A diffractive calibration device and a cascaded diffractive beam splitting device

Abstract

The application discloses a kind of diffractive calibration device and cascaded diffractive beam splitting device, belong to diffractive optical element technical field.The diffractive calibration device includes calibration grating array, which includes multiple one-to-one corresponding grating subunits with incident sub-beam;Subunit is equipped with calibration grating, and the calibration grating is formed by the flashing tooth structure of the sub-grating with the cross section of right trapezoid in turn splicing, and the grating structure parameters of each subunit are matched with the diffraction angle of corresponding sub-beam, for deflecting sub-beam of different incident angles into preset collimating direction.The cascaded diffractive beam splitting device includes beam splitting device and the above-mentioned diffractive calibration device sequentially arranged along optical axis.The application adopts pure diffractive two-stage cascaded architecture, can realize the accurate beam array splitting and collimation, and the device integration is high, and the diffractive efficiency is excellent, can be widely applied to optical communication, optical sensing and laser processing field.

Description

Technical Field

[0001] This invention relates to the field of diffractive optical element technology, specifically to a diffraction calibration device and a cascaded diffraction beam splitter. Background Technology

[0002] Diffractive optical elements (DOEs) are core devices in the field of optical beam splitting. They modulate the phase of incident light through micro- and nano-relief structures on their surfaces, and can distribute a single incident light into multiple sub-beams with different propagation directions according to a preset power ratio. They have the advantages of flexible and adjustable beam splitting scale, high power uniformity, planar thin-film structure, and easy integration, and have become commonly used components in laser processing, optical sensing, and optical interconnection systems.

[0003] However, DOEs are essentially angular beam splitters. Their working principle is to redistribute the energy of incident light at discrete spatial frequency points in the angular spectral domain. The resulting sub-beams inevitably propagate divergently along different diffraction angles, inherently lacking wavefront collimation capability. Theoretically, a single-layer DOE device possesses only one degree of freedom for phase modulation, unable to simultaneously perform both "beam splitting" and "collimation" functions, thus preventing the direct generation of long-distance parallel beam arrays. In chip-to-chip optical interconnects, divergent beams cannot match the fixed array spacing at the receiver, limiting transmission distance. In quantum sensing, non-parallel beams cannot construct stable and uniform optical potential wells, affecting atomic manipulation precision. In parallel laser processing, poor focusing consistency of divergent sub-beams leads to variations in energy density and size at different processing points, severely impacting processing accuracy and consistency.

[0004] To address the aforementioned issues, the industry's conventional solution is to add a microlens array (MLA) after the DOE beam splitter, collimating each sub-beam separately through refraction. However, this hybrid refraction-diffraction scheme has inherent drawbacks: First, microlenses are refractive curved surface elements, exhibiting aberrations such as spherical aberration and field curvature, which significantly degrade the collimation effect in large-angle beam splitting scenarios, making it unsuitable for large-field-of-view beam splitting requirements; second, the microlens array has a certain surface thickness, which is detrimental to the ultra-thin design and high-density integration of the device; third, in large-scale two-dimensional beam array scenarios, the fabrication consistency of the microlenses and the difficulty of array alignment increase significantly, resulting in high manufacturing costs.

[0005] Blazed gratings, as high-efficiency diffraction elements, can concentrate most of the diffraction energy to the target diffraction order through a sawtooth relief structure, thereby deflecting the beam propagation direction. They are currently widely used in spectral splitting, single-beam direction control, and laser beam combining. However, existing blazed gratings are all integral structures with a uniform period and blaze angle, which can only deflect a single beam or a uniform parallel beam at a fixed angle. There is currently no technical solution for precise collimation of diverging beam arrays after DOE beam splitting, which uses partitioned customized blazed grating sub-units to correspond one-to-one with sub-beams and matches diffraction angle parameters for each beam. Summary of the Invention

[0006] This invention provides a diffraction calibration device and a cascaded diffraction beam splitter, which can solve the technical problem that existing diffraction optical elements lack the function of collimating and calibrating the outgoing light field.

[0007] To achieve the above objectives, in a first aspect, the present invention provides the following technical solution: a diffraction calibration device, comprising a calibration grating array, wherein the calibration grating array includes a plurality of grating sub-units corresponding one-to-one with incident sub-beams, each grating sub-unit having a calibration groove, the calibration groove having a sawtooth-shaped calibration grating; the calibration grating is formed by sequentially splicing together a plurality of sub-gratings along the extension direction of the calibration groove, the cross-section of the sub-grating is a right trapezoid, the shorter base of each sub-grating is connected to the longer base of the adjacent sub-grating, forming a continuous blazed grating tooth structure; the sub-grating structure parameters of each grating sub-unit are matched with the diffraction angle of the corresponding incident sub-beam, for deflecting sub-beams with different incident angles into an outgoing beam with a preset collimation direction.

