The article explores the possibility of athermalizing a gradient-index (GRIN) lens so that the effective focal length (EFL) of the element remains constant over a change in temperature. This is accomplished by designing the lens so that the surface curvatures and index profile compensate for one another over a change in temperature to maintain constant optical power. The means to determine how the lens geometry and index profile change with temperature for both a homogeneous and radial GRIN are explained. An analytic model for the purpose of identifying athermalized GRIN singlets is described and validated against the previous work in this field. The model is used to identify an athermalized polymer radial GRIN element and compare it with four other polymer elements of the same focal length but different index profiles, including a homogeneous one. Comparison of these singlets in CODE V® optical design software shows that the athermalized GRIN element maintains its nominal EFL over a temperature change the best of the five in the group while the homogeneous element (having no GRIN profile to counteract the effect of temperature on the surface curvatures) has the poorest performance. A numerical model to analyze more complicated GRIN systems is discussed.
Sources of error associated with Single Point Diamond Turning of rotationally symmetric aspheres are examined and mathematically dissected to yield equations in the form of a superposition of errors. The equations are derived from manufacturing process considerations involving CNC machining mechanics or operator observations. The types of errors reviewed here include geometry errors, displacement errors, and dynamic errors but do not include errors associated with thermal gradients.
Micro-Electro-Mechanical Systems or MEMS are becoming increasingly important in several optical applications. In particular, devices composed of an array of active micro-optics can be used for wavefront correction, optical switching, and generic digital light control. Whatever the application, it is important for anyone seeking to employ this technology to use computer modeling to predict the performance of the subsystem that incorporates optical MEMS. In this paper we will show how commercially available software can be used to model these systems using several approaches.
Immediately following an optimization sequence, many designers typically implement sensitivity analysis prior to more intensive tolerance analysis and system error budgeting. This paper proposes a method of automating optical design optimization into a two stage process which incorporates design sensitivity into the optimization process. The first stage consists of the standard optimization approach where the error function is a user defined combination of system performance as well as optical and physical parameter constraints. The second stage amends the error function to include the minimization of incident ray angles on each optical surface as part of the error function. The amendment to the error function in the second stage targets the root mean square of incident angles of sample rays. These rays may typically consist of the marginal ray to the image center, as well as the upper and lower rim rays to the image corner. A priority is placed on reducing large angles as the result of a least squares method. This paper will address the detailed implementation of the proposed approach inside of the optical design program. Practical examples will be presented where the proposed optimization has reduced the system sensitivity to manufacturing errors without substantially effecting image quality. The results of incorporating the amended error function into an automated global optimization approach will be described.
Splines are commonly used to describe smooth freeform surfaces in Computer Aided Design (CAD) and computer graphic rendering programs. Various spline surface implementations are also available in optical design programs including lens design software. These surface forms may be used to describe general aspheric surfaces, surfaces thermally perturbed and interpolated surfaces from data sets. Splines are often used to fit a surface to a set of data points either on the surface or acting as control points. Spline functions are piecewise cubic polynomials defined over several discrete intervals. Continuity conditions are assigned at the intersections as the function crosses intervals defining a smooth transition. Bi-Cubic splines provide C2 continuity, meaning that the first and second derivatives are equal at the crossover point. C2 continuity is useful outcome of this interpolation for optical surface representation. This analysis will provide a review of the various types of spline interpolation methods used and consider additional forms that may be useful. A summary of the data inputs necessary for two and three-dimensional splines will be included. An assessment will be made for the fitting accuracy of the various types of splines to optical surfaces. And a survey of applications of spline surfaces in optical systems analysis will be presented.
The International Optical Design Conference traditionally includes one or more lens design problems for members of the optical design community to consider. This year, the design problem consists of designing a solid glass lens with no intervening air spaces between the first and last surfaces of the lens. This paper summarizes the design solutions submitted, highlights the best designs and considers some interesting points brought to light as a result of the endeavor.
The next generation of space-borne optical sensor will have to meet tight weight limitation, in order to be viable on smaller, less expensive, launch platforms, while supporting a wide range of mission scenarios. Wide spectral coverage, near-diffraction limited visible quality performance, and increased thermal and structural stability are becoming important features for future space-hardware. SiC represents an emerging technology which is gaining wider acceptance as the leading candidate for the next generation of space flight hardware. As a material for all-reflective flight telescopes and optical benches, SiC offers: the lightweight and stiffness characteristics of beryllium; glass-like inherent stability consistent with visible quality performance levels; superior thermal properties down to cryogenic temperatures and in the presence of large thermal gradients; and an existing, commercially based material and processing infrastructure like aluminum. This paper describes an all-SiC off-axis, three mirror anastigmatic telescope system which promises to meet these stressing technical requirements. The system described maintains a 35 cm entrance aperture with a weight of 14 kgs.
Many satellite-borne measurement applications require lightweight, reflective near diffraction limited telescopes with wide spectral bands (UV/visible to LWIR), for operation in space environments and over wide temperature ranges. Emerging silicon carbide (SiC) technology provides an attractive material for these telescope applications. It offers (1) the lightweight and stiffness of beryllium, (2) the diffraction limited visible optical performance of glass, (3) superior thermal stability to cryogenic temperatures, and (4) the cost and rapid fabrication advantages of aluminum. This paper describes the design, development, and test for a 50 cm dia. aperture on-axis imaging SiC telescope, and a 'goes like' 0.5 multiplied by 0.3 m scan flat for a geo-stationary earth observatory (GEO) mission. Optical, thermal, and structural design and analyses are described for the demonstration hardware. The scan mirror and telescope system have been optically tested over the temperature range of plus or minus 50 degrees Celsius. Temperature gradients have been induced on the scan mirror and telescope simulating non uniform thermal loading from the earth and sun. Test results are presented which show the excellent optical/thermal stability properties of SiC.
Many satellite-borne measurement applications require lightweight, reflective near diffraction limited telescopes with wide spectral bands (UV/visible to LWIR), for operation in space environments and over wide temperature ranges. Emerging silicon carbide (SiC) technology provides an attractive material for these telescope applications. The present paper describes the design and analysis of a 50 cm dia. aperture on-axis three mirror re-imaging SiC telescope, including the structure and a 'GOES like' scan flat for the GEO application. Optical, thermal and structural design and analyses are described for the demonstration hardware. Demonstration mirrors and structural hardware have been fabricated, tested and compared to design analyses with excellent agreement.
A 6-inch diameter aperture space-based visible telescope has been optimized to perform surveillance against the space background with earth albedo as a primary source of straylight. A three mirror off-axis anastigmat has been designed to cover a 1.4 degree(s) by 6.6 degree(s) field- of-view with 60 (mu) radian spatial resolution. The telescope body and optics are constructed of 6061-T6 aluminum to provide a thermally stable optical system. The optical elements are 'superfinished' to minimize scatter. Extensive baffles and stops are utilized to further reduce straylight. The telescope will be used on the Midcourse Space Experiment platform.
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