In this work, we demonstrate three ultra-compact integrated-photonics devices, which are designed via a machine-learning algorithm coupled with finite-difference time-domain (FDTD) modeling. Through digitizing the design domain into "binary pixels" these digital metamaterials are readily manufacturable as well. By showing a variety of devices (beamsplitters and waveguide bends), we showcase the generality of our approach. With an area footprint smaller than ${λ_0}^2$, our designs are amongst the smallest reported to-date. Our method combines machine learning with digital metamaterials to enable ultra-compact, manufacturable devices, which could power a new "Photonics Moore's Law."
The integration of two-dimensional (2D) periodic nanopattern defined by nanoimprint lithography and dry etching into aluminum induced crystallization (AIC) based polycrystalline silicon (Poly-Si) thin film solar cells is investigated experimentally. Compared to the unpatterned cell an increase of 6% in the light absorption has been achieved thanks to the nanopattern which, in turn, increased the short circuit current from 20.6 mA/cm2 to 23.8 mA/cm2. The efficiency, on the other hand, has limitedly increased from 6.4% to 6.7%. We show using the transfer length method (TLM) that the surface topo…
Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to mid-infrared, having an average power absorption of >95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband abs…
The interaction of light with subwavelength metallic nano-structures is at the heart of different current scientific hot topics, namely plasmonics, metamaterials and nanoantennas. Research in these disciplines during the last decade has given rise to new, powerful concepts providing an unprecedented degree of control over light manipulation at the nanoscale. However, only recently have these concepts been used to increase the capabilities of light processing in current photonic integrated circuits (PICs), which traditionally rely only on dielectric materials with element sizes larger than the …
Anomalous optical coupling properties between two silicon wires in a silicon slot waveguide embedded in epsilon-near-zero (ENZ) metamaterials are proposed and demonstrated. The dependences of optical field enhancement in the slot region and transverse optical force on the slot size and the permittivity of surrounding material are studied in details. It is demonstrated that the optical field in the slot region is significantly enhanced due to the giant index contrast at the slot interface between silicon wires and ENZ metamaterials, but the optical mode coupling between silicon wires is greatly…
Integrated mid-infrared micro-spectrometers have a great potential for applications in environmental monitoring and space exploration. Silicon-on-insulator (SOI) is a promising platform to tackle this integration challenge, due to its unique capability for large volume and low-cost production of ultra-compact photonic circuits. However, the use of SOI in the mid-infrared is restricted by the strong absorption of the buried oxide layer for wavelengths beyond 4 μm. Here, we overcome this limitation by utilizing metamaterial-cladded suspended silicon waveguides to implement a spatial heterodyne F…
We demonstrate ultrafast resonance switching of terahertz metamaterials through optical excitation of radiation damaged silicon placed in the gap of single split gap ring resonator. We observe the dynamic switching OFF of the fundamental resonance mode on a time scale of 4 picoseconds (ps) followed by the switching ON of the same resonance after 20 ps. Electric field distributions in the metamaterials unit cell derived through numerical simulations clearly support our experimental observations, showing that the high electric field at the resonator gaps, responsible for inductive-capacitive res…
Patterning the front side of an ultra-thin crystalline silicon (c Si) solar cell helps keeping the energy conversion efficiency high by compensating for the light absorption losses. A super-Gaussian mathematical expression was used in order to encompass a large variety of nanopattern shapes and to study their influence on the photonic performance. We prove that the enhancement in the maximum achievable photo-current is due to both impedance matching condition at short wavelengths and to the wave nature of light at longer wavelengths. We show that the optimal mathematical shape and parameters o…
In this letter, we study the near-field radiative heat transfer between two metamaterial substrates coated with silicon carbide (SiC) thin films. It is known that metamaterials can enhance the near-field heat transfer over ordinary materials due to excitation of magnetic plasmons associated with s polarization, while strong surface phonon polariton exists for SiC.By careful tuning of the optical properties of metamaterial it is possible to excite electrical and magnetic resonance for the metamaterial and surface phonon polaritons for SiC at different spectral regions, resulting in the enhanced…
Reconfigurable metamaterial-based apertures can play a unique role in both imaging and in beam-forming applications, where current technology relies mostly on the fabrication and integration of large detector or antenna arrays. Here, we report the experimental demonstration of a voltage-controlled, silicon-based electromagnetic metamaterial operating in the W-band (75-110 GHz). In this composite semiconductor metamaterial, patterned gold metamaterial elements serve both to manage electromagnetic wave propagation while simultaneously acting as electrical Schottky contacts that control the local…
