The shift in the central wavelength of fiber Bragg gratings (FBGs) during annealing of hydrogen-loaded optical fiber exposed to ultraviolet (UV) laser irradiation through a phase mask is studied and shown to be caused by thermal diffusion of hydrogen out of the fiber for both short-period and long-period FBGs. Reloading FBGs with hydrogen followed by a second annealing cycle without exposing the fiber to the UV laser reproduces the details of the wavelength evolution observed during first annealing following UV irradiation. This shows that the wavelength shift of the grating during annealing is determined by diffusion of hydrogen gas out of the optical fiber for both short-period and long-period FBGs.

The temperature distribution in an optical fiber during the fabrication of fiber Bragg gratings (FBGs) using a KrF excimer laser with a phase mask has been analyzed experimentally for typical fabrication conditions. The fluence of UV laser light at the fiber surface has been varied up to 420 mJ/cm 2. These experiments show that (1) scanning electron microscope (SEM) images of the fiber surface facing the excimer laser beam reveal partial physical damage apparently owing to partial melting, so that the surface temperature has increased beyond the softening point of silica glass, which is approximately 1200 C, (2) the optical spectrum transmitted through the FBG during laser irradiation contains spikes coincident in time with the laser pulses that correspond to a near instantaneous shift of the FBG spectrum to a higher temperature spectrum representing fiber core heating of approximately 8 C, and (3) analysis of the energy absorbed by the fiber indicates a bulk temperature rise of approximately 3 C in the fiber. The resulting large variation in the temperature rise over the fiber cross section from a few C to 1200 C, along with partial physical damage on the surface, will certainly induce large internal stresses in the fiber material and reduce the mechanical strength of the FBG.

We have investigated the electric transport properties of individual In 2 O 3 nanowire devices. We have found that the gate modulation characteristics depend strongly on the channel length. If the channel length is greater than 450 nm, the gate modulation curve exhibited field-effect transistor behavior with dominant n-channel current at room temperature. With the decrease of the channel length, the leakage current is increased due to the short-channel effect. For such short-channel devices, the gate modulation curve exhibited quasi-periodic current oscillations at low temperature, which are attributed to the Coulomb blockade of single-electron tunneling. Some devices showed two-fold periodicity in the Coulomb diamonds which may arise from the spin degeneracy of the single-particle energy levels.