Wavelength Tunable Second Harmonic Generation from Photonic Crystal Vertical Cavities

Abstract Flexible wavelength tunability is a critical specification for second‐harmonic generation (SHG) light sources. In the evolving landscape of future technologies, the photonic crystal (PhC) vertical cavity emerges as a promising platform for developing ultracompact SHG devices. However, the reduced size of PhC vertical cavities necessitates a departure from conventional tuning methodologies rooted in traditional phase‐matching frameworks. In this study, an SHG tuning strategy is presented that exploits the relationship between the resonance properties of the cavity and its SHG response. By systematically adjusting the incident angle of fundamental light, we demonstrate the precise tuning of cavity resonance, consequently tuning the SHG conversion efficiency spectra across a spectral bandwidth of about 30 nm. This research contributes to profound understanding of the physical process for flexible wavelength tunability at the nanoscale beyond conventional phase‐matching frameworks, offering insights for the development of tunable SHG sources in integrated photonics and nanoscale optical devices.