Diffractive optical waveguide device based on polarization coupling topology control

Abstract

The application discloses a diffraction optical waveguide device based on polarization coupling topological structure control, which comprises a waveguide medium, an in-coupling grating and an out-coupling grating, a plurality of non-grating areas are added in the out-coupling grating, and the plurality of non-grating areas divide the residual grating areas of the out-coupling grating into a one-dimensional array structure or a two-dimensional array structure; the grating areas are used for light diffraction and out-coupling, and the non-grating areas are used for light total reflection; and the optical waveguide is used for realizing uniform distribution of brightness and color in a full field of view. The application breaks through the limitation of uniformity of polarization holographic element efficiency distribution, can realize the out-coupling light energy regulation and control function on a single optical element while maintaining high diffraction efficiency, and has the advantages of high reliability, operability, low cost, rapidness and the like.

Description

Technical Field

[0001] This invention relates to diffractive waveguide devices based on polarization coupling topology control, belonging to the field of optical display technology. Background Technology

[0002] In recent years, with the development of near-eye display technologies such as augmented reality (AR) and head-mounted displays (HMD), diffractive waveguides have gradually become a research hotspot in the field of optical displays due to their advantages such as thinness and large field of view. Among them, surface relief gratings (SRGs) form surface relief structures through precise micro-nano fabrication techniques to achieve diffraction control of light, but they suffer from complex processing technology and high cost. Volume holographic gratings (VHGs) use volume holographic materials to record interference fringes to form gratings, which have high diffraction efficiency, but their optical performance is sensitive to environmental factors. In contrast, polarized volume holographic waveguide (PVG) technology combines the advantages of polarization optics and volume holography, effectively reducing complexity while ensuring optical performance.

[0003] Polarized volume holographic waveguide (PVG) technology disperses incident light into the user's eye through a diffraction grating. The coupling element plays a crucial role in coupling the image light field into the optical waveguide and coupling the pupil for output. For the output element, to achieve continuity and uniformity of the exit pupil, the diffraction efficiency usually needs to be controlled. Polarized volume holographic gratings, as a common type of existing optical coupling element, possess wide wavelength and angular response bandwidth, polarization sensitivity, high diffraction efficiency, lower manufacturing cost compared to other optical coupling elements, high transmittance to external light, and dynamic controllability.

[0004] However, while polarizing holographic gratings possess excellent diffraction characteristics, their high diffraction efficiency can lead to poor brightness uniformity. This is because after light enters the waveguide through diffraction by the input coupling grating, it must undergo total internal reflection to complete the exit pupil replication and expansion. The accumulated intensity loss from diffraction causes a gradual decrease in brightness, affecting the overall brightness uniformity across the entire field of view. Diffraction efficiency tuning can effectively reduce this attenuation and improve overall brightness uniformity. Furthermore, in color displays, due to the limitations of the grating dispersion equation, the diffraction efficiency of different wavelengths of light shifts with changes in the field of view, causing color unevenness. Efficiency tuning can minimize wavelength dependence, thereby improving color consistency. Therefore, moderately sacrificing diffraction efficiency to optimize exit pupil continuity and uniformity not only ensures consistency in intensity and color distribution across the entire field of view, avoiding the negative impact of uneven brightness and color difference on user experience, but also significantly improves visual comfort and immersion in dynamic scenes.

[0005] In summary, in existing diffractive waveguide technologies, the light intensity gradually attenuates when the light beam undergoes multiple total internal reflections within the waveguide, leading to uneven brightness and color in the display. Furthermore, traditional polarized holographic waveguides struggle to achieve efficiency control of the coupling grating on a single optical element. Summary of the Invention

[0006] Objective: To overcome the shortcomings of existing technologies, this invention provides a diffractive waveguide device based on polarization coupling topology control, which improves the display uniformity of polarization holographic waveguide devices.

[0007] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A diffractive optical waveguide device based on polarization coupling topology control includes: a waveguide medium, an input grating, and an output grating.

