OPTICAL ELEMENT

Conventional optical elements cannot emit circularly polarized light beams obtained by beam separation in the same direction. An optical element includes a polarization splitter element configured to split incoming light into a first circularly polarized light beam and a second circularly polarized light beam that has different handedness than the first circularly polarized light beam, where the polarization splitter element is configured to reflect the first circularly polarized light beam and allow the second circularly polarized light beam to transmit, and a reflector element configured to reflect the first circularly polarized light beam that has been reflected by the polarization splitter element, to proceed in a direction in which the second circularly polarized light beam is allowed to transmit.

BACKGROUND

1. Technical Field

The present invention relates to an optical element.

2. Related Art

It is known in the art to split light including a plurality of polarized light beams into a plurality of linearly polarized light beams by reflecting a linearly polarized light beam and allowing a different linearly polarized light beam to transmit (see, for example, Japanese Patent Application Publication No. 2003-167125).

The above-described technique, however, disadvantageously cannot split the light into circularly polarized light beams nor emit the circularly polarized light beams in the same direction.

SUMMARY

A first aspect of the innovations herein provide an optical element includes a polarization splitter element configured to split incoming light into a first circularly polarized light beam and a second circularly polarized light beam that has different handedness than the first circularly polarized light beam, where the polarization splitter element is configured to reflect the first circularly polarized light beam and allow the second circularly polarized light beam to transmit, and a reflector element configured to reflect the first circularly polarized light beam that has been reflected by the polarization splitter element, to proceed in a direction in which the second circularly polarized light beam is allowed to transmit.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1is a schematic view showing a projector apparatus50including an optical element10. The arrows inFIG. 1show the vertical or up-and-down direction of the projector apparatus50. As shown inFIG. 1, the projector apparatus50includes a light source52, a lens array54, an optical element10, a lens56and a liquid crystal panel58.

The light source52emits non-polarized white light L to the lens array54. The lens array54is located to receive the light emitted from the light source52. The lens array54includes a plurality of light concentrators60. The light concentrators60are provided in the same plane to which the traveling direction of the light L from the light source52is normal. The light concentrators60are, for example, arranged in matrix. The light concentrators60concentrate the light emitted from the light source52in a plurality of regions and allow the concentrated light to proceed toward the optical element10.

The optical element10splits the light L concentrated by the light concentrators60into a first circularly polarized light beam and a second circularly polarized light beam that has different handedness than the first circularly polarized light beam. The optical element10aligns the individual circularly polarized light beams to have the same handedness, then converts the resulting circularly polarized light beams into polarized light beams L aligned in the same direction of polarization, for example, linearly s-polarized light beams, which then proceed toward the lens56.

The lens56concentrates the polarized light beams L aligned by the optical element10in the same direction of polarization and allows the concentrated light beams to proceed to the liquid crystal panel58. The liquid crystal panel58allows part of the polarized light beams L concentrated by the lens56to transmit and blocks the rest, to create images.

FIG. 2is a partial cross-sectional view showing the optical element10. As shown inFIG. 2, the optical element10includes a plurality of base materials12, a plurality of polarization splitter elements14, a plurality of reflector elements16, a plurality of first polarization converter elements18, and a second polarization converter element20.

The base materials12are made of materials that allows light to transmit therethrough. The base materials12are isotropic to light. The base materials12can be made of triacetylcellulose (TAC), cyclo olefin polymer (COP), cyclo olefin copolymer (COC), which is a copolymer of COP, polycarbonate (PC) and the like. As a TAC film, FUJITAC T80SZ, TD 80 UL and the like available from FUJIFILM Corporation can be employed. As a COP film, ZeonorFilm®ZF14 available from Zeon Corporation can be employed. In order to use a cyclo-olefin-based film, it is preferable to use a film of high toughness due to the brittleness issues. The base materials12may be colorless and transparent glass substrates.

