Enhancing the monitoring sensitivity of DOP-based OSNR monitors in high OSNR region using off-center narrow-band optical filtering

Guo-Wei Lu,Lian-Kuan Chen

doi:10.1364/oe.15.000823

Abstract

Recently, OSNR monitoring based on the measurement of degree of polarization (DOP) has attracted much attention, thanks to its simplicity and high efficiency. However, the OSNR monitoring sensitivity is quite poor in the high OSNR region, resulting in high estimation error and narrow dynamic range. In this paper, we propose and experimentally demonstrate a narrow-band off-center optical filtering technique for DOP-based OSNR monitors. In 40-Gb/s RZ-OOK systems, OSNR monitoring sensitivity and DOP dynamic range are successfully enhanced to 3.14%/dB and 31.4%, respectively, in the high OSNR region (25~35dB/0.1nm).

Highlights

Optical signal-to-noise ratio (OSNR) is an important performance parameter to be monitored in future high-speed reconfigurable optical networks
Several in-band OSNR monitoring schemes have been proposed [1], such as the degree of polarization (DOP)-based scheme, the polarization nulling scheme, the fiber-loop-based scheme [2], the orthogonal polarization heterodyne scheme [3], and the scheme based on beating noise measurement [4]
As reported in Ref. [5], the OSNR monitoring sensitivity is severely degraded in the high OSNR region (≥25 dB/0.1nm), resulting in increased estimation errors

Summary

Introduction

Optical signal-to-noise ratio (OSNR) is an important performance parameter to be monitored in future high-speed reconfigurable optical networks. Using symmetric or off-center optical filtering with different filtering bandwidth before the DOP measurement, it is possible to enhance the DOP sensitivity to input OSNRs. the broad-band symmetric filtering will involve more ASE noise for DOP measurement, while the off-center narrow-band filtering will extract a smaller part of the signal's power Both of these approaches result in the de-polarization effect for the filtered signal, which will reduce the measured DOP value, intentionally. The monitoring sensitivity can be effectively improved in the high OSNR region For these two approaches, higher improvement could be achieved using off-center narrow-band filtering, especially in a system with a broad spectrum. Reconfigurable optical networks, the cascaded OADM filters may result in an aggregated filter response with time-variant profile and destroy the deterministic relation between the measured DOP and the OSNR. A numerical simulation is performed to verify the experimental result using a commercial simulator, OptSim, with a setup similar to that of the experiment

DOP Analyzer

Findings

Conclusions