This PDF file contains the front matter associated with SPIE Proceedings Volume 11290, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Recent progress of vertical-cavity surface-emitting lasers (VCSELs) using high contrast grating (HCG) and their applications will be reviewed. Replacing distributed Bragg reflectors (DBR) with a ultra-thin high contrast grating enables wavelength swept and far field pattern engineering. We will discuss review the basic concept and recent progress of HCG VCSEL arrays for phase engineering and beam steering. New applications in optical coherence tomography, 3D sensing and LIDAR will be discussed.

Standard designs for dielectric metasurfaces suffer from significant chromatic dispersion, impeding their use in broadband systems. We present a fundamental relation between ray trajectories in an optical system and its chromatic dispersion, and describe an associated design procedure to create cascaded optical systems with arbitrary dispersion. We use this procedure to design cascaded metasurface systems with various dispersive characteristics, including an achromatic metalens exploiting the orbital angular momentum of light. As experimental validation, we demonstrate beam deflectors exhibiting several different chromatic dispersions.

To date, the supersymmetric (SUSY) formalism in optics has been used to engineer the spatial distributions of refractive indices. Here, we use SUSY formalism to engineer the shape of the corrugated dielectric waveguide instead of its refractive index profile to enable the insertion of an arbitrary number of transmission peaks in the stopband. These peaks can be used to make low-power intensity-dependent optical switches. Moreover, at microwave frequencies, the embedded states can be used to design leaky wave antennas, capable of scanning continuously from forward to the backward direction through broadside without degradation in beam quality.

We review guided-mode resonant photonic lattices by addressing their functionalities and potential device applications. The 1D canonical model is rich in properties and conceptually transparent, with all the main conclusions being applicable to 2D metasurfaces and periodic photonic slabs. We explain the operative physical mechanisms grounded in lateral leaky Bloch modes. We summarize the band dynamics of the leaky stopband. With several examples, we demonstrate that Mie scattering is not causative in resonant reflection. Illustrated applications include a wideband reflector at infrared bands as well as resonant reflectors with triangular profiles. We quantify the improved efficiency of a silicon reflector operating in the visible region relative to loss reduction as realizable with sample hydrogenation. A resonant polarizer with record performance is presented.

We report metasurfaces capable of multiple frequency mixing processes of mixed nonlinear order. The metasurfaces are composed of multi-resonant metallic antennas and show prominent second harmonics, third harmonics, sum frequency generation and four-wave mixing. We report on their intrinsic efficiencies, which are surprisingly high, but with extrinsic efficiencies limited by material damage threshold due to heating. We use these wave mixers to demonstrate characterization of two unknown optical pulses at the pico-Joule level. We also explore the use of the Pancharatnam-Berry phase to control the nonlinear phase over a metasurface. This study reveals the important role that higher order multipoles play in nonlinear metasurfaces.

We demonstrate the versatility of dielectric metasurfaces to (i) shape the temporal evolution of ultrafast optical pulses, and (ii) discuss their applications towards creating integrated photonic interfaces with quantum systems.

Optical metasurfaces have shown an increasing promise to efficient nonlinear frequency conversion due to the presence of Mie-type resonances. Such enhanced nonlinear wave-mixing has opened an opportunity for frequency up-conversion of infrared images to visible in ultra-thin optical devices. Here we demonstrate GaAs metasurface infrared imaging with femtosecond time resolutions. Our results open new opportunities for the development of compact night-vision devices operating at room temperature and have multiple applications in defence and life sciences.

Recent developments in the physics of Mie-resonant high-index dielectric nanostructures suggested a promising pathway to improve efficiencies of the nonlinear light conversion beyond the limits imposed by plasmonics. Here, we employ the concept of bound states in the continuum to experimentally demonstrate a sharp enhancement of the second-harmonic generation efficiency at localized states formed via destructive interference of two leaky modes. For an AlGaAs subwavelength disk with optimized parameters, pumped with a structured light and placed on an engineered multilayered substrate, we observe the record-high conversion efficiency compared to the previous demonstrations with isolated subwavelength resonators.

