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Terahertz spectroscopy is a perfect tool to investigate the electronic intraband conductivity of graphene, but a phenom-enological model (Drude-Smith) is often needed to describe disorder. By studying the THz response of isotropically strained polycrystalline graphene and using a fully atomistic computational approach to fit the results, we demonstrate here the connection between the Drude-Smith parameters and the microscopic behavior. Importantly, we clearly show that the strain-induced changes in the conductivity originate mainly from the increased separation between the single-crystal grains, leading to enchanced localization of the plasmon excitations. Only at the lowest strain values explored, a behavior consistent with the deformation of the individual grains can instead be observed.

The continuously increasing interest in flexible and integrated photonics requires new strategies for device manufacturing on arbitrary complex surfaces and with smallest possible size, respectively. Terahertz (THz) technology can particularly benefit from this achievement to make compact systems for emission, detection and on-demand manipulation of THz radiation. Here, we present a novel fabrication method to realize conformable terahertz metasurfaces. The flexible and versatile character of polymeric nanomembranes is combined with direct laser writing via two-photon polymerization to develop free-standing ultra-thin quasi-perfect plasmonic absorbers with an unprecedentedly high level of conformability. Moreover, revealing new flexible dielectric materials presenting low absorption and permittivity in the THz range, this work paves the way for the realization of ultra-thin, conformable hybrid or all-dielectric devices to enhance and enlarge the application of THz technologies, and flexible photonics in general.

We analyse the effect of a strong perpendicular magnetic field on an intersubband transition in a disordered doped quantum well strongly coupled to an optical cavity. The magnetic field changes the lineshape of the intersubband optical transition due to the interface roughness of the quantum well from a Lorentzian to a Gaussian one. In this regime, a novel form of magnetic-field-induced cavity protection sets in, which strongly reduces the polariton linewidth to the cavity contribution only. Implications of our results for fundamental studies of nonlinear polariton dynamics and for technological applications to polariton lasers are finally highlighted.

The electronic and optical properties of graphene can be precisely tuned by generating deterministic arrangements of strain features. In this paper, we report the formation of widespread and controlled buckling delamination of monolayer graphene deposited on hexagonal boron-nitride promoted by a significant squeezing of the graphene flake and induced by polymeric micro-actuators. The flexibility of this method offers a promising technique to create arbitrary buckling geometries and arrays of wrinkles which could also be subjected to iterative folding-unfolding cycles. Further development of this method could pave the way to tune the properties of several kinds of other two-dimensional materials, such as transition metal dichalcogenides, by tailoring their surface topography.

Terahertz radiation is extremely suitable for various imaging applications. In real life, these range from food or pharmaceutical quality control to illegal materials or human security control inspections. Despite its great potential, the wide usage and commercialization of terahertz imaging systems are still limited by the lack of compact technologies. The emerging graphene-based devices can efficiently contribute to fill this gap, offering higher versatility, scalability, and superior electronic properties compared to conventional semiconductors. In this work, we study a new scheme for realizing a multielement terahertz sensor, which is capable of multipixel parallel detection. The array consists of linearly distributed antenna-coupled graphene field-effect transistors, which are realized by exploiting a deterministic growth by chemical vapor deposition of single-crystal graphene. This novel growth technique ensures high material quality and offers large adaptability to different electronic device architectures. Relatively uniform terahertz detection performances (with a maximum homogeneity degree of 80 $\%$ ) were obtained with a maximum responsivity of the order of 1 V/W and an estimated response time in the picosecond scale. These detectors have demonstrated to fulfill several main requirements for image sensors (pixel uniformity, operability, and scalability), becoming very promising candidates for the realization of commercial high-resolution room-temperature terahertz cameras.

