Nonlinear phenomena originating from the distributed coupling process were observed when distributed couplers, such as prisms and gratings, were used to couple light into nonlinear ZnS thin film waveguides. The efficiency of the nonlinear distributed coupling process was found to depend on two independent parameters, the angle of the incident beam and the power of the incident beam. Depending on the detuning of the incident angle, from the optimum incident angle at low powers, either optical limiting, power-dependent switching, or power-dependent bistability of the coupling efficiency, and thereby of the in-coupled power, was observed. At zero detuning, a twenty-fold decrease of the coupling efficiency with increasing powers was measured. At a nonzero detuning of the incident angle, power-dependent switching at milliwatt powers was observed. At larger angular detunings, corresponding to the angular width. FWHM, of the coupling peak at low powers, power-dependent bistability was observed, and the width of the bistability loop was found to increase with increasing detunings. All-optical beam scanning via a nonlinear grating coupler was also demonstrated, utilizing a control-signal beam configuration, where the signal beam scanned through an angle of 0.5° when the power of the control beam was varied. The observed nonlinearity in ZnS was positive and of thermal origin. The power-induced change in the refractive index was found to be 0.01 and a relaxation time of 10 μsec was measured. Problems with the long-term stability of the nonlinear distributed coupling process were traced to the occurrence of desorption and adsorption of water vapor in the ZnS films.

The switching energy and speed of a bistable GaAs etalon have been measured. At liquid nitrogen temperature, the switch-on was achieved by injecting a high density of carriers with an above-band-edge 600-nm external pulse. A minimum energy of 1 nJ was required. The measured switching time was 200 ps, limited by the detector response time. The switch-off was obtained by heating the device with a 300-nJ external pulse and consequently shifting the Fabry-Perot peak. Switch-off time was about 40 ns. Room-temperature bistability was first achieved in a GaAs-AlGaAs superlattice etalon. Switch-on by a near-band-edge 845-nm pulse of 10-pJ energy was observed.

基於光纖非線性效應的光學信號處理在光纖通信和傳感中起著重要作用。在各種非線性效應中，光纖中的布里淵散射不僅被廣泛應用於高速通信信號的處理，而且被用於建立光纖傳感器。本文研究基於布里淵散射的光學信號處理新技術在光通信和傳感中的應用。 / 近年來由於慢光技術在實現時間延遲和光學信號處理中的廣泛應用，它吸引了廣泛的注意力。 在各種實現慢光的技術中，基於布里淵散射的慢光技術展示了很大的潛力，因為它具有在常溫工作以及與現有光纖系統兼容的優勢。但是由於布里淵泵浦和信號之間嚴格的頻率要求，大多數的研究工作是建立於一個泵浦延遲一個信號的基礎上，所以只能獲得一個被延遲的信道。本文提出了一種在一個布里淵泵浦的慢光系統中實現同時產生多個延遲信號的技術。這種技術應用了基於四波混頻的廣播效應。輸入信號被布里淵泵浦延遲的同時，延遲通過三個四波混頻泵浦的廣播效應傳遞給其他六個新產生的信道。這種慢光廣播技術可以被應用於並行光學信號處理，比如實現多信道同步以及時分複用。 / 光纖傳感技術為結構的健康提供了一種優秀的監測方法，尤其是溫度和應力的監測。在過去的二十年間，基於布里淵散射的傳感技術吸引了大批人的興趣，因為布里淵光纖傳感器擁有高分辨率，長距離監測以及監測範圍廣的優點。本文提出了一種新的基於布里淵慢光的溫度和應力傳感技術。布里淵頻移的溫度和應力相關性使得輸入光脉衝的延遲也與溫度和應力相關，因此我們通過測量這個延遲來監測溫度和應力。我們分別實現了對100米和2米單模光纖的溫度測量。隨後我們也實現了分佈式溫度和應力監測。通過設置泵浦和探測光脉衝之間的延遲時間，我們可以監測特定位置的光纖。因此，通過控制整個延遲時間，我們實現了對整個光纖的溫度和應力分佈的監測。相比于普通的布里淵光纖傳感器，我們這種技術擁有以下優點：更加直接簡單的實現監測，快速的反應時間以及實時監測的潛力。 / 波長轉換在路由和交換中起了很重要的作用。在各種波長轉換的技術中，基於四波混頻的波長轉換非常優越因為它具有對調製格式，比特率以及通信協議透明的優點。但是，四波混頻只有在各個光波的相速度匹配的情況下才能有效的產生。這種匹配條件很難在一個很寬的頻段內保持，因此四波混頻的轉換帶寬是很有限的。本文提出了一種基於零增益受激布里淵散射的方法來動態地控制四波混頻的相位匹配。 通過布里淵泵浦和斯托克斯光引入自我補償的受激布里淵增益和損耗，四波混頻的相位匹配條件可以被受激布里淵散射激發的折射率改變來靈活的控制，並且不會影響四波混頻初始的參數。我們把這種零增益受激布里淵散射應用于增大簡並四波混頻的帶寬，增強通信信息波長轉換的效果，全光調控非簡並四波混頻的帶寬，實現偏振不敏感寬帶波長轉換以及延長基於四波混頻波長轉換和色散的延遲線的最大延遲時間。 / 低噪聲寬帶放大可以通過光學參量過程來實現。雖然光參量放大器可以提供高至70分貝的增益，但是這種參量放大器經常受限於各個光波的相位不匹配。在本文中，我們把零增益受激布里淵散射用於光參量放大器來動態的控制它的增益譜。基於這種技術，我們動態地改變了傳統的“M“型增益譜，並且由此得到了非常平滑的增益譜，增益的變換量僅僅在0.1分貝以內。 / Optical signal processing based on fiber nonlinearities plays an important role in both fiber-optic communications and sensing. Among various nonlinear effects, stimulated Brillouin scattering (SBS) in optical fibers has been widely employed not only in processing of high-speed communication signals, but also in constructing fiber-optic sensors. This thesis investigates new techniques of optical signal processing based on SBS for fiber-optic communications and sensing. / In the recent years, slow light has attracted considerable interest because of its numerous applications, in realizing variable true time delay and in optical information processing. Among various slow light mechanisms, the SBS based slow light shows great potential in all-optical signal processing due to the advantages of room-temperature operation and device compatibility with existing fiber systems. However, owing to the tight requirement of spectral alignment between the SBS pump and the signal, most of the published works are for the case where one SBS pump is used to delay a single channel. Hence, only one delayed channel is obtained. In this thesis, we demonstrate a technique to simultaneously generate multiple delayed signals through four-wave mixing (FWM) wavelength multicasting in a single-pump stimulated Brillouin scattering (SBS) based slow light system. The signal delay is achieved with a SBS pump while at the same time the delay is transferred to six other channels by three FWM pumps employed for wavelength multicasting. This slow light multicasting technique may find applications in parallel optical information processing such as simultaneous multichannel synchronization and time division multiplexing. / Fiber-optic sensor techniques provide a promising approach for structure health monitoring, especially the temperature and strain monitoring. The technique based on Brillouin scattering has attracted much interest in the past two decades because Brillouin fiber sensors offer advantages of high resolution, long distance sensing, and large sensing range. In the thesis, we propose and experimentally demonstrate a new method for temperature/strain sensing using stimulated Brillouin scattering based slow light. The approach relies on temperature/strain dependence of the Brillouin frequency shift in a fiber, hence the time delay of an input probe pulse. By measuring the delay, temperature/strain sensing can be realized. We achieve temperature measurement for both a 100 m single mode fiber (SMF) and a 2 m SMF. Distributed temperature/strain sensing has been demonstrated later. The temperature/strain of a particular fiber section can be monitored by setting an appropriate relative delay between the pump and probe pulses. By controlling the relative delay, we have achieved distributed profiling of the temperature/strain along the whole sensing fiber. Compared to conventional Brillouin fiber sensors, our scheme has the merits of more straightforward implementation, fast response and potential of real-time monitoring. / Wavelength conversion plays an important role in wavelength routing and switching. Among various schemes for wavelength conversion, the one based on FWM is superior as it offers advantages in being transparent to modulation formats, bit-rates, and communication protocols. However, significant FWM can occur only if the phase velocities of the interplaying waves are matched. The matching condition can hardly be satisfied over a wide spectral range and hence the conversion bandwidth is often limited. In this thesis, we propose and experimentally demonstrate an approach to dynamically control the FWM phase matching condition by using gain-transparent SBS. By introducing self-compensation of optical gain/loss with SBS pump and Stokes waves, the FWM phase matching condition can be flexibly controlled through SBS induced refractive index change without affecting the initial parameters of the FWM. The gain-transparent scheme is employed to enlarge the degenerate FWM conversion bandwidth, enhance the performance in wavelength conversion of communication signals, all-optically manipulate non-degenerate FWM conversion bandwidth, achieve both polarization-insensitive and wideband operation in a dual orthogonal pump wavelength converter, and