The elastic and vibrational properties of a material,bulk or planar waveguide,are studied by Brillouin and Raman spectroscopy to follow the process of nanocrystals growth in glass-ceramics. The nanoparticles cause the...The elastic and vibrational properties of a material,bulk or planar waveguide,are studied by Brillouin and Raman spectroscopy to follow the process of nanocrystals growth in glass-ceramics. The nanoparticles cause the appearance,in the low fre-quency Raman spectrum,of characteristic peaks,whose position depends on the size of the crystals. At the same time,sharp crystal peaks,due to optical phonons,appear in the Raman spectra,allowing the determination of the nucleated phase,and a frequency shift of the Brillouin peaks is observed.展开更多
In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strate...In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strategy to obtain highly ordered arrays of biological objects. To this purpose we fabricated a patterned surface wetted in the Cassie state, where we deposited a droplet containing genomic DNA. We observed that, when the droplet wets the surface in the Cassie state, an array of DNA filaments pinned on the top edges between pillars is formed. Conversely, when the Cassie-to-Wenzel transition occurs, DNA can be pinned at different height between pillars. These results open the way to the realization of tridimensional arrays of biological objects.展开更多
We present the details of the sol-gel processing used to realize inverse silica opal,where the silica was activated with 0.3 mol% of Er3+ ions. The template(direct opal) was obtained assembling polystyrene spheres of ...We present the details of the sol-gel processing used to realize inverse silica opal,where the silica was activated with 0.3 mol% of Er3+ ions. The template(direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating,into the void of the template,the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess a fcc structure with a air hollows of about 210 nm and a photonic band gap,in the visible range,was observed from reflectance measurements. Spectroscopic properties of Er3+-activated silica inverse opal were investigated by luminescence spectroscopy,where,upon excitation at 514.5 nm,an emission of 4I13/2 → 4I15/2 of Er3+ ions transition with a 21 nm bandwidth was observed. Moreover the 4I13/2 level decay curve presents a single-exponential profile,with a measured lifetime of 18 ms,corresponding a high quantum efficiency of the system.展开更多
Er3+/Yb3+ co-doped silica-alumina monolithic xerogels were prepared with the same concentration on 2 000 Er/Si ppm and 6 000 Al/Si ppm.The Yb/Si content was varied from 0 to 4 000 ppm.Densification of the samples was ...Er3+/Yb3+ co-doped silica-alumina monolithic xerogels were prepared with the same concentration on 2 000 Er/Si ppm and 6 000 Al/Si ppm.The Yb/Si content was varied from 0 to 4 000 ppm.Densification of the samples was achieved by thermal treatment in air at 950 ℃ for 120 hours with a heating rate 0.1 ℃/min.Photoluminescence spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb 3+ ions.The infrared-to-visible up-conversion luminescence has been investigated upon continuous wave excitation at 980 nm.The samples exhibit red,green and blue up-conversion emission.It is found that the intensity of up-conversion luminescence increases with increasing Yb3+ doping concentration.An opposite behavior is observed for the 4I13/2 luminescence of the Er3+ ions.展开更多
Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of t...Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of time reversal of a subsystem of discrete states coupled to an external environment characterized by a continuum of states, into which they generally decay. It is shown that, by flipping the discrete-continuum coupling from an Hermitian to a non-Hermitian interaction, thus resulting in a non unitary dynamics, time reversal of the subsystem of discrete states can be achieved, while the continuum of states is not reversed. Exact time reversal requires frequency degeneracy of the discrete states,or large frequency mismatch among the discrete states as compared to the strength of indirect coupling mediated by the continuum. Interestingly, periodic and frequent switch of the discrete-continuum coupling results in a frozen dynamics of the subsystem of discrete states.展开更多
Three-dimensional(3D)particle focusing in microfluidics is a fundamental capability with a wide range of applications,such as on-chip flow cytometry,where high-throughput analysis at the single-cell level is performed...Three-dimensional(3D)particle focusing in microfluidics is a fundamental capability with a wide range of applications,such as on-chip flow cytometry,where high-throughput analysis at the single-cell level is performed.Currently,3D focusing is achieved mainly in devices with complex layouts,additional sheath fluids,and complex pumping systems.In this work,we present a compact microfluidic device capable of 3D particle focusing at high flow rates and with a small footprint,without the requirement of external fields or lateral sheath flows,but using only a single-inlet,single-outlet microfluidic sequence of straight channels and tightly curving vertical loops.This device exploits inertial fluidic effects that occur