We describe the main recent technological approaches that associate micro-optical elements to VCSELs in order to control their output beam and to improve their photonic integration. These approaches imply either a hybrid assembly or a direct integration technique. They are compared with regards to their tolerance to alignment errors and to their ease of implementation onto arrays of devices at a wafer level. In particular, we detail the integration techniques we have developed for self-aligned polymer microlens fabrication for beam collimation and short distance beam focusing. Finally, designs to achieve active micro-optics or to exploit novel nanophotonic effects are discussed. 1. Introduction Due to their unique advantages such as low threshold, parallel operation, symmetrical and circular beam, on-wafer test capability, and high bandwidth modulation, VCSELs now constitute strategic light sources for photonic applications, ranging from optical communications to instrumentation as well as optical storage or printing [1]. Current research on these devices concerns enhancement of emission performances by means of novel confinement designs, spectral extension to UV-visible and mid-infrared ranges, but also improvement of their photonic integration. For this latter issue, precise beam control is strongly in demand. Despite a limited far-field beam divergence, typically in the range from 10° to 20°, (half angle at 1/e2), these laser diodes have indeed to be more and more associated with microoptical elements to improve the performance of the system in which they are inserted and to develop their use in novel application fields. In this paper, we review the main approaches recently proposed in the literature to combine free-space micro-optics with VCSEL arrays. In the first part, we sum up the main requirements for VCSEL beam shaping in function of the aimed application. In Sections 2 and 3, we review different fabrication methods for passive micro-optics integration on VCSELs, from hybrid report to direct fabrication on device surface. In Section 4, we describe recent advances in the field of active micro-optics for VCSEL beam adaptation to a dynamic environment. Finally, we discuss on emerging approaches based on nanostructured integrated lenses. 2. Micro-Optics for VCSELs: Main Requirements Up to now, the major market for VCSEL devices remains short-distance high-speed optical interconnects. In this area, key considerations concern coupling efficiency of VCSEL arrays to optical fibers. This efficiency depends strongly on the laser natural beam divergence
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