GRIN lens and GRIN lens array fabrication with diffusion-driven photopolymer
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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.Keywords:
Gradient-index optics
Optical power
Simple lens
of a dissertation at the University of Miami. Dissertation supervised by Professor Fabrice Manns. No. of pages in text. (112) The human crystalline lens is a complex and intricate structure that continuously grows throughout our lifetime. The crystalline lens has a non-uniform distribution of protein concentrations which produces an optical gradient within the lens in both the optical and equatorial axes. This gradient refractive index is a unique property of the crystalline lens that significantly contributes to its optical power and aberrations. The objective of this dissertation is to gain a better understanding of the relationship between the crystalline lens shape, its non-uniform gradient refractive index, the lens optical power and aberrations, and their changes with accommodation and age. The information acquired in this dissertation will be used to optimize vision correction procedures and to develop a more accurate lens model to predict the power and aberrations of the whole eye. The studies of this project include establishing techniques to quantify the gradient’s contribution to the accommodative amplitude, measuring the optical power and spherical aberration of the lens using laser ray tracing, and developing an enhanced laser ray tracing system which allows for on-axis and off-axis measurements of power and 2-D wavefront aberration maps of the crystalline lens.
Gradient-index optics
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Gradient-index optics
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X-ray optics
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Gradient index materials (GRIN) are defined as those in which the refractive index (n) varies spatially. Lenses possessing both radial and axial gradients of n, because of their unique ability to correct Petzval field curvature and chromatic aberration, are not equivalent to anything in current lens design. We have developed bulk GRIN materials for IR applications based on Ge x Si 1−x and Ge x Si 1−x Te(IV–VI) semiconducting compounds. The Ge x Si 1−x compound has an excellent transparency range, from 1.9 m to over 18 m, and shows no profound absorption peaks. By controlling the solidification parameters, both axial and radial profiles can be varied from linear to parabolic, a considerable departure from the simple law of normal freezing. The maximum gradients of the refractive index (n) in Ge x Si 1−x for radial and axial profiles are equal to 0.2 cm −1 and 0.1 cm −1 , respectively. Although having an inferior transparency characteristic, the Ge x Si 1−x Te compound shows higher n: 0.3 cm −1 and 0.2 cm −1 , respectively. Electrical resistivity () along with microhardness (H) measurements have also been performed. Both radial and axial variations of and H are in excellent agreement with optical tests. A model for the evaluation of the refractive index, resistivity, and microhardness is presented. Expressions interrelating n, and H are derived by using the energy-gap concept as an unified parameter. By measuring either resistivity or micro-hardness profiles, the refractive index gradient can be estimated. Assessments of the applicability and the limitations of the theory are given.
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The human crystalline lens is a layered structure. Unique protein solution in each individual cell layer gives a different refractive index value thus resulting in a gradient index (GRIN) lens. Crystalline lens GRIN not only provides extra optical power for both relaxed and accommodated eyes, but presumably plays an important role in balancing/reducing eye aberrations and maintaining image quality. In existing eye models, the crystalline lens is either treated as a homogeneous lens or a GRIN lens but with two separate GRIN equations for anterior and posterior segment due to its asymmetrical index distribution along the optical axis. In this study, a single continuous GRIN equation with optical power variability is constructed. A dynamic eye model incorporating this equation for various accommodative states is proposed and simulated in CODEV.
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An equation for the distribution of refractive index of a gradient refractive index square lens has been established, and such a lens has been fabricated using ion exchange. The distributions of refractive indices at different angles of incidence are discussed. Experimental and theoretical data are compared and show good agreement.
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Gradient-index optics
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A tunable optofluidic microlens configuration named Liquid Gradient Refractive Index (L-GRIN) lens is described. The variable light focusing is achieved through the diffusion based refractive index gradient within a microfluidic device.
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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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A simple method of constructing 3-D gradient refractive-index profiles in crystalline lenses is proposed. The input data are derived from 2-D refraction measurements of rays in the equatorial plane of the lens. In this paper, the isoindicial contours within the lens are modeled as a family of concentric ellipses; however, other physically more appropriate models may also be constructed. This method is illustrated by using it to model the 3-D refractive-index profile of a bovine lens.
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A novel nondestructive method of measuring the refractive indices and thicknesses of transparent lenses has been developed. Experimental measurements and numerical computations have been complementarily adopted in the paper. Experimentally, five selected lens samples will be used to quantitatively measure the radii of curvature and the best focusing positions on the both surfaces of the lenses. Subsequently, the refractive indices and thicknesses of the lens samples will be obtained through a derived numerical methodology. Such a measurement method of the refractive index and thickness of a lens has not been reported in the past. The results of the measured refractive index and thickness will be identified and compared with the nominal results. The uncertainties for both the refractive index and thickness of the lens will be deduced as well.
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This chapter will discuss on how GRIN (gradient index) can be used to build a collimating lenses. e also discuss what is GRIN and all the advantages that GRIN has which is suitable to be used as a material for a collimated lens compare to all the other types of lenses. A collimating lens is a lens used to collimate light, which is to gather it together in a parallel beam. There are a lot of type lenses to construct a collimating lens which varies from fiber lenses, ball lenses, a spherical lenses, spherical singlet and doublets, GRIN lenses, microscope objectives and cylindrical lenses. Lens materials can vary from glass to plastic to silicon. By a large margin, most of the fiber optic collimators used today are made using GRIN lenses. GRIN lenses are small, easy to handle, relatively low cost, and competitive in optical performance. They do have limitations though. GRIN lenses rarely come in large size and their performance is marginal in the visible spectrum range.
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