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1
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.
Texte intégralRésumé :
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
2
González, Xavier (Xavier R. González Barrios). « Edible photonic crystals tunable within the visible regime ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/112496.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 50-52).
An experimental study was performed to design and fabricate an edible photonic crystal made of alternating layers of food grade titanium dioxide and agar that is able to selectively reflect wavelengths of light within the visible spectrum and allow for dynamic color changes through the tuning mechanism of swelling its agar layers with the addition of edible solvents. After doing a literature search to discover which materials were available to create this edible photonic structure, a trial and error process was conducted using deposition and film thickness characterization techniques to optimize the physical and optical characteristics of the layers composing the photonic structure. The materials selected for the layers in the structure yield a high refractive index contrast, which allows for high reflectivity with a reduced amount of total layers. The multilayer stack can be designed to reflect particular wavelengths by selecting the thickness of the layers accordingly. Thin film characterization took place through the use of profilometry, ellipsometry, and atomic force microscopy. The feasibility and practicality of two manufacturing techniques, spin-coating and RF-sputtering, were analyzed in the process of learning how to assemble an edible multilayer stack for molecular gastronomy applications.
by Xavier González/
S.B.
3
Wong, Chee Wei 1975. « Strain-tuning of periodic optical devices : tunable gratings and photonic crystals ». Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17008.
Texte intégralRésumé :
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. [161]-173).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The advancement of micro- and nano-scale optical devices has heralded micromirrors, semiconductor micro- and nano-lasers, and photonic crystals, among many. Broadly defined with the field of microphotonics and microelectromechanical systems, these innovations have targeted applications in integrated photonic chips and optical telecommunications. To further advance the state-of-the-art, dynamically tunable devices are required not only for demand-based reconfiguration of the optical response, but also for compensation to external disturbances and tight device fabrication tolerances. In this thesis, specific implementations of strain-tunability in two photonic devices will be discussed: the fundamental diffractive grating element, and a photonic band gap microcavity waveguide. For the first part, we demonstrate high-resolution analog tunability in microscale diffractive optics. The design concept consists of a diffractive grating defined onto a piezoelectric-driven deformable membrane, microfabricated through a combination of surface and bulk micromachining. The grating is strain-tuned through actuation of high-quality thin-film piezoelectric actuators. Device characterization shows grating period tunability on the order of a nanometer, limited by measurement uncertainty and noise. The results are in good agreement with analytical theory and numerical models, and present immediate implications in research and industry. For the second part, we generalize the piezoelectric strain-tunable membrane platform for strain-tuning of a silicon photonic band gap microcavity waveguide. Additional motivation for this strain-tuning approach in silicon photonic crystals lies in:
(cont.) (a) the virtual absence of electro-optic effects in silicon, and (b) the ability to achieve tuning with low power requirements through piezoelectric actuation. Compared to current thermo-optics methods, piezoelectric actuation affords faster and more localized tuning in high-density integrated optics. The small-strain perturbation on the optical resonance is analyzed through perturbation theory on unperturbed full 3D finite-difference time-domain numerical models. Device fabrication involves X-ray nanolithography and multi-scale integration of micro- and nano-fabrication methods. Experimental characterization achieved dynamically-tunable resonances with 1.54 nm tunable range (at 1.55 Mum optical wavelengths), in good agreement with theory. This is the first demonstration of strain tunability in photonic crystals and contributes to the development of smart micro- and nano-scale photonics.
by Chee Wei Wong.
Sc.D.
4
Rey, Isabella H. « Active slow light in silicon photonic crystals : tunable delay and Raman gain ». Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3356.
Texte intégralRésumé :
In the past decade, great research effort was inspired by the need to realise active optical functionalities in silicon, in order to develop the full potential of silicon as a photonic platform. In this thesis we explore the possibility of achieving tunable delay and optical gain in silicon, taking advantage of the unique dispersion capabilities of photonic crystals. To achieve tunable optical delay, we adopt a wavelength conversion and group velocity dispersion approach in a miniaturised engineered slow light photonic crystal waveguide. Our scheme is equivalent to a two-step indirect photonic transition, involving an alteration of both the frequency and momentum of an optical pulse, where the former is modified by the adiabatic tuning possibilities enabled by slow light. We apply this concept in a demonstration of continuous tunability of the delay of pulses, and exploit the ultrafast nature of the tuning process to demonstrate manipulation of a single pulse in a train of two pulses. In order to address the propagation loss intrinsic to slow light structures, with a prospect for improving the performance of the tunable delay device, we also investigate the nonlinear effect of stimulated Raman scattering as a means of introducing optical gain in silicon. We study the influence of slowdown factors and pump-induced losses on the evolution of a signal beam along the waveguide, as well as the role of linear propagation loss and mode profile changes typical of realistic photonic crystal structures. We then describe the work conducted for the experimental demonstration of such effect and its enhancement due to slow light. Finally, as the Raman nonlinearity may become useful also in photonic crystal nanocavities, which confine light in very small volumes, we discuss the design and realisation of structures which satisfy the basic requirements on the resonant modes needed for improving Raman scattering.
5
Lu, Shin-Ying. « Electrically-tunable Colors of Chiral Liquid Crystals for Photonic and Display Applications ». Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1279299037.
Texte intégral
6
Welna, Karl P. « Electrically injected photonic-crystal nanocavities ». Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2528.
Texte intégralRésumé :
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.
7
Li, Jun. « REFRACTIVE INDICES OF LIQUID CRYSTALS AND THEIR APPLICATIONS IN DISPLAY AND PHOTONIC DEVICES ». Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2200.
