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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TL;DR: In this paper, a wave vector integral formula for the half-wave zones of a generalized FZP was derived from the wave vector distribution of the expected focusing beams, and the analytic expressions for calculating the corresponding half wave zones of expected FZPs were derived.
1 citations
TL;DR: In this article , a transport of amplitude into phase (TAP-GSA) algorithm was proposed to design multiplexed phase masks with high light throughput and low reconstruction noise.
Abstract: Fresnel incoherent correlation holography (FINCH) is a well-established incoherent digital holography technique. In FINCH, light from an object point splits into two, differently modulated using two diffractive lenses with different focal distances and interfered to form a self-interference hologram. The hologram numerically back propagates to reconstruct the image of the object at different depths. FINCH, in the inline configuration, requires at least three camera shots with different phase shifts between the two interfering beams followed by superposition to obtain a complex hologram that can be used to reconstruct an object's image without the twin image and bias terms. In general, FINCH is implemented using an active device, such as a spatial light modulator, to display the diffractive lenses. The first version of FINCH used a phase mask generated by random multiplexing of two diffractive lenses, which resulted in high reconstruction noise. Therefore, a polarization multiplexing method was later developed to suppress the reconstruction noise at the expense of some power loss. In this study, a novel computational algorithm based on the Gerchberg-Saxton algorithm (GSA) called transport of amplitude into phase (TAP-GSA) was developed for FINCH to design multiplexed phase masks with high light throughput and low reconstruction noise. The simulation and optical experiments demonstrate a power efficiency improvement of ~ 150 and ~ 200% in the new method in comparison to random multiplexing and polarization multiplexing, respectively. The SNR of the proposed method is better than that of random multiplexing in all tested cases but lower than that of the polarization multiplexing method.
1 citations
05 Mar 2021
TL;DR: In this paper, a five-dimensional imaging technique to resolve objects in three-dimensional space, spectrum and time has been developed using a single diffractive optical element consisting of a quasi-random array of pinholes.
Abstract: A five-dimensional imaging technique to resolve objects in three-dimensional space, spectrum and time has been developed using a single diffractive optical element consisting of a quasi-random array of pinholes. The object space and spectrum were sampled by axially scanning a point object with different wavelengths along the optical axis and recording the corresponding spatio-spectral signatures. The recorded spatio-spectral signatures were catalogued and stored in a library. A thick object emitting light at different wavelengths was placed in the object space within the axial boundaries of the library and illuminated by light sources within the spectral boundaries of the spatio-spectral library and a single object intensity pattern was recorded. The spatio-spectral images of the object were reconstructed by processing the object intensity pattern and the spatio-spectral library in the computer. Depth-wavelength reciprocity was exploited to see colour from depth and depth from colour. A computational approach utilizing the scaling factors in image formation was used to synthesize the spatio-spectral signatures. The application of depth-wavelength reciprocity and the synthesis of spatio-spectral signatures accelerated the training procedure leading to a faster multidimensional multispectral imaging technology in comparison to the existing coded aperture holography techniques. The developed technology was implemented for spatio-spectral-temporal imaging of a fast transient event such as a spark with a temporal resolution of 40 μs. A single camera shot of the spark recorded by a monochrome high-speed camera was converted into intensity cube data along depth for different wavelengths.
1 citations
Cites background from "Quasi-achromatic Fresnel zone lens ..."
...This characteristic is often observed in diffractive Fresnel zone lenses.(34) If the wavelength is increased by a factor, then if the propagation distances u and v are decreased by the same factor, the function IPSF will remain unchanged....
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06 Mar 2023
TL;DR: In this article , a novel computational algorithm based on the Gerchberg-Saxton algorithm (GSA) called transport of amplitude into phase (TAP-GSA), which was developed for multiplexed phase masks with high light throughput and low reconstruction noise.
