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- 实验方案
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Spin-Selective Transmission in Chiral Folded Metasurfaces
摘要： Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light-matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and bio-photonics.
关键词： sub-wavelength optics,Folded metasurface,intrinsic chirality,spin-selective transmission
更新于2025-09-23 15:23:52
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Nonlinear Optics in Dielectric Guided-Mode Resonant Structures and Resonant Metasurfaces
摘要： Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in nonlinear optics research is to realize high efficiency optical functionalities in ultra-small, sub-wavelength length scale structures by leveraging interesting optical resonances in surface relief metasurfaces. Such artificial surfaces can be engineered to support high quality factor resonances for enhanced nonlinear optical interaction by leveraging interesting physical mechanisms. The aim of this review article is to give an overview of the emerging field of nonlinear optics in dielectric based sub-wavelength periodic structures to realize efficient harmonic generators, wavelength mixers, optical switches etc. Dielectric metasurfaces support the realization of high quality-factor resonances with electric field concentrated either inside or in the vicinity of the dielectric media, while at the same time operate at high optical intensities without damage. The periodic dielectric structures considered here are broadly classified into guided-mode resonant structures and resonant metasurfaces. The basic physical mechanisms behind guided-mode resonances, electromagnetically-induced transparency like resonances and bound-states in continuum resonances in periodic photonic structures are discussed. Various nonlinear optical processes studied in such structures with example implementations are also reviewed. Finally, some future directions of interest in terms of realizing large-area metasurfaces, techniques for enhancing the efficiency of the nonlinear processes, heterogenous integration, and extension to non-conventional wavelength ranges in the ultra-violet and infrared region are discussed.
关键词： harmonic generation,guided-mode resonance,four-wave mixing,Mie scattering,optical resonances,nonlinear optics,sub-wavelength gratings,Fano resonances,optical switching
更新于2025-09-23 15:19:57
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Design of a Surface Plasmon Resonance-Enhanced ZnO Ultraviolet Photodetector Based on a Sub-wavelength Metal Grating Covered with a High-Refractive-Index Medium
摘要： To realize a surface plasmon resonance-enhanced zinc oxide (ZnO) ultraviolet photodetector based on a sub-wavelength metal grating, we take advantage of the sensitivity of the resonance condition of a sub-wavelength metal grating to the refractive index of the surrounding medium. We theoretically design a sub-wavelength Ag grating covered with a high-refractive-index medium layer and apply it to a ZnO ultraviolet photodetector. By optimizing the parameters (angle of incidence, grating period, grating spacing, grating thickness, high-refractive-index medium layer thickness, refractive index of the covering), the optical ?eld is localized at the interface of the sub-wavelength Ag grating and the ZnO thin ?lm; that is, surface plasmon resonance is realized within the device. Compared with the device without a high-refractive-index medium layer, the maximum absorption enhancement factor of the designed device can reach up to 108. This work will provide theoretical guidance to realize a surface plasmon resonance-enhanced ZnO ultraviolet photodetector with a sub-wavelength metal grating.
关键词： ultraviolet photodetector,ZnO,sub-wavelength metal grating,Surface plasmon resonance
更新于2025-09-23 15:19:57
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InGaAs Membrane Waveguide: A Promising Platform for Monolithic Integrated Mid-Infrared Optical Gas Sensor
摘要： Mid-infrared (mid-IR) absorption spectroscopy based on integrated photonic circuits has shown great promise in trace-gas sensing applications in which the mid-IR radiation directly interacts with the targeted analyte. In this paper, considering monolithic integrated circuits with quantum cascade lasers (QCLs) and quantum cascade detectors (QCDs), the InGaAs-InP platform is chosen to fabricate passive waveguide gas-sensing devices. Fully suspended InGaAs waveguide devices with holey photonic crystal waveguides (HPCWs) and sub-wavelength grating cladding waveguides (SWWs) are designed and fabricated for mid-infrared sensing at λ=6.15μm in the low index contrast InGaAs-InP platform. We experimentally detect 5 ppm ammonia with a 1 mm long suspended HPCW and separately with a 3 mm long suspended SWW, with propagation losses of 39.1 dB/cm and 4.1 dB/cm, respectively. Furthermore, based on the Beer-Lambert infrared absorption law and the experimental results of discrete components, we estimated the minimum detectable gas concentration of 84 ppb from a QCL/QCD integrated SWW sensor. To the best of our knowledge, this is the first demonstration of suspended InGaAs membrane waveguides in the InGaAs-InP platform at such a long wavelength with gas sensing results. Also, this result emphasizes the advantage of SWWs to reduce the total transmission loss and the size of the fully integrated device’s footprint by virtue of its low propagation loss and TM mode compatibility in comparison to HPCWs. This study enables the possibility of monolithic integration of quantum cascade devices with TM-polarized characteristics and passive waveguide sensing devices for on-chip mid-IR absorption spectroscopy.
