Comparison of optical-waveguide lens technologies
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Abstract:
Various materials, lens structures, and processes are examined relative to the lens requirements of an RF spectrum-analyzer implemented through the use of an integrated-optics format. Factors which distinguish optical-waveguide lenses and reflectors from conventional imaging lens systems are enumerated. It is concluded that a thin-film Luneburg lens is the most viable planar approach based upon the use of oxides and, when high refractive-index materials must be employed, the spherical depressed geodesic becomes a feasible alternate.Keywords:
Luneburg lens
Gradient-index optics
Waveguide
A Luneburg lens is described which has been fabricated from foam glass. The electrical performance is presented at X-band. The theoretical power-handling capability of this lens is conservatively estimated at 6 times that of an equivalent lens fabricated from expanded polystyrene.
Luneburg lens
Polystyrene
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Quantitative knowledge of the optical properties of the crystalline lens is essential if one expects to model accurately the optical properties of vertebrate eyes. The gradient of refracting index, GRIN, within the lens is responsible for a large part of the refractive properties of the crystalline lens. It is thus essential that the GRIN profile of crystalline lenses be accurately specified before a satisfactory understanding of the optical properties of vertebrate eyes is attained.
Gradient-index optics
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We present the design, fabrication, and experimental characterization of a modified two-dimensional Luneburg lens based on bulk metamaterials. The lens is composed by a number of concentric layers. By varying the geometric dimensions of unit cells in each layer, the gradient refractive index profile required for the modified Luneburg lens can be achieved. The cylindrical waves generated from a point source at the focus point of the lens could be transformed into plane waves as desired in the microwave frequency. The proposed modified Luneburg lens can realize wide-angle beam scanning when the source moves along the circumferential direction inside the lens. Numerical and experimental results validate the performance of the modified Luneberg lens.
Luneburg lens
Simple lens
Gradient-index optics
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Various aspects of implementing a gradient refractive index distribution using 3D printing are considered. These approaches are applied to two types of lens design: cylindrical Luneburg lens and thick flat lens. Based on simulated and measured results the main constraints for the lens design using additive manufacturing are defined. The novelty of the work consists of the study of the influence of different approaches to the implementation of lenses using additive technologies on the characteristics of the antenna. The approaches for a lens measured as a Luneburg lens and a thick flat lens are compared.
Luneburg lens
Gradient-index optics
Three dimensional printing
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This paper details the design of a printed-circuit-board implementation of a 2D Luneburg lens. The refractive index of the lens is controlled through a combination of meandering crossed microstrip lines and varying their widths. The 12.4lambda o diameter lens is designed to operate in the Transverse Electromagnetic (TEM) mode at 13 GHz. The lens was designed, fabricated, and measured. The measured half power beamwidth of the experimental lens is 5.26deg.
Luneburg lens
Beamwidth
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It is well-known that the conventional lens design suffers from the aberration, which will lead to imperfect imaging. One way to solve this problem is to use gradient index (GRIN) lenses such as Luneburg lens. However, the spherical geometry of Luneburg lens imposes difficulty for manufacturing. Also, it is desired to design the Luneburg lens with arbitrary focal length. To address these issues, in this paper, we propose to apply the transformation optics techniques to the general Luneburg lens design. In this way, the spherical lens surface will be transformed to flattened shapes, which can be practically fabricated on a flat substrate. Specifically, three-dimensional (3D) Luneburg lenses with different focal lengths will be studied. Moreover, discussion on the fabrications of proposed lens has been included. It is desired to ensure that the modified design lies within the available material properties of various polymer photoresists.
Luneburg lens
Gradient-index optics
Transformation Optics
Simple lens
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Luneburg lens
Waveguide
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We introduce a new method to make gradient index (GRIN) lenses and GRIN lens arrays by exposing diffusion-driven photopolymers using a low-power CW laser. By changing the size and power of the laser beam and the exposure time, the index profile of the GRIN lens can be controlled. A novel feature of this process is that the polymer can be cast on both sides of a micro-optic, followed by exposure and diffusion to develop perfectly aligned lenses.
Gradient-index optics
Optical power
Simple lens
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The Wire-Grid Lens Antenna is a unique realization of the Luneburg lens technique for frequencies in and near the HF frequency band. An effective refractive index which varies from the \sqrt{2} at the lens center to a value near unity at the lens edge, is attained by two layers of square-mesh wire grid positioned one above the other. [1],[2] At the center of the lens, the two grids are spaced close together; and at lens edge, the grids are spaced far apart compared to the mesh size of the grid. This paper presents the electromagnetic analysis of the wave propagation within the lens and of the radiation from the lens leading to the calculation of the radiation pattern of the lens. A typical Wire-Grid Lens Antenna is shown in Fig. 1. The inner circle is the lens proper; a flared horn is attached to the lens to provide an impedance match between the lens and free space.
Luneburg lens
Horn antenna
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Various materials, lens structures, and processes are examined relative to the lens requirements of an RF spectrum-analyzer implemented through the use of an integrated-optics format. Factors which distinguish optical-waveguide lenses and reflectors from conventional imaging lens systems are enumerated. It is concluded that a thin-film Luneburg lens is the most viable planar approach based upon the use of oxides and, when high refractive-index materials must be employed, the spherical depressed geodesic becomes a feasible alternate.
Luneburg lens
Gradient-index optics
Waveguide
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Citations (55)