Abstract: A reflecting-mirror-type variable optical attenuator based on a new principle is provided. A reflecting-mirror-type variable optical attenuator according to the present invention is formed of a collimator lens with optical fibers in which two optical fibers are attached to a rod lens in respective positions off-centered from the optical axis of the rod lens and a linearly movable reflecting mirror. A phenomenon that the optical axis of a light beam emitted from one optical fiber deviates from the optical axis of the collimator lens by the angle according to the off-centered distance on the surface of the rod lens is utilized. That is, by changing the distance between the surface of the reflecting mirror arranged to be linearly movable in the optical axial direction back and forth and the surface of the rod lens, input light from one optical fiber is attenuated to be output to the other optical fiber.

Abstract: A four polarization maintaining optical fiber ferrule is provided which comprises a cylindrical body with a throughhole at the center into which four polarization maintaining optical fiber elements having polarization maintaining planes are fastened, and at least one angular first reference portion on the outer surface of the cylindrical body of the ferrule, wherein the polarization maintaining planes of at least one pair of polarization maintaining optical fiber elements arranged symmetrically with respect to the central axis of the ferrule are fastened at certain angles with respect to the angular first reference portion. An optical coupler is provided which comprises a cylindrical sleeve, a pair of graded index rod lenses within the sleeve which are separated by a thin film for partially transmitting incident light and reflecting the remainder of the light, and the above-referenced four polarization maintaining optical fiber ferrules positioned at each end of the sleeve.