WOMBAT 2015 Tutorial
Stimulated Brillouin scattering
Applications:
• Fiber sensing
• Narrow linewidth laser
• Slow light/ delay line
• RF and optical filtering
• Microwave oscillator
• Microwave signal processing
Eggleton et al,. Adv. Opt. Photon 5 (2013)
Cavity optomechanics
Microwave photonic applications of Brillouin
scattering
Applications:
et al,. Sensors 11 (2011)
• Bao
Quantum
optical measurement
• Displacement sensing
• Tunable optical filter
• Slow light/ delay line
• Optomechanical oscillator
Metcalfe, App. Phys. Rev 1 (2014)
Aspelmeyer et al., Rev. Mod Phys. 86 (2014)
Fundamentals of Microwave Photonics
Stimulated Brillouin Scattering
Applications:
• Bandpass and bandstop filters
• Tunable delay lines and phase shifters
• Low noise microwave oscillators
Future of SBS microwave photonics
Microwave photonics
Microwave photonics (MWP): manipulation of RF signals using
photonic techniques/components
Capmany and Novak, Nat. Photon 1 (2007)
Yao, J. Lightwave Technol. 27 (2009)
Seeds and Williams, J. Lightwave Technol.24 (2006)
Marpaung et al., Laser Photon. Rev. 7 (2013)
vs.
• Heavy (copper, 567 kg/km)
• High loss(190 dB/km @ 6 GHz)
• Rigid and large cross section
• Lightweight
• Low loss(0.25 dB/km)
• Very flexible
•
•
•
•
Radio over fiber
Antenna remoting
Ultra-wideband (UWB)
Low phase noise
synthesizer
•
•
Filtering
Phase shifter, tunable delay
•
•
Spectrum analyzer
IFM receiver
E/O conversion
O/E conversion
f=0
f =p
f=0
LS
Optical frequency
Optical frequency
Optical frequency
Intensity modulation (IM)
Phase modulation (PM)
Single sideband (SSB) modulation
f=0
f =Df
Challenges
 E/O and O/E conversion losses
Optical frequency
Complex modulation
 Laser phase and intensity noise (RIN)
 Nonlinear distortion
 Photodetector shot and thermal noise
E/O conversion
O/E conversion
Figures of merit
 Link “gain”  RF to RF loss (typical:-30 dB, good: ~ 0 dB )
 Noise figure  SNR in/SNR out (typical: 30 dB, good: <10 dB)
 Dynamic range  margin of noise and distortion (typical: 80-90 dB, good >110 dB)
Functionalities
• filtering
• delay
• frequency
conversion…
Application
Spectrally crowded environments
• Wireless communications (5G)
• Radar and EW
Functionalities
• filtering
• delay
• frequency
conversion…
Application
Interference mitigation and filtering
Interferer Frequency agile
Tunable MWP interferer
filter
Power
Spectrally crowded environments
• Wireless communications (5G)
• Radar and EW
Solution
Signal
Radio frequency
Functionalities
• filtering
• delay
• frequency
conversion…
Application
Satellite communications
• On-board wifi and live television
Phased array
antenna
Solution
Tunable true time delay
AWG (Purdue)
Silicon modulator, WGs
Optical beamformer (U.Twente & LioniX)
Si3N4 Passive WGs, thermal tuners
Discriminator filters (UPV)
InP WGs, thermal tune, BPD
OEO (OEWaves)
LiNbO3 WGMR, electronics
Marpaung et al, Laser Photonics Rev. 7, No. 4, 506–538 (2013)
Stimulated Brillouin
Scattering
Stimulated Brillouin Scattering (SBS)
• One of the strongest nonlinear optical effects
• Results from a coherent interaction between vibrations and electromagnetic waves
The fundamental physical effects of the interaction are:
Electrostriction:
Electric field causes
material compression
[Light influences sound]
The photo-elastic effect:
Compressive strain
causes change in refractive index
[Sound influences light]
Robert W. Boyd, “Nonlinear Optics”, San Diego, CA: Academic press 2001.
