Double-cavity electrooptic Fabry-Perot tunable filter

The experimental development of an infrared multiple-cavity electrooptically tuned Fabry-Perot filter using LiNbO(3) is described. This filter, designed for operation in the 3-5-microm spectral band, was demonstrated by angle scanning using a He-Ne laser at 3.39 microm. The multiple-cavity configuration increased the free-spectral range of the 2-A bandwidth filter from 67 to 670 A as observed in the increased angular spacing of transmission peaks. Because of the large halfwave voltage of LiNbO(3) at these wavelengths, tuning was restricted to approximately 15% of the free-spectral range.