Liquid crystal spatial light modulator (versions)

FIELD: physics; measurements.

SUBSTANCE: present invention pertains to measurement techniques. The liquid crystalline substance used in the modulator, which fills the space between current conducting coatings, is a smectic C*-type composition with ferroelectric properties, capable of forming in its layer, spatially inhomogeneous structures, with high speed modulating phase of the transmitted light, under the effect of pulsed alternating electrical voltage. The light is modulated using one spatially inhomogeneous modulating element, whose surface area is equal to the aperture of the whole modulator, with solid current conducting coatings on the whole aperture. The pulsed control alternating electrical voltage is applied to the single pair of current conducting coatings. In the second version, one of the current conducting coatings is reflective.

EFFECT: faster operation with simplification of the structure of the device and manufacturing process.

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The invention relates to the field of optoelectronics and can be used in devices and systems for rendering and displaying information using lasers, in particular in projection displays, including television, in spatial light modulators, storage, conversion and processing images, etc.

Currently more widespread in the technique of visualization and display information receiving device and system using coherent or partially coherent light emitted in the first place, lasers of various types. When lighting them randomly inhomogeneous objects, such as rough surface of the screen or a transparent medium with curvature fluctuations in space refractive index, due to the interference of the scattered waves is formed spotted pattern or speckle structure. In fact, it is noise, and the speckle noise significantly reduces the image quality (see[1], [2]).

An enlarged fragment of the speckle field diffraction of the laser beam on a rough surface is shown in Figure 1 (type 1.1). In the scheme shown in Figure 1 (type 1.2), the speckle structure is formed in free space and is called the objective speckle pattern. These pictures easily observed using laser radiation. Subjective JV is CL-pattern observed in depicting optical systems, in which the conditions of the coherent illumination of the object is much less demanding. Therefore, subjective speckles can be seen with the naked eye even in polychromatic light extended sources. In the scheme shown in Figure 1 (type 1.3), the light passes through the scattering medium, and the speckles are observed in the image plane of the illuminating source. Subjective speckle pattern generated by the scheme of Figure 1 (type 1.3), clearly visible even while watching the street lamps through a steamy or frozen window of the vehicle (see [2]). Figure 1 shows a source 101 of the light randomly inhomogeneous object 102 (or the environment), schematic view of the longitudinal section 103 of the layer of speckle patterns, randomly distorted wavefront 104 depicting optical system 105.

Device and system visualization and information display, as a rule, provide for the display images on the screen for visual perception. Therefore, an urgent task is the elimination of speckle patterns that create noise in the image (speckle modulation) relatively low frequency, because the size of the individual speckles are determined by the resolution of the eye (see [1]). The problem is solved in different ways on the basis of the following two approaches, namely:

- the destruction of the speckle patterns directly on the screen

- destruction phase relationships, divodasa to create speckle patterns, in the light beam prior to its projection on the screen.

In both cases, the rate of destruction of the speckles should be significantly more reactions of the eye.

In the first approach it is necessary to consider the maximum angular resolution of the eye. It equals one minute, or 20-30 l/mm, but this value may vary depending on lighting conditions, screen layout, color image. Elimination of speckle patterns is achieved by its averaging when using matte screen-diffuser in the course of the observation image on it (see [3, 4]). Obviously, the movement frosted diffuser should be fast enough that the eye could not track the displacement of the speckle patterns relative to the image.

In [5] proposed a method of removing speckle patterns with two frosted diffusers, one of which is continuously moving relative to another. In this case there is no dependence on the transfer function of the optical system, since the value of the correlation function of the lens is usually a lot less impulse response of the output optical system. Elimination of speckle patterns with two frosted diffusers successfully implemented (see [6]).

