chapter5 optic fiber waveguides.ppt

Chapter 5
Optic Fiber Waveguides
core
纤芯
cladding
包层
coating
涂敷层
Step-Index Fiber
阶跃折射率光纤
Graded-Index Fiber
渐变折射率光纤
Intrinsic Absorption
本征吸收
Rayleigh Scattering
瑞利散射
optical time-domain reflectometer
光时域反射仪
Preform
预制棒
Fiber cable
光缆
Step-Index Fiber (SI Fiber)

n1
n2
Cladding index n2
Core index n1
n1 > n2
For total reflection we require > c
n1
n2
fractional refractive index change
Common SI Waveguides
Glass core Glass cladding
Glass core Plastic cladding
3) Plastic core Plastic cladding
All Glass
Lowest loss. Used for longest distances (up to about 100 km)
Glass/Plastic
Moderate loss. Moderate distances (up to about 100 m)
All Plastic
High loss. Short distances (up to about 10 m)
Typical fiber properties:
Cladding modes may also be trapped in the fiber by
total reflection at the outer boundary of the cladding.
The cladding modes are lossy and do not travel far.
n2
n1
Total Reflection
Graded-Index Fiber (GRIN Fiber)
Cladding
Core
z
2a
n1
n2
a
0
Ray Paths
Index
In the core
In the cladding
a is a design parameter. It is usually close to a = 2.
a
a
0
0
r
r
Snell’s Law
n(r)
1
2
c
n2
n1
2 > 1
SI Fiber
n2
n2
n1

0

0
The acceptance angle is independent of where the
incident ray enters the core.