DE102011003142A1 - Diode laser arrangement has dispersive optical device that diffracts laser beams collimated by collimator lens, and focusing device focuses laser beam on entry-side end of fiber - Google Patents

Abstract

The arrangement has several diode laser sources for creating several laser beams (3a-3n) with different wavelengths. Several optical fibers are provided to guide respective laser beams. The exit-side ends of optical fibers are arranged parallel to each other at specific distances (d1-dN). A collimator lens (6) collimates the laser beams. A dispersive optical device (7) diffracts collimated laser beams. The focusing device focuses laser beam on entry-side end of fiber.

Description

The present invention relates to a diode laser array having a plurality of diode laser sources.

Diode laser sources are characterized by high efficiency and can be provided in particular in a compact design. Due to the poorer beam quality compared to solid state lasers, the potential for the direct application of diode lasers has been limited. Due to the enormous power development in the semiconductor sector, however, diode laser sources are now available, the lamp-pumped solid-state lasers with simultaneously improved. Completely replace efficiency.

The core task for the further development of diode laser sources is to increase the brilliance. Known techniques for increasing the brilliance of diode lasers are polarization coupling and wavelength coupling with dichroic mirrors. However, these techniques have limited physical limits in terms of power scaling in the multi-kW range.

From the US 6,791,751 B2 It is known to spatially superimpose two optical pump beams with different polarization states with the aid of a birefringent crystal, so that a single (pump) laser beam is formed. However, the possibility of polarization superposition is limited to the use of two pump light sources. This results from the fact that only two polarizations can be separated and superimposed cleanly. A superposition of a plurality of laser sources is therefore not possible with the polarization coupling.

Another possibility for increasing the brilliance is the so-called wavelength coupling. In this case, laser radiation from diode laser sources of different wavelengths is superimposed by means of dichroic mirrors. Dichroic mirrors reflect only radiation at a given, predetermined wavelength, but are transparent to radiation of other wavelengths. However, dichroic mirrors as wavelength-coupling elements must cover a broad spectral range (typically 30-40 nm) due to the natural spectral width of the radiation of a single diode laser source and the wavelength increase as it increases the operating temperature (chirp) of the laser diodes. Therefore, also in this case, the number of combinable diode laser sources is limited.

If it is possible to narrow down the spectral bandwidth of the laser diodes, it is possible to increase the number of beam sources to be superimposed, as in the US Pat WO 2006/116477 A2 or the US 2010/0110556 A1 is described. For superimposition, dispersive optical elements are used, which exploit the property that laser beams of different wavelengths, which impinge on a dispersive optical element at different angles, with a suitable choice of angles or wavelengths, superimpose themselves into a single laser beam with several wavelengths ,

The US Pat. No. 6,697,192 B1 describes a fiber laser in which the overlay effect described above is exploited to form a common external resonator for a plurality of amplifier fibers. In this case, the laser beams emitted by the individual amplifier fibers are combined via the dispersive optical element in the form of a grating into a single laser beam having a plurality of wavelengths, which is reflected at an end mirror of the external resonator. By suitable choice of parameters, eg. As the orientation of the grating, the wavelengths of the laser beams generated by the amplifier fibers can be influenced.

Object of the invention

It is the object of the present invention to provide a diode laser arrangement which enables the generation of a laser beam with high brilliance.

Subject of the invention

This object is achieved by a diode laser array, comprising: a plurality of diode laser sources for generating a plurality of laser beams having different wavelengths, a plurality of optical fibers for guiding a respective laser beam of a diode laser source, wherein exit ends of the optical fibers are arranged parallel to each other and at predetermined intervals a collimating optics for collimating the plurality of laser beams emerging from the ends of the optical fibers, a dispersive optical device for diffracting the plurality of collimated laser beams to produce a single laser beam having a plurality of wavelengths, and focusing optics for focusing the beam generated by the dispersive optical device Laser beam on an inlet end of a Auskoppelfaser.

In such a diode laser arrangement can be realized by the dense wavelength coupling on the dispersive optical element, a compact and reliable design, which makes it possible to produce reproducible high laser performance with good beam quality and brilliance without great adjustment effort. As dispersive optical Element typically serves as a grid, but it may be possible to use other dispersive optical elements for superimposing the laser beams. It is understood that the properties of the grating - in particular the lattice constant and thus dispersion - must be adapted to the diode laser arrangement or to the wavelengths used must.

