A 194-nm cw laser is an essential part in the mercury ion optical frequency standard. We report the generation of over 2mW continuous-wave radiation at 194nm in a beta barium borate crystal using a simple sum frequenc...A 194-nm cw laser is an essential part in the mercury ion optical frequency standard. We report the generation of over 2mW continuous-wave radiation at 194nm in a beta barium borate crystal using a simple sum frequency mixing (SFM) system. One source beams at 718nm is resonantly enhanced with a cavity and the other at 266mn makes a single pass. Considering the walk-off effect in SFM, the source beam waists are designed to be elliptical, thus the conversion efficiency can be promoted. The 266-nm beam produced by frequency doubling of 532-nm laser is shaped close to the diffraction limit to achieve better mode matching.展开更多
We propose a method to determine the optimal power of the microwave resonance transition that simultaneously improves the signal-to-noise ratio and reduces line width based on saturation broadening theory and experime...We propose a method to determine the optimal power of the microwave resonance transition that simultaneously improves the signal-to-noise ratio and reduces line width based on saturation broadening theory and experiment. Saturation broadening spectra of the ground state hyperfine transition of trapped 199Hg+ ions are measured and analyzed. The value of the optimal microwave power is obtained by using the proposed method and is verified. Rabi oscillations decay spectra of trapped 199Hg+ ions are observed and the optimal microwave irradiation time for the maximum transition signal intensity is determined. This work will help to improve the short-term frequency stability of the mercury ion microwave frequency standard.展开更多
We experimentally realize the dual-wavelength bad cavity laser for the first time. As the Cs cell temperature is kept between 118℃ and 144℃, both the 1359nm and 147Ohm lasing outputs of dual-wavelength bad cavity la...We experimentally realize the dual-wavelength bad cavity laser for the first time. As the Cs cell temperature is kept between 118℃ and 144℃, both the 1359nm and 147Ohm lasing outputs of dual-wavelength bad cavity laser are detected. The laser output power of dual-wavelength bad cavity laser is measured when changing the 455 nm pumping laser frequency and power at 127℃ Cs cell temperature. Both the 1359 nm laser and the 1470 nm laser are working at the deep bad cavity regime, and the ratio between the linewidth of cavity mode and the laser gain bandwidth a ≈ 40 for 1359nm and 1470nm lasers. The 147Ohm laser linewidth is measured to be 407.3Hz. The dual-wavelength bad cavity laser operating on atomic transitions demonstrated here has a potential in the application as a stable optical local oscillator, even an active optical frequency standard directly in the future.展开更多
We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS)technology with good reproducibility.A frequency stability of 2.5×10^(-14)at 1 s ave...We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS)technology with good reproducibility.A frequency stability of 2.5×10^(-14)at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10^(-13),demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated,especially the contribution of the residual amplitude modulation(RAM).The contribution of the RAM in MTS cannot be evaluated directly.To solve this problem,we theoretically deduce the MTS signal with RAM under large modulation depth,and prove that the non-symmetric shape of the MTS signal is directly related to the MTS effect.The non-symmetric shape factor can be calibrated with a frequency comb,and in real experiments,this value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift.The full frequency uncertainty is evaluated to be 5.3 kHz(corresponding to a relative frequency uncertainty of 9.4×10^(-12)).The corrected transition frequency has a difference from the BIPM-recommended value of 2 kHz,which is within 1σ uncertainty,proving the validity of our evaluation.展开更多
The experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical frequency stan- dard is proposed, where He-Ne 633nm and Cs 1359nm stimulated emissions are working at good-cavity and bad-ca...The experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical frequency stan- dard is proposed, where He-Ne 633nm and Cs 1359nm stimulated emissions are working at good-cavity and bad-cavity regimes, respectively. The cavity length is stabilized by locking the 633nm output frequency to a super-cavity with the Pound Drever-Hall (PDH) technique. The frequency stability of 1359 nm bad-cavity stim- ulated emission output is then expected to be further improved by at least 1 order of magnitude than the 633nm PDH system due to the suppressed cavity pulling effect of active optical clock, and the quantum limited linewidth of 1359nm output is estimated to be 72.5 mHz.展开更多
