Introduction to Optical Communication

1. OPTICAL FIBER
COMMUNICATION
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22. What is an Optic Source?
• The heart of a fiber optical data system
• A Hybrid Device
– Converts electrical signals into optical signals
– Launches these optical signals into an optical fiber
for data transmission.
• Device consists of an interface circuit, drive
circuit, and components for optical source.
(LEDs, ELEDs, SLEDs, LDs, etc)
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23. LEDs – Light Emitting Diode
• Emits incoherent light through
spontaneous emission.
• Used for Multimode systems w/
100-200 Mb/s rates.
• Broad spectral width and wide
output pattern.
• 850nm region: GaAs and AlGaAs
• 1300–1550nm region: InGaAsP and
InP
• Two commonly used types: ELEDs
and SLEDs
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24. SLEDs – Surface Emitting LEDs
• Primary active region is a small circular area located below the
surface of the semiconductor substrate, 20-50µm diameter and
up to 2.5µm thick.
• Emission is isotropic and in lambertian pattern.
• A well is etched in the substrate to allow the direct coupling of
emitted light to the optical fiber
• Emission area of substrate is perpendicular to axis of optical
fiber
• Coupling efficiency optimized by binding fiber to the substrate
surface by epoxy resin with matching refractive index
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25. Surface Emitting LED
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26. ELEDs – Edge Emitting LEDs
• Primary active region is a narrow strip that lies beneath the
semiconductor substrate
• Semiconductor is cut and polished so emission strip region runs
between front and back.
• Rear face of semiconductor is polished so it is highly reflective while
front face is coated with anti-reflective, light will reflect from rear
and emit through front face
• Active Regions are usually 100-150µm long and the strips are 50-
70µm wide which are designed to match typical core fibers of 50-
100µm.
• Emit light at narrower angle which allows for better coupling and
efficiency than SLEDs
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27. Edge Emitting LED
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28. LDs – Laser Diodes
• Emit coherent light through
stimulated emission
• Mainly used in Single Mode
Systems
• Light Emission range: 5 to 10
degrees
• Require Higher complex driver
circuitry than LEDs
• Laser action occurs from three
main processes: photon
absorption, spontaneous
emission, and stimulated
emission.
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33. Splicing
There are several reasons for splicing a fiber cable,
these include:
To join two fibers due to a breakage.
To connect some of the cores straight through a
patch cabinet.
To extend a cable run.
To reduce losses, a fusion splice has much lower
losses than two connectorized cables joined
through a coupler.
Or to attach a pre-terminated pigtail.
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34. Definitions
Splicer
mechanical device for joining two pieces of paper or
film or magnetic tape
Splice
joint made by overlapping two ends and joining them
Splicing
process of the permanent connection of two pieces of
optical fibers
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35. Types of Splicing
• Mechanical
• Fusion (welding)
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36. Fusion Splicing
• Fusing the two fibers
• Flame heating sources
- micro-plasma burners, oxy-
hydric micro-burners, electric
arc..
• Advantage
- consistent and easily controlled
heat with adaptability
• Possible drawback
- weakening of fiber in the vicinity
of splice
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37. Mechanical Splicing
• bonding two fibers
together in an
alignment structure
• Transparent adhesive
- e.g. epoxy resin
• Commonly used
groove
- V-groove
• Alignment problems
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38. Comparison
Mechanical splicing Fusion splicing
Reflection losses
(-45 db to -55 db)
No reflection losses
Insertion loss
(0.2 db)
Very low insertion loss
(0.1 db to .15 db)
cost – high Comparatively less
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39. Fiber splicing
Fusion Splicing
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40. V-groove optical fiber splicing
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41. Optical Fiber Connectors
• Some of the principal requirements of a good
connector design are as follows:
1- low coupling losses
2- Interchangeability
3- Ease of assembly
4- Low environmental sensitivity
5- Low-cost and reliable construction
6- Ease of connection
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42. Splicing Losses
• Intrinsic
- Freznel reflection
• Extrinsic
- foreign particles on surfaces
• Reflection
- incident and reflected beam travel on the same
path
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47. Need of fiber optic communication
Fiber optic communication system has emerged as most
important communication system Compared to
traditional system because of following requirements:
• 1. In long haul transmission system there is need of low
loss transmission medium
• 2. There is need of compact and least weight
transmitters and receivers.
• 3. There is need of increased span of transmission.
• 4. There is need of increased bit rate-distrance product.
A fiber optic communication system fulfills these
requirements, hence most widely accepted
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