In situ method for power re-equalization of wavelength pulses inside of OCDMA codes

A simple in-situ method to equalize power among individual wavelengths pulses representing two-dimensional wavelength-hopping time-spreading OCDMA code originally generated by a fibre Bragg grating-based OCDMA encoder is presented. Experimental data obtained in a field-based multiuser OCDMA testbed shows that applying this method results in system performance enhancements which was demonstrated by observing improved bit error rate (BER) during the field trials

DESIGN AND PERFORMANCE ANALYSIS OF AN OPTICAL CDMA SYSTEM FOR 2-D PERFECT DIFFERENCE CODES USING SHIFTED SINE FUNCTIONS

A Dynamic Optical Code Division Multiple. Access (DOCDMA) communication system for Two Dimensional (2-D) Perfect Difference codes using Shifted Sine Functions (SSFs) is proposed here. The performance analysis for this OCDMA system has been done. This system is modeled and analyzed taking into account Multiple Access Interference (MAI) or Multiuser interference (MUI), Thermal Noise and Phase Induced Intensity (PIIN) noise. The performance of this system is compared to that of a DOCDMA system using SSFs as functional codes, Noncoherent spatial / spectral OCDMA system with 2-D perfect difference codes and OCDMA system for 2-D M-matrices codes. The results show that the proposed system improves the bit error rate (BER) performance for large number of users. Furthermore, it is found that for low values of the effective power for each user, the BER performance improves manifold. So, BER can be kept to very low values for lower power levels and hence, the system is more robust

Noncoherent Spatial/Spectral Optical CDMA System With Two-Dimensional Perfect Difference Codes

[[abstract]]A dynamic optical code division multiple access (DOCDMA) communication system is proposed for high-bandwidth communication systems. An implementation of the system is proposed based on a fast tunable optical filter (TOF) in each encoder and decoder. This technique actively modulates the central wavelength of a TOF according to a functional code at the transmitter during the bit period before the transmission of the data. The system is modeled and analyzed taking into account multiple access interference (MAI), thermal noise, and phase-induced intensity noise (PIIN). The performance of this system is compared to that of a spectral amplitude coding system that uses either a Hadamard code or a modified quadratic congruence (MQC) code. The results show that the proposed DOCDMA system reduces the PIIN effect on the performance of the system and improves the bit error rate (BER) performance at a large number of users. Furthermore, it is found that when the effective power is large enough, the MAI becomes the main factor that limits system performance, whereas when the effective power is relatively low, both thermal noise and PIIN become the main limiting factors with thermal noise having the main influence.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

Optimization of multicore optical fibers with fiber Bragg gratings towards bend and shape sensing

A shape sensor based on fiber Bragg gratings (FBGs) in multicore fibers is a complex device with multiple factors which have to be accounted for a successful measure- ment system. In this dissertation, I considered several aspects of such shape and curvature sensors

Investigation of the impact of fibre impairments and SOA-based devices on 2D-WH/TS OCDMA codes

