WO2004099856A1

WO2004099856A1 - Light beam splitting device

Info

Publication number: WO2004099856A1
Application number: PCT/EP2004/004924
Authority: WO
Inventors: Wieland Hill
Original assignee: Hentze-Lissotschenko Patentverwaltungs Gmbh & Co. Kg
Priority date: 2003-05-09
Filing date: 2004-05-07
Publication date: 2004-11-18
Also published as: DE10321102A1

Abstract

The invention relates to a light beam splitting device comprising at least one light beam splitter (20, 21, 22) enabling the first part of a divided light beam (26) to be reflected and the second part thereof to penetrate, thereby slitting said light beam (26) into at least two parts. Said invention is characterised in that the inventive beam splitting device also comprises at least one polarisation rotating element (23, 24, 25) which rotates the polarisation of the divided light beam (26), the beam splitter (20, 21, 22) selecting the polarisation

Description

"Splitting device for light rays"

The present invention relates to a splitting device for light beams comprising at least one beam splitter means which can reflect a first portion of a light beam to be split and can allow a second portion of the light beam to pass through such that the light beam is divided into at least two portions.

Splitting devices of the aforementioned type are well known from the prior art as so-called beam splitters. A partially transparent mirror can be used as the beam splitter, for example, which can be arranged in particular at an angle of 45 ° to the light beam to be split. The semitransparent mirror can be coated with one or more layers of a dielectric, so that for a certain wavelength an approximately predeterminable proportion of the light beam to be split is reflected and essentially the rest is transmitted through the mirror. A disadvantage of such beam splitters is that in practice the reflectivity only corresponds to the desired specifications to about ± 5%. For the corresponding specification of the intensities of the reflected or transmitted partial beam, this has the consequence that these fluctuate by, for example, approximately 10%. If a light beam to be split should not only be divided into two but into four partial beams, two or three beam splitters must be used for this purpose, so that the intensities of the partial beams can deviate considerably from the desired intensities. This proves to be disadvantageous, for example, if several holes are to be drilled simultaneously in one workpiece with one laser beam to be split. If the individual partial beams differ significantly in their intensity, the result is only an extremely unsatisfactory one

BESTATIGUNGSKOPIE Work product. The same applies to other areas of application such as the simultaneous labeling, marking, brazing, welding or structuring of materials, medical applications or printing technology.

Therefore, the problem on which the present invention is based is the creation of a splitting device of the type mentioned at the outset, with which a light beam can be split into partial beams, the intensity ratio of which can be specified more precisely.

This is achieved according to the invention in that the splitting device further comprises at least one polarization rotating means which can rotate the polarization of the light beam to be split, the at least one beam splitter being designed as a polarization-selective beam splitter. As a rule, light beams to be split are generated by lasers, so that the light beams to be split will mostly be at least partially linearly polarized. The beam splitter means according to the present invention offers the possibility of splitting the light beam to be split into two partial beams depending on the direction of the linear polarization of the light beam. In particular, the two partial beams will at least partially have a linear polarization perpendicular to each other. By previously rotating the linear polarization of the light beam to be split, the intensity ratio of the two partial beams to one another can therefore be set according to the invention. It is therefore possible to measure the intensities of the at least two partial beams and to change the setting of the polarization rotating means as a function of the measured intensities such that the measured intensity ratio corresponds to the intensity ratio to be achieved. For example, it can be achieved in this way that the at least two partial beams have substantially the same intensity. Such partial beams can thus be used, for example, for the simultaneous drilling of several holes in a workpiece.

In particular, the at least one beam splitter means can be designed such that a portion of the light beam to be split is essentially reflected with a first linear polarization, whereas a portion of the light beam to be split is essentially transmitted with a second linear polarization that is substantially perpendicular to the first. Such an embodiment of a beam splitter means can be implemented comparatively easily and offers the advantage that the partial beams of the split light beam diverge at a comparatively large angle, so that they can be processed further without any problems.

