Polarized single-lobed surface emission in mid-infrared, photonic-crystal, quantum-cascade lasers

摘要

We report single-mode, surface-emitting, mid-IR, photonic-crystal (PhC), quantum-cascade lasers with linearly polarized and highly directional single-lobed emission. A metallic square-lattice photonic crystal with elliptical air holes and π phase shift was used as the resonator. The 2D feedback coupling—necessary for the operation of the photonic-crystal resonator—is induced by the mismatch between the modes supported by metalized and nonmetalized regions and yields single-mode output with a side-mode suppression ratio >30 dB. The elliptical air holes modify the relative intensities of the TM field components (Hx and Hy) in the PhC plane, thus yielding linearly polarized emission. The π phase shift allows the system to produce a single-lobed pattern in the far field with a narrow divergence angle (2.4°×1.8°). The emission is perfectly orthogonal to the device surface, and the maximum operating temperature—still limited by the metallic ohmic losses—is 240 K.