Spatial-Polarization-Independent Parametric Up-Conversion of Vectorially Structured Light

Spatial-polarization-independent (SPI) parametric conversion is the basis of many optical applications, such as SPI frequency interfaces for communication channels carried by vector modes and up-conversion detection for polarization-resolved imaging. However, realizing such conversion remains a challenge. In the proof-of-principle study presented here, we demonstrate SPI parametric up-conversion using a polarization Sagnac nonlinear interferometer based on type-II second-harmonic generation. Our results show that the vector profile (including both polarization and intensity) and associated spin-orbit-coupling state of the vector signal beam can be transferred to the frequency-doubled beam with high fidelity. The principle lays the foundation for a SPI frequency interface for quantum and classical channels based on vector modes and also paves the way for up-conversion detection of polarization-resolved images in the mid- and far-infrared regions.