Metasurface-assisted phase-matching-free second harmonic generation in lithium niobate waveguides

Cheng Wang, Zhaoyi Li, Myoung Hwan Kim, Xiao Xiong, Xi Feng Ren, Guang Can Guo, Nanfang Yu, Marko Lončar

Research output: Contribution to journalArticlepeer-review

93 Scopus citations


The phase-matching condition is a key aspect in nonlinear wavelength conversion processes, which requires the momenta of the photons involved in the processes to be conserved. Conventionally, nonlinear phase matching is achieved using either birefringent or periodically poled nonlinear crystals, which requires careful dispersion engineering and is usually narrowband. In recent years, metasurfaces consisting of densely packed arrays of optical antennas have been demonstrated to provide an effective optical momentum to bend light in arbitrary ways. Here, we demonstrate that gradient metasurface structures consisting of phased array antennas are able to circumvent the phase-matching requirement in on-chip nonlinear wavelength conversion. We experimentally demonstrate phase-matching-free second harmonic generation over many coherent lengths in thin film lithium niobate waveguides patterned with the gradient metasurfaces. Efficient second harmonic generation in the metasurface-based devices is observed over a wide range of pump wavelengths (λ = 1580-1650 nm).

Original languageEnglish
Article number2098
JournalNature Communications
Issue number1
StatePublished - Dec 1 2017


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