Optical interferometer

In an optical interferometer, incident light 1 is divided into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other. The reflected light is subjected to total reflection by means of a first reflector 3, and the transmitted light is subjected to total reflection by means of a second reflector 4. The light reflected by the first reflector 3 and the light reflected by the second reflector 4 are again merged by means of the beam splitter 2 into a single ray, and the thus-merged ray falls on a photodetector 5. The optical interferometer is equipped with a third reflector 6 which reflects the incident light 1 at right angles so as to fall on the beam splitter 2, and a fourth reflector 7 which reflects the light, having been transmitted through the beam splitter 2, at right angles so as to fall on the second reflector 4. The beam splitter 2 and the third and fourth reflectors 6 and 7 are mounted on a moving member 8 which can be moved along an optical path extending between the first reflector 3 and the photodetector 5.