Large divergence fiber-coupled single-mode light source for laser interferometer

In this study, a large divergence fiber-coupled single-mode light source is presented for laser interferometer. The relationship between the fiber core diameter, numerical aperture and divergence of the fiber-coupled light sources is studied theoretically and experimentally. The guiding fiber of the large divergence fiber-coupled (LDFC) single-mode light source is then produced by fusion splicing the standard single-mode fiber (Nufern 630-HP) with the germanium-doped high numerical aperture (NA) few-mode fiber. The He-Ne laser coupled into the guiding fiber is used as the light source of the laser interferometer. The LDFC single-mode light source achieves the divergence angle of 12.7. and the beam quality factor of M-2 similar to 1.2. For comparison, we take the interferograms when different guiding fibers are used for the He-Ne laser. The background variation of the interferogram formed by the LDFC single-mode light source is 1/7 the variation of the interferogram formed by the standard single-mode fiber-coupled (Nufern 630-HP) laser. The experimental results indicate that the background uniformity of interferogram can be improved obviously by using the LDFC single-mode light source.