A study on the analysis of 2-stage fiber loop mirror and its applications

Abstract

The analysis and its applications of the 2-stage fiber loop mirror, which consists of fiber loop mirror concatenated with a unbalanced Mach-Zehnder interferometer, is presented. States of polarization and phase information through the structure are analyzed by using Jones matrix method with an assumption that polarization controllers inserted in the arms of the unbalanced Mach-Zehnder interferometer can be considered as arbitrary wave-plates. It is shown that the proposed structure can generate 3-pulse, 2-pulse and 1-pulse streams by the adjustment of the polarization controllers when one input pulse is given and the conditions for those cases are obtained analytically. It is demonstrated that the peak to side-lobe ratio is improved from 4:1 to 9:1 compared to conventional coherent matched filtering schemes using unbalanced Mach-Zehnder interferometer when this scheme is applied to coherent optical CDMA encoder/decoders. Consequently, the signal to noise ratio can be enhanced without increasing the required number of optical fiber delay lines. The proposed 2-stage fiber loop mirror is also applied to fiber-optic microwave notch filter. It is known that the proposed structure shows second order finite impulse response filter characteristics from the analysis of the 2-stage fiber loop mirror and the spectral response of the filter can be changed by adjusting arbitrary wave plates (polarization controllers) used in the structure. This capability to change the shape of the intensity transfer function enables us to control the filtering notches, for which the simulation results show that the depth can be up to 35 dB.