Optical Switch Tutorial from FiberStore

What is an Optical Switch?

Optical Switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another in telecommunication. Away from telecom, an optical switch is the unit that actually switches light between fibers, and a photonic switch is one that does this by exploiting nonlinear material properties to steer light (i.e., to switch wavelengths or signals within a given fiber).

An optical switch may operate by mechanical means, such as physically shifting an optical fiber to drive one or more alternative fibers, or by electro-optic effects, magneto-optic effects, or other methods. Slow optical switches, such as those using moving fibers, may be used for alternate routing of an optical switch transmission path, such as routing around a fault. Fast optical switches, such as those using electro-optic or magneto-optic effects, may be used to perform logic operations; also included in this category are semiconductor optical amplifiers, which are optoelectronic devices that can be used as optical switches and be integrated with discrete or integrated microelectronic circuits.
(Reference: WIKIPEDIA)


Optical Switching Technology

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. So, how does it work?

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.

Space Division Switching

It 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 Switching

This 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.

Wave 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.

There are also hybrid switching technologies which are 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 10Gbps) 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 (2.5Gbps 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.

Types of Optical Switches

Optical switches can be divided into mechanical and non-mechanical ones according to the driving methods.

Mechanical optical switch relies on the movement of optical fiber or optical elements to convert the optical path, such as a mobile optical fiber type, moving the sleeve to move the lens (including mirrors, prisms and self-focusing lens) types. The biggest advantage of this kind of optical switch is a low insertion loss and low crosstalk. Its disadvantage is slow and easy to wear, easy to vibration, impact shocks.

Non-mechanical optical switch relies electro-optic, magneto-optic, thermo-optic and other effects to change the refractive index of the optical waveguide, the optical path changes, such as electro-optic switch, magneto-optic switch, and thermo-optic switch. This kind of optical switch has good repeatability, fast switching speed, high reliability, long life and other advantages, and small size, can be monolithically integrated. The disadvantage is that the insertion loss and crosstalk performance is not ideal, which should be improved.
Here are three common optical switches.

Opto-Mechanical Switch
Opto-mechanical switch is the oldest type of optical switch and the most widely deployed at the time. These devices achieve switching by moving fiber or other bulk optic elements by means of stepper motors or relay arms. This causes them to be relatively slow with switching times in the 10-100 ms range. They can achieve excellent reliability, insertion loss, and crosstalk. Usually, opto-mechanical optical switches collimate the optical beam from each input and output fiber and move these collimated beams around inside the device. This allows for low optical loss, and allows distance between the input and output fiber without deleterious effects. These devices have more bulk compared to other alternatives, although new micro-mechanical devices overcome this.

Thermo-Optic Switch

Thermo-optic switches are normally based on waveguides made in polymers or silica. For operation, they rely on the change of refractive index with temperature created by a resistive heater placed above the waveguide. Their slowness does not limit them in current applications.

Electro-Optic Switch

These are typically semiconductor-based, and their operation depends on the change of refractive index with electric field. This characteristic makes them intrinsically high-speed devices with low power consumption. However, neither the electro-optic nor thermo-optic optical switches can yet match the insertion loss, backreflection, and long-term stability of opto-mechanical optical switches. The latest technology incorporates all-optical switches that can cross-connect fibers without translating the signal into the electrical domain. This greatly increases switching speed, allowing today's telcos and networks to increase data rates. However, this technology is only now in development, and deployed systems cost much more than systems that use traditional opto-mechanical switches.

Optical Switch Protection System for DWDM Network Security

Optical switch protection system for the security of communication network provides a set of economic, practical solutions, the formation of a non-blocking, high reliability, flexible, anti-disaster ability of the optical communication network. Optical switch protection system by the automatic switching and network management stations, you can achieve light switch protection, monitoring and the optical path of the optical power emergency dispatch three main functions.

DWDM system in the trunk and local fiber optic transmission network has a large number of applications. Due to the amount of traffic carried by focus on the importance of safety more and more attention in the event of full resistance will affect all business network hosted. The DWDM network security has always been the most important in the transmission maintenance work. However, DWDM protection technology by its own limitations, has problems such as not flexible, large investment, and the effect is not ideal. Then the optical switch protection technology comes to play a very important role in the DWDM network security.

