Which device is primarily responsible for modulating light in optical transmitters?

The device primarily responsible for modulating light in optical transmitters is the data encoder/modulator. This component plays a crucial role in the process of converting electrical signals into optical signals for transmission over fiber-optic cables. The modulation process involves varying the light signal's properties - such as amplitude, frequency, or phase - to encode the information being sent.

The data encoder/modulator ensures that the information is carried effectively through the medium, allowing for the successful transmission of data over long distances with minimal loss. In fiber optics, modulation techniques can include methods like On-Off Keying (OOK) or more advanced techniques such as Quadrature Amplitude Modulation (QAM), depending on the system requirements and desired data rates.

Other devices, such as optical detectors, optical amplifiers, and optical couplers, serve different functions within the optical communication system. Optical detectors convert the transmitted light signals back into electrical signals at the receiver end, while optical amplifiers boost signal strength over long distances. Optical couplers are used to combine or split optical signals within the network but do not have a role in modulation. Thus, the data encoder/modulator is the essential device that directly engages in the modulation process needed for optical transmission.