optical fiber
The optical fiber is the transmission channel of optical signals and is the key material for optical fiber communication.
The optical fiber consists of a core, a cladding, a coating layer, and a jacket, and is an asymmetrical cylinder of a multilayer dielectric structure. The main body of the core is
silica, which is doped with trace amounts of other materials to increase the refractive index of the material. The outer core has a cladding layer, and the cladding has a
different refractive index from the core and the core has a higher refractive index to ensure that the optical signal is mainly transmitted in the core. Outside the cladding is a
layer of paint that is used primarily to increase the mechanical strength of the fiber so that the fiber is not damaged by external damage. The outermost layer of the fiber is a
jacket and is also protective.
The two main features of an optical fiber are loss and dispersion. The loss is the attenuation or loss of the optical signal per unit length, expressed in dB/km. This parameter is
related to the transmission distance of the optical signal. The larger the loss, the shorter the transmission distance. Multi-microcomputer elevator control systems generally
have a short transmission distance, so in order to reduce costs, plastic optical fibers are mostly used. The dispersion of the fiber is mainly related to pulse broadening. In the
Mitsubishi elevator control system, optical fiber communication is mainly used for data transmission between group control and single ladder and data transmission between
two parallel single ladders. The fiber optic device used in the Mitsubishi elevator is mainly composed of a light source, an optical receiver, and an optical fiber, wherein the
light source and the optical receiver are packaged in a fixed plug of the optical fiber connector, and the optical fiber is connected to the movable plug.
Optical wavelength division multiplexing
WDM (Wavelength Division Multiplexing) technology refers to the use of multiple lasers to simultaneously transmit multiple wavelengths of light on the same fiber. It can
greatly increase the transmission capacity of the fiber transmission system. Currently, 1.6 Tbit/s WDM systems have been commercialized on a large scale. In order to further
increase the capacity of optical fiber transmission, the DWDM (Dense Wavelength Division Multiplexing) foundation became the main research object in the world after
1995. Lucent Bell Labs believes that the commercial DWDM system capacity can reach 100 Tbit/s. At present, DWDM based on 10 Gbit/s has gradually become the
mainstream of core networks among many operators in China. In addition to the increasing number of wavelengths and transmission capacity of the DWDM system, the
optical transmission distance has also increased from 600 km to over 2000 km. In addition, Coarse Wavelength Division Multiplexing (CWDM) has also emerged in the
expansion of metro optical transport networks, with advantages such as large capacity, short-distance transmission and low cost. The researchers also found that wavelength
division multiplexing of multiple optical time division multiplexed OTDM signals can greatly increase transmission capacity. As long as the appropriate combination can
achieve Tbit / s transmission, it is also the future development direction of optical fiber communication. Most of the transmission experiments in the laboratory over 3 Tbit/s
are implemented in this way.
Optical soliton communication technology
Light is a special ultra-short optical pulse on the order of ps. After long-distance transmission through the fiber, the waveform and speed remain unchanged. Optical soliton
communication uses optical soliton as a carrier to realize long-distance undistorted communication. In the case of zero error, information transmission can reach thousands
of miles. Numerous experiments have shown that it can be used for submarine cable communication, etc., and is suitable for combination with WDM systems to form ultra-
high-speed and large-capacity optical communication. When the single-channel rate reaches 40 Gbit/s or more, the advantages of optical soliton communication are fully
realized.
Fiber access technology
Fiber access using PON technology can be combined with a variety of technologies, such as ATMSDH and Ethernet, to generate APON, GPON, and EPON, respectively. In
contrast, EPON inherits the advantages of Ethernet and the cost is relatively low. After combining with fiber technology, EPON is not limited to local area networks, but also
extends to metropolitan area networks and even wide area networks. Now, fiber-to-the-home adopts EPON technology; GPON has the most advantages in circuit-switched
service support, and can fully utilize existing SDH technology, but the technology is more complicated and the cost is higher; APON will be used to implement FTTH solution.
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