Large Area and High Precision Machining of Aspheric Microlens Array

Microlens array (MLA), as a structure composed of two-dimensional micro scale lens array, has attracted the attention of academia and industry due to its unique optical properties and extensive applications. In recent years, MLA has gradually entered a variety of applications, such as wavefront sensing, virtual reality/augmented reality display, beam shaping, micro/wide angle imaging, optical field camera, optical communication and many other emerging applications.

Source:Shiyi Luan, Fei Peng,Guoxing Zheng, Chengqun Gui, Yi Song, and Sheng Liu

However, traditional MLA fabrication methods, such as thermal reflow, inkjet and self-assembly, are difficult to directly fabricate aspheric microlens arrays (AMLA) with ideal arrangement and contour, which determines the optical performance of AMLA. At the same time, the disadvantages of top-down writing, such as fragments, terrain control difficulties and complex processes, hinder the large-scale commercialization of these methods.

In a new paper published in the journal Light: Advanced Manufacturing, a team of scientists led by Professor Chengqun Gui of the State Key Laboratory of Advanced Lithography of the Institute of Technology and Science of Wuhan University and their colleagues demonstrated the preparation and characterization of AMLA through single beam exposure DLWL, which can meet the high requirements for optical performance.

Optical properties of manufactured AMLA.

In order to control the contour, they adopted an optimization method in their research to reduce the deviation between the AMLA contour and the required contour. The different optical properties of AMLA are tested with parallel light source and scattering light source, and the test results are consistent with the design. Due to the high flexibility of the method, AMLA and off-axis AMLA with different filling factors can also be easily fabricated by one-step lithography. Finally, the automatic stereoscopic display with flexible film is fabricated by using the above technology, which provides a new way to provide flexible holographic display with low cost.

a. Off axis MLA diagram. b. 3D terrain of manufactured off-axis MLA. c. The working wavelength of the focused spot array captured in the experiment is 635 nm. d. The off-axis MLA was characterized by SEM photos of the partial view of MLA with SEM. e-f and fill coefficient of 90.7% and 100% respectively.
Source: Shiyi Luan, Fei Peng, Guoxing Zheng, Chengqun Gui, Yi Song, and Sheng Liu

Compared with traditional MLA fabrication methods, this advanced lithography technology has a high degree of design flexibility and can significantly improve the performance of many functional devices based on MLA. Scientists summarized the advantages and application prospects of this advanced lithography technology:

"We show that the size is 30 × The 30 mm2 AMLA can be manufactured in 8 hours and 36 minutes, which corresponds to high-speed writing over 100 mm2/h. In fact, we can manufacture more than 500 × 500 mm2 MLA. At the same time, through three-dimensional optical proximity correction (the relative profile deviation is reduced to 0.28%), the contour of the manufactured AMLA has been successfully optimized, and the average surface roughness is less than 6 nm. "

"It has many application prospects, such as laser beam shapers and wavefront sensors. For example, to achieve a free form beam shaper, the microlenses in MLA should be aligned irregularly (that is, the focus spot array is randomly distributed) , which requires other methods to use complex grayscale masks. Using laser direct writing lithography technology with high degree of manufacturing freedom, we can directly manufacture off-axis MLA to generate irregular spot arrays without complex grayscale masks. " They added.

Schematic diagram of high-speed, large-area and high-precision AMLA manufacturing.

"The proposed AMLA manufacturing method based on direct laser writing lithography can not only reduce the preparation difficulty of MLA with complex morphology, but also is very suitable for industrial production. This can greatly reduce the preparation cost of devices composed of microlenses, such as endoscopes, infrared detectors, holographic displays, optical couplers, etc. Therefore, it will have a significant impact on medical care, rescue, optical communications, military and many other related fields." Scientists said.

Source: High-speed, large-area and high-precision fabrication of aspheric micro-lens array based on 12-bit direct laser writing lithography, Light: Advanced Manufacturing (2022). DOI: 10.37188/lam.2022.047