D.Ing. / Most optical fibre-based ambient refractive index sensors (including individual long-period gratings) rely on spectral attributes obtained in transmission. However, a probe refractometer has been proposed that is based on self-interference of a long-period grating (LPG), thus providing reflectance spectra containing the relevant data. This sensor operates as a Michelson interferometer by virtue of the fact that its constituent LPG acts as both a mode converter and coupler. Its construction is such that optical power coupled into the cladding (when light impinges on the LPG) is reflected at a fibre mirror and returns towards the grating, where it is re-coupled into the fundamental guided mode. Since light waves propagating along the core and cladding material of the fibre cavity beyond the LPG experience different optical path lengths (due to differing mode indices), a phase difference exists between these modes upon recombining at the grating location. This causes interference, which is manifested as a characteristic fringe pattern in the sensor’s reflectance spectrum (analogous to that obtained in the transmission of a twin LPG cascade operating as a Mach-Zehnder interferometer). Research was conducted towards implementing a unique method of temperature compensation in this LPG-based Michelson interferometer. Sensing attributes of individual LPGs were investigated first, with specific emphasis on the temperature characteristics of two different types of host fibre. It was found that LPGs manufactured in conventional ATC SMF-28 fibre (previously hydrogen-loaded to inscribe the grating and annealed after fabrication) and B/Ge co-doped PS1500 fibre from Fibercore exhibited temperature characteristics of opposite polarity. This led to the implementation of a compound-cavity Michelson interferometer whose constituent LPG is written in one type of fibre, while a specific length of the other type of fibre is fusion spliced onto the host fibre section. Experiments verified the success of this temperature-compensation technique, which caused a measured reduction in temperature sensitivity of up to in interferometer phase shift. Measurements of the refractive index of the test substance surrounding the cladding material of the Michelson interferometer’s fibre cavity (and not the LPG itself) could therefore be done without being adversely affected by environmental temperature fluctuations. This was demonstrated experimentally by comparing the interferometer’s phase shift – devoid of temperature-induced effects – due to increasing refractive index of the analyte (as a result of escalating temperature) with index of refraction readings from a temperature-controlled Abbe refractometer. Numerical gradients of linear curves fitted to these results differed by two orders of magnitude less than the resolution of readings obtained from an Abbe refractometer – proof of the success of the temperature compensation technique applied in this LPG-based Michelson refractometer.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 1975 / Vita. / Bibliography: p.168-172. / by Robert Wilson King, Jr. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

Phase shifting interferometry is one of the most promising methods for testing aspheres. However, one will encounter the following problems when it is applied to test an asphere: (1) very tight fringes produced by a strong asphere exceed the test system's resolution, (2) a test wavefront suffers from system aberrations of the interferometer that cause measurement errors, and (3) the wavefront immediately after reflection does not necessarily represent the shape of the test asphere. This thesis used a high density array sensor to detect the dense fringes. In order to solve the system aberration and the ray retrace problems, it is necessary to incorporate a ray trace code and phase shifting interferometry. This measurement principle was applied for an aspheric surface whose asphericity was 100 waves. A phase shifting Fizeau interferometer was incorporated with an optical design program. The attained accuracy was approximately one-tenth of a wave.

Submitted in fulfilment of the academic requirements for the Degree Master of Engineering: Electrical Engineering, Durban University of Technology. Durban. South Africa, 2015. / This dissertation describes the development and construction of the Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA) at the Durban University of Technology. The MITRA station consists of 2 antenna arrays separated by a baseline distance of 8 m. Each array consists of 8 Log-Periodic Dipole Antennas (LPDAs) operating from 200 MHz to 800 MHz. The design and construction of the LPDA antenna and receiver system is described. The receiver topology provides an equivalent noise temperature of 113.1 K and 55.1 dB of gain. The Intermediate Frequency (IF) stage was designed to produce a fixed IF frequency of 800 MHz. The digital Back-End and correlator were implemented using a low cost Software Defined Radio (SDR) platform and Gnu-Radio software. Gnu-Octave was used for data analysis to generate the relevant received signal parameters including total power, real, and imaginary, magnitude and phase components. Measured results show that interference fringes were successfully detected within the bandwidth of the receiver using a Radio Frequency (RF) generator as a simulated source. This research was presented at the IEEE Africon 2013 / URSI Session Mauritius, and published in the proceedings.

