SELF IMAGING OPTICAL ELEMENT USING MULTIMODE INTERFERENCE

摘要

Optical elements utilize multimode interference in a piece of an optical fiber of multimode type having a core in the shape of a ring or a tubular structure. Such a fiber can be compared to a planar waveguide, the core of which has been bent about a longitudinal axis located at some distance from the core. Such an optical fiber can be optically excited having an excitation centre in a point on or at the annular core by coupling from a single-mode fiber. Then different optical propagation modes are excited having approximately regular relations between their phase velocities so that, for example, for a suitable length of the fiber piece a light intensity is obtained in the other end of the fiber piece which is an approximate reflected image of the light intensity supplied at the input end of the fiber piece. Such an optical element can, for example, be used as a filter or as a passive 1 .times. N-coupler, where in the latter case the length of the fiber piece is adapted so that an N-fold image of the supplied light intensity is obtained at the output end of the fiber piece.