  Spatial polarization independent (SPI) parametric conversion is the basis of
many optical applications, such as SPI frequency interface for communication
channels carried by vector modes and upconversion detection for
polarization-resolved imaging. However, realizing such conversion remains a
challenge. In this proof-of-principle work, we demonstrated SPI parametric
upconversion using a polarization Sagnac nonlinear interferometer based on
type-II second-harmonic generation (SHG). Our results show that the vector
(including both polarization and intensity) profile and associated SOC state of
the vector signal beam could be transferred to the SHG beam with a high
fidelity. The principle lays a foundation of SPI frequency interface for
quantum/classical channels based on vector modes and also paves the way for
upconversion detection of polarization-resolved imaging in Mid-/far-infrared
region.
