JP4650931B2 - Polarization separation element - Google Patents

Description

  The present invention relates to a polarization beam splitting element, and more particularly to a polarization beam splitting element that reflects almost one orthogonally polarized light and transmits almost the other linearly polarized light.

  In the optical field, a polarization separation element that separates random polarized light (natural polarized light) into two orthogonally polarized light is used in many fields. A typical example is a liquid crystal display device.

  Conventionally, polarization beam splitter prisms, birefringent films, wire grid polarizers, and the like are known as polarization separation elements. The polarizing beam splitter prism has a structure in which a dielectric multilayer film is sandwiched between a birefringent prism and a right-angle prism, and the birefringent film includes, for example, two different polymers as shown in FIG. Alternating layers of materials are stacked in multiple layers, and one layer has a refractive index anisotropy by stretching, and the other layer has a constant refractive index regardless of stretching. Randomly polarized backlight is incident on the constituent layers so that linearly polarized light in one direction passes and linearly polarized light orthogonal thereto is reflected. This is actually used under the trade name DBEF.

  Further, the wire grid polarizer is composed of a linear grid-like conductive line layer made of a metal such as aluminum, silver, or Cr on the surface of a transparent substrate and arranged in parallel at a constant period below the wavelength. 1, Non-Patent Document 2 and the like.

Further, Patent Document 2 also discloses a polarization separation element in which a high refractive index layer and a low refractive index layer are alternately stacked on a relief grating type periodic groove array to have a periodic uneven structure. .
Japanese National Patent Publication No. 9-506984 JP 2000-131522 A Japanese Patent Laid-Open No. 7-235075 “Physics of Modern People 1—Light and Magnetism” (Katsuaki Sato, Tokyo University of Agriculture 1988, p. 103 (Asakura Shoten) JP Auton, "Infrared Transmission Polarizer by Photolithography", Applied.Optics.Vol.6.p.1023 (1967)

  However, the polarizing beam splitter prism is relatively bulky and it is difficult to increase the area. In addition, since the birefringent film is made of a polymer material, the heat resistance is difficult. In addition, since a conventional wire grid polarizer having heat resistance is manufactured using photolithography, it is expensive and difficult to increase in area. Furthermore, a polarization separation element in which high refractive index layers and low refractive index layers are alternately stacked on a periodic groove array is not easy to manufacture, and it is difficult to increase the area of a uniform element.

  The present invention has been made in view of such a situation in the prior art, and an object thereof is to provide a polarization separation element that is easy to manufacture, heat-resistant, and capable of increasing the area based on a novel principle. That is.

  The polarization separating element of the present invention that achieves the above object transmits one linearly polarized light of two orthogonal linearly polarized light at a higher ratio than that of reflection, and a higher ratio of the other linearly polarized light than that of transmission. Is a polarization separation element that reflects at 1 and has periodicity in one direction out of two orthogonal directions and is uniform in the other direction, and the cross-sectional shape along the one direction is continuous with a constant period of less than the wavelength. It consists of a thin triangular-shaped metal thin film.

  Another polarization separation element of the present invention is a polarization separation element that has a higher reflection ratio of one linearly polarized light of two orthogonally polarized lights and a lower reflection ratio of the other linearly polarized light, and has two orthogonal directions. It is characterized in that it has a periodicity in one direction, is uniform in the other direction, and a cross-sectional shape along the one direction is composed of a triangular wave-like metal thin film that repeats continuously at a constant period below the wavelength. Is.

  Still another polarization separation element of the present invention is a polarization separation element having a higher transmission ratio of one linearly polarized light of two orthogonal linearly polarized lights and a lower transmission ratio of the other linearly polarized light, and two orthogonal directions It has a periodicity in one direction, and is uniform in the other direction, and the cross-sectional shape along the one direction is composed of a triangular-shaped metal thin film that repeats continuously at a constant period below the wavelength. To do.

  In these cases, it is assumed that the metal thin film is supported so that one surface thereof is in close contact with the transparent body, and the surface opposite to the metal thin film side of the transparent body is a flat surface. it can.

