KR102476813B1 - Spatial Light Modulator and Digital Holography Using the Same - Google Patents

Abstract

The present invention relates to a spatial light modulator capable of reducing errors in diffraction through gap adjustment and digital holography using the same. And, a first electrode provided on each pixel on the first substrate, a second electrode located on the inner surface of the second substrate to face the first electrode, and between the first substrate and the second substrate A liquid crystal layer located on the outer surface of the second substrate, third electrodes and fourth electrodes spaced apart from each other and located on the outer surface of the second substrate corresponding to each pixel, and a liquid crystal film layer containing nano-liquid crystals on the outer surface of the second substrate. made including

Description

Spatial Light Modulator and Digital Holography Using the Same {Spatial Light Modulator and Digital Holography Using the Same}

The present invention relates to a 3D image display, and more particularly, to a spatial light modulator capable of reducing diffraction errors by adjusting a gap and digital holography using the same.

A display displaying an image started with a cathode ray tube (CRT) and has been developed as a flat panel display device. Examples of the flat panel display device include a thin film transistor-liquid crystal display device (TFT-LCD), a plasma display panel device (PDP), and an active matrix organic light emitting diode display device (AMOLED).

In addition, recently, there has been a demand for displaying a three-dimensional (3D) image so that viewers can perceive it more realistically, rather than simply displaying a two-dimensional image on such a display.

There are several types of 3D displays, typically a method of separating left and right eye images through an optical separation element such as a parallax barrier or an optical lens, and a method of separating an electronically generated hologram through a spatial light modulator (SLM). There is a digital holography method of a reproduction method, and the like.

Among them, the digital holography method is known as the display to be ultimately pursued by providing the most natural parallax. A spatial light modulator is required for such digital holography, and the spatial light modulator controls light transmittance or outputs light phase information. In the method of separating the left and right eye images described above, different information is provided to both eyes to recognize a 3D image through binocular parallax, whereas the digital holography method expresses distance and depth using the interference phenomenon of light, When light is emitted from a light source such as a coherent laser, information on an interference image is transmitted to the spatial light modulator, and the spatial light modulator diffracts the transmitted interference image information and outputs a 3D image.

Meanwhile, the spatial light modulator generally controls the intensity of light.

For example, the spatial light modulator is manufactured in a cell shape, and is formed in a state in which electrodes are formed on opposing glass substrates and liquid crystal is filled therebetween. This spatial light modulator operates differently depending on whether or not a vertical electric field is applied to electrodes located on both glass substrates. However, currently used spatial light modulators in which an intensity light modulator and a phase light modulator are separately manufactured require precise alignment of pixels of the intensity light modulator and the phase light modulator, and the distance between the two modulators is Accordingly, unintended parallax may occur. In addition, there is an error at the time of diffraction due to the thickness of the glass substrate, and the internal pixel size cannot be reduced beyond a certain level due to the limitation of resolution, and a sufficient diffraction angle is secured by the inverse relationship between the pixel pitch and the diffraction angle. Can not. Therefore, in the case of having a pixel pitch of a certain level or higher, there is a problem in that it is difficult to observe a 3D image.

The present invention has been made to solve the above problems, and an object thereof is to provide a spatial light modulator capable of reducing an error in diffraction by adjusting a gap and digital holography using the same.

The spatial light modulator of the present invention for achieving the above object comprises: a first substrate and a second substrate having a plurality of pixels facing each other; a first electrode provided on each pixel on the first substrate; , Corresponding to the second electrode located on the inner surface of the second substrate, the liquid crystal layer located between the first substrate and the second substrate, and each pixel on the outer surface of the second substrate so as to face the first electrode. A liquid crystal film layer including nano-liquid crystals is provided on the outer surface of the third and fourth electrodes and the second substrate, which are positioned and spaced apart from each other.

And, between the first substrate and the second substrate, a sealing material enclosing the liquid crystal layer while enclosing the plurality of pixels may be further included.

In addition, a polarizing film may be further included on the liquid crystal film layer.

On the other hand, in order to phase-modulate the light between the first and second substrates, a first voltage applying means for applying voltages to the first electrode and the second electrode, respectively, is further included. The liquid crystal film layer on the second substrate may further include a second voltage applying means for applying voltages to the third electrode and the fourth electrode, respectively, for amplitude modulation of light.

On the other hand, a first pad portion connected to the first voltage applying unit on the first substrate and located outside the sealant in a planar shape; and a second pad portion connected to the second voltage applying unit on an outer surface of the second base material and positioned outside the sealant in a plan view. In this case, the first pad part is connected to the first and second electrodes, respectively, and the second pad part is connected to the third and fourth electrodes, respectively.

In addition, the liquid crystal film layer is formed by combining nano liquid crystals in microcapsule units with a binder, and may be in a cured state.

Meanwhile, the liquid crystal layer includes liquid crystal in an electrically controlled birefringence (ECB) mode and is driven by a vertical electric field.

