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Clocks, Combs and OAWG
MIT Optics and Quantum Electronics
Erich P. Ippen
Massachusetts Institute of TechnologyCambridge, MA 02139
NEOSASeptember 15, 2011
Outline
MIT Optics and Quantum Electronics
Femtosecond lasers – few cycle pulses
Carrier envelope phase control
Optical frequency combs
Arbitrary optical waveforms
Applications
Clocks
Precision sampling and timing
The 5-fs Ti:sapphire Laser
Kerr lens modelocking (KLM)Double-chirped mirrorsAll-solid state, prismless cavity
MIT Optics and Quantum Electronics
5 fs = less than 2 cyclesOctave-spanning spectrum
Under Each Pulse is a Short Waveform
2nGL/c
The electric field waveform slips under the envelope from pulse to pulse – if group delay and phase delay differ.
MIT Optics and Quantum Electronics
Carrier-envelope phase slip
-80
-70
-60
-50
-40
-30
-20
RF
po
we
r sp
ect
rum
(d
Bm
)
200150100500
Frequency (MHz)
RBW: 100 kHz
fCE fR - fCE
BBO
570 nmfilter
PBS
RFspectrumanalyzer
PMT
Second harmonic generation
Control Over the Optical Phase
Carrier-envelope phase stabilization
An optical clockwork !
MIT Optics and Quantum Electronics
The optical frequency is an exact multiple of the pulse rep-rate.
A Clock
an oscillator a clockwork
Pendulum - Christiaan Huygens 1656
Chronometer - John Harrison (H4) 1761 (10-6 ~ 1 sec/ 9 days )
Quartz - W. Marrison, Bell Labs, 1928 (10-8 ~ 1 sec/3yrs )
Cesium atom - 1955 (10-10 ~ 1sec/300yrs)
Hg ion – 5x10-18 ~ 10sec since big bang
Atomic fountain - NIST-F1 (1.7x10-15 ~ 1sec/20Myrs)
and
MIT Optics and Quantum Electronics
From the 9.192 GHz Cs frequency standard to the 456 THz (657nm) Ca transition
Clockwork by Frequency Multiplication
1999
10-14 accuracy
MIT Optics and Quantum Electronics
10 lasers8 phase-lock loops
The Clockwork in the Frequency Domain
2 1 1g g
1mc mc f f f
2n L 2 L2f
n
MIT Optics and Quantum Electronics
d
dt
lasermodes
exactmultiples
of frep
1f 2f
repg
cf2n L
12f
2nd harmonics
f
1f-to-2f frequency locking
Octave-spanning frequency comb
This locks the rep rate to the optical frequency. Still need an optical reference.
Locking to the 3.39m HeNe Reference via DFG
g
c2n L m
g
mcf
2n L
He-Ne/CH4
Laser
3.39m
TransportableStability ~ 10-14
Difference frequency generation in PPLN
1f 2fDFG
2 1 rep reff f mf f
refref
c 3.39 mf
MIT Optics and Quantum Electronics
A Portable Optical Frequency Reference
Monolithic“sitall / zerodur”
resonator
• Compact• Ultrastable (< 10-14)• Transportable
Phase- locked He-Ne laser
3.39 m output
MIT Optics and Quantum Electronics
Mikhail Gubin, Lebedev Institute
Methane-stabilized He-Ne Laser: = 3.39m
L
1GHz Ti:sapphire Laser Frequency Comb
MIT Optics and Quantum Electronics
CEO locked
Frequency referenced
• 1f-to-2f in LBO
• CH4- stabilized HeNe
Optical Arbitrary Waveform Generation(OAWG)
MIT Optics and Quantum Electronics
Amplitudes and phases of all these frequencies are now determined. How about:
Completely Arbitrary Waveforms
G
ncf
2n L
G
mcf
2n L
G
cf
2n L
Fast modulator array
Spectrum lockedto “absolute” grid
Arbitraryelectrical field
waveform !
MIT Optics and Quantum Electronics
Pulse-to-pulseAM & PM
f
t
Arbitraryspectrum
Optical Arbitrary Waveform Generation
Sufficiently complicated temporally varying spectral phase masks create encoded optical signals.
