基于蓝绿光Micro-LED的可见光通信芯片调制带宽研究

基于氮化镓微米LED(Micro-LED)的可见光通信(Visible Light Communication,VLC)技术成为近年来的研究热点.通过深紫外光刻技术制备了小尺寸的氮化镓基蓝/绿光Micro-LED芯片,深入研究了40～10μm不同尺寸Micro-LED器件的性能,以及其作为VLC光源的调制带宽能力.研究发现,随着LED器件尺寸的缩小,其调制带宽显著增加.通过在电极间加入电磁屏障以及对LED器件侧壁进行钝化修复,直径为10 μm的绿光Micro-LED亮度可达1×108 cd/m2,直径为20 μm的蓝光Micro-LED的调制带宽可达372.6 MHz.研究结果表明,基于氮化镓的Micro-LED芯片在调制带宽上仍有较大的提升空间,经过进一步的研究,有望推动高速可见光通信的系统应用.     

基于无线可见光通信的双向语音对讲系统

设计并实现了基于无线可见光通信(VLC)的双向语 音对讲系统。上下行链路均使用普通的1W发光二极管(LED)手电筒作为发射端光源, 同时实现语音传输和照明功能。系统采用开关键控-非归零码(OOK-NRZ)调制方式,在测 试LED的光电特性后,设计了LED 驱动电路和接收电路;使用单片机控制音频编解码芯片实现语音信号的采集、处理和传输, 通过异步收发传输接口(UART) 进行数据传输,实现了最远通信距离为40m、最高传输速率为2.5Mbit/s的全双工实时语音 对讲。本文系统实现复杂度低、成 本低和功耗小,并可应用于其他数据传输场合,具有良好的实用性和广泛的适用性。     

双通道PWM的冷暖白光LED混色模型研究

LED光色度的动态调节是实现智能照明的基础, 采用冷暖白光LED和双通道脉冲宽度调制(PWM)法,基于1931CIE标准建立混合光源模型,推导出混合光源色坐标、相关色温 、最大亮度、显色指数与双通道调制脉冲 占空比比值的关系式。采用暖白光(色温3282 K)和冷白光(色温12930K)两种白光LED进行 混色实验, 通过微控制器输出PWM信号控制LED驱动电源,改变冷色光和暖色光的比重,得到的混合 光源色坐 标、最大亮度、相关色温及显色指数值与理论计算值吻合很好,证明了理论模型的正确性。 理论和实验结 果还表明,混合光源在双通道调制脉冲占空比比值为1的附近可得到低色温、高显色性和大 光通量的混合白光。     

用LED作光源的光纤乙炔气体传感器的研究

基于气体的近红外吸收机理,介绍了一种用LED作光源的光谱吸收型光纤乙炔气体传感器.该系统利用布拉格光纤光栅和压电陶瓷(PZT)的窄带滤波特性,对宽带光源LED进行波长调制,获得与乙炔气体吸收峰相对应的窄带反射出射光.利用谐波检测原理,获得探测器输出信号的二次谐波信号,以此二次谐波信号与光纤光栅透射光强的比值作为系统的输...     

基于双重调制技术的可见光通信系统研究

LED调制带宽制约着可见光通信(VLC) 系统的数据传输速率。为此,提出一种基于双重调制技术COB(chip on board)封装 的LED灯具,通过实现16级脉冲振幅 调制(PAM),将系统数据传输速率提升4倍;结合脉冲宽度调制(PWM)技术 进行调光,同时兼顾室内的照明及通信。采用Matlab软件模拟仿真视频传输试 验。结果表明,在相同信噪比(SNR)的情况下,基于双重 调制技术的VLC系统的误码率(BER)比传统使用开关键控(OOK)调控技术系 统的BER更低。本文系统在不增加器件带宽前提下,成倍提高了无线通信的 质量与 数据传输速率;从照明与通信的角度优化了VLC系统的信源,具有广阔的 应用前景。     

光纤光栅式甲烷浓度差分检测系统研究

基于甲烷气体的近红外光谱吸收特性,研究了一种全光纤差分吸收式甲烷检测系统.分析了差分吸收检测的基本原理,建立了甲烷检测的数学模型.系统选用发光二极管(LED)作光源,用光纤布拉格光栅进行滤波实现差分吸收检测,并结合光源强度调制技术和锁相放大技术,消除了光路干扰和光源强度波动的影响,提高了测试灵敏度.最后给出了该甲烷气体浓度检测系统的实验结果.     

