Projection system
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- APPOTRONICS CORP LTD
- Filing Date
- 2020-03-19
- Publication Date
- 2026-06-05
Smart Images
Figure CN113495405B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of projection technology, and more specifically to a projection system. Background Technology
[0002] Currently, the contrast ratio achievable by single-chip spatial light modulator projection display technology is roughly several hundred to one to two thousand to one, far below the brightness resolution of the human eye. Therefore, the brightness of projected images is insufficient in bright areas and fails to decrease in dark areas, resulting in poor image detail and loss of perceived depth. High dynamic range (HDR) projection systems aim to expand the display's brightness range, enabling rich grayscale information to be displayed in both bright and dark areas, thereby significantly improving image quality and the viewer's experience.
[0003] Currently, there are several main methods for achieving HDR display in projection systems:
[0004] The first method is dual-chip spatial light modulator technology. By adding another spatial light modulator after the DMD, a high contrast ratio can be achieved by multiplying the contrast ratios of the two chips. However, the addition of the second spatial light modulator significantly reduces the projector's brightness. Its luminous efficacy can only reach 50% or even less of that of a conventional projection system, making it difficult for the projection system to achieve higher peak brightness.
[0005] The second method is dynamic aperture technology. The contrast ratio of a DMD projection system is related to the aperture size of the projection lens. Generally, a larger numerical aperture corresponds to a higher contrast ratio. The disadvantages of this method are: First, the aperture control response is slow and cannot keep up with every frame. Second, using a mechanical mechanism to adjust the aperture structure raises reliability issues and increases system cost. Third, a smaller aperture means lower brightness; therefore, while increasing contrast, this approach also reduces peak brightness, affecting the viewing experience. Fourth, reducing the aperture cannot achieve a very high contrast ratio. Therefore, the contrast ratio of this method is far inferior to that of a projection system using a dual-panel spatial light modulator.
[0006] The third method is phase-shifting (light steering) technology. This involves adding a phase-modulated liquid crystal device (LCD) before the spatial light modulator. By controlling the phase delay distribution of the LCD, the light field distribution illuminating the spatial light modulator is controlled, achieving a high dynamic range projection system. HDR projection devices using phase-shifting technology can reduce light efficiency by approximately 10%-20% compared to traditional projection devices. However, phase-shifting technology requires coherent light sources, thus limiting its application to laser light sources. It is not ideal for fluorescent and LED light sources. Furthermore, the reliability of phase-modulated LCDs is not high, and their cost remains high, significantly increasing the overall cost of this technology. Moreover, phase-modulated LCDs cannot withstand high-power light sources. Additionally, because phase-modulated LCDs can only modulate coherent light, the high coherence of the light source can cause speckle effects due to undulations in the projection plane. While speckle can be mitigated by screen dithering, the additional dithering device increases system cost and reliability, limiting the application of pure laser projection.
[0007] The fourth method is similar to the local dimming technology used in LED-backlit LCDs. It employs a laser array as the light source for the projection device, with each laser responsible for illuminating a specific area. During projection, the laser intensity is dynamically controlled based on the peak brightness of each area of the image to achieve high contrast. This method achieves high contrast while avoiding unnecessary light energy loss; however, its light source structure and modulation process are relatively complex, and it cannot avoid the effects of varying aging rates.
[0008] It is evident that none of the above methods can effectively achieve high dynamic range projection. Summary of the Invention
[0009] The purpose of this application is to provide a projection system to achieve high dynamic range projection display.
[0010] This application provides a projection system including a light source, a spatial light modulator, and a beam deflector. The light source emits an illumination beam, and the beam deflector is disposed in the optical path of the illumination beam. The beam deflector includes a variable refractive index material arranged in an array. The refractive index of the variable refractive index material can change according to the intensity of the electric field applied to it. The beam deflector controls the electric field applied to the array of variable refractive index materials according to the image signal of the image to be projected, so that the refractive index of the variable refractive index material in at least a portion of the region changes, and the illumination beam passing through the region is deflected, so that the illumination beam incident on the spatial light modulator forms a brighter region and a darker region.
[0011] In some implementations, the variable refractive index unit is made of liquid crystal material.
