Effective control of terahertz radiation requires fast and efficient modulators with a large modulation depth-a challenge that is often tackled by using metamaterials.Metamaterial-based active modulators can be create...Effective control of terahertz radiation requires fast and efficient modulators with a large modulation depth-a challenge that is often tackled by using metamaterials.Metamaterial-based active modulators can be created by placing graphene as a tuneable element shunting regions of high electric field confinement in metamaterials.However,in this common approach,the graphene is used as a variable resistor,and the modulation is achieved by resistive damping of the resonance.In combination with the finite conductivity of graphene due to its gapless nature,achieving 100%modulation depth using this approach remains challenging.Here,we embed nanoscale graphene capacitors within the gaps of the metamaterial resonators,and thus switch from a resistive damping to a capacitive tuning of the resonance.We further expand the optical modulation range by device excitation from its substrate side.As a result,we demonstrate terahertz modulators with over four orders of magnitude modulation depth(45.7 dB at 1.68 THz and 40.1 dB at 2.15 THz),and a reconfiguration speed of 30 MHz.These tuneable capacitance modulators are electrically controlled solid-state devices enabling unity modulation with graphene conductivities below 0.7 mS.The demonstrated approach can be applied to enhance modulation performance of any metamaterial-based modulator with a 2D electron gas.Our results open up new frontiers in the area of terahertz communications,real-time imaging,and wave-optical analogue computing.展开更多
Metasurfaces consisting of artificial subwavelength structure arrays have shown unprecedented ability to manipulate the phase,amplitude,and polarization of light.Separate and complete control over different spin state...Metasurfaces consisting of artificial subwavelength structure arrays have shown unprecedented ability to manipulate the phase,amplitude,and polarization of light.Separate and complete control over different spin states,namely the orthogonal circular polarizations,has proven more challenging as compared to the control over orthogonal linear polarizations.Here,we present and experimentally demonstrate several spin-dependent wavefront control metasurfaces in the terahertz regime using all-silicon dielectric structures.Such spin-dependent allsilicon metasurfaces are easy to fabricate and have potential applications in spin-involved ultracompact and miniaturized terahertz optical systems as well as terahertz communication systems.展开更多
We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanesc...We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO_2∕Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.展开更多
Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low sp...Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence.However,for many applications ranging from sensing and spectroscopy to speckle-free imaging,it is essential to have high-radiance sources operating in continuous-wave(CW).In this paper,we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional(2D)random distribution of air holes is patterned into the top metal waveguide.We obtain a highly collimated vertical emission at ~3 THz,with a 430 GHz bandwidth,device operation up to 110 K,peak(pulsed)power of 21 mW,and CW emission of 1.7 mW.Furthermore,we show that an external cavity formed with a movable mirror can be used to tune a random laser,obtaining continuous frequency tuning over 11 GHz.展开更多
Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz(THz) spectral regions, which host a large variety of molecular absorpt...Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz(THz) spectral regions, which host a large variety of molecular absorptions and distinctive fingerprints to be exploited for sensing and tomography. Here, we characterize the spatial coherence of random multimode THz quantum cascade lasers(QCLs) emitting > m W optical power per mode and showing low divergence(10°–30°), performing a modified Young’s double-slit experiment. Partial spatial coherence values ranging between 0.16 and 0.34 are retrieved, depending on the specific degree of disorder. These values are significantly lower than those(0.82) of conventional Fabry–Perot THz QCLs exploiting an identical active region quantum design. We then incorporate the devised low spatial coherence random lasers into a confocal imaging system with micrometer spatial resolution and demonstrate notable imaging performances, at THz frequencies,against spatial cross talk and speckles.展开更多
Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,there...Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,therefore,beneficial to contrast themeasurements of hundreds of devices fabricated in a single chip in one cooldown process to promote the scalability,integrability,reliability,and reproducibility of quantum devices and to save evaluation time,cost and energy.Here,we used a cryogenic on-chip multiplexer architecture and investigated the statistics of the 0.7 anomaly observed on the first three plateaus of the quantized conductance of semiconductor quantum point contact(QPC)transistors.Our single chips contain 256 split gate field-effect QPC transistors(QFET)each,with two 16-branch multiplexed source-drain and gate pads,allowing individual transistors to be selected,addressed and controlled through an electrostatic gate voltage process.A total of 1280 quantum transistors with nano-scale dimensions are patterned in 5 different chips of GaAs heterostructures.From the measurements of 571 functioning QFETs taken at temperatures T[1.4 K and T[40 mK,it is found that the spontaneous polarisation model and Kondo effect do not fit our results.Furthermore,some of the features in our data largely agreed with van Hove model with short-range interactions.Our approach provides further insight into the quantum mechanical properties and microscopic origin of the 0.7 anomaly in QFETs,paving the way for the development of semiconducting quantum circuits and integrated cryogenic electronics,for scalable quantum logic control,readout,synthesis,and processing applications.展开更多
We demonstrate the generation of a spatiotemporal optical continuum in a highly nonlinear exciton–polariton waveguide using extremely low excitation powers(2-ps,100-W peak power pulses)and a submillimeter device suit...We demonstrate the generation of a spatiotemporal optical continuum in a highly nonlinear exciton–polariton waveguide using extremely low excitation powers(2-ps,100-W peak power pulses)and a submillimeter device suitable for integrated optics applications.We observe contributions from several mechanisms over a range of powers and demonstrate that the strong light–matter coupling significantly modifies the physics involved in all of them.The experimental data are well understood in combination with theoretical modeling.The results are applicable to a wide range of systems with linear coupling between nonlinear oscillators and particularly to emerging polariton devices that incorporate materials,such as gallium nitride and transition metal dichalcogenide monolayers that exhibit large light–matter coupling at room temperature.These open the door to low-power experimental studies of spatiotemporal nonlinear optics in submillimeter waveguide devices.展开更多
基金supported by the UK Engineering and Physical Sciences Research Council(EPSRC)grant EP/S023046/1 for the EPSRC Centre for Doctoral Training in Sensor Technologies for a Healthy and Sustainable Futurefunding from the Hyper Terahertz grant,no.EP/P021859/1the TeraCom grant,no.EP/W028921/1。
文摘Effective control of terahertz radiation requires fast and efficient modulators with a large modulation depth-a challenge that is often tackled by using metamaterials.Metamaterial-based active modulators can be created by placing graphene as a tuneable element shunting regions of high electric field confinement in metamaterials.However,in this common approach,the graphene is used as a variable resistor,and the modulation is achieved by resistive damping of the resonance.In combination with the finite conductivity of graphene due to its gapless nature,achieving 100%modulation depth using this approach remains challenging.Here,we embed nanoscale graphene capacitors within the gaps of the metamaterial resonators,and thus switch from a resistive damping to a capacitive tuning of the resonance.We further expand the optical modulation range by device excitation from its substrate side.As a result,we demonstrate terahertz modulators with over four orders of magnitude modulation depth(45.7 dB at 1.68 THz and 40.1 dB at 2.15 THz),and a reconfiguration speed of 30 MHz.These tuneable capacitance modulators are electrically controlled solid-state devices enabling unity modulation with graphene conductivities below 0.7 mS.The demonstrated approach can be applied to enhance modulation performance of any metamaterial-based modulator with a 2D electron gas.Our results open up new frontiers in the area of terahertz communications,real-time imaging,and wave-optical analogue computing.
基金National Key Research and Development Program of China(2017YFA0701004)National Natural Science Foundation of China(62075158,11974259,61735012,62025504,61875150,61935015)+1 种基金Tianjin Municipal Fund for Distinguished Young Scholars(18JCJQJC45600)Engineering and Physical Sciences Research Council(EP/P021859/1)。
文摘Metasurfaces consisting of artificial subwavelength structure arrays have shown unprecedented ability to manipulate the phase,amplitude,and polarization of light.Separate and complete control over different spin states,namely the orthogonal circular polarizations,has proven more challenging as compared to the control over orthogonal linear polarizations.Here,we present and experimentally demonstrate several spin-dependent wavefront control metasurfaces in the terahertz regime using all-silicon dielectric structures.Such spin-dependent allsilicon metasurfaces are easy to fabricate and have potential applications in spin-involved ultracompact and miniaturized terahertz optical systems as well as terahertz communication systems.
基金National Natural Science Foundation of China (NSFC) (61575125,61671308,61805148)Guangdong Foundation of Outstanding Young Teachers in Higher Education Institutions (YQ2015141)+4 种基金Guangdong Special Support Program of Top-notch Young Professionals (2015TQ01R453)Hong Kong Research Grants Council (14201415)Hong Kong Innovation and Technology Fund (ITS/371/16)UK Engineering and Physical Sciences Research Council (EPSRC)(EP/N022769/1)CUHK Global Travel Fund
文摘We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO_2∕Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.