in a laminar regime at sufficiently high flow rates,manipulating the particle positions by the combination of inertial lift forces and Dean drag forces.The device is fabricated by femtosecond laser irradiation followed by chemical etching,which is a simple two-step process enabling the creation of 3D microfluidic networks in fused silica glass substrates.The use of tightly curving three-dimensional microfluidic loops produces strong Dean drag forces along the whole loop but also induces an asymmetric Dean flow decay in the subsequent straight channel,thus producing rapid cross-sectional mixing flows that assist with 3D particle focusing.The use of out-of-plane loops favors a compact parallelization of multiple focusing channels,allowing one to process large amounts of samples.In addition,the low fluidic resistance of the channel network is compatible with vacuum driven flows.The resulting device is quite interesting for high-throughput on-chip flow cytometry.展开更多
Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation...Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model,we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, abovea "second" laser threshold, unidirectional emission is restored.展开更多
Particle indistinguishability is at the heart of quantum statistics that regulates fundamental phenomena such as the electronic band structure of solids, Bose-Einstein condensation and superconductivity.Moreover, it i...Particle indistinguishability is at the heart of quantum statistics that regulates fundamental phenomena such as the electronic band structure of solids, Bose-Einstein condensation and superconductivity.Moreover, it is necessary in practical applications such as linear optical quantum computation and simulation, in particular for Boson Sampling devices.It is thus crucial to develop tools to certify genuine multiphoton interference between multiple sources.Our approach employs the total variation distance to find those transformations that minimize the error probability in discriminating the behaviors of distinguishable and indistinguishable photons.In particular, we show that so-called Sylvester interferometers are near-optimal for this task.By using Bayesian tests and inference, we numerically show that Sylvester transformations largely outperform most Haar-random unitaries in terms of sample size required.Furthermore, we experimentally demonstrate the efficacy of the transformation using an efficient 3 D integrated circuits in the single-and multiple-source cases.We then discuss the extension of this approach to a larger number of photons and modes.These results open the way to the application of Sylvester interferometers for optimal assessment of multiphoton interference experiments.展开更多
Estimation of physical quantities is at the core of most scientific research,and the use of quantum devices promises to enhance its performances.In real scenarios,it is fundamental to consider that resources are limit...Estimation of physical quantities is at the core of most scientific research,and the use of quantum devices promises to enhance its performances.In real scenarios,it is fundamental to consider that resources are limited,and Bayesian adaptive estimation represents a powerful approach to efficiently allocate,during the estimation process,all the available resources.However,this framework relies on the precise knowledge of the system model,retrieved with a fine calibration,with results that are often computationally and experimentally demanding.We introduce a model-free and deep-learning-based approach to efficiently implement realistic Bayesian quantum metrology tasks accomplishing all the relevant challenges,without relying on any a priori knowledge of the system.To overcome this need,a neural network is trained directly on experimental data to learn the multiparameter Bayesian update.Then the system is set at its optimal working point through feedback provided by a reinforcement learning algorithm trained to reconstruct and enhance experiment heuristics of the investigated quantum sensor.Notably,we prove experimentally the achievement of higher estimation performances than standard methods,demonstrating the strength of the combination of these two black-box algorithms on an integrated photonic circuit.Our work represents an important step toward fully artificial intelligence-based quantum metrology.展开更多
Boson sampling is a computational problem that has recently been proposed as a candidate to obtain an unequivocal quantum computational advantage.The problem consists in sampling from the output distribution of indist...Boson sampling is a computational problem that has recently been proposed as a candidate to obtain an unequivocal quantum computational advantage.The problem consists in sampling from the output distribution of indistinguishable bosons in a linear interferometer.There is strong evidence that such an experiment is hard to classically simulate,but it is naturally solved by dedicated photonic quantum hardware,comprising single photons,linear evolution,and photodetection.This prospect has stimulated much effort resulting in the experimental implementation of progressively larger devices.We review recent advances in photonic boson sampling,describing both the technological improvements achieved and the future challenges.We also discuss recent proposals and implementations of variants of the original problem,theoretical issues occurring when imperfections are considered,and advances in the development of suitable techniques for validation of boson sampling experiments.We conclude by discussing the future application of photonic boson sampling devices beyond the original theoretical scope.展开更多
