A coupling prism and a design method thereof

Abstract

The application discloses a coupling prism and a design method thereof, relates to the technical field of holographic gratings, and can realize the preparation of a transmission type holographic grating while reducing the size of the coupling prism. R and S ; the angles between the vectors and the Y axis are R and S , and vectors L R and L S are drawn with the origin O as the top point of the vectors; circles O R and O S are drawn with the spot diameter as the diameter and with some points on L R and L S as the centers; the vertical lines l1 and l2 of L R and L S are drawn through the centers of the circles O R and O S , and the vertical line l1 intersects the vertical line l2 at the top point A; a straight line l3 is drawn, and the straight line l3 intersects the vertical line l1 at the point B and intersects the vertical line l2 at the point C; and the triangle determined by the top point A, the point B and the point C is stretched along the Z direction to form a coupling prism model. The coupling prism and the design method thereof can realize the preparation of a transmission type holographic grating while reducing the size of the coupling prism.

Description

Technical Field

[0001] This application relates to the field of holographic grating technology, and more specifically, to a coupling prism and its design method. Background Technology

[0002] The automotive head-up display (HUD) industry is developing rapidly, and diffractive waveguides based on volume holographic gratings are one of the most promising technological solutions in the AR-HUD industry. Volume holographic gratings can be divided into reflective and transmissive types. Transmissive holographic gratings have a significant advantage in diffraction efficiency, meeting the needs of HUDs operating outdoors, especially in strong sunlight. However, in reflective volume holographic gratings, two coherent beams are incident from opposite sides of the substrate during exposure, making the optical path setup relatively simple. Furthermore, only a standard right-angle prism is needed to couple the beams. Therefore, current AR-HUD research primarily focuses on reflective volume holographic waveguides. In contrast, transmissive holographic gratings use a dual-beam exposure method on the same side, where the incident angle of the signal light is greater than the total internal reflection angle at the waveguide interface. When the beam is directly incident, it cannot enter the waveguide to interfere with the reference light and complete the exposure. Therefore, a coupling prism needs to be designed to couple the signal light into the waveguide without changing the incident angle. Furthermore, for AR-HUD diffractive waveguides, the driver needs to observe the waveguide image over a large area, requiring the waveguide to have a large eyebox. This directly results in a large volume holographic grating area within the diffractive waveguide, and consequently, a larger beam area during exposure. Therefore, exposure of transmission-type holographic gratings requires a same-side coupling prism capable of simultaneously coupling two beams. The large incident angle and large beam size lead to an extremely large prism volume, which is detrimental to manufacturing and surface coating, ultimately resulting in excessively high costs. Summary of the Invention

[0003] The purpose of this application is to provide a coupling prism and its design method, which can reduce the size of the coupling prism while realizing the fabrication of a transmissive holographic grating.

[0004] One embodiment of this application provides a design method for a coupling prism. The coupling prism is used to couple a reference light and a signal light to a waveguide substrate. The reference light and the signal light interfere on the waveguide substrate to form a transmission holographic grating. The method includes: constructing a spatial rectangular coordinate system O-XYZ, where the Z direction is the axis of the coupling prism, and the coupling prism is prism-shaped; calculating θ according to Formula 1. R and θ S , where θ S θ is the angle of incidence of the signal light. Rn1 is the incident angle of the reference light; n2 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; θ2 is the refraction angle of the waveguide substrate, which is also the angle of the incident transmission holographic grating.

[0005]

[0006] In the OXY plane with θ R and θ S Let L be the angle between the vector and the Y-axis, and draw the vector L with the origin O as the vertex of the vector. R sum vector L S The spot diameters of the reference and signal lights are determined based on the maximum dimensions of the transmission holographic grating in each direction, and L is used as the diameter. R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O R and circle O S Tangent at point E; passing through circle O R Draw the center of the circle L R The perpendicular line l1 passes through circle O. S Draw the center of the circle L S Draw a perpendicular line l2, which intersects l1 and l2 at vertex A; draw a line l3 parallel to the X-axis, which intersects circle O. s and circle O S Tangent to the X-axis, line l3 intersects perpendicular lines l1 and l2 at points B and C respectively; stretch the triangle determined by vertices A, B and C along the Z direction to form a coupled prism model.

