Which dispersion type affects both single-mode and multimode fiber?

• A. Chromatic
• B. Modal
• C. Differential
• D. Polarization mode

Answer: (A)

Pulse broadening comes from how different parts of a light signal travel at different speeds inside the fiber. Chromatic dispersion is the wavelength-dependent speed of light in the fiber: the refractive index varies with wavelength, so spectral components travel at different velocities and arrive at different times. This effect occurs in both single-mode and multimode fibers because any signal with a range of wavelengths experiences these speed differences.

In a single-mode fiber, there’s essentially only one spatial path, so modal dispersion isn’t at play, but chromatic dispersion still broadens pulses. In a multimode fiber, you also have modal dispersion, since different spatial modes take different paths, adding to the spread, but chromatic dispersion remains a universal contributor. The other dispersion types stem from mechanisms that don’t affect both fiber types in the same way: modal dispersion is specific to multimode fibers, and polarization mode dispersion arises from birefringence and is a separate effect.