Non-reciprocal polarization conversion device based on Weyl semimetal

Abstract

The invention relates to a non-reciprocal polarization conversion device based on Weyl semimetal. The non-reciprocal polarization conversion device comprises a first WSM layer, a dielectric layer and a second WSM layer which are stacked in sequence, the first WSM layer is a Weyl semimetal layer; the second WSM layer is a Weyl semimetal layer which is arranged above the dielectric layer in a twisting manner; and a torsion angle is formed between the first WSM layer and the second WSM layer. According to the non-reciprocal polarization conversion device based on the Weyl semimetal, tunable non-reciprocal polarization conversion of light can be achieved, and the technical effects that the structure is simple, the size is small, and an external magnetic field is not needed are achieved.

Description

Technical Field

[0001] The present invention relates to the field of polarization conversion, and in particular to a non-reciprocal polarization conversion device based on Weyl semimetal. Background Art

[0002] Polarization conversion refers to the process of changing the polarization state of light from one form to another through specific methods or devices. In the field of optics, the polarization state of light is a key property that describes the direction and mode of vibration of the electric field vector in a light wave. Polarization conversion has a wide range of applications: in the field of communications, polarization conversion can be used to modulate and demodulate optical signals, improving the performance of communication systems; in display technology, polarization conversion can be used to control the polarization state of light, achieving high-quality image display; and in optical instruments and sensors, polarization conversion can be used to improve measurement accuracy and sensitivity, enabling more precise optical measurement and detection.

[0003] Non-reciprocal polarization conversion refers to the fact that when incident light enters a polarization conversion device from the forward and reverse directions, the polarization state of the incident light changes differently. This non-reciprocity is very useful in certain optical applications, especially when the polarization state of light needs to be controlled in a directional manner, such as in encrypted transmission.

[0004] Faraday rotators are a common nonreciprocal polarization conversion device in the prior art. Their principle is based on the Faraday effect: when a beam of plane-polarized light passes through a magneto-optical medium placed in a magnetic field, its polarization plane rotates in response to the magnetic field parallel to the direction of the light. This rotation is nonreciprocal, meaning that light passing through the rotator in the forward and reverse directions experiences different polarization states. However, existing Faraday rotators are complex, have limited functionality, are bulky, and require an external magnetic field. Summary of the Invention

[0005] Based on this, the object of the present invention is to provide a non-reciprocal polarization conversion device based on Weyl semimetal that has a simple structure, a compact size, and does not require the application of an external magnetic field.

[0006] A non-reciprocal polarization conversion device based on a Weyl semimetal comprises a first WSM layer, a dielectric layer, and a second WSM layer stacked in sequence; the first WSM layer is a Weyl semimetal layer; the second WSM layer is a Weyl semimetal layer twistedly arranged above the dielectric layer; a twist angle is formed between the first WSM layer and the second WSM layer.

[0007] The Weyl semimetal-based non-reciprocal polarization conversion device of the present invention can realize tunable non-reciprocal polarization conversion of light without an external magnetic field, and has the advantages of simple structure and compact size.

[0008] Furthermore, the thickness of the first WSM layer and the second WSM layer are both 300 nm.

[0009] Furthermore, the dielectric layer is made of silicon monoxide.

[0010] Furthermore, the thickness of the dielectric layer is 1800 nm.

[0011] Furthermore, a twist angle formed between the first WSM layer and the second WSM layer is 120° or 60°.

[0012] Furthermore, a twist angle formed between the first WSM layer and the second WSM layer is 120°.

[0013] Furthermore, the wavelength of the incident light is within the wavelength range of 4.1 μm to 4.5 μm.

[0014] Furthermore, the wavelength of the incident light is within the wavelength range of 4.2 μm to 4.4 μm.

[0015] Further, the dielectric constant and thickness of the dielectric layer are determined according to the expression of the transmission matrix and the desired transmittance and isolation;

[0016] The expression of the transmission matrix is:

[0017] in, Describes the electric and magnetic fields within the dielectric layer, E x and H x They represent the wave functions corresponding to the electric field and magnetic field in the x direction, E y and H y They represent the wave functions corresponding to the electric field and magnetic field in the y direction respectively; k0 represents the wave number of the incident light in a vacuum, D is the Berreman matrix, z is the distance of light propagation; i is the imaginary number symbol.

[0018] Furthermore, the first WSM layer and the second WSM layer are both made of Co3Sn2S2 material.

