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The class J design space is investigated with half wave current excitation for a solid-state RF amplifier capable of delivering hundreds of watts. Unlike conventional class J designs, the present analysis aims to explore a continuous design space in order to operate a commercially available device, within its practical limits of drain voltage. This design analysis together with package effects and the inclusion of non-linear capacitor is verified experimentally by fabricating a high-power (550 W CW) high-efficiency (62.8%) solid-state amplifier operating at 505.8 MHz. This power was obtained by in-phase combining two similar continuous class J stages, each one contributing half of the total power. For high-power lateral diffused metal-oxide semiconductor devices, the class J design space is found to be more realisable than popular modes of operation in view of the large non-linear output capacitance of the device. The measured output power, efficiency, spurious response and large signal output reflection coefficients are satisfactory and as anticipated from the design analysis. Since the final application of this amplifier is for a solid-state transmitter, a study of repeatability in terms of phase and amplitude imbalances was carried out by fabricating and evaluating multiple amplifiers, each one working with the proposed design principle.

Thin and lightweight retroreflectors of infrared light have been created from pairs of silicon metasurfaces. Metasurfaces are two-dimensional arrangements of subwavelength scatterers that control the propagation of optical waves 1 , 2 , 3 . Here, we show that cascaded metasurfaces, each performing a predefined mathematical transformation 4 , provide a new optical design framework 5 that enables new functionalities not yet demonstrated with single metasurfaces. Specifically, we demonstrate that retroreflection can be achieved with two vertically stacked planar metasurfaces, the first performing a spatial Fourier transform and its inverse, and the second imparting a spatially varying momentum to the Fourier transform of the incident light. Using this concept, we fabricate and test a planar monolithic near-infrared retroreflector composed of two layers of silicon nanoposts, which reflects light along its incident direction with a normal incidence efficiency of 78% and a large half-power field of view of 60°. The metasurface retroreflector demonstrates the potential of cascaded metasurfaces for implementing novel high-performance components, and enables low-power and low-weight passive optical transmitters 6 , 7 , 8 .

A novel concept for integrating visible light communications (VLC) with three‐dimensional indoor positioning is presented. A VLC link based on transmitter and receiver characteristics using experimental measurements was modelled. Proposed is a three‐dimensional positioning algorithm using received signal strength indication, which changes based on the angle and distance of the location based service. To reduce inter‐cell interference, the transmitter's location code was sent using different subcarriers. A demonstration shows that the proposed algorithm can obtain a user's position, including height, accurately and without inter‐cell interference.

With the advancement of solid-state devices for lighting, illumination is on the verge of being completely restructured. This revolution comes with numerous advantages and viable opportunities that can transform the world of wireless communications for the better. Solid-state LEDs are rapidly replacing the contemporary incandescent and fluorescent lamps. In addition to their high energy efficiency, LEDs are desirable for their low heat generation, long lifespan, and their capability to switch on and off at an extremely high rate. The ability of switching between different levels of luminous intensity at such a rate has enabled the inception of a new communication technology referred to as visible light communication (VLC). With this technology, the LED lamps are additionally being used for data transmission. This paper provides a tutorial and a survey of VLC in terms of the design, development, and evaluation techniques as well as current challenges and their envisioned solutions. The focus of this paper is mainly directed towards an indoor setup. An overview of VLC, theory of illumination, system receivers, system architecture, and ongoing developments are provided. We further provide some baseline simulation results to give a technical background on the performance of VLC systems. Moreover, we provide the potential of incorporating VLC techniques in the current and upcoming technologies such as fifth-generation (5G), beyond fifth-generation (B5G) wireless communication trends including sixth-generation (6G), and intelligent reflective surfaces (IRSs) among others.

In this paper, a novel technique is proposed to mitigate the so-called blind range on radars that use pulse compression. It is well known that the blind range is caused by the strong leak-through into the receiver during the transmission cycle. The proposed technique is called progressive pulse compression (PPC) and is based on partial decoding. PPC uses a portion of the uncontaminated received signal in conjunction with pulse compression to estimate the echoes from the incomplete signal. The technique does not require the use of a fill pulse or any hardware modifications. PPC can be divided into three steps. The fist step is to discard all the received signals during the transmit cycle and apply a smooth taper for continuous transition from zero to one. The second step is to perform the pulse compression using matched filter. The combination of these two steps is equivalent to performing pulse compression using a progressively changing template to partially extract the uncontaminated received signal for compression. The third step is to compensate for the progressively changing template so that proper reflectivity values can be recovered. This technique has been tested on the PX-1000 and will be implemented on PX-10k in the near future. These two radars are designed and operated by the Advanced Radar Research Center at the University of Oklahoma and are both X-band software-defined solid-state systems. The results presented in this paper are collected using the PX-1000 radar.

