C波段定义，L波段定义,S波段定义

Telecom Windows

Optical fiber communications typically operate in a wavelength region corresponding to one of the following “telecom windows”:

• The first window at 800–900 nm was originally used. GaAs/AlGaAs-based laser diodes and light-emitting diodes (LEDs) served as transmitters, and silicon photodiodes were suitable for the receivers. However, the fiber losses are relatively high in this region, and fiber amplifiersare not well developed for this spectral region. Therefore, the first telecom window is suitable only for short-distance transmission.
• The second telecom window utilizes wavelengths around 1.3 μm, where the loss of silica fibersis much lower and the fibers' chromatic dispersion is very weak, so that dispersive broadening is minimized. This window was originally used for long-haul transmission. However, fiber amplifiers for 1.3 μm (based on, e.g. on praseodymium-doped glass) are not as good as their 1.5-μm counterparts based on erbium. Also, low dispersion is not necessarily ideal for long-haul transmission, as it can increase the effect of optical nonlinearities.
• The third telecom window, which is now very widely used, utilizes wavelengths around 1.5 μm. The losses of silica fibers are lowest in this region, and erbium-doped fiber amplifiers are available which offer very high performance. Fiber dispersion is usually anomalous but can be tailored with great flexibility (→ dispersion-shifted fibers).

The second and third telecom windows are further subdivided into the following wavelength bands:

The second and third telecom windows were originally separated by a pronounced loss peak around 1.4 μm, but they can effectively be joined with advanced fibers with low OH content which do not exhibit this peak.

所以通讯中常用的C波段是指的是 1530nm-1565nm波段，L波段指的是156nm - 1625nm波段。