In addition, the first substrate or the second substrate may be a glass or plastic film.

Meanwhile, when voltage is applied to the first and second electrodes, phase modulation is performed between the first substrate and the second substrate, and at this time, the light incident to the first substrate passes through the second substrate and is emitted. .

In addition, when a voltage is applied to the third and fourth electrodes, the amplitude is modulated by passing through the liquid crystal film layer on the top of the second substrate, and the light incident on the top of the second substrate passes through the liquid crystal film layer and age is determined

Meanwhile, the spatial light modulator described above may include a light source unit transmitting coherent light to the spatial light modulator; and a lens system for concentrating the light emitted from the spatial light modulator to form a 3D image on a specific surface, and may be used for digital holography.

Here, the signal processing unit may further include transmitting hologram information to the spatial light modulator. In this case, the hologram information is transmitted as a voltage signal applied to the first to fourth electrodes.

In addition, the light source unit may include first to third light sources respectively emitting light of different wavelengths in the visible light region. For example, the first to third light sources may be red, green, or blue light. However, the emission color is not limited thereto, and can be changed to a light source having a different wavelength as long as white light can be obtained by adding the light. In any case, each of the light sources emits light of a single wavelength coherently. Also, the first to third light sources may be time-division driven.

The spatial light modulator and digital holography using the spatial light modulator of the present invention have the following effects.

First, in expressing information, it is possible to express information by dividing it into two modulations independently through a voltage application unit, thereby reducing data throughput. That is, the modulation of the phase and amplitude is free and the phase and amplitude can be individually adjusted at the same time, so the amount of data processing can be reduced. As a result, real-time images can be reproduced.

Second, since restoration is performed by combining the modulation values of the amplitude SLM and phase SLM during image reproduction, there are unique modulation values of amplitude and phase, which can reduce noise during the restoration process. can

Third, a spatial light modulator can be fabricated by attaching the curable nano liquid crystal to the outer surface of the second substrate in the form of a film, so that a thick substrate such as a glass substrate can be reduced in the upper cell while performing the same function as the stacked spatial light modulator. Yes, slimming is possible.

Fourth, by slimming the spatial light modulator, a diffraction error caused by a gap between two SLMs is prevented in the stacked spatial light modulator, thereby obtaining an effect of widening the viewing area.

Fifth, there is an advantage in preventing an alignment error due to an alignment error due to an error in vision equipment, etc., because coalescing between light modulators of different shapes is not required.

1 is a diagram schematically showing the digital holography of the present invention
2 is a diagram showing the principles of pixels and diffraction angles of a spatial light modulator;
3a and 3b are diagrams illustrating generation of a viewing area and an error area of a stacked spatial light modulator;
4 is a graph showing a change in viewing area according to a gap of a stacked spatial light modulator;
5 is a cross-sectional view showing the spatial light modulator of the present invention
6 is a plan view showing the spatial light modulator of the present invention
FIG. 7A is a graph showing voltage vs. refractive index change in the phase spatial light modulator of FIG. 5;
FIG. 7B is a graph showing change in transmittance versus voltage in the spatial light modulator for amplitude of FIG. 5
8A and 8B are diagrams showing light propagation in a spatial light modulator for phase and amplitude;
9 is a view showing the arrangement of light sources and spatial light modulators and light propagation in digital holography according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numbers throughout the specification indicate substantially the same elements. In the following description, if it is determined that a detailed description of a known technology or configuration related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, the component names used in the following description are selected in consideration of the ease of writing the specification, and may be different from the part names of the actual product.

1 is a diagram schematically showing digital holography of the present invention.

As shown in FIG. 1, the digital holography of the present invention spatially modulates the light source unit 10 that transmits coherent light, and the light transmitted from the light source unit 10 by receiving holographic image information and outputs the light with a specific interference pattern. It includes a spatial light modulator 200 that focuses the light emitted from the spatial light modulator 200 and a lens system 30 that focuses the hologram image 40 on a specific surface.

Here, the light source unit 10 emits light of a single wavelength in a coherent state, and may include, for example, a laser light source. In addition, a single light source or a plurality of light sources may be included according to an area required for the spatial light modulator 200 . If a single light source is provided in the light source unit 10, the wavelength of the emitted light may be a white wavelength or a shorter wavelength.

In addition, the spatial light modulator 200 may display an interference pattern corresponding to a hologram to be displayed, and the external signal processor 50 generates and transmits hologram information from the interference pattern. That is, the interference pattern appearing in the spatial light modulator 200 can be changed according to the signal applied to the spatial light modulator 200, and the signal processing unit 50 performs this change. Here, the hologram information processed by the signal processing unit 50 is called CGH (Computer Generated Hologram data), which is variable according to an event or a state of an object to be expressed.

