Abstract

We report on the highest cw power, fiber-coupled, air-cooled diode laser system, that delivers more than 35-W cw from a 1.5-mm fiber output with a low divergence angle of 15° or a numerical aperture (NA) of 0.13 FWHM. The crucial building block of our system is a proprietary fiber coupling technique that provides coupling efficiencies in excess of 70% with a unique combination of compact hermetic packaging and a low fiber divergence angle. Fig. 1 shows cw fiber output power for a single device that delivers 1.5 W from 200-pm core 0.13 NA fiber at a moderate drive current of 2.2 Amps. We fabricated the 150-μm broad area diode lasers from strained-layer, quantum-well InGaAs/GaAs material grown by the MOCVD technique. Our devices have a slope efficiency of 0.9 W/A and a low far-field divergence angle of 6° by 40° FWHM. Tire combined cw power of 35 Watts shown in Fig. 2 is achieved by bundling the fibers from many fiber-coupled devices. Because our system utilizes individual fiber-coupled devices, the devices can be spread out to lower the waste heat load, measured in Watts per unit area, to levels that can be handled by Peltier coolers and air heat-exchange fins. This is in marked contrast with array-based diode laser systems that must resort to cumbersome water cooling to handle the high waste heat density. The wall plug efficiency of our system running at full-rated power is 7%. This value includes the requirements for the Peltier coolers and fans, as well as the control electronics to maintain constant temperature and either constant current or constant light operation of the laser diodes.

© 1993 Optical Society of America