Waveguide system based on polarization liquid crystal grating and waveguide colorization view field expansion method

Abstract

The invention relates to the technical field of optics, in particular to a waveguide system based on a polarization liquid crystal grating and a waveguide colorization view field expansion method. PG is additionally added on the basis of a traditional scheme for realizing colorization of a single-layer waveguide to independently regulate and control the light angle of a certain wavelength, so that the FOV theoretical limit of the single-layer waveguide is broken through; the FOV size of a traditional double-layer waveguide is achieved, and meanwhile the light and thin appearance is kept.

Description

Technical Field

[0001] The present invention relates to the field of optical technologies, and particularly to a waveguide system based on a polarization liquid crystal grating and a method for expanding a waveguide colorized field of view. Background Art

[0002] When using a planar waveguide for output, some necessary conditions need to be met. When the input light source has a certain angle, the left-edge light rays need to satisfy the total reflection condition, and the right-edge light rays need to enter the waveguide and satisfy the restriction of exit pupil continuity for imaging performance. For a holographic optical waveguide, the horizontal FOV can be obtained from the first-order grating equation:

[0003]

[0004] where Λ x is the transverse period of the PVG, θ i is the angle of incidence in the incident medium, θ d is the diffraction angle of the exit medium, n i is the refractive index of the incident medium, which refers to air here, n g is the refractive index of the exit medium, which refers to the waveguide refractive index here, and λ is the wavelength in vacuum.

[0005] Combined with the above formula, in order to prevent chromatic dispersion, the gratings in the same layer of glass need to maintain the same transverse period. In addition, light of different wavelengths will have different diffraction angles.

[0006] Therefore, if a single-layer waveguide is used to implement the colorization scheme (multiple layers of gratings can be stacked on the single-layer waveguide), it can be seen from the K-vector diagram that the left half of the FOV of blue light is restricted by total reflection, and the right half of the FOV of red light is restricted by continuity. Therefore, the observable color FOVRGB is very small, and there is serious chromatic dispersion.

[0007] The currently most easily conceivable method is also the scheme of Hololens 2, which uses three layers of waveguides to achieve colorization, as shown in the figure above. Each layer of waveguide substrate transmits light of a single color separately, and finally realizes color within the designed FOV. However, three substrate layers are used. Needless to say, it is very thick and heavy.

[0008] A trade-off scheme is to achieve colorization through two layers of waveguides, as shown in the figure above. Initially, this scheme was to transmit red light through a single layer of waveguide to achieve the full FOV, and transmit blue-green light through another layer of waveguide. Among them, the left half of the FOV of blue light was still restricted; subsequently, the two-layer waveguide scheme was improved. Red light is transmitted through a single layer of waveguide to achieve the full FOV, and blue light is transmitted through another layer of waveguide to achieve the full FOV, while the green light FOV is divided into two parts and transmitted by two substrates respectively.

[0009] The maximum FOV of the above several solutions is affected by the maximum diffraction angle and the refractive index of the substrate. And when the refractive index of the substrate and the maximum diffraction angle are fixed, there is a limit value for the maximum value of the FOV.

[0010] It must be pointed out that in the waveguide display solution based on holography, although using a multi-layer waveguide transmission optical path can expand the colorized field of view angle, it inevitably increases the volume and weight of the waveguide system. In addition, the colorized FOV of a single-layer waveguide has a theoretical limit value and still cannot meet the requirements of a large field of view, and there are serious dispersion problems, which still need to be further solved.

[0011] In view of the above situation, in order to overcome the above technical problems, the present invention designs a waveguide system based on a polarization liquid crystal grating and a method for expanding the colorized field of view of the waveguide, and solves the above technical problems. Summary of the Invention

[0012] The technical purpose to be achieved by the present invention is: designing a waveguide system based on a polarization liquid crystal grating and a method for expanding the colorized field of view of the waveguide, adding a PG on the basis of the traditional single-layer waveguide colorization solution to separately control the angle of light of a certain wavelength to break through the FOV theoretical limit of the single-layer waveguide and achieve the FOV size of the traditional double-layer waveguide. At the same time, maintaining a thin and light appearance.

[0013] In order to achieve the above technical purpose, the present invention provides the following technical solutions:

[0014] A waveguide system based on a polarization liquid crystal grating, comprising: the described waveguide system includes an optical engine system, an input coupling region, a flat substrate, and an output coupling region;

[0015] The optical engine system can output a first type of circularly polarized light or a second type of circularly polarized light with a color image; the input coupling region includes a first input transmission element, a first input reflection element, and a second input reflection element, and the first input transmission element, the first input reflection element, and the second input reflection element have the property of being sensitive to circularly polarized light;

[0016] The output coupling region includes a first output reflection element and a second output reflection element, and the first output reflection element and the second output reflection element have the property of being sensitive to circularly polarized light.

