1) invariance to the operator of spreading in their environment,
2) preservation of the orthogonality of propagation,
3) smaller energy losses for modes with lower indices,
4) best mean approximation of the fields propagating in the given environment.
Thanks to these properties, the behaviour of different light fields in waveguides and free space is seen through the modal representation (light fields are represented as an infinite or finite linear superposition mode). The mode composition of the fields determines ...