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Full Stabilization of a Microcavity
Frequency comb
Pascal Del‘Haye, Olivier Arcizet, Albert Schliesser, Tobias Wilken, Ronald Holzwarth
and Tobias Kippenberg
Max-Planck-Institute for Quantum Optics, Germany
Conference on Lasers and Electro-Optics
May 2008
Outline
Environmental and Bio-
Chemical Sensing
1. Review Frequency Combs
2. Generation of Frequency Combs
using Microcavities
3. Control and Stabilization of Aoki, Dayan, Wilcut, Bowen,
Microcavity Combs Perkins, Kippenberg, Vahala,
Kimble (Nature, 2006)
4. “Low” Repetition Rate Frequency
Combs (<100 GHz)
• P. Del’Haye, A. Schliesser, T. Wilken, R.
Holzwarth, T. J. Kippenberg,
Nature 450, Dec. 20 2007
• EU & US Patent application “Optical
Comb Generator using Microresonators”
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 2
Frequency Combs
Pulse train in time domain
Equidistant lines in frequency
domain.
f n = f CE + n ⋅ f rep n = Integer number
2π ⋅ f rep =
Hz
S. T. Cundiff. Phase stabilization of ultrashort optical pulses. Journal Of Physics D-Applied Physics, 35(8):R43–R59, April 2002.
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 3
Frequency Comb Generators
Mode-locked lasers Intracavity phase modulation
Mode-locking with saturable
absorbers
• Electrooptic phase modulator
• can generate octave spanning installed in a Fabry-Perot cavity.
combs • 4 THz spanning frequency comb
• bulky setup • Modulation frequency ~ 6 GHz
• „low“ repetition rate
Kourogi et al, Ieee Journal of Quantum Electronics 29,
Spence et al, Optics Letters, 16(1):42–44, January 1991. 2693-2701 (1993).
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 4
A Monolithic Frequency Comb Generator
Micrometer size fused silica toroids
generate optical frequency combs.(1)
Image: S. Cundiff Nature News & Views, Nature, Dec. 20, 2007
(1) P.Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, T. J. Kippenberg (Nature 450, 1214-1217, 2007)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 5
Toroid Microcavities on-a-Chip
• Optical whispering gallery modes with very
long photon lifetimes:
Q>108 can be obtained
Photon lifetimes of several 100 ns
Finesse in excess of 1,000,000
Vahala Group
• Small mode volume
Circulating Intensities > 2.5 GW/cm2
• Silicon compatible
Fabricated on a silicon wafer
Armani, Kippenberg, Spillane, Vahala, Nature 421, 925-928 (2003).
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 6
Toroidal Microcavities
Fabrication using standard microfabrication techniques
(a) (b) (c)
2 μm silica layer Silica pads on silicon wafer after Free standing silica discs after
on silicon wafer lithography, HF-etching XeF2 dry etching
CO2 laser beam
Ultra-high-Q: Q=ωτ up to 6x108
silica
silicon CO2 laser assisted reflow
Wavelength λ=10.6 μm
absorbed by silica,
silicon transparent
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 7
Tapered Fiber Coupling
Fiber taper transition from conventional core
guiding region to a dielectric waveguide region
T
(125 μm)
40 μm
Pin
SMF-28
fiber ca. 1.5 um
Tapered region: ∅~λ
M. Cai, O.J. Painter, K. J. Vahala. Phys. Rev. Lett. (2002).
J. Knight, T.A. Birks, Optics Letters (1996)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 8
Tapered Fiber Coupling
critical coupling
Et Ecavity
T=|E-E|2=0
T
40 μm
Taper-microcavity junction exhibits Pin
extremely high ideality (coupling losses
<0.3%)
Coupling both to-and-from a 80-μm
microtoroid on a chip
Kippenberg, Spillane, Vahala, Optics Letters 27, 1669 (2002)
Spillane, Kippenberg, Painter, Vahala, PRL 91, 043902 (2003)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 9
Parametric Oscillations in χ(3) Materials
ωp
ωi ωs
Degenerate four- ωp
ωs
Silica Resonator (1)
wave mixing:
ωp ωi
CaF2 Resonator (2)
Annihilation of two pump photons ωp and emission of signal and
idler photon (ωs and ωi). Threshold powers ~ 1/Q2 (~100 μW)
The process can cascade with non- ωi ωs
degenerate four-wave mixing:
ωp ωi’
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
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 10
Generating Combs
(silica)
70 μm
- Up to 500 nm spanning combs observed.
- More than 1 mW optical power per comb line
P.Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, T. J. Kippenberg (Nature 450, 1214-1217, Dec 2007)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 11
Microcavity Dispersion
Dispersion contributions:
Waveguide Dispersion ΔωFSR < 0:
Material Dispersion ΔωFSR > 0 for λ > 1300 nm:
For wavelengths > 1300 nm, material and waveguide dispersion can compensate!
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 12
Microcavity combs?
Are the comb modes equidistant?!
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 13
Equidistance of Comb Lines
Superimposing two frequency combs... Microcavity Comb
Fiber Laser Comb
RF beat notes Photodiode
Multi-Heterodyne1) Measurement:
ωbeat1 ωbeat2 ωbeat3
Fiber Laser
Comb Line
100 MHz
1 THz
(100 MHz spacing)
Microcavity Comb
optical frequency (THz) (1 THz spacing)
ωbeat1 ωbeat2 ωbeat3
Beat Note
radio frequency (MHz)
Two equidistant frequency combs will generate an
equidistant beat note spectrum.