Alternatively, the beam splitter means could, for example, be designed such that at least two portions of the light beam to be split are transmitted at an angle to one another or offset with respect to one another. For example, a birefringent material could be used for such a beam splitter.

According to a preferred embodiment of the present invention, the splitting device comprises a first beam splitter means and at least a second beam splitter means, which can split the light beam to be split into at least three parts. By providing two or more beam splitter means, the light beam to be split can be divided into a larger number of parts. In this way, a plurality of holes can be drilled into a workpiece simultaneously using a single laser beam. According to the invention, it can be provided that the at least one beam splitter means is arranged behind the first beam splitter means with respect to the beam path, so that a partial beam reflected by the latter and / or a partial beam transmitted by the latter can be divided into at least two components. There are at least two different arrangement options. On the one hand, all of the beam splitting means can be arranged one behind the other such that, for example, the partial beam that has passed through the beam splitting means and is not reflected is always divided into two further partial beams. Alternatively, there is the possibility of splitting both the reflected and the transmitted partial beam into two partial beams by means of an additional beam splitter. Correspondingly, there is of course also the possibility of further dividing each of these partial beams by additional beam splitting means when the partial beams are transmitted at an angle to one another by the beam splitting means.

According to a preferred embodiment of the present invention, the splitting device comprises a first polarization rotation means for rotating the polarization of the light beam to be split and at least a second polarization rotation means for rotating the polarization of the partial beams already split. In this way, even when the light beam is divided into more than two partial beams, the intensity ratios of the individual partial beams can be set comparatively easily, because in this case in particular

Splitting device is designed such that the ratio of the intensities of the partial beams emerging from the splitting device can be predetermined by adjusting the at least one polarization rotating means or the at least two polarization rotating means. The reason for this is that each of the polarization-selective beam splitter means in Depending on the polarization of the light incident on the entry surface of the beam splitter means, for example, reflects a correspondingly large proportion and transmits a correspondingly large proportion. In the case of linearly polarized light in particular, the intensity of the reflected portion will correspond exactly to the intensity of the transmitted portion with a specific orientation of the polarization vector. Accordingly, when the polarization rotating means rotates the polarization vector of the linearly polarized light to be divided, the ratio of the intensity of the reflected portion to the intensity of the transmitted portion is changed.

According to a preferred embodiment of the present invention, the at least one beam splitter means is designed as a polarization-selective, partially transparent mirror. Such a polarization-selective semitransparent mirror can in particular have a coating with one or more dielectric layers, so that light of a predefined wavelength and a predefined linear polarization when it hits a certain angle on the entrance surface of the semitransparent mirror is divided into a reflected and a transmitted component, the proportion of which Intensities have a predetermined relationship to each other.

In particular, the normal of the entry surface of the polarization-selective partially transparent mirror is oriented at an angle to the light beam to be divided, which essentially corresponds to the Brewster angle of the material of the partially transparent mirror. At this angle there is in particular the advantage that the transmitted portion does not experience any losses when it emerges from the partially transparent mirror. As an alternative to this, the normal of the entry surface of the polarization-selective partially transparent mirror can also be oriented at an angle of 45 ° to the light beam to be divided. An angle of 45 ° can be advantageous under certain circumstances because in this case the reflected light beam forms an angle of 90 ° to the light beam to be split.

According to the invention, it can in particular be provided that the exit surface of the partially transparent mirror is anti-reflective, in particular provided with a reflection-reducing coating. In the event that the semitransparent mirror is not arranged under the Brewster angle, the antireflection coating can prevent the transmitted light beam from experiencing losses when it leaves the semitransparent mirror.

According to an alternative embodiment of the present invention, the at least one beam splitter means is designed as a polarization cube. Polarization cubes are well known and offer an effective way of dividing a light beam into two partial beams, the linear polarization of which is oriented perpendicular to one another. Furthermore, the division by means of a polarization throw has the advantage that the light beam to be split and the reflected partial beam as well as the reflected and the transmitted partial beam each form an angle of 90 ° with one another.

