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SYNCHRONIZATION IN ADVANCED OPTICAL COMMUNICATIONS
Title
SYNCHRONIZATION IN ADVANCED OPTICAL COMMUNICATIONS.
Creator
Kim, Inwoong, Li, Guifang, University of Central Florida
Abstract / Description
All-optical synchronization and its application in advanced optical communications have been investigated in this dissertation. Dynamics of all-optical timing synchronization (clock recovery) using multi-section gain-coupled distributed-feedback (MS-GC DFB) lasers are discussed. A record speed of 180-GHz timing synchronization has been demonstrated using this device. An all-optical carrier synchronization (phase and polarization recovery) scheme from PSK (phase shift keying) data is proposed...
Show moreAll-optical synchronization and its application in advanced optical communications have been investigated in this dissertation. Dynamics of all-optical timing synchronization (clock recovery) using multi-section gain-coupled distributed-feedback (MS-GC DFB) lasers are discussed. A record speed of 180-GHz timing synchronization has been demonstrated using this device. An all-optical carrier synchronization (phase and polarization recovery) scheme from PSK (phase shift keying) data is proposed and demonstrated for the first time. As an application of all-optical synchronization, the characterization of advanced modulation formats using a linear optical sampling technique was studied. The full characterization of 10-Gb/s RZ-BPSK (return-to-zero binary PSK) data has been demonstrated. Fast lockup and walk-off of the all-optical timing synchronization process on the order of nanoseconds were measured in both simulation and experiment. Phase stability of the recovered clock from a pseudo-random bit sequence signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5 % clock phase stability for large variations in power, bit rate and optical carrier frequency of the input data and therefore is suitable for applications in ultrafast optical packet switching. All-optical timing synchronization of 180-Gb/s data streams has been demonstrated using a MS-GC DFB laser. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB. All-optical carrier synchronization from phase modulated data utilizes a phase sensitive oscillator (PSO), which used a phase sensitive amplifier (PSA) as a gain block. Furthermore, all-optical carrier synchronization from 10-Gb/s BPSK data was demonstrated in experiment. The PSA is configured as a nonlinear optical loop mirror (NOLM). A discrete linear system analysis was carried out to understand the stability of the PSO. Complex envelope measurement using coherent linear optical sampling with mode-locked sources is investigated. It is shown that reliable measurement of the phase requires that one of the optical modes of the sampling pulses be locked to the optical carrier of the data signal to be measured. Carrier-envelope offset (CEO) is found to have a negligible effect on the measurement. Measurement errors of the intensity profile and phase depend on the pulsewidth and chirp of the sampling pulses as well as the detuning between the carrier frequencies of the data signal and the center frequency of the sampling source. Characterization of the 10-Gb/s RZ-BPSK signal was demonstrated using the coherent detection technique. Measurements of the optical intensity profile, chirp and constellation diagram were demonstrated. A CW local oscillator was used and electrical sampling was performed using a sampling scope. A novel feedback scheme was used to stabilize homodyne detection.
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Date Issued
2006
Identifier
CFE0001239, ucf:52894
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001239
ALL-OPTICAL REGENERATION FOR PHASE-SHIFT KEYED OPTICAL COMMUNICATION SYSTEMS
Title
ALL-OPTICAL REGENERATION FOR PHASE-SHIFT KEYED OPTICAL COMMUNICATION SYSTEMS.
Creator
Croussore, Kevin, Li, Guifang, University of Central Florida
Abstract / Description
All-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase...
