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In this paper, an active terahertz modulator based on optically controlled organometal halide perovskite M A P b I 2 B r is proposed. The terahertz wave time-domain transmission of the M A P b I 2 B r / A l 2 O 3 sample was measured by a terahertz time-domain spectrometer. Experimental results indicate that the M A P b I 2 B r / A l 2 O 3 sample showed an obvious optical-power-dependent modulation effect on transmission of the terahertz wave; the maximum modulation depth of the modulator can reach 59.99% at 0.3 THz when the external pump optical power is up to 1500 mW.

Transmission and dielectric properties of non-illuminated and illuminated barium titanate thin film were investigated by time-domain terahertz spectrometer and tuned by an electric field. Compared with the sample illuminated by 532 nm laser, the electric field could realize a higher modulation in the phase of the transmission for the nonilluminated sample. Results displayed that when the sample was illuminated by green laser, optical field suppressed the effect of electric field on transmission and dielectric properties of BTO thin film, because excited carriers from the substrate and ferroelectric thin film would form a built-in electric field to shield the external electric field. In addition, optical field and electrical field would play different roles in the lattice dynamics of the ferroelectric thin film.

The dielectric spectra of ferroelectric Pb(Zr0.52Ti0.48)O3/SrTiO3/PbTiO3 (PZT/STO/PT) superlattice under an external optical field were investigated at room temperature by time-domain terahertz (THz) spectroscopy. Results showed that the real and imaginary part of permittivity were increased roughly upon application of an external optical field, and tuned by 78.16% and 85.65% respectively. It could be interpreted as softening of the soft mode and increasing of the damping coefficient and oscillator strength. Furthermore, the central mode was observed in the tricolor thin film, and the frequency of the central mode was also increased along with the optical power.

We investigated the tunability of the dielectric characterization of the Ferroelectric Barium Strontium Titanate (Ba0.5Sr0.5TiO3) thin film on the Strontium Titanate substrate by a dc bias electric field through the terahertz time-domain spectroscopy. The tunability of the real part of the permittivity reached up to 74.8% and the imaginary part of the permittivity reached up to 33.6% when the bias electric field up to 30 V. And the results are attributed to the soft mode hardening caused by the electric field.

The absorption tunability of 100 nm thickness of ferroelectric Barium Strontium Titanate (Ba0.5Sr0.5TiO3) thin films with different densities of pumped optical field is measured by terahertz time-domain spectroscopy in the range of 0.2 THz – 1.2 THz at 19 °C. Experimental results show that the absorption coefficient of BST film is approximately at 5000 cm−1–20000 cm−1 in the range of 0.2 THz – 1.2 THz and the absorption coefficient reached up to 16% when we applied the optical field up to 600 mW. The theoretical calculations reveal that increasing photoexcitation fluences is responsible for the increasing of transmission change in the conduction current density cause the absorption coefficient varied.

An active multifunctional terahertz modulator based on plasmon-induced transparency (PIT) metasurface under the effect of external infrared light was investigated theoretically and experimentally. A distinct transparency window, which resulted from the near-field coupling between two resonators, could be observed in the transmission spectra. Experimental results showed a phenomenon infrared light induced blue shift on the both resonator with increasing optical powers. When the optical power was tuned from 0 mW to 400 mW, the amplitude tunability of transmission at transparency window reached to 34.01%, much larger than that at the two resonance frequencies. Moreover, the phase tunability of the transmission at 0.98 THz reached to 31.35%. Meanwhile, the amplitude variation was limited to 10%. Furthermore, a coupled Lorentz oscillator model was adopted to analyze the near-field interaction of the resonances. Experimental results were in good agreement with the analytical fitting results.

A broadband absorber, which is composed of graphene analog of electromagnetically induced transparency (EIT) and a metal ground plane spaced by a thin SiO 2 dielectric layer, is proposed and investigated. Numerical results reveal that the working bandwidth can be dynamically tuned between broadband absorption and narrowband absorption by varying the Fermi level of graphene through controlling of the electrostatic gating. Furthermore, absorption behaviors can be tuned to the state of off when the electric polarized is rotated to another axis. It is also found that the coupling strength between the radiative element and dark element is tuned by the distance between the disconnected vertical graphene strip and horizontal graphene strip. In addition, this type of graphene-based absorber is very sensitive to the incident angles.

A thermally tunable multiband terahertz metamaterial absorber comprising a periodic array of closed metallic square ring resonators and four metal bars parallel to the four side of the square ring, fabricated on the low-temperature co-fired ceramic (LTCC) strontium titanate (STO) dielectric layer dielectric substrate has been proposed. The resonance frequencies of the absorber are demonstrated to be continuously tuned in the terahertz regime by increasing the temperature. It is found that in the window between 0.05 and 0.35 THz the absorber has three distinctive absorption peaks at frequencies 0.129 THz, 0.198 THz and 0.316 THz (at the room temperature), whose peaks are attained 99.3%, 99.1% and 94.6% respectively. The tunability is attributed to the temperature-dependent permittivity of the substrate and attained to 67.3% frequency tuning depth at the room temperature, when the temperature varied from 400 K to 200 K. The proposed designs ensure broadband thermally tunable terahertz devices.

