Combining appropriate zero-order and first-order fields in an overmoded optical fibre, produces an offset intensity distribution whose radial position varies with their relative phase and polarization. This may be used to achieve phase (or polarization) diversity detection in a coherent optical receiver, by detection of this intensity distribution on a four segment photodetector. In-phase and Quadrature signals (or orthogonally polarized signals) are produced from each diametrically opposed pair of photodiode segments.
R. E. Epwor th,
A. R . L . Travis,
I. H. White,
"Overmoded Fibre For Multiport Coherent Detection", Proc. SPIE 0734, Fibre Optics '87, (17 September 1987); doi: 10.1117/12.938002; https://doi.org/10.1117/12.938002