03 Tt2530eu02al 01 Optical Fibres

8/13/2019 03 Tt2530eu02al 01 Optical Fibres

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Optical Fibers Siemens

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Contents

1 Silica Glass 32 Refraction and Reflection 53 Numerical Aperture 15

4 Types of Fibers 214.1 Multi-mode Fibers with Step Index Profile 224.2 Multi-mode Fiber with Graded Index Profile 244.3 Single-mode Fiber (Step Index Profile) 265 Fiber Profiles 296 Fresnel Reflection 317 V Parameter 358 Technical Data for MM, SM and DS Fibers 398.1 G50/125 Multiple Modes - Fiber Data 40

8.2 Single-Mode Fibers - Fiber Data 428.3 Transmission Characteristics (at Room Temperature) 448.4 Mechanical Characteristics 458.5 Dispersion-Shifted Fibers 459 Attenuation 4910 Dispersion 5310.1 Mode Dispersion 5610.2 Material Dispersion 6010.3 Wave Guide Dispersion 62

10.4 Chromatic Dispersion 6411 Bandwidth 67

Optical Fibers


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Siemens Optical Fibers

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12 Mode Field Diameter 6913 Cut Off Wavelength 7314 Exercise 79

15 Solution 83


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1 Silica Glass The material for fibers used in today's cables is exclusively silica glass.

The earth's crust consists of 26 % silicon.

Quartz appears in its pure crystalline form, as rock crystal for example. Silica glass,on the other hand, is an amorphous, solidified, molten mass. It has no melting point,but becomes increasingly soft at high temperatures and vaporizes without enteringthe liquid state.

Quartz appears in its natural form as the chemical compound SiO 2. As a product of erosion (e.g. of granite), it appears mainly as sand; and in practically unlimitedquantities.

Quartz is therefore a raw material in almost unlimited supply.

To obtain high-purity silica glass, SiO 2 is gained by deposition in the gaseous state.

High-purity SiO 2 is manufactured by distillation from the highly volatile compound of SiCl 4 and oxygen, releasing chlorine gas.

SiCl O 1700 C

SiO 2Cl4 2 2 2


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2 Refraction and Reflection


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Refraction of light

Critical angle

Axis of incidenceTotal reflection

Snellius' law of refraction

A beam of light meets a different, transparent medium at an angle.

A small part is reflected (angle of reflection = angle of incidence). A far greater partenters the other medium. The angle of propagation of the beam changes at this point.

It is refracted.

This effect is called refraction of light.

Example A:

If the transition is from a dense material to a less dense material, the beam isrefracted away from the axis of incidence .


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Axis of incidence

Less dense (air) n 2 = 1.0

Dense (glass) n 1 = 1.5

Fig. 1


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Example B:

If the transition is from a less dense to a more dense material, the refraction is toward

the axis of incidence .


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Axis of incidence

Dense (glaass) n 2 = 1.5

Less dense (air)n1 = 1.0

Fig. 2


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According to the Snellian law , the sines of the angles and are inversely relatedto the refraction factors n 1 and n 2.

n1 sin = n 2 sin

In fiber optics , only arrangement A can be used.

If the angle of incidence in arrangement A becomes steeper and steeper, onearrives at a situation where the beam of light is no longer refracted into the other medium. It then runs in the boundary layer between the two media. An angle 0 = 90

with sine "1" results. This special angle is called the critical angle ( 0).

It follows that it can be calculated with: sin 02

1

n

n.

All angles which are steeper than the critical angle cause the beam to be reflected

into the denser medium.Not only a small part is now reflected back, but rather the entire beam.

This means: total reflection takes place.

The critical angle is determined by the ratio of the refraction factors of the media.


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Example:

Axis of incidence

n2 = 1.46

n1 = 1.48

90

53,80

9865,048,1

46,1sin

0

1

20

anglecritical

nn

Cladding glas

Core glas

Cladding glas

Fig. 3


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Exercise:

Determine the critical angle for a beam of light which runs from the more optically

dense medium water with the index of refraction n 1 = 1.333 into the optically lessdense medium air with the index of refraction n 2 = 1.

Note

If a beam of light enters a less dense medium from a more dense one, refraction isaway from the axis of incidence.

Total reflection is only possible under this condition.

