Yttrium barium copper oxide photonic crystal filter and preparation method thereof

Abstract

The application discloses a yttrium barium copper oxide photonic crystal filter and a preparation method thereof. The photonic crystal filter is composed of a periodic asymmetric triangular hole and yttrium barium copper oxide (YBa2Cu3O(7-x)) superconducting material, and the lattice constant is 700 nm, and the side length of each triangular air hole is 210 nm. The photonic crystal filter can realize the opening of a photonic band gap by rotating a triangular hole by 40 degrees, and has a photonic band gap with a width of about 10 THz appearing in 1152-1162 THz and a photonic band gap with a width of about 10 THz appearing in 1020-1030 THz. The photonic crystal adopts a laser pulse deposition method to grow a yttrium barium copper oxide film on a MgO single crystal substrate, and then the yttrium barium copper oxide film is processed into a periodic porous nanostructure composed of a triangular hole and yttrium barium copper oxide, that is, a triangular hole yttrium barium copper oxide photonic crystal filter. The preparation process of the photonic crystal filter reported in the application is simple and easy to control.

Description

Technical Field

[0001] This invention belongs to the field of photonic crystal fabrication technology, and relates to a yttrium barium copper oxide photonic crystal filter and its fabrication method. Background Technology

[0002] A photonic crystal is an optical nanostructure composed of a periodic dielectric structure. It blocks the propagation of light at specific frequencies; this is known as the photonic bandgap, which is related to the crystal's geometry, duty cycle, and the difference in dielectric constant (refractive index) between the dielectric materials. The less symmetric the crystal's geometry, the more likely a photonic bandgap will appear; similarly, a greater difference in dielectric constant between the dielectric materials also increases the likelihood of a photonic bandgap. Photonic bandgaps can be classified as incomplete or complete. An incomplete photonic bandgap means that light waves of certain frequencies propagate only in specific directions, while propagation in other directions is prohibited. A complete photonic bandgap means that light waves within a specific range are prohibited from propagating regardless of their polarization or propagation direction.

[0003] Yttrium barium copper oxide (YBO) is a crystalline compound with a critical temperature around 92 K, serving as a high-temperature superconducting material. Compared to conventional metals, high-temperature superconductors offer advantages such as low dielectric constant, negligible dispersion, and a large bandgap. Because its dielectric constant is influenced by temperature, frequency, and magnetic field, high-temperature superconductors exhibit tunable bandgap characteristics. Furthermore, high-temperature superconducting YBO photonic crystals possess a wider bandgap, which can be modulated by utilizing the internal structural asymmetry of the crystal. By selecting a triangular aperture and altering its rotation angle, the symmetry of the YBO photonic crystal can be broken, effectively controlling the opening and closing of the photonic bandgap.

[0004] Optical filters are one of the fundamental components of photonics technology, with wide applications in fiber optic sensing, optical communication, and optical information processing. Photonic crystals possess a photonic frequency bandgap; photons with frequencies within the bandgap cannot exist within a photonic crystal. Therefore, a photonic crystal is a natural and ideal band-stop filter. By processing yttrium barium copper oxide (YTO) material into photonic crystals, the low dielectric constant of YTO creates a significant dielectric difference with air, resulting in a wider photonic bandgap and achieving broadband filter characteristics. Furthermore, the tunability of YTO allows for control of the bandgap position, enabling the creation of excellent photonic crystal filters to meet diverse needs. Summary of the Invention

[0005] (I) Purpose of the Invention

[0006] The purpose of this invention is to provide a yttrium barium copper oxide photonic crystal filter and its fabrication method, which forms a wider photonic bandgap and achieves broadband filter characteristics. By utilizing the tunability of yttrium barium copper oxide, the bandgap position can be controlled to create excellent photonic crystal filters that meet different requirements.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention provides a yttrium barium copper oxide photonic crystal filter, which is composed of periodic asymmetric triangular holes and yttrium barium copper oxide superconducting material. Each periodic structure forms a basic photonic crystal unit, and each basic photonic crystal unit structure contains four triangular holes.

