Low-light-leakage super-structure grating structure

Abstract

The invention discloses a low-light-leakage super-structure grating structure. An inverted goblet structure is defined by a first free-form curved surface structure and a second free-form curved surface structure. The first free-form curved surface structures are symmetrically distributed along the longitudinal center line of the super-structure grating unit, and openings of the first free-form curved surface structures face downwards. The free-form curved surface structures are symmetrically distributed along the longitudinal center line of the super-structure grating unit, and openings of the free-form curved surface structures face downwards. The distance between the two free-form curved surface structures can be adjusted; the super-structure grating structure is applied to a coupling-out area of a two-dimensional grating waveguide and serves as a two-dimensional coupling-out grating structure, and a light beam is coupled in through a coupling-in grating, is totally reflected and propagated in the two-dimensional grating waveguide, reaches the coupling-out area, and then is subjected to pupil expansion through the super-structure grating structure and is coupled out to human eyes. And meanwhile, as the structural form of the provided super-structure grating is an inverted goblet structure, the efficiency of coupling the light beam out of one side of the environment can be reduced.

Description

Technical Field

[0001] The present invention relates to a low light leakage meta-grating structure, belonging to the technical field of diffraction optics, and in particular to a two-dimensionally expanded meta-grating structure suitable for a light leakage near-eye display system. Background Art

[0002] After years of development, augmented reality technology has gradually matured. As the next generation computing platform, it has great potential to replace mobile phones and become the next generation of portable smart devices. Augmented reality near-eye display devices are an important part of augmented reality technology.

[0003] At present, the more mature augmented reality near-eye display solutions are mainly divided into prism solutions, birdbath solutions, free-form surface solutions, off-axis holographic lens solutions and waveguide solutions, but most of them require a combination of complex mirrors, resulting in a large overall module volume, which limits its application in smart wearables, namely augmented reality glasses. Waveguides have the potential to be applied to various fields of miniaturization requirements due to their compact and light advantages, making them the best augmented reality glasses solution at present.

[0004] The waveguide solution is specifically divided into two types: geometric waveguide and diffraction waveguide. The most common geometric waveguide solution is the array waveguide. The light beam emitted by the micro-projection optical machine is coupled into the waveguide by a reflector, and then enters the human eye after passing through a large number of semi-transparent and semi-reflective mirrors in the out-coupling area. This solution has limited field of view and orbital range, and due to the large number of coatings, it is difficult to guarantee product yield. Imaging is prone to black background stripes, uneven light brightness, ghosting, etc., so the geometric waveguide solution cannot present the best display effect to the human eye. The grating structure design process of the diffraction waveguide solution is relatively complicated, but it provides a large degree of design freedom. The diffraction waveguide augmented reality near-eye reality device after calculating and optimizing the grating structure parameters can obtain excellent imaging effects and a large field of view. The diffraction waveguide solution is divided into two types: surface relief grating waveguide and volume holographic grating waveguide. Among them, the volume holographic grating waveguide is difficult to achieve in large-scale mass production, which limits its scope of application. Surface relief grating waveguides have become the most studied technical solution at present because of the convenience of production using nanoimprint technology and semiconductor etching technology.

[0005] Surface relief grating refers to the periodic variation structure produced on the surface, that is, various periodic grooves formed on the surface. According to the different structural parameters such as the profile, shape and inclination of the grooves, surface relief gratings can be divided into one-dimensional gratings and two-dimensional gratings. The two-dimensional grating waveguide is divided into a coupling-in area and a coupling-out area. The coupling-out area uses a two-dimensional grating structure to take into account the functions of expansion and coupling-out, and can make full use of the effective area of ​​the optical waveguide. The common two-dimensional surface relief grating waveguides on the market currently have problems such as low coupling-out efficiency and serious light leakage.

[0006] CN118465901A discloses a two-dimensional coupled meta-grating structure, a two-dimensional grating waveguide and a wearable device for near-eye display, wherein the two-dimensional coupled meta-grating structure comprises a plurality of periodic grating periodic units, each of which comprises a double-waist free-form curved surface structure, a water drop-shaped structure, a free-form curved surface structure and a single-waist free-form curved surface structure, wherein the double-waist free-form curved surface structure is arranged at the center of the meta-grating unit, and the double-waist is symmetrically distributed along the transverse center line, and the longitudinal two-side regions of the double-waist free-form curved surface structure are symmetrically arranged as follows: the free-form curved surface structure and the water drop-shaped structures on both sides of the longitudinal direction are arranged at the front side of the two-side regions, and the single-waist free-form curved surface structure is relatively arranged at the rear side of the two-side regions and extends in the longitudinal direction. The provided two-dimensional coupled meta-grating structure is more effective in adjusting the coupling efficiency of multiple viewing angles, effectively increases the coupling efficiency, and improves the display brightness of the entire waveguide.