Axis of incidence

n2 = 1.46

n1 = 1.48

90

53,80

9865,048,1

46,1sin

0

1

20

anglecritical

nn

Cladding glas

Core glas

Cladding glas

Fig. 4


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3 Numerical Aperture


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Numerical Aperture

Angle of acceptance

The ratio of the refraction factor of the core glass n 1 to that of the surroundingcladding glass n 2 (n 1 n2) determines the critical angle.

On the end surface of the optical fiber there is also a refraction due to the differencein refraction factors between the air n 0 and the core glass n 1. There, the transitionfrom a less dense medium to a denser one causes the beam to bend towards theaxis of incidence.

The angle under which the beam is accepted by the optical fiber (OF) is called theacceptance angle - theta - ( max ).

The sine of the acceptance angle is the numerical aperture (NA) of the OF.


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Cladding glass n 2 = 1.46

Core glass n 1 = 1.48

Axis of incedence

Air n 0 = 1.0 a.)0

90-

Fig. 5


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snellian law:

12

sinsin

n

n

0

1

0 )90sin(sin

n

n

1

2

sin

sin

0

0

n

n

0

0 )90sin(1sinn

n 1sin0

10

n

1

2sin

0n

n

)90sin(sin 01 n

01 cossin n 2

0

2

0

2 1cossin

0

2

0 sin1cos

0

2

1 sin1sin n

)sin1(sin 022

1 n

2

1

2

2

2

12

1sin

n

nnn

2

2

2

1sin nn


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sin n n n1

2 2

1 48 1 462 2, ,

sin = 0.242

sin = NA

NA = 0.24

24,0sinarc

14

For larger NAs, the OF accepts more of the beam and the cone of light at the other

end is correspondingly wider.However, a greater acceptance angle also results in greater dispersion effects. Thisapplies to all fibers, even single-mode OFs.

Typical values for NAs:

Single-mode fibers = 0.13 (= 7.47 )

Multi-mode fibers = 0.20 (= 11.54 )

The acceptance angle is in relation to the axis of incidence. To obtain the completecone angle, the acceptance angle must be multiplied by 2.

Example:NA=0,13

Acceptance angel:

47,713,0sinarc

Cone angel:

94,1447,72 .


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4 Types of Fibers


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4.1 Multi-mode Fibers with Step Index Profile

The optical power of a light pulse is distributed over many (multi) modes. In multi-mode fibers, the modes propagate by different paths. The rays travel by differentpaths but all with the same velocity, and thus they have different transit times.Therefore the length of the pulses increases with increasing fiber length.

This type of fiber is employed only for short distances (approx. 50 - 100 m) at low data rates.


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n2

n1

n2

140 m

100 m

step index profile

input

P opt

mode 1

mode 2

mode 3

output

t

Fig. 6


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4.2 Multi-mode Fiber with Graded Index Profile

The graded index profile of the core is achieved by many layers of glass (more thanhundred), where each layer has its specific index of refraction (IOR).

These indices decrease gradually from the center toward the cladding.

Due to the continuous change of the IOR, the rays are refracted constantly whencrossing the borderline between the various layers.

The rays oscillating around the fiber axis still travel a longer path than the light raysalong the fiber axis; however, due to the lower refractive indices outside of the fiber axis these rays travel correspondingly faster.

The result is that the delay time difference of the various rays disappears almost

completely.Due to the difficult manufacturing process, the fiber is relatively expensive.

Therefore today it will not be employed for long distances.

Two types are standardized:

Type A with 50 m core dia. and 125 m cladding dia. (ITU-T Rec. G. 651)

Type B with 62.5 m core dia. and 125 m cladding dia.

(the larger diameter of this fiber increases the launching condition of this fiber

by 3 dB).

The relatively wide core diameter provides good (cheap) launching and receivingconditions.

Thus the main application for these fibers are the local area networks (LAN). Whereshort distances have to be bridged, but many patch panel have to be passed (thatmeans short, expensive, high-quality fiber and many low-cost transmitters andreceivers).


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

n2

n1 (r)

n2

125 m

graded index profile

n2

n1 (r) n2

n2

50 m

Fig. 7


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4.3 Single-mode Fiber (Step Index Profile)

Even in high-quality graded index fibers, a certain delay time caused by the variousmodes is still present. In order to reduce this effect, the number of modes has to bereduced.

