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Precise determination of characteristic laser frequencies by an Er-doped fiber optical frequency comb

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Chinese Physics B 2022年第7期31卷 327-335页

作者： Shiying Cao Yi Han Yongjin Ding Baike Lin Zhanjun Fang division of time and frequency Metrology National Institute of MetrologyBeijing 100029China

Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and ***,any optical frequency in visible to near-infrared region can be directly traced to a microwave *** a result,the length unit“meter”is directly related to the time unit“second”.This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared *** frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequencydoubling *** signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633,698,729,780,1064,and 1542 nm is better than 30 d *** frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1×10^(-13)at 1-s averaging *** measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylenestabilized 1542-nm *** results are within the uncertainty range of the international recommended *** results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb,which is not only important for the precise and accurate traceability and calibration of the laser frequencies,but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.

关键词： optical frequency measurement phase lock Er-doped fiber laser fiber optical frequency comb

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低噪声频率综合

现代雷达 1989年第6期11卷 47-54,16页

作者： F.L.Walls C.M.Felton 韦传安 time and frequency division nat-ional bureau of standards Felton Electronics Design 美国

本文综述了相位噪声的各种定义和经无噪声倍频、分频和变频后相位噪声的变化。其次综述了非致冷参考频率(rf)和微波振荡器的相位噪声。利用系统方法可以综合出一个微波信号,其近载频相位噪声受一个低频石英振荡器的控制,而高频相位噪声... 详细信息

本文综述了相位噪声的各种定义和经无噪声倍频、分频和变频后相位噪声的变化。其次综述了非致冷参考频率(rf)和微波振荡器的相位噪声。利用系统方法可以综合出一个微波信号,其近载频相位噪声受一个低频石英振荡器的控制,而高频相位噪声则受微波源的控制。用这种方法比用单个源可能得到的相位噪声性能优越。最后,比较了各种放大器、倍频器和分频器的相位噪声。虽然,分频器的相位噪声一般地比最好的倍频器要差,但是对大多数应用来说通常是足够了。应当特别指出两点,其一是对某些分频器,文献中引用的相位噪声或许悲观,其二是如果处于振动热应力条件下,系统的相位噪声常常会受到严重的影响。

关键词：低噪声频率综合相位噪声

Coherent Optical frequency Transfer via a 490 km Noisy Fiber Link

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Chinese Physics Letters 2022年第4期39卷 7-11页

作者： Xiang Zhang Xue Deng Qi Zang Dongdong Jiao Jing Gao Dan Wang Qian Zhou Jie Liu Guanjun Xu Ruifang Dong Tao Liu Shougang Zhang national time Service Center Chinese Academy of SciencesXi’an 710600China University of Chinese Academy of Sciences Beijing 100039China Key Laboratory of time and frequency standards Chinese Academy of SciencesXi’an 710600China

We demonstrate the coherent transfer of an ultrastable optical frequency reference over a 490 km noisy field fiber *** fiber-induced phase noise power spectrum density per-unit-length at 1 Hz offset frequency can reach up to 510 rad^(2)·Hz^(-1)·km^(-1),which is much higher than the fiber noise observed in previous *** extreme level of phase noise is mainly due to the fiber link laying underground along the *** phaselocked loop parameters are chosen to complete the active compensation of fiber noise by measuring the intensity fluctuation of additional phase noise and designing a homemade digital frequency division phase discriminator with a large phase detection range of 2^(12)π***,a noise suppression intensity of approximately 40 d B at1 Hz is obtained,with fractional frequency instability of 1.1×10^(-14 )at 1 s averaging time,and 3.7×10^(-19) at10000 *** transfer system will be used for remote atomic clock comparisons and optical frequency distribution over a long-distance communication network established in China.

关键词： fiber noise underground

Improved Evaluation of BBR and Collisional frequency Shifts of NIM-Sr2 with 7.2×10^(-18)Total Uncertainty

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Chinese Physics Letters 2022年第8期39卷 22-27页

作者： Bing-Kun Lu Zhen Sun Tao Yang Yi-Ge Lin Qiang Wang Ye Li Fei Meng Bai-Ke Lin Tian-Chu Li Zhan-Jun Fang division of time and frequency Metrology National Institute of MetrologyBeijing 100029China Department of Precision Instrument Tsinghua UniversityBeijing 100084China

NIM-Sr2 optical lattice clock has been developed on the Changping campus of national Institute of Metrology(NIM).Considering the limitations in NIM-Sr1,several improved parts have been designed including a differential pumping stage in the vacuum system,a permanent magnet Zeeman slower,water-cooled anti-Helmholtz coils,an extended viewport for Zeeman slower,etc.A clock laser with a short-time stability better than 3×10^(-16)is realized based on a self-designed 30-cm-long ultra-low expansion *** systematic frequency shift has been evaluated to an uncertainty of 7.2×10^(-18),with the uncertainty of BBR shift and the collisional frequency shift being an order of magnitude lower than the last evaluation of NIM-Sr1.

关键词： pumping slower Shift

An all-polarization-maintaining repetition-tunable erbium-doped passively mode-locked fiber laser

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Chinese Physics B 2013年第10期22卷 299-304页

作者：赵光贞肖晓晟孟飞梅佳伟杨昌喜 State Key Laboratory of Precision Measurement Technology and Instruments Department of Precision InstrumentsTsinghua University division of time and frequency Metrology National Institute of Metrology

An environmentally stable, repetition rate tunable, all-polarization-maintaining, Er-doped pulse fiber laser with a single-wall carbon nanotubes saturated absorber is demonstrated. The ring laser cavity includes a delay line enabling a tunable repetition rate to vary from 35.52 MHz to 35.64 MHz with continuous mode-locked operation. The laser output parameters confirm that the tunable mode-locked operations are stable. High environmental stability is also confirmed by the -130 dBc/Hz low phase noise, a 70-dB signal-to-noise ratio of radio frequency signals, a low amplitude fluctuation of 5.76 × 10-4, and a low fluctuation of reoetition rate of 12 Hz. The laser shows a high de^ree of oolarization of 93%.

