Mach-Zehnder fiber interferometer test of the anisotropy of the speed of light

TL;DR

This study used two temperature-stabilized Mach-Zehnder fiber interferometers with different arm orientations to test for anisotropy in the speed of light, observing azimuth-dependent phase differences in one configuration.

Contribution

It presents a novel experimental setup with controlled fiber lengths and orientations to investigate light speed anisotropy using fiber interferometers.

Findings

Phase difference depends on azimuth in the long, perpendicular arms interferometer.

No azimuth dependence observed in the short, parallel arms interferometer.

Temperature effects on phase differences are linked to fiber coupler interactions.

Abstract

Two optical fiber Mach-Zehnder interferometers were constructed in an environment with a temperature stabilization of better than 1 mK per day. One interferometer with a length of 12 m optical fiber in each arm with the main direction of the arms perpendicular to each other. Another with a length of 2 m optical fiber in each arm where the main direction of the arms are parallel as a control. In each arm 1 m of fiber was wound around a ring made of piezo material enabling the control of the length of the arms by means of a voltage. The influence of the temperature on the optical phase difference between the interferometer arms was measured. It is attributed to the temperature change induced variation of the interaction region of the optical fiber couplers. Further, the influence of rotation of the interferometers at the Earth surface on the observed phase differences was determined. For one interferometer (with the long and perpendicular arms) it was found that the phase difference depends on the azimuth of the interferometer. For the other one (with the short and parallel arms) no relevant dependence on the azimuth has been measured.