Optical attenuator used with optical fibers and compensation means

Abstract

An optical attenuator for attenuating the intensity of a light beam emerging from an optical fiber comprises a wedge-shaped attenuator disk made of an absorbing material and a transparent disk which is also wedge-shaped and fixed to the absorbing disk. For adjusting different attenuations, the attenuator disk together with the transparent disk are rotated around an axis by a motor. By rotating the disk, the thickness of the absorbing material through which the beam passes and thus the attenuation of the beam can be varied continuously. After passage through the attenuator disk, a corner cube reflects the beam back into the direction where it came from, so that it passes a second time through the transparent plate and the attenuator disk. This second passage occurs at a location which is shifted relative to the location of the first passage (in a direction perpendicular to the plane of the paper). The transmitted beam impinges on a prism from which it is directed via a lens into an optical fiber. Due to the twice repeated passage of the light beam through the attenuator disk and the transparent disk, any refractive index related beam deviations are compensated so that the outgoing attenuated light beam can efficiently be coupled into the optical fiber at all angular orientations of the attenuator disk.