If the number of modes is to be decreased, i.e. the V number diminished, either thecore diameter 2a or the numerical aperture A N must be reduced, or the wavelengthof the light must be increased.

If the V number in an optical fiber with a step index profile (g = ) becomes smaller than the constant V c = 2.405, then only a single mode, the fundamental modeLP 01 , can propagate in the core. Such an optical fiber with only one mode is called a

single-mode fiber.


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TT2530EU02AL_0127

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

n 2

n 1

n 2

125 m

step profile index

n 2

n 1 n 2

n 2

9 m

n 1

Fig. 8


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5 Fiber ProfilesSingle-mode OFs can be created with various profile structures.

Normal step index profilesimple-index

matched cladding

Steo index profile with loweredrefraction index in cladding

depressed cladding

1. Without dispersion shifting

2. With dispersions shifting

Normal step index profilesimple-index

matched cladding triangular profile

Segmented profile with doublystepped refraction index in

claddingdouble clad

3. With dispersion shifting

Segmented profile with quadruplygestufter stepped refraction

index in claddingquadruple clad

W profiledouble clad

Fig. 9


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6 Fresnel Reflection


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Fresnel reflection

Reflection coefficient

When light enters one medium from another, a small part is reflected. This effect isreferred to as Fresnel reflection. The ratio of reflected to incoming power isexpressed by the reflection coefficient "r".

The reflection coefficient of the optical power can be calculated when the refractionfactors (n1 and n0) of both materials are.

r n n

n n

1 0

1 0

2

.


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n1 = (glass) = 1.46

n0 = (air) = 1.0

P 0 -inc. Optical power; P r +reflected optical power; P 1 -transmitted optical power

P 0P r

P r

P 1

Fig. 10

Example:

0.1:0

nair

46.1:1ncoreglass

035.018699.00.146.10.146.1 2

22

01

01

nn

nnr

r = 0035

r = 35%


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TT2530EU02AL_0134

A end surface therefore reflects 3.5% of the supplied optical power. A mechanicalconnection has 2 end surfaces. The reflection therefore occurs twice. So the totalloss from reflection is 2 x 3.5% = 7%.

The reflected power (Pr) - the energy loss at the connection point - can be calculated with the following equation:

0.15dB=0.03511

10logReflection1

110logP r

We are dealing with two end surfaces. So this 0.15 dB occurs twice.

The Fresnellian loss at a mechanical connection point is therefore

approx. 0.3 dB.


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7 V Parameter


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1. V parameter

2. Structural parameter

3. Number of modes capable of propagation in a fiber

The V parameter or structural parameter is a dimensionless quantity which is usedto calculate the number of modes carried in the core of an OF, among other things.

The core of a fiber has a particular geometric size.

Depending on this size, a particular number of modes are capable of propagating inthe fiber.

The V parameter is determined by:

1. the core diameter of the fiber (d)

2. the numerical aperture (NA)

3. the operating wavelength ( )

NAd V

The number of modes (N) can be determined:

For graded index profiles:

4

2

V N

For step index profiles:

2

2

V N .

It is therefore an approximation. For lower values (with SM fibers), the inaccuracybecomes clearly visible.


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TT2530EU02AL_0137

Example:

A graded-index fiber with a core diameter d = 50 m and a NA= 0.2 is to be

operated at a wavelength of = 1 m.How many modes are capable of propagation in this fiber?

4.311

2.050V

m

m NAd

N V

4

31.4

4247

2 2

Approximately 247 modes are capable of propagation in this fiber. Such a fiber istherefore called a multi-mode fiber .

To obtain a single-mode fiber , one must reduce the number of modes by reducingthe V parameter. To do this,

a) the core diameter must be reduced,

b) the numerical aperture must be reduced, or

c) the wavelength must be increased.

If the value of the structural parameter becomes less than 2.405 , only a single mode,the basic mode LP 01 , is capable of propagation.


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TT2530EU02AL_0138

Example:

A fiber with a core diameter d = 9 m and a numerical aperture of 0.11 is to be

operated at a wavelength of = 1.3 m.How large is the V parameter of this fiber?

92.33.1

11.09V

m

m NAd

The V parameter of this fiber is 2.39 (< 2.405).

Under these conditions, the fiber is a single-mode fiber.

