CWDM system principles

CWDM mux is a low-cost WDM transmission technology for metro access layer. In principle, CWDM  mux is the use of different wavelengths of light multiplexer, optical signal multiplexing to a single optical fiber transmission link on the receiving end, with the optical demultiplexer mixed-signal in the fiber is broken down into different wavelengths signal connected to the receiving device. The principle shown in Figure 1. The main difference lies in DWDM mux: relative to DWDM systems in terms of the wavelength interval in the 0.2nm to 1.2nm, CWDM  mux has a wider wavelength interval, the industry accepted standard wavelength spacing of 20nm. The ITU-T G.694.2 wavelength is shown in Table 1. Each wavelength belongs to the band shown in Figure 2, covering the five single-mode fiber systems, O, E, S, C and L band.CWDM wavelength interval width, the technical specifications of the laser requirements are lower. The wavelength interval to reach 20nm, so the maximum wavelength shift of up to -6.5 ℃ ~ +6.5 ° C, the laser emission wavelength accuracy can be relaxed to ± 3nm, and the operating temperature range (-5 ° C ~ 70 ° C), temperature changes caused by wavelength drift is still within the permissible range, the laser without temperature control mechanism, so the structure of the laser is greatly simplified, the yield increase.In addition, the larger the wavelength interval means that the optical multiplexer / demultiplexer structure greatly simplified. Of CWDM systems, for example, the filter coating layers can be reduced to about 50 layers of 100GHz DWDM system filter coating layers of about 150 layers, which result in yield improvement, cost reduction, and supplier of filter greatly increase the pro-competitive. CWDM filter costs less than the cost of DWDM filter more than 50 percent, and will further reduce the automated production technology and increasing volume.