Conjugate nonlinear-optical loop mirror (Conj-NOLM)-based phase-preserving multilevel amplitude regenerator

Feng Wen,Baojian Wu,Stylianos Sygletos,Kun Qiu

doi:10.1364/oe.27.019940

Abstract

We propose a novel phase-preserving multilevel amplitude regenerator scheme by cascading two nonlinear-optical loop mirrors (NOLMs) with an intermediate optical phase conjugator (OPC) stage. Joint parameter optimization of the two NOLM units has been carried out to cancel the introduced phase distortion and enable a more power-efficient performance. Moreover, our scheme combines the operation of the NOLM and the OPC in a single subsystem, enabling the compensation of both amplitude and phase distortions when located symmetrically in a transmission link. To this end, extensive numerical simulations have been performed to evaluate the regeneration performance in a transmission link dominated by amplified spontaneous emission (ASE) noise and Kerr-induced nonlinear distortions (self-phase modulation-induced phase distortion), achieving over 100% reach extension compared to the cases of un-regenerative, or a mid-span OPC-based transmission links.

Highlights

Advanced modulation formats have found a commercial application in optical communication systems as they can bring significant increase of the fiber link capacity
A challenging design issue in their development is the mitigation of the nonlinear phase distortion they introduce to the input signals due to the self-phase modulation (SPM) effects in the highly nonlinear fiber (HNLF)
The rest of the paper is organized as follows: in Section 2 we introduce the theoretical model of the proposed Conj-nonlinear-optical loop mirrors (NOLMs) regenerator and perform the joint optimization of its parameters; in Section 3 we investigate the phase and amplitude response and perform comparison with the traditional single-NOLM scheme; in Section 4 we investigate the regenerative performance in cascaded transmission for 16-level quadrature amplitude modulation (16-QAM) signals; and in Section 5, we draw the conclusions of our study

Summary

Introduction

Advanced modulation formats have found a commercial application in optical communication systems as they can bring significant increase of the fiber link capacity. Mitigation of the nonlinear phase distortion and achievement of phase preserving operation in a single-NOLM based regenerator has been achieved through the design of a highly asymmetric interferometer scheme, enabled either with the use of a simple attenuator [6], or a bidirectional attenuator [7,11], or a bidirectional Erbium-doped fiber amplifier (Bi-EDFA) [8,12,13]. The rest of the paper is organized as follows: in Section 2 we introduce the theoretical model of the proposed Conj-NOLM regenerator and perform the joint optimization of its parameters; in Section 3 we investigate the phase and amplitude response and perform comparison with the traditional single-NOLM scheme; in Section 4 we investigate the regenerative performance in cascaded transmission for 16-level quadrature amplitude modulation (16-QAM) signals; and in Section 5, we draw the conclusions of our study

Theoretical model

Impact of ASE only noise

Findings

Conclusion