Nonreciprocal effects in a ring interferometer with a multimode fiber waveguide

An analysis is made of parasitic nonreciprocal effects in a ring interferometer utilizing a multimode fiber waveguide. These effects are associated with intermode exchange, which is a specific property of multimode waveguides. It is shown that these effects can be reduced significantly by utilizing a light source with a low spatial coherence. The results of the analysis yield dependences which are in order-of-magnitude agreement with those found experimentally.