Technical Insight
High-power 980nm VCSEL arrays in demand (Research Review)
Investigations into both edge-emitting laser diodes and VCSELs are being driven in part by demand for compact, high-power devices for use in materials processing, printing, medical applications and free-space data transmission. This paper by Miller and colleagues from the University of Ulm (Phot. Tech. Lett. 2001 13(3) 173) describes an array consisting of 19 high-power VCSELs operating at 980 nm. The devices (see ) were grown by MBE and contain C-doped upper Bragg reflectors made up of 30 pairs of Al0.9Ga0.1As/GaAs layers. The active region comprises three 8 nm thick In0.2Ga0.8As quantum wells. Above the p-type cladding, a 30 nm thick layer of AlAs is added, which is partially wet etched at 410C after mesa etching to form 50 m apertures, which are spaced 100 m apart. The total array size was 0.64 mm2. Backside light emission through the 150 m thick GaAs substrate is facilitated by an n-type DBR with only 20 Si-doped mirror pairs with the same composition as the p-type reflector. The GaAs substrate was coated with an anti-reflection layer and the device also employs a diamond heat spreader and copper heat sink. Each device provides 1.08 W of CW output at room temperature and 1.4 W at a heat sink temperature of 10C, corresponding to a total power density for the array of 1 kW/cm2. A beam divergence of 16 FWHM was also achieved, and the circularly symmetric far-field pattern allows for simple focusing of the beam with power densities of over 10 kW/cm2. Long-term testing has shown the device to be reliable for at least 10 000 h, with less than 1% degradation in output per 1000 h.
