JP2005208644A - Optical system, light source, projection display and direct-viewing display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization conversion optical system which is attained at a low cost, dispensing with an expensive polarized beam splitter, and also, in a state where required antireflection coating is comparatively little. <P>SOLUTION: The optical system includes a 1st polarizing lens array and a 2nd polarizing lens array. The 1st array lens functions as a converging lens for one polarized light, but, the 1st array lens does not substantially influence the other orthogonal polarization. Conversely, the 2nd lens array functions as a converging lens for the orthogonal polarization, but, the 2nd array lens does not substantially influence the 1st polarization. The 3rd lens array is arranged on the focusing plane of the lens array or adjacent to the focusing plane. The 1st and 2nd lens arrays are mutually offset in a lateral direction by half the lens pitch so that the spot of S-polarized light may alternate with the spot of P-polarized light in a patterned retarder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical system. Such a system may be used, for example, in a polarization conversion optical system (PCOS) that converts input non-polarized light into substantially single or uniform output polarized light. Such a system can be further used for a light source for a projection display, a projection display, a direct view display, or the like. The invention therefore further relates to a light source comprising such a system, a projection display / direct view liquid crystal display comprising such a light source, and a direct view display comprising such a system.

  One type of projection display is known to include a polarization converting optical system that receives unpolarized light from a lamp and converts it to uniformly polarized light. Projection illumination systems illuminate a spatial light modulator (SLM) such as a liquid crystal device (LCD) to convert the polarization of the illumination light into a substantially uniform polarization, thereby increasing the efficiency or brightness of the projection display. Improve. Accompanying FIG. 1 shows a typical display of this type as disclosed, for example, in US Pat. No. 5,978,136.

  The projection display shown in FIG. The lamp 1 includes a small arc lamp having, for example, a parabolic reflector, which emits a non-polarized, substantially collimated beam having a non-uniform intensity distribution. Light from the lamp 1 is supplied to a polarization conversion optical system (PCOS) / homogenizer 2. The polarization conversion optical system (PCOS) and homogenizer 2 includes first and second microlens arrays 3 and 4, a polarization beam splitter (PBS) 5, a ½ wavelength phase plate array 6, and a field lens 7. The emitted light is directed to the liquid crystal panel 8 to irradiate it.

  The first microlens array 3 forms an array of non-polarized spatially distributed bright spots on its focal plane. The second microlens array 4 is provided on the focal plane of the first microlens array 3, and the lenses of both arrays have the same focal length. Due to the field lens 7, the second microlens array 4 acts as part of a beam homogenization system that forms an image of a uniform light beam on the surface of the liquid crystal panel 8. The aspect ratio of the microlenses of the first array 3 is substantially the same as the aspect ratio of the panel 8. Thus, the light beam from lamp 1 is reshaped so that the homogenized beam illuminating panel 8 has substantially the same aspect ratio as the panel.

  For this type of homogenization system to work properly, the focal lengths of the microlenses in each array must be equal and the second array must be on the focal plane of the first array. (See Stupp and Brennesholtz, “Projection System”, Wiley, 1999).

  A polarizing beam splitter 5 is provided after the second array 4 and includes an array of elements. The pitch of the elements is about half of the pitch of the microlenses of the second array 4. The focused light beam is incident on the polarizing beam splitter 5 every other element or every other section. For example, the polarization separation film indicated by reference numeral 9 transmits one polarized light, for example, P-polarized light “forward”. Orthogonal polarized light such as S-polarized light is reflected in the direction of the reflective film (for example, indicated by reference numeral 10) in the adjacent portion of the beam splitter. In the beam splitter 5, the orthogonal polarization is reflected forward. Therefore, each non-polarized beam incident on the beam splitter 5 is separated into a space and propagates forward to generate two beams having orthogonal polarization.

  Element 6 includes an array of retarder film phase plates or phase strips. The phase plate or phase strip is arranged so that only the beam having one polarization is incident on the retarder film. The retardation is selected so that the incident polarized light is emitted from the retarder in a state where the polarized light is changed into orthogonal polarized light. Therefore, all forward propagating beams have substantially the same polarization state. These beams are condensed by the field lens 7 and irradiate the panel 8 uniformly.

  The F values of the microlenses of arrays 3 and 4 are selected to match the characteristics of lamp 1. The lamp 1 generally emits light that is slightly shifted. In order to shorten the length of the polarization conversion optical system 2 without substantially affecting the light collection efficiency of the polarization conversion optical system 2, both the focal length and pitch of the microlens are shortened to obtain a desired F value. It is necessary to maintain

  In any lamp, it is beneficial to use microlenses with a shorter pitch. This is because the irradiation beam is made more uniform in the panel 8, and as a result, the illuminance uniformity in the panel becomes higher. The reason why the uniformity is increased is that the number of lenses of the first array 3 that samples the non-uniform beam emitted from the lamp 1 increases. In other words, using a microlens with a shorter pitch, the light emitted from a light source having a smaller form factor can be efficiently uniformed, thereby providing a smaller “projection engine”. It becomes.

  When the pitch of the microlenses of the arrays 3 and 4 is shortened, the pitch of the beam splitter 5 is also shortened. Beam splitters are typically the most expensive parts in PCOS. Substantial shortening of the pitch increases manufacturing costs because more polarization separation and mirror coating is required. Further, when manufacturing elements with shorter pitches, tolerance becomes more important and light waste is increased. Because of these constraints, it is currently not business feasible to produce a polarizing beam splitter array having a pitch of less than about 0.5 mm, so the total length of PCOS using such an array is less than about 7 mm. I can't do it.

  The PCOS 2 shown in FIG. 1 includes four separate units: two microlens arrays 3 and 4, a beam splitter array 5 with a retarder strip, and a field lens 7. In order to reduce the loss of light due to Fresnel reflection from the surface of these units, it is necessary to index match the interface between these units or provide an anti-reflective coating. The former method increases the length of the system, and the latter method increases the cost of the system.

  US Pat. No. 6,621,533 (Patent Document 2) discloses a PCOS shown in FIG. The system includes microlens arrays 3 and 4 and a polarization rotation element 11. These function similarly to the microlens arrays 3 and 4 and the phase plate 6 of FIG. However, the PBS 5 is omitted and its action is provided by the polarization splitting element 12. The polarization branching element 12 includes, for example, an array of optically anisotropic microprisms 13 indicated by reference numeral 13 and an array of optically isotropic microprisms 14 indicated by reference numeral 14, for example. The array of microprisms 13 and the array of microprisms 14 are in contact with each other. Each microprism 13 and 14 has a wedge-shaped cross section.

