Light leakage prevention diffraction optical waveguide

Abstract

The invention relates to a light leakage prevention diffraction optical waveguide which comprises a waveguide substrate, an input diffraction optical element and an output diffraction optical element. Incident light is coupled into the waveguide substrate through the input diffractive optical element, and is coupled out of the waveguide substrate step by step through the output diffractive optical element after being totally reflected in the waveguide substrate; the input diffractive optical element and the output diffractive optical element are respectively and independently arranged to be of a periodic grating structure, and a grating of the output diffractive optical element is arranged to be an asymmetric surface relief grating. The grating tilt direction of the output diffractive optical element and at least one further grating structure parameter are modulated such that the diffraction efficiency of the output diffractive optical element towards the out-coupling side exceeds the diffraction efficiency away from the out-coupling side, and the diffraction efficiency towards the out-coupling side varies spatially. According to the invention, the inclined grating or blazed grating easy to process is used in the coupling-out area, and the optical performance of the diffraction optical waveguide is considered by modulating the grating parameters, so that the effects of effectively weakening light leakage and ensuring the privacy of a user are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of diffraction optical waveguides, and in particular to a light leakage-proof diffraction optical waveguide. Background Art

[0002] Waveguide is currently the best solution for augmented reality glasses. Waveguide solutions are divided into geometric waveguide solutions, diffraction waveguide solutions (embossed grating waveguide solutions and volume holographic waveguide solutions). Geometric waveguide solutions generally include sawtooth structure waveguides and polarization film array reflector waveguides. Among them, the mainstream polarization array waveguide uses an array of partially transmissive and partially reflective film mirrors to achieve the purpose of displaying virtual information. The polarization array waveguide solution has the advantages of lightness, large eye movement range and uniform color. The embossed grating waveguide solution can be mass-produced using nanoimprint technology, which has aroused great interest among AR optical module manufacturers. It has the advantages of a large field of view and a large eye movement range, but it also brings challenges to field of view uniformity and color uniformity. At the same time, related micro-nano processing technology is also a huge challenge. The volume holographic waveguide solution has advantages in color uniformity and the realization of a single full-color waveguide, but it is currently limited in large-scale mass production and large field of view.

[0003] Compared with the geometric waveguide solution and the volume holographic waveguide solution, the relief grating waveguide solution is more popular in the market due to its lower mass production cost. However, the light leakage problem of this solution has been criticized. At present, the strategy to reduce light leakage is mainly to use a film layer or grating on the other side of the outcoupling area to absorb or reflect the light escaping after the grating diffraction, or to use a two-dimensional grating with a special shape to suppress light leakage. The former may affect the optical properties of the diffraction light waveguide, such as uniformity and transmittance, while the latter is difficult to process and difficult to achieve, and has limited effect on improving light leakage. Therefore, how to use conventional and easy-to-process gratings to significantly improve the light leakage problem without damaging the optical performance of the modulated diffraction light waveguide has become a technical problem that needs to be solved urgently.

[0004] The Chinese patent with the publication number CN118091820A discloses a diffraction optical waveguide, including a waveguide substrate and an in-coupling grating area, an out-coupling area and a reflection area configured on the surface of the waveguide substrate; after the light enters the waveguide substrate from the in-coupling grating area, it is totally reflected and transmitted in the waveguide substrate; after the light is totally reflected and transmitted in the waveguide substrate and reaches the out-coupling area, a first diffraction light and a second diffraction light are generated, and the first diffraction light is coupled out of the waveguide substrate and enters the human eye; the reflection area is configured on the surface where the second diffraction light emerges from the waveguide substrate, corresponding to the out-coupling area, and the second diffraction light is selectively reflected back to the waveguide substrate after being transmitted to the reflection area. The above-mentioned diffraction optical waveguide is provided with a reflection area opposite to the out-coupling area. Although this design can reflect the light escaping after the grating diffraction and prevent it from leaking into the external environment, it does not take into account that these lights will pass through the grating diffraction of the coupling area again when returning to the waveguide, thereby interfering with the uniformity of the human eye's visual range. This undoubtedly increases the complexity of the design.

