Fiber links have proven to be the most robust tools for ultra-stable frequency dissemination over various distance ranges, thanks to an active compensation of the fiber propagation noise [1]. Here, we present our setup for local ultra-stable frequency distribution within an institute, fully based on digital electronics. We use a Red Pitaya SDRlab122 - 16 (RP16) platform to perform a Doppler cancellation scheme, based on a heterodyne Michelson interferometer using a single acousto-optic modulator (AOM) at 110 MHz, in order to cancel the phase noise arising from a 90 m-long fiber link at 1542 nm. The experimental setup is shown in Fig. 1.

SummaryWe present our progress on the construction of a ¹⁷¹Yb-based active optical atomic clock. The ytterbium (Yb) atoms, initially in a collimated thermal beam generated in an oven, are decelerated using a Zeeman slower to the capture velocity (~ 10 ms^-1) for a magneto-optical trap on the ¹S<inf>0</inf> → ³P<inf>1</inf> transition at 556 nm. This allows us to generate an ensemble of N >10⁶ atoms at temperatures below 100 μK, which will be transported using an optical conveyor belt to an ultra-stable (σ<inf>y</inf> ~ 10^-13) cavity of finesse on the order of 10⁴. Here, the atoms will be prepared in order to generate a superradiant emission which will serve as the frequency reference on the ¹S<inf>0</inf> → ³P<inf>0</inf> clock transition in ¹⁷¹Yb.

SummaryWe demonstrate a fiber link with instability in the 10-18 range for optical frequency dissemination. It relies on a fully-digital Doppler cancellation platform that makes a novel use of aliasing to generate signals above Nyquist frequency. Furthermore, we present an automatic method to measure the disturbance rejection of the system without a direct comparison between the input and the output of the fiber link. Finally, we have investigated the low-frequency noise at the Red Pitaya output.

SummaryActive optical atomic clocks are emerging as a new promising tool for time and frequency metrology. Such clocks have the potential to reach a fractional frequency instability in the 10-18 range at one second [1]. These references are based on the superradiant emission of an ensemble of atoms coupled to a single mode of the electromagnetic field [2]. For optical references, this coupling is achieved through a resonant high-finesse Fabry-Perot cavity that therefore plays a crucial role to reach superradiant lasing. Specific characteristics are required to permit superradiant emission in a metrologically relevant regime: tunability of the cavity resonant frequency, ability to accommodate atoms and low fractional length fluctuations, in the order of 10-13. This work shows the conception, through simulation, assembly and preliminary characterization of this Fabry Perot cavity.

This article reports on the use of a Field Programmable Gate Array (FPGA) platform for local ultra-stable optical frequency distribution through a 90 m-long fiber network. This platform is used to implement a fully digital treatment of the Doppler-cancellation scheme required by fiber links to be able to distribute ultra-stable frequencies. We present a novel protocol that uses aliased images of a digital synthesizer output to directly generate signals above the Nyquist frequency. This approach significantly simplifies the setup, making it easy to duplicate within a local fiber network. We demonstrate performances enabling the distribution of an optical signal with an instability below 10-17 at 1 s at the receiver end. We also use the board to implement an original characterization method. It leads to an efficient characterization of the disturbance rejection of the system that can be realized without accessing the remote output of the fiber link.