Which source is used in fiber cable to transmit data?

Fiber optic cables transmit data using modulated pulses of light. An electrical signal containing data is converted by a transmitter, typically a laser or a light-emitting diode (LED), into a light signal. This light travels through the core of the optical fiber, which is a thin strand of glass or plastic. The light is guided along the fiber's path by a principle called total internal reflection. At the destination, a photodetector receives the light pulses and converts them back into an electrical signal. This method provides high bandwidth, low attenuation, and immunity to electromagnetic interference, making it ideal for data centers.

A. Signals: This term is too general. A signal is the encoded information, but "light" is the specific physical medium used for transmission in fiber optic cables.
B. Electric: Electrical currents are the transmission source for copper-based cabling, such as twisted-pair or coaxial cables, not for fiber optic technology.
D. Pulse: Data is transmitted as pulses of light, but the pulse is a characteristic of the signal's modulation, not the fundamental energy source itself, which is light.

1. Stallings, W. (2014). Data and Computer Communications (10th ed.). Pearson. In Chapter 4, Section 4.3, "Optical Fiber," it is stated, "An optical fiber is a thin, flexible medium capable of guiding an optical ray... For optical fiber, the light source is either a light-emitting diode (LED) or an injection laser diode (ILD)."

2. Agrawal, G. P. (2010). Fiber-Optic Communication Systems (4th ed.). Wiley. Chapter 1, Section 1.1, "Need for Fiber-Optic Communications," explains, "In a fiber-optic communication system, the information is first converted into an electrical signal, which is then used to modulate the intensity of the light emitted by a semiconductor laser or a light-emitting diode (LED)."

3. MIT OpenCourseWare. (2003). 6.977 Optical Networks, Lecture 1: Introduction. Massachusetts Institute of Technology. Slide 4, titled "The Optical Layer," explicitly diagrams a fiber link with a "Light Source (Laser/LED)" and a "Light Detector (Photodiode)," identifying light as the transmission medium.