WO2009128744A1

WO2009128744A1 - Polarizer and a method for the production thereof

Info

Publication number: WO2009128744A1
Application number: PCT/RU2009/000165
Authority: WO
Inventors: Валентин Алексеевич ЦВЕТКОВ
Original assignee: Tzvetkov Valentin Alekseyevich
Priority date: 2008-04-15
Filing date: 2009-04-07
Publication date: 2009-10-22
Also published as: RU2008114190A

Abstract

The inventive light polarizer comprises six transparent polymer layers, including a converter for converting unpolarized light into quasi-parallel light for illuminating a light divider for dividing the light into two mutually orthogonal polarizations. The divider is in the form of a polymer layer with anisotropic, preferably sinusoidal, phase diffraction grating which is formed therein and decomposes light into two spectra of the order of ±1 having 50% intensity in each order. The changeless light concentrated in the diffraction spectra comes at a polarizer output. The orthogonal polarization light is concentrated in the focuses of the cylindrical raster object lenses and, passing across the birefringent sections of the second photopolymer layer, turns a plane of polarization by 90°, thereby obtaining the polarization coinciding with the diffraction spectra light. Thus, all of the light, which passed across all the layers practically without losses, has a single polarization. The method for producing the described polarizer is also disclosed.

Description

POLARIZER AND METHOD FOR ITS PRODUCTION

The invention relates to optics, in particular, to optical polarizers that can be used in various fields of science and industry, in particular, can be used in liquid crystal displays.

To date, the most widely used are polarizers, which are oriented uniaxially stretched polymer film, colored in bulk by dichroic dyes or iodine compounds [1]. When unpolarized light passes through such a polarizer, one component of light, the plane of oscillation of which is parallel to the axis of absorption of the dye, is almost completely absorbed and, naturally, is not used in the future. Another component of light, the plane of oscillations of which is perpendicular to the axis of absorption of the dye, passes through the polarizer with minimal absorption and is then used as linearly polarized light.

The main disadvantage of the known polarizer is a significant absorption of useful light energy - more than 50%. The closest in technical essence and the achieved effect to the proposed polarizer is a polarizer, the absorption of light energy in which is significantly reduced [2]. Such a polarizer contains a converter of incoming light into many converging beams - a cylindrical lens raster, a splitter of each of the converging beams of unpolarized light flux into two sub-streams with mutually opposite polarization directions: passing through with the first, for example, right, circular polarization direction, and reflected - with second left

SUBSTITUTE SHEET (RULE 26) direction of circular polarization. The splitter is made of a cholesteric liquid crystal having the ability to transmit all the light with the first direction of circular polarization, for example, the right, and reflect all the light with the left circular polarization. The left-directed sub-stream reflected from the splitter is subjected to additional reflection from the metal reflector located at the focus of the cylindrical raster, while the left-hand circular polarization changes to the right-hand circular polarization, and this sub-stream is again directed to the splitter. Now the second part of the input stream passes through the splitter, since the twice reflected light also has a right circular polarization. Thus, both parts of the unpolarized input light pass through a polaroid with a single direction of circular polarization. A quarter-wave plate converts circularly polarized light into plane-parallel, i.e. a linear polarizer is formed with a minimum of loss of useful light energy - almost 100% polaroid.

Despite the minimal loss of light energy, the known polarizer has significant drawbacks. These include structural complexity and significant thickness due to the presence of a cylindrical lens raster with areas of a metallized reflective layer, a cholesteric LC layer enclosed between substrates of significant thickness. The design is not suitable for manufacturing in continuous tape mode (roll-to-roll ppose).

The problem to which the invention is directed, is to develop a simplified design and reduce the cost of its manufacture while maintaining minimal losses

SUBSTITUTE SHEET (RULE 26) of useful light in the polarizer, as well as in the development of a technologically progressive method of manufacturing in continuous tape mode (roll-to-roll ppose).

The technical result is achieved due to the fact that in the known polarizer, consisting of a converter of unpolarized stray light, a light splitter into two mutually orthogonal polarizations, an additional cylindrical raster lens, a distance spacer, a protective film with the first layer of a photopolymer in which are formed optically isotropic and birefringent areas located in the foci of the lenses of the cylindrical raster lens, while the direction of the optical axis and the magnitude of the two-beam refractive index in areas selected with the possibility of phase incursion 90 ° (quarter-wave plate). The light splitter is made of a second photopolymer layer with an anisotropic phase diffraction grating formed, the refractive index within each grating element having preferably a sinusoidal distribution.

