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Chaos, an unstable steady-state phenomenon, arises in apparently random optical sequences from semiconductor lasers subjected to reflection. This condition, referred to as cacophony, might provide a new pseudo-random source for use in coherent fibre optic systems. Coherent optical signal processing is expected to find substantially increased application, especially in local data networks. An optical spread-spectrum source may suit two apparent needs of these networks: 1) a high resolution optical time-domain reflectometer, using correlation of sequences, which can identify the closely spaced features found in these systems; and 2) data security through optical frequency-hopping encryption, especially in broadcast data networks. The link between cacophony and chaotic processes suggests that, although noise like, the spectral evolution of cacophony is deterministic. This implied reproducibility, akin the binary pseudo-random sequences, would be advantageous in spread-spectrum applications. Experimental examination of reflection effects on lasers has explored various lasing and external reflection conditions. Computer simulation of cacophonous generators supplement the experimental work with quick trials of experiments under typical, hypothetical, or even unrealisable conditions. A new in-phase and quadrature equivalent circuit models optical magnitude with phase information, and with modest computing requirements. Cacophony has been generated experimentally and in the computer model, and reproducible sequences up to 10ns long have been demonstrated. Modelling shows that reproducibility may be improved if conditions, especially at the start of lasing, are better controlled. It is concluded that, in order to reach the kind of optical sequence reproducibility that is called for in the applications described above, it is probably necessary to introduce quantisation into the generator. The work has attempted to characterize optical cacophony, and has perhaps added some knowledge to the general problems of coherent optical signal processing.

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We propose and demonstrate the superiority of using a phase SLM only in a multi-reference phase encoded joint transform correlator(JTC) compared to an ordinary JTC. Maximal length sequences are shifted to form two dimensional orthogonal arrays referred as m-arrays. The phase mask is used in one step to encode multiple reference images and at the same time eliminate false correlation peaks through power spectrum dispersion. A theoretical model of the implemented JTC is mathematically expressed and explained in this thesis. Basic performance criteria, PSR (peak to side lobe ratio) and PCE (peak to correlation energy), are used for comparative analysis, and their relationship to joint input image size and SLM size are investigated and the results simulated.

Optical regeneration has the potential to significantly increase the reach of long-haul transmission systems. In this thesis, wavelength-preserving polarization-insensitive all-optical 3R regeneration is investigated and demonstrated for 10 and 40 Gb/s signals. The all-optical regenerator utilizes a self-pulsating laser for clock recovery, cross-phase modulation (XPM) based spectral broadening in a highly nonlinear fiber (HNLF) and offset filtering for retiming, and self-phase modulation based spectral broadening in a HNLF and offset filtering for reshaping. Raman amplification is used to increase the XPM-based spectral broadening and thus allow a design that meets the tradeoffs involved in simultaneously achieving good retiming and reshaping performance. The regenerator is shown to reduce amplitude noise and timing jitter while not causing a BER penalty. To fully validate the regeneration scheme, the cascadability is demonstrated using a recirculating loop. For a 10 Gb/s signal, with a regenerator spacing of 240 km, a return-to-zero, on-off-keyed (RZ-OOK) signal was transmitted over 18,000 km (75 loops) with a power penalty of 1.6 dB at a BER of 1E-9 compared to the back-to-back case. For a 40 Gb/s signal, with a regenerator spacing of 80 km, a RZ-OOK signal was transmitted over 8,000 km (100 loops) with a power penalty of 1.2 dB. In addition, all-optical 3R regeneration is demonstrated using a multimode quantum-dot Fabry Petot laser with ultra-low timing jitter. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2009-10-19 14:11:53.826

Photonic integration and all-optical signal processing are promising solutions to the increasing demand for high-bandwidth and high-speed communication systems. III-V semiconductor materials, specially AlGaAs, have shown potentials for photonic integration and efficient nonlinear processes due to their low nonlinear absorption, flexibility at controlling the refractive index, and mature fabrication technology. In this thesis, we report the designs of AlGaAs microring resonators optimized for efficient four-wave mixing. Four-wave mixing (FWM) is a nonlinear optical phenomenon which can be used to realize many optical signal processing operations such as optical wavelength conversion and optical time division multiplexing and demultiplexing. Our designed AlGaAs microring resonators are expected to have good optical confinement, transmission characteristics, and efficient coupling between the ring and waveguide. Here we also present our fabrication efforts to fabricate the microring resonators device and the insights gained in the process. The microring resonators devices have a potential to be used in optical communication networks for all-optical signal processing operations.

