When operation in the 1.30 or 1.55 micrometer infrared range of optical signal wavelength is desired for the fiber-optic receiver testing shown in FIG. 2, the optical fiber in the communications element 114 may be made of a material such as silica and may be obtained from suppliers such as Corning Glass Incorporated located in Corning, N.Y The fiber-optic conductor in the communications element 11