Optical Fiber Communication: Application of switching technology in Optical Networks

With the development of information technology, various new businesses have put forward higher requirements on the broadband and capacity of communication networks. However, in the current optical fiber communication system, each node of the network must undergo multiple optical-electrical and electrical-optical transformations, however, electronic devices have many disadvantages in adapting to high-speed and large-capacity demands, such as bandwidth restrictions, clock offset, severe crosstalk, and high power consumption, which leads to the "Electronic bottleneck" in the communication network. Moreover, the current development of electronic switches and information processing networks is close to the electronic speed limit. In order to solve this problem and give full play to the advantages of optical fiber communication in extremely wide band, anti-electromagnetic interference, strong confidentiality and low transmission loss, researchers began to introduce optical switching technology in the exchange system.

Optical switching refers to the direct exchange of information transmitted by optical fibers. Compared with electronic digital program-controlled switching, optical switching does not require the optical terminal to be set up between the optical fiber transmission line and the switch for optical and electro-optic conversion, in addition, in the exchange process, the advantages of high-speed, broadband, and electromagnetic induction of optical signals can be fully utilized. It has four main exchange modes: Air Separation optical switching, Time Division optical switching, wave splitting switching, and compound optical switching.

(1) Air Separation optical switching refers to space division switching. Spatial Optical Switches are the most basic functional switches in optical switching. The basic principle is to make the optical switching element a gate switch to form a path between any input optical fiber and any output optical fiber.

(2) Time Division optical switching is to convert the time position of the reused optical signal to another time position on the timeline. The switching principle is exactly the same as that of the time-division switching system in the off-the-shelf electronic program-controlled switching. Therefore, it can match the optical transmission system that adopts the all-optical time-division multiplexing method. In this way, each optical device can be reused at a time to reduce hardware devices and form a large-capacity optical switch.

(3) wavelength division switching is to convert any wavelength in the wavelength division multiplexing signal into another wavelength. The adjustable wavelength filter and wavelength converter are the basic components for achieving wavelength division switching. The former is used to select the desired wavelength optical signals from the Input Multi-Channel Wavelength Division optical signals, the latter converts the optical signals selected by the variable wavelength filter into appropriate wavelengths and then outputs them.

(4) composite optical switching refers to the application of more than two optical switching methods in one switching network at the same time. Air Separation + time division, Air Division + wavelength division, Air Division + time division + wavelength division are common composite optical switching methods.

Optical switching is a key node technology in all-optical networks. It performs optical signal switching and routing between any optical fiber port of an Optical Node. The most important task of optical switching is wavelength conversion.

Because it is essentially processing the wavelength of light, it is more accurate to say that the optical exchange should be called the wavelength exchange. The advantages of all-optical networks, such as bandwidth advantages, transparent transmission, and cost reduction, are all embodied in this technology. In terms of functions, optical switching, OXC Optical Crossover connectors), and OADM optical divider are sequential and inclusive. That is, OADM is a special case of OXC. Since OXC and optical exchange are still developing, the naming of optical exchange is currently chaotic. Some refer to the existing OADM and OXC as optical switching series, and some as optical routers. Therefore, most of the current optical exchanges use OXC and even OADM for the time being.

OXC has three methods: Optical Fiber crossover, wavelength crossover, and wavelength transformation crossover. Among them, the optical fiber cross-connection is based on the total capacity of all wavelengths on a single optical fiber, the capacity is large but not flexible; the wavelength crossover connection can be used to connect any wavelength on any optical fiber to any optical fiber with the same wavelength. For example, wavelength λ 1, λ 2, λ 3, and λ 4 are input from No. 1 fiber at the input end, the four wavelengths can be routed to the fibers 1, 2, 2, and 4 at the output ports through the wavelength crossover connection.

Some people now call this wavelength crossover connection a passive optical router, and its wavelength can be reused through spatial division. Wavelength selection is determined by the internal crossover matrix. a n × N crossover matrix can be used to establish N2 routes at the same time. The wavelength conversion crossover connection connects any wavelength on any optical fiber to any optical fiber with different wavelengths for maximum flexibility. The difference between it and wavelength crossover is that it can be used for wavelength conversion. Optical switching breaks through the speed bottleneck of electronic networks ". It can quickly provide customers with end-to-end high-speed broadband routing and virtual optical fiber networks.

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