Recent progress in pulsed optical synchronization systems
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Recent Progress in Pulsed Optical Synchronization Systems. Franz X. Kärtner Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology Cambridge, MA, USA. Acknowledgement. Students Hyunil Byun Jonathan Cox

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Recent Progress in Pulsed Optical Synchronization Systems

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Recent progress in pulsed optical synchronization systems

Recent Progress in Pulsed Optical Synchronization Systems

Franz X. Kärtner

Department of Electrical Engineering and Computer Science

and Research Laboratory of Electronics,

Massachusetts Institute of Technology

Cambridge, MA, USA


Recent progress in pulsed optical synchronization systems

Acknowledgement

Students

Hyunil Byun

Jonathan Cox

Anatoly Khilo

Michelle Sander

Postdocs:

J. Kim (KAIST, Korea)

Amir Nejadmalayeri

Noah Chang

Colleagues and Visitors:

E. Ippen, J. G. Fujimoto, L. Kolodziejski,

F. Wong and M. Perrott

DESY: F. Loehl, F. Ludwig, A. Winter


Recent progress in pulsed optical synchronization systems

Outline

  • Synchronization System Layout for Seeded FEL

  • Advantages of a Pulsed Optical Distribution System

  • Low Noise Optical Master Oscillators

  • Timing Distribution Over Stabilized Fiber Links

  • Optical-to-Optical Synchronization

  • RF-Extraction and Locking to Microwave References

  • Prospects for sub-fs timing distribution


Seeded x ray free electron laser

Seeded X-ray Free Electron Laser

Long-term sub-10 fs synchronization over entire facility is required.


Seeded x ray free electron laser1

Seeded X-ray Free Electron Laser

J. Kim et al, FEL 2004.


Why optical pulses mode locked lasers

TR = 1/fR

time

...

fR

2.fR

N.fR

frequency

Why Optical Pulses (Mode-locked Lasers)?

  • Real marker in time and RF domain, every harmonic can be extracted at the end station.

  • Suppress Brillouin scattering and undesired reflections.

  • Optical cross correlation can be used for link stabilization or for optical-to-optical synchronization of other lasers.

  • Pulses can be directly used to seed amplifiers, EO-sampling, ….

  • Group delay is directly stabilized, not optical phase delay.

  • After power failure system can auto-calibrate.


200 mhz soliton er fiber laser

200 MHz SolitonEr-fiber Laser

  • 200 MHz fundamentally mode locked soliton fiber laser

  • 167 fs pulses

  • 40mW output power

K. Tamura et al. Opt. Lett. 18, 1080 (1993).

J. Chen et al, Opt. Lett. 32, 1566 (2007).

Similar lasers are now commercially available!


Semiconductor saturable absorber modelocked 100mhz 1ghz er fiber lasers

Semiconductor Saturable Absorber Modelocked 100MHz - 1GHz Er-fiber Lasers

5”x4”x1.5”

out

pump

Long term output power with 270mW pump

Optical spectrum

RF spectrum

  • Compact, long-term stable femtosecond laser source at GHz reprate

  • SBR burning problem solved by SMF buffer and pump-reflective coating on SBR

  • 380mW pump  27.4mW output

  • Optical spectrum FWHM: 17.5nm

  • Pulse width: 187fs

  • Repetition rate: 967.4MHz

  • Intensity noise: 0.014% [10Hz,10MHz]

Autocorrelation


Sensitive time delay measurements by balanced optical cross correlation

Sensitive Time Delay Measurements byBalanced Optical Cross Correlation


Single crystal balanced cross correlator

Single-Crystal Balanced Cross-Correlator

Type-II phase-matched

PPKTP crystal

Reflect fundamental

Transmit SHG

Transmit fundamental

Reflect SHG

J. Kim et al., Opt. Lett. 32, 1044 (2007)


Single crystal balanced cross correlator1

Single-Crystal Balanced Cross-Correlator

80 pJ, 200 fs

1550nm input pulses

at 200 MHz rep. rate

In comparison:

Typical microwave mixer

Slope ~1 mV/fs @ 10GHz


Recent progress in pulsed optical synchronization systems

ML Fiber Laser Timing Jitter Measurement

Single crystal balanced

cross-

correlator

PBS

RF-pectrum

analyzer

Modelocked

Laser 1

Modelocked

Laser 2

Oscilloscope

HWP

Loop filter

J. Kim, et al. , Opt. Lett. 32, 3519 (2007).


Recent progress in pulsed optical synchronization systems

Timing Jitter in 200 MHz Fiber Lasers

Measured Jitter

Density

Integrated

Jitter

Theory

Noise Floor

Ultralow timing jitter (<1 fs) in the high frequency range [100 kHz, 10 MHz]

J. Kim, et al., Opt. Lett. 32, 3519 (2007).


Timing stabilized fiber links

Timing - StabilizedFiber Links


Recent progress in pulsed optical synchronization systems

Timing-Stabilized Fiber Links

Fiber link ~ several hundreds meters

to a few kilometers

PZT-based fiber stretcher

isolator

Mode-locked laser

Timing

Comparison

Faraday

rotating

mirror

Cancel fiber length fluctuations slower than the pulse travel time (2nL/c).

