In optical one-dimensional grating-on-layer planar structures, an optical resonance occurs when the incident light wave becomes phase-matched to a leaky waveguide mode excited in the layer underneath the grating by an appropriate tuning of the grating periodicity. Changing the refractive indices of the grating’s constituents, and/or thickness, changes the resonance frequency. In the case of a two-dimensional grating atop such a smooth layer, a similar and also cavity-mode resonance can occur. This idea has straightforward usage in diverse optical sensor applications. In this study, a novel guided-mode resonance sensor design for detecting glucose and hemoglobin in minute concentrations at a wide range of incidence angles is presented. In this design, materials of the grating, such as a polymer and cesium-lead halide with a perovskite crystal structure, are examined, which will allow flexible, low-cost fabrication by soft-lithography/imprint-lithography methods. The sensitivity, figure of merit, and quality factor are reported for one- and two-dimensional grating structures. The simulations performed are based on rigorous coupled-wave analysis. Optical resonance quality factor of ∼5·105 is achieved at oblique incidence for a structure comprising a one-dimensional grating etched in a poly-vinylidene chloride layer atop a silicon nitride waveguide layer on a substrate. Record values of the above-noted characteristics are achieved with a synergetic interplay of the materials, structural dimensions, incidence angle, polarization, and grating geometry.

Plasmonic designs for mid-infrared extraordinary optical transmission (EOT), a direct route to tailored filtering with broadband out-of-band rejection, have long been constrained by a fundamental trade-off between high transmission efficiency and narrow linewidths, a challenge rooted in the material properties of noble metals. Here, we theoretically propose and numerically demonstrate a versatile design paradigm that resolves this challenge by functionally decoupling the tasks of light coupling and resonant filtering. Our approach uses a dual-stacked noble metal-dielectric grating architecture to surpass the intrinsic limitations of single-layer structures. This paradigm provides the flexibility to engineer devices for ultra-high spectral selectivity and transmission efficiency. We demonstrate this with distinct designs: one at 10 mu m with a quality factor (Q-factor) > 2000 and > 91% transmission; a high-Q design at 4 mu m and > 80% transmission; and a high-efficiency design at 4 mu m with > 92% transmission over a uniquely broad spectral-angular range. These generic designs produce solitary, narrow EOT peaks originating from a "triple-coupling" mechanism that mitigates reflection and absorption losses, with symmetry-broken configurations capable of exceeding Q-factors of 16,000 while maintaining a peak transmission efficiency > 60%. Crucially, these compact two-layer designs exhibit exceptional robustness against fabrication variations, offering a broadly applicable route to ultra-compact, low-cost infrared components, enabling advanced architectures such as angular sensing, spectro-polarimetric imaging, and isotope-resolved gas diagnostics.

Novel concepts for efficient compact spectroscopy are extensively researched due to their fundamental applications in prominent fields such as chemistry, biology, and physics. Here, with an unprecedented spectral-azimuthal resolution, such a concept is introduced and exemplified in the mid-infrared, in which its advantages are paramount and have yet to be established industrially. The concept is based on the design and instrumentation of optical absorption spectral tuning (or sensitivity) to the relative azimuthal component of light impinging on specifically designed metamaterials (MMs). The inversely-designed MMs offer perfect photo-absorption inside λ0/200 ultra-thin layer of lead telluride. Two small-footprint system designs are proposed to instrument the spectral-azimuth-angle tuning for spectrometry. The first is based on a single or few spinning MM layout elements, and the second, to avoid spinning, utilizes a fixed focal-plane-array approach. The latter exploits the inherent variations in the local azimuthal-incidence angle. While low absorption is the Achilles heel of conventional mid-infrared photodetector spectrometers, the optimized MMs, besides their unique spectral-azimuth-angle tuning functionality, provide giant absorption enhancement, facilitating higher resolution and even smaller in-plane form factor. The highlighted concept opens an additional dimension to encode-decode spectral information, yielding profound advantages over conventional designs, such as those based on diffraction gratings.

