Fig. 1. Schematic diagram of optical-fiber-integrated DP-MS.

Fig. 2. Optical characteristics of unit cells in the DP-MS. (a), (b) Geometric parameters of a typical unit cell in the DP-MS: period P = 0.65 µm, height H = 0.8 µm, width W (0.15–0.6 µm), length L (0.15–0.6 µm), and rotation angle θ in the XY plane. (c) Phase shift ϕ_x and (d) transmittances T_x as a function of unit cell dimensions (L and W). Phase shifts ϕ_x and ϕ_y corresponding to unit cells with (e) varying lengths L and (f) varying transmittances T_x, derived by expanding the 92 × 92 database shown in (c) and (d) to a 500 × 500 database.

Fig. 3. Target phase profiles of the DP-MS are designed to generate (a) a single focal spot, (b) a vortex spot, and (c) multi-focal spots.

Fig. 4. Optical field rotation for the three DP-MSs excited by LMF fundamental modes with varying polarization directions: from left to right are 0°, 30°, 45°, 60°, 90°, 120°, 135°, and 150°. (a) Intensity distributions of the LMF fundamental modes, with white arrows indicating polarization directions. For the corresponding polarization directions shown in (a), the three DP-MSs respectively generate (b) a single focal spot, (c) a vortex spot (inset: phase distribution), and (d) multi-focal spots labeled as FP₁ and FP₂.

Fig. 5. Rotation angles of focal spots generated by the three DP-MSs corresponding to incident light with varying polarization directions (the green dashed lines indicate the ideal linear relationship between polarization angle and rotation angle). (a) A single focal spot (SP), (b) a vortex spot (VP), and (c) multi-focal spots (MP).

Fig. 6. FWHMs of the major axis (MA) and minor axis (mA) of focal spots (left axis), and their ratio (right axis) along the varying polarization directions of the LMF fundamental modes. (a) A single focal spot, (b) a vortex spot, (c) FP₁ in multi-focal spots, and (d) FP₂ in multi-focal spots (the blue dotted line represents the diffraction-limited spot size).

Fig. 7. Multi-focal fields generated by the DP-MS with overlapping different signal functions: (a) and (b) show the distance between the two focal spots controlled by different amplitudes (A₂ and A₇) of sawtooth wave functions (the white arrow represents the polarization direction). (c) Distance between the two focal spots corresponding to the amplitude of sawtooth wave. (d)–(f) Three focal spots rotating with the incident light with different polarization directions.