To see the other types of publications on this topic, follow the link: Photonic crystal.
Dissertations / Theses on the topic 'Photonic crystal'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Photonic crystal.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Zhou, Ying. "CHOLESTERIC LIQUID CRYSTAL PHOTONIC CRYSTAL LASERS AND PHOTONIC DEVICES." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2706.
Full textAbstract:
This dissertation discusses cholesteric liquid crystals (CLCs) and polymers based photonic devices including one-dimensional (1D) photonic crystal lasers and broadband circular polarizers. CLCs showing unique self-organized chiral structures have been widely used in bistable displays, flexible displays, and reflectors. However, the photonic band gap they exhibit opens a new way for generating laser light at the photonic band edge (PBE) or inside the band gap. When doped with an emissive laser dye, cholesteric liquid crystals provide distributed feedback so that mirrorless lasing is hence possible. Due to the limited surface anchoring, the thickness of gain medium and feedback length is tens of micrometers. Therefore lasing efficiency is quite limited and laser beam is highly divergent. To meet the challenges, we demonstrated several new methods to enhance the laser emission while reducing the beam divergence from a cholesteric liquid crystal laser. Enhanced laser emission is demonstrated by incorporating a single external CLC reflector as a polarization conserved reflector. Because the distributed feedback from the active layer is polarization selective, a CLC reflector preserves the original polarization of the reflected light and a further stimulated amplification ensues. As a result of virtually doubled feedback length, the output is dramatically enhanced in the same circular polarization state. Meanwhile, the laser beam divergence is dramatically reduced due to the increased cavity length from micrometer to millimeter scale. Enhanced laser emission is also demonstrated by the in-cell metallic reflector because the active layer is pumped twice. Unlike a CLC reflector, the output from a mirror-reflected CLC laser is linearly polarized as a result of coherent superposition of two orthogonal circular polarization states. The output linear polarization direction can be well controlled and fine tuned by varying the operating temperature and cell gap. Enhanced laser emission is further demonstrated in a hybrid photonic band edge - Fabry-Perot (FP) type structure by sandwiching the CLC active layer within a circular polarized resonator consisting of two CLC reflectors. The resonator generates multiple FP modes while preserving the PBE mode from the active layer. More importantly this band edge mode can be greatly enhanced by the external resonator under some conditions. Theoretical analysis is conducted based on 4×4 transfer matrix and scattering matrix and the results are consistent with our experimental observations. To make the CLC laser more compact and miniaturized, we have developed a flexible polymer laser using dye-doped cholesteric polymeric films. By stacking the mirror reflecting layer, the active layer and the CLC reflecting layer, enhanced laser emission was observed in opposite-handed circular polarization state, because of the light recycling effect. On the other hand, we use the stacked cholesteric liquid crystal films, or the cholesteric liquid crystals and polymer composite films to demonstrate the single film broadband circular polarizers, which are helpful for converting a randomly polarized light into linear polarization. New fabrication methods are proposed and the circular polarizers cover ~280 nm in the visible spectral range. Both theoretical simulation and experimental results are presented with a good match.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
2
Yamashita, Tsuyoshi. "Unraveling photonic bands : characterization of self-collimation in two-dimensional photonic crystals." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-06072005-104606/.
Full textAbstract:
Thesis (Ph. D.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2006.Summers, Christopher, Committee Chair ; Chang, Gee-Kung, Committee Member ; Carter, Brent, Committee Member ; Wang, Zhong Lin, Committee Member ; Meindl, James, Committee Member ; Li, Mo, Committee Member.
3
ANGELINI, ANGELO. "Photon Management on a Photonic Crystal Platform." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2611159.
Full textAbstract:
A multilayered dielectric structure, namely a one dimensional photonic crystal (1DPC), is proposed as a suitable platform for photon management, due to the low absorption of the dielectric materials. When properly designed, a 1DPC can sustain surface electromagnetic modes called Bloch Surface Waves (BSWs). In this PhD Thesis it is shown how light coupled to BSW can be focused or guided by means of ultrathin polymeric refractive structures directly patterned on the surface. Moreover, by patterning the surface with surface relief gratings, far-field radiation can be efficiently coupled to the surface modes, thus providing an enhanced electromagnetic field at the truncation interface of the 1DPC. By shaping the grating in a circular symmetry, light can be in-plane focused into a sub-wavelength spot. The same structure can be used to re-shape the radiation pattern of dipolar emitters. It is shown that an emitter lying on the surface of the 1DPC couples to the photonic structure and the fluorescence radiated couple with the surface modes. The so called BSW-coupled fluorescence propagates along the surface with low losses and a well-defined wavevector. By means of surface diffraction gratings properly designed, fluorescence can be extracted along any direction, thus improving the fluorescence collection with no need of high numerical aperture optics or critical alignements. A novel method for evaluating the enhancement gained with such photonic structures on the extraction efficiency is proposed. Such method is capable of providing at the same time spatial resolution, angular resolution and spectral resolution. A biosensing experiment to detect small amounts of labeled proteins is provided, in order to show the sensing capabilities of the photonic structure.
4
Pfeiffenberger, Neal Thomas. "Single Crystal Sapphire Photonic Crystal Fibers." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77179.
Full textAbstract:
A single crystal sapphire optical fiber has been developed with an optical cladding that is used to reduce the number of modes that propagate in the fiber. This fiber is the first single crystal sapphire photonic crystal fiber ever produced. Fabrication of the optical cladding reduces the number of modes in the fiber by lowering the effective refractive index around the core, which limits the amount of loss. Different fiber designs were analyzed using Comsol Multiphysics to find the modal volumes of each. The MIT Photonic Bands modeling program was used to see if the first photonic band gap fiber could be achieved theoretically. The fibers were qualified using far field pattern and photodetector measurements as well as gas sensing experiments. The fibers were then exposed to a harsh environment of 1000 °C with a coating of alumina to test the resistance to scattering of the fiber. The fibers were also examined using materials characterization equipment to see how the harsh environments impacted the optical and mechanical stability of the bundled fiber.Ph. D.
5
Chen, Vincent W. "Fabrication and chemical modifications of photonic crystals produced by multiphoton lithography." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45918.
Full textAbstract:
This thesis is concerned with the fabrication methodology of polymeric photonic crystals operating in the visible to near infrared regions and the correlation between the chemical deposition morphologies and the resultant photonic stopband enhancements of photonic crystals.
Multiphoton lithography (MPL) is a powerful approach to the fabrication of polymeric 3D micro- and nano-structures with a typical minimum feature size ~ 200 nm. The completely free-form 3D fabrication capability of MPL is very well suited to the formation of tailored photonic crystals (PCs), including structures containing well defined defects. Such structures are of considerable current interest as micro-optical devices for their filtering, stop-band, dispersion, resonator, or waveguiding properties. More specifically, the stop-band characteristics of polymer PCs can be finely controlled via nanoscale changes in rod spacings and the chemical functionalities at the polymer surface can be readily utilized to impart new optical properties.
Nanoscale features as small as 65 ± 5 nm have been formed reproducibly by using 520 nm femtosecond pulsed excitation of a 4,4'-bis(di-n-butylamino)biphenyl chromophore to initiate crosslinking in a triacrylate blend. Dosimetry studies of the photoinduced polymerization were performed on chromophores with sizable two-photon absorption cross-sections at 520 and 730 nm. These studies show that sub-diffraction limited line widths are obtained in both cases with the lines written at 520 nm being smaller. Three-dimensional multiphoton lithography at 520 nm has been used to fabricate polymeric woodpile photonic crystal structures that show stop bands in the visible to near-infrared spectral region.
85 ± 4 nm features were formed using swollen gel photoresist by 730 nm excitation MPL. An index matching oil was used to induce chemical swelling of gel resists prior to MPL fabrication. When swollen matrices were subjected to multiphoton excitation, a similar excitation volume is achieved as in normal unswollen resins. However, upon deswelling of the photoresist following development a substantial reduction in feature size was obtained. PCs with high structural fidelity across 100 µm × 100 µm × 32 layers exhibited strong reflectivity (>60% compared to a gold mirror) in the near infrared region. The positions of the stop-bands were tuned by varying the swelling time, the exposure power (which modifies the feature sizes), and the layer spacing between rods.
Silver coatings have been applied to PCs with a range of coverage densities and thicknesses using electroless deposition. Sparse coatings resulted in enhanced reflectivity for the stop band located at ~5 µm, suggesting improved interface reflectivity inside the photonic crystal due to the Ag coating. Thick coatings resulted in plasmonic bandgap behavior with broadband reflectivity enhancement and PC lattice related bandedge at 1.75 µm. Conformal titania coatings were grown onto the PCs via a surface sol-gel method. Uniform and smooth titania coatings were achieved, resulting in systematically red-shifted stopbands from their initial positions with increasing thicknesses, corresponding to the increased effective refractive index of the PC. High quality titania shell structures with modest stopbands were obtained after polymer removal.
Gold replica structures were obtained by electroless deposition on the silica cell walls of naturally occurring diatoms and the subsequent silica removal. The micron-scaled periodic hole lattice originated from the diatom resulted in surface plasmon interferences when excited by infrared frequencies. The hole patterns were characterized and compared with hexagonal hole arrays fabricated by focused ion beam etching of similarly gold plated substrate. Modeling of the hole arrays concluded that while diatom replicas lack long-ranged periodicity, the local hole to hole spacings were sufficient to generate enhanced transmission of 13% at 4.2 µm.
The work presented herein is a step towards the development of PCs with new optical and chemical functionalities. The ability to rapidly prototype polymeric PCs of various lattice parameters using MPL combined with facile coating chemistries to create structures with the desired optical properties offers a powerful means to produce tailored high performance photonic crystal devices.
6
Xiong, Chunle. "Nonlinearity in photonic crystal fibres." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512286.
