Simulation of grating interferometers and optical encoders using hybrid ray-trace/wavefront methods

Scott L. DeVore

doi:10.1117/12.455997

25 October 2002 Simulation of grating interferometers and optical encoders using hybrid ray-trace/wavefront methods

Scott L. DeVore

Proceedings Volume 4772, Electro-Optical System Design, Simulation, Testing, and Training; (2002) https://doi.org/10.1117/12.455997
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

Abstract

Optical linear displacement encoders are frequently used to measure and control the motion of high-precision machine tools and measurement systems. The encoder scales are typically fabricated as diffraction gratings, where the period of the grating is determined by the required resolution and other system design requirements. Coarse gratings - with a period of ~10 um - rely on incoherent sources and Talbot imaging to relay the moving scale pattern to a detector array without using lenses. Higher resolution encoders use finer encoder pitch (<1 um) and laser sources to form grating interferometers which can detect scale displacement to a resolution of better than 10 nm. In all cases, scale motion is detected by measuring interference between wavefronts diffracted by the scale. Although the first-order design of such systems is well understood, the need for high resolution and accuracy demands a detailed understanding of higher order effects resulting from misalignment, aberrations, coherence, and other physical optics effects. In this paper, we show how simulation methods based on wavefront models derived from ray-trace data can provide a detailed and accurate prediction of how system performance depends on a wide variety of design and construction parameters. The resulting simulation is a useful tool for optimizing encoder designs and establishing fabrication and alignment tolerance budgets.

Citation Download Citation

Scott L. DeVore "Simulation of grating interferometers and optical encoders using hybrid ray-trace/wavefront methods", Proc. SPIE 4772, Electro-Optical System Design, Simulation, Testing, and Training, (25 October 2002); https://doi.org/10.1117/12.455997

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KEYWORDS

Sensors

Computer programming

Diffraction gratings

Diffraction

Geometrical optics

Head

Interferometers

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