All-optical Switches And Tunable Filters Based On Fiber Bragg Grating Is Nonlinear

The optical fiber Bragg gratings have many advantages, such as small size, strong selectivity upon wavelength, low loss, large bandwidth, easy to connected to fiber, etc. It is an important device in all-optical signal processing. Now many applications of gratings make use of the linear properties of these structures. The nonlinearity of the gratings can be overviewed when the input power is low, the nonlinear coefficient is small, and the length of the fiber is short. But if we increase these parameters, the properties of the grating will change, and these can bring many new applications, such as, optical switch, optical logical gate, optical tunable filter, etc. The response time of the nonlinearity is in fs, which is coincidence the requirements of high speed optical signal processing. So it is reasonable to processing the optical signal by the nonlinearity of gratings. In this paper, the nonlinearity in gratings was studied and their applications in optical signal processing was discussed. The main work is listed in following:Coupled mode theory has been developed to describe the propagation of optical pulses through Bragg gratings. The mode functions of single and double channel input were deduced, and these functions can be used to analyze the transport characteristics in Bragg gratings.Due to the speciality of the boundary condition, the nonlinear modular of the core refractive index, the SPM and XPM nonlinear coupling of the pre and post waveform, it is nearly impossible to analyze and calculate the coupled function. So it is very important to find a approach to study the grating nonlinear characteristics numerically.The numerical solving technique of the reflective Bragg grating coupled function was studied based on perturbation approximation, slowly change amplitude approximation, and phase matching. And the Bragg grating calculation model was established according to the boundary condition and the ware transfer process in the gratings. This model can be used to study the linear and nonlinear characteristics the of the Bragg grating while continue wave and pulse input.The nonlinear reflection and power spectrum of the gratings by different Apodization Method were discussed. It shows that the reflection peak value changes with red-shift; phase-shifted grating has stronger nonlinear effect and has a more obvious shift; the pulse was compressed in different degree after passing through a fiber-grating. According to the results, we give some optimization principle for the optical switch based on nonlinear gratings.The optical switch based on nonlinear grating has been optimized. It shows that, the switch has short stabilizing time and the pulse wave-shape remains undistorted when the work point of grating is setted properlyThe nonlinearity-induced fiber grating Bragg wavelength shift was studied. It shows that, with the increase of the input power, the peak value of the reflection decreased, and the width of the reflection gap narrowed. A novel tunable filter scheme based on the nonlinearity is proposed. This all-optical filter is tuned by the input control power. The results show that the waveshape of the pulse keeps well.