A valley edge state waveguide using armchair boundaries and its application

Abstract

The present invention discloses a valley edge state waveguide using an armchair boundary and its application, and designs two boundaries with opposite structures. The valley edge state waveguide includes an armchair boundary composed of an SSBB-form boundary and a BBSS-form boundary; along a preset direction, the SSBB-form boundary is sequentially composed of a boundary between two adjacent small equilateral triangle holes and a boundary between two adjacent large equilateral triangle holes, and the BBSS-form boundary is sequentially composed of a boundary between two adjacent large equilateral triangle holes and a boundary between two adjacent small equilateral triangle holes. The valley edge state waveguide in this scheme can realize the direction-selective transmission of chiral light field signals, and always maintain the conservation of chirality during the transmission process. Combined with a zigzag boundary, a 90° and 180° signal rotation angle can be realized. At the same time, by constructing a vertical intersection structure of an armchair boundary and a zigzag boundary, a beam splitting function of equalizing the intensity of a chiral light field signal at a vertical intersection point can be realized.

Description

Technical Field

[0001] The invention relates to the field of optical waveguide transmission, and in particular to a valley edge state waveguide using an armchair boundary and applications thereof. Background Art

[0002] An optical waveguide is a dielectric device that guides light waves to propagate in it, also known as a dielectric optical waveguide. The loss of optical signals in the optical waveguide during transmission is an important issue in current optical communications and photonic integrated chips. This loss can be caused by a variety of factors: defects introduced during the preparation of the optical waveguide, losses caused by the optical signal in the optical waveguide when it is transmitted at a large angle, and losses introduced by the related beam splitting devices when splitting the optical signal in the optical waveguide. These losses will cause the intensity of the transmitted optical signal to attenuate and the diffusion of the optical signal, which can easily lead to problems such as distortion of the content of the transmitted optical signal and capture and monitoring.

[0003] The technical principle of topologically protected two-dimensional photonic crystal valley edge state waveguides is derived from the quantum valley Hall effect of electrons in condensed matter physics. Single-layer graphene can exist stably and has high electron mobility and linear dispersion characteristics of the Dirac cone. In the study of two-dimensional materials, people have used various methods to open the Dirac cone of graphene, thereby forming an energy band gap, which is more conducive to the application of graphene materials in semiconductor devices.

[0004] Analogous to electronic systems, people can also construct this kind of valley topology-protected edge state in photonic systems to form optical waveguides to achieve backscatter-free and lossless transmission of photons. First, starting from the photonic crystal structure of photonic graphene, the required Dirac cone is constructed, and then the spatial inversion symmetry is broken to open the energy band at the Dirac cone and form the required energy valley of the photonic crystal. Based on the flexibility of the preparation process, the method of drilling holes on the surface of silicon materials is the easiest way to achieve this photonic graphene structure.

[0005] In the prior art, two-dimensional circular holes are used to realize optical signal transmission of valley edge state waveguides. However, there is a problem with the circular hole solution, that is, its energy band gap is an indirect band gap. The indirect band gap causes the energy valley extremes to be not at the same reciprocal lattice position, and the noise appears at the passband edge of the photonic crystal transmission spectrum.

[0006] In the prior art, valley edge states protected by zigzag topology are also used to achieve low-loss straight-line, 120° and 60° angle transmission of optical signals near the 1560nm band. At the same time, a ring optical microcavity is constructed using valley edge state waveguides formed by two-dimensional graphene-like photonic crystals with equilateral triangular holes to achieve the screening and extraction of high-quality factor signals of 1569.5nm optical signals. However, based on the intersection of two zigzag boundaries, researchers discovered the phenomenon of unequal intensity splitting of chiral optical signals and the phenomenon of optical signal transmission path selection based on the conservation of valley chirality.

[0007] In summary, the zigzag boundary is presented, and only the chiral light signal angle transmission of 0°, 60° and 120° can be realized. The valley edge state waveguide cannot realize the angle transmission of other angles. In addition, in the valley edge state waveguide beam splitter formed by the intersection of two zigzag boundaries, the intensities of the two separated light signals are unequal, and cannot be used to realize the beam splitting function of equalizing the intensity of the chiral light signal. Summary of the invention

[0008] In view of this, the present invention proposes a valley edge state waveguide using an armchair boundary and its application, and the specific scheme is as follows:

[0009] In the first part, the present invention proposes a valley edge state waveguide using an armchair boundary, which is constructed in a graphene-like two-dimensional photonic crystal based on valley spin; wherein the graphene-like two-dimensional photonic crystal includes two hexagonal lattice primitive cells with opposite structures, namely a first hexagonal lattice primitive cell and a second hexagonal lattice primitive cell;

[0010] Each hexagonal lattice unit cell is composed of two types, a total of six sub-lattices, one of which is composed of large regular triangle holes, and the other is composed of small regular triangle holes.