The base materials12are shaped like a parallelogram in a cross-sectional view, except the top and bottom base materials12. Specifically speaking, each base material12has an entrance surface22and an exit surface24that are substantially orthogonal to incoming light beams L0. In addition, each base material12has a pair of inclined surfaces26that are inclined with respect to the entrance surface22and the exit surface24. The inclined surfaces26are parallel to each other. The inclined surfaces26form an angle of 45°, for example, with respect to the entrance surface22and the exit surface24.

The polarization splitter elements14are each formed like a film. The polarization splitter elements14are disposed on the inclined surfaces26of the base materials12. Accordingly, the polarization splitter elements14are inclined with respect to the direction in which the incoming light beams proceed. For example, the polarization splitter elements14are inclined at angle of 45° with respect to the direction in which the incoming light beams proceed.

The polarization splitter elements14split the incoming light by reflecting a first circularly polarized light beam L1and allowing a second circularly polarized light beam L2that has different handedness than the first circularly polarized light beam L1to transmit. The first circularly polarized light beam L1is a right-handed circularly polarized light beam, for example. The second circularly polarized light beam L2is a left-handed circularly polarized light beam, for example. It should be noted that the first circularly polarized light beam L1is a left-handed circularly polarized light beam, and the second circularly polarized light beam L2is a right-handed circularly polarized light beam. The polarization splitter elements14contain cholesteric liquid crystals. In a cholesteric liquid crystal film, the rod-like liquid crystal molecules are oriented helically. The helical axis is parallel to the normal direction to the plane of the polarization splitter elements14. The product of the helical cycle in the liquid crystal molecules and the refractive index of the liquid crystal molecules is set to be substantially equal to the wavelength of the light that can be split into the two circularly polarized light beams by reflection. Here, the light having a wavelength different than the helical cycle transmits through the polarization splitter elements14.

Specifically speaking, the following expression (1) is established when p denotes the helical cycle in the liquid crystal molecules, n denotes the average refractive index of the liquid crystals and λ denotes the wavelength of the light to be split.

If the liquid crystals have anisotropic refractive index, light having a range of wavelengths can be split by the reflection. When the magnitude of the range of refractive indices achieved by the anisotropy is denoted as Δn and the magnitude of the range of wavelengths of the light is denoted as Δλ, the following expression (2) is established.

Accordingly, if the refractive index of the liquid crystals has the variation Δn caused by the anisotropy, the light that can be split by the polarization splitter element14into the two circularly polarized light beams can have a range of wavelengths centered on the wavelength λ, which is expressed by the expression (1), or from (λ−Δλ/2) to (λ|Δλ/2).

If the light enters the optical element10at an angle with respect to the helical axis of the liquid crystal molecules, the expression (1) may be transformed into the following expression (3) due to the Bragg condition. Here, α denotes the angle between the incoming light and the helical axis.

Considering these expressions, the helical cycle in the liquid crystal molecules (p) is determined by the refractive index of the liquid crystal material (n), the wavelength of the light (λ) and the incident angle of the incoming light (α). The helical cycle of the liquid crystal molecules can be adjusted by controlling the concentration of the chiral agent added in the cholesteric liquid crystals.

The reflector elements16are each formed like a film. The reflector elements16are disposed on the inclined surfaces26of the base materials12. Accordingly, the reflector elements16are inclined with respect to the direction in which the incoming light proceeds. The angle of inclination of the reflector elements16is determined in such a manner that the first circularly polarized light beam L1can be reflected to proceed in the direction in which the second circularly polarized light beam L2travels. For example, the reflector elements16are arranged so as to be substantially parallel to the polarization splitter elements14. Therefore, in the present embodiment, the reflector elements16are inclined at an angle of 45° with respect to the traveling direction of the incoming light.

The reflector elements16are made of resins. The reflector elements16are made of a cholesteric-liquid-crystal-based material. More specifically, the reflector elements16are made of the same resin-based material as the polarization splitter elements14are. That is to say, the reflector elements16reflect right-handed circularly polarized light and allow left-handed circularly polarized light to transmit, like the polarization splitter elements14. Accordingly, the reflector elements16reflect the first circularly polarized light beam L1that has been reflected by the polarization splitter elements14to proceed in the direction in which the second circularly polarized light beam L2is allowed to transmit by the polarization splitter elements14and travels.

