Fiber-coupling technique for high-power diode laser arrays

Monolithic linear arrays of diode lasers, also known as diode laser bars, are the basic elements for most high-power laser applications such as solid-state laser pumping or material processing. Cylindrical microlenses used as fast- axis collimators for 10-mm diode bars require very high angles of aperture (up to 100 degree FW1/e2, equivalent to a numerical aperture of approx. 0.8) to capture most of the emitted laser power. For the efficient longitudinal pumping of laser rods, or the narrow focusing of the diode laser radiation (fiber coupling, material processing), high- quality microlenses with small lens aberrations are necessary to avoid power losses and beam quality degradation. A technique for coupling the output of high- power diode laser bars into one multimode fiber with high efficiency, easy alignment requirements and low manufacturing costs is demonstrated using a single fiber with core diameter down to 400 micrometers . This technique comprises two micro step-mirrors for beam shaping. The overall efficiency from one diode-laser bar to fiber is 71% with 20 W cm laser power through the fiber. Coupling of 12 diode laser bars and power of 200 W out of a fiber with core diameter of 0.8 mm and NA equals 0.2 is achievable with this technique.