Diffraction-reflection type flat optical waveguide beam splitter and design method thereof

Abstract

The invention discloses a diffraction-reflection type planar optical waveguide beam splitter and a design method thereof, and relates to the technical field of planar optical waveguide application. The parallel plate substrate is divided into a beam splitting area, collimation areas and reflection areas, the beam splitting area receives incident light vertically incident from the center of the upper surface and divides the incident light into multiple beams of diffracted light, the diffracted light is reflected for a specific number of times between the reflection areas and then enters the corresponding collimation areas to be adjusted to be in a vertical emergent state, and mutually parallel sub light beams are formed on the lower surface to be emitted; a single beam splitting area and a plurality of collimation areas are adopted, microstructures are uniformly distributed in the beam splitting areas, a transmission type or a reflection type is determined according to arrangement positions, an optical reflection film layer is plated in the reflection area, and light through holes are formed in the lower surface of the parallel plate substrate according to conditions. The device is compact in structure, easy and convenient to install and adjust and high in light intensity utilization rate, a single incident light beam can be symmetrically divided into a plurality of sub light beams which are parallel in propagation direction and equal in light intensity according to given interval parameters, and meanwhile the device has a reverse beam combining function.

Description

Technical Field

[0001] This invention relates to the field of planar optical waveguide application technology, specifically a diffraction-reflection planar optical waveguide beam splitter and its design method. Background Technology

[0002] A laser beam splitter is a core optical device whose core function is to split incident light into multiple independent, parallel, and uniformly intense outgoing beams. It has important applications in the field of interferometers, and is especially suitable for forming multi-axis interferometers or realizing multi-step phase shift measurements.

[0003] There are already various technical solutions for laser parallel beam splitting devices in the existing technology. For example, the four-reading head grating interferometry system developed by Tohoku University in Japan uses two beam splitting prisms placed at 45° with mutually perpendicular beam splitting interfaces to split an incident beam into four parallel outgoing beams (Meas.Sci.Technol.,25(9):094002); in the reading head of the one-dimensional grating two-dimensional measurement system designed by Tsinghua University, a set of several beam splitting prisms bonded together are used to split a laser beam into multiple parallel beams (Sensors,2019,19(10):2409); in a spatial separation grating interferometry system developed by Harbin Institute of Technology, a beam splitting prism placed at 45° is used for reverse beam splitting, that is, two parallel beams are combined into one beam (Applied Sciences,2019,9(2):263).

[0004] However, existing laser parallel beam splitter technologies generally have significant drawbacks: firstly, the devices are generally large in size, which is not conducive to the miniaturization and integration of measurement systems; secondly, the installation, adjustment, and positioning are difficult, making it difficult to effectively eliminate or compensate for the errors introduced into the measurement system; and thirdly, the utilization rate of light energy is low, resulting in significant light intensity loss during beam splitting, which affects measurement accuracy and system performance. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a diffraction-reflection planar optical waveguide beam splitter and its design method. It has a compact structure, is easy to assemble and adjust, and has a high light intensity utilization rate. It can symmetrically split a single incident beam into multiple sub-beams with parallel propagation directions and equal light intensity according to a given spacing parameter, and also has a reverse beam combining function.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A diffraction-reflection type planar optical waveguide beam splitter includes a parallel planar substrate and microstructures and optical reflective films located on its upper and lower surfaces. The parallel planar substrate is divided into three functional regions: a beam splitting region, a collimation region, and a reflection region.

[0008] The beam-splitting region receives incident light perpendicularly incident from the center of the upper surface of the parallel plate substrate. The light is diffracted and split into multiple diffracted beams. Each diffracted beam undergoes a specific number of reflections between the reflection regions located on the upper and lower surfaces of the parallel plate substrate to propagate a given distance. The reflected beams then enter the corresponding collimation region and are adjusted to a perpendicular exit state through diffraction, ultimately forming parallel sub-beams that exit from the lower surface of the parallel plate substrate. Both the beam-splitting and collimation regions contain microstructures, which are one-dimensional or two-dimensional planar gratings or metasurface structures. The reflection regions are coated with an optical reflective film, wherein:

[0009] The beam-splitting region is a single one arranged on the upper or lower surface of the center of the parallel plate substrate: if located on the upper surface, the microstructure in the beam-splitting region is transmissive; if located on the lower surface, the microstructure in the beam-splitting region is reflective.

[0010] The collimation zone is composed of multiple collimation zones arranged symmetrically on the upper or lower surface of the edge of the parallel plate substrate, corresponding one-to-one with the non-central sub-beam positions: if located on the upper surface, the microstructure in the collimation zone is reflective; if located on the lower surface, the microstructure in the collimation zone is transmissive; when the microstructure in the collimation zone is reflective, a light-passing hole is opened at the corresponding position on the lower surface of the parallel plate substrate to allow the sub-beam to exit.

