Diffractive waveguide and smart glasses
By designing a pupil-expanding grating structure in a diffraction waveguide with partitioning and setting an isolation layer and an absorption layer, the problem of coherent interference caused by multiple diffractions was solved, achieving brightness uniformity and clear image effect in AR display.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GOERTEK OPTICAL TECH CO LTD
- Filing Date
- 2026-03-24
- Publication Date
- 2026-05-29
Smart Images
Figure CN122110366A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of smart wearable device technology, and in particular to a diffractive waveguide and smart glasses. Background Technology
[0002] In the field of Augmented Reality (AR) displays, diffractive waveguide technology has become one of the key technologies for realizing AR glasses optical systems due to its advantages such as thinness, wide field of view, and high light transmittance. Diffractive waveguides typically include optical micro / nano structures such as coupling gratings, pupil gratings, and output gratings. Among them, the pupil grating is used to realize the two-dimensional expansion of the image within the waveguide, thereby expanding the user's viewing window (Eyebox).
[0003] However, due to the pupil-expanding properties of diffractive waveguides, the same incident light beam undergoes multiple diffraction, reflection, and coupling processes within the waveguide, generating multiple optical paths with fixed phase relationships. When these optical paths finally couple out, they coherently superimpose on the image plane; that is, the amplitudes of the light waves are superimposed according to their phase relationships and then squared to form an intensity distribution. This coherent interference phenomenon leads to uneven stripes or spots (i.e., "mottled patterns" or "coherent spots") in the final image pattern, severely affecting image uniformity and visual experience.
[0004] Therefore, how to effectively suppress coherent interference caused by multiple diffractions and improve the brightness uniformity of the imaging pattern is a technical problem that urgently needs to be solved. Summary of the Invention
[0005] The main purpose of this application is to provide a diffractive waveguide and smart glasses, which aims to solve the technical problem of how to effectively suppress coherent interference caused by multiple diffractions and improve the brightness uniformity of the imaging pattern.
[0006] To achieve the above objectives, this application provides a diffraction waveguide, which includes: a waveguide substrate, a coupling grating structure, a pupil-expanding grating structure, and an output grating structure.
[0007] The pupil-expanding grating structure includes an effective region and a suppression region. The effective region is configured to receive light from any region of the coupling grating structure and couple the light out to any region of the coupling grating structure. At least a portion of the pupil grating in the suppression region is filled with an isolation layer to suppress the generation of diffracted light from the pupil grating in the suppression region; And / or, at least a portion of the pupil dilation grating in the suppression region has a period smaller than that of the pupil dilation grating in the effective region, so as to suppress the generation of diffracted light from the pupil dilation grating in the suppression region.
[0008] In one embodiment, the pupil-expanding grating structure and the coupling grating structure are both located on the same side of the waveguide substrate, and the suppression region is located on the side of the effective region closer to the coupling grating.
[0009] In one embodiment, the thickness of the isolation layer gradually decreases in the direction away from the effective region.
[0010] In one embodiment, the absolute value of the difference between the refractive index of the isolation layer and the refractive index of the pupil grating in the suppression region is less than or equal to 0.2.
[0011] In one embodiment, at least some of the adjacent pupil gratings in the suppression region have different periods.
[0012] In one embodiment, the period of at least a portion of the pupil dilation grating in the suppression region is half the period of the pupil dilation grating in the effective region.
[0013] In one embodiment, the period of the pupil grating in the suppression region is a, the thickness of the isolation layer is d, the refractive index of the isolation layer is n1, the refractive index of the pupil grating is n2, and the operating wavelength of the diffraction waveguide is λ. Where, in the case that at least a portion of the pupil-expanding grating in the suppression region is filled with an isolation layer, and the period of at least a portion of the pupil-expanding grating in the suppression region is less than that of the pupil-expanding grating in the effective region, , a < λ.
[0014] In one embodiment, the diffraction waveguide further includes: an absorption layer; The absorption layer is disposed on the side of the isolation layer away from the waveguide substrate, and is used to absorb the diffracted light of the pupil grating in the suppression region.
[0015] In one embodiment, the absorption layer includes at least two absorber sublayers stacked sequentially, and the different absorber sublayers have different absorption rates for different center wavelengths within the operating band of the diffraction waveguide.