The optical switch protection system switching control module is a set of optical switches, optical power monitoring, stable light source monitoring in one of the high level of integration modules. Optical power monitoring module and optical switch control module coordination, selection of splitting ratio of 97:3 is more appropriate on the trunk, the equivalent of approximately 0.2dB attenuation on the transmission line; optical switching module contains 1x2 or 2x2 optical switch, controlled by the switch between the main and backup light routing operation.

Real-time monitoring of the optical power monitoring module communication optical fiber optical power value reported to the main control module; analysis and comparison of the main control module, found that the change in value of the optical power exceeds a preset threshold switching immediately issued instructions to the optical switch module; optical switch module by the Directive instantly switching action has occurred. In order to achieve a switching operation.

The optical path automatically switch protective equipment involved in trunk transmission system did not affect the transmission characteristics. In fact, switching equipment involved in the optical switch and splitter only two passive optical devices.

One end of the switching unit is connected to the transceiver of the transmission system, the main fiber optic cable and the spare cable, respectively connected to two output terminals of the 2x2 optical switch. When the optical path occurs when the optical power is abnormal, the optical switch is automatically switched to the alternate route.

It is understood that the optical switch protection system has the following advantages. Fast switching speed, the optical switch switching speed ships 5ms, plus system analysis, the response time of a single-ended switching time of less than 20ms, the switching time of less than 50ms for the entire system, the basic switching operation can be done without interrupting the communication, to achieve business grade level of protection.

Switching, high reliability, implemented through the optical power monitoring, to avoid false alarm of the optical frame, ensure switched judgment is correct. The spare fiber routing monitoring, to ensure the validity of the switch, and continue to be monitored after switching optical path.

Emergency dispatch function, simply switching command issued from the program, you can deploy routing to facilitate the realization of the non-blocking cutover and line maintenance work. The switch device for a transmission system is transparent, i.e. the switching device does not require the type of transmission system can use either SDH or DWDM.

The optical switch protection DWDM is an economical and safe a line protection method, but the the light automatic protection system intervention to DWDM systems, there are many issues to consider. Splitter 97:3 spectral, optical switching device insertion loss is about 2 dB intervention light switching device, the system has an additional two-fiber jumper whose fiber insertion loss is estimated as 1 dB, so the whole switching device Interventional theoretically maximum will bring 3dB attenuation, and many cases of practical use only in 1.5-2.5dB.

Optical automatic switching system for the DWDM line protection is both safe and economical means of protection. The future, as the size of the network continues to expand, optical switch protection systems will play a more important role to meet the requirements of the assessment indicators, to improve the safety of operation of the transmission network.

FiberStore's Optical Switch Solution

FiberStore's optical switches are based on Opto-Mechanical technology with proven reliability and available as optical switch 1x1, 1x2, 2x2 Non-Latching, Latching, Single-mode, Multimode versions. Besides these high performance Opto-Mechanical switch solutions, if you want to buy the other types such as thermo-optic and electro-optic ones, please contact the sales for special Custom Service.

Available Configuration

1X1 Mechanical              1X2 Mechanical

1X4 Mechanical              1X8 Mechanical

1X16 Mechanical            2X2 Mechanical

2X2B Mechanical            2X2BA Mechanical

D1X2 Mechanical            D2X2 Mechanical

D2X2B Mechanical

Available Mode

Single-mode

Multimode

Available Control Model

Latching

Non-lantching

All-optical switch introductionComments

The all-optical switch is the main element in the optical communication network. As the key to realize all optical network, it has a low pumping power, high switch efficiency, fast response time characteristics, so much attention in recent years has been paid.

From the late 1980s to the present, many research groups have conducted in-depth research of all kinds of all-optical switch. All-optical switch is a very important technology, it can be applied to the field of optical communications, optical computers, optical information processing and optical data processing. Optical switch as the key components of a new generation of all-optical network, mainly used to achieve light level routing, wavelength selection, optical add-drop multiplexing and optical cross-connect and self-healing protection. Therefore, the response speed optical switch, crosstalk, insertion loss performance will directly affect the quality of optical communication. The optical networking implementation depends on the light switches, optical filter, a new generation amplifier, dense wavelength division multiplexing technology devices and technological progress.

