Ultra-Fast 3D Printing of Assembly-Free Complex Optics with Sub-Nanometer Surface Quality at Mesoscale

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Article Overview

Optical lenses with complex spatial morphology are widely used in laser processing, machine vision, optical communication, and other fields. Traditional manufacturing methods for optical lenses mainly involve ultra-precision machining combined with grinding and polishing post-processing techniques, which typically involve multiple steps, high costs, and are difficult to meet complex degrees of freedom requirements. Additive manufacturing technology is showing significant advantages in preparing complex structured optical devices. However, the layer-by-layer additive manufacturing method faces issues such as low printing speed and poor surface quality caused by interlayer step effects. Recently, Professor Liu Yu from Jiangnan University’s School of Mechanical Engineering, PhD student Peng Shuai, and Professor Wang Xiaolong’s team from the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences jointly published a research paper titled “Ultra-fast 3D Printing of Assembly-Free Complex Optics with Sub-Nanometer Surface Quality at Mesoscale” in Extreme Manufacturing (International Journal of Extreme Manufacturing, IJEM), proposing the use of computed tomography volume printing technology combined with a meniscus balancing post-curing process to achieve high-speed printing (3.1 × 10⁴ mm³ h⁻¹) while ensuring sub-nanometer level (RMS = 0.3340 nm) surface quality of the printed structure.

Research Background

Optical devices, due to their good illumination, sensing, optical modulation, and display capabilities, can be directly applied to sensors, holographic reconstruction, human-computer interaction, and other optoelectronic devices. Traditional manufacturing methods for optical devices mainly include ultra-precision machining, casting, and injection molding. However, the current mainstream processing technologies are expensive, involve multiple steps, and have low degrees of freedom, limiting the further development of optical devices.

Recently, 3D printing has attracted significant attention in the manufacturing of highly complex morphology optical devices. Compared with two-photon polymerization (TPP), fused deposition modeling (FDM), direct ink writing (DIW), and stereolithography (SLA), which are based on points as basic manufacturing units, the digital light processing (DLP) technology, which uses layers as basic manufacturing units, is considered a more efficient method for high-speed manufacturing of polymer lenses. However, about 90% of the processing time is consumed in reapplying new photopolymer resin to ensure uniformity between layers. The Continuous Liquid Interface Printing (CLIP) process eliminates the time-consuming reapplication step, providing a significant opportunity to increase manufacturing speed. However, despite the significant increase in printing speed with CLIP, the surface quality of the printed structure is still somewhat limited by the step effect.

To address the issues of manufacturing speed and surface quality of printed structures for complex optical devices, Peng Shuai and others explored the feasibility of using TVP technology to further improve the manufacturing speed of complex optical lenses. As shown in Figure 1, the TVP technology first generates the lens structure within seconds. After removing the manufactured object from the resin container, the residual resin film on its surface is further cured to achieve sub-nanometer ultra-smooth surface. The printed optical lenses can be directly mounted on smartphone cameras for observing small features.

Figure 4. Manufacturing complex morphology lenses. (a-c) Complex morphology lenses. (d) Integrated printing of lens groups. (e) Schematic diagram of the experimental optical system used to demonstrate the functional characteristics of complex lenses. (f) Imaging of a green laser pen without printed lenses. (g) Imaging of a green laser passing through (a) along the Y-axis. (h) Imaging of a green laser passing through (c) along the Z-axis.

To demonstrate the imaging characteristics of TVP printed lenses, the experimental setup in Figure 5(a) uses a resolution test target with 8 sets of patterns ranging from 0 to +7. Figure 5(b) shows the target image captured by CCD. Figure 6(c) shows the stripes of the 3rd set, 6th unit. Figures 5(d-g) show that the TVP printed spherical lens can be directly mounted on a smartphone to capture two magnified images of the Arduino Mega 2560 surface, where the electrical components in focus and wires with a width of 500μm can be clearly seen. The authors used the coordinate lines in Figure 6(i) as the object. By directly mounting the printed compound eye lens on the smartphone shown in Figure 6(h), two blurred coordinate lines can be observed. The test results confirm that the TVP printed lenses can be effectively applied in commercial smartphones, providing high-quality images.

Professor Liu Yu

Researcher Wang Xiaolong