Topic 3 Dielectric Waveguides and Optical Fibers 2-1 Symmetric ...

Dispersion coefficient (ps km
30
-1 nm-1 )
20
10
0
-10
-20
-30
1.1
901 37500 ?1999 光電導論 S.O. Kasap, Optoelectronics (Prentice Hall)
λ 0
Dm
Dm + Dw
D w
1.2 1.3 1.4 1.5 1.6
λ (μm)
Material dispersion coefficient (D m) for the core material (taken as
SiO 2), waveguide dispersion coefficient (D w) (a = 4.2 μm) and the
total or chromatic dispersion coefficient D ch (= D m + D w) as a
function of free space wavelength, λ.
901 37500 光電導論
Chromatic Dispersion or Total Dispersion
Chromatic Dispersion
Chromatic Dispersion
Coefficient
Δτ
= | D
L
m
+ D | Δλ
w
D D D + =
m
Dispersion Shifted Fiber (DSF): to design the waveguide dispersion to
shift the zero (material) dispersion from 1330 nm to 1550 nm
by reducing the core radius and increasing the core doping
Dispersion flattened Fiber: to use multiple clad fiber to control the
total chromatic dispersion that is flattened between two wavelength
DFF
w
45
47
Waveguide Dispersion
Waveguide Dispersion
Coefficient
901 37500 光電導論
20
10
-10
-20
-30
Waveguide Dispersion
Δτ
=
L
D
w
Dw
901 37500 光電導論
?1999 S O K Ot l t i (P ti H ll)
Δλ
1.
984N
≈ − 2
( 2πa)
2cn
Dispersion coefficient (ps km -1 nm -1 )
30
0
λ 1
D w
D m
λ 2
1.1 1.2 1.3 1.4 1.5 1.6 1.7
λ (μm)
g 2
2
2
D ch = D m + D w
n
r
46
Thin layer of cladding
with a depressed index
Dispersion flattened fiber example. The material dispersion coefficient (Dm) for the
core material and waveguide dispersion coefficient (Dw) for the doubly clad fiber
result in a flattened small chromatic dispersion between λ1 and λ2. 48