Optical and hybrid convolutional neural networks(CNNs)recently have become of increasing interest to achieve low-latency,low-power image classification,and computer-vision tasks.However,implementing optical nonlineari...Optical and hybrid convolutional neural networks(CNNs)recently have become of increasing interest to achieve low-latency,low-power image classification,and computer-vision tasks.However,implementing optical nonlinearity is challenging,and omitting the nonlinear layers in a standard CNN comes with a significant reduction in accuracy.We use knowledge distillation to compress modified AlexNet to a single linear convolutional layer and an electronic backend(two fully connected layers).We obtain comparable performance with a purely electronic CNN with five convolutional layers and three fully connected layers.We implement the convolution optically via engineering the point spread function of an inverse-designed meta-optic.Using this hybrid approach,we estimate a reduction in multiply-accumulate operations from 17M in a conventional electronic modified AlexNet to only 86 K in the hybrid compressed network enabled by the optical front end.This constitutes over 2 orders of magnitude of reduction in latency and power consumption.Furthermore,we experimentally demonstrate that the classification accuracy of the system exceeds 93%on the MNIST dataset of handwritten digits.展开更多
We discuss the recent advances in meta-optics and nanophotonics associated with the physics of bound states in the continuum(BICs).Such resonant states appear due to a strong coupling between leaky modes in optical gu...We discuss the recent advances in meta-optics and nanophotonics associated with the physics of bound states in the continuum(BICs).Such resonant states appear due to a strong coupling between leaky modes in optical guiding structures being supported by subwavelength high-index dielectric Mieresonant nanoantennas or all-dielectric metasurfaces.First,we review briefly very recent developments in the BIC physics in application to isolated subwavelength particles.We pay a special attention to novel opportunities for nonlinear nanophotonics due to the large field enhancement inside the particle volume creating the resonant states with high-quality(high-Q)factors,the so-called quasi-BIC,that can be supported by the subwavelength particles.Second,we discuss novel applications of the BIC physics to alldielectric optical metasurfaces with broken-symmetry meta-atoms when tuning to the BIC conditions allows to enhance substantially the Q factor of the flat-optics dielectric structures.We also present the original results on nonlinear high-Q metasurfaces and predict that the frequency conversion efficiency can be boosted dramatically by smart engineering of the asymmetry parameter of dielectric metasurfaces in the vicinity of the quasi-BIC regime.展开更多
Nonlinear optical effects have enabled numerous applications such as laserfrequency conversion, ultrafast electro-optical, and all-optical modulation. Bothgaseous and bulk media have conventionally been used for free-...Nonlinear optical effects have enabled numerous applications such as laserfrequency conversion, ultrafast electro-optical, and all-optical modulation. Bothgaseous and bulk media have conventionally been used for free-space nonlinearoptical applications, yet they often require complex phase-matching techniques forefficient operation and may have limited operation bandwidth due to the materialabsorption. In the last decade, meta-optics made of subwavelength antennas or filmshave emerged as novel nonlinear optical media that may potentially overcomecertain limitations of bulk crystals. Due to resonant enhancements of the pump laserfield as well as the use of materials with extreme nonlinearity such as epsilon-nearzeromaterials, meta-optics can achieve strong nonlinear responses with asubwavelength thickness. Here, we review several nonlinear optical applications, suchas electric-field-induced second-harmonic generation, entangled photon pairgeneration, terahertz generation, all-optical modulation, and high-harmonicgeneration that we envision meta-optics may have distinct advantages over theirbulk counterparts. We outline the challenges still faced by nonlinear meta-optics andpoint out some potential directions.展开更多
The emergence of metalenses has impacted a wide variety of applications such as beam steering,imaging,depth sensing,and display projection.Optical distortion,an important metric among many optical design specification...The emergence of metalenses has impacted a wide variety of applications such as beam steering,imaging,depth sensing,and display projection.Optical distortion,an important metric among many optical design specifications,has however rarely been discussed in the context of meta-optics.Here,we present a generic approach for on-demand distortion engineering using compound metalenses.We show that the extra degrees of freedom afforded by a doublet metasurface architecture allow custom-tailored angle-dependent image height relations and hence distortion control while minimizing other monochromatic aberrations.Using this platform,we experimentally demonstrate a compound fisheye metalens with diffraction-limited performance across a wide field of view of 140°and a low barrel distortion of less than 2%,compared with up to 22%distortion in a reference metalens without compensation.The design strategy and compound metalens architecture presented herein are expected to broadly impact metasurface applications in consumer electronics,automotive and robotic sensing,medical imaging,and machine vision systems.展开更多
