  In multimode interferometers, the interaction between several modes brings a
high level of complexity to the interpretation of its light patterns. With
recent advances, it is possible to selectively excite only a couple of modes
inside the device. This paper presents an analytical method for determining the
phase difference between two propagating modes in the multimode interferometer,
in an effort to simplify the usage and expand the range of applications for
this type of optical devices.