The properties of all-optical nonlinear waveguide devices are investigated. In particular, the nonlinear directional coupler (NLDC) and nonlinear Mach-Zehnder interferometer (NLMZ) are analyzed using perturbation theory. The perturbation theory provides differential equations that describe the amplitude of the waveguide modes as a function of the propagation distance. To be practical, these waveguide devices require nonlinear phase shifts of π or more. Therefore, the theoretical investigation of these devices emphasizes their fabrication in bulk and multiple-quantum-well (MQW) gallium arsenide (GaAs). For the first time, absorption, carrier diffusion, and thermal effects are included in the theoretical investigation of the NLMZ and NLDC. The nonlinear dependence of the coupling terms, which has been neglected in all previous work, is shown to be significant for semiconductor based NLDC's. The effects of carrier diffusion on the nonlinear response of a GaAs waveguide is demonstrated using a self-consistent numerical method. The effects are heavily dependent on the waveguide geometry, and, therefore, should be included in the analysis of nonlinear semiconductor waveguide devices. However, if the diffusion length is large compared to the mode width, carrier diffusion simplifies the investigation since the nonlinear absorption and index change are uniform across the mode. This important conclusion is used in the models for the NLMZ and NLDC. The theoretical models predict the NLMZ and NLDC should work in bulk and MQW GaAs. To demonstrate that the required nonlinear phase shifts for the NLMZ and NLDC are indeed possible in bulk and MQW GaAs, the first experimental observation of electronic optical bistability in a MQW GaAs strip-loaded waveguide is recounted. This original research illustrated that phase shifts in excess of 2π are possible in MQW GaAs waveguides and, therefore, the future of all-optical waveguide devices in semiconductors is optimistic.

A study of the application of single-mode fiber optics to the multiple-beam interferometric recombination problem is presented. In the laboratory, the fibers have been used in wide bandwidth, two-arm, Mach-Zehnder test interferometers as well as a 5-telescope imaging interferometer connected to an all-fiber beam combiner. Based upon these experiments and some theoretical studies it is shown that fiber optics and fiber optic components such as directional couplers provide an excellent alternative to conventional optics such as mirrors, beamsplitters, and relay lenses. The equations describing the measurement of the complex degree of coherence in an interferometer with a single-mode fiber in each arm are derived. The equations reveal an important feature of the fibers: they filter phase fluctuations due to aberrations and turbulence at the input and convert them to intensity fluctuations at the output. This leads to a simplification of the calibration of measured visibilities. The coupling efficiency of light which has passed through a turbulent atmosphere is also studied as a function of fiber parameters and turbulence conditions for both image motion stabilized and non-stabilized cases. For the former case, coupling efficiency remains greater than 50% as long as telescope diameter is no larger than the turbulence coherence length. Beam combination architectures using arrays of directional couplers are fully discussed. Arrays accommodating up to 20 input beams are presented. The arrays require only N detector pixels for N input beams. A scheme of temporal multiplexing of the phase of each beam is used to identify individual fringe pairs. One possible scheme allows wide bandwidths even for large numbers of beams. A 5-telescope interferometer has been constructed and connected to an all-fiber beam combiner. Two extended objects were observed and reconstructed using standard radio astronomy VLBI software. The interferometer and beam combiner had good thermal and polarization stability and high throughput. Reconstructed images had dynamic ranges of about 50.

M.Ing. (Electrical and Electronic Engineering) / A distributed temperature fiber sensor based on the ratio of the Raman anti-Stokes to Rayleigh backscattered light components is studied. The aim of the study is to propose a method of quantifying the noise exhibited in the Rayleigh backscattered signal and further propose correlation coding techniques to reduce the noise in the Rayleigh and Raman backscattered signals. The noise in the Rayleigh backscattered signal is referred to as “interferometric noise”. When Rayleigh scattering along the length of an optical fiber occurs, some of the scattered light travels in a direction opposite to the direction of propagation, and is called backscattered light. When the coherence length of the optical source permits interactions between the Rayleigh backscattered light, there is a possibility for the interacting backscattered light, within a distance that is half the coherence length, to interfere with each other. Furthermore, when the sensing optical fiber is greater than the coherence length of the optical source, there will be several interference sections along the length of the sensing fiber causing the intensity of the Rayleigh backscattered light at the photo-detectors to vary randomly. The intensity variation gives the Rayleigh backscattered signal a jagged appearance indicating the presence of interferometric noise. The longer the coherence length of the optical sources, the larger the intensity variations in the backscattered light, that is, the more the interferometric noise exhibited. The more the interferometric noise in the Rayleigh backscattered signal, the poorer the temperature accuracy of the distributed temperature sensor based on the ratio of the Raman anti Stokes to Rayleigh backscattered components. To quantify the interferometric noise affecting the Rayleigh backscattered signal, a mathematical model based on well-known scattering and interferometry theories is developed. Using the developed mathematical noise model, noise powers of approximately -52dBm and -40dBm for coherence lengths of 4m and 24m are respectively obtained...

No description available.

