Introduction to Optical Fiber Cable

1
Introduction to Optical Fiber Cable
2
Course Outline

• Introduction
• Applications and future development
• Transmission to support broadband services
• Trends and market in optical fiber technology

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Introduction
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?????(wave) ????????
???????????????????????? CRESTS
???????????????????? TROUGHS. ??????????????
crest ???? troughs ???????????????????????????
???????????????? WAVELENGTH. ????????????????????
??????? meters.
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?????????????????
??????????????????? ??? ???????? ???? ????
Amplitude ??? ??????????? Frequency Amplitude
???????? ??????? ?????????????????????????????????
???????????????????????????????????????????????
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Frequency ????????????????????????????????????????
???????? Frequency ???????????????????????????????
?????????????? HERTZ. ????????????????????????????
?????????????
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Period ???????????????????????????????????????????
????????????. Period ??????????????????????? frequ
ency ????? periods ????. frequency ????? periods
???.
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?????????????????????????????????? Period ???
Frequency. Specifically Period 1 /
Frequency and Frequency 1 / Period ??????????
period 2 ??????, ?????????????????????? ½
?????????????????????????? 2 ?????????????????????
??? ???????????????????? ½ ??????????????????. ???
??????? period 10 ??????, ??????????????????????
1/10 ?????????????????????????? 10
???????????????????????? ????????????????????
1/10 ??????????????????.
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?????????????????????????? Frequency
??????????????????????? wavelength ??????????????
?????????????? ?????????????????????????????
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???????????? Waves

• ???????????????? ???????
• Mechanical ??? Electromagnetic

????? Mechanical ?????????????????????????????????
?????????? ??????????????????????????????????????
????? ?????????????????? medium
???????? ?????????????????????????????????????
???????????????????????? ??????????????
??????????? ????????????????????????????
??????????????????????????????????????????????????
????????
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Electromagnetic Waves ????????????????? Electroma
gnetic waves ??????????????????????
Electromagnetic Spectrum. Electromagnetic
Spectrum ?????????????????????????????????????????
?????? ??????????????????????????????? ???????
??????? ??????????????? ??????????????
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??????????????
?????????????????????????????????? ??
?????Mechanical ?????????????????? ???? AMPLITUDE
???????? ?????????????????????????! ?? ?????
Electromagnetic, ?????????????????????????????
frequency, ????????????????????????!
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At the low energy end are the long wavelength
Radio Waves. At the high energy end are the short
wavelength Gamma Rays.
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Visible Light
?????????? electromagnetic spectrum
?????????????????????????????? (Visible Light
region). ????????????????????????????????????????
??????????????????????????????????????????????
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????????????????????????????????????????????????
prism ????????????????????????????????????????????
????
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Principle of Light Guidance
How water can guide light

• ???????????????????????????????????
  ??????????????????????????????? refractive index,
  ?????????????
• ??????????????????????? ??????????????????????????
  ??????????????????
• ??????????????????????????????????????????????????
  ?
• ??????????????????????????????????????????????????
  ???????????

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???????????????????????????????
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Optical Fiber
Human hair for comparison
50 80 mm
Typical refractive indices Cladding ncl
1.4440 Core nco 1.4512 Light is guided
along the core by Total Internal
Reflection Cladding helps isolate light from edge
of fibre where losses and scattering are high
1 mm 1/1000000 m
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Total Internal Reflection
Rays striking an interface between two
dielectrics from the higher index side are
totally internally reflected if the refracted ray
angle calculated from Snells Law would otherwise
exceed 90.
If n1 1.470 and n2 1.475, say, then qcrit
85.28 within a fibre core
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Bound rays vs Refracting Rays
Bound rays zig-zag indefinitely along a fibre or
waveguide
Refracting rays decay rapidly as they propagate
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Optical Transmission System (Overview)

• ??????????????????????????????????????????????????
  ??????? ?????????????????? (light source)
  ??????????????????????? ??????????????
  light-emitting diode (LED) ??? laser diode
• ???????? (Attenuation)
• 1970 20 dB/km with purified glass
• Current 0.2 dB/Km
• ATT first standardized transmission at DS3 speed
  (45Mbps) with multimode fiber ?????????????????
  single-mode fiber ?????????????? single-mode
  fiber ??????????????????????????????? ??????
  ??????? multimode fiber ??????????
• Optical Spectrum
• 850 nm
• 1310 nm (S band)
• 1550 nm (C band)
• 1650 nm (L band) ??????????

