WO2005006054A2

WO2005006054A2 - Arrangement for transforming an optical radiation field

Info

Publication number: WO2005006054A2
Application number: PCT/EP2004/007219
Authority: WO
Inventors: Dieter Hoffmann; Martin Traub; Rudolf Meyer; Keming Du
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2003-07-10
Filing date: 2004-07-02
Publication date: 2005-01-20
Also published as: DE10331442B4; EP1651994A2; WO2005006054A3; DE10331442A1

Abstract

The invention relates to a system for transforming an optical radiation field propagating in a z direction and comprising a symmetrical beam radiation parameter product in x and y directions into a radiation field having an asymmetrical product of beam parameters by means of a transformation optics, wherein the x, y and z directions forming an orthogonal co-ordinate system. The inventive arrangement is characterised in that the radiation field is first and foremost segmented into at least two partial radiation fields by the transformation optics in the y direction which are afterwards offset in the x direction by the transformation optics, and said partial radiation fields are offset in the y direction by the transformation optics in such a way that the centres of gravity thereof is located on a line which is perpendicular with respect to the line where the centres of gravity of the partial radiation fields are situated before entering the transformation optics. Said arrangement is also characterised in that the radiation field is first and foremost segmented into at least two partial radiation fields by the transformation optics in the y direction, said transformation optics turns said partial radiation fields to 90° around the axis Z respectively and the partial radiation fields after being exposed to rotation are put together into a line in the direction y.

Description

"Arrangement for transforming an optical radiation field"

The present invention relates to an arrangement for transforming an optical radiation field, which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions, by means of transformation optics into a radiation field with an asymmetrical beam parameter product, the x, y - and z directions form a right-angled coordinate system.

Different applications of laser radiation require a linear beam shape or a beam cross section with asymmetrical beam parameters. However, the available output beams are usually radiation fields with a symmetrical beam parameter product. In order to obtain a linear radiation field from these available optical radiation fields, either cylindrical lenses are used or scanners are used which deflect the beam in time and generate a quasi-continuous, linear radiation field at high scanning frequencies. Such cylindrical lenses or scanners can be called transformation optics. In this case, cylindrical lenses are disadvantageous in that they do not change the beam quality of the fast and slow axes and therefore cannot be used in high aspect ratios. The disadvantage of using scanners is the temporal distraction, the segmentation of the line and the mechanical sensitivity of the structure.

On the basis of an arrangement as stated at the beginning and a state of the art in the form of the cylindrical lens described above or a scanner as transformation optics, the object of the present invention is to create an arrangement with which a radiation field with a symmetrical beam parameter product is transformed so that it becomes a linear focus at a large distance from the focusing element and at the same time very small dimensions in one direction with large dimensions in the direction orthogonal to it, while achieving a high efficiency and a high aspect ratio, without moving parts. This object is achieved by an arrangement for transforming an optical radiation field which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions, by means of transformation optics into a radiation field with an asymmetrical beam parameter product, the x, y and z directions form a rectangular coordinate system; the arrangement is characterized in that the radiation field with the transformation optics is first segmented into at least two partial radiation fields in the y direction, that the partial radiation fields are then shifted with the transformation optics in the x direction, and that these - partial radiation fields with the transformation optics in the y direction are shifted in such a way that the focal points of the partial radiation fields lie on a line that is perpendicular to the line on which the focal points of the partial radiation fields lie before entering the transformation optics.

The object is also achieved by an arrangement for transforming an optical radiation field which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions, by means of transformation optics into a radiation field with an asymmetrical beam parameter product, the x, y and z directions form a rectangular coordinate system; the arrangement is characterized in that the radiation field with the transformation optics is first segmented into at least two partial radiation fields in the y direction, and that these partial radiation fields are each rotated through the z axis by 90 ° with the transformation optics and the rotated partial radiation fields are closed a line in the x direction.

With an arrangement in the first-mentioned type, an optical radiation field with symmetrical parameter products in the x and y directions is subdivided into at least two partial radiation fields in the y direction in the transformation optics. These two partial radiation fields are then offset by means of the transformation optics in a direction perpendicular to it (y direction)), or in one direction with an essential vector component in the y direction, in order to then offset these offset partial radiation fields in a further step in the direction perpendicular to the first offset, ie in the x direction, push that the focal points of the power density distributions of the partial radiation fields lie on one line. The radiation field to be reshaped with a symmetrical beam parameter product can be, for example, a rotationally symmetrical field after a laser resonator with a cylindrical laser rod or a radiation field at the exit of a fiber; The shaping of a radiation emerging from a fiber has the advantage that the radiation is homogenized over the cross section of the fiber at the exit end. It is thus achieved with the specified arrangement that, for example, the radiation emerging from a glass fiber is generated in a linear focus with a large distance from the focusing optical element and at the same time very small dimensions in one direction with large dimensions in the direction orthogonal thereto. Such a mapping is also achieved with a high degree of efficiency.

