KR102519587B1 - Optical system and method for holographic display ujsing spatial light modulator - Google Patents

Abstract

A holographic optical system configuration and a holographic display method are disclosed. In particular, the present disclosure relates to a holographic optical system configuration and a holographic display method that can be efficiently applied when a spatial light modulator (SLM) is used. According to one aspect of the present disclosure, a holographic display device includes a spatial light modulator (SLM) for reproducing a hologram and a first lens and a second lens for performing Fourier transform on the hologram of the spatial light modulator with a pair of lenses. A configured optical system is configured such that a Fourier plane, which is a display reference image plane, is located in the same plane space as the second lens.

Description

Holographic optical system configuration and holographic display method using a spatial light modulator (SLM)

The present disclosure relates to a holographic optical system configuration and a holographic display method. In particular, the present disclosure relates to a holographic optical system configuration and a holographic display method that can be efficiently applied when a spatial light modulator (SLM) is used.

HOLOGRAM is a combination of 'HOLOS' meaning whole in Greek and 'GRAM' meaning message. In addition, a hologram is made using the principle of holography and refers to a fringe pattern that reproduces a three-dimensional image or a medium on which such an interference pattern is recorded.

The principle of holography is to split coherent light, for example, a beam from a laser, into two by a beam splitter so that one light directly hits the recording medium and the other light hits the object to be seen. . At this time, light directly illuminating the recording medium is referred to as reference light, and light illuminating the object is referred to as object light. Since object light is light reflected from each surface of an object, a phase difference (for example, a distance from the surface of the object to a recording medium) appears differently depending on the surface of the object. At this time, the unmodified reference light causes interference with the object light, and the hologram recording device records this fringe pattern of the object light and the reference light on a recording medium such as a photoplate or a camera (CCD or CMOS). . In addition, the hologram reproducing apparatus reproduces the hologram by re-radiating light to the recording medium on which the fringe pattern is recorded.

A spatial light modulator (SLM) is a key component of a holographic display that enables dynamic modulation of the phase or amplitude of incident light. Conventionally, various types of SLMs have been proposed, but recently, an Electrically Addressable Spatial Light Modulator (EASLM) based on LC (Liquid Crystal) technology has been used as a high-resolution device having 2π phase modulation.

In relation to this, as a general spatial light modulator (SLM) has a two-dimensional periodic pixel structure, the viewing angle of the display can be interpreted through a relationship between a lattice spacing and angles of incident and diffracted rays. For example, it is possible to interpret the viewing angle of the holographic display through the diffraction grating theory as shown in [Equation 1] below.

[Equation 1]

Grating equation: d*sinθ= mλ

Here, θ is the diffraction angle, d is the spacing between the slits or grating period or pixel period, and m is the order of diffraction (m= 0, ±1, ± 2, ...), and λ means a wavelength, respectively.

1 is a diagram for explaining a holographic display method using a general spatial light modulator (SLM). Since the viewing angle of the holographic display is determined by the diffraction angle θ according to the pixel period of the spatial light modulator (SLM, 100), research is being conducted in the direction of reducing the pixel pitch (pixel pitch, 101) of the SLM (100). .

In this regard, the viewing angle of the holographic display is limited to the maximum diffraction angle in a single diffraction order in [Equation 1] above. This is because diffraction orders are repeatedly generated in a specific angle direction at every integer multiple of the wavelength when the SLM pixels are arranged at regular intervals d. Here, since the reconstructed hologram image is repeated in each order to deliver inaccurate spatial information, it is perceived as noise by the user. Therefore, in order to implement a holographic display capable of providing a user with a reasonable viewing angle and expressing a high spatial frequency hologram, various SLM-related studies are being conducted.

In addition, in order to construct a digital holographic display, it is necessary to remove optical spatial noise according to the principle of holographic technology. In general, the optical spatial noise is generated by conjugate waves and high-order term diffracted light and non-diffracted light. In addition, a 4-f relay optic system may be applied to a general holographic display configuration. However, such a 4-f As the area of the SLM increases and the diffraction performance improves, the transfer optical system requires a lens having a larger diameter and higher lens power for convergence of diffracted light. Therefore, it will be said that a holographic display optical system suitable for the development of the SLM device is required for the configuration of the holographic display.

Hereinafter, in the present disclosure, 'optical system' may also be referred to as 'optical system' or 'optical system structure', and should be interpreted as having substantially the same meaning.

The present disclosure is to provide a holographic display optical system configuration and a holographic display method using the same.

In addition, the present disclosure is to provide an optical system configuration corresponding to a high-performance spatial light modulator and a holographic display device using the same.

In addition, the present disclosure is to provide an optical system configuration that does not require an additional optical element for noise filtering and a holographic display device using the same.

In addition, the present disclosure is to provide an optical system configuration in which an optical path is shortened and a holographic display device using the same.