Dispersion matchedgrating-lens pairs
Grating-lens pairs withphased mask inserted
The basic idea (Heritage and Weiner)
• A grating disperses the broad spectrum of an ultrashort pulse.• A phase and amplitude mask is inserted into the Fourier plane.• A second grating recombines the modified spectrum into a “shaped” waveform.
The advanced integrated version (UC Davis)
AWG1 AWG2
Phase modulators
IN OUT
Bond pads
Delay lines
AWG1 AWG2
Phase modulators
IN OUT
Bond pads
Delay lines
Modulatorarray
ArrayedWaveguide
Grating
In current technology, a small band of frequencies passes through each modulator element.
MIT Optics and Quantum Electronics
InP Encoder: 10channel
14.2 mm
MIT Optics and Quantum Electronics
UC DavisS.J. Ben Yoo et al.
Time (20ps/div)Time (20ps/div)
Trial output waveforms
10.7
mm
PMAM
Packaged InP OAWG(10 Ch AM+ 10 Ch PM) x 10 GHz
MIT Optics and Quantum Electronics
InPhi & UC Davis
1.5cm DCM11G
1% Inverse Gain OCDCM11G
1.5cm DCM11G
2.28mm Ti:Sa
5.5 GHz
1.5cm DCM11G
1% Inverse Gain OCDCM11G
1.5cm DCM11G 2.28mm Ti:Sa
3.3 GHz
10 GHz0.75cm
DCM11G
1% Inverse Gain OCDCM11G
0.75cm DCM11G
2.28mm Ti:Sa
Route to 10 GHz
• Precise dispersion compensation • Gain flattening• Optimized output mirror•Tight focusing; low loss
MIT Optics and Quantum Electronics
Mode Matching
Optics
Balanced Detector
Brewster Plate
PBS
λ/4
4%BS
Loop Filter
Piezo Driver
Output10xf
Piezo
ML Laser
LaserRep Rate: f
Super-invar
Hänsch-Couillaudlocking method
• F = 156 => 30dB sidemode suppression• F = 2100 => 55 dB sidemode suppression
J. Chen et al. Opt.Lett.32, 1556, 2007
MIT Optics and Quantum Electronics
Alternate Route: 10 x Rep-Rate Multiplication by Filtering
-70
-60
-50
-40
-30
-20
RF
Spectr
a (
dB
m)
1086420
10x F = 2100
MIT Optics and Quantum Electronics Group
+d1
+d2
frep
2frep
2frep
4frep
Interleaver 1
frequency comb
f
f
f
tTR
t
t
frep
pulse train
4frepTR/4
Interleaver 2
Rep Rate Multiplication withMonolithically Integrated Interleavers
19
2 4 6 8 10
-60
-50
-40
-30
-20
-10
0
Frequency (GHz)
Tra
nsm
issi
on
(d
B)
c=50%idealc = 60%
• Thermal tuning for optimizing• delays• coupling coefficients
• Side-mode suppression limited by• offsets in coupling coefficients• waveguide dispersion
M. Sander et al, CLEO 2011: CThY5
GHz Er:Fiber Laser Technology
MIT Optics and Quantum Electronics
Wider Goal: Two Octaves of Frequency Comb
Ti:sapphire Er/Yb glass/fiber
0.5 m 1.0 m 1.5 m 2.0 m
3.39 m /2
f-to-2f + DFG f-to-2f + DFG
repg
cf 10GHz2n L
• More power per comb line• Facilitates demultiplexing via AWG
HeNe-CH4
3.39mreference for DFG
MIT Optics and Quantum Electronics
22
1-GHz Er-doped Fiber Laser
121x94x33mm3
Poutput = 27.4 mW
Wintracav = 283 pJ
Ppump = 380 mW
967.1 967.7-100
-80
-60
-40
-20
0
frequency (MHz)
a) b)
c) d)
1 2 3 4 5 6 7 8 9 10-70
-60
-50
-40
-30
-20
-10
0
frequency (GHz)
inte
nsi
ty (
dB
m)
1540 1560 1580 16000
0.2
0.4
0.6
0.8
1
wavelength (nm)
inte
nsi
ty (
a.u
.)