  This arrangement provides microlenses with the very short pitch and focal length that have the F-number required to efficiently collect light. This is because the pitch of the microlenses can be determined regardless of whether it is necessary to use the polarizing beam splitter array 5 made of glass. As a result, the length of the system is a minimum value of about 4 mm. When perfectly parallel non-polarized light is incident on the polarization splitting element 12 in the normal direction, this light is inclined between the anisotropic prism 13 and the isotropic prism 14 (e.g., indicated by reference numeral 15). ) And is angularly separated into two orthogonally polarized beams. The angle between these beams is determined by the angle at which light enters the interface 15 and the change in the refractive index of the light at the interface 15.

  When the branch element 12 is illuminated by shifted light, as occurs in a real optical system, some of the light is incident on a vertical wall or interface (eg, indicated by reference numeral 16) and lost in the PCOS direction. This light is refracted in the wrong direction. Therefore, the light efficiency of such a system is reduced. A further disadvantage of this configuration is that it is formed by a relatively thick layer of polymer or liquid crystal material, for example, a layer of about 60-100 micrometers. Such thickness generally requires that the desired branch angle be achieved without compromising on the diffraction loss in the system, which occurs when the thickness and pitch are reduced. Although such thick polymer or liquid crystal materials can degrade when exposed to bright or high intensity light supplied from a high pressure arc lamp, the high pressure arc lamp is typically a light source in a projection engine. It is used. Thus, the lifetime of PCOS can be unacceptably low. Furthermore, in order to optimize the light efficiency, the anti-reflection coating must be applied to the outer surface of the three PCOS units, which increases costs.

U.S. Pat. No. 4,446,305 (Patent Document 3) discloses a light polarizing sheet member shown in FIG. The member or device functionality isotropic layer 20 having a relatively low refractive index n _1, highly birefringent polymer layer 21 having ordinary and extraordinary refractive index n _o and n _e, and relatively high refractive index n ₂ A functional isotropic layer 22 having Material of layer 21 and 22, _{n 1} is matched to _{n o} substantially, _{n 2} is selected to _{n e} substantially matches.

  For example, unpolarized light indicated by reference numeral 23 is incident on the upper surface of the layer 20. The interface between the birefringent layer 21 and the isotropic layers 20 and 22 forms lens structures 24 and 25. In this case, the lens structure 24 is effective only for light having the first polarization, and the lens structure 25 is effective only for light having orthogonal polarization. Thus, the P and S polarization components of incident light 23 are focused on different interlaced images.

  The birefringent material of layer 21 is a transparent and hard plastic film. By applying mechanical stress to this, molecular order is induced, resulting in optical anisotropy. The lens structure must be formed by modifying the surface of the layer 21 by embossing, grinding or polishing. Molecular rearrangement occurs by applying the heat or solvent necessary to soften the material before embossing. Stress birefringence is introduced by grinding and polishing. Thus, all these processes have the effect of changing the refractive index profile of the anisotropic material and thereby reducing the efficiency of the device.

  In order to manufacture the device, it is necessary to identify and select a material having an appropriate refractive index, particularly the appropriate matching conditions described above. In the case of broadband or white light, it is difficult to identify three materials that satisfy these index matching conditions over a fairly wide wavelength range. Therefore, the broadband efficiency of this device is low.

  Japanese Patent Laid-Open No. 3-005707 (Patent Document 4) discloses a configuration similar to US Pat. No. 4,446,305, but using a refractive lens as a Fresnel lens.

  US Pat. No. 5,671,034 (Patent Document 5) discloses a technique for manufacturing a polarization-dependent refractive optical element using a birefringent material.

  Japanese Patent Application Laid-Open No. 3-294803 (Patent Document 6) discloses a polarization branching system. This polarization splitting system includes a birefringent lens 17 that spatially splits random polarization from a light source into two orthogonal linear polarizations, a system 18 that converts one polarization state to the same state as the other, and substantially uniformly. A hologram lens 19 is used which combines polarized light into a parallel beam. This system is shown in the form of an array in FIG.

In order to make the light focused by the birefringent lens 17 parallel, the hologram lens 17 (focal length f _H ) must be provided at a position that is confocal with the birefringent lens (focal length f _B ). . In other words, the birefringent lens is separated from the hologram lens by a distance equal to the sum of the focal lengths of the two lenses (f _H + f _B ).

Due to the fact that the outgoing light is collimated, this known system cannot be used as a homogenizer in a polarization converting optical system. When the light is collimated, it is impossible to superimpose the images of the individual light sensitive microlenses and therefore it is impossible to form a uniform beam with uniform illumination on the panel surface. This system has a further disadvantage because it is limited to using the hologram lens 19. The performance efficiency of transmission holographic optical elements is highly wavelength dependent. Therefore, this system cannot be highly efficient in the case of white light. Furthermore, the hologram lens 19 is not sensitive polarization and cannot act to change the polarization of the incident light.
US Pat. No. 5,978,136 US Pat. No. 6,621,533 US Pat. No. 4,446,305 JP-A-3-005707 US Pat. No. 5,671,034 JP-A-3-294803

  An object of the present invention is to provide a simple polarization conversion optical system that can be provided at a low cost without requiring an expensive polarization beam splitter and with a relatively small amount of anti-reflection coating, and such polarization conversion. It is to provide a light source with an optical system and a display with such a light source.

  According to the first aspect of the present invention, the first polarized light is converged by the first convergence, and the second polarized light orthogonal to the first polarized light is transmitted by the second convergence smaller than the first convergence. A first array of polarizing lenses, receiving light from the first array, converging the second polarized light with a third convergence, and reducing the first polarized light with a third convergence smaller than the third convergence. An optical system comprising a second array of polarizing lenses that transmits at a convergence of four, as viewed from the first and second arrays, from one of the first and second image planes There is provided an optical system, further comprising a third array of lenses, provided at a position that is not substantially distant, thereby achieving the object.

  The first and second polarized light may be linearly polarized light.

  At least one of the second and fourth convergence may be substantially zero.

  The second polarization may not be substantially shifted by the first array.

  The first polarization may not be substantially shifted by the second array.

  The lenses of the first array may be substantially identical to one another.

  The lenses of the second array may be substantially identical to one another.

  The first and second image planes may be substantially coplanar.

  The third array may be substantially in the first and second image planes.

  The first and second image planes are not substantially coplanar, and the third array is substantially on one of the first and second image planes, or the first and the second It may be between the second image planes.

