基于光纤环选频特性的双环结构光电振荡器

提出并验证了一种借助于光纤环的选频特性实现辅助滤波的光电振荡器,利用偏振分束器(PBS)和偏振合束器(PBC)构成的双环路结构抑制掉部分光电振荡器的边模,同时借助于光纤环的光学梳状频率特性,对振荡器环路中的光信号模式再次进行选择,既起到边模抑制的作用,又提高了光电振荡器谐振腔的Q值.仿真结果表明:采用光纤环辅助滤波有利于光电振荡器的边摸抑制和单模输出,在保证光电振荡器输出低相位噪声和高频谱纯度微波信号的情况下,边模抑制比超过160 dB,模式间隔达到370 MHz,降低了对电域带通滤波器的性能要求,是一种新的光电振荡器设计方案.     

基于法布里-珀罗标准具的双环路光电振荡器

设计了一种基于法布里-珀罗(FP)标准具的双环路光电振荡器(OEO),该振荡器能将连续的光功率转换为稳定的频谱纯净的微波信号。FP标准具具有滤波的特性,因此可以替代普通OEO中的电滤波器从而降低电噪声,此外,FP标准具是一种高Q值的光学器件,可以缩短普通OEO所使用的光纤长度。双环路结构的引入能够更好地保证振荡器的单模输出,进一步降低相位噪声。仿真结果证明这种新型结构的OEO可以实现20GHz范围内振荡频率为15GHz的单模起振,边模抑制比超过150dB,使用的两条光纤环路长度分别为5m和36m。     

低相噪启钥式耦合微波光电振荡器研究北大核心

针对微波通信、雷达、电子战和导航等先进电子系统的应用发展需求,为了实现具有实用价值的极低相噪耦合微波光电振荡信号产生,提出了一种基于Sigma型光纤储能环腔架构的低相噪启钥式耦合微波光电振荡器。该方案通过Sigma型光纤储能技术消除了耦合微波光电振荡器中存在的偏振衰落问题,并且通过有源光纤环腔再生增益特性极大增强了振荡器品质因数,最终实现了10 GHz耦合微波光电振荡器的开机启钥稳定运行,起振信号在10 kHz频偏处的相位噪声达到-139.26 dBc/Hz。     

基于光电振荡器的光脉冲和电微波信号发生器

设计了一种基于相位调制器的用于产生光脉冲和电微波信号的光电振荡器。该方案采用直调激光器配合相位调制器产生大啁啾并由DCF压窄输出光脉冲。利用偏振分束器和合束器在不增加有源器件的基础上形成双环路结构抑制微波信号的边模。该系统可以产生9.8 GHz的重复频率，脉宽小于 12 ps的光脉冲同时输出该频率的电微波信号。测得相位噪声为-105 dBc/Hz@10 kHz，Q值大于10¹⁰。     

基于光电振荡器的低相噪光生微波技术及其应用北大核心CSCD

光电振荡器通过自振荡产生超低相位噪声微波信号,具有光、电两种输出,有望从源头突破现有雷达、电子战等射频系统性能瓶颈。文章介绍了光电振荡器的基本结构和理论模型,回顾了光电振荡器相位噪声、边模抑制比、工作频率、稳定度和小型化等关键性能提升的研究进展,并讨论了光电振荡器的功能拓展及光电振荡器在雷达等领域的应用。     

百瓦级全光纤线偏振激光振荡器

报道了一种全光纤结构的高消光比(PER)线偏振激光振荡器。该光纤激光振荡器的谐振腔由一段双包层掺镱保偏光纤和一对与增益光纤匹配的光栅组成。弯曲损耗使快轴方向上的偏振模和高阶模受到抑制,实现了消光比优于15 d B的线偏振激光输出。最高输出功率为93.2 W,中心波长为1080 nm,光谱半峰全宽(FWHM)约为1.2 nm。增加抽运功率有望进一步提升功率。     

基于电增益环腔选频特性的小型光电振荡器

为了进一步提高光电振荡器的实用性,提出了一种基于耦合型电增益环腔的小型化光电振荡器。利用电功分器和放大器构成电增益环腔,其梳状滤波效应可以有效对光电振荡器进行模式选择,结合直接调制半导体激光器,单模光纤和光电检测器,有效实现了小型化光电振荡器。理论上分析了电增益环腔的基本原理,并且通过仿真进行了验证。实验中获得了中心频率为12.624 GHz的微波信号,其相位噪声为-102 dBc/Hz@10 kHz。该方案在结构简单的条件下可以得到质量较高的射频信号,可以作为光电振荡器实用化的一种解决方法。     

K波段高稳光电振荡器

介绍了一种具有高稳定性、高谱纯度、低相位噪声的双环路光电振荡器(OEO)。理论上分析了光电振荡器的基本原理,采用光域双环路的方案有效地实现了边模抑制,通过检测输出信号频率的变化来控制光纤环路的长度,从而得到了高质量的20GHz微波信号,其频谱纯度高,线宽小于1Hz,相位噪声在10kHz时为-112dBc/Hz,而且在4h观测时间内,频率的稳定性小于10-10。     

光电振荡器的相位噪声特性

与传统的微波振荡器相比,光电振荡器利用光纤储能,能够产生低相位噪声的微波信号.论述了光电振荡器的特点、基本结构和工作原理,推导了相位噪声的表达式,对其特性进行了理论研究,并构建了光电振荡器的实验.理论分析表明,光纤延时、激光器的相对强度噪声以及微波放大器的噪声系数会影响光电振荡器的相位噪声,为减小相位噪声提供了理论依据.实验测量了3种光纤延时下的相位噪声,并与理论分析的结果进行了对比,证明了理论分析的正确性.     

微波超低相噪光电振荡器

介绍了一种基于光纤收发系统的新型微波振荡器.这种光电振荡器由两个反馈光纤延时环组成,各环路中包括光纤、光电探测器、放大器、滤波器和功分器/合成器.光电振荡器具有超低相噪、频谱纯、工作频率高和稳定度高的特点,可广泛应用于微波系统和光纤通信系统.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

A rigorous proof of MIMO channel capacity’s increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output（MIMO） communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas. The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.