Research On Multilevel All-optical Regenerator And Its Performance Characterization Method

With the application of high-order optical modulation signals in optical fiber communication systems,all-optical regeneration technology is no longer limited to switch keying(OOK)signal,and gradually to the development of amplitude and phase regeneration for optical multilevel signal.This thesis studies the implementation schemes of multilevel pulse amplitude modulation(MPAM)optical signal regenerators and the performance characterization method,and the feasibility of the proposed schemes is confirmed by the OptiSystem simulation.The main research contents and innovations are as follows:1.It is proposed to use the linear gain and gain slope to describe the amplification and reshaping characteristics of all-optical multilevel amplitude regenerators.The gain slope is defined as the derivative of the normalized gain of the regenerator to the normalized input power,which is closely related to the reshaping characteristic of the regenerator.The gain slope required for the multi-level all-optical amplitude regeneration function is derived as well.The results show that the gain slope curve can not only analyze the reshaping range of the all-optical regenerator conveniently,but also determine the number of regenerative levels and the optimal operating point of the all-optical regenerator.At the same time,the noise reduction ratio(NRR),defined as the ratio of the average normalized amplitude jitter of input signal to that of regenerative signal,can well reflect the signal quality improvement by regenerator: the greater the noise reduction ratio,the better the reshaping effect of the regenerator.2.Taking the MZI multi-level all-optical regenerator scheme as an example,we describe how to determine the linear gain and gain slope in detail.The gain slope curve of the MZI multi-level amplitude regenerator is a cosine oscillation function with a period of 1.The number of regenerative levels can be characterized by the amplitude of the oscillation: the smaller the amplitude of the oscillation,the more the number of regenerative levels.According to the distribution of the reshaping areas and the relation between the regenerative levels and the oscillation amplitude,a 4PAM regenerator based on the MZI structure is designed and dynamically simulated by the OptiSystem software.The simulation results show that,for a 4PAM signal degraded by ASE noise with average normalized amplitude jitter 0.0103,the resulting MZI-based all-optical regenerator has a noise reduction ratio of 6.79 dB,which can effectively suppress the amplitude noise of the degraded PAM optical signal.3.An optical-control multi-level all-optical regeneration scheme based on MZI and nonlinear fiber ring mirror(NOLM)is put forward,in which the optical clock control signal is used to realize the asymmetric phase shift of the optical fiber ring.The two methods of the parallel polarization pumping and orthogonal polarization pumping are discussed in detail.Parallel polarization scheme has a larger contribution to the cross phase shift,but it is also easy to be interfered by four wave mixing effect,while orthogonal polarization scheme can effectively avoid the influence of unfavorable factors.By optimizing the structural parameters for the NOLM regenerator,the power transfer function with the first-order approximation is obtained.The theoretical results are in agreement with the simulated ones...