  The first and second arrays may have substantially the same pitch.

  The lenses of the second array may be offset laterally with respect to the lenses of the first array.

  The lateral offset may be substantially equal to half the pitch of each of the first and second arrays.

  The lenses of the first and second arrays may include an optically anisotropic material.

  The lenses of the first and second arrays may be in contact with an optically isotropic material having a refractive index substantially equal to one of the refractive indices of the optically anisotropic material.

  The lenses of the first and second arrays may be formed of the same material, and the lenses of the first array may have an optical axis that is orthogonal to the optical axis of the lenses of the second array. .

  The lenses of the first and second arrays may be Fresnel lenses.

  The lenses of the first and second arrays may be positive and negative doublets.

  The first and second arrays may have substantially flat surfaces that face each other.

  The lenses of the first and second arrays may be gradient index lenses.

  The system may further comprise a fourth array of polarization changing elements that receive light from the second array and change at least one of the first and second polarizations, The four arrays may be modified so that the light from the fourth array is substantially uniform polarized.

  The fourth array may be provided to change one of the first and second polarizations to substantially the other of the first and second polarizations.

  The polarization changing element may be a polarization rotator.

  The polarization changing element may be a retarder.

  The third array may have a pitch substantially equal to half the pitch of the lenses of the first and second arrays.

  Each of the lenses of the third array may be optically aligned with a corresponding lens of the first or second array.

  The focal length of each of the lenses of the third array may be substantially equal to the focal length of the corresponding lens of the first or second array.

  The third array may comprise the fourth array, and at least some of the lenses of the third array may comprise polarization changing elements.

  At least some of the lenses may have optical anisotropy.

  The system may further include a field lens that converges light emitted from the system.

  According to a second aspect of the present invention there is provided a light source comprising a system according to the first aspect of the present invention and at least one light emitter, whereby the above object is achieved.

  According to a third aspect of the present invention, there is provided a projection display comprising a light source according to the second aspect of the present invention, whereby the above object is achieved.

  The display may further include a spatial light modulator provided to be illuminated by the light source.

  Each of the lenses of the first array may have an aspect ratio that is substantially equal to the aspect ratio of the spatial light modulator.

  According to a fourth aspect of the present invention, there is provided a direct view display provided with a system according to the first aspect of the present invention, provided between a backlight and a spatial light modulator, whereby the above object is achieved. Is done.

  Each of the lenses of the third array may be optically aligned with a corresponding pixel of the spatial light modulator.

  The spatial light modulator may be a liquid crystal device.

  It is possible to provide a polarization converting optical system with a very short length. For example, a length on the order of only 3 mm is possible. Furthermore, it is possible to provide a lens array with a very short pitch, which improves beam uniformity. Such a system can be used to provide efficient homogenization of very small form factor light sources such as individual light emitting diodes (LEDs) or small arrays of LEDs. This makes it possible to provide a small projection engine. A relatively thin layer of polymer can be used, which provides a system that provides good durability even in the very intense light used in projection systems. The cost of the system is relatively low because a relatively uncomplicated polarization converting optical system can be provided without the need for expensive polarizing beam splitters and with relatively little anti-reflective coating required.

  Alternatively, such a polarization converting optical system can be used to convert non-polarized light emitted from a narrow-angle backlight in a direct view display into substantial polarized light. Thus, more than half of the light from the backlight can be used, thereby improving the efficiency of, for example, a direct view liquid crystal device. In this case, the third array of microlenses acts as a field lens for the first and second arrays of microlenses and beneficially alters the convergence of the rays.

  Embodiments of the present invention will be further described with reference to the accompanying drawings.

  Like reference symbols in the accompanying drawings indicate like elements.

The polarization conversion optical system shown in FIG. 4 can be used, for example, in an illumination system of a projection system that projects an image displayed on a spatial light modulator such as a liquid crystal device. The system receives unpolarized light (indicated by reference numeral 30) from the lamp. Orthogonal P and S polarizations are indicated by reference numerals 31 and 32, respectively. Non-polarized light 30 is incident on a first array 33 having substantially the same polarization sensitive microlenses. The microlens is made of a birefringent material, and the optical axis of the lens is parallel to the direction of the S-polarized light 32. The lens material of the array 33 has positive birefringence. That extraordinary refractive index n _e is greater than the ordinary refractive index n _o. In the embodiments described herein, all anisotropic materials have positive birefringence. However, anisotropic materials having negative birefringence can also be used, and modifications necessary when using such materials will be apparent to those skilled in the art.

The lenses of array 33 are set in an isotropic material indicated by reference numerals 34 and 35. Refractive index n of the material is substantially matched to the ordinary refractive index n _o of the lens. In one embodiment, the lenses of array 33 are formed by a reactive mesogen known as RMM 34 available from Merck UK. The refractive index of RMM34 for green _light, n o = _1.53, a n e = 1.69. Materials 34 and 35 include a Norland optical adhesive known as NOA68. The refractive index of NOA 68 is n = 1.54 for green light. In another embodiment, the lenses of array 33 include a liquid crystal material known as MLC6697 available from Merck UK. The refractive index of MLC6697 for green _light, n o = _1.50, a n e = 1.66. Materials 34 and 35 include an adhesive known as SK9 available from Summers Optical. The refractive index of SK9 is n = 1.51 for green light. The lenses of the array 33 are plano-convex and are “optically positive”. Alternatively, by forming a negative lens array to the isotropic material is indexed matched to the extraordinary refractive index n _e of the anisotropic material within the anisotropic material to provide a lens array having a positive refractive index May be.

  S-polarized light 32 is focused by a series of spots in the focal plane 36 of the first array 33 by the lenses of the array 33. However, the P change 31 passes through the lenses of the array 33 without substantially converging or shifting. The second array 37 has substantially the same pitch as the first array 33 and is offset laterally relative to the first array 33 by substantially half the pitch of the lenses of each array. The lenses of the second array 37 are made of the same material as the lenses of the first array 33, but the optical axes of the lenses of the second array are substantially orthogonal to the optical axes of the lenses of the first array. doing. The lenses of the second array 37 allow the S-polarized light to pass through without substantially converging or shifting. The lens of the second array 37 focuses the P-polarized light 31 on the focal plane of the microlens array 37. The focal plane of the microlens array 37 substantially coincides with the focal plane 36 of the first array 33 or is coplanar.

