Mode Loss Measurement in Few-Mode Fibers With a Microwave Interferometric Technique

We measure the mode dependent loss (MDL) of a few-mode fiber (FMF) using an improved microwave interferometric technique. A frequency-swept microwave signal modulates a filtered optical incoherent source that is injected into the FMF under test. During propagation, the microwave signal carried by the various modes experiences different losses and delays before interfering at the photodetector. The fiber MDL, between mode groups, is computed from the interference pattern by measuring two different fiber lengths under the same excitation condition. This technique relies on the dominant excitation of the fundamental mode and therefore can measure high values of MDL.