All-optical in-band OSNR monitoring at 40 Gb/s using a nonlinear optical loop mirror

We present an all-optical in-band optical signal-to-noise ratio (OSNR) monitor using a nonlinear optical loop mirror. Monitoring is enabled from the nonlinear power transfer function of the loop mirror. Experimental results are provided at 40 Gb/s for three modulation formats: nonreturn-to-zero, carrier-suppressed return-to-zero, and return-to-zero. The monitor discriminates the various OSNR levels over a dynamic range of more than 25 dB with every modulation format.