  The focal spot of light formed on the plane 36 by the microlens arrays 33 and 37 forms a substantially regular pattern at half the pitch of each of the arrays 33 and 37. A patterned retarder 38 is provided adjacent to the plane 36. The patterned retarder 38 includes elements that are disposed at these positions having substantially the same pitch as the focal spot positions of the light formed by the microlens arrays 33 and 37. The elements of the patterned retarder 38 are arranged to act on S and / or P polarized light so that the light emitted from the patterned retarder 38 has substantially the same uniform polarization. For example, as shown in FIG. 5, the retarder 38 includes an element (e.g., indicated by reference numeral 39) that acts as a half-wave plate. The optical axis of the element 39 is oriented in such a direction that the S-polarized light 40 is converted into the P-polarized light 41. The element 39 is arranged alternately with the element 42, and the element 42 allows the P-polarized light 43 to pass through without substantially affecting the P-polarized light 43. Accordingly, substantially all incident light exits the patterned retarder 38 as P-polarized light.

  Light from elements 39 and 42 of the patterned retarder 38 passes through corresponding lenses in the isotropic microlens array 44. The array 44 forms part of a beam homogenization system, and the light emerging from the array is converged by a field lens of the type indicated by reference numeral 7 in FIG. As a result, a uniformed beam is generated on the input surface of the spatial light modulator of the type indicated by reference numeral 8 in FIG. The pitch of the lenses of array 44 is substantially equal to half the pitch of the lenses of each of arrays 33 and 37. Each microlens of the third array 44 collects polarized and focused light from a corresponding single lens of one of the arrays 33 and 37 and has the same focal length as the corresponding lens. Accordingly, the lenses of array 44 need not necessarily be identical to one another.

  Although the patterned retarder 38 is shown as being provided in front of the microlens array 44, it may be provided after the microlens array 44. The microlens array 44 is substantially located in the common focal plane of the microlens arrays 33 and 37.

  The pitch of the lenses of each of the arrays 33 and 37 may be selected according to system requirements. For example, a pitch between 80 micrometers and 500 micrometers can be provided. Alternatively, the F value of the lens can be selected to collect light from a light source used with the system. By minimizing the lens pitch of the arrays 33 and 37 while maintaining the F value of the lens, a short system can be provided that provides high efficiency and a high degree of uniformity.

  The lenses of the arrays 33, 37 and 44 are spherical or parabolic. The aspect ratio of the lens can be selected to substantially match the aspect ratio of the spatial light modulator that forms part of the projection system including the polarization converting optical system. A very small “projection engine” having high light utilization efficiency and high illumination uniformity over the entire image can be provided.

  When used in a direct view liquid crystal display, the lens aspect ratios of arrays 33 and 37 need not match the panel aspect ratio. The small lenses of the arrays 33, 37 and 44 may be two-dimensional or cylindrical (convex lens array).

  Polarization sensitive microlenses can be formed by a variety of different types of optically anisotropic materials. Such materials include low molecular weight liquid crystals, photopolymerizable liquid crystals (reactive mesogens), polymer liquid crystals and anisotropic crystalline solids. Various examples are described herein.

  FIG. 6 illustrates a technique that can be used during the manufacture of the system to ensure that the individual elements indicated by reference numerals 39 and 42 are correctly aligned. Elements 33 and 37 are formed or assembled as shown in FIG. 6, with a reactive mesogen layer 50 having a thickness corresponding to ½ wavelength adjacent to a common focal plane 36 of microlens arrays 33 and 37. Alternatively, it is formed on the common focal plane 36. Although the array 44 of isotropic microlenses 51 is shown as being formed on the layer 50, it may actually be formed after the layer 50 has been processed.

  S-polarized ultraviolet (UV) light 52 is incident on the microlenses of array 33 and is focused on a series of spots on layer 50. Layer 50 is planar aligned by being provided on a suitable matching layer 53. The incident angle range of the ultraviolet light 52 is selected such that a spot having a diameter substantially corresponding to half the pitch of the lenses of the array 33 is formed.

  The intensity of the incident ultraviolet light 52 is such that the reactive mesogenic material in the portion of the layer 50 where the ultraviolet light is incident is cured. The incident direction of the ultraviolet light 52 may be changed so that a series of stripes are formed instead of the spots. Alternatively, the substrate carrying the layer 50 may be translated laterally to provide substantially the same effect.

  After exposing layer 50 to ultraviolet light, the uncured portion of layer 50 is removed to provide a region that acts as a half-wave plate for visible light (e.g., indicated by reference numeral 39) and incident light An area (for example, indicated by reference numeral 42) that does not substantially affect the polarization is left.

  A two-layer (Pancharatnam) patterned retarder may be used as the retarder 38, which may be formed by a similar technique. For example, after forming the first layer by the method described above with reference to FIG. 6, a new matching layer may be formed on the existing layer. A thin layer of reactive mesogen may also be formed on the new matching layer. Similarly, the second layer may be cured by exposure to polarized ultraviolet light 52 thereafter. The uncured material can then be removed to provide a two-layer patterned retarder that has more efficient polarization conversion performance for white light than a single-layer retarder.

  Patterned retarder 38 may alternatively be formed from photoisomerizable reactive mesogens, for example, as described in US Patent Application No. 2002/0187282. According to this technique, the reactive mesogen layer 50 is exposed to polarized ultraviolet light 52 as described above, and in this case, photoisomerization occurs by exposure. Photoisomerization reduces the optical retardation of the reactive mesogens in the exposed areas, while the unexposed areas retain the original retardation. As a result, the entire layer 50 is polymerized by heating or photocuring. Thus, areas exposed to photoisomerization do not substantially affect the polarization of incident visible light in the final resulting system, and areas not originally exposed are ½ of incident visible light. Acts as a wave plate.

  It is also possible to form the patterned retarder 38 separately from other parts of the polarization converting optical system. For example, a birefringent liquid crystal material can be provided on a substrate carrying a patterned matching layer. Such a patterned matching layer can be obtained by using, for example, the multi-rubbing technique disclosed in EP 0 877 667, for example using the microstructure grating disclosed in GB 2384318, or for example by Matsusunaga et al. Optical manufacturing ", 14 pp 1477-1480, 2002, can be provided through the use of optical matching techniques.

  Reactive mesogens can be spun in solution onto the matching layer. When the solvent evaporates, a layer of nematic liquid crystal material remains later. The optical axis of the liquid crystal is aligned with the alignment direction of the alignment layer below it to form a retarder layer. Reactive mesogens are crosslinked by exposure to ultraviolet light. In order to enhance the performance of the patterned retarder against white light, for example, a second uniform retarder layer may be provided between the sensitive polarization microlenses 33 and 37 and the spatial light modulator of the projection system.

