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In present dissertation, field-driven quantum well (QW) device is proposed to obtain high-speed and high-efficiency all-optical wavelength converter (AOWC). A new type QW material, InGaAsP/InGaAlAs, is employed to improve not only quantum confined Stark effect, but also carrier life time during high electric field excitation. The bandwidth as well as efficiency can be enhanced. Thus, the slow gain recovery mechanism (~100ps) from conventional semiconductor optical amplifier (SOA)-based AOWC can be overcome. The dispersion- and efficient- limited fiber-based AOWC (~10ps) can also be avoided. -3dB frequency bandwidth exceeding 40GHz for both electrical-to-optical and photocurrent response has been observed from InGaAsP/InGaAlAs waveguide of AOWC, leading to above 40GHz bandwidth in optical-to-optical response. A 40 Gb/s measurement setup is finally used for testing eye-diagram and bit-error-ratio in order to verify the data transmission of AOWC. Low power penalty with 0.5 dB comparing with back-to-back system performance is measured, suggesting InGaAsP /InGaAlAs waveguide is applicable to all-optical processing. By exciting short optical pump pulse in such waveguide, as short as 6.4ps probe pulse is observed, breaking through 10ps order in conventional type of QW and thus indicating the plausibility of performing 100Gb/s all optical processing.

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In this dissertation I investigated a multi-channel and multi-bit rate all-optical clock recovery device. This device, a birefringent Fabry-Perot resonator, had previously been demonstrated to simultaneously recover the clock signal from 10 wavelength channels operating at 10 Gb/s and one channel at 40 Gb/s. Similar to clock signals recovered from a conventional Fabry-Perot resonator, the clock signal from the birefringent resonator suffers from a bit pattern effect. I investigated this bit pattern effect for birefringent resonators numerically and experimentally and found that the bit pattern effect is less prominent than for clock signals from a conventional Fabry-Perot resonator.I also demonstrated photonic balancing which is an all-optical alternative to electrical balanced detection for phase shift keyed signals. An RZ-DPSK data signal was demodulated using a delay interferometer. The two logically opposite outputs from the delay interferometer then counter-propagated in a saturated SOA. This process created a differential signal which used all the signal power present in two consecutive symbols. I showed that this scheme could provide an optical alternative to electrical balanced detection by reducing the required OSNR by 3 dB.I also show how this method can provide amplitude regeneration to a signal after modulation format conversion. In this case an RZ-DPSK signal was converted to an amplitude modulation signal by the delay interferometer. The resulting amplitude modulated signal is degraded by both the amplitude noise and the phase noise of the original signal. The two logically opposite outputs from the delay interferometer again counter-propagated in a saturated SOA. Through limiting amplification and noise modulation this scheme provided amplitude regeneration and improved the Q-factor of the demodulated signal by 3.5 dB.Finally I investigated how SPM provided by the SOA can provide a method to reduce the in-band noise of a communication signal. The marks, which represented data, experienced a spectral shift due to SPM while the spaces, which consisted of noise, did not. A bandpass filter placed after the SOA then selected the signal and filtered out what was originally in-band noise. The receiver sensitivity was improved by 3 dB.

All-optical devices allow improvements in the speed of optical communication and computation systems by avoiding the conversion between the optical and electronic domains. The focus of this thesis is the experimental investigation of a new type of all-optical switch that is based on the control of optical patterns formed by nonlinear interactions between light and matter. The all-optical switch consists of a pair of light beams that counterpropagate through warm rubidium vapor. These beams induce a nonlinear optical instability that gives rise to mirrorless parametric self-oscillation and generates light in the state of polarization that is orthogonal to that of the pump beams. In the far-field, the generated light forms patterns consisting of two or more spots. To characterize this instability, I observe experimentally the amount of generated power and the properties of the generated patterns as a function of pump beam intensity, frequency, and size. Near an atomic resonance, the instability has a very low threshold: with less than 1~mW of total pump power, >3~$\mu$W of power is generated. To apply this system to all-optical switching, I observe that the orientation of the generated patterns can be controlled by introducing a symmetry-breaking perturbation to the system. A perturbation in the form of a weak switch beam injected into the nonlinear medium is suitable for controlling the orientation of the generated patterns. The device operates as a switch where each state of the pattern orientation corresponds to a state of the switch, and spatial filtering of the generated pattern defines the output ports of the device. Measurements of the switch response show that it can be actuated by as few as 600~photons. For a switch beam with 1/e field radius $w_0=185\,\mu$m, 600 photons correspond to $5.4\times10^{-4}$ photons/\lambdasquared which is comparable to the best reported results from all-optical switches based on electromagnetically-induced transparentcy (EIT). This approach to all-optical switching operates at very low light levels and exhibits cascadability and transistorlike response. Furthermore, the sensitivity is comparable to switches using cold-atom EIT or cavity quantum-electrodynamics techniques but is achieved with a simpler system, requiring only one optical frequency and occurring in warm atomic vapor. I develop a numerical model for the switch that exhibits patterns that rotate in the presence of a weak applied optical field. Results from this model, and from my experiment, show that the switch response time increases as the input power decreases. I propose that this increase is due to critical slowing down (CSD). Mapping the pattern orientation to a simple one-dimensional system shows that CSD can account for the observed increase in response time at low input power. The ultimate performance of the device is likely limited by CSD and I conclude that the minimum number of photons capable of actuating the switch is between 400 and 600 photons. / Dissertation

In this thesis, the characteristics and the applications of Kerr-like nonlinear optical waveguide structures have been studied. The nonlinear optical waveguide is a medium whose refractive index changes with the electric field intensity. In the characteristics of Kerr-like nonlinear optical waveguide structures, we propose a general method for analyzing the three-layer optical waveguide structure with all nonlinear layers by using modal theory. Based on this method, the analysis of transforming arbitrary nonlinear layer into linear layer can be achieved easily by modifying nonlinear coefficient. All kinds of the transverse electric field distributions and the dispersion relation in the three-layer Kerr-like nonlinear optical waveguide structure have been obtained. In the application of Kerr-like nonlinear optical waveguide structures, the Mach-Zehnder waveguide interferometer structure will be discussed. Based on the asymmetric medium and asymmetric construction, the new all-optical router switching device and dense wavelength division multiplexing device have been proposed. The numerical results show that the proposed structures could function as all-optical switch devices and all-optical dense wavelength division multiplexing device.

Organic π-conjugated molecules and materials with large real parts and small imaginary parts of the third-order polarizability are of great interest for all-optical switching applications. In this dissertation, we use quantum-chemical and molecular-dynamics approaches to investigate the structure-property relationships that influence the nonlinear optical properties of π-conjugated molecules and materials. We begin with an overview of nonlinear optics, focusing in particular on the electronic properties of linear π-conjugated systems and some of the important problems that have limited device applications of these molecules to date. This is followed by a brief review of the computational methods employed in these studies. We then turn to the main results of the dissertation. Chapter 3 describes the structural dependence of the transition dipole moment between the first two polymethine excited states. Chapter 4 discusses the relationship between BLA, which depends on the geometric structure, and BOA, which probes electronic structure. Chapter 5 describes the benchmarking of computational methods to describe the symmetry-breaking of long polymethines and preliminary evidence regarding the role of vibrational modes in symmetry-breaking. Chapter 6 explains the negative third-order polarizability of tetraphenylphosphate and analogous systems. Chapter 7 focuses on molecular-dynamics studies of polymethine aggregation, particularly the relationships between chemical structure and the geometric and electronic structures of aggregates. Finally, Chapter 8 provides a synopsis of the work and discussion of further directions.

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.