GaAs optoelectronic logic devices.

She Tsz Chung William.Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.Includes bibliographical references (leaves 127-133).Chapter 1. --- IntroductionChapter 2. --- Review of Optical Logic --- p.11-28Chapter 2.1 --- All-Optical ApproachChapter 2.2 --- Optoelectronic ApproachChapter 2.3 --- Comparison of the Two ApproachesChapter 3. --- High Speed Photodetectors applied in Optoelectronic Logic Design --- p.29-40Chapter 3.1 --- Photoconductive SwitchChapter 3.2 --- Metal-Semiconductor-Metal PhotodetectorChapter 3.3 --- Design of Simple Logic GatesChapter 4. --- Device Fabrication and Characterization --- p.41-59Chapter 4.1 --- Design of Basic StructureChapter 4.2 --- FabricationChapter 4.3 --- Mounting of DeviceChapter 4.4 --- CharacterizationChapter 5. --- Experimental Technique --- p.60-74Chapter 5.1 --- Measurement ProcedureChapter 5.2 --- Optical SourcesChapter 5.3 --- Optical AlignmentChapter 5.4 --- Control of Optical Path DelayChapter 5.5 --- Measurement AutomationChapter 6. --- Demonstration of Optoelectronic Logic Devices --- p.75-110Chapter 6.1 --- OR GateChapter 6.2 --- Exclusive-OR GateChapter 6.3 --- Exclusive-NOR GateChapter 6.4 2 --- to 4 DecoderChapter 7. --- Discussion --- p.111-124Chapter 7.1 --- ImprovementsChapter 7.2 --- Extensions of this ProjectChapter 7.3 --- Prospects and Limitations of this ApproachChapter 8. --- Conclusion --- p.125-126References --- p.127-133AppendixChapter I. --- List of Instruments --- p.134-136Chapter II. --- Properties of GaAs --- p.137Chapter III. --- List of Accepted and Submitted Publications during the Period of Study --- p.13

Indium Phosphide Based Optical Waveguide MEMS for Communications and Sensing

Indium phosphide (InP) is extensively used for integrated waveguide and photonic devices due to its suitability as a substrate for direct bandgap materials (e.g. In1-XGaXAsYP1-Y) operating at the lambda=1550 nm communications wavelength. However, little work has been reported on InP optical waveguide micro-electro-mechanical systems (MEMS). In this work, InP cantilever and doubly-clamped beams were micromachined on an In0.53Ga0.47As "sacrificial layer" on (100) InP substrates. Young's modulus was measured using nanoindentation and microbeam-bending. Intrinsic stress and material uniformity (stress gradient) were obtained by measuring the profile of doubly-clamped and cantilever beams using confocal microscopy. The study resulted in a Young's modulus of 80.4-106.5 GPa (crystal orientation-dependent). Although InP was grown lattice-matched to the substrate, arsenic from the underlying In0.53Ga0.47As sacrificial layer resulted in intrinsic compressive stress. Adding trace amounts of gallium to the InP layer during epitaxial growth induced tensile stress to offset the effect of arsenic. The materials characterization was extended to develop optical waveguide switches and sensors. In the first device, two parallel waveguides were actuated to vary the spacing between them. By modulating the gap using electrostatic pull-in actuation, the optical coupling strength was controlled via the evanescent field. Low voltage switching (<10 V), high speed (4 us), low crosstalk (-47 dB), and low-loss (<10 %) were achieved. Variable coupling over a 17.4 dB dynamic range was also demonstrated. The second device utilized a single movable input waveguide, which was actuated via electrostatic comb-drives to end-couple with one of several output waveguides. Low voltage switching (<7 V), 140 us switching speed (2 ms settling time), low crosstalk (-26 dB), and low-loss (<3.2 dB) were demonstrated. Sensing techniques based on mass-loading were developed using end-coupled cantilever waveguides. Here, the mechanical resonance frequency was measured by actuating the cantilever and measuring the end-coupled optical power at the output waveguide. A proof-of-concept experiment utilized a focused-ion-beam to mill the cantilever tip and resulted in a measurable resonance shift with mass-sensitivity delta_m/delta_f=5.1 fg/Hz. The cantilever waveguide devices and measurement techniques enable accurate resonance detection in mass-based cantilever sensors and also enable single-chip sensors with on-chip optical detection to be realized

