The laser-induced holographic grating technique was employed to study the dynamic of the intensity grating formation in the azo-dye doped liquid crystals. The liquid crystal material in this study has several mesomorphic phases: smectic C, smectic A, and nematic. The first order of diffraction in the mesomorphic phases have been investigated by changing the concentration of dye, the polarizations of the writing beams and the probe beam

A optically controlled cholesteric grating is proposed. The dye-doped cholesteric grating (DDCLC grating) can be rotated by changing the polarization of the pump-beam. The experiment results reveal that the orientation of the cholesteric grating can be rotated in a specific range decided by the alignment direction of the two substrates. Moreover, the hybrid alignment condition for the cholesteric grating is also investigated. When the ratio of d/p is larger than 0.5,the cholesteric grating is observable without applying voltage in hybrid aligned cholesteric cell, and the cholesteric gratings with hybrid alignment can have a 360 rotation angle, thus achieve the two dimension beam steering cholesteric.

This document describes the design, analysis, construction and testing of KiwiSpec, a fibre-fed, high resolution astronomical spectrograph of an asymmetric white pupil design. The instrument employs an R4, 31.6 groove mm⁻¹ échelle grating for primary dispersion and a 725 lines mm⁻¹ volume phase holographic (VPH) based grism for cross-dispersion. Two versions of the prototype were designed and constructed: an 'in-air' prototype, and a prototype featuring a vacuum chamber (to increase the stability of the instrument). The KiwiSpec optical design is introduced, as well as a description of the theory behind a cross-dispersed échelle spectrograph. The results of tolerancing the optical design are reported for alignment, optical fabrication, and optical surface quality groups of parameters. The optical windows of an iodine cell are also toleranced. The opto-mechanical mounts of both prototypes are described in detail, as is the design of the vacuum chamber system. Given the goal of 1 m/s radial velocity stability, analyses were undertaken to determine the allowable amount of movement of the vacuum windows, and to determine the allowable changes in temperature and pressure within and outside of the vacuum chamber. The spectral efficiency of the instrument was estimated through a predictive model; this was calculated for the as-built instrument and also for an instrument with ideal, high-efficiency coatings. Measurements of the spectral efficiency of various components of the instrument are reported, as well as a description of the measurement system developed to test the efficiency of VPH gratings. On-sky efficiency measurements from use of KiwiSpec on the 1-m McLellan telescope at Mt John University Observatory are reported. Two possible exposure meter locations are explored via an efficiency model, and also through the measurement of the zero-order reflectivity of the échelle grating. Various stability aspects of the design are investigated. These include the stability of the optical mounts with temperature changes, and also the effect of the expansion and contraction of the supporting optical tables. As well, the stability of the in-air prototype was determined through measurement of the movement of thorium-argon emission lines within spectra as the temperature, atmospheric pressure and relative humidity (naturally) varied. Current and planned testing for determining the stability of the vacuum chamber prototype is discussed.

The laser-induced holographic gratings in the azo-dye-doped liquid crystals have been investigated by changing the temperature, and the concentration of the sample, the intensity of the two writing beams, and the polarization of probe beams. The cw Nd:YAG laser has been employed as the writing beams and the cw He-Ne laser has been employed as a real-time probe beam to detect the first order diffraction singals. The gratings are the results of photo-isomerization of azo dye and the structure alignment of liquid crystals. The model has been established to explain the first order diffraction signals, the mechanism of gratings formation and the temperature dependence.

Electron microscopes offer scientists an invaluable tool in probing matter at a very small scale. Rapid advancements over the past several decades has allowed electron microscopes to routinely image samples at the atomic scale. These advancements have been in all aspects of electron microscope design – such as more stable control voltages and currents, brighter and more coherent sources, beam aberration correction, and direct electron detectors, to name a few. One very recent advancement is in shaping the electron beam to provide an almost arbitrary set of possible beam profiles. Following the demonstration of electron vortex beams in 2010, there has been a surge of interest in the potential shaping electron beams. Utilizing holographic electron diffraction gratings, an almost arbitrary set of electron beams can be generated. These diffraction gratings are challenging to create due their tiny size and the precision with which they must be fabricated. We present a comprehensive study on the fabrication and design of electron diffraction gratings with the aim of being able to produce optimal gratings that result in bright, well separated beams which closely match a desired beam profile. We have developed and optimized fabrication of these gratings with focused ion beam milling, and have been able to use the fabricated gratings in a number of important experiments. These electron diffraction gratings have allowed us to perform various experiments such as aberration correction, electron helical dichroism, advanced phase-contrast imaging, and multi-beam interferometric techniques. Holographic beam shaping will continue to be an important tool for electron microscopists.

