In-band OSNR and chromatic dispersion monitoring using a fibre optical parametric amplifier

This paper presents an all-optical, in-band optical signal-to-noise ratio (OSNR) and chromatic dispersion monitor. We demonstrate monitoring over the 1 nm bandwidth of our signal, which is a 10 GHz pulse train of 8.8 ps pulses. The monitor output power, as measured on a slow detector, has a 1.9 dB dynamic range when the signal OSNR is varied by 20 dB, and a 1.6 dB dynamic range when +/- 150 ps/nm of chromatic dispersion is applied. Cascaded four-wave mixing occurring in the optical parametric amplifier provides the nonlinear power transfer function responsible for the monitoring. An analysis using the signals' probability density functions show that the nonlinear power transfer function provides preferential gain to clean undispersed pulses when compared to noisy and/or dispersed pulses. Our analysis includes a consideration of the applicability of the device to high duty cycle systems, and simulations on monitoring of a 40 Gb/s pulse train with a 50% duty cycle.