Longitudinally continuous varying high-order cylindrical vector fields enabled by spin-decoupled metasurfaces

Abstract

The manipulation of vector optical fields in three-dimensional (3D) space plays a vital role in both fundamental research and practical implementations of polarization optics. However, existing studies mostly focus on 3D vector optical fields with limited modes. Here, an approach of spin-decoupled spatial partitioning is proposed to generate complex 3D vector optical fields with a customizable number of modes on demand. The crosstalk among different modes is effectively suppressed by the decoupling capability of asymmetric photonic spin-orbit interactions (PSOIs) and the design of region displacement for opposite spin states. As a proof-of-concept demonstration, a metasurface is designed to generate longitudinally varying high-order cylindrical vector fields, ranging from the 2nd to the 10th order in even sequences along the propagation direction. The experimental results demonstrate the effectiveness and potential of our approach to enabling precise control of 3D vector optical fields with arbitrary mode combinations. This work holds promising applications in biophotonics, quantum optics, and communications.

Keywords: asymmetric PSOIs; control of vector optical fields; metasurfaces.

Figure 1:

Schematic diagram of generating 3D high-order cylindrical vector fields via a single metasurface. The case shows the 2nd-order, 4th-order, and 6th-order light spot diagrams of the x-component under the illumination of x-LP light.

Figure 2:

Principles for synthesizing longitudinally varying high-order vector fields. (a) Operating principle of the annular metasurface. The green and red lines represent LCP and RCP light, respectively. (b) LCP and RCP partition diagram of the metasurface. (c) Intensity distribution of the x-component and y-component in different regions under the x-LP light illumination. (d) Mode purity of synthetic vector optical fields.

Figure 3:

Schematic diagram of basic building blocks. (a) Schematic diagram of the unit cell, where H = 7.3 μm and P = 4.8 μm. The length L and width W of the eight nanorods are provided below. (b) Simulated propagation phase and polarization conversion amplitude of eight unit cells at a wavelength of 10.6 μm. (c) SEM images of a fabricated sample.

Figure 4:

Experimental setup and results. (a) Schematic diagram of the optical characterization setup. The numerical aperture of the objective lens is about 0.55. (b) Simulation and experiment diagram of the 2nd and 4th order of x-component, y-component, and total intensity on the x–y plane of LCP and RCP light incidence. (c) Transverse plane images of the x-component and y-component at each region at the x-LP light incidence. (d) Intensity distributions of the transverse plane of the x-component of the 2nd-order cylindrical vector field at the x-LP incidence. The yellow arrow represents the polarization direction of the incident LP light, while the white arrow represents the orientation of the linear polarizer. QWP: quarter-wave plate; HWP: half-wave plate.