Zhenyu Zhao

Shanghai Normal University | SHNU · Department of Physics

Photonic edge mode confining light in cavities of surface plasmons is beneficial in image and biosensor applications. In the terahertz band, however, the edge mode in a cavity of spoof localized surface plasmons has not matured sufficiently. Herein, a cost-effective strategy to achieve a terahertz photonic edge mode using a metasurface of strongly...

This work experimentally investigates and compares terahertz electromagnetic shielding of micrometer-thick Ti3C2Tx MXene on polyimide prepared by two methods: etched using LiF/HF or HCl/HF from the MAX phase precursor. The later process shows a larger absorption coefficient as well as higher electrical conductivity. Raman spectroscopy and scanning...

A new phenomenon of dual band symmetry-protected bound state in the continuum (SP-BIC) is revealed inside the plasmon-induced transparency (PIT) windows. A metasurface of circular periodically grooved cavity integrated with a complimentary symmetric double-gap split-ring resonator (DSRR) is employed. Intrinsic spoof localized surface plasmon (SLSP)...

Conventionally, a symmetry-protected quasi bound state of the continuum (BIC) becomes achievable by breaking the C2 symmetry of meta-atoms. Our work exhibits a novel approach to achieving dual band quasi-BIC by breaking the C2v symmetry into Cs symmetry. Also, we show that a single band quasi-BIC can be achieved by breaking the C2v symmetry into C2...

Achieving high-quality (Q)-factor resonances in metasurfaces is essential for various applications, including nano-lasers, nonlinear optics, and quantum optics. In this work, we propose a high-Q metasurface using a topological strategy: constructing the metasurface by stacking two conjugated nanopillar arrays with different topological invariants....

In a system of C2 symmetry, symmetry-protected bound states in the continuum (SP-BICs) exist with a continuous spectrum of radiating waves that can carry energy away and enable an infinite radiative quality (Q) factor and zero linewidth. However, the SP-BICs transform into quasi-BICs by breaking the C2 symmetry of the system, where the resonance li...

We numerically investigate the terahertz superlattice mode in a moiré metasurface containing fringe of squares and hexagonal structures. The edge of moiré fringes works as a route of uni-directional surface current driven by the incident terahertz polarization. As such, each lateral edge of moiré fringe works as dipole oscillator, which collectivel...

We have successfully fabricated Ti-based MXenes flakes, Ti3C2Tx, by chemical etching, then prepared it as an organic dispersion and finally spin-coated it on polyimide plastic substrate for terahertz wave shield. The shielding effectivity of the 12 μm ultra-thin film can reach up to 17 dB measured by the terahertz time-domain spectra. We can attrib...

In recent years, metasurfaces enabling a slow light effect in the terahertz band have seen considerable achievement. However, most of these advances demonstrated so far are polarization sensitive. In this work, we demonstrate polarization-insensitive terahertz slow light at spoof surface plasmon-induced transparency windows. Two types of metasurfac...

Metamaterials have been engineered to achieve electromagnetically induced transparency (EIT)-like behavior, analogous to those in quantum optical systems. These meta-devices are opening new paradigms in terahertz communication, ultra-sensitive sensing and EIT-like anti-reflection. The controlled coupling between a sub-radiant and a super-radiant pa...

We present a THz emission enhancement of 41 times at 0.92 THz from a metasurface made of T-shaped resonators excited in a quasi-near-field zone. Such a metasurface has an intrinsic transmission minimum with Q factor of 4 at 1.25 THz under far-field excitation. When this metasurface is coupled onto the backside of a 625-μm-thick photoconductive emit...

Low quality (Q) factors of the intrinsic inductive–capacitive (LC) mode as well as the parasitic dipole oscillation mode restrict high-resolution sensing using split-ring resonators (SRR). Although the trapped Fano-mode of the high-Q factor is found in asymmetric SRR, the conventional design limits the scaling down of resonators. As such, excitatio...

Herein, we demonstrate one of the highest terahertz group delay of 42.4 ps achieved experimentally at 0.23 THz, on a flexible planar metamaterial. The unit cell of metasurface is made up of a textured closed cavity and another experimentally concentric metallic arc. By tuning the central angle of the metallic arc, its intrinsic dipolar mode is in d...

A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. each MM contains a couple of identical size esRRs and a couple of structural inversed eSRRs twisted π/2 in check...

A novel phenomenon is observed in the meta-atoms composed of a complementary rectangular double split-ring resonator (SRR). An intrinsic Fano-resonance collapses with the outer SRR deformed asymmetrically. Alternatively, a trapped mode emerges at an adjacent frequency region, of which its strength grows up with increasing the asymmetric deviation....

This work theoretically proposed dual terahertz (THz) slow light plateaus by tuning the destructive interference between a toroidal magnetic momentum and magnetic dipole momentum. The metasurfaces are in a sandwich structure. A metallic cut-wire is patterned on one side of polyimide thin-film, and a rectangular split-ring resonator (SRR) on the oth...

