Optical fiber coupler

A fiber optic coupler comprises a multimode fiber bus (42), an input branch fiber (44), and an output branch fiber (46). Coupling between the fibers is accomplished by means of a reflector (60), disposed in the core (42a) of the multimode optical fiber (42). The reflector (60) is quite small, such that only a small fraction of the light propagating in the mulfimode fiber (42) is incident thereon. The incident light is reflected towards the output branch fiber (46) and coupled thereto through a lens (56). Light propagating in the input branch fiber (44) towards the multimode fiber (42) is focused on the reflector (60) by means of a lens (52). The reflector (60) is oriented to reflect the focused light in a generally cone-shaped beam directed longitudinally down the axis of a muftimode fiber (42). Preferably, the cone-shaped beam diverges so that substantially all the modes within the acceptance cone of the multimode fiber are excited. Such excitation of the modes is preferably equalized by selecting the numerical aperture of the multimode fiber (42) such that only the portion of the reflected beam which has a relatively uniform intensity is within the acceptance cone of the fiber (42). The invention is particularly advantageous for local area networks and distributed sensor systems.