The Mach- Zehnder interferometer is a further development of the Jamin interferometer. It was developed 1891/1892 independently from the Austrian Ludwig Mach ( son of Ernst Mach) and his Swiss colleague Ludwig Zehnder.
Incident light is split by a beam splitter into two arms. After passing through the two paths whose optical path length can be different, the two beams are overlaid with a second beam splitter again.
A Mach -Zehnder interferometer can be used both for the measurement of phase shifts, and for the modulation of light by targeted phase modulation in one arm of the interferometer.