WOMBAT 2015 Tutorial

Aspelmeyer et al., Rev. Mod Phys. 86 (2014)

Cavity optomechanics

Eggleton et al,. Adv. Opt. Photon 5 (2013)

Stimulated Brillouin scattering Applications:

• Fiber sensing

• Narrow linewidth laser

• Slow light/ delay line

• RF and optical filtering

• Microwave oscillator

• Microwave signal processing

Applications:

• Quantum optical measurement

• Displacement sensing

• Tunable optical filter

• Slow light/ delay line

• Optomechanical oscillator

Microwave photonic applications of Brillouin scattering

Bao et al,. Sensors 11 (2011) Metcalfe, App. Phys. Rev 1 (2014)

Fundamentals of Microwave Photonics

Stimulated Brillouin Scattering

• Bandpass and bandstop filters

• Tunable delay lines and phase shifters

• Low noise microwave oscillators

Applications:

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)

Seeds and Williams, J. Lightwave Technol.24 (2006)

Yao, J. Lightwave Technol. 27 (2009)

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

• Filtering

• Phase shifter, tunable delay

• Ultra-wideband (UWB)

• Low phase noise

synthesizer

• Spectrum analyzer

• IFM receiver

Optical frequency

Intensity modulation (IM)

Optical frequency

Phase modulation (PM)

f = 0 f =p

LS

Optical frequency

Single sideband (SSB) modulation

f = 0

E/O conversion

Optical frequency

Complex modulation

f = 0 f =Df

E/O and O/E conversion losses

Laser phase and intensity noise (RIN)

Nonlinear distortion

Photodetector shot and thermal noise

Challenges

O/E conversion

E/O conversion O/E conversion

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)

Figures of merit

Functionalities • filtering • delay • frequency conversion…

Spectrally crowded environments

• Wireless communications (5G)

• Radar and EW

Application

Functionalities • filtering • delay • frequency conversion…

Interference mitigation and filtering

Frequency agile

interferer

Radio frequency

Po

wer

Signal

Interferer Tunable MWP

filter

Spectrally crowded environments

• Wireless communications (5G)

• Radar and EW

Application Solution

Functionalities • filtering • delay • frequency conversion…

Satellite communications

• On-board wifi and live television

Application

Phased array

antenna

Solution

Tunable true time delay

Optical beamformer (U.Twente & LioniX)

Si3N4 Passive WGs, thermal tuners

Discriminator filters (UPV)

InP WGs, thermal tune, BPD

AWG (Purdue)

Silicon modulator, WGs

OEO (OEWaves)

LiNbO3 WGMR, electronics

Marpaung et al, Laser Photonics Rev. 7, No. 4, 506–538 (2013)

Stimulated Brillouin

Scattering

14

• 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

The photo-elastic effect:

Compressive strain

causes change in refractive index

[Light influences sound] [Sound influences light]

Robert W. Boyd, “Nonlinear Optics”, San Diego, CA: Academic press 2001.

Stimulated Brillouin Scattering (SBS)

11/12/12 15

Pump 1 w1

Eggleton et al,. Adv. Opt. Photon 5 (2013)

Robert W. Boyd, “Nonlinear Optics”, San Diego, CA: Academic press 2001.

Intensity

compresses material

(electrostriction)

Pump 2

w2=w1

Compression creates index grating

(photoelasticity) Excites acoustic wave

frequency W

Pump 2

w2 = w1 - W Doppler effect:

Pump reflected,

down-shifted to w2

waveguide

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.

11/12/12 16

• SBS leads to a narrow Stokes peak in the counter-propagating direction

w wp

W

Gain (Stokes)

Loss

(anti-Stokes)

W

Slow light

Fast light

W ~ 7-11 GHz

GB ~ 15-50 MHz Typical values (Silica)

GB

• The linewidth is determined by the acoustic lifetime (~ 9 ns for silica)

