Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical...
Transcript of Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical...
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7/30/2019 Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical Frequency Combs from Mode-locked Semiconductor Diode Lasers
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Ultrafast Coherent Optical Signal
Processing using Stabilized OpticalFrequency Combs from Mode-
locked Diode LasersPeter J. Delfyett
CREOL, The College of Optics and Photonics, University of Central Florida, Orlando,Florida 32816-2700
University of California
Santa Barbara, CADecember 5, 2012
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter
Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
Summary and Conclusions
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Ultrawideband Communications
Synthetic Aperture ImagingSensing, Detecting and Response
Applications Enabled By Optical Frequency Combs
Advanced Waveform Generation/Measurement
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Time Interleaved Pulse Trains Time Overlaid Pulse Trains
Interleaved Supermode SpectraOverlaid Supermode Spectra
Power
Time
P
ower
Optical Frequency
Amplitude
Time
Powe
r
Power
Time
Optical Frequency
Ampli
tude
Po
wer Time
ei
ei2
E(-)
E(-2)
E()
2
Power
eit
eit2t
fML
c/L
TC=L/c
c/L
fML
T= 1/fML
A1=1
A2=1
A3=0.5
Harmonic Modelocked LasersSchematic Representations
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0 200 400 600 800 1000 1200
0
50
100
150
200
250Intensity of Optical Pulse Train
Time
Intensity
0 100 200 300 400 500 600 700 800 900 1000
195
200
205
210
215
220
225
230
235
Intensity of Optical Pulse Train
Time
Intens
ity
210 220 230 240 250 260 270 280 290 300 3100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Optical Spectrum of Pulse Train
Frequency
Watts/Hz
20 40 60 80 100 120 140-80
-60
-40
-20
0
20
RF Power Spectrum of Pulse Train
Frequency
dB/Hz
Supermode Noise Spurs
(a)
(c)
(b)
(d)
Optical Pulse Train Intensity
Optical Pulse Train Intensity
Optical Spectrum of Pulse Train RF Power Spectrum of Pulse Train
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Low Noise Modelocked Diode Lasers
ViaStabilization of the Frequency Comb
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Fundamentally Modelocked Lasers
Time
Optical Frequency
fmod=c/L=10 GHz
L
c/L
T=100 ps
~
Powe
r
Pow
er
Log Frequency
RF Power Spectrum
Corner frequency moves to
large offset frequencies w/ short cavities
1 pulse in the cavity
Corner
Frequency
SOA
System Noise Floor
RF Power Spectrum
Frequency
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Harmonically Modelocked Lasers
Time
Optical Frequency
fmod=Nc/L=10 GHz
L
c/L
T=100 ps
~
SOA
Power
Power
Log Frequency
RF Power SpectrumSupermodes
System Noise Floor
Example: Ring Laser
Mode Spacing=10 MHz
fmod= 10 GHz
N=1000
N pulses in the cavity
N Independent longitudinal
mode groups
Coupled Modes
Corner
Frequency
10GHzRF Power Spectrum
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Harmonic Modelocking & Supermode
Suppression
Fmod=nc/L
= 10GHz
L
T=100 psec
~
Time
Optical Frequency
10GHz
T=100 psec
Power
Power
Time
Optical Frequency
10GHz
T=100 psec
Power
Power
SOA
=10GHz
Fmod=nc/L
=10GHz
L
~
SupermodeSuppression Filter
SOA
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0
0.2
0.4
0.6
0.8
1
1.2
0
0.2
0.4
0.6
0.8
1
1.2
Frequency
Transmission
Frequency
Transm
ission
(a)
(b)
Nested Optical Cavities
R1=R2=90%; T1=T2 =10%; FSR2 / FSR1 =8
Cavity Product Identical to R=99%; T=1%
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Harmonically Mode-locked Lasers &
Supermode Suppression
Modulation rate
The etalon free spectral range must match the mode-locking rate.
Laser cavity modes must coincide with etalon transmission peaks.
Mode spacing
Etalon transmission
Laser cavity
10.24 GHz
SOA
IM
PC I
PC
DCF
DC
etalon
PC
PC
DCF
FL
SOA: semiconductor optical amplifier
PC: polarization controller
IM: intensity modulator
I: isolator
DCF: dispersion compensating fiber
FL: fiber launcher
FL
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Setup
SOA
VODOPS
IM
II
PCPC
PC
Output
DC
PC
Free Space
OpticsFPE
PM
Cir
PBS
PID
OPS
PC
PC
PD
640 MHz
Laser Cavity
PDH Loop
I: isolator
SOA: semiconductor optical
amplifier
OPS: Optical phase shifter
PD: photodetector
PC: polarization controller
IM: intensity modulatorPBS: polarization beam splitter
FPE: Fabry-Perot etalon
PID: PID controller
PM: phase modulator
Cir : optical circulator
OPS: Optical Phase Shifter
VOD: Variable Optical DelayDCF: Dispersion Comp. Fiber
PDH: Pound Drever Hall
Ultra-low noise osc.
at 10.287GHz
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Laser is constructed on a optical breadboard and thermally andacoustically isolated with foam insulation.
