Recoated temperature-insensitive long-period gratings

Long-period gratings are now being used as gain equalizers in broadband amplifiers1 and as band-rejection filters in a variety of applications.2 While these devices provide elegant in-fiber solutions to many problems in fiber communications, they can exhibit high temperature sensitivities if sufficient care is not taken in their design. When written in conventional communication-grade fibers, their spectra can shift by 4 - 10 nm per 100°C change in temperature. Two solutions to this problem have been successfully demonstrated using specially designed fibers, one based on tailoring the fiber refractive index profile3 and the other based on the use of appropriate dopant materials in the core.4 In this paper, we present long-period gratings written in conventional communication-grade fibers that use the properties of a specially-designed polymer recoat to provide the temperature-independent performance.