MachZehnderinterferométer

The Mach-Zehnder interferometer is an optical instrument that splits a light beam into two separate paths and then recombines them to produce interference. It is named after James Clothier Mach and Ludwig Zehnder, who introduced the design in the late 19th century to study interference.

In the classic free‑space arrangement, a first beam splitter divides the incident beam into two arms that are reflected by mirrors toward a second beam splitter, where the beams interfere and exit through two output ports. In integrated optics or fiber systems, the beam splitters are realized by directional couplers or beam-splitting circuits, and a phase shifter in one arm provides the relative phase control.

The operation hinges on the relative phase phi between the two arms. For a balanced splitter, the output intensities follow I_out1 = I0 cos^2(phi/2) and I_out2 = I0 sin^2(phi/2). The phase difference can arise from differences in path length, refractive index, or external perturbations such as temperature, pressure, or mechanical strain.

Applications span precision metrology and sensing, where the device detects small changes in refractive index, length, or environmental conditions; optical modulators and switches in communications; and fundamental experiments in quantum optics using single photons or entangled states. On-chip Mach-Zehnder interferometers are central to modern photonic integrated circuits, enabling compact, stable phase control and high-speed modulation.

Practical considerations include sensitivity to vibrations and temperature drift, polarization effects, insertion loss, and fabrication tolerances in integrated implementations. Variants exist for free-space, fiber-based, and on-chip configurations, each tailored to specific spectral ranges and performance requirements.