Topological insulator grating structure for enhancing Faraday rotation angle

Abstract

The invention discloses a topological insulator grating structure for enhancing a Faraday rotation angle, and aims to improve the unit Faraday rotation angle. The topological insulator grating structure for enhancing the Faraday rotation angle comprises a grating and a magneto-optical material, the grating is formed on the surface of the magneto-optical material, the grating is a topological insulator material, the chemical formula of the topological insulator material is Bi < x > Sb < 2-x > Te < 3 >, x is equal to 0-2, and the magneto-optical material is bismuth ion doped yttrium iron garnet or cerium ion doped yttrium iron garnet. The grating structure of the topological insulator material shows an extremely high Faraday effect enhancement effect in the visible light and near-infrared range, the unit Faraday rotation angle of the magneto-optical material is increased, and compared with a plasma grating made of a metal material, back scattering of photons can be avoided, additional scattered light is reduced, light loss is reduced, and the photoelectric conversion efficiency is improved. And the requirement of a miniaturized and integrated optical isolator on a magneto-optical material can be met.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of Faraday magneto-optical single crystal thin films and devices. Specifically, it relates to a topological insulator grating structure for enhancing the magneto-optical effect. Background Art

[0002] Optical isolators have important application values in fields such as telecommunications and sensing due to their key roles in signal protection, system stability, and security. As the core component of optical isolators, magneto-optical materials have gradually become the focus of current research in the magneto-optical field. Among them, yttrium iron garnet Y3Fe5O 12 (YIG) has the Faraday effect and exhibits an extremely low Gilbert damping coefficient (10 -4 ), and is an ideal magneto-optical material. However, the unit Faraday rotation angle of YIG materials is relatively small and cannot play a role in the context of miniaturized and integrated applications. By doping with Bi 3+ , the Faraday rotation angle in the visible and infrared light bands can be effectively increased to make up for the gap in magneto-optical materials. However, increasing the unit Faraday rotation angle by using doped ions is restricted by factors such as lattice mismatch and growth technology.

[0003] Currently, constructing heavy metal structures (such as lattices, gratings, etc.) on magneto-optical materials to realize magnetoplasmonic photonic crystals for enhancing the magneto-optical effect has become a research hotspot. Magnetoplasmonic photonic crystals generate the excitation of local surface plasmons through the interaction between plasmon polaritons and photonic crystal structures, significantly enhancing the magneto-optical effect of materials. Usually, metal materials are used to construct plasmonic photonic crystals for enhancing the magneto-optical effect. However, when photons pass through metal structures, they inevitably generate backscattering with metal atomic nuclei, generating additional scattered light and increasing optical loss. In order to overcome the problem that it is difficult to increase the unit Faraday rotation angle of magneto-optical materials and meet the requirements of miniaturization of optical isolation devices, materials and structures that can greatly enhance the Faraday effect have become problems that need to be solved urgently. Summary of the Invention

[0004] The problem solved by the present invention is to increase the unit Faraday rotation angle to meet the application of magneto-optical materials in miniaturized optical isolation devices, and to provide a topological insulator grating structure for enhancing the Faraday rotation angle.

[0005] The topological insulator grating structure for enhancing the Faraday rotation angle of the present invention includes a grating and a magneto-optical material. A grating is formed on the surface of the magneto-optical material. The grating is a topological insulator material, and the chemical formula of the topological insulator material is Bi x Sb 2-x Te3, x = 0 - 2;

[0006] The magneto-optical material is yttrium iron garnet doped with bismuth ions or yttrium iron garnet doped with cerium ions. The chemical formula of the yttrium iron garnet doped with bismuth ions is Bi m A 3-m Fe 5-n B n O 12 , and the chemical formula of the yttrium iron garnet doped with cerium ions is Ce m A 3-m Fe 5-n B n O 12 , where m = 0.1 - 3 and n = 1 - 4.5; element A represents samarium (Sm), neodymium (Nd), lanthanum (La), terbium (Tb), lutetium (Lu), europium (Eu), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) or ytterbium (Yb); element B represents indium (In), chromium (Cr), aluminum (Al), gallium (Ga), cobalt (Co), scandium (Sc), manganese (Mn), zinc (Zn), titanium (Ti), tin (Sn), germanium (Ge) or zirconium (Zr).