In addition, the present disclosure is intended to provide an optical system configuration in which required optical system performance is lowered and a holographic display device using the same.

In addition, the present disclosure intends to provide an optical system configuration with improved display form factor and a holographic display device using the same.

In addition, the present disclosure is to provide an optical system configuration capable of reducing manufacturing cost and a holographic display device using the same.

In addition, the present disclosure is to provide an optical system configuration providing a large display area and a wide diffraction angle and a holographic display device using the same.

In addition, the present disclosure is to provide an optical system configuration having a viewing zone in a short distance and a holographic display device using the same without requiring a projection lens for magnification projection.

The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below. You will be able to.

The present disclosure can effectively provide a holographic display device through a holographic optical system configuration based on a Fourier transform using a pair of lenses.

According to one aspect of the present disclosure, a holographic display device includes a Fourier transform optical system composed of a first lens and a second lens for performing Fourier transform on a hologram reproduced from a spatial light modulator (SLM) with a pair of lenses. Here, the optical system is configured so that a Fourier plane, which is an image plane of the display, is located in the same plane space as the second lens.

In addition, a holographic display device according to another aspect of the present disclosure includes a spatial light modulator (SLM) in which a hologram is reproduced, and a first lens and a second lens that perform Fourier transform on the hologram of the spatial light modulator using a pair of lenses. A Fourier optical system composed of lenses may be included, and a focal length of the second lens corresponding to the first lens may be set to set a user viewing zone position at an adjacent distance d from the display Fourier plane. Also, for a large-area display configuration, the second lens may be configured with a diffractive optical element.

In addition, according to an aspect of the present disclosure, an optical system configuration in a holographic display device may include a Fourier optical system configured of a first lens and a second lens that perform Fourier transform as a pair. Here, the first lens and the second lens are arranged so that a Fourier plane, which is an image plane of the display by the optical system, is located in the same plane space as the second lens.

The features briefly summarized above with respect to the disclosure are merely exemplary aspects of the detailed description of the disclosure that follows, and do not limit the scope of the disclosure.

According to the present disclosure, since an optical path in a holographic display device is shortened and required performance of a component optical system is lowered, it is possible to improve a display form factor.

In addition, according to the present disclosure, optical noise can be removed through a Fourier holographic optical system configuration using a pair of lenses.

In addition, it is possible to provide a holographic display device that does not require an additional optical configuration for magnifying and projecting a hologram through the configuration of a Fourier holographic optical system using the pair of lenses.

In addition, according to the present disclosure, the manufacturing cost of the holographic display device can be reduced.

In addition, according to the present disclosure, it is possible to provide a holographic display device capable of forming a viewing area at a shorter distance.

Effects obtainable in the present disclosure are not limited to the effects mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the description below. will be.

1 is a diagram for explaining a holographic display method using a general spatial light modulator (SLM).
2 is a diagram for explaining an optical system configuration applied to a holographic display device according to an embodiment of the present disclosure.
FIG. 3 shows a mathematical relationship between input and output signals applied to the optical system configuration of FIG. 2 .
4 is a diagram for explaining a holographic display device including an optical system configuration of a holographic display according to an embodiment of the present disclosure.
FIG. 5 is a diagram illustrating a comparison of an optical system configuration of a holographic display according to an embodiment of the present disclosure with a conventional optical system configuration.
FIG. 6 is a diagram for explaining a holographic display optical system configuration and a holographic display device suitable for a near field of view according to another embodiment of the present disclosure.

Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described in detail so that those skilled in the art can easily carry out the present disclosure. However, the present disclosure may be implemented in many different forms and is not limited to the embodiments described herein.

In describing the embodiments of the present disclosure, if it is determined that a detailed description of a known configuration or function may obscure the gist of the present disclosure, a detailed description thereof will be omitted. And, in the drawings, parts irrelevant to the description of the present disclosure are omitted, and similar reference numerals are attached to similar parts.

In the present disclosure, when a component is said to be "connected", "coupled" or "connected" to another component, this is not only a direct connection relationship, but also an indirect connection relationship where another component exists in the middle. may also be included. In addition, when a component "includes" or "has" another component, this means that it may further include another component without excluding other components unless otherwise stated. .

In the present disclosure, components that are distinguished from each other are intended to clearly explain each characteristic, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated to form a single hardware or software unit, or a single component may be distributed to form a plurality of hardware or software units. Accordingly, even such integrated or distributed embodiments are included in the scope of the present disclosure, even if not mentioned separately.

In the present disclosure, components described in various embodiments do not necessarily mean essential components, and some may be optional components. Therefore, an embodiment composed of a subset of components described in one embodiment is also included in the scope of the present disclosure. In addition, embodiments including other components in addition to the components described in various embodiments are also included in the scope of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

The present disclosure relates to a holographic display optical system and a holographic display method using the same. The optical system of the present disclosure is functionally based on a Fourier holographic display structure.

