PHYSICAL ORIGIN OF THE TEMPERATURE-DEPENDENCE OF CHROMATIC DISPERSION IN FUSED-SILICA

The static and dynamic effects of temperature upon chromatic dispersion in fused silica are analyzed using a Sellmeier representation. By separately calculating the temperature modulation of the Sellmeier parameters induced by thermal expansion on the one hand, and by the dynamic vibrational motion of acoustic and optic phonons on the other, the individual contributions to the total effect have been analyzed. It is shown that all manifestations of chromatic dispersion in the silica optic window possess a temperature modulation which is dominated by a single term-namely the temperature derivative of the Sellmeier valence to conduction band energy gap. In addition, this term itself results overwhelmingly from a single physical process, namely the Debye-Waller-like modulation of one-electron band energies by the thermal activation of acoustic phonons.