FIBER OPTIC COMMUNICATION SYSTEM (TCT-4)122.252.230.113/content/ppt/tele/TCT_4hl.pdf · 2020. 10. 22. · 10 Gbps (STM-64: BSNL) 1.28 Tbps (128 Ch. DWDM) 20 Tbps (Possible) 5/24/2020

FIBER OPTIC COMMUNICATION SYSTEM(TCT-4)

Presentation

By

M.V.Satyanarayana

ILP-1

Cell no: 9030712960

[email protected]

5/24/2020 1TCT-4 OFC SYSTEMS

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1. Need For OFC 2. Propagation Fundamentals3. Optical Signal degradation issues4. Different types of cables and passive

components5. OFC Cable Laying Practices6. Splicing and Jointing 7. Testing and measurements8. Optical link Engineering


Contents

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Basic Fiber Optic Communication System

➢Fiber optics is a Transmission medium for carrying information from one point to another in the form of light.

➢Unlike the copper form of transmission, fiber optics is not electrical in nature.

➢A basic fiber optic system consists of a transmitting device that converts an electrical signal into a lightSignal.


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Global Internet Data Trends

Inter Net activity Quantity

Active net users 4549631870(4.5 billion)

websites 1768199049(1.76billion)

E- mails sent 1322476923889(1.3 trilion)

Google searches 3619936898 (3.6 billion)

YouTube video views 3695923569 (3.69 billions)

Twitter active users 359896111 (36 crore)

Face book active users 2489831392 (2.48 billion)

Internet traffic (data & voice)

5029699892GB (5.03ZB)

5/24/2020 TCT-4 OFC SYSTEMS 4

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Growth Rate of Net Users


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Global mobile subscribers


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Basic Fiber Optic Communication System contd………..

➢an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal.

➢The complexity of a fiber optic system can range from very simple (i.e., local area network) to extremely sophisticated and expensive (i.e., long distance telephone or cable television trunking).


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Basic Fiber Optic Communication System

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OFC components


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Why OFC ?

Medium / Link Carrier Information Capacity

Copper Cable (short distance)

10 MHz 1 Mb(ADSL Modem)

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: BSNL)

1.28 Tbps (128 Ch. DWDM)

20 Tbps (Possible)5/24/2020 10TCT-4 OFC SYSTEMS

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Parameter 6Quad OFC

Weight 2000kg/km 250kg/km

size 0.9mm 9µm

cost 3lakhs /km 1lakh/km

Bandwidth 2MHz 100 GHz

attenuation 0.63db/km 0.25db/km

Link protection Not available available

safety Not much Highly safe


Let us compare with 6 Quad cable

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OFC Operational / Transmission Windows

Window Operating Wavelength

800 – 900 nm 850 nm

1250 – 1350 nm 1310 nm

1500 – 1600 nm 1550 nm

➢There are ranges of wavelengths at which the fiber operates best.

➢Each range is known as an operating window. ➢Each window is centered on the typical operational

wavelength, as shown in table below.


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OFC Operational / Transmission Windows contd …….

Window Operating Wavelength

800 – 900 nm 850 nm

1250 – 1350 nm 1310 nm

1500 – 1600 nm 1550 nm

➢as shown in table above , these wavelengths were so -chosen because they offer very less loss.➢They best match the transmission properties of available light sources with the transmission qualities of optical fiber.5/24/2020 13TCT-4 OFC SYSTEMS

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Advantages of OFC

More information carrying capacity 10 Gbps

( 2.5 Gbps STM-16 : Railways)

Free from EMI(electromagnetic interference) and Electrostatic interference as no electric current flows through the fiber.

Low loss. The higher frequency, the greater the signal loss using copper cabling. With fiber, the signal loss is the same across frequencies, 0.25 db/km at 1550 nm

High bandwidth for voice, video and data applications


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Advantages of OFC contd…….

➢As fiber is non conductor it does not pick up or radiate electromagnetic radiation hence no WPC is required

➢Use of WDM(wavelength division multiplexing)

➢ Switching / routing at Optical signal level

➢No Cross talk as the signal transmission is digital modulation no chance of cross talk between channels.5/24/2020 15TCT-4 OFC SYSTEMS

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Advantages of OFCcontd ……..

➢Flexibility in system up gradation

➢Reliability - Fibber is more reliable than copper and has a longer life span

➢Secure - Fiber does not emit electromagnetic interference and is difficult to tap

➢High resistance to chemical effects & temp variations

➢Small size

➢Safety

➢Light weight5/24/2020 16TCT-4 OFC SYSTEMS

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OFC Limitations

➢Difficulty in splicing

➢Highly skilled staff required

➢Precision and costly instruments required

➢Tapping is difficult

➢Costly if under utilized

➢Special interface equipment required for block working

➢O-E-O conversion


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OFC applications in Railways

• Long haul circuits for administrative branch and data transmission circuits (PRS,FOIS etc.,)

• Short haul circuits for linking of telephone exchanges

• Control communications

• Signaling application for failsafe transmission


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Transmission windows

➢ Optical fiber transmission uses wavelengths that are in the near-infrared portion of the spectrum, just above the visible, and thus undetectable to the unaided eye.

➢ Typical optical transmission wavelengths are 850 nm, 1310 nm and 1550 nm.

➢ Both lasers and LEDs are used to transmit light through optical fiber.

➢ Lasers are usually used for 1310 or 1550 nm single mode applications

➢ LEDs are used for 850 or 1300 nm multimode applications.


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Optical Fiber Cable Structure


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Fibre Technology


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24 Fiber Armored cable


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CABLE CORE

HDPE OUTER JACKET

STAINLESS STELL ARMOUR CORRUGATED A ISI-304 0R 305

HDPE OUTER JACKET

CABLE CORE

INNER P.E.SHEATH

RIP CARD

INNER P.E.SHEATH

CORRUGATED STAINLESS STELL ARMOUR

ARMOURED OPTIC FIBRE CABLE

CROSS SECTIONAL VIEW OF

Cross sectional view of OFC


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TWO SUITABLE RIP CARDS UNDER THE ARMOUR

HDPE OUTER JACKET (2.0 mm minimum)

CORRUGATED A ISI-304 0R 305 STAINLESSSTELL ARMOUR [0.125 MM (maximum) ]

INNER P.E.SHEATH (1.5 mm minimum)

(OUTER DIA 2.4 mm +/- 0.1 mm)SECONDARY COATING TUBE

NON-HYGROSCOPIC DIELECTRIP TAPE (POLYSTER TAPE)

PRIMARY COATED FIBRE

CENTRAL STRENGTH MEMBER (2.5mm +/- 0.05mm)

WRAPPING ARMIDE YARN(IF REQUIRED)

WATER BLOCKING JELLY

WATER BLOCKING THIXOTROPIC JELLY

ONE SUITABLE RIP CARD UNDER THE INNER SHEATH

CONSTRUCTIONAL DIAGRAM OF

24 FIBRE ARMOURED OPTIC CABLE (TC. 55. 2006 Rev.1)

Constructional diagram of OFC


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Basic structure of Optical Fiber Cable

➢Optical fiber cable consists of one or more protective enclosures, each having one or more bare fibers and the entirety packaged with a strength member in an outer jacket.

➢Basic elements in OF cable are :

1. Bare fiber

2. Buffer tube

3. Strength member

4. Outer jacket


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Buffer tube description

➢Buffer tube is the first shield protecting fiber from damage

➢It can have one fiber or more

➢It can be tight buffer or loose buffer

➢It is color coded for identification


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Features of loose buffer tube

➢Buffer’s inner diameter is more than fiber’s outer diameter

➢Protects fiber from mechanical forces.

➢Force applied on buffer does not affect the fiber until the force is large enough to straighten the fiber inside the buffer


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Features of loose buffer tube contd…….

➢Loose buffer tube can be filled with gel to prevent entry of moisture

➢Eliminates micro bending of fiber

➢Loose buffer tube fiber cables are used out-door because they effectively isolate the fibers from external stresses such as changes in temperatures, preventing damages & resulting in lower fiber loss.


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Features of tight buffer tube

➢Tight buffer’s inner diameter is same as fiber’s outer diameter

➢It can keep the fiber operational despite break, as the fiber is held in position firmly.

➢Each buffer can hold one fiber only.


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Features of tight buffer tubecontd……..

