摘要
双焦点器件在高分辨率显微镜成像、激光切割等领域中有着广泛的应用。现有双焦点器件存在结构复杂、加工难度大等问题。提出了一种基于空间光调制器的远场超分辨双焦点聚焦光场构建方法。基于光学超振荡原理,结合二进制粒子群优化算法和角谱衍射理论,设计了两个具有不同焦距的单焦点聚焦二值相位超振荡掩模。通过布尔逻辑“与”运算,得到双焦点聚焦二值相位超振荡掩模。采用该方法,针对波长λ=632.8 nm的圆偏振光,设计了焦距分别为280000λ(177184μm)和300000λ(189840μm)的双焦点聚焦超振荡掩模。实验中,将超振荡掩模载入空间光调制器,成功实现了远场超分辨双焦点聚焦。实验结果与理论计算结果高度一致:两个聚焦焦斑的横向峰值半峰全宽分别为20.333μm和20.353μm,均低于对应的衍射极限,同时保持了较低的旁瓣。该方法具有易于实现、设计焦距可控等优点,在光通信、生物医学成像等领域中具有广阔的应用前景。
Objective Bifocal devices can generate two focal points in the vertical or transverse direction,have the advantages of improving the depth and resolution of imaging as well as the transmission efficiency and quality of optical signals,and have a wide range of applications in optical communications,optical imaging,microscopy technology,and optical sensors.Traditional bifocal devices are limited by the Abbe diffraction limit,but recently optical super-oscillation provides a new technology for far-field super-resolution focusing,which can make the focused focal spot break through the diffraction limit.However,the existing bifocal super-oscillatory lenses rely on complex optimization algorithms,the device processing is difficult,and the device size is limited.Based on the principle of optical super-oscillation,combined with the binary particle swarm optimization(BPSO)algorithm and the angular spectrum diffraction theory,two single-focal focused binary phase super-oscillation masks with different focal lengths are designed,and the bifocal focused binary phase super-oscillation masks can be obtained by using the Boolean logic“AND”operation.A bifocal super-oscillation mask is loaded into a spatial light modulator(SLM)to generate a super-resolution bifocal focusing device.This method has the advantages of easy implementation and controllable design focal length,and has significant application potential in optical communication,biomedical imaging and other fields.Methods This paper consists of three core steps:first,for circularly polarized light(wavelengthλ=632.8 nm),two binary phase super-oscillation masks(S-SOM1 and S-SOM^(2))are designed and optimized by using the BPSO algorithm and the angular spectrum diffraction theory with the corresponding focal lengths of f1=280000λ(177184μm)and f2=300000λ(189840μm),respectively.Second,a Boolean“AND”operation is performed on the phase distributions of the two masks to synthesize a bifocal super-oscillation mask(B-SOM),and the bifocal synchronous modulation is achieved by preserving the overlapping region of the phases.Finally,a farfield super-resolution bifocal focusing and measurement platform based on a spatial light modulator is designed and constructed,the BSOM is loaded into the SLM in the form of a grayscale map,the scanning shot of the optical field with a step size of 0.05 mm is taken through the electrically-controlled displacement stage to obtain the distribution of the optical field,and the key parameters are extracted to verify the performance.Results and Discussions The Boolean“AND”operation is performed on the phase distributions of the single-focal superoscillation masks S-SOM1 and S-SOM^(2) obtained from the optimized design to obtain the phase distributions of the bifocal superoscillation masks(Fig.3).From the theoretical results,it can be seen that the transverse full widths at half maximum(FWHMs)of the two focal spots are 21.846μm and 21.114μm,respectively,which are lower than the diffraction limits of 22.277μm and 23.495μm,and super-resolution focusing has been realized in theoretical calculations(Fig.5).The experimental results show that the designed bifocal device successfully realizes far-field super-resolution focusing.The longitudinal FWHMs of the bifocal are 4.523 mm and 4.198 mm,respectively(Fig.7),and the transverse FWHMs are 20.333μm and 23.353μm,respectively(Fig.8),which are lower than the Abbe diffraction limits of 22.225μm and 23.650μm.In addition,the bifocal sidelobe ratios are as low as 5.1%and 12.7%,respectively(Table 1),which effectively suppress the optical field crosstalk.The experimental focal spot positions(z=177.784 mm and z=189.184 mm)are in good agreement with the theoretical calculations,and the small deviations are due to the partial loss of the modulation phase after the logic“AND”operation.Conclusions In this paper,we propose a far-field super-resolution bifocal focusing method based on spatial light modulator,which is based on the principle of super-oscillation,and utilize the binary particle swarm optimization algorithm and the angular spectrum diffraction theory to design a single-focal binary-phase super-oscillation mask,and adopt the Boolean logic“AND”operation to generate a bifocal super-oscillation mask from two binary-phase super-oscillation masks with different focal lengths.Based on this method,the bifocal super-oscillation masks with working wavelength of 632.8 nm and focal lengths of 280000λ(177184μm)and 300000λ(189840μm)are designed and optimized,respectively.By loading the super-oscillation mask into a spatial light modulator without precision processing,far-field super-resolution bifocal focusing is experimentally demonstrated,with the peak intensity positions of the two focal spots located at 177784μm and 189184μm,respectively.The average FWHMs are 20.333μm and 23.353μm,respectively,which are lower than the Abbe diffraction limit.The low sidelobes are also maintained with ratios of 5.1%and 12.7%,respectively.The results significantly improve the control accuracy and resolution of far-field super-resolution bifocal imaging,which can be applied to the visible wavelength band and extended to other optical bands.
作者
李新羽
黄字文
李正羲
曹芸彬
李占锋
尚丽平
邓琥
武志翔
Li Xinyu;Huang Ziwen;Li Zhengxi;Cao Yunbin;Li Zhanfeng;Shang Liping;Deng Hu;Wu Zhixiang(School of Manufacturing Science and Engineering,Southwest University of Science and Technology,Mianyang 621010,Sichuan,China;School of Information Engineering,Southwest University of Science and Technology,Mianyang 621010,Sichuan,China;Joint Lab of Extreme Condition Matter Properties,Southwest University of Science and Technology,Mianyang 621010,Sichuan,China)
出处
《中国激光》
北大核心
2025年第11期39-47,共9页
Chinese Journal of Lasers
基金
国家自然科学基金(62105271)、四川省科技厅支撑计划(2020YJ0160)、西南科技大学研究生创新基金(24ycx2045)。
关键词
远场超分辨
双焦点聚焦
光学超振荡
空间光调制器
角谱衍射
far-field super-resolution
bifocal focusing
optical super-oscillation
spatial light modulator
angular spectrum diffraction
