Spatial mode exchange technique using volume holograms with a random optical diffuser to reduce modal cross-talks

摘要

In mode-division multiplexing (MDM) systems, transmission quality is restricted by differential mode delay (DMD). Wehave proposed and developed a spatial-mode exchange technique using volume holograms (VHET) as a leadingtechnology to reduce DMD. VHET can equilibrate the transmission time of each spatial mode which has differenttransmission speeds in a few mode fiber using a volume hologram. This technology enables low signal distortion andhigh spectral efficiency, which are indispensable to the long-haul transmission for the MDM system. However, in thistechnology, modal cross-talks (MXTs), which are caused by inter-page cross-talks in the volume hologram, seriouslydegrade the performance of VHET. In this study, we proposed a method of combining a volume hologram and a randomoptical diffuser to reduce the MXTs. In our method, the intensity distribution of the input spatial mode is diffuseduniformly by a random optical diffuser. The high exchange performance will be attained because the non-targetedholograms included in the multiplexed holograms do not affect most of the spatial mode. Moreover, our method can beapplied to the communication wavelength bands using the dual wavelength method. We confirmed the basic operation ofthe proposed scheme using a linearly polarized mode group comprising LP0,1, LP1,1, and LP2,1. Compared with theconventional VHET, the simulation results show that the maximum MXTs are significantly suppressed from 0.4 to -15.8dB.