A Bragg periodic scanning holographic imager

Abstract

The present invention relates to the field of 3D imaging, and discloses a Bragg periodic scanning holographic imager, which includes an imaging element, at least one galvanometer, an imaging lens group, and a depth-of-field scanning mechanism respectively arranged inside the holographic imager. The imaging element is used to provide a plurality of non-coincident or parallel first equivalent image planes; the position of the galvanometer corresponds to the first equivalent image plane, and is used to optically convert the plurality of first equivalent image planes into a plurality of second equivalent image planes; the imaging lens group is used for optical imaging and forms a plurality of two-dimensional sections; the depth-of-field scanning mechanism is connected to the galvanometer and is used to control the spatial position change of the galvanometer to realize volume scanning of the two-dimensional sections. By introducing the depth-of-field scanning mechanism and a plurality of galvanometers, the present invention realizes periodic volume scanning (Bragg periodic scanning) of the projection screen, greatly reduces the amplitude of volume scanning, increases the scanning frequency, and can stably realize the 3D imaging / projection display function with ultra-high resolution and ultra-fast frame rate.

Description

Technical Field

[0001] The present invention relates to the field of 3D imaging, and more particularly to a Bragg-period scanning holographic imager. Background Art

[0002] 3D display technology can provide additional depth information on the basis of traditional 2D displays, so it is considered the development direction of the next-generation display technology. However, there is currently no relatively effective solution for realizing 3D display. Most commercially successful cases are pseudo-3D technologies based on stereoscopic image pairs, which cannot provide users with a truly 3D picture with depth information. For example, in a 3D movie in a cinema, the principle is to project two 2D left and right eye image pairs on the screen using a projector. By wearing selective filtering glasses, the two eyes receive different pictures, thus creating an illusion of seeing a 3D picture. In fact, the projected picture is only a 2D picture. Prolonged viewing can also cause eye discomfort.

[0003] Using the volume scanning imaging method can achieve a true 3D effect, which is a very promising 3D solution. However, volume scanning imaging 3D often requires a high-speed rotating / moving screen, and the system has relatively large potential safety hazards, poor stability, a very limited display space, cannot be directly touched and interacted with, the display picture is transparent, and the correct occlusion relationship cannot be expressed.

[0004] Patents with authorization numbers CN106773469B, CN 207114903 U, and CN 206431409 U disclose a solution that can achieve true 3D display. Its key component is a stereoscopic display module, which can reproduce a true 3D picture through depth-of-field scanning. Its working principle is to reciprocally scan a focal plane in the depth direction (depth-of-field scanning) to form a continuous 3D picture. In this way, although a 3D picture can be projected, it relies on the scanning imaging of a single focal plane, and has extremely high requirements for the movement speed of the mechanical structure parts of the display system. The reliability of the system cannot be guaranteed, and the refresh speed of the picture and the overall brightness of the picture cannot be optimized. At the same time, it makes the operation and control system extremely complex, it is difficult to achieve stable picture display, and the manufacturing cost is extremely high. A full-solid-state holographic projector with application number 202010029144.5 achieves an effect of full-solid-state holographic display by setting multiple discrete focal planes in a projector. However, the 3D picture formed in this way is not continuous, but a slice-by-slice picture in real space, and a continuous 3D picture cannot be fully realized. At the same time, for 3D images with a relatively large depth-of-field change range, its visual performance ability cannot meet the psychological expectations of users.

[0005] To achieve 3D display, in addition to a device capable of displaying 3D images, a device capable of recording 3D videos is also required. According to the principle of reversibility of light paths, the light path used for 3D display can, conversely, be used to shoot 3D videos. Summary of the Invention

[0006] The technical problem to be solved by the present invention lies in: aiming at the deficiencies of the above-mentioned existing technologies, providing a Bragg-period scanning holographic imager, which realizes periodic volume scanning (Bragg-period scanning) of the projection image by introducing a depth-of-focus scanning mechanism and multiple galvanometric mirrors, greatly reducing the amplitude of volume scanning, increasing the scanning frequency, and stably realizing the 3D imaging / projection display function with ultra-high resolution and ultra-fast frame rate.

[0007] To solve the above technical problem, the present invention proposes a Bragg-period scanning holographic imager, including:

[0008] An imaging element for providing multiple non-coincident or parallel first equivalent image planes;

[0009] At least one galvanometric mirror, positioned corresponding to the first equivalent image plane, for optically converting the multiple first equivalent image planes into multiple second equivalent image planes, the number of both the first equivalent image planes and the second equivalent image planes being n;

[0010] An imaging lens group, positioned corresponding to the second equivalent image plane, for optical imaging and forming multiple two-dimensional sections; and

[0011] A depth-of-focus scanning mechanism, connected to the galvanometric mirror, for controlling the spatial position change of the galvanometric mirror to achieve volume scanning of the two-dimensional sections.

[0012] Further, the depth-of-focus scanning mechanism is also respectively connected to the imaging element and / or the imaging lens group for controlling the spatial position change of the imaging element and / or the imaging lens group to achieve volume scanning of the two-dimensional sections.

[0013] Further, the depth-of-focus scanning mechanism is also connected to the imaging lens group for controlling the effective focal length of the imaging lens group to achieve volume scanning of the two-dimensional sections.

[0014] Further, the imaging lens group includes at least a liquid zoom lens or a flexible zoom lens.

[0015] Further, the amplitude of a single second equivalent image plane in the depth-of-focus direction is L1 mm, and the depth of distribution of the multiple second equivalent image planes along the depth-of-focus direction is L2 mm, satisfying L1 < L2.

