Polarization conversion element

Abstract

The objective is to provide a polarization conversion element that can suppress increases in manufacturing costs and decreases in light utilization efficiency. [Solution] The polarization conversion element 1 has a first microstructure 14 formed on a first surface 11a and a phase difference member 13 arranged on a second surface 12a facing the first surface. The phase difference member 13 has a two-dimensional arrangement of a first region 131 that gives a first phase difference to incident light and a second region 132 that gives a second phase difference different from the first phase difference to incident light. The first microstructure 14 separates incident light incident on the first surface 11a into a first polarization and a second polarization with a different polarization direction from the first polarization, and emits the first polarization toward the first region 131 and the second polarization toward the second region 132. The first phase difference and the second phase difference are set so that the polarization direction of the first polarization that has passed through the first region and the polarization direction of the second polarization that has passed through the second region are the same.

Description

Technical Field

[0001] The present invention relates to a polarization conversion element.

Background Art

[0002] Polarization conversion elements that emit light radiated from a light source as S-wave or P-wave polarized light are known (see, for example, Patent Document 1). The polarization conversion element described in Patent Document 1 includes a first light-transmitting member having a polarization separation film, a second light-transmitting member having a reflection film, and a half-wave plate disposed between the first light-transmitting member and the second light-transmitting member. The polarization conversion element described in Patent Document 1 is manufactured by sandwiching the half-wave plate between the first light-transmitting member and the second light-transmitting member, so that workability is improved compared to a polarization conversion element manufactured by adhering the half-wave plate in a post-process.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of Invention

Problem to be Solved by the Invention

[0004] However, the polarization conversion element described in Patent Document 1 is formed of many components such as a polarization separation film, a reflection film, a housing that supports the polarization separation film and the reflection film, and a half-wave plate, and the manufacturing process is complicated, so there is a risk that the manufacturing cost may increase. Further, in the polarization conversion element described in Patent Document 1, the light utilization efficiency may decrease depending on the reflection efficiency of the reflection film.

[0005] The present invention solves such problems, and an object of the present invention is to provide a polarization conversion element capable of suppressing an increase in manufacturing cost and a decrease in light utilization efficiency.

Means for Solving the Problem

[0006] The polarization conversion element according to the present invention has a first microstructure formed on a first surface and a phase difference member arranged on a second surface facing the first surface. The phase difference member has a two-dimensional arrangement of a first region that gives a first phase difference to incident light and a second region that gives a second phase difference different from the first phase difference to incident light. The first microstructure separates incident light incident on the first surface into a first polarization and a second polarization with a different polarization direction from the first polarization, and emits the first polarization toward the first region and the second polarization toward the second region. The first phase difference and the second phase difference are set so that the polarization direction of the first polarization that has passed through the first region and the polarization direction of the second polarization that has passed through the second region are the same.

[0007] Furthermore, it is preferable that the polarization conversion element according to the present invention further comprises an optical element having at least one of the functions of an aberration correction lens function and a collimator lens function.

[0008] Furthermore, in the polarization conversion element according to the present invention, it is preferable that the optical element has a third surface on which a second microstructure having one of the functions of aberration correction lens function and collimator lens function is formed.

[0009] Furthermore, in the polarization conversion element according to the present invention, it is preferable that the optical element further has a fourth surface on which a third microstructure having the other function of aberration correction lens function and collimator lens function is formed.

[0010] Furthermore, the polarization conversion element according to the present invention further comprises a first substrate having a first surface, and a second substrate having a second surface and a third surface facing the second surface, and it is preferable that the optical element is disposed between the first substrate and the second substrate.

[0011] Furthermore, in the polarization conversion element according to the present invention, it is preferable that a recess for housing an optical element is formed on the second surface.

