Temperature-stable bandpass filters deposited with plasma ion-assisted deposition.

Plasma ion-assisted deposition with an advanced plasma source was investigated to produce narrow-bandpass filters in the near-infrared spectral range for telecommunication applications. The multilayer coatings were qualified by the optical performance, the vacuum-to-air behavior, the temperature stability, and the film stress. TiO(2)/SiO(2) and Ta(2) O(5)/SiO (2) material combinations were used and compared. The coating system produced low absorbing multilayers with a very low coefficient of expansion and low stress. The coefficient of expansion was in the low 10(-6) °C range, and film stress values in the range between 1 and 2 × 10(8) N/m(2) were obtained. TiO(2)/SiO(2) was the preferred material combination. The optical monitoring system allowed the production of bandpass filters with a performance close to that of the theoretical values.