Elliptical Zone Plates Research Articles

Novel fabrication and designs for hybrid optical elements with wider angle field of view by using integrated direct laser lithographic system

Hybrid optical elements, which are diffraction pattern arrays fabricated on curved refractive optical elements, have the ability to widen the field of view angle, and improve optical performance, by combining refraction and diffraction. As such, they have high potential in next-generation optical devices. However, manufacturing a high resolution diffraction pattern array that fully covers the curve of the refracted optical surface, so that the normal vectors of every pattern are perpendicular to the tangent plane of the refractive lens surface, is challenging. Furthermore, the lack of diffractive pattern designs corresponding to the curvature makes it difficult to replace curved microlens arrays with hybrid optics. In this study, a direct laser lithographic system combined with an auto-focus system and high accuracy rotational system was built to fabricate the diffractive patterns array on a cylindrical lens. This approach provides a method to manufacture hybrid optical elements with wider field of view. In addition, we proposed novel designs of a linear zone plate (LZP) and elliptical zone plate (EZP) on a cylindrical lens that can be used for focusing light beam into lines and points, respectively. These hybrid optics exhibit superior performance in both diffraction efficiency and resolution, 25% better than traditional diffractive optical elements. An array of two types of zone plates were fabricated fully along the curve of the cylindrical lens using the proposed system, giving a 20° angle field of view, which acts like a curved cylindrical lens array and 1D curved microlens array. The performance of these hybrid optical elements were evaluated by optical verification system and simulation.

Novel fabrication process for an array of elliptical zone plates by using direct laser lithography

An elliptical zone plate (EZP) is used to replace a Fresnel zone plate to focus a light beam when the optical axes of the incident and diffracted beams are not in a straight line. There are two advantages of using an EZP which contributes to improving the performance. First, the residual beam is not focused to the same direction of the main source. Second, the light returning from the focal plane is not directed to the light beam source. In this paper, we propose a method to fabricate an EZP with a direct laser lithographic system. In this paper, three types of writing (lithographic) paths were investigated to study the cause of the appearance of the ablation phenomenon and the side-wing effect. Then, we suggest a suitable fabricated motion to produce a fine EZP. In addition, an experiment setup for an optical evaluation system was introduced to verify the performance of the EZP array fabricated by the selected method.

Nonparaxial anamorphic diffractive lenses

Applications of anamorphic diffractive lenses, or in other words elliptical zone plates, are growing in number and diversity. Following this progress, the manufacturing methods of anamorphic diffractive lenses are also a subject of continuous improvement. On the other hand, their design is still based mainly on the paraxial approximation. In the present paper nonparaxial elliptical zone plates are presented and their difference from the paraxial version, termed as the elliptical aberration is shown. A comparison of their focusing quality was performed based on results of numerical modelling as well as experiments.

Monolithic integration of binary-phase fresnel zone plate objectives on 2-axis scanning micromirrors for compact microscopes

We demonstrated a unique monolithic integration of Fresnel elliptical zone plate (EZP) objective on a 2-axis staggered vertical comb-drive micromirror with 500 μm by 800 μm surface area via direct patterning of reflective binary phase modulation elements on a silicon chip. The need for focusing optics is thus obviated, simplifying the micro-endoscope assembly and improving its form factor. The design of binary phase EZP was guided by simulations based on FFT based Rayleigh-Sommerfeld diffraction model. For dual-axis scanning angles up to 9º by 9º at the image plane, the simulated diffracted Airy disks on a spatial map have been demonstrated to vary from 10.5 μm to 28.6 μm. Micromirrors scanning ±9º (optical) about both axes are patterned with elliptical zones designed for 7 mm focal length and 20þ off-axis 635-nm illumination using 635 nm laser. Videos of samples acquired with ~15 μm lateral resolution over 1mm × 0.35 mm field of view (FOV) at 5.0 frames/second using the device in both transmission and reflectance modes bench-top single-fiber laser scanning confocal microscope confirmed the applicability of the device to micro-endoscopy.

Application of Bragg-Fresnel lenses for microfluorescent analysis and microdiffraction

In creating an X-ray superprobe, the main characteristics are the focus size and the number of photons collected in it (efficiency). In Bragg-Fresnel focusing elements, both characteristics are related to the minimum zone size. However, an increase in the efficiency can be achieved by creating compound elliptical zone plates. To analyze the operation of zone plates of different constructions, an effective program for calculating the image of a point source was developed. The main advantage of the program is a new method for the fast calculation of Kirchhoff integral, detailed description of which is presented in Appendix A. The program allows to obtain a diffraction pattern from real lenses as well as to analyze their changes at different deviations of the lens position from the ideal position with respect to an incident X-ray beam. Different constructions of compound elliptical zone-plates designed on the base of the program and then fabricated are described in the work. The results of using a high-aperture Bragg-Fresnel lens for microfluorescent analysis and microdiffraction are presented.

Astigmatism correction in x-ray scanning photoemission microscope with use of elliptical zone plate

We report the impact of an elliptical, high resolution zone plate on the performance of an initially astigmatic soft x-ray scanning photoemission microscope. A zone plate with carefully calibrated eccentricity has been used to eliminate astigmatism arising from transport optics, and an improvement of about a factor of 3 in spatial resolution was achieved. The resolution is still dominated by the source size and chromatic aberrations rather than by diffraction and coma, and a further gain of about a factor of 2 in resolution is possible. Sub 100 nm photoemission microscopy with primary photoelectrons is now within reach.

Fabrication of holographic microlenses using a deep UV lithographed zone plate

Holographic microlens arrays and elliptical zone plates are fabricated on holographic plates and photoresists by interference between the first- and second-order diffracted waves from an ion etched Fresnel zone plate, which is made by electron-beam scanning and deep UV lithography. This method of fabrication is simple, and a holographic lens with a large numerical aperture and short focal length is obtained. Experimental results of focusing and imaging by a lens array and an elliptical zone plate are given. Two methods of fabricating holographic zone plates for an IR or UV wavelength are also proposed.

One-dimensional image and orthogonal Fourier transform with an elliptical zone plate

An elliptical zone plate is used for imaging along one direction the coherent light distribution and simultaneously obtaining the orthogonal 1-D Fourier transform. Experimental results are shown.

Display of phase-space functions by elliptical zone plates

A coherent processor to display the phase-space functions for 1-D signals is proposed. An elliptical zone plate is used as a single optical element. It is shown that, for a given 2-D input, the output plane shows the 1-D Fourier transform in one direction and the image in the other one. This lensless coherent processor can be used to display the Ambiguity Function, the Wigner Distribution Function and the Local Spectrum for some 1-D functions. Experimental results are presented.

Super Elliptical Zone Plates

The properties of zone plates with different boundary shapes are considered. These shapes are discussed as special cases of the super ellipse. For each case the Fresnel-Kirchhoff diffraction integral is numerically evaluated. It is shown that an elliptical zone plate yields an astigmatic image with axial intensity peaks corresponding to the semi-major and semi-minor axes. In the case of the super ellipse, an additional peak proportional to the square of the diagonal length is obtained. The results were experimentally confirmed in the elliptical case.