Model for Differential Model Delay Distribution in Multimode Fibers

A band-limited fixed frequency linearly polarized optical signal excites several modes of propagation when it is launched into a multi-mode dimensioned optical fiber waveguide. This signal will therefore propagate over multiple paths along the transmission medium resulting in different propagation time for each mode. Thus replicas of the input pulse launched into the multimode fiber arrive at the output at different times, with the fundamental mode arriving first. A Differential Modal Delay (DMD) distribution is thus produced at the output of the fiber. The mode distribution, and consequently the modal delay distribution, are both a function of the physical attributes (geometry, distance, launching angle) of the optical waveguide. In optical communication systems this DMD distribution creates signal distortion that limits system designs (power, modulation, noise) and network performance (reach, rate, capacity). Accurate quantification of this DMD distribution is therefore essential to the prediction and improvement of performance.