Optical metasurfaces,i.e.arrays of nanoantennas with sub-wavelength size and separation,enable the manipulation of light-matter interactions in miniaturized optical components with no classical counterparts.Six decade...Optical metasurfaces,i.e.arrays of nanoantennas with sub-wavelength size and separation,enable the manipulation of light-matter interactions in miniaturized optical components with no classical counterparts.Six decades after the first ob-servation of the second harmonic generation(SHG)in bulk crystals,these devices are expected to break new ground in the field of nonlinear optics,shifting the focus from the phase matching approach achieved within long propagation dis-tances to that of near-field resonances interplay in leaky nanocavities.Here we review the recent progress in SHG with all-dielectric metasurfaces.We discuss the most used technological platforms which underpinned such advances and analyze different SHG control approaches.We finally compare their performances with other well-established technolo-gies,with the hope to delineate the current state-of-the-art and figure out a few scenarios in which these devices might soon offer unprecedented opportunities.展开更多
Endoscopes are an important component for the development of minimally invasive surgeries.Their size is one of the most critical aspects,because smaller and less rigid endoscopes enable higher agility,facilitate large...Endoscopes are an important component for the development of minimally invasive surgeries.Their size is one of the most critical aspects,because smaller and less rigid endoscopes enable higher agility,facilitate larger accessibility,and induce less stress on the surrounding tissue.In all existing endoscopes,the size of the optics poses a major limitation in miniaturization of the imaging system.Not only is making small optics difficult,but their performance also degrades with downscaling.Meta-optics have recently emerged as a promising candidate to drastically miniaturize optics while achieving similar functionalities with significantly reduced size.Herein,we report an inverse-designed meta-optic,which combined with a coherent fiber bundle enables a 33%reduction in the rigid tip length over traditional gradient-index(GRIN)lenses.We use the meta-optic fiber endoscope(MOFIE)to demonstrate real-time video capture in full visible color,the spatial resolution of which is primarily limited by the fiber itself.Our work shows the potential of meta-optics for integration and miniaturization of biomedical devices towards minimally invasive surgery.展开更多
Metasurfaces,composed of two-dimensional nanostructures,exhibit remarkable capabilities in shaping wavefronts,encompassing phase,amplitude,and polarization.This unique proficiency heralds a transformative paradigm shi...Metasurfaces,composed of two-dimensional nanostructures,exhibit remarkable capabilities in shaping wavefronts,encompassing phase,amplitude,and polarization.This unique proficiency heralds a transformative paradigm shift in the domain of next-generation optics and photonics,culminating in the development of flat and ultrathin optical devices.Particularly noteworthy is the all-dielectric-based metasurface,leveraging materials such as titanium dioxide,silicon,gallium arsenide,and silicon nitride,which finds extensive application in the design and implementation of high-performance optical devices,owing to its notable advantages,including a high refractive index,low ohmic loss,and cost-effectiveness.Furthermore,the remarkable growth in nanofabrication technologies allows for the exploration of new methods in metasurface fabrication,especially through wafer-scale nanofabrication technologies,thereby facilitating the realization of commercial applications for metasurfaces.This review provides a comprehensive overview of the latest advancements in state-of-the-art fabrication technologies in dielectric metasurface areas.These technologies,including standard nanolithography[e.g.,electron beam lithography(EBL)and focused ion beam(FIB)lithography],advanced nanolithography(e.g.,grayscale and scanning probe lithography),and large-scale nanolithography[e.g.,nanoimprint and deep ultraviolet(DUV)lithography],are utilized to fabricate highresolution,high-aspect-ratio,flexible,multilayer,slanted,and wafer-scale all-dielectric metasurfaces with intricate nanostructures.Ultimately,we conclude with a perspective on current cutting-edge nanofabrication technologies.展开更多
The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric...The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric and magnetic Mie resonances,high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications.We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the resonator’s aspect ratio varies.We demonstrate that strong mode coupling results in resonances with high-quality factors,which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference.We explain the physics of these states in terms of multipole decomposition,and show that their appearance is accompanied by a drastic change in the far-field radiation pattern.We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra.Our theoretical findings are confirmed by microwave experiments for the scattering of high-index cylindrical resonators with a tunable aspect ratio.The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-quality factors helps to extend substantially functionalities of all-dielectric nanophotonics,which opens horizons for active and passive nanoscale metadevices.展开更多
基金supported by the National Science Foundation(Grant Nos.NSF-ECCS-2127235 and EFRI-BRAID-2223495)Part of this work was conducted at the Washington Nanofabrication Facility/Molecular Analysis Facility,a National Nanotechnology Coordinated Infrastructure(NNCI)site at the University of Washington with partial support from the National Science Foundation(Grant Nos.NNCI-1542101 and NNCI-2025489).