➢Easy to prepare for and provide connectors / splicing

➢Can be installed vertically

➢Very strong tight buffer tube cables are used in military and under-sea applications as small separation of fiber ends due to break does not interrupt services completely.


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Bare fiber description

➢ Two different types of highly pure, solid glass, composed to form the core and cladding.

➢ A protective Acrylate coating or primary coating surrounds the cladding

➢ This is applied to the glass fiber as the final step in the manufacturing process.

➢ This is color coded for identification of fiber ,


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Bare fiber descriptioncontd…..

➢ This primary coating protects the glass from dust and scratches

➢ This protective primary coating comprises of two layers:

➢ A soft inner layer that cushions the fiber and allows the coating to be stripped from the glass mechanically

➢ A hard outer layer that protects the fiber during handling, particularly the cabling, installation, and termination processes.


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➢Gel compound fills buffer tubes and cable interiors.

➢Gel making the cable impervious to water.

➢Gel needs to be completely cleaned off when the

cable end is stripped for termination.


Gel Compound

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➢ Ripcord is a thin but very strong thread

➢ Ripcord is embedded just below the cable jacket.

➢ Ripcord role is to split the cable easily without harming cable interiors.


Ripcord

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Strength member

➢Strength member runs along the center of the cable.

➢Strength member provides rigidity needed to keep it from buckling, as well as a core to build the cable structure around.

➢Strength member may be over coated with plastic to prevent friction with other parts of the cable.➢Flexible aramid yarn (Ex. Du pont Kevlar –widely used) used as strength member


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Cable Sheath

➢Cable sheath surrounds the entire assembly of buffer tube or tubes and strength member

➢Cable sheath purpose is to provide environmental protection to fibers

➢Cable sheath made of High Density Polyethylene (HDPE)


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Steel armor

➢ Steel armor is provided for armored cables to protect against crushing damage, rocks, and rodents.

➢ Steel armored cable is required when the OFC cable is laid at a depth less than 1.6 meters.

➢ If the OFC cable is laid at a depth 1.6 meters, then the armor is not necessary.


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Jacketing / Outer sheath

• Jacketing or Outermost sheath provides protection from chemical acids, alkalis etc.,

• Material used for this jacketing is high density polyethylene (HDPE) with anti termite


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24 fiber cable used in Indian Railways

24F armored cable➢ Normally used for under ground laying➢ It consists of 6 loose tubes

1. Blue2. Orange3. Green4. Brown5. Slate6. Natural (White)

➢Each loose tube contains 4 fibers1.Blue, 2.Orange, 3.Green, 4.Natural (White)


RDSO spec no.IRS:TC55-2006,Rev-1 with amendment 1.1

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➢ Optical fiber propagates light for angle of incidence > critical angle

➢ RI of core > RI of cladding

How does optical fiber propagate light ?

➢ Light injected into the core of the glass fiber will follow the physical path of that fiber due to total internal reflection of the light between the core cladding.


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Important Parameters of OFC

➢Refractive Index

➢Denser medium

➢Rarer medium

➢Incident ray

➢Refracted ray

➢Reflected ray


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Important Parameters of OFCcontd…….

➢Snell’s law

➢Angle of incidence

➢ Angle of refraction

➢Critical angle

➢ Total internal reflection

➢Snell’s law

➢Numerical Aperture


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Snell’s Law

➢ Snell’s Law gives relation ship between the different angles of light.

➢ As light passes from denser medium to rarer medium, (i.e. from one medium to another medium ) the light will looks bending in the rarer medium, this phenomenon is called refraction.

➢ If the angle of incidence is more than the critical angle, then the light will completely reflect back into the denser medium, this is explained by Snell's law.

n1 sin a = n2 sin b

a = Angle of incidence b = Angle of refraction

n1 = RI of Denser Medium n2 = RI of Rarer Medium


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What is Refractive Index ?

➢Refractive Index is the ratio of the velocity of light in a vacuum to the velocity of light in a material.

➢RI (n)=c/v

➢Refractive Index (n) = velocity of light in vacuum(c)

velocity of light in material(v)

➢ Velocity of light in vacuum (c) is 3 x 108 mtrs /sec

➢ Velocity of light in glass is (v) 2 x 108 mtrs / sec

➢Refractive Index (n) for air is 1.0

➢Refractive Index (n) for glass is 1.5


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Bending of Light Ray

Angle of incidence

Denser

Medium

RI = n1

Rarer

Medium

RI = n2

a

b

n1 > n2

a

Incident

Ray

Refracted

Ray

Reflected

Ray

Angle of refraction


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Critical Angle of Incidence

Rarer Medium RI = n2Denser

Medium RI = n1

c

90

n1 > n2

As per Snell’s Law : n1 sin a = n2 sin b

n1 sin c = n2 sin 90 = n2

Critical Angle of incidence (c) = sin-1 (n2/n1)

Incident Ray

Refraction angle 900

Critical angle is an angle at which the refraction angle will be 90 degrees to the normal


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LIGHT GUIDANCE (RAY THEORY)


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RAY THEORY (MERIDIONAL RAYS)


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Total Internal Reflection

Denser Medium RI = n1

Rarer Medium RI = n2

c

90

n1 > n2

Incident Rays

Refraction angle 900

Total Internal Reflection


When the angle of incidence is more than the critical angle, then the incident ray will be reflected back into the same denser medium and ray will move forward, within the medium this phenomenon is called total internal reflection.

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Optical fiber's Numerical Aperture

➢ Optical fibre's capability to collect light is not only determined by fibre core size, but also by its acceptance angle. Acceptance angle is the range of angles over which a light ray can enter the fibre and be trapped in its core.

➢ The sine of the half-angle of the acceptance angle is known as the numerical aperture

NA = sin 0IRIS

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➢The sine of the half-angle of the acceptance angle is known as the numerical aperture NA .

➢Fiber with a lower NA will allow fewer modes.

➢ Fewer modes means less dispersion and hence greater band width.


Optical fiber's Numerical ApertureContd…..

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http://www.fiberoptics4sale.com/wordpress/wp-content/uploads/2009/02/lightacceptanceangle.gif

TYPES OF FIBER

Multi ModeSingle Mode

Step-index Graded- index

FIBER


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TYPES OF FIBERcontd…..

➢ Step-index fiber has an abrupt change or step between the index of refraction of the core and the index of refraction of the cladding.

➢ Graded index fibre was designed to reduce modal dispersion inherent instep index fibre. Graded index fiber is made up of multiple layers with the highest index of refraction at the core. Each succeeding layer has a gradually decreasing index of refraction as the layers move away from the center.

➢ Fibers having very small diameter core that can carry only one mode which travels as a straight line at the center of the core are called Single mode step index fibers.


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TYPES OF FIBERcontd……


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➢One mode travels straight down the center of the core

➢Other modes travel at different steep angles and bounce back and forth by total internal reflection.

➢Different light waves travel down the fiber

➢normalized cut-off frequency

V = (πd/λ)(n12-n2

2)1/2

where, d= diameter of core, n1= RI of core

n2= RI of cladding , λ= wavelength of source

➢No. of modes in step-index fiber are N= V2/2

➢No. of modes in graded index fiber are N= V2/4

Propagation through Multimode step-index fiber


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Problems with Multi-mode Step-index fiber

➢Different modes travel different distances , resulting in different arrival times at the far end

➢This causes distortion in the transmitted signal

➢The disparity between arrival times of the different light rays is known as dispersion

➢High dispersion is an unavoidable characteristic of multimode step-index fiber.

➢Solutions are :

➢Use Graded Index Fiber

➢Use Single Mode Fiber


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Multimode grade-index fiber

➢Refractive index varies gradually from center of core to its periphery

➢Refractive index at the center of the core will be more and gradually decreases to ends.


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Propagation through Multimodegraded-index fiber

➢The core’s refractive index is parabolic, being higher at the center ( na> nb) and decreasing to the ends

➢The light rays follow a serpentine path being gradually bent back toward the center by the continuously declining RI.

➢The modes traveling in a straight line are in a higher refractive index, so they travel slower than the serpentine modes

➢Thus, the arrival time disparity is removed , as all modes arrive at about the same time


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Single mode fibre

Core

Diameter:

5 to 10 μm

Cladding

Diameter: 125 μm

Primary Coating

Diameter:

250 μm

Cladding refractive index < core refractive index


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Single mode step-index fiber

Core diameter 5 to 10 micro meter

Cladding diameter 125 micro meter


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➢Single mode fiber has a much smaller core that allows only one mode of light at a time to propagate through the core.