17.5nm
sech2 fit
measured
-500 0 5000
2
4
6
8
time delay (fs)
IAC
(a.u
.)
1.54x187fs
187 fs pulses17.5 nm BW
MIT Optics and Quantum Electronics
SBR
Partial Reflector OC 10%
OutputErbium Fiber
(92mm)
FC/PC connector
WDM
977 nm
SMF28e(11mm)
Integrated Femtosecond Waveguide Laser
4 cm 5cm10% out
outputLoop: 16 cmSBRpump
1520 1550 1580
-2000
0
2000
80
90
wavelength (nm)
a)
b)
refle
ctan
ce (
%)
disp
ersi
on (
fs2 )
70
100
4 cm 5cm10% out
outputLoop: 16 cmSBRpump
1520 1550 1580
-2000
0
2000
80
90
wavelength (nm)
a)
b)
refle
ctan
ce (
%)
disp
ersi
on (
fs2 )
70
100
4 cm 5cm
10% outoutputLoop: 16 cmSBRpump
• Integrated gain + dispersion compensation• Integrated pump coupling• Integrated loop mirror/output coupler• Butt-coupled SBR
44x18 mm2
• 400 MHz rep rate• 440 fs pulse duraton
MIT Optics and Quantum Electronics
MIT Optics and Quantum Electronics
• High power femtosecond amplifier• Octave-spanning continuum generation: = 1m - 2 m
1.55 m oscillator1 GHz, 200fs, 20mW
Output100fs2 W
PC
SMFPre-chirp Fiber
HNLFISO
Pre-Amplifier
PC ISO WDM
10W Raman Fiber Laser
LiekkiEr-doped Fiber
SMFPost-chirp
1480nm PUMP
Lens
980 nm
LiekkiEr-doped Fiber
(83 mm)PUMP
ISO
980 nmCollimator
DichroicLens Lens
SBROC(5%)
PZT
AOM
Lens
LoopFilter
~
PD
Amp
BPF
LO
Feedback Control Electronics
DFG
HeNe
SHG(f-2f)
LoopFilter
~
PD
Amp
BPF
LO
Feedback Control Electronics
Positive dispersionhigh power amplifier
1 GHz Er-Fiber Comb
D. Chao et al, to be published
1 GHz Octave-Spanning 1µm-2µm Continuum
MIT Optics and Quantum Electronics
1012nm7.09mW
2024nm65.37mW
1 GHz Source
1 GHz Supercontinuum
1082nm8.56mW
1590nm47.02mW
1f-2fDFG
• High field and coherent control science
• Optical coherence tomography
• Ultrahigh-resolution 3-D LADAR imaging
• Multi-dimensional spectroscopic sensing
• Bistatic LADAR
• Novel coherent optical communications
• Impairment avoidance in fiber communications
Some Applications
MIT Optics and Quantum Electronics
Application: Photonic analog –to- digital conversion
• Amplitude fluctuations of sampling pulse can be cancelled by balanced detection
• Resolution and dynamic range limited by timing jitter
• Modelocked lasers can achieve quantum-limited jitter
High Resolution Optical Sampling
MIT Optics and Quantum Electronics
optical sampling pulseI(t)
voltage waveformV(t)
timing jitter
V(t)
E-O Modulator
• Optical pulses sample analog signal on an electro-optical modulator
voltage waveform
Precision Sampling for ADC
G.C. Valley, Opt.Exp. 15, 1955 (2007)R. H. Walden IEEE J.Sel.Areas in Comm 17, 539 (1999)
ADC limited by timing jitter in sampler
MIT Optics and Quantum Electronics
The Walden Wall
• 4mm x 4mm chip
•20 HIC ring filters with 8 m radius, 20 nm FSR
• SiGe detectors with 2 GHz BW, 100 nW NEP
• Analog Si modulator bandwidth 50 GHz
• Ultra Low-jitter direct optical sampling
