Stimulated Brillouin scattering based optical signal processing for fiber-optic communications and sensing.

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.iACKNOWLEDGEMENT --- p.viTABLE OF CONTENT --- p.viiiChapter 1 --- INTRODUCTION --- p.1Chapter 1.1 --- Overview of Optical Signal Processing --- p.3Chapter 1.2 --- Outline of the Thesis --- p.6References --- p.10Chapter 2 --- STIMULATED BRILLOUIN SCATTERING IN OPTICAL FIBERS --- p.15Chapter 2.1 --- Physical Process of Brillouin Scattering --- p.16Chapter 2.2 --- Stimulated Brillouin Scattering Under Steady-State Conditions --- p.19Chapter 2.3 --- The Brillouin Gain --- p.22Chapter 2.3.1 --- Complex Brillouin Gain --- p.22Chapter 2.3.2 --- Brillouin Gain Spectrum --- p.24Chapter 2.4 --- Threshold of Brillouin Scattering --- p.30References --- p.32Chapter 3 --- SLOW LIGHT BASED ON SBS IN OPTICAL FIBERS --- p.34Chapter 3.1 --- Introduction to Slow Light --- p.35Chapter 3.2 --- Slow Light based on SBS in Optical Fibers --- p.39Chapter 3.2.1 --- Mathematical Description --- p.39Chapter 3.2.2 --- Delay of Optical Signals by SBS based Slow Light --- p.42Chapter 3.3 --- Generation of Multichannel Delayed Pulses by FWM Assisted SBS Slow Light System --- p.46Chapter 3.3.1 --- Principle and Experimental Setup --- p.47Chapter 3.3.2 --- Results and Discussion --- p.51References --- p.58Chapter 4 --- SBS SLOW-LIGHT-BASED FIBER-OPTIC SENSOR --- p.64Chapter 4.1 --- Introduction to Fiber-Optic Sensors --- p.66Chapter 4.2 --- Principle of Fiber-Optic Sensor based on SBS Slow Light --- p.69Chapter 4.3 --- Temperature Sensing by SBS Slow Light for a Whole Segment of Fiber --- p.73Chapter 4.3.1 --- Temperature Sensing for a 100 m Single-Mode Fiber --- p.73Chapter 4.3.2 --- Temperature Sensing for a 2 m Single-Mode Fiber --- p.76Chapter References --- p.80Chapter 5 --- DISTRIBUTED TEMPERATURE & STRAIN SENSING USING SBS-BASED SLOW LIGHT --- p.82Chapter 5.1 --- Introduction to Distributed Brillouin Fiber Sensor --- p.84Chapter 5.2 --- Distributed Fiber-Optic Temperature Sensor Using SBS-based Slow Light --- p.91Chapter 5.2.1 --- Principle and Experimental Setup --- p.92Chapter 5.2.2 --- Results and Discussion --- p.94Chapter 5.3 --- Distributed Fiber-Optic Strain Sensor Using SBS-based Slow Light --- p.101Chapter 5.3.1 --- Principle and Experimental Setup --- p.101Chapter 5.3.2 --- Results and Discussion --- p.104References --- p.109Chapter 6 --- DYNAMIC CONTROL OF PHASE MATCHING IN FWM WAVELENGTH CONVERSION BY GAIN-TRANSPARENT SBS --- p.114Chapter 6.1 --- Phase-matching Condition in FWM --- p.116Chapter 6.2 --- Conversion Bandwidth Enlargement in Degenerate FWM Using Phase-Matching Control by Gain-Transparent SBS --- p.119Chapter 6.2.1 --- Principle and Experimental Setup --- p.120Chapter 6.2.2 --- Results and discussion --- p.125Chapter 6.3 --- Wavelength Conversion of Communication Signals Using Degenerate FWM with Gain-Transparent SBS for Phase-Matching Control --- p.131Chapter 6.3.1 --- Principle --- p.131Chapter 6.3.2 --- Wavelength Conversion for Amplitude-Modulated Signals --- p.133Chapter 6.3.3 --- Wavelength Conversion for Phase-Modulated Signals --- p.139Chapter 6.3.4 --- Discussion --- p.145Chapter 6.4 --- All-Optical Manipulation of Non-Degenerate FWM Conversion Bandwidth by Gain-Transparent SBS --- p.150Chapter 6.4.1 --- Principle and Experiment Setup --- p.151Chapter 6.4.2 --- Results and Discussion --- p.153Chapter 6.5 --- Enhanced Performance of Polarization-insensitive Wavelength Conversion through Dynamic Control of Optical Phase --- p.157Chapter 6.5.1 --- Principle and Experiment Setup --- p.157Chapter 6.5.2 --- Results and Discussion --- p.160Chapter 6.6 --- Extension of the Maximum Optical Delay using Gain-Transparent-SBS-Controlled FWM Wavelength Conversion and Group Velocity Dispersion --- p.165Chapter 6.6.1 --- Principle and Experiment Setup --- p.166Chapter 6.6.2 --- Results and Discussion --- p.169References --- p.174Chapter 7 --- DYNAMIC CONTROL OF GAIN PROFILE IN FIBER OPTICAL PARAMETRIC AMPLIFIER BY GAIN-TRANSPARENT SBS --- p.182Chapter 7.1 --- Introduction to FOPA --- p.184Chapter 7.2 --- Dynamic Gain Profile in FOPA Assisted by Gain-Transparent SBS --- p.187Chapter 7.2.1 --- Principle and Experimental Setup --- p.187Chapter 7.2.2 --- Results and Discussion --- p.190References --- p.196Chapter 8 --- THESIS SUMMARY AND FUTURE WORK --- p.200Chapter 8.1 --- Summary --- p.201Chapter 8.2 --- Future Work --- p.206References --- p.208APPENDICES --- p.iChapter Appendix A. --- List of Publications --- p.iChapter Appendix B. --- List of Figures --- p.i