Texte intégralRésumé :
Liquid crystals (LCs) are important materials for flat panel display and photonic devices. Most LC devices use electrical field-, magnetic field-, or temperature-induced refractive index change to modulate the incident light. Molecular constituents, wavelength, and temperature are the three primary factors determining the liquid crystal refractive indices: ne and no for the extraordinary and ordinary rays, respectively. In this dissertation, we derive several physical models for describing the wavelength and temperature effects on liquid crystal refractive indices, average refractive index, and birefringence. Based on these models, we develop some high temperature gradient refractive index LC mixtures for photonic applications, such as thermal tunable liquid crystal photonic crystal fibers and thermal solitons. Liquid crystal refractive indices decrease as the wavelength increase. Both ne and no saturate in the infrared region. Wavelength effect on LC refractive indices is important for the design of direct-view displays. In Chapter 2, we derive the extended Cauchy models for describing the wavelength effect on liquid crystal refractive indices in the visible and infrared spectral regions based on the three-band model. The three-coefficient Cauchy model could be used for describing the refractive indices of liquid crystals with low, medium, and high birefringence, whereas the two-coefficient Cauchy model is more suitable for low birefringence liquid crystals. The critical value of the birefringence is deltan~0.12. Temperature is another important factor affecting the LC refractive indices. The thermal effect originated from the lamp of projection display would affect the performance of the employed liquid crystal. In Chapter 3, we derive the four-parameter and three-parameter parabolic models for describing the temperature effect on the LC refractive indices based on Vuks model and Haller equation. We validate the empirical Haller equation quantitatively. We also validate that the average refractive index of liquid crystal decreases linearly as the temperature increases. Liquid crystals exhibit a large thermal nonlinearity which is attractive for new photonic applications using photonic crystal fibers. We derive the physical models for describing the temperature gradient of the LC refractive indices, ne and no, based on the four-parameter model. We find that LC exhibits a crossover temperature To at which dno/dT is equal to zero. The physical models of the temperature gradient indicate that ne, the extraordinary refractive index, always decreases as the temperature increases since dne/dT is always negative, whereas no, the ordinary refractive index, decreases as the temperature increases when the temperature is lower than the crossover temperature (dno/dT<0 when the temperature is lower than To) and increases as the temperature increases when the temperature is higher than the crossover temperature (dno/dT>0 when the temperature is higher than To ). Measurements of LC refractive indices play an important role for validating the physical models and the device design. Liquid crystal is anisotropic and the incident linearly polarized light encounters two different refractive indices when the polarization is parallel or perpendicular to the optic axis. The measurement is more complicated than that for an isotropic medium. In Chapter 4, we use a multi-wavelength Abbe refractometer to measure the LC refractive indices in the visible light region. We measured the LC refractive indices at six wavelengths, lamda=450, 486, 546, 589, 633 and 656 nm by changing the filters. We use a circulating constant temperature bath to control the temperature of the sample. The temperature range is from 10 to 55 oC. The refractive index data measured include five low-birefringence liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 (delta_epsilon=-4.2), MLC-6241-000, and UCF-280 (delta_epsilon=-4); four middle-birefringence liquid crystals, 5CB, 5PCH, E7, E48 and BL003; four high-birefringence liquid crystals, BL006, BL038, E44 and UCF-35, and two liquid crystals with high dno/dT at room temperature, UCF-1 and UCF-2. The refractive indices of E7 at two infrared wavelengths lamda=1.55 and 10.6 um are measured by the wedged-cell refractometer method. The UV absorption spectra of several liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 and TL-216 are measured, too. In section 6.5, we also measure the refractive index of cured optical films of NOA65 and NOA81 using the multi-wavelength Abbe refractometer. In Chapter 5, we use the experimental data measured in Chapter 4 to validate the physical models we derived, the extended three-coefficient and two-coefficient Cauchy models, the four-parameter and three-parameter parabolic models. For the first time, we validate the Vuks model using the experimental data of liquid crystals directly. We also validate the empirical Haller equation for the LC birefringence delta_n and the linear equation for the LC average refractive index Ph.D.
Optics and Photonics
Optics
8
Kovalevich, Tatiana. « Tunable Bloch surface waves devices ». Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD022/document.
Texte intégralRésumé :
Cette thèse est consacrée au développement de dispositifs accordables sur la base de cristaux photoniques unidimensionnels qui peuvent supporter des ondes de surface de Bloch (BSW). Tout d'abord, nous explorons les possibilités de contrôler la direction de propagation des BSW par le biais de la polarisation de la lumière incidente. Dans ce cas, nous gravons sur le dessus du cristal photonique 1D des structures passives de type réseau, qui permettent à la fois de coupler la lumière incidente aux BSWs et de se comporter comme une lame séparatrice ultracompacte contrôlée par la polarisation lumineuse. Nous avons testé ce type de coupleur sur des cristaux photoniques 1D fonctionnant dans l’air et dans l’eau. Ensuite, nous démontrons l'accordabilité des BSWs en ajoutant une fine couche active dans la structure photonique multicouche. Il s’agit d’un film mince de niobate de lithium monocristallin qui permet d’introduire des propriétés anisotropes dans le cristal photonique 1D. Différentes façons de fabriquer des cristaux photoniques 1D contenant du niobate de lithium monocristallin ont été développées dans le cadre de ce travail. Ces travaux nous ont permis d’explorer le concept de contrôle électro-optique des BSWsThis thesis is devoted to develop tunable devices on the base of one-dimensional photonic crystals (1DPhC) which can sustain Bloch surface waves (BSWs).First, we explore the possibilities to control the BSW propagation direction with polarization of incident light. In this case we manufacture additional passive structures such as gratings on the top of the 1DPhC, which are working both as a BSW launcher and polarization–controlled “wave-splitters”. We test this type of launcher in air and in water as an external medium. Then, we demonstrate the tunability of the BSW by adding an active layers into the multilayer stack. Here a crystalline X-cut thin film lithium niobate (TFLN) is used to introduce anisotropic properties to the whole 1DPhC. Different ways to manufacture 1D PhCs with LiNbO3 on the top would be described. Finally, we explore the concept of the electro-optically tuned BSW
9
John, Jimmy. « VO2 nanostructures for dynamically tunable nanophotonic devices ». Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI044.
Texte intégralRésumé :
L'information est devenue le bien le plus précieux au monde. Ce mouvement vers la nouvelle ère de l'information a été propulsé par la capacité à transmettre l'information plus rapidement, à la vitesse de la lumière. Il est donc apparu nécessaire de mener des recherches plus poussées pour contrôler plus efficacement les supports d'information. Avec les progrès réalisés dans ce secteur, la plupart des technologies actuelles de contrôle de la lumière se heurtent à certains obstacles tels que la taille et la consommation d'énergie et sont conçues pour être passives ou sont limitées technologiquement pour être moins actives (technologie Si-back). Même si rien ne voyage plus vite que la lumière, la vitesse réelle à laquelle les informations peuvent être transportées par la lumière est la vitesse à laquelle nous pouvons la moduler ou la contrôler. Ma tâche dans cette thèse visait à étudier le potentiel du VO2, un matériau à changement de phase, pour la nano-photonique, avec un accent particulier sur la façon de contourner les inconvénients du matériau et de concevoir et démontrer des dispositifs intégrés efficaces pour une manipulation efficace de la lumière à la fois dans les télécommunications et le spectre visible. En outre, nous démontrons expérimentalement que les résonances multipolaires supportées par les nanocristaux de VO2 (NC) peuvent être réglées et commutées dynamiquement en exploitant la propriété de changement de phase du VO2. Et ainsi atteindre l'objectif d'adaptation de la propriété intrinsèque basée sur le formalisme de Mie en réduisant les dimensions des structures de VO2 comparables à la longueur d'onde de fonctionnement, créant un champ d'application pour un métamatériau accordable défini par l'utilisateurInformation has become the most valuable commodity in the world. This drive to the new information age has been propelled by the ability to transmit information faster, at the speed of light. This erupted the need for finer researches on controlling the information carriers more efficiently. With the advancement in this sector, majority of the current technology for controlling the light, face certain roadblocks like size, power consumption and are built to be passive or are restrained technologically to be less active (Si- backed technology). Even though nothing travels faster than light, the real speed at which information can be carried by light is the speed at which we can modulate or control it. My task in this thesis aimed at investigating the potential of VO2, a phase change material, for nano-photonics, with a specific emphasis on how to circumvent the drawbacks of the material and to design and demonstrate efficient integrated devices for efficient manipulation of light both in telecommunication and visible spectrum. In addition to that we experimentally demonstrate the multipolar resonances supported by VO2 nanocrystals (NCs) can be dynamically tuned and switched leveraging phase change property of VO2. And thus achieving the target tailoring of intrinsic property based on Mie formalism by reducing the dimensions of VO2 structures comparable to the wavelength of operation, creating a scope for user defined tunable metamaterial
10
Dorjgotov, Enkh-Amgalan. « Tunable Liquid Crystal Etalon and Photonic Devices ». Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1278035084.
Texte intégral
11
Du, Fang. « LIQUID CRYSTAL MATERIALS AND TUNABLE DEVICES FOR OPTICAL COMMUNICATIONS ». Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3375.