In addition, the holographic image is expressed on a plane corresponding to a certain focal distance from the lens system 30, which is called a focal plane. A viewer can view a hologram image.

The above-described digital holography is simply illustrated, and the light source unit 10 and the spatial light modulator 200 are disposed at a specific angle rather than on a horizontal plane, and a separate optical system such as a mirror or a lens may be further provided between them. . Such adjustment may be performed in consideration of the range and direction of light emitted from the light source unit 10 .

Meanwhile, the spatial light modulator will be described in more detail.

2 is a diagram showing the principle of pixels and diffraction angles of a spatial light modulator.

와 같은 조건을 만족한다.FIG. 2 shows the diffraction angle of a general spatial light modulator 20 thereof. As shown in FIG. 2 , the spatial light modulator 20 having a fixed shape may have regularly arranged openings, and when the width of one opening is set to one pitch p, the diffraction angle

satisfies the same conditions as

However, when this diffraction angle condition is met, since the wavelength of the incident light is determined, the diffraction angle changes in relation to the pitch value. In practice, the pitch value is almost impossible to implement below 1 μm due to the limit of resolution, and , there is a limit to reducing the pitch value as the internal pixel configuration of the spatial light modulator becomes more complicated. That is, it can be seen that if the pitch value is 10 μm, the diffraction angle Θ hardly exceeds 2° for incident light in the visible light region. Accordingly, the above-described digital holography of FIG. 1 includes a lens system 30 that collects light emitted from the spatial light modulator on a focal plane in order to compensate for a small diffraction angle caused by the pixel pitch of the spatial light modulator, so as to provide a clear hologram. It is to make the video acknowledgeable.

Meanwhile, the spatial light modulator 20 may have a viewing area of a holographic image corresponding to the diffraction angle.

The shape of the spatial light modulator can be divided into various methods depending on the variable means provided in the pixel, but, for example, among the methods that are electrically controllable and optically variable, a liquid crystal-based spatial light modulator (SLM) there is

In addition, these spatial light modulators include a phase SLM that adjusts only the phase information of light, an amplitude SLM that controls only the intensity of light, and a light It can be classified as an integrated spatial light modulator that simultaneously inputs phase information and light intensity. Among them, the integrated spatial light modulator is the best in terms of the speed of generating hologram information (CGH: Computer Generated Hologram) generated by the signal processing unit and the transmission efficiency of light. In the present invention, the integrated spatial light modulator using will be.

The spatial light modulator for phase changes the phase of light emitted from the light source, and the spatial light modulator for amplitude modulates only the amplitude of light. Also, light passing through the spatial light modulator is diffracted by each pixel of the spatial light modulator. Among conventional spatial light modulators, a spatial light modulator that modulates both the phase and amplitude within one cell has been proposed, but this structure is basically provided with electrodes on both substrates, which are the basic structure of a liquid crystal panel, and an electric field is generated between them. In operation, internal data processing is extensive, and there is a delay in data processing, so real-time 3D display is impossible, and it is difficult to accurately 3D display because it is difficult to combine amplitude and phase values. Accordingly, currently used spatial light modulators are used in such a way that a spatial light modulator for phase and a spatial light modulator for amplitude are separately formed and bonded to simultaneously implement phase modulation and amplitude modulation.

In the case of a spatial light modulator for phase, because it transmits all incident light, there is a lot of noise, and since an object having an amplitude value must be expressed as a phase, iterations are required to optimize it. Spatial light modulator for amplitude has the advantage of being effective in reproducing dynamic holograms in real time because it can adjust the transmittance of light, has low noise, and does not require repetitive calculation, but has twin noise in which reverse images are blurred Since a filter is required to remove twin noise and DC noise in which non-diffraction components are identified, it is difficult to implement in a cell structure.

Accordingly, there is a demand for a cell structure capable of simultaneously modulating the amplitude and phase, and a cell capable of individually controlling the amplitude and phase can significantly improve the quality of hologram 3D images by drastically reducing the size of noise.

Hereinafter, a stacked spatial light modulator will be described.

3A and 3B are diagrams illustrating generation of a viewing area and an error area of a stacked spatial light modulator.

3A and 3B, in the stacked spatial light modulator 30, the phase spatial light modulator 35 and the amplitude spatial light modulator 39 are formed as independent cells, and each spatial light modulator ( 35 and 39 are composed of substrates 21a and 21b/26a and 26b facing each other, liquid crystal layers 22 and 27 therebetween, and sealing materials 23 and 28 surrounding the liquid crystal layers.

By the way, the substrates 21a, 21b/26a, 26b used here are glass substrates, and their thickness is equivalent to 0.5 mm to 1 mm, respectively, so that the spatial light modulator 35 for phase and the spatial light modulator 35 for amplitude The gap between the modulators 39 is about 1 mm or more. Therefore, when the respective pitches of the spatial light modulator 35 for phase and spatial light modulator 39 for amplitude are aligned in place and there is no gap therebetween, the light has an accurate diffraction angle Θ corresponding to FIG. However, as shown in FIG. 3B, an error light region around the diffraction angle is generated due to the occurrence of a gap g between the spatial light modulator 35 for phase and the spatial light modulator 39 for amplitude. Thus, the stacked spatial light modulator has a problem in that the viewing angle of the viewable area is narrowed.

