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.
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.
ZnO thin layers were deposited on p-type silicon substrates by the sol-gel spin-coating method and, then, annealed at various temperatures in the range of 573–873 K. Photoluminescence was carried out in the temperature range of 20–300 K. All samples showed two dominant peaks that have UV emissions from 300 nm to 400 nm and visible emissions from 400 nm to 800 nm. Influence of temperature on morphology and chemical composition of fabricated thin layers was examined by XRD, SEM, FTIR, and Raman spectroscopy. These measurements indicate that ZnO structure is obtained for samples annealed at temperatures above 573 K. It means that below this temperature, the obtained thin films are not pure zinc oxide. Thus, annealing temperature significantly affected crystallinity of the thin films.
Graphene applications in electronic and optoelectronic devices have been thoroughly and intensively studied since graphene discovery. Thanks to the exceptional electronic and optical properties of graphene and other two-dimensional (2D) materials, they can become promising candidates for infrared and terahertz photodetectors.
Quantity of the published papers devoted to 2D materials as sensors is huge. However, authors of these papers address them mainly to researches involved in investigations of 2D materials. In the present paper this topic is treated comprehensively with including both theoretical estimations and many experimental data.
At the beginning fundamental properties and performance of graphene-based, as well as alternative 2D materials have been shortly described. Next, the position of 2D material detectors is considered in confrontation with the present stage of infrared and terahertz detectors offered on global market. A new benchmark, so-called “Law 19”, used for prediction of background limited HgCdTe photodiodes operated at near room temperature, is introduced. This law is next treated as the reference for alternative 2D material technologies. The performance comparison concerns the detector responsivity, detectivity and response time. Place of 2D material-based detectors in the near future in a wide infrared detector family is predicted in the final conclusions.
The perovskites XBiO3 (X = Al, Ga, In) have been studied in terms of mechanical, optical and thermoelectric behavior for energy harvesting application. Density functional theory is applied to study electronic, optical and thermoelectric properties of the studied materials. Structural, mechanical and thermodynamic stabilities are confirmed from the tolerance factor, Born mechanical stability and formation energy/specific heat capacity. Poisson and Plough ratios show the studied materials are ductile and have ability to withstand pressure. Band structure analysis shows the indirect band gap 3.0/2.1/1.0 eV for ABO/GBO/IBO. A complete set of optical spectra is reported by dielectric constants, refractive index, optical conduction, absorption of light and optical loss energy. Shifting of maximum absorption band to visible region increases the potential of perovskites XBiO3. Transport characteristics are also investigated by electrical conductivity, Seebeck coefficient and figure of merit.
The presented article examines aspects of a PV module testing using natural sunlight in outdoor conditions. The article discusses the physical sense of indexes: atmosphere purity, diffused component content, beam clear sky index. Procedures for their determination are given in relation to both instantaneous and daily values. Their close connection with the values of solar irradiance spectral distribution such as Average Photon Energy and Useful Fraction is demonstrated, as well as their usefulness in module testing in outdoor conditions. Their influence on the conversion of modules made from various absorbers and various technologies is demonstrated
This article proposes and examines a solution in which the base-station for the fifth generation radio access network is simplified by using a single millimeter-wave oscillator in the central-station and distributing its millimeter-wave signal to the base-stations. The system is designed in such a way that the low-phase-noise signal generated by an opto-electronic oscillator is transmitted from the central-station to multiple base-stations via a passive optical network infrastructure. A novel flexible approach with a single-loop opto-electronic oscillator at the transmitting end and a tunable dispersion-compensation module at the receiving end(s) is proposed to distribute a power-penalty-free millimeter-wave signal in the radio access network. Power-penalty-free signal transmission from 10 MHz up to 45 GHz with an optical length of 20 km is achieved by a combination of a tunable dispersion-compensation module and an optical delay line. In addition, measurements with a fixed modulation frequency of 39 GHz and discretely incrementing optical fiber lengths from 0.625 km to 20 km are shown. Finally, a preliminary idea for an automatically controlled feedback-loop tuning system is proposed as a further research entry point.
This paper presents a detailed review on a present confused situation related to defining and measurement of the eyepiece diopter range of optical/electro-optical devices to be used for a direct observation by human observers. On the basis of this review three precise definitions of a direct view imagers eyepiece diopter are presented. One of these definitions is determined as optimal fit to describe the perception of human observers. Further on, design and measurement uncertainties of diopter meters are discussed and rules of accurate measurements are formulated. Finally, recommendations for the maximum acceptable errors of the diopter scale of eyepieces of classic types of direct view imagers are presented, as well.
Photoelectrical characteristics of scanning IR detectors with implemented time delay and integration mode are analyzed. A new “shifted cellular” layout of photosensitive elements in the FPA structure is proposed. Advantages of the new FPA configuration in terms of threshold sensitivity for small-size/point objects are demonstrated. The analysis is based on the Monte Carlo simulation of the diffusion process of photogenerated minority charge carriers in the photosensitive layer photodiode arrays. The analysis is performed taking into account the main photoelectric parameters of FPA elements: photosensitive layer thickness, diffusion length of charge carriers, optical absorption length, their design parameters: geometric sizes of FPA elements, diameters of p-n junctions, and design parameters of the optical system: optical-spot diameter.