Optical add/drop multiplexer (OADM) and optical wavelength cross-connect (WXC) are two key components to enable greater connectivity and flexibility in dense wavelength division multiplexing (DWDM) networks. Fiber Bragg grating (FBG) based components have several inherent advantages such as compact, low-insertion loss, high reflectivity, no-linearity effect, polarization insensitivity and wavelength tunability. We experimentally investigate the system power penalty induced by the chromatic dispersion of the FBG as a function of the wavelength detuning of the reflection spectrum for 10 Gb/s signals, which was reflected by cascade of FBGs. Such power penalty limits the number of cascaded gratings and restricts the allowable range of wavelength detuning. In our experiments, we have used several FBG filters with 3-dB bandwidth of 0.43 nm. According to the experimental results, power penalty increases from the central wavelength to the edge wavelength of the reflection spectrum. There are 0.4 dB and 7 dB power penalty for one single FBG and ten cascaded-FBG filter, respectively, when the central wavelength was detuned to ¡Ó0.2 nm and ¡V0.1/+0.14 nm. This study result may give a design guideline of fiber grating-based optical add-drop multiplexers or optical wavelength cross-connects in DWDM nodes.

We study the dynamical behavior of the holographic grating formed in polymer-dispersed liquid crystal ( PDLC ) films. The grating is written by two coherent Ar+ laser ( l=514.5nm ) , while probed by a He-Ne laser ( l=632.8nm ).

No description available.

This thesis details the design, fabrication and measurement of an integrated optical Bragg grating filter, operating at a free space wavelength of 1532 nm, based on silicon-on-insulator (SOI) ridge waveguide. Grating-based integrated devices can interact with optical signals in photonic integrated circuits (PIC) in such a way as to selectively transmit, reflect or detect the signals that are resonant with these devices. Channel filters can access one channel of a wavelength division multiplexed signal without disturbing the other channels and are therefore important elements in WDM communications. Resonator filters are attractive candidates because they can potentially realize the narrowest linewidth for a given device size. Device models for this kind of device are developed by using the MATLAB programming language. Coupled mode theory (CMT) for filters, and the effective index method (EIM) which reduces a three dimensional (3D) analysis into two dimensions is used as modeling theoretical background. Computer modeling identifies the effect of device structure on the performance of the devices, and is also used to predict the output characteristics of this kind of device. This provides an understanding of device physics and operation, and a basis for comparison with experimental results. A common fabrication sequence for integrated optical Bragg grating filters based on SOI ridge waveguides is designed, developed and demonstrated. This includes the photomask for optical ridged waveguide, interferometic lithography for grating pattern and high accuracy RIE etching. This work demonstrates Bragg grating as a technology for realizing PIC in SOI material system, and presents the technology required to design, fabricate, characterize, and model these integrated devices. / Thesis / Master of Applied Science (MASc)

Design and Analysis of Arrayed Waveguide Grating Abstract Fiber optic communication provides extremely broad bandwidth making transferring large quantities of voice/data possible. Dense Wavelength Division Multiplexing (DWDM) is the most critical technology of the optical communication system. It allows the simultaneous transmission of up to hundreds of channels within a single fiber across a distance of thousands of kilometers. Arrayed waveguide grating (AWG) is the most critical component in the DWDM system. It takes a single input and separates different optical ¡§channels¡¨ into different output fibers. It is critical that we develop our own ability to design and fabricate such a device, so that we will not be left behind in the technological realm. Although there are many commercially available AWG designing software such as the Phaser package of the BPMPRO software, they fail to provide a solution to aide in the final design of the optical mask for the AWG. In this thesis, we present a detailed, step-by-step analysis of an AWG device, as well as a description of how the AWG device works. In the process, we have classified the free parameters from that of depending parameters and have solved the routing problem in the layout of the waveguides. To summarize the primary result of this thesis, we use five main points, which are: 1) We discuss the function of each block, the subsystems of the AWG. 2) We propose a novel, yet intuitive theory based on geometric optics ¡V how the device is able to perform its de-multiplexing functions. 3) We present an analytic formula showing the linear property of the optical path difference along the source and the receiver arrays. 4) We solved the routing problem of the various waveguide sections of the AWG. 5) We have automated the process of generating optical masks in AutoCAD format from within a Matlab environment.