Index-coupled multi-wavelength distributed feedback quantum cascade lasers based on sampled gratings

Single-mode, wide wavelength range, high output power and low threshold current density DFB QCLs emitting around 4.7 m were presented. The multi-wavelength lasers were fabricated simultaneously on a single wafer by different sampled gratings. Instead of electron beam lithography, conventional holographic exposure combined with the optical photolithography was used to fabricate the sampled grating. Single-mode lasing at different wavelengths with a mean side mode suppression ratio above 20 dB was obtained. A wide wavelength range of 238 nm (106 cm) was achieved in pulsed mode at room temperature with different sampling periods. All the DFB-QCLs showed a stable single-mode operation with threshold current density in the range from 1.067 to 1.3 kA/cm, and output power from a single facet in the range from 666.7 to 944.4 mW at 293 K.