[0011] The valley edge state waveguide includes an armchair boundary, and the armchair boundary can be divided into an SSBB form boundary and a BBSS form boundary;

[0012] A preset direction, a first direction, and a second direction are specified in the same plane, wherein the first direction and the second direction are respectively perpendicular to the preset direction and in opposite directions;

[0013] Along the preset direction, the SSBB form boundary is sequentially composed of a boundary between two adjacent small equilateral triangle holes and a boundary between two adjacent large equilateral triangle holes, and the first hexagonal lattice unit cell is located in a first direction of the SSBB form boundary, and the second hexagonal lattice unit cell is located in a second direction of the SSBB form boundary;

[0014] Along the preset direction, the BBSS form boundary is composed of the boundary between two adjacent large equilateral triangle holes and the boundary between two adjacent small equilateral triangle holes in sequence, and the second hexagonal lattice unit cell is located in the first direction of the BBSS form boundary, and the first hexagonal lattice unit cell is located in the second direction of the BBSS form boundary.

[0015] In a specific embodiment, the hexagonal lattice unit cell is a regular hexagon, and the side length of the hexagonal lattice unit cell is a:

[0016] The side length of the small equilateral triangle hole ranges from 0.3a to 0.45a, and the side length of the large equilateral triangle hole ranges from 0.5a to 0.7a.

[0017] In a specific embodiment, the valley edge state waveguide can transmit a chiral optical signal;

[0018] The excitation source of the chiral light signal may be located at the center of any equilateral triangle hole in the armchair boundary.

[0019] In a specific embodiment, the excitation source can excite a chiral light signal having a circular polarization characteristic in the direction of the electric field, and the excitation source is divided into a left-handed chiral excitation source and a right-handed chiral excitation source according to the rotation direction of the circularly polarized electric field;

[0020] By setting a left-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form, a left-propagating chiral light signal can be excited;

[0021] Setting a right-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form can excite a chiral light signal propagating to the right.

[0022] A left-handed chiral excitation source is set at the center of the first large equilateral triangle hole at the boundary of the BBSS form, which can excite a left-propagating chiral light signal.

[0023] By setting a right-handed chiral excitation source at the center of the first large equilateral triangle hole on the boundary of the BBSS form, a chiral light signal propagating to the right can be excited.

[0024] In a specific embodiment, the valley edge state waveguide further comprises a zigzag boundary;

[0025] The armchair boundary is linked with the zigzag boundary to realize a 90° turn and a 180° turn of the signal.

[0026] In a specific embodiment, the zigzag boundary can be divided into a BB form boundary and a SS form boundary;

[0027] In a 90° turn valley edge state waveguide:

[0028] If the horizontal armchair boundary is a SSBB form boundary:

[0029] Connecting the SS form boundary at the 90° corner of the SSBB form boundary can realize the propagation of right-handed optical signals upward along the SSBB form boundary;

[0030] Connecting the BB form boundary at the 90° corner of the SSBB form boundary can enable the right-handed optical signal to propagate downward along the SSBB form boundary.

[0031] In a specific embodiment, a 90° corner of a SSBB-shaped boundary is connected to a zigzag boundary, and a 90° corner of a zigzag boundary is connected to a BBSS-shaped boundary, so that a 180° turn of a right-handed optical signal can be achieved.

[0032] In the second part, the present invention proposes a transmission method of a chiral optical signal, using the valley edge state waveguide described in the first part; the transmission method comprises:

[0033] An excitation source is set at the center of any regular triangle hole in the armchair boundary;

[0034] When the excitation source is a left-handed chiral light signal, the light signal will be transmitted to the left along the valley edge state waveguide; when the excitation source is a right-handed chiral light signal, the light signal will be transmitted to the right along the valley edge state waveguide; and there is no backscattered signal returned during the transmission process and at the output of the waveguide end face;

[0035] The chiral light signal enters the zigzag boundary at the 90° corner of the armchair boundary for transmission, thus realizing a 90° turn of the chiral light signal; and then enters the armchair boundary at the 90° corner of the zigzag boundary for transmission, thus realizing a 180° turn of the chiral light signal.

