Distributed Raman optical amplification in phase coherent transfer of optical frequencies

We describe the application of Raman Optical-fiber Amplification (ROA) for the phase coherent transfer of optical frequencies in an optical fiber link. ROA uses the transmission fiber itself as a gain medium for bi-directional coherent amplification. In a test setup we evaluated the ROA in terms of on-off gain, signal-to-noise ratio, and phase noise added to the carrier. We transferred a laser frequency in a 200 km optical fiber link with an additional 16 dB fixed attenuator (equivalent to 275 km of fiber on a single span), and evaluated both co-propagating and counter-propagating amplification pump schemes, demonstrating nonlinear effects limiting the co-propagating pump configuration. The frequency at the remote end has a fractional frequency instability of 3e-19 over 1000 s with the optical fiber link noise compensation

Optically loaded Strontium lattice clock with a single multi-wavelength reference cavity

We report on the realization of a new compact strontium optical clock using a 2-D magneto-optical-trap (2D-MOT) as cold atomic source and a multi-wavelength cavity as the frequency stabilization system. All needed optical frequencies are stabilized to a zero-thermal expansion high-finesse optical resonator and can be operated without frequency adjustments for weeks. We present the complete characterization of the apparatus. Optical control of the atomic source allows us to perform low-noise clock operation without atomic signal normalization. Long- and short-term stability tests of the clock have been performed for the 88 Sr bosonic isotope by means of interleaved clock operation. Finally, we present the first preliminary accuracy budget of the system

Spectral purity transfer with 5 × 10−17 instability at 1 s using a multibranch Er:fiber frequency comb

In this work we describe the spectral purity transfer between a 1156 nm ultrastable laser and a 1542 nm diode laser by means of an Er:fiber multibranch comb. By using both the master laser light at 1156 nm and its second-harmonic at 578 nm, together with the 1542 nm slave laser, we investigate the residual noise between the main comb output, the octave-spanning output, and a wavelength conversion module including non-linear fibers, second-harmonic generation crystal and amplifiers. With an ultimate stability of the system at the level of 5E−17 at 1 s and accuracy of 3E−19, this configuration can sustain spectral transfer at the level required by the contemporary optical clocks with a simple and robust setup

Absolute frequency measurement of the 1S0 - 3P0 transition of 171Yb

We report the absolute frequency measurement of the unperturbed transition 1S0 - 3P0 at 578 nm in 171Yb realized in an optical lattice frequency standard. The absolute frequency is measured 518 295 836 590 863.55(28) Hz relative to a cryogenic caesium fountain with a fractional uncertainty of 5.4x10-16 . This value is in agreement with the ytterbium frequency recommended as a secondary representation of the second in the International System of Units.Comment: This is an author-created, un-copyedited version of an article accepted for publication/published in Metrologia. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/1681-7575/aa4e62. It is published under a CC BY licenc

Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this technique, the fiber noise was passively cancelled, and we compared two optical frequencies at the ultimate 1E-21 stability level. The experiment was performed on a 47 km fiber that is part of the metropolitan network for Internet traffic. The technique relies on the synchronous measurement of the optical phases at the two ends of the link, that is made possible by the use of digital electronics. This scheme offers several advantages with respect to active noise cancellation, and can be upgraded to perform more complex tasks

Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain

We used a Cs atomic fountain frequency standard to measure the Stark shift on the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the electric field generated by the blackbody radiation. The measures relative shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation -1.49(07)e-14. This value differs from the currently accepted one -1.69(04)e-14. The difference has a significant implication on the accuracy of frequency standards, in clocks comparison, and in a variety of high precision physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table

