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European Frequency and time Forum (EFTF)

作者： Xuwen Hu Fuyu Sun Chao Li Jie Liu Xiaofeng Li Shougang Zhang National Time Service Center Chinese Academy of Sciences Xi'an China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an China

ISBN: (数字)9798350354270

ISBN: (纸本)9798350354287

Efficient fluorescence detection is crucial in the field of precision spectral analysis. This paper presents an improved design of an atomic-beam fluorescence collector that utilizes the convergence characteristics of ellipsoidal surfaces and the reflection characteristics of spherical surfaces. It calculates the parameter relationship for achieving full-angle fluorescence collection. The study fine-tunes the structural parameters and simulates the fluorescence collection efficiency and losses under different conditions when emitting from a non-ideal point light source. The improved fluorescence collector captures photons with nearly 4n solid angle coverage, allowing photons to be reflected at most twice before reaching the photo detector, thereby increasing collection efficiency. This improved collector can be used in various fields for detecting weak fluorescence signals.

关键词： time-frequency analysis Europe Detectors Fluorescence Solids Reflection Structural engineering Spectral analysis Photonics Light sources

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A Compact Optically Pumped Cesium Beam Clock with a Differential Detection Scheme

A Compact Optically Pumped Cesium Beam Clock with a Differen...

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European Frequency and time Forum (EFTF)

作者： Chao Li Fuyu Sun Xuwen Hu Jie Liu Xiaofeng Li Shougang Zhang National Time Service Center Chinese Academy of Sciences Xi'an China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an China

ISBN: (数字)9798350354270

ISBN: (纸本)9798350354287

Compact optically pumped cesium beam clocks have become a focus in cesium clock research due to their high atomic utilization and excellent short-term frequency stability. However, stray light noise, one of the main noise sources, limits the stability improvement. In this paper, we present a compact optically pumped cesium clock that uses differential detection to reduce the impact of stray light on clock performance. It incorporates an additional fluorescence collector to capture stray light during detection and subtract it from the clock transition signal, effectively reducing stray light level. Consequently, this scheme significantly enhances the signal-to-noise ratio, improving the short-term frequency stability of the compact optically pumped cesium clock.

关键词： time-frequency analysis Atom optics Stray light Laser stability Cesium Optical pumping Optical noise Laser beams Optical beams Clocks

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Indoor UWB Localization Based on Improved Intelligent Optimization Algorithms 6

Indoor UWB Localization Based on Improved Intelligent Optimi...

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6th International Conference on Internet of Things, Automation and Artificial Intelligence, IoTAAI 2024

作者： Li, Shuaichen Wu, Jianfeng Chinese Academy of Sciences National Time Service Center Xian710600 China Chinese Academy of Sciences Key Laboratory of Time Reference and Applications Xi'an710600 China University of Chinese Academy of Sciences School of Integrated Circuits Beijing100049 China University of Chinese Academy of Sciences College of Electronic Electrical and Communication Engineering Beijing100049 China

ISBN: (纸本)9798350386974

In response to the slow convergence of the original intelligent optimization algorithm and the possibility of converging to locally optimal solutions, this paper proposes the Logistic Mapping-Gaussian Mutation-Spiral Flight improvement strategy. The improvement in performance by the proposed strategy for the intelligent optimization algorithm is verified using the Grey Wolf Optimization Algorithm (GWO) and Egret Swarm Optimization Algorithm (ESOA). First, the improved GWO algorithm was tested with both unimodal and multimodal standard test functions, and the results were compared. The results show that the improved algorithm has a significant improvement in the accuracy and stability. Next, the improvement strategy was applied to the ESOA algorithm to solve for indoor positioning in UWB. The experimental results show that the improved algorithm significantly reduces both positioning error and standard deviation, which was reduced by 17.69% compared with the algorithm before the improvement, and the standard deviation is approximately 1/10 of the pre improvement level. Moreover, Improved algorithm requires a smaller minimum population and fewer iterations and has better convergence ability. These results indicate that the proposed improvement strategy can effectively enhance the performance of intelligent optimization algorithms and provide new ideas and methods for better solving optimization problems and indoor UWB positioning problems. © 2024 IEEE.

关键词： Optimization algorithms

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Laser Frequency Offset Locking with Dual-modulation

Laser Frequency Offset Locking with Dual-modulation

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European Frequency and time Forum (EFTF)

作者： Wang Bisong Peter Yun Hao Qiang Key Laboratory of Time Reference and Applications National Time Service Center Chinese Academy of Sciences Xi'an Shaanxi China University of Chinese Academy of Sciences Beijing China

ISBN: (数字)9798350354270

ISBN: (纸本)9798350354287

We report a laser frequency offset locking scheme for coherent population trapping (CPT) atomic clock. Based on a usual half-wave modulation in CPT atomic clocks, we add a radio frequency signal to the laser driving current to form dual-modulation to compensate the frequency shift of optical transition due to buffer gas in the clock cell. The Doppler-free absorption enhanced spectrum produced by dual-modulation is observed and successfully applied to the laser frequency offset locking. In our scheme, a frequency shift device is no longer necessary, thus the clock's size, weight, power, complexity, environmental sensitivity, and cost are reduced, this is suitable for implementing compact and high-performance CPT and POP atomic clocks.

