Fig. 1. Schematic diagram of extending DoF and polarization imaging. (a) Traditional 4f system. Only a clear intensity image of the object in the front focal plane can be obtained. (b) 4f system with embedded LC PB-phase element. (c) Reconstructions of objects and their polarization information. Two spin component images of objects are reconstructed by the Wiener deconvolution algorithm using a defocus-insensitive PSF, from which clear images and polarization ellipticities of objects located in different planes can be obtained.

Fig. 2. LC element design and characterization. (a) Photograph of the LC element. (b) Local polarized micrograph of the LC element. Scale bar: 1 mm. (c) Schematic diagram of PSF formation. When a point source passes through the system with the LC element, two spin-dependent PSFs are generated. (d) Experimentally measured PSFs for LCP and RCP components from z = −5 to 5 cm. (e) Correlation between PSF at z = 0 cm and PSFs from z = −5 to 5 cm. (f) Imaging efficiency (IE) of the system at different object distances. (g) Measured and theoretical polarization splitting ratios of the system.

Fig. 3. Experiment for testing the capability of extending DoF. (a) Experimental setup for measurement. Imaging of a 1951 USAF target illuminated by LED light by the 4f system with added LC elements. L₁, L₂, L₃, lenses; P, polarizer. (b) Raw image directly captured by CCD. Scale bar: 1 mm. The images in the upper right corner and lower left corner are the LCP and RCP images, respectively, and the center is the zero-order light. When the zero-order light becomes blurred, the two untreated images remain relatively clear. (c) Images when the LC element is turned off, as well as the deconvolved LCP and RCP component images. (d) Intensity distributions along the lines in (c).

Fig. 4. Experiment for polarization imaging with extended DoF. (a) LC sample with designed Stokes vector S₃. (b) Micrograph of LC element under illumination of LCP light. (c) Reconstructed LCP and RCP images and Stokes vector S₃ with different object distances.

Fig. 5. Real-world object measurement by imaging a plastic ruler. (a) Photo of the plastic ruler. (b), (c) Raw images of two areas directly captured by a CCD. (d), (e) Reconstructed images of LCP and RCP components and Stokes vector S₃.

Fig. 6. Multi-object target recognition integrating the polarization dimension. (a) Schematic diagram of the scene. (b) Raw image directly captured by a CCD. Scale bar: 1 mm. (c) Reconstructed images of LCP and RCP components and Stokes vector S₃.