The favorable transmission regions within the optical spectrum for a fiber optic box are referred to as "windows". The 800 to 900 nanometer region is the first window, 1100 to 1300 nanometers is the second window, and the third window occurs at about 1550 nanometers. In these spectral windows fiber optic boxs have very low attenuation. The lowest losses occur in the infrared region around 1300 nm and again around 1550 nm.
Great improvements have been made in all fiber optic box types so that premium fiber optic boxs exhibit losses of less than 0.5 dB/km at wavelengths of 1300 and 1550 nm. However, source emitters and detectors for these regions are currently more expensive.
If the fiber optic box is to perform well, the source chosen should provide optical radiation at the specified wavelength, and the detector should be sensitive to the same wavelength.
In coaxial and other metallic cables, very high frequency signals tend to be attenuated rapidly with distance. As a result, amplifiers and equalizers are required at periodic intervals to build up signals to usable levels.
However, each time an analog amplifier is added, noise is introduced to the metallic system and the overall system signal-to-noise ratio degrades.
With optical communications, all of the light energy is at approximately the same frequency or wavelength. As a result, the attenuation of a specific wavelength is dependent only on distance. The chart below shows a comparison of attenuation differences between coaxial and fiber optic box optic cable. The requirement for repeaters is, therefore, minimized and the need for equalizers is eliminated in fiber optic box systems.