With the second arrangement, which solves the task, an essential feature is to rotate the respective partial radiation fields with the transformation optics about the z-axis by 90 °. Then, in a further step in the transformation optics, the rotated partial radiation fields can be brought together to form a line in the x direction. It can be seen that the dimensions of the line, composed of the partial radiation fields, can be influenced by the choice of the segmentation; If linear radiation cross sections are to be achieved on the output side of the transformation optics with a very large, different aspect ratio, the radiation field on the input side is segmented into a large number of partial radiation fields in the y direction.

For the transformation of the output radiation, cylindrical optics are preferably arranged on the input side of the transformation optics. Such cylinder optics first transform the radiation field with a symmetrical beam parameter product into an elliptical radiation field, the major axis of the ellipse lying in the y direction, taking into account the coordinate system specified above.

In order to obtain a uniform, linear radiation field on the output side of the transformation optics, ie with a uniform intensity distribution over the linear radiation field, it is advantageous that the individual, segmented partial radiation fields have approximately the same powers. This is achieved in that the Segments, ie the partial radiation cross-sectional areas, are selected in a different size, adapting the power.

In order to distribute the power of the radiation field equally over the partial radiation fields, the cross section of the partial radiation fields is imaged in the plane of the transformation optics in connection with a cylindrical lens.

With the use of a cylindrical lens on the input side of the transformation optics, the adaptation of the partial radiation fields so that they have approximately the same powers can be achieved by giving the cylindrical lens a changing radius of curvature.

The transformation optics preferably have a plurality of reflective elements; these reflective elements are used to separate the partial radiation fields. The reflective elements can be formed by mirror surfaces.

The reflective elements can also be formed by totally reflecting surfaces of a radiation-transparent element. Reflective elements in the form of mirror surfaces are to be preferred if the acceptance angle of totally reflecting surfaces would be exceeded. On the other hand, reflective elements in the form of the totally reflecting surfaces of a radiation-transparent element are to be used if this could be advantageous from a manufacturing point of view.

Furthermore, if the partial radiation fields are adjusted in their power by a changing radius of curvature of a cylindrical lens, the optical radiation field should have the same divergence angle in the x and y directions.

In connection with an arrangement in which the transformation optics rotate the partial radiation fields, a Dove prism is assigned to each partial radiation field in the transformation optics. Such a Dove prism has a base and two prism surfaces that run obliquely to the base surface, and is dimensioned and aligned such that one prism surface forms an entry surface for the corresponding partial radiation field and thus to the direction of propagation (z direction) of the partial radiation field under one Is aligned that the radiation is refracted towards the base; The radiation is then reflected at the base surface and towards the second prism surface directed, where it then, rotated by 90 ° to the z-axis, exits in the z-direction (with appropriate orientation of the second prism surface).

Further details and features of the invention will become apparent from the following description of an embodiment with reference to the drawing. In the drawing shows

1 shows two views, labeled A and B, of a radiation field which propagates in the z direction and emerges from the end of an optical fiber, on the one hand in the xz plane (illustration A) and on the other hand in its cross section in the yz plane (Representation B),

2 shows a representation of the respective xy planes assigned to FIG. 1 in order to indicate the respective beam cross section and the associated divergence angle in the x direction (θ _x ) and in the y direction (θ _y ) at the corresponding point in the z direction,

FIG. 3 shows a schematic illustration of a radiation field that propagates in the z direction, with a view of the x-z plane, which is focused by a cylindrical lens system and fed to a transformation lens system,

FIG. 4 shows the arrangement of FIG. 3, but in a view of the y-z plane of the radiation field on the input side and the x-z plane of the radiation field on the output side of the transformation optics,

FIG. 5 shows a three-dimensional representation of the arrangement, as is also shown in FIGS. 3 and 4,

FIG. 6 schematically shows the decomposition of an input-side radiation field with an elliptical beam cross section (illustration A), the partial radiation fields then being shifted in the x direction (illustration B), which in turn are shifted in a further step in the y direction (illustration C) .

FIG. 7 schematically shows a transformation optics with four Dove prisms for rotating the respective partial radiation fields by 90 ° around the z-axis, FIG. 8 schematically shows a radiation field which is segmented in the y direction into eight partial radiation fields (illustration A), and the corresponding radiation field after the transformation optics, rotated by 90 ° about the z-axis and combined to form a linear radiation field (illustration B), and

Figure 9 is a representation corresponding to Figures 1 and 2, but with a transformation optics 4 ', as shown in Figure 7 in the specific embodiment.

FIG. 1 schematically shows an arrangement for transforming an optical radiation field, generally designated by the reference number 1. The representations A and B show the x-z plane on the one hand and the y-z plane perpendicular to it on the other.

