WO1992010779A1

WO1992010779A1 - Method for transmission of visual information

Info

Publication number: WO1992010779A1
Application number: PCT/FI1991/000372
Authority: WO
Inventors: Jouko Viitanen
Original assignee: Jouko Viitanen
Priority date: 1990-12-12
Filing date: 1991-12-04
Publication date: 1992-06-25
Also published as: FI906095A0; FI906095A

Abstract

The object of the invention is a method for transmission of visual information, wherein the organs (20) transmitting visual information from the source of information are connected with a first surface for transmitting information and a second surface for illustrating information, whose opposite outer surface most preferably forms a display surface, such as a picture screen, a display screen, an optic surface, or the like. An optically anisotropic medium, such as a liquid crystal or the like, is arranged between the said first and second surfaces. For application of the method, a closed structure is formed, in which preferably essentially plane-like said first and second surfaces are located preferably essentially in the same direction in a housing (70) or the like. The said structure is also fitted with organs for condensing the structure and organs for separating the said surfaces from each other. The method can be applied in television sets, video displays, computers, control devices and other electronic devices for display of pictures on one hand and for converting the pictures into electronic form on the other hand. The said organs (20) transmitting visual information are arranged to function optically, i.e. by means of light beams reflected from an illuminator. The said structure is arranged to be affected by organs controlling the transmission of information from between the said surfaces, whose function is at least partly based on changing the refractive index of the said medium mechanically, or acoustically.

Description

Method for transmission of visual information

The object of the invention is a method for transmis¬ sion of visual information, wherein the organs trans- mitting visual information from the source of inform¬ ation are connected with a first surface for trans¬ mitting information and a second surface for illustrat¬ ing information, whose opposite outer surface most preferably forms a display surface, such as a picture screen, a display screen, an optic surface, or the like. An optically anisotropic medium, such as a liquid crystal or the like, is arranged between the said first and second surfaces. For application of the method, a closed structure is formed, in which preferably essentially plane-like said first and second surfaces are located preferably essentially in the same direction in a housing or the like. The said structure is also fitted with organs for condensing the structure and organs for separating the said surfaces from each other. The method can be applied in television sets, video displays, computers, control devices and other electronic devices for display of pictures on one hand and for converting the pictures into electronic form on the other hand.

The display of pictures in electronic form on a display screen is currently in most cases based on the use of a cathode-ray tube. The techniques involved is gener¬ ally known. A disadvantage of displays of this kind is their large size (especially thickness) , weight, and power consumption.

Other generally known types of display include electro¬ luminescence display, plasma display and liquid crystal display. Of these, especially the liquid crystal display has gained increasing popularity. In comparison with the cathode-ray tube, the advantages of the liquid crystal display include flatness, small weight and smaller power consumption. A display of this kind has been described, for example, in the PCT publication WO 84/04641. So far, the most difficult disadvantages of the liquid crystal display have been a complex structure requiring precision, which has made it expensive to manufacture display of great precision, poor contrast, difficulties in expressing natural colours and different levels of brightness, slow response time, which has prevented the display of quickly changing pictures, and the small size of the picture to be shown.

The disadvantages of the plasma display and the electroluminescence display are a limited choice of colours and the expensiveness of the applications due to the sophisticated manufacturing techniques.

using the method according to the invention provides a decisive improvement to the disadvantages presented above. For the application, the method according to the invention is generally characterized by the features given in the- characteristics of the claim 1.

One of the most important advantages of the invention is the fact that the apparatus related to the method is thin in the direction of depth. In addition, all colours of the spectrum of visible light and their different levels of brightness can be shown by applying the method; the control mechanism of the display is simple, thus enabling the manufacture of displays of even great precision at relatively low costs. By applying the principle of the invention, also displays of large size can be manufactured.

In the following, the invention is explained in detail and by referring to the attached drawings, in which Figure 1 shows an application of a display screen according to the invention in principle;

Figure 2 is a cross-sectional image of line A-A in Figure 1;

Figure 3 shows a detail of part B in Figure 2;

Figure 4 shows a detail of part C in Figure l; and

Figure 5 shows the principle of an electric arrange¬ ment of an embodiment according to the invention.

Figure 1 shows a display screen as an embodiment, seen from the normal direction of viewing. In the direction perpendicular to the viewing direction, the display screen comprises three layers with optic function seen in the cross-sectional image in Fig. 2.

As seen in Fig. 2, one side 22 of the optic fibres 20 forming the first layer has been formed as a surface. This surface 22 for transmitting information does not contain the cladding part used in conventional optic fibres, but the core of the fibre is in direct contact with the medium 40 constituting the second layer. However, the cladding 21 is maintained in the other surfaces of fibres 20. The fibres 20 are fixed on the support layer 25 which, in turn, is fixed to the housing 70 of the device. Optic plates 30 made of a light-permeable material form the third layer essential to the invention. One surface 32 of the optic plates 30, which is directed inwards and which il¬ lustrates information, is smooth, and the other, opposite surface which functions as the display surface 31 is formed in a shape shown in Fig. 3. According to Fig. 1, several optic plates 30 are placed beside each other in the display screen, and there are several optic fibres 20 underneath each plate. The optic fibres extend underneath several optic plates, as shown in Fig. 1, for example.

