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Refraction

Figure 7-13

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Critical Angle

Figure 7-14

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Total Internal Reflection (TIR)

Figure 7-15

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Figure 7-16

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Multimode Step-Index

Figure 7-17

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Multimode Graded-Index

Figure 7-18

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Single Mode

Figure 7-19

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Fiber Construction

Figure 7-20

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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How a light ray reacts when it meets the interface of twotransmissive materials that have different indexes of refraction

can be explained with Snells law . Snells law simply states

n1 sin 1 = n2 sin 2

Where n1 = refractive index of material 1(unit less)

n2 = refractive index of material 2(unit less)

1 = angle of incidence (degrees)2 = angle of refraction (degrees

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( n 1 n2 )

Refracted Ray

1 (angle of incidence)

( n 1 = n 2 ) Unrefracted

Ray Normal

Medium n1

Medium n2

2

2

Incident ray

( n 1 n2 )

Figure 2.5 Refractive model for Snells law

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Normal

Figure 2.6 Critical AngleRefraction

n2 less dense

1= C (minimum)

2

n1 more dense

Incident ray

Refracted ray (more to less dense)

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When 2 = 90 which result to sin 2 = 1, then 1 = C ,Therefore,

Cri tical Angle :

C =

1

21sinn

n

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Total Internal Reflection

2 conditions necessary for TIR to occur:

1. The refractive index of the first medium is greater thanthe refractive index of the second one (n1 > n2)

2. The angle of incidence, 1, is greater than or equal to thecritical angle, c : 1> c

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n 2 less dense

1 C

n 1 more dense

Incident ray Total InternalReflection ofIncident Ray

The Total Internal Reflection

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Example 1

let medium 1 be glass and medium 2 be ethyl alcohol. For an angle ofincidence of 30 , determine the angle of refraction .

47.335514.0sin

sin5514.030sin36.15.1

sinsin

1

2

2

21

2

1

n

n

n1 (glass) = 1.5n2 (ethyl alcohol) = 1.36

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Determine the critical angle for the fiber describe in Example 1

C =

1

21sinn

n

5.1

36.1sin 1

05.65

C =

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Determine the numerical aperture for the fiber describe in Example 1

633.0

36.15.1 22

2

2

2

1 nn NA