85.22

39.2

2

22V N

The result shows that two polarization modes oscillating rectangular to each other propagate in the single mode fiber. This two polarization modes are named andhandled as a single mode.


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8 Technical Data for MM, SM and DS Fibers


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8.1 G50/125 Multiple Modes - Fiber Data

Dimensions and tolerances

Material

Transmission characteristics

G 50/125 product line for operation at wavelengths around 1300 nm

Application as transmission element for telecommunications, video and datatransmission as well as in LANs.

Norms

Multi-mode fibers are described in the following: DIN VDE 0888 CCITT/ITU Rec. G651 IEC 793-2

8.1. Core glass8.1. Material

doped silica glass SiO 2 (silica)

Refraction index at 1300 nm 1.4469

8.1. Dimensions and tolerances

Core diameter

50 m 3 m

Concentricy tolerance (middle point position) between

core and cladding

3 m

3 m

Rotundity tolerance 3 m

8.1. Refraction index

Reduces parabolically towards the outside


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8.1. Cladding glass

8.1. Material

Silica glass SiO2 (silica) Deformation point approx. 20008.1. Dimensions and tolerances

Cladding diameter

Rotundity tolerance

125 m 3 m

2,5 m

8.1. Coating

8.1. Material

Interlaced urethane acrylate (two layers)

Refraction index Approx. 1.52


Diameter

Coloration (not done until fibers reachcable factory)

Nitro dyes (with solvent) - Herkula

250 m

8.1. Transmission characteristics (at roomtemperature)

Fiber type F = 1300 nm

highest attenuation value

lowest bandwidth value

Numerical aperture

G 50/125 0,7 F 1200

0.7 dB/km

1200 MHz at 1 km

0.20 0.02

8.1. Mechanical characteristics

All fibers are subjected to a tensilestrength test.

The tensile load is 5 N for a time of 1second.

If the time is shortened or extended, thetensile load decreases correspondingly.


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8.2 Single-Mode Fibers - Fiber Data



Mechanical data

E 9/125 product line for operation at wavelengths around 1300 nm and 1550 nm

Norms

Single-mode fibers are divided into the norms: DIN VDE 0888 CCITT/ITU Rec. 652 IEC 793-2

8.2. Core glass

8.2. Material

silica glass SiO 2 doped with germanium dioxide GeO 2

Deformation point approx. 100 -200 less than that of the cladding

glass 1800 - 1900

Refraction index: 1300nm = 1.4469

1500nm = 1.4446

1600nm = 1.4434

The refraction factor in the core is 0.3 % higher than in the cladding glass.


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TT2530EU02AL_0143


For single-mode fibers, the field diameter is given instead of the core diameter.

The field diameter is larger than the actual core diameter - for 1300 nm, approx.

A core diameter of 8.5 m gives, at 1300 nm, for example, afield diameter of 9.5 m (specification in data sheet 9.3 0.5

m). A core diameter of 8.5 m gives, at 1500 nm, for example, a field diameter of 11.3 m (specification in datasheet 10.5 1.0 m).

The concentricity tolerance (middle point position) betweenthe field and the cladding is less than or equal to 1 m.

10 - 12 %

8.2. Cladding glass

8.2. Material

Silica SiO 2

Deformation point approx. 2000

Refraction index: 0.3 % less than in the core


The cladding diameter isthe rotundity tolerance is

125 m 2 m 2.5 m

8.2. Coating

8.2. Material

Interlaced urethane acrylate (two layers)

Refraction index approx.

1.52


Diameter

Coloration (not done until fibers reach cable factory)

Nitro dyes (with solvent)

Herkula

250 m


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8.3 Transmission Characteristics (at RoomTemperature)

Fiber Typ F=1300m E 9/125 0.36 F 3.5

E 9/125 0.45 F 3.5

Attenuation coefficient at 1310 nm

Highest value for fibers in cable

(deviation < 0.1 dB)

0.36 dB/km

0.45 dB/km

Dispersion in range from 1285 to 1330 nm3.5 kmnm

ps

5kmnm

ps

Threshold wavelength c (fiber) 1170 nm to 1330 nm

cc (fiber in cable) 1270 nm

Numerical Aperture 0.13

Fiber Typ H=1500 nm E 9/125 0.21 H 18

E 9/125 0.27 H 18

Attenuation coefficient at 1300 nm

Highest value for fibers in cable

0.21 dB/km

0.27 dB/km

Dispersion in the 1550 nm rangekmnm

ps18

kmnm ps

18

Threshold wavelength c (fiber) 1170 nm to 1330 nmcc (fiber in cable) 1270 nm

Numerical Aperture 0.13

Fibers from lines 1 and 2 are also available for both wavelengths, e.g. E 9/125 0.36 F3.5 + 0.221 H18.