Texte intégralRésumé :
In this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic communications. The curing temperature is found to have significant effects on the PSLC performance. The electro-optic properties of nematic polymer network liquid crystal (PNLC) at different curing temperatures are investigated experimentally. At high curing temperature, a high contrast, low drive voltage, and small hysteresis PNLC is obtained as a result of the formed large LC micro-domains. With the help of curing temperature effect, it is able to develop PNLC based optical devices with highly desirable performances for optical communications. Such high performance is generally considered difficult to realize for a PNLC. In fact, the poor performance of PNLC, especially at long wavelengths, has hindered it from practical applications for optical communications for a long time. Therefore, the optimal curing temperature effect discovered in this thesis would enable PSLCs for practical industrial applications. Further more, high birefringence LCs play an important role for near infrared photonic devices. The isothiocyanato tolane liquid crystals exhibit a high birefringence and low viscosity. The high birefringence LC dramatically improves the PSLC contrast ratio while keeping a low drive voltage and fast response time. A free-space optical device by PNLC is experimentally demonstrated and its properties characterized. Most LC devices are polarization sensitive. To overcome this drawback, we have investigated the polymer-stabilized cholesteric LC (PSCLC). Combining the curing temperature effect and high birefringence LC, a polarization independent fiber-optical device is realized with over 30 dB attenuation, ~12 Vrms drive voltage and 11/28 milliseconds (rise/decay) response times. A polymer-stabilized twisted nematic LC (PS TNLC) is also proposed as a variable optical attenuator for optical communications. By using the polarization control system, the device is polarization independent. The polymer network in a PS TNLC not only results in a fast response time (0.9/9 milliseconds for rise/decay respectively), but also removes the backflow effect of TNLC which occurs in the high voltage regime.Ph.D.
Other
Optics and Photonics
Optics
12
Nishizawa, Norihiko, Youta Ito et Toshio Goto. « 0.78-0.90-μm wavelength-tunable femtosecond soliton pulse generation using photonic crystal fiber ». IEEE, 2002. http://hdl.handle.net/2237/6769.
Texte intégral
13
Garner, Brett William. « Multifunctional Organic-Inorganic Hybrid Nanophotonic Devices ». Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc6108/.
Texte intégralRésumé :
The emergence of optical applications, such as lasers, fiber optics, and semiconductor based sources and detectors, has created a drive for smaller and more specialized devices. Nanophotonics is an emerging field of study that encompasses the disciplines of physics, engineering, chemistry, biology, applied sciences and biomedical technology. In particular, nanophotonics explores optical processes on a nanoscale. This dissertation presents nanophotonic applications that incorporate various forms of the organic polymer N-isopropylacrylamide (NIPA) with inorganic semiconductors. This includes the material characterization of NIPA, with such techniques as ellipsometry and dynamic light scattering. Two devices were constructed incorporating the NIPA hydrogel with semiconductors. The first device comprises a PNIPAM-CdTe hybrid material. The PNIPAM is a means for the control of distances between CdTe quantum dots encapsulated within the hydrogel. Controlling the distance between the quantum dots allows for the control of resonant energy transfer between neighboring quantum dots. Whereby, providing a means for controlling the temperature dependent red-shifts in photoluminescent peaks and FWHM. Further, enhancement of photoluminescent due to increased scattering in the medium is shown as a function of temperature. The second device incorporates NIPA into a 2D photonic crystal patterned on GaAs. The refractive index change of the NIPA hydrogel as it undergoes its phase change creates a controllable mechanism for adjusting the transmittance of light frequencies through a linear defect in a photonic crystal. The NIPA infiltrated photonic crystal shows greater shifts in the bandwidth per ºC than any liquid crystal methods. This dissertation demonstrates the versatile uses of hydrogel, as a means of control in nanophotonic devices, and will likely lead to development of other hybrid applications. The development of smaller light based applications will facilitate the need to augment the devices with control mechanism and will play an increasing important role in the future.
14
Oliveira, Marcus Vinicius Nunes de. « Estudo de operaÃÃes lÃgicas atravÃs da modulaÃÃo por posiÃÃo de pulso no domÃnio da frequÃncia (PPFDM) em AOTF convencional e baseado em fibra de cristal fotÃnico ». Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=11498.
Texte intégralRésumé :
Neste trabalho, propomos um novo mÃtodo de modulaÃÃo Ãptica usando um filtro acÃstoÃptico sintonizÃvel (AOTF) convencional e um filtro acÃsto-Ãptico com polarizaÃÃo sintonizÃvel (AOTPF) baseado em fibra de cristal fotÃnico (PCF), onde portas lÃgicas Ãpticas E e OU sÃo obtidas pela operaÃÃo simultÃnea da modulaÃÃo em dupla banda lateral Ãptica (ODSB) e da modulaÃÃo por posiÃÃo de pulso no domÃnio da frequÃncia (PPFDM). Estes dispositivos sÃo operados com pulsos sÃlitons ultracurtos de 100 ps e 55,5 fs para o AOTF convencional e para o AOTPF baseado em PCF, respectivamente. Desta forma, um pulso leva dois bits de informaÃÃo apÃs ser criptografado pela modulaÃÃo proposta aqui. Em seguida, analisamos a modulaÃÃo ODSB-PPFDM para os pulsos de entrada, polarizados nos dois modos de entrada, permitindo uma variaÃÃo no parÃmetro de codificaÃÃo εcod para cada pulso de entrada. Para o AOTF convencional, consideramos uma diferenÃa de fase de dfi = pi rad entre ambos os pulsos de entrada. Como resultado, obtivemos vÃrios valores do parÃmetro de codificaÃÃo |εcod| onde as operaÃÃes lÃgicas E e OU foram possÃveis. JÃ para o AOTPF baseado em PCF, consideramos uma diferenÃa de fase de dfi = 1,28pi rad entre ambos os pulsos de entrada para obtermos valores do parÃmetro de codificaÃÃo |εcod| onde as operaÃÃes lÃgicas E e OU foram possÃveis.We propose a new method of optical modulation using a conventional Acousto-Optic Tunable Filter (AOTF) and an Acoustic Optic Tunable Polarization Filter (AOTPF) based on Photonic Crystal Fiber (PCF). In both devices the all-optical logic gates, namely AND and OR, are obtained by simultaneously operation of Optical Double Sideband (ODSB) modulation and a Pulse Position Frequency Domain Modulation (PPFDM). These devices shall operate with ultrashort soliton light pulses 100 ps and 55.5 fs for conventional AOTF and all-fiber AOTPF based on PCF, respectively. In this way, a pulse will carry two bits of information after been encoded by the modulation proposed here. We then analyze the modulation ODSB - PPFDM for input pulses, polarized in the two input modes, allowing a variation in the modulation parameter εcod for each input pulse. For conventional AOTF, a phase difference dfi = pi rad was considered between both input pulses, obtaining various values of the coding parameter offset |εcod| where the AND and OR logic operations were possible. For the all-fiber AOTPF based on PCF, a phase difference of dfi = 1,28pi rad was necessary between both input pulses to generate values of coding parameter offset |εcod|, for which AND and OR logic operations were possible.
15
Arsenault, Andre C. « Chemically tunable colloidal photonic crystals ». 2007. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=968442&T=F.
Texte intégral
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Chen, Zeguo. « Tunable topological phases in photonic and phononic crystals ». Diss., 2018. http://hdl.handle.net/10754/627143.