Technologies for single chip integrated optical gyroscopes

Optical gyroscopes are being employed for navigational purposes for decades now and have achieved comparable or better reliability and performance than rotor-based gyroscopes. Mechanical gyros are however generally bulky, heavy and consume more power which make them unsuitable for miniaturized applications such as cube satellites and drones etc. Therefore, much effort is being expended worldwide to fabricate optical gyros having tactical grade robustness and reliability, small size, weight, cost and power consumption with minimal sacrifice of sensitivity. Integrated optics is an obvious approach to achieving this. This work comprises detailed comparative analysis of different types and structures of integrated optical gyroscopes to find out the suitable option for applications which require a resolution of <10 o/h. Based on the numerical analysis, Add-drop ring resonator-based gyro is found to be a suitable structure for integration which has a predicted shot noise limited resolution of 27 o/h and 2.71 o/h for propagation losses of 0.1 dB/cm and 0.01 dB/cm respectively. An integrated gyro is composed of several optical components which include a laser, 3dB couplers, phase/frequency modulators, sensing cavity and photodetectors. This requires hybrid integration of multiple materials technologies and so choices about which component should be implemented in which technology. This project also undertakes theoretical optimization of few of the above-mentioned optical components in materials systems that might offer the most convenient/tolerant option, this including 3dB coupler, thermo-optic phase modulator and sensing cavity (resonator and waveguide loop). In particular, the sensing element requires very low propagation loss waveguides which can best be realised from Si3N4 or Ta2O5. The optimised Si3N4 or Ta2O5 waveguides however are not optimal for other functions and this is shown and alternatives explored where the Si3N4 or Ta2O5 can easily be co-integrated. The fabrication process of low loss Si3N4 and Ta2O5 waveguides are also reported in this thesis. Si3N4 films were grown by using low pressure chemical vapor deposition (LPCVD) technique. Dry etching of Si3N4 films have been optimized to produce smooth and vertical sidewalls. Experimental results predicted that the propagation loss of 0.009 dB/cm is achievable by using optimum waveguide dimensions and silica cladding with the relatively standard processes available within the Laser Physics Centre at the Australian National University. A CMOS back end of line compatible method was developed to deposit good quality Ta2O5 films and silica claddings through ion beam sputtering (IBS) method. Plasma etching of Ta2O5 waveguides has been demonstrated by using a gas combination of CHF3/SF6/Ar/O2. Oxygen was introduced into the chamber to produce non-vertical sidewalls, so the waveguides could be cladded without voids with IBS silica. Average propagation losses of 0.17 dB/cm were achieved from Ta2O5 waveguides which appeared after extensive investigation to be limited by the spatial inhomogeneity of the processing. Lastly, a detailed theoretical and experimental analysis was performed to find out the possible causes of the higher average propagation loss in Ta2O5 waveguides, some sections being observed with 0.02 dB/cm or lower losses

DARKNESS: The First Microwave Kinetic Inductance Detector Integral Field Spectrograph for Exoplanet Imaging