Figure 4 shows a light source with modulation mechan¬ isms 97 as used in the embodiment. As illuminators 94, 95, 96, any lamps can be used, such as ED-type semiconductor lamps with an intensity which can be modulated at a sufficient speed. The light is directed by condensing lenses 90 to the optic fibre 20. For showing pictures in colour, three illuminators 94, 95 and 96 are used as shown in the figure, radiating red, green and blue colour components at the cor¬ responding wavelengths of light. Each illuminator is connected to a separate modulator 97 which adjusts the momentary intensity of the current to the respect¬ ive illuminator so that the intensity of the respect¬ ive radiation emitted corresponds to the correct variety of colour and intensity of the location at each scanning moment.

As shown in Figs. 1 and 2, there is a medium 40 between the optic plates 30 and fibres 20, such as a "nematic" type liquid crystal which is optically anisotropic, i.e. its optic features depend on the angle between the optic axis of the molecules of the medium and the light beam falling on it. In addition, the medium 40 used in the application presented is positively dielectrically anisotropic; i.e. when it is placed in an electric field, the longitudinal axes of its molecules are turned in the direction of the electric field. Also, there are solid parts 50 which determine the distance between the plates 30 and fibres 20. The parts 50 are fixed to the optic fibres, but the plates 30 are slidable along the longitudinal axis of optic fibres 20 in the display plane^* of Fig. 1. This movement is achieved by the mechanical organs 60 which are fixed to one end of each plate 30. Further- more, the plates 30 have at both ends a suspension which allows movement in the plane according to Fig. but prevents any movement perpendicular to the plan

The slots between the plates 30, as well as the slo at the free ends of the plates, are filled with elastic material which allows movement of the plat but prevents the optically anisotropic liquid cry tal 40 from leaking out.

10

The refractive index n₃ of the optic plates 30 a the refractive index n., of the core of the opt fibres 20 are close to each other, as well as t higher refractive index n_e of the liquid crystal 4 15 However, the refractive index n₂ of the cladding 21 the optic fibres and the lower refractive index n₀ the liquid crystal 40 are lower than the first me tioned refractive indexes.

20 The surfaces of optic fibres 20 forming the fir surface 22 which are in contact with the liquid cryst material 40, are covered by a thin, transparent lay in a way known in liquid crystal technology (referenc J. Cognard, Alignment of Nematic Liquid Crystals a

25 Their Mixtures - Molecular Crystals and Liquid Crysta Supplement Series, Supplement 1, Gordon and Brea Science Publishers, New York, 1982) that the optic axes of the molecules of the liquid crystal 40 a directed at right angles to the display plane

30 Fig. 1 when no other active forces are present. T inner surfaces of optic plates 30 which form the sa second surface 32 have a similar finish. Because t molecules of liquid crystals in "nematic" state with a short distance are homogenously oriented, t

35 molecules of the entire liquid crystal layer 40 a in static state direc^ted at right angles to the displ plane of Fig. 1. Furthermore, there is a thin coa ing 33 between the said finishes and the plates 30 a light-permeable electroconductive material, such as indium tinoxide (ITO) , as is generally used in liquid crystal displays. Correspondingly, there is a similar coating 23 between the said finishes and the fibres 20. The coatings 23 and 33 are uniform, contrary to liquid crystal displays of the type previously in use.

When the mechanical organs 60 move the plates 30 in either direction along the longitudinal axis of the optic fibres 20, this movement results in the arrange¬ ment of liquid crystal molecules in the liquid crystal layer 40 so that the longitudinal axes of the molecules are turned in the direction of the movement, because the viscosity of a liquid is lowest when the molecules are directed along the movement, as is generally known in liquid crystal industry (reference: P. Ukleja, Liquid Crystals (Physics) , Encyclopedia of Physical Science and Technology_f vol. 7, Academic Press, 1987, pp. 365-390) . Due to the small size of the molecules and the thinness of the liquid crystal layer 40, only a very small movement is needed. The optical axes of the molecules are directed along their longitudinal axes, as is normal in liquid crystals.

When the molecules of the liquid crystal 40 are directed by the movement of plates 30 and light is directed at a suitable gentle angle to the fibres 20, the light proceeds within the fibre almost without any loss according to the law of total reflection, as is generally known in fibre optics, for the optical axes of liquid crystal molecules having the same direction as the travelling beam of light, so irres¬ pective of the polarization direction of the light, the light is reflected by the lower refractive in- dex n₀, and the refractive index n, of the core of the fibre 20 is greater than n₀. 'The refractive index n₂ of the cladding 21 is constant and smaller than n₁. When the movement of plates 30 in respect to the fibres 20 stops, an electric field is, according to an advantageous embodiment, connected between the electroconductive coatings 23 and 33 by an external power source 80. Thus at the moment when the movement stops, the orientation of the molecules of the liquid crystal 40 is influenced by two different forces, as is generally known in liquid crystal display techno- logy:

(i) The electric field between the coatings 23 and 33 induces a force acting to turn the longitudinal axes of the molecules from the direction of the movement to a direc¬ tion perpendicular to the surfaces 32 and 22, due to positive dielectric aniso- tropy.

