Transcript Ingen bildrubrik - Mittuniversitetet

Devices
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•
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•
•
•
•
Couplers
Isolators and Circulators
Multiplexers and Filters
Lasers and LEDs
Detectors
Amplifiers
Switches
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1
Couplers
• When two fibers are placed
in proximity to each other,
the signal are coupled from
one fiber to another.
• The coupler are treated
mathematically in exactly
the same manner as a
electrical RF-coupler with
scattering parameters.
• Bild s84
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2
Isolators and
Circulators
• Isolators couples the signals in one direction and
block the transmission in the other direction
• A circulator couples the signal to another port in a
circular manner
– Insertion loss is the power loss in the
coupled direction (As low as possible)
– Isolation is the loss in the blocked direction
(As high as possible)
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3
Isolator
• A isolator is using a
combination of polarization
filters and polarization
rotators.
– A single polarization
isolator is simple.
– A polarization
independent isolator
are using polarization
splitters, a rotator and a
/2-plate.
• Bild s88
• Bild s 89:1
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4
Circulator
• A circulator have
similar operation as
an isolator with more
than two ports.
• The signal are
coupled from port 1
to 2, 2 to 3 and so
on.
Bild s 89:2
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Electronic Simulation Group
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5
Multiplexers and
Filters
• In the optical domain
there exist
– Filters
– Multiplexers and
Demultiplexers
– Wavelength Routers
Bild s 91
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Filters
• Filters are usually designed
with Bragg grating
• Any periodic perturbation in the
propagating medium serve as a
Bragg grating (Usually
refractive index).
Bild s 98
– The wavelength corresponding to the
Bragg grating frequency are reflected
while all other are transmitted.
– The side lobes can be reduced by
having smaller refractive index
changes near the edges of the filter.
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Electronic Simulation Group
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7
Fabry-Perot Filters
• Fabry-Perot Filter (Etalon) is
fabricated by a cavity
surrounded by two mirrors
• The transfer function of an
etalon filter is periodical due
to the multiple of standing
waves in the cavity.
• Etalon is very simple and
cheap.
Bild s 103,105
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Electronic Simulation Group
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Multi Layer Filters
• A single Etalon filter
is very narrow
banded.
• The bandwidth can
be increased by using
multiple cavities.
Bild s 106,107:1
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Electronic Simulation Group
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9
Add/Drop elements
• Add/Drop elements can
be realized by a fiber
gratings (isolator), a
circulator and a coupler.
Bild s 100
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Electronic Simulation Group
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10
Multiplexers and
Demultiplexers
• Static multiplexers can
be realized using one
multi-layer filters for each
wavelength.
• The same device can be
used as a multiplexer as
well.
Bild s 107:2
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Electronic Simulation Group
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11
Wavelength
Routers
• A Static wave-length
router can be realized by
using a few multiplexers
and demultiplexers
Bild s 92
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12
Planar Lasers
• An amplifying medium is
surrounded by two
mirrors (one semitransparent)
• The amplifying medium
is mostly a quantum well
Bild Agrawal s
96, 98
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13
Planar Lasers
• The Laser must Be
confined in one direction
• Gain Guided Laser
– Oxide Strip
– Junction Strip
• Index Guided Laser
– Ridge wave guide
structure
– Etched mesa
structure
Bild Agrawal s
99,100
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Lasers
• The semiconductor amplifier is widebanded
• The monochromatic lasing wavelength
is determined by the cavity
surrounding the amplifier
• For low power, high reflectivity is
required for lasing operation.
– Cavity Laser (Fabry Perot Cavity)
– Distributed Feedback Reflector
(DFR)
– Distributed Bragg Reflector (DBR)
Bild Agrawal s
105, 107
Department of Information Technology and Media
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15
Vertical Cavity Surface
Emitting Lasers (VCSEL)
• The cavity is made of
epitaxial layers.
