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1.
Science ; 368(6498): 1487-1490, 2020 06 26.
Artigo em Inglês | MEDLINE | ID: mdl-32587020

RESUMO

The development of two-dimensional metasurfaces has shown great potential in quantum-optical technologies because of the excellent flexibility in light-field manipulation. By integrating a metalens array with a nonlinear crystal, we demonstrate a 100-path spontaneous parametric down-conversion photon-pair source in a 10 × 10 array, which shows promise for high-dimensional entanglement and multiphoton-state generation. We demonstrate two-, three- and four-dimensional two-photon path entanglement with different phases encoded by metalenses with fidelities of 98.4, 96.6, and 95.0%, respectively. Furthermore, four-photon and six-photon generation is observed with high indistinguishability of photons generated from different metalenses. Our metalens-array-based quantum photon source is compact, stable, and controllable, indicating a new platform for integrated quantum devices.

2.
Light Sci Appl ; 8: 99, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31728191

RESUMO

Tomography is an informative imaging modality that is usually implemented by mechanical scanning, owing to the limited depth-of-field (DOF) in conventional systems. However, recent imaging systems are working towards more compact and stable architectures; therefore, developing nonmotion tomography is highly desirable. Here, we propose a metalens-based spectral imaging system with an aplanatic GaN metalens (NA = 0.78), in which large chromatic dispersion is used to access spectral focus tuning and optical zooming in the visible spectrum. After the function of wavelength-switched tomography was confirmed on cascaded samples, this aplanatic metalens is utilized to image microscopic frog egg cells and shows excellent tomographic images with distinct DOF features of the cell membrane and nucleus. Our approach makes good use of the large diffractive dispersion of the metalens and develops a new imaging technique that advances recent informative optical devices.

3.
Nat Nanotechnol ; 14(3): 227-231, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30664753

RESUMO

A light-field camera captures both the intensity and the direction of incoming light1-5. This enables a user to refocus pictures and afterwards reconstruct information on the depth of field. Research on light-field imaging can be divided into two components: acquisition and rendering. Microlens arrays have been used for acquisition, but obtaining broadband achromatic images with no spherical aberration remains challenging. Here, we describe a metalens array made of gallium nitride (GaN) nanoantennas6 that can be used to capture light-field information and demonstrate a full-colour light-field camera devoid of chromatic aberration. The metalens array contains an array of 60 × 60 metalenses with diameters of 21.65 µm. The camera has a diffraction-limited resolution of 1.95 µm under white light illumination. The depth of every object in the scene can be reconstructed slice by slice from a series of rendered images with different depths of focus. Full-colour, achromatic light-field cameras could find applications in a variety of fields such as robotic vision, self-driving vehicles and virtual and augmented reality.

4.
Opt Express ; 26(18): 23397-23410, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-30184841

RESUMO

Enabling laser white-lighting at a correlated color temperature (CCT) of 6500K with the use of only red/green/blue (RGB) tri-color laser diodes (LDs) is demonstrated, which can further perform wavelength division multiplexing (WDM) communication with a high-spectral-usage 16 QAM-OFDM data stream at 11.2 Gbps over 0.5 m. The sampling rate of encoded data is optimized to avoid the aliasing effect and to effectively amplify the signal with high on/off extinction and modulation depth. Proper oversampling can decrease the peak-to-average power ratio (PAPR) of the OFDM data and filter out unwanted noise. There are also six different diffusers used to diverge the white-light mixed by the RGB LD beam. By analyzing the color-casting transmittance, surface roughness, CCT uniformity, divergent angle of the diffuser, and the data transmission capacity, the frosted glass (FG2.8) diffuser with high transmittance diverges the white light with the divergent angle of ± 20° and supports the highest data rate of 14 Gbps over 0.5 m. To fit the day-light CCT, the blue LD power at an optimized bias current is further attenuated with a 0.6-optical density filter for reducing CCT from 100000K to 6500K; however, such an adjustment also degrades the SNR ratio to sacrifice the achievable data rate of the blue LD. The polycarbonate (PC1.5) diffuser with proper surface roughness diverged white-light exhibits the best CCT uniformity and a divergent angle of ± 30° but supports a data rate of only 6.4 Gbps over 0.5 m. The poly (methyl methacrylate) PMMA1.5 diffuser scatters the white light with the largest angle of ± 40°; however, the data rate also decreases to 4.8 Gbps over 0.5 m.

5.
Nat Nanotechnol ; 13(3): 227-232, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29379204

RESUMO

Metalenses consist of an array of optical nanoantennas on a surface capable of manipulating the properties of an incoming light wavefront. Various flat optical components, such as polarizers, optical imaging encoders, tunable phase modulators and a retroreflector, have been demonstrated using a metalens design. An open issue, especially problematic for colour imaging and display applications, is the correction of chromatic aberration, an intrinsic effect originating from the specific resonance and limited working bandwidth of each nanoantenna. As a result, no metalens has demonstrated full-colour imaging in the visible wavelength. Here, we show a design and fabrication that consists of GaN-based integrated-resonant unit elements to achieve an achromatic metalens operating in the entire visible region in transmission mode. The focal length of our metalenses remains unchanged as the incident wavelength is varied from 400 to 660 nm, demonstrating complete elimination of chromatic aberration at about 49% bandwidth of the central working wavelength. The average efficiency of a metalens with a numerical aperture of 0.106 is about 40% over the whole visible spectrum. We also show some examples of full-colour imaging based on this design.

6.
Nanoscale ; 8(8): 4579-87, 2016 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-26842460

RESUMO

The catalytic solid-phase synthesis of self-organized nanoporous tin sulfide (SnS) with enhanced absorption, manipulative transmittance and depolarization features is demonstrated. Using an ultralow radio-frequency (RF) sputtering power, the variation of the orientation angle between the anodized aluminum oxide (AAO) membrane and the axis of the sputtered ion beam detunes the catalytically synthesized SnS from nanorod to nanoporous morphology, along the sidewall of the AAO membrane. The ultraslow catalytic sputtering synthesis on the AAO at the RF plasma power of 20 W and the orientation angle of 0° regulates the porosity and integrality of nanoporous SnS, with average pore diameter of 80-150 nm. When transferring from planar to nanoporous structure, the phase composition changes from SnS to SnS2-Sn2S3, and the optical bandgap shrinks from 1.43 to 1.16 eV, due to the preferred crystalline orientation, which also contributes to an ultralow reflectance of <1% at 200-500 nm when both the transmittance and the surface scattering remain at their maxima. The absorption coefficient is enhanced by nearly one order of magnitude with its minimum of >5 × 10(4) cm(-1) at the wavelength between 200 and 700 nm, due to the red-shifting of the absorption spectrum to at least 100 nm. The catalytically self-organized nanoporous SnS causes strong haze and beam divergence of 20°-30° by depolarized nonlinear scattering at the surface, which favors the solar energy conversion with reduced surface reflection and enhanced photon scattering under preserved transmittance.

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