[0012] In some embodiments, the variable refractive index unit includes a liquid crystal cell, each liquid crystal cell having a first incident surface, a first exit surface and a first connecting surface, the first incident surface being connected to the first exit surface and the first connecting surface, and the first incident surfaces of the plurality of liquid crystal cells constituting the light incident surface of the variable refractive index unit.
[0013] In some embodiments, the liquid crystal cell is wedge-shaped, and the angle between the first connecting surface and the first incident surface is greater than 90°.
[0014] In some embodiments, the angle between the normal of the first connecting surface and the first incident surface is equal to the dispersion angle of the illumination beam in the liquid crystal cell.
[0015] In some embodiments, the angle between the first connecting surface and the first incident surface is 120°-135°.
[0016] In some embodiments, the liquid crystal cell is made of nematic liquid crystal, and when no electric field is applied, the optical axis of the liquid crystal molecules in the liquid crystal cell is perpendicular to the incident light surface.
[0017] In some embodiments, the beam deflector further includes a fixed refractive index unit having a fixed refractive index, and a variable refractive index unit receiving the illumination beam emitted from the light source and being emitted by the fixed refractive index unit to the spatial light modulator.
[0018] In some embodiments, the fixed refractive index unit includes multiple crystal structures arranged side by side. Each crystal structure has a second incident surface, a second exit surface, and a second connecting surface. The second incident surface is connected to the second exit surface and the second connecting surface. Each second incident surface is attached to the first exit surface of a liquid crystal cell in the variable refractive index unit.
[0019] In some implementations, the second connection surface of each crystal structure is parallel to the first connection surface of a liquid crystal cell in a variable refractive index unit.
[0020] In some implementations, the second connection surface of each crystal structure is bonded to the first connection surface of the adjacent liquid crystal cell.
[0021] In some embodiments, the beam deflector further includes a first electrode and a second electrode for applying an electric field to the variable refractive index unit.
[0022] In some embodiments, the projection system further includes a control unit electrically connected to the first electrode and the second electrode, such that the control unit controls the electric field intensity applied to each region of the arrayed variable refractive index units according to the brightness of each region of the image to be projected.
[0023] In some embodiments, the light source includes a light-emitting device and a polarizer, the polarizer being used to receive the light beam emitted by the light-emitting device and emit a radiation-polarized illumination beam.
[0024] In some embodiments, the projection system further includes a display lens located in the optical path of the illumination beam emitted from the beam deflector.
[0025] In some embodiments, the display lens includes an objective lens and an eyepiece spaced apart, and the illumination beam is transmitted sequentially through the objective lens and the eyepiece to the spatial light modulator.
[0026] The projection system provided in this application, by setting a beam deflector with a variable refractive index unit, and by adjusting the electric field strength of the electric field applied to the beam deflector, achieves the deflection of the illumination beam passing through the variable refractive index unit, and makes the illumination beam incident on the spatial light modulator form a brighter area and a darker area, thereby realizing the modulation of the light-directing high dynamic projection system.
[0027] These or other aspects of this application will become more apparent in the following description of the embodiments. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0029] Figure 1 This is a schematic diagram of the structure of a projection system provided in an embodiment of this application;
[0030] Figure 2 This is a schematic diagram of a liquid crystal structure shown in an embodiment of this application;
[0031] Figure 3 This is a schematic diagram illustrating the propagation path of a light beam in a liquid crystal, as shown in an embodiment of this application.
[0032] Figure 4 This is a schematic diagram of the structure of a beam deflector provided in an embodiment of this application;
[0033] Figure 5 This is a schematic diagram of a partially disassembled structure of a beam deflector provided in an embodiment of this application;
[0034] Figure 6 This is a schematic diagram illustrating the working principle of the beam deflector provided in the embodiments of this application;
[0035] Figure 7This is the Δ-θ variation curve of the beam deflector shown in an embodiment of this application under a test environment;
[0036] Figure 8 This is a schematic diagram of another projection system provided in the embodiments of this application. Detailed Implementation
[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0038] See Figure 1 This embodiment provides a projection system 1, including a light source 20, a beam deflector 10, and a spatial light modulator 50. The light source 20 is used to emit an illumination beam, the beam deflector 10 is located in the optical path of the illumination beam emitted by the light source 20, and the spatial light modulator 50 is used to modulate the illumination beam emitted from the beam deflector 10.