Investigation of the Slow- and Fast-Light Effect on the Basis of Stimulated Brillouin Scattering for Application in Optical Communication and Information Systems.

In today\u27s information age demand for ultra-fast information transfer with ultra-high bandwidths has reached extraordinary levels. Hence, the transmission in the future internet-backbone will be increasingly constrained in the network nodes. At the same time, the power consumption of the network systems will increase to unsustainable levels. Nowadays, optical signal processing and switching can be implemented relatively easily. However, the realization of optical bu ers and short-term memories is still an unsolved challenge. The slow- and fast-light e ect has been investigated as one solution for the optical bu ering over the last few years. It means the slowing down and acceleration of the group velocity of light pulses in a medium. To realize this, many di erent methods and material systems have been developed but due to its signi cant advantages the nonlinear e ect of stimulated Brillouin scattering (SBS) is particularly promising. However, it also su ers from disadvantages which limit the slow- and fast-light performance

Slow and fast light in optical fibres

The ubiquitous role of optical fibres in modern photonic systems has stimulated research to realize slow and fast light devices directly in this close-to-perfect transmission line. Recent progress in developing optically controlled delays in optical fibres, operating under normal environmental conditions and at telecommunication wavelengths, has paved the way towards real applications for slow and fast light. This review presents the state-of-the-art research in this fascinating field and possible outcomes in the near future

Governing the speed of a light signal in optical fibers:Brillouin slow and fast light

