In which component in a fiber-optics communication system do changes to the intensity of the optical signal occur?

The optical transmitter is the component in a fiber-optic communication system where changes to the intensity of the optical signal occur. This is because the transmitter's primary function is to convert the electrical signals representing data into light signals. During this conversion process, the transmitter modulates the light’s intensity to encode the information being transmitted. This modulation can involve turning the light on and off, altering its brightness, or varying its other properties, all of which fundamentally changes the intensity of the optical signal before it travels through the optical fiber medium.

In contrast, the optical receiver is responsible for detecting the incoming light signals and converting them back into electrical signals but does not modify the signal's intensity itself. The optical fiber serves as the medium for transmitting the light signals, allowing the already modulated and transmitted signal to propagate from the transmitter to the receiver. While the optical amplifier can boost the strength of a signal that has weakened over long distances, it does not alter the signal's initial intensity encoding but rather enhances the existing signal to maintain quality over longer runs.