The implementation of terahertz (THz) wafer-level metadevices is critical to advance the science for applications including (I) integrated focal plane array which can image for biology and (II) integrated narrowband absorbers for high spectral resolution THz spectroscopy. Substantial progress has been made in the development of THz metamaterials; however, a wafer-level low-stress THz metadevices platform remains a challenge. This paper experimentally demonstrates a substrate-free THz metadevices platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films, achieving an…
We numerically propose an all-dielectric hybrid metamaterial (MM) to realize all-optical switch and logic gates in shortwave infrared (SWIR) band. Such MM consists of one silicon rod and one Ge2Sb2Te5 (GST) rod pair. Utilizing the transition from amorphous to crystalline state of GST, such MM can produce electromagnetically induced transparency (EIT) analogue with active control. Based on this, we realized all-optical switching at 1500 nm with a modulation depth 84%. Besides, three different logic gates, NOT, NOR and OR, can also be achieved in this device simultaneously. Thanks to the reversi…
We propose and demonstrate subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform for the first time. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which have critical dimensions greater than 100 nm, are fabricated using a commercial rapid turn-around silicon nitride prototyping foundry process using electron beam lithography. Experimental characterizat…
A recent computational result suggests that highly confined modes can be realized by all-dielectric metamaterials (S. Jahani et. al., Optica 1, 96 (2014)). This substantially decreases crosstalk between dielectric waveguides, paving the way for high-density photonic circuits. Here, we experimentally demonstrate, on a standard silicon-on-insulator (SOI) platform, that using a simple metamaterial between two silicon strip waveguides results in about a 10-fold increase in coupling length. The proposed structure may lead to significant reduction in the size of devices in silicon photonics.
Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic co-integration. However, the large spatial extent of evanescent waves arising from nanoscale confinement, ubiquitous in silicon photonic devices, causes significant cross-talk and scattering loss. Here, we demonstrate that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves. We experimentally show the reduction of cross-talk by gr…
Flexible control of the modal confinement in silicon photonic waveguides is an appealing feature for many applications, including sensing and hybrid integration of active materials. In most cases, strip waveguides are the preferred solution to maximize the light interaction with the waveguide surroundings. However, the only two degrees of freedom in Si strip waveguides are the width and thickness, resulting in limited flexibility in evanescent field control. Here, we propose and demonstrate a new strategy that exploits metamaterial engineering of the waveguide core and cladding to control the …
The ability to exploit the on-chip nonlinear generation of new frequencies has opened the door to a plethora of applications in fundamental and applied physics. Excitation of dispersive waves is a particularly interesting process that allows efficient nonlinear wavelength conversion by phase-matching of a soliton and waves in the normal dispersion regime. However, controlling the wavelength of dispersive waves in integrated waveguides remains an open challenge, hampering versatile shaping of the nonlinear spectral response. Here, we show that metamaterial silicon waveguides release new degrees…
Large imaging arrays of detectors at millimeter and submillimeter wavelengths have applications that include measurements of the faint polarization signal in the Cosmic Microwave Background (CMB), and submillimeter astrophysics. We are developing planar lenslet arrays for millimeter-wavelength imaging using metamaterials microlithically fabricated using silicon wafers. This metamaterial technology has many potential advantages compared to conventional hemispherical lenslet arrays, including high precision and homogeneity, planar integrated anti-reflection layers, and a coefficient of thermal e…
Metamaterials and meta-surfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, nonlinear optics, and even spaser lasing. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. The simplicity of free-space light coupling into sharply-resonant meta-surfaces with high resonance quality factors Q>>1 is a significant practical advantage over the extremely angle-sensitive diffractive structures or inherently inhomogeneous high-Q …
Hyperbolic metamaterials show exceptional optical properties, such as near-perfect broadband absorption, due to their geometrically-engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high-temperature stability. In this work we examine Ag/a-Si multilayers as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations and optical spectroscopy, we map the thermal and optical instability of the metamaterials. Although the thermal instability initiat…