[0009] The lattice constant of the basic unit of the photonic crystal is 700 nm, and the side length of each triangular hole is 210 nm.

[0010] In each basic unit of the photonic crystal, one of the triangles is rotated 40°, resulting in a photonic bandgap with a width of approximately 10 THz in the range of 1152–1162 THz and another photonic bandgap with a width of approximately 10 THz in the range of 1020–1030 THz.

[0011] This invention also provides a method for fabricating a yttrium barium copper oxide photonic crystal filter, which includes the following steps:

[0012] S1: Laser pulse deposition of yttrium barium copper oxide thin film, with bulk target material and MgO single crystal substrate;

[0013] S2: A 100 nm yttrium barium copper oxide thin film was etched by focused ion beam etching to obtain a yttrium barium copper oxide two-dimensional photonic crystal filter.

[0014] In step S1, during the deposition of the yttrium barium copper oxide thin film, the temperature of the MgO single crystal substrate is raised to 600–650 °C in a vacuum system, the oxygen flow pressure is 25–30 Pa, the target rotation speed is 1 rpm, and the incident laser energy density is 3–5 J / cm². 2 The pulse repetition frequency was 2–3 Hz, and the deposition time was 20 min. After the yttrium barium copper oxide thin film deposition was completed, the deposition chamber was isolated from the vacuum system, and oxygen was introduced into it to reduce the pressure to ambient level. Then, the pressure was reduced to room temperature at a rate of 1 °C / min to obtain the yttrium barium copper oxide thin film.

[0015] In step S2, the designed photonic crystal filter structure is fabricated on the barium yttrium copper oxide thin film. The focused ion beam processing conditions are: Ga ion beam, beam current 50pA, voltage 20kV, and etching time 60min.

[0016] (III) Beneficial Effects

[0017] The yttrium barium copper oxide photonic crystal filter and its fabrication method provided by the above technical solution have a simple structure and manufacturing process, making them suitable for mass production. Due to the low dielectric constant of yttrium barium copper oxide, a large dielectric difference is formed with air, which can create a wider photonic bandgap. By utilizing the tunability of yttrium barium copper oxide, the position of the bandgap can be controlled to meet the needs of different photonic crystal filters, achieving coverage of the corresponding waveband. It is easy to control and has high reliability. Attached Figure Description

[0018] Figure 1 Schematic diagram of the unit structure of triangular aperture yttrium barium copper oxide photonic crystal;

[0019] Area A is yttrium barium copper oxide material; Area B is air.

[0020] Figure 2 Band gap diagram of triangular aperture yttrium barium copper oxide photonic crystal.

[0021] Figure 3 A schematic diagram of a photonic crystal unit structure with one of the triangles (top left) rotated 40°.

[0022] Figure 4 Band diagrams of yttrium barium copper oxide photonic crystals at different rotation angles when rotating the upper left triangle.

[0023] (a) Rotation angle is 10°, (b) Rotation angle is 20°, (c) Rotation angle is 30°.

[0024] (d) Rotation angle is 40°, (e) Rotation angle is 50°, (f) Rotation angle is 60°.

[0025] Figure 5 Band diagrams of yttrium barium copper oxide photonic crystals at different rotation angles when rotating the upper left triangle.

[0026] (a) Rotation angle is 70°, (b) Rotation angle is 80°, (c) Rotation angle is 90°.

[0027] (d) The rotation angle is 100°, and (e) The rotation angle is 110°.

[0028] Figure 6 Schematic diagram and band structure of yttrium barium copper oxide photonic crystal when the upper left triangle is rotated.

[0029] (a) Photonic crystal structure diagram with a rotation angle of 40°, (b) corresponding single cell band diagram with a rotation angle of 40°. Detailed Implementation

[0030] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0031] The yttrium barium copper oxide photonic crystal filter of this invention consists of periodic asymmetric triangular apertures and yttrium barium copper oxide (YBa2Cu3O) (7-x) It is composed of superconducting materials, and each periodic structure forms a basic photonic crystal unit. Each basic photonic crystal unit contains 4 triangular holes.

