Miniature display device for double-focal-plane HUD (Head Up Display) system

Abstract

The invention relates to a micro display device for a bifocal plane HUD (head up display) system, which solves the problems of halved field of view, limited working bandwidth, low color saturation and low brightness of the existing bifocal plane HUD system, and comprises an image display module and a polarization modulation element arranged above the image display module, the polarization modulation element is used for polarization modulation of display pixels, the effective area of the sub-wavelength medium grating arrangement is equivalent to a 1 / 2 wave plate, the display pixels are separated in a row-by-row or column-by-column staggered mode through the sub-wavelength medium grating arrangement, and the problem that the view field is halved due to an existing target surface space partitioning scheme is solved. The two adjacent sub-wavelength medium gratings convert incident light into linear polarization states in two directions, the two directions are mutually orthogonal, and the two spaced sub-wavelength medium gratings are completely the same, so that the two images are respectively adjusted into the mutually orthogonal linear polarization states, and the two images are generated in a staggered manner.

Description

Technical Field

[0001] The present invention relates to a dual-focus HUD system, and more particularly to a micro-display device for a dual-focus HUD system. Background Art

[0002] A Head-Up Display (HUD) is an information display technology that projects key information directly in front of the user's line of sight, thereby reducing the distraction caused by eye movement. It was initially applied in the aviation field. In recent years, with the rapid development of display and optical technologies, HUD technology has gradually expanded to the automotive field, especially the dual-focus HUD system. This system superimposes key information such as navigation routes, speed data, and driving assistance prompts on the actual road environment and optimizes the information presentation through hierarchical display of the long-distance and short-distance views. That is, the long-distance view highlights navigation routes and road warnings, enhancing the driver's spatial perception and advance planning ability; the short-distance view focuses on key data such as vehicle speed and distance, facilitating the driver to quickly obtain operation information. This dual-focus display mode can effectively simplify the information transmission process, reduce visual interference caused by frequent projection switching, and significantly improve driving safety and user experience.

[0003] The Picture Generation Unit (PGU) is the core display device of the dual-focus HUD system and has become one of the key research directions. Currently, the main solutions for implementing the projection PGU of the dual-focus HUD system include three technical solutions: the target surface partition type, the channel multiplexing type, and the diffractive waveguide type.

[0004] The Chinese invention patent with the application number CN202210332331.X proposes a target surface partition type head-up display device. By dividing the PGU into two projection surface areas, the first and the second, and loading image information with different projection depths in each area, combined with the design of the subsequent optical system, the projection surfaces of different areas are modulated and focused respectively. This solution can achieve simultaneous imaging with two foci and multiple depths on a single target surface.

[0005] The Chinese invention patent with the application number CN202410101979.5 proposes a HUD display device based on a polarization dual-channel. It uses an optical superlens that can independently control left-handed and right-handed circularly polarized light and sets different focal positions for it. By controlling the polarization state of the projection light source and loading long-distance and short-distance images, using polarization as the information transmission channel, the function of dual-focus projection imaging is achieved.

[0006] The Chinese invention patent with the application number CN202410657693.5 proposes a vehicle-mounted HUD device based on a diffractive two-dimensional waveguide. A prism is used as the light-coupling end of the waveguide to align with the corresponding area of the corresponding PGU. By designing a grating structure on the waveguide surface and using the total internal reflection mechanism in the waveguide to transmit light, the optical path and pupil position are precisely controlled, realizing the splitting of light and imaging with different field angles and projection focal depths.

[0007] The above technology can achieve the simultaneous display of dual focal planes on a single PGU image plane, but there are the following deficiencies: 1) The target surface partitioning type scheme mainly divides the effective display area of a single PGU, resulting in the natural halving of the field of view size at two imaging distances, affecting the system's support ability for large field of view displays. In addition, the structure of the target surface partitioning has high requirements for the error precision of the optical system, increasing the difficulty and complexity of alignment and adjustment.

