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Range Sensing Using Dynamic Chromatic Aberration

IP.com Disclosure Number: IPCOM000043436D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Juetz, J: AUTHOR [+3]

Abstract

A method to sense the precise position of a surface over a long working distance utilizes dynamic chromatic aberration. This method is a type of autofocusing scheme. By applying the chromatic aberration property of a focusing holographic optical element (fHOE), the image of an illuminated object point is dynamically shifted along the optical axis according to the varying input wavelength from an illumination source. The position of any surface along this axis is therefore related to the wavelength of maximum reflected intensity, retrocollected and measured at the location of the original object point. This eliminates the need for mechanical motion of a focusing lens back and forth as in conventional autofocusing systems.

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Range Sensing Using Dynamic Chromatic Aberration

A method to sense the precise position of a surface over a long working distance utilizes dynamic chromatic aberration. This method is a type of autofocusing scheme. By applying the chromatic aberration property of a focusing holographic optical element (fHOE), the image of an illuminated object point is dynamically shifted along the optical axis according to the varying input wavelength from an illumination source. The position of any surface along this axis is therefore related to the wavelength of maximum reflected intensity, retrocollected and measured at the location of the original object point. This eliminates the need for mechanical motion of a focusing lens back and forth as in conventional autofocusing systems. The position of the image, as a function of input wavelength, can be derived from the grating equation for a fHOE formed on axis, by a converging and a diverging beam. As shown in Fig. 1, a laser 10 passes a beam 12 through a beam splitter 14 to provide beam 12A and 12B. Beam 12A passes through a collimator 16 to mirror 18 through lens 20 to convert beam 12A to a converging beam that is incident on and reflected by beam splitter
22. Beam 12B goes to mirror 24 and through a spatial filter 26 causing beam 12B to become a diverging beam that is incident on and transmitted by beam splitter 22. Beams 12A and 12B pass through hologram 28 as colinear means to record a focusing holographic element. The pos...