For singlemode fiber, the loss is about 0. 5 dB per km for 1310 nm sources, 0. 5 dB/km at either wavelength for outside plant max per EIA/TIA 568)This roughly translates into a loss of 0. 1. However, it is beneficial to make it standard practice to test all fiber optic cable assemblies at 1310 and 1550: the variation in insertion loss between the 1310nm and 1550nm test wavelengths can be very helpful in identifying serious problems with the product and/or process. The estimate, called a "loss budget" is calculated using typical component losses for. ic system. Fiber optic testing of a newly installed system not only verifies that the system meets its design requirements, but also creates a performance baseline for all future testing and troubleshooting of t at system. Understanding these principles ensures your custom assemblies perform reliably across.