A beautiful summary of physics and developments in optical fiber communication.

1. TRANSMISSION OF LIGHT IN FIBRE
FOR OPTICAL COMMUNICATION
Renjith Mathew Roy
International M.Sc. Physics
University of Stuttgart
Supervisor: Dr. Helga Kumric
http://www.criticalfrequency.com

2. OUTLINE
▪ 1. INTRODUCTION
o 1.1 Communication Modes
o 1.2 History
▪ 2. DATA LINK IN OPTICAL COMMUNICATION
o 2.1 Source: Laser
o 2.2 Transmission: Optical Fiber
• 2.2.1 Theory and Principle
• 2.2.2 Modes and Types of Fiber
• 2.2.3 Dispersion and Fiber Loss
o 2.3 Amplifier: EDFA
o 2.4 Receiver: Photodetectors
▪ 3. RESEARCH AND DEVELOPMENTS
• 3.1 Micro Structure Optical Fiber/ Photonic Crystal Fiber
o 3.1.1 Total Internal reflection: MOF
o 3.1.2 Photonic Band Gap :MOF
8/2/2021
OPTICAL
FIBER
COMMUNICATION
2
https://www.elprocus.com

3. 1. Copper wire : Frequency bandwidth- 16MHz .
Attenuation of 82 dB/km.
Speed- 100Mb/s- 1Gb/s Max, for 200 meters.
2. Radio wave, Microwave:
Mobile network frequency band of 1.8GHz- 2.5GHz.
Attenuation of 3.9 dB/100m.
beam divergence and atmospheric absorption.
3. Optical Communication:
Band width 100GHz .
Speed. 2 km 10Gb/s, Long Distance, durable.
8/2/2021 3
https://www.laserfocusworld.com
1. INTRODUCTION
1.1 COMMUNICATION MODES:

4. 1880
Alexander Graham
Bell:
Patented optical
telephone system.
‘Photophone’
1920
John Logie: Patented
for transmitting
Television Images
using Transparent
rods / hollow pipes
‘Televisor’
1954
Abraham Van Heel &
Harold H. Hopkins
Paper on Image
Bundles of uncladded
fibers (Just a transport
cover for protection).
1961
Narinder Singh &
Hopkins
Transmitted light out
of core- added
cladding / Bendable
fiber
1964
Charles K Kao.
Theoretical
Specification of Loss in
fiber.
4
en.wikipedia.org rts.org.uk www.circuitstoday.com
www.sbpmat.org.br www.researchgate.net
1977
Worlds 1st Telephone
traffic through fiber
optic system at 6 Mbps
for 2.4Km
In California
intotomorrow.com
1.2 HISTORY
1.2.1 TIMELINE:

5. 1.2.2 THE NOBEL PRIZE
NOBEL
PRIZE
• Charles K. Kao
• Nobel 2009 prize in physics.
• ‘Father of Optic Communications’.
8/2/2021 5
www.nobelprize.org
Two Necessity:
1. Optical Source – Is Laser a good source. (1964 Nobel prize)
2. Material Medium- What material has high transparency.
• He demonstrated that, high loss in fibre optics
is due to impurities.
• Identified Silica (SiO2) as the ideal candidate.
• Loss was 200 dB/ km.
• Shown the possibility to reduce the loss to
20 dB/km.
• The relative loss of various materials where
studied using surface resonances
[1]

6. ▪ 2. DATA LINK IN OPTICAL COMMUNICATION
o 2.1 Source: Laser
o 2.2 Transmission: Optical Fiber
• 2.2.1 Theory and Principle
• 2.2.2 Modes and Types of Fiber
• 2.2.3 Dispersion and Fiber Loss
o 2.3 Amplifier: EDFA
o 2.4 Receiver: Photodetectors

7. 8/2/2021
2: OPTICAL FIBER DATA LINK
7
A fibre optic datalink is a communications subsystem that
connects inputs and outputs (I/O) with optical and electrical
signals.
https://www.thefoa.org
The Fibre Optic Association, Inc.
Transmitter -
Source is Laser/LED. Transmitter gives out
optical pulses from electrical signal.
.
Medium- Optical fibre.
Receiver- Optical pulse converted back to
electrical signal.