4 is a graph illustrating a change in a viewing area according to a gap of a stacked spatial light modulator.

Experimentally examining the viewing area according to the gap in the stacked spatial light modulator as shown in FIG. 4 , if the gap is at a level of about 380 μm or less, the viewing area is constant, but when the gap exceeds 380 μm, the viewing area is gap It can be seen that this decreases in inverse proportion to the increase. Here, the viewing area may be referred to as a kind of viewing window through which a viewer can perceive a holographic image at a specific viewing distance. In the experiment, the viewing distance was set to 1m, the pixel size was set to 35㎛, and the wavelength of the light source was set to 532nm. However, when the gap increases beyond a predetermined value, the viewing area tends to decrease in inverse proportion to each other.

Hereinafter, in the present invention, a structure of a spatial light modulator with a reduced gap in order to reduce an error light region thereof while maintaining the advantages of signal processing of the stacked spatial light modulator will be described. In the spatial light modulator of the present invention, a spatial light modulator for phase is formed, an electrode is formed on the rear side of the spatial light modulator, and a spatial light modulator for amplitude is formed by coating a film containing nano-liquid crystals to form a stacked stack capable of individually driving. It is proposed to form spatial light modulation.

Through this structure, the gap of the entire spatial light modulator is reduced, so that error light generation is reduced and the viewing angle can be widened.

5 is a cross-sectional view showing the spatial light modulator of the present invention.

As shown in FIG. 5 , the spatial light modulator 200 of the present invention includes a first substrate 310 and a second substrate 320 having a plurality of pixels facing each other, each on the first substrate 310. The first electrode 311 provided on the pixel, the second electrode 321 located on the inner surface of the second substrate 320 to face the first electrode 311, and the first substrate 310 and the liquid crystal layer 315 located between the second substrate 320, and the third electrode 331 and the fourth electrode located on the outer surface of the second substrate 320 corresponding to each pixel and separated from each other 332) and a liquid crystal film layer 335 including nano-liquid crystals on the outer surface of the second substrate 320.

In particular, the spatial light modulator 200 of the present invention reduces the gap between the phase modulator (phase SLM) and the amplitude modulator (amplitude SLM) that act independently of each other, the inner and outer surfaces of the second substrate 320 It is used as a formation surface of the drive electrode of the different modulators. That is, descriptions of the phase modulator and the amplitude modulator are shared, the gap can be reduced, and the overall thickness of the spatial light modulator can be reduced and slimmed down.

Meanwhile, the first substrate 310 or the second substrate 320 may be a glass or plastic film. In the case of a plastic film, there is an advantage in that it can be implemented with a thickness thinner than that of glass. Even in the case of glass, a portion of the thickness may be etched and reduced to be adjusted to a thickness that can secure a certain viewing distance.

In addition, in the spatial light modulator of the present invention, the phase and amplitude changes in the phase SLM and the amplitude SLM are driven by a vertical electric field between the first and second electrodes 311 and 321, respectively. The internal liquid crystal layer 315 is driven by and the nano liquid crystal layer 335 is driven by the horizontal electric field driving between the third and fourth electrodes 331 and 332, thereby optically changing the liquid crystal arrangement.

Here, the liquid crystal layer 315 between the first and second substrates 310 and 320 has physical properties between liquid and solid phases of liquid crystal molecules, and prevents internal liquid crystal from being released to the outside, Between the first substrate 310 and the second substrate 320, a sealant 317 enclosing the liquid crystal layer 315 while enclosing the plurality of pixels is formed.

In addition, each pixel has a width of one pitch p, and the pixels are regularly arranged in a matrix in the sealing material 317. In addition, the first electrode 311 of the phase modulator (phase SLM) and the third and fourth electrodes 331 and 332 of the amplitude modulator (amplitude SLM) are provided within the one pitch p. Since the area of pixels is defined in common to the first substrate 310 and the second substrate 320, these electrodes 311, 331, and 332 do not require alignment during bonding and are positioned accurately within each pixel. can be formed in In addition, the second electrode 321 and the third and fourth electrodes 331 and 332 are formed on the inner and outer surfaces of the second base material 320, respectively, so that either the inner surface or the outer surface of the second base material 320 is formed. After forming the electrode on one side, the second substrate 320 is inverted to form the electrode on the other side, so that the electrode formed first can serve as a positional reference for the electrode to be formed later.

