Dissertations / Theses on the topic 'Multimode interference coupler'

Silicon-on-insulator (SOI) technology has become increasingly attractive because of the strong light confinement, which significantly reduces the footprint of the photonic components, and the possibility of monolithically integrating advanced photonic waveguide circuits with complex electronic circuits, which may reduce the cost of photonic integrated circuits by mass production. This thesis is dedicated to numerical simulation and experimental performance measurement of passive SOI waveguide devices. The thesis consists of two main parts. In the first part, SOI curved waveguide and corner turning mirror are studied. Propagation losses of the SOI waveguide devices are accurately measured using a Fabry-Perot interference method. Our measurements verify that the SOI corner turning mirror structures can not only significantly reduce the footprint size, but also reduce the access loss by replacing the curved sections in any SOI planar lightwave circuit systems. In the second part, an optical 90o hybrid based on 4 × 4 multimode interference (MMI) coupler is studied. Its quadrature phase behavior is verified by both numerical simulations and experimental measurements.

In this paper, the performance simulations of a novel ultra-compact balanced coherent photodetector for operation at a wavelength of 1.5 mu m are presented and design proposals for future fabrication processes are provided. It consists of a compact 2x2 MMI that is evanescently coupled into a germanium MSM photodetection layer. The simulations demonstrate dark current less than 10 nA, capacitance less than 20 fF, and optical bandwidth in the 10-30 GHz range. We propose utilizing the simplicity of direct wafer bonding to bond the detection layer to the output waveguides to avoid complicated epitaxial growth issues. This ultra-compact device shows promise as a high-speed, low-cost integrated silicon photonics solution for the telecommunications infrastructure.