• Possible to make very
small devices
• Devices can be tested
before assembly
Bild Pessa 22:2
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Electronic Simulation Group
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16
Pulse lasers
• For fast communication it
is necessary to modulate
the laser signal quickly.
Bild Oleg 1-2
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17
Saturable Absorber
• A saturable absorber
change the absorption
very quickly.
• By population inversion the
absorption decreases.
• For short decay time the
life-time of the absorber
must be reduced
– Introduce a trap level in
the band-gap
Bild Oleg 3-4
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18
Pulse Amplifier
Mode Lock Laser
• Short Pulse amplifier
– The gain in the amplifier is
constant
– At the pulse the absorber
bleaches, giving a net gain
– Prior and after the pulse the
absorber giving a net loss.
Bild Oleg 5-6
• Colliding Pulse Mode-Lock
Laser
– Two pulses together have
enough energy to saturate
the absorber.
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19
Light Emitting
Diodes (LEDs)
• Much Simpler and cheaper compared with
lasers
• For many applications with short distances
and low data rates LEDs are sufficient.
• A LED is a forward biased pn-junction, where
the injected minority carriers recombine by
spontaneous emission of light
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20
LEDs
Telecommunication LEDs
can either be surface or
edge emitting.
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21
Detectors
• Telecommunication detectors are traditional pndetectors
• PIN diodes are used to increase the efficiency
• Avalanche photodiodes are also used to increase the
signal
– To high amplification reduces noise performance
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22
Semiconductor Optical
Amplifiers (SOAs)
• A semiconductor amplifiers
is realized as a
semiconductor laser without
mirrors
• Very short compared with
fiber amplifiers
Bild Reale
Department of Information Technology and Media
Electronic Simulation Group
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23
SOAs
• For high amplification and
large bandwidth a very good
antireflective coatings are
necessary.
– Difficult to achieve.
• The antireflectivity can be
improved by:
– Tilted stripe structure
– Window faced structure
Bild s 370, 369
Department of Information Technology and Media
Electronic Simulation Group
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24
SOAs
• SOAs are polarization
dependent
• Multiple SOAs can be
used to realize a
polarization
independent amplifier.
Department of Information Technology and Media
Electronic Simulation Group
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Bild s 372
25
Electro-Optic
Switch
• Electro-optic directional
coupler switch
• Semiconductor Optical
Amplifier switch
– An optical amplifier
where the amplifier
bias switches the
signal
Bild s 155
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26
All-Optical
Regeneration
• Nonlinear Loop Mirror
– Without control pulse:
Reshaping
– With control pulse:
Retiming and reshaping
Bild Oleg 7-8
• A saturable absorber
can be used as an
optical gate for retiming
and reshaping.
Department of Information Technology and Media
Electronic Simulation Group
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27
All Optic Switch
Loop Mirror
– If the two signals are equal the
signal are coupled to the input.
– If the two signals experiences
different absorption or index the
signal are fully coupled to the
output.
• The control signal saturates the SOA
for a short moment.
• The two pulses reaches the SOA with
a time difference, one where the
amplified is saturated.
• The control pulse are filtered away
The two other are based on MachZehnder Interferometers.
Bild Toliver
Department of Information Technology and Media
Electronic Simulation Group
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28
All Optic Switch
• Each data-pulse induces an
non-linear refractive index
change in the SOAs.
• Each clock pulse is split in two
parts and passing the SOAs.
• The two pulses are interfering
either destructively or
constructively depending on
the clock pulse arrival.
Bild Nakamura,
2xUeno,
Department of Information Technology and Media
Electronic Simulation Group
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29
All-Optical Pulse
Regeneration
• Electro optical timing and
reshaping
– All Optical signal path
– Electrical signal for timing signal.
• For all Optical Pulse
Regeneration only the clock
recovery is missing
Bild Oleg 5-6
Department of Information Technology and Media
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30
Optical Clock
Recovery
• For Optical Clock recovery a lasers which are
able to create short pulses are required
– Self Pulsating Laser
– Mode Lock Laser
• Optical Clock recovery
up to 40 Gbit/s have
been achieved
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Electronic Simulation Group
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31
Large Switches
• A multi-port switches
can easily be realized
using several 2:2
switches in a matrix.