[0009] In this design, several non-grating regions are added to the coupling grating. These non-grating regions divide the remaining grating region of the coupling grating into a one-dimensional or two-dimensional array structure. The grating regions are used for light diffraction coupling, and the non-grating regions are used for total internal reflection. The optical waveguide is used to achieve uniform distribution of brightness and color across the entire field of view.

[0010] As a preferred embodiment, the coupling grating is a polarizing holographic grating.

[0011] As a preferred embodiment, the coupling grating is configured as a polarizing volume holographic grating with a diffraction efficiency ranging from 50% to 95% and consisting of composite or single polarization.

[0012] As a preferred embodiment, the waveguide medium has a refractive index of 1.5 to 2.2 and a thickness of 0.5 mm to 1.2 mm.

[0013] As a preferred embodiment, the polarization diffraction characteristics and diffraction efficiency characteristics of the grating region can be individually controlled.

[0014] As a preferred embodiment, the coupling grating has several gaps as non-grating regions, and the gaps divide the coupling grating into several spaced grating regions, which are arranged in a one-dimensional array structure.

[0015] As a preferred embodiment, the gap width is 50 nm to 1 mm, and the gap width gradually decreases along the direction of light propagation, while the width of the grating region gradually increases.

[0016] As a preferred embodiment, the coupling grating has several blank areas as non-grating areas, and the several blank areas divide the coupling grating into several spaced grating areas, which are arranged in a two-dimensional array structure.

[0017] As a preferred embodiment, along the direction of light propagation, the density of the blank area in the coupling grating gradually decreases, while the density of the grating area in the coupling grating gradually increases.

[0018] As a preferred embodiment, the grating region adopts a left-handed polarizing holographic grating, a right-handed polarizing holographic grating, or a combination of left-handed and right-handed polarizing holographic grating.

[0019] Beneficial Effects: The diffractive waveguide device based on polarization coupling topology control provided by this invention consists of an input and output polarization holographic grating and a waveguide medium. The output polarization holographic grating is composed of several grating regions divided by non-grating regions. By setting non-grating regions within the output polarization holographic grating, light propagating in the waveguide diffracts in the grating regions and undergoes total internal reflection in the non-grating regions when passing through the output element, achieving energy homogenization of the output light at different positions. The spacing between the non-grating regions between adjacent grating regions is achieved through laser etching, and the vector direction of the grating regions is achieved by spraying different solutions. This invention overcomes the limitation of uniform efficiency distribution in polarization holographic elements, maintaining high diffraction efficiency while enabling energy control of the output light on a single optical element. It offers advantages such as high reliability, operability, low cost, and speed. Compared to existing technologies, the advantages of this invention are as follows:

[0020] 1. This method precisely controls the energy distribution of emitted light in the coupling region by gradient-based microstructure modulation of the coupling grating, thereby improving the brightness uniformity of the entire display area. Especially in large field-of-view displays, it avoids the brightness unevenness problem that occurs in traditional diffraction waveguide technology.

[0021] 2. This method effectively reduces color unevenness by partitioning and controlling the diffraction characteristics of the coupled grating to minimize its dependence on different wavelengths of light. This is particularly important in color displays, as it ensures the uniformity of different colors of light across the entire field of view and avoids color differences. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a one-dimensional optical waveguide embodiment of a diffractive optical waveguide device controlled by polarization coupling topology.

[0023] Figure 2 This is a schematic diagram of the polarization characteristics of a polarizing holographic grating.

[0024] Figure 3 This is a schematic diagram of a polarizing holographic grating structure.

[0025] Figure 4 This is a simulation diagram showing the one-dimensional optical waveguide before and after optimization. Figure 4(a) shows the energy density distribution of the out-coupling region before optimization. Figure 4 (b) shows the optimized energy density distribution in the out-coupling region. Figure 4 (c) is the optimized optical waveguide model.

[0026] Figure 5 A schematic diagram of the diffraction efficiency distribution of a polarizing body holographic waveguide, representing the polarization state of the incident light.

[0027] Figure 6 This is a schematic diagram of the polarization diffraction characteristics of a polarizing holographic grating.

[0028] Figure 7 This is a schematic diagram of a two-dimensional optical waveguide embodiment based on polarization coupling topology control, wherein A in the figure is an enlarged view of a local structure of the coupling grating.

