  Nonlinear metamaterials (NLMMs) have been predicted to support new and
exciting domains in the manipulation of light, including novel phase matching
schemes for wave mixing. Most notable is the so-called nonlinear-optical
mirror, in which a nonlinear negative-index medium emits the generated
frequency towards the source of the pump. For the first time, we experimentally
demonstrate the nonlinear-optical mirror effect in a bulk negative-index NLMM,
along with two other novel phase matching configurations, utilizing periodic
poling to switch between the three phase matching domains.
