Fabrication and application of holographic Bragg gratings in lithium niobate channel waveguides

Permanent refractive-index gratings in waveguide devices are of high potential for optical communication systems that make use of the high spectral selectivity of holographic filters, e.g. dense wavelength division multiplexing (DWDM), optical sensors, or narrow-bandwidth mirrors for integrated waveguide lasers. In this contribution we review our results on holographically recorded refractive-index gratings in Cu-doped LiNbO3 channel waveguides. Elementary holograms are recorded with green light and read in reflection geometry in the insensitive infrared wavelength region around 1.5 μm. To enable long-term stability of the Bragg gratings a thermal fixing technique is applied. In this way strong and almost permanent refractive-index gratings are obtained and their application as narrow-bandwidth filters for DWDM applications is demonstrated. In comparison with Bragg gratings in silica fibres, the electro-optic effect in LiNbO3 allows for a direct wavelength tuning and a fast, reliable electrical switching of these gratings. (topical review)