Fabrication of polarization-maintaining and absorption-reducing fibers

Low-loss single-polarization fibers with stress-induced birefringence have been fabricated using VAD single-mode fiber preforms. Design criteria have also been clarified with due regard to optimum fiber structure that reduces transmission loss and increases birefringence. As a result of these criteria, the minimum loss of 0.4 dB/km at 1.54 μm, and the birefringence B s of 1.2 \times 10^{-4} at 1.15 μm was obtained. It has been shown that a large refractive-index difference between the core and the cladding Δ, as well as large birefringence, are very effective to stabilize the state of polarization. In a 5-km-long fiber with \Delta = 0.8 percent and B_{s}= 1.2 \times 10^{-4} , crosstalk lower than -20 dB has been obtained.

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