JP2877884B2 - Photothermal writing type spatial light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photothermal writing type spatial light modulator, and more specifically, to input an image or data pattern information to a spatial light modulator using writing light, This information is converted to 2
The present invention relates to a photothermal writing type spatial light modulator having a function of displaying a dimension.

[Summary of the Invention]

The present invention relates to a photothermal writing type spatial light modulator having a function of inputting an image or data pattern information to a spatial light modulator using writing light and displaying the information two-dimensionally using reading light, and in particular, The spatial light modulator is composed of a guest-host type liquid crystal in which a dye is mixed with a nematic liquid crystal, bias heat is applied to the spatial light modulator, and image and data pattern information is input by writing light having a wavelength in the light absorption region of the dye. ,
Since the photothermal writing type spatial light modulation element for displaying the reading light having a wavelength outside the light absorption region of the dye is formed, the writing light energy is small.

 Images can be written and displayed without scanning.

 Simple element structure and optical system.

 The contrast of the displayed image is high.

 Analog images can be displayed.

 Image processing using coherent light is possible.

 Image information can be written using a scanning optical system.

It has features such as.

[Conventional technology]

Conventionally, the following devices have been known as photothermal writing type spatial light modulators.

Reference 1 (Y. Nagae, E. Kaneko, Y. Mori and H. Kawakami: S
ID '86International Symposium (1986) .p.368-p.370)
As shown in FIG. 11, a transparent electrode 16, an alignment layer 3, a smectic liquid crystal 4, a metal reflector 17, a light absorbing layer 18 are provided between two glass substrates 2 each having an antireflection film 19, as shown in FIG. Is shown. 20 in the figure
Denotes an image erasing power supply.

In the above configuration, when there is no writing laser beam 7, the liquid crystal 4 is homogeneously aligned and the reading light 8
Is transmitted through the liquid crystal 4, reflected by the metal reflecting mirror, and is emitted again after passing through the glass substrate on the incident light side. On the other hand, when the writing laser light 7 enters from the glass substrate on the reflecting side, the laser light 7 absorbs light. Absorbed in layer 18 and converted to thermal energy. This heat energy is transmitted to the liquid crystal 4 through the metal reflecting mirror 17 and heats the liquid crystal. When the energy of the laser beam 7 is sufficiently large, the liquid crystal changes from a smectic phase to a liquid phase via a nematic phase. Here, when the laser light is cut off and the liquid crystal in the liquid phase is rapidly cooled, the liquid crystal is in a focal conic arrangement, and the readout light 8 is scattered. With the above operation, this device can be used for a dark image (2
Value image).

[Problems to be solved by the invention]

However, the above-mentioned conventional photothermal writing type spatial light modulator has a problem to be solved as described below.

Requires large light energy for writing. (Equation 10
0 mJ / cm ² to several J / cm ² ) Therefore, in order to write two-dimensional information such as an image or a data pattern, it is necessary to scan the writing laser beam in the horizontal and vertical directions.

 Therefore, the writing optical system becomes complicated.

Therefore, high-speed scanning cannot be performed (moving image display is difficult). The contrast of the displayed image is low.

 Only binary digital information can be displayed.

A complicated optical system (Schlieren optical system) is required.

 It is not suitable for image processing using coherent light.

Accordingly, an object of the present invention is to solve the above-described various problems and to write and display a high-resolution digital or analog image or data pattern at a high speed, thereby achieving high-definition image display and image processing. It is an object of the present invention to provide a photothermal writing type spatial light modulator suitable for the above.

[Means for solving the problem]

In order to achieve such an object, a first aspect of the present invention is to sequentially adhere a transparent substrate, a liquid crystal alignment layer, a guest-host type liquid crystal in which a nematic liquid crystal is mixed with a dye, a liquid crystal alignment layer, and a transparent substrate. In the configuration described above, the guest-host type liquid crystal is irradiated with writing light having a wavelength within the light absorption region of the dye and reading light having a wavelength outside the light absorption region, thereby generating heat based on the writing light absorption of the dye. By changing the birefringence of the guest-host type liquid crystal and modulating the readout light, the image or data pattern information is written and read.

According to a second aspect of the present invention, in the first aspect, a reflecting mirror is provided between one transparent substrate and a liquid crystal alignment layer adjacent thereto.

According to a third mode of the present invention, in the first or second mode, the guest-host type liquid crystal is heated.

According to a fourth aspect of the present invention, in any one of the first to third aspects, a planar heater or a Peltier element is closely attached to one of the transparent substrates.