[0007] As one feasible approach, in the OXY plane with θ R and θ S Let L be the angle between the vector and the Y-axis, and draw the vector L with the origin O as the vertex of the vector. R sum vector L S When, vector L R sum vector L S They are located on both sides of the Y-axis.

[0008] As an implementable approach, the design method for the coupling prism further includes determining circle O before stretching the triangle defined by vertices A, B, and C along the Z-direction. R and circle O S The edge points H and G are projected onto line l3; extending edge points H and G along the Y-axis forms a tangent line, and the circle O is tangent along the tangent line. R and circle O S The area not covered by the projection.

[0009] As an feasible approach, determine circle O R and circle O S After the edge points H and G projected onto the straight line l3, the design method of the coupling prism also includes: moving the edge points H and G a preset distance away from the origin O to the edge points H' and G'.

[0010] As one feasible approach, the preset distance is 5% of the spot diameter of the reference light or signal light.

[0011] As one feasible approach, in the triangle defined by vertices A, B, and C along the Z-direction, the stretching length is the larger 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 based on the maximum size of the transmissive holographic grating in each direction includes: obtaining the shape of the transmissive holographic grating and determining the maximum size D based on the size in each direction; 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.

[0013] As one feasible approach, the diameter of the reference light spot is the same as the diameter of the signal light spot.

[0014] As a feasible approach, with the spot diameter as the diameter and L... R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O R and circle O S After being tangent at a point E, the design method of the coupling prism also includes: connecting the origin O and point E to form a vector OE, where vector OE is the normal direction of the transmissive holographic grating.

[0015] Another embodiment of this application provides a coupling prism, which is designed and manufactured using the above-described 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 a reference light and a 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 this application include:

[0017] The design method for the coupling prism provided in this application uses a model to set various parameters of the coupling prism for the reference light and signal light based on the information of the grating to be formed, so that the designed coupling can reduce the size of the coupling prism while coupling all reference light and signal light. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a design method for a coupling prism provided in this application embodiment;

[0020] Figure 2 This is one of the state diagrams for a design method of a coupling prism provided in an embodiment of this application;

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

[0022] Figure 4 State diagram three of a design method for a coupling prism provided in this application embodiment;

[0023] Figure 5 State diagram four of a design method for a coupling prism provided in this application embodiment;

[0024] Figure 6 The fifth state diagram of a design method for a coupling prism provided in this application embodiment;

[0025] Figure 7 One of the model diagrams of a coupling prism provided in the embodiments of this application;

[0026] Figure 8 This is a second model diagram of a coupling prism provided for an embodiment of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0029] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0030] In the fabrication of a transmission holographic grating, the reference light and signal light are coupled through a coupling prism, illuminating the waveguide substrate from the same side and interfering to form the transmission holographic grating. When the incident angles of the reference and signal lights are known, their incident surfaces can be translated in three-dimensional space. If the coupling prism is arbitrarily set based solely on these incident angles, it may become too large or too small. If the prism's side length is too large, it increases fabrication difficulty, cost, and the area of ​​the exposure system; if the prism's side length is too small, the reference or signal light that needs to be coupled into the waveguide may not be fully coupled, resulting in grating defects.

[0031] This application provides a design method for a coupling prism, which is used to couple reference light and signal light to a waveguide substrate. The reference light and signal light interfere on the waveguide substrate to form a transmission holographic grating, such as... Figure 1 As shown, it includes:

[0032] S10: Construct a spatial rectangular coordinate system O-XYZ, where the Z direction is the axis of the coupling prism, and the coupling prism is prism-shaped;

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

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

[0035] S20: Calculate θ according to Formula 1 R and θ S , where θ S θ is the angle of incidence of the signal light. R n1 is the incident angle of the reference light; n2 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; θ2 is the refraction angle of the waveguide substrate, which is also the angle of the incident transmission holographic grating.

[0036]

[0037] When the grating is working, light enters the waveguide substrate from the air. The refractive index of the air and the waveguide substrate (θ1) can be used to calculate the refractive angle of the waveguide substrate (θ2) using the third line of Formula 1. Based on the principle of holographic grating recording, the incident angle during exposure is the same as the refractive angle of the waveguide substrate. Therefore, the incident angle θ of the reference light can be obtained using the second line of Formula 1. R Then, θ can be obtained from the first row of Formula 1. S .