[0005] The Chinese patent with the publication number CN115903240A discloses a diffraction light waveguide display device for reducing light leakage, characterized in that: it includes a diffraction light waveguide, an optical engine and an extinction film, the diffraction light waveguide has two waveguide surfaces facing each other, a diffraction grating area is arranged on at least one waveguide surface, and the diffraction grating area includes an entrance pupil area and at least one exit pupil area; the optical engine is located beside the entrance pupil area; the extinction film has at least one layer arranged on one of the waveguide surfaces and fully covers the exit pupil area; the central light of the optical engine forms an angle A with the vertical line of the waveguide surface. The above-mentioned diffraction light waveguide also has an extinction film arranged opposite to the outcoupling area, and the light entering the external environment is absorbed after being diffracted by the grating, but this configuration will reduce the transmittance of the waveguide in the structural area.

[0006] The Chinese patent with the publication number CN117608021A discloses a light leakage-proof diffraction waveguide device, comprising a waveguide substrate and an in-coupling grating and an out-coupling grating formed on the waveguide substrate, wherein the in-coupling grating is configured to couple an input light beam from the outside of the waveguide substrate into the waveguide substrate by diffraction and propagate it to the out-coupling grating by total reflection; the out-coupling grating comprises a two-dimensional grating structure formed on a substrate surface of the waveguide substrate, the two-dimensional grating structure comprises a structural surface extending in a direction parallel to the substrate surface and a plurality of optical unit structures arranged in an array along the structural surface, for expanding the light propagated therein in a plane parallel to the substrate surface by diffraction and coupling out from the waveguide substrate at the same time, wherein the optical unit structure is a columnar structure and is formed with an end face and a side wall connected between the end face and the structural surface, wherein the end face is inclined relative to the substrate surface. The above-mentioned diffraction waveguide uses a special three-dimensional cylindrical grating, and the energy level of reflection and transmission can be controlled by adjusting the grating shape of the coupling region. This grating can not only adjust the optical properties of the waveguide, but also effectively prevent light leakage. However, there are technical difficulties in manufacturing this special shape of three-dimensional grating structure, resulting in very low production yield. Summary of the invention

[0007] The problem to be solved by the present invention is to provide a light leakage-proof diffraction optical waveguide in view of the above-mentioned deficiencies existing in the prior art. The diffraction optical waveguide uses an easily processed inclined grating or a blazed grating in the outcoupling region, and by modulating the grating parameters, achieves the effect of taking into account the optical performance of the diffraction optical waveguide, effectively reducing light leakage and ensuring user privacy.

[0008] The above-mentioned object of the present invention is achieved through the following technical solutions: A light leakage-proof diffractive optical waveguide comprises a waveguide substrate, an input diffractive optical element and an output diffractive optical element; incident light is coupled into the waveguide substrate by the input diffractive optical element, and after total reflection occurs in the waveguide substrate, the output diffractive optical element couples the incident light out of the waveguide substrate in steps; the input diffractive optical element and the output diffractive optical element are each independently configured as a periodic grating structure, and the grating of the output diffractive optical element is configured as an asymmetric surface relief grating; the grating tilt direction of the output diffractive optical element and at least one other grating structure parameter are modulated so that the diffraction efficiency of the output diffractive optical element toward the outcoupling side exceeds the diffraction efficiency away from the outcoupling side, and the diffraction efficiency toward the outcoupling side varies with space.

[0009] Furthermore, the other grating structure parameters that are modulated include grating period P, duty cycle ff and grating height h.

[0010] Furthermore, the diffraction efficiency toward the out-coupling side and the diffraction efficiency away from the out-coupling side are regionally modulated or continuously modulated within an effective area of ​​the output diffractive optical element.

