CN111448484A

CN111448484A - Compound lens

Info

Publication number: CN111448484A
Application number: CN201880079692.XA
Authority: CN
Inventors: 石井太
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2017-12-22
Filing date: 2018-06-19
Publication date: 2020-07-24
Also published as: WO2019123689A1

Abstract

The invention provides a compound lens which has excellent tolerance and can inhibit the influence of birefringence. A compound lens (1) is provided with: a first lens (10) having a first curved surface section (12) and a first flat surface section (14) facing the first curved surface section (12), and being formed of a uniaxial crystal; and a second lens (20) which has a second curved surface section (22) and a second flat surface section (24) facing the second curved surface section (22), and which is formed of a uniaxial crystal, wherein the first lens (10) and the second lens (20) are arranged such that the first flat surface section (14) and the second flat surface section (24) face each otherThe optical axis (C) of the first lens (10)₁) And the optical axis (C) of the second lens (20)₂) Are substantially orthogonal to each other so that incident light incident from the first curved surface portion (12) is split in the first lens (10) and condensed in the second lens (20).

Description

Compound lens

Technical Field

The present invention relates to a compound lens.

Background

Conventionally, a structure using a crystal as a material of a lens through which light passes is known. For example, patent document 1 discloses an optical information reading apparatus having an optical pickup including a lens of uniaxial crystal. The uniaxial crystal has birefringence that separates transmitted light into ordinary light and extraordinary light according to an angle of incident light with respect to an optical axis. The optical pickup described above obtains two focal points at the same time by intentionally causing the birefringence.

Patent document 1: japanese laid-open patent publication No. 9-43401

The uniaxial crystal has advantages that deterioration progresses more slowly and resistance is excellent even when light having a shorter wavelength such as deep ultraviolet light is transmitted as compared with glass, for example. However, for example, when a uniaxial crystal is used as a lens for condensing light in a laser processing machine or the like, there is a problem that the emitted light is separated due to birefringence and the focus is blurred.

Disclosure of Invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a compound lens which is excellent in durability and can suppress the influence of birefringence.

A compound lens according to one aspect of the present invention includes: a first lens element having a first curved surface portion and a first flat surface portion opposed to the first curved surface portion, and being formed of a uniaxial crystal; and a second lens having a second curved surface portion and a second flat surface portion opposed to the second curved surface portion, and being formed of a uniaxial crystal, the first lens and the second lens being arranged such that the first flat surface portion and the second flat surface portion are opposed to each other, and an optical axis of the first lens and an optical axis of the second lens being substantially orthogonal to each other, so that incident light incident from the first curved surface portion is separated in the first lens and condensed in the second lens.

According to the present invention, a compound lens having excellent durability and capable of suppressing the influence of birefringence can be provided.

Drawings

Fig. 1 is a diagram showing a configuration example of a compound lens according to an embodiment of the present invention.

Fig. 2 is a plan view of a principal surface of a compound lens according to an embodiment of the present invention.

Fig. 3A is a diagram for explaining an optical path in the compound lens according to the embodiment of the present invention.

Fig. 3B is a diagram for explaining an optical path in the compound lens according to the embodiment of the present invention.

Fig. 3C is a diagram for explaining an optical path in the compound lens according to the embodiment of the present invention.

Detailed Description

Embodiments of the present invention will be described below. In the description of the drawings below, the same or similar structural elements are denoted by the same or similar reference numerals. The drawings are examples, the size and shape of each part are schematic, and it should not be understood that the claims of the present invention are limited to the embodiments.

Fig. 1 is a diagram showing a configuration example of a compound lens according to an embodiment of the present invention, and fig. 2 is a plan view of a main surface of the compound lens according to the embodiment of the present invention, and the compound lens 1 shown in fig. 1 is used as a lens for converging light rays and irradiating an object, for example, in a laser processing machine, a semiconductor device, or the like, and specifically, the compound lens 1 is formed in a convex lens shape, emits an incident light ray L so as to be converged at a focal point f on an optical axis (optical axis) OA, and the optical axis OA of the compound lens 1 is a virtual light ray which is representative of a light flux passing through the entire optical system of the compound lens 1, and is shown in parallel to the Y axis in fig. 1, and coordinate axes shown in fig. 1 to 3C are used for convenience of explanation and are not intended to show a crystal axis of the compound lens 1, and the light ray L may be a single-wavelength light ray, or may be natural light.

