Quantum communication provides a powerful tool for communication with information-theoretic security and high private capacity. However, until now, almost all studies on underwater quantum communication have been based on the polarization or orbital angular momentum of the single-photon state. Because quantum entanglement is an important resource in quantum communication, it is an interesting but still open question as to whether quantum entanglement still exists after interaction with water and underwater objects. In this study, we use the air-water-metal three-layer model as an example and investigate the dynamics of the output entangled state when both modes are sent through the water. Our results show that strong entanglement exists even after interaction with shallow water, and underwater quantum communication with two-mode quantum entanglement is thus feasible in typical quantum communication scenarios.
Quantum Illumination is a powerful tool for detecting a weakly-reflective target embedded in noise environment. Up to now, all quantum illumination techniques have been investigated in free-space scenario. Thus, it is still an open and interesting question whether quantum illumination could be applied to underwater target detection. Here, by using quantum entanglement generated by spontaneous parametric down conversion and joint quantum measurement of returned signal mode and idler mode, we construct a model of underwater target detection with quantum illumination technique. Further, we apply a set of typical experimental parameter and show that a 10-dB enhancement in the detection of a target embedded in 30-meter water can be observed. This work shows the potential applicability of quantum information technology in future underwater target detection.
Airborne laser bathymetric system has great advantages in shallow sea bathymetric mapping due to its no blind area, high accuracy and high density data. By using Monte Carlo method and radiation-transport equation, the spatial distribution of the signal spot on the sea surface is calculated respectively. The results show that the spatial distribution of the signal spot returned to the sea surface is more extensive with the increase of the depth, and the power attenuation of the center of the spot is more serious. In this paper, signal to noise ratio (SNR) is used as the performance evaluation criterion of laser bathymetry system, and the requirements of field of view for signal detection under different depth are analyzed. The analytic results will provide support for the design and optimization of the laser bathymetric system.
In optical systems, the lens is the most important element, which has been widely used. Conventional lens takes advantage of its convex interface to change the phase along the light path, in order to focus light to a point in the focal plane. However, their spatial resolution is limited to approximately half of the working wavelength restricting the fine observation of tiny objects particular biological samples. Recently superlenses with high resolution focusing property beyond diffraction limit have been proposed without phase compensation resulting in the lack of ability of focus plane wave. We proposed metalens at mid-infrared region made of metamaterials slab and a phase compensation based on mono-layered concave film realizing subwavelength focusing ability (λ/3). The metamaterials slab consists of 200-layered metal -dielectric structure (doped GaN-Si) possessing hyperbolic regime. The curve shape and electromagnetic property of phase compensation mono-layered concave film is obtained through restrict theoretical computation which related to the parameters of the metamaterials slab. The proposed metalens can also be easily extended to three dimension for realistic application as conventional optical lens.
Due to its advantages on the cost, power and size, the study of the CMOS image sensor is considered as an important direction of the development of low-light-level image sensor. However, the sensitivity of current CMOS image sensor does not satisfy the low-light-level application requirements. This paper introduces several key techniques on how to improve the sensitivity of CMOS image sensors. We introduce a novel CMOS low-light-level image sensor based on Geiger mode avalanche photodiode (GM-APD) and digital TDI technology. Noise characteristics and complete signal-tonoise ratio(SNR) theoretical models are constructed for both sensors. A comparison of SNR performance of two image sensors is also done by numerical simulation in this paper. The results show that the novel CMOS low-light-level image sensor outperforms EMCCD at the very low light level.
Due to the suddenness and complexity of modern warfare, land-based weapon systems need to have precision strike capability on roads and railways. The vehicle navigation system is one of the most important equipments for the land-based weapon systems that have precision strick capability. There are inherent shortcomings for single source navigation systems to provide continuous and stable navigation information. To overcome the shortcomings, the multi-source positioning technology is developed. The All Source Positioning and Navigaiton (ASPN) program was proposed in 2010, which seeks to enable low cost, robust, and seamless navigation solutions for military to use on any operational platform and in any environment with or without GPS. The development trend of vehicle positioning technology was reviewed in this paper. The trend indicates that the positioning technology is developed from single source and multi-source to ASPN. The data fusion techniques based on multi-source and ASPN was analyzed in detail.
Planar metalens composed of V-shaped nano-antennas which can realize subwavelength focusing has been fabricated by Focused Ion Beam etching technology. The metalens was completely flat due to the phase manipulation deriving from the different V-shaped nano-antennas aligned in concentric circles. Comparing to conventional curved lens, the as-made metalens was flat and ultrathin (less than thickness of 100 nm) with light weight. Simulation results demonstrated that the focal length can be accurately controlled by changing the arrangement of the nano-antennas.
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