Thanks to the proposed design, consisting of six layers of films, almost all incoming non-polarized light with minimal losses is converted to linearly polarized light.

The technical result in terms of the manufacturing method of the proposed polarizer is achieved by performing the bonding operation of four continuously moving tapes, the first of which is a strong transparent protective film on which the first layer of photopolymer is applied. The second tape is a transparent spacer. The third tape is a film with cylindrical lens rasters. Through the second and

SUBSTITUTE SHEET (RULE 26) the third tape is exposed to the first layer of the photopolymer by polarized radiation, with a plane of polarization directed under the angle of 45 ° to the direction of movement of the tape, and sections of a birefringent quarter-wave plate in the foci of cylindrical lenses are formed in the first layer of the photopolymer. A second layer of photopolymer is applied to the flat side of a film with cylindrical lens rasters, a second layer of photopolymer is exposed through a stencil with a system of transparent and opaque strips with polarized radiation with a plane of polarization directed along the direction of movement of the ribbons and form an anisotropic phase diffraction grating in it. When using opaque strips with a sinusoidal transmission distribution in a stencil, the formed diffraction grating will be sinusoidal and capable of efficiently decomposing light only by ± 1 orders of magnitude, which is the most optimal grating for the proposed polarizer.

The proposed method makes it possible to manufacture a polarizer in the form of a continuous tape of unlimited length (roll-to-roll ppress) with a tape speed limited by the photosensitivity of the photopolymer layers and the possible power of the exposure radiation sources.

The essence of the proposed polarizer and the method of its manufacture is illustrated with the use of graphic materials, which show: FIG. l is the design of the polarizer with three sub-elements from the set,

Figure 2 - the course of the rays in the polaroid, Figure.Z - an alternative design of a light converter,

SUBSTITUTE SHEET (RULE 26) Figure 4 - apparatus for the formation of a polaroid according to the invention in axonometric projection.

The polarizer consists of a converter 1 for incoming non-polarized radiation, a light splitter, which is a photopolymer layer 2 in which a phase anisotropic diffraction grating is formed with a period of 5 .... 50 μm, a cylindrical lens raster 3 with a focal length of 200 .... 2000 μm, a remote polymer optically isotropic film 4 with a calibrated thickness equal to the focal length of a cylindrical raster lens.

Close to the distance film 4, a photopolymer layer 5 is placed, which is deposited on a strong optically isotropic protective film 6.

Prior to exposure, layers 2 and 5 of the photopolymer are optically isotropic and, after exposure to polarized UV radiation, are able to form birefringent sections 2 \ 5 'with the direction of the optical axis coinciding with the plane of polarization of the exposure radiation. As such a polymer, it is proposed to use, in particular, the well-known polyvinylcinnamate, or any other photopolymer capable of forming birefringent layers.

An anisotropic diffraction grating is formed on layer 2 of the photopolymer. For this, the exposure of the layer of photopolymer 2 is carried out by actinic polarized UV radiation through a stencil, which is an alternating transparent and opaque stripes with a period of 5-50 microns. The direction of the plane of polarization of the exposure radiation is perpendicular to the plane of the drawing. As a result, a layer 2 of photopolymer is formed

SUBSTITUTE SHEET (RULE 26) b a periodic system of optically isotropic (2 ") and optically anisotropic (T), birefringent regions. This system acts as an anisotropic diffraction grating that decomposes light of the same polarization perpendicular to the plane of the drawing into ± 1 order diffraction spectra and, generally, higher Light with a polarization coinciding with the plane of the drawing passes through the anisotropic diffraction grating without any changes, since the profile of the refractive index does not change for light of this polarization therefore, for this polarization grating does not exist.

As a result, a system of illuminated areas with a mutually perpendicular direction of polarization is formed in the focal plane of the cylindrical raster lens: light with a plane of polarization coinciding with the plane of the drawing is focused on the optical axes of the raster lenses, and diffraction spectra with a plane of polarization perpendicular to the plane of the drawing are located outside the optical axis .

On the layer 5 of the photopolymer by exposure through a cylindrical lens raster by polarized UV radiation, a system of 5 'exposed and a system of 5' unexposed portions is formed, while the exposure of layer 5 should be done before the exposure of layer 2 of the photopolymer.

The unexposed sections of the 5 'system are optically isotropic. The exposed sections of the 5' system are birefringent with the optical axis at an angle of 45 ° to the plane of the drawing, which is ensured by the appropriate location of the polarizer during exposure. The birefringence of sections of the 5 'system is chosen such that light beams with a plane of polarization ,

SUBSTITUTE SHEET (RULE 26) lying in the plane of the drawing, acquire a phase shift of 90 ° and become linearly polarized with a plane of polarization perpendicular to the plane of the drawing.