[0039] Please continue reading for more details. Figure 1 The light source 20 can be a linearly polarized light source used to generate a linearly polarized light beam, i.e., the illumination beam is a linearly polarized beam. For example, a laser beam can be directly generated by a laser as the illumination beam. In some embodiments, the light source 20 includes a light-emitting device 21 and a polarizer 22. The polarizer 22 is used to receive the light beam emitted by the light-emitting device 21 and emit it to form a linearly polarized beam as the illumination beam. In this case, the light-emitting device 21 can be a visible light light-emitting device, such as an LED light source. It is understood that when a laser is used as the light source 20, the polarizer 22 is not required.
[0040] A beam deflector 10 is located in the optical path from the light source 20 to the spatial light modulator 50. The beam deflector 10 has a variable refractive index unit 100, which has a refractive index that changes according to the intensity of the applied electric field; that is, the refractive index of the variable refractive index unit 100 can be changed. Furthermore, when the intensity of the applied electric field to the variable refractive index unit 100 changes, the refractive index of at least a portion of the variable refractive index unit 100, or the refractive index of the entire variable refractive index unit 100, can change. When the illumination beam passes through the variable refractive index unit 100 with its changed refractive index, the illumination beam is deflected.
[0041] When the deflected illumination beam emitted by the beam deflector 10 is incident on the spatial light modulator 50, it can form a brighter region and a darker region. It is understood that the brighter region and the darker region only represent relative brightness, and the brightness of the brighter region is greater than that of the darker region.
[0042] The variable refractive index unit 100 can be made of a liquid crystal material, such as a nematic liquid crystal material or a ferroelectric liquid crystal material. The variable refractive index unit 100 can be formed into a generally prismatic structure or other shapes from the liquid crystal material.
[0043] Liquid crystals are classified into nematic liquid crystals, smectic liquid crystals, and cholesteric liquid crystals, and are widely used in displays, projection devices, and other applications. Taking nematic liquid crystals as an example, under the drive of an external electric field, the pointing vector of the liquid crystal molecules (equivalent to the direction of the crystal's optical axis) forms an angle θ with the electric field (referred to as the pointing angle). The pointing angle θ of the liquid crystal molecules depends on the magnitude of the applied electric field. Therefore, the refractive index of the liquid crystal material can be changed by applying an external electric field. Based on this, wedge-shaped liquid crystal cells can be fabricated, meaning that the deflection angle of the light path can be adjusted by applying an external electric field. Figure 1 As shown, liquid crystal molecules tend to align perpendicular to the direction of the electric field: when no electric field is applied, the pointing vectors of all liquid crystal molecules are parallel to the direction of the electric field; when an external electric field is applied, the pointing vectors of the molecules deflect in a direction perpendicular to the direction of the electric field, tending to align along the direction of the electric field. This type of liquid crystal is called vertically aligned nematic liquid crystal (VAN).
[0044] Please refer to the following: Figure 2 and Figure 3 For a time-harmonic plane wave propagating in a homogeneous medium, its wave equation is k×(k×E)+μ∈ω 2 E = 0. Expanded into vector form, it is k(k·E) - (k·k)E + μ∈ω 2 E = 0, its matrix form is
[0045]
[0046] Written
[0047]
[0048] in μ = μ r μ0,∈=∈ r ∈0.
[0049] For uniaxial birefringent liquid crystal materials, μ r =1, Where n o n represents the refractive index of O light. eThis represents the refractive index along the optical axis of a uniaxial birefringent crystal. If n e >n o If n e <n o If the electric field is zero, then the uniaxial birefringent crystal is called a negative birefringent crystal. Since there exists a non-zero electric field solution, we can obtain det(M) = 0. Therefore, we can deduce...
[0050]
[0051] It can be seen that two different types of plane waves can satisfy the above conditions: the first type, Its k-space iso-k surface is a sphere. The direction of the light wave group velocity (i.e., the direction of energy propagation, or the Poynting vector direction) is the same as the k-propagation direction. This type of light corresponds to o-ray. Another type... Its k-space iso-k surface is an ellipsoid. Generally, the direction of the light group velocity (i.e., the direction of energy propagation, or the Poynting vector direction) is not the same as the k-propagation direction; this type of light corresponds to e-rays.