[0007] The topological insulator grating structure for enhancing the Faraday rotation angle in the present invention can enhance the Faraday effect and can be used as an optical isolator, a Faraday rotator, a magneto-optical modulator or a silicon-based integrated optical device, etc.

[0008] The topological insulator in the topological insulator grating structure for enhancing the Faraday rotation angle in the present invention is a quantum material. Strong spin-orbit coupling and time-reversal symmetry ensure that the electron spins in the topological surface state are locked with each other in direction. When combined with a ferromagnetic material, the interfacial exchange coupling energy can induce a magnetic order in the topological insulator through magnetic proximity interaction and break the time-reversal symmetry. The magnetic proximity interaction existing in the topological insulator enables the topological surface state to affect the interfacial magnetic anisotropy of the magnetic material.

[0009] The present invention uses a topological insulator as the main material of the grating, and combining with a magneto-optical material to form a Faraday effect enhancement structure has the following advantages:

[0010] 1. The grating structure of the topological insulator material shows an extremely high Faraday effect enhancement effect in the visible light and near-infrared ranges. For example, at 500 nm, the Faraday rotation angle of a single-layer thin film is increased by more than 2 times.

[0011] 2. The topological properties of the topological insulator are relatively robust due to the protection of time-reversal symmetry. Even under the action of an external magnetic field or pressure, its topologically protected Dirac cone surface state remains stable. The topological insulator structure has relatively strong stability and is very stable when exposed to an environment of oxygen and water.

[0012] 3. Compared with the plasma grating of metal materials, the present invention can also avoid the backscattering of photons, reduce the additional scattered light, and reduce the optical loss. Description of the Drawings

[0013] Figure 1 Schematic diagram of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1, 1 - grating, 2 - magneto-optical material, 3 - incident light, 4 - outgoing light;

[0014] Figure 2 SEM image of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1;

[0015] Figure 3 Schematic diagram of the Faraday effect of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1;

[0016] Figure 4 Faraday loop diagram at a wavelength of 500 nm of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1;

[0017] Figure 5 Faraday loop diagram at a wavelength of 532 nm of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1;

[0018] Figure 6 Faraday loop diagram at a wavelength of 633 nm of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1;

[0019] Figure 7 Faraday rotation angle diagram of the grating structure for enhancing the magneto-optical effect using a topological insulator in Example 1 in the wavelength band of 410 - 950 nm. Detailed Implementation Manner

[0020] Detailed Implementation Manner 1: The topological insulator grating structure for enhancing the Faraday rotation angle in this implementation manner includes a grating and a magneto-optical material. A grating 1 is formed on the surface of the magneto-optical material 2. The grating 1 is a topological insulator material, and the chemical formula of the topological insulator material is Bi x Sb 2-x Te3, x = 0 - 2;

[0021] The magneto-optical material 2 is yttrium iron garnet doped with bismuth ions or yttrium iron garnet doped with cerium ions. The chemical formula of the yttrium iron garnet doped with bismuth ions is Bi m A 3-m Fe 5-n B n O 12 , and the chemical formula of the yttrium iron garnet doped with cerium ions is Ce m A 3-m Fe 5-n Bn O 12 , where m = 0.1 - 3, n = 1 - 4.5; element A represents samarium (Sm), neodymium (Nd), lanthanum (La), terbium (Tb), lutetium (Lu), europium (Eu), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) or ytterbium (Yb); element B represents indium (In), chromium (Cr), aluminum (Al), gallium (Ga), cobalt (Co), scandium (Sc), manganese (Mn), zinc (Zn), titanium (Ti), tin (Sn), germanium (Ge) or zirconium (Zr).

[0022] In this embodiment, the topological insulator grating enhances the Faraday effect because the incident light exhibits a waveguide resonance mode of TM wave under the topological insulator grating, and the linearly polarized light undergoes multiple reflections between the topological insulator grating and the magneto-optical material, and each reflection causes an increase in the Faraday rotation angle.

[0023] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that grating 1 is etched from a topological insulator thin film material.

[0024] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the height range of each grating in grating 1 is 10 -3 -200 μm, and the grating constant range is 0.35 - 3 μm.

