We demonstrate linear and nonlinear control of the ballistic trajectory of an optical beam. Such control is realized by
sending a Gaussian beam into a phase mask and then turn it into an accelerating Airy beam. We show how an optical
beam can be set into motion in a general ballistic trajectory, while the range and height of the trajectory can be
controlled at ease. In addition, we study linear propagation of deformed Airy beams in free space by varying the angle
between two "wings", which leads to wing flipping and change in acceleration. Finally, we demonstrate nonlinear
control of two-dimensional Airy beams with self-focusing and self-defocusing nonlinearities, and found that the Airy
beams initially driven by a self-defocusing nonlinearity exhibit anomalous diffraction and can be more robust as
compared to those driven by a self-focusing nonlinearity. Our results bring about a possibility to send an intense laser
beam into any desired location, passing through disordered media and getting over obstacles.
The feasibility of utilizing Bi<sub>4</sub>Gi<sub>3</sub>O<sub>12</sub> (BGO) crystals as sensing element for optical fiber current sensors (OCSs) with
enhanced sensitivity is demonstrated. Based on the theoretical analyses of the magneto-optical properties of BGO crystal,
the Verdet constants of the crystal at different wavelengths are measured by employing the double frequency method. By
combining the measured absorption coefficients with the relations between the Verdet constants and wavelengths, the
magneto-optical figure of merit of BGO crystal is obtained. After that an OCS based on a BGO crystal with a magnetic
field concentrator and enhanced Faraday rotation by critical angle reflections is designed and experimentally
demonstrated. Finally, the influences of the phase shift caused by reflection, which is the main resource of the deviation
between the measured and the real values, are theoretically analyzed and numerically simulated. It is demonstrated that
an OCS based on BGO crystals with enhanced Faraday rotation could be developed into a practical OCS with a good
linearity and a large dynamic range.
Photo-written waveguides employing binary optical masks are investigated in an iron-doped lithium niobate crystal. Planar and Y-branch waveguides are experimentally demonstrated. The index variations along the propagation direction of the writing beam in the crystal are experimentally measured and theoretically analyzed. The influence of the diffraction from the optical masks, which imposes a limitation for the applications of the waveguide fabrication method, is numerically specified. Additionally, the asymmetry of the index distribution in the waveguide region, which is related to the transport process of the photoexcited charge carriers, is revealed and qualitatively explained.
We present our experimental results on fabricating optical waveguides by laser micromachining, structure-light illuminating, and optical spatial dark solitons in iron doped lithium niobate (LiNbO<sub>3</sub>:Fe) crystals. After that we propose a novel approach to fabricate three-dimensional (3-D) optical circuits in LiNbO<sub>3</sub> crystals by combining the three light-induction techniques listed above. By employing laser micromachining, a curved and a Y-branches waveguides are successfully fabricated. With binary and SLM-prepared optical masks, Y-branches and gradient planar waveguides are experimentally demonstrated. By utilizing one-dimensional (1-D) optical spatial dark solitons, planar, Y-branches, and square channel waveguides are formed. The results show that each of the three methods can be employed to write optical waveguides in LiNbO3 crystals. By combing the three methods, 3-D light circuits can be created in 45<sup>o</sup>-cut bulk crystals by several procedures. Initially, a quasi-planar optical circuit is created in a thin layer of the crystal by structure-light illuminating with an optical mask. Then, a planar circuit is generated by utilizing a 1-D dark soltion. And then, form multi-layer planar circuits are formed by altering the positions of the crystal or writing beam. Finally, laser micromachining is used to link the different layers to form a 3-D light circuit. Furthermore, functional 3-D integrated optical system may be implemented by using the proposed approach.
The optimal exposure distances for 3-D optical waveguides induced by laser micromachining in LiNbO<sub>3</sub> crystals are theoretically and experimentally investigated. By solving the photorefractive dynamic equations, the optimal distances for waveguide fabrications are numerically specified when the focused laser beams scans along the different directions. The simulations show that the optimal exposure distance is not dependent on the scanning directions of the writing beam, but the index distributions of the fabricated waveguides are seriously dependent on them. When the writing beam scans the crystal along the axis c, optical waveguides cannot be fabricated efficiently. However, in this case, symmetric refractive index changes can be obtained, so called as sandwich illumination method. By scanning LiNbO<sub>3</sub>: Fe crystal with a focused green laser beam, experimental demonstrations are performed. The light-induced index changes are measured by employing digital holography. The experimental results coincide with the theoretical analyses. Additionally, a curved waveguide is experimentally formed. The near field pattern and the results of the guiding tests show that the waveguide are successfully written in the LiNbO<sub>3</sub>:Fe crystal.
Light-induced waveguide arrays pave a way to implement massive parallel and adaptive interconnection, and provide a fertile ground for investigating self-localized states, better known as discrete solitons. In this paper, creating planar and channel waveguide arrays by illuminations of two- or four-beam interference fields are investigated both theoretically and experimentally in LiNbO<sub>3</sub>:Fe, SBN:Cr, and KNSBN:Ce crystals. The distributions of refractive index changes induced by multi-beam interference fields with different orientations in various photorefractive crystals are numerically simulated. Employing illuminations of two-beam interference fields, planar waveguide arrays are experimentally demonstrated in an open circuit LiNbO<sub>3</sub>:Fe crystal and biased SBN:Cr and KNSBN:Ce crystals. An approach for fabricating channel waveguide arrays by employing illuminations of two-beam interference fields is presented. By fabricating a square and a rectangular channel waveguide arrays in a LiNbO<sub>3</sub>:Fe crystal this approach is experimentally demonstrated. Creating channel waveguide arrays using four-beam interference fields with different orientations are also performed in the three kinds of crystals. The index profiles of the light-induced waveguide arrays are measured employing the interferometric method or the digital holography. The near field patterns, diffraction patterns and the guiding test results show that the waveguide arrays are successfully fabricated.