2 is a diagram for explaining an optical system configuration applied to a holographic display device according to an embodiment of the present disclosure. In addition, FIG. 3 shows an optical relationship between input and output signals applied to the optical system configuration of FIG. 2 as a mathematical formula.

The optical system configuration of the present disclosure is based on a Fourier holographic display structure. Here, the optical Fourier transform applied to the present disclosure is characterized by having an optical structure that performs Fourier transform with a pair of lenses, rather than a conventional Fourier transform-based holographic display structure using a single lens.

2 illustrates a structure of two lenses 201 and 202 performing Fourier transform with a pair of lenses according to an example of the present disclosure. The focal length f1 of the first lens 201 and the focal length f2 of the second lens 202 are the same as the confocal fc. In addition, FIG. 3 shows the optical relationship between the two confocal lenses 201 and 202 as a mathematical formula. It can be seen from the equation of FIG. 3 that the input field g _in (x,y) of the first lens 201 and the output field g _out (u,v) of the second lens 202 have an optical Fourier transform relationship. . Hereinafter, in the present disclosure, the two confocal lenses are referred to as a first lens 201 and a second lens 202, or a first Fourier lens 201 and a second Fourier lens 202, respectively.

4 is a diagram for explaining a holographic display device including an optical system configuration of a holographic display according to an embodiment of the present disclosure.

Referring to FIG. 4 , the holographic display device according to the present disclosure includes a first Fourier lens 401 and a second Fourier lens 402 that Fourier transform a hologram reproduced by a spatial light modulator (SLM) with a pair of lenses. ), including an optical system composed of Here, an optical Fourier plane by the first Fourier lens 401 and the second Fourier lens 402 is located in the same plane space as the second Fourier lens.

In relation to this, the first Fourier lens 401 may be positioned close to the SLM, and the second Fourier lens may be positioned at a point spaced apart by the focal length f of the first Fourier lens. As an example, FIG. 4 illustrates a case where the first Fourier lens 401 is located after the SLM on an optical path.

On the other hand, it is also possible that the first Fourier lens 401 is located before the SLM on the optical path. In this case, if the first Fourier lens 401 is positioned before the SLM on the optical path, the focal length f1 of the first Fourier lens 401 may be set to f1=f2+d1. Here, d1 means the distance between the first Fourier lens 401 and the SLM, and f2 means the focal length between the SLM and the second Fourier lens 402.

5 is a diagram illustrating a comparison of an optical system configuration of a holographic display according to an embodiment of the present disclosure with a conventional optical system configuration.

Referring to FIG. 5, the upper part of FIG. 5 shows a structure using a conventional single Fourier lens using an SLM. On the other hand, the lower part of FIG. 5 shows a configuration of a holographic display optical system to which a confocal-based optical Fourier transform structure according to the present disclosure is applied using an SLM having the same performance.

Relatedly, in FIG. 5, N _x means the number of pixels of the SLM, f means the focal length of the lens, and λ means the wavelength. In addition, in each optical system configuration, the hologram is reconstructed on _a Fourier plane, and at this time, the maximum reproduced image reproduced on the Fourier plane has the same f* λ/ px size.

The configuration of the optical system according to an example of the present disclosure at the bottom of FIG. 5 has the following advantages compared to the conventional optical Fourier transform method using a single lens.

First of all, the optical system configuration of the present disclosure can perform the same optical function in half the optical path compared to the conventional one. Therefore, when a holographic display device is configured using the optical system configuration of the present disclosure, the display form factor can be improved by reducing the light path by half.

As another advantage, the performance of the Fourier lens required for the configuration of the optical system can be configured even with lower performance compared to the prior art. That is, assuming that a holographic image of the same size is reproduced, the required focal length of the Fourier lens is the same for both the conventional and proposed structures. On the other hand, the required aperture size of the lens is determined only by the diffraction angle according to the pixel period in the proposed structure of the lower part of FIG. 5, whereas in the conventional structure of the upper part of FIG. A lens of # is required.

In addition, the optical noise removal method of the optical system configuration according to the present disclosure shown in the lower portion of FIG. 5 can be configured more simply than in the prior art. For example, optical noise in a conventional holographic display structure is removed by applying a spatial filter to a Fourier plane in a 4-f transmission optical system. Therefore, the conventional optical system configuration requires a separate spatial filter element arrangement. On the other hand, in the configuration of the optical system according to the present disclosure shown in the lower portion of FIG. 5, since the Fourier plane coincides with the position of the second lens constituting the optical system, the position is determined through the phase shift of the hologram signal and the space between order noise. be able to move to Therefore, by disposing the aperture of the second lens between the order noise, it is possible to remove optical noise without a separate optical device.