According to the invention, it can further be provided that the at least one polarization rotating means is designed as a half-wave plate. A half-wave plate consists, for example, of birefringent material such as quartz and represents a simple and reliable possibility of rotating the linear polarization of a light beam. By rotating the The angle of rotation of the polarization and thus the division ratio on the beam splitter means can be adjusted in the plate around the direction of propagation. Alternatively, two quarter-wave plates or compensators such as Babinet compensators can be used. Alternatively, optically active materials of suitable thickness can also be used as the polarization rotating means. The angle of rotation is fixed by the material thickness.

For unpolarized or partially polarized light, the direction of polarization can naturally only be set to a limited extent. A first polarization of the beam splitter means, however, produces polarized partial beams which can be further divided as described above. Unpolarized light is divided into almost equally intense partial beams at the first beam splitter. For partially polarized light, the polarization direction and thus the division ratio can be set in a range determined by the degree of polarization using a polarization rotating means in front of the first polarizing beam splitter means. In particular, equally intense partial beams can be generated in this way.

According to the invention, it can be provided that means are provided for coupling the partial beams into optical fibers.

According to the invention, it can further be provided that the at least one beam splitter means and the at least one polarization rotating means are implemented in one component. For example, the exit surface of the polarization rotating means can be provided with a polarization-selective coating, which acts as a beam splitter. In this way, the manufacturing effort can be minimized. Further features and advantages of the present invention will become clear from the following description of preferred exemplary embodiments with reference to the accompanying figures. Show in it

Fig. 1 is a schematic side view of a first

Embodiment of a dividing device according to the invention;

2 shows a schematic side view of a second embodiment of a splitting device according to the invention;

3 shows a schematic side view of a third embodiment of a splitting device according to the invention;

Fig. 4 is a schematic side view of a fourth embodiment of a splitting device according to the invention.

1 that the embodiment of a splitting device according to the invention shown therein comprises two beam splitter means 1, 2 and two polarization rotating means 3, 4. The beam splitter means 1, 2 are designed in such a way that they reflect or pass light incident on them in a polarization-selective manner. The beam splitter means 1, 2 can be designed, for example, as polarization-selective, partially transparent mirrors, in particular with a corresponding dielectric coating, or as polarization cubes. The polarization rotation means 3, 4 can, for example, as Half-wave plates, optically active crystals or as compensators or the like.

In the embodiment shown in FIG. 1, the light beam 6 emerging from a glass fiber 5 is to be split into individual partial beams 6a, 6c, 6d, which for example have the same intensity. For this purpose, the light beam 6 emerging from the glass fiber 5 is collimated, for example, by a lens 7.

The light beam 6 emerging from the optical fiber 5 can be at least partially linearly polarized in the exemplary embodiment shown in FIG. 1. This will usually be the case when the light beam 6 is generated by a laser and the polarization in the optical fiber 5 is maintained. After passing through the lens 7, the collimated light beam 6 passes through the first polarization rotating means 3. By means of this polarization rotating means 3, the at least partially linear polarization of the light beam 6 can be rotated as desired.

After passing through the first polarization rotating means 3, the light beam 6 to be split strikes the first beam splitting means 1. In the exemplary embodiment shown, this is oriented such that the angle between the solder on the entry surface and the light beam 6 incident on this entry surface approximately corresponds to the Brewster angle of the material of the first beam splitter means 1. In the embodiment shown in FIG. 1, this is approximately 56 °. At the entry surface of the first beam splitter means 1, a portion of the light beam 6 is reflected into a partial beam 6a. Another part of the light beam 6, which has a linear polarization perpendicular to the reflected part, passes through the first beam splitter means 1 and leaves it as a partial beam 6b. Because of the arrangement of the beam splitter means 1 at the Brewster angle there are no reflection losses when the partial beam 6b emerges.

