Ultra-broadband semiconductor laser

Abstract

The fundamental mechanism behind laser action leads in general only to narrowband, single-wavelength emission. Several approaches for achieving spectrally broadband laser action have been put forward, such as enhancing the optical feedback in the wings of the gain spectrum^1,2, multi-peaked gain spectra^3,4, and the most favoured technique at present, ultrashort pulse excitation^5,6. Each of these approaches has drawbacks, such as a complex external laser cavity configuration, a non-flat optical gain envelope function, or an inability to operate in continuous mode, respectively. Here we present a monolithic, mid-infrared ‘supercontinuum’ semiconductor laser that has none of these drawbacks. We adopt a quantum cascade^7,8 configuration, where a number of dissimilar intersubband optical transitions are made to cooperate in order to provide broadband optical gain from 5 to 8 µm wavelength. Laser action with a Fabry–Pérot spectrum covering all wavelengths from 6 to 8 µm simultaneously is demonstrated with this approach. Lasers that emit light over such an extremely wide wavelength range are of interest for applications as varied as terabit optical data communications⁹ or ultra-precision metrology¹⁰ and spectroscopy¹¹.