Full textAbstract:
This thesis introduces the linear and nonlinear properties of photonic crystal fibre (PCF), describes the fabrication and characterisation of different PCFs, and demonstrates their applications to supercontinuum (SC) generation and single-photon sources. The linear properties of PCF include endlessly single-mode transmission, highly controllable dispersion and birefringence. These unique properties have made PCFs the best media to demonstrate all kinds of nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), Raman effects, four-wave mixing and modulation instability (FWM and MI), and soliton effects. The combination of these nonlinear effects has led to impressive spectral broadening known as SC generation in PCFs. The intrinsic correlation of signal and idler photons from FWM has brought PCF to the application of single-photon generation. Four projects about SC generation were demonstrated. The first was visible continuum generation in a monolithic PCF device, which gave a compact, bright (-20 dBm/nm), flat and single-mode visible continuum source extending to short wavelength at 400 nm. The second was polarised SC generation in a highly bire-fringent PCF. A well linearly polarised continuum source spanning 450-1750 nm was achieved with >99% power kept in a single linear polarisation. This polarised continuum source was then applied to tuneable visible/UV generation in a BIBO crystal. The third was residual pump peak removal for SC generation in PCFs. The fourth was to design an all-fibre dual-wavelength pumping for spectrally localised continuum generation. Two projects about photon pair generation using FWM were then demonstrated. One was an all-fibre photon pair source designed in the telecom band for quantum communication. This source achieved >50% heralding efficiency which is the highest in fibre photon pair sources reported so far. Another one was to design birefringent PCFs for naturally narrow band photon pair generation in the Si SPAD high detection efficiency range. 0.122 nm bandwidth signal photons at 596.8 nm were generated through cross polarisation phase matched FWM in a weakly birefringent PCF pumped by a picosecond Ti:Sapphire laser at 705 nm in the normal dispersion regime.
7
Kurt, Hamza. "Photonic crystals analysis, design and biochemical sensing applications /." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-06252006-174301/.
Full textAbstract:
Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007.Papapolymerou, John, Committee Member ; Adibi, Ali, Committee Member ; Citrin, David, Committee Chair ; Summers, Christopher, Committee Member ; Voss, Paul, Committee Member.
8
Chong, Harold Meng Hoon. "Photonic crystal and photonic wire structures for photonic integrated circuits." Thesis, University of Glasgow, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407719.
Full text
9
Fan, Yun-Hsing. "TUNABLE LIQUID CRYSTAL PHOTONIC DEVICES." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3926.
Full textAbstract:
Liquid crystal (LC)-based adaptive optics are important for information processing, optical interconnections, photonics, integrated optics, and optical communications due to their tunable optical properties. In this dissertation, we describe novel liquid crystal photonic devices and their fabrication methods. The devices presented include inhomogeneous polymer-dispersed liquid crystal (PDLC), polymer network liquid crystals (PNLC) and phase-separated composite film (PSCOF). Liquid crystal/polymer composites could exist in different forms depending on the fabrication conditions. In Chap. 3, we demonstrate a novel nanoscale PDLC device that has inhomogeneous droplet size distribution. In such a PDLC, the inhomogeneous droplet size distribution is obtained by exposing the LC/monomer with a non-uniform ultraviolet (UV) light. An electrically tunable-efficiency Fresnel lens is devised for the first time using nanoscale PDLC. The tunable Fresnel lens is very desirable to eliminate the need of external spatial light modulator. Different gradient profiles are obtained by using different photomasks. The nanoscale LC droplets are randomly distributed within the polymer matrix, so that the devices are polarization independent and exhibit a fast response time. Because of the small droplet sizes, the operating voltage is higher than 100 Vrms. To lower the driving voltage, in Chap. 2 and Chap. 3, we have investigated a polymer-network liquid crystal (PNLC) using a rod-like monomer structure. Since the monomer concentration is only about 5%, the operating voltage is below 10 Vrms. The PNLC devices are polarization dependent. To overcome this shortcoming, stacking two cells with orthogonal alignment directions is a possibility. In Chap. 3, another approach to lower the operating voltage is to use phase-separated composite film (PSCOF) where the LC and polymer are separated completely to form two layers. Without multi-domain formed in the LC cell, PSCOF is free from light scattering. Using PNLC and PSCOF, we also demonstrated LC blazed grating and Fresnel lens. The diffraction efficiency of these devices is continuously controlled by the electric field. Besides Fresnel lens, another critical need for imaging and display is to develop a system with continuously tunable focal length. A conventional zooming system controls the lens distance by mechanical motion along the optical axis. This mechanical zooming system is bulky and power hungry. To overcome the bulkiness, in Chap. 4 we developed an electrically tunable-focus flat LC spherical lens which consists of a spherical electrode imbedded in the top flat substrates while a planar electrode on the bottom substrate. The electric field from the spherical and planar electrodes induces a centrosymmetric gradient refractive index distribution within the LC layer which, in turn, causes the focusing effect. The focal length is tunable by the applied voltage. A tunable range from 0.6 m to infinity is achieved. Microlens array is an attractive device for optical communications and projection displays. In Chap. 5, we describe a LC microlens array whose focal length can be switched from positive to negative or vise versa by the applied voltage. The top spherical electrode glass substrate is flattened with a polymer layer. The top convex substrate and LC layer work together like a zoom lens. By tuning the refractive index profile of the LC layer, the focal length of the microlens array can be switched from positive to negative or vise versa. The tunable LC microlens array would be a great replacement of a conventional microlens array which can be moved by mechanical elements. The fast response time feature of our LC microlens array will be very helpful in developing 3-D animated images. A special feature for LC/polymer composites is light scattering. The concept is analogous to the light scattering of clouds which consist of water droplets. In Chap. 6, we demonstrate polymer network liquid crystals for switchable polarizers and optical shutters. The PNLC can present anisotropic or isotropic light scattering behavior depending on the fabrication methods. The use of dual-frequency liquid crystal and special driving scheme leads to a sub-millisecond response time. The applications for display, light shutters, and switchable windows are emphasized. Although polymer networks help to reduce liquid crystal response time, they tend to scatter light. In Chap. 7, for the first time, we demonstrate a fast-response and scattering-free homogeneously-aligned PNLC light modulator. Light scattering in the near-infrared region is suppressed by optimizing the polymer concentration such that the network domain sizes are smaller than the wavelength. As a result, the PNLC response time is ~300X faster than that of a pure LC mixture except that the threshold voltage is increased by ~25X. The PNLC cell also holds promise for mid and long infrared applications where response time is a critical issue.Ph.D.
Other
Optics and Photonics
Optics
10
Paturi, Naveen Kumar. "Analysis of photonic crystal defects for biosensing applications." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4861.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains viii, 70 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 55-57).
11
Høvik, Jens. "Photonic Crystal Waveguide Fabrication." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19277.
Full textAbstract:
This research is entirely devoted to the study and fabrication of structures with periodic dielectric constants, also known as photonic crystals (PhCs). These structures show interesting dispersion characteristics which give them a range of prohibited frequencies that are not allowed to propagate within the crystal. This property makes them suited for a wide array of photonic-based components. One-dimensional photonic crystals are already commercialized and are of widespread use in for example thin-film optics, and two-dimensional PhCs are available in the form of photonic crystal fibers.Much work is being done on the analysis of photonic crystals and their application in various photonic components. In designing any photonic crystal component the properties of the crystal must first be understood and analyzed. By using frequency-domain simulation software we have studied the properties of bulk photonic crystals and designed the ideal structure for confining light of any design wavelength within a three-dimensional photonic crystal slab.Through simulations, the ideal periodicity of the PhC has been found along with its optimal geometry for waveguiding purposes. The study was then extended to three dimensions and the optimal thickness of the PhC slab was found. By using these determined values we were able to properly confine light inside a defect in a photonic crystal structure. This phenomenon allowed us to briefly examine the use of a photonic crystal as a waveguide. This research was then continued by attempting to fabricate such a device. Methods entailing how to create a silicon-on-insulator wafer through plasma enhanced chemical vapor deposition were developed. Profilometry, refractometry and ellipsometry were used to characterize the quality of the SOI wafer. A surface roughness between 1.5-3.5 nm was found. The losses of the amorphous silicon was attempted to be measured through ellipsometry, but the ellipsometer was found incapable for loss meassurements. Better testing methods must therefore be developed.The PhC waveguiding structure is formed thorugh electron-beam lithography, and various thicknesses of photoresist are tested and characterized. Furthermore, various materials were attempted as an etch mask. Polymethyl methacrylate, $SiO_2$, and chromium were all utilized, where only the latter showed good enough selectivity for silicon etching. This lead to using both chromium and $SiO_2$ as the mask of choice. Several etching methods were tested. Both standard wet etching, room-temperature reactive ion etching recipes as well as cryogenic inductively coupled plasma reactive ion etching recipes were employed. Dry etching was found to be of insufficient quality, while the complete isotropy of wet etching rendered it impractical for fine structures needed for a PhC waveguide.The final solution which allowed the formation of the photonic crystal was a stacked structure, using both chromium, oxide, and PMMA throughout the etching process in order to achieve the wanted results. The PMMA was used as an etch mask to imprint the pattern in the oxide layer. The oxide layer was in turn used as an etch mask to imprint the pattern into the chromium, and the chromium served as the final mask to be used during cryogenic silicon etching. The cryogenic silicon etching recipe was characterized and shown to be sufficiently anisotropic as well as having a rather high maximum etch depth. The recipe show an unwanted formation of so-called silicon grass, and a high sidewall roughness is observed. Finally, a complete PhC waveguiding structure with both a grating, a taper, and a silicon waveguide is fabricated. Although they require more work to be optimized, the methods presented in this thesis provide the basis for fabricating a multitude of optical components, not only PhC's.
12
Scullion, Mark Gerard. "Slotted photonic crystal biosensors." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3405.