[0012] Furthermore, in the polarization conversion element according to the present invention, the phase difference member is arranged in two dimensions and comprises a first region, a second region, a third region that gives a phase difference to the incident light that is different from the first and second phase differences, and a fourth region that gives a phase difference to the incident light that is different from the first to third phase differences. The first microstructure converts the light incident on the first substrate into a first polarization, a second polarization, a third polarization with a different polarization direction from the first and second polarizations, and the first, second and third polarizations. Preferably, the light is separated into a fourth polarization with a different optical direction, the first polarization is emitted toward the first region, the second polarization toward the second region, the third polarization toward the third region, and the fourth polarization toward the fourth region, and the first to fourth phase differences are set so that the polarization direction of the first polarization that passed through the first region, the polarization direction of the second polarization that passed through the second region, the polarization direction of the third polarization that passed through the third region, and the polarization direction of the fourth polarization that passed through the fourth region are the same. [Effects of the Invention]

[0013] The polarization conversion element according to the present invention can suppress increases in manufacturing costs and decreases in light utilization efficiency. [Brief explanation of the drawing]

[0014] [Figure 1] (a) is a perspective view (1) of the polarization conversion element according to the first embodiment, (b) is a perspective view (2) of the polarization conversion element according to the first embodiment, and (c) is a front view of the polarization conversion element according to the first embodiment. [Figure 2] (a) is a diagram (part 1) showing the polarization state of the polarization conversion element shown in Figure 1(a), and (b) is a diagram (part 2) showing the polarization state of the polarization conversion element shown in Figure 1(a). [Figure 3] (a) is a perspective view (1) of the polarization conversion element according to the second embodiment, (b) is a perspective view (2) of the polarization conversion element according to the second embodiment, and (c) is a front view of the polarization conversion element according to the second embodiment. [Figure 4](a) is a perspective view (1) of the polarization conversion element according to the third embodiment, (b) is a perspective view (2) of the polarization conversion element according to the third embodiment, and (c) is a front view of the polarization conversion element according to the third embodiment. [Figure 5] (a) is a perspective view (1) of the polarization conversion element according to the fourth embodiment, (b) is a perspective view (2) of the polarization conversion element according to the fourth embodiment, (c) is a cross-sectional view along line AA shown in (a), and (d) is a partially exploded perspective view of the polarization conversion element according to the fourth embodiment. [Figure 6] (a) is a perspective view (1) of the polarization conversion element according to the fifth embodiment, (b) is a perspective view (2) of the polarization conversion element according to the fifth embodiment, and (c) is a front view of the polarization conversion element according to the fifth embodiment. [Figure 7] This figure shows the polarization state of the polarization conversion element shown in Figure 6(a). [Modes for carrying out the invention]

[0015] The polarization conversion element according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to those embodiments, but extends to the invention described in the claims and its equivalents.

[0016] (Configuration and function of the polarization conversion element according to the first embodiment) Figure 1(a) is a perspective view (part 1) of the polarization conversion element according to the first embodiment, Figure 1(b) is a perspective view (part 2) of the polarization conversion element according to the first embodiment, and Figure 1(c) is a front view of the polarization conversion element according to the first embodiment.

[0017] The polarization conversion element 1 includes a base 10, a first substrate 11, a second substrate 12, and a retardation member 13. When unpolarized incident light enters the first substrate 11, the polarization conversion element 1 outputs polarized outgoing light from the retardation member 13. Each of the base 10, the first substrate 11, and the second substrate 12 has a rectangular planar shape, and is formed of a light-transmissive member such as an inorganic glass material or silicon dioxide (SiO₂). The first substrate 11 is disposed on an upper surface, which is one surface of the base 10, and the second substrate 12 is disposed on a lower surface, which is the other surface of the base 10.

[0018] In the first substrate 11, a first microstructure 14 is formed on a first surface 11a that is a surface facing the base 10. The first microstructure 14 is formed so as to split unpolarized incident light entering the first surface 11a into P-polarized light and S-polarized light, and output the split P-polarized light and S-polarized light toward a first region 131 and a second region 132 of the retardation member 13, respectively. P-polarized light is also referred to as first polarized light, and S-polarized light is also referred to as second polarized light.

[0019] The first microstructure 14 is formed, for example, by arranging a plurality of columnar microstructures having a constant height on the first surface 11a. The plurality of microstructures forming the first microstructure 14 are also referred to as polarization splitting meta-atoms. The structure of the first microstructure 14 is not limited to such a structure, and the number of arranged microstructures, arrangement intervals, shapes, and arrangement patterns can be appropriately set.