Nowadays, polycrystalline lead telluride is one of the premier substances for thermoelectric devices while remaining a hopeful competitor to current semiconductor materials used in mid-infrared photonic applications. Notwithstanding that, the development of reliable and reproducible routes for the synthesis of PbTe thin films has not yet been accomplished. As an effort toward this aim, the present article reports progress in the growth of polycrystalline indium-doped PbTe films and their study. The introduction foregoing the main text presents an overview of studies in these and closely related research fields for seven decades. The main text reports on the electron-beam-assisted physical vapor deposition of n-type indium-doped PbTe films on two different amorphous substrates. This doping of PbTe is unique since it sets electron density uniform over grains due to pinning the Fermi level. In-house optimized parameters of the deposition process are presented. The films are structurally characterized by a set of techniques. The transport properties of the films are measured with the original setups described in detail. The infrared transmission spectra are measured and simulated with the original optical-multilayer modeling tool described in the appendix. Conclusions of films’ quality in terms of these properties altogether are drawn.

PbTe-based compounds are excellent candidates for the different types of optical detector applications from near to far IR ranges. In the present work, a technology has been developed for the fabrication of Pb1−xSnxTe compositions, doped with In, on a thin amorphous substrate (polyimide). The film preparation was performed by the electron gun evaporation method. The systematic study of structure and transport properties (Hall coefficient and electric conductivity) in the entire temperature range of 10–300 K for Pb1−xSnxTe:In films (x=0, 0.1, 0.2) was investigated. It was studied that the photoconductivity of the films in the telecom wavelength range, including kinetics, sensitivity, and noise equivalent power, has been conducted and it discovered persistent photoconductivity for all compositions at the temperature T<21 K. The results of the work have promising potential to use poly(nano) crystalline Pb1−xSnxTe:In films on an amorphous substrate both for photodetection in the telecom wavelength range and for the creation of all-optical neuromorphic systems, cooled memory, and logic elements operating at the low energy of laser pulses.

Submicron-structured films of thermoelectric materials, exhibiting an improved thermoelectric figure of merit, are reviewed, including methods of fabrication and characterization. The review emphasizes the beneficial role of the grain boundaries in polycrystalline films. The enhanced Seebeck coefficient of lead chalcogenide films is attributed to a potential relief that is built along the grain boundaries. It scatters charge carriers with low energy and does not affect carriers with higher energy. The model that accounts for the thermoelectric properties of the films is described and assessed experimentally. The application of a flexible thermoelectric device (module) based on the nanocrystalline film thermoelectric semiconductors as high sensitivity radiation detectors is suggested.

Polycrystalline PbTe:In films on a polyimide substrate were obtained and investigated. Their structural and transport properties in a wide range of temperatures (10–300 K) were studied. The unique feature of In impurity in PbTe is the stabilization of the Fermi level (pinning effect) that allowed for the preparation polycrystalline films with the same carrier concentration. We found that heat treatment in an argon atmosphere does not change the average grain size and carrier concentration for as-grown films but greatly increases the Hall mobility and the electron mean free path. By comparing the mobility in the bulk and in the film after heat treatment, we extracted the value of the mobility that arises due to scattering at the grain boundary barriers. The ultimate goal of the present study is the development of these films in designing portable uncooled photodetectors for the mid-IR range.

Ultrathin, all-dielectric, metamaterial design based on an asymmetrical optical micro-/nanocavity, enclosing a 10 nm thick Ge 2 Sb 2 Te 5 photoabsorber film, is inversely optimized for perfect tunable absorption in the mid-infrared. The absorption can be actively/geometrically pre-/post-fabrication spectrally tuned.

We inversely design a sub-vacuum-wavelength thick metamaterial comprising meta-surface, microcavity, and ultra-thin photo-absorber, with an absorptance spectrum ~99% peaked at 3.5µm, maintaining this level over a flattop range around this wavelength.

Two-dimensional optical nanostructures grating based on polymers were fabricated using dip-pen nanolithography. We investigated the influence of both the ink composition and dwell-time. Prototypes of phase masks were manufactured, and their main characteristics were analyzed.