关键词： time-frequency analysis Spectroscopy Frequency modulation Optical polarization Atom lasers Optical buffering Gas lasers Optical sensors Laser transitions Atomic clocks

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Spin-squeezing-enhanced optical lattice clocks with 10−19-level differential frequency stability at the averaging time of 1 s

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Physical Review A 2024年第1期110卷 013102-013102页

作者： Deshui Yu Jia Zhang Tongyan Xia Shougang Zhang Tiantian Shi Jingbiao Chen Key Laboratory of Time Reference and Applications State Key Laboratory of Advanced Optical Communication Systems and Networks Institute of Quantum Electronics School of Electronics Beijing 100049 China School of Integrated Circuits Beijing 100871 China Hefei National Laboratory Hefei 230088 China

Many-body entangled states allow precision measurement beyond the standard quantum limit. Yet they have not been effectively exploited in optical lattice clocks except for proof-of-principle demonstrations. Under the current experimental conditions, taking into account the lattice perturbation, atom-atom interactions, and local oscillator noise, we theoretically evaluate the performance of spin-squeezing-based shallow-lattice Yb optical clocks. The numerical simulation shows that the stability of differential frequency comparison between two Yb ensembles in squeezed spin states potentially accesses the 10−19 level at the averaging time of 1 s. The resultant Wineland parameter may be as low as ξW2=0.027, corresponding to a reduction of averaging time by a factor of 37, and is limited by the collision-induced degradation of spin squeezing. The metrological gain provided by spin squeezing opens up new opportunities for precision measurement and fundamental physics.

关键词： Atomic, optical & lattice clocks

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Optical frequency transfer link with remote site compensation

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Chinese Optics Letters 2024年第9期22卷 68-73页

作者： Qi Zang Xiang Zhang Xue Deng Qian Zhou Dan Wang Yucan Zhang Jing Gao Dongdong Jiao Guanjun Xu Tao Liu Ruifang Dong Shougang Zhang National Time Service Centre Chinese Academy of SciencesXi’an 710600China Key Laboratory of Time Reference and Applications Chinese Academy of SciencesXi’an 710600China School of Communications and Information Engineering and School of Artificial Intelligence Xi’an University of Posts and TelecommunicationsXi’an 710121China University of Chinese Academy of Sciences Beijing 100049China

In this paper,we present a remote time-base-free technique for a coherent optical frequency transfer system via *** the remote site,the thermal noise of the optical components is corrected along with the link phase noise caused by environmental *** this system,a 1×2 acousto-optic modulator(AOM)is applied at the remote site,with the first light being used to eliminate the noise of the remote time base and interface with remote users while the zeroth light is used to establish an active noise canceling *** this technique,a 10 MHz commercial oscillator,used as a time base at the remote site,does not contribute to the noise of the transferred *** experimental system is constructed using a 150 km fiber spool to validate the proposed *** compensation,the overlapping Allan deviation of the transfer link is 7.42×10^(-15)at 1 s integration time and scales down to 1.07×10^(-18)at 10,000 s integration *** uncertainty of the transmitted optical frequency is on the order of a few *** significantly reduces the time-base requirements and costs for multi-user applications without compromising transfer ***,these results show great potential for transferring ultra-stable optical frequency signals to remote sites,especially for point-to-multi-users.

关键词： optical frequency measurement remote site compensation ultra-stable laser fiber network

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A Novel Scheme of Doppler-Free Spectroscopy by Differential Detection

A Novel Scheme of Doppler-Free Spectroscopy by Differential ...

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European Frequency and time Forum (EFTF)

作者： Tenghui Yang Peter Yun Bisong Wang Qiang Hao Key Laboratory of Time Reference and Applications NTSC Chinese Academy of Science Xi'an Shaanxi China University of Chinese Academy of Sciences Beijing China

ISBN: (数字)9798350354270

ISBN: (纸本)9798350354287

We propose and implement a differential detection scheme of Doppler-free spectroscopy. By setting the proper relative polarization direction between the linearly polarized probe and pump beam, which are spatially counter-propagated and overlapped, simultaneous enhanced absorption and transmission are observed by detecting the parallel and perpendicular polarization components of the transmitted probe beam. The differential signal with improved signal-to-noise ratio (SNR) is also obtained, which is desired for compact optical reference, high-resolution spectroscopy and so on.

