Elenco Fiber Optics Voice and Data Kit - Manual (Page 12)

SNELL’S LAW
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Figure 2D
Figure 2D-1 Figure 2D-2 Figure 2D-3
θ
2
n
1
n
2
Critical Angle
Light is bent away from normal
Light does not enter
second material
Angle of
Refraction
Angle of Incidence
n
1
n
2
n
1
n
2
θ
1
Angle of
reflection
Angle of
incidence
=
When the angle of reflection is
more than the critical angle, light
is reflected.
n
1
is greater than n
2
7 The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGE 40)
By Donald J Sterling, Jr. - DELMAR PUBLISHERS, INC., Albany, New York, Copyright 1993
Snell’s Law states the relationship between the
incident and refracted rays.
n
1
sin
θ
1
= n
2
sin
θ
2
where: n
1
and n
2
are refractive indexes
θ
1
and
θ
2
are angle of incidence and angle of
refraction respectively.
The law shows that the angles depend on the
refracted indices on the two materials. Knowing any
three of the values, of course, allows us to calculate
the fourth through simple rearrangement of the
equation.
The critical angle of incidence
θc, where θ
2
=
90 O , is
θc = arcsin (n
2
/n
1
)
At an angle greater than
θc, the light is reflected.
Because reflected light means that n
1
and n
2
are
equal (since they are in the same material),
θ
1
and
θ
2
are also equal. The angle of incidence and
reflection are equal. These simple principles of
refraction and reflection form the basis of light
propagation through an optical fiber.
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