Grating assembly in a diffractive optical waveguide display system and method for controlling the diffraction efficiency thereof

Abstract

A grating combination device in a diffractive optical waveguide display system and a method for controlling the diffraction efficiency thereof. The device comprises an optical waveguide, an input coupling optical assembly, an output coupling grating group, a narrow-band phase retarder group, and a wide-band phase retarder group. The optical waveguide is a transparent optical medium plate. The input coupling optical assembly is located at one end of the optical waveguide and is used for coupling image-carrying light waves into the optical waveguide. The output coupling grating group is a plurality of polarization volume holographic gratings with red, green, and blue wave bands as the center wavelengths, and cooperates with the narrow-band phase retarder group stacked in the grating group to control the effective diffraction efficiency of the gratings at corresponding wavelengths. The wide-band phase retarder group is closely attached to the upper and lower surfaces of the waveguide plate and compensates for the polarization state of the image-carrying light waves when the image-carrying light waves propagate in the waveguide by total internal reflection. Under the condition of ensuring wave vector matching and position matching, the diffraction energy level can be reasonably distributed, and uniform display of red, green, and blue wave band image-carrying light waves in a single layer waveguide can be realized.

Description

Technical Field

[0001] This invention relates to the field of AR device technology, specifically to a grating assembly device and its diffraction efficiency control method in a diffractive waveguide display system. Background Technology

[0002] In existing technologies, diffractive waveguide display devices often require controlling the local diffraction efficiency of the grating to achieve uniform output after the extended exit pupil. The diffraction efficiency of the grating is closely related to its manufacturing process, and is generally achieved through conditions such as refractive index modulation, grating thickness, and exposure intensity. However, precisely controlling the refractive index modulation, grating thickness, and exposure intensity during the fabrication of volume holographic gratings in diffractive waveguide display devices presents significant technical challenges and high manufacturing costs. Therefore, how to achieve grating diffraction efficiency control in diffractive waveguide display systems through other means has become a highly anticipated technical issue.

[0003] Currently, color diffractive waveguide display systems are mostly implemented using multilayer grating waveguides. A common solution for achieving a color display system in a single-layer grating waveguide is to design a multilayer stacked single-wavelength or single-layer multi-wavelength composite grating combiner. For multilayer schemes, this method is effective if light of a specific wavelength interacts only with its designated layer. For example, green light should diffract from the green grating and pass unaffected through the red and blue grating layers. If green light is diffracted by the red or blue grating layer, it will cause stray light, blurring the image or producing chromatic aberration. The aforementioned problems can be solved by reducing the diffraction bandwidth of each layer, but this solution requires reducing the refractive index modulation of the material, which also reduces the field of view of the display system. Single-layer composite gratings use the same surface period, eliminating crosstalk issues, but the shared angular range of multiple wavelengths will be smaller, resulting in a too-small effective system field of view.

[0004] In summary, traditional single-layer color holographic waveguide display systems require complex grating designs and are prone to crosstalk and limited field of view. Furthermore, they are difficult to design and manufacture, have high processing costs, and are not suitable for large-scale production applications. Summary of the Invention

