JP2008511131A - Diode laser - Google Patents

Abstract

The diode laser has a plurality of partial beams (8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ 8 ⁾ generated by a plurality of diode laser elements (2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ ). ⁿ⁾ includes an optical device (10) for increasing the radiance of the emitted output laser beam (12) consisting of) at the location of the object (16). The optical device is placed behind the diode laser element and one spectral region (λ _B ⁽¹⁾ , Δλ _B ⁽¹⁾ ... Λ _B ^{(2 ) of the} partial beam emitted from the diode laser element. ⁾ , Δλ _B ⁽²⁾ ... Λ _B ⁽ⁿ⁾ , Δλ _B ⁽ⁿ⁾ ) are partially reflected to each diode laser element, and only the main part of the spectral region) is transmitted. The mean wavelengths of the spectral regions that include the volume Bragg grating (18) and are each filtered from different partial beams are different from each other. The second grating (24) superimposes the partial beam transmitted by the first volume Bragg grating on the coriner with the output laser beam (12).

Description

  The present invention relates to a diode laser including an optical device that increases the output of an emitted laser beam.

  The diode laser includes an optoelectronic semiconductor chip, a so-called laser diode, as a laser active element, and in particular in the case of a diode laser, the laser diode is composed of a plurality of individual emitters arranged side by side. In one embodiment for achieving high optical output, individual emitters are monolithically arranged in so-called laser diode bars. The laser diode bar typically has a width of about 5-10 mm (side), a height of 0.10-0.15 mm (vertical direction), and a resonance between 0.3-2.5 mm. Has vessel length (horizontal direction). In the case of so-called edge emitting emitters, the laser radiation produced at the pn junction of the laser diode is emitted at one of the side surfaces (output surface or front surface, emitter surface). The opposite surface (back surface) is mirror-finished to make a high degree of reflection, and forms a back mirror of the resonator.

  Each laser diode bar produces a thin laser beam that is approximately rectangular, which is combined with a number of partial beams emitted from individual emitters whose beam characteristics are measured in the transverse direction (width) of the laser diode bar. ), The so-called slow axis is clearly different from the beam characteristics in the axis perpendicular to this (epitaxy direction), the so-called fast axis.

  Based on the beam characteristics of the laser diode bar that is remarkably asymmetric as described above, and furthermore, in a high performance diode laser, it is necessary to arrange a plurality of such laser diode bars side by side or in layers. In particular, high performance diode laser structures typically require complex optics for beamforming, ie beam symmetrization and beam superposition. This is especially true for diode lasers where the laser beam is injected into an optical fiber and the linear beam of individual laser diode bars is to be converted to a substantially square or ideally circular cross-sectional shape. Diode lasers equipped with such a beamforming device are known, for example, from German Patent Nos. 19645150, 1984532 and 10015245.

  The symmetrization of the output laser beam by changing the arrangement of the partial beams respectively emitted from the individual emitters and the resulting beam symmetrization are possible in principle for any number of emitters. In order to increase the radiance of the light beam, it is necessary to spatially superimpose the individual partial beams on the coriner. However, the radiance (intensity per unit solid angle) or brightness (radiance) of radiation emitted from a beam source that is a combination of a plurality of individual sources that are spatially separated from each other and are not coherent with each other is It can only be enhanced if the individual partial beams differ with respect to their physical properties such that they can be spatially superposed by correspondingly acting beam splitters. This is possible if the partial beams are different for each polarization or wavelength.

  For example, the polarization coupling method known from DE 198 46 532 for the coupling of two laser diode bar stacks has only two independent degrees of polarization and can only increase the radiance by up to a factor of two. In contrast, wavelength coupling is possible in principle for a large number of partial beams, but each of these partial beams has a sufficiently different wavelength and is superposed with a spectrally selective dielectric mirror system with as little loss as possible. Only if you get. In this case, when a dielectric mirror system is used as a practical problem, it has been found that the minimum wavelength interval for combining unpolarized partial beams in the infrared region must be about 40 nm. Therefore, this wavelength coupling method is basically not applicable to partial beams of individual laser diode bars. This is because the emitters of the laser diode bars usually each have approximately the same wavelength. Therefore, the wavelength coupling by the dielectric mirror can be used only for coupling a plurality of laser diode bars or a plurality of stacked layers having different wavelengths.

