Compact, Lightweight, and Filter-Free: An All-Si Microspectrometer Chip for Visible Light Spectroscopy
Jasper J. Cadusch, Jiajun Meng, Dandan Wen, Vivek Raj Shrestha, Kenneth B. Crozier
Abstract
Spectroscopic optical measurements of visible light provide important real-time information in many research and industrial settings. Conventional spectrometers are well established in this context due to their accuracy and reliability; however, they have not found widespread use in field-deployed applications due to their bulk (size and weight) and susceptibility to mechanical shock. Here we demonstrate a compact, lightweight microspectrometer chip-scale solution based on doped silicon nanophotonic elements, known as waveguide array (WGA) pixels. Each pixel is an array of 2.7 μm tall vertically oriented slab waveguides with a subwavelength array period, etched into a P–I–N-doped silicon substrate. By adjusting the nanometric dimensions of each element we imbue our pixels with a structural color and each pixel’s responsivity spectrum with distinct features. In doing this, we forego the need for the optical elements, such as gratings or interferometers, that one would normally need for a spectrometer. This opens the possibility for dramatic miniaturization and for improvements in mechanical robustness. We fabricate and characterize 144 WGA pixels and use supervised machine learning techniques to perform spectroscopic measurements, including on biological samples, with our 6 mm × 6.5 mm chip. We find that our structurally colored microspectrometer chip offers performance comparable to that of commercial spectrometer, making it well suited to field deployment in hand-held devices.