光衰减器一般分为固定衰减和可调衰减器，可以使用OTDR计来准确地测量其衰减值（）

A.OTDR

B.光功率计

C.传输分析仪

D.光可变衰减器

A.调测前，必须先掌握单板要求的接收光功率参数，严格按照调测指导书说明的受光功率要求进行调测

B.输入光信号在接入单板接收光口前，必须先测试光功率是否满足调测要求，禁止光功率超过接收过载点时进行不加光衰自环的操作，保证输入光功率不超过器件允许的最大值

C.进行过载点测试时，达到国标即可，禁止超过国标2个dB以上，否则可能烧毁光模块

D.使用OTDR等能输出大功率光信号的仪器对光路进行测量时，要将通信设备与光路断开

E.不能采用将光纤连接器插松的方法来代替光衰减器

光时域反射法（OTDR）Optical time domain reflection method (OTDR) 基本原理：光源发出的光在沿光纤向前传输的过程中产生后向散射，后向散射光强在向后传播过程中随着距离增长而按一定规律衰减，在光速不变的情况下，距离与时间成正比。因此，根据探测器探测到的后向散射光强及其到达探测器的时间，就可以知道沿光纤路径上任一点的初始后向散射光强。Basic principle: the light emitted by the light source will generate backscattering in the process of forward transmission along the optical fiber, and the intensity of backscattered light will decrease in a certain rule as the distance increases in the process of backward propagation. Under the condition that the speed of light remains unchanged, the distance is proportional to time. Therefore, the initial backscattered light intensity at any point along the fiber path can be known based on the backscattered light intensity detected by the detector and the time it took to reach the detector. 光的后向散射包括瑞利散射、喇曼散射和布里渊散射3种形式。The backscattering of light includes Rayleigh scattering, Raman scattering and brillouin scattering.

A. 光功率计

B. OTDR测试仪

C. 光纤熔接机

D. 光话机

A、测量线路中断点

B、测量整体长度

C、测量光功率

D、测量光衰减