Download - Filtros fotónicos de radiofrecuencia
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Departamento de Comunicaciones
Curso de Doctorado
2004-2005
Aplicaciones de la Fotnica de
Microondas
Filtros fotnicos de radiofrecuencia
basados en dispositivos avanzados
Contents
Fundamental concepts
Filters operation
Implementations:
A little history
Filters based on a single source
Filters based on multiwavelength narrow sources
Filters based on broadband sources
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Fundamental Concepts
=
=
=M
r
r
r
N
k
k
k
zb
zazH
1
0
1
)(
Transfer functions for RF fi lters
Filter
=
=N
k
kTtkhnh0
)(][)(
h[2]
0 2 3
h[0]h[1]h[3]
h[N]Time Impulse
a) If N is finite: Finite Impulse Response (FIR) filter =
=N
k
k
kzazH0
)(
b) If N is infinite: Infinite Impulse Response (IIR) filter
=
=N
r
Tjr
reaH0
)(
=
=N
r
r rTtath0
)()(
Tz =1
Filter Frequency Response
Fundamental ConceptsTransfer functions for RF filters
The filter transfer function is always periodic in the frequency domain
0 1 2 3 4 5 6-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
FSR
f(Ghz)fr1 fr2
fr0
-3dB
f
MSSR
FSR [Hz]: Free Spectral Range or Spectral period FSR=1/f [Hz]: 3 dB Resonance bandwidth (same for all resonance orders)Q factor: Quality factor Q=frk/f (depends on the resonance)F: Finesse: F=FSR/f (indepndent of the resonance)MSSR [dB]: Main to secondary sidelobe ratio
Resonance
order 0Resonance
order 1
Resonance
order 2
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Fundamental Concepts
Transfer functions for RF fi lters
modulator
InputRF Signal
CW laserSource
T
2T
NT
ao1/2
aN1/2
a21/2
Input electric field
Output electric field
receiver
Output RF Signal
Delay line weight
Opticalsignaltapping
element
Opticalsignalcombining
element
( )tsi
( ) ( )[ ] ( ) ( )( )rTtrTtwjir
erTtsatE + = 0
21
0
( )[ ] ( )( )ttwji
oets +21
( ) ( ) ( ) == rTtsatEts ir2
00
Signal taps
Optical delay lines
Optical weights
Signal combination
(couplers, stars, etc.)
General Layout
Source coherence
Polarization
Positive coefficients
Limited Spectral period or FSR (Free Spectral Range)
Noise
Reconfigurability
Tunability
Practical realization of RF filters
Fundamental Concepts
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Fundamental ConceptsRequired photonics components
1) Optical signal tapping: Lasers, sliced broadband
sources, FBGs
2) Optical signal weighting:
3) Optical delay lines:
4) Optical signal combiners and switches
EDFAs, SOAs, EOMs, EAMs,
VCs, VOAS
Standard and HD fiber coils, LC-FBGs
Fundamental Concepts
Example: 3 tap transversal filter using fiber Coil delay lines
CW
optical
source1x3
T
2T
ao
a1
a2
3x1
=
=2
0
)()(r
r rTtxaty
Possible
optical
interference
(coherence)
RF signal
RF modulated
optical signalDelayed &Weighted
optical signals
Delayed &Weighted
RF signals
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CW
optical
source
CW
optical
source
CW
optical
source
RF signal
Dispersiveelement
to
to+T
to+2T
PossibleOptical
interference
(coherence )
Delayed &Weighted
optical signals
T
=
=2
0
)()(r
r rTtxaty
Delayed &Weighted
RF signalsPo
P1
P2Weighted
Optical
signals
Fundamental Concepts
Example: 3 tap transversal filter using Dispersive Delay Line
Filter Operation
The possibility to tune the RF bandpass position in a
sufficiently fast way either discretely or continuously
To tune the RF response of the filter, the FSR has to be
modified and therefore also the basic time delay T between
samples or taps.
Filter Tunability
0 1 2 3 4 5 6-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
FSR2
f(Ghz)fr1fr0
FSR1
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Filter Operation
A number of techniques to produce true time delays T
have been proposed:
Switched propagation paths (switched delay lines): Different
paths providing different basic propagation delays (that is
different values of T) can be chosen by means of an optical
space switch. It allows only step by step tunability, with the
tuning speed being limited by the switching time (1-10ms).