Yellow laser performance of Dy3+^{3+} in co-doped Dy,Tb:LiLuF4_4

We present laser results obtained from a Dy$^{3+}$-Tb$^{3+}$ co-doped LiLuF$_{4}$ crystal, pumped by a blue emitting InGaN laser diode, aiming for the generation of a compact 578 nm source. We exploit the yellow Dy$^{3+}$ transition $^{4}$F$_{9/2}$ $\Longrightarrow$ $^{6}$H$_{13/2}$ to generate yellow laser emission. The lifetime of the lower laser level is quenched via energy transfer to co-doped Tb$^{3+}$ ions in the fluoride crystal. We report the growth technique, spectroscopic study and room temperature continuous wave (cw) laser results in a hemispherical cavity at 574 nm and with a highly reflective output coupler at 578 nm. A yellow laser at 578 nm is very relevant for metrological applications, in particular for pumping of the forbidden $^{1}$S$_{0} \Longrightarrow ^{3}$P$_{0}$ Ytterbium clock transition, which is recommended as a secondary representation of the second in the international system (SI) of units. This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.39.006628. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Comment: 8 pages, 5 figure

Absolute frequency measurement of the 1S0 – 3P0 transition of 171-Yb with a link to International Atomic Time

Dataset of the INRIM Yb clock measured respect to TAI collected between October 2018 to February 2019. YbvsSIm-viaEAL.dat: montly data with columns MJDstart: start date in MJD MJDstop: stop date in MJD MJDmed: mid point date in MJD MJDbaro: baricenter date in MJD Ybduty: Yb clock duty time y0=Yb/HM3: ratio between Yb clock and H Maser 03 u0: statistical uncertainty of y0 uB0: systematic uncertainty of y0 y1=extrap.: extrapolation over HM3 udead1: uncertainty of y1 from dead times udrift1: uncertainty of y1 from HM3 drift HM3drift/d: HM3 drift per day udrift/d: uncertainty of HM3 drift y2=HM3/UTCit: ratio between HM3 and UTC(IT) u2: uncertainty of y2 y3=UTCit/TAI: ratio between UTC(IT) and TAI u3: uncertainty of y3 y4=EALext.: extrapolation over EAL udead4: uncertainty of y4 from dead times udrift4: uncertainty of y4 from EAL drift y5=-d: ratio between TAI and the SI second from Circular T u5: uncertainty of y5 uA5: statistical uncertainty of y5 uB5: systematic uncertainty of y5 y=Yb/SI: final ratio beween the Yb clock and the Si second uA: not used uB: not used u: uncertainty of y YbvsTAId.dat: data every 5 days with columns: MJDstart: start date in MJD MJDstop: stop date in MJD MJDmed: mid point date in MJD MJDbaro: baricenter date in MJD Ybduty: Yb clock duty time y0=Yb/HM3: ratio between Yb clock and H Maser 03 u0: statistical uncertainty of y0 uB0: systematic uncertainty of y0 y1=extrap.: extrapolation over HM3 udead1: uncertainty of y1 from dead times udrift1: uncertainty of y1 from HM3 drift HM3drift/d: HM3 drift per day udrift/d: uncertainty of HM3 drift y2=HM3/UTCit: ratio between HM3 and UTC(IT) u2: uncertainty of y2 y3=UTCit/TAI: ratio between UTC(IT) and TAI u3: uncertainty of y3 y=Yb/TAI: final ratio beween the Yb clock and TAI uA: not used uB: not used u: uncertainty of yWe acknowledge funding from the European Metrology Program for Innovation and Research (EMPIR) project 15SIB03 OC18, from the Horizon 2020 Marie Skłodowska-Curie Research and Innovation Staff Exchange (MSCA-RISE) project Q-SENSE (Grant Agreement Number 691156), from the Italian Space Agency (ASI) funding DTF-Matera, from the EMPIR project 18SIB05 ROCIT. The EMPIR initiative is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States

Phase noise cancellation in polarisation-maintaining fibre links

The distribution of ultra-narrow linewidth laser radiation is an integral part of many challenging metrological applications. Changes in the optical pathlength induced by environmental disturbances compromise the stability and accuracy of optical fibre networks distributing the laser light and call for active phase noise cancellation. Here we present a laboratory scale optical (at 578 nm) fibre network featuring all polarisation maintaining fibres in a setup with low optical powers available and tracking voltage-controlled oscillators implemented. The stability and accuracy of this system reach performance levels below 1 * 10^(-19) after 10 000 s of averagingComment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in "Phase noise cancellation in polarisation-maintaining fibre links", Rauf et al., Review of Scientific Instruments, 89, 033103 (2018) and may be found at https://doi.org/10.1063/1.501651