[0005] The purpose of this invention is to propose a grating combination device in a diffractive waveguide display system, thereby providing a design method and optical element composite structure for a single-layer color diffractive waveguide display system while ensuring a large field of view, a large exit pupil size, and a small volume; at the same time, based on the exit pupil expansion structure of the polarizer holographic diffraction grating in the single-layer color diffractive waveguide display system, a device for uniformly distributing exit energy and a method for controlling the effective diffraction efficiency of the grating are provided.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a grating assembly device in a diffractive waveguide display system, comprising an optical waveguide, an input coupling optical component, an output coupling grating group, a narrowband phase retarder group, and a broadband phase retarder group; the optical waveguide is a transparent optical medium plate; the input coupling optical component is composed of one or more of a prism, a semi-reflective lens, and a diffraction grating, used to couple the image-carrying light wave into the optical waveguide and make the image-carrying light wave satisfy the internal total internal reflection condition of the optical waveguide; the output coupling grating group is made of multiple polarizing holographic gratings stacked together, the twisted spirals of the multiple polarizing holographic gratings are in the same direction, the angular bandwidth is 10° to 120°, and the wavelength bandwidth is 1nm to 150nm; the narrowband phase retarder group is composed of multiple narrowband phase retarders with center wavelengths of red, green, and blue bands respectively; the broadband phase retarder group is closely connected to the upper and lower surfaces of the optical waveguide to compensate for the polarization state of the image-carrying light wave when it propagates within the optical waveguide by internal total internal reflection. After collimation, the image-carrying light wave is coupled into the optical waveguide via the input coupling optical component. Because the internal total internal reflection condition is met, it propagates within the optical waveguide. While propagating within the optical waveguide, the exit pupil can be expanded using components such as the output coupling grating group. Finally, it is coupled out of the waveguide via the output coupling grating group and enters free space for imaging or observation. The optical waveguide is a transparent optical medium plate, allowing the image-carrying light wave to undergo total internal reflection between its two parallel interfaces and propagate in a predetermined direction. The input coupling optical component is located at one end of the optical waveguide and is used to couple the image-carrying light wave into the optical waveguide, ensuring that the image-carrying light wave meets the total internal reflection condition of the optical waveguide. The output coupling grating group consists of multiple polarization holographic gratings with red, green, and blue wavelengths as their center wavelengths, located at the other end of the optical waveguide. It utilizes the diffraction of the gratings to break the total internal reflection condition and couple the image-carrying light wave out of the optical waveguide, allowing the image-carrying light wave to be imaged or observed in a certain region of free space outside the optical waveguide. The narrowband phase retarder group is a phase retarder with optimized bandwidth for red, green, and blue wavelengths, stacked in the grating group. It works in conjunction with the gratings of the corresponding wavelengths to control the effective diffraction efficiency of the gratings at the corresponding wavelengths. The broadband phase retarder group is closely connected to the upper and lower surfaces of the waveguide plate and compensates for the polarization state of the image-carrying light wave during total internal reflection propagation within the waveguide. The grating assembly in this diffractive waveguide display system, through the cooperation of a subwavelength polarizing holographic grating and a phase retarder, can achieve a reasonable distribution of diffraction energy levels while ensuring wave vector matching and position matching. This enables uniform display of image-carrying light waves in the red, green, and blue bands within a single-layer waveguide, while simultaneously reducing the design and fabrication difficulty of the grating and lowering the cost of commercial applications.

[0007] As a further improvement, the optical waveguide is a transparent optical medium plate, and its material can be transparent medium materials such as optical glass, optical plastics (including optical resins), and silicon carbide.

[0008] As a further improvement, the twisted spirals of the polarizing holographic grating are all in the same direction, either left-handed or right-handed; and their center wavelength peak diffraction efficiency is close to the ideal 100% high efficiency.

[0009] As a further improvement, the output coupling grating group is made of three stacked polarizer holographic gratings with center wavelengths of red, green and blue, respectively.

[0010] As a further improvement, the output coupling grating group is made of three polarizer holographic gratings stacked together, with the preferred stacking order from top to bottom being green, blue, and red. The wavelength bandwidth combination of the three gratings covers the visible light range that needs to be displayed.

[0011] As a further improvement, the output coupling grating group is made of two stacked polarizer holographic gratings, with the stacking order from top to bottom being cyan and orange. The combined wavelength bandwidth of the two polarizer holographic gratings covers the visible light range to be displayed. Its grating period is comparable to the visible light wavelength range and can be designed with different surface periods, while also ensuring that the diffraction angle is the same when incident light of two different center wavelengths is incident at the same angle.

[0012] Corresponding to the three-polarization holographic grating structure, the narrowband phase retarder group consists of three layers of narrowband phase retarders with center wavelengths of red, green, and blue, respectively. These layers are cross-stacked with the corresponding center wavelength gratings of the output coupling grating group formed by stacking the three-polarization holographic gratings. The narrowband phase retarder has the characteristic of modulating the polarization state of light within a narrow wavelength bandwidth at the corresponding center wavelength. Outside the corresponding narrow wavelength range, the polarization state of light does not change.

[0013] The broadband phase delayer group consists of circularly polarized optical elements applied to the upper and lower surfaces of the waveguide, ensuring that the full-band image-carrying light wave propagating through total internal reflection in the waveguide is still compensated to circularly polarized light after each total internal reflection.