P. Del‘Haye – Comb Stabilization, CLEO, May 2008
1) Schliesser, Brehm, Keilmann, van der Weide, Optics Express, 13, 1929 (2005) 14
Counting the sidebands
Frequency Counter
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 15
Equidistance of the comb lines
Difference between two mode spacings:
Accuracy relative to the optical
carrier:
5.5 mHz / 200 THz = 3 · 10 -17
P.Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, T. J. Kippenberg (Nature 450, 1214-1217, 2007)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 16
How to Stabilize the Comb?
Frequency
Two linearly independent actuators are
required for full stabilization of a
frequency comb.
f n = f CE + n ⋅ f rep
⇔ f n = f pump ± n ⋅ f modespacing
Mode Spacing
Offset Frequency
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 17
Controlling the Comb
I. The offset frequency is controlled
Transmission T
by the frequency of the pump laser,
while the microcavity resonance is
thermally locked(1) to the laser.
Actuator 1: Pump frequency
Tuning range > 10 GHz Frequency ν
Thermal bistability of a microcavity
(1) Thermal self locking: Carmon, Yang, Vahala, Optics Express, Vol. 12, pp. 4742-4750
II.
?
How to change the size of a monolithic microcavity?
Use fast thermal effects to change the optical
pathlength via the temperature dependent
refractive index.
Actuator 2: Pump power sent to microcavity
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 18
Experimental Locking Scheme
Pump power
control
Pump frequency
control
pump sideband
beat beat
No movable parts
for locking!
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 19
Thermal drift of the modespacing
Mode spacing drifts originating from intracavity power fluctuation and temperature drifts.
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 20
Stabilized Comb
Long term stabilization of the microcavity frequency comb!
Gatetime 1s
Kerr comb modes Pump Mode Sideband
(via frequency) (via pump power)
Stabilized reference
comb modes
Del’Haye, Arcizet, Schliesser, Holzwarth, Kippenberg, (arXiv:0803.1771)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008
ω 21
Mode Spacing Tuning Range
Mode spacing can be tuned by ~200 kHz per milliwatt pump power
Tuning range large enough to compensate for
thermal drifts and fluctuations (~60 kHz per hour)!
Del’Haye, Arcizet, Schliesser, Holzwarth, Kippenberg, (arXiv:0803.1771)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 22
Locking Bandwidth
Setup to determine locking bandwidth
The small mode volume in microtoroids yields
high actuation bandwidths in the kHz range.
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 23
Combs with Telecom Mode Spacing
775 μm diameter toroids and generated comb spectrum
Mode spacings in the microwave range can be
directly measured with fast photodiodes!
Del’Haye, Arcizet, Schliesser, Holzwarth, Kippenberg, (arXiv:0803.1771)
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 24
Microwave Beat Counting
er
lyz
A na
m
ctru
S pe
Stabilized Microwave Beat Note of the Frequency Comb Mode Spacing
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 25
Allan Deviation of the Mode Spacing Beat
N −1
The Allan deviation is a measure of the relative 1
σA = ⋅ ∑ ( yi +1 − yi ) 2
measurement accuracy within a certain gate time: 2( N − 1) i =1
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 26
Autocorrelation Measurement
~ 1 ps
Kerr comb from microcavity
Interferometric intensity autocorrelation trace.
Autocorrelator Setup
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 27
Applications of High Repetition Rate Comb Generators
• Advanced High Capacity Telecommunications (Channel Spacing
40/80/160 GHz)
• Spectrometer Calibration for Astronomy
Murphy, M. T. et al. Mon. Not. R.
Astron. Soc. 380, 839–847 (2007).
Wilken et. al, postdeadline session: CPDB9
• Generation of low-phase noise microwave oscillators
Figure from JPL Group/OE Waves:
PRL 93, 243905 (Maleki Group)
• Optical Arbitrary Waveform Generation
Weiner, A. M. Femtosecond pulse shaping using spatial light
modulators. Rev. Sci.Instrum. 71, 1929–1960 (2000).
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 28
Conclusion
Summary
• Generation and stabilization of
microcavity frequency combs has been
demonstrated
• Millimeter size resonators enabled direct
measurement of the mode spacing
Advantages
• Monolithic on-chip design
• High power per comb line
(>1 mW/combline)
• High repetition rate (>50 GHz)
Single comb lines accessible
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 29
Funding/Acknowledgments
We thank Prof. Kotthaus for cleanroom access
Nanosystems Initiative Munich
Max Planck Generalverwaltung via an
Independent Max Planck Junior Research Group
Marie Curie Reintegration Grant (IRG)
Marie Curie Excellence Grant (EXT)
Nano-Science European Research Area
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 30
Acknowledgments
Tobias Kippenberg Olivier Arcizet Albert Schliesser Remi Riviere Bastian Schroeter
Group Leader (Postdoc) (PhD) (PhD) (Diplom)
Cavity Cooling, combs Cavity Cooling Biochemical Sensing
Remi Riviere
(PhD)
Cooling Project
Georg Anetsberger Jens Dobrindt Xiaoqing Zhou Yang Yang
(PhD) (PhD) (PhD) (PhD)
Mechanical Dissipation Biochemical Sensing Coulomb Cooling Coulomb Cooling
Thank you for your attention!
www.mpq.mpg.de/k-lab
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 31
End
P. Del‘Haye – Comb Stabilization, CLEO, May 2008 32
