Repeatered Submarine Upgrade Solution

The Need for Upgrades to Existing Systems

New submarine systems are deployed with the latest technology available at the time of installation. However, although the systems are designed to operate for up to 25 years, technology enhancements that enable new functionality, improve capacity, and reduce cost inevitably become available after the initial equipment is installed.

The Xtera Solution: NXT for Upgrade of Ultra Long Haul Submarine Systems

Xtera’s NXT Submarine Line Terminal Equipment makes it possible to upgrade existing submarine systems with the latest technology whilst
smoothly integrating with the existing equipment. This enables addition of new capacity to any existing submarine cable at much lower cost per wavelength and with more functionality than the originally installed equipment.

The NXT transponder is also unique in that it delivers 20Gb/s per wavelength (vs 10Gb/s in typical transponders). This capability, combined with DPSK modulation, advanced receiver design, dynamic line adaption and improved FEC makes it possible to significantly increase transmission capacity of any submarine system. Upgrades to 40G solutions are also in design.

Deployment details

A new submarine cable typically consists of 4-6 fiber pairs. On the underwater section each of the fiber pairs will have all of the submarine repeaters installed during the initial cable deployment. This is necessary because of the expense incurred in changing repeaters after the cable is in the ocean.

The Submarine Line Terminal Equipment (SLTE) is placed at the ends of the cable and is located in landing stations that are on the shore. This equipment is easily accessible so normally SLTE’s are installed on only one or two of the fibers. The remaining fibers are left for future use.

The NXT is designed to connect to any of the unused fiber pairs in any submarine cable. It can also replace an older SLTE to provide more capacity or even be coupled together with an older SLTE to provide incremental wavelengths at a lower cost.

To use an existing fiber pair there are a number of challenges:

• The performance of the system must be equal to or better than the original equipment
• The new optical signals must be compatible with the original optical design
• The terminal equipment must also be able to manage the chain of repeaters connected to this fiber

The NXT has the optical flexibility and system performance to not only meet these requirements but also exceed the original design capacity of the submarine system. The exact amount of increase will vary according to the exact systems design and margins but can be easily calculated by systems simulation and design tools that Xtera has developed.

Figure 1. Typical submarine system

Figure 2. Xtera upgrade