[0029] Figure 8 This is a schematic diagram of the light propagation path in a polarizing holographic waveguide.

[0030] Figure 9 This is a schematic diagram of a two-dimensional optical waveguide simulation model. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] Example 1:

[0034] This embodiment introduces a diffractive optical waveguide device based on polarization coupling topology control, including: a waveguide medium, an input grating, and an output grating.

[0035] In this design, several non-grating regions are added to the coupling grating. These non-grating regions divide the remaining grating region of the coupling grating into a one-dimensional or two-dimensional array structure. The grating regions are used for light diffraction coupling, and the non-grating regions are used for total internal reflection. The optical waveguide is used to achieve uniform distribution of brightness and color across the entire field of view.

[0036] Furthermore, the coupled grating is a polarizing holographic grating.

[0037] Furthermore, laser etching is used to create non-grating regions in the coupled grating.

[0038] Furthermore, by changing the size of the grating region through the setting of the non-grating region, different diffraction efficiencies of the coupled grating can be achieved.

[0039] The working principle of the diffractive waveguide device based on polarization coupling topology control in this embodiment is as follows: Holographic waveguides are suitable for augmented reality and virtual reality display devices. When light propagates through total internal reflection within the waveguide medium, diffraction coupling occurs when it encounters a grating region; non-grating regions maintain total internal reflection. By selectively removing local gratings, the diffraction effect in that region is reduced, allowing more light to continue propagating forward, thus achieving efficiency control.

[0040] The coupling grating comprises grating regions of multiple polarizer holographic gratings, and the shape of the gap between adjacent polarizer holographic gratings can be any custom geometric pattern. The vector directions of adjacent polarizer holographic gratings can be different. The specific parameters such as the shape, size, and duty cycle of the non-grating regions need to be designed according to the specific application scenario.

[0041] Example 2:

[0042] This embodiment describes an example of a diffractive optical waveguide device based on polarization coupling topology control, used to realize a one-dimensional holographic optical waveguide, such as... Figure 1 As shown, it includes: waveguide medium 1, coupling grating 2, and coupling grating 3.

[0043] The coupling grating 3 has several gaps 301 as non-grating regions, and the gaps divide the coupling grating 3 into several spaced grating regions 302, which are arranged in a one-dimensional array structure.

[0044] This embodiment modulates the diffraction efficiency of the coupling grating by creating adjustable-width strip-shaped non-grating regions on the coupling grating. The width of these non-grating regions is gradient-distributed along the light propagation direction. When light propagates through total internal reflection within the waveguide, diffraction coupling occurs in the grating regions, while the non-grating regions maintain total internal reflection. By reducing diffraction in the non-grating regions, light energy waste is prevented.

[0045] Furthermore, waveguide medium 1, with a refractive index of 1.5 to 2.2 and a thickness of 0.5 mm to 1.2 mm, is used to transmit light through total internal reflection.

[0046] Furthermore, the coupling grating 2 is configured as a composite or single polarization holographic grating with a diffraction efficiency ranging from 50% to 95%, used to diffract more incident light and couple it to the waveguide medium.

[0047] Furthermore, the gap 301 has a width of 50 nm to 1 mm, and the width of the gap gradually decreases along the direction of light propagation, while the width of the grating region gradually increases.

[0048] Furthermore, the gap 301 is strip-shaped or square.

[0049] Furthermore, the waveguide medium 1 is made of glass or polymer.

[0050] Furthermore, the diffraction efficiency of each grating region 302 can be individually adjusted, such as... Figure 2 As shown, the efficiency η and angle θ of the grating region can be adjusted in real time according to specific conditions. By controlling the diffraction efficiency η of the grating region in the coupling grating 3 at a fixed incident angle θ, it is gradually increased along the light propagation direction, thus achieving zoned control of the diffraction efficiency characteristics of the coupling grating. One embodiment... Figure 2 The incident angle θ of the grating region can be set between -10° and 40°. In this invention, the incident angle of the grating region is preferably in the range of θ1-θ2, and the corresponding diffraction efficiency is in the range of η1-η2. Thus, while achieving a diffraction efficiency of 90%-100%, the incident angle of different grating regions can be adjusted along the direction of light propagation.

