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Results for “diffractive optical networks”
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Gain-phase grating based on spatial modulation of active Raman gain in cold atoms
In order to obtain an atomic grating which can diffract light into the high-order directions more efficiently, a gain-phase grating (GPG) based on the spatial modulation of active Raman gain is theoretically presented. This grating is induced by a pump field and a standing wave in ultracold atoms, and it not only diffracts a weak probe field propagating along a direction normal to the standing wave into the high-order directions, but also amplifies the amplitude of the zero-order diffraction. In contrast with electromagnetically induced grating or electromagnetically induced phase grating, the GPG has larger diffraction efficiencies in the high-order directions. Hence it is more suitable to be utilized as an all-optical router in optical networking and communication.
Decoding THz‐Driven Dynamic Fingerprints of Ferroelectric Nanotwin Networks
Ultrafast polarization dynamics in ferroelectrics are of considerable interest for high-speed tunable dielectrics and electro-optics. Extended domain wall networks formed in ferroelectric twin nanodomains can support collective dynamics in the terahertz regime but require techniques that track polarization and strain evolution driven by ultrafast stimulus. Here, we use multi-modal probing of THz-pulse-driven excitations in PbTiO 3 /SrTiO 3 superlattices by combining X-ray free electron laser measurements that directly tracks lattice changes, with optical second harmonic generation that tracks the electronic potential coupled with the lattice potential. Dynamical phase-field modeling enables fingerprinting of these collective modes as superpositions of domain “breathing” through wall oscillations and polarization “rotations” with still walls. Ultrafast domain wall motion at 0.1–0.5 THz is observed at practical fields of 100 kV/cm with wall velocities of >4000 m/s, approaching typical speed of sound in PbTiO 3 . A unique “charging” mode is discovered that can electrically charge and discharge domain walls on ∼4 ps time scale thus dynamically tuning wall conductivity. Integrated experimental and theoretical fingerprinting of the dynamical landscape presented here enables ultrafast control of ferroics for high-speed microelectronics and optical applications.
Design considerations for the beam-waveguide retrofit of a ground antenna station
Retrofitting an antenna that was originally designed without a beam waveguide introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dual-shaped reflector. To obtain an acceptable image, certain Geometrical Optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-meter dual-shaped DSN (Deep Space Network) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. GTD and FFT algorithms are particularly necessary at the higher frequencies, while Physical Optics and Spherical Wave Expansions proved necessary at the lower frequencies.
Massively parallel and universal approximation of nonlinear functions using diffractive processors
Nonlinear computation is essential for a wide range of information processing tasks, yet implementing nonlinear functions using optical systems remains a challenge due to the weak and power-intensive nature of optical nonlinearities. Overcoming this limitation without relying on nonlinear optical materials could unlock unprecedented opportunities for ultrafast and parallel optical computing systems. Here, we demonstrate that large-scale nonlinear computation can be performed using linear optics through optimized diffractive processors composed of passive phase-only surfaces. In this framework, the input variables of nonlinear functions are encoded into the phase of an optical wavefront—e.g., via a spatial light modulator (SLM)—and transformed by an optimized diffractive structure with spatially varying point-spread functions to yield output intensities that approximate a large set of unique nonlinear functions–all in parallel. We provide proof establishing that this architecture serves as a universal function approximator for an arbitrary set of bandlimited nonlinear functions, also covering wavelength-multiplexed nonlinear functions as well as multi-variate and complex-valued functions that are all-optically cascadable. Our analysis also indicates the successful approximation of typical nonlinear activation functions commonly used in neural networks, including the sigmoid, tanh, ReLU (rectified linear unit), and softplus. We numerically demonstrate the parallel computation of one million distinct nonlinear functions, accurately executed at wavelength-scale spatial density at the output of a diffractive optical processor. Furthermore, we experimentally validated this framework using in situ optical learning and approximated 35 unique nonlinear functions in a single shot using a compact setup consisting of an SLM and an image sensor. These results establish diffractive optical processors as a scalable platform for massively parallel universal nonlinear function approximation, paving the way for new capabilities in analog optical computing based on linear materials.
