A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically...A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically activated charge domain. The switching characteristics including rise time,delay and their relationship to electric field strength,optical trigger energies are discussed.The formation and radiation transit,accumulation of the charge domain are related with the triggering and sustaining phases of PCSS's,respectively.The results of the mathematical model on this mechanism agree with experimental results.展开更多
This work deals with the development of a decentralized optimal control algorithm, along with a robust observer,for the relative motion control of spacecraft in leader-follower based formation. An adaptive gain higher...This work deals with the development of a decentralized optimal control algorithm, along with a robust observer,for the relative motion control of spacecraft in leader-follower based formation. An adaptive gain higher order sliding mode observer has been proposed to estimate the velocity as well as unmeasured disturbances from the noisy position measurements.A differentiator structure containing the Lipschitz constant and Lebesgue measurable control input, is utilized for obtaining the estimates. Adaptive tuning algorithms are derived based on Lyapunov stability theory, for updating the observer gains,which will give enough flexibility in the choice of initial estimates.Moreover, it may help to cope with unexpected state jerks. The trajectory tracking problem is formulated as a finite horizon optimal control problem, which is solved online. The control constraints are incorporated by using a nonquadratic performance functional. An adaptive update law has been derived for tuning the step size in the optimization algorithm, which may help to improve the convergence speed. Moreover, it is an attractive alternative to the heuristic choice of step size for diverse operating conditions. The disturbance as well as state estimates from the higher order sliding mode observer are utilized by the plant output prediction model, which will improve the overall performance of the controller. The nonlinear dynamics defined in leader fixed Euler-Hill frame has been considered for the present work and the reference trajectories are generated using Hill-Clohessy-Wiltshire equations of unperturbed motion. The simulation results based on rigorous perturbation analysis are presented to confirm the robustness of the proposed approach.展开更多
Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in opt...Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in optical fibers. This paper obtains a new Mueller matrix analysis, which can be used under conditions that all these three factors are existing and changing. According to our transmission model, the state of polarization （SOP） changes along an optical mierostructure fiber with co-existence of birefringence-PDG-mode coupling were simulated. The simulated results, which show the phenomena of SOP constringency, are in good agreement with previous theoretical analyses.展开更多
The mode-division multiplexing technique combined with a few-mode erbium-doped fiber amplifier(FM-EDFA)demonstrates significant potential for solving the capacity limitation of standard single-mode fiber(SSMF)transmis...The mode-division multiplexing technique combined with a few-mode erbium-doped fiber amplifier(FM-EDFA)demonstrates significant potential for solving the capacity limitation of standard single-mode fiber(SSMF)transmission systems.However,the differential mode gain(DMG)arising in the FM-EDFA fundamentally limits its transmission capacity and length.Herein,an innovative DMG equalization strategy using femtosecond laser micromachining to adjust the refractive index(RI)is presented.Variable mode-dependent attenuations can be achieved according to the DMG profile of the FM-EDFA,enabling DMG equalization.To validate the proposed strategy,DMG equalization of the commonly used FM-EDFA configuration was investigated.Simulation results revealed that by optimizing both the length and RI modulation depth of the femtosecond laser-tailoring area,the maximum DMG(DMGmax)among the 3 linear-polarized(LP)mode-group was mitigated from 10 dB to 1.52 dB,whereas the average DMG(DMGave)over the C-band was reduced from 8.95 dB to 0.78 dB.Finally,a 2-LP mode-group DMG equalizer was experimentally demonstrated,resulting in a reduction of the DMGmax from 2.09 dB to 0.46 dB,and a reduction of DMGave over the C band from 1.64 dB to 0.26 dB,with only a 1.8 dB insertion loss.Moreover,a maximum range of variable DMG equalization was achieved with 5.4 dB,satisfying the requirements of the most commonly used 2-LP mode-group amplification scenarios.展开更多
文摘A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically activated charge domain. The switching characteristics including rise time,delay and their relationship to electric field strength,optical trigger energies are discussed.The formation and radiation transit,accumulation of the charge domain are related with the triggering and sustaining phases of PCSS's,respectively.The results of the mathematical model on this mechanism agree with experimental results.
文摘This work deals with the development of a decentralized optimal control algorithm, along with a robust observer,for the relative motion control of spacecraft in leader-follower based formation. An adaptive gain higher order sliding mode observer has been proposed to estimate the velocity as well as unmeasured disturbances from the noisy position measurements.A differentiator structure containing the Lipschitz constant and Lebesgue measurable control input, is utilized for obtaining the estimates. Adaptive tuning algorithms are derived based on Lyapunov stability theory, for updating the observer gains,which will give enough flexibility in the choice of initial estimates.Moreover, it may help to cope with unexpected state jerks. The trajectory tracking problem is formulated as a finite horizon optimal control problem, which is solved online. The control constraints are incorporated by using a nonquadratic performance functional. An adaptive update law has been derived for tuning the step size in the optimization algorithm, which may help to improve the convergence speed. Moreover, it is an attractive alternative to the heuristic choice of step size for diverse operating conditions. The disturbance as well as state estimates from the higher order sliding mode observer are utilized by the plant output prediction model, which will improve the overall performance of the controller. The nonlinear dynamics defined in leader fixed Euler-Hill frame has been considered for the present work and the reference trajectories are generated using Hill-Clohessy-Wiltshire equations of unperturbed motion. The simulation results based on rigorous perturbation analysis are presented to confirm the robustness of the proposed approach.
基金supported by the National Natural Science Foundation of China(Grants Nos.60877057 and 60907027)
文摘Birefringence （polarization-related phase-shift）, polarization dependent gain （PDG） and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in optical fibers. This paper obtains a new Mueller matrix analysis, which can be used under conditions that all these three factors are existing and changing. According to our transmission model, the state of polarization （SOP） changes along an optical mierostructure fiber with co-existence of birefringence-PDG-mode coupling were simulated. The simulated results, which show the phenomena of SOP constringency, are in good agreement with previous theoretical analyses.
基金supported by the National Natural Science Foundation of China(62305071)China Postdoctoral Science Foundation(2023M740747)Guangdong Introducing Innovative and Entrepreneurial Teams of“The Pearl River Talent Recruitment Program”(2021ZT09X044).
文摘The mode-division multiplexing technique combined with a few-mode erbium-doped fiber amplifier(FM-EDFA)demonstrates significant potential for solving the capacity limitation of standard single-mode fiber(SSMF)transmission systems.However,the differential mode gain(DMG)arising in the FM-EDFA fundamentally limits its transmission capacity and length.Herein,an innovative DMG equalization strategy using femtosecond laser micromachining to adjust the refractive index(RI)is presented.Variable mode-dependent attenuations can be achieved according to the DMG profile of the FM-EDFA,enabling DMG equalization.To validate the proposed strategy,DMG equalization of the commonly used FM-EDFA configuration was investigated.Simulation results revealed that by optimizing both the length and RI modulation depth of the femtosecond laser-tailoring area,the maximum DMG(DMGmax)among the 3 linear-polarized(LP)mode-group was mitigated from 10 dB to 1.52 dB,whereas the average DMG(DMGave)over the C-band was reduced from 8.95 dB to 0.78 dB.Finally,a 2-LP mode-group DMG equalizer was experimentally demonstrated,resulting in a reduction of the DMGmax from 2.09 dB to 0.46 dB,and a reduction of DMGave over the C band from 1.64 dB to 0.26 dB,with only a 1.8 dB insertion loss.Moreover,a maximum range of variable DMG equalization was achieved with 5.4 dB,satisfying the requirements of the most commonly used 2-LP mode-group amplification scenarios.
