极弱光信号图像探测中的几个问题

显微光子计数成像系统可以从细胞水平上获得生物超微弱发光图像,此系统需采用多项降噪声措施保证探测极限,引进同位素14C光源监测系统,对光子图像应用统计检验和处理,并用双路探测得到细胞背景上的超微弱发光信息。     

生物超弱发光采集系统及控制电路设计

生物超弱发光是生物系统在生命活动中的微弱发光现象。为了准确测量生物超弱发光,设计了一种用于生物超微弱发光的专用采集系统。系统的激发光源由单只大功率LED及光学系统构成,用压控恒流源调整LED光照强度,通过电子快门精确控制光探测器的采集时间。测量金心吊兰叶片的延迟发光结果表明,该系统测量精度高、重复性好。     

交流LED与高压LED的特性实验研究

高压LED和交流LED都是通过串联数十颗LED来增大整体导通电压,结构上高压LED是交流LED的一种特殊形式。介绍了高压LED和交流LED的驱动电路模型,其共同点是皆有一个限流电阻与光源串联。通过调整限流电阻的阻值和改变光源所含LED个数与连接形式,分别对高压LED和交流LED的输出特性进行了测量。在两种光源所含LED数量和工作电流均相同的情况下,高压LED的发光效率和光通量要高于交流LED;并联式高压LED的发光效率低于串联式高压LED的发光效率,光通量则相反;验证了交流LED的发光效率与限流电阻无关。     

交流发光二极管光源的工作特性研究

为得到交流发光二极管(AC LED)内部晶粒参数与其工作特性的关系,讨论了ACLED光源的内部结构和应用电路模型,分析了AC LED光源的工作特性,给出AC LED发光效率的解析表达式,理论上说明了AC LED的发光效率低于单颗LED晶粒的电光转换效率,且光效随着LED晶粒串联数量的增加而提高,AC LED的光效与限流电阻无关,增加串联晶粒的个数可减小限流电阻的损耗。因此,AC LED制造过程中宜降低晶粒的导通电压,以增加晶粒个数。     

LED单色平面光源并联支路中的电流均分

LED构成的半导体光源,在各个领域已被广泛应用.用LED单色光源在大学物理实验中取代传统的气体光源,也被不断的探索和尝试,并取得了有益的经验.为保证单色光源的发光阵列中每一支LED颜色一致,使LED光源具有良好的单色性,以满足物理实验的要求.必须控制并联方式的LED每路电流均等且保持不变,采用相应驱动电路可以达到这一目...     

基于ANSYS分析温度对荧光粉发光性能的影响

采用有限元方法模拟了LED集成封装光源和LED远程荧光集成封装(LED RPIP)光源各部分的热量分布。通过结合模拟和实验数据分析得到:随着LED结温升高,荧光粉温度随之上升,发光性能不断衰退,LED硅胶板和LED远程荧光板温度从室温35℃分别升高到73.794和73.156℃,光源光通量分别降低了30.53和22.39lm。最后得出硅胶板和远程荧光板中荧光粉发光性能分别下降了0.943%和0.78%。     

植物超弱发光的探测

采用超弱发光图像探测系统对蟛蜞菊、千日红花蕾、翠菊等植物样品进行了自发和光诱导的超弱发光图像探测,对大花紫薇叶片的延迟发光进行了初步的光谱探测。结果表明：植物自发发光与延迟发光的强度及其分布是有区别的,自发光光强度远小于延迟发光强度;与有丝分裂和生长代谢有关的植物超弱发光有光诱导下得以加强;千日红花蕾的延迟发光遵循双曲线衰减规律,说明生物光子具有一定的相干性;叶片的延迟发光光谱比离体叶绿素荧光光谱     

动手组装大功率LED灯

LED灯就是用发光二极管作为光源的射灯。传统射灯多采用卤素灯,发光效率较低比较耗电,使被照射环境的温度上升,使用寿命短。LED在发光原理、节能、环保的层面上都远远优于传统照明产品。而且LED发光的单向性形成了对射灯配光的完美支持。     

从LED特性看未来发展策略

1前言 1968年问世的单色发光二极管（light—emitting diode，LED），由于光强度低及单色缺乏全彩化，仅限于电子、电机设备的仪表与电器产品上的状态显示或观赏点缀等用途：虽然红黄绿LED已上市20多年，但由于光输出不高且亮度不足，发光效率又偏低，加上电子产品不耐热及易受屋外气候影响．因此难以发展为实用的照明光源与灯具。因全球能源短缺，节能新光源的研发成为全球的焦点，由此发展出了高亮度的LED（20世纪80年代中期）、高亮度蓝光LED（1993年）及白光LED，逐步实现了LED的全彩化。直到在消费电气商品领域找到新市场，才真正刺激了光电产业全心投入研究发展，开始大幅提升LED的光输出及红黄绿发光效率，从而成功地运用于交通信号灯及屋外的广告和各类型指示灯。从此，LED光源正式走入各类民生用途，包括汽车交通、通讯与信息产品、便利照明。近几年来更是在农业生产与生物医疗的生物产业上大放异彩，已为农作物栽培燃起了新希望。     

LED单色平面光源并联支路中的电流均分

LED构成的半导体光源,在各个领域已被广泛应用。用LED单色光源在大学物理实验中取代传统的气体光源,也被不断的探索和尝试,并取得了有益的经验。为保证单色光源的发光阵列中每一支LED颜色一致,使LED光源具有良好的单色性,以满足物理实验的要求。必须控制并联方式的LED每路电流均等且保持不变,采用相应驱动电路可以达到这一目的。     

用时间分辨荧光光谱研究乙酸-水溶液的聚合特性

对284nm激发光照射不同体积百分比乙酸一水溶液的峰值荧光强度时间衰变曲线进行了实验测量,并检测了不同紫外光激励下334nm荧光强度随时间的衰变过程,将获得的荧光衰减动力学曲线采用指数拟合方法进行了解卷积处理,测试了相应的荧光寿命。分析了乙酸-水溶液中线状二聚物（LD）缔合结构的变化规律,计算了混合物质中不同组分的浓度...     