[0008] 2) The channel multiplexing type scheme can theoretically achieve full field of view display, but its working bandwidth is limited, usually only supporting narrowband operation, making it difficult to meet the high-efficiency display requirements within a wide spectral range, restricting the versatility and stability of the system. Moreover, the sub-wavelength periodic structure of its components will generate strong zero-order images in actual imaging, introducing unnecessary optical noise and reducing the imaging contrast of the projected information.

[0009] 3) The diffractive waveguide type scheme can utilize its diffractive characteristics to achieve large field of view and multi-image plane projection, but it is sensitive to the incident angle, resulting in the angular resolution varying with the field of view, thus affecting the imaging accuracy under a large field of view. In addition, the wavelength dependence of the diffraction effect causes uneven light intensity distribution in the RGB broadband, leading to a decrease in color saturation and brightness uniformity. Especially in high-contrast scenes, this unevenness may affect the identifiability of key information in the HUD system. Summary of the Invention

[0010] The purpose of the present invention is to solve the technical problems existing in the existing dual focal plane HUD system, such as halved field of view, limited working bandwidth, low color saturation, and low brightness, and to provide a micro display device for a dual focal plane HUD system.

[0011] To achieve the above invention purpose, the present invention provides the following technical solutions: A micro display device for a dual focal plane HUD system, characterized in that: It includes an image display module and a polarization modulation element arranged above the image display module; The image display module includes a first polarizer, a glass substrate, a color filter layer, electrodes, a liquid crystal layer, a display pixel array, a second polarizer, and a backlight layer arranged in sequence from top to bottom; The polarization modulation element is disposed on the upper surface of the first linear polarizer. The polarization modulation element includes N sub-wavelength dielectric gratings, and the N sub-wavelength dielectric gratings are arranged along the length direction or the width direction of the first linear polarizer, where N≥2; The phase delay of the sub-wavelength dielectric grating satisfies the half-wave condition; The azimuth angles of two adjacent sub-wavelength dielectric gratings differ by 45°. The two adjacent sub-wavelength dielectric gratings convert the incident light into linearly polarized states in two directions, and the two directions are orthogonal to each other. The two spaced-apart sub-wavelength dielectric gratings are identical; The display pixel array includes a plurality of display pixels. The plurality of display pixels are divided into N groups. Each group of display pixels is arranged corresponding to a sub-wavelength dielectric grating in the vertical direction, and the width of the sub-wavelength dielectric grating matches the width of the display pixels in the corresponding group. The plurality of display pixels in each group are arranged along the length direction of the corresponding sub-wavelength dielectric grating; The electrode is used to connect to an external input signal.

[0012] Further, the sub-wavelength dielectric grating includes a substrate and a plurality of wire gratings uniformly distributed on the substrate along the width direction of the substrate; The half-wave condition is: ; where is the working wavelength, is the refractive index difference between the ordinary axis and the extraordinary axis of the sub-wavelength dielectric grating, is the wire grating thickness of the sub-wavelength dielectric grating.

[0013] Further, the wire grating thickness is 377.8 nm, the width is 100 nm, and the period is 166 nm; The wire grating is made of silicon carbide, and the substrate is made of fused quartz.

[0014] Further, the polarization modulation element is fixed on the upper surface of the first linear polarizer by optical bonding or material growth.

[0015] Further, the polarization modulation element is fixed on the upper surface of the first linear polarizer by optical bonding, and the material used for optical bonding is a transparent adhesive material.

[0016] Further, the transparent adhesive material is an optical glue.

[0017] Further, the backlight layer is a Lambert source.

