Color Sensing by Optical Antennas: Approaching the Quantum Efficiency Limit

Abstract

Color image sensing is commonly carried out by an array of color pixels. Each of the color pixels consists of at least three sensing elements in combination with optical filters for red, green and blue. The filters are arranged sideby-side limiting the total quantum efficiency of a color pixel to 1/N, where N is the number of color channels per color pixel. Hence, in the most basic filter arrangement, just consisting of a red, green, and blue filter, the upper limit of the quantum efficiency is equal to 1/3, limiting the dynamic range and color contrast of the detected optical input signal. In order to increase the quantum efficiency and improve the image quality, an alternative sensor device is proposed, which can be realized by using current semiconductor technology. The proposed sensor uses silicon optical antennas to detect the incident light. The sensor allows for detecting the color information, with quantum efficiencies approaching unity. The design of the optical antennas is described, and optimization strategies are discussed.

Nanophotonic Structural Colors

“…As illustrated in Figure c, Si disks are used along with an antireflection coating to achieve the so-called Kerker’s conditions that sharpen up reflectance transitions. Doing so brings one closer to the boxcar-shaped reflectance profiles leading to a color gamut exceeding the sRGB color space, that is, occupying ∼120% of the sRGB color space. , Another area where structural colors can be applied is in color filtering. − Due to their nanoscale footprint and the ability to be tuned over the visible spectra, structural colors can further miniaturize the imaging sensors by reducing the size of color filters. − Figure d depicts a configuration for color filtering. By adjusting the cavity thickness, the spectra can be continuously tuned over visible spectra .…”

Combining Photosynthesis and Photovoltaics: A Hybrid Energy-Harvesting System Using Optical Antennas

“…The solar cell consists of an array of nanowires or nanodisks. Each nanowire or nanodisk acts like a circular resonator. − The optical resonator supports whispering gallery or leaky modes . The light is repeatedly reflected by the circular boundary of the optical resonator.…”

“…The effective wavelength is given by λ eff = λ 0 / n eff , where n eff is the effective refractive index, which varies between the refractive index of the cladding (air) and the refractive index of the core and λ 0 is the vacuum wavelength . Optical mode theory can be used to calculate the effective refractive index. − , …”

“…Both approaches have been described in the literature. ,,,, We have investigated thin-film materials that can be directly deposited on a glass substrate at low temperatures. We investigated the use of crystalline, microcrystalline, and amorphous silicon materials. ,, All three materials have been intensively researched as photovoltaic materials. However, crystalline silicon requires the use of high deposition temperatures that are not compatible with the use of solar glass .…”

Nanophotonic color splitters for high-efficiency imaging

“…Theoretically, this can increase the photon collection on average by 3×, with additional improvements possible for front-illuminated CMOS configurations (where often only 50% of the illuminated surface is photoactive) ( Zhang et al., 2010 ), due to built-in lensing/funneling ( Sounas and Alu, 2016 ; Johlin et al., 2018 ). Color splitting for imaging applications has been investigated previously through fairly complex processes ( Chen et al., 2016 ), often involving high-index material processing steps ( Sounas and Alu, 2016 ; Miyata et al., 2019 ; Chen et al., 2017 ; Nishiwaki et al., 2013 ; Tamang et al., 2019 ; Zhao et al, 2020 ), new elements in the far-field of the sensor ( Miyata et al., 2019 ; Chen et al., 2017 ; Nishiwaki et al., 2013 ; Xiao et al., 2016 ; Camayd-Muñoz et al., 2020 ), and computationally expensive image reconstructions ( Wang and Menon, 2015 ; Sahoo et al., 2017 ). Many designs additionally only work with a specific polarization of light, limiting their efficiency for normal imaging applications ( Xu et al., 2010 ; Nguyen-Huu et al., 2011 ; Kanamori et al., 2006 ).…”