Research Of All Optical Format Conversion Based On Nonlinear Effects In SOA

The all-optical code switching based on SOA is studied based on the basic equation of Semiconductor Optical Amplifier(SOA). The propagation properties of optical wave in SOA are simulated. We use SOA and OBPF cascade structure to achieve all-optical NRZ to RZ and RZ to NRZ code conversion and analyzed the conversion effect. By analyzing the structure of MZI, the code switching of all optical NRZ-OOK to RZ-BPSK based on SOA-MZI structure is realized. Finally we use SOA and DI to achieve a multi-channel NRZ to RZ code conversion.According to the SOA carrier rate equation and the transmission equation of light wave in SOA, the relationship between the wave power and the carrier concentration is calculated by the method of subsection. The RZ to NRZ and NRZ to RZ format conversion scheme based on the SOA and OBPF cascade structure is analyzed on the OptiSystem simulation platform. In RZ to NRZ format conversion, mainly used the cross-phase modulation(XPM) in SOA. The choice of OBPF’s detuning is very important. When the detuning is blue shifted 0.9-1nm, the maximum signal extinction ratio is about 19.4dB. When detuning in antiphase region near, output signal extinction ratio(EXT) is very small, but whether it is in blue shift area or in the red region, the detuning is not the bigger the better, select appropriate detuning can obtain higher extinction ratio.In NRZ to RZ format conversion, mainly used the four wave mixing(FWM) effect, the peak of RZ signal after conversion has a certain jitter. so the output signal has nonlinear pattern effect(NLP). When the control signal pulse width is 2ps, the amount of NLP is 1.19 dB. When the control signal pulse width is 8ps, the amount of NLP is 4.96 dB. NLP effect increases with the increase of pulse width. In the case of the same extinction ratio, the conversion signal is easy to get a higher signal to noise ratio when the average power of the clock signal is higher. Therefore, when using this scheme, the code type conversion should consider the characteristics of signal to noise ratio and extinction ratio, and select the appropriate optical power.After that, according to the principle of SOA-MZI structure, the format conversion system based on SOA-MZI structure of all optical NRZ-OOK to RZ-BPSK is built. The effect of auxiliary optical injection power on conversion signal is analyzed. The results show that when the auxiliary optical power is low, the output signal distortion is more serious, with the increase of the auxiliary power, the quality of the output signal is getting better, but the gain is decreased.At the end of this paper, a delay interferometer(DI) and SOA are used to realize multi-channel NRZ to RZ code conversion. The results show that when the DI detuning increases, the converted RZ signal pulse width decreases. But DI is not able to increase indefinitely, which is due to the detuning is too large, will introduce the crosstalk of adjacent channels, resulting in the deterioration of the output signal waveform. The incident power of the clock signal is relatively small, the XGM effect of SOA is relatively strong, so that the output signal is modulated by the gain and the jitter of the peak is larger. With the increase of the clock signal input power, RZ signal peak jitter decreases. This is because the incident power increased to make SOA gradually in the gain saturation state, thereby weakening the XGM effect on the output signal.