Quantum cascade community heads for continuous devices

17 Jun 2002

Three of the most respected research groups on quantum cascade lasers (QCL) presented their latest results at the recent CLEO conference.

Claire Gmachl told delegates that Bell Labs had demonstrated the first short wavelength (4.6 micron) distributed feedback QCL targeted at the detection of carbon monoxide in the atmosphere. It uses a Bragg grating etched into the top surface of the laser ridges. The maximum output power in CW mode at 80 K is 150 mW. It is the first QCL to operate reliably in single mode in CW while employing the simpler etching technique to fabricate the top grating rather than a buried grating, says Gmachl. Distributed feedback lasers with buried Bragg gratings have also been made at 5.2 and 7.9 micron wavelengths to detect NO, N2O and CH4 at 80 K. They have been successfully carried on aircraft from the Jet Propulsion Laboratory to detect pollutants to 2 ppb.

Mattias Beck of the University of Neuchatel, Switzerland, said that there was still a lot of effort needed to get CW operation at room temperature, but his group had made progress with buried heterostructures. In pulsed mode at room temperature one device produced 250 mW of peak optical power with a slope efficiency of 120 mW/A. At 120 degC, the device still delivers 10 mW of optical power.

Carlo Sirtori at Thomson-CSF in France has been working on GaAs/AlInAs systems instead of the usual GaInAs/AlInAs grown on InP. Recently, he said, his group had tried to get rid of aluminium in the active layer. For a device operating at 77 K in pulsed mode, the collected optical power peak power is 1.5 W, the highest ever reported for lasers in this wavelength range (9.4 micron), he said.

Story courtesy of Opto and Laser Europe magazine.