Graded photonic crystal terahertz quantum cascade lasers

The use of integrated photonic structures to tailor the behavior of light is extremely promising for optimizing performance and for introducing advanced functionalities into optoelectronic devices. We demonstrate a powerful method based on photonic-band engineering which allows the optimization of the resonator quality factors of devices operating on band-edge photonic-crystal states. We also show that carefully designed pi-shifts in two-dimensional photonic-resonators give enhanced beam properties. The application of these general techniques to terahertz quantum cascade lasers yields improved maximum operating temperatures, and angularly narrow, single-lobed surface emission of approximate to 12 degrees x8 degrees. The devices operate at approximate to 2.8/2.9 THz, with peak output powers of 5 mW at 78 K.