The unpolarized scattered input radiation 7 consists of two mutually orthogonal polarizations P _p and P _s . The plane of polarization P _{p is} perpendicular to the plane of the drawing, the plane of polarization P _s is located in the plane of the drawing.

Radiation 7 enters the radiation converter 1 and, after passing through the converter, is converted into quasiparallel unpolarized radiation 8, which illuminates the phase anisotropic diffraction grating made from layer 2 of the photopolymer. Converter 1 can be made of two cylindrical rasters with matching focal lengths (Fig. L) or, alternatively, be a holographic screen with a system of holographic lenses that can direct incoming scattered light into pseudo-parallel beams (Fig. 2). Such holographic screens are well known, for example, [3]. Other types of converters can be used, for example, prismatic or any others. In the focal plane of the raster lens, zero-order spectra (zero) are formed on the optical axis of the raster lens and diffraction spectra outside the optical axis of the raster lens with a plane of polarization Pp for which an anisotropic grating 10 exists. For orthogonal polarization Ps, an anisotropic diffraction grating does not exist, since for this polarization both sections of the photopolymer have the same refractive index. All light beams with polarization P _{s are} focused by the raster-lens on the optical axes of the raster lenses, i.e. at the location of the spectrum 9

SUBSTITUTE SHEET (RULE 26) zero order (zero) for polarization P _p . Thus, in the focal plane of the raster lens outside the axis, diffraction spectra 10 are observed with an order of ± 1, ± 2 and higher orders with a polarization P _p . On the optical axis, a mixture of a spectrum of zero (zero) order with a polarization P _p and all focused light of orthogonal polarization P _{s is formed} , i.e. partially polarized light. If a sinusoidal distribution of the refractive index is created within each strip in the manufacture of an anisotropic phase grating, then only ± 1 order spectra (50% intensity in each order) are formed during diffraction, and no light intensity is observed in zero order.

Then light of only one polarization P _s will also be observed on the optical axes. Thus, in the presence of a sinusoidal polarization phase grating in the focal plane of the raster-lens, the following distribution of light intensity is observed: outside the optical axis there are completely polarized ± 1 order spectra with polarization P _p and light of only one orthogonal polarization P _s is observed on the optical axis.

Since birefringent portions of the system 5 'are formed on the photopolymer layer 5 in the region of the optical axes of the raster lenses with the direction of the optical axis at an angle of 45 ° to the plane of the drawing, and the magnitude of the birefringence induced in the portion of the birefringent system 5' is chosen such that for the polarization P _s the phase incursion was 90 ° (quarter-wave plate), then the light with the polarization P _s after passing through the parts of the 5 'system acquires the polarization P _p the same as in the diffraction spectra. Thus, at the output of the device there is radiation of only one polarization, i.e. This device is a linear polarizer. how

SUBSTITUTE SHEET (RULE 26) It can be seen from the foregoing that, for all evolutions of the polarization planes, almost no light loss occurred. Therefore, this is a linear polarizer with 100% transmission. The wavelengths of light that can be polarized include all visible light (400-700 nm). According to the principle of operation, the operating range of the polarizer can be significantly expanded towards UV or IR light, provided that all materials used are transparent in these ranges, and the photopolymer layers 2 and 5 retain photosensitivity in the UV range. Easily removable polymer films can be applied to both sides of the six-layer structure to protect the polaroid from mechanical damage and contamination during storage and transportation. An adhesive layer can be applied under one of the films to facilitate subsequent use. The polarizer of the proposed design can be used in projection displays because it is made of non-absorbing transparent materials, the transmitted radiation is not absorbed in the polarizers and the LC layer, therefore the thermal load on the polarizer and the LC layer is minimal. The proposed polarizer, which is a six-layer structure, can be manufactured on the equipment shown in Figure 4. The equipment includes five drums 12, 13, 14, 15, 16 and a pressure drum 17. All six layers that make up the polaroid are divided into four tape parts, each of which is moved using one of the drums 12, 13, 14 , fifteen .

The first of the tapes, moved by the drum 12, consists of a strong transparent base 6, on which with a sprayer 18,

SUBSTITUTE SHEET (RULE 26) the extruder, a doctor blade or other other device, the first layer 5 of the photopolymer is applied, which, after drying, enters the exposure zone 19, where birefringent sections of the system 5 'are formed in the focuses of the lenses of the cylindrical raster in the layer 5 of the photopolymer using UV illumination 20, with the direction of the optical axis directed at an angle of 45 ° to the direction of movement of the tapes. The magnitude of the induced birefringence is such that light with a plane of polarization perpendicular to the direction of movement of the ribbons rotates the plane of polarization by 90 ° (quarter-wave plate).

