44!

Outline Part II

!  Femtosecond to attosecond precision timing distribution for large scale facilities: Example X-ray FEL

!  Synchronization system layout for a seeded X-ray FEL

!  Advantages of a pulsed optical distribution system

!  Timing jitter of femtosecond lasers

!  Timing distribution over stabilized fiber links

!  Optical-to-optical synchronization

!  RF-Extraction and locking to microwave references

!  Outlook: Photonic ADCs!

45!

Next Generation X-ray Source Schematic

Today long-term sub-10 fs synchronization over entire facility desired. 300 m - 3 km

Tomorrow sub-fs synchronization will be required.

fs x-ray pulses

Seeding with various schemes demonstrated: For lasers the challenge comes with high repetition rates

(Seeded, high repetition rate X-Ray FELs)

46!

Pulsed femtosecond timing distribution

J. Kim et al, FEL 2004.

fs x-ray pulses

Other approaches: R. Wilcox, LBNL, cw-distribution, or post stamping

47!

10 -6

Femtosecond Laser!

TR

time!

τ"

Δt Optical Cavity

Electronic Oscillator!

time!

ampl

itude! T0 Δt

Timing jitter of femtosecond lasers!

J. Kim et al., Laser & Phot. Rev., 1–25 (2009). H. A. Haus et al., IEEE JQE 29, 983 (1993).

10 -4

kTc 50~ω!

2 2 1 cML

pulse cav

d tdt W

ωτ

τ< Δ >≈ ⋅ ⋅

h

pulse width ~100fs

ħωc = photon energy

Dissipation-Fluctuation!Theorem!

2 20

mod

1RF

e cav

d kTt Tdt W τ< Δ >≈ ⋅ ⋅

cavity lifetime

period ~100ps

kT = thermal energy

48!

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!

frequency

… ...

fR 2fR NfR

TR = 1/fR

time

Single-Crystal Balanced Cross-Correlator

49!

Reflect fundamental Transmit SHG Transmit fundamental

Reflect SHG

Type-II phase-matched PPKTP crystal

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

T. Schibli et al, OL 28, 947 (2003)

Single-Crystal Balanced Cross-Correlator

50!

Reflect fundamental Transmit SHG Transmit fundamental

Reflect SHG

Type-II phase-matched PPKTP crystal

Single-Crystal Balanced Cross-Correlator

51!

Reflect fundamental Transmit SHG Transmit fundamental

Reflect SHG

Type-II phase-matched PPKTP crystal

Single-Crystal Balanced Cross-Correlator

52!

In comparison: Typical microwave mixer Slope ~1 µV/fs @ 10 GHz Greatly reduced thermal drifts!

80 pJ, 200 fs 1550nm input pulses at 200 MHz rep. rate

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

200 MHz Soliton Er-fiber Laser

53!

•  167 fs pulses

•  200 pJ intracavity pulse energy

•  50% loss

ISO

PBS

λ/4

λ/2

λ/4

collimatorcollimator

WDM980 nm Pump

10 cmSMF

50 cmEr doped fiber 10 cm

SMF

10 cmSMF

10 cmSMF

ISO

PBS

λ/4

λ/2

λ/4

collimatorcollimator

WDM980 nm Pump

10 cmSMF

50 cmEr doped fiber 10 cm

SMF

10 cmSMF

10 cmSMF

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

Timing Jitter of Fiber Lasers

54!

Modelocked Laser 1

Modelocked Laser 2

HWP

PBS Single crystal balanced

cross- correlator

Oscilloscope

RF-pectrum analyzer

-1

0

1

-800 0 800

Time delay (fs)D

ete

cto

r outp

ut

(V)

Loop filter

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

Phase detector method ! Timing Detector method

103 104 105 106 107 108

10-12

10-10

10-8

10-6

10-4

10-2Ji

tter S

pect

ral D

ensi

ty (f

s2 /H

z)

103 104 105 106 107 1080

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Jitte

r (fs

rms)

Timing Jitter in Stretched Pulse Lasers

55!

!  3 fs rms [100 kHz, 40 MHz] !  Additional noise present at frep/2 and frep/4

80 MHz Er-fiber Stretched Pulse Laser

Frequency (Hz)

model

J. Cox et al. Opt. Lett., 35, 3522 (2010)

Attosecond Timing ?

56!

How do we get to Attosecond Jitter Lasers?

Intracavity losses down (Factor of 50)

Intracavity energy up (Factor of 50)

10-fs pulses (Factor of 100)

2 2 1 cML

pulse cav

d tdt W

ωτ

τ< Δ >≈ ⋅ ⋅

h

~ 106 Is it true?

