Arrays of focused beams generated by the integration of Fresnel microlenses with vertical cavity surface-emitting laser arrays

The advent of vertical cavity surface emitting laser arrays (VC-SELAs) creates new possibilities of integration and miniaturization in a host of optical information processing and interconnection applications.1,2 Beams of individual lasers in a VC-SELA exit through the substrate while diverging due to diffraction causing beam overlap after short distances. Here, we present results of integrating an easy to fabricate binary phase Fresnel microlens array (BP-FMA) on the substrate of a VC-SELA to focus individual beams making them suitable for above applications. A VC-SELA with 10 m aperture laser on 100 m pitch was first fabricated detail of which is given elsewhere.2 By the selective ion beam milling of the substrate, the BP- FMA pattern was fabricated in the exit interface. The generated step height was 0.19 m (to induce 180 phase shift between neighboring zones of Fresnel microlenses). Each microlens in the array has an aperture of 80 m situated 100 m apart. In one case, we used such microlenses to reduce the beam divergence of 10 m aperture lasers (situated 200 m away) from 11 (diffraction without the lens) to 4 (with the lens). In this paper, we will present the quality of beams generated in addition to the diffraction and the throughput efficiencies of the fabricated microlenses. The effect of back reflection on the performance of laser resonators will also be examined.