[0016] Further, the mass of the imaging element is M g, and it satisfies the following relationship with the number n of the first equivalent image planes:

[0017] Further, the number of galvanometers is N, and the mass of any one of the galvanometers is M N g, the amplitude is A mm, and the mass of the outermost lens of the holographic imager is mg, satisfying:

[0018] Further, the scanning frequency or equivalent frequency of the depth of focus scanning mechanism is greater than

[0019] Further, the imaging element is a projection display element or a photographing light-sensitive element.

[0020] Further, a plurality of projection display chips and photographing light-sensitive chips are simultaneously provided in the imaging element to realize the dual functions of projection and photographing.

[0021] Further, a plurality of projection display chips are provided in the imaging element, and all the projection display chips can be replaced with photographing light-sensitive chips to realize the photographing function.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] 1. The present invention can realize a completely continuous 3D scene reproduction, which is a holographic display in the true sense;

[0024] 2. During the working process of the present invention, only a small amplitude (Bragg period scanning) scanning is required to realize continuous full-scene reproduction. Compared with the conventional volume scanning 3D method, the reliability is guaranteed, and at the same time, the refresh rate can be increased by more than one order of magnitude, greatly improving the user viewing experience; there is no safety hazard, and the touch operation of the 3D picture can be realized, and the occlusion relationship can be correctly represented;

[0025] 3. When the present invention is applied, the eyes need to perform dynamic adjustment of the depth of focus like viewing real objects, rather than the fixed depth of focus of ordinary 2D display pictures, so visual fatigue will not be caused, which is helpful for protecting eyesight.

[0026] 4. The present invention can simultaneously realize the functions of projection and photographing, which is convenient for simultaneously outputting picture information and receiving external image information during actual application. For example, user interaction actions and expression information can be recognized while displaying. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure 1 Schematic diagram of the imager of the present invention where the imaging element 1 is a projection display element and the system of Example 1

[0029] Figure 2 is based on Figure 1 and is a schematic diagram of the system of the imager of the present invention in which the projection display element is replaced with a photosensitive element for shooting

[0030] Figure 3 Schematic diagram of the system of Example 2

[0031] Figure 4 Schematic diagram of the system of Example 3

[0032] Figure 5 Schematic diagram of the system of Example 4

[0033] Figure 6 Schematic diagram of the state of one vibration period of the second equivalent image plane 4

[0034] Figure 7 Schematic diagram of the principle of mechanical zoom of the imaging lens group 5

[0035] Figure 8 Schematic diagram of the zoom principle of the imaging lens group 5 using a flexible zoom lens

[0036] Figure 9 Schematic diagram of the amplitude correspondence relationship between the galvanometer mirror 3 and the two-dimensional imaging element 1 when the galvanometer mirror 3 is at a 45° angle to the two-dimensional imaging element 1

[0037] Figure 10 Schematic diagram of the system of the imager of the present invention when the number of galvanometer mirrors 3 is two

[0038] The reference signs are as follows:

[0039] Imaging element 1, first equivalent image plane 2, galvanometer mirror 3, second equivalent image plane 4, imaging lens group 5, two-dimensional section 6, depth-of-field scanning mechanism 7 Detailed implementation manners

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not have any limiting effect on the protection scope of the present invention

[0041] Referring to Figures 1 to 10 , the present invention provides a Bragg period scanning holographic imager, which internally includes an imaging element 1, at least one galvanometer mirror 3, an imaging lens group 5, and a depth-of-field scanning mechanism 7

[0042] The imaging element 1 is used to provide a plurality of non - overlapping or parallel first equivalent image planes 2. The number of the first equivalent image planes 2 is n. The first equivalent image plane 2 can be a real physical one, or a virtual image plane or a real image plane obtained through optical conversion, etc. The specific implementation method is described in detail in a fully solid - state holographic projector with the application number 202010029144.5, and will not be elaborated here;

[0043] The position of the galvanometer 3 corresponds to the position of the first equivalent image plane 2, and is used to optically convert the plurality of first equivalent image planes 2 into a plurality of second equivalent image planes 4. The second equivalent image plane 4 is a virtual image plane or a real image plane obtained through optical conversion, etc. The number of the first equivalent image planes 2 and the second equivalent image planes 4 is equal, both being n;

[0044] The position of the imaging lens group 5 corresponds to the second equivalent image plane 4, and is used for optical imaging and forming a plurality of two - dimensional sections 6;

[0045] The depth - of - field scanning mechanism 7 is connected to the galvanometer 3, and is used to control the spatial position change of the galvanometer 3 to realize volume scanning of the two - dimensional section 6. Preferably, reciprocating motion back and forth is used to realize volume scanning;

[0046] This kind of scanning is equivalent to the depth - of - field scanning of a 3D image, and can scan out an imaging space, in which an array of denser two - dimensional sections 6 or a continuous 3D image is formed. The present invention preferably realizes periodic volume scanning by controlling the periodic position change of each component.

