Bell Labs builds ultra-broadband semiconductor laser

Bell Labs has said its researchers have built what they believe is the first semiconductor laser that emits light continuously over a broad spectrum of infrared wavelengths.

The device could potentially be used in applications ranging from advanced optical communications to sensitive chemical detectors, and the technique used to produce the laser could be the basis for future high-performance semiconductor lasers for fibre optics, as well as other technology applications, according to Bell Labs.

"An ultra-broadband semiconductor laser could be used to make an extremely sensitive and versatile detector that can detect minute traces of pollutants in the atmosphere, said Claire Gmachl, a physicist at Bell Labs. "It could also be used to produce new medical diagnostic tools such as breath analysers."

Semiconductor lasers are typically narrowband devices, emitting light of a single colour at a characteristic wavelength. But an ultra-broadband laser offers significant advantages for sampling of a wide swath of wavelengths at the same time, the company said, and making a reliable one that can operate under a variety of operating conditions.

The new laser belongs to a class of high-performance semiconductor lasers known as quantum cascade lasers, which was invented at Bell Labs. A QC laser operates much like an electronic waterfall, the company said. When an electric current flows through the laser, electrons cascade down an energy staircase; every time they hit a step, they emit a photon of infrared light.

The emitted photons are reflected back and forth inside the semiconductor resonator that contains the electronic cascade, stimulating the emission of other photons. "The wavelength range can in principle be made much wider, or also narrower," Gmachl said. "We picked the range of 6 to 8 micrometer for laser action as a good range for a convincing demonstration of the idea. In the future, we may be able to custom tailor the laser to the specific needs of individual applications, including fibre optics."