[0016] In addition, to achieve the above objectives, this application also provides smart glasses, which include the diffractive waveguide as described above.
[0017] This application provides a diffractive waveguide and smart glasses. The diffractive waveguide includes: a waveguide substrate, an input grating structure, a pupil-expanding grating structure, and an output grating structure. The pupil-expanding grating structure includes an effective region and a suppression region. The effective region is configured to receive light from any region of the input grating structure and couple the light out to any region of the output grating structure. At least a portion of the pupil-expanding grating in the suppression region is filled with an isolation layer to suppress the generation of diffracted light from the pupil-expanding grating in the suppression region. And / or, the period of at least a portion of the pupil-expanding grating in the suppression region is smaller than that of the pupil-expanding grating in the effective region to suppress the generation of diffracted light from the pupil-expanding grating in the suppression region.
[0018] This application relates to a diffractive waveguide and smart glasses, which can be configured with a waveguide substrate, a coupling grating structure, a pupil-expanding grating structure, and a coupling-out grating structure. The pupil-expanding grating structure can be divided into an effective region and a suppression region, and an isolation layer or adjustment of the grating period can be set in the suppression region to suppress stray diffraction. In actual operation, the coupling grating guides light into the waveguide, the effective region of the pupil-expanding grating receives light and performs pupil-expanding transmission, while the suppression region suppresses the generation of unnecessary diffracted light through an isolation layer or a small period design. Finally, the light is extracted by the coupling-out grating to form an image. Compared to existing diffractive waveguides, which are prone to stray light and image crosstalk due to full-area diffraction of the grating, this application, by dividing the pupil-expanding grating and designing a suppression region, can suppress interference effects in non-imaging areas while achieving effective pupil expansion. Therefore, when using smart glasses, users can directly obtain a clear image with uniform brightness, improving display quality and visual experience. Attached Figure Description
[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of the pupil expansion characteristics of a diffraction waveguide. Figure 2 This is a front view of the diffraction waveguide structure proposed in the first embodiment of this application; Figure 3 This is a top view of the diffraction waveguide structure proposed in the first embodiment of this application; Figure 4 This is a side view of the diffraction waveguide structure proposed in the first embodiment of this application; Figure 5This is a schematic diagram of the diffraction waveguide structure when the period of the pupil-expanding grating decreases according to the first embodiment of this application; Figure 6 This is a side view of the diffraction waveguide structure proposed in the second embodiment of this application; Figure 7 This is a diagram of the diffraction waveguide structure after the pupil-expanding grating structure is trimmed in the second embodiment of this application.
[0022] Explanation of icon numbers:
[0023] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0024] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.
[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0026] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application 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.
[0027] Furthermore, the use of terms such as "first" and "second" in this application is 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. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.
[0028] Understandably, in the field of Augmented Reality (AR) displays, diffractive waveguide technology has become one of the key technologies for realizing AR glasses optical systems due to its advantages such as thinness, wide field of view, and high light transmittance. Diffractive waveguides typically include optical micro / nano structures such as coupling grating structure 1, pupil-expanding grating structure 2, and output grating structure 3. Among them, pupil-expanding grating structure 2 is used to realize the two-dimensional expansion of the image within the waveguide, thereby expanding the user's viewing window (Eyebox).
[0029] However, due to the pupil-expanding properties of diffractive waveguides, the same incident light beam undergoes multiple diffraction, reflection, and coupling processes within the waveguide, resulting in multiple optical paths with fixed phase relationships. (Refer to...) Figure 1 , Figure 1 This is a schematic diagram illustrating the pupil-expanding characteristics of a diffractive waveguide. (Example:) Figure 1 As shown, the light ray 1001 entering from the coupling grating structure 1 undergoes multiple diffractions within the pupil-expanding grating structure 2, for example, splitting into light rays 1002 and 1003, and further diffracting into light rays 1004 and 1005, finally combining into light ray 1006. The key issue is that coherent light rays like 1004 and 1005 do not simply add up their intensities when forming 1006, but rather undergo vector superposition of their amplitudes, the result of which follows the formula... , where δ is the phase difference between the two beams.
