Tuning of photorefractive interference filters in LiNbO3

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Abstract
Fine tuning of narrow-bandwidth interference filters based on volume holographic gratings fixed in photorefractive LiNbO3 has been demonstrated. A filter with a peak wavelength at 518.45 nm, peak reflectivity 32.5% and bandwidth of 50 pm was used. Filter tuning has been achieved both by varying the filter temperature and by applying an electric field. By varying the filter temperature between 35 and 60 degrees C a temperature tuning coefficient of 5.1 pm K-1 was obtained. The effect is induced by the temperature-dependent change of refractive index and by the lattice thermal expansion. By applying a direct current electric field, an electrical tuning coefficient of 5.9 pm kV-1 has been measured 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% has been demonstrated.