According to a fifth aspect of the present invention, in the fourth aspect, a polarizing beam splitter is adhered to one of the transparent substrates.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, an image or data pattern information is written without scanning.

According to a seventh aspect of the present invention, in any one of the first to fifth aspects, an image or data pattern information is written by scanning.

[Operation] Since the present invention is configured as described above, it is possible to display images and data pattern information by either a non-scanning method or a scanning method, which is suitable for displaying high-definition digital and analog images. In addition, image processing using coherent light can be performed.

That is, since the photothermal writing type spatial light modulator of the present invention utilizes the birefringence of liquid crystal, an image can be written and displayed without scanning with a small writing light energy.
For this reason, a point that a scanning optical system is required for writing, a point that a writing and reading optical system is complicated, and a point that are peculiar to the conventional photothermal writing type spatial light modulator described in the above-mentioned document 1
There are no problems such as that only the digital information of the value can be displayed, that the contrast of the displayed image is low, and that it is not suitable for coherent light image processing.

Further, according to the present invention, image display using a scanning optical system is also possible.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<< Configuration >> FIG. 1 schematically shows the configuration of an embodiment of the photothermal writing type spatial light modulator according to the present invention. In the figure, 1 is
This is a photothermal writing type spatial light modulator of the present invention in which a transparent substrate 2 and a guest-host type liquid crystal 6 in which a liquid crystal is mixed with a dye 5 are adhered and integrated. In the figure, 7 is a writing light,
8 is a reading light. The liquid crystal shown in the figure is a nematic liquid crystal.

In the guest-host type liquid crystal and the dye shown in FIG. 1, in the initial state where there is no writing light, the long axes of the molecules are arranged uniformly (homogeneous alignment) parallel to the transparent substrate. A guest-host type liquid crystal in which the major axis of the dye is arranged non-parallel to the transparent substrate can also be used in the photothermal writing type spatial light modulator of the present invention. For example,
As shown in FIG. 2, homeotropic alignment in which liquid crystal molecules and dye molecules are uniformly vertically aligned with the substrate, or, as shown in FIG. A well-known liquid crystal material and a liquid crystal alignment method utilizing birefringence of liquid crystal, such as so-called hybrid alignment, which are aligned and homeotropically aligned near the other substrate, are used for the photothermal writing type spatial light modulator of the present invention. Can be.

As the dye to be mixed with the liquid crystal, for example, a material that strongly absorbs light of a specific wavelength is used, as shown by the light absorptance vs. spectral characteristics in FIG.

Light having a wavelength (for example, λ _{1 in} FIG. 4) that is easily absorbed by the dye is used for writing, and light having a wavelength (for example, λ _{2 in} FIG. 4) that is hardly absorbed by the dye is used for reading. As the writing light and the reading light, incoherent light such as xenon lamp light and halogen lamp light or laser light (coherent light) is used. However, when linearly polarized light is used as the writing light, it is necessary to determine the polarization direction of the writing light in consideration of the absorption anisotropy of the dye. For example, a dye having a positive (or negative) absorption anisotropy (a dichroic dye)
Since the major axis (or minor axis) direction of the dye molecule has a large light absorptivity, the major axis (or minor axis) direction of the dye molecule should be aligned with the polarization direction of the writing light in order to save writing light energy. Is desirable. On the other hand, as the reading light, light linearly polarized in a direction other than the major axis and the minor axis of the liquid crystal molecules is used.

<< Operation >> Next, the operation of the photothermal writing type spatial light modulator of the present invention will be described.

The operation of the photothermal writing type spatial light modulator of the present invention will be described with reference to an example of a device in which the element shown in FIG. 1 is inserted between a polarizing plate and an analyzer whose polarization directions are orthogonal to each other. The angle between the polarization direction of the polarizing plate on the incident side and the long axis of the liquid crystal molecules is ζ,
Assuming that the thickness of the liquid crystal layer 6 is d and the wavelength of the reading light 8 is λ ₂ ,
The read light transmittance _IO is Given by Here, dΔn / dT is the amount of change in the birefringence of the liquid crystal per unit temperature change, T _O is the temperature of the liquid crystal (generally, room temperature) without artificial heating (hereinafter referred to as bias heat), and ΔT is temperature increased by the bias heat, dT / dP temperature variation of the liquid crystal with respect to the unit writing light energy, P _W is the writing light energy, theta _O is the initial optical phase difference.

zeta = 45 to °, and by controlling the theta _O Then, equation (1) becomes Becomes The expression (3) indicates that the transmittance of the reading light can be periodically changed by individually applying the bias heat and the writing light, or by adding both at the same time.