[0030] This phase difference δ is not random, but a fixed value determined by the difference in the geometric path length of light propagating within the waveguide and the diffraction characteristics of the grating. Within the pupil-expanding grating structure 2, light rays with different diffraction orders (such as 1004 and 1005) experience different physical paths, resulting in a fixed optical path difference, which is then converted into a fixed phase difference δ. For example, when split into light rays 1002 and 1003, their phases are Φ1 and Φ2, respectively. When these two light rays re-enter region 102, they generate light rays 1004 and 1005, respectively, with added phases of Φ2 and Φ2. When these two light rays re-enter region 102, they combine to form light ray 1006, with added phases of Φ1 and Φ2. Because the path lengths of the two light rays are the same, the intensity of light ray 1006 is no longer simply 1004 plus 1005, but rather a coherent superposition of the two, forming a fixed phase difference δ. (Φ1-Φ2).
[0031] Due to the existence of this phase difference δ, the light intensity at each point on the final image plane will change periodically with the cos(δ) term: when δ = 2mπ (m is an integer), the interference is constructive, forming a bright area; when δ = (2m+1)π, the interference is destructive, forming a dark area. In a complete imaging process containing multiple similar 1006 rays, rays at different angles and positions have different δ values, resulting in fixed interference fringes with alternating and discontinuous intensity (i.e., uneven brightness) appearing on the final image pattern.
[0032] Therefore, how to effectively suppress coherent interference caused by multiple diffractions and improve the brightness uniformity of the imaging pattern is a technical problem that urgently needs to be solved.
[0033] To address the aforementioned shortcomings, this embodiment provides a diffractive waveguide comprising a waveguide substrate 4, an input grating structure 1, a pupil-expanding grating structure 2, and an output grating structure 3. The pupil-expanding grating structure 2 can be divided into an effective region 21 and a suppression region 22. An isolation layer 5 is provided in the suppression region 22, or the grating period is adjusted to suppress stray diffraction. In actual operation, the input grating structure 1 guides light into the waveguide, the effective region 21 of the pupil-expanding grating structure 2 receives the light and performs pupil-expanding transmission, while the suppression region 22 suppresses the generation of unnecessary diffracted light through the isolation layer 5 or a small period design. Finally, the light is extracted and imaged by the output grating structure 3. Compared to existing diffractive waveguides, which are prone to stray light and image crosstalk due to full-area diffraction of the grating, this embodiment, by dividing the pupil-expanding grating structure 2 and designing a suppression region 22, can suppress interference effects in non-imaging areas while achieving effective pupil expansion. Consequently, users can directly obtain a clear image with uniform brightness when using smart glasses, improving display quality and visual experience.
[0034] For ease of understanding, the following is combined with Figures 2 to 7 The diffraction waveguide provided in the embodiments of this application will be described in detail.
[0035] refer to Figure 2 as well as Figure 3 , Figure 2 This is a front view of the diffraction waveguide structure proposed in the first embodiment of this application. Figure 3 This is a top view of the diffraction waveguide structure proposed in the first embodiment of this application. Figure 2 as well as Figure 3 As shown, the diffraction waveguide includes: a waveguide substrate 4, a coupling grating structure 1, a pupil expanding grating structure 2, and a coupling out grating structure 3. The pupil-expanding grating structure 2 includes an effective region 21 and a suppression region 22. The effective region 21 is configured to receive light from any region of the coupling grating structure 1 and couple the light out to any region of the coupling grating structure 3. At least a portion of the pupil grating of the suppression region 22 is filled with an isolation layer 5 to suppress the generation of diffracted light from the pupil grating of the suppression region 22; And / or, at least a portion of the pupil dilatation grating in the suppression region 22 has a period smaller than that of the pupil dilatation grating structure 2 in the effective region 21, so as to suppress the generation of diffracted light from the pupil dilatation grating in the suppression region 22.
