Which specialized component allows telephone companies to send multiple calls over a single fiber optic line?

The correct choice, which pertains to allowing telephone companies to send multiple calls over a single fiber optic line, is the multiplexing splitter. This component specifically utilizes the technique of multiplexing, which is essential for combining multiple signals for transmission over a single medium.

In the context of fiber optics, multiplexing enables the simultaneous transmission of various signals over the same fiber cable by allocating unique wavelengths or time slots to each signal. This is particularly advantageous for telephone companies as it maximizes the use of the fiber optic infrastructure, reducing costs and increasing efficiency by enabling multiple conversations to occur at once without interference.

This foundational principle of multiplexing is vital for modern telecommunications, as it supports the increasing demand for bandwidth and multiple services such as voice, video, and data over the same fiber optic line.