Actively MLL with intracavity 1000 Finesse
etalon
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The pulses are compressed to 1.1 ps autocorrelation FWHM by using a
dual grating compressor.
Sampling scope and autocorrelation traces
Actively MLL with intracavity 1000 Finesse
etalon
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The 10 dB spectral width of the optical spectrum is ~8.3nm.
The comb line has a ~50dB signal-to-noise ratio
Optical spectrum
Actively MLL with intracavity 1000 Finesse
etalon
High Resolution Comb Line
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Timing jitter and amplitude noise:
Actively MLL with intracavity 1000 Finesse
etalon
Integrated timing jitter (1 Hz100 MHz) is ~3fs
and up to Nyquist it is 14fs.
Integrated amplitude noise (1 Hz100
MHz) is 230ppm.
Note the overall dynamic range of the measurement 1016
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The linewidth of the laser with the 1000 Finesse etalon was measured as ~ 500 Hz
(Note the relative ratio of the carrier frequency to the linewidth ~ 1012)Stability of 150 kHz over 30 sec
(NB: Measurements are limited by the CW laser linewidth & stability)
MLL
CW laser
PC RFSA
OSA
-20 -10 0 10 20-70
-60
-50
-40
-30
-20
-10
0
Amplitude(dBm)
Frequency (GHz)
High Resolution Spectrum Analyzer
CW laser
Stabilized Frequency Comb lines
Optical linewidth/stability measurement.
Actively MLL with intracavity 1000 Finesse
etalon
Stability
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SCOW AmplifierSCOWA Slab-Coupled Optical Waveguide Amplifier
J. J. Plant, et. al. IEEE Phot. Tech. Lett., v. 17, p.735
(2005)
W. Loh, et. al. IEEE J. Quant. Electron., v. 47, p. 66
(2011)
0 5 10 15 20 25 300
3
6
9
12
15
Pout
(dBm)
Gain(dB)
1 A
2 A
3 A
4 A
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Etalon stabilized HMLLExperimental setup
CIR: Circulator
DBM: Double Balanced Mixer
FPE: Fabry-Perot Etalon
ISO: Isolator
LPF: Low-Pass Filter
OC: Output Coupler (Variable)PC: Polarization controller
PD: Photodetector
PID: Proportional-Integral-Differential Controller
PM: Phase Modulator
PS: Phase Shifter
PZT: Piezoelectric Transducer (Fiber Stretcher)
SOA: Semiconductor Optical Amplifier (SCOWA)
VOD: Variable Optical Delay
Pound-Drever-Hall Loop
Optical Path
Electrical Path
SCOWA
IM
PC
PC
ISO ISO
FPE (FSR = 10.287 GHz)
OC
PS
PID
DBM
PD
CIR
LPF
PM
PC
PCPC
10.287 GHz
500 MHz
PC
Laser Output
Ultra-low
noise oscillator
Long fiber cavity provides narrow resonances
Fabry-Prot Etalon provides wide mode spacing
Pound-Drever-Hall loop locks both cavities
An ultra-low noise oscillator is used to drive the laser
VODPZT
I. Ozdur, et. al., PTL, v. 22, pp. 431-433 (2010)
F. Quinlan, et. al., Opt. Express 14, 5346-5355 (2006)
PBS
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-80
-70
-60
-50
-40
-30
-20
Power(dBm)
Frequency (100 MHz/div)
Span: 1 GHz
Res. BW: 1 MHz
~60 dB
High-Resolution Optical SpectrumOptical Spectrum
1544 1546 1548 1550
-70
-60
-50
-40
-30
-20
-10
Power(dBm)
Wavelength (nm)
~60 dB
10.24 10.26 10.28 10.30 10.32-110
-100
-90
-80
-70-60
-50
-40
-30
-20
-10
0
Relative
Power(dB)
Frequency (GHz)
Span: 100 MHz
Res. BW: 3 kHz
Radio-Frequency Spectrum
1 10 100 1k 10k 100k 1M 10M 100M
-170
-160
-150
-140
-130-120
-110
-100
-90
-80
-70Residual Phase Noise
Noise Floor
Poseidon Oscillator Absolute Noise
L(f)(dBc/Hz)
Frequency Offset (Hz)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
IntegratedT
imingJitter(fs)
Single sideband phase noise spectrum
Etalon-
stabilized
laser
(10.287 GHz)
Etalon-
stabilized
laser
(10.285 GHz)Real-time
Spectrum
Analyzer
Real-time spectrogram
Time(35s)
420-2-4
Frequency Offset (MHz)
Optical Frequency Stability
Measurement
Etalon-based Ultralow-noise Frequency
Comb Source
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Oscillator characterization
-40 -30 -20 -10 0 10 20 30 40
0.0
0.5
1.0
Compressed AC
Transform Limited AC
ACTrace(a.u.)