Defects in the lattice are of primal importance to tune graphene chemical, thermal and electronic properties. Electron-beam irradiation is an easy method to induce defects in graphene following pre-designed patterns, but no systematic study of the time evolution of the resulting defects is available. In this paper, the change over time of defected sites created in graphene with low-energy ($\leq 20$ keV) electron irradiation is studied both experimentally via micro-Raman spectroscopy for a period of $6\times 10^3$ hours and through molecular dynamics simulations. During the first 10 h, the structural defects are stable at the highest density value. Subsequently, the crystal partially reconstructs, eventually reaching a stable, less defected condition after more than one month. The simulations allow the rationalization of the processes at the atomic level and confirm that the irradiation induces composite clusters of defects of different nature rather than well-defined nanoholes as in the case of high-energy electrons. The presented results identify the timescale of the defects stability, thus establishing the operability timespan of engineerable defect-rich graphene devices with applications in nanoelectronics. Moreover, long-lasting chemical reactivity of the defective graphene is pointed out. This property can be exploited to functionalize graphene for sensing and energy storage applications., Comment: 21 pages, 5 figures

In this Letter we report the realization of a femtosecond-laser-written diode-pumped Pr:LiLuF4 visible waveguide laser. The waveguide studied in this work consisted of a depressed-index cladding, whose design and fabrication were optimized to minimize the propagation loss. Laser emission has been achieved at 604 nm and 721 nm, with output power of 86 mW and 60 mW, respectively, and slope efficiencies of 16% and 14%. In addition, we obtained, for the first time in a praseodymium-based waveguide laser, stable continuous-wave laser operation at 698 nm (3 mW of output power and 0.46% of slope efficiency), corresponding to the wavelength necessary for the clock transition of the strontium-based atomic clock. The waveguide laser emission at this wavelength is mainly in the fundamental mode (i.e., the larger propagation constant mode) showing a nearly Gaussian intensity profile.

Refractive freeform components are becoming increasingly relevant for generating controlled patterns of light, because of their capability to spatially-modulate optical signals with high efficiency and low background. However, the use of these devices is still limited by difficulties in manufacturing macroscopic elements with complex, 3-dimensional (3D) surface reliefs. Here, 3D-printed and stretchable magic windows generating light patterns by refraction are introduced. The shape and, consequently, the light texture achieved can be changed through controlled device strain. Cryptographic magic windows are demonstrated through exemplary light patterns, including micro-QR-codes, that are correctly projected and recognized upon strain gating while remaining cryptic for as-produced devices. The light pattern of micro-QR-codes can also be projected by two coupled magic windows, with one of them acting as the decryption key. Such novel, freeform elements with 3D shape and tailored functionalities is relevant for applications in illumination design, smart labels, anti-counterfeiting systems, and cryptographic communication., Comment: 31 pages, 22 figures, Advanced Materials Technologies 2022

We demonstrate a graphene-MoS2 architecture integrating multiple field-effect transistors (FETs), and we independently probe and correlate the conducting properties of van der Waals coupled graphene-MoS2 contacts with those of the MoS2 channels. Devices are fabricated starting from high-quality single-crystal monolayers grown by chemical vapor deposition. The heterojunction was investigated by scanning Raman and photoluminescence spectroscopies. Moreover, transconductance curves of MoS2 are compared with the current-voltage characteristics of graphene contact stripes, revealing a significant suppression of transport on the n-side of the transconductance curve. On the basis of ab initio modeling, the effect is understood in terms of trapping by sulfur vacancies, which counterintuitively depends on the field effect, even though the graphene contact layer is positioned between the backgate and the MoS2 channel.

Pseudo-magnetic field (PMF) in deformed graphene has been proposed as a promising and flexible method to quantum-confine electronic states and create gaps in the local density of states. Motivated by this perspective, we numerically analyze various different configurations leading to electronic localization and band flattening in periodically strained graphene. In particular, we highlight the existence of a fine structure in the pseudo-Landau levels confined in large-PMF regions, the emergence of states confined to PMF nodes as well as of snake-like orbits. In our paper, we further analyze the importance of the relative rotation and asymmetry of the strain lattice with respect to the atomic lattice and show how it can be used to modulate the PMF periodicity and to create localized orbits far from the strain points. Possible implementations and applications of the simulated structures are discussed.