Guided Mode Resonant Filters (GMRFs) have long been studied as a support surface for nonlinear optical interactions due to their intrinsically high Q-factor. However, their operation relies on a non-localized and large-area guided mode that limits the achievable power density and requires complex phase-matching approaches. Conversely, photonic crystal nano-cavities have shown promising results due to both their high-Q factors to enhance the pump field and their localized nature that allows phase-matching-free implementation and high power density excitation. However, their intrinsic small size restricts the supported input power and hinders the coupling efficiency of the pump into the mode. In this paper, we report the first experimental demonstration of continuous-wave second harmonic generation in a Cavity-Resonator Integrated Grating Filter (CRIGF). This intermediary device, which can be described as a cavity-enhanced finite-size GMRF or, equivalently, as a low-index-contrast photonic crystal micro-cavity, will be shown to offer a practical route to nonlinear interactions with viable power (<20 mW) and excitation conditions (surface excitation with a ~10-μm-waist spot size). In practice, the devices under study make use of a lithium-niobate on insulator (LNOI) waveguide with a nanostructured silicon nitride upper cladding as a pragmatic way to implement a high second-order nonlinearity platform with established processing technology. The already-demonstrated versatility of the CRIGF design (demonstrated at wavelengths of 850 nm using S₃iN₄/SiO₂ platform, 4.5 μm with the GaAs/AlGaAs technology and, here, at 1.55 μm with the LiNbO₃ platform) coupled to the electro-optical tuning afforded by lithium niobate system makes this approach extremely promising for pixelated non-linear systems.

This talk will cover our past and ongoing work on light-sensitive and tunable optical devices for sensor protection and imaging in the mid-infrared spectral range. These devices use phase-transition materials, especially vanadium dioxide, as tunable and light-sensitive elements that can be integrated with micro/nanophotonic structures. I will present optical diodes that feature asymmetric transmission, limiters based on frequency-selective surfaces, and temperature-tunable spectral filters based on thin-film stacks.

Metasurfaces can be used for free-space wavefront shaping, which can generate an arbitrary phase shift with subwavelength thickness. We designed an integrated metasurface that can achieve on-chip spatial signal convertion with a ultracompact dimension and low loss (<1dB). The dielectric metalens integration can significantly reduce the taper length as well as making mechanically robust photonic crystal coupler with high transmission. The proposed integrated metasurfaces can be easily cascaded to achieve on-chip meta-system for signal processing. Here we demonstrated a metasystem that can perform the spatial differentiation and a deep learning meta-system that can achieve wavelength demultiplexing.

An RF-Photonic phased array antenna beamformer was previously demonstrated using cascaded fiber Bragg gratings with 1 x 2 couplers for true-time-delay beamforming. This work's focus is to design, build, and test an integrated Si-photonic beamforming circuit to replace the fiber-optics system, allowing for chip-scale beamformers with low size, weight, power, and cost. Several metastructure waveguides were designed to provide a strong slowlight effect near their transmission band edge. By tuning the wavelength near the band edge, tunable optical truetime delay is achieved. We report the design, simulation, fabrication and test of these high-contrast metastructure waveguides to provide group velocity variation against wavelength near the band-edge. Wavelength-tunable delay was verified using both an interferometric approach using an integrated Mach-Zehnder interferometer, and using a direct measurement of the true-time delay of an RF signal modulated onto a C-band optical carrier. We have also designed an integrated photonic beamforming circuit for a small array, including photodetectors, fabricated by AIM Photonics. Experimental test results for those integrated photonic circuits will be discussed. We will continue to improve our integrated photonic circuit to pursue larger array implementation. The goal is to further integrate this photonic circuit with an RF phase array antenna and demonstrate the scan of an RF beam by optical control.

