KR100816473B1 - Polarization splitter and backlight unit using the same - Google Patents

Abstract

The present invention is to provide a polarization splitting device and a backlight unit that does not recognize moire when the transmitted light is observed.

1st and 2nd optical which has the curved surface 12A, 13A which formed the mountain part and the valley part alternately and mutually parallel on one surface, has a flat surface on the other surface, and transmits P polarization more than S polarization. The air layer 11 is provided with plate members 12 and 13, and the curved surfaces 12A and 13A of the first and second optical plate members 12 and 13 are arranged so that the ridges of the peaks are substantially parallel to each other. It was arranged so as to face each other, and moire was made indistinguishable by making the pitch of the said one of the 1st and 2nd optical plate members 12 and 13 different from the pitch of the said other part.

Polarization Separation Device, Backlight Unit, Optical Plate Member

Description

Polarization splitter and backlight unit using the same}

1 is a schematic view showing a liquid crystal display device in the first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the polarization splitting element of FIG. 1.

3 is a graph showing the relationship between the ratio of the pitch of each optical plate member and the moire pitch.

4 is a graph showing the relationship between the ratio of the pitch of each optical plate member and the moire pitch.

5 is a cross-sectional view showing a polarization splitting element in a second embodiment of the present invention.

<Short description of symbols>

2 backlight units

5 light source

7, 31 polarization splitter

11 air layer

12, 32 first optical plate member

13, 33 2nd optical plate member

12A, 13A, 32A, 33A Curved Surface

34, 35 polarization amplifier

The present invention relates to, for example, a polarization splitting element used for a liquid crystal display device and the like and a backlight unit having the same.

Generally, as a display method in a liquid crystal display device, the alignment state of a liquid crystal is electrically performed using the liquid crystal panel which has a pair of glass substrate which clamps a liquid crystal layer and a liquid crystal layer, and the polarizing plate provided in each of a pair of glass substrate. And a visible light transmitted through the liquid crystal panel by a backlight unit that irradiates the liquid crystal panel with illumination light from the rear surface side thereof.

In the backlight unit used for such a liquid crystal display device, in order to obtain a clearer display by irradiation, the direct type backlight unit which can irradiate a large amount of illumination light with a liquid crystal panel is used.

In such a backlight unit, a polarization splitting element is provided in order to improve light use efficiency. As a polarization splitting element, a plurality of birefringent material layers are laminated to transmit one linearly polarized light and reflect the other linearly polarized light, or a cholesteric liquid crystal is laminated on a substrate to form one circle. Background Art A polarization splitting element that transmits polarized light and reflects circularly polarized light in reverse rotation has been proposed. By the way, both are complicated in structure and difficult to manufacture. Therefore, when large area is made, there exists a problem that it is difficult to make uniform a polarization splitting element in surface.

On the other hand, one side is a curved surface formed by alternately paralleling the peaks and valleys, and the other surface has at least one pair of optical plate members that transmit P polarized light more than S polarized light in a plane. A polarization splitting element has been proposed in which the curved surface of the optical plate member is disposed so that the ridges of the mountain portions are substantially parallel to each other via the air layer. (See Non-Patent Document 1, for example). Since this polarization splitting element uses an optical plate member using a Brewster angle, the structure is simple, and the polarization splitting function is increased by interposing an air layer between a pair of optical plate members.

[Non-Patent Document 1] Suzuki et al., "Reflective Polarizer Sheet on the Backlighting Unit," SID Digest, 1997, p. 813-816

However, the following subjects remain in the said conventional polarization splitting element. In other words, the optical plate member having the same pitch is arranged such that its curved surfaces face each other. Therefore, there exists a problem that moire is visually recognized because a deviation of a pitch occurs because of some manufacturing error.

This invention is made | formed in view of the above-mentioned subject, and an object of this invention is to provide the polarization splitting element and backlight unit which did not recognize moire when the transmitted light was observed.

