On the Phase of the Modulation Transfer Function of a Multimode Optical-Fiber Guide

Abstract

We consider the range of validity of a Hilbert‐transform approach in which the measured magnitude of the modulation‐transfer‐function of an optical fiber is used to compute the fiber's impulse response. It is argued that a key “minimum‐phase assumption” can fail to be satisfied in important cases, and a few closely related experimental and analytical results are presented.

A Note Concerning Optical-Waveguide Modulation Transfer Functions

“…1 to the effect that, for a fiber guide that can propagate a finite number of discrete modes without mode mixing, the modulation-transfer-function (more precisely, the Laplace transform version of the modulation-transfer-function) is zero-free in the closed right half of the complex plane, and that property is structurally stable in a certain sense, if and only if a certain condition is met. The theorem described in Section II is concerned with a more realistic and far more interesting case in which mode mixing is not ruled out.…”