Relationship between link budget and transmission distance in optical modules

      1.  the meaning of the link budget
      Link budget (link budget), is in a communication system on the transmitter, communication system links, propagation environment and the receiving end of all the gain and attenuation of the accounting. Usually can be used to estimate the signal can be successfully transmitted from the transmitting end to the receiving end of the farthest distance between.
      2. link budget and the relationship between the transmission distance
      Ideal conditions, the farthest transmission distance of the optical module = link budget / module light-emitting wavelength in the unit length of the attenuation value of the fiber, where the link budget = the minimum transmit optical power - receive sensitivity, the unit is dB.

Figure 1 Attenuation diagram of different wavelengths of light transmitted in the optical fiber

      As shown in the figure above, this is the attenuation diagram of different wavelengths of light transmitted in an optical fiber, where the vertical coordinate is the attenuation value in dB/km and the horizontal coordinate is the wavelength. As can be seen from the figure, there are four wavelength windows for optical communication, and the most commonly used in single-mode fibers are the 1310nm window and the 1550nm window: at 1550nm (1.5um), the fiber attenuation is about 0.2-0.3dB/km, while at 1310nm (1.3um) the fiber attenuation is about 0.3-0.4dB/km.
      Take the 10G ER optical module with wavelength of 1550nm as an example, the transmission distance is required to be greater than or equal to 40km:
Optical module transmit optical power range of -4dBm ~ 4dBm, the minimum receive sensitivity of -16dBm, the light-emitting wavelength of 1550nm (the third window), the fiber attenuation we take the middle value of 0.25dB/km.
      Then link Budget = -4dBm (minimum transmit power) - (-16dBm (sensitivity) ) = 12dB, the theoretical transmission of the farthest distance of 12/0.25 = 48km.
      In fact, there will be external losses in the transmission process, such as bending loss, connector loss, etc., so the actual transmission distance of the optical module will be shorter than the theoretical transmission distance, so we claim that the transmission distance of the ER module is 40km.
      Moduletek Limited can provide different transmission distance optical modules, welcome to buy.
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