4. 1.Information is encoded into
electrical signals
2.Electrical signals are
converted into light signals
3.Light travels down the3.Light travels down the
fibre
4.A detector changes the light
signals into electrical signals
5.Electrical signals are
decoded into
information
5. Introduction
• An optical fiber is essentially a waveguide
for light
• It consists of a core and cladding that
surrounds the core
• The index of refraction of the cladding is• The index of refraction of the cladding is
less than that of the core, causing rays of
light leaving the core to be refracted back
into the core
• A light-emitting diode (LED) or laser
diode (LD) can be used for the source
7. ADVANTAGES
(I) Optical Fibres are non conductive
(Dielectrics)
(II) Electromagnetic Immunity :
(III) Large Bandwidth (> 5.0 GHz for 1 km
length)
(IV) Low Loss (5 dB/km to < 0.25 dB/km typical)(IV) Low Loss (5 dB/km to < 0.25 dB/km typical)
(v) Small, Light weight cables.
(vi) Available in Long lengths (> 12 kms)
(vii) Security - Being a dielectric
(ix) Universal medium
8. APPLICATION OF FIBRE OPTICS
IN COMMUNICATIONS
Common carrier nationwide networks.
Telephone Inter-office Trunk lines.
Customer premise communication networks.
Undersea cables.
High EMI areas (Power lines, Rails, Roads).High EMI areas (Power lines, Rails, Roads).
Factory communication/ Automation.
Control systems.
Expensive environments.
High lightening areas.
Military applications.
Classified (secure) communications.
9. Optical Fiber
• Optical fiber is made from thin strands of either
glass or plastic
• It has little mechanical strength, so it must be
enclosed in a protective jacket
• Often, two or more fibers are enclosed in the• Often, two or more fibers are enclosed in the
same cable for increased bandwidth and
redundancy in case one of the fibers breaks
• It is also easier to build a full-duplex system
using two fibers, one for transmission in each
direction
11. Total Internal Reflection
• Optical fibers work on the principle of total
internal reflection
• With light, the refractive index is listed
• The angle of refraction at the interface• The angle of refraction at the interface
between two media is governed by Snell’s
law:
n1 sin 1 n2 sin 2
12. Refraction & Total Internal
Reflection
By Snell's law,
n1 sin 1 = n2 sin 2
The critical angle of
incidence c
where 2 = 90o
Is = arc sin (n2 / n1)Is = arc sin (n2 / n1)
14. PROPAGATION OF LIGHT
THROUGH FIBRE
meridional rays
Skew rays
core
refractive
index of
1.47 and a
cladding
index of
1.46
The index of
the cladding
is less than
1%
15. The specific characteristics of light
propagation through a fibre
• The size of the fibre.
• The composition of the fibre.
• The light injected into the fibre• The light injected into the fibre
16.
17. Modes and Materials
• Since optical fiber is a waveguide, light can propagate in a
number of modes
• If a fiber is of large diameter, light entering at different
angles will excite different modes while narrow fiber may
only excite one mode
• Multimode propagation will cause dispersion, which• Multimode propagation will cause dispersion, which
results in the spreading of pulses and limits the usable
bandwidth
• Single-mode fiber has much less dispersion but is more
expensive to produce. Its small size, together with the fact
that its numerical aperture is smaller than that of
multimode fiber, makes it more difficult to couple to light
sources
18. Types of Fiber
• Both types of fiber described earlier are known as step-index fibers
because the index of refraction changes radically between the core
and the cladding
• Graded-index fiber is a compromise multimode fiber, but the index of
refraction gradually decreases away from the center of the core
• Graded-index fiber has less dispersion than a multimode step-index
fiberfiber
19. FIBRE TYPES
1. Step Index
2. Graded Index
• By this classification there are three types of
fibresfibres
(I) Multimode Step Index fibre (Step Index fibre)
(II) Multimode graded Index fibre (Graded Index
fibre)
(III) Single- Mode Step Index fibre (Single Mode
Fibre)
20. COMMON FIBRE SIZES
50 µm 62.5 µm 100 µm 8 -10 µm
125 µm 125 µm 140 µm
125 µm
Multi Mode Graded Index Single Mode
Core
(m)
Cladding (
m)
8 125
50 125
62.5 125
100 140
22. Single-Mode Fiber (SMF)
• Step-Index type with very small core
• Most common design: 9/125 μm or
10/125 μ m, NA ~ 0.1
• Bitrate x Distance product: up to 1000
Gb/s • km (limited by CD and PMD - see next slides)
OFC SDE RTTC,
BSNL,BHUBANESWAR
6/30/2020
Gb/s • km
n
r
1.465
1.460
22
23. Step-Index Multimode (MM)
Dispersion
OFC SDE RTTC,
BSNL,BHUBANESWAR
6/30/2020
Pulse broadening due to multi-path transmission.
