How to choose the optical module in the case of known link attenuation

      1. The concept of fiber optic link attenuation
vFiber optic link attenuation includes fiber attenuation, connector attenuation and splice attenuation. Therefore, all these factors should be considered when calculating the attenuation of a fiber optic link. In addition, we need to calculate the system margin. System margin includes fiber bending and some unpredictable light attenuation, etc. Leave at least 3dB margin.
      Method of testing link attenuation: One end of the fiber under test is a light source and the other end is an optical power meter. The optical power from the light source is P0. After the optical power of the fiber under test is reduced to P1, (P0-P1) is the link attenuation of the fiber under test.

Figure 1. Link attenuation test schematic (Loss = P0-P1)

      2. In the case of known fiber link attenuation, how to choose the optical module
      The following conditions need to be met:
      RX2 sensitivity < TX1 power - link attenuation - 3dB < RX2 received optical overload value
      RX1 sensitivity < TX2 power - link attenuation - 3dB < RX1 receive optical overload value

Figure 2. Module Application Schematic

      For example, if you use our SFP10-10G-ZR module, the link attenuation of the application environment is 15dB (1550nm light source). The actual parameters of our SFP10-10G-ZR module are as follows:

Table 1 Actual parameters of our SFP10-10G-ZR module

      Calculation:
      TX1 Emitted Optical Power - Loss-3dB=1.3-15-3=-16.7dBm
      TX2 Emitted Optical Power - Loss-3dB=2.1-15-3=-15.9dBma
      Because:
      RX2 sensitivity (-25.2dBm) < -16.7dBm < -7dBm
      RX1 sensitivity (-24.5dBm) < -15.9dBm < -7dBm
      Therefore, our SFP10-10G-ZR module can be used in the 15dB (1550nm light source) link attenuation environment.
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