  Alternatively, the metal thin film may be supported by being stretched in a frame.

  The metal thin film is preferably made of any one of aluminum, gold, and silver.

The period in the cross-sectional shape of the metal thin film is Λ, the depth h of the groove having a triangular triangular cross section, and the thickness of the metal thin film in the depth direction of the groove having the triangular triangular cross section is d. When λ _min
Λ / λ _min <0.5 (1)
h> 1.5Λ (2)
d> 0.010 μm (3)
It is desirable to satisfy the following conditions.

  The polarization separation element of the present invention has periodicity in one direction out of two orthogonal directions and is uniform in the other direction, and the cross-sectional shape along the one direction is continuously at a constant period below the wavelength. Since it consists of a repetitive triangular wave-shaped metal thin film, once the original plate having such a cross-sectional shape is produced, the original plate is duplicated by the 2P method or the like, and then a single layer of metal thin film is formed. It can be manufactured as a product. Here, the original plate can be manufactured by a method such as nano / micro cutting or a two-beam interference exposure method in addition to the method by photolithography, and the area can be increased. And since the main component of the polarization splitting element is a metal thin film, an element having excellent heat resistance can be obtained.

  The polarization separation element of the present invention will be described below based on the principle and examples.

  1A and 1B are a side view and a plan view of a polarization beam splitting element according to an embodiment of the present invention. This polarization separation element 1 is provided with a transparent resin layer 12 on a transparent flat substrate 11, and the surface of the transparent resin layer 12 is a groove that repeats continuously in a horizontal direction in FIG. A concavo-convex surface having a triangular wave cross section composed of a line 13 and a ridge line 14 and having a uniform concavo-convex surface in a direction perpendicular to the paper surface of FIG. 1A (vertical direction of FIG. 1B). The metal thin film 15 having a certain thickness such as aluminum is laminated on the uneven surface. Therefore, when only the metal thin film 15 is viewed, the cross-sectional shape in the paper surface of FIG. 1A is a triangular wave shape that repeats continuously at a constant period Λ, and is uniform in the direction orthogonal to the paper surface of FIG. It has a continuous surface shape. The period Λ of the continuously repeating pattern having a triangular wave cross section of the metal thin film 15 is set to be smaller than the operating wavelength.

  When randomly polarized light (naturally polarized light) 2 is incident substantially perpendicularly on the substrate 11 to the polarization separating element 1 having such a configuration, linearly polarized light (S polarized light) having an electric field vector oscillating in parallel with the groove line 13 and the ridge line 14. ) Component radiates a polarized light component in the same direction as the incident light in the opposite direction to vibrate electrons in the metal thin film 15 in parallel with the groove line 13 and the ridge line 14, and as a result, S-polarized light is reflected as reflected light 3. The component of linearly polarized light (P-polarized light) having an electric field vector that vibrates in a direction perpendicular to the groove line 13 and the ridge line 14 cannot excite such vibration of electrons and enters the metal thin film 15 on the back surface. And transmitted as transmitted light 4. When random polarized light 2, which is a combined light of S-polarized light and P-polarized light, is incident on the polarization separating element 1, the reflected light 3 becomes S-polarized light and the transmitted light 4 becomes P-polarized light. It can be separated.

  As one specific example, the polarization separation element 1 is in the air with a refractive index of 1, the refractive index of the transparent flat substrate 11 and the transparent resin layer 12 is 1.5, and the wavelength used is 0.4 μm to 0.7 μm. , A period Λ = 0.12 μm of a continuously repeating pattern having a triangular wave cross section, and the height of the ridge line 14 with respect to the groove line 13 (the height of the protrusion having the triangular wave shape in the cross section, the depth of the groove having the triangular wave shape in the cross section) h = 0. S-polarized light in the case where the thickness d of the metal thin film 15 in the direction perpendicular to the transparent flat substrate 11 (direction perpendicular to the plane of the polarization separation element 1) d = 0.03 μm and the metal thin film 15 is made of an aluminum thin film The transmittance and reflectance characteristics of P-polarized light are shown in FIG. However, the transmittance is the transmittance in the transparent flat substrate 11.