Surface channel waveguides(WGs) were fabricated in a monoclinic Tm^(3+):KLu(WO_4)_2 crystal by femtosecond direct laser writing(fs-DLW). The WGs consisted of a half-ring cladding with diameters of 50 and 60 μm locate...Surface channel waveguides(WGs) were fabricated in a monoclinic Tm^(3+):KLu(WO_4)_2 crystal by femtosecond direct laser writing(fs-DLW). The WGs consisted of a half-ring cladding with diameters of 50 and 60 μm located just beneath the crystal surface. They were characterized by confocal laser microscopy and μ-Raman spectroscopy,indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In continuous-wave(CW)mode, under Ti:sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm,corresponding to a slope efficiency η of 37.8% for the 60 μm diameter WG. The WG propagation loss was0.7 0.3 d B∕cm. The top surface of the WGs was spin-coated by a polymethyl methacrylate film containing randomly oriented(spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched(PQS) operation was achieved. The PQS60 μm diameter WG laser generated a record output power of 150 m W at 1846.8 nm with η = 34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics(energy/duration)were 105.6 nJ/98 ns at a repetition rate of 1.42 MHz.展开更多
We predict theoretically a regime of photon-pair generation driven by the interplay of multiple bound states in the continuum resonances in nonlinear metasurfaces.This nondegenerate photon-pair generation is derived f...We predict theoretically a regime of photon-pair generation driven by the interplay of multiple bound states in the continuum resonances in nonlinear metasurfaces.This nondegenerate photon-pair generation is derived from the hyperbolic topology of the transverse phase matching and can enable orders-of-magnitude enhancement of the photon rate and spectral brightness,as compared to the degenerate regime.We show through comprehensive simulations that the entanglement of the photon pairs can be tuned by varying the pump polarization,which can underpin future advances and applications of ultracompact quantum light sources.展开更多
On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing tec...On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing technologies.While integrated vortex beam generators have been previously demonstrated in different optical settings,ultrafast control and sweep of FOAM light with low-power control,suitable for high-speed optical communication and computing,remains challenging.Here we demonstrate fast control of the FOAM from a vortex semiconductor microlaser based on fast transient mixing of integer laser vorticities induced by a control pulse.A continuous FOAM sweep between charge 0 and charge+2 is demonstrated in a 100 ps time window,with the ultimate speed limit being established by the carrier recombination time in the gain medium.Our results provide a new route to generating vortex microlasers carrying FOAM that are switchable at GHz frequencies by an ultrafast control pulse.展开更多
Recently,there has been a growing interest in integrated THz photonics for various applications in communications,spectroscopy and sensing.We present a new integrated photonic platform based on active and passive elem...Recently,there has been a growing interest in integrated THz photonics for various applications in communications,spectroscopy and sensing.We present a new integrated photonic platform based on active and passive elements integrated in a double-metal,high-confinement waveguide layout planarized with a low-loss polymer.An extended top metallization keeps waveguide losses low while improving dispersion,thermal and RF properties,as it enables to decouple the design of THz and microwave cavities.Free-running on-chip quantum cascade laser combs spanning 800 GHz,harmonic states with over 1.1 THz bandwidth and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed using a homogeneous quantum-cascade active core.With a strong external RF drive,actively mode-locked pulses as short as 4.4 ps can be produced,as measured by SWIFTS.We demonstrate as well passive waveguides with low insertion loss,enabling the tuning of the laser cavity boundary conditions and the cointegration of active and passive elements on the same THz photonic chip.展开更多
基金The present work has been funded partly with the financial supportof MIUR-FIRB RBNE012N3X, MIUR PRIN, PAT FAPVU 2004-2006.
文摘The elastic and vibrational properties of a material,bulk or planar waveguide,are studied by Brillouin and Raman spectroscopy to follow the process of nanocrystals growth in glass-ceramics. The nanoparticles cause the appearance,in the low fre-quency Raman spectrum,of characteristic peaks,whose position depends on the size of the crystals. At the same time,sharp crystal peaks,due to optical phonons,appear in the Raman spectra,allowing the determination of the nucleated phase,and a frequency shift of the Brillouin peaks is observed.