[0047] Since each two - dimensional section 6 is covered with a pixel array (two - dimensional), a three - dimensional pixel array can be formed after volume scanning. The advantage of this structure with the galvanometer 3 is that as long as scanning is carried out within a very small range, a relatively larger equivalent scanning space can be achieved, and after optical conversion, the equivalent scanning space can be further enlarged. For example, the movement range of the second equivalent image plane 4 is the equivalent scanning range (that is, 2 times the area of the second equivalent image plane 4 multiplied by the scanning amplitude in its vertical direction, which can be denoted as V 等效 )), while the actual scanning movement range is the movement range of the galvanometer 3 (that is, 2 times the area of the galvanometer 3 multiplied by the scanning amplitude in its vertical direction, which can be denoted as V 扫描 ). The ratio of the two is preferably set to be greater than 1.2 (a specific magnification setting mode can be achieved through optical geometric relationships, which will not be elaborated here), so as to achieve the purpose of primary magnification, and the optical conversion of the imaging lens group 5 can further enlarge the equivalent scanning range. For example, a lens with a magnification greater than 5 is selected to further enlarge the imaging space to more than 5 3 times.

[0048] Another advantage of this scanning system is that key components such as the two-dimensional imaging element 1 and the imaging lens group 5 can be in a completely stationary state or a very slight moving state, making the system more reliable.

[0049] Among them, the imaging element 1 can be a projection display element or a photographic light-sensitive element:

[0050] Such as Figure 1 , when the projection display element is used as the imaging element 1, the scanning imager of the present invention is used as a holographic projector:

[0051] The light of the projection display element forms multiple two-dimensional sections 6 in space after being optically transformed by the galvanometer 3 and the imaging lens group 5, and forms an array of two-dimensional sections 6, which is equivalent to the imaging lens group 5 directly projecting the multiple first equivalent image planes 2 and second equivalent image planes 4 shown in Figure 1 and Figure 2 that are optically conjugate to the array of two-dimensional sections 6. By controlling the vibration of the galvanometer 3 through the depth of focus scanning mechanism 7, preferably with periodic changes, the relative position or the overall position between the first equivalent image plane 2 and the second equivalent image plane 4 and the imaging lens group 5 changes periodically, and the array of two-dimensional sections 6 in space also vibrates in the depth of focus direction to perform volume scanning. The previous multi-layer section type and discontinuous three-dimensional display effect forms a denser array of two-dimensional sections 6 or a continuous 3D picture after scanning, realizing a continuous 3D display effect;

[0052] Moreover, the above two-dimensional sections 6 are optically conjugate to the first equivalent image plane 2 and the second equivalent image plane 4 respectively. Therefore, when performing volume scanning on the two-dimensional sections 6, the first equivalent image plane 2 and the second equivalent image plane 4 are also performing volume scanning at the same time. The above two-dimensional sections 6 are real image planes after optical transformation, and the first equivalent image plane 2 and the second equivalent image plane 4 are virtual image planes obtained through optical transformation;

[0053] Such as Figure 2 , when the photographic light-sensitive element is used as the imaging element 1, the scanning imager of the present invention is used as a holographic camera:

[0054] Similar to the above projection process, according to the principle of reversibility of light paths, the light of the external scene forms multiple real image two-dimensional sections 6 on the photographic light-sensitive element after being optically transformed by the galvanometer 3 and the imaging lens group 5 and is recorded, which is equivalent to the effect of directly generating multiple first equivalent image planes 2 and second equivalent image planes 4 shown in Figure 2 that are optically conjugate to the external scene after the light of the external scene is optically imaged by the imaging lens group 5;

[0055] This is very similar to the working principle of an ordinary camera. The difference is that an ordinary camera has only one photosensitive chip and can only record the scene information at the optically conjugate position corresponding to it. However, the photosensitive element of the present invention contains multiple photosensitive chips, so it can record multiple images simultaneously, and each image corresponds to the scene at a different depth of field, achieving a slice-like 3D shooting record. By controlling the spatial position change of the photosensitive element and / or the imaging lens group 5 through the depth-of-field scanning mechanism 7, preferably a periodic change, the relative position or the overall position between the first equivalent image plane 2 and the second equivalent image plane 4 and the imaging lens group 5 changes periodically. Correspondingly, the depth-of-field space optically conjugate to the photosensitive chip, the first equivalent image plane, and the second equivalent image plane 4 also undergoes a periodic scan, so that the information at different depths of the scene is recorded separately, thereby recording a complete and continuous 3D scene and achieving the purpose of 3D shooting. According to the reversibility of the optical path, during the process of the depth-of-field space optically conjugate to the second equivalent image plane 4 undergoing a periodic scan, the second equivalent image plane 4 undergoes a corresponding periodic scan. And the above-mentioned second equivalent image plane 4 and the two-dimensional section 6 are in an equivalent relationship, so the scan of the second equivalent image plane 4 can be equivalent to the scan of the two-dimensional section 6. The above two-dimensional section 6 is the real image plane after optical conversion, and the first equivalent image plane 2 and the second equivalent image plane 4 are virtual image planes obtained through optical conversion.

[0056] The present invention controls the spatial position change of the galvanometer mirror 3 through the provided depth-of-field scanning mechanism 7, so that the relative position between the second equivalent image plane 4 corresponding to the first equivalent image plane 2 and the imaging lens group 5 changes, preferably a periodic change, to achieve a volumetric scan of the two-dimensional section 6. For example, by mechanically causing the galvanometer mirror 3 to perform a periodic reciprocating scanning motion in space, a continuous space can be swept out in space. In practical applications, it can reciprocate at a fixed frequency or scan at different frequencies according to the needs of the displayed content. Among them, the design of the scanning mechanism belongs to the common knowledge in the art, and the specific implementation method can be designed according to the actual situation and will not be elaborated here.

