Optical element and uses thereof

Abstract: Two polarisation conversion element arrays (320a) and (320b), each composed of a plurality of polarisation conversion elements for converting light incident thereupon to a linearly polarised light beam with a predetermined polarisation direction which are arranged in at least one of the array arrangement directions, either the direction of the lens array row or the direction of the lens array column, are disposed so as to oppose each other, with a predetermined space (Cp) provided therebetween at about the centre of the light-outgoing surface of a lens array (310) in the direction of arrangement. Of the light beams (s-polarised + p-polarised light beams) gathered by the lens array (310), light beam (L2) that is not incident upon the polarisation conversion element (320a) and passes through the predetermined space (Cp) is a light beam including a predetermined polarised light beam (s-polarised light beam) that is primarily made to leave the array (320a) and an ineffective polarised light beam (p-polarised light beam). Of the light passing through and leaving the space (Cp), the required polarised light beam alone can be made to leave as an effective light beam by providing a polarisation plate or the like at the light-outgoing side of the space (Cp).

Description: The present invention relates to an optical element for converting light incident thereto to a predetermined polarised light beam, as well as a polarisation illumination device and a projection display apparatus using the same. In order to increase the efficiency with which light is utilised to provide a bright display, illuminating optical systems of projection display apparatuses make use of a method that converts polarised light with random polarisation directions to polarised light with one polarisation direction. A known optical element (polarisation conversion element) for converting light with random polarisation directions to light with one polarisation direction is disclosed in Japanese Patent Laid-Open No. 7-294906. Fig. 14 herein is a plan view of such an optical element comprising a polarisation beam splitter array 20 formed by alternately bonding together linear polarisation beam splitters 30 including polarisation separating films 36 and linear prisms 40 including reflecting films 46. A lens array composed of a plurality of focus lenses is provided at the light-incoming surface of the polarisation beam splitter array 20, with λ/2 phase plates 24 selectively provided at the light-outgoing surface of the splitter array 20. As shown in Fig. 14A, light incident upon the lens array 10 is gathered and converted by the lens array 10 into a plurality of separated light beams (or intermediate light beams) that are incident upon the polarisation beam splitters 30 disposed in correspondence with the lens array 10 in the form of light beams containing s-polarised components and p-polarised components. The incident light is separated into s-polarised light beams and p-polarised light beams by the polarisation separating films 36. Each s-polarised light beam is reflected substantially vertically by its corresponding polarisation separating film 36 formed at an angle of 45 degrees with respect to the light-incoming plane. Then, each s-polarised light beam is reflected again by its corresponding reflecting film 46 formed at an angle of 45 degrees with respect to the light-incoming plane, and leaves its associated prism 40. On the other hand, each p-polarised light beam passes through its corresponding polarisation separating film 36, and is converted into an s-polarised light beam by its associated λ/2 phase plate and leaves it. Thus, this optical element is of the type that converts all of the incident light beams with random polarisation directions to be converted into s-polarised light beams before leaving the optical element. Ideally, all of the light incident upon the lens array 10 and gathered by each of the focus lenses of the lens array 10 should be incident upon the polarisation beam splitters disposed in correspondence with each of the focus lenses. As shown in Fig. 14B, however, there are actually portions of the light incident upon the lens array 10 that are not completely gathered by the array 10, causing them to be incident upon their corresponding prisms 40. The light portions incident upon the prisms 40 are totally reflected at their corresponding reflecting films 46, and strike the polarisation beam splitters 30 adjacent thereto. The light incident upon the polarisation beam splitters 30 is separated into s-polarised light beams and p-polarised light beams by the polarisation separating films 36. The s-polarised light beams produced by the separation are reflected by their respective polarisation separating films 36, and are converted into p-polarised light beams by their respective λ/2 phase plates and leave them. On the other hand, the p-polarised light beams pass through their respective polarisation separating films 36, and are reflected by and leave the reflecting films 46 disposed in the direction of passage of the light beams. Thus, some of the light incident upon the optical element leaves the optical element as s-polarised light beams, and some of the light incident upon the optical element leaves the optical element as p-polarised light beams. Here, the light-incoming surface of the polarisation conversion element can be divided into effective light-incoming areas EA and ineffective light-incoming areas UA. The effective light-incoming areas EA are areas of the light-incoming surface of the polarisation conversion element where the incident light beams are converted into the desired polarised light beams and leave the polarisation conversion element. On the other hand, the ineffective light-incoming areas UA are areas of the light-incoming surface of the polarisation conversion element where the incident light beams leave the polarisation conversion element after being converted into undesired polarised light beams. Thus, in the present embodiment, the light-incoming surfaces of each of the plurality of polarisation beam splitters 30 correspond to the effective light-incoming areas EA, and the light-incoming surfaces of each of the plurality of prisms 40 correspond to the ineffective light-incoming areas UA. When there is a desire to use only one type of polarised light beam, it is necessary to cut off the light beams travelling toward the ineffective light-incoming areas UA using a polarisation plate or the like. In other words, in this case, the aforementioned outgoing p-polarised light beams are not used, thereby reducing the efficiency with which light is used. Accordingly, in view of the above-described prior art problem, it is an object of the present invention to provide a technique permitting more efficient use of light of an optical element used in a polarisation illumination device or a projection display apparatus. To this end, according to a first aspect of the present invention, there is provided polarisation illumination device for separating and converging a light with random polarisation directions into a plurality of sub-beams, and for converting each of the plurality of