This work numerically investigates a localized terahertz (THz) slow light phenomenon by tuning the spoof localized surface plasmon-induced transparency (PIT). A binary meta-molecule supports the interaction of the spoof localized surface plasmon (spoof-LSP), which is composed of a metallic arc and a textured circular cavity of periodic grooves. By...

We experimentally investigate the terahertz (THz) response of conductively coupled asymmetric split ring resonator-based meta-molecules in the layout of reflection and rotational symmetry. In the reflectional symmetry case, the horizontally polarized THz excites a couple of trapped modes: the low-order one is a coupled Fano-resonance, and the high-...

We experimentally investigate the terahertz (THz) electromagnetically-induced transparency (EIT)-like phenomenon in a metamolecule (MM) of three-body system. This system involves a couple of geometrically identical split-ring resonators (SRRs) in orthogonal layout conductively coupled by a cut-wire resonator. Such a three-body system exhibits two f...

The interaction between terahertz (THz) resonance modes and element deformation in rectangular split-ring resonator (RSRR)-based meta-atoms (MAs) is investigated experimentally. Two types of RSRR-based MAs are presented: lateral-varied SRR (LV-SRR) and arm-twisted SRR (AT-SRR). When the distances from the gaps to the opposite sides of above meta-at...

We demonstrate a localized slow light phenomenon in a symmetry broken metamolecule (MM) of conductively coupled dark resonators at a terahertz band. Under a dark-mode excitation condition, the single mode resonance becomes dual modes by breaking the uniaxial symmetry of MM. Thus, a transparency window exists in between dual modes. An interaction of...

The evolution of terahertz resonance modes in an individual split-ring resonator (SRR) is investigated experimentally by locally structural deformation. The length reduction of opposite-side results in a frequency blueshift of resonance modes. Simultaneously, the Q factor of inductive–capacitive oscillation mode is enhanced while the dipole oscilla...

We present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of <100>-oriented semi-insulating gallium arsenide (SI-GaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the...

We reported a broadband terahertz (THz) plasmon-induced transparency (PIT) phenomenon owing to asymmetric coupling in between the bright-and-dark resonators in meta-molecules (MMs). Each MM contains a cut-wire resonator and a couple of identical size and gap opposite-directed U-shaped resonators in mirror symmetry. An upside displacement of cut-wir...

We investigate the terahertz (THZ) responses of fractal concentric rectangular square resonators (CRS) induced by different mode coupling mechanisms. Near-field coupling results in the resonant mode redshift, while conductive coupling cause the results in the resonant mode blueshift. One can achieve a high Q mode with strong modulation depth by swi...

We measure the opto-electronic properties of femtosecond-laser-ablated GaAs and demonstrate its utility towards THz devices. In particular, we show that laser-ablated THz antennas are 65% more efficient than non-ablated antennas at high powers. Our results demonstrate the possibility of using femtosecond-laser-ablation as a cost-effective technique...

By integrating the graphene layer with the dielectric loaded surface plasmon waveguides, the tunable propagation properties have been investigated in the near-IR region, including the influences of operation frequency, the Fermi level of the graphene layer, and dielectric layer thickness. To improve the modulation properties, multiple unit cell (gr...

We investigate a plasmon-induced transparency (PIT)-like behavior at terahertz (THz) region induced by resonance detuning in a hybrid planar metamaterial (MM). Each unit cell of the MM contains two types of dipole oscillation resonators: a cut-wire and a couple of U-shaped resonators in mirror symmetry. The hybridization of above resonators splits...

The modulation of dielectric constant and loss at terahertz (THz) frequency of CaCu3Ti4O12 (CCTO) ceramics is achieved by doping Nd2O3. Nd2O3 doped CCTO samples are prepared by solid-state reaction method. Structure analysis shows that the Nd ions do not affect the basic crystalline structure of CCTO. With the help of morphologic characterization,...

We investigate the terahertz electromagnetic responses of fractal meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) resonators are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each resonator works as an independent dipole so as to result in the m...

We theoretically investigate the feasibility of terahertz generation and detection in a (110)-oriented 3C-SiC single crystal excited by a frequencydoubled Yb-doped femtosecond pulse laser. The phase-matching condition of optical rectification (OR) and electro-optic (EO) sampling are analyzed on the basis of the dispersion relation of 3C-SiC. The TH...

Due to the excellent optical,mechanical and thermal properties,graphene is one of the most important topics in many research fields.Since the linear dispersion relationship near the Dirac point can be tuned conveniently by using the applied gate voltage,magnetic fields,and temperature,graphene layer is a good platform to investigate the tunable dev...

A novel semi-insulated GaAs interdigitated photoconductive antenna is presented in this paper and its THz emission waveform and spectra bandwidth are recorded at different exciting carrier density in temperature range from 4.2 K to 270 K.The experimental results show that the THz radiation amplitude reaches to maximum at 70 K.THz waveform and bandw...

An efficient terahertz (THz) emission from sol-gel grown Cu 2 ZnSnSe 4 (CZTSe) film is evaluated using THz time domain spectroscopy. Comparing the polarity of THz emission waveforms of CZTSe and GaAs, we suggest the acceleration of photo-carriers in the surface accumulation layer of CZTSe to be the dominant mechanism of radiation emission.