[0019] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of the non-reciprocal polarization conversion device based on Weyl semimetal of the present invention;

[0021] Figure 2 Schematic diagram of the working principle of the non-reciprocal polarization conversion device based on Weyl semimetal of the present invention;

[0022] Figure 3 Schematic diagram of the structure of a non-reciprocal polarization conversion device based on Weyl semimetal according to Example 1 of the present invention;

[0023] Figure 4 Schematic diagram of the non-reciprocal polarization conversion effect of the Weyl semimetal-based non-reciprocal polarization conversion device according to Example 1 of the present invention at different incident angles with a twist angle of 120°;

[0024] Figure 5 Schematic diagram of the isolation coefficient and insertion loss of the Weyl semimetal-based non-reciprocal polarization conversion device in the wavelength band of 4.1μm to 4.5μm according to Example 1 of the present invention;

[0025] Figure 6 Schematic diagram of the non-reciprocal polarization conversion effect of the Weyl semimetal-based non-reciprocal polarization conversion device of the present invention under vertical incidence and different twist angles. DETAILED DESCRIPTION

[0026] It should be clear that the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the embodiments of the present application.

[0027] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the embodiments of the present application. The singular forms "a," "the," and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0028] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims. In the description of the present application, it should be understood that the terms "first", "second", etc. are only used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0029] It should be understood that the embodiments of the present application are not limited to the precise structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the embodiments of the present application is limited only by the appended claims.

[0030] In recent years, the nonmagnetic, nonreciprocal properties of Weyl semimetals (WSMs) have attracted widespread attention. Inspired by twist electronics, the inventors designed a three-layer nonreciprocal polarization conversion device (first WSM layer, dielectric layer, second WSM layer) based on the asymmetry of the dielectric constant tensor of Weyl semimetals. This device can achieve tunable nonreciprocal polarization conversion of light without an applied magnetic field. Compared to traditional Faraday rotators, it has a simpler structure, a smaller size, and does not require an external magnetic field.

[0031] See also Figure 1 , Figure 1 The figure is a schematic structural diagram of a non-reciprocal polarization conversion device based on a Weyl semimetal according to the present invention. The non-reciprocal polarization conversion device based on a Weyl semimetal according to the present invention comprises a first WSM layer, a dielectric layer, and a second WSM layer stacked in sequence. The first WSM layer is a Weyl semimetal layer. The dielectric layer is fixedly arranged above the first WSM layer. The second WSM layer is a Weyl semimetal layer twistedly arranged above the dielectric layer. A twist angle is formed between the first WSM layer and the second WSM layer. By adjusting the twist angle, the isolation amplitude of the polarization conversion device for incident light of different wavelengths can be dynamically adjusted, thereby achieving a tuning effect.

[0032] Among them, the Weyl semimetal layer is made of Co3Sn2S2 material, and its preparation method belongs to the existing technology, as shown in the paper "Preparation and Electromagnetic Properties of Weyl Semimetal Co3Sn2S2 Thin Film" by Li Shouhan, Cui Chi, Li Wei and others, which will not be repeated here.

[0033] See also Figure 2 , Figure 2The diagram is a schematic diagram of the working principle of the non-reciprocal polarization conversion device based on Weyl semimetal of the present invention. The incident light entering from the second WSM layer is the incident light in the forward direction, and the incident light entering from the first WSM layer is the incident light in the reverse direction. The working principle of the non-reciprocal polarization conversion device based on Weyl semimetal of the present invention is as follows: for TM linear polarized light of a specific wavelength band incident in the forward direction, the twisted second WSM layer is equivalent to a coupler, which can convert most of the incident TM linear polarized light into TE linear polarized light. After the incident TM linear polarized light passes through the second WSM layer, most of it is converted into TE linear polarized light, and a small part remains TM linear polarized light. These TM linear polarized lights and TE linear polarized lights are incident on the dielectric layer. The dielectric layer can support Fabry-Perot resonance, so that the electric field of the polarized light is concentrated in the dielectric layer, thereby effectively reducing the loss of polarized light energy and improving the light transmission effect.

[0034] After passing through the dielectric layer, the TM linear polarized light and the TE linear polarized light are incident on the first WSM layer. The first WSM layer is equivalent to a TE polarizer, which can filter out the TM linear polarized light and only allow the TE linear polarized light to pass through. Therefore, when the TM linear polarized light of a specific wavelength band is incident on the non-reciprocal polarization conversion device based on Weyl semimetal of the present invention in the forward direction, it will be converted into TE linear polarized light, that is, converted into the orthogonal state of the original incident TM linear polarized light. However, for the TM linear polarized light of a specific wavelength band incident in the reverse direction, the fixed first WSM layer is equivalent to a TE polarizer, and most of the incident TM linear polarized light is filtered by the first WSM layer and cannot be transmitted to the subsequent links. Therefore, the non-reciprocal polarization conversion device based on Weyl semimetal of this scheme can allow the forward incident light (incident from the second WSM layer) to pass through and be converted into the orthogonal state; at the same time, it prevents the reverse incident light (incident from the first WSM layer) from passing through, thereby achieving non-reciprocal polarization conversion.

