Sensitive and accurate femtosecond pulse characterization via two-photon absorption in Fabry-Pérot laser diodes

• Semiconductor lasers as accurate two-photon detectors for optical autocorrelation measurements in the several-dozen femtosecond regime, • Validation of the pulse width and autocorrelation shape using conventional photodiodes and crystal-based autocorrelators, • Analysis of waveguiding effects causing distortion of ultrashort pulses, • Prediction of the optimal operating point by examining the nonlinear current–voltage (I-V) curve at different optical intensities. This lifts the requirement for an autocorrelator setup to determine the detector bias, • Our findings will help researchers to develop accurate two-photon (non-interferometric) dual-comb ranging systems and pulse diagnostic tools. Semiconductor lasers offer native bifunctionality enabling coherent light emission and linear photodetection. They can also operate as sensitive two-photon absorption detectors due to the third-order nonlinearity of the heterostructure constituting the active region. The strong two-photon response at room temperature is highly desired in ultrafast optics, where such detectors are used for interferometric characterization of femtosecond light pulses for shape and duration. Another niche is pulse detection in dual-comb ranging. While prior studies have focused on the two-photon response of commercial photodiodes or proprietary semiconductor microcavities for intensity autocorrelation measurements, a systematic analysis of the semiconductor lasers’ ability to accurately characterize the optical pulse width is missing. To address this niche, here we measure autocorrelation traces of femtosecond pulses with varying durations from sub-55-fs to 260 fs at the common 1.5 µm wavelength using AlGaAs and InGaAsP laser diodes designed to operate at emission wavelengths of 0.95 µm and 1.3 µm, respectively. We validate the obtained waveforms using a silicon avalanche photodetector and conventional crystal-based second-harmonic autocorrelator. We consider the effects of optical polarization, operation mode and electrical load resistance on the shape and intensity of generated electrical signals. Our results prove the suitability of Fabry-Pérot laser structures for interferometric autocorrelation measurements of 53 μW (212 fJ pulse energy) average power pulses as short as 36 fs with a mean square error of 7 × 10 -3 .