An asymmetric transmission magnetic tunable subwavelength slow light waveguide

Abstract

The application discloses an asymmetric transmission magnetic adjustable subwavelength slow light waveguide, which comprises a photonic crystal medium column array, a metal plate waveguide, wave-absorbing material and a metal electric conductor; the photonic crystal medium column array is a two-dimensional triangular lattice structure, one side of the photonic crystal medium column array is the metal electric conductor, and the other three sides are the wave-absorbing material. Unlike the one-way transmission of the photonic crystal topological boundary state in the prior art, the slow light system is designed by symmetric coupling of two photonic crystals, and the application provides a new model that only one photonic crystal can realize slow light design; the application only uses two rows of photonic crystals to achieve a subwavelength slow light waveguide; and the electromagnetic wave field distribution propagating in opposite directions in the application is asymmetric, and the inconsistent characteristics of the forward transmission and the backward transmission can be used in the fields of communication and sensor detection. The application has the advantages of low density and expanded magnetic band gap width, and solves the defect that the band gap width of a common slow light system is constrained.

Description

Technical Field

[0001] This invention relates to the field of photonic crystals and optoelectronic devices, and in particular to a subwavelength slow optical waveguide based on the surface states of a magnetic photonic crystal. Background Technology

[0002] Slow light, generally referring to pulsed light waves with group velocities much lower than the speed of light in a vacuum, is a phenomenon often observed in special crystals and superstructures, where energy transfer speeds are significantly slower than those of ordinary light waves. Slow light has many applications, such as enhancing nonlinear effects, creating highly sensitive optical switches, and storing photons.

[0003] The excitation magnetoplasmic resonance frequency of magnetic photonic crystals mainly depends on the applied bias magnetic field and their own saturation magnetization, exhibiting magnetically tunable properties. By adjusting the applied magnetic field, the operating frequency domain of the system can be directly changed, thus creating a wideband slow-light system that is easy to adjust.

[0004] The Mie resonance and Mie bandgap of magnetic photonic crystals realize edge states based on magnetic surface plasmons. The edge states generated in the bandgap above the Mie resonance frequency are characterized by magnetic chirality and are insensitive to boundary defects, exhibiting resistance to backscattering. By utilizing the magnetic chirality edge states generated by magnetic surface plasmons in magnetic photonic crystals, a defect-resistant slow-light system can be designed and implemented.

[0005] Previous slow-light systems relied on the unidirectional transmission characteristics exhibited by the topological boundary states of photonic crystals, employing symmetrical coupling of two photonic crystals to complete the initial design. This invention differs from previous systems, designing a system that achieves the slow-light effect using only a single low-density photonic crystal. Furthermore, addressing the generally constrained bandgap width of current slow-light systems, this invention features the ability to be adjusted using a magnetic field. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to design an asymmetric transmission magnetically tunable subwavelength slow optical waveguide, which has the advantages of breaking through the bandgap width constraint and changing the bandgap frequency by adjusting the applied magnetic field.

[0007] Technical solution: To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A magnetically tunable subwavelength slow-light waveguide for asymmetric transmission includes a photonic crystal dielectric pillar array, a metal plate waveguide, an absorbing material, and a metal conductor. The photonic crystal dielectric pillar array is a two-dimensional triangular lattice structure. Three sides of the photonic crystal dielectric pillar array are absorbing material, and one side is a metal conductor. A point source is located above the center of the region. A gap is left between the photonic crystal dielectric pillar array and the metal conductor on the point source side. Adjacent dielectric pillars in the array are placed close together. The photonic crystal dielectric pillar array, the absorbing material, and the metal conductor are all located between the metal plate waveguide. Under the action of an external magnetic field, the boundary states of the photonic crystal exhibit transmission characteristics with a slow-light effect, and the slow-light indexes of the electromagnetic waves on the left and right sides are different. The performance and frequency range of the slow-light effect can be adjusted by adjusting the external magnetic field.

[0009] Preferably, the photonic crystal dielectric pillar is a cylindrical photonic crystal pillar.

[0010] Preferably, the lattice constant of the photonic crystal dielectric pillar array is equal to the diameter of the cylinder, and this special duty cycle enables the photonic crystal boundary states to exhibit transmission characteristics with a slow light effect.

[0011] Furthermore, as the applied magnetic field strength increases, the bandgap frequency exhibiting the slow light effect rises overall; the greater the magnetic field strength, the greater the frequency of the electromagnetic wave exhibiting the slow light effect.