[0020] When the incident light entering the polarization conversion element 1 is visible light, the plurality of microstructures forming the first microstructure 14 are preferably formed of materials such as silicon nitride (Si₃N₄), silicon carbide (SiC), titanium dioxide (TiO₂), and gallium nitride (GaN). Further, when the incident light entering the polarization conversion element 1 is near-infrared light, the plurality of microstructures forming the first microstructure 14 are preferably formed of materials such as silicon (Si), SiC, SiN, TiO₂, gallium arsenide (GaAs), and GaN. Further, when the incident light entering the polarization conversion element 1 has a wavelength in the optical communication band, the plurality of microstructures forming the first microstructure 14 may be formed of a material such as indium phosphide (InP). The shape of the microstructures may be a shape other than a columnar shape having a cross-sectional shape such as a hollow square, a cross, a circle, or a hollow circle. Note that specific configurations for realizing the function of the first microstructure 14 are described, for example, in Japanese Patent No. 6857163 and "Efficient Polarization Beam Splitter Based on All-Dielectric Metasurface in Visible Region" (Jing Li et al., Nanoscale Research Letters (2019)).

[0021] The second substrate 12 has a second surface 12a which is a surface opposite to the surface facing the base 10. The phase difference member 13 is disposed on the second surface 12a of the second substrate 12.

[0022] The phase difference member 13 comprises a plurality of half-wave plates 15 and has a first region 131 where the plurality of half-wave plates 15 are arranged, and a second region 132 where the plurality of half-wave plates 15 are not arranged, and is arranged on the second surface 12a of the second substrate 12. The first region 131 and the second region 132 are arranged alternately in a two-dimensional array, so as to be arranged in a staggered pattern. Each of the plurality of half-wave plates 15 of the phase difference member 13 is incident on P-polarized light separated from the incident light by the first microstructure 14, and a 90° phase difference is given to the incident P-polarized light, that is, the incident P-polarized light is rotated by 90° and emitted as S-polarized light. The phase difference member 13 is formed, for example, by supporting and integrating the plurality of half-wave plates 15 in the first region 131 by a support member (not shown).

[0023] Figure 2(a) is a diagram (part 1) showing the polarization state of the polarization conversion element 1, and Figure 2(b) is a diagram (part 2) showing the polarization state of the polarization conversion element 1.

[0024] The unpolarized incident light L1 is incident on the first surface 11a of the first substrate 11. The incident light L1 incident on the first surface 11a of the first substrate 11 is separated into P-polarized LP and S-polarized LS as it passes through the first microstructure 14 formed on the first surface 11a. The P-polarized LP is incident on each of the first regions 131 of the phase difference member 13, which is placed on the second surface 12a of the second substrate 12, via the base 10 and the second substrate 12. The P-polarized LP incident on each of the first regions 131 of the phase difference member 13 is rotated by 90° and polarized to S-polarized as it passes through each of the plurality of half-wave plates 15 placed in the first region 131, and is emitted as S-polarized output light L2. On the other hand, the S-polarized LS is incident on each of the first regions 131 of the phase difference member 13, which is placed on the second surface 12a of the second substrate 12, via the base 10 and the second substrate 12. S-polarized light LS incident on each of the second regions 132 of the phase difference member 13 is emitted from the second region 132 as S-polarized emitted light L2 without rotation. As S-polarized emitted light L2 is emitted from each of the multiple half-wave plates 15 arranged in the first region 131, and S-polarized emitted light L2 is also emitted from the second region 132, the emitted light L2 is emitted over the entire surface of the phase difference member 13. Since the emitted light L2 is emitted over the entire surface of the phase difference member 13, the polarization conversion element 1 functions as a polarization conversion element that emits S-polarized emitted light L2 in response to the incident light L1 which is unpolarized.

[0025] The polarization conversion element 1 is manufactured by fixing a first substrate 11 to one side of a base 10, fixing a second substrate 12 to the other side of the base 10, and placing a phase difference member 13 on the second surface 12a of the second substrate 12.