Bit rate x Distance product is severely limited!
100/140 μm Silica Fiber: ~ 20 Mb/s • km
0.8/1.0 mm Plastic Optical Fiber: ~ 5 Mb/s • km
23
24. Gradient-Index (GI) Fiber
• Doping profile designed to minimize “race” conditions
(“outer” modes travel faster due to lower refractive index!)
• Most common designs: 62.5/125 or 50/125 m, NA ~ 0.2
• Bitrate x Distance product: ~ 1 Gb/s • km
OFC SDE RTTC,
BSNL,BHUBANESWAR
6/30/2020
n
r
1.475
1.460
24
25. 11
n2n2
n1n1
CladdingCladding
CoreCore
Different Types of Fiber
• Multi-mode fiber
– Core diameter is about
50 µm (step index) or 62.5 µm
(graded)
– Light propagates in the
form of multiple modes,
each taking
n2n2 CladdingCladding
11
n1n1 CoreCore
each taking
a slightly different path
– Used primarily in systems with
short transmission distances
(under 2km)
• Single-mode fiber
– Core radius is smaller
(8-10 µm) cladding
around (250 µm)
– Only one mode in which light
can propagate
– Used for long distance and
high bandwidth applications
27. STEP INDEX MULTIMODE FIBRE
• The maximum number of modes (N)
depends on the core diameter (d),
wavelength and numerical aperture (NA)
x d x N A x d x N A
N= 0.5 x (---------------------- ) 2
28. GRADED INDEX MULTI-MODE
FIBRE
dxNA
N= 0.25 x ( ---------------- )2
()
The maximum number of modes (N)
depends on the core diameter (d),
wavelength and numerical aperture
(NA)
29. OPTICAL FIBRE PARAMETERS
Optical fibre systems have the following
parameters.
(I) Wavelength.
(II) Frequency.(II) Frequency.
(III) Window.
(IV) Attenuation.
(V) Dispersion.
(VI) Bandwidth.
34. Optical Attenuation
• Specified in loss per kilometer
(dB/km)
–0.40 dB/km at 1310 nm
–0.25 dB/km at 1550 nm
• Loss due to absorption 1550
• Loss due to absorption
by impurities
–1400 nm peak due to OH ions
• EDFA optical amplifiers
available in 1550 window
1310
Window
1550
Window
35. Optical Attenuation
• Pulse amplitude reduction limits “how
far”
• Attenuation in dB
• Power is measured in dBm:
ExamplesExamples
10dBm10dBm 10 mW10 mW
0 dBM0 dBM 1 mW1 mW
-3 dBm-3 dBm 500 uW500 uW
-10 dBm-10 dBm 100 uW100 uW
T T
Pi P0
-10 dBm-10 dBm 100 uW100 uW
-30 dBm-30 dBm 1 uW1 uW
)
36. ATTENUATION
• INTRINSIC ATTENUATION
• Absorption - Natural Impurities in the
glass absorb light energy.
• Scattering - Light rays travelling in the• Scattering - Light rays travelling in the
core reflect from small imperfections
into a new pathway that may be lost
through the cladding.
38. Dispersion
• Dispersion in fiber optics results from the fact that in
multimode propagation, the signal travels faster in some
modes than it would in others
• Single-mode fibers are relatively free from dispersion except
for intra-modal dispersion
• Graded-index fibers reduce dispersion by taking advantage of
higher-order modes
• One form of intra-modal dispersion is called material
dispersion because it depends upon the material of the core
• Another form of dispersion is called waveguide dispersion.
• Dispersion increases with the bandwidth of the light source.
39. DispersionDispersion
T
In the optical signal, the different wavelengths
have the different speed in optical fiber. And it
will cause such kind of phenomenon-dispersion .
