What is the significance of the cutoff wavelength in single-mode fibers?

The cutoff wavelength is a critical parameter in the design and operation of single-mode optical fibers. It signifies the boundary between multi-mode and single-mode operation. Specifically, the cutoff wavelength defines the threshold above which the fiber supports only a single propagation mode. When light is transmitted at wavelengths longer than the cutoff wavelength, the fiber allows only one mode to propagate, minimizing the dispersion and allowing for better performance over long distances.

In practical terms, if the transmission wavelength is below this cutoff wavelength, the fiber may support multiple modes, leading to modal dispersion which can degrade signal quality. Therefore, fibers designed for single-mode operation are optimized to have a specific cutoff wavelength, ensuring efficient and reliable data transmission in high-bandwidth applications. This characteristic is essential for applications that require high fidelity and low losses over longer distances, such as in telecommunications and data centers.