32 GBaud PDM coherent transmission over 8000 km based on recirculating optical fiber loop controller

A recirculating optical fiber loop controller (ROFLC) is essential equipment for experimental verification of long-haul optical fiber communication transmission. In this experiment, the integrated acousto-optic modulators are controlled by a timing circuit composed of counters and comparators in a field programmable gate array (FPGA) to control the on–off of the optical signal. The ROFLC is introduced into the communication system to achieve 4 quadrature-amplitude-modulation (QAM) signal at 32 GBaud, over 8000 km single-mode fiber (SMF) transmission utilizing polarization division multiplexing (PDM). The ROFLC makes possible a low-cost and lightweight optical fiber communication system, and strongly promotes the application of optical fiber communication systems.