[0036] In the third part, the present invention proposes a chiral light signal equal beam splitting device based on a valley edge state waveguide, including the valley edge state waveguide described in any one of the first parts;

[0037] The beam splitting device includes an SSBB form boundary, a BBSS form boundary, an SS form boundary and a BB form boundary, and the excitation source of the chiral light signal is located at the SSBB form boundary or the BBSS form boundary;

[0038] In a preset first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point;

[0039] In the preset second direction, the SS form boundary and the BB form boundary are connected at the beam splitting point;

[0040] The first direction is perpendicular to the second direction.

[0041] In a specific embodiment, after a chiral light signal enters a beam splitting point from an armchair boundary of a certain form, it will not enter an armchair boundary of another form based on the chirality conservation principle;

[0042] There are two forms of zigzag boundaries at the splitting point, and the transmission directions of the chiral light signal in the two forms of zigzag boundaries are opposite after the splitting, so as to achieve equal splitting.

[0043] Beneficial effects: The present invention discloses a valley edge state waveguide using an armchair boundary and its application, and designs a boundary composed of two two-dimensional photonic crystals with opposite structures to realize the transmission of chiral light signals in the valley edge state waveguide with topological protection. The valley edge state waveguide constructed by the armchair boundary can realize the direction-selective transmission of the chiral light field signal, and always maintain the conservation of chirality during the transmission of the chiral light signal. And by combining the valley edge state waveguide constructed by the armchair boundary and the zigzag boundary, the transmission of the chiral light field with a 90° turn angle and the transmission of a 180-degree turn formed by two consecutive 90° turns can be realized, and there is no loss of backscattered signals during the transmission process. By constructing a vertical intersection structure of the armchair boundary and the zigzag boundary, a valley edge state waveguide beam splitter device with topological protection of a two-dimensional photonic crystal is formed, which realizes the beam splitting function of equally dividing the intensity of the transmitted chiral light field signal at the vertical intersection point. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the structure of the valley edge state waveguide in an embodiment of the present invention;

[0045] Figure 2 This is a diagram showing the effect of transmission of a chiral optical signal in one direction in an embodiment of the present invention;

[0046] Figure 3 This is a diagram showing the effect of transmission of a chiral optical signal in another direction in an embodiment of the present invention;

[0047] Figure 4 This is a diagram showing the transmission effect of a chiral light signal at a 90° angle in an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the structure of a 90° rotation angle of a chiral light signal in an embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram of the structure of a chiral light signal turning 180° in an embodiment of the present invention;

[0050] Figure 7 A schematic diagram of the chiral light field intensity equalization and beam splitting function formed by vertical crossing in an embodiment of the present invention;

[0051] Figure 8Schematic diagram of the chiral light field intensity averaging and beam splitting effect in an embodiment of the present invention.

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work. DETAILED DESCRIPTION

[0053] In the following, various embodiments of the present disclosure will be described more fully. The present disclosure may have various embodiments, and adjustments and changes may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the present disclosure to the specific embodiments disclosed herein, but the present disclosure should be understood to cover all adjustments, equivalents and / or alternatives that fall within the spirit and scope of the various embodiments of the present disclosure.

[0054] It should be noted that the scheme of the present invention is an edge state waveguide transmission scheme based on valley spin, which is different from the existing waveguide transmission scheme based on pseudospin. Valley spin is to break the C6 symmetry in the graphene lattice, thereby opening a band gap at the high symmetry point K in the reciprocal space. The two states above and below the band gap correspond to two pseudospins with opposite handedness.

[0055] In the present invention, a certain boundary can be expressed as a certain form of a certain boundary. For example, a BBSS boundary can be expressed as a BBSS form of an armchair boundary.

[0056] Since the edge state waveguide transmits optical signals, they need to be captured in a dark environment, so the experimental result graphs of the present invention are all based on a black background.

[0057] The terms used in the various embodiments disclosed in the present invention are only used for the purpose of describing specific embodiments and are not intended to limit the various embodiments disclosed in the present invention. As used herein, singular form boundaries are intended to also include plural form boundaries, unless the context clearly indicates otherwise. Unless otherwise specified, all terms used herein (including technical terms and scientific terms) have the same meaning as the meanings commonly understood by ordinary technicians in the field of various embodiments disclosed in the present invention. The terms (such as the terms defined in the generally used dictionary) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in the various embodiments disclosed in the present invention.