[0011] Furthermore, a global coordinate system is established based on the parallel flat plate substrate, and the position of the emitted sub-beam can be extended along one dimension to form a one-dimensional beam splitting mode, or extended along two dimensions to form a two-dimensional beam splitting mode.

[0012] Furthermore, the global coordinate system takes the center of the upper surface of the parallel plate substrate as the origin, the incident light incident direction as the z-axis, and defines mutually orthogonal x-axis and y-axis in the upper surface of the parallel plate substrate along the periodic extension direction of the microstructure, forming a right-handed rectangular coordinate system.

[0013] Furthermore, the number of sub-beams emitted is set according to requirements, and each sub-beam is symmetrically distributed about the central axis of the parallel flat substrate and has equal light intensity.

[0014] Furthermore, the total number of diffraction orders emitted by the microstructure in the beam-splitting region is equal to the set number of emitted sub-beams, and the microstructure in the collimation region emits only diffraction orders perpendicular to the surface of the parallel flat substrate.

[0015] Furthermore, the beam splitter can split a single beam of light into multiple parallel beams, and it can also reverse the process to combine multiple parallel beams of light into a single beam.

[0016] A design method for a diffraction-reflection type planar optical waveguide beam splitter includes the following steps:

[0017] S1: Choose between one-dimensional or two-dimensional beam splitting mode based on actual application requirements;

[0018] S2: Based on the selected beam splitting mode, the positions of the beam splitting region and the collimation region on the parallel flat substrate are determined, thereby determining the microstructure type;

[0019] S3: Based on the lower bound constraint condition of the thickness of the parallel plate substrate, set the number of reflections N of the beam on the lower surface of the parallel plate substrate.

[0020] S4: Based on the incident light wavelength, the refractive index of the substrate material and the target diffraction angle, the spatial period of the microstructure in the diffraction dimension is calculated and determined by combining the grating equation.

[0021] S5: Based on the set distance Δ between the sub-beam exit position and the beam splitter center axis, the number of reflections N, and the cotangent value cotθ0 corresponding to the diffraction angle, the thickness of the parallel plate substrate is calculated using geometric relationship formulas, while considering the setting of lower bound constraint conditions to avoid beam interference.

[0022] S6: With the optimization objective of maximizing the efficiency of the vertical diffraction order while minimizing the efficiency of other orders, the period and structural depth parameters of the collimated region microstructure are optimized to obtain the maximum efficiency η of the collimated diffraction order of the collimated region microstructure. m , m is the order of the diffracted light from the beam-splitting region from which the corresponding sub-beam originates;

[0023] S7: Let the efficiency of each diffraction order in the beam-splitting region be... … … The optimization objective is set based on the parity of the number of emitted beams:

[0024] If the number of outgoing sub-beams is odd, for any desired diffraction orders i and j, i ≠ j ≠ 0, the following condition is met: For any diffraction order u that does not require an outgoing emission, the following condition is satisfied: ;

[0025] If the number of outgoing sub-beams is even, for any desired diffraction orders i and j, where i ≠ j, the following condition is met: For any diffraction order u that does not require an outgoing emission, the following condition is satisfied: ;

[0026] S8: Based on actual engineering application scenarios, a tolerance analysis of the three-axis rotation angle of the beam splitter is performed;

[0027] S9: Determine the number and size of the light-transmitting holes to be set on the lower surface of the parallel plate substrate, and at the same time determine the boundary shape and size of the beam splitting area, collimation area and reflection area, as well as the boundary shape and size of the parallel plate substrate.

[0028] Compared with existing technologies, the advantages of this invention are as follows: This invention innovatively combines micro-nano optics with traditional geometric optics, achieving an integrated design of beam splitting and collimation through a parallel plate optical waveguide. The optical path undergoes multiple reflections and folds between the upper and lower surfaces of the parallel plate substrate, effectively enhancing the compactness of the optical path, significantly improving space utilization, and greatly reducing the device size, which is beneficial for system miniaturization and integration. Moreover, the device has a thin-film structure, which can be flexibly bonded to other devices, greatly reducing the difficulty of assembly and positioning in the optical path structure and reducing system error sources. At the same time, by optimizing the microstructure parameters of the beam splitting and collimation regions, the incident light, after being incident perpendicularly, can achieve highly parallel and uniform light output in one-dimensional or two-dimensional directions on the other side of the parallel plate substrate according to the given beam splitting spacing and number of beams, ensuring uniform light intensity of the output sub-beams, improving light energy utilization, and reducing light intensity loss in the beam splitting stage. In addition, the beam splitter of this invention has bidirectional beam splitting and beam combining functions, making its application scenarios more flexible and providing more flexible and miniaturized components for interferometer applications. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the optical waveguide path model of the two-output planar optical waveguide beam splitter in Embodiment 1 (the symmetrical parts are omitted).

[0030] Figure 2 This is a complete three-dimensional optical path diagram of the two-output planar optical waveguide beamsplitter in Embodiment 1;

[0031] Figure 3 This is a schematic diagram of the optical waveguide path model of the three-output planar optical waveguide beam splitter in Example 2 (the symmetrical parts are omitted).