MEANS TO SOLVE THE PROBLEM This invention employ | adopted the following structures in order to solve the said subject. That is, the polarization splitting device of the present invention has a curved surface in which the peaks and valleys are alternately formed or parallel to each other on one surface, have a flat surface on the other surface, and the first linearly polarized light has a polarization direction. At least one pair of optical plate members which transmit more than 2nd linearly polarized light which is orthogonal to 1 linearly polarized light, and each said curved surface of the said pair of optical plate members has an air layer so that the ridgeline of the said mountain part may be substantially parallel with each other. In the polarization splitting element disposed to face each other, the moire is made indistinguishable by changing the pitch of the peak of one of the pair of optical plate members different from the pitch of the peak of the other. do.

In this invention, by making the moire indistinguishable because the pitches of the curved surfaces arranged opposite are different, the luminance unevenness can be reduced in the plane of the illumination light transmitted through the polarization splitting element. In addition, since the pitches of the peaks of the curved surfaces that are arranged opposite are different, the curved surfaces do not closely contact each other, so that the air layer can be reliably formed. For this reason, the polarization separation function by a polarization separation element can be maintained.

Here, when the bend angle of the curved surface is assumed to be θ _B (deg), the Brewster angle of light incident on the polarization splitting element is preferably 180 ° -2θ _B or more and 180 ° -2 (θ _B + 15 °) or less. . As a result, since the first linearly polarized light of one of the light incident in the thickness direction of the polarization splitting element is transmitted through the air layer with substantially no reflection, the first linearly polarized light is transmitted more than the second linearly polarized light, thereby increasing the polarization splitting function. have.

<Example>

EMBODIMENT OF THE INVENTION Hereinafter, the 1st Example of the polarization splitting element and backlight unit which concerns on this invention is described, referring drawings.

In this embodiment, the direct type backlight unit is used as the lighting means of the liquid crystal display device 1 as shown in FIG. The liquid crystal display device 1 includes a backlight unit 2 and a liquid crystal panel 3.

The backlight unit 2 includes a light source 5, a diffuser plate 6, a polarization splitting element 7, and a housing 8 for housing them.

The light source 5 is comprised, for example with a cold cathode fluorescent lamp, and emits light of unpolarized light. In addition, the light source 5 is provided with a drive circuit (not shown), an inverter (not shown), etc. for driving control of such a cold cathode fluorescent lamp.

The diffusion plate 6 diffuses the light emitted from the light source 5 and makes the traveling direction of the illumination light from the light source 5 toward the polarization splitting element 7 uniform.

The polarization splitting element 7 is constituted by a pair of first and second optical plate members 12 and 13 arranged to face each other via an air layer 11.

The first and second optical plate members 12 and 13 are made of, for example, PMMA (polymethyl methacrylate) having a refractive index of 1.493, and one side of the first and second optical plate members 12 and 13 are alternately constant at regular intervals. It is the curved surface 12A, 13A formed repeatedly, and the other surface is planar. The first optical plate member 12, and acid addition and the angle of bend (θ _P1) parts of the valley is set to 112.4 °, the vertex of the crest pitch interval (P _1), for example, is to 50μm. In addition, the second optical plate member 13 is disposed between the diffusion plate 6 and the first optical plate member 12, and the bend angle θ _P2 is 112.4 ° and the pitch P ₂ is first. one pitch of the optical plate member 12 is a (P ₁₎ and the other 75μm. Therefore, the ratio P ₂ / P ₁ between the pitch P ₁ and the pitch P ₂ is 1.5.

Here, the bending angles θ _P1 and θ _{P2 of} the first and second optical plate members 12 and 13 will be described. First, the Brewster angle (θ _B ) of the light traveling from the medium _{A with} the refractive index n _A toward the interface with the medium _{B with} the refractive index n is

θ _B = tan ^-1 (n _B / n _A )

It becomes By making the angle of incidence at the boundary between the medium A and the medium B the Brewster angle θ _B , the P-polarized light of one linearly polarized light is transmitted without reflection and the S polarized light of the other linearly polarized light is transferred to the interface. Reflect. In this embodiment, since the refractive index n _A of the first optical plate member 12 which is the medium _A is 1.493, and the refractive index n _B of the air layer 11 which is the medium _B is 1, the first and the second In 2 optical plate members 12 and 13, Brewster angle (theta) _B becomes 33.8 degrees.