➢Single-mode fiber exhibits no dispersion caused by multiple modes

➢Single-mode fiber also enjoys lower fiber attenuation than multimode fiber

➢Thus, more information can be transmitted per unit of time because it can retain the fidelity of each light pulse over longer distances

➢DISADVANTAGE is coupling light into the core is difficult.

Propagation through Single mode step-index fiber


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Important Parameters of Single mode fiber

Parameter Description Typical value

Attenuation Loss of signal strength 0.35 db/km at 1310 nm

0.25 db/km at 1550 nm

Core diameter Diameter of core 8 to 10 micro meter

Cladding diameter Diameter of cladding 125 micro meter

Core-cladding RI ratio

Ratio of RI of core to cladding

Less than 1%

Cut-off wavelength Minimal wavelength at which fiber supports only one wavelength

> 1260 nm

Numerical aperture

Ability of Optical Fiber to gather light from source and guide it inside through total internal reflection

0.10 to 0.17


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Important Parameters of Single mode fibercontd……

Parameter Description Typical value

Mode field

diameter

(MFD)

➢MM fiber carries all light energy

through core as core diameter is large.

➢SM fiber carries 80% light energy

through core and 20% through

cladding as core diameter is small.

➢Mode field diameter (MFD) is the

effective diameter available for

propagation.

➢MFD is dependent on wavelength – it

reduces with wavelength. Shorter the

wavelength, more focused the beam is

and more stringent confinement of

beam to core , hence less MFD

➢When 2 fibers are connected, not only

core-cladding diameters to match but

also MFDs to match

9.3 micro meters

for core diameter of

8.3 micro meters


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Application of MM and SM Fibers

➢Multimode fiber is used primarily in systems with short transmission distances (under 2 km), such as premises communications, private data networks, and parallel optic applications.

➢Single-mode fiber is typically used for longer-distance and higher-bandwidth applications .Its tremendous information-carrying capacity and low intrinsic loss have made single-mode fiber the ideal transmission medium for a multitude of applications.


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Optical Fiber Sizes Available commercially

➢To ensure compatibility among splices/connectors, sizes of core & cladding have been standardized

➢International standards for SM fiber

➢Cladding diameter : 125 microns (micro meter)

➢Cladding + coating : 245 microns (micro meter)

➢Core diameter : 5 to 10 micro meter

➢International standards for MM fibers

➢Cladding diameter : 125 microns (micro meter)

➢Cladding + coating : 245 microns (micro meter)

➢Core diameter : 50 to 62.5 micro meter


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➢ Attenuation is the loss of optical power as lighttravels through the fiber and is measured indb/km

➢ It ranges from over 300 dB/km for plastic fibers to0.21 dB/km for single mode.

➢ Attenuation varies with wave length.

➢ Single Mode with 1310 nm is 0.35 dB/km & with1550 nm it is 0.25 dB/km.

Attenuation in Optical fiber


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850nm

1300/1310 1380nm

1550nm

Attenuation vs. wavelength


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1. Absorption

2. Scattering

3. Micro bending

4. Macro bending


Causes of attenuation

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Factors causing light absorption

➢Light absorption due to presence of ions (OH) in silica, impurities in silica, residual materials within the fiber core and inner cladding.

➢These water ions that cause the “water peak” region on the attenuation curve, typically around 1380 nm.

➢absorption of optical energy by tiny impurities in the fiber such as iron, copper, or cobalt


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Factors causing Scattering

➢Scattering of light due to molecular level irregularities in the physical construction of fiber.

➢The well known form is Rayleigh Scattering.

➢Rayleigh Scattering is caused by metal ions in the silica matrix.

➢Rayleigh Scattering limits the use of wavelengths below 800nm shorter wavelengths more.


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Absorption LossScattering Loss

Absorption loss & Scattering loss


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Macro-bending loss

➢Micro bending is caused by a nick or dent in the fiber that disrupts the mode

➢Macro-bending loss is caused by bending of the entire fiber axis

➢The bending radius shall not be sharper than ’30D’ where ‘D’ is diameter of cable = 20 mm

(30 x 20 mm) = 600 mm

➢One single bend sharper than 30D can cause loss of 0.5 dB

➢If bending is even sharper, fiber may break


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Micro-bending loss

➢ Micro-bending loss is caused by micro

deformations of fiber axis at the time of

manufacturing, which leads to failures in achieving

total internal reflection conditions.

➢ Micro-bends are small-scale perturbations along

the fiber axis, the amplitude of which are on the

order of microns. These distortions can cause light

to leak out of a fiber.5/24/2020 75TCT-4 OFC SYSTEMS

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➢ Due to thermal expansion / variations enough load may

be exerted on the glass to cause micro bends.

➢ Coating material is selected by manufacturers to

minimize loss due to micro-bending. The linear thermal

expansion coefficient of coating material shall be

compatible with that of fiber


Micro-bending loss contd……

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Dispersion

➢Dispersion is the time distortion of an optical signal

➢It results from the differences of time of travel and arrival of the signal at the destination, typically resulting in pulse broadening.

➢In digital transmission, dispersion puts a limit on the maximum data rate and the maximum distance i.e. the information-carrying capacity of a fiber link.


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Types of dispersion

There are 2 types of dispersion :

➢ Inter-modal dispersion (MODAL DISPERSION)

➢ Chromatic dispersion (Material dispersion + Wave guide dispersion)

➢ Dispersion is measured as picoseconds/nm -km and represented with a symbol Δt .


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Types of dispersion contd…..


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➢ As a pulse of light propagates through a fiber, elements such as numerical aperture, core diameter, refractive index profile, wavelength & and laser line width cause the pulse to broaden.

➢ This poses a limitation on the overall bandwidth of the fiber.


Dispersion

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➢Total dispersion is a function of fiber length. ➢The longer the fiber, the more the dispersion.

Δt total = L × (Dispersion/km) ➢The overall effect of dispersion on the performance of a fiber optic system is known as inter symbol interference .


Dispersion contd……..

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Model Dispersion in Multimode Fibres

➢Multimode fibres can have many different light modes since they have much larger core size.

➢Each mode enters the fibre at a different angle and thus travels at different paths in the fibre.

➢Each mode ray travels a different distance and arrives at different times at the fibre output.

➢So the light pulse spreads out in time which can cause signal overlapping.

➢Model dispersion is not a problem in single mode fibres since there is only one mode that can travel in the fibre.


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Chromatic Dispersion


➢Chromatic dispersion is pulse spreading due to different wavelengths of light propagates at slightly different velocities through the fiber.

➢Whether Laser or LED have finite line widths, means they emit the light in more than one wavelength.

➢Different wavelengths propagate at different velocities.➢Chromatic dispersion is expressed in Nano seconds or

Pico seconds per (km-nm).➢Chromatic dispersion consists of two parts

1. Material dispersion. 2. Waveguide dispersion.

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Material Dispersion


➢ Material dispersion is a type of chromatic dispersion.

➢ Material dispersion is due to the wavelength dependency on the index of refraction of glass.

➢ Material dispersion is the result of the finite line width of the light source and the dependence of refractive index of the material on wavelength.

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Chromatic Dispersion


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➢ Waveguide dispersion is due to the physical structure of the waveguide.

➢ In a simple step-index profile fiber, waveguide dispersion is not a major factor, but in fibers with more complex index profiles, waveguide dispersion can be more significant.

➢ Material dispersion and waveguide dispersion can have opposite signs depending on the transmission wavelength. In the case of a step-index single-mode fiber, these two effectively cancel each other at 1310 nm, yielding zero dispersion.

Waveguide Dispersion


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Waveguide Dispersion

contd......

•Wave guide dispersion is only important in single mode fibres. It is caused by the fact that some light travels in the fibre cladding compared to most light travels in the fibre core.


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http://www.fiberoptics4sale.com/wordpress/wp-content/uploads/2009/02/waveguidedispersion.gif

Dispersion in Single Mode Fiber

➢ The difference in refractive indices of single mode fibber's core and cladding are minuscule.

➢ The different RI of core and cladding will cause the variation of speed of light and it becomes a factor over greater distances.

