Optical fibre Basic physics of OFC Merits & Demerits of OFC Nomenclature of OFC Absorption & attenuation Jointing & termination of OFC Optical sources & Detectors FBG & Applications

1. A
“SEMINAR ON ”
Submitted to:-
Ravi Goyal Sir
Submitted by:-
Ram Niwas Bajya
OPTICAL FIBER

2. Contents
RAM NIWAS BAJIYA
 Optical fibre
 Basic physics of OFC
 Merits & Demerits of OFC
 Nomenclature of OFC
 Absorption & attenuation
 Jointing & termination of OFC
 Optical sources & Detectors
 FBG & Applications

3. OPTICAL FIBER
 OFC have Fibres which are long, thin strands made with
pure glass about the diameter of a human hair
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4. Total internal reflection
 At some angle, known as the critical angle θc, light traveling from a higher
refractive index medium to a lower refractive index medium will be refracted at
90° i.e. refracted along the interface.
 If the light hits the interface at any angle larger than this critical angle, it will not
pass through to the second medium at all. Instead, all of it will be reflected back
into the first medium, a process known as total internal reflection
Incident angle =
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5. Optical fiber mode
Fibbers that carry
more than one mode
at a specific light
wavelength are called
multimode fibres.
Some fibres have
very small diameter
core that they can
carry only one mode
which travels as a
straight line at the
centre of the core.
These fibres are
single mode fibres.
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6. Optical fiber's Numerical
Aperture(NA)
Multimode optical fiber will
only propagate light that
enters the fiber within a
certain cone,
known as the acceptance
cone of the fiber. The half-
angle of this cone is called the
acceptance angle θmax. For
step-index multimode fiber,
the acceptance angle is
determined only by the
indices of refraction:
Where
n is the refractive index of the medium light is traveling
before entering the fiber
nf is the refractive index of the fiber core
nc is the refractive index of the cladding
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7. Medium / Link Carrier Information Capacity
Copper Cable
(short distance)
1 MHz 1 Mbps
Coaxial Cable
(Repeater every 4.5 km)
100 MHz 140 Mbps (BSNL)
UHF Link 2 GHz 8 Mbps (BSNL), 2 Mbps (Rly.)
MW Link
(Repeater every 40 km)
7 GHz 140 Mbps (BSNL), 34 Mbps (Rly.)
OFC 1550 nm 2.5 Gbps(STM-16 – Rly.)
10 Gbps (STM-64)
1.28 Tbps (128 Ch. DWDM)
20 Tbps (Possible)RAM NIWAS BAJIYA

