published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The properties of photo-induced gratings in germania doped glass fibers were studied. Permanent phase gratings in a fiber core were fabricated by the mixing of two contra propagating waves. Experiments are described and results are presented which show that the strength of a photoinduced grating is strongly dependent on the writing power as well as the laser writing wavelength. A rigorous development of linear coupled mode theory for the contra propagation geometry is given and used to model the experimentally observed grating responses as a function of fine tuning frequency of probing light. Measurements have been done of the amplitude and phase response of the grating structure and compared with theoretical models of uniform and chirped gratings. The theoretically predicted negative group velocity dispersion in fiber grating was observed interferometrically and described in detail. The nonlinear coupled mode theory has been fully implemented in a computer program and some numerical results are given in the second part of this thesis. The dynamics of a pulse propagating in the fiber grating is simulated and the results show its dependence on pulse energy, frequency detuning, and the type of grating geometry. A limitation is found in the dispersion property of a constant amplitude fiber grating so that the pulse compression ratio and the width of a compressible pulse is strictly limited to ≅250 picoseconds.

M.Phil. (Electrical and Electronic Engineering) / A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.

In this paper, we propose a rate-compatible forward error-correcting (FEC) scheme based on low-density-parity check (LDPC) codes together with its software reconfigurable unified field-programmable gate array (FPGA) architecture. By FPGA emulation, we demonstrate that the proposed class of rate-compatible LDPC codes based on puncturing and generalized LDPC coding with an overhead from 25% to 46% provides a coding gain ranging from 12.67 to 13.8 dB at a post-FEC bit-error rate (BER) of 10(-15). As a result, the proposed rate-compatible codes represent one of the strong FEC candidates of soft-decision FEC for both short-haul and long-haul optical transmission systems.

Dai, Yongheng. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Lei, Kin Pang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

by Ka Suen Lee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / Chapter Chapter I --- Introduction --- p.1 / Chapter 1.1 --- The evolution of communication networks --- p.1 / Chapter 1.2 --- The development of lightwave communication systems --- p.2 / Chapter 1.3 --- System architecture --- p.9 / Chapter 1.4 --- The motivation of the researches --- p.11 / References --- p.13 / Chapter Chapter II --- Theories --- p.15 / Chapter 2.1 --- The optical time-division multiple-access --- p.15 / Chapter 2.2 --- The operations of 2 x 2 fiber coupler --- p.18 / References --- p.21 / Chapter Chapter III --- Optical loop mirror multiplexer --- p.23 / Chapter 3.1 --- Self Phase Modulation in optical fiber --- p.23 / Chapter 3.2 --- Current developments of the optical loop mirror --- p.24 / Chapter 3.3 --- The principle of the novel time-division multiplexer --- p.30 / Chapter 3.4 --- The experiment and results --- p.31 / Chapter 3.5 --- Analysis on the splitting ratios of the optical loop mirror multiplexer --- p.34 / Chapter 3.6 --- Analysis on the phase of the optical outputs --- p.36 / Chapter 3.7 --- The theories of the optical loop mirror multiplexer --- p.39 / Chapter 3.8 --- The advantages on the optical loop mirror multiplexer --- p.41 / Chapter 3.9 --- The optical bit pattern generation --- p.48 / Chapter 3.10 --- The conclusions of the optical loop mirror multiplexer --- p.49 / References --- p.51 / Chapter Chapter IV --- Optical matrix for high-speed operation in two-dimensional array devices --- p.55 / Chapter 4.1 --- Recent developments in two-dimensional array devices --- p.55 / Chapter 4.2 --- The principle of the novel optical matrix --- p.58 / Chapter 4.3 --- The experiment and results --- p.62 / Chapter 4.4 --- The applications of the novel optical matrix --- p.66 / Chapter 4.5 --- Comparison on the operation modes of the optical matrix --- p.74 / Chapter 4.6 --- Comparison on the construction of the optical matrix --- p.77 / Chapter 4.7 --- The conclusions of the optical matrix --- p.80 / References --- p.81 / Chapter Chapter V --- Conclusions and Future Works --- p.84 / Chapter 5.1 --- The conclusions --- p.84 / Chapter 5.2 --- The future works --- p.86 / Chapter 5.3 --- List of publications --- p.87 / References --- p.88 / Appendix 1 The 1.319 μm Nd:YAG laser system --- p.A-l / Chapter A1.1 --- The laser action of the Neodymium-YAG solid-state laser --- p.A-l / Chapter A1.2 --- The four-level laser system --- p.A-4 / Chapter A1.3 --- The installation and operations of a 1.319μm Nd:YAG laser --- p.A-8 / References --- p.A-21 / Appendix 2 Mode-locking in the Nd:YAG Laser --- p.A-22 / Chapter A2.1 --- The mode-locking technique --- p.A-22 / References --- p.A-26

by Han Dejun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves [117]-[129]). / Abstract --- p.ii / Acknowledgment --- p.iv / Table of Contents --- p.v / Chapter 1. --- Introduction --- p.1-1 / Chapter 1.1 --- The Current Situation of Space-division Optical Switches --- p.1-1 / Chapter 1.1.1 --- Digital Optical switches (DOS) --- p.1-2 / Chapter 1.1.2 --- Twin-guide amplifier (TGA) --- p.1-3 / Chapter 1.1.3 --- Direction coupler with amplifiers --- p.1-4 / Chapter 1.1.4 --- Total internal reflection type switch with amplifier --- p.1-5 / Chapter 1.1.5 --- Semiconductor optical amplifier gate switches --- p.1-6 / Chapter 1.2 --- Existing Problems --- p.1-9 / Chapter 1.3 --- New Proposals --- p.1-10 / Chapter 1.3.1 --- New features --- p.1-11 / Chapter 1.3.2 --- New technology for OEIC --- p.1-13 / Chapter 1.3.3 --- Expected improvement in performance --- p.1-14 / Chapter 1.4 --- Organization of thesis --- p.1-17 / Chapter 2. --- Band Lineup And Optical Gain Calculation --- p.2-1 / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Band Lineup for InGaAsP MQW Structures --- p.2-3 / Chapter 2.2.1 --- Derivation According to Ishikawa et al.'s Scheme --- p.2-3 / Chapter 2.2.2 --- Derivation According to Krijn's scheme --- p.2-5 / Chapter 2.2.3 --- Improved band lineup calculation scheme --- p.2-7 / Chapter 2.3 --- Gain and Spontaneous Emission Rate Expressions --- p.2-13 / Chapter 2.3.1 --- Optical gain expressions --- p.2-13 / Chapter 2.3.2 --- Spontaneous Emission Rate Expressions --- p.2-16 / Chapter 2.3.3 --- Polarization characteristics --- p.2-17 / Chapter 2.4 --- Optical Absorption and Its Polarization Sensitivity --- p.2-18 / Chapter 2.4.1 --- Absorption in an intermixed QW Structure --- p.2-18 / Chapter 2.4.2 --- Electro-optical Absorption --- p.2-19 / Chapter 3. --- Design of the Optical Switches --- p.3-1 / Chapter 3.1 --- Design of Material Layer Structure --- p.3-2 / Chapter 3.2 --- Design of Device Geometrical Structure --- p.3-7 / Chapter 3.3 --- Optical Gain in Polarization