[0032] Figure 4 This is a complete three-dimensional optical path schematic diagram of the three-output planar optical waveguide beam splitter of Embodiment 2;

[0033] Figure 5 This is a schematic diagram of the optical waveguide path model of the four-output planar optical waveguide beam splitter in Example 3 (the symmetrical parts are omitted).

[0034] Figure 6 This is a complete three-dimensional optical path schematic diagram of the four-output planar optical waveguide beam splitter in Example 3;

[0035] Figure 7 This is a flowchart of the design method of the present invention.

[0036] In the diagram: 1. Beam splitting region; 2. Collimation region; 3. Reflection region; 4. Light passage aperture. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] like Figures 1-6 As shown, a diffraction-reflection type planar optical waveguide beam splitter includes a parallel planar substrate and microstructures and optical reflective films located on its upper and lower surfaces. Its key technical features are as follows:

[0039] ① Functional area setting: The surface of the parallel plate substrate is divided into three functional areas, namely beam splitting area 1, collimation area 2 and reflection area 3. Each functional area works together to realize the beam splitting-reflection-collimation function.

[0040] ② Light propagation process: After the incident light is perpendicularly incident on the center of the upper surface of the parallel plate substrate, it is diffracted at the beam splitting region 1 and split into multiple diffracted beams. Each diffracted beam is reflected a specific number of times between the reflection regions 3 located on the upper and lower surfaces of the parallel plate substrate to propagate a given distance. After reflection, the beam enters the collimation region 2 and is adjusted to a perpendicular exit state through the diffraction effect. Finally, multiple parallel sub-beams are formed and emitted from the lower surface of the parallel plate substrate.

[0041] ③ Beam-splitting region structure: The core function of beam-splitting region 1 is to generate multiple diffracted beams as the source of sub-beams. It contains microstructures, which are one-dimensional or two-dimensional planar gratings or metasurface structures. Beam-splitting region 1 can be located on the upper or lower surface of the parallel plate substrate: if located on the upper surface, the microstructures within beam-splitting region 1 are transmissive; if located on the lower surface, the microstructures within beam-splitting region 1 are reflective.

[0042] ④ Collimation Region Structure: The core function of collimation region 2 is to adjust the obliquely incident beam to a vertically exiting beam through diffraction. It consists of several discrete, identical, and symmetrical closed regions about the central axis of the parallel plate substrate. The center of each collimation region 2 coincides with the center of the exit position of each of the other sub-beams except the central exit sub-beam, corresponding one-to-one with each non-central sub-beam. Collimation region 2 also contains microstructures, which can be one-dimensional or two-dimensional planar gratings or metasurface structures. Collimation region 2 can be located on the upper or lower surface of the parallel plate substrate: if located on the upper surface, the microstructures within collimation region 2 are reflective; if located on the lower surface, the microstructures within collimation region 2 are transmissive.

[0043] ⑤ Reflection zone structure: The core function of reflection zone 3 is to reflect the light beam a certain number of times to propagate a given distance. It is located on the upper and lower surfaces of the parallel plate substrate. Reflection zone 3 is coated with a high-reflectivity optical reflective film layer and is an opaque area. If necessary, a light-transmitting hole 4 can be opened at the corresponding position of reflection zone 2 on the lower surface of the parallel plate substrate to allow the sub-beam to exit.

[0044] ⑥ Characteristics of the emitted beam: The number of emitted parallel sub-beams can be set to any number as required. The sub-beams are symmetrically distributed about the central axis of the parallel flat substrate, and the light intensity is equal.

[0045] ⑦ Beam Splitting Mode: Define a global coordinate system associated with the parallel plate substrate. With the center of the upper surface of the parallel plate substrate as the origin, and the incident light direction (i.e., the direction perpendicular to the upper surface and pointing towards the lower surface) as the z-axis, define mutually orthogonal x-axis and y-axis within the upper surface of the parallel plate substrate along the periodic extension direction of the microstructure units. The x, y, and z axes form a right-handed rectangular coordinate system. Based on this coordinate system, the position of the emitted parallel sub-beam can be extended along one dimension (the x-axis direction) to form a one-dimensional beam splitting mode; or it can be extended along two dimensions (the x-axis direction and the y-axis direction) to form a two-dimensional beam splitting mode.

[0046] ⑧ Diffraction order correspondence: Each outgoing sub-beam corresponds one-to-one with each diffraction order that the microstructure in beam-splitting region 1 needs to emit, that is, the total number of diffraction orders that the microstructure in beam-splitting region 1 needs to emit is equal to the set number of outgoing sub-beams; the microstructure in collimation region 2 only needs to emit one diffraction order, that is, the diffraction order perpendicular to the surface of the parallel plate substrate.

