Robust EO comb generation in high-Q photonic crystal microresonator

We demonstrate broadband and coherent electro-optic (EO) frequency comb generation in a thin-film lithium niobate (TFLN) photonic crystal Fabry–Pérot (PhC-FP) microresonator. By leveraging the strong second-order nonlinearity, low optical loss, and microwave-optical field overlap of TFLN, our platform enables efficient cascaded EO modulation. The standing-wave PhC-FP cavity provides spectral confinement that eliminates cavity modes near Raman-active wavelengths, thereby excluding stimulated Raman scattering even under high optical power. We achieve intrinsic quality factors exceeding 10⁶ and generate EO combs spanning over 600 resonant modes. The measured comb spectra match theoretical predictions based on the extracted Q distribution and dispersion profile, confirming that the comb dynamics are governed by the phase-matching condition between modulation frequency and integrated dispersion. High-power measurements further validate Raman-free operation at on-chip pump powers up to 200 mW. These results establish the PhC-FP resonator as a scalable and power-efficient platform for integrated EO comb sources suitable for quantum photonics, metrology, and coherent communications.