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Design and analysis of a micro-optical speckle displacement sensor

: Schreiber, P.; Zeitner, U.D.


Sasian, J.M. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Novel optical systems design and optimization V : 9 July 2002, Seattle, USA, Fifth Conference of Novel Optical Systems Design and Optimization
Bellingham/Wash.: SPIE, 2002 (SPIE Proceedings Series 4768)
ISBN: 0-8194-4535-5
Conference on Novel Optical Systems Design and Optimization <5, 2002, Seattle/Wash.>
Conference Paper
Fraunhofer IOF ()
micro-optical speckle displacement sensor design; reference beam interference; back-scattered speckle light; moving surface; inspection; incremental sensor; special pattern; arbitrary surface; design goal; micro-optical system; injection-molded plastic component; replicated grating; lithographic technology; ray tracing; design layout; laser diode module; beam splitter grating; refocusing optic; geometric optic; first order design; buried reflection beam splitter grating; diffractive optic design tool; maximum efficiency; diffraction orders; aberration; scattering surface; displacement sensing; system tolerancing; wave-optical modelling; changing interference signal

The presented displacement sensor is based on the interference of a reference beam and the back-scattered speckle light from the moving surface under inspection. In contrast to incremental sensors this system works on nearly arbitrary surfaces without any special patterns. The design goal is a micro-optical system assembled with injection-molded plastic components and replicated gratings manufactured with lithographic technologies. The system design starts with ray tracing for the layout of the laser diode module, the beam splitter grating and the refocusing optics. After this geometric optics first order design the profile of the buried reflection beam splitter grating is optimized with special diffractive optics design tools to achieve maximum efficiency in the required diffraction orders. The evaluation of the design is carried out mainly under two aspects: First part of analysis deals with investigation of aberrations and system tolerancing by ray tracing. The second part concentrates on wave-optical modeling of the changing interference signals, caused by the movement of the scattering surface.