Apparatus and method for manufacturing large holographic screen

Abstract

An apparatus and a method for manufacturing a large holographic screen are provided. The apparatus for manufacturing a holographic screen, according to an embodiment of the present invention, comprises: a first optical system for modulating and expanding a signal beam; an imaging lens for converging the signal beam expanded by the first optical system; a unidirectional diffuser, which scatters the converged signal beam only in the forward direction such that the scattered beam is incident on a holographic optical element surface; and a second optical system for causing a reference beam to be incident on the holographic optical element. Therefore, the unidirectional diffuser can be used as a reference optical element and combined with a photopolymer for recording without a gap, thereby enabling optical loss and an optical path to be reduced and the required time necessary for exposure to be shortened, and a large imaging lens for concentrating a signal beam can be replaced with an array-type optical element composed of small-sized lenses, thereby simplifying an apparatus and reducing manufacturing costs.

Description

Device and method for producing a large holographic screen

[0001] The present invention relates to a technology for manufacturing holographic screens, and more specifically, to an apparatus for manufacturing a large-area holographic screen capable of projecting images while possessing high transparency, which can be utilized for providing images in the form of augmented reality and as a transparent projection screen.

[0002] A holographic optical element (HOE) can be fabricated by patterning the mutual interference pattern between a reference beam and a signal beam onto a holographic recording medium, such as a photopolymer. The recorded interference pattern forms a volume grid that repeats periodically within the holographic recording medium; subsequently, during the playback stage, if the incoming projected beam satisfies the Bragg condition of the volume grid, it outputs a diffracted beam through a diffraction phenomenon. Leveraging its advantages of high transparency and thin medium structure, this element is highly suitable for use as a transparent screen.

[0003] However, due to the bidirectional scattering of the diffuser, which is a reference optical element, a separation distance between the diffuser and the photopolymer is required during holographic screen optical recording, which unnecessarily increases the size of the recording setup and causes optical loss.

[0004] In addition, large-area optical recording requires large-aperture imaging lenses for collimating or focusing laser light; however, there are difficulties in manufacturing large holographic screens due to the physical limitations of actually implementable large-aperture lenses and cost issues.

[0005] The present invention has been devised to solve the above-mentioned problems, and the objective of the present invention is to provide a large holographic screen manufacturing apparatus capable of recording by aligning a unidirectional diffuser with a photopolymer without separation, as a method to reduce light loss and optical path and shorten the required exposure time when manufacturing a large holographic screen using a holographic optical element.

[0006] Another objective of the present invention is to provide a large holographic screen manufacturing device in which a large imaging lens for light concentration is replaced with an array-type optical element as a means to simplify the system and reduce manufacturing costs.

[0007] A holographic screen manufacturing device according to one embodiment of the present invention for achieving the above objective comprises: a light source; a beam splitter that splits a beam emitted from the light source into a signal beam and a reference beam; a first optical system that modulates and expands the split signal beam; an imaging lens that converges the signal beam expanded by the first optical system; a unidirectional diffuser that scatters the converged signal beam only forward and causes the scattered beam to be incident on the surface of a holographic optical element; and a second optical system that causes the split reference beam to be incident on the holographic optical element.

[0008] A unidirectional diffuser can be combined with a holographic optical element without separation.

[0009] A unidirectional diffuser consists of arrays of micro-lenses arranged in a line, which can scatter a signal beam only forward.

[0010] The spacing between microlens arrays can be smaller than the size of the microlens.

[0011] The imaging lens can focus the signal beam at an observation position separated by a predetermined distance from the holographic optical element.

[0012] The fixed distance (c) is,

[0013]

[0014] It is determined through the above formula,

[0015] a is the distance from the exit surface of the first optical system to the imaging lens, and

[0016] b is the distance from the imaging lens to the unidirectional diffuser, and

[0017] f can be the focal length of the imaging lens.

[0018] The first optical system divides and expands a signal beam into multiple parts, and the imaging lens may be an imaging lens array comprising multiple imaging lenses that converge each of the divided multiple signal beams.

[0019] The first optical system can split the signal beam into multiple parts by splitting the optical fiber receiving the signal beam into multiple optical fibers using a splitter.

[0020] The second optical system can split the reference beam into multiple optical fibers by splitting the optical fiber receiving the reference beam into multiple reference beams and causing each reference beam to be incident on different regions of the holographic optical element.

