We report on a widely tunable synchronously pumped picosecond optical parametric oscillator (OPO) combining an aperiodically poled MgO-doped LiNbO₃ crystal as a broadband gain medium and an axially chirped volume Bragg grating as a spectral filtering dispersive element. Translation of the Bragg grating along the beam axis enables wavelength tuning over 215 nm around 3.82 μm and provides spectral narrowing. Rapid continuous tuning over 150 nm in 100 ms is demonstrated.

We investigate and model a picosecond synchronously pumped optical parametric oscillator (OPO) based on an aperiodically poled lithium niobate (APPLN) nonlinear crystal with a chirped quasi-phasematching (QPM) grating. We observe remarkable spectral features with an asymmetric OPO spectrum consisting of a main peak with lower side-lobes. Depending on the sign of the QPM chirp rate, the sidelobes are located either on the red or on the blue side of the main peak. Meanwhile, side-bands develop in the depleted pump spectrum. We attribute these features to cascaded sum-/difference-frequency generation processes which are quasi-phase matched at different positions in the APPLN crystal. A terahertzgeneration cascading effect is also observed and characterized at high pump power.

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