It should be noted that in all figures the z direction is the direction of propagation of the radiation field 1, even if this changes its direction in space, i.e. the z direction is carried along with the direction of propagation of the radiation field 1.

Furthermore, respective planes are in the x-y directions with corresponding lines in the figure

Denotes I; The respective beam cross sections are assigned to these planes in the xy direction in FIG. 2, and the divergence angles of the radiation in the x and y directions, denoted by θ _x and θ _y , are given.

In the arrangement of FIG. 1, the radiation field becomes an optical fiber on the output side

II provided. At the exit end of the optical fiber 11, the divergence angle in the x direction, θ _Xl and the divergence angle in the y direction, θ _y , are the same, as can be seen in FIG. The diverging radiation field 1 then enters collimating optics, preferably a spherical lens 2, wherein θ _x = θ _{y also} applies to lens 2. The radiation field aligned in parallel is then guided into a cylinder optics 3, the radiation field 1 emerging from the cylinder optics 3 then having a larger divergence angle in the x direction than in the y direction, so that: θ _x > θ _y . As can be seen from FIG. 1, the cylindrical lens 3 is aligned with its cylinder axis in the y direction. The radiation field 1, which is focused in the x-direction after the cylinder optics 3, while it is spreading in the y-direction as a parallel radiation field, then enters a transformer mation optics 4, with respect to the divergence angle on the input side of the transformation optics θ _x > θ _y . By means of the transformation optics 4, the radiation field 1 is segmented into a predetermined number of partial radiation fields in the y direction; these partial radiation fields are then shifted in the x direction by means of the transformation optics 4 and then shifted again in the y direction such that the centers of gravity of the partial radiation fields lie on a line. On the output side of the transformation optics 4, the divergence angle in the x direction, θ _x , is then greater than the divergence angle in the y direction, θ _y , whereas on the input side of the transformation optics 4, the following applies to the divergence angles: θ _x > θ _y .

While the beam quality of the radiation field 1, as it emerges from the exit surface of the light guide 2, is the same in the x and y directions, on the output side of the transformation optics 4 the beam quality in the x direction is very much better than in the y direction.

Depending on the number of partial radiation fields in which the radiation field 1 is broken down in the transformation optics 4, line-shaped radiation fields can be generated on the output side of the transformation optics 4, which, using the coordinate system shown in the drawings, have a width of 70 μm in the x direction. while the length in the y direction can be, for example, 14 mm, ie the dimensions of the radiation field in the x and y directions differ by a factor of about 200.

FIGS. 3, 4 and 5 show an arrangement, comparable to that shown schematically in FIG. 1, in a more detailed representation of the transformation optics 4. However, in FIGS. 3 to 5 the radiation field 1 is shown directly entering the cylinder optics 3. This radiation field 1 is segmented into partial radiation fields on a first reflection optics 5, made up of reflecting mirror surfaces, about 40 partial radiation fields being shown. After this segmentation in the y direction, the partial radiation fields are shifted in the x direction by appropriate alignment of the mirror surfaces. These partial radiation fields shifted in the x direction are then guided to a second reflection optics 6, which is part of the transformation optics 4, which then, by means of individual mirror surfaces assigned to each partial radiation field, causes the partial radiation fields to be shifted again in the y direction so that they lie in line on the output side of the transformation optics. The cross sections of the beam 5 of the transformation field on the input side and on the output side of the transformation optics.

The mode of operation of the transformation optics 4 is shown schematically in FIG. The representation A shows an elliptical radiation field as it enters the transformation optics 4. This radiation field A is segmented in the transformation optics 4 in the y direction, with the illustration A showing six partial radiation fields by way of example. The segmentation takes place in the direction of the major axis of the ellipse. It can also be seen from the representation A that the respective cross-sectional areas of the partial radiation fields are selected such that they have approximately the same area, i.e. the power of the partial radiation fields is matched to each other by the cross-sectional size. As illustration B of FIG. 6 shows, these partial radiation fields are then shifted in the x direction, so that they are offset in steps from one another, but essentially connect directly to one another in the x direction. In a third stage, indicated by the representation C, these partial radiation fields are then brought together again in the y direction in such a way that they, i.e. the focal points of the beam cross-sections lie on a line.

FIGS. 7 and 9 now show an alternative arrangement for transforming an optical radiation field which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions.

Insofar as components are shown in FIG. 9 which are identical or comparable to those of FIG. 1, the corresponding reference symbols are used as in FIG. 1; A description of these components is not made, so that reference is made to the corresponding explanations for FIG. 1 above. The same applies to the representation of the divergence angles in the lower half of FIG. 9 and the respective beam cross sections on the corresponding planes; the ratios of the divergence angles in the x direction (θ _x ) and (θ _y ) result directly from FIG. 9.