[0052] When a beam of light is incident perpendicularly on a liquid crystal interface, assuming the angle between the orientation vector of the liquid crystal molecules and the interface normal is θ, as follows: Figure 3 As shown in the diagram, the o-ray continues to propagate along the direction of the incident light, while the e-ray's propagation direction is deflected, and the deflection angle α satisfies the following relationship:
[0053]
[0054] It can also be expressed as α is also called the dispersion angle.
[0055] Therefore, when θ = 0 or At this time, α = 0, meaning that neither the o-ray nor the e-ray is deflected.
[0056] Based on the above principles, light beams can be deflected using liquid crystals, and the refractive index of the liquid crystals can be adjusted by controlling the electric field strength, thereby controlling the deflection angle.
[0057] In one implementation, the variable refractive index unit 100 includes a plurality of liquid crystal cells 110 arranged side by side, please refer to the accompanying document. Figure 4 and Figure 5Each liquid crystal cell 110 is approximately wedge-shaped, with a roughly triangular longitudinal cross-section, where the longitudinal cross-section refers to the cross-section along the direction of the liquid crystal cell's direction vector. Each liquid crystal cell 110 has a first incident surface 111, a first exit surface 113, and a first connecting surface 112. The first incident surface 111 is connected to the first exit surface 113 and the first connecting surface 112. Specifically, one side of the first incident surface 111 is connected to one side of the first exit surface 113, the other side of the first exit surface 113 is connected to one side of the first connecting surface 112, and the other side of the first connecting surface 112 is connected to the other side of the first incident surface 111. The first incident surface 111, the first connecting surface 112, and the first exit surface 113 form an approximately triangular prism liquid crystal cell.
[0058] In some embodiments, the angle between the first connecting surface 112 and the first incident surface 111 can be greater than 90°. It can be understood that the angle β between the first connecting surface 112 and the first incident surface 111 refers to the angle formed by the intersection of the first connecting surface 112 and the first incident surface 111, opposite to the first exiting surface 113. When light enters from the first incident surface 111, it propagates through the liquid crystal cell 110 and exits from the first exiting surface 113. The first exiting surface 113 is also inclined relative to the first incident surface 111, effectively forming a wedge-shaped structure.
[0059] The angle β between the first connecting surface 112 and the first incident surface 111 is greater than 90°, indicating that the first connecting surface 112 is inclined relative to the first incident surface 111. The advantage of this design is that during the propagation of the light beam incident from the first incident surface 111 in the liquid crystal cell 110, the amount of scattered light escaping from the first connecting surface 112 and becoming stray light is reduced. β can be set, for example, as π / 2 + α, i.e., α + 90°, where α is the dispersion angle of the light beam in the liquid crystal cell 110, which is the angle between the normals of the first connecting surface 112 and the first incident surface 111. The normal of the first incident surface 111 refers to the ray that is perpendicular to the first incident surface 111 and extends towards the first exit surface 113. Since the first connecting surface 112 is inclined relative to the first incident surface 111, when the light beam enters from the first incident surface 111 and is deflected in the liquid crystal cell 110, the deflected light will be dispersed. However, since the included angle β = π / 2 + α, the dispersed light cannot escape from the first connecting surface 112, but will exit from the first exiting surface 113, thus avoiding the formation of stray light.
[0060] In some embodiments, the angle between the first exit surface 113 and the first incident surface 111 may be, for example, 30° to 60°. It can be understood that the angle between the first exit surface 113 and the first incident surface 111 refers to the angle opposite to the first connecting surface 112.
[0061] The liquid crystal cell 110 has the following characteristics: in an electric field, when the magnitude of the electric field changes, the tilt angle of the optical axis of the liquid crystal molecules in the liquid crystal cell 110 changes, thereby changing the direction of the emitted light. Liquid crystals include thermotropic liquid crystals (LCs) and lyotropic liquid crystals (LCs), with thermotropic liquid crystals further including nematic, smectic, and cholesteric phases. It is understood that in this embodiment, the liquid crystal cell 110 can be any one of a nematic, smectic, or cholesteric phase. In some embodiments, the liquid crystal cell 110 is composed of nematic liquid crystals, and when no electric field is applied, the optical axis direction of the liquid crystal molecules in the liquid crystal cell 110 is perpendicular to the incident light surface.
