This paper presents a 2×2 channel mode-wavelength division multiplexing (MWDM) scheme for a radio-over-free-space optics (Ro-FSO) system. The key features of the MWDM system are four dual-core PCF mode (de)multiplexers for the conversion of the fundamental mode to two mode groups at the transmitter/combination of two mode groups at the receiver, and four single-core PCFs for equalization of the modal power in the received signals to compensate for mode coupling from the FSO channel. The PCFs are designed and analyzed using the full-vector finite element method at a wavelength of 1550nm. Numerical results demonstrate that the dual-core PCFs at the transmitter successfully convert the fundamental mode into two distinct mode groups at a ratio of 46.4% to 41.2%, and 43.6% to 44.5%. At the receiver, a single-core PCF equalizer restores the output power to 96.7%, 96.3%, 95.4% and 95.1% of the maximum transmitted power in the designated mode group for each channel. The improvement in achievable distance for the MWDM Ro-FSO system at the same BER level is evident under medium and heavy fog.