Full textAbstract:
Optical biosensors are increasingly being considered for lab-on-a-chip applications due to their benefits such as small size, biocompatibility, passive behaviour and lack of the need for fluorescent labels. The light guiding mechanisms used by many of them result in poor overlap of the optical field with the target molecules, reducing the maximum sensitivity achievable. This thesis presents a new platform for optical biosensors, namely slotted photonic crystals, which engender higher sensitivities due to their ability to confine, spatially and temporally, the peak of optical mode within the analyte itself. Loss measurements showed values comparable to standard photonic crystals, confirming their ability to be used in real devices. A novel resonant coupler was designed, simulated, and experimentally tested, and was found to perform better than other solutions within the literature. Combining with cavities, microfluidics and biological functionalization allowed proof-of-principle demonstrations of protein binding to be carried out. High sensitivities were observed in smaller structures than most competing devices in the literature. Initial tests with cellular material for real applications was also performed, and shown to be of promise. In addition, groundwork to make an integrated device that includes the spectrometer function was also carried out showing that slotted photonic crystals themselves can be used for on-chip wavelength specific filtering and spectroscopy, whilst gas-free microvalves for automation were also developed. This body of work presents slotted photonic crystals as a realistic platform for complete on-chip biosensing; addressing key design, performance and application issues, whilst also opening up exciting new ideas for future study.
13
Smith, Cameron. "Reconfigurable Photonic Crystal Cavities." Thesis, The University of Sydney, 2009. http://hdl.handle.net/2123/4988.
Full textAbstract:
Photonic crystals are optical structures that contain a periodic modulation of their refractive index, allowing them to control light in recent years of an unprecedented capacity. Photonic crystals may take on a variety of configurations, in particular the photonic crystal cavity, which may “hold” light in small volumes comparable to the light’s wavelength. This capability to spatially confine light opens up countless possibilities to explore for research in telecommunications, quantum electrodynamics experiments and high-resolution sensor applications. However, the vast functionality potentially made available by photonic crystal cavities is limited due to the difficulty in redefining photonic crystal components once they are formed in their (typically) solid material. The work presented in this thesis investigates several approaches to overcome this issue by reconfiguring photonic crystal cavities.
14
Smith, Cameron. "Reconfigurable Photonic Crystal Cavities." University of Sydney, 2009. http://hdl.handle.net/2123/4988.
Full textAbstract:
Doctor of Philosophy (PhD)Photonic crystals are optical structures that contain a periodic modulation of their refractive index, allowing them to control light in recent years of an unprecedented capacity. Photonic crystals may take on a variety of configurations, in particular the photonic crystal cavity, which may “hold” light in small volumes comparable to the light’s wavelength. This capability to spatially confine light opens up countless possibilities to explore for research in telecommunications, quantum electrodynamics experiments and high-resolution sensor applications. However, the vast functionality potentially made available by photonic crystal cavities is limited due to the difficulty in redefining photonic crystal components once they are formed in their (typically) solid material. The work presented in this thesis investigates several approaches to overcome this issue by reconfiguring photonic crystal cavities.
15
Azabi, Y. O. "Spiral photonic crystal fibers." Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/19372/.
Full textAbstract:
This thesis is concerned with the study of special types of photonic crystal fibers (spiral) and their optical properties. The work is carried out using simulation techniques to obtain the modal field profile and properties for the designs. The method used in solving the Maxwell’s equations is the full vectorial finite element method with the implementation of penalty function and perfectly matched layer. The penalty function is used to eliminate nonphysical solutions. The perfectly matched layer is integrated to absorb rays of light traveling away from the core. These rays are absorbed by the layer and do not reflect back to negatively influence the results. The spiral shapes are implemented in the distribution of the holes in the cladding region of the photonic crystal fiber to determine the photonic crystal fiber properties. Three different spirals have been introduced which are equiangular, Archimedean and Fermat’s spiral. The study of the effective refractive index, effective area and dispersion with varying spiral parameters have been carried out and the results are analyzed to understand the effect of each parameter. The variation of similar parameters in the spirals leads to similar variation in the optical properties under consideration. Furthermore, the equiangular spiral photonic crystal fibers (ES-PCF) have been investigated in two different dimensional scales. The scales are in comparison with the wavelength of operation in the first case when core size is larger than the operating wavelength. In this case the total dispersion of the fiber has slightly higher values than the material dispersion but similar curve and slope. On the other hand, when the core size is comparable with the wavelength of operation, the dispersion is varying significantly with varying the spiral parameters. The effective area can be made very small and therefore the nonlinearity of the fiber very large to facilitate non-linear applications such as super continuum generation. The equiangular spiral photonic crystal fiber has been modified slightly where the position of holes in the third ring are shifted further from the center and their size is much bigger. This manipulation is proposed in an algorithm in this thesis to facilitate the fabrication of ES-PCF using an adaptive stack and draw technique. The design shows similar optical behavior to an ideal spiral and its dispersion has been tailored for supercontinuum generation.
16
Liles, Alexandros Athanasios. "Hybrid photonic crystal cavity based lasers." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/12081.
Full textAbstract:
In recent years, Silicon Photonics has emerged as a promising technology for cost-effective fabrication of photonic components and integrated circuits, the application of which is recently expanding in technological fields beyond tele- and data-communications, such as sensing and biophotonics. Compact, energy-efficient laser sources with precise wavelength control are crucial for the aforementioned applications. However, practical, efficient, electrically-pumped lasers on Silicon or other group IV elements are still absent, owing to the indirect bandgap of those materials. Consequently, the integration of III-V compounds on Silicon currently appears to be the most viable route to the realization of such lasers. In this thesis, I present and explore the potential of an External Cavity (EC) hybrid III-V/Silicon laser design, comprising a III-V-based Reflective Semiconductor Optical Amplifier (RSOA) and a Silicon reflector chip, based on a two-dimensional Photonic Crystal (PhC) cavity vertically coupled to a low-refractive-index dielectric waveguide. The vertically coupled system functions as a wavelength-selective reflector, determining the lasing wavelength. Based on this architecture mW-level continuous-wave (CW) lasing at room temperature was shown both in a fiber-based long cavity scheme and die-based short cavity scheme, with SMSR of > 25 dB and > 40 dB, respectively. Furthermore, by electrically modulating the refractive index of the PhC cavity in the reflector chip, tuning of the emitted wavelength was achieved in the die-based short cavity EC laser configuration. In this way, I demonstrated the suitability of the examined EC configuration for direct frequency modulation. The proposed scheme eliminates the need for wavelength matching between the laser source and a resonant modulator, and reveals the potential of employing low-power-consumption resonant modulation in practical Silicon Photonics applications.
17
Chen, Parry. "Group velocity analysis of metamaterial photonic crystals and multipole simulation of photonic crystal slabs." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10525.
Full textAbstract:
Group velocity analysis of metamaterial photonic crystals and multipole simulation of photonic crystal slabs Periodicity is a feature of two topical areas of optics, photonic crystals and metamaterials. Photonic crystals scatter passing light coherently, introducing structural dispersion and creating band gaps where light cannot propagate. Metamaterials use resonant structures much smaller than the wavelength to produce negative effective refractive indexes. When metamaterials are constituents of photonic crystals, new phenomena arise. Firstly, new band gaps appear whenever the average refractive index is zero, occurring independently of Bragg reflections. However, only one dimensional examples have been reported, and its existence in higher dimensions is unknown. Secondly, the group velocity of dispersion relations can be infinite and turn negative, which violates conservation theorems obeyed by lossless structures. These open questions are resolved by using multipole methods, a two dimensional method specialized cylindrical inclusions. Analytical dispersion relations are derived for long wavelengths, demonstrating that zero average refractive index is neither necessary nor sufficient to obtain band gaps. Then, an analytical criterion for infinite group velocity points is derived, existing whenever the modal field is balanced between the positive and negative group index constituents of a photonic crystal. To derive this condition, an analytical tool is developed to calculate group velocities from modal field distributions and material parameters in general lossy dispersive periodic media. Finally, the strengths of the multipole method are applied to simulate a widely fabricated photonic crystal structure: the planar dielectric slab periodically perforated with cylindrical holes. Two structural symmetries are exploited, the vertical translational invariance of the slab, and the rotational invariance of the inclusions, to create a rapidly convergent numerical method. Extensions of the method are possible to defect structures and plasmonic extraordinary transmission gratings.
18
Saulnier, Nicole A. "Computational Modeling of Photonic Crystal Microcavity Single-Photon Emitters." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/53.
Full textAbstract:
Conventional cryptography is based on algorithms that are mathematically complex and difficult to solve, such as factoring large numbers. The advent of a quantum computer would render these schemes useless. As scientists work to develop a quantum computer, cryptographers are developing new schemes for unconditionally secure cryptography. Quantum key distribution has emerged as one of the potential replacements of classical cryptography. It relies on the fact that measurement of a quantum bit changes the state of the bit and undetected eavesdropping is impossible. Single polarized photons can be used as the quantum bits, such that a quantum system would in some ways mirror the classical communication scheme. The quantum key distribution system would include components that create, transmit and detect single polarized photons.
The focus of this work is on the development of an efficient single-photon source. This source is comprised of a single quantum dot inside of a photonic crystal microcavity. To better understand the physics behind the device, a computational model is developed. The model uses Finite-Difference Time-Domain methods to analyze the electromagnetic field distribution in photonic crystal microcavities. It uses an 8-band k · p perturbation theory to compute the energy band structure of the epitaxially grown quantum dots. We discuss a method that combines the results of these two calculations for determining the spontaneous emission lifetime of a quantum dot in bulk material or in a microcavity. The computational models developed in this thesis are used to identify and characterize microcavities for potential use in a single-photon source. The computational tools developed are also used to investigate novel photonic crystal microcavities that incorporate 1D distributed Bragg reflectors for vertical confinement. It is found that the spontaneous emission enhancement in the quasi-3D cavities can be significantly greater than in traditional suspended slab cavities.
19
Cordier, Martin. "Photon-pair generation in hollow-core photonic-crystal fiber." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT024/document.
