Angle selection device for covering visible light wave band based on non-reciprocal grating

Abstract

The invention discloses a non-reciprocal grating-based visible light wave band covering angle selection device, and relates to the technical field of micro-nano optics. According to the device, an array of a micron-sized asymmetric geometric structure is utilized, and a forward and reverse differentiated angle selection function is realized 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 unit is in an asymmetric cone shape or a funnel shape, and the aperture areas of the two ends are not equal. By changing the area ratio of the light inlet aperture to the center aperture, the device shows different angle cut-off characteristics during forward incidence and reverse incidence. Meanwhile, due to the change of the filling factor caused by the change of the light inlet aperture, the peak transmittances of forward and reverse incidence also show geometric difference. The aperture and side wall shape of the microstructure unit can be any geometric structure, and the reflecting layer covers the metal and medium structure. The device can automatically switch the angle screening range according to the incident direction, and is suitable for an optical system needing non-reciprocal field angle regulation and control.

Description

Technical Field

[0001] This invention relates to the fields of micro-nano optics, optical communication devices, and optoelectronic stealth technology, specifically to an angle-selective device covering the visible light band based on a non-reciprocal grating. This device breaks the reversibility of the optical path through an asymmetric aperture structure, enabling unidirectional angle-selective transmission. It is particularly suitable for scenarios requiring protection against echo interference, laser protection, unidirectional stealth coatings, and high signal-to-noise ratio optical communication systems. Background Technology

[0002] In modern optical and optical communication systems, precise control over the propagation direction of optical signals is crucial. Traditional angle selection devices, such as interference filters or photonic crystals based on multilayer dielectric films, can filter light at specific angles, but most are based on symmetrical structural designs. According to the principle of optical reversibility, the transmission characteristics of these devices are completely identical in the forward and reverse optical paths. That is, if light can travel from point A to point B, it can also travel back from point B to point A with the same efficiency.

[0003] However, in many cutting-edge applications, this "reciprocity" has become a limiting factor:

[0004] Optical communication and laser systems: In lasers or optical amplifiers, reflected light signals can cause instability in the resonant cavity and even damage expensive pump sources. Therefore, there is an urgent need for a unidirectional device that can allow signal light output while blocking external reflected light.

[0005] Optoelectronic stealth and detection: In certain stealth or detection scenarios, it is desirable to achieve "one-way transparency", that is, to allow internal detectors to receive external signals while preventing internal light from leaking or reflecting external detection light, thereby achieving the effect of "seeing the outside, but not seeing the inside from the outside".

[0006] Interference-resistant communication: In complex electromagnetic environments, non-reciprocal devices can effectively isolate backscattered noise and significantly improve the signal-to-noise ratio.

[0007] Existing non-reciprocal optical devices primarily rely on magneto-optical materials (such as Faraday rotators) to break time-reversal symmetry using magnetic fields. However, these devices are typically bulky, difficult to integrate, require external magnetic fields, and are costly, making them unsuitable for large-area or miniaturized systems. Another approach, based on nonlinear optical effects or time-varying modulation, while not requiring a magnetic field, often necessitates high-intensity incident light or complex dynamic modulation circuitry, limiting its application in low-light detection or passive systems.

[0008] In recent years, passive non-reciprocal devices based on micro / nano structures have gradually attracted attention. By designing structural asymmetries (such as asymmetric metasurfaces or gratings), asymmetric optical transmission can be achieved under linear passive conditions. However, existing asymmetric grating schemes are mostly in the theoretical research stage, or their structures are too complex (such as requiring multi-layer nanoscale alignment), making them difficult to fabricate; or their materials are limited, making it difficult to achieve efficient unidirectional transmission and high-contrast angle cutoff over a wide spectral range.

