Parallel Polarization Illumination with a Multifocal Axicon Metalens for Improved Polarization Imaging.

Polarization imaging is an important branch of the microscopy technique that can provide additional information and enhanced contrast. The illumination system of a polarization microscope enables many different polarizations but makes the setup bulky, complicated, and slow. Here, we design and fabricate an ultrathin planar axicon metalens that also enables parallel illumination with different polarizations. Our results reveal a diffraction-limited size and high degree of linear polarization. To verify our approach, we accurately map the polarization angle of an aluminum grating, which is used as a polarizer. Furthermore, we demonstrate that elliptical polarization can be generated without additional design. A single metalens has the same capabilities as a conventional illumination module containing a polarizer, compensator, and rotation-stage/optical modulator. In addition, our device has the potential to enable rapid super-resolution polarization imaging. The new method could be useful in many applications and areas, including, e.g., materials research and biomedicine.

Design of diffractive optical element projector for a pseudorandom dot array by an improved encoding method.

Here we achieved the structured light patterns of a pseudorandom dot array by a single diffractive optical element. The dot array can be applied to achieve three-dimensional imaging. First, the pseudorandom dot array was generated by the proposed improved encoding methods, which are an improved formula-method-based encoding algorithm and an improved enumeration-method-based encoding algorithm. Second, diffractive optical elements were designed as dot projectors to generate pseudorandom dots by the Gerchberg-Saxton algorithm. Pseudorandom dot arrays with different sizes were generated to validate the proposed encoding methods. A pseudorandom dot array with a maximal size of 713×449 was experimentally achieved. By analyzing the intensity distribution of the projecting pattern, the projected dots have a unique window of 7×7, and the dot array is distortion free. The proposed encoding methods, optimization algorithm, and applied fabrication technology have potential applications in three-dimensional imaging, three-dimensional sensing, shape measurement, and deformation measurement with high decoding speed.