JPH02221918A - Transparent laser address type liquid crystal light modulation cell - Google Patents

Abstract

PURPOSE: To effectively utilize light for writing and projecting, execute recording with high resolution and to obtain a long service life by joining the structures of an inorg. type cell and a dye type cell together in to a single cell. CONSTITUTION: The laser address type liquid crystal cell 15 constituted by providing the outside surface of the cell with transparent substrate layers 36, 38 and inserting a liquid crystal material layer doped with dichromatic dyes between the substrates. A thin absorption layer 42 consisting of nickel, etc., is arranged between the substrate layer 36 and the liquid crystal layer 40. The IR laser entering from an arrow 44 direction of this constitution is partly absorbed by the dyes and heats the liquid crystal material, by which large and small dots 46, 48 are formed. The remaining beams which are not absorbed are absorbed in the absorption layer 42 and are converted to heat, thereby, the dots 46, 48 are joined with the absorption layer 42. The dots are projected in this state by the projecting light. The dots are, therefore, cable of effectively utilizing the stable light.

Description

BACKGROUND OF THE INVENTION The present invention generally relates to liquid crystal devices used as light modulators for image projection. More particularly, the invention relates to a liquid crystal cell in which information can be written by a laser beam for subsequent projection. This liquid crystal cell operates in transmission mode with projection being made directly through it.

Devices using liquid crystal materials have become increasingly popular in recent decades. Most of these liquid crystal devices use nematic liquid crystal. Such devices cannot store data and must be continuously addressed or refreshed; however, this may be difficult if the desired display is dynamic and updated continuously or frequently. is not a drawback.

A second type of liquid crystal material, known as smectic, has storage capabilities in that image information only needs to be written once into the liquid crystal cell. Information subsequently written is substantially permanent until erased.

Laser-addressed liquid crystal light modulators have been developed using smectic materials as high-resolution projection display devices. The writing mechanism of this device is primarily thermal. An imaged infrared laser beam is used to heat the smectic liquid crystal material, "melting" it into an isotropic state. The liquid crystal is then cooled to a smectic state, forming a diffused region. The written diffuse area is stable within the smectic temperature range of the particular liquid crystal material and will retain the written information. The liquid crystal cell has an electric field of about 10' V/CI,
Or it can be erased by a combination of heating and applying an electric field.

Following writing of the cell, any written image is projected onto a display screen, photosensitive material, etc. by projecting visible light through the cell.

Some of these display devices are based on optical technology (
Optical Engineering) J 23
(3) Discussed in "Laser Addressed Liquid Crystal Displays" by Dewey, May-June 1984, pp. 230-240.

Two approaches to laser addressed liquid crystal light modulators have been developed for use in conjunction with infrared diode lasers. Both are described in Dewey, supra. One device, known as a reflective device, uses a thin film infrared absorber formed on the support layer of a liquid crystal cell. When the infrared beam is scanned across the absorber layer, the radiation is converted to heat creating a diffuse region within the cell.

However, thin film infrared absorbers are opaque not only to infrared radiation but also to the visible radiation used to project the image. The image thus written on the liquid crystal cell must be projected by reflection of visible radiation from the cell, which also requires the use of relatively complex optical systems.

A second approach to liquid crystal light modulators is a transmissive device. In such a case, the cell is provided with means for absorbing infrared radiation and converting it into heat and allowing visible radiation to be transmitted with relatively little absorption. Of course, the advantage of such a device is the relatively simple optical system required for writing the cell and subsequently projecting the image.

Two different types of transmission cells are known.

Devices known as dye-based cells, on the other hand, are doped into the liquid crystal material and electrolyzed with an infrared absorbing dye that has an absorption peak at the laser wavelength; when the writing beam scans the cell, the dye absorbs the laser radiation and heats it up. Convert to The dye has little or no effect on visible radiation; the projection light simply passes through the device in the same manner as is used in conventional slide projectors. However, such cells have some drawbacks in that they exhibit sub-integral dot instability of the writing beam as well as a deleterious effect on the liquid crystal material by the high concentrations of dyes that are sometimes used.

