Effective Verdet constant in a terbium-doped-core phosphate fiber.

The concept of an effective Verdet constant is proposed and experimentally validated. The effective Verdet constant of light propagation in a fiber includes contributions from the materials in both the core and the cladding. It is measured in a 25 wt.% terbium-doped-core phosphate fiber to be -6.2+/-0.4 rad/(Tm) at 1,053 nm, which is six times larger than silica fiber. The result agrees well with Faraday rotation theory in optical fiber.