The compound lens 1 is formed by joining two

lenses

10 and 20. Specifically, the lens 10 (first lens) is a plano-convex lens having a convex surface 12 (first curved surface) which is a convex curved surface portion extending in the XZ plane direction, and a flat surface 14 (first flat surface) facing the convex surface 12. The lens 20 (second lens) is a plano-convex lens having a convex surface 22 (second curved surface) which is a convex curved surface portion extending in the XZ plane direction, and a flat surface 24 (second flat surface) facing the convex surface 22. Both the lens 10 and the lens 20 have a thickness in the Y-axis direction, and the plane 14 and the plane 24 are disposed to face each other. That is, in the compound lens 1, incident light entering from the convex surface 12 passes through the plane 14 and the plane 24 and exits from the convex surface 22. In the present embodiment, the

convex surfaces

12 and 22 are convex spherical surfaces, for example, but the two convex surfaces are not limited to spherical surfaces, and one or both of the two convex surfaces may be aspherical surfaces.

As shown in fig. 1, the flat surface 14 of the lens 10 and the flat surface 24 of the lens 20 directly engage each other. In this case, for example, the flat surface 14 and the flat surface 24 after the high-precision polishing can be joined by optical coupling of pressure bonding or interatomic bonding. Alternatively, the lens 10 and the lens 20 may be arranged such that the flat surface 14 and the flat surface 24 face each other, and another member (for example, a bonding member or the like) may be interposed therebetween. Specifically, for example, the flat surface 14 and the flat surface 24 may be bonded by an adhesive. Further, the lens 10 and the lens 20 may be physically fixed by a jig or the like so that the plane 14 faces the plane 24.

Fig. 2 is a plan view of the compound lens 1 viewed from the convex surface 12 side of the lens 10. Thus, the

lenses

10 and 20 have circular shapes with equal diameters in a plan view of the main surfaces. The shape of the

lenses

10 and 20 in plan view is not limited to a circle, and may be an ellipse, a polygon, or the like.

The

lenses

10, 20 are each composed of a crystal (i.e., uniaxial crystal) having an optical axis (optical axis) in only one direction. Examples of the uniaxial crystal include artificial crystal, natural crystal, quartz, calcite, zircon and the like, but the case of the artificial crystal is described as an example in the present specification. The artificial crystal has high transmittance in a wide wavelength range as compared with other materials (e.g., synthetic quartz glass). In addition, the artificial crystal has a characteristic that optical characteristics are not easily damaged and deterioration progresses slowly even in a case where the wavelength of light is short and energy is strong (for example, deep ultraviolet light). Further, artificial crystals are excellent in water resistance because they are not deliquescent. Therefore, the artificial crystal suitably functions as a lens for transmitting light.

On the other hand, for a uniaxial crystal, the phase velocity of light differs depending on the propagation direction. Thus, when the surface of the uniaxial crystal including the optical axis and the traveling direction of the incident light is set as the main cross section, the refractive index of the ordinary ray (S-polarized light) vibrating perpendicular to the main cross section is different from the refractive index of the extraordinary ray (P-polarized light) vibrating parallel to the main cross section. Therefore, incident light incident on the uniaxial crystal is separated into ordinary light and extraordinary light in the process of transmitting the lens according to its incident angle, resulting in birefringence. Therefore, when the convex lens is formed using a uniaxial crystal, the emitted light is not focused at one focal point, and the focal point is blurred. In view of this problem, for example, if a light ray passing through the convex lens is made incident so as to be parallel to the direction of the optical axis of the convex lens, the refractive indices of the ordinary ray and the extraordinary ray are equal, and therefore the separation of the ordinary ray and the extraordinary ray is eliminated. However, in this case, there is also a problem that the focus is blurred due to spherical aberration caused by the curved surface of the convex lens.

Therefore, in the present embodiment, as shown in fig. 1 and 2, the optical axis C of the lens 10 is adopted₁(solid line in fig. 2) and the optical axis C of the lens 20₂The structure of the

lenses

10, 20 is joined in a substantially orthogonal manner (dashed lines in fig. 2). Specifically, the optical axis of the artificial crystal is in the same direction as the Z axis, which is the crystal axis of the artificial crystal. Therefore, the

lenses

10 and 20 may be Y-cut artificial quartz in which a plane parallel to a specific plane of X-axis and Z-axis among X-axis, Y-axis and Z-axis, which are crystal axes of the artificial quartz, is cut out as a main surface. Alternatively, the

lenses

10 and 20 may be X-cut artificial quartz in which a plane parallel to a plane specified by the Y-axis and the Z-axis is cut out as a main surface. Thus, the Z-axis of the crystal axis (i.e., the optical axis C)₁、C₂) Arranged parallel to the

flat surfaces

14, 24 of the

lenses

10, 20 and having an optical axis C₁、C₂The two

lenses

10 and 20 are joined to each other in a substantially orthogonal manner. The cutting direction of the

lenses

10 and 20 is not limited to the Y-cut type or the X-cut type, and may be any cutting direction as long as the optical axes of the lenses can be arranged substantially perpendicular to each other. The optical axes of the lenses may not be arranged parallel to the

planes

14 and 24.

