A small spectroscope with 25 color sensors was fabricated by combining metamaterial color filters and Si photodiodes. The metamaterial color filters consisted of guided-mode resonant metal gratings with subwavelength two-dimensional periodic structures. Transmittance characteristics of the color filters were designed to obtain peak wavelengths proportional to grating periods. For each color sensor, a peak wavelength of the spectral sensitivity could be tuned in the range of visible wavelengths by adjusting each grating period. By performing spectrum reconstruction using Tikhonov regularization, the spectrum of an incident light was obtained from the signal of photodiodes. Several monochromatic lights were made incident on the fabricated device and the spectral characteristics of the incident light were reconstructed from the output signals obtained from the respective color sensors. The peak wavelengths of the reconstructed spectra were in good agreement with the center wavelengths of the monochromatic lights.

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SUMMARY Arrayed plasmonic color filters integrated on Si photodiodes with 21 elements were experimentally demonstrated. The plasmonic color filters consisted of nanodot subwavelength periodic structures. Optical characteristics of the color filters were measured and compared with calculated results. In order to obtain spectrum of an incident light from the signal of photodiodes, spectrum reconstruction using Tikhonov regularization was adapted. In the spectral sensitivity of each photodiode, the peak wavelength was adjusted between 400 and 850 nm in wavelength by the period of nanodot structure on each photodiode. The measured peak wavelengths roughly agreed with calculated values with errors less than 30 nm in wavelength. Spectral characteristics of a monochromatic light were measured by fabricated device and spectrum reconstruction was carried out. The position of the center wavelength could be successfully detected.

Color filters are indispensable for imaging devices, liquid crystal displays, and so on. Color filters are divided by two types that are transmissive and reflective types. In the field of electrical device applications such as image sensors and displays, transmissive color filters are more useful than reflective filters. Currently, transmissive color filters with pigments are commonly used.