Long-distance frequency transfer over an urban fiber link using optical phase stabilization

Journal of the Optical Society of America B (Impact Factor: 1.97). 07/2008; 25(12). DOI: 10.1364/JOSAB.25.002029
Source: arXiv


We transferred the frequency of an ultra-stable laser over 86 km of urban fiber. The link is composed of two cascaded 43-km fibers connecting two laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically demonstrate a link of 172 km without using spooled fiber extensions, we implemented a recirculation loop to double the length of the urban fiber link. The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz linewidth. The fiber-induced phase noise is measured and cancelled with an all fiber-based interferometer using commercial off the shelf pigtailed telecommunication components. The compensated link shows an Allan deviation of a few 10-16 at one second and a few 10-19 at 10,000 seconds.

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Available from: Michel Lours, Aug 18, 2014
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    • "From Eq.4 and following considerations, one expects that the amplitude and the bandwidth of the noise correction are decreasing linearly with L. The performance of the link can then be improved by dividing a link into smaller subsections. This is the cascaded link approach [23] [24]. For instance, dividing a link in N independent subsections of equal length, and considering that the power of the free fiber noise scales as the length of each subsection, both the amplitude and the bandwidth of the noise rejection are increased by a factor N . "
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    ABSTRACT: We theoretically and experimentally investigate relevant noise processes arising in optical fiber links, which fundamentally limit their relative stability. We derive the unsuppressed delay noise for three configurations of optical links: two-way method, Sagnac interferometry, and actively compensated link, respectively designed for frequency comparison, rotation sensing, and frequency transfer. We also consider an alternative two-way setup allowing real-time frequency comparison and demonstrate its effectiveness on a proof-of-principle experiment with a 25-km fiber spool. For these three configurations, we analyze the noise arising from uncommon fiber paths in the interferometric ensemble and design optimized interferometers. We demonstrate interferometers with very low temperature sensitivity of respectively -2.2, -0.03 and 1 fs/K. We use one of these optimized interferometers on a long haul compensated fiber link of 540km. We obtain a relative frequency stability of 3E-20 after 10,000 s of integration time.
    Full-text · Article · Dec 2014 · Journal of the Optical Society of America B
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    • "An RF transfer using amplitude modulation of the laser carrier has demonstrated frequency stability of 10 -15 at a 1 s averaging period and near 10 -18 at one day [22- 24]. An optical carrier frequency transfer can reach stabilities below 10 -18 after 1000 s [25] [26] [27]. In addition, the recorded distance for frequency transfer has increased from 251 km in 2007 [28] to 920 km in 2011 [29] "
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    • "To measure f rep fluctuations, it is convenient to increase the sensitivity by measuring N×f rep , with N a large integer. By beating the comb output with an ultra stable laser (linewidth<1Hz) [17] of optical frequency ν cw (near the 1.55 µm central wavelength of the comb), we have access to f b =N×f rep +f 0 -ν cw . This radio-frequency (RF) signal mixed with f 0 leads to two sidebands, highly sensitive to f rep fluctuations (because of the large multiplicative factor N). We select, with a bandpass filter, the sideband which is independent from f 0 (since f b -f 0 = N×f rep -ν cw ). "
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    ABSTRACT: We report on the characterization of a commercial- core fiber-based frequency comb equipped with an intracavity free-space electro-optic modulator (EOM). We investigate the relationship between the noise of the pump diode and the laser relative intensity noise (RIN) and demonstrate the use of a low-noise current supply to substantially reduce the laser RIN. By measuring several critical transfer functions, we evaluate the potential of the EOM for comb repetition rate stabilization. We also evaluate the coupling to other relevant parameters of the comb. From these measurements, we infer the capabilities of the femtosecond laser comb to generate very-low-phase-noise microwave signals when phase-locked to a high-spectral-purity ultra-stable laser.
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