[0021] According to another aspect of the present invention, a method for manufacturing a holographic screen is provided, characterized by comprising: a step in which a light source emits a beam; a step in which a beam splitter divides the emitted beam into a signal beam and a reference beam; a step in which a first optical system modulates and expands the divided signal beam; a step in which an imaging lens converges the signal beam expanded by the first optical system; a step in which a unidirectional diffuser scatters the converged signal beam only forward and causes the scattered beam to be incident on the surface of a holographic optical element; and a step in which a second optical system causes the divided reference beam to be incident on the holographic optical element.

[0022] According to another aspect of the present invention, an optical system for a holographic screen manufacturing device is provided, characterized by comprising: a signal beam optical system for expanding a signal beam; an imaging lens for converging a signal beam expanded in a first optical system; and a unidirectional diffuser that scatters the converging signal beam only forward and causes the scattered beam to be incident on the surface of a holographic optical element.

[0023] According to another aspect of the present invention, a light processing method for producing a holographic screen is provided, characterized by comprising: a step in which a signal beam optical system expands a signal beam; a step in which an imaging lens converges the expanded signal beam; and a step in which a unidirectional diffuser scatters the converged signal beam only forward so that the scattered beam is incident on the surface of a holographic optical element.

[0024] As explained above, according to the embodiments of the present invention, when fabricating a large holographic screen using a holographic optical element, a unidirectional diffuser is used as a reference optical element to record by aligning it with the photopolymer without separation, thereby reducing optical loss and optical path and shortening the required exposure time.

[0025] In addition, according to embodiments of the present invention, by replacing a large imaging lens for focusing a signal beam in the production of a large holographic screen with an array-type optical element composed of small-sized lenses, it is possible to simplify the device and reduce manufacturing costs.

[0026] FIG. 1 is a device for manufacturing a large holographic screen according to one embodiment of the present invention,

[0027] Figure 2 shows a bidirectional diffuser,

[0028] Fig. 3 shows a unidirectional diffuser,

[0029] FIG. 4 shows a unidirectional diffuser utilizing a micro-lens array,

[0030] FIG. 5 is a device for manufacturing a large holographic screen using an imaging lens array according to another embodiment of the present invention,

[0031] FIG. 6 is a device for manufacturing a large holographic screen utilizing an optical fiber array in a signal beam and a reference beam according to another embodiment of the present invention.

[0032] FIG. 7 is a device for manufacturing a large holographic screen utilizing an optical fiber array only for a signal beam according to another embodiment of the present invention,

[0033] FIG. 8 is a device for producing a large holographic screen using a moving stage according to another embodiment of the present invention.

[0034] The present invention will be described in more detail below with reference to the drawings.

[0035] An embodiment of the present invention presents an apparatus and method for manufacturing a large holographic screen. This technology is designed to simplify the apparatus and reduce manufacturing costs for producing a holographic screen capable of performing the optical function of a projection screen using a holographic optical element (HOE).

[0036] In an embodiment of the present invention, a unidirectional diffuser is used as a reference optical element to record by aligning it with a holographic optical element without separation, thereby reducing optical loss and optical path and shortening the required exposure time. Additionally, a large imaging lens for focusing is replaced with an array-type optical element composed of small lenses, thereby simplifying the device and reducing manufacturing costs.

[0037] FIG. 1 is a diagram illustrating the configuration of a device for producing a large holographic screen according to an embodiment of the present invention. The device for producing a large holographic screen according to an embodiment of the present invention is a device for producing a holographic screen capable of diffusing an image projected from a projector pixel by pixel at a corresponding location.

[0038] As illustrated, the manufacturing device for a large holographic screen according to an embodiment of the present invention comprises a laser light source (110), a beam splitter (BS, 120), a signal beam optical system (130), an imaging lens (140), a unidirectional diffuser (150), a stage (160), and a reference beam optical system (170).

[0039] The beam splitter (120) splits the beam emitted from the laser light source (110) into a signal beam and a reference beam, and transmits the signal beam to the signal beam optical system (130) and the reference beam to the reference beam optical system (170).

[0040] The signal beam optical system (130) comprises an SLM that modulates a signal beam branched from a beam splitter (120) into a signal beam for producing a holographic screen, and a High NA lens (beam expander) that expands a mirror-reflected signal beam that reflects the modulated beam and is incident on a High NA lens.

[0041] The imaging lens (140) is a lens for converging a signal beam that is expanded and emitted from the signal beam optical system (130) toward the unidirectional diffuser (150).

