Dispersion engineering is critical for the creation of integrated broadband laser frequency combs.In the long wavelength infrared range(LWIR,8-13µm),frequency combs based on quantum cascade lasers are attractive ...Dispersion engineering is critical for the creation of integrated broadband laser frequency combs.In the long wavelength infrared range(LWIR,8-13µm),frequency combs based on quantum cascade lasers are attractive since they are monolithic,fundamental oscillators with high power levels and efficiencies.One effective approach for expanding quantum cascade laser gain bandwidth is by stacking multiple gain media with different center lasing frequencies,as this leads to flatter broadband gain spectra.However,as the gain bandwidth is increased,dispersion becomes the main limiting factor for comb bandwidth.Therefore,achieving broadband combs requires schemes that can flexibly engineer the dispersion over broad bandwidths.Here,we demonstrate the ultimate nanophotonic dispersion compensation scheme:an air-dielectric slab double-chirped mirror,which we fully integrate with the quantum cascade laser gain section.This scheme relies on the highest possible index contrast and therefore provides the maximum correction per unit length over a very broad bandwidth.With this approach,we report the successful demonstration of a broadband room-temperature LWIR laser frequency comb on a gain medium that normally does not form combs without deliberate dispersion compensations.Our air-dielectric mirrors are versatile and can be extended to other integrated laser frequency combs in different material platforms and frequency bands.展开更多
Power systems around the world have been registering a degenerating inertial response in view of the growth of inverter-based resources along with the withdrawal of conventional coal units.Therefore,there is a need fo...Power systems around the world have been registering a degenerating inertial response in view of the growth of inverter-based resources along with the withdrawal of conventional coal units.Therefore,there is a need for swift frequency support and its control,preferably by means of power electronic-interfaced storage devices,owing to their beneficial capabilities.Despite being particularly efficient,pragmatically,the traditional model-based non-linear control techniques are not highly popular in power system control design,primarily due to the complications faced in obtaining accurately suitable models for certain power system components.Lately,the modelfree Koopman operator-based model predictive control(KMPC)has proven to be highly conducive for data-driven non-linear control design.The principle behind KMPC is to change the coordinates in a manner to get an approximately linear model,which can then be controlled using a linear model predictive control.In this study,we employed time-delayed embedding of measurements to reconstruct a new set of preferable coordinates,thereby suggesting an approach for finding the optimal number of time lags and the embedding dimensions which are the key parameters of this algorithm.The efficacy of this KMPC framework is established by adopting a decentralized frequency control problem through a decoupled synchronous machine system,which we proposed for both the Kundur two-area system as well as the IEEE 39-bus test system.展开更多
基金supported in part by the Spectral Combs from UV to THz(SCOUT)and SIGMA+programs from the Defense Advanced Research Project Agency(DARPA)support from the Gordon and Betty Moore Foundation through Grant GBMF11446 to the University of Texas at Austin.
文摘Dispersion engineering is critical for the creation of integrated broadband laser frequency combs.In the long wavelength infrared range(LWIR,8-13µm),frequency combs based on quantum cascade lasers are attractive since they are monolithic,fundamental oscillators with high power levels and efficiencies.One effective approach for expanding quantum cascade laser gain bandwidth is by stacking multiple gain media with different center lasing frequencies,as this leads to flatter broadband gain spectra.However,as the gain bandwidth is increased,dispersion becomes the main limiting factor for comb bandwidth.Therefore,achieving broadband combs requires schemes that can flexibly engineer the dispersion over broad bandwidths.Here,we demonstrate the ultimate nanophotonic dispersion compensation scheme:an air-dielectric slab double-chirped mirror,which we fully integrate with the quantum cascade laser gain section.This scheme relies on the highest possible index contrast and therefore provides the maximum correction per unit length over a very broad bandwidth.With this approach,we report the successful demonstration of a broadband room-temperature LWIR laser frequency comb on a gain medium that normally does not form combs without deliberate dispersion compensations.Our air-dielectric mirrors are versatile and can be extended to other integrated laser frequency combs in different material platforms and frequency bands.
文摘Power systems around the world have been registering a degenerating inertial response in view of the growth of inverter-based resources along with the withdrawal of conventional coal units.Therefore,there is a need for swift frequency support and its control,preferably by means of power electronic-interfaced storage devices,owing to their beneficial capabilities.Despite being particularly efficient,pragmatically,the traditional model-based non-linear control techniques are not highly popular in power system control design,primarily due to the complications faced in obtaining accurately suitable models for certain power system components.Lately,the modelfree Koopman operator-based model predictive control(KMPC)has proven to be highly conducive for data-driven non-linear control design.The principle behind KMPC is to change the coordinates in a manner to get an approximately linear model,which can then be controlled using a linear model predictive control.In this study,we employed time-delayed embedding of measurements to reconstruct a new set of preferable coordinates,thereby suggesting an approach for finding the optimal number of time lags and the embedding dimensions which are the key parameters of this algorithm.The efficacy of this KMPC framework is established by adopting a decentralized frequency control problem through a decoupled synchronous machine system,which we proposed for both the Kundur two-area system as well as the IEEE 39-bus test system.