[0047] ⑨ Material Selection: The microstructure material can be selected from one of the following: silicon, silicon nitride, silicon-rich silicon nitride, silicon oxynitride, titanium dioxide, diamond, gallium nitride, quartz, glass, or polymer; the cross-sectional shape of the one-dimensional or two-dimensional planar grating can be one of the following: rectangular, stepped, or sawtooth; the metasurface structure is a columnar structure, and its top-view shape can be one of the following: circular, square, elliptical, rectangular, ring-shaped, cross-shaped, I-shaped, or polygonal. The parallel plate substrate material can be selected from one of the following: silicon, silicon nitride, titanium dioxide, diamond, gallium nitride, quartz, or glass.

[0048] ⑩ Two-way function: This beam splitter can be used to split a beam of light into multiple parallel beams, or in reverse, to combine multiple parallel beams into one beam.

[0049] like Figures 1-7 As shown, a design method for a diffraction-reflection type planar optical waveguide beam splitter is presented, and its process is combined with... Figure 7 As shown, it includes the following steps:

[0050] S1: Determine the beam splitting mode: Select either a one-dimensional or two-dimensional beam splitting mode based on the actual application requirements.

[0051] S2: Determine the location of the functional area: Based on the selected beam splitting mode, determine the location of beam splitting area 1 and collimation area 2 on the parallel plate substrate. The selection of this location directly determines the microstructure type (transmission type or reflection type) of beam splitting area 1 and collimation area 2.

[0052] S3: Determine the number of reflections: Based on the lower bound constraint of the thickness of the parallel plate substrate calculated later, set the number of reflections N of the beam on the lower surface of the parallel plate substrate. The value of N will directly affect the thickness c of the parallel plate substrate, and the larger N is, the smaller c is, which is beneficial to the miniaturization of the beam splitter.

[0053] S4: Determine the spatial period of the microstructure: Based on the incident light wavelength, the refractive index of the substrate material, and the target diffraction angle, calculate and determine the spatial period T of the microstructure in the diffraction dimension using the grating equation.

[0054] S5: Determine the substrate thickness: Based on the set distance Δ between the sub-beam exit position and the beam splitter central axis, the number of reflections N, and the cotangent value cotθ0 corresponding to the diffraction angle, calculate the thickness c of the parallel plate substrate using geometric relationship formulas, while considering the setting of lower bound constraints to avoid beam interference.

[0055] S6: Optimize the microstructure parameters of the collimation region: With the optimization objective of maximizing the efficiency of the vertical diffraction order while minimizing the efficiency of other orders, optimize the period and structural depth parameters of the microstructure in collimation region 2 to ultimately obtain the maximum efficiency η of the collimation diffraction order of the microstructure in collimation region 2. m (where m is the order of the diffracted light from the beam-splitting region from which the sub-beam corresponding to collimation region 2 originates).

[0056] S7: Optimize the microstructure parameters of the beam-splitting region, assuming the efficiency of each diffraction order in beam-splitting region 1 is... … … The optimization objective is set based on the parity of the number of emitted beams:

[0057] If the number of exiting sub-beams is odd, the optimization objective is: for any diffraction orders i and j (i ≠ j ≠ 0) that need to be emitted, satisfying the following... For any diffraction order u that does not require outgoing emission, the following condition is satisfied: ;

[0058] If the number of exiting sub-beams is even, the optimization objective is: for any diffraction orders i and j (i≠j) that need to be emitted, satisfying the following... For any diffraction order u that does not require outgoing emission, the following condition is satisfied: .

[0059] S8: Tolerance Analysis: Based on actual engineering application scenarios, tolerance analysis is performed on key parameters such as the three-axis rotation angle of the beam splitter to ensure the stability and reliability of the beam splitter during actual processing and use.

[0060] S9: Determine the boundary and light-transmitting hole parameters: Determine the number and size of the light-transmitting holes to be set on the lower surface of the parallel plate substrate, and at the same time determine the boundary shape and size of the beam splitting area 1, collimation area 2 and reflection area 3, as well as the boundary shape and size of the parallel plate substrate, to complete the complete design of the beam splitter.

[0061] By using the above design, selecting a suitable beam splitting mode according to the given light source size, wavelength and beam splitting spacing, and determining the number of reflections, diffraction angle and substrate thickness, and by optimizing the microstructure parameters of the corresponding region, a symmetrical, parallel and uniform light output diffraction-reflection planar optical waveguide beam splitter can be realized.

[0062] Example 1: Two-output planar optical waveguide beam splitter

[0063] 1. Implementation Objectives

[0064] This embodiment aims to provide a two-output planar optical waveguide beam splitter that splits incident light into two parallel sub-beams of equal intensity at a given spacing. The incident light wavelength is λ = 780 nm, and the spacing between the two parallel sub-beams is 12 nm (i.e., the distance Δ = 6 mm between the exit position of the sub-beams and the central axis of the beam splitter). The beam diameter... =2mm.