Figure 2 presents the design of the matte screen 201 with two diffusers (see [6]), which is made in the form of a decorative carrier frame. At its close the flax stationary frosted diffuser 202 and a mechanism to move the movable diffuser. The transfer mechanism (in this case, rotation), as shown in figure 2, includes a low-speed engine DSM-60-220 with duplechin symmetrical bevel gear, where shown: engine 203, a leading gear 204, the intermediate gears 205 and 206, the leading output gear 207 and 208, the eccentric axis 209 and 210, which is the driving member movable frame 211 with frosted glass 212. When the movement of the movable frame 211 is based on hardened regulatory gap screws 213. Springs 214 press frame 211 at its rotation. Options the following motion: the angular velocity of 1 rpm, the radius of the circular movement is 1 mm, the rotation speed of the movable plate - 38 rpm Screen size is 230×330 mm²and resolution of 25 l/mm In this design provides reliable suppression of speckle noise in reconstructed from holograms images.

An obvious disadvantage of the solution to eliminate speckle noise directly on the screen is the use of a complex mechanical device moving screen, and the more complex and cumbersome, the greater the aperture of the screen. Although this approach was proposed and implemented over 20 years ago, the technical implementation for many years remained practically unchanged.

The second approach is to eliminate the speckle noise associated with the destruction temporarily and spatial coherence of the radiation, is implemented by using a more compact technical means, but requires a much higher spatial resolution, due to subsequent expansion of the beam aperture to fit the screen. Another important condition is to maintain a direction of a light beam that does not allow the use of light-scattering environments.

Known solution to this problem using managed spatial phase masks (filters). An example of a mask (see [1]) is illuminated with a diffuser and then bleached holographic plate with the overwhelming interference depth π phase delay, distributed by the aperture of the beam (i.e. the square plate) randomly. Obviously, such a record, as in the above case, the scattering screens, you need to quickly move transverse to the beam direction, which is a significant disadvantage of this solution.

As the phase mask can be used in the liquid crystal phase spatial light modulator, generating a Walsh function or other orthogonal functions in the management of electrical power or light on a specially designed computer program (see [7]). Such a spatial light modulator according to its purpose, the control principle and the technical implementation is selected by the operation of the prototype.

Diagram and working principle of a liquid crystal display (LCD) electrically controlled spatial light modulator [7] illustrated in figure 3. The basis for the design of such a modulator and similar devices is a liquid crystal cell, which typically contains two parallel spaced transparent dielectric plate 301, the external sides of which are covered with antireflection coating 302, and the inner transparent conductive coating 303 (usually with an anti-reflective sub-layer), one or both of which is covered with a layer of transparent anisotropic dielectric substance (orientate) 304. The space between the plates is filled with liquid crystal substance 305, which can change its optical anisotropy depending on the amplitude and/or pulse duration of the alternating voltage applied to the conductive coating. The initial orientation of the liquid crystal molecules in the absence of an external electric field is set anisotropic coating. The image is observed or when light passes through the layer in one direction, if both the conductive coating is made transparent (type 3.1), or by double passage of light, if the second conductive coating 306 is made reflective (type 3.2).

In practice, the phase modulation LAZ is REGO radiation was used spatial light modulators based on the S-effect in the liquid crystal of the nematic type with a limited number of elements (maximum 256× 256) in the matrix that is applicable to suppress the speckle noise only in the case of simple observation images. In the case of highly informative display of images, the spatial resolution of such a spatial modulator must be hundreds reverse mm. In fact, this liquid-crystal active-matrix microdisplay working on light transmission. Light loss in this device is quite large due to the decrease of the working aperture, due to the presence of electronic control elements (typically, thin-film transistor) and the spacing between the elements of the matrix. Moreover, the periodic structure of the matrix distorts the wavefront of the coherent light, leading to image distortion on the screen. Control of the spatial light modulator is a separate challenge.

In the liquid crystal spatial modulators and displays the liquid crystal of the nematic type is the most prevalent (see [8]). As is known, optical response (reaction) of the liquid crystal to the influence of the electric field is the result of changes in the anisotropy of the optical properties, due to the General orientation of the long axes of the molecules in the volume layer. The physical orientation (reorientation) of molecules of nematic liquid cu is Stella (NLC, or nematic) the electric field is the anisotropy of the dielectric constant, due to their anisotropic (elongated) shape.