Wavelength tuning of one or multiple sources combined with
dispersive optical devices: based on tuneable sources anddispersive devices (Standard Fibre, High dispersive (dispersion
compensating) fibre, Linearly Chirped Fibre Bragg Gratings
(LCFBG)).Can provide continuous or step tunability at high
speed, limited by the tuning speed of the sources (depending on
the tuneable source technology from 100ns to >100ms).
Filter Tunability
A number of techniques to produce true time
delays T have been proposed:
Fixed wavelength multiple sources or sliced broad-
band sources combined with tuneable dispersive
devices: Based on novel devices and tuneabledispersion properties as Special Chirped FBGs with
actuators to change their dispersion properties. It can
provide continuous and step tunability but in this case
the time and accuracy to perform a dispersion change
on the fibre device is not so well controlled (100 ms-
1s).
Filter Operation
Filter Tunability
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Brings the possibility of changing dynamically the values
of the filter taps (ak, br coefficients) to reshape its
spectral response:
The windowing / weighting or apodisation of the
amplitude of the filter taps is also a fundamental aspect
to ensure enough rejection of the avoided bands.
Different apodisation functions have been demonstrated
for MSLR improvement:
By adjusting the power of the optical sources
By controlling the attenuation/gain suffered by the taps when
they travel though the optical processor
Filter Operation
Filter Reconfigurability
Implementations: a little historyFiber optic delay lines for microwave signal processing
Optical fiber as a delay medium for signal processing applications was proposed by Wilner
and van den Heuvel (1976).
Ohlhaber and Wilner (1977) reported an experimental demonstration of an optical fiber
transversal filter based on three multimode fiber delay paths to generate and correlate a 4-
bit, 88-Mb/s coded sequence.
An optical fiber frequency filter was demonstrated by Chang, Cassaboom, and Taylor
(1977), who illuminated a bundle of fifteen multimode fibers that provided fifteen different
delays spaced by 5.2 ns yielding a filter with a transfer function having a fundamentalpassband at 193 MHz.
Optical fiber as a delay medium for signal processing applications was proposed by Wilner
and van den Heuvel (1976).
Ohlhaber and Wilner (1977) reported an experimental demonstration of an optical fiber
transversal filter based on three multimode fiber delay paths to generate and correlate a 4-
bit, 88-Mb/s coded sequence.
An optical fiber frequency filter was demonstrated by Chang, Cassaboom, and Taylor
(1977), who illuminated a bundle of fifteen multimode fibers that provided fifteen different
delays spaced by 5.2 ns yielding a filter with a transfer function having a fundamentalpassband at 193 MHz.
K.P.Jackson et al., IEEE Trans. MTT, 33, pp. 193-210 (1985)
Implementation of single-mode fiber delay-line networks capable of synthesizing many
sophisticated time- and frequency-domain filtering operations (tapping mechanisms, basic
signal processing, etc.)
Implementation of single-mode fiber delay-line networks capable of synthesizing many
sophisticated time- and frequency-domain filtering operations (tapping mechanisms, basic
signal processing, etc.)
FSR=740 MHz
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A lit tle history
Wavelength tunable
fiber laser3 dB
coupler
Digitizing
oscilloscope
Signal
generatorDetector
1 m 1 m 1 m 1 m 1 m
G1 G6G2 G3 G4 G5
Ball et al, PTL pp.741-743 (1994)
Fiber-grating-based optical processors
50 ns true time delay in discrete 10 ns intervals
Grating spacing set to yield the desired delay
50 ns true time delay in discrete 10 ns intervals
Grating spacing set to yield the desired delay
LiNO3Modulator
Implementations
Laser
Polarization
controller
couplerTemperature
controller
Chirped fibre
gratingOptical receiver
MZ-EOM
Fibre delay line
Network analyser
Tunable RF transversal filters by using chirped FBGs
Zhang et al.,EL, pp. 1770-1772 (1998)
Linear and continuous tuning.
The time delay introduced by the grating is wavelength dependent.
Linear and continuous tuning.
The time delay introduced by the grating is wavelength dependent.
Filters based on a single source
Implementations
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Tunable laser
LCA OC
1x8
splitter
attenuator
4
1 4
...
1 4
l1 l4
Tunable bandpass transversal filters
Zhang et al.,EL, pp.
