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Microwave Photonics
Jianping Yao
Microwave Photonics Research Laboratory
School of Information Technology and EngineeringUniversity of Ottawa
Outline
Introduction to Microwave Photonics
Bragg gratings for Microwave Photonics applications
Optically controlled phased array antennas
All-optical microwave signal processing
Photonic generation of microwave, mm-wave and THz
Radio over fiber and UWB (Ultra-WideBand) over fiber
Photonics ADC
Conclusions
OThH1.pdf
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978-1-55752-855-1/08/$25.00 2008 IEEE
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Microwave photonics is an interdisciplinary area that studies the
interaction between microwave and optical signals for microwaveand millimeter-wave signal generation, distribution, controland
processingby means of photonics.
The broadband and low loss capability of photonics (optical fiber)
has led to great interest in their use to generate, distribute, control
and process microwave and millimeter-wave signals. Application
areas include
Optically controlled phased array antennas
All-optical processing of microwave signals (filtering, mixing, etc)
Low phase-noise microwave, mm-wave and THz generation Radio over fiber and UWB over fiber
Photonic ADC
Introduction to Microwave Photonics
Outline
Introduction to Microwave Photonics
Bragg gratings for Microwave Photonics applications
Optically controlled phased array antennas
All-optical microwave signal processing
Photonic generation of microwave, mm-wave and THz
Radio over fiber and UWB (ultra-wideband) over fiber
Photonics ADC
Conclusions
OThH1.pdf
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Fiber Bragg gratings for Microwave-Photonics
Applications
oeffn =2
0
Fiber Bragg gratings forMicrowave-Photonics Applications
1
5
4
3
2
TLS PC EOM
RF
PD
12
3
TLS PC EOM
RF
PD
51
1 ~
5
0
Uniform Fiber ragg Grating
2 eff on =
Chirped fiber grating based delay line
Uniform fiber grating based delay line
mi
n ma
x
mi
n ma
x
Chirped Fiber ragg Grating
mi2 =effn max2 =effn
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Outline
Introduction to Microwave Photonics Bragg gratings for Microwave Photonics applications
Optically controlled phased array antennas
All-optical microwave signal processing
Photonic generation of microwave, mm-wave and THz
Radio over fiber and UWB (ultra-wideband) over fiber
Photonics ADC
Conclusions
Phased-Array Antenna using True Time Delay (TTD)
Phased Array Antenna System based on phase shifters
Phased Array Antenna System based on TTD
2
3
4
2
3
4
0
30
6090
120
150
180
-30
-60-90
-120
-
150
1800
30
6090
120
150
-30
-60-90
-120
-150
Example of
beam squintwith electrical
phase shift
technique
Example of beam
squint-free pattern with
true-time delay
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Optically Controlled Phased Array Beamforming
Difficulty: to write the FBGs with very small spacing, especially for the first delay line.
4
3
1
TLS - tunable laser source, PC - polarization controller, EOM -electrooptic
modulator, FBG - fiber Bragg grating, PD - photodetector
H. Zmuda, R. A. Soref, P. Payson, S. Johns, and E. N. Toughlian, Photonic beamformer for phased array
antennas using a fiber grating prism, IEEE Photon. Technol. Lett., vol. 9, pp. 241243, Feb. 1997.
Wideband true-time-delay unit for phased arrayantenna using discrete-chirped fiber Bragg grating prism
The beam-pointing direction is determined by the grating
spacing difference and is independent of the microwave
frequency.
Y. Liu, J. P. Yao and J. Yang, "Wideband true-time-delay unit for phased array antenna using discrete-chirped
fiber Bragg grating prism," Optics Communications, vol. 207, pp. 177-187, June 2002.
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Y. Liu and J. P. Yao "Wideband true time-delay beamformer employing a tunable chirped fiber grating prism," OSA Applied Optics,
vol. 42, no. 13, pp. 2273-2277, May 2003.
