Single resonant cavity enhances the second harmonic generation of layered ferroelectric NbOCl2

Second harmonic generation (SHG) is a common nonlinear optical process with wide applications. Recent studies have found that the van der Waals crystal material NbOCl2 has a high efficiency in SHG, and this material does not undergo any change in electronic structure or weakening of excitonic effect during stacking, making it a scalable SHG crystal. Here, we designed and fabricated a single resonant Fabry–Pérot (FP) microcavity to enhance the SHG of NbOCl2 by amplifying the local electric field of the excitation light. The cavity was fabricated by plasma-enhanced chemical vapor deposition, and the deposition process was optimized to avoid the damage of the NbOCl2 sample. Our measurements confirmed that the SHG of the NbOCl2 sample can be amplified more than 30 times on the distributed Bragg reflector (half of the FP cavity), and more than 200 times inside the FP cavity. This method provides ideas for efficiently enhancing harmonics and directions for on-chip integrated photonic devices.