FIELD-ASSISTED FIBER SPINNING FOR THE PREPARATION OF OPTICAL FIBERS HAVING NON-LINEAR OPTICAL ACTIVITY

摘要

A method for the preparation of polymer-based optical fibers with nonlinear optical activity using a field-assisted fiber spinning technique has been developed. Example nonlinear optical activity includes electrooptic effects and second harmonic generation. A homogeneous mixture of a high-glass-transition-temperature polymer and a rigid-rodlike noncentrosymmetric molecule with nonlinear optical activity is employed in a specialized fiber-spinning operation. Equivalently, the noncentrosymmetric moieties can be chemically attached to the polymer backbone. A special spinneret is designed in such a manner as to allow a strong electric or magnetic field to be externally applied in the die (extrudate) swell region prior to fiber draw-down. In the die swell region, the imposed electric or magnetic field imparts a preferential orientation to the rod-like molecules (segments), where the molecular dipoles acquire an anisotropic spatial orientational distribution. This preferential alignment is subsequently accentuated and trapped in fiber draw-down, where the mixture cools and vitrifies. Elongational deformation experienced by the mixture in the draw-down region hydrodynamically forces the rod-like molecules (segments) to align with the fiber axis. Hence, the final product is nonlinearly-active polymer optical fibres doped with noncentrosymmetric rod-like molecules (segments) whose molecular axis is aligned with the fiber axis. In addition, the alignment is such that the net dipole moment of the system as a whole is non-zero due to the strong electromagnetic field imposed prior to fiber draw-down. This invention is useful in a wide variety of electrooptic and optoelectronic applications.