[0062] The first incident surfaces 111 of the plurality of liquid crystal cells 110 constitute the light incident surface of the variable refractive index unit 100. In some embodiments, the first incident surfaces 111 of the plurality of liquid crystal cells 110 are located on the same plane and are connected end to end in sequence to form a continuous plane.
[0063] In some embodiments, the angle β between the first connecting surface 112 and the first incident surface 111 can be, for example, 120° to 135°. Within this angle range, it roughly corresponds to the dispersion angle of the laser beam, which can more effectively prevent scattered light from escaping the liquid crystal cell 110 and becoming stray light.
[0064] In some embodiments, the beam deflector 10 may further include a fixed refractive index unit 200, wherein the fixed refractive index unit 200 has a fixed refractive index, that is, the refractive index of the fixed refractive index unit 200 is constant. The fixed refractive index unit 200 is attached to the variable refractive index unit 100. The illumination beam emitted from the variable refractive index unit 100 is incident on the fixed refractive index unit 200 and exits from the fixed refractive index unit 200 to the spatial light modulator 50. In some embodiments, the fixed refractive index unit 200 may be attached to the variable refractive index unit 100, that is, during the propagation of the illumination beam from the variable refractive index unit 100 to the fixed refractive index unit 200, there is no other propagation medium, and it directly enters the fixed refractive index unit 200 from the variable refractive index unit 100. Of course, in other embodiments, there may also be a predetermined distance between the variable refractive index unit 100 and the fixed refractive index unit 200.
[0065] In one implementation, the fixed refractive index unit 200 includes a plurality of crystal structures 210 arranged side by side. The plurality of crystal structures 210 can be configured to cooperate with a plurality of liquid crystal cells 110. For example, the plurality of crystal structures 210 can be arranged alternately with the plurality of liquid crystal cells 110.
[0066] The crystal structure 210 has a fixed refractive index, meaning that its refractive index remains essentially unchanged or completely unchanged under the influence of an electric field. For example, the crystal structure 210 can be made of resin, such as epoxy resin. In some embodiments, the crystal structure 210 can also be made of materials such as glass, quartz, polycarbonate, or polypropylene.
[0067] The crystal structure 210 has a second incident surface 211, a second exit surface 213, and a second connecting surface 212. The second incident surface 211 is connected to the second exit surface 213 and the second connecting surface 212, and the second exit surface 213 is also connected to the second incident surface 211, forming a roughly wedge-shaped structure. Specifically, one side of the second incident surface 211 is connected to one side of the second exit surface 213, the other side of the second incident surface 211 is connected to one side of the second connecting surface 212, and the other side of the second exit surface 213 is also connected to one side of the second incident surface 211. When the light beam exits from the first exit surface 113, it enters from the second incident surface 211 and exits from the second exit surface 213.
[0068] Each second incident surface 211 is correspondingly attached to a first exit surface 113 of a liquid crystal cell 110 in the variable refractive index unit 100. It is understood that the attachment of the second incident surface 211 to the first exit surface 113 can be complete, meaning the area of the first exit surface 113 completely overlaps with the area of the second incident surface 211. Furthermore, in some embodiments, the second connecting surfaces 212 can be parallel to or attached to the first connecting surfaces 112 of a liquid crystal cell 110 in the variable refractive index unit 100.
[0069] When the second connecting surface 212 is in one-to-one contact with the first connecting surface 112 of one of the liquid crystal cells 110 in the variable refractive index unit 100, it can mean that the second connecting surface 212 is completely in one-to-one contact with the first connecting surface 112 of one of the liquid crystal cells 110 in the variable refractive index unit 100. That is, the areas of the second connecting surface 212 and the first connecting surface 112 are exactly equal, and the first connecting surface 112 and the second connecting surface 212 are also parallel to each other. It can be understood that for a crystal structure 210, its second connecting surface 212 is in contact with the second connecting surface 212 of one liquid crystal cell 110, and its second incident surface 211 is in contact with the first exit surface 113 of another adjacent liquid crystal cell 110. That is, the crystal structure 210 is embedded between two adjacent liquid crystal cells 110, and correspondingly, one liquid crystal cell 110 is embedded between two adjacent crystal structures 210.
