FOT Lessons: Key technologies of optical networks

  The main advantage of the future all-optical network is that the optical signal does not need to undergo optical-electrical and electro-optical conversion when passing through the optical switching unit. Therefore, it is not limited by the response speed of photoelectric devices such as detectors and modulators, but it needs to be solved. Some key technical issues.

Optical signal amplification

  The signal transmission distance of the optical fiber communication system is limited by the transmission loss and dispersion delay of the optical fiber. In order to transmit signals farther, in traditional fiber-optic communication systems, the use of electro-optical-electric conversion regenerator transmissions not only complicates the communication equipment, increases the cost, but also affects the advantageous performance (bandwidth) of optical fiber transmission. The play. If optical amplifiers are used to amplify and transmit optical signals directly on the optical path, ie, all-optical relay technology, more line equipment can be saved, economic benefits can be improved, and the advantages of optical fiber transmission can be more clearly demonstrated. Erbium doped fiber amplifiers (EDFA) can provide fairly flat gain characteristics in the 1530 to 1565 nm wavelength range. If we add EDFA to gain equalization, we can make the amplifier’s wavelength range up to 90nm (about 10^13Hz). Dispersion compensation, forward error correction, EDFA preamplifier and post-amplifier, remote pumping preamplifier and post-rearrangement technology are currently used to enable signals with a transmission rate of 2.5 Gbit/s to reach a distance of over 500 kilometers without relay transmission.

Wavelength Division Multiplexing to Achieve Multiplexing of Optical Signals

  In order to solve the transmission capacity problem of the channel, optical multiplexing technology is mostly used in optical fiber communication systems. Optical multiplexing techniques include Optical Time Division Multiplexing (OTDM) and Optical Code Division Multiplexing (OCDM). In order to further increase the transmission capacity, Dense Wavelength Division Multiplexing (DWDM) technology may also be used.

Wavelength Selection and Wavelength Conversion Technology

  In wavelength division multiplexing (WDM) technology, the number of wavelengths λ represents the number of channels. In optical fiber communication systems, optical filters can be used to select useful wavelengths.
If the same wavelength is output from two channels from the same port, it will cause the phenomenon of wavelength contention and blocking. This requires the use of wavelength conversion technology.

Optical switching technology

  It is well known that the Public Switched Telephone Network (PSTN) uses circuit-switched technology and the computer network uses packet-switched technology. If the optical switching technology is adopted in the optical fiber communication network, that is, optical cross-connect equipment (OXC) is adopted, the advantages of high transmission rate, large capacity, and strong anti-interference capability of the optical fiber communication system can be embodied.

Optical Add-drop Multiplexing

  In telecommunication networks, add/drop multiplexing is the processing of electrical signals. In the wavelength division multiplexing system of optical fiber communication, Optical Add and Drop Multiplexer (OADM) technology is used to avoid an unnecessary demultiplexing process in the process of information transmission to simplify the structure of the node hardware. Reduce related management operations and increase network node throughput.

Optical Network Intelligent Control Technology

  After optical transmission channels are adopted, new network control and network management technologies need to be developed to implement Intelligent Optical Network (ION), for example, implementation of optical channels, adjustment of optical channels (wavelength allocation and management), and optical network layer. Structure, optical network nodes and interface technologies etc.

Integrated optical technology

  The structure of an all-optical network is inseparable from various functions and different types of optical devices to complete the transmission, transmission, and reception of optical signals, such as optical transmitter/receivers, optical wavelength division multiplexing/demultiplexers, Optical filters, wavelength converters, optical amplifiers, dispersion compensators, etc. Currently, a variety of optical devices for optical fiber communication systems have been manufactured using photonic integration technologies, such as multi-wavelength laser arrays, photodetector arrays, optical couplers, optical multiplexers, optical filters, and the like.
  All of the key technologies discussed above, namely, the basis of fiber optic communications, are based on the production of ultra-pure silica glass fibers and the production of semiconductor lasers.

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