In general, the polarization separation function, which is a ratio between the transmittance of P-polarized light and the transmittance of S-polarized light, which enters the interface between medium A and medium _B , is maximized at an angle of incidence slightly larger than Brewster's angle θ _B. In this embodiment, the polarization splitting function is maximized at an incidence angle that is about 15 degrees larger than the Brewster angle θ _B. As mentioned above, the preferable range as an incident angle into the air layer 11 is 33.8 degrees-48.8 degrees.

As a result, the bend angles θ _P1 and θ _{P2 of} the first and second optical plate members 12 and 13 correspond to the first and second optical plate members 12 and 13 with respect to the polarization splitting element 7. It is preferable that it is 82.4 degrees-112.4 degrees so that the incidence angle of the light which advances in the superimposition direction of ie, ie, the arrow X direction shown to FIG. 1 and FIG. 2 may be 33.8 degrees-48.8 degrees.

In addition, an inner surface reflection layer 18 is provided on the inner wall of the housing 8 to reflect the light reflected by the diffusion plate 6 or the polarization splitting element 7 to the inner wall of the housing 8.

The liquid crystal panel 3 is disposed on the liquid crystal layer 21, a pair of glass substrates 22 and 23 disposed on both sides of the liquid crystal layer 21, and outer surfaces of the glass substrates 22 and 23, respectively. The polarizing plates 24 and 25 are provided.

On the inner surface of the pair of glass substrates 22 and 23 facing each other, a transparent electrode (not shown) formed of ITO (Indium Tin Oxide) or the like which applies a voltage to the liquid crystal layer 21 is provided. .

The illumination light emitted from the light source 5 and diffused in the diffuser plate 6 enters into the polarization splitting element 7 and is separated into a P polarization component which is one linear polarization component and an S polarization component which is the other linear polarization component. , The P-polarized component penetrates the polarization splitting element 7 more than the S-polarized component. Then, it enters into the liquid crystal panel 3. Here, the separation method of polarization by the polarization splitting element 7 will be described.

As shown in Fig. 2, the P-polarized light that enters the second optical plate member 13 in the arrow X direction and reaches the curved surface 13A is curved when the bending angle θ _P2 is 112.4 ° as in the present embodiment. Since it is incident on the surface 13A at an incident angle of 33.8 ° (= 90-112.4 ° / 2), most of the light incident on the second optical plate member 13 passes through and enters the air layer 11.

The P-polarized light incident on the air layer 11 reaches the curved surface 12A of the first optical plate member 12, but similarly to the above-described second optical plate member 13, most of the incident light is made of 1 The optical plate member 12 is transmitted.

As shown in FIG. 2, since the S-polarized light incident on the second optical plate member 13 in the arrow X direction and reaching the curved surface 13A is incident on the curved surface 13A at a grain angle of 33.8 °, A part is reflected by the curved surface 13A, and the remaining part passes through the second optical plate member 13 and enters the air layer 11. And a part of S-polarized light which permeate | transmitted through the 2nd optical plate member 13 is reflected by the 1st optical plate member 12 similarly to the 2nd optical plate member 13, and the remainder is 1st optical It penetrates the plate member 12. However, by repeating the reflection and the transmission on the curved surfaces 12A and 13A of the first and second optical plate members 12 and 13 in order, the S polarized light transmitted through the first optical plate member 12 is Less

As described above, the P-polarized light and the S-polarized light are separated by the polarization splitting element 7.