This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The st...This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.展开更多
A method is presented to improve the laser frequency stabilization for the optical pumping cesium clock. By comparing the laser frequency stabilization of different schemes, we verify that the light angle is an import...A method is presented to improve the laser frequency stabilization for the optical pumping cesium clock. By comparing the laser frequency stabilization of different schemes, we verify that the light angle is an important factor that limits the long-term frequency stability. We minimize the drift of the light angle by using a fiber- coupled output, and lock the frequency of a distributed-feedback diode laser to the fluorescence spectrum of the atomic beam. The measured frequency stability is about 3.5 ×10^-11 at i s and reaches 1.5 × 10^-12 at 2000s. The Allan variance keeps going down for up to thousands of seconds, indicating that the medium- and long-term stability of the laser frequency is significantly improved and perfectly fulfills the requirement for the optical pumping cesium clock.展开更多
Frequencies of frequency standards are shifted by the local static gravity red shifts and also modulated by the tidal relativistic red shifts. We compute the tidal relativistic red shifts using a time-domain method an...Frequencies of frequency standards are shifted by the local static gravity red shifts and also modulated by the tidal relativistic red shifts. We compute the tidal relativistic red shifts using a time-domain method and present the numerical results for the National Institute of Metrology (NIM) in Beijing, Laboratoire National de Metrologie et Essais-Systeme de References Temps-Espaee (LNE-SYRTE) in Paris and Physikalisch-Teehnische Bundesanstalt (PTB) in Braunschweig. The differences of the tidal relativistic red shift approach as large as 1.1 × 10^-16 when frequency standards at NIM are compared with those at SYRTE and PTB. Moreover, the tidal relativistic red shifts of frequency standards in space stations are also computed.展开更多
The SI "second"is realized by caesium primary frequency standards( PFSs) using laser cooled atoms in a fountain configuration. Four sub systems and operation procedure of the NTSC-F1 primary frequency standa...The SI "second"is realized by caesium primary frequency standards( PFSs) using laser cooled atoms in a fountain configuration. Four sub systems and operation procedure of the NTSC-F1 primary frequency standard are introduced in the paper.The frequency stability of NTSC-F1 is 3.0×10-13/ τ-1 / 2compared to hydrogen maser. Four terms of frequency shift and uncertainty including second order Zeeman frequency shift,cold collision shift,gravity shift and blackbody shift are evaluated. The improvement of NTSC-F1 is introduced.展开更多
We report a 42Ohm external cavity diode laser with an interference filter (IF) of 0.5am narrow-bandwidth and 79% high transmission, which is first used for Rb optical frequency standard. The IF and the cat-eye refle...We report a 42Ohm external cavity diode laser with an interference filter (IF) of 0.5am narrow-bandwidth and 79% high transmission, which is first used for Rb optical frequency standard. The IF and the cat-eye reflector are used for selecting wavelength and light feedback, respectively. The measured laser linewidth is 24 kHz when the diode laser is free running. Using this narrow-linewidth IF blue diode laser, we realize a compact Rb optical frequency standard without a complicated PDH system. The preliminary stability of the Rb optical frequency standard is 2 × 10^-13 at I s and decreases to 1.9 ×10^-14 at 1000s. The narrow-linewidth characteristic makes the IF blue diode laser a well suited candidate for the compact Rb optical frequency standard.展开更多
The Dick effect is one of the main limits to the frequency stability of a passive frequency standard, especially for the fountain clock and ion dock operated in pulsed mode which require unavoidable dead time during i...The Dick effect is one of the main limits to the frequency stability of a passive frequency standard, especially for the fountain clock and ion dock operated in pulsed mode which require unavoidable dead time during interrogation. Here we measure the phase noise of the interrogation oscillator applied in the microwave frequency standard based on laser-cooled 113^Cd+ ions, and analyze the Allan deviation limited by the Dick effect. The results indicate that the Dick effect is one of the key issues for the cadmium ion dock to reach expected frequency stability. This problem can be resolved by interrogating the local oscillator continuously with two ion traps.展开更多
