JP2022020360A - Optical element and method of manufacturing the same - Google Patents

Abstract

To provide a technique reducing variance in retardation of a retardation layer.SOLUTION: An optical element includes a lens having a curved surface and a retardation layer formed on the curved surface of the lens. The retardation layer includes a liquid crystal layer having a slow axis and a fast axis. When viewed from a normal direction at the center of gravity of the curved surface, a division line which divides respective segments connecting the center of gravity and respective points at a peripheral edge of the curved surface in the proportion of 4:1 from the center of gravity to the peripheral edge of the curved surface, a first virtual line parallel with the slow axis passing the center of gravity, and a second virtual line parallel with the fast axis passing the center of gravity are set. When viewed from the normal direction, the first virtual line and the division line cross each other at a first point and a second point, and the second virtual line and the division line cross each other at a third point and a fourth point. The sum of thicknesses of the liquid crystal layer at the third point and the fourth point on the second virtual line is smaller than the sum of thicknesses of the liquid crystal layer at the first point and the second point on the first virtual line.SELECTED DRAWING: Figure 6

Description

The present disclosure relates to an optical element and a method for manufacturing the same.

Patent Document 1 describes a retardation film formed in a curved surface shape. The retardation film is a stretched film. The retardation film is bent at a high temperature and bonded to the curved surface of the lens. The retardation film contains a cycloolefin copolymer (COC) resin or a cycloolefin polymer (COP) resin as a main polymer. A retardation film containing a COC resin or a COP resin has a smaller change in birefringence due to heat and stress than a retardation film containing a polycarbonate (PC) resin.

The retardation layer described in Patent Document 2 is coated on a curved surface. As a coating method, for example, a spin coating method is used. When the retardation layer is coated on the curved surface of the lens, wrinkles can be suppressed and uneven thickness can be suppressed as compared with the case where the retardation film is bonded to the curved surface of the lens.

Japanese Unexamined Patent Publication No. 2012-220853 Japanese Unexamined Patent Publication No. 2012-32527

The optical element includes a lens having a curved surface and a retardation layer formed on the curved surface of the lens.

The present inventor has found a problem that when a retardation layer having a uniform thickness is formed on a curved surface of a lens by an experiment or the like, the variation in retardation of the retardation layer becomes large.

One aspect of the present disclosure provides a technique for reducing variation in retardation of retardation layers.

The optical element according to one aspect of the present disclosure includes a lens having a curved surface and a retardation layer formed on the curved surface of the lens. The retardation layer includes a liquid crystal layer having a slow phase axis and a phase advance axis. When viewed from the normal direction at the center of gravity of the curved surface, it passes through a dividing line that divides each line segment connecting the center of gravity and each point on the peripheral edge of the curved surface from the center of gravity to the peripheral edge of the curved surface at a ratio of 4: 1 and the center of gravity. A first virtual line parallel to the slow axis and a second virtual line parallel to the phase advance axis passing through the center of gravity are set. When viewed from the normal direction, the first virtual line and the dividing line intersect at the first point and the second point, and the second virtual line and the dividing line are the third point and the fourth point. Cross at. The sum of the thicknesses of the liquid crystal layers at the third point and the fourth point on the second virtual line is the sum of the thicknesses of the liquid crystal layers at the first point and the second point on the first virtual line. Thinner than.

According to one aspect of the present disclosure, variation in retardation of the retardation layer can be reduced.

1 (A) is a cross-sectional view perpendicular to the Y-axis direction of the optical element according to the reference embodiment, and FIG. 1 (B) is a cross-sectional view perpendicular to the X-axis direction of the optical element of FIG. 1 (A). 1 (C) is a plan view of the optical element of FIG. 1 (A). FIG. 2 is an enlarged perspective view showing the liquid crystal layer of FIG. 1 (A). 3A is a view of the liquid crystal molecule at the point P101 of FIG. 1 as viewed from the Y-axis direction, and FIG. 3B is a view of the liquid crystal molecule at the point P101 of FIG. 1 as viewed from the X-axis direction. FIG. 4A is a view of the liquid crystal molecule at the point P103 of FIG. 1 as viewed from the Y-axis direction, and FIG. 4B is a view of the liquid crystal molecule at the point P103 of FIG. 1 as viewed from the X-axis direction. FIG. 5 is a diagram showing an example of the relationship between the tilt angle of the flat plate-shaped liquid crystal layer and Rd. 6 (A) is a cross-sectional view perpendicular to the Y-axis direction of the optical element according to the embodiment, and FIG. 6 (B) is a cross-sectional view perpendicular to the X-axis direction of the optical element of FIG. 6 (A). 6 (C) is a plan view of the optical element of FIG. 6 (A). FIG. 7 is a plan view showing the positions of the mask for dry etching and the liquid crystal layer. FIG. 8 is a diagram showing the distribution of Rd on the first virtual line and the second virtual line of the optical element of Example 1. FIG. 9 is a diagram showing the distribution of Rd on the first virtual line and the second virtual line of the optical element of Example 2. FIG. 10 is a diagram showing the distribution of Rd in the region within the dividing line of the optical elements of Examples 1 and 2.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding configurations may be designated by the same reference numerals and description thereof may be omitted. Further, in the specification, "-" indicating a numerical range means that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

First, the optical element 101 according to the reference embodiment will be described mainly with reference to FIG. As shown in FIGS. 1A and 1B, the optical element 101 includes a lens 102. The lens 102 includes a curved surface 102a.

