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The real-time characterization of the polarization state of a light beam is of importance for a variety of applications in Optics and Photonics. We have designed a device that includes a Vector Diffractive Optical Element (VDOE) to determine the polarization state of an incident light beam. The device is able to simultaneously evaluate the four Stokes parameters of the light under analysis. The VDOE is sectorized into several Fresnel zone plates, enabling a compact arrangement and facilitating optoelectronical integration. We have also developed a procedure to remove diffractive effects and systematic errors. From the simulated results, our device is able to identify any polarization incident state with an averaged uncertainty of 0.006%. Finally, we have experimentally verified the VDOE with non-ideal polarization elements to further validate and test our proposed design. The averaged uncertainty of our experimental realization is 3.33%.

The generation of surface plasmon resonances (SPR) in laser-induced periodic surface structures (LIPSS) allows their application in the field of optical sensing, such as the detection of refractive index variations in gases and liquids. We have fabricated gold-coated LIPSS nanostructures on stainless steel substrates by using femtosecond laser nano-ablation. This technique is a low-cost and high-throughput fabrication method applicable to fast and large-scale manufacturing. The depth profile of the fabricated LIPSS shows a central dip at the top of each ripple that split the geometry. The actual topography is modeled and included in a computational electromagnetism package to obtain the expected optical response under the experimental conditions. The measured and simulated spectral reflectances are compared, and the differences are explained by the departure of the fabricated LIPSS from the ideal topography. The experiments and simulations showed excellent agreement for the main spectral characteristics, like the Fano-like lineshapes of the spectral reflectance. This fitting provides the values used to determine the refractometric performance of the fabricated device, that shows a sensitivity of 518 nm/RIU and a figure of merit of 32 RIU−1 for an aqueous analyte. Our experimental results show that the fabricated devices are competitive in terms of cost and simplicity when compared to existing devices with similar performance.

Low-cost hydrogenated amorphous silicon solar cells (a-Si:H) can perform better and be more competitive by including nanostructures. An optimized nano-dimer structure embedded in close contact with the back electrode of an aSi:H ultra-thin solar cells can enhance the deliverable short-circuit current up to 27.5 %. This enhancement is the result of an increase in the absorption at the active layer, that is the product of an efficient scattering from the nanostructure. From our calculations, the nano-dimer structure must be made out of a high-index of refraction material, like GaP. The evaluation of the scattering and absorption cross section of the structure supports the calculated enhancement in short-circuit current, that is always accompanied by a decrease in the total reflectance of the cell, which is reduced by about 50 %.

Stainless steel is a basic raw material used in many industries. It can be customized by generating laser-induced periodic surface structure (LIPSS) as subwavelength gratings. Here, we present the capabilities of an LIPSS on stainless steel to modify the polarization state of the reflected radiation at the IR band. These structures have been modeled using the finite element method and fabricated by femtosecond laser processing. The Stokes parameters have been obtained experimentally and a model for the shape has been used to fit the simulated Stokes values to the experimental data. The birefringence of the LIPSS is analyzed to explain how they modify the polarization state of the incoming light. We find the geometry of the subwavelength grating that makes it work as an optical retarder that transforms a linearly polarized light into a circularly polarized wave. In addition, the geometrical parameters of the LIPSS are tuned to selectively absorb one of the components of the incoming light, becoming a linear axial polarizer. Appropriately selecting the geometrical parameters and orientation of the fabricated LIPSS makes it possible to obtain an arbitrary pure polarization state when illuminated by a pure linearly polarized state oriented at an azimuth of 45°. The overall reflectance of these transformations reaches values close to 60% with respect to the incident intensity, which is the same reflectivity obtained for non-nanostructured stainless steel flat surfaces.

Refractometric sensors based on plasmonic resonances can be modified to operate using an interrogation method based on the optoelectronic response of the device. In this contribution we show how the bolometric effect can be used to generate a signal depending on the change of the refractive index of the analyte. The design has been tuned to sense variations in the range of aqueous media. We have also proposed a modification of a perovskite solar cell to sense variations in the index of refraction of air. These changes in the interrogation method have required a modification of the definitions of the sensitivity and Figure of Merit of such types of sensors. The results show a performance that is competitive with other refractometric sensors and allows an operation method that relies on the measurement of electric, or electronic, parameters.