[0009] In summary, there is an urgent need to develop a novel optical device that is simple in structure, easy to fabricate over large areas, has a wide range of material choices (compatible with metals and dielectrics), and possesses efficient unidirectional angle selection characteristics. The device based on an asymmetric aperture grating proposed in this invention innovatively utilizes the asymmetry of geometric optics and the principle of luminous flux conservation to achieve broadband, efficient non-reciprocal angle selection at the micrometer scale, effectively solving the aforementioned technical bottlenecks. Summary of the Invention

[0010] To overcome the limitations of existing optical angle selection devices, such as fixed field of view and inability to dynamically adjust the angle threshold according to the transmission direction, this invention proposes an angle selection device covering the visible light band based on a non-reciprocal grating.

[0011] The device designed in this invention utilizes an array of micrometer-scale asymmetric geometric structures, based on the principle of luminous flux conservation, to break the spatial symmetry of the light transmission angle response. By constructing light transmission channels with inconsistent port sizes, the device achieves direction-dependent field-of-view angle modulation characteristics under linear passive conditions without external magnetic fields or nonlinear materials; that is, forward-incident light and reverse-incident light have different cutoff angles (inflection points). Furthermore, this invention employs a widely applicable reflective material system and a flexible geometric configuration.

[0012] This invention is achieved through the following technical solutions:

[0013] An angle selection device covering the visible light band based on a non-reciprocal grating comprises a substrate, a microstructure array layer, and a functional modification layer. The microstructure array layer is composed of multiple microstructure units arranged periodically. Each microstructure unit has a through-hole optical transmission channel, and the cross-sectional area S1 of the first port on the light incident side is not equal to the cross-sectional area S2 of the second port on the light emitting side, forming an asymmetric conical, frustum-shaped, or funnel-shaped cavity structure. The aperture cross-section of the microstructure unit is of arbitrary geometry, and the sidewalls are arbitrary planes or curved surfaces with reflective functions. The angle selection device is based on the principle of light flux conservation and utilizes the constraint relationship between the asymmetric aperture area ratio and the light receiving angle to achieve the non-reciprocal angle selection characteristic of electromagnetic waves. That is, the transmission power-angle response curves of forward and reverse incident light have different cutoff angles, thus exhibiting different angle selection ranges in different transmission directions.

[0014] Furthermore, the non-reciprocal angle selection characteristic is specifically manifested as follows: when light is incident from the large aperture port, i.e., the first port, the device has a first cutoff angle θ. c1 When light enters through the small aperture port, i.e., the second port, the device has a second cutoff angle θ. c2 , and θ c1 ≠θ c2 By adjusting the aperture area ratio of the first and second ports, the difference between the first and second cutoff angles can be precisely controlled, thereby achieving differentiated control of the field of view in both forward and reverse transmission directions. Specifically, when light enters from the smaller aperture end, since the central limiting aperture (pupil) remains unchanged, reducing the entrance aperture inevitably leads to an increase in the relative proportion of the physical wall thickness between adjacent microstructure units on the incident surface (i.e., a decrease in the effective fill factor). This results in a larger vertical reflection area during reverse incidence, with more incident light being directly reflected by the top wall thickness, thus reducing the peak transmittance at small angles compared to forward incidence (e.g., from approximately 0.9 to around 0.75). This phenomenon is a physical effect accompanying the change in the structural geometric fill factor when the aperture area ratio is changed to control the cutoff angle.

[0015] Furthermore, the aperture cross-section of the microstructure unit can be designed with any geometric structure, including but not limited to regular shapes (such as regular hexagons, squares, triangles, circles, ellipses) or irregular complex shapes (irregular polygons, fractal structures, or closed figures enclosed by free curves); and the cross-sectional shapes of the first port and the second port can be the same (only scaled) or different (both shape and size change, forming a gradient channel). The reflective sidewalls connecting the two ports can be any plane or curved surface with reflective function, including straight inclined planes, parabolic curved walls, ellipsoidal curved walls, or higher-order curved surfaces, to adapt to different light field modulation requirements. Specifically:

[0016] When the sidewall geometry of the microstructure unit is designed as a curved reflective wall, the sidewall takes the form of a parabolic, ellipsoidal, hyperboloid, or any higher-order curved shape. The curved reflective wall utilizes the focusing or collimating properties of geometric optics to optimize the transmission path of light in the asymmetric cavity.

