Surface emitting photonic crystal mid-infrared quantum cascade lasers

We demonstrate spectrally single-mode, low-divergence surface-emission from photonic-crystal quantum cascade lasers operating in the mid-infrared spectral range (lambda~7.2 mum). The photonic-crystal resonator is defined by the sole top metallization. No semiconductor etch is employed. The effective index contrast is induced by the different profiles of surface plasmon and air-confined modes. Numerical electromagnetic simulations show that the resonator Q-factor depends strongly on the r/a ratio. The devices - which operate up to 220 K - exhibit single mode emission with a side mode suppression ratio ges20/25 dB. The far-field emission pattern is doughnut-shaped, with a full divergence angle of ~12 degrees.