Hey, fellow engineers! As engineers from Hengtong, we often encounter a rather tricky issue when working on projects related to 100/200G DWDM networks, and that is which optical fiber to choose for ADSS cable design, G.655 or G.652D? Today, I'd like to share some of my thoughts with you.
Let's start with the G.655 optical fiber. It has non-zero dispersion near the 1550nm wavelength. This is really crucial! In our DWDM networks with large transmission capacity and small channel spacing, nonlinear effects like four-wave mixing are the "big enemies" of signal quality. And the G.655 optical fiber can suppress them effectively, ensuring a stable signal transmission, just like paving a "smooth road" for signal transmission. Moreover, it has a relatively moderate effective area and quite good ability to carry optical power. When multiple wavelength signals are transmitted simultaneously, it can handle the optical power distribution properly, and we don't need to worry about signal degradation caused by excessive optical power. As for the loss characteristic, its loss is relatively low in the 1550nm wavelength range which is commonly used in DWDM systems. When ADSS cables need to be installed overhead for long distances to transmit large-capacity 100/200G signals, it can reduce the requirement for repeater equipment. How convenient that is! It also makes our design work much easier.
Now, let's take a look at the G.652D optical fiber. It has a small dispersion coefficient near the 1310nm wavelength, close to zero dispersion. However, at the 1550nm wavelength, its dispersion is relatively large. This is a bit of a "hindrance" when we have multi-wavelength multiplexing and high-speed transmission in DWDM systems. Usually, we need to add additional dispersion compensation modules to adjust the dispersion to ensure signal quality. As a result, when we design, we have to consider making room for these devices, and the cost will increase accordingly. It will be even more troublesome when it comes to long-distance transmission. Besides, compared with the G.655 optical fiber, its effective area is not so advantageous in carrying high-power optical signals. When the optical power is high during multi-wavelength multiplexing, problems are likely to occur and affect the signal transmission quality. Also, although its loss in the 1550nm window is still at a reasonable level, it is slightly higher than that of the G.655 optical fiber. When transmitting large-capacity signals over long distances, the attenuation of optical signals is faster, and repeater equipment needs to be arranged more frequently. This will increase both the cost and the maintenance difficulty for our ADSS cable long-distance and large-capacity transmission design.
So, how should we choose? It depends on a comprehensive consideration. If our network focuses on long-distance and large-capacity transmission, and we want to achieve high-quality 100/200G DWDM signal transmission without too much trouble in dispersion compensation, while relying on the fiber's own characteristics to suppress nonlinear effects, then the G.655 optical fiber is definitely more suitable. For example, in some backbone long-distance transmission networks with extremely high requirements, it is the right choice. However, if the transmission distance of the network is not that long, we are more concerned about cost control, and we can solve the dispersion problem by reasonably configuring dispersion compensation equipment and other means, and the optical power in the network is also relatively easy to control, then the G.652D optical fiber can also be used. Just like in some local areas of metropolitan area networks where the requirements are not so strict, using it and combining it with appropriate measures can also achieve a quite good transmission solution.
In conclusion, when we design ADSS cables in 100/200G DWDM networks, we need to take into account various aspects such as network planning, transmission distance, cost budget and requirements for signal quality in order to select the most suitable optical fiber. How do you usually make the choice in your projects? Come and share your experiences with us!