[0036] It should be noted that, in this embodiment, the coupling-in grating structure 1, the pupil-expanding grating structure 2, and the coupling-out grating structure 3 can be disposed on the same side or opposite side of the waveguide substrate 4. For example, the pupil-expanding grating structure 2 and the coupling-out grating structure 3 can be located on the upper and lower surfaces of the waveguide, respectively, or they can be integrated on the same surface. The relative positions of the suppression region 22 and the effective region 21 are also possible in various ways. For example, the suppression region 22 can be located on the side of the effective region 21 that is closer to the coupling end and farther from the coupling end, or it can be disposed around the effective region 21.
[0037] In order to ensure that the light propagating from the effective region 21 to the suppression region 22 is precisely the critical path that may cause multiple diffraction interferences, an isolation layer 5 is applied in this region or the grating period is reduced to block or weaken the harmful light path, thereby effectively suppressing coherent interference and improving the uniformity of the output image while maintaining the complete window function.
[0038] In this embodiment, the layout is explained with the pupil-expanding grating structure 2 and the coupling grating structure 3 located on the same side of the waveguide substrate 4, and the suppression region 22 disposed on the side of the effective region 21 close to the coupling grating structure 3. However, this embodiment is not specifically limited.
[0039] It is understood that the aforementioned coupling grating structure 1 can be a periodic micro / nano structure located on or inside the waveguide surface, used to couple external incident light into the waveguide, such as a surface relief grating or a volume holographic grating. The aforementioned waveguide substrate 4 can be a flat optical material with high light transmittance, such as glass or optical plastic, used to guide light to propagate through total internal reflection within it. The aforementioned pupil-expanding grating structure 2 can be a diffraction structure disposed on or inside the waveguide surface, used to expand the light beam in at least one direction, such as a one-dimensional or two-dimensional grating array. In this embodiment, the aforementioned pupil-expanding grating structure 2 includes several pupil-expanding gratings. The aforementioned effective region 21 can be the smallest continuous region in the pupil-expanding grating structure 2 that can completely realize the functions of light reception, expansion, and guided coupling, and its size is determined by the incident pupil and the field of view.
[0040] In addition, refer to Figure 4 , Figure 4 This is a side view of the diffraction waveguide structure proposed in the first embodiment of this application. Figure 3 as well as Figure 4As shown, it can also be understood that the aforementioned suppression region 22 can be a region used to weaken or eliminate coherent interference caused by multiple diffractions, for example, to partially disable the grating function through structural modification. The aforementioned isolation layer 5 can be a thin film material filled on the grating in the suppression region 22, with a refractive index similar to the grating material, used to reduce the diffraction efficiency of the grating, such as silicon dioxide or a resin coating. Figure 4 As shown, in this embodiment, the aforementioned isolation layer 5 can be filled between at least a portion of the pupil-expanding gratings in the pupil-expanding grating structure 2. Alternatively, it can completely fill and cover the pupil-expanding gratings. The top of the isolation layer 5 can be flat or uneven. This embodiment describes it as completely filling and covering the pupil-expanding gratings with a flat top. Figure 4 As shown. The above-mentioned coupling grating structure 3 can be a diffraction structure located in the waveguide light-emitting region, used to couple the light propagating in the waveguide to the direction of the human eye, such as a tilted grating or a gradient periodic grating.
[0041] As another implementation method, refer to Figure 5 , Figure 5 This is a schematic diagram of the diffraction waveguide structure when the period of the pupil-expanding grating structure 2 in the first embodiment of this application is reduced. In this embodiment, the period of the pupil-expanding grating structure 2 can also be reduced to weaken or eliminate coherent interference caused by multiple diffractions in the suppression region 22. Specifically, the period can be smaller than the period of the pupil-expanding grating structure 2 in the effective region 21, and this embodiment does not impose any restrictions on this.
[0042] In practical applications, after the optical signal enters the diffraction waveguide from the self-coupled grating structure 1, it propagates within the waveguide substrate 4 via total internal reflection. When the light propagates to the pupil-expanding grating structure 2, this structure expands the optical signal to increase the viewing window. The pupil-expanding grating structure 2 includes an effective region 21 and a suppression region 22. In the effective region 21, the light undergoes multiple diffractions to achieve pupil expansion and is guided to the output grating structure 3. In the suppression region 22, because at least a portion of the pupil-expanding grating is filled with an isolation layer 5 and / or a pupil-expanding grating with a period smaller than that of the effective region 21, the interference effect of the light in this region is suppressed or blocked, thereby avoiding the generation of multiple diffracted light paths with a fixed phase difference. Finally, all the expanded and suppressed coherent interference light is coupled out by the output grating structure 3, forming a uniformly bright imaging signal.
