Coupling prism and design method thereof

Abstract

The invention discloses a coupling prism and a design method thereof, and relates to the technical field of holographic grating, and the design method of the coupling prism comprises the steps: constructing a space rectangular coordinate system O-XYZ; calculating theta R and theta S according to a formula 1; drawing a vector LR and a vector LS by taking the theta R and the theta S as included angles between vectors and the Y axis and taking the original point O as a vector vertex; respectively drawing a circle OR and a circle OS by taking the diameter of the light spot as the diameter and taking a certain point on the LR and the LS as the circle center; vertical lines l1 and l2 of the LR and the LS are drawn through the circle centers of the circle OR and the circle OS respectively, and the vertical line l1 and the vertical line l2 intersect at the vertex A; drawing a straight line l3, wherein the straight line l3 is intersected with the vertical line l1 and the vertical line l2 at a point B and a point C respectively; and stretching a triangle determined by the vertex A, the point B and the point C along the Z direction to form a coupling prism model. According to the coupling prism and the design method thereof provided by the invention, the size of the coupling prism can be reduced on the basis of realizing the preparation of the transmission-type holographic grating.

Description

Technical Field

[0001] The present application relates to the technical field of holographic gratings, and in particular to a coupling prism and a design method thereof. Background Art

[0002] The development of the vehicle head-up display (HUD) industry is changing with each passing day. The diffraction optical waveguide based on volume holographic grating is one of the most promising technical solutions in the AR-HUD industry. Volume holographic gratings can be divided into reflective volume holographic gratings and transmissive holographic gratings. Among them, the transmissive holographic grating has obvious advantages in diffraction efficiency and can meet the needs of HUD working outdoors, especially in scenes with strong sunlight. However, since the two coherent beams of the reflective volume holographic grating are incident from both sides of the substrate during exposure, the construction of the optical path is relatively simple, and when coupling the beam, only an ordinary right-angle prism is needed to meet the coupling requirements. Therefore, the current research work related to AR-HUD is mainly based on reflective volume holographic optical waveguides. In contrast, the exposure method of the transmissive holographic grating is the same-side double-beam exposure, in which the incident angle of the signal light is greater than the total reflection angle of the waveguide interface. When the light beam is directly incident, it cannot enter the waveguide to form interference with the reference light to complete the exposure. Therefore, it is necessary to design a coupling prism to couple the signal light into the waveguide without changing the incident angle. In addition, for AR-HUD diffraction waveguides, the driver needs to observe the image of the waveguide in a larger range, which requires the waveguide to have a larger eyebox, which will directly lead to a larger volume holographic grating area in the diffraction waveguide. Correspondingly, the area of ​​the light beam during exposure will also increase. Therefore, the exposure of the transmission holographic grating requires a same-side coupling prism that can couple two beams of light at the same time. Among them, the large incident angle and large beam size will cause the prism to be extremely large, which is not conducive to processing and manufacturing and prism surface coating, and ultimately leads to excessive costs. Summary of the invention

[0003] The purpose of the present application is to provide a coupling prism and a design method thereof, which can reduce the size of the coupling prism on the basis of realizing the preparation of a transmission-type holographic grating.

[0004] On the one hand, an embodiment of the present application provides a design method for a coupling prism, wherein the coupling prism is used to couple a reference light and a signal light to a waveguide substrate, and the reference light and the signal light interfere on the waveguide substrate to form a transmission holographic grating, comprising: constructing a spatial rectangular coordinate system O-XYZ, wherein the Z direction is the axial direction of the coupling prism, and the coupling prism is prism-shaped; calculating θ according to formula 1 R and θ S , where θ S is the incident angle of the signal light; θ Ris the incident angle of the reference light; n1 is the refractive index of the incident medium when the waveguide substrate is used; θ1 is the incident angle of the incident medium, n2 is the refractive index of the waveguide substrate, and θ2 is the refractive angle of the waveguide substrate, which is also the angle of the incident transmission holographic grating;

[0005]

[0006] In the OXY plane, θ R and θ S is the angle between the vector and the Y axis, and draws the vector L with the origin O as the vector vertex R and vector L S ; Determine the spot diameter of the reference light and the signal light according to the maximum size of the transmission holographic grating in each direction, and take the spot diameter as the diameter, L R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO R and circle O S Tangent at point E; through circle O R Draw L at the center of the circle R The perpendicular line l1 passes through the circle O S Draw L at the center of the circle S The perpendicular line l2 of the circle O intersects the perpendicular line l1 and the perpendicular line l2 at vertex A. Draw a straight line l3 parallel to the X-axis. The straight line l3 intersects the circle O s and circle O S The line l3 is tangent to the point closest to the X-axis and intersects the vertical line l1 and the vertical line l2 at points B and C respectively; the triangle determined by the vertices A, B and C is stretched along the Z direction to form a coupled prism model.

