  Modal dispersion characterization of multimode optical fibers can be
performed using the recently-proposed mode-dependent signal delay method. This
method consists of sending optical pulses using different combinations of modes
though the multimode optical fiber and measuring the mode group delay at the
fiber output. From these measurements, it is possible to estimate the modal
dispersion vector, the principal modes, and their corresponding differential
mode group delays. In this paper, we revise and extend the theoretical
framework of the mode-dependent signal delay method to include the impact of
receiver noise and mode-dependent loss. We compute optimal launch modes,
minimizing the noise error in the estimation of the fiber modal dispersion
vector. We show that, for a 40-mode fiber, the electronic signal-to-noise ratio
(SNR) is improved asymptotically by almost 6 dB compared to conventional mode
combinations.