That is, even if the angle of incidence of light incident on the plane of the second optical plate member 13 has an angle intersecting with the arrow X direction shown in FIG. 2, the second optical plate member is a medium having a large refractive index from air, which is a medium having a small refractive index. Since it enters (13), the angle with respect to the arrow X direction shown in FIG. 2 becomes small by Snell's law. For example, when light having an angle of approximately 90 ° to the arrow X direction is incident on the second optical plate member 13, the angle to the arrow X direction in the second optical plate member 13 is about 42 °. It becomes For this reason, light can be condensed in the second optical plate member 13. Therefore, the angle of incidence of light on the curved surface 13A becomes close to the Brewster angle θ _B , and the polarization separation function can be improved.

Further, the relationship between the first optical plate pitch (P ₁₎ and the ratio (P ₂ / P ₁₎ with a pitch (P ₂₎ of the second optical plate member 13 of the member 12, the moire pitch, 2 In the case where even the primary moire is considered, it is as shown in FIG. 3, and in the case where the third moire is also considered, it is as shown in FIG. 4.

In addition, when the resolution of the human eye is 1 minute (1/60 °) and a point 1000 mm away from the liquid crystal display device 1 is an observation position,

tan (1/60) × 1000 = 0.290

From the above, about 290 μm becomes the identification lower limit value. Therefore, if the moire pitch is smaller than 290 μm, the moire becomes impossible to identify. In the present embodiment, the ratio P ₂ / P ₁ between the pitch P ₁ and the pitch P ₂ is 1.5 and is smaller than 290 μm, which is the lower limit of identification when the second moire is considered. Moire becomes indistinguishable when 1) is observed. That is, in the case where even the third moire is considered, the moire pitch is at a level at which the moire can be distinguished. However, as the order of the moire increases, the moire shade becomes smaller. Therefore, even when the third moire is considered, even if the moire pitch is at a level at which the moire can be identified, the identification of the moire can be sufficiently reduced.

According to the polarization splitting element 7 configured as described above and the backlight unit 2 having the same, the ratio P ₂ / P of the pitches P ₁ and P _{2 of} the first and second optical plate members 12 and 13 is shown. _{Since 1} ) is 1.5, the moire can be made indistinguishable when the second moire is considered. Therefore, the polarization unevenness of the illumination light transmitted through the polarization splitting element 7 can be reduced.

In addition, since the curved surfaces 12A and 13A are not in close contact with each other, the air layer 11 is reliably formed between the curved surface 12A and the curved surface 13A, and polarization separation between P-polarized light and S-polarized light is performed. Maintain functionality.

Next, a second embodiment will be described with reference to FIG. That is, the embodiment described here is basically the same as the first embodiment described above, and adds other elements to the first embodiment described above. Therefore, in FIG. 5, the same code | symbol is attached | subjected to the same component as FIG. 2, and the description is abbreviate | omitted.

The difference between the second embodiment and the first embodiment is that the polarization splitting element 31 is formed on the curved surfaces 32A and 33A of the first and second optical plate members 32 and 33, respectively. This is the point with the amplification films 34 and 35.

The first optical plate member 32, the angle of bend (θ _P1) of the curved surface (32A) is in a 112.4 °, the pitch (P ₃₎ 50μm. The second optical plate member 33 has a bending angle θ _P2 of the bending surface 33A of 112.4 ° and a pitch P ₄ of 82.5 μm. Therefore, the ratio P ₄ / P ₃ between the pitch P ₃ and the pitch P ₄ is 1.65.

The polarization degree amplifying films 34 and 35 are made of, for example, TiO ₂ (titanium oxide) having a refractive index of 2.28, and are curved surfaces 32A and 33A of the first and second optical plate members 32 and 33. Are formed by the vapor deposition method, respectively. The thicknesses of the polarization degree amplifying films 34 and 35 are set to, for example, 63 nm so as to be 1/4 wavelength in light having a typical wavelength of 550 nm from the wavelengths of 380 nm to 780 nm, which are visible regions, respectively. Therefore, the polarization degree amplification films 34 and 35 are all incrementally reflective films due to the interference phenomenon of light.

Therefore, most of the P-polarized light incident on the second optical plate member 33 is the second optical plate member 33, the polarization degree amplification film 35, the polarization degree amplification film 34, and the first optical plate member ( 32).

