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Backward Second-harmonic Generation in Periodically-poled LiNbO₃

Xinhua Gu and Yujie J. Ding, Dept. of Physics and Astronomy, Centers for Photochemical and Materials Sciences, Bowling Green State Univ., Bowling Green, OH; Jin U. Kang, Naval Research Lab., Washington, DC; Jacob B. Khurgin, Dept. of Electrical and Computer Engin., Johns Hopkins Univ., Baltimore, MD

second-harmonic waves, some of the waves propagate in the direction opposite to the fundamental waves and are thus known as backward second-harmonic (BSH) waves. Because of the extremely large phase-mismatch that occurs in such a process, the BSH effect is negligible. Conventional phase-matching techniques using either angle or temperature tuning cannot compensate for large phase-mismatching. Thus, the backward process has been virtually ignored by most of the nonlinear optics community. While there were some early theoretical studies, it is only recently that the backward parametric processes have been analyzed theoretically in detail. In general, the backward nonlinear processes are important since they can lead to mirrorless optical parametric oscillators (OPOs) and other novel effects