➢ It can also combine with material dispersion to create a nightmare in single mode chromatic dispersion.

➢ Only Chromatic dispersion exists in Single mode fiber and no modal dispersion 5/24/2020 89TCT-4 OFC SYSTEMS

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Dispersion in Single Mode Fiber contd …..

➢ Dispersion varies with wavelength it’s unit is pS/nm-km

➢The wavelength at which dispersion equals zero is called the zero-dispersion wavelength (λ0).

➢This is the wavelength at which fiber has its maximum information-carrying capacity.

➢For standard single-mode fibers, this is in the region of 1310 nm.

➢ This makes very high-bandwidth communication possible at this 1310 nm wavelength.

➢However, the drawback is that, even though dispersion is minimized at 1310 nm, attenuation is not.


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Dispersion vs. Wavelength curve


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Classes of Single mode fiber

There are 3 different classes of single mode fiber are used

1.Non dispersion-shifted fiber (NDSF) (ITU-T/G.652)

2.Dispersion-shifted fiber (DSF) (ITU-T/G.653)

3.Non zero-dispersion-shifted fibers (NZ-DSF) (ITU-T/G.653)


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Classes of Single mode fiber contd…….

Non dispersion-shifted fiber (NDSF) (ITU-T/G.652)➢ This fiber is used for 1310 nm.

➢ This fiber has high dispersion at 1550 nm, hence not suitable for 1550 nm systems

Dispersion-shifted fiber (DSF) (ITU-T/G.653)➢ To address the shortcoming of NDSF fiber, fiber

manufacturers developed, dispersion-shifted fiber (DSF)

➢ This has moved the zero-dispersion point to the 1550 nm region


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Classes of Single mode fiber contd…….

Non zero-dispersion-shifted fibers (NZ-DSF) (ITU-T/G.653)

➢ Though DSF worked extremely well with a single 1550 nm wavelength, it exhibits serious non linearity when multiple, closely-spaced wavelengths in the 1550 nm were transmitted in DWDM systems.

➢ To address the problem of non linearity, non zero-dispersion-shifted fibers (NZ-DSF) were designed by manufacturers. Exclusively for DWDM


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Cable laying practices


There are different stages are involved in cable laying. They are➢ Initial / First survey & estimation➢ Second survey➢ Final survey➢ Drum testing➢ Trenching➢ Laying HDPE duct➢ Duct integrity test➢ Laying of OFC➢ Loop Chambers➢ Joint Chambers➢ Protection of OFC using spare cable.➢ Cable markers➢ Testing of OFC

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Initial / First survey

➢by train with Engineering drawing

➢Verify culverts, bridges and LC gates

➢Observe nature of land i.e. sand, black cotton soil, red soil, morrum and rocky

➢Prepare a chart with schedule items for rough estimation

Second survey

➢by trolley along with concerned PWI, S&T staff maximum one block section per day

➢Take alignment along the Railway boundary

➢Note the off sets existing cables

➢Enter the protection works required i.e. GI Pipe, RCC Pipe etc.

Site Survey and Estimation


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➢Final survey is by on foot with sufficient labors

➢Do the test pit for every 200 m and note down the nature of soil.

➢Compile the estimation for one block section with 10 to 15% extra quantities.

➢Prepare the proposed cable route drawing.

➢Ensure the station yard, location boxes, signal posts, culverts and LC gates in the drawing.

➢Submit drawings for Engineering department approval.

Final survey


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➢As-made drawings to be prepared with proper off sets of cable trench, Joint chambers, loop chambers etc.

➢After verification of as made drawings, do correction if any

➢Hand over the as made drawings to S&T, Electrical and Engineering departments with acknowledgement.➢Store the sufficient number of soft and hard copies for further use & future reference.

As made drawings


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Cable laying practices

➢Hand over the approved drawings to the contractor and take acknowledgement

➢Ask them to visit the site along with drawings for their convenient

➢ Ensure the material on hand before starting trenching work

➢Show the cable plane and ask them to start work in one block section


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Trenching for cable laying

➢Trenches for telecom cable shall be dug to a depth of 1.2 meters.

➢Width of 300mm (or as per requirement adequate to accommodate cables and their protections)

➢Mettled, mechanized concrete and stone paved roads shall also be cut to a depth of 1.2 meters. The cable shall be laid through RCC pipe.

➢All cable crossing across railway tracks shall be done in horizontal boring method through G.I pipes

➢All cable crossing across road crossing shall be done in horizontal boring method through RCC pipes


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➢HDPE drum length is 1KM and dia is 40/33mm.

➢Permit trenching for 1km length and ask them to lay the HDPE duct immediately

➢Unwind the duct by keeping it on Duct wheel.

➢Complete the duct laying for one block section

➢Do the Duct Integrity Test (DIT) for one block section and cable blowing to be started

➢Keep the drum at the middle of 3km trench on jacks

➢Cable to be blown through ducts using cable blowing machine in one direction

Laying HDPE Duct


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➢ After backfilling ducts shall be tested for duct integrity test.

➢ The sole purpose of duct integration testing is to prove that the installed ducts are ready for blowing of cable without any hindrance from one manhole to other.

➢ There are two types of tests.

1. Air tightness test

2. kink-free shape test.5/24/2020 106TCT-4 OFC SYSTEMS

Duct Integration Test

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➢ Air tightness test is done by pressurizing 2 km duct stretches at a time.

➢ One end of duct will be closed and compressed air at 5 to 6kg/cm2 pressure is sent from the other end.

➢ At about 5kg/cm2 pressure the inlet of compressed air

will be closed.

➢ Fall in pressure should not be more than 50% in one hour.5/24/2020 107TCT-4 OFC SYSTEMS

Duct Integration Test / Air Tightness Test

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Duct Integration Test / kink-free shape test.

➢To check that the duct has not collapsed a kink-free shape test is done

➢In this test a kinked wooden cylindrical piece (shuttle) is blown into the duct with far end fitted with flexible wire

grip/stocking.

➢The wooden shuttle should pass through duct at far end with out any obstruction and within approximately 10 minutes or less.

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Duct Integration Test Apparatus

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Drum Testing

➢Before laying every cable drum to be tested

➢ Normally drum length is about 3 km

➢ Drum No. , length of the cable, Running meters to be noted

➢ All fibers to be tested with OTDR and traces to be stored

➢ If any event/break observed, avoid laying5/24/2020 110TCT-4 OFC SYSTEMS

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➢Place the cable drum at the center i.e. at 1.5 KM ( as the OFC drum size is 3 KM length) and thereby the cable can be pulled easily in both directions, so that pulling portion can be minimized.

➢Now blow the cable to one side i.e. either 1 KM or 1.5 KM using blowing machine.

➢Un wind the balance cable (2 KM or 1.5 KM) from the drum and put it in the shape of ‘8’ coil, so that it becomes each to pickup layer by layer for further blowing.

➢Blow the balance cable on the other side

Laying of OFC cable


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➢Place the loop chamber for every 1 KM

➢Complete the blowing in one block section.

➢Test the cable after blowing and splicing to be done in the joint enclosure.

➢Drum wise and section wise OTDR traces to be stored.

➢During blowing ensure proper or uniform pressure to be applied and speed should not exceed 10 meters/minute.

Laying of OFC cablecontd……


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Laying of OFC through bridges

➢The optic fiber cable is required to be laid through HDPE pipe in GI pipes over steel girder bridges. The GI pipes should be fitted on the girder bridges with suitable clamp/U bolt without drilling holes in the girder

➢Where ever the water flow is less, the cable shall be laid under the bed of the dry culvert at a depth of 1.2 meters or through RCC/Double wall corrugated (DWC) pipes.

➢In case of wet culverts or un-friendly terrains where it is not possible to lay cable under the bed of culverts, the cable may be laid over the culvert in G.I pipes.

➢In rocky soil HDPE duct pipe shall be laid and concreted up to ground level5/24/2020 113TCT-4 OFC SYSTEMS

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Laying of OFC while Road & Track crossings

➢While road or track crossings the width of thetrench should be 300 mm and depth should be 1.6meters .

➢The trench should be done using horizontal boringmethod.

➢Especially during track crossings the cable shouldbe drawn through G.I pipes.

➢ During road crossings the cable can be drawnthrough RCC pipes.5/24/2020 114TCT-4 OFC SYSTEMS

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Laying of OFC near FP

➢While laying near feeding post ,as far as possiblethe cable shall be laid on the side of trackopposite to the feeding post.

