DWDM System Principle
DWDM technology utilizes the bandwidth and low loss characteristics of single-mode fiber, uses multiple wavelengths as carriers, and allows each carrier channel to be transmitted simultaneously in the fiber
Compared with the general single-channel system, dense WDM (DWDM) not only greatly improves the communication capacity of the network system and makes full use of the bandwidth of the optical fiber, but also has many advantages such as simple expansion and reliable performance, especially it can directly connect Entering a variety of businesses makes its application prospects very bright.
In the analog carrier communication system, in order to make full use of the bandwidth resources of the cable and improve the transmission capacity of the system, the method of frequency division multiplexing is usually used. That is, the signals of several channels are simultaneously transmitted in the same cable, and the receiving end uses a band-pass filter to filter out the signals of each channel according to the different carrier frequencies.
Similarly, the optical frequency division multiplexing method can also be used in the optical fiber communication system to improve the transmission capacity of the system. In fact, such multiplexing methods are very effective in optical fiber communication systems. Different from the frequency division multiplexing in the analog carrier communication system, in the optical fiber communication system, the light wave is used as the signal carrier, and the low loss window of the optical fiber is divided into several parts according to the frequency (or wavelength) of each channel light wave. channels, so as to realize the multiplexed transmission of multiple optical signals in one optical fiber.
Since some optical devices (such as filters with very narrow bandwidth, coherent light sources, etc.) are not yet mature, it is very difficult to realize optical frequency division multiplexing (coherent optical communication technology) with very dense optical channels. Based on the current device level, frequency division multiplexing of separated optical channels has been realized. People usually call the multiplexing of optical channels with large spacing (even on different windows of optical fibers) optical wavelength division multiplexing (WDM), and then call DWDM with small channel spacing in the same window as dense wavelength division multiplexing (DWDM). ). With the advancement of science and technology, modern technology has been able to achieve multiplexing with a wavelength interval of nanometers, and even multiplexing with a wavelength interval of several tenths of a nanometer, but the technical requirements of the device are more stringent, so the 1270nm The wavelength band from 1610nm to 20nm is called Coarse Wavelength Division Multiplexing (CWDM).
Schematic diagram of the composition and spectrum of the DWDM system. The optical transmitter at the sending end sends out optical signals with different wavelengths but with certain precision and stability, which are multiplexed by the optical wavelength multiplexer and sent to the erbium-doped fiber power amplifier (the erbium-doped fiber amplifier is mainly used to compensate for the It can reduce the power loss and improve the transmission power of the optical signal), and then send the amplified multi-path optical signal into the optical fiber for transmission. In the middle, it can be determined whether there is an optical line amplifier or not according to the situation, and it reaches the receiving end through an optical preamplifier (mainly used for Improve the receiving sensitivity in order to extend the transmission distance) After amplification, it is sent to the optical wavelength demultiplexer to decompose the original optical signals.
