peter delfyett seminar: ultrafast coherent optical signal processing using stabilized optical...

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

[email protected]

University of California

Santa Barbara, CADecember 5, 2012


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2

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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10

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


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


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


etalon

High Resolution Comb Line


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Timing jitter and amplitude noise:


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.


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)


(i)

0

2

4

6

8

10

IntegratedJitter(fs)

and SCOWA

Timing JitterSSB Phase Noise Comparison


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Outline


Key Technologies



Direct Phase Detection (w/o external local oscillator) w/ Comb Filter Applications




High Precision Laser Radar w/ Unambiguous Ranging &

Velocimetry



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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


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


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


Key Technologies



Direct Phase Detection (w/o external local oscillator) w/ Comb Filter Applications




High Precision Laser Radar w/ Unambiguous Ranging &

Velocimetry


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


PM: phase modulator

IM: intensity modulator

CIR: circulator

OSA: optical 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


Key Technologies




Applications






40/84

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



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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


Key Technologies




Applications





Optical DACs using Frequency


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Comb Filtering Static Approach

T

T

1/T

1/T

Time

Time

Frequency

Frequency

Intensity

Intensity

Intensity



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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


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


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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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)



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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


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


Key Technologies




Applications






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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


Key Technologies




Applications






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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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67

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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68

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


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



PZT: piezoelectric transducer

PD: photo detector

CIR: circulator

High-res OSA: High resolution optical

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



PZT: piezoelectric transducer

PD: photo detector

PID: proportional-integrated-differential controller

CIR: circulator

OSA: optical 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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75

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


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.



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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)


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)


Directly from MLL

Amplified

0.00

0.02

0.04

0.06

0.08

0.10

Integrated

AMNoise(%)

Pulse-to-pulse energy fluctuations



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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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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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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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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

peter delfyett seminar: ultrafast coherent optical signal processing using stabilized optical...

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