[0017] When the sidewall geometry of the microstructure unit is designed as a flat reflective wall, the microstructure unit takes the shape of a truncated pyramid (such as a hexagonal frustum or a quadrangular frustum) or a frustum of a cone, with flat inclined sidewalls connecting two apertures of different sizes.

[0018] Furthermore, this invention protects a wide range of reflective materials and structural systems: the functional modification layer can be any medium or structure with light-reflecting capabilities. Specifically, it includes:

[0019] 1. Metallic reflective materials: encompassing any form of highly reflective metallic materials, including silver, gold, copper, aluminum, chromium, and their alloys;

[0020] 2. Dielectric Reflection Structures: These encompass photonic crystal structures that reflect light using the photonic bandgap principle, distributed Bragg mirrors composed of multilayer dielectric films, or high-refractive-index dielectric coatings. This reflective layer is attached to the inner wall of the microstructure through deposition or micro / nano fabrication processes, achieving highly efficient reflection of incident light.

[0021] Furthermore, the substrate material of the microstructure array layer is a polymer, semiconductor, or optical glass, which is integrally formed by two-photon polymerization, electron beam lithography, or nanoimprint lithography. The size of the microstructure unit is set to the micrometer scale (height 50–1000 μm, period range 15–50 μm, wall thickness 1–20 μm), so that its working mechanism is based on geometric optics, thereby maintaining a stable non-reciprocal angle selection function in a wide range of visible and mid-infrared light.

[0022] Furthermore, the angle selection device exhibits non-reciprocal transmission in the visible and mid-infrared bands. In a preferred embodiment, when incident forward (from a large aperture), the receiving angle range is 0–θ1 (e.g., 16°); when incident backward (from a small aperture), the receiving angle range becomes 0–θ2 (e.g., 14°), achieving an asymmetric definition of the angle selection threshold for forward and reverse incident light. Simultaneously, with reverse incident light, the reduced aperture leads to an increase in the effective wall thickness area ratio (i.e., the non-transmitting area) of the microstructure unit's top, resulting in a decrease in the geometric fill factor on the incident surface, thus slightly reducing its peak transmittance compared to forward incident light.

[0023] Furthermore, in order to eliminate stray light illuminating the wall thickness region during reverse incidence, the end face region on the small aperture side of the microstructure unit or the gap region between array units can be covered with a light-absorbing material layer to absorb stray light during reverse incidence and prevent it from causing secondary interference through external reflection of the structure.

[0024] Furthermore, the microstructure array can also adopt an irregular periodic arrangement. By introducing random perturbations into the aperture size, wall thickness, or spatial position of the asymmetric microstructure units, the strict periodic phase condition of the grating is disrupted, thereby effectively suppressing diffraction effects while maintaining unidirectional transmission characteristics.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) Significant unidirectional conduction characteristics (optical path non-reciprocity): Unlike traditional symmetrical gratings, this invention achieves passive unidirectional light transmission through an asymmetrical aperture design without the need for magneto-optical materials or an external magnetic field. It exhibits high forward incident transmittance (>0.9) and extremely low reverse incident transmittance, making it suitable as an on-chip integrated "optical isolator" to effectively prevent echo interference.

[0027] (2) High versatility of materials and structure: This invention breaks the limitation of specific materials. The reflective layer can be flexibly selected from various metals such as gold, silver, and copper, or all-dielectric structures such as photonic crystals. The aperture shape can also be designed as any polygon or circle according to the pixel arrangement requirements. This versatility enables the device to adapt to various manufacturing environments such as CMOS compatible processes and flexible electronics processes.

[0028] (3) Broadband operating capability: Based on the principle of geometric optics (micrometer-scale structure), the non-reciprocal effect of the device does not depend on the resonant characteristics of the material. Therefore, it can operate in an extremely wide frequency band covering the visible light to mid-infrared, overcoming the narrow bandwidth defect of traditional resonant non-reciprocal devices.

