Fabrication of waveguides with arbitrary index profiles in LiNbO₃:Fe crystal by white light irradiation

On the basis of the theoretical analysis of the relations between the distributions of light-induced index changes and the intensity profiles of writing beams, a novel optical approach for fabricating waveguides with arbitrary index profiles is proposed. Waveguide structures with index profiles of an error function distribution and a square law distribution are fabricated respectively employing writing beams with different intensity profiles generated by a white light beam reading out gray patterns from an electrically addressed spatial light modulator (SLM). Employing the interferometric technique, the light-induced index changes in the crystal sample are measured, which are well fitted by using the deduced analytic expressions of the index change distributions. Experimental results show that the method is feasible. High quality waveguide devices with arbitrary index profiles may be fabricated in various photorefractive media employing white light irradiations and spatial light modulators with high resolutions.