The curved surface 102a is, for example, a concave curved surface. The concave curved surface is a curved surface in which the center of gravity P100 is recessed from the peripheral edge. The center of gravity P100 of the concave curved surface is recessed from the peripheral edge of the concave curved surface regardless of whether the cross section is perpendicular to the X-axis direction or the Y-axis direction. The X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The Z-axis direction is the normal direction at the center of gravity P100 of the concave curved surface. The XY plane is parallel to the tangent plane at the center of gravity P100 of the concave curved surface.

The optical element 101 further includes a retardation layer 103 formed on the curved surface 102a of the lens 102. The retardation layer 103 includes, for example, an alignment layer 104 formed on the lens 102 and a liquid crystal layer 105 formed on the alignment layer 104. However, the alignment layer 104 may not have an arbitrary configuration.

The liquid crystal layer 105 has a slow phase axis and a phase advance axis. In the Z-axis direction, the slow-phase axis is the X-axis direction and the phase-advance axis is the Y-axis direction. The slow axis is the direction with the highest refractive index, and the phase advance axis is the direction with the lowest refractive index.

As shown in FIG. 2, the liquid crystal layer 105 contains a plurality of liquid crystal molecules 105a parallel to each other. In the Z-axis direction, the major axis direction of the liquid crystal molecule 105a is the X-axis direction, and the minor axis direction of the liquid crystal molecule 105a is the Y-axis direction.

The present inventor has found a problem that when a liquid crystal layer 105 having a uniform thickness is formed on a curved surface 102a of a lens 102 by an experiment or the like, the variation of the retardation Rd of the liquid crystal layer 105 becomes large.

Rd is the product of the difference Δn (Δn = ne-no) between the refractive index ne of the slow phase axis and the refractive index no of the phase advance axis and the dimension d in the Z-axis direction of the liquid crystal layer 105. That is, Rd is obtained from the equation of Rd = Δn × d.

The reason why the above problem occurs when the thickness of the liquid crystal layer 105 is uniform will be described. As shown in FIGS. 1A and 1B, the liquid crystal layer 105 is formed on the curved surface 102a of the lens 102. As a result, the liquid crystal molecule 105a is tilted with respect to the XY plane at a position away from the center of gravity P100 of the curved surface 102a.

The inclination of the liquid crystal molecule 105a is different between the points P101 and P102 on the first virtual line L101 and the points P103 and P104 on the second virtual line L102 shown in FIG. 1 (C). In the Z-axis direction view, the first virtual line L101 is a virtual line that passes through the center of gravity P100 and is parallel to the slow phase axis. Further, in the Z-axis direction view, the second virtual line L102 is a virtual line that passes through the center of gravity P100 and is parallel to the phase advance axis.

FIG. 3 shows the inclination of the liquid crystal molecule 105a at the point P101 on the first virtual line L101. In FIG. 3, the broken line indicates the liquid crystal molecule 105a at the center of gravity P100, and the solid line indicates the liquid crystal molecule 105a at the point P101. As is clear from FIG. 3, at the point P101, the X-axis direction dimension of the liquid crystal molecule 105a is smaller than that of the center of gravity P100, whereas the Y-axis direction dimension of the liquid crystal molecule 105a does not change. The same applies to the point P102.

As a result, at the points P101 and P102 on the first virtual line L101, ne is smaller and no is unchanged as compared with the center of gravity P100, so that Δn is smaller. Further, at points P101 and P102, d is larger than that of the center of gravity P100. The decrease in Rd due to the decrease in Δn is larger than the increase in Rd due to the increase in d. As a result, at points P101 and P102, Rd, which is the product of Δn and d, is smaller than that of the center of gravity P100.

FIG. 4 shows the inclination of the liquid crystal molecule 105a at the point P103 on the second virtual line L102. In FIG. 4, the broken line indicates the liquid crystal molecule 105a at the center of gravity P100, and the solid line indicates the liquid crystal molecule 105a at the point P103. As is clear from FIG. 4, at the point P103, the Y-axis direction dimension of the liquid crystal molecule 105a is slightly smaller than that of the center of gravity P100, whereas the X-axis direction dimension of the liquid crystal molecule 105a does not change. The same applies to the point P104.

As a result, at the points P103 and P104 on the second virtual line L102, no is smaller and ne does not change as compared with the center of gravity P100, so Δn becomes larger. Further, at points P103 and P104, d is larger than that of the center of gravity P100. Therefore, at points P103 and P104, Rd is larger than that of the center of gravity P100.

FIG. 5 shows an example of the relationship between the tilt angle of the flat plate-shaped liquid crystal layer and the measured value of Rd. In FIG. 5, the inclination angle of 0 ° means that the flat plate-shaped liquid crystal layer is oriented parallel to the XY plane.

The black circles in FIG. 5 are data in which the flat plate-shaped liquid crystal layer is rotated clockwise and counterclockwise around the second virtual line L102 and tilted. A positive tilt angle means that the direction of rotation is clockwise. Further, a negative tilt angle means that the rotation direction is counterclockwise.

The absolute value of the horizontal axis of the inclination angle of the black circle in FIG. 5 corresponds to the distance between the points P101 and P102 on the first virtual line L101 and the center of gravity P100. The larger the distance between the points P101 and P102 and the center of gravity P100, the larger the absolute value of the inclination angle of the liquid crystal molecule 105a and the smaller Rd.