The second type of transmission type cell is called an inorganic type cell. In a simple example, such a cell includes a liquid crystal layer sandwiched between transparent support layers. A layer of material that selectively absorbs light at the wavelength of the writing beam is disposed between the liquid crystal layer and at least one of the support layers.This material is typically an indium-tin oxide that absorbs light in the infrared region. Become a thing. Thus, when the writing beam is directed onto the cell through the absorption layer, a portion of the writing beam is absorbed by that layer and converted to heat. This heat is then supplied to the liquid crystal material to write image information, the absorbing layer being transparent to a significant portion of the projection beam directed through the cell to project the written image. Inorganic type cells have the disadvantage that they use the writing beam radiation less efficiently and tend to attenuate the projection beam. Such cells have low sensitivity and are difficult to form small high-contrast dots or lines; such cells are also susceptible to non-uniformity in the surface alignment layer, which may cause the written image to transfer. Prone to exhibit "ghost" image effects after being altered.

What is needed, therefore, is a laser-addressed liquid crystal light modulator that overcomes the disadvantages of both the dye-based and transmission-based devices discussed above. Such devices utilize writing and projection light effectively, can record high resolution images, and have a long service life.

SUMMARY OF THE INVENTION In meeting the aforementioned needs, the present invention is used in transmission mode to project a written image onto a cell with a writing laser beam. The present invention, which provides a laser-addressed liquid crystal cell, overcomes the drawbacks of known transmission-type cells by combining the structures of dye-type cells and inorganic-type cells.

This laser-addressed liquid crystal cell therefore includes first and second transparent substrate layers for forming the outer surface of the cell.
A smectic liquid crystal material is disposed between the substrate layers.

The liquid crystal material is dye-mixed. The dye is at least the first
A first absorption means is disposed between the first support layer and the liquid crystal layer, which exhibits significant absorbance at a wavelength of , and exhibits significant transmission at at least a second wavelength. This absorption means is formed in such a way that it exhibits a significant absorbance at the third wavelength and a significant transmittance at least at the fourth wavelength;
There is ζ.

In many applications, the first wavelength at which the dye absorbs light and the third wavelength at which the absorbing means absorbs light will be at odds.
Furthermore, these wavelengths may be in the infrared; however, in some cases the dye and the absorbing means may exhibit absorbance at different wavelengths.

Furthermore, it is believed that it is most common for the dye and the absorbing means to exhibit transmission within a certain wavelength range, the wavelengths of which both the dye and the absorbing means are within the visible spectrum.

Preferably, the dye is a dichroic dye.

The absorption means may be formed of a single layer of metallic material, such as for example indium-tin oxide, or the absorption means may comprise a layer selectively reflecting the light to be absorbed, a layer of radiation-absorbing material, It may be a multilayer structure comprising a spacer layer of dielectric material disposed between an absorbing material and a selectively reflecting layer.

In yet another construction, a second absorption means may be arranged adjacent to the liquid crystal layer and on the opposite side of the first absorption means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To better understand and appreciate the present invention, consider a writing mechanism with transmissive cells of a known type.

Referring to FIG. 1, a simple inorganic type liquid crystal cell is shown. Substrate layers IO and 12 are formed of a suitable transparent material such as quartz or glass.

A layer of smectic liquid crystal material 14 such as CBOA is the substrate layer 1.
It is located between 0 and 12. An absorption layer 16 is arranged between one substrate layer 10 and the liquid crystal layer 14. The absorption layer 16 is made of a material that selectively absorbs light at the wavelength of the writing beam. In the case of an infrared writing laser, layer 16 would be formed of a thin layer of indium-tin oxide.

A writing beam from, for example, a Nd:YAG laser (not shown) is directed onto the cell from the direction generally indicated by arrow 18. The beam passes through substrate layer 12 and liquid crystal layer 14 and enters absorption layer 16 . A significant portion of the infrared beam is absorbed by layer 16 and converted to heat. This heat passes from the absorption layer 16 into the liquid crystal layer 14 by conduction. When thermal energy enters the liquid crystal material from the plane of layer L4, the liquid crystal material is heated to an isotropic state and melts the liquid crystal in this region. A written point is thus formed consisting of an image of only one pixel being written.

According to one theory or model of operation, a relatively large point is indicated at 20 in FIG. To form such spots a considerable amount of heat is directed into the absorption layer and further into the liquid crystal layer. This allows the melted portion of the liquid crystal material to reach far inside the liquid crystal layer. 22 in Figure 1
The small dots shown at will be very narrow as a result of the relatively small amount of heat entering the liquid crystal material from the absorption layer 16, and thus such dots will have low optical contrast.