The reflector elements16do not change the handedness of the first circularly polarized light beam L1. Accordingly, the handedness of the first circularly polarized light beam L1remains right-handed even after the first circularly polarized light beam L1is reflected by the reflector elements16. Here, the first circularly polarized light beam L1that has been reflected by the reflector elements16will be referred to as a circularly polarized light beam L3.

The first polarization converter elements18are provided on the inclined surfaces26of the base materials12. The first polarization converter elements18entirely cover the exit surfaces of the polarization splitter elements14. The first polarization converter elements18convert circularly polarized light of particular handedness into circularly polarized light of the reversed handedness. The first polarization converter elements18are half wave plates, for example. Specifically speaking, the first polarization converter elements18convert the left-handed second circularly polarized light beam L2into a right-handed circularly polarized light beam. In this manner, the first polarization converter elements18change the handedness of the second circularly polarized light bean L2that has transmitted through the polarization splitter elements14to align the handedness of the second circularly polarized light beam L2with the handedness of the first circularly polarized light beam L1that has been reflected by the polarization splitter elements14. Here, the second circularly polarized light beam L2will be referred to as a circularly polarized light beam L3after the handedness is changed by the first polarization converter elements18.

Here, a pair of each polarization splitter element14and a corresponding first polarization converter element18faces one of the reflector elements16with a base material12placed therebetween. Each polarization splitter element14and a corresponding first polarization converter element18are provided on the upper inclined surface26of one of the base materials12, and each reflector element16is provided on the same side or the upper inclined surface26of an adjacent one of the base materials12. The pairs of one polarization splitter element14and one first polarization converter element18alternate with the reflector elements16. In other words, a plurality of sets of one polarization splitter element14, one first polarization converter element18and one reflector element16are periodically arranged in the up-and-down direction.

The second polarization converter element20converts, into linearly polarized light beams L4, the circularly polarized light beams L3having the same handedness achieved by the first polarization converter elements18. The second polarization converter element20converts the circularly polarized light beams L3into, for example, linearly s-polarized light beams L4. The second polarization converter element20is formed like a film. The second polarization converter element20is formed to substantially entirely cover the exit surfaces24of the base materials12. The second polarization converter element20is formed on the plane, to which the traveling direction of the incoming light is normal. The second polarization converter element20is a quarter wave plate.

The light concentrators60of the lens array54are provided in a one-to-one correspondence with the sets of one polarization splitter element14, one reflector element16and one first polarization converter element18. The light beams L0concentrated by the light concentrators60enter the polarization splitter elements14. Here, the light beams concentrated by the light concentrators60do not directly enter the first polarization converter elements18.

The following describes how the above-described optical element10behaves.

Non-polarized white light beams L0, which are emitted from the light source52and concentrated by the light concentrators60of the lens array54, are incident on the polarization splitter elements14of the optical element10. The polarization splitter elements14reflect the right-handed first circularly polarized light beams L1of the incident light beams toward the reflector elements16. On the other hand the polarization splitter elements14allow the left-handed second circularly polarized light beams L2of the incident light beams to transmit toward the first polarization converter elements18.

Configured to reflect right-handed circularly polarized light, the reflector elements16reflect the first circularly polarized light beams L1in the direction parallel to the traveling direction of the incoming light beams L0, in other words, toward the second polarization converter element20. The first polarization converter elements18, which are half wave plates, convert the left-handed second circularly polarized light beams L2into the right-handed circularly polarized light beams L3and allow the circularly polarized light beams L3to proceed toward the second polarization converter element20without changing the traveling direction. In this manner, the first circularly polarized light beams L1and the second circularly polarized light beam L2, into which the light beams L0have been split by the polarization splitter elements14, are converted to have the same handedness or into the right-handed circularly polarized light beams L3and also converted to proceed in the direction in which the light beams enter the optical element10.

The second polarization converter element20, which is a quarter wave plate, converts the right-handed circularly polarized light beams L3into linearly polarized light beams, for example, a linearly s-polarized light beams L4and allows the linearly s-polarized light beams L4to proceed toward the lens56. The linearly polarized light beams L4from the second polarization converter element20all have the same direction of polarization. Thus, almost all of the light beams L0emitted from the light source52can be utilized.

