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Optical frequency comb generation from a monolithic microresonator


Optical frequency combs1,2,3 provide equidistant frequency markers in the infrared, visible and ultraviolet4,5, and can be used to link an unknown optical frequency to a radio or microwave frequency reference6,7. Since their inception, frequency combs have triggered substantial advances in optical frequency metrology and precision measurements6,7 and in applications such as broadband laser-based gas sensing8 and molecular fingerprinting9. Early work generated frequency combs by intra-cavity phase modulation10,11; subsequently, frequency combs have been generated using the comb-like mode structure of mode-locked lasers, whose repetition rate and carrier envelope phase can be stabilized12. Here we report a substantially different approach to comb generation, in which equally spaced frequency markers are produced by the interaction between a continuous-wave pump laser of a known frequency with the modes of a monolithic ultra-high-Q microresonator13 via the Kerr nonlinearity14,15. The intrinsically broadband nature of parametric gain makes it possible to generate discrete comb modes over a 500-nm-wide span (70 THz) around 1,550 nm without relying on any external spectral broadening. Optical-heterodyne-based measurements reveal that cascaded parametric interactions give rise to an optical frequency comb, overcoming passive cavity dispersion. The uniformity of the mode spacing has been verified to within a relative experimental precision of 7.3 × 10-18. In contrast to femtosecond mode-locked lasers16, this work represents a step towards a monolithic optical frequency comb generator, allowing considerable reduction in size, complexity and power consumption. Moreover, the approach can operate at previously unattainable repetition rates17, exceeding 100 GHz, which are useful in applications where access to individual comb modes is required, such as optical waveform synthesis18, high capacity telecommunications or astrophysical spectrometer calibration19.

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Figure 1: Broadband parametric frequency conversion from a monolithic toroidal microresonator.
Figure 2: Multi-heterodyne beat note detection.
Figure 3: Probing the equidistance of the comb structure.
Figure 4: Verification of the equidistant mode spacing.


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We thank T. W. Hänsch, T. Udem, K. J. Vahala and S. A. Diddams for critical discussions and suggestions. T.J.K. acknowledges support via an Independent Max Planck Junior Research Group. This work was funded as part of a Marie Curie Excellence Grant (RG-UHQ), the DFG funded Nanosystems Initiative Munich (NIM) and a Marie Curie Reintegration Grant (JRG-UHQ). We thank J. Kotthaus for access to clean-room facilities for sample fabrication.

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Correspondence to T. J. Kippenberg.

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Del’Haye, P., Schliesser, A., Arcizet, O. et al. Optical frequency comb generation from a monolithic microresonator. Nature 450, 1214–1217 (2007).

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