Deformable, Programmable, and Shape-Memorizing Micro-Optics
The use of shape memory polymers is demonstrated for deformable, programmable, and shape-memorizing micro-optical devices. A semi-crystalline shape memory elastomer, crosslinked poly(ethylene-co-vinyl acetate), is used to prepare various micro-optic components, ranging from microlens and microprism arrays to diffraction gratings and holograms. Here, the precise replication of surface features at the micro- and nanoscale and the formation of crosslinked shape memory polymer networks can be achieved in a single step via compression molding. Further deformation via hot pressing or stretching of micro-optics formed in this manner allows manipulation of the microscopic surface features, and thus the corresponding optical properties. Due to the shape memory effect, the original surface structures and the optical properties can be recovered and the devices be reprogrammed, with excellent reversibility in the optical properties. Furthermore, arrays of transparent resistive microheaters can be integrated with deformed micro-optical devices to selectively trigger the recovery of surface features in a spatially programmable manner, thereby providing additional capabilities in user-definable optics.
Synthesis, growth, structural and optical studies of a new organic three dimensional framework: 4-(aminocarbonyl)pyridine 4-(aminocarbonyl)pyridinium hydrogen L-malate
4-(aminocarbonyl)pyridine 4-(aminocarbonyl)pyridinium hydrogen L-malate [(4ACP)(4ACP).(LM)] a new organic nonlinear optical (NLO) crystal was grown by the slow evaporation method. Single crystal X-ray diffraction analysis revealed that the [(4ACP)(4ACP).(LM)] crystal belongs to monoclinic crystal system, space group P2{sub 1}/n, with a three dimensional network. Thermogravimetry (TG) and differential thermal (DT) analyses showed that [(4ACP)(4ACP).(LM)] is thermally stable up to 165 °C. The optical transmittance window and the lower cut-off wavelength of [(4ACP)(4ACP).(LM)] were found out by UV–vis–NIR spectral study. The molecular structure of [(4ACP)(4ACP).(LM)] was further confirmed by FTIR spectral studies. The relative dielectric permittivity and dielectric loss were determined as function of frequency and temperature. The third order nonlinear optical property of [(4ACP)(4ACP).(LM)] was studied by the Z-scan technique using a 532 nm diode pumped CW Nd:YAG laser. Nonlinear refractive index, nonlinear absorption coefficient and third order nonlinear susceptibility of the grown crystal were found to be 7.38×10{sup −8} cm{sup 2}/W, 0.08×10{sup −4} cm/W and 5.36×10{sup −6} esu, respectively. The laser damage threshold value is found to be 1.75 GW/cm{sup 2} - Graphical abstract: In the crystal structure of the title complex, the asymmetric unit contains one hydrogen L-malate anion, 4-(aminocarbonyl)pyridinium cation and a neutral isonicotinamide molecule. It is stabilized by intermolecular N-H…O, C-H…O and O-H…O hydrogen bonds which generate a three dimensional network.
Piezoelectric Diffraction-Based Optical Switches
Piezoelectric diffraction-based optoelectronic devices have been invented to satisfy requirements for switching signals quickly among alternative optical paths in optical communication networks. These devices are capable of operating with switching times as short as microseconds or even nanoseconds in some cases.
