OPTOELECTRONIC SEMICONDUCTOR DEVICES slides/Optical fibers... · 2009. 11. 19. · OPTOELECTRONIC...
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ELEKTRONIKOS ĮTAISAI 2009
VGTU EF ESK [email protected]
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OPTOELECTRONIC
SEMICONDUCTOR DEVICES
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ELEKTRONIKOS ĮTAISAI 2009
VGTU EF ESK [email protected]
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• Optical effects in fibers
• Structure and types of optical fibers
• Dispersion in single mode fibers
• Attenuation
• Communication windows
• Optical cables
Optical fibers
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• 1. In vacuum rays travel at velocity of 3⋅108 m/s. In any other medium rays travel at a slower speed given by v = c / n. The factor n is the index of refraction or refractive
index of the medium.
• 2. If any power crosses the boundary, the transmitted ray direction is given by Snell’s
law:
• 3. If n2 < n1 , the transmitted ray is bent away from the normal when traveling from
media having a high refractive index into a media with a lower refractive index.
• 4. At the critical incident angle, the transmission angle becomes π/2. For , the total internal reflection occurs..
•5. At a plane boundary between two media a ray is reflected at
an angle equal to the angle of incidence.
ELEKTRONIKOS ĮTAISAI 2009
VGTU EF ESK [email protected]
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t2i1 sinsin ϕϕ nn =
crϕϕ >
Optical fibers
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At n2
Optical fiber is round
cross-section waveguide.1966 m.: 1000 dB/km.
K.C.Kao : 20 dB/km.
1975 m.: 2 dB/km, 1979 m.: 0,2 dB/km.
• Why are only certain optical wavelengths used
in telecommunication systems?
• What are reasons of attenuation? How can we
reduce attenuation?
• What materials are used for optical fibers?
• What are reasons of distortions of optical
pulses?
SiO2
Optical fibers
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In 1965, Charles K. Kao and George A. Hockham of the British company
Standard Telephones and Cables were the first to recognize that
attenuation of contemporary fibers was caused by impurities, which could
be removed, rather than fundamental physical effects such as scattering.
They demonstrated that optical fiber could be a practical medium for
communication, if the attenuation could be reduced below 20 dB per
kilometer.
The first practical optical fiber for communications was invented in 1970
by researchers Robert D. Maurer, Donald Keck, Peter Schultz, and Frank
Zimar working for American glass maker Corning Glass Works. They
manufactured a fiber with 17 dB optic attenuation per kilometer by doping
silica glass with titanium.
On 22 April, 1977, General Telephone and Electronics sent the first live
telephone traffic through fiber optics, at 6 Mbit/s, in Long Beach,
California.
http://en.wikipedia.org/wiki/Optical_fiber
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Step-index fiber
c// 11 lnvlt ==
cnlnlnt 221cr12 /sinc/ == ϕ
c2
1 n
n
n
l
t ∆∆=
nn
n
t
lBl
∆∆c
1
2=≅t
B∆1
≅
↓↓
==
−==
−=
−=
=
==
↓↑
0
20
22
21ma
a22
21m
122
21cr
12cr
cr1m1ma
,
)( ,cos)(
sin
sin
cos
/sin
cossinsin
if ,
ΦΦ∆
ΦΦθθ
α
α
ϕ
ϕ
ϕθα
∆
/n
NA/I
nnNAn
nnn
nnn
nn
nnn
nBl
How can we reduce dispersion?
SiO2
Pulse
spreads
out.
Multipath (delay) time dispersion,… bit-rate,…
n1 = 1.5, n2 = 1, … Bl = 0.4 (Mb/s)km
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t = 0 X
Initially the density of runners
can be approximated by δ
function.
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t = 4 min
X
After some time the pulse
characterizing density of
runners is spread.
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( )
[ ]( )
18
,8cc8
),2(1 If
2 ,)/()(
if ,)(21)(
:ionApproximat
...5,01cosh)(
02
0
20
22
20
2/10
2200
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• If α = 2, dispersion is minimal.
• The refractive index profile
must be precise.
µm 102 ,π
405,22
22
21
<−
< ann
aλ
wm ,/ DDDDlt +== λ∆∆
Multimode and single mode fibers
Propagation of light can be considered as
propagation of electromagnetic waves.
SI and GRIN fibers are multimode
fibers. Many types of electromagnetic
waves can propagate along the fibers as
dielectric waveguides. Then the
dispersion is due to different phase
velocities of the waves.
We can reduce the number of the
waves that can propagate and
reduce the mode dispersion
reducing the core diameter.
Dispersion is minimal in the
single-mode fibers. The core
diameter of a single-mode fiber is
less than 10 µm.
Chromatic dispersion
α
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A typical single-mode optical fiber,
showing diameters of the
component layers.
Single-mode fiber
Dispersion is minimal in
the single-mode fibers.
The core diameter of a
single-mode fiber is less
than 10 µm.
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Dispersion in the single-mode fibers
( )αβω
jc
'j* +=+= nnn
n is dependent on λ and Npr
2
2
m
m2
2g
d
d
c
,d
d
c
λ
λ
λ∆λ∆λ
λ∆
nD
Dn
l
t
−=
=−≅
Visible light
Infrared rays
Ultraviolet rays
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2wwm )π2(c ,
anDDDD
λ−≅+=
The chromatic dispersion is
minimal at λ = 1300 nm.
In DSF (dispersion shifted fibers):
dispersion is minimal at λ = 1550 nm
In DFF (dispersion flattened fibers)
dispersion is small in the range from
1300 to 1700 nm.