Bild s158
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Electronic Simulation Group
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32
Wavelength
converters
• Opto-electric approach
• Cross Gain Modulation in
a SOA
Bild s162, 164
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33
Solitons
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•
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•
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Introduction
Robustness
Sliding-Frequency Filter
Tapered Fibers
Dispersion Managed Fibers
Pulse-to-Pulse Interaction
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34
Introduction
• Narrow pulses with high peak power and
special shape.
• A soliton is not affected by dispersion.
– The dispersion is exactly compensated by
nonlinear effects in the fiber.
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35
Robustness
• A soliton is, when once created very robust.
• A pulse where nonlinear effects not exactly
compensate the dispersion is shifted towards this
case.
• Solitons ”feels” only average parameters (fiber
dispersion, fiber mode area, pulse energy) as long
as the variations are faster than the soliton
dispersion length.
– Stable in systems with lumped amplifiers (Lamp< zdisp).
– Slow variation can be used for pulse reshaping
(compression and broadening)
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36
SlidingFrequency Filter
• Etalon Filter can be
used due to the narrow
bandwidth of the soliton
– Cheap and simple,
compared with
Gaussian filters
– Same filter can be
used for multiple
channels
• Bild 17:1
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37
SlidingFrequency Filter
• The soliton adapts to
successive slowly
sliding-frequency shifting
filters and moves in
frequency
– The noise cannot be
moved in frequency,
which is removed
efficiently
• Bild 19:2
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38
SlidingFrequency Filter
Noise Reduction
• Bild 20:2
• Bild 21:1
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39
SlidingFrequency Filter
Transfer Function
• In a long transmission
line the transfer function
looks like a step
function.
– Removing small
signals and noise
– Large signals are all
given the same
energy
24:2
25:1
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40
Wavelength Division
Multiplexing (WDM)
In WDM, Solitons of
different channels
overtake and pass
thought (Collide with)
each other, which
results in.
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41
Tapered Fibers
• Some of the problems can
be corrected by using a
tapered fibers, where the
dispersion decays exactly
as the intensity.
• Bild 35:2
– Behaves like loss less,
constant D-fiber
• The exponential dispersion
can be replaced with an 3step approximation.
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42
Gain Flatness
• Optical amplifiers have
not a flat gain over several
channels.
• After multiple amplifiers
the signal power differs
very much between
channels.
• In Soliton transmission
with filters the amplitude
can be kept relative
constant between the
different channels.
• Bild 39:1
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43
Gain Flatness
• Bild 39:2
• Bild 40:2
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44
Dispersion
Managed Fibers
• Fibers with alternating dispersion where the pulses
are true solitons only in a few points along the fiber.
– All advantages of ’classical solitons’
– Power enhancement
– Inexpensive and flexible design
– High stability range
– WDM
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45
Pulse-to-Pulse
Interaction
• The pulse-to-pulse
interaction depends on
the pulse width-spacing
ratio.
• Bild 60:1
• The interaction increases
as the pulses starts
overlap
• At large overlap the
interaction vanishes
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46
Pulse overlapped dispersion
managed Fibers
• Use the non-pulse
interaction regime just at
the transmitter and
receiver
• Move quickly across the
partially overlapped
regime
• Spend most of the time
in /t >10 regime
• Bild 61:2
Department of Information Technology and Media
Electronic Simulation Group
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47
State of The Art
•
•
•
•
320 Gbit/s Transmission over 200 km.
10 GHz Clock Recovery from a 160 Gbit/s stream.
168 Gbit/s Demultiplexing
84 Gbit/s All Optical 3R Regeneration (No clock
recovery)
• 40 Gbit/s All Optical Clock Recovery
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Electronic Simulation Group
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48