Unrepeatered transmission systems provide a cost-effective solution to transmit high capacity channels in submarine networks to communicate between coastal population centers or in terrestrial networks to connect remote areas where service access is difficult. The main goal of unrepeatered systems has traditionally been to achieve the longest reach, however, increasing traffic demands now require unrepeatered systems to support both longer reach and higher transport capacity. As a result, transmission rate of unrepeatered systems has quickly moved from 10 Gb/s to 40 Gb/s or 100 Gb/s. This paper reviews the key basic technologies, with a specific focus on Raman amplification, required for long-reach, high-capacity unrepeatered optical transmission systems. We will discuss novel Raman amplification schemes, enhanced remote optically pumped amplifiers (ROPA), ultra-low loss / large effective area fibers, and coherent transmission with advanced modulation format and high FEC coding gain. We will also report recent experimental demonstrations that show how these technologies have been combined to achieve industry’s leading capacity and reach transmission.
As transmission rates in fiber-optic networks increase, routing optical signals using electronic processing will become increasingly difficult. This limitation can be overcome by performing the required processing optically. Self-routing of optical signals through a switching node using optically processed control is demonstrated. Packet headers are encoded with packet destination addresses using either optical code-division or time-division encoding schemes. An optical routing controller reads the destination addresses and appropriately sets the photonic switch using an optical look-up table. The results of several experiments demonstrating optical control of a photonic switch are described.