(ii) The above mentioned finish of surfaces 32 and 22 induces in the orientation of molecules a force acting in the same direction near the surfaces 32 and 22.

The action of the forces (i) and (ii) on the light travelling normally in fibre 20 by total refraction is such that the refractive index effective on the electric component of light polarized in the direction of the plane of light encounter (i.e. the plane on which the incoming, reflected, and outgoing beams of light are located) approaches the index n_e upon turning of the optical axes of the molecules. Since ne is close to the refractive index n, of the core of the optic fibre, no total refraction takes place any longer but the light component polarized in a manner described above travels straightforward, almost without any loss to the liquid crystal and further, because n₃_n_e_n₁ , into the plate 30. It is advantageous to arrange the relative intensities between the said forces (i) and (ii) on one hand and the mechanical movement of the plate 30 on the other hand with respect to directing the molecules using an electric field of suitable effect so that, in any case, the mechanical movement is the strongest factor, when the liquid crystal layer 40 is thin. The next strongest factor is the electric field for molecules located far from the surfaces 22 and 32, but the directing effect of finish for the molecules near the surfaces. The same relations apply naturally also to the velocity at which the direction of molecules can be effected. Therefore, when plate 30 is moved at a suitable velocity, its directing force surpasses the other forces (i) and (ii) prevailing at the moment when the plate is stopped.

The aim is to make the stop of plates 30 as sudden as possible. Because all changes of motive state in media advance at a maximum velocity of the sonic speed specific to the medium from the point of action by the force changing the motive state, the movement stops first at the end of plate 30 where the stopping force acts on; from this end, the stopping action is transmitted as a mechanical wave motion or an acoustic pulse to the other end of the plate 30 at the sonic speed specific to the medium. Thus also forces (i) and (ii) have an action first on one end of the plate 30 and the action is then transmitted at the sonic speed specific to the material of plate 30 to the other end of the plate.

Further, immediately after the plate 30 is stopped, its direction of movement is changed to the opposite. The effect of this sudden stop and"start of a movement in the opposite direction on the orientation of molecules in liquid crystal 40 is explained as follows: Using a liquid crystal, the ends of the molecules having the greatest anchoring force on the surface material of plate 30, and also with the molecules anchored generally from their one end due to the occasional inequalities of the surface and the direct¬ ing finishes of the said surfaces 32 and 22, a change takes place from the orientation in the direction of the surface again to the direction of the surface with respect to the longitudinal axes of the molecules after a rotation of almost 180° for those molecules anchored to the surface.

Also molecules located farther from the surface are disturbed by the rotation distracting their orienta¬ tion. The said forces (i) and (ii) contribute to the rotation of 180°. (The phenomenon can be illustrated for example by comparing it to a situation in which a magnet is swinged backward and forward in a viscose medium, and sticks with one end of a magnetic material are attached to the magnet.) Also the effect of this mechanically induced change of molecular orientation on the electric components of light polarized in the direction of the encounter plane of light travelling in fibres 20 is in accordance with the description above.

The said sudden stop of the movement and the start of a movement in the opposite direction are carried out in the embodiment presented so that the mechanical organs 60 are coils, known for example from loud¬ speakers, in a magnetic field where the movement of the coil is induced by electric current led into it. The direction of the force caused by the organs 60 can be changed by changing the direction of the current transmitted in the coil. The sudden stop and the start of a movement in the opposite direction is arranged so that the plate 30 hits elastically the massive and hard edge 62 of the housing 70 simul- taneously as the direction of the current transmitted in the coil is changed.

According to the enlarged detail shown in Fig. 3, the shape of the vertical cross-section of the outer surface 31 of plate 30 is such that the outer surface of the first form part 36 in the outer surface 31 encountered by the narrow cone formed by the light beams travelling in the plate upon exiting the liquid crystal 40 is at an angle of 90° to the direction of travel of the light beams of cone 35 so that the light exits the plate almost without any loss. On the other hand, the second form part 34 of the outer surface 31 has a concave shape as shown in Fig. 3, and the concave surface is coated with a light-reflect¬ ing layer to make it a mirror, so that the exiting narrow cone 35 disperses in as many diretions as possible, thus providing the display with a large angle of viewing. The number of the said form parts 34, 36 in the display must exceed the number of image points desired on the display perpendicular to the said form parts, because upon travel of the cone 35 in the fibre 20, the beams of a cone 35 starting at a certain point can screen two form parts 34, 36 at a time.

As it is known, raster scanning is used for picture forming for example in display devices based on a cathode-ray tube. Thus the brightness of each image is defined so that the display surface is scanned in order by an electron beam, for example by one horizon¬ tal line at a time, and the momentary intensity of the electron flow is adjusted to correspond to the desired brightness of each image to be scanned. The principle of raster scanning is used also in this invention. The scanning action is ' induced by the method described above, when the phenomenon of light distraction caused by the stop of mechanical movement proceeds in the apparatus formed by the plate 30, the liquid crystal 40 and the optic fibre 20 at a maximum speed of the sonic speed specific to the medium in question. On the other hand, the light emitted to the optic fibres 20 travels in a direction opposite to the direction of the distracting phenomenon in plates 30. The velocity of light substantially exceeds the sonar speed, so that its delay of propagation can be disregarded in this context. The effect of the said other forces (i) and (ii) is only to accelerate the transition of molecules of the liquid crystal 40.

