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Phase variations of the interrogation field lead to frequency shifts in Ramsey-type atomic clocks. This paper reports the development of a 300 MHz Mach–Zehnder (MZ) switch that effectively suppresses phase-transient effects. Similar to MZ interferometers, this radio-frequency (RF) MZ switch comprises two arms that are power- and phase-matched with each other. By inserting a PIN diode RF switch in one arm, the other arm remains undisturbed, freeing it of the phase transient. Trigger phase fluctuation measurements are implemented by using a lock-in amplifier to extract the in-phase and quadrature (I/Q) demodulation data. The results show that the extinction ratio of the RF MZ switch phase fluctuations is −16.

Magnetic shielding is an important part in atomic clock’s physical system. The demagnetization of the assembled magnetic shielding system plays an important role in improving atomic clock’s performance. In terms of the drawbacks in traditional attenuated alternating-current demagnetizing method, this paper proposes a novel method — automatically attenuated alternating-current demagnetizing method. Which is implemented by controlling the demagnetization current waveform thorough the signal source’s modulation, so that these parameters such as demagnetizing current frequency, amplitude, transformation mode and demagnetizing period are precisely adjustable. At the same time, this demagnetization proceeds automatically, operates easily, and works steadily. We have the pulsed optically pumped (POP) rubidium atomic clock’s magnetic shielding system for the demagnetization experiment, the magnetic field value reached 1nT/7cm. Experiments show that novel method can effectively realize the demagnetization of the magnetic shielding system, and well meets the atomic clock’s working requirements.

This paper presents the design and phase noise measurement of microwave frequency synthesizer for atomic fountain frequency standard. In this synthesizer, a voltage-controlled DRO is locked to 100MHz hydrogen maser signal through a divider chain. The required interrogation frequency 9192631770 Hz is generated by mixed with 7368230 Hz and 400 MHz signals. The experimental results show that the phase noise of interrogation signal at 9.192 GHz is -88dBc/Hz@ offset 1Hz. With such performances, the expected Dick effect contribution to atom fountain frequency standard is reported at a level of 1.0×10-15 at 1 s integrating time, that is a factor 10 higher than quantum noise limit of atom frequency standard. The carrier spectral spur of microwave synthesizer signal impacted on atomic fountain frequency standard is also discussed.

In view of the application of modulation transfer spectroscopy (MTS) in laser frequency stabilization can not only completely remove the Doppler background but also avoid extra frequency noise due to the frequency dither to laser in the normally used saturation absorption locking technique. Employ the nonlinear spectroscopy method of modulation transfer (MTS) replaces the saturated absorption for the cesium D 2 line transition to stabilize the laser frequency aims to improve the frequency stability of cesium atomic fountain clock’s optical system. We conducted two sets of modulation transfer spectroscopy apparatuses to stabilize two independent lasers, and the analysis of the beat signal between two independent laser systems has showed a frequency stability of $4.46\times 10^{-12}$ @ls, and a 3dB linewidth about 85KHz.

The mathematical model of automatic short-circuit calculation is proposed, that is directly used in coal mine high-voltage grid. The model combinates incidence matrix with short-circuit calculation in mine high-voltage grid. According to the connectivity of single-direction graph, the model describes the power supply relation matrix of branches node in coal mine high-voltage grid by the incidence matrix of bus node and branch node. The short-circuit calculation of all short-circuit points is achieved, according to the short-circuit matrix of three-phase and two-phase short-circuit current in all short circuit points given by the model. The analysis results show that the model can realize automatic short-circuit calculation accurately in coal mine high-voltage grid, and it provides a foundation for studying the performance of automatic short-circuit calculation and adaptive setting calculation of multiple fault operation mode.

The traditional switch exhibits phase discontinuity and transients in few hundreds microradian which will induce the larger microwave leakage shift in the atomic fountain clock. The RF Mach-Zehnder interferometric switch is developed in order to decrease the phase variations without inducing phase discontinuity. To detect the phase variations, the phase transient measurement system is also built and described in detail in this paper. The result shows the peak to peak phase variations of RF Mach-Zehnder interferometric is 10 microradians within the measurement resolution of a few microradians after five days averaging.

