The Effect Of Nonlinear Polarization Evolution On The Power Transmission Characteristics Of NALM

Nonlinear amplifying loop mirror (NALM) has been used in so many fiber optical systems and devices. Several important applications of NALM are all-optical switches, clock-pulse extracting, all-optical signal regularizing/regeneration and optical time domain multiplexing/de-multiplexing, etc.. Based on achieving the power equalization by NALM, this thesis is devoted to the theoretical analysis and experimental investigations on the power transmission characteristics of NALM. Including the cross-phase modulation (XPM) effect between the components of the co-propagating signal and the counter-propagating signal on the principle axes, not only are the original equations of NALM power transmission amended and extended, but also the corresponding experiments are done. Firstly, based on the fundamental equations of NALM power transmission, the effects of structure parameters of NALM are analyzed. If the NALM power transmission curves are normalized, the dynamic range of input power will be uniquely dependent on the nonreciprocal phase shift bias, which also determines the operating points and their selected principles are described. Secondly, considering the cross-phase modulation (XPM) effect between the clockwise and counter-clockwise signals, the extension of the fundamental equations of NALM power transmission is achieved and used to compare the effects of several modulation formats and duty ratios on the difference of nonlinear phase shifts between the clockwise and counter-clockwise signals.Thirdly, the equations of NALM power transmission are amended including the nonlinear polarization evolution (NPE) induced by nonlinear birefringence at high input power. The relative strength of linear birefringence and nonlinear birefringence is calculated. The results of numerical simulations illustrate that the asymmetric NPE of the clockwise and counter-clockwise signal make them interfere incompletely at the both of the reflected and transmitted output ports. The analysis based on experiment results shows that the NPE strength is approximately one-third of that of the accumulated nonlinear phase shifts of the components of optical signal on both the two principle axes. When the input signal is RZ format with small duty ratio, the results of experiment of NALM power transmission point out that NALM has some power equalization effect because of the approximate flatten part due to incomplete interference. When the variation range of output signal is less than 1dB, the dynamic range of input power is varied from 3.7 to 4.1dB. Finally, considering the XPM effect between the components of the clockwise and counter-clockwise signals on both the two principle axes, the equations of NALM power transmission are extended further.