1708-1710 (2000)
Changing the wavelength of the tunable laser selects operating gratings
Each grating array gives a filtering frequency
Possibility of designing the filter response (Hamming window)
A Mach-Zehnder section doubles the number of taps (so does Q factor)
Changing the wavelength of the tunable laser selects operating gratings
Each grating array gives a filtering frequency
Possibility of designing the filter response (Hamming window)
A Mach-Zehnder section doubles the number of taps (so does Q factor)
Filters based on a single source
Implementations
Laser Recirculatingdelay line
Polarization
controller
MZ EOM
Optical Power
Meter
LCA
1
42 3
1
32
4
RF
Notch filter by using an optical fiber recirculating line
Zhang et al., IEEE MWCL, pp. 217-219 (2001)
The frequency response is controlled by the coupling coefficient of the
coupler and the length of the recirculating loop.
The fiber grating array enables to get a tunable FSR.
Continuous tunability can be achieved by using a chirped fiber grating
The frequency response is controlled by the coupling coefficient of the
coupler and the length of the recirculating loop.
The fiber grating array enables to get a tunable FSR.
Continuous tunability can be achieved by using a chirped fiber grating
IIR (Infinite Impulse Response filters)
Filters based on a single source
Implementations
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Filters based on multiwavelength narrow sources
Tunable source 3
Tunable source 4
DFB laser Vectorial
Network
Analyser
5x1Coupler
2x2Coupler
Fiber Grating
Adapted
Terminals
Electro-Optical
Modulator
Tunable source 1
Tunable source 2
Sample amplitudes are controlled by
laser output powers (reconfigurability)
The basic delay T is set by the spectral separation ofadjacent wavelengths. Thus T can be changed(tunability)
The linear chirp provides avariable delay with wavelength:
Each sample is carried using adifferent wavelength (=0.533nm)
1547 1548 1549 1550 1551-40
-30
-20
-10
0
0
1
2
3
4
Reflectivity(dB)
GroupDelay(ns)
N 2k
Wavelength (nm)
01
Tunable and reconfigurable filter based on a laser array and a LCFBG
0 1 2 3 4 5 6-5 0
-4 5
-4 0
-3 5
-3 0
-2 5
-2 0
-1 5
-1 0
-5
0
Frequency (GHz)
Modulus(dB)
Experimental resultTheoretical result
2.125 GHz
12dB
D. Pastor, J. Capmany and B. Ortega, OFC99 (1999)
Implementations
APODISATION
By the proper weighting of the tap
contributions controlling the output power
of the lasers in the array, the secondary to
main lobe ratio can be increased.
The figure shows a Gaussian apodisationas (0.5 0.8 1 0.8 0.5) that reduces the main
to secondary sidelobe ratio up to -20 dB.
APODISATION
By the proper weighting of the tap
contributions controlling the output power
of the lasers in the array, the secondary tomain lobe ratio can be increased.
The figure shows a Gaussian apodisationas (0.5 0.8 1 0.8 0.5) that reduces the main
to secondary sidelobe ratio up to -20 dB.
Filters based on multiwavelength narrow sourcesTunable and reconfigurable filter based on a laser array and a LCFBG
RECONFIGURABILITY
0 1 2 3 4 5 6-60
-50
-40
-30
-20
-10
0
0 1 2 3 4 6-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
Frequency (GHz)
Modulus(dB)
Experimental resultTheoretical result
Frequency (GHz)
Modulus(dB)
4 Taps 3 Taps
Laser 5 is switched off Laser 1 and 5 are switched off
By switching off one
or more lasers.
Bandpass positions
are maintained.
0-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
1 1.5 2 2.5 3 3.5 40.50.5 3.5
Frequency (GHz)
Modulus(dB)
No apodisedtaps
Gaussian Apodised tapsTheoretical apodised filter
Implementations
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By adjusting of spectral spacing between sources to 0.266 nm (half of theprevious) the resonance separation increases up to 4.25GHz.
The figure shows results extended up to 10 GHz, and the CSE is observed. Thefirst notch is at 8.5 GHz for the dispersion parameter of the grating.
By adjusting of spectral spacing between sources to 0.266 nm (half of theprevious) the resonance separation increases up to 4.25GHz.
The figure shows results extended up to 10 GHz, and the CSE is observed. The
first notch is at 8.5 GHz for the dispersion parameter of the grating.
Carrier Suppression
Effect
The third main lobe is
just cancelled with this
particular parameters.
