Phase-amplitude relationships for the frequency response of a monomode optical fibre

Abstract

It is shown theoretically that a relationship exists between the phase and amplitude components of the modulation transfer function (MTF) for a monomode optical fibre, provided that the source coherence time is very much less than the reciprocal modulation bandwidth: this condition is normally satisfied in practice. It follows that only the amplitude component need be measured; the phase component can then be derived. A similar relationship is also shown to exist for the phase and amplitude components of the complex amplitude transfer function. The result allows the MTF to be measured conveniently for a variety of propagation conditions, such as differing optical carrier frequencies or differing polarisation states. The corresponding relationship for the amplitude transfer function could be useful in spectroscopic applications.