We demonstrate a graphene–MoS2 architecture integrating multiple field-effect transistors (FETs), and we independently probe and correlate the conducting properties of van der Waals coupled graphene–MoS2 contacts with those of the MoS2 channels. Devices are fabricated starting from high-quality single-crystal monolayers grown by chemical vapor deposition. The heterojunction was investigated by scanning Raman and photoluminescence spectroscopies. Moreover, transconductance curves of MoS2 are compared with the current–voltage characteristics of graphene contact stripes, revealing a significant suppression of transport on the n-side of the transconductance curve. On the basis of ab initio modeling, the effect is understood in terms of trapping by sulfur vacancies, which counterintuitively depends on the field effect, even though the graphene contact layer is positioned between the backgate and the MoS2 channel.

We report on the design, fabrication by 3D printing and soft molding, and characterization of magic windows, which are 3D optical components capable of generating structured light patterns by refraction of an incident beam.

Artificial photonic materials, nanofabricated through wavelength-scale engineering, have shown astounding and promising results in harnessing, tuning, and shaping photonic beams. Metamaterials have proven to be often outperforming the natural materials they take inspiration from. In particular, metallic chiral metasurfaces have demonstrated large circular and linear dichroism of light which can be used, for example, for probing different enantiomers of biological molecules. Moreover, the precise control, through designs on demand, of the output polarization state of light impinging on a metasurface, makes this kind of structures particularly relevant for polarization-based telecommunication protocols. The reduced scale of the metasurfaces makes them also appealing for integration with nanomechanical elements, adding new dynamical features to their otherwise static or quasi-static polarization properties. To this end we designed, fabricated and characterized an all-dielectric metasurface on a suspended nanomembrane. Actuating the membrane mechanical motion, we show how the metasurface reflectance response can be modified, according to the spectral region of operation, with a corresponding intensity modulation or polarization conversion. The broad mechanical resonance at atmospheric pressure, centered at about 400 kHz, makes the metasurfaces structure suitable for high-frequency operation, mainly limited by the piezo-actuator controlling the mechanical displacement, which in our experiment reached modulation frequencies exceeding 1.3 MHz.

Nowadays, simple and non-destructive methods able to recognize pathogens in real time and in living tissues are still missing. This study has been designed to evaluate the presence of fungi (i.e. Gnomoniopsis spp.) in chestnuts. To this aim, a measurement setup based on terahertz radiation has been used to highlight the presence of fungal diseases in chestnut samples. A population of fifty chestnuts that was known to be partially infected by Gnomoniopsis spp., has been imaged in the low terahertz range by a compact and portable active imaging system equipped with a 100 GHz (0.1 THz) source. The relationship between the chestnut physical parameters, such as mass or volume, and the light attenuation in healthy and infected fruits has been tentatively explained by assuming a different water density and a different physical structure in healthy and unhealthy fruits, due to carbohydrates hydrolysis by the fungi. The preliminary results here described suggest that the sole analysis of the light attenuation combined with the measurement of weight or volume of a chestnut can provide an immediate indication of the presence of fungi in the fruits.

We present the first steps to develop radiation sensors based on the graphene field effect transistor technology. Such a sensor exploits the ambipolar behavior of graphene near its Dirac point and it is not dependent on collecting charges, but it senses ionizing radiation trough the change in conductivity of the graphene layer induced by changes of the electric field. We designed the layout of the sensors with the help of Sentaurs TCAD. We simulated static operations and the dynamic response to radiation and calculated the source–drain current through the graphene layer with a quasi-analytical model. The transistors were produced at the National Enterprise for nanoScience and nanoTechnology by depositing high quality graphene on silicon chips manufactured by the Fondazione Bruno Kessler foundry. To reduce the high contact resistance between graphene and aluminum contacts caused by oxidation of the aluminum surface, we used gold/chromium interfaces. We investigated the sensors behavior by mean of electrical measurements, extracting the graphene properties, such as mobility and doping. We observed modulation of the source–drain current, determined the Dirac point and found the optimal voltage levels to be sensitive to pulsed IR laser light and β -particles.

