Robust and broadband frequency conversion in composite crystals with tailored segment widths and χ(2) nonlinearities of alternating signs.

We propose an efficient, robust, and broadband nonlinear optical frequency conversion technique, which uses segmented crystals constructed in analogy with the composite pulses in nuclear magnetic resonance and quantum optics. The composite crystals are made of several macroscopic segments of nonlinear susceptibilities of opposite signs and specific thicknesses, which are determined from the condition to maximize the conversion efficiency with respect to variations in the experimental parameters. These crystals deliver broadband operation for significantly lower pump intensities than single bulk crystals. We demonstrate this technique by numerical simulation of sum-frequency generation in MgO:LiNbO3 crystal.