The reflected partial beam 6a can be coupled into a glass fiber 11 by a further lens 8. The partial beam 6b which has passed through the first beam splitter means 1 passes through the second polarization rotating means 4 and then hits the second beam splitter means 2. Like the first beam splitter means 1, the second beam splitter means 2 is arranged in such a way that the partial beam 6b is incident on the entrance surface of the beam at a Brewster angle second beam splitter means 2 strikes. Correspondingly, a first part of the partial beam 6b is converted into a reflected partial beam 6c and a second part, which has a linear polarization rotated by 90 ° with respect to the first part, passes through the second beam splitter means 2 as a partial beam 6d. The partial beam 6d in turn experiences no losses when it emerges from the second beam splitter means 2 due to the alignment at the Brewster angle.

The partial beams 6c and 6d can be coupled into further glass fibers 12, 13 by further lenses 9, 10.

With a corresponding rotation of the polarization rotating means 3, 4 it can be achieved, for example, in the case of a linearly polarized light beam 6 to be split that the intensities of the partial beams 6a, 6c, 6d are of the same size. Furthermore, the intensities of the partial beams 6a, 6c, 6d can be set in any desired relationship to one another by appropriate settings of the polarization rotating means 3, 4. For example, it can be achieved that the intensities of the partial beams 6c, 6d are of the same size, whereas the intensity of the partial beam 6a is as large as the intensity of the partial beams 6c, 6d together. According to the invention, there is also the possibility of using a plurality of additional polarization rotating means and beam splitting means in the beam direction behind the second beam splitting means 2 in the partial beam 6d and corresponding partial beams resulting therefrom. Furthermore, there is also the possibility of introducing further polarization rotating means and beam splitting means into the partial beams 6a and 6c. This is particularly useful if the light beam 6 to be split is not or only slightly linearly polarized, as is often the case with multimode fibers. Then, by adjusting the polarization rotating means 3, no change in the ratio of the intensities of the partial beams 6a and 6b can be brought about because these are then usually of the same intensity. In this case, an arrangement as described below in relation to FIG. 3 is particularly useful.

2 shows a further embodiment of a splitting device according to the invention, in which three beam splitter means 13, 14, 15 and three polarization rotating means 16, 17, 18 are provided. These beam splitter means 13, 14, 15 serve to split a light beam 19, which in the exemplary embodiment shown is designed as a collimated laser beam. After passing through the first polarization rotating means 16, the laser beam 19 is divided into two partial beams 19a, 19b by the first beam splitting means 13. The division takes place analogously to the division of the light beam 6 into the partial beams 6a and 6b by the first beam splitter means 1 according to FIG. 1. In particular, in the exemplary embodiment according to FIG. 2, the beam splitter means 13, 14, 15 are also aligned at a Brewster angle to the incident light beams 19 or partial beams 19b, 19d.

The partial beam 19b which has passed through the first beam splitting means 13 passes through the second polarization rotating means 17 and becomes thereon then split by the second beam splitter means 14 into two partial beams 19c and 19d. The partial beam 19d which has passed through the second beam splitting means 14 passes through the third polarization rotating means 18 and is then subsequently divided into two partial beams 19e, 19f by the third beam splitting means 15.

Again, there is the possibility of arbitrarily selecting the intensity ratios of the partial beams 19a, 19c, 19e, 19f to one another by appropriately adjusting the polarization rotating means 16, 17, 18. For example, there is in particular the possibility of selecting the intensities of the partial beams 19a, 19c, 19e, 19f all of the same size.

According to the invention, there is of course the possibility in the embodiment according to FIG. 2 to arrange a further polarization rotation means and a further beam splitting means in the individual partial beams, for example in the partial beam 19f, so that the partial beam 19f is again divided into two partial beams. In particular, there is the possibility of arranging any number of polarization rotating means and beam splitting means one behind the other, so that the light beam 19 can be divided into any number of partial beams.