This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634nm referencing on the hyperfine B-X transition R(80)8-4 of 127I2. The lasers are stabilized on the...This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634nm referencing on the hyperfine B-X transition R(80)8-4 of 127I2. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8 × 10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.展开更多
A novel frequency hopping(FH) sequences generator based on advanced encryption standard(AES) iterated block cipher is proposed for FH communication systems.The analysis shows that the FH sequences based on AES algorit...A novel frequency hopping(FH) sequences generator based on advanced encryption standard(AES) iterated block cipher is proposed for FH communication systems.The analysis shows that the FH sequences based on AES algorithm have good performance in uniformity, correlation, complexity and security.A high-speed, low-power and low-cost ASIC of FH sequences generator is implemented by optimizing the structure of S-Box and MixColumns of AES algorithm, proposing a hierarchical power management strategy, and applying the dynamic clock gating technology based on finite state machine and clock gating.SMIC 0.18 μm standard CMOS technology shows that the scale of ASIC is only about 10.68 kgate, power consumption is 33.8 μW/MHz, and the maximum hop-rate is 1 098 901 hop/s.This design is suitable for portable FH communication system for its advantages in high-security and hop-rate, low-power and low-cost.The proposed FH sequences generator has been employed in Bluetooth SoC design.展开更多
A method for evaluating the benign and malignant breast tumors based on radio?frequency(RF)data was explored by extracting the characteristic parameters of breast ultrasound RF signals.The breast biopsy data were used...A method for evaluating the benign and malignant breast tumors based on radio?frequency(RF)data was explored by extracting the characteristic parameters of breast ultrasound RF signals.The breast biopsy data were used as the reference data for judging the lump benign or malignant.The extracted ultrasound RF data were reconstructed and segmented by computer aided method to obtain the breast tumor region of interest(ROI)and its characteristic parameters(entropy and standard deviation).The characteristic parameters were statistically analyzed to evaluate the relationship between characteristic parameters and benign or malignant breast tumors.The results indicate the entropy and standard deviation of normal region is much higher than that of lump region,which shows that the standard deviation and entropy characteristic parameters of ultrasonic RF signals are meaningful in the diagnosis of breast tumors.The proposed method provides a new direction for computer?aided diagnosis of benign and malignant breast tumors.展开更多
Up to the present time gravitational-wave detectors, such as LIGO and Virgo, have been sensitive to frequencies on the order of a few thousand to a small fraction of an Hz. They have been most effective in the study o...Up to the present time gravitational-wave detectors, such as LIGO and Virgo, have been sensitive to frequencies on the order of a few thousand to a small fraction of an Hz. They have been most effective in the study of black-hole mergers. We suggest that high-frequency relic gravitational wave (HFRGW) detectors be developed, especially the Li-Baker HFRGW detector, in the gigahertz and higher frequency range. We believe collecting cosmological, primordial observational data especially generated during the first few seconds after the beginning of our Universe is extremely important. One motivation for this paper is, therefore, that we are confident that observation of relic gravitational waves will provide vital information about the birth of our Universe and its early dynamical evolution. Other astrophysical applications of HFRGW detectors involve the entropy growth of the early Universe, an ability to study alternatives to inflation and to provide clues about the symmetries underlying new physics at the highest energies. A working hypothesis or theory, based upon the rollout of our Universe from infinitesimal Planck Length and Planck Time is presented. This theory involves the rapid motion of time and matter during that early time having frequencies on the order of trillions of cycles per second or more. Several alternative HFRGW detectors are described and the proposed Li-Baker HFRGW detector, which is theoretically sensitive to GW amplitudes, A, as small as 10-32, is discussed in detail. Such sensitivity may provide a means for verifying or falsifying the rollout of our Universe working hypothesis. Essentially a combination of theory and experimentation is presented. It is recommended that plans and detailed specifications for the Li-Baker HFRGW detector be prepared in order to expedite its fabrication.展开更多