The inactivation of pathogens through the irradiation of ultraviolet light depends on how light propagates within the medium where the microorganism is immersed. A simple geometrical optics analysis, and a fluence evaluation reveal some reservoirs where the pathogen may hide and be weakly exposed to the incoming radiation. This geometrical hide-outs also generate a tail in the plot of the total inactivation plot vs. the incoming fluence. We have analyzed these facts using geometrical optics principles and illumination engineering computational packages. The results obtained from previous biomedical measurements involving SARS-CoV-2 have been used to evaluate the inactivation degree for an spherical geometry applicable to airborne pathogens, and for an spherical cap geometry similar to that used in biomedical experiments. The case presented here can be seen as the worst-case scenario applicable under collimated illumination.

Absorption of amorphous-Si hydrogenated (aSi-H) solar cells can be enhanced by using dielectric nanostructures made of Si3N4 that work like antireflection coatings. The analysis focus on the short-circuit current delivered by the cell under solar irradiance, and it is made taking into account every layer and structure of an aSi-H cell. A customized design of the antireflection coating in the form of nanostructured dielectric layers, produces a short-circuit current enhancement of 15.2% with respect to the reference flat solar cell, and a lower reflectivity of the cell. Three different geometries of linear nanostructures have been analyzed and compared with quite similar results among them. An improvement in performance has been also obtained for realizable geometrical dimensions that could be fabricated while maintaining electric conductivity of the front contact.

The bolometric effect allows us to electrically monitor spectral characteristics of plasmonic sensors, it provides a lower cost and simpler sample characterization compared with angular and spectral signal retrieval techniques. In our device, a monochromatic light source illuminates a spectrally selective plasmonic nanostructure. This arrangement is formed by a dielectric low-order diffraction grating that combines two materials with a high-contrast in the index of refraction. Light interacts with this structure and reaches a thin metallic layer, that is also exposed to the analyte. The narrow absorption generated by surface plasmon resonances hybridized with low-order grating modes, heats the metal layer where plasmons are excited. The temperature change caused by this absorption modifies the resistance of a metallic layer through the bolometric effect. Therefore, a refractometric change in the analyte varies the electric resistivity under resonant excitation. We monitor the change in resistance by an external electric circuit. This optoelectronic feature must be included in the definition of the sensitivity and figure of merit (FOM) parameters. Besides the competitive value of the FOM (around 400 RIU - 1 , where RIU means refractive index unit), the proposed system is fully based on opto-electronic measurements. The device is modeled, simulated and analyzed considering fabrication and experimental constrains. The proposed refractometer behaves linearly within a range centered around the index of refraction of aqueous media, n ≃ 1 . 33 , and can be applied to the sensing for research in bio-physics, biology, and environmental sciences.

We present a refractometric sensor realized as a stack of metallic gratings with subwavelength features and embedded within a low-index dielectric medium. Light is strongly confined through funneling mechanisms and excites resonances that sense the analyte medium. Two terminations of the structure are compared. One of them has a dielectric medium in contact with the analyte and exploits the selective spectral transmission of the structure. The other design has a metallic continuous layer that generates surface plasmon resonances at the metal/analyte interface. Both designs respond with narrow spectral features that are sensible to the change in the refractive index of the analyte and can be used for sensing biomedical samples.

Perovskite solar cells are currently considered a promising technology for solar energy harvesting. Their capability to deliver an electrical signal when illuminated can sense changes in environmental parameters. We have numerically analyzed the variation of the current delivered by a perovskite cell as a function of the index of refraction of air, that is in contact with the front surface of the cell. This calculation identifies which geometrical and material structures enhance this behavior. After replacing the top transparent electrode of a solar cell by an optimized subwavelength metallic grating, we find a large variation in the responsivity of the cell with respect to the change in the index of refraction of the surrounding medium. Such a refractometric sensor can be interrogated electronically, avoiding the cumbersome set-ups of spectral or angular interrogation methods. We present an adaptation of the performance parameters of refractometric sensors (sensitivity and figure of merit) to the case of opto-electronic interrogation methods. The values of sensitivity and Figure of Merit are promising for the development of refractometric perovskite-based sensors.