By arranging the

lenses

10 and 20 as described above, in the compound lens 1, when the light ray L enters a certain position on the convex surface 12 of the lens 10, the light ray is separated into the ordinary light and the extraordinary light in the lens 10 and passes through different points M and n between the plane 14 and the plane 24, respectively.

Fig. 3A to 3C are diagrams for explaining an optical path in the compound lens according to the embodiment of the present invention. In fig. 3A to 3C, the ordinary rays in the

lenses

10 and 20 are shown by solid lines, and the extraordinary rays are shown by broken lines. In the following, a case where the lens 10 is an incident side and the lens 20 is an outgoing side will be described, but the same principle holds even if the traveling direction of the light beam is reversed.

FIG. 3A shows a light ray L parallel to the optical axis OA of the compound lens 1 entering a position P on the convex surface 12 of the lens 10 and passing through the lens 10. Here, the incident angle of the light ray L is α₁The refraction angle of the ordinary ray on the incident surface of the lens 10 is β₁The refraction angle of the extraordinary ray is set as gamma₁The refractive index of the ordinary ray of the lens 10 is n_oThe refractive index of the extraordinary ray is n_e(<n_o). In addition, the curvature radius of the lens 10 is R₁H is the height of the lens 10 from the optical axis OA at the position P₁D represents the length (thickness) of the lens 10 in the optical axis OA direction at the position P₁。

First, the incident angle of the light ray L (i.e., the angle formed by the normal of the incident surface and the light ray L) is α₁Therefore, the angle formed by the optical axis OA and the normal is also α₁The light ray L is split into ordinary rays (S-polarized light) when passing through the lens 10: solid line) and extraordinary rays (P-polarized light: dashed line). Here, since the effective refractive index of the extraordinary ray depends on the incident angle, if the effective refractive index of the extraordinary ray is n_e(theta) (theta: incident angle), the effective refractive index n of the extraordinary ray_e(α₁) Represented by the following formula (1).

[ formula 1]

In addition, the vertical angle of incidence is also α₁And thus the path length T of the ordinary ray passing through the lens 10_o1And the path length T of the extraordinary ray_e1Represented by the following formulae (2) and (3).

[ formula 2]

[ formula 3]

The optical path length (optical path L ength) of a light ray is represented by the product of the refractive index and the path length, therefore, the optical path length OP of the ordinary ray transmitted through the lens 10_o1And optical path length OP of the extraordinary ray_e1Represented by the following formulae (4) and (5).

[ formula 4]

[ formula 5]

In addition, the incident angle α in the above-described formulas (4) and (5)₁Is an angle satisfying the following equation (6) according to fig. 3A, and further, the refraction angle β₁And angle of refraction gamma₁According to the light ray LSnell's law of the incident surface satisfies the angles of the following equations (7) and (8).

[ formula 6]

[ formula 7]

sinα₁＝n_osinβ₁…(7)

[ formula 8]

sinα₁＝n_e(α₁)sinγ₁…(8)

Fig. 3B shows the optical paths of ordinary rays and extraordinary rays at the boundary surface B between the lens 10 and the lens 20. As described above, the optical axis C of the lens 10₁And the optical axis C of the lens 20₂Are substantially orthogonal. Thus, the main cross section of lens 10 is also orthogonal to the main cross section of lens 20. Thereby, the ordinary ray in the lens 10 becomes an extraordinary ray in the lens 20, and the extraordinary ray in the lens 10 becomes an ordinary ray in the lens 20. That is, the ordinary rays and the extraordinary rays are switched at the boundary surface B between the lens 10 and the lens 20.

The refraction angle of the extraordinary ray in the lens 20 was set to β₂Let the refraction angle of the ordinary ray be gamma₂According to fig. 3A, the incident angle of the ordinary ray transmitted through the lens 10 to the lens 20 is α₁-β₁The incident angle of the extraordinary ray transmitted through the lens 10 to the lens 20 is α₁-γ₁Angle of refraction β₂And angle of refraction gamma₂Is an angle satisfying the following expressions (9) and (10) according to snell's law of the boundary surface B between the lens 10 and the lens 20.