As an example, the I-ΔT characteristic when the readout light (λ ₂ = 633 nm) is incident on the spatial light modulator (d = 25 μm) of the present invention in which a dichroic dye is mixed into a nematic liquid crystal is described as a fifth example.
Shown in the figure. The figure shows that if the temperature (ΔT _B ) due to the bias heat is set near ΔT _C (ΔT _C = T _C −T _O : T _C is the phase transition temperature from the nematic phase to the liquid phase), light modulation can be performed with small thermal energy. Indicates what can be done. However, the sum of the temperature increased by the bias heat and the temperature increased by the writing light must be smaller than ΔT _C ｛[ΔT _B + (dT / dP) P _W ] <ΔT
_C ｝ is the condition.

FIG. 6 shows an embodiment of an image or data pattern writing / display apparatus using the photothermal writing type spatial light modulator of the present invention. In the same figure, 9 is a constant temperature tube for keeping the temperature of the spatial light modulator constant, 10 is a heater, 11 is a temperature controller, 12 is a polarizing plate for adjusting the polarization direction of readout light, 13 is a lens, and 14 is an input image. , 15 are screens for projecting display images. The writing light 7 and the reading light 8 are incident on the spatial light modulator 1 perpendicularly or almost perpendicularly, and the traveling directions of both lights do not necessarily have to be the same direction. T ₀ = 25 ° C, Δ
An image was formed on the spatial light modulator of the present invention by setting T _B = 32 ° C.
Writing with laser light (λ ₁ = 488 nm) resulted in a resolution of 20 line pairs / mm or more. The light energy required for writing was ² mJ / cm ² , and an image could be written / displayed with much less energy than a conventional photothermal writing type spatial light modulator without scanning. , Also Θ
By controlling _O or rotating the polarizing plate, it was confirmed that the level of the image could be changed in an analog manner, and that an image whose level was inverted from the input image could be displayed.

There are the following two reasons why the spatial light modulator of the present invention has higher sensitivity than the conventional photothermal writing type spatial light modulator.

In general, the refractive index of the liquid crystal greatly changes near T _C , not limited to the embodiment. For example, 5CB (homeotropic4-cyano-4
-Pentylbiphenyl) nematic ordinary refractive index of the liquid crystal (n _o) and extraordinary refractive index (n _e), as shown in FIG. 7, showing a very large temperature dependence. (Here, it is the refractive index of the liquid crystal in the liquid phase.) As shown in FIG.
One of the values of the refractive index, because the general approach each other with increasing temperature, n _o or than to use only n _e, birefringence Δ
better with n (= n _o -n _e) is, it is possible to obtain a large refractive index change. That is, if the temperature dependence of the birefringence of the liquid crystal is used, a large optical change can be generated by a small temperature change. Conventional photothermal writing type spatial light modulators utilize the state change of the smectic liquid crystal phase → nematic phase → liquid phase of the smectic liquid crystal, and two types of phase transitions are generated to display images and data patterns. There is a need. On the other hand, in the spatial light modulator of the present invention, an image is displayed by utilizing a change in birefringence within a single phase (nematic phase), so that light energy required for writing is small.

Further, in the present invention, since the guest-host type liquid crystal is used, the writing light is absorbed by the dye and converted into heat energy in the liquid crystal layer, so that the liquid crystal can be efficiently heated. On the other hand, in the conventional photothermal writing type spatial light modulator, as shown in FIG.
The liquid crystal 4 is absorbed by the light absorbing layer 18 and then propagates to the liquid crystal 4. Most of the heat energy generated in the light absorbing layer is transmitted to the glass substrate, and the liquid crystal cannot be heated effectively.

So far, the transmission type photothermal writing type spatial light modulation element for displaying an image with the read light passing through the spatial light modulation element has been described. Next, the reflecting mirror 30 is provided between the guest-host type liquid crystal 6 and the substrate 2. The reflection type spatial light modulator (FIG. 8) will be described. However, reference numeral 31 in the figure denotes a polarizing beam splitter. In the reflection type spatial light modulator, the writing light 7 and the reading light 8 reciprocate in the guest-host type liquid crystal 6, so that the reading light birefringence requires less writing light energy than the transmission type spatial light modulator. The effect can be increased. However, in order to prevent the resolution of the displayed image from lowering, it is necessary to vertically write the writing light and the reading light into the spatial light modulator. In order to prevent the writing light from being mixed into the display image, the writing light needs to be linearly polarized in the major axis direction or the minor axis direction of the liquid crystal molecules. However, if the reflecting mirror 30 is provided with a wavelength dispersion characteristic such that the writing light is transmitted and the reading light is reflected, the optical paths of the writing light and the reading light are changed as shown in FIG. 1 or FIG. Can be prevented from being mixed with writing light.

