## Abstract

Using a novel self-cascaded first-order second-harmonic generation (SHG) and third-order sum-frequency generation (SFG) in a $\mathrm{ZnO}$ periodically poled lithium niobate crystal fiber, tunable blue–green light was demonstrated. At a domain pitch of $15.45\phantom{\rule{0.2em}{0ex}}\mathrm{\mu}\mathrm{m}$, the SHG signal and its fundamental signal at $1423.9\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$ can satisfy the third-order SFG quasi-phase-matched (QPM) condition. The measured SHG power at $714.2\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$ was $12.25\phantom{\rule{0.2em}{0ex}}\mathrm{mW}$ under $100\phantom{\rule{0.2em}{0ex}}\mathrm{mW}$ input power, and the estimated nonlinear coefficient $\left({d}_{33}\right)$ achieved was $25.3\phantom{\rule{0.2em}{0ex}}\mathrm{pm}\u2215\mathrm{V}$. The self-cascaded $\mathrm{SHG}+\mathrm{SFG}$ power measured at $477.1\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$ was $\sim 700\phantom{\rule{0.2em}{0ex}}\mathrm{\mu}\mathrm{W}$ under $350\phantom{\rule{0.2em}{0ex}}\mathrm{mW}$ input power. The maximum internal efficiency of the SHG is 14.84%. The tuning range of the self-cascaded SHG and SFG generated tunable blue–green light was more than $40\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$, from 471.3 to $515\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$. The maximum simulated $3\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$ bandwidth achieved using a gradient-period QPM structure is $196\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$, which is from 1476 to $1672\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$. The gain-bandwidth product of the self-cascaded SHG and SFG processes decreases drastically as the bandwidth is broadened.

© 2007 Optical Society of America

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