The review exposes basic concepts and manifestations of the singular and structured light fields. The presentation is based on deep intrinsic relations between the singularities and the rotational phenomena in light; it involves essentially the dynamical aspects of light fields and their interactions with matter. Due to their topological nature, the singularities of each separate parameter (phase, polarization, energy flow, etc.) form coherent interrelated systems (singular networks), and the meaningful interconnections between the different singular networks are analysed. The main features of singular-light structures are introduced via generic examples of the optical vortex and circular vortex beams. The review describes approaches for generation and diagnostics of different singular networks and underlines the role of singularities in formation of optical field structures. The mechanical action of structured light fields on material objects is discussed on the base of the spin-orbital (canonical) decomposition of electromagnetic momentum, expressing the special roles of the spin (polarization) and spatial degrees of freedom. Experimental demonstrations spectacularly characterize the topological nature and the immanent rotational features of the light-field singularities. The review is based on the results obtained by its authors with a special attention to relevant works of other researchers.

New ways of calculating narrow microparticle size distributions based on using the Tikhonov and the modified Twomey methods for the laser diffraction technique are presented. These allow to have reduced the broadening (over-smoothing) of the result occurring in these methods for narrow distributions both singular and their sum. The calculated singular distributions and their distribution sum were then approximated by a Gaussian function and a bimodal Gaussian function, respectively, using the Levenberg-Marquardt method. The angular distribution of scattering power was measured for polystyrene particles with radii of 0.676 µm and 1.573 µm, and for their sum. The tests were carried out for linearly polarized He-Ne laser light scattered by a dilute aqueous suspension of these particles. The results obtained were compared with those obtained with the nanoDS instrument (CILAS). It turned out that using the way based on the Twomey method, the parameters of the narrow distribution sought could be determined quite well.

Optical waveguides (WGs) are widely used as interconnects in integrated optical circuits both for telecommunication and sensing applications. There are different kind of optical WG designs that offers different guiding parameters, opening a vast number of possibilities. A silica-titania (SiO2:TiO2) rib WG is discussed and examined by a numerical analysis in this article with a great emphasis on the analysis of bending losses and optimization. A modal analysis for different basic parameters of the WG is presented with a detailed wavelength-based modal analysis. Various potential fabrication methods are discussed, however, a sol-gel method and dip-coating deposition technique are proposed for the low-cost development of such WGs. Moreover, an approach towards minimizing the bending losses by adding an upper cladding layer on the rib WG is presented and described.

Absorption of the below-bandgap solar radiation and direct pre-thermalizational impact of a hot carrier (HC) on the operation of a single-junction solar cell are ignored by the Shockley-Queisser theory. The detrimental effect of the HC is generally accepted only via the thermalization-caused heating of the lattice. Here, the authors demonstrate experimental evidence of the HC photocurrent induced by the below-bandgap 0.92 eV photon energy radiation in an industrial silicon solar cell. The carriers are heated both through direct free-carrier absorption and by residual photon energy remaining after the electron-hole pair generation. The polarity of the HC photocurrent opposes that of the conventional generation photocurrent, indicating that the total current across the p-n junction is contingent upon the interplay between these two currents. A model of current-voltage characteristics analysis allowing us to obtain a reasonable value of the HC temperature was also proposed. This work is remarkable in two ways: first, it contributes to an understanding of HC phenomena in photovoltaic devices, and second, it prompts discussion of the HC photocurrent as a new intrinsic loss mechanism in solar cells.

A graphene/NPB structure with Re₂O₇ as an interfacial layer in the context of its potential use in the design of an organic light-emitting diode (OLED) is investigated. The X-ray photoelectron spectroscopy (XPS) study shows the formation of the Re₂O₇ phase on a monolayer graphene on quartz during thermal deposition in ultra-high vacuum (UHV). The ultraviolet photoelectron spectroscopy (UPS) study shows an enhancement of the work function of the graphene heterostructure after deposition of the Re₂O₇ layer up to 5.4 eV. The hole injection barrier between the Re₂O₇/graphene heterostructure and the N-bis-(1-naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB) layer was estimated to be 0.35 eV, which is very promising for a good OLED performance.

