Journal
OPTICS COMMUNICATIONS
Volume 393, Issue -, Pages 72-76Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.optcom.2017.02.031
Keywords
Subwavelength structures; Diffraction; Polarization; Superresolution; Binary optics
Categories
Funding
- National Natural Science Foundation of China (NSFC) [61505158, 51575440]
- China Postdoctoral Science Foundation [2016T90909, 2014M560767]
- Shaanxi
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A new method is proposed for shaping a far-field uniform optical needle based on a regular nanostructured metasurface, viz. high-NA (numerical aperture) micro-Fresnel zone plate (FZP). The designed microstructure is comprised of two planar FZP-fragments with different focal lengths. Delicate interference of diffracted beams results in an optical needle at a required working distance in the post-evanescent field. For a 44.88 gm-diameter microstructure illuminated with a linearly x-polarized beam, a 5.77 lambda-long uniform optical needle is produced at a distance of 12.88 lambda away from the mask surface. The transverse beam sizes are 0.97 lambda and 0.39 lambda in x and y directions, respectively. The designed result calculated by the vectorial angular spectrum theory is in good agreement with the rigorous electromagnetic calculation using the three-dimensional finite-difference time domain (3D FDTD) method. The designed microstructure is easy-to-fabricated with required NA and working distance. The proposed method can be readily modified for other polarized beams. These far-field uniform optical needles potentially suit the fields of nanolithography, optical trapping, and microscopy.
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