[0038] S30: As Figure 2 As shown, in the OXY plane with θ R and θ S Let L be the angle between the vector and the Y-axis, and draw the vector L with the origin O as the vertex of the vector. R sum vector L S ;

[0039] Specifically, vector L R sum vector L S Physically, these represent the light vectors of the reference light and the signal light, respectively, with the reference light having a length of θ. R The signal light is incident on the surface of the waveguide substrate at an angle of θ. S The angle at which the incident waveguide substrate is incident on its surface.

[0040] S40: As Figure 3 As shown, the spot diameters of the reference light and signal light are determined based on the maximum dimensions of the transmissive holographic grating (hereinafter referred to as the grating) in each direction, and the spot diameter is used as the diameter, with L as the reference diameter. R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O R and circle O S Tangent at point E;

[0041] The aforementioned coupling prism is used to couple the reference light and signal light during grating fabrication, thus determining the shape and size of the grating. To enable interference in forming the grating, the light spots of the reference light and signal light should cover the grating. Therefore, in this embodiment, the light spot diameters of the reference light and signal light are determined based on the maximum dimensions of the grating in each direction. The maximum dimensions of the grating in each direction refer to multiple dimensions along a straight line within the plane containing the grating, with the largest value among these dimensions being 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 reference light and signal light spot diameters can be the same or different. Those skilled in the art can make specific settings according to the actual situation, as long as the spot diameters of the reference light and signal light are both greater than the maximum size of the grating.

[0043] After determining the spot diameters of the reference light and the signal light, the spot diameter of the reference light is taken as the diameter, and L is used as the reference beam diameter. R Draw a circle O with a point on it as its center. R Using the diameter of the signal light spot as the diameter, and L S Draw a circle O with a point on the graph as its center. S Among them, circle O R and circle O S Tangent at point E, circle O R and circle O S Setting the prism tangent to a single point allows full utilization of the side lengths of the two sides of the triangle, thus minimizing the tangential area of ​​the coupling prism and correspondingly minimizing its volume.

[0044] S50: such as Figure 4 As shown, through circle O R Draw the center of the circle L R The perpendicular line l1 passes through circle O. S Draw the center of the circle L S The perpendicular line l2 intersects the perpendicular line l1 at 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. Therefore, based on the above vector L... R sum vector L S Physically representing the light vectors of the reference light and the signal light respectively, draw the two coupling surfaces of the coupling prism. Specifically, through circle O... R Draw the center of the circle L R The perpendicular line l1 serves as a coupling surface; passing through circle O S Draw the center of the circle L S The perpendicular line l2 serves as another coupling surface, and the perpendicular lines l1 and l2 intersect at vertex A, which is a vertex of the coupling prism.

[0046] S60: As Figure 5 As shown, draw a straight line l3 parallel to the X-axis, with line l3 intersecting circle O. R and circle O S The line l3 is tangent to the perpendicular line l1 and the 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, making circle O R and circle O S Located above line l3 and intersecting with circle O R and circle O SThe distance is the shortest, so that while ensuring the coupling of the reference light and the signal light, the cross-sectional area of ​​the coupling prism is minimized, and the volume of the coupling prism is minimized.

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

[0049] The design method for the coupling prism provided in this application uses a model to set various parameters of the coupling prism for the reference light and signal light based on the information of the grating to be formed, so that the designed coupling can reduce the size of the coupling prism while coupling all reference light and signal light.

[0050] Optional, such as Figure 2 As shown, in the OXY plane with θ R and θ S Assuming the vector direction, draw vector L with the origin O as the vector vertex. R sum vector L S When, vector L R sum vector L S They are located on both sides of the Y-axis.

[0051] Based on the aforementioned vector L R sum vector L S Physically, these represent the light vectors of the reference light and the signal light, respectively. They are coupled into the reference light and the signal light by two coupling planes, respectively. Vector L R sum vector L S Located on both sides of the Y-axis, the two coupling surfaces are positioned on opposite sides of the Y-axis, facilitating subsequent design.

