High‐Polarization‐Extinction Raman Conversion in Gas‐Filled Polarization‐Maintaining Hollow‐Core Fibers

Abstract

ABSTRACT Gas‐filled hollow‐core fibers (HCFs) are versatile platforms for high‐power nonlinear optics, yet integrating robust polarization control remains crucial for advanced practical applications. Here, we demonstrate the generation of highly polarized Stokes light via stimulated Raman scattering (SRS) in a nitrogen‐filled polarization‐maintaining anti‐resonant HCF (PM‐HCF). By exploiting strong structural birefringence, the Raman interaction decouples along the principal axes, enabling threshold‐selective amplification and an intrinsic polarization purification mechanism. Consequently, the vibrational Raman Stokes emission achieves a polarization extinction ratio (PER) of 35 dB, even with an incident pump PER as low as ∼2 dB. Analytical theory and numerical modeling validate the polarization‐selective dynamics and identify the fiber platform as the dominant factor governing PER saturation. Furthermore, high polarization purity and conversion efficiency persist under tight bending with radii down to 5 cm. These results establish PM‐HCFs as a robust architecture for generating polarization‐stable, frequency‐shifted light, paving the way for practical applications in fields such as optical communications and remote sensing.