8. 8/2/2021
2.1 SOURCE: LASER
8
Why laser ?
It gives coherent waves > All wave in phase > Powerful beam >
Very little dispersion.
https://global.canon/en/technology/
(VCSEL) Vertical Cavity Surface Emitting Laser
This is a semiconductor-based laser diode that emits optical beam
vertically from its top surface.
• Usually 850nm -GaAs
• 1500 nm- AllnGaAs
• Low beam divergence
• High beam quality
https://www.21semiconductors.com
[2]

9. • Core - A cylindrical dielectric waveguide.
• Cladding – It has slightly lower refractive
index.
• Protective Jacket- This enhances
durability.
8/2/2021 9
www.community.fs.com
2.2 OPTICAL FIBER
• OFC is the backbone of internet.
• Transmitting about 99% of all data.
• Stretching over 1.1 million km around the world.
https://www.submarinecablemap.com
mammothmemory.net

10. 2.2.1 TOTAL INTERNAL REFLECTION
8/2/2020 10
CONDITIONS:
1. Light incident from a material of high refractive index on to
material with low refractive index .
2. Angle of incidence 𝜃𝑖 > critical angle (𝜃𝑐)
http://wordpress.mrreid.org
https://www.miniphysics.com
ቇ
𝜽𝒄 = 𝐬𝐢𝐧−𝟏 ቆ
𝒏𝟐
𝒏𝟏
𝜃𝑐 = 𝜃𝑐 𝜃𝑖 > 𝜃𝑐
𝜃𝑖 < 𝜃𝑐
Light incident on surface will be completely reflected back.
𝑛2
𝑛1
https://www.sciencesource.com
[3]

11. 2.2.1.1 EVANESCENT WAVE
8/2/2021 11
Total internal reflection: No propagation to the 2nd medium.
But there should be a transmitted wave, which cannot carry any energy across the
boundary
for sin 𝜃𝑡 > 1 this is imaginary
𝐸𝑡 = 𝐸0𝑡𝑒𝑖 𝑘𝑡 sin 𝜃𝑡 𝑥
𝑒−𝑖𝜔𝑡
𝑒−𝐾𝑒𝑣𝑎𝑍
• E -continuously oscillates w.r.t x and t.
• And amplitude decays exponentially along z.
(3rd term).
https://en.wikipedia.org
https://www.slideshare.net
Requirements of cladding:
1. Should be transparent to light.
2. Sufficiently thick.
[4]
z
y

12. 2.2.1.2 NUMERICAL APERTURE
Cone of external ray that can be guided by the fibre.
i.e. It describes the light gathering capability of a fibre.
If 𝜽𝒊𝒏 > 𝜽𝒂 (ACCEPTANCE ANGLE): refracted , short lived,
does not undergo total Internal reflection.
8/2/2021 12
NA :characterizes the range of angles over which the system can accept light.
[5]
researchgate.net

13. 2.2.2 MODES IN FIBRE OPTICS
SINGLE MODE FIBER
• Small core diameter and refractive index
• Index difference- 0.3% ; Core diameter – 8-10 μm
• Great power confinement within core.
8/2/2021 13
https://www.sciencedirect.com
MULTIMODE FIBER
• Core diameter 50-100𝜇𝑚 Cladding-
125𝜇𝑚
• Index difference -1 -1.5%
• Higher Bandwidth 10-100Gb/sec
Number of paths taken by light beam defines mode.
Each mode travel with a distinct group velocity
[7]
[6]

14. • Core and cladding have two different refractive
indices.
• Small fractional change between 𝑛1 and 𝑛2.
• 𝑛1 = 1.44 to 1.46 (Fused Silica) ∆𝒏 𝒃𝒆𝒕𝒘𝒆𝒆𝒏 0.001
and 0.02.
• Refractive index changes are made by doping
(Titanium, Germanium, Boron etc).
8/2/2021
2.2.2.1 STEP INDEX FIBER
14
https://www.fiberoptics4sale.com
Step index – good for single more
Multimode – Problem!
Model Dispersion.
[8]

15. 8/2/2021 15
Solution: GRIN (GRADED REFRACTIVE INDEX FIBER)
• Refractive Index- Maximum at centre minimum at the edge.
• No total internal reflection, rather gradual bending.
• Travel velocity increases with radial distance from core
• Equal travel time for all modes.
https://www.fiberoptics4sale.com
[8]
fiberoptics4sale.com fiberoptics4sale.com
fiberoptics4sale.com

16. 8/2/2021
2.2.3: DISPERSION
16
MATERIAL DISPERSION:
• Depends on Wavelength of light used as it depend on refractive index.
• Higher the index, slower the light travels. 𝜇 𝛼
1
𝜆
TYPES OF DISPERSION:
Modal Dispersion, Material dispersion, Chromatic dispersion, Polarisation dispersion.
MODAL DISPERSION:
• Occurs in multi-mode fibres:
• Each mode has different group velocities.
• Spreading of travel time causes broadening of pulse.
• Cannot Distinguish 2 signals 0,1. https://wiki.metropolia.fi
[8]
[8]

