To provide a grating capable of improving the thermal stability and quality reliability for a long period of time, without need of hydrogen filling treatment.
The grating II is formed by irradiating a core of quartz glass co-doped with Sn and Al in addition to Ge with ultraviolet laser light without hydrogen filling treatment. In the state of the grating II, peaks (1)e, (3)e, (5)e and (6)e of Raman scattering, obtained in Raman spectral analysis, are shifted to low frequency side (low wave number side) from the state obtained before irradiating with the ultraviolet laser light. The density of bonding structure in the network structure of the glass is made to be changed to become higher and the stability to thermal load is enhanced by the shift to low frequency side.
NAKAI TADAHIKO
SUDO TAKAHIDE
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