➢Further the optic fiber cable shall be at least onemeter away from any metallic part of the O.H.E.

➢ The cable shall be laid in RCC/DWC pipes for alength of 300 meters on the either side of thefeeding point


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Spare OFC cable for protection at loop chamber

➢Spare OFC cable has to be kept as a coil at various locations i.e., at loop chambers, at LC gates, at bridges, at culverts, at prefabs / OFC rooms, at road crossings, at track crossings, and finally at joint chambers.

➢ at every 1 KM one loop chamber to be provided with a spare cable of 10 meters.

➢It should be ensured that there will be at least 1 KM distance between loop chambers. If there is an LC gate or a bridge or a track crossing or prefab and then the next loop chamber will be at 1 KM.


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Spare OFC cable for protection at LC gates & Bridges

➢LC gate: One chamber will be provided at all LC gates at least 10 meters away from the center point of the road, a coil of 15 meters will be kept as spare in this chamber.

➢Bridges: For all bridges of length less than 25 meters, one chamber will be provided at a distance of 10 meters from the edge.

➢For all bridges of length less more than 25 meters, two chambers will be provided on either side of bridge at a distance of 10 meters from the edge.

➢At these chambers a coil of 15 meters will be kept as a spare in each chamber.


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Spare OFC cable for protection at Prefab/OFC rooms, Road & Track crossings

➢ All prefab/ OFC rooms will be provided with one chamber with a coil of 15 meters

➢ Road / Track crossing: One loop chamber with 15 meters coil to be provided at every track crossing. The chamber to be placed at a distance of 2.5 meter away from the track.


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Track Crossing diagram


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Road Crossing


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Culvert/ bridges


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Spare OFC cable for protection at Joint chamber

➢At every 3 km, one joint chamber will be provided by providing a coil of 10 meters for each side of the cable.

➢Stations: Every station will be provided with one number joint chamber where ’T’ joint is made.

➢Only those fibers which are required to be derived only are to be spliced with derivation cable with ”T” joint without disturbing the other fibers.

➢For through cable 15 meters to be left as coil and for derivation cable 15 meters to be left as a coil in the chamber


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OFC cable route markers

➢ Cable route markers shall be provided at the distance of every 50 meters on the cable route with circuit details, like “IRISET OFC”.

➢ Also at places or corners wherever the route of cable changes.

➢ The joint indicators shall be provided at all types of cable joints


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Testing of Fibers

➢All terminated fibers to be tested with OTDR and traces to be stored.

➢Power measurements to be done for every fiber with laser source meter and power meter.

➢Average loss to be

< 0.25 dB/km for at 1550 nm

&

< 0.35 dB/km at 1310 nm5/24/2020 125TCT-4 OFC SYSTEMS

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OPTICAL SOURCES, DETECTORS, AMPLIFIERS,

COUPLERS, SPLITTERS, ATTENUATORS,

CONNECTORS, PIG TAILS, PATCH CORDS & FDMS


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Optical Source

➢ The Main function of optical source is to Convert electrical energy into optical energy.

➢ There are basically two types of optical sources are used. They are

➢Light Emitting diodes ( LEDs) (Spontaneous emission)

➢LASER diodes (LDs) (stimulated emission)

•LASER stands for Light Amplification by Stimulated Emission of Radiation


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Optical Source Requirements

➢ Directivity Size and configuration compatible with launching light into the fiber and light should be highly directional.

➢ Output Power: should be as high as possible.

➢ Linearity Should be linear (accurately track the electrical input signal ,minimize the distortion & noise).

➢ Wavelength Emit light at wavelengths where fiber has low losses, dispersion and where detectors are efficient.


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Optical Source Requirementscontd…..

➢ Direct modulation Capable of simple signal modulation ranging from audio frequencies to GHz range.

➢ Coupling Efficiency Should couple sufficient optical power to overcome attenuation in the fiber

➢ Spectral bandwidth: Should have narrow spectralbandwidth (line width) in order to minimize dispersion

➢ Stable optical output: Must be capable of maintaining stable optical output (that does not change with ambient conditions)

➢ Should be Economical comparatively cheap and highly reliable in order to compete with conventional transmission techniques5/24/2020 129TCT-4 OFC SYSTEMS

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Features of Laser Diode (LD’s)stimulated emission

➢External stimulation :

External photon forces photon of similar energy to be emitted. This is reflected back to active region to continue the process; hence Spectral width is narrow ( 1 nm ).

➢High output power

All photons propagate in same direction , hence contribute to high output power (LD requires 10 mA current to radiate 1 mW whereas LED requires 150 mA)

➢Better directivity

Stimulated photons propagate in same direction, hence better directivity

➢Coherence

➢All photons are synchronized, hence coherent radiation5/24/2020 130TCT-4 OFC SYSTEMS

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Important parameters of Laser diodes

Threshold current and its significance:

Threshold current is the current at which the laser operates, normal range is 50-70 mA.

This threshold current should be minimum to maintain junction temperature low to have reliable output and low noise

• fOutput power

currentThreshold current

Normal operating rage

0


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Important parameters of Laser diodescontd…….

Spectral width :Spectral width is the band width of emitted light.This spectral is very narrow 1.3 nm in laser diode.

Power output

WavelengthSpectral

width 1-3nm

30-60nm

LED response

Laser response


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Important parameters of Laser diodescontd…….

100%

90%

10%

0

Power output

Rise and Fall Time:

Rise and Fall Time is a measure of how

quickly the laser can be switched on or off .

Rise and Fall Time is measured between the

output levels of 10-90% of maximum time

Rise

timeFall

time5/24/2020 133TCT-4 OFC SYSTEMS

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Laser Diode (LD’s) specifications

➢Wavelength : 1310 nm (or) 1550 nm

➢Rise and fall time : 0.3 nS

➢Threshold current : 50 mA

➢normal operating current : 70 mA

➢Spectral Width : 1-3 nm

➢Operating temp : -100 C to +650 C

➢Output power : Hundreds of mille watts


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Features of LED’s spontaneous emission

➢Wide spectral widthThe transition of electrons from many energy levels of conduction band and valence bands contributes to the radiation. Spectral width is naturally high (170 nm at 1310 nm)

➢Low intensityThe photons are radiated in arbitrary directions, very few of them create light in desired direction i.e. LEDs have poor current-to-light conversion

➢Poor directivityEven the photons which contribute to light do not move in one direction; they propagate in a cone.

➢IncoherenceThe photons are incoherent i.e. they get created without any phase relation


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Semiconductor material used as Optical Sources

➢Gallium-Aluminum-Arsenic:

This semi conductor material is used as optical source for LED diodes.

This semi conductor material is used as optical source for the s wave length 800-900nm

➢Indium-Gallium-Arsenic- Phosphide:

This semi conductor material is used as optical source for LDs (Laser diodes).

This semi conductor material is used as optical source for the s wave length 1000-1600nm


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Optical sources comparison

LED source

➢Produces incoherent light

➢Spontaneous emission

➢High spectral with 30-60nm

➢Less launching power100 micro watt

➢Poor coupling efficiency 1%

➢Used only for MM

➢LAN application

LASER Source

➢ Produces coherent light

➢Stimulated emission

➢Narrow spectral width 1 to 3nm (reduces dispersion)

➢High output power100mW

➢High coupling efficiency 50%

➢Used only for SM

➢Can be modulated directly with high frequency due to short recombination time


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Precautions for handling laser diode

➢Visible and Infrared light can damage eye permanently.

➢While handling laser source never look into a live laser source

➢Never look into an unknown light source

➢Never look into any fiber until it is ascertained it is safe


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Optical Detectors

➢Converts the light into electricity through photoelectric effect. The requirements of optical detectors are.

1.High sensitivity

2.Fast response

3.low noise

4.high reliability

5. low cost5/24/2020 139TCT-4 OFC SYSTEMS

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Types of Optical Detectors

There are basically two types of Optical Detectors are used.

1. PIN diode2. Avalanche Photo Diode (APD)

PIN Diode: ➢It is a photo diode with intrinsic (un-doped)

region between n & p doped regions.

➢Most of the photons are absorbed in the intrinsic region and carriers are generated and contributes to the photocurrent.


