Conformal optics

(optics) The design of optical systems whereby the shape of the outer surfaces is chosen to optimize the interaction with the environment in which the optical system is being used.

Conformal optical systems have outer surfaces whose shape is chosen to optimize the interaction with the environment in which the optical system is being used. The imaging through such conformal optical windows is likely to suffer from extreme aberration, requiring special techniques for correction. Computer-intensive methods of design, fabrication, and testing of optics have reached a level where the development of cost-effective methods for insertion of these conformal optics concepts into operational systems appears to be practical. See also Aberration (optics).

Important applications of conformal optics are found in missile and aircraft systems. Missiles and aircraft carry optical sensors for imaging, detection, and ranging that must look at the world through the outer skin of the vehicle. Traditionally, the windows for viewing through the skin of missiles and aircraft have had simple optical forms, such as flats or spheres, that enable the optical tracking systems to operate by using well-known technology. But these optically advantageous windows degrade the performance of the vehicle through increased drag, aerodynamic heating, or other undesirable effects. One example is the use of an optical tracker or seeker on the front end of a missile. The use of a conformal window, whose shape conforms more closely to the optimal, pointed ogival shape, reduces the drag of the missile and provides significant gains in the missile's performance. Such ogival shapes produce considerable optical aberration, however (see illustration).

Geometric optics of an optical tracker behind a conformal window that is shaped to provide an improved drag profile for a missile. Paths of rays through the optical system are shown. (a) Side view. (b) Oblique view. (Optical Research Associates)

The approach to design with conformal optics does not call for complete abandonment of current understanding of the image-formation process. Optical design methods are based on the description of the wavefront passing through surfaces by use of numerical ray tracing. The understanding of the aberrations arising at surfaces is obtained from an analytic method for describing the surface and the wavefront to stated levels of accuracy. The aberrations produced by general aspheric surfaces defy simple analytic descriptions but can be obtained by fitting of the numerical ray-tracing results. See also Geometrical optics.