The number of modes in an optical fiber increases as the _______ decreases.

As the wavelength decreases, the number of modes that an optical fiber can support increases. This is primarily because the modal index, which defines the propagation characteristics of light within the fiber, is influenced by the wavelength of the light being transmitted.

When the wavelength of light is decreased, the ability of light to behave as multiple modes within the core of the fiber is enhanced. Fewer wavelengths allow for more efficient coupling into the core and the support of additional propagation paths or modes. This phenomenon is rooted in the principles of waveguide theory, where a shorter wavelength can more easily "fit" into the dimensions of the core, thus allowing multiple paths for the light to travel.

In contrast, as the wavelength increases, the capacity for modes to propagate effectively diminishes due to limitations imposed by the physical structure and refractive indices of the fiber. Therefore, the correct association is that a decrease in wavelength leads to an increase in the number of modes supported by the fiber, highlighting the intricate relationship between these optical properties.