[0014] In this invention, the circularly polarized light from the input coupling optical component, taking left-handed circularly polarized incident light as an example, undergoes total internal reflection within the optical waveguide. With compensation from the broadband phase retarder group, it remains left-handed circularly polarized incident light after each total internal reflection. When it propagates to the region where the exit pupil needs to be extended, the left-handed circularly polarized light passes through the uppermost narrowband phase retarder in the green band. The image-carrying light wave in the green band is partially converted into right-handed circularly polarized light according to the required proportion, while other light waves outside the green band remain left-handed circularly polarized light. The second-layer green band polarizing holographic grating is a right-handed polarizing grating with a peak efficiency close to the ideal 100%. It diffracts all the right-handed circularly polarized light converted by the narrowband phase retarder in the green band, thus realizing the extension of the exit pupil of the green band light wave. Other light waves remain unaffected and continue to propagate at their original angles, passing through the narrowband phase retarder in the third blue band. The image-carrying light waves within the blue band are partially converted into right-hand circularly polarized light according to the required proportion, while other light waves outside the blue band remain left-hand circularly polarized light. The fourth layer, a right-hand polarizing holographic grating in the blue band, has a peak efficiency close to the ideal 100%. It diffracts all the right-hand circularly polarized light converted by the narrowband phase retarder in the blue band, achieving the extended exit pupil required for the energy of the blue band light waves. Other light waves remain unaffected and continue propagating at their original angles. Upon passing through the fifth layer of the narrowband phase retarder in the red band, the image-carrying light waves within the red band are partially converted to right-hand circularly polarized light according to the desired proportion. Other light waves outside the red band remain left-hand circularly polarized incident light. The bottommost red band polarizing holographic grating is a right-hand polarizing grating with a peak efficiency close to the ideal 100%. It diffracts all the right-hand circularly polarized light converted by the narrowband phase retarder in the red band, achieving the extended exit pupil required for the red band light waves. Other light waves remain unaffected and continue propagating at their original angles, further undergoing total internal reflection and the aforementioned polarization conversion and diffraction processes. Similarly, right-hand polarized light, or two-layer or four-layer narrowband phase retarder and grating groups, employ a similar design, wherein the input coupling optical component involved in this invention can be a polarizing holographic grating.

[0015] By controlling the conversion degree of the narrowband phase retarders in each band, the effective diffraction efficiency of the grating is controlled, thereby expanding the exit pupil while ensuring a uniform distribution of the final coupled energy. The above-mentioned combination of the narrowband phase retarder group and the output coupling grating group can realize the design of a single-layer waveguide color display system, which further avoids crosstalk between image carrier light waves of different bands while ensuring a large field of view bandwidth.

[0016] As a further improvement, the method for fabricating the narrowband phase delayer group includes the following steps:

[0017] A single, uniformly oriented optical alignment layer is used to align the upper liquid crystal layer. Subsequently, two or more twisted polymer liquid crystal layers are used, with the upper liquid crystal layer directly aligned with the lower liquid crystal layer to generate a continuously changing optical axis. The layers are then photopolymerized into a thin film to produce a narrowband phase retarder assembly.

[0018] As a further improvement, the material of the photoalignment layer is an azo dye, and the azo material includes one or more of Brilliant Yellow, Congo Red, SD1, SD2, LIA-C001, and ROP-108; the material of the polymer liquid crystal layer is one or more of RM257, RM82, RMS03-001c, and RMS10-025; and the chiral agent of the polymer liquid crystal layer is one or more of CB-15 / C45S, MLC-6247, S5011, and R5011.

[0019] As a further improvement, the narrowband phase retarder group converts the polarization state of the incident circularly polarized light according to the required ratio. The incident circularly polarized light is left-handed circularly polarized incident light, and its design method is as follows:

[0020] One unit of left-hand circularly polarized incident light is converted into a right-hand circularly polarized component with an electric field strength of cosβ units and a sinβ unit after passing through a corresponding narrowband phase retarder group. This corresponds to a linear retarder with a phase retardation of 2β and a fast axis relative rotation of π / 4. Its Jones matrix is ​​expressed as follows:

[0021] , where β ranges from 0 to 90°; i is the imaginary unit.