Metamaterials comprising assemblies of dielectric resonators have attracted much attention due to their low intrinsic loss and isotropic optical response. In particular, metasurfaces made from silicon dielectric resonators have shown desirable behaviors such as efficient nonlinear optical conversion, spectral filtering and advanced wave-front engineering. To further explore the potential of dielectric metamaterials, we present all-dielectric metamaterials fabricated from epitaxially grown III-V semiconductors that can exploit the high second-order optical susceptibilities of III-V semiconducto…
We report on the fabrication of two-dimensional periodic photonic nanostructures by nanoimprint lithography and dry etching, and their integration into a 1-μm-thin mono-crystalline silicon solar cell. Thanks to the periodic nanopatterning, a better in-coupling and trapping of light is achieved, resulting in an absorption enhancement. The proposed light trapping mechanism can be explained as the superposition of a graded index effect and of the diffraction of light inside the photoactive layer. The absorption enhancement is translated into a 23% increase in short-circuit current, as compared to…
Optical switches are one of the most important elements of integrated photonics. Here, we designed, fabricated and characterized several nanophotonic optical switches (NOSs) in silicon that exhibit ultra-compact footprint, along with excellent extinction ratios and operating bandwidths. Simulations indicate that our best device of dimensions 3umX3um and 0.3um device height can provide about 10dB extinction ratio with a bandwidth of 12nm, centered at the design wavelength of 1550nm. Three-dimensional finite-difference time-domain analysis in conjunction with a modified version of direct binary …
Using full opto-acoustic numerical simulations, we demonstrate enhancement and suppression of the SBS gain in a metamaterial comprising a subwavelength cubic array of dielectric spheres suspended in a dielectric background material. We develop a general theoretical framework and present several numerical examples using technologically important materials. For As$_2$S$_3$ spheres in silicon, we achieve a gain enhancement of more than an order of magnitude compared to pure silicon, and for GaAs spheres in silicon, full suppression is obtained. The gain for As$_2$S$_3$ glass can also be strongly …
Hyperbolic Metamaterials, as a non-magnetic anisotropic artificial structure, show metal properties in one direction and dielectric behavior in orthogonal directions. The proposed hyperbolic metamaterial filter in this project is designed with the metal wire mesh perpendicular to the alternative layers of dielectric materials, keeps TM center wavelength unchanged for the different angle of incident light in MDIR regime. The geometric size of this nanostructure is smaller than the working wavelength and supports big wavevectors due to hyperbolic dispersion. In contrast with conventional Bragg s…
Zero-index materials exhibit exotic optical properties that can be utilized for integrated-optics applications. However, practical implementation requires compatibility with complementary metallic-oxide-semiconductor (CMOS) technologies. We demonstrate a CMOS-compatible zero-index metamaterial consisting of a square array of air holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design is achieved through a Dirac-cone dispersion. The metamaterial is entirely composed of silicon and offers compatibility through low-aspect-ratio structures that can be simply fabricated in a standard …
We present optically tunable magnetic 3D metamaterials at terahertz (THz) frequencies which exhibit a tuning range of ~30% of the resonance frequency. This is accomplished by fabricating 3D array structures consisting of double-split-ring resonators (DSRRs) on silicon-on-sapphire, fabricated using multilayer electroplating. Photoexcitation of free carriers in the silicon within the capacitive region of the DSRR results in a red-shift of the resonant frequency from 1.74 THz to 1.16 THz. The observed frequency shift leads to a transition from a magnetic-to-bianisotropic response as verified thro…
Boundary-dominated optomechanics in silicon metamaterial membranes
Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Saclay（纳米科学和纳米技术中心，法国国家科学研究中心，巴黎萨克雷大学）；Telecommunication Research Institute (TELMA), Universidad de Málaga（马拉加大学电信研究所）；Photonic Systems Laboratory, École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院光子系统实验室）；National Research Council Canada（加拿大国家研究委员会）
Nanomechanical photonic metamaterials provide a wealth of active switching, nonlinear and enhanced light-matter interaction functionalities by coupling optically and mechanically resonant subsystems. Thermal (Brownian) motion of the nanostructural components of such metamaterials leads to fluctuations in optical properties, which may manifest as noise, but which also present opportunity to characterize performance and thereby optimize design at the level of individual nanomechanical elements. We show that Brownian motion in an all-dielectric metamaterial ensemble of silicon-on-silicon-nitride …
This letter proposes a 50:50 TE terahertz (THz) power splitter based on digitized metamaterials. The device is optimized using particle swarm optimization algorithm. The structure of the digitized metamaterials contains circular air holes in silicon slab which are deposited on silicon dioxide substrate. The optimized structure shows insertion loss (IL) of less than 3.9 dB over the frequency range of 0.9-1.1 THz. The proposed device has the footprint of 400 $\times$ 350 $μ$m$^2$. The proposed device has excellent merits such as compactness, efficient, all-dielectric, and compatible with CMOS fa…
