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Full Stabilization of a Microcavity Frequency comb

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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

				
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