Insensitive Gain Medium-- An Example --- p.3-8 / Chapter 3.4 --- Optical Absorption in Polarization Insensitive Gain Medium-- An Example --- p.3-15 / Chapter 4. --- Fabrication Technology --- p.4-1 / Chapter 4.1 --- Passive Waveguide Formation --- p.4-2 / Chapter 4.1.1 --- Impurity-free vacancies diffusion technology --- p.4-3 / Chapter 4.1.2 --- High energy ion implantation enhanced intermixing technology --- p.4-4 / Chapter 4.1.3 --- Elevated temperature O+ HE-IIEI of MQWs --- p.4-6 / Chapter 4.2 --- Oxygen Implant Isolation --- p.4-6 / Chapter 4.3 --- Self Aligned Ridged Waveguide Technology --- p.4-7 / Chapter 4.4 --- Reduction of Effective Facet Reflectivity --- p.4-11 / Chapter 4.5 --- Fabrication Process Flow --- p.4-12 / Chapter 4.5.1 --- Layer structure of the material --- p.4-12 / Chapter 4.5.2 --- Fabrication process flow for the Y-junction optical switches --- p.4-14 / Chapter 4.6 --- Schematic Structure of the Fabricated Switches --- p.4-19 / Chapter 5. --- Experimental Results --- p.5-1 / Chapter 5.1 --- High Energy Ion Implantation Enhanced Intermixing of Quantum Wells --- p.5-2 / Chapter 5.1.1 --- High energy ion implantation --- p.5-2 / Chapter 5.1.2 --- Rapid thermal annealing --- p.5-4 / Chapter 5.2 --- Photoluminescence --- p.5-6 / Chapter 5.3 --- Electroluminescence --- p.5-9 / Chapter 5.4 --- Current-Voltage characteristics --- p.5-12 / Chapter 5.5 --- Guided-Wave Optoelectronic Measurement --- p.5-14 / Chapter 5.5.1 --- Setup of the measurement --- p.5-14 / Chapter 5.5.2 --- Measurement of absorption loss for the blue-shifted QW structure --- p.5-16 / Chapter 5.5.3 --- Optical losses measurement by Fabry-Perot interference method --- p.5-18 / Chapter 5.5.4 --- Electroabsorption peak shift in IIEI wafer --- p.5-21 / Chapter 5.6 --- Oxygen Implant Isolation --- p.5-21 / Chapter 5.7 --- Characteristics of Optical Switches --- p.5-23 / Chapter 5.7.1 --- Current-voltage characteristics --- p.5-23 / Chapter 5.7.2 --- Optical mode and transmission characteristics --- p.5-24 / Chapter 5.7.3 --- Switch characteristics --- p.5-29 / Chapter 5.7.4 --- Discussion --- p.5-32 / Chapter 6. --- Conclusion and Future Studies --- p.6-1 / Chapter 6.1 --- Conclusion --- p.6-1 / Chapter 6.1.1 --- The major contributions to the Y-JOS --- p.6-1 / Chapter 6.1.2 --- The major contribution to the bandgap engineering for InGaAs(p)/InP heterostructure --- p.6-3 / Chapter 6.1.3 --- The major contributions to the HE-IIEI technology --- p.6-4 / Chapter 6.2 --- Topics for Future Studies --- p.6-5 / Chapter 6.2.1 --- Band lineup and optical gain calculation --- p.6-5 / Chapter 6.2.2 --- Optimization of HE-IIEI technology --- p.6-6 / Chapter 6.2.3 --- Optimization of the Fabrication of Y-JOS --- p.6-7 / Reference --- p.R1 / Appendix A Characteristics Of Strained Quantum Wells --- p.A1 / Appendix B Effective Index Change Induced by Quantum Well Intermixing --- p.A3 / Appendix C Abbreviation --- p.A13 / Appendix D List of Publications --- p.A14

這篇論文討論了三個重要的全光網絡的網絡管理方向，分別為在全光封包交換網絡的光路追踪問題，光封包的暫存及在波分複用無源光網絡（WDM-PON）的能源節省運作。 / 使用全光編碼器進行光路追踪 / 在所有全光封包交換網絡中，數據包的路由光路是可以被通過光學交叉連接（OXC）的網絡節點重新配置。要監控任何可能的路由錯誤、信號質量下降的任何可能的原因、發現任何惡意或攻擊流量的來源、或提供服務質量（QoS）的路由策略，光學數據包的光路監測是必要的。此方案編碼光路信息到光學數據的標籤，每個網絡節點被分配一個獨特的質數為識別標記的光路信息。使用位於OXC輸出端的光學編碼器，每次當數據包通過該網絡節點時，數據包的標籤值將乘以特定的質數。網絡數據包已經走過的節點將被編碼的標籤為代表的網絡節點的所有素數的乘積。因此，在標籤的檢示器中，光數據包走過的每個網絡節點都可以很容易地通過標籤值的因式分解求得。 / 相比使用時間延遲識別技術，我們的設計大幅減少了光纖線的長度要求。此外，與導頻訊號檢測方法相比，它提供了快速檢測的好處。此外，網絡循環的問題也可以檢測。編碼標籤也可以作為的光封包的保存週期指示器（TTL）。 / 功率控制的全光封包緩衝器 / 全光封包緩衝區全光交換網絡中是非常重要的。為了實現簡單而有效的光學數據包緩衝操作，我們提出使用功率控制時間延遲的全光數據包緩衝區。