Dynamic characteristics and noise modelling of directly modulated quantum well-dots microdisk lasers on silicon

The small-signal amplitude modulation, threshold, and spectral characteristics of microdisk lasers with InGaAs/GaAs quantum well-dots active region were studied jointly with the spectral and threshold parameters of edge-emitting lasers made from the same epitaxial heterostructure. Using the obtained material parameters, the relative intensity noise of the microdisk lasers was calculated as a function of the bias current and side-mode suppression ratio. It is shown that the integral noise is low enough for error-free optical data transmission with the maximum possible bitrate limited by the microdisk modulation bandwidth, if the bias current is above 1.7× threshold current (for side mode suppression ratio > 20 dB).

Research on Hysteresis Modeling and Compensation Method of Giant Magnetostrictive Force Sensor

Linearity is an important index for evaluating the performance of various sensors. Under the Villari effect, there may be some hysteresis between the input force and the output voltage of a force sensor, meaning that the output will be multivalued and nonlinear. To improve the linearity and eliminate the hysteresis of such sensors, an output compensation method using a variable bias current is proposed based on the bidirectional energy conversion mechanism of giant magnetostrictive material. First, the magnetization relationship between the input force, bias current, and flux density is established. Second, a nonlinear neural network model of the force-magnetization hysteresis and a neural network model for the compensation control of the force sensor are established. These models are trained using the magnetic flux density-force curve and the magnetic flux density-current curve, respectively. Taking the optimal linearity as the objective function, the bias current under different input forces is optimized. Finally, a bias current control system is developed and an experimental test platform is built to verify the proposed method. The results show that the proposed variable bias current hysteresis compensation method enables the linearity under the return of the force sensor to reach 1.6%, which is around 48.3% higher than under previous methods. Thus, the proposed variable bias current method effectively suppresses the hysteresis phenomenon and provides improved linearity for giant magnetostrictive force sensors.

Evaluation of Self-Field Effects in Magnetometers Based on Meander-Shaped Arrays of Josephson Junctions or SQUIDs Connected in Series

Arrays of superconducting quantum interference devices (SQUIDs) are highly sensitive magnetometers that can operate without a flux-locked loop, as opposed to single SQUID magnetometers. They have no source of ambiguity and benefit from a larger bandwidth. They can be used to measure absolute magnetic fields with a dynamic range scaling as the number of SQUIDs they contain. A very common arrangement for a series array of SQUIDs is with meanders as it uses the substrate area efficiently. As for most layouts with long arrays, this layout breaks the symmetry required for the elimination of adverse self-field effects. We investigate the scaling behavior of series arrays of SQUIDs, taking into account the self-field generated by the bias current flowing along the meander. We propose a design for the partial compensation of this self-field. In addition, we provide a comparison with the case of series arrays of long Josephson junctions, using the Fraunhofer pattern for applications in magnetometry. We find that compensation is required for arrays of the larger size and that, depending on the technology, arrays of long Josephson junctions may have better performance than arrays of SQUIDs.

Current biased gradiometric flux qubit in a circuit-QED architecture

We propose a scheme for controlling the gradiometric flux qubit (GFQ) by applying an ac bias current in a circuit-QED architecture. The GFQ is insensitive to the magnetic flux fluctuations, which at the same time makes it challenging to manipulate the qubit states by an external magnetic field. In this study, we demonstrate that an ac bias current applied to the $\alpha$-junction of the GFQ can control the qubit states. Further, the present scheme is robust against the charge fluctuation as well as the magnetic flux fluctuations, promising a long coherence time for quantum gate operations. We introduce a circuit-QED architecture to perform the single and two-qubit operations with a sufficiently strong coupling strength.

Photonic implementation of spike timing dependent plasticity with weight-dependent learning window based on VCSOA

Based on the well-known Fabry–Pérot approach, after taking into account the variation of bias current of the vertical-cavity semiconductor optical amplifier (VCSOA) according to the present synapse weight, we implement the optical spike timing dependent plasticity (STDP) with weight-dependent learning window in a VCSOA with double optical spike injections, and numerically investigate the corresponding weight-dependent STDP characteristics. The simulation results show that, the bias current of VCSOA has significant effect on the optical STDP curve. After introducing an adaptive variation of the bias current according to the present synapse weight, the optical weight-dependent STDP based on VCSOA can be realized. Moreover, the weight training based on the optical weight-dependent STDP can be effectively controlled by adjusting some typical external or intrinsic parameters and the excessive adjusting of synaptic weight is avoided, which can be used to balance the stability and competition among synapses and pave a way for the future large-scale energy efficient optical spiking neural networks based on the weight-dependent STDP learning mechanism.

Performance optimization of RSOA based mm-wave radio-over-fibre access network

In this paper, a Reflective Semiconductor Optical Amplifier based, Radio-over-Fibre access network configuration has been proposed to feed future millimeter-wave radio systems. The system architecture combines several approaches to overcome the challenges of millimeter-wave signal transmission. Reflective semiconductor optical amplifier modulator realizes a colorless and relatively cost-effective Remote Antenna Unit. The same optical carrier is used for both downlink and uplink. Optical single-sideband modulation is used at the downlink, which is robust against chromatic dispersion, but the complex realization of this modulation format is not possible at the Remote Antenna Unit. Optical intermediate frequency transmission is applied at the uplink direction, and the required local oscillator signal originates from the central station. The critical element is the reflective optical amplifier, as it compensates for the optical loss and works as an external intensity modulator. The operation of the reflective optical amplifier is modeled by multisection rate and wave equation-based description. The amplification and modulation behaviors of an available reflective optical amplifier are also measured. The experimental work validated the colorless operation and the quality of the modulation versus bias current and input optical power. Finally, system simulation was realized. The uplink and downlink power budgets were balanced, and optimal values for the optical coupling rate and RSOA bias current have been selected.