[0018] Furthermore, the polarization degree of the first linear polarizer is greater than or equal to 99%, and the extinction ratio is greater than or equal to 1000:1; The color filter layer selectively transmits light within the wavelength ranges corresponding to the three primary colors of red, green, and blue. The central wavelength of the red light of the color filter layer is 610 - 640 nm, and the peak transmittance is greater than 85%; the central wavelength of the green light is 520 - 550 nm, and the peak transmittance is greater than 85%; the central wavelength of the blue light is 440 - 470 nm, and the peak transmittance is greater than 85%; the full width at half maximum of the color filter layer is less than or equal to 50 nm, and the transmission suppression ratio between adjacent channels is greater than 0.1%; The electrode is made of the transparent conductive material ITO, and its surface resistance is lower than 100 Ω / m 2 , the adjustable range of the voltage between the electrodes is 0 - 10 V, the response time is less than 10 ms, the parasitic capacitance is lower than 0.5 pF, and the edge light leakage suppression ratio is higher than 30 dB; The response time of the liquid crystal layer is 1 - 10 ms, the light transmittance is 80% - 90%, the thickness is 3 - 10 μm, the viewing angle is 60° - 170°, the driving voltage is 2 - 15 V, and the color contrast ratio is greater than 1000:1; The polarization degree of the second linear polarizer is greater than or equal to 99%, and the extinction ratio is greater than or equal to 1000:1; Furthermore, the glass substrate is made of SiO2 material and has a thickness of 0.5 mm.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) A microdisplay device for a dual - focal - plane HUD system provided by the present invention includes an image display module and a polarization modulation element disposed above the image display module. The polarization modulation element includes N sub - wavelength dielectric gratings for polarizing modulation of display pixels. The effective area of the arrangement of the sub - wavelength dielectric gratings is equivalent to a half - wave plate. The display pixels are separated row - by - row or column - by - column in an interleaved manner according to the arrangement of the sub - wavelength dielectric gratings, avoiding the problem of halving the field of view caused by the existing target - surface partitioning type scheme. In addition, by making the phase delay of the sub - wavelength dielectric gratings Meet the half-wave condition, and the azimuth angles of two adjacent sub-wavelength dielectric gratings differ by 45°, so that two adjacent sub-wavelength dielectric gratings convert the incident light into linearly polarized states in two directions respectively, and the two directions are orthogonal to each other. The two spaced sub-wavelength dielectric gratings are exactly the same, so that two images are respectively polarization-modulated into linearly polarized states orthogonal to each other, and two images are generated in an interleaved manner, ensuring the independent display of the dual-channel images, avoiding spatial crosstalk, and the sub-wavelength dielectric grating has uniform phase delay performance in the visible light range, can maintain imaging stability in a wide band, and avoid color deviation and imaging fluctuation caused by wavelength dependence. Compared with the channel multiplexing type and diffraction waveguide type schemes, the present invention is superior in terms of brightness, contrast and color uniformity, ensuring high-quality display of dual-channel images.

[0020] (2)The microdisplay device provided by the present invention for a dual-focus HUD system has a simple structure, not only adapts to existing display technologies, but also can be integrated into an existing dual-focus optical system, simplifies system design, and provides an efficient and simple solution for the dual-focus HUD system. Brief Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of an embodiment of a microdisplay device for a dual-focus HUD system of the present invention; Figure 2 It is a schematic diagram of the functional principle of an embodiment of the present invention; Figure 3 It is a schematic structural diagram of a sub-wavelength dielectric grating in an embodiment of the present invention; Figure 4 It is a broadband phase delay curve diagram of an embodiment of the present invention; Figure 5 It is a broadband transmittance curve diagram of an embodiment of the present invention; Figure 6 It is a schematic diagram of the azimuth angle of a sub-wavelength dielectric grating in an embodiment of the present invention; Figure 7 It is a schematic diagram of the incident light after passing through two adjacent sub-wavelength dielectric gratings in an embodiment of the present invention.

[0022] The description of the reference numerals is as follows: 1 - polarization modulation element, 11 - sub-wavelength dielectric grating, 111 - substrate, 112 - wire grid; 2 - first linear polarizer, 3 - glass substrate, 4 - color filter layer, 5 - electrode, 6 - liquid crystal layer, 7 - display pixel array, 8 - second linear polarizer, 9 - backlight layer. Detailed Embodiments

[0023] The present invention will be further described below with reference to the drawings and exemplary embodiments.

