Today's customer is concerned with cost reduction programs and many "grade" their suppliers by their contribution the these programs. Actually, the time to cost reduce is in the design phase, not after production has begun. To assure the most moldable and least cost part, the customer and supplier should begin discussions early in the design process when there is the opportunity to change things.
Versatility, low cost, limited materials, and unfamiliar manufacturing and assembly processes generate opportunities, obstacles and confusion in the transition from glass to high volume plastic lens assemblies. From concept to final assembly, many factors must be considered. Different experiences and capabilities lead to different preferences among injection molding shops for materials, surface types, mechanical features, doublet assembly, subassembly processes, vacuum coatings, final assemblies, etc. Because the low cost and great versatility of polymer optics make them very attractive, care must be taken to ensure that appropriate quality standards can be met. The authors' experiences are drawn upon to address a number of such issues, from design through assembly and testing, from manually stuffed clam shells and tubes to diffractive optical element eyepieces and robot assembled endoscopes.
Kodak Optical Products has embarked on a journey that will ultimately lead to manufacturing excellence and total customer satisfaction. With quality as our compass we have already obtained ISO 9001 and Manufacturing Resource Planning (MRP) II certifications. Seeking and attaining these certifications enabled us to understand and enhance fundamentals relative to the operation of our business. This has provided a solid foundation from which we can launch continuous improvement activities. Now we continue our journey to such destinations as 10X reduction in both defects and cycle time, measuring and reducing our cost of poor quality, and upgrading our quality information system. Our presentation will emphasize our 10X improvement process and how it applies to high-volume production of precision plastic optics.
A precisely modeled acrylic lightpipe is combined with micro-structured films, reflective films, adhesives, and other mechanical components in the construction of a thin, high performance LCD backlight. We focus here on the manufacturing issues associated with the injection molded lightpipe.
Various methods of manufacturing are reviewed for large area (6 inch diameter and greater) microstructured optical components that are used for light management in non-imaging applications. All of the manufacturing methods discussed will relate to the processing of various optical grade polymers. This paper will start with a review of the traditional methods used to make plastic Fresnel lenses over the past forty or more years. The evolution of precision compression molding will be analyzed. Quality/cost trade-offs of the various methods currently used to produce large-area, thin cross-section, microstructured optical components will be discussed. Examples of products made by compression molding, transfer molding, hot stamping, thermal and UV casting and other various processing methods will be discussed. The paper will conclude with a look into the future. Where is non-traditional, non- glass optical component manufacturing technology headed?
With the advent of low-cost electro-optic components such as LEDs, laser diodes and CCD imaging devices, the cost and performance demands now fall upon the optical subsystems in order to achieve realistic marketing targets for many emerging commercial and consumer products. One of the many benefits of injection-molded plastic optics is the diversity of features that are available to the design team. Once designed and incorporated into the tooling, many features are virtually free in high-volume production. These features can include mechanical details as well as optical functions. Registration features can be included for precisely positioning optical elements to one another or to other assemblies such as printed circuit boards or housings. Snaps, compression features, spring-loading elements, standoffs, self-tapping screws or ultrasonically weldable features can greatly facilitate ease of assembly.
This paper is a general overview of optical coatings and optical coating processes for plastic. It details the basic operations and concepts in these areas. A description of coating methods, properties and possible uses are presented.
Diffractive optics technology offers optical system designers new degrees of freedom that can be used to optimize the performance of optical systems. The zone spacing of a diffractive lens can be chosen to impart focusing power as well as aspheric correction to the emerging wavefront. The surface (or blaze) profile within a given zone determines the diffraction efficiency of the element, or in other words, determines how the incident energy is distributed among the various diffraction orders. Unless the zone profile is generated with high fidelity, incident energy will be distributed into extraneous diffraction orders, which generally reduces the optical system performance. Several diffractive optical components have been fabricated using replication techniques that provide high-efficiency and accurate wavefront generation. Typical minimum efficiency measurements at the design wavelength for diffractive zone spacings greater than 10 micrometers are 95% or above. For minimum zone features as small as 5 micrometers , the measured efficiency is greater than 85% at the design wavelength. The integrated diffraction efficiency, which is a weighted measure of the efficiency across the clear aperture, is typically 2 - 3% more than the efficiency measurement at the minimum feature.