In order to realize the wavelength coupling, diode laser sources are used in the diode laser arrangement which generate laser radiation with a small spectral width (for example of approximately 0.3 nm). In this way, an accurate, predetermined wavelength difference between the individual diode laser sources can be generated, which is typically between about 1 nm and about 4 nm. The number of diode laser sources may be more than ten, or even more than fifteen, in such a structure.

In a dense wavelength coupling, it is important that the exit-side ends of the optical fibers are accurately and reproducibly arranged or aligned. In one embodiment, the diode laser arrangement for this purpose has a common carrier for parallel alignment of the exit ends of the optical fibers at predetermined distances from each other.

The provision of a common support for the exit-side ends of the optical fibers allows a reproducible, parallel alignment of the optical fibers, so that the end faces of the exit-side fiber ends can be arranged in a common plane, the z. B. can correspond to the focal plane of the collimating optics. By the common carrier, in particular, the distances of the optical fibers to each other can be set reproducible.

In a further development, the common carrier has a plurality of parallel, in particular V-shaped recesses for receiving a respective exit-side end of an optical fiber. With the help of the recesses, the optical fibers can be guided parallel to each other, wherein the distance of adjacent recesses determines the distance between the fiber ends to each other. It is understood that instead of V-shaped depressions and wells with another, z. B. round geometry can be used.

In an alternative development, the carrier has a flat base surface on which the outlet-side ends of the optical fibers are arranged and fixed next to one another, wherein the lateral surfaces of adjacent optical fibers touch. In this way, a distance between the respective centers of the optical fibers can be set, which corresponds to the diameter of the optical fibers. For fixing the optical fibers on the carrier, the z. B. may be in the form of a glass plate, fixed by gluing or otherwise. For example, a clamping device, for. As a rectangular sleeve, with the dimensions of the juxtaposed fiber ends of the optical fibers are used for fixing. In this case, care should be taken not to clamp the fiber ends too much as this would cause a deterioration of the numerical aperture.

In a further embodiment, a distance between the lateral surfaces of the outlet ends of adjacent optical fibers is less than 20 microns. If a dense wavelength coupling is realized in which the wavelength difference between the individual diode laser sources is only a few nanometers, it is necessary to arrange the fiber ends at intervals which are in the micrometer range. The distances should be set as exactly as possible to the value that is optimal for the construction of the diode laser array. This is made possible by means of the carrier described above without complex adjustment.

In a further embodiment, the collimating optics simultaneously serve as focusing optics for focusing the laser beam with the plurality of wavelengths, whereby a compact construction of the diode laser arrangement can be realized. The use of a collimating optics as a focusing optics is also referred to as a Littrow arrangement. The angle at which the grating is tilted to the ends of the optical fibers to allow such an application is also referred to as the Littrow angle. The Littrow angle results from the wavelength used, the diffraction order used and the lattice constant of the lattice. As a diffraction order, preferably the 1st diffraction order is chosen, since the diffraction losses are lowest there. The lattice constant is determined to match the structure and the wavelength difference. In such a construction, the angle at which each of the laser beams strikes the grating corresponds to the first diffraction order of the central wavelength grating, i. H. the mean value of the wavelengths of the laser beams of the diode laser sources, while the laser beam produced by the superimposition of the -1. Diffraction order of the grid corresponds.

In the Littrow arrangement, both the end faces of the exit-side fiber ends of the plurality of optical fibers and the front side of the entry-side end of the coupling-out fiber are typically arranged in the focal plane of the collimation and focusing optics. The entrance side In this case, the end of the coupling-out fiber preferably runs parallel and offset relative to the outlet-side ends of the optical fibers. Also, the distance of the inlet end of the Auskoppelfaser should be as small as possible to a common plane in which the exit-side ends of the plurality of optical fibers. In particular, this distance should be less than 10 mm in order to minimize aberrations as far as possible.

As an alternative to using the collimating optics as focusing optics, both optics can of course also be designed as physically separate assemblies. In this case, the exit-side ends of the plurality of optical fibers and the entrance-side end of the decoupling fiber are spaced further apart from each other than in the Littrow arrangement, and typically at an angle to each other.