[0008] Preferably, the calibration grating array includes a first grating array, a second grating array, a third grating array, and a fourth grating array. The first grating array and the second grating array are arranged side by side along a first direction, the third grating array and the fourth grating array are arranged side by side along the first direction, the first grating array and the fourth grating array are arranged side by side along a second direction, and the second grating array and the third grating array are arranged side by side along a second direction.

[0009] Preferably, the calibration slots of the first grating array and the third grating array extend in parallel directions, the calibration slots of the second grating array and the fourth grating array extend in parallel directions, and the calibration slots of the first grating array and the second grating array extend in non-parallel directions.

[0010] Preferably, the shorter bottom edge of the sub-gratings of the first grating array faces away from the third grating array, the shorter bottom edge of the sub-gratings of the third grating array faces away from the first grating array, the shorter bottom edge of the sub-gratings of the second grating array faces away from the fourth grating array, and the shorter bottom edge of the sub-gratings of the fourth grating array faces away from the second grating array.

[0011] Preferably, for a single-path incident sub-beam, the apex angle formed by the longer base of the sub-grating and the oblique waist at the corresponding position is γ, the period of the sub-grating is d, the refractive index of the grating material is n, the operating wavelength of the device is λ, and the deflection angle of the sub-beam after calibration is δ. The parameters satisfy the following relationship: sinγ=λ / [(n-1)d]; sinδ=(n-1)sinγ; By matching the values ​​of the apex angle γ and the period d, the incident sub-beam is deflected into an outgoing beam in a preset direction.

[0012] Preferably, when the incident light is a two-dimensionally distributed sub-beam array, the diffraction angular component of the (i,j)th order sub-beam in the first direction is θ. （x,i） The diffraction angular component in the second direction is θ （y,j） The total diffraction angle θ corresponding to this sub-beam （i,j） Satisfy: θ （i,j） =arccos(cosθ （x,i） ・cosθ （y,j） ); γ at the apex of the corresponding sub-grating （i,j） Satisfy: sinγ （i,j） =sinθ （i,j） / (n-1); The period d of the corresponding sub-grating （i,j） Satisfy: d （i,j） =λ / [(n-1)sinγ （i,j） Furthermore, the periodic extension direction of each sub-grating is orthogonal to the deflection plane formed by the corresponding sub-beam and the optical axis.

[0013] In a second aspect, the present invention also provides a cascaded diffraction beam splitter, comprising a beam splitter and a diffraction calibration device as described in the first aspect, wherein the beam splitter and the diffraction calibration device are arranged sequentially along the optical axis, and the right-angle waist side of the sub-grating of the diffraction calibration device is disposed facing the beam splitter.

[0014] Preferably, a transparent intermediary layer is provided between the beam splitter and the diffraction calibration device, the intermediary layer being used to fix the axial spacing between the beam splitter and the calibration grating array.

[0015] Preferably, the beam splitting device is a DOE diffraction beam splitter with a periodic relief surface structure, used to diffract and split the incident beam into multiple sub-beams propagating in different directions. Each sub-grating in the calibration grating array is set in one-to-one correspondence with each sub-beam, used to correct the diverging sub-beams into mutually parallel outgoing beams.

[0016] Preferably, the cross-sectional area of ​​the intermediate layer is not less than 1.25 times the cross-sectional area of ​​the emitted beam array, and the beam splitting device, the intermediate layer and the calibration grating array are integrated into one unit by photopolymerization, anodic bonding or ultraviolet bonding process.

[0017] Compared with the prior art, the technical solution of the present invention can achieve the following technical effects: 1. Overcoming the theoretical limitation that single-layer diffractive optical elements cannot simultaneously achieve beam splitting and collimation, a two-level pure diffraction cascade architecture consisting of beam splitting and calibration is adopted to decouple the beam splitting and wavefront direction correction functions, which can generate a beam array with uniform power and long-distance collimated transmission, meeting the application requirements of chip optical interconnection, optical quantum sensing, laser parallel processing and other scenarios.

[0018] 2. By adopting partitioned and customized grating sub-units that correspond one-to-one with the sub-beams, the grating parameters of each sub-unit are independently matched with the diffraction angle of the corresponding sub-beam, which can accurately correct the diverging sub-beams at different angles one by one. The beam parallelism is high and the array regularity is good, which solves the technical problem that traditional integral gratings cannot adapt to multi-angle diverging beam arrays.

[0019] 3. The blazed grating structure, which is spliced ​​with right-angle trapezoidal sub-gratings, has high diffraction efficiency and low energy loss. The device has an overall planar structure, which is thin and highly integrated. All of them can be fabricated by photolithography, which has strong process compatibility and low mass production cost. Compared with the traditional microlens collimation scheme, there is no aberration degradation problem in large-angle beam splitting scenarios, and the performance is more stable and reliable. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a single beam passing through a calibration grating according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a calibration grating showing that the sub-beams of this invention are scattered in a point-like pattern and are on the same horizontal plane. Figure 3 This is a schematic diagram of a calibration grating showing that the sub-beams of this invention are scattered in a point-like pattern and are not on the same horizontal plane. Figure 4 This is a schematic diagram of a cascaded diffraction beam splitter according to an embodiment of the present invention.