  As can be seen from FIG. 2, according to the present invention, it is possible to very efficiently separate the polarized light with the S-polarized light as the reflected light 3 and the P-polarized light as the transmitted light 4.

Here, the range of the above period Λ, height h, and thickness d will be described. To efficiently separate S-polarized light and P-polarized light,
Λ / λ _min <0.5 (1)
h> 1.5Λ (2)
d> 0.010 μm (3)
It is preferable to satisfy the following conditions. Here, λ _min is the minimum wavelength at the used wavelength. When the thickness d of the metal thin film 15 is smaller than 0.010 μm, the transmittance of S-polarized light is increased and the extinction ratio is deteriorated. Even if the thickness d is increased, if the height h with respect to the period Λ is increased, the thickness in the direction perpendicular to the slope of the protrusion of the metal thin film 15 is reduced, and the extinction ratio between S-polarized light and P-polarized light is improved. Therefore, the upper limit of the thickness d of the metal thin film 15 cannot be set.

  As a metal material that can be used for the metal thin film 15, aluminum (Al) having a refractive index close to 0 and an extinction coefficient of about 5 is preferable, and gold (Au) and silver (Ag) are suitable accordingly.

  In FIG. 3, the side view of another Example of the polarization splitting element 1 of this invention is shown. The polarization separation element 1 of this embodiment is the same as that of the polarization separation element 1 of FIG. 1, the transparent resin layer 12 and the transparent plane that are the supports of the triangular-shaped metal thin film 15 whose cross-sectional shape repeats continuously at a constant period Λ. The substrate 11 is removed and only the metal thin film 15 is supported in the air. Similarly to the embodiment shown in FIG. 1, random polarized light 2 that is a combined light of S-polarized light and P-polarized light is used as the polarization separating element 1. , S-polarized light can be separated as reflected light and P-polarized light can be separated as transmitted light. The principle is the same as in FIG. Further, the period Λ, the height h (in this case, the depth of the groove having a triangular wave cross section), the range of the thickness d, and the type of metal are the same as those in the embodiment of FIG.

  FIG. 4 shows an example of a support structure of the polarization separation element 1 in the form of FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view thereof. A metal thin film 15 is stretched on a rectangular frame 20, and the cross-sectional shape of the stretched metal thin film 15 has a constant period. 3 is provided in the rectangular frame 20 in a stable manner by providing the triangular-wave-like parallel grooves 21 that are continuously repeated in FIG.

  When the configuration of FIG. 1 is compared with the configuration of FIG. 3, in the configuration of FIG. 1, the transparent resin layer 12 can be easily adhered to the metal thin film 15. On the other hand, in the configuration of FIG. 3, the height h of the triangular wave shape of the cross-sectional shape can be easily made.

  As one specific example of the polarization separation element for visible light (wavelength 0.4 to 0.7 μm) of the present invention as described above, a polarization separation element 1 as shown in FIG. 1 was produced by the following steps. For the 2P replication method, see Patent Document 3, for example.

  (1) Manufacture of original plate: A surface linear lattice-shaped original plate having a cross-sectional shape of one cycle of an isosceles triangle, a period Λ = 0.12 μm, and a height of 0.33 μm was manufactured by nano / micro cutting. Of course, other methods such as lithography and two-beam interference exposure may be used for producing the original plate.

  (2) 2P replication: The surface shape of the linear lattice-shaped original plate is changed to ultraviolet rays by applying an ultraviolet curable resin to the linear lattice-shaped original plate obtained in (1) and curing it with ultraviolet light. Duplicated on the surface of the curable resin. This original copy may be performed by other methods. At that time, the period Λ of the replica was not changed, but the height of the one-dimensional protrusion having an isosceles triangle cross section was reduced by about 10%. Therefore, the height of the protrusion on the original plate is set to 0.33 μm, which is an expected height.

