Y. Wakayama

We demonstrated switching operation of lasing wavelength in GaAs-based mid-infrared coupled-cavity quantum cascade lasers. Our cavity structures consist of a ridge-waveguide Fabry–Perot cavity coupled with a microcylindrical cavity. Individual control of currents injected into both cavities enabled single-mode operation and facilitated intentional mode switching between coupled-cavity modes with spacing over 120 nm. The integrated microcylindrical cavity expanded the separation of coupled-cavity modes due to the small size of the cavity and enabled switching the lasing wavelength over a wide spectral range.

A high-Q photonic crystal (PC) microcavity for TM-like modes, which can be applied to quantum cascade lasers (QCLs), was successfully designed in an air-hole based PC slab with semiconductor cladding layers. In spite of no photonic badgaps for TM-like modes in air-hole based PC slabs, cavity Q reached up to 2,200 by utilizing a graded square lattice PC structure. This is ~18 times higher than those previously reported for PC defect-mode microcavities for QCLs. This large improvement is attributed to a suppression of the coupling between the cavity mode and the leaky modes thanks to the dielectric perturbation in the graded structure. We also predicted a dramatic reduction of the threshold current in the designed cavity down to one-fifteenth of that of a conventional QCL, due to a decreased optical volume.

We report a numerical demonstration of photonic crystal microcavities for high functional surface emitting QCLs. Localized mode for TM-like mode was achieved by introducing a point defect.