Motif discovery is a powerful and insightful method to quantify network structures and explore their function. As a case study, we present a comprehensive analysis of regulatory motifs in the connectome of the model organism Caenorhabditis elegans ( C. elegans ). Leveraging the Efficient Subgraph Counting Algorithmic PackagE (ESCAPE) algorithm, we identify network motifs in the multi-layer nervous system of C. elegans and link them to functional circuits. We further investigate motif enrichment within signal pathways and benchmark our findings with random networks of similar size and link density. Our findings provide valuable insights into the organization of the nerve net of this well-documented organism and can be easily transferred to other species and disciplines alike. Graphical abstract

Accurate three-dimensional (3D) imaging is essential for machines to map and interact with the physical world 1 , 2 . Although numerous 3D imaging technologies exist, each addressing niche applications with varying degrees of success, none has achieved the breadth of applicability and impact that digital image sensors have in the two-dimensional imaging world 3 – 10 . A large-scale two-dimensional array of coherent detector pixels operating as a light detection and ranging system could serve as a universal 3D imaging platform. Such a system would offer high depth accuracy and immunity to interference from sunlight, as well as the ability to measure the velocity of moving objects directly 11 . Owing to difficulties in providing electrical and photonic connections to every pixel, previous systems have been restricted to fewer than 20 pixels 12 – 15 . Here we demonstrate the operation of a large-scale coherent detector array, consisting of 512 pixels, in a 3D imaging system. Leveraging recent advances in the monolithic integration of photonic and electronic circuits, a dense array of optical heterodyne detectors is combined with an integrated electronic readout architecture, enabling straightforward scaling to arbitrarily large arrays. Two-axis solid-state beam steering eliminates any trade-off between field of view and range. Operating at the quantum noise limit 16 , 17 , our system achieves an accuracy of 3.1 millimetres at a distance of 75 metres when using only 4 milliwatts of light, an order of magnitude more accurate than existing solid-state systems at such ranges. Future reductions of pixel size using state-of-the-art components could yield resolutions in excess of 20 megapixels for arrays the size of a consumer camera sensor. This result paves the way for the development and proliferation of low-cost, compact and high-performance 3D imaging cameras that could be used in applications from robotics and autonomous navigation to augmented reality and healthcare. A compact, high-performance silicon photonics-based light detection and ranging system for three-dimensional imaging is developed that should be amenable to low-cost mass manufacturing

The NASA/Goddard Space Flight Center’s (GSFC’s) W-band (94 GHz) Cloud Radar System (CRS) has been comprehensively updated to modern solid-state and digital technology. This W-band (94 GHz) radar flies in nadir-pointing mode on the NASA ER-2 high-altitude aircraft, providing polarimetric reflectivity and Doppler measurements of clouds and precipitation. This paper describes the design and signal processing of the upgraded CRS. It includes details on the hardware upgrades (SSPA transmitter, antenna, and digital receiver) including a new reflect array antenna and solid-state transmitter. It also includes algorithms, including internal loop-back calibration, external calibration using a direct relationship between volume reflectivity and the range-integrated backscatter of the ocean, and a modified staggered-PRF Doppler algorithm that is highly resistant to unfolding errors. Data samples obtained by upgraded CRS through recent NASA airborne science missions are provided.

Nanomagnets in a spin Magnetic thin film multilayers have many applications for data storage, semiconductor memories and as sensors. The spin-torque effect, which uses an electric current to rapidly spin the material's magnetic constituents, could lead to new applications for this technology at ever-smaller scales: think in terms of a radio set the size of a bacterium. Two groups have now independently achieved synchronization — or phase-locking — of the magnetic oscillations of two such nanomagnets placed just 400–500 nm apart. These oscillations can generate microwave signals for telecommunication and an array of these nanomagnets could also act as a receiver, enabling microchips to communicate without being in physical contact, greatly enhancing computing speed. The spin torque 1 , 2 effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current 3 , 4 , 5 , 6 , 7 , 8 . This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements 9 . The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators 10 , 11 , 12 . Here we show that two STNOs in close proximity mutually phase-lock—that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems 13 , 14 , 15 . The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the lidar transmitter and receiver. A new quasi-solid-state lidar optical architecture employs a transmitter with a two-dimensional MEMS mirror for fine beam steering at a fraction of the degree of the angular resolution and is combined with a digital micromirror device for wide FOV scanning over 37 degree while sustaining a large aperture area of 140 mm squared. In the receiver, a second digital micromirror device is synchronized to the transmitter DMD, which enables a large FOV receiver. An angular resolution of 0.57°(H) by 0.23° (V) was achieved with 0.588 fps for scanning 1344 points within the field of view.