Titania dioxide (TiO₂) layers were synthesized via the acid-catalysed sol-gel route using titania (IV) ethoxide, and then annealed at temperatures varying in the range of 150–700 °C. The research concerned the effect of annealing temperature on the structure of TiO₂ layers, their surface morphology, and their optical properties. Further, X-ray diffractometry, and Raman spectroscopy were used to determine the structure of TiO₂ layers. Scanning electron and atomic force microscopy were used to study the surface morphology of TiO₂ layers. Transmittance, reflectance, absorption edge, and optical homogeneity were investigated by UV-VIS spectrophotometry, while the refractive index and thicknesses of TiO₂ layers were measured using a monochromatic ellipsometer. Chromatic dispersion characteristics of the complex refractive index were determined using spectroscopic ellipsometry. Structural studies have shown that the TiO₂ layers annealed at temperatures up to 300 °C are amorphous, while those annealed at temperatures exceeding 300 °C are polycrystalline containing only anatase nanocrystals with sizes increasing from 6 to 20 nm with the increase of the annealing temperature. Investigations on the surface morphology of TiO₂ layers have shown that the surface roughness increases with the increase in annealing temperature. Spectrophotometric investigations have shown that TiO₂ layers are homogeneous and the width of the indirect optical band gap varies with annealing temperature from 3.53 eV to 3.73 eV.

External light outcoupling structures provide a cost-effective and highly efficient solution for light extraction in organic light-emitting diodes. Among them, different microtextures, mainly optimized for devices with isotopically oriented emission dipoles, have been proposed as an efficient light extraction solution. In the paper, the outcoupling for a preferential orientation of emission dipoles is studied for the case of a red bottom-emitting organic light-emitting diode. Optical simulations are used to analyse the preferential orientation of dipoles in combination with three different textures, namely hexagonal array of sine-textures, three-sided pyramids, and random pyramids. It is shown that while there are minimal differences between the optimized textures, the highest external quantum efficiency of 51% is predicted by using the three-sided pyramid texture. Further improvements, by employing highly oriented dipole sources, are examined. In this case, the results show that the top outcoupling efficiencies can be achieved with the same texture shape and size, regardless of the preferred orientation of the emission dipoles. Using an optimized three-sided pyramid in combination with ideally parallel oriented dipoles, an efficiency of 62% is achievable. A detailed analysis of the optical situation inside the glass substrate, dominating external light outcoupling, is presented. Depicted results and their analysis offer a simplified further research and development of external light extraction for organic light-emitting devices with highly oriented dipole emission sources.

The paper presents a comprehensive look at the perspectives on the use of THz in digital communication systems. The publication aims to focus on arguments that justify a significant increase in the frequency of radio links and their integration with fibre-based networks. Comparison of THz links with their microwave and optical counterparts is discussed from basic physical limitations to technological constraints. Main attention is paid to the available channel capacity resulting from its bandwidth and signal-to-noise ratio. The short final discussion is about technology platforms that seem to be crucial to the availability of suitable THz sources. According to the author, the biggest advantage of using bands in the range of several hundred GHz for a digital data transmission is their use for mobile communication over short distances, as well as for broadband indoor links. However, these applications require a development of compact electronic THz sources with low noise and power reaching single watts. This is beyond the range of the most popular silicon-based technology platform, although a significant progress can be expected with the development of technologies based on wide bandgap semiconductors. Fibre optic connections remain the unquestioned leader in communication over long distances and permanent links.

The paper presents a dual-band plasmonic solar cell. The proposed unit structure gathers two layers, each layer consists of a silver nanoparticle deposited on a GaAs substrate and covered with an ITO layer, It reveals two discrete absorption bands in the infra-red part of the solar spectrum. Nanoparticle structures have been used for light-trapping to increase the absorption of plasmonic solar cells. By proper engineering of these structures, resonance frequencies and absorption coefficients can be controlled as it will be elucidated. The simulation results are achieved using CST Microwave Studio through the finite element method. The results indicate that this proposed dual-band plasmonic solar cell exhibits an absorption bandwidth, defined as the full width at half maximum, reaches 71 nm. Moreover, It can be noticed that by controlling the nanoparticle height above the GaAs substrate, the absorption peak can be increased to reach 0.77.