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8.4 Mechanical Characteristics

All fibers are subjected to a tensile strength test. The tensile load is 8 N for a time of 1 second.

If the time is shortened or extended, the tensile load decreases correspondingly.

8.5 Dispersion-Shifted Fibers



Mechanical data

Norm

CCITT/ITU Rec. G 653

8.3. Core glass

8.3. Material

group refraction index at 1300 nm 1.4760


The field diameter according to CCITT/ITU is 8.1 m 0.65 m

Core/cladding offset 1.0 m

8.3. Cladding glass

8.3. Material

8.3. Dimensions and tolerancesCladding glass diameter 125 m 2.0 m

Core/cladding offset 1.0 m

Eccentricity of the cladding 2 % defined as 1 100 min.cladding diametermax.cladding diameter


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8.3. Coating

8.3. CJPC3 Acrylate coating

8.3. Dimensions and tolerancesCoating diameter

Roundness 0.70

250 mm 15 mm

Dry stripping force 3.0 N (0.67 lb.)

Wet stripping force


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8.3. Behavior under the influence of the environment

Testing criteria Attenuation causedTemperature dependency 0.03 dB/km

Temperature/humidity cycles

- 10 C to 85 C and 4% to 98% rel. humidity 0.10 dB/km

Storage in water at 23 C 0.05 dB/km

Storage in water at 85 C 0.05 dB/km


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9 Attenuation


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Absorption

Diffusion

Rayleigh diffusion

Attenuation coefficient

Absorption bands

Attenuation

Attenuation is the loss of power between two points (unit: dB)

dBPowerPPowerP

log10=a out2

in1

It consists of diffusion and absorption losses.

Diffusion

Diffusion is caused by density fluctuations (non-homgenities).

Absorption

Losses due to absorption are caused by foreign substances (impurities) in the silicaglass.

The degree of impurity is indicated in PPM (parts per million) or PPB (parts per billion).

For example: 1 PPM Cu at 800 nm several hundred dB/km attenuation

1 PPM OH at 880 nm 0.1 dB/km

at 950 nm 1 dB/kmat 1240 nm 1.7 dB/km

at 1390 nm 35 dB/km

Absorption is particularly in specific wavelengths. One refers to absorption bands.

The fiber loss is dependent on the operating wavelength. It is therefore important tomeasure the fiber loss spectrally (as a function of the wavelength).


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

6

4

2

1

600 800 1000 1200 1400 1600

Wavelength

Attentuation

Fig. 11


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TT2530EU02AL_0152

Attenuation coefficient

This coefficient describes the fiber loss in relation to the length (unit: dB/km).

dB/kmPowerPPowerPlog

L10

out2

in1

Rayleigh diffusion

Rayleigh diffusion is the material-related diffusion of the glass.

The diffusion loss decreases with increasing wavelength to the fourth power of .

and influences .

1

4 .


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10 Dispersion


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TT2530EU02AL_0154

Dispersion types

Mode dispersion only with multi-mode fibers

Material dispersion with multi-mode and single-mode fibers

Optical fiber dispersion with single-mode fibers

Chromatic dispersion is the effect of material and optical fiber dispersion

The word comes from the Latin "dispersus", which means "spread-out, widened".

The term was first used to describe the process which takes place when whitesunlight is separated in a prism.

"Dispersion" was then used for the wavelength dependence of the refraction index of the glass.

Today, the term is used for all effects which are responsible for delay differences,pulse broadening and pulse distortion.

The pulse distortion T in ps, caused by dispersion, is determined as follows:

L M T 2

M( )= chromatic dispersionps

nm km

= spectral half power width

L= length of the OF in km

Example:M( )= 3.5

psnm km

= 5 nm

L = 25 km

Solution: T =3.5

psnm km

5nm 25km

T = 437.5 ps


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

P 0 P 1 P 2

t

Fig. 12


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10.1 Mode Dispersion

Mode dispersion

Differences in delay

In multi-mode fibers, the energy of the light pulse is divided among all the modes.The signal is not completely transmitted until all the modes have arrived at thereceiver.