The advent of subwavelength dielectric gratings enables narrowband spectral filtering on a compact, low-loss, and readily fabricable platform. Subwavelength gratings realize narrow spectral features via coupling to laterally propagating leaky modes (guided mode resonance). Given their minimal number of layers and geometrically-tunable pass bands, these structures are particularly useful in infrared hyperspectral applications. We previously demonstrated long-wave IR (8 – 12 μm) infrared filters based on high-index contrast suspended silicon/air gratings. High-contrast gratings placed above a slab of the same index are zero-contrast gratings (ZCGs) and possess several advantages. In this study, we present mid-wave IR (MWIR, 3 – 6 μm) ZCG filters using air/Si/SiO₂ gratings fabricated on commercial silicon-on-insulator wafers. Geometric parameters are optimized using a genetic algorithm. We demonstrate ZCG filters with quality factors (Q) as high as 175 at oblique incidence for a 4.4 μm wavelength, and with a background high-reflectivity window from about 4.0 to 5.5 μm. The filters are optimized for coupling to light polarized with the electric field perpendicular to the gratings (transverse magnetic, TM). We also demonstrate coupling to transverse electric (TE) modes under azimuthally oblique incidence. For the same mode order, TE modes are more weakly coupled than TM, and therefore enable narrower spectral linewidths. To obtain an experimental Q of 175, full conical mounting allows strong TM mode coupling for the background reflection, and weak TE mode coupling for a narrow transmission band. Experimental results closely agree with transmittance spectra calculated via rigorous coupled wave analysis. The ZCG approach also offers a means for the design and fabrication of 2D gratings that offer polarization independent operation. We present polarization-independent filter response on square and hexagonal lattice designs.

We demonstrate photon-pair generation via spontaneous parametric down-conversion (SPDC) from two types of metasurfaces composed by AlGaAs nanocylinders: 1) monolithically fabricated on a selectively oxidized layer of AlAs epitaxially grown on a GaAs wafer; 2) fabricated by reporting the AlGaAs nanostructures on a transparent wafer via wafer bonding. In these samples, we observed SPDC both in back- and forward-scattering configurations, under excitation with a CW pump around 775 nm and single-photon detection on the signal and idler channels. The Bragg modulation of Mie-resonances enables paraxial SPDC, which demonstrates the potential of all-dielectric metasurfaces for quantum applications like on-axis quantum imaging.

I will introduce a new method for designing ultra-high efficiency metamaterials using global topology optimization networks (GLOnets). These networks combine deep generative neural networks with adjoint-based topology optimization to perform a global search and topology optimization within the design space. Importantly, these concepts utilize a population-based approach to optimize a distribution of device instances, which ensures that the full design space is properly sampled and vetted during network training. These hybrid algorithms that combine machine learning with physical calculations will set the stage for big data approaches to assist in defining the next generation of nano-based optical devices.

Valley-contrasting physics is gaining growing attraction for its potentials as a promising information carrier in electric and classical systems. In this work, we present a new realization of topological edge states based on locally defined valley-Hall effect, which enables direction-locked polarizations and robust transmission through sharp corners. Unlike existing photonic topological insulators (PTIs), the proposed implementation does not strictly demand distinct claddings (domains) across the waveguide interface. In fact, the interfaced bulks (slabs) are identical -away from the interface- and have a triangular lattice of circular air holes as in common photonic crystal (PhC) waveguides. Here, the interface is defined along a one-dimensional line created by opposite shifts of the centers of the respective unit cells on the two sides, which result in a glide-symmetric holes arrangement. The region near the interface locally lacks mirror inversion symmetry, and electromagnetic fields exhibit opposite orbital-angular-momentum states on the two sides of the interface. These observations are known to be responsible for the distinct topological phases in typical valley PTIs. In our proposed structure, it is clear that the topological modes can be understood as a result of discontinuity in the fields at the interface. Intuitively, one may also regard the proposed structure as a typical valley PhC, which is based on graphene-like lattice but with either A or B site being vanishingly small (i.e. missing). Advantageously, our proposed approach can enable robust waveguiding in a simpler implementation than current PTI designs, thus benefiting practical applications and fabrication at optical frequencies.

The work delves into designing practical finite slab implementations of PTIs that are not constrained by the requirement of a complete bandgap. These structures are characterized by a topological ‘Zak Phase’ along one axis (transverse to propagation). The interface mode is established by means of a transverse impedance match of the bandgaps on either side of the interface. If the gap impedances on both sides match, field concentration at the interface is seen while the partial gap prevents coupling to bulk bands, reflections and leakage. The proposed structure is extremely practical as it has a narrow finite width that provides a 1-D waveguide with spin momentum locking and can easily be integrated into opto-electronic systems.