Wideband true time-delay beamformer
employing a tunable chirped fiber grating prism
y = -13.714x + 21297
R2= 0.999
y = -18.801x + 29198
R2= 0.9989
y = -24.052x + 37347
R2= 0.9956
y = -29.417x + 45682
R2= 0.9961
-150
-100
-50
0
50
100
150
1548 1550 1552 1554 1556 1558
Wavele ngth (nm)
Timedelay(ps)
Experimental time delay measurements of the tunable fiber
grating delay lines at the microwave frequency of 10 GHz.Experimental setup of the tunable chirped fiber grating prism
beamformer for a 4-element wideband phased array antenna system.
Y. Liu, J. P. Yao, X. Dong and J. Yang, "Tunable chirpingof a fibre Bragg grating without center wavelength shift
using simply supported beam," Optical Engineering vol.
41, pp. 740 - 741, April 2002.
The difficulty in implementing this system is the fabrication of the 4chirped gratings. The chirped gratings were fabricated using our
grating tuning techniques: chirped gratings can be obtained from
uniform gratings.
J. P. Yao, J. Yang and Y. Liu, "Continuous true-time-delay beamforming employing a multiwavelength tunable fiber laser
source," IEEE Photonics Technology Letters, vol. 14, no.5, pp. 687 -689, May 2002.
Continuous true-time-delay beamformingemploying a multiwavelength tunable fiber laser source
Tunable TTD beamformer configuration
Multiwavelength spacing tuning
Multiwavelength spacing tunable laser
Time delays versus increased
wavelength spacing.
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Y. Liu, J. Yang and J. P. Yao, "Continuous true-time-delay beamforming for phased array antenna using a tunable chirped fiber
grating delay line," IEEE Photonics Technology Letters, vol. 14, no. 8, pp. 1172 -1174, August 2002.
Continuous true-time-delay beamforming for phased array
antenna using a tunable chirped fiber grating delay line
Time delay response when the
chirped FBG is tunedTunable TTD beamformer configuration
Applications
1. Radar 2. Broadband wireless access networks
BS
Radio over fiber system
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Outline
Introduction to Microwave Photonics Bragg gratings for Microwave Photonics applications
Optically controlled phased array antennas
All-optical microwave signal processing
Photonic generation of microwave, mm-wave and THz
Radio over fiber and UWB (ultra-wideband) over fiber
Photonics ADC
Conclusions
All-Optical Microwave Signal Processing
Digital signal processing - speed is limited.
Advantages of all-optical microwave filters:
Wideband
Low loss
Light weight
Immune to electromagnetic interference (EMI)
Finite Impulse Response (FIR) Filter Optical Delay Line FIR Filter
][][][][][1
0
nxnhknxkhnyN
k
==
=
8 GHz 16 GHz2 GHz
-10 dB
-50 dB
-40 dB
-30 dB
-20 dB
Frequency response of an all-optical
microwave filter
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Optical Delay Line Microwave Filter
Limitation of an Optical Delay Line FIR Filter
Incoherent detection All-positive coefficients Low-pass filters only
Fr
equency
Response
(dB)
Fr
equency
Response
(dB)
4-tap Lowpass Filter with
All-positive Coefficients [1 1 1 1]4-tap Bandpass Filter with
Negative Coefficients [1 -1 1 -1]
Optical Delay Line Microwave Filter
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BroadbandOptical
Source
Modulator
RF
T
R1 R2 R3 R4 Rn
1 2 3 4 n
OutputPD
Optical
Source
Modulator
RF Input RF Output
b1
b0
T-
1x2Coupler
Photonic microwave filter using a FBG-based tapped delay line.
1.S. Sales, J. Capmany, J. Marti, and D. Pastor, Experimental demonstration of fiber-optic delay line filters with
negative coefficients, Electron. Lett., vol. 31, pp. 1095-1096, Jul. 1995.
