Freeform metasurface color router for deep submicron pixel image sensors

Kim, Changhyun; Hong, Jongwoo; Jang, Junhyeok; Lee, Gun-Yeal; Kim, Youngjin; Jeong, Yoonchan; Lee, Byoungho

doi:10.1126/sciadv.adn9000

Cited by 9 publications

(3 citation statements)

References 52 publications

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“…(c) A schematic and SEM images of a free-form polarization-sensitive single layer nanophotonic color router based on the automatic differentiation of RCWA. Reproduced with permission from [46]. CC BY-NC 4.0.…”

Section: Adjoint Methodsmentioning

confidence: 99%

“…In this context, the automatic differentiation (AD) method, which utilizes AD libraries to train artificial neural networks, provides an alternative way to efficiently compute FoM gradients by removing the need for manual constructions of the adjoint problem [116]. Kim et al designed a free-form polarization-sensitive single layer color router with 600 nm pixel pitch employing the AD of RCWA as shown in figure 6(c) [46]. The fabricated device exhibited the measured color routing efficiencies of 42%, 52%, and 33% at wavelengths of 660 nm, 530 nm, and 455 nm, respectively.…”

Section: Adjoint Methodsmentioning

confidence: 99%

“…The initial implementation of nanophotonic color routers was conducted based on physics-inspired fixed-form design approaches, where devices are composed of optical elements of simple primitive shapes such as rectangles and cylinders that are chosen based on physical intuitions. Design optimizations of these devices were performed by varying only the structural parameters such as length, height, or radius of 42.3% (experiment) [46] a…”

Section: Fixed-form Color Routersmentioning

confidence: 99%

See 2 more Smart Citations

Towards subwavelength pixels: nanophotonic color routers for ultra-compact high-efficiency CMOS image sensors

Park,

Lee,

Lee

et al. 2024

J. Opt.

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The proliferation of smartphones and the widespread use of camera modules necessitate CMOS image sensors with high pixel density. The recent competitive race to miniaturize pixels has enabled commercial CMOS sensors with submicron pixels to reach sizes as small as 0.5 μm. However, further downsizing towards subwavelength pixels faces fundamental challenges as the conventional focus-and-filter approach suffers from the diminishing focusing ability of conventional microlens arrays and optical efficiency constraints imposed by absorptive color filters. Nanophotonic color routers have emerged to overcome these challenges via efficient spatiospectral splitting, thereby directing incident light into corresponding pixels. In particular, recent developments in free-form device optimization methods enable the design of highly efficient color routers by exploring a large combinatorial design space, which was previously considered to be intractable with conventional design methods. In this review, we comprehensively introduce a multitude of research achievements in the field of nanophotonic color routers for CMOS image sensors with a special emphasis on their design methodologies.

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Section: Adjoint Methodsmentioning

confidence: 99%

Section: Adjoint Methodsmentioning

confidence: 99%

Section: Fixed-form Color Routersmentioning

confidence: 99%

See 1 more Smart Citation

Towards subwavelength pixels: nanophotonic color routers for ultra-compact high-efficiency CMOS image sensors

Park,

Lee,

Lee

et al. 2024

J. Opt.

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A Polarization‐Insensitive and Adaptively‐Blazed Meta‐Grating Based on Dispersive Metasurfaces

Zang,

Liu,

Feng

et al. 2024

Laser & Photonics Reviews

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The diffraction efficiency of blaze gratings is optimized only at a specific frequency due to a fixed blaze angle, resulting in reduced and variable diffraction efficiencies over the working frequency band. Additionally, blazed gratings demonstrate polarization dependence due to their groove structures and the interaction of light with their surfaces. Consequently, designing gratings with constant diffraction efficiencies across a wide frequency bandwidth while maintaining polarization independence remains a challenge. Here, a design paradigm of dispersion engineerable meta‐grating inspired by orthogonal harmonic oscillations (OHO) is presented. Utilizing the OHO model, the phase dispersion of a metasurface can be precisely controlled, which applies to any unit cell featuring two orthogonal electromagnetic resonances. As a proof of concept, a polarization‐insensitive meta‐grating is showcased, where the blazed angle adapts with the incident frequency, ensuring broadband performance. In the experiment, the adaptively‐blazed grating measured an optimized and constant diffraction efficiency of ≈80% over the working wavelength range, i.e., 8.7–12.2 µm. The difference in diffraction efficiency between the two perpendicular linear polarization states remains within 4.6%. The proposed paradigm paves the way for meta‐device design based on precise dispersion engineering, which has potential applications in spectrometers, broadband beam forming and steering, hyperspectral imaging, etc.

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Light‐to‐Spike Encoding Using Indium‐Gallium‐Zinc Oxide Phototransistor for all‐Color Image Recognition with Dynamic Range and Precision Tunability

Huang,

Chen,

Chen

et al. 2024

Small Methods

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To enhance the efficiency of machine vision system, physical hardware capable of sensing and encoding is essential. However, sensing and encoding color information has been overlooked. Therefore, this work utilizes an indium‐gallium‐zinc oxide (IGZO) phototransistor to detect varying densities of red, green, and blue (RGB) light, converting them into corresponding drain current (ID) states. By applying stochastic gate voltage (VG) pulses to the IGZO phototransistor, the fluctuations are generated in these ID states. When the ID exceeds the threshold current (ITC), a spike signal is generated. This approach enables the conversion of light densities into spike signals, achieving spike‐rate encoding. Moreover, adjusting the standard deviation (σ) of the VG pulses controls the range of light densities converted into spike rates, while altering the mean (μ) of the VG pulses changes the baseline level of spike rates. Remarkably, separate RGB channels offer a tunable encoding process, which can emphasize individual colors and correct color bias. The encoded spike rates are also fed into a spiking neural network (SNN) for CIFAR‐10 pattern recognition, achieving an accuracy of 86%. The method allows the operation of SNN and shows the tunability in the process of light‐to‐spike encoding, opening possibilities for color image processing.

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Freeform metasurface color router for deep submicron pixel image sensors

Cited by 9 publications

References 52 publications

Towards subwavelength pixels: nanophotonic color routers for ultra-compact high-efficiency CMOS image sensors

Towards subwavelength pixels: nanophotonic color routers for ultra-compact high-efficiency CMOS image sensors

A Polarization‐Insensitive and Adaptively‐Blazed Meta‐Grating Based on Dispersive Metasurfaces

Light‐to‐Spike Encoding Using Indium‐Gallium‐Zinc Oxide Phototransistor for all‐Color Image Recognition with Dynamic Range and Precision Tunability

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