Show moreAll-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase-preserving amplitude regeneration, phase regeneration, and phase-regenerative wavelength conversion are analyzed and demonstrated experimentally. The single-pump phase-conjugation process was used to regenerate RZ-DPSK pulse amplitudes with different input noise distributions, and the impact on output phase characteristics was studied. Experiments revealed a limited range over which amplitude noise could effectively be suppressed without introduction of phase noise, particularly for signals with intensity pattern effects. Phase regeneration requires use of phase-sensitive amplification (PSA), which occurs in nonlinear interferometers when the pump and signal frequencies are degenerate (NI-PSA), or in fiber directly through single-stage (degenerate) or cascaded (non-degenerate) FWM processes. A PSA based on a Sagnac interferometer provided the first experimental demonstration of DPSK phase and amplitude regeneration. The phase-regenerative capabilities of the NI-PSA are limited in practice by intrinsic noise conversion (amplitude to phase noise) and to a lesser extent by the requirement to modulate the pump wave to suppress stimulated Brillouin scattering (SBS). These limitations are relaxed in novel materials with higher SBS thresholds and nonlinearities. Degenerate FWM provides PSA in a traveling-wave configuration that intrinsically suppresses the noise conversion affecting the NI-PSA, while providing stronger phase-matched gain. Experiments confirmed superior phase-regenerative behavior to the NI-PSA with simultaneous reduction of amplitude noise for NRZ-DPSK signals. Phase-regenerative wavelength conversion (PR-WC) provides the regenerative properties of PSA at a new wavelength, and was proposed and demonstrated for the first time in this research. The parallel implementation of two FWM processes, phase-conjugation and frequency conversion, provides two idlers which exhibit interesting and useful regenerative properties. These were investigated theoretically and experimentally. Ideal phase-regenerative behavior is predicted when the contributing FWM processes are equally phase-matched, which can be maintained over any interaction length or wavelength shift provided the pump powers are properly adjusted. Depleted-pump regime PR-WC provides simultaneous phase and amplitude regeneration. Experiments confirmed regenerative behavior for wavelength shifts of the idlers up to 5 nm. Two techniques for phase regeneration of 4-level PSK signals were developed and evaluated. The first is based on parallel operation of PSAs suitable for processing 2-level PSK signals, where phase projection and regeneration are combined to recover the input data. Analysis of this scheme outlined the conditions required for effective phase regeneration and for practical implementation using known PSAs. A novel process based on FWM (parallel phase-conjugation followed by PSA) was developed and analyzed, and demonstrated using numerical simulations. These studies provide a basis for further work in this area.
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Date Issued
2007
Identifier
CFE0001923, ucf:47473
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001923
ELECTRO-OPTICAL AND ALL-OPTICAL SWITCHING IN MULTIMODE INTERFERENCE WAVEGUIDES INCORPORATING SEMICONDUCTOR NANOSTRUCTURES
Title
ELECTRO-OPTICAL AND ALL-OPTICAL SWITCHING IN MULTIMODE INTERFERENCE WAVEGUIDES INCORPORATING SEMICONDUCTOR NANOSTRUCTURES.
Creator
Bickel, Nathan, LiKamWa, Patrick, University of Central Florida
Abstract / Description
The application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered...
Show moreThe application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered advantages such as a very compact device footprint, low polarization sensitivity, large bandwidth and relaxed fabrication tolerances when compared with conventional single-mode waveguide formats. The first portion of this dissertation focuses on the characterization of the materials and material processing techniques for the monolithic integration of In0.15Ga0.85As/GaAs self-assembled quantum dots (SAQD) and InGaAsP/InGaAsP multiple quantum wells (MQW). Supplemental methods for post-growth bandgap tuning and waveguide formation were developed, including a plasma treatment process which is demonstrated to reliably inhibit thermally induced interdiffusion of Ga and In atoms in In0.15Ga0.85As/GaAs quantum dots. The process is comparable to the existing approach of capping the SAQD wafer with TiO2, while being simpler to implement along-side companion techniques such as impurity free vacancy disordering. Study of plasma-surface interactions in both wafer structures suggests that the effect may be dependent on the composition of the contact layer. The second portion of this work deals with the design, fabrication, and the testing of MMI switches which are used to investigate the limits of electrical current control when employing SAQD as the active core material. A variable power splitter based on a 3-dB MMI coupler is used to analyze the effects of sub-microsecond electrical current pulses in relation to carrier and thermal nonlinearities. Electrical current controlled switching of the variable power splitter and a tunable 2 x 2 MMI coupler is also demonstrated. The third part of this dissertation explores the response of In0.15Ga0.85As/GaAs SAQD waveguide structures to photogenerated carriers. Also presented is a simple, but effective, design modification to the 2 x 2 MMI cross-coupler switch that allows control over the carrier distribution within the MMI waveguide. This technique is combined with selective-area bandgap tuning to demonstrate a compact, working, all-optical MMI based switch.
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Date Issued
2010
Identifier
CFE0003220, ucf:48568
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003220