sub-beams to substantially one type of polarised light beam by two polarisation conversion element arrays and transmitting the plurality of sub-beams such that each of the sub-beams illuminates an entire illumination area; wherein each of said two polarisation conversion element arrays includes polarisation separating surfaces for separating the plurality of sub-beams into two types of linearly polarised light reflecting surfaces for reflecting one of the two types of the linearly polarised light separated by said polarisation separating surfaces and phase plates for converting the two types of linearly polarised light to substantially one type of polarisation, said polarisation separating surfaces and said reflecting surfaces being arranged alternately with light-transmissive members disposed therebetween; a light-incoming surface of each of said polarisation conversion element arrays has alternately disposed effective light-incoming areas, in which light incident on said polarisation separating surfaces is converted into light having a desired polarisation direction, and ineffective light-incoming areas, in which light incident on said reflecting surfaces is converted into light having an undesired polarisation direction; said two polarisation conversion element arrays are disposed so that central effective light-incoming areas in the device are adjacent each other; and said central effective light-incoming areas are separated by a predetermined space. The light-incoming surface of each polarisation conversion element array is divided into a first area where light incident thereupon directly impinges upon a polarisation separating film surface and into a second area where light incident thereupon directly impinges upon a reflecting surface. Of the incident light, the portion of the light incident upon the first light-incoming area is converted into a predetermined type of polarised light beam (effective polarised light beam), while the portion of the light incident upon the second light-incoming area is converted into an ineffective polarised light beam. According to the construction of the first aspect of the invention, light passing through a predetermined space is not incident upon the second area, so that it leaves the optical element, without being converted into an ineffective light beam, as a light beam with random polarisation directions. Thus, the effective polarised component of the light beam with random polarisation directions that passes through the predetermined space can be utilised, thereby increasing the efficiency with which the light of the optical element is used. It is preferable that dummy regions not including the aforementioned polarisation separating surface and the reflecting surface are formed using a transmissive material at the predetermined space side end of the two ends of each of the two polarisation conversion element arrays. This makes it possible to make the length of the path of light passing through each polarisation conversion element array and the length of the path of light passing through the predetermined space to be close to each other. The light reflected by the predetermined space side end of the two ends of each of the two polarisation conversion element arrays may not be effectively used, since it cannot effectively irradiate the irradiating surface depending on the direction of reflection. This problem can be mitigated using the above-described construction. Regions not including the aforementioned polarisation separating surfaces and the reflective surfaces may be formed using a transmissive material at the other one of the two sides of each of the two polarisation conversion element arrays which is not disposed at the side of the predetermined space. In general, the optical element of the first aspect of the invention is used by setting the centre thereof midway between the two conversion element arrays, that is in a predetermined space, so as to lie on the optical axis of the light source. Light leaving the light source, in general, tends to become weaker with increasing distance from the optical axis of the light source, so that even when light incident upon the end of each of the two polarisation conversion element arrays which is not disposed at the side of the predetermined space is converted into a predetermined type of polarised light beam, there is almost no increase in the efficiency with which light is used. Thus, by virtue of the above-described construction, it is possible to use fewer polarisation separating surfaces and reflecting surfaces, thereby reducing the cost of the optical element. According to a second aspect of the present invention, there is provided an optical element comprising: a lens array composed of a plurality of lenses disposed in a matrix arrangement; and two polarisation conversion element arrays according to the first aspect of the invention, affixed to one of the surfaces of the lens array. As in the first aspect of the invention, in the second aspect of the invention, the light-incoming surface of each polarisation conversion element array is divided into a first area where light incident thereupon directly impinges upon a polarisation separating film surface and into a second area where light incident thereupon directly impinges upon a reflecting surface. It is preferable that all of the light gathered by the lens arrays is incident upon the first area, but there are some parts of the light that are incident upon the second area. According to the construction of the second aspect of the invention, of the light beams leaving the lens arrays, those that are not incident upon the polarisation conversion element arrays and pass through a predetermined space are not incident upon the second area, so that the light beams with random polarisation directions leave the optical element unchanged. Therefore, it is possible to use the effective polarised component included in the polarised light beams with random polarisation directions that pass through such a predetermined space, thereby allowing more efficient use of the light of the optical element. It is preferable that the polarisation separating surfaces and the reflecting surfaces along the light-incoming surfaces of the polarisation conversion element arrays be arranged at a pitch which is greater than 1/2 the pitch with which the lens arrays are arranged along the direction of arrangement of the polarisation separating surfaces and the reflecting surfaces. According to the above-described construction, each of the polarisation conversion element arrays can be constructed to allow the light beams from the lens arrays to efficiently impinge thereupon, thereby allowing more efficient use of the light of the optical element. According to a third aspect of the present invention, there is provided a polarisation illumination device comprising: a light source; and an optical element according to the second aspect of the invention. According to the third aspect of the invention, an optical element allowing light to be used with high efficiency is provided, so that light can be used with greater efficiency in an illumination device. It is preferable that the polarisation separating surfaces