Solid-state lasers

Two 10-fs Ti:Sapphire Lasers Synchronized within 13 as

57!

13 as

Ref @ 10 GHz

A. Benedick, et al. Nat. Photonics 6, 97-100, 2012

Timing jitter of OneFive:Origami Laser

58!

1k 10k 100k 1MFrequency (Hz)

Jitte

r Spe

ctra

l Den

sity

(fs2 /H

z)

10-9

Pha

se N

oise

@ 1

0GH

z (d

Bc/

Hz)

-180

10-7

10-5

10-3

-160

-140

-120

Inte

grat

ed J

itter

at [

f,1M

Hz]

(fs)

0

0.1

0.2

0.3

f > 15 kHz

K. Safak et al., Struct. Dyn. 2, 041715 (2015)

59!

Timing - Stabilized

Fiber Links

60!

Timing-stabilized fiber links

PZT-based fiber stretcher

Mode-locked laser

Fiber link ~ several hundreds meters

to a few kilometers SMF/DCF

isolator

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

1-week operation with SMF/DCF

61!

0 50 100 150-5

0

5

10

15

20

25

Tim

ing

Link

Drif

t (fs

)

Time (hours)0 50 100 150

-15

-10

-5

0

5

10

15

Fibe

r Flu

ctua

tions

(ps)

Timing Link System Performance

5 fs (rms) drifts over one week of operation

FLASH, FERMI, and tests at PAL and LCLS (2008-2014)

62!

Clocking the European XFEL

3.5 km

Injector laser�Probe laser�

M. Y. Peng et al. Opt. Exp. 21, 19982 (2013).

High precision PM-link developed jointly with OFS

Dispersion-compensating PM Fiber D = -102.5 ps/nm·km @1550nm, slow axis D’ = -0.33 ps/nm2·km, slow axis

Splice

Fiber 1 Std. PM 1550 Length: 4m

Fiber 2 Std. PM 1550

Length: 2946m

Fiber 3 Bridge Fiber Length: 2m

Fiber 4 PM DCF

Length: 511m

Fiber 5 Bridge Fiber Length: 2m

Fiber 6 Bridge Fiber Length: 19m

Fiber 7 Std. PM 1550 Length: 3m

63!

High precision PM-link results (OFS)

3.5 km

Injector laser�Probe laser�

0 4 8 12 16 20 24 28 32-1

-0.5

0

0.5

1

Out

loop

Drif

t (fs

)

36 40 44

0 4 8 12 16 20 24 28 32Time (hours)

36 40 4444454647

50

Rel

.Tem

pera

ture

(K)

-0.6-0.4-0.2

0

0.6

Rel

. Hum

idity

(%)

0.20.4

4849

Laser-to-Laser Remote Synch.: 100 as RMS & 0.6 fs Pk-Pk drift (< 1Hz) over 44 h

M. Xi et al. Opt. Exp. 22, 14904 (2014) M. Y. Peng et al. Opt. Exp. 21, 19982 (2013)

64!

Optical-to-Optical Synchronization

65!

Ti:sapphire Laser + Cr:Forsterite Laser

Ti:sapphire Cr:forsterite

Spanning over 1.5 octaves

5fs 30 fs

65!

66!

Sub-femtosecond Residual Timing Jitter

J. Kim et al, EPAC 2006.

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

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

67!

Optical-to-RF Conversion or

Optical-to-RF Locking

Excess Phase Noise in Photo Detection

68!

RF frequency

… ...

fR 2fR nfR

TR = 1/fR

time Photodetector

t

TR/n (E. N. Ivanov et al, IEEE JQE 2003, IEEE UFFC 2005 and 2007)

It is difficult to stabilize the phase of microwave signals To better than 10 fs precision over many hours or days of operation.

Thermal phase drift (~350 fs/K), B. Lorbeer et al, PAC 2007 Amplitude-to-phase conversion (~ ps/mW)

Balanced Optical-Microwave Phase Detector

69!

Microwave Signal

Electro-optic sampling of microwave signal with optical pulse train

Passive Lasergyro for Navigation Systems

Convert Phase /Timing information in optical domain into intensity modulation

(BOM-PD)

Optical Pulse Train

DC current

J. Kim et al., Opt. Lett. 29, 2076 (2004), 31, 3659 (2006).

Optoelectronic Phase-Locked Loop (PLL)

70!

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) Stable Pulse

Train Output

Modelocked Laser

71!

