Whether connecting communities or spanning continents, speed and accuracy are the two key requirements for fiber optic networks that carry critical task communications. Users need faster FTTH links and 5G mobile connections to achieve telemedicine, autonomous vehicle, video conferencing and other bandwidth intensive applications. With the emergence of a large number of data centers and the rapid development of artificial intelligence and machine learning, coupled with faster network speeds and support of 800G and above, all fiber characteristics have become crucial.
According to the ITU-T G.650.3 standard, optical time domain reflectometer (OTDR), optical loss testing device (OLTS), chromatic dispersion (CD), and polarization mode dispersion (PMD) tests are required to perform comprehensive fiber identification and ensure high network performance. Therefore, managing CD values is key to ensuring transmission integrity and efficiency.
Although CD is a natural characteristic of all optical fibers, which is the extension of broadband pulses over long distances, according to the ITU-T G.650.3 standard, dispersion becomes a problem for optical fibers with data transmission rates exceeding 10 Gbps. CD can seriously affect signal quality, especially in high-speed communication systems, and testing is the key to addressing this challenge.
What is CD?
When light pulses of different wavelengths propagate in optical fibers, the dispersion of light can cause pulse overlap and distortion, ultimately leading to a decrease in the quality of the transmitted signal. There are two forms of dispersion: material dispersion and waveguide dispersion.
Material dispersion is an inherent factor in all types of optical fibers, which can cause different wavelengths to propagate at different speeds, ultimately resulting in wavelengths reaching the remote transceiver at different times.
Waveguide dispersion occurs in the waveguide structure of optical fibers, where optical signals propagate through the core and cladding of the fibers, which have different refractive indices. This results in a change in the diameter of the mode field and a variation in the signal velocity at each wavelength.
Maintaining a certain degree of CD is crucial to avoid the occurrence of other nonlinear effects, therefore zero CD is not advisable. But CD must be controlled at an acceptable level to avoid negative impacts on signal integrity and service quality.
What is the impact of fiber type on dispersion?
As mentioned earlier, CD is an inherent natural characteristic of any optical fiber, but the type of fiber plays a crucial role in managing CD. Network operators can choose “natural” dispersion fibers or fibers with dispersion curves offset to reduce the impact of CD within a specific wavelength range.
The most commonly used fiber in today’s networks is the standard ITU-T G.652 fiber with natural dispersion. ITU-T G-653 zero dispersion shifted fiber does not support DWDM transmission, while G.655 non-zero dispersion shifted fiber has a lower CD, but has been optimized for long distances and is also more expensive.
Ultimately, operators must understand the types of fiber optics in their networks. If most of the optical fibers are standard G.652, but some are other types of fibers, then if the CDs in all links cannot be seen, the service quality will be affected.
In conclusion
Chromatic dispersion remains a challenge that must be addressed to ensure the reliability and efficiency of high-speed communication systems. Fiber characteristics and testing are key to solving dispersion complexity, providing insight for technicians and engineers to design, deploy, and maintain infrastructure that carries global critical mission communications. With the continuous development and expansion of the network, Softel will continue to innovate and launch solutions to the market, leading the way in supporting the adoption of advanced technologies.
Post time: Mar-20-2025