• The Brillouin shift W is determined by the acoustic wave frequency

• Kramers-Kroenig relation: gain resonance refractive index change

sharp amplitude and phase (delay) responses

High-Q resonators Waveguides with large Brillouin gain

1. Brillouin, Annals of Physics 17, 88, (1922)

2. Mandelstahm, Rus. J. Phys. Chem (1926)

3. Chiao et al. Phys. Rev. Letters 12, 592 (1964).

4. Brewer et al. Phys. Rev. Letters 13, 334 (1964).

5. Hagenlocker et al. Appl. Phys. Letters 7, 236 (1965)

6. Ippen et al. Appl. Phys. Lett. 21, 539 (1972)

7. Hill et al., App. Phys. Lett, 28 (1976)

8. Dainese et al. Nature Physics 2, 388 (2006)

9. Grudinin et al. Phys. Rev. Lett. 102, (2009)

10. Pant et al. Opt. Exp. 19, 8285 (2011)

11. Lee et al. Nat. Photon. 6, 369 (2012)

12. Shin et al. Nature Comm. 4, (2013).

SBS in optical fibres6

SBS in silicon12

SBS in WGM

resonators9 SBS in wedge

resonators11

On-chip SBS10

First theoretical predictions1,2

First Brillouin laser7

First demonstration

of SBS3

SBS in liquids4

SBS in PCF8

Year of

discovery

Invention

of the laser

SBS in gases5

1920 2000 2010 1970 1980 1960

SBS on chip-scale devices

Eggleton et al,. Adv. Opt. Photon 5 (2013)

How to get enough gain in a chip scale device?

On-chip SBS is challenging because the waveguides are very short.

g0 = Brillouin gain coefficient

Pp = Pump power

Leff = Waveguide length

Aeff = optical mode area

The gain is

1) Material with high refractive index

2) Small mode area

4) Good opto-acoustic overlap

3) Low loss optical waveguides

cladding

Core

x

y

z

Guiding/confinement of acoustic mode

Determined by acoustic velocity in materials

Poulton et al. JOSA B 30 (2013)

Pant et al., Opt. Express 19 (2011)

vIPG ~ 1500 m/s

vchalc ~ 2600 m/s

vsilica ~ 6000 m/s

7 cm

Chalcogenide waveguide:

• 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)

Key parameters:

• GB ~ 34 MHz

• g0 ~0.74*10-9 m/W (~100 x silica)

• W ~ 7.7 GHz

• 16 dB gain for 300 mW pump

Pant et al., Opt. Express 19 (2011)

(va ~ 8000 m/s)

(va ~ 6000 m/s)

(n =3.48)

(n =1.45)

Phonon leakage

Si

SiO2

SOI waveguide • Silicon has high refractive index

• But no acoustic confinement in Si core

• Phonon lifetime is very short for small

waveguides Poulton et al. JOSA B 30 (2013)

Shin et al, Nature Communications. 4 (2013)

• 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

Application: filtering

11/12/12 22

Probe

RF out

Po

wer

RF Frequency

f = 0 Df = ±p

Optical frequency

SBS gain

Phase

modulator

RF in

Pump

Gain Loss

SBS

medium

Zhang et al., IEEE Photon. Tech. Lett. 23 (2011)

6 MHz

3-dB width

Pagani and Shania., (unpublished)

> 50 dB

extinction

On chip SBS bandpass filter

• 2-12 GHz tuning

• 20 dB extinction

• 20-40 MHz tunable bandwidth

Byrnes et al., Opt. Express 20, (2012)

11/12/12 23

Stern et al., Photon. Res. 2 (2014)

• Broad reconfigurable bandwidth

(tens of MHz-to GHz)

• Flat passband

• Sharp and high extinction

• 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

11/12/12 24 Wei et al., IEEE Photon. Tech. Lett.. 27 (2015)

• 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

Wei et al., Opt. Express 22 (2014)

• 50 MHz to 4 GHz tunable bandwidth

• > 40 dB suppression up to 2 GHz width

• ~ 1 dB passband flatness

• Improve SNR

11/12/12 25

Probe

RF out

SSB

modulator

RF in

Pump

Gain Loss

Optical frequency

SBS loss (anti-Stokes)

Po

wer

RF Frequency

Notch

Morrison et al., Opt. Comm. 313 (2014)

SBS

medium

• 2-8 GHz tuning

• 20 dB extinction

• 120 MHz 3-dB width (FWHM)

• High pump power (350 mW)

RF Frequency

3-dB

Bandwidth

No

tch

att

en

uati

on

Desired properties

• High peak attenuation (>50 dB)

• High resolution (FWHM ~ 10 MHz)

• Large frequency tuning (tens GHz)