Background:The theory of pulse diagnosis is to assess the physiological condition of the human body using radial pulse.However,pulses can vary markedly from person to person.Further,pulse diagnosis is difficult to lea...Background:The theory of pulse diagnosis is to assess the physiological condition of the human body using radial pulse.However,pulses can vary markedly from person to person.Further,pulse diagnosis is difficult to learn and requires one-on-one teaching.Methods:To address this problem,we built a home-made pulse diagnoser and measured human pulses for studying the standardization of pulse diagnosis.Our pulse diagnoser was composed of a piezoelectric transducer,differential amplifier,data acquisition instrument,and a Matlab analysis program.The measured pulses were converted into electronic signals by a piezoelectric transducer and saved on a computer.The digitalized data were then refined and analyzed by fast Fourier transform for frequency analysis.Simulations were performed to assess the factors that affected the pulse,including phase shifts of reflected pulse waves (generate sub-peaks in pulses),inconsistent heart rates (deform pulse waves),the vessel stiffness (alter harmonic frequencies of the pulses),and the wave amplitudes (determined by the pulse strength).Results:By comparing a published report and our simulation findings,we characterized the pulse types and the effects of various factors,and then applied the findings to study actual pulses in patients.Three types of pulses were determined from the frequency spectrumchoppy pulse (Se mai) without apparent harmonic peaks,the harmonic frequencies of wiry pulse (Xian mai) that are non-integer multiples of the fundamental frequency,and surging pulse (Hong mai) that exhibit strong amplitudes in the spectrum of frequency.A normal pulse and a slippery pulse were differentiated by a phase shift,but not by assessing the frequency spectrum.Conclusion:These findings confirm that frequency domain analysis can avoid ambiguity arising in assessing the three types of pulses in the time domain.Further studies of other pulses in the frequency domain are required to develop a precise electronic pulse diagnoser.展开更多
An adjustable mixer for surface acoustic wave( SAW)-less radio frequency( RF) front-end is presented in this paper. Through changing the bias voltage,the presented mixer with reconfigurable voltage conversion gain( VC...An adjustable mixer for surface acoustic wave( SAW)-less radio frequency( RF) front-end is presented in this paper. Through changing the bias voltage,the presented mixer with reconfigurable voltage conversion gain( VCG) is suitable for multi-mode multi-standard( MMMS) applications. An equivalent local oscillator( LO) frequency-tunable high-Q band-pass filter( BPF) at low noise amplifier( LNA) output is used to reject the out-of-band interference signals. Base-band( BB) capacitor of the mixer is variable to obtain 15 kinds of intermediate frequency( IF) bandwidth( BW). The proposed passive mixer with LNA is implemented in TSMC 0. 18μm RF CMOS process and operates from 0. 5 to 2. 5 GHz with measured maximum out-of-band rejection larger than 40 d B. The measured VCG of the front-end can be changed from 5 to 17 d B; the maximum input intercept point( IIP3) is0 d Bm and the minimum noise figure( NF) is 3. 7 d B. The chip occupies an area of 0. 44 mm^2 including pads.展开更多
This paper describes a high security data transmission system over X-band microwave frequency. The paper has two parts. The first part deals with encryption of binary data by Advanced Encryption Standard (AES) using V...This paper describes a high security data transmission system over X-band microwave frequency. The paper has two parts. The first part deals with encryption of binary data by Advanced Encryption Standard (AES) using VHDL modeling of Field Programmable Gate Array (FPGA). The second part deals with a novel idea of transmitting the encrypted data by using a single klystron. This requires the simultaneous generation of a pair of two independent RF frequencies from a reflex klystron working for X-band frequency range. In this scheme, the klystron is suitably biased on the repeller terminal and superimposed on a train of AES encrypted binary data so as to create two RF frequencies one corresponding to negative peaks and the other one to the positive peaks of the data resulting in an Frequency Shift Keying (FSK) signal. The results have been verified experimentally.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 91436103 and 11204374
