Optical cross-connect - AbsoluteAstronomy.com

An optical cross-connect (OXC) is a device used by telecommunications carriers to switch

Switch

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

high-speed optical signals

Optical communication

Optical communication is any form of telecommunication that uses light as the transmission medium.An optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the...

in a fiber optic

Optical fiber

An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

network, such as an optical mesh network

Optical mesh network

Optical mesh networks are a type of telecommunications network.Transport networks, the underlying optical fiber-based layer of telecommunications networks, have evolved from DCS -based mesh architectures in the 1980s, to SONET/SDH ring architectures in the 1990s...

.

There are several ways to realize an OXC:

Opaque OXCs (electronic switching) - One can implement an OXC in the electronic domain: all the input optical signals are converted into electronic signals after they are demultiplexed
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...

by demultiplexers. The electronic signals are then switched by an electronic switch module. Finally the switched electronic signals are converted back into optical signals by using them to modulate
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...

laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

s and then the resulting optical signals are multiplexed by optical multiplexer
Multiplexer
In electronics, a multiplexer is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output...

s onto outlet optical fibers. This is known as an "OEO" (Optical-Electrical-Optical) design. Cross-connects based on an OEO switching process generally have a key limitation: the electronic circuits limit the maximum bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...

of the signal. Such an architecture prevents an OXC from performing with the same speed as an all-optical cross-connect, and is not transparent
Transparency (telecommunication)
In telecommunications, transparency can refer to:#The property of an entity that allows another entity to pass through it without altering either of the entities....

to the network protocols used. On the other hand, it is easy to monitor signal quality in an OEO device, since everything is converted back to the electronic format at the switch node. An additional advantage is that the optical signals are regenerated, so they leave the node free of dispersion and attenuation. An electronic OXC is also called an opaque OXC.

Transparent OXCs (optical switching) - Switching optical signals in an all-optical device is the second approach to realize an OXC. Such a switch is often called a transparent OXC or photonic cross-connect (PXC). Specifically, optical signals are demultiplexed, then the demultiplexed wavelengths are switched by optical switch
Optical switch
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....

modules. After switching, the optical signals are multiplexed onto output fibers by optical multiplexers. Such a switch architecture keeps the features of data rate and protocol transparency. However, because the signals are kept in the optical format, the transparent OXC architecture does not allow easy optical signal quality monitoring.

Translucent OXCs (optical and electronic switching) - As a compromise between opaque and transparent OXC's, there is a type of OXC called a translucent OXC. In such a switch architecture, there is a switch stage which consists of an optical switch module and an electronic switch module. Optical signals passing through the switch stage can be switched either by the optical switch module or the electronic switch module. In most cases, the optical switch module is preferred for the purpose of transparency. When the optical switch module's switching interfaces are all busy or an optical signal needs signal regeneration
Signal regeneration
In telecommunications, signal regeneration is signal processing that restores a signal, recovering its original characteristics.The signal may be electrical, as in a repeater on a T-carrier line, or optical, as in an OEO optical cross-connect....

through an OEO conversion process, the electronic module is used. Translucent OXC nodes provide a compromise of full optical signal transparency and comprehensive optical signal monitoring. It also provides the possibility of signal regeneration at each node.

An optical add-drop multiplexer

Optical add-drop multiplexer

An optical add-drop multiplexer is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber . This is a type of optical node, which is generally used for the construction of optical telecommunications...

(OADM) can be viewed as a special case of an OXC, where to node degree

Degree (graph theory)

In graph theory, the degree of a vertex of a graph is the number of edges incident to the vertex, with loops counted twice. The degree of a vertex v is denoted \deg. The maximum degree of a graph G, denoted by Δ, and the minimum degree of a graph, denoted by δ, are the maximum and minimum degree...

is two.

See also