Delay (ps)
p
= 930 fs
10.24 10.26 10.28 10.30 10.32
-100
-80
-60
-40
-20
0
Relative
Power(dB)
Frequency (GHz)
Span: 100 MHz
Res. BW: 3 kHz
Pulses are compressible to close to the transform limit
Photodetected RF tone has >90 dB dynamic range
Intensity Autocorrelation RF Power Spectrum
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AmplificationOutput power and spectral characteristics
-60
-40
-20
-60
-40
-20
1552 1554 1556 1558 1560 1562 1564
-60
-40
-20 I=4A, Pout
=320 mW
I=4A, Pout
=214 mW
Directly from MLL
OpticalPow
er(dBm)
Wavelength (nm)
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1 10 100 1k 10k 100k 1M 10M 100M
-170
-160
-150
-140
-130-120
-110
-100
-90
-80
-70
(iv)
(iii)
(ii)(i) All-anomalous Cav.
(ii) Disp. Comp. Cav.
(iii) All-anomalous and Covega
(iv) Poseidon Oscillator
Noise Floor
L(f)(dB
c/Hz)
Frequency Offset (Hz)
(i)
0
2
4
6
8
10
IntegratedJitter(fs)
and SCOWA
Timing JitterSSB Phase Noise Comparison
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
High Precision Laser Radar w/ Unambiguous Ranging &
Velocimetry
Summary and Conclusions
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General Ideas for OFC Modulation
Desirable Modulator Qualities for real time OFC applications:
Current methods of modulating light intensity:
Direct modulation of diode driving current Frequency chirp
External modulation:
Electro-optic modulators (EOM) Nonlinear modulation transfer function
and Relatively high V
Electro-absorption modulators (EAM) Poor optical power handling,
High insertion loss and Sensitive to temperature and wavelength
Proposed concept for OFC modulation:
Injection locking a resonant cavity w/ gain (VCSEL) arcsine phase modulation
NB: Linear intensity modulator in an interferometric configuration
- Linear modulation transfer function
- Large modulation bandwidth
- Low Insertion Loss (negative..?)
- Low V
- Good power handling capability
- Comb filtering, tunable, arrays
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Injection-Locked Resonant Cavity as an Arcsine Phase
Modulator
1
0
Master laser
1
Slave laser0
Adlers equation*:
= 1
=
2: locking range
*A. E. Siegman, Lasers, 1986
=
Locking range
0
1
R t C it I t f t i M d l t
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V
f(t) ~
/2
Iin
V
T(V)))((sin 1 tf
I0,1 )2
)(1(
tfIIinout
Resonant cavity linear modulator Phase response
Stable locking range Calculate SFDR
f(t) ~
Iin
T(V)
)2
)cos(1(
inout II
Electro-optic Mach-Zehnder modulator
VtV /)(0
Resonant Cavity Interferometric ModulatorComparison to a Conventional MZ Modulator
outI
outI
Ph M d l i & Fil i
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Filtering &
Modulation
Optical SpectrumRF Spectrum
f1
VCSEL
Bias T
AC Modulation; f1,
DC current= I1
Phase Modulation & Filtering-Channel selection concept
I()
f
P(f)
Ch. 1
DC=I1
Ch. 2
DC=I2
Ch. 1
Ch. N
Ch. 2
Comb Modulated Output
0
= +f1
Ph M d l ti & Filt i
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Filtering &
Modulation
VCSEL
Bias T
AC Modulation; f2
DC current= I2
Phase Modulation & Filtering-Channel selection concept
Ch. 1
Ch. N
Ch. 2
Comb Modulated Output
RF spectrum
f2f
P(f)
= +f2
I()
Ch. 1
DC=I1
Ch. 2
DC=I2
0
Optical Spectrum8.6 8.7 8.8 8.9 9.0
193.405
193.410
193.415
193.420
193.425
193.430Measurement
Linear fit
Frequenc
y(THz)
DC Driving Current (mA)
Slope ~ 50 GHz/mA
Frequency vs. Current
Li M d l
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Linear ModulatorExperimental Results
0 1 2 3 4 5 6
-80
-75
-70
-65
-60
-55
-50
Power(d
Bm)
Frequency (GHz)
10 dB
0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
00 0 0 0 0 0 Measurement
Fit
Staticphase(radian)
DC Current Deviation (mA)
1 GHz
1.0001 GHz
CW
laser
PID
RFSA
VCSEL
High-res
OSA
+
Bias
Tee
EDFA
IDCRF
VOA PC
50/50Iso
PD
PD
90/10
PZT
VCSEL: vertical cavity surface emitting laser
Iso: isolator
VOA: variable optical attenuator
PC: polarization controller
PZT: piezoelectric transducerPD: photo detector
PID: proportional-integrated-differential controller
CIR: circulatorOSA: optical spectrum analyzer
RFSA: RF spectrum analyzer
CIR
Spur free dynamic range of ~130 dB.Hz2/3
Very low V of ~ 2.6 mV
Multi-gigahertz bandwidth (~ 5 GHz)
Possible gain
PC
-80 -70 -60 -50 -40 -30 -20
-160
-140
-120
-100
-80
-60
-40
-20
0
Fundamental
IM3
Fundam
ental&intermodulatio
n
power(dBm)
RF Input (dBm)
Noise floor
SFDR = 130
dB.Hz2/3
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
High Precision Laser Radar w/ Unambiguous Ranging &
Velocimetry
Summary and Conclusions
Di t d d l ti f h
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Direct demodulation of phase
modulated signals
Operating principle: Detecting light-induced changes in the
forward voltage of an optically injection locked VCSEL operating
above threshold.
