In a process for the production of an optical coupler for polymeric optical fibers using ultrasound welding, the fibers are warmed, before the welding, to a temperature of from 50.degree. to 250.degree. C. for from 0.2 to 3 hours. The polymeric optical fibers are introduced into a plastic tube which melts with the fibers during the welding operation to form a unit. In another embodiment, a connector bar which has the same refractive index as the core material of the polymeric optical fibers can be inserted into the plastic tube, the polymeric optical fibers are brought into contact with the connector, and the plastic tube, the connector bar and the fibers are welded to one another under the action of ultrasound.