Full textAbstract:
Les sources de paires de photons sont un composant essentiel des technologies émergentes en information quantique. De nombreux travaux ont permis des avancées importantes utilisant des processus non linéaires d'ordre 2 dans les cristaux et les guides d'ondes, et d'ordre 3 dans les fibres. Les limitations viennent dans le premier cas, des pertes et en particulier des pertes de couplage avec les fibres optiques et dans le second cas, du bruit dû à l'effet Raman dont le spectre est très large dans les fibres de silice. Ce projet propose une nouvelle architecture basée sur des fibres à cristal photonique à coeur creux (FCPCC) que l'on peut remplir de liquide ou de gaz non linéaire. Cette configuration permet la génération paramétrique de paires de photons corrélés par mélange à quatre ondes sans l'inconvénient de la diffusion Raman. Cette technologie offre une large gamme de paramètres à explorer en s'appuyant sur les propriétés physiques et linéaires contrôlables des FCPCC et la possibilité de remplissage de ces fibres avec des fluides aux propriétés non-linéaires variées. En effet, par une conception judicieuse de la FCPCC et un choix approprié du liquide ou du gaz, il est possible de (i) contrôler la dispersion et la transmission pour générer des photons corrélés sur une large gamme spectrale avec la condition d'accord de phase la plus favorable, (ii) d'ajuster la taille de coeur de la fibre et/ou sa forme pour augmenter sa non-linéarité ou son efficacité de couplage avec d'autres fibres et (iii) de s'affranchir totalement de l'effet Raman si on utilise par exemple un gaz monoatomique, ou d'obtenir des raies Raman fines, aisément discriminables des raies paramétriques dans le cas d'un liquidePhoton pair sources are an essential component of the emerging quantum information technology. Despite ingenious proposals being explored in the recent years based on either second order nonlinear processes in crystals and waveguides or on third order processes in fibers, limitations remain, due to losses and specifically coupling losses in the former case and due to Raman generation in silica, giving rise to a broad spectrum noise in the latter. These limitations have been challenging to lift because of the limited alternative nonlinear materials that fulfil the conditions for the generation of bright and high fidelity photon pairs in integrable photonic structures. In the present project, we develop a new and versatile type of photonic architecture for quantum information applications that offers access to a variety of nonlinear optical materials that are micro-structured in optical fiber forms to generate photon pairs, without the drawback of Raman scattering and with a large design parameter-space. Indeed, with a careful design of the HCPCF along with the appropriate choice of fluid, one can (i) control the dispersion and the transmission to generate photons with the most favourable phase-matching condition over a large spectral range, (ii) adjust the fibre core size and/or shape to enhance nonlinearity or the coupling efficiency with other fibres, (iii) totally suppress the Raman effect in monoatomic gases for instance or have only narrow and separated Raman lines that can thus be easily separated from the useful parametric lines in liquids
20
Leirset, Erlend. "Photonic crystal light emitting diode." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10014.
Full textAbstract:
This master's thesis describe electromagnetic simulations of a gallium antimonide (GaSb) light emitting diode, LED. A problem for such devices is that most of the generated light is reflected from the surface due to total internal reflection, and is therefore prevented from coupling out of the semiconductor material. Etching out a 2D photonic crystal grating on the LED surface would put aside the absolute rule of total internal reflection, and could therefore be used to increase the total transmission. The simulation method which was developed was supposed to find geometry parameters for the photonic crystal to optimize the light extraction. A set of plane waves were therefore simulated using FDTD to build an equivalent to the Fresnel equations for the photonic crystal surface. From that the total transmittance and radiation patterns for the simulated geometries were calculated. The results indicated an increase in the transmission properties of up to 70% using a square grating of holes where the holes have a radius of 0.5µm, the hole depth is 0.4µm, and the grating constant is 1µm. A hexagonal grating of holes and a square grating of isotropically etched holes were also simulated, and featured improvements on the same scale, but with different dimensions for the holes. The simulations were computationally very demanding, and the simulation structure therefore had to be highly trimmed to limit the calculation time to reasonable values. This might have reduced the accuracy of the results. Especially the optimum grating constant, and the value of the optimum improvement itself is believed to be somewhat inaccurate.
21
Liu, Tao. "Photonic Crystal Based Optical Devices." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1294%5F1%5Fm.pdf&type=application/pdf.
Full text
22
Welna, Karl P. "Electrically injected photonic-crystal nanocavities." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2528.
Full textAbstract:
Nano-emitters are the new generation of laser devices. A photonic-crystal cavity, which highly confines light in small volumes, in combination with quantum-dots can enhance the efficiency and lower the threshold of this device. The practical realisation of a reliable, electrically pumped photonic-crystal laser at room-temperature is, however, challenging. In this project, a design for such a laser was established. Its properties are split up into electrical, optical and thermal tasks that are individually investigated via various device simulations. The resulting device performance showed that with our design the quantum-dots can be pumped in order to provide gain and to overcome the loss of the system. Threshold currents can be as low as 10’s of μA and Q-factors in the range of 1000’s. Gallium arsenide wafers were grown according to our specifications and their diode behaviour confirmed. Photonic-crystal cavities were fabricated through a newly developed process based on a TiOₓ hard-mask. Beside membraned cavities, also cavities on oxidised AlGaAs were fabricated with help to a unique hard-mask removal method. The cavities were measured with a self-made micro-photoluminescence setup with the highest Q-factor of 4000 for the membrane cavity and a remarkable 2200 for the oxide cavity. The fabrication steps, regarding the electrically pumped photonic-crystal laser, were developed and it was shown that this device can be fabricated. During this project, a novel type of gentle confinement cavity was developed, based on the adaption of the dispersion curve (DA cavity) of a photonic-crystal waveguide. Q-factors of as high as 600.000 were measured for these cavities made in Silicon.
23
Calcraft, Alexander Robert Andrew. "Air-bridge photonic crystal cavities." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505430.
Full textAbstract:
Photonic crystal cavities can confine light to volumes smaller than a cubic wavelength, coupling their photonic modes to embedded quantum dots. Structures with sufficiently low losses and modal volumes can render photon emission reversible, a regime with potential for applications in quantum information processing. Three dimensional photonic crystal cavities are extremely difficult to produce, however two dimensional structures, bound above and below by air, can use the photonic band gap for in-plane confinement, and total internal reflection for 'to the plane' confinement. This thesis concerns itself with the development and utilisation of a method for calculating the mode structure and characteristics of such 'airbridge' cavities. An expansion in terms of the guided modes of an unpatterned dielectric membrane allows us to find the energies and fields of confined states. Loss calculations using periodic boundary conditions are shown to be flawed, and a method is devised, which effectively modifies the bound-ary conditions prior to the loss calculation. Losses are then calculated using Fermi's golden rule, allowing for full analyses of emission rate, directionality and polarisation. This method is highly accurate, and orders of magnitude faster than the widely used finite difference time domain codes. Multiple cavity designs are analysed and optimised. The 'L3' cavity which consists of a line of three holes missed from a hexagonal lattice, with the holes at either end slightly displaced, is then used to consider the effect of membrane refractive index, showing an exponential relationship between refractive index and achievable quality factors. The effects of in-plane disorder are shown to hold influence over the design preference of cavities. Finally, as a step towards a scalable quantum information processing architecture, several geometries are considered for the coupling of parallel 'L3' cavities; splittings are shown to exist in energy, quality factor, and emission polarisation.
24
Szymanski, Dominik. "Photonic crystal cavities and waveguides." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538086.
Full text
25
Hedley, Thomas. "Modelling of photonic crystal fibre." Thesis, University of Bath, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433962.
Full text
26
Corbett, Jason C. W. "Photonic crystal fibres in astronomy." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2661/.
Full textAbstract:
Photonic crystal fibres (PCF) are a new generation of optical fibre that guide light via a periodic air-silica, photonic crystal structure instead of the more traditional step change in refractive index associated with traditional fibre. Careful design of the photonic structure causes the fibres to behave in interesting new ways and one of main aims of this thesis is to begin the investigation of the uses of PCF's in astronomy. Step index and large mode area (LMA) PCF's are introduced in Chapters 2 and 3, respectively. Chapter 4 then deals with the instrumental simplifications associated with the use of LMA PCF'ร in fibre stellar interferometry showing that up to four step index fibres and associated optics can be replaced with a single LMA fibre. One of the key features of LMA fibres, for astronomy, is that, unlike the step index fibre, the mode field size is independent of wavelength and the fibre can therefore be fed with a pupil image via a field lens. Chapter 5 investigates this important new parameter space showing that contiguous sampling using single mode fibres is now possible for the first time. Further, unlike the direct feed to the LMA fibre, maximised coupling over very large wavebands is now possible using just a single fibre. Chapter 6 deals with another new fibre technology in astronomy: Multi-mode fibre (MMF) to single-mode array (SMA) transitions. These fibre systems break out the modes of the multi-mode fibre into an array of single-mode fibres upon which Bragg gratings can be etched. The SMA is then refused into an output MMF resulting in a multimode device but with single-mode line suppression. The number of modes transmitted is numerically equal to the number of fibres in the SMA and the performance of these devices is investigated on a model telescope showing that only a few tens of modes is required to efficiently transmit either the J or н bands. Finally, Chapter 7 details the experimental investigation of fibre modal noise in high dispersion spectroscopy. This is a photometric error on a resolution element due to fibre modes interfering with each other at very high spectral dispersion. Worryingly, the results show that no current theory exists that can predict the performance of a fibre based high R spectrometer.
27
Chen, Lei. "Modelling of photonic crystal fibres." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516842.
Full textAbstract:
The work in this thesis is to understand, through theory and simulation, a guidance mechanism due to the weak interaction of modes in photonic crystal fibres (PCFs). Firstly, two common kinds of PCFs, that guide light by total internal reflection and by photonic bandgaps, are reviewed. Several typical PCF structures for which light propagation is governed by weak mode interaction are then discussed and particularly compared with bandgap-guiding PCFs. Two independent methods are developed to model a set of related rectangular hollow-core PCF structures. The boundary element method is derived for a general PCF configuration and applied to our model structures. This method numerically provides some basic features about the guided modes, such as the propagation constant and field profile. The calculations show an ideal confinement in our model structure by considering a scalar wave equation and a high dielectric constant at the glass intersections. However, in realistic guidance, both confinement loss and the field of the guided modes indicate a raised leakage due to mode interactions. The analytic methodology starts by solving the ideal case considered in boundary element calculations and leads to analytic solutions for the perfectly guided modes. A perturbation method corresponding to the realistic guidance is then applied to these analytic solutions. This method can provide insight into understanding the formation of leakage through an analysis of mode interactions. An approximate analytic method for obtaining the attenuation of guided modes from the perturbation interaction is demonstrated. Attenuations calculated in this way give good agreement with boundary element results in magnitude and trends in variation. The influences of frequency and fibre parameters on features of the attenuation are also investigated. An overall interpretation of this guidance mechanism and suggestions for fibre optimisation are made in the final chapter, where further development of this work is also proposed.