[0021] Reference numerals: 1. Calibration grating array; 2. Beam splitter; 3. Intermediate layer; 4. Sub-beam; 5. Outgoing beam; 11. Calibration slot; 12. Calibration grating; 13. First grating array; 14. Second grating array; 15. Third grating array; 16. Fourth grating array; 121. Sub-grating; 122. Vertex. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0023] like Figure 1-4 As shown, to address the technical problem that existing diffractive optical elements lack the function of collimating and calibrating the outgoing light field, this invention provides the following technical solution: a diffraction calibration device, comprising a calibration grating array 1, wherein the calibration grating array 1 includes multiple grating sub-units corresponding one-to-one with the incident sub-beams 4, each grating sub-unit having a calibration groove 11, the calibration groove 11 having a sawtooth-shaped calibration grating 12; the calibration grating 12 is formed by sequentially splicing multiple sub-gratings 121 along the extension direction of the calibration groove 11, the cross-section of the sub-grating 121 being a right trapezoid, the shorter base of each sub-grating 121 connecting with the longer base of the adjacent sub-grating 121, forming a continuous blazed grating tooth structure; the structural parameters of the sub-grating 121 of each grating sub-unit are matched with the diffraction angle of the corresponding incident sub-beam 4, used to deflect the sub-beams 4 at different incident angles into an outgoing beam 5 with a preset collimation direction.

[0024] Among them, the calibration grating array 1 serves as the overall carrier substrate, providing a unified processing reference and coplanar reference for all grating sub-units, ensuring the positional accuracy and flatness of each sub-unit, avoiding deflection direction errors caused by substrate deformation, and providing a unified mounting and bonding interface for subsequent integration with beam splitting devices; the grating sub-unit, as the smallest independent functional unit corresponding to a single sub-beam, is the carrier for realizing customized calibration for each beam, and the grating parameters can be designed independently for each sub-beam, breaking through the limitation of the traditional integral grating with uniform parameters and only able to deflect at a fixed angle; the calibration groove 11 provides a positioning processing area for the calibration grating, ensuring that the grating lines within the same sub-unit are parallel to each other, avoiding grating direction deviation from the process; at the same time, the groove structure facilitates pattern transfer and depth control in the photolithography process, improving the consistency and yield of batch production; the sub-grating 121 adopts a right-angled trapezoidal cross-section structure, forming the basic toothed unit of the blazed grating. Compared to ordinary binary gratings, the right-angled trapezoidal blazed surface can concentrate most of the diffraction energy to the target deflection order, greatly improving diffraction efficiency and reducing energy loss of the zeroth order and other higher orders.

[0025] The splicing structure of this embodiment eliminates the step-like discontinuity at the unit splicing points, avoiding energy loss and wavefront distortion caused by step scattering. Simultaneously, this modular splicing structure allows for flexible adjustment of the grating period and blaze angle of the corresponding sub-unit by adjusting the apex angle and height of individual sub-gratings, providing a structural basis for the fabrication of customized partitioned grating arrays. The grating sub-units are arranged in a one-to-one correspondence with the incident sub-beams, and the sub-grating structural parameters of each sub-unit match the diffraction angle of the corresponding sub-beam. This allows divergent sub-beams with different incident angles to be uniformly deflected to a preset collimation direction, fundamentally solving the problem that traditional monolithic gratings cannot adapt to multi-angle divergent beam arrays. This enables blazed gratings to be used for the first time for collimating beam arrays after DOE beam splitting.

[0026] In this embodiment, the calibration grating array 1 includes a first grating array 13, a second grating array 14, a third grating array 15, and a fourth grating array 16. The first grating array 13 and the second grating array 14 are arranged side by side along a first direction, the third grating array 15 and the fourth grating array 16 are arranged side by side along the first direction, the first grating array 13 and the fourth grating array 16 are arranged side by side along a second direction, and the second grating array 14 and the third grating array 15 are arranged side by side along a second direction. The four grating arrays are arranged in a rectangular symmetrical arrangement along the first and second directions, corresponding one-to-one with the spatial position of the four-quadrant divergent beam array output by the two-dimensional DOE beam splitter, ensuring that each divergent sub-beam can be incident on the grating sub-unit of the corresponding partition, without light leakage or cross-regional crosstalk. At the same time, the partitioned design reduces the processing difficulty of a single area and improves the yield and pass rate of large-scale two-dimensional array fabrication.