文摘A 194-nm cw laser is an essential part in the mercury ion optical frequency standard. We report the generation of over 2mW continuous-wave radiation at 194nm in a beta barium borate crystal using a simple sum frequency mixing (SFM) system. One source beams at 718nm is resonantly enhanced with a cavity and the other at 266mn makes a single pass. Considering the walk-off effect in SFM, the source beam waists are designed to be elliptical, thus the conversion efficiency can be promoted. The 266-nm beam produced by frequency doubling of 532-nm laser is shaped close to the diffraction limit to achieve better mode matching.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11074282 and 11474320
文摘We propose a method to determine the optimal power of the microwave resonance transition that simultaneously improves the signal-to-noise ratio and reduces line width based on saturation broadening theory and experiment. Saturation broadening spectra of the ground state hyperfine transition of trapped 199Hg+ ions are measured and analyzed. The value of the optimal microwave power is obtained by using the proposed method and is verified. Rabi oscillations decay spectra of trapped 199Hg+ ions are observed and the optimal microwave irradiation time for the maximum transition signal intensity is determined. This work will help to improve the short-term frequency stability of the mercury ion microwave frequency standard.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874009,11074011 and 91436210the International Science and Technology Cooperation Program of China under Grant No 2010DFR10900
文摘We experimentally realize the dual-wavelength bad cavity laser for the first time. As the Cs cell temperature is kept between 118℃ and 144℃, both the 1359nm and 147Ohm lasing outputs of dual-wavelength bad cavity laser are detected. The laser output power of dual-wavelength bad cavity laser is measured when changing the 455 nm pumping laser frequency and power at 127℃ Cs cell temperature. Both the 1359 nm laser and the 1470 nm laser are working at the deep bad cavity regime, and the ratio between the linewidth of cavity mode and the laser gain bandwidth a ≈ 40 for 1359nm and 1470nm lasers. The 147Ohm laser linewidth is measured to be 407.3Hz. The dual-wavelength bad cavity laser operating on atomic transitions demonstrated here has a potential in the application as a stable optical local oscillator, even an active optical frequency standard directly in the future.
基金the National Key Research and Development Program of China(Grant No.2017YFA0304401)Key-Area Research and Development Program of GuangDong Province,China(Grant No.2019B030330001)the National Natural Science Foundation of China(Grant Nos.11174095,61875065,91536116,and 11804108).
文摘We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS)technology with good reproducibility.A frequency stability of 2.5×10^(-14)at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10^(-13),demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated,especially the contribution of the residual amplitude modulation(RAM).The contribution of the RAM in MTS cannot be evaluated directly.To solve this problem,we theoretically deduce the MTS signal with RAM under large modulation depth,and prove that the non-symmetric shape of the MTS signal is directly related to the MTS effect.The non-symmetric shape factor can be calibrated with a frequency comb,and in real experiments,this value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift.The full frequency uncertainty is evaluated to be 5.3 kHz(corresponding to a relative frequency uncertainty of 9.4×10^(-12)).The corrected transition frequency has a difference from the BIPM-recommended value of 2 kHz,which is within 1σ uncertainty,proving the validity of our evaluation.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874009,11074011 and 91436210the International Science&Technology Cooperation Program of China under Grant No 2010DFR10900
文摘The experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical frequency stan- dard is proposed, where He-Ne 633nm and Cs 1359nm stimulated emissions are working at good-cavity and bad-cavity regimes, respectively. The cavity length is stabilized by locking the 633nm output frequency to a super-cavity with the Pound Drever-Hall (PDH) technique. The frequency stability of 1359 nm bad-cavity stim- ulated emission output is then expected to be further improved by at least 1 order of magnitude than the 633nm PDH system due to the suppressed cavity pulling effect of active optical clock, and the quantum limited linewidth of 1359nm output is estimated to be 72.5 mHz.
