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1、Special English金钟燮考试安排考试安排时间：11月27日 周六周六 9：00-11：00地点：A区 8111-8112成绩：平时分30分（测验及点名）内容：课堂内容，老教材内容，摘要题型题型：1.缩略语展开，翻译（十选五，共10分）2.公式的英语表达 （五选三，共15分）3.英译汉（七选四，共40分）4.汉译英（三选二，共20分）5.总结摘要（标题，摘要，关键词；共15分）The material compositions of core and cladding, as well as their dimensions and index profiles, determine
2、 the optical attenuation and signal dispersion characteristics of the fiber. These properties are also dependent on the wavelength used. Nowadays 850nm is mostly used, but in the near future, 1300nm will probably be referred because of the demonstrated lower dispersion and attenuation values.Semicon
3、ductor junction photodiodes are small, light, sensitive, fast, and can operate with just a few bias volts. They are almost ideal for fiber systems. We will investigate three forms of these devices: the pn, PIN, and avalanche photodiodes. The simple pn photodiode, drawn in Fig.7-4, illustrates the ba
4、sic detection mechanism of a junction detector. When reverse biased, the potential energy barrier between the p and n regions increases. Free electrons (which normally reside in the n region) and free holes (which normally in the p region) cannot climb the barrier, so no current flows. 请将缩略语展开，并写出中文
5、含义请将缩略语展开，并写出中文含义（共（共10分）分）SNRlaserIPmodemCPUDCACLEDPDWDMITUFMAMSMFPhase = X equals (is equal to) negative (minus) B plus (or) minus root of B square minus four A C over （divided by）two A X square over A square plus Y square over B square equal one Phase equals two pi N D over lambda plus thetaF equ
6、als one over two pi R (sub) F C (sub) FY equals A times X plus B 翻译（翻译（10分分/每小题，共每小题，共40分）分）Semiconductor device produce a slowly fluctuating current called current noise or 1/f noise. It is limited to low frequencies, varying as 1/f below 1Hz. Current noise can be minimized by passing the amplified
7、 signals through filters that severely attenuate frequencies below about 10 Hz. In an atmospheric optic communication system, light can enter the photodetector from sources other than the desired one. Energy from sunlight, street lamps, or car lights can be detected, increasing the receivers dc curr
8、ent and, consequently, increasing the shot noise. This background noise is easily eliminated from fiber links because they are normally completely enclosed. Laser diode modulationLaser diode present more problems to the circuit designer than LEDs. The trouble arise from 1.The existence of a threshol
9、d current2.The threshold currents age dependence3.The threshold currents temperature dependence4.The emission wavelengths temperature dependence阅读下列文字，并写出一篇英文摘要（阅读下列文字，并写出一篇英文摘要（15分）分）在光纤传感领域,光纤光栅传感技术是十多年来发展最为迅速的技术之一,传感系统本身和应用领域均有了很大发展1。但是鉴于分布式光纤光栅传感的结构局限，传统的光纤光栅传感器在解调的精密度方面有些欠缺，特别在静态测量，大范围测量中误差较大，影
10、响检测质量，并容易引起误报等事故2。本研究采用了新的解调方法，采用ITU（International Telecommunication Union, 国际通讯联盟）标准信道作为多重参考（multi reference），可有效提高测量精度，并可实现宽带光源全光谱范围测量，有效扩大测量范围，增加传感信道。同时降低了成本，简化了结构。1978年加拿大渥太华通信研究中心的K. O. Hill等人首次在掺锗石英光纤中发现光纤的光敏效应，并采用驻波写入法制成世界上第一根光纤光栅3。光纤光栅具有以下特点：耐高压，耐腐蚀、抗电磁场干扰、体积小、重量轻、便于实现远端传输等。特别是易于耦合，可在一根光纤内集成
11、多个传感头复用，实现大面积多信道的分布式测量。并且由于光纤光栅传感器是一种波长调制型传感器，波长编码信号不受光源强度的起伏、光纤微弯损耗引起的随机起伏和耦合损耗等因素的影响，对环境干扰也不敏感。作为分布式的光纤光栅传感器系统，最为成功的当属1993年英国的A. D. Kersey发表在Optics Letters上的文章4。这种方法成功地实现了分布式测量，且结构简单，但是由于该系统使用宽带光源作为光源，而光纤光栅又只反射宽带光源中的一小部分光，所以信号较小，SNR(Signal to Noise ratio, 信噪比)低。1998年韩国的S. H. Yun博士留美期间，在Optics Lett
12、ers 上发表了一篇文章5。但是以上方案都是在假设F-P滤波器对电压的线性响应基础上。而实际上，F-P滤波器是由内置的PZT进行调制，而PZT的电压响应由于磁滞效应，是非线性响应。所以，测量结果会有不可克服的误差，特别是在静态测量，准静态测量，大范围测量时，误差较大。2001年香港理工大学靳伟教授小组首先提出由气体吸收谱线作为多重参考的方案2，减少了F-P滤波器非线性响应带来的误差。此方法经。所以，没有实现真正意义上的线性解调。本研究将采用ITU标准信道作为多重参考，可以实现宽带光源全光谱测量，大大提高了测量范围。另外，对通过ITU标准信道的光信号峰顶位置进行多项式拟合，重现F-P滤波器的实际
13、扫描曲线，对应光纤光栅反射峰顶的位置，解调光纤光栅反射波长。从而实现真正的线性解调。用多项式拟合法拟合信号峰顶位置信息，得到了更准确的，较少受外界干扰的峰顶位置，即波长信息，同时拟合结果也可以用于误差分析。实验结果表明，本方案可以对光源光纤光栅传感器进行线性解调，并且在20Hz扫描频率下，得到了1pm的解调精度。由于测量范围扩大到80nm，可以进行更多信道的同步测量，在实际应用中会有更好的应用。 Fiber grating sensor array interrogation with time-delayed sampling of a wavelength-scanned fiber la
14、serAbstractA novel method for fiber Bragg grating (FBG) sensor array interrogation based on a wavelength-scanned fiber laser is presented. The wavelength of the scanning fiber laser is monitored by time-delayed sampling and assigned to return peaks as Bragg wavelengths of the sensor gratings. From e
15、xperiments with an array of four FBG sensors, the scheme showed the same measurement results using different wavelength scanning waveforms, which verified that this scheme demodulated the sensor signals linearly, regardless of nonlinearities in the wavelength-tuning mechanism. Overall, 20 pm of meas
16、urement accuracy was obtained which could have been greatly enhanced with faster phase modulation. Linear interrogation of fiber Bragg grating sensor array using a Etalon filterA scanned Fabry-Perot(F-P) filter and a Multi-Channel Wavelength Locker(MCWL) were used to interrogate fiber Bragg grating
17、sensor array. When the F-P filter scans over the MCWL which works as a multi-reference, the temporal peaks profiles correspond to the locking wavelengths. To solve the linearity, stability, and accuracy problems caused by the nonlinear response of F-P filter, a polynomial fitting algorithm was used
18、to calculate the relationship between the peak locations and the wavelengths in all the scanning range. Then from the reflected peaks locations and the best fitting line, the Bragg wavelengths can be obtained. The measurement linearity was greatly enhanced with wavelength resolution of about 4 pm in 10 scanning frequency.