A teeter-totter effect of terahertz (THz) resonant modes in C-shaped complementary split-ring resonators (CSRRs) is observed. The dual resonant mode transmission enhancement was investigated using THz time-domain spectroscopy. The intensity of the lower-frequency resonance modes increases monotonically with the CSSR gap width, which is accompanied...

We report on the first terahertz (THz) emitter based on femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to the nonablated device. Counter-intuitively, the ablated device shows significantly lower photocurrent and carrier mobility. We understand this behavior in terms...

We report on the first terahertz (THz) emitter based on femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to the nonablated device. Counter-intuitively, the ablated device shows significantly lower photocurrent and carrier mobility. We understand this behavior in terms...

A terahertz (THz) extraordinary transmission from a complementary circular split-ring resonance (CSRR) on polyimide film is investigated via THz time-domain spectroscopy. A distinct single-peak resonance is observed due to the inductive-capacitive (LC) resonance when the THz polarization is perpendicular to the gap of CSRR. When the THz polarizatio...

By integrating the metallic metamaterials (MMs) with a graphene layer, the resonant properties of an active tunable device based on the metal-SiO2-graphene (MSiO2G) structure have been theoretically investigated in the near-IR spectral region. The results manifest that the influences of the graphene layer on the propagation properties are significa...

We observed efficient terahertz (THz) emission from sol-gel grown Cu2ZnSnSe4 (CZTSe) thin films using THz time domain spectroscopy technique. The THz emission bandwidth exceeds 2 THz with a dynamic range of 20 dB in the amplitude spectrum. The THz emission amplitude from CZTSe is found to be independent of external magnetic fields. Comparing the po...

We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorp...

We theoretically investigate terahertz (THz) emission and detection from 〈110〉-oriented electro-optic (EO) crystals adapted for Yb-doped femtosecond pulse laser. According to the principles of phase-matching condition, the dispersion relation between optical velocity and THz pulse, THz absorption spectra, and coherence lengths of CdTe, GaP, and GaA...

We theoretically investigate the feasibility of terahertz detection via electro-optic (EO) sampling using 6H-SiC single crystal. The frequency response is simulated based on the principle of phase-matching condition. The optical dispersion of 6H-SiC was calculated by Sellmeier equation. In collinear incidence approach, the THz detectable bandwidths...

We observed efficient transient optical grating effect from the TiO2–Nb2O5–TeO2 glasses excited by femtosecond laser pulses. The glass samples were prepared via melt-quenching technique. The optical nonlinearities were calibrated by forward degenerate four wave mixing (DFWM) experiment with 50 fs laser pulse at 800 nm. The magnitude of the third or...

Laser beam scanners are important optical elements with a large variety of applications in the measurement techniques, optical communications, laser imaging ladar, etc. Agile beam steering of optical radiation using phased arrays offers significant advantages, such as weight, stability and power requirements over conventional beam steering systems....

We experimentally study the thickness dependence of the terahertz (THz) response in {110}-oriented GaAs crystals for free space electro-optic sampling at 1.55 microm. The THz response bandwidths are analyzed and simulated under phase-matching condition with a model frequency response function. The results indicate that the detection bandwidth incre...

We characterize ErAs:In0.53Ga0.47As superlattices as substrates for photoconductive terahertz emitters excited at 1.55 μm. The bandwidth of the emitted radiation is studied as a function of the superlattice period (or equivalently the electron lifetime) and the applied bias field. The results show that a variation in the electron lifetime from 0.2...

ErAs:In0.53Ga0.47As superlattice THz emitters are fabricated and characterized at an excitation wavelength of 1.55 μm. Photocurrent-voltage characteristics, carrier lifetimes and bandwidth of the THz output are discussed as a function of the superlattice period.

Niobic tellurite glass doped by silver chloride nanocrystal was prepared with the melting-quenching and heat treatment method, and the self-trapped exciton absorption band of the silver chloride nanocrystal was observed at 532 nm in the UV-visible absorption spectrum. The glass structure characteristics were investigated by Raman spectroscopy, and...

Silver chloride (AgCl) nanocrystal doped niobic tellurite glass (80TeO2–20Nb2O5) was synthesized by melting-quenching and heat treatment technique, and its non-resonant ultrafast nonlinear optical properties were investigated. Longer thermal treatment time can enlarge the AgCl nanocrystal grain size and increase the AgCl nanocrystal density, and it...

Terahertz time-domain spectroscopy is used to determine gain related parameters of terahertz quantum-cascade lasers. Due to the techniquespsila insensitivity to the QCL emission, spectral gain narrowing is observed above laser threshold. By correlating these measurements with bandstructure simulations, insight into the subband alignment as a functi...

We present a study of the terahertz (THz) generation by optical rectification in a 2 mm thick <110> ZnTe crystal. The conditions for the most efficient THz generation are described. We investigate the competition between optical rectification (OR), second harmonic generation (SHG), two-photon absorption (TPA) and free-carrier absorption in the diff...