[0011] By optimizing these parameters, the diffraction efficiency can be precisely controlled, thereby effectively reducing the light leakage phenomenon in the optical waveguide and improving the overall performance of the system. Among them, continuous modulation, that is, the use of a gradient grating solution, refers to the design concept of CN117148499B authorized by the applicant a few days ago, which is conducive to improving the uniformity of light output; but in the present invention, the regional modulation method, that is, the grating in the area uses the same structural parameters, which is the most obvious in improving the comprehensive performance of diffraction efficiency and suppressing light leakage; the specific method of regional modulation or continuous modulation is optimized according to the path and method of waveguide pupil expansion.

[0012] Preferably, the output diffractive optical element comprises a transmissive tilted grating, and a tilt angle α of the transmissive tilted grating is greater than 10°.

[0013] More preferably, the transmission-type tilted grating has a grating period P of 200-500 nm, a duty cycle ff of 20-80%, and a grating height h of 30-500 nm.

[0014] Alternatively, the output diffractive optical element comprises a reflective tilted grating, and a tilt angle α of the reflective tilted grating is less than 0°.

[0015] More preferably, the reflective tilted grating has a grating period P of 200-500 nm, a duty cycle ff of 20-80%, and a grating height h of 30-500 nm.

[0016] Alternatively, the output diffractive optical element comprises a transmissive blazed grating, wherein a blaze angle α and a reverse blaze angle β of the transmissive blazed grating are independently set to 0-90°, and cosα / cosβ>1.

[0017] More preferably, the transmission blazed grating has a grating period P of 200-500 nm, a duty cycle ff of 20-80%, and a grating height h of 30-500 nm.

[0018] Alternatively, the output diffractive optical element comprises a reflective blazed grating, wherein a blaze angle α and a reverse blaze angle β of the reflective blazed grating are independently set to 0-90°, and cosα / cosβ<1.

[0019] More preferably, the reflective blazed grating has a grating period P of 200-500 nm, a duty cycle ff of 20-80%, and a grating height h of 30-500 nm.

[0020] Most preferably, the output diffractive optical element is arranged as a transmissive grating structure or a reflective grating structure, the grating correspondence of the output diffractive optical element is inclined in a direction away from the side of the input diffractive optical element or towards the side of the input diffractive optical element, and the grating period P, duty cycle ff and grating height h of the output diffractive optical element are modulated so that the diffraction efficiency of the output diffractive optical element toward the outcoupling side exceeds the diffraction efficiency away from the outcoupling side, and the ratio of the two diffraction efficiencies varies with space.

[0021] At the same time, the input diffractive optical element can be only a coupling-in grating, or it can include a coupling-in grating and a turning grating. The output diffractive optical element corresponds to an out-coupling grating. The incident light from the projection optical machine passes through the coupling-in area, the turning area and the out-coupling area on the waveguide substrate, couples out the virtual image, and enters the human eye (towards the out-coupling side). Since the output diffractive optical element can diffract light in two directions at the same time, namely, toward the out-coupling side and away from the out-coupling side, the outgoing light propagating in the direction away from the out-coupling side may be received by the eyes of the person opposite the wearer of the AR glasses, thereby causing information leakage, and also affecting the eye contact between the wearer of the AR glasses and other people. In order to minimize the risk of information leakage, during the waveguide design process, the output diffractive optical element needs to improve the difference in diffraction efficiency in the two directions.

[0022] For the transmission-type outcoupling grating, T-1 is the diffraction efficiency in the direction toward the outcoupling side, and R-1 is the diffraction efficiency away from the outcoupling side. When T-1>R-1, light leakage can be effectively alleviated; similarly, for the reflection-type outcoupling grating, when R-1>T-1, light leakage can be effectively alleviated; at the same time, in order to ensure the uniformity of light outcoupling in the outcoupling area, the grating parameters will be adjusted in the outcoupling area, that is, the grating tilt direction of the output diffraction optical element and at least one other grating structure parameter are modulated. Taking the transmission-type outcoupling grating as an example, it is necessary to satisfy that T-1 gradually increases in the direction away from the turning area, and in this process, T-1>R-1 is always controlled; in this way, under the premise of effectively suppressing light leakage, the uniformity of the optical waveguide outcoupling efficiency can also be guaranteed; similarly, the reflection-type waveguide needs to satisfy that R-1 gradually increases in the direction away from the turning area, and in this process, R-1>T-1 is always controlled.

