Resonant waveguide vs Fabry-Perot cavity: A comparative study for CMOS spectral sensor technology

The ubiquitous use of versatile smart devices fuels a rapid growth in spectral sensor technology. Ambient Light Sensors (ALS), with 3-6 spectral channels in the visible and near-infrared are the most common version today. Their architecture comprises a pixel and a filter atop. While the compliance of the pixel to CMOS technology is built-in, the compliance of the filter in terms of materials and of process parallelism is not obvious. The process demand discards the pixel-scale variable-thickness Fabry-Perot solution, notably, and rather points to single-step nanophotonic structures whose pattern is specific to each ALS pixel/channel. In this study, we provide a performance comparison between two such candidate filters, the resonant waveguide (RWG) rejection filter, and the hybrid Fabry Perot (FP) band-pass filter. The evaluation is carried out in terms of spectral response, tunability, angular and polarization tolerance, and noise sensitivity, assessing the collective ability of an ALS array to retrieve spectral information. Through this analysis from the photon to the system, we pave a methodological frame for engineers and manufacturers facing a variety of application choices and sensing capabilities.