We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band...We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band,wide-angle,and p-polarized thermal emission spectra.This approach,employing molecular beam epitaxy,circumvents the complexities associated with current layered structures and yields temperature-resistant emission wavelengths.Our findings contribute a promising route towards simpler,more efficient MIR optoelectronic devices.展开更多
We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two di...We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two different frequencies close to the epsilon-near-zero(ENZ)frequency,where large values of reflection coefficients|r_(pp)|/|r_(ss)|are obtained due to the ENZ response induced different rapid increasing trends of|r_(pp)|and|r_(ss)|.Particularly,the tunable ENZ effect with tilt degree of Weyl cones and Fermi energy enables the enhanced spatial IF shift at different frequencies.The enhanced spatial IF shift also shows the adjustability of WSM thickness,incident angle and Weyl node separation.Our findings provide easy and available methods to enlarge and adjust the reflected IF shift of TE-polarized light with a WSM.展开更多
The lossy nature of indium tin oxide(ITO) at epsilon-near-zero(ENZ) wavelength is used to design an electrically tunable metasurface absorber. The metasurface unit cell is constructed of a circular resonator comprisin...The lossy nature of indium tin oxide(ITO) at epsilon-near-zero(ENZ) wavelength is used to design an electrically tunable metasurface absorber. The metasurface unit cell is constructed of a circular resonator comprising two ITO discs and a high dielectric constant perovskite barium strontium titanate(BST) film. The ENZ wavelength in the accumulation and depletion layers of ITO discs is controlled by applying a single bias voltage. The coupling of magnetic dipole resonance with the ENZ wavelength inside the accumulation layer of ITO film causes total absorption of reflected light. The reflection amplitude can achieve ~84 d B or ~99.99% modulation depth in the operation wavelength of 820 nm at a bias voltage of-2.5 V. Moreover, the metasurface is insensitive to the polarization of the incident light due to the circular design of resonators and the symmetrical design of bias connections.展开更多
Epsilon-near-zero(ENZ)modes have attracted extensive interests due to its ultrasmall mode volume resulting in ex-tremely strong light-matter interaction(LMI)for active optoelectronic devices.The ENZ modes can be elect...Epsilon-near-zero(ENZ)modes have attracted extensive interests due to its ultrasmall mode volume resulting in ex-tremely strong light-matter interaction(LMI)for active optoelectronic devices.The ENZ modes can be electrically toggled between on and off states with a classic metal-insulator-semiconductor(MIS)configuration and therefore allow access to electro-absorption(E-A)modulation.Relying on the quantum confinement of charge-carriers in the doped semiconductor,the fundamental limitation of achieving high modulation efficiency with MIS junction is that only a nanometer-thin ENZ confinement layer can contribute to the strength of E-A.Further,for the ENZ based spatial light modulation,the require-ment of resonant coupling inevitably leads to small absolute modulation depth and limited spectral bandwidth as restric-ted by the properties of the plasmonic or high-Q resonance systems.In this paper,we proposed and demonstrated a dual-ENZ mode scheme for spatial light modulation with a TCOs/dielectric/silicon nanotrench configuration for the first time.Such a SIS junction can build up two distinct ENZ layers arising from the induced charge-carriers of opposite polar-ities adjacent to both faces of the dielectric layer.The non-resonant and low-loss deep nanotrench framework allows the free space light to be modulated efficiently via interaction of dual ENZ modes in an elongated manner.Our theoretical and experimental studies reveal that the dual ENZ mode scheme in the SIS configuration leverages the large modulation depth,extended spectral bandwidth together with high speed switching,thus holding great promise for achieving electric-ally addressed spatial light modulation in near-to mid-infrared regions.展开更多
