New world record for spectral bandwidth


Semiconductor lasers

Surface emitters developed at the TU Darmstadt set a new world record for spectral bandwidth Semiconductor Lasers for the Fiberoptic Communications Networks of the Future

Working in collaboration with their partners under the EU’s “Subtune” project, scientists at the TU Darmstadt have developed semiconductor lasers that emit light over a wavelength range of 100 nm, a new world record for a single semiconductor laser. Such lasers might allow more efficient, lower-cost operation of future fiberoptic telecommunications networks and the development of high-responsivity gas sensors.

Design of TU Darmstadt’s semiconductor laser. Picture: Institute for Microwave Technology and Photonics

Surface-emitting semiconductor lasers emit light at a right angle to the plane of the semiconducting wafer on which they have been fabricated. They require very little power for their operation and are thus utilized as light sources on, e.g., computer mice and laser printers. Christian Gierl and Karolina Zogal of the TU Darmstadt’s Institute for Microwave Technology and Photonics have recently significantly extended the tunabilities of such lasers.

Their approach involves taking advantage of yet another benefit of surface-emitting semiconductor lasers, namely, their very large resonator-length/emitting-area ratios, which greatly increases the spacings of their emitted wavelengths. Their broad free spectral range allows tuning the wavelength of their strongest emission line over a broad range, i.e., converting them into transmitters whose output may be set to any wavelength falling within a certain, broad range, just as radio transmitters may be tuned to various frequencies/wavelengths.

A flexible membrane varies the wavelength of the emitted light:

Under the EU’s “Subtune” project, Gierl, a physicist, and Zogal, a materials scientist, managed to tune the wavelength of the output beam of a semiconductor laser provided by one of their Subtune partners, the Walter Schottky Institute at the TU München, over a range of more than 100 nm, the broadest tuning range thus far achieved by any semiconductor laser, while retaining its other, excellent, emission characteristics, such as its high output power and high spectral purity.

Gierl explained that, “The telecommunications industry is extremely interested in this technology because in the future it will need to service households via fiberoptic networks operating at various wavelengths.” If there were no tunable lasers, a special type of semiconductor laser would have to be fabricated for each wavelength to be involved. Gierl added that, “Tunable lasers obviate that necessity, since only a single type of laser will have to be fabricated.”



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