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Transmission of IM/DD Signals at 2 μm Wavelength Using PAM and CAP

Advanced modulation formats with intensity modulation and direct detection (IM/DD) have shown promise in a short-reach optical communication system like data center interconnect. However, the conventional fiber transmission spectral window is mostly located at 850, 1310, and 1550 nm. Here, we experimentally demonstrated an amplifierless IM/DD link at the 2-μm spectral band. The signal is encoded with pulse amplitude modulation (PAM) and 3-D carrier-less amplitude and phase modulation (3-D-CAP). The encoded signal is transmitted through a 100 m-long solid-core fiber designed for single mode at 2-μm. We achieve a transmission with bit-rate of 40 Gbit/s using PAM-4 and 24 Gbit/s using CAP16. The measured bit error rates of both formats are below the forward error correction (FEC) limit of 3.8 × 10-3. This study is the first demonstration of PAM4 and CAP transmission at 2-μm, and the results show a significant potential of advanced modulation for 2-μm optical communication.