Why does optical fiber need many wavelengths?

The core reason why optical fiber communication needs multiple wavelengths is to overcome physical limitations, increase transmission capacity and adapt to different scenarios. The main basis is as follows:

Solve the transmission loss and dispersion problems

Loss characteristics difference: Different wavelengths have different attenuation degrees in optical fiber. Short wavelengths (such as 850nm) have a loss of up to 5dB/km, which is only suitable for short-distance multimode optical fiber transmission; while long wavelengths (such as 1310nm and 1550nm) have significantly lower losses (1310nm is about 0.4dB/km, 1550nm can be as low as 0.19dB/km), supporting longer distance transmission.
Dispersion control requirements: 1310nm is close to the zero dispersion point in standard single-mode optical fiber, which is suitable for medium-distance high-speed transmission; although 1550nm has the lowest loss, it has a large dispersion and needs to be combined with dispersion compensation technology or special optical fiber (such as G.655) to achieve ultra-long-distance transmission.

Improve fiber capacity: wavelength division multiplexing (WDM) technology

Spectrum resource utilization: Through wavelength division multiplexing technology, optical signals of different wavelengths are combined into the same optical fiber for transmission. For example

C band (1530-1565nm): It has the lowest loss and is the core band of dense wavelength division multiplexing (DWDM). A single fiber can support more than 100 wavelength channels.

L band (1565-1625nm): As a supplement to the C band, it further expands capacity. Single-fiber bidirectional communication: Use paired wavelengths (such as 1310nm/1550nm) to achieve bidirectional data transmission on one optical fiber, saving optical fiber resources.

Adapt to diverse application scenarios

‌ Wavelength 850nm: short-distance transmission of multimode optical fiber (≤550 meters), low cost, compatible with multimode systems

Wavelength 1310nm: metropolitan area network/regional network (≤60 kilometers), low dispersion, no amplifier required.

‌ Wavelength 1550nm: long-distance/submarine communication (≤160 kilometers), ultra-low loss, can be used with optical fiber amplifiers.

In summary, multiple wavelengths are the optimal solution for balancing loss, dispersion, capacity and cost, and are also the basis for wavelength division multiplexing technology to achieve exponential growth in optical fiber capacity.