40. Dispersion results in distortion of the signal,
which limits the bandwidth of the fiber.
41. Dispersion Classification
• Modal Dispersion
– Affects multimode fiber only
• Graded index profile is used to overcome this
• Chromatic Dispersion
– Limits the transmission capacity of SMF (single mode fibre)
– Dispersion Compensation techniques are used to address
thisthis
• Consists of Material dispersion and waveguide
dispersion
• Is lowest at 1310 window and zero at 1310nm for normal
fiber
• Polarization Mode Dispersion (ps/km)
– Is caused change of polarization of the wave in the fiber
– Is a concern only at high bit rates. Various techniques exist
to address this
• Using polarization maintaining fiber is one solution
43. Modal Dispersion
Each ray (mode) travels a different
distance, so it
arrives at a distant point of the
fiber at a different timefiber at a different time
Modal Dispersion is zero in Single Mode Fiber
45. MATERIAL DISPERSION
n = c/v
where n is index of
refraction,
c is the speed of light inc is the speed of light in
vacuum
v is the speed of the same
wavelength in the material.
The value of V in the equation changes for each wavelength, Thus Index of
refraction changes according to the wavelength.
46. Light Source for Optical
Transmission
Power
Laser
LED 35nm
2 to 3 nm
Wavelength ()
• The range of light wavelengths injected into the fibre. A source
does not normally emit a single wavelength, it emits several.
This range of wavelengths, expressed in nanometer is the
spectral width of the source. An LED has a much higher
spectral width than a LASER - about 35 nm for a LED and 2 to
3 nm for a LASER.
47. • Around 850nm, longer (reddish) wavelengths travel
faster than the shorter (Bluish) ones.
• At 1550nm however the situation is reversed. The
shorter wavelengths travel faster than the longer ones .
• At some point, the cross over must occur where the
bluish and reddish wavelengths travel at the same
• At some point, the cross over must occur where the
bluish and reddish wavelengths travel at the same
speed. This crossover occurs around 1300nm, the zero-
dispersion wavelength. At wavelengths below 1300nm,
dispersion is negative. So wavelengths travel or arrive
later. Above 1300 nm, the wavelengths lead or arrive
faster.
48. Waveguide dispersion
Waveguide dispersion, occurs because optical energy
travels in both the core and cladding, which have slightly
different refractive indices. The energy travels at slightly
different velocities in the core and cladding because of
the slightly different refractive indices of the materials
tmint
tmintmax
49. How Far Can I Go Without
Dispersion?
Distance (Km) =
Specification of Transponder (ps/nm)
Coefficient of Dispersion of Fiber (ps/nm*km)
A laser signal with dispersion tolerance of 3400 ps/nm
is sent across a standard SMF fiber which has a Coefficient of
Dispersion of 17 ps/nm*km.
It will reach 200 Km at maximum bandwidth.
Note that lower speeds will travel farther.
50. Polarization Mode Dispersion (PMD)
1st-order PMD
Ideal Practical
Core
Cladding
Cross-section of
optical fiber
Fast axis
Slow axis
- Well defined, frequency independent eigenstates
- Deterministic, frequency independent Differential Group Delay (DGD)
- DGD scales linearity with fiber length
1st-order PMD Fast
Slow
Dt
D t : Differential Group Delay (DGD)
Dt
51. Fibre core elipticity
The cross-section of a real fiber core, however, is usuallyThe cross-section of a real fiber core, however, is usually
elliptical due to manufacturing defects or external stresses
Consequently and the two orthogonally polarized modes of a
modulated signal will travel at the same speed. the light polarized
along one axis will travel faster than that along the orthogonal
axis. After propagation through a certain length of fiber, a delay
between the two polarization modes will occur . This is called a
differential group delay (DGD), i.e., a first-order polarization
mode dispersion (PMD).
52. SM Fiber Standards
• ITU Defines four types of single
mode fibres
– G.652: Standard Single Mode Fiber (SSMF/NDSF)
– G.653: Dispersion Shifted Fiber (DSF)
– G.654 :Very Low Loss Fiber (Cut-off shifted fiber)– G.654 :Very Low Loss Fiber (Cut-off shifted fiber)
– G.655: Non-Zero Dispersion Shifted Fiber(NZDSF)
– G.656: Non-Zero Dispersion for Wideband optical
transport
53. Non-Dispersion-Shifted Fiber(NDSF)
• ITU-T G.652 – Standard Single Mode Fiber
(SSMF)
– The most commonly deployed fiber (95% of worldwide
deployments).
