Mode Multiplication of Cylindrical Vector Beam Using Raytracing Control

Abstract Cylindrical vector beams (CVBs) hold significant promise in mode division multiplexing communication owing to their inherent vector mode orthogonality. However, existing studies for facilitating CVB channel processing are confined to mode shift conversions due to their reliance on spin-dependent helical modulations, overlooking the pursuit of mode multiplication conversion. This challenge lies in the multiplicative operation upon inhomogeneous vector mode manipulation, which is expected to advance versatile CVB channel switching and routing. Here, we tackle this gap by introducing a raytracing control strategy that conformally maps the light rays of CVB from the whole annulus distribution to an annular sector counterpart. Incorporated with the multifold conformal annulus-sector mappings and polarization-insensitive phase modulations, this approach facilitates the parallel transformation of input CVB into multiple complementary components, enabling the mode multiplication conversion with protected vector structure. Serving as a demonstration, we experimentally implemented the multiplicative operation of four CVB modes with the multiplier factors ofN= +2 andN= –3, achieving the converted mode purities over 94.24% and 88.37%. Subsequently, 200 Gbit/s quadrature phase shift keying signals were successfully transmitted upon multiplicative switching of four CVB channels, with the bit-error-rate approaching 1 × 10⁻⁶. These results underscore our strategy’s efficacy in CVB mode multiplication, which may open promising prospects for its advanced applications.