[0012] Furthermore, the photonic crystal dielectric pillar array uses only two rows of photonic crystal dielectric pillars to achieve the low-density design requirement.

[0013] Beneficial Effects: Compared with existing technologies, the photonic crystal slow waveguide proposed in this invention features unconstrained frequency and bandgap, as well as magnetic tunability. It requires only a single photonic crystal plate, and moreover, this invention achieves subwavelength-level slow waveguide performance using only a low-density photonic crystal array with two rows of magnetic pillars. Unlike the left-right symmetry of previous slow optical systems, the propagation performance and dispersion curves of electromagnetic waves on the left and right sides of this invention are different, resulting in an asymmetrical field distribution of electromagnetic waves propagating in opposite directions. This inconsistent forward and backward propagation characteristic can be applied to fields such as communication and sensor detection. This invention offers advantages such as low density and extended magnetic bandgap width, overcoming the limitation of constrained bandgap width in common slow optical systems. Attached Figure Description

[0014] Figure 1 This is a perspective structural diagram of a three-dimensional model according to an embodiment of the present invention.

[0015] Figure 2 This is a two-dimensional schematic diagram of an embodiment of the present invention.

[0016] Figure 3 This is a schematic diagram of the projected energy band structure when the magnetic field is 500oe in an embodiment of the present invention.

[0017] Figure 4 This is an electric field distribution diagram on the boundary of the photonic crystal in this embodiment of the invention, under the action of an electromagnetic wave with a magnetic field strength of 500oe and a frequency of F = 3.04GHz, and a schematic diagram of the dispersion curves of ω and κ on the left and right sides in two propagation directions after fast Fourier transform. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0019] like Figure 1 As shown, this embodiment of the invention discloses an asymmetric transmission magnetically tunable subwavelength slow optical waveguide, comprising a photonic crystal dielectric pillar array 1, a metal plate waveguide 2, an absorbing material 3, and a metal conductor 4; the photonic crystal dielectric pillar array is a two-dimensional triangular lattice structure, with one side of the photonic crystal dielectric pillar array being the metal conductor 4 and the other three sides being the absorbing material 3; the point source is located above the centerline of the photonic crystal array, and the photonic crystal dielectric pillar array 1, the absorbing material 3, and the metal conductor 4 are all located between two metal plate waveguides 2. Figure 1 (This is a perspective view, so only the bottom metal plate is shown.) There is a gap between the photonic crystal dielectric pillar array 1 and the metal conductor 4. The gap spacing is determined by the flatness of the dispersion curve of the slow optical waveguide in the test frequency band. In this example, the gap spacing W = 30 mm.

[0020] This invention is based on a two-dimensional triangular lattice dielectric pillar array structure, in which dielectric pillars are arranged at equal intervals along the x-axis and y-axis. Due to the spatial periodic distribution of the dielectric constant of the photonic crystal, there is a strong dispersion effect at the edge of the photonic bandgap. Therefore, slow light can be obtained by using a two-dimensional photonic crystal waveguide.

[0021] In a specific example of this invention, the photonic crystal dielectric pillar array is composed of periodically arranged yttrium iron garnet (YIG) cylinders with a gyromagnetic ratio of 1750 and a relative permittivity of 15.26 (other ferrite materials can also be used). The radius of the ferrite cylinders is r = 4 mm, the height is h = 10 mm, and the lattice constant of the array is a = 8 mm. The quasi-two-dimensional structure composed of the triangular lattice is placed in parallel plate waveguides composed of two aluminum plates of thickness D1, where D1 is 1 mm to 2 mm. The lattice is surrounded by a wave-absorbing material and a metallic conductor of thickness D, where D is 10 mm to 20 mm.

[0022] In this embodiment of the invention, when the lattice constant is equal to the diameter of the cylinder, a specific duty cycle causes the boundary states of the photonic crystal to exhibit slow-light transmission characteristics. The lattice constant and the size of the cylinder do not affect the performance of the slow-light effect; only the specific duty cycle where the lattice constant equals the diameter needs to be satisfied. By measuring the electric field values ​​at various points along the transmission path within a certain frequency bandwidth, the dispersion curves of ω and κ can be obtained through a Fast Fourier Transform. The slow-light index can be calculated from the dispersion curves, achieving the slow-light effect. Furthermore, the performance and frequency range of the slow-light effect can be adjusted by regulating the applied magnetic field.