[0024] Refer to Figures 1-7, a microdisplay device for a dual-focus HUD system of the present invention includes an image display module and a polarization modulation element 1 disposed above the image display module.

[0025] In this embodiment, as Figure 1 shown, the image display module includes a first linear polarizer 2, a glass substrate 3, a color filter layer 4, an electrode 5, a liquid crystal layer 6, a display pixel array 7, a second linear polarizer 8, and a backlight layer 9 arranged in sequence from top to bottom; The polarization modulation element 1 is disposed on the upper surface of the first linear polarizer 2. The polarization modulation element 1 can be fixed on the upper surface of the first linear polarizer 2 by optical bonding or material growth. In this embodiment, the polarization modulation element 1 is fixed on the upper surface of the first linear polarizer 2 by optical bonding, and the material used for optical bonding is a transparent adhesive material. In this embodiment, the transparent adhesive material is selected as optical glue.

[0026] The polarization modulation element 1 includes N sub-wavelength dielectric gratings 11, N≥2, and the N sub-wavelength dielectric gratings 11 are arranged along the length direction or width direction of the first linear polarizer 2. The working wavelength band of the sub-wavelength dielectric grating 11 covers the visible light wavelength band range.

[0027] The phase delay of the sub-wavelength dielectric grating 11 satisfies the half-wave condition: ; wherein, is the working wavelength, is the refractive index difference between the ordinary axis and the extraordinary axis of the sub-wavelength dielectric grating 11, is the thickness of the wire grid 112 of the sub-wavelength dielectric grating 11; As Figure 3 shown, it is a schematic structural diagram of the sub-wavelength dielectric grating 11, which includes a substrate 111 and a plurality of wire grids 112 uniformly arranged on the substrate 111. In this embodiment, the thickness of the wire grid 112 is 377.8 nm, the width is 100 nm, and the period is 166 nm.

[0028] As Figure 6 shown, it is a schematic diagram of the azimuth angle θ. Since the grating itself is strip-shaped, different line polarization modulation angles can be achieved with different directions. The ordinary axis is the Figure 6 horizontal direction in Figure 6 , and the extraordinary axis is the

[0029] vertical direction in Figure 7As shown, two adjacent sub-wavelength dielectric gratings 11 convert incident light into linearly polarized states in two directions respectively, and the two directions are orthogonal to each other. The two spaced-apart sub-wavelength dielectric gratings 11 are identical.

[0030] The display pixel array 7 includes a plurality of display pixels, which are divided into N groups. Each group of display pixels is correspondingly provided with a sub-wavelength dielectric grating 11 in the vertical direction, and the width of the sub-wavelength dielectric grating 11 matches the width of the display pixels in this group. The plurality of display pixels in each group are arranged along the length direction of the corresponding sub-wavelength dielectric grating 11. In this way, the width of the sub-wavelength dielectric grating 11 precisely matches the width of a single display pixel in the image display module, forming a highly registered structure.

[0031] The electrode 5 is connected to an external input signal. The external input signal controls the molecules of the liquid crystal layer 6 through the electrode 5, and the distribution of the image is realized in each display pixel.

[0032] In this embodiment, the finite-difference time-domain (FDTD) method is adopted, and modeling and simulation are carried out based on the sub-wavelength grating theory. Taking the case of light beam perpendicular incidence as an example, during FDTD simulation, the phase delay amounts of incident light of a pair of orthogonal polarization states (TE light and TM light) after passing through the sub-wavelength dielectric grating 11 are respectively obtained. In the wide wavelength band of 400nm - 700nm, achromatic design is carried out for five wavelengths to achieve a specific uniform phase delay in the entire visible light spectrum range. Through sampling and selection, the materials of the wire grid 112 and the substrate 111 of the sub-wavelength dielectric grating 11 are finally determined to be silicon carbide and fused quartz respectively.