BOM-PD 1: timing synchronization BOM-PD 2: out-of-loop timing characterization

Stability of BOM-PDs

J. Kim et al., Optics Express 15, 8951 (2007).

72!

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

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

Long-term stability: 6.8 fs drift over 10 hours

~ rf-stability 2 10-19 .

CONFiDENTiAL+ 73)

< 1 fs synchronization of Laser and RF-Networks

Timing Distribution Systems Ultrashort Pulse Synchronization

DESY Spin-Off Company Products: Timing & Synchronization

•  Accelerators and X-ray Free-Electron Lasers •  Ultrafast Laser Labs •  Radio Telescopes •  Jitter Characterization •  Low Noise Microwave Generation

Laser-Microwave Synchronization

< 1 fs Synchronisation of two femtosecond lasers

< 1 fs Synchronisation of microwave sources

to lasers

00 TΔt2π

VΔV

=N23

1⋅

=

Voltage!

time!

T!o!

Δt!V!o!

ΔV!

Challenge in High-Speed ADCs

Targeted resolution

10 GHz

50 GHz 14-bit 0.5 fs 0.1 fs 12-bit 2 fs 0.4 fs 10-bit 9 fs 1.8 fs 8-bit 36 fs 7.2 fs 6-bit 144 fs 30 fs

Required sampling jitter

0TΔt2π 3 2N

=⋅

74!

Photonic ADCs

104 105 106 107 108 109 1010 101102468

101214161820

this

0.1 fs

work

1 fs10 fs

100 fs (2007)

EN

OB

Analog input frequency, Hz

1 ps (1999)

Photon

ic

ADCs

104 105 106 107 108 109 1010 101102468

101214161820

this

0.1 fs

work

1 fs10 fs

100 fs (2007)

EN

OB

Analog input frequency, Hz

1 ps (1999)

Photon

ic

ADCs

Voltage!

t!T!o!

Δt!V!o!ΔV!

75!G. C. Valley, Opt. Express 15, 1955 (2007) R. H. Walden, ADC in the early 21st century, IMS 2007.

„Walden Plot“

State of the Art Electronic ADC and Beyond

Nortel Inc.: 40 GSa/s CMOS Y. M. Greshishchev, et al. ISSCC, paper 21.7 (2010). Fujitsu Inc.: 65 GSa/s CMOS http://www.fujitsu.com RPI: 40 GSa/s SiGe ADC M. Chu, et al. IEEE J. Solid State Circuits 45, 380 (2010).

Wavelength Multiplexed Optical Sampling

76!

!  Effective sampling rate = laser rep rate (1/T) x number of multiplexed channels (N)

!  Sampling jitter is set by MLL timing jitter !  Digitization is performed in electronic domain !  Down counting by WDM

Eliminate aperture jitter, demultiplex to lower rate channels T. Clark, Time and wavelength interleaved phot. Sampler , PTL 99.

Integrated Silicon Photonic ADC

77!

Modulator input Photodetector outputs (8 total)

Ring and bias heater controls

ADC chip (7×3.25

mm) input coupler

12 microring heater contact pads

metal layer

8 photodetector contact pads

MZ modulator with RF and bias heater pads

photodetectors

ring filters with heaters

1 mm

silicon structures

ch1

ch2

ch3

ch1

ch2

ch3

ch2, bottom

ch3, bottom

through, bottom

through, top

ch3, top

ch2, top

ch1, top

ch1, bottom

Si metal

Grein et al., CLEO 2011, paper CThI1 Khilo et al., Opt. Exp. (20) 4454 (2012)

Acknowledgement!Students: M. Peng (JPL) and P. Callahan, K. Safak, A. Kalaydzyan J. Kim (Prof. KAIST); A. Benedick and C. Sorace-Agaskar (MIT Lincoln Laboratory) A. Khilo and M. Dahlem (both Prof. MASDAR Institute of Technology) J. Cox (Sandia National Laboratory), M. Sander (Prof. Boston University) A. Motamedi (INTEL) Postdocs: M. Xi, Q. Zhang, T. Schibli and M. Popovic (both Prof. University of Colorado, Boulder) F. O. Ilday (Prof. Bilkent University) Research Scientists: O.D. Mücke, N. Chang, A. Nejadmalayeri (Samsung) Collaborators: Holger Schlarb and Ingmar Hartl (DESY) E. Ippen, F. Wong, M. Watts, R. Ram, J. Orcutt (MIT) E. Monberg, M. Yan, L. Grüner-Nielsen, J. Fini (OFS) S. Spector, T. Lyscczarz, M. Geis, M. Grein, J. Wang, J. Yoon (MIT – Lincoln Lab.)

78!