Which of the following wavelengths is not commonly used for fiber optic communications?

In fiber optic communications, specific wavelengths are standardized for optimal performance and minimal signal loss. The commonly used wavelengths include 850 nm, 1300 nm, and 1550 nm, which correspond to the three main windows of operation for fiber optics.

850 nm is primarily utilized for short-distance communication, particularly in multimode fibers, where LEDs are often employed as light sources. This wavelength is beneficial for data centers and local area networks.

1300 nm offers improved performance over distances compared to 850 nm and is often used in multimode applications and some single-mode applications as well. This wavelength uses laser diodes for higher data rates and longer distances.

1550 nm is known for its low attenuation characteristics and is predominantly used in long-distance communications and single-mode fibers. This wavelength allows for longer transmission distances without significant signal degradation, making it suitable for telecommunications.

The wavelength of 1800 nm, however, is not standard for fiber optic communications. While it may be used in specialized applications or experimental setups, it does not fall within the commonly accepted wavelength windows for typical fiber optic systems, which makes it the correct response for the question.