[0022] Compared with existing technologies, the advantages of this invention are as follows: This invention utilizes a band-segmented polarization compensation structure to achieve the propagation of red, green, and blue primary color wavelengths within a single-layer optical waveguide, with no crosstalk between them, resulting in spurious image formation. The central fields of view for each of the red, green, and blue center wavelengths can propagate at the same angle within the waveguide, increasing the system's field of view. Full-color fusion is free of rainbow effects, resulting in excellent performance. Polarization management is used to control the efficiency of the exit pupil expansion grating, achieving uniform output of the image-carrying light wave. The exit pupil expansion grating can be uniformly implemented using ideal high efficiency, eliminating the need for complex regional modulation of grating efficiency, thus simplifying design and fabrication. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the grating assembly device in the diffractive waveguide display system of this invention.

[0024] Figure 2 This is a schematic diagram of a one-dimensional and two-dimensional exit pupil extended waveguide display composite structure in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of a method for achieving grating efficiency variation through thickness variation in an embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of a traditional single-layer waveguide display system that uses composite gratings to achieve color display.

[0027] Figure 5 This is a schematic diagram of a Poincaré sphere implementing the polarization management principle in an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram illustrating the structural principle of a narrowband phase delayer according to an embodiment of the present invention;

[0029] Figure 7 This is a schematic diagram of the Stokes parameter S3 bandwidth of a narrowband phase delayer for red, green, and blue bands in an embodiment of the present invention.

[0030] In the figure, 1-optical waveguide; 2-narrowband phase retarder in the green band; 3-green band polarizer holographic grating; 4-narrowband phase retarder in the blue band; 5-blue band polarizer holographic grating; 6-narrowband phase retarder in the red band; 7-red band polarizer holographic grating; 8-first broadband phase retarder group; 9-second broadband phase retarder group; 11-red band; 12-green band; 13-blue band; 14-output coupling grating; 15-intermediate transition grating; 16-multiple polarizer holographic grating stack; 17-grating stack with consistent surface period; 18-crosstalk beam; 19-angle of rotation of the stocks vector towards the negative axis of S3; 20-polarization state corresponding to the top dashed circle; 21-first polymer liquid crystal layer; 22-second polymer liquid crystal layer; 23-third polymer liquid crystal layer; 24-fourth polymer liquid crystal layer; 25-optical alignment layer. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0032] This invention discloses a grating combination device in a diffractive waveguide display system. It utilizes multi-layer, multi-wavelength polarizing holographic gratings in conjunction with multi-layer, corresponding narrowband phase retarders to achieve crosstalk-free single-layer color waveguide display while ensuring a large field of view. Furthermore, by controlling the local polarization of the target image-carrying light wave through the narrowband phase retarder, the effective diffraction efficiency of the corresponding grating is controlled, thereby achieving uniformity in the final exit pupil display of the system.

[0033] In the optical waveguide 1, the multilayer waveband polarizer holographic grating and the multilayer narrowband phase retarder stacked structure corresponding to the waveband are as follows: Figure 1As shown, the top layer is a narrowband phase retarder 2 in the green band; the second layer is a green band polarizer holographic grating 3; the third layer is a narrowband phase retarder 4 in the blue band; the fourth layer is a blue band polarizer holographic grating 5; the fifth layer is a narrowband phase retarder 6 in the red band; and the bottom layer is a red band polarizer holographic grating 7. All polarizer holographic gratings are right-handed polarization gratings, with peak efficiency close to the ideal 100%. The wavelength bandwidth is limited by the refractive index modulation of the grating medium and is maximized, allowing for bandwidth overlap. The total wavelength bandwidth of the three layers covers the visible light image source wavelength bandwidth to achieve maximum color and energy transmission. Under these conditions, the angular bandwidth of each grating layer is also maximized, which is beneficial for achieving a large field of view in the display system. Taking the central field beam of the imaging light waves in bands 11 (red), 12 (green), and 13 (blue) as an example, before being incident on the narrowband phase delayer 2 in the green band, the light is adjusted to be left-hand circularly polarized. After being delayed by the corresponding band narrowband phase delayer, the right-hand circularly polarized part will be diffracted out of the pupil by the corresponding band grating. The left-hand circularly polarized light will continue to propagate along the original direction and will not be diffracted to other directions by any grating, thus avoiding stray light. The first broadband phase delay unit group 8 is located at the bottom layer of the narrowband phase delay unit 2 in the green band. It is used to compensate for the polarization changes caused by the red band 11, green band 12, and blue band 13 passing through the green band polarizer holographic grating 3, blue band polarizer holographic grating 5, red band polarizer holographic grating 7, and mainly by internal total internal reflection. This ensures that the red band 11, green band 12, and blue band 13 continue to maintain a left-handed circular polarization state after internal total internal reflection. The function of the first broadband phase delay unit group 8 can be specifically implemented by the optimized phase a plate. The second broadband phase retarder group 9 is located on top of the narrowband phase retarder 2 in the green band. It is used to compensate for the polarization changes caused by the red band 11, green band 12, and blue band 13 passing through the green band polarizer holographic grating 3, blue band polarizer holographic grating 5, red band polarizer holographic grating 7, and internal total internal reflection. It also needs to further compensate for the partial right-handed circular polarization caused by the red band 11, green band 12, and blue band 13 passing upward through the narrowband phase retarder 2 in the green band, the narrowband phase retarder 4 in the blue band, and the narrowband phase retarder 6 in the red band. The output coupling grating group includes the green band polarizer holographic grating 3, the blue band polarizer holographic grating 5, and the red band polarizer holographic grating 7. The narrowband phase retarder group includes the narrowband phase retarder 2 in the green band, the narrowband phase retarder 4 in the blue band, and the narrowband phase retarder 6 in the red band.