[0007] CN116299816A discloses a fork-shaped metasurface grating, optical waveguide and near-eye display device for suppressing high-order light, including at least one first grating structure and at least one second grating structure, the size of the first grating structure is larger than the size of the second grating structure, and the coupling efficiency can be adjusted by changing the size ratio of the two grating structures; the first grating structure and the second grating structure are fork-shaped structures, the cross angle of the first grating structure and the cross angle of the second grating structure are the same, and the cross-shaped structure can better reduce the leakage of light outside; the edge of the first grating structure and the edge of the second grating structure are sawtooth-shaped, and the distance between two adjacent sawtooths in the edge of any grating structure is the same, and each sawtooth is randomly normally distributed along the vector direction of the one-dimensional grating. By setting the edge of the grating structure to be sawtooth-shaped, it is beneficial to suppress the high-order diffraction components of light, thereby improving the imaging quality.

[0008] At present, conventional solutions use diamond or other shaped structures for coupling out regions, such as Figure 4 As shown, in the usual scheme, due to the characteristics of the conventional grating, there is diffraction order energy coupling in the direction of the human eye and the direction of the external environment, and the coupling energy in the two directions is approximately the same. The light leakage to the external environment will leak information and become stray light on the one hand, and on the other hand, it will reduce the actual coupling efficiency of the waveguide to the human eye. Summary of the invention

[0009] The purpose of the present invention is to innovatively propose a new meta-grating structure based on the design of a two-dimensional extended diffraction optical waveguide, which is easy to process and has more adjustable parameters, suppresses light leakage efficiency, and improves coupling efficiency. When used in waveguides, the efficiency of light beam coupling to the eye direction is equivalent to the efficiency of light beam leakage to the environment direction. On the one hand, light leakage will form stray light output to the environment, exposing the display content, and at the same time affecting the effective efficiency of coupling to the human eye direction. Innovation is made in the grating structure, and a new form of two-dimensional grating structure is proposed. In the application of grating waveguides, this structure greatly suppresses the light beam coupling to the environment direction, thereby avoiding the problems encountered by the above-mentioned conventional two-dimensional grating structure to a great extent.

[0010] The technical solution adopted by the present invention is a low light leakage meta-grating structure, which is surrounded by a first free-form curved surface structure 1 and a second free-form curved surface structure 2 to form an inverted goblet structure. The first free-form curved surface structure 1 is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward. The free-form curved surface structure 2 is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward; the spacing d between the two free-form curved surface structures can be adjusted; the lateral period size range is 50-200nm, and the height range of the inverted goblet structure is 20-1000nm.

[0011] The metagrating structure is applied to the out-coupling region of the two-dimensional grating waveguide. As a two-dimensional out-coupling grating structure, the light beam is coupled in through the coupling-in grating, propagates through total reflection in the two-dimensional grating waveguide, and after reaching the out-coupling region, it is expanded through the metagrating structure and coupled out to the human eye. At the same time, since the proposed metagrating structure is in the form of an inverted goblet structure, the efficiency of light beam coupling out to the environment can be reduced.

[0012] Furthermore, a coating is performed on the basis of the super-grating structure, and the coating is performed by common coating or deposition coating. The coating material is, for example, TIO 2， Metal oxides such as Si3N4 and AL2O3, the coating thickness ranges from 10nm to 200nm.

[0013] Furthermore, the period range of the grating is 200nm-1000nm, and the ratio of the longitudinal period to the transverse period of the grating structure is For the two-dimensional grating two-dimensional pupil expansion solution, the coupling-in grating period needs to satisfy the K-domain principle, and the coupling-in and coupling-out grating periods must be consistent to ensure the normal outcoupling of the light beam.

[0014] The incident beam must satisfy the following grating equation conditions:

[0015]

[0016] where sinθin >1 / n, n is the refractive index of the waveguide substrate, λ is the wavelength, d is the grating period, θ air is the incident beam elevation angle, φ air is the incident angle of the light beam, θ in is the coupling angle of the light beam in the waveguide, sinθ in >1 / n can ensure that the light beam propagates through total reflection in the waveguide and meet the total reflection condition.

[0017] Furthermore, for the propagation of the light beam in the entire waveguide, the K vector closure condition must be satisfied. The K vector closure condition is described as follows: in is the grating vector when the beam is coupled in, K EPE is the grating vector obtained when the pupil of the beam is expanded, K out is the grating vector obtained when the light beam is coupled out, ensuring that the angle of the light beam coupled out to the human eye is consistent with the angle of the light beam emitted from the optical machine, that is, satisfying K in +K EPE +K out =0.