As the beam of light travels along the optic fibre 20 almost without loss when the plate 30 is in motion but exits via the plate 30 almost without loss in the manner described above upon stopping of the plate 30, the respective site of exit of light is determined by the distance how far the change in state of motion has advanced as an acoustic pulse in plates 30. Thus the content of colourfulness and brightness of the picture displayed in the apparatus according to the invention for each image contained in a line can be determined by modulation of momentary brightness and colour content 94, 95, 96 of the light fed into fibres 20 according to the site of advancement of the acoustic pulse in plates 30.

One sequence of oscillation caused by organ 60 cor¬ responds in the video display embodiment to the time of one image field. During the time of each image field, each plate 30 hits edge 62 once. Because the impact induces simultaneous scanning in several fibres 20, the velocity of the acoustic pulse advancing in them may be considerable slower than the scanning velocity of an ordinary video display line.

In accordance with the invention, the change in the direction of the optical axes of molecules of liquid crystal 40 from the orientation in the direction of fibres 20 described above should essentially take place as quickly as possible. If the change is slow compared to the speed of advancement of the acoustic pulse, the refractive index on the beam of light exiting the fibre 20 changes in the longitudinal direction of the fibre on a long distance in the direction of the beam slowly from n₀ to n_e. Thus (a) only part of the energy of the beams travelling in the fibre 20 at a more sheer angle than the critical angle of total reflection is transferred to the refracted beam, and the rest continues in the partly reflected beam. In addition, (b) all those beams which are transmitted in the fibre 20 at a more gentle angle than the critical angle of total reflection corresponding to the refractive index n., of the core and the momentary refractive index of each site of the liquid crystal 40, are retained in the fibre 20 until they achieve the site where the critical angle is sufficiently small. Thus in an ideal situation, the beam of light exiting in a spot-like manner can extend to a great width, thus causing summing up of image points in the picture to be viewed at.

In the invention, the disadvantage of point (a) is alleviated by using a thin fibre 20 and as sheer an angle as possible for the light travelling in the fibre. Thus as many reflections and refractions occur as possible within a certain distance, and the energy of the reflected beam is reduced within as short a distance as possible. In an extreme case, a very thin single mode fibre is to be used.

The disadvantage of point (b) can also be reduced by using as sheer an angle of reflection as possible which is close to the critical angle^* of total reflec¬ tion according to the refractive indexes n₀ and τι. . Thus even a small change in the orientation of the liquid crystal 40 and the increase in the refractive index corresponding to it results in a partial refrac¬ tion of the beam from the fibre 20.

Further, in the alternative embodiments presented herebelow, other ways are shown for changing the orientation as abruptly as possible.

A two-dimensional display, such as a television screen, contains a large number of lines whose presentation would require a corresponding number of arrangements like those presented above. However, it is usually not economical to construct each line to function separately but it is advantageous to place several optic fibres 20 underneath each optic plate 20 as shown in Fig. 1 so that the scanning by one and the same acoustic pulse has an effect on several optic fibres 20, each having a separate light modulator of the type described above.

Further, it may not be economical to construct the said illuminators 90, 94, 95, 96 with their modula¬ tors 97 for each optic fibre 20 corresponding to a separate line, so that the same fibres 20 extend underneath several optic plates 30 as shown in Fig. 1. Thus those modulators 97 which are used for the fibres 20 underneath one plate 30 can also be used for other plates 30 in the same display. However, a requirement for this is naturally that the said scanning can be performed by changing the state of movement in only one of the plates 30 at a time. There¬ fore, if the scanning mechanism explained in the invention is compared with scanning by a conventional cathode-ray tube, the difference in the scanning order is in that whereas lines are scanned successive¬ ly one at a time by the cathode-ray beam, the invention presents a method for simultaneous scanning of as many lines at a time as there are optic fibres 20 underneath plates 30.

The scanning order is such that the plate 30 farthest from the illuminator of the optic fibre 20 is activated first, the one next closest second, etc. Thus the possibly slow return of the molecules in plate 30 back to the direction of fibre 20 does not disturb the action in other plates 30; only after functioning of the plate closest to the illuminator, is a period of turn-off needed for all illuminators, after which activation can be re-started from the plate farthest from the illuminator. During the turn-off period, also the direction of motion of all plates 30 is changed.

The invention is not limited to the embodiment pre¬ sented in the above explanation and in the drawings, but it can be modified within the basic idea to a great extent as shown in the following. ^•

Instead of moving the optic plates 30 in relation^" to the liquid crystal 40 and the fibres 20 as presented in the embodiment above, the mechanism can naturally be also constructed so that the fibres 20, or the fibres 20 and the support layer 25 move and the other parts are kept in place, or a third plate is moved which is located for example between the plates 30 and the liquid crystal 40.