[0034] Figure 2The diagram shows a schematic of a one-dimensional and two-dimensional exit pupil extended waveguide display composite structure. The difference lies in that the two-dimensional exit pupil extended structure, in addition to the input coupling grating and output coupling grating 14 of the one-dimensional exit pupil extended structure, includes an intermediate turning grating 15. This allows the grating assembly in the diffraction waveguide display system to replicate the exit pupil in two relatively orthogonal dimensions, enabling a larger and more comfortable viewing eyebox. To achieve this function, the efficiency of the polarization volume holographic gratings used for exit pupil extension, such as the output coupling grating 14 and the intermediate turning grating 15, needs to be controlled so that part of the light to be transmitted continues to propagate forward, while the other part passes through the diffraction turning direction of the polarization volume holographic grating. Furthermore, to achieve uniform exit pupil energy in this type of waveguide display system, complex design and precise implementation of the local efficiency of the exit pupil extended grating are required. Moreover, in volume holographic gratings, the factors affecting the efficiency of polarization volume holographic gratings mainly include refractive index modulation and grating thickness; precisely achieving the efficiency of polarization volume holographic gratings is even more difficult. Figure 3 As shown, using variations in the thickness of a polarizing holographic grating to alter diffraction efficiency is a common practice. Generally, the thickness of a polarizing holographic grating ranges from hundreds of nanometers to tens of micrometers. Precisely controlling the thickness within this range is costly and difficult to achieve on a large scale. However, the structure described in this invention uniformly employs a high-efficiency grating and achieves the required effective diffraction efficiency through the design of a delay unit, significantly reducing the complexity and manufacturing cost.

[0035] Furthermore, to achieve the wide-bandwidth optical wave transmission required for color display within a single-layer holographic waveguide, a composite grating covering the visible light band of the image source is needed. A multi-layer stack of polarizing holographic gratings 16 is an advantage of using holographic gratings to achieve composite gratings. Optimizing the stacked gratings for the red, green, and blue bands ensures that the center wavelength and center field of view of each band achieve the same diffraction angle, reducing the complexity of exit pupil uniformity optimization and suppressing rainbow effects. However, with a large wavelength bandwidth of the stacked polarizing holographic grating, crosstalk beams 18 are inevitably generated, affecting the final display clarity, such as... Figure 4 As shown. While a grating stack 17 with consistent surface period can solve the above problems, in this case, the diffraction angle ranges of long and short wavelengths are separated, the overlapping area is reduced, resulting in a significant decrease in the final display field of view and performance degradation. The structure described in this invention uniformly uses high-efficiency gratings and achieves the required effective diffraction efficiency through the design of a delay unit, significantly reducing process difficulty and manufacturing costs.

[0036] In this embodiment of the invention, the narrowband phase retarder, also called a waveplate, causes a phase delay between two mutually perpendicular polarization components of polarized light, thereby achieving polarization state control of the light. Figure 5As shown. In this invention, the polarizing holographic grating responds to circularly polarized light with a diffraction efficiency close to 100%. Taking left-handed circularly polarized light as an example, the polarizing holographic grating has a right-handed structure and diffracts right-handed circularly polarized light. The ratio by which the narrowband phase retarder converts the left-handed circularly polarized light portion into right-handed circularly polarized light is the effective diffraction efficiency, denoted as η. Taking the left-handed and right-handed circularly polarized states as a set of orthogonal bases, in this circularly polarized coordinate system, rotating 1 unit of left-handed circularly polarized light towards the right-handed circularly polarized axis by an angle β results in a polarization with a left-handed circularly polarized component and a right-handed circularly polarized component with an electric field strength of cos(β) units. Therefore, the effective diffraction efficiency is denoted as η = sin(β). 2 (β); where the operation of rotating angle β in circular polarization coordinates is a rotation matrix, denoted as .

