1. Optical Fibre Communication
N. Jayaprakash

2. Course Contents Fundamentals of Communication
Fundamentals of Optical Communication
Construction and Type of Cables
O.F Components and Connectors
Railtel
Light Sources ,Detectors and Receivers
O.F Measurements Instruments
Optical System Design
Fibre Splicing
PCM Principles & Line Codes
SDH
DWDM & FTTH

3. 1. Fundamentals of Communication
E -> O
O ->E
inf
Encoder
Light Source
Light Detector
Decoder
inf
OF Cable

4. Transmission Impairment using Copper Cable
Attenuation :Repeaters and Signal to Noise Ratio( SNR)
Noise
Distortion

5. Digital Transmission- Performance Criteria
1 in : Better
1 in 105 : Good
1 in 104 : Reasonably Good
1 in 103 : Just Acceptable
< 1 in : Unacceptable

6. 2.Fundamentals of Optical Fibre Communication
Introduction(Content Material)
What is Fiber Optics?
How are Fiber Optics Used today?
What are the advantages of Fiber Optics over Copper wire?
Where will Fiber Optics take me in the next 20 years?

7. Need for Fibre Optic Communication??
In long haul transmission system there is a need of low loss transmission medium.
There is need of compact and least weight transmitters and receivers
There is need of increased span of transmission
There is need of increased bit rate-distance product

8. Block Diagram of OFC systems
Transmitter
Receiver
Optical Detector
Channel Coupler
Repeater
Carrier Source
Amplifier
Optical Fiber
Modulator
Processing
Message Origin
Message Output

9. Modulator :
1) Converts the electrical message into the proper format.
2) It Impresses the signal onto the wave generated by carrier source.
Carrier Source :
It generates the wave on which the information is transmitted. This wave is called Carrier.
Channel Coupler:
It feeds the power into the information channel. The Channel Coupler design is an important part of fiber system because of possibility of high losses.

10. Transmission Sequence
Information is Encoded into Electrical Signals
Electrical Signals are Converted into Light Signals
Light Travels Down the Fiber.
A Detector Changes the Light Signals into Electrical Signals
Electrical Signals are Decoded into Information.

11. Advantages of Fibre Optics
Optical Fibres are non Conductive (Dielectrics)
Electromagnetic Immunity
Large Bandwidth (>5 GHz for 1 Km length)
Low loss
Security
Small, Light weight Cables etc….

12. Application of Fibre Optics
Military applications
Medical applications
Undersea cables
Control Systems
Factory Communications
Railways
Communication networks…. Etc…,

13. Principle of Fibre Optics
Total Internal Reflection (TIR)
Single Mode Fibre
Multimode Fibre
Core (um)
Cladding(um) 8
125 50
62.5
100
140

14. Total Internal Reflection (TIR)
Refractive index of core(n1) is higher than the cladding(n2) n1>n2
When a ray of light strikes the boundary at an angle greater than critical angle it gets reflected and no light passes through Fiber Optic Cables | Group

15. Single Mode Fibre
Carries light pulses along single path. Only the lowest order mode (fundamental mode) can propagate in the fiber and all higher order modes are under cut-off condition (non-propagating) .
Uses Laser Light source

16. Cont.… Advantages Less dispersion Less degradation
Large information capacity
Core diameter is about 10 μm
Difference between the RI of core and cladding is small
Drawbacks
Expensive to produce
Joining two fibers is difficult
Launching of light into single mode is difficult

17. Multi-Mode Optical Fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus.
Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters.

18. About MMF
Multi-mode fibers are described by their core and cladding diameters. example: 62.5/125 μm multi-mode fiber.
The two types of multi-mode optical fibers are:
Step index multi-mode optical fibers
Graded index multi-mode optical fibers
The transition between the core and cladding can be sharp, which is called a step-index profile, or a gradual transition, which is called a graded-index profile.

19. Cont.…

20. Types of MMF

21. Step Index Fiber
Step-index multimode fiber has a large core, up to 100 microns in diameter.
As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding.
These alternative pathways cause the different groupings of light rays, referred to as modes, to arrive separately at the receiver.

22. Cont.
The pulse begins to spread out, thus losing its well-defined shape.
The need to leave spacing between pulses to prevent overlapping limits bandwidth that is, the amount of information that can be sent.
Consequently, this type of fiber is best suited for transmission over short distances, in an endoscope, for instance.

23. Light Propagation in Step Index Fiber

24. Modal Dispersion
The arrival of different modes of the light at different times is called Modal Dispersion.
Modal dispersion causes pulses to spread out as they travel along the fiber, the more modes the fiber transmits, the more pulses spread out.
This significantly limits the bandwidth of step-index multimode fibers.
For example, a typical step-index multimode fiber with a 50 μm core would be limited to approximately 20 MHz for a one kilometer length, in other words, a bandwidth of 20 MHz·km.

25. Graded-Index Multimode Fiber
Graded-index multimode fibers solves the problem of modal dispersion to a considerable extent.
Graded-index multimode fiber contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding.
The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding.

