Calculating the EX Series Switch Fiber-Optic Cable Power Budget

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.

1. Determine values for the link's minimum transmitter power (P_T ) and minimum receiver sensitivity (P_R ). For example, here, (P_T ) and (P_R ) are measured in decibels, and decibels are referred to one milliwatt (dBm).

   P_T = –15 dBm

   P_R = –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 (P_B ) by subtracting (P_R ) from (P_T ):

   –15 dBm – (–28 dBm) = 13 dBm