extend the maximum optical delay of a delay line based on FWM wavelength conversion and dispersion. / Low noise and broadband amplification are possible by using optical parametric processes. Although fiber-optic parametric amplifier (FOPA) can provide gain as high as 70 dB, its operation is often confined by phase mismatch of the interplaying fields. In this thesis, we apply gain-transparent SBS to a FOPA and dynamically control its gain profile. The conventional “M“ shape gain profile can be dynamically changed. Flattening of the gain profile to within 0.1 dB variation has been achieved. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Liang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Abstract also in Chinese. / ABSTRACT --- p.i / ACKNOWLEDGEMENT --- p.vi / TABLE OF CONTENT --- p.viii / Chapter 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Overview of Optical Signal Processing --- p.3 / Chapter 1.2 --- Outline of the Thesis --- p.6 / References --- p.10 / Chapter 2 --- STIMULATED BRILLOUIN SCATTERING IN OPTICAL FIBERS --- p.15 / Chapter 2.1 --- Physical Process of Brillouin Scattering --- p.16 / Chapter 2.2 --- Stimulated Brillouin Scattering Under Steady-State Conditions --- p.19 / Chapter 2.3 --- The Brillouin Gain --- p.22 / Chapter 2.3.1 --- Complex Brillouin Gain --- p.22 / Chapter 2.3.2 --- Brillouin Gain Spectrum --- p.24 / Chapter 2.4 --- Threshold of Brillouin Scattering --- p.30 / References --- p.32 / Chapter 3 --- SLOW LIGHT BASED ON SBS IN OPTICAL FIBERS --- p.34 / Chapter 3.1 --- Introduction to Slow Light --- p.35 / Chapter 3.2 --- Slow Light based on SBS in Optical Fibers --- p.39 / Chapter 3.2.1 --- Mathematical Description --- p.39 / Chapter 3.2.2 --- Delay of Optical Signals by SBS based Slow Light --- p.42 / Chapter 3.3 --- Generation of Multichannel Delayed Pulses by FWM Assisted SBS Slow Light System --- p.46 / Chapter 3.3.1 --- Principle and Experimental Setup --- p.47 / Chapter 3.3.2 --- Results and Discussion --- p.51 / References --- p.58 / Chapter 4 --- SBS SLOW-LIGHT-BASED FIBER-OPTIC SENSOR --- p.64 / Chapter 4.1 --- Introduction to Fiber-Optic Sensors --- p.66 / Chapter 4.2 --- Principle of Fiber-Optic Sensor based on SBS Slow Light --- p.69 / Chapter 4.3 --- Temperature Sensing by SBS Slow Light for a Whole Segment of Fiber --- p.73 / Chapter 4.3.1 --- Temperature Sensing for a 100 m Single-Mode Fiber --- p.73 / Chapter 4.3.2 --- Temperature Sensing for a 2 m Single-Mode Fiber --- p.76 / Chapter References --- p.80 / Chapter 5 --- DISTRIBUTED TEMPERATURE & STRAIN SENSING USING SBS-BASED SLOW LIGHT --- p.82 / Chapter 5.1 --- Introduction to Distributed Brillouin Fiber Sensor --- p.84 / Chapter 5.2 --- Distributed Fiber-Optic Temperature Sensor Using SBS-based Slow Light --- p.91 / Chapter 5.2.1 --- Principle and Experimental Setup --- p.92 / Chapter 5.2.2 --- Results and Discussion --- p.94 / Chapter 5.3 --- Distributed Fiber-Optic Strain Sensor Using SBS-based Slow Light --- p.101 / Chapter 5.3.1 --- Principle and Experimental Setup --- p.101 / Chapter 5.3.2 --- Results and Discussion --- p.104 / References --- p.109 / Chapter 6 --- DYNAMIC CONTROL OF PHASE MATCHING IN FWM WAVELENGTH CONVERSION BY GAIN-TRANSPARENT SBS --- p.114 / Chapter 6.1 --- Phase-matching Condition in FWM --- p.116 / Chapter 6.2 --- Conversion Bandwidth Enlargement in Degenerate FWM Using Phase-Matching Control by Gain-Transparent SBS --- p.119 / Chapter 6.2.1 --- Principle and Experimental Setup --- p.120 / Chapter 6.2.2 --- Results and discussion --- p.125 / Chapter 6.3 --- Wavelength Conversion of Communication Signals Using Degenerate FWM with Gain-Transparent SBS for Phase-Matching Control --- p.131 / Chapter 6.3.1 --- Principle --- p.131 / Chapter 6.3.2 --- Wavelength Conversion for Amplitude-Modulated Signals --- p.133 / Chapter 6.3.3 --- Wavelength Conversion for Phase-Modulated Signals --- p.139 / Chapter 6.3.4 --- Discussion --- p.145 / Chapter 6.4 --- All-Optical