In this thesis, new techniques to generate slow and fast light are proposed and investigated. The use of the slow and fast light for microwave photonics applications is also investigated. This thesis consists of four parts. In the first part, the generation of slow and fast light based on fiber Bragg gratings (FBGs) is studied. Two techniques are proposed. In the first technique, slow and fast light is generated based on a linearly chirped fiber Bragg grating (LCFBG); and in the second technique, slow and fast light is generated based on a tilted fiber Bragg grating (TFBG). Theoretical analysis is performed which is verified by experiments. In the second part, the applications of FBG-based slow and fast light in microwave photonics are studied. These applications include all-optical tunable microwave frequency multiplication, tunable microwave chirped pulse generation, tunable phase shifting, tunable fractional order differentiation, and tunable microwave photonic filtering. In the third part, the generation of slow and fast light based on microring resonators (MRRs) is studied. Novel methods to obtain continuously tunable slow to fast light are proposed and experimentally demonstrated by using a silicon-on-insulator (SOI) MRR with MMI (multi-mode interference) couplers, and a high-contrast Ge-doped silica-on-silicon (SOS) MRR. In the fourth part, the applications of the MRR-based slow and fast light in microwave photonics are studied. These applications include all-optical tunable fractional order differentiation, and tunable fractional order Hilbert transformation.

This thesis describes the development of optical wavelength converters with an integrated coupling structure, fabricated on periodically poled MgO doped lithium niobate (MgO:LN) for optical fiber communication and other all-optical signal processing applications. Wavelength converter is an integral part of any broadband communication system. The ability to transfer information between carrier wavelengths allows for efficient use of the available bandwidth in a transmission medium. Wavelength converters based on PPLN waveguides are among the most efficient nonlinear optical devices available today, due to highspeed operation, low noise, parallel operation on multiple wavelength channels and preservation of information carried in the optical domain. However, low conversion efficiency is an issue for wavelength converter based on PPLN waveguide. Compared to pure LN, MgO doped LN decrease restriction in optical damage and increase conversion efficiency. Integrated coupling structure demonstrates a solution to mode-coupling of the input wave to the fundamental mode of DFG device and increase the conversion efficiency. Therefore, a periodically poled MgO doped lithium niobate (MgO:LN) waveguides with integrated coupling structure is fabricated. The components of integrated coupling structure are compatible with lithium nobate waveguides, including directional couplers, small radius bends, adiabatic taper, and mode filter. The integrated coupling structure combines the pump and signal waves into the DFG conversion section, and makes the single mode conversion of the pump from input waveguide to conversion section. Theoretical models and simulations are provided in this thesis, and performances of the device with this structure are also presented. / Thesis / Master of Applied Science (MASc)

An increasing adoption of digital signal processing (DSP) in optical fiber telecommunication has brought to the fore several interesting DSP enabled modulation formats. One such format is orthogonal frequency division multiplexing (OFDM), which has seen great success in wireless and wired RF applications, and is being actively investigated by several research groups for use in optical fiber telecom. In this dissertation, I present three implementations of OFDM for elastic optical networking and distributed network control. The first is a field programmable gate array (FPGA) based real-time implementation of a version of OFDM conventionally known as intensity modulation and direct detection (IMDD) OFDM. I experimentally demonstrate the ability of this transmission system to dynamically adjust bandwidth and modulation format to meet networking constraints in an automated manner. To the best of my knowledge, this is the first real-time software defined networking (SDN) based control of an OFDM system. In the second OFDM implementation, I experimentally demonstrate a novel OFDM transmission scheme that supports both direct detection and coherent detection receivers simultaneously using the same OFDM transmitter. This interchangeable receiver solution enables a trade-off between bit rate and equipment cost in network deployment and upgrades. I show that the proposed transmission scheme can provide a receiver sensitivity improvement of up to 1.73 dB as compared to IMDD OFDM. I also present two novel polarization analyzer based detection schemes, and study their performance using experiment and simulation. In the third implementation, I present an OFDM pilot-tone based scheme for distributed network control. The first instance of an SDN-based OFDM elastic optical network with pilot-tone assisted distributed control is demonstrated. An improvement in spectral efficiency and a fast reconfiguration time of 30 ms have been achieved in this experiment. Finally, I experimentally demonstrate optical re-timing of a 10.7 Gb/s data stream utilizing the property of bound soliton pairs (or "soliton molecules") to relax to an equilibrium temporal separation after propagation through a nonlinear dispersion alternating fiber span. Pulses offset up to 16 ps from bit center are successfully re-timed. The optical re-timing scheme studied here is a good example of signal processing in the optical domain and such a technique can overcome the bandwidth bottleneck present in DSP. An enhanced version of this re-timing scheme is analyzed using numerical simulations.