Such a narrow spot would also be highly influenced by surface boundary conditions that would tend to enhance non-uniformity problems and fouling along the interface between the liquid crystal material and the absorbing material, which would ultimately result in thermal degradation of the liquid crystal material. Because of the relatively low conductivity, much of the incident laser energy is lost into the support layer and other parts of the cell.

Referring to FIG. 2, a typical dye type cell is shown. The supports 1124 and 26 are formed of a dye-doped smectic liquid crystal material, one layer 28 of which contains a liquid crystal 11i2B. Suitable dyes for use in such liquid crystal materials are described, for example, in U.S. Pat. No. 4.465.33.
8, and ``Optica Technology (Optica)''.
l Engineering) J 23(3), 23
0 (May-June 1984 issue), pages 239-240, "Laser Addressable Liquid Crystal Display" by Dewey
and its references.

According to one theory or model of this type of cell operation:
Information from the laser beam is directed onto the cell from the direction shown schematically by arrow 30.

In the case of inorganic cells, laser radiation is absorbed not only near the surface but also inside the liquid crystal material and converted into heat. The large and small points 32 and 34 thus form a cylinder that spans most of the liquid crystal layer 2. Since the substrate layers 24 and 26 act as heat sinks, the regions near the surface of the liquid crystal layer will not melt quickly inside (the depth of the point structure formed will be very large). Although the optical contrast is correspondingly high, the point structure will not be strongly (anchored) to the liquid crystal surface; the liquid crystal structure consists of many parallel layers that are highly fluid within the individual layers. Therefore, the written points may have a tendency to shrink or coalesce.

The present invention is obtained by combining an inorganic type cell and a dye type cell into a single cell. One embodiment of the present invention is shown in FIG. Again, the transparent substrate layer 36
and 38 form the outer surfaces of the cell, with a layer 40 of liquid crystal material provided between the substrate layers.

The liquid crystal material is preferably doped with a dye, such as a dichroic dye. In this embodiment an absorbing layer 42, such as a thin layer of a metallic material such as nickel, is disposed between the substrate layer 36 and the liquid crystal layer 40.

In operation, a laser writing beam, preferably from an 830na infrared laser diode (not shown), will be directed onto the cell from the direction generally indicated by arrow 44, the beam passing through a layer of liquid crystal 40, where A portion of the beam is absorbed by the dye, heating the liquid crystal material. Small and large dots 46 and 48 are formed, each having a portion that spans the interior of the generally cylindrical layer of liquid crystal 40 similar to the dots formed within the cell of FIG.

The dye in the liquid crystal layer allows a significant portion of the infrared writing beam to pass through unabsorbed, so that the remaining portion of the beam is directed onto the absorbing layer 42.

There, a significant portion of the remaining beam is absorbed and converted into heat. This heat passes by conduction into the liquid crystal layer 40 where a portion of the liquid crystal material melts in a manner similar to that shown in the cell of FIG. This melted part is liquid crystal JI
40, thereby forming points 46 and 48 which extend completely to the absorber/liquid crystal layer boundary.

The cell of FIG. 3 may also be used with the writing beam directed into the cell from the direction indicated by arrow 50. In this case a significant portion of the writing beam is first absorbed by layer 42 before passing into liquid crystal layer 40.

A significant portion of the remaining beam is then absorbed by the dichroic dye. However, the advantage of directing the writing beam as shown by arrow 44 is that the absorbing layer 42 tends to reflect the portion of the writing beam that is not absorbed by either the liquid crystal layer 40 or the absorbing layer 42, thereby causing the writing beam to be directed toward the liquid crystal layer. It acts as a double pass. This would go a long way towards increasing the writing efficiency of the cell.

As an alternative embodiment, the cell of FIG. 3 may include an absorbing layer included on each side of the liquid crystal layer 40; such a structure (not shown) may extend completely to the layer boundaries on each side of the liquid crystal layer 40. It would help the points within.

Many benefits result from absorption of the writing beam using both dyes and inorganic absorber structures. Firstly, because the dots formed include cylindrical portions formed over the interior of the liquid crystal layer, the cell will be able to record small, high-contrast details; secondly, said cells may be dye-type cells or inorganic-type cells. Dye-based cells tend to be more sensitive than inorganic-based cells, which may be more effective than having only one side of the cell, but there are no other undesirable effects from the high dye concentrations that should be used (the writing beam In the present invention, the addition of an inorganic layer makes it possible to fully utilize the energy of the remaining writing beam, thus improving the efficiency of the cell.