We demonstrate frequency stabilization of DFB laser via modulation transfer spectroscopy, which avoids the interference of Doppler absorption spectrum. By modulating the frequency of laser beam(pump laser beam), the other laser beam(probe laser beam) overlap pump laser beam is modulated as the same frequency by nonlinear interaction. By demodulating the signal from detection beam, an error signal is generated through the low pass filter. The frequency is stabilized at the 0 point position of the MTS frequency discrimination curve by PID loop which shows frequency fluctuation is less than 149 kHz, and the relative frequency stability is improved by nearly two orders of magnitude.

The optical system plays a significant role to cesium atomic fountain clocks, which manipulates and detects population of cesium atoms. This paper presents a compact optical system for cesium atomic fountain clocks. The optical system provides two beams with 32mW separately for cooling atoms and six beams of 12mW respectively for trapping atoms with the frequency tuning from 80MHz to 220MHz. The relative intensity noise of the detect laser beam reduces from 1.33×10-6 Hz to 1.52×10-10 Hz at 1Hz by the laser power stabilization system. The optical system operates continuously for 30 days with the fluctuation of optical power less than 3% approximately. And the frequency stability is 3×10-15 at 1000s. The results show the optical system satisfies with the needs of our cesium atomic fountain clock developed and establishes the foundation for cesium atomic fountain continuous operation.

This paper present an optical system for Cs atomic fountain clock that is located on a 1.2 m×1.2 m optical table. Taking advantage of this system, we trap about 10 8 cesium atoms in the magneto-optic trap (MOT) and get the Ramsey fringe of the fountain by scanning the microwave frequency of the interrogation cavity. The full-width at half-maximum of the central fringe (FWHM) is 1.4 Hz.

The control system for Cesium atomic fountain clock is described in detail in this paper. It consists of five parts, automatic digital frequency locking system of extended cavity diode laser (ECDL), the time serial control system, the data acquisition system, the microwave frequency synthesizer control system and the servo control system. With automatic digital frequency locking system, the frequency of ECDL can be locked to any saturated absorption curve automatically and remains locked throughout a series of abrupt disturbance. And moreover, the laser system can relock itself in few seconds when the frequency of the laser is out of range. The time serial control system generate thirteen time serial signals synchronously, including Transistor-Transistor Logic (TTL) signals and arbitrary waveform signals. Moreover, the result shows that these signals are synchronized within 10 μs. The time of flight (TOF) signals are obtained combined with data acquisition system. The resulting Ramsey resonance signal is obtained by sweeping frequency of the synthesizer. The frequency of the 9.2 GHz synthesizer is square-wave modulated by the servo control system so that the frequency of the quartz crystal oscillator is locked to the atomic resonance of the fountain.

In this paper we present experimental results on the laser power stabilization of the detection system in Cs fountain clock. In order to stabilize the laser power, we have constructed a feedback loop by using an acousto-optic modulator, a photodetector, and a servo controller. The control-loop can make the relative intensity noise of the laser beam reduce from 1.33×10 -4 Hz -1/2 to 7.16×10 -6 Hz -1/2 at 2 Hz. However, if the beam used in the control-loop is obtained by using PBS, the two detection beams in fountain clock cannot be stabilized at the same time. Therefore, we propose a new scheme by using a piece of uncoated optical glass plate as a splitter to obtain the branch beam used in the control-loop. Experimental results demonstrate that the power stabilities of the two detection beams are both at 10 -5 level (based on rms value) for 1.5 hours at the same time.

The deep study of anomaly feature based on the particular server was made in this paper. By continuously monitoring on the honeypot deployed in Internet Data Center for more than two months, the experimental results were summarized and some initial exploratory models were built. The models show that the number of attackers for the main attack types and ports can be described by normal distribution; meanwhile, the average packet number that each attacker generates per day can be described by log-normal distribution. This research aims to contribute to endeavor in the wider security research community to build methods and obtain some statistical models, grounded on strong empirical work, for assessment of the robustness of systems in hostile environments, and the anomaly traffic sampling, detection and classification on the backbone.

Pneumatic clutch system of heavy truck is nonlinear and its state parameters are variable. The common PID controller is difficult to obtain good performance. Neural network is adopted to tune the PID parameter online. The output of neural network is used to adjust the PID controller parameter and the controller adjusts the pulse width to control the displacement of the clutch. The experimental result demonstrates the algorithm can obtain good control performance.