Loss (dB) = 10 lg ( mW1 / mW2 ) When both gains are equal, the loss is 0 dB, so there is no loss (doesn't happen obviously). A passive optical splitter divides an incoming light signal across two or more output ports. Excess loss accounts for manufacturing imperfections, typically 0. DISCLAIMER: These calculators are provided for. To calculate the power requirements for each optical link, you can use the formula: Pi is the driving power needed for each optical link. 5 dB depending on splitter type. Optional: patch panels, attenuators, or extra components. Example: 0 dBm. Let's say you have a laser output at 0 dBm (which is 1 milliwatt of optical power). in Watts – W), the loss value in dB is calculated by the formula: Loss (dB) = 10 lg (.