Dynamic control of the speed of a light signal, based on stimulated Brillouin scattering in optical fibers, was theoretically studied and also experimentally demonstrated as the core object of this thesis. To date, slow light based on stimulated Brillouin scattering has shown the unmatched flexibility to offer an efficient timing tool for the development of all-optical future router. Nevertheless, the seeming perfect Brillouin slow light suffered from three major obstacles: naturally narrow signal bandwidth, strong change of signal amplitude, and significant signal distortion. The essential contribution of this work has been mostly dedicated to resolve all those impairments so as to make Brillouin slow light a completely operating all-optical delay line for practical applications. Actually, high capability of tailoring the spectral distribution of the effective Brillouin resonance makes possible to resolve partially or completely all those problems. First of all, a broadband spectral window was passively obtained in between two Brillouin gain/loss resonances by simply appending two segments of fibers showing different Brillouin frequency shifts. The global Brillouin gain of the concatenated fibers manifests a gain/loss doublet resonance showing a broad window in between gain/loss peaks. In practice, this configuration has a crucial advantage that it removes the need of the pump modulation, generally used to create a polychromatic pump source. Therefore, a broadband Brillouin slow and fast light was simple realized with a reduced distortion. Secondly, the signal amplification or attenuation associated to the signal delay was completely compensated by superposing Brillouin gain and loss resonances with identical depth but different width. As a result, the Brillouin gain led to effectively a spectral hole in the center of the broadband absorption and opened a transparent window while the sharp change in the refractive index was preserve. This way it makes possible to realize zero-gain Brillouin slow light. This configuration was also exploited to produce Brillouin fast light with a total absence of signal loss, simply by swapping the spectral position of the two pumps. At last, a signal was continuously delayed through a Brillouin fiber delay line without any distortion. Due to the strong induced dispersion, pulse broadening is a major difficulty in all slow light systems and it is impossible to compensate such broadening using a linear system. Therefore, a conventional Brillouin slow light system was combined with a nonlinear optical fiber loop mirror that gives a nonlinear quadratic transmission. Using this configuration, the inevitable pulse broadening was completely compensated at the output of the loop and a signal was delayed up to one symbol without any distortion. Brillouin slow light systems were further studied in the spectral domain. For a given Brillouin resonance the spectrum of a light pulse was optimized to better match the Brillouin bandwidth. When the time envelope of a pulse was properly shaped, it was clearly observed that the spectral width of the pulse became minimized while preserving the pulse duration. This way the maximum time delay through Brillouin slow light could be enhanced for a fixed pulse width. Brillouin fast light was even realized in total absence of any pump source, which is a plain requirement for the generation of Brillouin slow or fast light. This self-generated delay line, key contribution of this thesis, relies on both spontaneous and stimulated Brillouin scattering in optical fibers. In this implementation, a light signal was strongly boosted above the so-called Brillouin threshold, so that most power of the signal was transferred to a backward propagating wave, namely the generation of amplified spontaneous Stokes wave. Since the center frequency of the intense Stokes wave is below the signal frequency by exactly Brillouin shift of the fiber used, this wave led to a Brillouin loss band centered at the signal frequency. Consequently, the signal experienced fast light propagation and the propagation velocity of the signal was self-controlled, simply by varying the signal input power. This technique has many practical advantages such as its high simplicity of the configuration and an invariant signal power in the output of this delay line. Additionally, this system self-adapts the signal bandwidth as the spectrum of the amplified Stokes wave matches the spectral distribution of the signal. An alternative method to generate all-optical delay line was proposed instead of slow light. This scheme makes use of the combination of wavelength conversion and group velocity dispersion. This type of delay line was mainly aimed at improving the storage capability of delaying element. The wavelength of a signal was simply and efficiently converted at a desired wavelength using cross gain modulation in semiconductor optical amplifiers. Then the converted signal was delivered to a high dispersive medium and arrived at the end of the medium with relative time delay due to the group velocity dispersion. A fractional delay of 140 was continuously produced through this delay line for a signal with a duration of 100 ps, preserving signal bandwidth and wavelength. The effect of slow light on linear interactions between light and matter was experimentally investigated to clarify the current scientific argument regarding slow light-enhanced Beer-Lambert absorption. It was predicted that real slowing of the light group velocity could enhance the molecular linear absorptions so as to improve the sensitivity of this type of sensing. However, the experimental results unambiguously show that material slow light (slow light in traveling wave media) does not enhance the Beer-Lambert absorption

Microwave Photonic Signal Processing Using On-Chip Nonlinear Optics

The field of microwave photonics (MWP) emerged as a solution to the challenges faced by electronic systems when dealing with high-bandwidth RF and microwave signals. Photonic devices are capable of handling immense bandwidths thanks to the properties of light. MWP therefore employs such devices to process and distribute the information carried by RF and microwave signals, enabling significantly higher capacity compared to conventional electronics. The photonic devices traditionally used in MWP circuits have mainly comprised bulky components, such as spools of fibre and benchtop optical amplifiers. While achieving impressive performance, these systems were not capable of competing with electronics in terms of size and portability. More recently, research has focused on the application of photonic chip technology to the field of MWP in order to reap the benefits of integration, such as reductions in size, weight, cost, and power consumption. Integrated MWP however is still in its infancy, and ongoing research efforts are exploring new ways to match integrated photonic devices to the unique requirements of MWP circuits. This work investigates the application of on-chip nonlinear optical interactions to MWP. Nonlinear optics enables light-on-light interactions (not normally possible in a linear regime) which open a vast array of powerful functionalities. In particular, this thesis focuses on stimulated Brillouin scattering, resulting from the interaction of light with hypersonic sound waves, and four-wave mixing, where photons exchange energies. These two nonlinear effects are applied to implement MWP ultra-high suppression notch filters, wideband phase shifters, and ultra-fast instantaneous frequency measurement systems. Experimental demonstrations using integrated optical waveguides confirm record results

All-optical switching and variable delay using nonlinear optical signal processing techniques.