日盲紫外LED实时视频传输系统设计

针对当前紫外光通信中气体灯与激光光源调制速率慢、体积较大,光电倍增管工作电压过高等问题,提出了一种基于现场可编程门阵列技术的日盲紫外LED实时视频传输系统,其发射光源采用波长为265 nm的单紫外LED,探测器采用紫外PIN;通过电路和逻辑模块设计搭建了视频传输系统,研究了系统的光功率密度与通信距离之间的关系;基于二进制开关键控调制方式,实现日盲紫外LED实时视频传输系统最大传输速率为2.88 Mbit/s,当通信距离为4 m时,传输速率达到1.92 Mbit/s。     

基于LED的紫外光通信系统研究

针对现有基于低压汞蒸气灯日盲紫外光通信系统通信速率低、驱动电压高、光源响应速度慢、电光转换效率低和功耗过高等问题,提出并设计了一套基于LED的日盲紫外光通信系统。该系统以深紫外LED作为光源,用光电倍增管探测微弱光信号,采用脉冲位置调制(PPM)技术和最大似然解调技术,并用现场可编程门阵列完成了调制解调部分的设计与仿真。实验表明,采用深紫外LED和PPM技术,可以大幅度提高系统的通信速率、电光转换效率,同时显著降低驱动电压和系统功耗。     

基于室内可见光照明的位置服务系统

设计并实现了一种基于室内LED照明光源的位置服务系统。系统利用LED标签(LED ID)技术,LED提供照明的同时广播自身的位置ID信息,移动终端将接收到的ID信息与位置关联,实现自身的被动定位。可见光通信的调制编码以及解调解码模块均采用单片机处理器(PC)实现,并提供UART接口分别与PC控制端和手机显示端进行通信。PC控制端向LED信号源发送位置服务信息,LED信号源通过空间光传输方式将自身位置ID和接收到的位置服务信息广播出去。手机使用终端加载有Android操作环境下的室内定位导航软件,可以实时更新位置和位置服务信息。     

高压倒装LED照明组件的热性能

高压(HX)倒装LED是一种新型的光源器件,在小尺寸、高功率密度发光光源领域有广泛的应用前景.设计了4种不同工作电压的高压倒装LED芯片,进行了流片验证,并对其进行了免封装芯片(PFC)结构的封装实验,在其基础上研制出一种基于高压倒装芯片的PFC-LED照明组件.建立了9V高压倒装LED芯片、PFC封装器件及照明组件的模型,利用流体力学分析软件进行了热学模拟和优化设计;利用T3Ster热阻测试分析仪进行了热阻测试,验证了设计的可行性.结果表明,基于9V高压倒装LED芯片的PFC封装器件的热阻约为0.342 K/W,远小于普通正装LED器件的热阻.实验结果为基于高压倒装LED芯片的封装及应用提供了热学设计依据.     

适用于可见光通信的LED器件

认为研究发光二极管(LED)器件调制特性以及在高速调制状态下的发光特性是提升新型可见光通信系统性能的关键问题之一,LED器件调制特性的提升可以显著拓展可见光通信系统的应用范围。基于LED器件的调频特性,通过分析发光器件和封装的结构及其他关键光电性能,提出建议:通过降低RC时间以及载流子自发辐射寿命,有效改善LED器件的响应速率,提高LED的调制带宽。     

室内VLC白光LED调制带宽拓展

针对室内照明场景应用需求,探究了驱动电流的变化对四种常用LED光源频率特性所产生的影响效果,得出荧光粉LED的频率特性响应几乎不受驱动电流变化的影响的结论。结合硬件预均衡策略对1 W荧光粉LED的调制带宽拓展进行了理论分析和硬件电路设计,测试结果表明:在不对蓝光过滤的条件下,荧光粉LED调制带宽由1 MHz提高到了32 MHz,单盏荧光粉LED在非归零-开关键控（non-return-to-zero on-off-keying,NRZ-OOK）调制下可达到26 Mbit/s的传输速率,误码率7.5510-6,传输距离达到3 m,符合于室内照明通信对传输距离的要求。     

A real-time VLC to UART protocol conversion system

A real-time visible light communication(VLC) to universal asynchronous receiver/transmitter(UART) conversion system is made up of a transmitter with a light emitting diode(LED) and a receiver with a photodiode(PD), by which a VLC system is connected to traditional communication modes, and the data are transferred by wireless visible light. UART packets are converted to light packets by the modulation of a 10 k Hz on-off-keying(OOK) light signal, and the data losses in the transportation are avoided by the protection of a data buffer mechanism. The experimental results reveal that the real-time VLC to UART conversion system can provide a real-time VLC transmission way for two UART devices in not less than 10 m at a baud rate not less than 19 200 Bd with stable ambient lighting at the same time.     