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Types of Optical Detectorscontd……

Avalanche photodiode (APD):➢ It is a semiconductor based photodiode.➢ It is operated with relatively high reverse voltage

ranging about ten to hundreds of volts & some times just below the breakdown voltage.

➢ In this system, carriers are excited by absorbed photons.

➢ These photons are strongly accelerated in the strong internal electric field , so that they can generate secondary carriers as it occurs in photo multipliers.

➢ The avalanche process effectively amplifies the photo current significantly.5/24/2020 141TCT-4 OFC SYSTEMS

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Important Parameters of optical detectors

Responsibility:

➢ The ratio of electrical output current Id from detector to the input optical power.

➢ It is measured in ampere/watt (A/W)

➢ For example 0.6 A/W means that incident light having 50uW of power results in 30uA of current

Id= 50uW X 0.6 A/W = 30 uA


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Important Parameters of optical detectorscontd…..

Quantum efficiency(n):

➢ It indicates how well incident optical photons are absorbed and then used to generate primary charge carriers.

➢ It is the ratio of number of electron-hole pairs generated to the number of incident photons on the surface of the photo detector.

➢ A typical quantum efficiency of 70% means 7 out of every 10 photons create carriers (electron current).

➢ It should be as high as possible.


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Important Parameters of optical detectorscontd……

Dark Current(I):

➢ Dark current is the current flowing through the photodiode without light input.

➢ Dark current develops from stray light or from thermally generated electron-hole pairs.

➢ Dark current for a good photo detector should be less than 10 nA.


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Important Parameters of optical detectorscontd……

Rise Time:

Rise time is defined as the time difference between the point at which the detector has reached 10% of its peak output current

Rise time is the point at which it has reached 90% of its peak response, when it is irradiated by a very short pulse of light.

Fall time :

Fall time is defined as the time between the 90% point and the 10% point on the trailing edge of the pulse waveform. This is also called the decay time.


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Typical characteristics of PIN & APDs

Characteristic PIN APD

Responsivity (A/W) 0.5 - 0.95 5 - 20

Quantum efficiency (%) 60 - 70 --

Dark current (nA) 1- 20 1- 5

Bandwidth (GHz) 1 - 10 1-10

Bias voltage (V) 5 - 6 20 - 30


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Typical parameters for long haul & short haul communication

Characteristic Tx power Rx sensitivity

Short haul communication

-8dBm to -15dBm rlys use

-10.6 dBm

-28dBm

Long haul communication

0dBm to -5dBm

rlys use

-2.2dBm

-36 dBm


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Opto electronic repeaters

➢In OFC, system the maximum optical signal transmission distance is limited by fibre attenuation & distortion.

➢ By using opto-electronic repeaters, the optical signal is converted into an electrical signal.

➢This electrical signal is amplified at a higher intensity using transmitter and again converted back to optical signal and send through the fibre, further.

➢These repeaters are to be installed at about every 20 KM distance , the cost of repeater is very high.

➢ For the modern wavelength-division multiplexed signals it is very complex and difficult to convert into O-E-P5/24/2020 148TCT-4 OFC SYSTEMS

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➢ An alternative approach for opto electronic repeater is to use an Optical Amplifier

➢ Optical amplifier, amplifies the optical signal directly without having to convert the signal into the electrical domain.

➢ This optical amplifier is made by doping a length of fibre with the rare-earth mineral called erbium.

➢ When this erbium is excited, it emits light around 1.54 micro meters the low loss wave length required for OFC transmission.


Optical Amplifier

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Couplers

➢Couplers are the devices that combine differentoptical signals on different paths into a singlefiber optical signal.

➢Each of these different optical signal hasdifferent wavelengths.

➢Each wavelength carries a different datastreams.

➢Use of couplers increases capacity of fiber.➢The can be used to transmit full-duplex signal

over a single fiber


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Couplerscontd……


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Couplerscontd……

T Couplerinput

Tree coupler

Star Couplers

output

out

One input

Multiple

outputs

Multiple inputs

Multiple outputs

or


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Attenuators:

➢ Attenuators are Used for

reducing the amplitude of

optical signal without

appreciably distorting the

waveform

➢ Attenuators are used to

stop the overloading of

receivers.

➢ Attenuators are used in

testing & checking

Attenuators


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“0 dB” couplers & “10 dB” attenuators


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Splitters:➢Using splitters a single optical signal is splitted into

multiple optical signals.➢Splitters can be used to increase system reliability

and to reduce system cost

Optical Splitters


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CONNECTORS


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OFC Connectors

➢ OFC connector facilitates for connection / disconnection / reconnection of fiber to the equipment.

➢ Connectors are used in applications where ➢Flexibility is required in routing an optical signal

from lasers to receivers ➢Termination of cables is required

➢Connector consists of 4 parts :➢Ferrule➢Connector body➢Cable➢Coupling device


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Characteristics of connectors

Parameter Description

Insertion loss 1. Loss due to use of connector (unavoidable)

2. Manufacturers specify typical value

Repeatability (loss)

Difference between successive measurement of the same connector. Shall be 0.1 to 0.3 db

Suitability Suitable to SM / MM fiber

Return loss The amount of power reflected from the connector to connector interface. Return loss values are expressed as dB. A typical specification could range from -15 to -60 dB, where, in most cases, -60 is more desirable.

-60 is more desirable.


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Insertion loss Repeatability Fiber type Application

0.5 to 1.0 db 0.20 db SM / MM Transmission NW

FC - Ferrule Connector

Gradually being replaced with SC and LC connectors


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0.2 to 0.45 db

0.10 db SM / MM Transmission NW

SC - Subscriber Connector (or) Standard Connector


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0.2 to 0.45 db

0.10 db SM / MM Transmission NW

SC Duplex Connector


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0.40 db (SM)

0.50 db (MM)

0.40 db (SM)

0.20 db (MM)

SM / MM Inter/Intra Building

ST - Straight Tip connector

Popular connector for multimode fiber, LAN applications


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0.15 db (SM) 0.20 db SM / MM High density interconnection

LC - Lucent Connector or Local Connector


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Fiber Distribution Management System

(FDMS)


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FDMS with SC couplers


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FDMS with E2000 couplers


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E2000 pigtails


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SC-E2000 Patch cord


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LC-FC Patch cord


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SC-FC patch cord


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Optical Interface SpecificationsSTM-1

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➢ It is a compact optical transceiver.

➢ It is used in optical communications for both telecommunication and data communications applications.

➢ It interfaces a network device to a fibre optic cable.

Small Form-factor Pluggable (SFP)

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SPLICING


1G Optical interface specifications

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10G Optical interface specifications -XFP

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➢ It is a kind of optical transceiver which combines the CWDM technology.

➢ Similar with the traditional SFPs, CWDM SFP is also a hot-swappable input/output device that plugs into an SFP port or slot of a switch or router, and links the port with the fiber-optic network.

➢ It is a convenient and cost-effective solution for the adoption of Gigabit Ethernet and Fiber Channel (FC) in campus, data-center, and

metropolitan-area access networks.

Coarse Wave length Division Multiplexing

(CWDM SFP)


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CWDM SFP Transceivers


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CWDM Color Coding


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➢ CWDM SFPs come in eight wavelengths that range from1470 nm to 1610nm.

➢ For better identify the wavelength to which the GigabitEthernet channel is mapped when using these CWDMSFPs.

➢ we use the color markings on the devices, such as colorarrow on label and color coded bale clasp to achieve it.

➢ This is why there are many SFPs with different colors forapplications.

➢ The following table lists the CWDM SFPs with theirwavelength and color codes.

CWDM SFP Transceivers


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What is splicing

➢Splicing is a permanent connection of two pieces of fiber➢Two types of splices :1) Mid-span splicing of two fibers➢Fibers from two cables are spliced after laying drum by drum➢Cuts in fiber run are attended by splicing certain minimum length cable piece at either end2) Pig-tail splicing➢Pig-tail is a fiber cable with factory installed connector at one end and the free fiber of pig-tail is spliced connected to cable➢Methods of splicing➢Mechanical splicing➢Fusion splicing


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Mechanical Splicing

➢Mechanical splicing is used only in emergency restoration cases.

➢This mechanical splicing is fast, inexpensive and easy.

