Name: demonstration of spin-multiplexed and direction-multiplexed all-dielectric visible metaholograms
Uploaded: 2020-09-25T14:00:00
Description: Watch this Scientific Journal Video about Demonstration of Spin-Multiplexed and Direction-Multiplexed All-Dielectric Visible Metaholograms at JoVE.com

This work was financially supported by the National Research Foundation (NRF) grants (NRF-2019R1A2C3003129, CAMM-2019M3A6B3030637, NRF-2019R1A5A8080290) funded by the Ministry of Science and ICT of the Korean government. I.K. acknowledges the NRF Global Ph.D. fellowship (NRF-2016H1A2A1906519) funded by the Ministry of Education of the Korean government.

1. Device fabrication
NOTE: Figure 1 shows the fabrication process of a-Si:H metasurfaces17.
<ol>
	<li>Prepare a fused silica wafer piece (size = 2 cm x 2 cm, thickness = 500 &#181;m) as a substrate. Rinse the substrate with acetone and isopropyl alcohol (IPA) then blow nitrogen gas over the substrate to dry it.</li>
	<li>Deposit a 380 nm thick a-Si:H film on the substrate using plasma-enhanced chemical vapor deposition (PECVD) with the f...

<ol>
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The a-Si:H metasurfaces were fabricated in three major steps: a-Si:H thin film deposition using PECVD, precise EBL, and dry etching. Among these steps, the EBL writing process is the most important. First, the pattern density on metasurfaces is quite high, so the process requires precise control over the electron dose (energy) and scanning parameters such as number of dots per unit area. The development condition should also be chosen carefully. The density of the pattern is very high, so when the development process is ...

Optical metasurfaces composed of sub-wavelength nanostructures have enabled many interesting optical phenomena, including optical cloaking1, negative refraction2, perfect light absorption3, color filtering4, holographic image projection5, and beam manipulation6,7,8. Optical metasurfaces that have appropriately-designed scatterers can modulate the spectrum, wavefront and polarization of light. Early optical metasurfaces were mainly fabricated using noble metals (e.g., Au, Ag) due to their high reflectivity and ease of nanofabrication, but they have high Ohmic losses, so the metasurfaces have low efficiency at short visible wavelengths.
Development of nanofabrication techniques for dielectric materials that have low losses in visible light (e.g., TiO29, GaN10, and a-Si:H11) has enabled realization of highly efficient flat optical devices with optical metasurfaces. These devices have applications in optics and engineering. One intriguing application is optical holography for projective volumetric display and information encryption. Compared to conventional holograms that use spatial light modulators, the metahologram has numerous advantages such as miniaturization of optical setup, higher resolution of holographic images and larger field of visibility.
Recently, encoding of multiple holographic information in a single-layered metahologram device has been achieved. Examples include metaholograms that are multiplexed in spin12,13, orbital angular momentum14, incident light angle15, and direction16. These efforts have overcome the critical shortcoming of metaholograms, which is a lack of design freedom in a single device. Most conventional metaholograms could only produce single encoded holographic images, but multiplexed device can encode multiple holographic images in real time. Hence, the multiplexed metahologram is a crucial solution platform towards real holographic video display or multifunctional anticounterfeiting holograms.
Reported here are protocols to fabricate spin- and direction-multiplexed all-dielectric visible metaholograms, then to optically characterize them13,16. To encode multiple visual information in a single metasurface device, metaholograms are designed which show two different holographic images when the spin or direction of incident light are changed. To fabricate highly efficient holographic images in a manner comparable with CMOS technology, a-Si:H is used for the metasurfaces and dual magnetic resonances and antiferromagnetic resonances induced inside them are exploited. The fabrication protocol consists of film deposition, electron beam writing, and etching. The fabricated device is characterized using a customized optical setup composed of a laser, a linear polarizer, a quarter waveplate, a lens and a charge-coupled device (CCD).

