aplicaciones de la fotónica de microondas 1

8/13/2019 Aplicaciones de la Fotnica de Microondas 1

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Introduction

Departamento de ComunicacionesCurso de Doctorado

2004-2005

Aplicaciones de la Fotnica deMicroondas

Contents

Introduction

Concept of photonic processing of RF signals

Potential applications

Advantages Examples of applications:

Mobile, wireless and RoF

Antenna beamsteering

Radars

Optical prefiltering of SCML


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CURRENT EUROPEAN PROJECTS

IST-2001-37435 Lightwave Architectures forthe Processing of Broadband ElectronicSignals (LABELS)

IST-2001-32786 Network of Excellence on

Broadband Fiber Radio Techniques and its

Integration technologies (NEFERTITI)

Introduction

In RF systems it is interesting to use photonic devices toimplement flexible filters for microwave and radiofrequency(RF) signals free from bandwidth constraints

This involves using photonics technology and devices toperform the required signal processing tasks over RF signals

conveyed by an optical carrier directly in the optical domain. Also there is an increased use of the RF and microwave

spectrum apart from baseband within optical channels inWDM systems and a need to access or process them directlyin the optical domain

Thus there are two main driving application fields

RF systems and applications

Optical Transmission systems and networks


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RF circuit

antenna

Rf input

signalRf output

signal

Optical

CW source

Rf input

signal

Optical Signal

Processormodulator

Optical

Receiver

Rf output

signal

Optical

output

signal

Optical

input

signal

antenna

TRADITIONAL APPROACH

Band limitation

Poor flexibility

EMI

Frequency dependent losses

PHOTONIC SOLUTION

OPRFS (Optical Processing

of RF Signals)

Incoherent regime (tc


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Introduction: What for? (II)Optical Transmission

The concept of photonic processing of RF signals for opticalTransmission systems and networks

To headerprocessingInput multiwavelength

SCM signal

Payload CH#1

Payload CH#N

Header CH#1

Header CH#N

Photonic

Filter

Baseband

Signals

Improve performance of Radio over Fiber systems

Payload and header separation in Label swappingoptical networks

Pilot tone extraction within WDM channels for control,

protection and management purposes Service separation in WDM transmission carrying

multiple RF services within an optical wavelength.

Potential Applications

Introduction: What for? (II)Optical Transmission


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Introduction: Advantages

Optical delay lines have very low loss (independent ofthe RF signal frequency),

ODLs provide very high time bandwidth products

Are immune to electromagnetic interference (EMI).

Lightweight

Can provide very short delays which result in very highspeed sampling frequencies (over 100 GHz in

comparison with a few GHz with the available electronictechnology)

Optics provides the possibility of spatial and wavelengthparallelism using WDM techniques.

Examples of applications

Radio

Microwaves

IREHFSHFUHFVHFHFMFLFVLFELF IR

1 KHz 1 MHz 1 GHz 1 THz

1 m1 km1000 km 1 mm 1 m

KXCSL

Mobile, ROF& Wireless Coms

Satellite

Radar

mm and sub THzImaging and sensing


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Photonic filters can be applied: For channel rejection

For channel selection applications

Directly in the RF domain with no required previousdown-conversion

In the first case, we deal with an optical link where notonly the desired signal is carried by the fiber, but alsounwanted interfering signals that are also picked up by

the antenna. Example: radio astronomy applications the signal transmission

from several stations to a central site requires the removingstrong man-made interfering signals from the astronomy bands.

Noise suppression and channel interference mitigation in thefront-end stage after the receiving antenna of i.e an UMTS basestation prior to a highly selective SAW filter.

Mobile, Wireless & Radio over Fiber Systems

In the second case, the signal carried by the optical linkis composed of a frequency plan that comprises severaldisjoint parts of the RF spectrum (UMTS, HIPERLAN,LMDS) .

A band-pass photonic filter can be employed to select a givenRF band or spectral region

Or for noise suppression and channel interference mitigation.

In both cases the position of the frequency notch or thefilter band-pass can be as low as a few MHZ or as highas several tens of GHz due to the broadbandcharacteristics of photonic delay lines.




