Calculating the Fiber-Optic Cable Power Budget for a QFX Series Device

 

Calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at the worst-case levels.

To calculate the worst-case estimate for the fiber-optic cable power budget (PB) for the link:

  1. Determine values for the link's minimum transmitter power (PT) and minimum receiver sensitivity (PR). For example, here, (PT) and (PR) are measured in decibels, and decibels are referenced to 1 milliwatt (dBm):

    PT = –15 dBm

    PR = –28 dBm

    Note

    See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.

  2. Calculate the power budget (PB) by subtracting (PR) from (PT):

    –15 dBm – (–28 dBm) = 13 dBm