Single-mode laser action in quantum cascade lasers with spiral-shaped chaotic resonators

The authors have fabricated and characterized quantum cascade lasers with spiral-shaped microresonators. The lasers operate in pulsed mode at room temperature with peak optical power greater than 20 mW and in continuous wave at temperatures up to 125 K. They exhibit single-mode emission in both pulsed mode and continuous wave operation, with a 30 dB side-mode suppression ratio at injection currents well above threshold. Subthreshold spectral measurements indicate that the spiral cavities support whispering-gallery-like modes. Single-mode lasing occurs on one of these modes. Far-field profiles reveal enhanced directionality compared to microdisk lasers. (C) 2007 American Institute of Physics.