的循環迴路的數量是由輸入信號的功率控制（即具有較高的功率輸入信號將經歷更長的時間延遲）。我們把偱環延遲緩衝器重新設計成信號功率依賴過濾的問題。光信號首先通過在不同的時刻，每延遲副本將減半功率與前一個通過循環生成多個副本的循環。然後，它會通過信號的功率大子而使用非線性光學效應來實施過濾。過濾器只與特定功率水平的信號，可以輸出，而別人得到減毒，因此清除的特點。因此，為了改變延遲量，我們只需要改變輸入信號功率等具體延遲的信號，將陷入電源依賴的濾波器的通帶和輸出。 / 比起使用許多的SOA來控制循環延遲或使用可調諧波長轉換器及波長依賴時滯的方案，我們的計劃提供更容易的延遲控制。 / 信號電源效率的WDM-PON的操作技巧 / 在WDM-PON中，光網絡單元（ONU）的上傳信號通過對由光線路終端（OLT）的下傳信號的重新編寫產生。傳統上，這設計產生功耗的問題。例如：如果沒有下傳信號，光網絡單元不能發送上傳數據。因此，即使沒有數據傳送，光線路終端也要不斷傳送下傳信號，為了確保光網絡單元總是能夠發送上傳數據。在這種網絡中，突發傳送模式可以提供電源效率上的節省。我們提出了一個信號傳送技術來由光網絡單元向光線路終端發送“喚醒消息，以通知光線路終端的收發器從睡眠模式恢復。這技術是通過對在RSOA放大自發輻射（ASE）噪聲進行特定導頻信號的，因而不需要重新調制下游信號。在光線路終端，額外的模塊將負責檢測不同光網絡單元的導頻信號，然後啟動相應的收發器。我們的計劃提供了在WDM-PON的簡單和高成本效益的能源節省方案。 / This thesis addresses three important network management aspects of optical networks, namely, optical lightpath tracing problem for all-optical networks, all-optical packet buffering in optical packet switching networks, power-efficient operation in wavelength division multiplexing passive optical networks (WDM-PON). / Lightpath tracing through all-optical encoder / In an all-optical reconfigurable wavelength routing network, the lightpath of the optical data packets can be reconfigured, via the optical cross connects (OXC) residing at each network node. In order to monitor any possible routing errors, any possible causes of signal quality degradation, detect any source of malicious or attack traffic and provide quality of service (QoS) aware next-hop routing strategy, monitoring of lightpath of optical data packets is necessary. This scheme encodes the lightpath information into the label of individual optical packet. Each network node is assigned with a distinct prime number as an identification tag. By using the optical encoders located at the outputs of OXCs, the label value of the packets will be multiplied by the prime number designated to the respective OXC, residing at the network node. Hence, the information of the network nodes that the packet has traversed will be encoded to the label as the product of all the prime numbers assigned to all traversed network nodes. Therefore, at the destination node, the whole physical lightpath of each received optical data packet can be easily identified through factorization of the encoded label value. / Our scheme provides substantial reduction in the requirement of fiber delay lines, as compared to the time-delay recognition techniques. It offers fast detection when comparing with pilot tone detection method. Besides, possible network looping problem can be detected and the encoded label can be acted as time-to-live (TTL) identifier of the optical packet. / All-optical power-controlled optical packet buffer / All-optical packet buffer is essential for the contention resolution in all-optical packet switching network. In order to realize simple and efficient operation of optical packet buffer, we propose the use of all-optical power-controlled packet buffer for which the number of circulating loops is controlled by the input signal power (i.e. input signal with higher power will experience longer delay). We formulate the problem of designing a re-circulating delay buffer into signal power dependent filtering problem. The optical OOK signal first passes through a re-circulating loop generating multiple copies at different time instants that each delayed copy will have halved power as the previous one. Then it will pass through the signal power dependent filter implemented by using optical nonlinear effect. The filter has the characteristics that only signal (packet copy) with specific power level can be outputted while the others get