17. 8/2/2021
2.2.3.1 FIBER LOSSES
17
ABSORPTION:
• SiO2 has strong wavelength dependence.
• IR, UV- Vibrational & electron transitions.
• 𝑶𝑯−
ion dissolved in glass.
• Absolute minimum at 1.55𝝁𝒎
• Attenuation 0.15dB/km
SCATTERING:
• Rayleigh Scattering (causes 96% Attenuation)
• Due to localized molecular positions in glass.
Scattering Intensity ∝
1
𝜆4
https://www.fiberoptics4sale.com
[9]
[1]

18. 8/2/2021
2.3: AMPLIFIER
18
ADVANTAGES:
▪ No coupling loss to the transmission fibre.
▪ Low noise compared to electronic amplifiers.
▪ Easily integrate with other optical devices.
http://www.fiber-optical-networking.com
Boost the intensity of optical signal carried through a fibre.
FIBER AMPLIFIER- Erbium-Doped Fibre Amplifiers (EDFA)
• Core doped with erbium ion Er 3+.
• Fibre absorb light of one frequency and
emit another amplified frequency by
Stimulated emission.
• Operates in the 1550 nm range
https://www.fs.com
[10]
[10]

19. • Receiver- Converts optical to electrical signal.
• Light absorption > electron hole pair generation if 𝒉𝝊 ≥ 𝑬𝒈 result in photo current in external circuit.
8/2/2021
2.4: RECEIVER: PHOTODETECTORS
19
ADVANTAGE:
High quantum efficiency =
𝐼𝑝𝑑 - photogenerated current.
𝑃𝑜𝑝𝑡 - optical input power
P-I-N PHOTODIODE
https://www.fiberoptics4sale.com
• Lightly doped I (intrinsic) region sandwiched
between p and n . They are reverse biased.
• When Light falls on i region, e-h pair generation
(current flow) occurs.
• Wide ‘i’ region – more absorption probability
• More carrier pair generation.
https://www.electrical4u.com
[16]

20. 3. RESEARCH AND DEVELOPMENTS
▪ 3.1 Micro Structure Optical Fiber/ Photonic Crystal Fiber
o 3.1.1 Total Internal reflection-MOF
o 3.1.2 Photonic Band Gap -MOF

21. • Instead of doping to change refractive index, here
airholes are made along the length.
3.1.1 TOTAL INTERNAL REFLECTION-MOF:
• Fibre with solid Core.
• Effective refractive index of cladding (air holes) is less
than that of core(solid material).
• Total internal reflection take place.
• Used for broadband single-mode guidance.
8/2/2020
3.1: MICRO STRUCTURED OPTICAL FIBER /PCF
21
[11]
Solid Silica Core
• Limitations of Silica: Losses (0.2-20 dB/Km) limited by scattering,
Need amplifier in every 50 Km, Dispersion, power loss.
.
• SOLUTION: PHOTONIC CRYSTAL FIBER.
[11] J.C. Knight, Nature, 424, 847-851 (2003)

22. 8/2/2020
3.1.2 PHOTONIC BANDGAP FIBERS
22
PHOTONIC CRYSTAL:
• Periodic dielectric structures that can modulate light propagation.
• Light is prevented from propagation of certain frequency in certain
direction due to Bragg reflection.
• Photonic bandgaps are made similar to energy bandgap in solid
state crystals.
[12]
[12]

23. 8/2/2020 23
HOW IS LIGHT GUIDED IN HOLLOW CORE BAND GAP FIBER?
No total internal reflection, instead Bragg reflection from periodic grid in fibre cladding.
Bragg Fibre or 1D- Photonic bandgap fibre (Bragg Fibre).
[14] R.F Cregan et al., Science 285, 1537 (1999)
[13]

24. AIR CORE BANDGAP FIBER
24
• Cladding is regarded as 2D photonic crystal with holes
are arranged periodically.
• Core- Air hole of different size.
• Cladding - Periodic array of large number of air holes.
[15]: R. Philip, 299, 358-362(2003)
• If optical frequency lie within photonic bandgap –propagation through
cladding Is prohibited.( Light is controlled within fibre ever than before.)
https://www.researchgate.net
8/2/2020
[14]
[15]
[14]

25. 8/2/2020 25
MODES IN PCF:
• Fundamental mode is trapped.
• Higher order modes leak away through
the gaps between the air holes.
[11]
[15]
• Low loss- only surface scattering from around air holes.
• Loss- 0.28 dB/km at 1550 nm.

