Efficient Beam Shaping of Linear, High-Power Diode Lasers by Use of Micro-Optics

We have designed, fabricated, and characterized a micro-optical beam-shaping device that is intended to optimize the coupling of an incoherent, linearly extended high-power diode laser into a multimode fiber. The device uses two aligned diffractive optical elements (DOEs) in combination with conventional 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 approximately 50%. The device is compact, and its fabrication is suited for mass production at low cost. This micro-optical device, used in a range-finder measurement system, will extend the measurement range. In addition to the direct 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 were multiple-projection photolithography in combination with reactive-ion etching in fused silica and high-energy beam-sensitive glass gray-tone lithography in photoresist. We found that refractive-type elements (gray tone) yield better efficiency for large deflection angles, whereas diffractive elements (multilevel or laser written) give intrinsically accurate deflection angles.