8. Frequency Vs Attenuation In
Various Types of Cable
• More
information
carrying
capacity
fibbers can
handle
much
higher data
rates than
copper.
More
information
can be sent
in a second
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9. Limitations of OFC
 Difficulty in jointing (splicing)
 Highly skilled staff would be required for maintenance
 Precision and costly instruments are required
 Tapping for emergency and gate communication is difficult.
 Costly if under- utilised
 Special interface equipment’s required for Block working
 Accept unipolar codes i.e. return to zero codes only.
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10. Nomenclature for Optical Interface
 X can be I or S or L or V or U & denotes haul
 I for intra station (up to 2 km)
 S for short haul (15 km)
 L for long haul (40 km at 1310 nm & 80 km at 1550 nm)
 V for very long haul (60 km at 1310 nm & 120 km at 1550
nm)
 U for ultra-long haul (160 km at 1550 nm)
 Optical Interface specified as X.Y.Z
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11.  • Y can be 1 or 4 or 16 or 64 & denotes STM Level
 – 1 for STM-1
 – 4 for STM-4
 – 16 for STM-16
 – 64 for STM-64
 • Z can be 1 or 2 or 3 & denotes fibre type
 – 1 for 1310 nm over NDSF (G.652 fibre)
 – 2 for 1550 nm over NDSF (G.652 fibre)
 – 3 for 1550 nm over DSF (G.653 fibre)
 – 5 for 1550 nm over NZDSF (G.655 fibre)
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12. Examples of Nomenclature for
Optical Interface
 I.16.1 – Intra station STM-16 link on 1310 nm fibre
 S.16.2 – Short haul STM-16 link on 1550 nm fibre (G.652)
 L.16.2 & L.16.3 – Long haul STM-16 link on 1550 nm fibre (G.652 &
G.653)
 S.4.1 – Short haul STM-4 link on 1310 nm fibre
 L.4.1 – Long haul STM-4 link on 1310 nm fibre (40 km)
 S.1.1 – Short haul STM-1 link on 1310 nm fibre
 L.1.1 – Long haul STM-1 link on 1310 nm fibre (40 km)
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13. Absorption & Attenuation
 Scattering of light due to molecular level irregularities in the glass
 Light absorption due to presence of residual materials, such as
metals or water ions, within the fiber core and inner cladding.
 These water ions that cause the “water peak” region on the
attenuation curve, typically around 1380 nm.
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14. • Three peaks in attenuation
a). 1050 nm b). 1250 nm c). 1380 nm
• Three troughs in attenuation (Performance windows)
a.) 850 nm: 2 dB/km b). 1310 nm: 0.35 dB/km c). 1550 nm: 0.25 dB/km
Absorption loss & Scattering loss
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15. JOINTING AND TERMINATION OF OFC
There are two methods for jointing Optical fibre cable.
a). splicing
b.) connectors
a). splicing
1.Fusion Splicing-
• Fusion splicing provides a fast, reliable, low-loss, fibre-to-fibre
connection by creating a homogenous joint between the two
fibre ends.
• The fibres are melted or fused together by heating the fibre
ends, typically using an electric arc.
• Fusion splices provide a high-quality joint with the lowest loss
(in the range of 0.01 dB to 0.10 dB for single-mode fibres) and
are practically non-reflective.
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16. 2. Mechanical Splicing-
• Mechanical splicing is of slightly higher losses (about 0.2 db) and
less-reliable performance
• System operators use mechanical splicing for emergency restoration
because it is fast, inexpensive, and easy.
• Mechanical splices are reflective and non-homogenous
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17. b). Basics about connectors-
• Fibre optic connector facilitates re-mateable connection i.e. disconnection /
reconnection of fibre
• Connectors are used in applications where – Flexibility is required in routing an
optical signal from lasers to receivers
– Reconfiguration is necessary
– Termination of cables is required
• Connector consists of 4 parts:
– Ferrule
– Connector body
– Cable
– Coupling device
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18. Optical sources
An optical source is a major component of optical transmitters. Fiber
optic communication systems often use semiconductor optical
sources such as Light emitting diodes ( LEDs) and semiconductor
lasers.
Some of the advantages are:
•Compact in size
• High efficiency
• Good reliability
• Right wavelength range
• Small emissive area compatible with fibre core dimensions
• Possibility of direct emulation at relatively high frequencies
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19. Optical Detectors
The role of an optical receiver is to convert the optical signal back into
electrical signal and recover the data transmitted through the optical
fibre communication system. Its vital component is a photo detector
that converts light into electricity through the photoelectric effect.
Some the advantages are:
· high sensitivity
· fast response
· low noise
· low cost
· high reliability
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20. FBG and
Applications
The Filter that Bragg Grading