In seeking efficient last-mile solutions for high-capacity, optical code division multiple access (OCDMA) emerges as a promising alternative high-speed optical network that can securely support a multitude of simultaneous users without requiring extensive equipment. This multiplexing technique has recently been the subject of comprehensive research, highlighting its potential for facilitating high-bandwidth multi-access networking. When contrasted with techniques such as wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM), OCDMA offers a more effective and equitable split of available fibre bandwidth among the users. This thesis presents my research focused on the incoherent OCDMA under the influence of optical fibre impairments that uses picosecond multiwavelength pulses to form two-dimensional wavelength hopping time-spreading (2D-WH/TS) incoherent OCDMA codes. In particular, self-phase modulation, temperature induced fibre dispersion, chromatic dispersion, as well as the impact of semiconductor optical amplifier SOA devices deployment on 2D-WH/TS OCDMA code integrity were investigated. These aspects were investigated using a 17-km long bidirectional fibre link between Strathclyde and Glasgow University. In particular, I investigated the impact of temporal skewing among OCDMA code carriers and the importance of selecting small range of wavelengths as code carriers where wide range manifest high dependency on wavelength. This wavelength dependency is exploited furthermore to measure the induced temperature dispersion coefficient accurately and economically. I have conducted experiments to characterise the impact of SOA-device on 2D OCDMA code carries which is evaluated under different bias conditions. This evaluation addressed the potential challenges and ramifications of the gain recovery time of SOA and its wavelength dependency with respect to gain ratio and self-phase modulation (SPM). The OCDMA code was built using multiplexers and delay lines to create a 2D OCDMA code to allow studying the impact of deploying a SOA under different conditions on each wavelength. The concept described above is then extended to the investigation of the SOA’s impact on a 2D-WH/TS OCDMA prime code under high bias current/gain conditions. The overall performance of two different 2D-WH/TS OCDMA systems deploying the SOA was also calculated. I have also investigated the possibility of manipulating chirp in 2D-WH/TS incoherent OCDMA to counteract the self-phase modulation-induced red shift by using single mode fibre and lithium crystals. I have investigated the performance of the picosecond code based optical signal when subjected to temperature variations similar to that experience by most buried fibre systems. I have proposed and demonstrated a novel technique, which I examined analytically and experimentally, that utilises a SOA at the transmitter to create a new code with a new wavelength hopping and spreading time sequences to achieve a unique physical improved secure incoherent OCDMA communication method. A novel fully automated tuneable compensation testbed is also proposed of an autonomous dispersion management in a WH/TS incoherent OCDMA system. The system proposed manipulates the chirp of OCDMA code carriers to limit chromatic dispersion detrimental effect on transmission systems.In seeking efficient last-mile solutions for high-capacity, optical code division multiple access (OCDMA) emerges as a promising alternative high-speed optical network that can securely support a multitude of simultaneous users without requiring extensive equipment. This multiplexing technique has recently been the subject of comprehensive research, highlighting its potential for facilitating high-bandwidth multi-access networking. When contrasted with techniques such as wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM), OCDMA offers a more effective and equitable split of available fibre bandwidth among the users. This thesis presents my research focused on the incoherent OCDMA under the influence of optical fibre impairments that uses picosecond multiwavelength pulses to form two-dimensional wavelength hopping time-spreading (2D-WH/TS) incoherent OCDMA codes. In particular, self-phase modulation, temperature induced fibre dispersion, chromatic dispersion, as well as the impact of semiconductor optical amplifier SOA devices deployment on 2D-WH/TS OCDMA code integrity were investigated. These aspects were investigated using a 17-km long bidirectional fibre link between Strathclyde and Glasgow University. In particular, I investigated the impact of temporal skewing among OCDMA code carriers and the importance of selecting small range of wavelengths as code carriers where wide range manifest high dependency on wavelength. This wavelength dependency is exploited furthermore to measure the induced temperature dispersion coefficient accurately and economically. I have conducted experiments to characterise the impact of SOA-device on 2D OCDMA code carries which is evaluated under different bias conditions. This evaluation addressed the potential challenges and ramifications of the gain recovery time of SOA and its wavelength dependency with respect to gain ratio and self-phase modulation (SPM). The OCDMA code was built using multiplexers and delay lines to create a 2D OCDMA code to allow studying the impact of deploying a SOA under different conditions on each wavelength. The concept described above is then extended to the investigation of the SOA’s impact on a 2D-WH/TS OCDMA prime code under high bias current/gain conditions. The overall performance of two different 2D-WH/TS OCDMA systems deploying the SOA was also calculated. I have also investigated the possibility of manipulating chirp in 2D-WH/TS incoherent OCDMA to counteract the self-phase modulation-induced red shift by using single mode fibre and lithium crystals. I have investigated the performance of the picosecond code based optical signal when subjected to temperature variations similar to that experience by most buried fibre systems. I have proposed and demonstrated a novel technique, which I examined analytically and experimentally, that utilises a SOA at the transmitter to create a new code with a new wavelength hopping and spreading time sequences to achieve a unique physical improved secure incoherent OCDMA communication method. A novel fully automated tuneable compensation testbed is also proposed of an autonomous dispersion management in a WH/TS incoherent OCDMA system. The system proposed manipulates the chirp of OCDMA code carriers to limit chromatic dispersion detrimental effect on transmission systems

Fiber Bragg Grating Based Sensors and Systems

This book is a collection of papers that originated as a Special Issue, focused on some recent advances related to fiber Bragg grating-based sensors and systems. Conventionally, this book can be divided into three parts: intelligent systems, new types of sensors, and original interrogators. The intelligent systems presented include evaluation of strain transition properties between cast-in FBGs and cast aluminum during uniaxial straining, multi-point strain measurements on a containment vessel, damage detection methods based on long-gauge FBG for highway bridges, evaluation of a coupled sequential approach for rotorcraft landing simulation, wearable hand modules and real-time tracking algorithms for measuring finger joint angles of different hand sizes, and glaze icing detection of 110 kV composite insulators. New types of sensors are reflected in multi-addressed fiber Bragg structures for microwave–photonic sensor systems, its applications in load-sensing wheel hub bearings, and more complex influence in problems of generation of vortex optical beams based on chiral fiber-optic periodic structures. Original interrogators include research in optical designs with curved detectors for FBG interrogation monitors; demonstration of a filterless, multi-point, and temperature-independent FBG dynamical demodulator using pulse-width modulation; and dual wavelength differential detection of FBG sensors with a pulsed DFB laser

Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application

With the explosive growth of bandwidth requirement in optical fiber communication networks, optical code division multiple access (OCDMA) has witnessed tremendous achievements as one of the promising technologies for optical access networks over the past decades. In an OCDMA system, optical code processing is one of the key techniques. Rapid optical code reconfiguration can improve flexibility and security of the OCDMA system. This thesis focuses on advanced optical modulations and en/decoding techniques for applications in fast reconfigurable OCDMA systems and secure optical communications. A novel time domain spectral phase encoding (SPE) scheme which can rapidly reconfigure the optical code and is compatible with conventional spectral domain phase en/decoding by using a pair of dispersive devices and a high speed phase modulator is proposed. Based on this scheme, a novel advanced modulation technique that can simultaneously generate both the optical code and the differential-phase-shift-keying (DPSK) data using a single phase modulator is experimentally demonstrated. A symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using a similar setup for both the transmitter and receiver is further proposed, based on which a bit-by-bit optical code scrambling and DPSK data modulation technique for secure optical communications has been successfully demonstrated. By combining optical encoding and optical steganography, a novel approach for secure transmission of time domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over public wavelength-division multiplexing (WDM) network has also been proposed and demonstrated. To enable high speed operation of the time domain SPE/SPD scheme and enhance the system security, a rapid programmable, code-length variable bit-by-bit optical code shifting technique is proposed. Based on this technique, security improvements for OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable optical codes of up to 1024-chip have been achieved. Finally, a novel tunable two-dimensional coherent optical en/decoder which can simultaneously perform wavelength hopping and spectral phase encoding based on coupled micro-ring resonator is proposed and theoretically investigated. The techniques included in this thesis could be potentially used for future fast reconfigurable and secure optical code based communication systems

Coherent optical code division multiple access based on superstructure fiber bragg grating encoders and decoders.

Li Xin.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.Includes bibliographical references (leaves 81-86).Abstracts in English and Chinese.COHERENT OPTICAL CODE DIVISION MULTIPLE ACCESS BASED ON SUPERSTRUCTURE FIBER BRAGG GRATING ENCODERS AND DECODERS --- p.1ACKNOWLEDGEMENT --- p.2ABSTRACT --- p.III摘要 --- p.VCONTENTS --- p.VILIST OF FIGURES --- p.1Chapter CHAPTER 1 --- INTRODUCTION --- p.3Chapter 1.1 --- Overview of OCDMA --- p.3Chapter 1.2 --- Classification of OCDMA Schemes --- p.6Chapter 1.3 --- Introduction of Coherent OCDMA Schemes --- p.9Chapter 1.4 --- Introduction of superstructure Fiber Bragg Gratings and Other Encoding and Decoding Components --- p.10Chapter 1.5 --- Outline of the Thesis --- p.13Chapter CHAPTER 2 --- COUPLED MODE THEORY AND SUPERSTRUCTURE FIBER BRAGG GRATING SIMULATION MODEL --- p.16Chapter 2.1 --- Fiber Bragg Grating Model Based on Coupled Mode Theory --- p.16Chapter 2.1.1 --- Introduction of FBG and the Coupled Mode Theory --- p.16Chapter 2.1.2 --- FBG Model Based on CMT --- p.18Chapter 2.1.3 --- FBG Model When there are Phase Discontinuities Between Different Parts --- p.20Chapter 2.2 --- Properties of Fiber Bragg Gratings --- p.22Chapter 2.3 --- Simulation Model of superstructure Fiber Bragg Gratings --- p.27Chapter 2.4 --- Summary --- p.31Chapter CHAPTER 3 --- COHERENT OCDMA CODING SCHEME BASED ON THE SUPERSTRUCTURE FIBER BRAGG GRATING ENCODER/DECODER --- p.33Chapter 3.1 --- Introduction and Theoretical Derivation of the Coding Scheme --- p.33Chapter 3.1.1 --- Introduction of the Coding Scheme --- p.33Chapter 3.1.2 --- Derivation of SSFBG Encoder --- p.34Chapter 3.1.3 --- Encoding for the SSFBG --- p.39Chapter 3.2 --- Introduction of the Simulation Model and the Research on It …… --- p.44Chapter 3.3 --- Summary --- p.47Chapter CHAPTER 4 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN IDEAL CASE --- p.48Chapter 4.1 --- Introduction of the ideal case and factors that affect the system performance --- p.48Chapter 4.2 --- Effects by Refractive Index Modulation of the SSFBG Encoder --- p.49Chapter 4.3 --- Effects by Code Type --- p.54Chapter 4.4 --- Effect by the Code Length --- p.57Chapter 4.5 --- Summary --- p.60Chapter CHAPTER 5 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN PRACTICAL ENVIRONMENT --- p.62Chapter 5.1 --- Introduction --- p.62Chapter 5.2 --- Comparison of System Performance in Synchronous and Asynchronous Cases --- p.63Chapter 5.3 --- Discussion on the System Performance When Users are In Different Power Levels --- p.65Chapter 5.4 --- Analysis of Channel Noise In the Coherent OCDMA System --- p.68Chapter 5.5 --- Summary --- p.70Chapter CHAPTER 6 --- CONCLUSIONS AND FUTURE WORK --- p.72Chapter 6.1 --- Conclusions --- p.72Chapter 6.2 --- Future Work --- p.75APPENDIX A PROOF OF SSFBG THEORETICAL MODEL APPROXIMATION --- p.77"APPENDIX B RANDOM SEQUENCE, M-SEQUENCE AND WALSH SEQUENCE" --- p.80REFERENCES --- p.8

