JP2893769B2 - Polarizing element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element that converts random polarized light into linear polarized light having a plane of polarization in one direction.

[Conventional technology]

Conventionally, in order to obtain unidirectional polarized light from random polarized light, a method of selectively extracting only linearly polarized light having a specific polarization plane using a polarizer or a birefringent crystal has generally been used. A representative example is a polarizing plate. This is the incident light, which is random polarized light having polarization components orthogonal to each other,
By selectively absorbing only one linearly polarized light component and transmitting only the other linearly polarized light component, the light is converted into emission light having only one direction of polarized light component. Other examples using a birefringent crystal include a lotion prism and a Nicol prism.

[Problems to be solved by the invention]

However, conventional polarizers use the dichroic nature of light absorption, so the conversion efficiency to unidirectional polarized light is as low as about 45% at the maximum, and the polarizer itself is thermally destroyed by the heat generated by light absorption. Had the danger of producing In the case of using a birefringent crystal, unnecessary polarization components having different polarization directions are removed by means such as reflection, so that the conversion efficiency to unidirectional polarization is also 50% or less in this method. And low is a problem.

Therefore, the present invention solves the above-mentioned problems, and an object of the present invention is to compactly convert random polarized light into unidirectional polarized light with little loss due to light absorption or reflection. It is to provide a simple polarizing element.

[Means for solving the problem]

The polarizing element of the present invention is a polarizing element that separates incident light into two types of linearly polarized light whose polarization planes are orthogonal to each other, and condenses the light at different positions in a substantially same plane; And a λ / 2 retardation layer, one of which is selectively formed on the optical path on which light is condensed, and which makes the polarization direction of the one polarized light coincide with the polarization direction of the other polarized light. The polarized light separating means includes a first isotropic layer having a plurality of lenses formed on a light exit side surface and a second isotropic layer having a plurality of lenses formed on a light incident side surface. And a birefringent layer sandwiched between the first isotropic layer and the second isotropic layer.

Further, in the polarizing element, a lens that converts the other polarized light and the one polarized light emitted from the λ / 2 phase difference layer into parallel rays on a light emission side of the λ / 2 phase difference layer. Is provided.

[Action]

According to the above-mentioned means, first, random polarized light is converted into two linearly polarized lights whose polarization planes are orthogonal to each other by a birefringent lens composed of three layers of an isotropic layer, a birefringent layer, and an isotropic layer. (Light component). next,
A retardation plate that rotates the polarization plane of the incident light by 90 degrees is placed at the condensing position of one polarized light (for example, ordinary light component), and the polarization plane of the transmitted light is rotated by passing through it, and the polarization direction of the transmitted light is changed to the other polarization. And the polarization direction. Finally, by passing through the lens again polarized light that is position-selectively separated and condensed and the polarization directions are all aligned in the same direction, most of the random polarized light that is incident light is converted to unidirectional polarized light. . In the above conversion process, there is almost no decrease in the amount of light due to light absorption or reflection due to the difference in polarization direction. Also,
Since the lens adapted to the lens characteristics of the birefringent lens is arranged on the exit side of the polarizing element, the width of the light beam hardly changes in the polarization conversion process by the present polarizing element.
Therefore, when incident light having excellent parallelism is incident on the present polarizing element, emission light having similarly excellent parallelism can be obtained.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples.