[0057] It is also possible to further control the periodic change of the effective focal length of the imaging lens group 5 through the depth-of-field scanning mechanism 7, which can also achieve a volumetric scan of the two-dimensional section 6. The periodic change of the effective focal length of the imaging lens group 5 can be achieved by changing the relative position and / or the overall position of the optical elements in the imaging lens group 5 (mechanical zoom), or by setting a liquid zoom lens and / or a flexible zoom lens with a zoom function in the imaging lens group 5;

[0058] Furthermore, the depth-of-field scanning mechanism 7 can also be connected to the two-dimensional imaging element 1 and / or the imaging lens group 5 respectively, for controlling the spatial position change of the two-dimensional imaging element 1 and / or the imaging lens group 5, achieving a volumetric scan of the two-dimensional section 6, and can also achieve the above-mentioned 3D imaging effect.

[0059] In addition to performing simple one-dimensional depth-of-field scanning, the display effect can be further enhanced by means of three-dimensional scanning. For example, adding scanning parallel to the equivalent image plane can further increase the horizontal resolution and make the image quality more delicate.

[0060] The design of the scanning mechanism is a general knowledge in the field and can be designed according to the actual application scenario, so it will not be elaborated here.

[0061] The following takes the holographic imager of the present invention that only includes one galvanometer 3, the imaging element 1 as the projection display element, and the number n = 3 of the first equivalent image planes 2 as an example to further illustrate the present invention:

[0062] Example 1

[0063] As Figure 1 , the Bragg period scanning holographic imager includes a projection display element, a galvanometer 3, an imaging lens group 5, and a depth-of-field scanning mechanism 7 respectively arranged inside. The depth-of-field scanning mechanism 7 is connected to the galvanometer 3 and controls the reciprocating scanning (or periodic change) of the spatial position of the galvanometer 3 back and forth, so that the relative positions between the first equivalent image plane 2 provided by the projection display element and the second equivalent image plane 4 optically converted by the galvanometer 3 and the imaging lens group 5 change periodically. The two-dimensional section 6 optically conjugated to the second equivalent image plane 4 changes periodically in the depth-of-field direction accordingly, realizing the reciprocating scanning of the two-dimensional section 6 back and forth, thereby presenting a continuous 3D picture.

[0064] Example 2

[0065] As Figure 3 , the Bragg period scanning holographic imager includes a projection display element, a galvanometer 3, an imaging lens group 5, and a depth-of-field scanning mechanism 7 respectively arranged inside. The depth-of-field scanning mechanism 7 is respectively connected to the imaging element 1 and the galvanometer 3 and controls the periodic changes of their spatial positions, so that the relative positions between the first equivalent image plane 2 provided by the projection display element and the second equivalent image plane 4 optically converted by the galvanometer 3 and the imaging lens group 5 change periodically. The two-dimensional section 6 optically conjugated to the second equivalent image plane 4 changes periodically in the depth-of-field direction accordingly, realizing the reciprocating scanning of the two-dimensional section 6 back and forth, thereby presenting a continuous 3D picture.

[0066] Example 3

[0067] As Figure 4, The Bragg periodic scanning holographic imager includes a projection display element, a galvanometer 3, an imaging lens group 5, and a depth of focus scanning mechanism 7 disposed inside respectively. The depth of focus scanning mechanism 7 is connected to the galvanometer 3 and the imaging lens group 5 respectively and controls the periodic changes in their spatial positions, so that the relative positions between the first equivalent image plane 2 provided by the projection display element and the second equivalent image plane 4 after optical conversion by the galvanometer 3 and the imaging lens group 5 change periodically. The two-dimensional section 6 optically conjugated to the second equivalent image plane 4 then changes periodically in the depth of focus direction, realizing the reciprocating scanning of the two-dimensional section 6 back and forth, thereby presenting a continuous 3D image.

[0068] Embodiment 4

[0069] As Figure 5 , The Bragg periodic scanning holographic imager includes a projection display element, a galvanometer 3, an imaging lens group 5, and a depth of focus scanning mechanism 7 disposed inside respectively. The depth of focus scanning mechanism 7 is connected to the projection display element, the galvanometer 3, and the imaging lens group 5 respectively and controls the periodic changes in their spatial positions, so that the relative positions between the first equivalent image plane 2 provided by the projection display element and the second equivalent image plane 4 after optical conversion by the galvanometer 3 and the imaging lens group 5 change periodically. The two-dimensional section 6 optically conjugated to the second equivalent image plane 4 then changes periodically in the depth of focus direction, realizing the reciprocating scanning of the two-dimensional section 6 back and forth, thereby presenting a continuous 3D image.

[0070] Embodiment 5

[0071] The Bragg periodic scanning holographic imager includes a projection display element, a galvanometer 3, an imaging lens group 5, and a depth of focus scanning mechanism 7 disposed inside respectively. The depth of focus scanning mechanism 7 is connected to the galvanometer 3 and the imaging lens group 5 respectively and controls the periodic changes in the spatial position of the galvanometer 3 and the effective focal depth of the imaging lens group 5, so that the relative positions between the first equivalent image plane 2 provided by the projection display element and the second equivalent image plane 4 after optical conversion by the galvanometer 3 and the imaging lens group 5 change periodically. The two-dimensional section 6 optically conjugated to the second equivalent image plane 4 then changes periodically in the depth of focus direction, realizing the reciprocating scanning of the two-dimensional section 6 back and forth, thereby presenting a continuous 3D image.

