TUNING OF PHOTOREFRACTIVE INTERFERENCE FILTERS IN LINBO3

Fine tuning of narrow-bandwidth interference filters based on volume h olographic gratings fixed in photorefractive LiNbO3 has been demonstra ted. A filter with a peak wavelength at 518.45 nm, peak reflectivity 3 2.5% and bandwidth of 50 pm was used. Filter tuning has been achieved both by varying the filter temperature and by applying an electric fie ld. By varying the filter temperature between 35 and 60-degrees-C a te mperature tuning coefficient of 5.1 pm K-1 was obtained. The effect is induced by the temperature-dependent change of refractive index and b y the lattice thermal expansion. By applying a direct current electric field, an electrical tuning coefficient of 5.9 pm kV-1 has been measu red too. In this case the tuning mechanisms are the electro-optic and piezoelectric effects. On the other hand, with an applied alternating current electric field, a beam intensity modulation from 90% to 20% ha s been demonstrated.