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Remote Optically Pumped Amplifier (ROPA) for Submarine and Ultra-long-haul Fiber-optic Systems
Tools Used: OptSim
Overview
Ultra-long-haul terrestrial and submarine links benefit from unrepeatered fiber-optic deployments because one can save on capex and opex by avoiding intermediate amplification sites and related operational expenses. A number of field trials and deployments have been reported over the last decade increasing both data rates and unrepeatered distances [1-5].
The Challenge
A ROPA is a piece of erbium-doped fiber amplifier typically kept at 100-km distance from the terminal and is remotely pumped from the receiving end. Since there’s no electrical power feeding at the amplifier itself, the system is considered unrepeatered. As you can see from the references, a number of schemes exists with regards to the pumping configuration. Due to the availability of high-power lasers in 1480nm range, it’s a common choice as pump. Each submarine and ultra-long-haul deployment is different, and simulations is a key to technology selection.
The Solution
In this application case study, we demonstrate a repeaterless ROPA system that is pumped by a back-pumped Raman amplifier in OptSim. The benefit of such an arrangement is that the Raman amplifier not only compensates for the fiber loss but also provides amplification to its output pump which is then reused as a pump for ROPA. The schematic is shown in Figure 1.
Figure 1. Schematic of a backward pumped ROPA.
The topology comprises of two Raman amplifiers – one at the transmitting and the other at the receiving terminals. The ROPA is a backward pumped, 15m of EDF placed at 100km from the receiving terminal. The Raman amplifier at the transmitted end is a single-mode fiber (SMF) with forward pumping at 1485nm. The dispersion compensating fiber (DCF) compensates for the total chromatic dispersion in the 200-km link. The Raman amplifier at the receiving end is also a 100-km SMF but is backward pumped at 1485nm.
Simulation and Results
Figure 2 shows the signal at the ROPA input (left) and output (right). As can be seen, the power gain is around 17dB of gain at 1550nm.
Figure 2. Input (left) and output (right) optical signals at ROPA.
Figure 3 shows an eye diagram at the receiving terminal.
Figure 3. Received eye diagram.
The received eye diagram is shows an excellent transmission considering ~200km of transmission. Optical noise is clearly visible due to amplified spontaneous emission (ASE) from optical amplification process at Raman and ROPA.
The case study demonstrated design of a ROPA-based system. The placement of pump needs careful considerations so as to optimize power budget and guarantee a specified quality of service (QoS). For more information and to request a demo, please contact photonics_support@synopsys.com.
Author
Jigesh K. Patel, Product Manager
References
1. Philippe Perrier, Daryl Chaires: “Advances in unrepeatered systems,” a presentation at NANOG45, https://archive.nanog.org/meetings/nanog45/presentations/Tuesday/Chaires_submarine_N45.pdf
2. Tiejun J. Xia, et al., “557-km unrepeatered 100G transmission with commercial Raman DWDM system, enhanced ROPA, and cabled large Aeff ultra-low fiber in OSP environment,” OFC 2014, Paper # Th5A.7
3. Submarine telecoms forum: https://xtera.com/wp-content/uploads/2017/05/Latest-Developments-for-Unrepeatered-Cable-Systems-Submarine-Telecoms-Forum-Issue-82-Xtera-May-2015.pdf
4. Do-il Chang, et al., “Ultra-long unrepeatered transmission over 607km at 100G and 632km at 10G,” Optics Express, vol. 23, no. 19, Sept. 2015, pg. 25028-25033
5. Nicolas Tranvouez, et al., “Unrepeatered systems: State of the art capability,” https://www.suboptic.org/wp-content/uploads/2014/10/We2.19.pdf