[0032] To facilitate observation and analysis of its symmetry and periodicity, and to avoid overly complex structures, four triangles were placed in each larger unit cell, thus forming a new periodic structure. The lattice constant of this structure is 700 nm, with each triangular aperture having a side length of 210 nm. A schematic diagram of the photonic crystal structure is shown below. Figure 1 As shown.

[0033] The bandgap diagram of yttrium barium copper oxide photonic crystal in the 750–1500 THz (20–400 nm) range was obtained through theoretical simulation calculations, as follows: Figure 2 As shown. In both the horizontal and vertical directions, the symmetry and periodicity of the photonic crystal are intact, therefore the band gap is not opened.

[0034] By rotating one of the triangles (top left) 40° counterclockwise around the center of the triangle, as shown... Figure 3 As shown, further theoretical simulation calculations were performed to analyze the band diagram under different rotation angles.

[0035] The band gap diagrams of yttrium barium copper oxide photonic crystals corresponding to rotation angles of 10°, 20°, 30°, 40°, 50°, and 60° are as follows: Figure 4 The bandgap diagrams of yttrium barium copper oxide photonic crystals corresponding to rotation angles of 70°, 80°, 90°, 100°, and 110° in (a), (b), (c), (d), (e), and (f) are as follows: Figure 5 (a), (b), (c), (d), (e).

[0036] Based on existing theoretical knowledge, the photonic bandgap is related to the geometry of the photonic crystal, its duty cycle, and the difference in dielectric constant (refractive index difference) of the dielectric materials. The worse the geometric symmetry of the photonic crystal and the greater the difference in dielectric constant of the dielectric materials, the easier it is for a photonic bandgap to appear. Correspondingly, we can see that as the rotation angle of the triangle changes, the original symmetry of the photonic crystal is broken, and a bandgap appears.

[0037] Similar to the unrotated photonic crystal structure, when the triangle is rotated by 10° and 20°, as... Figure 4 As shown in (a) and (b), no photonic bandgap was observed.

[0038] When the triangle is rotated 30°, as follows Figure 4As shown in (c), we can observe an extremely narrow photonic bandgap near the frequency of 1023 THz. This is due to the rotation of the triangle, which breaks the original symmetry of the crystal structure in the horizontal direction and the original periodicity in the vertical direction, resulting in the appearance of the photonic bandgap.

[0039] Similarly, when the triangle is rotated by 40°, 50°, and 60°, as... Figure 4 As shown in (d), (e), and (f), a photonic bandgap with a width of approximately 10 THz appears in the frequency range of 1152–1162 THz, and another photonic bandgap with a width of approximately 10 THz appears in the frequency range of 1020–1030 THz. This is due to the rotation of the triangle, which breaks the original symmetry in the horizontal direction and the original periodicity in the vertical direction of the crystal structure, resulting in a photonic bandgap. Compared to other rotation cases, 40°, 50°, and 60° correspond to the maximum values ​​of the photonic bandgap width, and the bandgap opening effect is more obvious. If other parameters of the bandgap need to be adjusted later, rotations around 40°, 50°, and 60° can be selected for easier observation.

[0040] When the rotation angle is 70°, such as Figure 5 As shown in (a), an extremely narrow photonic bandgap appears around 1155 THz.

[0041] When the rotation angle is 80°, such as Figure 5 As shown in (b), no photonic bandgap appears in this frequency band.

[0042] When the rotation angle is 90°, it is similar to rotating 30°, such as... Figure 5 As shown in (c), an extremely narrow photonic bandgap appears at a frequency of around 1023 THz.

[0043] When the rotation angle is 100° or 110°, the band gap also disappears.

