title: Phase mismatch-free nonlinear propagation in optical zero-index materials.
abstract: Phase matching is a critical requirement for coherent nonlinear optical processes such as frequency conversion and parametric amplification. Phase mismatch prevents microscopic nonlinear sources from combining constructively, resulting in destructive interference and thus very low efficiency. We report the experimental demonstration of phase mismatch-free nonlinear generation in a zero-index optical metamaterial. In contrast to phase mismatch compensation techniques required in conventional nonlinear media, the zero index eliminates the need for phase matching, allowing efficient nonlinear generation in both forward and backward directions. We demonstrate phase mismatch-free nonlinear generation using intrapulse four-wave mixing, where we observed a forward-to-backward nonlinear emission ratio close to unity. The removal of phase matching in nonlinear optical metamaterials may lead to applications such as multidirectional frequency conversion and entangled photon generation.
authors: NSF Nanoscale Science and Engineering Center, University of California, Berkeley, CA 94720, USA.
authors: Haim
authors: H
authors: Suchowski
authors: Kevin
authors: K
authors: O'Brien
authors: Zi Jing
authors: ZJ
authors: Wong
authors: Alessandro
authors: A
authors: Salandrino
authors: Xiaobo
authors: X
authors: Yin
authors: Xiang
authors: X
authors: Zhang