On the other hand, the white circles in FIG. 5 are data in which the flat plate-shaped liquid crystal layer is rotated clockwise and counterclockwise around the first virtual line L101 and tilted. A positive tilt angle means that the direction of rotation is clockwise. Further, a negative tilt angle means that the rotation direction is counterclockwise.

The absolute value of the horizontal axis of the inclination angle of the white circle in FIG. 5 corresponds to the distance between the points P103 and P104 on the second virtual line L102 and the center of gravity P100. The larger the distance between the points P103 and P104 and the center of gravity P100, the larger the absolute value of the inclination angle of the liquid crystal molecule 105a and the larger Rd.

As is clear from comparing the black circles and the white circles in FIG. 5, the tendency of the change of Rd is different between the first virtual line L101 and the second virtual line L102. On the first virtual line L101, the larger the distance from the center of gravity P100, the smaller the Rd. On the other hand, on the second virtual line L102, the larger the distance from the center of gravity P100, the larger the Rd.

The curved surface 102a of the lens 102 is a concave curved surface in this reference embodiment, but may be a convex curved surface. The convex curved surface is a curved surface in which the center of gravity P100 is convex (protruding) from the peripheral edge. The center of gravity P100 of the convex curved surface is more convex than the peripheral edge of the convex curved surface regardless of whether the cross section is perpendicular to the X-axis direction or the Y-axis direction.

The absolute value of the inclination angle of the liquid crystal molecule 105a is about the same between the convex curved surface and the concave curved surface. Therefore, the distribution of Rd is about the same on the convex curved surface and the concave curved surface.

Next, the optical element 1 according to the present embodiment will be described with reference to FIG. As shown in FIGS. 6A and 6B, the optical element 1 includes a lens 2. The lens 2 includes a curved surface 2a. The curved surface 2a is, for example, a concave curved surface. The concave curved surface is a curved surface in which the center of gravity P0 is recessed from the peripheral edge. The center of gravity P0 of the concave curved surface is recessed from the peripheral edge of the concave curved surface regardless of whether the cross section is perpendicular to the X-axis direction or the Y-axis direction.

The optical element 1 further includes a retardation layer 3 formed on the curved surface 2a of the lens 2. The retardation layer 3 includes, for example, an alignment layer 4 formed on the lens 2 and a liquid crystal layer 5 formed on the alignment layer 4. However, the alignment layer 4 may not have an arbitrary structure.

The liquid crystal layer 5 has a slow phase axis and a phase advance axis. In the Z-axis direction, the slow-phase axis is the X-axis direction and the phase-advance axis is the Y-axis direction. The slow axis is the direction with the highest refractive index, and the phase advance axis is the direction with the lowest refractive index. The X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The Z-axis direction is the normal direction at the center of gravity P0 of the concave curved surface. The XY plane is parallel to the tangent plane at the center of gravity P0 of the concave curved surface.

As shown in FIG. 6C, in the Z-axis direction view, the first virtual line L1 is a virtual line that passes through the center of gravity P0 and is parallel to the slow phase axis. Further, in the Z-axis direction view, the second virtual line L2 is a virtual line that passes through the center of gravity P0 and is parallel to the phase advance axis.

In the Z-axis direction view, the dividing line L3 divides each line segment connecting the center of gravity P0 and each point on the peripheral edge of the curved surface 2a at a ratio of 4: 1 from the center of gravity P0 side to the peripheral edge of the curved surface 2a. Further, in the Z-axis direction view, the first virtual line L1 and the dividing line L3 intersect at the first point P1 and the second point P2, and the second virtual line L2 and the dividing line L3 are the third point P3 and the third point P3. It intersects with 4 points P4.

The distance between the first point P1 and the center of gravity P0 is 0.8 times that of X1. X1 is the distance between the center of gravity P0 and the intersection of the straight line extending in the positive direction of the X-axis from the center of gravity P0 and the peripheral edge of the curved surface 2a. The distance between the second point P2 and the center of gravity P0 is 0.8 times that of X2. X2 is the distance between the center of gravity P0 and the intersection of the straight line extending from the center of gravity P0 in the negative direction of the X axis and the peripheral edge of the curved surface 2a.

The distance between the third point P3 and the center of gravity P0 is 0.8 times that of Y1. Y1 is the distance between the center of gravity P0 and the intersection of the straight line extending in the positive direction of the Y axis from the center of gravity P0 and the peripheral edge of the curved surface 2a. The distance between the fourth point P4 and the center of gravity P0 is 0.8 times that of Y2. Y2 is the distance between the center of gravity P0 and the intersection of the straight line extending from the center of gravity P0 in the negative direction of the Y axis and the peripheral edge of the curved surface 2a.

According to the present embodiment, the sum of the thicknesses ty1 and ty2 of the liquid crystal layer 5 at the third point P3 and the fourth point P4 on the second virtual line L2 is the first point P1 and the first on the first virtual line L1. It is smaller than the sum of the thicknesses tx1 and tx2 of the liquid crystal layer 5 at the two points P2. That is, the following equation (1) holds.