关键词： Spectroscopy time-frequency analysis Optical polarization Atom optics Absorption Resonant frequency Laser stability Optical pumping Probes Signal to noise ratio

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Derivation and Simulation of Beidou System QMBOC Signal Distortion Model

Derivation and Simulation of Beidou System QMBOC Signal Dist...

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Aerospace Engineering and Systems (ISAES), International Symposium on

作者： Xin Gao Yongnan Rao Xiaogang Zheng School of Electrical and Electronic Engineering Wuhan Polytechnic University Wuhan China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an China

ISBN: (数字)9798350350418

ISBN: (纸本)9798350350425

This study examines the distortion characteristics of the QMBOC (Quadrature Multiplexed Binary Offset Carrier) modulation signal. The QMBOC ideal signal creation formula extends the digital and analog distortion model suited for QMBOC by mathematical modeling, based on the 2-OS distortion model and BOC distortion model. The legend is then generated using a simulation platform. The inconsistency in the weight proportion of the distortion of the in-phase and orthogonal components of the QMBOC signal is attributed to the γ power factor of the signal. The simulation results indicate that the primary signal distortion is primarily associated with the Q branch in the investigation and examination of the duty ratio and distortion value. Additionally, the simulation analysis of distortion also supports the corresponding experimental findings. This offers a theoretical backing for examining the distortion properties of QMBOC.

关键词： Accuracy Correlation Simulation Stability criteria Interference Distortion Satellite navigation systems Signal generators Mathematical models Correlators

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Incorporating a Cesium fountain frequency standard into a Real-time time Scale UTC(k)

Incorporating a Cesium fountain frequency standard into a Re...

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IEEE International Symposium on applications of Ferroelectrics (ISAF)

作者： Shuhong Zhao Shaowu Dong Shanshan Bai Jihai Zhang Sufang Liu Shouxiang Lu National Time Service Center Chinese Academy of Sciences Xi’an China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi’an China University of Chinese Academy of Sciences Beijing China

ISBN: (数字)9798350371901

ISBN: (纸本)9798350371918

The integrity and dependability of reference time scales are increasingly critical across various fields, notably in the realm of global navigation satellite systems (GNSS) and essential services requiring synchronized timing. The cesium fountain clock is the most accurate infrastructure for reproducing the time interval unit "second" in the International System of Units (SI). It exhibits almost no frequency drift and has excellent long-term stability in reproducing the standard second length. The cesium fountain clock NTSC-CsF2, along with the clock assembly, is jointly involved in timekeeping. This study focuses on the performance analysis of the cesium fountain clock, the joint time scale algorithm based on the cesium fountain clock, and the frequency steering algorithm aimed at generating a real-time time scale. The final experiment proves that the participation of the fountain clock can improve the performance of the standard time UTC(k).

关键词： time-frequency analysis Global navigation satellite system Cesium Real-time systems Stability analysis Performance analysis Synchronization Standards Frequency control Clocks

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Purification Technique with a Hertz-Linewidth Laser for Fiber-Based Optical Frequency Coherence Dissemination

SSRN

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SSRN 2024年

作者： Wang, Dan Liu, Jie Jiao, Dongdong Zang, Qi Zhang, Xiang Zhou, Qian Zhang, Yucan Xu, Guanjun Dong, Ruifang Liu, Tao Zhang, Shougang National Time Service Center Chinese Academy of Sciences Xi’an China University of Chinese Academy of Sciences Beijing China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi’an China

We propose a purification relay station for optical frequency dissemination over long-distance communication fiber links particularly in complex environments. This technique addresses the challenge of phase noise suppression limitation due to dissemination delay in laser traversing fiber links. Utilizing a cavity-stabilized hertz-linewidth laser, we synchronized the phase with that of the signal received from the previous link within a 10 Hz bandwidth and followed the phase noise of the hertz-linewidth laser beyond 10 Hz (much lower than the phase noise of the previously disseminated optical frequency), effectively reducing high-frequency phase noise. Furthermore, to ensure continuous coherence and stability of the disseminated laser, the data processing based on FPGA was employed to eliminate phase cycle slips in the previously disseminated optical frequency. We applied this technique to the optical frequency disseminated along with a 106 km communication fiber link. After optical frequency purification, the fractional frequency instability at a 1 s averaging time is reduced by a factor of three. Additionally, with the elimination of the phase cycle slips, the fractional frequency instability of purified optical frequency scales as 1/τ which matches with a signal dominated by phase-modulated white noise. At a 10,000 s averaging time, the purified optical frequency achieves a stability of 6.15×10-19, representing a reduction of two orders of magnitude compared to that of the previously disseminated optical frequency. This work establishes the foundation for the development of a nationwide optical frequency dissemination network involving long-distance fiber links in complex environments. © 2024, The Authors. All rights reserved.

关键词： Phase noise

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