Furthermore, the dyes used in the present invention, typically used in dye-type cells, are often dichroic in the aligned liquid crystal material, so that the absorption efficiency of the dye is limited to a fraction of the liquid crystal. is lowered until it is heated to an isotropic state.

At this point the radiation absorption increases and therefore the point writing speed increases. In the present invention, there is an inorganic absorber layer so that it operates at a constant efficiency regardless of the state of the liquid crystal material. The liquid crystal can thus melt relatively quickly near the boundary between the liquid crystal layer and the absorption layer.

Since a portion of the liquid crystal is in the isotropic phase, the higher efficiency exhibited by the cell of the present invention is less expensive because the dye will cause the dots to grow rapidly through the interior of the liquid crystal material. This means higher writing speeds can be obtained with the laser and other parts of the device.

Dye-based cells tend to have lower written point stability. However, in the present invention the dots are strongly anchored at the liquid crystal layer/absorbing layer boundary, and therefore the coalescence of the written dots will be reduced, caused by the part of the dots extending through the interior of the liquid crystal layer at the same time. The high contrast would prevent other normal deleterious surface effects from contributing significantly to the written image, which is thought to reduce the "ghosting" problem typically associated with inorganic type cells. It will be done.

In such cases, previously written images are sometimes seen in the cells. The strong light scattered inside the written liquid crystal layer will make any ghost images less noticeable.

Referring to FIG. 4, a more complex embodiment of the invention is illustrated. A pair of transparent substrate layers 54 and 56
forms the outer surface of the cell. A layer 58 of liquid crystal material within the cell
is contained, and this liquid crystal material is doped with a suitable dye. An inorganic absorption means 60 is formed between layer 58 and substrate layer 56.
The liquid crystal material 58 is disposed between the liquid crystal material 58 and the liquid crystal material 58 . As in the previous embodiment, an infrared writing beam is directed onto the cell from the direction generally indicated by arrow 62. This beam is absorbed by both the dye and the inorganic absorption means 60 within the liquid crystal layer 58, causing small and large dots 64 and 66 to be written in the liquid crystal layer 58.

In this embodiment, the absorption means 60 consists of a three-layer stack of dielectric and metal thin films. The absorption means 60 includes a dielectric wavelength selective mirror 68, an absorption layer 70, and a spacer layer 72 disposed therebetween, these three layers collectively exhibiting a high absorption for the incident laser light when properly tuned. The absorption means 60, which may constitute an interference cavity, remains partially transparent to visible light.

In the three-layer absorption means 60, the absorption layer 70 cooperates with the spacer 72 to receive the incident infrared radiation.

Part of the light is reflected at the interface between the absorbing layer 70 and the liquid crystal material 58, and the remaining light passes through the absorbing layer 70 and passes through the spacer layer 72.
Go inside. This light is then reflected by the mirror 68, returns to the absorption layer/liquid crystal interface after warping, and interferes with the light reflected at this interface. By tuning the optical thickness of spacer layer 72, the amount of net reflected light is minimized. 9 of the incident writing beam radiation in this way.
More than 0% is absorbed.

Mirror 68 is preferably formed as a multilayer structure consisting of a stack of dielectric layers. Such mirrors provide a high reflectivity for the writing beam radiation, on the order of 95-99%, but are substantially transparent to visible light. The layers of the mirror are made of two different materials and stacked one on top of the other. In a preferred embodiment, the odd numbered layers of the stack are formed of a material with a high index of refraction. In one embodiment, a suitable material for these layers is titanium dioxide. Each even numbered layer is formed of a material having a relatively low refractive index. A preferred example of such a material is silicon dioxide. Each layer of the stack absorbs one quarter of the light of the writing beam.
It is formed to have an optical thickness equal to the wavelength. In this way the mirror is brought into a specific state of tuning with respect to the incident radiation.

A more detailed description of the structure of absorbent means 60 can be found in US Pat. No. 4,787,313, which is incorporated herein by reference.

