Certified Fiber Optics Practice Exam

What is one method to reduce modal dispersion in an optical fiber system?

1. Increase the core diameter

2. Decrease the wavelength of the transmitter

3. Increase the wavelength of the transmitter

4. Use fewer modes

The correct answer is: Increase the wavelength of the transmitter

To reduce modal dispersion in an optical fiber system, using fewer modes is an effective strategy. Modal dispersion occurs when different light modes travel through the fiber at varying speeds, leading to spreading of the signal over time. This is particularly significant in multimode fibers, where multiple paths (or modes) are available for light to travel through. By using fewer modes, you limit the number of paths that light can take, which minimizes the differences in arrival times among them. In practical terms, this often means opting for single-mode fibers instead of multimode fibers, as single-mode fibers support only one mode of light propagation. This inherently reduces the modal dispersion because there is no competition among different modes for the same path, resulting in a clearer signal with less distortion over long distances. The other options, such as altering the core diameter or changing the wavelength of the transmitter, do not directly contribute to reducing modal dispersion in the context of the question. Increasing or decreasing the wavelength can affect other aspects of fiber performance, but it does not inherently address the modal dispersion issue in multimode fibers. Therefore, focusing on reducing the number of modes ensures better performance by maintaining signal integrity over longer distances.