Data is sent through the fiber-optic cable by a(n):

Data is transmitted through fiber-optic cables using a laser device, which converts electrical signals into light pulses. These light pulses travel through the glass or plastic fibers of the cable at high speeds, allowing for efficient and high-capacity data transmission over long distances. The fundamental operation of fiber optics relies on the principle of light transmission and total internal reflection, which enables the fiber to carry signals without significant loss of quality.

While other devices like routers and multiplexers are used in networking to manage data traffic or combine multiple signals, they do not perform the task of converting electrical signals to light for transmission through fiber. Optical devices may refer to a broader category that includes any component that uses light, but the specific functionality necessary for transmitting data via fiber optics is primarily attributed to the laser device. Therefore, the laser device is the correct choice in this context for the process of sending data through fiber-optic cables.