[0065] 2. Material Selection

[0066] In this embodiment, the microstructure material and substrate (parallel flat plate substrate) of the planar optical waveguide beam splitter are both made of JGS1 glass.

[0067] 3. Determination of functional area location and beam splitting pattern

[0068] Beam splitting region location: Beam splitting region 1 is selected as the center of the upper surface of the parallel plate substrate;

[0069] Collimation zone location: Collimation zone 2 is selected as the location on both sides of the lower surface of the parallel plate substrate;

[0070] Beam splitting mode: The x-direction is determined as the diffraction direction of the microstructure, and a one-dimensional beam splitting mode is adopted.

[0071] 4. Calculation of key parameters

[0072] Parameter definition: Let the thickness of the parallel plate substrate be c, the number of reflections of the beam on the lower surface of the parallel plate substrate be N, and the diffraction angle from the beam splitting region 1 be θ0.

[0073] Determining the number of reflections: Based on the beam diameter constraint, to avoid spatial interference between the portion of the actual beam transmitted in beam-splitting region 1 and emitted in collimation region 2 and the portion reflected and folded in reflection region 3, the thickness of the parallel plate substrate must satisfy the lower bound constraint. Further deduction leads to Substituting Δ=6mm, =2mm, calculated N<2.5. Since the larger N is, the smaller c is, in order to achieve miniaturization of the beam splitter, N=2 is determined;

[0074] Determination of the microstructure period T in the beam-splitting region: The positive and negative first-order diffracted beams of the microstructure in beam-splitting region 1 are selected as the source of the outgoing sub-beam, and the microstructure period T of beam-splitting region 1 is determined to be 2μm.

[0075] Diffraction angle calculation: based on the grating equation (where n is the refractive index of the jgs1 glass material), and cotθ0≈3.6 is calculated;

[0076] Parallel plate substrate thickness calculation: based on Figure 1 The geometric relationships of the optical waveguide optical path model shown are expressed using the formula. Substituting Δ=6mm, N=2, and cotθ0≈3.6, we calculate that c is 4.32mm.

[0077] 5. Microstructure selection and parameter optimization

[0078] Collimation region microstructure: A one-dimensional sawtooth transmission grating is selected as the microstructure of collimation region 2, with structural parameters including period T2 and structural depth z2. The period of the microstructure in collimation region 2 is determined to be the same as that in beam-splitting region 1, i.e., T2 = 2 μm. Therefore, the diffracted light emitted perpendicularly from collimation region 2 is the negative first-order transmitted light. The optimal structural parameters for collimation region 2 are obtained through optimization: z2 = 1.89 μm, corresponding to the maximum diffraction efficiency η of the negative first-order transmitted light. -1 =59.01%;

[0079] Beam-splitting region microstructure: A one-dimensional rectangular transmission grating is selected as the microstructure of beam-splitting region 1, with structural parameters including period T, linewidth a1, and structural depth z1, to maximize the positive and negative first-order diffraction efficiency. To optimize the target, the optimal structural parameters for beam splitting region 1 were obtained: a1 = 600 nm. The corresponding diffraction efficiency in the beam-splitting region ;

[0080] Light intensity ratio verification: The ratio of the light intensity of each sub-beam to the incident light intensity is approximately .

[0081] 6. Determination of Boundary and Light Passage

[0082] Region boundary shape: The boundary shape of both the beam splitting region 1 and the collimation region 2 is rectangular, and the boundary shape of the parallel plate base is circular;

[0083] Light-transmitting hole setting: Light-transmitting hole 4 is not required in this embodiment.

[0084] 7. Tolerance Analysis

[0085] Establish as Figure 2 The two-output planar optical waveguide beamsplitter and its internal optical path are shown in a three-dimensional model. A three-axis rotation angle tolerance analysis is performed to ensure the performance stability of the beamsplitter during actual processing and assembly. Finally, the boundary dimensions l in the x-direction of beam splitting region 1 and collimation region 2 are determined. x =2.5mm, dimension l in the y direction y =3mm, the boundary diameter of the parallel plate base is Φ=20mm.

[0086] Example 2: Three-output planar optical waveguide beam splitter

[0087] 1. Implementation Objectives

[0088] This embodiment aims to provide a three-output planar optical waveguide beam splitter that splits incident light into three parallel sub-beams of equal intensity at a given spacing. The incident light wavelength is λ = 633 nm, and the spacing between adjacent parallel sub-beams is 5 mm (i.e., the distance Δ = 5 mm between the exit position of the sub-beam and the central axis of the beam splitter). The beam diameter... =2mm.

[0089] 2. Material Selection

[0090] In this embodiment, the microstructure material and substrate (parallel flat plate substrate) of the planar optical waveguide beam splitter are both made of JGS1 glass.

