An Extended Light Source Based on Multimode Fiber in Interferometers

In interferometers, defects on the surface of optical elements can generate coherent noise, such as "Newton's rings," in interferograms, thereby affecting measurement accuracy. To address this issue, this paper proposes a method for extending the light source using a multimode fiber. By adjusting the parallel beam coupling into the multimode fiber, the coherent noise of the light source can be eliminated. The proposed method is verified in a Twyman-Green interferometer with a 25.4 mm diameter, employing a multimode fiber with a core diameter of 1 mm. Experimental results demonstrate a 36.9% reduction in scattering contrast and a 43% improvement in signal-to-noise ratio (SNR) of the interferometer when the fiber is moved +/- 1 mm perpendicular to the optical axis, while maintaining a fixed incidence angle of 1 degrees to the optical axis. These findings confirm the effectiveness of the proposed method.