JP6852895B2 - Beam expander - Google Patents

Description

The present invention relates to a beam expander capable of receiving, for example, a laser beam and expanding the beam light in a uniaxial direction or expanding the diameter of the beam light as a whole.

For example, a laser beam emitted from a semiconductor laser element often has an elliptical cross section orthogonal to the beam light, which is generally about 2: 1. As a means for bringing such an elliptical beam light closer to a perfect circle, a beam expander in which two convex lenses or one convex lens and one concave lens are combined has been proposed. In addition, a beam expander that combines a convex lens and a cylindrical lens has also been proposed.

Further, FIG. 7 of Patent Document 1 discloses a beam expander using two cylindrical lenses. In the example shown in Patent Document 1, a semiconductor laser element is used as a light source of a projection type display device (projector), and an elliptical beam light from the semiconductor laser element is emitted from the two cylindrical lenses. An example of getting closer to a perfect circle is shown.

That is, the beam light from the semiconductor laser element is parallelized via the collimating lens by the convex lens, and the parallelized beam light is passed through the first cylindrical lens and the second cylindrical lens, and the short axis of the beam light. The side is expanded in the axial direction.
On the other hand, on the long axis side of the beam light, the first and second cylindrical lenses are transmitted as they are, so that the elliptical beam light from the semiconductor laser element becomes close to a perfect circle.

On the other hand, in Patent Document 2, an optical element (prism) in which the incident side of the beam light is formed into a concave conical surface and the outgoing side is formed into a convex conical surface is used to convert the incident beam light into a beam light having an annular cross section (ring band shape). An example of expanding to is shown.
The annular cross-section laser beam generator shown in Patent Document 2 seeks to obtain high resolution in combination with a multiphoton microscope, which irradiates the central portion of the optical axis with laser light. Is intended to avoid and expand the irradiation area of the laser beam in a ring shape (ring band shape).

Japanese Patent No. 3767623 Japanese Unexamined Patent Publication No. 2003-344285

By the way, in the conventional beam expander in which two convex lenses or a combination of a convex lens and a concave lens are combined, including the beam expander disclosed in Patent Document 1, it is necessary to adjust the focus of the combined lenses. is there.
Therefore, the optical system and the focus adjustment mechanism become complicated, the configuration of the beam expander portion inevitably becomes large, and the cost rise is inevitable.

Note that FIG. 9 of Patent Document 1 shows an example in which a conical transparent body (prism) is used in the optical system of the projector described above, and the vicinity of the apex of the cone of the transparent body is processed into a spherical shape. There is.
This can be regarded as a point that approximates the configuration of the optical element of the beam expander according to the present invention, which will be described later. However, the optical system of the projector disclosed in Patent Document 1 and the optical system of the beam expander according to the present invention are different in their action and effect, such as the direction of light incident on the apex of the cone is opposite. Is clear.

On the other hand, the annular cross-section laser light beam generator disclosed in Patent Document 2 aims to spread the laser beam in a ring shape by using a prism having a conical surface, and as described at the beginning, the beam. It is clear that the problem to be solved is different from that of the beam expander according to the present invention, which attempts to expand the light in a uniaxial direction or to expand the diameter of the beam light as a whole.

Therefore, the main problem to be solved by the present invention is to easily expand the light beam in the uniaxial direction or increase the beam diameter as a whole (biaxial direction) by arranging the optical elements on the parallelized optical axes. ) Is to provide a beam expander that can be expanded.
In addition, a beam expander that can obtain a light beam with relatively uniform light intensity characteristics by adopting a configuration that effectively compensates for the decrease in light intensity near the center of the optical axis of the magnified light beam. Is intended to provide.

In the form of the beam expander according to the present invention made to solve the above-mentioned problems, an inner concave portion having an arcuate cross section and an outer convex portion having an arcuate cross section are formed, and the inner surface side is an incident surface of a light beam. At the same time, an optical element having an outer surface side formed on the exit surface of the light beam is provided, and the center of the incident light beam is projected onto the inner recess to obtain a light beam having an enlarged beam diameter on the exit surface side. It is characterized by.

Further, as a form of the beam expander according to the present invention, in the optical element, light-transmitting flat plates having the same thickness intersect with each other in a V shape, and the inner surface thereof is along the inner surface and the outer surface of the intersection. It is a roof-shaped optical element in which a concave portion and an outer convex portion are formed, and is characterized in that the beam diameter is enlarged in the uniaxial direction.