[0091] 3. Determination of functional area location and beam splitting pattern

[0092] Beam splitting region location: Beam splitting region 1 is selected as the center of the upper surface of the parallel plate substrate;

[0093] Collimation zone location: Collimation zone 2 is selected as the location on both sides of the upper surface of the parallel plate substrate;

[0094] Beam splitting mode: The x-direction is determined as the diffraction direction of the microstructure, and a one-dimensional beam splitting mode is adopted.

[0095] 4. Calculation of key parameters

[0096] Parameter definition: Let the thickness of the parallel plate substrate be c, the number of reflections of the beam on the lower surface of the parallel plate substrate be N, and the diffraction angle from the beam splitting region 1 be θ0.

[0097] Determining the number of reflections: Based on the beam diameter constraint, to avoid spatial interference between the portion of the actual beam transmitted in beam-splitting region 1 and reflected in collimation region 2, and the portion reflected and folded in reflection region 3, the thickness of the parallel plate substrate must satisfy the lower bound constraint. Further deduction leads to Substituting Δ=5mm, =2mm, calculated N<1.25. Since a larger N results in a smaller c, to achieve miniaturization of the beam splitter, N=1 is determined;

[0098] Determination of the microstructure period T in the beam-splitting region: The positive and negative first-order and zero-order diffracted beams of the microstructure in beam-splitting region 1 were selected as the source of the outgoing sub-beam, and the microstructure period T of beam-splitting region 1 was determined to be 1.111 μm.

[0099] Diffraction angle calculation: based on the grating equation (where n is the refractive index of the jgs1 glass material), and cotθ0≈2.36 is calculated;

[0100] Parallel plate substrate thickness calculation: based on Figure 3 The geometric relationships of the optical waveguide optical path model shown are expressed using the formula. Substituting Δ=5mm, N=1, and cotθ0≈2.36, we calculate that c is 5.88mm.

[0101] 5. Microstructure selection and parameter optimization

[0102] Collimation region microstructure: A one-dimensional sawtooth reflection grating is selected as the microstructure of collimation region 2, with structural parameters including period T2 and structural depth z2. The period of the microstructure in collimation region 2 is determined to be the same as that in beam-splitting region 1, i.e., T2 = 1.111 μm. Therefore, the diffracted light emitted vertically from collimation region 2 is the negative first-order reflected light. The optimal structural parameters for collimation region 2 are obtained through optimization: z2 = 233 nm, corresponding to the maximum diffraction efficiency of the negative first-order reflected light. ;

[0103] Beam-splitting region microstructure: A one-dimensional rectangular transmission grating is selected as the microstructure of beam-splitting region 1, and its structural parameters include period T, linewidth a1, and structural depth z1. And minimize the efficiency of non-target diffraction orders. To optimize the target, the optimal structural parameters for beam splitting region 1 were obtained: a1 = 300 nm, z1 = 600 nm, corresponding to the diffraction efficiency of the beam splitting region. , ;

[0104] Light intensity ratio verification: The ratio of the light intensity of the two sub-beams to the incident light intensity is approximately... The intensity of the central sub-beam accounts for approximately 26% of the incident light intensity.

[0105] 6. Determination of Boundary and Light Passage

[0106] Region boundary shape: The boundary shape of both the beam splitting region 1 and the collimation region 2 is rectangular, and the boundary shape of the parallel plate base is circular;

[0107] Light transmission hole setting: Three light transmission holes 4 need to be set in this embodiment.

[0108] 7. Tolerance Analysis

[0109] Establish as Figure 4 The three-dimensional model of the three-output planar optical waveguide beamsplitter and its internal optical path is shown, and a three-axis rotation angle tolerance analysis is performed to ensure the performance stability of the beamsplitter during actual processing and assembly. Finally, the boundary dimension l in the x-direction of beam splitting region 1 and collimation region 2 is determined. x =3mm, dimension l in the y direction y =3mm, the boundary diameter of the parallel plate substrate is Φ=18mm, and the diameter of the light-transmitting hole 4 is D=2.5mm.

[0110] Example 3: Four-output planar optical waveguide beam splitter

[0111] 1. Implementation Objectives

[0112] This embodiment aims to provide a four-output planar optical waveguide beam splitter that splits incident light into four parallel sub-beams of equal intensity at a given spacing. The exit positions of the four sub-beams form the four vertices of a square in space. The incident light wavelength is λ = 633 nm, and the distance between two sub-beams on the diagonal of the square is 10 mm (i.e., the distance Δ = 5 mm between the exit position of the sub-beam and the central axis of the beam splitter). The beam diameter is... =2mm.

[0113] 2. Material Selection

[0114] In this embodiment, the microstructure material and substrate (parallel flat plate substrate) of the planar optical waveguide beam splitter are both made of JGS1 glass.

[0115] 3. Determination of functional area location and beam splitting pattern

[0116] Beam splitting region location: Beam splitting region 1 is selected as the center of the upper surface of the parallel plate substrate;

[0117] Collimation zone location: Collimation zone 2 is selected as the area around the upper surface of the parallel plate substrate;

[0118] Beam splitting mode: The x and y directions are determined as the diffraction directions of the microstructure, and a two-dimensional beam splitting mode is adopted.