Cheng, Lap Kei.Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.Includes bibliographical references.Abstracts in English and Chinese.ABSTRACT --- p.I摘要 --- p.IIACKNOWLEDGEMENTS --- p.VTABLE OF CONTENTS --- p.IVINTRODUCTION --- p.0Chapter 1.1 --- Different ways to achieve all-optical tunable delay --- p.2Chapter 1.1.1 --- Optical buffer realized with optical switching --- p.2Chapter 1.1.2 --- Slow light technique --- p.3Chapter (i) --- Basics of slow light --- p.4Chapter (ii) --- Slow light via electromagnetically induced transparency (EIT) --- p.6Chapter (iii) --- Slow light via coherent population oscillation (CPO) --- p.7Chapter (iv) --- Slow light via optical parametric amplification (OPA) --- p.8Chapter (v) --- Slow light via stimulated Raman and Brillouin scattering --- p.8Chapter 1.1.3 --- Tunable delay using wavelength conversion together with chromatic dispersion --- p.10Chapter 1.1.4 --- Comparison of different schemes for constructing all-optical delay line --- p.11Chapter 1.2 --- Overview of the thesis --- p.12References --- p.14ALL-OPTICAL SWITCHING OF DPSK SIGNAL IN AN SOA USING NONLINEAR POLARIZATION ROTATION --- p.18Chapter 2.1 --- Introduction --- p.19Chapter 2.2 --- Birefringence and nonlinear polarization rotation --- p.20Chapter 2.3 --- Differential-phase-shift keying (DPSK) modulation format --- p.22Chapter 2.4 --- Experimental setup --- p.23Chapter 2.5 --- Experimental results --- p.25Chapter 2.6 --- Conclusion --- p.29References --- p.30WIDEBAND SLOW LIGHT VIA STIMULATED BRILLOUIN SCATTERING IN AN OPTICAL FIBER USING A PHASE-MODULATED PUMP --- p.32Chapter 3.1 --- Introduction --- p.33Chapter 3.2 --- Stimulated Brillouin scattering (SBS) --- p.34Chapter 3.3 --- Slow light via SBS --- p.35Chapter 3.4 --- Experimental setup --- p.37Chapter 3.5 --- Experimental result --- p.39Conclusion --- p.42References --- p.43SIGNAL WAVELENGTH TRANSPARENT SBS SLOW LIGHT USING XGM BASED WAVELENGTH CONVERTER AND BRILLOUIN FIBER LASER --- p.45Chapter 4.1 --- Introduction --- p.46Chapter 4.2 --- Brillouin fiber laser and XGM wavelength converter --- p.47Chapter 4.3 --- Operating principle --- p.50Chapter 4.4 --- Experimental setup and results --- p.51Conclusion --- p.56References --- p.57ALL-OPTICAL TUNABLE DELAY LINE FOR CHANNEL SELECTION IN A 40-GB/S OPTICAL TIME DIVISION MULTIPLEXING SYSTEM --- p.59Chapter 5.1 --- Introduction --- p.60Chapter 5.2 --- Principle of four-wave mixing --- p.61Chapter 5.3 --- Channel selection in an OTDM system --- p.63Chapter 5.4 --- Experimental setup --- p.64Chapter 5.5 --- Experimental results --- p.67Conclusion --- p.70References --- p.71TUNABLE OPTICAL DELAY WITH CSRZ-OOK TO RZ-OOK OPTICAL DATA FORMAT CONVERSION USING FOUR-WAVE MIXING WAVELENGTH CONVERSION AND GROUP VELOCITY DISPERSION --- p.73Chapter 6.1 --- Introduction --- p.74Chapter 6.2 --- Carrier-Suppressed Return-to-Zero --- p.76Chapter 6.3 --- Operating Principle --- p.77Chapter 6.4 --- Experimental setup --- p.79Chapter 6.5 --- Experimental result --- p.81Conclusion --- p.86References --- p.87CONCLUSION --- p.90Chapter 7.1 --- Summary of work --- p.90Chapter 7.2 --- Prospects of future work --- p.92APPENDIX: LIST OF PUBLICATIONS