Texte intégralRésumé :
Topological photonics/phononics, inspired by the discovery of topological insulators, is a prosperous field of research, in which remarkable one-way propagation edge states are robust against impurities or defect without backscattering. This dissertation discusses the implementation of multiple topological phases in specific designed photonic and phononic crystals.
First, it reports a tunable quantum Hall phase in acoustic ring-waveguide system. A new three-band model focused on the topological transitions at the Γ point is studied, which gives the functionality that nontrivial topology can be tuned by changing the strengths of the couplings and/or the broken time-reversal symmetry. The resulted tunable topological edge states are also numerically verified.
Second, based on our previous studied acoustic ring-waveguide system, we introduce anisotropy by tuning the couplings along different directions. We find that the bandgap topology is related to the frequency and directions. We report our proposal on a frequency filter designed from such an anisotropic topological phononic crystal.
Third, motivated by the recent progress on quantum spin Hall phases, we propose a design of time-reversal symmetry broken quantum spin Hall insulators in photonics, in which a new quantum anomalous Hall phase emerges. It supports a chiral edge state with certain spin orientations, which is robust against the magnetic impurities. We also report the realization of the quantum anomalous Hall phase in phononics.
17
Zhang, Nai-wen, et 張乃文. « Negative refraction of tunable elliptical-rod photonic crystals achieved by liquid crystals ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/41444520142353213370.
Texte intégralRésumé :
碩士國立成功大學
機械工程學系碩博士班
96
Photonic crystals (PhCs) are synthetic periodic structures that,when suitably designed, have the ability to change the propagation of light. Recently, it was proved that the diffraction effects of PhCs can produce the effective negative refraction or the negative index. Hence, the studying of PhCs is not limited in the band gap region. The anomalous refractive properties (especially negative refraction) of PhCs have become hot topics of scientific research over the past few years. In this thesis, the plane wave expansion method is used to get the equifrequency surface. The anomalous refractive properties of photonic crystal are analyzed by using the equifrequency surface. Then we use the finite difference time domain method and the finite element method to simulate the light propagation in PhCs and compare the refractive angle with that predicted by the equifrequency surface. In order to change the direction of the light propagation, the two-dimension columns within photonic crystals are replaced by elliptic rod. Due to the geometric anisotropy of elliptic rods, we can rotate the elliptic rods to obtain different structure factors. The anisotropic property can then be used to tune the refraction direction. The results can be applied to develop various photonic crystal devices, such as optical switches and tunable optical splitters. The material properties of liquid crystals (LCs) can be altered easily by applying an external electric field. The LCs are infiltrated into the photonic crystal of elliptic rods and the relationship between the refractive angle and the angle of the director is studied. Owing to the large anisotropy consisting of elliptic rods, the range of negative refraction angle is superior to column. The direction of the negative refraction is controlled by changing the direction of the LCs director. The tunability was analysed at the specified frequency and a large tunable range of the negative refraction is achieved. The refraction of a tunable PhCs with nematic liquid crystals can be used to design an optical switch. Besides, the transmission of the optical switch can be improved by properly adjusting the boundary conditions.
18
Shih, Chih-Chang, et 施志昌. « Study on magnetically tunable metallic terahertz wave photonic crystals infiltrated with liquid crystal ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/43421200307249105151.
Texte intégral
19
Chang-HongWu et 吳承鴻. « optically tunable photonic crystals base on blue phase liquid crystals doped with azo-chiral material ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/rb88yf.
Texte intégral
20
Bellis, Isabella De. « Photonic crystals based on smart polymers. A new route for tunable devices ». Doctoral thesis, 2021. http://hdl.handle.net/2158/1236030.
Texte intégralRésumé :
The results of this Ph.D. thesis demonstrate the tunability of photonic platforms by introducing stimuli responsive polymers as constituents of the photonic structure itself or as thermally driven mechanical actuators. In particular, liquid crystalline networks (LCNs) were patterned by lithographic techniques, such as direct laser writing (DLW) and UV polymerization to develop and fabricate tunable photonic crystals for different applications, from tunable telecom filters to tunable structural colors and intelligent sensors, featuring good optical properties that can be controlled and modulated by multiple tuning mechanisms (e.g. temperature and light).
In order to optimize the structure design and the tunability of LCN photonic devices, the refractive index and the tunable optical anisotropy (determined by the chemical composition of the material, the fabrication parameters, and the molecular ordering) have been precisely characterized. As first, it has been demonstrated, using a refractometer method, that optical properties of these new photonic materials can be tuned by adjusting mesogenic concentration both in LCN macro- and micro-structures. The tailored chemical formulation allows not only the determination of the shape changing properties of LCNs but also the modulation of the refractive indices and the optical anisotropy of liquid crystalline mixtures, which can be tuned at different temperatures or alternatively by laser light irradiation. Aiming to increase the fabricated structure resolution, a second result demonstrated how refined fabrication resolutions, never yet reached for liquid crystalline networks, can be achieved at low polymerization temperatures (5°C-10°C) using opportune writing parameters. The resulting 3D polymerizable unit, now comparable with the typical voxel of commercial resists, enlarges the application field of photo-responsive elastic materials without degradation of the patterned structure rigidity. Indeed, a spheroidal voxel would be the best polymerization unit to fabricate three-dimensional structures, especially in 3D photonic structures as woodpile photonic crystals for which isotropic voxel dimensions are needed. The best fabrication parameters using the DLW lithographic technique at controlled temperature enabled the fabrication of the first 3D woodpile photonic crystal made by LCN, having a geometric resolution and a light transmission attenuation at the stop band comparable with photonic crystal fabricated with commercial resists. This demonstrates the effectiveness of our previous study. Such photonic crystal has been characterized using temperature as an external stimulus to tune its optical properties in order to demonstrate its potential as a tunable filter at telecom wavelength. Finally, the first proof-of-concept of a smart millimetric optical sensor was developed during a six-month period in collaboration with Prof. Li and Prof. Keller group in Paris, at ChimieParis Tech. A temperature responsive actuator has been combined with the back side of the Morpho Menelaus wing, owing an optimized structural coloration due to its natural photonic crystal structure. Two different strategies have been proposed to control the visual sensor: a macroscopic deformation of the combined system induces an iridescence variation, whereas a nanoscale contraction generates a color shift through the lamellae interspacing variation, parameter that determines the structural coloration.
In conclusion, this thesis focused on the material characterization of smart polymers and their nanopatterning for tunable photonic shows as the employ of smart LCNs can be extended from mechanical actuators and microrobotics to micrometric photonic structures for new multifunctional devices.
21
Sun, Mao-Guo, et 孫茂國. « Fabrication of Alternative Plasmonic Materials and Design of Tunable Tamm Plasmon by Hybrid Photonic Crystals ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/98437272798590609769.