基金partly supported by the European Union ERC Consolidator Grant SPRINT(681379)the EPSRC Programme Grant‘HyperTerahertz’(EP/P021859/1)the support of the Royal Society and the Wolfson Foundation.
文摘Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence.However,for many applications ranging from sensing and spectroscopy to speckle-free imaging,it is essential to have high-radiance sources operating in continuous-wave(CW).In this paper,we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional(2D)random distribution of air holes is patterned into the top metal waveguide.We obtain a highly collimated vertical emission at ~3 THz,with a 430 GHz bandwidth,device operation up to 110 K,peak(pulsed)power of 21 mW,and CW emission of 1.7 mW.Furthermore,we show that an external cavity formed with a movable mirror can be used to tune a random laser,obtaining continuous frequency tuning over 11 GHz.
文摘Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz(THz) spectral regions, which host a large variety of molecular absorptions and distinctive fingerprints to be exploited for sensing and tomography. Here, we characterize the spatial coherence of random multimode THz quantum cascade lasers(QCLs) emitting > m W optical power per mode and showing low divergence(10°–30°), performing a modified Young’s double-slit experiment. Partial spatial coherence values ranging between 0.16 and 0.34 are retrieved, depending on the specific degree of disorder. These values are significantly lower than those(0.82) of conventional Fabry–Perot THz QCLs exploiting an identical active region quantum design. We then incorporate the devised low spatial coherence random lasers into a confocal imaging system with micrometer spatial resolution and demonstrate notable imaging performances, at THz frequencies,against spatial cross talk and speckles.
基金financial support from EPSRC,UK.the China Scholarship Council(CSC)for its financial support.
文摘Themass production and the practical number of cryogenic quantum devices producible in a single chip are limited to the number of electrical contact pads and wiring of the cryostat or dilution refrigerator.It is,therefore,beneficial to contrast themeasurements of hundreds of devices fabricated in a single chip in one cooldown process to promote the scalability,integrability,reliability,and reproducibility of quantum devices and to save evaluation time,cost and energy.Here,we used a cryogenic on-chip multiplexer architecture and investigated the statistics of the 0.7 anomaly observed on the first three plateaus of the quantized conductance of semiconductor quantum point contact(QPC)transistors.Our single chips contain 256 split gate field-effect QPC transistors(QFET)each,with two 16-branch multiplexed source-drain and gate pads,allowing individual transistors to be selected,addressed and controlled through an electrostatic gate voltage process.A total of 1280 quantum transistors with nano-scale dimensions are patterned in 5 different chips of GaAs heterostructures.From the measurements of 571 functioning QFETs taken at temperatures T[1.4 K and T[40 mK,it is found that the spontaneous polarisation model and Kondo effect do not fit our results.Furthermore,some of the features in our data largely agreed with van Hove model with short-range interactions.Our approach provides further insight into the quantum mechanical properties and microscopic origin of the 0.7 anomaly in QFETs,paving the way for the development of semiconducting quantum circuits and integrated cryogenic electronics,for scalable quantum logic control,readout,synthesis,and processing applications.
基金support from EPSRC Grants Nos.EP/J007544/1 and EP/N031776/1the ERC Advanced Grant EXCIPOL 320570+2 种基金support from the Leverhulme Trust Grant No.RPG-2013-339the Russian Foundation for Basic Research(16-52-150006)the ITMO University Fellowship through the Government of Russia Grant No.074-U01.
文摘We demonstrate the generation of a spatiotemporal optical continuum in a highly nonlinear exciton–polariton waveguide using extremely low excitation powers(2-ps,100-W peak power pulses)and a submillimeter device suitable for integrated optics applications.We observe contributions from several mechanisms over a range of powers and demonstrate that the strong light–matter coupling significantly modifies the physics involved in all of them.The experimental data are well understood in combination with theoretical modeling.The results are applicable to a wide range of systems with linear coupling between nonlinear oscillators and particularly to emerging polariton devices that incorporate materials,such as gallium nitride and transition metal dichalcogenide monolayers that exhibit large light–matter coupling at room temperature.These open the door to low-power experimental studies of spatiotemporal nonlinear optics in submillimeter waveguide devices.