NASA Tech Briefs, November 2003
Topics covered include: Computer Program Recognizes Patterns in Time-Series Data; Program for User-Friendly Management of Input and Output Data Sets; Noncoherent Tracking of a Source of a Data-Modulated Signal; Software for Acquiring Image Data for PIV; Detecting Edges in Images by Use of Fuzzy Reasoning; A Timer for Synchronous Digital Systems; Prototype Parts of a Digital Beam-Forming Wide-Band Receiver; High-Voltage Droplet Dispenser; Network Extender for MIL-STD-1553 Bus; MMIC HEMT Power Amplifier for 140 to 170 GHz; Piezoelectric Diffraction-Based Optical Switches; Numerical Modeling of Nanoelectronic Devices; Organizing Diverse, Distributed Project Information; Eigensolver for a Sparse, Large Hermitian Matrix; Modified Polar-Format Software for Processing SAR Data; e-Stars Template Builder; Software for Acoustic Rendering; Functionally Graded Nanophase Beryllium/Carbon Composites; Thin Thermal-Insulation Blankets for Very High Temperatures; Prolonging Microgravity on Parabolic Airplane Flights; Device for Locking a Control Knob; Cable-Dispensing Cart; Foam Sensor Structures Would be Self-Deployable and Survive Hard Landings; Real-Gas Effects on Binary Mixing Layers; Earth-Space Link Attenuation Estimation via Ground Radar Kdp; Wedge Heat-Flux Indicators for Flash Thermography; Measuring Diffusion of Liquids by Common-Path Interferometry; Zero-Shear, Low-Disturbance Optical Delay Line; Whispering-Gallery Mode-Locked Lasers; Spatial Light Modulators as Optical Crossbar Switches; Update on EMD and Hilbert-Spectra Analysis of Time Series; Quad-Tree Visual-Calculus Analysis of Satellite Coverage; Dyakonov-Perel Effect on Spin Dephasing in n-Type GaAs; Update on Area Production in Mixing of Supercritical Fluids; and Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure.
Biocompatibility of Hydrogen-Diluted Amorphous Silicon Carbide Thin Films for Artificial Heart Valve Coating
Amorphous silicon carbide (a-SiC:H) thin films were synthesized using trichloromethylsilane by a hot wire chemical vapor deposition process. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy to confirm its chemical bonding, structural network and composition of the a-SiC:H films. The optical microscopy images reveal that hydrogen dilution increased the surface roughness and pore density of a-SiC:H thin film. The Raman spectroscopy and FTIR spectra reveal chemical network consisting of Si-Si, C-C and Si-C bonds, respectively. The XRD spectroscopy and Raman spectroscopy indicate a-SiC:H still has short-range order. In addition, in vitro cytotoxicity test ensures the behavior of cell–semiconductor hybrid to monitor the proper coordination. The live–dead assays and MTT assay reveal an increase in green nucleus cell, and cell viability is greater than 88%, respectively, showing non-toxic nature of prepared a-SiC:H film. Moreover, the result indicated by direct contact assay, and cell prefers to adhere and proliferate on a-SiC:H thin films having a positive effect as artificial heart valve coating material.
Pulsed laser powder bed fusion additive manufacturing of A356
Highlights: • Dense A356 specimens (98 ± 0.4%) were fabricated using a customized P-LPBF system. • Microstructure and grain morphology were examined using LOM, SEM, and EBSD. • Solidification front velocities (R) were evaluated through the KGT model. • A columnar grain structure was observed and predicted by the Hunt's criterion. - Abstract: A356 (Al7SiMg) specimens were fabricated through pulsed laser powder bed fusion (P-LPBF) additive manufacturing. Microstructural examinations and analyses were carried out through the usage of light optical microscopy (LOM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The results revealed a fine cellular microstructure with the intercellular network consisting of Al cells and defined by a network of Si arms. The Al cells at the center of the melt pools and within the melt pool boundary bands were measured to be 423 ± 49 nm and 664 ± 76 nm, respectively. The presence of a fine columnar grain structure and epitaxial growth on partially melted grains was observed and explained by the KGT model and Hunt's criterion.
Optical Computation Of Matrices From Vectors
Proposed optical apparatus generates rectangular pattern of light and dark areas, brightnesses of which represent elements of matrix product of two vectors. Photorefractive effect gives rise to four-wave mixing, which generates output beam modulated spatially by matrix product xy(SupT). Optical multipliers used as real-time analog tensor generators, components of neural networks, and generators of patterns to steer electromagnetic beams by diffraction or to effect temporary interconnections in very-large-scale integrated circuits.