One of the major issues in graphene-based optoelectronics is to scale-up high-performing devices. In this work, we report an original approach for the fabrication of efficient optoelectronic devices from scalable tungsten disulfide (WS2)/graphene heterostructures. Our approach allows for the patterned growth of WS2 on graphene and facilitates the realization of ohmic contacts. Photodetectors fabricated with WS2 on epitaxial graphene on silicon carbide (SiC) present, when illuminated with red light, a maximum responsivity R ~220 A W-1, a detectivity D* ~2.0 × 109 Jones and a -3 dB bandwidth of 250 Hz. The retrieved detectivity is 3 orders of magnitude higher than that obtained with graphene-only devices at the same wavelength. For shorter illumination wavelengths we observe a persistent photocurrent with a nearly complete charge retention, which originates from deep trap levels in the SiC substrate. This work ultimately demonstrates that WS2/graphene optoelectronic devices with promising performances can be obtained in a scalable manner. Furthermore, by combining wavelength-selective memory, enhanced responsivity and fast detection, this system is of interest for the implementation of 2d-based data storage devices.

Quantum cascade lasers (QCLs) represent a most promising compact source at terahertz (THz) frequencies, but efficiency of their continuous wave (CW) operation still needs to be improved to achieve large-scale exploitation. Here, we demonstrate highly efficient operation of a subwavelength microcavity laser consisting of two evanescently coupled whispering gallery microdisk resonators. Exploiting a dual injection scheme for the laser cavity, single mode CW vertical emission at 3.3 THz is obtained at 10 K with 6.4 mA threshold current and 145 mW/A slope efficiency up to 320 μ W emitted power measured in quasi-CW mode. The tuning of the laser emission directionality is also obtained by independently varying the pumping strength between the microdisks. By connecting the resonators through a suspended gold bridge, the laser out-coupling efficiency in the vertical direction is strongly enhanced. Owing to the high brightness, low-power consumption and CW operation, the proposed microcavity laser design could allow the realization of high-performance CW THz QCLs ready for massive parallelization.

Dataset for the publication "Broadband Dynamic Polarization Conversion in Optomechanical Metasurfaces", Front. Phys. 2020,https://doi.org/10.3389/fphy.2019.00231

The development of terahertz based technology has given the opportunity for the realization of non destructive techniques capable of gaining meaningful information on delicate systems such as biological samples. Here, the health status of leaves in vivo has been monitored through a portable terahertz imaging system. The data have been extracted and analysed from the images acquired and compared with analogous results reported in the literature on similar systems. The possibilty of extracting additional information from the images regarding leaf details has also been explored.

The interaction between graphene surface plasmons and a semiconductor quantum well has been investigated by means of scattering matrix simulations. Due to the strong confinement factor of the graphene layer, a large Rabi splitting arises from the interaction with intersubband transitions. By varying the Fermi energy in the graphene and the doping in the quantum well, the resulting polariton states show features of strong and ultra-strong coupling. The system has been modeled with the coupled-mode theory to find the highest quality factor for the polariton resonance, reaching a “highly resolved” ultra-strong coupling regime.

