Microoptical components for fiber coupling of high power laser

A microoptical beam transformation system for coupling of high power laser diode bars into multimode optical fibers is introduced. The key components are a gradient-index (GRIN) cylindrical lens for the collimation Of the fast-axis radiation and an array of blazed gratings for beam deflection of the single emitter bundles in the slowaxis. Excellent optical performance and high numerical aperture is required for the cylindrical lens. The lenses are fabricated by Ag+/Na+ ion exchange and exhibit diffiraction-limited performance up to N.A. = 0.5. The array of blazed gratings is produced by e-beam lithography in a variable dose writing mode. The diffraction efficiency into the desired order is higher than 85% for each element. Using these elements coupling of more than 60% of the output power of a 19 emitter high power laser diode bar (Pout = 20 W) into a 200 mm fiber of N.A. = 0.2 is achieved. Applications in fiber laser pumping, solid state laser pumping as well as laser soldering and pl astic welding are discussed.