[0007] As an practicable method, in the OXY plane, θ R and θ S is the angle between the vector and the Y axis, and draws the vector L with the origin O as the vector vertex R and vector L S When the vector L R and vector L S Located on both sides of the Y axis.

[0008] As an practicable manner, before stretching the triangle defined by vertex A, point B and point C along the Z direction, the design method of the coupling prism further includes: determining a circle O R and circle O S The edge points H and G of the projection on the straight line l3; the edge points H and G are extended along the Y axis to form a cutting line, and the circle O is cut along the cutting line R and circle O S The area not covered by the projection.

[0009] As an practicable approach, determine the circle O R and circle O S After the edge points H and G are projected on the straight line l3, the design method of the coupling prism further includes: the edge points H and G are moved away from the origin O by a preset distance to edge points H' and G'.

[0010] As an implementable manner, the preset distance is 5% of the spot diameter of the reference light or the signal light.

[0011] As an implementable manner, in a triangle defined by stretching vertices A, point B, and point C along the Z direction, the stretching length is a larger value of the spot diameters of the reference light and the signal light.

[0012] As an implementable method, determining the spot diameters of the reference light and the signal light according to the maximum size of the transmission holographic grating in each direction includes: obtaining the shape of the transmission holographic grating, and determining the maximum size D according to the sizes in each direction; the spot diameter of the reference light is between 1.1D-1.3D, and the spot diameter of the signal light is between 1.1D-1.3D.

[0013] As an implementable manner, the spot diameter of the reference light is the same as the spot diameter of the signal light.

[0014] As an implementable method, the spot diameter is taken as the diameter and L is taken as the R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO R and circle O S After being tangent to a point E, the design method of the coupling prism further includes: connecting the origin O and the point E to form a vector OE, where the vector OE is the normal direction of the transmission holographic grating.

[0015] On the other hand, an embodiment of the present application provides a coupling prism, which is designed and manufactured using the above-mentioned coupling prism design method. The coupling prism is a triangular prism, including a bottom surface and two coupling surfaces. The two coupling surfaces are connected to couple reference light and signal light to a waveguide substrate, respectively. The reference light and the signal light interfere on the waveguide substrate to form a transmission holographic grating.

[0016] The beneficial effects of the embodiments of the present application include:

[0017] The design method of the coupling prism provided in the present application uses a model to set various parameters of the coupling prism for reference light and signal light according to various information of the grating to be formed, so that the designed coupling can reduce the volume of the coupling prism under the premise of coupling all reference lights and signal lights. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application 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 paying creative work.

[0019] Figure 1 A flow chart of a design method for a coupling prism provided in an embodiment of the present application;

[0020] Figure 2 One of the state diagrams of a method for designing a coupling prism provided in an embodiment of the present application;

[0021] Figure 3 A second state diagram of a method for designing a coupling prism provided in an embodiment of the present application;

[0022] Figure 4 A third state diagram of a method for designing a coupling prism provided in an embodiment of the present application;

[0023] Figure 5 A fourth state diagram of a method for designing a coupling prism provided in an embodiment of the present application;

[0024] Figure 6 A fifth state diagram of a method for designing a coupling prism provided in an embodiment of the present application;

[0025] Figure 7 One of the model diagrams of a coupling prism provided in an embodiment of the present application;

[0026] Figure 8 This is a second model diagram of a coupling prism provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0029] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0030] In the process of preparing a transmission holographic grating, the reference light and the signal light are coupled through a coupling prism, and are irradiated to the waveguide substrate from the same side of the waveguide substrate and interfere on the waveguide substrate to form a transmission holographic grating. When the incident angles of the reference light and the signal light are known, in three-dimensional space, the incident planes of the reference light and the signal light can be translated in the plane. If the coupling prism is set arbitrarily only according to the incident angles of the reference light and the signal light, the coupling prism will be too large or too small. If the side length of the coupling prism is too large, it will increase the difficulty of processing and increase the cost, and also increase the area of ​​the exposure system; if the side length of the coupling prism is too small, the reference light or signal light that needs to be coupled into the waveguide cannot be fully coupled into, resulting in grating defects.

