The correct answer is: D. Normalized frequency.
Normalized frequency is a dimensionless parameter used to characterize the propagation of light in a single-mode fiber. It is defined as the ratio of the wavelength of light to the core radius of the fiber. The normalized frequency is a key parameter in determining the performance characteristics of a single-mode fiber, such as its bandwidth, loss, and dispersion.
The intermodal delay effect is a phenomenon that occurs in multimode fibers, where light travels in multiple modes. This can cause a delay between the different modes, which can limit the bandwidth of the fiber. Single-mode fibers do not suffer from this effect, as light only travels in a single mode.
The geometric distribution of light in a propagating mode is a measure of how the light is distributed within the core of the fiber. This can affect the performance of the fiber, such as its loss and dispersion. However, the geometric distribution of light is not a key parameter in determining the performance of a single-mode fiber.
Fractional power flow in the cladding of fiber is a measure of how much power from the light source is lost to the cladding. This can affect the performance of the fiber, such as its loss. However, fractional power flow in the cladding is not a key parameter in determining the performance of a single-mode fiber.