Pulse duration retrieval using a commercial laser diode with a monitor photodiode

Semiconductor lasers merge coherent light emission with photodetection and, owing to third-order nonlinearities in their active region, function as sensitive room temperature two-photon absorption (TPA) detectors. Here, we leverage these capabilities offered by a commercially available InGaAsP semiconductor laser diode with an integrated InGaAs monitor photodiode to measure the duration of femtosecond pulses at telecom wavelengths. The nonlinear and linear signals obtained from both detectors enable the retrieval of pulse duration with femtosecond accuracy without moving parts. This capability is demonstrated down to 2 $\mu$W average optical power for a 250 MHz repetition rate laser.