The research described work in this thesis is concerned with the development and realisation of high brightness array laser diodes operating in single spatial mode. The fabrication of the high brightness laser devices was carried out on 830 nm GaAs/AlGaAs material system. Broad area lasers were fabricated to evaluate the material quality. The material design was based on the high d/Г concept, by which the optical power is maximised prior to thermal roll-over or the catastrophic optical mirror damage (COMD). A quantum well intermixing (QWI) process was developed for integrating the non absorbing mirrors (NAMs), the gain section, the MMI coupler and the single spatial mode output waveguide. The quantum well intermixing (QWI) was used to fabricate nonabsorbing mirrors (NAMs) with a blue shift of 58 nm. The annealing for the optimum process was 810º C for 90 seconds. The QWI was evaluated using the photoluminescence method, band gap shift of 58 nm was realised. The fabricated NAMs ranged from 30 to 100 μm in length. The gain section length was set at 975 μm. In the passive sections, the MMI and output waveguide are 1 mm long. The total device length was around 2 mm. No COMD was observed in the fabricated devices meaning that the quantum well intermixing has worked well. The propagation loss measurement for 830 nm passive waveguide, intermixed with a QWI blue shifted 58 nm and 9.8 mm long was 4.48 dB/cm. This is comparable to the loss that was measured from broad area laser material, which had a loss of 6.9 dB/cm. Fimmwave and beam propagation method (BPM) were used for the modelling. The results of the modelling for the single mode ridge waveguide were that, a ridge depth of 1.84 μm supported a single mode. The selected ridge width was 2.5 μm. Modelling of a 1x4 MMI array laser and a 1x2 MMI array was undertaken using the beam propagation method (BPM). The optimum lateral spacing of the gain waveguides was found to be in a range of 2.5-3.5 μm for high power operation. In the 1x4 MMI array laser, the phase was modelled. The inner gain sections have a phase difference of π/2 with respect to the outer gain sections, while the 1x2 MMI array laser has zero phase shift between the two gain sections. 1x4 and 1x2 MMI array lasers were fabricated. In the case of 1x4 MMI array laser, different MMI coupler lengths were fabricated. The MMI lengths were between 617 μm and 709 μm. The devices were tested electrically using 10 μs pulses and a 1 KHz repetition rate. They were tested to a Abstract iii current level of 22xIth. The power achieved was > 440 mW in pulsed mode from the single output facet. This power was equivalent to an optical intensity of 17.6 MW/cm2. The threshold current measured for the device was 145 mA. The external quantum efficiency (ηext) was 32.1 %. The MMI array laser device design with an MMI width of 24 μm, length of 617 μm and gain section spacing of 3.5 μm had a strong phase locking up to an applied current of 5.2xIth. The far-field pattern width of the central lobe of the phase locked 1x4 MMI array laser was 2.1 º measured from the array facets side. This value is comparable to the diffraction limited value of 1.96 º calculated simply from (λ/N.p). The quality factor (M2 emitter) for the 2.5 μm wide single ridge emitter was estimated to be close to 1. The beam quality factor of the 1x4 MMI array bar (M2 bar) was estimated to be 1.07. The visibility (V) of the pattern was very close to 1. The phase locked power (P) was 152.0 mW per facet for an operating current of 5.2xIth (Ith=145 mA). The corresponding brightness was 19.6 MW/cm2.sr. The operating wavelength for a 1x4 MMI laser diode array was a 0.822 μm. The single emission wavelength was measured from the four array side with a narrow spectral width (Δλ) of 0.22 nm at the FWHM for an operating current of 5.2xIth. The narrow spectral width of 0.22 nm for the array was a much smaller than that for a ridge waveguide laser. The ridge waveguide laser had a spectral width of a 0.65 nm at FWHM. This spectral width was measured for a current of 200 mA in pulsed mode with a 5 μs pulse width. The lasing spectra of the array showed four individual peaks, when the current was increased to 6.2xIth. At this point, the array is no longer phase locked. The wavelength peaks were as follows: λ1=821.35 nm, λ2=821.59 nm, λ3=821.83 nm and λ4=822.08 nm, respectively. The spectral width (Δλ) was around 0.22 nm at FWHM for the each of the individual peaks. The 1x2 MMI array devices were pulsed to a current level of 30xIth. The output power was around 332 mW from the single output facet. The threshold current was 85 mA. The largest optical output power was realised for the device with an MMI length of 480 μm. The external quantum efficiency was around 33%. The phase relationship between the gain sections for the 1x2 MMI array laser is an identical one (i.e.Ф1=Ф2). The phase locking was achieved in the 1x2 MMI array laser. However, the phase locking was only evident up to 3xIth (Ith=85 mA) CW. The width of the central lobe of the far-field pattern was 4.49 º (equivalent to 1.33x the diffraction limit). There was also a reasonable correlation between the far-field pattern from the measurement and the far-field pattern from the simulation. The quality Abstract iv factor for the emitter (M2 emitter) was 1, while the beam quality factor (M2 bar) of the 1x2 MMI array (bar) was estimated to be 1.33. The visibility (V) of the pattern was estimated to be around 0.5. The lasing spectra showed a single wavelength emission with a peak of 823.55 nm and a very narrow spectral width of 0.3 nm at the FWHM. The optical power at an injection current of 3.2xIth was a mere 60mW CW per facet, which corresponded to a brightness of 5.02 (MW/cm2. sr). The results for a 1x2 MMI laser array indicated that the length of the MMI section promoted the phase locking. An accurately designed MMI length resulted in a narrow spectral width of 0.3 nm at FWHM for an MMI length of 480 μm. The spectral width increased with a reduction of the MMI length. The spectral width was 0.86 nm at FWHM for an MMI length of 465 μm, whereas it increased to 3.1 nm at the FWHM for an MMI length of 444 μm. Therefore, the phase locking and the bandwidth of the 1xN MMI array laser is a self imaging and MMI cavity length dependent.

The Multimode Interference (MMI) mechanism is a powerful toool used in the analysis and design of a certain class of optical, microwave and millimeter wave devices. The principles of the MMI method and the self-imaging principle is described. Using this method, NXM MMI couplers, MMI splitter/combiners are analyzed. Computer simulations for illustrating the "
Multimode Interference Mechanism"
are carried out. The MMI approach is used to analyze overmoded '
rectangular metallic'
and '
dielectric slab'
type of waveguides and devices. The application of the MMI technique is investigated experimentally by using a metallic waveguide structure operating in the X-band. The construction of the related structure and the related experimental work are reported.