激光激发微弱荧光信号的光电探测

提出一种微弱荧光光电探测的实验装置，同时研究这种系统的噪声产生和抑制问题，信号噪声比的改善使得这种装置可以使用小功率氦氖激光作为激光发条件下探测荧光信号。这些工作为肿瘤早期诊断系统设备的实用化创造了基础。     

基于LPFG滤噪和混合放大的长距离FBG传感器系统

设计的基于长周期光纤光栅(LPFG)滤噪和掺Er光纤(EDF)/喇曼混合放大的长距离光纤布拉格光栅(FBG)传感器系统,不但优化了系统的信噪比(SNR),而且使传感距离提高到50 km.该系统以高功率扫描激光器作为传感光源和解调系统,加入的LPFG减小了双向喇曼放大的自发辐射(ASE)噪声和FBG后向反射噪声,同时双环形器的EDF结构利用剩余的泵浦功率产生ASE光和放大传感信号,为后端FBG提供了光源以及提高了后端FBG的SNR.带LPFG的混合放大与EDF/喇漫混合放大相比,实验表明,FBG 1和FBG 2的SNR分别提高了4.40 dB和4.38 dB,而且分布在50 km光纤上的4个FBG均获得了大于15 dB的SNR.     

Bit-Error-Rate Degradation in a Multimode Fiber Optic Transmission Link Due to Modal Noise

A review is given of the statistics of modal noise and of the expressions for the signal-to-noise ratio for the cases of a monochromatic and a nonmonochromatic light source including the effects of source frequency fluctuations. Using the results, a quantitative analysis is made of how modal noise degrades the bit-error-rate performance of a digital transmission link with multimode fiber. Plots of the bit-error rate versus the received optical power show the characteristic asymptotic behavior (BER floor); expressions are derived for the asymptotic BER. The power penalty due to modal noise can be considerably reduced by suitable system modifications, e.g., by optimization of the decision threshold setting or by application of a low coherent light source such as an LED or a laser diode operating with several spectral emission lines of low coherence and low partition noise.     

普通单模光纤中光孤子传输问题的研究

在使用普通单模光纤的光孤子传输系统中,放大器自发辐射（ASE）噪声和色散波逸出是限制光孤子传输的两个主要因素,它们将引起孤子能量科动和定时抖动,从而导致系统误码。本文分别研究了带限光滤波器对ASE噪声的抑制和非线性增益对色散波的抑制以及对孤子传输系统的稳定作用,并设计了使用普通单模光纤的光孤子传输系统。     

Organic Light Emitting Field Effect Transistors: Advances and Perspectives

Light emitting field effect transistors based on molecular and polymeric organic semiconductors are multifunctional devices that integrate light emission with the current modulating function of a transistor. The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors. OLEFETs show great potential for technological applications such as active matrix full color electroluminescent displays. In this Feature Article we review advances in OLEFETs since their first demonstration in 2003 and we highlight exciting challenges associated with their future development.     

Quadratic antenna systems and noise excited antennas

A quadratic receiving antenna system is defined as a multiport antenna whose outputs are passed through square-law detectors, or, in pair, through correlators (product detectors). These detected signals are then linearly combined with different weights to give the output or response of the receiving system. A reciprocity relation is derived which relates the electromagnetic field radiated by a multiport transmitting antenna excited by quasi-monochromatic noise sources to the response of a quadratic receiving antenna system. The noise sources exciting the transmitting antenna may be independent or they may be correlated. In general, the radiated field is partially polarized. The weights used in combining the signals from the square-law detectors and the correlators in the associated receiving system are determined by the intensities of, and the correlations between, the noise sources exciting the transmitting antennas. Practical use has been made of the derived reciprocity relation. The radiation properties of noise-excited multiport antennas have been determined by measurements made on the associated quadratic receiving system.     

Reduction of shot noise with light emitting diodes

The authors find that the optical shot noise and the electrical shot noise in light emitting diodes have the identical fluctuation due to spontaneous emission as far as the quantum efficiency is unity. The 0.45-dB reduction of noise below the standard shot-noise limit is achieved by using such correlation between the two kinds of shot noise     

Semiconductor laser noise in an interferometer system

The noise of semiconductor laser light after passing a Michelson interferometer has been measured for gain guided as well as index guided double-heterostructure injection lasers. This noise is mainly due to the partition noise and the frequency noise of the laser emission. Unless the interferometer is perfectly balanced, the observed noise is several orders of magnitude larger than the usual intensity noise of semiconductor lasers.     

Low Level Light Intensity Measurement from Repetitive Signals†

Background noise is a limiting factor in many cases where photo-electric measurement of light intensities is made. In the present case this problem is dealt with and the effect of noise reduced by special electronic circuit techniques for the study of temporal variations of light emission from microsecond transient discharges. The electronic circuits are dealt with in some detail, and examples are given of the uses to which the apparatus can be put.