For example, molecules with positive dielectric anisotropy (ε_1l>ε_⊥), seeking the lowest energy state, upon reaching a certain threshold U_n ^sneeded to overcome the elastic forces are oriented with their long axes (Director) along the field lines and the direction of light propagation (Figure 4). In the General case, the result of the reorientation of the molecules of the layer of NLC feels Splay-deformation, and its birefringent properties change (S electro-optical effect). This display cell can modulate both the phase of the transmitted light and its intensity (using polarizers). While often other for phase modulation of light use it's effect. Figure 4 shows a diagram of the reorientation of the NLC molecules with splay deformation of the layer (S-effect), where n₀is the refractive index for the ordinary ray, n_eis the refractive index for the extraordinary ray. Δn is the difference of refractive index (birefringence), U^S _n- threshold voltage reorientation, D is the direction of polarization of the incident light wave. The direction of the light beam and electric on the I (E) are the same.

Nematics have a number of advantages, but do not provide sufficient performance, since the time of their electro-optical response is in the range of units and tens of milliseconds and cannot be reduced without a sharp increase in the control voltage. The main reason for this is the standard mechanism of interaction of nematic liquid crystal with the electric field and the deformation of the layer of nematic liquid crystal as a continuous elastic medium.

On the other hand, it is known that liquid crystals smectic type ferroelectric properties (smectite With^*or^*LCD), have substantially more than nematics fast electro-optical switching - from tens to hundreds of microseconds [9]. Them in the direction of preferred orientation of the long axes of the molecules is determined by the polar angle Θthey tilted relative to the normal to the smectic layers, and the azimuthal angle (in the plane of the smectic layer (Figure 5). Due to the stoichiometry of molecules in the absence of external influences each layer of molecules possesses a spontaneous polarization (P_s), and the polar axis different smectic layers are rotated relative to each other so that equilibrium is formed spirally twisted structure (helix). The macroscopic polarization of the cell, however, is not required because the angle ϕ in smecta the definition of the layers varies from 0 to π at a distance equal to the pitch of the helix R₀. Thanks a specified polarization layers smectite With^*LCDS are much greater than the nematic susceptibility to the action of an electric field and provide 100-1000 times greater frequency of light modulation. Figure 5 shows the physical model of display cells with ferroelectric smectic LCD with large helix pitch distance (view 5.1) and smaller (view 5.2) layer thickness, which shows: plane 508 smectic layers of the liquid crystal perpendicular to the surface of the wafer 501; vectorelectric field, located in the plane of the smectic layer; vectorshowing the direction of orientation of the long axes of the molecules in the smectic layers of ferroelectric liquid crystal; vectorspontaneous polarization; step R₀helix; normal L to the smectic layers; the coordinate axis x, perpendicular to the plates 1; coordinate axis y parallel to the plate 1; the coordinate z-axis coinciding with the direction vector; angle Θ the slope of the long axes of the molecules with respect to the vector(the angle between the vectorsand); the angle in the XY plane between the normal to the plates and in the ktoroy ; direction P and the axes of the polarizer and analyzer; the intensity of I₀falling on the cell light, the intensity I of the modulated cell light; the diameter D of the incident light beam; angle β between the polarizer and the axis of the helix (type 5.1), between R and a (form 5.2).

Created ferroelectric liquid crystal composition of the organization of the achiral smectic liquid crystal mixture of the substituted phenylpyrimidine and phenylbenzoate in the amount of 60-90% by weight of the total liquid crystal composition and chiral additives of optically active derivatives trifenilmetanovogo acid in the amount of 10-40% by weight of the total liquid crystal composition (see [10]). These compositions provide indexing of the helix with a pitch of the spiral than 1 μm, the spontaneous polarization over 50 NC/cm²and the smectic tilt angle of more than 10°. This cell has the property of bistability (called "surround bistability"), which is caused not only due to the interaction With^*LCD layer with its bounding surfaces, many thanks to the stoichiometry of the liquid crystal composition, and therefore manifests itself even when the layer thickness of more than 10 μm.

