Modal delay and modal bandwidth measurements of bi-modal optical fibers through a frequency domain method

We propose a simple and robust frequency domain method for measuring modal delay and bandwidth of bimodal optical fibers. An analytical transfer function model is formulated showing excellent agreement with experimental results for relatively short fibers. Using the model, a full set of information can be extracted, including modal delay and modal bandwidth under any launch conditions. As a result, one can obtain a worst-case modal bandwidth that can gauge the fiber modal bandwidth under general conditions. In addition, the frequency domain measurement method and the analytical model are validated through the excellent agreements with the time domain measurement results. The analytical model is also generalized for longer fiber lengths when additional degradation effects become significant to alter the behavior of the transfer function. Through the detailed study, we show that the simple frequency domain measurement method as facilitated by the analytical model can deliver a full set of modal delay and modal bandwidth information that otherwise requires more complex method of differential mode delay measurements.