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

1

4

3

12

3

4

1 2 3 4

Fig. 13


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A short light impulse is sent through an OF with a step index profile.

Core diameter d = 50 m

Refraction index in core n 1 = 1.48Refraction index in cladding n 2 = 1.46

Operating wavelength = 850 nm = 0.85 m

From this, one obtains: NA = n n12

22

= 0.24 (13.9 )

the V parameter V = 44

0,850

0.2450 NAd

.

The number of modes can now be determined 4844

444

22

V N

This means that 484 modes capable of propagation are present in this fiber.

The energy of the light pulse is divided among these 484 modes, which all runthrough the fiber at different angles. The speed is the same for all

c c

n

300.000km / s

1.48202.703km / s

10

1

However, due to the difference in distances, the transit time of the outer paths islonger than that of the core ray.

Not until all 484 modes have arrived at the end of the fiber is the signal transmissionfinished and a new impulse can be transmitted.

The duration of the transmission pulse is significantly shorter compared to the sum of all received pulses.

The difference is called the transit time difference.

The effect which is caused by the different paths of the modes is called modedispersion.

As fiber lengths increase, transit time differences increase, limiting the length of the

transmission path.


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


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10.2 Material Dispersion

Material dispersion M 0 ( )

Group velocity

Dispersion zero point

Material dispersion is caused by the wavelength dependence of the refractionindex n of the core glass. This dependence is expressed with M0 ( ).

The material dispersion is a material-dependent quantity. By doping the core glass,one can change it slightly within strict limits, thereby influencing the zero point.

Material dispersion is effective both in multi-mode and single-mode fibers.

However, in multi-mode fibers the mode dispersion is far greater. Light pulses

propagate in an OF with the group velocity c cn

g

g

.

The group refraction index (n g) and therefore the propagation velocity c g of the coreglass is wavelength-dependent.

The spectral width ( ) of a light source includes several wavelengths.

The portions of the light (the individual wavelengths) of therefore propagate atvarious speeds within the core glass.

The measure for the change in the group refraction index n g for the various wavelengths of is the material dispersion M 0 .

The material dispersion M 0 is usually indicated inps

nm km.

The group refraction index n g for silica glass has its minimum in the range of the 1300nm wavelength.

Therefore, the material dispersion is also at a minimum at 1300 nm.

The material dispersion M 0 ( ) becomes infinitesimally small at 1300 nm.


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

n1 ( i)

iv1

iv2

Fig. 14


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10.3 Wave Guide Dispersion

Threshold wavelength

Above the cut off wavelength c, only one mode - the basic mode LP 01 - is capableof propagation in the fiber.

Single-mode fibers are best operated with larger wavelengths (threshold wavelength!).

Larger wavelengths have more energy than shorter ones.

The light energy spreads out of the core glass area into the cladding glass.

Due to their greater energy, larger wavelengths penetrate farther into thecladding glass.The optical fiber dispersion value is therefore also greater at larger wavelengths.

A part of the basic mode is directed into the cladding glass.

The difference in refraction indices between the core glass and the cladding glasscauses different propagation velocities. However, a balanced average results.

The basic mode therefore propagates faster on the whole.

Optical fiber dispersion therefore causes a negative "pulse prolongation". Thisnegative effect counters the positive material dispersion.


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

i i 2

r r

Fig. 15


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10.4 Chromatic Dispersion

Chromatic dispersion M ( )

Zero point of the dispersion

"Chromatic dispersion" refers to the sum of the effects of material dispersion plusoptical fiber dispersion.

Chromatic dispersion is designated with M ( ).

M ( )

Chromatic dispersion

=

=

M0 ( )

Material dispersion

+

+

M1 ( )

Wave guide dispersion

The wavelength at which chromatic dispersion disappears is called the zero point of the dispersion.