[0070] The second emitting surfaces 213 of multiple crystal structures 210 constitute the light-emitting surface of the fixed refractive index unit 200. In some embodiments, the second emitting surfaces 213 of the multiple crystal structures 210 are located on the same plane and constitute a continuous light-emitting surface. Light incident through the incident surface of the variable refractive index unit 100 is emitted from the light-emitting surface of the fixed refractive index unit 200. In some embodiments, the light-emitting surface and the incident surface are parallel to each other to more precisely control the emission angle of the emitted light.
[0071] In some embodiments, the beam deflector 10 further includes a first electrode 300 and a second electrode 400, which are used to apply an electric field to the variable refractive index unit 100. The direction of the electric field can be parallel to or perpendicular to the direction of the liquid crystal's guide vector. The first electrode 300 and the second electrode 400 can be distributed on a glass cover plate located on the light-incident surface and a glass cover plate located on the light-exit surface. The first electrode 300 and the second electrode 400 can be, for example, metal electrodes, calomel electrodes, etc., and can be applied to the light-incident surface and the light-exit surface respectively, such that the direction of the formed electric field is parallel to the direction of the guide vector of the liquid crystal when it is not deflected.
[0072] In some embodiments, the projection system 10 further includes a control unit (not shown), which may be, for example, a central processing unit (CPU). The control unit may be electrically connected to the first electrode 300, the second electrode 400, and the light source 20 to control the electric field intensity applied to the variable refractive index unit 100. When the projection system 10 performs projection display, it first receives a signal of an image to be projected. Each frame of the image signal may include multiple partitions (each partition may, for example, match the area of the first incident surface 111 of a variable refractive index unit 100), and the brightness and color of the images on these partitions may be different. When the image signal to be projected is input to the projection system 10, the control unit controls the light source 20 to generate an illumination beam of the corresponding color according to the signal and guides it to the beam deflector 10. At this time, the control unit can control the first electrode 300 and the second electrode 400 according to the brightness information of each zone of the real-time image, and then control and adjust the electric field intensity applied to each array of variable refractive index units 100 on the beam deflector 10, thereby adjusting the brightness of the light on each variable refractive index unit 100, that is, forming relatively brighter and darker areas. Then the beam is guided to the spatial light modulator 50 and projected outward to achieve the HDR display effect.
[0073] The working principle of the beam deflector 10 provided in this embodiment will be explained in detail below, taking the use of a nematic liquid crystal as the liquid crystal cell 110 as an example.
[0074] See Figure 6In nematic liquid crystals, under the influence of an external electric field, the pointer of the liquid crystal molecules forms an angle θ = θ(V) with the point, resulting in birefringence. When the normal to the extraordinary ray (e-ray) is in the same direction as the electric field, its refractive index n² can be expressed by the following formula:
[0075]
[0076] Where n o n is the refractive index of the ordinary ray o. e Let θ be the refractive index of the e-ray when the direction of the liquid crystal molecule is perpendicular to the direction of the electric field, and let θ be the refractive index of the liquid crystal material, since the angle depends on the magnitude of the applied electric field.
[0077] Specifically, assuming the selected refractive index matches the refractive index n of the material F With n o Similarly, without an applied voltage, incident light with a certain linear polarization will not be deflected. When a certain voltage V is applied to both ends of the unit, the VAN liquid crystal molecules deflect, and the angle between the director of the liquid crystal molecules and the direction of the electric field becomes θ. The incident light polarized in the plane becomes the e-ray of this liquid crystal unit, which will be deflected by a certain angle α. When it propagates to the first exit surface 113, due to n eff At this point, it becomes related to n F The difference lies in the fact that refraction occurs further at the interface.
[0078] After the liquid crystal is deflected, the refractive index of the liquid crystal cell 110 is n. eff The refractive index of crystal structure 210 is n F According to the law of refraction:
[0079]
[0080] The angle between the incident light and the normal direction of the refracting surface is θ1 = α. F The reason is that Figure 4 The wave vector of an e-ray incident in a neutral polarized direction is also vertical. However, due to the dispersion angle α, the light will be deflected to some extent within the birefringent crystal. At the wedge-shaped interface, the light is deflected again, and after being refracted, it enters the isotropic crystal, where its wave vector direction is consistent with the energy propagation direction. Therefore, the direction of the outgoing light can be uniquely determined by the law of refraction.