  (3) Metal coating: One layer of Al thin film was coated with a thickness of d = 0.03 μm by vacuum-depositing Al on the lattice-like surface of the replica of (2).

  The performance of the obtained polarization separation element was as shown in FIG. In addition, the steps (2) and (3) can be easily and repeatedly performed as long as the original plate is produced once in the step (1), and can be easily and inexpensively and have a large area with heat resistance. It is possible to produce the polarization separation element.

  Although the polarization separation element of the present invention has been described based on the embodiments, the polarization separation element of the present invention is not limited to these embodiments and can be variously modified.

It is the side view (a) and top view (b) of the polarization beam splitting element of one Example of this invention. It is a figure which shows the transmittance | permeability and reflectance characteristic of the polarization splitting element of one specific example. It is a side view of another Example of the polarization splitting element of this invention. It is the top view (a) and sectional drawing (b) which show an example of the support structure of the polarization splitting element of the form of FIG.

Explanation of symbols

1... Polarization separating element (present invention)
2 ... Incident light (natural polarization)
3 ... Reflected light (S-polarized light)
4 ... Transmitted light (P-polarized light)
DESCRIPTION OF SYMBOLS 11 ... Transparent planar substrate 12 ... Transparent resin layer 13 ... Groove line 14 ... Edge line 15 ... Metal thin film 20 ... Rectangular frame 21 ... Groove

Claims (6)

A polarization separation element that transmits one linearly polarized light of two orthogonally polarized light beams at a higher ratio than that of reflection and reflects the other linearly polarized light at a higher ratio than that of transmitted light. has periodicity in one direction in the direction, is uniform in the other direction, Ri Do from the triangular wave-shaped metal thin film sectional shape along its direction continuously repeated at a constant period of less than the wavelength, the the period in the cross-sectional shape of the metal thin film lambda, and the depth h of the cross section triangular groove, the metal thin film in the depth direction of the cross section triangular groove a thickness of d, and the _min the minimum wavelength λ in the used wavelength band and when,
Λ / λ _min <0.5 (1)
h> 1.5Λ (2)
d> 0.010 μm (3)
A polarization separation element satisfying the following conditions: A polarization separation element having a higher reflection ratio of one linearly polarized light of two orthogonally polarized lights and a lower reflection ratio of the other linearly polarized light, and having periodicity in one of the two orthogonal directions is uniform in the other direction, Ri Do from the triangular wave-shaped metal thin film sectional shape along its direction continuously repeated at a constant period of less than the wavelength, the period in cross-sectional shape of the metal thin film lambda, sectional triangular When the depth h of the wavy groove, the thickness of the metal thin film in the direction of the depth of the triangular wave cross section is d, and the minimum wavelength in the operating wavelength range is λ _min ,
Λ / λ _min <0.5 (1)
h> 1.5Λ (2)
d> 0.010 μm (3)
A polarization separation element satisfying the following conditions: A polarization separation element having a higher transmission ratio of one linearly polarized light of two orthogonal linearly polarized lights and a lower transmission ratio of the other linearly polarized light, and having periodicity in one of the two orthogonal directions is uniform in the other direction, Ri Do from the triangular wave-shaped metal thin film sectional shape along its direction continuously repeated at a constant period of less than the wavelength, the period in cross-sectional shape of the metal thin film lambda, sectional triangular When the depth h of the wavy groove, the thickness of the metal thin film in the direction of the depth of the triangular wave cross section is d, and the minimum wavelength in the operating wavelength range is λ _min ,
Λ / λ _min <0.5 (1)
h> 1.5Λ (2)
d> 0.010 μm (3)
A polarization separation element satisfying the following conditions: 4. The metal thin film has one surface closely supported by a transparent body and is supported on a surface opposite to the surface on the metal thin film side of the transparent body. 5. The polarization separation element according to any one of the above. 4. The polarization separation element according to claim 1, wherein the metal thin film is supported while being stretched in a frame. The polarization separation element according to claim 1, wherein the metal thin film is made of any one of aluminum, gold, and silver.

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