[0026] (Effects of the polarization conversion element according to the first embodiment) Since the polarization conversion element 1 is formed from a base 10, a first substrate 11, a second substrate 12, and a phase difference member 13, the manufacturing process is simplified compared to the polarization conversion element described in Patent Document 1, and the manufacturing cost can be reduced compared to the polarization conversion element described in Patent Document 1.

[0027] Furthermore, the polarization conversion element 1 converts the polarization state of the unpolarized incident light incident on the first substrate 11 and emits polarized light from the phase difference member 13 without using a reflective film, thus reducing the risk of decreased utilization efficiency.

[0028] (Configuration and function of the polarization conversion element according to the second embodiment) Figure 3(a) is a perspective view (1) of the polarization conversion element according to the second embodiment, Figure 3(b) is a perspective view (2) of the polarization conversion element according to the second embodiment, and Figure 3(c) is a front view of the polarization conversion element according to the second embodiment.

[0029] Polarization conversion element 2 has a base 20 in place of base 10, first substrate 11, and second substrate 12. The configuration and function of the components of polarization conversion element 2 other than base 20 are the same as those of the components of the polarization conversion element with the same reference numeral, so a detailed explanation is omitted here. Polarization conversion element 2 functions like polarization conversion element 1, emitting S-polarized output light L2 in response to incident light L1 which is unpolarized.

[0030] The base 20, also referred to as the first substrate, has a rectangular surface shape and is formed from an inorganic glass material and a light-transmitting material such as silicon dioxide (SiO2). A first microstructure 23 is formed on one surface of the base 20, the first surface 21, and a phase difference member 13 is arranged on the other surface of the base 20, the second surface 22.

[0031] The first microstructure 23 is formed, similar to the first microstructure 14, by arranging a plurality of columnar microstructures of constant height on the first surface 21. The first microstructure 23 is formed to separate unpolarized incident light incident on the first surface 21 into P-polarized and S-polarized light, and to emit the separated P-polarized and S-polarized light toward the first region 131 and the second region 132 of the phase difference member 13, respectively.

[0032] Since the polarization conversion element 2 is formed with a base 20 and a phase difference member 13, the manufacturing process can be simplified compared to the polarization conversion element 1, and thus the manufacturing cost can be further reduced compared to the polarization conversion element 1.

[0033] Furthermore, the polarization conversion element 2 converts the polarization state of the unpolarized incident light incident on the first surface 21 of the base 20 without using a reflective film, and emits it as polarized light from the phase difference member 13, thus reducing the risk of decreased utilization efficiency.

[0034] (Configuration and function of the polarization conversion element according to the third embodiment) Figure 4(a) is a perspective view (1) of the polarization conversion element according to the third embodiment, Figure 4(b) is a perspective view (2) of the polarization conversion element according to the third embodiment, and Figure 4(c) is a front view of the polarization conversion element according to the third embodiment.

[0035] Polarization conversion element 3 differs from polarization conversion element 1 in that it has an optical element 30. The configuration and function of the components of polarization conversion element 3 other than the optical element 30 are the same as those of the components of polarization conversion element 1, which is given the same reference numeral, so a detailed explanation is omitted here. Like polarization conversion element 1, polarization conversion element 3 functions as a polarization conversion element that emits S-polarized output light L2 in response to incident light L1 which is unpolarized.

[0036] The optical element 30, like the first substrate 11, has a rectangular surface shape and is a lens formed from an inorganic glass material and a light-transmitting member such as silicon dioxide (SiO2). The optical element 30 is positioned on an opposing surface 12b that is opposite to the second surface 12a on which the phase difference member 13 is placed and faces the base 10, so as to be sandwiched between the base 10 and the second substrate 12. The optical element 30 is subjected to predetermined optical processing such as aberration correction and collimation to the P-polarized LP and S-polarized LS incident on the second substrate 12.

[0037] The polarization conversion element 3 can improve the optical characteristics of the emitted light L2 compared to the polarization conversion element 1 by applying a predetermined optical treatment to the P-polarized LP and S-polarized LS incident on the second substrate 12 using the optical element 30 arranged on the opposing surface 12b.