[0081] The angle between the refracted light and the normal direction of the refracting surface is θ2, with clockwise direction being positive. Define the angle α between the first exit surface 113 and the vertical direction. F The direction of clockwise rotation is positive, and the angle Δ between the vertical direction and the refracted light is positive in the clockwise direction. Therefore, the overall deflection angle of the light ray relative to the incident direction is positive.
[0082] Δ=θ2-α F (Eq.1)
[0083] in
[0084] Substituting Eq.2-3 into Eq.1 yields...
[0085]
[0086] It can be seen that, on the one hand, when α F When n = 0, the device degenerates into a parallel liquid crystal panel, Δ = 0, indicating that common parallel liquid crystal panels do not have the function of deflecting light. On the other hand, when n... F ≤n o hour, We can obtain Δ≥0; when n F ≥n e hour, At this time, Δ≤0; when n o <n F <n e When Δ is positive or negative.
[0087] As an example, let's take the typical VAN liquid crystal TL216 as an example. The refractive index n of TL216 at 550nm wavelength under 25°C conditions is... o =1.53, n e =1.74.
[0088] from Figure 7 It can be seen that choosing a suitable n F The initial angle of the liquid crystal can achieve a light deflection of at least 2 degrees. This deflection can be converted into a movement of the spatial position of the light spot using subsequent optical techniques.
[0089] The beam deflector 10 provided in this embodiment can provide a deflection angle for the light beam, and by setting the first connecting surface 112 in an inclined form relative to the first incident surface 111, it can prevent the scattered light from escaping from the first connecting surface 112 and becoming stray light, that is, prevent the beam from escaping from the side of the beam deflector 10.
[0090] Please refer to it again. Figure 1 In some embodiments, the projection system 1 may further include a display lens 40, which is disposed in the optical path of the illumination beam emitted from the beam deflector 10 and located in the optical path between the beam deflector 10 and the spatial light modulator 50. The beam deflector 10 is disposed on the front focal plane of the display lens 40; the beam deflector 10 may be disposed on the front focal plane of the display lens 40, forming an f-θ lens system. The spatial light modulator 50 may be a DMD, LCD, or LCoS, etc. The spatial light modulator 50 is used to receive the illumination beam transmitted through the display lens 40, modulate it, and then emit it.
[0091] In some embodiments, referring to Figure 8 , the display lens 40 may include an objective lens 41 and an eyepiece 42 arranged at intervals, and the deflected beam is transmitted through the objective lens 41 and the eyepiece 42 in sequence to the spatial light modulator 50.
[0092] Assume that the focal length of the objective lens 41 is f1, the focal length of the eyepiece 42 is f2, and the distance between the two lenses is d. The beam deflector 10 is located on the front focal plane of the display lens 40, and the spatial light modulator 50 is located on the rear focal plane of the display lens 40. Under the thin lens approximation, the distance from the objective lens 41 to the beam deflector 10 The distance from the eyepiece 42 to the spatial light modulator 50 To ensure clear imaging, the selection of d needs to satisfy f FFL , f BFL > 0, that is, d < f1, f2. In some embodiments, the distance from the objective lens 41 to the beam deflector 10 can be less than the distance from the eyepiece 42 to the spatial light modulator 50, which can control the size of the spot reaching the lens, thereby reducing the size of the subsequent optical elements.
[0093] By forming the display lens 40 with the spaced objective lens 41 and eyepiece 42, the telecentricity of the system can be improved, making the light space irradiated on the spatial light modulator 50 more uniform in angular distribution, which is helpful for the design of the illumination light on the subsequent light modulator. Among them, telecentricity is a physical quantity that measures the parallel degree of the chief rays and the optical axis. The better the telecentricity, the better the parallelism of the chief rays and the optical axis.