– The most conventional fiber being used by BSNL.– The most conventional fiber being used by BSNL.
– Has chromatic dispersion minimum at 1310nm and high
at 1550nm(17-20PS/nm-km).
Lasers and Detectors at 1310 nm are inexpensive.
• Suitable for TDM (single-channel) use in the 1310-nm
region or DWDM use in the1550nm region (with dispersion
compensator).
54.
55. Single Mode Fiber Standards II
• ITU-T G.652c - Low Water Peak Non
Dispersion Shifted Fiber.
Source www.corning.com
56. Water Peak Region
• Water Peak Region”: it is the wavelength region of
approximately 80 nanometers (nm) centered on
1383 nm with high attenuation.
58. Dispersion-Shifted Fiber (DSF)
• ITU-T G.653 – Dispersion Shifted
Fiber (DSF)
– Suitable for TDM use in the 1550-nm region but
unsuitable for DWDM in this region.
– Intended for single channel operation at 1550 nm.– Intended for single channel operation at 1550 nm.
– It shifts the zero dispersion value within the C-
band.(from 1310 to 1550nm)
– Destructive nonlinearities in optical fiber near the
zero dispersion point.
– Channels allocated at the C-band are seriously
affected by noise due to nonlinear effects (Four Wave
Mixing).
60. Design features for DSF
• The level of dispersion depends on
– Doping levels of impurities
– Values of refractive indices difference(D)
– Core Radius ( R )
• By using various combination between
doping profiles,D and R ,it is possible to
achieve zero dispersion at wavelength
between 1300nm to 1700nm.
• Its primary application for Submarine
Systems.
61. Single Mode Fiber Standards III
• ITU G.654-1550nm loss minimized
fiber
– It has very low loss(0.15db/km) at 1550nm
wavelength.
– Low loss is achieved by using pure silica glass– Low loss is achieved by using pure silica glass
in the fiber core.
– Also maintains a high Cut-off wavelength to
reduce fiber sensitivity to bending induced
loss.
– It is expensive
– Its main application is in non repeaters
submarines systems
62. Non-Zero Dispersion-Shifted Fiber
(NZ-DSF)
• ITU-T G.655 – Non Zero Dispersion Shifted
Fiber (NZDSF)
• Low dispersion in the 1550 nm region, but not zero
• Designed specifically to meet the needs of DWDM.
• Good for both TDM and DWDM use in the 1550nm region.
• Small amount of chromatic dispersion at C-band: minimization• Small amount of chromatic dispersion at C-band: minimization
of nonlinear effects.
• Optimized for DWDM transmission (C and L bands)
– This fiber specially designed for use in the latest
generation of amplified DWDM systems.
– This fiber ensures that individual channel rates of
10Gb/s to distance greater than 250km without
dispersion compensation.
