Nonreciprocal transmission of EM waves by a chain of ferrite rods

Abstract

Nonreciprocal optical effects have become a popular topic of research because of their wide range of applications, such as optical isolators and optical diodes for on-chip applications. With the rapid advances of meta-materials and photonic crystals, many new nonreciprocal phenomena were found and associated mechanisms were proposed over the past years. For example, one-way electromagnetic space wave can be realized by means of two-dimensional magnetic photonic crystals, which is due to simultaneously breaking the time-reversal and parity symmetries of the magnetic photonic crystals designed [1]. Similar phenomena was also found in a chain of high-refractive-index dielectric nanorods when wave beam passing through the chain. The mechanism is believed to be due to the symmetry of resonant modes of different angular momentum channels in the dielectric nanoparticles [2]. In this work, we studied the spatial non-reciprocal phenomenon induced by a chain of ferrite rods from the point of view of higher order diffraction of gratings. When incident waves obliquely imping on rod chain in a bias magnetic field, we observed the total reflection at certain incident angles, but total transmission with negative deflection when the direction of bias magnetic field is reversed. We found the non-reciprocal transmission was associated with the diffraction orders of rod chain; the total refraction comes from the 0 order diffraction, while the total transmission was mainly caused by the −1 order diffraction. Other higher order diffraction could be ignored because of their very small amplitude. It was believed that the photon eigenfrequencies of a circular gyromagnetic cylinder experience a splitting that is proportional to the photonic angular momentum density at the cylinder surface is responsible for the non-reciprocal transmission. These photonic angular momentum states (PAMSs) give some unusual decoupling properties, which could be useful for designing novel photonic devices [3, 4] Experimentally, we designed and fabricated a rod chain by strontium ferrite, and the non-reciprocal transmission and negative deflection were observed in experiments by field mapping method.