  The object of the present invention is therefore to provide a diode with an optical device that has a simple structure and clearly allows the spatial coupling of a large number of partial beams compared to the prior art, and that increases the radiance of the emitted output laser beam. It is to provide a laser.

  The present invention solves the above-described problems with a diode laser having the constituent features of claim 1. According to these components, the diode laser is composed of a plurality of partial beams generated by a plurality of laser diode elements, and includes an optical device that enhances the radiance of the emitted output laser beam at the application plane, the optical device comprising: After the diode laser element. In the present invention, the optical device has a first volume in which only one spectral region of the partial beam emitted from the diode laser element is partially reflected to each diode laser element, and only the main part of the spectral region is transmitted. The average wavelengths of the spectral portions that include the Bragg grating and are each filtered from different partial beams are different from each other. The first volume Bragg grating is followed by a second grating, preferably also a volume Bragg grating, for spatially superimposing the partial beam transmitted by the first volume Bragg grating on the collier with the output laser beam. The

  Furthermore, the wavelength coupling according to the invention improves the beam parameter product of the laser diode bar in the slow axis plane, ie the beam quality, by a factor of 10 mm / 0.15 mm formed from the ratio of the bar width to the individual emitter width, When the bar width is 10 mm, it is typically from 500 mm · mrad to about 10 mm · mrad.

  By using the first holographic grating or volume Bragg grating, the partial beam already emitted from the diode laser element in a relatively narrow band can be narrowed again for each spectral bandwidth. Thus, it is sufficiently different with respect to each average wavelength, and it is stabilized in a narrow band according to those wavelengths, so that partial beams with different spectra that can be superimposed by the second grating almost without loss are generated. it can.

  The use of holographic gratings to realize wavelength division multiplexing is already known in principle from US Pat. No. 5,69,1989. However, the purpose of this known application method is not to increase the radiance or brightness of the laser beam at the location of the object whose physical characteristics are to be changed by the laser beam, for example, the location where thermal processing is performed, but the spectrum can be divided. The laser beam is transmitted simultaneously and subsequently separated by a demultiplexer to increase the bandwidth in optical information transmission using an optical fiber.

  In the sense of the present invention, a diode laser is an assembly positioned at the top, which is a combination of a plurality of laser diode elements. This diode laser has a structure constituted by a group of individual emitters referred to as a diode laser element in the present invention, as well as a group of laser diodes each including a number of individual emitters, for example, a group of laser diode bars. It may be a structure. In the latter case, the laser diode bar is called a diode laser element.

  In order to allow as little lossless coupling of the partial beams, in a preferred embodiment of the present invention, the difference in the average wavelength of the spectrally adjacent and transmitted partial beams is half the sum of the half widths of each spectrum. Bigger than.

  The first and / or second volume Bragg gratings are composed of a single volume Bragg grating element whose grating characteristics are position dependent, and preferably each volume Bragg grating element has a constant but different grating characteristic. When the number of regions corresponding to the number of diode laser elements is provided, a particularly compact structure can be achieved.

  Instead of the above, the first and / or second volume Bragg gratings are constituted by a plurality of discrete volume Bragg grating elements each having different grating characteristics, and the number of discrete volume Bragg grating elements is particularly determined by the diode laser element. It should be equivalent to a number. A volume Bragg grating made up of individual volume Bragg grating elements can be manufactured particularly easily.

  In a preferred embodiment, each first and / or second volume Bragg grating structure is preceded by a micro-optical system, in particular incorporated in each volume Bragg grating structure. As a result, it is possible to reduce the loss when the partial beam is transmitted to the volume Bragg grating and when it is coupled to the volume Bragg grating.

