The optical fiber network, as the pronoun of high-speed and effective, has been deeply rooted in the people's mind, and the deployment and application have been realized on a large scale in the communication system. And the full-optical communication network which realizes the transparent and high survivability is the development goal of the broadband communication network.

As an important basic technology in all-optical communication network, the development and application of optical switching technology determine the direction of optical communication network in the future to a great extent. The concept and development of optical switching technology and its application in communication are briefly introduced for the research and discussion of scientific researchers.

Optical switching product

The advantage of optical fiber communication is that the great information capacity and strong anti-interference ability, its superior performance has long been confirmed, and the communication network which is mainly composed of the conventional electronic circuit is gradually replaced in the modern communication system, and becomes an important component of modern communication. The lack of the electronic circuit in the original communication system is the bottleneck of the performance of the advantage of the optical fiber communication system.

In an optical fiber communication system, only a scientific and reasonable communication system can play an advantage of an optical fiber system, form an ideal high-speed, large-capacity and high-quality optical fiber network, and the original electronic circuit communication is a great hindrance in the implementation of all-optical networks, The need to remove the influence of the electronic circuit requires the progress of the technology of the optical fiber communication system. the traditional communication network and the optical fiber network coexist in the process of photoelectric conversion, and the combination of the two is limited by the electronic device, the capacity of the photoelectric exchange information is determined in the working speed of the electronic part, the optical fiber network with large bandwidth becomes narrow when the photoelectric exchange is carried out, So that the bandwidth of the entire network is also limited. Therefore, it is necessary to directly perform optical switching on the switching node in the optical communication network without the process of photoelectric conversion, so that the communication bandwidth of the optical fiber can be released, and the communication capacity of the optical fiber is high and the communication rate is high. So the technology of optical switching is attracting attention, and is considered to be the most important part of the next generation of broadband technology.

1. Way of optical switching

There are three ways of optical signal reuse: free division reuse, time division reuse and wavelength division multiplex. There are also space division switching, time division switching and wavelength division switching to complete the switching of three kinds of multiplex channels.

Space division switching is to exchange optical signals in spatial domain, and its basic functional component is spatial optical switch. The principle of space optical switch is that the optical switching element is composed of gate array switch, and the path can be established arbitrarily in multi-input and multi-output optical fiber. It can form a space division optical switching unit, or it can form a time division or wavelength division switching unit together with other types of switches. There are two kinds of space separation switches: optical fiber type and space type. Space division switching is the division of switching space.

Time division multiplexing is a commonly used signal multiplexing method in a communication network, a channel is divided into a plurality of different time slots, each optical path signal is allocated to occupy different time slots, and a baseband channel is fitted into a high-speed optical data stream for transmission. Time-division switching requires the use of time-slot switches. The time slot switch sequentially writes the input signal into the optical buffer, and then reads out according to a given sequence, so that any time slot in one frame is switched to another time slot and is output, and the sequence exchange program is completed. A general bi-stable laser can be used as an optical buffer, but it can only be output by bit, which does not meet high-speed switching and large capacity requirements. and the optical fiber delay line is a time division switching device which uses more time division switching equipment, and the time division multiplexing optical path signals are input into the optical splitter, so that only one optical signal of the same time slot is arranged on each output path, and the signals passing through different optical delay lines are combined, The signals of different time delay lines have different time delays, and finally, the signals are combined exactly to the original signal before the signal multiplexing, so that time division switching is completed.

Wavelength division multiplexing technology is widely used in optical transmission system. In optical wavelength division multiplexing system, the source and destination end need to transmit signals with the same wavelength. For example, each multiplexing terminal needs to use additional multiplexing equipment in case of multiplexing, which increases the cost and complexity of the system. Therefore, if wavelength division optical switching is used on intermediate transmission nodes in the wavelength division multiplexing system, it can be satisfied that the source and destination of the wavelength division multiplexing system are interconnected without additional devices, and the system resources can be saved and the resource utilization rate can be improved.

Wave dividing switching system firstly divides optical wave signals into multiple wavelength channels required for wavelength division exchange. After wavelength exchange is performed for each channel, the resultant signal is multiplexed into a dense wavelength multiplexing signal, which is outputted by one optical cable, which uses the characteristics of optical fiber broadband, multiplexing multi-channel optical signals in the band with low loss, greatly improves the utilization rate of fiber channel and improves the capacity of communication system.

Hybrid switching technology is the optical path connection of multistage links composed of a variety of switching technologies in large-scale communication networks. Because it is necessary to divide the multi-channel signals into different links in large-scale networks, the advantages of WDM can not be brought into play, so it is necessary to use WDM technology in the connection links at all levels, and then use the space division switching technology to complete the connection between links. Finally, the destination uses wavelength Division switching technology to output the corresponding optical signals, and then carries on the signal merging and final shunt output. There are several common switching techniques, such as free division-time division mixing, space division-wavelength division mixing, space division-time division-wavelength division mixing and so on. In the first step of all-optical switching, wavelength switching is realized by using optical add / drop multiplex (OADM) and optical cross-connected (OXC) technology based on circuit switching, and then optical packet switching is further realized.

The wavelength exchange is a circuit exchange in which the optical domain is carried out in units of wavelength, and the wavelength exchange is to provide an end-to-end routing and distribution wavelength channel for the optical signal. The key to wavelength switching is to use the corresponding network node device, i. e., optical add/ drop multiplexing or optical cross-connection. The principle of optical add/ drop multiplexing is to drop and insert the required wavelength path in all-optical way in the network node. The main components include a multiplexer and a demultiplexer, and an optical switch and an adjustable harmonic. The operation principle of the optical add/ drop multiplexing is similar to the function of the add/ drop multiplexer in the synchronous digital system (SDH), but one is in the time domain and the other is in the optical domain. While the optical cross-connection is similar to the digital cross connector (dxc) in the synchronous digital system, but is a cross-connection to the wavelength path at the optical network node.

The optical wavelength exchange is still an inefficient optical switching mode, and its connection-oriented property makes it impossible to reallocate the wavelength channel that has been established to achieve the maximum utilization efficiency, even if the communication is in an idle state. And the optical packet switching can realize the multiplexing of the bandwidth resources with extremely small switching granularity and improve the communication efficiency of the optical network. Optical packet switching is currently in general light transparent packet switching (OTPS), optical burst switching (OBS) and optical label switching (OMPLS) technology. The main characteristic of the optical transparent packet switching is that the packet length is fixed, and in a synchronous exchange mode, all input packets need to be synchronized in time, thereby increasing the technical difficulty and increasing the using cost. And the optical burst uses the variable length packet, the control information of the transmission header and the transmission mode of the data of the packet body are separated in time and space, and the defect of the synchronization time is overcome, but the problem that the packet loss is likely to be generated. And the optical mark exchange is a method for adding a mark at the access point of the core network to re-package the IP packet, and performing route selection according to the mark inside the core network.

While the way in which the optical exchange requires a higher (generally 10 gb/ s) communication situation for a digital transmission rate, a lower transmission cost and greater system capacity can be achieved; however, when the transmission rate required by the system is required to be lower (refer to less than 2.5 gb/ s), When the connection configuration is flexible, access to the old-fashioned way of photoelectric conversion may be more appropriate. Therefore, in the practical application, the appropriate system deployment should be selected according to the application scene.

With the development of communication network technology and the realization of all-optical network in the future, optical switching technology will contribute to the all-optical of communication network in a more novel and efficient way, and become an important part of social development and people's life.