Observation Of Photorefractive Surface Nonlinear Apodized And Chirp Waveguide Arrays

Recent years, waveguide arrays have important applications in the investigation of many exciting nonlinear propagation, trapping, switching, and steering beam dynamics, and offer a tunable platform for studying discretizing light behavior and quantum simulator. Thus the fabrication and wave-guiding of waveguide arrays become a hotspot. Compare with the conventional method, light-induced waveguide arrays are of many advantages such as rapid, real-time, simple and low cost etc. Owing to recyclable, photosensitive and non-transient response, photorefractive materials are often used to fabricate various waveguide arrays by optical induction.Photorefractive surface waves(PR SWs) can propagate along the surface of the photorefraetive materials and confine the beam energy in the narrow layer near surface. It has vast applications in fast mutually pumped phase conjugation, signal amplification, surface enhanced second harmonic generation and exciting long-range surface plasmon. As we all know, it will write a waveguide as a beam propagating along the photorefraetive materials, however, the waveguide arrays induced by PR SWs have not been investigated. The investigation of such waveguide arrays is of a great significance to control surface optical phenomenon and design integrated optical components. In this dissertation, the waveguide arrays induced by PR SWs are studied systematically, and the main contents are shown as follows:1. A new type of nonlinear waveguides, photorefractive surface apodized waveguide arrays are suggested, which can be induced by PR SWs based on diffusion nonlinearity. The disturbed refractive index distribution of such waveguide behaves as a periodic lattice with apodized envelope. Moreover, the dispersion relation and corresponding modes are analyzed by using the transfer matrix method. It is very interesting that the dispersion curves of index-guided modes(IGMs) and Bragg-guided modes(BGMs) couple and intertwine with each other, and anti-crossings instead of crossings between them hence generate some mini-gaps. Moreover, there exists a type of extraordinary modes constituted by the splice of index-guided modes and Bragg-guided modes.2. We suggest a new type of nonlinear waveguide, photorefractive surface nonlinearly chirped and apodized waveguide arrays, which can be directly induced by PR SWs in virtue of diffusion and drift nonlinearities. The disturbed refractive index of apodized tails converges to a nonzero value which can be handily adjusted by external electric field. Then the guided-wave properties of such waveguide arrays are analyzed by using the transfer matrix method. It is very intriguing that the dispersion curves of IGMs can be tailored by external electrical field, which can help to control the modes excitation; the dispersion curves of ordinary and extraordinary BGMs couple, intertwine and anti-cross with each other, which can provide more abundant anti-crossings; the corresponding modes near such anti-crossing have a clear coupling and ‘competition’ in the evolution of dispersion curves.3. We study the regulation of background illumination, electric field and write beam on apodized waveguide arrays induced by PR SWs. With the intensity of write beam increasing, the index-guided mode bands degenerating or spliting and eventually become saturation; the wavelength and incident angle of write beam can effectively adjust the period of apodized waveguide arrays. There is a tunable chirp for a larger write angle, which location can be contolled by the intensity and angle of write beam and background illumination, the maximum amplitude and sign can be adjusted by the wavelength and angle of write beam and external electric field.