How do I calculate an optical budget?
This calculation depends on the laser and its operating wavelength. The general rule is the higher the wavelength, the lower the loss.
For every 1Km of fiber, you will incur a loss of 0.25dB at 1550nm or 0.4dB at 1310nm. When calculating optical budget, one needs to include optical connector or patch panel losses, which is approx. 0.1dB for each point of connection. For example, the total fiber loss of a 2Km fiber run, when using a 1550nm laser and two optical patch panels on each side, will be 0.9dB (0.25dB+0.25dB+0.2dB+0.2dB).
The converted RF power is related to the square of the optical power, and due to this relationship, a 1dB loss of optical power will become a 2dB loss of RF power.