Measurement of the dc Kerr and electrostrictive phase modulation in silica

We report, to our knowledge, the first polarization-resolved measurement of the frequency dependence of both the electronic and the electrostrictive contributions to the dc Kerr coefficient in silica. At the acoustic resonance the perpendicular polarization phase shift is a factor of 2.3 times greater than in the parallel polarization, confirming the presence of strong electrostriction. We find good agreement between the phase-shift measurements and theoretical models of both the polarization and frequency dependence. The analysis indicates the dc Kerr coefficient χ1111(3)(-ω;ω, 0, 0) to be 1.9×10-22 m2/V2. From these results the electrostrictive contribution to a poled-silica device near the device acoustic resonance is expected to be r33,Es=28 pm/V, over an order of magnitude greater than the electronic Kerr electro-optic coefficient r33,Kerr=0.2 pm/V.