Download - Introduction Fiber Optical Communication

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Introduction

Fiber Optical Communication

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http://www.fiber-optics.info/

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Agenda

• Advantages of Fiber Optics.

• Fiber-Optic Communications

• How Does an Optical Fiber Transmit Light?

• How Are Optical Fibers Made?

• What You Need to Know?

• What Do Fiber Optics Benefit Us?

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How Fiber Optics Work?

You hear about fiber-optic cables whenever people talk about the telephone system, the cable TV system or the Internet. Fiber-optic lines are strands of optically pure glass as thin as a human hair that carry digital information over long distances. They are also used in medical imaging and mechanical engineering inspection

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Advantages of Fiber Optics

Less signal degradation - The loss of signal in optical fiber is less than in copper wire.

Light signals - No interference with those of other fibers in the same cable.

Low power - Signals in optical fibers degrade less and need lower-power transmitters.

Light weight - An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground

Thinner - Optical fibers can be drawn to smaller diameters than copper wire.

Higher bandwidth – The information-carrying capacity of a fiber is greater that that id twisted-pair cable.

Digital signals - Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.

Non-flammable - Because no electricity is passed through optical fibers, there is no fire hazard..

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Fiber-Optic Communications

Optical Fiber

Conducts the light signals over a distance.

Optical Regenerator - May be necessary to boost the light signal (for long distances)

Transmitter Produces and encodes the light signals

Optical Receiver

Receives and decodes the light signals

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Transmitter

The transmitter is like the sailor on the deck of the sending ship. It receives and directs the optical device to turn the light "on" and "off" in the correct sequence, thereby generating a light signal.

Produces and encodes the light signals.

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Transmitter

Light Source

Lasers-narrow spectrum 1~3 nm, high speed Gb/s

LEDs-10BASE-FL LED 830 ~870 nm, low band width

VCSELs are faster, more efficient, and produce a smaller divergence beam than LEDs.

Wavelength (infrared, non-visible portions of the spectrum)

1,550 nm-high speed, long distance, single mode loss<1 dB/km

1,300 nm- single mode/multi mode(1.5 dB/km)

850 nm - multi mode loss 3.5 dB/km

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Fiber Optic Connectors

MT-RJ (AMP, Tyco Electronics)

SC Subscriber Connector (NTT)

LC (Lucent Technology, 1.25 mm ferrule)

ST Straight Tip (AT&T Trademark)

.

Small-Form-Factor, SFF connectors

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Fiber Optic Connectors

                              

Opti-JackVolition

E2000/LX-5 MUMT is a 12 fiber connector for ribbon cable.

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Fiber Optic Connector Alignment

Ferrule-most traditional connector use 2.5 mm ferrule as fiber-alignment mechanism

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Connector Ferrule Shapes & Polishes

Insertion loss is the loss of optical power contributed by adding a connector to a line.

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Connector and Splice Loss Mechanisms

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Optical Regenerator

Signal loss occurs when the light is transmitted through the fiber,

especially over long distances

Optical Regenerators is spliced along the cable to boost the

degraded light signals.

Consists of optical fibers with a special coating (doping).

Regenerator is a laser amplifier for the incoming signal.

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Optical Receiver

Optical receiver is like the sailor on the deck of the receiving ship.

Takes the incoming digital light signals, decodes them and sends the electrical signal to the other user's computer, TV or telephone (receiving ship's captain).

The receiver uses a photocell or photodiode to detect the light.

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How Does an Optical Fiber Transmit Light?

Shine a flashlight beam down a long, straight hallway

Total internal reflection.

Light signal degrades within the fiber

Signal degrades depends on the purity of the glass and the wavelength of the transmitted light

850 nm = 60 to 75 percent/km

1,300 nm = 50 to 60 percent/km

1,550 nm is greater than 50 percent/km

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Physics of Total Internal Reflection

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What are Fiber Optics?

Core - Thin glass center of the fiber where the light travels.

Cladding - Outer optical material surrounding the core that reflects the light back into the core.

Buffer coating - Plastic coating that protects the fiber from damage and moisture.