[0037] ;

[0038] The above-mentioned rotation by β angle can be achieved using a linear retarder with a phase delay of 2β and a fast axis rotation of π / 4 relative to the coordinate axes. The Jones matrix characterizing the optical properties of this linear retarder is as follows:

[0039] ;

[0040] The aforementioned delay transformation process for polarization in a Poincaré sphere is as follows: Figure 5 As shown, left-handed circularly polarized light is the vector from the origin along the S3 axis to the sphere. After rotating by an angle 2β in the direction of the negative S3 axis, it becomes... Figure 5 The angle 19, where the stocks vector is rotated towards the negative axis of S3, represents the delayed polarization state. The linear delay unit with a delay of 2β and a fast axis rotated π / 4 relative to the coordinate axes is a special case satisfying this polarization delay transformation. In fact... Figure 5 The polarization state 20 corresponding to the top dashed circle in the diagram all meet the requirements of the polarization delay conversion; there are also many delay devices required to achieve this conversion that meet the conditions, and the design flexibility is very high.

[0041] Furthermore, the phase delayers in this invention need to be designed as narrowband or wideband according to specific functions, so as to realize the functions of narrowband phase delayer 2 in the green band, narrowband phase delayer 4 in the blue band, narrowband phase delayer 6 in the red band, first wideband phase delayer group 8, second wideband phase delayer group 9, etc., and their structures are as follows: Figure 6As shown. A specific embodiment of the structure includes a single, uniformly and uniformly oriented light alignment layer 25, providing alignment for the upper polymer liquid crystal layer. Subsequently, there are two or more twisted polymer liquid crystal layers, such as a first polymer liquid crystal layer 21, a second polymer liquid crystal layer 22, a third polymer liquid crystal layer 23, and a fourth polymer liquid crystal layer 24. The upper polymer liquid crystal layer is directly aligned with the lower polymer liquid crystal layer, generating an optical axis with continuous variation, which is then photopolymerized into a thin film. Furthermore, different layers can be combined by doping with different concentrations of chiral agents and controlling different thicknesses to form a highly flexible phase retardation. Meanwhile, the existence of a layer with a 0° rotation angle is not excluded as one possible solution. Through multilayer spin coating or coating processes, the entire thin film can be easily manufactured, and almost arbitrary bandwidth and shape bandstop control can be achieved. Theoretically, higher precision and near-ideal performance can be expected with increasing layer count.

[0042] As one embodiment, the photo-alignment material in the structure can be an azo dye such as Brilliant Yellow; the polymeric liquid crystal material is RM257; and the chiral agent is R5011. The dispersion of the liquid crystal material is described by the Cauchy equation, the general form of which is:

[0043] ;

[0044] in Let λ be the birefringence, and λ be the wavelength of light in vacuum. For the red, green, and blue wavelengths of the image source, we take red light as 615–630 nm, green light as 515–535 nm, and blue light as 460–475 nm. A, B, and C are material-dependent constants; for example, for liquid crystal material RM235, we take A=0.128, B=8350, and C=0. For the selected material and number of layers, the twist and thickness of each layer are designed, including the initial angle of the alignment layer. The Mueller matrix can be used to characterize the optical features of each layer, thereby obtaining the overall bandwidth and delay characteristics of the phase retarder. Intelligent algorithms such as annealing and particle swarm optimization can be used to optimize the above parameters of each layer, making the overall bandwidth and delay characteristics of the phase retarder consistent with the target characteristics.

[0045] In one embodiment of the present invention, the narrowband phase retarder 4 in the green band; the fourth layer is a blue band polarizer holographic grating 5; and the bandwidth and delay characteristics of the fifth layer, a narrowband phase retarder 6 in the red band, are as follows: Figure 7 As shown.

