Fig. 1. Schematic illustration of (a) concentric bilayer microsphere, (b) eccentric bilayer microsphere, and (c) trapped Janus microsphere. (d) Optical path difference of Janus microspheres of the radius 4 μm with different ratios.

Fig. 2. Changes in (a) positions and (b) orientations of the Janus microsphere with ratio PS:PMMA = 5:1 during trapping. Changes in trapped microsphere (c) positions and (d) orientations with light polarization directions.

Fig. 3. Changes in (a) positions and (b) orientations of the Janus microsphere with ratio PS:PMMA = 1:5 during trapping. Changes in trapped microsphere (c) positions and (d) orientations with light polarization directions.

Fig. 4. (a) Positions and (b) orientations of Janus microspheres vary with the ratios (or the optical path difference). (c), (d) Alternative steady postures when initial orientation changes.

Fig. 5. (a) Preparation of the Janus microspheres. (b) Histogram of the Janus microspheres’ diameters and fitted normal distribution curve in orange. The illustrations of the Janus microsphere with the ratio 5:1 under (c) optical microscope and (d) scanning electron microscope. The scale is 2 μm.

Fig. 6. (a) Schematic diagram of the optical tweezers system. (b) Change in the light polarization direction after passing through the half-wave plate.

Fig. 7. (a) Free and (b) trapped Janus microspheres with different ratios. The scale is 2 μm. (c) Positions and (d) orientations of Janus microspheres vary with the ratios (or the optical path difference).

Fig. 8. Changes in (a) positions and (b) orientations of Janus microspheres with ratio 5:1 when light polarization direction rotates. (c) Changes in positions of Janus microspheres with ratios 5:1, 4:1, 2:1, and 1:1. The black curves are fitted circles, and the legend indicates rotation radii. (d) Statistical results for rotation radii. Changes in (e) positions and (f) orientations of Janus microspheres with ratio 1:5 when light polarization direction rotates.

Fig. 9. Coordinate systems of the optical field and the microsphere.