Thermal tuning of a fixed Bragg grating for IR light fabricated in a LiNbO3 : Ti channel waveguide

We investigate a thermally tunable integrated narrow-bandwidth interference filter for light in the infrared wavelength region around lambda = 1550 nm fabricated in a channel waveguide in lithium niobate, The filter is based on a holographically recorded and thermally fixed refractive-index Bragg gr ating. The device is connected to optical single-mode fibers and works pola rization-independent. We measure a peak reflectivity of 95% and a linewidth (FWHM) of 0.09 nm, By temperature-controlling the peak wavelength of the f ilter is tuned, For the linear thermal expansion coefficient of lithium nio bate along the c axis the value alpha 33 = (4.5 +/- 0.5) x 10(-6) K-1 is ob tained, Permanent illumination of the filter with incoherent light allows u s to adjust the peak reflectivity.