UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS: Structure of Optical Fiber Cable ...

63
UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:

Transcript of UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS: Structure of Optical Fiber Cable ...

Page 1: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

UNIT 2LIGHT PROPAGATION IN AN OPTICAL FIBER:

Page 2: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

CONTENTS:

Structure of Optical Fiber Cable

Classification of Fibers

Based on fiber materials

Based on Modes : Single mode / multi mode fiber

Based on RI profile: Step index / Graded index fiber

Ray Theory

Critical angle, Acceptance angle, Acceptance cone,

Numerical Aperture, V number, cutoff wavelength

Linearly polarized modes

Mode Coupling

Page 3: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Structure of Optical Fiber Cable:

CORE CADDING JACKET

Page 4: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

CORE:

Innermost section

Made of glass/plastic

Glass: SILICA,

Plastic: acrylic - PMMA (Poly methyl methacrylate) It is the actual fiber through which light travels

Light travels in the core by Total Internal Reflection (TIR)

μcore > μclad

μ = c/v

RI is adjusted in Glass or plastic by proper doping.

Plastic fiber also called as Polymer Fibers

Page 5: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

CLADDING:

Core is surrounded by glass / plastic coating Optical properties of Glass is different from core,

μcore > μclad

This causes the optical beam to propagate in the core by Total internal reflection at the core clad interface.

Adds to the mechanical strength Protects the core from contamination Cladding reduces losses due to scattering of light due

to surface discontinuities at the core clad interface.

Page 6: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

JACKET:

Made of plastic / Polymer to provide protection to the fiber against Moisture, abrasion, crushing,

environmental damages, stress, fracture, over use over prolonged period of time.

Provides tensile strength to the fiber.

Page 7: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Classification of Fibers (Materials):

• μcore > μclad (Essential condition for light propagation)

• Dense materials have high RI Plastic core, Plastic Clad Glass core, Plastic Clad (PCS, Plastic Clad Silica) Glass core , Glass clad (SCS, Silica Clad Silica)

Page 8: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Comparison between Glass fiber and Plastic Fiber:

Plastic fibers: Advantages

More flexible

More rugged

Easier to install

Can withstand stress

Less expensive

Light weight

Limitations

More signal attenuation ( as light does not propagate through plastic as effectively as glass)

Due to losses : limited for short distance communication as within a building.

Page 9: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Comparison:

Glass fibers: PCS better than SCS: SCS has best propagation characteristics as it is pure (no

impurities to change the ray propagation)

SCS has low transmission loss

Limitation : Least rugged, Easily susceptible to attenuation when exposed to radiations.

PCS less affected by radiations and hence immune to external interference in comparison to SCS.

Selection of fiber depends on the applications or system requirement.

Page 10: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

General Structure of Fiber-Optic Cables:

Page 12: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

RAY THEORY:

Ray : Narrow beam of light

Light is modeled as a number of discrete rays that can propagate through the fiber.

Using ray theory and applying SNELL’S LAW we can find cable parameters.

Ray theory : Reflection , Refraction, TIR

Page 13: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

How Light Travels Through Fiber?

TIR is the basis of fiber-optic communication

When a light ray strikes a boundary of two materials with different RIs, it bends, or in other terms, refracts to an extent that depends on the ratio of the RIs of the two materials

Page 14: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Cable parameters:

Critical angle Acceptance angle Numerical aperture Solid angle

Page 15: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Concept of TIR (TOTAL INTERNAL REFLECTION):

Speed of light in free space = 3 x 108 m/s

Light travels slow through more dense materials than free space.

Light travelling from one medium to other gets either reflected / refracted

Page 16: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Reflection coefficient (μ):

Refractive index (μ) of the material is defined as: μ = c/v

c is the velocity of light in free space

V is the velocity of light in medium

μ =1 for air

μ > 1 for all known materials.

Light travels slowly in optically dense material (high RI) than in the one that is less dense material (low RI).

Page 17: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

SNELL’S LAW:

Snell's law gives us the information on how a light ray reacts when it meets a interface of 2 medium having different RI.

Page 18: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Snell’s Law Continued……..

Page 19: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Continued…….

Optical fibers work on the principle of total internal reflection

The angle of refraction and incidence at the interface between two media is governed by Snell’s law:

2211 sinsin nn

Page 20: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

μ1<μ2 : Less dense to more dense

Ray bent towards normal μ1=μ2: same medium

Ray travels un reflected μ1>μ2: More dense to less dense

Ray bent away from normal

μ1

μ2

μ1<μ2 μ1=μ

2

NORMAL

μ1>μ2

Page 21: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Total Internal Reflection

μ1>μ2: More dense to less dense Ray bent away from normal

More denseCOREΜ1

INCIDENT WAVE

Less denseCLADDINGμ2

Refracted ray

Internal reflection

θi

θr

By adjusting θi we can initiate TIR and hence light starts propagating in the core

Page 22: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Refraction & Total Internal Reflection:

When reflection occurs : θi = θr

Page 23: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

c

a

Acceptanceangle

Acceptance Cone

B

A

Lost by radiation

Core

Cladding

Acceptance angle

Page 24: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

25 A meridinal ray A is to be incident at an angle a in the core

– cladding interface of the fiber. The ray enters the fiber core at an angle a to the fiber

axis. The ray gets refracted at the air – core interface at angle c

and enters into the core – cladding interface for transmission Therefore, any ray which is incident at an angle greater

than a will be transmitted into the core – cladding interface

at an angle less than c and hence will not undergo total

internal reflection.