基金supported by the Joint Research Fund in Astronomy(Grant Nos.U1931129,U1631115 and U1831117)under cooperative agreement between NSFC and Chinese Academy of Sciences(CAS)NSFC-STINT Grant 11611130023(CH2015-6360)the National Natural Science Foundation of China(NSFC,Grant No.11403054)
文摘This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.
基金Supported by the National Fundamental Research Program of China under Grant No 2011CB921501the National Natural Science Foundation of China under Grant Nos 91336103,10934010 and 61078026
文摘A method is presented to improve the laser frequency stabilization for the optical pumping cesium clock. By comparing the laser frequency stabilization of different schemes, we verify that the light angle is an important factor that limits the long-term frequency stability. We minimize the drift of the light angle by using a fiber- coupled output, and lock the frequency of a distributed-feedback diode laser to the fluorescence spectrum of the atomic beam. The measured frequency stability is about 3.5 ×10^-11 at i s and reaches 1.5 × 10^-12 at 2000s. The Allan variance keeps going down for up to thousands of seconds, indicating that the medium- and long-term stability of the laser frequency is significantly improved and perfectly fulfills the requirement for the optical pumping cesium clock.
基金Supported by the National Key R&D Program of China under Grant No 2016YFF0200200
文摘Frequencies of frequency standards are shifted by the local static gravity red shifts and also modulated by the tidal relativistic red shifts. We compute the tidal relativistic red shifts using a time-domain method and present the numerical results for the National Institute of Metrology (NIM) in Beijing, Laboratoire National de Metrologie et Essais-Systeme de References Temps-Espaee (LNE-SYRTE) in Paris and Physikalisch-Teehnische Bundesanstalt (PTB) in Braunschweig. The differences of the tidal relativistic red shift approach as large as 1.1 × 10^-16 when frequency standards at NIM are compared with those at SYRTE and PTB. Moreover, the tidal relativistic red shifts of frequency standards in space stations are also computed.
文摘The SI "second"is realized by caesium primary frequency standards( PFSs) using laser cooled atoms in a fountain configuration. Four sub systems and operation procedure of the NTSC-F1 primary frequency standard are introduced in the paper.The frequency stability of NTSC-F1 is 3.0×10-13/ τ-1 / 2compared to hydrogen maser. Four terms of frequency shift and uncertainty including second order Zeeman frequency shift,cold collision shift,gravity shift and blackbody shift are evaluated. The improvement of NTSC-F1 is introduced.
基金Supported by the China Academy of Space Technology Foundation under Grant No CAST-2015-5-10the National Hi-Tech Research and Development Programthe National Natural Science Foundation of China under Grant No 91436210
文摘We report a 42Ohm external cavity diode laser with an interference filter (IF) of 0.5am narrow-bandwidth and 79% high transmission, which is first used for Rb optical frequency standard. The IF and the cat-eye reflector are used for selecting wavelength and light feedback, respectively. The measured laser linewidth is 24 kHz when the diode laser is free running. Using this narrow-linewidth IF blue diode laser, we realize a compact Rb optical frequency standard without a complicated PDH system. The preliminary stability of the Rb optical frequency standard is 2 × 10^-13 at I s and decreases to 1.9 ×10^-14 at 1000s. The narrow-linewidth characteristic makes the IF blue diode laser a well suited candidate for the compact Rb optical frequency standard.
