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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.

Correcciones en el texto del artículo original., We report on a minor correction in our article: “High frequency mechanical excitation of a silicon nanostring with piezoelectric aluminum nitride layers”...

Metamaterials are structures engineered at a small scale with respect to the wavelength of the excitations they interact with. These structures behave as artificial materials whose properties can be chosen by design, mocking and even outperforming natural materials and making them the quintessential tool for manipulation of wave systems. In this Letter we show how the acoustic properties of a silicon nitride membrane can be affected by nanopatterning. The degree of asymmetry in the pattern geometry induces an artificial anisotropic elasticity, resulting in the splitting of otherwise degenerate mechanical modes. The artificial material we introduce has a maximum Ledbetter-Migliori anisotropy of 1.568, favorably comparing to most bulk natural crystals. With an additional freedom in defining arbitrary asymmetry axes by pattern rotation, our approach can be useful for fundamental investigation of material properties as well as for devising improved sensors of light, mass or acceleration based on micromechanical resonators.

Enhancing the resolution of 3D patterning techniques in functional soft polymers enlarges the application areas of responsive shape-changing materials, for tunable nanophotonics and nanorobotics. Thanks to the recent advances of polymer science, the palette of available materials for nanomanufacturing is becoming wider and wider--although the comprehension of their polymerization process by two-photon polymerization is still incomplete. In this work, both shrinking of the minimal polymerizable unit and a significant improvement of the mechanical stability of microstructured soft polymers, in particular of liquid crystalline networks, are demonstrated. To this aim, temperature control enhances the resolution and reduces the swelling of the polymerized structures, thus avoiding deviations of the final structure from the intended design. This fine control on the nanoscale features enables the use of soft responsive materials not only for bulky microelements, but also for high-resolution structures with more complex design.

Symmetry principles and theorems are of crucial importance in optics. Indeed, from one side, they allow obtaining direct insights into phenomena by eliminating unphysical interpretations; from the other side, they guide the designer of photonic components by narrowing down the parameter space of design variables. In this Letter, we illustrate a significant departure from the Babinet spectral complementarity in a very common and technologically relevant situation: that of a patterned conducting screen placed on a subwavelength dielectric slab. The symmetry property predicted by the Babinet theorem is correctly recovered for pairs of geometrically complementary–but less realistic in terms of applications–free-standing patterned screens. Our analysis merges experimental data with fully vectorial electromagnetic modeling and provides an alternative form of the Babinet theorem that highlights a connection with the concept of electromagnetic duality.

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

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.

A strong trend for quantum-based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nanomechanical devices are particularly suitable for hybrid integration due to the ease of fabrication at multiscales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, surface acoustic waves (SAWs) are injected in the Si layer where the material has been locally patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we find an external excitation peak efficiency in excess of 500 pm/V at 1-GHz mechanical frequency. Exploiting the long-term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a candidate for hybrid quantum systems., This work is supported by the FET-Open PHENOMEN project (GA 713450). D.N.U. gratefully acknowledges funding from a Ramon y Cajal postdoctoral fellowship (RYC-2014-15392).

Amplitude and phase are the basic properties of every wave phenomena; as long as optical waves are concerned, the ability to act on these variables is at the root of a wealth of switching devices. To quantify the performance of an optical switching device, an essential aspect is to determine the tradeoff between the insertion loss and the amplitude or phase modulation depth. Here it is shown that every switching optical device is subject to such a tradeoff, intrinsically connected to the dielectric response of the materials employed inside the switching element itself. This limit finds its roots in fundamental physics, as it directly derives from Maxwell's equations for linear dielectrics, and is hence applicable to a wide class of optical components. Furthermore it results that concepts as filtering, resonance and critical coupling could be of advantage in approaching the limit.