[0029] (4) Compact structure and easy integration: Compared with the bulk Faraday isolator, the microstructure array of the present invention is only micrometer thick and thin film in shape, which can be easily integrated directly with photodetectors, laser arrays or display panels to achieve miniaturization and weight reduction of the system.

[0030] (5) Excellent anti-diffraction and noise suppression capabilities: Combining irregular arrangement and light-absorbing layer design, the device can not only block the reverse echo, but also eliminate the ghosting interference caused by the periodic structure, which significantly improves the imaging quality and signal-to-noise ratio of the optical system. Attached Figure Description

[0031] Figure 1 This is a three-dimensional structural diagram of the asymmetric microstructure unit in Embodiment 1 of the present invention. The left side is a schematic diagram of two ports, and the right side is a side perspective view, showing the asymmetric conical transmission channel.

[0032] Figure 2This is a schematic diagram of two incident modes of a non-reciprocal grating array in Embodiment 1 of the present invention. The left side shows the array with the first port (large aperture) facing upwards, and the right side shows the array with the second port (small aperture) facing upwards.

[0033] Figure 3 The diagram shows the microstructure units and corresponding arrays of different aperture shape variants (hexagonal, circular, quadrilateral) in Embodiment 2 of the present invention, demonstrating the arbitrariness of aperture geometry.

[0034] Figure 4 This is a comparison curve of the transmission power as a function of the incident angle under forward incident (large aperture light) and reverse incident (small aperture light) conditions in Embodiment 1 of the present invention, showing the difference between the cutoff angle shift and the transmittance.

[0035] Explanation of markings in the diagram:

[0036] 1—First port of the microstructure unit (large aperture / incident end); 2—Second port of the microstructure unit (small aperture / outcrystal end); 3—Sidewall with reflective function; 4—Height of the microstructure unit. Detailed Implementation

[0037] 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.

[0038] Example 1: Non-reciprocal grating based on hexagonal asymmetric aperture

[0039] This embodiment provides an angle selection device covering the visible light band based on a non-reciprocal grating. 1. Structural design as follows: Figure 1 As shown, the device consists of a substrate, a microstructure array layer, and a functional modification layer. The microstructure units are asymmetrical hexagonal frustum-shaped (funnel-shaped). (Stereoscopic view) Figure 1Left): Shows the overall shape of the cell. Its first port (marked 1) is a large-aperture regular hexagon with a side length of L1 (e.g., 25 μm); the second port (marked 2) is a small-aperture regular hexagon with a side length of L2 (e.g., 5.6 μm), and L1 > L2. Side perspective view ( Figure 1 Right): Shows the elongated shape of the microstructure unit in the height direction (marked 4), with the height h set at 500 μm (as indicated in the figure). The sidewalls (marked 3) connect the upper and lower ports, and a reflective layer is attached to the inner surface. Figure 2 As shown, the array layer is formed by periodically and densely covering the aforementioned cells. Figure 2 The left side shows the first port (large aperture) facing upwards, defined as the positive incident port; Figure 2 The right side shows the state with the second port (small aperture) facing upwards, defined as the reverse incident port. 2. Performance Verification and Mechanism Analysis Figure 4 The transmission power-angle response curves of this structure under forward and reverse incident conditions are shown for comparison. The non-reciprocal shift of the cutoff angle (inflection point) is illustrated. Figure 4 As shown, the light transmission curve for a large aperture (corresponding to) Figure 4 The curve with a larger cutoff angle (i.e., the solid line Port1) shows a sharp decrease in transmittance at an incident angle of approximately 12° (corresponding to x = 12° in the figure), indicating the first cutoff inflection point; the small aperture light-gathering curve (corresponding to...) Figure 4 The curve with the smaller cutoff angle (i.e., the dashed line Port2) begins to decline when the incident angle is approximately 14° (corresponding to x = 14° in the figure), exhibiting the second cutoff inflection point. This shift in cutoff angle (Δθ ≈ 2°) confirms that this device can dynamically adjust the field of view range based on the principle of luminous flux conservation according to different incident directions. Peak transmittance difference analysis: Observation Figure 4 In the small to medium angle region (0°–10°), it can be observed that the peak transmittance of the large aperture (corresponding to the high transmittance curve) is relatively high, close to 0.9; while the peak transmittance of the small aperture (corresponding to the low transmittance curve) decreases to around 0.75. The physical mechanism is that when light enters from the small aperture end, in order to maintain non-reciprocal angle selection, the aperture is reduced, resulting in a significant increase in the proportion of the solid wall thickness region (dead zone) at the top of the microstructure unit in the total surface area of ​​the array. More perpendicularly incident light directly illuminates the wall thickness and is reflected, leading to a decrease in the effective fill factor, thereby causing a decrease in transmittance.