28
Tekeste, Meron Yemane. "Photonic Crystal Based Wavelength Demultiplexing." Miami University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=miami1155299701.
Full text
29
Sevim, Koray Sözüer H. Sami. "One dimensional photonic crystal waveguide/." [s.n.] [s.l.], 2004. http://library.iyte.edu.tr/tezler/master/fizik/T000446.pdf.
Full text
30
Stewart, Justin William. "Photonic Crystal-Based Flow Cytometry." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5396.
Full textAbstract:
Photonic crystals serve as powerful building blocks for the development of lab-on-chip devices. Currently they are used for a wide range of miniaturized optical components such as extremely compact waveguides to refractive-index based optical sensors. Here we propose a new technique for analyzing and characterizing cells through the design of a micro-flow cytometer using photonic crystals. While lab scale flow cytometers have been critical to many developments in cellular biology they are not portable, difficult to use and relatively expensive. By making a miniature sensor capable of replicating the same functionality as the large scale units with photonic crystals, we hope to produce a device that can be easily integrated into a lab-on-chip and inexpensively mass produced for use outside of the lab.
Using specialized FDTD software, the proposed technique has been studied, and multiple important flow cytometry functions have been established. As individual cells flow near the crystal surface, transmission of light through the photonic crystal is influenced accordingly. By analyzing the resulting changes in transmission, information such as cell counting and shape characterization have been demonstrated. Furthermore, correlations for simultaneously determining the size and refractive indices of cells has been shown by applying the statistical concepts of central moments.
31
Hu, Zhen. "Modeling photonic crystal devices by Dirichlet-to-Neumann maps /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ma-b30082559f.pdf.
Full textAbstract:
Thesis (Ph.D.)--City University of Hong Kong, 2009."Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [85]-91)
32
Ayre, Melanie. "Photonic crystal interfaces : a design-driven approach." Thesis, St Andrews, 2006. http://hdl.handle.net/10023/143.
Full text
33
Khetani, Altaf. "Photonic crystal fiber as a biosensor." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/27596.
Full textAbstract:
With the era of technological change at its all time high, advancements in the field of photonics offer us a wide range of innovative potential applications. Over the years photonics has played an important role in modern industries such as telecommunication, sensors and medical imaging. One of the fields which has received a lot of attention is Photonic Crystal Fibers (PCF) for biosensor application. Photonic crystal fiber is a unique type of optical fiber in which continuous channels of (typically) air run their entire length. These 'holes' serve to both confine electromagnetic waves within the core of the fiber and to tailor its transmission properties. The classification of photonic crystal fiber can be solid core PCF where the light is guided by total internal reflection, and Hollow core photonic bandgap fibers (PBF) in which light is guided through the photonic bandgap effect. Simulation of PCF has been done through commercial software known as COMSOL which follows the finite element approach.
The focus of this thesis is on the application of PCF for different sensing applications. Traditionally, solid core PCF has been used for sensing purposes as the cladding channels can be filled with gas or liquid, thus serving as an efficient type of evanescent wave sensing. Hollow core PBF offers huge improvements as the interaction between light and matter is increased by the presence of sample in the core where most of the light is confined.
Conventionally, HC-PBF is used for sensor purposes by selectively filling the core. Here we have used a non-selective filling technique wherein all the channels of PCF are being filled with samples. When the fiber is empty it guides a particular band, and upon filling with other samples, the bandgap is shifted, and depending on this shift one can determine the refractive index of the sample. This type of sensor has been able to detect as low as 10 -5 change in refractive index just by taking a few centimeters of HC-PBF.
Laser Flash Photolysis is one of the leading methods used in photochemistry to determine the transient species such as radicals, excited states or ions, in chemical and biological systems. By using HC-PBF we have replaced the conventional technique of LFP where in a test-tube is used to hold the sample. The sample is excited through a laser and a monitoring beam is used to observe the amount of absorption. The sample required here is on the order of a milliliter which can be scaled down to pico liter by the use of PCF. The LFP results using PCF showed signal enhancement of at least an order of magnitude for samples like xanthone in toluene, xanthone in acetonitryl and water soluble benzoin in methyl viologen.
Raman Spectroscopy is yet another area which had a surge of growth for label free detection of samples. One of the reasons for its popularity is that it provides a unique optical fingerprint of chemicals and biomolecules. In this thesis we have focused on developing HC-PBF for enhancing the Raman signal from the sample. We have obtained an enhancement of over 40 times when using a HC-PBF with a length of 9.5cm. We have also used HC-PBF to study the enhancement of Raman signal from colloidal nanoparticles in an aqueous solution.
Supercontinuum generation is yet another area which has seen tremendous growth through the use of solid core PCF. Here we have covered the excitation of cladding and core mode in an endlessly single mode PCF which has the potential to be used as an effective type of biosensor as the penetration of light in the cladding channels is very strong compared to an evanescent wave field.
34
Khorshidahmad, Amin. "Controlling light with slab photonic crystal." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104667.
Full textAbstract:
This thesis presents novel designs and schemes for wavelength demultiplexing, frequency conversion and multi-wavelength generation applications, achieved by engineering the band structure and dynamic control of the dispersion in planar photonic crystal (PhC) platform. The composite superprism demultiplexer, whereby simultaneous diffraction compensation and angular channel separation considerably reduces the footprint required in conventional superprisms, is proposed. A design model is developed and applied to optimize and analyze the scaling properties of the demultiplexer. Expanding the bandwidth of the conventional superprism in a compact stratified hetero-lattice operating in reflective scheme is also investigated. Increasing the adiabatically achievable frequency shift by the structural change induced via tuning the slab refractive index of a nested cavity is shown. Wavelength conversion using the proposed dynamically reconfigurable nested resonators is further studied. In this scheme, ultrafast modulation of the refractive index, e.g. via induced free carriers, transforms the photons stored within the original cavity into the distinct set of eigenmodes of a dynamically formed resonator. As a result, an arbitrary frequency shift, determined by the spectral separation of the resonances of the initial and the tuned cavities, is achievable provided a fast enough tuning. This scheme may also eliminate the adiabatic frequency conversion that normally co-exists with intermodal transitions in a static cavity. Optical comb sources with tunable spectrum by dynamically controlling the reconfiguration, tailoring the dispersion and utilizing the symmetry of the mode profiles in nested resonators is also proposed and numerically demonstrated.Cette thèse présente des concepts et plans originaux pour des applications en démultiplexage de longueur d'onde, conversion de fréquence et génération de multi-longueur d'onde, obtenue par la conception de la structure de bande et le contrôle dynamique de la dispersion de la plate-forme de cristaux photoniques (CPh) planaires.Un démultiplexeur superprisme composite, par lequel la compensation de la diffraction ainsi que la séparation angulaire des canaux réduit considérablement l'encombrement requis par les superprismes classiques, est proposé. Un modèle de conception est développé et appliqué afin d'optimiser et d'analyser les propriétés de mise à l'échelle du démultiplexeur. L'élargissement de la bande passante du superprisme classique dans une exploitation compacte hétéro-réseau stratifiée dans un schéma de réflexion est également étudiée. L'augmentation du décalage de fréquence adiabatique réalisable par le changement structurel qui est induit par la modification de l'indice de réfraction de la dalle dans une cavité imbriquée est présenté. De plus, la conversion de longueur d'onde grâce aux résonateurs imbriqués et dynamiquement reconfigurables qui sont proposés dans cette thèse est étudiée. Dans ce schéma, la modulation ultra-rapide de l'indice de réfraction, par exemple via des porteurs libres induits, transforme les photons accumulés dans la cavité d'origine en un ensemble distinct de modes propres d'un résonateur configuré dynamiquement. En conséquence, un décalage en fréquence arbitraire, déterminé par la séparation spectrale des résonances de la cavité initiale et celles du résonateur accordé, est réalisable à condition qu'un réglage soit fait rapidement. Ce système peut aussi éliminer la conversion de fréquence adiabatique qui accompagne normalement la transition entre les modes dans une cavité statique. La conception de sources peigne de fréquences optiques à spectres accordables par le contrôle dynamique de la configuration, l'adaptation de la dispersion et l'utilisation de la symétrie des profils des modes dans les résonateurs imbriqués est également proposée et démontrée numériquement.
35
Spurny, Marcel. "Photonic crystal waveguides in chalcogenide glasses." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2111.
Full textAbstract:
The growing speed and bandwidth requirements of telecommunication systems demand all-optical on-chip solutions. Microphotonic devices can deliver low power nonlinear signal processing solutions. This thesis looks at the slow light photonic crystals in chalcogenide glasses to enhance low power nonlinear operation. I demonstrate the development of new fabrication techniques for this delicate class of materials. Both, reactive ion etching and chemically assisted ion beam etching are investigated for high quality photonic crystal fabrication. A new resist-removal technique was developed for the chemical, mechanical and light sensitive thin films. I have developed a membraning method based on vapor phase etching in combination with the development of a save and economical etching tool that can be used for a variety of vapour phase processes. Dispersion engineered slow light photonic crystals in Ge₃₃As₁₂Se₅₅ are designed and fabricated. The demonstration of low losses down to 21±8dB/cm is a prerequisite for the successful demonstration of dispersion engineered slow light waveguides up to a group index of around n[subscript(g)] ≈ 40. The slow light waveguides are used to demonstrate highly efficient third harmonic generation and the first advantages of a pure chalcogenide system over the commonly used silicon. Ge₁₁.₅As₂₄24Se₆₄.₅ is used for the fabrication of photonic crystal cavities. Quality factors of up to 13000 are demonstrated. The low nonlinear losses have enabled the demonstration of second and third harmonic generation in those cavities with powers up to twice as high as possible in silicon. A computationally efficient model for designing coupled resonator bandpass filters is used to design bandpass filters. Single ring resonators are fabricated using a novel method to define the circular shape of the rings to improve the fabrication quality. The spectral responses of the ring resonators are used to determine the coupling coefficient needed for the design and fabrication of the bandpass filters. A flat top bandpass filter is fabricated and characterized as demonstration of this method. A passive all-optical regenerator is proposed, by integrating a slow-light photonic crystal waveguide with a band-pass filter based on coupled ring resonators. A route of designing the regenerator is proposed by first using the dispersion engineering results for nonlinear pulse propagation and then using the filter responses to calculate the nonlinear transfer function.
