A System View of Optical Fiber Communication prt.2

AbdulRahman AlKhayyat 223218

Mohamed Felimban224304

OUTLINE

I. The Fiber Optic Data Communication System

II. Components of the Transmission SystemI. TransmittersII. ReceiversIII. Transmission Medium

III. PerformanceI. AttenuationII. Interference

IV. Conclusion

I. The Fiber Optic Data Communication SystemFiber Optic communication systems generally include:

A Transmitter

Transmission Medium including amplifiers and repeaters

A Receiver

A model of this System is shown in the figureThe illustration indicates the Source-User pair,

Transmitter & ReceiverIt also clearly shows the Transmission Medium.

1. Transmitter to convert an electrical signal into an optical signal

serves two functions:• A light emitter

works as a source of the light coupled into the fiber optic cable

• A regulatorto modulate this light to represent the binary data it receive

II. Components of the Transmission System

There are some requirements for the transmitter that should be met

1. physical dimensions must be compatible with size of the fiber optic being used

• emit light in a cone within cross sectional diameter

2. optical source must be able to generate enough power• desired BER should be met

3. high efficiency in coupling the light into the fiber optic cable

4. sufficient linearity• to prevent the generation of harmonics & inter-modulation distortion• if such interference is generated it is extremely difficult to remove• this would cancel the interference resistance benefits of the fiber optic

cable

5. Should be easily modulated with an electrical signal & capable of high-speed modulation

6. The usual requirements of small size, low weight, low cost and high reliability

II.1. Transmitters: Optical Source Component

• Types of Diodes that can be used as an optical source of the Transmitter:1. laser diode (LD)2. light emitting diode (LED)

• LD's advantages over LED's• can be modulated at very high speeds• produce greater optical power• higher coupling efficiency

to the fiber optic cable

II.1. Transmitters cont’d

• LED's advantages over LD's• higher reliability • better linearity • lower cost

LED and laser diodes: P-I characteristics

II.1. Transmitters cont’d

Verschiedene LED’s

2. Receivers to recover the signal as an electrical signal

serves two functions:• A sensor

to detect the light coupled out of the fiber optic cable then convert the light into an electrical signal

• A demodulatordemodulate this light determine the identity of the binary data that it represents

II. Components of the Transmission System

Indoor & Outdoor Receivers

• receiver performanceis generally characterizedby a parameter called the Sensitivity

• usually a curve indicatingthe minimum opticalpower that the Receivercan detect versus the data rate,in order to achieve a particular BER

II.2. Receivers cont’dReceiver sensitivities for BER = 10-9, with different devices

• The Transmission distance is limited by• fiber attenuation & fiber distortion

• Solution: i. repeaters• convert the signal to an electrical signal• send the signal again at a higher intensity

• high complexity & needing to be installed once every 20km = very high cost

• Solution: ii. optical amplifiers• amplifies the optical signal directly

without converting the signalinto the electrical domain

• Amplifiers have largely replaced repeaters in new installations

II.3. Transmission Medium

III. Performance

• The more light that can be coupled into the core the more light will reach the Receiver and the lower BER

• The lower attenuation in propagating down the core the more light reaches the Receiver & the lower BER

• The less time realized in propagating the faster the signaling rate and the higher the end-to-end data rate from Source-to-User

III. Performance cont’d

1. Attenuation• Caused by a combination of material absorption, Raleigh

scattering, Mie scattering, and connection losses• Is about 1000 db/km in modern fiber• Other causes of attenuation are physical stresses to the

fiber, microscopic fluctuations in density, and imperfect splicing techniques.

Attenuation vs. Wavelength Attenuation spectrum of standard single-mode fiber

III. Performance cont’d

2. Interference• a key concern is the problem of interference

• Presence of high current equipment results in the propagation of electromagnetic pulses that interfere with the data communications links

• In the past UTP copper cable was the transmission medium choice

• Using Fiber optic cables as the Transmission Medium• great interference protection• is simply not affected by the electromagnetic

interference

• Has been slow in coming to the industrial environment due to cost

• however, this is changing as the price of fiber optic cable steadily decreases

IV. In ConclusionThank You

for listening

If any question..We’d be happy to answer