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The combination of high-absorption indium gallium arsenide (InGaAs) with Si material (excellent avalanche characteristic) is an ideal solution for the achievement of high-gain low-noise near-infrared avalanche photodetector (APD). Traditional Si-based epitaxial InGaAs thin film suffers from high threading dislocations (TDs), leading to deterioration of noise and gain-bandwidth product (GBP) of APD. InGaAs/Si APD with GBP exceeding terahertz (THz) is reported for the first time theoretically in this work. The calculated APD is based on the semiconductor interlayer bonding in which a thin polycrystalline Si (poly-Si) bonding layer is inserted at the bonded interface to isolate the mismatched lattices of InGaAs and Si single crystals. Extreme low dark current of 10−12 A of APD at room temperature is achieved due to the absence of TDs in InGaAs layer and it is located at 10−5 A near breakdown voltage (${V}_{\text{br}}$). More importantly, a deviation of the dark and optical currents near ${V}_{\text{br}}$ due to the trapping effect of holes at InGaAs/Si bonded interface is identified. The change in gain with bias is inconsistent with the 3-dB bandwidth (BW). The 3-dB BW becomes linear versus bias with the increase in poly-Si thickness, leading to high 3-dB BW (8–10 GHz) near ${V}_{\text{br}}$. Finally, ultrahigh GBPs of 1.2 and 1.3 THz are achieved for APD with 3- and 5-nm-thick poly-Si bonding layer, respectively. This may give guidance for the fabrication of semiconductor APDs which can meet next-generation high bit-rate applications. [ABSTRACT FROM AUTHOR]

Single-photon avalanche diode (SPAD) is an ultrasensitive device for the detection of weak signals. Epitaxial InP-based devices exhibit poor avalanche characteristics and poor compatibility with Si complementary metal oxide semiconductor (CMOS) circuit, and epitaxial Si-based devices show high dark count rate (DCR) and limited detection wavelength. Here we first show a new generation of InGaAs-on-Si SPADs, achieved by semiconductor interlayer bonding, for the detection of 1550-nm infrared signals theoretically. This wafer-bonded InGaAs/Si SPAD has enabled a significant step-change in performance. The dark current of this SPAD is four orders of magnitude lower than that of the epitaxial ones (300 K). High gain-bandwidth-product of 254 and 353 GHz is achieved at the gain of ~ 24 and ~ 36, respectively, for the wafer-bonded SPAD with polycrystalline Si bonding layer at InGaAs/Si bonded interface. In comparison with epitaxial SPADs, the wafer-bonded ones exhibit low DCR (~ 105 Hz at 10% Vbr), high single photon detection efficiency (~ 24 % at 10% Vbr), and high pulse repetition rate (1 GHz at 5% Vbr) at 300 K. These results indicate that utilizing the wafer-bonded platform, the route toward high-performance InGaAs-on-Si SPAD arrays for use in future eye-safe laser radar (LIDAR) and quantum communication at room temperature (RT) is expected to be achieved. [ABSTRACT FROM AUTHOR]

Due to high ramping rates on the Booster Ring (BRing), which is the key part of the high-intensity heavy-ion accelerator facility (HIAF) complex at the Institute of Modern Physics (IMP), thin-wall vacuum chambers are required for all magnets to maintain the eddy currents at a tolerable level. A novel thin-wall vacuum chamber supported by ceramic rings was discussed and evaluated for the HIAF at the IMP to reduce the manufacturing cost, reduce the difficulty, shorten the production cycle, and improve the quality. Because the beam coupling impedance aspects are highly important for beam stability, several approaches were used to evaluate the impedance on the ceramics-loaded tube. In this article, we describe the results from the single- and two-wire bench measurements and the numerical simulations. The simulated and measured impedance results are consistent with each other. Several effective methods to mitigate the impedance were proposed and investigated in detail. According to the simulation and measurement results of the beam coupling impedance mitigation, this novel ceramic-ring copper-coated thin-wall vacuum chamber structure will be considered for application to the HIAF project with the highest priority. [ABSTRACT FROM AUTHOR]

In the ground-based astronomical telescope, the imaging quality is usually affected by tip-tilt vibrations induced by the telescope structure. Long exposure time of the image sensor is usually required for a good signal-to-noise ratio, which brings the amount of time delays into the control loop of the tip-tilt mirror. Thus, a low control bandwidth is insufficient to compensate telescope vibrations. In this paper, an improved disturbance observer (DOB) control based on only the image sensor is proposed to reject structural vibrations. This new DOB controller is added into the original loop in the tip-tilt mirror control system, so the closed-loop performance can be optimized by designing an appropriate Q-filter. An improved Q-filter is presented to reject large-magnitude vibrations and also to reduce amplifications induced by this controller at nondisturbance frequencies. This proposed controller can achieve a satisfying result in vibration mitigations when vibration frequencies are provided to design the Q-filter. Furthermore, in the tilt–tilt mirror control system, this improved DOB is not restricted by an accurate model such that noise in the loop cannot provide serious influence on vibration mitigation. Both simulations and extensive experiments are carried out to demonstrate that the DOB can earn an extra improvement on the control performance in comparisons with the conventional feedback controller. [ABSTRACT FROM AUTHOR]

The automatic train operation which integrates knowledge-based intelligent algorithm to develop safe and efficient control system has become one of the most important developing directions in the field of railway transit equipment. Multi-objective optimization is a strictly incompatible problem, and such contradiction is one of the main reasons that lead to the best multi-objective optimization difficult to achieve. In this paper, the multi-objective optimization feature information is transformed into the association function first, and then the matter-element theory is introduced to establish models for the speed trajectory to achieve the multi-objective optimization to fuse knowledge-based safety requirement constrained condition. Performance indices weighting of different performance in different stages are determined with the Hierarchical Mahalanobis distance method, and the decision speeds are calculated with goodness evaluation method. Taking Shanghai Railway Transit Equipment in China as a case study, this paper selected the multi-objective performance indices including passenger comfort, running stability, energy efficiency, and parking accuracy as objectives to support the decision-making. The multi-objective performance indices are evaluated by a field investigation and simulation. The test result shows that the comfort level, running stability, energy saving property, and parking accuracy are better than those derived by the traditional control algorithm. It indicates that the model has the advantage that it conveniently quantifies the qualitative indices, and it can integrate the data source information to improve the multi-objective performance indices, so that it is very useful to apply multi-source data and prior knowledge to multi-objective optimization of the automatic train operation control system. [ABSTRACT FROM AUTHOR]

Studies the problem of fair rate allocation, specifying the requirements of a fair rate allocation algorithm, and providing a survey of various proposed fair rate allocation strategies in the context of available bit rate service in Asynchronous Transfer Mode networks. Congestion control framework; Design criteria; Network configuration; Dynamic max rate control.