一, In this era of optical communication, the wavelength division multiplexer is one of the passive components. The wavelength division multiplexer is also one of the core components of optical fiber communication transmission. A wavelength division multiplexer is an optical passive device that uses two or more wavelengths of optical signals to be combined into the same optical fiber for transmission. The types of filter wavelength division multiplexers are: coarse wavelength division multiplexer and dense wavelength division multiplexer. The coarse wavelength division multiplexer is divided into: three-port wavelength division multiplexer, mini wavelength division multiplexer, common wavelength division multiplexer, etc. It is characterized by low insertion loss, high isolation and so on.

二，The function of the wavelength division multiplexer is to combine the light of different wavelengths on different optical fibers into one optical fiber for transmission, or to separate many wavelengths on the same optical fiber. To put it more simply, the function of a wavelength division multiplexer is to combine or separate wavelengths, and in terms of land, it is to combine and separate wavelengths. All wavelengths of the coarse wavelength division multiplexer are from 1270 to 1610.

三，In 2014, the export volume of China‘s WDM device industry was 345,100 pieces, and in 2018, the export volume of China‘s WDM device industry was 550,000 pieces, a year-on-year increase of 15.9%.

四，Wavelength division multiplexer is a low-cost WDM transmission technology for the access layer of the metropolitan area network. In principle, CWDM is to use an optical multiplexer to multiplex optical signals of different wavelengths into a single optical fiber for transmission. signal, connect to the corresponding receiving equipment. Its principle is shown in Figure 1. The main difference with DWDM is: Compared with the wavelength interval of 0.2nm to 1.2nm in the DWDM system, CWDM has a wider wavelength interval, and the standard wavelength interval in the industry is 20nm. The wavelengths specified in ITU-T G.694.2 are shown in Table 1. The bands to which each wavelength belongs are shown in the figure below, covering the five bands of O, E, S, C, and L of the single-mode fiber system.

五，Due to the wide wavelength interval of the CWDM system, the requirements for the technical indicators of the laser are relatively low. Since the wavelength interval reaches 20nm, the maximum wavelength shift of the system can reach -6.5°C～+6.5°C, the emission wavelength accuracy of the laser can be relaxed to ±3nm, and within the working temperature range (-5°C～70°C), the temperature The wavelength drift caused by the change is still within the allowable range, and the laser does not need a temperature control mechanism, so the structure of the laser is greatly simplified and the yield is improved.

六，In addition, the larger wavelength interval means that the structure of the optical multiplexer/demultiplexer is greatly simplified. For example, the number of coating layers of the filter in the CWDM system can be reduced to about 50 layers, while the number of coating layers in the 100GHz filter in the DWDM system is about 150 layers. conducive to competition. The cost of CWDM filters is more than 50[%] less than that of DWDM filters, and will be further reduced with the increase of automated production technology and batches.