We introduce a silicon photonics meta-detector for perfect 850-950 nm band tunable absorption. Optimized < λ /4.5 thin designs of 10 nm Si film wrapped by a laterally asymmetric dual SiO 2 -Air Si-SiO 2 gratings cavity, fully absorbs light of > 15µm penetration depth, in < 25 nm effectively thin Si absorber.

The demand for miniature, low-cost, utmost efficient optical absorbers triggered ongoing research efforts to minimize the overall design thickness, particularly the photo-active layer, while still maintaining a high optical absorptance. In this study, we present all-dielectric nanophotonic metamaterials of optimized, fabrication compatible and tolerant, architecture for perfect mid-wave infrared absorptance. Overall sub-vacuum-wavelength thick designs are intended to couple and confine light inside an ultrathin 100 nm PbTe photo-absorbing film. Three application-oriented structures, with dimensions inversely designed to provide diverse requirements, are introduced: a two-dimensional metasurface embedded design for unpolarised wide-band absorption and two, one-dimensional metasurface embedded designs for s-polarised wide-band and non-polarised narrow-band absorption. A comprehensive study of the structures' spectral absorptance under normal- and oblique-incidence irradiation is performed. The conical-mounting absorptance analysis elucidates that the high absorption can be continuously spectrally tuned with the azimuthal component of the incidence angle. To the best of our knowledge, this property is discussed for the first time for all-dielectric metamaterials. Also, the ranges of geometrical tuning of the peak absorptance are investigated in detail, and usage of another prospective semiconductor absorber is explored. To unfold the mutual, and essentially different, physical mechanisms that fuel the perfect absorptance, an elaborated analysis is presented. The electromagnetic power transport, portrayed by the Poynting vector, displays three-dimensional singular flows around points, such as vorticity centers, saddles, sinks, and spirals. The potential mid-infrared applications which can benefit from the peculiar properties of the designed structures, such as spectroscopy, sensing, thermal radiation manipulations, and communication, are also discussed.

We introduce a 5µm-thick meta-structure design showing ~100% ultra-narrow, angular-sensitive resonant absorptance, MWIR peaked with Q ≈ 2650 for tunable sensing applications. Light trapping inside a 22nm absorber is visualized by Poynting vector vortex topology.

We suggest a novel design for CO2 sensors. This design could be adjusted for various gas sensing approaches and other MWIR range applications, such as free-space communication, imaging systems, and light detection and ranging systems. (C) 2020 The Author(s)

A new resonant-cavity photodetector architecture, where mirrors are surrogated by grating-patterned meta-surfaces is suggested. We show by design that thus structured, sub-10 μm thick mid-IR photodetectors, with 75nm thick HgCdTe photo-absorber, can attain unsurpassable peak efficiency.

We propose a novel concept of designing silicon photonics metamaterials for perfect near-infrared light absorption. The study’s emphasis is an in-depth investigation of various physical mechanisms behind the ∼ 100 % ultra-narrowband record peak absorptance of the designed structures, comprising an ultrathin silicon absorber. The electromagnetic power transport, described by the Poynting vector, is innovatively explored, which shows combined vortex and crossed-junction two-dimensional waveguide-like flows as outcomes of optical field singularities. These flows, though peculiar for each of the designed structures, turn out to be key factors of the perfect resonant optical absorption. The electromagnetic fields show tight two-dimensional confinement: a sharp vertical confinement of the resonant-cavity type combined with a lateral metasurface supported confinement. The silicon-absorbing layer and its oxide environment are confined between two subwavelength metasurfaces such that the entire design is well compatible with silicon-on-insulator microelectronics. The design concept and its outcomes meet the extensive challenges of ultrathin absorbers for minimum noise and an ultra-narrowband absorptance spectrum, while maintaining an overall very thin structure for planar integration. With these materials and such objectives, the proposed designs seem essential, as standard approaches fail, mainly due to a very low silicon absorption coefficient over the near-infrared range. Tolerance tests for fabrication errors show fair tolerability while maintaining a high absorptance peak, along with a controllable deviation off the central-design wavelength. Various applications are suggested and analyzed, which include but are not limited to: efficient photodetectors for focal plane array and on-chip integrated silicon photonics, high-precision spectroscopic chemical and angular-position sensing, and wavelength-division multiplexing.

