CWDM System Principle
CWDM ( Coarse Wavelength Division Multiplexing ) system, namely the coarse wavelength division multiplexing system, is a metropolitan area network oriented access layer and low cost WDM transmission technology. From the principle of speaking, CWDM is the use of optical multiplexer different wavelength multiplexed optical signal to a single optical fiber for transmission, the receiving end of the link, by means of optical demultiplexer optical fiber in the mixed signal into signals of different wavelengths, is connected to a corresponding receiving equipment. Its principle as shown in figure 1. With DWDM the main difference is that: compared with DWDM system of 0.2nm to 1.2nm wavelength interval, CWDM has a wide wavelength interval, the industry standard wavelength spacing of 20nm. ITU-T G.694.2 specified wavelength as shown in table 1. The wavelength of the band as shown in Figure 2, covered the single mode fiber system O, E, S, C, L five band.
Because the CWDM system of laser wavelength interval width, low technical requirements. Due to the wavelength interval to achieve a 20nm, so the system maximum wavelength shift of 6.5℃ ~ 6.5℃, laser emission wavelength accuracy can be relaxed to± 3nm, but also in the operating temperature range ( 5～ 70 ℃), caused by temperature variation of wavelength shift is still within the acceptable range, laser without temperature control mechanism, so laser greatly simplifies the structure, improve the rate of finished products.
In addition, the larger wavelength interval mean optical multiplexer / demultiplexer greatly simplified structure. For example, the CWDM system filter coating layers can be reduced to about 50 stories, while the DWDM system in the 100GHz filter coating layer is about 150, which leads to improve the rate of finished products, cost is reduced, and the filter suppliers greatly increased competition in favor of. CWDM filter cost than DWDM filter will cost 50% less than, but with the automated production technology and mass increase will further reduce.
In addition, CWDM located in the metropolitan area network within short distance transmission (80 kilometers ), and the passage rate is generally not more than 2.5Gbps, so the transmission lines also without the need for optical amplification, dispersion, nonlinear and other aspects to consider, so you can make the system simplified.
Through the above means, through to the wavelength spacing of expansion and simplification of the equipment, make CWDM system unit optical channel cost can be reduced to DWDM system 1/2 or even 1/5, in the metropolitan area network access layer has a strong advantage.