Search query: dielectric metasurface silicon

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abstract: As the hole mobility increases with free carrier absorption (FCA) heavily doped p type silicon has emerged as a promising candidate for detecting near infrared (NIR) light with photonic energy below the semiconductor bandgap, and the hot carrier photodetector is capable of high responsivity approaching commercially available devices. To enhance performance related FCA of the semiconductor, here we demonstrate an all silicon metasurface absorber designed in nanohole arrays and present an in depth analysis on the electromagnetic resonance mechanism in the NIR spectral of interest. Multipole decomposition under a Cartesian coordinate system reveals that combining with the dielectric loss introduced by the doping, magnetic dipole resonances contribute predominantly to the absorption enhancement. This simple and easy fabricated architecture has great potential for silicon hot carrier photodetectors.
author_names: Honghao Yu

Qing Xiong

Hong Wang

Ye Zhang

Jianjun Lai

Changhong Chen
title: Near infrared free carrier absorption enhancement of heavily doped silicon in all dielectric metasurface
year: 2020

abstract: The achievement of structural color has shown advantages in large gamut, high saturation, high brightness, and high resolution. While a large number of plasmonic/dielectric nanostructures have been developed for structural color, the previous approaches fail to match all the above criterion simultaneously. Herein we utilize the Si metasurface to demonstrate an all in one solution for structural color. Due to the intrinsic material loss, the conventional Si metasurfaces only have a broadband reflection and a small gamut of 78% of sRGB. Once they are combined with a refractive index matching layer, the reflection bandwidth and the background reflection are both reduced, improving the brightness and the color purity significantly. Consequently, the experimentally demonstrated gamut has been increased to around 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020. Meanwhile, high refractive index of silicon preserves the distinct color in a pixel with 2 x 2 array of nanodisks, giving a diffraction limit resolution. Here, the authors fabricate a metasurface with high brightness and large gamut structured colors by combining a silicon metasurface with a refractive index matching layer. The experimentally demonstrated gamut is 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020.
author_names: Wenhong Yang

Shumin Xiao

Qinghai Song

Yilin Liu

Yunkai Wu

Shuai Wang

Jie Yu

Jiecai Han

Din Ping Tsai
title: All dielectric metasurface for high performance structural color
venue: Nature Communications
year: 2020

abstract: An all dielectric metasurface is deemed to serve a potential platform to demonstrate spectral filters. Silicon rich silicon nitride (SRN) which contains a relatively large portion of silicon, can exhibit higher refractive indices, when compared to silicon nitride. Meanwhile, the extinction coefficient of SRN is smaller than that of hydrogenated amorphous silicon, leading to reduced absorption loss in the shorter wavelength. SRN is therefore recommended as a scattering element from the perspective of realizing all dielectric metasurfaces. In this work, we propose and embody a suite of highly efficient structural color filters, capitalizing on a dielectric metasurface that consists of a two dimensional array of SRN nanodisks that are embedded in a polymeric layer. The SRN nanodisks may support the electric dipole (ED) and magnetic dipole (MD) resonances via Mie scattering, thereby leading to appropriate spectral filtering characteristics. The ED and MD are identified from field profile observation with the assistance of finite difference time domain simulations. The manufactured color filters are observed to produce various colors in both transmission and reflection modes throughout the visible band, giving rise to a high transmission of around 90% in the off resonance region and a reflection ranging up to 60% A variety of colors can be realized by tuning the resonance by adjusting the structural parameters such as the period, diameter, and height of the SRN nanodisks. The spectral position of resonances might be flexibly tuned by tailoring the polymer surrounding the SRN nanodisks. It is anticipated that the proposed coloring devices will be actively used for color displays, imaging devices, and photorealistic color printing.
author_names: Chul-Soon Park

