1 Fiber Optic's Type
More than 1.1 multimode fiber optic multimode fiber is the optical fiber that can transmit multiple optical conduction modes. At the beginning of the optical fiber communication, is the use of multimode fiber (g. 651 fiber), the working wavelength at 850 nm and 1300 nm, the attenuation constant of the < 4 db/km respectively and < 3 db/km, the dispersion coefficient of < 120 ps/respectively (nm) km) and < 6 ps/(nm) km). Due to its attenuation and dispersion, it can only be used for short distance communication. However, it has a large diameter and is not high enough for connectors and connectors. It is easier to use than single-mode fiber and is currently used in computer networks.
A single mode fiber optic single mode fiber is the optical fiber that transmits only one optical conduction module (schema). Its main advantage is that the attenuation is small, the transmission is long, the transmission capacity is large, and it is widely used in the long distance backbone network, the metropolitan area network, the connecting network and so on. Single-mode fiber due to transmit only base model, it does not exist delay difference between mold, with much larger bandwidth than multi mode fiber, the bandwidth of the single-mode fiber can reach more than dozens of GHz. So single mode fiber is especially suitable for long-distance, high-volume communication systems. With the development of optical fiber manufacturing technology and communication technology, the type of single-mode fiber is also developing.
Common single-mode fiber is the following:
The 1.2.1 g. 652 fibre-optic g. 652 fiber optic cable is a regular optical fiber, and it has both 1310 nm and 1550nm Windows. The zero dispersion point is located in the 1310nm window, while the minimum attenuation is in the 1550nm window. The typical values of the two Windows are: 1310 nm window attenuation is 0.3 ~ 0.4 dB/km, the dispersion coefficient of 0 ~ 3.5 ps/(nm) km), 1550 - nm window of attenuation is 0.19 ~ 0.25 dB/km, dispersion coefficient is 15 ~ 20 ps/(nm) km).
The 1.2.2 G. 653 optical fiber g. 653 optical fiber is the dispersion-shifted fiber, and is called the optimal optical fiber for the 1550nm window. People through the optical refraction profile design, to move the zero dispersion point to a 1550 - nm window, with the minimum of the fiber attenuation window with matches, make 1550 nm window has a minimum at the same time the dispersion and the minimum decay. The typical value of its 1550nm window is: the attenuation coefficient is 0.19 ~ 0.25 dB/km, the zero dispersion point is in 1525 ~ 1575nm wavelength area, and the dispersion coefficient of this interval is < 3.5 ps/(nm. Km). The excellent properties of this optical fiber in the 1550nm window make it the best choice for single wavelength, large capacity, and long distance transmission. If the TDM system is expanded purely along the way, the 20Gbit/s system can be launched directly without any dispersion compensation. The important defect of the g. 653 fiber is that the four-wave mixing limit is restricted by the use of the waveform multiplexing (WDM). So-called four-wave mixing phenomenon is caused by the nonlinear of the fiber, when different wavelengths in a single fiber transmission at the same time, due to the interaction, can produce new and, difference of wave component.
1.2.3 g. 655 optical fiber g. 655 optical fiber or non-zero dispersion-shifted fiber, it is in order to solve the g. 653 optical fiber in serious four-wave mixing effect, of g. 653 optical fiber the zero dispersion point of the move, to keep the dispersion coefficient of 1540 ~ 1565 nm range from 1.0 ~ 4.0 ps/(nm) km), avoiding the zero dispersion area, maintain a dispersion value, at least in order to more convenient to open multiple wavelength WDM systems. In the properties of the g. 655 fiber, the other features are the same as the G. 653, except for the zero dispersion point. It has a minimum attenuation coefficient and dispersion coefficient in the 1550nm window. Although its dispersion coefficient is slightly greater than G. 653 fiber, it has greatly reduced the dispersion limit distance relative to g. 652 fiber. It successfully solved the disadvantages of the g.652 fiber optic dispersion and g. 653 fiber in the 1550nm wavelength region, and the advantages of these two fibers. It can open a high speed 10Gbit/s, 20Gbit/s TDM system, and it can also be expanded by WDM mode.
