Bingcheng Zhu

Improvement of BER performance by tilting receiver plane for indoor visible light communications with input-dependent noise

In this paper, an indoor visible light communication (VLC) system with the input-dependent noise is considered. In the system, the main noise is caused by Gaussian noise, however, with a noise variance depending on the current input signal strength. In the presence of the input-dependent noise, the theoretical expression of the bit error rate (BER) for the VLC using on-off keying is derived. Based on the derived BER, an optimization problem is formulated to improve the BER performance by tilting the receiver plane. The proposed optimization problem is proven to be a convex optimization problem, which can be efficiently solved by using the specialized solver such as the CVX toolbox for MATLAB. To verify the accuracy of the derived expression of the BER, all theoretical results are thoroughly confirmed by using the Monte-Carlo simulations. Moreover, simulation results show that the larger the variance of the input-dependent noise is, the worse the BER performance becomes. Additionally, the BER performance can be dramatically improved by tilting the receiver plane properly.

On-chip optical interconnect using visible light

We propose and fabricate a monolithic optical interconnect on a GaN-on-silicon platform using a wafer-level technique. Because the InGaN/GaN multiple-quantum-well diodes (MQWDs) can achieve light emission and detection simultaneously, the emitter and collector sharing identical MQW structure are produced using the same process. Suspended waveguides interconnect the emitter with the collector to form in-plane light coupling. Monolithic optical interconnect chip integrates the emitter, waveguide, base, and collector into a multi-component system with a common base. Output states superposition and 1×2 in-plane light communication are experimentally demonstrated. The proposed monolithic optical interconnect opens a promising way toward the diverse applications from in-plane visible light communication to light-induced artificial synaptic devices, intelligent display, on-chip imaging, and optical sensing.

Simultaneous Light-Emitting Light-Detecting Functionality of InGaN/GaN Multiple Quantum Well Diodes

The InGaN/GaN multiple-quantum-well (MQW) diode has selectable functionalities with emission and detection in the visible region due to the MQW-based p-n junction structure, which is employed to achieve on-chip optocoupling. Here, we propose to fabricate a suspended InGaN/GaN MQW diode on an III-nitride-on-silicon platform by a combination of silicon removal and III-nitride backside etching. Spatial simultaneous light-emitting light-detecting functionality, in which the detected light comes from an external light source, is experimentally demonstrated, endowing the MQW diode with the capability of contributing to intelligent displays as well as full-duplex visible light communication. As a transmitter, the InGaN/GaN MQW diode demonstrates out-of-plane data transmission at 120 Mb/s using visible light.

Spatiotemporal summation and correlation mimicked in a four-emitter light-induced artificial synapse

In the brain, each postsynaptic neuron interconnects many presynaptic neurons and performs functions that are related to summation and recognition as well as correlation. Based on a convolution operation and nonlinear distortion function, we propose a mathematical model to explore the elementary synaptic mechanism. A four-emitter light-induced artificial synapse is implemented on an III-nitride-on-silicon platform to validate the device concept for emulating the synaptic behaviors of a biological synapse with multiple presynaptic inputs. In addition to a progressive increase in the amplitude of successive spatiotemporal excitatory postsynaptic voltages, the differences in the stimulations are remembered for signal recognition. When repetitive stimulations are simultaneously applied and last over a long period of time, resonant spatiotemporal correlation occurs because an association is formed between the presynaptic stimulations. Four resonant spatiotemporal correlations of each triple-stimulation combination are experimentally demonstrated and agree well with the simulation results. The repetitive stimulation combinations with prime number-based periods inherently exhibit the maximum capacity of resonant spatiotemporal correlation. Our work offers a new approach to building artificial synapse networks.

Full-duplex light communication with a monolithic multicomponent system

A monolithic multicomponent system is proposed and implemented on a III-nitride-on-silicon platform, whereby two multiple-quantum-well diodes (MQW-diodes) are interconnected by a suspended waveguide. Both MQW-diodes have an identical low-In-content InGaN/Al0.10Ga0.90N MQW structure and are produced by the same fabrication process flow. When appropriately biased, both MQW-diodes operate under a simultaneous emission-detection mode and function as a transmitter and a receiver at the same time, forming an in-plane full-duplex light communication system. Real-time full-duplex audio communication is experimentally demonstrated using the monolithic multicomponent system in combination with an external circuit.Light communication: Quantum wells pump up the audioA chip-scale device that uses confined light to emit and detect audio signals simultaneously has been developed by researchers from China and Japan. Recent findings have shown that quantum wells, thin semiconductors films that trap electric charges, can act as light-emitting diodes (LEDs) at the same time. It is termed the simultaneous emission-detection phenomenon. Yongjin Wang at the Nanjing University of Posts and Telecommunications and colleagues now report a technique to use light-emitting quantum wells for high-speed signal communication. The team fabricated two quantum wells on a III-nitride chip and then connected them through a suspended optical waveguide. Photocurrent measurements revealed that light generated on one side of the device could travel through the waveguide and modulate the output of the second LED. Connection to an external audio circuit enabled the quantum wells to receive sound signals and amplify them almost instantaneously.