SINGLE-EXCIMER-PULSE WRITING OF FIBER GRATINGS BY USE OF A ZERO-ORDER NULLED PHASE MASK - GRATING SPECTRAL RESPONSE AND VISUALIZATION OF INDEX PERTURBATIONS

Optical fiber Bragg reflectors have been written by irradiating the fiber from the side through a phase mask with a single pulse of high-power 249-nm excimer-laser light. Efficient tapping of light to the radiation modes has been achieved for light at wavelengths shorter than the Bragg wavelength. The photoinduced periodic refractive-index perturbations have been observed directly with an optical microscope and are shown to have the same period as the phase mask and to be highly localized on one side, the irradiated side of the fiber core-cladding boundary.