Study Of Optical Modulation Format Conversion Based On Silicon Photonic Waveguide Devices

With the development of optical communication technology, different types of optical networks are emerging, and different networks have different optimal optical modulation formats. When the signal communicates across the network, it is necessary to convert the optical modulation format between the exchange nodes in the network. Non-return-to-zero (NRZ) and return-to-zero (RZ) are the most popular optical modulation formats in the optical communication system. So, the optical modulation format conversion between NRZ and RZ will become an important technology for future optical networks.Now, the above modulation format conversion is mainly based on the nonlinear effects in nonlinear optical fibers and semiconductor optical amplifiers (SOA) at home and abroad. These modulation format converters can directly realize the format conversion in the optical domain, without the conversion procession of optical-electrical-optical. The optical modulation format conversion based on nonlinear fibers is with high speed and efficiency, but the low nonlinear coefficient of the nonlinear fibers results in a long interaction length. The nonlinear coefficient of SOA is high, but SOA is a kind of active device that requires current injection electronics and a heat-sink platform. So we use silicon photonic waveguide devices, such as silicon optical waveguides and silicon micro-ring devices, to achieve the optical modulation format conversion, in order to achieve the all-optical network and integrated.Silicon photonic waveguide devices have significant nonlinear effects, and satisfy the Schrodinger equations. Model the silicon photonic waveguide devices using the Matlab software, and build the optical modulation format conversion system based on the devices by OptSim optical communication system software. When the pump and the probe are coupled into the silicon photonic waveguide devices, the two signals will produce the nonlinear effects of self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM), and cause the changes of the input signals spectra. By setting the center frequency and bandwidth of the optical bandpass filter (OBPF) reasonably, we can achieve the optical modulation format conversion from NRZ to RZ. In addition, two-photon absorption (TPA) and free carrier absorption (FCA) in the silicon waveguide will not only reduce the optical power, but also cause the spectral distortion, so TPA and FCA can not be ignored in the optical modulation format conversion. The results show that the changeable bandwidth of the OBPF leads to tunable-pulsewidth RZ signal. The conversion efficiency (CE) and the pattern effect of the RZ signal are attributed to the parameters of the pump pulse and the OBPF.