OPTICAL FIBRE COMMUNICATION 2011 AUGUST. Pcm equipment.
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Transcript of OPTICAL FIBRE COMMUNICATION 2011 AUGUST. Pcm equipment.
OPTICAL FIBRE COMMUNICATION
2011 AUGUST
Pcm equipment
Pcm equipment(2) contd
Global Capacity TrendWORLD INTERNET USAGE AND POPULATION STATISTICS
World RegionsPopulation (Est 2007) Million
Population % of the World
Internet Usage, Latest Data (Million)
% Population ( Penetration )
Usage % of World
Usage Growth 2000-2007
Africa 933 14.2% 34 3.6% 2.9% 643.1%
Asia 3,713 56.5% 437 11.8% 37.2% 282.1%
Europe 810 12.3% 322 39.8% 27.4% 206.2%
Middle East 193 2.9% 20 10.1% 1.7% 494.8%
North America 335 5.1% 233 69.5% 19.8% 115.2%
Latin America/Caribbean 557 8.5% 110 19.8% 9.4% 508.6%
Oceania / Australia 34 0.5% 19 54.5% 1.6% 146.7%
WORLD TOTAL 6,575 100.00% 1,173 17.84% 100.00% 225.00%
Source: www.internetworldstats.com
Current Estimated Capacities between Continents
North America
335 Million
Latin America/
Caribbean
557 Million
Africa
933 Million
Europe
810 Million
Asia
3.7 Billion
Oceania/
Australia
34 Million
Middle East
193 Million
8Tbs
12Tbps
6Tbps
5Tbp
s
6Tbps
9Tbps
2-3Gbps
Internet Usage by World Region
EXPLOSIVE GROWTH OF INTERNET
SEA-ME-WE 4 Cable System Configuration Diagram
FTTH, PON(passive Optical Network)
Power Line Communication System
LIGHT
Light is an is electromagnetic radiation of a wavelength that is visible to the human eye
CHARACTERISTICS OF LIGHT• Light is made up of , either electromagnetic
wave or particles called photons. Light can be considered as rays that follows straight line between or within optical elements, bending only at surfaces.
• Light is composed of electrical & magnetic fields, which vary in amplitude as they move through space together at the speed of the light. The two fields are perpendicular to each other and to the direction on which the light travels.
MEDIUM
Medium is a material substance which can transmit energy waves.
E.g. Air, Liquid, Solid
Liquid
Solid
Air
What is Optical Fibre?
An optical fibre consists 3 different parts.– Core– Cladding– Buffer Coating
Basic Theory :Light has to be confined to the core so that the digital signal can be transmitted from one place to another through light.
Basic Elements of the Optical Fibre System :
Light Source
Glass Fibre
LIGHT
Transmitter
ELECTRICITY
LED/LaserLightSource
Receiver
ELECTRICITY
Avalanche Photo Diode
• Refractive IndexLight changes its speed when it travels from one material to another, such as from air into glass. This cause an effect called refraction. Hence bending of the light at the surface of a material is expected. The speed of the light in the vacuum is highest.
Basic Theorems behind Optical Fibre (a)
• Snell’s LawSnell's law states that the ratio of the sines (Sin) of the angles of incidence and refraction is equivalent to the ratio of velocities in the two media, or equivalent to the opposite ratio of the indices of refraction.
Sin Ө 1 n 2 Sin Ө 2 n 1
Sin Ө 1 n 2
Sin Ө 2 n 1
n1 SinӨ1 = n2 SinӨ2
n1< n2
Ө1
Ө2
Medium 1n1
Medium 2n2
• When the refraction angle reaches 90°, there is no refraction and the incident angle reaches its critical angle (ΦC)
• When incident angle reaches the critical angle, there is no refraction.• Beyond the critical angle, light ray becomes totally internally reflected .
• Critical Angle & Total Internal Reflection
Basic Theorems behind Optical Fibre (b)
Φ1ΦC
Medium 2n2
Medium 1n1
Φ2
Total Internal Reflection
• According to the increase of the angle of incidence, the angle of refraction increases.
Special points to be considered in optical fibre (a)
1. Numerical Aperture (NA)– NA is defined as the sine of half the angle of a fibre’s light
acceptance cone (see Figure). – All modes of light entering the fiber at angles less than that which
correspond to the NA, will be bound or confined to the core of the fiber.
– The larger the NA of a fiber, the larger the light acceptance cone.
