Holographic fabricated photonic-crystal distributed-feedback quantum cascade laser with near-diffraction-limited beam quality

We demonstrate the fabrication and characterization of photonic-crystal distributed-feedback quantum cascade laser emitting at 4.7 μm. The tilted rectangular-lattice PCDFB structure was defined using a multi-exposure of two-beam holographic lithography. The devices exhibit the near-diffraction-limited beam emission with the full width at half maximum of the far-field divergence angles about 4.5° and 2.5° for stripe widths of 55 μm and 95 μm, respectively. Single-mode emission with a side mode suppression ratio of ≈20 dB is achieved in the temperature range (80-210 K). The single-facet output power is above 1 W for a 95 μm × 2.5 mm laser bar at 85 K in pulsed operation.