Simultaneous Linear and Nonlinear Optical Autocorrelation Measurement With Fabry-Pérot Laser Diodes

Semiconductor lasers exhibit intrinsic bifunctionality, enabling coherent light emission and linear photodetection. Additionally, their active-region heterostructures, characterized by third-order nonlinearity, facilitate their operation as highly sensitive two-photon absorption (TPA) detectors [1]. This strong TPA response, sustained at room temperature, is particularly valuable in ultrafast optics, where such detectors are employed for precise interferometric characterization of femtosecond light pulses, including their temporal shape and duration. Various autocorrelation techniques have been proposed, each serving distinct purposes. Linear interference (interferogram, IGM) is primarily used to analyze the spectral characteristics of a light source, while intensity autocorrelation (IAC) and fringe-resolved autocorrelation (FRAC) are commonly employed to estimate pulse duration generated by mode-locked lasers. Unlike FRAC, which relies on nonlinear optical effects and thus requires high-intensity pulses, linear IGM can analyze weak signals, making it particularly advantageous for low-power laser sources.