Birefringence- and Optical Distortion-Free Isotropic Polymer Lens Assisted by Photonic Microspheres

Development of low-cost and light polymer optical devices to substitute for inorganic materials is a major trend. Traditional molten processing methods are direct and have been extensively applied in optical product manufacturing. However, the inevitable intrinsic birefringence and optical distortion due to polymer molecular chain anisotropy limit their application in high-end optical devices. Here, we report a novel thermocompression strategy for isotropic polymer lens fabrication, in which a cross-linked photonic crystal (PC) consisting of closely stacked polymer microspheres is used as a precursor and then heated and pressed under the rubbery state. A polymethyl methacrylate microsphere-based PC is used as a demonstration, and the obtained isotropic lenses exhibit superior performance compared to the traditional counterpart, which are birefringence-free (Δn < 1 × 10^-5) and optical distortion-free and have excellent mechanical properties (hardness reaches 0.28 GPa), and the hidden mechanism is carefully studied. These properties enable the isotropic lens to be applied in precision optical components such as the lens of spectacles, microscope, telescope and endoscope, industrial camera, and astronaut helmet, and the proposed general method can extend to various polymers and provide new opportunities for the development of three-dimensional PCs.