As described above, having the polarization splitter elements14, the optical element10can split the incoming light beams L0into the first circularly polarized light beams L1and the second circularly polarized light beams L2of different handedness without blocking any of the incoming light beams L0. Having the reflector elements16, the optical element10can emit the separated first circularly polarized light beams L1and the second circularly polarized light beams L2in the same direction. Furthermore, having the first polarization converter elements18, the optical element10can convert the first circularly polarized light beams L1and the second circularly polarized light beams L2, which are obtained by the beam separation, into the circularly polarized light beams L3all of which have the same handedness. Having the second polarization converter element20, the optical element10can convert the circularly polarized light beams L3having the same handedness into the linearly polarized light beams L4having the same direction of polarization and emit the linearly polarized light beams L4. Thus, the optical element10can utilize the light beams L0from the light source52more efficiently.

The following describes how to manufacture the above-described optical element10.FIGS. 3, 4, 5 and 6show the steps of manufacturing the optical element10.

As shown inFIG. 3, in one of the steps of manufacturing the optical element10, a polarization splitter element14is formed by application on one of the surfaces of a plate-like base material12a. A reflector element16is formed by application on one of the surfaces of another plate-like base material12b. It should be noted that the base materials12aand12bare the some as the base materials12but distinguished from each other in order to provide clear description of the manufacturing method. The polarization splitter element14and the reflector element16can be each formed by applying an alignment film and orienting the molecules of the alignment film, and then applying and curing a cholesteric liquid crystal film. In addition, a first polarization converter element18is formed on the other of the surfaces of the base material12b. The first polarization converter element18may be formed in accordance with the known method of manufacturing a half wave plate. For example, the first polarization converter element18can be formed by applying a photo-alignment film and orienting the molecules of the photo-alignment film and then applying and curing nematic liquid crystals. Alternatively, the first polarization converter element18may be formed by attaching a completed half wave plate film on the other of the surfaces of the base material12b. Note that the order of the steps of manufacturing the polarization splitter element14, the reflector element16and the first polarization converter element18can be varied as appropriate. Furthermore, the polarization splitter element14and the reflector element16are made of the same cholesteric liquid crystals. In this case, cholesteric liquid crystals, which are to provide both the polarization splitter element14and the reflector element16, are formed on one of the surfaces of every base material12. After this, the first polarization converter element18may be formed on the other of the surfaces of half of the base materials12.

Subsequently, as shown inFIG. 4, the base materials12ahaving the polarization splitter element14formed thereon and the base materials12bhaving the reflector element16and the first polarization converter element18formed thereon are alternately stacked on one another. Here, one base material12aand one base material12bare stacked together in such an orientation that the polarization splitter element14is in contact with the first polarization converter element18. Furthermore, when stacked one another, the base materials12aand12bare preferably shifted in the same direction in such a manner that the dotted line DL1shown inFIG. 4, which connects the corresponding corners of the base materials12aand12b, is inclined with respect to the surfaces of the base materials12aand12b. In this manner, more optical elements10can be manufactured from the same number of base materials12aand12b. Here, the angle θ of inclination of the dotted line DL1with respect to the surfaces of the base materials12aand12bis equal to the angle of inclination of the polarization splitter elements14with respect to the incoming direction of the light beams L0incident on the completed optical element10.

Subsequently, the base materials12aand12bstacked along the dotted line DL1shown inFIG. 4are cut into the structures shown inFIG. 5. Furthermore, the base materials12aand12bare subjected to cutting along the dotted lines DL2shown inFIG. 5so that the structures shown inFIG. 6are obtained. On the exit surfaces of the base materials12aand12bof these structures, the second polarization converter element20is formed. In this manner, the optical element10is completed.

