This paper reports simulation results for 1550 nm wavelength absorption efficiency of a superconducting NbN nanowire coupled to a single-mode Si3N4 waveguide depending on SiO2 cladding thickness. Simulation results for straight, U-and W-shaped strips show that with perfect planarization (no top cladding) the absorption coefficient per unit length is 0.031, 0.07 and 0.11 dB/pm, respectively.

In this paper, we present a technological method for creating high-density luminescent structures based on up-conversion NaYF4:Yb3+, Er3+ particles and experimentally demonstrate the possibility of their creation. This technology is applicable for large-scale fabrication of patterned media with a level of filling with microparticles of more than 96% for the fabrication of planar structures applicable in photonics and optoelectronics.

We present the result of the creation and investigation of the multi-element superconducting single photon detectors, which can recognize the number of photons (up to six) in a short pulse of the radiation at telecommunication wavelengths range. The best receivers coupled with single-mode fiber have the system quantum efficiency of ⁓85%. The receivers have a 100 ps time resolution and a few nanoseconds dead time that allows them to operate at megahertz counting rate. Implementation of the multi-element architecture for creation of the superconducting single photon detectors with increased sensitive area allows to create the high efficiency receivers coupled with multi-mode fibers and with preserving of the all advantages of superconducting photon counters.

Quantum cascade lasers (QCL) are widely adopted as prominent and easy-to-use solid-state sources of terahertz radiation. Yet some applications require generation and detection of very sharp and narrow terahertz-range pulses with a specific spectral composition. We have studied time-resolved light-current (L-I) characteristics of multimode THz QCL operated with a fast ramp of the injection current. Detection of THz pulses was carried out using an NbN superconducting hot-electron bolometer with the time constant of the order of 1 ns while the laser bias current was swept during a single driving pulse. A nonmonotonic behavior of the L-I characteristic with several visually separated subpeaks was found. This behavior is associated with the mode competition in THz QCL cavity, which we confirm by L-I measurements with use of an external Fabry-Perot interferometer for a discrete mode selection. We also have demonstrated the possibility to control the L-I shape with suppression of one of the subpeaks by simply adjusting the off-axis parabolic mirror for optimal optical alignment for one of the laser modes. The developed technique paves the way for rapid characterization of pulsed THz QCLs for further studies of the possibilities of using this approach in remote sensing. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)

In this article, present the first detailed study of cascade switching in superconducting photon number resolving detectors. The detectors were made in the form of four parallel nanowires, coupled with the single-mode optical fiber and mounted into a closed-cycle refrigerator with a temperature of 2.1 K. We found out the value of additional false pulses (N cas.sw. ) appearing due to cascade switching and showed that it is possible to set up the detector bias current that corresponds to a high level of the detection efficiency and a low level of N cas.sw. simultaneously. We reached the detection efficiency of 60% and N cas.sw. = 0.3%.

The article outlines methods for providing automatic test design for testing integrated structures that implement ultra-large integrated circuits (VLSI). An original route for designing test solutions for ultra-large integrated circuits testing is presented. These solutions include a set of functional tests and electrical equipment with a contacting device. The paper provides a description of the original CAD Functional Test Studio (FT Studio), which provides a solution to this problem and operates on the basis of the original object-and-machine-oriented language STeeL (Smirnov Test Electrical Exposition Language). This system allows automating the verification of almost all types of VLSI, the composition of which is determined by the current standard OST B 11.073.012 -87 "Integrated circuits. General and specific specifications.", including VLSI qualification tests. The proposed method is based on the two-way communication of the VLSI mathematical and topological model implemented in the FT Studio system, supported continuously within a unified information environment, and really provides an automatic process of functional control of integrated structures. FT Studio CAD provides hardware support and multi-platform support for process equipment

The purpose of the present work is to minimize time for and improve the quality of automatic placement of fragments of Very Large Scale Integration circuits on a crystal as compared to the known algorithms. Modern methods of solving this problem use search procedures, which produce the results appropriate for use in practice, requiring much computer time. Method of placement, suggested in this paper, instead of search procedures uses a procedure of dichotomous division of crystal area into sectors with further redistribution of VLSI fragments across crystal. Sector-wise placement of VLSI fragments implements a formal mechanism of ―attracting‖ fragments to each other that optimizes the structure of connections between fragments. The method allows to optimally place several thousands of VLSI fragments on a crystal in minutes. Placement enables to reduce the total length of connections between fragments and order their structure. The paper presents the results of comparing effectiveness of the suggested algorithm with effectiveness of the method for placing VLSI fragments using fractal aggregation and genetic algorithm. A gain (12,5%) is yielded in total length of connections, with substantially shorter time duration for processor functioning.