In addition, the liquid crystal film layer 335 is a combination of nano liquid crystals in microcapsule units by a binder, and in the spatial light modulator 200, the microcapsules in the binder are fixed and cured, and the third and fourth electrodes ( 331 and 332), it is possible to vary the propagation of light by changing the arrangement of the nano liquid crystals in the microcapsules according to the application of the horizontal electric field.

For example, the microcapsule is obtained by encapsulating a plurality of liquid crystal single molecules in a polymer material, and emits light emitted in an isotropic state as it is without change in an electric field unapplied state, and when an electric field is applied, the microcapsule It has the property of aligning liquid crystal single molecules in the direction perpendicular or horizontal to the direction of the electric field. That is, liquid crystal single molecules in the microcapsules are switched when an electric field is applied. The binder filling the spaces between the microcapsules is a UV curable material, and after forming the binder including the microcapsules on the second substrate 320 on which the third and fourth electrodes 331 and 332 are formed, a UV curing process is performed. Through this, it is cured into a liquid crystal film layer 335 onto a film.

Meanwhile, a polarizing film 340 may be further included on the liquid crystal film layer 335 to change the direction of light emission. In this case, the curing process of the liquid crystal film layer 335 may be performed after attaching the polarizing film 340 .

Hereinafter, detailed operations of the phase modulator and the amplitude modulator will be described.

6 is a plan view showing the spatial light modulator of the present invention, FIG. 7a is a graph showing the change in refractive index versus voltage in the spatial light modulator for phase of FIG. 5, and FIG. 7b is a graph showing the voltage in the spatial light modulator for amplitude in FIG. It is a graph showing the change in transmittance versus transmittance.

As shown in FIG. 6, in order to phase-modulate light between the first and second substrates 310 and 320, a first voltage applying means for applying voltages to the first electrode 311 and the second electrode 321, respectively ( 341). And, in the liquid crystal film layer 335 on the second substrate 320, a second voltage applying means for applying voltages to the third electrode 331 and the fourth electrode 332, respectively, to modulate the amplitude of light. (342) is further included.

In the illustrated example, the first voltage applying means 341 has been shown to be formed on the surface of the first base material 310 on which the first electrode 311 is formed, and the second voltage applying means 342 is the third, second voltage applying means 342. 4 electrodes 331 and 332 are shown formed on the outer surface of the second substrate 320 . These first and second voltage applying units 341 and 342 protrude to the outside and may be connected to a signal processor (see 50 in FIG. 1 ) provided outside the spatial light modulator 200 .

In addition, a first pad part PAD1 connected to the first voltage applying means 341 on the first substrate 310 and located outside the seal member 317 in a plan view and the second substrate ( 320) may further include a second pad part PAD2 connected to the second voltage applying unit 342 and positioned outside the seal member 317 in a plan view. At this time, the first pad part PAD1 is connected to the first and second electrodes 311 and 321 through separate link wires (not shown), and the second pad part PAD2 is connected to the first and second electrodes 311 and 321. It may be connected to the third and fourth electrodes 331 and 332 through link wires (not shown), respectively. On the other hand, the first pad part PAD1 is on the surface of the first substrate 310 on which the first electrode 311 is formed, and can be electrically connected to the first electrode 311 through planar connection. However, since the second electrode 321 is located on the inner surface of the second base material 320, electrical connection is not possible with only link wiring. For example, components of the sealant 317 located on the second electrode 321 The second electrode 321 and the sealant 317 include a conductive material and include a link wire (not shown) connected to the first pad part PAD1 on the side of the first substrate 310 in contact with the sealant 317. ), link wiring, and sequential connection to the first pad part PAD1.

In some cases, the second electrode 321 may be conductively grounded without electrical connection to the lower first substrate 310 . In this case, the second electrode 321 is always in a grounded state, and as a voltage is applied to the first electrode 311, whether or not an electric field is formed in the phase modulator (phase SLM) can be controlled.

Meanwhile, the liquid crystal layer 315 includes ECB (Electrically Controlled Birefringence) mode liquid crystal and is driven by a vertical electric field between the first and second electrodes 311 and 321 . The first electrode 311 is divided for each pixel so that the phase SLM can be driven for each pixel. The second electrode 321 may be formed by dividing each pixel or by grouping a plurality of pixels as needed.

As shown in FIG. 7A, the phase modulator (phase SLM) obtains the effect of phase change by changing the effective refractive index according to the voltage applied to the liquid crystal layer 315 when voltage is applied. The phase modulator (phase SLM) generates a vertical electric field when a voltage is applied in the liquid crystal layer 315 between the first substrate 310 and the second substrate 320, and the wavelength of the incident light is proportional to or inversely proportional to the voltage value. At (λ), phase modulation between 0 and λ is performed. Before applying the voltage, the liquid crystal layer 315 of the phase modulator (phase SLM) is designed to have a retardation value approximately equivalent to a red wavelength (λred). That is, the phase modulator ( phase SLM) can be phase-modulated within a range of the maximum value λred (0 to λred). In addition, as shown in FIG. 7B, the amplitude modulator (amplitude SLM) adjusts the transmittance of the liquid crystal film layer 335 according to voltage application. This changes, thereby obtaining the effect of a change in the intensity of light, that is, a change in amplitude.

