Research On Key Technologies Of Optical Signal Processing

Optical signal processing is a key technology in future high-speed and large- capacity optical network. In this dissertation, optical signal processing technologies including all-optical wavelength conversion, optical format conversion and all-optical regeneration as well as optical pulse-amplitude-equalization technology are intensively studied based on optical devices such as semiconductor optical amplifier (SOA), delayed interferometer (DI) and optical modulators.Firstly, we present numerical models for SOA and DI, and analyze the operation principle of the SOA-DI optical gate. Based on the numerical model of SOA, a method of optical pulse-amplitude-equalization is proposed and theoretically studied. Experiments are also carried out to verify the proposed scheme. The experimental and numerical results agree well. Amplitude equalization of optical pulses with amplitude fluctuation of more than 40% at a repetition rate of 20 GHz is demonstrated. The scheme also works well when it is applied to the amplitude equalization of 40 GHz optical pulses with amplitude fluctuation of greater than 30%.All-optical wavelength conversion of RZ signals at 10 Gb/s and 40 Gb/s is demonstrated based on the SOA-DI optical gate. Wavelength converter based on a nonlinear polarization switch (NPS) and a DI is proposed and demonstrated for the wavelength conversion of NRZ signals. The extinction ratio and the Q-factor of the wavelength-converted signal based on NPS are effectively improved due to the reshaping function of the DI, leading to the receiver sensitivity improvement of the NPS-converted signal before and after transmission.By using a DI with variable delays, we demonstrate an all-optical NRZ-to-RZ format converter. The scheme can be used to convert input signals at different bit rates and can obtain converted signals with tunable duty cycles. The format converter is insensitive to the power fluctuation of the optical clock as the SOA works in the saturation regime. Besides, we also propose and demonstrate NRZ-to-RZ format conversion based on cascaded lithium niobate phase and intensity modulators followed by a section of DCF. By using this scheme, RZ signal with a low duty cycle and low timing jitter can be obtained. The converted RZ shows excellent transmission performance.Finally, all-optical regeneration based on SOA-DI configuration is investigated. The SOA-DI-based all-optical 2R regenerator is theoretically and experimentally studied. The blue-shifted optical filtering technique is used to mitigate the impact of pattern effects at a bit rate of 40 Gb/s. A novel all-optical 2R regenerator based on SOA-DI-SOA configuration is proposed and demonstrated. The cross-gain modulation in a second SOA is utilized to achieve the regenerative amplification of the optical signal out of DI. The performance of the SOA-DI regenerator is greatly improved and is more tolerant to the degradation of the input signal. Furthermore, 40 Gb/s 3R regeneration of degraded signals is also demonstrated by incorporating the SOA-DI as the optical decision gate and a self-pulsating laser as the clock recovery unit. The waveform of the PMD-degraded signal is successfully restored after the 3R regeneration. The bit-error rate floor of the ASE-degraded signal is removed and error-free operation is achieved.