Ishwor Koirala

Song Gao

Vivek Raj Shrestha

Sang-Shin Lee

Duk-Yong Choi
title: Structural color filters based on an all dielectric metasurface exploiting silicon rich silicon nitride nanodisks.
venue: Optics express
year: 2019

abstract: Structural color has been particularly attractive as it provides a highly promising approach for next generation color printing. Plasmonic nanostructures have been intensively investigated for color printing, while suffering from intrinsic loss that degrades the quality of the coloration. Dielectric materials have emerged as an alternative because of their high refractive index that enables highly confined optical modes within the nanostructure at the diffraction limit. Here, we demonstrate an all dielectric nanoring metasurface for coloration. By harnessing the intrinsic nanoring structure design, vivid structural color has been achieved in the visible range. The color gamut is expected to occupy 115% of the standard color space (sRGB) on the chromaticity diagram of the International Commission on Illumination (CIE) 1931 in theory. Our structure can be applied to various complex devices and materials and find potential applications such as displays, information, and art works.
author_names: Xin Liu

Zhao Huang

Jianfeng Zang
title: All Dielectric Silicon Nanoring Metasurface for Full Color Printing.
venue: Nano letters
year: 2020

abstract: Dielectric metasurfaces are promising optical components due to lossless nature and broad functionality including lenses, polarizers, waveplates, routers, holography, and so on. These metasurfaces consist of meta atoms made of transparent and high index materials at the designed wavelength. Silicon (n 4 3.5 at 700 nm 1 mm) is very promising material at the near infrared range[1] although it has absorption in the visible region. In addition, as the band gap increases, dielectric constant decreases so it requires much higher aspect ratio in the visible range, which makes fabrication difficult. Meta atoms consists of a high aspect ratio pillars, posts or holes with circular, rectangular, or polygonal two dimensional shape. Since subwavelength feature size is required, electron beam lithography (EBL) is essential, including production of mask reticle for stepper or nanoimprint molds. However, complicated and massively parallel pattern of metafurfaces for enough functionality makes EBL difficult through both increase of exposure data file size and lengthening of exposure time.
author_names: Kentaro Iwami

Chikara Ogawa
title: Characterization of octagonal silicon pillar for meta atom of dielectric metasurface
year: 2019

abstract: DOI: 10.1002/adom.201801191 plasmonic or dielectric nanoantennas.[20] Mode conversions between the trans electric (TE) modes TE0, TE1, and TE2 were achieved with a length of 10 mm at 1550 nm using silicon nanoantennas on LiNbO3 or Si3N4 waveguides by simulations.[20] A nanoscale mode converter was theoretically proposed[11] and experimentally demonstrated[21] by introducing a periodic perturbation in its effective refractive index along the propagation direction and a graded effective index profile along its transverse direction. Mode conversion between TE0 and TE1 modes was successfully achieved with a length of 23 mm at 1550 nm. However, no experimental results on the crosstalk of the TE mode conversion were provided in the previous reports.[20,21] It is highly desired to miniaturize the device footprint and realize a compact waveguide mode converter. In this article, we propose and demonstrate a compact silicon waveguide mode converter based on all dielectric metasurface structure with a tilted subwavelength periodic perturbation. The mode coupling coefficient changes along the propagation direction, which can help the mode conversion process. Our proposed waveguide mode converter can be scaled to realize arbitrary waveguide mode conversion. As examples, we experimentally demonstrate two silicon waveguide mode converters employing all dielectric metasurface structures that can convert TE0 mode to TE1 mode and TE0 mode to TE2 mode, respectively. The mode conversion lengths are 5.75 and 6.736 mm for the TE0 to TE1 and TE0 to TE2 waveguide mode converters, respectively, which are shorter than previously reported results.[20,21] Mode demultiplexers are cascaded after the metasurface mode converter to measure the crosstalk values and conversion losses. The insertion losses are lower than 1 dB and the crosstalk values are below 10 dB in a wavelength range of 20 nm for the TE0 to TE1 and TE0 to TE2 waveguide mode conversions. Figure 1a depicts the 3D view of the proposed waveguide mode converter based on dielectric metasurface structure with a tilted subwavelength periodic perturbation. Propagation of optical field in a perturbed dielectric structure can be described by the coupled mode theory. Attributed to the perturbation on the silicon waveguide, one waveguide mode can be coupled into another mode, and the amplitude of each waveguide mode along the propagation direction is determined by a set of differential equations[11,25]
author_names: Hongwei Wang

