Commonly used light sources for fiber optic communication include

The most commonly used light sources in fiber optic communication are Light Emitting Diodes (LEDs) and semiconductor lasers, including Fabry-Perot, Distributed Feedback (DFB), and VCSELs.

Light Emitting Diodes (LEDs)

LEDs are semiconductor devices that emit light when current flows through them. They are typically used in short-distance, low-speed fiber optic systems due to their broad spectral width, lower cost, and robustness. LEDs emit light over a range of wavelengths, commonly 850 nm to 1300 nm, which is suitable for multimode fibers. Their light is non-coherent and spreads out as it travels, which can limit long-distance transmission due to chromatic dispersion. LEDs are valued for their long lifespan and reliability in simpler applications .

Semiconductor Lasers

Semiconductor lasers, or laser diodes, are preferred for long-distance, high-speed transmission because they produce high-intensity, narrow spectral width, and coherent light. They operate at wavelengths optimized for minimal fiber loss, typically 1300 nm and 1550 nm, where silica fibers have the lowest attenuation. Laser diodes include several types:

• Fabry-Perot (F-P) lasers: Emit from a cavity within the chip and are simpler but have broader spectral width than DFB lasers.
• Distributed Feedback (DFB) lasers: Provide narrow linewidth and stable wavelength, ideal for long-haul communication.
• Vertical Cavity Surface-Emitting Lasers (VCSELs): Emit vertically from the chip surface, commonly used in short-reach, high-speed networks .

Wavelength Considerations

Fiber optic systems primarily use infrared light rather than visible light because it experiences lower attenuation in silica fibers. Common operating wavelengths are 850 nm for short-range multimode fibers, and 1310 nm or 1550 nm for long-distance single-mode fibers. The 1550 nm window is particularly important for long-haul and submarine cables due to minimal fiber loss (~0.2 dB/km) and compatibility with optical amplifiers .

Summary

• Short-distance, low-speed systems: LEDs at 850–1300 nm
• Long-distance, high-speed systems: Semiconductor lasers (F-P, DFB, VCSEL) at 1300–1550 nm
• Infrared light is preferred for minimal attenuation and efficient transmission
• Choice of light source depends on distance, speed, cost, and required signal quality .