[0023] In the above-mentioned diffraction waveguide design, commonly used one-dimensional gratings include straight gratings, tilted gratings and blazed gratings. These grating structures are relatively mature in processing, easy to achieve mass production and preparation, and compared with other special structures, the design and processing costs are relatively low. In the study, we found that these tilted gratings and blazed gratings can very effectively suppress light leakage under specific grating parameters, and in a large parameter variation range, that is, in the process of obvious changes in the grating diffraction efficiency, they can always meet the diffraction efficiency of the output diffractive optical element toward the out-coupling side exceeds the diffraction efficiency away from the out-coupling side, thereby taking into account both uniformity and light leakage suppression.

[0024] The input diffractive optical element and the output diffractive optical element are arranged along the YZ plane of the waveguide substrate. For the tilted grating, h represents the grating height of the grating, ff represents the duty cycle of the grating, and α represents the tilt angle of the tilted grating. It is stipulated that when the out-coupling grating deviates toward the positive X axis (away from the side of the in-coupling grating), the value of α is positive, and when it deviates toward the negative X axis, the value of α is negative; for the blazed grating, α and β represent the blaze angle and the anti-blaze angle respectively, h is the grating height, and ff is the duty cycle; for the convenience of description, for the transmission-type out-coupling grating, the size of the leakage light is represented by the size of the R-1 / T-1 value, and the smaller the ratio, the more obvious the leakage suppression effect; for the reflection-type out-coupling grating, the size of the leakage light is represented by the size of the T-1 / R-1 value, and the smaller the ratio, the more obvious the leakage suppression effect.

[0025] Gratings with a period of P=200~500nm are studied. Without loss of generality, multiple field angles are selected to calculate the actual angles of the out-coupling grating after the waveguide turns and the T-1 and R-1 of the out-coupling grating as well as their ratio. The changes of T-1 and R-1 with the grating parameters and the changes of their ratio with the grating parameters are investigated. Through analysis, it is found that the tilted grating can effectively suppress the light leakage of the transmission waveguide when α>10°, and can effectively suppress the light leakage of the reflection waveguide when α<0°. The blazed grating can effectively suppress the light leakage of the transmission waveguide when cosα / cosβ>1, and can effectively suppress the light leakage of the reflection waveguide when cosα / cosβ<1.

[0026] Specifically, the input diffractive optical element and the output diffractive optical element are each independently configured as a sub-wavelength grating structure composed of a plurality of straight tooth gratings, a plurality of tilted gratings and / or a plurality of blazed gratings and arranged in a one-dimensional or two-dimensional array, and the output diffractive optical element has at least one group of tilted gratings or blazed gratings covering the light transmission path.

[0027] Specifically, the waveguide substrate is configured as a flat plate structure made of an optical material transparent to visible light; the input diffractive optical element and the output diffractive optical element are each independently and tightly attached to the surface of the waveguide substrate or embedded in the material of the waveguide substrate.

[0028] Specifically, the etching processing methods available for the input diffractive optical element and the output diffractive optical element include electron beam etching, reactive ion beam etching, magnetic enhanced reactive ion etching, high density plasma etching, inductively coupled plasma etching, variable voltage coupled plasma etching and electron cyclotron resonance etching. Modulation of structural parameters can be achieved by controlling the exposure of electron beams or ion beams on the master substrate. The periodic structure on the master can be copied into the resin material of the replica by nanoimprinting, casting, molding, injection molding, etc., to meet the needs of large-scale mass production and reducing manufacturing costs.

[0029] This design enables precise control of the light transmission path in the optical waveguide; the arrangement and angle of each grating unit can be optimized according to specific application requirements to achieve the best diffraction effect; for example, the light beam transmitted in the optical waveguide may need to be guided at a specific output angle, or the light intensity needs to be distributed in multiple different output directions. By adjusting the period, duty cycle and height of the grating, these parameters can be finely controlled to meet different application requirements.