On the other hand, S polarized light is partially reflected from the incident side surface of the polarization degree amplification film 35 and the remaining part is transmitted. However, since the polarization degree amplification film 35 is provided to increase the reflectance, the curved surface 33A Most S-polarized light is reflected.

In addition, in the present embodiment, the ratio P ₄ / P ₃ between the pitch P ₃ and the pitch P ₄ is 1.65, and even when the third order moire is taken into consideration, the liquid crystal display is smaller than the lower limit of 290 μm. The moire becomes indistinguishable when the device is observed.

The polarization splitting element 31 and the backlight unit including the same have the same effect and effect as the above-described first embodiment, but the polarization degree amplification films 34 and 35 increase the reflectance, and consequently S The light transmittance of the light source 5 can be improved by making the transmittance | permeability of polarization smaller, and making a polarization separation function high.

In addition, since the ratio P ₄ / P ₃ of the pitches P ₃ and P _{4 of} the first and second optical plate members 32 and 33 was 1.65, the moire was identified in the case of considering the third order moire. You can make it impossible. Therefore, the luminance unevenness of the illumination light transmitted through the polarization splitting element 31 can be further reduced.

Here, since the film thickness of the polarization degree amplification films 34 and 35 is set to 63 nm which is 41.7 (= 380 / (4x2.28)) nm or more and 85.5 (= 780 / (4x2.28)) nm or less, the wavelength of the visible light region It can have a reflection effect on S polarization.

<Example 1>

Next, an Example demonstrates the polarization splitting element which concerns on this invention more concretely.

A polarization splitting element having the first and second optical plate members having the same materials, bending angles, and pitches as shown in Table 1 below were formed, and the first to fifth examples and the first and second comparative examples were formed, respectively. . That is, in the third to fifth embodiments, the polarization degree amplifying film is formed on each curved surface of the first and second optical plate members.

Here, the refractive index of PMMA is 1.493, the refractive index of COP (cycloolefin polymer) is 1.53, the refractive index of TiO ₂ is 2.28, and the refractive index of Pb ₂ O ₅ (lead oxide) is 2.20. Therefore, when COP is used as the first and second optical plate members, the Brewster angle θ _B is 133.6 °.

TABLE 1

Plate member Polarization degree amplifier Bend angle Pitch (1st / 2nd, μm) Example 1 PMMA - 112.4 50 / 67.5 Example 2 COP - 113.6 50/75 Example 3 PMMA TiO ₂ 112.4 50 / 82.5 Example 4 PMMA Pb ₂ O ₅ 112.4 50/125 Example 5 COP TiO ₂ 113.6 50/200 Comparative Example 1 PMMA - 112.4 50/55 Comparative Example 2 COP - 113.6 50/95

In the polarization splitting element thus formed, the transmittance and reflectance of P-polarized light and S-polarized light were measured, and the polarization degree P.d was calculated. In addition, the light utilization efficiency (T. L. T) was measured in the state which incorporated these polarization split elements into the backlight unit. In addition, it was determined whether or not the moire was identified at the observation position 1000 mm away from the liquid crystal display device. The results are shown in Table 2.

((TP-TS)/(TP＋ TS)) 로 나타난다.That is, when the degree of polarization is that the transmittance of P-polarized T _P, TS the transmittance of S polarized light,

((TP-TS) / (TP + TS))

Moreover, when light use efficiency is larger than TP * 50%, the effect as a polarization separation element can be recognized. This is because the natural light contains 50% of the P-polarized component and the S-polarized component, so that in the absence of the polarizing element, the light utilization efficiency for P-polarized light is theoretically 50% of TP.

