<title>Gradient index microlenses for laser diode applications</title>

Abstract

Gradient index micro lenses for laser diode applicationsR. Goering, T. Possner, B. MesserschmidtFraunhofer Institution for Applied Optics and Precision EngineeringSchillerstrasse 1 , 07745 Jena, GermanyABSTRACTCollimating and diverging cylindrical micro lenses with N.A. up to 0.60 fabricated by thermal silver ion exchangein a special designed glass type are reported. Cylindrical microlens arrays are fabricated by field assistet ion-exchange. Applications to fiber coupling as well as to diode bar collimation are discussed.Keywords: ion-exchange, GRIN-components, laser diode beam shaping, laser bar collimation, fiber coupling1. INTRODUCTIONMicrooptical GRIN-lenses with high N.A. are very useful for the transformation of the strongly divergent andasymmetric beam emitted from semiconductor laser diodes and laser diode bars to a well-collimated beam orto a focused spot. Preferred applications are the coupling between laser diodes and optical fibres, the pumpingof solid state lasers as well as optical scanning. High N.A., a nearly diffraction limited pertormance and lensdimensions of a few hundred microns are required. In a previous paper we presented the formation of one-dimensional cylindrical microlenses by a two step silver ion-exchange process1. Here we would like to discussthe optimization of these components and a number of new elements fabricated by similar ion-exchangeprocesses and applications which could not be realized by standard SELFOC-lenses.Figures 1 and 2 show flat GRIN-components and ion-exchange techniques for their realization. The formationof diverging lenses is possible in a single ion-exchange step. For the generation of cylindrical collimating lenseswe use a two step process, proposed by Ohmi2. Cylindrical microlens-arrays are produced by a field-assistedexchange using a masked substrate.Fig. 1: Thermal ion-exchanged GRIN components