The effectiveness of self-mixing interferometry has been demonstrated across the electromagnetic spectrum, from visible to microwave frequencies, in a plethora of sensing applications, ranging from distance measurement to material analysis, microscopy and coherent imaging. Owing to their intrinsic stability to optical feedback, quantum cascade lasers (QCLs) represent a source that offers unique and versatile characteristics to further improve the self-mixing functionality at mid infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision deeply subwalength (< {\lambda}/6000) mechanical vibrations of a suspended Si3N4-membrane used as the external element of a THz QCL feedback interferometric apparatus. Besides representing a platform for the characterization of small displacements, our self-mixing configuration can be exploited for the realization of optomechanical systems, where several laser sources can be linked together through a common mechanical microresonator actuated by radiation pressure., Comment: 5 pages, 4 figures

Actuation of thin polymeric films via electron irradiation is a promising avenue to realize devices based on strain engineered two-dimensional materials. Complex strain profiles demand a deep understanding of the mechanics of the polymeric layer under electron irradiation; in this article, we report a detailed investigation on electron-induced stress on a poly-methyl-methacrylate (PMMA) thin film material. After an assessment of stress values using a method based on dielectric cantilevers, we directly investigate the lateral shrinkage of PMMA patterns on epitaxial graphene, which reveals a universal behavior, independent of the electron acceleration energy. By knowing the stress-strain curve, we finally estimate an effective Young's modulus of PMMA on top of graphene, which is a relevant parameter for PMMA-based electron-beam lithography and strain engineering applications. Published under license by AIP Publishing.

Rare earth-doped crystals and fibers have long been used as laser active media in the UV, VIS, and NIR spectral regions, but only a limited number of materials have shown laser emission beyond 3 μm, mainly because of the competition between radiative and non-radiative processes that limit the emission efficiency of these materials at long wavelengths. The ideal material must have excellent crystal quality, good thermo-physical parameters, wide transparency region in the mid infrared (MIR) and low phonon energies. Most of the research has been focused on fluorides, bromides and chlorides [1], but these compounds are often hygroscopic and/or the optical quality of grown samples (especially chlorides and bromides) is low both for the presence of scattering centers and contamination with quenching centers.

The control of the local strain profile in 2D materials offers an invaluable tool for tailoring the electronic and photonic properties of solid-state devices. In this paper, we demonstrate a local engineering of the exciton photoluminescence (PL) energy of monolayer tungsten disulfide (WS2) by means of strain. We apply a local uniaxial stress to WS2 by exploiting electron-beam patterned and actuated polymeric micrometric artificial muscles (MAMs), which we implement onto monolithic synthetic WS2/graphene heterostructures. We show that MAMs are able to induce an in-plane stress to the top WS2 layer of the van der Waals heterostructure and that the latter can slide on the graphene underneath with negligible friction. As a proof of concept for the local strain-induced PL shift experiments, we exploit a two-MAM configuration in order to apply uniaxial tensile stress on well-defined micrometric regions of WS2. Remarkably, our architecture does not require the adoption of fragile suspended microstructures. We observe a spatial modulation of the excitonic PL energy of the WS2 monolayers under stress, which agrees with the expected strain profile and attains a maximum redshift of about 40 meV at the maximum strain intensity point. After the actuation, a time-dependent PL blueshift is observed in agreement with the viscoelastic properties of the polymeric MAMs. Our approach enables inducing local and arbitrary deformation profiles and circumvents some key limitations and technical challenges of alternative strain engineering methods requiring the 2D material transfer and production of suspended membranes., Comment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in APL and may be found at https://aip.scitation.org/doi/10.1063/1.5122262

The terahertz (THz) quantum cascade laser (QCL) provides a versatile tool in a plethora of applications ranging from spectroscopy to astronomy and communications. In many of these fields, compactness, single mode frequency emission, and low threshold are highly desirable. The proposed approach, based on line defects in a photonic crystal (PhC) matrix, addresses all these features while offering unprecedented capabilities in terms of flexibility, light waveguiding, and emission directionality. Nine line-defect QCLs were realized in a triangular lattice of pillars fabricated in the laser active region (AR), centered around ∼2 THz by tuning the photonic design. A maximal 36% threshold reduction was recorded for these ultraflat dispersion line-defect QCLs in comparison to standard metal-metal QCL. The mode selectivity is an intrinsic property of the chosen fabrication design and has been achieved by lithographically scaling the dimension of the defect pillars and by acting on the PhC parameters in order to match the AR emission bandwidth. The measured line-defect QCLs emitted preferentially in the single frequency mode in the propagation direction throughout the entire dynamic range. An integrated active platform with multiple directional outputs was also fabricated as proof-of-principle to demonstrate the potential of this approach. The presented results pave the way for integrated circuitry operating in the THz regime and for fundamental studies on microcavity lasers.