In the arrangement in FIG. 9, a transformation optic 4 'is provided, which is shown in more detail in FIG. This transformation optics 4 ′ has three Dove prisms 7, one of these prisms being assigned to a partial radiation field. Each Dove prism 7 has a base area 8 as well as a first prism area 9 and a second prism area. che 10 on. The respective partial radiation field enters the first prism surface 9, forming an entry surface, is refracted towards the base surface 8 and is reflected from there to the second prism surface 10, forming an exit surface. The angle of the first prism surface 9 and the second prism surface 10 to the base surface 8 or to the direction of propagation of the partial radiation field is so designed, including the base surface 8, that the partial radiation field from the second prism surface 10 has a propagation direction that corresponds to the z direction corresponds, emerges, namely at 90 ° to the z-axis, compared with the orientation of the input-side partial radiation field, rotated. A total of three partial radiation fields with three Dove prisms 7 are shown in FIG. 7 in order to illustrate the principle of this arrangement. However, it can be seen that the transformation optics 4 'can be expanded as desired by segmenting a radiation field into a corresponding number of partial radiation fields and assigning a prism 7 to each partial radiation field in the transformation optics 4'.

FIG. 8 shows a radiation field with an elliptical beam cross section, which is aligned with its large ellipse axis in the y direction. This radiation field is segmented in the y-direction into eight partial radiation fields, which are then rotated around the z-axis with a transformation optic 4 ′, as shown in FIG. 7, so that the radiation field is obtained in accordance with the representation B. It can be seen that the individual, rotated partial radiation fields in the y direction can be brought together by suitable optical measures in order to obtain a coherent radiation field.

With the arrangements as described above, a line with a large aspect ratio without moving components can be generated via a compact optical system. A power density distribution can thus be generated, with essentially the same divergence angles and different beam radii for two directions oriented orthogonally to one another, which are defined by the directions with the maximum and minimum extent of this power density distribution.

Claims

claims

1. Arrangement for transforming an optical radiation field, which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions, by means of a transformation optics in a radiation field with an asymmetrical beam parameter product, the x, y and z -Directions form a right-angled coordinate system, characterized in that first the radiation field (1) with the transformation optics (4) is segmented into at least two partial radiation fields in the y direction, that the partial radiation fields are then shifted in the x direction with the transformation optics (4) , and that these partial radiation fields are shifted in the y-direction with the transformation optics (4) in such a way that the centers of gravity of the partial radiation fields lie on a line that is perpendicular to the line on which the centers of gravity of the partial radiation fields exist before entering the transformation optics (4 ) lie.

2. Arrangement for transforming an optical radiation field, which propagates in the z direction and which has a symmetrical beam parameter product in the x and y directions, by means of a transformation optics into a radiation field with an asymmetrical beam parameter product, the x, y and z Directions form a right-angled coordinate system, characterized in that the radiation field (1) with the transformation optics (4 ') is first segmented into at least two partial radiation fields in the y direction, and that these partial radiation fields are each rotated by 90 ° about the z-axis with the transformation optics (4 ') and the rotated partial radiation fields are combined to form a line in the y direction.

3. Arrangement according to claim 1 or 2, characterized in that a cylindrical optics (3) is arranged on the input side of the transformation optics (4; 4 '), which transforms the radiation field (1) into an elliptical radiation field, with the large axis of the ellipse in y- Lying in the direction, reshaped.

4. Arrangement according to one of claims 1 to 3, characterized in that the segmented partial radiation fields have approximately the same powers.

5. Arrangement according to claim 3 and 4, characterized in that the cross section of a partial radiation field provided is imaged in the plane of the transformation optics (4, 4 ').

6. Arrangement according to claim 4, characterized in that the adjustment of the power of the partial radiation fields is achieved by a changing radius of curvature of the cylindrical lens.

7. Arrangement according to claim 6, characterized in that the optical radiation field (1) in the x and y directions has the same divergence angle (θ _x , θ _y ).

8. Arrangement according to claim 1, characterized in that the transformation optics (4) has a plurality of reflective elements (5, 6), with the reflective elements of the transformation optics (4) being broken down into the partial radiation fields.

9. Arrangement according to claim 8, characterized in that the reflective elements are mirror surfaces (5, 6).

10. The arrangement according to claim 8, characterized in that the reflective elements (5, 6) are formed by totally reflecting surfaces of a radiation-transparent element.

1. Arrangement according to claim 2, characterized in that in the transformation optics (4 ') each partial radiation field is assigned a Dove prism (7) which has a base area and has two prism surfaces which run obliquely to the base area (8), and is thus dimensioned and is oriented such that one prism surface (9) forms an entry surface for the corresponding partial radiation field in such a way that the radiation is refracted towards the base surface, is reflected on the base surface and is rotated through 90 ° to the z-axis on the second prism surface (10) z-direction emerges.