[0035] Example 1

[0036] See also Figure 3 , Figure 3 Figure 1 is a schematic diagram of the structure of a non-reciprocal polarization conversion device based on a Weyl semimetal according to Example 1 of the present invention. In this embodiment, the thickness of the first and second WSM layers is 300 nm. The dielectric layer is made of silicon monoxide (SiO) and has a thickness of 1800 nm. The twist angle formed between the first and second WSM layers is 120°.

[0037] In other embodiments, the dielectric layer may be made of other dielectric materials. However, when using other materials with different dielectric constants, the thickness of the dielectric layer needs to be adjusted accordingly.

[0038] In other embodiments, the twist angle formed between the first WSM layer and the second WSM layer may not be equal to 120°.

[0039] Experiments have shown that the Weyl semimetal-based non-reciprocal polarization conversion device of Example 1 of the present invention has a good non-reciprocal polarization conversion effect on incident light with a wavelength in the range of 4.1 μm to 4.5 μm.

[0040] See also Figure 4 , Figure 4 Schematic diagram of the non-reciprocal polarization conversion effect of the Weyl semimetal-based non-reciprocal polarization conversion device according to Example 1 of the present invention at different incident angles with a twist angle of 120°. Figure 4 The left figure is a diagram of the polarization conversion effect of forward incidence (incident from the second WSM layer). The x-axis coordinate represents the wavelength of the incident light (ranging from 3.0μm to 6.0μm), and the y-axis coordinate represents the incident angle of the incident light (ranging from 0° to 85°). The color of the corresponding point represents the transmission effect of the incident light with forward incidence under the combination of wavelength and incident angle. The more the color tends to red, the better the transmission effect, and the more the color tends to purple, the worse the transmission effect. Figure 4 The right figure is a polarization conversion effect diagram of reverse incidence (incident from the first WSM layer), the x-axis coordinate represents the wavelength of the incident light (range is 3.0μm ~ 6.0μm), the y-axis coordinate represents the incident angle of the incident light (range is 0° ~ 85°), and the color of the corresponding point represents the transmission effect of the reverse incident light under the combination of the wavelength and the incident angle; the more the color is biased towards red, the better the transmission effect, and the more the color is biased towards purple, the worse the transmission effect. Figure 4 It can be seen that within the wavelength band of 4.1-4.5 μm, the non-reciprocal polarization conversion device based on Weyl semimetal in Example 1 of the present invention has a better transmission effect on the incident light of the forward direction, and a poorer transmission effect on the incident light of the reverse direction. It can be seen that the non-reciprocal polarization conversion device based on Weyl semimetal in Example 1 has good non-reciprocity.

[0041] See also Figure 5 , Figure 5 This is a schematic diagram of the isolation coefficient and insertion loss of the non-reciprocal polarization conversion device based on Weyl semimetal in the wavelength band of 4.1μ~4.5μm of Example 1 of the present invention. Insertion loss refers to the degree of reduction in signal power when a component or device is inserted into a transmission line or circuit. Isolation refers to the degree to which a component or device can effectively separate two signals or channels. These two physical quantities are important parameters used to characterize the performance of components and equipment in a transmission system. Figure 5It can be seen that within the wavelength band of the incident light of 4.1μ-4.5μm, the non-reciprocal polarization conversion device based on Weyl semimetal in Example 1 of the present invention has a high isolation coefficient and a low insertion loss: the isolation coefficient is not less than 20dB and can reach up to 100dB; at the same time, the insertion loss does not exceed 6dB; in the band of 4.2μm to 4.4μm, the insertion loss does not even exceed 2dB.

[0042] Example 2

[0043] The Weyl semimetal-based non-reciprocal polarization conversion device of Example 2 of the present invention is substantially the same as Example 1, differing in that the twist angle formed between the first and second WSM layers in Example 2 is 60°. Experiments have demonstrated that the Weyl semimetal-based non-reciprocal polarization conversion device of Example 2 of the present invention also exhibits excellent non-reciprocal polarization conversion performance for incident light within the wavelength range of 4.1 μm to 4.5 μm.

[0044] Since vertical incident light is the most representative, the incident angle of the incident light is fixed at 90°. By changing the twist angle between the first and second WSM layers, the effect of the twist angle on the non-reciprocal polarization conversion effect is studied. Figure 6 , Figure 6 Schematic diagram of the non-reciprocal polarization conversion effect of the Weyl semimetal-based non-reciprocal polarization conversion device of the present invention under vertical incidence and different twist angles.

