Pulse Generation by On‐Chip Dispersion Compensation at 8 µm Wavelength

ABSTRACT The mid‐infrared spectral region holds growing importance for applications such as gas sensing and spectroscopy, and compact ultrashort pulse laser sources are essential to enable these applications. However, the fast gain dynamics of intersubband transitions hinders the direct generation of pulses from quantum cascade lasers (QCL). In this work, we take advantage of the linear chirp of mid‐infrared frequency modulated (FM) QCLs and the possibility to engineer group delay in passive photonic circuits to convert a quasi‐continuous signal into ultrashort pulses in the mid‐infrared, converting the source into an amplitude modulated (AM) comb. Our approach relies on chirped Bragg gratings implemented in Silicon Germanium graded‐index photonic circuits for operation around 8 wavelength. With this approach, pulses as short as 1.39 ps were obtained. This establishes an FM‐to‐AM conversion strategy based on a passive photonic circuit that enables new approaches to integrated ultrafast pulse generation in the mid‐infrared.