Wednesday 4 May 2011

Transmission windows

Transmission windows

Each effect that contributes to attenuation and dispersion depends on the optical wavelength. The wavelength bands (or windows) that exist where these effects are weakest are the most favorable for transmission. These windows have been standardized, and the currently defined bands are the following:[11]
Band Description Wavelength Range
O band original 1260 to 1360 nm
E band extended 1360 to 1460 nm
S band short wavelengths 1460 to 1530 nm
C band conventional ("erbium window") 1530 to 1565 nm
L band long wavelengths 1565 to 1625 nm
U band ultralong wavelengths 1625 to 1675 nm

Note that this table shows that current technology has managed to bridge the second and third windows that were originally disjoint.

Historically, there was a window used below the O band, called the first window, at 800-900 nm; however, losses are high in this region so this window is used primarily for short-distance communications. The current lower windows (O and E) around 1300 nm have much lower losses. This region has zero dispersion. The middle windows (S and C) around 1500 nm are the most widely used. This region has the lowest attenuation losses and achieves the longest range. It does have some dispersion, so dispersion compensator devices are used to remove this.

No comments:

Post a Comment