Research On All-optical Differentiator Based On Grating

With the development of the information technology,it is an inevitable trend that electro-optical hybrid system will be replaced by all-optical signal processing system.In all-optical signal processing system,all-optical temporal differentiator is an import device which can differentiate the input light pulses in the time domain.Compared to optical-electric-optical conversion,All-optical temporal differentiator is able to reduce power consumption,system complexity and cost.All-optical temporal differentiator has a wide range of applications such as ultrafast optical operations,pulse shaping and coding,dark soliton detection in all-optical signal processing.All-optical differentiator based on grating has a a broad prospect with benefits such as mature technology?strong compatibility?high flexibility.In this thesis,the all-optical differentiators based on gratings have been researched,and the main works are as follows:(1)The coupled-mode theory of long-period fiber grating,nonlinear effect and the mechanism of double-beams input in silicon waveguide grating are studied.The theoretical model of all-optical temporal differentiator is established and the amplitude-frequency response and phase-frequency response of the gratings are analyzed.(2)By changing the coupling state between the core mode and the cladding mode,the fractional-order differentiation is demonstrated.For a Gaussian pulse with bandwidth of 12ps,the cross-correlation coefficient between the ideal output and the the actual output is 90.2%for the first-order differentiation.The effects of duty ratio are also investigated.(3)An all-optical temporal differentiator is designed based on the silicon waveguide grating,and the optical-control tuning of differential order is realized by using the optical nonlinear effects.For picosecond Gaussian pulse,the tunable differential order at the vicinity of the first order is demonstrated using the cross-phase modulation and the self-phase modulation respectively.The N-order differentiation are also studied,and the second,third and fourth order differential error comparing with the ideal differentiators are 5.6%,7.2%and 10%.The effects of grating parameters and signal pulse width on the performance are investigated at the same time.