Resonant cavity-assisted enhancement of optical absorption was a photodetector designing concept emerging about two and half decades ago that responded to the challenge of thinning the photoactive layer while outperforming the efficiency of the monolithic photodetector. However, for many relevant materials, meeting that challenge with such a design unrealistically requires many layer deposition steps, so that the efficiency at goal hardly becomes attainable because of inevitable fabrication faults. Under this circumstance, we suggest a new approach for designing photodetectors with an absorber layer as thin as those in respective resonant cavity-enhanced ones, but concurrently, the overall detector thickness would be much thinner and top-performing. The proposed structures also contain the cavity-absorber arrangement but enclose the cavity by two dielectric one-dimensional grating-on-layer structures with the same grating pitch, instead of the distributed Bragg reflectors typical of the resonant cavity enhancement approach. By a design based on in-house software, the theoretical feasibility of such ∼7.0-8.5  μm thick structures with ∼100% efficiency for a linearly polarized (TE or TM) mid-infrared range radiation is demonstrated. Moreover, the tolerances of the designed structures' performance against the gratings' fabrication errors are tested, and fair manufacturing tolerance while still maintaining high peak efficiency along with a small deviation of its spectral position off initially predefined central-design wavelength is proved. In addition, the electromagnetic fields amplitudes and Poynting vector over the cavity-absorber area are visualized. As a result, it is inferred that the electromagnetic fields' confinement in the designed structure, which is a key to their upmost efficiency, is two-dimensional, combining in-depth vertical resonant-cavity-like confinement with the lateral microcavity like one set by the presence of gratings.

When observing sea water, a specular reflection of a light source may appear in the form of bright points of light that come and go. These bright points of light, called glints, blend together to form a smooth path of glittering light when viewed from a distance. For detection and observation systems, glints may produce severe saturation in different parts of the image, generating blinding glares and increased fatigue for the observer, which causes hardships in marine remote sensing and target detection. In our work, we have advanced the state-of-the-art analysis of the polarization-based approach to glint reduction and target imaging for a modern remote sensing system by adding external linear polarizers to an observation system on the Red Sea shore. The results of our experiments are presented, analyzed, and discussed, qualitatively and quantitatively, using image processing tools. We performed: 1) an analysis of the RGB histograms of the overall image, the sea and the background; 2) an auto segmentation using the MATLAB image processing toolbox on colored and grayscale images; and 3) saturated frame pixel analysis. An operator survey was added to validate the proposed method. The results show that a polarizer at the optimal angle can help reduce the glints, and, as a result, leads to image enhancement for oceanic applications in general, and for oceanic detection and remote sensing systems in particular.

Internal inverse effects of magnetostriction and piezoelectricity are conceptually introduced for a laterally wide magnetostrictive-piezoelectric-layered structure and studied for a cubic polycrystalline ferromagnetic layer bonded to an out-of-laminate plane-poled piezoelectric. It is shown that these concurrent effects may crucially contribute to the mechanism of magnetoelectric (ME) coupling over that known from previous analytical modeling. It is shown that the studied effect gives rise to an additional magnetic anisotropy in each specific ferromagnetic crystallite. This excess anisotropy has non-cubic symmetry and depends on the orientation of the crystallite's local crystallographic frame relative to the frame set by the laminate geometry. We explain the saturation lag in the magnetization curve as compared to the corresponding standalone ferromagnetic layer. Our consideration provides useful insight into the fundamental issue of the strain-mediated ME coupling.

We study a triangular arrangement of two flat mirrors and a grating mirror for coupling a -1st diffracted order light beam into a traveling-wave intra-cavity light recirculation and out-of-cavity output, combining the 0 th and the repeatedly diffracted secondary +1st order beams. The thus designed and then optimized grating Fabry-Perot ring cavity demonstrates high output contrast and detection resolution for wavelength, cavity length and incidence angle.