In a further embodiment, the optical fibers have an identical or smaller core diameter than the coupling-out fiber. When imaging the end faces of the fiber ends of the optical fibers on the front side of the fiber end of the coupling fiber in this case, the beam quality is maintained and the brilliance is increased by the wavelength coupling. Typically, Auskoppelfasern be used with a core diameter between about 50 microns and about 200 microns, with which a power between typically about 150 watts and about 1.5 KWatt or more can be transported.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and the features listed further can be used individually or in combination in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Show it:

1a , b show schematic representations of a side view and a top view of a first embodiment of a diode laser arrangement according to the invention,

2 a three-dimensional representation of a detail of the diode laser array of 1a , b with a carrier,

3 a sectional view of a carrier with a plurality of contacting optical fibers, and

4 a plan view of a second embodiment of a diode laser array according to the invention.

1a , b show a diode laser arrangement 1 in a side view and in a plan view. The diode laser array 1 has a plurality of diode laser sources 2a , ..., 2n in the form of wavelength-stabilized diode laser modules having a corresponding number of laser beams 3a , ..., 3n each with different wavelengths λ ₁ , ..., λ _N , which directly into a plurality of optical fibers 4a , ..., 4n be coupled. It is understood that alternatively between the diode laser sources 2a , ..., 2n and the optical fibers 4a , ..., 4n a (not shown) coupling optics may be provided, for. B. in the form of a plurality of microlenses.

The number of diode laser sources 2a , ..., 2n This typically varies between three and fifteen, with the spectral width of that of a respective diode laser source 2a , ..., 2n generated laser radiation to the spectral intensity maximum typically about 0.3 nm.

The spectral distance between the wavelengths λ ₁ ,..., Λ _{N of} the individual diode laser sources 2a , ..., 2n is constant in the present example and is in each case 2 nm, ie the wavelengths λ ₁ ,..., λ _N differ by 2 nm in each case. B. the first wavelength λ ₁ in a wavelength range between 900 nm and 1070 nm, z. At 930 nm, the second wavelength λ ₂ at 930 + 2 nm, etc. Typical values for the spectral distance are between about 1 nm and about 4 nm. It is understood that the spectral distance between the wavelengths λ ₁ , ..., λ _{N of} the diode laser sources 2a , ..., 2n not necessarily constant, but may also vary, in which case, the distance between the optical fiber cable to each other is not constant and must be varied accordingly.

The from the diode laser sources 2a , ..., 2n generated laser beams 3a , ..., 3n occur at the front of a respective exit end 5a , ..., 5n the optical fibers 4a , ..., 4n out. The exit-side fiber ends 5a , ..., 5n are here arranged in a common plane (X, Z plane of an XYZ coordinate system) with predetermined distances d ₁ ,..., d _N between adjacent optical fibers 4a , ..., 4n , The distances d ₁ ,..., D _N are in this case between the centers or the center lines of adjacent fiber ends 5a , ..., 5n measured and are typically in the micrometer range. The distances r ₁ , ..., r _N between the lateral surfaces of adjacent fiber ends 5a , ..., 5n the optical fibers 4a , ..., 4n are typically less than 20 microns.

The at the end faces of each fiber end 5a , ..., 5n emerging laser beams 3a , ..., 3n meet a collimator optics, which in the present example as a single lens 6 (With focal length f) is formed in the focal plane, the end faces of the fiber ends 5a , ..., 5n are arranged. The spatial distribution of the laser light in the focal plane is through the lens 6 in an angular distribution on a dispersive optical element in the form of a grating 7 converted, ie the laser beams 3a , ..., 3n meet at different angles on the grid 7 on, which is near another focal plane of the lens 6 is positioned.

By the dispersion of the grid 7 become the individual spatially separated, incident at different angles laser beams 3a , ..., 3b due to their respective different wavelengths λ ₁ , ..., λ _N at a common angle from the grating 7 reflects and thus a dense wavelength coupling of the individual laser beams 3a , ..., 3n to a single laser beam 8th achieved, which has a plurality of wavelengths λ ₁ , ..., λ _N due to the superposition. To achieve this, the lattice constant of the grid must be 7 to the wavelengths λ ₁ , ..., λ _{N of} the laser beams 3a , ..., 3n be adjusted. The lattice constant depends primarily on the required resolution, ie on the angles of the incident beams and the wavelength difference. The smaller the wavelength difference, the higher the resolution and the lower the lattice constant. It is understood that the lattice constant manufacturing technology can not be made arbitrarily small, so that a suitable combination of all parameters must be found, which takes into account the production limits. The lattice constant is typically in the range between about 0.5 microns and 1.5 microns in the present applications.