We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection. The significant feature differing fro...We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection. The significant feature differing from all other means based on whatever natural materials or metamaterials is that for TM incident wave, the reflected phase is a constant, while for TE wave, the reflected phase is a linear function of the incident angle. The phase difference between them covers the range from -180°to 0°, and the polarization conversions from linear states to elliptical or circular states can be obtained by only adjusting the incident angle. Because no complex structures are employed, our proposal promises a simple approach for manipulating polarization conversion at both terahertz and optical frequencies.展开更多
CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric res...CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric response of GRCB/CCTO ternary metacomposites were systematically investigated.The weakly real permittivity(ε′)-negative response(ε′~−1×10^(2))was achieved which originated from weakly low-frequency plasmonic state of free carriers within constructed GRCB networks.With enhancing three-dimensional GRCB network,the plasma frequency of metacomposites increased while the damping factor decreased.Herein,theε′-negative values of metacomposites were tuned from−10^(2) to−10^(4) orders of magnitude andε′-near-zero(ENZ)frequencies from~142 to~340 MHz which substantially benefited from the moderate carrier concentration of GRCB dual fillers.The Drude model and equivalent circuit models were adopted to demonstrate dielectric and electrical characteristics.The obtained metacomposites show strong EM shielding effect along with enhanced plasmonic oscillation and even better achieving perfect EM shielding effect in ENZ media.This work achieves the tunableε′-negative andε′-near-zero response and more importantly clarifies its regulation mechanism in ceramic-based ternary metacomposites,which opens up the possibility of designing high-performance EM shielding materials based on metacomposites.展开更多
We present a novel method to achieve the decoupling between the transmission and reflection waves of non-Hermitian doped epsilon-near-zero(ENZ)media by inserting a dielectric slit into the structure.Our method also al...We present a novel method to achieve the decoupling between the transmission and reflection waves of non-Hermitian doped epsilon-near-zero(ENZ)media by inserting a dielectric slit into the structure.Our method also allows for independent control over the amplitude and the phase of both the transmission and reflection waves through few dopants,enabling us to achieve various optical effects,such as perfect absorption,high-gain reflection without transmission,reflectionless high-gain transmission and reflectionless total transmission with different phases.By manipulating the permittivity of dopants with extremely low loss or gain,we can realize these effects in the same configuration.We also extend this principle to multi-port doped ENZ structures and design a highly reconfigurable and reflectionless signal distributor and generator that can split,amplify,decay and phase-shift the input signal in any desired way.Our method overcomes limitations of optical manipulation in doped ENZ caused by the interdependent nature of the transmission and reflection,and has potential applications in novel photonic devices.展开更多
We report the modulation of epsilon-near-zero(ENZ)wavelength and enhanced third-order nonlinearity in indium tin oxide(ITO)/Au multilayer films.The samples consisting of five-layer 40 nm ITO films spaced by four-layer...We report the modulation of epsilon-near-zero(ENZ)wavelength and enhanced third-order nonlinearity in indium tin oxide(ITO)/Au multilayer films.The samples consisting of five-layer 40 nm ITO films spaced by four-layer ultrathin Au films of different thickness,i.e.,ITO(40 nm)/[Au(x)/ITO(40 nm)]4,were prepared by magnetron sputtering at room temperature.The ENZ wavelength in the multilayer films is theoretically calculated and experimentally confirmed.The nonlinear refractive index and nonlinear absorption coefficient of the samples of x=0,2,3,4 nm were determined using the Z-scan method at a wavelength of 1.064μm.The large nonlinear refractive index n2=1.12×10^(−13) m^(2)=W and nonlinear absorption coefficient β=−1.78×10^(−7) m=W in the sample of x=4 nm are both four times larger than those in the single-layer ITO film.The large optical nonlinearity due to the ENZ enhancement and carrier concentration is discussed.The results indicate that the ITO/Au multilayer films are promising for advanced all-optical devices.展开更多
