What are the three most common wavelength windows used for communications through optical fibers?

The three most common wavelength windows used for optical fiber communications are indeed 850 nm, 1300 nm, and 1550 nm. Each of these wavelengths has specific characteristics that make them suitable for different types of fiber optic systems.

At 850 nm, multimode fibers are commonly used, which allow for high data rates over short distances. This wavelength takes advantage of the low loss and high efficiency of light transmission through the core of multimode fiber. It's frequently used in local area networks and data centers.

At 1300 nm, the performance of both multimode and singlemode fibers is optimized, with lower attenuation and dispersion, making it suitable for medium-range communications. This wavelength is advantageous for longer links because it can carry data over greater distances than 850 nm without significant loss of signal quality.

The 1550 nm wavelength is particularly significant for long-haul singlemode fiber communication systems. It experiences the lowest attenuation and also allows for the use of dense wavelength division multiplexing (DWDM), which enables multiple signals to be transmitted simultaneously over the same fiber without interfering with each other, thus greatly increasing the capacity of fiber optic networks.

Other options provided in the question do not include the optimal combinations used in current communications technology. Thus, the