[0040] Example 2: Variant Structure Based on Arbitrary Geometric Aperture

[0041] To verify the universality of the "arbitrary geometric structure" claim in this invention, this embodiment constructs variants with different cross-sectional shapes. For example... Figure 3 As shown, from top to bottom, three different microstructural units and their arrays are displayed:

[0042] Hexagonal aperture (top row): has the highest fill factor and is suitable for dense arrays.

[0043] Circular aperture (middle row): forms a frustum-shaped asymmetric structure with complete rotational symmetry and is insensitive to the polarization state of incident light.

[0044] Quadrilateral apertures (bottom row): Forming a frustum-shaped structure, suitable for integration with rectangular pixel arrays (such as CMOS sensors). Simulation results show that regardless of the change in aperture cross-sectional shape, as long as the asymmetry of the aperture areas at both ends is maintained, the device can exhibit similar non-reciprocal angle selection characteristics.

[0045] Example 3: Verification based on different reflective material systems

[0046] This embodiment aims to illustrate the broad applicability of the "reflective functional layer" material in the claims of this invention. In the above embodiments, the reflective layer is typically made of metallic silver. However, this invention is also applicable to other reflective systems: other metals: gold, copper, or aluminum are used as the reflective layer. Simulations show that in their respective high-reflectivity bands (e.g., gold in the infrared band), their non-reciprocal transmission performance is essentially consistent with that of the silver layer structure. Dielectric reflective structure: alternating deposition of high and low refractive index dielectric materials (e.g., TiO2 / SiO2) on the sidewalls of the microstructure to construct a one-dimensional photonic crystal (or distributed Bragg mirror). This structure utilizes the photonic bandgap effect to achieve total internal reflection. Experiments show that the all-dielectric non-reciprocal grating based on the photonic crystal not only possesses unidirectional conduction function but also avoids the ohmic loss of metallic materials, making it particularly suitable for high-power laser protection scenarios.

[0047] In summary, the device proposed in this invention has a high degree of freedom in the selection of aperture shape, sidewall curvature, and reflective material, and can achieve efficient non-reciprocal angle selection function.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, 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 therein; 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 non-reciprocal grating-based angle selection device covering the visible wavelength band, characterized in that, The microstructure array layer is formed by periodically arranging a plurality of microstructure units, each of which has a through optical transmission channel, and the first port aperture cross-sectional area S1 at the light incident side and the second port aperture cross-sectional area S2 at the light exit side are not equal, forming an asymmetric conical, table-shaped or funnel-shaped cavity structure; the aperture cross section of the microstructure unit is any geometric structure, and the sidewall is any plane or curved surface with a reflection function; the angle selection device realizes the non-reciprocal angle selection characteristics of electromagnetic waves based on the light flux conservation principle and the constraint relationship of the asymmetric aperture area ratio on the light acceptance angle, that is, the transmission power-angle response curves of forward incidence and reverse incidence have different cutoff angles, thereby presenting different angle selection ranges in different transmission directions.

2. The nonreciprocal grating-based, angle-selective device covering the visible wavelength band according to claim 1, characterized in that, The non-reciprocal angular selection characteristic specifically represents that when light is incident from a large-aperture port, i.e., a first port, the device has a first cutoff angle θ c1 ; when light is incident from a small-aperture port, i.e., a second port, the device has a second cutoff angle θ c2 , and θ c1 ≠ θ c2 ; by adjusting the aperture area ratio of the first port to the second port, the difference between the first cutoff angle and the second cutoff angle is accurately controlled, thereby realizing differential control of the field angles in the two transmission directions.