[0051] Furthermore, the polarizing holographic grating includes a liquid crystal solution, such as... Figure 3 As shown, the liquid crystal molecules in the liquid crystal solution adopt an elliptical structure, and the different lengths of the elliptical structure represent the different angles of the periodic spiral rotation of the liquid crystal molecules inside the grating.

[0052] Furthermore, the liquid crystal solution is a reactive liquid crystal doped with an appropriate amount of chiral material, thereby enabling the generation of the longitudinal (perpendicular to the substrate direction) periodic rotation of the liquid crystal required for the polarizer holographic grating, wherein the longitudinal period can be modulated according to the concentration of the helical torsion constant of the chiral material.

[0053] Furthermore, the liquid crystal solution is divided into R5011 and S5011, where R5011 and S5011 correspond to the left-handed and right-handed liquid crystal helical directions, respectively.

[0054] Furthermore, the polarization diffraction characteristics of the grating region can be individually controlled. When the helical structure of the liquid crystal molecules in the liquid crystal solution is right-handed, the diffraction efficiency of PVG reaches its highest point when the incident light is right-handed circularly polarized and its lowest point when the incident light is left-handed circularly polarized.

[0055] Furthermore, by adjusting the concentration of the helical torsion constant of the chiral material in the liquid crystal solution, controllable polarization diffraction characteristics of the grating region are achieved, so that after two orthogonal circularly polarized beams are subjected to interference exposure, the diffraction efficiency of each grating region in the coupled grating 3 gradually increases along the direction of light propagation.

[0056] Example 3:

[0057] This embodiment describes a specific implementation of a diffractive waveguide device based on polarization coupling topology control for realizing a one-dimensional holographic waveguide. A waveguide structure with dimensions of 60 mm × 40 mm is used, the coupling grating is set to 25 mm × 8 mm, the output grating is set to 30 mm × 20 mm, and the light source configuration is consistent with the experimental setup, with dimensions of 12.3 mm × 9.2 mm.

[0058] The waveguide structure has an input grating thickness of 4 μm and an output grating thickness of 3 mm. Both the input and output gratings are polarizing holographic gratings with a transverse period of 420 nm, a longitudinal period of 215 nm, a field of view of 40°, a center wavelength of 530 nm for the image source, and right-hand circularly polarized light.

[0059] The efficiency-adjustable coupling grating period is set to 3 mm, with each non-grating region closer to the grating region side of the input light region. The grating region widths are 0.6 mm, 0.8 mm, 1 mm, 1.3 mm, 1.7 mm, 1.7 mm, 2.2 mm, 2.2 mm, 2.2 mm and 2.6 mm respectively.

[0060] The holographic waveguide simulation model effect in this embodiment is as follows: Figure 4 As shown, where, Figure 4 In Figure (a), the energy density distribution of the out-coupling region before optimization is shown. Figure 4 (b) shows the optimized energy density distribution in the out-coupling region. Figure 4 (c) is the optimized waveguide model, in which the output coupling grating region is divided into 10 periods of non-grating regions, each non-grating region being about 3 mm wide. The comparison before and after optimization shows that the uniformity of the exit pupil of the one-dimensional polarizer holographic waveguide structure is significantly improved by efficiency control.

[0061] Exit pupil uniformity is calculated by dividing the pupil into nine equal regions and calculating the average emitted light intensity in each region. The brightness uniformity (UFOV) of the exit pupil region can be used as a relative reference for brightness uniformity. The calculation formula is as follows:

[0062]

[0063] Where i represents the i-th measurement point, and Let represent the minimum and maximum illuminance at the i-th measurement point, respectively.

[0064] The uniformity of the exit pupil of the optimized structure is 42.92%, while that of the unoptimized structure is 24.42%. The uniformity of the exit pupil is improved by about one time through efficiency control.

[0065] The diffraction efficiency characteristics of the coupled-in and coupled-out gratings are as follows: Figure 3 As shown, the diffraction efficiency, angle, and bandwidth of each controllable grating region in the input and output gratings can be adjusted in real time according to specific circumstances. The overall field of view uniformity and exit pupil uniformity of the input and output gratings can be achieved through zoned control.