➢Mechanical splices are reflective and non-homogenous

➢Mechanical splicing offers slightly higher losses about

0.2 db, less-reliable and less performance.

fiberfiber

Alignment sleeve


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Fusion Splicing

➢Fusion splicing provides a fast, reliable, low-loss, fiber-to-fiber connection by creating a homogenous joint between the two fiber ends.

➢The fibers are melted or fused together by heating the fiber ends, typically using an electric arc.

➢Fusion splices provide a high-quality joint with the lowest loss (in the range of 0.01 dB for single-mode fibers) and are practically non-reflective.

Electric arc

fiber fiber


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ARC Fusion Splicing Machine – Fujikura


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Straight joint for OFC cable

Preparation of cable for jointing

➢ Stripping/cutting the cable

➢ Preparation of cable and joint closure for splicing

➢ Stripping and cleaving of fibres

➢ Organising fibres and finishing joints

➢ Sealing of joint closure and

➢ Placing joint in pit


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TEST AND MEASUREMENTS


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Power Meter


➢ Power meter by itself can be used to measure source power

➢ With a source it can measure loss of a cable called insertion loss

➢ Most power measurements are in the range of +10dBm to -40dBm

➢ DWDM systems can have power up to +30 dBm (1 watt)

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DETECTORS ARE SILICON, GERMANIUM, OR

INDIUM-GALLIUM-ARSENIDE SEMICONDUCTORS

NETWORK TYPE WAVELENGTH POWER RANGE (DBM)

TELECOM 1310, 1550 nm +3 TO -45

TELECOM DWDM 1550 nm +20 TO -30

CATV 1300, 1550 nm +10 TO -6

Optical power levels


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Power measurement in OFC system / Insertion loss measurement


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Power measurement in OFC system / Insertion loss measurement

The OFC cable under test is connected to optical source to one end using launch cable and other end is connected to power meter using receive cable.

Here the launch cable & receive cables are nothing but OFC patch chords.

First connect the optical source to the power meter using patch chord and measure the loss.

Connect actual OFC cable and measure the loss.

Now minus the patch chord from the total loss, it will give actual OFC cable loss.5/24/2020 190TCT-4 OFC SYSTEMS

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Optical Time Domain Reflector(OTDR)

➢ The OTDR is useful for testing the integrity of fibreoptic cables.

➢ The aim of this instrument is to detect, locate andmeasure events at any location in the fibre link.

➢ One of the main benefits of the OTDR is that itcan fully test a fibre from only one end.

➢ OTDR meter is most effective when testing longcables (more than approximately 250 meters or

800 feet) or cable plants with splices.


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Optical Time Domain Reflecto Meter(OTDR)


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Advantages of OTDR

➢Produces the graphic display of fiber status with

different events

➢OTDR measured data can be stored for

documentation in the form of soft & hard copies

for future reference.

➢The biggest advantage of OTDR is, all the cable

parameters can be measured from one end.5/24/2020 193TCT-4 OFC SYSTEMS

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Parameters to be measured using OTDR

➢ OTDR traces are used for troubleshooting, since they can show where cable break is occurred.

➢ These traces are compared with the traces taken at the time of installation.

➢ By comparing these traces the cable performance can be assessed.

➢ OTDR can measure the following parameters.1. Measures the cable brakes with almost exact distance.2. Measures the splice and connector loss3. Measure the loss between two points4. Measures the transmission loss5. Gives the length of the cable.


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OTDR working principle

➢ The OTDR works on the back scattering principle.

➢ It detects a small reflected signal in response to the injected a large signal.

➢ There are two types of reflections.

1. Rayleigh Back scattering

2. Fresnel Reflections.


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Incident light

Backscattered light

1/1000 of scattered light

➢ It is intrinsic to the fibre material itself and is present along the entire length of the fibre. When a pulse of light is sent down a fibre, some of the photons of light arescattered.

➢ This effect is referred as Rayleigh scattering,.➢ It provides amplitude and temporal information along

the length of cable.

Rayleigh scattering


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Fresnel reflection

➢Fresnel reflection is due to the light reflecting off when it hits the material having different refractive indexes, like connector, mechanical splice and cable brake.

➢The amount of light reflected depends upon the boundary surface smoothness and the index difference


➢ Connectors using gel can reduce the Fresnel reflection. The gel acts as an index matching materialminimizing the glass/air index difference

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Typical OTDR traceFusion

spliceConnector pairCoupler Fiber bend

Mechanical

splice break

Distance (km)

Dead zone


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➢ The OTDR is designed to detect the backscattering level all along the fiber link.

➢ It measures backscattered signals which are much smaller than the signal sent to the fiber.

➢ The component which receive those values is the photodiode.

➢ It is designed to receive a given level range. ➢When there is a strong reflection, then the power

received by the photodiode can be more than 4000 times higher than the backscattered power and can saturate the photodiode.

DEAD ZONE


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➢ The photodiode requires some time to recover from this saturated condition; during this time, it will not detect the backscatter signal accurately.

➢ The length of fiber which is not fully characterized during the recovery period is termed the Dead Zone.

➢ This dead zone length depends upon the incident pulse signal, stronger the pulse, more is the dead zone

➢ To overcome this dead zone problem , dummy / spare cable length (around 100 meters) to be used.

DEAD ZONEcontd…….


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DEAD ZONEcontd……

They are of two types of dead zones.1)Launch dead zone and 2) Event dead zoneLaunch dead zone:➢This launch dead zone occurs due to the connector present while

launching the pulse in OTDR➢Nothing can be measured for the first 100 meters.➢The solution for dead zone add a patch cord of length 100 meters

at beginning of the system

Event dead zone:➢Event dead zone is the minimum distance on the trace.➢where two separate events can still be distinguished.➢ The distance to each event can be measured, but the separate loss

of each events cannot be measured.5/24/2020 201TCT-4 OFC SYSTEMS

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Dead zone


DEAD ZONEcontd……

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Range discrimination in OTDR

➢ Range discrimination is the minimum distance separating two events that can be displayed as separate events

➢ Two events too close together cannot be resolved, especially with long pulses hence proper pulse width has to be selected

➢ Use the shortest pulse that will provide the required range

➢ Pulse length determines the range discrimination


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Important terms of OTDR

Dynamic range:This is the difference between the highest value of input thatcan be given to the detector and the minimum detectablepower

Ghosts are very confusing, as they seem to be real reflectiveevents like connectors, but will not show any loss.Ghosts can be eliminated using Index matching Gel.

Ghosts (false reflections):Ghosts are repetitions of a trace or portion of a trace. Theyare caused by a large reflection in a short fibre, causing lightto bounce back and forth.


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Information in the OTDR Trace


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Study of OTDR Traces

The slope of the fibre trace shows the attenuation coefficient of the fibre and is calibrated in dB/km by the OTDR.

Connectors and splices are called "events" in OTDR jargon. Both should show a loss, but connectors and mechanical splices will also show a reflective peak. The height of that peak will indicate the amount of reflection at the event

Sometimes, the loss of a good fusion splice will be too small to be seen by the OTDR. That's good for the system but can be confusing to the operator. It is very important to know the lengths of all fibres in the network, so you know where to look for events and won't get confused when unusual events show up


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Making measurements with the OTDR

Fibre Attenuation by Two Point Method.


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Visual Fault Locators

➢ Visual Fault Locators are red light lasers.

➢ They visually locate faults, up to around 5 kilometres.

➢ By sending visual light, the operator can easily see breaks and important bends in the fibre; as the light escapes out. This function makes them useful for continuity testing of patch cords, jumpers, or short sections of fibre.


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Visual Fault Locatorscontd.......

Visual fault locators are used in conjunction with:

➢Splicing machines to identify fibres to be jointed.

➢ OTDR to analyse failures which occur within the dead zone.

➢The most popular fault finders are made with a He - Ne source.

➢ Visual Fault Locators can use 670 nm or 635 nm lasers or LEDs,

➢670 nm VFL provides long distance fault location and correctlight intensity

➢ 635 nm VFL provides excellent visibility by shorter faultlocation.


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OPTICAL LINK ENGINEERING


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Constituents of Link

➢An optical power loss model for a point-to-point link is shown below :

➢Power received on photo detector PR

= Power output of the source PS - Total power loss PT

Optical

Tx

Optical

Rx

Splice ( Joints)Connector Connector

Optical Fibre


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Optical link design


➢ An optical link design must meet both the link power budget analysis and the system rise time analysis.