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Fiber Optic Technology
Multimode fiber " Multiple paths" for
the light to travel
Single mode fiber "Single path" for the
light to travel
LED
Laser
Light Emitting Diode
Core 50 or 62.5 micron diameter
Core 9 micron diameter
Cladding 125 micron diameter
Cladding 125 micron diameter
Outer coating 250 micron diameter
Outer coating 250 micron diameter
?????????? telecom, CATV, Broadcast, Data
communciation
?????????? LAN ??????????????
For comparison purposes this is the relative
size of a human hair ( _at_ 70 microns)
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Fiber types
refractive index
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Modes in Fiber
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????????????
TRANSMITTER
FIBER
Performance ????????????? modulation ????????????
????? fiber

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Light Emitting Diode (LED)

Typical performance data Power in MM-fiber 100
mW Power in SM-fiber 1 mW Direct Modulation
Bandwidth 100 MHz
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Laser
Typical performance Power (in fiber) 5-10 mW Max
100-300 mW Direct Modulation Bandwidth 1-10
GHz
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Photodiode detector
Typical performance data Responsivity 1 mA /
mW Bandwidth 1-20 GHz
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Transmitter and Receiver

• Light emitter ???????????????? ???????????????????
  
• LED (light emitting diode) ??????????????????
  (lt1Gbps), ????????????? multimode fiber
• Laser diode
• Light detector ??????????????????????????
• PIN photodiode ?????????? LED
• Avalanche photodiode ???????? PIN
  ?????????????????????????????

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Optical Transmission System (Attenuation)

• ???????????
• ????????? (scattering)
• Rayleigh scattering ??????????????????
  ???????????????????????????????????????
  ????????????????????????????????? wavelength
  ??????????????????????????????? scattering
  ????????????????????? wavelength ?????????????
  ??? limit ?????????????????????????????? 800 nm
• ????????? (absorption)
• ??????????????????????????????????????????????
  ??????????????? wavelength ???????????????????????
  ????????????? wavelength ??????? 1700 nm
• ????????????
• ?????????????????????????
• ????????????
• ???????????????
• Attenuation ??????????????????????????????????????
  ??????? ??????

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Attenuation
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Attenuation mechanisms
????????????????????????????????????????????
?????????????????????? molecular bonds (???? Si -
O)
??????????????????????????????????? (eg, OH- ion)
Rayleigh Scattering ??????????????????????????????
?????????????????????????????????
???????????????????????????????????????????
?????????? (????????????)
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Dispersion

• Dispersion ????????????? (spreading)
  ?????????????????????????????? dispersion
  ??????????????????????????????????
  ???????????????? bandwidth ?????????????????????
• Chromatic dispersion linear
• Polarization Mode Dispersion (PMD) nonlinear
• Chromatic dispersion ??????????????????
  wavelength ???????????????????????????
  ??????????????? bandwidth ??????? 2.5 Gbps
• Material dispersion
• Wavelength dispersion
• PMD ?????????????????????????? polarization
  ???????? (vertical and horizontal)

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Chromatic Dispersion
Even if we eliminate all types of multimode
dispersion, pulses of light having different
wavelengths still travel at different velocities
in silica, so pulse spreading is still possible
if we use a spread of wavelengths. This is called
Material Dispersion and is responsible for
rainbows etc.
Together, Material Dispersion and Waveguide
Dispersion are termed Chromatic Dispersion. The
pulse spread is proportional to fibre length L
and wavelength spread Dl.
In the fundamental mode, the light spreads out
differently into the cladding depending on
wavelength. Hence, different wavelengths have
different effective refractive indices. This is
Waveguide Dispersion.
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Polarization Mode Dispersion (PMD)
nx
ny

• pulse ????????????????????????????????????????
  PMD ???????????? chromatic dispersion
  ??????????????????????? bit rates 10Gb/s
  ????????????

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Fiber performance
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The 3 Rs of Optical Networking
A Light Pulse Propagating in a Fiber Experiences
3 Type of Degradations
Pulse as It Enters the Fiber
Pulse as It Exits the Fiber
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The 3 Rs of Optical Networking (Cont.)
The Options to Recover the Signal from
Attenuation/Dispersion/Jitter Degradation Are
Pulse as It Enters the Fiber
Pulse as It Exits the Fiber
Phase Variation
t
ts Optimum Sampling Time
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WDM (wavelength division Multiplexing)-transmissio
n
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Highway of Lights
DWDM Dense Wavelength Division Multiplexing
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Nonlinear effect

• ??????????? PMD ????????? nonlinear effect
  ???????? nonlinear effect ????????????????????
  power ??????????????? DWDM
• Nonlinear effect ?????????????????????????????????
  ???????
• ?? DWDM, four wave mixing ???? nonlinear effect
  ???????????????????
• ??????????????????????????????????????????
  interact ?????????????????????????????????????????
  ?????? cross talk ?????????????????????????
• Four-wave mixing ?????????????????????????????????
  ??????????????????????????????????????????????????
  ?? capacity ?? DWDM ???????

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Four Wave Mixing (FWM)
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Characterizing Optical Sngals and Performance

• BER ???? bit error rate ??????????????????????????
  ??????????????????????????????? ???????????
• Noise
• Intersymbol interference ????????????????????????
• Interchannel interference ????????????????????
  channel ????? ?????????????????????????????
  channel ??????? bandwidth 2.5 Gbps ?????????????
  100 GHz
• Nonlinear effects
• ????????????????????????????????????? modulation
  ??????
• On-off keying (OOK)

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An optical communications link
So, where does this optical fibre fit into the
overall picture?