26. 8/2/2021 26
OPTICAL
FIBER
COMMUNICATION
THANK YOU
Renjith Mathew Roy
renjithmathewroy@gmail.com
.fiberoptics4sale.com
lightwaveonline.com
SUMMARY
wired.com

27. REFERANCES
8/2/2021 27
[1] K.C Kao and G.A Hockham, IEE Proceedings, 133, 191-198 (1986)
[2] Michael Bass, Handbook of Optics (McGraw-Hill, USA,2001).Sec 4.45
[3] Max Born and Emil Wolf, Principles of Optics (Cambridge University Press,
Cambridge, 2019).Page-49
[4] M. Milan., Applied Spectroscopy, 67, 126-2301 (2013)
[5] B.E.A Salech and M.C Teich, Fundementals of Photonics( Wiley, USA, 2019).page 395
[6] Michael Bass, Handbook of Optics (McGraw-Hill, USA,2001) Sec. 1.3
[7] B.E.A Salech and M.C Teich, Fundementals of Photonics( Wiley, USA, 2019).page 415
[8] B.E.A Salech and M.C Teich, Fundementals of Photonics( Wiley, USA, 2019).page 419
[9] B.E.A Salech and M.C Teich, Fundementals of Photonics( Wiley, USA, 2019).page 417
[10] Michael Bass, Handbook of Optics (McGraw-Hill, USA,2001) Sec. 2.12
[11] J.C. Knight, Nature, 424, 847-851 (2003)
[12] J. D. Joannopoulos, et al., Photonic Crystals: Molding the Flow of Light (Princeton University Press,
Princeton, 2008)
[13] V. Matejec, Optical fibre for future telecommunication and energy transfer (Czech Republic,
2003)
[14] R.F Cregan et al., Science, 285, 1537 (1999)
[15] Russell Philip, Science, 299, 358-362(2003)
[16] Herbert Vanghaus, Fibre Optics Communication (Springer ,Switzerland, 2017) chapter 6

28. 8/2/2020 28
• https://www.wireandcabletips.com/copper-vs-fiber-wire-cable-design
• https://community.fs.com/blog/a-guide-on-fiber-optic-cable.html
• https://www.businessinsider.com/map-the-worlds-network-of-undersea-cables-2017-8?IR=T
• https://www.nobelprize.org/prizes/physics/2009/kao/lecture/
• https://rfphotonicslab.org/2020/02/25/optical-waveguides/
• https://www.ciscopress.com/articles/article.asp?p=170740
• https://wiki.metropolia.fi/display/Physics/%28M%29+Dispersion+in+Fiber+Optics
• https://community.fs.com/blog/types-of-optical-fiber-dispersion-and-compensation-
strategies.html
• https://www.ciena.com/insights/what-is/What-Is-Coherent-Optics.html
• https://global.canon/en/technology/s_labo/light/003/08.html
• https://www.rp-photonics.com/fiber_coupled_diode_lasers.html
• http://www.fiber-optical-networking.com/the-application-of-edfa.html
WEBSITE REFERANCES

29. BACKUP SLIDES

30. PRESENTATION
TITLE
9/3/20XX 30
STACK and Draw Technique

31. Splicing
( Mechanical- Just precisely align two ends
together)
FUSION SPLICING.
1. Prepare the fibre- remove coatings.
2. Cleave the fibre- precisely cut mirror smooth
and perpendicular to fibre axis.
3. Fuse fibre with electrical arc heating.
4. Protect the fibre https://tecratools.com
9/3/20XX
PRESENTATION TITLE
31
Want to enable light to pass from one fibre to other
https://circuitglobe.com
https://www.indiamart.com

32. To overcome high data transmission- Ultrafast pulse
propagation
Optoelectronic integrated circuits -interconnections-
through silicon waveguide.
Kind of small wire to transport optical data from fibre to
electronic device for conversion
9/3/20XX
. SILICON WAVEGUIDE
32
[1] Z. Fang and C.Z Zhao, ISRN Optics, 428690 (2012)
[2] K. Liu, et al, Scientific Reports, 16734 (2015)
[1]
[1]
[2]

33. 9/3/20XX PRESENTATION TITLE 33
• Optical signals are fed into core of fibre using Laser
Diode modules.
• 2 lenses are used. – A collimating lens and a rod
shaped
• Line generation lens focuses laser light into optical
fibre
Fibre Coupling:

34. It is a forward biased p-n Junction.
Electroluminescence
Light emitted from semiconducting material as a result
of electron- hole recombination.( spontaneous
recombination)
At room temperature- few thermally excited electrons
and holes- need potential.
9/3/20XX
LED- LIGHT EMITTING DIODE
34
For OFC – InGaAsP LED with 1.3 𝛍𝐦
B.E.A Salech and M.C Teich, Fundementals of Photonics( Wiley, USA, 2019). Chapter 18

35. 8/02/2021 OPTICAL FIBER COMMUNICATION 35
https://teams.femto-st.fr
Measurement of optical property:
• For quantitative assessment of waveguide performance live the light patterns produced by modes.
[1]
EXPERIMENT :For Measuring Material Property:
• The relative loss of various materials where studied using surface resonances
• Surface Acoustic Wave propagate through material surface