Research On All-optical Signal Processing Based On Nonlinear Effect Of Fiber

To meet the demand of modern high-speed and high-capacity optical fibre transmission and to overcome the restriction of electronic bottleneck, All-optical 3R regeneration is one of the pivotal technologies for all-optical transparent networks. The clock Recovery, delayed buffers and optical decision are the three important processes in the realization of all-optical 3R regeneration. Optical fibre, endowed with femtosecond response speed, is the preferred nonlinear material for high-speed all-optical signal processing. Fiber Bragg grating (FBG) with small size is convenient for integration and can be directly adapted in optical fiber communication line. Due to its characteristic of controllable switching, FBG can realize the function of all-optical decision. Furthermore, it can be used as delay line since the optical transmission delay is tunable. However, the nonlinear effect in optical fiber is polarization-dependent. Since the magnitude of the clock component in optical spectrum is various with different modulated signal patterns, the clock recovery by using the resonance mechanism encounters the problem of pattern effect. In this dissertation, four aspects are studied and explored by theoretical analysis, numeric calculation and system simulation, including the delayed buffers and optical decision in fiber Bragg grating, the polarization dependence of nonlinear effect in optical fiber, and the elimination of pattern dependence of clock recovery in regeneration. The main contents are listed as follow:1. The method based on Semi-implicit Runge-Kutta method and simple iterative is proposed to solve the nonlinear coupling mode equations in FBG. This greatly reduces the computational complexity, simplifies the calculating procedure and avoids the numerical divergence. The smoothing technology in simulation is designed, which reduces the stabilizing time in numerical simulation. The general numerical simulation platform is established both for static and dynamic state of FBG. An allover simulation on FBG properties is achieved.2. The characteristics of tuning delay and power jitter in optical fiber Bragg Grating is researched. It is found that phase-shifting grating (PSG) is not suitable for tuning delay of short pulses. The tuning delay performance of FBG without phase-shift depends on the optimal combination of the corresponding parameters, such as power, working central wavelength, pulse width and grating length. By adjusting these parameters, the maximal delay time can be achieved with no pulse deformation. The dispersionless all-optical tunable delay is implemented, and power fluctuation of output pulse has been reduced.3. The timing jitter and power fluctuation of output pulses are researched when FBG is used in all-optical decision. It is found that suppressing sidelobe of the transmission spectrum in apodized grating is conducive to reduce the output power fluctuation caused by changing in pump power. With the increase of wavelength difference between pump and probe signal, the timing jitter caused by changing in signal power is decreased.4. The method of all-optically determining output lightwave polarization is suggested based on the cascading SPM power equalizer and the combinational logic OR gate. With input return-to-zero signal with random polarization direction, output polarization direction is determined and output power is balanced. The method can be used to resolve the problem of polarization-dependence in the nonlinear effect of optical fiber.5. The scheme of all-optical separator and equalizer for two-level power signal is designed, which is based on the cascaded NOLM. The scheme can not only directly separate or balance two-level power signal, but also eliminate pulse pedestal and convert output wavelength.6. Based on NOLM, doubling frequency for NRZ/RZ clock is suggested. Intensity and phase of continue wave are modulated simultaneously by XOR in NOLM. Two pulse series with?phase difference are produced and carrier suppression is obtained in output spectrum at the transmission port of NOLM. Then doubling frequency for NRZ/RZ clock is achieved. With this method, the pattern correlation in doubling frequency for clock is eliminated.7. The general scheme of clock extraction for NRZ/RZ signal is suggested. By XOR in NOLM, the carrier line and even harmonics of the original signal are suppressed, and clock lines of NRZ signal is enhanced. The suppressed lines are recovered by AND in NOLM. With this scheme, the clock can be extracted directly by the F-P filter even in the extreme condition of inputting the full duty square-wave pulse series. As a result, the pattern effect in the clock recovery is overcome.