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RF Photonics

Notch/bandpass

filter

Downconversion

DSP

Down

conversionADC DSP

ADC

Less stringentrequirements



RF in

FBG 1 FBG N

L 2L 4L

Optical

switchesRFout

DispersiveMedia

SSMF or DCF

8L

EOMSLD

Detector

1540 1545 1550 1555 1560 1565 1570 1575

-35

-30

-25

-20

-15

-10

-5

0

30 UFBG 1nm wavelength spaced

FBG array spectrum ->

MWP tuneable filter for UMTS applications

App licati on: Tunable photonic filter for noise suppression and channel interference mitigation in thefront-end stage of a UMTS base station. The inclusion of such a filter can increase the capacity ofUMTS systems. Objectives: a) High Q factor (select 1 UMTS channel 5MHz at 2 GHz), Tunability,Realizable cost.

Design of UMTS microwave photonic filter:1. Classical FIR transversal but combining some different techniques.2. Spectral slicing of a high power broadband optical source to obtain an equivalent multi-

wavelength source.3. Slicing by an array of fibre Bragg gratings which also introduces a fixed time delay between the

reflected slices.4. Finally, we employ a reconfigurable chain of dispersive modules to introduce tunability.

D. Pastor et al, Electron Lett. vol. 4, no 16, August 2004.

Radio over Fiber Systems



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MWP tuneable filter for UMTS applicationsRequirements: High Q-factor (about 400) & Tunability of the RF passband within the 12 channels

along the 60 MHz band.1. The transversal filter operates at a higher-order resonance of its periodic response. (we employ

the resonances n18 to reduce the required number of samples. The FSR of the filter has beenset to 109 MHz, and the corresponding spacing between the (adjacent) gratings was 930 mm.

2. Other goals: 3 dB bandwidth within 56 MHz, a 1 dB bandwidth larger 3 MHz, and anacceptable sidelobe rejection level (>20 dB). Gaussian apodisation of the taps weights wasemployed, and the total number of FBGs was fixed to 30. The FBG wavelength spacing wasset to 1 nm to allocate properly the FBG along the SLED spectrum (40 nm).

1 . 8 1 . 8 5 1 . 9 1 . 9 5 2 2 . 0 5 2 . 1

x 1 09

-2 0

-1 8

-1 6

-1 4

-1 2

-1 0

-8

-6

-4

-2

0

0 km10.7 km

Frequency (GHz)

(dB)

FSR=1977MHz/18=109MHz

17th 19th18th



1.93 1.94 1.95 1.96 1.97 1.98 1.99

-18

-16

-14

-12-10

-8

-6

-4

-2

0

Frequency(GHz)

0 2 4 6 8 10 121.935

1.94

1.945

1.95

1.955

1.96

1.965

1.97

1.975

1.98x 10

9

Standard Fibre Length (km)

-30

-20

-10

0

1.85 1.90 1.95 2.00 2.05 2.10

f (GHz)

>22dB

RFResonacefrequency

MWP tuneable filter for UMTS applications

Slope of 3.577 MHz / km(i.e. 1.39 km fibre is requiredfor the shift of 5 MHz).

Coverage of the UMTS band v.s. the length of theSMF-28 fibre used as dispersive medium.

1.80 1.85 1.90 1.95 2.00 2.05 2.10 2.15

-40

-30

-20

-10

0

Transferfunction(dB)

dB21MSLR

353Q

MHz6.5f

MHz44.1976f

dB3

o

=

=

=

=

MeasuredSimulated




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Multifrequencysource

1, 2,........NOptical carriers

RF signalgenerator

Amplitude modulatorFiber BraggGrating

1

2

= 2 1

WDM

d1

(1,1)2

(2,2)

(,)i

(i,i)

ArrayAntenna

( ) ( ) ( )[ ]10 = iid

csin

( ) ( )

+

==

sindc

iii

j

eN

i ii

EAF

,1

0

,

( )=

RF


Radiation

pattern

Modulating RF signal: RF Optical carrier: B

Non-uniformFBGLeff

BOptical fiber

B. Ortega et al.,IEEE Trans. onMTT, 48 pp.1352-1360 (2000).


Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(a)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(b)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(c)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(a)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(b)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(c)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(a)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(b)

Intensidad (dB)-40 -30 -20 -10 0-40-30-20-100

ngulo (grados)

-80

-60

-40

-200

20

40

60

80

(c)

0 43.6 80

2 GHz

4 GHz

7 GHz

DSB modulation: 32 elements, d = 21.4 mm (fmax = 7 GHz)

Wideband operation: 2 - 7 GHz

Stable beampointing angle

Spatial range: 0 - 90 with continuous tuning angle

DSB modulation : 32 elements, d = 21.4 mm (fmax = 7 GHz)

Wideband operation: 2 - 7 GHz

Stable beampointing angle

Spatial range: 0 - 90 with continuous tuning angle

SSB modulation : 32 elements, d = 8.3 mm (fmax = 18 GHz)