Beam synthesizing antenna arrays are essentially demanded for on-chip millimeter wave and terahertz systems.In order to achieve a par-ticular radiation beam,specific amplitude and phase distributions are required for ...Beam synthesizing antenna arrays are essentially demanded for on-chip millimeter wave and terahertz systems.In order to achieve a par-ticular radiation beam,specific amplitude and phase distributions are required for all the array elements,which is conventionally realized through a properly designed feeding network.In the current work,a low-loss feeding network design approach based on epsilon-near-zero(ENZ)medium was proposed for large-scale antenna arrays with different beam requirements.Due to the infinite wavelength within the ENZ medium,a newly-discovered stair-like resonant mode was adopted for assigning a uniform phase distribution to each element,while the amplitudes and positions of these elements were optimized for generating particular beams.To implement the design philosophy in a low-loss manner,a hollow air-filled waveguide near cutoff fre-quency was employed to emulate the ENZ medium,and the bulk sil-icon microelectromechanical systems(MEMS)micromachining tech-nology was utilized for chip-scale integration.As a specific example,a low-sidelobe antenna array at 60.0 GHz was designed,which realized an impedance bandwidth of 2.57%,a gain of 13.6 dBi and a sidelobe level as low as-20.0 dB within the size of 0.5×3.4λ_(0)(2).This method is also compatible with a variety of applications,such as the high-directivity antenna array,non-diffractive Bessel beam antenna array,and so on.Based on this innovative concept of applying ENZ medium to the on-chip antenna array,it shows the advantages of simple struc-ture and low loss for on-chip beam synthesis without complex lossy feeding networks.展开更多
Transparent conductive oxides exhibit attractive optical nonlinearity with ultrafast response and giant refractive index change near the epsilon-near-zero(ENZ) wavelength, originating from the intraband dynamics of co...Transparent conductive oxides exhibit attractive optical nonlinearity with ultrafast response and giant refractive index change near the epsilon-near-zero(ENZ) wavelength, originating from the intraband dynamics of conduction electrons. The optical nonlinearity of ENZ materials has been explained by using the overall-effective-mass and the overall-scattering-time of electrons in the extended Drude model. However, their response to optical excitation is yet the last building block to complete the theory. In this paper, the concept of thermal energy is theoretically proposed to account for the total energy of conduction electrons exceeding their thermal equilibrium value. The time-varying thermal energy is adopted to describe the transient optical response of indium-tin-oxide(ITO), a typical ENZ material. A spectrally-resolved femtosecond pump-probe experiment was conducted to verify our theory. By correlating the thermal energy with the pumping density, both the giant change and the transient response of the permittivity of ITO can be predicted. The results in this work provide a new methodology to describe the transient permittivities of ENZ materials, which will benefit the design of ENZ-based nonlinear photonic devices.展开更多
It has been found that the dielectric constants of transparent conductive oxides(TCOs)can be adjusted in an extremely large range by tuning the carrier density.Due to the remarkable light confinement property of the e...It has been found that the dielectric constants of transparent conductive oxides(TCOs)can be adjusted in an extremely large range by tuning the carrier density.Due to the remarkable light confinement property of the epsilon-near-zero(ENZ)effect of TCOs,it has attracted extensive interests of light modulation.However,the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction.In this work,a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement.In a metallic subwavelength grating structure with deep trenches backed by a ground plane,the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias.Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration.Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.展开更多
Strong nonlinearity of plasmonic metamaterials can be designed near their effective plasma frequency in the epsilon-near-zero(ENZ) regime. We explore the realization of an all-optical modulator based on the Au nonline...Strong nonlinearity of plasmonic metamaterials can be designed near their effective plasma frequency in the epsilon-near-zero(ENZ) regime. We explore the realization of an all-optical modulator based on the Au nonlinearity using an ENZ cavity formed by a few Au nanorods inside a Si photonic waveguide. The resulting modulator has robust performance with a modulation depth of about 30 dB/μm and loss less than 0.8 dB for switching energies below 600 fJ. The modulator provides a double advantage of high mode transmission and strong nonlinearity enhancement in the few-nanorod-based design.展开更多
Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexi...Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexible electronics,wearable devices,sensors,etc.The ENZ materials are mostly reported at visible,infrared and terahertz wavelengths,while the report about ENZ materials at radio frequency is rare.In this work,flexible and biocompatible poly(vinyl alcohol)/multi-walled carbon nanotubes(PVA/MWCNTs)hydrogels,which were successfully fabricated by an environmentally friendly method,were used as ENZ materials at radio frequency for the first time.Cytotoxicity experiments proved that the experimental process and products are green,environmentally friendly and biocompatible.The microstructure,crystalline structure,chemical composition and dielectric properties were investigated.Two different water states,which were free water molecules and bound water molecules,coexisted in these PVA/MWCNTs hydrogels and accounted for about 37.5 wt%and 15.9 wt%respectively by analyzing the thermogravimetric analysis curves.When the MWCNTs content reached 12 wt%and 15 wt%,the continuous conductive MWCNTs network was formed in the hydrogel,and ENZ phenomenon was observed at about 760 k Hz and 580 k Hz respectively,which was attributed to the interband transition.Considering the flexibility and non-toxicity of PVA/MWCNTs hydrogels,the ENZ properties of this structure at the radio frequency can be well used in wearable invisibility cloak,flexible electronics,skin sensors and other wearable devices.展开更多
The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in th...The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.展开更多
可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零...可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零介电常数(epsilon near zero,ENZ)超材料单元结构的设计,并利用ENZ超材料的窄通道隧穿效应有效实现了窄带滤波功能,通过将3个ENZ超材料单元结构串联从而完成了带通滤波器基本结构的设计。在此基础上,将微波液晶材料引入ENZ超材料的隧穿通道中,利用液晶材料在外部驱动电压作用下介电参数可变的特性,最终实现了对带通滤波特性的有效调控。全波数值仿真结果表明,所提出的基于ENZ超材料的液晶带通滤波器能够实现中心频率15.88~16.73 GHz的调控,从而验证了设计方法的有效性。展开更多
文摘We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band,wide-angle,and p-polarized thermal emission spectra.This approach,employing molecular beam epitaxy,circumvents the complexities associated with current layered structures and yields temperature-resistant emission wavelengths.Our findings contribute a promising route towards simpler,more efficient MIR optoelectronic devices.
基金the National Natural Science Foundation of China(Grant Nos.61875133 and 11874269).
文摘We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two different frequencies close to the epsilon-near-zero(ENZ)frequency,where large values of reflection coefficients|r_(pp)|/|r_(ss)|are obtained due to the ENZ response induced different rapid increasing trends of|r_(pp)|and|r_(ss)|.Particularly,the tunable ENZ effect with tilt degree of Weyl cones and Fermi energy enables the enhanced spatial IF shift at different frequencies.The enhanced spatial IF shift also shows the adjustability of WSM thickness,incident angle and Weyl node separation.Our findings provide easy and available methods to enlarge and adjust the reflected IF shift of TE-polarized light with a WSM.
基金supported by the Agency for Science, Technology and Research (A*STAR) under AME IRG Grant No. A2083c0058AME IAF-PP Grant No. 182 24 30030+1 种基金HBMS IAF-PP Grant No. H19H6a0025by MOE Tier 3 program LUNI170919a PUBMOE。
文摘The lossy nature of indium tin oxide(ITO) at epsilon-near-zero(ENZ) wavelength is used to design an electrically tunable metasurface absorber. The metasurface unit cell is constructed of a circular resonator comprising two ITO discs and a high dielectric constant perovskite barium strontium titanate(BST) film. The ENZ wavelength in the accumulation and depletion layers of ITO discs is controlled by applying a single bias voltage. The coupling of magnetic dipole resonance with the ENZ wavelength inside the accumulation layer of ITO film causes total absorption of reflected light. The reflection amplitude can achieve ~84 d B or ~99.99% modulation depth in the operation wavelength of 820 nm at a bias voltage of-2.5 V. Moreover, the metasurface is insensitive to the polarization of the incident light due to the circular design of resonators and the symmetrical design of bias connections.
