Resonant cavity-enhanced photodiode array for miniaturised spectroscopic sensing

Optical spectroscopic sensing is a technique that is commonly employed for the identification and compositional analysis of a wide variety of substances, from biological samples to greenhouse gases. High-resolution spectrometers are well established, however, attempts to miniaturise the designs can suffer from adverse effects due to the miniaturisation, for both Fourier transform based interferometric designs, as well as dispersive designs. In this work, a linear array of resonant cavity-enhanced photodiodes is realised with spatially chirped resonance wavelength, offering chip-scale free-space hyperspectral sensing. Resonant cavity-enhanced photodiodes sense over a narrow spectral band, which can be tuned by the thicknesses of the heterostructure. Through this work, multiple narrow spectral bands can be sensed by resonant cavity-enhanced photodiodes on a single chip by grading the thicknesses across the wafer. Photocurrent measurements from a fabricated array determine the wavelength of incident light with an accuracy of ± 2 nm.