[0058] Example 1

[0059] Embodiment 1 of the present invention discloses a valley edge state waveguide using an armchair boundary. Starting from the quantum valley Hall effect of photons and utilizing the topological protection of valley edge states, a boundary composed of two two-dimensional photonic crystals with opposite structures is designed to realize chiral light signal transmission of the topologically protected valley edge state waveguide. The structure of the valley edge state waveguide is shown in the attached manual. Figure 1 The specific plan is as follows:

[0060] A valley edge state waveguide using an armchair boundary is constructed from a specific graphene-like two-dimensional photonic crystal based on the valley spin principle. The graphene-like two-dimensional photonic crystal can be obtained by drilling holes on the surface of a silicon material. The valley edge state waveguide of this embodiment can only be obtained based on a two-dimensional photonic crystal structure with a specific structure.

[0061] Among them, the graphene-like two-dimensional photonic crystal is composed of hexagonal lattice primitive cells. Each hexagonal lattice primitive cell has six equilateral triangular holes, and the six equilateral triangular holes are distributed in the hexagonal lattice primitive cell in a graphene-like honeycomb form. There are two types of hexagonal lattice primitive cells, namely the first hexagonal lattice primitive cell and the second hexagonal lattice primitive cell. The two types of hexagonal lattice primitive cells present opposite spatial structural characteristics, as shown in the attached manual. Figure 1 As shown in A1 and A2.

[0062] Each hexagonal lattice unit cell is composed of two types, a total of six sub-lattices, one of which is composed of large equilateral triangle holes, and the other is composed of small equilateral triangle holes. The two different sizes of equilateral triangle holes break the spatial inversion symmetry of the honeycomb hexagonal lattice unit cell. Figure 1 In the figure, the hexagonal lattice primitive cell A1 and the hexagonal lattice primitive cell A2 present opposite spatial structural characteristics, that is, the hexagonal lattice primitive cell A1 needs to be spatially inverted around the center point of the primitive cell, or mirrored along the y-axis, in order to obtain the shape of the hexagonal lattice primitive cell A2.

[0063] Through Figure 1 The connection between the hexagonal lattice unit cell A1 and the hexagonal lattice unit cell A2 shown in the figure can construct two forms of armchair boundaries, namely SSBB and BBSS. The valley edge state waveguide is composed of a series of boundaries, among which the main boundary is the armchair boundary. According to the morphology, the armchair boundary can be divided into SSBB form boundary and BBSS form boundary.

[0064] The preset direction, the first direction and the second direction are defined in the same plane, and the first direction and the second direction are respectively perpendicular to the preset direction and in opposite directions. The preset direction, the first direction and the second direction can be understood as the positive direction of the x-axis, the positive direction of the y-axis and the negative direction of the y-axis.

[0065] Along the preset direction (i.e., the positive direction of the x-axis), the SSBB form boundary is composed of the boundary between two adjacent small equilateral triangle holes and the boundary between two adjacent large equilateral triangle holes in sequence, and the first hexagonal lattice unit cell is located in the first direction of the SSBB form boundary (i.e., the positive direction of the y-axis), and the second hexagonal lattice unit cell is located in the second direction of the SSBB form boundary (i.e., the negative direction of the y-axis).

[0066] Along the preset direction (i.e., the positive direction of the x-axis), the BBSS formal boundary is composed in sequence of the boundary between two adjacent large equilateral triangular holes and the boundary between two adjacent small equilateral triangular holes, and the second hexagonal lattice unit cell is located in the first direction of the BBSS formal boundary (i.e., the positive direction of the y-axis), and the first hexagonal lattice unit cell is located in the second direction of the BBSS formal boundary (i.e., the negative direction of the y-axis).

[0067] The armchair boundary is the boundary between two adjacent congruent triangular holes. From left to right, the boundary types are named SSBB (small-small-big-big) and BBSS (big-big-small-big-small). The optical signal will not be completely confined to this boundary. A part of the signal will diffuse to both sides, but this part of the signal will quickly attenuate. The remaining optical signal can only be transmitted along the armchair boundary. Figure 1 In the figure, the bold line in the B1 region is the SSBB boundary, and the bold line in the B2 region is the BBSS boundary. Along the positive direction of the x-axis, the SSBB form refers to small triangles, small triangles, large triangles, and large triangles. The boundary between two small triangles and the boundary between two large triangles together constitute a SSBB boundary. The BBSS form is a large triangle, a large triangle, a small triangle, and a small triangle. The boundary between two large triangles and the boundary between two small triangles together constitute a BBSS boundary, which is an inverted structural form of the SSBB form. The SSBB form is composed of hexagonal lattice unit cell A1 on the top and hexagonal lattice unit cell A2 on the bottom; on the contrary, in the BBSS form, the hexagonal lattice unit cell A2 is on the top and the hexagonal lattice unit cell A1 is on the bottom.

