HW #4
due 2/23/12 5PM
No later than 2/27/12 5PM
1. An optical fiber has a core diameter of 10
μ
m
and numerical aperture of 0.2.
a) What is the maximum source diameter and numerical aperture for optimum coupling?
b) For a laser beam with wav elength of 1. 55
μ
m
and the maximum source diameter in a), what is the divergence
angle? Considering the size and angle issues, does this beam provide optimum coupling?
c) To ensure optimum coupling, what is the maximum distance between the laser and the fiber.
d) Is it wise to reduce the beam diameter to 25% of the value used in b)?
Justify your answer with the new
divergence angle.
Notice: This has advantage of relaxing the requirements on alignment.
2. Consider a fiber with a core diameter of 100
μ
m
, core refractive index of 1.485 and a cladding refractive
index of 1.455 at
λ
o
=
850
nm
.
Consider operating this fiber at
λ
o
=
850
nm
and laser source with linewidth of
2nm.
Assume
the material has zero dispersion wav elength
λ
0
=
1360
nm
and dispersion slope of
S
0
=
0. 09
ps
/
km

nm
2
.
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 Spring '11
 Rahmir

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