Structure-light-induced Photorefractive Waveguide Arrays

At the beginning of a new millennium, humanity enters into a multimedia internet age with information (e.g. data, sound, and videos) transmitted at a high speed. As the basis of the internet, the microprocessor speed and the amount of available bandwidth increase as Moore's Law, the traditional fabrication techniques of the key photonics and electronics components face a critical challenge. Currently, there exists no low-cost integrated optical component in commercial systems. Recently, light-induced optical waveguide formation attracts much research interest as a recognized technology for direct, rapid, and cost-effective fabricating of various integrated optical waveguides.This dissertation mainly investigates writing various waveguide structures in photorefractive (PR) crystals by structure light irradiation method. The main contents of this dissertation are as follows: (1)According to the set of equations governing the PR process, index changes in PR crystals induced by writing beams with different intensity profiles are theoretically analyzed and numerically simulated. (2)The index changes induced by cw laser at milliwatt in LiNbO3:Fe crystals are studied experimentally in detail. Furthermore the experimental results are theoretically analyzed and numerically simulated. The results show that waveguide structures can be effectively induced employing structure light irradiation in LiNbO3:Fe crystals. (3) Fabrication methods of planar, Y-branches, and channel waveguides employing structure lights formed by cylindrical lenses and optical binary masks are investigated experimentally in detail. And a novel approach to prepare optical masks by using spatial light modulator for light-induced various waveguides, even a whole circuits is proposed. (4)Fabricating planar and channel waveguide arrays in SBN:Cr, LiNbO3:Fe and KNSBN:Ce crystals under illuminations of two-beam and four-beam interferograms are detailedly investigated both theoretically and experimentally. Moreover a novel approach to fabricate array of three-dimensional waveguides in PR crystals employing illuminations of a pair of mutually coherent or incoherent two-beam interference fields is proposed. Employing writing beams with appropriate intensity distributions and external electric fields along proper directions, arrays of planar and channel waveguides can be fabricated in various PR crystals. (5) Based on Mach-Zehnder interferometer setup, slice-interferometry for measuring light-induced index changes in PR crystal is investigated. And employing digital holography for visualizations of the index changes in PR crystal is first proposed. Additionally, the two approaches are used for measuring the index distributions of light-induced waveguides successfully.Various optical waveguides and waveguide arrays can be fabricated by irradiations of different structure lights. This technique is very convenience, and combines with the electrical/thermal fixing and optical/thermal erasing techniques both permanent and instantaneous waveguides can be obtained. Structure-light-induced waveguide devices in PR crystals can be used for the current optical communication systems, and may be used for optical dynamic interconnection and optical neural network systems.