Page 25: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

26 Contd.•The ray B entered at an angle greater than a and

eventually lost propagation by radiation. •It is clear that the incident rays which are incident on fiber core within conical half angle c will be refracted

into fiber core, propagate into the core by total internal reflection. •This angle a is called as acceptance angle, defined

as the maximum value of the angle of incidence at the entrance end of the fiber, at which the angle of incidence at the core – cladding surface is equal to the critical angle of the core medium.

Page 26: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

27Acceptance cone : The imaginary light cone with twice the acceptance angle as the vertex angle, is known as the acceptance cone.

Numerical Aperture (NA) :Numerical aperture (NA) of the fiber is the

light collecting efficiency of the fiber and is a measure of the amount of light rays can be accepted by the fiber.

 

Page 27: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Numerical Aperture

The numerical aperture of the fiber is closely related to the critical angle and is often used in the specification for optical fiber and the components that work with it

The numerical aperture is given by the formula:

The angle of acceptance is twice that given by the numerical aperture

22

21.. nnAN

Page 28: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

29

Numerical aperture

A ray of light is launched into the fiber at an angle 1 is less than

the acceptance angle a for the fiber as shown.

1

2

Ø

Page 29: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

30This ray enters from a medium namely air of refractive index n0 to the fiber with a core of refractive

index n1 which is slightly greater than that of the

cladding n2 . Assume that the light is undergoing total

internal reflection within the core.Applying Snell’s law of refraction at A,

10

1

2

1

sin

sinn

n

n

211 sinsin n

In the triangle ABC,

22

22

or

Page 30: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

31

cos2

sinsin 111 nn

21

2sin1cos

21

211 sin1sin n

From the above two equations,

When the total internal reflection takes place, θ = θc and θ1 = θa . Therefore,

21

21 sin1sin ca n

Page 31: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

32 Also, at B, applying the Snell’s law of refraction, we get

1

2

1

2 sin (or) 90sin

sin

n

n

n

nc

c

21

22

21

21

2

1

21 1sin nn

n

nna

From the above equation, we get

This is called the numerical aperture (N.A). The numerical aperture is also defined as the sine of the half of the acceptance angle .

ca nAN sinsin. 1

Page 32: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

33 In terms of refractive indices n1 and n2, where n1 is the core index and n2 the cladding index

2122

21 )(. nnAN

The half acceptance angle a is given by ).(sin 1 ANa

212

22

11 )(sin nn

21

22

21

2n

nn

21

2

2

).(

n

AN

211 )2(N.A n

From the above eqns, we get

Page 33: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

UNIT III Lecture 6

34PHYSICAL STRUCTURE OF OPTICAL FIBER :

An optical fiber is a transparent rod, usually made of glass or clear plastic through which light can propagate.

The light signals travel through the rod from the transmitter to the receiver and can be easily detected at the receiving end of the rod, provided the losses in the fiber are not excessive.

The structure of the modern fiber consists of an optical rod core coated with a cladding.

The core and the cladding have different refractive indices and hence different optical properties

Page 34: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

35 Countd.•The refractive index of the core is always greater than that of the cladding (i.e.) n1 > n2.

The light travels within the core by the principle of total internal reflection

An unclad fiber and a clad rod through which the light travels.

With the unclad rod, only a small potion of the light energy is kept inside; most of the light leaks to the surroundings.

The clad fiber is a much more efficient light carrier.

Page 35: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

36Countd.•The losses of the light as it travels through the fiber are much smaller for the clad fiber than for the unclad one.• The thickness of the core of a typical glass fiber is nearly 50 μm and that of cladding is 100 – 200 μm. • The overall thickness of an optical fiber is nearly 125 – 200 μm. • Thus an optical fiber is small in size and light weight unlike a metallic cable.

Page 36: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

37 Propagation characteristics of optical fiber :Meridinal rays and Skew rays :

The light rays, during the journey inside the optical fiber through the core, cross the core axis. Such light rays are known as meridinal rays.

The passage of such rays in a step index fiber is Similarly, the rays which never cross the axis of the core are known as the skew rays.

Skew rays describe angular ‘helices’ as they progress along the fiber.

Page 37: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

38

Countd.

•They follow helical path around the axis of fiber.

• A typical passage of skew rays in a graded index fiber is shown in the following Fig.