关键词： sub-wavelength waveguides,gas sensing,absorption spectroscopy,photonic crystal waveguides,mid-infrared,photonics integrated circuits,quantum cascade devices,parts-per-billion
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 16th International Conference on Group IV Photonics (GFP) - Singapore, Singapore (2019.8.28-2019.8.30)] 2019 IEEE 16th International Conference on Group IV Photonics (GFP) - Sub-Decibel Off-Chip Fiber Couplers Based on L-Shaped Waveguides and Subwavelength Grating Metamaterials
摘要： Uniform grating couplers based on versatile L-shaped waveguides are experimentally demonstrated, with coupling loss of -2.7 dB and back-reflections of -20 dB. Apodized couplers with subwavelength-grating metamaterials predict improved fiber-chip coupling down to -0.46 dB within device layouts compatible with lithographic technologies available in nanophotonic foundries.
关键词： silicon-on-insulator,sub-wavelength grating metamaterials,deep-ultraviolet technology,silicon nanophotonics,grating couplers,mass-scale production
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 16th International Conference on Group IV Photonics (GFP) - Singapore, Singapore (2019.8.28-2019.8.30)] 2019 IEEE 16th International Conference on Group IV Photonics (GFP) - Sub-Decibel Off-Chip Fiber Couplers Based on Z-Shaped Waveguides and Subwavelength Grating Metamaterials
摘要： Uniform grating couplers based on versatile L-shaped waveguides are experimentally demonstrated, with coupling loss of -2.7 dB and back-reflections of -20 dB. Apodized couplers with subwavelength-grating metamaterials predict improved fiber-chip coupling down to -0.46 dB within device layouts compatible with lithographic technologies available in nanophotonic foundries.
关键词： deep-ultraviolet technology,mass-scale production,sub-wavelength grating metamaterials,silicon-on-insulator,silicon nanophotonics,grating couplers
更新于2025-09-16 10:30:52
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Metal-insulator-metal plasmonic grating filter with suppressed Rayleigh anomaly
摘要： Plasmonic grating filters can be fabricated in single lithography process and reduce the cost of colour filters used in hyperspectral cameras. Due to the presence of Rayleigh Anomaly (RA) peak, however, it has not been possible to design filter array spanning wide-spectral-range without sacrificing spectral purity. In this paper, a plasmonic grating filter design using Metal-Insulator-Metal (MIM) with suppressed RA peak is presented. Proposed filter allows extending spectral range without sacrificing spectral purity. Using proposed MIM structure, surface plasmon polariton (SPP) mode supported on air side of bottom grating structure is cancelled by second set of SPP mode on top grating structure. This allows designing filter array with improved spectral range and achieves better than 2x improvement in suppression of the Rayleigh Anomaly peak.
关键词： sub-wavelength grating,plasmonics,wavelength filtering devices
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Ultra-Deep Sub-Wavelength Mode Confinement in Graphene Waveguides
摘要： In this paper, a nano-structured device is designed using two adjacent graphene-based waveguides which is capable of con?ning an incident light-wave at the deep nano-scale. The Fermi energy of graphene in both waveguides are tuned by electrostatic gating, providing an active control on the working frequency of the device.
