Fourier-domain mode delay measurement for multimode fibers using phase detection

We have proposed a powerful method based on a phase detection reflectometric technique to solve the difficulty of the small signal discrimination in the amplitude-detection method for differential modal delay measurement of multimode optical fibers (MMFs). The phase is radically shifted to π at the time delay positions among the excited modes even when the amplitudes of the peaks cannot be distinguished with the noise level. The modal dispersion of the MMF under test can be simply determined by choosing the time delay in the last phase shift in the Fourier domain. In addition, we confirmed that the phase-sensitive interferometric measurement does not need to scramble the excited modes in the fiber. We subsequently conclude that a portable modal dispersion or mode analysis equipment can be developed by using the phase-detection intermodal interferometric technique proposed here.