[0038] (Configuration and function of the polarization conversion element according to the fourth embodiment) Figure 5(a) is a perspective view (part 1) of the polarization conversion element according to the fourth embodiment, and Figure 5(b) is a perspective view (part 2) of the polarization conversion element according to the fourth embodiment. Figure 5(c) is a cross-sectional view along line AA shown in Figure 5(a), and Figure 5(d) is a partially exploded perspective view of the polarization conversion element according to the fourth embodiment.

[0039] Polarization conversion element 4 differs from polarization conversion element 2 in that it has a second substrate 40 and an optical element 41. The configuration and function of the components of polarization conversion element 4 other than the second substrate 40 and optical element 41 are the same as those of the components of polarization conversion element 2, which are given the same reference numerals, so a detailed explanation is omitted here. Polarization conversion element 4 functions like polarization conversion element 1, emitting S-polarized output light L2 in response to incident light L1 which is unpolarized.

[0040] The second substrate 40, like the second substrate 12, has a rectangular surface shape and is formed from an inorganic glass material and a light-transmitting member such as silicon dioxide (SiO2). The second substrate 40 has a second surface 40a, which is the surface opposite to the surface facing the base 10, and an opposing surface 40b, which is the surface opposite to the second surface 40a and faces the base 10. The phase difference member 13 is arranged on the second surface 40a. The opposing surface 40b has a recess 42 in which the optical element 41 is housed.

[0041] The optical element 41, like the optical element 30, has a rectangular surface shape and is formed from an inorganic glass material and a light-transmitting member such as silicon dioxide (SiO2). It has a third surface 41a facing the base 20 and a fourth surface 41b facing the bottom surface of the recess 42. The third surface 41a has a second microstructure 43 formed thereon, which has an aberration correction function to correct the aberrations of P-polarized LP and S-polarized LS incident on the second substrate 40. The fourth surface 41b has a third microstructure 44 formed thereon, which has a collimating function to collimate P-polarized LP and S-polarized LS incident on the second substrate 40. The second microstructure 43 and the third microstructure 44 are formed, like the first microstructure 14, by arranging a plurality of columnar microstructures of constant height on the third surface 41a and the fourth surface 41b, respectively. Multiple microstructures that form the second microstructure 43 are also called aberration-correcting metaatoms, and multiple microstructures that form the third microstructure 44 are also called collimated metaatoms.

[0042] Polarization conversion element 4 corrects aberrations and collimates P-polarized LP and S-polarized LS incident on the second substrate 12 by arranging an optical element 41, which has a microstructure having aberration correction and collimation functions, between the first substrate 11 and the second substrate 40. By correcting aberrations and collimating P-polarized LP and S-polarized LS incident on the second substrate 12, polarization conversion element 4 can further improve the optical characteristics of the emitted light L2 compared to polarization conversion element 2.

[0043] (Configuration and function of the polarization conversion element according to the fifth embodiment) Figure 6(a) is a perspective view (1) of the polarization conversion element according to the fifth embodiment, Figure 6(b) is a perspective view (2) of the polarization conversion element according to the fifth embodiment, and Figure 6(c) is a front view of the polarization conversion element according to the fifth embodiment.

[0044] Polarization conversion element 5 differs from polarization conversion element 1 in that it has a first substrate 50 and a phase difference member 51 instead of the first substrate 11 and the phase difference member 13. The configuration and function of the components of polarization conversion element 5 other than the first substrate 50 and the phase difference member 51 are the same as those of the components of polarization conversion element 1 which are given the same reference numerals, so a detailed explanation is omitted here. Polarization conversion element 5 functions like polarization conversion element 1, emitting S-polarized output light L2 in response to incident light L1 which is unpolarized.

