Highly birefringent lamellar core fiber

We report a polarization-maintaining fiber in which the birefringence is due to artificially introduced anisotropy in the core material. The beat length was measured by direct observation at three different wavelengths, giving a shortest result of 85 µm at a wavelength of 543 nm. The measured phase-index birefringence is about one third of that expected, which is explained by diffusion between the core layers, which are each less than 200 nm thick. By taking account of this diffusion, we can accurately model the experimental beat length and differential group delay over a wide wavelength range.