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Continuous-wave operation of a distributed-feedback quantum cascade laser emitting at around 4.6 µm grown by solid source molecular beam epitaxy combined with metal organic vapour phase epitaxy is presented. These devices display an ultra-low threshold current density of 0.85 kA/cm2 at 30 °C. The low threshold characteristics resulted in continuous-wave operating temperature up to 100 °C for thermoelectrically cooled devices and room-temperature continuous-wave output power in excess of 8.5 mW for uncooled devices.

The singlemode operation of a distributed feedback terahertz quantum cascade laser with complex-coupled metallic relief gratings emitting at 3.09 THz (λ=97.07 µm) is reported. The side-mode suppression ratio is about 20 dB at all operating temperatures. The highest working temperature of up to 88 K is obtained, with the optical power of 10 mW at 10 K and 1 mW at 88 K.

A tapered distributed feedback quantum cascade laser emitting at lambda similar to 8.1 mu m is reported. utilising a tapered waveguide structure with a surface metal grating, the device exhibited singlemode operation over the temperature range of 100 to 214 k, with sidemode suppression ratio > 20 db and a nearly diffraction limited far-field beam divergence angle of 5.4 degrees.

Electrically pumped, edge-emitting, singlemode operation of a two-dimensional photonic crystal distributed feedback (PCDFB) quantum cascade laser emitting at similar to 7.8 mu m is demonstrated. The two-beam holographic technique combined with wet-etching process is successfully used to de. ne a square-lattice PCDFB structure on the top grating layer of the laser. This simple PC fabrication method may open exciting opportunities for the wide application of PCDFB lasers.