We configure and analyze a nanostructured device that hybridizes grating modes and surface plasmon resonances. The model uses an effective index of refraction that considers the volume fraction of the involved materials, and the propagation depth of the plasmon through the structure. Our geometry is an extruded low-order diffraction grating made of dielectric nano-triangles. Surface plasmon resonances are excited at a metal/dielectric interface, which is separated from the analyte by a high-index dielectric layer. The optical performance of the refractometric sensor is highly competitive in sensitivity and figure of merit (FOM) because of the the ultra-narrow spectral response (below 0.1 nm). Moreover, it is operative within a wide range of the index of refraction (from 1.3 till 1.56), and also works under normal incidence conditions. This work was supported in part by the Ministerio de Economía y Competitividad of Spain under Grant TEC2016-77242-C3-1-R and Grant DPI2016-75272-R, in part by the Comunidad de Madrid SINFOTON2-CM under Grant (S2018/NMT-4326), and in part by the European Fund for Regional Development. The work of M. H. Elshorbagy was supported by the Ministry of Higher Education of Egypt (missions section).

When optical antennas are used as light detectors, temperature changes their spectral response. Using this relation, we determine the spectrum of a light beam from an optical antenna’s signal. A numerical evaluation of the temperature-spectral response has been completed with a model for the noise of the device. Using both the response and the noise model, we have established the capabilities of the device by quantifying the error in the spectrum determination both for broadband spectrum and monochromatic radiation.

This work reports on a computational analysis of how a modified perovskite cell can work as a refractometric sensor by generating surface plasmon resonances at its front surface. Metal-dielectric interfaces are necessary to excite plasmonic resonances. However, if the transparent conductor (ITO) is replaced by a uniform metal layer, the optical absorption at the active layer decreases significantly. This absorption enhances again when the front metallic surface is nanostructured, adding a periodic extruded array of high aspect-ratio dielectric pyramids. This relief excites surface plasmon resonances through a grating coupling mechanism with the metal surface. Our design allows a selective absorption in the active layer of the cell with a spectral response narrower than 1 nm. The photo-current generated by the cells becomes the signal of the sensor. The device employs an opto-electronic interrogation method, instead of the well-known spectral acquisition scheme. The sensitivity and figure of merit (FOM) parameters applicable to refractometric sensors were adapted to this new situation. The design has been customized to sense variations in the index of refraction of air between 1.0 and 1.1. The FOM reaches a maximum value of 1005 RIU &minus, 1 , which is competitive when considering some other advantages, as the easiness of the acquisition signal procedure and the total cost of the sensing system. All the geometrical and material parameters included in our design were selected considering the applicable fabrication constrains.

These days, when computational power and resources are widely available, it is commonplace to rely on numerical tools that have demonstrated their capabilities to simulate physical phenomena involving electromagnetic radiation and its interaction with materials. However, we should recall that the scientific method is based on the comparison of the outputs given by physical models to the results of measurements of those outputs. Furthermore, from an engineering point of view, simulation is just an extension of the design process, and only through measurement and testing can the fabricated devices reach their final realization. A well-executed measurement is always more certain than simulations and provides the true values of the physical parameters being analyzed. Therefore, all of our efforts to understand, model, and simulate how antennas behave within the IR/optical regime should be compared against the actual measurements of the as-fabricated devices. In this chapter we explain how experimental conditions and setups have been adapted for the testing and evaluation of antenna-coupled sensors. Characterization of antenna-coupled IR sensors falls into several categories: spatial, angular, spectral, and polarization response. Signal-to-noise ratio and specific detectivity are also of primary importance when characterizing optical antennas.

Classical electromagnetism and photonics share a common foundation. Light propagation and interaction, even at the nanoscale, is driven by Maxwell’s equations and macroscopic parameterization of materials through their optical and electromagnetic properties. These equations relate the spatial and temporal variations of the displacement electric field.