be arranged in accordance with a distribution of light from the lens array. This allows light from the lens array to be used effectively, so that light of an illumination device can be used with even greater efficiency. It is preferable that a polarisation separating surface be disposed at a location closest to the predetermined space in each of the two polarisation conversion element arrays, such that the centre of this polarising separating surface is shifted towards the predetermined space from the centre axis of the lens, among the plurality of lenses of each of the lens arrays, which is disposed closest to the polarisation separating surface. A large amount of light leaves the light source at around the optical axis of the light source. The light quantity distribution of light leaving a portion around the optical axis of the light source is shifted towards the optical axis of the light source from the centre axis of the lens disposed closest to the polarisation separating surface disposed closest to the predetermined space between the two polarisation conversion element arrays. Thus, by virtue of such a construction, it is possible to effectively use the light present near the optical axis of the light source, thereby allowing even more efficient use of the light of the illumination device. According to a fourth aspect of the invention, there is provided a projection display apparatus comprising: a polarisation illumination device according to the third aspect of the invention; modulating means for modulating light from the polarisation illumination device in accordance with a received image signal; and projection optical means for projecting the light beam modulated by the modulating means. According to the fourth aspect of the invention, an illumination device using an optical element allowing light to be used with higher efficiency is used, thereby allowing a brighter image to be projected onto a projection surface. Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings and by way of further example only; wherein Fig. 1 is a schematic structural view as viewed in a plane of the main portion of a polarisation illumination device of an embodiment of the present invention. Fig. 2 is a perspective view of the optical element 200 of Fig. 1. Fig. 3 is a view illustrating the basic operation of the polarisation conversion element array 320b (320a). Fig. 4 is a front view showing the light-incoming surface of the optical element 300 of a first embodiment. Fig. 5 is a rear view showing the light-outgoing surface of the optical element 300 of the first embodiment. Fig. 6 is a sectional view taken along line A-A of Fig. 5. Fig. 7 is a side view of the optical element 300 of the first embodiment. Fig. 8 is a perspective view of the structure of the polarisation conversion element arrays 320a, 320b. Fig. 9 is a view showing an example of how the polarisation beam splitter array 340 is manufactured. Fig. 10 is an enlarged partial sectional view taken along the line A-A of Fig. 5. Fig. 11 is an enlarged views of the predetermined space side ends of the polarization conversion element arrays 320a and 320b, shown in Fig. 8. Fig. 12 is a view showing an optical element 300 of Embodiment 2. Fig. 13 is a schematic structural view of the main portion of a projection display apparatus 800 provided with the polarisation illumination device 50 of Fig. 1. Fig. 14 is a plan view of a conventional optical element. A. Polarisation Illumination Device: Fig. 1 is a schematic structural view as viewed from a plane of the main portion of a polarisation illumination device 50 of an embodiment of the present invention. The polarisation illumination device 50 comprises a light source 60 and a polarisation portion 70. Light with random polarisation directions that include an s-polarised component and a p-polarised component leave the light source 60. The light leaving the light source 60 is converted into one type of polarised light beam (such as an s-polarised light beam) in which the polarisation directions are substantially the same by means of the polarisation portion 70, thereby illuminating an illumination area 80. The light source 60 comprises a lamp 101 and a parabolic surface reflector 102. The light emitted from the lamp 101 is reflected unidirectionally by the parabolic surface reflector 102, and converted into substantially parallel light beams that are incident upon the polarisation portion 70. The polarisation portion 70 comprises a first optical main element 200 and a second optical main element 400. Fig. 2 is a perspective view of the first optical main element 200. The first optical main element 200 comprises tiny and rectangular light beam separating lenses 201 arranged in a matrix arrangement with M rows and 2N columns. Thus, there is an N column of lenses on the left side of a centre CL in the lens horizontal direction, and an N column of lenses on the right side of the centre CL in the lens horizontal direction. In the example, M = 10 and N = 4. The first optical main element 200 is disposed such that the optical axis lies on the centre of the first optical main element 200. As seen from the direction of arrow Z, the external shape of each of the light-beam separating lenses 201 is similar to the shape of the illumination area 80. Since, in the present embodiment, the illumination area 80 is assumed to be long in the x direction, the external shape of each of the light beam separating lenses is also long horizontally in the X-Y plane. The second optical main element 400 of Fig. 1 comprises an optical element 300 and a light-outgoing side lens 390. The element 300 and the lens 390 are disposed such that their centres lie on the optical axis. The optical element 300 comprises a focus lens array 310 and two polarisation conversion element arrays 320a and 320b. The focus lens array 310 has the same structure as that of the first optical main element 200, and opposes the first optical main element 200. The focus lens array 310 gathers a plurality of light beams separated by each of the light beam separating lenses 201 of the first optical main element 200. The polarisation conversion element arrays 320a and 320b each convert the light beams incident thereupon into one type of linearly polarised light beams (such as s-polarised light beams or p-polarised light beams), so that the light beams leave the arrays 320a and 320b as one type of polarised light beams. Fig. 3 is a view illustrating the basic operation of the polarisation conversion element array 320b (320a). Light beams with random polarisation directions, each including an s-polarised component and a p-polarised component, impinge upon the light-incoming surface of the polarisation conversion element array. Each incident light beam is first separated into s-polarised light beams and p-polarised light beams by each polarisation separating film 331. The s-polarised light beams are reflected substantially vertically by each polarisation separating film 331. Then, they are reflected vertically by and leave the reflecting films 332. On the other hand, the p-polarised light beams pass through the polarisation separating films 331. λ/2 phase plates 381 are disposed at the surface