The study of the bolometer response to terahertz (THz) radiation from a double-barrier resonant tunneling diode (RTD) biased into the negative differential conductivity region of the I–V characteristic revealed that the RTD emits two pulses in a period of intrinsic self-oscillations of current. The bolometer pulse repetition rate is a multiple of the fundamental frequency of the intrinsic self-oscillations of current. The bolometer pulses are detected at two critical points with a distance between them being half or one-third of a period of the current self-oscillations. An analysis of the current self-oscillations and the bolometer response has shown that the THz photon emission is excited when the tunneling electrons are trapped in (the first pulse) and then released from (the second pulse) miniband states.

Abstract WSi thin films have the advantages for creating SNSPDs with a large active area or array of detectors on a single substrate due to the amorphous structure. The superconducting properties of ultrathin WSi films substantially depends on their structure and thickness as the NbN films. Scientific groups investigating WSi films mainly focused only on changes of their thickness and the ratio of the components on the substrate at room temperature. This paper presents experiments to determine the effect of the bias potential on the substrate, the temperature of the substrate, and the peak power of pulsed magnetron sputtering, which is the equivalent of ionization, a tungsten target, on the surface resistance and superconducting properties of the WSi ultrathin films. The negative effect of the substrate temperature and the positive effect of the bias potential and the ionization coefficient (peak current) allow one to choose the best WSi films formation mode for SNSPD: substrate temperature 297 K, bias potential -60 V, and peak current 3.5 A.

We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000 mu m and film thicknesses d similar to 4-6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T *(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.

The paper presents the experimental results of studying the dynamics of electron energy relaxation in structures made of thin (d ≈ 6 nm) disordered superconducting vanadium nitride (VN) films converted to a resistive state by high-frequency radiation and transport current. Under conditions of quasi-equilibrium superconductivity and temperature range close to critical (~ Tc), a direct measurement of the energy relaxation time of electrons by the beats method arising from two monochromatic sources with close frequencies radiation in sub-THz region (ω ≈ 0.140 THz) and sources in the IR region (ω ≈ 193 THz) was conducted. The measured time of energy relaxation of electrons in the studied VN structures upon heating of THz and IR radiation completely coincided and amounted to (2.6–2.7) ns. The studied response of VN structures to IR (ω ≈ 193 THz) picosecond laser pulses also allowed us to estimate the energy relaxation time in VN structures, which was ~ 2.8 ns and is in good agreement with the result obtained by the mixing method. Also, we present the experimentally measured volt-watt responsivity (S~) within the frequency range ω ≈ (0.3–6) THz VN HEB detector. The estimated values of noise equivalent power (NEP) for VN HEB and its minimum energy level (δE) reached NEP@1MHz ≈ 6.3 × 10–14 W/√Hz and δE ≈ 8.1 × 10–18 J, respectively.

Abstract Spectral characteristics of WSi and NbN superconducting single-photon detectors with different surface resistance and width of nanowire strips have been investigated in the wavelength range of 1.3-2.5 μm. WSi structures with narrower strips demonstrated better performance for detection of single photons in longer wavelength range. The difference in normalized photon count rate for such structures reaches one order of magnitude higher in comparison with structures based on NbN thin films at 2.5 μm.

The use of improved fabrication technology, highly disordered NbN thin films, and intertwined section topology makes it possible to create high-performance photon-number-resolving superconducting single-photon detectors (PNR SSPDs) that are comparable to conventional single-element SSPDs at the telecom range. The developed four-section PNR SSPD has simultaneously an 86 +/- 3% system detection efficiency, 35 cps dark count rate, similar to 2 ns dead time, and maximum 90 ps jitter. An investigation of the PNR SSPD's detection efficiency for multiphoton events shows good uniformity across sections. As a result, such a PNR SSPD is a good candidate for retrieving the photon statistics for light sources and quantum key distribution systems. (C) 2019 Optical Society of America

We study parametric down-conversion (PDC) of optical laser radiation in the strongly frequency non-degenerate regime which is promising for the generation of quantum-correlated pairs of extremely different spectral ranges, the optical and the terahertz (THz) ones. The possibility to detect tenuous THz-frequency photon fluxes generated under low-gain spontaneous PDC is demonstrated using a hot electron bolometer. Then experimental dependences of the THz radiation power on the detection angle and on the pump intensity are analyzed.

Abstract We present development of large active area superconducting single-photon detectors well coupled with standard 50 μm-core multi-mode fiber. The sensitive area of the SSPD is patterned using the photon-number-resolving design and occupies an area of 40×40 μm2. Using this approach, we have obtained excellent specifications: system detection efficiency of 47% measured using a 900 nm laser and low dark count rate of 100 cps. The main advantages of the approach presented are a very short dead time of the detector of 22 ns and FWHM jitter value of about 130 ps.

