30 Nov 2004
Applying high hydrostatic pressures to a 2.4 micron laser diode tunes its emission to 1.7 microns.
Midinfrared diode lasers with a tuning range of 700 nm have been unveiled by a team of researchers from Poland and France. By applying hydrostatic pressures up to 19 kbar, the diode lasers tune from 2.4 microns down to 1.7 microns. (Applied Physics Letters 85 4292)
"We are aiming at spectroscopic applications and at replacing tunable sources such as Ti:Sapphire lasers," Witold Trzeciakowski from the Polish Academy of Sciences told Optics.org. "In telecoms, a tunable laser could be useful for diagnosis of fiber networks. Gas detection and pollution control also need tunable diode lasers."
Applying hydrostatic pressure to a semiconductor device modifies its bandgap and emission wavelength. Trzeciakowski and colleagues have used this phenomenon to tune a variety of laser diodes with emission wavelengths starting from 635 nm right through to longer wavelengths such as 1550 nm.
In this work, the team grew InGaAsSb/AlGaAsSb lasers which emitted 2.4 microns continuous wave at room temperature. A single laser was mounted in a piston-cylinder cell and subjected to pressures up to 20 kbar. A microlens helps couple light out either through a sapphire window or a fiber.
For each pressure, the team measured the current-voltage and power-current characteristics. "We had up to 7 mW from 2.4 microns down to 1.9 microns and below 1.9 microns we had 5 mW," said Trzeciakowski. "When the pressure was increased up to 19 kbar, the threshold current varied from 240 to 400 A/cm2, showing a minimum of 200 A/cm2 close to 8 bar."
The researchers now hope to limit the degradation of their devices after multiple pressure cycles and say that special mounting and processing may be required. "We also want to increase the reliability of our pressure cell by reducing its diameter," explained Trzeciakowski.