上記式（１）が成立すれば、重心Ｐ０から離れた位置でのＲｄの差（図５の黒丸と白丸の差）を低減できる。Ｒｄの差が小さくなるように、液晶層５の厚みに差が付けられるからである。従って、色調のムラを抑制できる。

If the above equation (1) is established, the difference in Rd (difference between the black circle and the white circle in FIG. 5) at a position away from the center of gravity P0 can be reduced. This is because the thickness of the liquid crystal layer 5 is different so that the difference in Rd is small. Therefore, unevenness in color tone can be suppressed.

The thickness of the liquid crystal layer 5 is measured in the normal direction at each point of the curved surface 2a of the lens 2. The thickness of the liquid crystal layer 5 is calculated, for example, from spectroscopic interference or from a photograph of a scanning electron microscope (SEM).

In addition to the above formula (1), the following formula (2) is preferably established.

上記式（２）が成立すれば、上記式（１）のみが成立する場合に比べて、液晶層５のＲｄのムラがより小さくなる。従って、色調のムラをより抑制できる。（ｔｙ１＋ｔｙ２）／（ｔｘ１＋ｔｘ２）は、好ましくは０．８０よりも大きく、より好ましくは０．８５よりも大きい。また、（ｔｙ１＋ｔｙ２）／（ｔｘ１＋ｔｘ２）は、好ましくは０．９９よりも小さく、より好ましくは０．９８よりも小さい。

If the above formula (2) is satisfied, the unevenness of Rd of the liquid crystal layer 5 becomes smaller than that in the case where only the above formula (1) is satisfied. Therefore, unevenness in color tone can be further suppressed. (Ty1 + ty2) / (tx1 + tx2) is preferably greater than 0.80, more preferably greater than 0.85. Further, (ty1 + ty2) / (tx1 + tx2) is preferably smaller than 0.99, more preferably smaller than 0.98.

Further, in addition to the above formula (1), the following formula (3) is preferably established.

上記式（３）が成立すれば、上記式（１）のみが成立する場合に比べて、液晶層５のＲｄのムラがより小さくなる。従って、色調のムラをより抑制できる。

If the above formula (3) is satisfied, the unevenness of Rd of the liquid crystal layer 5 becomes smaller than that in the case where only the above formula (1) is satisfied. Therefore, unevenness in color tone can be further suppressed.

Further, in addition to the above formula (3), the following formula (4) is preferably established.

上記式（４）が成立すれば、上記式（３）のみが成立する場合に比べて、液晶層５のＲｄのムラがより小さくなる。従って、色調のムラをより抑制できる。ｔｙ１／ｔｘ１、ｔｙ１／ｔｘ２、ｔｙ２／ｔｘ１及びｔｙ２／ｔｘ２は、それぞれ、好ましくは０．８０よりも大きく、より好ましくは０．８５よりも大きい。である。また、ｔｙ１／ｔｘ１、ｔｙ１／ｔｘ２、ｔｙ２／ｔｘ１及びｔｙ２／ｔｘ２は、それぞれ、好ましくは０．９９よりも小さく、より好ましくは０．９８よりも小さい。

If the above formula (4) is satisfied, the unevenness of Rd of the liquid crystal layer 5 becomes smaller than that in the case where only the above formula (3) is satisfied. Therefore, unevenness in color tone can be further suppressed. ty1 / tx1, ty1 / tx2, ty2 / tx1 and ty2 / tx2 are each preferably greater than 0.80 and more preferably greater than 0.85, respectively. Is. Further, ty1 / tx1, ty1 / tx2, ty2 / tx1 and ty2 / tx2 are each preferably smaller than 0.99 and more preferably smaller than 0.98, respectively.

Further, according to the present embodiment, the thicknesses tx1 and tx2 of the liquid crystal layer 5 at the first point P1 and the second point P2 on the first virtual line L1 are thicker than the thickness to of the liquid crystal layer 5 at the center of gravity P0. .. That is, the following equation (5) holds.

上記式（５）が成立すれば、第１仮想線Ｌ１上でのＲｄのムラ（図５の黒丸の上下動）を低減できる。第１仮想線Ｌ１上でのＲｄの差が小さくなるように、ｔｘ１、ｔｘ２と、ｔｏと、に差が付けられるからである。従って、色調のムラを抑制できる。

If the above equation (5) is satisfied, the unevenness of Rd (vertical movement of the black circle in FIG. 5) on the first virtual line L1 can be reduced. This is because the difference between tx1, tx2, and to is added so that the difference in Rd on the first virtual line L1 becomes small. Therefore, unevenness in color tone can be suppressed.

Further, in addition to the above formula (5), the following formula (6) is preferably established.

If the above formula (6) is satisfied, the unevenness of Rd of the liquid crystal layer 5 becomes smaller than that in the case where only the above formula (5) is satisfied. Therefore, unevenness in color tone can be further suppressed. To / tx1 and to / tx2 are each preferably greater than 0.80 and more preferably greater than 0.85, respectively. Further, to / tx1 and to / tx2 are each preferably smaller than 0.99 and more preferably smaller than 0.98, respectively.

Further, according to the present embodiment, the thicknesses ty1 and ty2 of the liquid crystal layer 5 at the third point P3 and the fourth point P4 on the second virtual line L2 are thinner than the thickness to of the liquid crystal layer 5 at the center of gravity P0. .. That is, the following equation (7) holds.

