Modified S2 schemes for estimating differential mode group delay in polarization-maintaining few-mode fiber

Abstract

In the mode-division-multiplexed (MDM) system, the few-mode fiber (FMF) replaces the single-mode fiber (SMF) as the transmission medium, to increase the per-fiber transmission capacity. The polarization-maintaining few-mode fiber (PM-FMF) can greatly enhance the optical communication system, since it can both preserve the polarization state and allow the transmission of multiple modes. To obtain the differential mode group delay (DMGD) value of the PM-FMF, which determines the computational complexity of the equalization algorithm at the receiver, the characterization of the fiber is essential. The conventional S2 method, which can estimate the DMGD of the FMF, cannot be directly applied to the PM-FMF, because it is impossible to determine which of the LP01x and the LP01y mode is the dominant mode. In this work, two new approaches are developed, for the first time to our knowledge, to measure the DMGD in the PM-FMF. The former method is to measure the DMGD in both polarization directions, and LP01x and LP01y are selected as dominant modes, respectively. The latter approach is to realize a simultaneous DMGD measurement of all LP modes, and only LP01y is selected as the dominant mode. It is demonstrated in the experiments that a good agreement has been achieved between the measurement results from both schemes.