of the polarisation separating films where the p-polarised light beams leave. The plates 381 convert the p-polarised light beams into s-polarised light beams that leave the plates 381. Thus, almost all of the light beams that have passed through the polarisation conversion elements leave them as s-polarised light beams. When one wants light to leave the polarisation conversion element as p-polarised light beams, a λ/2 phase plate 381 is placed at the surface where the s-polarised light beams reflected by the reflecting films 332 leave. An important feature of this embodiment of the present invention is the structure of the optical element 300, which will be described in detail below. The light-outgoing side lens 390 of Fig. 1 is used for transmitting the plurality of separated light beams leaving the optical element 300 (that is, the separated linearly polarised light beams formed by means of the polarisation conversion element arrays 320a and 320b) such that each of them illuminate the entire illumination area 80. The light leaving the light source section 60 and impinging upon the first optical main element 200 is separated into intermediate light beams 202 by means of the light beam separating lenses 201 and the focus lenses 311 gather the light. The intermediate light beams 202 converge within a plane (in the XY plane in Fig. 1) perpendicular to the optical axis by means of the light beam separating lenses 201 and the focus lenses 311 that gather the light beams. Light source images are formed at the location where the intermediate light beams converge, with the number of light source images being the same as the number of light beam separating lenses 201. The light source images are formed near the polarisation separating films 331 (see Fig. 3) in the polarisation conversion element arrays 320a and 320b. Of the light beams incident upon the optical element 300, those that are gathered by the focus lens array 310 and irradiate the polarisation separating films 331 are converted into one type of linearly polarised light beams and leave the polarisation separating films 331. The light beams that have left the optical element illuminate the illumination area 80 by means of the light-outgoing side lens 390. The whole illumination area 80 is uniformly illuminated by the plurality of light beams separated by means of the plurality of light beam separating lenses 201. B: First Embodiment: Fig. 4 is a front view showing the light-incoming surface of the optical element 300 of the first embodiment. Fig. 5 is a rear view of the light-outgoing surface thereof. Fig. 6 is a sectional view taken along line A-A of Fig. 5. Fig. 7 is a side view of the optical element 300. In the optical element 300, two polarisation conversion element arrays 320a and 320b are affixed to the flat light-outgoing surface of the light-gathering focus lens array 310, using an optical adhesive. The two polarisation conversion element arrays 320a and 320b are arranged opposed to each other, and are disposed on the left and right sides of a centre CL in the horizontal direction of the focus lens array 310 so as to be spaced apart by a predetermined space Cp which is described later. Like the first optical main element 200 (of Fig. 2), the focus lens array 310 comprises substantially rectangular focus lenses 311 in a matrix arrangement with M rows and 2N columns. Thus, there are N columns on the left side of and N columns on the right side of the centre CL in the lens horizontal direction. In this example, M = 10 and N = 4. Fig. 8 is a perspective view of the structure of the polarisation conversion element arrays 320a and 320b. The polarisation conversion element arrays 320a and 320b each comprise a polarisation beam splitter array 340 and λ/2 phase plates 381 (represented by slanted lines in the figure) selectively disposed at portions of the light outgoing surface of the polarisation beam splitter array 340. The shape of the polarisation beam splitter array 340 is formed by successively adhering a plurality of light-transmissive members 323 parallelogrammic and column-like in sections. At the interfaces of the light-transmissive members 323 are alternately disposed polarisation separating films 331 and reflecting films 332. λ/2 phase plates 381 are selectively disposed at the image portions in the X direction of the light-outgoing surfaces of the polarisation separating films 331 or the reflecting films 332 in the X direction thereof. In the present embodiment, λ/2 phase plates 381 are selectively disposed at the image portions in the X direction of the light-outgoing surfaces of the polarisation separating films 331. As described above using Fig. 3, light incident upon the polarisation separation film 331 either passes through the polarisation separation film 331 and is converted into a predetermined linearly polarised light beam by the λ/2 phase plate 381 and leaves it or is reflected by the polarisation separation film 331 and then by the reflecting film 332 and leaves it as a predetermined linearly polarised light beam. Accordingly, one block including one polarisation separation film 331, one reflecting film 332 adjacent thereto, and one λ/2 phase plate 381 can be considered as one polarisation conversion element 350. The polarisation conversion element arrays 320a and 320b are each formed by a plurality of such polarisation conversion elements 350 arranged in the X direction. In the present embodiment, N = 4 for one side of the focus lens array 310, so that there are four columns of polarisation conversion elements 350 on one side of the array 310. It is to be noted that a portion 360 equivalent to the polarisation conversion element of the 4th column is only formed by a light-transmissive material, so that it does not include a polarisation separation film 331 or a reflecting film 332. For description purposes, the portion 360 will be called light-transmissive portion that will be described later. In Fig. 8, a dummy portion 370 composed of a light-transmissive material is provided at a side (end) surface of the polarisation conversion element 350 in the leftmost column. A comer of an edge 372 at the light-incoming surface (adhered surface) of the dummy portion 370 is rounded or removed. The reason for this will be discussed later. Fig. 9 is a view illustrating an example of how the polarisation beam splitter array 340 is manufactured. The polarisation beam splitter array 340 is formed by alternately bonding together plate glasses 321, each provided with, for example, a polarisation separation film 331 and a reflecting film 332 such that they are alternately disposed, and plate glasses 322 that is not provided with anything, using an adhesive 325. Here, a plate glass 322b (dummy portion 370 (Fig. 8)) and 322c (light-transmissive portion 360 (Fig. 8)), each of which does not have the same thickness as the plate glasses 322, are bonded to the beginning and end of the bonded structure. This forms the dummy portion 370 and the light-transmissive portion 360. Accordingly, light-transmissive blocks are formed by cutting out virtually parallel sections (represented by broken lines in the figure) of the plurality of light-transmissive members 321, 322, 