Theoretical investigation on the third harmonic generation by double resonances in waveguide directional couplers

The cascaded third harmonic generation in waveguide directional couplers is analyzed theoretically. It is found that the phase-matching conditions for the cascaded third harmonic generation can be realized by the double resonances of the directional coupler. The core thickness and the internal separation of the two waveguides in the directional coupler can be adjusted to meet the resonance conditions. As an example, we have designed a directional coupler structure for efficient cascaded THG at 0.5167 μm, and the optimized parameters for the structure have been obtained. The results above have been well verified by numerical calculations.