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 transversal concepts of weak, strong and critical coupling, and of Fano resonances, are analyzed within a unified framework which relies on a simple classical model of driven-dissipative coupled oscillators. A careful exploration of the system’s parameter space has led to the emergence of certain intriguing phenomena, which we named lineshape inheritance, universal absorption lineshape, and strong critical coupling. These concepts may be of relevance when attempting to understand the response of a diversity of systems, especially in the fields of (quantum) light-matter coupling, and of solid-state nanophysics, where the basic scheme of multi-oscillator dissipative resonances is often encountered.

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.

Materials of which the optical response is determined by their structure are of much interest both for their fundamental properties and applications. Examples range from simple gratings to photonic crystals. Obtaining control over the optical properties is of crucial importance in this context, and it is often attempted by electro-optical effect or by using magnetic fields. In this paper, we introduce the use of light to switch and tune the optical response of a structured material, exploiting a physical deformation induced by light itself. In this new strategy, light drives an elastic reshaping, which leads to different spectral properties and hence to a change in the optical response. This is made possible by the use of liquid crystalline networks structured by Direct Laser Writing. As a proof of concept, a grating structure with sub-millisecond time-response is demonstrated for optical beam steering exploiting an optically induced reversible shape-change. Experimental observations are combined with finite-element modeling to understand the actuation process dynamics and to obtain information on how to tune the time and the power response of this technology. This optical beam steerer serves as an example for achieving full optical control of light in broad range of structured optical materials.

In this contribution, a rigorous numerical calibration is proposed to characterize the excitation of propagating mechanical waves by interdigitated transducers (IDTs). The transition from IDT terminals to phonon waveguides is modeled by means of a general circuit representation that makes use of Scattering Matrix (SM) formalism. In particular, the three-step calibration approach called the Thru-Reflection-Line (TRL), that is a well-established technique in microwave engineering, has been successfully applied to emulate typical experimental conditions. The proposed procedure is suitable for the synthesis/optimization of surface-acoustic-wave (SAW) based devices: the TRL calibration allows to extract/de-embed the acoustic component, namely resonator or filter, from the outer IDT structure, regardless of complexity and size of the letter. We report, as a result, the hybrid scattering parameters of the IDT transition to a mechanical waveguide formed by a phononic crystal patterned on a piezoelectric AlN membrane, where the effect of a discontinuity from periodic to uniform mechanical waveguide is also characterized. In addition, to ensure the correctness of our numerical calculations, the proposed method has been validated by independent calculations.

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.

In this article we demonstrate that a grating fabricated through nanoscale volumetric crosslinking of a liquid crystalline polymer enables remote polarization control over the diffracted channels. This functionality is a consequence of the responsivity of liquid crystal networks upon light stimuli. Tuning the photonic response of the device is obtained thanks to both a refractive index and a shape change of the grating elements induced by a molecular rearrangement under irradiation. In particular, the material anisotropy allows for nontrivial polarization state management over multiple beams. Absence of any liquid component and a time response down to 0.2 milliseconds make our device appealing in the fields of polarimetry and optical communications., Comment: 16 pages,8 figures, featured article in ALP

Analytical formulas are derived describing the coherent absorption of light from a realistic multilayer structure composed by an optically conducting surface on a sup- porting substrate. The model predicts two fundamental results. First, the absorption regime named coherent perfect transparency theoretically can always be reached. Second, the optical conductance of the surface can be extrapolated from absorption experimental data even when the substrate thickness is unknown. The theoretical predictions are experimentally verified by analyzing a multilayer graphene structure grown on a silicon carbide substrate. The graphene thickness estimated through the coherent absorption technique resulted in good agreement with the values obtained by two other spectroscopic techniques. Thanks to the high spatial resolution that can be reached and high sensitivity to the probed structure thickness, coherent absorp- tion spectroscopy represents an accurate and non-destructive diagnostic method for the spatial mapping of the optical properties of two-dimensional materials and of metasurfaces on a wafer scale.

In this paper we investigate the effect of a static magnetic field and of optical pumping on the transmittance of a hybrid graphene-split ring resonator metasurface. A significant modulation of the transmitted spectra is obtained, both by optical pumping, and by a combination of optical pumping and magnetostatic biasing. The transmittance modulation features spectral fingerprints that are characteristic of a non-Trivial interplay between the bare graphene response and the split ring resonance.

