Symmetric grating-based angle selection device with reciprocity

Abstract

The invention discloses a reciprocity angle selection device based on symmetrical gratings, which realizes an efficient and accurate angle selection function in a broadband range by utilizing an array of a micron-sized highly-symmetrical geometric structure and based on a luminous flux conservation principle. The device is composed of a substrate, a microstructure array layer and a functional modification layer. The microstructure array layer is formed by periodically and densely paving a plurality of hollow microstructure units in geometric symmetry, the interior of each unit is a funnel-shaped or conical light transmission channel with a large upper part and a small lower part, and a functional modification layer is attached to the side wall of each unit. According to the invention, only light in a specific acceptance angle range is allowed to pass through by regulating and controlling the geometrical parameters of the side wall of the microstructure and utilizing the limiting effect of geometrical optics, so that transmission response with a sharp cut-off characteristic is realized. According to the present invention, the defects of narrow bandwidth, polarization sensitivity, high processing difficulty and the like of the traditional device are overcome, the frequency insensitivity, the polarization insensitivity, good optical path reciprocity and the like are provided, the diffraction effect can be inhibited through the irregular arrangement, and the device is suitable for the high signal-to-noise ratio optical communication system.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics and optical communication devices, specifically to an angle selection device with reciprocity based on a symmetrical grating. Background Technology

[0002] With the rapid development of modern information technology, optical communication technology has become a core pillar of information transmission. In complex application scenarios such as high-speed, high-capacity wavelength division multiplexing systems and submarine optical cable communication, optical signals often carry different wavelengths and angles. To ensure the accuracy and efficiency of signal transmission, precise separation and integration of optical signals are required. Among these, filtering optical signals in specific propagation directions (i.e., angle selection) is a key technology for reducing inter-channel crosstalk and improving the system signal-to-noise ratio. Furthermore, effective control of the direction of light propagation is equally crucial in fields such as precision optical imaging, solar concentrators, and privacy displays.

[0003] However, existing optical angle selection technologies still face many technical bottlenecks and challenges:

[0004] First, traditional angle-selective devices, such as interference filters or photonic crystal structures based on multilayer dielectric thin films, mainly rely on the interference effect of light or the photonic bandgap characteristics to operate. These devices are usually highly sensitive to wavelength, have narrow operating bandwidths, and their angle response characteristics often drift with wavelength, making it difficult to maintain consistent performance over a wide spectral range.

[0005] Secondly, while novel micro / nano structures based on surface plasmons or metasurfaces can achieve subwavelength-scale optical field manipulation, their physical mechanisms are mostly based on electromagnetic resonance. This resonance mechanism not only limits the operating bandwidth of the devices but is also often accompanied by high absorption losses. More importantly, such structures typically require high-precision nanoscale fabrication processes (such as electron beam lithography), resulting in high fabrication costs and making large-scale, low-cost manufacturing difficult.

[0006] Furthermore, many existing grating structures or micro-visor structures often suffer from polarization sensitivity issues. Due to the lack of high symmetry, their responses to transverse electric (TE) and transverse magnetic (TM) waves are inconsistent, leading to performance degradation when handling randomly polarized natural light or complex signal light. In addition, some designs sacrifice optical path reversibility (reciprocity) in pursuit of unidirectional transmission characteristics, limiting their application in bidirectional communication or specific optical systems.

[0007] In summary, traditional optical angle selection devices generally suffer from narrow operating bandwidth, polarization sensitivity, low transmission efficiency, and high fabrication difficulty. These shortcomings severely limit their widespread application in modern broadband optical communication and high-performance imaging. Therefore, there is an urgent need to develop a novel angle selection device that is simple in structure, easy to fabricate, possesses broadband response characteristics, and is insensitive to polarization. The angle selection device based on a symmetric grating proposed in this invention innovatively utilizes a micrometer-level highly symmetric geometry and the principle of luminous flux conservation to successfully solve the aforementioned problems while ensuring optical path reciprocity, providing a completely new solution for high-performance optical filtering and directional transmission. Summary of the Invention

[0008] To overcome the shortcomings of existing optical angle selection technologies, such as limited bandwidth, polarization sensitivity, poor optical path reciprocity, and difficulty in nanoscale fabrication, this invention proposes a reciprocal angle selection device based on a symmetrical grating. The device designed in this invention utilizes an array of micrometer-scale highly symmetrical geometric structures and, based on the principle of luminous flux conservation, achieves efficient and precise angle selection in a wide band of visible and mid-infrared light.

