Numerically Modelled Evaluation of all Optical RZ OOK Conversion to Higher Order M–QAM Format Conversion using Photic Fiber Nonlinearity

Abstract

This study shows how to convert all-optical RZ-OOK to 8QAM code using a nonlinear photonic looped mirror (NOLM), which takes advantage of power-dependent phase alteration and interferometry. The methodology uses Gaussian-pulse RZ-OOK transmissions at 20-30 Gbps to study the effect of duty cycles (20-66%) and nonlinear components (γ = 1.0-2.5 W⁻¹km⁻¹) on constellation formation. Key findings show that a 33-50% duty cycle with γ = 1.5-2.0 produces identifiable 8QAM constellations, with "1" bits forming four phase-rotated high-amplitude regions and "0" bits clustering at the origin. The system is unique in that it allows for DSP-free higher-order control conversion, which is useful for minimal latency optical connection networks. However, performance is constrained by nonlinear interference correlation and phase asymmetry.