This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and...This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and a related altitude motion model is established.Then,the designed controller is divided into the outer part and inner part,where the outer part is devised by a combination of the back-stepping method and command filter technique so that the’explosion of complexity’problem is eliminated.Moreover,the integrator structure of the altitude motion model is exploited to simplify the back-stepping design,and disturbance observers inspired from the idea of extended state observer are devised to obtain estimations of the system disturbances.The control input switches from the outer part to the inner part when the altitude tracking error converges to a small value and linear approximation of the altitude motion model is applied.The inner part is generated by the Q-learning algorithm which learns the optimal command in the presence of unknown system matrices and disturbances.It is proved rigorously that all signals of the closed-loop system stay bounded by the developed control method and controller switching occurs only once.Finally,comparative simulations are conducted to validate improved control performance of the proposed scheme.展开更多
We demonstrate a passively Q-switched tunable erbium-doped fiber laser （EDFL） based on graphene as a saturable absorber （SA）. A three-port optical circulator （OC） and a strain-induced tunable fiber Bragg grating...We demonstrate a passively Q-switched tunable erbium-doped fiber laser （EDFL） based on graphene as a saturable absorber （SA）. A three-port optical circulator （OC） and a strain-induced tunable fiber Bragg grating （TFBG） are used as the two end mirrors in an all-fiber linear cavity. The Q-switched EDFL has a low pump threshold of 23.8 mW. The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from 23.8 mW to 219.9 mW. The minimum pulse duration is 1.7 p.s and the highest pulse energy is 25.4 nJ. The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.展开更多
Due to the remarkable carrier mobility and nonlinear characteristic, MoS2 is considered to be a powerful competitor as an effective optical modulated material in fiber lasers. In this paper, the MoS2 films are prepare...Due to the remarkable carrier mobility and nonlinear characteristic, MoS2 is considered to be a powerful competitor as an effective optical modulated material in fiber lasers. In this paper, the MoS2 films are prepared by the chemical vapor deposition method to guarantee the high quality of the crystal lattice and uniform thickness. The transfer of the films to microfiber and the operation of gold plated films ensure there is no heat-resistant damage and anti-oxidation. The modulation depth of the prepared integrated microfiber-MoS2 saturable absorber is 11.07%. When the microfiber-MoS2 saturable absorber is used as a light modulator in the Q-switching fiber laser, the stable pulse train with a pulse duration of 888 ns at 1530.9 nm is obtained. The ultimate output power and pulse energy of output pulses are 18.8 mW and 88 nJ, respectively. The signal-to-noise ratio up to 60 dB indicates the good stability of the laser. This work demonstrates that the MoS2 saturable absorber prepared by the chemical vapor deposition method can serve as an effective nonlinear control device for the Q-switching fiber laser.展开更多
We presented a passively Q-switched(PQS) diode-pumped c-cut Tm, Ho:LuVO_4 laser with a black phosphorus saturable absorber for the first time.Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 ...We presented a passively Q-switched(PQS) diode-pumped c-cut Tm, Ho:LuVO_4 laser with a black phosphorus saturable absorber for the first time.Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of 2.89 μs,a pulse repetition rate of 71.84 kHz, and a pulse energy of about 6.70 μJ.展开更多
A transmission-type tungsten disulfide（WS_2）-based saturable absorber（SA） is fabricated and applied to passively Q-switched Nd：YVO_4 laser.The WS_2 nanosheets are deposited on a quartz substrate by the vertical e...A transmission-type tungsten disulfide（WS_2）-based saturable absorber（SA） is fabricated and applied to passively Q-switched Nd：YVO_4 laser.The WS_2 nanosheets are deposited on a quartz substrate by the vertical evaporation method.By inserting the WS2 SA into the plano-concave laser cavity,we achieve 153-ns pulses with an average output power of1.19 W at 1064 nm.To the best of our knowledge,both of them are the best results among those obtained by the Q-switched solid-state lasers with WS_2-based absorbers.The repetition rate ranges from 1.176 MHz to 1.578 MHz.As far as we know,it is the first time that MHz level Q-switched pulses have been generated in all solid state lasers based on low-dimensional materials so far.展开更多
We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr：YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power...We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr：YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power of 680 mW at 532 nm. The corresponding pulse width of the Q-switched envelope of the green laser is 170 ＋ 20 ns. The mode-locked pulses have a repetition rate of approximately 183 MHz and the average pulse duration is estimated to be around sub-nanosecond. It is found that the intra-cavity frequency doubling greatly improves the modulation depth and stability of the mode-locked pulses within the Q-switched envelope.展开更多