  In a particularly advantageous embodiment of the invention, the first and / or second volume Bragg grating is composed of one or more PTR elements. This PRT element enables exceptionally narrow-band stabilization of the wavelength of the partial beam emitted from each diode laser element, and as a result, the exceptionally efficient and lossless wavelength of the partial beam thus stabilized. Allows coupling.

  For a more detailed explanation of the invention, reference is made to the examples in the drawings.

In the embodiment of FIG. 1, the diode lasers are arranged side by side in a row to form a diode laser module 4, n pieces of many diode laser device 2 ^(1), 2 ⁽²⁾ ... 2 ⁽ including ⁿ⁾ . The illustrated diode laser elements 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ are laser diode bars arranged one above the other even if they are individual emitters of the laser diode bar. Also good. Each of the diode laser device ^{2 (1), 2 (2} ) ··· 2 (n) , the partial beam 8 ^(1), to release 8 ⁽²⁾ · · · 8 ^(n).

Partial beams 8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ^{(n )} respectively emitted from the diode laser elements 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ on the output side of the diode laser module 4. ⁾ Is followed by a micro-optical system 6 that causes collimation in the direction of the fast axis.

This micro optical system 6 has individual cylindrical lenses when the diode laser module 4 is an individual laser diode bar and the diode laser elements 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ are individual emitters. It is. In this case, if the illustrated diode laser module is formed by combining a plurality of laser diode bars serving as diode laser elements 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ , n micro-optical systems 6 are provided. An array of microlenses is used. In an alternative embodiment, the micro-optical system 6 additionally performs collimation in the direction of the slow axis.

The partial beams 8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ⁿ⁾ emitted from the diode laser module 4 or the collimator 6 are combined by an optical device 10 that generates an output laser beam 12 on the output side. In the beam, all the partial beams 8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ⁿ⁾ are superimposed on the corinier, and the beam guide and beam shaping apparatus which are suggested directly or only in the drawing are suggested. For example, by optical fibers, guided to the object 16 in a superposed state, where the physical effect required for each purpose of use is brought about with high strength. This object is, for example, a laser active medium of a workpiece to be processed or a solid state laser to be optically pumped with a diode laser.

The optical device 10 includes, on the input side, each partial beam 8 ^(1), of the 8 ⁽²⁾ · · · 8 ^(n), the mean wavelength _{^{λ B (1), λ B}} (2) ··· λ B ( and ^n), each partial beam 8 is emitted ^(1), 8 ⁽²⁾ ... 8 (lower half-width than the half-value width of _{^{n) Δλ B (1),}} Δλ B (2) ··· Δλ B ⁽ⁿ⁾ and a narrow spectral region only each diode laser element 2 with ^(1), 2 ⁽²⁾ partially reflected ... 2 to ^(n), and transmits only the main part of the spectral region, the 1 holographic grating or volume Bragg grating 18. The feedback caused by the reflected part leads to so-called self-seeding of each diode laser element 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ , resulting in spectral narrowing of each output radiation, diode laser device ^{2 (1), 2 (2} ) ··· 2 (n) at the time of steady state, the wavelength average wavelength lambda _B ^(1), the _{^{λ B (2) ··· λ B}} (n) The half-value widths Δλ _B ⁽¹⁾ , Δλ _B ⁽²⁾ ... Δλ _B ⁽ⁿ⁾ are also correspondingly narrowed, that is, clearly narrower than the partially emitted partial beam. Only partial beams 8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ⁿ⁾ with bandwidth are emitted. If, without the first volume Bragg grating 18, the diode laser device 2 ^(1), 2 ⁽²⁾ partial beams 8 ^(1), each of which is emitted from · · · 2 ^(n), 8 ⁽²⁾ · · 8 ⁽ⁿ⁾ will have approximately the same wavelength λ _A and the same half-value width Δλ _A. A suitable volume Bragg grating is, for example, a photothermorefractive device known from US Pat. No. 6,586,141. Based on such a so-called PTR element, a volume Bragg grating is known that exhibits very excellent spectral selectivity and high refractive efficiency. The PTR element also has a feature of high mechanical, optical and thermal stability.