Photonic microwave filter with negative coefficients using differential detection
Optical Delay Line Microwave Filter
J. Capmany, D. Pastor, A. Martinez, B. Ortega, and S. Sales,
Microwave photonics filter with negative coefficients based on
phase inversion in an electro-optic modulator, Opt. Lett., vol. 28,
pp. 1415-1417, Aug. 2003.
Optical Microwave Filter: differential detection
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All-optical microwave bandpass filter with negativecoefficients based on PM-IM conversion
LD 1
LD 2
EOPM
RFInput
PD
RFOutput
2x1Coupler
AWG
LCFBG 1 (-)
LCFBG 2 (+)
F. Zeng, J. Wang, and J. P. Yao, "All-opticalmicrowave bandpass filter with negative
coefficients based on a phase modulator and
linearly chirped fiber Bragg gratings," Opt. Lett.,
vol. 30, no. 17, pp. 2203-2205, Sep. 2005.
J. Wang, F. Zeng, and J. P. Yao, "All-optical
microwave bandpass filter with negativecoefficients based on PM-IM conversion," IEEE
Photon. Technol. Lett., vol. 17, no.10, pp. 2176-
2178, Oct. 2005.
Group
Delay
Group
Delay
0
DC
t
t
0
After
Photodetector
Directly detected by a photodetector
After
Dispersive Device
0
+0
0
t
Amplitude
0>
=
D
010
GHz) periodic sequence of optical pulses with timing jitter
significantly below that of electronic circuitry.
2. The sampling process can be made to be highly linear with
negligible back-coupling between optical sampling pulsesand the electrical signal being sampled.
R S
( )x t
( )Sx nT ( )Sq nT
( )SnT
An Electrooptic Analog-to-Digital Converter
The first photonic ADC was proposed in 1975 by Taylor using Mach-
Zehnder interferometer
H. F. Taylor, An electrooptic analog-to-digital converter, Proc. IEEE. vol. 63, no. 10, pp. 1524-1525, Oct. 1975.
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Advantages:
1. Linear in complexity:
each additional bit of
resolution requires anaddition MZ
interferometer.
2. Decoupling of the
analog sampled signal
from the optical
sampling signal.
Drawback:
A limitation of this
approach is that each
additional bit of
resolution
requires a doubling of
the length of the MZmodulator.
A photonic ADC scheme using Mach-Zehndermodulators with identical half-wave voltages
A 4-channel ADC using four MZMs with identical half-
wave voltages.
111
0
110
0
1000
000
0
000
1
0011
011
1
111
1
1110
intensity(au)
comparator
output
quantized
s()
The operation of the 4-channel photonic ADC. (a) The transfer
functions of the four MZMs; (b) The linear binary code at the
outputs of the comparators; (c) Quantized value (solid) v.s. theinput phase modulation (dotted).
Experimental results. (a) The measured 8 waveformscorresponding to 8 bias phase shifts; (b) The digitized signal
(solid) and the fitted sinusoidal signal (dashed).
H. Chi and J. P. Yao, A photonic analog-to-digital
conversion scheme using Mach-Zehnder modulators with
identical half-wave voltages, Optics Express, submitted.
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Conclusions
Microwave photonics has compelling benefits for many current
applications (mm-wave and THz generation, broadbandtunable signal processors, etc).
Microwave photonics has great potential for next generation
broadband wireless access networks.
Transparent to the modulation format
Microwave photonics will also find important applications in
wireless sensor networks (transmission of sensing data for
environmental, medical, traffic surveillance, defense and
homeland security applications)
Acknowledgements Students and post-doctoral fellows in the Microwave
Photonics Research Laboratory, University of Ottawa
NSERC
Canada Foundation for Innovation (CFI)
Ontario Innovation Trust (OIT)
National Capital Institute for Telecommunications (NCIT)
Canadian Institute for Photonics Innovation (CIPI)
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