Determining principal modes in a multimode optical fiber using the mode dependent signal delay method

Mode dispersion can negatively impact optical fiber communication over multimode optical fibers (MMFs). Principal modes are a basis of spatial modes that do not experience mode dispersion up to the first order in frequency. In this work, a method to determine the principle modes of a MMF is proposed. This method is referred to as the mode dependent signal delay method, being the extension to a MMF of the analogous method to determine the principal states of polarization of a single-mode optical fiber. Using this method, principal modes can be determined by measuring N super(2) - 1 mean signal time delays at a MMF input for N super(2) - 1 launch conditions generated at a MMF output. The differences of the mode dependent signal delay method from the polarization signal delay method and its experimental implementation are discussed.