Semiconductor Laser Sets Surface-Emission Record

A semiconductor laser that emits light over a wavelength range of 100 nm sets a record for a single semiconductor laser and could enable more efficient telecommunications networks and gas sensors.

Surface-emitting semiconductor lasers emit light at a right angle to the plane of the semiconducting wafer on which they are built. These devices require little power to operate, making them a reliable solution for light sources on computer mice and laser printers.

Now, scientists at the Technical University of Darmstadt's Institute for Microwave Technology and Photonics, working with partners under the European Commission's Subtune project, have extended the tunability of these lasers even further. They took advantage of a characteristic of surface-emitting lasers; namely, their large resonator-length/emitting-area ratio, which causes emitted wavelengths to be spaced significantly apart. Their broad spectral range can be tuned to any wavelength, similar to a radio transmitter being tuned to a desired frequency or wavelength.

The design of the Technical University of Darmstadt's semiconductor laser, which sets a surface-emission record. (Images: Institute for Microwave Technology and Photonics)

To tune the output light's wavelength, they applied a flexible membrane with a reflectiveness of more than 99 percent to the emitting surface. The membrane, developed by Walter Schottky Institute at the Technical University of Munich, functioned as an output mirror with an external control over the flexing. The wavelength of the emitted light was determined by the mirror spacing.

The new technology can be extended to practical applications that require an operating range of 1.55 µm, the wavelength used by fiber optic telecommunications systems.

"The telecommunications industry is extremely interested in this technology because, in the future, it will need to service households via fiber optic networks operating at various wavelengths," said physicist Christian Gierl of TU Darmstadt. Without tunability, special lasers would have to be fabricated for each wavelength needed, adding complexity and cost.

The method has also been used to develop tunable lasers with a range centered around 2 µm, a wavelength of particular interest for gas detection.

More broadly tunable lasers such as this might enable more efficient, lower-cost fiber optic networks and better gas sensors.

"Gas sensors based on our technology have high responsivities, in addition to being extremely compact and highly energy-efficient," Gierl said.

A follow-on project to close the remaining gaps is needed before the chip is ready for practical applications. One such gap involves providing that the output be modulated at high frequencies so data can be transmitted at high transfer rates. The team also would like to incorporate the chips into modules similar to USB sticks that can be readily integrated into telecommunications sytems.

The laser was successfully tested on a communications network at Subtune partner Tyndall's research facility in Cork, Ireland.

For more information, visit: www.tu-darmstadt.de