The network nodes of 5g load-carrying network are connected with optical modules and optical fiber. Unlike 4G networks, 5g signal has a higher frequency and a reduced coverage of a single base station. The number of base stations to be deployed in 5g network will be 2-3 times that of 4G network.
Optical fiber transmission technology has become the dominant and widely used in the fields of telecommunication backbone network and data center. WDM transmission is widely used in order to increase transmission capacity. However, the specific transmission technology is different for different application scenarios. The main factors that affect the selection are the loss and dispersion of optical fiber link; the light source (including modulator) and detector adopted have an important influence on the cost of transmission system, and also the consideration factor in the selection of technical scheme. In addition, the inheritance of industrial chain has an important impact on cost and has become one of the important factors.
In the early low-speed transmission system, FP laser with low cost but wide spectrum line was usually used; for high-speed transmission over 10Gbps, DFB laser with narrow spectral line was often used. In order to control the cost, when the transmission distance is not long, people tend to modulate DFB laser directly, called DML. The chirp effect will be produced by the direct modulation laser, which will widen the spectrum line and produce more dispersion. Therefore, in order to not affect the linewidth of the semiconductor laser and thus transmit a longer distance, people connect an electric absorption modulator EAM after the laser. This dfb+eam combination structure is called EML laser.
WDM technology was first applied in telecommunication field, but it was mainly used in backbone and core network of long-distance transmission. The C-band (1530-1570nm) DWDM transmission was adopted. The selection basis is that the optical fiber transmission loss in this band is the lowest, but the cost of various optical devices in this industry chain is higher. With the development of mobile Internet and the rise of large-scale data center construction, optical fiber transmission technology has been widely used in data center, and has become the second and bigger blue sea market of optical fiber communication technology.
