Abstract

It is well known that hydrogen loading¹ drastically enhances the photosensitivity of germanosilicate glass. Hydrogen loading has made it possible to write strongly reflective gratings even into standard telecommunication fibers. However, the mechanism is not yet clearly known. On the other hand, photosensitive absorption band (~240 nm) of germanosilicate fiber can be excited by two-photon absorption (TPA) of blue-green light. It has been known that Hill gratings² are formed by TPA of 488 (514) nm Ar-laser light. TPA in the blue-green region has been studied by index change, induced loss, and electron-spin resonance. However, effects of hydrogen loading on TPA have not been reported. Such studies are expected to contribute to clarify the mechanisms of hydrogen loading, and possibility of enhancement of photosensitivity in the blue-green region. Although one-photon absorption in hydrogen-loaded germanosilicate glass has been measured, the TPA obeys a different selection rule. Hence, TPA should not be determined by an analogy with one-photon absorption and therefore should be determined by direct measurement.

© 1996 Optical Society of America