Physical origin: Voltage change is due to the change in the
carrier density in the active region of the VCSEL when driven by
an external phase modulated light.
V()
hl o
I () &
()
Locking
range N. Hoghooghi, et. al, IEEE Photonics TechnologyLetters, 22(20), pp. 1509-1511, 2010.
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Phase
detector
0
0
Optical spectrum RF spectrum
0
0
f1 f2
VCSEL
Bias T
AC voltage
DC voltage
Channel filtering concept
I()
f
P(f)
Ch. 1
fmod
=f1
Ch. 2
fmod=f2
Ch. 1
Ch. N
Ch. 2
D d l ti & h l filt i ith
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Demodulation & channel filtering with
an injection-locked VCSEL
PC: polarization controller
PM: phase modulator
IM: intensity modulator
CIR: circulator
OSA: optical spectrum analyzer
RFSA: RF spectrum analyzer
CW
laserIM
PM
PM
PM
VCSEL
12.5 GHz
Ch.3
(1 GHz)
Ch.2
(0.9 GHz) Ch.1(0.8 GHz)
RFSA
OSA
DC
RF
CIRBias T
WDM
filter N
x1
combiner
PC
PC
PC
PC
Electrical path
Optical path
1538.2 1538.4 1538.6-60
-50
-40
-30
-20
-10
0
Power(d
B)
Wavelength (nm)
Ch.1Ch.2Ch.3
VCSEL
E i t l lt f th h l
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Experimental results of three channel
system
1538.1 1538.2 1538.3 1538.4 1538.5-60
-50
-40
-30
-20
-10
0
Wavelength (nm)
Power(dB)
1538.1 1538.2 1538.3 1538.4 1538.5-60
-50
-40
-30
-20
-10
0
Power(dB)
Wavelength (nm)
1538.1 1538.2 1538.3 1538.4 1538.5-60
-50
-40
-30
-20
-10
0
Power(dB)
Wavelength (nm)
Ch.1 Ch.2 Ch.3
750 800 850 900 950 1000-95
-90
-85
-80
-75
-70
-65
RBW 30 kHz
Span 270 MHz
Power(dBm)
Frequency (MHz)
SNR ~ 60
dBc/Hz
750 800 850 900 950 1000-95
-90
-85
-80
-75
-70
-65
Power(dBm)
Fre uenc MHz
RBW 30 kHz
Span 270 MHz
SNR ~ 60
dBc/Hz
750 800 850 900 950 1000-95
-90
-85
-80
-75
-70
-65RBW 30 kHz
Span 270 MHz
Power(dBm)
Fre uenc MHz
SNR ~ 62
dBc/Hz
Optical
spectra
Corresponding
detected RF
spectra
First demonstration of direct demodulation and channel filtering of
phase modulated signals with SNR of 60 dBc/Hz.
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Linear Modulator Concept for Pulsed Light
Received RF signal
- A resonant cavity (Fabry-Perot) with multiple resonances, injection locked by a mode-
locked laser as the frequency comb.
- By simultaneous modulation of the period combs, one imparts arcsine phase modulation
on each injected comb.
1/frep
MLL
Fabry-Perot LaserFSR=frep
FPOpticalFrequency
FP resonances
Corresponding phase responses
Injected comb lines from the MLL
Imparted phase on each injected combs
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter
Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
Summary and Conclusions
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Multi heterodyne Detection of
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ff(1)rep 2f(1)
repf(2)rep
RF
Power
Spectr
alDensity
f(1)rep
Photo-
detection
+ +2
f(1)rep
f(2)
repOpt
icalPower
Spec
tralDensity
Comb
Source
CombSource
D
Oscilloscope
RFSA
Diagnostics
frepPLL
LPF
(a)
(b)
Multi-heterodyne Detection of
Frequency Combs (Optical Sampling)
Each pair of comb-lines generates a unique RF beat-note
The RF beat-note retains the relative phase between the comb-lines
Multi heterodyne detection of
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Multi-heterodyne detection of
frequency combsExperimental results Mode-locked laser combs
Effective repetition rate detuning ~600 kHz
Total Optical BW ~ 17nm ~2.12THzCompression factor ~ 17,000x
10 GHz spacing optical comb is mapped into a 600 kHz spacing RF comb
Optical spectra
1500 16001475 157515501525Wavelength (nm)
Power(5dB/div.)