文摘Optical and hybrid convolutional neural networks(CNNs)recently have become of increasing interest to achieve low-latency,low-power image classification,and computer-vision tasks.However,implementing optical nonlinearity is challenging,and omitting the nonlinear layers in a standard CNN comes with a significant reduction in accuracy.We use knowledge distillation to compress modified AlexNet to a single linear convolutional layer and an electronic backend(two fully connected layers).We obtain comparable performance with a purely electronic CNN with five convolutional layers and three fully connected layers.We implement the convolution optically via engineering the point spread function of an inverse-designed meta-optic.Using this hybrid approach,we estimate a reduction in multiply-accumulate operations from 17M in a conventional electronic modified AlexNet to only 86 K in the hybrid compressed network enabled by the optical front end.This constitutes over 2 orders of magnitude of reduction in latency and power consumption.Furthermore,we experimentally demonstrate that the classification accuracy of the system exceeds 93%on the MNIST dataset of handwritten digits.
基金financial support from the Australian Research Councilthe Strategic Fund of the Australian National University+3 种基金the Alexander von Humboldt Foundationfinancial support by the Russian Science Foundation(grant 18-72-10140)financial support by the Ministry of Education and Science of the Russian Federation(3.1500.2017/4.6)support from the Foundation for the Advancement of Theoretical Physics and Mathematics“BASIS”(Russia)
文摘We discuss the recent advances in meta-optics and nanophotonics associated with the physics of bound states in the continuum(BICs).Such resonant states appear due to a strong coupling between leaky modes in optical guiding structures being supported by subwavelength high-index dielectric Mieresonant nanoantennas or all-dielectric metasurfaces.First,we review briefly very recent developments in the BIC physics in application to isolated subwavelength particles.We pay a special attention to novel opportunities for nonlinear nanophotonics due to the large field enhancement inside the particle volume creating the resonant states with high-quality(high-Q)factors,the so-called quasi-BIC,that can be supported by the subwavelength particles.Second,we discuss novel applications of the BIC physics to alldielectric optical metasurfaces with broken-symmetry meta-atoms when tuning to the BIC conditions allows to enhance substantially the Q factor of the flat-optics dielectric structures.We also present the original results on nonlinear high-Q metasurfaces and predict that the frequency conversion efficiency can be boosted dramatically by smart engineering of the asymmetry parameter of dielectric metasurfaces in the vicinity of the quasi-BIC regime.
基金supported by the National Natural Science Foundation of China(NSFC)(61975251).
文摘Nonlinear optical effects have enabled numerous applications such as laserfrequency conversion, ultrafast electro-optical, and all-optical modulation. Bothgaseous and bulk media have conventionally been used for free-space nonlinearoptical applications, yet they often require complex phase-matching techniques forefficient operation and may have limited operation bandwidth due to the materialabsorption. In the last decade, meta-optics made of subwavelength antennas or filmshave emerged as novel nonlinear optical media that may potentially overcomecertain limitations of bulk crystals. Due to resonant enhancements of the pump laserfield as well as the use of materials with extreme nonlinearity such as epsilon-nearzeromaterials, meta-optics can achieve strong nonlinear responses with asubwavelength thickness. Here, we review several nonlinear optical applications, suchas electric-field-induced second-harmonic generation, entangled photon pairgeneration, terahertz generation, all-optical modulation, and high-harmonicgeneration that we envision meta-optics may have distinct advantages over theirbulk counterparts. We outline the challenges still faced by nonlinear meta-optics andpoint out some potential directions.
基金funding support provided by the Defense Advanced Research Projects Agency Defense Sciences Office Program: Enhanced Night Vision in Eyeglass Form (ENVision)
文摘The emergence of metalenses has impacted a wide variety of applications such as beam steering,imaging,depth sensing,and display projection.Optical distortion,an important metric among many optical design specifications,has however rarely been discussed in the context of meta-optics.Here,we present a generic approach for on-demand distortion engineering using compound metalenses.We show that the extra degrees of freedom afforded by a doublet metasurface architecture allow custom-tailored angle-dependent image height relations and hence distortion control while minimizing other monochromatic aberrations.Using this platform,we experimentally demonstrate a compound fisheye metalens with diffraction-limited performance across a wide field of view of 140°and a low barrel distortion of less than 2%,compared with up to 22%distortion in a reference metalens without compensation.The design strategy and compound metalens architecture presented herein are expected to broadly impact metasurface applications in consumer electronics,automotive and robotic sensing,medical imaging,and machine vision systems.
基金financial support by ANR through the NANOPAIR project.
文摘Optical metasurfaces,i.e.arrays of nanoantennas with sub-wavelength size and separation,enable the manipulation of light-matter interactions in miniaturized optical components with no classical counterparts.Six decades after the first ob-servation of the second harmonic generation(SHG)in bulk crystals,these devices are expected to break new ground in the field of nonlinear optics,shifting the focus from the phase matching approach achieved within long propagation dis-tances to that of near-field resonances interplay in leaky nanocavities.Here we review the recent progress in SHG with all-dielectric metasurfaces.We discuss the most used technological platforms which underpinned such advances and analyze different SHG control approaches.We finally compare their performances with other well-established technolo-gies,with the hope to delineate the current state-of-the-art and figure out a few scenarios in which these devices might soon offer unprecedented opportunities.