[ formula 9]

n_osin(α₁-β₁)＝n_e(α₁-β₁)sinβ₂…(9)

[ formula 10]

n_e(α₁)sin(α₁-γ₁)＝n_osinγ₂…(10)

FIG. 3C shows the ordinary and extraordinary rays entering the lens 20 at the plane 24 and passing through the lens20 from the position Q of the convex surface 22, the exit angle of the light ray L is set to α₂The curvature radius of the lens 20 is R₂H is the height of the lens 20 from the optical axis OA at the position Q₂D represents the length (thickness) of the lens 20 in the optical axis OA direction at the position Q₂The angle formed by the normal of the emission surface and the optical axis OA is represented by phi.

Path length T of ordinary ray passing through lens 20_o2And the path length T of the extraordinary ray_e2Represented by the following formulae (11) and (12).

[ formula 11]

[ formula 12]

Therefore, the optical path length OP of the ordinary ray transmitted through the lens 20_o2And optical path length OP of the extraordinary ray_e2Represented by the following formulae (13) and (14).

[ formula 13]

[ formula 14]

The condition that the ordinary rays and the extraordinary rays separated in the lens 10 are condensed in the lens 20 and exit from one point (position Q) of the convex surface 22 is as follows: the sum (OP) of the optical path length of the ordinary ray in the lens 10 and the optical path length of the extraordinary ray in the lens 20_o1+OP_e2) Equal to the sum (OP) of the optical path length of the extraordinary ray in the lens 10 and the optical path length of the ordinary ray in the lens 20_e1+OP_o2). Therefore, according to the above-mentioned equations (4), (5), (13) and (14), when the following equation (15) is established,ray L emerges from a point on convex surface 22.

[ formula 15]

Further, the refraction angle β in the above formula (15)₂And angle of refraction gamma₂Is an angle satisfying the above equations (9) and (10).

Since the angle formed by the normal of the exit surface and the optical axis OA is also phi as shown in fig. 3C, the incident angle of the ordinary light transmitted through the lens 20 to the convex surface 22 is phi + γ₂In addition, the extraordinary ray transmitted through the lens 20 is incident on the convex surface 22 at an incident angle of φ + β₂Therefore, the exit angle α of the light ray L₂Is an angle satisfying the following expressions (16) and (17) according to snell's law of the exit surface of the light ray L.

[ formula 16]

n_osin(φ+γ₂)＝sinα₂…(16)

[ formula 17]

n_e(α₁-β₁)sin(φ+β₂)＝sinα₂…(17)

Further, according to fig. 3C, the angle Φ formed by the normal line of the exit surface and the optical axis OA is an angle of the satisfied expression (18).

[ formula 18]

As described above, according to the present embodiment, the light ray L is split into the ordinary ray and the extraordinary ray in the lens 10, but is condensed in the lens 20 and ideally exits from one point of the convex surface 22, whereby the composite lens 1 can suppress the influence of birefringence and eliminate the focus blur.

Further, since the composite lens 1 of the present embodiment is made of artificial quartz, the water resistance can be improved as compared with a lens made of calcium fluoride, magnesium fluoride, or the like, for example.

The mode of converging the outgoing light at the focal point F of the compound lens 1 is not limited to the mode of converging the incoming light entering all regions of the compound lens 1 at exactly one point, but includes a width of the focal point of such a degree as to fall within aberration generated in a general convex lens made of glass or the like. In addition, the above expression (15) does not necessarily need to be satisfied in the entire region of the

lenses

10, 20 as long as the

lenses

10, 20 include a region satisfying the above expression (15).

In the above-described embodiment, the lens has a convex curved surface portion, but the present invention is not limited to this, and may have a concave curved surface portion. Specifically, both lenses constituting the compound lens may be plano-concave lenses each having a spherical surface with a concave curved surface portion. In this case, for example, the flat surfaces of the plano-concave lenses are joined to face each other to form the shape of a concave lens as a whole. Even in this case, the sum of the optical path lengths of the ordinary ray and the extraordinary ray passing through the compound lens is equal in both paths, and the influence of birefringence can be suppressed.

In the above embodiment, the embodiment in which both the two

lenses

10 and 20 are made of artificial quartz has been described, but the present invention is not limited to this, and the two

lenses

10 and 20 may be made of a material different from artificial quartz. The

lenses

10 and 20 may be made of different materials and may have the same refractive index.