Motivated by the theoretical observation that isotropic chirality can exist even in completely random systems, we design a dielectric metamaterial consisting of a random colloid of meta-atoms, which exhibits unprecedentedly high isotropic optical activity. Each meta-atom is composed of a helically arranged cluster of silicon nanospheres. Such clusters can be fabricated by large-scale DNA self-assembly techniques. It is demonstrated that the use of a high concentration of the meta-atoms in the colloid provides significant suppressions of incoherent scattering losses. As a result, the proposed s…
We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial, HMM resonator. The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitters spontaneous emission, we placed a simple gold based cyli…
Silicon photonics enables on-chip ultra-high bandwidth optical communications networks which is critical for the future of microelectronics1,2. By encoding information on-chip using multiple wavelength channels through the process of wavelength division multiplexing (WDM), communication bandwidths in excess of 1 Tbit s-1 are possible3. Already several optical components critical to WDM networks have been demonstrated in silicon, however a fully integrated multiple wavelength source capable of driving such a network has not yet been realized. Optical amplification, a necessary component for pro…
We present a theory which explains how to achieve an enhancement of nonlinear effects in a thin layer of nonlinear medium by involving a planar periodic structure specially designed to bear a trapped-mode resonant regime. In particular, the possibility of a nonlinear thin metamaterial to produce the bistable response at a relatively low input intensity due to a large quality factor of the trapped-mode resonance is shown. Also a simple design of an all-dielectric low-loss silicon-based planar metamaterial which can provide an extremely sharp resonant reflection and transmission is proposed. The…
We present a guide for the design and fabrication of a CMOS-compatible metamaterial microstructure as an absorber of visible light with exceptionally high absorption efficiency (~ 98%), for wavelengths 400nm-700nm. The structural parameters of the microstructure have been optimized by using Finite Element method (FEM) based COMSOL multyphysics software simulations. An optimized 2D unit cell of the structure consists of 4um by 160 nm TiN base on glass substrate covered with 70 nm thick silicon dioxide (SiO2). A periodic structure of titanium nitride (TiN) straps (each of 90 nm thick and 2-micro…
Tunable dielectric meta-surface nanostructures offer incredible performance in optical application due to their extraordinary tunability of the polarization and engineering the dispersion of light with low loss in infrared range. In this article, we designed and experimentally measured the tunability of all-dielectric subwavelength silicon nanoparticles with the help of the temperature-based refractive index of the liquid crystal in the telecom regime. The proposed structure composed of high dielectric nanodisk surrounded by nematic liquid crystal (NLC) is simulated with numerical software, as…
In this article, we propose and numerically analyze an all dielectric biaxial metamaterial [ADBM] constructed by multilayer pattering of a sub-wavelength ridge array of Silicon and a flat SiO2 layer. The proposed ADBM can support Dyakonov Surface Waves [DSWs] with infinite propagation length which can propagate in a wide angular domain. Though natural uniaxial and biaxial materials and also nanowire all dielectric metamaterials can also support DSWs, the angular existence domain [AED] is limited to a very narrow range. Our proposed ADBM can support can overcome this limitation and it can achie…
Photonic crystal slabs are the state of the art in studies for the light confinement, optical wave modulating and guiding, as well as nonlinear optical response. Previous studies have shown abundant real-world implementations of photonic crystals in planar optics, metamaterials, sensors, and lasers. Here, we report a novel full 2π phase control method in the reflected light beam over the interaction with a photonic crystal resonant mode, verified by the temporal coupled-mode analysis and S-parameter simulations. Enhanced by the asymmetric coupling with the output ports, the 2π phase shift can …
We present a modal analysis of metal-insulator-metal (MIM) based metamaterials in the far infrared region. These structures can be used as resonant reflection bandcut spectral filters that are independent of the polarization and direction of incidence because of the excitation of quasimodes (modes associated with a complex frequency) leading to quasi-total absorption. We fabricated large area samples made of chromium nanorod gratings on top of Si/Cr layers deposited on silicon substrate and measurements by Fourier Transform spectrophotometry show good agreement with finite element simulations.…
