The amplification of non-linear travelling waves through a tree of 3-strings

A 3-string is a planar network of 3 sections of strings which are tied together at one common mobile extremity. We describe the propagation and the interaction of non-linear travelling perpendicular waves in a 3-string. We also explain how to use a network of 3-strings having the shape of a tree to amplify such a travelling wave. This method is applied to the cases of KdV solitons and plane gravitational waves.