[0031] The present application provides a design method of a coupling prism, wherein the coupling prism is used to couple reference light and signal light to a waveguide substrate, and the reference light and signal light interfere on the waveguide substrate to form a transmission holographic grating, such as Figure 1 As shown, including:

[0032] S10: constructing a spatial rectangular coordinate system O-XYZ, wherein the Z direction is the axial direction of the coupling prism, and the coupling prism is prismatic;

[0033] Specifically, the coupling prism is a triangular prism, wherein two of the three faces of the triangular prism serve as coupling faces of the reference light and the signal light respectively, and the other face serves as the contact face with the waveguide substrate (also called the bottom face). The reference light and the signal light are coupled into the coupling prism from the coupling faces respectively, and are emitted into the waveguide substrate from the bottom face.

[0034] It can be understood that when the axial direction of the coupling prism is the Z-axis direction, in the OXY plane, the cross-section of the coupling prism is a triangle, one side of the triangle is in contact with the waveguide substrate, and the other two sides correspond to coupling surfaces, which are used for coupling signal light and reference light respectively.

[0035] S20: Calculate θ according to formula 1 R and θ S , where θ S is the incident angle of the signal light; θ R is the incident angle of the reference light; n1 is the refractive index of the incident medium when the waveguide substrate is used; θ1 is the incident angle of the incident medium, n2 is the refractive index of the waveguide substrate, and θ2 is the refractive angle of the waveguide substrate, which is also the angle of the incident transmission holographic grating;

[0036]

[0037] When the grating is working, it enters the waveguide substrate from the air. The refractive angle of the waveguide substrate θ2 can be calculated from the incident angle θ1 of the grating, the refractive index of the air and the refractive index of the waveguide substrate according to the third line of formula 1. According to the principle of holographic grating recording, the incident angle during exposure is the refractive angle of the waveguide substrate. According to the second line of formula 1, the incident angle θ of the reference light can be obtained. R , and then according to the first line of formula 1, we can get θ S .

[0038] S30: Figure 2 As shown, in the OXY plane, θ R and θ S is the angle between the vector and the Y axis, and draws the vector L with the origin O as the vector vertex R and vector L S ;

[0039] Specifically, the vector L R and vector L S Physically, they represent the light vectors of the reference light and the signal light respectively. The reference light is θ R The signal light is incident on the surface of the waveguide substrate at an angle of θ S The angle of incidence is the surface of the waveguide substrate.

[0040] S40: Figure 3 As shown, the spot diameters of the reference light and the signal light are determined according to the maximum size of the transmission holographic grating (hereinafter referred to as grating) in each direction, and the spot diameter is taken as the diameter, L R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO R and circle O S Tangent at point E;

[0041] According to the aforementioned coupling prism, it is used to couple the reference light and the signal light when preparing the grating, that is, the shape and size of the grating are determined. In order to be able to interfere to form a grating, the light spots of the reference light and the signal light should cover the grating. Based on this, the light spot diameters of the reference light and the signal light in the embodiment of the present application are determined according to the maximum size of the grating in each direction. Among them, the maximum size of the grating in each direction refers to a plurality of sizes along a straight line direction in the plane where the grating is located, and the maximum value among the plurality of sizes is the maximum size. For example, for a circular grating, the maximum size is the diameter of the circle; for a square grating, the maximum size is the value of the diagonal.

[0042] The spot diameters of the reference light and the signal light may be the same or different, and those skilled in the art may make specific settings according to actual conditions, as long as the spot diameters of the reference light and the signal light are both larger than the maximum size of the grating.

[0043] After determining the spot diameters of the reference light and the signal light, take the spot diameter of the reference light as the diameter and L as the R Draw a circle O with a point on it as the center R , with the spot diameter of the signal light as the diameter, L S Draw a circle O with a point on it as the center S , where circle O R and circle O S Tangent to point E, circle O R and circle O S The tangent point setting can fully utilize the lengths of the two sides of the triangle, thereby minimizing the cross-sectional area of ​​the coupling prism and minimizing the volume of the corresponding coupling prism.