[0009] This invention is achieved through the following technical solutions:

[0010] An angle selection device based on a symmetrical grating with reciprocity is disclosed. The upper surface of the device is the light incident surface, and the lower surface is the light exit surface. The device consists of a substrate, a microstructure array layer, and a functional modification layer. The microstructure array layer is composed of multiple geometrically symmetrical hollow microstructure units arranged periodically in a horizontal direction. Each microstructure unit has a through-hole light transmission channel, and the cross-sectional area of ​​the upper opening aperture is larger than the cross-sectional area of ​​the lower opening aperture or the central aperture, forming a funnel-shaped or cone-shaped light transmission channel. Based on the principle of light flux conservation, the device restricts and guides the light propagation path through the reflective functional layer attached to the sidewall, thereby achieving the transmission of incident light within a specific angle range and the blocking of light beyond the angle range.

[0011] Furthermore, the aperture cross-section of the microstructure unit can be designed as a polygon (such as a regular hexagon or square), a circle, or any arbitrary geometric structure; the reflective sidewall can be any plane or curved surface with reflective function (such as a semi-ellipsoid, parabola, or plane). This highly symmetrical structural design endows the device with excellent polarization insensitivity and optical path reciprocity. Simultaneously, the geometric symmetry of the overall structure of the device gives it bidirectional isotropic angle-selective response characteristics (optical path reciprocity), meaning that the transmittance is substantially equal when light is incident from the upper or lower surface of the device at the same angle, supporting bidirectional equivalence of optical signals.

[0012] Furthermore, the substrate material of the microstructure array layer is a polymer material, which is integrally formed by two-photon polymerization (TPP) lithography technology, and has the ability to form three-dimensional structures with micron-level precision, ensuring the geometric fidelity of the sidewall curvature or plane of the microstructure unit.

[0013] Furthermore, a wide range of reflective materials and structural systems are protected: the functional modification layer is deposited or attached to the inner surface of the microstructure unit and can be any material or structure with light reflection function. Specifically, this includes: 1. Metallic reflective materials: such as high-reflectivity metals and their alloys, such as silver (Ag), gold (Au), copper (Cu), and aluminum (Al); 2. Dielectric reflective structures: such as photonic crystal structures based on the photonic bandgap principle, distributed Bragg reflectors (DBRs or high-refractive-index dielectric coatings) composed of multilayer dielectric films, etc. This reflective layer is attached to the inner wall of the microstructure through deposition or micro / nano fabrication processes to achieve efficient reflection of incident light (preferably with a reflectivity greater than 95%). Preferably, when metallic silver is used, its reflectivity in the mid-infrared and visible light bands is greater than 95%, and its thickness is 0.4 μm to 1 μm.

[0014] Furthermore, the broadband characteristics resulting from the micrometer-scale design are preserved: the size of the microstructure units is on the micrometer scale, enabling its working mechanism to be based on geometric optics rather than subwavelength resonance; specifically, the microstructure height is 100 μm. ～ The size is 200 μm, the period (i.e., the center-to-center distance between adjacent cells) is 30 μm to 40 μm, and the wall thickness between adjacent cells is 1 μm to 2 μm. This size is much larger than the operating wavelength (e.g., 420 nm to 680 nm), which makes it follow the laws of geometric optics, thereby achieving a frequency-insensitive broadband operating mode.

[0015] Furthermore, this invention defines in detail three preferred reflector wall surface shapes and their corresponding aperture structures to adapt to different application requirements:

[0016] The semi-ellipsoidal reflector has an upper hexagonal opening and a lower central aperture that transitions to a circle. The curved sidewalls utilize the geometric optical focusing properties of the semi-ellipsoidal surface to guide incident light within the receiving angle to the bottom circular aperture for transmission. Preferably, the microstructure height is 178 μm, the side length of the upper hexagon is 36 μm, and the diameter of the lower central circular aperture is 27.31 μm.

[0017] Parabolic reflector: Both the upper opening aperture and the lower central aperture are regular hexagons, and the sidewalls are parabolic curved hexagonal pyramids. The collimation or focusing characteristics of the parabola limit the divergence angle of the beam. Preferably, the side length of the central hexagonal aperture is 13.92 μm.

[0018] Flat reflective wall: The microstructure unit is truncated pyramidal in shape, with flat inclined sidewalls. When a regular hexagonal array is used, a hexagonal pyramidal cavity is formed, and the side length of the central hexagonal hole is preferably 12 μm; when a regular square array is used, a square pyramidal cavity is formed, and the side length of the central square hole is preferably 12 μm.

