Photosensitivity and application with 157-nm F2 laser radiation in planar lightwave circuits

Photosensitivity studies of germanosilica planar waveguides were carried out with short-wavelength 157-nm light from an F₂ laser. More than a 5×10^-3 refractive-index change was induced in a nonuniform index profile concentrated near the cladding-core interface and confirmed by an atomic force microscopy in 157-nm radiated fiber. This profile geometry narrows with the laser exposure to offer practical application in trimming phase errors and controlling birefringence in frequency domain modulators where a 1.7×10^-3 effective index change and a 5×10^-4 birefringence change were induced, respectively. The 157-nm photosensitivity response is more than 15 times stronger than that by a 248-nm KrF laser and more than twofold stronger than that by a 193-nm ArF laser.