Metasurfaces, especially those made from high refractive index materials, have gain notable success in recent years in different applications. Devices such as meta-gratings/lenses are usually composed of properly designed unit cells with specific phase or polarization manipulation functions. Typical design usually consists two steps: 1) rigorous analysis of the unit cells; 2) spatial arrangement of unit cells with varying structural parameters. For the intuitive correspondence relation between optical functionality and the structural parameters, it often assumes that the coupling between adjacent unit cells is negligible, which is actually a question to be verified. We will present a physical-optics-based approach to deal with the modeling of the whole metasurfaces, with a locally extended rigorous analysis of several unit cells so to include possible coupling effects, while the computational efficiency remains high. Examples on meta-gratings and lenses will be presented.

In In this paper, we show two novel approaches for photonic device optimization. Both approaches exploit the Lippmann- Schwinger equation, and can be applied with significant gains in computational efficiency when used with adjoint variable method. The first method optimizes a binarized device by greedily proposing and evaluating the effect of changing different pixels in the design region. Using the update of the Green’s function of the system with Dyson’s equation, one can guarantee the improvement of the figure of merit even for a large discrete binary change. The final structure is binary and guarantees fabricability with varying minimum feature sizes. In the second approach, we develop a fast algorithm to perform a line search for continuous optimization with gradient descent. The algorithm enables the line search to be executed faster than evaluating a new gradient, making such a line search extremely valuable. This line search is based on a Shanks transformation of the series expansion of the Lippmann-Schwinger equation, which enables us to determine the optimal learning rate in the search direction and minimize the number of separate iterations needed to achieve an optimal device.

Quantitative phase imaging systems enable label-free imaging of transparent bio-samples. Miniaturization of these imaging systems will extend their potentials in biomedical and diagnostic applications. Here, we demonstrate a novel quantitative phase gradient microscope using two multifunctional metasurface layers. Thanks to the multi-functionality and compactness of the dielectric metasurfaces, the device simultaneously captures three differential interference contrast images to retrieve a quantitative phase gradient image in a single shot. Imaging experiments with diverse phase samples verify the capability to capture quantitative phase gradient data, with low noise levels and single cell resolution.

There are two physical effects that are exploited nowadays to implement flat metalenses requiring 2𝜋-phase excursion, either subwavelength guidance implementing varying propagation delays, or resonant confinement combining two resonances. We compare both approaches and identify possible limitations with the second approach.

The recent development of efficient dielectric metasurfaces has enabled practical optical components and systems composed of multiple cascaded metasurfaces. In this talk, I present an overview of our work on modeling, design, and implementation of cascaded metasurface components and systems. In particular, I present accurate system-level models for metasurfaces, techniques for designing efficient metasurfaces, multifunctional cascaded metasurfaces, and bilayer birefringent metasurfaces that provide the ultimate control over the wavefront and polarization of light. Furthermore, I will introduce a novel technique for engineering chromatic dispersion by cascading and briefly discuss a single-snapshot hyperspectral imager enabled by cascading multiple metasurfaces.

Hyperspectral imaging divides a scene into many spectral channels with narrow spectral width. Here we present a compact hyperspectral imaging system based on dielectric metasurfaces. Our system has nine channels spanning 795 nm to 970 nm, which are arranged in a rectangular array and acquired in a single snapshot, in contrast to many commercial systems. The system's narrowband filters, necessary for hyperspectral operation, also reduce chromatic aberration, a common problem in metasurface imaging systems. The small footprint of the device (2.5 mm × 2.5 mm × 1.5 mm) facilitates its potential integration into a handheld system (e.g., a mobile phone).

We use the chromaticism induced by the resonance of Metal-Insulator-Metal structure and the interaction surface which is greater than the geometrical surface of the nano-rod to combine locally different dimensions of nano-antennas in order to create two optical functions on the same surface. The purpose is to create a phase mask that spread a point source reflected by our system so that at 3 μm this point is horizontally duplicated and vertically at 5 μm. Thus our device changes color information into shape information which permitted another way to differentiate infrared signature of objects.