[0017] Preferably, the output coupling region can be set as a first output reflection element, a second output reflection element, and a first output transmission element.

[0018] Preferably, the first input reflection element, the second input reflection element, the first output reflection element, and the second output reflection element are all set as polarization volume holographic gratings;

[0019] Preferably, the first input transmissive element and the first output transmissive element are configured as polarization gratings or phase-type metasurfaces.

[0020] Preferably, the first input transmissive element only responds to the first type of circularly polarized light and diffracts it into the second type of circularly polarized light, does not respond to the second type of circularly polarized light and directly transmits it without changing the polarization.

[0021] Preferably, the first output transmissive element only responds to the second type of circularly polarized light and diffracts it into the first type of circularly polarized light, does not respond to the first type of circularly polarized light and directly transmits it without changing the polarization state.

[0022] Preferably, the first input reflective element and the first output reflective element only respond to the first type of circularly polarized light and diffract it without changing the polarization state, do not respond to the second type of circularly polarized light and directly transmit it without changing the polarization state.

[0023] Preferably, the second output reflective element only responds to the second type of circularly polarized light and diffracts it without changing the polarization state, does not respond to the first type of circularly polarized light and directly transmits it without changing the polarization state.

[0024] A method for waveguide color field expansion based on a polarization liquid crystal grating, which is used in cooperation with the above-mentioned waveguide system based on a polarization liquid crystal grating. Through the coupling structure of the waveguide system, the red light or blue light can be individually regulated, so that the fields of view lacking red light or blue light in the full-color scheme of a single-layer waveguide can all reach the human eye through total internal reflection of the waveguide, thereby expanding the field of view of red light and thus expanding the color field of view.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The present invention proposes another method idea for expanding the FOV RGB to break through the theoretical upper limit of the FOV. Compared with the traditional reflective waveguide display system, the proposed solution in this patent stacks r-PVGs that respond to LCP and RCP respectively on one surface of the r-PVG waveguide to achieve diffraction of the response optical path, and a PG is added on the other surface to compensate for the diffraction angle of red light. The RCP light with a certain field of view emitted from the entire optical engine passes through the compensation grating. Due to the polarization response and diffraction characteristics of the PVG, the red light in the 630nm band is pre-deflected by a certain angle and the polarization state changes from RCP to LCP, and finally diffracts into the waveguide by the r-PVG that responds to LCP. For light in the 460nm and 532nm bands, in an ideal case, it can be directly diffracted into the waveguide by the r-PVG that responds to RCP. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Now the above and other aspects of the present invention will be described by way of example only with reference to the drawings, in which:

[0029] Figure 1 is a schematic diagram of the full-colorization of each layer of waveguide in k-space;

[0030] Figure 1 (a) is a schematic diagram of the full-colorization of a single-layer waveguide in k-space;

[0031] Figure 1 (b) is a schematic diagram of the full-colorization of a double-layer waveguide in k-space;

[0032] Figure 1 (c) is a schematic diagram of the full-colorization of a triple-layer waveguide in k-space;

[0033] Figure 2 is a schematic diagram of the color structures of single-layer, double-layer, and triple-layer waveguides;

[0034] Figure 3 is a schematic diagram of various properties of the present invention;

[0035] Figure 3 (a) is a schematic diagram of the full-colorization structure of the single-layer waveguide proposed by the present invention;

[0036] Figure 3 (b) is a schematic diagram of the polarization beam splitting of the present invention to realize the RGB optical path transmission;

[0037] Figure 3 (c) is a schematic diagram of the full-colorization of the single-layer waveguide proposed by the present invention in k-space;

[0038] Figure 3 (d) is a relationship diagram of the field-of-view limit of the present invention with the waveguide refractive index and the maximum diffraction angle;

[0039] Figure 4 is a schematic diagram of the first embodiment of the present invention;

[0040] Figure 5 is the field-of-view diagram of blue light, green light, and red light of the present invention;

[0041] Figure 6 is the diagram of the first and second PG wavelength bandwidths, the first and second r-PVG wavelength bandwidths, and the third r-PVG wavelength bandwidth of the present invention;

[0042] Figure 7 It is a diagram showing the relationship between the field of view limit of the present invention, the waveguide refractive index, and the maximum diffraction angle; Figure 8 It is a schematic diagram of the second embodiment of the present invention; Figure 9 It is a schematic diagram of the third embodiment of the present invention. Detailed implementation manners

[0043] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0044] As Figures 1-9 shown,

[0045] Embodiment 1: As Figure 1 shown, when using a planar waveguide for output, some necessary conditions need to be met. When the input light source has a certain angle, the left-edge light rays need to satisfy the total reflection condition, and the right-edge light rays need to enter the waveguide and, for the imaging performance, need to satisfy the restriction of exit pupil continuity. For a holographic optical waveguide, the horizontal FOV can be obtained from the first-order grating equation:

[0046]

[0047] where, Λ x is the transverse period of the PVG, θ i is the incident angle in the incident medium, θ d is the diffraction angle of the exit medium, n i is the refractive index of the incident medium, which refers to air here, n g is the refractive index of the exit medium, which refers to the waveguide refractive index here, and λ is the wavelength in vacuum. To better analyze the horizontal field of view limit intuitively, we use Figure 1 k-space analysis.