[0068] The entire photonic crystal plate is made of silicon material. By drilling holes on it, the desired photonic crystal structure and armchair armchair boundary can be formed. The hexagonal lattice unit cell is a regular hexagon. If the side length of the hexagonal lattice unit cell is a, the side length of the small regular triangle hole ranges from 0.3a to 0.45a, and the side length of the large regular triangle hole ranges from 0.5a to 0.7a. Preferably, the side length of the small regular triangle hole is 0.4a, and the side length of the large regular triangle hole is 0.6a. Figure 1 As shown in . Further preferably, a=423nm.

[0069] The valley edge state waveguide protected by the topological protection of the two-dimensional photonic crystal constructed by the armchair boundary can realize the direction-selective transmission of the chiral light field signal, and the conservation of chirality is always maintained during the transmission of the chiral light signal. The excitation source of the chiral light signal is located at the center of the equilateral triangle hole of the armchair boundary. This equilateral triangle hole can be the center of any one of the four equilateral triangle holes in the form of SSBB or BBSS. The chiral light signal of the excitation source is a chiral light signal with circular polarization characteristics in the direction of the electric field. According to the rotation direction of the circularly polarized electric field, the excitation source of the chiral light signal can be classified into left-handed chiral excitation source (counterclockwise rotation) and right-handed chiral excitation source (clockwise rotation). The transmission process of the chiral light signal in the valley edge state waveguide is as shown in the attached manual. Figure 2 and attached Figure 3 shown.

[0070] By setting a left-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form, a left-propagating chiral light signal can be excited;

[0071] Setting a right-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form can excite a chiral light signal propagating to the right.

[0072] A left-handed chiral excitation source is set at the center of the first large equilateral triangle hole at the boundary of the BBSS form, which can excite a left-propagating chiral light signal.

[0073] By setting a right-handed chiral excitation source at the center of the first large equilateral triangle hole on the boundary of the BBSS form, a chiral light signal propagating to the right can be excited.

[0074] After experimental verification, when the valley edge state waveguide of this embodiment is used to transmit chiral light signals, no backscattered signal is returned during the transmission process and at the output of the waveguide end face, verifying that the Sarmchair armchair boundary valley edge state waveguide has the characteristics of direction-selective transmission of chiral light signals and can play a role in suppressing backscattering loss.

[0075] In addition, the valley edge state waveguide of the present embodiment also includes a zigzag boundary, and the zigzag boundary is combined with the armchair boundary to realize 90° and 180° steering of the transmission signal. Specifically, the armchair boundary is linked and combined with the zigzag boundary at the corner to construct a valley edge state waveguide with a 90° corner and a 180° corner. An excitation source can also be set in the zigzag boundary so that the chiral light signal starts from the zigzag boundary and enters the armchair boundary through the corner.

[0076] Zigzag boundaries can be divided into BB-type boundaries and SS-type boundaries. The SS-type boundary is a zigzag boundary constructed by two adjacent small equilateral triangle holes. The BB-type boundary is a zigzag boundary constructed by two adjacent large equilateral triangle holes.

[0077] In a valley edge state waveguide with a 90° angle: if the armchair boundary in the horizontal direction is an SSBB boundary, connecting the SS boundary at the 90° angle of the SSBB boundary can realize the right-handed optical signal to propagate upward along the SSBB boundary; connecting the BB boundary at the 90° angle of the SSBB boundary can realize the right-handed optical signal to propagate downward along the SSBB boundary. Figure 4 and attached Figure 5 shown.

[0078] After two 90° turns, a 180° turn can be achieved. Connecting the 90° turn of the SSBB boundary to the zigzag boundary, and connecting the 90° turn of the zigzag boundary to the BBSS boundary, a 180° turn of the right-handed optical signal can be achieved. The 180° turn is shown in the attached figure. Figure 6 shown.

