Optical fiber communication, as one of the main pillars of modern communication, plays an important role in modern telecommunication networks.
The development trend of optical fiber communication can be expected from the following aspects.
1.In order to realize increasing information capacity and long-distance transmission, single-mode fiber with low loss and low dispersion must be used. At present, G.652 conventional single-mode optical fiber is widely used in communication network optical cable lines. Although this fiber has a minimum loss of 1.55 μm, it has a large dispersion value of about 18 ps / (nm.km). It is said that when the conventional single-mode fiber is used at a wavelength of 1.55 μm, the transmission performance is not ideal.
If the zero-dispersion wavelength is shifted from 1.31 μm to 1.55 μm, it is called dispersion-shifted fiber (DSF), but when this fiber and erbium-doped fiber amplifier (EDFA) is used in a wavelength division multiplexing system (WDM), it will Due to the non-linearity of the fiber, four-wave mixing occurs, which prevents the normal use of WDM, which means that zero fiber dispersion is not good for WDM.
In order for the optical fiber communication technology to be successfully applied to the WDM system, the fiber dispersion should be reduced, but it is not allowed to be zero. Therefore, the new single-mode fiber designed is called non-zero dispersion fiber (NZDF), which ranges from 1.54 ~ The dispersion value in the 1.56μm range can be maintained at 1.0 ~ 4.0ps / (nm.km), which avoids the zero dispersion area, but maintains a small dispersion value.
Many examples have been reported publicly using NZDF’s EDFA / WDM transmission system.
2.Photonic devices used in optical fiber communication systems have also developed significantly in recent years. In order to meet the needs of WDM systems, multi-wavelength light source devices (MLS) have been developed in recent years. It mainly arranges multiple laser tubes in an array and makes a hybrid integrated optical component with a star coupler.
For the receiving end of the optical fiber communication system, its photodetector and preamplifier are mainly developed in the direction of high-speed or wide-band response. PIN photodiodes can still meet the requirements after improvement. For broadband photodetectors used in the long-wavelength 1.55μm band, a metal semiconductor-metal photodetection tube (MSM) has been developed in recent years. Traveling wave distributed photodetector. According to reports, this MSM can detect 78dB of 3dB frequency bandwidth for 1.55μm light waves.
The FET’s preamplifier is likely to be replaced by a high electron mobility transistor (HEMT). It is reported that the 1.55μm optoelectronic receiver using the MSM detector and HEMT pre-amplified optoelectronic integration (OEIC) process has a frequency band of 38GHz and is expected to reach 60GHz.
3. The point-to-point transmission PDH system in the optical fiber communication system has been unable to adapt to the development of modern telecommunications networks. Therefore, the development of optical fiber communication towards networking has become an inevitable trend.
SDH is a brand-new transmission network constitution with the basic characteristics of networking. It is a comprehensive information network that integrates multiplexing, line transmission and switching functions and has strong network management capabilities. It is currently being widely used.