文摘In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strategy to obtain highly ordered arrays of biological objects. To this purpose we fabricated a patterned surface wetted in the Cassie state, where we deposited a droplet containing genomic DNA. We observed that, when the droplet wets the surface in the Cassie state, an array of DNA filaments pinned on the top edges between pillars is formed. Conversely, when the Cassie-to-Wenzel transition occurs, DNA can be pinned at different height between pillars. These results open the way to the realization of tridimensional arrays of biological objects.
基金The work has been supported by the MIUR-FIRB RBNE012N3X,MIUR PRIN, PAT FAPVU 2004-2006,GRICES-CNR.
文摘We present the details of the sol-gel processing used to realize inverse silica opal,where the silica was activated with 0.3 mol% of Er3+ ions. The template(direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating,into the void of the template,the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess a fcc structure with a air hollows of about 210 nm and a photonic band gap,in the visible range,was observed from reflectance measurements. Spectroscopic properties of Er3+-activated silica inverse opal were investigated by luminescence spectroscopy,where,upon excitation at 514.5 nm,an emission of 4I13/2 → 4I15/2 of Er3+ ions transition with a 21 nm bandwidth was observed. Moreover the 4I13/2 level decay curve presents a single-exponential profile,with a measured lifetime of 18 ms,corresponding a high quantum efficiency of the system.
基金This research is performed in the context of the Italy-Vietnamre-search project 6 BS 2 MAE2006-2008 .MIUR-FIRB RBNE012N3X,PAT FAPVU2004-2006 ,MIUR-PRIN2004-2006 .
文摘Er3+/Yb3+ co-doped silica-alumina monolithic xerogels were prepared with the same concentration on 2 000 Er/Si ppm and 6 000 Al/Si ppm.The Yb/Si content was varied from 0 to 4 000 ppm.Densification of the samples was achieved by thermal treatment in air at 950 ℃ for 120 hours with a heating rate 0.1 ℃/min.Photoluminescence spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb 3+ ions.The infrared-to-visible up-conversion luminescence has been investigated upon continuous wave excitation at 980 nm.The samples exhibit red,green and blue up-conversion emission.It is found that the intensity of up-conversion luminescence increases with increasing Yb3+ doping concentration.An opposite behavior is observed for the 4I13/2 luminescence of the Er3+ ions.
文摘Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of time reversal of a subsystem of discrete states coupled to an external environment characterized by a continuum of states, into which they generally decay. It is shown that, by flipping the discrete-continuum coupling from an Hermitian to a non-Hermitian interaction, thus resulting in a non unitary dynamics, time reversal of the subsystem of discrete states can be achieved, while the continuum of states is not reversed. Exact time reversal requires frequency degeneracy of the discrete states,or large frequency mismatch among the discrete states as compared to the strength of indirect coupling mediated by the continuum. Interestingly, periodic and frequent switch of the discrete-continuum coupling results in a frozen dynamics of the subsystem of discrete states.
文摘Three-dimensional(3D)particle focusing in microfluidics is a fundamental capability with a wide range of applications,such as on-chip flow cytometry,where high-throughput analysis at the single-cell level is performed.Currently,3D focusing is achieved mainly in devices with complex layouts,additional sheath fluids,and complex pumping systems.In this work,we present a compact microfluidic device capable of 3D particle focusing at high flow rates and with a small footprint,without the requirement of external fields or lateral sheath flows,but using only a single-inlet,single-outlet microfluidic sequence of straight channels and tightly curving vertical loops.This device exploits inertial fluidic effects that occur in a laminar regime at sufficiently high flow rates,manipulating the particle positions by the combination of inertial lift forces and Dean drag forces.The device is fabricated by femtosecond laser irradiation followed by chemical etching,which is a simple two-step process enabling the creation of 3D microfluidic networks in fused silica glass substrates.The use of tightly curving three-dimensional microfluidic loops produces strong Dean drag forces along the whole loop but also induces an asymmetric Dean flow decay in the subsequent straight channel,thus producing rapid cross-sectional mixing flows that assist with 3D particle focusing.The use of out-of-plane loops favors a compact parallelization of multiple focusing channels,allowing one to process large amounts of samples.In addition,the low fluidic resistance of the channel network is compatible with vacuum driven flows.The resulting device is quite interesting for high-throughput on-chip flow cytometry.
