Control of crystal orientation in an organic-crystal-cored fibre

The authors have succeeded in controlling organic-crystal orientation in glass capillaries using the modified Bridgman-Stockbarger method, in which the pulling direction of the capillary is at an angle theta to the temperature gradient. The controllability of the crystal orientation in the organic-crystal-cored fibre (OCCF) of 2-methyl-4-nitroaniline (MNA) was examined by the measurement of the second-harmonic generation power. It was confirmed that the second-harmonic power of the controlled OCCF is three times higher than that of the uncontrolled OCCF, since the axis with the largest second-order nonlinear optical susceptibility coefficient is tilted from the fibre axis in the controlled OCCF. The control mechanism for the crystal orientation is also discussed.