On the relation between retarded and advanced arrival of a pulse at the output of an optical system

Abstract

It is shown that the possibility of negative delay time of a pulse at the output of an optical system (compared to the pulse at its input) is a necessary consequence of the possibility of positive delay time of the pulse and the superposition principle. In particular, two optical systems with different positive delay times are sufficient for creating an optical system with a negative delay time. The negative delay time of a pulse can be considered as a spline extrapolation of its time dependence resulting from the interference of several copies of the pulse with different delays. It is shown that a negative delay time of a pulse arises necessarily in any interferometer in an area of destructive interference of two copies of the initial pulse that are similar in amplitude and undergo different delay times.