Dispersion in the single-mode fibers
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Attenuation
zWW dd α=−
)exp()0()( zWzW α−=
)/exp()/exp(
)/exp()/exp(
uvuvuvuvuv
iririririr
λλα
λλα
AWWA
AWWA
==
−=−=
Attenuation in glass is
caused by
absorption and
scattering of light.
Slopes of ...
Rayleigh scattering...
4RR /λα A=
Attenuation is minimal at
wavelength of 1.55 µm.
Attenuation
Rayleigh scatteringAbsorption
Impurities cause increase
of attenuation.
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• Glass (silicon dioxide, also called silica) is used
usually for optical fibers.
• An optical fiber consists of core and cladding,
having less refractive index.
• In multi-mode fibers light propagates reflecting from
cladding.
• To reduce distortions of optical pulses, we must
reduce dispersion and attenuation.
• In the single mode fibers minimal dispersion is
achieved at wavelength of 1.3 µµµµm, minimal attenuation is at wavelength of 1.55 µµµµm.
Optical fibers
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• Three communication windows are used in
practice.
• The first communication window is at the
wavelength of 0.85 µm. It is related to GaAs light sources.
• The second window is at 1.3 µm. At this wavelength attenuation is small and dispersion is minimal.
• The third window is at 1.55 µm. At this wavelength attenuation in a glass fiber is minimal.
• Minimal dispersion at 1550 nm is achieved using the
dispersion-shifted fibers. Small dispersion in
the range 1300–1600 nm is achieved in the
dispersion-flattened fibers.
Optical fibers
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Optical cable
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Optical cable
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Indoor/Outdoor Breakout Cable
Armored Cable
Optical cables
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Optical cable
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Optical cable
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202020102000199019801970
Year
Transmission Capacity (b/s)
1011
1010
109
108 100 M
400 M
2.5 G
1.6 G
10 G
1.3 µm SMF
FP-LD
HIC
: Under Development
1.55 µm DS-SMF
DFB-LD
Si-MIC
Optical Amplifier
External Modulator
Si-/GaAs-MIC
Soliton Transmission
Optical FDM
Quantum Effect Devices
OEIC
Evolution of Technology (T. Miki, IEEE Proc. Nov. 1993, pp 1594-1609)
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VGTU EF ESK [email protected]
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In mathematics and physics, a soliton is a self-reinforcing solitary
wave (a wave packet or pulse) that maintains its shape while it
travels at constant speed; solitons are caused by a delicate balance
between nonlinear and dispersive effects in the medium.
The soliton phenomenon was first described by John Scott
Russell (1808-1882) who observed a solitary wave in the Union
Canal, reproduced the phenomenon in a wave tank, and named it
the "Wave of Translation".
In 1973, Akira Hasegawa of AT&T Bell Labs was the first to
suggest that solitons could exist in optical fibers, due to a balance
between self-phase modulation and anomalous dispersion. He
also proposed the idea of a soliton-based transmission system to
increase performance of optical telecommunications.
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ELEKTRONIKOS ĮTAISAI 2009
VGTU EF ESK [email protected]
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Solitons
In mathematics and physics, a soliton is a self-reinforcing solitary
wave (a wave packet or pulse) that maintains its shape while it
travels at constant speed; solitons are caused by a delicate balance
between nonlinear and dispersive effects in the medium.
The soliton phenomenon was first described by John Scott Russell
(1808-1882) who observed a solitary wave in the Union Canal,
reproduced the phenomenon in a wave tank, and named it the
"Wave of Translation".
In 1973, Akira Hasegawa of AT&T Bell Labs was the first to
suggest that solitons could exist in optical fibers, due to a balance
between self-phase modulation and anomalous dispersion. He also
proposed the idea of a soliton-based transmission system to increase
performance of optical telecommunications.
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ELEKTRONIKOS ĮTAISAI 2009
VGTU EF ESK [email protected]
25
In 1988, Linn Mollenauer and his team transmitted soliton pulses over 4,000
kilometers using a phenomenon called the Raman effect, named for the
Indian scientist Sir C. V. Raman who first described it in the 1920s, to
provide optical gain in the fiber.
In 1991, a Bell Labs research team transmitted solitons error-free at 2.5
gigabits over more than 14,000 kilometers, using erbium optical fiber
amplifiers (spliced-in segments of optical fiber containing the rare earth
element erbium).
In 1998, Thierry Georges and his team at France Télécom R&D
Center, combining optical solitons of different wavelengths
(wavelength division multiplexing), demonstrated a data
transmission of 1 terabit per second.
In 2001, the practical use of solitons became a reality when
Algety Telecom deployed submarine telecommunications
equipment in Europe carrying real traffic using John Scott
Russell's solitary wave.
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In 1988, Linn Mollenauer and his team transmitted soliton
pulses over 4,000 kilometers using a phenomenon called the
Raman effect, named for the Indian scientist Sir C. V. Raman
who first described it in the 1920s, to provide optical gain in
the fiber.
In 1991, a Bell Labs research team transmitted solitons error-
free at 2.5 gigabits over more than 14,000 kilometers, using
erbium optical fiber amplifiers (spliced-in segments of optical
fiber containing the rare earth element erbium).
ELEKTRONIKOS ĮTAISAI 2009
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Solitons
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In 1998, Thierry Georges and his team at France Télécom
R&D Center, combining optical solitons of different
wavelengths (wavelength division multiplexing),
demonstrated a data transmission of 1 terabit per second.
In 2001, the practical use of solitons became a reality when
Algety Telecom deployed submarine telecommunications
equipment in Europe carrying real traffic using John Scott
Russell's solitary wave.
Solitons
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The refractive indices of the core and cladding are 1.45
and 1.43 respectively. Light wavelength is 1.55 mm.
Find the maximal core diameter of the single-mode fiber.
Optical fibers