Manipulation of Non-Degenerate FWM Conversion Bandwidth by Gain-Transparent SBS --- p.150 / Chapter 6.4.1 --- Principle and Experiment Setup --- p.151 / Chapter 6.4.2 --- Results and Discussion --- p.153 / Chapter 6.5 --- Enhanced Performance of Polarization-insensitive Wavelength Conversion through Dynamic Control of Optical Phase --- p.157 / Chapter 6.5.1 --- Principle and Experiment Setup --- p.157 / Chapter 6.5.2 --- Results and Discussion --- p.160 / Chapter 6.6 --- Extension of the Maximum Optical Delay using Gain-Transparent-SBS-Controlled FWM Wavelength Conversion and Group Velocity Dispersion --- p.165 / Chapter 6.6.1 --- Principle and Experiment Setup --- p.166 / Chapter 6.6.2 --- Results and Discussion --- p.169 / References --- p.174 / Chapter 7 --- DYNAMIC CONTROL OF GAIN PROFILE IN FIBER OPTICAL PARAMETRIC AMPLIFIER BY GAIN-TRANSPARENT SBS --- p.182 / Chapter 7.1 --- Introduction to FOPA --- p.184 / Chapter 7.2 --- Dynamic Gain Profile in FOPA Assisted by Gain-Transparent SBS --- p.187 / Chapter 7.2.1 --- Principle and Experimental Setup --- p.187 / Chapter 7.2.2 --- Results and Discussion --- p.190 / References --- p.196 / Chapter 8 --- THESIS SUMMARY AND FUTURE WORK --- p.200 / Chapter 8.1 --- Summary --- p.201 / Chapter 8.2 --- Future Work --- p.206 / References --- p.208 / APPENDICES --- p.i / Chapter Appendix A. --- List of Publications --- p.i / Chapter Appendix B. --- List of Figures --- p.iv

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Ultrafast optical signal processing, which shares the same fundamental principles of electrical signal processing, can realize numerous important functionalities required in both academic research and industry. Due to the extremely fast processing speed, all-optical signal processing and pulse shaping have been widely used in ultrafast telecommunication networks, photonically-assisted RFlmicro-meter waveform generation, microscopy, biophotonics, and studies on transient and nonlinear properties of atoms and molecules. In this thesis, we investigate two types of optical spectrally-periodic (SP) filters that can be fabricated on planar lightwave circuits (PLC) to perform pulse repetition rate multiplication (PRRM) and arbitrary optical waveform generation (AOWG). / First, we present a direct temporal domain approach for PRRM using SP filters. We show that the repetition rate of an input pulse train can be multiplied by a factor N using an optical filter with a free spectral range that does not need to be constrained to an integer multiple of N. Furthermore, the amplitude of each individual output pulse can be manipulated separately to form an arbitrary envelope at the output by optimizing the impulse response of the filter. / Next, we use lattice-form Mach-Zehnder interferometers (LF-MZI) to implement the temporal domain approach for PRRM. The simulation results show that PRRM with uniform profiles, binary-code profiles and triangular profiles can be achieved. Three silica based LF-MZIs are designed and fabricated, which incorporate multi-mode interference (MMI) couplers and phase shifters. The experimental results show that 40 GHz pulse trains with a uniform envelope pattern, a binary code pattern "1011" and a binary code pattern "1101" are generated from a 10 GHz input pulse train. / Finally, we investigate 2D ring resonator arrays (RRA) for ultraf ast optical signal processing. We design 2D RRAs to generate a pair of pulse trains with different binary-code patterns simultaneously from a single pulse train at a low repetition rate. We also design 2D RRAs for AOWG using the modified direct temporal domain approach. To demonstrate the approach, we provide numerical examples to illustrate the generation of two very different waveforms (square waveform and triangular waveform) from the same hyperbolic secant input pulse train. This powerful technique based on SP filters can be very useful for ultrafast optical signal processing and pulse shaping.