Silica Fiber with Large and Thermodynamically Stable Second Order Optical Nonlinearity

Abstract

In this thesis, we demonstrate, theoretically, that, by depositing a regular fused-silica fiber with optical nonlinear molecules, strong and thermodynamically stable SHG can be obtained. Our experiments also provide strong evidence for the theory.

Start from the basic Maxwell equation, we derive the SHG efficiency that the excited power translates into the SHG signal. According to the SHG efficiency equation, a small radius and a long length will help to result in a high SHG efficiency, which also increases with the excited power. We fabricate silica fiber tapers with radius less than 5 μm through either wet etching or heating while stretching. Through improving the stretching setup, and adroitly manipulating both the stretching rate and the heating temperature, we are able to control the taper loss less than 1 dB. Then we dip taper part into cationic solution and anionic solution alternatively to have ISAM/CHISAM film on it. By improving the surface quality of film around a silica fiber taper, we are able to control film loss of PAH/PR film to less than 2 dB for 5 bilayers.

We set up a SHG measurement stage for a nonlinear fiber, and develop a measurement method during the experiments. We have shown that by depositing (PAH/PB)10 films around a fiber taper with a diameter around 5 µm, we can obtain high SHG signal. The ratio of the obtained SHG signal to the excitation power for such a nonlinear fiber is more than 10 times of that of a 125 µm single mode fiber with the same length. Our experiment result provides strong evidence that centrosymmetric material can be used as SHG material.