In addition to this bistability With^*LCD cell has the property of multistability that allows you to provide with the swarm of scale in information displays. Gray scale can be realized physically, i.e. not through electronic tricks and excessive requirements on the resolution or to the performance of display cells, and directly through electro-optical switching of liquid-crystalline substances. It is reproduced in the form of an almost continuous sequence of stable optical state within the state with zero intensity to maximum (6), and therefore the above conditions, in essence, are conditions of the manifestations of multistability. Both extreme and all the intermediate States are inverting pulse of appropriate amplitude and duration during tens or hundreds of microseconds. Figure 6 shows the change with time of the electro-optic response With^*LCD cells (upper line) to control the electrical pulses (bottom line) for the three types of response: monostable (without memorizing optical state to the left), bistable (two stable optical States - the right of bold line) and multistable (with gray levels that can be saved after turning off the impulse to the right, all the lines). Clearly multistability is manifested as a change in the ratio between the width observed for the analyzer of light and dark bands (7, type 7.3)due to the s spatial-periodic modulation of the direction of orientation of the polarization vector (Fig) above some threshold voltage. On Fig shows the orientation of the polarization vector and the distribution of the azimuthal angle of the Director along the normal (z) to the smectic layers at different values of the electric voltage (U₁<U₂<U₃).

Period bands (units-tens of micrometers) is given by the magnitude of spontaneous polarization of the liquid crystal (Fig.7, type 7.1). When the threshold is exceeded switch the first cell region, in which ϕ maximum, while other areas do not switch. In the source domains are broken, and the change of polarity of the field does not allow you to set a regular lattice of domains. During this phase modulation of the transmitted light reaches π and more depending on the thickness of the layer With^*LCD (usually from 5 to 30 μm) and applied voltage (from units to tens of volts). The presence of domains, the periodic modulation angle (along the z-coordinate and memorizing variable periodic lattice at any point of the hysteresis loop is caused only material parameters of the liquid crystalline substance.

Compositions With^*LCD with surround bistability, under certain conditions electrical excitation allow intense diffuse light (see [11]).

Properties built With^*The LCD layer domain spatially inhomogeneous patterns and high speed upravlat is their interest from the point of view of their use as the basis for creating spatial speckle vast modulator. However, the information on this application, With^*The LCD cell is missing and unknown used design, suitable With^*LCD compositions, electro-optical effects and modes of handling any^*LCD modulator with such appointment.

The technical problem to be solved proposed variants of the invention, forming a single General inventive concept is the creation of a liquid crystal device for suppressing speckle noise in images with compared to similar substantially simpler design and manufacturing technology, higher spatial resolution, higher settings of transmittance and higher performance.

The solution of this task is ensured by the fact that in the known liquid crystal spatial light modulator, comprising two parallel spaced transparent dielectric plate on the outer sides of which are covered with antireflection coating, and on the inner side of the transparent conductive coating, and the liquid crystal substance filling the space between the conductive coating and changes its optical anisotropy under the influence of an electric field applied to such a liquid crystal substance, which is composed of smectic^*-the IPA with ferroelectric properties, having the ability to form in the layer spatially inhomogeneous patterns, with high speed modulation under the action of pulsed alternating electrical voltage phase of the transmitted light; for light modulation using one inhomogeneous spatial modulating element size equal to the aperture of the entire modulator with continuous across the aperture of the conductive coatings and the control pulse alternating voltage to make a single pair of conductive coatings.

In the first embodiment of the technical solution proposed spatial modulator that suppresses speckle noise when passing through the laser beam in one direction (according to the scheme shown in figure 3, a view 3.1). Enclosed in the modulator layer With^*LCD due to its properties when the control voltage destroys the phase relations in the beam, resulting in the creation of speckle patterns in images. Applied to the liquid crystal substance based on the composition of smectic^*-type ferroelectric properties, Chevron has no defects and allows to achieve high stability when switching States of light transmission, which provides high quality image passing through the cell.

The second is ariante instead of cells, working in the lumen, it is proposed to use a liquid crystal cell of the reflective type, which is enough to do one of the conductive reflective coatings (see figure 3, view 3.2). Such cell aperture is the size of the screen on which the image is projected, may serve to suppress speckles when installing directly in front of the screen or instead of it. In the latter case, the composition is used With^*LCD, intensely light-scattering when the application of the alternating electric voltage.

