Single mode emitting ridge waveguide quantum cascade lasers coupled to an active ring resonator filter

Quantum cascade ridge waveguide lasers with coupled ring resonators have been fabricated. Coupling of an actively pumped microring resonator to a ridge waveguide device allows for filtering the numerous Fabry-Perot modes emerging in the ridge waveguide. Due to the large free spectral range of the ring resonators mode selection is accomplished, resulting in stable single mode emission for an optimized design. Thus, side mode suppression ratios of up to 26 dB over a temperature range of 140 K are attained by on-chip coupling of a ridge waveguide device with a microsquare ring resonator. The tuning rate of the microring resonator laser is 0.40 nm/K. Output powers of several milliwatts are obtained.