The skew rays will not utilize the full area of the core and they travel farther than meridinal rays and undergo higher attenuation.

Page 38: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

39

MERIDINAL AND SKEW RAYS

Page 39: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Modes and Materials:

Since optical fiber is a waveguide, light can propagate in a number of modes

If a fiber is of large diameter, light entering at different angles will excite different modes while narrow fiber may only excite one mode

Multimode propagation will cause dispersion, which results in the spreading of pulses and limits the usable bandwidth

Single-mode fiber has much less dispersion but is more expensive to produce. Its small size, together with the fact that its numerical aperture is smaller than that of multimode fiber, makes it more difficult to couple to light sources

Page 40: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Comparison :

Standard single mode Optical Fiber

Most common single mode optical fiber SMF28 from corning

Core diameter dcore = 8.2micro meter

Outer cladding diameter = 125 micro meter

Standard Multimode optical Fiber

Most common multimode optical fiber 62.5/125 from corning

Core diameter= 62.5 micro meter

Outer cladding diameter=125 micrometer

Step index Fiber Graded Index Fiber

Page 41: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Continued……

Single Mode Numerical Aperture NA=0.14

NA=sin(q)

Dq=8°

lcutoff = 1260nm (single mode for >l lcutoff)

Single mode for both l=1300nm and l=1550nm standard telecommunications wavelengths

Multimode Numerical Aperture

NA=0.275

NA=sin(q)

Dq=16°

Many modes

Page 42: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Types of Fiber: Both types of fiber described earlier are known as step-index fibers

because the index of refraction changes radically between the core and the cladding

Graded-index fiber is a compromise multimode fiber, but the index of refraction gradually decreases away from the center of the core

Graded-index fiber has less dispersion than a multimode step-index fiber

Page 43: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 44: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 45: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 46: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 47: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

V Number:

The number of propagating modes in a fiber is proportional to its V-Number

The equation is given as

V=2π/λ * a √ η12 – η2

2

Page 48: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Number of Modes:

The number of modes can be characterized by the normalized frequency

Most standard optical fibers are characterized by their numerical aperture

Normalized frequency is related to numerical aperture

The step index optical fiber is single mode if V<2.405The step index optical fiber is multi mode if V>2.405

For Graded Index Single mode fiber V< 3.4For Graded Index Multi mode fiber V > 3.4

Page 49: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Number of Modes:

The number of Modes in Step Index Fiber is

N = V2 / 2

Where α is refractive index profile

Page 50: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Linearly Polarized Modes:

Meriodianal Ray

TE mode

TM mode

Skew ray

Hybrid Mode

EH mode

HE mode

The modes degenerate to give LP modes

Page 51: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Electromagnetic Field distribution:

Electromagnetic wave in free space:

TEM mode

Ex ≠ 0

Ey ≠ 0

Hx ≠ 0

Hy ≠ 0

Ez=0

Hz=0

Page 52: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 53: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Electromagnetic wave through a waveguide:

Mode of Propagation is either :

TE, TM, EH, HE mode

TE: Ex, Ey ≠ 0, Ez=0

Hx, Hy, Hz ≠ 0

TM: Ex, Ey,Ez ≠ 0,

Hx, Hy ≠ 0, Hz=0

Hybrid: Ex, Ey,Ez ≠ 0,

Hx, Hy,Hz ≠ 0

EH mode: Ez dominates

HE mode : Hz dominates

Page 54: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Phase velocity (mode):

z

Page 55: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Phase velocity

Vp = ω / β

ω : angular frequency of waveβ : Phase constantγ : Propagation Constant γ = α + jβThe attenuation constant defines the rate at which the fields of the wave are attenuated as the wave propagates.An electromagnetic wave propagates in an ideal (lossless) media without attenuation (α= 0)The phase constant defines the rate at which the phase changes as the wave propagates..

Page 56: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Group velocity

Page 57: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

58Group velocity (pulse)

z

0d

d t

ddgV

Page 58: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Linearly polarized modes

•All modes travelling down has their own phase velocity.•Group of modes having same phase velocity will degenerate•Their modal patterns are not seen distinctively•The new mode formed by combination of the degenerated modes : LINEARLY POARLIZED MODES

Page 59: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

LP modes

LP modes Exact modesLP01 HE11

LP11 HE21, TE01, TM01

LP21 HE31, EH11

LP02 HE12

LP31 HE41, EH21

LP12 HE22, TE02, TM02

LPlm HE2m,TE0m,TM0m

LPlm(l≠0or1) HEl+1,m,EHl-1,m

Page 60: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

LPlm :

l : half of number of maxima around the circumference

m: number of maxima along the radius.

Page 61: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.

Intensity Profiles

Page 62: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.
Page 63: UNIT 2 LIGHT PROPAGATION IN AN OPTICAL FIBER:. CONTENTS:  Structure of Optical Fiber Cable  Classification of Fibers  Based on fiber materials  Based.