322b, and 322c at a predetermined angle  from the surfaces thereof. It is preferable that  be about 45 degrees. The protrusions at both ends are cut to a substantially rectangular shape. Grinding the cut surfaces of the light-transmissive blocks produces the polarisation beam splitter array 340 (Fig. 8). It is to be noted that in the specification, a light-transmissive member is also called "base", and that the block formed by bonding together the plurality of light-transmissive members and a block portion cut out from this block are called " base block". Fig. 10 is a partial enlarged view taken along line A-A of Fig. 5. The polarisation conversion element arrays 320a and 320b are symmetrically disposed on opposite sides of the lens centre, and have exactly the same functions, so that a description of only the polarisation conversion element array 320a will be given below. The light-incoming surface of the polarisation conversion element array 320a has alternately disposed effective light-incoming areas EA (the light-incoming surface portions corresponding to the polarisation separation films 331) in which light incident to the polarisation separation films 331 is converted into effective polarised light beams and ineffective light-incoming areas UA (the light-incoming surface portions corresponding to the reflecting films 332) in which light incident upon the reflective films 332 is converted into ineffective polarised light beams. The width Wp of each effective light-incoming area EAand each ineffective light-incoming area UA in the X direction is 1/2 of the width WL of the focus lens 311 in the X direction. The centre 311c of the focus lenses 311 is disposed so as to match the centre of each effective light-incoming area EA in the X direction. Here, the effective polarised light beams produced by the polarisation conversion element 350 are s-polarised light beams. The light gathered by the focus lens array 310 (that is light with random polarisation directions that include an s-polarised component and a p-polarised component) is incident upon the polarisation conversion element array 320a. Of the light incident thereupon, light beam L1 incident upon an effective light-incoming area EA is separated into an s-polarised component and an p-polarised component by the associated polarisation separation film 331, as described earlier using Fig. 3. The s-polarised light beam is reflected by the associated polarisation separation film 331 and then by the associated reflecting film 332 and leaves it. The p-polarised light beam passes through the associated polarisation separation film 331 and is converted into an s-polarised light beam by the associated λ/2 phase plate 381 and leaves it. Thus, almost all of the light incident upon the effective light-incoming areas EA of the polarisation conversion element array 320a is converted into s-polarised light beams and leave it. If λ/2 phase plates 381 are selectively provided at the light-outgoing surfaces of the reflecting films 332, substantially only p-polarised light beams can be obtained by the polarisation conversion elements. As described in the prior art section, the portions of the light incident upon the ineffective light-incoming areas UA are converted into undesired polarised light beams (p-polarised light beams in the present embodiment). Ordinarily, the efficiency with which light is used is reduced, since the light is cut off by a light-shielding plate or the like provided at an ineffective light-incoming area UA. In a structure such as that of the polarisation illumination device 50 of Fig. 1, in particular, the quantity of light becomes greatest around the optical axis of the light source, so that when there is an ineffective light-incoming area UA around the optical axis, the efficiency with which light is used is considerably reduced. The present invention makes it possible to overcome such a problem in a way described below. In the present embodiment, the polarisation conversion element 350a of the polarisation conversion element array 320a closest to the optical axis (see Fig. 10) and the polarisation conversion element 350b of the polarisation conversion element array 320b closest to the optical axis (see Fig. 10) are disposed on the left and right side of the space Cp so as to oppose each other. The dummy portions 370 of the two polarisation conversion element arrays 320a and 320b as well as a gap Gp therebetween are located in the space Cp. Thus, of the light beams incident upon the focus lens array 310 around the optical axis, light beam L2 that cannot irradiate the polarisation separation film 331, since the focus lens array 310 cannot completely gather a portion of the light, passes through the space Cp within which neither a polarisation separating film 331 nor a reflecting film 332 are present and leaves the gap Cp unchanged. The light beam passing through the space Cp is a light beam consisting of an effective s-polarised component as well as an ineffective p-polarised component. Of the components of the outgoing light beam passing through the space Cp, the required polarised component (the s-polarised component in the present embodiment) alone can be made to leave the space Cp by placing a polarisation plate at the light-outgoing plane side for effective use. When the polarisation illumination device 50 (Fig. 1) is applied to a projection display apparatus described later, a polarisation plate is ordinarily provided at the light-incoming surface of a liquid crystal light valve being an illumination area 80. Therefore, in this case, it is not necessary to provide a separate polarisation plate. The light-transmissive portion 360 at the outermost side of the polarisation conversion element array 320a is a portion through which light from the lens at the outermost side of the focus lens array 310 passes. The light source of the polarisation illumination device 50 having the structure of the present embodiment is ordinarily disposed on a centreline extending through the centre of the light-incoming surface of the focus lens array 310 and being perpendicular to the light-incoming surface (see Fig. 4), so that the quantity of light incident upon the outer side of the lens array 310, that is the light-transmissive portion 360, is smallest. In such a situation, there is often not much difference between the quantities of light that can be effectively used in the entire first optical main element 300 (see Fig. 1) when the light incident upon the outermost side of the focus lens array 310 is converted into a polarised light beam by the polarisation conversion element for use compared to when the light just passes through the array 310 unchanged. Thus, the light-transmissive portion 360 at the outmost side of the focus lens array 310 of the polarisation conversion element array 320a is formed only by a light-transmissive member, so that it does not take structure of the polarisation conversion element 350 (see Fig. 8), and is not provided with a λ/2 phase plate 381. This causes light beam L3 passing through the lens at the outermost side of the focus lens array 310 to pass through and leave the light-transmissive portion 360 unchanged. The light beam leaving the