[0019] Furthermore, with the optimized configuration of the above structural parameters (such as setting the center aperture size to 12μm~27.31μm), the device achieves sharp cutoff angle selection characteristics: when the receiving angle is set to ±15°, the transmission power remains above 0.85 when the incident light angle is within the receiving angle range; when the incident light angle exceeds the receiving angle and gradually increases, the transmission power decreases sharply and becomes negligible before reaching the 30° cutoff angle.

[0020] Finally, the present invention also provides an implementation scheme of irregular periodic arrangement, in which the central aperture size or wall thickness of a single microstructure unit is randomly selected and arranged within a preset tolerance range (e.g., 13.5 μm to 17.6 μm). This irregular arrangement, while maintaining the angle selectivity characteristics, breaks the strict periodic phase condition of the grating and effectively suppresses the strong diffraction effect caused by the periodic structure.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) Broadband frequency response characteristics: This invention adopts a micrometer-level geometric structure, rather than a traditional nanometer-level resonant structure or multilayer film interference structure. The working principle is based on the conservation of light flux in geometric optics. Therefore, the device has no specific resonant wavelength limitation and can maintain stable angle selectivity performance in a wide spectral range from visible light to mid-infrared, solving the problems of narrow bandwidth and wavelength sensitivity in existing technologies.

[0023] (2) Excellent optical path reciprocity and bidirectional transmission capability: Benefiting from the highly symmetrical design of the microstructure units in three-dimensional space (such as the geometric correspondence between the upper and lower apertures and the symmetrical curvature of the sidewalls), this device strictly adheres to the principle of optical path reversibility. Combined with... Figure 7 The verification results show that, unlike traditional unidirectional light guides or non-reciprocal gratings, this device exhibits highly consistent angle selection characteristics (transmittance curve overlap > 99%) in both forward and reverse optical paths. This characteristic enables the device to achieve bidirectional homogeneous signal transmission in transceiver integrated optical communication systems (such as optical transceiver modules and bidirectional WDM systems) without the need for additional expensive optical isolators or complex path switching switches, significantly reducing system complexity and cost.

[0024] (3) Sharp cutoff angle selectivity: Through precise design of the microstructure sidewalls (such as hemispherical or parabolic surfaces), this device achieves excellent angle selectivity. The transmittance is high (>85%) within the acceptance angle range (e.g., ±15°), while once it exceeds this angle range, the transmittance drops sharply and achieves sharp cutoff, effectively filtering out stray light and resulting in a high signal-to-noise ratio.

[0025] (4) Mature processing technology and controllable cost: The main structure of this invention is based on mature two-photon polymerization (TPP) and metal deposition processes. The material system is simple (polymer + silver), eliminating the need for complex heterogeneous material integration or nanoscale alignment and stacking of hundreds of thin films. This "single structure + single material" paradigm significantly reduces processing difficulty and manufacturing costs, and has good mass production potential.

[0026] (5) It has the ability to resist diffraction interference: The irregular arrangement scheme proposed in this invention effectively destroys the diffraction conditions of the periodic grating by introducing the randomness of the structural parameters, and solves the problem of "ghosting" or diffraction fringes that are common in the imaging applications of periodic arrays. Attached Figure Description

[0027] Figure 1 The diagram shows the three-dimensional structure and geometric parameters of the microstructure unit in the embodiment of the present invention (left) and the three-dimensional structure of the microstructure array (right).

[0028] Figure 2 This is a top view of the microstructure unit and array with a hexagonal central aperture in Embodiment 1 of the present invention;

[0029] Figure 3 This is a top view of the microstructure unit and array using a circular central aperture (corresponding to a semi-ellipsoidal or parabolic reflector wall) in Embodiment 1 of the present invention.

[0030] Figure 4 This is a top view schematic diagram of the microstructure unit and array with a quadrilateral central aperture in Embodiment 2 of the present invention;

[0031] Figure 5 This is a characteristic curve of the transmittance of the device of the present invention as a function of incident angle under different incident light wavelengths (420nm~680nm).

[0032] Figure 6 This is a graph showing the response characteristics of the transmittance of the irregularly periodically arranged grating array as a function of the incident angle in Embodiment 3 of the present invention.

[0033] Figure 7 This is a comparison curve showing the transmittance of the device of the present invention as a function of the incident angle under forward incident (light source located on the upper surface) and reverse incident (light source located on the lower surface) conditions.

