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Proceedings Paper

Dimensional metrology for the fabrication of imaging optics using a high accuracy low coherence interferometer
Author(s): Rainer Wilhelm; Alain Courteville; Fabrice Garcia
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Paper Abstract

This paper presents a fibre-based low coherence interferometric sensor developed by FOGALE nanotech. Based on the well-established principle of low coherence interferometry the sensor works as a comparator of optical path lengths. The optical path length in the measurement interferometer arm containing a target object is compared with the optical path length in an internal delay line. Multiple, partially reflecting surfaces of the target can be detected during one scan of the delay line. Measurement ranges are between a few mm up to 400 mm (optical thickness). The measurement zone can be placed at a distance of up to several meters away from the instrument's exit. The sensor reaches an absolute accuracy down to 100 nm over the full measurement range. The system has been applied both for the glass and for the optical industry. This paper focuses on innovative applications of the sensor in the optics manufacturing industry. First, the measurement technique and the system concept including the detection scheme and signal processing are explained. We present a modeling-based approach for the dimensional metrology of optical components (e.g. single lenses, windows, prisms) or complete lenses where the positions of all individual elements can be detected. A comprehensive propagation model including dispersion and phase effects is used to extract the distances from the optical path differences. Prior to a measurement, the optimum tailoring of the measurement beam is obtained by a simulation of the beam propagation through the target object. This ensures that each surface to be measured delivers a sufficiently strong signal. To illustrate our approach we present its successful application in the fabrication process of high-performance imaging optics.

Paper Details

Date Published: 13 June 2005
PDF: 12 pages
Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005); doi: 10.1117/12.612563
Show Author Affiliations
Rainer Wilhelm, FOGALE nanotech (France)
Alain Courteville, FOGALE nanotech (France)
Fabrice Garcia, FOGALE nanotech (France)


Published in SPIE Proceedings Vol. 5856:
Optical Measurement Systems for Industrial Inspection IV
Wolfgang Osten; Christophe Gorecki; Erik L. Novak, Editor(s)

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