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Evaluation of Sinusoidally Varying Light Signals

IP.com Disclosure Number: IPCOM000052553D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Schedewie, F: AUTHOR

Abstract

The parameters of sinusoidally varying signals (relative phase Epsilon( amplitude A, bias B in Fig. 1) can be obtained from three sampling points a, b, c which are preferably chosen with a phase difference of 120 Degrees.

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Evaluation of Sinusoidally Varying Light Signals

The parameters of sinusoidally varying signals (relative phase Epsilon( amplitude A, bias B in Fig. 1) can be obtained from three sampling points a, b, c which are preferably chosen with a phase difference of 120 Degrees.

In optics, such signals occur frequently, for example, in two-beam interferometry, where the path difference DeltaX of two light waves of the same wavelength determines the relative phase of the resulting interference pattern. In Fig. 2, a laser beam 1 is directed, via partially reflecting mirror 2, to a double- refracting crystal (calcite) 3, where it is split into two beams 4a, 4b with mutually perpendicular directions of polarization. After reflection at sample surface 5, which may have a step with a height difference Z, the two beams are recombined by calcite crystal 3. The relative phase difference of the two partial beams is indicative of the step height, it can be determined from the relative phase of the interference pattern which is obtained when an analyzer is placed in the output beam with an azimuth of 45 Degrees relative to the directions of polarization.

A novel, alternative detector arrangement for determining the relative phase of the interference pattern is shown in the upper part of Fig. 2; output beam 6 traverses a Lambda/4 plate 7 to be transformed into left and right circular, polarized beans impinging on grating 8. In the diffracted light, three diffraction orders (0, +1, -1) are each recorded by a combination of an analyzer 9 and a photodetector 10. The azimuths of the three analyzers are set to -60 Degrees, 0 ...