Example 1 FIG. 1 is a schematic cross-sectional view of the configuration of the polarizing element of the present invention. An example of the present invention will be described with reference to FIG. The isotropic layer 11 is made of an isotropic transparent material having a refractive index of n1, and a lenticular lens-like pattern (pitch: 100 μm) having a concave cross section on one side and having a unidirectional light-collecting shape is formed in an array. Are arranged. The isotropic layer 15 has a refractive index of
n2 is also made of isotropic transparent material (however,
n2> n1), a lenticular lens-like pattern (pitch is 100 μm) having a one-way light-collecting property in which the cross-sectional shape corresponding to the concave cross-sectional shape is convex on one surface. (Which is slightly smaller than the interface 12). Using the two isotropic layers 11 and 15 described above, about 5 cm according to the method of assembling a normal liquid crystal cell.
A cell having a gap of μm was produced by bonding. After that, a nematic liquid crystal material (ordinary refractive index no, above light refractive index ne, where no
<Ne) was injected, sealed, and aligned to form a three-layer structure of an isotropic layer 11, a birefringent layer 13, and an isotropic layer 15. However, two isotropic materials and a liquid crystal material were selected so that n1 = no and n2 = ne. With the above configuration, it is possible to spatially separate and condense random polarized light of incident light into two linearly polarized lights (ordinary light component and extraordinary light component) whose polarization planes are orthogonal to each other. That is, the liquid crystal material behaves as a uniaxial birefringent material by performing the alignment treatment here.

Now, in FIG. 1, the ordinary light component (the polarization direction is perpendicular to the paper surface) is indicated by a broken line 18, and the extraordinary light component (the polarization direction is parallel to the paper surface).
Is indicated by a solid line 19, the refractive index n1 of the isotropic layer 11 and the birefringent layer
Since the ordinary light refractive index no of 13 is equal, the extraordinary light component of the light incident on the polarizing element undergoes the refraction of light at the first lens interface 12 due to the refractive index difference. However, since the relationship between the refractive index of the birefringent layer 13 and the refractive index of the isotropic layer 15 regarding the extraordinary light component is ne = n2 at the interface of the second lens, no refraction of light is received. Therefore, the extraordinary light component is condensed by the refraction of light only at the first lens interface 12 and is focused (in this case, strictly speaking, the interface formed by the isotropic layer 11 and the birefringent layer 13). Is a one-way lenticular lens shape and therefore forms a focal line.) On the other hand, the ordinary light component is refracted by the light only at the second lens interface, contrary to the abnormal light component, and is similarly condensed to form a focal point (focal line). This is because the relationship between the refractive indexes of the isotropic layer 11, the birefringent layer 13, and the isotropic layer 15 with respect to the ordinary light component is n1 = no <n2.

Next, the width of about 40μ only at the focus (focal line) position of the ordinary light component
The [lambda] / 2 retardation layer 16 having a pitch of 100 [mu] m and a pitch of 100 [mu] m is formed in a position-selective manner, so that the polarization plane of the ordinary light component passing through this portion is rotated by 90 degrees. Forming a focal line). Further, a substrate 17 made of an isotropic material having a unidirectional lenticular lens (lens pitch: 50 μm) formed on the back surface was attached so as to sandwich the λ / 2 retardation plate 16. Here, the thickness of the substrate 17 is the thickness of the isotropic layer 15 × n2 / (n3 × 2).
And the parallel incident light collected at the second lens interface 14 is
The configuration was such that the light was converted into parallel light again by a lens formed on the back surface of the substrate 17. Strictly speaking, since the curvatures of the lenses between the first lens interface 12 and the second lens interface 14 are not equal, the curvature of the third lens 20 is set every other row to the above-mentioned value.
It is necessary to change according to the kind of lens, but if the thickness of the isotropic layer 15 is made large (for example, 10 times) with respect to the lens diameter of the two kinds of lenses, the lens curvature of the third lens 20 becomes large. Even if uniform, emitted light with good parallelism can be obtained. With the above configuration, light transmitted through the present polarizing element is almost completely converted into an extraordinary light component without being absorbed. Also, it can be seen that when light with good parallelism is incident on the present polarizing element, the emitted light obtained is also light with good parallelism.

Random polarized light having good parallelism was incident from the front of the polarizing element, and the light transmittance of the present polarizing element and the ratio of the extraordinary light component in the emitted light were measured.
The rate was as high as 94%.