[0023] In this embodiment of the invention, the projected energy band of a photonic crystal when a magnetic field of 500e is applied is measured using the multiple scattering method (e.g., Figure 3 As shown in the diagram, the projected band structure reveals a typical slow light effect in the photonic crystal boundary states within the 2.98-3.2 GHz frequency range.

[0024] In this embodiment of the invention, the electric field value at each point is detected by setting several equally spaced measurement points along the electromagnetic wave transmission path. Then, a fast Fourier transform is performed using a signal detector to obtain the dispersion curves of ω and κ. The slow light indexes for both the left and right propagation directions can be calculated, both meeting the requirements for slow light. Furthermore, the electromagnetic wave propagation performance differs between the left and right sides; that is, the dispersion curves and slow light indexes are different, indicating asymmetry.

[0025] Figure 4 (a) shows the electric field distribution at a frequency of 3.04 GHz when a magnetic field of 500oe is applied.

[0026] Figure 4 In the diagrams (b) and (c), the dispersion curves of electromagnetic waves ω and κ on the left and right transmission paths are shown when a magnetic field of 500oe is applied. The slow light indexes are calculated to be 116.1 and 109.6, respectively.

[0027] In this embodiment of the invention, by changing the magnetic field and observing the electric field values ​​at different frequencies, electric field diagrams exhibiting the slow-light effect and dispersion curves of ω and κ are obtained for different magnetic field strengths. The slow-light index is calculated using group velocity. Furthermore, it is found that the bandgap frequency producing the slow-light effect increases with increasing magnetic field strength. This demonstrates that the invention has magnetically tunable functionality.

[0028] The table below illustrates the slow light index for two transmission directions with magnetic field strengths ranging from approximately 200oe to 800oe.

[0029] Table 1 Results of the Slow Light Index

[0030]

[0031] In summary, the photonic crystal slow waveguide implementation scheme disclosed in this invention is not only different from the previous design that uses two photonic crystals for coupling, but can be realized with only a single photonic crystal array. It also has the characteristics of asymmetric transmission and magnetic tunability, breaking through the constraints on the bandgap width of previous slow optical systems. Subwavelength-level slow waveguides can be realized with only a low-density photonic crystal array of two rows of magnetic pillars.

Claims

1. A magnetically tunable subwavelength slow optical waveguide with asymmetric transmission, characterized in that, The system comprises a photonic crystal dielectric pillar array, a metal plate waveguide, an absorbing material, and a metal conductor. The photonic crystal dielectric pillar array is a two-dimensional triangular lattice structure. Three sides of the photonic crystal dielectric pillar array are absorbing material, and one side is a metal conductor. The point source is located above the central region. A gap is left between the photonic crystal dielectric pillar array and the metal conductor on the point source side. Adjacent dielectric pillars in the array are placed close together. The photonic crystal dielectric pillar array, the absorbing material, and the metal conductor are all located between the metal plate waveguide. Under the action of an external magnetic field, the boundary states of the photonic crystal exhibit transmission characteristics with a slow light effect, and the slow light indexes of the electromagnetic waves on the left and right sides are different. The performance and frequency range of the slow light effect can be adjusted by adjusting the external magnetic field. The photonic crystal dielectric pillars are made of ferrite material.

2. The asymmetric transmission magnetically tunable subwavelength slow optical waveguide according to claim 1, characterized in that, The photonic crystal dielectric pillar is made of yttrium iron garnet (YIG) material.

3. The asymmetric transmission magnetically tunable subwavelength slow optical waveguide according to claim 1, characterized in that, The photonic crystal dielectric pillar is a cylindrical photonic crystal pillar.

4. The asymmetric transmission magnetically tunable subwavelength slow optical waveguide according to claim 3, characterized in that, The lattice constant of the photonic crystal medium pillar array is equal to the diameter of the cylinder.

5. The asymmetric transmission magnetically tunable subwavelength slow optical waveguide according to claim 1, characterized in that, As the applied magnetic field strength increases, the bandgap frequency exhibiting the slow light effect rises overall; the stronger the magnetic field, the higher the frequency of the electromagnetic wave exhibiting the slow light effect.

6. The asymmetric transmission magnetically tunable subwavelength slow optical waveguide according to claim 1, characterized in that, The photonic crystal dielectric pillar array uses only two rows of photonic crystal dielectric pillars to achieve the low-density design requirement.

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