9/125/250, 62.5/125/250

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Single Mode v.s. Multi Mode

Single Mode

Multi Mode

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Step Index Core v.s. Graded Index Core for Multi Mode

Step-index Fiber: Fiber that has a uniform index of refraction throughout the core that is a step below the index of refraction in the cladding

Graded-index Fiber: Optical fiber in which the refractive index of the core is in the form of a parabolic curve, decreasing toward the cladding

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Classes of Fiber Optics

Cores diameterCladding diameter

Wavelength Light source

Single-mode fibers

5~10 microns 125 microns1,300 to 1,550 nm

Laser,VCSEL infrared

Multi-mode Step Index fibers

50, 62.5 or above microns

125~140 microns

850 to 1,300 nmLED, ,VCSEL infrared

Multi-mode Step Index fibers

400~600 microns230~630 microns

750~2000 microns

LED, ,VCSEL infrared

Multi-mode plastic fibers

750~2000 microns 750~2000

microns650 nm LED, visible red

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How Are Optical Fibers Made?

Optical fibers are made of extremely pure optical glass.

Making a preform glass cylinder

Drawing the fibers from the preform

Testing the fibers

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Making a preform glass cylinder

Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals.

Precise mixture governs the various physical and optical properties (index of refraction, coefficient of expansion, melting point, etc.).

The gas vapors are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe

As the lathe turns, a torch is moved up and down the outside of the tube.

Modified Chemical Vapor Deposition (MCVD)

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Making a preform glass cylinder

The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2)

The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass.

The purity of the glass is maintained by using corrosion-resistant plastic in the gas delivery system (valve blocks, pipes, seals) and by precisely controlling the flow and composition of the mixture.

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Drawing Fibers from the preform blank

Graphite furnace (1,900 to 2,200 Celsius)

Laser micrometer- Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s)

measure the diameter of the fiber

feed the information back to the tractor

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Testing the Finished Optical Fiber

Tensile strength - Must withstand 100,000 lb/in2 or more

Refractive index profile - Determine numerical aperture as well as screen for optical defects

Fiber geometry - Core diameter, cladding dimensions and coating diameter are uniform

Attenuation - Determine the extent that light signals of various wavelengths degrade over distance

Information carrying capacity (bandwidth) - Number of signals that can be carried at one time (multi-mode fibers)

Chromatic dispersion - Spread of various wavelengths of light through the core (important for bandwidth)

Operating temperature/humidity range

Temperature dependence of attenuation

Ability to conduct light underwater - Important for undersea cables

                                           

                       

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What You Need to Know?

Transmitter Power-Transmitters are rated in dBm.

Receiver Sensitivity-The minimum acceptable value of received power needed to achieve an acceptable BER or performance.

Optical Power Budget-Related to transmitter power and receiver sensitivity

Delay Budget-propagation factor is 0.67c or 5 ns/m

Optical Power Budget

Transmitter Power Receiver Sensitivity

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What You Need to Know?

Multi Mode

[(Transmitter Output Power Specifications Minimum Value - Receiver Input Sensitivity Specifications Maximum Value) - safety factor dBm] ÷ M dB/km (λ=1310nm)[((OP): dBm  - (ST): dBm) - 5(SF) dBm] ÷ M dB/km =  km

•Single Mode

[(Transmitter Output Power Specifications Minimum Value - Receiver Input Sensitivity Specifications Maximum Value) - safety factor dBm] ÷ S dB/km (λ=1310nm) or 0.25 (λ=1550nm)[((OP): dBm  - (ST): dBm) - 9(SF) dBm] ÷ =  km

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Case Studying

Single Mode Optical Fiber Cables with Loose Fibers( ITU-T G.652 Standard Single Mode Fibre ) in stranded Tubes for Duct Applications ( Dry Core Cable Design ), 6 cores with cable specifications No. LOFC-10001 A;  Type of Fiber :  Single Mode, Step IndexMax. Attenuation at 1310 nm  :  0.40 dB/kmMax. Attenuation at 1550 nm  :  0.25 dB/kmMode Field Dia. at 1310 nm   :  9.2 um +/- 0.4 umMode Field Dia. at 1550 nm   :  10.4 um +/- 0.8 umCable Cut-off Wavelength     :  < 1260 nmFlooding material            :  Jelly compoundFibres     :  Fibre Reinforced Plastic Rod, FRP dia. :  2.2 mmLoose Tubes :  Material :  Thermoplastic (PBT) ( Page 2 to 6 )

Wavelength: 1310 nmTX Output: -15 dBm (Single), -20 dBm (Multi)Max. TX Output: -6 dBm (Single), -14 dBm (Multi) Sensitivity: -36 to -32 dBm (Single), -34 to -30 dBm (Multi) Moxa: [ -15 - (-32) - 9 dBm] ÷ 0.4 dB/km =  20 km

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What You Need to Know?

Optical Power Budget

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What Do Fiber Optics Benefit Us?

Immunity for EMI

High Bandwidth

Long Transmission Distance

Safety and Security

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