Our recent research work on artificial birefringence and broadband polarization converter in terahertz (THz) functional devices was reviewed in this paper, we proposed the subwavelength dielectric gradient grating structure with artificial high birefringence, broadband and low dispersion, and the dielectric metasurface with line-square compound lattice which can realize polarization dependent EIT effect with a large artificial birefringence effect. On the basis, we presented a compound metasurface and a coupled dielectric-metal grating for broadband THz wave polarization conversion and asymmetric transmission. Moreover, we introduced two-dimensional materials into THz polarization devices, and proposed a switchable quarter-wave plate based on graphene grating and a carbon nanotube attached subwavelength grating for broadband THz polarization conversion and dispersion control. This work has greatly promoted the development and practical application of THz polarization devices.
In this paper, we have reviewed our research on terahertz (THz) isolators and nonreciprocal transmission devices. In addition, we present a new kind of THz isolator based on asymmetry magneto-metasurface. A structured InSb layer coats on the silica substrate in which the numerical simulation shows that this metasurface has isolation over 60dB at 0.646 THz and a 10dB operating bandwidth of 13 GHz under an external magnetic field of 0.3T with an insertion loss less than 2.5dB. This kind of low-loss, high isolation, easy coupling THz magneto-metasurface isolator has broadly potentials for THz application systems. Importantly, we discuss and conclude the necessary conditions of forming THz nonreciprocal transmission in the magneto-material devices, which is strongly related with magneto-material and asymmetric transmission system.
A narrow-band filter with a broad tuning range is designed based on a magnetic field controlled ferrite defect in photonic crystal for a terahertz (THz) wave. The resonance defect modes of a ferrite defect in photonic crystal in the THz region are studied by using the finite difference time domain method. Detailed calculations on the shifts of the defect mode frequency and transmission properties reveal that the peak frequency of transmission spectra can continuously vary from 0.77 to 0.95 THz under the external magnetic field and the bandwidth of the filter is about 0.015 THz.
In this work, we present a terahertz (THz) isolator in metal parallel plate waveguide (PPWG). A magneto-optical film with 30μm thickness is coated on one side of the metal plate of PPWG with 100μm width, forming a metal- magnetoair- metal hybrid waveguide. Due to the non-reciprocity of magneto-optical medium and the asymmetry of the waveguide structure, this waveguide show a strong one-way transmission property. The numerical simulation shows that this THz isolator has a maximum isolation of 30dB and a 20dB operating bandwidth of 90GHz under a magnetic field of 0.3T, and its insertion loss is smaller than 0.5dB. Moreover, this operating frequency band can be widely tuned by changing the external magnetic field and temperature. This low-loss, high isolation, broadband tunable nonreciprocal THz waveguide has a great potential for THz application systems.
Our recent important progress in terahertz (THz) functional devices based on photonic crystals and plasmonics was reviewed in this paper, involving THz modulator, isolator and sensor. For THz modulators, we demonstrate the transmission and modulation properties of a state conversion photonic crystals and a metal-semiconductor-metal plasmonic waveguide based on theoretical and experimental investigations. We also show the nonreciprocal transmission and enhancement mechanism of the structured metal/magneto-optical plasmonic waveguide and plasmonic lens for THz isolator and circulator. Moreover, a real-time quantitative THz microfluidic sensing based on photonic crystal pillar array is introduced by experimental results. These THz functional subwavelength devices exhibit great promising potential in THz application systems.