Nonideal behaviour of singlemode fibre-optic 3 ×3 directional couplers

Abstract

The phase shifts of 3 × 3 singlemode couplers deviate from 120° because of losses and asymmetries. The dependence of the phase shifts on the input states of polarisation is shown. Furthermore, the phase shift deviations due to power splitting asymmetries can be predicted numerically to some extent without phase sensitive measurements.