FIG. 1 shows an embodiment in which the lattice constant of the first volume Bragg grating changes continuously as a function of position coordinates, as illustrated by the arrow 20 in the drawing. Instead of the continuous change of the lattice constant, a discontinuous change of the lattice constant inside the first volume Bragg grating is also possible. As a result, each diode laser element 2 ⁽¹⁾ , 2 ^{(2 )} ... 2 ⁽ⁿ⁾ can each be assigned a region having a certain lattice characteristic.

The partial beam emitted from the first volume Bragg grating 18 hits a second grating 24 arranged inside the optical device 10 after collimation on the slow axis by the micro-optical system 22, which is preferably also the volume Bragg grating, at its inside, spectrum narrowband component beams 8 ^(1), 8 ⁽²⁾ collinear superposition occurs in incoherent · · · 8 ^(n). The second grating is also preferably a PTR element, and has a position-dependent internal grating structure according to the first volume Bragg grating 18. At the position i, the grating structure is such that the partial beam having the wavelength λ _B ⁽ⁱ⁾ is reflected to the maximum while the wavelengths λ _B ^{(i + 1)} , λ _B ^{(i + 2)} ·・ ・ Partial beams of λ _B ^{(i + n)} must be configured to transmit as little as possible.

Partial beams 8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ^{(n )} where the spectra are adjacent and transmitted in order to enable efficient wavelength coupling and concomitant increase in radiance or brightness. mean wavelength lambda _{B ^{of) (1), λ B (}} 2) the difference ··· λ _B ^(n), each spectral half width _{^{Δλ B (1), Δλ B}} (2) ··· Δλ B (n) Is greater than half of the sum of, so the following condition is satisfied:
1/2 (Δλ _B ⁽¹⁾ + Δλ _B ^(i-1) ) ≦ λ _B ⁽¹⁾ −λ _B ⁽ⁱ −1 ⁾

  For example, PD-LD Inc. (Pennington, NJ, USA) and Ondax Inc. Using a known PTR element provided by (Monrovia, Calif., USA), a laser beam emitted from an individual diode laser element at a half-width of about 3 to 6 nm is narrow-band with a half-width of less than 0.2 nm. For example, a maximum of 30 individual emitters of the laser diode bar can be sufficiently separated for each wavelength to be confined to the region, so that wavelength coupling is possible. Furthermore, since the laser diode bars arranged in layers can be adjusted to different central wavelengths, which differ from each other by a few nanometers at the time of manufacture, in principle all the partial beams of such a stack can be collimated by wavelength coupling. Can be overlaid. Instead, the partial beams emitted from one stack of laser diode bars are tuned to a unique wavelength using a first volume Bragg grating and narrowbands emitted from individual laser diode bars. The laser beam can also be superimposed on the collier by wavelength coupling.

In the embodiment shown in FIG. 2, the first volume Bragg grating 18 is a plurality of discrete volume Bragg gratings corresponding to the number n of diode laser elements 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ^(n). It is composed of elements 18 ⁽¹⁾ , 18 ⁽²⁾ ... 18 ⁽ⁿ⁾ . In principle, the second grating 24 can also be composed of a plurality of discrete volume Bragg grating elements. Furthermore, the micro-optical system 6, the first volume Bragg grating 18 and the second grating 24 can be integrated into a monolithic component, so that, based on a compact structure, the micro-optical system 22 shown in FIGS. It becomes unnecessary.

Since the first volume Bragg grating 18 can be assembled directly into the collimator 6 or manufactured with the collimator 6 as a monolithic component as described above, the arrangement according to the invention allows a very compact and stable structure. Since the distance d from the output surface of the diode laser element 2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ to the first volume Bragg grating 18 is only a few mm, typically less than 3 mm, it is mechanical. Sensitivity to heavy loads is greatly reduced.

