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Dynamically reconfigurable topological edge state in phase change photonic crystals

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Science Bulletin 2019年第12期64卷 814-822页

作者： Tun Cao Linhan Fang Ying cao Nan Li Zhiyou Fan Zhiguo Tao School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024China China North Vehicle Research Institute Beijing 100072China

The observation of topological edge states(TESs) revolutionized our understanding of scattering and propagation of electromagnetic(EM) waves. Supported by topological robustness, the TES at the interface between trivial and non-trivial insulators was not reflected from the structural disorders and imperfections. Recently topological photonic crystals(PhCs) were demonstrated to obtain remarkable one-way propagation of the TES, having the advantages of lossless propagation, dense integration, and high fabrication tolerance over conventional PhCs. Nevertheless, the lack of reversible switching of TES possesses significant limitations in helicity/spin filtering and tunable photonic devices. We proposed a topological PhC based on a prototypical phase-change material, Ge2 Sb2 Te5(GST225) to solve the problem. We find that at a particular frequency, the TES within the structure can be reversibly switched between "on"and "off" by transiting the GST225 structural state between amorphous and crystalline. Moreover, the topology of the PhC was maintained since the tuning of TES was achieved by varying the refractive index of GST225 instead of the structural geometry. This provides a continuous change of the spectral position of the photonic bandgap and TES by gradually crystallising the GST225. We show that the phase change of GST225 from amorphous to crystalline and vice versa can be engineered in nanoseconds. Our proof of concept may offer a platform for dynamically tuning the TESs that might otherwise be challenging to attain in photonic systems. We expect it to have potential applications for photonic devices in topological optical circuits and scatter-free one-way light propagation.

关键词： Phase change materials Photonic crystals Topological edge states tunability Reconfigurability

Microsphere femtosecond laser sub-50 nm structuring in far field via non-linear absorption

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Opto-Electronic Advances 2023年第6期6卷 8-17页

作者： Zhenyuan Lin Kuan Liu Tun Cao Minghui Hong Pen-tung Sah Institute of Micro-Nano Science and Technology Xiamen UniversityXiamen 361102China School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024China Department of Electrical and Computer Engineering National University of Singapore4 Engineering Drive 3117576Singapore

Creation of arbitrary features with high resolution is critically important in the fabrication of nano-optoelectronic devices.Here,sub-50 nm surface structuring is achieved directly on Sb2S3 thin films via microsphere femtosecond laser irradi-ation in far field.By varying laser fluence and scanning speed,nano-feature sizes can be flexibly tuned.Such small patterns are attributed to the co-effect of microsphere focusing,two-photons absorption,top threshold effect,and high-repetition-rate femtosecond laser-induced incubation effect.The minimum feature size can be reduced down to~30 nm(λ/26)by manipulating film thickness.The fitting analysis between the ablation width and depth predicts that the feature size can be down to~15 nm at the film thickness of~10 nm.A nano-grating is fabricated,which demonstrates desirable beam diffraction performance.This nano-scale resolution would be highly attractive for next-generation laser nano-lithography in far field and in ambient air.

关键词： non-linear effect microsphere femtosecond laser far field

Reversible switching of electromagnetically induced transparency in phase change metasurfaces

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Advanced Photonics 2020年第5期2卷 74-83页

作者： Libang Mao Yang Li Guixin Li Shuang Zhang Tun Cao Dalian University of Technology School of Optoelectronic Engineering and Instrumentation ScienceDalianChina Southern University of Science and Technology Department of Materials Science and EngineeringShenzhenChina University of Birmingham School of Physics and AstronomyBirminghamUnited Kingdom

Metasurface analogue of the phenomenon of electromagnetically induced transparency(EIT)that is originally observed in atomic gases offers diverse applications for new photonic components such as nonlinear optical units,slow-light devices,and biosensors.The development of functional integrated photonic devices requires an active control of EIT in metasurfaces.We demonstrate a reversible switching of the metasurface-induced transparency in the near-infrared region by incorporating a nonvolatile phase change material,Ge2Sb2Te5,into the metasurface design.This leads to an ultrafast reconfigurable transparency window under an excitation of a nanosecond pulsed laser.The measurement agrees well with both theoretical calculation and finite-difference time-domain numerical simulation.Our work paves the way for dynamic metasurface devices such as reconfigurable slow light and biosensing.