의 식을 따른다. 여기서 각도 α는 전압 인가시 편광 필름(340)의 투과축과 액정 광축 사이의 각도로, 각도 α가 45˚일 때, 투과율이 최대가 됨을 알 수 있다. 그리고, 진폭 변조부(amplitude SLM)는 상기 액정 필름층(335) 내의 나노 액정의 배향 각도를 전압으로 조절함으로써, 상기 투과율, 즉, 빛의 세기를 조절할 수 있는 것이다. 한편, 상기 진폭 변조부(amplitude SLM)의 투과율에 관계된 것으로, 액정 필름층(335)은 가장 시감 특성이 좋은 녹색 파장(λgreen)에 대해 λ/2의 지연 값(retardation value)를 갖도록 설계한다. 그런데, 전압 인가 전 초기 상태에서는 각도 α가 0˚인 것으로, 진폭 변조부(amplitude SLM)는 내부 액정 필름층(335)에서, 지연 값에 관계없이 투과율은 0이 되며, 인가하는 전압 값을 올리면 점차 투과율의 상승을 얻을 수 있다. 여기서, 각도 α를 결정하는 것은, 액정 필름(335) 내의 나노 액정의 배향 과 상기 액정 필름(335) 상의 편광 필름(340)과의 관계이며, 각도 α가 45˚일 때, 투과율이 최대가 되도록 하기 위해, 상기 제 3, 제 4 전극(331, 332)은 편광 필름(340)의 투과축에 대해 +45˚ 또는 -45˚ 의 길이 방향을 갖도록 설계할 수 있다.It is the liquid crystal film layer 335 that determines the transmittance in the amplitude modulator (amplitude SLM), and its transmittance is

follow the formula Here, the angle α is an angle between the transmission axis of the polarizing film 340 and the liquid crystal optical axis when voltage is applied, and it can be seen that the transmittance is maximized when the angle α is 45 degrees. And, the amplitude modulator (amplitude SLM) can adjust the transmittance, that is, the intensity of light, by adjusting the alignment angle of the nano liquid crystals in the liquid crystal film layer 335 with a voltage. Meanwhile, as related to the transmittance of the amplitude modulator (amplitude SLM), the liquid crystal film layer 335 is designed to have a retardation value of λ/2 for a green wavelength (λgreen) having the best luminous properties. However, in the initial state before voltage application, the angle α is 0°, and the amplitude modulator (amplitude SLM) is in the internal liquid crystal film layer 335, the transmittance becomes 0 regardless of the delay value, and when the applied voltage value is raised, A gradual increase in transmittance can be obtained. Here, determining the angle α is the relationship between the alignment of the nano liquid crystals in the liquid crystal film 335 and the polarizing film 340 on the liquid crystal film 335, and when the angle α is 45°, the transmittance is maximized. To do this, the third and fourth electrodes 331 and 332 may be designed to have a length direction of +45° or -45° with respect to the transmission axis of the polarizing film 340 .

8A and 8B are diagrams illustrating light propagation in the spatial light modulator for phase and amplitude.

As shown in FIG. 8A, the phase modulator (phase SLM) modulates the phase Ф of the incident light pixel by pixel (φ1', φ2', φ3') by changing the voltage value applied to the first electrode 311 for each pixel. let it

In this case, when voltage is applied to the first and second electrodes 311 and 322, the phase is modulated between the first substrate 310 and the second substrate 320, and at this time, the first substrate 310 The light incident to passes through the second substrate 320 and modulates the phase of light incident on the first substrate 310 and is emitted. This is possible due to a change in effective refractive index in the liquid crystal layer 315 according to voltage application.

And, as shown in FIG. 8B, the amplitude modulator (amplitude SLM) changes the amplitude to A1, A2, and A3 according to the strength of the voltage, and this can also be controlled for each pixel.

In the present invention, the pixel-by-pixel control is performed by allowing each pixel to be independently connected to the first and second voltage application means 341 and 342 to the first and second pad portions PAD1 and PAD2 of FIG. 6 .

In addition, when a voltage is applied to the third and fourth electrodes 331 and 332, the amplitude SLM passes through the liquid crystal film layer 335 on the second substrate 320 and is amplitude-modulated. Light incident on the second substrate 320 passes through the liquid crystal film layer 335 and is emitted with a delay value equivalent to half (λ/2) of the wavelength of the incident light.

Meanwhile, the first to fourth electrodes 311, 321, 331, and 332 provided in the aforementioned spatial light modulator 200 may be transparent electrodes, and in some cases, the first electrode 311 and the third and fourth The electrodes 331 and 332 may be replaced with metal when their width is smaller than the pixel pitch.

