ABSTRACT
We measure full interferograms of telecom signals impaired by noise and investigate their applicability to in-band optical signal-to-noise ratio (OSNR) monitoring in practical systems. We experimentally establish that the dependence of overall shape of the interferogram on a signal's extinction ratio (ER) is strong but not unique. As the ER is being degraded the interferogram evolves in two distinct ways depending on the modulation conditions. The resulting ambiguity in the interferogram shape prevents OSNR measurements on completely unknown signals and necessitates a calibration for each modulator condition. With appropriate calibration, we experimentally demonstrate reliable OSNR measurements in the 5 to 25 dB range for 42.8 Gb/s nonreturn-to-zero, return-to-zero, and carrier-suppressed return-to-zero on-off-keyed signals.