Optical switches applications in all-optical networks in addition should have a fast response speed, low insertion loss, low channel crosstalk and polarization insensitive, should also have integration and scalability and low-cost, low-power, good thermal stability and other characteristics. All-optical switch is expected to reflect its huge potential in the following applications.

(1) The calculation speed of computer depends on the increased speed of the switching elements and chip size reduction, in which regard has encountered a bottleneck. The development of optical computer is a possible way out. Optical computers may be fast photonic switching chip and chip the outside optical interconnects constitutes. Accordingly, the optical switch is the key to the development of optical computers.

(2) Electronic communication is gradually optical fiber communication replaced in order to meet the growing demand for communication capacity. Dense Wavelength Division Multiplexing technology, optical fiber communication signal transmission to achieve all optical signal exchange also rely on electronics, limiting the improvement of optical communication rate. Therefore, all-optical communication is the key to all-optical switch.

(3) Fiber optic communication systems in the long-haul network, metropolitan area network, the access network between the optical switch required by the optical cross-connects to complete; optical switch network between users rely on the OADM. The optical cross-connect and add-drop multiplexer is constituted by an optical switch array Thus, the optical switch is the basis for all-optical switching.

From the 1970s began to study the optical bistability has more than 30 years of history. However, the study of all-optical switching is also faced with many practical problems, mainly due to three reasons.

(1) All-optical switch is based on the third-order nonlinear effect. The desired optical power of switch is too high, which often takes more than the light intensity of the signal light more than five orders of magnitude. Not like the low-power electronic switch, it can’t achieve low-power light control.

(2) Due to the strong input light caused by the strong thermal effect, particularly in the dielectric absorption peak at a wavelength switching device, the heat absorption so that the device is very unstable and difficult to achieve a cascading operation of the device.

(3) The laser beam propagation in the medium microns, the power density is not high, but the nonlinear effect limited distance required to produce nonlinear power is too difficult to compress to the transverse dimension of the beam.

Therefore, reducing the switching power is the study of all-optical switch is an important task. Subject the light through the fiber waveguide or a planar integrated optical waveguide having a wavelength order of magnitude transverse dimension, can obtain a higher light power density and a longer interaction length, thereby greatly improving the efficiency of generating nonlinear optical effects, and may lower optical power to achieve all-optical switch. Waveguide-type optical switch become the main object of study. Silicon waveguides (including optical fiber) in the communication band absorption is small, but non-linear too weak, the accumulation of available ring cavity nonlinear.

Source: FiberStore

A new type of Optical Switch using a quantum dot

An optical switch developed at the Joint Quantum Institute (JQI) spurs the mark integration of photonics and electronics.

What, isn’t electronics adequate? Well, nothing travels faster than light, as well as in your time and effort to hurry in the processing andtransmission of knowledge, the combined use of photons along with electrons is desirable for developing a workable opto-electronic protocol. The JQI switch can steer a beam of light from one direction toanother in only 120 picoseconds, requiring hardly any power, no more than 90 atto joules. At the wavelength used, in the near infrared,this amounts to about 140 photons. This is actually the setup of a waveguide made from a photonic crystal, a great device put into the fiber optic transmission area.

A quantum dot is placed inside a tiny zone free from holes. Light is distributed into and from the waveguide via endcaps. If properly timed, a pump laser pulse allows probe pulse to exit the side. When the probe and pump beams are not aligned, the probe beam will exit the farend of the waveguide. The center piece of most electronic gear is the transistor, a solid-state component where a gate signal is used to a nearby tiny conducting pathway, thus switching on and off the passage of the information signal.

The analogous process in photonics would be a solid-state component which provides a gate, enabling or disabling the passage of light through a nearby waveguide, or as a router,for switching beams in different directions. Within the JQI experiment, prepared and conducted in the University of Maryland and at the National Institute for Standards and Technology (NIST) by Edo Waks and his colleagues, an all-optical switch has been created utilizing a quantum dot placed in the resonant cavity. The dot, consisting of a nm-sized sandwich of the elements indium and arsenic, is so tiny that electrons moving inside can emit light at only discrete wavelengths, as though the dot were an atom. The quantum dot sits inside a photonic crystal, a material that has been tired of many tiny holes.