[0030] In addition, the functionality of the optical waveguide can be further enhanced by designing the input diffractive optical element and the output diffractive optical element as a one-dimensional or two-dimensional array of periodic grating structures; this array structure allows for complex optical path design over a larger area, thereby enabling more complex optical functions in the optical waveguide, such as multiplexing, beam shaping, and optical path switching. The flexibility and versatility of this design provide broad prospects for the application of optical waveguide technology in the AR field.

[0031] In summary, the present invention provides a highly customizable anti-leakage diffractive optical waveguide. By optimizing the structural parameters of the output diffractive optical element, the optical transmission path can be precisely controlled and optimized. This optical waveguide can not only improve the efficiency and stability of optical transmission, but also expand the application scope of optical waveguide technology, providing new possibilities for the design and integration of optical systems. With the continuous advancement of optical technology, this anti-leakage diffractive optical waveguide is expected to play an important role in future optoelectronic devices.

[0032] In summary, the beneficial technical effects of the present invention are as follows: with the flexibility of design and low mass production cost, diffraction optical waveguides are gradually becoming the preferred solution for AR near-eye display technology due to their advantages such as easy realization of a large field of view; in diffraction optical waveguides, the gratings in the out-coupling region can simultaneously produce diffraction effects on the side close to and far from the human eye, which enables images to be formed on both sides of the waveguide sheet, but also brings the risk of information leakage; in addition, individuals facing the wearer may notice the luminous phenomenon at the position of the wearer's eyes, which may affect the wearer's interaction with others; in order to solve these problems, the present invention proposes an innovative design scheme, in which tilted gratings and / or blazed gratings are used as output diffraction optical elements in the out-coupling region, and by adjusting the tilt angle, blaze angle and anti-blaze angle of the grating, the grating period, the duty cycle and the grating height, not only the optical performance of the diffraction optical waveguide is ensured, but also the light leakage is effectively reduced, thereby ensuring the privacy and security of the user. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of the light leakage prevention diffraction waveguide of Example 1 of the present invention.

[0034] Figure 2 It is a schematic diagram of the connection relationship between the waveguide substrate and the output diffractive optical element of Example 1 of the present invention.

[0035] Figure 3 3 is a diffraction efficiency diagram of the diffraction optical waveguide according to Example 3 of the present invention.

[0036] Figure 4 It is a diffraction efficiency diagram of the diffraction optical waveguide according to Example 4 of the present invention.

[0037] Figure 5 It is a diffraction efficiency diagram of the diffraction optical waveguide according to Example 6 of the present invention.

[0038] Figure 6 It is a diffraction efficiency diagram of the diffraction optical waveguide according to Example 7 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical means, creative features, objectives and functions achieved by the present invention clearer and easier to understand, the present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods.

[0040] Example 1: Reference Figure 1 and Figure 2, is a light leakage-proof diffractive optical waveguide disclosed in the present invention, comprising a waveguide substrate, an input diffractive optical element and an output diffractive optical element; incident light is coupled into the waveguide substrate by the input diffractive optical element, and after total reflection occurs in the waveguide substrate, the output diffractive optical element couples the incident light out of the waveguide substrate in steps; the input diffractive optical element and the output diffractive optical element are independently configured as periodic grating structures, and the grating of the output diffractive optical element is configured as an asymmetric surface relief grating; the grating tilt direction of the output diffractive optical element and at least one other grating structure parameter (grating period P, duty cycle ff and grating height h) are regionally modulated, so that the diffraction efficiency of the output diffractive optical element toward the outcoupling side exceeds the diffraction efficiency away from the outcoupling side, and the diffraction efficiency toward the outcoupling side varies with space.