[0018] Compared with the prior art, the performance of the grating waveguide designed in the present invention depends on the grating structure used. The diffraction order and corresponding efficiency of the grating structure in each direction affect the pupil expansion and coupling efficiency of the waveguide. In the conventional two-dimensional grating structure, the efficiency of coupling to the human eye direction and coupling to the environment direction is equivalent, which will cause light pollution to the environment direction or leakage of display information, and will also affect the efficiency of the entire waveguide. Therefore, the shape of the grating structure causes the above-mentioned light leakage disadvantage. The present invention solves the above-mentioned problem from the perspective of the grating structure and proposes a new form of two-dimensional super-structure grating structure, namely, an inverted goblet-like structure. Because of the innovation in the grating shape, the structure effectively suppresses the coupling of the light beam from the waveguide to the environment direction, namely, light leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of micro-projection optical machine through coupling into grating near-eye display.

[0020] Figure 2 Schematic diagram of a two-dimensional pupil-expanding diffractive optical waveguide based on a one-dimensional grating.

[0021] Figure 3 Schematic diagram of a two-dimensional pupil-expanding diffractive optical waveguide based on a two-dimensional grating.

[0022] Figure 4 This is a schematic diagram of the structure proposed by the present invention.

[0023] Figure 5 Schematic diagram of two free-form surface structures.

[0024] Figure 6This is a diagram of a periodically arranged super-configuration grating structure.

[0025] Figure 7 is the K-vector diagram using this grating structure.

[0026] Figure 8 A schematic diagram of an embodiment. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the micro-projection optical machine couples light into the waveguide substrate through a coupling grating, so that the light meets the total reflection condition and propagates by total reflection in the substrate. In the coupling grating area, part of the light is expanded and propagated, and part of the light is coupled out to the human eye, thereby achieving the purpose of near-eye display.

[0029] like Figure 2 The figure shows a schematic diagram of a two-dimensional pupil-expanding diffraction optical waveguide based on a one-dimensional grating. The light beam coupled into the coupling-in region undergoes pupil expansion in two directions in the turning region and the out-coupling region, and finally the light beam is coupled out to the human eye in the out-coupling region.

[0030] like Figure 3 The figure shows a schematic diagram of a two-dimensional pupil expansion diffraction waveguide based on a two-dimensional grating. The function of the coupling-in region is to couple the light into the waveguide base so that the light satisfies the total reflection propagation condition; the function of the coupling-out region is to couple part of the light out to the human eye, and part of the light expands and propagates in the coupling-out region. The ratio of the longitudinal period to the transverse period of the grating structure in the coupling-out region is The two-dimensional classical grating structures currently used in the outcoupling region are cylindrical structures and diamond structures.

[0031] The present invention proposes a two-dimensional coupled metagrating structure for a two-dimensional extended diffraction optical waveguide, such as Figure 4 The figure shows a schematic diagram of the structure proposed by the present invention, which is a top view of four periods, and the shaded part is the grating structure. It is composed of a first free-form curved surface structure 1 and a second free-form curved surface structure 2. The free-form curved surface structure 1 is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward. The free-form curved surface structure 2 is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward, and the spacing d between the two structures can be adjusted. The lateral period size range is 50-200nm, and the proposed structure height range is 20-1000nm. Figure 5 a and b belong to different forms of structures according to the above description. The grating structure is applied to Figure 3 The outcoupling region shown is used to suppress the energy of leakage light, while preventing information leakage to the environment and stray light, and at the same time improves the effective outcoupling efficiency of the waveguide to the human eye by suppressing leakage light.

[0032] Figure 6 It is a periodically arranged super-configuration grating structure. Figure 7 The K vector diagram using the grating structure is shown, which illustrates the vector direction of some diffraction orders of the grating structure. Films can be coated on the basis of this structure, such as metal oxides such as TIO2 and AL2O3, with a coating thickness ranging from 10nm to 200nm.

[0033] The grating period ranges from 200nm to 1000nm, and the ratio of the longitudinal period to the transverse period of the grating structure is For the two-dimensional grating two-dimensional pupil expansion scheme, the coupling grating period needs to satisfy the following Figure 7 As shown in the K-domain schematic, the consistency of the coupling-in and coupling-out grating periods ensures the normal coupling-out of the light beam.