Chan Wai-Leung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Abstracts in English and Chinese. / ABSTRACT --- p.I / 摘要 --- p.III / Acknowledgements --- p.V / Table of Contents --- p.VII / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Different All-Optical Signal Processing Functions --- p.3 / Chapter 1.1.1 --- Periodic optical signal generation --- p.3 / Chapter 1.1.2 --- Optical clock recovery and clock synchronization --- p.4 / Chapter 1.1.3 --- Wavelength conversion and signal regeneration --- p.5 / Chapter 1.1.4 --- Optical multicasting --- p.6 / Chapter 1.1.5 --- All-optical time division multiplexing and demultiplexing --- p.6 / Chapter 1.2 --- SOA-MZI as the Prime Candidate --- p.7 / Chapter 1.3 --- Overview of the Thesis --- p.8 / References --- p.10 / Chapter 2 --- basic Properties of Semiconductor Optical Amplifier Based Mach-Zehnder Interferometer --- p.16 / Chapter 2.1 --- Semiconductor Optical Amplifier Based Mach-Zehnder Interferometer --- p.16 / Chapter 2.1.1 --- Characteristics of SOA-MZI --- p.17 / Chapter 2.2 --- Review on Different Reported Applications of SOA-MZI --- p.19 / Chapter 2.2.1 --- Format converter --- p.19 / Chapter 2.2.2 --- Mode-locked fiber ring laser --- p.20 / Chapter 2.2.3 --- OTDM ADD/DROP Multiplexer --- p.21 / Chapter 2.2.4 --- Optical Switch --- p.21 / References --- p.23 / Chapter 3 --- Self-Starting All-Optical Photonic Clock --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Principle of Photonic Clock Generation --- p.26 / Chapter 3.3 --- Basic Configuration --- p.27 / Chapter 3.3.1 --- Basic results --- p.28 / Chapter 3.3.2 --- Effects of state of polarization --- p.31 / Chapter 3.3.3 --- Effects of an isolator within the feedback loop --- p.34 / Chapter 3.3.4 --- Phase noise characteristics --- p.35 / Chapter 3.4 --- Multi-Loop Configuration --- p.36 / Chapter 3.4.1 --- Results examined in time domain --- p.38 / Chapter 3.4.2 --- Results examined in frequency domain --- p.38 / Chapter 3.4.3 --- More multi-loop results --- p.40 / Chapter 3.5 --- Other Proposed Scheme --- p.40 / Chapter 3.6 --- Summary --- p.43 / References --- p.44 / Chapter 4 --- All-Optical Clock Recovery --- p.46 / Chapter 4.1 --- Introduction --- p.46 / Chapter 4.2 --- Principle of All-Optical Clock Recovery --- p.47 / Chapter 4.3 --- Experiments Setup --- p.48 / Chapter 4.4 --- Clock Recovery Demonstration --- p.50 / Chapter 4.5 --- External Clock Synchronization Demonstration --- p.53 / Chapter 4.6 --- Summary --- p.55 / References --- p.56 / Chapter 5 --- Wavelength Conversion Optimization Using a Holding Beam --- p.57 / Chapter 5.1 --- Introduction --- p.57 / Chapter 5.2 --- Principle of Wavelength Conversion Under Injection of a Holding Beam --- p.58 / Chapter 5.3 --- Wavelength Conversion Using a Holding Beam --- p.62 / Chapter 5.4 --- Effect of a Holding Beam on Wavelength Conversion --- p.63 / Chapter 5.5 --- Optimizing the Effect of Holding Beam Assisted Wavelength Conversion --- p.67 / Chapter 5.6 --- Summary --- p.68 / References --- p.69 / Chapter 6 --- All-Optical Multicasting of Digital Signal with Format Conversion --- p.70 / Chapter 6.1 --- Introduction --- p.70 / Chapter 6.2 --- Principle of Switching-Wavelength Pulses Generation --- p.72 / Chapter 6.3 --- Principle of Multicasting Using SOA-MZI --- p.75 / Chapter 6.4 --- Experiment on Multicasting --- p.76 / Chapter 6.5 --- Performance of the Multicasting Scheme --- p.79 / Chapter 6.6 --- Summary --- p.84 / References --- p.85 / Chapter 7 --- Optical Demultiplexing for Time Division Multiplexed Data Source With Wavelength Conversion --- p.87 / Chapter 7.1 --- Introduction --- p.87 / Chapter 7.2 --- Principle of Optical Time Division Demultiplexing Using SOA-MZI --- p.90 / Chapter 7.3 --- Demonstration of Optical Time Division Demultiplexing --- p.91 / Chapter 7.4 --- Results and Discussions --- p.93 / Chapter 7.5 --- Summary --- p.96 / Chapter 8 --- Conclusion and Future Works --- p.100 / Chapter 8.1 --- Conclusions --- p.100 / Chapter 8.2 --- Future Works --- p.102 / Appendices --- p.A-1 / Appendix A. List of Publications --- p.A-1 / Appendix B. List of Figures --- p.A-2

Graduation date: 1967