光学超构表面原理与应用

Abstract: Metasurfaces are subwavelength structured thin films consisting of arrays of units that allow the control of polarization, phase, and amplitude of light over a subwavelength thickness. Recent developments in topological photonics have greatly broadened the horizon in designing metasurfaces for novel functional applications. In this review, we summarize recent progress in the research field of topological metasurfaces, first from the perspectives of passive and active in the classical regime, and then in the quantum regime. More specifically, we begin by examining the passive topological phenomena in TWo-dimensional photonic systems, including both time-reversal broken systems and time-reversal preserved systems. Subsequently, we discuss the cutting-edge studies of active topological metasurfaces, including nonlinear topological metasurfaces and reconfigurable topological metasurfaces. After overviewing topological metasurfaces in the classical regime, we show how they could provide a new platform for quantum information and quantum many-body physics. Finally, we conclude and describe some challenges and future directions of this fast-evolving field.

Abstract: The field of metasurface research has rapidly developed in the past decade. Electron-beam lithography (EBL) is an excellent tool used for rapid prototyping of metasurfaces. However, Gaussian-beam EBL generally struggles with low throughput. In conjunction with the recent rise of interest in metasurfaces made of low-index dielectric materials, we propose in this study the use of a relatively unexplored chemically amplified resist, SU-8 with EBL, as a method for rapid prototyping of low-index metasurfaces. We demonstrate the use of SU-8 grating on silicon for cost-efficient fabrication of an all-dielectric multilevel security print for anti-counterfeiting purposes, which encrypt different optical information with different light illumination conditions, namely, bright-field reflection, dark-field reflection, and cross-polarized reflection. The large-scale print (1 mm2) could be exposed in a relatively short time (∼11 min) due to the ultrahigh sensitivity of the resist, while the feature size of ∼200 nm was maintained, demonstrating that SU-8 EBL resist serves as a good candidate for rapid prototyping of metasurface designs. Our results could find applications in the general area of increasing EBL patterning speed for a variety of other devices and structures.

Abstract: Multi-dimensional optical imaging systems that simultaneously gather intensity, depth, polarimetric, and spectral information have numerous applications in medical sciences, robotics, and surveillance. Nevertheless, most current approaches require mechanical moving parts or multiple modulation processes and thus suffer from long acquisition time, high system complexity, or low sampling resolution. Here, a methodology to build snapshot multi-dimensional lensless imaging is proposed by combining planar-optics and computational technology, benefiting from sufficient flexibilities in optical engineering and robust information reconstructions. Specifically, a liquid crystal diffuser based on geometric phase modulation is designed to simultaneously encode the spatial, spectral, and polarization information of an object into a snapshot detected speckle pattern. At the same time, a post-processing algorithm acts as a special decoder to recover the hidden information in the speckle with the independent and unique point spread function related to the position, wavelength, and chirality. With the merits of snapshot acquisition, multi-dimensional perception ability, simple optical configuration, and compact device size, our approach can find broad potential applications in object recognition and classification.

Abstract: Integrated optical phased arrays (OPAs) have attracted significant interest to steer laser beams for applications including free-space communications, holography, and light detection and ranging. Although many methods have been proposed to suppress grating lobes, OPAs have also been limited by the trade-off between field of view (FOV) and beamforming efficiency. Here, we propose a metasurface empowered port-selected OPA (POPA), an OPA steered by port selection, which is implemented by an aperiodic waveguide array with an average pitch less than the wavelength and phase controlled by coupling among waveguides. A metasurface layer above the POPA was designed to increase wide FOV steering, aliasing-free by polarization division. As a result, we experimentally demonstrate beam scanning over a±41.04°×7.06°±41.04°×7.06° FOV. The aliasing-free POPA with expanded FOV shows successful incorporation of the waveguide-based OPA technique with an emerging metasurface design, indicating much exploration in concepts for integrated photonic devices.

Abstract: We theoretically and experimentally demonstrate an RGB achromatic metalens that operates concurrently at three visible wavelengths (λ=450, 532, and 700 nm) with a high numerical aperture of 0.87. The RGB metalens is designed by simple integration of metalens components with the spatial interleaving method. The simulated spatial interleaving metalens shows RGB achromatic operation with focusing efficiencies of 25.2%, 58.7%, and 66.4% at the wavelengths of 450, 532, and 700 nm, respectively. A 450 μm diameter metalens operating at three designated wavelengths is fabricated with low-loss hydrogenated amorphous silicon. The fabricated metalens has the measured focusing efficiencies of 5.9%, 11.3%, and 13.6% at λ=450, 532, and 700 nm, respectively. The Strehl ratios of 0.89, 0.88, and 0.82 are obtained at given wavelengths, which show a capability of diffraction-limited operation.

