# Quasi-achromatic Fresnel zone lens with ring focus.

TL;DR: Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL, which is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not.

Abstract: The phase of a standard Fresnel zone lens (FZL) is periodically modulated in the radial direction using the phase of a binary fraxicon. The resulting element (rf-FZL) focuses light into a ring. The ring is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not. The binary rf-FZL is fabricated using electron beam direct writing. Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL. An efficiency of 24% was obtained. The variation in radius of ring pattern was reduced from 61 μm to less than 10 nm for a corresponding wavelength variation from 532 to 633 nm.

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##### Citations

16 citations

### Cites background from "Quasi-achromatic Fresnel zone lens ..."

...Quasi-achromatic lenses with capabilities to change focal distance by changing wavelength wavelength have been investigated [7]....

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### Cites background from "Quasi-achromatic Fresnel zone lens ..."

...Therefore, the increase in diffraction angle of the spiral axicon and the decrease in focal length of the FZL cancel each other out, resulting in a wavelength independent diameter of the flower-like pattern.(33) The wavelength dependency is analyzed for a variation of wavelength by 50 nm for Λ 1⁄4 190 μm....

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...The combination of a binary axicon with a binary FZL enables the wavelength independent ring diameter property.(33) As seen earlier,(33) when the wavelength changes, the diameter of the irradiance profile remains constant although there is a shift in the focal plane position....

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..., and Ba 832 (1-9) (20 con: a new l ical FZL....

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##### References

183 citations

### "Quasi-achromatic Fresnel zone lens ..." refers background in this paper

...A FZL is designed to be a phase-only element [1,19] in the u − v configuration [18] for the phase condition shown in 1559-128X/14/091970-05$15....

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135 citations

### "Quasi-achromatic Fresnel zone lens ..." refers background in this paper

...65 times the diffraction-limited value [5]....

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...Therefore, axicons are normally used together with a lens [5,7]....

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126 citations

68 citations

### "Quasi-achromatic Fresnel zone lens ..." refers background in this paper

...A binary fraxicon (BF) with a period of Λ can generate a ring pattern [6,9]....

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