Metastructures enabled quasi-phase matching in nonlinear waveguides
Authors: Zhang, Y., Deng, J., Zhang, X., Zhang, J., Zhang, J.
Journal: Journal of Optics United Kingdom
Publication Date: 01/04/2026
Volume: 28
Issue: 4
eISSN: 2040-8986
ISSN: 2040-8978
DOI: 10.1088/2040-8986/ae5e89
Abstract:One of the key conditions for efficient nonlinear process lies in phase matching (PM). In nonlinear waveguides, this is commonly fulfilled by modal PM or quasi-PM (QPM) through periodic poling. However, these methods are subject to certain dimension of the waveguide or certain type of nonlinear material. In this work, we introduce a new QPM technique based on periodic phase jump (PPJ) between interacting waves during the propagation. For the second harmonic generation (SHG) process, we first prove that a periodic π-phase jump between fundamental frequency (FF) and second harmonic (SH) plays the same role of the periodic sign change of nonlinear coefficient in the dynamic of waves. Then, we implement this PPJ-QPM technique in an AlGaAs-on-insulator waveguide by periodic arrangement of metalines in the waveguide to induce the needed π-phase jump. We design the dimension of the metalines such that the two waveguide modes at FF and SH both have high transmission but experience a phase difference near π. With these metalines, QPM-SHG for both infinite-width slab waveguide and finite-width stripe waveguide are numerically demonstrated for a fundamental wavelength of 1550 nm. The normalized SHG efficiencies reach 90.6% W−1 cm−2 (66.9% W−1 cm−2) for the slab (stripe) waveguide, representing 96 (37) times improvement when compared to the best efficiencies of the waveguide without the metalines. The principle of the proposed PPJ-QPM technique is applicable to any nonlinear material, waveguide with any size, and other nonlinear processes, making it a general QPM technique for nonlinear integrated photonics.
Source: Scopus