Research On Optical Temporal Differentiator Based On Fiber Sagnac Loop

Optical signal processing,which could overcome "electronic bottlenecks"effectively,can process optical signals directly.It has many advantages such as ultra-high processing speed and large working bandwidth,and it is one of the key technologies of all-optical communications networks.The optical temporal differentiator(OTD)enables signal processing directly in optical domain.Compared with electrical differentiator,OTD has the merits of high operation speed,resistance to electromagnatic interference,low power consumption,and compactness.Thus,the study of OTD is of great value.In this thesis,based on the theoretical,simulation and experimental research on the transmission spectrum characteristics of a Sagnac loop with high birefringence(HiBi)fiber,a second-order optical temporal differentiator(SO-OTD)based on this kind of Sagnac loop is proposed and studied.The performances of the SO-OTD are analyzed by theoretical analysis and numerical simulations.Furthermore,an OTD implemented for wavelength-division multiplexed(WDM)system and a high-order optical temporal differentiator(HO-OTD)based on this kind of Sagnac loop are also proposed and analyzed.The main research achievements are summarized as follows:(1)According to the Jones matrix theory,the theoretical and simulation research on the transmission spectrum characteristics of the Sagnac loop based on HiBi fiber have been carried out.The influence of the parameters of HiBi fiber,polarization controller state and coupler power ratio on the transmission spectrum characteristics are mainly analyzed.A Sagnac loop based on a length of HiBi is made and studied in the lab.The results show that the experimental and theoretical results are in good consistence.(2)A SO-OTD based on HiBi Sagnac loop is analyzed and verified.The results present that the tunability of central frequency of differentiator can be realized by choosing appropriate Hibi fiber length or refractive index difference.Furthermore,when the input Gaussian pulse’s attenuation factor is 0.5ps,the maximum 3dB bandwidth of the differentiator can reach to 30THz,the minimum error factor is only about 0.0077.This result shows that the SO-OTD can perform high-precision second-order differential processing on Gaussian pulses.(3)A HO-OTD and a WDM system SO-OTD based on HiBi Sagnac loop are also analyzed and verified.Validated by theoretical research and numerical simulation,the proposed two differentiors can achieve high-precision differential function.The performances have also been analyzed by deviation factor,energetic efficiency,and 3 dB bandwidth.The results show that the two OTDs have good accuracy and large working bandwidth.