Due to the high efficiency of the absorption means 60, the incident writing beam radiation directed onto the cell first passes through the liquid crystal layer 58 and then enters the absorption means 60. The dye in the liquid crystal layer 58 does not absorb all of the incident writing beam, but the absorbing means 6
Another example (not shown) would be to support a simple absorbing layer of a material such as indium-tin oxide, which would be very effective at collecting all of the light passed by the dye. This layer could be disposed between layer 54 and liquid crystal layer 58, which layer directs a portion of the incident writing beam radiation to liquid crystal layer 5.
8, such a structure would give the written points anchored to the boundaries of the liquid crystal layer on both sides, in this embodiment the reflective layer and the substrate layer 54. It may be necessary to apply an anti-reflective coating to the interface between the two.

The cell of the invention is used as part of an optical system for projecting an image, preferably onto a photosensitive medium. An example of such an optical system can be understood with reference to FIG. A cell 76 formed according to any of the previously described embodiments forms the center of the projection system. The writing laser beam is generated by a laser emitting source, for example 83
It may also be a conventional laser diode that generates a laser beam with a wavelength in the infrared range of 0n11. The beam passes through a suitable modulator 80 which modulates the beam according to the image to be formed on cell 76.

Galvo mirror 82 scans the laser beam so that the entire surface of cell 76 is written. From mirror 82, the beam is directed to dichroic mirror 84, which reflects the writing beam radiation, and then the beam is directed to liquid crystal cell 76.

After the image is completely written on the self 6, the image is projected by the projection light R86.
The light source 86 may also be any suitable projection light source, such as a tungsten lamp. A condenser lens 88 collimates the projection beam, which passes through the dichroic mirror 84 and enters the liquid crystal self 6 .

As it passes through cell 76, the projection beam picks up image information corresponding to the image originally written in cell 76, projection optics 9.
0 images the projection beam to exclude scattered light through an aperture 91 and directs the beam onto a photosensitive medium 92 supported by a suitable screen 94. Media 92 may be any photosensitive medium suitable for the projection light used.
A preferred example of a photosensitive medium is U.S. Pat. No. 4,399,2.
There is a microencapsulated medium disclosed in No. 09.

By forming the cell 76 in accordance with the present invention, the cell includes both an inorganic infrared absorber and an infrared absorbing dye, often both the inorganic absorber and the dye are included in the laser light source 76.
8 may be selected to be sensitive to infrared radiation produced by 8. Many dyes commonly used in liquid crystal materials are 63
Sensitive to 3na or 780ns+ laser radiation. 1 of the absorption means described in connection with the embodiment of FIG.
One advantage is that the structure of this absorption means is tunable to any desired wavelength, including the wavelength corresponding to the dye in question.

It is also possible to use dye absorbers and inorganic absorbers that correspond to different wavelengths. In such a case it would be necessary to use two laser sources, with two absorbers producing laser beams of corresponding wavelengths. Such an optical system is shown in FIG. 6, where laser source 78 generates a laser beam with a first wavelength and laser source 96 generates a laser beam with a second wavelength. The beams would be combined through a suitable beam splitter 98 and the combined beam would be scanned onto the liquid crystal cell by a single scanning mirror 82. In the simplest case the combined beam is the sixth
It will be integrally modulated by modulation means arranged as shown at 100 in the figure. Alternatively, each laser light source 78 and 96 may have its own modulator 102, 104, which also allows the writing of points within the cell and within the liquid crystal layer at the surface of the liquid crystal layer to be controlled separately. , thereby providing greater control over the characteristics of the image being written. Since dye-based cells are more sensitive than inorganic-based cells, a standard helium-neon or argon-ion laser is used for the corresponding dye in conjunction with a diode laser for absorption by the inorganic absorption layer. Advantages of such an approach include making dyes sensitive to shorter wavelengths produced by gas lasers more stable and facilitating closer imaging of the gas laser's output.

Although the configuration of the device described above constitutes a preferred embodiment of the invention, it will be appreciated that the invention is not limited to the detailed configuration of the device and that modifications may be made without departing from the scope of the invention. Will.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a portion of a liquid crystal cell illustrating the theory of operation of a typical inorganic type cell. FIG. 2 is a cross-sectional view of a portion of a liquid crystal cell illustrating the theory of operation of a cell typical of the dye type. FIG. 3 is a cross-sectional view of a portion of a liquid crystal cell formed in accordance with the present invention illustrating the theory of operation of the cell. FIG. 4 is a cross-sectional view of a cell similar to FIG. 3 showing another embodiment of the present invention. FIG. 5 is a schematic diagram of an optical system for image projection using the liquid crystal cell of the present invention. FIG. 6 is a diagram similar to FIG. 5 showing an optical system using two laser light sources. In the figure 10.12, 24, 26, 36, 38, 54.56...
- Substrate layers 14.28, 40.58...Liquid crystal layer 16.42.60...Absorption layer. 20.32, 34.46.48, 64.66... points (
dot) 76...LCD selfie 8, 96...laser light source (4 people in addition)