Abstract: Spin splitting of light originates from the interplay between the polarization and spatial degrees of freedom as a fundamental constituent of the emerging spin photonics, providing a prominent pathway for manipulating photon spin and developing exceptional photonic devices. However, previously relevant devices were mainly designed for routing monotonous spin splitting of light. Here, we realize an oscillatory spin splitting of light via metasurface with two channel Pancharatnam–Berry phases. For the incidence of a linearly polarized light, the concomitant phases arising from opposite spin states transition within pathways of the metasurface induce lateral spin splitting of light with alternately changed transport direction during beam guiding. We demonstrate the invariance of this phenomenon with an analogous gauge transformation. This work provides a new insight on steering the photon spin and is expected to explore a novel guiding mechanism of relativistic spinning particles, as well as applications of optical trapping and chirality sorting.

Abstract: High-performance solid-state quantum sources in the telecom band are of paramount importance for long-distance quantum communications and the quantum Internet by taking advantage of a low-loss optical fiber network. Here, we demonstrate bright telecom-wavelength single-photon sources based on In(Ga)As/GaAs quantum dots (QDs) deterministically coupled to hybrid circular Bragg resonators (h-CBRs) by using a wide-field fluorescence imaging technique. The QD emissions are redshifted toward the telecom O-band by using an ultra-low InAs growth rate and an InGaAs strain reducing layer. Single-photon emissions under both continuous wave (CW) and pulsed operations are demonstrated, showing high brightness with count rates of 1.14MHz and 0.34 MHz under saturation powers and single-photon purities of g⁽²⁾(0)=0.11±0.02 (CW) and g⁽²⁾(0)=0.087±0.003 (pulsed) at low excitation powers. A Purcell factor of 4.2 with a collection efficiency of 11.2%±1%11.2%±1% at the first lens is extracted, suggesting efficient coupling between the QD and h-CBR. Our work contributes to the development of highly efficient single-photon sources in the telecom band for fiber-based quantum communication and future distributed quantum networks.

Abstract: Active devices have drawn considerable attention owing to their powerful capabilities to manipulate electromagnetic waves. Fast and periodic modulation of material properties is one of the key obstacles to the practical implementation of active metamaterials and metasurfaces. In this study, to circumvent this limitation, we employ a cascaded phase-matching mechanism to amplify signals through spatiotemporal modulation of permittivity. Our results show that the energy of the amplified fundamental mode can be efficiently transferred to that of the high harmonic components if the spatiotemporal modulation travels at the same speed as the signals. This outstanding benefit enables a low-frequency pump to excite parametric amplification. The realization of cascaded parametric amplification is demonstrated by finite-difference time-domain (FDTD) simulations and analytical calculations based on the Bloch–Floquet theory. We find that the same lasing state can always be excited by an incidence at different harmonic frequencies. The spectral and temporal responses of the space-time modulated slab strongly depend on the modulation length, modulation strength, and modulation velocity. Furthermore, the cascaded parametric oscillators composed of a cavity formed by photonic crystals are presented. The lasing threshold is significantly reduced by the cavity resonance. Finally, the excitation of cascaded parametric amplification relying on the Si-waveguide platform is demonstrated. We believed that the proposed mechanism provides a promising opportunity for the practical implementation of intense amplification and coherent radiation based on active metamaterials.

Abstract: Integrated optical phased arrays (OPAs) have attracted significant interest to steer laser beams for applications including free-space communications, holography, and light detection and ranging. Although many methods have been proposed to suppress grating lobes, OPAs have also been limited by the trade-off between field of view (FOV) and beamforming efficiency. Here, we propose a metasurface empowered port-selected OPA (POPA), an OPA steered by port selection, which is implemented by an aperiodic waveguide array with an average pitch less than the wavelength and phase controlled by coupling among waveguides. A metasurface layer above the POPA was designed to increase wide FOV steering, aliasing-free by polarization division. As a result, we experimentally demonstrate beam scanning over a ±41.04°×7.06°±41.04°×7.06° FOV. The aliasing-free POPA with expanded FOV shows successful incorporation of the waveguide-based OPA technique with an emerging metasurface design, indicating much exploration in concepts for integrated photonic devices.