[0042] The unidirectional diffuser (150) scatters the signal beam converged by the imaging lens (140) only forward, and directs the scattered beam to the photopolymer (P), which is a holographic optical element. The unidirectional diffuser (150) is in close contact with the photopolymer (P) without any gap.

[0043] The stage (160) is equipped with a photopolymer (P) to record the interference pattern of a large holographic screen.

[0044] The reference beam optical system (170) is configured to include a lens (beam expander) that expands the incident beam and directs it onto the photopolymer (P), and a mirror that reflects the reference beam branched from the beam splitter (120) and directs it onto the lens.

[0045] A unidirectional diffuser (150) is described in detail below. In order to record a holographic screen on a photopolymer (P), a reference diffuser is required that can convert the waveform of a signal beam into scattered light on the surface of the photopolymer (P).

[0046] Since a conventional diffuser scatters the incoming beam without distinguishing between the front and back as shown in Fig. 2, a sufficient separation distance is required between the diffuser and the photopolymer to prevent additional scattering of the reference beam that has passed through the photopolymer. Because such a bidirectional diffuser inevitably causes unnecessary backscattering of the incoming beam, the light loss is significant, and the light loss due to the separation distance is also a problem.

[0047] To prevent such problems, in an embodiment of the present invention, a unidirectional diffuser that primarily generates forward scattering, as shown in FIG. 3, is utilized as a reference diffuser. Such a unidirectional diffuser can be implemented based on a high-transmittance diffuser, a diffractive optical element, a holographic optical element, a microlens array, etc.

[0048] FIG. 4 is a diagram illustrating the structure of a unidirectional diffuser utilizing a micro-lens array. In the case of a micro-lens array having a sufficiently small lens pitch (p), it can perform a role similar to a diffuser by diverting incoming laser light at a specific radiation angle. In particular, by stacking multiple micro-lens arrays that are shifted by a spacing (s) smaller than the lens size (p), the radiation characteristics can be improved to exhibit more homogeneous characteristics.

[0049] If the optical element is utilized as a reference diffuser, the beam passing through the photopolymer is not re-scattered backward; therefore, during holographic screen recording, the reference diffuser can be aligned with the photopolymer without a separate separation distance, thereby reducing the space required for the holographic screen fabrication device (thus reducing the coherence distance requirement for the laser light) and improving the light efficiency up to exposure.

[0050] In this way, in an embodiment of the present invention, the unidirectional diffuser (150) can scatter a signal beam only forward using arrays of micro-lenses arranged in a row, and the spacing between the arrays of micro-lenses can be implemented to be smaller than the size of the micro-lenses.

[0051] The imaging lens (140) is described in detail below. Since the diffracted light scattered from each position of the recording holographic screen must all reach the user position located in the viewing area, the signal beam must be focused to the entire observation position. Accordingly, as shown in FIG. 1, the laser light passing through the High NA lens (beam expander) of the signal beam optical system (130) does not enter the unidirectional diffuser (150) in the form of collimated light, but must be composed of converged light that is focused to a distance of b+c through a separate imaging lens (140). That is, the imaging lens (140) must focus the signal beam to an observation position separated by a predetermined distance from the photopolymer (P). The optimal viewing distance c (distance between the photopolymer and the viewing area) of the holographic screen can be determined according to the following formula.

[0052]

[0053] Here, a is the distance from the exit surface of the signal beam optical system (130) to the imaging lens (140), b is the distance from the imaging lens (140) to the unidirectional diffuser (150), and f is the focal length of the imaging lens (140). The convergent light formed by the imaging lens (140) passes through the unidirectional diffuser (150) and is partially scattered, but can provide an optimal observation position at position c where the Chief ray converges.

[0054] Meanwhile, for the production of a large holographic screen, the width w of the target photopolymer (P) d An imaging lens (140) with a larger diameter is required. Specifically, in the configuration shown in FIG. 1, the diameter w of the imaging lens (140) lens is determined according to the formula below, and the width of the target holographic screen (w) depends on the ratio of distances b and c. d It can be seen that an imaging lens with an enlarged aperture is required.

[0055]

[0056] In addition, in a structure as illustrated in FIG. 1, since a signal beam having a very narrow beam width must be expanded into a signal beam to cover the entire large aperture of the imaging lens (140), the optical element for the signal beam expander necessarily requires a very large NA, which increases the cost and difficulty of configuring the device. That is, when manufacturing the imaging lens (140), large aperture lenses have limitations such as manufacturing costs, physical processing limitations, and aberration problems due to the difficulty of aspherical processing, making it difficult to manufacture large screens such as projector screens.