If the fibres 20 and the support layers 25 are moved, the advantage is that the moving surface 22 is the same as the one through which the beam of light passes to the liquid crystal 40. Thus, to distract the beam of light from the fibre 20, there is no need for the change of orientation of molecules in the entire field 40 from the direction of the surface to the direction perpendicular to the surface, but the said orientation by an acoustic pulse of molecules of even a small layer of liquid crystal near the surface 22 is sufficient, because the shape of the field directed is not a plane in three dimensions. Thus the beam of light escaped from the fibre 20 is not totally re¬ flected back, but it will be partly refracted from the prism formed by differently oriented fields of liquid crystal.

Furthermore, if the fibres 20 and possibly the support layers 20 are moved, and the fibres 20 are thin compared with the support layers 25, the material of the fibres can be selected so that all of their acoustic features need not be taken into account, and in the selection of the material of the support layers 25, on the other hand, their optic features need not be taken into account at all.

In view of manufacturing techniques, it is difficult to use a finish of surfaces 32 and 22 which directs the liquid crystal molecules perpendicularly, i.e. at an angle of 90° to the display surface of Fig. 1 as presented above. Thus also such finishes can be used which provide a direction in an angle of less than 90°, because, as noted above, the effect of the finish was the weakest of the said mechanisms of direction outside the layer in close contact to the surface.

In the embodiment presented above, use was made in addition to the primary mechanism for changing the direction of molecules by the acoustic pulse of also (i) electric orientation and (ii) orientation by surface treatment. According to the main principle of the invention, however, one or neither of the auxiliary mechanism mentioned above is not necessarily needed, depending on the characteristics of the liquid crystal 40 and the plates 30 or the fibres 20 used. This is because as the liquid crystal molecules are anchored on the surface of a solid material, their orientation can, due to the quality of the material, without any separate finish, be directed so that the refractive index for at least one of the said direc- tions of light polarization is greater than during the said movement.

Instead of the finish presented, the surfaces 32 and 22 can be treated so that the molecules of liquid crystal 40 are directed in state of rest along the direction of the plane in Fig. 1 but at an angle of 90° to the longitudinal axes of fibres 20. Thus as the direction of motion of plates 30 is changed, at least those molecules close to the surf ce are turned in the display plane of Fig. 1, wherein the polariza¬ tion components of light perpendicular to the encounter plane of beams travelling in fibres 20 are subjected to a similar refraction as described above for the component in the direction of the encounter plane.

In the embodiment in the example, a longitudinal mechanical wave motion, or an acoustic pulse, was used in the plates 30 or the fibres 20. However, the acoustic pulse may also be transverse or contain also transverse components. Thus either surface finish, negatively dielectric anisotropical liquid crystal material, or both of these together can be used to direct the molecules of the liquid crystal 40 in state of rest along the longitudinal axes of the fibres 20. Thus in state of rest the light travels in the fibres 20 without loss, but by an acoustic pulse perpendicular to the fibres, light can be distracted from the fibre, because the refractive index effective on the polarization component transverse to the encounter plane of light increases.

An acoustic pulse according to the embodiment in the example can also be generated in another generally known way than by hitting plate 30 to the edge 62 of the housing 70.

The fibres 20 do not necessarily need the support layers 25, and they can also be completely surrounded by the liquid crystal 40 as long as there is a cladding 21 in a direction other than that towards the plate 30, or, for example, if the beams of light travelling in different directions on reflecting surfaces are directed so that they exit in the direc¬ tion of plate 30.

The optic plates 30 (or the fibres 20 and their possible support layers 25, if they are movable) may be composed of more than one material which have different elastic coefficients so that the velocity of the acoustic pulse may be different in different parts of the plate 30. This way the differentiation of successive image points can be improved in the scanning direction (by using an acoustically slower material between the fields corresponding to separate image points) and the sufficient amplitude of the acoustic pulse can be allowed without damaging the material. For changing the velocity of the pulse, also treatment of the materials can be used. For example by using spring-like structures, a different velocity of mechanical oscillation is achieved than by using rods of a pure material.

In the explanation above, it was assumed that one acoustic pulse corresponds to each scanning action. However, using a suitable liquid crystal material, also continuous mechanical oscillation can be used which forms a stationary wave. Although there is no scanning in this kind of a wave similar to that in a single pulse, the amplitudes of the parts representing different phases of oscillation are different. Thus at the site corresponding to a smaller amplitude of the motion, the liquid crystal is settled in the state of rest sooner than at the site corresponding to a greater amplitude, although the extreme site of oscillation is achieved simultaneously. If the maximum site of oscillation is at one end of the fibre 20 and the minimum site is at the other end, the scanning by a beam of light as described above proceeds thus from the minimum to the maximum.

Further, the phenomenon of scanning can be induced or the velocity of change in the orientation of molecules can be affected by changing the thickness of the liquid crystal layer 40 from one end of the plates 30 and fibres 20 to the other end. Using a voltage of constant amplitude, the intensity of the electric field decreases upon increasing the distance between the coatings 23 and 33 functioning as electrodes. Thus the directing force (i) of the electric field, as well as the velocity of change induced by it, is greater at the thinner end of the liquid crystal layer 40 and decreases towards the thicker end.