0 2 4 6 8 10-4 5
-4 0
-3 5
-3 0
-2 5
-2 0
-1 5
-1 0
-5
0
Frequency (GHz)
Modulus(dB)
Experimental result
Theoretical result
4.25 GHz
To overcome the CSE SSB
modulation was employed and
operation up to 20GHz with 3
taps was demonstrated.
To overcome the CSE SSB
modulation was employed and
operation up to 20GHz with 3
taps was demonstrated.
Filters based on multiwavelength narrow sourcesTunable and reconfigurable filter based on a laser array and a LCFBG
TUNABILITY
D. Pastor and J. Capmany, EL 34, pp 1684-1685 (1998)
Implementations
MAGNETIC TUNABLE
CHIRP DEVICE
Multiwavelengthsource
EOMCirculator
Uniform FBG
Network
Analyser
I
3A 0.39nm 916ps/nm
5A 0.56nm 475ps/nm
Curren t Bandwid th Delay s lope
Filters based on multiwavelength narrow sourcesMultiwavelength source with tunable chirped grating
-25
-20
-15
-10
-5
0
REFLECTIVITY(dB)
1 54 4. 4 1 54 4.7 15 45. 0 1 54 5. 3 1 54 5. 6
0
125
250
375
500
DELAYTIME(ps)
WAVELENGTH (nm)
0 2 4 6 80
20
4060
80
100
5 A
3 A
AXIAL DISTANCE (cm)
Coil
Uniform Bragg Grating Magnetostrictive
Rod
MAGNETIC FIELD -25
-20
-15
-10
-5
0
REFLECTIVITY(dB)
-25
-20
-15
-10
-5
0
REFLECTIVITY(dB)
0 3 6 9 12 15
-25
-20
-15
-10
-5
0
REFLECTIVITY(dB)
FREQUENCY (GHz)
6.36GHz
8.14GHz
9.39GHz
0 A
2 A
4 ACONTINUOUSTUNABILITY
CONTINUOUS
TUNABILITY
Implementations
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(b)
MultiwavelengthSource EOM
z axis
Coils
TFBG
RF input
(a)
Out toLCA (bar)
Out toLCA(cross)
I1
LCA
I2Y-junction Coupler
Optical
switch
z axis
1542 1543 1544 1545
-40
-30
-20
-10
(nm)
Reflectivity(dBm)
0.2
0.4
0.6
0.8
Group
DelayTime(ns)
(a)
MagneticField
0 1 2 3 4
4
6
8
10
12
14
FSR(
GHz)
I (A)
1543 15440.0
0.5
1.0 BS
CS(ns)
(nm)
0 2 4 6 8 10
-30
-20
-10
0 (b)
H(
dB)
f (GHz)
-30
-20
-10
0 (a)
H(
dB)
SWITCHED DELAY LINESWITCHED DELAY LINESWITCHED DELAY LINE
LARGER
TUNABILITY
LARGER
TUNABILITY
Filters based on multiwavelength narrow sourcesMultiwavelength source with tunable chirped grating
(ps/nm) 0 A 2 A 4 A
BAR 351 297 230
CROSS 715 580 420
(ps/nm) 0 A 2 A 4 A
BA R 351 297 230
CROSS 715 580 420J. Mora et al., EL, 39, p. 1799-1800 (2003)
Implementations
Filters based on multiwavelength narrow sourcesCurrent Injection in multimode lasers
Fabry- Perot
Lasernear
the threshold
current
Isolator
EOM EDFA
Dispersiveelement.
46 km SSMF
Receiver
RF Network
AnalyserIbias Input
1540 1542 1544 1546 1548 1550 1552 1554 15560
20
40
60
80
100
120
140
Wavelength (nm)
LinearArbitraryUnits
A Fabry-Perot laser was employed toprovide a CW multi-wavelength source
The entire optical signal is RF modulated
and applied to a dispersive media (46 km
SSMF).
The bias current of the FP laser was
controlled near the threshold to providedifferent weighing profiles and thereforealso different MSLR and 3dB BW values.