Air n0 = 1 Core n1
Cladding n2
αmax
ΦC
90 - ΦC
n0Sinαmax = n1Sin(90 - ΦC) n1Sin ΦC = n2Sin90
Numerical Aperture consideration
From Snell’s Law :
n1Sin ΦC = n2Sin90
Numerical Aperture Calculation
n0Sinαmax = n1Sin(90 - ΦC)
Therefore, nosinαmax = NA
NA determines the light gathering
capabilities of the fibre
What is Acceptance Angle?
Fibre accepting angle:
Question 1
A silica optical fibre with a core diameter large enough to be considered by ray theory analysis has a core refractive index of 1.50 and a cladding refractive index of 1.47
Determine: (a) the critical angle at the core cladding interface; (b) the NA for the fibre; (c) the acceptance angle in air for the fibre
Solution: (a) The critical angle at the core-cladding interface
(b) The numerical aperture is:
(c) The acceptance angle in air θa is:
E.g. The speed of light in water V(l) is 2.24 x 10 8 ms -1 and the speed of light in a vacuum V(V) is 2.99 x 10 8 ms -1. What is the Refractive index of Water(n w)?
V(l) = 2.24 x 10 8 ms -1
V(V) = 2.99 x 10 8 ms -1
Refractive index of water = V(V) V(l)
= 2.99 x 10 8 ms -1
2.24 x 10 8 ms -1
= 1.33
So The Refractive Index of water is 1.33 (No units).
What is Snell’s Law?• This describes the bending of light rays when it
travels from one medium to another.
Glass
Air
Air
Water
Snell's law states that the ratio of the sines (Sin) of the angles of incidence and refraction is equivalent to the ratio of velocities in the two media, or equivalent to the opposite ratio of the indices of refraction.
Sin Ө 1 n 2 =Sin Ө 2 n 1
Sin Ө 1 n 2 =Sin Ө 2 n 1
n 1 Sin Ө 1 = n 2 Sin Ө 2
PO - Ray of Incidence n 1 - RI for medium 1 OQ - Ray of Refraction n 2 - RI for medium 2Ө 1 - Angle of IncidenceӨ 2 - Angle of Refraction
TOTAL INTERNAL REFLECTIONn 1 Sin Ө 1 = n 2 Sin Ө 2
With the increase of the angle of incidence, the angle ofrefraction increases accordingly.
When reaches φ2 90°, there is no refraction and φ1 reaches a critical angle (φc )
Beyond the critical angle, light ray becomes totally internally reflected
EQUATIONS ASSOCIATED WITH RAY PROPAGATION
• CRITICAL ANGLE
• NUMERICAL APERTURE
LIGHT GATHERING CAPACITY• An optical fibre will pick up light from any source. However collecting
light for small core fibres will be a important step towards communication fibres. This means collecting light from one source and transferring that light to the optical fibre. This demands COUPLING light from core to the fibre, in a efficient way. Larger light sources are generally easy to align with fibres, but their lower intensity generally delivers less light. Transferring light between fibres requires careful alignment and tight tolerance. When two fibres’ are permanently joined are called SPLICING. Temporary joints made by two fibres are called as CONNECTORS. Special device named COUPLERS are needed to join 3 or more fibres. Losses in transferring signals in copper can be neglected but it is not so with fibres. Hence it should account for the losses deriving from coupling , from connectors, splices and the efficiency of the light source into the fibre.
NUMERICAL APPERATURE
• LIGHT GATHERING CAPACITY OF A OPTICAL FIBRE CABLE IS DEFINED AS THE NUMERICAL APPERTURE
• THE ACCEPTANCE ANGLE IS THE ANGLE WHERE THE OF SOURCE ISINTRODUCED TO THE FIBRE
• ACCEPTANCE ANGLE
Optical Fibre
• An optical fibre consists of two parts the core and the cladding• The core is a narrow cylindrical strand of glass and the cladding
is a tubular jacket surrounding it• The core has a (slightly) higher refractive index than the claddingTherefore, total Reflection of light ncore > ncladding
OPTICAL FIBRE FREQUENCIES
• Question 1: A silica optical fibre with a core diameter large enough to be considered by ray theory analysis has a core refractive index of 1.50 and a cladding refractive index of 1.47
• Determine: (a) The critical angle at the core cladding
interface; (b) The NA for the fibre(c) The acceptance angle in air for the fibre
This means the angle over which the light rays entering the fibre
, to be guided along it’s core. Acceptance angle is measured in air outside the fibre ,it defers from confinement angle of the
MODES OF FIBRE
• There are 2 main type of modes in optical Fibre
• SINGLE MODE STEP INDEX
• MULTIMODE STEP INDEX GRADED INDEX
TYPES OF FIBRE
Elements of Optical Transmission System
Optical Fibre Transmission System
Major components1. Modulator2. Light source3. Connectors (Couplers)4. Optical glass Fibre5. Light sensor/Detector6. Optical amplifiers/Repeaters7. Optical fibre joints (splices)