Further, as another embodiment of the beam expander according to the present invention, the optical element has an incident surface of a light beam formed of a concave conical surface and an exit surface of a light beam formed of a convex conical surface, and has a concave conical surface. The thickness between the convex conical surface and the convex conical surface is uniformly formed, and the inner concave portion and the outer convex portion are formed along the inner surface of the concave conical surface and the outer surface of the convex conical surface, respectively, to reduce the beam diameter. It is characterized by being enlarged in the biaxial direction.

In this case, the thickness of the optical element constituting the beam expander is t, the radius of curvature of the inner concave portion of the optical element is R1, the opening angle of one side of the line orthogonal to the exit surface of the optical element is θ, and the optical element When the refraction angle determined by the refractive index n of the material is α, it is desirable that the radius of curvature R2 of the outer convex portion of the optical element is set to a value obtained by the following equation 1.
R2 = R1 + t− (t · cos θ) / (n · cos α) …… Equation 1

According to the beam expander according to the present invention described above, by using the optical element described above, the light beam diameter can be expanded and the configuration of the beam expander can be simplified.

In addition, since an arcuate inner recess and an arcuate outer convex portion in which the cross section of the optical element is spherical or aspherical, respectively, are formed, the light beam incident on the inner concave portion is formed on the outer convex portion. It is gradually enlarged toward and emitted. As a result, it is possible to effectively compensate for the decrease in light intensity in the vicinity of the central portion of the optical axis, and it is possible to obtain a light beam having relatively uniform light intensity characteristics.

It is a perspective view which showed the beam expander of the 1st form which concerns on this invention. It is also a perspective view which showed the beam expander of the 2nd form. It is a schematic diagram explaining the basic concept which expands an incident beam. It is a schematic diagram explaining the magnifying action of the incident beam which concerns on this invention. It is a schematic diagram explaining the main parameter of an optical element. It is a schematic diagram explaining the example which obtains the radius of curvature of the outer convex part of an optical element. It is a schematic diagram which showed an example of preferable numerical value of each part of an optical element.

The beam expander according to the present invention will be described based on the embodiment shown in the figure.
First, FIG. 1 shows a perspective view of the basic configuration of the beam expander (uniaxial expand type) of the first form. In the example shown in FIG. 1, a roof-shaped optical element 1A in which light-transmitting flat plates having the same thickness are crossed in a V shape is used.

Then, an inner recess 2 having an arcuate cross section is formed along the inner surface of the V-shaped intersection. Further, an outer convex portion 3 having an arcuate cross section is formed along the outer surface of the V-shaped intersection.
That is, the inner concave portion 2 and the outer convex portion 3 in this embodiment form a concave shape that is long in the axial direction and a convex shape that is long in the axial direction, respectively, as in the form along the axial direction of the cylindrical body.
In this roof-shaped optical element, the V-shaped inner surface side of the optical element 1A is formed on the incident surface 4 of the light beam, and the outer surface side is formed on the emitting surface 5 of the light beam.

For example, the laser beam from the semiconductor laser element is parallelized via a collimating lens such as a convex lens (not shown), and the center of the parallelized light beam (incident beam 6a) is the arc shape of the optical element 1A shown in FIG. It is projected onto the inner recess 2 of the lens.
As a result, the incident beam 6a can obtain a light beam (emission beam 6b) whose beam diameter is enlarged in the uniaxial direction by the optical element 1A.

According to the optical element 1A constituting the beam expander of the first form described above, the incident beam 6a is oriented in a direction orthogonal to the arcuate ridge line intersecting in a V shape (uniaxial direction) as described later. An enlarged emission beam 6b can be obtained.
Therefore, as shown in FIG. 1 as an example, the slightly vertically long incident beam 6a can be converted into an emitted beam 6b having substantially the same vertical and horizontal dimensions.

FIG. 2 shows a perspective view of the basic configuration of the beam expander (biaxial expand type) of the second form. The example shown in FIG. 2 has an incident surface 4 of a light beam formed of a concave conical surface and an exit surface 5 of a light beam formed of a convex conical surface, and is located between the concave conical surface 4 and the convex conical surface 5. An optical element 1B having a conical prism having a uniformly formed thickness is used.
Then, along the inner surface of the concave conical surface, an arcuate inner concave portion 2 having a spherical or aspherical cross section is formed. Further, an arc-shaped outer convex portion 3 having a spherical or aspherical cross section is formed along the outer surface of the convex conical surface.
That is, spherical or aspherical inner concave portions 2 and outer convex portions 3 are formed at the apex portions of the concave conical surface and the convex conical surface, respectively.

