Phase shifted Fresnel axicon: erratum
TL;DR: The acknowledgement in the Letter “Phase-shifted Fresnel axicon” [Opt Lett 37, 1980 (2012)] was incomplete and is therefore corrected in this erratum as discussed by the authors.
Abstract: The acknowledgement in the Letter “Phase-shifted Fresnel axicon” [Opt Lett 37, 1980 (2012)] was incomplete and is therefore corrected in this erratum
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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.
17 citations
TL;DR: In this paper, a comparison of the beam generated by different beam generation and focused ion beam milling methods is presented. And in order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.
Abstract: Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory, several functions can be combined, the efficiency is reduced with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 μm limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. Two different techniques, namely, a modulo-2π phase addition technique and an analog technique for design and fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. In order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.
15 citations
15 Jun 2015
TL;DR: In this article, the phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an element labelled as conical FZL, which can generate a focused ring pattern at the focal plane of the lens.
Abstract: The phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an element labelled as
conical FZL, which can generate a focused ring pattern at the focal plane of the FZL. The phase integration is achieved
by modifying the location and width of zones of FZL in accordance with the phase variation of the negative axicon. The
element was designed for a high power laser with a wavelength of 1064 nm, focal length and diameter of conical FZL of
30 mm and 8 mm respectively and for a ring diameter of 50 μm. The element was fabricated using photolithography. The
pattern was transferred from the resist layer to the borosilicate glass plates by dry etching to achieve an etch depth of
1064 nm. The etch depth measured using confocal microscope was 1034 nm at the central part and 930 nm for the
outermost part of the device with a maximum error of 12.5% at the outermost part and 3% at the central part. The
element was used in an optical trapping experiment. The ring pattern generated by the conical FZL was reimaged into the
trapping plane using a tightly focusing microscopic objective. Polystyrene beads with diameters of 3 μm were
suspended in deionized distilled water at the trapping plane. The element was found to trap multiple particles in to the
same trap.
6 citations
Additional excerpts
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TL;DR: In this article, a focused ion beam system (Nova Nanolab 600 from FEI) was used to write diffractive optical elements (DOEs) directly on a single mode fiber tip.
Abstract: In the past, UV lithography has been used extensively for the fabrication of diffractive optical elements (DOEs). The advantage of this technique is that the entire structure can be written at one time, however, the minimum feature size is limited to about 1 μm. Many 1-d and 2-d periodic grating structures may not need such fine details but it is essential for diffractive optics with circular structures. This is because the spacing between features typically decreases towards the edge of the element resulting in the smallest feature falling well below 1 μm. 1-d structures such as sub-wavelength gratings will also have smaller feature sizes throughout the structure. In such cases, advanced techniques such as Focused Ion Beam and Electron-beam Lithography are required for the fabrication of finer structures. In this paper, we present results of DOEs fabricated with a focused ion beam system (Nova Nanolab 600 from FEI) directly on a single mode fibre tip. The ability to write DOEs directly on fibre tip is of great importance in fields such as endoscopy and optical trapping. The DOE itself, transforms the laser beam to a phase and intensity profile that matches the requirement. Because it is located directly on the fibre, no extra alignment is required. In addition, the system becomes more compact, which is especially important for applications in the field of endoscopy. The main goal of the present work was to develop the most accurate method for creating the desired pattern (that is, the DOE structure) into an actually working element. Different exposure strategies for writing test structures directly with the ion beam on the fibre tip have been tested and carefully evaluated. The paper will present in detail the initial fabrication and optical test results for blazed and binary structures of 1-d and circularly symmetric Fresnel axicons on optical fibres.
6 citations
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 "Phase shifted Fresnel axicon: errat..."
...In Diffractive Optical Elements (DOEs), it is possible to integrate multiple functions in a single element.(4) Hence, single DOEs capable of generating focused ring patterns were designed using different techniques(5,6), fabricated and high quality ring patterns were generated....
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References
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TL;DR: An optical element: a phase-shifted Fresnel axicon for generation of multiple Bessel beams by giving a binary phase modulation to the standard Fresnels axicon is generated.
Abstract: We propose an optical element: a phase-shifted Fresnel axicon for generation of multiple Bessel beams. By giving a binary phase modulation to the standard Fresnel axicon, the proposed element is generated. The phase profile of the binary phase modulation is engineered to generate two and three Bessel beams of equal intensities. This composite optical element is fabricated using electron beam direct writing. The performance of the fabricated device is evaluated using a semiconductor laser, and the generation of two and three Bessel beams is successfully demonstrated.
8 citations