According to the above-described method of manufacturing the optical element10, the polarization splitter elements14and the reflector elements16are made of cholesteric liquid crystals. This makes it possible to form the polarization splitter elements14and the reflector elements16in the same manufacturing or applying step, which can improve the productivity. The productivity can be improved in particular by shortening the time required to form the reflector elements16, when compared with the case where the reflector elements16are formed as a metal film or the like and vapor deposition is thus required. In addition, the reflector elements16can be formed on the base materials12having a larger area than when the reflector elements16are formed as a metal film using a vapor deposition apparatus that often has a circular-dome-shaped chamber. Therefore, the completed optical elements10can have a larger area and small optical elements10can be produced more efficiently. Furthermore, if the base materials12are flexible, the completed optical element10can be flexible.

The following describes an alternative embodiment to the above-described optical element.

FIG. 7is a partial cross-sectional view showing an optical element110. As shown inFIG. 7, the optical element110includes base materials12, polarization splitter elements14, reflector elements16, first polarization converter units30and second polarization converter units32. The optical element110is different from the optical element10in that the first polarization converter elements18are not provided on the polarization splitter elements14.

The first polarization converter units30are provided on exit surfaces24of the base materials12. The first polarization converter units30are located to receive the light emitted from the reflector elements16. Accordingly, the first polarization converter units30receive the first circularly polarized light beams L1reflected by the reflector elements16. The first circularly polarized light beams L1are right-handed. The first polarization converter units30convert the first circularly polarized light beams L1that are incident thereon after being reflected by the reflector elements16into the linearly polarized light beams L4and allow the linearly polarized light beams L4to proceed. The first polarization converter units30are quarter wave plates.

The second polarization converter units32are provided on the exit surfaces24of the base materials12. The second polarization converter units32are located to receive the light emitted from the polarization splitter elements14. In other words, the second polarization converter units32are differently positioned than the first polarization converter units30on the exit surfaces24of the base materials12. The first polarization converter units30and the second polarization converter units32are alternately arranged on the exit surfaces24, which are in the same plane. The second polarization converter units32receive the second circularly polarized light beams L2that have transmitted through the polarization splitter elements14. The second circularly polarized light beams L2have different handedness than the first circularly polarized light beams L1, i.e., are left-handed. The second polarization converter units32convert the second circularly polarized light beams L2that are incident thereon after having transmitted through the polarization splitter elements14into the linearly polarized light beams L4and allow the linearly polarized light beams L4to proceed. The second polarization converter units32are quarter wave plates.

Here, the optic axis of the second polarization converter units32is orthogonal to the optic axis of the first polarization convener units30. As used herein, the term “optic axis” denotes the slow or fast axis. The direction of polarization of the linearly polarized light beams L4from the second polarization converter units32, which receive the left-handed second circularly polarized light beams L2, is the same as the direction of polarization of the linearly polarized light beams L4from the first polarization converter units30, which receive the right-handed first circularly polarized light beams L1.

The following describes how above-described optical element110behaves.

Non-polarized white light beams L0, which are emitted from the light source52and concentrated by the light concentrators60of the lens array54, are incident on the polarization splitter elements14of the optical element110. The polarization splitter elements14reflect the right-handed first circularly polarized light beams L1of the incident light beams toward the reflector elements16. In addition, the polarization splitter elements14allow the left-handed second circularly polarized light beams L2of the incident light beams to transmit.

Configured to reflect right-handed circularly polarized light, the reflector elements16reflect the first circularly polarized light beams L1in the direction parallel to the traveling direction of the incoming light beams L0, in other words, toward the first polarization converter units30. The first polarization converter units30convert the incoming first circularly polarized light beams L1into the linearly polarized light beams L4and allow the linearly polarized light beams L4to proceed. The second polarization converter units32convert the second circularly polarized light beams L2that have transmitted through the polarization splitter elements14into the linearly polarized light beams L4that have the same direction of polarization as the linearly polarized light beams L4from the first polarization converter unit30, and allow the linearly polarized light beams L4to proceed. The first polarization converter units30and the second polarization converter units32allow the resulting linearly polarized light beams L4to proceed to the liquid crystal panel58via the lens56.

The following describes how to manufacture the above-described optical element110.FIGS. 8, 9, 10 and 11show the steps of manufacturing the optical element110.

