InGaAs/InP Negative Feedback Avalanche Diode (NFAD), with a quenching negative feedback resistor integrated, is a new type of high-sensitivity and all-solid-state semiconductor device based on Single Photon Avalanche Diode (SPAD) structure. This paper proposes a near-infrared free-running single photon counting integrated module based on InGaAs/InP NFAD. It contains an active quench and extraction circuit, sampling and processing circuit, upper computer software design and TEC etc., and is designed to serve a NFAD adopting absorption-attenuation-charge-multiplication (SAGCM) structure with InGaAs/InP materials and operating in Geiger mode. In this module, we specifically design a full differential amplifier and comparator to exploit the performance of NFAD by detecting and extracting the weak avalanche signal and converting it into TTL pulse. The avalanche detection discrimination threshold voltage is adjustable by external high-precision DAC, and a programmable dead time could be set by Field Programmable Gate Array (FPGA). The module system provides timing logic in order to avoid false counting caused by the coupling noise of the differential amplifier. By developing Graphical User Interface (GUI) program, we are able to setup detector working parameters configuration, to display real-time counting data and to further meet different application requirements. The fabricated module exhibits good NFAD performance with PDE of 7.9% and 15.8%, DCR of 1.37 kHz and 1.06 kHz and the after-pulse probability of 34.2% and 16.8% at 223 K, 1550 nm with dead time of 200 ns and 1 μs, respectively. It turns out that a near-infrared single photon counting system possessing fast detection speed, fast quenching time, flexible dead time adjustment, small size and high integration will be available in the near future to strongly support lidar and quantum information facilities.
This paper presents a laser protection idea to form a two-dimensional subwavelength metasurfaces structure with phasechange vanadium dioxide (VO2) material. By using the phase change characteristics of VO2, the signal light can be focused to the infrared focal plane at room temperature, and VO2 undergoes a phase change under the action of a strong laser, which causes the spot on the focal plane to diverge, reducing the light intensity and energy density to protect the focal plane. The final imaging spot diameter of the metasurfaces designed in this paper is 4.4μm, which can intercept 76% of the incident energy from the outside after the phase change.
The self propagating welding of Kovar and sapphire was carried out with NiAl nano multilayers. The samples were tested by X-ray machine, scanning acoustic microscope, scanning electron microscope and bonding tester. The results show that sapphire and Kovar can be well self propagating welded using multilayer NiAl nano multilayers as heat source and solder to form uniform weld joint. The void ratio of the weld joint is 1.1%, and the welding strength is ~ 3.38 MPa. This study lends credible the welding of sapphire and similar metal materials.
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