14
Stimulated Brillouin Scattering (SBS)
The main effect of SBS is to resonantly excite an acoustic grating,
which back-reflects the pump at exactly the acoustic frequency W.
Intensity
compresses material
(electrostriction)
Pump 1 w1
Doppler effect:
Pump reflected,
down-shifted to w2
Compression
Excites creates
acousticindex
wavegrating
(photoelasticity)
frequency W
waveguide
Pump 2
w2w=2=w
w1 1- W
Robert W. Boyd, “Nonlinear Optics”, San Diego, CA: Academic press 2001.
Eggleton et al,. Adv. Opt. Photon 5 (2013)
11/12/12
15
W
W
GB
Fast light
Gain (Stokes)
Slow light
wp
w
Loss
(anti-Stokes)
• SBS leads to a narrow Stokes peak in the counter-propagating direction
• The Brillouin shift W is determined by the acoustic wave frequency
• The linewidth is determined by the acoustic lifetime (~ 9 ns for silica)
Typical values (Silica)
W ~ 7-11 GHz
GB ~ 15-50 MHz
• Kramers-Kroenig relation: gain resonance  refractive index change
sharp amplitude and phase (delay) responses
11/12/12
16
First theoretical predictions1,2
First demonstration
of SBS3
SBS in liquids4
On-chip SBS10
SBS in silicon12
SBS in gases5
Invention
of the laser
1920
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
1960
Brillouin, Annals of Physics 17, 88, (1922)
Mandelstahm, Rus. J. Phys. Chem (1926)
Chiao et al. Phys. Rev. Letters 12, 592 (1964).
Brewer et al. Phys. Rev. Letters 13, 334 (1964).
Hagenlocker et al. Appl. Phys. Letters 7, 236 (1965)
Ippen et al. Appl. Phys. Lett. 21, 539 (1972)
Hill et al., App. Phys. Lett, 28 (1976)
Dainese et al. Nature Physics 2, 388 (2006)
Grudinin et al. Phys. Rev. Lett. 102, (2009)
Pant et al. Opt. Exp. 19, 8285 (2011)
SBS
Lee et al. Nat. Photon. 6, 369 (2012)
Shin et al. Nature Comm. 4, (2013).
in optical fibres6
1970
First Brillouin laser7
1980
2000
SBS in PCF8
2010
Year of
discovery
SBS in WGM SBS in wedge
resonators9
resonators11
SBS on chip-scale devices
High-Q resonators
Eggleton et al,. Adv. Opt. Photon 5 (2013)
Waveguides with large Brillouin gain
On-chip SBS is challenging because the waveguides are very short.
The gain is
g0 = Brillouin gain coefficient
Pp = Pump power
Leff = Waveguide length
Aeff = optical mode area
How to get enough gain in a chip scale device?
1) Material with high refractive index
cladding
2) Small mode area
3) Low loss optical waveguides
4) Good opto-acoustic overlap
Guiding/confinement of acoustic mode 
Determined by acoustic velocity in materials
Pant et al., Opt. Express 19 (2011)
Poulton et al. JOSA B 30 (2013)
y
x
z
Core
Chalcogenide waveguide:
7 cm
•
High index material As2S3 (n~2.45, g0~n8)
•
Small mode area (Aeff ~ 2.3 µm2)
•
Low propagation loss (~0.2 dB/cm)
•
Large overlap of acoustic and optical modes
Eggleton et al., Nature Photonics, (2011)
vIPG ~ 1500 m/s
vchalc ~ 2600 m/s
vsilica ~ 6000 m/s
Key parameters:
•
g0 ~0.74*10-9 m/W (~100 x silica)
•
W ~ 7.7 GHz
•
GB ~ 34 MHz
•
16 dB gain for 300 mW pump
Pant et al., Opt. Express 19 (2011)
• Silicon has high refractive index
• But no acoustic confinement in Si core
• Phonon lifetime is very short for small