light-transmissive portion 360 is, like the light beam passing through and leaving the space Cp, a light beam containing an effective s-polarised component and an ineffective p-polarised component. Of the outgoing polarised components leaving the light-transmissive portion 360, only the required polarised component (the s-polarised component in the present embodiment) is utilised by providing a polarisation plate at the light-outgoing side of the light-transmissive portion 360, allowing the light beam to be utilised as an effective light beam. Fig. 11 is an enlarged view of the predetermined space side ends of the polarization conversion element arrays 320a and 320b of Fig. 8. In Fig. 11A, it is assumed that polarisation conversion element arrays 320a and 320b that do not have dummy portions 370 are disposed in the horizontal direction of the light-outgoing surface of the focus lens array 310, with a predetermined space Cp provided therebetween with respect to the centre CL. Here, there is a difference between the light path lengths of the light beam passing through the space Cp and the light beam passing through the polarisation conversion element arrays 320a and 320b. If possible, it is preferable that lengths of the light paths be as close to each other as possible. Depending on the direction of reflection, the light beam Lex1 reflected by the ends 371 of the polarisation conversion element arrays 320a or 320b cannot be used effectively. The focus lens array 310 and the polarisation conversion element arrays 320a and 320b are bonded together using, for example, an adhesive 375 shown in Fig. 11A. Here, an adhesive protruding portion 376 is produced at the predetermined space Cp. The light beam Lex2 passing through such an adhesive protruding portion 376 is reflected irregularly, since the adhesive surface is not even, thereby preventing effective use of the light. In Fig. 11B, it is assumed that dummy portions 370 composed of the same material as the light-transmissive members 323 of the polarisation conversion element arrays 320a and 320b are disposed in the predetermined space Cp. When the dummy portions are provided, it is possible to mitigate problems regarding differences in the lengths of the light paths and differences in the reflection directions of the light beam Lex1 reflected at an end surface of the polarisation conversion element arrays 320a or 320b. As shown in Fig. 11B, the amount of protrusion of the adhesive is made smaller by providing dummy portions 370, and either rounding or removing the corners of the sides of the dummy portions 370 at the light-incoming surfaces (adhered surfaces). The gap Gp at the centre portion does not have to be formed. Taking into account the accuracy of alignment of the polarisation conversion element arrays 320a and 320b with the light-outgoing surface of the focus lens array 310 when bonding them together, however, it is preferable there be a slight gap between the dummy portions 370 at the centre portion, when the polarisation conversion element arrays 320a and 320b have been bonded to the light-outgoing surface of the focus lens array 310. C. Embodiment 2 Fig. 12 is a diagram illustrating an optical element of Embodiment 2. The middle portion of Fig. 12 shows the distributions of the quantities of light illuminating the light-incoming surface of a polarisation conversion element array 320a, after gathering of the light by each of the lenses La to Ld of the lens array 310 in a structure such as that of the polarisation illumination device 50 (Fig. 1). In general, the intensity Ia of the light gathered by the lens La nearest the optical axis is the strongest, while the intensity of the light gathered by the lens furthest from the optical axis is weakest. In Fig. 12, the intensity Id of the light gathered by the fourth lens is the weakest. The light quantity distribution shifts from its associated lens centre towards or away from the optical axis starting from a certain lens position (the position of the third lens Lc in Fig. 12), so that for the light quantity distributions of the lenses La to Ld, the closer the lens is to the optical axis the more the distribution is shifted towards the optical axis from its associated lens centre, and the further away the lens is from the optical axis the more the distribution is shifted towards the opposite side of the optical axis from its associated lens centre. In Fig. 12, the light quantity distribution Pc of the lens Lc is centred at about the lens centre, while the light quantity distributions Pb and Pa of the lenses Lb and La that are closer to the optical axis than the lens Lc are shifted towards the optical axis. The light quantity distribution Pd of the lens Ld is shifted away from the optical axis with respect to its lens centre. In such a case, when the centres of the effective light-incoming areas of the polarisation conversion element arrays are aligned with their corresponding lens centres, without exception, light loss occurs as a result of a shift in the light quantity distribution as described above. This loss of light becomes particularly large at around the optical axis of the light source when the distribution of light from a lens array and an effective light-incoming area are not aligned. Thus, it is preferable that the centres of each of the effective light-incoming areas of the polarisation conversion element array 320a be arranged in accordance with the distributions of light leaving the lens array 310, that is in accordance with the peak interval of the distributions of the light from the lens array 310. In addition, in order to utilise the light gathered by the lens array 310 more effectively, it is preferable that the light gathered by the lenses closer to the optical axis be used more effectively. In particular, it is preferable to substantially align the centre of the effective light-incoming area EA1 1 of the polarisation conversion element array 320a that is disposed closest to the optical axis of the light source with the peak position of the light distribution Pa, when the light quantity around the optical axis of the light source is large, or when the distribution Pa of light from the lens La disposed near the optical axis of the light source is shifted towards the optical axis of the light source with respect to the centre of the La. According to the second embodiment, it is possible to overcome problems related to light intensities and light quantity distributions that depend on a lens position of the focus lens array. The optical element of the second embodiment has the same basic structure as that of the optical element of the first embodiment, but differs from it in that it utilises polarisation conversion element arrays 320a and 320b whose effective light-incoming areas EA (designated EA1 to EA4 in the figure) and ineffective light-incoming areas (designated UA1 to UA4 in the figure) each have a width in the X direction that is larger than 1/2 the width WL in the X direction of each of the lenses La to Ld of the lens array 310. Fig. 12 only shows the polarisation conversion element array 320a side. The polarisation conversion element array 320b side, which is simply symmetrical to the