OSNR Monitoring for NRZ-PSK Signals Using Silicon Waveguide Two-Photon Absorption

We study the use of two-photon absorption (TPA) in a silicon optical waveguide for measuring the optical signal-to-noise ratio (OSNR) of a nonreturn to zero phase-shift keying (NRZ-PSK) signal. The average photocurrent generated in the silicon waveguide increased by 70 nA (from 375 to 445 nA) for a change in OSNR from 28 to 6 dB and a constant total input power of 10 dBm. The nonresonant nature of the silicon waveguide TPA detector enables the simple measurement of OSNR over a continuous wide (>; 10 nm) wavelength range. For a 10-Gb/s NRZ-PSK signal, we show that when the residual dispersion in the optical signal exceeds 425 ps/nm, further increases in dispersion have little effect on the photocurrent. Thus, this TPA-based OSNR monitor can be used in practical systems with large dispersion.