26. Light Propagation in MMF

27. Multi-Mode v/s Single-Mode

28. Advantages of Multi-Mode
Easily supports most distances required for premises and enterprise networks
Can support 10 Gb/s transmission upto 550 meters
Easier to install and terminate in the field
Connections can be easily performed in the field, offering installation flexibility and cost savings
Have larger cores that guide many modes simultaneously

29. Applications
Step-index multimode fibers are mostly used for imaging and illumination.
Graded-index multimode fibers are used for data communications and networks carrying signals for typically no more than a couple of kilometers.

30. Optical Fiber Components
Fiber Connector: an optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection
Broadband light source (BBS):a light source that emit lights over a large wavelength range Example: ASE source, EELED,SLED
Fiber coupler: an optical device that combines or splits power from optical fibre's
Circulator: a passive three-port device that couple light from Port 1 to 2 and Port 2 to 3 and have high isolation in other directions

31. Cont.…
Mode scrambler: an optical device that mixes optical power in fiber to achieve equal power distribution in all modes
Index matching fluid: A liquid with refractive index similar to glass that is used to match the materials at the ends of two fibers to reduce loss and back reflection
Wavelength division multiplexer: a device that combines and split lights with different wavelengths

32. Optical Fibre Parameters
Wavelength
Frequency
Window
Attenuation
Dispersion
Bandwidth

33. Wavelength
It is a Characteristic of light that is emitted from the light source and is measured in nanometers(nm).
In the Visible spectrum , wavelength can be described as the colour of the light.
Frequency
It is a number of pulse per second emitted from a light source.
Frequency is measured in units of hertz (Hz)
1Hz= 1 pulse/sec

34. Operational Wavelength
Window
A narrow window is defined as the range of wavelengths at which a fiber best operates .
Window
Operational Wavelength
800nm-900nm
850nm
1250nm-1350nm
1300nm
1500nm-1600nm
1550nm

35. Attenuation
It is defined as a loss of optical power over a set distance, a fibre with lower attenuation will allow more power to reach a receiver
Intrinsic Attenuation
Absorption
Scattering
Extrinsic Attenuation
Micro bending
Macro bending

36. Bandwidth
It is defined as the amount of information that a system can carry such that each pulse of light is distinguishable by receiver.
Numerical Aperture :
Numerical aperture(NA) is the “light- gathering ability” of a fibre.
Light injected into the fibre at angles greater than the critical angle will be propagated .
NA= n12 - n22
where n1 and n2 are refractive indices of Core and Cladding resp..

37. Dispersion
Modal Dispersion
Material Dispersion
Waveguide Dispersion

38. Optical Fibre Construction

39. Parts O.F Cables Component Function Material Buffer
Protect fibre from Outside
Nylon, Plastic
Central Member
Facilitate Stranding Temperature Stability Anti-Bulking
Steel, Fibre Glass
Cable Jacket
Contain and Protect cable Core
PVC, Teflon
Cable Filling Compound
Prevent Moisture intrusion
Water Blocking Compound
Strength Member
Tensile Strength
Aramid Yam, Steel

40. Buffer Loose Buffer – For Outdoor applications
Tight Buffer - for indoor applications

41. Colour Codes 6 F OF Cable Fiber No. Blue Orange Green Brown Slate
White
12 F OF Cable
Blue
Orange
Green
Brown
Slate
White
Red
Black
Yellow
Violet
Pink
Glass/Natural

42. O.F Components Components like pig tail, patch cord , FDF & Connectors
Connector Requirement
The attenuation in optical fibre connectors should be less than 1 dB.
The Connector must provide consistent performance on each remating .
The connector must provide protection to the fibre so that it does not break while being handled
Connector must be cost effective.

43. O.F Measuring Instruments
Main Tests on OFC
Cable loss
Splice loss
Connector loss
Fibre Length
Continuity of Fiber
Fault Localization/ Break Fault

44. Main Instruments Required
Calibrated Light Source
Optical Power Meter
Optical Attenuator
Optical Time Domain Reflectometer (OTDR)

45. Calibrated Light Source
Generates Light Signals of Known Power and Wavelength
Calibrated Power Source
Measures Optical Power over wide range
It is never measured directly, but Measured through Electrical Conversion using Photo Electric conversion. It is known as Optical Sensor of known Wavelength.
Accuracy depends upon the stability of the Detector’s power to current conversion.

46. Power Attenuator Applications Types
Fixed Attenuators
Variable Attenuators
Applications
To Simulate the Regenerator Loss at the FDf
To provide Local Loop Back for Testing
To measure the Bit Error Rate by varying the Optical Signal at the Receiver Input

47. OTDR is used for measuring
Fiber Loss
Splice Loss
Connector Loss
Fiber Length
Continuity of Fiber
Fault Localization

48. PCM-Principles
PCM system use TDM technique to provide a number of circuits on the same transmission medium.
Basic Requirements for PCM System
Filtering
Sampling
Quantization
Encoding
Line Coding

49. Enclosure

50. Termination box

51. PDH

53. PDH

54. FDF

55. PDH

56. Cooler

57. OTDR

58. Indicators in SDH,PDH

59. OTDR