[0041] Embodiment 2 is a light leakage-proof diffractive optical waveguide disclosed in the present invention, which is different from Embodiment 1 in that the waveguide substrate is configured as a flat plate structure composed of an optical material transparent to visible light (such as ordinary optical glass, high-refractive glass, lithium niobate, SiC, diamond, etc.), and the input diffractive optical element and the output diffractive optical element are each independently and tightly attached to the surface of the waveguide substrate; The input diffractive optical element is configured as a sub-wavelength grating structure composed of a plurality of straight tooth gratings, a plurality of tilted gratings and / or a plurality of blazed gratings, and arranged in a one-dimensional array in the coupling region and the turning region of the waveguide substrate. In this embodiment, a tilted grating is preferably used, and the grating period P of the coupling grating is 300nm, the tilt angle α is -20°, the duty cycle ff is 60%, and the grating height h is 150nm. The grating period P of the turning grating is 300nm, the tilt angle α is 0°, the duty cycle ff is 50%, and the grating height h is 180nm. The output diffractive optical element is configured as a sub-wavelength grating structure composed of multiple tilted gratings and arranged in a one-dimensional array in the outcoupling region of the waveguide substrate. The grating period P of the outcoupling grating is 300nm, the tilt angle α is 35°, the duty cycle ff is 50%, and the grating height h is 200nm.

[0042] Embodiment 3 is a light leakage prevention diffraction waveguide disclosed in the present invention, which is different from Embodiment 1 in that the inclination angle of the outcoupling grating is α=-40~40°.

[0043] A tilted grating with a period of P = 300nm is selected as the grating structure of the out-coupling area. Three field angles are randomly selected to couple into the waveguide, and the incident angles are 57°, 64°, and 60°, respectively. The light is transmitted to the out-coupling area through the diffraction waveguide and diffracted under the action of the grating in the out-coupling area. Figure 3As shown in the figure, when the grating tilt angle α>10°, T-1>R-1 in all viewing fields, and as the tilt angle increases, R-1 / T-1 gradually decreases, and the light leakage suppression effect is more obvious; when α<0°, in all viewing fields, R-1>T-1, and as the tilt angle increases negatively, T-1 / R-1 gradually decreases, and the light leakage suppression effect is more obvious. That is, for a transmission grating, tilting the grating in the positive direction is beneficial to suppressing light leakage, while for a reflection grating, tilting the grating in the negative direction is beneficial to suppressing light leakage. That is, the direction and size of the tilt angle of the tilted grating determine the direction and degree of suppression of light leakage.

[0044] Embodiment 4 is a light leakage-proof diffraction waveguide disclosed in the present invention, which is different from Embodiment 1 in that the duty cycle of the outcoupling grating is ff=30~60° or the grating height h=100~250nm.

[0045] On the basis of Example 2, a tilted grating with a positive tilt angle α=35° is selected to further analyze the influence of the change of height h and duty cycle ff on the grating diffraction efficiency T-1 and R-1. Figure 4 As shown in the figure, when the duty cycle ff varies from 30 to 60%, T-1 increases approximately linearly with the duty cycle, while R-1 increases relatively slowly and decreases with the duty cycle at some incident angles. That is, within the range of duty cycle ff, R-1 / T-1 gradually decreases. The linear increase of T-1 with the duty cycle is conducive to maintaining good outcoupling uniformity, while the reduction of R-1 / T-1 ensures that the light leakage effect can be clearly reflected in the entire outcoupling grating area.

[0046] When the height h of the tilted grating varies from 100 to 250 nm, T-1 and R-1 both show parabolic changes with height, that is, within the grating height range, there is a certain height value that maximizes T-1 and R-1. Overall, within the height variation range, R-1 / T-1 can always remain less than 0.5, that is, the light efficiency on the light leakage side is less than 50% of the normal outcoupling efficiency.

[0047] The above results show that no matter changing ff or h, the tilted grating can not only realize the change of T-1 and R-1 diffraction efficiency and adjust the optical properties such as uniformity and light efficiency of the diffraction waveguide, but also can always keep the diffraction efficiency of T-1 much greater than the diffraction efficiency of R-1. The value of R-1 / T-1 can also be adjusted to prevent light leakage, and the grating parameters are all within the easy processing range.

[0048] Similarly, for the reflective diffraction waveguide, when α<0, changing the duty cycle ff and the height h can also achieve changes in the T-1 and R-1 diffraction efficiencies, adjust the uniformity and optical efficiency of the diffraction waveguide and other optical properties, and always keep the R-1 diffraction efficiency much greater than the T-1 diffraction efficiency. The value of T-1 / R-1 can also be adjusted to prevent light leakage, and the grating parameters are all within the easy processing range.