[0034] In the figure: 1—Length of the upper opening of the microstructure unit (e.g., 36 μm); 2—Diameter of the center of the microstructure unit (e.g., 27.31 μm or 12 μm); 3—Wall thickness between adjacent units (e.g., 1 μm); 4—Height of the microstructure unit (e.g., 178 μm). Detailed Implementation

[0035] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] Example 1: Angle Selection Device Based on Hexagonal Periodic Semi-ellipsoidal Reflector Wall

[0037] like Figure 1 and Figure 2 , Figure 3 As shown, this embodiment provides a reciprocal angle selection device based on a symmetric grating. The microstructure array layer is made of polymer material, and the array units are arranged in a close-packed hexagonal pattern on a horizontal plane. Figure 1 As shown, the height of a single microstructure unit (marked 4) is set to 178 μm. This unit presents a funnel-shaped hollow structure, with the upper opening (marked 1) corresponding to a hexagonal side length of 36 μm. Depending on the sidewall design, the central aperture (marked 2) can exhibit different shapes.

[0038] When a semi-ellipsoidal reflector is used, the central aperture is circular (e.g., ...). Figure 3 As shown), its diameter is 27.31 μm;

[0039] When using hexagonal straight or curved walls, the central aperture is hexagonal (e.g., Figure 2 As shown in the figure, the side length is adjusted accordingly. The wall thickness between adjacent units (marked 3) is reserved at 1μm. The inner wall surface is covered with a metallic silver reflective layer. This structure utilizes the principle of light flux conservation to achieve high transmittance for perpendicularly incident light (0°) while effectively blocking light exceeding the designed acceptance angle (e.g., 15°), thus realizing sharp cutoff characteristics.

[0040] It should be noted that although this embodiment uses metallic silver (Ag) as the reflective functional layer for simulation and illustration, in practical applications, the reflective layer is not limited to silver. Any material with high reflectivity can be used in this device, such as metallic materials like gold (Au), copper (Cu), and aluminum (Al); or dielectric structures such as photonic crystal structures and Bragg reflective layers that utilize the periodic change of the refractive index of the medium to generate a reflection effect, all of which fall within the scope of protection of this invention.

[0041] Example 2: Angle Selection Device Based on Quadrilateral Periodic Straight Reflector Wall

[0042] like Figure 4 As shown, in this embodiment, the cross-section of the microstructure unit is designed as a regular quadrilateral (square). The structural height of a single unit is maintained at 178 μm, the side length of the quadrilateral is set at 30 μm, and the central aperture diameter is 12 μm. The sidewalls adopt a flat reflective wall design and are also covered with a metallic silver reflective layer. This structure maintains high symmetry, preserves good polarization insensitivity characteristics, and better meets the parallelism requirements of the outgoing and incoming light for S-waves or P-waves.

[0043] Example 3: Broadband Feature Verification

[0044] like Figure 5 As shown, this embodiment verifies the broadband characteristics of the device. Simulations were performed within the 420nm–680nm range (covering the visible light band). The results show the transmittance-angle curves at different wavelengths ( Figure 5 The fact that the curves (in the middle) highly overlap indicates that the working mechanism of the device of the present invention is based on geometric optics and does not rely on subwavelength resonance. Therefore, it has an extremely wide operating frequency band and can work stably in the visible light and mid-infrared bands.

[0045] Example 4: Irregularly Periodically Arranged Anti-Diffraction Array

[0046] like Figure 6 As shown, to address the problem of diffraction effects easily generated by periodic grating structures, this embodiment introduces randomized parameter design. Geometric parameters such as the center aperture and side length of the microstructure unit are randomly selected within a certain tolerance range (e.g., 13.5 μm to 17.6 μm). Figure 6 The curves in the figure show that even with irregular arrangement, the device still maintains excellent angular cutoff characteristics (transmittance drops sharply at about 25° to 30°). At the same time, this irregularity effectively destroys the coherence of the diffracted light and significantly suppresses the "observable diffraction effect".

[0047] Example 5: Verification of Optical Path Reciprocity and Bidirectional Transmission