  The retarder performance can be optimized to compensate for the wavelength dependent performance of other parts of the polarization conversion system. For example, the variation in the refractive index of the microlens leads to chromatic aberration, and as a result, better polarization conversion can be performed at a wavelength of blue than red, for example. In this embodiment, the retarder performance can be designed such that the retarder is more efficient for red light for the purpose of enhancing the system performance for white light or colorless light.

  Another example of a patterned retarder 38 has planarly aligned reactive mesogens and homeotropically aligned reactive mesogens in staggered stripes. The plane-aligned stripe acts as a half-wave retarder for incident polarized light. Homeotropically aligned stripes are optically isotropic and have no substantial effect on the polarization of incident light. Such a patterned retarder can be manufactured using optical matching techniques.

  As yet another example, the patterned retarder 38 may include an array of retarder film strips having a width substantially equal to half the pitch of the polarization sensitive microlenses of the arrays 33 and 37.

  In yet another example, the patterned retarder 38 is a liquid crystal in which a region of twisted nematic liquid crystal or a region of reactive mesogen operating in the Mauguin regime is an isotropic material, such as a region of isotropic polymer, or a homeotropically aligned liquid crystal. It may include cells provided alternately with the material region or the reactive mesogen region. The region containing the twisted nematic material rotates the plane of polarization of the incident light and the other regions do not substantially affect the polarization state of the incident light.

FIGS. 7 a and 7 b show a configuration in which the microlens array 44 also acts as a patterned retarder 38. Accordingly, the patterned retarder 38 can be omitted in this configuration, resulting in a simplified system. In the configuration shown in FIG. 7a, a microlens formed of an optically isotropic material (e.g., indicated by reference numeral 55) is replaced with a microlens formed of a twisted nematic liquid crystal material operating in the Mauguin regime (e.g., indicated by reference numeral 56). Are shown alternately. The liquid crystal material of these lenses, when immersed in an optically isotropic dielectric in medium index matches the ordinary refractive index n _o of the liquid crystal material such as a lens 56, the refractive index of the isotropic micro lenses 55 such as a lens 56 substantially equal to the extraordinary refractive index n _e.

  In this configuration, the twisted nematic liquid crystal of the lens 56 rotates the polarization plane of incident light from S-polarized light to P-polarized light. The isotropic microlens 55 or the like does not substantially change the P-polarized light of the incident light. Accordingly, substantially uniform P-polarized light is emitted from the microlens array 44. Such a configuration has the advantage of reduced size and complexity. This is because both the polarization conversion and homogenization functions are incorporated into a single element constituted by the microlens lens 44. Furthermore, the number of elements that need to be correctly aligned is reduced, and as a result, the manufacture of the system becomes easier.

  The configuration shown in FIG. 7B is different from the configuration shown in FIG. 7A in that a liquid crystal microlens 57 that is plane-matched or homeotropically matched is provided in place of the isotropic microlens 55. Therefore, the microlens 57 does not substantially affect the polarization of incident light. However, the lenses 56 and 57 can be made of the same nematic liquid crystal material so that the dispersion of light by the lenses substantially matches.

8a and 8b show an example of a manufacturing technique for the microlens array 44 shown in FIG. 7a. Providing a substrate 60 including an isotropic medium with a refractive index n _o, the isotropic micro lens 55 formed as an array of isotropic medium with a refractive index n _e. A gap is provided between the micro lenses 55. A uniform matching layer 61 is formed on the upper surfaces of the microlens 55 and the substrate 60.

  A counter substrate 62 made of an isotropic medium is provided with the bottom surface of the microlens lens array having no gap. A uniform matching layer 63 is formed on the lower surface of the counter substrate 62. The matching layer 63 is oriented so that the matching directions of the matching layers 61 and 63 are orthogonal. A gap for the microlens 56 is formed by combining the substrate 60 and the counter substrate 62. These gaps are filled with nematic liquid crystal, and nematic liquid crystal is aligned by matching layers 61 and 63 to form a twisted nematic liquid crystal lens (for example, indicated by reference numeral 56).

  9a and 9b show a manufacturing technique for the microlens array shown in FIG. 7b. A patterned matching layer 65 is formed on the optical isotropic substrate 60 as an array of regions having matching directions orthogonal to each other (e.g., indicated by reference numerals 66 and 67). The matching layer 65 can be formed by, for example, a multi-rubbing technique, the use of a grating microstructure, or optical patterning as described above.

  The optically isotropic counter substrate 62 is the same as that shown in FIG. 8a, and an unpatterned or uniform matching layer 63 is formed on the lower surface thereof. The matching direction of the matching layer 63 is parallel to the matching direction of the region of the patterned matching layer 65 (eg, indicated by reference numeral 66).

  The substrates 60 and 62 are combined to define an air gap array that forms the microlens lenses of the array 44. The gap is filled with nematic liquid crystal to form a planarly aligned microlens (eg, indicated by reference numeral 57) and a twisted nematically aligned microlens 56.

  FIG. 9c shows yet another configuration. In this configuration, the curved surface for the microlens is formed on the substrate 60 by stamping or the like, and the unpatterned matching layer 63 is formed on the curved surface. On the other hand, the counter substrate 62 has a flat lower surface on which a patterned matching layer 65 is formed.

In order for the microlens lenses 33 and 37 to form a light spot in substantially the same common focal plane 36, the radius of curvature of the microlenses of the second array 37 is set to be the same as that of the first array 33, as shown in FIG. The focal length of the microlenses of the second array 37 can be reduced by making it smaller than that of the lens. Alternatively, as shown in FIG. 10a, the birefringent medium 70 is placed between the microlenses of the second array 37 and the patterned retarder 38 so that both microlenses of the arrays 33 and 37 have the same radius of curvature. It may be provided. Birefringent medium 70 has a ordinary refractive index _{n o2} and extraordinary refractive index _{n e2.}

S-polarized light indicated by reference numeral 71 'saw' the extraordinary refractive index n _e2 of the medium 70, P-polarized light indicated by reference numeral 72 Ru "see" the ordinary refractive index n _o2 of the lower of the medium 70. This has the effect of reducing the focal length of the microlenses of the array 37.