On the other hand, a voltage U with an amplitude decreasing in a linear manner at an increasing distance from the power source 80 can be induced according to Fig. 5 as follows: The resistances of the electrodes formed by coatings 23 and 33 are for their entire length R., . The power source 80 (voltage U) and an external load 85 with a resistance R₂ are connected to the opposite ends of the electrodes 23, 33, as shown in Fig. 5. Thus the voltage of the ends of the elect¬ rodes 23 and 33 connected to the power source 80 is U, but the voltage of the ends connected to the resistance R₂ is U x R₂ : (2R, + R₂) . If the coat- ings 23 and 33 are homogenous, the amplitude of the voltage between them is linearly changed as a function of distance. By feeding to the connection shown in Fig. 5 an alternating voltage with an amplitude increasing from the moment of collision instead of an alternating voltage with a constant amplitude, an intensity of electric field effective on the liquid crystal 40 is achieved which is sufficiently high to cause the orientation of molecules in state of rest at different times at different sites in the lon¬ gitudinal direction of the fibres 20. It is advant¬ ageous to adjust the velocity of change of the voltage amplitude so that the site in the liquid crystal 40 corresponding to this intensity of the electric field proceeds at the same velocity as the acoustic pulse used in the embodiment of the example. Thus the joint effects of the different directing factors accelerate the change of orientation, and an abrupt change takes place within a short distance, which improves the differentiation of images.

The load 85 mentioned above can naturally be also an active component changing with respect to time; on the other hand, the amplitude of the power source 80 may remain constant, also providing an electric field changing with time and location as described above.

In addition, the structure of the display can be such that there is only one optic plate 30 for the whole display, wherein each optic fibre 20 is of the length of one line only, and each is supplied with a light modulator of its own. The display can also be con¬ structed so that there is a plate 30 for each line, and each one and the same optic fibre 20 extends underneath all plates, or part or all of the plates 30 have the fibres 20 of their own. Further, there is no need for using one fibre 20 for the entire length of a plate 30, but this distance can be subdivided for different fibres. Furthermore, different non-homogenous combinations can be used, depending'on the financial and technical requirements set for the application. In the embodiment described above, the different colour components of light were led into the same light fibre. However, According to the principle of the invention, a separate light fibre can be used for each colour component. In this case, the colour display can also be arranged so that the wavelength of the light travelling in the light fibre is smaller than the wavelength of visible light; according to the principle of connection described above, as such light enters the liquid crystal containing a fluores¬ cent substance, the light is absorbed into the fluores¬ cent substance which, in turn, emits the wavelength of visible light specific to the substance in question. Thus, a separate fibre is to be used for each colour component, red, green, and blue; and the liquid crystals corresponding to them is to be mixed with a fluorescent substance emitting a suitable wavelength. Therefore, the liquid crystals corresponding to the different colours must be prevented from mixing by adding an elastic concentre to the structure according to Fig. 1, although the fibres representing different colour components are beside each other. In the reference: T. Urisu, T. Sugeta and Y. Mizushima, Liquid crystal display device for total reflection switching with fluorescent dye addition. Applied Optics. Vol. 20, No. 4, Feb. 15, 1981, pp. 633-635, a principle of application using fluorescent substances for the connection with total reflection is presented as prior art, which differs from the invention essen- tially in that it is based on electric controlling.

It is also possible to use such carefully selected fluorescent substances which emit only when lighted at one or a few certain wavelengths. In this system, three separate combinations of fibre and mixed liquid crystal are not needed but three different ultraviolet frequencies are led into the fibres 20; the liquid crystal 40 is mixed with each of the three said fluorescent substances, each reacting at only one o the ultraviolet frequencies and radiating as th frequencies of visible red, green and blue light.

Instead of the said LED lamps, also other illuminator can be used, such as a LASER illuminator. It shoul be especially noted that by suitable selection o material for the plates 30, by their number, and b using fluorescent substances, the scanning velocit can be reduced to a great extent without causin disturbing flicker in the display. Thus it is possibl to use also such illuminators which do not have sufficiently wide modulation bandwidth to correspond, for example, to that of the conventional video signal. Of course, also illuminators emitting white light ca be used, equipped with colour filters.

Instead of the concave shape of the outer surface 3 of the plate 30 shown in Fig. 3, also another shap requiring less precision can be used, for example layer dispersing and reflecting light more occasional ly, or a shape retaining the narrowness of the cone, or a shape converging the cones, wherein the inventio as described can also be used in other scannin applications.

It is obvious that in the drawings shown as examples, the direction of the longitudinal axes of the fibres 2 and the plates 30 do not have any significance i relation to the principle of action; the horizonta direction is applicable as well.

Instead of liquid crystals, the medium layer 40 ca also consist of another elastic, liquid or amorphi substance which is optically anisotropic and whos optical axis can be mechanically disturbed. The function of the invention presented can also be turned to the opposite, because if a beam of light travels a certain route, it can always also return the same route; by replacing the illuminator 90, 94, 95, 96 ^"and 97 with light detectors and by placing the device towards a lighted picture, it can be used as a scanning input device for colour pictures into elect¬ ronic devices.