基金Supported by the Young Scientists Fund of the National Natural Science Foundation of China under Grant No 11304177the National Basic Research Program of China under Grant No 2010CB922901
文摘The Dick effect is one of the main limits to the frequency stability of a passive frequency standard, especially for the fountain clock and ion dock operated in pulsed mode which require unavoidable dead time during interrogation. Here we measure the phase noise of the interrogation oscillator applied in the microwave frequency standard based on laser-cooled 113^Cd+ ions, and analyze the Allan deviation limited by the Dick effect. The results indicate that the Dick effect is one of the key issues for the cadmium ion dock to reach expected frequency stability. This problem can be resolved by interrogating the local oscillator continuously with two ion traps.
基金Project supported by the National Fundamental Research Program of China (Grant Nos 2005CB3724500 and 2006CB921400)the Major Program of National Natural Science Foundation of China (Grant No 60490280)National Natural Science Foundation of China (Grant No 10574005)
文摘This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634nm referencing on the hyperfine B-X transition R(80)8-4 of 127I2. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8 × 10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.
基金Supported by National Natural Science Foundation of China (No.60676053)
文摘A novel frequency hopping(FH) sequences generator based on advanced encryption standard(AES) iterated block cipher is proposed for FH communication systems.The analysis shows that the FH sequences based on AES algorithm have good performance in uniformity, correlation, complexity and security.A high-speed, low-power and low-cost ASIC of FH sequences generator is implemented by optimizing the structure of S-Box and MixColumns of AES algorithm, proposing a hierarchical power management strategy, and applying the dynamic clock gating technology based on finite state machine and clock gating.SMIC 0.18 μm standard CMOS technology shows that the scale of ASIC is only about 10.68 kgate, power consumption is 33.8 μW/MHz, and the maximum hop-rate is 1 098 901 hop/s.This design is suitable for portable FH communication system for its advantages in high-security and hop-rate, low-power and low-cost.The proposed FH sequences generator has been employed in Bluetooth SoC design.
基金financially supported by the National Natural Science Foundation of China (No. 61703201)the National Natural Science Foundation of Jiangsu Province (No. BK20170765)
文摘A method for evaluating the benign and malignant breast tumors based on radio?frequency(RF)data was explored by extracting the characteristic parameters of breast ultrasound RF signals.The breast biopsy data were used as the reference data for judging the lump benign or malignant.The extracted ultrasound RF data were reconstructed and segmented by computer aided method to obtain the breast tumor region of interest(ROI)and its characteristic parameters(entropy and standard deviation).The characteristic parameters were statistically analyzed to evaluate the relationship between characteristic parameters and benign or malignant breast tumors.The results indicate the entropy and standard deviation of normal region is much higher than that of lump region,which shows that the standard deviation and entropy characteristic parameters of ultrasonic RF signals are meaningful in the diagnosis of breast tumors.The proposed method provides a new direction for computer?aided diagnosis of benign and malignant breast tumors.
文摘Up to the present time gravitational-wave detectors, such as LIGO and Virgo, have been sensitive to frequencies on the order of a few thousand to a small fraction of an Hz. They have been most effective in the study of black-hole mergers. We suggest that high-frequency relic gravitational wave (HFRGW) detectors be developed, especially the Li-Baker HFRGW detector, in the gigahertz and higher frequency range. We believe collecting cosmological, primordial observational data especially generated during the first few seconds after the beginning of our Universe is extremely important. One motivation for this paper is, therefore, that we are confident that observation of relic gravitational waves will provide vital information about the birth of our Universe and its early dynamical evolution. Other astrophysical applications of HFRGW detectors involve the entropy growth of the early Universe, an ability to study alternatives to inflation and to provide clues about the symmetries underlying new physics at the highest energies. A working hypothesis or theory, based upon the rollout of our Universe from infinitesimal Planck Length and Planck Time is presented. This theory involves the rapid motion of time and matter during that early time having frequencies on the order of trillions of cycles per second or more. Several alternative HFRGW detectors are described and the proposed Li-Baker HFRGW detector, which is theoretically sensitive to GW amplitudes, A, as small as 10-32, is discussed in detail. Such sensitivity may provide a means for verifying or falsifying the rollout of our Universe working hypothesis. Essentially a combination of theory and experimentation is presented. It is recommended that plans and detailed specifications for the Li-Baker HFRGW detector be prepared in order to expedite its fabrication.
