Optical Frequency Comb Generation from a Monolithic Microresonator

Pascal Del‘Haye, Albert Schliesser, Olivier Arcizet, Tobias Wilken, Ronald Holzwarthand Tobias Kippenberg

Max-Planck-Institute for Quantum Optics, Germany

Frontiers in Optics 2007/Laser Science XXIIISeptember 2007

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Frequency Combs

S. T. Cundiff. Phase stabilization of ultrashort optical pulses. Journal Of Physics D-Applied Physics, 35(8):R43–R59, April 2002.

repCE fnffn ⋅+=

Equidistant lines in frequency domain.

Pulse train in time domain

n = Integer number

Hz

chirped mirror

Ti:Al2O3

pumpoutcoupling mirror

pulse train

ApertureKerr lens mode-locked laser:

=⋅ rep2 fπ

cavity roundtrip time repf/1=τ

P. Del‘Haye – Kerr Combs – FIO 2007 3Armani, Kippenberg, Spillane, Vahala, Nature 421, 925-928 (2003).

Toroid Microcavities on-a-Chip

• Optical whispering gallery modes with verylong photon lifetimes:

Q>108 can be obtainedPhoton lifetimes of several 100 nsFinesse in excess of 1,000,000

• Small mode volume• Silicon compatible

Built on a silicon waferIntegration with other function

Vahala Group

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Toroidal Microcavities

silica

silicon CO2 laser assisted reflow

Fabrication using standard microfabrication techniques

2 μm silica layer on silicon wafer

(a) (b) (c)

Silica pads on silicon wafer after lithography, HF-etching

Free standing silica discs after XeF2 dry etching

Wavelength λ=10.6 μmabsorbed by silica,silicon transparent

Ultra-high-Q: Q=ωτ up to 6x108CO2 laser beam

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Coupling both to-and-from a 80-μmmicrotoroid on a chip

Taper-microcavity junction exhibits extremely high ideality (coupling losses <0.3%)

Pin

T

40 μm

EcavityEt

critical coupling

T=|E-E|2=0

Kippenberg, Spillane, Vahala, Optics Letters 27, 1669 (2002)Spillane, Kippenberg, Painter, Vahala, PRL 91, 043902 (2003)

Tapered Fiber Coupling

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Parametric Oscillations

ωp

ωpωs

ωi

Degenerate four-wave mixing:

Annihilation of two pump photons ωp and emission of signal and idler photon (ωs and ωi). Threshold powers ~100 μW

1) Kippenberg, T. J.; Spillane, S. M. & Vahala, K. J., Physical Review Letters, 2004, 93, 083904 2) Savchenkov, Matsko, Strekalov, Mahageg, Ilchenko, Maleki, PRL, 2004, 93, 243905

CaF2 Resonator (2)

Silica Resonator (1)

ωp

ωi ωs

ωp

ωsωi

ωi’The process can cascade with non-degenerate four-wave mixing:

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Generating Combs

More than 130 lines, pump power 500 mW177-μm-diameter cavity

Modespacing = 1 THz, 70 μm-diameter cavity

70 μm(silica)

- Up to 500 nm spanning combs observed.- Conversion efficiencies of more than 80 % can be achieved!

P.Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, K. Vahala, R. Holzwarth, T. J. Kippenberg (arXiv:0708.0611)

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Cold Microcavity ModesThe microcavity modes are not expected to be a priori equidistant due to dispersion.

ωFSR1

ω

ωFSR2

ΔωFSR = ωFSR2 -ωFSR1

ωSolutions:- Nonlinear: Modes can be pulled equidistant by self-phase modulation and cross-phase modulation. 1)

- Linear: Dispersion compensation1) Kippenberg, T. J.; Spillane, S. M. & Vahala, K. J., Physical Review Letters, 2004, 93, 083904

XPM XPMSPM

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Microcavity DispersionDispersion contributions:

For wavelengths > 1300 nm, material and waveguide dispersion can be compensated!

Waveguide Dispersion ΔωFSR < 0:

Material Dispersion ΔωFSR > 0 for λ > 1300 nm:

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Dispersion Measurement

repoffset fnff ⋅+=Δ

Utilizing a fiber laser frequency comb to measure the FSR of a microcavity.

n = Number of fiber comb lines between two microcavity resonances

Distance between cold microcavity modes:

foffset

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Dispersion Measurement

Accumulated dispersion in a 70 μm diameter microcavity over a wavelength range of 61 nm [1577nm…1516nm]

1577 nm

1516 nm

ωFSR1

ω

ωFSR2 ωFSR4ωFSR3

Dispersion of a cold toroidal microcavity: ~3 MHz/FSR

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Microcavity combs?

