Birefringent splittable composite (BISPEC) fiber and polarization-maintaining couplers

A novel technique for the fabrication of birefringent splittable composite (BISPEC) fiber is reported. We describe in details the design consideration, practical fabrication, and characterization of this fiber. The distinctive feature of this fiber is that the principal axes of the constituent fibers can be accurately aligned in the preform stage so that long lengths of well-aligned fiber can be drawn. We further demonstrate the application of this fiber by fabricating a polarization-maintaining coupler by simply introducing a local taper. Measurements show that such a coupler can have polarization extinction ratio as large as 31 dB (in the best case)