The description of the role of absorption in interference resonators is important for characterization of metal-insulator-metal structures. To study the resonance characteristics of the interference structures the conditions of excitation of their eigenmodes were analyzed. The mode excitation conditions determined by the dispersion relations were obtained for the waveguide, Fabry-Pérot, symmetric and antisymmetric plasmonic normal modes. The approximations of the dispersion relations in the form of analytical functions were implemented to describe the behavior of the resonance positions in far-field spectra depending on the parameters of the layers.

The design of resonant planar metal-insulator-metal (MIM) structures offers promising applications in the optical image processing field, especially for developing efficient and ultrafast systems for optical computing and edge detection. The present work extends approaches based on electromagnetic theory and coupled-mode theory to describe nature and characteristics of the resonances in absorptive interference structures. Obtained analytical expressions based on Fano representation relate the resonance properties of the interference structures with their geometrical and optical parameters. This approach was efficiently employed to describe optical properties of the MIM structures and optimize their geometrical parameters for applications in optical filtration and image processing. The review of recent developments for all-optical edge detection both in reflection and transmission highlights various challenges encountered.

Dielectric nanoparticles not showing distinct Mie resonances have been discarded as useful elements of resonant nanophotonics. However, the incorporation of the excitonic transition into such nanoparticles may allow us to generate sharp resonances, in particular, Fano resonances, thereby enhancing the utility of such nanoparticles. In this work, on the basis of the Mie theory and its electrostatics approximation, we analyze analytically and numerically optical responses and resonant behaviors of internal fields in spherical excitonic nanoparticles. The excitonic sphere is characterized by a dielectric constant consisting of a background dielectric constant and a Lorentzian response of the exciton excitation. From equations of the electrostatics approximation, by appropriately accounting for the background scattering, it is shown analytically that the absorption efficiency is expressed as a Lorentzian function, while the efficiencies of the scattering and extinction are expressed in the form of the generalized Fano function (external Fano resonance). From the same procedures, it is also shown that the spectra of the enhancement factor of internal fields are described by the same generalized Fano function (internal Fano resonance). Equations appearing in the derivation clearly indicate that both the external and internal Fano resonances are caused by the interference between a nonresonant component and a resonant component, corresponding to a broad background and sharp excitonic transition, respectively. Assuming a model excitonic sphere that mimics a polymer sphere doped with J-aggregates of excitonic molecules, spectra of scattering, absorption and extinction efficiencies, as well as that of the enhancement factor of internal fields, are calculated including a size range beyond the small particle limit, for which the exact Mie theory is used. The generalized Fano functions are shown to reproduce very well the calculated spectra even beyond the small particle limit, provided that the sphere radius is less than an upper bound. The results of the present paper provide a firm basis for discussing the formation of the Fano line shapes in optical responses and spectra of internal fields of excitonic nanospheres.

To reveal origins of resonance characteristics of multilayer interference structures, we developed an ab initio spatial coupled-mode theory using the approximations of general electromagnetic theory of wave propagation in stratified media. In contrast to the conventional coupled-mode theory, the coefficients of developed coupled-mode models, which describe the Fano resonance behavior of interference field enhancement, are given by analytical functions of structural and optical parameters of the resonance systems. The results of analytical modeling of low- and high-loss resonator systems supporting waveguide, Fabry-Perot, symmetric, and antisymmetric plasmonic normal modes agree very well with electromagnetic numerical simulations. We demonstrate also that the conventional spatial phenomenological coupled-mode theory is accurate only for low-loss structures.

Based on electromagnetic calculations, the formation mechanism of the Fano line shape in the attenuated total reflection (far-field) spectrum of a coupled waveguide multilayer structure is studied in detail by tracing back to the behaviors of local electric fields. The Fano line shape of absorptance A directly related to the reflectance by R=1−A is shown to be generated by a superposition of a Fano line shape exhibited by local absorption in one of the waveguide layers and a Lorentzian line shape exhibited by local absorption in another waveguide layer. It is also shown that the Fano line shape of the first waveguide layer is generated by a superposition of different Fano line shapes exhibited by local electric fields at different positions inside the waveguide layer. These results unveil the nested mechanisms of the Fano line shape formation hidden in the behaviors of local electric fields. The Fano resonance inside the first waveguide layer is thought to be an example of the multiple Fano resonance arising from the interaction between multiple continua with a discrete state.

CdTe thin films have been deposited by thermal evaporation on heated glass substrates. Structural properties of the CdTe thin films were studied by scanning electron microscopy and Raman spectroscopy. Optical properties were examined by ellipsometry and Fourier spectroscopy. We revealed the low absorption of the synthesized thin films in the infrared (IR) region. We investigated the sensing capability of metal / dielectric / dielectric structures based on a CdTe waveguide layer and gold thick film. The reflectivity spectra of the structures with the water, ethanol, and isopropanol as sensing media exhibit resonance line shapes. The positions of the resonances correspond to those of local maximal values of the solvents absorption. The obtained results can be used for developing the applications of optical resonances in the IR region.