We demonstrate a passively Q-switched Yb：LSO laser based on tungsten disulphide （WS2） saturable absorber op- erating at 1034 nm and 1056 nm simultaneously. The saturable absorbers were fabricated by spin coating me...We demonstrate a passively Q-switched Yb：LSO laser based on tungsten disulphide （WS2） saturable absorber op- erating at 1034 nm and 1056 nm simultaneously. The saturable absorbers were fabricated by spin coating method. With low speed, the WS2 nanoplatelets embedded in polyvinyl alcohol could be coated on a BK7 glass substrate coated with high-refractive-index thin polymer. The shortest pulse width of 1.6 gs with a repetition rate of 76.9 kHz is obtained. As the pump power increases to 9 W, the maximum output power is measured to be 250 mW, corresponding to a single pulse energy of 3.25 μJ. To the best of our knowledge, this is the first time to obtain dual-wavelength Q-switched solid-state laser using few-layer WS2 nanoplatelets.展开更多
An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was rea...An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs,and the highest single pulse energy of 40.6 nJ respectively.展开更多
In this paper, the effect of injected energy on low energy single longitudinal mode (SLM) pre-lase Q-switched is analyzed and the optimization procedure is shown in detail. Here, taking the Pr:YLF laser as an example ...In this paper, the effect of injected energy on low energy single longitudinal mode (SLM) pre-lase Q-switched is analyzed and the optimization procedure is shown in detail. Here, taking the Pr:YLF laser as an example of low energy laser, and the parameters of Pr:YLF laser by using pre-lase have been shown. Compared with normal Q-switched laser, the single pulse energy reaches 60.16% and the pulse width exceeds 39.73% when the same maximum energy is injected and SLM is achieved in pre-lase. The analysis results show that pre-lase is suitable for low energy laser to obtain SLM and there be an optimal performance to achieve the optimal energy output.展开更多
An efficient 1064-nm Nd：YVO_4laser in-band pumped by a wavelength-locked laser diode（LD） at 913.9 nm was demonstrated. The maximum continuous wave（CW） output power of 23.4 W at 1064 nm was realized with the incid...An efficient 1064-nm Nd：YVO_4laser in-band pumped by a wavelength-locked laser diode（LD） at 913.9 nm was demonstrated. The maximum continuous wave（CW） output power of 23.4 W at 1064 nm was realized with the incident pump power of 40 W, corresponding to a total optical-to-optical efficiency of 58.5%. This is to the best of our knowledge the highest total optical-to-optical efficiency and output power of Nd：YVO_4laser in-band pumped by a 913.9-nm laser diode.The Q-switched operation of this laser was also investigated. Through a contrast experiment of pumping at 808 nm, the experimental results showed that an Nd：YVO_4laser in-band pumped by a wavelength-locked LD at 913.9 nm had excellent pulse stability and beam quality for high repetition rate Q-switching operation.展开更多
基金supported by the National Natural Science Foundation of China(Nos.61873295,61833016)the Aeronautical Science Foundation of China(No.2016ZA51011).
文摘This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and a related altitude motion model is established.Then,the designed controller is divided into the outer part and inner part,where the outer part is devised by a combination of the back-stepping method and command filter technique so that the’explosion of complexity’problem is eliminated.Moreover,the integrator structure of the altitude motion model is exploited to simplify the back-stepping design,and disturbance observers inspired from the idea of extended state observer are devised to obtain estimations of the system disturbances.The control input switches from the outer part to the inner part when the altitude tracking error converges to a small value and linear approximation of the altitude motion model is applied.The inner part is generated by the Q-learning algorithm which learns the optimal command in the presence of unknown system matrices and disturbances.It is proved rigorously that all signals of the closed-loop system stay bounded by the developed control method and controller switching occurs only once.Finally,comparative simulations are conducted to validate improved control performance of the proposed scheme.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.61077017 and 61378028)the Program for New Century Excellent Talents in University,China (Grant Nos.NCET-11-0069 and NCET-10-0291)the 111 Project (Grant No.B13042)
文摘We demonstrate a passively Q-switched tunable erbium-doped fiber laser （EDFL） based on graphene as a saturable absorber （SA）. A three-port optical circulator （OC） and a strain-induced tunable fiber Bragg grating （TFBG） are used as the two end mirrors in an all-fiber linear cavity. The Q-switched EDFL has a low pump threshold of 23.8 mW. The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from 23.8 mW to 219.9 mW. The minimum pulse duration is 1.7 p.s and the highest pulse energy is 25.4 nJ. The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.
