Beam forming device for laser diode arrays

A device forms laser radiation which has partial beams interspaced in a first direction that is perpendicular to the direction of propagation of the laser radiation, especially for forming laser radiation which is emitted by a laser diode bar. The device contains a plurality of reflective surfaces on which at least one of the interspaced partial beams can be reflected in such a manner that the distances of the partial beams are smaller relative to each other after reflection than before reflection.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a device for shaping laser radiation having partial beams spaced apart from one another in a first direction, which is perpendicular to the propagation direction of the laser radiation, in particular for shaping laser radiation that emerges from a laser diode bar.

Definitions: in the propagation direction of the light to be influenced means the average propagation direction of the light, particularly if the latter is not a plane wave or is at least partly convergent or divergent. Light beam, partial beam or beam, unless expressly indicated otherwise, does not mean an idealized beam from geometric optics, but rather a real light beam, such as a laser beam having a Gaussian profile, for example, which has an extended beam cross section rather than an infinitesimally small beam cross section.

Laser diode bars have a plurality of emitters, for example 19 emitters, which are arranged in a manner spaced apart from one another in the so-called slow axis. The slow axis is the first direction mentioned in the introduction, in which the active layer of the semiconductor diode extends, whereas the fast axis is the direction perpendicular thereto. By way of example, each of the emitters has a length of approximately 150 μm in the slow axis, wherein the distance between two adjacent emitters in this direction is approximately 400 μm. That has the consequence that dark regions are present between the partial beams emerging from the individual emitters, said dark regions proving to be disadvantageous for the brightness (specific intensity) of the laser radiation.

In the prior art, the partial beams of the laser diode bars which emerge from the individual emitters are collimated by micro-optics in the fast axis and partly also in the slow axis without the periodicity of the beams of the individual emitters being manipulated in this case. One example of this is found in WO 2005/085934 A1. In this prior art, accordingly, depending on the application purpose, further beam-shaping optics are used in order to obtain a specific beam profile. In this case, the dark region between the emitters is accepted, which sets a limit on the brightness that can be obtained. Consequently, a structurally imposed limit for the brightness of the entire laser system arises on account of the bar structure, said limit being countably distant from the physical limit.

A further example of a beam-shaping optical unit is found in DE 101 06 155 A1, where the laser radiation emerging from a laser diode bar is split into two parts in the slow axis, wherein these parts are subsequently arranged one above the other in the fast axis. As a result, the cross section of the laser radiation is converted from an elongated rectangular form into a less elongated rectangular form, which can be better focused onto the end of an optical fiber.

A further example of a beam-shaping optical unit is found in German patent application 10 2007 061 358. 1, which has not been published heretofore. The device described therein is depicted inFIG. 1and comprises a first substrate1having a first refractive interface2, which serves as an entrance surface and which can deflect at least a plurality of the partial beams of the laser radiation to be shaped differently in such a way that they run at least partly more convergently with respect to one another after passage through the first interface than before passage through the first interface. The exit surface3of the first substrate1is embodied in plane fashion. The device furthermore comprises a second substrate4having a plane entrance surface5and an exit surface, which serves as a second refractive interface6and through which the laser radiation that has passed through the first interface2can pass, wherein the second interface6can deflect at least some of the partial beams in such a way that the convergence thereof is reduced. In this case, as a result of reducing or eliminating the distance between the partial beams in the first direction, it is possible for the dark region between the individual partial beams to be reduced in size, such that the brightness that can be obtained can be brought closer to the physical limit.

The two refractive interfaces2,6are structured and have, in particular, a multiplicity of surfaces inclined with respect to one another. On account of the fact that two structured surfaces are provided, a low effectiveness (performance) of the device known from the prior art arises on account of shape deviations and microroughnesses of these structured surfaces.

BRIEF SUMMARY OF THE INVENTION

The problem addressed by the present invention is that of providing a device of the type mentioned in the introduction which is more effective.

In accordance with the invention, it is provided that a device contains a plurality of reflective surfaces at which in each case at least one of the partial beams spaced apart from one another can be reflected in such a way that the distances between the partial beams are smaller after reflection than before reflection. On account of the fact that rather than two substrates with two structured surfaces being provided, in particular only one substrate with one structured surface is provided, which surface forms the plurality of reflective surfaces, a series of advantages are afforded. Firstly, the production costs can be reduced. Secondly, on account of the reduction of the number of structured surfaces, the faults can be reduced and the effectiveness (performance) can thus be increased.

In accordance with another embodiment of the invention, it is provided that the device contains a substrate having a first refractive interface, which serves as an entrance surface, and a second refractive interface, which serves as an exit surface, wherein the first and/or the second interface are/is configured in such a way that the distances between the partial beams are smaller after passage through the substrate than before said passage.

In this case, in particular, only one of the two interface is structured, whereas the other of the two interfaces is plane. The same advantages as discussed above are afforded as a result.

Furthermore, the device can be configured such that the beam parameters of the laser radiation can be altered.