In addition, in both cases, the liquid crystal substance is a composition of smectic type ferroelectric properties in which the organization of the achiral smectic liquid crystal mixture contains substituted phenylpyrimidine and phenylbenzoate in a mass ratio of 3:1 to 2:1, and the substituted phenylpyrimidine include at least one organic compound selected from the group (I, II), consisting of:

(I)

where n≥8, m≤10

(II)

where n≥6, m≤10

phenylbenzoate include at least one organic compound selected from the group (III, IV), consisting of:

(III)

where n≥8, m≤10

(IV)

where n≥6, m≤10

and chiral additive includes an organic compound (V, VI), consisting of:

(V)

n≥4, m≤6

where n=0,1; m≥2

(VI)

where n≥3, m≤6

the mass ratio of from 1:1 to 2:1 and the organic compound (VII):

weight is 15-30% of the total mass of chiral additives.

The advantages of the proposed speckle overwhelming With^*LCD spatial modulator is provided through:

- design^*LCD cell,

- composition of the liquid crystal and

control mode cell.

Replacement NLC on With^*LCD significantly (more than 100 times) to increase the speed. The composition of^*The LCD provides the conditions for creating managed spatially inhomogeneous structures in the layer. The refusal of the matrix of the modulating elements and the use of one uniform aperture With^*LCD cell as a flat single large aperture of the modulator allows continuous across the aperture spatially inhomogeneous phase modulation of the laser radiation and to exclude multiplex or active-matrix addressing elements Mat the Itza. The control mode pulsed alternating voltage provides the necessary speed and depth of the phase modulation in the absence of light scattering and distortion of images. The modulator can be manufactured with an aperture suitable for used power and cross section of the laser beam, to avoid leaving temperature regime or to provide the most favorable conditions for phase modulation of light.

While the prior art it is not clear that suppress speckles of the laser radiation can be achieved by applying fast^*LCD with bistable and multistable properties, without affecting its stability or violations of these properties, caused by the influence of the bounding^*LCD layers of electric impulse control or passing laser radiation.

To enhance the performance of speckle suppressing With^*LCD modulators suitable individually or in the aggregate, to use different areas of improvement, such as changing the type and composition of the liquid crystal, the mode change control cell, modification of the design of the modulator and the like, for Example, to enhance the effect of suppressing the speckle noise in the design of the modulator is proposed to provide two after avatele located From the ^*LCD cell. In the modulator, it is advisable the use of polymer-liquid crystal layers, antiferroelectric compositions LCD, flexoelectric effect and other

Thus, using the proposed design of the modulator, the liquid crystal composition and mode control pulse alternating voltage allows you to get the device to suppress speckles of the laser radiation with high speed (tens of microseconds), high resolution (up to units of micrometers) and stability parameters of light transmission without distortion of the image, which makes possible the use of a modulator according to the purpose and creation on the basis of such modulators and lasers devices imaging and display of video information, including the projection of high resolution and good image quality and meet the requirements of current and future systems, storage, conversion, image processing and displaying information with the aid of laser radiation, while simplifying their design and manufacturing techniques.

The inventive modulator as a device to suppress the speckle noise in images can be widely used in the development of displays and other optoelectronic devices C is Azania, using a laser to visualize information.

Sources of information

1. Collier, R., Burchard K., L. Lin, Optical holography. Moscow: Mir, p.390 (1973).

2. Ryabukho VP // SOG, N 5, pp. 102-109 (2001).

3. Lohmann A.V., J. Opt. Soc. Am., v.55, 1030 (1965).

4. Arsenault H., S. Lowenthal Opt. Commun., v.57, 493 1970).

5. Lowenthal, S., D. Joyeux, J. Opt. Soc. Am., v.61, 7, 847 (1971).

6. Turegano astray freight Disk system holographic memory. In the book "Optical holography. Practical application", Leningrad: Nauka, p.75-95 (1985).

7. Vasiliev A.A., Casasent D., I. N. Kompanets., Parfenov AV Spatial light modulators, Ed. Innonence/, Moscow: Radio and communication (1987).

