The mode-division multiplexing (MDM) technique enables the transmission of multiple signals within a multi-mode
fiber (MMF) or a few-mode fiber (FMF). To construct an efficient and flexible MDM network in the same way as a
wavelength-division multiplexing network, a mode conversion method with low modal crosstalk is required for
switching between arbitrary spatial modes. However, in general, modal crosstalk is strongly dependent on the intensity
pattern before mode conversion, and it is increased particularly for higher order modes. In order to reduce modal
crosstalk, we propose a method using a random diffuser and a spatial light modulator (SLM). In the proposed method,
firstly, the input spatial mode is dispersed uniformly by the random diffuser. Subsequently, the diffused phase
distribution is canceled and converted into the desired spatial mode by the SLM, which displays phase difference
between desired and diffused modes. Consequently, every spatial mode can be evenly converted into a desired mode.
Here, we numerically simulate and confirm that the proposed method can reduce modal crosstalk compared to the
conversion method without the random diffuser.