关键词： fiber laser modulation tuning and mode locking nanotubes

First Evaluation and frequency Measurement of the Strontium Optical Lattice Clock at NIM

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Chinese Physics Letters 2015年第9期32卷 17-20页

作者：林弋戈王强李烨孟飞林百科臧二军孙震房芳李天初方占军 division of time and frequency National Institute of Metrology (NIM) Beijing 100013 Department of Precision Instrument Tsinghua University Beijing 100084

An optical lattice clock based on 87Sr is built at national Institute of Metrology （NIM） of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10-16. To measure its absolute frequency with respect to NIM＇s cesium fountain clock NIM5, the frequency of a flywheel H-maser of NIM5 is transferred to the Sr laboratory through a 50-kin-long fiber. reference frequency of this H-maser, is used for the optical this Sr clock is measured to be 429228004229873.7（1.4）Hz. A fiber optical frequency comb, phase-locked to the frequency measurement. The absolute frequency of

关键词： AOM First Evaluation and frequency Measurement of the Strontium Optical Lattice Clock at NIM

A Hertz-Linewidth Ultrastable Diode Laser System for Clock Transition Detection of Strontium Atoms

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Chinese Physics Letters 2014年第2期31卷 66-69页

作者：李烨林弋戈王强王少凯赵阳孟飞林百科曹建平李天初方占军臧二军 division of time and frequency Metrology National Institute of Metrology Beijing 100013 State Key Laboratory of Precision Measurement Technology and Instruments Tsinghua University Beijing 100084

The frequencies of two 698 nm external cavity diode lasers （ECDLs） are locked separately to two independently located ultrahigh finesse optical resonant cavities with the Pound Drever-Hall technique. The linewidth of each ECDL is measured to be -4.6 Hz by their beating and the fractional frequency stability below 5 × 10^-15 between 1 s to lOs averaging time. Another 698nm laser diode is injection locked to one of the cavity-stabilized ECDLs with a fixed frequency offset for power amplification while maintaining its linewidth and frequency characteristics. The frequency drift is H1 Hz/s measured by a femtosecond optical frequency comb based on erbium fiber. The output of the injection slave laser is delivered to the magneto-optical trap of a Sr optical clock through a iO- ta-long single mode polarization maintaining fiber with an active fiber noise cancelation technique to detect the clock transition of Sr atoms.

关键词： Locks (fasteners)

A Longitudinal Zeeman Slower Based on Ring-Shaped Permanent Magnets for a Strontium Optical Lattice Clock

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Chinese Physics Letters 2015年第10期32卷 22-25页

作者：王强林弋戈高坊林李烨林百科孟飞臧二军李天初方占军 division of time and frequency National Institute of Metrology Beijing 100013 Department of Precision Instrument Tsinghua University Beijing 100084 Research Institute of Petroleum Exploration and Development Langfang 065007

We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter but different inner diameters. The maximum variation of the axial field from its target values is less than 2%. In most parts of the Zeeman slower, the intensity variations of the field in radial spatial distribution are less than 0.1 roT. With this Zeeman slower, the strontium atoms are slowed down to 95m/s, and approximately 2% of the total atoms are slowed down to less than 50m/s.

关键词： A Longitudinal Zeeman Slower Based on Ring-Shaped Permanent Magnets for a Strontium Optical Lattice Clock

Enhancing Deepfake Detection:Proactive Forensics Techniques Using Digital Watermarking

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Computers, Materials & Continua 2025年第1期82卷 73-102页

作者： Zhimao Lai Saad Arif Cong Feng Guangjun Liao Chuntao Wang School of Automation Guangdong University and TechnologyGuangzhou510006China School of Immigration Administration(Guangzhou) China People’s Police UniversityGuangzhou510663China Department of Mechanical Engineering College of EngineeringKing Faisal UniversityAl Ahsa31982Saudi Arabia Cyber Police division Guangzhou Public Security BureauGuangzhou510030China School of Forensic Science and Technology Guangdong Police CollegeGuangzhou510320China College of Mathematics and Informatics South China Agricultural UniversityGuangzhou510642China

With the rapid advancement of visual generative models such as Generative Adversarial Networks(GANs)and stable Diffusion,the creation of highly realistic Deepfake through automated forgery has significantly *** paper examines the advancements inDeepfake detection and defense technologies,emphasizing the shift from passive detection methods to proactive digital watermarking *** detection methods,which involve extracting features from images or videos to identify forgeries,encounter challenges such as poor performance against unknown manipulation techniques and susceptibility to counter-forensic *** contrast,proactive digital watermarking techniques embed specificmarkers into images or videos,facilitating real-time detection and traceability,thereby providing a preemptive defense againstDeepfake *** offer a comprehensive analysis of digitalwatermarking-based forensic techniques,discussing their advantages over passivemethods and highlighting four key benefits:real-time detection,embedded defense,resistance to tampering,and provision of legal ***,the paper identifies gaps in the literature concerning proactive forensic techniques and suggests future research directions,including cross-domain watermarking and adaptive watermarking *** systematically classifying and comparing existing techniques,this review aims to contribute valuable insights for the development of more effective proactive defense strategies in Deepfake forensics.

关键词： Deepfake proactive forensics digital watermarking traceability detection techniques