OPTICAL INTERFEROMETER

PROBLEM TO BE SOLVED: To make stable measurements with an optical interferometer by eliminating unwanted reflected light. SOLUTION: In the optical interferometer, incident light beams are split by a beam splitter 4 into two mutually perpendicular optical paths, one formed by reflected light beams and the other by transmitted light beams, with the reflected light beams and the transmitted light beams being totally reflected respectively by a first reflector 5 and a second reflector 6 on the respective optical paths. The light beams reflected by both reflectors 5 and 6 are recombined by the beam splitter 4 and received by a receiver 7. The beam splitter 4 for splitting and recombining the incident light beams is disposed to be slightly tilted from a direction normal to the incident light beams.