Photosensitivity in Ge-doped silica is a well-known effect used for the fabrication of fiber Bragg gratings. Because the UV-induced index change of hydrogen-loaded Ge-doped silica films can be made larger than 0.0001, the direct writing of channel waveguides is possible. Channel waveguides~(1,2) and couplers~4 can be patterned in this way with a mask brought in contact with the film. However, defining the channel waveguides with a tightlyfocussed UV-beam without a mask yields a more versatile fabrication technique for photonic components.~3
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