In the above-described embodiment, the embodiment in which the compound lens is a pair of two lenses has been described, but the present invention is not limited to this, and the compound lens may further include two additional lenses between the

lenses

10 and 20. In this case, the other two lenses are also made of uniaxial crystals having the same refractive index, and are joined so that the optical axes of the lenses are substantially orthogonal to each other. In this case, the compound lens has a structure including four lenses in total. Alternatively, the compound lens may be a combination of two new lenses, each of which is further inserted into a plurality of such pairs of two lenses, and may have a configuration including six or eight lenses in total. The new lens in a pair of two pieces may be formed into a flat plate shape, for example, and bonded between the flat surface 14 of the lens 10 and the flat surface 24 of the lens 20.

One embodiment of the present invention has been described above. The compound lens according to the present embodiment includes: a first lens having a first curved surface portion and a first flat surface portion opposed to the first curved surface portion, and being formed of a uniaxial crystal; and a second lens having a second curved surface portion and a second flat surface portion opposed to the second curved surface portion, and being formed of a uniaxial crystal, the first lens and the second lens being arranged such that the first flat surface portion and the second flat surface portion are opposed to each other, and an optical axis of the first lens and an optical axis of the second lens being substantially orthogonal to each other, so that incident light incident from the first curved surface portion is separated in the first lens and condensed in the second lens.

Thus, the light ray L is separated into ordinary and extraordinary rays in the lens 10, but is condensed and emitted in the lens 20, and therefore, a compound lens having excellent resistance and suppressed influence of birefringence can be provided as compared with a lens such as glass.

The embodiments described above are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention can be modified or improved without departing from the gist thereof, and the present invention also includes equivalents thereof. That is, those skilled in the art can appropriately modify the design of each embodiment and include the features of the present invention within the scope of the present invention. For example, the elements provided in the embodiments, and the arrangement, materials, conditions, shapes, sizes, and the like thereof are not limited to those exemplified, and can be appropriately changed. In addition, the elements provided in the embodiments can be technically combined as much as possible, and the combination of the elements is included in the scope of the present invention as long as the features of the present invention are included.

Description of the reference numerals

1 … compound lens; 10. a 20 … lens; 12. 22 … convex surface; 14. 24 … plane; c₁、C₂… optical axis; OA … optical axis; b … boundary surface; p, Q … position.

Claims

1. A compound lens is provided with:

a first lens element having a first curved surface portion and a first flat surface portion opposed to the first curved surface portion, and being formed of a uniaxial crystal; and

a second lens having a second curved surface portion and a second flat surface portion opposed to the second curved surface portion, and formed of a uniaxial crystal,

the first lens and the second lens are arranged such that the first planar portion and the second planar portion are opposed to each other,

an optical axis of the first lens and an optical axis of the second lens are substantially orthogonal to each other, so that incident light incident from the first curved surface portion is separated by the first lens and condensed by the second lens.

2. The compound lens of claim 1,

the incident light has ordinary rays and extraordinary rays in the first lens and the second lens respectively,

the sum of the optical path length of the ordinary ray in the first lens and the optical path length of the extraordinary ray in the second lens is approximately equal to the sum of the optical path length of the extraordinary ray in the first lens and the optical path length of the ordinary ray in the second lens.

3. The compound lens of claim 2,

a length of the first lens in an optical axis direction at a position where the incident light is incident on the first curved surface part is set to d₁D represents a length of the second lens in the optical axis direction at a position where the outgoing light is emitted from the second curved surface portion₂Setting the refractive index of the ordinary rays in the first lens and the second lens to n_oN is a refractive index of the extraordinary ray in the first lens and the second lens when the incident angle of the extraordinary ray is theta_e(θ), the incident angle of the incident light is α₁A refraction angle of the ordinary ray in the first lens is set to β₁Setting the refraction angle of the extraordinary ray in the first lens to gamma₁Refracting the ordinary rays in the second lensThe angle is set to gamma₂A refraction angle of the extraordinary ray in the second lens is set to β₂In the case of (1), the first curved surface portion and the second curved surface portion include a region satisfying the following expression.

[ formula 1]

4. A compound lens according to any one of claims 1 to 3,

the first curved surface portion and the second curved surface portion are convex spherical surfaces.

5. A compound lens according to any one of claims 1 to 3,

the first curved surface portion and the second curved surface portion are concave spherical surfaces.

6. The compound lens according to any one of claims 1 to 5,

the uniaxial crystal is an artificial crystal.