Group delay time is the difference in travel time through a cable for the light of different wavelengths. This is an important concept when considering optical fiber cables, as the speed at which light travels through an optical fiber can vary depending on the wavelength of the light.
Group delay time is measured in picoseconds per nanometer of wavelength, and is usually expressed as a “group delay dispersion” (GDD). It is the time difference between two different wavelengths of light as they travel through the same fiber. This is significant as it can cause pulse broadening and temporal dispersion, which can cause distortion in the signal, and can even lead to complete signal attenuation.
Group delay time can be affected by a number of factors, including the material the cable is made of, its size, the temperature of the environment, and the length of the cable. It is also affected by the type of optical fiber used, such as multimode or single-mode fibers. The core size of the cable also affects the group delay time, as the core size affects the number of reflections of the light within the cable.
To reduce group delay time, optical fibers are typically designed with special materials and with a small core size. This allows for fewer reflections of the light within the cable, resulting in less time for the light to travel and reducing the group delay time. Additionally, careful selection of the optical fiber type can help reduce the group delay time, as single-mode fibers have a smaller core size than multimode fibers, and are less prone to pulse broadening and temporal dispersion.
In conclusion, group delay time is the difference in travel time through fiber for light of different wavelengths, and is an important concept to consider when designing and deploying optical fiber cables.