In this paper we investigate the potentials of liquid crystalline elastomer microstructures for the realization of optically tunable photonic microstructures. While certain limitations regarding the compromise between feature size and structure warping have been observed, it turns out that the simultaneous presence of a refractive index tuning effect and of a shape tuning effect intrinsic to the LCE material can be harnessed to design tunable photonic devices with unique behavior.

The insertion of mobile ions and coupled changes of electron concentration are exploited to induce a non-volatile and reversible change of the optical properties of mixed ionic and electronic conductors (MIECs). The physical mechanisms responsible for the change of the real and imaginary part of the MIECs' refractive index upon ion-intercalation are extensively investigated in the visible and near-IR range. Applications of the proposed electrochemically driven optical actuators are discussed for the manipulation of the light in an optical chip.

We demonstrate room-temperature strong coupling between a mid-infrared (? = 9.9 ?m) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k = 0 where - potentially - polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and - simultaneously - to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the strong critical coupling concept is highlighted. © 2014 AIP Publishing LLC.

Scientific Reports 6: Article number: 24592; Published online: 19 April 2016; Updated: 02 June 2016 The Acknowledgements section in this Article is incomplete. “The authors gratefully acknowledge Raffaele Colombelli for precious suggestions and insights on the application of coupled-mode models to strongly-coupled systems”.

In this paper we report about linear and nonlinear optical properties of intersubband cavity polariton samples, where the resonant photonic mode is a defect state in a metallodielectric photonic crystal slab. By tuning a single geometric parameter of the resonator, the cavity Q factor can reach values as large as 85, with a consequent large cooperativity for the light-matter interaction. We show that a device featuring large cooperativity leads to sharp saturation, or even bistability, of the polariton states. This nonlinear dynamics occurs at the crossover between the weak-and the strong-coupling regimes, where the weak critical coupling concept plays a fundamental role. In this paper we report about linear and nonlinear optical properties of intersubband cavity polariton samples, where the resonant photonic mode is a defect state in a metallodielectric photonic crystal slab. By tuning a single geometric parameter of the resonator, the cavity Q factor can reach values as large as 85, with a consequent large cooperativity for the light-matter interaction. We show that a device featuring large cooperativity leads to sharp saturation, or even bistability, of the polariton states. This nonlinear dynamics occurs at the crossover between the weak- and the strong-coupling regimes, where the weak critical coupling concept plays a fundamental role.

In this article we discuss a model describing key features concerning the lineshapes and the coherent absorption conditions in Fano-resonant dissipative coupled oscillators. The model treats on the same footing the weak and strong coupling regimes, and includes the critical coupling concept, which is of great relevance in numerous applications; in addition, the role of asymmetry is thoroughly analyzed. Due to the wide generality of the model, which can be adapted to various frameworks like nanophotonics, plasmonics, and optomechanics, we envisage that the analytical formulas presented here will be crucial to effectively design devices and to interpret experimental results.

In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation. In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation. (C) 2015 Optical Society of America

By placing a material in close vicinity of a resonant optical element, its intrinsic optical response can be tuned, possibly to a wide extent. Here, we show that a graphene monolayer, spaced a few tenths of nanometers from a split ring resonator metasurface, exhibits a magneto-optical response which is strongly influenced by the presence of the metasurface itself. This hybrid system holds promises in view of thin optical modulators, polarization rotators, and nonreciprocal devices, in the technologically relevant terahertz spectral range. Moreover, it could be chosen as the playground for investigating the cavity electrodynamics of Dirac fermions in the quantum regime. By placing a material in close vicinity of a resonant optical element, its intrinsic optical response can be tuned, possibly to a wide extent. Here, we show that a graphene monolayer, spaced a few tenths of nanometers from a split ring resonator metasurface, exhibits a magneto-optical response which is strongly influenced by the presence of the metasurface itself. This hybrid system holds promises in view of thin optical modulators, polarization rotators, and nonreciprocal devices, in the technologically relevant terahertz spectral range. Moreover, it could be chosen as the playground for investigating the cavity electrodynamics of Dirac fermions in the quantum regime. (C) 2015 AIP Publishing LLC.

