Integrated Optomechanical Analysis

Excerpt

The numerical simulation of optical performance is typically a multidisciplinary effort comprising thermal, structural, and optical analysis tools. Performing detailed design trades such as computing optical performance as a function of temperature and mounting configuration requires the passing of data between the various models. In addition, it is common to develop finite element models to determine the thermal and structural response of an optical instrument due to environmental factors. The goals of this text are twofold; the first is to present finite element modeling techniques specific to optical systems and second, to present methods to integrate the thermal and structural response quantities into the optical model for detailed performance predictions.

The first two chapters provide a review and act as reference material for the rest of the chapters. The first chapter reviews mechanical engineering basics and finite element theory. Included in this section are the equations of elasticity, fracture mechanics, failure theories, heat transfer, structural dynamics, and a discussion on finite element modeling issues. The second chapter discusses optical fundamentals, optical performance metrics, and image formation. Included are discussions on polarized light, wavefront error, diffraction, the point spread function, and the modulation transfer function. Also presented is the use of orthogonal polynomials such as the Zernike polynomials to represent optical surface data.

Finite element model construction and analysis methods for predicting displacements of optical elements and support structures are discussed in Chapter 3. Topics include modeling methods for individual optical components, adhesive bond models, surface coating effects, flexure mounts, test supports, and assembly processes. The next two chapters discuss methods of integrating structural and thermal response quantities into the optical model and their effects on optical performance. Chapter 4 presents methods to integrate rigid-body errors and optical surface deformations, predict optical errors due to stress birefringence, compute line-of-sight jitter, and predict the effect mechanical obscurations have on image quality. Optothermal analysis methods are discussed in Chapter 5, including thermo-elastic and thermo-optic modeling techniques. Also discussed are methods to model bulk volumetric absorption, map temperatures from the thermal to structural model, and to account for moisture effects and adhesive curing.

Chapter 6 provides an introduction to the analysis of adaptive optics. Concepts and definitions including correctability and influence functions are discussed. Also, the mathematics to compute actuator inputs to minimize optical surface deformations are presented along with examples. Chapter 7 discusses structural optimization theory and applications, including the use of optical responses as constraints in structural optimization models, and an application of multidisciplinary optimization is reviewed. In Chapter 8, a simple telescope serves as an example for many of the analysis techniques discussed in earlier chapters. Model and results files are included in electronic format on a CD so that readers can review specific details of input and output and even run the example cases as desired. In Chapter 9, an integrated optomechanical analysis of a lens assembly is presented. Thermal, structural, and optical analyses are demonstrated to compute the change in focus, wavefront error, the point spread function, and the modulation transfer function as a function of laser power.

Keith B. Doyle

Victor L. Genberg

Gregory J. Michels

September 2002