Fuyu Sun

Measuring microwave cavity response using atomic Rabi resonances

In this letter, an atom-based approach for measuring the microwave (MW) cavity response (including cavity frequency and Q-factor) is presented, which utilizes a MW magnetic field detection technique based on atomic Rabi resonances. We first identify the Rabi resonances on seven π transitions in Cs atoms and demonstrate their uses in continuously frequency-tunable field detectors. With the atom-based field detectors, we then indicate the possibility of reconstructing the MW cavity response by measuring the MW frequency-dependent Rabi frequency (i.e., MW field strength) inside the cavity. To demonstrate this approach, we measured the response curves of a 9.2-GHz cavity and a cavity resonating at 8.3 GHz and 9.7 GHz using π transitions and σ transitions, respectively. We compared the results measured by our approach with those measured by Vector Networker Analyzer and obtained good agreement. From such atom-based, SI-traceable measurements, the MW cavity response can be linked directly to the Rabi frequency,...

Microwave magnetic field detection based on Cs vapor cell in free space

In this study, we demonstrate the direct measurement of a microwave (MW) magnetic field through the detection of atomic Rabi resonances with Cs vapor cells in a free-space low-Q cavity. The line shape (amplitude and linewidth) of detected Rabi resonances is investigated versus several experimental parameters such as the laser intensity, cell buffer gas pressure, and cell length. The specially designed low-Q cavity creates a suitable MW environment allowing easy testing of different vapor cells with distinct properties. Obtained results are analyzed to optimize the performances of a MW magnetic field sensor based on the present atom-based detection technique.

The prediction, simulation and verification of the phase noise in low-phase-noise crystal oscillator

In order to achieve the prediction of the phase noise of low phase noise crystal oscillator, based on the classic phase noise model of Leeson, the load Q value (QL) is calculated according to the selected oscillator circuit parameters. Thus, on the basis of Lesson phase noise formula, the predicted results of the phase noise of low phase noise crystal oscillators are obtained. Then, the nonlinear transistor model is constructed to simulate the phase noise of low phase noise crystal oscillator by using the ADS (Advanced Design System) simulation software of Agilent and obtain the simulated curve of the phase noise. At last, practical measurement has been performed on these low phase noise crystal oscillator prototypes. The measured results show that: the predicted phase noise of the oscillators and the ADS simulation results obtained by using nonlinear transistor model are both close to the actual measured phase noise, which are at 100Hz and far away offset the carrier frequency. After that, the existence of the deviation, which is near carrier frequency, is analyzed. The prediction and simulation methods given by this paper might be beneficial to simplify the design progress of the low phase noise crystal oscillator.

Femtosecond-level timing fluctuation suppression in atmospheric frequency transfer with passive phase conjunction correction

We demonstrate femtosecond-level timing fluctuation suppression in indoor atmospheric comb-based frequency transfer with a passive phase conjunction correction technique. Timing fluctuations and Allan deviations are both measured to characterize the excess frequency instability incurred during the frequency transfer process. By transferring a 2 GHz microwave over a 52-m long free-space link in 5000 s, the total root-mean-square (RMS) timing fluctuation was measured to be about 280 fs with a fractional frequency instability on the order of 3 × 10-13 at 1 s and 6 × 10-17 at 1000 s. This atmospheric comb-based frequency transfer with passive phase conjunction correction can be used to build an atomic clock-based free-space frequency transmission link because its instability is less than that of a commercial Cs or H-master clock.

Femtosecond atmospheric frequency transfer using diode laser with electronic phase compensation

We demonstrated an atmospheric radio-frequency transfer over a 50 m outdoor free-space link using a compact diode laser with an electronic phase compensation technique. With transferring a 1 GHz microwave signal in 5000 seconds, the total root-mean-square (RMS) timing fluctuation was measured to be about 560 fs, with fractional frequency instability on the order of 4 × 10−13 at 1 s, and order of 4 × 10−16 at 1000 s. This atmospheric frequency transfer scheme can be used to disseminate a commercial Rb or Cs clock via a free-space transmission link.

Simulation of the Ramsey cavity response

Ceramic Sealing Window (CSW) and Frequency Tuning Rod (FTR) are two important components of the Ramsey cavity. Here, a complete electromagnetic model of the Ramsey cavity is built with Finite-element tool HFSS, and the effects of CSW and FTR on the cavity response are simulated and analyzed in detail. To achieve high coupling efficiency, the estimated parameter ranges of CSW and FTR are investigated. The results obtained here offer a helpful guide for Ramsey cavity design in Cs and Rb beam clocks.

Attosecond synchronization of passive mode-locked lasers using optical heterodyne techniques

We demonstrate an attosecond synchronization of mode-locked lasers using optical heterodyne technique. The measured RMS timing fluctuation between two mode-locked Er:fiber lasers with same color was about 800 attosecond within 60 s.

Direct loop gain and bandwidth measurement of phase-locked loop

A simple and robust technique for directly measuring the loop gain and bandwidth of a phase-locked loop (PLL) is proposed. This technique can be used for the real-time measurement of the real loop gain in a closed PLL without breaking its locking state. The agreement of the measured loop gain and theoretical calculations proves the validity of the proposed measurement technique. This technique with a simple configuration can be easily expanded to other phase-locking systems whose loop gain and bandwidth should be measured precisely.

Dual-mode Ramsey cavity for a dual Rb/Cs atomic clock

In this paper, we propose a dual-mode Ramsey cavity for a dual Rb/Cs atomic clock, with resonances at 6.83GHz and 9.19GHz under the two different operating modes, respectively. Thus, the proposed cavity can excite Rb atoms and Cs atoms clock transition in the same environment (e.g., static magnetic field, temperature, and/or the asymmetric length between the two arms due to a single U-shaped structure). This design provides a compact physical package for a dual Rb/Cs clock. Another potential application of the dual-mode is high-accuracy comparison measurement. As an example, a dual-mode cavity with TE105 and TE109 modes was simulated.

The effect of bend on the Ramsey cavity

Ramsey cavity is one of core components that compose the Cs beam tube in the Cs atomic beam clocks. In this work, the contribution from the waveguide bend on the field distribution of the cavity is carefully investigated by using combination method of Maxwell equations and Finite element simulation. We find that there exists TM11 mode inside cavity in addition to standing wave TE10p mode. Meanwhile, we also find that the cavity resonance frequency is closely related to the bend radius. These results demonstrate a better description of the microwave properties than previous work where the Ramsey cavity was usually studied as an ideal rectangular microwave cavity.