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# Fringe Counting System

IP.com Disclosure Number: IPCOM000093306D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 34K

IBM

## Related People

Schools, RS: AUTHOR [+2]

## Abstract

In interferometry it is often necessary to observe and count the relative displacement of a fringe pattern as some component of the system is altered. This system accomplishes the counting by performing a frequency analysis of the light patterns supplied to it.

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Fringe Counting System

In interferometry it is often necessary to observe and count the relative displacement of a fringe pattern as some component of the system is altered. This system accomplishes the counting by performing a frequency analysis of the light patterns supplied to it.

A fringe generator supplies fringe pattern 1 to input plane 2 of the system. The fringes are alternating dark and light patterns of light in which there is relative motion between one set of fringes 3, the solid lines, and another set of fringes 4, the dashed lines. The fringe systems are supplied to frequency analyzer lens 5.

As the fringe patterns are in relative motion, the spatial frequency of the combined pattern varies periodically from one with a basic spatial frequency to another with a spatial frequency that is twice the basic frequency. Between these extremes there is an infinite number of frequencies. However, the fringes are centered at only one frequency. This is the spatial frequency equivalent to twice the basic spatial frequency. All other frequencies occur twice for one full fringe displacement.

In this system, the presence of the double spatial frequency is determined by detecting the presence of light in that position. Detector array 6 is located in output plane 7 of frequency analyzer lens 5 to accomplish this. Counting of the detected fringes is performed in circuitry 8.

The input fringe pattern can be supplied in one of several forms. It can be provided from two...