Optical or infrared antennas are devices that receive optical radiation and transform it into a current within the resonant structure. This high-frequency current is transduced by a given mechanism to a change in voltage or current that is read by external electronics. From this point of view, optical antennas are light detectors. Over time, several transduction mechanisms have been proposed and realized. One of the first used is the rectification of the currents flowing through the antenna by means of tunnel and Schottky junctions properly placed at the appropriate location, typically where the current density reaches the largest value. These elements are considered generically as diodes. Another simpler transduction mechanism is based on the heating of a bolometric material due to Joule dissipation. In this case, the mechanism is dissipative and needs electronic biasing to sense variations in resistivity of the bolometric element. It happens that most of the metals used in the fabrication of optical antennas have a similar value of the parameter responsible for the change in resistance with temperature, the temperature coefficient of resistance (TCR). Some designs use this effect to make the whole resonant element act as a bolometric transducer, which can be termed a distributed bolometer. Using the change in temperature caused by thermal dissipation of currents, thermoelectric transducers based on the Seebeck effect have also been proposed and tested. In this section we present the basic principles of these transduction mechanisms.

Infrared antennas and resonant structures take advantage of the successful designs in the radioelectric and microwave spectra. A quite simple and naive approach would be to consider the geometry and shape of those designs and transfer them into the optical regime with simple wavelength structure size scaling. However, this translation misses the specific behavior of metals and dielectrics at optical frequencies, and how these characteristics can strongly change the geometries and arrangements of a working antenna in the infrared. Fabrication of optical antennas and resonant structures has been possible only since technology has provided tools and processes able to produce smooth metallic surfaces with sizes ranging in the subwavelength scale for the optical domain. This means that resonant elements are nanophotonic devices and systems. This tiny size also needs an appropriate approach for the design of working elements. The first constraint is related to the physical substrate that the antennas are placed on or embedded in. Most of the antenna-coupled detectors and resonant structures are written on a dielectric substrate or on a dielectric stand-off layer deposited on top of a metallic surface that typically has been evaporated on a dielectric substrate. The thicknesses of these layers are a fraction of a wavelength, and the substrates are dielectric wafers, or plastic flexible substrates. When the device is illuminated from the substrate side, the substrate has to be transparent enough for the given wavelength of operation. In any case, the optical properties of every material involved in the proposed design have to be properly included in the design and modeling of the device. But not only optical properties are important. When thermal effects are at play, thermal conductivity and electrothermal coefficients are also of interest and need to be considered.

Silicon microlenses are a very important tool for coupling terahertz (THz) radiation into antennas and detectors in integrated circuits. They can be used in a large array structures at this frequency range reducing considerably the crosstalk between the pixels. Drops of photoresist have been deposited and their shape transferred into the silicon by means of a Reactive Ion Etching (RIE) process. Large silicon lenses with a few mm diameter (between 1.5 and 4.5 mm) and hundreds of μm height (between 50 and 350 μm) have been fabricated. The surface of such lenses has been characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), resulting in a surface roughness of about ∼3 μm, good enough for any THz application. The beam profile at the focal plane of such lenses has been measured at a wavelength of 10.6 μm using a tomographic knife-edge technique and a CO2 laser. © 2013 Published by Elsevier B.V., J. Bueno acknowledges support through Grants AYA2008-06166-C03-02 and AYA2010-21697-C05-01. N. Llombart acknowledges support through Grant AYA2010-10054-E and the program “Ramón y Cajal” RYC-2009-04924. J.L. Costa-Krämer acknowledges support from MAT2008-06330.

A periodic array of extruded nanoprisms is proposed to generate surface plasmon resonances for sensing applications. Nanoprisms guide and funnel light towards the metal-dielectric interface where the dielectric acts as the medium under test. The system works under normal incidence conditions and is spectrally interrogated. The performance is better than the classical Kretschmann configurations, and the values of sensitivity and figure of merit are competitive with other plasmonic sensor technologies. The geometry and the choice of materials have been made taking into account applicable fabrication constraints.

A metallic nanostructured array that scatters radiation toward a thin metallic layer generates surface plasmon resonances for normally incident light. The location of the minimum of the spectral reflectivity serves to detect changes in the index of refraction of the medium under analysis. The normal incidence operation eases its integration with optical fibers. The geometry of the arrangement and the material selection are changed to optimize some performance parameters as sensitivity, figure of merit, field enhancement, and spectral width. This optimization takes into account the feasibility of the fabrication. The evaluated results of sensitivity (1020 nm/RIU) and figure of merit (614 RIU−1RIU−1) are competitive with those previously reported.