基金National Science Foundation(NSF)(DMR-1506884)Army Research Office(ARO)(W911NF-15-1-0152)
文摘Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model,we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, abovea "second" laser threshold, unidirectional emission is restored.
基金supported by ERC-Starting Grant 3D-QUEST (3DQuantum Integrated Optical Simulation Grant agreement No.307783)+3 种基金H2020-FETPROACT-2014 Grant QUCHIP (Quantum Simulation on a Photonic Chip Grant agreement No.641039)Brazilian National Institute for Science and Technology of Quantum Information (INCT-IQ/CNPq)in part by Perimeter Institute for Theoretical Physics
文摘Particle indistinguishability is at the heart of quantum statistics that regulates fundamental phenomena such as the electronic band structure of solids, Bose-Einstein condensation and superconductivity.Moreover, it is necessary in practical applications such as linear optical quantum computation and simulation, in particular for Boson Sampling devices.It is thus crucial to develop tools to certify genuine multiphoton interference between multiple sources.Our approach employs the total variation distance to find those transformations that minimize the error probability in discriminating the behaviors of distinguishable and indistinguishable photons.In particular, we show that so-called Sylvester interferometers are near-optimal for this task.By using Bayesian tests and inference, we numerically show that Sylvester transformations largely outperform most Haar-random unitaries in terms of sample size required.Furthermore, we experimentally demonstrate the efficacy of the transformation using an efficient 3 D integrated circuits in the single-and multiple-source cases.We then discuss the extension of this approach to a larger number of photons and modes.These results open the way to the application of Sylvester interferometers for optimal assessment of multiphoton interference experiments.
基金the ERC Advanced grant QU-BOSS(Grant Agreement No.884676)Ministero dell’Istruzione dell’Universitàe della Ricerca(Ministry of Education,University and Research)program“Dipartimento di Eccellenza”(Grant No.CUP:B81I18001170001).
文摘Estimation of physical quantities is at the core of most scientific research,and the use of quantum devices promises to enhance its performances.In real scenarios,it is fundamental to consider that resources are limited,and Bayesian adaptive estimation represents a powerful approach to efficiently allocate,during the estimation process,all the available resources.However,this framework relies on the precise knowledge of the system model,retrieved with a fine calibration,with results that are often computationally and experimentally demanding.We introduce a model-free and deep-learning-based approach to efficiently implement realistic Bayesian quantum metrology tasks accomplishing all the relevant challenges,without relying on any a priori knowledge of the system.To overcome this need,a neural network is trained directly on experimental data to learn the multiparameter Bayesian update.Then the system is set at its optimal working point through feedback provided by a reinforcement learning algorithm trained to reconstruct and enhance experiment heuristics of the investigated quantum sensor.Notably,we prove experimentally the achievement of higher estimation performances than standard methods,demonstrating the strength of the combination of these two black-box algorithms on an integrated photonic circuit.Our work represents an important step toward fully artificial intelligence-based quantum metrology.
基金The authors declare no conflicts of interest.This work was supported by the European Research Council Advanced Grant CAPABLE(Composite integrated photonic platform by femtosecond laser micromachining,Grant Agreement No.742745)the QuantERA ERA-NET Cofund in Quantum Technologies 2017 project HiPhoP(High-Dimensional Quantum Photonic Platform,Project ID 731473)the European H2020-FETPROACT-2014 Grant QUCHIP(Quantum Simulation on a Photonic Chip,Grant Agreement No.641039).This work was also supported by CNPq project INCT de Informação Quântica.
文摘Boson sampling is a computational problem that has recently been proposed as a candidate to obtain an unequivocal quantum computational advantage.The problem consists in sampling from the output distribution of indistinguishable bosons in a linear interferometer.There is strong evidence that such an experiment is hard to classically simulate,but it is naturally solved by dedicated photonic quantum hardware,comprising single photons,linear evolution,and photodetection.This prospect has stimulated much effort resulting in the experimental implementation of progressively larger devices.We review recent advances in photonic boson sampling,describing both the technological improvements achieved and the future challenges.We also discuss recent proposals and implementations of variants of the original problem,theoretical issues occurring when imperfections are considered,and advances in the development of suitable techniques for validation of boson sampling experiments.We conclude by discussing the future application of photonic boson sampling devices beyond the original theoretical scope.
