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Microresonator soliton dual-comb spectroscopy

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Science  04 Nov 2016:
Vol. 354, Issue 6312, pp. 600-603
DOI: 10.1126/science.aah6516
  • Fig. 1 Microresonator-based dual-comb spectroscopy.

    Two soliton pulse trains with slightly different repetition rates are generated by continuous-wave (CW) laser pumping of two microresonators. The pulse trains are combined in a fiber bidirectional coupler to produce a signal output path that passes through a test sample as well as a reference output path. The output of each path is detected (on Reference and Signal photo detectors) to generate an electrical interferogram of the two soliton pulse trains. The interferogram is Fourier-transformed to produce comb-like radio-frequency (RF) electrical spectra having spectral lines spaced by the repetition rate difference of the soliton pulse trains. The absorption features of the test sample can be extracted from this spectrum by normalizing the signal spectrum by the reference spectrum. Also shown are two silica disk resonators. The disks have a diameter of 3 mm and are fabricated on a silicon chip. The nth optical comb frequency (νn1 and νn2) for each soliton pulse train is given in terms of the respective repetition rate (fr1 and fr2) plus an offset frequency (fc1 andfc2). In the RF domain spectrum, the nth line occurs at a multiple of the difference in the repetition rates (Δfr = fr2fr1) plus an offset frequency (Δfc = fc2fc1).

  • Fig. 2 Soliton comb spectral characterization.

    (A and B) Optical spectra of the microresonator soliton pulse streams. (C and D) Electrical spectra showing the repetition rates of the soliton pulse streams. The rates and resolution bandwidth (RBW) are given within the panels.

  • Fig. 3 Measured electrical interferogram and spectra.

    (A) The detected interferogram of the reference soliton pulse train. (B) Typical electrical spectrum obtained by Fourier transform of the temporal interferogram in (A). Ten spectra each are recorded over a time of 20 μs and averaged to obtain the displayed spectra. (C) Resolved (multiple and individual) comb lines of the spectrum in (B) are equidistantly separated by 2.6 MHz, the difference in the soliton repetition rate of the two microresonators. The linewidth of each comb line is <50 kHz and is set by the mutual coherence of the pumping lasers. (D and E) Fourier transform (black) of the signal interferogram produced by coupling the dual-soliton pulse trains through the synthetic absorber (WaveShaper; see fig. S1) with programmed absorption functions (spectrally flat and sine-wave). The obtained dual-comb absorption spectra (red) are compared with the programmed functions (blue curves) from 1545 to 1565 nm.

  • Fig. 4 Measured molecular absorption spectra.

    (A) Absorption spectrum of 2ν3 band of H13CN measured by direct power transmission using a wavelength-calibrated scanning laser and comparison to the microresonator-based dual-comb spectrum. The residual difference between the two spectra is shown in green. (B) Overlay of the directly measured optical spectrum and the dual-comb spectrum, showing line-by-line matching. The vertical positions of the two spectra are adjusted to compensate for insertion loss.

Supplementary Materials

  • Microresonator soliton dual-comb spectroscopy

    Myoung-Gyun Suh, Qi-Fan Yang, Ki Youl Yang, Xu Yi, Kerry J. Vahala

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Fig. S1
    • References

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