We demonstrate birefringence enhancement in an optical fiber with artificial core anisotropy. A nanostructured fiber core in the form of a glass slab with layers of germanium-doped silica interleaved with the layers of fluorine-doped silica enabled an increase of the birefringence of 0.54 × 10 ⁻⁴ without any stress zones. The experimental result confirms the numerical prediction of birefringence enhancement over previously presented fibers by increasing the refractive index contrast between the two core base glasses. Birefringence improvement has been achieved only by core material engineering and not by adding any stress zones or other approaches involving cladding shaping and core geometry design. The modification introduced to core had no impact on the guiding performance of the realized fiber, which remained perfectly matched to the SMF-28 standard in terms of its numerical aperture NA = 0.11 and the effective mode-field diameter MFD = 10.1 μm at the wavelength of 1550 nm.