Yong Zhang

Yu He

Qingming Zhu

Lu Sun

Yikai Su
title: Compact Silicon Waveguide Mode Converter Employing Dielectric Metasurface Structure
year: 2018

abstract: It is advantageous to construct a dielectric metasurface in silicon due to its compatibility with cost effective, mature processes for complementary metal oxide semiconductor devices. However, high quality crystalline silicon films are difficult to grow on foreign substrates. In this work, we propose and realize highly efficient structural color filters based on a dielectric metasurface exploiting hydrogenated amorphous silicon (a Si:H) known to be lossy in the visible regime. The metasurface is comprised of an array of a Si:H nanodisks embedded in a polymer, providing a homogeneously planarized surface that is crucial for practical applications. The a Si:H nanodisk element is deemed to individually support an electric dipole (ED) and magnetic dipole (MD) resonance via Mie scattering, thereby leading to wavelength dependent filtering characteristics. The ED and MD can be precisely identified by observing the resonant field profiles with the assistance of finite difference time domain simulations. The completed color filters provide a high transmission of around 90% in the off resonance band longer than their resonant wavelengths, exhibiting vivid subtractive colors. A wide range of colors can be facilitated by tuning the resonance by adjusting the structural parameters like the period and diameter of the a Si:H nanodisk. The proposed devices will be actively utilized to implement color displays, imaging devices, and photorealistic color printing.
author_names: Chul-Soon Park

Vivek Raj Shrestha

Wenjing Yue

Song Gao

Sang-Shin Lee

Eun-Soo Kim

Duk-Yong Choi
title: Structural Color Filters Enabled by a Dielectric Metasurface Incorporating Hydrogenated Amorphous Silicon Nanodisks
venue: Scientific Reports
year: 2017

author_names: Dimitrios C Zografopoulos

Antonio Ferraro

Jose Francisco Algorri

Pedro Martin-Mateos

Braulio Garcia-Camara

Aldo Moreno-Oyervides

Viktor Krozer

Pablo Acedo

Ricardo Vergaz

Jose Manuel Sanchez-Pena

Romeo Beccherelli
title: All Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance
venue: Advanced Optical Materials
year: 2019

abstract: Metasurfaces can be programmed for a spatial transformation of the wavefront, thus allowing parallel optical signal processing on chip within an ultracompact dimension. On chip metasurfaces have been implemented with two dimensional periodic structures, however, their inherent scattering loss limits their large scale implementation. The scattering can be minimized in single layer high contrast transmitarray (HCTA) metasurface. Here we demonstrate a one dimensional HCTA based lens defined on a standard silicon on insulator substrate, with its high transmission <1 dB loss) maintained over a 200 nm bandwidth. Three layers of the HCTAs are cascaded for demonstrating meta system functionalities of Fourier transformation and differentiation. The meta system design holds potential for realizing on chip transformation optics, mathematical operations and spectrometers, with applications in areas of imaging, sensing and quantum information processing. Metasurfaces can be programmed for a spatial transformation of the wavefront, allowing on chip optical signal processing. Here, the authors demonstrate a one dimensional high contrast transmitarray metasurface based lens on SOI substrate and demonstrate functionalities of Fourier transformation and differentiation.
author_names: Zi Wang

Tiantian Li

Anishkumar Soman

Dun Mao

Thomas Kananen

Tingyi Gu
title: On chip wavefront shaping with dielectric metasurface
venue: Nature Communications
year: 2019

abstract: In metamaterial systems, toroidal dipole (TD) plays an important role in determining their optical properties. Here, we proposed an all dielectric metasurface consisting of two silicon split ring resonators (SRRs) that can support strong TD resonance. The TD resonance is excited by TD moments both inside the unit cell and between the neighboring unit cells, and can be easily manipulated by altering the gap size or distance of the SRRs, leading to powerful electric and magnetic near field enhancement. In addition, symmetric unprotected TD bound state in the continuum (TD BIC) was achieved in closed ring resonator (CRR) metasurface, and transformed into leaky resonances with ultrahigh Q factors by adjusting the distance of CRRs. The proposed structure provides a good platform for us to better understand the coupling of SRRs, which is useful for the design and application of TD metasurfaces in biological sensors, nonlinear interactions and other photonic devices.
author_names: Xin Luo

Xiangjun Li

Tingting Lang

Xufeng Jing

Zhi Hong
title: Excitation of high Q toroidal dipole resonance in an all dielectric metasurface
year: 2020