[0044] S50: Figure 4 As shown, through the circle O R Draw L at the center of the circle R The perpendicular line l1 passes through the circle O S Draw L at the center of the circle S The perpendicular line l2, the perpendicular line l1 and the perpendicular line l2 intersect at the vertex A;

[0045] The two coupling surfaces on the coupling prism couple the signal light and the reference light respectively, and the signal light and the reference light are incident perpendicular to the coupling surfaces respectively. Therefore, based on the above vector L R and vector L S Physically, the light vectors representing the reference light and the signal light are drawn to draw the two coupling surfaces of the coupling prism. Specifically, through the circle O R Draw L at the center of the circle R The perpendicular line l1 of the circle O is used as a coupling surface; S Draw L at the center of the circle S The perpendicular line l2 serves as another coupling surface, and the perpendicular lines l1 and l2 intersect at vertex A, which serves as a vertex of the coupling prism.

[0046] S60: Figure 5 As shown, draw a straight line l3 parallel to the X axis, and the straight line l3 and the circle O R and circle O S Tangent to the X-axis, straight line l3 intersects perpendicular line l1 and perpendicular line l2 at points B and C respectively;

[0047] Line l3 and circle O R and circle O S The point closest to the X axis is tangent, so that circle O R and circle O S Located above the straight line l3 and in contact with the circle O R and circle O SThe distance between the two prisms is the shortest. Thus, on the basis of ensuring the coupling of reference light and signal light, the cross-sectional area of ​​the coupling prism is minimized, and the corresponding volume of the coupling prism is minimized.

[0048] S70: Figure 7 As shown, the triangle defined by vertex A, point B and point C is stretched along the Z direction to form a coupled prism model.

[0049] The design method of the coupling prism provided in the present application uses a model to set various parameters of the coupling prism for reference light and signal light according to various information of the grating to be formed, so that the designed coupling can reduce the volume of the coupling prism under the premise of coupling all reference lights and signal lights.

[0050] Optional, such as Figure 2 As shown, in the OXY plane, θ R and θ S is the vector direction, and draws vector L with the origin O as the vector vertex R and vector L S When the vector L R and vector L S Located on both sides of the Y axis.

[0051] According to the above vector L R and vector L S Physically, the light vectors representing the reference light and the signal light are coupled into the reference light and the signal light respectively by two coupling surfaces. The vector L R and vector L S They are respectively located on both sides of the Y axis, so that the two coupling surfaces are located on both sides of the Y axis, which is convenient for subsequent design.

[0052] In one achievable manner of the embodiment of the present application, before stretching the triangle defined by vertex A, point B, and point C along the Z direction, the design method of the coupling prism further includes:

[0053] S41: Determine circle O R and circle O S The edge points H and G of the projection on the line l3;

[0054] S42: Figure 6 and Figure 8 As shown, the edge points H and G are extended along the Y axis to form a cutting line, and the circle O is cut along the cutting line. R and circle O S The area not covered by the projection.

[0055] After the triangle is formed, some parts of the triangle have no light passing through them. In order to further reduce the volume of the coupling prism, the embodiment of the present application cuts off the parts where no light passes through and only retains the parts where light passes through. Specifically, determine the circle O Rand circle O S The edge points H and G of the projection on the straight line l3 are used to determine the application space of the light within the triangle ABC; then the edge points H and G are extended along the Y axis to form a cutting line, cutting off the part not covered by the circle O R and circle O S The area not covered by the projection can be reduced, thereby reducing the volume of the coupling prism.

[0056] Optionally, determine circle O R and circle O S After the edge points H and G of the projection on the straight line l3, the design method of the coupling prism also includes:

[0057] S411: Figure 6 As shown, the edge points H and G move away from the origin O by a preset distance to edge points H' and G'.

[0058] In order to avoid affecting the normal transmission of the light beam after the excess part is cut off, the edge points H and G are moved away from the origin O by a preset distance to the edge points H' and G' to reserve activity space for the light beam.

[0059] In one achievable manner of the embodiment of the present application, the preset distance is 5% of the spot diameter of the reference light or the signal light.

[0060] Specifically, those skilled in the art can set the preset distance according to actual conditions.

[0061] Optionally, in a triangle determined by stretching vertices A, point B, and point C along the Z direction, the stretching length is a larger value of the spot diameter of the reference light and the signal light.

[0062] The stretching length is the axial length of the coupling prism. In order to ensure that the light spots of the reference light and the signal light fall on the two coupling surfaces, and the light spots of the reference light and the signal light are circular spots, the stretching length is the larger value of the light spot diameter of the reference light and the signal light, so that the light spots of the reference light and the signal light can fall on the corresponding coupling surfaces.

