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Generation of a sub-diffraction hollow ring by shaping an azimuthally polarized wave

View Article: PubMed Central - PubMed

ABSTRACT

The generation of a sub-diffraction optical hollow ring is of great interest in various applications, such as optical microscopy, optical tweezers, and nanolithography. Azimuthally polarized light is a good candidate for creating an optical hollow ring structure. Various of methods have been proposed theoretically for generation of sub-wavelength hollow ring by focusing azimuthally polarized light, but without experimental demonstrations, especially for sub-diffraction focusing. Super-oscillation is a promising approach for shaping sub-diffraction optical focusing. In this paper, a planar sub-diffraction diffractive lens is proposed, which has an ultra-long focal length of 600 λ and small numerical aperture of 0.64. A sub-diffraction hollow ring is experimentally created by shaping an azimuthally polarized wave. The full-width-at-half-maximum of the hollow ring is 0.61 λ, which is smaller than the lens diffraction limit 0.78 λ, and the observed largest sidelobe intensity is only 10% of the peak intensity.

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(a) The SEM images of the micro lens, and (b) the zoom-in of the lens central part.
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f4: (a) The SEM images of the micro lens, and (b) the zoom-in of the lens central part.

Mentions: A micro lens was fabricated using electron-beam lithography and dry etching. The detailed geometrical structure of the micro lens is shown in Table 1 in the Supplementary Information. A 500-μm thick sapphire glass was used as the lens substrate. A Si3N4 layer was first deposited on the substrate with PECVD coating, and its refractive index was characterized with ellipsometry, which yielded a refractive index of 1.91. The thickness of this dielectric layer was about 348 nm, corresponding to the relative phase change of π. Dry etching was adopted to form the Si3N4 dielectric ring structures. Figure 4(a,b) shows the SEM images of the micro lens.


Generation of a sub-diffraction hollow ring by shaping an azimuthally polarized wave
(a) The SEM images of the micro lens, and (b) the zoom-in of the lens central part.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120339&req=5

f4: (a) The SEM images of the micro lens, and (b) the zoom-in of the lens central part.
Mentions: A micro lens was fabricated using electron-beam lithography and dry etching. The detailed geometrical structure of the micro lens is shown in Table 1 in the Supplementary Information. A 500-μm thick sapphire glass was used as the lens substrate. A Si3N4 layer was first deposited on the substrate with PECVD coating, and its refractive index was characterized with ellipsometry, which yielded a refractive index of 1.91. The thickness of this dielectric layer was about 348 nm, corresponding to the relative phase change of π. Dry etching was adopted to form the Si3N4 dielectric ring structures. Figure 4(a,b) shows the SEM images of the micro lens.

View Article: PubMed Central - PubMed

ABSTRACT

The generation of a sub-diffraction optical hollow ring is of great interest in various applications, such as optical microscopy, optical tweezers, and nanolithography. Azimuthally polarized light is a good candidate for creating an optical hollow ring structure. Various of methods have been proposed theoretically for generation of sub-wavelength hollow ring by focusing azimuthally polarized light, but without experimental demonstrations, especially for sub-diffraction focusing. Super-oscillation is a promising approach for shaping sub-diffraction optical focusing. In this paper, a planar sub-diffraction diffractive lens is proposed, which has an ultra-long focal length of 600 λ and small numerical aperture of 0.64. A sub-diffraction hollow ring is experimentally created by shaping an azimuthally polarized wave. The full-width-at-half-maximum of the hollow ring is 0.61 λ, which is smaller than the lens diffraction limit 0.78 λ, and the observed largest sidelobe intensity is only 10% of the peak intensity.

No MeSH data available.