As described above, for example, the laser beam from the semiconductor laser element is parallelized via the collimating lens, and the center of the parallelized light beam (incident beam 6a) is the circle of the optical element 1B as shown in FIG. It is projected onto the arc-shaped inner recess 2.
As a result, the incident beam 6a can obtain an optical beam (emission beam 6b) whose beam diameter is expanded in the biaxial direction by the optical element 1B.

According to the optical element 1B constituting the beam expander of the second form described above, as will be described later, the incident beam 6a is a beam light expanded in two axes (vertical and horizontal directions), that is, the entire beam diameter is increased. It is possible to obtain an emitted beam 6b that is magnified to.
Therefore, as shown in FIG. 2 as an example, when the incident beam 6a that is close to a perfect circle arrives, it is enlarged as it is in the vertical and horizontal directions (biaxial direction), and the enlarged exit beam that is close to a perfect circle. It can be converted to 6b.

FIG. 3 is a schematic diagram illustrating a basic concept of magnifying and emitting an incident beam, and the example shown in FIG. 3 shows a case where the intersections intersect linearly in a V shape. Further, FIG. 4 shows the optical characteristics of the roof-shaped optical element 1A shown in FIG. 1 and the optical element 1B of the conical prism shown in FIG. 2, and the arc-shaped inner recess 2 and the arc-shaped The optical characteristics of the beam expander according to the present invention provided with the outer convex portion 3 of the above are shown. Note that FIGS. 3 and 4 show the shape of the end face of the cut surface cut along the transmission axis of the beam light at the central portion of each of the optical elements 1A and 1B.

As shown in FIG. 3, in the optical element in which the roof-shaped intersections intersect in a V shape and the optical element in which the vertices of the conical surface by the conical prism intersect in a V shape, both the intersections and the vertices are linear. Since it intersects with, the intersection has a sharp cross section. Therefore, the optical path near the central portion of the incident beam 6a is divided into either of two hands at the V-shaped intersection position (intersection point) of the optical element, as shown in FIG.
As a result, the central portion of the emitted beam 6b has a low light intensity (light intensity reduction portion 7) as indicated by reference numeral 7. This has the same effect as the example of spreading the incident beam disclosed in Patent Document 2 in a ring shape (ring band shape).

Therefore, according to the optical element provided with the arc-shaped inner concave portion 2 and the arc-shaped outer convex portion 3 as shown in FIG. 4, the optical path near the central portion of the incident beam 6a incident on the optical elements 1A and 1B is It goes straight in the inner recess 2 as it is, and the degree of refraction in the radial direction increases as the distance from the center of the beam increases. Then, it is refracted at the arc-shaped outer convex portion 3, and the incident beam 6a is emitted as an enlarged parallel emission beam 6b.

As a result, the beam expander according to the present invention shown in FIG. 4 can effectively compensate for the decrease in light intensity near the central portion of the optical axis as compared with the example shown in FIG. 3, and is relatively uniform. It is possible to obtain an emitted beam 6b having various light intensity characteristics.
That is, according to the beam expander according to the present invention, for an incident beam having a so-called Gaussian light intensity distribution obtained from a semiconductor laser device, for example, the light intensity at the center thereof is appropriately reduced to make the light more uniform. It can contribute to obtaining an emitted beam having an intensity distribution.

5A to 5C explain the preferable relationship between the parameters of each part and the radii of curvature of the arcuate inner concave portion 2 and the outer convex portion 3 with respect to the optical elements 1A and 1B constituting the beam expander described above. is there.
5A to 5C are schematic views of the portion of the optical element shown in FIG. 4 including the inner concave portion 2 and the outer convex portion 3.

FIG. 5A shows the parameters of each part of the optical elements 1A and 1B. The thickness of the optical element is t, the radius of curvature of the inner recess 2 of the optical element is R1, and the line orthogonal to the exit surface 5 of the optical element. The opening angle on one side is shown as θ, the refraction angle determined by the refractive index n of the material of the optical element is shown as α, and the radius of curvature of the outer convex portion 3 of the optical element is shown as R2.

In the configuration of the optical elements 1A and 1B shown in FIG. 5A, the thickness t, the radius of curvature R1 of the inner recess 2, the opening angle θ on one side of the line orthogonal to the exit surface 5, and the refractive index n are arbitrarily determined. The calculation formula for obtaining the radius of curvature R2 of the outer convex portion 3 determined by FIG. 5B can be derived as follows based on FIG. 5B.

