Application of Optical Switching Technology in Communication Networks

As a synonym for high-speed and effective network, optical fiber networks are widely used in communication systems. Achieving transparent and high-survivability all-optical communication networks is the development goal of broadband communication networks. As an important basic technology in all-optical communication networks, the development and application of optical switching technology determine the future direction of optical communication networks. Brief Introduction to the concept and development of optical Exchange Technology and Its Application in communication for the Research and Discussion of researchers.

The advantage of optical fiber communication lies in its huge information capacity and strong anti-interference capability. Its superior performance has been proved, and it gradually replaces the communication network consisting of Electronic lines in modern communication systems, it has become an important form of modern communication. However, the lack of electronic lines in the original communication system hinders the advantage of the optical fiber communication system and becomes a performance bottleneck.

In an optical fiber communication system, only a scientific and reasonable communication architecture can give full play to the advantages of the optical fiber system to form an ideal high-speed, large-capacity, high-quality optical fiber network, the original electronic line communication is a huge obstacle in the implementation of the all-optical network. To remove the impact of electronic lines, the progress of the optical fiber communication system technology is required [1]. when traditional communication networks and optical fiber networks coexist, there is a process of photoelectric transformation, and the combination of the two is limited by electronic devices. The size of photoelectric exchange information depends on the working speed of the electronic part, originally, the optical fiber network with a large bandwidth became narrower during the photoelectric switching, and the bandwidth of the entire network was also limited. Therefore, in optical communication networks, it is necessary to directly perform optical switching on the switching node without the photoelectric conversion process. In this way, the optical fiber communication bandwidth can be released and the advantage of large communication capacity and high communication rate can be achieved. Therefore, the optical switching technology has attracted a lot of attention and is considered the most important part of the next-generation broadband technology.

1. Optical Switching

Optical Signal multiplexing generally involves three methods: Air division multiplexing, time division multiplexing, and wavelength division multiplexing. There are also air division switching, time division switching, and wavelength division switching for the exchange of three multiplexing channels [2].

The Air Separation switch is used to swap optical signals in the spatial domain. Its basic function component is the spatial optical switch. The principle of the Spatial Optical Switch is to form a gate switch, which can be used to establish any path in the optical fiber of multiple inputs and outputs. It can constitute an Air Separation optical switching unit, or it can constitute a time division or wavelength division switching unit together with other types of switches. Air Separation optical switches generally have two types of optical fiber type and space type, and the Division of swap space is used for air separation.

Time division multiplexing is a common method of signal multiplexing in communication networks. A channel is divided into several different time slots, and each optical path signal is allocated to occupy different time slots, A baseband channel is fitted to a high-speed optical data stream for transmission. Time division switching requires the use of time slot switches. The Time Slot Switch writes the input signal to the Light cache in sequence and reads the data in the sequence. In this way, any time slot in one frame is switched to another time slot for output, the Program for time sequence switching is completed. Generally, a bistability laser can be used as an optical cache, but it can only output by bit and cannot meet the needs of high-speed switching and large capacity. The optical fiber delay line is a time-division switching device that inputs time-division multiplexing optical signals into the optical splitter so that each output channel has only one optical signal with the same time slot, then, the signals passing through different optical delay lines are combined, and the signals passing through different delay lines obtain different time latencies. The final combination is exactly in line with the original signal before signal multiplexing, this completes the time-based exchange.

In optical transmission systems, the optical division multiplexing technology is widely used. Generally, in optical Division Multiplexing Systems, the source and destination must use the same wavelength of light to transmit signals, for example, when the multiplexing is not performed, additional multiplexing devices are required for each multiplexing terminal, which increases the cost and complexity of the system [3]. therefore, if Wave Optical splitting switching is used on the intermediate transmission node in the wavelength division multiplexing system, the source and target ends of the wavelength division multiplexing system can be interconnected without additional devices, in addition, it can save system resources and improve resource utilization.

The wave splitting switching system first splits the light wave signal into multiple wavelength channels required for the wave splitting switching, and performs wavelength switching for each channel, after the signal is reused, a dense wavelength division multiplexing signal is formed and output by a optical fiber cable. This utilizes the fiber broadband feature to reuse the optical fiber signals in low-loss bands, this greatly improves the utilization of optical fiber channels and the capacity of the communication system.

Hybrid exchange technology is a multi-level link optical path connection that uses a combination of multiple exchange technologies in a large-scale communication network. Because multiple signal channels need to be connected to different links in a large-scale network, the advantages of Wavelength Division Multiplexing cannot be realized. Therefore, wavelength division multiplexing technology must be used in Connection links at all levels, then, the Air Separation switching technology is used for link exchange at all levels, and the destination end outputs the corresponding optical signals by using the wavelength division switching technology. Then, the signals are merged and output separately. Common exchange technologies include air division-Time Division mixing, Air Division-wavelength division mixing, and Air Division-Time Division-wavelength division mixing.

2. All-optical network switching technology

The first step in the implementation of all-optical switching is to use the optical multiplexing (OADM) and optical crossover (OXC) Technology Based on the circuit switching method to achieve wavelength switching, then we further implement optical packet switching [4].

Wavelength exchange is a circuit exchange in Optical Fields in units of wavelength. wavelength exchange provides end-to-end Routing and Wavelength distribution channels for optical signals. The key to wavelength switching is to use the corresponding network node equipment, that is, optical insertion and multiplexing or optical cross-connection. The principle of optical insertion and multiplexing is to separate and insert the required wavelength path in all-optical mode in network nodes. Its main components include multiplex and demultiplexing, as well as optical switches and tunable harmonic filters. The working principle of optical multiplexing is similar to that of Synchronous Digital System (SDH), but one is in the time domain and the other is in the optical domain. Optical cross-connection works similar to the digital cross-connector (DXC) in the Synchronous Digital System, but implements the cross-connection of the wavelength path at the optical network node.

In essence, optical wavelength switching is not efficient. Its connection orientation makes it unable to reallocate established wavelength channels to maximize utilization efficiency, even if the communication is idle. However, optical packet switching can reuse bandwidth resources at a very small granularity, improving the communication efficiency of optical networks. Currently, the optical packet switching (OTPS), optical burst switching (OBS), and optical mark switching (OMPLS) technologies are generally used for optical packet switching. The main feature of transparent optical packet switching is that the group length is fixed and the synchronous switching mode is adopted. It is necessary to synchronize all input groups in time, which increases the technical difficulty and costs. In light of sudden use of variable length grouping, the use of the control information of the transmission packet header and the packet body data separation in time and space transmission mode, overcome the shortcomings of synchronization time, however, packet loss may occur. In contrast, optical tag switching adds a tag in the access area of the core network to re-package the IP packet, and selects routes based on the tag in the core network.

Although the optical switching method is more suitable for communication scenarios with high digital transmission rate requirements (generally 10 Gb/s or more), it can achieve lower transmission costs and larger system capacity; however, when the system requires a low transmission rate (less than 2.5 Gb/s) and flexible connection configuration methods, it may be more appropriate to use the old photoelectric conversion method for access. Therefore, in the current practical application, you should select the appropriate system deployment based on the Application Scenario.

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