FIG. 9 is a schematic diagram of an image display device using a reflection type spatial light modulator. In the figure, 32 is a sheet heater or Peltier element, 33 is a lead wire, and 34 is a dichroic mirror that reflects (or transmits) write light and transmits (or reflects) read light. The device shown in FIG. 9 is more compact than the device shown in FIG.
In addition, there is an advantage that an image can be displayed with less writing light energy. FIG. 10 is a top view of a further miniaturized device of FIG. In the figure
35 is a dichroic prism having the same function as 34.

〔The invention's effect〕

As described above, according to the present invention, the following specific effects can be obtained.

Since the photothermal writing spatial light modulator of the present invention utilizes the birefringence of liquid crystal, the writing light energy is smaller than that of the conventional photothermal writing spatial light modulator.

Therefore, it is possible to write / display two-dimensionally at once without scanning information such as images and data patterns.

For this reason, the writing optical system is simple, and an image can be displayed at a higher speed as compared with the conventional photothermal writing type spatial light modulator.

Further, since the birefringence of the liquid crystal is used, the contrast of the displayed image is high.

The conventional photothermal writing type spatial light modulator can display only binary digital images, but the spatial light modulator of the present invention can display digital and analog images.

The conventional photothermal writing type spatial light modulator requires a schlieren optical system for reading, but the spatial light modulator of the present invention does not require the optical system and the reading optical system is simple.

The conventional photothermal writing type spatial light modulation element is an image display using scattered light, and is not suitable for optical image processing. On the other hand, since the spatial light modulator of the present invention displays an image using birefringence, it is suitable for optical image processing.

Further, writing of image information using a scanning optical system is also possible.

It has features such as.

[Brief description of the drawings]

1 to 3 are schematic diagrams showing examples of the configuration of a photothermal writing type spatial light modulator according to the present invention, respectively. FIG. 4 is a graph showing the light absorptivity of the dyes of the constituent elements of FIGS. 1 to 3. FIG. 5 is a diagram showing an example of wavelength dependence, FIG. 5 is a diagram showing an example of the temperature dependence of the read light transmittance of the photothermal writing type spatial light modulator of the present invention, and FIG. 6 is a photothermal writing type of the present invention. schematic diagram of a configuration example of an image writing / display apparatus using a spatial light modulation element, FIG. 7 is a normal refractive index of the nematic liquid crystal of the components of Figure 1-Figure 3 (n _o) and extraordinary refractive FIG. 8 is a diagram showing an example of a temperature-dependent characteristic of the rate ( _ne ), FIG. 8 is a schematic diagram showing another configuration example of the photothermal writing type spatial light modulator of the present invention, and FIG. 9 and FIG. FIG. 11 is a schematic diagram showing another configuration example of an image writing / display device using the photothermal writing type spatial light modulation element of the present invention. FIG. 1 is a schematic diagram showing a configuration of a conventional photothermal writing type spatial light modulator described in FIG.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/137 500 G02F 1/13 102

Claims (7)

(57) [Claims] A transparent substrate, a liquid crystal alignment layer, a guest-host type liquid crystal in which a nematic liquid crystal is mixed with a dye, a liquid crystal alignment layer, and a transparent substrate are sequentially brought into close contact with each other. A write light having a wavelength and a read light having a wavelength outside the light absorption region are irradiated on the guest-host type liquid crystal, and the birefringence of the guest-host type liquid crystal is changed by heat generated based on absorption of the dye by the write light. And a photothermal writing type spatial light modulator, wherein an image or data pattern information is written and read by modulating the reading light. 2. The photothermal writing type spatial modulation device according to claim 1, wherein a reflecting mirror is provided between one of the transparent substrates and a liquid crystal alignment layer adjacent to the transparent substrate. 3. The photothermal writing type spatial modulation device according to claim 1, wherein the guest-host type is heated. 4. A photothermal writing type spatial modulation device according to claim 1, wherein a sheet heater or a Peltier device is adhered to one of said transparent substrates. 5. The photothermal writing spatial modulation device according to claim 4, wherein a polarization beam splitter is adhered to one of the transparent substrates. 6. The photothermal writing type spatial modulation device according to claim 1, wherein an image or data pattern information is written without scanning. 7. The photothermal writing type spatial modulation device according to claim 1, wherein an image or data pattern information is written by scanning.