[0025] Specific Embodiment 4: The difference between this embodiment and Specific Embodiment 3 is that the height range of each grating in grating 1 is 5 - 20 nm, and the grating constant range is 0.35 - 0.6 μm.

[0026] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the thickness of the magneto-optical material 2 is 50 - 200 nm.

[0027] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that the topological insulator material is Bi 0.5 Sb 1.5 Te3 or Bi2Se3.

[0028] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that the topological insulator thin film material is prepared by a pulsed laser deposition process.

[0029] Specific Embodiment 8: The difference between this embodiment and Specific Embodiment 7 is that Bi 0.5 Sb 1.5A Te3 target or a Bi2Se3 target is used. The laser energy is controlled to be 150 - 350 mJ, the pulsed laser frequency is 1 - 10 Hz, and the growth temperature is 350 - 550 °C. Pulsed laser deposition is carried out to obtain a topological insulator thin film material.

[0030] Specific Embodiment Nine: The difference between this embodiment and Specific Embodiment Eight is that the pulsed laser deposition process is carried out under an inert gas condition.

[0031] Specific Embodiment Ten: The difference between this embodiment and any one of Specific Embodiments One to Nine is that the magneto - optical material 2 is Bi1Y2Fe5O 12 、Bi1Y2Fe5O 12 or Y3Fe5O 12 .

[0032] Example One: The topological insulator grating structure for enhancing the Faraday rotation angle in this example includes a grating and a magneto - optical material. A grating 1 is formed on the surface of the magneto - optical material 2. The grating 1 is a topological insulator material, and the chemical formula of the topological insulator material is Bi 0.5 Sb 1.5 Te3 (BST), which is prepared by a pulsed laser deposition process. A target with the chemical formula Bi 0.5 Sb 1.5 Te3 is used. The laser energy is controlled to be 200 mJ, the pulsed laser frequency is 1 Hz, the growth temperature is 400 °C, the target - substrate distance is 3 cm, and the argon gas pressure used is 10 Pa. A BST thin film is deposited, and then the BST thin film is etched into a grating by using a FIB focused ion beam processing technology. The height of each grating is 5 nm, the width of the grating is 150 nm, and the grating constant is 450 nm;

[0033] The magneto - optical material 2 is a bismuth - doped yttrium iron garnet thin film, and the chemical formula of the bismuth - doped yttrium iron garnet is Bi1Y2Fe5O 12 (Bi:YIG). This thin film is deposited on an SGGG substrate by a pulsed laser deposition process, and the thickness is 30 nm.

[0034] Figures 4 - 7 In, the black line represents the magneto - optical effect of the single - layer Bi:YIG thin film; the red line represents the magneto - optical effect of the Bi:YIG thin film when the BST thin film is prepared and the grating structure is not constructed; the blue line represents the magneto - optical effect of the Bi:YIG thin film when the BST grating structure is constructed. Comparing the magneto - optical effects in the three cases can prove that it is the grating structure of BST rather than the BST thin film material that enhances the magneto - optical effect of Bi:YIG.

[0035] Figures 4 - 7The effects of BST thin films and BST gratings on the Faraday rotation angle of Bi:YIG thin films under linearly polarized light at wavelengths of 500, 532, and 633 nm are listed. For example Figure 5 , the black line represents the Faraday loop of single-layer Bi:YIG at a wavelength of 532 nm. When an external saturated magnetic field is applied, the unit Faraday rotation angle is approximately 3×10 4 deg / cm. A layer of BST thin film is prepared on Bi:YIG, which completely covers the Bi:YIG thin film. When an external saturated magnetic field is applied, the Faraday rotation angle decreases to 1.9×10 4 deg / cm. The BST thin film is etched into a grating structure. When an external saturated magnetic field is applied, the Faraday rotation angle increases to approximately 5×10 4 deg / cm. Therefore Figures 4 - 7 it is proved that the grating structure design of BST enhances the Faraday effect.