[0072] In Embodiment 5, the depth of focus scanning mechanism 7 can control the effective focal depth of the imaging lens group 5 in the following way:

[0073] As Figure 7 , The depth of focus scanning mechanism 7 controls the relative positions and / or the overall positions of a plurality of optical elements provided inside the imaging lens group 5 to change (mechanical zoom), realizing the control of the periodic change of the effective focal length of the imaging lens group 5;

[0074] A flexible zoom lens with a zoom function can also be provided in the imaging lens group 5, and the focal length of the flexible zoom lens is controlled by the focal depth scanning mechanism 7 to realize the control of the periodic variation of the effective focal length of the imaging lens group 5. The principle of the flexible zoom lens is as Figure 8 shown. The flexible zoom lens can also be replaced by other lenses with a zoom function, such as a liquid zoom lens, etc.;

[0075] Of course, the imaging lens group 5 in Embodiment 3 and Embodiment 4 can also be added with a zoom function and uniformly regulated by the focal depth scanning mechanism 7 to realize the reciprocating scanning of the two-dimensional section 6 back and forth. In addition, the number of galvanometers 3 can also be multiple, Figure 10 which is the case where the number of galvanometers 3 is 2.

[0076] Embodiments 1 to 5 respectively reflect different implementation methods of the reciprocating scanning of the two-dimensional section 6 back and forth, and finally achieve a continuous 3D display effect.

[0077] In the actual application of the present invention, when the focal depth scanning mechanism 7 operates to perform a volume scan on the two-dimensional section 6, the first equivalent image plane 2 and the second equivalent image plane 4 that are optically conjugate to the two-dimensional section 6 are also performing volume scans simultaneously;

[0078] The vibration controlled by the focal depth scanning mechanism 7 has a linear correspondence with the scans of the first equivalent image plane 2 and the second equivalent image plane 4. However, based on the lens imaging law, the scans of the two-dimensional section 6 in the focal depth direction and the scans of the first equivalent image plane 2 and the second equivalent image plane 4 are not linearly corresponding. Therefore, it is more convenient to design the relevant design parameters with reference to the first equivalent image plane 2 or the second equivalent image plane 4:

[0079] Such as Figure 6 , the amplitude of the second equivalent image plane 4 in the focal depth direction (i.e., the maximum displacement of the second equivalent image plane 4 deviating from the equilibrium position in the focal depth direction) is L1 mm. The equilibrium position of the above-mentioned second equivalent image plane 4 is the midpoint between the two points of the amplitude point in the focal depth direction and the amplitude point in the opposite direction of the focal depth of the second equivalent image plane 4. And the amplitude points of the second equivalent image plane 4 are as Figure 6 shown: The maximum displacement position of the second equivalent image plane 4 along the focal depth direction is defined as the amplitude point in the focal depth direction, and the maximum displacement position along the opposite direction of the focal depth is defined as the amplitude point in the opposite direction of the focal depth;

[0080] Due to the presence of the galvanometer 3, there should be a geometric correspondence between the amplitude L1 of the second equivalent image plane 4 after optical conversion by the galvanometer 3 and the amplitude in the vertical direction of the galvanometer 3. The amplitude in the vertical direction of the galvanometer 3 is A mm. It should be noted that the above-mentioned amplitude A in the vertical direction of the galvanometer 3 should be interpreted as the maximum displacement of the galvanometer 3 deviating from the equilibrium position of the galvanometer 3 in the direction perpendicular to its own direction during the vibration of the galvanometer 3, and the equilibrium position of the galvanometer 3 is the midpoint position of the maximum displacements in the forward and reverse directions of the vibration of the galvanometer 3;

[0081] The amplitude of the galvanometer mirror 3 in the vertical direction is A, which is associated with the angle between the galvanometer mirror 3 and the two-dimensional imaging element 1. Taking the angle between the galvanometer mirror 3 and the imaging element 1 as 45° as an example, the following is an illustration:

[0082] As Figure 9 shown, the number of galvanometer mirrors 3 is 1, the amplitude is A mm, and the scanning amplitude L1 of the second equivalent image plane 4 is 2√2A mm;

[0083] When the number of galvanometer mirrors 3 is 2 and they are arranged in parallel with the same vibration frequency and the amplitude is also A mm, then the amplitude L1 of the second equivalent image plane 4 is 4√2A mm;

[0084] When the number of galvanometer mirrors 3 is 3 and they are arranged in parallel with the same vibration frequency and the amplitude is also A mm, then the amplitude L1 of the second equivalent image plane 4 is 6√2A mm;

[0085] And so on, when the number of galvanometer mirrors 3 is N and they are arranged in parallel with the same frequency and the amplitude is also A mm, then the amplitude L1 of the second equivalent image plane 4 is 2√2N*A mm;

[0086] In actual application, when the number of galvanometer mirrors 3 is multiple and they are not arranged in parallel, the amplitude L1 of the second equivalent image plane 4 along the depth of focus direction can be obtained through geometric operations;

[0087] The depth of distribution of multiple second equivalent image planes 4 along the depth of focus, that is, the central distance between the second equivalent image plane 4 closest to the imaging lens group 5 and the second equivalent image plane 4 farthest from the imaging lens group 5 is L2 mm, and the amplitude L1 of the second equivalent image plane 4 along the depth of focus should satisfy L1 < L2. Only in this way can the scanning amplitude be relatively smaller.