Optical code-division multiple access system and optical signal processing

This thesis presents our recent researches on the development of coding devices, the investigation of security and the design of systems in the optical cod-division multiple access (OCDMA) systems. Besides, the techniques of nonlinear signal processing used in the OCDMA systems fire our imagination, thus some researches on all-optical signal processing are carried out and also summarized in this thesis. Two fiber Bragg grating (FBG) based coding devices are proposed. The first coding device is a superstructured FBG (SSFBG) using ±π/2-phase shifts instead of conventional 0/π-phase shifts. The ±π/2-phase-shifted SSFBG en/decoders can not only conceal optical codes well in the encoded signals but also realize the reutilization of available codes by hybrid use with conventional 0/π-phase-shifted SSFBG en/decoders. The second FBG based coding device is synthesized by layer-peeling method, which can be used for simultaneous optical code recognition and chromatic dispersion compensation. Then, two eavesdropping schemes, one-bit delay interference detection and differential detection, are demonstrated to reveal the security vulnerability of differential phase-shift keying (DPSK) and code-shift keying (CSK) OCDMA systems. To address the security issue as well as increase the transmission capacity, an orthogonal modulation format based on DPSK and CSK is introduced into the OCDMA systems. A 2 bit/symbol 10 Gsymbol/s transmission system using the orthogonal modulation format is achieved. The security of the system can be partially guaranteed. Furthermore, a fully-asynchronous gigabit-symmetric OCDMA passive optical network (PON) is proposed, in which a self-clocked time gate is employed for signal regeneration. A remodulation scheme is used in the PON, which let downstream and upstream share the same optical carrier, allowing optical network units source-free. An error-free 4-user 10 Gbit/s/user duplex transmission over 50 km distance is reazlied. A versatile waveform generation scheme is then studied. A theoretical model is established and a waveform prediction algorithm is summarized. In the demonstration, various waveforms are generated including short pulse, trapezoidal, triangular and sawtooth waveforms and doublet pulse. ii In addition, an all-optical simultaneous half-addition and half-subtraction scheme is achieved at an operating rate of 10 GHz by using only two semiconductor optical amplifiers (SOA) without any assist light. Lastly, two modulation format conversion schemes are demonstrated. The first conversion is from NRZ-OOK to PSK-Manchester coding format using a SOA based Mach-Zehnder interferometer. The second conversion is from RZ-DQPSK to RZ-OOK by employing a supercontinuum based optical thresholder

Force Sensing in Arthroscopic Instruments using Fiber Bragg Gratings

Minimally-invasive surgery has revolutionized many medical procedures; however, it also impedes the ability to feel the interaction between the surgical tool and the anatomical part being operated on. In order to address this problem, it is necessary to obtain accurate measurements of the interaction forces exerted on the surgical tools during surgery. These forces can then be manifested to the surgeon via a haptic device or presented visually (visual-force feedback). This thesis describes the use of a fiber optic device to measure and display to the surgeon interaction forces acting on an arthroscopic tool. The sensorization of the tool involves a simple, highly efficient and robust design and is ideally suited for use in a surgical training environment aimed at narrowing the gap between trainees and expert surgeons before the trainees proceed to their first surgery in vivo. The major advantages of using fiber optics include their small size, their local simplicity, their ease of sterilization, and their high sensitivity. In this thesis, a complete low-cost sensing solution is described, including 1) the use of fiber Bragg grating and long period grating sensors, 2) design of a low-cost optical interrogator, 3) high resolution electronic signal processing, and 4) fabrication of the tool using wire EDM, CNC, and 3D metal sintering technologies. The full design of an arthroscopic grasper is presented, along with the preliminary design and manufacturing of an arthroscopic probe and shaver. The designed low-cost system was compared with a commercially-available optical interrogator. The calibration and experimental results for this system are presented and discussed for accuracy and performance of the sensorized tool before and after an axial element was added for increased sensitivity. Sources of error and methods of improvement for the optical system, arthroscopic tool, and testing procedures are discussed to inform the design of future generations of these instruments