[0036] In this embodiment, the enhancement of the magneto-optical properties of the Bi:YIG thin film by the topological insulator is closely related to the relationship between the interface effect of the BST grating and the Bi:YIG and the wavelength. Incident light of different wavelengths will cause changes in the energy band structure at the interface, thereby affecting the magneto-optical properties. In addition, the magneto-optical enhancement effect of the Bi:YIG / BST grating also depends on the transmission mode of the incident light. Another reason for the enhancement of the Faraday effect is the generation of the waveguide resonance mode of the TM wave under the BST grating, and the multiple reflections of the linearly polarized light between the BST and the Bi:YIG thin films. Each reflection promotes the increase of the Faraday spin angle. Therefore, when the linearly polarized light passes through the Bi:YIG / BST grating, the polarization plane deflects greatly.

[0037] Example 2: The difference between this example and Example 1 is that the grating height of the topological insulator material Bi 0.5 Sb 1.5 Te3 is 10 nm, the grating width is 135 nm, and the grating constant is 500 nm; the thickness of the magneto-optical material Bi1Y2Fe5O 12 is 60 nm.

[0038] Example 3: The difference between this example and Example 1 is that the topological insulator material used is Bi2Se3, which is prepared by pulsed laser deposition technology. The Bi2Se3 thin film is etched into a grating with a grating constant of 500 nm and a height of 5 nm by using FIB focused ion beam processing technology. The magneto-optical material used is a Y3Fe5O thin film with a thickness of 100 nm prepared by pulsed laser deposition technology. 12 film.

[0039] Example 4: The difference between this example and Example 3 is that the grating constant of the topological insulator material Bi2Se3 is 450 nm, the height is 10 nm, and Y3Fe5O12 The thickness of the thin film is 100 nm.

[0040] Example 5: The difference between this example and Example 3 is that the grating constant of the topological insulator material Bi2Se3 is 350 nm, the height is 10 nm, and Y3Fe5O 12 The thickness of the thin film is 150 nm.

Claims

1. A topological insulator grating structure with enhanced Faraday rotation angle, characterized in that The topological insulator grating structure for enhancing the Faraday rotation angle comprises a grating (1) and a magneto-optical material (2). The grating (1) is formed on the surface of the magneto-optical material (2). The material of the grating (1) is a topological insulator material. The chemical formula of the topological insulator material is Bi x Sb 2-x Te3, x = 0-2; The magneto-optical material (2) is yttrium iron garnet doped with bismuth ions or yttrium iron garnet doped with cerium ions, and the chemical formula of the yttrium iron garnet doped with bismuth ions is Bi m A 3-m Fe 5-n B n O 12 The chemical formula of the cerium ion-doped yttrium iron garnet is Ce m A 3-m Fe 5-n B n O 12 , wherein m=0.1-3, n=1-4.5; element A represents samarium, neodymium, lanthanum, terbium, lutetium, europium, gadolinium, dysprosium, holmium, erbium, thulium or ytterbium; element B represents indium, chromium, aluminum, gallium, cobalt, scandium, manganese, zinc, titanium, tin, germanium or zirconium.

2. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 1, characterized in that The grating (1) is formed by etching a topological insulator thin film material.

3. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 1, characterized in that The height range of each grating in grating (1) is 10 -3 -200μm, and the grating constant ranges from 0.35-3μm.

4. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 3, characterized in that The height of each grating in the grating (1) is in the range of 5-20 nm, and the grating constant is in the range of 0.35-0.6 μm.

5. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 1, characterized in that The thickness of the magneto-optical material (2) is 50 to 200 nm.

6. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 1, characterized in that The topological insulator material is Bi 0.5 Sb 1.5 Te3 or Bi2Se3.

7. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 2, characterized in that Topological insulator thin film materials are prepared by pulsed laser deposition process.

8. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 2, characterized in that Adopt Bi 0.5 Sb 1.5 Te3 target or Bi2Se3 target, control the laser energy to 150-350mJ, the pulse laser frequency to 1-10Hz, and the growth temperature to 350-550℃ to perform pulse laser deposition to obtain topological insulator thin film material.

9. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 8, characterized in that The pulsed laser deposition process is carried out under inert gas conditions.

10. The topological insulator grating structure with enhanced Faraday rotation angle according to claim 1, characterized in that The magneto-optical material (2) is Bi1Y2Fe5O 12 、Bi1Y2Fe5O 12 or Y3Fe5O 12 .

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