Claims

1. Method for transmission of visual informatio wherein the organs (20) transmitting visual informati from the source of information are connected with first surface (22) for transmitting information and second surface (32) for illustrating information, who opposite outer surface most preferably forms a displ surface (31) , such as a picture screen, a displ screen, an optic surface, or the like, whereby optically anisotropic medium (40) , such as a liqu crystal or the like, is arranged between the sai first (22) and second (32) surfaces, whereby, f application of the method, a closed structure i formed, in which preferably essentially plane-lik said first (22) and second (32) surface are locate preferably essentially in the same direction in housing (70) or the like, whereby the said structur is also fitted with organs for condensing the structur and organs (50) for separating the said surfaces (22 32) from each other, characterized in that th said organs (20) transmitting visual information ar optically arranged to function, i.e. by means of ligh beams reflected from an illuminator, and the sai structure is arranged to be affected by organs con trolling the transmission of information from betwee the said surfaces (22, 32), whose function is a least partly based on changing the refractive inde of the said medium (40) mechanically, or acousti cally.

2. Method according to claim 1, characterized i that the organs controlling the transmission o information from between the said surfaces (22, 32 is formed on one hand by the organs reducing th refractive index of the said medium (40) , whereby th reflection of light beams from the said medium (40 is effected at least in one direction as a functio of time so that the transmission of light beams through the said medium (40) is essentially prevented or reduced, and on the other hand by the organs increasing the refractive index of the said medium (40) , whereby the transmission of light is induced essentially through the said medium (40) , wherein for changing the refractive index in the first phase by the said organs reducing the refractive index, the orientation of the optical axes of the molecules of the medium (40) is induced so that the refractive index of the medium (40) is preferably at its minimum, after which in the second phase the said organs increasing the refractive index are used to induce the orientation of the optical axes of the molecules of the medium (40) so that the refractive index of the medium (40) is preferably at its maximum, wherein, for transmission of information, the said phases are preferably con¬ tinuously repeated in turn and in succession to generate a preferably continuous scanning motion of beams of light over the said display surface (31), such as a picture screen, display screen, an optic surface, or the like.

3. Method according to claim 2, characterized in that the said organs controlling the transmission of information between the surfaces (22, 32) is formed of a mechanical, or acoustic arrangement, which is arranged to function by at least one mechanical organ (60) or the like having an effect on the said medium (40) , such as a liquid crystal or the like, wherein upon effect of the said mechanical organ (60) or the like, such as by a change in state of motion or the like, a change is effected in the refractive index of the liquid crystal (40) or the like at least between two essentially different functional values.

4. Method according to claim 2, characterized in that the organs used for reducing the refractive index of the medium (40) is a mechanical or acoustic arrangement formed by at least one mechanical or¬ gan (60) or the like having an effect on the med¬ ium (40) , such as a liquid crystal or the like, and that the organs used for increasing the refractive index are a generally known coating arrangement which is arranged to function by the cooperation on one hand of finish or the like of the said first (22) and/or second (32) surface opposite each other or of separate light-permeable surface organs in connection with them, and, on the other hand, of the liquid crystal or the like, preferably of a "nematic" type, functioning as the said medium (40) , and/or a generally known electric arrangement which is arranged to function by the cooperation on one hand of the said first (22) and second (32) surfaces opposite each other, or of separate light-permeable surface organs in connection with them, preferably homogenous electro- conductive coatings (23, 33), such as indium tinoxide- (ITO) or the like, and on the other hand, of preferably positively dielectric anisotropic liquid crystal or the like, wherein a preferably adjustable potential difference (U) is arranged between the said sur¬ faces (23, 33) .

5. Method according to claim 4, characterized in that for reducing the refractive index of the said medium (40) , the said mechanical organ (60) is used for inducing a mechanical wave, such as an acoustic pulse or the like, proceeding preferably in the direction of the main plane as a function of time in the said medium (40) or a substance layer in it, wherein the orientation of the optical axes of the molecules in the said medium (40) or in a substance layer in it is induced essentially in the direction of the said first (22) and/or second '(32) surfaces or separate surface organs connected to them, and wherein, for increasing the said refractive index, the said coating arrangement and/or electric arrangement is used to induce the orientation of the optical axes of the molecules in the said medium (40) or in a substance layer in it preferably essentially at right angles to the said first (22) and/or second (32) surface or separate surface organs connected to them.

6. Method according to claim 4 or 5, characterized in that the said mechanical arrangement is formed preferably in the direction of the main plane of the said medium (40) of two or more mechanical organs (60) having a preferably parallel effect on the medium (40) or the substance layer in it, wherein the said medium (40) is divided into at least two or more functional part.

7. Method according to claim 3, 5 or 6, characterized in that the said mechanical wave or the like is induced by oscillation preferably essentially in the direction of the plane defined by the said first surface (22) caused by the said mechanical organ (60) , such as a coil or the like in a magnetic field, wherein a standing wave is induced, wherein, for changing the said refractive index, the orientation of the molecules in the said medium (40) or a substance layer in it is effected at different velocities, at the extreme sites of the said wave corresponding to the different amplitudes of the standing wave.

