High-dynamic-range microwave sensing using atomic Rabi resonances.

Detection of the microwave (MW) field with high accuracy is very important in the physical science and engineering fields. Herein, an atomic Rabi resonance-based MW magnetic field sensor with a high-dynamic-range is reported, where α and ß Rabi resonances are used to measure MW fields. In MW measurement experiments, the sensor successfully measured a magnetic field of about 10 nT at 9.2 GHz using the α Rabi resonance line on the cesium clock transition and continuously detected the MW magnetic field in the X-band over a high dynamic power range of >60 dB from the ß Rabi resonance. Finally, the MW power frequency shift and power broadening are investigated to support more sensitive field measurements. The proposed MW detection method can be extended to cover a higher dynamic range and a wider frequency band by applying stronger excitations and exploring non-clock atomic transitions, respectively. In addition to MW magnetic field sensing, other potential application of the proposed method can be explored, including SI-traceable MW calibration and atomic communication.

Highly stable multiple-access underwater frequency transfer with terminal phase compensation.

A multiple-access underwater frequency transfer scheme using terminal phase compensation is demonstrated. With this scheme, a highly stable 100 MHz frequency signal was disseminated over a 3 m underwater link for 5000 s. The timing fluctuation and fractional frequency instability were both measured and analyzed. The experimental results show that with the phase compensation technique, the total root-mean-square (RMS) timing fluctuation is about 3 ps, and the fractional frequency instabilities are on the order of 5.9×10-13 at 1 s and 5.3×10-15 at 1000 s. The experiment results indicate that the proposed frequency transfer technique has a potential application of disseminating an atomic clock to multiple terminals.

Analysis and experimental demonstration of underwater frequency transfer with diode green laser.

We demonstrated an underwater frequency transfer technique with a green diode laser. The characteristic of the timing fluctuation and instability for the transfer technique was analyzed and simulated. With this technique, we had transferred a highly stable 100-MHz frequency signal over an underwater link with distances of 3 m, 6 m, and 9 m for 5000 s, respectively. The experimental results involving the underwater transfer of the 100-MHz radio-frequency signal shows that the rms timing fluctuations are 5.9 ps (3-m link), 6.4 ps (6-m link), and 8.4 ps (9-m link). The calculations also show that the relative Allan deviations for the 3-m, 6-m, and 9-m transmission links are 5.6 × 10-13 at 1 s and 5.3 × 10-15 at 1000 s, 5.8 × 10-13 at 1 s and 1.1 × 10-14 at 1000, and 6.8 × 10-13 at 1 s and 1.1 × 10-14 at 1000 s, respectively. The measured instabilities were lower than Rb and Cs atomic clocks, implying that the proposed frequency transfer scheme can potentially be used to transfer the signals of these atomic clocks over underwater links.

The design of a wide bandwidth time marker generator.

The Time Marker Generator (TMG) is an important instrument that is used to calibrate the time base of an oscilloscope. If a direct digital frequency synthesizer is used to generate the necessary waveforms, there is serious distortion in the generated square wave when the ratio of the sampling frequency to the output frequency is non-integer. In addition, the look-up table (LUT) in the direct digital waveform synthesizer needs a large storage capacity to generate a narrow triangular wave at a low output frequency. This paper proposes a design that will generate the time marker whose samples are synthesized by real-time calculation instead of storing them in a LUT. We also propose an M waveform data synthesizer with a parallel structure (M-WDSPS) to reduce the operating clock frequency of the field programmable gate array (FPGA). We built a 4-WDSPS TMG based on this design and reduced the required clock frequency from 1 GHz to 250 MHz, thus making the implementation possible in an FPGA. Our proposed TMG design can provide square wave, pulse wave, narrow triangular wave, and linear triangular wave with different amplitudes in two operating modes: normal mode and highlight mode. The TMG we constructed can provide the time marker with an output frequency range from 10 mHz to 111 MHz, a rising/falling edge time lower than 1 ns, regardless of whether the output frequency is low or high, and a frequency stability lower than 0.1 ppm.

Precisely synchronous and cascadable multi-channel arbitrary waveform generator.

The output bandwidth and the capability to generate multiple analog outputs with accurately adjustable relative phase are important specifications of arbitrary waveform generator (AWG). To increase the output bandwidth, AWG with a multi-memory paralleled direct digital synthesizer structure (DDS) was proposed to break through operating speed limitations of memory and field programmable gate array. But this structure does complicate synchronization of the analog outputs. This paper proposes a structure for synchronization of the outputs of multi-channel high speed AWG that generates arbitrary waveforms using a multi-memory paralleled DDS. Careful distribution of the clock and trigger signals enables elimination of the random initial phase caused by the frequency divider. Based on this structure, a four-channel 600 mega samples per second AWG is designed. An embedded clock synchronization calibration module is designed to eliminate the random phase difference caused by a frequency divider inside a digital-to-analog converter. The AWG provides a 240 MHz bandwidth, 16 mega-samples storage depth, inter-channel initial skew accuracy less than 150 ps, and 0.0001° phase resolution, which can be used to generate two pairs of I/Q signals or a pair of differential I/Q signals for the quadrature modulator. Additionally, more AWGs can be cascaded to obtain more output channels with an output timing skew between adjacent channels of less than 1.6 ns.