Measurement of OSNR in the presence of partially polarized ASE

We investigate the effect of partially polarized amplified spontaneous emission (ASE) on the measurement and interpretation of the optical signal-to-noise ratio (OSNR) using the polarization-nulling method. OSNR measurement is widely used to estimate bit-error rate (BER) in transparent photonic networks, but we find that significant errors in OSNR and in estimated BER could occur if the degree of ASE polarization becomes high.