Ways to increase the capacity of optical fiber transmission
In theory, increase the transmission capacity can have the following several ways: air separation of multiplexing (SDM), the electric time-division multiplexing (TDM), wavelength division multiplexing (WDM) and optical frequency division multiplexing (FDM) O, optical time-division multiplexing (TDM) O technology and optical soliton (So liton). Based on the practicality, only the TDM and WDM are briefly introduced.
TDM technology (TDM) TDM technology is a technique that is used to multiplex signals and is a traditional method of ampliation. PDH's 34,140, 565 Mbit/s, and the SDH's 155,622,2488,9952 Mbit/s are all used for reuse on electrical signals. According to the statistics, at 215Gbit/s, the price per bit of the system is reduced by about 30 percent per bit. That's why, in the past, people started using TDM technology. With the improvement of reuse rate, for example reaches 10 gbit/s is close to the limit of the silicon and the technology of arsenic, don't have much potential, the effect of fiber dispersion is also more serious, to put forward higher requirements to optical fiber. 2.2 wavelength division multiplexing (WDM) technology by WDM technology is to make full use of the single mode fiber low loss area has the huge bandwidth resources (about 25 THZ), USES the wavelength division multiplexer (wave) to different rules in the sender will wavelength of the signal light transmitted carrier and combined into a single fiber. At the receiving end, a wave separator (splitter) separates the light carriers that carry different signals from different wavelengths.
WDM technology of the main features are: (1) can make full use of optical fiber huge bandwidth resource, make a single fiber transmission capacity than single wavelength transmission increases several times or more. The use of N wavelengths to be transmitted in single mode fiber, which can be used to save the fiber in large volumes. (3) because of the same optical fiber transmission signal wavelength independent of each other, thus it can be completely different signal transmission properties, complete various business signal synthesis and separation, including digital signal and analog signal, synthesis and separation of the SDH and PDH signals. The channel is transparent to the data format, which is independent of the signal speed and the mode of modulation, which is the ideal method for network expansion and development. The use of WDM technology is used to enable network exchange and recovery to enable transparent, highly survivable optical networks in the future.
Suggestions for selecting fibre correctly
Choice must consider three key parameters of optical fiber types: (1) the biggest WuZhongJi each wavelength of the maximum bitrate transmission distance (2) (3) each number of the wavelength of the fiber. Of course, all these parameters should consider the requirements of the optical fiber final phase, not the initial requirements. According to the above parameters, if the maximum WuZhongJi transmission distance in 50 ~ 100 km (depending on the types of laser), then the g. 652 conventional fiber because of its low price is a more appropriate choice. If the distance is longer, and each wavelength of maximum bit rate is less than 10 gbit/s, so should be preferred to conventional optical fiber. If the distance is long, but only need single wavelength high rate (more than 10 gbit/s), then can choose g. 653 dispersion-shifted fiber. If the distance is long and requires a multi-wavelength load of 10 Gbit/s or higher speed, the g. 655 non-zero-dispersion-shifted fiber is the best option.
Thus put forward the following optical fiber selection principles: (1) short trunk optical cable access network and fiber because the distance is short, use more fiber core to increase the investment is not big, therefore generally should choose g. 652 conventional optical fiber. (2) the long-distance optical cable for long transmission distance, using more fiber core investment increase, so must have a high rate and multiple wavelengths of WDM technology, priority should be given by g. 655 dispersion-shifted fiber.
It is reported that in recent years in North America are starting a new round of fiber laying a climax, but on the trunk line has stopped using g. 652 optical fiber, but all adopt the g. 655 non-zero dispersion-shifted fiber. This trend deserves attention.
Whether choose g. 652 optical fiber or g. 655 optical fiber, in addition to conventional index for the attenuation and dispersion of the fiber and other request, generally can be put forward according to the requirement of the transmission rate of 10 gbit/s, PMD parameters, thus for later use WDM means to rapidly expand the capacity of the transmission system.