We proposed and experimentally demonstrated a new method to engineer ultra-high efficiency and linear polarization achromatic meta-lens from visible to telecommunication wavelength: 660 nm to 1200 nm with 90 % efficiency. Our proposed method is a promising approach for broadband structured interfaces. This new design surpasses the current state of the art of metalens which is mainly focus on circular polarization with limited bandwidth and efficiency.

Transmissive and reflective all-dielectric metastructures will be presented that offer tailored polarization con- versions and spectral responses. The metastructures consist of stacked deeply subwavelength, high contrast gratings of different fill factors and rotations. Broadband metastructures that perform a given polarization conversion over a wide continuous bandwidth will be shown, as well as multiband metastructures that perform a common polarization conversion over different bands. Multifunctional metastructures that realize different polarization conversions over different bands will also be reported at the conference. Unlike earlier stacked grating geometries, the transmissive metastructures do not require antireflection layers since impedance matching is incorporated into their design. The subwavelength gratings are modeled as homogeneous anisotropic layers, allowing an overall metastructure to be treated as a stratified dielectric medium. Quasi-static analysis is used to homogenize the subwavelength gratings and represent them with effective dielectric constants. Plane-wave transfer matrix techniques are employed to model the interactions between gratings, allowing for rapid design and optimization. In the metastructures, higher-order Floquet harmonics are bound to the gratings due to their subwavelength periodicities. As a result, only zeroth-order coupling between the gratings needs to be considered. The multifunctional performance and compactness (wavelength-sized thickness) of the proposed devices will find use at millimeter-wave wavelengths and beyond. Two example designs are described in this paper. Measured performance of prototypes will also be reported at the conference and various fabrication approaches reviewed. This work demonstrates the flexibility with which cascaded subwavelength gratings can realize unprecedented polarization control with varied spectral responses.

The functionality of biomolecules is largely relevant to their structural chirality, especially the handedness. Discriminating between enantiomers, namely mirror-imaged chiral molecule pairs, and physically separating them are thus vitally important in life sciences. However, completing these tasks by an optical means is very challenging, because the molecular chirality is intrinsically weak. Here we numerically study a design of dielectric metasurfaces for enhancing the near-ultraviolet circular dichroism of chiral molecules and for enantioselective separation of chiral nanoparticles by optical forces. The proposed device can also function as a helicity-preserving meta-mirror. Our findings may pave the way toward practical chiroptical devices.

Metasurface optics provide an ultra-thin alternative to conventional refractive lenses. A present challenge is in realizing metasurfaces that exhibit tunable optical properties and achromatic behavior across the visible spectrum. I will discuss the design, fabrication, and characterization of metasurface lenses ("metalenses") that use asymmetric TiO2 nanostructures to induce a polarization-dependent optical response. These metalenses were used to demonstrate varifocal color imaging with white light from a halogen source. I will also provide an update on our efforts to fabricate stacked metasurfaces with multiple interacting layers that may offer enhanced performance across the visible spectrum.

High contrast gratings (HCGs) are nowadays very popular in research due to small dimensions and their highly reflective or transmissive properties. By proper alignment of HCG bars they may become focusing reflectors or lenses. Here we present simulations of GaAs-based planar focusing reflectors realized by monolithic HCGs. We present how to design focusing reflectors and discuss how to tune their reflectivity.

We demonstrate a free-space amplitude modulator for mid-IR radiation ( λ around 10 µm) that can operate up at least 400 MHz (-3dB cut-off at ∼100/150 MHz) and at room-temperature. The device is based on a semiconductor hetero-structure enclosed in a judiciously designed optical resonator based on a metallic meta-surface. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime: the important change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR laser source up to at least 400 MHz .

We design and process more than 100 different 980 nm MHCG mirror designs, to determine optimal parameters for the use of the MHCGs as mirrors for VCSELs. We present measured power reflectance spectra and compare the results to our with numerical simulations. We discuss the impact of the actual processed geometric shape of the MHCG stripes on the measured power reflectance of the MHCGs..

