Chinese Optics Letters, Vol. 19, Issue 7, 071902 (2021)
Robust modal phase matching in subwavelength x-cut and z-cut lithium niobate thin-film waveguides
Lingzhi Peng1, Lihong Hong1, Baoqin Chen1, Peng He2,3,**, and Zhiyuan Li1,*
- 1School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China
- 2Guangdong Full-Spectra Laser Technology Co., Ltd., Dongguan 523808, China
- 3Dongguan Sanhang Innovation Research Institute, Dongguan 523808, China
We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation (SHG) in subwavelength x-cut and z-cut lithium niobate (LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly. Under the scheme of optimal modal phase matching (MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them. Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.
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