Visible light communication(VLC) is an emerging technology in optical wireless communication(OWC) that has attracted worldwide research in recent years. VLC can combine communication and illumination together, which could be applied in many application scenarios such as visible light communication local area networks(VLANs), indoor localization, and intelligent lighting. In recent years, pioneering and significant work have been made in the field of VLC. In this paper, an overview of the recent progress in VLC is presented. We also demonstrate our recent experiment results including bidirectional 100 Mbit/s VLAN or Li-Fi system based on OOK modulation without blue filter. The VLC systems that we proposed are good solutions for high-speed VLC application systems with low-cost and low-complexity. VLC technology shows a bright future due to its inherent advantages, shortage of RF spectra and ever increasing popularity of white LEDs.
A design for a CMOS frontend integrated circuit(chip) for neural signal acquisition working at wide voltage supply range is presented in this paper.The chip consists of a preamplifier,a serial instrumental amplifier(IA) and a cyclic analog-to-digital converter(CADC).The capacitive-coupled and capacitive-feedback topology combined with MOS-bipolar pseudo-resistor element is adopted in the preamplifier to create a –3 d B upper cut-off frequency less than 1 Hz without using a ponderous discrete device.A dual-amplifier instrumental amplifier is used to provide a low output impedance interface for ADC as well as to boost the gain.The preamplifier and the serial instrumental amplifier together provide a midband gain of 45.8 d B and have an input-referred noise of 6.7 V rms integrated from 1 Hz to 5 k Hz.The ADC digitizes the amplified signal at 12-bits precision with a highest sampling rate of 130 k S/s.The measured effective number of bits(ENOB) of the ADC is 8.7 bits.The entire circuit draws165 to 216 A current from the supply voltage varied from 1.34 to 3.3 V.The prototype chip is fabricated in the0.18-m CMOS process and occupies an area of 1.23 mm2(including pads).In-vitro recording was successfully carried out by the proposed frontend chip.
An implantable optrode composed of fiber and multi-channel flexible thin-film electrode is developed. The flexible recording electrode is made from polyimide and is wrapped around the optical fiber. The front end of the fiber is tapered by wet etching. With the tapered shape, the light can leak from the sidewall of the fiber, and the tapered tip makes it easy to be implanted. The flexible electrode is attached with its recording sites aligning to the tapered part on the fiber. With this method, the fiber acts as an optical waveguide, as well as a support probe for flexible thin-film electrode. This novel device simplifies the fabrication process and decreases the size of the optrode. The device works well in vivo and the optical caused spike can be recorded with signal-to-noise ratio of 6:1.
In order to ensure stable,correct and real-time high-speed transmission of indoor visible light communication(VLC),the key modulation and demodulation technologies of orthogonal frequency division multiplexing(OFDM) are studied in this paper. The time-domain synchronization,frequency synchronization and channel equalization of receiver are analyzed and optimized by utilizing short and long training preamble. Moreover,field programmable gate array(FPGA) development board(Xilinx Kintex-7) and Verilog hardware description language are used to realize the design of proposed OFDM-VLC system. Simulation and experiment both verify the feasibility of the hardware designs of this system. The proposed OFDM-based VLC system can process signal in real-time,which can be used in actual VLC application systems.
Electro-deposition, electrical activation, thermal oxidation, and reactive ion sputtering are the four primary methods to fabricate iridium oxide film. Among these methods, reactive ion sputtering is a commonly used method in standard micro-fabrication processes. In different sputtering conditions, the component, texture, and electrochemistry character of iridium oxide varies considerably. To fabricate the iridium oxide film compatible with the wafer-level processing of neural electrodes, the quality of iridium oxide film must be able to withstand the mechanical and chemical impact of post-processing, and simultaneously achieve good performance as a neural electrode. In this study, parameters of sputtering were researched and developed to achieve a balance between mechanical stability and good electrochemical characteristics of iridium oxide film on electrode. Iridium oxide fabricating process combined with fabrication flow of silicon electrodes, at wafer-level, is introduced to produce silicon based planar iridium oxide neural electrodes. Compared with bare gold electrodes, iridium oxide electrodes fabricated with this method exhibit particularly good electrochemical stability, low impedance of 386 kW at 1 kH z, high safe charge storage capacity of 3.2 m C/cm^2, and good impedance consistency of less than 25% fluctuation.
A wireless powered small volume light source composed of light emitting diode(LED) array is developed for implantation. According to the volt-ampere characteristics of LED and the load characteristics of coil coupling power supply, the light power and work distance of implant LED-array are optimized by changing the number and series-parallel connection mode of LEDs in receiver. The wireless powered implant can provide 5.4 m W light. The entire implant is seamlessly packaged within parylene, a biocompatible material, coating by chemical vapor depositing. The volume of the implant is 9 mm×4 mm×3 mm, the weight of which is only 0.25 g. The device can work continuously for more than three weeks in 0.9% saline and the prime prototype of the device has been validated by animal implantation.
A novel linear microprobe array(LMPA)has been developed by a conventional microfabrication method from silicon.The LMPA leverages the properties of conventional microwire with additional features of naturally formed regular spacing.With the help of periodic microprobe arrays and double-side V-grooves fabricated in advance between each pair of the two microprobes’rear ends,the number of microprobe units for assembly in one array can be flexibly chosen by cleavage fracture from the LMPA.The fabrication method was demonstrated and the prototype device was assessed by electrochemical impedance spectroscopy(EIS)and in vivo test.The SNR of the spikes recorded was 6.
ZHAO Shan ShanPEI Wei HuaZHAO HuiWANG Yi JunCHEN San YuanCHEN Yuan FangZHANG HeGUO Dong MeiGUI QiangCHEN Hong Da
Silicon photonics is an emerging competitive solution for next-generation scalable data communications in different application areas as high-speed data communication is constrained by electrical interconnects.Optical interconnects based on silicon photonics can be used in intra/inter-chip interconnects, board-to-board interconnects, short-reach communications in datacenters, supercomputers and long-haul optical transmissions. In this paper, we present an overview of recent progress in silicon optoelectronic devices and optoelectronic integrated circuits(OEICs) based on a complementary metal–oxide–semiconductor-compatible process, and focus on our research contributions. The silicon optoelectronic devices and OEICs show good characteristics, which are expected to benefit several application domains, including communication, sensing, computing and nonlinear systems.