The absorption properties of a resonator can be tuned by varying the phase between incoming coherent light beams. Such control is now shown under strong coupling conditions, allowing all incoming energy to be converted into polaritons. The ability to drive a system with an external input is a fundamental aspect of light–matter interaction. The key concept in many photonic applications is the ‘critical coupling’ condition1,2: at criticality, all the energy fed to the system is dissipated within the system itself. Although this idea was crucial to enhance the efficiency of many devices, it was never considered in the context of systems operating in a non-perturbative regime. In this so-called strong-coupling regime, the matter and light degrees of freedom are mixed into dressed states, leading to new eigenstates called polaritons3,4,5,6,7,8,9,10. Here we demonstrate that the strong-coupling regime and the critical coupling condition can coexist; in such a strong critical coupling situation, all the incoming energy is converted into polaritons. A general semiclassical theory reveals that such a situation corresponds to a special curve in the phase diagram of the coupled light–matter oscillators. In the case of a system with two radiating ports, the phenomenology shown is that of coherent perfect absorption (CPA; refs 11, 12), which is then naturally understood in the framework of critical coupling. Most importantly, we experimentally verify polaritonic CPA in a semiconductor-based intersubband-polariton photonic crystal resonator. This result opens new avenues in polariton physics, making it possible to control the pumping efficiency of a system independent of the energy exchange rate between the electromagnetic field and the material transition.

Phase-locked multi-terahertz transients map out the full photonic bandstructure of a one-dimensional photonic crystal while a 12-fs control pulse activates ultrastrong interaction on a sub-cycle time scale with quantized electronic transitions in semiconductor quantum wells. We trace the build-up dynamics of a large vacuum Rabi splitting and observe an unexpected asymmetric formation of the upper and lower polariton bands. The pronounced flattening of the photonic bands causes a slow-down of the group velocity by one order of magnitude on the time scale of the oscillation period of light. published

In the latest years the optical engineer's toolbox has welcomed a new concept, the metasurface. In a metasurface, properly tailored material inclusions are able to reshape the electromagnetic field of an incident beam. Change of amplitude, phase and polarization can be addressed within a thickness of only a fraction of a wavelength. By means of this concept, a radical gain in compactness of optical components is foreseen, even of the most complex ones; other unique features like that of analog computing have also been identified. With this huge potential ready to be disclosed, lack of tunability is still a main barrier to be broken. Metasurfaces must now be made reconfigurable, i.e. able to modify and memorize their state, possibly with a small amount of energy. In this Communication we report low-energy, self-holding metasurface reconfiguration through lithium intercalation in a vanadium pentoxide layer integrated within the photonic device. By a proper meta-atom design, operation on amplitude and phase of linearly polarized light has been demonstrated. In addition, manipulation of circularly polarized light in the form of tunable chirality and tunable handedness-preserving reflection has been implemented. These operations are accomplished using as low as 50 pJ/{\mu}m^{2}, raising lithium intercalation in transition metal oxides as one of the most energy efficient self-holding tuning mechanisms known so far for metasurfaces, with significant perspectives in the whole field of nanophotonics.

This work reports a detailed study of quasi-guided mode resonances in metallodielectric photonic crystal slabs, focusing on the interaction with the intersubband transition supported by a multiple quantum well embedded in the photonic crystal itself. The strong light-matter coupling regime is obtained at room temperature in the mid-infrared spectral range, and its spectral fingerprints are analyzed in the framework of a Fano line-shape model. We propose an estimate of the light-matter coupling coefficient for arbitrarily shaped resonant cavities embedding multiple quantum wells supporting intersubband transitions, obtaining good agreement between theoretical calculations and experimental results.