Texte intégralRésumé :
碩士國立交通大學
影像與生醫光電研究所
105
Optical Tamm state is a localized surface mode that plamonic resonance occurred at the boundary between a photonic crystal and metal. Conventional optical Tamm states have been used distributed Bragg reflector (DBR) as the photonic crystal. By varying the thickness of the top layer of DBR or making DBR porous, it could possibly tune the resonant wavelengths. However, it is very difficult to control the quality or modify the thickness of DBR after a sample is fabricated. In this thesis, we choose 3D photonic crystal fabricated by nanosphere to replace DBR to excite optical Tamm state. This structure is called "Hybrid Photonic Crystal ". Hybird photonic crystal can easily tune the resonant wavelengths of Tamm state by changing the environment. In the second part of this thesis, we report the titanium nitride (TiN) as an alternative plasmonic material in visible and near-infrared region. The multi-target magnetron co-sputter system with combined high power impulse magnetron sputtering (HIPIMS) is used to fabricate TiN thin film. The optimization processing condition as well as optical characterization of TiN is introduced. We also replace the metal in optical Tamm state structure by TiN thin film to observe the Tamm plasmon resonance.
22
Hsieh, Hao-Yu, et 謝濠宇. « Integrated Intensity Tunable Optical Filter and High-efficiency Acousto-optical Interaction Based on Photonic Crystals Nano-beam Structure ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/73611532835768118754.
Texte intégral
23
Li, Guan-Huei, et 李冠輝. « Tunable photonic crystal waveguide based on liquid crystal ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/51739561733198217895.
Texte intégral
24
NOCENTINI, SARA. « Tunable polymeric photonic structures ». Doctoral thesis, 2017. http://hdl.handle.net/2158/1088792.
Texte intégralRésumé :
In this work is demonstrated how, combining soft materials and photonic structures thank to a 3D lithographic technique, is possible to create microstructured polymeric photonic devices able to reconfigure their photonic properties under a remote light stimulus.
25
Schaub, Dominic Etienne. « Dynamically Tunable Photonic Bandgap Materials ». 2010. http://hdl.handle.net/1993/4275.
Texte intégralRésumé :
Photonic bandgap materials are periodic structures that exclude electromagnetic field propagation over frequency intervals known as bandgaps. These materials exhibit remarkable wave dispersion and have found use in many applications that require control over dynamic electromagnetic fields, as their properties can be tailored by design. The two principal objectives of this thesis are the development of a liquid crystal-based microwave photonic bandgap device whose bandgap could be tuned during operation and the design and implementation of a spectral transmission-line modeling method for band structure calculations.
The description of computational methods comprises an overview of the implemented numerical routines, a derivation of the spectral properties of the transmission-line modeling method in periodic domains, and the development of an efficient sparse matrix eigenvalue algorithm that formed the basis of the spectral transmission-line modeling method. The discussion of experimental methods considers the use of liquid crystals in microwave applications and details the design and fabrication of several devices. These include a series of modified twisted nematic cells that were used to evaluate liquid crystal alignment and switching, a patch resonator that was used to measure liquid crystal permittivity, and the liquid crystal photonic bandgap device itself.
Numerical experiments showed that the spectral transmission-line modeling method is accurate and substantially faster and less memory intensive than the reference plane wave method for problems of high dielectric contrast or rapidly varying spatial detail. Physical experiments successfully realized a microwave photonic bandgap structure whose bandgap could be continuously tuned with a bias voltage. The very good agreement between simulated and measured results validate the computational and experimental methods used, particularly the resonance-based technique for permittivity measurement. This work's results may be applied to many applications, including microwave filters, negative group velocity/negative refraction materials, and microwave permittivity measurement of liquid crystals.
26
Guo, Chao-Jie, et 郭朝傑. « Tunable Photonic Crystal Wavelength Division Multiplexer with Liquid Crystal Defects ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/52433621534845304328.
Texte intégralRésumé :
碩士國立成功大學
機械工程學系碩博士班
94
Two dimensional photonic crystal slabs have formed photonic band gap that forbids wave propagation. With the defects in photonic crystals, the defect modes will be found at a resonance frequency within the photonic band gap. Photonic crystal waveguides and cavities are the two fundamental devices used to spatially localize the light in a planar photonic crystal. We design a channel filter of a two dimensional photonic crystal with triangular lattices. We present a method for tuning a photonic crystal microcavity by rotating electromagnetically the director axis of the liquid crystal surrounding the microcavity. The index of the refraction can be actively modulated after infiltrating anisotropic liquid crystals into a two dimensional photonic crystal lattice of air cylinders in silicon. By implementing the two dimensional finite difference time domain method, we demonstrate the ability to tune wavelengths of a photonic crystal filter by modulating the director axis of the liquid crystal. Multiple wavelengths can be selected. We analyze the quality factor and the resonance wavelength of a tunable channel filter to enhance the performance of the photonic crystal wavelength division multiplexer applications. The tunable cavities allow the wavelength division multiplexer to actively select many wavelengths from the waveguides.
27
Liu, Fang-Yu, et 劉芳妤. « A Tunable Photonic Crystal Device with Multi-stable Photonic Band Gap ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/3d3487.
Texte intégralRésumé :
碩士國立中山大學
光電工程學系研究所
107
Photonic crystals are composed of periodic dielectric and has tiny volume. One of the important properties of photonic crystal is that electromagnetic wave cannot transmit in some specific frequency called photonic band gap(PBG). Photonic crystals can be applied in optic devices and systems such as beam splitter and photonic crystal fibers. However, most of the PBG in photonic crystal is not able to be tuned and therefore limit the applications. On the other hand, blue phase liquid crystal is a kind of self-assembly photonic crystal which has a high tenability and can be tuned by light and electric treatment, but the narrow temperature range restrict the application of blue phase. To broaden the temperature range of blue phase Kikuchi et al. add monomer into blue phase liquid crystal. The polymer stabilized blue phase liquid crystal broaden the temperature range but confine the lattice constant. Someone found that through applying DC voltage, the PBG of PSBP could be tuned and therefore expand the applications of PSBP. However, the tuned PBG is not able to be fixed and therefore limit the applications of photonic crystal. Thus we want to fabricate a device with multi-stable state. In this research, we doped self-assembly material, HSA, into PSBP to fabricate a tunable photonic crystal device with multi-stable PBG. The HSA will disperse in the device with increasing the temperature. Therefore, we can tune the PBG in higher temperature. In contrast, the HSA will aggregate in the device and fix the tuned PBG with decreasing the temperature. After analyzing the influence of cell gap, percentage of monomer and curing intensity, we successfully fabricate a tunable photonic crystal device with multi-stable PBG.
28
Wülbern, Jan Hendrik [Verfasser]. « Tunable photonic crystal devices / von Jan Hendrik Wülbern ». 2010. http://d-nb.info/100592211X/34.
Texte intégral
29
Hsu, Chung-jen, et 許忠仁. « Design of Tunable Y-Shaped Photonic Crystal Waveguides ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/k333zk.
Texte intégralRésumé :
碩士國立中山大學
光電工程研究所
97
Photonic crystals (PCs) are structures with spatially periodic variations in dielectric constants. The prime property of PCs is the existence of the photonic band gaps (PBGs) which could prohibit the propagation of light within a certain frequency range. Once the PC structures are fabricated, it is hard to tune their optical properties for the fixed geometries. Thus, it is important to develop tunable PC waveguide devices for the applications in the photonic integrated circuits. We utilize the mode-gap effect to design two-dimensional (2-D) tunable Y-shaped PC waveguides with the polyaniline type electrorheological (ER) fluids. The propagation of light on the Y-shaped waveguide can be controlled by applying the electric field in specific regions. Besides, we also propose a tunable multi-channel PC waveguide with the polyaniline type ER fluids. We then investigate the tunable propagation characteristics of a 2-D single line-defect PC waveguide with liquid crystals (LCs) by varying the direction of LCs and the hole sizes. We also simulate the tunable optical properties of a 2-D Y-shaped PC waveguide utilizing LCs. Finally, we consider a 3-D Y-shaped PC slab waveguide with LCs. The effects of the direction of LCs and the slab thickness are discussed.