➢ In the link power budget analysis, one first determines the power margin between the optical transmitter output and the minimum receiver sensitivity needed to establish a link. ( analysed for link feasibility )

➢ Once the link power budget has been established, the designer makes a system rise time analysis to ensure that the dispersion limit of the link has not been exceeded. ( analysed for data carrying capacity )

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Link power budget analysis

➢While planning an OFC link we have to provide

sufficient margin against losses on the link.

➢ Consider an OFC link with a laser diode source(+3dBm)

and an the APD detector with sensitivity of -32 dBm .

Considering a connector loss of 1dB, fiber attenuation

of 0.25dB/KM, patch cord loss of 3dB and splice loss of

0.1dB /splice , find the system margin over a 60km link.


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Link power budget analysis

➢ Tx (laser diode) power output = + 3dBm.

➢ Rx ( InGaAs / APD) sensitivity = - 32dBm

➢ connector loss = 1dB

➢ Optical cable of loss = 0.25 dB/km.

➢ patch cord loss = of 3dB

➢ splice loss = 0.1dB / splice

➢ Cable Distance = 60 km.5/24/2020 214TCT-4 OFC SYSTEMS

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Link power budget calculation

Available power budget = Source power – receiver sensitivity

➢ Availability power margin = +3 - (-32) = 35dB

➢Attenuation in cable = 0.25X 60 = 15 dB

➢ splice loss = 21X 0.1 = 2.1 dB

( Assuming 3 km drum we require 20 drums i.e., 21 joints)

➢Patch card losses = 3 dB on either side = 6 dB

➢Connector losses = 1 dB on either side = 2 dB

➢ future margin, keeping in mind aging of equipment = 3 dB

➢Total losses = 15+2.1+6+2+3 = 28.1 dB

➢Available system margin = 35 – 28.1 = 6.9 dB

This link is feasible5/24/2020 215TCT-4 OFC SYSTEMS

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➢ A rise-time budget analysis is a convenient method for determining the dispersion limitation of an optical fibre link. This is particularly useful for digital systems. The four basic elements that may significant are

1.The transmitter rise time (t1)

2.The group-velocity dispersion (GVD) rise time of the fibre (t2)

3.The modal dispersion rise time of the fibre,

4. The receiver rise time. (t3)

➢ Single-mode Fibre do not experience modal dispersion, so in these fibres the rise time is related to only GVD. Therefore, for single-mode fibres, we will only consider three basic elements

Rise-time budget


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➢ In digital transmission, dispersion puts a limit on the maximum data rate and the maximum distance i.e. the information-carrying capacity of a fiber link.

➢ Rise Time budget analysis is a means for ensuring the minimum permissible data rate over an optical fiber link.

➢ Total system rise time is given by equation below :

➢ t = t12 + t2

2 + t32

➢The following are the 3 commonly encountered rise time elements in link designing :➢Transmitter Rise Time. = t1➢Dispersion Rise Time of the fiber. = t2➢Receiver Rise Time. = t35/24/2020 217TCT-4 OFC SYSTEMS

Rise-time budgetContd....

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➢Consider an OFC link operating at 1310nm. The laser source rise time is 25 pS, spectral width of the laser is 2nm and fiber dispersion is 2pS/nm-km. Find the feasibility for a 100 km on E4 link.

➢Operating Wavelength =1310 nm

➢Laser Source rise time = 25 psec = t1

➢Spectral width of laser = 2 nm.

➢Fibre dispersion = 2 psec/nm-km

➢Total length =100km

➢Fibre respnse time= fibre dispersionxspectral widthxcable length=2x2x100 = 400 psec = t2


Rise time budget analysis

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Limits for Rise-time

➢ For a signal to be received correctly, the over all time response of a system must be less than the bit rate.

➢ Conventionally, the total transition time degradation of a digital link should not exceed 70% of an NRZ bit rate or 35% of RZ bit rate.

➢ The bit rate is defined as the reciprocal of the data rate


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Receiver Rise time

➢Receiver rise time is the time interval between 10% and 90% of the rise of output.

➢This is related to the bandwidth with the following empirical formula

➢t3 = 0.35 / Brx ( Brx is Rx bandwidth)➢t3 = 0.35 / 140 Mbps➢t3 = 0.35 / 140 x 106

➢t3 = 2500 ps


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Calculation of rise time budget

➢ Receiver band width = 140 Mbps

➢ Receiver rise time = 0.35/ 140Mbps = 2.5 nsec=. 2500ps

➢ Substituting all these values we get the total rise time

➢ = (25 ² +400 ² +2500 ²) =2532 p sec = 2.532ns

➢ This value is less than the maximum allowable 70 % of bit interval time for 140 Mbps NRZ data string ( which is 5nS)

➢ 70% of 1/140Mbps = 70X1/140X1/100 = 5 nS.

➢ Since the system rise time is less than 70% of the bit interval time for NRZ coding , we can finalize the link.

This link is feasible


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System rise-Time & Information Rate

➢ In digital transmission system, the system rise-time limits the bit rate of the system according to the following criteria:

➢Tsys< 70% of NRZ bit period

➢tsys< 35% of RZ bit period

➢ The bit period is defined as the reciprocal of the data rate.


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FTTH( Fibre To The Home)

➢ FTTH is a fibre optic cable that replaces the standard copper wire of the local Telco.

➢ FTTH is desirable because it can carry high-speed broadband services integrating voice, data and video, and runs directly to the junction box at the home or building.

➢ Traditional copper telephone wires carry analog signals, by nature a less precise.

➢ Fibre optic cable is superior for relaying these signals and allows for faster transfer rates and virtually unlimited bandwidth.

➢ FTTH is better Internet speed, streaming video, and other demanding applications.5/24/2020 223TCT-4 OFC SYSTEMS

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➢ It is a telecommunications network that uses point-to-multipoint fibre to the end-points.

➢ In this unpowered optical splitters are used to enable a single optical fibre to serve multiple end-points.

➢ PON consists of an optical line terminal (OLT) at the service provider's central office and a number of optical network units (ONUs) or Optical Network Terminals (ONTs),near end users.

PON ( Passive Optical Network)

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➢PON reduces the amount of fibre and central office equipment required compared with point-to-point architectures.

➢A passive optical network is a form of fibre-optic access network.

➢In most cases, downstream signals are broadcast to all premises sharing multiple fibres. Encryption can prevent eavesdropping.

➢Upstream signals are combined using a multiple access protocol, usually time division multiple access (TDMA).


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Wave Length Division Multiplexing (WDM)

Presented By The Fiber Optic Association

©2004, The Fiber Optic Association, Inc.

Wavelength-Division Multiplexing


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WDM works on a principle of a prism, just like we separate the "white"light from the sun into a spectrum of colors with the prism.

The input end of a WDM system is really quite simple. It is a simple couplerthat combines or multiplexes all the signal inputs into one output fiber.

The de multiplexer separates the light at the end of the fiber.

It shines the light on a grating, which separates the light into the differentwavelengths by sending them off at different angles.

Optics capture each wavelength and focuses it into another fiber, creatingseparate outputs for each wavelength of light.

Current systems offer from 4 to 32 channels of wavelengths. The highernumbers of wavelengths has lead to the name “Dense” WavelengthDivision Multiplexing or DWDM.



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Wavelength division multiplexing (WDM)

First

wavelength

second wavelength

Transmitter at first

wavelength

Transmitter at

second wavelength

receiver at first wavelength

receiver at second

wavelength


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TX-A

ITU Ch.1

TX-A

ITU Ch.2

TX-A

ITU Ch.3

TX-A

ITU Ch.4

RX-A

ITU Ch.1

RX-A

ITU Ch.2

RX-A

ITU Ch.3

RX-A

ITU Ch.4

4 CH

WDM

MUX

4 CH

WDM

MUX

Optic fiber

EDFA

25 db gain

Data in Data Out

(λ1).

(λ2 )

(λ3 )

(λ4 )

(λ1).

(λ2 )

(λ3 )

(λ4 )


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Thank You

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Documents

FIBER OPTIC COMMUNICATION SYSTEM (TCT-4)122.252.230.113/content/ppt/tele/TCT_4hl.pdf · 2020. 10. 22. · 10 Gbps (STM-64: BSNL) 1.28 Tbps (128 Ch. DWDM) 20 Tbps (Possible) 5/24/2020