[0088] Considering that as long as the gap between adjacent second equivalent image planes 4 can be completely scanned through the scanning action, a continuous 3D picture space can be realized. Therefore, as long as the scanning amplitude is greater than the maximum distance between adjacent second equivalent image planes 4, the scanning of a complete continuous space can be realized. Therefore, in design, it can be preferably selected: Within this design parameter range, on the premise of making the amplitude very small, it is still possible to ensure finding appropriate design parameters so that the second equivalent image plane 4 can sweep out a complete continuous space in the space (in fact, there is a certain overlap in the space swept by adjacent second equivalent image planes 4, completely avoiding the problem of discontinuous longitudinal depth of field, and at the same time leaving enough design margin to allow a part of a scanning cycle to be used to update the display screen during design, increasing design flexibility), and the scanning amplitude can be reduced to a very small value.

[0089] In actual application, in order to show a more delicate picture effect, the scanning amplitude can be made larger, or for scenarios with low requirements for depth resolution, it can also be smaller.

[0090] In actual application, the scanning frequency or the equivalent frequency of the depth of focus scanning mechanism 7 is preferably greater than The frequency here refers to the reciprocal of the time interval for the moving part to pass through a certain spatial point twice in the same direction continuously. For example, during the reciprocating scanning of the imaging element 1, it is the reciprocal of the time for passing through the equilibrium position twice in the same direction continuously. In addition, for the case of zooming for scanning, it can be equivalent to the reciprocal of the time for the focal length of the imaging lens group 5 to change back to the same focal length from the initial focal length. The initial focal length refers to the focal length of the imaging lens group 5 when the depth of focus scanning mechanism 7 is not operating. Of course, it can also be obtained by measuring the reciprocal of the time interval for the projection focal plane to sweep across a certain position in space twice in the same direction continuously.

[0091] When displaying a 3D image within a certain space, it is necessary to make the focal plane scan back and forth within a certain space to complete the update of the full-space image. Therefore, the frame frequency of the 3D image is the depth of focus scanning frequency.

[0092] In addition, there is a special case, that is, when the display space undergoes overall movement, such as the process of moving from a close view to a distant view. During the switching process, the depth of focus usually only requires one-way movement without reciprocating scanning. Then there is no concept of depth of focus scanning at this time. However, the switching process of the display depth of focus also needs to be completed at a relatively appropriate speed, otherwise, problems such as image jitter or trailing are likely to occur. For this situation, we introduce the concept of equivalent frequency: The equivalent frequency refers to the reciprocal of the time used during the process when the equivalent image plane moves one-way relative to the imaging lens group 5 and the moving distance is equal to the maximum adjacent distance between adjacent second equivalent image planes 4.

[0093] For the case of zooming for scanning, the reciprocal of the time for the equivalent focal length to change back to the same focal length from the initial focal length (or the reciprocal of the time interval for changing back to the maximum focal length from the maximum focal length) can be used. The initial focal length refers to the focal length of the imaging lens group 5 when the depth of focus scanning mechanism 7 is not operating. Of course, it can also be obtained by measuring the reciprocal of the time interval for the projection focal plane to sweep across a certain position in space twice along the same direction continuously.

[0094] In actual application, it is found that the larger the number n of the first equivalent image plane 2 and the second equivalent image plane 4, the denser the two-dimensional cross-sections will be. In general display situations, a relatively good stereoscopic display effect can basically be presented. Therefore, only when there is a large change in the overall depth of field of the displayed content, it is necessary to re-match the depth of field of the display space through the depth-of-focus scanning operation. For example, when the displayed content of a movie scene changes from an indoor scene to an open outdoor scene or an outer space galaxy scene, at this time, the depth of field of the display changes significantly. Usually, such a large depth-of-field difference scene switch is usually completed within multiple frames of images, and the conversion process is relatively slow. Therefore, only if the display system can achieve a relatively slow depth-of-field switch is sufficient. So the scanning frequency (equivalent frequency) can be much lower than the frame rate of 3D video. This can also greatly reduce the requirements for the computing and control systems, making the system more stable;

[0095] However, on the other hand, the larger n is, the greater the total mass of the corresponding components will be, and the natural frequency of the system will decrease. In this way, it is relatively difficult to achieve a high scanning frequency. Therefore, it is necessary to lower the lower limit of the scanning frequency to protect the reliability of the system.

[0096] Usually, the display screen is within a relatively small range, such as an indoor scene. At this time, the projection space of the equivalent image plane may completely meet the display requirements of this small space range. At this time, even if the depth-of-focus scanning operation is not performed, the 3D scene can be relatively realistically restored. Or, in order to make the display effect more delicate, only a very small amplitude of scanning is required.

[0097] Only when the change range of the display depth of field is large, or when the overall depth of field changes significantly, the depth-of-focus scanning needs to perform a large amplitude of scanning or overall translation.

[0098] It should be noted that in many cases, the depth-of-field switch does not need to complete a full scanning cycle.

[0099] For example, when the scene of the screen slowly switches from a close-up to a long-shot and then stays at the long-shot for a period of time, then the depth-of-focus scanning only needs to adjust the depth of field of the screen accordingly. At this time, the concept of equivalent frequency can be used.

[0100] The following are the feedback situations of several users during actual tests:

[0101]

[0102] Judging from the data, for application scenarios with general requirements not being particularly high, the scanning frequency (or equivalent frequency) is preferably greater than When this value is reached, the comprehensive score of users is higher than 60, which can meet the needs of general users;

[0103] Of course, in order to further improve the 3D display effect and increase the comprehensive performance score, for some special application scenarios, it is preferable to have n≥2, and the scanning frequency

[0104] For some users who pursue the ultimate experience, it is preferable to have n≥3, and the scanning frequency

[0105] Generally, the depth resolution of the human eye is much lower than the horizontal resolution. Therefore, even if the pixel pitch in the depth direction is relatively large, it will not cause resolution distortion. Thus, the pixel pitch in the depth direction of the projection screen can be set larger, so that a very realistic 3D image can be projected while effectively reducing the device and process costs.