[0063] In one achievable manner of the embodiment of the present application, determining the spot diameters of the reference light and the signal light according to the maximum size of the transmission holographic grating in each direction includes:

[0064] Obtain the shape of the transmission holographic grating, and determine the maximum size D according to the sizes in various directions;

[0065] In practical applications, when the size of the grating is different in various directions and the directions of the reference light and the signal light relative to the grating can be determined, the maximum size can be determined based on the size relative to the reference light and the signal light. For example, when it is determined that the reference light and the signal light interfere in the length direction of the grating, the maximum size can be set to the length direction of the grating.

[0066] The spot diameter of the reference light is between 1.1D and 1.3D, and the spot diameter of the signal light is between 1.1D and 1.3D.

[0067] In practical applications, whether it is reference light or signal light, the uniformity of the spot edge is lower than that of the center part. In order to avoid the loss of grating structure caused by uneven spot edge, the embodiment of the present application sets the spot diameter of the reference light and the spot diameter of the signal light between 1.1D-1.3D to improve the stability of the grating structure.

[0068] Optionally, the spot diameter of the reference light is the same as the spot diameter of the signal light.

[0069] The spot diameters of the reference light and the signal light are set to be the same, which can reduce the design difficulty and facilitate calculation during the design process.

[0070] In addition, when the spot diameter of the reference light is the same as the spot diameter of the signal light, and circle O R and circle O S Tangent to point E, so that the ray formed by the origin O and point E is vector L R and vector L S The angle bisector of the angle formed. According to the angle bisector law, the distance from any point on the angle bisector to both sides is equal. Since the perpendicular line l1 and the perpendicular line l2 are perpendicular to L R and L S , that is, point A is located on the ray formed by the origin O and point E.

[0071] In one achievable method of the embodiment of the present application, the diameter of the light spot is taken as the diameter, and L is taken as the diameter. R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO R and circle O S After being tangent to point E, the design method of the coupling prism also includes:

[0072] Connect the origin O and point E to form a vector OE, which is the normal direction of the transmission holographic grating. In the process of designing the coupling prism, the normal direction of the grating can be determined, which is convenient for the subsequent processing of the grating.

[0073] In order to further illustrate the design method of the coupling prism in the embodiment of the present application, the present application takes specific numerical values ​​as an example for specific description, as follows:

[0074] Step 1: Construct a spatial rectangular coordinate system O-XYZ;

[0075] Step 2: Calculate θ according to Formula 1 R and θ S;

[0076] The grating period ∧ of the grating is 0.31μm, the working wavelength of the grating is 0.532μm, the grating is a square 25*25mm, the refractive index of the waveguide substrate is 1.5168, and the incident angle θ1 of the grating is 33.5°. When the grating is working, it enters the waveguide substrate from the air, and the refractive index of the air is 1. According to the third line of formula 1, n1sinθ1=n2sinθ2, θ2 is 21.34°. According to the principle of holographic grating recording, the incident angle during exposure is the refractive angle of the waveguide substrate (that is, the second line of formula 1 θ2=θ R ), and then θ R = 21.34° Substitute into the first line of formula 1 Calculate θ S =50.13°.

[0077] Step 3: Draw vector L from origin O in the OXY plane R and vector L S , where the vector L R and vector L S θ R and θ S is the angle between the vector and the Y axis, vector L R and vector L S Physically, they represent light vectors of reference light and signal light respectively;

[0078] Step 4: Since the grating size is 25*25mm, considering that the uniformity of the edge of the spot is lower than that of the center, the spot size of the reference light and the signal light is appropriately expanded to 30mm, with 30mm as the diameter and vector L R and vector L S Draw a circle O with a point on it as the center R and circle O S , circle O R and circle O S Tangent at point E.

[0079] Step 5: Connect the origin O and point E as the grating direction;

[0080] Step 6: Cross the circle O R Draw a perpendicular line l1 from the center of L2 through circle O S Draw L at the center of the circle S The perpendicular line l2 of the circle O intersects the perpendicular line l1 and the perpendicular line l2 at the vertex A. R and circle O S The diameters are the same, and vertex A is located on the straight line formed by the origin O and point E;

[0081] Step 7: Draw a straight line l3 parallel to the X-axis. The straight line l3 and the circle O R and circle OS Tangent to the X-axis, straight line l3 intersects perpendicular line l1 and perpendicular line l2 at points B and C respectively, forming triangle ABC;

[0082] Step 8: Cut off the part of triangle ABC where no light passes;

[0083] Step 9: Stretch along the Z direction to form a coupled prism model.

