|Author:||Qureshi, Khurram Karim|
|Title:||Fiber ring lasers and all-optical signal processing devices for wavelength-division multiplexing systems|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Wavelength division multiplexing
|Department:||Department of Electrical Engineering|
|Pages:||vi, 220 leaves : ill. ; 31 cm|
|Abstract:||The wavelength division multiplexing (WDM) optical fiber system is an important enabling technology to satisfy the requirements of bandwidth of today's information age. The main objective of this research project is to develop novel devices with the potential applications in WDM systems. In particular, novel semiconductor fiber ring lasers based on a recently introduced linear optical amplifier (LOA) and all-optical signal processing devices based on an entirely new type of highly nonlinear fiber as well as devices based on injection-locking in Fabry Perot laser diodes are investigated. We proposed and demonstrated a simple configuration of a widely tunable single wavelength semiconductor fiber ring laser and a multiwavelength semiconductor fiber ring laser based on a linear optical amplifier (LOA). In an LOA, a vertical-cavity surface-emitting laser is integrated, perpendicularly, along the entire length of the amplifier, serves as a ballast to provide a constant gain to the amplifier and helps to clamp the gain competition in a laser cavity. In case of a single wavelength laser, ultra-wide continuous wavelength tuning range of over 90 nm was achieved using a scanning Fabry Perot filter. In addition a stable multiwavelength semiconductor fiber ring laser was also realized using F-P etalon. Thirty eight lasing lines were obtained with a fixed channel spacing of 0.8 nm, which is defined by the free-spectral range of the F-P etalon. Power stability of less than 0.15 dB during a 3-hour test for a single channel of the multiwavelength laser demonstrated the stability of this laser. A gain clamped SOA scheme is also realized using optical feedback. Using this scheme a stable multiwavelength semiconductor fiber laser was demonstrated. In the second part of this research project, all-optical signal processing devices were investigated. An all-optical switch is a key component in high capacity optical fiber communication networks such as optical time division multiplexed and wavelength division multiplexed systems. In this study an all optical on-off switch based on FWM in only 1.9-m long Bismuth Oxide Highly Non Linear Fiber (Bi2O3-HNLF) was demonstrated. The principle of the switch is that in the presence of the control signal, i.e., when the control signal is ON, the data will be transmitted, whereas when the control signal is OFF, the data signal will be blocked. The switch has a fast response time and high ON/OFF switching ratio. Robust optical pulse trains sources, capable of producing width-tunable pulses with high repetition rate and high extinction ratio are important sources for many applications, such as all optical sampling, ultrafast spectroscopy, all-optical reshaping and high speed optical communication. In this project width tunable train pulses were generated by employing FWM effect in 1.9-m of Bi2O3-HNLF. The scheme involves generating two optical pulse trains at different wavelengths, combining them in a short length HNLF to generate FWM and then varying the delay between the pulse trains. Due to FWM process the product term carries an optical pulse whose width depends on the overlap time between the two original pulses. The high nonlinearity of the fiber also compresses the pulsewidth of the generated pulse. The all-optical AND operation is one of the fundamental logic gates because it provides on-the-fly bit level functions such as address recognition or packet header modification, binary adders and binary counters. In this study an all-optical AND gate working at 10 Gb/s was implemented using the FWM effect in 1.9-m of Bi2O3-HNLF for NRZ signals. No additional input beam such as clock signal or continuous wave light other than input signals is used which is required in other schemes. All-optical signal quality monitoring system (SQMS) is crucial for fault management, quality of service, optical layer protection and eye monitoring for adaptive polarization-mode dispersion (PMD) compensation in high capacity transport and access networks. Typical error monitoring schemes require expensive optical-electrical conversions and high speed large-scale integration chips. Real-time all-optical signal quality monitoring is useful for future all-optical networks as the generated optical error signals can be forwarded to the corresponding network node for processing using the same network. It is, however, difficult to implement a real-time error-monitoring system all-optically because of the limited signal processing capabilities of current all-optical devices. In this study we proposed an all-optical signal quality monitoring system at 10 Gb/s using two multi-wavelength mutual injection-locked Fabry Perot laser diodes (FP-LDs) without employing any high speed electronics. Relatively complex logic operations, two threshold, one NOT, and one NOR, functions are realized. The proposed SQMS uses two threshold levels to determine the error bits. The resulting optical indicator signal, sometimes known as the "pseudo-error" signal, identifies both the positions and the durations of the error bits.|
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