In expressing information, the spatial light modulator 200 of the present invention can independently express information by dividing it into two modulations through the first and second voltage application units 341 and 342, thereby reducing the amount of data processing. there is That is, the spatial light modulator of the present invention can form a layered structure with a small thickness, so that the phase and amplitude can be freely modulated, and at the same time, the phase and amplitude can be individually adjusted, so the amount of data processing can be reduced. . As a result, real-time images can be reproduced.

In addition, since restoration is performed by combining the modulation values of the amplitude modulator (amplitude SLM) and the phase modulator (phase SLM) during image reproduction, there are unique modulation values of amplitude and phase, which can reduce noise during the restoration process. can

In addition, a spatial light modulator can be fabricated by attaching the curable nano-liquid crystal to the outer surface of the second substrate in the form of a film, so that in the amplitude light modulator, which is the upper cell, while having the same function as the stacked spatial light modulator, a thick substrate such as a glass substrate can be reduced, making slimming possible.

In addition, by slimming the spatial light modulator, a diffraction error caused by a gap between two SLMs is prevented in the stacked spatial light modulator, thereby obtaining an effect of widening the viewing area.

In addition, there is an advantage in that coalescence errors can be prevented because it is not required to coalesce optical modulators of different shapes, and errors due to alignment due to errors in vision equipment can be prevented.

Meanwhile, in the following, hologram reproduction capable of displaying color in digital holography will be reviewed using the modified example of the light source unit 10 described in FIG. 1 and using the same.

FIG. 9 is a view showing arrangement of light sources and spatial light modulators and light propagation in digital holography according to the present invention.

As shown in FIG. 9 , the light source unit 10 may include first to third light sources 12a, 12b, and 12c respectively emitting light of different wavelengths in the visible light region, which is, for example, red, green, It may be a blue light source. However, the emission color is not limited thereto, and can be changed to a light source having a different wavelength as long as white light can be obtained by adding the light. In any case, each of the light sources emits light of a single wavelength coherently. In addition, a spatial light modulator 200 may be included on the first to third light sources 12a, 12b, and 12c, and a waveguide 11 for controlling parallel-side light emission. Each of the first to third light sources 12a, 12b, and 12c may be a laser light source. If the light source has good directivity, good coherence, and each emits single wavelength light, it may be replaced.

In addition, when the plurality of first to third light sources 12a, 12b, and 12c are provided, the spatial light modulator 200 can process only a single wavelength at a point in time, and thus is driven in time division.

The first to third light sources 12a, 12b, and 12c each have a single different wavelength, and can be summed together to represent white light. In addition, the first to third light sources 12a, 12b, and 12c are time-division driven, so that the spatial light modulator 200 converts light of a corresponding wavelength into phases φ1', φ2', and φ3' and amplitudes ( A1, A2, and A3) are modulated, and light is emitted to have delay values of λ and λ/2.

As shown in FIG. 1, the spatial light modulator 200 is connected to the signal processing unit 50, receives interference fringe image information according to voltage application to electrodes provided for each pixel, and modulates phase and amplitude by diffracting the spatial light modulator 200. . In addition, the spatial light modulator 200 applies voltage signals corresponding to the hologram to be displayed to the first to fourth electrodes 311, 321, 331, and 332 with image information of the interference fringe, so that the pattern can be displayed. have. That is, the interference pattern appearing in the spatial light modulator 200 can be changed according to the signal applied to the spatial light modulator 200, and the signal processing unit 50 performs this change. Here, the hologram information processed by the signal processing unit 50 is called CGH (Computer Generated Hologram data), which is variable according to an event or a state of an object to be expressed.

Although not shown, when the diffraction angle is small, a lens system (30 in FIG. 1) for concentrating the light emitted from the light modulator and concentrating a 3D image on a specific surface is further provided for focusing light and displaying a hologram perceptible at a viewing distance. can be included The lens system is a component that may be omitted when it is possible to form internal pixels of the spatial light modulator 200 to a level of 1 μm or less.

On the other hand, the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be clear to those skilled in the art.

10: light source unit 11: waveguide
12a to 12c: light source 20: SLM
30: lens system 40: hologram
50: signal processing unit 310: first substrate
311: first electrode 315: droplet layer
317 seal material 320 second substrate
321: second electrode 331: third electrode
332: fourth electrode 335: liquid crystal film layer
340: polarizer 341: first voltage application unit
342: second voltage application unit phase SLM: phase modulator
Amplitude SLM: Amplitude modulator

