{'fraction_non_alphanumeric': 0.021361815754339118, 'fraction_numerical': 0.0, 'mean_word_length': 5.6371681415929205, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Photochemical changes in hydrogen-loaded optical fibres with application to Bragg grating formation

The sensitization to UV-induced refractive-index changes, by hydrogen, of germanosilicate glass is important in the production of in-fibre Bragg gratings. During grating formation fluorescence from germanium lone-pair centres is excited in the core of the fibre by the UV exposure. This fluorescence has been used to monitor photochemical reduction of substituted tetravalent germanium atoms by hydrogen. The photoreduced atoms occupy sites and absorb fluorescent radiation. Together with ions they are responsible for the refractive-index changes exploited in the holographic formation of Bragg gratings in hydrogen-loaded, germanium-doped fibres.