Large second harmonic generation enhancement in Si<sub>3</sub>N<sub>4</sub> waveguides by all-optically induced quasi-phase-matching.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29044113.
- Also identified by DOI 10.1038/s41467-017-01110-5 and PMC identifier 5725590.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Efficient second harmonic generation in integrated platforms is usually achieved by resonant structures, intermodal phase-matching or quasi-phase matching by periodically poling ferroelectric waveguides. However, in all these structures, it is impossible to reconfigure the phase-matching condition in an all-optical way. Here, we demonstrate that a Watt-level laser causes a periodic modification of the second-order susceptibility in a silicon nitride waveguide, allowing for quasi-phase-matching between the pump and second harmonic modes for arbitrary wavelengths inside the erbium band. The grating is long-term inscribed, and leads to a second harmonic generation enhancement of more than 30 dB. We estimate a χ <sup>(2)</sup> on the order of 0.3 pm/V, with a maximum conversion efficiency of 0.05% W<sup>-1</sup>. We explain the observed phenomenon with the coherent photogalvanic effect model, which correctly agrees with the retrieved experimental parameters.