1 km fiber: travel time = 10 μs  ~100 kHz BW


2 link test system

2 Link Test System

J. Cox et al. CLEO 2008.


Experimental apparatus

Experimental Apparatus

~300 m optical fiber

Piezo stretcher

EDFA

200 MHz Laser

In-Loop

PPKTP

Out-of-Loop PPKTP

Invar Board

Motor


Balanced cross correlation signals

Balanced Cross-Correlation Signals

Link 1

Link 2

Out of

Loop


Results timing jitter

Results – Timing Jitter

360 as (rms) timing jitter from 1 Hz to 100 kHz

3.3 fs (rms) timing jitter from 35 μHz to 100 kHz

 Out-off loop jitter limited by quantum noise


Optical to optical synchronization

Optical-to-Optical Synchronization


Optical to optical synchronization1

Optical-to-Optical Synchronization


Ti sapphire laser cr forsterite laser

Spanning over 1.5 octaves

Ti:sapphire Laser + Cr:Forsterite Laser

Cr:forsterite

Ti:sapphire

30 fs

5fs


Sub femtosecond residual timing jitter

Sub-femtosecond Residual Timing Jitter

Balanced optical cross-correlator based on GDD (T. Schibli et al, OL 28, 947 (2003))

Long-term drift-free sub-fs timing synchronization over 12 hours

J. Kim et al, EPAC 2006.


Optical to rf conversion or optical to rf locking necessary for locking omo to rmo

Optical-to-RF Conversion orOptical-to-RF Lockingnecessary forLocking OMO to RMO


Recent progress in pulsed optical synchronization systems

TR/n

t

...

fR

2fR

nfR

RF frequency

Direct Extraction of RF from Pulse Train

E. Ivanov et al, IEEE UFFC 52, 1068 (2005).

IEEE UFFC 54, 736 (2007).

AM-to-PM conversion,

Temperature drift

of photodetectors and mixers

TR = 1/fR

time

Photodetector


Recent progress in pulsed optical synchronization systems

TR/n

t

...

fR

2fR

nfR

RF frequency

Direct Extraction of RF from Pulse Train

55 fs drift

in 100 sec

A. Bartels et al, OL 30, 667 (2005).

TR = 1/fR

time

Photodetector

More in: B. Lorbeer et al, PAC 2007.


Balanced optical microwave phase detector bom pd

Balanced Optical-Microwave Phase Detector(BOM-PD)

Microwave

Signal

Electro-optic sampling of microwave signal with optical pulse train

J. Kim et al., Opt. Lett. 31, 3659 (2006).


Opt oelectronic phase locked loop pll

Optoelectronic Phase-Locked Loop (PLL)

Regeneration of a high-power, low-jitter and drift-free microwave

signal whose phase is locked to the optical pulse train.

Balanced Optical-Microwave Phase Detector (BOM-PD)

Regenerated

Microwave

Signal Output

Tight locking of modelocked laser to microwave reference

Balanced Optical-Microwave Phase Detector (BOM-PD)

Modelocked

Laser

Stable Pulse

Train Output


Testing stability of bom pds

Testing Stability of BOM-PDs

BOM-PD 1: timing synchronization

BOM-PD 2: out-of-loop timing characterization


Long term stability 6 8 fs drift over 10 hours

Long-Term Stability: 6.8 fs drift over 10 hours

RMS timing jitter integrated in 27 μHz – 1 MHz: 6.8 fs

J. Kim et al, Nature Photonics 2, 733 (2008).


Delay locked looop 2 9 fs drift over 8 hours

Delay Locked Looop: 2.9 fs drift over 8 hours

RMS timing jitter integrated in 0.1 Hz – 1MHz, 2.4 fs

J. Kim et al, submitted to CLEO 2010.


Recent progress in pulsed optical synchronization systems

1 GHz diode pumped CrLiSAF Laser: Modelocked

Jointly with Jim Fujimoto


Recent progress in pulsed optical synchronization systems

Prospects for Attosecond Timing Distribution

(100 MHz Cr:LiSAF Laser, SSB scaled to 1GHz)

U. Demirbas, submitted to CLEO 2010


Recent progress in pulsed optical synchronization systems

Conclusions

  • Long term stable (10h) sub-10 fs timing distribution system is completed.

  • True long term stability (forever): Implement Polarization Control

  • Master Oscillators commercially available + amplifier >400mW of

  • output power > 10 links)

  • 300 m Fiber Links, over 10h < 5 fs ( < 1fs possible)

  • Optical-to-Optical Synchronization, over 12h < 1fs

  • Optical-to-Microwave Synch., over 10h < 7fs ( < 1fs possible)

  • Solid-State Lasers show timing jitter [1kHz – 10 MHz] < 200as (<50as)

  • Continued development of this technology seems to enable < 100as long term stable timing distribution.


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