Soraa Propels Green Lasers Beyond 100 MW
The Californian pioneer of semi-polar and non-polar light emitters drives green and blue laser performance to new levels
Soraa has improved the performance of its semi-polar and non-polar green and blue lasers that it is developing for displays and medical markets.
James Raring revealed to delegates at the ninth International Conference on Nitride Semiconductors that the continuous-wave output of the company's 516 nm green lasers now exceeds 100 mW. Other characteristics of these packaged diodes included threshold currents and voltages of 125 mA and 5.9 V, a slope efficiency of 0.4 W/A and a wall-plug efficiency that peaks at 4.1 percent.
Soraa has recently focused on improving the beam-quality of its single-mode green lasers. Divergence along the fast axis is 14-22 degrees, and in the slow axis it is 10-14 degrees.
Improvements have also been made to Soraa's blue lasers, which have similar levels of beam divergence. Packaged single-mode variants have a slope efficiency of more than 1.6 W/A, and the threshold current and voltage are 30 mA and 3.9V. When emitting 500 mW, wall plug efficiency is more than 20 percent and it hits 22 percent at 200 mW.
The West-coast outfit has also made more powerful, multi-mode variants that can produce 1.4 W and have a wall-plug efficiency of more than 23 percent.
Raring believes that the excellent performance produced by these lasers stems from the use of non-polar and semi-polar planes.
Turning to these orientations improves the radiative recombination rate of these devices through increased overlap of the electrons and holes in the quantum wells. What’s more, it aids hole injection, thanks to a reduction in the effective mass of this carrier. However, Raring believes that the most exciting aspect of these novel planes is the far greater design freedom that they enable.
The most promising market for Soraa's lasers is projection displays, which employ a combination of red, green and blue lasers to form colour images. In this market lasers are competing with lamps and LEDs, but the latter two deliver an inferior optical throughput, typically by a factor of three.
Most commercial green lasers on the market today employ some form of frequency doubling of an infra-red source. Replacing such devices with a single, green-emitting chip will lead to improvements in efficiency, compactness, ruggedness and speckle, according to Raring.
He estimates that the pico-projector market could consume 200 million units per year, and a similar number may be needed to supply desktop and high-end projectors.