21. Fiber Grating
 Fiber grating is made by periodically changing the refraction index
in the glass core of the fiber. The refraction changes are made by
exposing the fiber to the UV-light with a fixed pattern.
Glass core
Glass cladding Plastic jacket Periodic refraction index change
(Gratings)
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22. Fiber Grating Basics
 When the grating period is half of the input light wavelength, this
wavelength signal will be reflected coherently to make a large
reflection.
 The Bragg Condition
Λ
λr = 2neff Λ
in
Reflection spectrum
reflect
Transmission spectrum
trans.
∆ n (refraction index difference)
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23. Creating Gratings on Fiber
 One common way to make gratings on fiber is using Phase Mask for
UV-light to expose on the fiber core.
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24. Characteristics of FBG
 It is a reflective type filter
 Not like to other types of filters, the demanded
wavelength is reflected instead of transmitted
 It is very stable after annealing
 The gratings are permanent on the fiber after proper
annealing process
 The reflective spectrum is very stable over the time
 It is transparent to through wavelength signals
 The gratings are in fiber and do not degrade the through
traffic wavelengths, very low loss
 It is an in-fiber component and easily integrates to
other optical devices
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25. Temperature Impact on FBG
 The fiber gratings is generally sensitive to temperature change
(10pm/°C) mainly due to thermo-optic effect of glass.
 Athermal packaging technique has to be used to compensate the
temperature drift
1533.8
1534.0
1534.2
1534.4
1534.6
1534.8
1535.0
1535.2
-5 15 35 55 75
Temperature (℃ )
CenterWavelength(nm)
Athermal
Normal
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26. Types of Fiber Gratings
TYPES CHARACTERS APPLICATIONS
Simple reflective
gratings
Creates gratings on the fiber that
meets the Bragg condition
Filter for DWDM,
stabilizer, locker
Long period
gratings
Significant wider grating periods
that couples the light to cladding
Gain flattening filter,
dispersion
compensation
Chirped fiber
Bragg gratings
A sequence of variant period
gratings on the fiber that reflects
multiple wavelengths
Gain flattening filter,
dispersion
compensation
Slanted fiber
gratings
The gratings are created with an
angle to the transmission axis
Gain flattening filter
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27. Typical FBG Production
Procedures
Select
Proper
fiber
H2
loading
Laser
writing
Annealing
Athermal
packaging
Testing
Different
FBG
requires
different
specialty
fiber
Increase
photo
sensitivity
for easier
laser
writing
Optical
alignment &
appropriate
laser writing
condition
Enhance
grating
stability
For
temperature
variation
compensation
Spec test
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28. Current Applications of FBG
 FBG for DWDM
 FBG for OADM
 FBG as EDFA Pump laser stabilizer
 FBG as Optical amplifier gain flattening filter
 FBG as Laser diode wavelength lock filter
 FBG as Tunable filter
 FBG for Remote monitoring
 FBG as Sensor
 ….
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29. Possible Use of FBG in System
Multiplexer
Dispersion
control EDFA
OADM
SwitchEDFA
Demux
ITU FBG filter
Dispersion
compensation filter
Pump stabilizer &
Gain flattening filter
ITU FBG filter
Tunable filter
ITU FBG filter
Pump stabilizer &
Gain flattening filter
E/O
Wave locker
Monitor
Monitor sensor
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30. ITU FBG Filter for DWDM
λ1, λ2 … λn
FBG at λ1
λ1 λ2
Circulator Circulator
FBG at λ2
λ3
Circulator
FBG at λ3
...
λ1, λ2 … λn
FBG at λ1
λ1 λ2
Circulator Circulator
FBG at λ2
λ3
Circulator
FBG at λ3
...
Multiplexer
De-multiplexerRAM NIWAS BAJIYA

31. ITU FBG Filter for OADM
Circulator Circulator
FBG
Through signal
Dropped signal Added signal
Outgoing signal
Incoming signal
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32. Dispersion Compensation
Filter
Dispersed
pulse
circulator
ChirpedFBG
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33. Pump Laser Stabilizer
980
spectrum
Focal lens
Fiber
980 Stabilizer
+
-
Pump Laser
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34. Gain Flattening Filter
1 5 0 0 1 5 2 0 1 5 4 0 1 5 6 0 1 5 8 0 1 6 0 0
W a v e l e n g t h ( n m )
- 1 5
- 1 0
- 5
0
5
1 0
1 5
2 0
Gain(dB)
Gain profile
GFF profile
Output
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