关键词： Fermi energy tuning,graphene waveguides,surface plasmon polaritons,ultra-deep sub-wavelength mode con?nement
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - On Chip Sub-Wavelength Grating Fabry-Perot Cavity, toward Integrated Cavity Optomechanics Applications
摘要： Sub-Wavelength Grating (SWG) periodic media are comprised of alternative dielectric layers with a pitch Λ small enough in comparison to the wavelength to supress any diffraction or interference effect. As a good first approximation, SWG media can be considered as uniform and lossless ones, with an averaging effect over the dielectric permittivity [1]. The use of SWG media as core and/or cladding materials of optical waveguides was first proposed and demonstrated in 2010 [2] as a way to realize easy engineering of the refractive guided index of light with simple lithographic patterning. Since then, SWG waveguides have found various applications such as waveguide crossing, multimode interferometers, optical filters, mid-infrared waveguides, or even optical biosensing [3]. We propose to include SWG waveguides within a suspended Fabry-Perot (FP) cavity (see Fig. 1a). The core of the cavity is formed by alternative Silicon and Air SWG layers, while the input and output mirrors are two Direct Bragg Reflectors (DBR). The whole structure is fully suspended through the use of two support arms. We present the theoretical modelization, technological realization and optical characterisations of such a cavity. The design was conducted through both an analytical model that treats SWG media with equivalent refractive indexes, and two dimensional effective index Finite-Difference Time-Domain (FDTD) simulations. Actual devices were realized on 200 mm silicon on insulator (SOI) wafers in our clean room facilities with e-beam patterning of the waveguide level, and characterized via full-scale wafer optical spectrum measurement between 1520 nm and 1580 nm. At time of writing, we measured optical quality factors of 10 000 over 2 μm long cavities. We believe this kind of suspended structure can be used in the field of Cavity Optomechanics, where an optical cavity is coupled to a mechanical resonator [4]. Indeed, because it is fully suspended, we await mechanical resonance to occur, the cavity behaving similarly to a doubly clamped holey cantilever (see Fig. 1c). Apart from the traditional optical phase shift occurring with propagation length variations of the cavity, there should also be a phase shift arising from the SWG nature of the waveguide, whose equivalent refractive index depends on the pitch Λ (and thus length) of the cavity. Due to this additional effect, we expect a strong optomechanical coupling rate.
关键词： Sub-Wavelength Grating,silicon on insulator,optical waveguides,Fabry-Perot cavity,cavity optomechanics
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Cherenkov Generation of Wideband Terahertz Radiation using a Sub-Micron LiNbO <sub/>3</sub> Slab Waveguide
摘要： Terahertz (THz) radiation is critical to the areas of security, medicine, communications, and consumer applications. THz generation is often achieved using lithium niobate, LiNbO3, since it has a high nonlinear coefficient in this regime (d33=180 pm/V [1]). Dramatic improvement to the generation efficiency has been achieved by incorporating this material into waveguiding configurations [2,3], since waveguides allow the pump pulse to remain confined over large distance (millimeters or longer). To date, waveguides investigated for THz generation utilize transverse core dimensions larger than a few microns. However, when the waveguide core is sub-wavelength with respect to the pump wavelengths, as well as the generated THz wavelengths, another benefit is observed: substantial broadening of the generated THz bandwidth. Here, we report on a sub-wavelength SiO2-LiNbO3-SiO2 slab waveguide that produces wideband THz radiation and emits it in the form of Cherenkov waves. The investigated LiNbO3 slab waveguide has transverse core dimensions of 720 nm × 4 mm and a length of 100 μm. This waveguide is excited using an electric field pulse having a duration of 50 fs and a central-wavelength of 780 nm. Figure 1(a) shows the generated THz electric field pulse, which has the short duration of <1 ps. The power spectrum of the generated THz pulse is shown in Fig. 1(b), having a central-frequency of 6.9 THz and a full-width half-maximum (FWHM) bandwidth of 2.1 THz. Notably, LiNbO3 has a strong phonon resonance at 7.6 THz [4]. However, since the generated THz radiation is emitted as Cherenkov waves, it exits the sub-wavelength LiNbO3 core after propagating a distance much less than a wavelength. This characteristic minimizes the high loss of the LiNbO3 phonon resonance, allowing for generation to occur directly at this phonon resonance. As such, the sub-wavelength nature of the LiNbO3 core allows for dramatic improvement to the THz radiation bandwidth. The data is Fig. 1 is obtained by performing finite-difference time-domain simulations. Experimental verification of this result is currently underway. In this experimental work, the LiNbO3 slab waveguide instead has a length of 1 cm and the excitation pulses will have energies ranging up to 200 nJ.
关键词： wideband THz generation,Terahertz radiation,LiNbO3,Cherenkov waves,sub-wavelength waveguide
更新于2025-09-12 10:27:22