We map out the band structure of a one-dimensional photonic crystal while a 12-fs control pulse activates ultrastrong interaction with quantized electronic transitions in semiconductor quantum wells. Phase-locked multi-terahertz transients trace the buildup of a large vacuum Rabi splitting and an unexpected asymmetric formation of the upper and lower polariton bands. The pronounced flattening of the photonic bands causes a slow-down of the group velocity by one order of magnitude on the time scale of the oscillation period of light.

We report on the transition from the strong to the weak light-matter coupling regime between an intersubband excitation and a photonic crystal resonance in a nanostructured semiconductor membrane. Such a transition is induced by varying the intensity of an ultrafast light pulse, which is employed for pumping and probing the system eigenmodes. The phenomenon is interpreted in terms of the saturation of the intersubband transition due to the large number of photoexcited electrons in the quantum well, as confirmed by a thorough analysis performed both in frequency and time domain.

We present the observation of the strong light–matter coupling regime between intersubband transitions of semiconductor quantum wells and the plasmonic-like resonances of a one dimensional metallic grating. Polariton spectra have been recorded in transmission employing a suspended membrane sample and are consistent with theoretical calculations. This arrangement, avoiding the complexity of dispersive substrate, is particularly attractive for the development of time-resolved pump–probe experiments.

We present a theoretical study of amorphous and crystalline thin-film solar cells with a periodic pattern on a sub-micron scale realized in the silicon layer and filled with silicon dioxide right below a properly designed antireflection coating. The study and optimization of the PV structure as a function of all the photonic crystals parameters allows to identify the different roles of the periodic pattern and of the etching depth in determining an increase of the absorption. By patterning thin-film silicon solar cells with a periodic etching in addition to an antireflection coating, we found an increase of the short-circuit current up to 36.5% for crystalline silicon. These results demonstrate the advantage of a wavelength-scale, photonic-crystal based approach.

We present a theoretical study of amorphous and crystalline thin-film solar cells with a periodic pattern on a sub-micron scale realized in the silicon layer and filled with silicon dioxide right below a properly designed antireflection coating. The study and optimization of the PV structure as a function of all the photonic crystals parameters allows to identify the different roles of the periodic pattern and of the etching depth in determining an increase of the absorption. From one side, the photonic crystal acts as an impendence matching layer, thus minimizing reflection of incident light over a particularly wide range of frequencies. Moreover a strong absorption enhancement is observed when the incident light is coupled into the quasi guided modes of the photonic slab. We compare the efficiency of this structure to that of PV cells characterized by the sole antireflection coating. We found a substantial increase of the short-circuit current when the parameters are properly optimized, demonstrating the advantage of a wavelength-scale, photonic-crystal based approach.

We present a theoretical study of crystalline and amorphous silicon thin-film solar cells with a periodic pattern on a sub-micron scale realized in the silicon layer and filled with silicon dioxide right below a properly designed antireflection (AR) coating. The study and optimization of the structure as a function of all the photonic lattice parameters, together with the calculation of the absorption in a single layer, allows to identify the different roles of the periodic pattern in determining an increase of the absorbance. From one side, the photonic crystal and the AR coating act as impedance matching layers, thus minimizing reflection of incident light over a particularly wide range of frequencies. Moreover a strong absorption enhancement is observed when the incident light is coupled into the quasi guided modes of the photonic slab. We found a substantial increase of the short-circuit current when the parameters are properly optimized, demonstrating the advantage of a wavelength-scale, photonic crystal based approach for patterning of thin-film silicon solar cells.

In this work we demonstrate the achievement of light-matter strong coupling regime between an intersubband transition and the photonic bandlike mode supported by a metallic grating. Polaritonic resonances have been identified in the reflectivity spectra at 10 degrees incidence, with a clear anticrossing appearing when the photonic mode is tuned across the transition line. Experimental results are in good agreement with the simulations performed with a scattering-matrix approach. This cavity design can be further optimized and is likely to open the way to a new class of time-resolved measurements, as it allows pump-and-probe measurements to be performed in collinear geometries. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3524823]