Abstract

Polarization-maintaining fiber couplers are useful in optical-fiber communication and optical-fiber sensors. In making a polarization-maintaining coupler, the principal polarization axes of the two birefringent fibers must be perfectly aligned and must be kept parallel to preserve the polarization states in the coupling region. This requirement is essential for achieving a good extinction ratio. However, perfect alignment of the polarization axes of the two separate fibers before fabrication is difficult, and maintaining such an alignment during coupler fabrication by either a polishing or a tapering process is even more difficult.^1,2 An alternative method of making a polarization-maintaining fiber coupler is the use of polarization-maintaining twin-core fiber. A twin-core fiber can be made highly birefringent, and polarization-maintaining couplers or polarization beam splitters can be fabricated from it.³ The problem with twin-core fibers is that they cannot be easily connected to standard optical fibers because of their small core separation, which is required for achieving significant evanescent coupling.

© 1993 Optical Society of America