[0033] The broadband phase delay curve of this embodiment is as Figure 4 shown. It can be seen from this figure that under the conditions of TE and TM polarized incident light, the phase delay in the visible light range of 450nm - 650nm is controlled near π, the average value is 1.002π, and the root mean square error is 3.42×10 -4 . This result shows that the sub-wavelength dielectric grating 11 exhibits good broadband phase delay characteristics in the visible light range, can effectively cover the red, green, and blue wavelength bands, and meets the design requirements for broadband polarization state modulation in this embodiment. The broadband transmittance curve is as Figure 5 shown, and the average transmittance also reaches 80% under the conditions of TE and TM polarized incident light.

[0034] Among them, the backlight layer 9 is a Lambert source, which can provide unpolarized light with uniform intensity. The second linear polarizer 8 is used to convert the unpolarized light emitted by the backlight layer 9 into linearly polarized light, with a polarization degree greater than or equal to 99% and an extinction ratio greater than or equal to 1000:1. The response time of the liquid crystal layer 6 is 1 - 10 ms, the transmittance is 80% - 90%, the thickness is 3 - 10 μm, the viewing angle is 60° - 170°, the driving voltage is 2 - 15 V, and the color contrast ratio is greater than 1000:1. The electrode 5 is used to control the orientation of liquid crystal molecules in the liquid crystal layer 6 to adjust the polarization state of the transmitted light and achieve grayscale and image display. Therefore, the transparent conductive material ITO is used, and its surface resistance is lower than 100 Ω / m 2 , the adjustable range of the voltage between the electrodes is 0 - 10 V, the response time is less than 10 ms, the parasitic capacitance is lower than 0.5 pF, and the edge light leakage suppression ratio is higher than 30 dB. The color filter layer 4 selectively transmits light in the wavelength ranges corresponding to the three primary colors of red, green, and blue. The central wavelength of the red light of the color filter layer 4 is 610 - 640 nm, and the peak transmittance is greater than 85%; the central wavelength of the green light is 520 - 550 nm, and the peak transmittance is greater than 85%; the central wavelength of the blue light is 440 - 470 nm, and the peak transmittance is greater than 85%; the full width at half maximum of the color filter layer 4 is less than or equal to 50 nm, and the transmission suppression ratio between adjacent channels is greater than 0.1%. The glass substrate 3 is made of SiO2 material and has a thickness of 0.5 mm. The polarization degree of the first linear polarizer 2 is greater than or equal to 99%, and the extinction ratio is greater than or equal to 1000:1.

[0035] As Figure 2 shown, it is a schematic diagram of the functional principle of this embodiment. The backlight layer 9 uses a Lambert source to provide unpolarized light with uniform intensity. After passing through the second linear polarizer 8, it is converted into linearly polarized light, passes through the display pixel array 7 and the liquid crystal layer 6 in sequence, applies an external voltage to the liquid crystal layer 6 through the electrode 5 to control the display state of each display pixel, and realizes the loading of the image. Then it passes through the color filter layer 4, the glass substrate 3, and the first linear polarizer 2 in sequence. At this time, the polarization state of the image is linearly polarized light in a unified state. According to the arrangement rule of the sub-wavelength dielectric gratings 11 in the polarization modulation element 1, that is, two adjacent sub-wavelength dielectric gratings 11 modulate the polarization of the incident light into linearly polarized states in two directions, and the two directions are orthogonal to each other. At this time, the effective area of the arrangement of the sub-wavelength dielectric gratings 11 is equivalent to a half-wave plate, and two images will be generated in an interleaved manner to form a complete display scheme.