[0106] In addition, the mass Mg of the imaging element 1 and the number n of the first equivalent image planes 2 satisfy Among them, the mass M of the imaging element 1 refers to the mass of the remaining part after removing the imaging lens group, support mechanism, wiring harness and other auxiliary components in the holographic imager.

[0107] Here, a holographic projector is taken as an example for illustration. Generally, the main application field of a holographic projector is a geometric holographic display system (refer to the patent document with the application number 201910875975.1). In such a system, the holographic projector often needs to be in a motion state. Therefore, its mass cannot be too large. Otherwise, controlling the motion of a component with too large a mass will have a very large inertia due to the mass, resulting in extremely difficult operation and extremely high energy consumption. On the other hand, it will cause a great burden on the support structure, and the whole system will be very bulky and impractical. Therefore, its mass needs to be reasonably designed. Ideally, the smaller the overall mass, the better. However, the first equivalent image plane 2 must rely on a physical entity to exist. Thus, the larger the number of the first equivalent image planes 2, the larger the overall mass will be. If you want to design a holographic projector as light as possible, then the number of the first equivalent image planes 2 must be sacrificed. If you want to obtain denser first equivalent image planes 2, you have to accept the increase in mass. The two cannot reach the optimal state at the same time. The present invention gives a design criterion for weighing the relationship between the two, that is

[0108] This design relationship indirectly limits the size of the total mass and gives the upper limit boundary of the holographic projector in the case of different numbers of the first equivalent image planes 2. When exceeding this upper limit boundary, the practicality of the manufactured holographic projector will be very poor. For example, for living room display, using 11 first equivalent image planes 2 for depth of field performance can achieve a very perfect display effect. And the maximum mass of moving objects in the living room should not exceed 5000g. Otherwise, on the one hand, there may be potential safety hazards to personnel, and on the other hand, the support structure will be very bulky, occupy a large amount of space, and be not very beautiful. For this boundary situation As the design upper limit. In actual tests, it was also found that the vast majority of families are not willing to accept products that exceed this design boundary.

[0109] In addition, for desktop office scenarios, when designing, it is preferable to select more stringent design specifications as much as possible. At this time, the overall structure and display performance are more ideal. The actual measurement results show that users generally rate products that meet the design rules higher than 60 points.

[0110] Furthermore, it is preferable to At this time, the entire system is more compact, flexible, and beautiful. The actual measurement results show that users generally rate products that meet the design rules higher than 70 points.

[0111] Furthermore, it is preferable to At this time, it is equivalent to further tightening the design boundary. The system is not only compact, but also some appearance design elements can be added to make the customer attraction of the system stronger. The actual measurement results show that users generally rate products that meet the design rules higher than 90 points.

[0112] In addition, in order to pursue the optimal comprehensive display effect, fine design of each component is required.

[0113] On the one hand, it is necessary to improve the large-angle display ability, so the area of the galvanometer 3 should be as large as possible, so as to better utilize the effective optical area of the lens. On the other hand, it is also necessary to ensure excellent depth-of-field detail performance as much as possible, that is, it is necessary to increase the system scanning frequency. For a mechanical scanning system, the best configuration for scanning is to use its natural frequency for scanning, and usually there is a negative correlation between the natural frequency of the mechanical system and the mass of the vibrating components. Therefore, the mass of the lens needs to be made smaller, and correspondingly its area will also be smaller. In addition, for a product, improving the stability of the system is also very important. The smaller the amplitude of vibration during scanning, the closer the system is to a solid state and the better the stability. However, if the amplitude is too small, the depth-of-field performance range will be restricted, and it is difficult to achieve the performance of a very large depth of field. In addition, if the mass and amplitude of the moving parts are relatively large, the recoil effect on the system will be obvious, and situations such as image jitter are likely to occur.

[0114] In summary, for this new solution, it is necessary to simultaneously consider three mutually contradictory indicators: effective optical utilization area, scanning frequency, and scanning amplitude. And the three cannot reach the optimal design at the same time, and certain trade-offs and optimizations are required to obtain a relatively excellent comprehensive performance.

[0115] Since there was no design experience to draw on before, although the imaging principle is relatively easy to understand, it is still quite difficult to actually design a product with excellent performance. Therefore, the present invention provides an easily implemented guiding design rule to help ordinary practitioners in the field design products with excellent performance.

[0116] Generally, for a specific lens imaging application scenario, the thickness range of the main lens is very narrow. For example, in a single-lens reflex camera, the thickness (central thickness) of the outermost lens is generally between 1 and 5 mm. Without considering some extremely special cases in actual situations, this range will be even narrower, which is mainly restricted by the design rules of imaging lenses. Therefore, the quality of imaging lenses often mainly depends on the size of their apertures. In order to match the imaging lens, the area of the galvanometer 3 also needs to be within a suitable range. In addition, the problem of mirror surface deformation caused by vibration during scanning also needs to be considered, that is, the stiffness problem of the lens. That is, for a galvanometer 3 with a specific area, its thickness needs to be designed to ensure sufficient stiffness. Therefore, the volume of the scanning mirror is also determined within a very small range. Usually, the density difference of the lens materials is relatively small, so its mass can also be further determined within a reasonable range.

