Quantime - A miniature cesium atomic clock using CPT technique for telecom application

The Quantime project aims at developing a miniature atomic clock suited for the telecom market, requiring a wide operating temperature range (from -40 to +85°C), and a low production cost. The CPT (Coherent Population Trapping) technique for atomic interrogation is used for miniaturization and low power consumption. In the first phase of the project, the clock architecture was chosen, and the main sub-systems were developed. A clock breadboarding demonstrator was assembled and the measured Allan deviation of 1E-11 at 400 s confirms the operation of all the sub-systems

Effect of Quartz Crystal Thermal Structure on its Performances in Ultra Stable Oscillators

5 pagesInternational audienceThe aim of this work is to improve efficiency of quartz crystal oscillators, and particularly Space Ultra Stable Oscillators (USO). Space USOs have to resist severe environment including vibrations (in particular during the launch), cosmic radiations, large external temperature change... At the same time, as for all devices for space, those types of oscillators have to be as light and small as possible while being the lowest energy consumers and the best in term of frequency stability performances (whatever the outside temperature is). We focused on the thermal structure aspect in order to reduce volume and consumption while preserving performances in comparison with present products. It is well known that temperature is the most influent parameter on the frequency of bulk acoustic wave resonators. Temperature has two types of effects. First, frequency is sensitive to the average steady state temperature of the resonant part of the resonator. Second, frequency is also sensitive to temperature gradients. This second effect is more difficult to evaluate and strongly depends on the mechanical packaging of the resonator. This is why we pay particular attention to the effect of the structure on these gradients. In the field of space we have to work in vacuum, so the mechanisms of heat transfer we are working with are conduction and radiation. Convection cannot be present. The architecture of the inside of the resonator as well as its conditioning in the oscillator will have a large influence on the distribution of temperature in the sensitive areas: geometry of the whole structure has to be precisely defined to control heat transfer effects. A detailed analysis of the mechanisms of heat transfer between resonators and their environment is carried out on different types of resonators: standard ones, QAS (adherent electrodes) and BVA (electrodeless resonator). This study is based on theoretical developments and on numerical simulations based on finite element software. It leads to an assessment and comparison of effects of various important time constants involving the different parts of the oscillator, depending on whether they exchange by conduction and/or radiation. Thus we can really see the effect of the structure set and can make a projection on the packaging of the thermal environment of the resonator, inside the oscillator, which is necessary to fulfill the specifications in operating conditions

CPT Cesium-Cell Atomic Clock Operation With a 12-mW Frequency Synthesizer ASIC

In this paper, we present the design, fabrication, and electrical characterization of a low-power microwave source for interrogation of cesium atomic hyperfine transition frequency using the coherent population trapping (CPT) technique. The 4.6-GHz frequency generation and signal buffering is performed by a single-chip frequency synthesizer ASIC with a frequency tuning resolution of 1 x 10(-13) and a programmable RF output power from -10 to 0 dBm. The circuit was used to modulate the current of a vertical-cavity surface-emitting laser through a dedicated impedance matching network and low thermal conductivity transmission line. Strong modulation sidebands with >60% of carrier amplitude were obtained with an ASIC power consumption of 12 mW. The system was used as optical source for atomic interrogation in an experimental cesium CPT clock. The measured clock stability of 5 x 10(-11) at tau = 1 s, going down to 4.5 x 10(-12) at tau = 200 s, is limited by the signal-to-noise ratio of the detected CPT signal