First two sets of RF beat notes
50 2500 200150100Frequency (MHz)
Power(dBm)-50
-60
-70
Frequency (MHz)140 160 180
-50
-60
-70
-80Pow
er(dBm)
Pulse Combs Time Domain
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Pulse Combs Time DomainExperimental Results (10 GHz & 250 MHz)
As the optical pulse is stretched and compressed, the RF
waveform does the same Optical waveform is mapped to RF
waveform
Normal
Anomalous
Dispersion
1 2 3 40 5Time (s)
Amp
litude(a.u.)
Time domain waveform
Stretched
Direct output
Compressed
Phase Modulated CW Combs
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Phase Modulated CW CombsExperimental Results
Real time
oscilloscope
RFSACW LaserPhase
Modulator
~10 GHz
Erbium Fiber
Mode-locked
Laser
Multi-heterodyne detection of
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Multi-heterodyne detection of
frequency combsExperimental results Phase modulation combs
1 2 3 4Time (s)
0
0
-20
-40
20
40
A
mplitude(mV) Time domain waveform
1 2 3 4Time (s)
0
70
60
80
90
Instantaneous
Frequency(MHz)
Instantaneous frequency
65 70 75 80Frequency (MHz)
60
Amplitude(a.u.)
Fourier transform
Phase()
-1
0
1
The optical waveform chirp is mapped to the
RF waveform
Spectral phase information can be retrieved
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter
Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
Summary and Conclusions
Optical DACs using Frequency
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Optical DACs using Frequency
Comb Filtering Static Approach
T
T
1/T
1/T
Time
Time
Frequency
Frequency
Intensity
Intensity
Intensity
Optical DACs using Frequency
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Modelocked
Comb Generator
N Combs
WDM DeMux Modulator Array
Maximum Modulation Rate F~WDM Mux
Arbitrary Waveform
Instantaneous Bandwidth Nx
Ultra-Pure CW channels Modulated CW Channels
Comb Spacing
Temporal
Gate
Pulse Shaping at the Highest Possible Spectral Resolution
Challenges: Some waveforms require phase modulation well beyond 2
Optical DACs using Frequency
Comb Filtering Dynamic Approach
A Novel Concept for Ultra-High-Speed Optical Pulse Shaping
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A Novel Concept for Ultra-High-Speed Optical Pulse Shaping
Our novel idea is different than the conventional approaches in 4 ways:
Instead of manipulating the existing optical combs, we regenerate the optical
combs with the desired amplitudes and phases
The refresh rate is limited by the modulation speed of the VCSELs (10s of GHz)
The channel count can easily be scaled by going from 1-D array into 2-D array
geometry
Simultaneous modulation and amplification
Phase / Amplitude
> 106 increase in
the refresh rate !!!
High speed Reconfigurable Optical
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High-speed Reconfigurable Optical
Arbitrary Waveform Generation
Four optical comblines, independently modulated and
coherently combined
Wavelength demux and mux pair
6.25 GHz channel spacing
Each modulator Injection-locked VCSEL with
current modulation
Experimental Setup
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1538
.80
1538
.85
1538
.90
1538
.95
1539
.00
1539
.05
1539
.10
1539
.15
1539
.20
1539
.25
1539
.30
1539
.35
1539
.40
1539
.45
1539
.50
1539
.55
1539
.60
-70
-60
-50
-40
-30
-20
-10
0
Pow
er(dBm)
Wavelength (nm)
0.0 0.1 0.2 0.3 0.4 0.5-5.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0160 ps
Volta
ge(mV)
Time (ns)
~30 ps
Experimental SetupOptical Frequency Comb Source
Generated by modulation
of CW laser
Adjust DC bias voltages,
RF phases and amplitudes
to achieve five combs ofequal power
Experimental Setup
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Experimental SetupDemux, Mux Specifications
Essex Hyperfine WDM filters
Fiber-pigtailed input and outputs
Channel spacing of 6.25 GHz
Adjacent channel isolation ~ 22
dB
Gaussian shaped passband
3 dB channel bandwidth ~ 3.5
GHz Mux, Demux are a matched pair
Intensity Profile of Rapidly
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Intensity Profile of Rapidly
Updated Optical WaveformsVCSEL 1 2 3 4
RF frequency (MHz) 4 5 6 7
VCSEL 1 2 3 4
RF frequency (MHz) 1562.5 3125 781.25 2343.75
5.120n 6.400n
0
100m
200m
Voltage(V)
Time (s)
0.0
0
1.28
n
2.56
n
3.84
n
5.12
n
6.40
n
7.68
n
8.96
n0
100m
200m
Voltage(V)
Time (s)
Photodetected RF spectrum
0.00 6.25G 12.50G 18.75G 25.00G
-60
-40
-20
Power(dBm)
Frequency (Hz)
Intensity Profile of Rapidly
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VCSEL 1 2 3 4
RF frequency (MHz) 1562.5 3125 781.25 2343.75
194.74
7
194.75
4
194.76
0
194.76
6
194.77
2
194.77
8
194.78
5
-60
-50
-40
-30
-20
-10
VCSEL 3 IL 2010-10-13-1.trc
Power(dBm)
Frequency (THz)
Optical Spectrum
Intensity Profile of Rapidly
Updated Optical Waveforms
Reconfigurable Cross Connect Switch /
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Reconfigurable Cross Connect Switch /
Pulse Shaping Code Reconfiguration
Information from any wavelength can be arbitrarily switchedbetween channelsat rates approaching channel spacing. 100 times faster that the existing MEMS technology.