polarisation conversion element array 320a side with reference to the optical axis, is not shown in the figure. For instance, the polarisation conversion element array 320a disposed such that the centre of lens Lc in the third column is aligned with the centre of its associated effective light-incoming area EA3. Ordinarily, the width of each of the ineffective light-incoming areas UA (designated UA1 to UA4 in the figure) is equal to the width of each of the effective light-incoming areas EA, so that the left two effective light-incoming areas EA2 and EA1 are shifted from the centres of their corresponding lenses Lb and La towards the optical axis. On the other hand, the rightmost effective light-incoming area EA4 is shifted from the centre of the lens Ld away from the optical axis . As a result, each of the effective light-incoming areas EA1 to EA4 substantially is aligned with the location of its corresponding light quantity distribution of the lens array 310. Since a predetermined number of lenses, such as two or three lenses, disposed close to the optical axis has a strong light intensity, it is particularly preferable to align the distributions of the quantity of light gathered by each of these lenses substantially with their respective effective light-incoming areas. By virtue of such a construction, according to the second embodiment, it is possible to use the light with greater efficiency. How much larger the width of an effective light-incoming area should be made than 1/2 the width of the associated lens, or which lens should be used as a reference to place an effective light-incoming area can be experimentally determined easily from the number of lens arrays and the relationship between the light quantity distribution and its associated lens. The widths of the effective light-incoming areas and ineffective light-incoming areas do not have to be made greater than 1/2 the widths of their corresponding lenses. The widths are determined by the actual distribution of the quantity of light irradiating the light-incoming surface of the polarisation conversion array. D. Projection display apparatus: Fig. 13 is a structural schematic view of the main portion of a projection display apparatus provided with the polarisation illumination device 50 of Fig. 1. The projection display apparatus includes the polarisation illumination device 50, dichroic mirrors 801 and 804, reflecting mirrors 802, 807, and 809, lenses 806, 808, and 810, three liquid crystal light valves 803, 805, and 811, a cross dichroic prism 813, and a projection lens assembly 814. The dichroic mirrors 801 and 804 each functions as a colour light separating means for separating white light into three colour components, red, blue, and green. The three liquid crystal light valves 803, 805, and 811 each functions as a light modulating means for modulating the three colour components in order to form an image, in accordance with the image information or signal received. The cross dichroic prism 813 functions as a colour light combining means for combining the three colour components to form a colour image. The projecting lens assembly 814 functions as a projection optical system for projecting the light carrying the combined colour image onto a screen 815. The red component of white light from the polarisation illumination device 50 passes through the dichroic mirror 801 reflecting a blue component and a green component, whereas the blue component and the green component are reflected thereby. The red component that has passed therethrough is reflected by the reflecting mirror 802 and arrives at the red component liquid crystal light valve 803. On the other hand, of the blue component and the green component reflected by the first dichroic mirror 801, the green component is reflected by the green component reflective dichroic mirror 804 and arrives at the green component liquid crystal light valve 805. The blue component passes through the second dichroic mirror 804. In the present embodiment, the path of the blue component is the longest. Thus, for the blue component, following the dichroic mirror 804, a light-guiding means 850 formed by a relay lens unit including a light-incoming lens 806, a intermediate lens 808, and a light-outgoing lens 810 is provided. The blue component, after passing through the green component reflective dichroic mirror 804, passes through the light-incoming lens 806, is reflected by the reflecting mirror 807, and is guided to the intermediate lens 808. Then, after being reflected by the reflecting mirror 809, it is guided to the light-outgoing lens 810 and reaches the blue component liquid crystal light valve 811. The three liquid crystal light valves 803, 805, and 811 correspond to the illumination area 80 of Fig. 1. In accordance with the image signal (information) provided by an external control circuit (not shown), the three liquid crystal light valves 803, 805, and 811 modulate their corresponding colour components to generate colour light beams containing image information of the light components. The modulated three colour components are incident upon the cross dichroic prism 813. A dielectric multi-layered film reflecting a red component and a dielectric multi-layered film reflecting a blue component are formed into the shape of a cross at the cross dichroic prism 813. These dielectric multi-layered films combine the three colour components, forming a light beam representing the colour image. The light beam in which the light components have been combined is projected onto the screen 815 by the projecting lens assembly 814 being a projection optical system in order to enlarge the image for display. The projection display apparatus projection display apparatus uses liquid crystal light valves 803, 805, and 811 serving as light modulating means of the type that modulates a light beam polarised in a particular direction (that is, an s-polarised light beam or a p-polarised light beam). Polarisation plates (not shown) are ordinarily affixed onto the light-incoming side and the light-outgoing side of each of the liquid crystal light valves. Therefore, a light beam polarised in a predetermined direction, such as an s-polarised light beam, is modulated and impinges upon the cross dichroic prism 813. Here, of the light beams incident upon the optical element 300, those gathered by the focus lens array 310 and irradiating the polarisation separating films 331, as shown in Fig. 10are all converted into s-polarised light beams and leave the optical element 300. The light beams from the optical element 300 illuminate the liquid crystal light valves 803, 805, and 811 through a light-outgoing side lens 390. Of the light beams incident upon the optical element 300, those that could not be completely gathered by the focus lens array 310 and irradiate their respective reflecting films 332 are converted into p-polarised light beams, as described in the conventional example, and leave the optical element 300 to illuminate the liquid crystal light valves 803, 805, and 811. As mentioned above, however, polarising plates are provided at the light-incoming surfaces of the liquid crystal light valves 803, 805, and 811 to block p-polarised light beams, whereby