基金the National Natural Science Foundation of China(81473597)China National Funds for Distinguished Young Scientists(30825046)Chang Jiang Scholars Program,and the 111 Project(B07007).
文摘Background:The theory of pulse diagnosis is to assess the physiological condition of the human body using radial pulse.However,pulses can vary markedly from person to person.Further,pulse diagnosis is difficult to learn and requires one-on-one teaching.Methods:To address this problem,we built a home-made pulse diagnoser and measured human pulses for studying the standardization of pulse diagnosis.Our pulse diagnoser was composed of a piezoelectric transducer,differential amplifier,data acquisition instrument,and a Matlab analysis program.The measured pulses were converted into electronic signals by a piezoelectric transducer and saved on a computer.The digitalized data were then refined and analyzed by fast Fourier transform for frequency analysis.Simulations were performed to assess the factors that affected the pulse,including phase shifts of reflected pulse waves (generate sub-peaks in pulses),inconsistent heart rates (deform pulse waves),the vessel stiffness (alter harmonic frequencies of the pulses),and the wave amplitudes (determined by the pulse strength).Results:By comparing a published report and our simulation findings,we characterized the pulse types and the effects of various factors,and then applied the findings to study actual pulses in patients.Three types of pulses were determined from the frequency spectrumchoppy pulse (Se mai) without apparent harmonic peaks,the harmonic frequencies of wiry pulse (Xian mai) that are non-integer multiples of the fundamental frequency,and surging pulse (Hong mai) that exhibit strong amplitudes in the spectrum of frequency.A normal pulse and a slippery pulse were differentiated by a phase shift,but not by assessing the frequency spectrum.Conclusion:These findings confirm that frequency domain analysis can avoid ambiguity arising in assessing the three types of pulses in the time domain.Further studies of other pulses in the frequency domain are required to develop a precise electronic pulse diagnoser.
基金Supported by the National Basic Research Program of China(No.2010CB327404)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘An adjustable mixer for surface acoustic wave( SAW)-less radio frequency( RF) front-end is presented in this paper. Through changing the bias voltage,the presented mixer with reconfigurable voltage conversion gain( VCG) is suitable for multi-mode multi-standard( MMMS) applications. An equivalent local oscillator( LO) frequency-tunable high-Q band-pass filter( BPF) at low noise amplifier( LNA) output is used to reject the out-of-band interference signals. Base-band( BB) capacitor of the mixer is variable to obtain 15 kinds of intermediate frequency( IF) bandwidth( BW). The proposed passive mixer with LNA is implemented in TSMC 0. 18μm RF CMOS process and operates from 0. 5 to 2. 5 GHz with measured maximum out-of-band rejection larger than 40 d B. The measured VCG of the front-end can be changed from 5 to 17 d B; the maximum input intercept point( IIP3) is0 d Bm and the minimum noise figure( NF) is 3. 7 d B. The chip occupies an area of 0. 44 mm^2 including pads.
文摘This paper describes a high security data transmission system over X-band microwave frequency. The paper has two parts. The first part deals with encryption of binary data by Advanced Encryption Standard (AES) using VHDL modeling of Field Programmable Gate Array (FPGA). The second part deals with a novel idea of transmitting the encrypted data by using a single klystron. This requires the simultaneous generation of a pair of two independent RF frequencies from a reflex klystron working for X-band frequency range. In this scheme, the klystron is suitably biased on the repeller terminal and superimposed on a train of AES encrypted binary data so as to create two RF frequencies one corresponding to negative peaks and the other one to the positive peaks of the data resulting in an Frequency Shift Keying (FSK) signal. The results have been verified experimentally.