Transparent electrodes are essential components of optoelectronic devices, however, increasing requirements with respect to transmission at a level approaching 100% and sheet resistance below 1 Sq-1 are still a challenge. In this talk, we show that monolithic deep-subwavelength grating integrated with metal enables to reach those requirements for broad spectrum of polarized light. It facilitates injection of very high current densities exceeding 20 kA cm-2 not causing noticeable heat generation that meets the requirements of the most demanding optoelectronic devices such as semiconductor lasers.

Two major trends in dielectric nanoantenna research related to achieving their active and tunable functionalities will be discussed. Interfacing of dielectric nanoantennas with light emitters provides opportunities to enhance their emission and shape its directivity. By making the nanoantennas themselves out of active III-V semiconductor materials, lasing action with controllable directionality can be achieved. On the other hand, by endowing nanoantennas with tuneable properties dynamic control of light wavefront can be achieved pawing way to spatial light modulators with sub-micrometre resolution.

An electrically tunable filter based on a plasmonic phase retarder and liquid crystal cells is reported. The plasmonic phase retarder consists of a periodic array of deep-subwavelength metallic nanostructures. A first entrance polarizer prepares the incident light in a polarization state oriented at 45° from the nanowires orientation. A strong phase retardation between TM and TE polarizations is induced by the plasmon resonances. A polarization analyzer based on liquid crystal cells allows to project the transmitted light onto a polarization state whose orientation depends on the applied voltage. Using this approach, a range of 8V is enough to span more than 70% of the area covered by standard RGB filters in CIE color coordinates with a single filter, including yellow, orange, red, magenta, purple, blue, cyan and green as well as different tones of white. In order to ensure the applicability to large area production, UV nanoimprint lithography (UV-NIL) and thin film coatings have been used to fabricate the plasmonic phase retarder. The evaporation is performed with an angle, so that a self-shadowing effects prevents full coverage of the surface. The resulting structure consists in a periodic array of silver nanowires. Multiple interfering resonances are observed so that the nominal transmission can reach levels above 70%. The construction of the colors transmitted by the tunable filter is modeled and validated through a series of optical characterization of the individual elements.

Metasurfaces manipulate light through engineering the amplitude, phase and polarization across arrays of meta-atom antenna resonators. Adding tunability and active functionality to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, LIDAR, tunable metalenses, reconfigurable meta-holograms and many more. We present here high-index reconfigurable meta-atoms, resonators and metasurfaces that can dynamically and continuously tune their frequency, amplitude and phase, across the infrared spectral ranges. We utilize narrow linewidth resonances along with peak performance of tunable mechanisms for efficient and practical reconfigurable devices.

In this talk, we will present our recent results towards dynamic control of individual dielectric nanoantennas. The goal is to develop a platform enabling the new generation of Spatial Light Modulators with sub-wavelength pixel size for visible light applications. In particular, we will present a transmissive device based on resonant titanium dioxide nanoantennas embedded in liquid crystals, with a pixel size of only one micrometer and operating at a wavelength og 660 nm. We demonstrate full re-configurability of the device via dynamic beam steering, with as large as 40% diffraction efficiency with respect to incident light and more than 20 degrees field of view. We will also show future prospects to further increase this efficiency and further miniaturize the pixel size.

In this talk, we present and discuss our recent advances on meta-gratings, in particular their tunability and nonlinearity enabled by their implementation with TMD materials. We have recently shown that gradient metasurfaces suffer from fundamental limits on the overall efficiency of wavefront manipulation. To overcome this issue, we have introduced the concept of meta-gratings, formed by periodic arrays of carefully tailored bianisotropic inclusions. This concept enables wavefront engineering with unitary efficiency and significantly lower fabrication demands both in transmission and reflection. Beyond beam-steering, we have also shown metagratings for focusing and lensing. In this work, we extend these concepts to tunable, highly non-linear and/or non-reciprocal metasurfaces based on TMD materials, exploiting the unusual light-matter interactions enabled by exciton-photon coupling in these materials. We discuss the broad opportunities of this material platform for metasurfaces.