36
Boedecker, Geesche. "Resonance Fluorescence in a Photonic Crystal." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6959/.
Full textAbstract:
The problem under consideration in the thesis is a two level atom in a photonic crystal and a pumping laser. The photonic crystal provides an environment for the atom, that modifies the decay of the exited state, especially if the atom frequency is close to the band gap. The population inversion is investigated als well as the emission spectrum.
The dynamics is analysed in the context of open quantum systems. Due to the multiple reflections in the photonic crystal, the system has a finite memory that inhibits the Markovian approximation. In the Heisenberg picture the equations of motion for the system variables form a infinite hierarchy of integro-differential equations. To get a closed system, approximations like a weak coupling approximation are needed.
The thesis starts with a simple photonic crystal that is amenable to analytic calculations: a one-dimensional photonic crystal, that consists of alternating layers. The Bloch modes inside and the vacuum modes outside a finite crystal are linked with a transformation matrix that is interpreted as a transfer matrix. Formulas for the band structure, the reflection from a semi-infinite crystal, and the local density of states in absorbing crystals are found; defect modes and negative refraction are discussed.
The quantum optics section of the work starts with the discussion of three problems, that are related to the full resonance fluorescence problem: a pure dephasing model, the driven atom and resonance fluorescence in free space.
In the lowest order of the system-environment coupling, the one-time expectation values for the full problem are calculated analytically and the stationary states are discussed for certain cases.
For the calculation of the two time correlation functions and spectra, the additional problem of correlations between the two times appears. In the Markovian case, the quantum regression theorem is valid. In the general case, the fluctuation dissipation theorem can be used instead. The two-time correlation functions are calculated by the two different methods. Within the chosen approximations, both methods deliver the same result. Several plots show the dependence of the spectrum on the parameters. Some examples for squeezing spectra are shown with different approximations.
A projection operator method is used to establish two kinds of Markovian expansion with and without time convolution. The lowest order is identical with the lowest order of system environment coupling, but higher orders give different results.Die Arbeit befasst sich mit der Emission eines 2-Niveau-Atoms in einem photonischen Kristall mit einem treibenden Laser. Der photonische Kristall stellt für das Atom eine Umgebung dar, die seinen Zerfall verändert, insbesondere wenn die Übergangsfrequenz des Atoms nahe an der Bandkante ist. Es werden sowohl die Besetzungen als auch das Emissionsspektrum untersucht. Die Dynamik wird im Kontext offener Quantensysteme analysiert. Durch die vielfachen Reflexionen im photonischen Kristall hat das System ein endliches Gedächtnis, das die Markov-Näherung verhindert. Im Heisenberg-Bild stellen die Bewegungsgleichungen für die Systemvariablen eineunendliche Hierachie von Integro-Differentialgleichungen dar. Um ein geschlossenes System zu erhalten, sind Näherungen wie eine schwache Kopplung nötig. Zunächst wird ein einfacher photonischer Kristall betrachtet.: Der eindimensionale photonische Kristall, der aus wechselnden Lagen besteht. Die Blochmoden innerhalb und die Vakuummoden außerhalb des endlichen photonischen Kristalls sind durch eine Transformationsmatrix, die als Transfermatrix interpretiert werden kann, miteinander verbunden. Einfache Formeln für die Bandstruktur, Reflexion eines halb-unendlichen Kristalls, die lokale Zustandsdichte im absorbierenden Kristall werden gefunden; außerdem werden Defektmoden und negative Brechung diskutiert. Im quantenoptischen Teil der Arbeit werden zu Anfang drei Probleme diskutiert, die im Zusammenhang zum Problem der Resonanzfluoreszenz stehen und die analytisch berechnet werden können: Ein Dephasierungsmodell, das getriebenen Atom und Resonanzfluoreszenz im freien Raum. In der niedrigsten Ordnung der System-Bad-Kopplung werden die Erwartungswerte analytisch berechnet und die stationären Zustände werden für bestimmte Fälle diskutiert. Bei der Berechnung der Zweizeitkorrelationsfunktion und der Spektren taucht das zusätzliche Problem der Korrelationen zwischen den beiden Zeiten auf. Im Markov-Fall gilt das Quantenregressionstheorem. Im allgemeinen Fall kann stattdessen das Fluktuations-Dissipations-Theorem benutzt werden. Die Korrelationsfunktionen werden mit zwei verschiedenen Methoden berechnet. Innerhalb der gewählten Näherungen liefern beide Methoden dasselbe Resultat. Einige Plots zeigen die Abhängigkeit des Spektrums von den verschiedenen Parametern. Mehrere Beispiele für Squeezing-Spektren werden mit den verschiedenen Näherungen gezeigt. Eine Projektions-Operator-Methode wird benutzt, um zwei Arten einer Markov-Entwicklung zu implementieren, mit und ohne Faltungsintegral. Die niedrigste Ordnung ist identisch mit der niedrigsten Ordnung der System-Bad-Kopplung, wohingegen höhere Ordnungen andere Resultate ergeben.
37
Chen, Yong. "Hole control in photonic crystal fibres." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616649.
Full textAbstract:
Photonic crystal fibres (PCFs) are special fibres with air holes which run along the whole fibre length. These holes not only determine the fibres' unique properties, but also provide a new degree of freedom for fibre modications. In this thesis, we focus on hole control in PCFs from two perspectives: during their fabrication and after they have been made. We found for the first time that the direct information of viscosity was not necessary for description of the fibre drawing process. This conclusion matched our experimental results without recourse to any adjustable fitting parameters. By post-processing of PCFs, which modifies the cladding and core structure and shape, we have achieved a series of novel devices for both linear and nonlinear applications. We have demonstrated fibre devices with cores resembling Young's double slits that have good performance in terms of compatibility and intensity enhancement for a specific application in fibre optic spectrometers. The bulk of this thesis reports on higher-order modes and their nonlinear applications. We achieved all-fibre, low loss and broadband mode converters in highly nonlinear PCFs (HNPCFs) which converted the fundamental mode (LP01) to a higher-order mode (LP02), which can then be converted back if necessary. This higher-order mode has been used for supercontinuum (SC) generation and four wave mixing (FWM) at wavelengths unobtainable for the fundamental mode. This is achieved by utilising the profound dispersion properties of the higher-order mode. We also demonstrated another kind of mode conversion: from the fundamental mode to a Bessel-like beam or its Fourier transform version, an annular beam. Three different methods were implemented experimentally to achieve this non-diffractive, self-healing beam.
38
Chen, Raymond M. Eng Massachusetts Institute of Technology. "Photoacoustic photonic crystal fiber gas sensor." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41258.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 89-93).
Photoacoustic spectroscopy (PAS) is a form of laser spectroscopy that has demonstrated very high sensitivity for gas detection. Typically, PAS involves the absorption of a modulated laser beam by the gas species of interest, and the subsequent generation of acoustic waves at the modulation frequency. The amplitude of the acoustic signal, which can be measured by a microphone, can be amplified by several orders of magnitude with a properly designed gas cell used as an acoustic resonator. In recent times, hollow-core photonic crystal fiber (HC-PCF) has emerged as superior gas cell for standard absorption-based laser spectroscopy due to its small size, compatibility with fiber-based optical components, and easily attainable long light-gas interaction path lengths. However, the possibility of utilizing HC-PCF as a gas cell for PAS has yet to be explored. The size and structure of HC-PCF demands that a new method of PA signal detection must be proposed, because the conventional use of microphones for PAS is not applicable. This thesis describes the development of a proposed novel use of HC-PCF as a PA gas cell from theoretical support to experimental realization. A number of unresolved experimental issues prevented data on the performance of the constructed system from being obtained. These problems are discussed, and recommendations for further study, including several proposed measures to overcome these experimental issues, are made in the conclusion to the thesis.
by Raymond Chen.
M.Eng.
39
Cowan, Benjamin M. "Photonic crystal laser-driven accelerator structures /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
40
Kiliç, Onur. "Fiber based photonic-crystal acoustic sensor /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
41
Zhu, Rui. "Integrated nano-optomechanics in photonic crystal." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS258/document.