In accordance with a further preferred configuration of the embodiment in accordance with the invention, it can be provided that the substrate can rotate the partial beams, in particular can rotate them by 90° about the propagation direction. By way of example, in this case, each of the two interfaces can have a plurality of cylindrical lenses, the cylinder axes of which are inclined, preferably inclined by 45°, with respect to the direction in which the partial beams are arranged alongside one another. In this way, the device, in addition to reducing the distances between the partial beams, can perform the function of beam rotation, which is fulfilled for example by the device in accordance with EP 1 006 382 A.

Further features and advantages of the present invention will become clear from the following description of preferred exemplary embodiments with reference to the accompanying drawings, in which:

In the figures, identical or functionally identical parts are provided with identical reference symbols.

DESCRIPTION OF THE INVENTION

FIG. 2shows a device comprising a substrate10, which has a structured surface11. Said structured surface11forms a plurality of reflective surfaces12, between which steps13are arranged.

Instead of one substrate10, it is also possible for a plurality of substrates to be provided, which have in each case at least one structured surface at which in each case a plurality of reflective surfaces are formed.

Partial beams14incident from the left inFIG. 2impinge on the reflective surfaces12and are reflected from the latter downward inFIG. 2. As a result of the steps13between the reflective surfaces12, the distance a between the partial beams14before reflection is reduced with respect to a distance b between the reflected partial beams15after reflection.

FIG. 3shows a comparable device. The distance b between the reflected partial beams15can be influenced by the height of the steps13.

The reflective surfaces12can be metal mirrors or glass having a highly reflective coating. There is also the possibility of using other materials such as semiconductors or ceramics. Furthermore, the reflections at the reflective surfaces can also be effected by total internal reflections.

On account of the individual partial beams14,15having beam paths of different lengths, a slanted slow-axis collimation means16is arranged downstream of the substrate10(seeFIG. 4). The beam paths of different lengths are taken into account and compensated for by the slanted positioning. In this case, the slow-axis collimation means16can be embodied in aspherical fashion.

There is also the possibility of arranging a slow-axis collimation means upstream of the substrate10, although said collimation means is not slanted in this case.

In the case of the embodiment in accordance withFIG. 5, a transparent substrate20is provided, which comprises a structured first interface21, which serves as an entrance surface, and a plane second interface22, which serves as an exit surface. The first interface21has prism sections23on which the incident partial beams24impinge. In the exemplary embodiment depicted, the prism sections23correspond to one another and are oriented parallel to one another. The partial beams24are refracted by the prism sections23in such a way that they run parallel to the imaginary base surface25of the prism sections23within the substrate. After repeated refraction at the plane second interface22, the distance a between the partial beams24prior to passage through the substrate is reduced with respect to the distance b between the partial beams26.

In the case of the abovementioned beam course parallel to one another or to the imaginary prism base surfaces, the beam parameters of the partial beams are not altered.

By altering the topology of the first and/or the second interface, the beam parameters can be altered.

By way of example, the beams can have a smaller divergence with a larger diameter or vice versa. In this case, there is indeed the possibility that the prism sections23and base surfaces are embodied in such a way that, or the partial beams24impinge on the prism sections23at an angle such that, the partial beams24do not run parallel to the base surfaces25within the substrate.

For the collimation of the partial beams24,26, a slanted slow-axis collimation means is likewise expedient as a result of the beam paths of different lengths.

FIG. 6shows a perspective view of a device for beam rotation in accordance with EP 1 006 382 A. Said device comprises a substrate30having a structured first interface31, which serves as an entrance surface, and a structured second interface32, which serves as an exit surface, wherein each of the interface31,32has a plurality of cylindrical lenses33,34arranged at an angle of 45° with respect to the direction in which the partial beams35are arranged alongside one another.

The cylindrical lenses33,34of the interface31,32form a telescope arrangement. A respective one of the partial beams35impinges on one of the cylindrical lenses33. By means of a device of this type, the partial beams35are rotated by 90° about the propagation direction (see the rotated partial beams36inFIG. 6).

FIG. 7shows that a partial beam35impinging centrally on one of the cylindrical lenses33also leaves the opposite cylindrical lens34centrally again as a partial beam36.FIG. 8shows that a partial beam35impinging eccentrically, in particular here above the center, likewise leaves the opposite cylindrical lens34eccentrically again, although here below the center, as a partial beam36. This effect is exploited by the fourth embodiment of a device according to the invention, as depicted inFIG. 9.

The cylindrical lenses33on the first interface31are extended and arranged in such a way that although the central partial beam35aimpinges centrally on the corresponding cylindrical lens33a, the partial beams35b,35carranged further above and further below impinge eccentrically. In particular, the degree of eccentricity increases with increasing distance from the center of the first interface31.

As a result, the partial beams35b,35care deflected toward the center, such that they emerge from the correspondingly extended and arranged cylindrical lenses34a,34b,34ccloser to one another. The distances a between the partial beams35a,35b,35cbefore passage through the lenses are therefore reduced to the distances b between the partial beams36a,36b,36c. In this case, the pitch (center-to-center distance) of the cylindrical lenses34a,34b,34cis smaller than that of the cylindrical lenses33a,33b,33cbecause the partial beams move closer together.

FIG. 10schematically shows the displacement of the emerging partial beams36a,36b,36crelative to the entering partial beams35a,35b,35cinward.