  We report the fabrication of artificial unidimensional crystals exhibiting an
effective bulk second-order nonlinearity. The crystals are created by cycling
atomic layer deposition of three dielectric materials such that the resulting
metamaterial is non-centrosymmetric in the direction of the deposition.
Characterization of the structures by second-harmonic generation Maker-fringe
measurements shows that the main component of their nonlinear susceptibility
tensor is about 5 pm/V which is comparable to well-established materials and
more than an order of magnitude greater than reported for a similar crystal
[1-Alloatti et al, arXiv:1504.00101[cond-mat.mtrl- sci]]. Our demonstration
opens new possibilities for second-order nonlinear effects on CMOS-compatible
nanophotonic platforms.