attenuated and therefore cleared. As a result, in order to change the amount of delay, we just need to change the input signal power such that the signal with specific delay will fall into the pass band of the power dependent filter and get outputted. / Compared with other delay schemes which use many SOAs as gates to control the number of re-circulating delay or implementing tunable wavelength converter and passes through wavelength dependent delay, our scheme provides easy control of the delay required. / Signaling techniques for power-efficient operation of WDM-PON / In WDM-PON, the upstream signal at the optical network unit (ONU) can be generated by re-modulating the downstream signal received from the optical line terminal (OLT). However, the conventional architecture may suffer from power consumption problem. When there is no downstream signal, the ONU is not able to send any upstream data. Thus even if there is no traffic on the line, the OLT has to send the downstream signal continuously, in order to ensure the ONU can always be able to send its upstream data. In such networks, burst-mode traffic transmission can provide improvement on power efficiency. We propose a signaling technique to send “Wake Up message from the ONU to OLT, to notify the transceiver of the OLT to recover from sleep mode. It is done by modulating the Amplified Spontaneous Emission (ASE) noise in RSOA at the ONU with the particular ONU specific pilot tone monitoring signal. Thus, it does not require the presence of the remodulating downstream signal. At the OLT, a specific module is needed for the detection of the pilot tones from different ONUs and then activate the corresponding transceiver. Our scheme offers simple and cost-effective approach for power-efficient operation in the WDM-PON. / 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. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Tse, Kam Hon. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 90-97). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.i / Acknowledgements --- p.viii / Chapter Chapter 1 --- Background --- p.1 / Chapter 1.1 --- All-Optical Packet Switching Networks --- p.3 / Chapter 1.1.1 --- Packet Buffering --- p.4 / Chapter 1.1.2 --- Route Tracing --- p.7 / Chapter 1.2 --- Wavelength Division Multiplexing Passive Optical Networks (WDM-PON) --- p.12 / Chapter 1.2.1 --- ONU Upstream Re-Modulation in WDM-PON --- p.12 / Chapter 1.2.2 --- Green Networking --- p.13 / Chapter 1.3 --- Contributions --- p.17 / Chapter 1.3.1 --- Path Tracing Scheme for All-Optical Packet-Switched Networks --- p.17 / Chapter 1.3.2 --- All-Optical Power-Controlled Optical Packet Buffer for All-Optical Packet-Switched Networks --- p.18 / Chapter 1.3.3 --- Signaling Techniques for Power-Efficient Operation of WDM-PON --- p.19 / Chapter 1.4 --- Organization of Thesis --- p.19 / Chapter Chapter 2 --- Path Tracing Scheme for All-Optical Packet-Switched Networks --- p.21 / Chapter 2.1 --- Introduction --- p.21 / Chapter 2.2 --- Path Tracing Using Prime-Number Tags --- p.26 / Chapter 2.2.1 --- Network Node Tracing --- p.26 / Chapter 2.2.2 --- Network Link Tracing --- p.28 / Chapter 2.2.3 --- Network Looping Problem --- p.29 / Chapter 2.3 --- Optical Implementation --- p.30 / Chapter 2.4 --- Experimental Results --- p.38 / Chapter 2.5 --- Multi-Level Amplitudes Of The Label --- p.41 / Chapter 2.6 --- Required Maximum Fiber Delay --- p.44 / Chapter 2.7 --- Summary --- p.47 / Chapter Chapter 3 --- A Novel Fiber-based Variable All-Optical Packet Buffer based on Self-Phase Modulation Induced