Microwave Photonic Signal Processing Using On-Chip Nonlinear Optics

The field of microwave photonics (MWP) emerged as a solution to the challenges faced by electronic systems when dealing with high-bandwidth RF and microwave signals. Photonic devices are capable of handling immense bandwidths thanks to the properties of light. MWP therefore employs such devices to process and distribute the information carried by RF and microwave signals, enabling significantly higher capacity compared to conventional electronics. The photonic devices traditionally used in MWP circuits have mainly comprised bulky components, such as spools of fibre and benchtop optical amplifiers. While achieving impressive performance, these systems were not capable of competing with electronics in terms of size and portability. More recently, research has focused on the application of photonic chip technology to the field of MWP in order to reap the benefits of integration, such as reductions in size, weight, cost, and power consumption. Integrated MWP however is still in its infancy, and ongoing research efforts are exploring new ways to match integrated photonic devices to the unique requirements of MWP circuits. This work investigates the application of on-chip nonlinear optical interactions to MWP. Nonlinear optics enables light-on-light interactions (not normally possible in a linear regime) which open a vast array of powerful functionalities. In particular, this thesis focuses on stimulated Brillouin scattering, resulting from the interaction of light with hypersonic sound waves, and four-wave mixing, where photons exchange energies. These two nonlinear effects are applied to implement MWP ultra-high suppression notch filters, wideband phase shifters, and ultra-fast instantaneous frequency measurement systems. Experimental demonstrations using integrated optical waveguides confirm record results

The concept of "slow light" and nature of Stokes pulse delay in stimulated Brillouin scattering

This work addresses the nature of the delay experienced by pulsed Stokes radiation when amplified by stimulated Brillouin scattering (SBS), topically referred to as “slow light in SBS”. The term “slow light” refers to the propagation of a light pulse in a medium in which the group velocity of the pulse is considerably lower than the phase velocity of light. A comprehensive review of the literature on “slow light” has revealed a range of inconsistencies in attributing experimentally observed pulse delays to the group velocity effect. For the case of SBS the controversies are resolved through analytic solutions of the basic coupled SBS equations in both the frequency and time domains. The solutions provide the first mathematically rigorous and physically non-contradictory description of the temporal, spectral and energy characteristics of the Stokes radiation and of the induced acoustic wave in an SBS amplifier. Based on these solutions, a theoretical model of Stokes pulse propagation through a CW-pumped SBS medium is developed, the so called “inertial” model. The solutions are verified experimentally through study of the Stokes pulse dynamics in a set of fibers with different inhomogeneous SBS bandwidths and acoustic wave relaxation times. The results obtained confirm that the delay, shape and amplitude of the output Stokes pulse follow the predictions of the “inertial” model and that, contrary to popular opinion, the phenomenon of group delay, or “slow light”, is irrelevant to the observed delays

High-Performance On-Chip Microwave Photonic Signal Processing Using Linear and Nonlinear Optics

Manipulating and processing radio-frequency (RF) signals using integrated photonic devices has recently emerged as a paradigm-shifting technology for future microwave applications. This emerging technique is referred to as integrated microwave photonics (IMWP) which enables the high-frequency processing and unprecedentedly wideband tunability in compact photonic circuits, with significantly enhanced stability and robustness. However, to find widespread applications, the performance of IMWP devices must meet or exceed the achievable performance of conventional electronic counterparts. The work presented in this thesis investigates high-performance IMWP signal processing from two aspects: the optimized IMWP processing schemes and the photonic integration. Firstly, we explore novel schemes to improve the performance of chip-based microwave photonic subsystems, such as RF delay lines and RF filters which are basic building blocks of RF systems. A phase amplification technique is demonstrated to achieve a Si3N4 chip-based RF time delay with a delay tuning speed at gigahertz level. A new scheme to achieve an all-optimized RF photonic notch filter is demonstrated, producing a record-high RF link performance and complete functionalities. To unlock the potential of RF signal processing, we investigate a new filter concept of pairing linear and nonlinear optics for a high-performance RF photonic filter. To reduce the footprint of the novel IMWP filter, the photonic integration of both the ring resonators and Brillouin-active circuits on the same photonic chip is achieved. To eliminate the use of integrated optical circulators for on-chip SBS, on-chip backward inter-modal stimulated Brillouin scattering is predicted and experimentally demonstrated in a Si-Chalcogenide hybrid integrated photonic platform. The study and demonstrations presented in this thesis make the first viable step towards high-performance IMWP signal processing for real-world RF applications