[0066] The PVG diffraction efficiency distribution of the incident light polarization states of the coupled-in and coupled-out gratings, as shown in the figure... Figure 5 As shown, when the liquid crystal molecule helical structure is right-handed, the diffraction efficiency of PVG reaches its highest point when the incident light is right-handed circularly polarized and its lowest point when the incident light is left-handed circularly polarized.

[0067] The polarization diffraction characteristics of the coupled-in and coupled-out gratings are as follows: Figure 6 As shown, when the incident beam is left-handed circularly polarized (LCP) and its rotation direction is consistent with the twisted spiral direction of the liquid crystal molecules inside the PVG, Bragg diffraction occurs and the circular polarization direction of the outgoing beam will be reversed; when the incident beam is right-handed circularly polarized (RCP) and its rotation direction is opposite to that of the liquid crystal molecules inside the PVG, Bragg diffraction does not occur, and the beam will pass directly through the PVG and exit in a 0th-order diffraction state without any change in polarization.

[0068] Example 4:

[0069] This embodiment describes an example of a diffractive optical waveguide device based on polarization coupling topology control, used to realize a two-dimensional holographic optical waveguide, such as... Figure 7 As shown, it includes: waveguide medium 1, coupling grating 2, and coupling grating 3.

[0070] The coupling grating 3 has several blank areas 303 as non-grating areas. The several blank areas divide the coupling grating 3 into several spaced grating areas 302. The several spaced grating areas 302 are arranged in a two-dimensional array structure.

[0071] Under two-dimensional pupil expansion conditions, the beam used for coupling grating 3 is introduced into waveguide medium 1 through a diffraction angle that satisfies the total internal reflection condition of the waveguide medium, and propagates to the grating region of the two-dimensional array structure. The grating region is composed of two polarizer holographic gratings with different grating vector directions or a composite of two polarizer holographic gratings with different grating vector directions. The grating region can change the propagation path of the beam within the waveguide by multiple bends of the beam, allowing the beam to propagate simultaneously in two directions and be extracted from the waveguide medium 1 during the beam replication process.

[0072] Furthermore, waveguide medium 1, with a refractive index of 1.5 to 2.2 and a thickness of 0.5 mm to 1.2 mm, is used to transmit light through total internal reflection.

[0073] Furthermore, the coupling grating 2 is configured as a composite or single polarization holographic grating with a diffraction efficiency ranging from 50% to 95%, used to diffract more incident light and couple it to the waveguide medium.

[0074] Furthermore, along the direction of light propagation, the density of the blank area 303 in the coupling grating 3 gradually decreases, while the density of the grating area 302 in the coupling grating 3 gradually increases.

[0075] Furthermore, the grating region 302 adopts a left-handed polarizing holographic grating (Lpvg), a right-handed polarizing holographic grating (Rpvg), or a combination of left-handed and right-handed polarizing holographic gratings (Lpvg and Rpvg combined).

[0076] Furthermore, the blank area can be any custom geometric pattern.

[0077] Furthermore, by adjusting the area of ​​the liquid crystal solution coating, the duty cycle of the grating region in the coupling grating can be dynamically adjusted, thereby controlling the distribution of light coupling efficiency within the optical waveguide.

[0078] Furthermore, the grating region can be coated with liquid crystal solutions of different liquid crystal spiral directions to control the grating vector direction, thereby regulating the distribution of light coupling efficiency within the optical waveguide.

[0079] Furthermore, the vector direction of the grating region is divided into two types, namely Lpvg and Rpvg.

[0080] Furthermore, the polarization diffraction characteristics and diffraction efficiency characteristics of the grating region can be individually controlled.

[0081] This embodiment describes the propagation path of light in a two-dimensional polarizer holographic waveguide structure, as follows: Figure 8 As shown, when light enters the waveguide medium, its rotation direction is reversed after each total internal reflection in the optical waveguide structure; after each coupling grating in the optical waveguide structure, the light is diffracted out of the optical waveguide.

