THE OPEN ROAD TO SUBMARINE CAPACITY
Managing Optical Power Levels in Open Submarine Cables
By Geoff Bennett
January 26, 2021
The submarine network market is experiencing unprecedented demand growth, and it has even seen a boost from the changes in our working patterns brought about by the COVID-19 pandemic. A major trend over the past five years has been the move to open cable systems, where the wet plant and the transponders are sourced from different vendors, whether on different fiber pairs or even within the same fiber pair. Decoupling the choice of wet plant and transponders allows the cable operator to choose the best-of-breed transponders at any given point in the cable’s lifecycle. But open cables also have challenges around fiber characterization, capacity deployment, and optical power management. This article explains why open submarine cables are so vital to today’s market and how intelligent optical power management can help to solve their major challenges.
Open Submarine Cables
Submarine cable systems are basically composed of two major elements: the wet plant and the dry plant. As its name suggests, the wet plant includes anything that goes under the water, including the cable itself and the optical amplifiers that are spaced at regular intervals along the cable. The dry plant includes the high-voltage electrical equipment that powers the amplifier chain, the terminal (or ROADM) unit, and the transponders. The latter two, the terminal and transponders, are also known as the submarine line terminating equipment, or SLTE.
Given the fact that the wet plant portion of the cable, including the electrical power management, cannot be changed once it has been deployed, this article will focus on the SLTE portion of the system, and in particular the need for optical power management.
Figure 1 shows a breakdown of the elements within the SLTE, shown within the dotted line box. The cable itself connects into a flexible grid ROADM, and this provides an open demarcation point for the insertion of wavelengths from a variety of different vendors’ transponders. One of the key capabilities that has been highlighted by the move to open cables is the need to control and maintain the stability of optical power levels along the entire cable system. This is achieved using optical power sources such as amplifier spontaneous emission (ASE) generators and idlers. Both these devices generate optical power over a certain range of frequencies, and their power level and frequency range are controlled by intelligent power management software working in conjunction with the flexible grid ROADM. ASE and idlers do not transmit data – they simply generate light.