The laser beam 8th meets on his way back from the grid 7 on the lens 6 , which now serves as a focusing lens. The Lens 6 focuses the laser beam 8th on the front side of an entrance end 10 a decoupling fiber 9 , The optical fibers 4a to 4n and the decoupling fiber 9 have a fiber core and a fiber cladding, wherein the laser radiation is coupled into the fiber core. In the present example, the decoupling fiber 9 the same core diameter d _K (see. 3 ) like the optical fibers 4a , ..., 4n on. The entrance end 10 the decoupling fiber 9 runs parallel to the outlet ends 5a , ..., 5n the optical fibers 4a , ..., 4n , wherein the front side of the Auskoppelfaser 9 also in the focal plane of the lens 6 is arranged. The decoupling fiber 9 here has an in 1b shown distance S to the exit ends 5a , ..., 5n the optical fibers 4a . 4n on, which in the present example is about 3 mm and typically should not be greater than about 5 mm or 10 mm in order to minimize aberrations as possible.

Since the core diameter of the Auskoppelfaser 9 (Receiver fiber) with the core diameter d _{K of} the optical fibers 4a , ..., 4n (Transmission fibers), the beam quality is preserved in the image and the brilliance is increased by the wavelength coupling. It is understood that for this purpose the core diameter d _{K of} the optical fibers 4a , ..., 4n can also be chosen smaller than the core diameter of the Auskoppelfaser 9 , At a core diameter of the decoupling fiber 9 of about 100 microns can with the diode laser array 1 an output power of about 1.5 kW can be achieved. Typical core diameter of the decoupling fiber 9 are between about 50 microns and 200 microns, typical output power of the individual diode laser sources 2a , ..., 2n are between about 50 and 500 watts.

At the in 1a , b construction shown will be the lens 6 for the majority of laser beams 3a , ..., 3n used as a common Kollimationsoptik and serves at the same time to focus of the grid 7 produced laser beam B. In this so-called Littrow arrangement corresponds to an angle α, which the grid 7 with the X-direction along which the optical fibers 4a , ..., 4n run, the so-called Littrow angle. This one is chosen so that an angle under which a respective laser beam 3a , ..., 3n on the grid 7 meets, just the 1st diffraction order of the grid 7 corresponds to the central wavelength, ie for the average of the respective wavelengths λ ₁ , ..., λ _N , wherein the laser beam formed by the superimposition 8th the -1. Diffraction order of the lattice 7 equivalent. The Littrow angle α is typically between about 20 ° and about 50 ° in the present applications. It is understood that in place of the single lens 6 also a combination of a plurality of successively arranged optical elements, for. B. from multiple lenses, can serve as a collimator or as focusing optics.

As described above, the exit-side ends 5a to 5n the optical fibers 4a to 4n at predetermined intervals d ₁ , ..., d _N positioned from each other, which inter alia of the wavelengths λ ₁ , ..., λ _{N of} the respective laser beams 3a , ..., 3n the diode laser sources 2a , ..., 2n depend. In order to be able to fix the respective spatial distance d ₁ ,..., D _N , which is in the micrometer range dense wavelength coupling present here, reproducibly and with high accuracy, the diode laser arrangement has 1 one in 2 represented carrier 11 in the form of a metal plate, at the top thereof V-shaped, parallel and at predetermined intervals d ₁ , ..., d _N arranged depressions 12 are provided, the inclusion of a respective exit-side end 5a to 5n a respective optical fiber 4a , ..., 4n serve, from those in 2 for simplicity, only the fiber ends 5a , ..., 5n are shown. Such a carrier, also referred to as a V-pit array 11 allows easy and reproducible fixation and alignment of the individual fiber ends 5a , ..., 5n parallel to each other and at a defined distance d1, ..., d _N from each other.

An alternative possibility for the realization of a carrier 11 , which reproducibly generates predetermined distances d ₁ , ..., d _N between the optical fibers 4a , ..., 4n or from their fiber ends 5a , ..., 5n allows, is in 3 shown. The carrier 11 in this case consists of a plate-shaped body, z. B. glass, with a flat base 13 on which the optical fibers 3a , ..., 3n are fixed, with the lateral surfaces 14 adjacent fiber ends 5a , ..., 5n Touch, making one for all optical fibers 3a , ..., 3n identical distance d is generated, which corresponds to the diameter d of the respective optical fiber 3a , ..., 3n equivalent.