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			<td height="21" style="height:21px;width:327px;">Aceton</td>
			<td style="width:187px;">J.T. Baker</td>
			<td style="width:201px;">925402</td>
			<td style="width:167px;"></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Beam splitter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CCM1-BS013/M</td>
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			<td height="21" style="height:21px;width:327px;">Chromium etchant</td>
			<td style="width:187px;">KMG</td>
			<td style="width:201px;">Cr-7</td>
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			<td height="21" style="height:21px;width:327px;">Chromium evaporation source</td>
			<td style="width:187px;">Kurt J. Lesker</td>
			<td style="width:201px;">EVMCR35D</td>
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			<td height="21" style="height:21px;width:327px;">Clamp</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CP175</td>
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			<td height="21" style="height:21px;width:327px;">Conducting polymer</td>
			<td style="width:187px;">Showa denko</td>
			<td style="width:201px;">E-spacer</td>
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			<td height="21" style="height:21px;width:327px;">Diode laser</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CPS635</td>
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			<td height="21" style="height:21px;width:327px;">E-beam evaporation system</td>
			<td style="width:187px;">Korea Vacuum Tech</td>
			<td style="width:201px;">KVE-E4000</td>
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			<td height="21" style="height:21px;width:327px;">E-beam resist</td>
			<td style="width:187px;">Microchem</td>
			<td style="width:201px;">495 PMMA A2</td>
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			<td height="21" style="height:21px;width:327px;">Electron beam lithography</td>
			<td style="width:187px;">Elionix</td>
			<td style="width:201px;">ELS-7800</td>
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			<td height="21" style="height:21px;width:327px;">Half-wave plate</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AHWP05M-600</td>
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			<td height="21" style="height:21px;width:327px;">Inductively-coupled plasma reactive ion etching</td>
			<td style="width:187px;">DMS</td>
			<td style="width:201px;">-</td>
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			<td height="21" style="height:21px;width:327px;">Iris</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">SM1D12</td>
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			<td height="21" style="height:21px;width:327px;">Isopropyl alcohol</td>
			<td style="width:187px;">J.T. Baker</td>
			<td style="width:201px;">909502</td>
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			<td height="21" style="height:21px;width:327px;">Kinematic mirror mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">KM100/M</td>
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			<td height="21" style="height:21px;width:327px;">Lens</td>
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			<td style="width:201px;">LB1630</td>
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			<td height="21" style="height:21px;width:327px;">Lens Mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">LMR2/M</td>
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			<td height="21" style="height:21px;width:327px;">Linear polarizer</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">GTH5-A</td>
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			<td height="21" style="height:21px;width:327px;">Mirror</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">PF10-03-G01</td>
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			<td height="21" style="height:21px;width:327px;">Neutral density filter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">NDC-50C-4</td>
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			<td height="21" style="height:21px;width:327px;">Plasma enhanced chemical vapor deposition</td>
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			<td height="21" style="height:21px;width:327px;">Post</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">TR75/M</td>
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			<td height="21" style="height:21px;width:327px;">Post holder</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">PH75E/M</td>
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			<td height="21" style="height:21px;width:327px;">Quarter-wave plate</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AQWP10M-580</td>
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			<td height="21" style="height:21px;width:327px;">Resist developer</td>
			<td style="width:187px;">Microchem</td>
			<td style="width:201px;">MIBK:IPA=1:3</td>
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			<td height="21" style="height:21px;width:327px;">Rotational mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">RSP1/M</td>
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			<td height="21" style="height:21px;width:327px;">Scanning electron microscopy</td>
			<td style="width:187px;">Hitachi</td>
			<td style="width:201px;">Regulus8100</td>
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			<td height="21" style="height:21px;width:327px;">XY translation mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">XYF1/M</td>
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			<td height="21" style="height:21px;width:327px;">1-inch adapter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AD11F</td>
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			<td height="21" style="height:21px;width:327px;">1-inch lens mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CP02/M</td>
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demonstration of spin-multiplexed and direction-multiplexed all-dielectric visible metaholograms

The optical holography technique realized by metasurfaces has emerged as a novel approach to projective volumetric display and information encryption display in the form of ultrathin and almost flat optical devices. Compared to the conventional holographic technique with spatial light modulators, the metahologram has numerous advantages such as miniaturization of optical setup, higher image resolution and larger field of visibility for holographic images. Here, a protocol is reported for the fabrication and optical characterization of optical metaholograms that are sensitive to the spin and direction of incident light. The metasurfaces are composed of hydrogenated amorphous silicon (a-Si:H), which has large refractive index and small extinction coefficient in the entire visible range resulting in high transmittance and diffraction efficiency. The device produces different holographic images when the spin or direction of incident light are switched. Therefore, they can encode multiple types of visual information simultaneously. The fabrication protocol consists of film deposition, electron beam writing and subsequent etching. The fabricated device can be characterized using a customized optical setup that consists of a laser, a linear polarizer, a quarter waveplate, a lens and a charge-coupled device (CCD).

The a-Si:H metasurfaces enable high cross-polarization efficiency and can be fabricated using a method (Figure 1) that is compatible with CMOS; this trait may enable scalable fabrication and near-future commercialization. The SEM image shows the fabricated a-Si:H metasurfaces (Figure 2). Furthermore, a-Si:H has a larger refractive index than TiO2 and GaN, so even with low aspect ratio nanostructure of around 4.7, an a-SiH meta-hologram with high diffr...

Watch this Scientific Journal Video about Demonstration of Spin-Multiplexed and Direction-Multiplexed All-Dielectric Visible Metaholograms at JoVE.com

Demonstration of Spin-Multiplexed and Direction-Multiplexed All-Dielectric Visible Metaholograms

We present a protocol for fabrication of spin- and direction-multiplexed visible metaholograms, then conduct an optical experiment to verify their function. These metaholograms can easily visualize encoded information, so they can be used for projective volumetric display and information encryption.

The optical holography technique realized by metasurfaces has emerged as a novel approach to projective volumetric display and information encryption ...

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