High-power InAlAs/InGaAs Schottky barrier photodiodes for analog microwave signal transmission

The design, manufacturing and DC and microwave characterization of high-power Schottky barrier InAlAs/InGaAs back-illuminated mesa structure photodiodes are presented. The photodiodes with 10 and 15 μm mesa diameters operate at ≥40 and 28 GHz, respectively, have the output RF power as high as 58 mW at a frequency of 20 GHz, the DC responsivity of up to 1.08 A/W depending on the absorbing layer thickness, and a photodiode dark current as low as 0.04 nA. We show that these photodiodes provide an advantage in the amplitude-to-phase conversion factor which makes them suitable for use in high-speed analog transmission lines with stringent requirements for phase noise.

Precise spectrophotometric method for semitransparent metallic thin-film index determination using interference enhancement

A precise spectrophotometric method to determine the refractive index of a semitransparent metallic thin film is presented. This method relies on interference enhancement of the measured spectra, employing an opaque substrate with a dielectric spacer layer beneath the absorbing layer of interest to create interference fringes.The resulting spectral oscillations of the stack are highly sensitive to the properties of the top absorbing layer, allowing precise determination of the refractive index via fitting. The performance of this method is verified using simulations in comparison to the typical method of depositing the absorbing thin film directly onto a transparent substrate. An experimental demonstration is made for titanium thin films over the visible range (370-835 nm). The refractive index of these films is extracted from experimental data using a combination of the Modified Drude and Forouhi-Bloomer models. This method showed high repeatability and precision, and is verified for Ti films between 6-70 nm thickness.

Study of Structural Characteristics of Asphalt Overlays on Airport Pavement with Damaged Load Transfer Efficiency of Joints

In this paper, the real joint load transfer efficiency of airport pavement is calculated by combining the results of airport pavement deflection detection and ground-penetrating radar detection. Spring elements are used to simulate the actual load transfer efficiency of joints in ABAQUS. The impact of different asphalt overlays on the stress state of the critical point in the pavement is analyzed by the airport cement concrete pavement model. The result shows that adding a thin stress-absorbing layer with fine-graded and low modulus can effectively disperse the load transferred from the asphalt pavement to the cement pavement and the stress concentration at the joint under the asphalt overlay. Compared with airport pavement without a stress-absorbing layer, the tensile stress and shear stress at the critical point in the airport pavement asphalt overlay decreased by 24.62% and 22.49%, respectively. Therefore, the combination of the high-modulus upper layer and low-modulus lower layer can effectively reduce the tensile stress and shear stress at the critical point. In addition, increases in the thickness of the asphalt overlay can effectively improve the stress state at the critical point. When the thickness of the asphalt overlay changed from 13 cm to 21 cm, the maximum tensile and shear stress decreased by 8.82% and 8.92%, respectively. Finally, based on the analysis of the numerical simulation and field test verification, the optimal airport pavement asphalt overlay scheme is proposed.

Synthesis, Properties and Applications of Lead-Free Perovskites:A Review

Perovskites are the materials or compounds having a structure similar to calcium titanium oxide (CaTiO3). These materials possess the basic structure of ABX3, in which A & B are the cations with +1 and +2 electron vacancy and X is an anion which may be either halogen or oxygen. Perovskites are chiefly being used in solar cells in the photo absorbing layer for solar to electrical energy conversion with relatively high efficiencies, besides their use in LEDs, photodetectors, X-ray detectors, lasers etc. The power conversion efficiency (PCE) of Perovskite solar cell (PSC) has increased from 10% in the year 2012 to 29.1% in 2020 and are promising to cross the theoretical maximum (Shockley-Queisser) limit of 33% for conventional silicon solar cells, besides having great thermal and mechanical stability values. Toxicity due to the presence of lead and associated instability of PSCs have led to the intensive research in lead-free perovskite solar cells (LF-PSCs). In this review article we have tried to explore the current status of synthesis, properties and applications of perovskites in PSCs,particularly lead-free perovskites, and will suggest future prospects in this widely attracted field of non-conventional energy generation.

Investigation of the Effect of Temperature Stabilization in Radiation–Heat Converters Based on a Strong Absorbing Coating

Light–heat converters are promising for further development of contact laser surgery. The simplest converter consists of an optical fiber with a strong absorbing layer at the tip. We studied the time dependence of the tip temperature at different CW laser powers and revealed that, in several seconds, the temperature evolution becomes almost power-independent. Mathematical modeling showed that laser ablation of the tip coating is the main reason for this phenomenon.

Layered shock-resistant element parts shape change process selection and modeling

An impact-resistant layered element consisting of two outer layers from highly rigid material and an inner layer from viscoelastic material has been developed. The item reduces the barring effect on the protected object. The design peculiarity is that the outer part has a bend with a deflection arrow within 10… 15 thicknesses, and has a connection of the outer layers from high-stiff material on opposite edges with staples from plastic material, which during plastic deformation flows into the edge holes coaxially in the outer layers, on the inner side of the impact-resistant element is attached a shock-absorbing layer from elastic foamed polymeric material, the back surface of which corresponds to the surface of the protected object. For the parts manufacture it has been developed bending sheet parts method in which the bending the part shelves with a bending element with their subsequent straightening. The aim is to increase the process productivity and the geometric dimensions’ accuracy of the part. Modeling the process of parts spontaneous forming "Impact-resistant element upper sheet" on the reverse and direct schemes is performed by the finite element method in the AnSYS / AutoDYN system. The study purpose is to develop technology and modeling the process of the impact-resistant element sheet parts deformation.

Methodology of optimisation for a nanostructured two-photon absorption photodetector

We introduce a 3-step method to optimise a nanostructured photodetector for infrared sensing through non degenerated two-photon absorption (NDTPA). First, the nanostructure is designed to tailor the distribution and concentration of both pump and signal intensities within the absorbing layer, thus leading to a gain in two-photon absorption. Second, the issue of the competition between NDTPA and other sub-bandgap transitions is tackled with a new figure of merit to favor as much as possible NDTPA while minimising other absorption processes. Third, a refined computation of the gain and the figure of merit is done to consider focused beams. Finally, two scenarios based on low power infrared photodetection are investigated to illustrate the flexibility and adaptibility of the method. It is shown that the gain is up to 7 times higher and the figure of merit is up to 20 times higher compared to the literature.