[0027] In this embodiment, the calibration slots 11 of the first grating array 13 and the third grating array 15 extend in parallel directions, and the calibration slots 11 of the second grating array 14 and the fourth grating array 16 extend in parallel directions. However, the calibration slots 11 of the first grating array 13 and the calibration slots 11 of the second grating array 14 do not extend in parallel directions. The beam deflection planes of the first and third quadrants correspond to the same set of grating directions, while the beam deflection planes of the second and fourth quadrants correspond to another set of grating directions. This ensures that the diffraction deflection direction of the grating is coplanar with the incident deflection direction of the sub-beam, ensuring that the deflected beam exits along the optical axis without generating additional lateral offset. Through the design of two sets of calibration slots in different directions, sub-beams incident from any direction in three-dimensional space can be decomposed into the deflection plane of the corresponding grating for direction correction. Omnidirectional collimation of two-dimensional beams can be achieved using only a planar grating array without the need for additional three-dimensional deflection elements, further ensuring the ultra-thin and planar characteristics of the device. Meanwhile, sharing the calibration slot direction in the same diagonal quadrant can reduce the number of process layout designs and improve processing efficiency.

[0028] In this embodiment, the shorter bottom edge of the sub-grating 121 of the first grating array 13 faces away from the third grating array 15, the shorter bottom edge of the sub-grating 121 of the third grating array 15 faces away from the first grating array 13, the shorter bottom edge of the sub-grating 121 of the second grating array 14 faces away from the fourth grating array 16, and the shorter bottom edge of the sub-grating 121 of the fourth grating array 16 faces away from the second grating array 14; wherein, the sub-beams of the first quadrant and the third quadrant, and the second quadrant and the fourth quadrant, are centrally symmetrical about the deflection direction relative to the optical axis, and the required deflection correction directions are also opposite. By reversing the short bottom edge of the corresponding sub-grating, the blaze deflection direction of the grating is aligned with the required correction direction of the beam, deflecting the diverging beams in all four quadrants towards the optical axis. The symmetrical orientation design of the four-quadrant gratings ensures the deflection symmetry of the entire beam array, avoiding distortion of the output beam array caused by inconsistent grating orientation. This ensures uniform spacing and regular arrangement of the collimated beam array, significantly improving the accuracy of the beam spot position and the consistency of the array. Simultaneously, the symmetrical orientation design also aligns with the symmetrical characteristics of two-dimensional DOE beam splitting, ensuring consistent diffraction efficiency in each quadrant and improving the uniformity of output power.

[0029] In this embodiment, for a single-path incident sub-beam 4, the apex angle 122 formed by the longer base of the corresponding sub-grating 121 and the oblique waist is γ, the period of the sub-grating 121 is d, the refractive index of the grating material is n, the operating wavelength of the device is λ, and the deflection angle of the sub-beam 4 after calibration is δ. The parameters satisfy the following relationship: sinγ=λ / [(n-1)d]; sinδ=(n-1)sinγ; By matching the values ​​of the apex angle γ and the period d, the incident sub-beam 4 is deflected into an outgoing beam 5 in a preset direction.

[0030] The above calculation method clarifies the mathematical relationship between the geometric parameters of the sub-grating and the deflection angle, providing a precise calculation basis for the design of grating sub-units. The required grating size can be directly deduced from the target deflection angle, ensuring that the accuracy of the beam deflection angle is controllable.

[0031] In this embodiment, when the incident light is a two-dimensionally distributed array of sub-beams, the diffraction angular component of the (i,j)th order sub-beam in the first direction is θ. （x,i） The diffraction angular component in the second direction is θ （y,j） The total diffraction angle θ corresponding to the sub-beam (4) （i,j） Satisfy: θ （i,j） =arccos(cosθ （x,i） ・cosθ （y,j） ); The γ at the apex 122 of the corresponding sub-grating 121 （i,j） Satisfy: sinγ （i,j） =sinθ （i,j） / (n-1); The period d corresponding to sub-grating 121 （i,j） Satisfy: d （i,j） =λ / [(n-1)sinγ （i,j） Furthermore, the periodic extension direction of each sub-grating 121 is orthogonal to the deflection plane formed by the corresponding sub-beam 4 and the optical axis.

[0032] The above formula decomposes the diffraction angle of a sub-beam in three-dimensional space into components in two orthogonal directions. The total deflection angle is obtained through vector synthesis, solving the problem of directly calculating the spatial beam angle in two-dimensional beam-splitting scenarios and providing accurate angle input for grating parameter design. For each (i,j)-order sub-beam, the apex angle and period parameters of the corresponding sub-grating can be calculated independently, enabling customized calibration of the parameters for each beam and ensuring that sub-beams at different positions and diffraction angles can be accurately corrected to a parallel state.

