Data for "Comparing ultrastable lasers at 7×10-17 fractional frequency instability through a 2220 km optical fibre network"
<p>Here we share the relevant data of the manuscript “Comparing ultrastable lasers at 7×10<sup>-17</sup> fractional frequency instability through a 2,220 km optical fibre network”.</p>
<p>Raw data was acquired using multiple synchronised, dead-time free frequency counters in Lambda-mode [1]. The integration time for each data point was 1 s. The data provided here have been processed to reflect the fractional frequency difference between the ultrastable lasers at NPL and PTB, scaled to 1542 nm. Specifically,<br>
<span class="math-tex">\(y=(\nu_{\text{NPL(ULE)}}\frac{777327}{1126090}-\frac{767233}{767235}\nu_{\text{PTB(Si)}})/194.4 \ \text{THz}\)</span></p>
<p>where <span class="math-tex">\(y\)</span> is the value recorded in the data files, <span class="math-tex">\(\nu_{\text{NPL(ULE)}}\)</span> and <span class="math-tex">\(\nu_{\text{PTB(Si)}}\)</span> are the optical frequencies of the ultrastable lasers at NPL (referenced to a ULE cavity) and PTB (referenced to Si cavity), respectively. The numerators and the denominators of the scaling factors correspond to mode numbers of the optical frequency comb at NPL and PTB, respectively. The expression for <span class="math-tex">\(y\)</span> corresponds to the fractional transfer beat [2] between the NPL and PTB ultrastable lasers.</p>
<p>The file</p>
<ul>
<li>“833000_s_874000_s_data_for_fig_2.txt”</li>
</ul>
<p> contains the timeseries data used to compute the modified Allan deviation reported in <strong>Fig. 2a</strong>. The “0” values correspond to invalid data due to glitches in the operation of the optical fibre link. A linear drift of 40 mHz s<sup>-1</sup> has been removed in these data.</p>
<p>The file</p>
<ul>
<li>“432000_s_912077_s_data_for_fig_3.txt”</li>
</ul>
<p>contains the timeseries data used in <strong>Fig. 3.</strong> The “0” values correspond to invalid data due to glitches in the operation of the optical fibre link. These data have additionally been high pass filtered with a cut off frequency of 1 mHz to decouple the short-term instability of the optical fibre link from the drift of the ultrastable lasers (with a characteristic time >1000 s), as described in the manuscript.</p>
<p>The files</p>
<ul>
<li>“222000_s_232000_s_data_for_supp_fig_1.txt”,</li>
<li>“270000_s_288000_s_data_for_supp_fig_1.txt”,</li>
<li>“754000_s_765000_s_data_for_supp_fig_1.txt”,</li>
<li>“832000_s_890000_s_data_for_supp_fig_1.txt”,</li>
</ul>
<p>contain the timeseries data used to compute the modified Allan deviation reported in <strong>Supplementary Fig. 1</strong>. The “0” values correspond to invalid data due to glitches in the operation of the optical fibre link. A linear drift of 40 mHz s<sup>-1</sup> has been removed in these data.</p>
<p>The temporal starting point is displayed in seconds in the title of the files relative to 00:00 UTC of 2019/07/06.</p>
<p> </p>
<p><strong>References</strong></p>
<p>[1] Dawkins, S. T., McFerran, J. J. & Luiten, A. N. Considerations on the Measurement of the Stability of Oscillators with Frequency Counters. <em>IEEE Transactions on ultrasonics, ferroelectrics, and frequency control</em> <strong>54</strong>, 918-925 (2007).</p>
<p>[2] Telle, H.R., Lipphardt, B. & Stenger, J. Kerr-lens, mode-locked lasers as transfer oscillators for optical frequency measurements. <em>Appl. Phys. B</em> <strong>74</strong>, 1-6 (2002).</p>
<p> </p>
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