[0079] Instructions attached Figure 4 The experimental results of the 90° rotation angle are shown in Figure 2. Figure 5 It is a schematic diagram of the transmission of optical signals in the valley edge state waveguide. The horizontal waveguide is an SSBB form boundary, and then connects to the SS form boundary at a 90° corner. The right-handed chiral optical signal source is located at the center of the first small equilateral triangle hole in the SSBB form boundary. The frequency of the right-handed optical signal is 157.79THz. The right-handed chiral light field generated by the excitation can only propagate to the right along the valley edge state waveguide, and continue to propagate upward along the SS form boundary after a 90° turn. Although it undergoes a 90° turn, no backscattering signal is generated. Even if the chiral optical signal undergoes one or two 90° turns in the transmission path, no obvious backscattering signal is present in the valley edge state waveguide, proving that the valley edge state waveguide of this embodiment can transmit chiral optical signals.

[0080] This embodiment discloses a valley edge state waveguide using an armchair boundary, and designs a boundary composed of two-dimensional photonic crystals with opposite structures to realize the transmission of chiral light signals in the topologically protected valley edge state waveguide. The valley edge state waveguide constructed by the armchair boundary can realize the direction-selective transmission of the chiral light field signal, and the conservation of chirality is always maintained during the transmission of the chiral light signal. And by combining the valley edge state waveguide constructed by the armchair boundary and the zigzag boundary, the transmission of the chiral light field with a 90° turn angle and the transmission of a 180-degree turn formed by two consecutive 90° turns can be realized, and there is no loss of backscattered signals during the transmission process.

[0081] Example 2

[0082] Embodiment 2 of the present invention discloses a method for transmitting a chiral optical signal, which applies the valley edge waveguide of embodiment 1 to the transmission of a specific signal. The scheme is as follows:

[0083] A method for transmitting a chiral optical signal, using the valley edge state waveguide in Example 1 to transmit the chiral optical signal; the transmission method comprises the following steps:

[0084] An excitation source is set at the center of any regular triangle hole in the armchair boundary;

[0085] When the excitation source is a left-handed chiral light signal, the light signal will be transmitted to the left along the valley edge state waveguide; when the excitation source is a right-handed chiral light signal, the light signal will be transmitted to the right along the valley edge state waveguide; and there is no backscattered signal returned during the transmission process and at the output of the waveguide end face;

[0086] The chiral light signal enters the zigzag boundary at the 90° corner of the armchair boundary for transmission, thus realizing a 90° turn of the chiral light signal; and then enters the armchair boundary at the 90° corner of the zigzag boundary for transmission, thus realizing a 180° turn of the chiral light signal.

[0087] An excitation source may also be arranged at the zigzag boundary, so that the chiral light signal starts from the zigzag boundary and enters the armchair boundary after passing 90°.

[0088] This embodiment discloses a method for transmitting a chiral light signal, which uses the valley edge state waveguide in Embodiment 1 to transmit a chiral light signal, and can achieve 90° and 180° rotation angles of the chiral light signal, without loss of backscattered signals during the transmission process.

[0089] Example 3

[0090] This embodiment discloses a chiral light signal equal beam splitting device based on valley edge state waveguide, which uses the valley edge state waveguide of embodiment 1 to perform equal beam splitting on the chiral light signal. The specific scheme is as follows:

[0091] A chiral light signal equal beam splitting device based on valley edge state waveguide adopts the valley edge state waveguide of Example 1, combines two forms of armchair boundaries and two forms of zigzag boundaries to construct a vertical cross valley edge state waveguide, so as to realize the equal beam splitting function of the transmitted chiral light field signal intensity.

[0092] The beam splitting device includes four types of edges: SSBB edge, BBSS edge, SS edge and BB edge. One of the SSBB edge and the BBSS edge is used to carry the excitation source of the chiral light signal, and one of the SSBB edge and the BBSS edge is used to guide the chiral light signal to be equally split to both sides.

[0093] In the first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point; in the second direction, the SS form boundary and the BB form boundary are connected at the beam splitting point; the first direction is perpendicular to the second direction.

[0094] After the chiral light signal enters the splitting point from a certain form of armchair boundary, it will not enter another form of armchair boundary based on the principle of chirality conservation; and there are two forms of zigzag boundaries at the splitting point. After the chiral light signal is split, the transmission directions in the two forms of zigzag boundaries are opposite to achieve equal splitting.