上記式（７）が成立すれば、第２仮想線Ｌ２上でのＲｄのムラ（図５の白丸の上下動）を低減できる。第２仮想線Ｌ２上でのＲｄの差が小さくなるように、ｔｙ１、ｔｙ２と、ｔｏと、に差が付けられるからである。従って、色調のムラを抑制できる。

If the above equation (7) is satisfied, the unevenness of Rd (vertical movement of the white circle in FIG. 5) on the second virtual line L2 can be reduced. This is because the difference between ty1, ty2, and to is added so that the difference in Rd on the second virtual line L2 becomes small. Therefore, unevenness in color tone can be suppressed.

Further, in addition to the above formula (7), the following formula (8) is preferably established.

上記式（８）が成立すれば、上記式（７）のみが成立する場合に比べて、液晶層５のＲｄのムラがより小さくなる。従って、色調のムラをより抑制できる。ｔｙ１／ｔｏ及びｔｙ２／ｔｏは、それぞれ、好ましくは０．８０よりも大きく、より好ましくは０．８５よりも大きい。また、上記式（８）において、ｔｙ１／ｔｏ及びｔｙ２／ｔｏは、それぞれ、好ましくは０．９９よりも小さく、より好ましくは０．９８よりも小さい。

If the above formula (8) is satisfied, the unevenness of Rd of the liquid crystal layer 5 becomes smaller than that in the case where only the above formula (7) is satisfied. Therefore, unevenness in color tone can be further suppressed. ty1 / to and ty2 / to are each preferably greater than 0.80 and more preferably greater than 0.85, respectively. Further, in the above formula (8), ty1 / to and ty2 / to are each preferably smaller than 0.99, more preferably smaller than 0.98, respectively.

Further, according to the present embodiment, the standard deviation σ of Rd of the light (wavelength 543 nm) parallel to the Z-axis direction in the region (including the dividing line L3) in the dividing line L3 is 3.0 nm or less. That is, the following equation (9) holds.

標準偏差σが３．０ｎｍ以下であると、分割線Ｌ３内の領域でのＲｄのムラを低減できる。なお、分割線Ｌ３内の領域におけるＲｄの測定点は、Ｐ１、Ｐ２、Ｐ３及びＰ４を含み、合計１００点以上設定される。標準偏差σは、例えば０．０ｎｍ～３．０ｎｍであり、好ましくは０．０ｎｍ～２．０ｎｍである。

When the standard deviation σ is 3.0 nm or less, the unevenness of Rd in the region within the dividing line L3 can be reduced. The measurement points of Rd in the region within the dividing line L3 include P1, P2, P3 and P4, and a total of 100 points or more are set. The standard deviation σ is, for example, 0.0 nm to 3.0 nm, preferably 0.0 nm to 2.0 nm.

The curved surface 2a of the lens 2 is a concave curved surface in the present embodiment, but may be a convex curved surface. The convex curved surface is a curved surface in which the center of gravity P0 is more convex than the peripheral edge. The center of gravity P0 of the convex curved surface is more convex than the peripheral edge of the convex curved surface regardless of whether the cross section is perpendicular to the X-axis direction or the Y-axis direction.

The absolute value of the tilt angle of the liquid crystal molecule has the same tendency between the convex curved surface and the concave curved surface. Therefore, even if the curved surface 2a is a convex curved surface, the above equation (1) may be satisfied. Further, even if the curved surface 2a is a convex curved surface, it is preferable that one or more of the above equations (2) to (9) is satisfied.

Next, the optical element 1 will be described with reference to FIG. 6 and the like again. The lens 2 included in the optical element 1 is desired to have a curved surface 2a from the viewpoint of performance depending on the application.

The lens 2 may be a spherical lens or an aspherical lens. Further, the lens 2 may be any of a biconcave lens, a plano-concave lens, a concave meniscus lens, a biconvex lens, a plano-convex lens, and a convex meniscus lens. The lens 2 may have a curved surface 2a.

The outer shape of the lens 2 is not limited to the circle shown in FIG. 6C, and may be, for example, an ellipse or a polygon. The above equation (1) may be satisfied regardless of the outer shape of the lens 2. Further, it is preferable that one or more of the above equations (2) to (9) is satisfied regardless of the outer shape of the lens 2.

The material of the lens 2 may be resin or glass. The resin of the resin lens is, for example, polycarbonate, polyimide, polyacrylate, or cyclic olefin. The glass of the glass lens is, for example, BK7, synthetic quartz.

The retardation layer 3 is, for example, a 1/4 wave plate. A 1/4 wave plate and a linear polarizing plate (not shown) may be used in combination. The absorption axis of the linear polarizing plate and the slow axis of the 1/4 wave plate are offset by 45 °. A circular polarizing plate is composed of a linear polarizing plate and a 1/4 wave plate.

The linear polarizing plate may be arranged on the side opposite to the lens 2 with respect to the retardation layer 3, may be arranged between the retardation layer 3 and the lens 2, or may be arranged with the lens 2 as a reference. It may be arranged on the opposite side of the retardation layer 3.

Although not shown, the retardation layer 3 may be a broadband retardation layer further including a second liquid crystal layer laminated on the liquid crystal layer 5. In the second liquid crystal layer, the above formula (1) may or may not hold, but the above formula (1) preferably holds. The above equations (2) to (9) are also the same as the above equation (1).

The number of liquid crystal layers included in the broadband retardation layer may be two or more, and may be three or more. In Z-axis orientation, the plurality of liquid crystal layers have slow axes in different orientations from each other. The above formula (1) may be satisfied with at least one liquid crystal layer. Preferably, the above formula (1) is established in all the liquid crystal layers. The above equations (2) to (9) are also the same as the above equation (1).

