New planar optical coupler for a data bus system with single multimode fibers.

We report an optical coupler suitable for use as an access coupler in a data bus T-system with single multimode fibers as transmission lines. The in- and out-coupling factors are determined by a lateral displacement of the main trunk-fibers which are butt joined. The fabrication of the coupler takes advantage of a simple, sufficiently reproducible, and cheap planar photolithographic process. Using fibers with 100-microm o.d. and 90-microm core diam a total insertion loss of about 1.5 dB and an out-coupling of about -14 dB was measured with a lateral displacement of 20 microm.