This work summarises investigations focused on the photoanode impact on the photovoltaic response of dye-sensitized solar cells. This is a comparison of the results obtained by the authors’ research team with literature data. The studies concern the effect of the chemical structure of the applied dye, TiO2 nanostructure, co-adsorbents addition, and experimental conditions of the anode preparation. The oxide substrates were examined using a scanning electron microscope to determine the thickness and structure of the material. The TiO2 substrates with anchored dye molecules were also tested for absorption properties in the UV-Vis light range, largely translating into current density values. Photovoltaic parameters of the fabricated devices with sandwich structure were obtained from current-voltage measurements. During tests conducted with the N719 dye, it was found that devices containing an 8.4 µm thick oxide semiconductor layer had the highest efficiency (5.99%). At the same time, studies were carried out to determine the effect of the solvent and it was found that the best results were obtained using an ACN : tert-butanol mixture (5.46%). Next, phenothiazine derivatives (PTZ-1–PTZ-6) were used to prepare the devices; among the prepared solar cells, the devices containing PTZ-2 and PTZ-3 had the highest performance (6.21 and 6.22%, respectively). Two compounds designated as Th-1 and M-1 were used to prepare devices containing a dye mixture with N719.

Cellular mobile communication networks are experiencing an important evolution with the emerging deployment of 5G networks and the successive decline in the use of previous generations in the years to come. In parallel, policies promoting ecological transition are gaining social impact and economic interest and this seems to be the trend in the near future. In the telecommunications market, the shift between two dominant generations could be an important opportunity to introduce renewable energy sources to green the sector, reducing the carbon footprint of the world-wide extended activity. This work analyses the current situation and provides an insight into the possibilities to incorporate renewable energy supplies, specifically photovoltaics (as it seems to be the most promising among clean electric sources), perhaps combined with small wind turbines in off-grid systems. Paper also compares the characteristics of standard facilities in Spain and Poland, two different European countries in terms of weather and insolation hours.

Thermo-optic properties enhancement of the bi-stable temperature threshold sensors based on a partially filled photonic crystal fiber was reported. Previously tested transducers filled with a selected group of pure n-alkanes had in most cases differences between switching ON and OFF states. Therefore, the modification of filling material by using additional crystallization centers in the form of gold nanoparticles was applied to minimize this undesirable effect. The evaluation of the thermodynamic properties of pentadecane and its mixtures with 14 nm spherical Au nanoparticles based on the differential scanning calorimetry measurements was presented. Optical properties analysis of sensors prepared with these mixtures has shown that they are bounded with refractive index changes of the filling material. Particular sensor switches ON before melting process begins and switches OFF before crystallization starts. Admixing next group of n-alkanes with these nanoparticles allows to design six sensors transducers which change ON and OFF states at the same temperature. Thus, the transducers with a wider temperature range for fiber-optic multi-threshold temperature sensor tests will be used.

In this paper, we present the electrical and electro-optical characterizations of an InAs/GaSb type-2 superlattice barrier photodetector operating in the full longwave infrared spectral domain. The fabricated detectors exhibited a 50% cut-off wavelength around 14 μm at 80 K and a quantum efficiency slightly above 20%. The dark current density was of 4.6 × 10 2 A/cm2 at 80 K and a minority carrier lateral diffusion was evaluated through dark current measurements on different detector sizes. In addition, detector spectral response, its dark current-voltage characteristics and capacitance-voltage curve accompanied by electric field simulations were analyzed in order to determine the operating bias and the dark current regimes at different biases. Finally, dark current simulations were also performed to estimate a minority carrier lifetime by comparing experimental curves with simulated ones.

In perovskite solar cells, series of symmetrical and asymmetrical imino-naphthalimides were tested as hole-transporting materials. The compounds exhibited high thermal stability at the temperature of the beginning of thermal decomposition above 300 °C. Obtained imino-naphthalimides were electrochemically active and their adequate energy levels confirm the application possibility in the perovskite solar cells. Imino-naphthalimides were absorbed with the maximum wavelength in the range from 331 nm to 411 nm and emitted light from the blue spectral region in a chloroform solution. The presented materials were tested in the perovskite solar cells devices with a construction of FTO/b-TiO2/m-TiO2/perovskite/ HTM/Au. For comparison, the reference perovskite cells were also performed (without hole-transporting materials layer). Of all the proposed materials tested as hole-transporting materials, the bis-(imino-naphthalimide) containing in core the triphenylamine structure showed a power conversion efficiency at 1.10% with a short-circuit current at 1.86 mA and an open-circuit voltage at 581 mV.