Spectral Broadening --- p.48 / Chapter 3.1 --- Introduction --- p.48 / Chapter 3.2 --- Input signal power dependent delay --- p.51 / Chapter 3.3 --- Numerical Simulation Studies --- p.54 / Chapter 3.4 --- Experimental Results --- p.64 / Chapter 3.5 --- Discussion --- p.68 / Chapter 3.6 --- Summary --- p.71 / Chapter Chapter 4 --- A Cost-effective Pilot-Tone-based Monitoring Technique for Power Saving in RSOA-based WDM-PON --- p.73 / Chapter 4.1 --- Introduction --- p.73 / Chapter 4.2 --- Proposed System Architecture --- p.75 / Chapter 4.3 --- Experimental Setup and Result --- p.78 / Chapter 4.4 --- Power Saving Efficiency Calculation --- p.82 / Chapter 4.5 --- Summary --- p.86 / Chapter Chapter 5 --- Conclusions and Future Work --- p.87 / Chapter 5.1 --- Conclusions --- p.87 / Chapter 5.2 --- Future Work --- p.88 / Bibliography --- p.90 / Publications during PhD Study --- p.98

Silicon photonics is considered to have the potential to enable future communication systems with optical input-outputs to circumvent the shortcomings of electronics. Today silicon is the material of choice for photonic and optoelectronic circuits, mainly due to its excellent material properties, established processing technology, low-cost, compact device footprint, and high-density integration. From sensing and detection to computing and communications, silicon photonics has advanced remarkably in the last couple of decades and found numerous applications. This thesis work focusses on three novel applications of silicon photonics for optical communications. The first application is the design and demonstration of a differential phase shift keying (DPSK) demodulator circuit using a ring resonator. DPSK-based transceivers are being actively considered for short-haul optical communication systems due to their advantages in terms of high extinction ratio, dispersion tolerance, and improved sensitivity. The ring resonator utilizes the concept of coherent perfect absorption and results into a compact demodulator circuit that can be easily integrated into an all-optical system. The next application involves a nonlinear optical process, namely, four wave mixing (FWM) inside a silicon nanowire. For FWM to occur efficiently, phase matching between the real propagation constants of all the frequency components is a key requirement. However, this condition cannot be easily satisfied in integrated optics semiconductor platforms. We propose an altogether new approach to achieve signal gain within the context of non-Hermitian photonics and parity-time (PT) symmetry and show that the phase matching criterion is not necessary to achieve efficient nonlinear interactions. Instead by introducing losses only to the idler components while leaving the pump and signal waves intact, we analyze a coupled-wave system of silicon nanowires using finite difference time domain technique and find that signal gain is indeed possible in such a system, irrespective of the fulfillment of the phase-matching condition. The final application of silicon photonics in this thesis is the engineering of zero group velocity dispersion (GVD) point in the C-band of communication channel. The problem of pulse broadening due to chromatic dispersion is becoming an increasingly important factor for signal degradation. We propose a hybrid silicon/plasmonic waveguide that can change the zero-GVD point by altering the geometry and material of the waveguide components. In addition, such hybrid system also has the potential to transmit both optical and electronic signals along the same circuitry.