Fiber Optical Communication

1

• Introduction
• Fiber Optical Communication

http//www.fiber-optics.info/
www.lcsi.com.tw
2
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?

3
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

4
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..

5
Fiber-Optic Communications
Optical Regenerator - May be necessary to boost
the light signal (for long distances)
Optical Fiber Conducts the light signals over a
distance.
Optical Receiver Receives and decodes the light
signals
Transmitter Produces and encodes the light
signals
6
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.

7
Transmitter

• Light Source
• Lasers-narrow spectrum 13 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
  losslt1 dB/km
• 1,300 nm- single mode/multi mode(1.5 dB/km)
• 850 nm - multi mode loss 3.5 dB/km

8
Fiber Optic Connectors
SC Subscriber Connector (NTT)
ST Straight Tip (ATT Trademark)
Small-Form-Factor, SFF connectors
MT-RJ (AMP, Tyco Electronics)
LC (Lucent Technology, 1.25 mm ferrule)
9
Fiber Optic Connectors
10
Fiber Optic Connector Alignment

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

11
Connector Ferrule Shapes Polishes

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

12
Connector and Splice Loss Mechanisms
13
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.

14
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.

15
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

16
Physics of Total Internal Reflection
17
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

18
Single Mode v.s. Multi Mode
Single Mode
Multi Mode
19
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
20
Classes of Fiber Optics
21
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

22
Making a preform glass cylinder
Modified Chemical Vapor Deposition (MCVD)

• 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.

23
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.

24
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

25
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

26
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
Receiver Sensitivity
Transmitter Power
27
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
  (?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
  (?1310nm) or 0.25 (?1550nm)
• ((OP) dBm - (ST) dBm) - 9(SF) dBm
    km

28
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       lt 1260 nmFlooding
material              Jelly compoundFibres    
  Fibre Reinforced Plastic Rod, FRP dia.   2.2
mmLoose Tubes   Material   Thermoplastic (PBT)
( Page 2 to 6 )
Wavelength 1310 nm TX 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
29
What You Need to Know?

• Optical Power Budget

30
What Do Fiber Optics Benefit Us?

• Immunity for EMI
• High Bandwidth
• Long Transmission Distance
• Safety and Security

31
If you have any questions or comments about this
topic, email us at service_at_lcsi.com.tw Skype us
at lcsiservice