By Gary Thomas
Scientists at TU Darmstadt in conjunction with their partners in the European Union’s ‘Subtune’ project have devised semiconductor lasers that emit light over a broad spectral range of 100 nm.
This is the first ever single semiconductor laser with such capability. These new lasers herald the development of gas sensors with high responsiveness and fiber optic telecommunication networks that are economical and efficient.
Light emitted from surface emitting semiconductor lasers are perpendicular to the wafer plane on which the lasers are fabricated. They are employed as light sources in devices like laser printers and computer mice since they do not consume much power. The work carried out at the Institute for Microwave Technology and Photonics at TU Darmstadt has enhanced the operable range of these lasers. The scientists leveraged a characteristic of surface emitting lasers, namely, their high resonator length to emitting area ratio which causes emitted wavelengths to be spaced further apart. The resultant broad spectral range can be tuned to any wavelength akin to a radio transmitter being tuned to desired frequency or wavelength. In order to tune the output light’s wavelength, the scientists applied a flexible membrane with greater than 99% reflectivity to the emitting surface. The membrane functioned as an output mirror with an external control over the flexing. The wavelength of the emitted light is determined by the spacing of the mirror.
The new technology can be extended to practical applications requiring operating range of 1.5 mm typical of fiber optic communications. It has also been used to develop tunable lasers whose range is centered around 2 mm and can thus be used in gas sensors. The tunable single laser source eliminates the necessity for multiple semiconductor lasers corresponding to each wavelength.