[0036] The embodiments described above are only descriptions of the specific implementation manners of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A micro display device for a dual-focal plane HUD system, characterized in that: It comprises an image display module and a polarization modulation element (1) arranged above the image display module; The image display module comprises, arranged in order from top to bottom, a first linear polarizer (2), a glass substrate (3), a color filter layer (4), an electrode (5), a liquid crystal layer (6), a display pixel array (7), a second linear polarizer (8), and a backlight layer (9); The polarization modulation element (1) is arranged on the upper surface of the first linear polarizer (2), the polarization modulation element (1) comprises N sub-wavelength dielectric gratings (11), the N sub-wavelength dielectric gratings (11) are arranged along the length direction or the width direction of the first linear polarizer (2), and N is greater than or equal to 2; Phase delay of the sub-wavelength dielectric grating (11) Satisfy the half-wave condition; The azimuth angles of two adjacent sub-wavelength dielectric gratings (11) differ by 45°, the two adjacent sub-wavelength dielectric gratings (11) convert incident light into linear polarization states in two directions, and the two directions are orthogonal to each other, and the two spaced sub-wavelength dielectric gratings (11) are completely identical; The display pixel array (7) comprises a plurality of display pixels, the plurality of display pixels are divided into N groups, each group of display pixels is arranged corresponding to a sub-wavelength dielectric grating (11) in the vertical direction, the width of the sub-wavelength dielectric grating (11) matches the width of the display pixels corresponding to the group, and the plurality of display pixels in each group are arranged along the length direction of the corresponding sub-wavelength dielectric grating (11); The electrode (5) is used to connect to an external input signal.

2. The micro display device for a dual-focal plane HUD system according to claim 1, characterized in that: The sub-wavelength dielectric grating (11) comprises a substrate (111) and a plurality of wire gratings (112) uniformly distributed on the substrate (111); The half-wave condition is: ； in, is the working wavelength, is the refractive index difference between the ordinary axis and the extraordinary axis of the subwavelength dielectric grating (11), is the thickness of the wire grating (112) of the sub-wavelength dielectric grating (11).

3. The micro display device for a dual-focal plane HUD system according to claim 2, characterized in that: The wire grid (112) has a thickness 377.8nm, width 100nm, period 166nm; The wire grid (112) is made of silicon carbide, and the substrate (111) is made of fused quartz.

4. The micro display device for a dual-focal plane HUD system according to claim 3, characterized in that: The polarization modulation element (1) is fixed on the upper surface of the first linear polarizer (2) by optical bonding or material growth.

5. The micro display device for a dual-focal plane HUD system according to claim 4, characterized in that: The polarization modulation element (1) is fixed on the upper surface of the first linear polarizer (2) by optical bonding, and the material used in the optical bonding is a transparent adhesive material.

6. The micro display device for a dual-focal plane HUD system according to claim 5, characterized in that: The transparent adhesive material is optical glue.

7. The micro display device for a dual-focal plane HUD system according to claim 6, characterized in that: The backlight layer (9) is a Lambertian light source.

8. The micro display device for a dual-focal plane HUD system according to claim 1, characterized in that: The polarization degree of the first linear polarizer (2) is greater than or equal to 99%, and the extinction ratio is greater than or equal to 1000:1; The color filter layer (4) selectively transmits light in the wavelength range corresponding to the three primary colors of red, green and blue. The central wavelength of red light of the color filter layer (4) is 610-640nm, and the peak transmittance is greater than 85%; the central wavelength of green light is 520-550nm, and the peak transmittance is greater than 85%; the central wavelength of blue light is 440-470nm, and the peak transmittance is greater than 85%; the half-width of the color filter layer (4) is less than or equal to 50nm, and the transmission suppression ratio of adjacent channels is greater than 0.1%; The electrode (5) is made of a transparent conductive material ITO, and its surface resistance is less than 100Ω / m 2 , the inter-electrode voltage adjustable range is 0-10V, the response time is less than 10ms, the parasitic capacitance is less than 0.5pF, and the edge light leakage suppression ratio is higher than 30dB; The liquid crystal layer (6) has a response time of 1-10 ms, a light transmittance of 80%-90%, a thickness of 3-10 μm, a viewing angle of 60°-170°, a driving voltage of 2-15 V, and a color contrast ratio greater than 1000:1; The second linear polarizer (8) has a polarization degree greater than or equal to 99% and an extinction ratio greater than or equal to 1000:

1.

9. The micro display device for a dual-focal plane HUD system according to claim 8, characterized in that: The glass substrate (3) is made of SiO2 and has a thickness of 0.5 mm.

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