[0044] The opening and closing of the bandgap is relatively easy to observe and judge when the angle changes, but the change in the bandgap width is not significant. This indicates that the bandgap width is not heavily dependent on fine-tuning such as rotation of the structure itself, but rather on adjustable parameters such as the size of the structure, the incident angle, and the operating temperature. A larger photonic bandgap is achieved when a triangle is rotated by 40°. Figure 6 As shown, a photonic bandgap of approximately 10 THz appears in the range of 1152–1162 THz, and another photonic bandgap of approximately 10 THz appears in the range of 1020–1030 THz. This result has two band gaps of 10 THz each, indicating a relatively good filtering effect.

[0045] like Figure 6As shown, the yttrium barium copper oxide photonic crystal filter has a lattice constant of 700 nm and a triangular aperture side length of 210 nm. In the unit cell structure, the upper left triangle is rotated by 40°. The fabrication process steps for this photonic crystal filter are as follows:

[0046] S1: Laser pulse deposition of yttrium barium copper oxide thin films, with a bulk target and a MgO single crystal substrate. The MgO single crystal substrate is heated to 600–650°C under vacuum, with an oxygen flow pressure of 25–30 Pa, a target rotation speed of 1 rpm, and an incident laser energy density of 3–5 J / cm². 2 The pulse repetition frequency was 2-3 Hz, and the deposition time was 20 min. After deposition, the deposition chamber was immediately isolated from the vacuum system and oxygen was rapidly introduced into it to reduce the pressure to atmospheric pressure. Then, the pressure was reduced to room temperature at a rate of 1 °C / min to obtain a yttrium barium copper oxide film.

[0047] S2: A 100 nm yttrium barium copper oxide thin film was etched using focused ion beam etching. On the yttrium barium copper oxide thin film, according to... Figure 6 The photonic crystal filter structure shown was fabricated. Focused ion beam fabrication conditions: Ga ion beam, beam current 50 pA, voltage 20 kV, etching time 60 min, yielding a yttrium barium copper oxide two-dimensional photonic crystal filter.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A yttrium barium copper oxide photonic crystal filter, characterized in that, It consists of periodic asymmetric triangular holes and yttrium barium copper oxide superconducting material. Each periodic structure forms a basic photonic crystal unit, and each basic photonic crystal unit contains 4 triangular holes. The lattice constant of the basic unit of the photonic crystal is 700 nm, and the side length of each triangular hole is 210 nm. In each basic unit of the photonic crystal, one of the triangles is rotated 40°, resulting in a photonic bandgap with a width of approximately 10 THz in the range of 1152–1162 THz and another photonic bandgap with a width of approximately 10 THz in the range of 1020–1030 THz.

2. A method for fabricating a yttrium barium copper oxide photonic crystal filter based on the yttrium barium copper oxide photonic crystal filter of claim 1, characterized in that, Includes the following steps: S1: Laser pulse deposition of yttrium barium copper oxide thin film, with bulk target material and MgO single crystal substrate; S2: A 100 nm yttrium barium copper oxide thin film was etched by focused ion beam etching to obtain a two-dimensional yttrium barium copper oxide photonic crystal filter. In step S1, during the deposition of yttrium barium copper oxide thin film, the temperature of the MgO single crystal substrate is raised to 600-650ºC in a vacuum system, the oxygen flow pressure is 25-30Pa, and the target rotation speed is 1 rpm. In step S1, during the deposition of the yttrium barium copper oxide thin film, the incident laser energy density is 3–5 J / cm². 2 The pulse repetition frequency is 2-3 Hz; In step S1, the deposition time for the yttrium barium copper oxide thin film is 20 minutes. In step S1, after the yttrium barium copper oxide thin film deposition is completed, the deposition chamber is isolated from the vacuum system and oxygen is introduced into it to reduce the pressure to ambient level. Then, the pressure is reduced to room temperature at a rate of 1ºC / min to obtain the yttrium barium copper oxide thin film. In step S2, the designed photonic crystal filter structure is fabricated on the barium yttrium copper oxide thin film. The focused ion beam processing conditions are: Ga ion beam, beam current 50pA, voltage 20kV, and etching time 60min.

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