[0057] Accordingly, in another embodiment of the present invention, a signal beam optical system (130) divides and expands the signal beam into a plurality of signal beams (signal beam array), and an imaging lens (140) is composed of a plurality of imaging lenses that converge each of the divided plurality of signal beams, thereby presenting a method to resolve the difficulty of manufacturing.

[0058] FIG. 5 is a diagram illustrating the configuration of a large holographic screen manufacturing device according to another embodiment of the present invention. The holographic screen manufacturing device according to an embodiment of the present invention replaces the High NA lenses and large aperture imaging lenses (140) of FIG. 1 with general NA lenses and arrayed imaging lenses.

[0059] This allows for 1) the absence of a need to cover an area that is excessively large relative to the beam width of the laser light from the perspective of individual beam paths, thus eliminating the need for High NA lenses for Beam Expanding, and 2) the ease of implementing a recording device by utilizing an array of lenses that can be manufactured at an appropriate level instead of large-aperture imaging lenses that are physically difficult to manufacture.

[0060] In FIG. 5, which utilizes an array of three imaging lenses, the diameter w required for each individual imaging lens lens The diameter can be reduced to 30% of that of a large-aperture imaging lens (Fig. 1). Additionally, if the number of segmented lens arrays is increased, the required diameter of the imaging lens is reduced proportionally.

[0061] FIG. 6 is a diagram illustrating the configuration of a large holographic screen manufacturing device according to another embodiment of the present invention. In the large holographic screen manufacturing device according to an embodiment of the present invention, the signal beam optical system (130) splits the signal beam into multiple parts by splitting an optical fiber receiving the signal beam into multiple optical fibers using a splitter, and the reference beam optical system (170) splits the reference beam into multiple parts by splitting an optical fiber receiving the reference beam into multiple optical fibers using a splitter, and each of these parts is incident on different regions of the photopolymer (P).

[0062] This simplifies the beam splitting and expansion structure in free space through a combination of an optical fiber and a beam splitter capable of coupling the signal beam optical system (130) and the reference beam optical system (170). In particular, since the alignment between spectroscopic and optical elements becomes very easy by utilizing an optical fiber, there is an advantage in that the number of imaging lenses (140) can be variably adjusted to match the required size of the holographic screen.

[0063] The optical fiber array structure is applied not only to the signal beam but also to the reference beam. In particular, if the divergence angle required for the reference beam is very large, such as in screens for ultra-short throw projectors, a High NA lens is required for the reference beam as well; however, if this is replaced with an optical fiber array as shown in Fig. 6, it is possible to simulate the wavefront of a reference beam with a large divergence angle with a simplified device configuration. By utilizing optical fibers as beam expanders instead of conventional lenses, the physical spacing p between fibers is typically f It is possible to form it very small, at the level of 1~2mm, so that it can approximate and satisfy the NA condition of the reference beam as if it were expanded from a single focal point.

[0064] Meanwhile, as with a projector using a general projection system, if the required divergence angle of the reference beam is not large, as shown in FIG. 7, the signal beam may be implemented using a single optical fiber for the reference beam even if an optical fiber array is used.

[0065] Up to now, a large holographic screen manufacturing apparatus and method have been described in detail with reference to preferred embodiments.

[0066] In the above embodiment, a unidirectional diffuser is used as a reference optical element to record by aligning it with the photopolymer without separation, thereby reducing optical loss and optical path and shortening the required exposure time. Additionally, an array-type optical element capable of replacing a large imaging lens for focusing is proposed, simplifying the system and reducing manufacturing costs.

[0067] Meanwhile, the holographic screen manufacturing device and method according to an embodiment of the present invention can be implemented in various applications such as window-mounted screens, transparent displays, automotive infotainment systems, and solar cell concentrators.

[0068] Furthermore, it is possible to configure the optical system for the holographic screen manufacturing device according to an embodiment of the present invention, such as a signal beam optical system (130), an imaging lens (140), a unidirectional diffuser (150), and a reference beam optical system (170), or to configure the optical system for the holographic screen manufacturing device with a signal beam optical system (130), an imaging lens (140), and a unidirectional diffuser (150), and in this case, the technical concept of the present invention may also be applied.

