Phase noise suppression in multilevel optical code-division multiple-access network coding system with embedded orthogonal polarizations

This study proposes a novel spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) scheme with four optical intensity levels by polarization division multiplexing (PDM) to increase the maximum permissible number of simultaneous subscribers using an optical broadband source of finite bandwidth. In the proposed system, each encoder/decoder pair is shared by two subscribers, and the requirement for complex polarization compensator schemes at the receiver is removed. The phase-induced intensity noise (PIIN) induced at high optical intensities significantly degrades the performance of a conventional SAC-OCDMA scheme. Therefore, this study uses two methods to suppress the PIIN effect: 1. two users share the same encoder and transmit signals on mutually orthogonal polarizations, such that some PIIN terms are canceled out; and 2. the receiver structure is equipped with multiple balanced detectors (MBDs) to reduce the PIIN power impinging on each photodiode (PD). The numerical evaluation results demonstrate that under PIIN-limited conditions, the proposed system achieves a higher performance than that of the conventional SAC-OCDMA scheme.