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).
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