Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperatur...Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.展开更多
With the continuous expansion of the enrolment scale in universities in China,the number of graduates has rapidly increased,which has brought certain difficulties to the employment of college students.In order to ensu...With the continuous expansion of the enrolment scale in universities in China,the number of graduates has rapidly increased,which has brought certain difficulties to the employment of college students.In order to ensure smooth employment,college students need to have strong employability.There is a close relationship between the quality of higher education and the employability of college students.Universities need to improve the employment rate of college students by ensuring the quality of education.The problems in higher education and the relationship between education quality and college students’employability are discussed in this paper,and effective strategies for improving the education quality and college students’employability are proposed.This study will likely contribute to the employment of college students.展开更多
A key point in building a contemporary energy system is the search for sustainable and green energy.Many green energy sources exist in the road or pavement domain,such as solar,thermal,wind,and mechanical energy,etc.U...A key point in building a contemporary energy system is the search for sustainable and green energy.Many green energy sources exist in the road or pavement domain,such as solar,thermal,wind,and mechanical energy,etc.Under the repeated vehicle loads,stresses and strains are generated in the pavement,which can generate substantial mechanical energy.In recent two decades,there has been a growing scholarly preference for utilizing the piezoelectric effect to convert mechanical energy from pavement into electricity to supply low-power transportation facilities,pavement sensors,etc.This paper provides an in-depth review of state-of-the-art advances in road piezoelectric energy harvesters.The basic principle of piezoelectric energy harvesting and common piezoelectric materials were briefly introduced.The piezoelectric energy harvesters suitable for roads are thoroughly reviewed from five perspectives:structure,finite element analyses,protective packaging,management circuit,and application.Finally,the challenges faced by piezoelectric energy harvesters for pavements were summarized,and the potential research directions were also proposed.This review serves as a valuable reference for advancing road piezoelectric harvesting technology development.展开更多
We demonstrate a robust femtosecond LIDAR setup by using two free-running environmentally stable allpolarization-maintaining nonlinear amplified loop mirror mode-locked fiber lasers. Based on the asynchronous optical ...We demonstrate a robust femtosecond LIDAR setup by using two free-running environmentally stable allpolarization-maintaining nonlinear amplified loop mirror mode-locked fiber lasers. Based on the asynchronous optical sampling method, a ranging accuracy of ±2 μm within 65 m has been achieved, as tested in an 80-m-long underground optical tunnel. Through the Kalman filter in real-time data processing, the measurement accuracy can be maintained at a 200 Hz update rate. This setup provides a practical tool for various large-scale industrial and astronomical ranging applications.展开更多
We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two...We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle.By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.展开更多
We demonstrate the stabilization of an optical frequency comb(OFC) using a segment of fiber delay line as a reference. A mode-locked Er-doped fiber laser is phase locked to a kilometer-long fiber delay line using thre...We demonstrate the stabilization of an optical frequency comb(OFC) using a segment of fiber delay line as a reference. A mode-locked Er-doped fiber laser is phase locked to a kilometer-long fiber delay line using three different schemes. The short-term stability of the comb modes in the OFC stabilized by these schemes is obviously enhanced, down to the 10;level at millisecond average time. Among these three schemes, phase locking two bunches of comb modes in the OFC to the same fiber delay line exhibits the lowest residual phase noise. Fiber-delay-line-referenced OFCs can provide reliable laser sources in precise metrology owing to the advances of low cost, compactness, and high integration.展开更多
基金supported by National Natural Science Foundation of China (Grant Nos.61475162,61675150,and 61535009)Tianjin Natural Science Foundation (Grant No.18JCYBJC16900)Tianjin Research Program of Application Foundation and Advanced Technology (Grant No.17JCJQJC43500)
文摘Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.
文摘With the continuous expansion of the enrolment scale in universities in China,the number of graduates has rapidly increased,which has brought certain difficulties to the employment of college students.In order to ensure smooth employment,college students need to have strong employability.There is a close relationship between the quality of higher education and the employability of college students.Universities need to improve the employment rate of college students by ensuring the quality of education.The problems in higher education and the relationship between education quality and college students’employability are discussed in this paper,and effective strategies for improving the education quality and college students’employability are proposed.This study will likely contribute to the employment of college students.
基金partly supported by the National Natural Science Foundation of China under Grant No.5247082732the Shaanxi Provincial Transportation Technology Project under Grant No.24-58k+2 种基金the Fundamental Research Funds for the Central Universities of CHD under Grant No.300102214909the Scientific Innovation Practice Project of Postgraduates of Chang'an University under Grant No.300103723024Scientific Research Fund of Xinjiang Transportation Design Institute under Grant No.KY2022080901 and KY2022042501。
文摘A key point in building a contemporary energy system is the search for sustainable and green energy.Many green energy sources exist in the road or pavement domain,such as solar,thermal,wind,and mechanical energy,etc.Under the repeated vehicle loads,stresses and strains are generated in the pavement,which can generate substantial mechanical energy.In recent two decades,there has been a growing scholarly preference for utilizing the piezoelectric effect to convert mechanical energy from pavement into electricity to supply low-power transportation facilities,pavement sensors,etc.This paper provides an in-depth review of state-of-the-art advances in road piezoelectric energy harvesters.The basic principle of piezoelectric energy harvesting and common piezoelectric materials were briefly introduced.The piezoelectric energy harvesters suitable for roads are thoroughly reviewed from five perspectives:structure,finite element analyses,protective packaging,management circuit,and application.Finally,the challenges faced by piezoelectric energy harvesters for pavements were summarized,and the potential research directions were also proposed.This review serves as a valuable reference for advancing road piezoelectric harvesting technology development.
基金supported by the Natural Science Foundation of Tianjin(No.18JCYBJC16900)the National Natural Science Foundation of China(NSFC)(Nos.61675150,61827821,and 61535009)
文摘We demonstrate a robust femtosecond LIDAR setup by using two free-running environmentally stable allpolarization-maintaining nonlinear amplified loop mirror mode-locked fiber lasers. Based on the asynchronous optical sampling method, a ranging accuracy of ±2 μm within 65 m has been achieved, as tested in an 80-m-long underground optical tunnel. Through the Kalman filter in real-time data processing, the measurement accuracy can be maintained at a 200 Hz update rate. This setup provides a practical tool for various large-scale industrial and astronomical ranging applications.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.U1730115,61535009,and 11527808)the Open Fund of State Key Laboratory of High Field Laser Physics(Shanghai Institute of Optics and Fine Mechanics)
文摘We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle.By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.
基金This work was supported by the National Natural Science Foundation of China(Nos.61975144 and 61827821)the Tianjin Research Program of Application Foundation and Advanced Technology of China(No.17JCJQJC43500)。
文摘We demonstrate the stabilization of an optical frequency comb(OFC) using a segment of fiber delay line as a reference. A mode-locked Er-doped fiber laser is phase locked to a kilometer-long fiber delay line using three different schemes. The short-term stability of the comb modes in the OFC stabilized by these schemes is obviously enhanced, down to the 10;level at millisecond average time. Among these three schemes, phase locking two bunches of comb modes in the OFC to the same fiber delay line exhibits the lowest residual phase noise. Fiber-delay-line-referenced OFCs can provide reliable laser sources in precise metrology owing to the advances of low cost, compactness, and high integration.