[0082] By controlling the energy I and diffraction efficiency of each part of the grating region in the coupling grating 3, a two-dimensional coupling grating structure with high efficiency near the input coupling grating and low efficiency far from the input coupling grating can be formed, thereby achieving brightness uniformity across the entire field of view.

[0083] By controlling the polarization of each part of the grating region in the output grating 3, a two-dimensional output grating structure can be formed with single polarization near the input coupling grating and composite polarization away from the input coupling grating, thereby achieving efficiency control.

[0084] Example 5:

[0085] This embodiment describes a specific implementation of a diffractive waveguide device based on polarization coupling topology control for realizing a two-dimensional holographic waveguide. The simulation model uses a waveguide structure with a size of 20×40mm, the input coupling region is set as a 3mm×3mm circle, the output coupling region is set as 13mmx26mm, and the light source configuration is consistent with the experimental setup.

[0086] The aforementioned two-dimensional efficiency-tunable polarizing holographic waveguide simulation model, such as Figure 9 As shown, the grating region of the coupled grating includes several square blank non-grating regions, the size of which is 0.5mm × 0.5mm.

[0087] Specifically, the density of the non-grating region distribution gradually decreases from the lower left corner to the upper right corner of the coupled grating, and the duty cycle of the non-grating region in the coupled grating decreases linearly from 0.562 to 0.173, with a linear growth rate of 0.695.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A diffractive optical waveguide device based on polarization coupling topology control, comprising a waveguide dielectric, an input grating, and an output grating, characterized in that: Several non-grating regions are added to the coupling grating, and these non-grating regions divide the remaining grating region of the coupling grating into a one-dimensional array structure; each grating region is used for light diffraction coupling, and the non-grating regions are used for total internal reflection; the optical waveguide is used to achieve uniform distribution of brightness and color throughout the entire field of view. The coupling grating is configured as a polarizing volume holographic grating with a diffraction efficiency ranging from 50% to 95% and either composite or single polarization. The coupling grating is a polarizing volume holographic grating; The polarization diffraction characteristics and diffraction efficiency characteristics of the grating region can be individually controlled; The coupling grating has several gaps as non-grating regions, and the gaps divide the coupling grating into several spaced grating regions, which are arranged in a one-dimensional array structure. The gap width is 50 nm to 1 mm, and the gap width gradually decreases along the direction of light propagation, while the width of the grating region gradually increases. The polarizer holographic grating includes a liquid crystal solution, wherein the liquid crystal solution is a chiral material.

2. The diffractive waveguide device based on polarization coupling topology control according to claim 1, characterized in that: The waveguide medium has a refractive index of 1.5 to 2.2 and a thickness of 0.5 mm to 1.2 mm.

3. A diffractive optical waveguide device based on polarization coupling topology control, comprising a waveguide dielectric, an input grating, and an output grating, characterized in that: Several non-grating regions are added to the coupling grating, and these non-grating regions divide the remaining grating region of the coupling grating into a two-dimensional array structure; each grating region is used for light diffraction coupling, and the non-grating regions are used for total internal reflection; the optical waveguide is used to achieve uniform distribution of brightness and color throughout the entire field of view. The coupling grating is configured as a polarizing volume holographic grating with a diffraction efficiency ranging from 50% to 95% and either composite or single polarization. The polarization diffraction characteristics and diffraction efficiency characteristics of the grating region can be individually controlled; The coupling grating has several blank areas as non-grating areas. These blank areas divide the coupling grating into several spaced-apart grating areas, which form a two-dimensional array structure. Along the direction of light propagation, the density of the blank area in the coupling grating gradually decreases, while the density of the grating area in the coupling grating gradually increases. The grating region employs a left-handed polarizing holographic grating, a right-handed polarizing holographic grating, or a combination of left-handed and right-handed polarizing holographic grating; The grating region is coated with liquid crystal solutions of different liquid crystal spiral directions to control the grating vector direction.

4. The diffractive waveguide device based on polarization coupling topology control according to claim 3, characterized in that: The waveguide medium has a refractive index of 1.5 to 2.2 and a thickness of 0.5 mm to 1.2 mm.

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