The feasibility of an optical image edge detection based on metal-insulator-metal (MIM) resonance transmission structures is experimentally investigated. The structures are fabricated on a glass substrate and consist of thin aluminum layers separated by a quartz layer. The excitation of Fabry-Perot modes by an incident wave produces resonance line shapes in angular and wavelength transmission spectra. Resonance enhancement and suppression of beams using the MIM structures can be implemented for suppressing the illuminating beam and amplifying the field scattered by an object. By using the MIM structure under oblique incidence, we experimentally observe the efficient image edge detection for phase optical elements at a set of wavelengths. The obtained images of edges of the elements exhibit a directionality of image edge detection that depends on the direction of inhomogeneity gradient in the object plane, as suggested by the angular transmission spectra of the MIM structures. The results of the present work can find applications in optical information processing and optical filtering systems.

The morphology of thin metal films has a great influence on their optical properties and resonance characteristics of plasmonic modes excited at metal-dielectric interfaces. Using the optical characteristics of metal layers fabricated by three different techniques we estimate the resonance characteristics of planar plasmonic structures consisting of silver, gold, and aluminum layers in the Kretschmann configuration. In the case of air environment, the physical vapour deposition leads to higher values of the sensing sensitivity and field enhancement as compared to other types of metal films. In the case of water environment, the resonance characteristics are close for all the considered types of metal layers. The present study demonstrates the influence of the metal layer morphology on the performance of planar plasmonic structures in optical sensing, filtration, and signal processing.

Strong coupling of surface plasmon polaritons with molecular oscillators is an active topic of research. The realization of strong coupling regime using surface plasmon-polaritons was reported for various types of molecules. In this work, we study the response of a planar plasmon structure in the Kretschmann configuration in aqueous environment. The structure supports excitation of the surface plasmon polaritons and the vibrational mode of water molecules. The anticrossing behavior of dispersion curves of the modes caused by their coupling is investigated. The results of the present work can be implemented in studies of light-matter interaction for sensing applications and molecular and material sciences.

Except for a few cases to which sophisticated techniques are applicable, it is difficult to observe experimentally local electric fields or near fields associated with excitation of electromagnetic modes supported by building blocks of nanostructures. Although elucidating the behavior of the local electric fields or near fields is very useful to develop potential applications of the nanostructures, in many cases, their behaviors have been only speculated from simulations based on the electromagnetic theory. Here, we develop a simple technique that allows us to study experimentally the average behavior of the local electric fields inside two planar waveguide layers interacting with each other in all-dielectric multilayer structures. The study is made possible by doping the two waveguide layers with two different fluorophores. Fluorescence intensities detected at two different wavelengths allow us to study separately the behaviors of the local electric fields inside each waveguide layer. Angle-scan fluorescence excitation spectra are measured for two different series of multilayer samples by exciting the samples in an attenuated total reflection geometry. The line shapes observed are in good agreement with theoretical ones calculated based on the electromagnetic theory, confirming that the experimental fluorescence excitation spectra reflect well the average behaviors of the local electric fields. Applying the developed technique, we investigate systematically the changes in the local electric fields inside the waveguide layers caused by the change in the strength of coupling between the two waveguide modes. In one series of the samples, a gradual transition in the behavior of the local electric fields, from a Fano-resonant behavior to a double-peak behavior, is demonstrated with increasing the coupling strength. In another series of the samples, the coupling strength is widely changed and the formation of the coupled modes in a strong coupling regime is clearly observed. The observed changes in the local electric fields can be reproduced very well by simple analytical calculations based on a coupled oscillator model. The model is helpful to gain physical insights into the coupling of the waveguide modes, which cannot be obtained by the electromagnetic calculations.

We have succeeded in controlling the line shape of Fano-like resonances in all-dielectric multilayer structures in a wide range by UV light irradiation. Multilayer structures consisting of a waveguide layer supporting a half-leaky guided mode, a spacer layer, and another waveguide layer supporting a planar waveguide mode are known to exhibit Fano-like line shapes in attenuated total reflection spectra due to coupling between the half-leaky guided mode and the planar waveguide mode. Using a photochromic layer, i.e., a layer doped with spiropyran molecules, as one of the waveguide layers, we controlled the amount of light absorption in the waveguide layer by varying the UV irradiation dose. We demonstrated that the line shape changes dramatically depending on the UV dose, from the electromagnetically induced transparency-like to electromagnetically induced absorption-like line shape (or vice versa) passing through the Fano-like line shape. We also demonstrated that the photochromic response induced by UV irradiation in the Fano-resonant multilayer structure is enhanced by a factor of ∼100 relative to that in a single photochromic layer. Our analyses based on electromagnetic calculations suggest that the dramatic line shape change and the enhanced photochromic response are the consequences of enhanced local electric fields inside the photochromic waveguide layer combined with the photoinduced increase in the imaginary part of the dielectric constant.