[0117] Through the above theoretical analysis to balance the performance of all aspects and combined with experimental assembly and testing, the present invention determines the parameter design space that can better show the depth-of-field detail effect on the premise of ensuring a certain viewing angle (since the design of this system is mainly aimed at the 3D imaging field, the depth-of-field performance ability needs to be prioritized during the design process). The mass of any one of the galvanometers 3 is M N g, the amplitude is A mm, and the mass of the outermost lens of the holographic imager is mg, satisfying:

[0118] It should be noted that for the case of using multiple galvanometers 3, the mass of the scanning lens closest to the outermost lens of the imaging lens is defined as M1g, and the masses of other scanning lenses are defined as M2g, M3g, M4g... M n g, and satisfy:

[0119] For different users, the required scenarios are different, and their requirements are also different. For game users who have relatively high requirements for the movement speed of the scenario, it is preferred In the office application scenario, users have relatively low requirements for image quality, and it is preferred For users with relatively high requirements for 3D experience, it is preferred

[0120] The following case takes the mass of the outermost lens as 80 g as an example for experimental testing, as shown in the following table:

[0121]

[0122] Although the mass of the outermost lens in the above embodiments is 80 g, when designing, the overall system can be scaled, and thus designs with other sizes and masses can be obtained. This is very similar to the situation in fluid design. As long as the Reynolds numbers of fluids are similar, their mathematical solutions will be very similar. Therefore, when large models cannot be implemented, small models with the same Reynolds number are usually used for experimental testing. In fact, we have also verified the above experimental scheme under the conditions of 50 g, 20 g, 10 g, 5 g, 2 g, etc. The user experience feedback is consistent with the feedback results in the above table, further proving the generality of the design formula.

[0123] In addition, a relatively rough but relatively effective simplified design rule can be summarized from the above implementation feedback, that is In some scenarios with less strict requirements, the simplified design rule can be directly used, and relatively perfect products can also be obtained.

[0124] Generally, the depth resolution of the human eye is much lower than the horizontal resolution. Therefore, even if the pixel pitch in the depth direction is relatively large, it will not cause resolution distortion. Thus, the pixel pitch in the depth direction of the projection screen can be set larger, so that a very realistic 3D image can be projected while effectively reducing the equipment and process costs.

[0125] A plurality of projection display chips and photographing photosensitive chips can be provided in the imaging element 1 at the same time to achieve the dual functions of projection and photographing.

[0126] It should be noted that the Bragg period scanning holographic imager of the present invention with the projection display element as the imaging element 1 is used as a holographic projector, and the Bragg period scanning holographic imager of the present invention with the photographing photosensitive element as the imaging element 1 is used as a holographic camera. The above design description is mainly for the explanation of the situation of the holographic projector. However, since the application situations of the holographic camera are very similar, based on the principle of reversibility of light paths, the problems that need to be considered by the holographic projector will also be encountered by the holographic camera. Therefore, the above design description also applies to the holographic camera.

[0127] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A Bragg periodic scanning holographic imager, characterized in that, Including those respectively arranged inside the holographic imager: An imaging element (1) for providing a plurality of non-coincident or parallel first equivalent image planes (2); At least one galvanometer (3), whose position corresponds to the first equivalent image plane (2), for optically converting the plurality of first equivalent image planes (2) into a plurality of second equivalent image planes (4), and the number of both the first equivalent image plane (2) and the second equivalent image plane (4) is n; An imaging lens group (5), whose position corresponds to the second equivalent image plane (4), for optical imaging and forming a plurality of two-dimensional sections (6); and A depth-of-field scanning mechanism (7), connected to the galvanometer (3), for controlling the spatial position change of the galvanometer (3) to realize volume scanning of the two-dimensional section (6); wherein, The amplitude of a single said second equivalent image plane (4) in the depth of focus direction is mm, and the depth of distribution of a plurality of said second equivalent image planes (4) along the depth of focus direction is mm, satisfying L1 < L2; The mass of the imaging element (1) is Mg, and it satisfies the following relationship with the number n of the first equivalent image planes (2): ; The number of the galvanometric mirrors (3) is N, and the mass of any one of the galvanometric mirrors (3) is g, the amplitude is A mm, and the mass of the outermost lens of the holographic imager is mg, satisfying: .

2. The Bragg periodic scanning holographic imager according to claim 1, characterized in that: The depth-of-field scanning mechanism (7) is also respectively connected to the imaging element (1) and / or the imaging lens group (5), for controlling the spatial position change of the imaging element (1) and / or the imaging lens group (5) to realize volume scanning of the two-dimensional section (6).

3. The Bragg periodic scanning holographic imager according to claim 1, characterized in that: The depth-of-field scanning mechanism (7) is also connected to the imaging lens group (5), for controlling the effective focal length of the imaging lens group (5) to realize volume scanning of the two-dimensional section (6).

4. The blazed periodic scanning holographic imager according to claim 3, wherein: The imaging lens group (5) at least includes a liquid zoom lens or a flexible zoom lens.

5. A Bragg periodic scanning holographic imager according to claim 1, characterized in that: The scanning frequency or equivalent frequency of the depth of focus scanning mechanism (7) is greater than Hz.

6. A Bragg periodic scanning holographic imager according to any one of claims 1 to 5, characterized in that: The imaging element (1) is a projection display element or a photographing and light-sensitive element.

7. A Bragg periodic scanning holographic imager according to any one of claims 1 to 5, characterized in that: A number of projection display chips and photographing and light-sensitive chips are simultaneously provided inside the imaging element (1) to realize the dual functions of projection and photographing.

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