TABLE 2

P.D T.L.T (%) Pitch Ratio (2nd / 1st) Moire pitch (μm, up to 2nd order) Identification (observation distance 1m) Example 1 38.3 53.5 1.35 192.9 Impossible Example 2 41.7 54.3 1.50 150.0 Impossible Example 3 69.6 61.5 1.65 235.7 Impossible Example 4 68.1 61.5 2.50 250.0 Impossible Example 5 69.6 61.7 4.00 200.0 Impossible Comparative Example 1 38.3 53.8 1.10 550.0 end Comparative Example 2 41.7 54.3 1.90 950.0 end

From Table 2, the ratio between the pitch of the first optical plate member and the pitch of the second optical plate member (the pitch of the second optical plate member / the pitch of the first optical plate member) is 1.35, 1.5, 1.65, 2.5 in both cases. Or, since it is one of three or more, the moire pitch became a value smaller than 290 micrometers which is a lower limit of identification when the observation distance is 1000 mm. Therefore, we confirmed that moire could not be identified.

In addition, in Examples 3 to 5, by forming a polarization degree amplification film, it was confirmed that the reflectance was increased, the transmittance of S polarized light was reduced, and the degree of polarization was increased.

That is, in any of the examples, it was confirmed that T.L.T is a value larger than 50% and the light beam utilization efficiency is increased in comparison with the case where no polarization splitting element is provided.

That is, this invention is not limited to the said Example, It is possible to add various changes in the range which does not deviate from the meaning of this invention.

For example, a high refractive index film having a higher refractive index than each optical plate member and a low refractive index film having a lower refractive index than the high refractive index film are alternately arranged on the curved surfaces of the first and second optical plate members, respectively. You may laminate more than one. Here, the film thickness of the high refractive index film (refractive index: n ₁ ) and the low refractive index film (refractive index: n ₂ ) are respectively (380 / (4 × n ₁ )) nm or more ((780 / (4 × n)). ₁ )) nm or less, and (380 / (4 × n ₂ )) nm or more and (780 / (4 × n ₂ )) nm or less are preferable. With this configuration, the reflective amplification film functions as a multiple reflection film and the visible light region It can make higher reflection effect with respect to S polarization | polarized-light of the wavelength of, and can increase than the 2nd Example which improved polarization degree.

Here, as the high refractive index film, TiO used for the polarization amplification film in the above-described second embodiment₂ In addition, Nb₂O₅A material having transparency in a visible light region such as ITO (indium oxide) and a higher refractive index than a resin material used for each optical plate member can be used. In addition, as the low refractive index film, SiO₂(Silicon oxide), MgF₂Materials having a light transmittance in the visible light region such as (magnesium fluoride) and having a lower refractive index than those of the high refractive index material used for the high refractive index film can be used.

In addition, although the diffusion sheet is arrange | positioned between a polarization separation element and a light source, you may make it the structure which does not arrange | position a diffusion sheet. Moreover, it is good also as a structure which arrange | positioned the diffusion sheet and the prism sheet between the polarization separation element and the liquid crystal panel.

In addition, the polarization splitting element has a configuration in which the second optical plate member is disposed on the light source side than the first optical plate member, but the first optical plate member may be disposed on the light source side.

In the above embodiment, the polarization splitting element has only a pair of first and second optical plate members, but two or more pairs of first and second optical plate members may be laminated via an air layer. .

In addition, although PMMA is used as the 1st and 2nd optical plate members, as long as it is a resin material which does not have optical anisotropy and has high transmittance | permeability in visible region, you may use COP similarly to an Example, and acryl and PS (polystyrene) Or other resin materials may be used. Moreover, even if it is a birefringent resin material like PC (polycarbonate) etc., it can apply as a 1st and 2nd optical plate member by creating by the method which can suppress the expression of optical anisotropy, such as the casting method.

In addition, you may change suitably the thickness of a 1st and 2nd optical plate member according to a design.

In addition, if the bending angle in each curved surface of the first and second optical plate members is equal to or greater than 180 ° -2θ _{B and} less than 180 ° -2 (θ _B + 15 °) with respect to θ _B (deg), You may change your enemy. In addition, a value different from the bending angle in the curved surface and the second optical plate member in the first optical plate member may be used.