We report on the development of a heterodyne receiver at mid-infrared wavelength for high-resolution spectroscopy applications. The receiver employs a superconducting NbN hot electron bolometer as a mixer and a room temperature distributed feedback quantum cascade laser operating at 10.6 μm (28.2 THz) as a local oscillator. The stabilization of the heterodyne receiver has been achieved using a feedback loop controlling the output power of the laser. Improved Allan variance times as well as a double sideband receiver noise temperature of 5000 K and a noise bandwidth of 2.8 GHz of the receiver system are demonstrated.

We optimized technology of thin VN films deposition in order to study VN-based superconducting single-photon detectors. Investigation of the main VN film parameters showed that this material has lower resistivity compared to commonly used NbN. Fabricated from obtained films devices showed 100% intrinsic detection efficiency at 900 nm, at the temperature of 1.7 K starting with the bias current of 0.7·I

Invention and demonstration of solid-state terahertz-range quantum cascade lasers (THz QCLs), followed by inevitable development of the fabrication technology, brought in a new era for the terahertzrange related fundamental and practical applications, such as spectroscopy and astrophysics, imaging and communication. With increase of the THz QCL research papers (with details found elsewhere, e.g., [14]), optimization of the lasing characteristics, improvement of its performance and development of the laser characterization techniques attracts a special attention among the researchers. There is a wide variety of different techniques for the detection of THz QCL. However, most of them are based on incoherent thermal detection with the slow time-constant of thermal process ~ 1 ms. In this paper, we present a new characterization method of THz QCL operated in the pulsed mode. In the proposed method the THz QCL is biased by applying a smooth gradual (i.e., with a “slow-rising” front edge) voltage pulse, and the laser output power was measured using NbN superconducting hot electron bolometer (HEB) within a single voltage pulse front edge, which was possible due to sufficiently short response time (of the order of 1 ns) of the HEB. The HEB which we used was similar to that described elsewhere [5]. The primary advantage of this method over the most common THz detection techniques derives from its ability to measure THz QCL output power-current relationship within a single voltage pulse. In addition, the use of a smooth gradual voltage pulse makes it possible to avoid strong fluctuations of the current flowing through the THz QCL at the beginning and the end of the driving pulse in the case of using a driving pulse with sharp edges [6]. In our setup, THz QCL was mounted onto a cold plate of a closed-cycle refrigerator, whose base temperature was varied in a range of 5 – 60 K. Principally, a very short measurement time set by duration of the driving pulse and its repetition rate (~ 5 μs and 200 Hz, respectively), prevents the QCL from overheating by the driving current. Amplitude of the driving pulse was chosen to be slightly higher than the laser threshold voltage. Fig. 1 depicts a driving pulse along with the measured lasing power which is given in arbitrary units. THz radiation was focused by a couple of off-axis parabolic mirrors onto the detector block. HEB was installed onto a cold plate of a wet helium cryostat. DC voltage and a resistive heater were used to bias the HEB to its optimal bias point where a high responsivity is obtained. THz QCL power incident on the detector was kept within detector’s dynamic range. The HEB signal was amplified using a low noise cold amplifier and an R&S oscilloscope was used for the signal analysis. THz QCL based on four tunnel-coupled quantum wells GaAs/Al0.15Ga0.85As with a resonance-phonon depopulation scheme emitting near 2.3 THz was investigated by the proposed method. The laser was processed into a double metal waveguide based on Au with dimensions 1 mm × 100 μm ×10 μm using the conventional technology described in [7]. The laser is die bonded to a copper submount with wire bonding to ridge structures. No coatings or lens were deposited on the laser facet. A THz QCL emits radiation when the value of voltage exceeds the laser threshold level (i.e. when the laser gain coefficient is exactly balanced by the sum of waveguide and mirror losses). Applying a smooth gradual voltage pulse it becomes possible to smoothly approach the threshold condition which was examined at different operating temperatures of the QCL. As deduced from data given in Fig. 1, the laser threshold and peak power are achieved at voltages of 10.7 V and 10.8 V at 5 K, respectively. A further increase in the laser voltage is accompanied by a sharp drop in the optical power until lasing ceases at 11.3 V. After a sharp increase in output power beyond the laser threshold,

We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range 452-2300 nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric downconversion, where one photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as 4×104 in our detection setting. A photon detection efficiency as high as 64% at 1550 nm and 15% at 2300 nm was observed.

We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range $457$ nm - $2300$ nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric down conversion, where one of photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as $4times 10^4$ in our detection setting. A photon detection efficiency as high as $64$ % at $1550$ nm and $15$ % at $2300$ nm was observed.