4 finally shows a diode laser array 1 (so-called "Conical Mount"), which differ from the in 1a , Federation 2 shown arrangement differs in that for outward and return two spatially separated lenses 6 . 15 are provided as Kollimationsoptik and as focusing optics. It is understood that in place of the respective lenses 6 . 15 It is also possible to provide a plurality of lenses arranged one behind the other as collimating optics or as focusing optics.

At the in 4 shown construction is the receiver (Auskoppelfaser 9 ) further from the optical fibers 3a , ..., 3n removed as in the 1a , b shown construction, ie the in 4 The structure shown is less compact. In addition, by compared to 1b additionally required deflection angle β on the grid 7 Aberrations which typically have to be corrected by additional optical elements (not shown).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6791751 B2 [0004]
• WO 2006/116477 A2 [0006]
• US 2010/0110556 A1 [0006]
• US Pat. No. 6,697,192 B1 [0007]

Claims (9)

Diode laser arrangement ( 1 ) comprising: a plurality of diode laser sources ( 2a to 2n ) for generating a plurality of laser beams ( 3a to 3n ) having different wavelengths (λ ₁ , ..., λ _N ), a plurality of optical fibers ( 4a to 4n ) for guiding a respective laser beam ( 3a to 3n ) of a diode laser source ( 2a to 2n ), with exit ends ( 5a to 5n ) of the optical fibers ( 4a to 4n ) are arranged parallel to one another and at predetermined intervals (d ₁ to d _N ) to each other, a collimating optics ( 6 ) for collimation of the ends ( 5a to 5n ) of the optical fibers ( 4a to 4n ) leaving a plurality of laser beams ( 3a to 3n ), a dispersive optical device ( 7 ) for diffracting the plurality of collimated laser beams ( 3a to 3n ) for generating a single laser beam ( 8th ) having a plurality of wavelengths (λ ₁ , ..., λ _N ), and a focusing optics ( 6 . 15 ) for focusing the beam from the dispersive optical device ( 7 ) generated laser beam ( 8th ) to an entrance end ( 10 ) a decoupling fiber ( 9 ). A diode laser array according to claim 1, further comprising: a common carrier ( 11 ) for parallel alignment of the exit ends ( 5a to 5n ) of the optical fibers ( 4a to 4n ) at predetermined intervals (d ₁ , ..., d _N ) from each other. Diode laser arrangement according to claim 2, in which the carrier ( 11 ) a plurality of parallel, in particular V-shaped recesses ( 12 ) for receiving a respective exit-side end ( 5a to 5n ) an optical fiber ( 4a to 4n ) having. Diode laser arrangement according to claim 2, in which the carrier ( 11 ) a flat base ( 13 ), on which the outlet ends ( 5a to 5n ) of the optical fibers ( 4a to 4n ) are arranged side by side and fixed, wherein the lateral surfaces ( 14 ) of adjacent optical fibers ( 4a to 4n ) touch. Diode laser arrangement according to one of the preceding claims, wherein a respective distance (r ₁ , ..., r _N ) between the lateral surfaces of the outlet-side ends ( 5a to 5n ) of adjacent optical fibers ( 4a to 4n ) is less than 20 microns. Diode laser arrangement according to one of the preceding claims, in which the collimating optics ( 6 ) simultaneously as focusing optics ( 6 ) for focusing the laser beam ( 8th ) with the plurality of wavelengths (λ ₁ , ..., λ _N ). A diode laser array according to claim 6, wherein the entrance end ( 10 ) the decoupling fiber ( 9 ) parallel and offset to the exit ends ( 5a to 5n ) of the optical fibers ( 4a to 4n ) is arranged. A diode laser array according to claim 7, wherein the entrance end ( 10 ) the decoupling fiber ( 9 ) to a common plane (X, Z) in which the exit ends ( 5a to 5n ) of the plurality of optical fibers ( 4a to 4n ) are arranged, a distance (S) of less than 10 mm. Diode laser arrangement according to one of the preceding claims, in which the optical fibers ( 4a to 4n ) an identical or smaller core diameter (d _K ) than the Auskoppelfaser ( 9 ) exhibit.

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