Optical fiber with a pure silica core having a bragg grating formed in its core and a process for providing same

摘要

A process for adapting a length of optical fiber with a pure silica core to enable imprinting a Bragg grating in the core without doping the core, the process using an optical fiber having some fluorine in its cladding, and besides the process, a pure silica core optical fiber having a Bragg grating. The process causes fluorine to diffuse from the cladding into the core for a selected length, and then by one of several alternative methods, creates defects in the core within the length. The alternatives include heating and reducing or oxidizing the length; performing flame brushing; or irradiating the length using ionizing radiation, such as gamma radiation. Next, the process uses hydrogenation to load the core with hydrogen, and then exposes the length to a pattern of UV light as is normally done in imprinting a Bragg grating. Finally, the process heats the length, causing hydrogen fluoride to form in the regions exposed to appreciable UV light. Since the hydrogen fluoride is volatile, it boils out of the optical fiber while the optical fiber is being heated. What remains is a length having a variation in concentration of fluorine, which is an index lowering agent, according to the pattern of UV light to which the length was exposed, or, in other words, a chemical (Bragg) grating.