FIG. 10b shows yet another configuration. In this configuration, the microlenses of the arrays 33 and 37 are formed of birefringent materials having different birefringences. The microlenses of the array 33 are formed of a birefringent material having an ordinary light refractive index n _o1 that matches the ordinary light refractive index of the isotropic material 34. The microlenses of the array 37 are formed of a birefringent material having an ordinary refractive index n _o2 that matches the ordinary refractive index of the isotropic material 35. The effects of this on S-polarized light and P-polarized light are indicated by 71 and 72, respectively. By appropriate selection of material and refractive index, the microlenses of the second array 37 will have a shorter focal length than the microlenses of the first array 33. The difference in focal length determines the distance between the microlens array 33 and the microlens array 37 in the light propagation direction of the entire system.

  Actually, it is not essential that the focal plane of the microlens array 33 and the focal plane of the microlens array 37 coincide with each other, and these focal planes only need to be sufficiently close to each other. This can be achieved by using substantially identical microlenses for arrays 33 and 37 if the arrays are sufficiently close together in the direction of light propagation of the entire system. For example, as shown in FIG. 11a, the microlenses of the array 37 may be reversed so that the planar sides of the microlenses of the arrays 33 and 37 face each other and are separated by a relatively thin layer 75 of isotropic material. Good. A relatively thin layer 75 of isotropic material may be an adhesive or a thin substrate. In systems where polarization conversion efficiency needs to be substantially constant with wavelength, it may be beneficial to have a greater distance between the same sensitive microlenses.

  FIG. 11b shows yet another configuration. In this configuration, the microlenses of the arrays 33 and 37 are Fresnel lenses. The thickness of a Fresnel lens with a given diameter and focal length depends on the number of sections but is smaller than the thickness of a conventional optically equivalent lens. The Fresnel lens shown in FIG. 11b includes two sections and has a thickness about half that of the lens shown in FIG. 11a.

  FIG. 11c shows yet another configuration. In this configuration, the lens arrays 33 and 37 include Fresnel lenses, but the array 37 faces in the opposite direction, and the flat surfaces of the arrays 33 and 37 face each other and are adjacent to each other.

  When light enters the Fresnel lens in a direction parallel to the optical axis of the Fresnel lens, as shown in FIG. 12a, substantially all the light passes through the lens. However, as shown in FIG. 12b, when light is incident on the Fresnel lens with an angle with respect to the optical axis of the Fresnel lens, a part of the light, for example, a portion incident on a flat surface (for example, indicated by reference numeral 76) Is not focused by, and as a result the efficiency of the system is reduced. However, such losses are relatively small when the angle of incidence is small.

  Fresnel lenses tend to be diffracted because they have many sections and a short pitch. Furthermore, the sharp shape can affect the alignment of the liquid crystal material during manufacture as described above. If the number of sections is relatively small, e.g. 1 or 2, the thickness of the lens is greatly reduced, but the smallest width y of a section is smaller than the acceptable limit, e.g. 10-20 micrometers. In other words, no significant diffraction occurs, and the liquid crystal molecules do not match the shape of the lens. For example, for a lens with a diameter of 200 micrometers, y is substantially equal to 28 micrometers if there are two sections, and y is substantially equal to 17 micrometers if there are three sections. The lens shown in FIGS. 12a and 12b has two sections, the thickness of which is half that of a conventional equivalent lens.

  A problem of a single element lens can be a problem of chromatic aberration caused by a variation in refractive index and, as a result, a variation in the focal length of the lens that varies with the wavelength of light. This increases the minimum size of the light spot focused on the patterned retarder, as shown in FIG. If the spot diameter is greater than half of the lens pitch and thus larger than the size of the patterned retarder element, some light will be “lost” from the system because its polarization is not changed correctly.

  FIG. 18a shows that the position and minimum diameter of the white light spot focused by the lens is determined by extreme red and extreme blue light from the edge of the lens. FIG. 18b shows only the red and blue rays that define the minimum diameter of the white light focusing spot for simplicity. Immediately following the plane containing the least focused spot or circle with the least disruption, the beam diameter is rapidly increasing. This feature should be considered when designing an efficient polarization conversion system. Therefore, if the focal planes of the arrays 33 and 37 are not in the same plane, it is beneficial to provide the polarization changing element array closer to the focal plane of the first microlens array 33 than to the focal plane of the second microlens array 37. It is. Further, the preferred position of the polarization changing element array may not be the least disruptive circle plane. In this circle plane, the red and blue focusing spots are closest and overlap. Such positioning provides the highest average polarization conversion efficiency, but the blue light polarization conversion efficiency is significantly higher than the red light polarization conversion efficiency, which is not preferred.

  In order to reduce the effects of chromatic aberration, one or both of the microlens arrays 33 and 37 are replaced with a pair of negative and positive microlenses so that each microlens of each “composite” array is a doublet (one pair). May be included.

  In each of FIGS. 14a to 14d, an array pair equivalent to the array 33 is indicated by reference numerals 33a and 33b, and an array pair equivalent to the array 37 is indicated by reference numerals 37a and 37b. The sign of the positive lens array is followed by “a” and the sign of the negative lens array is followed by “b”.

  If the microlens array 37 is incompletely index matched to the optical isotropic material 35 surrounding it, the array 37 is a negative lens that is very weak to the light focused by the microlens array 33. Can act as an array. This makes it possible to reduce the influence of chromatic aberration of the microlens array 33 by bringing the focal planes of red light and blue light close to each other.

  A similar effect can be provided by the birefringent medium 70 shown in FIG. 10a. For example, the variability characteristics of the birefringent medium 70 can be selected to minimize chromatic aberration, and the distance between the microlens arrays 33 and 37 can be changed so that their focal planes are substantially coincident.

  FIG. 15 a shows a manufacturing technique of the microlens arrays 33 and 37. A polymer layer 80 is formed on the substrate 81, and the upper surface of the polymer 80 is shaped so as to define a microlens profile. For example, the polymer 80 may include a UV curable optical adhesive such as Norland NOA 61 or Summers Optical SK9. In this case, these UV-curable optical adhesives have a lens profile formed by a mold shaped in accordance with the lens. Thereafter, the ultraviolet curable optical adhesive is cured. A matching layer 82 is formed on the top surface of the polymer 80. The matching layer 82 is, for example, rubbed polyimide, a grating microstructure, or an optical matching layer.

  A similar matching layer 84 is formed on the counter substrate 83. The matching layers 82 and 84 have a uniform matching direction and are oriented so that the matching direction of the matching layer 84 is anti-parallel to the matching direction of the matching layer 82.