[0052] In one possible implementation of this application embodiment, before stretching the triangle defined by vertices A, B, and 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 onto line l3;

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

[0055] After forming a triangle, some parts of the triangle do not allow light to pass through. To further reduce the volume of the coupling prism, this embodiment of the application removes the parts where no light passes through, retaining only the parts where light passes through. Specifically, circle O is determined. Rand circle O S The edge points H and G projected onto line l3 determine the application space of the light ray within triangle ABC; then, the edge points H and G are extended along the Y-axis to form a cutting line, cutting off the portion not covered by circle O. R and circle O S The area not covered by the projection is reduced, thereby decreasing the volume of the coupling prism.

[0056] Optionally, define circle O. R and circle O S Following the edge points H and G of the projection on line l3, the design method for the coupling prism also includes:

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

[0058] To avoid affecting the normal transmission of the beam after removing the excess part, the edge points H and G are moved a preset distance away from the origin O to the edge points H' and G' to reserve space for the beam to move.

[0059] In one possible implementation of this application embodiment, the preset distance is 5% of the spot diameter of the reference light or signal light.

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

[0061] Optionally, in the triangle defined by vertices A, B, and C stretched along the Z direction, the stretching length is the larger of the spot diameters of the reference light and the signal light.

[0062] The stretch 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 that the light spots of the reference light and the signal light are circular, the stretch 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 possible implementation of this application embodiment, determining the spot diameters of the reference light and signal light based on the maximum dimensions of the transmissive holographic grating in each direction includes:

[0064] Obtain the shape of the transmissive holographic grating and determine the maximum size D based on the dimensions in each direction;

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

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

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

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

[0069] Setting the same spot diameter for both the reference light and the signal light reduces design complexity and facilitates calculations during the design process.

[0070] Additionally, when the diameter of the reference light spot is the same as the diameter of the signal light spot, and circle O R and circle O S Tangent at point E, such that the ray formed by the origin O and point E is vector L. R sum vector L S The angle bisector of the formed angle, according to the angle bisector law, means that any point on the angle bisector is equidistant from the two sides. Since perpendicular lines l1 and l2 are perpendicular to L... R and L S That is, point A lies on the ray formed by the origin O and point E.

[0071] In one possible implementation of this application embodiment, the diameter is taken as the spot diameter, and L... R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O R and circle O S After being tangent at point E, the design methods for the coupling prism also include:

[0072] Connecting the origin O and point E forms vector OE, which is the normal direction of the transmissive holographic grating. The normal direction of the grating can be determined during the design of the coupling prism, facilitating subsequent processing of the grating.

[0073] To further illustrate the design method of the coupling prism in the embodiments of this application, this application uses specific numerical examples for detailed explanation, 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 ∧ is 0.31 μm, the operating wavelength is 0.532 μm, the grating is square (25*25 mm), the waveguide substrate has a refractive index of 1.5168, and the incident angle θ1 is 33.5°. During operation, the grating enters the waveguide substrate from air, and the refractive index of air is 1. Using formula 1 (third row), n1sinθ1=n2sinθ2, θ2 is calculated to be 21.34°. Based on the principle of holographic grating recording, the incident angle during exposure is the refractive angle of the waveguide substrate (i.e., θ2=θ in formula 1, second row). R ), then θ R Substituting 21.34° into the first row of Formula 1 θ was calculated S =50.13°.

[0077] Step 3: Draw vector L in the OXY plane starting from the origin O. R sum vector L S , where vector L R sum vector L S Using θ respectively R and θ S Let L be the angle between the vector and the Y-axis. R sum vector L S Physically, these represent the light vectors of the reference light and the signal light, respectively.

[0078] Step 4: Since the grating size is 25*25mm, and considering that the uniformity of the light spot edge is lower than that of the center, the light spot size of the reference light and signal light is appropriately expanded to 30mm, with a diameter of 30mm and a vector L... R sum vector L S Draw a circle O with a point on the graph as its 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: Pass through circle O R Draw a perpendicular line l1 from the center of circle O to L2, passing through circle O. S Draw the center of the circle L S Perpendicular line l2, perpendicular lines l1 and l2 intersect at vertex A, since circle O R and circle O S With the same diameter, vertex A lies 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, with line l3 intersecting circle O. R and circle OS The line l3 is tangent to the perpendicular line l1 and the perpendicular line l2 at points B and C respectively, forming triangle ABC.

