Environmental-friendly microlens array for field curvature correction

Fig (a) Working principle of the microlens array, (b) scanning electron microscope (SEM) characterization, (c) microscope photographs, (d) dark field focus image.

Field curvature is a widespread matter in large field optical imaging systems, which means even if you are imaging a planar object, you can only achieve high sharpness at the focus position, and the image in the edge area may become blur. However, the existing optical systems and imaging components are mostly planar designs, so it is particularly important to eliminate field curvature aberrations.

As a natural biomacromolecular material, the protein materials have the advantages of wide source, renewable, biocompatible, non-polluting, and absorbable degradation. In recent years, with the help of growing maturity of micro-nano processing technology, many special functions of protein-based micro-nano structures, including micro-devices and even integrated systems have been successfully realized.

Based on hereinbefore background, the researchers from the group of Prof. Hong-Bo Sun (the Key Laboratory of Integrated Optoelectronics of Jilin University) demonstrated a three-dimensional microlens array with different curvature unit lenses (MLADC) based on bovine serum albumin (BSA) fabricated by femtosecond laser two-photon polymerization direct writing (FsDLW). The MLADC possesses unique and characteristic optical performance, as the curvatures of unit lenses are different along with their different positions, which will play a significant role in optimizing optical system structure and reducing optical elements, especially in field curvature correction. In addition, due to the unique advantages of FsDLW, such as non-contact and low thermal damage, the biological activity of the protein is partially retained. Therefore, it is easy to achieve a fine adjustment of the focal plane by utilizing the equilibrium swelling of the protein hydrogel in the solution. These results are reported in Chinese Optics Letters Vol. 17, No. 6 2019 (Zhishan Hou, et al., Tunable protein microlens array).

"These results show the application prospects of protein-based materials in new biophotonics and biomedical fields, indicating the great potential of femtosecond laser direct writing technology in building "smart" integrated photonic micro/nano-biological systems," said Dr. Zhi-Shan Hou from this group.

Their further work will focus on the dual controllable design of femtosecond laser direct writing in device geometry and material functional properties, and give the device novel and diverse features and functions by fully exploiting and utilizing the intrinsic properties of proteins.

环境友好的场曲矫正微透镜阵列

图 （a）微透镜阵列工作原理，（b）器件扫描电镜（SEM）表征，（c）器件显微镜照片，（d）器件暗场成像照片。

场曲是光学系统的一种固有像差，就是即便是对着标靶等平面物体拍摄，也只能在对焦点位置实现高锐度，边缘区域的图像就会变得模糊。然而现有的光学系统和成像部件多为平面设计，因此，消除场曲像差就变得尤为重要。

蛋白质材料作为一种天然的生物大分子材料，具有来源广泛可再生、生物兼容无污染、可吸收降解等优点。近年来，在日益发展成熟的微纳加工技术的帮助下，利用蛋白质及其衍生物，已经成功实现了许多特殊功能的微纳结构、微器件乃至集成系统，成为一个重要的前沿研究方向和发展趋势。

基于以上背景，来自吉林大学集成光电子重点实验室的杨罕教授课题组提出了利用飞秒激光双光子聚合直写制备基于牛血清白蛋白的三维场曲矫正微透镜组，它通过排列焦距不同的多组微透镜阵列，实现了对弯曲像平面的平面矫正。另外，得益于飞秒激光超快脉冲非接触、低附带热损伤的独特优势，使得蛋白质的生物活性得以部分保留。因此，可以通过利用蛋白质水凝胶自身在溶液中的平衡溶胀，实现透镜组矫正焦平面的再度微调。该成果发表在Chinese Optics Letters 2019年第17卷第6期上(Zhishan Hou, et al., Tunable protein microlens array)。

研究小组认为，该研究成果显示出蛋白质基材料在新型生物光子和生物医学等领域的应用前景，表明了飞秒激光直写技术在构建“智能”集成光子微/纳米-生物系统的巨大潜力。

该课题组接下来的工作将会继续聚焦飞秒激光直写在器件几何构型和材料功能特性的双重可控设计，充分挖掘、利用蛋白质本征性质，赋予器件新颖多样的特性和功能。