[0033] In addition, this embodiment also provides a cascaded diffraction beam splitter, including a beam splitter 2 and a diffraction calibration device as described in the first aspect. The beam splitter 2 and the diffraction calibration device are arranged sequentially along the optical axis, and the right-angle waist side of the sub-grating 121 of the diffraction calibration device faces the beam splitter 2. The beam splitter 2 performs the beam splitting function, dividing a single incident beam into multiple sub-beams in different directions, achieving spatial distribution of optical power. The number of beams, power ratio, and array arrangement can be flexibly designed to adapt to the needs of different application scenarios. The right-angle waist side of the sub-grating faces the beam splitter, ensuring that the incident beam enters from the right-angle face of the grating and exits from the blazing slope, fully conforming to the working mode of a transmission blazed grating, ensuring the blazing effect functions normally, maximizing diffraction efficiency, and reducing interface reflection and energy loss.

[0034] In this embodiment, a transparent intermediary layer 3 is provided between the beam splitter 2 and the diffraction calibration device. The intermediary layer 3 is used to fix the axial spacing between the beam splitter 2 and the calibration grating array 1. As an intermediate transparent support structure, the intermediary layer 3 provides a stable and precise axial spacing for the beam splitter and the calibration grating array, ensuring that the spatial position of the split sub-beams accurately corresponds to the grating sub-units when they propagate to the grating array. At the same time, the intermediary layer provides mechanical support for the device, improving the overall structural strength and resistance to environmental interference. The intermediary layer integrates the beam splitter and the calibration grating array into a single device, eliminating the need for additional optical mounting brackets and alignment structures, significantly reducing the device size and improving system integration. Furthermore, the fixed spacing ensures stable performance after the device leaves the factory, allowing downstream users to use it directly without on-site alignment, thus lowering the application threshold.

[0035] In this embodiment, the beam splitting device 2 is a DOE diffraction beam splitter with a periodic relief surface structure, used to diffract and split the incident beam into multiple sub-beams 4 propagating in different directions. Each sub-grating 121 in the calibration grating array 1 is correspondingly set with each sub-beam 4, used to correct the diverging sub-beams 4 into mutually parallel outgoing beams 5. The beam splitting device 2 has the advantages of flexible beam splitting scale, high power uniformity, and thin device thickness, and can generate beam arrays of arbitrary size in one-dimensional or two-dimensional form, adapting to different application scenarios. Both the DOE beam splitter and the blazed grating array are pure diffraction planar elements, and the two are cascaded to form a fully diffractive beam splitting collimating device. Compared with the traditional hybrid refractive and diffractive scheme of DOE and microlens array, the overall device thickness of this scheme is thinner, the integration is higher, and there is no aberration problem of refractive elements. The collimation effect is better in large-angle and large-scale beam splitting scenarios. At the same time, both can be fabricated by photolithography, and the processing technology is fully compatible, which is convenient for mass production and reduces manufacturing costs.

[0036] In this embodiment, the cross-sectional area of ​​the intermediate layer 3 is not less than 1.25 times the cross-sectional area of ​​the output beam array 5. The beam splitting device 2, the intermediate layer 3, and the calibration grating array 1 are integrated into one unit through photopolymerization, anodic bonding, or ultraviolet bonding processes. The cross-sectional area of ​​the intermediate layer is reserved with sufficient process and installation margins to avoid the edge beams exceeding the light transmission aperture due to assembly errors and beam drift, ensuring that the entire beam array is effectively output. Various integration processes such as photopolymerization, anodic bonding, and ultraviolet bonding can be adapted to different device materials such as glass, quartz, and optical plastics. While ensuring the bonding strength of the devices, the optical quality of the light transmission surface is maintained, and additional wavefront distortion is avoided by the bonding layer.

[0037] For ease of understanding, this embodiment uses a unified coordinate system: the main propagation direction of the incident light is defined as the z-axis, the plane where the calibration grating array is located is the xy plane, the first direction is the x-axis direction, and the second direction is the y-axis direction.

[0038] The main structural innovation of this embodiment lies in the use of right-angled trapezoidal sub-gratings spliced ​​together to form a transmissive blazed grating, whose beam deflection principle is based on the phase modulation effect of the blazed grating. A single sub-grating 121 has a right-angled trapezoidal cross-section, containing a right-angled waist surface and an inclined waist surface. Multiple sub-gratings are spliced ​​end-to-end along the periodic direction to form a continuous sawtooth relief structure. When the beam is incident perpendicularly along the z-axis onto the right-angled waist surface, it enters the interior of the grating medium and then incident onto the inclined waist surface. Due to the tilt angle (i.e., apex angle γ) of the inclined waist surface, the beam is refracted within the medium, and its propagation direction is deflected. Finally, when it exits the grating from the exit surface into the air, the overall propagation direction is deflected by an angle δ relative to the incident direction.

[0039] When the grating structure satisfies the blaze condition, most of the diffraction energy will be concentrated in the target deflection order. At this time, the structural parameters and optical parameters satisfy the following relationship: 1. Blazing condition: sinγ=λ / [(n-1)d], where γ is the apex angle of the sub-grating, λ is the working wavelength, n is the refractive index of the grating material, and d is the grating period (i.e. the width of a single sub-grating along the periodic direction).