Are the lines equidistant?!Are the lines equidistant?!

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Frequency combs for metrology

Hz

ν

Frequency comb lines with known frequencies(Mode spacing ~ 100 MHz)

Unknown optical frequency

νN

ν0

νN+1νN-1νN-2

Radio frequency beat note with νB = νN - ν0

The beat note frequency can be measured with radio frequency counters.

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Equidistance of Comb Lines

100 MHz1 THz

ωbeat3ωbeat2ωbeat1

optical frequency (THz)

ωbeat1 ωbeat2 ωbeat3

radio frequency (MHz)

Fiber Laser Comb Line(100 MHz spacing)

Kerr Comb Line(1 THz spacing)

Beat Note

An equidistant beat note spectrum can be generated by superimposing two equidistant combs.

Superimposing two frequency combs... Kerr Comb

Multi-Heterodyne1) Measurement:PhotodiodeRF beat notes

Fiber Laser Comb

1) Schliesser, Brehm, Keilmann, van der Weide, Optics Express, 13, 1929 (2005)

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Equidistance of Comb Lines

⊗ =Fiber Laser Comb

Kerr Comb

Beat note spectrum:Optical Domain Radio Frequency Domain

Kerr lines are proved to be equidistant to a level of

=THz 200

kHz 21 x 10 -13

First demonstration of frequency comb generation in a monolithicFirst demonstration of frequency comb generation in a monolithic microcavity!microcavity!

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Counting the sidebands

Frequency Counter

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Counting the sidebands

Allan deviation:Measure of the relative accuracy that can be obtained with a certain gate time.

Accuracy relative to the optical carrier:5.5 mHz / 200 THz = 3 · 10 -17

∑−

=+ −⋅

−=

1

1

21 )(

)1(21 N

iiiA yy

Nσ

P.Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, K. Vahala, R. Holzwarth, T. J. Kippenberg (arXiv:0708.0611)

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Thermal drift of the modespacing

ω

Stabilized referencecomb modes

Kerr comb modes

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Kerr Comb ActuatorsTwo control variables to define all lines of a frequency comb:

Carrier envelope offset frequency fCEORepetition rate frep

Modelocked Laser:Pump frequency fPMode spacing Δν

Microcavity comb:

Controlled by pump power

Pump frequencycontrol

Pump powercontrol

pumpbeat

sidebandbeat

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Stability of the Kerr Comb Lock

Locked with microcavity

pump power

Gatetime 1s

Standard lock of a diode laser to a reference laser

Modespacing

Pump Frequency

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• Frequency combs spanning 500 nm have been generated

• Equidistance has been proved to a level of 7.3x10-18

• Locking has been demonstrated

Conclusion

• Pulse shaping• Spectrometer calibration• Multi-channel

telecommunication

Future Applications• Increase cavity diameter for mode

spacings in the microwave domain• Generate octave spanning spectra• Time domain behaviour?!

Future Research

Advantages• Monolithic on-chip design• High power per comb line

(1 mW/combline can be easily achieved)• High repetition rate (>100 GHz)

Single comb lines accessible

Summary

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FundingMax Planck Generalverwaltung via an Independent Max Planck Junior Research Group

MPQ

Marie Curie Reintegration Grant (IRG)Marie Curie Excellence Grant (EXT)

NIM Initiative

Nano-Science European Research Area

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Acknowledgments

Thank you for your attention!

Jens Dobrindt(Diplom)Cooling Theory

Tobias KippenbergGroup Leader

Georg Anetsberger (Diplom)Mechanical Dissipation

Remi Riviere(PhD)Cooling Project

Bastian Schroeter(Diplom)Biochemical Sensing

Yang Yang(PhD)Coulomb Cooling

Albert Schliesser (PhD)Cavity Cooling, combs

Xiaoqing Zhou(PhD)Coulomb Cooling

Olivier Arcizet (Postdoc)

Remi Riviere (PhD)Cavity Cooling

www.mpq.mpg.de/k-lab

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End