[0048] Combined with the above formula, in order to prevent chromatic dispersion, the gratings in the same layer of glass need to maintain the same transverse period. In addition, light of different wavelengths will have different diffraction angles.

[0049] Therefore, if a single-layer waveguide is used to implement the colorization scheme (multiple gratings can be stacked on a single-layer waveguide), it can be seen from the K-vector diagram that the left half of the field of view of blue light is restricted by total reflection, and the right half of the field of view of red light is restricted by continuity. Therefore, the observable color FOV RGB is very small, and there is serious chromatic dispersion.

[0050] The currently most straightforward method is also the solution of Hololens 2, which uses three-layer waveguides to achieve colorization, as shown in the figure above. Each layer of waveguide substrate transmits light of a single color separately, and finally, a color image is achieved within the designed FOV. However, three-layer substrates are used. Undoubtedly, using three-layer substrates is thick and heavy.

[0051] Another trade-off solution is to achieve colorization through two-layer waveguides, as shown in the figure above. Initially, this solution used one layer of waveguide to transmit red light alone to achieve the full field of view, while blue and green light were transmitted through another layer of waveguide. However, the left half of the field of view of the blue light was still restricted. Subsequently, the two-layer waveguide solution was improved. Red light was transmitted alone through one layer of waveguide to achieve the full field of view, blue light was transmitted through another layer of waveguide to achieve the full field of view, and the green light field of view was divided into two parts, which were transmitted through two substrates respectively.

[0052] The maximum FOV of the above several solutions is affected by the maximum diffraction angle and the refractive index of the substrate. And when the refractive index of the substrate and the maximum diffraction angle are fixed, there is a limit value for the maximum value of the FOV.

[0053] The present invention proposes another method and idea for expanding the FOV RGB to break through the theoretical upper limit of the FOV. Compared with the traditional reflective waveguide display system, the solution proposed in this patent stacks r-PVG that responds to LCP and RCP respectively on one surface of the r-PVG waveguide to achieve diffraction of the response optical path, and a PG is added on the other surface to compensate for the diffraction angle of the red light. The RCP light with a certain field of view emitted from the overall optical engine passes through the compensation grating. Due to the polarization response and diffraction characteristics of the PVG, the red light in the 630nm band is pre-deflected by a certain angle and the polarization state changes from RCP to LCP, and finally diffracts into the waveguide by the r-PVG that responds to LCP. For light in the 460nm and 532nm bands, in an ideal situation, it can be directly diffracted into the waveguide by the r-PVG that responds to RCP.

[0054] The optical engine system can be a microdisplay projection optical machine such as LCoS, Micro-LED, Micro-OLED, DLP, etc., and can emit left-handed circularly polarized light or right-handed circularly polarized light. In this embodiment, taking the optical engine system emitting right-handed circularly polarized (RCP) RGB light as an example, the first, second, fourth, and fifth r-PVGs are r-PVGs responsive to RCP, the third and sixth r-PVGs are r-PVGs responsive to LCP, and the lateral period sizes of all r-PVGs are kept consistent. G light and B light pass through the first PG without diffraction and then pass through the first and second r-PVGs to introduce the light into the waveguide for total reflection and transmission to the coupling-out area where the human eye is located. Subsequently, the fourth and fifth r-PVGs introduce G light and B light into the human eye without being responsive to the second PG; for R light, after passing through the first PG, a small-angle deflection occurs, and at the same time, the polarization state of R light is converted from RCP to LCP. Subsequently, it is introduced into the waveguide by the third r-PVG responsive to LCP for total reflection. Through design, the diffraction angle of R light can be made the same as that of G light. In the coupling-out area, it is reflected out of the waveguide by the sixth r-PVG, and then the second PG corrects the field of view of R light. Finally, it is received by the human eye.

[0055] The field of view angle that can be achieved through the configuration of this waveguide can also be analyzed by k-space, as shown in the above figure. In k-space, all possible light propagation directions form a circular region, and the grating performs a certain vector displacement on the light in K space. In our assumption, the length and width of the FOV are equal, and the FOV is symmetric about 0°. At this time, the horizontal FOVRGB can be expressed as:

[0056]

[0057] where n g represents the refractive index of the waveguide substrate, and θ dmax represents the maximum diffraction angle. When the maximum diffraction angle θ dmax is 75° and the refractive index n g of the waveguide is 1.57, the maximum FOV RGB that can be achieved by the solution proposed in this patent is 22.12°, which is about 15.7° higher than the traditional solution.

