Beam splitter

Adding up all these, we see that the total difference between the two paths is that the U path has gone through one additional phase change of one-half a wavelength. Therefore, there will be complete destructive interference, and no light will reach detector 2.

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MZI

Adding up all the contributions for the two paths, we see that they are the same. Thus light entering detector 1 via the two paths is in phase. Thus we get constructive interference for the light entering detector 1.

The interferometer is used to measure the phase shift of a thin sample of, say, glass. The sample is placed in either the U or D beam. The phase shift of the sample alters the phase relationships between the two beams that we have just described, and there is no longer complete destructive interference at detector 2. Measuring the relative amount of light entering detector 1 and detector 2 allows a calculation of the phase shift produced by the sample.

It turns out that, despite the figure, all of the light from the source ends up at detector 1; no light gets to detector 2. We will prove that this is so.

马赫曾德尔调制器

This document is Copyright 1999 © David M. Harrison. This is version $Revision: 1.3 $, date $Date: 2018/10/15 16:47:43 $ (y/m/d UTC).

Note we have labelled the two detectors 1 and 2, and have labelled the upper path of the light U and the down path of the light D. We consider the two paths for light arriving at detector 1:

The Mach-Zehnder interferometer, invented over one hundred years ago, is still used for many optical measurements. "Mach" is the son, Ludwig, of the man, Ernst, who proposed Mach's Principle and for whom a unit for the measurement of the speed of sound is named. Here we describe the details of how a simple version of the interferometer works; the discussion is largely non-mathematical but somewhat lengthy. A figure of the interferometer appears to the right.