Dicationic ionic liquids (DILs) are a subclass of the ionic liquid (IL) family and are characterized by two cationic head groups linked by means of a spacer. While DILs are increasingly attracting interest due to their peculiar physico-chemical properties, there is still a lack of understanding of their intermolecular interactions. Herein, we report our investigations on the intermolecular vibrational modes of two bromide DILs and of a bistriflimide DIL. The minimal possible neutral cluster of ions was studied as a simplified model of these systems and was optimized at the DFT level. Normal modes of two sandwich-like conformers were then calculated using the harmonic approximation with analytical computation of the second derivatives of molecular energy with respect to the atomic coordinates. The calculated spectra were compared to far-infrared experimental spectra and two groups of peaks over three, for the two bromide DILs, and three over five, for the Tf2N- DIL, were described by the proposed neutral cluster model. Therefore, this model represents a reliable and computationally affordable model for the exploration of the intermolecular interactions of this kind of system.

We report spectroscopic characterization of Pr3+:Lu2O3 in the MIR region from 1 to 10 µm. Lu2O3 possesses good thermo-physical properties, has relatively low phonon energies, and can be grown in good quality. Moreover, Pr3+ ions possess several low-energy levels that in principle, can give rise to mid-infrared emission. For these reasons, we investigated this material as a potential mid-infrared emitter. From absorption measurements, we identified absorption from the first five multiplets. Moreover, low temperature measurements allowed us to extract the Stark sublevel positions of all these five multiplets and we revised the classical Dieke diagram for Pr3+ in this compound. We also observed near- and mid-infrared emission bands under diode laser pumping. The pump power dependence of the corresponding emission intensities proved the main energy transfer mechanisms that populate the lower lying levels to be cross-relaxation processes and permitted us to discern among the various possibilities and assign the different emission bands to specific transitions. In particular, we observed for the first time MIR emission at 4.4 and 7 µm in this compound, that is, in the latter case, an emission energy equal to less than three phonons in this crystal host.

The ability to drive a system with an external input is a fundamental aspect of light-matter interaction. The coherent perfect absorption (CPA) phenomenon extends to the general multibeam interference phenomenology the well known critical coupling concepts. This interferometric control of absorption can be employed to reach full delivery of optical energy to nanoscale systems such as plasmonic nanoparticles, and multi-port interference can be used to enhance the absorption of a nanoscale device when it is embedded in a strongly scattering system, with potential applications to nanoscale sensing. Here we review the two-port CPA in reference to photonic structures which can resonantly couple to the external fields. A revised two-port theory of CPA is illustrated, which relies on the Scattering Matrix formalism and is valid for all linear two-port systems with reciprocity. Through a semiclassical approach, treating two-port critical coupling conditions in a non-perturbative regime, it is demonstrated that the strong coupling regime and the critical coupling condition can indeed coexist; in this situation, termed strong critical coupling, all the incoming energy is converted into polaritons. Experimental results are presented, which clearly display the elliptical trace of absorption as function of input unbalance in a thin metallo-dielectric metamaterial, and verify polaritonic CPA in an intersubband-polariton photonic-crystal membrane resonator. Concluding remarks discuss the future perspectives of CPA with photonic structures., arXiv admin note: substantial text overlap with arXiv:1605.08906

The interplay between interference and absorption leads to interesting phenomena like coherent perfect absorption and coherent perfect transparency (CPA and CPT), which can be exploited for fully optical modulation. While it is known that it is possible to harness CPA and CPT for switching a strong signal beam with a weak control beam, it is not immediate that this process su ers from a fundamental compromise between the device e ciency (quantified by device loss and modulation depth) and the asymmetry between signal and control intensity desired for operation. This article quantifies this compromise and outlines a possible way to overcome it by means of a combination of optical gain and loss in the same photonic component. A general formulation and a specific device realization are both discussed. © 2018 Optical Society of America.