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TT2530EU02AL_0165

Dispersion

nmxkm ps

1100 1200 1300 1400 1500 1600

Wellenleiterdispersion waveguide dispersion

ChromatischeDispersionTotal chromaticdispersion

MaterialdispersionMaterial dispersion

+20

+10

0

-10

-20

SMF Einmodenfaser 28 Chromatische DispersionSingle Mode Fiber Chromatic dispersion

Fig. 16


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11 Bandwidth


68/86


TT2530EU02AL_0168

Bandwidth

Bandwidth length product

Length exponent

Dispersion effects (mode dispersion and material dispersion) prolong thetransmission pulses. With a 850 nm LED with a large spectral half power width, thematerial dispersion is greater. With 1300 nm LED with a narrow spectral half power

width, the mode dispersion is greater.

The pulse prolongation increases with increasing route length. As the route becomeslonger, a point is reached where flawless recognition of the pulses is no longer guarantied. This is the point at which either the transmission route or thetransmission frequency must be reduced.

Bandwidth is the frequency at which the total transmission function of an OF falls tohalf of its value at the frequency zero. The attenuation of the light signal hasincreased by 3 dB. The bandwidth of a OF decreases approximately proportionally toits length. The bandwidth/length product is often specified as an indication of quality.

Bandwidth/length product (MHz x km) = band width of an OF in MHz at 1 km

b1= B1 x L1 L1=L

The bandwidth does not decrease linearly when several lengths of cable areconnected. One calculates with the so-called length exponent " ". Its value liesbetween 0.6 and 1.0. It can be calculated with the experimental value 0.8.

Example:

A 34-Mbit system has a system bandwidth of 50 MHz

L = 25 km

= 1300 nm

The required bandwidth/length product must be determined.

b1 = B1 x L1

= 50 MHz x 25 0,8

= 657 MHz x km

At the operating wavelength = 1300 nm, the bandwidth/length product is dividedinto steps of 200 MHz x km. (600 - 800 - 1000 - 1200 MHz x km).

Therefore an OF with a bandwidth/length product of 800 MHz x km is required for our example of 657 MHz x km.


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12 Mode Field Diameter


70/86


TT2530EU02AL_0170

Field diameter

Mode field radius

Field radius

With single-mode fibers, the energy of the basic mode partially penetrates into thecladding glass. The penetration depth and therefore the intensity distribution isdetermined by:

the numerical aperture the operating wavelength

the geometric core diameter

The light distribution of the basic mode for SM fibers plays an essential role in theevaluation of coupling, twisting, and splicing losses. This is why the field diameter rather than the core diameter is indicated for single-mode fibers.

Only fibers with the same field diameter may be connected to each other.

The field diameter is defined as 2w 0

w 0 designates the radius at which the radial field amplitude falls to the 1/e-tuple (

37% because e = 2.71828) of its maximum value at the OF axis (r = 0). The fielddiameter depends on the wavelength. It increases as the wavelength increases. Thefield radius w 0 , in relation to the core radius is only a function of the structuralparameter V, which is dependent on the wavelength and the numerical aperture NAin the following way:

NAd

V

.


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TT2530EU02AL_0171

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100

%

80

60

40

20

0

-10 -8 -6 -4 -2 0 2 4 6 8 m 10

1

e

Light transmission

Distance travelled

Fig. 17


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For single-mode OFs, there is a simple approximation for the structural parameter range 1.6 V 2.6 which does a good job of showing the relation between the fieldradius w 0 , the core radius a and the structural parameter.

Example:

A single-mode OF with a step index profile and a core diameter d = 8.5 m and athreshold wavelength c = 1255 (V c = 2.405) has a field diameter 2w 0 at the

wavelengths = 1300 nm and 1550 nm:

2 02 6

2 wVc c

a,

= 1300 nm: m9.5m8.51255nm2.405

1300nm2.6w 20

= 1550 nm: m11.3m8.51255nm2.405

1550nm2.6w 2

0

The field diameter is larger than the core diameter

(for 1300 nm, approx. 10 - 12%).

The core diameter 8.5 m, for example at 1300 nm , gives a field diameter of

9.5 m (9.3 m 0.5 m according to data sheet).

The core diameter 8.5 m, for example at 1550 nm , gives a field diameter of

11.3 m (10.5 m 1.0 m according to data sheet).