[EN] Microwave photonics (MWP) is a well-established research field that investigates the use of photonic technologies to generate, distribute, process and analyze RF waveforms in the optical domain. Despite its great potential to solve long-standing problems faced by both the microwave and electronics industries, MWP systems are bulky, expensive and consume a lot of power. Integrated microwave photonics (IMWP) is an emerging area of research that promises to alleviate most of these drawbacks through the use of photonic integrated circuits (PIC). In this work, we have aimed at further closing the gap between the worlds of MWP and integrated optics. In particular, we have focused on the design and experimental characterization of PICs with reconfigurable, ring-assisted Mach-Zehnder interferometer filters (RAMZI), and demonstrated its potential use in different IMWP applications. These filters consist of a symmetric MZI loaded with ring resonators, which are coupled to the MZI branches by different optical couplers. The contributions of this thesis can be split into two sections. In the first one, we demonstrate integrated optical couplers and reflectors with variable power splitting and reflections ratios. These exploit the well-known properties of tapered multimode interference couplers (MMI), and their inherent robustness makes them highly suitable for the implementation of both RAMZI and reflective filters. Besides, we study in detail the impact of manufacturing deviations in the performance of a 4x4 MMI-based 90º hybrid, which is a fundamental building block in coherent optical communication systems. In the second section, we demonstrate the use of integrated RAMZI filters for three different IMWP applications, including instantaneous frequency measurement (IFM), direct detection of frequency-modulated signals in a MWP link, as well as in tunable, coherent MWP filters. A theoretical analysis of the limits and trade-offs that exist in photonics-based IFM systems is also provided. Even though these are early proof-of-concept experiments, we hope that further technological developments in the field will finally turn MWP into a commercial reality.
[ES] La fotónica de microondas (MWP) es un campo de investigación que estudia el uso de tecnologías ópticas para generar, distribuir, procesar y analizar señales de RF. A pesar de su gran potencial para resolver algunos de los problemas a los que se enfrentan las industrias electrónica y de microondas, estos sistemas son voluminosos, caros y consumen mucha potencia. La fotónica de microondas integrada (IMWP) es un área emergente que promete solucionar todos estos inconvenientes a través de la utilización de circuitos ópticos integrados (PIC). En esta tesis, hemos pretendido avanzar un poco más en el acercamiento entre estas dos disciplinas. En concreto, nos hemos centrado en el diseño y caracterización experimental de PICs con filtros reconfigurables basados en interferómetros Mach-Zehnder cargados con anillos (RAMZI), y demostrado su potencial uso en diferentes aplicaciones de IMWP. Los filtros RAMZI están hecho básicamente de un MZI simétrico cargado con anillos, los cuales a su vez se acoplan a las ramas del interferómetro a través de distintos acopladores ópticos. Las contribuciones de este trabajo se pueden dividir en dos partes. En la primera, hemos demostrado acopladores y reflectores ópticos integrados con coeficientes de acoplo y reflexión variables. Éstos explotan las propiedades de los acopladores por interferencia multimodal (MMI), y su robustez les hace muy atractivos para la implementación de filtros RAMZI y de tipo reflectivo. Además, hemos analizado el impacto que las tolerancias de fabricación tienen en el rendimiento de un híbrido óptico de 90º basado en un MMI 4x4, el cual es un elemento fundamental en los sistemas de comunicaciones ópticas coherentes. En la segunda parte, hemos demostrado el uso de filtros RAMZI en tres aplicaciones distintas de IMWP. En concreto, hemos utilizado dichos filtros para implementar sistemas de medida de frecuencia instantánea (IFM), detección directa de señales moduladas en frecuencia para enlaces fotónicos, así como en filtros coherentes y sintonizables de MWP. También hemos desarrollado un análisis teórico de las limitaciones y problemas que existen en los sistemas IFM. A pesar de que todos los experimentos realizados han consistido en prototipos para una prueba de concepto, esperamos que futuros avances tecnológicos permitan que la fotónica de microondas se convierta algún día en una realidad comercial.
[CAT] La fotònica de microones (MWP) és un camp d'investigació que estudia l'ús de tecnologies òptiques per a generar, distribuir, processar y analitzar senyals de radiofreqüència. A pesar del seu gran potencial per a resoldre alguns dels problemes als que s'enfronten les indústries electrònica i de microones, estos sistemes son voluminosos, cars i consumixen molta potència. La fotònica de microones integrada (IMWP) és un àrea emergent que promet solucionar tots estos inconvenients a través de la utilització de circuits òptics integrats (PIC). En esta tesi, hem pretés avançar un poc més en l'acostament entre estes dos disciplines. En concret, ens hem centrat en el disseny i caracterització experimental de PICs amb filtres reconfigurables basats en interferòmetres Mach-Zehnder carregats amb anells (RAMZI), i demostrat el seu potencial en diferents aplicacions d' IMWP. Els filtres RAMZI estan fets bàsicament d'un MZI simètric carregat amb anells, els quals, al seu torn, s'acoblen a les branques del interferòmetre a través de distints acobladors òptics. Les contribucions d'este treball es poden dividir en dos parts. En la primera, hem demostrat acobladors i reflectors òptics integrats amb coeficients de transmissió i reflexió variables. Estos exploten les propietats dels acobladors per interferència multimodal (MMI), i la seua robustesa els fa molt atractius per a la implementació de filtres RAMZI i de tipo reflectiu. A més a més, hem analitzat l'impacte que les toleràncies de fabricació tenen en el rendiment d'un híbrid òptic de 90 graus basat en un MMI 4x4, el qual és un element fonamental en els sistemes de comunicacions òptiques coherents. En la segona part, hem demostrat l'ús de filtres RAMZI en tres aplicacions diferents de IMWP. En concret, hem utilitzat estos filtres per a implementar sistemes de mesura de freqüència instantània (IFM), detecció directa de senyals modulades en freqüència per a enllaços fotònics, així com en filtres coherents i sintonitzables de MWP. També hem desenvolupat una anàlisi teòrica de les limitacions i problemes que existixen en els sistemes IFM. A pesar de que tots els experiments realitzats han consistit en prototips per a una prova de concepte, esperem que futurs avanços tecnològics permeten que la fotònica de microones es convertisca algun dia en una realitat comercial.
Sánchez Fandiño, JA. (2016). Integrated Optical Filters for Microwave Photonic Applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/67690
TESIS