63. dispersion in single-mode fibers
Standard single-mode
Nonzero dispersion-shifted
+10
Dispersion(ps/nm-km)
1300 1400 1500 1600
(wavelength-nm)
Nonzero dispersion-shifted
Zero dispersion shifted
-10
Dispersion(ps/nm
64. Dispersion
Most installed
fibres are
N-DSF
Most installed
fibres are
N-DSF
DSF
LSF
(Corning)
True
Wave;
LEAF
NZ-DSFNZ-DSF
15
20
25
Dispersion
ps/(nm.km)
Fibre Dispersion Summary
Dispersion compensation needed on standard fibres at bit rates > 2.5Gb/s
Dispersion
Wavelength
1530 15601310 1550
- 30
- 25
- 20
- 15
- 10
- 5
0
5
10
65. Different Solutions for Different Fiber Types
SMF
(G.652)
•Good for TDM at 1310 nm
•OK for TDM at 1550
•OK for DWDM (With Dispersion Mgmt)
DSF
(G.653)
•OK for TDM at 1310 nm
•Good for TDM at 1550 nm
•Bad for DWDM (C-Band)
NZDSF •OK for TDM at 1310 nm
The primary Difference is in the Chromatic Dispersion Characteristics
NZDSF
(G.655)
•OK for TDM at 1310 nm
•Good for TDM at 1550 nm
•Good for DWDM (C + L Bands)
Extended Band
(G.652.C)
•Good for TDM at 1310 nm
•OK for TDM at 1550 nm
•OK for DWDM (With Dispersion Mgmt
•Good for CWDM (>8 wavelengths)
66. Types of Fibre
OFC Characteristics
ITU-T G.652 Single-mode optical fibre and cable
ITU-T G.653 Dispersion-shifted single-mode optical
fibre and cablefibre and cable
ITU-T G.654 Cut-off shifted single-mode optical
fibre cable
ITU-T G.655 Non-zero dispersion-shifted single-
mode optical fibre and cable
ITU-T G.656 Non-Zero Dispersion for Wideband
Optical Transport
67. Recommendation G.656
G.656 – will allow the easier deployment of Coarse Wave Division
Multiplexing (CWDM) in metropolitan areas, and increase the
capacity of fibre in Dense Wave Division Multiplexing (DWDM)
systems. Wave Division Multiplexing (WDM) increases the data
carrying capacity of an optical fibre by allowing simultaneous
operation at more than one wavelength.
G.656 allows operators using CWDM to deploy systems without the
need to compensate for chromatic dispersion, a phenomenon that atneed to compensate for chromatic dispersion, a phenomenon that at
low levels counteracts distortion, but at high-levels can make a
signal unusable. Although complicated, the management of
chromatic dispersion is crucial as the number of wavelengths used
in WDM systems increase. ITU has a history of providing the
specifications that allow operators to most efficiently handle this.
G.656 also means that at least 40 more channels can be added to
DWDM systems. In this case chromatic dispersion is used to control
harmful interference over this – unprecedented – range of the optical
spectrum.
68. Characteristics of Recommendation G.656
The most important new feature in Recommendation
G.656 fibre is the chromatic dispersion coefficient. In
G.656 this coefficient has an allowed range of 2 to 14
ps/nm*km in the 1460-1625 nm band, compared to 1 to
10 ps/nm*km for G.655.B and G.655.C which is only
related to the 1530-1565 nm band. This low value of the
chromatic dispersion coefficient in the S-C-L bands is the
real novelty of G.656 because it allows the utilization of a
larger wavelength band.larger wavelength band.
The range of mode field diameter permitted in G.656 of
7 to 11 µm compares to 8 to 11 µm in the G.655 non-
zero dispersion-shifted fibre. G.656 fibre has a maximum
PMD link design value of 0.20 ps/sqrtkm, which is the
lowest value recommended by ITU-T (the same value
that ITU-T recently adopted for G.655.C). G.656 has the
same cable cut-off wavelength and cable attenuation
coefficients in the C and L bands as G.655.
71. Fiber Optic Connectors &
Splices
• Connectors
– Demountable
terminations for fiber
– Connect to transmitters– Connect to transmitters
and receivers
• Splices
– Permanent termination
of two fibers
72. Fiber Optic Splices
• Permanent terminations for fiber
• Specifications
– Loss
– Repeatability– Repeatability
– Environment
– Reliability
– Back reflection
– Ease of termination
– Cost
73. Connectors
• There are four types
– Rigid Ferrule (most common)
– Resilient ferrule
– Grooved plate hybrids– Grooved plate hybrids
– Expanded beam
• Top image shows ferrules from
swiss-jewel.com (link Ch 6e)
• Lower image shows LC, SC,
Biconic, and the obsolete
Deutsch 1000
80. Ferrule Polish
• To avoid an air gap
• Ferrule is polished flat, or
• Rounded (PC—Physical
Contact), orContact), or
• Angled (APC)
– Reduces reflectance
– Cannot be mated with the other
polish types
81. Tight-Buffer
Cable
• PVC Buffer is extruded directly onto the coating
• Diameter is 900 microns
• Makes cable more flexible
• Easier to terminate
• The most common indoor cable type
• Not good for outside use
• Because the buffer strains the fiber as temperature
fluctuates, increasing attenuation
• Image from mohawk-cdt.com (link Ch 4f)
82. Ribbon cable
• Dozens of fibers packed together
• Can be mass fusion spliced or mass terminated