The dielectric spectra of single-layer PbTiOsub3/sub(PT), single-layer PbZrsubx/subTisub1-x/subOsub3/sub(PZT) and multilayer PZT/PT thin films under an external optical field were investigated at room temperature by time-domain terahertz (THz) spectroscopy. Results showed that the real part of permittivity increased upon application of an external optical field, which could be interpreted as hardening of the soft mode and increasing of the damping coefficient and oscillator strength. Furthermore, the central mode was observed in the three films. Among the dielectric property of the three thin films studied, the tunability of the PZT/PT superlattice was the largest.

In this paper, a dual-band perfect absorber, composed of a periodically patterned elliptical nanodisk graphene structure and a metal ground plane spaced by a thin SiO(2) dielectric layer, is proposed and investigated. Numerical results reveal that the absorption spectrum of the graphene-based structure displays two perfect absorption peaks in the terahertz band, corresponding to the absorption value of 99% at 35μm and 97%at 59μm, respectively. And the resonance frequency of the absorber can be tunned by controlling the Fermi level of graphene layer. Further more, it is insensitive to the polarization and remains very high over a wide angular range of incidence around ±60(0). Compared with the previous graphene dual-band perfect absorption, our absorber only has one shape which can greatly simplify the manufacturing process.

A microwave miniaturized bandpass filter using (Mg 0.95 Ca 0.05 )TiO 3 (abbreviated as 95MCT hereafter) ceramic substrate is investigated in the present paper. The paper studies the sintering and microwave dielectric properties of Al 2 O 3 , La 2 O 3 and SiO 2 co-doped 95MCT. The XRD pattern shows that a secondary phase MgTi 2 O 5 is easily segregated in 95MCT ceramic, however, through co-doping it can be effectively suppressed, and the microwave dielectric properties, especially, the Qf value can be significantly improved. Through optimizing the co-doping ratio of Al 2 O 3 , La 2 O 3 and SiO 2 , the sintering temperature of 95MCT ceramic can be lowered by 80°C, and the microwave dielectric properties can reach Qf=61856GHz and e r =19.84, which indicates the modified 95MCT ceramic have a great potential application in microwave communication devices. Based on this, we also designed a miniaturized microwave bandpass filter (BPF) on modified 95MCT substrate. Through a full wave electromagnetic structure simulation, the results show that the center frequency of the BPF is 2.45GHz and the relative bandwidth is 4.09% with the insertion loss of less than 0.2dB in the whole bandpass.

The phase evolution, crystal structure and dielectric properties of (1 − x )Nd(Zn 0.5 Ti 0.5 )O 3 + x Bi(Zn 0.5 Ti 0.5 )O 3 compound ceramics (0 ≤ x ≤ 1.0, abbreviated as (1 − x )NZT– x BZT hereafter) were investigated. A pure perovskite phase was formed in the composition range of 0 ≤ x ≤ 0.05. The B-site Zn 2+ /Ti 4+ 1:1 long range ordering (LRO) structure was detected by both XRD and Raman spectra in x ≤ 0.05 samples. However, this LRO structure became gradually degraded with an increase in x . The dielectric behaviors of the compound ceramic at various frequencies were investigated and correlated to its chemical composition and crystal structure. A gradually compensated τ f value was obtained in (1 − x )NZT– x BZT microwave dielectrics at x = 0.03, which was mainly due to the dilution of dielectric constant in terms of Claussius–Mossotti differential equation.

The crystal structure evolution and microwave (MW) dielectric properties of xCa(Al0.5Nb0.5)O3+(1−x)SrTiO3 (xCAN+(1−x)ST, 0≤x≤1.0, ) dielectric ceramics were investigated. X-ray diffraction patterns illustrated that a single perovskite solid solution could be formed between the two end members; however, minor amount of pyrochlore phase was also detected in the composition range of 0.5≤x≤0.9. With the increase of x value, the crystal structure gradually evolved from a simple Pm3m cubic to a monoclinic P21/n space group with the octahedral tilting and the B-site ordering structure transition subsequently developed. The MW dielectric properties of xCAN+(1−x)ST solid solutions were elaborately investigated and correlated to their crystal structures. The microscopic structure-related thermal parameters in the xCAN+(1−x)ST solid solution were analyzed in terms of the Claussius–Mossotti equation to reveal the original contributors in temperature coefficients. Temperature coefficient-compensated ceramic could be obtained in the xCAN+(1−x)ST system in the range of 0.5

The dielectric properties of 0.6CaTiO3-0.4NdAlO3 ceramics under external optical fields were investigated by terahertz time-domain spectroscopy in a frequency range of 0.2 THz to 1 THz at room temperature. It could be found that the variation of the real part of complex permittivity is approximately 0.31 in the frequency range of 0.2 THz to 1 THz. However the imaginary part of the dielectric constant does not change appreciably with the external optical field. The micromechanism of these results was attributed to the built-in electric field caused by the excited free carriers in the ceramics.