A novel scheme for broadband second-harmonic generation was developed with type I quasi phase matching by use of an off-digital nonlinear optical coefficient <i>d</i><sub>31</sub> . This was achieved by matching of the group velocities of the second harmonic and the fundamental, while the phase velocities were quasi phase matched. The desired group-velocity dispersion could be obtained with LiNbO<sub>3</sub> doped with 5 mol. % of MgO. Efficient second-harmonic generation with a bandwidth of 52 nm was obtained for the fundamental wavelength centered at 1566 nm in MgO-doped periodically poled LiNbO<sub>3</sub> , compared with a bandwidth of 1.3 nm for the conventional scheme using <i>d</i><sub>33</sub> . Efficient frequency doubling of an ultrafast pulse is expected without group-velocity walk-off or pulse distortion.
© 2002 Optical Society of America
(160.3730) Materials : Lithium niobate
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4360) Nonlinear optics : Nonlinear optics, devices
(320.7110) Ultrafast optics : Ultrafast nonlinear optics
Nan Ei Yu, Jung Hoon Ro, Myoungsik Cha, Sunao Kurimura, and Takunori Taira, "Broadband quasi-phase-matched second-harmonic generation in MgO-doped periodically poled LiNbO_3 at the communications band," Opt. Lett. 27, 1046-1048 (2002)