光纤复习 2014.doc

复习 一、Fill in the blank（30 points, 2% per blank ） (1) As the temperature increases, the diodes gain decreases, the threshold current becomes greater. 二、Judgement, only one is correct （16 points, 4% per blank ） (1) What is the output current of a photodetector whose quantum efficiency is 0.9. The wavelength is 1300nm, and the incident power level is -37dBm. ( a ) a. 0.188(A b. 0.190(A c. 0.192(A d. 0.194(A 三、简述题（24 points, 8% per blank） 1、简述光纤通信系统对光源、光纤和光检测器的要求。 ( carrier Source: stable, single-frequency, sufficient power, the information is contained in the variation of the optic power (fiber: attenuation, distortion, acceptance angle ( photodetectors: long life, low power consumption, high sensitivity, fast response 2、SiO2折射率特点 Describe the characteristics of refractive index for pure silicon dioxide glass. (The refractive index decreases with increasing wavelengths. (At a particular wavelength, there is an inflection point on the refractive index curve. The magnitude of the slope is minimum at this wavelength. (For pure silica, the refractive index is close to 1.45 and the inflection point is near 1.3 (m. 色散如何导致的模拟信号、数字信号畸变 How does dispersion create signal distortion? (Digital signal: The several pulses travel at different velocities, reaching the end of the fiber at slightly different times. When summed at the output, the slightly displaced pulses add together, yielding an output that is lengthened, or spread, relative to the input signal. (Analog signal: At the input several wavelengths vary together in phase with each other, creating a large signal variation. After travel through the dispersive media, these wavelengths are no longer in phase. When added together theyproduce a signal variation lower in amplitude than the input signal variation. 4、导模条件 Explaining mode condition. Stable interference patterns occurred only when the phase shift for a complete round trip was equal to an int