The broadband retardation layer is, for example, an alignment layer 4 and a liquid crystal layer 5 alternately laminated. From the lens 2 side, the alignment layer 4 and the liquid crystal layer 5 are laminated in this order. The liquid crystal layer formed on the transparent base material different from the lens 2 and the liquid crystal layer formed on the lens 2 may be bonded to each other to form a broadband retardation layer.

The alignment layer 4 aligns the liquid crystal molecules of the liquid crystal layer 5. The alignment layer 4 is formed by, for example, rubbing of polyimide, photodecomposition of a silane coupling agent or polyimide by irradiation with polarized UV, utilization of photodimerization or photoisomerization by irradiation with polarized UV, flow alignment treatment by shearing force, or diagonal vapor deposition of an inorganic substance. It has been subjected to treatment such as alignment treatment. Multiple processes may be used in combination. Among these, the use of photodimerization or photoisomerization by polarized UV irradiation is preferable from the viewpoint of orientation control force, applicability to curved surfaces, and reduction of foreign substances.

Coumarin, diphenylacetylene, or anthracene is used as a material that causes photodimerization by polarized UV irradiation. As a material that causes photoisomerization by polarized UV irradiation, azobenzene, stilbene, α-imino-β ketoester, or spiropyran is used. As a material that causes both photodimerization and photoisomerization by polarized UV irradiation, cinnamate, chalcone, or stillbazole is used.

The alignment layer 4 is coated on the curved surface 2a of the lens 2. The coating method is, for example, spin coat method, bar coat method, dip coat method, cast method, spray coat method, bead coat method, wire bar coat method, blade coat method, roller coat method, curtain coat method, slit die coat method. , Gravure coat method, slit reverse coat method, micro gravure method, comma coat method and the like. The resin composition is applied to the curved surface 2a of the lens 2 and dried. The solvent of the resin composition is removed by heating after coating. The coating method may be a vapor deposition method that does not use a solvent.

The thickness of the alignment layer 4 is, for example, 1 nm to 10 μm, preferably 10 nm to 5 μm, and more preferably 50 nm to 2 μm. The thickness of the alignment layer 4 is measured in the normal direction at each point of the curved surface 2a of the lens 2, similarly to the thickness of the liquid crystal layer 5.

As described above, the alignment layer 4 has an arbitrary structure and may be omitted. In that case, the curved surface 2a of the lens 2 may be subjected to a treatment for orienting the liquid crystal molecules of the liquid crystal layer 5.

The liquid crystal layer 5 contains a plurality of liquid crystal molecules oriented in parallel with each other, similarly to the liquid crystal layer 105 shown in FIG. In the Z-axis direction, the long-axis direction of the liquid crystal molecules is the X-axis direction, and the short-axis direction of the liquid crystal molecules is the Y-axis direction. The liquid crystal molecule is a rod-shaped liquid crystal in this embodiment, but may be a discotic liquid crystal.

The liquid crystal layer 5 contains an energy curable resin such as a photocurable resin or a thermosetting resin. The liquid crystal layer 5 is formed by applying and drying the liquid crystal composition. The liquid crystal composition is, for example, a photocurable polymer liquid crystal containing an acrylic group or a methacrylic group. The liquid crystal composition may be composed of a component that does not exhibit a liquid crystal phase by itself. It suffices if the liquid crystal phase is generated by the polymerization. The polymerizable liquid crystal composition may contain additives. As the additive, a polymerization initiator, a leveling agent, a polymerization inhibitor, a chiral agent, an ultraviolet absorber, an antioxidant, a light stabilizer, a dichroic dye or the like is used. A plurality of types of additives may be used in combination.

The method of applying the liquid crystal composition may be a general one. The method for applying the liquid crystal composition is, for example, a spin coating method, a bar coating method, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method, or the like. The solvent of the liquid crystal composition is removed by heating after coating.

The solvent of the liquid crystal composition is, for example, an organic solvent. Organic solvents include amides (eg N, N-dimethylformamide), sulfoxides (eg dimethyl sulfoxides), hydrocarbons (eg benzene or hexanes), esters (eg methyl acetate, ethyl acetate, butyl acetate, or propylene glycol monoethyl). Ether acetate), ketones (eg acetone, or methyl ethyl ketone), or ethers (eg tetrahydrofuran, or 1,2-dimethoxyethane). Two or more kinds of organic solvents may be used together. The liquid crystal layer 5 may be formed by a vapor deposition method or a vacuum injection method that does not use a solvent.

The thickness of the liquid crystal layer 5 is determined based on the wavelength of light, the phase difference, and Δn (Δn = ne-no). For example, when the wavelength of light is 543 nm and the phase difference is 1/4 wavelength, Rd is 136 nm. When Rd is 136 nm and Δn is 0.1, the thickness of the liquid crystal layer 5 is 1360 nm.

As described above, the thickness of the liquid crystal layer 5 is determined based on the wavelength of light, the phase difference, and Δn, and is not particularly limited, but is, for example, 0.1 μm to 20 μm, preferably 0.2 μm to 10 μm, more preferably. Is 0.5 μm to 5 μm. The liquid crystal layer 5 is not limited to the 1/4 wave plate, and may be a 1/2 wave plate or the like.

