A quantum-dot (QD) laser created by a team of Japanese researchers is capable of continuous-wave output at temperatures up to 220ºC, making it usable in extreme environments such as those encountered deep underground in oil and gas drilling. Gain at such high temperatures was achieved by suppressing indium out-diffusion as the indium arsenide QDs were being fabricated by molecular-beam epitaxy. The resulting eight-layer structure had a high density of 5.9 × 1010 QDs per square centimeter per layer. In addition, because the ground state and first excited state were separated by a large amount (80 mV), higher-order lasing at very high temperatures was suppressed. The team was made up of scientists from QD Laser and Fujitsu Laboratories (both in Kanagawa) and from the University of Tokyo.
The laser consists of n and p aluminum gallium arsenide (AlGaAs) cladding layers and partially p-doped GaAs barriers. It emits at a wavelength of 1268 nm at 30ºC, which changes approximately linearly as a function of temperature to a wavelength of 1359 nm at 220ºC (all wavelengths fall well within the low-loss window of fused silica optics). Optical output is 2 mW at 210ºC and 1 mW at 220ºC; threshold currents are 15, 27, and 55 mA at 30ºC, 125ºC, and 200ºC.
Contact Yasuhiko Arakawa at [email protected].