[0119] 4. Calculation of key parameters

[0120] Parameter definition: Let the thickness of the parallel plate substrate be c, the number of reflections of the beam on the lower surface of the parallel plate substrate be N, and the diffraction angle from the beam splitting region 1 be θ0.

[0121] Determining the number of reflections: Based on the beam diameter constraint, to avoid spatial interference between the portion of the actual beam transmitted in beam-splitting region 1 and reflected in collimation region 2, and the portion reflected and folded in reflection region 3, the thickness of the parallel plate substrate must satisfy the lower bound constraint. Further deduction leads to Substituting Δ=5mm, =2mm, calculated N<1.25. Since a larger N results in a smaller c, to achieve miniaturization of the beam splitter, N=1 is determined;

[0122] Determination of the period T of the microstructure in the beam-splitting region: The positive and negative first-order diffracted light from the x and y directions of the microstructure in beam-splitting region 1 are selected as the source of the outgoing sub-beams, and the period of the microstructure in the x and y directions of beam-splitting region 1 is determined to be T=2μm.

[0123] Diffraction angle calculation: based on the grating equation (where n is the refractive index of the jgs1 glass material), and cotθ0≈3.6 is calculated;

[0124] Parallel plate substrate thickness calculation: based on Figure 5 The geometric relationships of the optical waveguide optical path model shown are expressed using the formula. Substituting Δ=5mm, N=1, and cotθ0≈3.6, we calculate that c is 9.0mm.

[0125] 5. Microstructure selection and parameter optimization

[0126] Collimation region microstructure: A one-dimensional sawtooth reflection grating is selected as the microstructure of collimation region 2, with structural parameters including period T2 and structural depth z2. The period of the microstructure in collimation region 2 is determined to be the same as that in beam-splitting region 1, i.e., T2 = 2 μm. Therefore, the diffracted light emitted perpendicularly from collimation region 2 is the negative first-order reflected light. The optimal structural parameters for collimation region 2 are optimized to z2 = 220 nm, corresponding to the maximum diffraction efficiency of the negative first-order reflected light. ;

[0127] Beam-splitting region microstructure: A two-dimensional rectangular transmission grating is selected as the microstructure of beam-splitting region 1, and its structural parameters include the x-direction period T. x Period T in the y-direction y x-direction line width a x y-direction line width a y and structural depth z1, where T x =T y =T=2μm, let... .by And minimize the zero-order diffraction efficiency To optimize the objective, the optimal structural parameters for beam splitting region 1 were obtained: a x =a y =1.2μm, z1=810nm, corresponding to the diffraction efficiency in the beam-splitting region , ;

[0128] Light intensity ratio verification: The proportion of the light intensity of each sub-beam to the incident light intensity is approximately... .

[0129] 6. Determination of Boundary and Light Passage

[0130] Region boundary shape: The boundary shape of both the beam splitting region 1 and the collimation region 2 is rectangular, and the boundary shape of the parallel plate base is circular;

[0131] Light transmission hole setting: This embodiment requires four light transmission holes 4.

[0132] 7. Tolerance Analysis

[0133] Establish as Figure 6 The four-output planar optical waveguide beamsplitter and its internal optical path 3D model are shown, and a three-axis rotation angle tolerance analysis is performed to ensure the performance stability of the beamsplitter during actual processing and assembly. Finally, the boundary dimensions l in the x-direction of beam splitting region 1 and collimation region 2 are determined. x =3mm, dimension l in the y direction y =3mm, the boundary diameter of the parallel plate substrate is Φ=18mm, and the diameter of the light-transmitting hole 4 is D=2.5mm.

[0134] The above three embodiments illustrate the specific implementation of the present invention. Those skilled in the art can adjust parameters such as the number of beams, beam spacing, and incident light wavelength according to the design method disclosed in the present invention, based on actual application needs, to realize diffraction-reflection planar optical waveguide beam splitters of different specifications, all of which fall within the protection scope of the present invention.