Increasing the
Bias current
D.Pastor, et al. IEEE Photon. Tech. Lett., vol. 13, pp. 1224-1226, (2001)
0 1 2 3 4 5 6-3 5
-3 0
-2 5
-2 0
-1 5
-1 0
-5
0
Frecuency (GHz)
|H(f)|dB
Frequency (GHz)
Implementations
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Filters based on broadband sourcesBragg grating based acousto-optic superlattice modulator
(a)
0 1 2 3 4 5 60.0
0.5
1.0
1.5
Wavelength
shift(nm)
fs(MHz)
0,0 0,5 1,0 1,5 2,0
0,00
0,25
0,50
0,75
1,00
Reflectivity(dB)
PS(mW)
(b)
1542 1543 1544-70
-60
-50
-40
R(
dB)
(nm)
-70
-60
-50
-40
R(
dB)
0 5 10 15 20
-45
-30
-15
0
|H|2
(dB)
f (GHz)
-45
-30
-15
0
|H|2
(dB)
The interaction between a longitudinal acoustic
wave and a strong FBG can generate a fiberBragg grating array suitable for RF applications.
Tunability and reconfigurability of the device are
demonstrated.
The interaction between a longitudinal acousticwave and a strong FBG can generate a fiberBragg grating array suitable for RF applications.
Tunability and reconfigurability of the device are
demonstrated.
EOM
Tap
Power
Wavelength
Broadband
Source
90/10
Coupler
10
90
Wavelength
Group
Delay
Time
Tapping
Element
OSA
LCA
fiber
length
Optical
Power
Wavelength
Broadband
Source
Horn
Transducer
RF supply-2 -1 0 1 2-20
-10
0
Reflectivity(dB)
-B/
-20
-10
0
Reflectivity(dB) (a)
(b)
Tapered
fiber
FBG
Circulator
M.Delgado-Pinar et al., MWP04
Implementations
Multitap filter using in-fiber Bragg grating arrays
Spectral slicing of a broadband source
Bragg gratings equispaced in time
Possibility of designing the filter response (Kaiser window)
Spectral slicing of a broadband source
Bragg gratings equispaced in time
Possibility of designing the filter response (Kaiser window)
Hunter et al.,IEEE MGWL, pp. 103-105 (1996)
Grating sets3 dB couplerElectro-optic
modulator
Network analyser and
display
RF oscillator
1480nm
pump
diode
IsolatorWDM
15m Erbium
doped fiber
Photodetector
Filters based on broadband sources
Implementations
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Filters based on broadband sourcesLED sliced by tunable gratings
Electro-optic modulatorOSAOSA
23 kmfiber
SLED
1L2
EDFAEDFA
LCALCA
UFBGs
90-10 Coupler
RF signal
Mechanical stageReflected signals
2
3
0
glue
1545 15460.0
0.5
1.0
R(a.u.)
(nm)
( ) NeinitN
LLpN
= 1
,LNN
NLLN
=
0 50 100 150
1545
1546
1547
1548
1549 3
2
1
0
N(nm)
L (m)
0.0 0.5 1.0 1.5 2.0 2.50
1
2
3
4
5
6
FSR(GHz)
-1(nm-1)
J. Mora et al., Opt. Express10, 1291-1298 (2002).
Implementations
Mechanical stage
0
L2
UFBGs4x4 coupler
AT
Variable
attenuator
3
2
1
From LED
Reflected signals
To modulator
glue
-3 -2 -1 0 1 2 3-30
-25
-20
-15
-10
-5
P(a.u.)
P(a.u.)
MSLR(dB)
AT
(dB)
-3 0
-2 0
-1 0
0
H(dB)
-3 0
-2 0
-1 0
0
H(dB)
0 2 4 6 8 1 0
-3 0
-2 0
-1 0
0
f (GHz)
H(dB)
(a)
(b)
(c)
Sidelobe Supressed Filters
Filters based on broadband sourcesLED sliced by tunable gratings
Implementations
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D. Pastor et al, Opt. Lett. 2003, 28, pp. 18021804.
SLED
EDFA
1X40
AWG
1X40
AWG EOM
Network
Analyser
SOA 23 kmSSMF
1 540 1 54 5 1 55 0 1 55 5 15 60 1 56 5-40
-38
-36
-34
-32
-30
-28
-26
-24
-22
-20
Wavelength(nm)
Amplitude(dB)
Array of:
SwitchesVariable
attenuators.
Broadband Source sliced by AWGs Two Combined BB sources arespectrally sliced by means of a pair of
Arrayed Waveguide Gratings (AWGs)
AWG are standard ITU for DWDMapplic (0.8 nm channel spacing and
0.4nm channel BW)
Switches and/or Variable attenuatorsbetween AWGs provides weighing andtuneability features.
