Optical signal-to-noise ratio monitoring based on tracking of principal states of polarization

Abstract

Feature Issue on Optical Performance Monitoring (OPM). We propose and demonstrate a simple method for monitoring optical signal-to-noise ratio (OSNR) of each channel in wavelength-division multiplexing networks based on tracking of principal states of polarization (PSP) and scrambling at the transmitter part. This technique reduces measurement error caused by the effect of PMD, which limits the performance of a previous polarization extinction method. PSP tracking uses bandpass-filtered power at clock frequency for a non-return-to-zero signal as a feedback signal to separate the two PSPs by aligning them to the axes of a polarization beam splitter (PBS). The scrambling makes it possible to extinguish the polarization of an optical signal from one output of the PBS and to provide maximum and minimum optical powers, thus enabling us to obtain OSNR regardless of the effect of PMD. In a transmission experiment over a 400-km single-mode fiber-dispersion-compensating fiber (SMF+DCF) link, the results showed that the difference between the OSNRs measured by use of the proposed method and by an optical spectrum analyzer (OSA) was less than 1.0 dB.