[0046] The first broadband phase delayer group 8 and the second broadband phase delayer group 9 are also designed and prepared using the same material structure system and optimization method as described above.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A grating assembly device in a diffractive waveguide display system, characterized in that, This includes optical waveguides, input coupling optical components, output coupling grating groups, narrowband phase retarder groups, and broadband phase retarder groups; The optical waveguide is a transparent optical medium plate; The input coupling optical component is composed of one or more of the following: prism, semi-reflective lens, and diffraction grating. The output coupling grating group is made of multiple polarizing holographic gratings stacked together. The twisted spirals of the multiple polarizing holographic gratings are in the same direction, with an angular bandwidth of 10° to 120° and a wavelength bandwidth of 1nm to 150nm. The narrowband phase retarder group consists of multiple layers of narrowband phase retarders with center wavelengths of red, green, and blue bands, respectively. The broadband phase delay unit group is closely connected to the upper and lower surfaces of the optical waveguide to compensate for the polarization state of the image-carrying light wave when it undergoes total internal reflection propagation within the optical waveguide.

2. The grating assembly device in a diffractive waveguide display system according to claim 1, characterized in that, The material of the optical waveguide is one of optical glass, optical resin, and silicon carbide.

3. The grating assembly device in a diffractive waveguide display system according to claim 1, characterized in that, The twisted spirals of the polarizing holographic grating have the same direction of rotation, either left-handed or right-handed.

4. The grating assembly device in a diffractive waveguide display system according to claim 1, characterized in that, The output coupling grating group is made of three stacked polarizer holographic gratings with center wavelengths of red, green and blue, respectively.

5. The grating assembly device in a diffractive waveguide display system according to claim 4, characterized in that, The output coupling grating group is made of three polarizing holographic gratings stacked together, with the stacking order from top to bottom being green, blue, and red. The wavelength bandwidth combination of the three polarizing holographic gratings covers the visible light range that needs to be displayed.

6. The grating assembly device in a diffractive waveguide display system according to claim 4, characterized in that, The output coupling grating group can be made by stacking two polarizing holographic gratings, with the stacking order from top to bottom being cyan and orange. The wavelength bandwidth combination of the two polarizing holographic gratings covers the visible light range to be displayed.

7. The grating assembly device in a diffractive waveguide display system according to claim 1, characterized in that, The broadband phase retarder group is composed of circularly polarized optical elements; the narrowband phase retarder group consists of three layers of narrowband phase retarders with center wavelengths of red, green and blue, respectively, which are cross-layered with the corresponding center wavelength gratings of the output coupling grating group made by stacking three polarizing holographic gratings. The narrowband phase retarder group modulates the polarization state of light within a narrow wavelength range at the corresponding center wavelength, and the polarization state of light does not change outside the corresponding narrow wavelength range.

8. The grating assembly device in a diffractive waveguide display system according to claim 7, characterized in that, The method for fabricating the narrowband phase delay array includes the following steps: A single, uniformly oriented optical alignment layer is used to align the upper liquid crystal layer. Subsequently, two or more twisted polymer liquid crystal layers are used, with the upper liquid crystal layer directly aligned with the lower liquid crystal layer to generate a continuously changing optical axis. The layers are then photopolymerized into a thin film to produce a narrowband phase retarder assembly.

9. The grating assembly device in the diffractive waveguide display system according to claim 8, characterized in that, The photoalignment layer is made of an azo dye, which includes one or more of the following: Brilliant Yellow, Congo Red, SD1, SD2, LIA-C001, and ROP-108; the polymer liquid crystal layer is made of one or more of the following: RM257, RM82, RMS03-001c, and RMS10-025; and the chiral agent of the polymer liquid crystal layer is one or more of the following: CB-15 / C45S, MLC-6247, S5011, and R5011.

10. The grating assembly device in a diffractive waveguide display system according to claim 7, characterized in that, The narrowband phase retarder group converts the polarization state of the incident circularly polarized light according to the required ratio. The incident circularly polarized light is left-handed circularly polarized incident light, and its design method is as follows: One unit of left-hand circularly polarized incident light is converted into a right-hand circularly polarized component with an electric field strength of cosβ units and a sinβ unit after passing through a corresponding narrowband phase retarder group. The conversion element can be a linear retarder with a phase delay of 2β and a fast axis relative rotation of π / 4, and its Jones matrix is ​​expressed as follows: , where β ranges from 0 to 90°; i is the imaginary unit.

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