Few-mode fiber (FMF) compatible optical add/drop multiplexer (OADM) is indispensable for the future flexible high-speed mode-division multiplexed (MDM) optical networks. In this paper, we demonstrate a proof of concept of FMF compatible OADM which enables add/drop functionality for MDM superchannels. The OADM consists of two cascaded free-space thin-film filters with 5° incident angle. We demonstrate the rerouting of 3 × 318 Gb/s MDM CO-OFDM superchannels via the proposed OADM. The experimental results show 2.6, 2.4, and 0.7 dB OSNR penalties for add, drop, and through ports, respectively. Additionally, we demonstrate a heterodyne receiver configuration which can handle multiband detection without incurring penalty of spectral efficiency.