In this paper, we proposed and theoretically simulated the tunable all-dielectric metasurface by varying the bisecting angular gap. The Fano-resonance position for the proposed silicon-on-silica structure shows the blue-shift with an increase in the angular gap. We have also observed the steep rise in the linewidth (FWHM) due to the increase in the angular gap. Such designs of the metasurfaces can provide a customized solution for various applications like modulator, filter, biochemical sensors.

We demonstrate how to tailor the size-dependent enhanced transmission and absorption of 1D subwavelength semiconductor-based metamaterial high contrast gratings. We focus on 3 spectral regimes generic for most semiconductors, where the refractive index (n) and extinction coefficient (k) of the semiconducting material satisfy the following conditions: n >> k, n ~ k and n < k. We show that the transmission into such structures can be enhanced by reducing the bar width, increasing the grating period, or tapering the grating sidewalls. Moreover, thanks to the slow-light phenomenon, the absorption of the grating can be enhanced as compared to bulk semiconductors.

Quadriwave lateral shearing interferometry (QWLSI) is a wave front sensing technology based on the analysis of an interferogram created by waves diffracted by an optical grating set in front of a camera sensor. Since QWLSI is a single-arm interferometry modality is has the advantage of being very compact, robust and easy to implement. It enables to achieve a phase resolution of 5nm. In this paper, we will describe the QWLSI system and apply it to metasurface shape and laser-induced refractive index variation measurements like waveguides and LIDT.

Silicon photonics has emerged as an intense field of research due to its unique capabilities to integrate photonics and electronics into the same platform using standard semiconductor fabrication facilities. Subwavelength grating (SWG) structures, i.e. periodic nanostructured waveguides with a pitch below half the wavelength of light, allow the lossless propagation of Bloch-Floquet modes which closely resemble propagation through a homogenous waveguide with optical properties (refractive index, dispersion, birefringence) that can be tailored to fulfill specific design goals. SWG engineering is now routinely used for novel and advanced device design. Fiber-chip couplers, polarization and mode multiplexers, multimode interference couplers (MMIs), lenses, and bragg filters have been successfully designed in our group based in these concepts. In this invited talk we will review some of our last advances in the field.

Microcavities using high mechanical quality suspended thin films as flexible mirrors can be exquisitely sensitive to gas or radiation pressure changes. We demonstrate how to directly pattern thin (200 nm), suspended silicon nitride membranes with subwavelength gratings in order to enhance their reflectivity. We discuss how using such nanostructured trampolines to form ultrashort microcavities may lead to a combination of small modevolume and remarkably narrow linewidth which is interesting for improving the sensitivity of optical sensors or for cavity optomechanics. Using high mechanical quality nanotrampolines to form few-micron long sandwiches we realize squeeze film pressure sensors in which the modifications of their vibrations due to the compression of the gas between them are measured optically and whose state-of-the-art responsitivity and sensitivity are promising for absolute pressure measurements in the free molecular flow regime.

Artificial subwavelength dielectric meta-lens (ML), realization of ultrathin and light-weight, provides a potential candidate to replace traditional bulky curved lens with high image quality. A ML with 1.5 mm in diameter having numerical aperture NA ~ 0.60 at the near-infrared wavelength λ = 0.94 μm was designed by finite-difference timedomain (FDTD) method with speeding up optimization of MLs’ scheme by deep neural network (DNN) model. Additionally, an ultra-thin high NA ML was achieved by cost effective semiconductor manufacturing technology. The fabricated ML can focus an incident light down to a spot as small as ~ 5.2 μm with high optical efficiency of ~88.4% (focusing efficiency achieved 23.7%). We also provided efficient MLs’ semiconductor manufacturing technology for the development of optical device in the near-infrared image technology.

Plasmonic metamaterial is a new class science which can regulate the electromagnetic response characteristics, including frequency, phase and polarization characteristics, by the specific design of structure and distribution of materials. But how to design the structure and material effectively becomes a issue worth studying. Inverse design has experienced rapid development in the past 20 years. When we applied some algorithms into the design of metamaterial, the efficiency can be improved greatly. In this paper, we proposed and improved a fully automatic genetic algorithm for the optimization of polarization-selective broadband absorber for 3μm-5μm, and we successfully achieved an average absorption of up to 0.7522 in 3-5um for transverse magnetic wave.