Metasurface-assisted phase-matching-free second harmonic generation in lithium niobate waveguides
Cheng Wanga, Zhaoyi Lib, Myoung-Hwan Kimc, Xiao Xionga d, Xi‐Feng Rend, Guang‐Can Guod, Nanfang Yub e✉, Marko Lončara f✉
- aJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
- bDepartment of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA
- cDepartment of Physics, The University of Texas Rio Grande Valley, Brownsville, TX, 78520, USA
- dKey Laboratory of Quantum Information & Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China
- eDepartment of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA. ny2214@columbia.edu
- fJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA. loncar@seas.harvard.edu
- ✉Corresponding author
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Abstract
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).