[0049] Embodiment 5 is a light leakage-proof diffractive optical waveguide disclosed in the present invention, which is different from Embodiment 1 in that the waveguide substrate is set to a flat plate structure composed of an optical material transparent to visible light (such as ordinary optical glass, high-refractive glass, lithium niobate, SiC, diamond, etc.), and the input diffractive optical element and the output diffractive optical element are each independently and tightly attached to the surface of the waveguide substrate; The input diffractive optical element is configured as a sub-wavelength grating structure composed of a plurality of straight tooth gratings, a plurality of tilted gratings and / or a plurality of blazed gratings, and arranged in a one-dimensional array in the coupling region and the turning region of the waveguide substrate. In this embodiment, a tilted grating is preferably used, and the grating period P of the coupling grating is 410nm, the tilt angle α is -30°, the duty cycle ff is 55%, and the grating height h is 120nm. The grating period P of the turning grating is 410nm, the tilt angle α is 0°, the duty cycle ff is 50%, and the grating height h is 200nm. The output diffractive optical element is set to a sub-wavelength grating structure composed of multiple blazed gratings and arranged in a one-dimensional array in the outcoupling area of ​​the waveguide substrate. The grating period P of the outcoupling grating is 410nm, the blaze angle α is 36°, the anti-blaze angle β is 20.1°, and cosα / cosβ is 0.5 (that is, the length of the base on both sides of the triangle height line a / b is 0.5), the duty cycle ff is 100%, and the grating height h is 100nm.

[0050] Embodiment 6 is a light leakage prevention diffraction waveguide disclosed in the present invention, which is different from Embodiment 5 in that the duty cycle of the outcoupling grating is ff=50~100° or the grating height is h=50~300nm.

[0051] A blazed grating with a period of P = 410nm is selected as the grating structure of the outcoupling area. Three field angles are randomly selected to couple into the waveguide, and the light is transmitted to the outcoupling area through the diffraction waveguide and diffracted under the action of the grating in the outcoupling area. Figure 5As shown, taking a / b = 0.5, that is, the angle on the left side of the triangle is greater than the angle on the right side. At this time, the efficiency of the R-1 level is always higher than that of the T-1 level, and light leakage can be effectively eliminated in the reflective grating. As the duty cycle ff of the blazed grating increases, both R-1 and T-1 increase approximately linearly, that is, T-1 < R-1 is always satisfied; similarly, as the grating height h increases, R-1 and T-1 increase approximately parabolically. Within a certain height range, R-1 > T-1 can be achieved, and T-1 / R-1 gradually decreases. That is, while ensuring the uniformity of light output, light leakage is effectively suppressed.

[0052] Example 7: A light-leakage-proof diffractive optical waveguide disclosed in the present invention is different from Example 5 in that the grating period P of the output grating is 280 nm, the blaze angle α is 21°, the anti-blaze angle β is 78°, and cosα / cosβ = 12.5, the duty cycle ff is 50 - 100°, or the grating height h is 50 - 300 nm.

[0053] Select a grating with a period P = 280 nm. For a blazed grating with a / b = 12.5, that is, the angle on the left side is less than the angle on the right side, as Figure 6 shown. At this time, the efficiency of the T-1 level is higher than that of the R-1 level, which is suitable for transmissive optical waveguides. By changing the duty cycle of the grating, the diffraction efficiency of T-1 gradually increases as the duty cycle increases, while the diffraction efficiency of R-1 decreases slowly, that is, R-1 / T-1 decreases as the duty cycle increases, and light leakage can be effectively suppressed. By changing the grating height, both T-1 and R-1 increase as the grating height increases. When the grating height is greater than 100 nm, R-1 / T-1 decreases significantly, effectively suppressing light leakage. That is, when the a / b ratio is determined, by adjusting the duty cycle and the grating height, it can be effectively ensured that T-1 increases significantly within a certain range, and R-1 / T-1 < 1.