DC3
DC4
DC1
DC2
DC1
DC2
DC3
DC4
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter
Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
Summary and Conclusions
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Matched Filtering using OFCs
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Comparison to OCDMA Optical Code Division Multiple
Access (OCDMA) Spectral modulation, temporal
spread
Decoding:
Needs non-linear opticalthresholding because of slow
response time of photodetectors
Coherent detection technique
is linear
Requires less optical power
Heritage and Weiner,IEEE JSTQE, 2007
Jiang et al., IEEE PTL, 2004
Complete Experimental Setup
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Complete Experimental Setup
Interference using Orthogonal
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g gCodes Using orthogonal codes gives best contrast between
different binary sequences
- PD
PD
Differential
signal
0,,0,
1 2 3 4
0,0,0,0
1 2 3 4
1 2 3 4
1 2 3 4
0
- PD
PD
Differential
signal
0,0,0,0
1 2 3 4
0,0,0,0
1 2 3 4
1
1 2 3 4
1 2 3 4
1111
1111
1111
1111
DCode
CCode
BCode
ACode
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5.11
mismatchmatch
mismatchmatchQ
3010
22
1
QerfcBER
,Summary of Results of Matched Filtering
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Outline
Motivation Background
Key Technologies
Stabilized Optical Frequency Combs
Arcsine Phase & Linear Intensity Modulators w/ Comb Filter
Direct Phase Detection (w/o external local oscillator) w/ Comb Filter
Applications
Arbitrary Waveform Measurements
Arbitrary Waveform Generation
Pattern Recognition using Matched Filtering Techniques
Summary and Conclusions
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Summary Demonstrated key technologies and applications using OFCs
Key Technologies Stabilized optical frequency combs (1.5 fsec jitter; 60 dBc/Hz)
Applications
Arbitrary waveform measurements (A to D Converter )
Reconstruction of Incoherent (Independent) Sources
Arbitrary waveform generation (D to A Converter) Fastest true real-time waveform generation (Mod Rates: >3GHz; IB: >22 GHz)
Matched filtering w/ differential photodetection (BER=10-30)
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Fundamentals of Injection Locking
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Optical intensity and
phase response vs. controlled via
current modulation ofVCSEL
Intensity change is small Phase difference betweenmaster and slave light, 0 :
j gUsing VCSELs as Modulators
Locking range = L
fr 1
A.E. Siegman,Lasers, Chap. 29, University Science Books, 1986
F. Mogensen, et al.,IEEE J. Quantum Electronics., vol. 21, 1985
Phase response
Output intensity
tansin
11
0
f
L
Linewidth enhancement factor
Phase
=1fr f
10 cot
2
Slave Laser
(VCSEL)
Master
Laser
Resonant Cavity Interferometric Modulator
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- Theory
)(sin)( 1011m
0: slave frequency
1: master frequency
)2
)cos(1(
inI
)2
)(1()
2
)2/))((cos(sin1(
1 tfI
tfII ininout
Linear Modulator
))((sin1
tf
inI
inI outI
Mach-Zehnder Interferometer
Injection-locked laser phase response
1
/2
-/2
o
-1 LockingRange
Put them together
Resonant Cavity Interferometric Modulator
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V
f(t) ~
/2
Iin
V
T(V)
))((sin 1 tf
I0,1 )2
)(1(
tfIIinout
Resonant cavity linear modulator Phase response
Stable locking range Calculate SFDR
f(t) ~
Iin
T(V)
)2
)cos(1
(
inout II
Electro-optic Mach-Zehnder modulator
VtV /)(0
- Comparison to a conventional MZ modulator
outI
outI
Phase Modulation & Filtering
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Filtering &
Modulation
Optical SpectrumRF Spectrum
f1
VCSEL
Bias T
AC Modulation; f1,
DC current= I1
ase odu at o & te g-Channel selection concept
I()
f
P(f)
Ch. 1
DC=I1
Ch. 2
DC=I2
Ch. 1
Ch. N
Ch. 2 Comb Modulated Output
0
= +f1
Phase Modulation & Filtering
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Filtering &Modulation