3. The nonreciprocal grating-based, covering-visual-band, angle-selective device according to claim 1, wherein The functional modification layer is a reflection function layer deposited or attached to the inner wall surface of the microstructure unit, and the material covers any medium or structure with a reflection function, including: (1) Metal reflective material: including but not limited to silver, gold, copper, aluminum, chromium and any form of high-reflectivity metal material of their alloys; (2) Dielectric reflection structure: including photonic crystal structure reflecting light using photonic bandgap principle, distributed Bragg reflector composed of multilayer dielectric film or high refractive index dielectric coating.

4. The nonreciprocal grating-based, covering-visual-light-band, angle selection device according to claim 1, wherein The sidewall geometry profile of the microstructure unit is designed as a curved reflective wall; wherein the sidewall is curved in the shape of a parabolic surface, an ellipsoidal surface, a hyperboloidal surface or any high-order curved surface; the curved reflective wall utilizes the focusing or collimating characteristics of geometric optics to optimize the transmission path of light in the asymmetric cavity.

5. The nonreciprocal grating-based, visible wavelength band covering, angle selection device according to claim 1, characterized by The sidewall geometry profile of the microstructure unit is designed as a flat reflective wall; wherein the microstructure unit is in the shape of a truncated pyramid or a circular truncated cone, and the sidewall is a flat inclined surface connecting the two apertures of different sizes.

6. The nonreciprocal grating-based, visible wavelength band covering, angle selection device according to claim 1, characterized by The cross-sectional shape of the first port and the second port of the microstructure unit is any geometric structure, including: (1) Regular geometric shape: such as regular hexagon, regular quadrilateral, triangle, circle, ellipse; (2) Irregular or complex shape: such as irregular polygon, fractal structure or closed figure enclosed by free curve; and the cross-sectional shape of the first port and the second port is the same or different only in size scaling.

7. The nonreciprocal grating-based, covering-visual-light-band, angle selection device according to claim 1, wherein The base material of the microstructure array layer is a polymer material, a semiconductor material or an optical glass, which is integrally formed by two-photon polymerization lithography technology, electron beam lithography or nanoimprint technology; the size of the microstructure unit is in the order of microns, the height ranges from 50 to 1000 μm, the period ranges from 15 to 50 μm, and the wall thickness is set to 1-20 μm, so that its working mechanism is based on geometric optics rather than subwavelength resonance.

8. The nonreciprocal grating-based, covering-visual-light- band angular selection device according to claim 1, wherein The angle selection device exhibits non-reciprocal transmission effect in the visible light and mid-infrared waveband. When forward incidence, i.e. the first port, the acceptance angle range is 0-θ1; when reverse incidence, i.e. the second port, the acceptance angle range becomes 0-θ2, realizing the asymmetric definition of the angle screening threshold for forward and reverse incidence; at the same time, due to the reduction of the light entrance aperture during reverse incidence, the effective wall thickness area ratio of the top of the microstructure unit increases, resulting in the reduction of the geometric filling factor on the incident surface, so that the peak transmittance is reduced compared with forward incidence.

9. The nonreciprocal grating-based, visible wavelength band covering, angle selection device according to claim 1, characterized by In order to eliminate the stray light irradiated on the wall thickness area during reverse incidence, the end surface area of the small aperture side of the microstructure unit or the gap area between the array units is covered with a light-absorbing material layer.

10. The nonreciprocal grating-based, covering-visual-light- band angular selection device according to claim 1, wherein The arrangement mode of the microstructure array layer also includes irregular periodic arrangement; by introducing random disturbance in the aperture size, wall thickness or spatial position of the asymmetric microstructure unit, the strict periodic phase condition of the grating is destroyed, and the diffraction effect is suppressed.

Images