基金Ministerio de Economía y Competitividad(MINECO)(FIS2013-44174-P,FIS2015-71933-REDT,MAT2016-75716-C2-1-R(AEI/FEDER,UE),TEC2014-55948-R)Agència de Gestiód’Ajuts Universitaris i de Recerca(AGAUR)(2017SGR755)+1 种基金Consejería de Educación,Junta de Castilla y León(SA046U16,UIC016)Generalitat de Catalunya(2016FI_B00844,2017FI_B100158,2018FI_B2 00123)
文摘Surface channel waveguides(WGs) were fabricated in a monoclinic Tm^(3+):KLu(WO_4)_2 crystal by femtosecond direct laser writing(fs-DLW). The WGs consisted of a half-ring cladding with diameters of 50 and 60 μm located just beneath the crystal surface. They were characterized by confocal laser microscopy and μ-Raman spectroscopy,indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In continuous-wave(CW)mode, under Ti:sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm,corresponding to a slope efficiency η of 37.8% for the 60 μm diameter WG. The WG propagation loss was0.7 0.3 d B∕cm. The top surface of the WGs was spin-coated by a polymethyl methacrylate film containing randomly oriented(spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched(PQS) operation was achieved. The PQS60 μm diameter WG laser generated a record output power of 150 m W at 1846.8 nm with η = 34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics(energy/duration)were 105.6 nJ/98 ns at a repetition rate of 1.42 MHz.
基金the support by the Australian Research Council(Nos.DP190101559,CE200100010,and FT170100331)the support of the European Union Horizon 2020 Research and Innovation Programme through the METAFAST project(Grant No.899673).
文摘We predict theoretically a regime of photon-pair generation driven by the interplay of multiple bound states in the continuum resonances in nonlinear metasurfaces.This nondegenerate photon-pair generation is derived from the hyperbolic topology of the transverse phase matching and can enable orders-of-magnitude enhancement of the photon rate and spectral brightness,as compared to the degenerate regime.We show through comprehensive simulations that the entanglement of the photon pairs can be tuned by varying the pump polarization,which can underpin future advances and applications of ultracompact quantum light sources.
基金the support from the National Science Foundation(NSF)(ECCS-1932803,OMA-1936276,ECCS-1842612,DMR-1809518,and CNS-2011411)U.S.Army Research Office(ARO)(W911NF-19-1-0249 and W911NF-18-1-0348)+2 种基金Office of Naval Research MURI(N00014-20-1-2558)partially supported by the NSF through the University of Pennsylvania Materials Research Science and Engineering Center(MRSEC)(DMR-1720530)supported by the NSF National Nanotechnology Coordinated Infrastructure Program under grant NNCI-1542153.
文摘On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing technologies.While integrated vortex beam generators have been previously demonstrated in different optical settings,ultrafast control and sweep of FOAM light with low-power control,suitable for high-speed optical communication and computing,remains challenging.Here we demonstrate fast control of the FOAM from a vortex semiconductor microlaser based on fast transient mixing of integer laser vorticities induced by a control pulse.A continuous FOAM sweep between charge 0 and charge+2 is demonstrated in a 100 ps time window,with the ultimate speed limit being established by the carrier recombination time in the gain medium.Our results provide a new route to generating vortex microlasers carrying FOAM that are switchable at GHz frequencies by an ultrafast control pulse.
基金funding from the ERC Grant CHIC(No.724344)in part by the NATO Science for Peace and Security Programme under grant G5721 THESEUsActphast 4 Researchers P2020-41 for financial support.
文摘Recently,there has been a growing interest in integrated THz photonics for various applications in communications,spectroscopy and sensing.We present a new integrated photonic platform based on active and passive elements integrated in a double-metal,high-confinement waveguide layout planarized with a low-loss polymer.An extended top metallization keeps waveguide losses low while improving dispersion,thermal and RF properties,as it enables to decouple the design of THz and microwave cavities.Free-running on-chip quantum cascade laser combs spanning 800 GHz,harmonic states with over 1.1 THz bandwidth and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed using a homogeneous quantum-cascade active core.With a strong external RF drive,actively mode-locked pulses as short as 4.4 ps can be produced,as measured by SWIFTS.We demonstrate as well passive waveguides with low insertion loss,enabling the tuning of the laser cavity boundary conditions and the cointegration of active and passive elements on the same THz photonic chip.