HIGH-PERFORMANCE AND HIGHLY STABLE 0.3-NM-FULL-WIDTH-AT-HALF-MAXIMUM INTERFERENCE OPTICAL FILTERS

Fabrication of very-narrow-bandpass optical tunable filters [(0.3 nm f ull width at half-maximum) (FWHM)] is reported. To improve the film de nsities, the O2 ion-assisted deposition method is used in the fabricat ion. In the succession of high-and low-refractive-index layers, the co mmonly used TiO2 material is replaced by Ta2O5, which suits the ion-as sisted fabrication technique. The relative thicknesses of the filter m ultilayer structure of 1/2/1 are modified to 0.998/2.007/0.998, which reduces the shift difference in the central wavelengths with regard to the p and s polarizations when the filter is tilted. These improvemen ts enabled fabrication of 0.3-nm-FWHM optical tunable filters with imp roved stability characteristics.