A dispersive media (SSMF) is used to
imprint the proper time delay to eachslice (sample) after the modulation of
the RF signal over the entire spectrum
at the EOM
12 slices (channels)
spaced 2 x 0.8 nm = 1.6 nmUniform weighing
Dispersive Med: 400ps/nm
RF response: FSR=1.56 GHz3dB B W=125 MHz
MSLR=15 dB0 2 4 6 8 10-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (GHz)
Amplitude(dB)
1 .1 1 .2 1 .3 1 .4 1 .5 1 .6 1 .7 1 .8 1 .9 2
-30
-25
-20
-15
-10
-5
0
Frequency(GHz)
Amplitude(dB)
0 Hz lobe out
of measure
>130MHz
Filters based on broadband sources
Implementations
1 2 3 4 5 6 7 8 9 10-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (GHz)
Amplitude(dB)
1540 1550 1560Wavelength(nm)
1 2 3 4 5 6 7 8 9 10-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (GHz)
Amplitude(dB)
1540 1545 1550 1555 1560 1565Wavelength(nm)
24 slices (channels)spaced 0.8 nm
Uniform weighing (aprox)
Dispersive Med: 400ps/nmRF response: FSR=3.1 GHz
3dB BW=125 MHz (aprox)
MSLR=14 dB
6 slices (channels)
spaced 4 x 0.8 nm = 3.2 nmApodized samples
Dispersive Med: 400ps/nmRF response: FSR= 780 MHz
3dB B W=200 MHzMSLR=15 dB (with half samples
as previous)
Examples of Tuneability and Apodization
Filters based on broadband sources
Broadband Source sliced by AWGs
Implementations
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Practical Limits
Intrinsic to the Slicing approach:1. Spectral power inefficiency if the ratio
SliceBW / SliceSpacing is low or/and theBandwidth of the BB source is larger than
slices range.2. RF decaying envelope due to the low pass
filtering effect produced by the Slicebandwidth and the dispersive media.
We can appreciate in the simulation as the
product (GVD) determinates the 3dBbandwidth of the decaying slope in RF
domain.
(1) and (2) move in opposite directions
Extrinsic to the Slicing approach:
1. Precise amplitude control of each tap was
difficult due to the PDL of the AWG and EOM(mainliy the EOM) devices in combination witha polarized source like it was the SLED.
Filters based on broadband sourcesBroadband Source sliced by AWGs
Implementations
A single bandpass RF filter based on a MZI illuminated with a
broadband source.
A tuning range of several tens of GHz is achieved by changing
the optical paths of the MZI and the dispersion.
The bandwidth of the RF filter is kept constant along the RF
range, when the dispersion in the system is invariant.
Potential high Q values can be achieved by choosing the
appropriate broadband source.
A single bandpass RF filter based on a MZI illuminated with a
broadband source.
A tuning range of several tens of GHz is achieved by changing
the optical paths of the MZI and the dispersion.
The bandwidth of the RF filter is kept constant along the RF
range, when the dispersion in the system is invariant.
Potential high Q values can be achieved by choosing the
appropriate broadband source.
Filters based on broadband sourcesBroadband source sliced by a MZI
J. Mora et al., Intl. Topical Meeting on MWP, pp. 251-254 (2003).
Implementations
-
8/13/2019 Filtros fotnicos de radiofrecuencia
17/17
EDFA 1
1
FABRY-PEROTFILTER
Electro-Optical
Modulator70 km SSMF
EDFA 2
vectorial
networkanalyser
0 1 2 3 4 5 6-60
-50
-40
-30
-20
-10
0
Frequency (GHz)
NormalisedModulus
ofH(f),dB
1526 1528 1530 1532 1534 1536 15380
20
40
60
80
1526 1528 1530 1532 1534 1536 15380
0.5
1
)(nm
)(nm
Normalised
Weights
OpticalPower
(arbitrarynaturalunits) (a)
(b)
(a)-(b)
A fibre based Fabry-Perot filter of 35 GHz
of FSR and high Finesse was employed toslice the 1530 nm peak of ASE noise from
an EDFA. Almost 35 naturally aposized resonances(samples) can be distinguished over the
noise floor at the receiver input.
3dB BW=250MHz
>35dB
J. Capmany, et. al. Electron. Lett., pp. 494-496, (1999).
Filters based on broadband sourcesBroadband source sliced by Fabry-Perot
Implementations