The triangle ABC and the triangle A'B'C'shown in FIG. 5B are similar figures, and the line segments A, B, C and A', B', C'of each triangle are as follows.
A: Length of the line segment from the center point on the optical axis of the radius of curvature R1 to the point where the straight line extending from this center point at the opening angle θ intersects the exit surface 5 B: The exit surface 5 of the line segment A. Length C from the intersection with the line to the point where the line orthogonal to the line A intersects the optical axis: The length A'between the points on the optical axis of the line A and B. : The length of the line segment from the point where the inner recess 2 intersects the optical axis and the point where the straight line extending from this intersection at the opening angle θ intersects the emission surface 5 B': The emission surface 5 of the line segment A' Length of the line from the intersection with and to the point where the line orthogonal to the line A'intersects the optical axis C': The line between the points on the optical axis of the line A'and B' length

As described above, since the triangle ABC shown in FIG. 5B and the triangle A'B'C'are similar figures,
A: A'= B: B'
A'= A ・ B'/ B
From B = Atanθ to A'= B'/ tanθ
From B'= Bt ・ tanα to A'= At ・ tanα / tanθ
sinα = sinθ / n
From the relationship of tanα = sinα / cosα, A'= A− (t · cosθ) / (n · cosα)
A'= R2
From A = R1 + t to R2 = R1 + t- (t · cos θ) / (n · cos α) …… Equation 1
The above formula 1 shows an example in which the arc-shaped inner concave portion 2 and the arc-shaped outer convex portion 3 each have a spherical cross-sectional shape.

Then, in FIG. 5C, the value of R2 when t = 15, R1 = 10, θ = 25 °, and n = 1.5 was obtained based on Equation 1, and specific numerical values were entered in each part. Shown in state. In this case, when n = 1.5, α = 16.36 °, and therefore the ideal value of R2 is the result shown below from the above equation 1.
R2 = R1 + tt ・ cosθ / n ・ cosα = 15.554

As described above, according to the beam expander according to the present invention, the incident beam can be expanded in the uniaxial direction by using, for example, the optical element 1A illustrated in FIG. Therefore, for example, the elliptical beam light described at the beginning can be effectively used as a means for bringing the beam light closer to a perfect circle.
Further, the incident beam can be expanded in the X-axis direction and the Y-axis direction by using the two optical elements 1A illustrated in FIG. 1, and the axial directions of the plurality of optical elements 1A can be arbitrarily set according to the application and the requirement. It can also be set and combined.

Further, according to the beam expander according to the present invention, including the optical element 1B illustrated in FIG. 2, a laser pointer, an optical vibration sensor, a position detection sensor, and a communication device using a laser beam (laser beam). It can also be effectively used for the function of expanding the beam diameter in the previous stage of diffusion and transmission), and at the same time, the action and effect described in the above-mentioned effect column of the present invention can be obtained.

1A optical element (uniaxial expand type)
1B optical element (biaxial expand type)
2 Inner concave part 3 Outer convex part 4 Incident surface 5 Exit surface 6a Incident beam 6b Exit beam 7 Light intensity reduction part

Claims (4)

An optical element is provided in which an inner concave portion having an arcuate cross section and an outer convex portion having an arcuate cross section are formed, the inner surface side is an entrance surface of a light beam, and the outer surface side is an emission surface of a light beam.
A beam expander characterized in that the center of an incident light beam is projected onto the inner recess to obtain a light beam having an enlarged beam diameter on the exit surface side. The optical element has a roof-shaped shape in which light-transmitting flat plates of the same thickness intersect each other in a V shape, and the inner concave portion and the outer convex portion are formed along the inner surface and the outer surface of the intersection. It is an optical element
The beam expander according to claim 1, wherein the beam diameter is expanded in the uniaxial direction. The optical element has an incident surface of a light beam formed of a concave conical surface and an exit surface of a light beam formed of a convex conical surface, and the thickness between the concave conical surface and the convex conical surface is uniformly formed. At the same time, the inner concave portion and the outer convex portion are formed along the inner surface of the concave conical surface and the outer surface of the convex conical surface, respectively.
The beam expander according to claim 1, wherein the beam diameter is expanded in a biaxial direction. Refraction determined by t for the thickness of the optical element, R1 for the radius of curvature of the inner recess of the optical element, θ for the opening angle on one side of the line orthogonal to the exit surface of the optical element, and n for the refractive index of the material of the optical element. The beam according to any one of claims 1 to 3, wherein the radius of curvature R2 of the outer convex portion of the optical element is set to a value obtained by the following equation 1 when the angle is α. Expander.
R2 = R1 + t− (t · cos θ) / (n · cos α) …… Equation 1

Images