Distributed electrode boosts laser output and improves mode quality
Addition of a distributed electrode to an indium gallium arsenide phosphide (InGaAsP) laser allowed researchers at Alcatel (Marcoussis, France) to create a device that emits up to 1.1 W of 1480-nm light in the fundamental mode. The laser has four compressively strained quantum wells and uses a flared unstable cavity as an amplifier. By comparison, a similar laser with a uniform electrode emits 0.7 W of poor-quality multimode light.
The distributed electrode, which is unbroken along its center, shades to half-tone dots of decreasing diameter toward its two edges. Its electrical resistance depends on lateral position, being lowest at its center and increasing gradually away from center. The effect is to partially compensate for carrier depletion induced by high power densities, thus keeping beam quality close to diffraction-limited. The flared amplifying section over which the electrode is placed is 1150 µm long with an angle of 7, resulting in an emission width of 140 µm. The external efficiency of the laser is 0.45 W/A and the threshold current 0.6 A, compared to values of 0.27 W/A and 1 A for a laser with a uniform electrode. Contact: Paul Salet at [email protected].