[0058] In order to make the PG not responsive to G and B light, additional designs need to be made for the bandwidths of the first and second PGs and the first, second, and third r-PVGs to ensure that stray light does not enter the waveguide in the polarization multiplexing manner. The above figure shows the wavelength bandwidths of the first and second PGs and the first, second, and third r-PVGs in this embodiment.

[0059] k-space analysis:

[0060] As Figure 7As shown, the theoretical limit of the traditional single-layer waveguide FOV RGB can be obtained from K-space analysis as follows:

[0061]

[0062] Compare the theoretical limit of the FOV of this solution with the theoretical limit of the traditional single-layer colorized FOV.

[0063] Example 2: The layout is the same as that of the first embodiment, except that it is the B light rather than the R light that is regulated. Specifically, as follows, the G light and the R light pass through the first PG without diffraction and directly transmit through, and then pass through the first and second r-PVGs to introduce the light into the waveguide for total reflection and transmission to the coupling-out region where the human eye is located. Then, the G light and the R light are introduced into the human eye through the fourth and fifth r-PVGs and are not responded to by the second PG; for the B light, after passing through the first PG, a small-angle deflection occurs, and at the same time, the polarization state of the B light is converted from RCP to LCP, and then it is introduced into the waveguide by the third r-PVG that responds to LCP for total reflection. By design, the diffraction angle of the B light can be made the same as that of the G light. It is reflected out of the waveguide by the sixth r-PVG in the coupling-out region, and then the second PG corrects the field of view of the B light. Finally, it is received by the human eye.

[0064] Example 3: The layout is similar to that of Example 1 as shown in the following figure. The difference is that the lateral period of the sixth r-PVG in the coupling-out region is different from the lateral periods of the other r-PVGs, and the coupling-out region only includes r-PVGs and does not require PGs.

[0065] For those of ordinary skill in the art, various modifications to the present disclosure will be obvious, and the general principles defined herein can be applied to other variations without departing from the scope of the present disclosure. Therefore, the present disclosure is not limited to the examples and designs described herein, but should be given the broadest scope consistent with the principles and novel features disclosed herein. Although one or more exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, those of ordinary skill in the art will understand that various changes in form and detail can be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims.

Claims

1. A waveguide system based on polarization liquid crystal grating, characterized in that: include: The waveguide system comprises an optomechanical system, an input coupling region, a planar substrate and an output coupling region; The optical-mechanical system can output a first type of circularly polarized light or a second type of circularly polarized light with a color image; the input coupling region includes a first input transmission element, a first input reflection element, and a second input reflection element, and the first input transmission element, the first input reflection element, and the second input reflection element have a property of being sensitive to circularly polarized light; The output coupling region includes a first output reflective element and a second output reflective element, wherein the first output reflective element and the second output reflective element have a property of being sensitive to circularly polarized light.

2. A waveguide system based on polarization liquid crystal grating according to claim 1, characterized in that: The output coupling region may be configured as a first output reflective element, a second output reflective element, and a first output transmissive element.

3. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The first input reflection element, the second input reflection element, the first output reflection element and the second output reflection element are all configured as polarization volume holographic gratings.

4. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The first input transmission element and the first output transmission element are configured as a polarization grating and a phase-type metasurface.

5. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The first input transmission element only responds to the first type of circularly polarized light and diffracts and converts it into the second type of circularly polarized light, and does not respond to the second type of circularly polarized light and directly transmits it without changing its polarization.

6. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The first output transmission element only responds to the second type of circularly polarized light and diffracts and converts it into the first type of circularly polarized light, and does not respond to the first type of circularly polarized light and directly transmits it without changing its polarization state.

7. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The first input reflecting element and the first output reflecting element only respond to the first type of circularly polarized light and diffract without changing the polarization state, and do not respond to the second type of circularly polarized light and directly transmit without changing the polarization state.

8. A waveguide system based on polarization liquid crystal grating according to claim X, characterized in that: The second output reflecting element only responds to the second type of circularly polarized light and diffracts without changing the polarization state, and does not respond to the first type of circularly polarized light and directly transmits the light without changing the polarization state.

9. A method for expanding the field of view of a waveguide colorization based on a polarization liquid crystal grating, the method being used in conjunction with a waveguide system based on a polarization liquid crystal grating as claimed in any one of claims 1 to 8, characterized in that: The coupling structure of the waveguide system is used to separately control red light or blue light, so that the field of view where red light or blue light is missing in the full-colorization solution of a single-layer waveguide can reach the human eye through total reflection of the waveguide, thereby expanding the field of view of red light and thus expanding the field of view of colorization.

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