30
Liu, Chen-Yang, et 劉承揚. « Design and Analysis of Tunable Photonic Crystal Electro-optical Devices ». Thesis, 2005. http://ndltd.ncl.edu.tw/handle/67748236059530834430.
Texte intégralRésumé :
博士國立成功大學
機械工程學系碩博士班
93
Photonic crystals are artificial dielectric or metallic structures in which the refractive index modulation gives rise to stop bands for optical waves within a certain frequency. The waveguide creates a band of conduction inside the bandgaps. These crystals have many potential applications because of their ability to control lightwave propagation. Such structures can be use to design highly efficient new optical devices. We investigated the properties of the photonic crystal waveguides and the tunable photonic crystal devices with liquid crystals numerically by using the plane wave expansion method, the finite-difference time-domain method, and the extended Jones matrix method. The design and analysis of tunable photonic crystal devices, such as tunable photonic bandgap, tunable photonic crystal field-sensitive polarizer, tunable photonic crystal waveguide Mach-Zehnder interferometer, tunable photonic crystal waveguide coupler, tunable photonic crystal channel drop filter, and tunable wavelength division multiplexing are discussed. The novel tunable components may provide novel application in the photonic integrated circuits and optical communication systems.
31
Wang, Liang-Jhih, et 王良誌. « 1D Photonic Crystal Tunable Nanocavity Lasers with Novel Nanoclamp Structure ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/3wvq59.
Texte intégralRésumé :
碩士國立交通大學
光電工程研究所
107
In this thesis, based on the large wavelength response per percentage strain (7.8 nm) of 1D photonic crystal (PhC) tunable nanocavity laser, we further propose and setup novel nanoclamps nearby both sides of 1D PhCs. It can create a non-ideal elastic region to produce non-uniform structural deformation distribution under an applied linear stress. Owing to the different deformation between the clamped and unclamped regions, the wavelength response of the device can be significantly enhanced. At first, via the mechanical/optical numerical simulation based on finite-element method, we confirm the non-uniform deformation of 1D PhC nanocavity with nanoclamp under different strains, as well as the corresponding tunable properties of the resonance mode inside. By further discussing the optical properties of 1D PhC nanocavities with different nanoclamp parameters, the enhancing mechanism is initially clarified and used for establishing simple design rules. Based on our previous nanofabrication techniques, we further optimize the process to meet the requirements of nanoclamp structure, which realizes this design and improves its yielding rate. The devices not only show single mode lasing operations with low lasing thresholds in measurements, but also show good matchings with the simulation results. The experimental wavelength responses can be enhanced to 10–12 nm under different nanoclamp parameters. In addition, we also theoretically propose an optimized design with wavelength response as large as 15.9 nm. On the other hand, the nanoclamp is also applied on 1D PhC waveguide without defect design both in simulation and experiment. Via the non-uniform deformation caused by nanoclamp under stress, a nanocavity with high quality factor can be created. This implies that an on-demanded and reproducible nanocavity laser could be achieved by this strain-induced waveguide-nanocavity conversion. We believe our proposed novel mechanical/optical hybrid design in this study would provide interesting and highly potential possibilities for optical strain sensors and nanolasers in flexible photonic integrated circuits.
32
Wu, Chia-Cheng, et 吳家政. « Optical Strain Sensors Based on 1D Photonic Crystal Tunable Nanolasers ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/zg8w2r.
Texte intégralRésumé :
碩士國立交通大學
光電工程研究所
106
In this thesis, we propose and study on 1D photonic crystal (PhC) tunable nanolasers buried in deformable material via compressing. Comparing with 2D PhC, 1D PhCs shows smaller device footprints and high compatibility with conventional optical ridge waveguide in photonic integrated circuits. We firstly simulate the optical properties of 1D PhC tunable nanocavity in PDMS under compression to decrease the lattice constants for demonstrating reproducible wavelength tuning. And then the 1D PhC tunable nanolasers in PDMS are realized by a series of nano-fabrication processes. Single mode lasing with low threshold from the device is obtained in measurement. Because of its discontinuous structure, we further decrease/increase the lattice constants by applying compressing and stretching strain to the PDMS. We successfully realize the large wavelength tunability and wide wavelength tuning range in the telecommunication bands. In addition, the repeating compression/relaxing process in measurements are also executed for proving the high reliability and reproducibility of wavelength tuning by our devices. Owning to the large wavelength tunability of this device, we utilize this device to realize optical strain sensors. By studying the optical properties of the devices under non-axial strain, we successfully build a database for our strain sensor. The strain sensor we proposed is consisted of three nanolasers arranged in arbitrary angles, which shows the capabilities of identifying different unknown planar strain. We believe the proposed tunable nanolasers and optical strain sensors in this thesis could provide new scenario in flexible telecommunication photonic integrated circuits and ambient strains sensing.
33
Yu, Sheng-pin, et 游勝濱. « Study on the characteristics of some tunable photonic crystal devices containing liquid crystal ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/77682791238472563014.
Texte intégralRésumé :
碩士國立中央大學
光電科學研究所
100
In this thesis we use the plane wave expansion method together with the finite element method (COMSOL Multiphysics 3.5a) to investigate the optical properties of some silicon based two-dimensional photonic crystals infiltrated with liquid crystals. We show that the photonic band gaps can be tuned by changing the orientation of the director of the liquid crystal (the direction of preferred orientation of liquid crystal molecules in the neighborhood of any point), which is controlled by the externally applied electric field. Large and useful photonic band gaps can be found from the calculations of the photonic band structures. Such a mechanism of controlling light waves should be useful in designing components in photonic integrated circuits. As an example of application, we design a Y-shaped photonic crystal waveguide and study its properties. The waveguide contains a photonic crystal cavity located at the branch point, which is infiltrated with liquid crystal material. With this cavity inside, only those guided modes within a frequency range near the specific resonance frequencies of the cavity can be propagated. We found that the propagating direction of the guided waves are determined by the orientation of the cavity mode patterns, which can be controlled by changing the direction of the applied external electric field since the cavity is infiltrated with liquid crystal material. We expect that similar devices can be developed to be used as frequency-selective or switching devices in optical circuits.
34
Mahnkopf, Sven. « Photonic crystal based widely tunable laser diodes and integrated optoelectronic components ». Doctoral thesis, 2005. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-13860.