3 shows an exemplary embodiment which essentially corresponds to the exemplary embodiment according to FIG. 2. Three beam splitter means 20, 21, 22 and three polarization rotating means 23, 24, 25 are also provided here by way of example. In the exemplary embodiment in FIG. 3, a collimated laser beam 26 is likewise to be divided into individual partial beams 26c, 26d, 26e, 26f. The first beam splitter means 20 is divided into a reflected partial beam 26a and a transmitted one Partial beam 26b instead. In contrast to the exemplary embodiment according to FIG. 2, however, in the exemplary embodiment according to FIG. 3, a polarization rotating means 24, 25 and a beam splitting means 21, 22 are provided both in the beam path of the reflected partial beam 26a and in the beam path of the transmitted partial beam 26b. In this way, the reflected partial beam 26a is divided into two partial beams 26c, 26d, whereas the transmitted partial beam 26b is divided into two partial beams 26e and 26f.

Such an arrangement proves to be particularly advantageous in the case of a non-polarized light beam 26 to be split. In this case, the intensities of the partial beams 26a, 26b split by the first beam splitter means 20 are the same because the light from a first linear polarization is reflected and the light from a second linear polarization perpendicular to it is transmitted, and at the same time the unpolarized light is picked out arbitrarily by these two Linear polarizations includes equally large portions. The intensities of the partial beams 26c, 26d, 26e, 26f can nevertheless be set correspondingly to one another by the corresponding setting of the second polarization rotation means 24 and the third polarization rotation means 25.

According to the invention, there is definitely the possibility, in addition to the beam splitter means 20, 21, 22 shown in FIG. 3 or in addition to the polarization rotating means 23, 24, 25 shown in FIG. 3, additional beam splitter means and polarization rotating means in the individual partial beams 26c, 26d, 26e, 26f in order to divide them up under certain circumstances. Furthermore, there is of course also the possibility of using an arrangement shown in FIG. 3 for light beams to be collimated emerging from an optical fiber in accordance with the embodiment according to FIG. 1. 4 shows an embodiment of a splitting device according to the invention, which comprises two beam splitter means 27, 28 and two polarization rotating means 29, 30 by way of example. These divide together a light beam 31, for example a collimated laser beam, into partial beams 31 a, 31 c, 31 d. In contrast to the embodiments according to FIGS. 1 to 3, in the embodiment according to FIG. 4, however, the beam splitter means 27, 28 are not oriented at a Brewster angle to the incident light beam 31 or 31 b, but at an angle of 45 °. Because of the reflection of the reflected steep rays 31 a, 31 c at an angle of 90 °, this angle can offer advantages for various applications. In order to prevent losses of the partial beams 31b, 31d passing through the beam splitter means 27, 28 at the exit, in such an arrangement the exit surfaces of the beam splitter means 27, 28 arranged on the right in FIG. 4 can be anti-reflective, for example by a corresponding one anti-reflective coating.

According to the invention, there is of course the possibility, also in the embodiments according to FIGS. 1 to 3 or in the variations described in connection with FIGS. 1 to 3, the beam splitter means 1, 2, 13, 14, 15, 20, 21, 22 to be arranged at an angle of 45 ° to the incident light beams or partial beams or at any other angle.

Claims

claims:

1 . Splitting device for light beams comprising at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28) which reflect a first portion of a light beam (6, 19, 26, 31) to be split and a second portion of the light beam (6, 19, 26, 31) can pass through such that the light beam (6, 19, 26, 31) is divided into at least two parts, characterized in that the distribution device further comprises at least one polarization rotation means (3, 4 , 16, 17, 18, 23, 24, 25, 29, 30) which can rotate the polarization of the light beam (6, 19, 26, 31) to be split, the at least one beam splitter means (1, 2, 13, 14 , 15, 20, 21, 22, 27, 28) is designed as a polarization-selective beam splitter.