VCSEL
Bias T
AC Modulation; f2
DC current= I2
g-Channel selection concept
Ch. 1
Ch. N
Ch. 2
Comb Modulated Output
RF spectrum
f2f
P(f)= +f2 I()
Ch. 1DC=I
1
Ch. 2
DC=I2
0
Optical Spectrum8.6 8.7 8.8 8.9 9.0
193.405
193.410
193.415
193.420
193.425
193.430Measurement
Linear fit
Frequen
cy(THz)
DC Driving Current (mA)
Slope ~ 50 GHz/mA
Frequency vs. Current
f
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Linear interferometric modulator setup
CW
laser
Piezo
driver
RFSA
VCSEL
High-res
OSA
Bias
Tee
IDC
RF
VOA PC
50/50Iso
PDPZT
CIR
PC
VCSEL: vertical cavity surface emitting
laser
Iso: isolator
VOA: variable optical attenuator
PC: polarization controller
PZT: piezoelectric transducer
PD: photo detector
CIR: circulator
High-res OSA: High resolution optical
spectrum analyzer
RFSA: RF spectrum analyzer
Electrical path
Optical path
0 1 2 3 4 5 6
-80
-75
-70
-65
-60
-55
-50
Power(dBm
)
Frequency (GHz)
10 dB
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
00 0 0 0 0 0 Measurement
Fit
Staticphase(radian)
DC Current Deviation (mA)
0.00 0.05 0.10 0.15 0.20 0.250.15
0.20
0.25
0.30
0.35
0.40
Voltage(V)
Time(sec)
V ~ 2.6 mV
-10 dB bandwidth
~5 GHz
How to measure linearity of a modulator?
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V(t)
F
1 2 2221 31 32
221212
2
1
21-2
22-1
32
31
22
21
=
+
+
+
Noise floor
Spur-free
dynamic range(SFDR)
How to measure linearity of a modulator?-Two-tone experiment
Iin IoutModulator
N. Hoghooghi and P. J. Delfyett, IEEE Journal of Lightwave
Technology, 29(22), pp.3421-342, 2011.
A l li k l i li d l t
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Analog link employing linear modulator
1 GHz
1.0001 GHz
CW
laser
PID
RFSA
VCSELHigh-res
OSA
+
Bias
Tee
EDFA
IDCRF
VOAPC
50/50Iso
PD
PD90/10
PZT
CIR
PC
VCSEL: vertical cavity surface emitting laser
Iso: isolator
VOA: variable optical attenuator
PC: polarization controller
PZT: piezoelectric transducer
PD: photo detector
PID: proportional-integrated-differential controller
CIR: circulator
OSA: optical spectrum analyzer
RFSA: RF spectrum analyzer
1 km of
fiber
Electrical path
Optical path
Spur-free dynamic range measurement
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Spur free dynamic range measurement
of the link
-80 -70 -60 -50 -40 -30 -20
-160
-140
-120
-100
-80
-60
-40
-20
0
Fundamental
IM3
Fundamental&intermodulation
power
(dBm)
RF Input (dBm)
Noise floor
Power of the fundamental is a factor of >3,000,000^2
higher than third-order intermodulation power.
Order of the magnitude better than DARPA project
goal.
0.999 1.000 1.001 1.002
-60
-50
-40
-30
-20
-100
10
Power(dBm)
Frequency (GHz)
Sample RF spectrum
10 20 30 40 50 60 70 80 90 100
-160
-150
-140
-130
-120
-110
-100
-90
-80
RIN[dBc/Hz]
10 20 30 40 50 60 70 80 90 1000
0.05
0.1
0.15
0.2
0.25
Frequency Offset [MHz]
IntegratedR
MSRIN(%)
RIN
SFDR = 130 dB.Hz2/3
Modelocking Basics
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L
c/2L
gA Review
Optical CavityAllowed Modes
Laser Medium
Laser Cavity
Spontaneous Emission Spectrum
Laser Spectrum
Modelocking Basics
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c=o=2
m o
oo+ mo- m
T=2L/c
P
=2/
E-Field
E-Field Spectrum
Modulated
E-Field
E-Field Spectrum
Modelocked Spectrum
Modulator
A Review
Coherent Optical Signal Processing &
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Communications using Optical Frequency Combs
What are optical frequency combs?
Coherent, stabilized cw optical frequencies generated on a periodic frequency grid, (e.g.,
a set of longitudinal modes from a modelocked laser).
Why re-visit coherent communications/signal processing?
Allows the use of E(t) as compared to I(t) high spectral efficiency.
(80x -200xincrease)
Coherent combs of stabilized optical frequencies are easily obtainable from mode-
locked lasers.
Channel conditioning can be done simply ((frequency stabilization of the entire comb as
compared to individual lasers).
