No abstract

We determined that refractive index change of Ge-doped silica can be induced by vacuum ultraviolet (VUV) light irradiation from Xe 2 Ã , Kr 2 Ã , and Ar 2 Ã excimer lamps using fabricated fiber Bragg grating (FBG) in the core of the hydrogen-loaded fiber as the material. It was found that irradiation with light from Xe 2 Ã and Kr 2 Ã excimer lamps can change the refractive index in the core and irradiation with light from Ar 2 Ã excimer lamps cannot. The change in refractive index under 146 nm light irradiation was greater than that under 172 nm light irradiation. The change in refractive index induced by irradiation with VUV light can be maintained up to approximately 130 C.

We have developed a new laser that emits radiation at a wavelength of 335.5 nm for the fabrication fi ber Bragg gratings (FBGs) without the need to remove the polymer jackets which are covering fibers. Subsequently, we have investigated the effect of Ge concentration in the core using the laser. It was found that a Ge concentration of more than 6 7 mol% in the core is needed for practical writing of FBG. In spite of use of the laser, the polymer jackets were thermally damaged by cw irradiation. The intermittent irradiation was thus necessary, and we have clarifi ed the irradiation conditions for writing FBGs without removing the polymer jacket. The refl ectivity of FBG increased with the length of FBG. We estimated that a 16 19-mm long FBG has enough refl ectivity to fabricate a distortion monitoring device that can be widely used in the civil and architectural fi elds.