Influence of Temperature on the Optical Properties of Narrow-band Interference Filters

Abstract

For narrow-band interference filters, we generally observe a small variation of peak wavelength with time; this variation of filter characteristics depends to a large degree on the materials of which these filters are made, and on the manufacturing process. Several explanations have been given to take account of this effect, which is particularly dramatic in the case of very narrow-band filters, so it is of the utmost importance to study in detail the influence of parameters such as the shift of temperature within the plant during deposition. The aim of this work is to know how to produce filters whose optical characteristics are steady with time. A significant advance in the study of this problem has been obtained by simulating the monitoring process on a computer. However, it is necessary, for each material used, to determine the dilatation coefficients of both refractive index and thickness. In this work we show how these coefficients may be deduced from measurements of shifts with temperature of the peak wavelength of complete narrow-band filters of two different designs. A theoretical study of the effect of temperature on the position of the passband of a dielectric narrow-band filter is performed, and from experimental measurements on complete filters we estimate the dilatation coefficients of the optical thicknesses of the component materials. The results obtained are slightly different from those given by other authors; this can be easily explained because the approximations made in their calculations of the dilatation coefficients are not accurate enough. Good agreement is obtained if an accurate check is performed from their experimental results.