Linear-polarized terahertz isolator by breaking the gyro-mirror symmetry in cascaded magneto-optical metagrating

To realize nonreciprocal transmission, it is necessary to break the time-reversal symmetry of the transmission system, but it is very challenging to keep the linear polarized (LP) input and output unchanged in the free space transmission system. Magnetized semiconductor InSb can realize terahertz (THz) nonreciprocal transmission for the two conjugated photonic spin states, but it cannot realize efficient one-way transmission of LP state due to gyro-mirror symmetry. In this work, by introducing a pair of orthogonal uniaxial anisotropies from the meta-gratings on both sides of InSb, both the gyro-mirror and time-reversal symmetries are broken for the LP state, thus making this cascaded grating–InSb–grating structure serves as a high-performance isolator for the LP light. The experiment results indicate isolation of 50 dB at 0.4 THz for the same LP input and output under a weak biased magnetic field of 0.17 T. Moreover, we further illustrate the factors affecting the isolation bandwidth of the device, also demonstrated another broadband structure with the 10 dB isolation bandwidth from 0.2–0.7 THz, and the relative bandwidth achieves 110%. The mechanisms of THz nonreciprocal transmission and polarization manipulation proposed in this work will contribute to the development of efficient THz magneto-optical devices.

Magnetically Induced Transparency in Media with Helical Dichroic Structure

In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific properties of reflection, transmission, absorption, rotation, ellipticity spectra and also the spectra of ellipticity and azimuth of eigen polarization were investigated. The existence of a tunable linear and nonreciprocal transmission band was shown.

Nonreciprocal transmission in a parity-time symmetry system with two types of defects

In this paper, we have studied two different mechanisms of nonreciprocal and asymmetric transmission in the one-dimensional asymmetric optical system composed of parity-time (PT) and magneto-optical materials with different defect layers. It is shown that there are three pairs of nonreciprocal dispersive curves with the perfect transmission in the three different band gaps, when the defect layer is filled with normal material. When the defect layer is filled with magneto-optical material, the transmittivity of two nonreciprocal frequencies can be modulated by the magnitude and direction of the defect layer’s external magnetic field and appears to be asymmetric nonreciprocal transmission. One-way frequency corresponding to one direction has extraordinary transmission, and the other one-way frequency corresponding to the opposite direction is suppressed. When the defect layer is filled with loss or gain material, the transmittivity of two nonreciprocal frequencies can be amplificated or attenuated simultaneously, respectively. The nonreciprocal propagation is originated from the resonant modes in the system due to the defect layer, and the nonreciprocal and asymmetric transmission is determined by the broken PT system due to magneto-optical and gain/loss material in the defect layer. Such controllable and asymmetric nonreciprocal propagation in the composite system may have broad potential applications in nonreciprocal communication and integration devices.