Self-biased magneto-optical non-reciprocal metasurface device

Abstract

The disclosure provides a self-biased magneto-optical non-reciprocal metasurface device. The device includes substrate layer and a sub-wavelength structure layer. The substrate layer is a material layer with a refractive index of 1 to 5 in a microwave frequency band. The sub-wavelength structure layer includes a plurality of square columnar elements arranged in a matrix period with equal period in row and column directions. The square columnar elements include magneto-optical material. The adjustment of phase and amplitude of a circularly polarized electromagnetic wave is achieved by changing the length, width and height of the square columnar elements, and thus the device attains a desired isolation and insertion loss at a center frequency f.sub.0. The parameters of the magneto-optical material are: coercivity Hc≥1000 A/m; remanence Br≥1 kGs; a voigt parameter of a permittivity tensor or permeability tensor in a working frequency band≥0.01.

Claims

1. A device, comprising: a substrate layer; and a sub-wavelength structure layer; wherein: the substrate layer is a material layer with a refractive index of 1 to 5 in a microwave frequency band; the sub-wavelength structure layer comprises a plurality of square columnar elements arranged in a matrix period with equal period in row and column directions; the square columnar elements comprise a magneto-optical material; adjustment of phase and amplitude of a circularly polarized electromagnetic wave is achieved by changing the length, width and height of the square columnar elements, and thus the device attains a desired isolation and insertion loss at a center frequency f.sub.0; parameters of the magneto-optical material are: coercivity Hc≥1000 A/m; remanence Br≥1 kGs; a voigt parameter of a permittivity tensor or permeability tensor in a working frequency band≥0.01; self-biased work state is achieved by utilizing the remanence, and a magneto-optical effect provides non-reciprocity; a thickness of the substrate layer is L, the square columnar elements have a height of h, a length of w.sub.1 and a width of w.sub.2; the square columnar elements are arranged to form a matrix array with equal row and column periods p; the device size is D.sub.1×D.sub.2; the device responds to circularly polarized incident electromagnetic waves; dimensions of the device satisfy the relationship: w.sub.1≤10 mm, w.sub.2=0.75 w.sub.1−1.25 w.sub.1, h=w.sub.1−3 w.sub.1, p=3 w.sub.1−4 w.sub.1, L=1/2 w.sub.1−2 w.sub.1, D.sub.1=10λ.sub.0−15λ.sub.0, D.sub.2=10λ.sub.0−15λ.sub.0, λ.sub.0=c/f.sub.0, and c is a speed of light in vacuum; and a thickness of the device is sub-wavelength; the device is magnetized only once; and a remanence direction is parallel to an incident electromagnetic wave direction.

2. The device of claim 1, wherein the magneto-optical material comprises ferrite or Yttrium iron garnet (YIG).

3. The device of claim 1, wherein the substrate layer comprises polytetrafluoroethylene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an intensity-type non-reciprocal metasurface device working under circularly polarized electromagnetic waves; and

(2) FIG. 2 shows the forward and reverse transmission spectra of an intensity-type non-reciprocal metasurface device working under circularly polarized electromagnetic waves.

DETAILED DESCRIPTION

(3) To further illustrate the disclosure, embodiments detailing a self-biased magneto-optical non-reciprocal metasurface device are described below. It should be noted that the following embodiments are intended to describe and not limit disclosure.

(4) As described in the background section, the feasible solutions for realizing non-reciprocal metasurfaces mainly include nonlinearity, time-modulation and magneto-optical effects. Non-reciprocal devices based on nonlinearity require very high input power and have dynamic reciprocity problems; non-reciprocal devices based on time-modulation systems have large power consumption, narrow bandwidth and relatively large device sizes; non-reciprocal devices based on magneto-optical effects require a large magnet to provide a magnetic field and are difficult to achieve in the optical band. The advantages of the magneto-optical effect are broadband, low power consumption, and stability. Therefore, the realization of a self-biased magneto-optical non-reciprocal metasurface device is of great significance.

(5) In this example, a self-biased intensity-type metasurface device operates under circularly polarized electromagnetic waves.

(6) The self-biased intensity-type metasurface device includes a substrate layer with a thickness of L; the elements have a height h, length w.sub.1 and width w.sub.2, and a period p, and the entire device size is D1×D2. The device responds to circularly polarized incident electromagnetic waves. The direction of residual magnetization is parallel to the incident direction of electromagnetic waves. The adjustment of phase and amplitude of the circularly polarized electromagnetic wave is achieved by changing the length, width and height of the element, and thus the device attains the desired isolation and insertion loss at the center frequency f.sub.0.

(7) The hexagonal barium ferrite material with high coercivity and magneto-optical effect in the microwave frequency band is used as the elements, and the remanence is used to realize self-bias. At the same time, the square column with high direction ratio is used as the form of elements for circularly polarized electromagnetic wave. By designing the Mie resonator unit with sub-wavelength periodic structure, the unidirectional transmission function of circularly polarized electromagnetic wave is realized.

(8) In certain embodiments, the circularly polarization intensity-type device comprises a polytetrafluoroethylene (PTFE) substrate layer with a thickness of 2 mm; and the matrix array comprises square columnar hexagonal barium ferrite material with a height of h=6 mm, a width of w.sub.1=w.sub.2=3 mm, and a period of p=10 mm. The device size is 20×20 cm. The device responds to circularly polarized incident electromagnetic waves. The schematic structure of the device is shown in FIG. 1. The direction of residual magnetization is parallel to the incident direction of electromagnetic waves, that is, along the height direction of the hexagonal barium ferrite material.

(9) Testing and analysis of the device prepared in this Example: the function of unidirectional transmission with isolation of 9.18 dB and insertion loss of 1.35 dB at 15.67 GHz is observed, as shown in FIG. 2.

(10) In summary, when electromagnetic waves are incident on the magnetic elements with remanence of the disclosure, due to the non-reciprocity of the materials, the amplitude and phase of the forward and the reverse electromagnetic waves are different. Moreover, only one magnetization is required, and dispenses with continuous external magnetic field. The entire device with sub-wavelength dimension is conducive to the miniaturization and integration of the device. This device has important application prospects in radar shielding (unidirectional transmission), free space isolators, non-reciprocal lenses, non-reciprocal holographic imaging and other fields.

(11) It would be obvious to those skilled in the arts that changes and modifications may be made; therefore, the aim of the appended claims is to cover all such changes and modifications.