关键词： metasurfaces electromagnetically induced transparency surface plasmon resonance reconfigurable phase change material

Non-volatile dynamically switchable color display via chalcogenide stepwise cavity resonators

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Opto-Electronic Advances 2024年第1期7卷 16-27页

作者： Kuan Liu Zhenyuan Lin Bing Han Minghui Hong Tun Cao School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024China Pen-tung Sah Institute of Micro-Nano Science and Technology Xiamen UniversityXiamen 361102China Institute of Laser Engineering Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China

High-resolution multi-color printing relies upon pixelated optical nanostructures,which is crucial to promote color display by producing nonbleaching colors,yet requires simplicity in fabrication and dynamic switching.Antimony trisulfide(Sb_(2)S_(3))is a newly rising chalcogenide material that possesses prompt and significant transition of its optical characteristics in the visible region between amorphous and crystalline phases,which holds the key to color-varying devices.Herein,we proposed a dynamically switchable color printing method using Sb_(2)S_(3)-based stepwise pixelated Fabry-Pérot(FP)cavities with various cavity lengths.The device was fabricated by employing a direct laser patterning that is a less timeconsuming,more approachable,and low-cost technique.As switching the state of Sb_(2)S_(3) between amorphous and crystalline,the multi-color of stepwise pixelated FP cavities can be actively changed.The color variation is due to the profound change in the refractive index of Sb_(2)S_(3) over the visible spectrum during its phase transition.Moreover,we directly fabricated sub-50 nm nano-grating on ultrathin Sb_(2)S_(3) laminate via microsphere 800-nm femtosecond laser irradiation in far field.The minimum feature size can be further decreased down to~45 nm(λ/17)by varying the thickness of Sb_(2)S_(3) film.Ultrafast switchable Sb_(2)S_(3) photonic devices can take one step toward the next generation of inkless erasable papers or displays and enable information encryption,camouflaging surfaces,anticounterfeiting,etc.Importantly,our work explores the prospects of rapid and rewritable fabrication of periodic structures with nano-scale resolution and can serve as a guideline for further development of chalcogenide-based photonics components.

关键词： tunable color displays Fabry-Pérot cavity resonators color printing chalcogenide materials

Acoustic transmissive cloaking with adjustable capacity to the incident direction

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Microsystems & Nanoengineering 2022年第5期8卷 43-51页

作者： Meng Lian Linqiu Duan Junjie Chen Jingyuan Jia Ying Su Tun Cao School of Optoelectronic Engineering and Instrumentation Science Dalian University of Technology116024 DalianChina

Zero-refractive-index(ZRI)phononic crystals(PhCs),in which acoustic waves can be transmitted without phase variations,have considerable potential for engineering wavefronts and thus are applicable to invisibility cloaking.However,the creation of the transmissive cloaking achieved by ZRI-PhCs is challenging under an oblique incidence,which substantially hinders their practical applications.Here,we experimentally demonstrate acoustic transmissive cloaking with the adjustable capacity to the incident direction.Acoustic transmissive cloaking of arbitrarily shaped obstacles can be obtained through a hybrid acoustic structure consisting of one outer layer of a programmable phaseengineered metasurface(PPEM)and one inner layer of a double zero-refractive-index(DZRI)-PhC.The DZRI-PhC is functionally the same as an equiphase area and can guide acoustic waves around the obstacle,a process known as acoustic tunneling.The PPEM perpendicularly transfers the incident acoustic waves to the DZRI-PhC and allows the emergent waves from the DZRI-PhC to transmit along the original incident direction.The DZRI-PhC is made of an array of iron squares in the air.The reciprocal of the effective bulk modulus and the effective mass density is approximately zero at a frequency of 3015 Hz(0.5187 v0/a)originating from the zeroth-order Fabry–Pérot(FP)resonance that possesses infinite phase velocities.Each meta-atom of the outer metasurface consists of a line channel and four shunted Helmholtz resonators,which have effective masses that are engineered by a mechanics system.The amplitude and phase of the sound waves propagating through each meta-atom can be controlled continuously and dynamically,enabling the metasurface to obtain versatile wavefront manipulation functions.Acoustic cloaking is visually demonstrated by experimentally scanning the acoustic field over the hybrid structure at a frequency of 3000 Hz(0.5160 v0/a).Our work may provide applications with great potential,including underwater ultrasound,airborne sound,acoustic communication

关键词： incident Acoustic outer

Chirality Enhancement Using Fabry-Pérot-Like Cavity

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Research 2020年第1期2020卷 1400-1408页

作者： Jiaxin Bao Ning Liu Hanwei Tian Qiang Wang Tiejun Cui Weixiang Jiang Shuang Zhang Tun Cao School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024China State Key Laboratory of Millimeter Waves School of Information Science and EngineeringSoutheast UniversityNanjing 210096China School of Physics&Astronomy University of BirminghamBirminghamB152TTUK

Chiral molecules that do not superimpose on their mirror images are the foundation of all life forms on earth.Chiral molecules exhibit chiroptical responses,i.e.,they have different electromagnetic responses to light of different circular polarizations.However,chiroptical responses in natural materials,such as circular dichroism and optical rotation dispersion,are intrinsically small because the size of a chiral molecule is significantly shorter than the wavelength of electromagnetic wave.Conventional technology for enhancing chiroptical signal entails demanding requirements on precise alignment of the chiral molecules to certain nanostructures,which however only leads to a limited performance.Herein,we show a new approach towards enhancement of chiroptical effects through a Fabry-Pérot(FP)cavity formed by two handedness-preserving metamirrors operating in the GHz region.We experimentally show that the FP cavity resonator can enhance the optical activity of the chiral molecule by an order of magnitude.Our approach may pave the way towards state-of-the-art chiral sensing applications.