Application of molded plastics to precision optical systems has required significant advances in both the design and fabrication of these optical components. Tighter fabrication tolerances and improved transmitted wavefront quality are being achieved with each passing year. Recently, interest has focused on the particular challenge of injection molded diffractive optic structures. Binary optics are generated using VLSI techniques of microlithography and dry etching to produce a diffractive structure with submicron accuracy. The cost incurred in wafer scale fabrication of individual elements is quite high. By precise mastering, detailed mold design and careful process control, binary optics can be successfully replicated in plastic materials allowing significantly lower costs. This paper will address three specific applications of mass produced diffractive structures. A hybrid refractive/diffractive lens has been designed and produced in acrylic; a set of complex diffractive fanout gratings has been produced in acrylic, polycarbonate, polymethylpentene, and cyclic olefin copolymer; and a diode laser collimator/corrector has recently been successfully molded in polycarbonate. Detailed results highlighting the fidelity of the replicated surface will be included.
Binary optical elements are finding increased use in a wide range of applications. Fabrication of binary optical elements generally remains a time consuming and expensive process. Even in high volume, costs can be prohibitive, especially for elements larger than a few millimeters in diameter. Replications techniques, such as injection molding, have recently begun to show promise as a means of manufacturing binary optical elements, and doing so at a significant cost reduction over conventional photolithographic means. We report on recent improvements in the application of injection molding techniques to the replication of binary optical elements. Several examples of binary elements fabricated by these techniques, as well as present process capability, will be discussed.
Diffractive optics allow for increased optical performance, decreased size and weight, and decreased systems costs in numerous applications. Many types of optics can be fabricated using diffractive surfaces which are not possible, or not cost competitive, using standard refractive lenses. Diffractive optics technology has been developed at Kodak to the point where low cost, mass produced, plastic-molded diffractive optics are available on a commercial basis. Rotationally symmetric, aspheric, refractive/diffractive hybrid lenses have been injection molded in 100,000 part test runs and the lenses demonstrated consistent quality throughout the test. In this paper we will discuss design, analysis, and fabrication of diffractive optics for some typical applications. These applications include diffractive hybrid achromats for visual applications, such as fixed focus and zoom camera lenses, achromatized laser diode objectives, asymmetric anamorphic concentrating and spectral filtering lenses for rangefinding and autofocus applications, the use of diffractive optics in high quality, grayscale laser writers as beam deflectors and F(theta) lenses. Kodak's diamond turning capability for fabricating diffractive optics and our capacity for fabricating plastic injection mold tooling utilizing diamond turning is discussed. Finally, a discussion of our meteorology technology for examining diffractive surfaces will be discussed.
A symmetric two element, 10X eyepiece has been designed using a combination of refractive and diffractive surfaces. Each element consists of a diffractive and refractive surface to form a hybrid optic. The symmetry of the design combined with loose manufacturing tolerances provides an extremely cost effective approach to obtaining high-quality imaging. The diffractive surfaces achromatize the design which enables manufacture with a single optical material. During injection molding production of the hybrid element, the measured diffraction efficiency at the edge of the clear aperture ranges between 96 - 98% at the design wavelength of 558 nm. The lateral color, which is a critical aberration to correct in high- performance eyepieces, has been measured for the hybrid design and found to match within 1.2 micrometers of its theoretical value.
We discuss the design of CCD imaging lenses with hybrid diffractive/refractive optics. The hybrid lenses are made of optical grade plastic materials. We have been able to significantly reduce the number of elements while maintaining very high optical quality. This paper describes the conception, design and development of hybrid lenses which combine excellent optical quality with low manufacturing costs. The new lens has high resolution, ultra-low geometric distortion, very light weight and low production cost.
Precision plastic optical systems frequently depart from traditional design geometries and often require unusual design methods to incorporate mechanical structures with optical surfaces, to evaluate radiometric performance, or to study stray light issues. This paper discusses modeling techniques that have been used successfully to design and analyze several unusual plastic optical systems. Examples include use the of non-sequential ray tracing in conventional optical design programs as well as solid-model-based design programs for the purposes of evaluating stray light and radiometry features associated with integrated optical and mechanical surfaces in molded components.
