Online tuning of active photonic crystal quantum-cascade lasers

Here, we present the design and realization of active PhC semiconductor lasers. The PhC used is based on a hexagonal lattice of free-standing pillars which are surrounded by air. Such structures have typically full bandgaps for TM-polarized light, which is the polarization of light emitted by QCLs. A calculated bandstructure of the PhC for a ration r/a of 0.3, where r is the radius of the pillars and a the period. The pillars are fabricated from an active THz quantum-cascade layer sequence. The device is embedded in a double-metal waveguide which suppresses any out-of-plane scattering and allows for an electrical contact of every pillar. The combination of the extremely low group velocity and the strong modal confinement leads to the gain enhancement. This leads to a lithographic tuning range of 400 GHz, which is significantly larger than the measured FWHM gain bandwidth of THz-QCLs of only 130 GHz.