Texte intégralRésumé :
In a first aspect of this work, the development of photonic crystal based widely tunable laser diodes and their monolithic integration with photonic crystal based passive waveguide and coupler structures is explored theoretically and experimentally. In these devices, the photonic crystal is operated in the photonic bandgap which can be used for the realization of effective reflectors and waveguide structures. Such tunable light sources are of great interest for the development of optical network systems that are based on wavelength division multiplexing. In a second aspect of this work, the operation of a photonic crystal block near the photonic band edge is investigated with respect to the so-called superprism effect. After a few introductory remarks that serve to motivate this work, chapter 3 recapitulates some aspects of semiconductor lasers and photonic crystals that are essential for the understanding of this work so that the reader should be readily equipped with the tools to appreciate the results presented in this workIn einem ersten Aspekt der vorliegenden Arbeit wird die Entwicklung von weit abstimmbaren Halbleiterlasern auf der Basis photonischer Kristalle sowie deren monolithische Integration mit passiven, auf photonischen Kristallen basierenden Wellenleiter- und Kopplerstrukturen theoretisch und experimentell untersucht. In diesen Bauelementen werden die photonischen Kristalle im Bereich der photonischen Bandlücke betrieben, was zur Realisierung effektiver Reflektoren und Wellenleiterstrukturen ausgenutzt werden kann. Kompakte, weit abstimmbare Halbleiterlaser sind für die Entwicklung von optischen Netzwerksystemen, die auf dem wavelength division multiplexing (WDM) beruhen, von fundamentaler Bedeutung. In einem zweiten Aspekt der Arbeit wird der Betrieb von photonischen Kristallen im Bereich der photonischen Bandkante im Hinblick auf den sogenannten Superprisma-Effekt untersucht. Nach einigen einleitenden Worten, die diese Arbeit motivieren, werden in Kapitel 3 die für das Verständnis der Arbeit wesentlichen Grundlagen von Halbleiterlasern und photonischen Kristallen rekapituliert
35
Chia-ChinTsai et 蔡佳晉. « Design and Analysis of Tunable Photonic Crystal Devices Using Magneto-optical Defects ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/89261953202306304120.
Texte intégralRésumé :
碩士國立成功大學
機械工程學系
102
In this research a series of tunable photonic crystal (PhC) devices are proposed. The magneto-optical (MO) materials are infiltrated into the PhC structure to become point or line defects. With out-of-plane magnetization, the degenerate resonant modes splits into two counter-rotating modes at different frequencies. Furthermore, the quality factor of two splitting modes significantly increases to about 4000, which is suitable for applications of dense wavelength-division-multiplexing (DWDM) systems and refractive index sensors. When the out-of-plane magnetization is applied to the MO line defects in the PhCs, the fundamental waveguide mode vanishes in specific frequency region. This phenomenon causes the fundamental mode waves blocked by the PhC structure. Based on the effect, the power can be switched by applying external magnetic fields. When two MO line defects are put side by side in the PhC structure with opposite direction of magnetization, the time-reversal and space inversion symmetries breaks, which causes the difference of the dispersion curves for opposite propagating directions. Using this effect a PhC diode can be achieved. Computations are performed using plane wave expansion (PWE) and finite difference time domain (FDTD) method.
36
王昭龍. « Design of tunable filter and dispersion compensator by one-dimensional photonic crystal ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/55583227055848884727.
Texte intégral
37
Suh, Myoung-Gyun. « Theoretical Analysis on the Liquid Crystal Infiltrated Tunable 2D Photonic Crystal Laser using Finite-Difference Time-Domain Method ». 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2001200612060800.
Texte intégral
38
Suh, Myoung-Gyun, et 徐明均. « Theoretical Analysis on the Liquid Crystal Infiltrated Tunable 2D Photonic Crystal Laser using Finite-Difference Time-Domain Method ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/33260491544218447513.
Texte intégralRésumé :
碩士國立臺灣大學
物理研究所
94
In recent years, with growing interests to Photonic Crystals (PhCs) and their applications, many researchers have studied PhCs. 2-Dimensional PhC laser is one of the interesting research topics due to its strong light confinement in a small wavelength-scale volume. Liquid Crystal (LC) infiltrated 2D PhC laser has also been investigated for the laser wavelength tuning, yet its theoretical study seems insufficient. Thus, in this research, we developed 3D Finite-Difference Time-Domain (FDTD) program which can simulate the light propagation in LCs, and analyzed the characteristics of LC infiltrated 2D PhC laser. In several characteristic PhC structures, the lasing wavelength shift of a single mode, the degeneracy splitting, the lasing mode change and the quality factor (Q-factor) change are found as the arrangement of LCs changes. Moreover, by properly designing the defect, we can expect the intrinsic polarization of the lasing mode.
39
Mahnkopf, Sven [Verfasser]. « Photonic crystal based widely tunable laser diodes and integrated optoelectronic components / vorgelegt von Sven Mahnkopf ». 2005. http://d-nb.info/979674492/34.
Texte intégral
40
Hsin-YuLin et 林星玗. « Thermally-controlled laser-mode conversion based on spatially tunable photonic bandgap cholesteric liquid crystal templates ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/24492245437224774317.
Texte intégralRésumé :
碩士國立成功大學
光電科學與工程學系
102
A spatially tunable dye-doped liquid crystal (DDLC) refilling cholesteric liquid crystal (CLC) polymer template device with a thermally controlled laser-mode conversion is successfully developed in this study. This laser device is fabricated through four stages: before curing, after curing, after washing out, and after refilling. Experimental results show that the tunable spectral range for the photonic bandgap (PBG) of the laser device covers nearly the entire white region (405 nm to 752 nm). The spatially tunable laser mode can be converted between random lasing operation at low temperatures and bandedge lasing operation at high temperatures. The mismatch between the refractive indices of the refilling nematic LC (NLC) in the nanopores and the template leads to multiple scattering of pumped fluorescence emission and to random lasing. After the refilling LCs become isotropic, the index match between the LC and the template causes the PBG of the template to appear and results in bandedge lasing emission. The refilling template laser fabricated by forming a gradient-pitched CLC through nature diffusion has many drawbacks, including the formation of defects, relatively high energy threshold, wide linewidth, narrow tunable spectral range, and long processing time. The experimental results show that the structural and lasing features of the gradient-pitched refilling CLC template laser improve if rapid thermal annealing is repeatedly adopted during thermal diffusion, particularly the ultralow energy threshold of 60 nJ/pulse. The developed device has many advantages, such as having a highly stable and defect-free structure, an ultralow lasing threshold, and wide spatial tunability and lasing-mode convertibility. Hence, the device has high application potential in photonics and display.
41
Jia-LunChang et 張家綸. « Broadband low-voltage tunable photonic bandgap and lasing devices based on ferroelectric liquid crystal and cholesteric liquid crystal composites ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/44k8e7.
Texte intégralRésumé :
碩士國立成功大學
光電科學與工程學系
106
This thesis mainly develops and studies the optical properties of ferroelectric liquid crystal and cholesteric liquid crystal (FLC-CLC) composite devices and further develops dye-doped FLC-CLC (DDFLC-CLC) lasers by means of electrothermal effect. Experimental results show that the device has photonic bandgap (PBG) control in the entire white light region in low-voltage range and at near room temperature, and the spectral range for tuning the lasing wavelength can be as wide as 100 nm. In first part, this study measures the temperature response of the electrothermal heating sheet and the low-voltage regulation of the reflection band of the FLC-CLC device in the visible region. In second part, the properties of the laser output and electrical controllability of the DDFLC-CLC laser are investigated. The wide tuning of the reflection band (~321 nm) in the entire visible region can be obtained in a low voltage range (0‒2.8 V) with less deformation of reflection band. This study also uses the Keating model and the electrothermal heating model to simulate the relationship between the reflection center wavelength and the applied voltage, which result fits well with the experimental results. In addition, the study also regulates the laser output wavelength of the DDFLC-CLC up to 100 nm in a low-voltage range (0 V – 0.8 V). The lasing threshold of the lasers is between 0.21 – 1.38 μJ/pulse.
42
Tsai, Chia-Chen, et 蔡佳珍. « ZnO Microspheres Made of High Synthesis Efficiency for Electrophoretically Self-Assembled Photonic Crystal Templates and Tunable Nanostructures ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/19911064683285607195.