基金supported by NSF-GCR-2120774the National Science Foundation via awards NNCI-1542101 and NNCI-2025489.
文摘Endoscopes are an important component for the development of minimally invasive surgeries.Their size is one of the most critical aspects,because smaller and less rigid endoscopes enable higher agility,facilitate larger accessibility,and induce less stress on the surrounding tissue.In all existing endoscopes,the size of the optics poses a major limitation in miniaturization of the imaging system.Not only is making small optics difficult,but their performance also degrades with downscaling.Meta-optics have recently emerged as a promising candidate to drastically miniaturize optics while achieving similar functionalities with significantly reduced size.Herein,we report an inverse-designed meta-optic,which combined with a coherent fiber bundle enables a 33%reduction in the rigid tip length over traditional gradient-index(GRIN)lenses.We use the meta-optic fiber endoscope(MOFIE)to demonstrate real-time video capture in full visible color,the spatial resolution of which is primarily limited by the fiber itself.Our work shows the potential of meta-optics for integration and miniaturization of biomedical devices towards minimally invasive surgery.
基金supported by the National Key Research and Development Project of China (Nos.2022YFA1404700,2023YFB2806700,and 2021YFA1400802)National Natural Science Foundation of China (Nos.6233000076,12334016,12025402,62125501,11934012,12261131500,92250302,and 62375232)+3 种基金Shenzhen Fundamental Research Project (Nos.JCYJ20210324120402006,JCYJ20220818102218040,and GXWD20220817145518001)University Grants Committee/Research Grants Council of the Hong Kong Special Administrative Region,China (Project No.AoE/P-502/20,CRF Project Nos.C5031-22G and C1015-21E,GRF Project Nos.CityU15303521 and CityU11305223and Germany/Hong Kong Joint Research Scheme:GCityU101/22)Project of City University of Hong Kong (Nos.9380131,9610628,and 7005867).
文摘Metasurfaces,composed of two-dimensional nanostructures,exhibit remarkable capabilities in shaping wavefronts,encompassing phase,amplitude,and polarization.This unique proficiency heralds a transformative paradigm shift in the domain of next-generation optics and photonics,culminating in the development of flat and ultrathin optical devices.Particularly noteworthy is the all-dielectric-based metasurface,leveraging materials such as titanium dioxide,silicon,gallium arsenide,and silicon nitride,which finds extensive application in the design and implementation of high-performance optical devices,owing to its notable advantages,including a high refractive index,low ohmic loss,and cost-effectiveness.Furthermore,the remarkable growth in nanofabrication technologies allows for the exploration of new methods in metasurface fabrication,especially through wafer-scale nanofabrication technologies,thereby facilitating the realization of commercial applications for metasurfaces.This review provides a comprehensive overview of the latest advancements in state-of-the-art fabrication technologies in dielectric metasurface areas.These technologies,including standard nanolithography[e.g.,electron beam lithography(EBL)and focused ion beam(FIB)lithography],advanced nanolithography(e.g.,grayscale and scanning probe lithography),and large-scale nanolithography[e.g.,nanoimprint and deep ultraviolet(DUV)lithography],are utilized to fabricate highresolution,high-aspect-ratio,flexible,multilayer,slanted,and wafer-scale all-dielectric metasurfaces with intricate nanostructures.Ultimately,we conclude with a perspective on current cutting-edge nanofabrication technologies.
基金We acknowledge fruitful discussions with H.Atwater,I.V.Shadrivov,P.A.Belov,A.N.Poddubny,A.Polman,and A.Moroz.The numerical calculations were performed with support from the Ministry of Education and Science of the Russian Federation(Project 3.1500.2017/4.6)the Australian Research Council.The experimental study of the cylinder SCS in the microwave frequency range was supported by the Russian Science Foundation(17-79-20379)The analytical calculations with resonant-state expansion method were performed with support from the Russian Science Foundation(17-12-01581)。
文摘The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric and magnetic Mie resonances,high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications.We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the resonator’s aspect ratio varies.We demonstrate that strong mode coupling results in resonances with high-quality factors,which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference.We explain the physics of these states in terms of multipole decomposition,and show that their appearance is accompanied by a drastic change in the far-field radiation pattern.We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra.Our theoretical findings are confirmed by microwave experiments for the scattering of high-index cylindrical resonators with a tunable aspect ratio.The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-quality factors helps to extend substantially functionalities of all-dielectric nanophotonics,which opens horizons for active and passive nanoscale metadevices.