[0069] FIG. 8 is a diagram illustrating the configuration of a large holographic screen manufacturing device according to another embodiment of the present invention. The large holographic screen manufacturing device according to an embodiment of the present invention uses a single / small imaging lens instead of an arrayed imaging lens, and performs the recording on the photopolymer by dividing it into small individual cells (hogels).

[0070] To this end, a precision moving stage capable of moving the photopolymer in two axial directions is required, and at each position, the scattering pattern of the holographic screen is exposed and recorded using a signal beam and a reference beam that interfere in a local area. At this time, the main axis of the scattered light of the signal beam must be variable depending on the position of the individual hogel, and to this end, the imaging lens must also be positioned on the moving stage capable of moving in two axial directions.

[0071] In the recording stage of individual cells, the position of the photopolymer is adjusted to specify the recording position of the individual cell on the holographic screen, and the angle of incidence of the Chief Ray is adjusted by adjusting the relative position of the imaging lens relative to the expander. Since the adjusted directionality of the Chief Ray gives light-gathering ability to the holographic screen that is finally recorded, it becomes possible to implement a holographic screen that can receive projected light from the entire viewing area without a lens group.

[0072] Furthermore, although preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above. Various modifications are possible by those skilled in the art without departing from the essence of the invention as claimed in the claims, and such modifications should not be understood individually from the technical spirit or perspective of the present invention.

Claims

1. Light source; A beam splitter that splits a beam emitted from a light source into a signal beam and a reference beam; A first optical system that modulates and expands a branched signal beam; An imaging lens that converges the signal beam expanded in the first optical system; A unidirectional diffuser that scatters a converging signal beam only forward, causing the scattered beam to be incident on the surface of a holographic optical element; A holographic screen manufacturing device characterized by including a second optical system that incidents a branched reference beam on a holographic optical element.

2. In Claim 1, A unidirectional diffuser is, A holographic screen manufacturing device characterized by being combined with a holographic optical element without separation.

3. In Claim 1, A unidirectional diffuser is, A holographic screen manufacturing device characterized by a series of micro-lens arrays that scatter a signal beam only forward.

4. In Claim 3, The spacing between the microlens arrays is, A holographic screen manufacturing device characterized by being smaller than the size of a micro lens.

5. In Claim 1, Imaging lenses, A holographic screen manufacturing device characterized by focusing a signal beam at an observation position separated by a predetermined distance from a holographic optical element.

6. In Claim 5, The fixed distance (c) is, It is determined through the above formula, a is the distance from the exit surface of the first optical system to the imaging lens, and b is the distance from the imaging lens to the unidirectional diffuser, and A holographic screen making device characterized in that f is the focal length of an imaging lens.

7. In Claim 1, The first optical system is, Split the signal beam into multiple beams and expand it, Imaging lenses, A holographic screen manufacturing device characterized by being an imaging lens array comprising a plurality of imaging lenses that converge each of a plurality of divided signal beams.

8. In Claim 7, The first optical system is, A holographic screen manufacturing device characterized by splitting a signal beam into multiple signals by splitting an optical fiber that receives a signal beam into multiple optical fibers using a splitter.

9. In Claim 8, The second optical system is, A holographic screen manufacturing device characterized by receiving an optical fiber as a reference beam, splitting the reference beam into multiple optical fibers using a splitter, and dividing the reference beam into multiple beams to be incident on different regions of a holographic optical element.

10. A step in which the light source emits a beam; A beam splitter divides the emitted beam into a signal beam and a reference beam; A first optical system modulates and expands a branched signal beam; An imaging lens, in the step of converging a signal beam expanded in a first optical system; A step in which a unidirectional diffuser scatters a converging signal beam only forward, causing the scattered beam to be incident on the surface of a holographic optical element; A method for producing a holographic screen characterized by including the step of a second optical system injecting a branched reference beam into a holographic optical element.

11. Signal beam optical system for expanding the signal beam; An imaging lens that converges the signal beam expanded in the first optical system; An optical system for a holographic screen manufacturing device characterized by including a unidirectional diffuser that scatters a converging signal beam only forward and causes the scattered beam to be incident on the surface of a holographic optical element.

12. A signal beam optical system, a step of expanding the signal beam; A step in which an imaging lens converges an expanded signal beam; A light processing method for manufacturing a holographic screen, characterized by including the step of a unidirectional diffuser scattering a converging signal beam only forward and causing the scattered beam to be incident on the surface of a holographic optical element.

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