High-speed real-time visible light communication system based on InGaN/GaN-base multi-quantum well blue micro-LED

Visible light communication (VLC) technology is a new type of wireless communication technology, which employs a light source as the carrier of information to realize illumination and communication simultaneously. This paper adopts a single InGaN/GaN-base multi-quantum well blue micro-light emitting diode (LED) as the light source, designs pre-emphasis circuit, LED driver circuit, impedance matching network, etc., and builds a high-speed real-time VLC system. It has been verified that the LED achieves a 3 dB modulation bandwidth of 450 MHz or more; and the real-time communication rate reaches over 800 Mbit/s at a distance of 2 m. The communication bit error rate (BER) is as low as at a communication rate of 622 Mbit/s. Experimental indicators including 3 dB bandwidth, communication rate, and communication BER are all taken into account. Therefore, this VLC system supports high-quality high-speed real-time communication.     

Energy Efficient Lighting System for Indoor Parking with Ubiquitous Communication

This paper presents visible light communication (VLC) based energy efficient lighting system in indoor parking area for illumination and at the same time would offer ubiquitous data communication. Light emitting diodes (LEDs) based VLC is used for communication and illumination at the same time. We have optimized the position of LED emitters on the ceiling in the parking area to obtain the desired signal-to-noise ratio (SNR) and bit error rate (BER). Two lighting configurations in the parking area are discussed. We compared the power transmission from LED emitters, number of emitters, SNR distribution, BER and cost for both the configurations. Multi-level pulse modulations are used in this work along with simple on off keying (OOK) for modulation. We compared OOK with M-PAM, multi-level pulse position modulation and invert multi-level pulse position modulation to obtain the required SNR and power to achieve the same BER. Simulation results are presented and discussed. It is observed that the system allows uniform illumination in the parking area and at the same time high data rate communication.     

Visible Light Communication Method for Personalized and Localized Building Energy Management

The Paris agreement at the 21st Conference of the Parties (COP21) emphasizes the reduction of greenhouse gas emissions and increase in energy consumption in all areas. Thus, an important aspect is energy saving in buildings where the lighting is a major component of the electrical energy consumption. This paper proposes a building energy management system employing visible light communication (VLC) based on LED lighting. The proposed management system has key characteristics including personalization and localization by utilizing such VLC advantages as secure communication through light and location‐information transmission. Considering the efficient implementation of an energy‐consumption adjustment using LED luminaires, this paper adopts variable pulse position modulation (VPPM) as a VLC modulation scheme with simple controllability of the dimming level that is capable of providing a full dimming range. This paper analyzes the VPPM performances according to variable dimming for several schemes, and proposes a VPPM demodulation architecture based on dimming‐factor acquisition, which can obtain an improved performance compared to a 2PPM‐based scheme. In addition, the effect of a dimming‐factor acquisition error is analyzed, and a frame format for minimizing this error effect is proposed.     

Half‐duplex visible light communication using an LED as both a transmitter and a receiver

In typical visible light communication (VLC) systems, light‐emitting diodes (LEDs) are used as optical transmitters and photodiodes are used as optical receivers. Currently, many communication devices such as smart phones have a built‐in LED lamp whereas they usually do not have a built‐in photodiode. If we find a way to receive VLC signals without the need to add an additional photodiode on the communication devices, it will contribute to the spread of VLC. Therefore, we propose and demonstrate a VLC scheme without the need for a photodiode. As the first step, we investigate the characteristics of an LED as a VLC receiver and find out that an LED can also be used as a VLC receiver in certain conditions. Then, we demonstrate a half‐duplex VLC system using an LED as both an optical transmitter and an optical receiver, without the need for a photodiode. This technique could be used in various applications such as the VLC between smart phones with a built‐in LED lamp and the VLC between LED traffic lights. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of the effects of LED direction on the performance of visible light communication system

Visible light communication (VLC) is expected to be the next generation of indoor wireless communication. A VLC system uses many LED chips, and its performance is greatly affected by the direction of light-emitting diodes (LEDs). Normally, the LEDs are directed vertically downward to the floor. In this paper, we introduce an LED layout scheme in which the LEDs tilt toward the room corners. The effects of changing LED direction on system performance, including illuminance, received power, and SNR, are analyzed. The analysis is then verified by the simulations.     

Performance study of an OFDM visible light communication system based on white LED array

By introducing orthogonal frequency division multiplexing (OFDM) technology, a visible light communication (VLC) system using a 5x5 white LED array is studied in this paper. The OFDM transmitter and receiver are modeled through MATLAB/Simulink tool. The electrical-optical-electrical (EOE) response of the VLC channel, which is also the response of the detector, is derived based on Lambert’s lighting model. Then the modeling on the overall OFDM/VLC system is established by combining the above three models together. The effects of the factors which include the digital modulation, Reed-Solomon (RS) coding, pilot form, pilot ratio (PR) and communication distance on the bit error rate (BER) of the system are discussed. The results show that through the use of RS coding, block pilot, quadrate phase shift keying (QPSK) modulation and a suitable pilot ratio about 1/3, under the communication rate about 550 kbit/s, the BER can be dropped to below 10-5, and the communication distance can reach 0.9 m.