waveguides
SOI waveguide
(n =3.48)
Si
(n =1.45) SiO2
(va ~ 8000 m/s)
(va ~ 6000 m/s)
Poulton et al. JOSA B 30 (2013)
Phonon leakage
• Si3N4 membrane for
acoustic confinement
• Forward SBS
• Low gain ( <1 dB)
• Breakthrough in SBS on chip
• Under etched silicon
• Forward SBS with ~4 dB of gain
Shin et al, Nature Communications. 4 (2013)
Application: filtering
Loss
RF out
Power
Gain
On chip SBS bandpass filter
RF Frequency
Probe
Pump
SBS
medium
Phase
modulator
RF in
•
•
•
2-12 GHz tuning
20 dB extinction
SBS gain
20-40 MHz tunable bandwidth
Df = ±p
f=0
Byrnes et al., Opt. Express
20,frequency
(2012)
Optical
> 50 dB
extinction
6 MHz
3-dB width
11/12/12 Pagani and Shania., (unpublished)
Zhang et al., IEEE Photon. Tech. Lett. 23 (2011)
22
•
•
•
Broad reconfigurable bandwidth
(tens of MHz-to GHz)
Flat passband
Sharp and high extinction
•
Stern et al., Photon. Res. 2 (2014)
11/12/12
Polarization pulling to enhance
filter suppression
• Pump sweeping for broad SBS
• Result : 44 dB selectivity, 250
MHz -1 GHz tunable bandwidth
• 3 dB passband flatness
23
• Electrical comb for SBS pump
• Digital feedback for shape control
• Non-uniform pump spacing to mitigate
FWM  improve flatness
• Dual fiber stage to limit SRS and
FWM  improve selectivity
• 50 MHz to 4 GHz tunable bandwidth
• > 40 dB suppression up to 2 GHz width
• ~ 1 dB passband flatness
• Improve SNR
Wei et al., Opt. Express 22 (2014)
Wei11/12/12
et al., IEEE Photon. Tech. Lett.. 27 (2015)
24
Loss
RF out
Notch
Power
Gain
RF Frequency
Probe
SSB
modulator
Pump
SBS
medium
RF in
SBS loss (anti-Stokes)
Optical frequency
• 2-8 GHz tuning
• 20 dB extinction
• 120 MHz 3-dB width (FWHM)
• High pump power (350 mW)
Morrison et al., Opt. Comm. 313 (2014)
11/12/12
25
Notch
attenuation
3-dB
Bandwidth
Desired properties
• High peak attenuation (>50 dB)
• High resolution (FWHM ~ 10 MHz)
• Large frequency tuning (tens GHz)
• Bandwidth reconfigurability
State-of-the-art RF filter
RF Frequency
IMWP filter
•
•
•
•
SOI ring
Rejection 30 dB
FWHM 910 MHz
Tuning 12 GHz
M. Rasras, J. Lightwave Technol. (2009)
• Attenuation >50 dB
• Bandwidth ~ 10 MHz
• Tuning: 3-4 GHz
B. Kim, IEEE Trans. Elect. Dev. (2013)
Input
RF signal
Output
RF signal
Power
Power
Novel MWP filter
RF frequency
Notch
RF Frequency
Laser
f=0
LS
EO
modulator
f =Df
Df = ±p
LS
US
Optical frequency
Amplitude matching
SBS gain
filter
Photodetector
f=0
US
Optical frequency
Phase cancellation
Phase and amplitude control
Filter response
Phase and amplitude filter
Conventional
Conventional SSB
SSB
G
G=
=1
1 dB
dB
Rejection:
Rejection: 1
1 dB
dB
Novel filter
G = 0.8 dB
Rejection: 55 dB
Pump = 8 mW
D. Marpaung et al, Postdeadline paper Frontiers in Optics 2013 FW6B
Conventional SSB
G = 20 dB
Rejection: 20 dB
Pump = 350 mW
2900% fractional tuning
Q= 375
at 30 GHz
D. Marpaung et al., Optica, 2, 76-83 (2015)
Conventional filter
D. Marpaung et al., Optica, 2, 76-83 (2015)
Cancellation filter
Application: delay and phase shift
Extreme broadening: 25 GHz
bandwidth slow light
Ultra-long delay: High gain SBS
10.9 ps
delay