The planar metal/dielectric structures based on a CdTe waveguide separated from a metal layer by a layer of silicon dioxide support excitation of propagating hybrid plasmon-waveguide modes. The intercoupling of plasmon and waveguide modes results in the appearance of asymmetric resonance line shapes in spectra. The field enhancement of the hybrid modes is characterized by the Fano and plasmon-induced transparency-like line shapes in the attenuated total reflection spectra. The rigorous electromagnetic theory is used to analyze the field distribution in resonance regions. In this paper, redistribution of the electromagnetic field between the coupled modes is demonstrated. We demonstrate the appearance of hybrid symmetric and antisymmetric plasmon-waveguide modes in the structure. Obtained results can lead to development of applications in sensing and enhanced spectroscopies.

We report the experimental studies on the thermal deposition of CdTe films. The deposition of thin CdTe films is performed onto the substrate of varying temperature. The characteristics of the deposited CdTe films are studied using Raman spectroscopy, scanning profilometry, and scanning electron microscopy. According to the measurements, thin CdTe films deposited on substrates with temperatures of 300 °C and 450 °C demonstrate the best stoichiometry. The processes of changing the stoichiometric composition of CdTe films were studied by exposing the films to plasma at a high-voltage gas discharge. The optimal regimes were obtained to achieve 5 % excess and 12% deficiency of Te in the fabricated CdTe films. The optical properties of CdTe films in the visible and infrared ranges were studied. We experimentally demonstrate the resonances in spectra of CdTe-based metal-dielectric structures including layers of water, isopropanol, and ethanol, which can be used to determine the concentration of these solvents.

We estimate the resonance properties of SPP modes excited at water-metal interfaces using Fano approximations in the ultraviolet, visible and infrared regions. The results obtained by Fano approximation correspond to the exact estimations and suggest more simple approach to analysis and design of resonance structures.

We consider planar metal/dielectric/metal structures based on silver and quartz, which support excitation of the Fabry-Pérot modes in the case of close to normal light incidence. The resonance line shapes in the transmission spectra of the structures can be approximated by Fano line shapes. Based on analytical expressions for characteristics of resonances in lossy structures, the width, height, and slope of the Fabry-Pérot resonance line shapes are estimated. The characterization of Fabry-Pérot resonances may find potential applications in opto-informatics and sensing.

Using a reverse attenuated-total-reflection geometry, we measured angle-scan fluorescence emission spectra of all-dielectric multilayer samples containing a waveguide layer doped with fluorescent dye molecules (fluorescent waveguide layer). A sample containing only one fluorescent waveguide layer showed a highly directional emission spectrum with a Lorentzian line shape caused by the radiative decay of an excited planar waveguide mode into a traveling wave in a decoupling prism. Addition of another waveguide layer containing absorptive dye molecules was found to greatly modify the spectrum and generate a Fano line shape in the emission spectrum. The observed Lorentzian and Fano emission spectra could be well reproduced by electromagnetic calculations based on the Lorentz reciprocity theorem. Calculated results of electric field distributions indicate that the Fano line shape is generated by the suppression of local electric fields inside the fluorescent waveguide layer resulting from coupling between two waveguide modes.

The motion of matter containing photoreactive units, such as azo dyes, occurs when the latter undergo cyclic photoisomerization in gradients of light intensity; an effect referred to by photochemical tweezing. Matter motion is polarization sensitive owing to photo-selection of the azo dyes, and it has been described in detail by the recently developed theory of photoinduced vectorial motion of matter (PVMM). Indeed, motion occurs in the direction of the vector gradient of the actinic light with an efficiency that depends on the respective orientations of light polarization and gradient vectors. This paper uses rigorous numerical simulations to reproduce the motion of matter by photochemical tweezing in gradients of intensities produced by a Gaussian beam as well as by an interference pattern resulting from two coherent beams. The simulations are based on the PVMM theory and reproduce very well experimental observations. In particular, and in agreement with the published literature, the parameters used in our simulations impose mobility enhancement of solid azo-polymers by photoisomerization to the viscous flow level, and matter motion is due to the concomitant effects of the enhancement of molecular mobility and the photoisomerization force in the gradients of light fields.

In this work, we analyze the characteristics of the Brewster effect at the air-glass interface for monochromatic and broadband polarized light. The obtained broadband light reflectivity spectrum demonstrates the modified resonance line shape. The effeciency of the Brewster effect for optical image processing is discussed.

The resonance characteristics of the Fabry-Pérot resonator modes supported by metal/dielectric/metal planar structures are studied in the case of absorbing media for near-to-normal light incidence. Approximations based on rigorous solution and field-transfer model for the field and resonance line shapes in spectra are attributed to the class of Fano and Lorentz resonances. The analytical expressions are obtained for the propagation constant and field enhancement of the mode, width, height and slope of resonance line shapes in spectra as functions of structural parameters. With estimation of field characteristics of the fabricated loss structures based on aluminum and quartz, the peaks in the transmission spectra can be attributed to the excitation of Fabry-Pérot modes. Fundamental characterization of Fabry-Pérot resonances may find applications in optical processing and sensing.