Hao Xu
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Hao Xu has a total of 8 co-authors. Here are the top co-authors by number of shared publications:
- Jianye Zhao
School of Electronics, Peking Universityhttps://ror.org/02v51f717, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China
3 shared publications - Lin Dan
Department of Electronics, Peking University, Beijing 100871, China
2 shared publications - Ping Guo
Department of Electronics, Peking University, Beijing 100871, China
2 shared publications - Dong Hou
School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
1 shared publication - Haitao Wu
School of Electronics, Peking University, Beijing 100871, China
1 shared publication - Haoyuan Lu
Department of Electronics, Peking University, Beijing 100871, China
1 shared publication
Latest Publications
- Open Access
Yoctosecond Timing Jitter Sensitivity in Tightly Synchronized Mode-Locked Ti:Sapphire Lasers
Higher sensitivity in timing jitter measurement has great importance in studies related to precise measurements. Timing jitter noise floors contribute one of the main parts in existing measurements. In this article, a phase error signal is obtained by superposition of outputs of two optical heterodyne discrimination apparatus to suppress the noise floor. Excess phase noise of the electrical amplifier is avoided. We demonstrate 2.6 × 10−14 fs2/Hz (~160 ys/√Hz) timing jitter noise floor between two identical 99 MHz repetition-rate mode-locked Ti:sapphire lasers after their repetition rates are tightly synchronized. The performance is extensible to reach an integrated timing jitter resolution of one attosecond.
Open AccessYoctosecond Timing Jitter Sensitivity in Tightly Synchronized Mode-Locked Ti:Sapphire Lasers
Higher sensitivity in timing jitter measurement has great importance in studies related to precise measurements. Timing jitter noise floors contribute one of the main parts in existing measurements. In this article, a phase error signal is obtained by superposition of outputs of two optical heterodyne discrimination apparatus to suppress the noise floor. Excess phase noise of the electrical amplifier is avoided. We demonstrate 2.6 × 10−14 fs2/Hz (~160 ys/√Hz) timing jitter noise floor between two identical 99 MHz repetition-rate mode-locked Ti:sapphire lasers after their repetition rates are tightly synchronized. The performance is extensible to reach an integrated timing jitter resolution of one attosecond.
- Open Access
Optical Frequency Comb-Based Direct Two-Photon Cooling for Cold Atom Clock
The performance of the cold atom clock based on coherent population trapping (CPT) improved when the temperature decreased. In order to obtain a lower temperature in the cold atom clock, we proposed a cooling scheme in this paper that employs direct two-photon transition using optical frequency combs (OFCs). Two trains of time-delayed pulses from opposite directions were utilized to interact with atoms. It was found that the temperature of the cold atoms reached the minimum if the pulse area was and the time delay between the absorption pulse and the stimulated emission pulse was in the range from to . In this paper, it was confirmed that the proposed cooling process allowed for faster and more efficient momentum exchange between light and atoms, and the proposed cooling process could be applied to the atoms or molecules that could not be cooled to desired temperature through the single-photon cooling process. The 87Rb cooling, together with the CPT interrogating scheme using OFCs reduced the ratio value of linewidth/contrast, and the frequency stability of the cold atom clock hence improved by more than six times as per our calculation.Open AccessOptical Frequency Comb-Based Direct Two-Photon Cooling for Cold Atom Clock
The performance of the cold atom clock based on coherent population trapping (CPT) improved when the temperature decreased. In order to obtain a lower temperature in the cold atom clock, we proposed a cooling scheme in this paper that employs direct two-photon transition using optical frequency combs (OFCs). Two trains of time-delayed pulses from opposite directions were utilized to interact with atoms. It was found that the temperature of the cold atoms reached the minimum if the pulse area was and the time delay between the absorption pulse and the stimulated emission pulse was in the range from to . In this paper, it was confirmed that the proposed cooling process allowed for faster and more efficient momentum exchange between light and atoms, and the proposed cooling process could be applied to the atoms or molecules that could not be cooled to desired temperature through the single-photon cooling process. The 87Rb cooling, together with the CPT interrogating scheme using OFCs reduced the ratio value of linewidth/contrast, and the frequency stability of the cold atom clock hence improved by more than six times as per our calculation. - Open Access
- 14 September 2021
- Published by MDPI AG in Applied Sciences
- Vol. 11 (18) , 8536
High Vacuum Packaging of MEMS Devices Containing Heterogeneous Discrete Components
Vacuum packaging of Micro-electro-mechanical system (MEMS) devices is a hot topic for its advantages of improving performance and reducing power consumption. In this paper, the physics package of a chip scale atomic clock (CSAC), as a typical kind of MEMS device, is performed by vacuum packaging based on a systematic method proposed by us. The whole process, including low outgassing and thermal stable materials selection, prebaking for desorption, getter firing for absorption and solder reflow for vacuum sealing is introduced thoroughly. The thermogravimetric analysis or thermal gravimetric analysis (TGA) is used to analyze the thermal stability and desorption of materials. The leak rate of physics packages is measured to be less than 4 × 10−10 Pa·m3/s by helium leak detection. The residual gas pressure and composition in physics packages are analyzed after vacuum packaging. The results show a high vacuum ~0.1 Pa in the physics package. The frequency stability is improved from 4.68 × 10−11 to 1.07 × 10−11 @40,000 s. The presented method for high vacuum packaging is also applicable to other MEMS devices.
- 14 September 2021
- Published by MDPI AG in Applied Sciences
- Vol. 11 (18) , 8536
Open AccessHigh Vacuum Packaging of MEMS Devices Containing Heterogeneous Discrete Components
Vacuum packaging of Micro-electro-mechanical system (MEMS) devices is a hot topic for its advantages of improving performance and reducing power consumption. In this paper, the physics package of a chip scale atomic clock (CSAC), as a typical kind of MEMS device, is performed by vacuum packaging based on a systematic method proposed by us. The whole process, including low outgassing and thermal stable materials selection, prebaking for desorption, getter firing for absorption and solder reflow for vacuum sealing is introduced thoroughly. The thermogravimetric analysis or thermal gravimetric analysis (TGA) is used to analyze the thermal stability and desorption of materials. The leak rate of physics packages is measured to be less than 4 × 10−10 Pa·m3/s by helium leak detection. The residual gas pressure and composition in physics packages are analyzed after vacuum packaging. The results show a high vacuum ~0.1 Pa in the physics package. The frequency stability is improved from 4.68 × 10−11 to 1.07 × 10−11 @40,000 s. The presented method for high vacuum packaging is also applicable to other MEMS devices.