[0043] Furthermore, considering that during the pupil expansion process of the diffraction waveguide, the interference fringes that cause uneven brightness in the final image are often generated in the later stages of pupil expansion and occur along a specific diffraction path with a long propagation path, therefore, in this embodiment, as... Figure 3 As shown, the pupil-expanding grating structure 2 and the coupling grating structure 3 are both located on the same side of the waveguide substrate 4, and the suppression region 22 is located on the side of the effective region 21 close to the coupling grating structure 3.
[0044] In the specific implementation, after the light enters the waveguide substrate 4 through the coupling grating structure 1, it first undergoes pupil expansion propagation within the effective region 21 of the pupil-expanding grating structure 2 located on the same surface. When it continues to propagate to the suppression region 22 near the coupling grating structure 3, the diffraction function of the original grating is effectively suppressed because this region is filled with an isolation layer 5 and / or uses a small-period grating, thereby cutting off the multiple diffraction light paths that would lead to fixed phase difference interference. Finally, the light enters the coupling grating structure 3 on the same surface and is coupled out.
[0045] Furthermore, considering that the further away the light source is from the effective region 21, the smaller the light source becomes, which allows for a reduction in thickness and thus lower costs. Therefore, in this embodiment, the thickness of the isolation layer 5 gradually decreases along the direction away from the effective region 21.
[0046] It should be noted that in this embodiment, the isolation layer 5 can be thinner the further away from the effective area 21. Combined with... Figure 3 As can be seen, the closer to the right side, the smaller the thickness of the isolation layer 5 can be. This is because the thicker the isolation layer is, the better the suppression effect, and the less light is transmitted to the right side. This allows for a reduction in the thickness of the right-side isolation layer 5, thus achieving the desired effect while further reducing costs.
[0047] In one embodiment, in order to achieve isolation, the absolute value of the difference between the refractive index of the isolation layer 5 and the refractive index of the pupil grating of the suppression region 22 is less than or equal to 0.2.
[0048] It is understood that the refractive index mentioned above is a physical quantity describing the degree to which the speed of light is slowed down in a medium. Its value is equal to the ratio of the speed of light in a vacuum to the speed of light in a medium. For example, the refractive index of glass is about 1.5. The aforementioned isolation layer 5 can be an optical thin film filled on the grating of the suppression region 22. Its material refractive index can be close to that of the grating material below. For example, if the grating is silicon nitride (refractive index ~2.0), then the isolation layer 5 can be made of aluminum oxide (refractive index ~1.8) or a specific polymer material.
[0049] It is important to emphasize that when light propagates from the waveguide substrate 4 to the suppression region 22 of the pupil-expanding grating structure 2, if the grating surface in this region is filled with an isolation layer 5, the light will be refracted and reflected when passing through the interface between the grating structure and the isolation layer 5. In this embodiment, the absolute value of the difference between the refractive index of the isolation layer 5 and the refractive index of the pupil-expanding grating in the suppression region 22 is set to be less than or equal to 0.2. Because the refractive index difference is small, the diffraction efficiency of the light at the interface is extremely low, and the phase modulation capability of the grating is weakened. As a result, the incident light can hardly excite an effective diffraction order (such as ±1st order diffraction) in the suppression region 22. Therefore, the generation of multiple diffraction light paths with a fixed phase relationship is avoided, and the light superposition mode is changed from coherent superposition to incoherent superposition. Finally, a uniform image is output through the coupling grating structure 3.
[0050] Furthermore, considering that when light propagates to the suppression region 22 of the pupil grating structure 2, if the periods of at least some adjacent pupil gratings in the suppression region 22 are different, the grating structure constants encountered by the incident light at different microscopic positions within the suppression region 22 will differ. This results in inconsistent diffraction angles and additional phases in the secondary diffracted light generated when the light is diffracted by local gratings of different periods within the same suppression region 22. This disrupts the fixed phase matching relationship between the diffracted light paths, making it difficult for the diffracted light emitted from these adjacent but periodically different grating regions to form stable and regular interference patterns. The superposition effect is closer to incoherent superposition, thereby effectively suppressing the spatially regular brightness unevenness caused by the repetition of the periodic structure. Therefore, in this embodiment, the periods of at least some adjacent pupil gratings in the suppression region 22 are different.