基金financial supports from National Key Research and Development Program of China (No.2019YFB2203402)National Natural Science Foundation of China (Nos.11874029 and 92050108)+4 种基金Guangdong Science and Technology Program International Cooperation Program (Nos.2021A0505030038)Guangdong Basic and Applied Basic Research Foundation (Nos.2020B1515020037 and 2022B1515020069)Pearl River Talent Plan Program of Guangdong (No.2019QN01X120)Fundamental Research Funds for the Central Universities (No.21621108)supported by UK EPSRC Grant EP/T00097X/1
文摘Epsilon-near-zero(ENZ)modes have attracted extensive interests due to its ultrasmall mode volume resulting in ex-tremely strong light-matter interaction(LMI)for active optoelectronic devices.The ENZ modes can be electrically toggled between on and off states with a classic metal-insulator-semiconductor(MIS)configuration and therefore allow access to electro-absorption(E-A)modulation.Relying on the quantum confinement of charge-carriers in the doped semiconductor,the fundamental limitation of achieving high modulation efficiency with MIS junction is that only a nanometer-thin ENZ confinement layer can contribute to the strength of E-A.Further,for the ENZ based spatial light modulation,the require-ment of resonant coupling inevitably leads to small absolute modulation depth and limited spectral bandwidth as restric-ted by the properties of the plasmonic or high-Q resonance systems.In this paper,we proposed and demonstrated a dual-ENZ mode scheme for spatial light modulation with a TCOs/dielectric/silicon nanotrench configuration for the first time.Such a SIS junction can build up two distinct ENZ layers arising from the induced charge-carriers of opposite polar-ities adjacent to both faces of the dielectric layer.The non-resonant and low-loss deep nanotrench framework allows the free space light to be modulated efficiently via interaction of dual ENZ modes in an elongated manner.Our theoretical and experimental studies reveal that the dual ENZ mode scheme in the SIS configuration leverages the large modulation depth,extended spectral bandwidth together with high speed switching,thus holding great promise for achieving electric-ally addressed spatial light modulation in near-to mid-infrared regions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51406126 and 11604229
文摘We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection. The significant feature differing from all other means based on whatever natural materials or metamaterials is that for TM incident wave, the reflected phase is a constant, while for TE wave, the reflected phase is a linear function of the incident angle. The phase difference between them covers the range from -180°to 0°, and the polarization conversions from linear states to elliptical or circular states can be obtained by only adjusting the incident angle. Because no complex structures are employed, our proposal promises a simple approach for manipulating polarization conversion at both terahertz and optical frequencies.
基金This work was financially supported by the National Natural Science Foundation of China(No.52205593)the Fund of Natural Science Special(Special Post)Research Foundation of Guizhou University(No.2023-032)the Platform of Science and Technology and Talent Team Plan of Guizhou Province(No.GCC[2023]007).
文摘CaCu_(3)Ti_(4)O_(12)(CCTO)ceramic nanocomposites incorporating graphene–carbon black(GRCB)fillers were fabricated by spark plasma sintering process.The percolative effects of conductive GRCB fillers on dielectric response of GRCB/CCTO ternary metacomposites were systematically investigated.The weakly real permittivity(ε′)-negative response(ε′~−1×10^(2))was achieved which originated from weakly low-frequency plasmonic state of free carriers within constructed GRCB networks.With enhancing three-dimensional GRCB network,the plasma frequency of metacomposites increased while the damping factor decreased.Herein,theε′-negative values of metacomposites were tuned from−10^(2) to−10^(4) orders of magnitude andε′-near-zero(ENZ)frequencies from~142 to~340 MHz which substantially benefited from the moderate carrier concentration of GRCB dual fillers.The Drude model and equivalent circuit models were adopted to demonstrate dielectric and electrical characteristics.The obtained metacomposites show strong EM shielding effect along with enhanced plasmonic oscillation and even better achieving perfect EM shielding effect in ENZ media.This work achieves the tunableε′-negative andε′-near-zero response and more importantly clarifies its regulation mechanism in ceramic-based ternary metacomposites,which opens up the possibility of designing high-performance EM shielding materials based on metacomposites.
基金the National Natural Science Foundation of China(Nos.12104191 and 11204195)the Natural Science Research of Jiangsu Higher Education Institutions of China(No.21KJB140006)the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘We present a novel method to achieve the decoupling between the transmission and reflection waves of non-Hermitian doped epsilon-near-zero(ENZ)media by inserting a dielectric slit into the structure.Our method also allows for independent control over the amplitude and the phase of both the transmission and reflection waves through few dopants,enabling us to achieve various optical effects,such as perfect absorption,high-gain reflection without transmission,reflectionless high-gain transmission and reflectionless total transmission with different phases.By manipulating the permittivity of dopants with extremely low loss or gain,we can realize these effects in the same configuration.We also extend this principle to multi-port doped ENZ structures and design a highly reconfigurable and reflectionless signal distributor and generator that can split,amplify,decay and phase-shift the input signal in any desired way.Our method overcomes limitations of optical manipulation in doped ENZ caused by the interdependent nature of the transmission and reflection,and has potential applications in novel photonic devices.
基金supported by the National Natural Science Foundation of China(No.12174228)Natural Science Foundation of Shandong Province(No.ZR2019MA024).