Sets of combs at separate locations can be made coherent (frequency and phase)
Modelocked Spectrum
T=2L/c
P=2/Modulator
Optical Frequency Combs
Ultrafast Photonics Group
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Ultrafast Photonics Group
Fundamental PhysicsQuantum Dot
Ultrafast Light- Matter
Dynamics
New Device DevelopmentQ-Dot Optical Amplifiers
Modulators & Photodetectors
Active Optical Filters
Systems ApplicationsOptical Networks for Signal Processing &
Communications
Optical Sampling for A-to-D Converters
Arbitrary Waveform Generation
Precision Laser Radar
[email protected]://creol.ucf.edu
http://up.creol.ucf.edu
Stabilized Comb Source Specs
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Stabilized Comb Source Specs
1.1ps pulse width with and 50 dB suppresion
to the next observable optical mode.
500 Hz optical linewidth and sub 150 kHzmaximum frequency deviation in 30 seconds.
3 fs integrated timing jitter from (1 Hz100
MHz) and 14 fs timing jitter extrapolated toNyquist (1 Hz 5.14 GHz).
Simultaneous optical frequency stabilization and supermode suppression
of a 10.287 GHz harmonically mode-locked laser with:
Ozdur I., et al, A semiconductor based 10-GHz optical comb source with 3 fs integrated timing jitter
(1Hz-100MHz) and ~500 Hz comb linewidthPhotonic Technology Letters Vol. 22, No. 6, March 15, 2010.
Oscillator characterization
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Oscillator characterizationOptical Spectra
1550 1555 1560
-80
-70
-60
-50
-40
-30
Power(dBm)
Wavelength (nm)
Optical Spectrum
0 10 20 30 40 50 60
-0.2
-0.1
0
0.1
0.2
time (s)
FrequencyOffset(MHz)
Spectrogram
-1.0 -0.5 0.0 0.5 1.0
-80
-70
-60-50
-40
-30
-20
-10
0
Rel.Po
wer(dB)
Frequency Offset (MHz)
Span: 2 MHz
Res. BW. 100 Hz
Single comb-line
beat-note2 kHz FWHM Lorentzian
1 kHz FWHM Lorentzian
Phase and amplitude noise
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Phase and amplitude noise
1 10 100 1k 10k 100k 1M 10M 100M
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
L(f)(d
Bc/Hz)
Frequency Offset (Hz)
0
2
4
6
8Directly from MLL
Amplified (Pout
~ 200 mW)
Integrated
TimingJitter(fs)
Single Sideband Phase Noise
1 10 100 1k 10k 100k 1M 10M 100M
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
M(f)(dBc/Hz)
Frequency Offset (Hz)
Directly from MLL
Amplified
0.00
0.02
0.04
0.06
0.08
0.10
Integrated
AMNoise(%)
Pulse-to-pulse energy fluctuations
Oscillator characterization
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81
Oscillator characterizationPulses
-40 -30 -20 -10 0 10 20 30 40
0.0
0.5
1.0
Compressed AC
Transform Limited AC
ACT
race(a.u.)
Delay (ps)
p
= 930 fs
10.24 10.26 10.28 10.30 10.32
-100
-80
-60
-40
-20
0
Relativ
ePower(dB)
Frequency (GHz)
Span: 100 MHz
Res. BW: 3 kHz
Pulses are compressible to close to the transform limit
Photodetected RF tone has >90 dB dynamic range
Conclusions
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7/30/2019 Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical Frequency Combs from Mode-locked Semiconductor Diode Lasers
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Conclusions An optical comb source has been built with:
Stable (instability < 300 kHz @ 194 THz over 60 s), low line-width (< 1
kHz) optical comb
High repetition rate (10 GHz) optical pulse-train
Short pulses generated from a dispersion compensated cavity (p 5 mW per comb-line)
No evident degradation in Phase (14 fs jitter integrated to Nyquist) and
Amplitude Noise (< 0.03%, 1 Hz to 100 MHz)
Linear Intensity Modulator
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7/30/2019 Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical Frequency Combs from Mode-locked Semiconductor Diode Lasers
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System Configuration
-Iso: Isolator
-PC: Polarization Controller-PS: Optical Phase Shifter
-VOA: Variable Optical Attenuator
-TEC: Temperature Controller
-Cir : Circulator
-VCSEL: Vertical Cavity Surface Emitting Laser
-RFSA: Radio Frequency Spectrum Analyzer
-OSA: Optical Spectrum Analyzer
Concept of Photonic Arbitrary Waveform Generation
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7/30/2019 Peter Delfyett Seminar: Ultrafast Coherent Optical Signal Processing using Stabilized Optical Frequency Combs from Mode-locked Semiconductor Diode Lasers
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Static Fourier Analysis
K
k
kktkA
Atf
1
00 )cos(2
)(
k: periodic frequency components
Ak: amplitude of the kth frequency component
kphase of the kth frequency component
Performance Characteristics
Limited to periodic signals
Minimum periodicity ~ Mode spacing - filter spacing
Accuracy determined by number of combs