Selective Poling Of Polymers By Laser-heating

Several techniques have been demonstrated to fabricate electrooptic (EO) waveguide devices in poled polymer thin films . Most of these procedures produce lateral variations in the film composition to provide the index structure necessary for lateral waveguiding. One technique, selective poling, utilizes localized poling electric fields to induce lateral variations of the birefringence in the film to form waveguide channels. Though all the methods require poling the active polymer to induce an electrooptic response, the selective poling procedure is distinguished by the fact that lateral waveguides are formed as a consequence of the poling and no modification of the composition of the film is required.Poling generally entails heating the entire polymer slab to temperatures near or above its glass transition temperature, T g, and applying an electric field between electrodes disposed to either side of the film while the film poles and cools. Typically all structures of the electrode are connected to a common point and thus all poled regions are poled identically and simultaneously. We propose and demonstrate a new technique for forming channel waveguides in a single-composition film. This technique produces a structured poling pattern by heating the polymer only in selected regions using a laser beam. By selectively heating the polymer, the poling process can be ooth spatially resolved and temporally resolved. The temporal aspect of the laser poling allows different regions between the same poling electrodes to be poled under the influence of different electric fields. Novel device structures that require variable degrees and orientations of poling are thus possible without requiring complicated poling electrode geometries. Also, selective heating of the polymer film in the presence of a uniform field produces a uniform orientation of the birefringence over the poled region, whereas the electric fields produced by patterned electrodes induce rotations of the birefringence at the electrode edges. Other exciting possible uses of laser-heating include clean-up poling of selectively poled slabs that have flaws (component trimming) and depoling of regions near patterned reflective poling electrodes.