[0045] The first substrate 50 has a first microstructure 52 formed on the first surface 50a, which is the surface facing the base 10. Similar to the first microstructure 14, the first microstructure 52 is formed of multiple columnar microstructures of constant height. The first microstructure 52 separates unpolarized incident light incident on the first surface 50a into P-polarized and S-polarized light, and a pair of polarized light whose polarization planes are tilted ±45° with respect to the polarization planes of the respective P-polarized and S-polarized light. The first microstructure 52 is formed to emit the separated P-polarized and S-polarized light, and the pair of polarized light whose polarization planes are tilted ±45° with respect to the polarization planes of the respective P-polarized and S-polarized light, toward the first region 511 to the fourth region 514 of the phase difference member 51.

[0046] The phase difference member 51 comprises a first polarization portion 53, a second polarization portion 54, and a third polarization portion 55, and has a first region 511 located in the second quadrant, a second region 512 located in the third quadrant, a third region 513 located in the fourth quadrant, and a fourth region 514 located in the first quadrant. Each of the first to fourth regions 511 to 514 is arranged two-dimensionally on the second surface 12a. The first polarization portion 53 is located in the first region 511, the first polarization portion 53, the second polarization portion 54, and the third polarization portion 55 are not located in the second region 512, the second polarization portion 54 is located in each of the third regions 513, and the third polarization portion 55 is located in the fourth region 514.

[0047] The first polarization section 53 is a half-wave plate and is positioned in the first region 511 of the phase difference member 51. The first polarization section 53 receives P-polarized light separated from the incident light by the first microstructure 52, rotates the incident P-polarized light by 90°, and emits it as S-polarized light.

[0048] The second polarization section 54 is a Faraday rotator that rotates the polarization plane by 45° and is positioned in the third region 513 of the phase difference member 51. The second polarization section 54 receives light whose polarization plane is tilted by -45° to the polarization plane of S-polarized light separated from the incident light by the first microstructure 52, rotates the incident light by 45°, and emits it as S-polarized light.

[0049] The third polarization section 55 is a Faraday rotator that rotates the polarization plane by -45° and is positioned in the fourth region 514 of the phase difference member 51. The third polarization section 55 receives light whose polarization plane is tilted by 45° to the polarization plane of S-polarized light separated from the incident light by the first microstructure 52, rotates the incident light by -45°, and emits it as S-polarized light.

[0050] Figure 7 shows the polarization state of the polarization conversion element 5.

[0051] Unpolarized incident light L1 is incident on the first surface 11a of the first substrate 11. The incident light L1 incident on the first surface 11a of the first substrate 11 is separated into first polarization LD1, second polarization LD2, third polarization LD3, and fourth polarization LD4 as it passes through a plurality of first microstructures 14 formed on the first surface 11a. The first polarization LD1 is P-polarized, and the second polarization LD2 is S-polarized. The third polarization LD3 is polarized with a polarization plane tilted at -45° with respect to the polarization plane of the second polarization LD2, and the fourth polarization LD4 is polarized with a polarization plane tilted at 45° with respect to the polarization plane of the second polarization LD2.

[0052] The first polarized LD1, which is P-polarized, is incident on the first polarized portion 53 located in the first region 511 of the first microstructure 52 via the base 10 and the second substrate 12. The first polarized LD1, which is P-polarized, is rotated by 90° and polarized to S-polarized as it passes through the first polarized portion 53, and is emitted as S-polarized emitted light L2.

[0053] The second polarized light LD2, which is S-polarized, is incident on the second region 512 of the first polarized portion 53 via the base 10 and the second substrate 12, and is emitted from the second region 512 as S-polarized emitted light L2 without rotation.

[0054] The third polarized light LD3, whose polarization plane is tilted at -45° relative to the polarization plane of the second polarized light LD2, is incident on the second polarized portion 54 located in the third region 513 of the first microstructure 52 via the base 10 and the second substrate 12. The third polarized light LD3 incident on the second polarized portion 54 is rotated by 45° as it passes through the second polarized portion 54, becoming S-polarized, and is emitted as S-polarized light L2.

[0055] The fourth polarized light LD4, whose polarization plane is tilted 45° with respect to the polarization plane of the second polarized light LD2, is incident on the third polarized portion 55 located in the fourth region 514 of the first microstructure 52 via the base 10 and the second substrate 12. The fourth polarized light LD4 incident on the third polarized portion 55 is rotated by -45° as it passes through the third polarized portion 55, becoming S-polarized, and is emitted as S-polarized light L2.