High-contrast imaging is a powerful technique for the study of exoplanets. Combining extreme adaptive optics to correct for atmospheric turbulence, a coronagraph to suppress diffraction from the telescope aperture, and an integral field spectrograph to obtain a spectrum at every spatial element in the final image, ground-based high contrast instruments can effectively remove on-axis star light to characterize nearby faint companions and disks. Current state-of-the-art high-contrast imagers operating at near-infrared wavelengths regularly achieve contrast ratios &lt; 10−6 at 0.5” separations. For young systems (&lt;~10 Myr) at 10 pc, this roughly translates to detectability of Jupiter mass planets in 5 AU orbits. Tighter separations may be achieved with larger telescope apertures, but deeper contrasts are limited from the ground by residual atmospheric aberrations. Unsensed and uncorrected wavefront aberrations lead to a pattern of coherent speckles in the final image that evolve on a range of timescales from a few milliseconds to tens of minutes. The most problematic speckle population, referred to as atmospheric speckles, have lifetimes of roughly 1 s causing them to average slowly in long exposures. After subtraction of the long lived quasi-static speckles in post-processing, atmospheric speckle noise sets the ultimate contrast limits.In this thesis we present DARKNESS (the DARK-speckle Near-infrared Energy- resolving Superconducting Spectrophotometer), the first demonstration platform to utilize optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs enable real-time speckle control techniques and post-processing speckle suppression at framerates capable of resolving the atmospheric speckles. We describe the motivation, design, and characterization of DARKNESS, its deployment behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory, early speckle characterization results at ∼ms timescales, and future prospects for implementing this data in useful speckle removal schemes

Development and testing of a micromachined probe card.

This thesis is concerned with the design, fabrication and testing of micro scale probes. The probes were designed to act as temporary electrical connections to allow wafer level testing of integrated circuits. The work initially focused on the creation of free standing nickel cantilevers, angled up from the substrate with probe tips at the free end. These were fabricated using a novel method, combining pseudo grey scale lithography and thick photoresist sacrificial layers. Detailed analysis of the fabrication method, in particular the resist processing and lithography was undertaken and the limitations of the method explored.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Free-space holographic optical interconnects in dichromated gelatin

Abstract unavailable please refer to PDF

Micro-optics for Opto-genetic Neuro-stimulation with Micro-LED Arrays

The breakthrough discovery of a nanoscale optically gated ion channel protein, Channelrhodopsin 2 (ChR2), in combination with a genetically expressed optically activated ion pump, Halorhodopsin, allowed the direct stimulation and inhibition of individual action potentials with light alone. This thesis describes the development of optics and micro-optics which when used with micro-led array sources, collects and projects light efficiently and uniformly onto such opto-genetically modified specimens. When used with enhanced light gated ion channels and pumps these systems allow us to further our understanding of both brain and visual systems. Micro-LED arrays permit spatio-temporal control of neuron stimulation on sub-millisecond timescales. However, micro-led arrays are disadvantaged by the broad-angular spread of their light emission and their low spatial fill factor. We present the design of macro and micro-optics systems for use with a micro-LED arrays consisting of a matrix of 25μm diameter micro-LEDs with 150 or 80μm centre-to-centre spacing. On one system, the micro-LED array is imaged onto off-the-shelf micro-optics using macro-optics and in the other system; micro-LED array and custom micro-optics are optimised and integrated together. The two systems are designed to improve the fill-factor from 2% to more than 78% by capturing a larger fraction of the LED emission and directing it correctly to the sample plane. This approach allows low fill factor arrays to be used effectively, which in turn has benefits in terms of thermal management and electrical drive from CMOS backplane electronics. These systems were implemented as an independent set that could be connected to a variety of different microscopes available for Patch-clamp and Multi-electrode measurements. As well, the feasibility of an eye prosthesis was tested using virtual reality optics and a fake eye to stimulate ganglion cells and by doing in-vivo stimulation of the genetically modified retina of a mouse.Open Acces

Conference on Binary Optics: An Opportunity for Technical Exchange

The papers herein were presented at the Conference on Binary Optics held in Huntsville, AL, February 23-25, 1993. The papers were presented according to subject as follows: modeling and design, fabrication, and applications. Invited papers and tutorial viewgraphs presented on these subjects are included

Apertureless scanning near-field optical microscopy and manipulation of nanostrucutres at electrified interfaces

Der Einfluss unterscheidlicher geometrischer und material-typischer Parameter wurde simuliert und mittels experimentellen Untersuchungen bestätigt um den Mechanismus der Oberflächenstrukturierungen unterhalb des Beugungslimits von Licht zu klären.The influence of geometrical and material-specific parameters was simulated and confirmed experimentally to clarify the origin of surface modification below the diffraction limit of ligh