Experimental confirmation of the general solution to the multiple-phase-matching problem

We recently described a general solution to the phase-matching problem that arises when one wishes to perform an arbitrary number of nonlinear optical processes in a single medium [Phys. Rev. Lett. 95, 133901 (2005)]. Here we outline in detail the implementation of the solution for a one-dimensional photonic quasicrystal, which acts as a simultaneous frequency doubler for three independent optical beams. We confirm this solution experimentally using an electric-field poled KTiOPO₄ crystal. In optimizing the device, we find - contrary to common practice - that simple duty cycles of 100% and 0% may yield the highest efficiencies, and we show that our device is more efficient than a comparable device based on periodic quasi-phase matching.