The calculation considers the optical source, wavelengths, type of fiber, distance, core diameter and lens, and a number of different parameters that affect power loss. The basics for doing the calculation are distance and damping. For example, how long is the fiber from point to point and the degree of signal attenuation. The damping is affected by the fiber cable age, which often relates to joints / welds, stations, contacts and damage. By doing measurements with an Optical Time Domain Reflectometer (OTDR), you can evaluate the fiber’s status. With the right information about the damping, you can also calculate how much you can expand your fiber network before you need to add active equipment.
Power budget (PB)
Least possible “transmitter power” (PT)
Least possible “receiver sensitivity” (PR)
PB = PT – PRThe equation below is in decibel (dB) with reference to 1 mW (dBm):
PB = PT – PR
PB = 0 dBm – (–16 dBm)
PB = 16 dB