The limitations for suppressing modal noise induced in a graded-index multimode fibre in a white light interferometer

Modal noise induced in a multimode fibre can be greatly suppressed if the coherence length of the light source used is less than the optical path difference (OPD) between two adjacent fibre modes. In this work, using an accurate modal analysis, the OPDs between each pair of adjacent fibre modes at the far end of a multimode fibre were calculated and compared with supporting experimental results, obtained by varying both the values of the coherence length of a low coherence light source and the length of the multimode fibres employed in an interferometric system. The results from this work can be used both to understand theoretically, and thus determine the practical limitations of, the use of multimode fibres in an interferometric system with a low coherence light source.