The integration of multiple optical elements on a common substrate to create photonic integrated circuits (PIC) has been successfully applied in: fibre-optic communications, photonic computing and optical sensing. The push towards III-Vs on silicon promises a new generation of integrated devices that combine the advantages of both integrated electronics and optics in a single substrate. III-V edge emitting laser diodes offer high efficiency and low threshold currents making them ideal candidates for the optically active elements of the next generation of PICs. Nevertheless, the highly divergent and asymmetric beam shapes intrinsic to these devices limits the efficiency with which optical elements can be free space coupled intra-chip; a capability particularly desirable for optical sensing applications e.g. . Furthermore, the monolithic nature of the integrated approach prohibits the use of macroscopic lenses to improve coupling. However, with the advent of 3D direct laser writing, three dimensional lenses can now be manufactured on a microscopic-scale , making the use of micro-lens technology for enhanced free space coupling of integrated optical elements feasible.
Here we demonstrate the first use of 3D micro-lenses to improve the coupling efficiency of monolithically integrated lasers. Fabricated from IP-dip photoresist using a Nanoscribe GmbH 3D lithography tool, the lenses are embedded directly onto a structured GaInP/AlGaInP substrate containing arrays of ridge lasers free space coupled to one another via a 200 μm air gap. We compare the coupling efficiency of these lasers with and without micro-lenses through photo-voltage and beam profile measurements and discuss optimisation of lens design.
Robert Thomas, Gwilym I. Williams, Sam Ladak, and Peter M. Smowton, "3D micro-lenses for free space intra-chip coupling in photonic-integrated circuits (Conference Presentation)," Proc. SPIE 10123, Novel In-Plane Semiconductor Lasers XVI, 101230W (Presented at SPIE OPTO: February 01, 2017; Published: 20 April 2017); https://doi.org/10.1117/12.2252213.5398643852001.
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