Research On Optical Switch Based On "Dynamic"Photorefractive Spatial Soliton

Optical switch is an essential device in optical network, especially in all-optical network:All-optical switch as the foundation of signal routing, exchanging and processing is the key of realizing all-optical network. However, the high drive power has substantially limited its application, the researchers therefore focus on reducing the drive power of all-optical switch. With the development of nonlinear material, photorefractive spatial soliton which can be driven only by milli-watt order power has draw substantial attention. There have been recent reports on optical switches and optical logic gates using "light-by-light" interactions, however there are few reports of optical switch based on self-bending soliton. This thesis starts form photorefractive effect and "dynamic" photorefractive soliton, the main research contents are as following:1. A method based on digital image processing to measure the refractive index changes was proposed. We took photovoltataic crystal LiNbO3(LN) as an example, analyzed process of its light-induced refractive index changes and designed the experiment. Based on this method, we recorded the relation of minor refractive index changes with exposure time. Experiment results showed the refractive index changes reached saturation after about60s of light exposure, for ordinary light and extraordinary light, the saturated refractive index changes were1.2×10-4and6.6x10-4, respectively. This result showed good consistency with former research.2. The self-bending of transversely shifted Ce:SBN crystal under biased electric field was studied. Experiment showed the shifting of the crystal prolonged the existence time of quasi-steady-state soliton, the soliton that was formed and maintained by the shifting of photorefractive crystal was called "dynamic" soliton. The shifting along the optical axis first caused asymmetric tilt of refractive index waveguide, the shifting velocity influenced the free-carrier diffusion speed and spatial electric field creation time, and higher shifting velocity largely shortened the time to reach saturated refractive index. The shifting of crystal was seen as the perturbation to quasi-steady-state soliton, and its influence to soliton propagation can be interpreted as particles’movement in diffusion field. We obtained the relation of shifting velocity and beam center position according to this theory.3. An optical switch based on "dynamic" photorefractive soliton was designed, its key structure was a transversely shifted photorefractive crystal in a biased electric field. The output ports were chosen by controlling different crystal shifting direction and velocity. The proposed optical switch was simulated and then verified in transversely shifted Ce:SBN crystal under biased electric field. The self-bending of soliton responded to different shifting direction and velocity, and realized9different output positions. The largest bending difference reached500um in a5.8%mm propagation length-far larger than the diameter of common optic fibers. At last, the future application of this optical switch in vibration detection was looked into. A real-time experiment system was constructed to monitor the vibration direction and velocity.