[0040] 2. Beam deflection angle: sinδ=(n-1)sinγ, where δ is the total deflection angle of the beam after passing through the grating.

[0041] By adjusting the apex angle γ and period d of the sub-grating, the deflection angle of the beam can be precisely controlled, enabling directional calibration of the sub-beam at any incident angle. Compared to ordinary binary gratings, the diffraction efficiency of this right-angled trapezoidal blazed structure can be increased to over 85%, with a significant reduction in energy loss.

[0042] For a one-dimensional diverging beam array output by a one-dimensional DOE beam splitter, such as Figure 1 As shown, each sub-beam diverges in a fan shape along the x-direction, and the diffraction angle θ of the i-th order sub-beam 4 is... i Satisfies the grating equation: sinθ i =iλ / Λ, where Λ is the period of the DOE beam splitter and i is the diffraction order.

[0043] A calibration grating array 1 is placed at an axial distance L after the DOE beam splitter, with each sub-beam corresponding to an independent grating sub-unit. To correct the diverging sub-beams into collimated beams parallel to the z-axis, the sub-gratings need to deflect the incident beams θ along the optical axis. i Angle, i.e., target deflection angle δ i =θ i .

[0044] δ i Substituting these values ​​into the above formula for blazed gratings, the structural parameters of the corresponding sub-gratings can be calculated: Vertex angle: γ i =arcsin[sinθ i / (n-1)] Period: d i =λ / [(n-1)sinγ i ] By designing sub-gratings with matching parameters for each sub-beam, all divergent sub-beams can be deflected to propagate parallel to the z-axis, achieving collimated output of a one-dimensional beam array.

[0045] For a two-dimensional beam array output from a two-dimensional DOE beam splitter, the diffraction angle of the (i,j)th order sub-beam 4 can be orthogonally decomposed into the x-direction component θ. （x,i） With the y-direction component θ（y,j） They respectively satisfy: sinθ （x,i） =iλ / Λ x sinθ （y,j） =jλ / Λ γ ; where Λ x Λ γ These are the periods of the DOE beam splitter in the x and y directions, respectively.

[0046] The total diffraction angle θ of the sub-beam （i,j） The spatial angle between its propagation direction and the z-axis can be obtained through vector composition: θ （i,j） =arccos(cosθ （x,i） ·cosθ （y,j） ); To correct the sub-beam to be parallel to the z-axis, the deflection direction of the grating must be consistent with the deflection plane of the beam (the plane formed by the sub-beam propagation direction and the z-axis). Therefore, the following conditions must be met: the grating lines must be orthogonal to the deflection plane, and the grating period must lie within the deflection plane. The corresponding structural parameters of the sub-grating are: Vertex angle: γ （i,j） =arcsin[sinθ （i,j） / (n-1)]; Period: d （i,j） =λ / [(n-1)sinγ （i,j） ]; Since the two-dimensional beam splitting exhibits a symmetrical distribution across four quadrants, the calibration grating array is divided into four quadrant subarrays (the first to fourth grating arrays), each corresponding to a beam in one of the four quadrants. The beam deflection planes in the first and third quadrants correspond to the same set of grating directions, while the second and fourth quadrants correspond to a different set of grating directions. Furthermore, the grating teeth in opposite quadrants face opposite directions, thus achieving symmetrical collimation of the entire array beam and ensuring the regularity of the output array.

[0047] The cascaded diffraction beam splitter consists of a beam splitter 2, an intermediate layer 3, and a calibration grating array 1, arranged sequentially along the optical axis. These three components are integrated into one unit through optical bonding. The incident parallel light first enters the beam splitter 2, and after being split by DOE diffraction, it forms multiple divergent sub-beams 4 that propagate in different directions. After propagating an axial distance L within the transparent intermediate layer 3, the sub-beams are precisely incident on the corresponding grating sub-units of the calibration grating array 1. According to preset structural parameters, the sub-gratings 121 in each sub-unit deflect the corresponding sub-beams at a specific angle along the optical axis. Finally, all sub-beams exit in a direction parallel to the optical axis, forming a regular output beam array 5 with uniform power and collimated transmission.

[0048] To further illustrate the specific technical solution of this application, this embodiment provides a 5×5 two-dimensional cascaded diffraction collimator beam splitter, which can be applied to chip optical interconnect scenarios in the 1550nm communication band. The following detailed description is provided in conjunction with specific parameters and a complete calculation process to ensure that those skilled in the art can repeat the implementation based on this description.

[0049] 1. Operating wavelength: λ = 1550nm = 1.55μm; 2. Beam splitter: Two-dimensional DOE diffraction beam splitter, with a period of Λ in the x-direction. x =20μm, period Λ in the y direction γ =20μm; effective diffraction orders are -2, -1, 0, +1, +2, with a total of 5×5 sub-beams; power uniformity target ≤5%; 3. Device material: fused silica, refractive index n=1.444 at 1550nm wavelength; 4. Intermediate layer: fused silica material, axial thickness L=10mm, light transmission aperture 10mm×10mm; 5. Output specifications: After collimation, the parallelism of the beam is ≤0.1°, and the diffraction efficiency of the array is ≥85%.