One of the many benefits of injection-molded plastic optics is the diversity of optical elements that can be incorporated into a design. Aspheres, toroids, irregular apertures and stops, prismatic and diffractive elements are available to the designer with little impact on high- volume production costs. By utilizing off-axis design and total internal reflection (TIR), a series of optical functions can be integrated into an inexpensive, compact unitary structure that can simulate complex conventional optical systems or subsystems. An examples of this philosophy is presented in the form of a fingerprint scanner that includes the entire optical system in a single molded element; accepting radiation from a light-emitting diode, relaying it to an integral fingerpad, and on to a CCD imaging device. The entire structure measures approximately 1 by 3 inches by 1/2 inch thick. It incorporates two off-axis aspheres, three planar TIR surfaces, and two reflective toroids with intermediate aperture stops. The resolution of the system exceeds that of the CCD in center field. The higher-order curvatures of the various elements were played off against one another to minimize distortion resulting from the off-axis design.
An injection molding process development has been conducted to demonstrate the feasibility of manufacturing, by injection molding, mirrors with sufficient surface accuracy for utilization in laser printers and mechanical stiffness for ease of assembly.
With the proliferation of aspheric and unusual optical surfaces in many optical systems, manufacturers are finding that conventional optical metrology methods are no longer suitable when characterizing these systems. For example, monochromatic interferometric measurements of individual components are being replaced by methods which determine system performance by analyzing the actual image produced by the optical system. This presentation will cover MTF and how it is used to characterize optical assemblies and systems employing unusual optical components.
This paper describes a machine vision based technique to measure the profile of small aspheric convex optics. The proposed technique uses a video camera to view the horizontal profile of convex optics. A vision processor captures the image and calculates the best-fitted surface profile expression and related parameters based on a priori knowledge of the lens. This technique offers an efficient and easy way to measure small aspheric optics in manufacturing environment.
This paper introduces an optimization method of precision aspheric lenses for advanced small sensor heads of large numerical aperture. The approach is different from the numerical method adopted in commercial software packages. Analytically optimized results of an aspheric lens of large numerical aperture are obtained from solving differential equations strictly bounded by the condition of minimum angle of divergence and without spherical aberration. It is concluded that the optimized lens of a certain type, with minimum power losses and minimum angle of divergence, uniquely depends on the refractive index of the plastic or glass material. Criteria of manufacturing aspheric lenses in different types according to the indexes are given in the paper as well. Considering the difficulty of fabricating a lens module with two aspheric surfaces, a simplified ideal form of an aspheric lens is also proposed in this paper. Obviously, the optimized results allow more tolerances especially in manufacturing integrated plastic optics with an electrooptic device. It is proved to be useful as a tool in precision optical design software packages.
Optical and therefore nontactile 3D-measurement techniques are of increasing interest in industrial automation, especially in quality control and guidance of automotive vehicles. In connection with these demands, a new type of optical modulator jacketed in rotational plastic optics is introduced in the paper. Furthermore first results obtained by simulation studies will be presented. A simple nevertheless effective way of obtaining 3D information is to illuminate the whole 3D object or scene simultaneously with rf-modulated light. This can be well achieved by using the suggested optical modulator that incorporates the properties of a high aperture and minimum aberration in the 3D-imaging process. The mentioned modulator makes use of the effect of Frustrated Total Reflection (FTR). To exploit this FTR effect in an optical 2D mixer, the gap width between media of higher dense has to be modulated by an rf-voltage applied to a piezo crystal as an rf-controlled tuning medium. Considering the limited modulation bandwidth due to the parasitic capacity of the piezo crystal, the geometrical dimension of the modulator must be made as small as possible. Therefore the spot of the light is collimated at the focal point of the jacketing rotational ellipsoid. The integrated component made of plastic optics and piezo crystal plays a substantial role for the optical modulation and imaging. Some simulation results of this optical device show that the inherent non-linearity of the FTR modulator may be neglected in practical applications, thus yielding a high modulation depth. Furthermore, a 3D-image system adopting this plastic-made optics is also depicted in the paper, which is robust and handy for several industrial applications.
Injection and embossing is an economical method of producing HOE (holographic optical element) in large or small quantities and variable types. We use CIM (computer integrated manufacturing) system to obtain the proper parameters of the manufacturing system. The CAEMOLD computer simulation software and photoelasticity measurement can assist in calculating and modifying injection and embossing process. These technique can obtain the uniform distribution and lower value of residual stress in the plastic HOE product from the results of the computer simulation.
We demonstrate that transmission kinoforms for visible light applications can be injection molded in acrylic in production volumes. A camera is described that employs molded Fresnel lenses to change the convergence of a projection ranging system. Kinoform surfaces are used in the projection system to achromatize the Fresnel lenses.