Atomic Structure, Dynamics, Changes in Chemical Bonding and Semiconductor-Metal Transition in Sb 2 Se 3 : A Remarkable Material for Quantum Networks and Energy Applications
Antimony sesquiselenide has become an outstanding functional material for photovoltaics, energy storage and transformation, memory and photonic applications. Sb 2 Se 3 is one of the most successful emerging solar light absorbers and has also been identified as a highly promising ultralow-loss phase-change material (PCM) for next-generation coherent nanophotonic processors, photonic tensor cores, quantum and neuromorphic networks. Unlike benchmark telluride PCMs, Sb 2 Se 3 features a quasi-one-dimensional (1D) crystalline structure consisting of (Sb 4 Se 6 ) ∞ ribbons, lacks the typical PCM chemical bonding, and undergoes an extended semiconductor-metal transition above the melting point. Consequently, the origin of high optical contrast between crystalline (SET) and amorphous (RESET) logic states remains elusive and presents a significant challenge. Using high-energy X-ray diffraction and Raman spectroscopy over a wide temperature range, supported by first-principles simulations and complemented by thermal, optical and electrical measurements, as well as by 121 Sb-Mossbauer spectroscopy, the quasi-1D network of orthorhombic antimony sesquiselenide was found to undergo significant evolution in amorphous and supercooled Sb 2 Se 3 , leading to lower coordination, shorter interatomic distances and a higher p-electron density on antimony, indicating changes in chemical bonding. The observed novel Sb 2 Se 3 nanocrystalline polymorph, characterized by trigonal antimony coordination and more isolated Sb-Se ribbons, could help reduce multiple trapping defect states in the bandgap, which are typical of orthorhombic Sb 2 Se 3 , thereby enhancing the power-conversion efficiency of photovoltaic devices. Semimetallic and metallic liquid Sb 2 Se 3 exhibit a gradual transformation into a denser 2D and/or 3D network with higher antimony coordination. Localized electron states in the pseudogap are becoming extended, leading to an increase in electronic conductivity σ following the relationship σ ∝ N(E F ) 2 . Liquid Sb 2 Se 3 also appears to be strongly fragile, with a nonmonotonic change in viscosity and higher atomic mobility in the metallic liquid. Furthermore, these results explain extraordinary functionalities of Sb 2 Se 3 for photonic and energy applications.
Fully Polarimetric Passive W-band Millimeter Wave Imager for Wide Area Search
We describe the design and phenomenology imaging results of a fully polarimetric W-band millimeter wave (MMW) radiometer developed by Pacific Northwest National Laboratory for wide-area search. Operating from 92 - 94 GHz, the W-band radiometer employs a Dicke switching heterodyne design isolating the horizontal and vertical mm-wave components with 40 dB of polarization isolation. Design results are presented for both infinite conjugate off-axis parabolic and finite conjugate off-axis elliptical fore-optics using optical ray tracing and diffraction calculations. The received linear polarizations are down-converted to a microwave frequency band and recombined in a phase-shifting network to produce all six orthogonal polarization states of light simultaneously, which are used to calculate the Stokes parameters for display and analysis. The resulting system performance produces a heterodyne receiver noise equivalent delta temperature (NEDT) of less than 150m Kelvin. The radiometer provides novel imaging capability by producing all four of the Stokes parameters of light, which are used to create imagery based on the polarization states associated with unique scattering geometries and their interaction with the down welling MMW energy. The polarization states can be exploited in such a way that man-made objects can be located and highlighted in a cluttered scene using methods such as image comparison, color encoding of Stokes parameters, multivariate image analysis, and image fusion with visible and infrared imagery. We also present initial results using a differential imaging approach used to highlight polarization features and reduce common-mode noise. Persistent monitoring of a scene using the polarimetric passive mm-wave technique shows great promise for anomaly detection caused by human activity.