Song et al., Opt. Lett. 32 (2007)
On chip SBS slow light
Song et al., Opt. Lett. 30 (2005)
Analog applications
230 ps delay 1 GHz bandwidth
Pant et al., Opt. Lett. 37 (2012)
Zadok et al., IEEE Photon. Tech Lett. 19 (2007)
Problem:
require tunable large delays (~ns), large bandwidths
• Applications
(~GHz), high carrier frequency (microwave, mm-wave)
it is difficult to achieve a (1) tunable, (2) large slope (3) wide band
• But…
linear phase response
 (w)
Real phase
response
“True-time-delay”
bandwidth
Ideal phase
response
Actual phase
Desired phase
wc
Burla et al., Opt. Express 19(22) (2011)
wc wc
w
w
ww
w
c 
c 
RFRF
c 
RFw
w
•
•
•
100 MHz delay bandwidth
0.03 ns to 9.9 ns tunable delay
300o carrier phase tuning
Chin et al., Opt. Express 18 (2010)
Carrier
Sideband
𝜔𝑐 − 𝜔𝑅𝐹
SBS pump
spectrum:
Ω𝐵
𝜔
𝜔𝑐
Ω𝐵
RF frequency
cancelrange (360o)
•Amplitudes
Full tuning
𝜔
𝑝1
• 3 dB 𝜔
amplitude
fluctuations
• Bandwidth limited to 2WB
Phase
𝜔𝑝2
RF frequency
response
Magnitude
Optical signal
spectrum:
SBS phase
shift:
Loayssa
Lahoz,
Phases&add
upIEEE Photon. Tech Lett. 18 (2006)
𝜔
RF frequency
•
•
•
Two degrees of freedom: amplitude
and phase
Ultra-wideband operation: 1 – 31 GHz
Record-low amplitude fluctuations
(< 0.5 dB)
Pagani, et al., Opt. Lett., 39 (2014)
Application: signal generation
•
•
•
•
Silica on silicon wedge resonator
Q = 875 million
FSR matched to SBS shift
Narrow linewdith SBS laser
H. Lee, et al., Nat. Photon, 6 (2012)
•
•
•
1st and 3rd Stokes beating to generate
microwave frequency (~ 21 GHz)
Electronic frequency division to
achieve lower frequencies
Low phase noise, comparable to
commercial RF synthesizers
J. Li, et al., Nat. Commun. (2013)
Future direction
Computer-controlled smart RF filter
with high performance
1-30 GHz continuous
frequency tuning
tuning
Tunable notch extinction
Tunable filter resolution
Tunable bandpass
Marpaung et al., “Nonlinear integrated microwave photonics”,
Journal of Lightwave Technol. 32 (invited, 2014)
• AOM operating at 10 GHz
• Reconfigurable filtering (?)
• Link and interaction with SBS
•
•
Potential for wider comb (?)
Miniaturizing high quality light
and RF source
Microwave photonics
• Manipulation of RF signals using photonic techniques
• Promise: reduced footprint and weight, wide bandwidth
• Challenge: conversion losses, noise, distortion
SBS applications in MWP
• Tunable filtering with performance unmatched by any
technology
• RF phase shifter with record-low amplitude fluctuation
• RF synthesizer with low phase noise
What the future holds:
• High SBS gain in CMOS compatible chip
• Functional SBS circuit (modulator, detectors, SBS engine)
• Chip scale optical and RF sources
Alvaro Casas-Bedoya, Amol Choudhary, Irina Kabakova, David Marpaung, Birgit Stiller, and
Benjamin J. Eggleton
University of Sydney
Duk-Yong Choi, Steve J. Madden, Barry Luther-Davies
Australian National University
Christopher G. Poulton, Christian Wolff
University of Technology Sydney (UTS)
Main contributors
Mattia Pagani
Blair Morrison
Shayan Shania
Hengyun Jiang
Iman Aryanfar
Thank you