Key Research For SOA-based Switch In Optical Delay Line

Thanks to the intrinsic features like high time-bandwidth product, good Electro Magnetic Compatibility(EMC) and high operating frequency, fiber delay line(FDL) is widely used in phasearray radar, optical communication system, optical signal processing, optical computer system and electronic countermeasures etc. The FDL based on optical switch is one of the most widely used type. Due to short switching time and capability of integration, semiconductor optical amplifier is attractive for optical switches.In this paper, the work mainly focused on solving the problem induced by nonlinear effects of SOA, and the major studies can be divided into three parts:Firstly,the structure of SOA and working principle are discussed, the theoretical equation and nonlinear effects in SOA are also studied.Secondly,to suppress the distortion induced by SOA, the scheme using phase modulation is proposed. A comparison between the SOA-based optical RF switches using phase modulation and intensity modulation is carried out. The waveforms, noise floor and spurious free dynamic range(SFDR) are measured to confirm the ability of phase modulation to suppress the distortion induced by SOA. Results show that the scheme using optical phase modulation has ignorable nonlinear distortion even when the SOA is operated at deep saturated region.Lastly,to suppress the pattern effect in SOA, the scheme using polarization modulation is proposed. A comparison between SOA-based photonic systems using polarization modulation and intensity modulation is carried out theoretically and experimentally, in which both analog and digital photonic systems are considered. The pattern effect suppression for different input power of SOA and the optical spectral properties are also investigated. Experimental results show that the scheme using polarization modulation has ignorable pattern effect even though the SOA is operated at the deep saturated region.