[0054] The results show that when the value of a / b is greater than 1, by changing the duty cycle and height of the blazed grating, not only can the changes in the diffraction efficiencies of T-1 and R-1 be achieved, and the optical properties such as the uniformity and light efficiency of the diffractive optical waveguide be adjusted, but also the diffraction efficiency of T-1 can always be much greater than that of R-1, and the value of R-1 / T-1 can also be adjusted, thereby preventing light leakage. In addition, the grating parameters are all within the easy processing range.

[0055] If it is a reflective diffractive optical waveguide, when the value of a / b is less than 1, by changing the duty cycle and height of the blazed grating, not only can the changes in the diffraction efficiencies of R-1 and T-1 be achieved, and the optical properties such as the uniformity and light efficiency of the diffractive optical waveguide be adjusted, but also the diffraction efficiency of R-1 can always be much greater than that of T-1, and the value of T-1 / R-1 can also be adjusted, thereby preventing light leakage. In addition, the grating parameters are all within the easy processing range.

[0056] In addition, the scheme is applicable to all cases where a one-dimensional grating is used in the outcoupling region, and is not limited to the layout of the diffraction waveguide and whether it is a transmission or reflection diffraction waveguide.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A light leakage-proof diffraction optical waveguide, characterized in that: The invention comprises a waveguide substrate, an input diffractive optical element and an output diffractive optical element; incident light is coupled into the waveguide substrate by the input diffractive optical element, and after total reflection occurs in the waveguide substrate, the output diffractive optical element couples the incident light out of the waveguide substrate in steps; the input diffractive optical element and the output diffractive optical element are each independently configured as a periodic grating structure, and the grating of the output diffractive optical element is configured as an asymmetric surface relief grating; the grating tilt direction of the output diffractive optical element and at least one other grating structure parameter are modulated so that the diffraction efficiency of the output diffractive optical element toward the outcoupling side exceeds the diffraction efficiency away from the outcoupling side, and the diffraction efficiency toward the outcoupling side varies with space.

2. The anti-light leakage diffraction optical waveguide according to claim 1, characterized in that: The other grating structure parameters that are modulated include the grating period P, the duty cycle ff and the grating height h.

3. The anti-light leakage diffraction optical waveguide according to claim 2, characterized in that: The output diffractive optical element comprises a transmissive tilted grating, and a tilt angle α of the transmissive tilted grating is greater than 10°.

4. The anti-light leakage diffraction optical waveguide according to claim 3, characterized in that: The grating period P of the transmission-type tilted grating is 200-500 nm, the duty cycle ff is 20-80%, and the grating height h is 30-500 nm.

5. The anti-light leakage diffraction optical waveguide according to claim 2, characterized in that: The output diffractive optical element comprises a reflective tilted grating, and a tilt angle α of the reflective tilted grating is less than 0°.

6. The anti-light leakage diffraction optical waveguide according to claim 5, characterized in that: The grating period P of the reflective tilted grating is 200-500 nm, the duty cycle ff is 20-80%, and the grating height h is 30-500 nm.

7. The anti-light leakage diffraction optical waveguide according to claim 2, characterized in that: The output diffractive optical element comprises a transmission blazed grating, wherein a blaze angle α and a reverse blaze angle β of the transmission blazed grating are independently set to 0-90°, and cosα / cosβ>1.

8. The anti-light leakage diffraction optical waveguide according to claim 7, characterized in that: The transmission blazed grating has a grating period P of 200-500 nm, a duty cycle ff of 20-80%, and a grating height h of 30-500 nm.

9. The anti-light leakage diffraction optical waveguide according to claim 2, characterized in that: The output diffractive optical element comprises a reflective blazed grating, wherein a blaze angle α and a reverse blaze angle β of the reflective blazed grating are independently set to 0-90°, and cosα / cosβ<1.

10. The anti-light leakage diffraction optical waveguide according to claim 9, characterized in that: The grating period P of the reflective blazed grating is 200-500 nm, the duty cycle ff is 20-80%, and the grating height h is 30-500 nm.

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