Research On Silicon-based Waveguide All-Optical Differentiator

All-optical differentiator is an important component of all optical signal processing system.With the continuous development of signal processing system,more requirements for the response speed and frequency of the system are proposed.The traditional information processing generally adopts the optical-electrical-optical conversion route,and the frequency response of the electrical signal processing part is limited,which makes the whole system unable to respond to high-frequency signals.Therefore,this route can not meet the needs of high frequency signal processing.The future development trend of information technology is to break through the all-optical signal processing technology,and the existing optical-electrical-optical signal processing system will be replaced by all-optical signal processing system.The differentiators based on silicon waveguide grating have many advantages in all-optical system.It has a high refractive index of about 3.47,which can better limit the light field.It is also compatible with the widely used CMOS technology,and has the advantages of high integration and low cost.Silicon waveguide grating differentiator also has a wide range of application prospects,which is of great value in pulse shaping and coding,ultrafast all-optical operation and other frontier fields.Therefore,this paper focus on all-optical differentiators based on silicon waveguide grating,and the main content is divided into the following two parts:(1)The all-optical time domain differentiator based on silicon waveguide phase-shift Bragg grating is studied.This differentiator utilizes the response characteristics of the PSBG reflective end of the silicon-on-insulator platform to the optical signal,and realizes the function of differentiating the Gaussian incident signal.First,the structure of the SOI waveguide grating model was established and the integer-order differentiation was realized.Then,the influence of various structural parameters of PSBG on the performance of grating filtering is discussed in detail.By changing some structural characteristics of PSBG,the fractional differentiation of the incident signal is realized.Finally,based on the analysis of the influencing factors of the differential order in this paper,a light-controlled order adjustment method is proposed that uses the optical nonlinear effect of silicon material to control the differential order of the differentiator by adding pump light.And for the two structures of the differentiator whose order is less than 1 and greater than 1,the simulation has realized the light control and adjustment process of PSBG differentiator.In the process of applying the pump light power of 0-2.7W,the PSBG differentiators of less than 1 st order and greater than 1 st order produced 0.842-0.906 order and 1.189-1.230 order differential effects on the 20ps incident signal,respectively.(2)The all-optical time-domain differentiator based on silicon waveguide long-period grating is studied.The three-layer waveguide structure and grating design method of the long period grating on the SOI platform are discussed.The integer-order all-optical time-domain differentiator is designed using the fully coupled state of LPWG.Then,the effects of coupling coefficient and length of LPWG,etching depth,FWHM and bandwidth of incident signal on the differential effect are simulated,and the realization method of fractional-order long-period grating differentiator is proposed.Finally,this article discusses the use of optical nonlinear effects to achieve differential order adjustment.Using the non-linear effects such as Kerr effect,free carrier absorption and two-photon absorption,self-phase modulation and cross-phase modulation generated by silicon material under high-power pump light,the light-controlled modulation of the differential order of the LPWG differentiator is realized.In the process of applying pump power of 0-0.9W,the LPWG differentiator can generate 1-1.072-order differential for the incident signal of 20ps.