关键词： Chiral chiral circular

Wideband mid-infrared thermal emitter based on stacked nanocavity metasurfaces

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International Journal of Extreme Manufacturing 2022年第1期4卷 133-141页

作者： Tun Cao Meng Lian Kuan Liu Xianchao Lou Yaoming Guo Dongming Guo School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalianPeople’s Republic of China Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education Dalian University of TechnologyDalianPeople’s Republic of China

Efficient thermal radiation in the mid-infrared(M-IR)region is of supreme importance for many applications including thermal imaging and sensing,thermal infrared light sources,infrared spectroscopy,emissivity coatings,and camouflage.The ability to control light makes metasurfaces an attractive platform for infrared applications.Recently,different metamaterials have been proposed to achieve high thermal radiation.To date,broadening the radiation bandwidth of a metasurface emitter(meta-emitter)has become a key goal to enable extensive applications.We experimentally demonstrate a broadband M-IR thermal emitter using stacked nanocavity metasurface consisting of two pairs of circular-shaped dielectric(Si;N;)–metal(Au)stacks.A high thermal radiation can be obtained by engineering the geometry of nanocavity metasurfaces.Such a meta-emitter provides wideband and broad angular absorptance of both p-and s-polarized light,offering a wideband thermal radiation with an average emissivity of more than 80%in the M-IR atmospheric window of 8–14μm.The experimental illustration together with the theoretical framework establishes a basis for designing broadband thermal emitters,which,as anticipated,will initiate a promising avenue to M-IR sources.

关键词： mid-infrared wideband perfect thermal radiation surface plasmon resonance metasurface nanocavity

Reconfigurable,graphene-coated,chalcogenide nanowires with a sub-10-nm enantioselective sorting capability

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Microsystems & Nanoengineering 2018年第1期4卷 337-344页

作者： Tun Cao Long Tian Huawei Liang Kai-Rong Qin Department of Biomedical Engineering Dalian University of TechnologyDalianChina Shenzhen Key Laboratory of Laser Engineering College of Optoelectronic EngineeringShenzhen UniversityShenzhenChina

Chiral surface plasmon polaritons(SPPs)produced by plasmonic nanowires can be used to enhance molecular spectroscopy for biosensing applications.Nevertheless,the switchable stereoselectivity and detection of various analytes are limited by a lack of switchable,chiral SPPs.Using both finite-element method simulations and analytic calculations,we present a graphene-coated chalcogenide(GCC)nanowire that produces mid-infrared,chiral SPPs.The chiral SPPs can be reversibly switched between“on”(transparent)and“off”(opaque)by non-volatile structural state transitions in the dielectric constants of the chalcogenide glass Ge2Sb2Te5.Furthermore,by controlling the Fermi energy of the graphene-coating layer,the nanowire can output either non-chiral or chiral SPPs.A thermal-electric model was built to illustrate the possibility of ultrafast on/off switching of the SPPs at the terminus of the nanowire.Finally,we show that a selective,lateral sorting of sub-10-nm enantiomers can be achieved via the GCC nanowire.Chiral nanoparticles with opposite handedness experience transverse forces that differ in both their sign and magnitude.Our design may pave the way for plasmonic nanowire networks and tunable nanophotonic devices,which require the ultrafast switching of SPPs,and provide a possible approach for a compact,enantiopure synthesis.

关键词： synthesis chiral Chiral

Nonvolatile chirality switching in terahertz chalcogenide metasurfaces

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Microsystems & Nanoengineering 2022年第5期8卷 197-205页

作者： Jiaxin Bao Xieyu Chen Kuan Liu Yu Zhan Haiyang Li Shoujun Zhang Yihan Xu Zhen Tian Tun Cao School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024P.R.China Center for Terahertz waves and College of Precision Instrument and Optoelectronics Engineering Tianjin Universityand the Key Laboratory of Optoelectronics Information and Technology(Ministry of Education)Tianjin 300072P.R.China

Actively controlling the polarization states of terahertz(THz)waves is essential for polarization-sensitive spectroscopy,which has various applications in anisotropy imaging,noncontact Hall measurement,and vibrational circular dichroism.In the THz regime,the lack of a polarization modulator hinders the development of this spectroscopy.We theoretically and experimentally demonstrate that conjugated bilayer chiral metamaterials(CMMs)integrated with Ge_(2)Sb_(2)Te_(5)(GST225)active components can achieve nonvolatile and continuously tunable optical activity in the THz region.A THz time-domain spectroscopic system was used to characterize the device,showing a tunable ellipticity(from‒36°to 0°)and rotation of the plane polarization(from 32°to 0°)at approximately 0.73 THz by varying the GST225 state from amorphous(AM)to crystalline(CR).Moreover,a continuously tunable chiroptical response was experimentally observed by partially crystallizing the GST225,which can create intermediate states,having regions of both AM and CR states.Note that the GST225 has an advantage of nonvolatility over the other active elements and does not require any energy to retain its structural state.Our work allows the development of THz metadevices capable of actively manipulating the polarization of THz waves and may find applications for dynamically tunable THz circular polarizers and polarization modulators for THz emissions.

关键词： polarization tunable modulator