LIMITATIONS TO TRANSMISSION
ATTENUATION
Example
• To calculate the ratio of 1 kW (one kilowatt, or 1000 watts) to 1 W in decibels, use the formula
• Similarly for amplitude, current or voltage (power is proportional to the square of the above 3 quantities. )
Laser Output Power, Receiver Sensitivity and dBm
Example 1
Answer (Example 1)
• Connector loss= 8*1dB= 8dB• Cable loss= (4*100)/1000=0.4dB• System margin = 5dB• Sensitivity= -30 dB • Transmitter Power = connector loss+cable
loss+system margin+sensitivity • Therefore, 8 + 0.4 + 5 – 30 = -16.6dB
ReceiverTransmitter 8 Connectors
Example 2
Answer (Example 2)
• Connector loss= 2*1.5dB = 3 dB• Cable loss= 0.4dB * 50 = 20 dB• System margin = 8 dB• Sensitivity= -34 dB • Transmitter Power = connector loss+ cable loss + system
margin + sensitivity • = 3+20+8-34= -3 dB• No: of splices= 3/ 0.15 = 20 splices
Transmitter Receiver2 Connectors
Answer (Example 2)
• Connector loss= 2*1.5dB = 3 dB• Cable loss= 0.4dB * 50 = 20 dB• System margin = 8 dB• Sensitivity= -34 dB • Transmitter Power = connector loss+ cable loss + system
margin + sensitivity • = 3+20+8-34= -3 dB• No: of splices= 3/ 0.15 = 20 splices
Transmitter Receiver2 Connectors
Question
If the System Margin is -10dB, calculate the receiver sensitivity.
Give your overall observation?
Answer
Question on Practical system – 1
Long haul telephone optical fibre system consist with the following components
Part One Question Contd
Calculate the Power Budget and estimate whether the system will Function?
Part 1 Answer
Part Two Question – Use of Optical Amplifiers
The Previous system has been re engineered with two optical amplifiers as detail out below
Verify the Power budget for correct operation?
Part Two Answer – Use of Optical Amplifiers
Part Two Answer Contd – Use of Optical Amplifiers
Example 3 (f)Part Two Answer Contd– Use of Optical Amplifiers
Part Three Questions – Onsite Re engineering Problems
Due to site and optical amplifier operational problem, the above system was again re engineered as follows
By calculating the Power Budget verify whether the system can be operational or not?
Then the Calculation for segments 2 and 3 are given below;
Part Three Answer – Onsite Re engineering Problems
Part Three Answer Contd– Onsite Re engineering Problems
DISPERSION
• Data carried in an optical fibre consists of pulses of light energy composed of a large number of frequencies travelling at a
given rate.• There is a limit to the highest data rate (frequency) that can be sent down a fibre and be expected to emerge intact at the
output.• This is because of a phenomenon known as Dispersion (pulse spreading), which limits the "Bandwidth” of the fibre.
Consequences of Dispersion• Frequency Limitation
• Distance : A given length of fibre, has a maximum frequency(bandwidth) which can be sent along it. To increase the bandwidth for the same type of fibre one needs to decrease the length of the fibre.
TYPES OF DISPERSION
DISPERSION
CHROMATICDISPERSION
MODALDISPERSION
MATERIALDISPERSION
WAVEGUIDE DISPERSION
CHROMATIC DISPERSION• It is a result of group velocity being a function of
wavelength. In any given mode different spectral components of a pulse travelling through the fibre at different speed.
• It depends on the light source spectral characteristics.
• May occur in all fibre, but is the dominant in single mode fibre
CHROSMATIC DISPERSION
Material dispersion - different wavelengths => different speeds
Waveguide dispersion – different wavelengths => different angles
MATERIAL DISPERSION
• Refractive index of silica is frequency dependent. Thus different frequency (wavelength) components travel at different speed
M is the material dispersion parameter. It characterizes the amount of pulse broadening by material dispersion per unit length of fibre and per unit of spectral width.
WAVEGUIDE DISPERSION• This results from variation of the group velocity with
wavelength for a particular mode. Depends on the size of the fibre.
• The angle between the ray and the fibre axis varying with wavelength which subsequently leads to a variation in the transmission times for the rays, and hence dispersion.
• This can usually be ignored in multimode fibres, since it is very small compared with material dispersion. It is significant in monomode fibres.
• Changing the design of the core-cladding interface can alter waveguide dispersion.