  The substrate 81 and the counter substrate 83 are combined, but the cell gap is defined by increasing the distance by the glue spacer 85. The cell gap is filled with a liquid crystal material such as MLC6647 or a reactive mesogen such as RMM34. In the case of reactive mesogenic materials, the material is then cured by ultraviolet light irradiation. For relatively thin lens arrays, it may be sufficient to provide a single matching layer on one side of the reactive mesogen or liquid crystal material 86. For example, as shown in FIG. 15 b, only the counter substrate 83 has a matching layer 84. This is sufficient to ensure that the material 86 (in this case, a reactive mesogen) is properly aligned.

  Once the material 86 is cured, the counter substrate 83 having the matching layer 84 may be removed. Therefore, the thickness of the system can be reduced. In the case of a rubbed polyimide matching layer 84, the lack of a matching layer in the final system avoids problems that can occur due to the limited durability of the matching layer of the projection system.

FIG. 16 shows a further polarization conversion optical system. The system shown in FIG. 16 differs from that shown in FIG. 4 in that the microlens arrays 33 and 37 include an array of graded index (GRIN) microlenses. Such lenses can be formed by polymer network liquid crystals or reactive mesogens, examples of suitable methods being disclosed in US Pat. No. 5,671,034. Light in one polarization state is focused by each GRIN lens in one array. This is because light in one polarization state encounters a radial change in refractive index from the refractive index n _{2 at} the center of the lens to the refractive index n ₁ <n ₂ at the lens edge. The orthogonal polarization encounters a substantially isotropic refractive index profile and does not substantially shift while propagating through the sensitive polarization GRIN lens layer.

In one embodiment of such a GRIN microlens array, the refractive index profile (n _L ) as a function of lens radius r is given by:

n _L = n ₂ (1-Ar ² )
Here, A is a constant defined below, and n ₂ is the maximum refractive index of the lens. For a given optical anisotropic medium having a refractive index n _o and n _e, the maximum lens refractive index n ₂ is not greater than n _e. The constant A is related to the lens thickness t, the focal length f of the lens, and n ₂ as follows.

A = 1/2 tfn ₂
The thickness of the GRIN lens layer is determined by the required lens F-number or focal length, material and processing parameters. For example, to achieve a lens diameter of 200 micrometers and a focal length in air of 1260 micrometers (F / 6.3), the lens profile is n ₂ = 1.69 at r = 0 to n at r = 100. _When changing to ₁ = 1.53, the required thickness of the anisotropic material is 24.8 micrometers.

The same optically anisotropic material can be used to achieve a given F value for lenses of different thickness. This is made possible by changing the manufacturing process parameters to change the refractive index profile and the values of the maximum and minimum refractive indices n ₁ and n ₂ .

  As another example, a GRIN lens can be formed from an inorganic birefringent material, such as lithium niobate. Inorganic birefringent materials exhibit a definable change in birefringence as a function of ion concentration. This type of configuration is shown in FIG. The use of inorganic materials can improve the durability of the system.

  The advantage of the GRIN lens is that the lens has no curvature, so that even if the lens material is not index matched to its periphery, the sensitive polarization GRIN lens aligned to focus the S-polarized light is a lens for the P-polarized light. As it does not work at all. The GRIN lens appears as a sheet with isotropic plane parallel walls of dielectric material for P-polarized light, and therefore the GRIN lens has very little effect on P-polarized light.

  It is also possible to use a non-sensitive polarized GRIN lens in the array 44 instead of the conventional lens. The use of such a lens reduces the length of the system.

  A polarization conversion system may be used to convert non-polarized light emitted by a directional backlight in a direct view display into substantially polarized light. This increases the efficiency of the direct view liquid crystal device because the second polarization is reused.

  In a direct-view display polarization conversion system, the fourth array of microlenses acts as a microlens field lens for the sensitive array, beneficially changing the convergence of the light rays. FIG. 20a shows the focusing effect of the lens acting on the shifted light. FIG. 20b shows the effect on optical polarization of the optically anisotropic lens and the additional lens provided in the focal plane of the anisotropic lens. The additional lens has the same focal length as the anisotropic lens. The second lens acts as a field lens with respect to the first lens and bends light rays in the direction of the optical axis of the system to reduce light shift.

  FIG. 20b shows two birefringent microlens arrays 33 and 37 and an isotropic microlens array 44 provided in the focal plane 36 of the anisotropic array. When an array of polarization rotating elements is provided adjacent to and aligned with the isotropic microlens array 44, the system converts the non-polarized light from the backlight to substantially polarized light and acts as a polarization conversion system for direct view displays. To do. In the preferred embodiment, the individual lenses of the isotropic array 44 are aligned with the respective corresponding pixel apertures of the direct view liquid crystal display. The isotropic array 44 reduces light shift, thereby allowing the liquid crystal layer of the panel to be located further away from the polarization conversion element without loss of light in the gaps between the pixels.

  FIG. 21 shows a projection engine that includes, for example, the same general type of lamp 1 as shown in FIG. 1 and a polarization converting optical system and beam homogenizer 2. The polarization conversion optical system / beam homogenizer 2 may be, for example, any type described above and shown in FIG. In particular, subsystem 2 includes birefringent microlens arrays 33 and 37, patterned retarder 38, and isotropic microlens 44. Furthermore, a field lens 7 is provided.

  The lamp 1 and the subsystem 2 illuminate the liquid crystal panel 8 with substantially uniform illumination intensity throughout the panel 8 and a substantially uniform single polarization that meets the input polarization requirements of the panel 8. The panel 8 modulates light with image data, and the modulated light from the panel 8 is supplied to the projection lens 90. The projection lens 90 projects each displayed image on a projection screen (not shown).