  Yet another preferred effect is that the first volume Bragg grating stabilizes the wavelength according to the narrow band region, so that the temperature dependence of the wavelength of the emitted laser radiation is reduced by the first volume Bragg grating 18. It is to become.

A diode laser according to the present invention is shown in a schematic diagram. Another embodiment of a diode laser according to the invention is shown in a schematic principle diagram.

Explanation of symbols

2 ⁽¹⁾ , 2 ⁽²⁾ , 2 ⁽ⁿ⁾ diode laser element, 4 diode laser module, 6 micro optical system, 8 ⁽¹⁾ , 8 ⁽²⁾ , 8 ⁽ⁿ⁾ partial beam, 10 optical device, 18 First volume Bragg grating, 24 second grating

Claims (10)

From a plurality of partial beams (8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ⁿ⁾ ) generated by a plurality of diode laser elements (2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ ) A diode laser with an optical device (10) that increases the radiance of the emitted output laser beam (12) at the location of the object (16),
The optical device (10) is placed behind the diode laser element (2 ⁽¹⁾ , 2 ⁽²⁾ ... 2 ⁽ⁿ⁾ ) and the diode laser element (2 ⁽¹⁾ , 2 ^(2).・ ・ ・ 2 ⁽ⁿ⁾ ) One spectral region (λ _B ⁽¹⁾ , Δλ _B ⁽¹⁾ ... Of the partial beams (8 ⁽¹⁾ , 8 ⁽²⁾ , 8 ⁽ⁿ⁾ ) emitted from ^{_{· λ B (2), Δλ}} B (2) ··· λ B (n), Δλ B (n)) only each diode laser element ^{(2 (1), 2 (} 2) ··· 2 (n) ) To each of the spectral regions (λ _B ⁽¹⁾ , Δλ _B ⁽¹⁾ ... Λ _B ⁽²⁾ , Δλ _B ⁽²⁾ ... Λ _B ⁽ⁿ⁾ , Δλ _B ^{( n)} includes a first volume Bragg grating (18) that transmits only the main part of
Different partial beam the spectral region each are filtered from ^{(8 (1), 8 (} 2) ··· 8 (n)) (λ B (1), Δλ B (1) ··· λ B (2), Δλ _B ⁽²⁾ ... λ _B ⁽ⁿ⁾ , Δλ _B ⁽ⁿ⁾ ) mean wavelengths (λ _B ⁽¹⁾ , λ _B ⁽²⁾ ... λ _B ⁽ⁿ⁾ ) are different from each other,
In addition, the partial beams (8 ⁽¹⁾ , 8 ⁽²⁾ ... 8 ⁽ⁿ⁾ ) transmitted by the first volume Bragg grating (18) are spatially superimposed on the corinier by the output laser beam (12). Diode laser comprising a second grating (24) for.   The diode laser according to claim 1, comprising a volume Bragg grating as the second grating.   3. The diode laser according to claim 1, wherein the difference in the average wavelength of the transmitted partial beams adjacent to each other in the spectrum is larger than half of the sum of the half widths of the respective spectra.   4. The diode laser according to claim 2, wherein the first and / or second volume Bragg grating is composed of a single volume Bragg grating element whose grating characteristics are position dependent.   5. The diode laser according to claim 4, wherein each of the volume Bragg grating elements has a number of regions corresponding to the number of the diode laser elements, each having a constant but different lattice characteristic.   4. The diode laser according to claim 2, wherein the first and / or second volume Bragg grating is composed of a plurality of discrete volume Bragg grating elements having different grating characteristics.   7. The diode laser according to claim 6, wherein the number of the discrete volume Bragg grating elements is equal to the number of the diode laser elements.   8. The diode laser according to claim 1, wherein a micro optical system is respectively placed in front of the first volume Bragg grating and / or the second grating.   9. The diode laser according to claim 2, wherein each of the micro optical systems is incorporated in the volume Bragg grating.   The diode laser according to one of claims 2 to 9, wherein the first volume Bragg grating and / or the second grating is composed of one or more PTR elements.

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