Optimization of microlens arrays for photon detectors

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Zanella, Frédéric
Schneider, Christian
Ciric, Luka
Basset, Guillaume
Microlenses, and especially microlens arrays (MLA), are commonly used as stand-alone optical components, for beam homogenization and shaping. Or integrated as wafer-level optics (WLO), either on top of light sources for beam shaping (e.g., on micro-LED or vertical-cavity surface-emitting laser – VCSEL), or on top of light or image sensors as light concentrators. In the latter case, each microlens of the MLA, also known in the photography domain as On-Chip Lens (OCL), redirects the light to the active volume of the pixel located underneath. This increases the external quantum efficiency (EQE) by increasing the pixel effective fill-factor, especially for front-illuminated image sensors and their limited fill-factors. We report various MLA optimizations and the concentration factors achieved when addressing challenges encountered with advanced photon detectors such as single-photon avalanche diodes (SPAD) or silicon photon multiplier (SiPM). For example: substrate size and type (wafer, bare or packaged die), optical transmission range from NUV to NIR, microlens geometrical parameter space (diameters from micrometers to millimeters) and stability to temperature, vibrations and irradiation (UV, gamma and proton).
Publication Reference
SPIE Optics + Optoelectronics, Quantum Optics and Photon Counting 2023, PC1257005, Prague, Czech Republic
The UV stability test campaign was funded by the EU H2020 project Phabuloμs (grant 871710) and the shown nearly gapless MLA by the Innosuisse project SPADLens (agreement 2155010564).