Controllable pulse width of bright similaritons in a tapered graded index diffraction decreasing waveguide
We obtain the bright similariton solutions for generalized inhomogeneous nonlinear Schrödinger equation (GINLSE) which governs the pulse propagation in a tapered graded index diffraction decreasing waveguide (DDW). The exact solutions have been worked out by employing similarity transformations which involve the mapping of the GINLSE to standard NLSE for the certain conditions of the parameters. By making use of the exact analytical solutions, we have investigated the dynamical behavior of optical similariton pairs and have suggested the methods to control them as they propagate through DDW. Moreover, pulse width of similariton is controlled through various profiles. These results are helpful to understand the similaritons in DDW and can be potentially useful for future experiments in optical communications which involve optical amplifiers and long-haul telecommunication networks.
A new strontium antimonate{sup III} Sr{sub 5}Sb{sub 22}O{sub 38}: Synthesis, crystal structure and characterizations
A new strontium antimonate{sup III}, Sr{sub 5}Sb{sub 22}O{sub 38}, has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. It crystallizes in the P2{sub 1}/n space group of the monoclinic system with a=11.739(9) Å, b=12.014(10) Å, c=16.412(13) Å, β=91.460(8)°, V=2314.0(3) Å{sup 3}. The crystal structure is built of seven trigonal–pyramidal SbO{sub 3} and four sphenoid SbO{sub 4} polyhedra which are connected through sharing corner-oxygen atoms to form the complex three-dimensional {sub ∞}{sup 3}[Sb{sub 22}O{sub 38}]{sup 10−} anionic network with two different intersectant tunnels along the [111-bar ] and [11-bar 1-bar ] directions accommodating the electric charge balanced Sr{sup 2+} cations. First-principles electronic structure calculations based on the density functional theory (DFT) and the UV–vis diffuse reflectance spectroscopy measurements both indicate that the compound belongs to a direct band insulator with an optical gap value of 3.3 eV. - Graphical abstract: The 2D Sb–O slabs are stacked through sharing oxygen atoms to form the 3D network structure of the new strontium antimonate{sup III} Sr{sub 5}Sb{sub 22}O{sub 38}. - Highlights: • A new strontium antimonate{sup III}, Sr{sub 5}Sb{sub 22}O{sub 38}, has been hydrothermally synthesized. • The single crystal structure was determined by X-ray diffraction. • The powder XRD and UV–vis absorption spectroscopy were studied. • Theoretical studies interpret the relationships between optical absorption and crystal structure.
Reduced graphene oxide based silver sulfide hybrid films formed at a liquid/liquid interface
Free-standing, ultra-thin films of silver sulfide and reduced graphene oxide (RGO) based silver sulfide hybrids are prepared at a liquid/liquid interface employing in situ chemical reaction strategy. Ag{sub 2}S and RGO−Ag{sub 2}S hybrid films are characterized by various techniques such as UV-visible and photo luminescence spectroscopy, X-ray diffraction and scanning electron microscopy. The morphology of hybrid films consists of Ag{sub 2}S nanocrystals on RGO surface while Ag{sub 2}S films contains branched network of dendritic structures. RGO−Ag{sub 2}S exhibit interesting optical and electrical properties. The hybrid films absorb in the region 500–650 nm and show emission in the red region. A higher conductance is observed for the hybrid films arising from the RGO component. This simple low cost method can be extended to prepare other RGO based metal sulfides.
Spontaneous formation of InGaN nanowall network directly on Si
We present the study on epitaxial growth of an InGaN nanowall network directly on Si by plasma-assisted molecular beam epitaxy. Scanning electron microscopy, high-resolution X-ray diffraction, and transmission electron microscopy together with energy-dispersive X-ray analysis infer the crystalline nature of the InGaN nanowall network, oriented along the C-axis, with In composition ranging from pure GaN to 40%. Room temperature photoluminescence is observed, indicating good optical quality. The nanowall network is highly in-plane electrically conductive.