Fig. 1. Schematic diagram of the principle and device configurations of on-chip multispectral photodetectors

Fig. 2. Interferometric type—schematic diagram of Michelson interferometer

Fig. 3. (a) The imaging principle of the hyperspectral sensor; (b) The exemplar hyperspectral imaging results of the sensor^[20]

Fig. 4. Long-wave infrared multispectral imaging system^[25]

Fig. 5. (a) Comparison between the filtering principles of traditional BCF and the routing principle of the MBCR; (b) Comparison of imaging results between MBCR and BCFs^[40]

Fig. 6. (a) Schematic of GaAsSb NW array photodetectors; (b) Normalized photocurrent versus wavelength of GaAsSb NW array photodetectors; (c) Reconstructed image and RGB images for a representative photodetector (D_{NW tip} of 86 nm); (d) Major transverse electric field (E_x) distribution of fundamental mode of GaAsSb NW (D_{NW tip} of 171 nm at z=0 and peak wavelength of 912 nm (HE_1,1 mode)) (The inset shows the spectrum of absorption in the NW ^[56])

Fig. 7. (a) Schematic of fabricated InAs nanowire array photodetectors; (b) Simulated absorption spectrum of the InAs nanowire array (green line with circle), 300 nm InAs substrate (blue line with triangle) and their sum (red line), respectively; (c) Photoresponse spectrum from 1200 to 4000 nm measured by a ‌Fourier transform infrared spectroscopy at 0 V and room temperature; (d) Temporal response of the InAs nanowire array photodetector^[61]

Fig. 8. (a) Scanning electron microscopy (SEM) images of typical nanodisk arrays with area of 1 μm×1 μm; (b) Comparison of experimentally measured RGB photocurrent response (dots) and simulation result (solid curves) of devices with areas of 1 μm×1 μm and 5 μm×5 μm^[64]

Fig. 9. (a) Fabrication process of a hybrid NA-NP photodetectors illustrated by SEM images; (b) J-V characteristics under dark and 1 Sun illumination conditions; (c), (d) Measured responsivity spectra of the photodetectors with D_NA ranging from 180 to 320 nm at visible (VIS)-near infrared (NIR) and short-wave infrared (SWIR) range^[62]

Fig. 10. (a) SEM images of patterned quantum dot films; (b) Array of three-pixel photodetectors fabricated on a 0.5 inch × 0.5 inch flat substrate; (c) Bias voltage-dependent spectral responsivities of a 4.8 μm IR pixel, a 6 μm IR pixel, and a 9.5 μm IR pixel, respectively^[69]

Fig. 11. (a) Schematic view of the CdSe photodetector; (b) Experimental setup of the single-pixel scanning imaging process; (c) Full-color image and the corresponding RGB mono-color images^[86]

Fig. 12. (a) Optical system of switching the infrared cutoff filter; (b) Multispectral imaging of the iris and periocular^[99]

Fig. 13. (a) Device structure of the perovskite-based RGBW PDs; (b) Experimental transmittance spectra of PFLs and experimental absorption spectra of the PPLs; (c) Imaging results of perovskite-based color camera under different light intensities^[100]

Fig. 14. Applications of multispectral photodetectors; (a) Used for cloud top height estimation^[107]; (b) Used for monitoring cotton wilt disease^[116]; (c) Used for marine debris detection^[120]; (d) Used for archaeology^[122]