How is Optical Switching Technology use in the Communication Network

Fiber optic network, as synonymous with high-speed and effective in the communication system has been for a large scaled deployed and applied. However, the transparent, high survivability of optical communication network is a goal of broadband communication network. Optical switching technology as an important foundation for all-optical communication network technology, its development and application will greatly affect the development direction of future optical communication networks. 

 

Advantage of optical fiber communication is the huge capacity and strong anti-jamming capability, superior performance of which has already been confirmed, and in modern communication systems gradually replace the electronic circuits in the past as the main components of the communication network, becoming an important component of modern communication.

 

Optical switching

 

The optical signals are multiplexed in three ways, space division, time division, and WDM, the corresponding optical switching methods space division switching, time division switching and wave division switching to complete the three multiplexed channels.

 

The space division switching is the domain swap space on the optical signal, the basic functional components of the spatial light switch. Spatial light switch is the principle of optical switching components gate array switch can be in any of the multiple input multiple output fiber established path. It can constitute an empty spectroscopic switching unit, and other types of switches can also together constitute a time-division switching unit or wave stars. Empty spectral switches generally have both fiber-based and space-based space division switching is a division of swap space.

 

Time division multiplexed signal multiplexing method is a communication network, a channel is divided into a number of different time slots, each optical path signal distribution occupy different time slots, a baseband channel to fit the high-speed optical data stream transmission. Need to use time division switching time slot interchange. The time slot interchanger of the input signal is sequentially written to the optical buffer, and then read out in accordance with established order, thus achieving a one frame at any one time slot exchange to another time slot and outputs completed the timing exchange program. Usually bistable lasers can be used as an optical buffer, but it is only the bit output, and can not meet the demand of high-speed switching and large capacity. While the optical fiber delay line is a more time-division switching device, the time-division-multiplexed signal light input to the optical splitter, so that each of its output channels are only a light signal of the same timeslot, then these signals combined through different optical delay line, after a signal of the type of delay line to obtain a different time delay, the final combination fits before the signals are multiplexed with the original signal, thereby completing a time-division switching.

 

Ships in WDM systems, the source and destination are required to transmit signals using the same wavelength, such as non-multiplexed so multiplexed in wavelength division multiplexing technology is widely used in the optical transmission system, each multiplex terminal using additional multiplexers, thus increasing system cost and complexity. In the WDM system, wave spectral exchange in the intermediate transmission nodes, to meet no additional devices to achieve wavelength division multiplexing system source and destination communicate with each other, and you can save system resources, improve resource utilization rate.

 

Wave spectroscopic switching system first lightwave signal demultiplexer is divided into plural wave splitting is required to exchange the wavelength channels in each channel wavelength switching the last signal obtained after multiplexing composed of a dense wave division multiplexing signal from an optical output, which take advantage of the characteristics of the fiber-optic broadband, low-loss band multiplexing multiple optical signals, greatly improving the utilization of the Fiber Channel, to improve the communication system capacity.

 

Hybrid switching technology is used in large-scale communication network in a variety of the optical path switching technology a mixture of multi-level link connection. In large-scale networks need to be multi-channel signal splitter and then access different link, making the advantages of wavelength division multiplexing can not play, so using wavelength division multiplexing technology levels connecting link, and then space division switching technology used in all levels of link exchange to complete the interface between the link, finally destination and then wave of the exchange of technical output corresponding optical signals, signal combined final sub output. Mixed-use switching technology time mixed, air separation - after midnight - wavelength division mixed several minutes - hours of mixing, air separation - wavelength division.

 

All-optical network switching technology

To realize the all optical network switching, the first is to use the circuit switch based optical add-drop multiplexing (OADM) and OXC (optical cross connect) technology to achieve wavelength switching, and then further realization of optical packed switching.

 

Wavelength switching is based on wavelength in units of optical circuit switched domain, wavelength switching optical signals to provide end-to-end routing and wavelength assignment channel. Wavelength switching key is to use the corresponding network node equipment, optical add-drop multiplexing optical cross-connect. Optical add-drop multiplexing the working principle is based on all-optical network nodes drop and insert the required wavelength path. Its main constituent elements of the multiplexer reconciliation multiplexer, as well as optical switches and tunable harmonic, etc.. Optical add-drop multiplexing of the working principle and the synchronous digital hierarchy (SDH) multiplexer separate interpolation function is similar, but in the time domain, while the other is acting in the optical domain. The optical cross-connect and the synchronous digital system digital cross-connect (DXC) similar effect, but to achieve the cross-connection to the passage in the wavelength at which the optical network node.

 

Optical wavelength to exchange essentially took office contingent is not efficient optical switching, connection-oriented attribute it established wavelength channel re-distribution to achieve maximum utilization efficiency can not be achieved, even if the communication is idle. Optical packet switching can be implemented with a minimum switching granularity multiplexing of bandwidth resources, improve the communication efficiency of the optical network. Optical packet switching is generally light and transparent packet-switched (OTPS), optical burst switching (OBS) and optical label switching (OMPLS). The optical the transparent packet switching characteristics is the packet length is fixed, the use of synchronous switching manner, the need for all input packets are synchronized in time, thus increasing the technical difficulty and increase the use of cost. The transmission optical burst the use of a variable-length packet data transfer header control information and separated in time and space, to overcome the shortcomings of the synchronization time, but it is possible to generate the packet loss problem. Optical label switching is carried out to add a tag in the IP packet in the core network access re-packet, and the routing method according to the tag inside the core network.

Although optical switching communication Occasion require a higher (generally more than 10Gb / s) is more suitable for lower transmission costs and greater system capacity can be achieved; via digital transmission rate when the system requirements require a lower transmission rate (2.5Gb / s or less), the connection configuration more flexible access may be more appropriate to use the old-fashioned way of photoelectric conversion. Therefore, the practical application of the current should be selected according to the application scenarios appropriate system deployment.

 

With the future communication network technology development and all-optical network, optical switching technology will be more innovative and more efficient ways for communication network photochemical contribute to become an important part of social development and people's lives.

 

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