As shown inFIG. 8, in one of the steps of manufacturing the optical element110, a polarization splitter element14is formed by application on one of the surfaces of a plate-like base material12a. A reflector element16is formed by application on one of the surfaces of another plate-like base material12b. The polarization splitter element14and the reflector element16can be each formed by forming an alignment film in which the molecule orientations are aligned and then forming a cholesteric liquid crystal film. The polarization splitter element14and the reflector element16are made of the same cholesteric liquid crystals.

Subsequently, as shown inFIG. 9, the base materials12ahaving the polarization splitter element14formed thereon and the base materials12bhaving the reflector element16formed thereon are alternately stacked on one another. When stacked on one another, the base materials12aand12barc preferably shifted in the same direction.

Subsequently, the base materials12aand12bstacked along the dotted line DL1shown inFIG. 9are cut into the structures shown inFIG. 10. Furthermore, the base materials12aand12bare subjected to cutting along the dotted lines DL2shown inFIG. 10so that the structures shown inFIG. 11are obtained. On the exit surfaces of the base materials12aand12bof these structures, the first polarization converter units30and the second polarization converter units32are formed. Specifically speaking, an alignment film is formed on the exit surfaces of the base materials12aand12b. In the formed alignment film, the alignment film in the region that is positioned to receive light from the reflector elements16is oriented to be orthogonal to the alignment film in the region that is positioned to receive the light from the polarization splitter elements14. After this, nematic liquid crystals are formed on the alignment film and the liquid crystal molecules are oriented along the alignment film. In this way, the first polarization converter units30and the second polarization converter units32are patterned. Alternatively, a quarter wave plate in which the first polarization converter units30and the second polarization converter units32have been patterned may be attached to the exit surfaces of the base materials12aand12b. In this manner, the optical element110is completed.

The shapes, arrangements, numerical values such as the number of the components, materials and the like mentioned in relation to the components of the above-described embodiments may be changed as appropriate. Furthermore, some of the features of an embodiment may be combined with some of the features of another embodiment.

For example, if light having a plurality of wavelengths is split into two circularly polarized light beams, the number of the polarization splitter elements14stacked on one another may be equal to the number of the resulting light beams of different wavelengths into which the light is split. For example, if light is split into red, green and blue light beams, a polarization splitter element14in which cholesteric liquid crystal molecules are helically arranged with the cycle equal to the red light wavelength, a polarization splitter element14in which cholesteric liquid crystal molecules are helically arranged with the cycle equal to the green light wavelength and a polarization splitter element14in which cholesteric liquid crystal molecules are helically arranged with the cycle equal to the blue light wavelength may be stacked on one another. Note that, if Δn has a large value in the above-mentioned expression (2), a single layer-like polarization splitter element14can be sufficient to split light containing a plurality of colors into two circularly polarized light beams.

In the above-described embodiments, the optical elements10,110are utilized in the projector apparatus50, for example. The optical elements10,110, however, may be utilized in other apparatuses. For example, the optical elements10,110may be utilized in a backlight provided in a liquid crystal display device to allow the backlight to emit a single type of linearly polarized light beams. Alternatively, the optical elements10,110may be utilized in tm optical pickup.

The optical element10and110may be utilized in a 3D image display apparatus that requires different polarized light beams for left and right eyes. In this case, the first polarization converter elements18are omitted from the optical element10. By doing so, the optical element10can emit linearly polarized light beams orthogonal to each other as the light beams to form the right-eye and left-eye images. Alternatively, the first polarization converter elements18and the second polarization converter elements20may be omitted from the optical element10. By doing so, the optical element10can emit right-handed and left-handed circularly polarized light beams as the light beams to form the right-eye and left-eye images. Alternatively, the first polarization converter units30and the second polarization converter units32may be omitted from the optical element110. By doing so, the optical element110can emit right-handed and left-handed circularly polarized light beams as the light beams to form the right-eye and left-eye images.

DESCRIPTION OF REFERENCE NUMERALS

18first polarization converter element

20second polarization converter element

30first polarization converter unit

32second polarization converter unit

58liquid crystal panel