Kaertner, Ippen, Hoyt, Smith, Ram, MIT Lincoln Lab
40 Gs/s 8-bit Optical Bit Interleaved ADC
MIT Optics and Quantum Electronics
Synchronization of a Large Scale X-Ray FEL
MIT Optics and Quantum Electronics
Kim et al., MIT/DESY
Acknowledgments
Andrew Benedick
Hyunil Byun
Jeff Chen
David Chao
Jonathan Morse
Michelle Sander
Jason Sickler
Franz Kärtner
MIT Optics and Quantum Electronics
Noah Chang
Jung-Won
Kim
-50 -40 -30 -20 -10 0 10 20 30 40 500
0.5
Frequency (GHz)
Spectral Domain
Inte
nsi
ty
-50 -40 -30 -20 -10 0 10 20 30 40 50
-3
-2
-1
0
1
2
3
ph
ase
(ra
ds)
-100 -80 -60 -40 -20 0 20 40 60 80 1000
2000
4000
6000
8000
10000
12000
time (ps)
Inte
nsi
ty
Comparison of Chirped vs. Unchirped pulse
Chirp
No Chirp
-50 -40 -30 -20 -10 0 10 20 30 40 50
-3
-2
-1
0
1
2
3
Time (ps)
ph
ase
(ra
ds)
temporal phase
-50 -40 -30 -20 -10 0 10 20 30 40 500
500
1000
1500
2000
2500
time (ps)
Time Domain
Inte
nsi
ty
-50 -40 -30 -20 -10 0 10 20 30 40 50-100
-80
-60
-40
-20
0
20
40
60
80
100
Ch
irp
(G
Hz)
exp(-(n/3.5355)8) apodization, 2p radians of phase across spectrum
• 10 x 10GHz (10ps pulses)• Supergaussian amplitude apodized• 2p quadratic phase• Chirp over timeslot - 100GHz/100ps
Linearly Chirped Waveform – 10 Modes
Spectral domain Time domain – chirped pulse
Phase vs. time
Chirp
Amplitude
Initial vs. chirped pulse
MIT Optics and Quantum Electronics
Theory
100 x 10GHz (1ps pulses), Supergaussian amplitude apodized27p quadratic phaseChirp over timeslot - 1THz/100ps
Linearly Chirped Waveform – 100 Modes
-500 -400 -300 -200 -100 0 100 200 300 400 5000
0.5
Frequency (GHz)
Spectral Domain
Inte
nsity
-500 -400 -300 -200 -100 0 100 200 300 400 500
-3
-2
-1
0
1
2
3
phas
e (r
ads)
-100 -80 -60 -40 -20 0 20 40 60 80 1000
2
4
6
8
10
12
14x 10
5
time (ps)
Inte
nsity
Comparison of Chirped vs. Unchirped pulse
Chirp
No Chirp
-50 -40 -30 -20 -10 0 10 20 30 40 50
-3
-2
-1
0
1
2
3
time (ps)
phas
e (r
ads)
temporal phase
-50 -40 -30 -20 -10 0 10 20 30 40 500
5000
10000
15000
time (ps)
Time Domain
Inte
nsity
-50 -40 -30 -20 -10 0 10 20 30 40 50-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Chi
rp (
GH
z)
exp(-(n/1490.712)10) apodization, 27p radians of phase across spectrumSpectral domain Time domain – chirped pulse
Phase vs. time
Chirp
Amplitude
Initial vs. chirped pulse
MIT Optics and Quantum Electronics
Linearly Chirped Waveform 10-Modes
-50 0 500
0.2
0.4
0.6
0.8
1
Inte
nsity
(au
)
-50 0 50-3
-2
-1
0
1
2
3
Time (ps)
Pha
se (
rad)
Blue Curve – Target Intensity Black Curve -- Measured IntensityBlue dots – Target PhaseRed Curve – Measured Phase
Circles – Target Intensity Black Stems -- Measured Intensity Blue X – Target PhaseRed Dots – Measured Phase
-50 0 500
0.2
0.4
0.6
0.8
1
Frequency (GHz)In
tens
ity (
au)
-50 0 50-3
-2
-1
0
1
2
3
Pha
se (
rad)
MIT Optics and Quantum Electronics
Experiment