[0048] To verify the bidirectional transmission capability of this device in practical applications, this embodiment conducted a reciprocity simulation test on the hexagonal semi-ellipsoidal reflector structure. The test plan is as follows: First, the light source was set to be incident from the upper surface of the device (Port 1), and the incident angle was scanned from 0° to 60°. The forward transmission power curve T was recorded. 12 Subsequently, keeping the structural parameters unchanged, the light source was placed on the lower surface of the device (Port 2), and the incident angle was scanned from 0° to 60°, recording the reverse transmission power curve T. 21 .like Figure 7 As shown, simulation results demonstrate that the forward transmission curve (solid line) and the reverse transmission curve (dashed line) perfectly coincide across the entire scanning angle range, with their root mean square error being almost zero. This physically confirms that the symmetrical grating structure does not introduce any non-reciprocal phase delay or loss, perfectly supporting lossless bidirectional angle filtering of optical signals and fully meeting the stringent requirements of high-performance bidirectional optical communication systems.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A reciprocal angle selection device based on a symmetrical grating, characterized in that, The device has an upper surface as the light incident surface and a lower surface as the light exit surface, and is composed of a substrate, a microstructure array layer, and a functional modification layer. The microstructure array layer is composed of multiple geometrically symmetrical hollow microstructure units arranged periodically in the horizontal direction. Each microstructure unit has a through light transmission channel inside, and the cross-sectional area of ​​the upper opening aperture is larger than the cross-sectional area of ​​the lower opening aperture or the central aperture, forming a funnel-shaped or cone-shaped light transmission channel. The aperture cross-section of the microstructure unit is polygonal, circular, or arbitrary geometric, and the sidewalls are arbitrary planes or curved surfaces with reflective functions. Based on the principle of light flux conservation, the device restricts and guides the light propagation path through the functional modification layer attached to the sidewalls, thereby achieving the transmission of incident light within a specific angle range and the blocking of light beyond the angle range.

2. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The substrate material of the microstructure array layer is a polymer material, which is integrally formed by two-photon polymerization lithography technology. It has the ability to form three-dimensional structures with micron-level precision, ensuring the geometric fidelity of the sidewall curvature or plane of the microstructure unit.

3. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The functional modification layer is deposited or attached to the inner wall surface of the microstructure unit, and its material includes, but is not limited to, any one of the following: (1) a highly reflective metallic material, including silver, gold, copper, aluminum and their alloys; (2) a dielectric reflective structure, including a photonic crystal structure, a distributed Bragg mirror or a high refractive index dielectric coating; when metallic silver is used, its reflectivity in the mid-infrared and visible light bands is greater than 95%, and its thickness is 0.4μm to 1μm.

4. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The microstructure unit has a size on the order of micrometers, enabling its working mechanism to be based on geometric optics rather than subwavelength resonance. Specifically, the height h of the microstructure unit ranges from 100 μm to 200 μm, the period (i.e., the center-to-center distance between adjacent units) ranges from 30 μm to 40 μm, and the wall thickness between adjacent units is set to 1 μm. ～ 2μm.

5. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The sidewall geometry of the microstructure unit is designed as a semi-ellipsoidal reflective wall; the upper opening aperture is a regular hexagon, and the lower central aperture transitions to a circle; the sidewall curved surface utilizes the geometric optical focusing characteristics of the semi-ellipsoidal surface to guide the incident light within the receiving angle to the bottom circular aperture for transmission; its microstructure height is 178μm, the side length of the upper hexagon is 36μm, and the diameter of the lower central circular aperture is 27.31μm.

6. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The sidewall geometry of the microstructure unit is designed as a parabolic reflector wall; the upper opening aperture and the lower central aperture are both regular hexagons, and the sidewall is a parabolic curved hexagonal pyramid surface, which limits the divergence angle of the beam through the collimation or focusing characteristics of the parabola; the side length of the central hexagonal aperture is 13.92 μm.

7. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The sidewall geometry of the microstructure unit is designed as a flat reflective wall; wherein, the microstructure unit is in the shape of a truncated pyramid with a flat inclined sidewall; when a regular hexagonal array is used, a hexagonal pyramid cavity is formed, and the side length of the central hexagonal hole is preferably 12μm; when a regular quadrilateral array is used, a quadrilateral pyramid cavity is formed, and the side length of the central square hole is preferably 12μm.

8. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, By precisely configuring the aspect ratio and aperture ratio of the semi-ellipsoidal reflector, parabolic reflector, or flat reflector, the device achieves sharp cutoff angle selection characteristics: when the receiving angle is set to ±15°, the transmission power remains above 0.85 when the incident light angle is within the receiving angle range; when the incident light angle exceeds the receiving angle and gradually increases, the transmission power decreases sharply and becomes negligible before reaching the 30° cutoff angle.

9. The angle selection device with reciprocity based on a symmetric grating according to claim 1, characterized in that, The arrangement of the microstructure array also includes an implementation method of irregular periodic arrangement; wherein, the central aperture size or wall thickness of a single microstructure unit is randomly selected and arranged within a preset tolerance range; while maintaining the angle selection characteristics, the strict periodic phase condition of the grating is destroyed, and the strong diffraction effect caused by the periodic structure is suppressed.

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