The pitch of the first and second optical plate members has a ratio of the pitch of the first optical plate member and the pitch of the second optical plate member (the pitch of the second optical plate member / the pitch of the first optical plate member) to be 1.35, If the value satisfies any one of 1.5, 1.65, 2.5, or 3 or more, the enemy may be changed. Here, the case where the difference of about +/- 3% generate | occur | produces in the pitch of each optical member by manufacturing error etc. is also included. Thus, by setting the ratio of the pitch to 1.5 or 3 or less, the moire pitch can be made smaller than the moire lower identification value when the second order is considered. In addition, by setting the ratio of the pitch to 1.35, 1.65, 2.5, or 4.0 or more, the moire pitch can be made smaller than the lower limit of the moire when the third moire is considered.

In addition, as long as the moire pitch is a value smaller than the moire lower identification limit, the value may be different.

In addition, you may change suitably the thickness of each air layer according to a design.

Further, in the second embodiment, the film thickness of the polarization degree amplification film is equal to or greater than (380 / (4 x n)) nm or less ((780 / (4 x n)) nm when the refractive index of the high refractive index film is n. If TiO ₂ is used as the polarization degree amplification film, however, similarly to the examples and the high-refractive index film described above, it has light transmittance in visible light regions such as Nb ₂ O ₅ and TiO ₂ , and each optical As long as the material has a higher refractive index than the resin material used for the plate member, another member may be used.

In addition, a polarization degree amplification film is not limited to the vapor deposition method, You may form by another thin film formation method by the sputtering method. Moreover, it is good also as a structure which laminates on the surface of an optical plate member what disperse | distributes nanoparticles of higher refractive index than resin film used for an optical plate member in resin.

In addition, although the polarization degree amplification film is provided in both of the 1st and 2nd optical plate members, it is good also as a structure provided only in either one.

According to the polarization splitting element and the backlight unit of the present invention, since the pitches of the curved surfaces arranged opposite to each other are configured to be different from each other, the moire can be made indistinguishable. In addition, the air layer can be reliably formed to maintain the polarization separation function between the first linearly polarized light and the second linearly polarized light.

Claims (8)

A second linearly polarized light having a curved surface in which the peaks and valleys are alternately or parallelly formed on one surface, having a flat surface on the other surface, and having the first linearly polarized light perpendicular to the first linearly polarized light; At least one pair of optical plate members to transmit more than In the polarization splitting element in which the curved surfaces of each of the pair of optical plate members face each other via an air layer such that the ridges of the peaks are parallel to each other, The pitch of the peaks of one of the pair of optical members is different from the pitch of the peaks of the other, A polarization degree amplifying film is formed on at least one surface of the optical plate member to reduce the transmittance of the second linearly polarized light. delete The method of claim 1, The film thickness of the said polarization degree amplification film is (380 / (4xn)) nm or more ((780 / (4xn)) nm or less when the refractive index of the polarization degree amplification film is n, The polarization separation characterized by the above-mentioned. device. The method of claim 1, The polarization splitting element is formed by alternately stacking a high refractive index film having a higher refractive index than the optical plate member and a low refractive index film having a lower refractive index than the high refractive index film. The method of claim 4, wherein Said high refractive index film has a thickness, and high when the refractive index of the film refractive index as _{n 1, (380 / (4} × n 1)) nm or more ((780 / (4 × n 1)) polarization, characterized in that nm or less Separation element. The method according to claim 4 or 5, Wherein the low refractive index film has a thickness, when said that the low refractive index film, the refractive index _{n 2, (380 / (4} × n 2)) nm or more ((780 / (4 × n 2)) polarization, characterized in that nm or less Separation element. A polarization splitting element according to any one of claims 1 to 3 and 5 and a light source for illuminating illumination light on the polarization splitting element. The method of claim 1, The ratio of the pitch of the first light diffusing member and the pitch of the second light diffusing member (the pitch of the second light diffusing member / the pitch of the first light diffusing member) of the pair of light diffusing members is 1.35, 1.5, 1.65, 2.5 Or a moire cannot be identified by setting any one of three or more.

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