Based on the diffraction neural network, a small-volume diffractive optical element for optical logic calculation in the terahertz band is designed. The optical logic calculation ability and calculation accuracy of the diffraction neural network are calculated. The results show that after training, the diffraction neural network can accurately calculate eight kinds of optical logic and has 100% recognition accuracy when the number of network layers is greater than 5. This article mainly introduces the design principle and calculation process of the diffraction neural network, and compares the recognition accuracy of different network layers.
We propose a type of hybrid structure metalens composed of a graphene-loaded metallic metasurface sandwiched by two mutually orthogonal gratings, which can work in transmission modes for dynamic terahertz wavefront manipulation with tunability and enhanced focusing efficiency. Experimental results show that due to the multi-reflection between the metasurface layer and the grating layers, the focusing efficiency is enhanced by 1.8 times, and the focal length of the metalens is increased by 0.61mm by increasing the applied gate voltage on the graphene from 0V to 1.4V. We hope the proposed structure may open a new avenue for reconfigurable THz metasurfaces with high efficiencies.
Battlefield situational awareness is the core condition that determines the success or failure of the battlefield, and it is also an important application direction of photodetectors. The rapid development of AI technology in recent years is about to cause major changes in future wars. The new AI battlefield will also put forward new urgent needs for situational awareness. This article summarizes the current main modes of collaborative detection of battlefield situation awareness and its research status, including radar / infrared composite detection, multi-source data fusion of radar / infrared detection, cooperative target recognition, target tracking, etc. On this basis, combined with the current development trend of the intelligence level of the main battlefield equipment, we get the development needs of future intelligent battlefield situational awareness for new types of collaborative detection, including requirements for its style, angle, speed, and detection targets of distributed collaborative detection. Based on this, the key development directions and core issues to be solved for intelligent battlefield situational awareness in the future are proposed.
Laser-induced graphene (LIG) has received extensive attention due to its excellent properties such as high electrical conductivity, high thermal stability and electrical conductivity, simple synthesis, and low manufacturing cost of patterned structures. However, most research on LIG has focused on electrical applications. In this work, we first examine the influence of the substrate on the LIG generated on polyimide, and then fabricate patterned LIG structures, including gratings and Fresnel zone plates for terahertz (THz) wave modulation. The function of the structure is proved through the experiment of the terahertz focal plane imaging system. It is expected that the LIG-based structure can widen the application of THz technology.
Control of terahertz (THz) wave polarization state is of great significance for imaging and communication. Dynamically control of THz wave polarization state is achieved by an electronically controlling composite metasurface consisting of the gold cross antennas and a monolayer graphene. The graphene composite metasurface acts as a quarter-wave plate when the external control voltage is 0 V, by which the polarization state of the incident THz wave is converted from linear polarization to circular polarization. When voltage is increased, the chemical potential of graphene is increased gradually, transmitted polarization state of the THz wave is changed from right circular polarization to right elliptical polarization, and to linear polarization. Furthermore, the polarization state of the THz wave is able to be changed from left circular polarization to left elliptical polarization, and to linear polarization if the device is clockwise rotated by 90°. Our work will offer a new avenue for tunable THz polarization modulation devices.
This article summarizes the reports and researches on detection system of STSS published in domestic and foreign literature, summarizes the development process of STSS detection system from a single geostationary orbit to a combined large elliptical orbit, then to the development process of the high-track network and the low-track network cooperate with each other. It also summarizes the development process of infrared detectors from single-band to multi-band, from line scan with less detection pixels to line scan with more detection pixels and large-area staring array. The application scenarios, overall scheme, and overall parameters of the STSS detection system are sorted out, and the core technical indicators are analyzed for the overall parameters. From the perspective of the development process of the US early warning satellite system and the technical characteristics of the space-based infrared system, US early warning satellite technology is of great significance to research on US defense programs, equipment, and system capabilities.
Metasurfaces are widely applied to realize miniaturized optical devices with high performance, because of the high design freedom. Recently, with the help of optical design, cascaded metalenses with two-layered metasurface, which can correct monochromatic aberration have been proposed for a well-focused light spot in the focal plane at large incident angles. However, the focal length is fixed in these systems. In this paper, we report a wide-angle metalens with continuously tunable focus. Through the optical design method, we obtain a lens phase profile with large field of view. And referring to the principle of Moiré lens, a wide angle (±30°) and continuously zoomed metalens with well focusing at infrared wavelength (810nm) was designed, and its characteristics are verified by numerical simulations. Our metalens has great potential in areas where high imaging quality and tunability.
To reduce the plasmonic line width of the metallic nano-structures and improve its performance when used in sensing, a hybrid structure consisting of a graphene stripe and a gold gap-ring is proposed and studied numerically. The structure works at Middle-IR band(3-6μm). Through strong coupling, some narrow dips caused by absorption of graphene appear on the wide background scattering spectrum of the metallic structure. Due to the high plasmonic confinement of graphene, the line width of these dips is around several tens nano-meters. In addition, the resonance intensity of graphene is enhanced significantly. By index changing, the sensing property of this composite structure is also studied. Simulation results show that its sensitivity exceeds 3000 nm/RIU (refractive index unit) and the figure of merit can reach up to 109 which prove our structure a good sensor.
'Micro- and nano-photonics' is a course for PhD candidates in School of Optoelectronics, Beijing Institute of Technology. The aim of the course is to introduce the recent development of micro- and nano-photonics to PhD students of optical engineering. The teaching content includes new branches of photonics, including basic theories and developments of plasmonics, matamaterials, photonics crystals and fibers. Then theoretical analysis of nanophotonics, as well as the simulation methods and software are introduced. The fabrication methods of nanophotonic devices are also introduced. More than 30 PhD students have been taught by this course since 2012. In this paper, we give an introduction about our course and its effects on the students' research. We also give a discussion about how to give class to PhD students with backgrounds of optics and photonics.
KEYWORDS: Holograms, Computer generated holography, Modulation, 3D displays, 3D image processing, Holography, Phase shift keying, 3D image reconstruction, Spatial frequencies, Signal to noise ratio
The real-time holographic display encounters heavy computational load of computer-generated holograms and precisely intensity modulation of 3D images reconstructed by phase-only holograms. In this study, we demonstrate a method for reducing memory usage and modulating the intensity in 3D holographic display. The proposed method can eliminate the redundant information of holograms by employing the non-uniform sampling technique. By combining with the novel look-up table method, 70% reduction in the storage amount can be reached. The gray-scale modulation of 3D images reconstructed by phase-only holograms can be extended either. We perform both numerical simulations and optical experiments to verify the practicability of this method, and the results match well with each other. It is believed that the proposed method can be used in 3D dynamic holographic display and design of the diffractive phase elements.
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