[0050] Taking the first quadrant (+2,+2) order sub-beam as an example, the structural parameters of the corresponding grating sub-unit are calculated in full: Step 1: Calculate the diffraction angular components of the sub-beam: According to the DOE grating equation, the diffraction angular component in the x-direction is: sinθ （x,2） =iλ / Λ x =2×1.55μm / 20μm=0.155θ （x,2） =arcsin(0.155)≈8.91°; Similarly, the diffraction angular component in the y-direction: sinθ （y,2） =jλ / Λ γ =2×1.55μm / 20μm=0.155θ （y,2） ≈8.91°; Step 2: Calculate the total diffraction angle of the sub-beam: According to the formula for the composition of spatial angle vectors: cosθ （2,2） =cosθ （x,2） ·cosθ （y,2） ≈cos8.91°×cos8.91°≈0.9879×0.9879≈0.9759; θ （2,2） =arccos(0.9759)≈12.62°; Step 3: Calculate the apex angle and period of the corresponding sub-grating: To correct the sub-beam to be parallel to the z-axis, the target deflection angle is δ = θ.（2,2） =12.62°.

[0051] According to the blazed grating formula, the sub-grating apex angle satisfies: sinγ （2,2） =sinθ （2,2） / (n-1)=sin12.62° / (1.444-1)≈0.2185 / 0.444≈0.4921; γ （2,2） =arcsin(0.4921)≈29.47°; The sub-grating period satisfies: d （2,2） =λ / [(n-1)sinγ （2,2） ]=1.55μm / (0.444×0.4921)≈7.09μm; Step 4: Determine the direction and orientation of the sub-grating: The (+2,+2) level subbeam is located in the first quadrant, and the angle between its deflection plane and the x-axis is: φ=arctan(tanθ （y,2） / tanθ （x,2） ) = 45°; Therefore, the grating lines are orthogonal to the deflection plane, making an angle of 135° with the x-axis; the grating period is along a 45° direction and lies within the deflection plane. The short bottom edge of the sub-grating faces upward and to the right, away from the array center, ensuring that the beam is deflected along the optical axis.

[0052] Step 5: Parameter verification at other levels: Using the same algorithm, the subgrating parameters for all orders can be calculated, with typical values ​​as follows: (0,0) order: The diffraction angle is 0, the corresponding position is a light-transmitting window, there is no grating structure, and the light beam passes through directly; (+1,0) order: total diffraction angle ≈ 4.44°, γ ≈ 10.02°, d ≈ 20.0μm; (-1,-1) order (third quadrant): The total diffraction angle, γ, and d parameters are completely consistent with those of the (+1,+1) order, except that the grating orientation is reversed and the short bottom edge faces the lower left. (-2,0) level: The parameters are the same as those of (+2,0) level, but the grating orientation is opposite.

[0053] All level parameters are derived using the same algorithm, and the design process can be completely reproduced.

[0054] The following is an example of the structural arrangement of a grating array: The calibration grating array is a 10mm × 10mm square fused silica substrate, divided into four rectangular sub-arrays according to the four quadrants: 1. First grating array 13: Located in the first quadrant (x>0, y>0), corresponding to the sub-beams i>0, j>0, containing 6 grating sub-units; the calibration slot extends at 135°, and the short bottom edge of the sub-grating faces the upper right. 2. Second grating array 14: Located in the second quadrant (x<0,y>0), corresponding to the sub-beams i<0, j>0, containing 6 grating sub-units; the calibration slot extends at 45°, and the short bottom edge of the sub-grating faces the upper left. 3. Third grating array 15: Located in the third quadrant (x<0, y<0), corresponding to the sub-beams i<0, j<0, containing 6 grating sub-units; the calibration slot extends at 135°, and the short bottom edge of the sub-grating faces downward to the left; 4. Fourth grating array 16: Located in the fourth quadrant (x>0, y<0), corresponding to the sub-beams i>0, j<0, containing 6 grating sub-units; the calibration slot extends at 45°, and the short bottom edge of the sub-grating faces the lower right.

[0055] The size of a single grating sub-unit is designed to be 0.8mm × 0.8mm, which is larger than the spot diameter of the sub-beam in the plane, ensuring that the beam is fully incident without edge truncation; the size of the central (0,0) level light transmission window is 0.8mm × 0.8mm.