only s-polarised light beams are used. On the other hand, the light beams passing through the space Cp in the optical element of the above-described embodiment of the present invention leave the space Cp and illuminate the liquid crystal light valves 803, 805, and 811, without being converted into a polarised light beam. Since the illuminating light is white light including an s-polarised component usable at the liquid crystal light valves 803, 805, and 811, it is possible to use only the s-polarised component of the light irradiating the liquid crystal light valves 803, 805, and 811. Thus, since the projection display apparatus 800 of Fig. 13 incorporates the polarisation illumination device 50 using the optical element 300 of the above-described embodiment of the present invention, it is possible to use the light more efficiently than in the conventional case. As can be understood from the foregoing description, the optical elements of the present embodiments of the present invention can allow light in the projection display apparatus to be used more efficiently than in conventional projection display apparatuses. Therefore, the image projected onto the screen 815 can be made brighter. While the preferred embodiments of the present invention have been described, it is to be understood that various modifications may be made without departing from the scope of the appended claims. The polarisation illumination device of the present invention may be used in apparatuses other than the projection display apparatus of Fig. 13. For example, the polarisation beam splitter array in accordance with the present invention may also be applied to a projection display apparatus that does not project a colour image, but projects a black-and-white image. In this case, compared to the apparatus of Fig. 13, only one liquid crystal light valve needs to be used, and the colour light separating means for separating a light beam into its three colour components and a colour light combining means for combining the three colour components of the light beam are not required. In addition, the present invention can be applied to a projection-type colour display apparatus using only one light valve. Further, the present invention can be applied to a projection display apparatus using a reflective light valve or an image display apparatus using the polarisation illuminating light of a rear-type display apparatus or the like.

Claims: A polarisation illumination device (50) for separating and converging a light with random polarisation directions into a plurality of sub-beams, and for converting each of the plurality of sub-beams to substantially one type of polarised light beam by two polarisation conversion element arrays (320a, 320b) and transmitting the plurality of sub-beams such that each of the sub-beams illuminates an entire illumination area; wherein each of said two polarisation conversion element arrays includes polarisation separating surfaces (331) for separating the plurality of sub-beams into two types of linearly polarised light, reflecting surfaces (332) for reflecting one of the two types of the linearly polarised light separated by said polarisation separating surfaces, and phase plates (381) for converting the two types of linearly polarised light substantially one type of polarisation, said polarisation separating surfaces and said reflecting surfaces being arranged alternately with light-transmissive members (322) disposed therebetween; a light-incoming surface of each of said polarisation conversion element arrays has alternately disposed effective light-incoming areas, in which light incident on said polarisation separating surfaces is converted into light having a desired polarisation direction, and ineffective light-incoming areas, in which light incident on said reflecting surfaces is converted into light having an undesired polarisation direction; said two polarisation conversion element arrays are disposed so that central effective light-incoming areas in the device are adjacent each other; and said central effective light-incoming areas are separated by a predetermined space (Cp, Gp). A polarisation illumination device according to claim 1 wherein the element has an optical axis and said polarisation separating surfaces are inclined towards the optical axis on the light incident side of the element. A polarisation illumination device according to claim 1 or claim 2, wherein each polarisation conversion element array comprises a dummy region (370) including neither said polarisation separating surface nor said reflecting surface, said dummy region being made of a light-transmissive material and being disposed at the end of each array adjacent said predetermined space. A polarisation illumination device according to claim 3 wherein a corner of each dummy region adjacent said predetermined space is removed at the light incident side of the element. A polarisation illumination device according to any one of the preceding claims, wherein each polarisation conversion element array comprises a region (360) including neither said polarisation separating surface nor said reflecting surface, said region being made of a light- transmissive material and being disposed at the end of the array opposite said predetermined space. A polarisation illumination device according to any one of the preceding claims, farther comprising a lens array (310) composed of a plurality of lenses (311) disposed in a matrix arrangement, wherein said two polarisation conversion element arrays (320a, 320b) are affixed to one of the surfaces of said lens array. A polarisation illumination device according to claim 6, wherein said polarisation separating surfaces are arranged in accordance with a distribution of light leaving said lens array. A polarisation illumination device according to any one of claim 6 and 7, wherein in each array the polarisation separating surface (331) disposed at a location closest to the predetermined space (Cp, Gp) is positioned such that the centre of said polarisation separating surface is off-set from the centre axis of its respective lens in said lens array towards the said predetermined space. A polarisation illumination device according to any preceding claim, wherein said polarisation separating surfaces and said reflecting surfaces along the light-incoming surface of each of said polarisation conversion element arrays are arranged at a pitch (Wp') that is greater than 1/2 the arrangement pitch (W L ) of said lens array disposed along the direction of arrangement of said polarisation separating surfaces and said reflecting surfaces. A projection display apparatus comprising: a polarisation illumination device as claimed in any one of preceding claims; modulation means for modulating light from said polarisation illumination device in accordance with a received image signal; and projection optical means for projecting the light beam modulated by said modulating means.

Inventors: OGAWA YASUNORI, USHIYAMA TOMIYOSHI, YAJIMA AKITAKA, OGAWA, YASUNORI, USHIYAMA, TOMIYOSHI, YAJIMA, AKITAKA
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1997
Main classification: G02B27
IPC codes: G02B5, H04N9, G02B27, G02F1, G03B21