The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands.

Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems.

A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W).

The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering.

Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler.

Keywords:silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.

This thesis presents an introduction to the design and simulation of a novel class of integrated photonic phased array switch elements. The main objective is to use nano-electromechanical (NEMS) based phase shifters of cascaded under-etched slot nanowires that are compact in size and require a small amount of power to operate them. The structure of the switch elements is organized such that it brings the phase shifting elements to the exterior sides of the photonic circuits. The transition slot couplers, used to interconnect the phase shifters, are designed to enable biasing one of the silicon beams of each phase shifter from an electrode located at the side of the phase shifter. The other silicon beam of each phase shifter is biased through the rest of the silicon structure of the switch element, which is taken as a ground. Phased array switch elements ranging from 2×2 up to 8×8 multiple-inputs/multiple-outputs (MIMO) are conveniently designed within reasonable footprints native to the current fabrication technologies. Chapter one presents the general layout of the various designs of the switch elements and demonstrates their novel features. This demonstration will show how waveguide disturbances in the interconnecting network from conventional switch elements can be avoided by adopting an innovative design. Some possible applications for the designed switch elements of different sizes and topologies are indicated throughout the chapter. Chapter two presents the design of the multimode interference (MMI) couplers used in the switch elements as splitters, combiners and waveguide crossovers. Simulation data and design methodologies for the multimode couplers of interest are detailed in this chapter. Chapter three presents the design and analysis of the NEMS-operated phase shifters. Both simulations and numerical analysis are utilized in the design of a 0º-180º capable NEMS-operated phase shifter. Additionally, the response of some of the designed photonic phased array switch elements is demonstrated in this chapter. An executive summary and conclusions sections are also included in the thesis.

碩士
國立臺灣科技大學
電子工程系
91
The purpose of the paper is that to improve an optical switch via a 2x2 multimode interference coupler. We have proposed the reduction of the length in the new optical switch. First we should know, any variation of the component must conform the excellent characteristics of the MMI: fabrication in tolerance、insensitive in wavelength、low excess loss、stable splitting ratio and insensitive in polarization. In the paper we successfully use the BPMCAD simulation tool to prove the correctness of the 2x2 optical switch. And we replace the rectangular shape of the multimode interference section with the parabolic shape. In this study, we successfully reduce length of the optical switch about 40% of the general multimode interference coupler. The fabrication tolerance in width of improved multimode interference is 4.5 times of the general multimode interference. The wavelength sensitivity and fabrication tolerance in length are about 2% in variation of the general multimode interference coupler.

