Homodyne displacement measuring interferometer probe for optical coordinate measuring machine with tip and tilt sensitivity

Sam C. Butler, Michael A. Ricci, Chen Wang, Qun Wei, Jonathan D. Ellis

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


In this proceedings, we present a 3DoF (one linear, two angular) optical probe for measuring freeform optics in conjunction with an optical coordinate measuring machine (OCMM). This probe uses homodyne interferometry in a Michelson configuration and position sensing detection to simultaneously measure displacement, tip, and tilt. The goal of this work is to investigate point-to-point methods for measuring freeform optics and establish a probing methodology that can perform self-alignment with respect to the local optical surface. We present the design and preliminary benchtop validation of the probe's performance. Benchtop validation shows successful measurements with 5 nm linear and 20 μrad angular noise levels, with a 15 μm spot size. A CMOS sensor is used for visual confirmation of proper focus on measurement surface to minimize initial defocus error. A PSD detects linear horizontal and vertical displacement of the reflected beam from the measurement surface using autocollimation. In-phase and quadrature signals are measured by two photodetectors and post-processed to obtain displacement information. Periodic error caused by polarization effects and beam mixing is compensated by FPGA-based signal processing.

Original languageEnglish (US)
Title of host publicationOptifab 2015
EditorsSebastian Stoebenau, Julie L. Bentley
ISBN (Electronic)9781628418385
StatePublished - 2015
EventOptifab 2015 - Rochester, United States
Duration: Oct 12 2015Oct 15 2015

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOptifab 2015
Country/TerritoryUnited States


  • 3DOF
  • angular interferometry
  • displacement measuring interferometry
  • freeform metrology
  • homodyne interferometry

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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