The holes preclude the passage of sunshine with the crystal except for a narrow wavelength range. Actually, the dot sits in the small hole-free arcade which acts just like a resonant cavity. When light travels on the nearby waveguide a lot of it gets into the cavity, where it interacts using the quantum dot. And it is this interaction which could transform the waveguide’s transmission properties. Although 140 photons are needed in the waveguide to create switching action,only about 6 photons actually are required to bring about modulationof the quantum dot, thus throwing the switch.

Previous optical switches happen to be able to work only by utilizing bulky nonlinear-crystals and high input power. The JQI switch, by comparison, achieves high-nonlinear interactions using a single quantum dot and very low power input. Switching required only 90 atto joules of power, some five times less than the very best previous reported device made at labs in Japan, which itself used 100 times less power than other all-optical switches. Japan switch, however, has the advantage of operating at room temperature, as the JQI switch needs a temperature close to 40 K.

Continuing our analogy with electronics: light traveling on the waveguide by means of an information-carrying beam could be switched from one direction to another using the presence of asecond pulse, a control beam. To steer the probe beam the side from the device, the slightly detuned pump beam needs toarrive simultaneously with the probe beam, that is on resonance with the dot. The dot lies just off the middle tabs on the waveguide, inside the cavity. The temperature from the quantum dot is tuned to become resonant using the cavity, leading to strong coupling. If the pump beam doesn’t reach the same time as the probe, the probe beam will exit in another direction.

Source: http://www.fiberstore.com/

Brief Introduction to Optical Switch

The advent and development of fiber optic communication technology has brought a revolutionary change to the communications industry. Nowadays in the world, about 85% of communication services via optical fiber transmission, long haul network and local relay network has been widely using fiber optics.

Dense Wavelength Division Multiplexing (DWDM) technology development and maturation has opened up a vast space for the full application of the bandwidth and capacity of optical fiber transmission. With a high rate, large bandwidth obvious advantage, DWDM optical communication network has become the development of communication network trend. Especially in recent years, an IP-based Internet business explosive growth, this growth trend has not only changed the relationship between the IP network layer and the underlying transport network, and the networking of the entire network, the node design, management and control new requirements.

An intelligent network architecture – Automatic Switched Optical Network (ASON) has become a research hotspot of today’s systems. Its core node optical cross-connect (OXC). Constitute dynamic wavelength routing and optical network flexible and effective management can be realized by the OXC equipment. OXC technology is one of the key technologies increasingly complex DWDM network, optical switch for switching the optical path of functional devices, is a key part of the OXC. Optical switch matrix is ​​the core part of the OXC, it can achieve dynamic optical path management, optical network fault protection, wavelength dynamic allocation function, the solution to the current complex network of wavelength contention and improve the wavelength reuse, flexible configuration of the network are There is of great significance.

Optical switch is not only the core device in OXC, but also widely used in the following areas.

(1) Optical network protection switching system, the actual optical transmission system have left spare fibers when working channel transmission interruption or performance degradation to a certain extent, the main signal light switch automatically go to standby fiber system transmission, so that the receiving end received normal signal and feeling less than the network has a fault, the network nodes connected in a ring to further improve the survivability of the network.

(2) Real-time network performance monitoring system, remote fiber test points, 1 × N multi-channel optical switch, a plurality of optical fibers connected to the Optical Time Domain Reflectometer, real-time network monitoring, computer-controlled optical switch switching sequence and time to achieve the detection of all fiber, and test results are returned to the network control center, once found a road problems, can be processed directly in the network management center.

(3) The light switch is also used in optical fiber communication device testing system and metropolitan area networks, the poor access network/multiplexing and switching equipment. The introduction of the light switch in the future all-optical networks more flexible, intelligent, survivability. Optical switching technology has become the key to future optical networking, optical switching technology plays an increasingly important role in the field of communication, automatic control.

In many types of optical switches, MEMS optical switch is considered most likely to become the mainstream of the optical switch device. In this paper, an overview of the basis of the principle characteristics of a variety of optical switch on, the focus of several major MEMS optical switch, and outlined their structure and performance characteristics.