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Optical receiver Test

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  • 光接收机测试
  • 一、工作原理
  • 二、主要指标
  • 三、实作
  • 四、关于中继
  • Question and Answer

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光接收机测试

一、工作原理

放大器: 补偿衰减

前置放大器: 低噪声放大,放大倍数低

主放大器: 多级放大电路

自动增益电路(AGC, Automatic gain control): 调节输出光功率

均衡器: 消除信号(0 or 1)在传输中变宽的问题,使其不影响判决

判决器: 斯密特触发器(Schmitt trigger)。 当输入电压高于正向阈值电压,输出为高;当输入电压低于负向阈值电压,输出为低

眼图: 展示 信号的非线性回归特性(即大概率在一条曲线上)。一般由均衡器处理后的信号得来。

二、主要指标

  1. 灵敏度(PminP_{min}Pmin​): 最小能接受的信号(要求此时的误码率 Bit Error Rate满足要求),单位dBm,越小越好

    当 收到的信号功率<灵敏度功率,误码率会很大

  2. 过载光功率(PmaxP_{max}Pmax​): 功率高于这个值,就不行,机器会坏

  3. 动态范围()

三、实作

假设一台光发送接收机的绿灯亮,表示接收没有问题

两台光发送接收机,用加了衰减器的光纤互相连接,左边的不亮,右边的亮

可能的故障(检错点)有:

  1. 光纤断了

  2. 连接不牢

  3. 右边发送器坏了 (用自己的发送器接自己的接收器(自环)这种方式来检验,是否真的是这种情况)

  4. 左边接收器坏了 (用自环验证)

  5. 绿灯坏了

  6. 衰减器不行(衰减过多 或 太少)

  7. 没接电源

四、关于中继

= 60 km, 加光中继

光中继的作用:

  1. 补偿衰减 (再放大)

  2. 对畸变失真的波形做整形 (再整形)

  3. 重新定时 (再定时)

光中继的类型:

  1. 光电型中继器 (变成电后再操作)

  2. 全光中继器 (只能用于光的放大)

Question and Answer

Pmax−PminP_{max} - P_{min}Pmax​−Pmin​