[0051] It should be noted that the period of the aforementioned pupil grating refers to the repetition distance between the center points of adjacent optical micro / nano structural units (such as grooves, protrusions, or refractive index modulation regions) that constitute the pupil grating structure 2. This parameter directly determines the diffraction angle of the light. For example, a period of 400nm is designed for the diffraction of light at a specific wavelength.
[0052] In this embodiment, it is sufficient to ensure that the periods of at least any two adjacent pupil-expanding gratings within the suppression region 22 are different. The specific interval can be set according to the actual situation, or it can be set randomly; this embodiment does not impose any restrictions on this.
[0053] Furthermore, to ensure the inhibitory effect, continue as follows Figure 5 As shown, in one specific embodiment, the period of at least a portion of the pupil dilation grating of the suppression region 22 is 1 / 2 of the period of the pupil dilation grating structure 2 of the effective region 21.
[0054] When light propagates from the effective region 21 to the suppression region 22, if the period of at least a portion of the pupil-expanding grating in the suppression region 22 is set to half the period of the pupil-expanding grating in the effective region 21, it means that the light enters a grating region with a smaller spatial modulation scale. According to diffraction theory, when the grating period decreases to the order of the working wavelength or smaller, its higher-order (e.g., ±1st order) diffraction efficiency drops sharply, and it may even fail to excite effectively. Therefore, the light propagating to this small-period suppression region 22 has its interaction with the grating weakened, and cannot generate effective diffracted light for pupil expansion and steering as it does in the effective region 21. This blocks multiple diffracted light paths with specific phase relationships generated within the suppression region 22, thereby suppressing coherent superposition and resulting in a more uniform intensity distribution of the light ultimately output from the coupling grating structure 3.
[0055] This embodiment includes a waveguide substrate 4, a coupling grating structure 1, a pupil-expanding grating structure 2, and a coupling-out grating structure 3. The pupil-expanding grating structure 2 can be divided into an effective region 21 and a suppression region 22. An isolation layer 5 is provided in the suppression region 22, or the grating period is adjusted to suppress stray diffraction. In actual operation, the coupling grating structure 1 guides light into the waveguide, the effective region 21 of the pupil-expanding grating structure 2 receives the light and performs pupil-expanding transmission, while the suppression region 22 suppresses the generation of unnecessary diffracted light through the isolation layer 5 or a small period design. Finally, the light is extracted and imaged by the coupling-out grating structure 3. Compared to existing diffractive waveguides, which are prone to stray light and image crosstalk due to full-area diffraction of the grating, this embodiment, by dividing the pupil-expanding grating structure 2 and designing a suppression region 22, can suppress interference effects in non-imaging areas while achieving effective pupil expansion. Therefore, when using smart glasses, users can directly obtain a clear image with uniform brightness, improving display quality and visual experience.
[0056] Based on the first embodiment described above, a second embodiment of this application is proposed.
[0057] Furthermore, considering that while both the isolation layer 5 and the period are reduced, in order to effectively select the thickness and thus reduce manufacturing costs, the period of the pupil grating of the suppression region 22 is a, the thickness of the isolation layer 5 is d, the refractive index of the isolation layer 5 is n1, the refractive index of the pupil grating is n2, and the operating wavelength of the diffraction waveguide is λ. Where at least a portion of the pupil-expanding grating in the suppression region 22 is filled with an isolation layer 5, and the period of at least a portion of the pupil-expanding grating in the suppression region 22 is less than that of the pupil-expanding grating in the effective region 21, , a < λ.
[0058] It should be noted that the above-mentioned operating wavelength λ refers to the center wavelength of the optical signal or its band range targeted by the diffraction waveguide design. For example, 550nm can be selected as the design reference wavelength in the visible light band.
