Scott W. Sparrold

Conformal dome correction with counterrotating phase plates

Windows and domes that are shaped to aerodynamic requirements can increase range and speed for the host platform. This class of optical systems is referred to as conformal optics. The solution discussed here is intended for conformal missile systems having gimbals that point the optical line of sight through different parts of the dome. A conformal dome induces large amounts of varying aberration, tens to hundreds of waves across gimbal angle, and therefore requires dynamic correction. Space is very constricted in missile sensors, and it is therefore highly desirable to limit the number of motors used for aberration correction. This paper describes the performance of a new class of optical systems that employ counterrotating phase prisms to correct conformal dome aberrations while gimbaling the optical system. The phase surfaces on the prisms are described by Zernike circular polynomials. Since the shear across the phase surfaces is rotational, the only aberrations that are generated are those without rotational symmetry, such as tilt, coma, or astigmatism. Using this approach, CODE V® was used to analyze and design a compact, high-performance conformal optical system.

Conformal dome aberration correction with counter-rotating phase plates

ABSTRACT Domes have been designed that conform to the aerodynamic requirements of airborne systems, as well as the opticalrequirements. Such domes have large amounts of aberrations - lOs to lOOs of waves. Typical systems also have gimbals thatpoint the optical line of sight through different parts of the domes. Aberrations vary significantly with pointing angle andtherefore require dynamic correction. This paper describes the performance of a new class of optical systems that employcounter-rotating phase plates to correct conformal dome aberrations. The correctors are described by Zernike circularpolynomials. Since the shear is rotational, only aberrations with non-rotational symmetry can be created, like coma orastigmatism. A theoretical development shows the relationship between the corrector surface shapes and the aberrationscreated. Code V was used to model the correction capabilities of the angular shear corrector plates.Keywords: conformal optics, dome, window, aberration, correction, phase plate

Capabilites of an arch element for correcting conformal optical domes

This paper presents an approach for correcting conformal missile domes with a non-rotationally symmetric optical element called an arch. A parametric study in terms of aerodynamics, fineness ratio, maximum seeker look angle and dome index of refraction will demonstrate its capabilities for correcting conformal domes. A nomograph for trading optical performance versus relative missile range will also be presented.

Leveraging off genetic algorithms for optimizing AGRIN lenses

While researching various gradient index glass families for superb color correction using ZEMAX1 optical design program, the authors found that certain solutions could only be found using the Hammer routine2. Hammer is a genetic algorithm that breeds a particular lens configuration with variations of itself3. It is not intended to be a global search routine. Hammer is typically used after the best performance is obtained using the standard damped least squares (DLS) algorithm with the default merit function (MF) based on minimizing root mean square (RMS) spot size. Upon this discovery, the authors proceeded to explore the benefit of using the genetic Hammer algorithm on three different lens systems. To make the solution space more complicated, two axial gradient index (AGRIN) elements were used in each lens type; a bi- AGRIN cemented doublet; a bi-AGRIN air spaced triplet with CaF2 as the center element, and a double Gauss with four AGRIN elements and two CaF2 elements. AGRIN elements were used in each lens to provide a more complex solution space and to make optimization more difficult. After optimization, the performance of each lens was compared wiht the conventionally optimized counterpart using the default MF with a DLS algorithm. After this comparison was made, another trade study was done between the Hammer and DLS algorithms, but in this case, the optimization used a custom MF instead of the default MF. The authors believe this study shows the importance of MF construction over that of using the default RMS spot size metric. A significant improvement was obtained for all lenses with the default MF using the Hammer over the DLS technique, but that improvement was less obvious when a custom MF was used.