Claims (20)

facing each other, a first substrate and a second substrate having a plurality of pixels;
a first electrode provided on each pixel on the first substrate;
a second electrode positioned on an inner surface of the second substrate to face the first electrode;
a liquid crystal layer positioned between the first substrate and the second substrate;
a third electrode and a fourth electrode located on the outer surface of the second substrate to correspond to each pixel and spaced apart from each other;
On the outer surface of the second substrate, a liquid crystal film layer containing nano-liquid crystals; and
A polarizing film in contact with the liquid crystal film layer,
The third electrode and the fourth electrode have a longitudinal direction of +45 ° or -45 ° with respect to the transmission axis of the polarizing film,
The liquid crystal layer varies an effective refractive index according to a voltage difference applied to the first electrode and the second electrode and transmits incident light toward the second substrate,
In the liquid crystal film layer, before voltage is applied to the third and fourth electrodes, the nano-liquid crystal is oriented so that the optical axis coincides with the transmission axis of the polarizing film, and when the voltage difference applied to the third and fourth electrodes increases, the A spatial light modulator in which transmittance of light passing through a liquid crystal film layer is increased. According to claim 1,
The spatial light modulator further comprising a sealant between the first substrate and the second substrate, enclosing the plurality of pixels and enclosing the liquid crystal layer. delete According to claim 2,
The spatial light modulator further comprises a first voltage application means for applying voltages to the first electrode and the second electrode, respectively. According to claim 4,
The spatial light modulator further comprises a second voltage application means for applying voltages to the third electrode and the fourth electrode, respectively. According to claim 5,
a first pad portion connected to the first voltage applying unit on the first base material and positioned outside the sealant in a plane view; and
The spatial light modulator further comprising a second pad part connected to the second voltage application unit and positioned on an outer surface of the second base material and positioned outside the seal member in a plan view. According to claim 6,
The first pad part is connected to the first and second electrodes, respectively;
The second pad part is connected to the third and fourth electrodes, respectively, of the spatial light modulator. According to claim 1,
The liquid crystal film layer is a spatial light modulator in which nano liquid crystals in microcapsule units are bonded by a binder. According to claim 1,
The liquid crystal layer includes a liquid crystal of an electrically controlled birefringence (ECB) mode,
The spatial light modulator of claim 1 , wherein the liquid crystal layer has a delay value corresponding to a red wavelength before voltage is applied to the first and second electrodes. According to claim 1,
The spatial light modulator of claim 1 , wherein the first or second substrate is a glass or plastic film. According to claim 5,
When a voltage is applied to the first and second electrodes, the liquid crystal layer phase-modulates between 0 and the wavelength of the incident light according to a voltage difference applied to the first and second electrodes, and emits light. According to claim 11,
When voltage is applied to the third and fourth electrodes, the spatial light modulator is amplitude-modulated by passing through the liquid crystal film layer on the second substrate. A first substrate and a second substrate having a plurality of pixels facing each other, a first electrode provided on each pixel on the first substrate, and an inner surface of the second substrate facing the first electrode. a second electrode, a liquid crystal layer located between the first substrate and the second substrate, and a third electrode and a fourth electrode located on the outer surface of the second substrate corresponding to each pixel and spaced apart from each other; 2, a spatial light modulator including a liquid crystal film layer containing nano-liquid crystals, and a polarizing film in contact with the liquid crystal film layer, on an outer surface of the substrate;
a light source unit transmitting coherent light to the spatial light modulator; and
A lens system for focusing the light emitted from the spatial light modulator to focus a three-dimensional image on a specific surface;
The third electrode and the fourth electrode have a longitudinal direction of +45 ° or -45 ° with respect to the transmission axis of the polarizing film,
The liquid crystal layer varies an effective refractive index according to a voltage difference applied to the first electrode and the second electrode and transmits incident light toward the second substrate,
In the liquid crystal film layer, before voltage is applied to the third and fourth electrodes, the nano-liquid crystal is oriented so that the optical axis coincides with the transmission axis of the polarizing film, and when the voltage difference applied to the third and fourth electrodes increases, the Digital holography in which the transmittance of light passing through a liquid crystal film layer increases. According to claim 13,
Digital holography further comprising a signal processing unit transmitting hologram information to the spatial light modulator. According to claim 14,
The hologram information is transmitted as a voltage signal applied to the first to fourth electrodes. According to claim 13,
The light source unit includes first to third light sources respectively emitting light of different wavelengths in the visible light region. According to claim 16,
The first to third light sources are time-division driven digital holography. According to claim 15,
and a first voltage application means for applying voltages to the first electrode and the second electrode, respectively, and a second voltage application means for applying voltages to the third and fourth electrodes, respectively. According to claim 18,
The liquid crystal layer
It has a delay value of a red wavelength before voltage is applied to the first and second electrodes,
When a voltage is applied to the first and second electrodes, the incident light is phase modulated between 0 and the wavelength range of the incident light in proportion or inverse proportion to the voltage difference applied to the first electrode and the second electrode. Digital holography. According to claim 19,
When a voltage is applied to the third and fourth electrodes, the phase-modulated light passing through the second substrate passes through the liquid crystal film layer on top of the second substrate and is amplitude-modulated.

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