[0056] As S-polarized light L2 is emitted from the first polarization sections 53 to the third polarization sections 55, which are located in the first region 511, the third region 513, and the fourth region 514, and from the second region 512, the emitted light L2 is emitted over the entire surface of the first microstructure 52. Since the emitted light L2 is emitted over the entire surface of the first microstructure 52, the polarization conversion element 5 functions as a polarization conversion element that emits S-polarized emitted light L2 in response to the incidence of unpolarized incident light L1.

[0057] (Modified example of the polarization conversion element according to the embodiment) In polarization conversion elements 1 to 4, no polarizing member is placed in the second region 132 of the phase difference member 13. Also, in polarization conversion element 5, no polarizing member is placed in the second region 512 of the phase difference member 51. However, in the polarization conversion element according to the embodiment, a polarizing member may be placed in the second region of the phase difference member. In the polarization conversion element according to the embodiment, the first and second phase differences provided by the polarizing members placed in the first and second regions are set so that the polarization direction of the first polarization that has passed through the first region is the same as the polarization direction of the second polarization that has passed through the second region. Also, the first, second, third, and fourth phase differences provided by the polarizing members placed in the first to fourth regions are set so that the polarization directions of the polarization that has passed through the first to fourth regions are the same.

[0058] Furthermore, in polarization conversion elements 1 to 4, the first microstructures 14 and 23 are formed to emit P-polarized light into the first region 131 and S-polarized light into the second region 132. However, in the polarization conversion element according to the embodiment, the first microstructure may be formed to emit S-polarized light into the first region 131 and P-polarized light into the second region 132. In the polarization conversion element according to the embodiment, the first microstructure may be formed to separate incident light incident on the first surface into a first polarization and a second polarization having a different polarization direction from the first polarization, and to emit the first polarization toward the first region and the second polarization toward the second region.

[0059] Furthermore, in polarization conversion elements 1 to 4, the first microstructures 14 and 23 are formed to emit P-polarized light into the first region 131 and S-polarized light into the second region 132. However, in the polarization conversion element according to the embodiment, the first microstructure may be formed to emit S-polarized light into the first region 131 and P-polarized light into the second region 132. In the polarization conversion element according to the embodiment, the first microstructure may be formed to separate incident light incident on the first surface into a first polarization and a second polarization having a different polarization direction from the first polarization, and to emit the first polarization toward the first region and the second polarization toward the second region.

[0060] Furthermore, the polarization conversion element 5 is formed to separate the incident light into first polarization, second polarization, third polarization, and fourth polarization, and to emit each of the first to fourth polarizations toward the first region 511 to the fourth region 514. However, in the polarization conversion element according to the embodiment, the first microstructure may be formed to separate the light incident on the first substrate into first polarization, second polarization, third polarization, and fourth polarization, and to emit each of the first to fourth polarizations toward the first region to the fourth region.

[0061] Furthermore, while polarization conversion elements 1 to 4 have a phase difference member 13 equipped with a plurality of half-wave plates 15, in the polarization conversion elements according to the embodiment, the phase difference member does not need to be equipped with a plurality of half-wave plates 15. In the polarization conversion elements according to the embodiment, instead of a plurality of half-wave plates 15, a microstructure having the function of providing a 90° phase difference is formed in the first region of the phase difference member.

[0062] Furthermore, the polarization conversion element 5 has a phase difference member 51 that includes a first polarization portion 53 to a third polarization portion 55. However, in the polarization conversion element according to the embodiment, the phase difference member does not need to include the first polarization portion 53 to the third polarization portion 55. In the polarization conversion element according to the embodiment, the phase difference member may have a microstructure formed in the first region that has the function of providing a phase difference of 90°, and the phase difference member may have microstructures formed in the third and fourth regions that have the function of providing a phase difference of ±45°.