[0095] Instructions attached Figure 7 The armchair boundary and the zigzag boundary are constructed to vertically cross the valley edge state waveguide to achieve the equal beam splitting function of the transmitted chiral light field signal intensity. Figure 8 The figure is a schematic diagram of the effect of light field signal splitting. The vertical direction is the armchair boundary, and the boundary form from top to bottom is: SSBB-BBSS; the horizontal direction is the zigzag boundary, and the boundary form from left to right is: BB-SS. The excitation source is located at the center of the first S small equilateral triangle hole of the SSBB boundary, which excites the right-handed chiral light field signal and transmits it along the armchair boundary valley edge state waveguide, and realizes equal beam splitting of the right-handed chiral light signal intensity at the intersection with the zigzag boundary. The transmitted right-handed light field signal does not continue to transmit along the lower half of the BBSS boundary, but is split with equal intensity at the intersection, with one beam transmitted to the right along the SS form of the zigzag boundary, and the other beam transmitted to the left along the BB form of the zigzag boundary. The characteristic of valley edge state waveguide transmission is to maintain the conservation of chirality during the transmission process, and the chirality of the SSBB form of the armchair boundary is opposite to that of the BBSS form. Therefore, the chiral light field will not continue to transmit to the lower half of the armchair boundary. After beam splitting at the intersection, the chirality of the SS form and the BB form of the zigzag boundary is also opposite. After beam splitting, the transmission directions along SS and BB are also exactly opposite. Therefore, the right-handed chiral light field will be divided into two beams and continue to transmit along SS and BB respectively. And at the intersection, the intensity of the beam split to the two SS and BB forms of the Zigzag zigzag boundary is equal, and the beam splitting geometry condition of the 90° angle determines the situation of equal beam splitting of the intensity of the transmitted chiral light signal.

[0096] The present invention discloses a valley edge state waveguide using an armchair boundary and its application. Two boundaries formed by two-dimensional photonic crystals with opposite structures are designed to realize the chiral light signal transmission of the valley edge state waveguide with topological protection. The valley edge state waveguide constructed by the armchair boundary can realize the direction-selective transmission of the chiral light field signal, and the conservation of chirality is always maintained during the transmission process of the chiral light signal. And by combining the valley edge state waveguide constructed by the armchair boundary and the zigzag boundary, the transmission of the chiral light field with a 90° angle and the transmission of two consecutive 90° angles to form a 180-degree angle can be realized, and there is no loss of backscattered signals during the transmission process. By constructing a vertical intersection structure of the armchair boundary and the zigzag boundary, a valley edge state waveguide beam splitter device with topological protection of a two-dimensional photonic crystal is formed, and the beam splitting function of the transmitted chiral light field signal at the vertical intersection point is realized.

[0097] Those skilled in the art will appreciate that the accompanying drawings are only schematic diagrams of a preferred implementation scenario, and the modules or processes in the accompanying drawings are not necessarily necessary for the implementation of the present invention. Those skilled in the art will appreciate that the modules in the devices in the implementation scenario can be distributed in the devices of the implementation scenario according to the description of the implementation scenario, or can be changed accordingly and located in one or more devices different from the present implementation scenario. The modules of the above-mentioned implementation scenarios can be combined into one module, or can be further split into multiple sub-modules. The above disclosure is only a few specific implementation scenarios of the present invention, but the present invention is not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A valley edge state waveguide using an armchair boundary, characterized in that: The method is constructed based on valley spin in a graphene-like two-dimensional photonic crystal; wherein the graphene-like two-dimensional photonic crystal includes two hexagonal lattice primitive cells with opposite structures, namely a first hexagonal lattice primitive cell and a second hexagonal lattice primitive cell; Each hexagonal lattice unit cell is composed of two types, a total of six sub-lattices, one of which is composed of large regular triangle holes, and the other is composed of small regular triangle holes. The valley edge state waveguide includes an armchair boundary, and the armchair boundary can be divided into an SSBB form boundary and a BBSS form boundary; A preset direction, a first direction, and a second direction are specified in the same plane, wherein the first direction and the second direction are respectively perpendicular to the preset direction and in opposite directions; Along the preset direction, the SSBB form boundary is sequentially composed of a boundary between two adjacent small equilateral triangle holes and a boundary between two adjacent large equilateral triangle holes, and the first hexagonal lattice unit cell is located in a first direction of the SSBB form boundary, and the second hexagonal lattice unit cell is located in a second direction of the SSBB form boundary; Along the preset direction, the BBSS form boundary is composed of the boundary between two adjacent large equilateral triangle holes and the boundary between two adjacent small equilateral triangle holes in sequence, and the second hexagonal lattice unit cell is located in the first direction of the BBSS form boundary, and the first hexagonal lattice unit cell is located in the second direction of the BBSS form boundary.