By the way, in the present embodiment, as described above, the thickness of the liquid crystal layer 5 satisfies at least the formula (1). That is, the sum of the thicknesses ty1 and ty2 of the liquid crystal layer 5 at the third point P3 and the fourth point P4 on the second virtual line L2 is the sum of the first point P1 and the second point P2 on the first virtual line L1. It is smaller than the sum of the thicknesses tx1 and tx2 of the liquid crystal layer 5.

The thickness of the liquid crystal layer 5 is adjusted by, for example, a dry etching method. As the dry etching method, for example, a plasma etching method is used. In the plasma etching method, an exposed portion of the liquid crystal layer 5 is etched with plasma such as oxygen using a mask that covers a part of the liquid crystal layer 5.

As shown in FIG. 7, the mask M covers, for example, the first point P1 and the second point P2 on the first virtual line L1. The third point P3 and the fourth point P4 on the second virtual line L2 are exposed from the mask M. If the liquid crystal layer 5 is etched in this state, the sum of ty1 and ty2 becomes smaller than the sum of tx1 and tx2. A plurality of masks M having different sizes may be used in order so that the change in the thickness of the liquid crystal layer 5 becomes smooth.

In the plasma etching method, for example, a RIE (Reactive Ion Etching) apparatus is used. The gas used to generate the plasma contains, for example, oxygen gas, and may further contain a halogen-containing gas such as CF ₄ or CCl ₄ in addition to the oxygen gas. The etching amount can be controlled by the etching time, gas flow rate, and the like.

Although not shown, the optical element 1 may further include a protective layer such as a hard coat layer or an antifouling layer. The protective layer protects the retardation layer 3 and is arranged on the side opposite to the lens 2 with the retardation layer 3 as a reference.

The experimental data will be described below. Example 1 below is an example, and Example 2 below is a comparative example.

[Example 1]
In Example 1, an optical element composed of a lens, an alignment layer, and a liquid crystal layer was produced. As a lens, a plano-concave lens (manufactured by Edmond Optics, product code # 45-038) was prepared. The diameter of this lens was 50 mm.

As the alignment layer, a photoalignment film that exerts an orientation regulating force by irradiation with polarized UV was used. A solution containing the material of the photoalignment film was applied to the concave curved surface of the plano-concave lens with a spin coater. Drying after application was carried out at 100 ° C. for 10 minutes. After drying, the surface of the alignment layer was irradiated with light of 240 mW / cm ² using a polarization exposure apparatus (HC-1001 manufactured by Yamashita Denso Co., Ltd.) to impart an orientation regulating force. The thickness of the oriented layer was about 0.1 μm.

The liquid crystal layer was formed by applying and drying the liquid crystal composition. As the liquid crystal composition, a photopolymerization initiator (BASF, Darocure TPO) and a leveling agent were added to an ultraviolet curable liquid crystal (BASF, LC242) and dissolved in ethyl acetate. The liquid crystal composition was applied onto the alignment layer with a spin coater. Drying after application was carried out at 100 ° C. for 10 minutes. After drying, the liquid crystal composition was cured by irradiating with light of 3000 mW / cm ² using an ultraviolet irradiation device (LC6 manufactured by Hamamatsu Photonics Co., Ltd.).

The thickness of the liquid crystal layer was adjusted by a dry etching method. As the mask, a glass plate of borosilicate glass (manufactured by Schott AG, D263) was used. The glass plate was placed on the liquid crystal layer as shown in FIG. The glass plate had a Y-axis direction dimension of 35 mm, an X-axis direction dimension of 76 mm, and a Z-axis direction dimension (thickness) of 0.5 mm. As the etching apparatus, a reactive ion etching apparatus (RIE-10NR manufactured by SAMCO) was used. The flow rate of oxygen gas was 20 sccm, the atmospheric pressure was 5.3 Pa, and the etching time was 20 seconds.

[Example 2]
In Example 2, the optical element was manufactured under the same conditions as in Example 1 except that the dry etching of the liquid crystal layer was omitted.

[evaluation]
(1. Thickness of liquid crystal layer)
The thickness of the liquid crystal layer is determined by using a near-infrared microspectroscopy measuring device (USPM-RU-W manufactured by Olympus Co., Ltd.) to reflect light reflected at the interface between air and the liquid crystal layer and the interface between the liquid crystal layer and the alignment layer. It was measured from the waveform of the interference wave with the light reflected by. In this measurement, the refractive index of the liquid crystal layer was set to 1.56.

Table 1 shows the measurement results of the thickness of the liquid crystal layer.

表１から明らかなように、例１では、液晶層のドライエッチングを実施したので、上記式（１）～（４）が成立した。一方、例２では、液晶層のドライエッチングを省略したので、上記式（１）～（４）が成立しなかった。

As is clear from Table 1, in Example 1, since the liquid crystal layer was dry-etched, the above formulas (1) to (4) were established. On the other hand, in Example 2, since the dry etching of the liquid crystal layer was omitted, the above equations (1) to (4) did not hold.

In Example 2, tx1, tx2, ty1, and ty2 were substantially the same and greater than to. The thickness of the liquid crystal layer before dry etching mainly depended on the distance from the center of gravity P0 of the concave curved surface, and did not depend on the orientation from the center of gravity P0.

The farther the concave curved surface is from the center of gravity P0, the thicker the liquid crystal layer before dry etching. This is because, at a position where the concave curved surface is far from the center of gravity P0, the gradient is steep, the liquid crystal composition tries to crawl up against gravity, and the flow of the liquid crystal composition is hindered.

