IM-DD and DPSK heterodyne transmission experiments at 2.55 μm using single-mode fluoride optical fibers

This paper describes 200 ∼ 940 Mbit/s intensity modulation - direct detection (IM-DD) and 200 Mbit/s differential phase shift keying (DPSK) heterodyne transmission experiments at 2.55 μm. The experiments were performed using color center lasers, external modulators, single-mode fluoride fibers and pin photodiodes. In the IM-DD system, the attained minimum received powers were -17.5 dBm at 200 Mbit/s and -13.5 dBm at 940 Mbit/s. On the other hand, the minimum received power in the 200 Mbit/s DPSK system was -41.0 dBm for a local oscillation (LO) power of -7.0 dBm. The result means that a coherent transmission is superior to an IM-DD transmission for a long span mid-infrared transmission. Finally, this paper discusses the problems to be solved regarding constituent device such as light sources, modulators, fibers and optical detectors.