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13 Cut Off Wavelength


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Single-mode fibers

Cut-off wavelength c

Basic mode LP 01

Many modes are always capable of propagation in a fiber with a step index profile.The number of modes decreases as the operating wavelength increases. For operations, it is important to know at which wavelength only the basic mode iscarried in the OF. "Threshold wavelength" refers to the lowest operating wavelengthat which only one mode (the basic mode) is capable of propagation.

If the V parameter is less than 2.405, only one mode is capable of propagation.Only then does the fiber become a single-mode fiber!

NAd V

Examples:

Given: d = 50 m d = 8.5 m

= 1.3 m = 1.3 m

NA = 0.2 NA = 0.113

V = 24.16 V = 2.32


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One must distinguish between:

Threshold wavelength for fibers outside of cables c = 1170...1315 nmand Fibers in cables or in maxibundles cc = 1250 nm

It is best to indicate the value for fibers in cables, because this is indicative for use incables.

If the fiber is operated at operating wavelengths less than the cut off wavelength,the fiber is "multi-mode".

Measurement procedure

One measures the optical power spectrally using a 2 m long, straight (bend radiusgreater than 140 mm) piece of fiber. One then carries out the same measurement

with a bend of 30 mm.

One then calculates the attenuation caused by the bend as a function of the wavelength and records it in a diagram. Several clearly defined attenuation peaks with steep flanks toward the greater wavelengths result.

These flanks mark the cut off wavelengths of the lower modes.

The cut off wavelength is then the wavelength at which the flank of the peak with thelongest wave is less than the value 0.1 dB .


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1400 nm

0 =1230 nm

160012001000800600

20.0

dB

10.0

5.0

2.0

1.0

0.5

0.2

0.1

Fig. 18


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Example:

Determine the cut off wavelength for a fiber with the core diameter d =9 m and the

numerical aperture NA = 0.11.The structural parameter V c for the cut off wavelength is 2.405.

m NAv

d

NAd

293,1405,2

11,05,9

V

This means that above the wavelength 1293 nm, the fiber is a single-mode fiber .The wavelength at which the fiber becomes a single-mode fiber is called c . The

term cut-off wavelength is also used for the threshold wavelength.One must distinguish between: cut off wavelength for the fibers

and Fibers in cables or in maxibundles cc = 1250 nm

It is best to indicate the value for fibers in cables, because this is indicative for use incables.

If the fiber is operated at operating wavelengths less than the cut off wavelength , thefiber is "multi-mode".

Measurement procedure:

One measures the optical power spectrally using a 2 m long, straight (bend radiusgreater than 140 mm) piece of fiber. One then carries out the same measurement

with a bend of 30 mm. One then calculates the attenuation caused by the bend as afunction of the wavelength and records it in a diagram. Several clearly definedattenuation peaks with steep flanks toward the greater wavelengths result. Theseflanks mark the cut off wavelengths of the lower modes . The cut off wavelength isthen the wavelength at which the flank of the peak with the longest wave is less thanthe value 0.1 dB.


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14 Exercise


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Exercise

1. How does the speed of light change in glass with the refraction index 1.5?

2. What does the term "fiber profile" mean?

3. Explain the term "step index profile".

4. Explain the construction of a graded index fiber.

5. What do "NA" and "A N 0.245" mean?

6. What does "transmission window" mean?

7. Name the types of dispersion

a) which exist in multi-mode fibers:

b) which exist in single-mode fibers:


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15 Solution


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Solution

1. The speed of light is slower by a factor of 1.5.

c c

n

300,000 km / s

1.5200,000 km s1

0

1

/

2. "Fiber profile" refers to the course of the refraction index within the fiber

3. A fiber has a step index fiber when the refraction indices of the core and thecladding glass differ by a clear step.

4. Graded index fibers are fibers in which the refraction index decreasescontinuously (usually parabolically) from the fiber axis to the cladding.

5. NA and AN stand for numerical aperture.

The NA is the sine of the angle of acceptance.

0.245 is the sine of 14.18 .

6. Transmission window refers to the ranges of the course of the spectralattenuation curve where the curve shows a minimum of attenuation

a)

a)

a)

1. Window at 850 nm

2. Window at 1300 nm

3. Window at 1550 nm7. a) Mode dispersion

Material dispersion

b) Material dispersionOptical fiber dispersionChromatic dispersion


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03 Tt2530eu02al 01 Optical Fibres

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Transcript of 03 Tt2530eu02al 01 Optical Fibres