Full textAbstract:
Les oscillateurs de référence de haute pureté sont actuellement utilisés dans un grand nombre d’applications allant du contrôle de fréquence aux horloges pour les radars, les GPS et l’espace... Les tendances actuelles dans ce domaine requièrent des architectures miniaturisées avec la génération de signaux directement dans la gamme de fréquences d’intérêt, autour de quelques GHz. Récemment, de nouvelles architectures basées sur les principes de l’optomécanique ont vu le jour dans ce but. De tels oscillateurs optomécanique génèrent non seulement des signaux hyperfréquences directement dans la gamme de fréquences GHz avec éventuellement un faible bruit de phase, mais permettent également un degré élevé d'intégration sur puce. Ce travail de thèse s'inscrit dans cette démarche. L’oscillateur optomécanique étudié se compose de cavités à cristaux photoniques suspendues couplées à des guides d’ondes silicium sur isolant intégrés dans une architecture tridimensionnelle. Ces cavités abritent des modes optiques fortement confinés autour de 1550nm et des modes mécaniques dans le GHz. De plus, ces structures présentent un recouvrement spatial entre phonon et photon élevé. Il en résulte un couplage optomécanique amélioré. Cette force de couplage optomécanique améliorée est ici sondée optiquement sur des structures à cristaux photoniques de conception optimisée. Ces cavités sont réalisées dans des matériaux semi-conducteurs III-V dont la piézoélectricité nous permet d'intégrer des outils supplémentaires pour sonder et contrôler les vibrations mécaniques via un pilotage capacitif, piézoélectrique ou acoustique. Ce contrôle total des modes mécaniques et de l’interaction optomécanique ouvre la voie à la mise en œuvre de circuits intégrés pour le verrouillage par injection et des boucles de rétroaction permettant de réduire le bruit de phase de l’oscillateurHigh purity reference oscillators are currently used in a wide variety of frequency control and timing applications including radar, GPS, space... Current trends in such fields call for miniaturized architectures with direct signal generation in the frequency range of interest, around few GHz. Recently, novel optomechanically-enhanced architectures have emerged with this purpose. Such optomechanically-driven oscillators not only generate microwave signals directly in the GHz frequency range with possibly low phase noise but also are amenable to a high degree of integration on single chip settings. This PhD work falls within this scope. The optomechanically-driven oscillator under study consists of suspended photonic crystal cavities coupled to integrated silicon-on-insulator waveguides in a three-dimensional architecture. These cavities harbor highly-confined optical modes around 1,55 µm and mechanical modes in the GHz and most importantly, feature a high phonon-photon spatial overlap, all resulting in an enhanced optomechanical coupling. This enhanced optomechanical coupling strength is here probed optically on photonic crystal structures with optimized design. These cavities are hosted in III-V semiconductor materials whose piezoelectricity enable us to integrate additional tools for probing and controlling mechanical vibrations via capacitive, piezoelectric or acoustic driving. This full control over the mechanical modes and optomechanical interaction, paves the way towards the implementation of integrated injection locking circuits of feedback loops for reducing the phase noise of the oscillator
42
CLEMENTI, MARCO. "Nonlinear Optics in Photonic Crystal Cavities." Doctoral thesis, Università degli studi di Pavia, 2020. http://hdl.handle.net/11571/1317094.
Full textAbstract:
Harnessing the properties of light for technological applications is perhaps the ultimate objective of photonics, whereas the generation, manipulation and detection of light in chip-based structures has an important impact both on industry and on fundamental research1. The integration to semiconductor-based nanostructures makes possible the application of the photonics paradigm to compact devices which on one hand enable the processing of information at high speed, and on the other hand allow to include, onto a single chip, complex experimental apparatuses, opening the way towards novel technological and physical applications. In this perspective, an effective light-matter interaction is primarily important, as this feature greatly enhances capability of integrated optical and opto-electronic devices, in terms of switching time, energy consumption and spectrum of applications.
For these reasons, the development of structures capable to enhance the interaction of light and matter covers great interest in the field of integrated optics. In this thesis work, we investigate on the linear and nonlinear properties of photonic crystal (PhC) microresonators2, a specific type of integrated optical cavity which capabilities to confine the electromagnetic field both in time and space are particularly suited for enhanced photonic devices. In particular, this type of nanostructure benefits from an enhanced nonlinear response with respect to bulk or non-resonant nonlinear devices, and they are characterized by a minimal footprint, a crucial feature in view of integration, thanks to a Bragg-type physical confinement mechanism.
Throughout the work, we focus on three specific topics. The first one consists in the design, fabrication and characterization of PhC cavities realized in silicon suspended membranes, designed for the demonstration of integrated optical frequency combs. These rely on a specific cavity design, engineered to provide equally spaced resonances in energy, as a consequence of the effective confinement potential3. We discuss experimental results showing comb-like resonant spectra and we investigate the possibility to use the structures for the implementation of triply-resonant nonlinear processes, such as four-wave mixing (FWM), with unprecedented conversion efficiency.
In a second part, we investigate on the suitability of a novel material, silicon-rich silicon nitride (SRSN)4, for the fabrication of PhC cavities and their operation as nonlinear devices. We show how SRSN deposited films can be successfully used to fabricate high-quality factor PhC cavities and we experimentally study the generation of second- and third-harmonic under resonant pumping regime.
Finally, we investigate the suitability of otherwise parasitic nonlinear effects, related to two-photon absorption in silicon microcavities, for the implementation of nonlinear properties based on the dynamical thermo-optic response of the material. We show that the PhC platform provides a way to achieve narrow spectral holes and gain windows, associated to a pronounced dispersion. This feature, associated to a dramatic decrease in group velocity, can be exploited to achieve slow-light on a chip exclusively via thermo-optic effect, in a completely novel approach.
1. Thomson, D. et al. Roadmap on silicon photonics. J. Opt. 18, 073003 (2016).
2. Notomi, M. Manipulating light with strongly modulated photonic crystals. Reports Prog. Phys. 73, 096501 (2010).
3. Alpeggiani, F., Andreani, L. C. & Gerace, D. Effective bichromatic potential for ultra-high Q-factor photonic crystal slab cavities. Appl. Phys. Lett. 107, 261110 (2015).
4. Clementi, M. et al. Cavity-enhanced harmonic generation in silicon rich nitride photonic crystal microresonators. Appl. Phys. Lett. 114, 131103 (2019).
43
Williams, Gareth Owen Scott. "Photochemical kinetics and fluorescence spectroscopy in photonic crystal fibres." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/11747.
Full textAbstract:
This thesis describes work carried out to demonstrate the use of photonic crystal fibres for the study of photochemistry reaction kinetics and fluorescence spectroscopy. Photonic crystal fibre allows the guidance of light, in a well-defined mode, over long path lengths. When the fibre’s microstructure is filled with a sample solution this, therefore, provides a greatly increased measurement path length and greater light-sample interaction than is possible in conventional spectroscopic systems, leading to enhanced sensitivity whilst greatly reducing the required sample volumes. The use of photonic crystal fibre as a micro reaction chamber for carrying out photochemical reactions and the study of their kinetics was achieved through monitoring the photoisomerisation of two azobenzene-based dyes, Disperse Red 1 and Disperse Orange 1, using real-time UV/Vis absorption spectroscopy. Both the 488 nm excitation laser and the broadband light source for the measurements were co-coupled through the fibre, giving perfect overlap of both with the sample. The fibre used for the measurements was a hollow core kagomé-type fibre with a core diameter of 19μm, giving a sample volume of 2.8 nL cm-1. The 30 cm path-length of the fibre allowed the use of sample concentrations down to 5×10-6 M, over an order of magnitude lower than in a conventional 1cm cuvette, with a sample volume of 90 nl in the core, a reduction of five orders of magnitude over conventional measurements. The kinetics of the photoisomerisation from the trans to the cis isomers of the dyes and the thermally driven cis-to-trans isomerisation could be tracked on the ms timescale, using a grating spectrometer which recorded the entire absorption spectrum of the dye. The data were numerically fitted using a custom model to take into account the properties of the fibre system. This led to the calculation of rate constants for the isomerisation processes in good agreement with those previously measured for these dye systems in bulk solution. Furthermore, the measurement of the dyes in pentane, in which they are highly insoluble, could be achieved due to the low concentrations that could be used; such measurements have not previously been reported. For the study of photonic crystal fibre as a system for the excitation and collection of fluorescence, two types of fibre were used; the same kagomé hollow-core fibre used for the photochemistry absorption measurements and a suspended-core “Mercedes” fibre. This allowed for the excitation of fluorophores in two contrasting environments. In the kagomé fibre fluorophores in bulk solution are excited whilst, in the Mercedes fibre, only fluorophores either on or in close proximity to the silica core interact with the evanescent field of the excitation light. The Fluorescein fluorophore was used initially to measure the detection limits in both fibre types and limits of 2x10-11 M in the kagomé and 10-9 M in the Mercedes fibre were obtained. This equates to 106 molecules in the kagomé fibre, which displays the lower detection limit due to greater light-sample interaction. Two-photon excitation of the Fluorescein fluorophore was then carried out using a mode-locked Ti-Sapphire laser as an excitation source, demonstrating the ability of the fibre system to sustain two-photon excitation of a long (30 cm) path length. The two-photon measurements showed remarkable detection sensitivity allowing detection of fluorescence from 10-9 M solutions of Fluorescein, showing the potential of using PCF for two-photon based experiments which are of particular interest in fields such as photodynamic therapy. A further study was carried out, using the two fibre types, for measurement of the fluorescence lifetime of the Rhodamine B fluorophore. Unperturbed lifetimes could be measured in the fibres showing no interference from the fibre. The measurements confirmed, in reference to known lifetime values, that in the kagomé fibre the excited fluorophores are in the bulk solution with only a minor influence from surface effects, whilst in the Mercedes fibre all of the excited molecules experience interaction with the surface of the silica core. This, therefore, gives a method of locating the fluorophores with respect to the fibre surface and the ability to choose between measurement of bulk solution and long path-length evanescent field-induced fluorescence.
44
Schulz, Sebastian Andreas. "Propagation loss in slow light photonic crystal waveguides." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2837.
Full textAbstract:
The field of nanophotonics is a major research topic, as it offers potential solutions to important challenges, such as the creation of low power, high bandwidth interconnects or optical sensors. Within this field, resonant structures and slow light waveguides are used to improve device performance further. Photonic crystals are of particular interest, as they allow the fabrication of a wide variety of structures, including high Q-factor cavities and slow light waveguides. The high scattering loss of photonic crystal waveguides, caused by fabrication disorder, however, has so far proven to be the limiting factor for device applications. In this thesis, I present a detailed study of propagation loss in slow light photonic crystal waveguides. I examine the dependence of propagation loss on the group index, and on disorder, in more depth than previous work by other authors. I present a detailed study of the relative importance of different components of the propagation loss, as well as a calculation method for the average device properties. A new calculation method is introduced to study different device designs and to show that photonic crystal waveguide propagation loss can be reduced by device design alone. These “loss engineered” waveguides have been used to demonstrate the lowest loss photonic crystal based delay line (35 dB/ns) with further improvements being predicted (< 20 dB/ns). Novel fabrication techniques were investigated, with the aim of reducing fabrication disorder. Initial results showed the feasibility of a silicon anneal in a nitrogen atmosphere, however poor process control led to repeatability issues. The use of a slow-fast-slow light interface allowed for the fabrication of waveguides spanning multiple writefields of the electron-beam lithography tool, overcoming the problem of stitching errors. The slow-fast-slow light interfaces were combined with loss engineering waveguide designs, to achieve an order of magnitude reduction in the propagation loss compared to a W1 waveguide, with values as low as 130 dB/cm being achieved for a group index around 60.