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

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

[0084] This application also discloses a coupling prism, designed and manufactured using the above-described coupling prism design method. The coupling prism is a triangular prism, such as... Figure 7 and Figure 8 As shown, the device includes a bottom surface and two coupling surfaces. The two coupling surfaces are connected to couple a reference light and a 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. The coupling prism disclosed in this application has a small volume while achieving the coupling of the reference light and the signal light.

[0085] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A design method of a coupling prism for coupling a reference light and a signal light to a waveguide substrate on which the reference light and the signal light interfere to form a transmission type holographic grating, characterized by, The method comprises the following steps: A rectangular coordinate system O-XYZ is constructed, wherein the Z direction is the axial direction of the coupling prism, and the coupling prism is in the shape of a prism; θ is calculated according to formula 1 R and θ S where θ S is the angle of incidence of the signal light; θ R is the angle of incidence of the reference light; n1 is the refractive index of the incident medium when the waveguide substrate is applied; θ1 is the angle of incidence of the incident medium, n2 is the refractive index of the waveguide substrate, θ2 is the angle of incidence of the waveguide substrate, and is also the angle of incidence of the incident transmission-type holographic grating; In the OXY plane, θ R and θ S are the angles between the vectors and the Y axis, and the origin O is the vertex of the vectors L R and L S ; The spot diameters of the reference and signal lights are determined based on the maximum dimensions of the transmission holographic grating in each direction, and L is used as the diameter. R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O R and circle O S Tangent at point E; the circle O R the perpendicular line l1 drawn from the center of the circle L R the perpendicular line l2 drawn from the center of the circle L S the perpendicular line l1 drawn from the center of the circle L S the perpendicular line l2 drawn from the center of the circle L the perpendicular line l1 and the perpendicular line l2 intersect at the vertex A A straight line l3 parallel to the X axis is drawn, the straight line l3 intersecting the circle O R and the circle O S The straight line l3 is tangent at the point closest to the X axis, the straight line l3 intersecting the perpendicular line l1 and the perpendicular line l2 at points B and C, respectively; A triangle defined by the vertices A, B and C is stretched along the Z direction to form a coupling prism model.

2. The design method of a coupling prism according to claim 1, wherein The θ R and θ S are the angles between the vectors and the Y axis, and the vectors L R and L S are drawn with the origin O as the top point of the vectors. When the vectors L R and L S are drawn, they are located on the two sides of the Y axis, respectively.

3. The design method of a coupling prism according to claim 1, wherein Before stretching the triangle defined by the vertices A, B and C along the Z direction, the method further comprises the following steps: determining the circle O R and the circle O S edge points H and G of the projection on the straight line l3; The edge points H and G extending in the Y-axis direction form a cutting line along which the circle O is cut s and the projection of the circle O S does not cover the area.

4. The design method of a coupling prism according to claim 3, wherein said circle O R and the circle O S The method further comprises, after the edge points H and G of the projection on the straight line l3: The edge points H and G are moved away from the origin O to the edge points H' and G' by a preset distance.

5. The design method of a coupling prism according to claim 4, wherein The preset distance is 5% of the spot diameter of the reference light or the signal light.

6. The design method of a coupling prism according to claim 1, wherein In the step of stretching the triangle defined by the vertices A, B and C along the Z direction, the stretching length is the value of the spot diameter of the reference light and the signal light.

7. The design method of a coupling prism according to claim 1, wherein The step of determining the spot diameter of the reference light and the signal light according to the maximum size of the transmission type holographic grating in each direction comprises the following steps: The shape of the transmission type holographic grating is obtained, and the maximum size D is determined according to the size in each direction. 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 design method of a coupling prism according to claim 7, wherein The spot diameter of the reference light is the same as the spot diameter of the signal light.

9. The design method of a coupling prism according to claim 8, wherein Using the diameter of the light spot as the diameter, and L R and L S Draw circles O with a certain point on the surface as the center. R and circle O S , circle O s and circle O S After being tangent at point E, the method further includes: A vector OE is formed by connecting the origin O and the point E, and the vector OE is the normal direction of the transmission type holographic grating.

10. A coupling prism, characterized by, The coupling prism is designed and manufactured by using the design method of any one of claims 1-9, the coupling prism is a triple prism, comprising a bottom surface and two coupling-in surfaces, the two coupling-in surfaces are connected for coupling the reference light and the signal light into a waveguide substrate respectively, and the reference light and the signal light interfere on the waveguide substrate to form a transmission type holographic grating.

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