8. Method according to claim 1 or 2, characterized in that the said organs for transmission of visual information are formed by one or more optic fibres (20) comprising both the cladding (21) and the core, wherein the said transmission of information is carried out in a generally known manner by beams of light according to the law of total reflection, herein the said first surface (22) or a part of it is formed at least partly in the longitudinal direction by one or more of the said optic fibres (20) or the like preferably fixed to the support layer (25) or the like so that the said first surface (22) or a part of it is formed by the said core part of the optic fibre (20) or the like.

9. Method according to claim 5 and/or 7, charac¬ terized in that the said mechanical organ (60) , such as a coil in a magnetic field or the like, is arranged in power connection with the said second surface (32) or its opposite outer surface, which preferably forms the said display surface (31) , the side or edge part of which is preferably in connection with the said housing (70) or the like, or in a corresponding manner.

10. Method according to one of the claims 6-8 above, characterized in that the said medium (40) , such as the liquid crystal or the like is divided into said functional parts by forming the said second sur¬ face (32) , whose opposite outer surface preferably forms the said display surface (31) , of two or more preferably parallel sections located in the longi¬ tudinal direction of one or more optic fibres (20) forming the said first surface (22) , wherein the corresponding mechanical organs (60) , such as coils in a magnetic field, or the like, are fixed in a power connection with the sides or edge parts of the inner surfaces (32) or outer surfaces (31) of the said sections, preferably in connection with the said housing (70) or the like, or likewise.

11. Method according to one of the claims 1-10 above, characterized in that the said mechanical wave or the like is arranged to have an effect on the said section or a limited part of it so that the interface separating surfaces of fields with a different refrac¬ tive index in the medium (40) is essentially in a different direction to the plane defined by the said first surface (22) , wherein the said section or a limited part of it functions as a prism defracting beams of light, or the like.

12. Method according to claim 4, characterized in that the said potential difference (U) is induced by a voltage with a constant amplitude between the said electroconductive coatings (23, 33).

13. Method according to claim 4, characterized in that the said potential difference is arranged by an alternating voltage (U) with an amplitude changing by time and/or location between the said electroconductive coatings (23, 33).

14. Method according to claim 13, characterized in that the said opposite electroconductive coatings (23, 33) in connection with one or more sections are connected to each other with a series arrangement, wherein the one ends of the said coatings (23, 33) are joined by a wire organ fitted with a load (85) , such as a regulating resistance or the like, and the other ends are connected to the power source (80) , wherein the said changing alternating voltage (U) is achieved by changing the amplitude of the power source (80) and/or the resistance of the said load (85) .

15. Method according to one of the claims 1-14 above, characterized in that the distance between the said first (22) and the second (32) surfaces is essentially changed, preferably linearly, at least in one direc¬ tion, preferably in the longitudinal direction of one or more optic fibres (20) forming the said first sur¬ face (22) .

16. Method according to one of the claims 1-15 above, characterized in that the said second surface (32) , whose outer surface forms the display surface (31) , such as a picture screen, a display screen, an optic surface or the like, is formed of one or more optic plates (30) or the like arranged preferably to the plane-like inner surface (32) of the plate (30) , essentially without any loss with respect to the cone (35) formed by beams of light entering or exiting the said medium (40) .

17. Method according to claim 16, characterized in that the said outer surface (31) , such as a picture sreen, a display screen, an optic screen, or the like, is formed of the first and the second form part, alternatively placed on the said outer surface, preferably transverse to the longitudinal axis of one or more optic fibres (20) forming the said first surface (22) , the length of the form parts correspond- ing preferably to the length of the outer surface (31) in the corresponding direction, wherein the said first form part is formed of a preferably essentially plane-like surface (36) comprising a part allowing the light beams of the cone (35) to permeate directly through it, and the said second form part is formed of a preferably essentially concave surface (34) comprising a part reflecting the light beams of the cone (35) , such as a mirror surface or the like.

18. Method according to one of the claims 1-17 above, characterized in that the wavelength of the beams of light reflected from the illuminator is shorter than the wavelength of visible light, and that the said medium (40) , such as a liquid crystal or the like, comprises fluorescent material, wherein as the beams of light enter the said medium (40) , emission of visible light is induced from the said fluorescent material.

19. Method according to one of the claims 1-18 above, characterized in that the source of light comprising the said source of information is placed in connection with the said organs (20) for transmission of visual information, wherein the beams of light are modu¬ lated (97) by one or more illuminators (94, 95, 96), such as a light emitting diode (LED) , preferably by a wide band radiator supplied with colour filters, or the like, for transmission of information by reflection from the said source of light (90, 94, 95, 96, 97) to the said display surface (31) , such as a display screen, picture screen, or the like.

20. Method according to claim 19, chεiracterized in that the said light source (90, 94, 95, 96, 97) is formed of three diodes emitting light of different wavelengths, preferably red, green and blue (94, 95, 96) , or the like.

21. Method according to one of the claims 1-18 above, characterized in that the said source of information, such as a picture, drawing or the like, and the light source are placed in connection with the said display surface (31) , such as an optic surface or the like, wherein the said organs (20) for transmission of visual information is connected to organs of light detection, such as light detectors preferably equipped with colour filters, or the like.