Mechanical stress in transmissive optical elements causes index of refraction changes in the optical material. This effect, known as the stress optic effect, results in wavefront and polarization errors in the optical system. In addition, temperature changes alter the index of refraction of optical materials affecting the system’s optical performance. Both temperature changes and stresses are an issue for many applications including systems for optical lithography, data storage, LCD projection, and telecommunications.

SigFit allows engineers to convert the stress and temperature predictions from a finite element model into average optical path difference, birefringence, and crystal axis orientation for import to optical analysis. An example of such an analysis is shown at the left. The deformations, temperatures, and stresses due to absorption of the transmitted light in a lens barrel are predicted by a finite element analysis. With SigFit the optical surface deformations are characterized by the motions and Zernike polynomials for each lens surface. Additionally, the effects due to the temperature changes and stresses are formatted into optical path difference maps in Zernike polynomial format. All of these description were imported into optical analysis software to generate the modulation transfer function shown.

If polarization were important for this application, then the birefringence and crystal axis orientationdue to the stress birefringence can be generated for import into CODEV.