[0084] The present application also discloses a coupling prism, which is designed and manufactured using the above-mentioned coupling prism design method. The coupling prism is a triangular prism, such as Figure 7 and Figure 8 As shown, it includes a bottom surface and two coupling surfaces, the two coupling surfaces are connected to couple the reference light and the signal light to the waveguide substrate respectively, and the reference light and the signal light interfere on the waveguide substrate to form a transmission holographic grating. The coupling prism disclosed in the embodiment of the present application has a smaller volume while achieving the coupling of the reference light and the signal light.

[0085] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for designing a coupling prism, wherein the coupling prism is used to couple reference light and signal light to a waveguide substrate, wherein the reference light and the signal light interfere with each other on the waveguide substrate to form a transmission holographic grating, characterized in that: include: Constructing a spatial rectangular coordinate system O-XYZ, wherein the Z direction is the axial direction of the coupling prism, and the coupling prism is prism-shaped; Calculate θ according to formula 1 R and θ S , where θ S is the incident angle of the signal light; θ R is the incident angle of the reference light; n1 is the refractive index of the incident medium when the waveguide substrate is used; θ1 is the incident angle of the incident medium, n2 is the refractive index of the waveguide substrate, and θ2 is the refractive angle of the waveguide substrate, which is also the angle of the incident transmission holographic grating; In the OXY plane, θ R and θ S is the angle between the vector and the Y axis, and draws the vector L with the origin O as the vector vertex R and vector L S ; The spot diameters of the reference light and the signal light are determined according to the maximum size of the transmission holographic grating in each direction, and the spot diameter is taken as the diameter, L R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO R and circle O S Tangent at point E; Over the circle O R Draw L at the center of the circle R The perpendicular line l1 passes through the circle O S Draw L at the center of the circle S The perpendicular line l2, the perpendicular line l1 and the perpendicular line l2 intersect at the vertex A; Draw a straight line l3 parallel to the X axis. The straight line l3 and the circle O R and circle O S Tangent to the X-axis, straight line l3 intersects perpendicular line l1 and perpendicular line l2 at points B and C respectively; The triangle defined by vertex A, point B and point C is stretched along the Z direction to form a coupled prism model.

2. The method for designing a coupling prism according to claim 1, characterized in that: The OXY plane is θ R and θ S is the angle between the vector and the Y axis, and draws the vector L with the origin O as the vector vertex R and vector L S When the vector L R and vector L S They are respectively located on both sides of the Y axis.

3. The method for designing a coupling prism according to claim 1, characterized in that: Before stretching the triangle defined by vertex A, point B and point C along the Z direction, the method further includes: Determine circle O R and circle O S The edge points H and G of the projection on the line l3; Extend edge points H and G along the Y axis to form a cutting line, and cut circle O along the cutting line s and circle O S The area not covered by the projection.

4. The method for designing a coupling prism according to claim 3, characterized in that: The determined circle O R and circle O S After the projected edge points H and G on the straight line l3, the method further comprises: The edge points H and G move away from the origin O by a preset distance to edge points H' and G'.

5. The method for designing a coupling prism according to claim 4, characterized in that: The preset distance is 5% of the spot diameter of the reference light or the signal light.

6. The method for designing a coupling prism according to claim 1, characterized in that: In the triangle determined by stretching vertices A, point B, and point C along the Z direction, the stretching length is the larger value of the spot diameter of the reference light and the signal light.

7. The method for designing a coupling prism according to claim 1, characterized in that: Determining the spot diameters of the reference light and the signal light according to the maximum size of the transmission holographic grating in each direction comprises: Obtaining the shape of the transmission holographic grating, and determining the maximum size D according to the sizes in various directions; The spot diameter of the reference light is between 1.1D and 1.3D, and the spot diameter of the signal light is between 1.1D and 1.3D.

8. The method for designing a coupling prism according to claim 7, characterized in that: The spot diameter of the reference light is the same as the spot diameter of the signal light.

9. The method for designing a coupling prism according to claim 8, characterized in that: With the spot diameter as the diameter, L R and L S Draw a circle O with a point on it as the center R and circle O S ,CircleO s and circle O S After being tangent to a point E, the method further comprises: The origin O and point E are connected to form a vector OE, and the vector OE is the normal direction of the transmission holographic grating.

10. A coupling prism, characterized in that: The coupling prism is designed and manufactured using the design method of the coupling prism described in any one of claims 1 to 9. The coupling prism is a triangular prism, including a bottom surface and two coupling surfaces. The two coupling surfaces are connected to couple the reference light and the signal light to the waveguide substrate respectively. The reference light and the signal light interfere on the waveguide substrate to form a transmission holographic grating.

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