Agile low phase noise radio-frequency sine wave generator applied to experiments on ultracold atoms

We report on the frequency performance of a low cost (~500$) radio-frequency sine wave generator, using direct digital synthesis (DDS) and a field-programmable gate array (FPGA). The output frequency of the device may be changed dynamically to any arbitrary value ranging from DC to 10 MHz without any phase slip. Sampling effects are substantially reduced by a high sample rate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. By using a low noise external oscillator to clock the DDS, we demonstrate a phase noise as low as that of the master clock, that is at the level of -113 dB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. The device is successfully used to confine an ultracold atomic cloud of rubidium 87 in a RF-based trap, and there is no extra heating from the RF source.Comment: 10 pages, 6 figure

Une introduction au nouveau Système international d'unités

International audienceBy deciding to set certain universal constants, metrologists are about to change the way we measure the world. This historical development will be marked by a major reform of the International System of Units aimed at establishing a more coherent, stable and universal measurement system. We present the main issues of this reform before explaining the steps involved in building the new system.En décidant de fixer certaines constantes universelles, les métrologues s'apprêtent à changer notre façon de mesurer le monde. Cette évolution historique sera marquée par une réforme majeure du Système international d'unités dont l'ambition est d'établir un système de mesure plus cohérent, plus stable et universel. Nous pré-sentons les grands enjeux de cette réforme avant d'expliquer les étapes de la construction du nouveau système qui entrera en vigueur en mai 2019

Frequency Stability Transfer in Passive Mode-Locked Quantum-dash Laser Diode using Optical Injection Locking

In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 µm with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level

Frequency Stability Transfer in Passive Mode-Locked Quantum-dash Laser Diode using Optical Injection Locking

In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 µm with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level

Comparison of time profiles for the magnetic transport of cold atoms

International audienceWe have compared different time profiles for the trajectory of the centre of a quadrupole magnetic trap designed for the transport of cold sodium atoms. Our experimental observations show that a smooth profile characterized by an analytical expression involving the error function minimizes the transport duration while limiting atom losses and heating of the trapped gas. Using numerical calculations of single atom classical trajectories within the trap, we show that this observation can be qualitatively interpreted as a trade-off between two types of losses: finite depth of the confinement and Majorana spin flips

Cascaded optical link on a telecommunication fiber network for ultra-stable frequency dissemination

The transfer of ultra-stable frequencies between distant laboratories is required by many applications in time and frequency metrology, fundamental physics, particle accelerators and astrophysics. Optical fiber links have been intensively studied for a decade and brought the potential to transfer frequency with a very high accuracy and stability thanks to an active compensation of the propagation noise. We are currently developing an optical metrological network using the fibers of the French National Research and Education Network. Using the so-called dark-channel approach, the ultrastable signal is copropagating with data traffic using wavelength division multiplexing. Due to significant reflections and losses along the fibers, which cannot be compensated with amplifiers, we have developed some repeater stations for the metrological signal. These remotely-operated stations amplify the ultrastable signal and compensate the propagation noise. The link is thus composed of a few cascaded spans. It gives the possibility to increase the noise correction bandwidth, which is proportional to the inverse of the fiber length for each span. These stations are a key element for the deployment of a reliable and large scale metrological network. We report here on the implementation of a two-spans cascaded link of 740 km reaching a relative stability of a few 10^-20 after 1000s averaging time. Extension to longer links and alternative transfer methods will be discussed

Progress on a cascaded optical link between Paris and Strasbourg

We are currently developing a cascaded optical frequency link between Paris and Strasbourg using the French National Research and Education Network RENATER. The ultrastable signal is copropagating with data traffic using wavelength division multiplexing. We have developed some repeater stations to amplify and filter the ultrastable signal between each sections of the link and compensate the propagation noise. The remote operation of these stations is a key element for the deployment of a reliable and large scale metrological network. We report on the first implementation of such a remote station on a 540km cascaded link between Paris and Reims. The stability (modified Allan deviation with lambda-type counter) reaches a few 10-^20 at 1000 s averaging time

Ultra-stable optical frequency and accurate timing signal dissemination using telecommunication network

Optical fibre links have been developed to transfer an ultrastable optical frequency between distant laboratories for time and frequency metrology and high-precision measurements. We will review the specificity of this technique, its performance and a few applications

Limitations due to residual interference in a fiber-based optical frequency reference at 1.55 µm

We present an experimental investigation of the stability limits specific to optical frequency standards using a fiber-optic architecture and semiconductor lasers. A compact setup composed of a semiconductor laser frequency-locked onto an acetylene transition detected in saturated absorption has been implemented using only fiber-optic components. Fiber optic technology allows compact and reliable solutions for various applications. However, for high sensitivity and stability applications such as metrology, residual reflections induced by optical index inhomogeneities in connectors and fiber-coupled components leading to spurious interference significantly limit performance. We have examined the origin of the interference fringes superimposed on the detected signal and the limitations they cause to the frequency stability of the reference. The effects of temperature and beam power fluctuations are also examined. Our results show that the frequency stability is limited in the 10-13 range by the effect of interference fringes due to use of fiber components

Cascaded optical fiber link using the internet network for remote clocks comparison

We report a cascaded optical link of 1100 km for ultra-stable frequency distribution over an Internet fiber network. The link is composed of four spans for which the propagation noise is actively compensated. The robustness and the performance of the link are ensured by five fully automated optoelectronic stations, two of them at the link ends, and three deployed on the field and connecting the spans. This device coherently regenerates the optical signal with the heterodyne optical phase locking of a low-noise laser diode. Optical detection of the beat-note signals for the laser lock and the link noise compensation are obtained with stable and low-noise fibered optical interferometer. We show 3.5 days of continuous operation of the noise-compensated 4-span cascaded link leading to fractional frequency instability of 4x10 −16 at 1-s measurement time and 1x10 −19 at 2000 s. This cascaded link was extended to 1480-km with the same performance. This work is a significant step towards a sustainable wide area ultra-stable optical frequency distribution and comparison network at a very high level of performance