[0094] The working principle of the projection system 1 provided in this embodiment is: The light source 20 emits an illumination beam, and the illumination beam is incident on the variable refractive index unit 100. At this time, by controlling the electric field strength applied to the variable refractive index unit 100, the illumination beam is deflected on the variable refractive index unit 100 at a predetermined deflection angle, and the deflected illumination beam exits from the fixed refractive index unit 200 and is incident on the lens system 40. The lens system 40 transmits the illumination beam and then is incident on the spatial light modulator 50.
[0095] By setting the beam deflector 10 with the variable refractive index unit 100, by regulating the electric field strength of the electric field applied to the beam deflector 10, the deflection of the illumination beam passing through the variable refractive index unit 100 is achieved, and the illumination beam incident on the spatial light modulator 50 forms a brighter area and a darker area, thereby realizing the modulation of the light-steering type high-dynamic projection system.
[0096] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A projection system, characterized in that, include: A light source, used to emit a beam of illumination; Spatial light modulator; as well as A beam deflector is disposed in the optical path of an illumination beam. The beam deflector includes variable refractive index units arranged in an array. The refractive index of the variable refractive index units can change according to the intensity of the electric field applied to them. The beam deflector controls the electric field applied to the variable refractive index units according to the image signal of the image to be projected, so that the refractive index of the variable refractive index units in at least a portion of the region changes, and the illumination beam passing through this region is deflected, so that the illumination beam incident on the spatial light modulator forms brighter and darker regions. The variable refractive index unit is made of liquid crystal material; the variable refractive index unit includes a liquid crystal cell, each liquid crystal cell having a first incident surface, a first exit surface and a first connecting surface, the first incident surface being connected to the first exit surface and the first connecting surface, and the first incident surfaces of multiple liquid crystal cells constituting the light incident surface of the variable refractive index unit; the liquid crystal cell is wedge-shaped, and the angle between the first connecting surface and the first incident surface is greater than 90°.
2. The projection system according to claim 1, characterized in that, The angle between the first connecting surface and the normal of the first incident surface is equal to the dispersion angle of the illumination beam in the liquid crystal cell.
3. The projection system according to claim 1, characterized in that, The angle between the first connecting surface and the first incident surface is 120°-135°.
4. The projection system according to claim 1, characterized in that, The liquid crystal cell is made of nematic liquid crystal. When no electric field is applied, the optical axis of the liquid crystal molecules in the liquid crystal cell is perpendicular to the incident light surface.
5. The projection system according to any one of claims 1-4, characterized in that, The beam deflector also includes a fixed refractive index unit with a fixed refractive index, wherein the variable refractive index unit receives the illumination beam emitted from the light source and is emitted by the fixed refractive index unit to the spatial light modulator.
6. The projection system according to claim 5, characterized in that, The fixed refractive index unit includes multiple crystal structures arranged side by side. Each crystal structure has a second incident surface, a second exit surface, and a second connecting surface. The second incident surface is connected to the second exit surface and the second connecting surface. Each second incident surface is attached to the first exit surface of a liquid crystal cell in the variable refractive index unit.
7. The projection system according to claim 6, characterized in that, The second connection surface of each crystal structure is parallel to the first connection surface of one of the liquid crystal cells.
8. The projection system according to claim 6, characterized in that, The second connection surface of each crystal structure is attached to the first connection surface of the adjacent liquid crystal cell.
9. The projection system according to any one of claims 1-4, characterized in that, The beam deflector also includes a first electrode and a second electrode, which are used to apply an electric field to the variable refractive index unit.
10. The projection system according to claim 9, characterized in that, The projection system further includes a control unit electrically connected to the first electrode and the second electrode, so that the control unit controls the electric field intensity applied to each region of the arrayed variable refractive index units according to the brightness of each region of the image to be projected.
11. The projection system according to any one of claims 1-4, characterized in that, The light source includes a light-emitting device and a polarizer, the polarizer being used to receive the light beam emitted by the light-emitting device and output the radiation-polarized illumination beam.
12. The projection system according to any one of claims 1-4, characterized in that, The projection system also includes a display lens located in the optical path of the illumination beam emitted from the beam deflector.
13. The projection system according to claim 12, characterized in that, The display lens includes an objective lens and an eyepiece spaced apart, and the illumination beam is transmitted sequentially through the objective lens and the eyepiece to the spatial light modulator.