Texte intégralRésumé :
碩士逢甲大學
材料科學所
98
The major objectives of this study are aimed at achieving (a) high synthetic efficiency fabrication of monodispersive submicron-sized zinc oxide (ZnO) spheres with high sphericity by sol-gel process, (b) synthesis of monodispersed ZnO microspheres with narrow size distribution by chemical bath deposition (CBD) method, (c) electrophoretic self-assembly (EPSA) formation and microstructural characterization of 3-D photonic crystal (PhC) templates of polystyrene (PS) microspheres at average size of 250 nm by emulsion polymerization. Our goal is to investigate the photonic properties of such closely packed, ordered 3-D templates of PS spheres, which can manifest photonic bandgap (PBG) in accordance with our modeling results out of planar-wave expansion (PWE) simulation work for face-centered cubic (FCC) structures to verify the existence of real PBG in our tunable nanostructures PhC samples. The results showed that two-step sol-gel process can produce monodispersed ZnO microspheres of 90~500 nm and CBD process is able to formulate ZnO microspheres of even smaller particle size (50~300 nm) in a narrow particle size distribution. It is essential to control the acidity of EPSA colloid with reasonably good stability. At basic conditions, the PS colloid can be obtained with good dispersivity by adding suitable amount of surfactant such as sodium dodecyl sulfate (SDS). These uniformly sized ZnO and microspheres can be successfully formed as 3-D ordered templates of opal structure on transparent, conductive substrates such as indium-tin oxide (ITO) glasses through our novel EPSA route. To acquire pronounced PBG effect for photonic applications in developing LEDs or solar cells of high conversion efficiency, most of polystyrene microsphere templates are currently used due to its material flexibility to avoid defect or void introduction during the drying stage and to easily transform into inverse opal structure by infiltrating other oxides with high dielectric constant (e.g. ZnO or TiO2) through potential thermal or chemical material removal schemes such as pyrolysis or solvent dissolution or etching.
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Jia-DeLin et 林嘉德. « Tunable Photonic Bandgap Device and Laser Based on Cholesteric and Blue Phase Liquid Crystal and Their Applications ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/93825852878819275868.
Texte intégralRésumé :
博士國立成功大學
光電科學與工程學系
103
Self-assembled photonic crystals (PhCs) based on liquid crystals (LCs) with chirality have high potential for the applications (e.g., soft matter-based integrated photonic circuit) because of their simple fabrication process as well as excellently controllable photonic properties. Cholesteric liquid crystal (CLC) and blue phase (BP) liquid crystal are two most representative materials with chiralities. With the addition of the chiral molecules, the LC molecules in CLC and BP can spontaneously self-organize as helical structures. The self-assembled helical structures may induce photonic bandgap (PBG) structure for circularly polarized light in CLC and BP. Lasers based on such soft-matter PhCs can also be developed by simply doping active materials into the CLC and BP systems. This dissertation, entitled “Tunable photonic bandgap device and laser based on cholesteric and blue phase liquid crystals and their applications”, mainly includes three works, which are briefly described as follows: (1) The topic of the first work is “Optically tunable/switchable omnidirectionally spherical microlaser based on a dye-doped cholesteric liquid crystal microdroplet with an azo-chiral dopant.” This work presents an optically wavelength-tunable and intensity-switchable dye-doped CLC (DDCLC) spherical microlaser with an azo-chiral dopant. Experimental results present that two functions of optical control — tunability of lasing wavelength and switchability of lasing intensity — can be obtained for this spherical microlaser at low and high intensity regimes of non-polarized UV irradiation, respectively. The 3D DDCLC spherical microlaser is a highly promising controllable 3D micro-light source or microlaser for applications of 3D all-optical integrated photonics, laser displays, and biomedical imaging and therapy, and as a 3D UV microdosagemeter or microsensor. (2) The topic of the second work is “Photosensitive and all-optically fast-controllable photonic bandgap device and laser in a dye-doped blue phase with a low-concentration azobenzene liquid crystal.” This work demonstrates the feasibility of a novel photosensitive and all-optically fast-controllable PBG device based on a dye-doped blue phase (DDBP), embedded with a low-concentration azobenzene liquid crystal (azo-LC). The PBG of the DDBP can be reversibly fast-tuned off and on with the successive illumination of a weak UV and green beams. The UV irradiation can transform the trans azo-LCs into bend cis isomers, which can easily disturb LCs at the boundary between the double twisting cylinders (DTCs) and the disclinations, and, then, quickly destabilize BPI to become a BPIII-like texture with randomly-oriented DTCs. With the successive illumination of a green beam, the BPI PBG device can be fast-turned on, owing to the fast disappearance of the disturbance of the azo-LCs on the boundary LCs via the green-beam-induced cis→trans back isomerization. The BP PBG device can significantly contribute to efforts to develop a photosensitive and all-optically fast-controlling LC laser. (3) The topic of the third work is “Spatially tunable photonic bandgap of wide spectral range and lasing emission based on a blue phase wedge cell.” This study demonstrates for the first time a continuously tunable PBG of wide spectral range based on a BP wedge cell. A continuously shifting PBG of the BP wedge cell occurs due to the thickness gradient of the wedge cell at a fixed temperature. The wedge cell provides a gradient of boundary force on the LCs and thus forms a distribution of BP crystal structure with a gradient lattice. Additionally, a spatially tunable lasing emission based on a DDBP wedge cell is also demonstrated. The tunable band of the PBG and lasing emission is about 130 nm and 70 nm, respectively, which tuning spectral ranges are significantly wider than those of CLC and DDCLC wedge cells, respectively. Such a BP device has a significant potential in applications of tunable photonic devices and displays.
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Guan-JoungWei et 韋冠中. « Wide-band spatially tunable and hyper-reflective photonic bandgap based on a refilled cholesteric liquid crystal polymer template ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/66647918187925597616.
Texte intégralRésumé :
碩士國立成功大學
光電科學與工程學系
102
The scientists in the field of liquid crystal (LC) exploited chiral LC polymer to fabricate novel cholesteric LC (CLC) polymer template (simply called template) in recent years. The template can effectively overcome the limitation in the optical features of traditional CLCs, such as enhancement of reflectivity over 50%, multiple photonic bandgaps (PBGs), and changeable optical characteristics by flexibly replacing the refillingLC materials, and so on. This thesis fabricates two gradient-pitched CLC templates with two opposite handednesses, which are then merged as a spatially tunable and hyper-reflective CLC template sample. This sample can simultaneously reflect right- and left-circularly polarized lights and the tunable spectral range includes the entire visible region. In addition, this study investigates the causes to limit the reflectance of the template sample and a method to improve the reflectance. By increasing the temperature of the template sample exceeding the clearing point of the refilling LC, the light scattering significantly decreases and the reflectance effectively increases. In summary, this study fabricates a merged template sample to develop a wide-band spatially tunable and hyper-reflective PBG device. This device has a maximum reflectance over 85% and a wide-band spatial tunability in PBG between 400 nm and 800 nm which covers the entire visible region. This hyper-reflective PBG template device with a wide-band tunability over entire visible region can not only be employed as a wide-band spatially tunable filter, but also used to develop a low-threshold mirror-less laser with a spatial tunability at entire visible region and simultaneous emission of left- and right-circular polarizations.