文摘We report the modulation of epsilon-near-zero(ENZ)wavelength and enhanced third-order nonlinearity in indium tin oxide(ITO)/Au multilayer films.The samples consisting of five-layer 40 nm ITO films spaced by four-layer ultrathin Au films of different thickness,i.e.,ITO(40 nm)/[Au(x)/ITO(40 nm)]4,were prepared by magnetron sputtering at room temperature.The ENZ wavelength in the multilayer films is theoretically calculated and experimentally confirmed.The nonlinear refractive index and nonlinear absorption coefficient of the samples of x=0,2,3,4 nm were determined using the Z-scan method at a wavelength of 1.064μm.The large nonlinear refractive index n2=1.12×10^(−13) m^(2)=W and nonlinear absorption coefficient β=−1.78×10^(−7) m=W in the sample of x=4 nm are both four times larger than those in the single-layer ITO film.The large optical nonlinearity due to the ENZ enhancement and carrier concentration is discussed.The results indicate that the ITO/Au multilayer films are promising for advanced all-optical devices.
基金supported by National Natural Science Foundation of China(NSFC)under grant U22B2016,62022045,the National Key Research and Development Program of China under Grant 2021YFA0716600the Shenzhen Science and Technology Program under Grants JSGG20210802153800002.
文摘Beam synthesizing antenna arrays are essentially demanded for on-chip millimeter wave and terahertz systems.In order to achieve a par-ticular radiation beam,specific amplitude and phase distributions are required for all the array elements,which is conventionally realized through a properly designed feeding network.In the current work,a low-loss feeding network design approach based on epsilon-near-zero(ENZ)medium was proposed for large-scale antenna arrays with different beam requirements.Due to the infinite wavelength within the ENZ medium,a newly-discovered stair-like resonant mode was adopted for assigning a uniform phase distribution to each element,while the amplitudes and positions of these elements were optimized for generating particular beams.To implement the design philosophy in a low-loss manner,a hollow air-filled waveguide near cutoff fre-quency was employed to emulate the ENZ medium,and the bulk sil-icon microelectromechanical systems(MEMS)micromachining tech-nology was utilized for chip-scale integration.As a specific example,a low-sidelobe antenna array at 60.0 GHz was designed,which realized an impedance bandwidth of 2.57%,a gain of 13.6 dBi and a sidelobe level as low as-20.0 dB within the size of 0.5×3.4λ_(0)(2).This method is also compatible with a variety of applications,such as the high-directivity antenna array,non-diffractive Bessel beam antenna array,and so on.Based on this innovative concept of applying ENZ medium to the on-chip antenna array,it shows the advantages of simple struc-ture and low loss for on-chip beam synthesis without complex lossy feeding networks.
基金supported by the National Natural Science Foundation of China(Grant Nos.91950207,12174310,61805157,and 11974282)。
文摘Transparent conductive oxides exhibit attractive optical nonlinearity with ultrafast response and giant refractive index change near the epsilon-near-zero(ENZ) wavelength, originating from the intraband dynamics of conduction electrons. The optical nonlinearity of ENZ materials has been explained by using the overall-effective-mass and the overall-scattering-time of electrons in the extended Drude model. However, their response to optical excitation is yet the last building block to complete the theory. In this paper, the concept of thermal energy is theoretically proposed to account for the total energy of conduction electrons exceeding their thermal equilibrium value. The time-varying thermal energy is adopted to describe the transient optical response of indium-tin-oxide(ITO), a typical ENZ material. A spectrally-resolved femtosecond pump-probe experiment was conducted to verify our theory. By correlating the thermal energy with the pumping density, both the giant change and the transient response of the permittivity of ITO can be predicted. The results in this work provide a new methodology to describe the transient permittivities of ENZ materials, which will benefit the design of ENZ-based nonlinear photonic devices.
基金financial supports from the National Key Research and Development Program of China(No.2019YFB2203402)the National Natural Science Foundation of China(Nos.92050108,11774383,11774099 and 11874029)+2 种基金Guangdong Science and Technology Program International Cooperation Program(No.2018A050506039)Guangdong Basic and Applied Basic Research Foundation(No.2020B1515020037)Pearl River Talent Plan Program of Guangdong(No.2019QN01X120).