6 is a diagram for explaining a holographic display optical system configuration and a holographic display device suitable for a short-range viewing zone according to another embodiment of the present disclosure.

According to the holographic display device according to the present disclosure, it is possible to set a user viewing zone position at a distance adjacent to the display. That is, by adjusting the focal length of the second Fourier lens 602 corresponding to the first Fourier lens 601, it is possible to set the user's viewing zone position to a position d adjacent to the displayed Fourier plane.

로 설정할 수 있다. For example, in constructing the optical system constituting the holographic display device of FIG. 6, if f ₁ is the focal length of the first Fourier lens 601, the focal length of the second Fourier lens is

can be set to

Here, in constructing the Fourier holographic display optical system of the present disclosure, the size of the second Fourier lens 602 is the same as the size of the image to be reproduced. Therefore, in the case of expanding and reproducing a holographic image, it is more effective if the second Fourier lens 602 is formed of a diffractive optical element (DOE), which is easy to manufacture as a large-area element.

In addition, in the Fourier plane formed in the same plane space as the position of the second Fourier lens 602 in FIG. 6, the aperture of the second Fourier lens is placed between order noise, and the hologram signal is phase shifted ( It is possible to remove optical spatial noise by moving it to a space between the order noise through a phase shift. That is, it is possible to remove optical noise without a separate optical device by using only a focal point formed on one side of the second Fourier lens 602 by the zero-order diffracted light of the first Fourier lens 601. Accordingly, the spatial filter illustrated in FIG. 6 for explanation does not mean a separate optical filter element, but merely means a focal point formed on one side of the second Fourier lens 602 .

Various embodiments of the present disclosure are intended to explain representative aspects of the present disclosure, rather than listing all possible combinations, and matters described in various embodiments may be applied independently or in combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For hardware implementation, one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), It may be implemented by a processor (general processor), controller, microcontroller, microprocessor, or the like.

The scope of the present disclosure is software or machine-executable instructions (eg, operating systems, applications, firmware, programs, etc.) that cause operations according to methods of various embodiments to be executed on a device or computer, and such software or It includes a non-transitory computer-readable medium in which instructions and the like are stored and executable on a device or computer.

201, 401, 501, 601: first lens
202, 402, 502, 602: second lens

Claims (11)

In the holographic display device,
a spatial light modulator (SLM) that reproduces a hologram; and
An optical system composed of a confocal first lens and a second lens for performing Fourier transform on the hologram of the spatial light modulator with a pair of lenses, wherein a Fourier plane, which is a display reference image plane, is the second lens Located in the same plane space as the, holographic display device.
According to claim 1,
The first lens is positioned closely to the spatial light modulator,
The second lens is configured to be spaced apart by a focal length (f) of the first lens, the holographic display device.
According to claim 2,
The first lens is positioned closely after the spatial light modulator on an optical path.
According to claim 2,
The first lens is positioned before the spatial light modulator on an optical path.
According to claim 4,
The focal length f1 of the first lens is defined as f1=f2+ when the distance between the first lens and the spatial light modulator is d1 and the distance between the spatial light modulator and the second lens having a focal length of f2 is f2. A holographic display device, set to d1.
According to claim 1,
In the Fourier plane formed in the coplanar space with the position of the second lens, an aperture of the second lens is disposed between the order noises, and a hologram signal is phase shifted to a space between the order noises. A holographic display device that removes optical spatial noise by moving to .
In the holographic display device,
a spatial light modulator (SLM) capable of reproducing holograms; and
An optical system composed of a pair of first and second lenses for Fourier transforming the hologram of the spatial light modulator,
In order to set the user viewing zone position to the distance d from the display Fourier plane to the user viewing zone, the focal length f ₂ of the second lens corresponding to the first lens

set,
f ₁ represents the focal length of the first lens, and d represents the distance from the display Fourier plane to the user's viewing zone.
delete According to claim 7,
In the Fourier plane formed in the coplanar space with the position of the second lens, an aperture of the second lens is disposed between the order noises, and a hologram signal is phase shifted to a space between the order noises. A holographic display device that removes optical spatial noise by moving to .
According to claim 7,
For a large-area display configuration, the second lens is composed of a diffractive optical element (diffractive optical element), the holographic display device.
In the configuration of the optical system in the holographic display device,
The optical system includes a first lens and a second lens performing Fourier transform as a pair,
The first lens and the second lens are arranged so that a display Fourier plane by the optical system is located in the same plane space as the second lens,
The focal length (f ₂ ) of the second lens corresponding to the first lens is determined by considering the distance from the Fourier plane to the user's viewing zone.

set,
f ₁ represents the focal length of the first lens, and d represents the distance from the display Fourier plane to the user's viewing zone.

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