[0034] The incident beam must satisfy the following grating equation conditions:

[0035]

[0036] where sinθ in >1 / n, n is the refractive index of the waveguide substrate, λ is the wavelength, d is the grating period, θ air is the incident beam elevation angle, φ air is the incident angle of the light beam, θ in is the coupling angle of the light beam in the waveguide, sinθ in >1 / n can ensure that the light beam propagates through total reflection in the waveguide and meet the total reflection condition.

[0037] For the propagation of the light beam in the entire waveguide, Figure 1 and Figure 2 As shown, the K vector closure condition must be satisfied. The K vector closure condition can also be described as follows: in is the grating vector when the beam is coupled in, K EPE is the grating vector obtained when the pupil of the beam is expanded, K out The grating vector is obtained when the light beam is coupled out, so as to ensure that the angle of the light beam coupled out to the human eye is consistent with the angle of the light beam emitted from the optical machine.

[0038] K in +K EPE +K out =0

[0039] In the embodiment, the structure designed according to the above description is as follows Figure 8 As shown in a, it is the structure actually used. Figure 7In the case of various levels of efficiency of forward transmission and pupil expansion shown in the figure, the efficiency of coupling out to the human eye is 1.89%, and the efficiency of coupling out to the environment can be suppressed to 0.23%, where the grating period is 760nmx440nm, the grating height is 150nm, the refractive index of the grating layer and the substrate layer is 1.9136, and the incident wavelength is green light 530nm. Figure 8 FIG. 8 b shows a calculated comparative structure, which is a commonly used cylindrical structure with a cylinder height of 150nm, a diameter of 200nm, a grating period of 760x440nm, an incident green light wavelength of 530nm, and a refractive index of the grating layer and the substrate layer of 1.9136. The simulated efficiency of coupling out to the human eye is 2.39%, and the efficiency of coupling out to the environment is 1.64%. The difference between the two efficiencies is not large, and the efficiency of coupling out to the environment is not suppressed. The efficiency comparison of the two structures reflects the superior performance of the current structure in suppressing light leakage.

[0040] Without increasing the difficulty of processing, improving the adjustment freedom of the two-dimensional grating in the diffraction optical waveguide can better control the outcoupling efficiency, further suppress the light leakage efficiency, achieve higher outcoupling efficiency, and avoid information leakage and ambient stray light.

Claims

1. Low light leakage supergrating structure, characterized by: An inverted goblet structure is formed by a first free-form curved surface structure and a second free-form curved surface structure; the first free-form curved surface structure is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward; the free-form curved surface structure is symmetrically distributed along the longitudinal center line of the meta-grating unit and opens downward; the spacing d between the two free-form curved surface structures can be adjusted; the lateral period size range is 50-200nm, and the height range of the inverted goblet structure is 20-1000nm; The metagrating structure is applied to the out-coupling region of the two-dimensional grating waveguide. As a two-dimensional out-coupling grating structure, the light beam is coupled in through the coupling-in grating, propagates through total reflection in the two-dimensional grating waveguide, and after reaching the out-coupling region, it is expanded through the metagrating structure and coupled out to the human eye. At the same time, since the proposed metagrating structure is in the form of an inverted goblet structure, the efficiency of light beam coupling out to the environment can be reduced.

2. The low light leakage metagrating structure according to claim 1, characterized in that: A coating is applied on the basis of the super-grating structure, and the coating is a common coating or a deposited coating; the coating material is TIO 2， Si3N4 and AL2O3 metal oxides, coating thickness range is 10nm-200nm.

3. The low light leakage metagrating structure according to claim 1, characterized in that: The period range of the grating is 200nm-1000nm, and the ratio of the longitudinal period to the transverse period of the grating structure is For the two-dimensional grating two-dimensional pupil expansion solution, the coupling grating period needs to meet the K-domain principle, and the coupling-in and coupling-out grating periods must be consistent to ensure the normal coupling-out of the light beam; The incident beam must satisfy the following grating equation conditions: where sinθ in >1 / n, n is the refractive index of the waveguide substrate, λ is the wavelength, d is the grating period, θ air is the incident beam elevation angle, φ air is the incident angle of the light beam, θ in is the coupling angle of the light beam in the waveguide, sinθ in >1 / n can ensure that the light beam propagates through total reflection in the waveguide and meet the total reflection condition.

4. The low light leakage metagrating structure according to claim 1, characterized in that: For the light beam to propagate in the entire waveguide, the K vector closure condition must be satisfied. The K vector closure condition is described as follows: in is the grating vector when the beam is coupled in, K EPE is the grating vector obtained when the pupil of the beam is expanded, K out is the grating vector obtained when the light beam is coupled out, ensuring that the angle of the light beam coupled out to the human eye is consistent with the angle of the light beam emitted from the optical machine, that is, satisfying K in +K EPE +K out =0.

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