• Bandwidth reconfigurability

• Attenuation >50 dB

• Bandwidth ~ 10 MHz

• Tuning: 3-4 GHz

State-of-the-art RF filter

B. Kim, IEEE Trans. Elect. Dev. (2013)

• SOI ring

• Rejection 30 dB

• FWHM 910 MHz

• Tuning 12 GHz

IMWP filter

M. Rasras, J. Lightwave Technol. (2009)

EO

modulator

SBS gain

filter Laser Photodetector

Input

RF signal

Po

wer

RF frequency

Output

RF signal

Po

wer

RF Frequency

Novel MWP filter Notch

LS US

Optical frequency

Phase and amplitude control

f = 0 f =Df

US LS

f = 0 Df = ±p

Phase and amplitude filter

Optical frequency Amplitude matching Phase cancellation Filter response

G = 1 dB

Rejection: 1 dB

Conventional SSB

G = 1 dB

Rejection: 1 dB

Conventional SSB

G = 20 dB

Rejection: 20 dB

Pump = 350 mW

Conventional SSB

G = 1 dB

Rejection: 1 dB

Conventional SSB

G = 20 dB

Rejection: 20 dB

Pump = 350 mW

Conventional SSB

G = 0.8 dB

Rejection: 55 dB

Pump = 8 mW

Novel filter

D. Marpaung et al, Postdeadline paper Frontiers in Optics 2013 FW6B

D. Marpaung et al., Optica, 2, 76-83 (2015)

2900% fractional tuning

Q= 375

at 30 GHz

D. Marpaung et al., Optica, 2, 76-83 (2015)

Conventional filter Cancellation filter

Application: delay and phase shift

Zadok et al., IEEE Photon. Tech Lett. 19 (2007)

230 ps delay 1 GHz bandwidth

Analog applications

Extreme broadening: 25 GHz

bandwidth slow light

10.9 ps

delay

Song et al., Opt. Lett. 32 (2007)

Song et al., Opt. Lett. 30 (2005)

Ultra-long delay: High gain SBS

Pant et al., Opt. Lett. 37 (2012)

On chip SBS slow light

Problem:

• Applications require tunable large delays (~ns), large bandwidths

(~GHz), high carrier frequency (microwave, mm-wave)

• But… it is difficult to achieve a (1) tunable, (2) large slope (3) wide band

linear phase response

)(w

w

Ideal phase

response

Real phase

response

“True-time-delay”

bandwidth

cw

RFc ww cw

RFc ww cw

RFc ww

Desired phase

Actual phase

Burla et al., Opt. Express 19(22) (2011)

Chin et al., Opt. Express 18 (2010)

• 100 MHz delay bandwidth

• 0.03 ns to 9.9 ns tunable delay

• 300o carrier phase tuning

Ca

rrie

r

Sid

eba

nd

Optical signal

spectrum:

SBS pump

spectrum:

𝜔𝑐 − 𝜔𝑅𝐹 𝜔𝑐 𝜔

𝜔 𝜔𝑝1

Ω𝐵

𝜔𝑝2

Ω𝐵

𝜔

SBS phase

shift:

Amplitudes cancel

Phases add up

RF frequency

Mag

nitud

e

RF frequency

response

RF frequency

Ph

ase

• Full tuning range (360o)

• 3 dB amplitude fluctuations

• Bandwidth limited to 2WB

Loayssa & Lahoz, IEEE Photon. Tech Lett. 18 (2006)

Pagani, et al., Opt. Lett., 39 (2014)

• Two degrees of freedom: amplitude

and phase

• Ultra-wideband operation: 1 – 31 GHz

• Record-low amplitude fluctuations

(< 0.5 dB)

Application: signal generation

H. Lee, et al., Nat. Photon, 6 (2012)

J. Li, et al., Nat. Commun. (2013)

• 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

• Silica on silicon wedge resonator

• Q = 875 million

• FSR matched to SBS shift

• Narrow linewdith SBS laser

Future direction

Computer-controlled smart RF filter

with high performance

1-30 GHz continuous tuning

Tunable filter resolution

Tunable bandpass

Tunable notch extinction

1-30 GHz frequency tuning

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

Christopher G. Poulton, Christian Wolff

University of Technology Sydney (UTS)

Duk-Yong Choi, Steve J. Madden, Barry Luther-Davies

Australian National University

Alvaro Casas-Bedoya, Amol Choudhary, Irina Kabakova, David Marpaung, Birgit Stiller, and

Benjamin J. Eggleton

University of Sydney

Main contributors

Mattia Pagani

Blair Morrison

Shayan Shania

Hengyun Jiang

Iman Aryanfar

Thank you