Manipulating the polarisation of light is crucial for sensing and imaging applications. One such aspect in particular is selective transmission of one circular polarisation (spin) when light is transmitted through a medium or a device. However, most present methods of achieving this have relatively low efficiency and selectivity, whilst high selectivity examples rely on lossy and complex three-dimensional helical or multilayer structures. Here, we propose a dielectric metamaterial approach for achieving spin-selective transmission of electromagnetic waves, utilizing spin-controlled constructiv…
In this article, a few-layered graphene-dielectric multilayer (metamaterial) electro-optic modulator has been proposed in the mid and far infrared range that works on electro-absorption mechanism. Graphene, both mono layer and few layer, is an actively tunable optical material that allows control of inter-band and intra-band transition by tuning its chemical potential. Utilizing this unique feature of graphene, we propose a multilayer graphene dielectric stack where few layer graphene is preferred over mono layer graphene. Although the total thickness of the stack still remains in the nanomete…
A 2-D photonic crystal was integrated experimentally into a thin-film crystalline-silicon solar cell of 1-μm thickness, after numerical optimization maximizing light absorption in the active material. The photonic crystal boosted the short-circuit current of the cell, but it also damaged its open-circuit voltage and fill factor, which led to an overall decrease in performances. Comparisons between modeled and actual optical behaviors of the cell, and between ideal and actual morphologies, show the global robustness of the nanostructure to experimental deviations, but its particular sensitivity…
Silicon photonic integrated circuits routinely require 3-dB optical power dividers with minimal losses, small footprints, ultra-wide bandwidths, and relaxed manufacturing tolerances to distribute light across the chip and as a key building block to form more complex devices. Symmetric Y-junctions stand out among other power splitting devices owing to their wavelength-independent response and a straightforward design. Yet, the limited resolution of current fabrication methods results in a minimum feature size (MFS) at the tip between the two Y-junction arms that leads to significant losses for …
We report on a method and an associated open source software, Fit@TDS, working on an average personal computer. The method is based on the fitting of a time-trace data of a terahertz time-domain-spectroscopy system enabling the retrieval of the refractive index of a dielectric sample and the resonance parameters of a metasurface (quality factor, absorption losses, etc.). The software includes commonly used methods where the refractive index is extracted from frequency domain data. However, these methods are limited, for instance in case of a high noise level or when an absorption peak saturate…
Optical microresonators are of paramount importance in photonic circuits requiring fine spectral filtering or resonant light recirculation. Key performance metrics improve with increasing resonance quality factor (Q) across all applications. The performance of silicon photonic circuits is often hampered by the low-quality factor of planar silicon microresonators, typically of Q~10^4-10^5. On the other hand, bulk whispering gallery mode resonators provide a wide range of materials with intriguing optical properties and exceptionally high resonant quality factors Q>10^7. However, the efficient c…
Two-dimensional hexagonal boron nitride (hBN) that hosts bright room-temperature single-photon emitters (SPEs) is a promising material platform for quantum information applications. An important step towards the practical application of hBN is the on-demand, position-controlled generation of SPEs. Several strategies have been reported to achieve the deterministic creation of hBN SPEs. However, they either rely on a substrate nanopatterning procedure that is not compatible with integrated photonic devices or utilize a radiation source that might cause unpredictable damage to hBN and underlying …
In this article, we introduce the concept of a dielectric nanolaser that is nanoscopic in all spatial dimensions. Our proposal is based on dielectric nanoparticles of high refractive index, e.g., silicon, acting as a (passive) cavity (without intrinsic gain) that is decorated with a thin film of organic gain media. Its resonance frequencies can be tuned over the entire visible range and bright and dark modes can be addressed. So called "magnetic" modes can be utilized, which makes this dielectric nanolaser a complementary source of coherent nearfields similar to the surface plasmon laser (whic…
Centre de Nanosciences et Nanotechnologies, CNRS, UMR 9001, Université Paris-Sud, Université Paris-Saclay（纳米科学与技术中心）；École Centrale de Lyon, INSA Lyon, CNRS, Université Lyon 1, CPE Lyon, INL（里昂中央理工学院）
The technologically-relevant task of feature extraction from data performed in deep-learning systems is routinely accomplished as repeated fast Fourier transforms (FFT) electronically in prevalent domain-specific architectures such as in graphics processing units (GPUs). However, electronics systems are limited with respect to power dissipation and delay, both, due to wire-charging challenges related to interconnect capacitance. Here we present a silicon photonics-based architecture for convolutional neural networks that harnesses the phase property of light to perform FFTs efficiently by exec…
Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities t…