The article presents a study of a hybrid structure based on the combination of a tapered optical fibre and gold nanoparticles dispersed in a liquid crystal material. Sensitivity to changes of the refractive index of the environment in which the structure is located, as well as the possibility of changing the refractive index of liquid crystals by external factors, such as temperature and electric field, were investigated. Electro- and thermally-induced changes of the refractive index of a liquid crystal through the rotation of a molecule director, which cause changes in the light propagated in a tapered optical fibre, were described. The most important issue in the article is to determine the influence of doping a liquid crystal with gold nanoparticles the concentration of which varies between 0.1 and 0.3 wt.%. The paper presents transmission measurements in a wide optical range depending on voltage, temperature, and frequency changes. Additionally, time courses of the obtained signal were measured. The study shows that the appropriate selection of nanoparticle concentration has a huge impact on the optical wave propagation. The experimental results show that the optical changes obtained for the investigated hybrid structure prefer it for use as an electro-optical switcher, filter, or sensor.

Optical sampling based on ultrafast optical nonlinearities is a useful technique to monitor the waveforms of ultrashort optical pulses. In this paper, we present a new implementation of optical waveform sampling systems by employing our newly constructed free-running mode-locked fibre laser with a tunable repetition rate and a low timing jitter, an all-optical waveform sampler with a highly nonlinear fibre (HNLF), and our developed computer algorithm for optical waveform display and measurement, respectively. Using a femtosecond fibre laser to generate the highly stable optical sampling pulses and exploiting the four-wave mixing effect in a 100 m-long HNLF, we successfully demonstrate the all-optical waveform sampling of a 10 GHz optical clock pulse sequence with a pulse width of 1.8 ps and a 80 Gbit/s optical data signal, respectively. The experimental results show that waveforms of the tested optical pulse signals are accurately reproduced with a pulse width of 2.0 ps. This corresponds to a temporal resolution of 0.87 ps for optical waveform measurement. Moreover, the optical eye diagram of a 10Gbit/s optical data signal with a 1.8 ps pulse width is also accurately measured by employing our developed optical sampling system.

As long as high resolution or long-range observation is to be achieved using infrared detection, it will be necessary to cool down the detector in order to reach the best sensitivity and dynamics. This paper describes different cooling solutions currently used for this purpose discussing advantages and drawbacks. Some guideline is given for cooler choice and selection. The focus is on rotary Stirling coolers illustrated by description of the RMs1 cooler dedicated to high operating temperature size, weight, and power infrared detectors. A user case study is presented with cooler power consumption and cool down time of the RMs1 cooler when integrated in IRnova’s Oden MW IDDCAs.

The paper presents experimental results of the lifetime of light induced excess carriers in the n-type silicon. The lifetimes of carriers of silicon crystals were analysed as a function of the intensity of light illuminating the sample. As a measurement method of the lifetime of carriers, the photoacoustic method in a transmission configuration with different surfaces was used. The dependence character was next analysed in the frame of the Shockley Reed Hall statistics in approximation of the light low intensity.

Number of trace compounds (called biomarkers), which occur in human breath, provide an information about individual feature of the body, as well as on the state of its health. In this paper we present the results of experiments about detection of certain biomarkers using laser absorption spectroscopy methods of high sensitivity. For NO, OCS, C₂H₆, NH₃, CH₄, CO and CO(CH₃)₂ an analysis of the absorption spectra was performed. The influence of interferents contained in exhaled air was considered. Optimal wavelengths of the detection were found and the solutions of the sensors, as well as the obtained results were presented. For majority of the compounds mentioned above the detection limits applicable for medicine were achieved. The experiments showed that the selected optoelectronic techniques can be applied for screening devices providing early diseases detection.

Dye-sensitized solar cells (DSSCs) were prepared using various food dyes. Food dyes are economically superior to organometallic dyes since they are nontoxic and inexpensive. The spectrophotometric evaluation of chosen food dyes in solution and on a TiO₂ substrate show that the dyes form J-aggregation on the photoelectrode substrate. Oxidation of potential measurements for used food dyes ensured an energetically permissible and thermodynamically favorable charge transfer throughout the continuous cycle of a photo-electric conversion. The performance of dye-sensitized solar cells based on food dyes was studied. The results illustrate that the dye containing carboxylic acid and sulfonic acid as the acceptor group gave the maximum conversion efficiency 4.20%.

In this study a metal clad waveguide sensor with a metamaterial guiding layer is analyzed. Sensitivity of the proposed sensor is derived using dispersion and Fresenal’s equations for waveguiding mode and reflection mode. While efficiently analyzing and comparing the results with the existing one, some interesting findings are achieved. It is observed that the proposed sensor shows larger cover layer sensitivity and larger adlayer sensitivity compared to the dielectric guiding layer sensor due to adsorbtive properties of metamaterial. Henceforth, it concludes that the proposed sensor shows sensitivity improvement over a dielectric guiding layer sensor.

Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards (110). The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.