Conversion and selection of Laguerre-Gaussian modes via a variable aperture in a geometric-phase-plate-assisted...

We numerically analyze the conversion and selection of intracavity modes in a two-mirror optical resonator, which is assisted by a geometric phase plate (GPP) and a circular aperture, along with its output performance of high-order Laguerre-Gaussian (LG) modes. Based on the iterative Fox-Li method and the analysis of modal decomposition, transmission losses, and spot sizes, we find that various self-consistent two-faced resonator modes could be formed by fixing the GPP but changing the size of aperture. Such a feature not only enriches transverse-mode structures inside the optical resonator, but also provides a flexible way to directly output high-purity LG modes for high-capacity optical communication, high-precision interferometers, high-dimensional quantum correlation, etc.