碩士
中華技術學院
機電光工程研究所碩士班
93
The subject of this thesis on the design and analysis of multimode interference (MMI) based optical passive devices for directional coupler. We propose a novel 1.3/1.55-μm wavelength demultiplexer on the LiNbO3 material system. A chirp grating is placed inside a MMI and periodically segmented waveguides in a directional coupler structure to shorten the device length and increase wavength tolerance. Simulation results show that a demultiplexer with an insertion loss of 0.156dB and 0.223dB can be obtained at 1.55- and 1.3-μm wavelengths, respectively. A new principle that can reduce the N-fold self-images interval of the MMI waveguide is presented. By placing some partial index-modulation regions in this multimode waveguide, a paired-interference mechanism and a symmetric-interference mechanism will exist simultaneously. The formulas in this thesis provide a simple design option to shorten the device length. The coupling characteristics have good tolerance on the device length and wavelength variation. Design of the device was carried out and it is showed that the device performance can be optimized by proper allocation of the periodically segmented waveguides.

碩士
國立高雄應用科技大學
電子工程系碩士班
103
In this thesis, a novel inverse power splitter coupler is designed by the 60-degree crossing as a fold plane. The 60 degree of a center-fold plane made by the self-image as the turning mirror is achieved to 2×2 60-degree multimode waveguide turning mirror coupler with inverse power splitter. The inverse power splitter of the 2×2 60-degree multimode waveguide turning coupler is demonstrated by finite-difference time-domain methods (FDTD) from K=0.85/0.72/0.15/0.28 to K=0.15/0.28/0.85/0.72. The excess loss of 2×2 60-degree multimode waveguide turning couplers with K=0.15/0.28/0.5/0.72/0.85 is almost 0.1~0.69 dB by FDTD. Two/four 2×2 60-degree multimode waveguide couplers are composed to get the all power splitter ratio of 0~1. The device height of two/four components of 2×2 60-degree multimode waveguide couplers is decreased max. 13.5/7.4 times than two/four components of 2×2 straight multimode waveguide couplers. The device length of two/four components of 2×2 60-degree multimode waveguide couplers is decreased max. 2/2.5 times than two/four components of 2×2 straight multimode waveguide couplers. The power splitter ratio of two/four components of 2×2 60-degree multimode waveguide couplers is max. 0.96/min. 0.01. The device will be useful to make the photonic integrated circuit.

碩士
國立臺灣科技大學
電子工程系
97
The optical power splitters are widely utilized in photonic integrated circuits for signal transmission, multiplexer, demultiplexer, amplification, receiving, and protection. In this thesis, two novel approaches based on multimode interferences and directional couplers were proposed, designed, and simulated on a 5-um-thick silicon-on-insulator platform. The numerical calculation was carried with the help of the BeamPROP commercial software. In the single mode region of silicon-on-insulator waveguides with 4-um width and 2.5-um etch depth for an efficient coupling to traditional fibers, a S-shape multimode interference was first demonstrated on the flexible splitting ratio at two output ports. The mode-shifting phenomena and self-imaging principles were simultaneously implemented to illustrate low polarization dependent loss and wavelength insensitivity. Followed by the conformal mapping on the effective index, the multimode interference beat length and waveguide bend radius were theoretically optimized and obtained for the tap monitoring functions on a 5.2% coupling ratio over 1310-1550 nm wavelength range under the multimode interference S-shape with 1035-um straightness, 11-mm bend radius, and 13-um width besides that the polarization dependent loss was less than -0.1 and -0.7dB, respectively, for the primary and tap ports. The other approach for the optical power splitting was achieved by the compensated mode profiles in the interactive region of a 2x2 directional couplers for the equal photonic intensity on two output ports. The numerical calculation showed that both of the 50% coupling ratio with 10% variation and ~0.3dB polarization dependent loss were demonstrated between 1400-nm and 1650-nm wavelengths, contributed by the two asymmetric waveguide widths of 4.5 um and 4.0um under the 1.6um gap and 2.5um etch depth in the parallel coupling region. A S-bend multimode interference could not only demonstrate the splitting ratio arbitrarily distributed at the two output ports for waveguide tap monitoring, but also show attractive properties on the compactness, tolerance to fabrication parameters, inherent balance and low optical insertion loss. And the alternative approach for the equal optical power splitting by the asymmetric waveguides in the parallel coupling region of optical directional couplers was then proposed and illustrated to the lowest birefringence and chromaticity. Our novel approaches for the optical power splitter on silicon-on-insulator waveguides could applicably be developed to a highly integrated photonic and electronic circuitry by complementary metal-oxide-semiconductor technologies for size, weight, and cost reduction, compared with the traditional optical systems, for future monolithic integration.

