One-by-two polarizing beam splitter for 1550nm with 40dB return loss. The input fiber is Corning SMF-28 fiber, while the two output fibers are 8/125 polarization maintaining fibers. All three fibers are one meter long, 3mm OD Kevlar reinforced PVC cabled, with no connectors on the. Excess loss is the ratio of the optical power launched at the input port of the splitter to the total optical power measured from all output ports. A splitter with 1×2 certain ratio configuration means that it has one input and. The theoretical loss assumes perfect splitting with no imperfections. In practice, losses are slightly higher due to: Insertion loss tells you how much weaker the signal becomes after passing through the splitter. Let's say you have a laser output at 0 dBm (which is 1 milliwatt of optical power). Enter excess loss from the splitter datasheet for your wavelength. Include any additional component losses and an engineering margin. in Watts – W), the loss value in dB is calculated by the formula: 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).