Tunable characteristic of phase-locked quantum cascade laser arrays

A multimode interference (MMI) structure is designed to simplify the fabrication of quantum cascade laser (QCL) phase-locked arrays. The MMI geometry is optimized with a sufficient output channel distance to accommodate conventional photolithography and wet etching process by which power amplifier array is fabricated without using the complicated two-step etching-regrowth or dry etching technique. The far-field pattern with periodically modulated peaks reveals that the beams from the arrays are phase-locked. Furthermore, the frequency tuning performance of the MMI-based phase-locked arrays is studied using the Littrow-configuration external cavity structure. A wavelength tuning range of more than 60 cm^-1 is demonstrated, which will eventually realize the high power, frequency tunable, large-scale phase-locked arrays, and their application in spectroscopy.