Transmissive fiber optic packaging for reflective modulators

The authors describe an optical package where light from an input fiber is collimated by a GRIN (gradient index) lens and incident at a slight angle on a reflective modulator in the Fourier plane. The modulated output is reflected and focused by the same lens into a separate output fiber placed symmetrically across the optical axis. Conventional ceramic fiber ferrules, with a single hole at the center, are fabricated with submicron tolerances. But the same manufacturing processes do not allow a ferrule with two holes positioned with the required accuracy. Instead we use a radially symmetric ceramic ferrule with a 250 /spl mu/m hole-exactly twice the 125 /spl mu/m fiber diameter-and put both fibers in the same hole. The "transmissive" single mode fiber package has an excess loss of 1 dB.