Design of Polarization-Maintaning Optical Fiber Suitable for Thermally-Diffused Expanded Core Techniques (Special Issue on Optical Fibers and Their Applications)

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Thermally-diffused expanded core (TEC) techniques brought the fibers with the mode fields expanded by thermal diffusion of core dopants. The techniques are effective to the reduction of splice or connection losses between the different kind of fibers, and are applied to the integrations of thin film optical devices in fiber networks, the fabrications of chirped fiber gratings, and so on. In the practical use of TEC techniques, the fibers are heated high temperature of about 1650℃ because of a short period of time in processing by microburners. The mode field diameter expansion (MFDE) ratio, which is defined as the ratio of the mode field diameter in the fiber section having the core expanded and that unexpanded, is desired to be more than 2.0 from the viewpoint of loss reduction in industrial uses of the TEC techniques. When the TEC techniques are applied to polarization-maintaining optical fibers (PM fibers), such as PANDA fibers, both core dopants and stress applying part (SAP) dopants diffuse simultaneously. So the MFDE ratio is less than two without mode field deformation in conventional PANDA fibers which are practically used as PM fibers. In this paper a PANDA fiber design suitable for the TEC techniques is newly proposed. The fiber has 1.28 μm cutoff wavelength and the mode field diameter is about 11 μm before core expansion at 1.3 μm wavelength. As the result of our design by the stress analysis, it is shown that the MFDE ratio in the newly designed PANDA fiber can take 2.0 without mode field deformation under the condition that a modal birefringence is more than 1.5 × 10^lt-4gt. The MFDE ratio with newly designed PANDA fiber can be larger than that in the conventional PANDA fiber. The mode fields in the fiber sections having the cores expanded and unexpanded are calculated by the finite difference beam propagation method. When the MFDE ratio takes about 2.0, the small mode field non-circularity of 49% in the newly designed PANDA fiber is gained in comparison with that of 110% in the conventional PANDA fiber.
社団法人電子情報通信学会の論文
1997-04-25

Design of Polarization-Maintaning Optical Fiber Suitable for Thermally-Diffused Expanded Core Techniques (Special Issue on Optical Fibers and Their Applications)

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