Which technology is primarily utilized for increasing the capacity of fiber optic networks?

Wavelength Division Multiplexing (WDM) is the correct choice as it allows multiple wavelengths (or channels) of light to be transmitted simultaneously through a single fiber optic cable. This technique significantly increases the data capacity of fiber optic networks by combining various wavelengths, each carrying its own separate information stream.

WDM essentially expands the available bandwidth of the fiber without needing to lay more physical cables. It is particularly effective in modern telecommunications, where there is a high demand for data transmission and infrastructure efficiency. By sending data over multiple wavelengths, WDM enables service providers to optimize their fiber infrastructure and support a larger number of users and higher data rates.

The other technologies listed have their specific applications but do not primarily focus on increasing the capacity of fiber optics in the same manner as WDM. For instance, Time Division Multiplexing (TDM) works by allocating time slots for data transmission on a single channel but does not take advantage of multiple wavelengths. Frequency Division Multiplexing (FDM) divides bandwidth into different frequency channels, which is more common in traditional radio and television communications. Code Division Multiplexing (CDM) allows multiple signals to occupy the same frequency channel but is different in its approach and application from WDM within fiber optic systems.