Abstract: Abstract Fresnel incoherent correlation holography (FINCH) is a well-established incoherent digital holography technique. In FINCH, light from an object point splits into two, differently modulated using two diffractive lenses with different focal distances and interfered to form a self-interference hologram. The hologram numerically back propagates to reconstruct the image of the object at different depths. FINCH, in the inline configuration, requires at least three camera shots with different phase shifts between the two interfering beams followed by superposition to obtain a complex hologram that can be used to reconstruct an object’s image without the twin image and bias terms. In general, FINCH is implemented using an active device, such as a spatial light modulator, to display the diffractive lenses. The first version of FINCH used a phase mask generated by random multiplexing of two diffractive lenses, which resulted in high reconstruction noise. Therefore, a polarization multiplexing method was later developed to suppress the reconstruction noise at the expense of some power loss. In this study, a novel computational algorithm based on the Gerchberg-Saxton algorithm (GSA) called transport of amplitude into phase (TAP-GSA) was developed for FINCH to design multiplexed phase masks with high light throughput and low reconstruction noise. The simulation and optical experiments demonstrate a power efficiency improvement of ~ 150% and ~ 200% in the new method in comparison to random multiplexing and polarization multiplexing, respectively. The SNR of the proposed method is better than that of random multiplexing in all tested cases but lower than that of the polarization multiplexing method.
TL;DR: In this paper, a binary Fresnel Zone Axilens (FZA) is designed for the infinite conjugate mode and the phase profile of a refractive axicon is combined with it to generate a composite Diffractive Optical Element (DOE).
Abstract: A binary Fresnel Zone Axilens (FZA) is designed for the infinite conjugate mode and the phase profile of a refractive axicon is combined with it to generate a composite Diffractive Optical Element (DOE). The FZA designed for two focal lengths generates a line focus along the propagation direction extending between the two focal planes. The ring pattern generated by the axicon is focused through this distance and the radius of the ring depends on the propagation distance. Hence, the radius of the focused ring pattern can be tuned, during the design process, within the two focal planes. The integration of the two functions was carried out by shifting the location of zones of FZA with respect to the phase profile of the refractive axicon resulting in a binary composite DOE. The FZAs and axicons were designed for different focal depth values and base angles respectively, in order to achieve different ring radii within the focal depth of each element. The elements were simulated using scalar diffraction formula and their focusing characteristics were analyzed. The DOEs were fabricated using electron beam direct writing and evaluated using a fiber coupled diode laser. The tunable ring patterns generated by the DOEs have prospective applications in microdrilling as well as microfabrication of circular diffractive and refractive optical elements.
Cites background from "Quasi-achromatic Fresnel zone lens ..."
...s the ring pat tion results dium Tin O ickness of 6 patterning.(5) chosen for lcohol in th zed water....
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References
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TL;DR: In this paper, a phase Fresnel lens is inserted in the pupil of the optical system to deform the wave surface passing through an optical system by the amount ϕ(u,v).
Abstract: In order to deform the wave surface passing through an optical system by the amount ϕ(u,v), it is suggested that a phase Fresnel lens be inserted in the pupil of the optical system. Assuming 0⩽ϕ(u,v)
189 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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TL;DR: The purpose of this paper is to show that when a lens-axicon combination is illuminated by a Gaussian beam, the transverse distribution of the focal ring is also aGaussian distribution.
Abstract: An axicon and a lens are combined to form an optical system producing a ring-shaped pattern. The purpose of this paper is to show that when a lens-axicon combination is illuminated by a Gaussian beam, the transverse distribution of the focal ring is also a Gaussian distribution. The typical width of this distribution was found to be, in the case of the lens-axicon combination, 1.65 times greater than the typical width of the Gaussian beam obtained by focusing the same beam using the lens alone. This focusing system is well suited for the drilling of good quality large diameter holes using a high power laser beam.
144 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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Journal Article•
127 citations
TL;DR: In this paper, the Fraunhofer and Fresnel diffraction patterns produced by a thin linear axicon when it is illuminated by a plane wavefront were determined, and an interferometric method of recording zone plates using linear axicons was presented.
Abstract: We determine the Fraunhofer and Fresnel diffraction patterns produced by a thin linear axicon when it is illuminated by a plane wavefront. An interferometric method of recording zone plates using linear axicons is presented.
70 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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