The insertion loss method uses a calibrated source and power meter to measure loss across the fiber non-destructively. Divide loss by length to get attenuation. You measure optical power in dBm or insertion loss in dB. Consistent procedures ensure accuracy.
[pdf] A beam splitter or beamsplitter is an that splits a beam of into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as, also finding widespread application in.
[pdf] Unlike, single-mode fiber does not exhibit. This is due to the fiber having such a small cross section that only the first mode is transported. Single-mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. For these reasons, single-mode fibers can have a higher than multi-mode fibers. Equipment for single-mod.
[pdf] 