[0063] Furthermore, in the polarization conversion element according to the embodiment, the first microstructure may be formed to emit not only P-polarized light, S-polarized light, and a pair of polarizations whose polarization planes are tilted ±45° with respect to the respective polarization planes of P-polarized and S-polarized light, but also linearly polarized light and left and right circularly polarized light with different polarization plane tilt angles. The polarization conversion element according to the embodiment can improve light utilization efficiency by increasing the number of polarizations emitted from the first microstructure.

[0064] Furthermore, while the polarization conversion elements 1 and 3 have a first substrate 11, the polarization conversion elements according to the embodiment do not necessarily have a first substrate 11. When the polarization conversion elements according to the embodiment do not have a first substrate 11, a first microstructure is formed on the surface of the base 10 opposite to the surface facing the second substrate 12.

[0065] Furthermore, although the polarization conversion element 3 has an optical element 30, the polarization conversion element according to the embodiment does not have to have an optical element 30. When the polarization conversion element according to the embodiment does not have an optical element 30, a second microstructure having the same function as the optical element 30 is formed on the surface of the second substrate 12 facing the base 10.

[0066] Furthermore, in the polarization conversion element 3, the optical element 30 is positioned between the first substrate 11 and the phase difference member 13, and in the polarization conversion element 4, the optical element 41 is positioned between the base 20 and the phase difference member 13. However, in the polarization conversion element according to this embodiment, an optical element having at least one of the aberration correction lens function and the collimator lens function may be positioned at the location where the polarized light transmitted through the phase difference member 13 is incident.

[0067] Furthermore, in the polarization conversion element 4, the optical element 41 is held by being housed in a recess 42 formed in the second substrate 40. However, in the polarization conversion element according to this embodiment, the optical element 41 may be held by a spacer arranged to surround the side surface of the optical element 41. [Explanation of symbols]

[0068] 1 Polarization conversion element 11. First circuit board 12 Second board 13 Phase difference member 14 1st fine structure

Claims

1. The first microstructure formed on the first surface, It has a phase difference member disposed on a second surface which is positioned opposite to the first surface, The phase difference member has a first region that gives a first phase difference to the incident light and a second region that gives a second phase difference different from the first phase difference to the incident light arranged in two dimensions. The first microstructure separates the incident light incident on the first surface into a first polarization and a second polarization having a different polarization direction from the first polarization, and emits the first polarization toward the first region and the second polarization toward the second region. The first phase difference and the second phase difference are set such that the polarization direction of the first polarization that has passed through the first region and the polarization direction of the second polarization that has passed through the second region are the same. A polarization conversion element characterized by the following features.

2. The polarization conversion element according to claim 1, further comprising an optical element having at least one of the functions of an aberration correction lens function and a collimator lens function.

3. The polarization conversion element according to claim 2, wherein the optical element has a third surface on which a second microstructure having one of the functions of an aberration correction lens function and a collimator lens function is formed.

4. The polarization conversion element according to claim 3, wherein the optical element further has a fourth surface on which a third microstructure having the other function of aberration correction lens function and collimator lens function is formed.

5. A first substrate having the first surface, The present invention further comprises a second substrate having the second surface and a third surface facing the second surface, The polarization conversion element according to claim 4, wherein the optical element is disposed between the first substrate and the second substrate.

6. The polarization conversion element according to claim 5, wherein the second surface has a recess formed for housing the optical element.

7. The phase difference member is arranged in two dimensions, comprising: a first region, a second region, a third region that gives a third phase difference to the incident light that is different from the first phase difference and the second phase difference, and a fourth region that gives a fourth phase difference to the incident light that is different from the first to third phase differences. The first microstructure separates the light incident on the first substrate into a first polarization, a second polarization, a third polarization with a different polarization direction from the first and second polarizations, and a fourth polarization with a different polarization direction from the first, second and third polarizations, and emits the first polarization toward the first region, the second polarization toward the second region, the third polarization toward the third region, and the fourth polarization toward the fourth region. The first to fourth phase differences are set such that the polarization direction of the first polarization that has passed through the first region, the polarization direction of the second polarization that has passed through the second region, the polarization direction of the third polarization that has passed through the third region, and the polarization direction of the fourth polarization that has passed through the fourth region are the same. A polarization conversion element according to any one of claims 1 to 6.

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