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光学时域反射仪主要用来测试光纤损耗,所测得的瑞利散射信号与耦合进光纤中的光功率成正比,光功率的变化将直接影响仪器的测量精度。另外,由于瑞利散射产生的背向反射信号很微弱,于是,要从大干信号两个数量级的噪声中提取信号,这就必须以时间作代价。激光器的输出光功率是随周围温度变化和使用时间的增加而变化的,图1是美国RCA生产的激光器的输出功率随温度变化的曲线。图2是随使用时间增加引起输出功率变化的曲线。我们采用的上海半导体器件六厂生产的性能类似RCA产品的单异质结砷化镓激光器(2EJD2B)的温度系数较大,在常温下每升高10℃光功率将下降10％左右。为提高仪器的测量精度,我们试制了脉冲式激光稳功率源,它是利用激光器在其工作区域里光功率随工作电流线性增加的特点,对激光器发出的光脉冲采样,通过自动调节系统,使激光器的输出功率保持稳定。
Optical time-domain reflectometer is mainly used to test the fiber loss, the measured Rayleigh scattering signal is proportional to the optical power coupled into the optical fiber, optical power changes will directly affect the measurement accuracy of the instrument. In addition, since the backscattered signal due to Rayleigh scattering is very weak, then it takes time to extract the signal from two orders of magnitude of the noise of a large signal. The output optical power of the laser varies with the ambient temperature and the operating time. Figure 1 shows the curve of the output power of a laser manufactured by RCA in the United States with temperature. Figure 2 shows the change in output power as a function of time. The single heterojunction gallium arsenide laser (2EJD2B) with RCA-like performance produced by Shanghai Semiconductor Device No. 6 Factory has a large temperature coefficient. At every 10 ℃ increase in temperature, the optical power will decrease by about 10%. In order to improve the measurement precision of the instrument, we tried out a pulsed laser steady power source, which utilizes the characteristic that the laser power increases linearly with the working current in the working area of the laser, and samples the light pulse emitted by the laser. By automatically adjusting the system, The output power of the laser remains stable.