Proceedings PaperTemperature stability of thin film narrow bandpass filters produced by ion-assisted deposition
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Four types of single-cavity thin-film narrow bandpass filters whose FWHM range from 0.5 to 1.1 nm are produced by ion-assisted deposition of alternating TiO2/SiO2 or Ta2O5/SiO2 layers onto eight substrates having differing coefficients of linear expansion, and the temperature stability of their center wavelengths are examined in the 1540-nm wavelength region. For the eight substrates, whose coefficients of linear expansion range from 0 to 142 X 10-7/ degree(s)C, the temperature stability of the filters ranges from +0.018 to -0.005 nm/ degree(s)C. Calculations based on a newly developed elastic strain model reveal the main reason temperature stability of the center wavelengths exhibits substrate dependency is due to a reduction in film packing density brought about by volumetric distortion of the film, which is caused by stress induced from the substrate.