Photodetectors exploiting photoejected hot electrons have the potential to achieve ultrahigh sensitivity and broadband detection capabilities, which are controlled by the structure of the device rather than the bandgap of the employed materials. However, the achievement of photodetectors of long-wavelength photons with both high responsivity and bandwidth is still challenging. Here, a novel class of high-gain photodetectors based on the manipulation of intrinsic hot carriers by exploiting the electromagnetic engineering of a graphene-based active channel is presented. Light field is focused in a split-finger gated structure to create a potential gradient in the channel, which is able to trap and detrap the charges laterally transferred from low resistive Au-graphene interface, finally leading to a high photoconductive gain. Correspondingly, the device activity can be easily switched from photovoltaic to photoconductive, depending on the photoinduced hot-carrier distribution, just by controlling the electric field. The device shows tunable sensitivity, higher energy efficiency, and photoconductive gain. In particular, the responsivity (0.6-6.0 kV W-1) and the noise-equivalent power (less than 0.1 nW Hz-0.5 at room temperature) are significantly improved even at low-energy terahertz band with respect to state-of-the-art devices based on extrinsically coupled hot carriers operating in the near infrared. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

© 2018 OSA. We report on the development of terahertz (THz) saturable-absorbers exploiting printable graphene inks. The achieved 80% transparency modulation at 3.5 THz makes these devices potential candidates as passive components for THz solid-state lasers., EPSRC

In the present article we numerically investigated the magneto-optical behaviour of a sub-wavelength structure composed by a monolayer graphene and a metallic metasurface of optical resonators. Using this hybrid graphene-metal structure, a large increase of the non-reciprocal polarization rotation of graphene can be achieved over a broad range of terahertz frequencies. We demonstrate that the symmetry of the resonator geometry plays a key role for the performance of the system: in particular, increasing the symmetry of the resonator the non-reciprocal properties can be progressively enhanced. Moreover, the possibility to exploit the metallic metasurface as a voltage gate to vary the graphene Fermi energy allows the system working point to be tuned to the desired frequency range. Another peculiar result is the achievement of a structure able to operate both in transmission and reflection with almost the same performance, but in a different frequency range of operation. The described system is hence a sub-wavelength, tunable, multifunctional, effective non-reciprocal element in the terahertz region.

Electromagnetic fields coupled with mechanical degrees of freedom have recently shown exceptional and innovative applications, ultimately leading to mesoscopic optomechanical devices operating in the quantum regime of motion. Simultaneously, micromechanical elements have provided new ways to enhance and manipulate the optical properties of passive photonic elements. Following this concept, in this article we show how combining a chiral metasurface with a GaAs suspended micromembrane can offer new scenarios for controlling the polarization state of near-infrared light beams. Starting from the uncommon properties of chiral metasurface to statically realize target polarization states and circular and linear dichroism, we report mechanically induced, ~300 kHz polarization modulation, which favorably compares, in terms of speed, with liquid-crystals commercial devices. Moreover, we demonstrate how the mechanical resonance can be non-trivially affected by the input light polarization (and chiral state) via a thermoelastic effect triggered by intracavity photons. This work inaugurates the field of Polarization Optomechanics, which could pave the way to fast polarimetric devices, polarization modulators and dynamically tunable chiral state generators and detectors, as well as giving access to new form of polarization nonlinearities and control.

This publisher’s note corrects the funding declaration in J. Opt. Soc. Am. B 37, 19 (2020)JOBPDE0740-322410.1364/JOSAB.37.000019.