  FIG. 22 shows a direct view display. This direct view display includes a polarization conversion optical system 2 described above and shown in FIG. The system 2 is provided between a backlight 100 having a narrow angle and a liquid crystal panel 8 having a pixel layer denoted by reference numeral 95, for example. A polarizer 101 is provided on the exit side of the panel 8. System 2 converts the light from backlight 100 into a substantially single uniform polarization that meets the input requirements of panel 8.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, this invention should not be limited and limited to this embodiment. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments of the present invention. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

1 is a cross-sectional view of a known type of projection system including a known type of polarization converting optical system. It is sectional drawing which shows another type of polarization conversion optical system. 1 is a cross-sectional view showing a known type of polarization conversion optical system. It is sectional drawing which shows the polarization conversion optical system by embodiment of this invention. It is sectional drawing which shows an example of the detail of the system of FIG. FIG. 5 is a cross-sectional view showing a manufacturing technique of the system of the type shown in FIG. 4. It is a figure which shows an example of the detail of the system shown in FIG. It is a figure which shows an example of the detail of the system shown in FIG. It is a figure which shows the manufacturing technique of the example shown to FIG. 7a. It is a figure which shows the manufacturing technique of the example shown to FIG. 7a. FIG. 7b shows the manufacturing technique of the example shown in FIG. 7b. FIG. 7b shows the manufacturing technique of the example shown in FIG. 7b. FIG. 7b shows the manufacturing technique of the example shown in FIG. 7b. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. It is a figure which shows passage of the light which injected into the normal line direction with respect to the Fresnel lens. It is a figure which shows passage of the light which entered with an angle with respect to the Fresnel lens. It is a figure which shows the influence of the chromatic aberration in a lens. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 shows another example of a lens array that can be used in the type of system shown in FIG. 4. FIG. 5 is a diagram showing a manufacturing technique of an example of a lens array used in the system of the type shown in FIG. 4. FIG. 5 is a diagram showing a manufacturing technique of an example of a lens array used in the system of the type shown in FIG. 4. FIG. 6 is a cross-sectional view of a polarization conversion optical system according to another embodiment of the present invention. FIG. 17 shows a GRIN lens that can be used in the system of FIG. It is a figure which shows the influence of the color dispersion | variation of the microlens irradiated with the shift light, and beam shift. It is a figure which shows the influence of the color dispersion | variation of the microlens irradiated with the shift light, and beam shift. It is sectional drawing which shows a well-known polarization system. It is a figure which shows the focusing effect of the lens which acts on shift incident light. It is a figure which shows the focusing effect of the lens which acts on shift incident light. 1 is a cross-sectional view showing a projection engine according to an embodiment of the present invention. It is sectional drawing which shows the direct view type display by embodiment of this invention.

Explanation of symbols

33 First microlens array 37 Second microlens array 44 Third microlens array

Claims (37)

A first array of polarizing lenses for converging a first polarization with a first convergence and transmitting a second polarization orthogonal to the first polarization with a second convergence less than the first convergence; ,
A first polarizing lens that receives light from the first array, converges the second polarization with a third convergence, and transmits the first polarization with a fourth convergence less than the third convergence; An optical system comprising two arrays, wherein the first and second arrays are substantially first and second image planes, respectively, and the first and second polarizations are first and second, respectively. Convert it to a second image,
An optical further comprising a third array of lenses provided at a position substantially no further than one of the first and second image planes when viewed from the first and second arrays system.   The optical system of claim 1, wherein the first and second polarizations are linear polarizations.   The optical system according to claim 1, wherein at least one of the second and fourth convergence is substantially zero.   4. An optical system according to any preceding claim, wherein the second polarization is not substantially shifted by the first array.   The optical system according to claim 1, wherein the first polarization is not substantially shifted by the second array.   6. An optical system according to any preceding claim, wherein the lenses of the first array are substantially identical to one another.   The optical system according to claim 1, wherein the lenses of the second array are substantially identical to each other.   The optical system according to claim 1, wherein the first and second image planes are substantially coplanar.   The optical system of claim 8, wherein the third array is substantially at the first and second image planes.   The first and second image planes are not substantially coplanar, and the third array is substantially on one of the first and second image planes, or the first and the second The optical system according to claim 1, wherein the optical system is between the second image planes.   The optical system according to any of claims 1 to 10, wherein the first and second arrays have substantially equal pitch to each other.   The optical system of claim 11, wherein the second array of lenses is offset laterally with respect to the first array of lenses.   The optical system of claim 12, wherein the lateral offset is substantially equal to half the pitch of each of the first and second arrays.   The optical system according to claim 1, wherein the lenses of the first and second arrays comprise an optically anisotropic material.   15. The lens of claim 14, wherein the lenses of the first and second arrays are in contact with an optically isotropic material having a refractive index substantially equal to one of the refractive indices of the optically anisotropic material. Optical system.   15. The lenses of the first and second arrays are formed of the same material, and the lenses of the first array have an optical axis that is orthogonal to the optical axis of the lenses of the second array. 15. The optical system according to 15.   The optical system according to claim 1, wherein the lenses of the first and second arrays are Fresnel lenses.   The optical system according to claim 1, wherein the lenses of the first and second arrays are positive and negative doublets.   19. An optical system according to any of claims 1 to 18, wherein the first and second arrays have substantially flat surfaces opposite each other.   20. The optical system according to claim 1, wherein the lenses of the first and second arrays are gradient index lenses.   The apparatus further comprises a fourth array of polarization changing elements that receive light from the second array and change at least one of the first and second polarizations, the fourth array comprising the fourth array. 21. An optical system according to any preceding claim, wherein the light from the array is modified to be substantially uniform polarized light.   The optical system of claim 21, wherein the fourth array is provided to change one of the first and second polarizations to substantially the other of the first and second polarizations.   23. An optical system according to claim 21 or 22, wherein the polarization changing element is a polarization rotator.   23. An optical system according to claim 21 or 22, wherein the polarization changing element is a retarder.   25. An optical system according to any of claims 1 to 24, wherein the third array has a pitch substantially equal to half the pitch of the lenses of the first and second arrays.   26. An optical system according to any preceding claim, wherein each of the lenses of the third array is optically aligned with a corresponding lens of the first or second array.   27. The optical system of claim 26, wherein the focal length of each of the third array of lenses is substantially equal to the focal length of the corresponding lens of the first or second array.   25. An optical system according to any of claims 21 to 24, wherein the third array comprises the fourth array and at least some of the lenses of the third array comprise polarization changing elements.   30. The optical system of claim 28, wherein at least some of the lenses have optical anisotropy.   The optical system according to any one of claims 1 to 29, further comprising a field lens for converging light emitted from the system. An optical system according to any of claims 1 to 30,
At least one light emitter;
With light source.   A projection display comprising the light source according to claim 31.   The projection display according to claim 32, further comprising a spatial light modulator provided to be illuminated by the light source.   34. A projection display according to claim 33, wherein each of the lenses of the first array has an aspect ratio substantially equal to the aspect ratio of the spatial light modulator.   A direct-view display comprising the optical system according to any one of claims 1 to 29, provided between a backlight and a spatial light modulator.   36. The direct view display of claim 35, wherein each of the lenses of the third array is optically aligned with a corresponding pixel of the spatial light modulator. 37. The direct view display according to claim 33, wherein the spatial light modulator is a liquid crystal device.

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