碩士
國立中山大學
光電工程學系研究所
97
This study uses vertical mirror optical waveguide reflector and bending waveguide to fabricate semiconductor ring resonators. By using multimode interference couplers with specific width and length that generate distinctive energy distribution to achieve the power splitting of 85:15. We integrate vertically deep etching turning mirror to reflect optical mode, and reduce the component size to 37.6%. In fabrication process, this study applies multiple wet etching technique to form the waveguide structure. First, we use wet etching technique to etch ridge waveguide and turning mirror, and then perform deep etching in the periphery of bending and turning region to reduce the bending loss. Finally, the etching mask is lifted off, and the wafer is polished and sliced for measurement. After measuring the signal, we can compute waveguide loss by Fabry-perot resonant situation. The waveguide loss is 59.6dB/cm. Power splitting of 90:10 is achieved. The free spectral range (FSR) is 72GHz for the ring resonators.

碩士
國立清華大學
光電工程研究所
97
A novel low-loss silicon photonic wire with 3-D taper couplers fabricated on silicon-on-insulator (SOI) by the deep etching and the thermal annealing processes was presented. The propagation loss and the coupler loss were measured to be 1.26dB/cm and 2.5dB/coupler [10][11]. In order to realize highly compact photonic integrated circuits based on silicon photonic wires, multimode interference (MMI) couplers were introduced for performing light splitting and combing due to the advantages of wide optical bandwidth, polarization independence and large fabrication tolerance. In this thesis, we have demonstrated monolithically integrated 2-D and 3-D MMI couplers with the novel silicon photonic wires via self-profile transformation [14]. The power splitting ratios of 50:50 and 15:85 were designed for preliminary study. For the 50:50 and 15:85 2-D MMI devices, the power splitting ratios were measured to be 46:54 and 10:90 for TE-polarized, and 48:52 and 13:87 for TM-polarized. The wide optical bandwidth according to the BPM simulation was also proven experimentally by measuring 2-D MMI devices. The preliminary measurement results for 3-D MMI couplers were also presented.

碩士
中華技術學院
機電光工程研究所碩士班
97
The optical waveguide integrated optical components with curved forms are part of the waveguide at present. Therefore the components design of the bending form of waveguide is particularly important. The bending waveguide is designed to focus on wide-angle and low-loss. The angle of bending for the traditional design of bending waveguide has to be restricted to less than 2 °. There will be a serious loss of radiation modes if angle is too large. This paper is interpreting to use coherently-coupled transfer mode to improve the above-mentioned defects. This paper is interpreting to use Beam Propagation Method (BPM) to simulate analysis and design and to use Coherently-Coupled Transfer mode and Multi-Mode interference structure to design bending-type demultiplexer components. When the input light, respectively, for the 1.55μm and 1.31μm wavelength and the bend angle of 5 °, the efficiency of transmission of those two wavelengths is more than 94%.

碩士
國立成功大學
微電子工程研究所
103
Mode converter and ring resonator are fabricated on the GaN wafer. Both of the devices are composed of several MMI waveguides and fabricated by ICP-RIE dry etching. We measure the characteristic of the device by CCD camera and the optical spectrum analyzer. First, mode converter output port shows exactly two light spot and frequency spectrum characteristic is similar with the input source. These result present that the mode converter can work properly under input source wavelength range. Second, the through port and drop port of the ring resonator has the contrast 10dB and 5dB, respectively. The through port spectrum is opposite to the drop port spectrum, same as the theory describing. Mode converter shows the function of converting fundamental mode into the first order mode but there is ripple on the spectrum. This is a problem that can be improved in the future. The ring resonator has the function of filtering wavelength but the contrast of the drop port is only 5dB which is smaller than the through port. The contrast can be improved by optimize the fabrication process or using the tapered MMI waveguide.