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Generation of multiple ultrastable optical frequency combs from an all-fiber photonic platform

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Science Advances  27 Mar 2020:
Vol. 6, no. 13, eaax4457
DOI: 10.1126/sciadv.aax4457
  • Fig. 1 Schematic of generating ultrastable optical frequency combs based on an all-fiber photonics platform.

    The comb-line frequency νi (i = 1, 2, …, n) of each comb source is directly locked to the stability of the fiber reference (δτ/τ) while stabilizing the carrier-envelope offset frequency fceo,i (i = 1, 2, …, n) of each comb. Using WDM couplers and tunable delay, multiple optical frequency combs are simultaneously locked to the fiber reference. AMP, radio frequency amplifier; AOFS, acousto-optic frequency shifter; BPF, radio frequency bandpass filter at 2fao; EDFA, erbium-doped fiber amplifier; FRM, Faraday rotating mirror; OC, 2 × 2 optical coupler; WDM, wavelength-division multiplexer; VCO, voltage-controlled oscillator. Photo credit: Dohyeon Kwon, KAIST

  • Fig. 2 Absolute phase noise, frequency noise, linewidth, and frequency instability of the fiber delay–stabilized frequency comb.

    (A) Measured single-sideband (SSB) optical phase noise PSD of the fiber delay–stabilized comb at 1540 nm (black), phase noise PSD projected from thermomechanical and thermoconductive fiber length fluctuation (blue dashed curve), and measured optical phase noise PSD of the free-running comb (gray dotted curve). (B) Measured frequency noise PSD of the fiber delay–stabilized comb at 1540 nm (black) and frequency noise PSD projected from thermomechanical and thermoconductive fiber length fluctuation (blue dashed curve). (C) Measured linewidth at 1550 nm of the fiber delay–stabilized comb using a frequency-stabilized CW fiber laser. (D) Fractional frequency instability of the fiber delay–stabilized comb (black, squares) and projected instability from thermomechanical and thermoconductive length fluctuation (blue, diamonds). The inset gray curve is the fractional frequency instability of the free-running comb.

  • Fig. 3 Absolute phase noise of repetition rate (i.e., timing jitter) of the fiber delay–stabilized frequency comb.

    Curve (i), measured optical phase noise of the fiber delay–stabilized comb scaled to the 10-GHz carrier (black). Curve (ii), measured residual fceo noise scaled to 10 GHz (gray). For comparison, the phase noise of a 10-GHz oven-controlled crystal oscillator (OCXO) (21) [curve (iii), red circles], 10-GHz sapphire-loaded cavity oscillator (SLCO) (22) [curve (iv), purple triangles], 10-GHz optoelectronic oscillator (OEO) (23) [curve (v), right green diamonds], and 10-GHz microwaves generated by OFD (6, 7) [curve (vi), blue squares; curve (vii), green squares] are also shown. Curve (viii), integrated RMS timing jitter of the measured repetition-rate phase noise.

  • Fig. 4 Two optical frequency combs locked to a single fiber delay line.

    (A) Concept of dual-comb source stabilization using a single fiber delay line. (B) Fourier-transformed interferogram of the fiber delay–stabilized comb-A and comb-B. (C) Relative linewidth between each comb and the CW laser when both lasers are stabilized to the same fiber delay line.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/13/eaax4457/DC1

    Section S1. Optical frequency comb sources

    Section S2. Out-of-loop comb-line frequency noise measurement method

    Section S3. Absolute linewidth measurement method

    Section S4. Dual-comb source experiment

    Section S5. Impact of acoustic noise, vibrations, and temperature fluctuations on the fiber delay line–based stabilization system

    Fig. S1. Free-running frep phase noise PSD and locked fceo noise PSD of comb-A and comb-B.

    Fig. S2. Experimental setup for out-of-loop optical phase noise measurement.

    Fig. S3. Measured in-loop and out-of-loop optical phase noise of the fiber delay line–stabilized comb.

    Fig. S4. Linewidth measurement at 1550 nm.

    Fig. S5. Optical phase noise of the fiber delay line–stabilized dual-comb source.

    Fig. S6. Relative linewidth measurement experiment between the comb and CW laser.

    Fig. S7. Impact of acoustic shielding on the measured out-of-loop optical phase noise PSDs.

    Fig. S8. Vibration sensitivity measurement.

    Fig. S9. Comparison between the measured frequency noise PSDs (black) and the estimated frequency noise PSDs computed from the measured vibration PSDs (red).

    Fig. S10. Frequency noise and vibration sensitivity reduction by a spring-mass mount.

    References (34, 35)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Optical frequency comb sources
    • Section S2. Out-of-loop comb-line frequency noise measurement method
    • Section S3. Absolute linewidth measurement method
    • Section S4. Dual-comb source experiment
    • Section S5. Impact of acoustic noise, vibrations, and temperature fluctuations on the fiber delay line–based stabilization system
    • Fig. S1. Free-running frep phase noise PSD and locked fceo noise PSD of comb-A and comb-B.
    • Fig. S2. Experimental setup for out-of-loop optical phase noise measurement.
    • Fig. S3. Measured in-loop and out-of-loop optical phase noise of the fiber delay line–stabilized comb.
    • Fig. S4. Linewidth measurement at 1550 nm.
    • Fig. S5. Optical phase noise of the fiber delay line–stabilized dual-comb source.
    • Fig. S6. Relative linewidth measurement experiment between the comb and CW laser.
    • Fig. S7. Impact of acoustic shielding on the measured out-of-loop optical phase noise PSDs.
    • Fig. S8. Vibration sensitivity measurement.
    • Fig. S9. Comparison between the measured frequency noise PSDs (black) and the estimated frequency noise PSDs computed from the measured vibration PSDs (red).
    • Fig. S10. Frequency noise and vibration sensitivity reduction by a spring-mass mount.
    • References (34, 35)

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