基金Project supported by the National Natural Science Foundation of China(Grant No.11674036)the Beijing Youth Top-notch Talent Support Program,China(Grant No.2017000026833ZK08)the Fund of State Key Laboratory of Information Photonics and Optical Communications,Beijing University of Posts and Telecommunications,China(Grant Nos.IPOC2016ZT04 and IPOC2017ZZ05)
文摘Due to the remarkable carrier mobility and nonlinear characteristic, MoS2 is considered to be a powerful competitor as an effective optical modulated material in fiber lasers. In this paper, the MoS2 films are prepared by the chemical vapor deposition method to guarantee the high quality of the crystal lattice and uniform thickness. The transfer of the films to microfiber and the operation of gold plated films ensure there is no heat-resistant damage and anti-oxidation. The modulation depth of the prepared integrated microfiber-MoS2 saturable absorber is 11.07%. When the microfiber-MoS2 saturable absorber is used as a light modulator in the Q-switching fiber laser, the stable pulse train with a pulse duration of 888 ns at 1530.9 nm is obtained. The ultimate output power and pulse energy of output pulses are 18.8 mW and 88 nJ, respectively. The signal-to-noise ratio up to 60 dB indicates the good stability of the laser. This work demonstrates that the MoS2 saturable absorber prepared by the chemical vapor deposition method can serve as an effective nonlinear control device for the Q-switching fiber laser.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61775053,51572053,51777046,and 61705140)
文摘We presented a passively Q-switched(PQS) diode-pumped c-cut Tm, Ho:LuVO_4 laser with a black phosphorus saturable absorber for the first time.Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of 2.89 μs,a pulse repetition rate of 71.84 kHz, and a pulse energy of about 6.70 μJ.
基金Project supported by the National Natural Science Foundation of China(Grant No.61378024)
文摘A transmission-type tungsten disulfide（WS_2）-based saturable absorber（SA） is fabricated and applied to passively Q-switched Nd：YVO_4 laser.The WS_2 nanosheets are deposited on a quartz substrate by the vertical evaporation method.By inserting the WS2 SA into the plano-concave laser cavity,we achieve 153-ns pulses with an average output power of1.19 W at 1064 nm.To the best of our knowledge,both of them are the best results among those obtained by the Q-switched solid-state lasers with WS_2-based absorbers.The repetition rate ranges from 1.176 MHz to 1.578 MHz.As far as we know,it is the first time that MHz level Q-switched pulses have been generated in all solid state lasers based on low-dimensional materials so far.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 60278024 and 60438020）.
文摘We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr：YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power of 680 mW at 532 nm. The corresponding pulse width of the Q-switched envelope of the green laser is 170 ＋ 20 ns. The mode-locked pulses have a repetition rate of approximately 183 MHz and the average pulse duration is estimated to be around sub-nanosecond. It is found that the intra-cavity frequency doubling greatly improves the modulation depth and stability of the mode-locked pulses within the Q-switched envelope.
基金Project supported by the National Scientific Research Project of China(Grant No.61177047)Beijing Municipal Natural Science Foundation+1 种基金China(Grant No.1102005)the Basic Research Foundation of Beijing University of Technology,China(Grant No.X3006111201501)
文摘We demonstrate a passively Q-switched Yb：LSO laser based on tungsten disulphide （WS2） saturable absorber op- erating at 1034 nm and 1056 nm simultaneously. The saturable absorbers were fabricated by spin coating method. With low speed, the WS2 nanoplatelets embedded in polyvinyl alcohol could be coated on a BK7 glass substrate coated with high-refractive-index thin polymer. The shortest pulse width of 1.6 gs with a repetition rate of 76.9 kHz is obtained. As the pump power increases to 9 W, the maximum output power is measured to be 250 mW, corresponding to a single pulse energy of 3.25 μJ. To the best of our knowledge, this is the first time to obtain dual-wavelength Q-switched solid-state laser using few-layer WS2 nanoplatelets.
基金Project supported by the National Key Scientific Instruments Development Program of China(Grant No.2012YQ120047)
文摘An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs,and the highest single pulse energy of 40.6 nJ respectively.
文摘In this paper, the effect of injected energy on low energy single longitudinal mode (SLM) pre-lase Q-switched is analyzed and the optimization procedure is shown in detail. Here, taking the Pr:YLF laser as an example of low energy laser, and the parameters of Pr:YLF laser by using pre-lase have been shown. Compared with normal Q-switched laser, the single pulse energy reaches 60.16% and the pulse width exceeds 39.73% when the same maximum energy is injected and SLM is achieved in pre-lase. The analysis results show that pre-lase is suitable for low energy laser to obtain SLM and there be an optimal performance to achieve the optimal energy output.
基金Project supported by Tianjin City High School Science&Technology Fund Planning Project(Grant No.20140703)
文摘An efficient 1064-nm Nd：YVO_4laser in-band pumped by a wavelength-locked laser diode（LD） at 913.9 nm was demonstrated. The maximum continuous wave（CW） output power of 23.4 W at 1064 nm was realized with the incident pump power of 40 W, corresponding to a total optical-to-optical efficiency of 58.5%. This is to the best of our knowledge the highest total optical-to-optical efficiency and output power of Nd：YVO_4laser in-band pumped by a 913.9-nm laser diode.The Q-switched operation of this laser was also investigated. Through a contrast experiment of pumping at 808 nm, the experimental results showed that an Nd：YVO_4laser in-band pumped by a wavelength-locked LD at 913.9 nm had excellent pulse stability and beam quality for high repetition rate Q-switching operation.