[0135] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0136] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A diffraction-reflection type planar optical waveguide beamsplitter, characterized in that: It includes a parallel plate substrate and microstructures and optical reflective film layers located on its upper and lower surfaces. The parallel plate substrate is divided into three functional areas: a beam splitting area (1), a collimation area (2), and a reflection area (3). The beam splitting region (1) receives incident light perpendicularly incident from the center of the upper surface of the parallel plate substrate. The light is diffracted through the beam splitting region (1) and split into multiple diffracted beams. Each diffracted beam undergoes a specific number of reflections between the reflection regions (3) located on the upper and lower surfaces of the parallel plate substrate to propagate a given distance. The reflected beams then enter the corresponding collimation region (2) and are adjusted to a perpendicular exit state through diffraction, ultimately forming parallel sub-beams that exit from the lower surface of the parallel plate substrate. Both the beam splitting region (1) and the collimation region (2) contain microstructures, which are one-dimensional or two-dimensional planar gratings or metasurface structures. The reflection region (3) is coated with an optical reflection film, wherein: The beam splitting region (1) is a single one arranged on the upper or lower surface of the center of the parallel plate substrate: if it is located on the upper surface, the microstructure in the beam splitting region (1) is transmissive; if it is located on the lower surface, the microstructure in the beam splitting region (1) is reflective. The collimation zone (2) is arranged in multiple ways and is centrally symmetrically on the upper or lower surface of the edge of the parallel plate substrate, corresponding one-to-one with the position of the non-central sub-beam: if it is located on the upper surface, the microstructure in the collimation zone (2) is reflective; if it is located on the lower surface, the microstructure in the collimation zone (2) is transmissive; when the microstructure in the collimation zone (2) is reflective, a light-transmitting hole (4) is opened at the corresponding position on the lower surface of the parallel plate substrate to allow the sub-beam to exit.

2. The diffraction-reflection type planar optical waveguide beamsplitter according to claim 1, characterized in that: A global coordinate system is established based on the parallel flat plate substrate. The position of the emitted sub-beam can be extended along one dimension to form a one-dimensional beam splitting mode, or extended along two dimensions to form a two-dimensional beam splitting mode.

3. A diffraction-reflection type planar optical waveguide beamsplitter according to claim 2, characterized in that: The global coordinate system has the center of the upper surface of the parallel plate substrate as the origin, the z-axis along the incident light direction, and the x-axis and y-axis, which are orthogonal to each other, defined in the upper surface of the parallel plate substrate along the periodic extension direction of the microstructure. The x, y, and z axes form a right-handed rectangular coordinate system.

4. The diffraction-reflection type planar optical waveguide beamsplitter according to claim 1, characterized in that: The number of sub-beams emitted is set according to requirements, and each sub-beam is symmetrically distributed about the central axis of the parallel plate substrate and has equal light intensity.

5. A diffraction-reflection type planar optical waveguide beamsplitter according to claim 1, characterized in that: The total number of diffraction orders that the microstructure of the beam splitting region (1) needs to emit is equal to the set number of emitted sub-beams, and the microstructure of the collimation region (2) only emits diffraction orders perpendicular to the surface of the parallel plate substrate.

6. A diffraction-reflection type planar optical waveguide beamsplitter according to claim 1, characterized in that: The beam splitter can split a single beam of light into multiple parallel beams, and it can also reverse the process to combine multiple parallel beams of light into a single beam.

7. A design method for a diffraction-reflection type planar optical waveguide beam splitter, characterized in that: The design method of the diffraction-reflection type planar optical waveguide beamsplitter according to claim 2 includes the following steps: S1: Choose between one-dimensional or two-dimensional beam splitting mode based on actual application requirements; S2: Based on the selected beam splitting mode, the positions of the beam splitting region (1) and the collimation region (2) on the parallel plate substrate are determined, thereby determining the microstructure type; S3: Based on the lower bound constraint condition of the thickness of the parallel plate substrate, set the number of reflections N of the beam on the lower surface of the parallel plate substrate. S4: Based on the incident light wavelength, the refractive index of the substrate material and the target diffraction angle, the spatial period of the microstructure in the diffraction dimension is calculated and determined by combining the grating equation. S5: Based on the set distance Δ between the sub-beam exit position and the beam splitter center axis, the number of reflections N, and the cotangent value cotθ0 corresponding to the diffraction angle, the thickness of the parallel plate substrate is calculated using geometric relationship formulas, while considering the setting of lower bound constraint conditions to avoid beam interference. S6: With the optimization objective of maximizing the efficiency of the vertical diffraction order while minimizing the efficiency of other orders, the periodicity and structural depth parameters of the collimated region (2) microstructure are optimized to obtain the maximum efficiency η of the collimated diffraction order of the collimated region (2) microstructure. m , m is the order of the diffracted light from the beam-splitting region from which the corresponding sub-beam originates; S7: Let the efficiency of each diffraction order in the beam-splitting region (1) be... … … The optimization objective is set based on the parity of the number of emitter beams: If the number of outgoing sub-beams is odd, for any desired diffraction orders i and j, i ≠ j ≠ 0, the following condition is met: For any diffraction order u that does not require an outgoing emission, the following condition is satisfied: ; If the number of outgoing sub-beams is even, for any desired diffraction orders i and j, where i ≠ j, the following condition is met: For any diffraction order u that does not require an outgoing emission, the following condition is satisfied: ; S8: Based on actual engineering application scenarios, a tolerance analysis of the three-axis rotation angle of the beam splitter is performed; S9: Determine the number and size of the light-transmitting holes to be set on the lower surface of the parallel plate substrate, and at the same time determine the boundary shape and size of the beam splitting area (1), collimation area (2) and reflection area (3), as well as the boundary shape and size of the parallel plate substrate.

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