The second of the tapes, moved by the drum 13, is a transparent, optically isotropic film 3 of strictly controlled thickness, and for the present process is a component product, or can be manufactured as part of the same process using one of the known technologies.

The third of the tapes, moved by the drum 14, is a film 4 with cylindrical raster lenses. For the present process, it is a component product or can be manufactured as part of the same process using one of the known technologies that are not the subject of the present invention.

The first, second and third tapes connected into a single tape are continuously moved to the spraying and illumination zone 24, where the second layer 2 of photopolymer is applied to the flat side of the film with cylindrical raster lenses. After drying, the photopolymer layer 2, located on a flat surface, moves to the exposure zone 23. In projection zone 24, projection UV illumination 20, a stencil 25, and polaroid 26 on the photopolymer layer 2 form birefringent portions of system V with an optical direction

SUBSTITUTE SHEET (RULE 26) axis coinciding with the direction of movement of the tapes. Stencil 25 has a system of transparent and opaque sections and their period is chosen so that, taking into account the increase in the projection system, a phase anisotropic diffraction grating is formed on layer 2 of the photopolymer. If a pattern of opaque regions with a sinusoidal distribution of the degree of opacity is present on screen 25, then a sinusoidal anisotropic phase diffraction grating will be formed.

All four tapes are moved by drums 12,13,14,15 at the same speed. The speed of their movement is determined by the exposure time necessary for the formation of birefringent sections on layers 2 and 5 of photopolymers.

After the exposure processes, all four tapes are connected using a drum 16 and a clamping device 17 into a single monolithic polarizing unit. To ensure solidity and structural strength, it is possible to use thin adhesive layers between individual tapes that do not change the ray path in the polaroid.

Cathodoluminescent lamps with polarizers can be used as a source of UV radiation, providing radiation of sufficient power in the sensitivity range of the layers of photopolymers. It is possible, and even preferable, to use high-power lasers emitting in the sensitivity range of photopolymers and emitting polarized radiation. The length of the manufactured polarizers can be unlimited.

The width of the manufactured polarizer is limited only by the width of the drums and the power of UV radiation sources and the ability of projection systems to form fairly narrow beams

SUBSTITUTE SHEET (RULE 26) exposure radiation. At the current level, these widths can be several meters, namely polarizers of this area are required for displays with a diagonal of 100 inches or more.

References:

[1] - US Patent No. 5,007,942.

[2] - Patent of Russia No. 2.143, 128.

[3] - DNP holographic backlight screens (see www.dpr.com).

SUBSTITUTE SHEET (RULE 26)

Claims

CLAIM

1. A polarizer consisting of a converter of unpolarized scattered light into many beams of unpolarized quasiparallel light and a light splitter into two mutually orthogonal polarizations, which is due to the fact that an additional cylindrical lens raster lens is introduced into it, remote laying, protective film, with the first layer of photopolymer applied, in which optically isotropic and birefringent sections are formed, located in the foci of the lenses of a cylindrical raster lens, while optical axis and birefringence in the regions selected with the possibility of phase incursion of 90 °, the light splitter is made of the second layer of the photopolymer with the formed phase anisotropic diffraction grating.

2. The polarizer according to claim 1, with the fact that the formed phase anisotropic diffraction grating is made with a sinusoidal profile of the distribution of the refractive index

3. A method of manufacturing a polarizer, which consists in processing and bonding four continuously moving tapes, and on the first of the tapes, which is a transparent protective film, put the first layer of photopolymer, the second tape is made in the form of a transparent remote strip, the third tape is made in the form films with cylindrical lens rasters, while through the second and third tapes the first layer of the photopolymer is exposed to polarized radiation with a plane of polarization directed minutes at an angle of 45 ° to the direction of tape movement, are formed in the first layer of photopolymer portions

SUBSTITUTE SHEET (RULE 26) a derefringent quarter-wave plate in the foci of cylindrical lenses, a second layer of photopolymer is applied to the flat side of a film with cylindrical lens rasters, a second layer of photopolymer is exposed through a stencil with a system of transparent and opaque stripes with polarized radiation along a polarization plane directed along the direction of movement of the ribbons and form an anisotropic in it phase diffraction grating, to the second layer of the photopolymer is attached a fourth tape, configured to convert seeded light in quasi-parallel light.

SUBSTITUTE SHEET (RULE 26)