[0059] It is important to emphasize that when light propagates to the suppression region 22, which simultaneously possesses a small-period grating (period a < λ) and is filled with an isolation layer 5, its transmission process is affected by both the subwavelength characteristics of the grating and the refractive index matching of the interface. The grating period a is smaller than the operating wavelength λ, making it difficult to support effective diffraction; simultaneously, the isolation layer 5 (refractive index n1, thickness d) is designed to further suppress any residual modulation effects. To ensure sufficient suppression, the thickness d of the isolation layer 5 must satisfy the following relationship: .
[0060] This condition ensures that even with a small difference in refractive index (|n2-n1|), the isolation layer 5 can provide sufficient physical thickness to attenuate the evanescent field coupling of the grating, allowing light to pass through the region with almost no diffraction, thereby blocking the generation of coherent light paths and ensuring that subsequent light is output from the coupled grating structure 3 in a manner dominated by incoherent superposition.
[0061] refer to Figure 6 , Figure 6 This is a side view of the diffraction waveguide structure proposed in the second embodiment of this application. Considering that some light may still directly penetrate the suppression region 22 (or be scattered), an absorption region can be specially set on the side of the structure (for example, a thin film with high absorption rate for the working wavelength can be deposited on the waveguide surface) to improve the display effect. Therefore, in this embodiment, the diffraction waveguide further includes: an absorption layer 6; The absorption layer 6 is disposed on the side of the isolation layer 5 away from the waveguide substrate 4, and is used to absorb the diffracted light of the pupil grating of the suppression region 22.
[0062] It should be noted that the aforementioned absorption layer 6 is a functional thin film deposited or bonded to the surface of an optical element, which has a high absorption rate for light of a specific wavelength and is used to eliminate stray light. For example, a black dye coating or a metal-dielectric composite absorption film may be used in the visible light band.
[0063] Therefore, as Figure 6 As shown, in this embodiment, an absorption layer 6 is additionally provided on the side of the isolation layer 5 away from the waveguide substrate 4, that is, on the top of the isolation layer 5. Light is absorbed through the absorption layer 6, thereby further eliminating stray light and improving the effect.
[0064] It should be emphasized that the material and thickness of the specific absorption layer 6 can be set according to the actual situation, and this embodiment does not impose any restrictions on this.
[0065] Furthermore, in order to provide a corresponding absorber layer for each center wavelength, the absorber layer 6 includes at least two absorber layers stacked sequentially, and the different absorber layers have different absorption rates for different center wavelengths within the operating band of the diffraction waveguide.
[0066] It should be noted that the above-mentioned absorption sublayers are single-function thin films constituting the composite absorption layer 6. Each sublayer has a specific material composition and thickness to achieve selective high absorption of the target wavelength band, for example, it is composed of titanium nitride or carbon-based thin films of different thicknesses.
[0067] The aforementioned center wavelength refers to the wavelength value where light energy distribution is most concentrated within a specific band. It is typically used as a design and performance evaluation benchmark for optical components (such as filters and absorption layers). For example, in an RGB display system, it corresponds to the three center wavelengths of red, green, and blue, respectively. The aforementioned absorptivity is a physical quantity describing a material's ability to absorb light energy. It is defined as the ratio of the intensity of absorbed light to the intensity of incident light, usually expressed as a percentage. For example, a material may have an absorptivity of up to 95% for 550nm green light.
[0068] It is important to emphasize that when a composite optical signal containing multiple wavelength components (e.g., red, green, and blue) is incident as residual stray light onto absorption layer 6, different absorption sublayers exhibit varying absorption rates for different center wavelengths within the diffraction waveguide's operating band (e.g., 650nm for red light, 550nm for green light, and 450nm for blue light). For instance, the uppermost sublayer may have the highest absorption rate for red light, the middle layer for green light, and the lower layer for blue light. This ensures that during light transmission, residual light of different wavelengths is selectively absorbed sequentially by the corresponding absorption sublayers as it penetrates absorption layer 6.
[0069] Therefore, this embodiment sets up at least two absorber sub-layers, stacking each absorber sub-layer sequentially, with different absorber sub-layers corresponding to different center wavelengths of absorption rate, thereby ensuring that all light is absorbed by the absorber sub-layers and improving the absorption effect.