Larger wideband operation : 4 - 18 GHz (C-X-Ku)

SSB modulation: 32 elements, d = 8.3 mm (fmax = 18 GHz)

Larger wideband operation : 4 - 18 GHz (C-X-Ku)




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Clutter Elimination at RF in MTI Radars

PRF

Landclutter

Landclutter

Target

Seaclutter

Rainclutter

Noise PRI

=1/PRF

Doppler shift=-(2/)(dR/dt)

R(t)=

Ro+d

R/dt(

t-to)

MTI: Moving Target Indicator Radaruses Doppler effect to separate

targets of interest from clutter



Downconversion

A/DDigitalNotchfilter

Filtering of clutter and noise is performed using a digitalnotch filter placed after frequency down-conversion tobase-band and analogue to digital (ADC) conversion.

To distinguish the small echo from the target from largeecho from the fixed objects high performance (14-18 bitresolution) ADCs are required which represents a majorbottleneck in the system



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If the clutter can be removed directly in the opticaldomain by means of a photonic filter, then the highresolution requirements on the ADCs can be relaxed.

For example, with a 30 dB clutter attenuation therequired ADC resolution is reduced by 5bits.

RF Photonics

Notch/bandpass

filter

Downconversion

A/D DSP


Al l-Opt ical Microwave Inter ference Mit igation Fil ter Single Bandpass filter

Port 4

EOM

LCA

Fiber length

RF signal

TunableLaser

Port 1 Port 2

L

PL(-L)

Port 3

1520 1560-80

-60

(a)

S(dBm)

(nm)

1530 1535

-60

-40

(c)

T(dBm)

(nm)

1530 1535

-60

-50

(b)

TSBF

(dBm)

(nm)

BroadbandOptical Source

OSA

OSA

0 5 1 0 1 5 2 00.0

0.5

1.0

1.5

2.0

M u lt i -No tc h

Re g io n

S in g le

Not ch

Re g io n

f3dB

f(GHz)

( n s )

7 8 9

-30

-20

-10

0

10

(a) n = 0

f (GHz)

|H

(dB)|2

7 8 9

(b) n = 22

f (GHz)

7 8 9

-30

-20

-10

0

10

(a) n = 52

|H(d

B)|2

f (GHz)

7 8 9

(b) n = 112

f (GHz)

Notch filters by combining a tunable laser and a broad band source sliced by a Mach-Zehnder interferometer for applications as interference mitigation filters.

Using a single bandpass filter centered at 7.89 GHz with a 3dB bandwidth of 250 MHz,single and multi notch filters have been implemented by tuning the optical wavelength of thetunable laser.

The single and multi-notch regions are given by the bandwidth of the single bandpass filter.

Notch filters by combining a tunable laser and a broad band source sliced by a Mach-Zehnder interferometer for applications as interference mitigation filters.

Using a single bandpass filter centered at 7.89 GHz with a 3dB bandwidth of 250 MHz,single and multi notch filters have been implemented by tuning the optical wavelength of thetunable laser.

The single and multi-notch regions are given by the bandwidth of the single bandpass filter.

f=280MHz f=67MHz

f=30MHz f=15MHz

for RADAR

applications

J.Mora et al.,Intl Topical Meetingon MWP, MC-12, pp.77-80 (2004).



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Optical Prefiltering Using FBGs Rf photonic filters can also be used to extract a microwave

signal carried by an optical channel (wavelength). Thisapplication is known as OPTICAL PREFILTERING

fo fo+fRFfo-fRF

Optical filter

fo fo+fRFfo-fRF

fo


Optical Prefiltering using an Uniform FBG

circulator

Payload

f

label

f

Payload

label

f RF

Through port

OSCM extraction

PortFBG filter

Lee et al IEEE PTL,vol13, pp. 635,2001

Optical Prefiltering Using FBGs



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f

f

Lee et al IEEE PTL,vol13, pp. 635,2001

Channel payload @ 2.5 Gb/sChannel header @ 622 Mb/s anda subcarrier at 14 GHz

Optical channel before the FBG

Optical channel after the FBG

Optical Prefiltering Using FBGs


Optical Prefiltering Using FBGs: IST LABELSexperiment at 10 Gb/s

f

f

622Mbps

10Gbps

fs=18GHz

OSALSA

FBG

Payload @10GbsHeader @622 Mb/s

Optical channel before the FBG

Optical channelafter the FBG

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