The present invention relates to a surface interaction type multimode optical fiber coupler. A representative embodiment of the present invention comprises a plurality of optical fibers with each having an expanded core section. The expanded core sections of the optical fibers are fused together forming a fused section. Each of the optical fibers is optically coupled with at least one other optical fiber primarily through surface interaction in the fused section. The optical fibers are suitable for multimode operations. According to an embodiment of the present invention, a method of fabrication an optical fiber coupler comprises: providing a plurality of optical fibers with each having an expanded core section; and maintaining at least a portion of the expanded core sections in contact and simultaneously heating at least a portion of the expanded core sections that are in contact to form a fused section until a predetermined end condition is reached.