文摘It has been found that the dielectric constants of transparent conductive oxides(TCOs)can be adjusted in an extremely large range by tuning the carrier density.Due to the remarkable light confinement property of the epsilon-near-zero(ENZ)effect of TCOs,it has attracted extensive interests of light modulation.However,the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction.In this work,a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement.In a metallic subwavelength grating structure with deep trenches backed by a ground plane,the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias.Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration.Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.
基金Engineering and Physical Sciences Research Council(EPSRC)H2020 European Research Council(ERC)project iPLASMM(321268)+2 种基金Royal SocietyWolfson FoundationEuropean Commission(EC)FP7 project(304179)(Marie Curie Actions)
文摘Strong nonlinearity of plasmonic metamaterials can be designed near their effective plasma frequency in the epsilon-near-zero(ENZ) regime. We explore the realization of an all-optical modulator based on the Au nonlinearity using an ENZ cavity formed by a few Au nanorods inside a Si photonic waveguide. The resulting modulator has robust performance with a modulation depth of about 30 dB/μm and loss less than 0.8 dB for switching energies below 600 fJ. The modulator provides a double advantage of high mode transmission and strong nonlinearity enhancement in the few-nanorod-based design.
基金the financial supports from the National Natural Science Foundation of China(51871146)the Natural Science Foundation of Shanghai(22ZR1426800)+3 种基金Young Elite Scientist Sponsorship Program by China Association for Science and Technology(YESS20200257)the Innovation Program of Shanghai Municipal Education Commission(2019-01-07-0010-E00053)China National Postdoctoral Program for Innovative Talents(BX2021174)China Postdoctoral Science Foundation(2021M692033)。
文摘Epsilon-near-zero(ENZ)material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index,showing great potentials in the fields of flexible electronics,wearable devices,sensors,etc.The ENZ materials are mostly reported at visible,infrared and terahertz wavelengths,while the report about ENZ materials at radio frequency is rare.In this work,flexible and biocompatible poly(vinyl alcohol)/multi-walled carbon nanotubes(PVA/MWCNTs)hydrogels,which were successfully fabricated by an environmentally friendly method,were used as ENZ materials at radio frequency for the first time.Cytotoxicity experiments proved that the experimental process and products are green,environmentally friendly and biocompatible.The microstructure,crystalline structure,chemical composition and dielectric properties were investigated.Two different water states,which were free water molecules and bound water molecules,coexisted in these PVA/MWCNTs hydrogels and accounted for about 37.5 wt%and 15.9 wt%respectively by analyzing the thermogravimetric analysis curves.When the MWCNTs content reached 12 wt%and 15 wt%,the continuous conductive MWCNTs network was formed in the hydrogel,and ENZ phenomenon was observed at about 760 k Hz and 580 k Hz respectively,which was attributed to the interband transition.Considering the flexibility and non-toxicity of PVA/MWCNTs hydrogels,the ENZ properties of this structure at the radio frequency can be well used in wearable invisibility cloak,flexible electronics,skin sensors and other wearable devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.11734012,62105213,12074267,516022053,and 12174265)the Young Innovative Talents Project of Universities in Guangdong Province(Grant No.2019KQNCX123)+4 种基金the Guangdong Basic and Applied Basic Research Fund(Grant No.2020A1515111037)the Science and Technology Project of Guangdong(Grant No.2020B010190001)the Guangdong Natural Science Foundation(Grant No.2020A1515010467)the Shenzhen Fundamental Research Program(Grant No.20200814113625003)the Open Fund of State Key Laboratory of Applied Optics(Grant No.SKLAO2020001A06)。
文摘The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.
文摘可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零介电常数(epsilon near zero,ENZ)超材料单元结构的设计,并利用ENZ超材料的窄通道隧穿效应有效实现了窄带滤波功能,通过将3个ENZ超材料单元结构串联从而完成了带通滤波器基本结构的设计。在此基础上,将微波液晶材料引入ENZ超材料的隧穿通道中,利用液晶材料在外部驱动电压作用下介电参数可变的特性,最终实现了对带通滤波特性的有效调控。全波数值仿真结果表明,所提出的基于ENZ超材料的液晶带通滤波器能够实现中心频率15.88~16.73 GHz的调控,从而验证了设计方法的有效性。