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

•Standard single-mode fiber is bi-modal fiber when operated below the cable cutoff wavelength of around 1260 nm, in which case two modes including LP01 and LP11 are supported. The system performance highly depends on the modal bandwidth of the fiber, therefore, it is valuable to develop a simple and robust method to measure the modal bandwidth of such fiber.•We propose a simple and robust frequency domain method for measuring modal delay and bandwidth of bi-modal 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 condition.•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. We propose a simple and robust frequency domain method for measuring modal delay and bandwidth of bi-modal 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.