[0056] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0057] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0058] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A diffraction calibration device, comprising a calibration grating array (1), characterized in that: The calibration grating array (1) includes multiple grating sub-units that correspond one-to-one with the incident sub-beams (4). Each grating sub-unit is provided with a calibration groove (11), and the calibration groove (11) is provided with a sawtooth calibration grating (12). The calibration grating (12) is composed of multiple sub-gratings (121) sequentially spliced ​​along the extension direction of the calibration groove (11). The cross-section of the sub-grating (121) is a right trapezoid. The shorter bottom edge of each sub-grating (121) is connected to the longer bottom edge of the adjacent sub-grating (121) to form a continuous blazed grating tooth structure. The structural parameters of the sub-grating (121) of each grating sub-unit are matched with the diffraction angle of the corresponding incident sub-beam (4) to deflect the sub-beams (4) with different incident angles into an outgoing beam (5) with a preset collimation direction.

2. The diffraction calibration apparatus according to claim 1, characterized in that: The calibration grating array (1) includes a first grating array (13), a second grating array (14), a third grating array (15), and a fourth grating array (16). The first grating array (13) and the second grating array (14) are arranged side by side along a first direction. The third grating array (15) and the fourth grating array (16) are arranged side by side along a first direction. The first grating array (13) and the fourth grating array (16) are arranged side by side along a second direction. The second grating array (14) and the third grating array (15) are arranged side by side along a second direction.

3. The diffraction calibration apparatus according to claim 2, characterized in that: The calibration slots (11) of the first grating array (13) and the third grating array (15) extend in parallel directions, the calibration slots (11) of the second grating array (14) and the fourth grating array (16) extend in parallel directions, and the calibration slots (11) of the first grating array (13) and the calibration slots (11) of the second grating array (14) extend in non-parallel directions.

4. The diffraction calibration apparatus according to claim 2, characterized in that: The shorter bottom edge of the sub-grating (121) of the first grating array (13) faces away from the third grating array (15), the shorter bottom edge of the sub-grating (121) of the third grating array (15) faces away from the first grating array (13), the shorter bottom edge of the sub-grating (121) of the second grating array (14) faces away from the fourth grating array (16), and the shorter bottom edge of the sub-grating (121) of the fourth grating array (16) faces away from the second grating array (14).

5. The diffraction calibration apparatus according to claim 1, characterized in that: For a single-path incident sub-beam (4), the apex angle (122) formed by the longer base of the corresponding sub-grating (121) and the oblique waist is γ, the period of the sub-grating (121) is d, the refractive index of the grating material is n, the operating wavelength of the device is λ, and the deflection angle of the sub-beam (4) after calibration is δ. The parameters satisfy the following relationship: sinγ=λ / [(n-1)d]; sinδ=(n-1)sinγ; By matching the values ​​of the apex angle γ and the period d, the incident sub-beam (4) is deflected into an outgoing beam (5) in a preset direction.

6. The diffraction calibration apparatus according to claim 2, characterized in that: When the incident light is a two-dimensional array of sub-beams (4), the diffraction angular component of the (i,j)th order sub-beam in the first direction is θ. （x,i） The diffraction angular component in the second direction is θ （y,j） The total diffraction angle θ corresponding to the sub-beam (4) （i,j） Satisfy: θ （i,j） =arccos(cosθ （x,i） ・cosθ （y,j） ); The apex angle (122) γ of the corresponding sub-grating (121) （i,j） Satisfy: sinγ （i,j） =sinθ （i,j） / (n-1); The period d of the corresponding sub-grating (121) （i,j） Satisfy: d （i,j） =λ / [(n-1)sinγ （i,j） Furthermore, the periodic extension direction of each sub-grating (121) is orthogonal to the deflection plane formed by the corresponding sub-beam (4) and the optical axis.

7. A cascaded diffraction beam splitter, characterized in that: The device includes a beam splitter (2) and a diffraction calibration device as described in any one of claims 1 to 6. The beam splitter (2) and the diffraction calibration device are arranged sequentially along the optical axis, and the right-angle waist side of the sub-grating (121) of the diffraction calibration device is set towards the beam splitter (2).

8. The cascaded diffraction beam splitter according to claim 7, characterized in that: A transparent intermediary layer (3) is provided between the beam splitter (2) and the diffraction calibration device. The intermediary layer (3) is used to fix the axial spacing between the beam splitter (2) and the calibration grating array (1).

9. The cascaded diffraction beam splitter according to claim 7, characterized in that: The beam splitting device (2) is a DOE diffraction beam splitter with a surface periodic relief structure, used to diffract and split the incident beam into multiple sub-beams (4) propagating in different directions. Each sub-grating (121) in the calibration grating array (1) is set in correspondence with each sub-beam (4), used to correct the diverging sub-beams (4) into mutually parallel outgoing beams (5).

10. The cascaded diffraction beam splitter according to claim 8, characterized in that: The cross-sectional area of ​​the intermediate layer (3) is not less than 1.25 times the cross-sectional area of ​​the outgoing beam (5) array. The beam splitting device (2), the intermediate layer (3) and the calibration grating array (1) are integrated into one unit by photopolymerization, anodic bonding or ultraviolet bonding process.

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