45
Quan, Qimin. "Photonic Crystal Nanobeam Cavities for Biomedical Sensing." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10421.
Full textAbstract:
Manipulation of light at the nanoscale has the promise to enable numerous technological advances in biomedical sensing, optical communications, nano-mechanics and quantum optics. As photons have vanishingly small interaction cross sections, their interactions have to be mitigated by matters (i.e. quantum emitters, molecules, electrons etc.). Waveguides and cavities are the fundamental building blocks of the optical circuits, which control or confine light to specific matters of interest. The first half of the thesis (Chapters 2 & 3) focuses on how to design various photonic nanostructures to manipulate light on nano- to micro- scale, especially to modify the light-matter interaction properties. Chapter 2 discusses how nano-slot waveguides and photonic crystal nanobeam waveguides are able to modify the emission of quantum emitters, in a different way that normal ridge waveguides are not able to. Chapter 3 focuses on a more complicated and powerful structure: the photonic crystal nanobeam cavity. The design, fabrication and characterization of the photonic crystal nanobeam cavities are described and demonstrated in detail, which lays out the foundation of the biomedical sensing applications in the second half of the thesis. The second half of the thesis (Chapters 4 & 5) focuses on the application of photonic crystal nanobeam cavities in the label-free sensing of biomedical substances. Chapter 4 demonstrates detection of solutions with different refractive index (aceton, methanol, IPA etc.), glucose concentration, single polystyrene nanoparticles and single streptavidin bio-molecules. Chapter 4 proposes a novel nonlinear optical method to further enhance the sensitivity. Chapter 4 also demonstrates high quality nanobeam cavities fabricated in polymers, that open up a new route to decrease the cost, as well as to achieve novel applications with functional polymers. The broader impact of this technology lies in its potential of commercialization of a new generation of biosensors with high sensitivity and high integration. Chapter 5 discusses progresses towards instrumentation of the nanobeam cavity sensing technology for research & development apparatus, as well as point-of-care diagnostic tools.Engineering and Applied Sciences
46
Lee, Jonathan Chaosung. "Fabrication and Characterization of Single-Crystal Diamond Photonic Cavities." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10964.
Full textAbstract:
Cavity quantum electrodynamics provide a platform to form a quantum network which connects individual quantum bits (qubits) via photon. Optical cavity, a device which traps photons in a confined volume can enhance the interaction between photons and the qubits serves as fundamental building block for a quantum network. Nitrogen vacancy (NV) centers in diamond has emerged as one of the leading solid-state qubits because of its long spin coherence time and single photon emission properties at room temperature. Diamond optical micro-cavities are highly sought after for coupling with NV centers. Fabrication of optical cavities from nano-crystalline diamond film has been demonstrated previously. The quality factor (Q) of such devices was limited by the material properties of the nano-crystalline diamond film. Fabrication of single-crystal diamond photonic cavities is challenging because there is no trivial way to form thin diamond film with optical isolation. In this thesis, we describe an approach to fabricate high quality single-crystal diamond optical cavities for coupling to NV centers in diamond. ingle-crystal diamond membranes were generated using an ion-slicing method. Whispering gallery modes were observed for the first time from microdisk cavities made from such material. However, the cavity Q (∼ 500) was limited by the ion damage created during processing. By using an homo-epitaxial overgrowth method, a high quality diamond film can be grown on the ion damaged membranes. Microdisk cavities with Q ∼ 3,000 were fabricated on these improved materials. Diamond membranes with a delta-doped layer of NV can be made using a slow overgrowth process which demonstrate the position and density of NV centers can be controlled in these membranes. Photonic crystal cavities with Q ∼ 4,000 were fabricated from the delta-doped membranes with cavity resonance near the zero phonon line of NV centers. Different color centers can also be introduced during the overgrowth process, and optical coupling of an ensemble of silicon vacancy centers is demonstrated by coupling to a diamond microdisk cavity. We believe the techniques developed in this thesis could contribute to building of a quantum photonic network using diamond as a platform.Engineering and Applied Sciences
47
Bergenek, Krister. "Thin-film photonic crystal LEDs with enhanced directionality." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/912.
Full text
48
Khankhoje, Uday Kiran. "Photon Confinement in Photonic Crystal Cavities." Thesis, 2010. https://thesis.library.caltech.edu/5873/1/thesis-uday-full.pdf.
Full textAbstract:
In this thesis, the use of photonic crystal cavities for experiments in cavity quantum-electrodynamics is described. To this end, the propagation of light in photonic crystals, and the creation of cavities by making defects in the photonic crystal lattice, is discussed. By drawing an analogy with Fabry-Perot etalons, the mechanism of light confinement in these cavities is explained. It is shown that by engineering the immediate cavity neighborhood, the mirror reflectivities can be increased, resulting in a very high quality factor (Q) and low mode volume. Photonic crystal cavity designs used in this thesis are introduced, along with numerically computed data of their performance.
Device fabrication in gallium arsenide wafers is described in detail, with special attention to address factors that lead to a lack of reproducibility. Over the course of this thesis effort, several thousand cavities were fabricated, and a wide range of Qs were recorded. Careful experiments were performed to determine the causes of low Qs, both at the wafer growth level, and at the fabrication level. Technological improvements in wafer growth are reported, as well as fabrication techniques to improve cavity Q.
These cavities contain indium arsenide quantum dots (QDs) as internal light sources. Cavity-induced enhancement of QD light emission is discussed, along with interferometric measurements of photon correlations. It is found that light emission from coupled QD-cavity systems is highly non-classical, and this quantum nature is characterized by means of a second order correlation function.
To conclude, a novel application of high-Q cavities is discussed, that of an electrically-pumped laser fabricated in a 1D nanobeam cavity. The salient feature of such a geometry is that a high Q is retained even with the introduction of gold in the cavity vicinity. Finally, approaches to improve cavity Q by material system optimizations are explored. In the first approach, QD growth in III-V material systems with light emission wavelengths in the telecommunications wavelength range (λ ≈ 1.55 μm) is discussed, and in the second, the growth of III-V-based active media in silicon structures is considered.
49
Lin, Jian-Hung, and 林建宏. "Photonic Crystal and Circular Photonic Crystal-Design and Fabrication." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/14241637516895754577.
Full textAbstract:
博士國立中正大學
物理所
96
Different methods for fabrication of photonic crystals (PhCs) and photonic quasicrystals (PQCs) were theoretically and experimentally investigated. Firstly, we demonstrated a simple and useful method based on multi-exposure of two-beam interference pattern, to fabricate different kinds of 2D and 3D periodic structures. Square and hexagonal 2D structures were fabricated by a double-exposure with a rotation angle of 90o and 60o between two exposures, respectively. Three-exposure, in particular, resulted in different kinds of 3D structures (face-centered cubic, simple cubic, hexagonal-hexagonal, hexagonal-rectangular, etc.), with close lattice constants in transverse and longitudinal directions, which is difficult to be obtained by the commonly used multi-beam interference technique. The experimental results obtained with either SU-8 negative or AZ-4620 positive photoresist are well in agreement with the theoretical predictions. Secondly, we demonstrated that the combination of the interference and the direct laser writing employing multi-photon polymerization effect is an ideal method to fabricate periodic structures with desired defects. In particular, the defect has been embedded in desired position and orientation by adopting a double-step scanning microscopy. Indeed, multi-exposure of two-beam interference technique was first used to create 2D PhCs template. Low power femtosecond laser combined with high numerical aperture objective lens was then used to map the periodic structure in order to determine the positions and orientations of air-holes or material-cylinders, without the intermediate development. Based on mapping results, desired defects were written precisely into these structures by increasing the power of femtosecond laser to induce multi-photon polymerization effect. The experimental results show that defects are patterned with accurate positions and orientations. These proposed techniques should be useful for fabrication of PhCs without and with well-defined defects. Finally, we investigated theoretically the optical properties of a new PQC, so called circular photonic crystals (CPCs). Namely, we compared the photonic gap properties of air-rods CPC with and without phase shift and found the original reason for its isotropic gap property. The simulations results show that the air-rods CPC without phase shift has a small anisotropic photonic gap. With increasing the phase shift term, the photonic gap of CPC becomes more isotropic. Indeed, with a phase shift of 45 degree, the variations of upper gap edge, lower gap edge, and gap width become less than 1%. This excellent property is attributed to the complete circular symmetry of the CPC with a large phase shift, indicated by the Fourier transform calculation and the diffraction pattern measurement. In particular, we found an existent whispering galley mode for the CPC having phase shift, which could serve for many applications such as defect-free photonic crystal laser, etc.
50
Yang, Lu-Lin, and 楊玉麟. "Investigation on ARROW-Based Photonic Crystal Waveguide Devices and 3D Copper Photonic Crystals." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/70212597042301889780.
Full textAbstract:
博士國立交通大學
電子工程系所
97
The photonic crystal slab waveguides based on antiresonant reflecting optical waveguide (ARROW) structures are proposed for improving the butt-coupling efficiency with a single-mode fiber. Lightwaves propagating in this waveguide are confined by the photonic band gaps in lateral and antiresonance reflection in vertical. Numerical methods for analyzing and designing this devices are introduced. Modal characteristics of the ARROW structures are revealed. The photonic band structures and transmission behaviors of the two-dimensional photonic crystal waveguides are discussed. By combining the advantages of these two devices, the ARROW-based photonic crystal waveguides are analyzed and designed. In this platform, the important devices such as the 60, 120 sharp bends, and Y-branch waveguides are designed for substantially reducing the areas of the photonic integrated circuits. The three-dimensional copper photonic crystals with two feature sizes were fabricated layer-by-layer. The optical properties of the photonic band gaps for both structures have been investigated by experimental observation and simulation verification. With these devices, the suppression of the thermal emission in the ranges of band gaps and the narrow-band emission near the band-edge wavelengths have been experimentally observed.