Osram Opto Semiconductors has produced a broad area laser diode with a lateral brilliance of up to 4.8 W/(mm*mrad) in the laboratory. The more brilliant the laser, the more efficiently it can inject its light into optical fibers. This then increases the output power of modules for pumping fiber lasers used for material processing. This progress is one of the results of the project “Integrated microoptical and microthermal elements for diode lasers of high brilliance” (IMOTHEB) which was funded by the German Federal Ministry of Education and Research and which has now been successfully completed. 

Brilliance is a measure of the combination of optical output power and beam quality. 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 fibercoupled laser systems. The more brilliant the laser, the more light can be injected into an optical fiber. 

Improved chip design

A lateral brilliance of up to 4.8 W per millimeter and milliradiant (W/(mm*mrad)) was achieved in the laboratory – one of the highest known values for broad area laser diodes. Optimization of the chip design provided the basis for this success, particularly the integration of microthermal and microoptical 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 delivered greater optical output power with constant beam quality. As one of the project partners the Max Born Institute provided considerable support for the chip development work in the form of extensive methodologies and analyses. The findings will now successively flow into product development. 

Ten percent boost of pump module output power

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”, explained Dr. Alexander Bachmann, Project Coordinator at Osram Opto Semiconductors. “The same module produces a higher output power than is possible with the laser diodes currently used in this application.” 

The IMOTHEB research project aimed at an increase of the efficiency of laser systems and an reduction of their production costs. The project (FKZ 13N12312) started in October 2012 and was supported by the German Federal Ministry of Education and Research (BMBF) as part of the “Integrated Microphotonics” initiative. Osram Opto Semiconductors coordinated the project. The other partners were DILAS Diodenlaser and the Max Born Institute.