Optical splitter/coupler and optical communication system

An optical splitter/coupler comprising:

• a multimode waveguide having an electrooptic effect, and propagating multimode light;
• one pair of incident waveguides propagating single mode lights, and inputting the single mode lights to one end of the multimode waveguide;
• one emitting waveguide guiding-out a single mode light which has propagated through the multimode waveguide;
• at least one pair of individual electrodes provided so as to be positioned in vicinities of respective side edges of the multimode waveguide, on one surface of the multimode waveguide;
• and
• a ground electrode provided on another surface of the multimode waveguide,
• wherein the multimode waveguide has a length such that 3(n+1) (where n is a natural number) bright spots arise at a central portion and at both side edge portions due to the single mode lights incident from the incident waveguides,
• the individual electrodes are provided at positions corresponding to a one pair of the bright spots which one pair is second from an upstream side, and
• the emitting waveguide is connected to a position corresponding to a downstream-most one of the bright spots at the multimode waveguide.

An optical splitter/coupler comprising:

• a multimode waveguide having an electrooptic effect, and propagating multimode light;
• one incident waveguide propagating a single mode light, and inputting the single mode light to one end of the multimode waveguide;
• one pair of emitting waveguides guiding-out a single mode lights which have propagated-in through the multimode waveguide;
• at least one pair of individual electrodes provided so as to be positioned in vicinities of respective side edges of the multimode waveguide, on one surface of the multimode waveguide;
• and
• a ground electrode provided on another surface of the multimode waveguide,
• wherein the multimode waveguide has a length such that 3(n+1) (where n is a natural number) bright spots arise at a central portion and at both side edge portions due to the single mode light incident from the incident waveguide,
• the individual electrodes are provided in pairs at predetermined positions, and
• the emitting waveguides are connected to positions corresponding to a downstream-most one pair of the bright spots at the multimode waveguide.