Efficient beam shaping of linear, high-power diode lasers by use of micro-optics

We have designed, fabricated, and characterized a micro-optical beam-shapin g device that is intended to optimize the coupling of an incoherent, linear ly extended high-power diode laser into a multimode fiber. The device uses two aligned diffractive optical elements (DOEs) in combination with convent ional optics. With a first prototype, we achieved an overall efficiency of 28%. Straightforward improvements, such as antireflective coatings and the use of gray-tone elements, are expected to lead to an efficiency of approxi mately 50%. The device is compact, and its fabrication is suited for mass p roduction at low cost. This micro-optical device, used in a range-finder me asurement system, will extend the measurement range. In addition to the dir ect laser writing technique, which was used for fabrication of the DOEs of the prototype, we applied two other technologies for the fabrication of the micro-optical elements and compared their performance. The technologies we re multiple-projection photolithography in combination with reactive-ion et ching in fused silica and high-energy beam-sensitive glass gray-tone lithog raphy in photoresist. We found that refractive-type elements (gray tone) yi eld better efficiency for large deflection angles, whereas diffractive elem ents (multilevel or laser written) give intrinsically accurate deflection a ngles. (C) 2001 Optical Society of America.