[0045] Figure 6 The left figure shows the polarization conversion effect of forward incidence (incident from the second WSM layer). The x-axis coordinate represents the wavelength of the incident light, the y-axis coordinate represents the twist angle, and the color of the corresponding point represents the transmission effect of the incident light in the forward direction under the combination of wavelength and twist angle. The more the color tends to red, the better the transmission effect, and the more the color tends to purple, the worse the transmission effect. Figure 6 The right figure shows the polarization conversion effect of reverse incidence (incident from the first WSM layer). The x-axis coordinate represents the wavelength of the incident light, the y-axis coordinate represents the twist angle, and the color of the corresponding point represents the transmission effect of the reverse incident incident light under the combination of wavelength and twist angle. The more the color tends to red, the better the transmission effect, and the more the color tends to purple, the worse the transmission effect.

[0046] according to Figure 6It can be seen that the polarization conversion effects corresponding to a pair of complementary twist angles are almost identical. Similar to the situation in Example 1, within the wavelength band of 4.1-4.5 μm, the Weyl semimetal-based non-reciprocal polarization conversion device of Example 2 of the present invention has a good transmission effect for incident light in the forward direction, but a poor transmission effect for incident light in the reverse direction. The Weyl semimetal-based non-reciprocal polarization conversion device of Example 2 of the present invention also has good non-reciprocity.

[0047] Furthermore, the present invention can also calculate the light transmittance and isolation based on the incident light and the dielectric constant and thickness of the dielectric layer through the Berreman 4×4 transmission matrix method. The calculation method is as follows:

[0048] Solve the Berreman equation:

[0049] The expression of the transfer matrix is ​​obtained:

[0050] in, Used to describe the electric and magnetic fields within a dielectric layer, E x and H x They represent the wave functions corresponding to the electric field and magnetic field in the x direction, E y and H y where represents the wave functions corresponding to the electric and magnetic fields in the y-direction, respectively; k0 represents the wave number of the incident light in a vacuum; D is the Berreman matrix; z is the distance the light propagates; and i is the imaginary sign. By substituting the relevant parameters into the transmission matrix expression, the transmittance and isolation of light can be calculated. Alternatively, by substituting the desired transmittance and isolation into the expression, the required dielectric constant and thickness of the dielectric layer can be calculated, thereby enabling the design of the non-reciprocal polarization conversion device based on Weyl semimetals according to the present invention.

[0051] The Weyl semimetal-based nonreciprocal polarization conversion device of the present invention can achieve tunable nonreciprocal polarization conversion of light without an external magnetic field. Compared to traditional Faraday rotators, it offers a simpler structure, a smaller size, and the absence of an external magnetic field. Furthermore, the Weyl semimetal-based nonreciprocal polarization conversion device of the present invention achieves excellent nonreciprocal conversion performance, a high isolation coefficient, and low insertion loss when the WSM layer thickness is 300nm, the dielectric layer thickness is 1800nm, the twist angle is 120° or 60°, and the incident light wavelength is 4.1μm to 1.5μm.

[0052] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, and the present invention is intended to encompass such modifications and variations.

Claims

1. A non-reciprocal polarization conversion device based on a Weyl semimetal, characterized in that: The invention comprises a first WSM layer, a dielectric layer and a second WSM layer stacked in sequence; the first WSM layer is a Weyl semimetal layer; The second WSM layer is a Weyl semimetal layer twistedly disposed above the dielectric layer; A twist angle is formed between the first WSM layer and the second WSM layer.

2. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 1, characterized in that: The thickness of the first WSM layer and the second WSM layer are both 300 nm.

3. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 2, characterized in that: The dielectric layer is made of silicon monoxide.

4. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 3, characterized in that: The thickness of the dielectric layer is 1800 nm.

5. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 4, characterized in that: The twist angle formed between the first WSM layer and the second WSM layer is 120° or 60°.

6. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 5, characterized in that: The twist angle formed between the first WSM layer and the second WSM layer is 120°.

7. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 6, characterized in that: The wavelength of the incident light is within the range of 4.1 μm to 4.5 μm.

8. The non-reciprocal polarization conversion device based on Weyl semimetal according to claim 7, characterized in that: The wavelength of the incident light is within the range of 4.2 μm to 4.4 μm.

9. The non-reciprocal polarization conversion device based on a Weyl semimetal according to any one of claims 1 to 8, characterized in that: Determining the dielectric constant and thickness of the dielectric layer according to the expression of the transmission matrix and the desired transmittance and isolation; The expression of the transmission matrix is: in, Describes the electric and magnetic fields within the dielectric layer, E x and H x They represent the wave functions corresponding to the electric field and magnetic field in the x direction, E y and H y They represent the wave functions corresponding to the electric field and magnetic field in the y direction respectively; k0 represents the wave number of the incident light in a vacuum, D is the Berreman matrix, z is the distance of light propagation; i is the imaginary number symbol.

10. The non-reciprocal polarization conversion device based on Weyl semimetal according to claims 1-8, characterized in that: The first WSM layer and the second WSM layer are both made of Co3Sn2S2 material.

Images