Polarization-maintaining optical fibers for coupler fabrication

Mount for a polarization-maintaining coupler comprising

• a pair of biconically-tapered-fused lengths of optical fiber wherein the optical fibers form leads to the fused portion, the leads of which have protective coverings and the fused portion of which is bare,
• a rigid substrate having approximately the same thermal coefficient of expansion as does the fused portion of the coupler,
• means for mounting said leads to suspend the fused portion tautly out of contact with both the substrate and the mounting means, and
• means enclosing the coupler within a protective package with the coupler suspended in air.

Method of making a polarization-maintaining coupler comprising the steps of

• (1) placing side-by-side two short lengths of an optical fiber, each comprising a jacket having an index of refraction substantially lower than that of the core, which jacket includes an oval stress-applying region that
• has a thermal coefficient of expansion that affords to the fiber a birefringence of from 1 to 3.times.10.sup.-4,
• substantially contacts the core, and has an area of less than 10 percent that of the fiber;
• (2) aligning the polarization axes of the two fiber lengths,
• (3) fusing the two fiber lengths together, and
• (4) while launching light into one of the fiber lengths, drawing the fused lengths until light being emitted from the lengths reaches a predetermined relationship.