MODAL DISPERSION - SIMMF
• Lower order modes travel travelling almost parallel to the centre line of the fibre cover the shortest distance, thus reaching the end of fibre sooner.
• The higher order modes (more zig-zag rays) take a longer route as they pass along the fibre and so reach the end of the fibre later.
• Mainly in multimode fibres
The time taken for ray 1 to propagate a length of fibre L gives the minimum delay time:
The time taken for the ray to propagate a length of fibre L gives the maximum delay time:
Since The delay difference :
MODAL DISPERSION - GIMMF• The rays follow smooth curves rather than the
zig-zags of step-index fibres
Ray paths in a graded-index fibre
(a) a central ray;
(b) a meridional ray
(c) a helical ray avoiding the centre
MODAL DISPERSION - GIMMF• The intermodal dispersion is smaller than in
step-index fibres.• A helical ray, for example, although traversing
a much longer path than the central ray, does so in a region where the refractive index is less and hence the velocity greater
• To a certain extent the effects of these two factors can be made to cancel out, resulting in very similar propagation velocities down the fibres for the two types of ray
EQUATIONS FOR SINGLE MODE
• Number of modes
• Diameter
• Cut off wavelength
• For single-mode transmission: λ > λc• If λ < λc, two or more modes propagate
(multimode fibers)
EQUATIONS FOR SINGLE MODE
• Number of modes
• Diameter
• Cut off wavelength
• For single-mode transmission: λ > λc• If λ < λc, two or more modes propagate
(multimode fibers)
Wave division multiplexing
• 1. Concepts• 2.How to multiply the capacity in a given
optical fibre core by adding electronics at the terminal equipement without installation of new optical fibre systems
• Hence cost saving is evident in WDM or dense WDM (DWDM)
• Let’s study !!
Attenuation in Fibreoptical fibre behaves differently for different wavelength of light. The following diagram shows that. The three windows of wavelengths where the attenuation is lower is given
below. Hence these 3 windows are mostly used for practical purposes.
1. General Observation on Attenuation and the Present Day Technology
• Attenuation is low between 1500nm-1700nm in wavelength.• This gives rise to operate 24Tbps speed • How?
C=fλ where C=3*108
• And f1-f2=[c/(1500nm)]-[c/1700nm]=24Tbps• The present day technology goes up to 10Gbps or 40Gbps.
• STM1 STM4 STM16 STM64…… STM256 155.52Mbps 620Mbps 2.5Gbps 10Gbps 40Gbps
6.4ns 1.6ns 400ps 100ps 25ps
Present day technology adapting to the optical fibre
The following 2 major factors play a vital role in designing the maximum capacity of an optical fibre• How far the digital multiplexing can be achieved
• As at present , 488ns micro information of a bit pertaining to 2Mbps PCM stream will be reduced to 25ps when it goes through STM64 (10Gbps). If the technology improves to shrink less than 25ps , then the number of bits in the higher order PCM will be more than 10Gbps.
•To transmit 10Gbps, the optical fibre requires a bandwidth of around 0.078ns = 78ps ( for 1 wavelength)•If the available bandwidth in the optical fibre is 200ns , the number of wavelengths that can be produced is around 2400 , which will result in producing a total of 24Tbps.•Hence both Time Division Multiplexing and Dense Wave Division Multiplexing can further improve the traffic carrying capacity of an optical fibre up to a total of 24Tbps.
Optical Fibre
Optical Fibre
96
Overview of WDMDigital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Single Pair of Fibers
Single Pair of Fibers
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
WDM MUX WDM MUX
Single Pair of Fibers
Traditional Digital Fiber Optic Transport
Digital Fiber Optic Transport using WDM
Number of wavelengths = ( 24 * 103 Gb ) / 10 Gb = 2400 wavelengths
Future ScenariosTheoretical Maximum of an Optical Fibre Cable
Only 1 core is needed
Transponders
Optical Fibre
1 λ1
2 λ2
2399 λ2399
2400λ2400
TDM
10Gbps2Mbps
488ns 100 ps
Optical tools for maintanance
• OTDR• Splicing machine
Optical Time Domain ReflectometryPrinciple (OTDR)
Fusion splicing • It is the process of fusing or welding two fibers together usually by an
electric arc. Fusion splicing is the most widely used method of splicing as it provides for the lowest loss and least reflectance, as well as providing the strongest and most reliable joint between two fibers.
• Virtually all singlemode splices are fusion.• Fusion splicing may be done one fiber at a time or a complete fiber ribbon
from ribbon cable at one time. First we'll look at single fiber splicing and then ribbon splicing.