[0070] Furthermore, in another implementation, reference Figure 1 as well as Figure 7 , Figure 7 This is a diagram of the diffraction waveguide structure after trimming the pupil-expanding grating structure 2 in the second embodiment of this application. Figure 1 As shown, the directions of light rays 1003 and 1004 are the same as the direction of light ray 1006 emitted through the coupling grating structure 3. Therefore, this embodiment also proposes that by cutting the suppression region 22 of the pupil-expanding grating structure 2, the path that generates 1005 can be fundamentally and directly cut off, thereby avoiding coherent superposition caused by the superposition of too many rays with the same path. Figure 7 As shown.
[0071] It should be emphasized that the specific cutting size can be either directly cutting off the suppression area 22 or cutting off at least a portion of the suppression area 22. For the remaining part of the suppression area 22, the above-mentioned method of setting the isolation layer 5 and / or reducing the cycle can be adopted. That is, any one of the three methods can be used, or any two methods can be used, or all three methods can be used directly. This embodiment does not limit this.
[0072] In addition, to achieve the above objectives, this application also provides a smart glasses, which includes a diffractive waveguide as described above.
[0073] It should be emphasized that, since the specific implementation of the smart glasses in this embodiment can refer to the above-described diffractive waveguide embodiment, the smart glasses in this embodiment can have all the beneficial effects achieved by the above-described diffractive waveguide embodiment, and this embodiment will not elaborate on this.
[0074] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A diffractive waveguide, characterized in that, The diffraction waveguide includes: a waveguide substrate, a coupling grating structure, a pupil-expanding grating structure, and a coupling output grating structure. The pupil-expanding grating structure includes an effective region and a suppression region. The effective region is configured to receive light from any region of the coupling grating structure and couple the light out to any region of the coupling grating structure. At least a portion of the pupil grating in the suppression region is filled with an isolation layer to suppress the generation of diffracted light from the pupil grating in the suppression region; And / or, at least a portion of the pupil dilation grating in the suppression region has a period smaller than that of the pupil dilation grating in the effective region, so as to suppress the generation of diffracted light from the pupil dilation grating in the suppression region.
2. The diffraction waveguide as described in claim 1, characterized in that, The pupil-expanding grating structure and the coupling grating structure are both located on the same side of the waveguide substrate, and the suppression region is located on the side of the effective region closer to the coupling grating.
3. The diffraction waveguide as described in claim 1, characterized in that, The thickness of the isolation layer gradually decreases in the direction away from the effective region.
4. The diffraction waveguide as described in claim 1, characterized in that, The absolute value of the difference between the refractive index of the isolation layer and the refractive index of the pupil grating in the suppression region is less than or equal to 0.
2.
5. The diffraction waveguide as described in claim 1, characterized in that, The periods of at least some of the adjacent pupil gratings in the suppression region are different.
6. The diffraction waveguide as described in claim 1, characterized in that, The period of at least a portion of the pupil dilation grating in the suppression region is half the period of the pupil dilation grating in the effective region.
7. The diffraction waveguide as described in claim 1, characterized in that, The period of the pupil-expanding grating in the suppression region is a, the thickness of the isolation layer is d, the refractive index of the isolation layer is n1, the refractive index of the pupil-expanding grating is n2, and the operating wavelength of the diffraction waveguide is λ. Where, in the case that at least a portion of the pupil-expanding grating in the suppression region is filled with an isolation layer, and the period of at least a portion of the pupil-expanding grating in the suppression region is less than that of the pupil-expanding grating in the effective region, , a < λ.
8. The diffractive waveguide as described in any one of claims 1 to 7, characterized in that, The diffraction waveguide further includes: an absorption layer; The absorption layer is disposed on the side of the isolation layer away from the waveguide substrate, and is used to absorb the diffracted light of the pupil grating in the suppression region.
9. The diffraction waveguide as described in claim 8, characterized in that, The absorption layer includes at least two absorber sublayers stacked sequentially, and the absorption rates of different absorber sublayers are different for different center wavelengths within the operating band of the diffraction waveguide.
10. A type of smart glasses, characterized in that, The smart glasses include a diffractive waveguide as described in any one of claims 1 to 9.