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  • Ultrafast Coherent Optical Signal

    Processing using Stabilized Optical

    Frequency Combs from Mode-

    locked Diode Lasers Peter J. Delfyett

    CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816-2700

    delfyett@creol.ucf.edu

    University of California

    Santa Barbara, CA

    December 5, 2012

  • 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

  • 3

    Motivation

    Why Diode Based Fiber Lasers? Diode lasers are small (100s microns), electrically efficient

    (>70%), wavelength agile (300 nm to >10 microns via

    bandgap engineering).

    Robust, no moving / mechanical parts

    Broad bandwidth potential for large tuning bandwidth.

    Operates over very broad temperature ranges.

    Cost effective, direct electrically (battery) pumped.

    Can engineer the cavity Q to be >> than conventional cavities

    Potential for photonic integrated circuits, e.g., electronics,

    lasers, modulators & detectors full functioning

    optoelectronic systems on a chip

    computing & signal processing at the speed of light!

  • 4

    Ultrawideband Communications

    Synthetic Aperture Imaging Sensing, Detecting and Response

    Applications Enabled By Optical Frequency Combs

    Advanced Waveform Generation/Measurement

  • 5

    Time Interleaved Pulse Trains Time Overlaid Pulse Trains

    Interleaved Supermode Spectra Overlaid Supermode Spectra

    P

    ow

    er

    Time

    Po

    wer

    Optical Frequency

    Am

    pli

    tud

    e

    Time

    Po

    wer

    Po

    wer

    Time

    Optical Frequency

    Am

    pli

    tud

    e

    Po

    wer Time

    ei

    ei2

    E(-)

    E(-2)

    E()

    2

    Po

    we

    r

    eit

    eit2t

    fML

    c/L

    TC=L/c

    c/L

    fML

    T= 1/fML

    A1=1

    A2=1

    A3=0.5

    Harmonic Modelocked Lasers Schematic Representations

  • 6

    0 200 400 600 800 1000 12000

    50

    100

    150

    200

    250Intensity of Optical Pulse Train

    Time

    Inte

    nsity

    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

    Inte

    nsity

    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

    Watt

    s/H

    z

    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

  • 7

    Low Noise Modelocked Diode Lasers

    Via

    Stabilization of the Frequency Comb

  • 8

    Fundamentally Modelocked Lasers

    Time

    Optical Frequency

    fmod=c/L

    =10 GHz

    L

    c/L

    T=100 ps

    ~

    Po

    wer

    Po

    wer

    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

  • 9

    Harmonically Modelocked Lasers

    Time

    Optical Frequency

    fmod=Nc/L

    =10 GHz

    L

    c/L

    T=100 ps

    ~

    SOA

    Po

    wer

    Po

    wer

    Log Frequency

    RF Power Spectrum

    Supermodes

    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

    10GHz RF Power Spectrum

  • 10

    Harmonic Modelocking & Supermode

    Suppression

    Fmod=nc/L

    = 10GHz

    L

    T=100 psec

    ~

    Time

    Optical Frequency

    10GHz

    T=100 psec

    P

    ow

    er

    Po

    wer

    Time

    Optical Frequency

    10GHz

    T=100 psec

    Po

    wer

    Po

    wer

    SOA

    =10GHz

    Fmod=nc/L

    =10GHz

    L

    ~

    Supermode

    Suppression Filter

    SOA

  • 11

    Ii

    T

    1 R exp i d i

    64

    0.0 I2i

    T2

    1 R2 exp i di

    8

    0.0

    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

    Tran

    smis

    sio

    n

    Frequency

    Tran

    smis

    sio

    n

    (a)

    (b)

    Nested Optical Cavities

    R1=R2=90%; T1=T2 =10%; FSR2 / FSR1 =8

    Cavity Product Identical to R=99%; T=1%

  • 12

    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

  • 13

    Setup

    SOA

    VOD OPS

    IM

    I I

    PC PC

    PC

    Output

    DC

    PC

    Free Space

    Optics FPE

    PM

    Cir

    PBS

    PID

    O PS

    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 modulator

    PBS: polarization beam splitter

    FPE: Fabry-Perot etalon

    PID: PID controller

    PM: phase modulator

    Cir : optical circulator

    OPS: Optical Phase Shifter

    VOD: Variable Optical Delay

    DCF: Dispersion Comp. Fiber

    PDH: Pound Drever Hall

    Ultra-low noise osc.

    at 10.287GHz

  • 14

    Laser is constructed on a optical breadboard and thermally and

    acoustically isolated with foam insulation.

    Actively MLL with intracavity 1000 Finesse

    etalon

  • 15

    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

  • 16

    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

  • 17

    Timing jitter and amplitude noise:

    Actively MLL with intracavity 1000 Finesse

    etalon

    Integrated timing jitter (1 Hz 100 MHz) is ~3fs

    and up to Nyquist it is 14fs.

    Integrated amplitude noise (1 Hz 100

    MHz) is 230ppm.

    Note the overall dynamic range of the measurement 1016 )

  • 18

    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

    Am

    plit

    ude

    (d

    Bm

    )

    Frequency (GHz)

    High Resolution Spectrum Analyzer

    CW laser

    Stabilized Frequency Comb lines

    Optical linewidth/stability measurement.

    Actively MLL with intracavity 1000 Finesse

    etalon

    Stability

  • 19

    Low Noise Modelocked Diode Lasers

    The Effect of Intracavity Power

  • 20

    SCOW Amplifier SCOWA 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)

    Ga

    in (

    dB

    )

    1 A

    2 A

    3 A

    4 A

  • 21

    Etalon stabilized HMLL Experimental 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

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