8. Limblines, Electro - and magneto-optics of liquid crystals, Moscow: Nauka (1978).

9. V.G.Chigrinov, Liquid crystal devices: physics and applications, Artech House, Boston, London, UK (1999).

10. Andreev A.L., I. N. Kompanets., Pozhidaev, H.E. ferroelectric Liquid crystal display cell. Patent of Russia №2092883 from 10.10.1997 (application No. 95109563 with priority dated 07.06.1995).

11. Andreev A.L., P. Bobylev, Guberan N.A., I. N. Kompanets., Pozhidaev, H.E., Fedorenkova T.B., chosen V.M., Sumkin P. electric field-Controlled light scattering in ferroelectric liquid crystals. Optical journal, t, No. 9, 58-65 (2005).

1. Liquid crystal spatial light modulator, comprising two parallel spaced transparent dielectric PLA is Tina, on the outer sides of which are covered with antireflection coating, and on the inner side of the deposited transparent conductive coating, and the liquid crystal substance filling the space between the conductive coating and changes its optical anisotropy under the influence of an electric field, characterized in that the applied liquid crystal substance, which is the composition of smectic^*-type ferroelectric properties, which are able to form in the layer spatially inhomogeneous patterns, with high speed modulation under the action of pulsed alternating electrical voltage phase of the transmitted light; light modulation is one inhomogeneous spatial modulating element whose square is equal to the aperture of the entire modulator with continuous across the aperture of the conductive coating, and the control pulse alternating voltage make it the only pair of conductive coatings.

2. Liquid crystal spatial light modulator according to claim 1, characterized in that the liquid crystal substance is a composition smectic^*-type ferroelectric properties in which the organization of the achiral smectic liquid crystal mixture contains someoneeeeeeee and phenylbenzoate in a mass ratio of 3:1 to 2:1, when this is substituted phenylpyrimidine include at least one organic compound selected from the group (I, II), consisting of:

where n≥8, m≤10

where n≥6, m≤10,

phenylbenzoate include at least one organic compound selected from the group (III, IV), consisting of:

where n≥8, m≤10

where n≥6, m≤10,

and chiral additive includes an organic compound (V, VI), consisting of:

(V)

n≥4, m≤6

where n=0,1; m≥2

(VI)

where n≥3, m≤6

the mass ratio of from 1:1 to 2:1 and the organic compound (VII):

where n≥3

(VII)

where n≥3

weight is 15-30% of the total mass of chiral additives.

3. Liquid crystal spatial light modulator, comprising two parallel spaced transparent dielectric plate, at least one of which is made of the transparent is Noah and equipped with anti-reflective coating, applied to its outer side, the conductive coating on the inner side plates, one of which is drawn on the plate with antireflection coating made transparent and more reflective, and the liquid crystal substance filling the space between the conductive coating and changes its optical anisotropy under the influence of an electric field, characterized in that the applied liquid crystal substance, which is the composition of smectic C*-type ferroelectric properties, which are able to form in the layer spatially inhomogeneous patterns, with high speed modulation under the action of pulsed alternating electrical voltage phase of the transmitted light; light modulation is one spatially inhomogeneous modulation element whose square is equal to the aperture of the entire modulator with continuous across the aperture of the conductive coating, and the control pulse alternating voltage make it the only pair of conductive coatings.

4. Liquid crystal spatial light modulator according to claim 3, characterized in that the liquid crystal substance is a composition of smectic C*-type ferroelectric properties in which the organization of the achiral with actionsa With the liquid crystal mixture contains substituted phenylpyrimidine and phenylbenzoate in a mass ratio of 3:1 to 2:1, when this is substituted phenylpyrimidine include at least one organic compound selected from the group (I, II), consisting of:

where n≥8, m≤10

where n≥6, m≤10,

phenylbenzoate include at least one organic compound selected from the group (III, IV), consisting of:

where n≥8, m≤10

where n≥6, m≤10,

and chiral additive includes an organic compound (V, VI), consisting of:

(V)

n≥4, m≤6

where n=0,1; m≥2

(VI)

where n≥3, m≤6

the mass ratio of from 1:1 to 2:1 and the organic compound (VII):

where n≥3,

weight is 15-30% of the total mass of chiral additives.