Claims (1)

[Claims] 1. A laser-addressed liquid crystal cell, comprising first and second transparent substrate layers forming the outer surface of the cell; a dye mixed therein; a liquid crystal layer of a smectic liquid crystal material disposed between said substrate layers exhibiting some absorbance at a wavelength of at least a certain degree of transmission at least at a second wavelength; a first absorption means arranged between the first substrate layer and the liquid crystal layer, the first absorption means being formed so as to exhibit a certain degree of transmittance at a fourth wavelength;・Address type liquid crystal cell. 2. The laser addressed liquid crystal cell according to claim 1, wherein the first wavelength at which the dye exhibits a certain degree of absorbance is in the infrared region. 3. The liquid crystal cell according to claim 2, wherein the dye exhibits a certain degree of transmittance at a plurality of second wavelengths;
A laser-addressed liquid crystal cell characterized by having wavelengths in the visible range. 4. A laser-addressed liquid crystal cell according to claim 1, wherein the wavelength at which the absorption means exhibits a certain degree of absorbance is within the infrared region. 5. The liquid crystal cell according to claim 4, wherein the absorption means exhibits a certain degree of transmittance at a plurality of second wavelengths, and the second wavelengths are in the visible region.
Address type liquid crystal cell. 6. The liquid crystal cell according to claim 1, wherein the first wavelength and the third wavelength are the same.
Address type liquid crystal cell. 7. A laser addressed liquid crystal cell according to claim 1, wherein the first wavelength and the third wavelength are different. 8. A liquid crystal cell according to claim 6, wherein the dye and the absorbing means each exhibit a degree of transparency at a plurality of equivalent second and fourth wavelengths, the second and fourth wavelengths being visible. A laser-addressed liquid crystal cell characterized by being located in the area. 9. A laser-addressed liquid crystal cell according to claim 1, wherein the absorption means is formed of a layer of metal material. 10. A laser-addressed liquid crystal cell according to claim 9, wherein the metal material is indium-tin oxide (110). 11. The laser-addressed liquid crystal cell according to claim 1, wherein the dye is a dichroic dye. 12. The liquid crystal cell according to claim 1, wherein the absorption means comprises a layer of radiation absorbing material disposed in close proximity to the liquid crystal layer and selectively reflective to light of the third wavelength. and a spacer layer of dielectric material disposed between the layer of material and the selectively reflective layer. A laser-addressed liquid crystal cell featuring: 13. further comprising a second absorption means disposed between the second substrate layer and the liquid crystal layer, the second absorption means having at least a certain degree of absorbance at the third wavelength and at least a certain degree of absorbance at the fourth wavelength; 1. A laser-addressed liquid crystal cell, characterized in that the cell is formed so as to exhibit a certain degree of transmittance at a wavelength of . 14. first and second transparent substrate layers forming the outer surfaces of the liquid crystal cell; and a dye is incorporated therein, the dye having a certain degree of absorbance at least at a first wavelength and a degree of transmittance at least at a second wavelength. a liquid crystal layer made of a smectic liquid crystal material disposed between said substrate layers and formed to exhibit some degree of absorbance at least at the third wavelength and some degree of transmission at least at said second wavelength a first absorption means disposed between the first substrate and the liquid crystal layer; a liquid crystal cell that generates a laser beam having at least one of the first wavelength and the third wavelength; , the first of the above liquid crystal cells
and laser means for directing the laser beam onto the second substrate layer; scanning means for scanning the laser beam onto the cell; modulation means for modulating the laser beam in accordance with the image to be projected; and projection beam means for generating a projection beam of a second wavelength and directing the projection beam onto one of the first and second substrate layers. 15. The projection device according to claim 14, wherein the first wavelength and the third wavelength are the same. 16. The projection apparatus according to claim 14, wherein the first wavelength and the third wavelength are different, and the laser beam means has a first laser beam having the first wavelength and the third wavelength. a second laser beam, and both the first and second beams are directed onto the liquid crystal cell. 17. The projection apparatus according to claim 16, wherein the modulating means independently modulates the first and second laser beams according to the image to be projected.