DEVELOPMENT OF GLASSES FOR HIGH EFFICIENT BRAGG REFRACTION GRATINGS

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(1) Origin of photo-induced refractive index changes(PIRC)in GeO_2-SiO_2 glasses were found to be due to photochemical conversion of an oxygen vacancy(neutral oxygen monovacancy, NOMV,)coordinated by two Ge^<4+> ions into a GeE'center which has an intense absorption band at around 6eV.Thus, we concluded that enhancement of the NOMV leads to that of photosensitivity in SiO_2 : Ge glasses.(2) Heat treatment of SiO_2 : Ge glasses in a H_2 atmosphere at 500 C,which is far below Tg, for 70 hincreased selectively the concentrations of the NOMV by an order of magnitude.(3) It was found that concentrations of the NOMV were enhanced by one or two orders of magnitude by rf-sputtered deposited thin glass films of SiO_2 : Ge by heating at 350C for 30 min in vacuum.(4) Concentrations of the NOMV were successfully enhanced over 3 to 4 orders of magnitude by implanting protons into SiO_2 : Ge glasses. Photobleachable optical band peaking at 5 eV were created in SiO_2 glasses implanted with implanted ions with electropositive nature such as P and B.These bands were simply bleached with illumination with 5 ev light and no formation of Si E' center was seen. The former and the latter gave positive and negative refractive index changes after uvbleaching.(5) Although various optical bands associated with Al ions were identified in synthetic SiO_2 : Alglasses irradiated with gamma and excimer lasers, none of the bands showed photobleaching nature.