Osram Opto Semiconductors GmbH of Regensburg, Germany has produced a broad-area laser diode with a lateral brilliance of up to 4.8W per millimeter and milliradiant (W/(mm*mrad)) in the laboratory. The more brilliant the laser, the more efficiently it can inject its light into optical fibers, increasing the output power of modules for pumping fiber lasers used in material processing. This progress is a result of the project 'Integrated micro-optical and micro-thermal elements for diode lasers of high brilliance' (IMOTHEB) to increase laser system efficiency and reduce their production costs. The project was funded by the German Federal Ministry of Education and Research (BMBF) as part of the 'Integrated Microphotonics' initiative, and has now been completed (after beginning in October 2012).
Brilliance is a measure of the combination of optical output power and beam quality, so brilliant laser sources generate a narrow beam of light with extremely small beam divergence and high power density. This property is crucial for the efficiency of fiber-coupled laser systems, says Osram Opto. The more brilliant the laser, the more light can be injected into an optical fiber.
Improved chip design
The lateral brilliance of up to 4.8W/(mm*mrad) achieved in the laboratory is one of the highest values achieved for broad-area laser diodes, says Osram Opto. Optimization of the chip design provided the basis for this, particularly the integration of micro-thermal and micro-optical elements for beam shaping on the chip.
The improvements were made in the course of the IMOTHEB research project coordinated by Osram. One of the aims of the project was to further develop laser chips so that they deliver greater optical output power with constant beam quality. Project partner Max Born Institute supported chip development work in the form of extensive methodologies and analyses. The findings will now flow into product development.
Pump module output power boosted by 10%
An important application of fiber-coupled lasers is the pumping (injection of optical energy) of high-power lasers for material processing. Fiber lasers in particular are gaining in importance, for example for cutting and welding sheet metal in the automobile industry. At the same time, there is growing pressure on costs. The aim of IMOTHEB was therefore to reduce the system costs for such pump modules.
Project partner DILAS Diodenlaser researched concepts for the automated assembly of diode lasers. Another key factor was the brilliance of the laser sources. DILAS used a demonstration module to show that the improved Osram chips were capable of increasing the output power of the module by 10%. "Because the chip is more brilliant, more light goes into the fiber," says Dr Alexander Bachmann, project coordinator at Osram Opto. "The same module produces a higher output power than is possible with the laser diodes currently used in this application."