2. Splitting device according to claim 1, characterized in that the at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28) is designed such that a portion of the light beam to be split (6, 19 , 26, 31) is essentially reflected with a first linear polarization, whereas a portion of the light beam (6, 19, 26, 31) to be split is essentially transmitted with a second linear polarization that is essentially perpendicular to the first.

3. Splitting device according to claim 1, characterized in that the at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28) is designed such that at least two portions of the light beam to be split (6, 19, 26, 31) are transmitted at an angle to one another or offset from one another, preferably using a birefringent material for the at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28).

4. splitting device according to one of claims 1 to 3, characterized in that the splitting device comprises a first beam splitter means (1, 13, 20, 27) and at least a second beam splitter means (2, 14, 15, 21, 22, 28), which can divide the light beam (6, 19, 26, 31) to be divided into at least three parts.

5. Splitting device according to claim 4, characterized in that the at least one second beam splitter means (2, 14, 15, 21, 22, 28) is arranged behind the first beam splitter means (1, 13, 20, 27) with respect to the beam path, so that a partial beam (6a, 19a, 26a, 31a) reflected by this and / or a partial beam (6b, 19b, 26b, 31b) transmitted by it can be divided into at least two parts.

6. Splitting device according to one of claims 4 or 5, characterized in that the splitting device comprises a first polarization rotation means (3, 16, 23, 29) for rotating the polarization of the light beam to be split (6, 19, 26, 31) and at least a second Polarization rotating means (4, 17, 18, 24, 25, 30) for rotating the polarization of the already divided partial beams (6a, 6b, 19b, 19d, 26a, 26b, 31b).

7. Distribution device according to one of claims 1 to 6, characterized in that the distribution device is designed such that by adjusting the at least one polarization rotating means (3, 4, 16, 17, 18, 23, 24, 25, 29, 30) that Ratio of the intensities of from the Splitting device emerging partial beams (6a, 6c, 6d, 19a, 19c, 19e, 19f, 26c, 26d, 26e, 26f, 31 a, 31 c, 31 d) can be specified.

8. Splitting device according to one of claims 1, 2, 4 to 7, characterized in that the at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28) is designed as a polarization-selective partially transparent mirror ,

9. Splitting device according to claim 8, characterized in that the normal of the entrance surface of the polarization-selective partially transparent mirror is oriented at an angle to the light beam to be split (6, 19, 26, 31), which essentially corresponds to the Brewster angle of the material of the partially transparent mirror.

10. Splitting device according to claim 8, characterized in that the normal of the entry surface of the polarization-selective partially transparent mirror is oriented at an angle of 45 ° to the light beam to be split (6, 19, 26, 31).

1 1. Distribution device according to one of claims 7 to 10, characterized in that the exit surface of the partially transparent mirror is anti-reflective, in particular is provided with a reflection-reducing coating.

12. Splitting device according to one of claims 1, 2, 4 to 7, characterized in that the at least one beam splitter means (1, 2, 13, 14, 15, 20, 21, 22, 27, 28) is designed as a polarization cube.

13. Splitting device according to one of claims 1 to 12, characterized in that the at least one polarization rotation means (3, 4, 16, 17, 18, 23, 24, 25, 29, 30) is designed as a half-wave plate.

14. Distribution device according to one of claims 1 to 13, characterized in that the at least one polarization rotating means (3, 4, 16, 17, 18, 23, 24, 25, 29, 30) is designed as an optically active material of suitable thickness.

15. Splitting device according to one of claims 1 to 14, characterized in that means are provided for coupling the partial beams (6a, 6c, 6d) in light guide fibers (1 1, 12, 13).

16. Splitting device according to one of claims 1 to 15, characterized in that the at least one beam splitter means and the at least one polarization rotating means are realized in one component.