The distribution of the thickness of the liquid crystal layer before dry etching is determined by the gradient of the concave curved surface, the viscosity of the liquid crystal composition, the concentration of the solid content, the boiling point of the solvent, the rotation speed of the spin coat, and the like. Incidentally, in Examples 1 and 2, the inclination angles at the measurement points of tx1, tx2, ty1 and ty2 were about 20 °.

The thickness of the liquid crystal layer can also be measured using a scanning electron microscope (SEM). The SEM sample is prepared by cutting an optical element with the first virtual line L1 and the second virtual line L2 shown in FIG. 6 (C). The thickness of the liquid crystal layer can be measured by using the SEM photograph of the cut surface.

(2. Rd of liquid crystal layer)
The Rd of the liquid crystal layer was collectively measured on the entire curved surface 2a using a two-dimensional birefringence rate evaluation device (WPA-200, manufactured by Photonic Lattice). The wavelength of light used for the measurement of Rd was 543 nm.

FIG. 8 shows Rd on the first virtual line L1 and the second virtual line L2 of the optical element of Example 1. In FIG. 8, black circles indicate the measured values of Rd on the first virtual line L1, and white circles indicate the measured values of Rd on the second virtual line L2. As is clear from FIG. 8, in the optical element of Example 1, the distribution of Rd was uniform on both the first virtual line L1 and the second virtual line L2.

FIG. 9 shows Rd on the first virtual line L1 and the second virtual line L2 of the optical element of Example 2. In FIG. 9, black circles indicate the measured values of Rd on the first virtual line L1, and white circles indicate the measured values of Rd on the second virtual line L2. As is clear from FIG. 9, in the optical element of Example 2, the distribution of Rd was uniform on the first virtual line L1, but the distribution of Rd was non-uniform on the second virtual line L2.

FIG. 10 shows the distribution of Rd in the region in the dividing line L3 of the optical elements of Examples 1 and 2. In each example, the measurement points of Rd are about 16000 points. In Example 1, since the liquid crystal layer was dry-etched, the standard deviation σ of Rd was 1.7 nm, and the above formula (9) was established. On the other hand, in Example 2, since the dry etching of the liquid crystal layer was omitted, the standard deviation σ of Rd was 3.4 nm, and the above formula (9) did not hold.

Although the optical element and the method for manufacturing the optical element according to the present disclosure have been described above, the present disclosure is not limited to the above-described embodiment and the like. Various changes, modifications, replacements, additions, deletions, and combinations are possible within the scope of the claims. Of course, they also belong to the technical scope of the present disclosure.

1 Optical element 2 Lens 2a Curved surface 3 Phase difference layer 5 Liquid crystal layer L1 First virtual line L2 Second virtual line L3 Dividing line P0 Center of gravity P1 First point P2 Second point P3 Third point P4 Fourth point

Claims (9)

A lens with a curved surface and
Including a retardation layer formed on the curved surface of the lens.
The retardation layer includes a liquid crystal layer having a slow phase axis and a phase advance axis.
When viewed from the normal direction at the center of gravity of the curved surface, it passes through a dividing line that divides each line segment connecting the center of gravity and each point on the peripheral edge of the curved surface from the center of gravity to the peripheral edge of the curved surface at a ratio of 4: 1 and the center of gravity. A first virtual line parallel to the slow axis and a second virtual line parallel to the phase advance axis passing through the center of gravity are set.
When viewed from the normal direction, the first virtual line and the dividing line intersect at the first point and the second point, and the second virtual line and the dividing line are the third point and the fourth point. Cross at
The sum of the thicknesses of the liquid crystal layers at the third point and the fourth point on the second virtual line is the sum of the thicknesses of the liquid crystal layers at the first point and the second point on the first virtual line. Smaller than an optical element. The thickness of the liquid crystal layer at the third point and the fourth point on the second virtual line is smaller than the thickness of the liquid crystal layer at the first point and the second point on the first virtual line. The optical element according to claim 1. The optical element according to claim 1 or 2, wherein the thickness of the liquid crystal layer at the first point and the second point on the first virtual line is thicker than the thickness of the liquid crystal layer at the center of gravity. The optical element according to any one of claims 1 to 3, wherein the standard deviation of the retardation of light parallel to the normal direction (wavelength 543 nm) in the region within the dividing line is 3.0 nm or less. The optical element according to any one of claims 1 to 4, wherein the retardation layer is a 1/4 wave plate. The optical element according to any one of claims 1 to 5, wherein the retardation layer is a broadband retardation layer further including a second liquid crystal layer laminated on the liquid crystal layer. The optical element according to any one of claims 1 to 6, wherein the liquid crystal layer contains an energy curable resin. The optical element according to any one of claims 1 to 7, wherein the retardation layer further includes an alignment layer for orienting liquid crystal molecules contained in the liquid crystal layer between the lens and the liquid crystal layer. The manufacturing method for manufacturing the optical element according to any one of claims 1 to 8.
By applying the liquid crystal composition on the curved surface of the lens to form the liquid crystal layer,
The liquid crystal layer is dry-etched, and the thickness of the liquid crystal layer at the third point and the fourth point on the second virtual line is measured by the first point and the second point on the first virtual line. To make it thinner than the thickness of the liquid crystal layer,
A method for manufacturing an optical element, including.

Images