Optical Switching

A Paper Presentation on

Optical Switch

Content• Introduction• Optical Fiber Communication• Optical Switching • Need of Optical Switching• Types of Optical Switching• Optical packet Switching• Optical Burst Switching

Introduction• Now a days we are using optical fiber

communication for data transmission.• In this data can be transmitted through optical

fiber.• Today fibers are pure enough that a light signal

can travel for about 80 kilometers without the need for amplification. But at some point the signal still needs to be boosted.

• The speed and capacity of such a network - with hundreds, if not thousands, of channels per fiber strand -would be practically limitless.

Optical fiber communication• A fiber consists of a glass core and a surrounding

layer called the cladding.• Based on total internal reflection.• A transmitter either a light emitting diode or a

laser sends electronic data that have been converted to photons over the fiber.

• Data can be transmitted but after some distance we need to boost data.

• These points where data has boosted known as nodes.

Cont.….• This is generally referred to as an 'optical-to-

electronic-to-optical' (OEO) conversion and is a significant bottleneck in transmission.

• signal converted to electrical ones, to be amplified, regenerated or switched, and then reconverted to optical signals.

• In this there are following problems:-o Slow O/E/O conversion.o Electronic equipment is dependent on the data rate & protocol.

Optical Switch• Optical switches will switch a wavelength or an

entire fiber form one pathway to another.

The need for Optical Switching

• High bit rate transmission must be matched by switching capacity

• Optical or Photonic switching can provide such capacity

• Important parameterso Switching time (↓)o Insertion loss (↓ and loss uniformity at all input-output connections)o Crosstalk (↓)o Extinction ratio (ratio of ON-OFF power) (↑)o Polarization-dependent loss (↓)o Reliability, energy usage, scalability, temperature resistance

Type of Optical switches

• MEMS• Thermo optic Switch• Bubble Switch• Liquid Crystal Switch• Non-Linear Optical Switching

MEMS• MEMS stands for "Micro-ElectroMechanical System" • Systems are mechanical but very small• Fabricated in silicon using established semiconductor

processes• MEMS first used in automotive, sensing and other

applications• Optical MEMS switch uses a movable micro mirror• Fundamentally a space division switching element

Two axis motion

Micro mirror

2D MEMS based Optical

Switch Matrix

• Mirrors have only two possible positions• Light is routed in a 2D plane• For N inputs and N outputs we need N2 mirrors• Loss increases rapidly with N

Input fibre

Output fibre

3D MEMS based Optical Switch Matrix

Mirrors require complex closed-loop analog controlHigher port counts possible

Thermo optic Switch

• The basic Thermo-optical switching element has an input waveguide and two possible output waveguides.

• In between there are two short, internal waveguides that first split the input light and then couple the two internal waveguides together again. The recombined light would proceed down the “default” output waveguide.

• But thermo-optical effect makes it possible to use this coupling of the light as a switching element.

Cont.…

Bubble Switch

• The switch consist of a silica waveguide with arrays of Intersecting light pipes that form a mesh.

• A small hole sits at a point where these light pipes intersect.

• It contains an index-matching fluid.• If no bubble is present then light move to default

waveguide otherwise light is shifted to second waveguide.

• The bubble act as a mirror that reflects the light wave to another branch of the switching element.

• Based on a combination of Planar Lightwave Circuit (PLC) and inkjet technology

Liquid Crystal Switch

• The liquid crystal switches rely on a change in the polarization of optical signals with the application of electrical voltage to make a switching element.

• Liquid crystal switching elements are built with two active components, the cell and the displacer.

• The main function of the cell is to reorient the polarized light entering the cell as required.

• The displacer is a composite crystal that directs the polarized light leaving the cell.

Cont.…• Liquid crystal switches work

by processing polarization state of the light. Apply a voltage and the liquid crystal element allows one polarization state to pass through. Apply no voltage and the liquid crystal element passes through the orthogonal polarization state.

• These polarization states are steered to the desired port, are processed, and are recombined to recover the original signal’s properties.

• With no moving parts, liquid crystal is highly reliable and has good optical performance, but can be affected by extreme temperatures.

Non-Linear Optical Switching

• If more light is shined on a mirror, the surface reflects more of the incident light and the imaged room appears brighter.

• Glass optical fibers experience non-linear effects, some of which can be used to design very fast switching elements, capable of changing their state in a femtosecond (quadrillionth of a second time scale).

• In general, non-linear optical switching requires the use of very short optical pulses that contain sufficient power to elicit nonlinear effects from the glass in the fiber.

• In one instance each segment travels through the loop in opposite directions recombines after completing the circle and exist on the same fiber on which it entered the loop.

• In cases, though, after the two beams split, an additional beam is send down one side of the loop but not the other.

• The intensity of light produced by the interaction of the coincident beams changes the index of refraction in the fiber, which in turn changes the phase of the light.

Cont.…

Advantage• Fast• Power Reduction• Stability• Economical• low loss• short switching time• Low power consumption• Low crosstalk • Low polarization effect

Comparison

Optical Packet Switching• Optical Circuit Switching

o Limited circuito Low efficiency (due to fixed bandwidth)

• Optical Packet Switchingo Using Packet ( = Header (for routing) + Data )

• If Optical Packet Switching is realized, it cano allocate WDM channels on demand (microsecond)o share network resource efficientlyo support burst traffic efficientlyo offer high-speed data rate/format transparency &

configurability

Architecture

OPS• What is the problem in implementing OPS?

o Long Switching timeo Buffer is needed

• Long switching time is due too Extracting the routing information from the headero Controlling switching matrix electronicallyo Performing the switching and buffering functions

• Buffer at Optical domain is neededo Data should be buffered while header is processedo When a contention is occurredo When the bandwidth is not sufficient

Optical Burst Switching

• Switch the channels entirely in the optical domain using electronic tech.

• Processo Assemble the packets (have same destination) -> make bursts at the

edgeo Bursts are assigned to wavelength channelso Switched through transparently without any conversiono Disassemble into the original packets

• No need for Optical buffer.

Optical Burst Switching

• Before burst transmission a control packet is generated and sent to the destination to set up path

• Each optical burst switch reads burst size & arrival time.

• Burst switch schedules an appropriate time period on a wavelength whish is called burst scheduling.

Conclusion• Data can be transmitted with very high speed

using optical fiber communication.• Photonic packet – switched networks offer the

potential of realizing packet-switched networks with much higher capacities than may be possible with electronic packet-switched networks.

Reference• Georgios I. Papadimitriou, Chrisoula Papazoglou, and Andreas S.

Pomportsis,”,Optical Switching: Switch Fabrics, Techniques, and Architectures”,IEEE Commun,Meg.,pp384‐405,Feb‐2003.

• Optical Burst Switching (OBS): A New Area in Optical Networking ResearchYang Chen, Chunming Qiao and Xiang Yu, Computer Science and Engineering Department,State University of New York at Buffalofyangchen,qiao,[email protected]

• Gerd Keiser,”Optical Fiber Communication”,Tata Mcgraw-hill Edition.

• Walter Goralski, Optical Networking and WDM, Tata McGrawhill edition.

• NONLINEAR EFFECTS IN OPTICAL FIBERS: ORIGIN,MANAGEMENT AND APPLICATIONS by S. P. Singh and N. Singh,Department of Electronics and Communication†,University of AllahabadAllahabad-211002, India

Thank you

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