Example 2 FIG. 2 shows a cross-sectional view of the structure of a polarizing element according to the present invention, similar to Example 1. The shape of the lens formed at the interface between the isotropic layer 11, the birefringent layer 13, and the isotropic layer 15 is different from that of the first embodiment. By making the lens shape a Fresnel shape, the distance between the two lenses formed between the interfaces can be made shorter than in the case of Example 1, and when a liquid crystal material is used as the birefringent layer 13, it is easy to align. There are features. When the light transmittance of the present polarizing element and the ratio of the extraordinary light component in the transmitted light were measured in the same manner as in Example 1, they were about 89% and about 92%, respectively, which were almost the same values as in Example 1. there were.

In the two embodiments of the anomaly, a linear lenticular lens array having one-way focusing is used as the focusing lens body formed at the interface, but of course, a lens configured using other general circular or elliptical lenses Arrays may be used.
However, in order to increase the conversion efficiency of light into one-way polarized light, it is important to two-dimensionally close-pack the lens body so that non-lens portions do not occur. It can be said that it is rational to have a linear lenticular shape. In the above embodiment, a liquid crystal material is used as a material for forming the birefringent layer. However, if the material has a high birefringence (for example, a polymer material maintaining an alignment state), the liquid crystal material is limited. Obviously it can be used without being done.

〔The invention's effect〕

As described above, the polarizing element of the present invention separates and condenses incident light, which is random polarized light, into two linearly polarized light components whose polarization planes are orthogonal to each other. By rotating the plane of polarization of the polarized light so that it matches the plane of polarization of the other polarized light, and then combining them again using a lens, it is possible to change from random polarized light to unidirectional polarized light with almost no light absorption. It can be said that the conversion can be performed. Further, since light absorption is scarcely involved, even when a strong light beam is incident, polarization conversion can be performed stably without causing self-destruction due to heat generation. As described in the above embodiment, it is considered that the polarization conversion efficiency of the polarizing element of the present invention is approximately 80% or more including the light transmittance, and the conversion efficiency of the conventional polarizing plate is at most about 45%. It can be seen that the polarizing element of the present invention is very excellent in terms of polarization conversion efficiency.

The polarizing element of the present invention makes use of the above-mentioned characteristics, and is widely used for various display elements requiring polarization, especially for liquid crystal display elements, optical isolators, optical switches, optical filters, and various optical devices including them. Application is possible.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of the configuration of a polarizing element of the present invention in Example 1.
FIG. 2 is a schematic cross-sectional view of a polarizing element when the birefringent lens of Example 2 is formed of a Fresnel lens. 11 First substrate (isotropic layer) 12 First lens interface 13 Birefringent layer 14 Second lens interface 15 Second substrate (isotropic layer) 16 Λ / 2 phase difference layer 17 Third substrate (isotropic layer) 18 Normal light 19 Extraordinary light 20 Third lens 21 First lens interface with Fresnel lens 22 ... Second lens interface by Fresnel lens

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-265206 (JP, A) JP-A-1-273002 (JP, A) JP-A-1-127329 (JP, A) JP-A-60- 63503 (JP, A) JP-A-1-118805 (JP, A) JP-A-62-71905 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 5/30

Claims (2)

(57) [Claims] 1. A polarized light separating means for separating incident light into two kinds of linearly polarized lights whose polarization planes are orthogonal to each other, and condensing the lights at different positions in a substantially same plane; A polarizing element having a λ / 2 retardation layer that is selectively formed on the optical path where one of the light beams is condensed, and matches the polarization direction of the one polarized light beam with the polarization direction of the other polarized light beam, A first isotropic layer in which a plurality of lenses are formed on a surface on a light emission side; a second isotropic layer in which a plurality of lenses are formed on a surface on a light incidence side; A polarizing element, comprising: a birefringent layer sandwiched between the first isotropic layer and the second isotropic layer. 2. The polarizing element according to claim 1, wherein the other polarized light is provided on a light exit side of the λ / 2 retardation layer.
A polarizing element, comprising: a lens that converts the one polarized light beam emitted from the λ / 2 retardation layer into a parallel light beam.