Electric-field thermally poled optical fibers for quasi-phase-matched second-harmonic generation

We report on quasi-phase-matched frequency doubling to the blue in electric-held poled optical fibers. An increase of a factor of /spl sim/10 in the conversion efficiency in comparison with the previous results is obtained. Our experiments show that the structure of the induced nonlinear grating is not uniform, both longitudinally and transversely. For this reason the value of the effective nonlinear coefficient is still far from the optimum expected from the measured value, through Maker's oscillation, for a uniformly poled fiber.