The amplitude of vibration of an array of micro‐cantilevers piezoelectrically excited has been measured by analyzing the diffraction pattern given by the structure. A model for the simulation of this situation, and some out‐of‐plane interferometric measurements based on diffraction pattern, have been developed and performed to fully understand the dynamic of the elements and the diffraction pattern produced by them.

In this work principal component analysis (PCA), a multivariate pattern recognition technique, is used to characterize the noise contribution of the experimental apparatus and two commonly used methods for fluorescence removal used in biomedical Raman spectroscopy measurements. These two methods are a fifth degree polynomial fitting and an iterative variation of it commonly known as the Vancouver method. The results show that the noise in Raman spectroscopy measurements is related to the spectral resolution of the measurement equipment, the intrinsic variability of the biological measurements, and the fluorescence removal algorithm used.

In this work the resonance, frequency response, and far-field patterns of an optical nano-antenna placed on an interface between air and a metamaterial substrate is obtained through finite element calculations. The metamaterial is characterized by an effective, macroscopic index of refraction which can take negative and near-zero values, or by published values of the effective permittivity and permeability for metamaterials. The results show that the resonant wavelength and response can be fitted to analytical functions that are even functions of the index of refraction, this is consistent with the knowledge that negative indices of refraction allows for wave propagation in the same magnitude but opposite direction observed with positive indices of refraction. The simulations also show that substrates with near-zero index of refraction will enhance the antenna response by 62% compared to substrates with n > 1. Lossy metamaterials are also considered in the simulations. The far-field pattern of the antenna, obtained through a near-field to far-field transformation, behaves the same independently of the sign of the index of refraction, also the far-field pattern for the emission towards near-zero substrates is nearly constant and independent of the angle for the evaluated angular range.

Background Filaggrin (FLG) gene mutations, which result in complete or incomplete loss of proFLG/FLG peptides, have been reported as an important predisposing factor for atopic dermatitis (AD) and secondary atopic phenotypes such as atopic asthma. Method The presence of the protein FLG in the skin was evaluated at birth on 12 infants using Raman spectroscopy; these 12 infants were monitored for 1 year to see whether they developed AD. Three different statistical analysis procedures, two of which involved principal component analysis (PCA), were performed on the Raman spectra in order to determine the FLG content. Results The infants who had a lower FLG content, determined using any of the three statistical analysis procedures proposed, were also the ones that clinically developed AD. Conclusion The results suggest that Raman spectroscopy and statistical analysis such as PCA could be used as an early detection procedure for FLG -related AD and as a possible quantitative marker for FLG gene mutations

The performance of dipole nanoantennas coupled to two different waveguides, a cylindrical waveguide and a photonic crystal waveguide, illuminated with a polarized electromagnetic wave incident from the air and from the substrate is analyzed by numerical simulations. When illuminated from the air, the photonic crystal waveguide antenna showed two resonances spectrally far apart from each other: one of them corresponds to the main antenna resonance and the other one to the modes excited in the photonic crystal cavity. The cylindrical waveguide antenna shows only the main antenna resonance. No significant antenna response was observed at a polarization perpendicular to the main axis of the antenna. Illumination from the substrate did not increase the response of the waveguide-coupled antenna. These results show that antenna-coupled waveguides could be used as detectors for near-field applications where polarization sensitivity and dual band operation are desired.

In this paper the optical parameters at infrared frequencies of metallic thin films were obtained experimentally using a variable angle spectroscopic ellipsometer and used to simulate numerically the frequency response of antennas and antenna-coupled detectors at infrared frequencies (5–15 μm). The simulation results agree with previously published data and practical guidelines are presented for the design and fabrication of dipole and bowtie antennas at infrared frequencies.

A dual-dipole structure is demonstrated at 10.6 μm, which facilitates electronic cancellation of the non-antenna-coupled thermal response of an infrared antenna-coupled bolometer. Structures of this type may also find utility in high-spatial-resolution measurement of Stokes parameters of a beam of radiation.

The performance of Fresnel zone plates having polygonal boundaries between zones has been studied for polygons with a low number of sides. An optimized polygonal shape has been analytically defined by minimizing the mismatched area between the circular and the polygonal pseudo-Fresnel zones. The square polygon has been analyzed in more depth than the others because of its simple symmetry. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 536–541, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23125