2. The valley edge state waveguide according to claim 1, characterized in that: The hexagonal lattice unit cell is a regular hexagon, and the side length of the hexagonal lattice unit cell is assumed to be a: The side length of the small equilateral triangle hole ranges from 0.3a to 0.45a, and the side length of the large equilateral triangle hole ranges from 0.5a to 0.7a.

3. The valley edge state waveguide according to claim 1, characterized in that: The valley edge state waveguide can transmit chiral optical signals; The excitation source of the chiral light signal may be located at the center of any equilateral triangle hole in the armchair boundary.

4. The valley edge state waveguide according to claim 3, characterized in that: The excitation source can excite a chiral light signal with circular polarization characteristics in the direction of the electric field. According to the rotation direction of the circular polarization electric field, the excitation source is divided into a left-handed chiral excitation source and a right-handed chiral excitation source. By setting a left-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form, a left-propagating chiral light signal can be excited; Setting a right-handed chiral excitation source at the center of the first small equilateral triangle hole at the boundary of the SSBB form can excite a chiral light signal propagating to the right. A left-handed chiral excitation source is set at the center of the first large equilateral triangle hole at the boundary of the BBSS form, which can excite a left-propagating chiral light signal. By setting a right-handed chiral excitation source at the center of the first large equilateral triangle hole on the boundary of the BBSS form, a chiral light signal propagating to the right can be excited.

5. The valley edge state waveguide according to claim 1, characterized in that: The valley edge state waveguide further includes a zigzag boundary; The armchair boundary is linked with the zigzag boundary to realize a 90° turn and a 180° turn of the signal.

6. The valley edge state waveguide according to claim 5, characterized in that: The zigzag boundary can be divided into a BB form boundary and a SS form boundary; In a 90° turn valley edge state waveguide: If the horizontal armchair boundary is a SSBB form boundary: Connecting the SS form boundary at the 90° corner of the SSBB form boundary can realize the propagation of right-handed optical signals upward along the SSBB form boundary; Connecting the BB form boundary at the 90° corner of the SSBB form boundary can enable the right-handed optical signal to propagate downward along the SSBB form boundary.

7. The valley edge state waveguide according to claim 6, characterized in that: The 90° corner of the SSBB form boundary is connected to the zigzag boundary, and the 90° corner of the zigzag boundary is connected to the BBSS form boundary, so that a 180° turn of the right-handed optical signal can be achieved.

8. A method for transmitting a chiral optical signal, characterized in that: Using the valley edge state waveguide described in claim 1; the transmission method comprises: An excitation source is set at the center of any regular triangle hole in the armchair boundary; When the excitation source is a left-handed chiral light signal, the light signal will be transmitted to the left along the valley edge state waveguide; when the excitation source is a right-handed chiral light signal, the light signal will be transmitted to the right along the valley edge state waveguide; and there is no backscattered signal returned during the transmission process and at the output of the waveguide end face; The chiral light signal enters the zigzag boundary at the 90° corner of the armchair boundary for transmission, thus realizing a 90° turn of the chiral light signal; and then enters the armchair boundary at the 90° corner of the zigzag boundary for transmission, thus realizing a 180° turn of the chiral light signal.

9. A chiral light signal equal beam splitting device based on valley edge state waveguide, characterized in that: A valley edge state waveguide comprising any one of claims 1 to 7; The beam splitting device includes an SSBB form boundary, a BBSS form boundary, an SS form boundary and a BB form boundary, and the excitation source of the chiral light signal is located at the SSBB form boundary or the BBSS form boundary; In a preset first direction, the SSBB form boundary and the BBSS form boundary are connected at a preset beam splitting point; In the preset second direction, the SS form boundary and the BB form boundary are connected at the beam splitting point; The first direction is perpendicular to the second direction.

10. The chiral light signal equal beam splitting device according to claim 9, characterized in that: After a chiral light signal enters the beam splitting point from a certain form of armchair boundary, it will not enter another form of armchair boundary based on the principle of chirality conservation; There are two forms of zigzag boundaries at the splitting point, and the transmission directions of the chiral light signal in the two forms of zigzag boundaries are opposite after the splitting, so as to achieve equal splitting.

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