High-Speed All-Optical Signal Processing Based On Semiconductor Optical Amplifier

Optical fiber communication technology has greatly expedited the growing of Internet, whose traffic is increasing with a speed exceeding the"Moore's Law". As a consequence, the so-called"electronic bottleneck"emerges. All-optical signal processing (AOSP) is a kind of technology that processes the signal directly in the optical domain, so it avoids the O/E and E/O conversions, as an alternative to prevent the"electronic bottleneck", while achieving a very high speed of signal processing. All-optical signal processing has a lot of functions such as amplification, wavelength conversion, regeneration, logic, memory, multiplexing and de-multiplexing, clock recovery etc. Since it avoids the repetitive conversions of O/E/O with expensive high-speed electronic devices, all-optical signal processing will play a very important role in the next generation optical fiber networks, which are supposed to be green, with high power efficiency, and low cost.Semiconductor optical amplifier (SOA) is one of the key devices as a nonlinear element to realize the all-optical signal processing, because it has many advantages, such as high optical nonlinearity, capable of being integrated, compact size, and low power consumption. Lots of all-optical functions have been proposed through exploring the various nonlinear effects in SOAs via cross gain modulation (XGM), cross phase modulation (XPM), four wave mixing (FWM), or cross polarization modulation (XPolM). The thesis will focus on the specific studies of all-optical signal processing based on SOA in aspects as follows: Time-domain model of SOAA new time-domain model of SOA was proposed, which included many physical effects, like carrier heating (CH) process, spectrum hold burning (SHB) process, bidirectional amplified spontaneous emission (ASE), and gain dispersion. Moreover, a detailed numerical algorithm was also provided to solve the model. Turbo-switch based on SOATurbo-switch (TS) is a novel all-optical switch scheme, which consists of two cascaded SOAs and an intermediate optical band-pass filter (OBF). Turbo-switch can be used to enhance the operation speed of SOA switches. As for the researches of turbo-switch, the following areas are focused:(1) The fundamental working principles of the turbo-switch are theoretically investigated for the first time. The simulation results show that, turbo-switch can accelerate the operation speed of SOA by 4 times for the two reasons as: Firstly, the slow recovery tails in the gain / phase dynamics of SOA1 are compensated by SOA2. Secondly, the intermediate OBF prevents the pump from consuming the carriers in SOA2.(2) The pattern effect associated with SOA is evaluated for the turbo-switch. In addition, the 160 Gb/s wavelength conversion using turbo-switch is also simulated.(3) Novel schemes to further improve the switching speed are analyzed. The simulation results show that, cascading more SOAs after turbo-switch will help to accelerate the operation speed of the switch. A switch with three cascaded SOAs has a carrier recovery time of about 10 ps.(4) The impact of the biased current on turbo-switch is studied. Both simulation and experimental results show that, reducing the biased current of SOA1 will decrease the extinction ratio of the output, while adjusting that of SOA2 will help to mitigate the pattern effect of the switch. Therefore, it is better to keep the current of SOA1 high, and adjust that of SOA2 to optimize the switching speed.High-speed all-optical memory based on SOAHigh-speed all-optical memory is one of the key components in optical packet switching (OPS) networks. A novel all-optical memory based on SOA is proposed to store optical data for long-term. The key elements of the memory are Mach-Zehnder Interferometers (MZIs) incorporating SOAs, acting as AND gate and regenerator in a loop configuration. The initial data burst is loaded into the memory through the AND gate, and the regenerator improves the quality of the optical signal during circulating. Simulations are carried out to investigate the operation behaviors of the MZIs. Moreover, the results show the error free operation of the memory when operated at 20, 40 and 80 Gb/s even after 500 times circulation.All-optical edge detector based on SOAAll-optical edge detection can be used to identify the rising and falling edges of the non-return-to-zero (NRZ) signal. Since the output of the edge detector is usually picosecond pulses, it can find applications in many areas, including clock extraction from the NRZ signal, NRZ to pseudo-return-to-zero (PRZ) format conversion, and ultra-wideband (UWB) signal generation.A novel all-optical edge detector is proposed for the high-speed NRZ signals. A single Mach-Zehnder interferometer (MZI) incorporating SOAs was used, so the structure is very simple, and can be fully integrated. The basic working principle of the new device is that, the CW probes in the upper and bottom arms always undergo a phase difference of ? via inputs of NRZ data and NRZ complementary data at the upper and lower arms of MZI, except during the rising and falling transition edges of the NRZ signal. Therefore, the output after the two probes interfering at the constructive port of the MZI will be a series of pulses at only the edges of the NRZ signal. The output signals of the edge detectors are numerically evaluated in terms of Q-factors (>20dB) and extinction ratios (>11dB) at 20 and 40 Gb/s, which indicate the high quality of output.