DE102007009380A1 - Diode laser stack, comprises multiple laser-bar chips, which are arranged one above other and have multiple emission zones, which are arranged parallel to each other - Google Patents

Abstract

The diode laser stack comprises multiple laser-bar chips (1), which are arranged one above the other. The laser-bar chips have multiple emission zones, which are arranged parallel to each other. The width of the each emission zone is between 25 to 400 micrometers and the distance between the emission zones is 50 to 200 micrometers. The laser-bar chips are connected with a driver for periodic stimulation of the emission zones with a pulse-duty factor less than or equal to thirty percent. Independent claims are also included for the following: (1) a system with two or more diode laser stack (2) a method for generating laser radiation with a diode laser stack.

Description

The The invention relates to a semiconductor pulse diode laser in a stacked arrangement and a method of generating pulsed laser radiation, in particular The invention relates to a diode laser, characterized by its compact Construction a simple coupling of the emitted laser radiation into a multimode fiber.

Known are laser diodes in the form of so-called laser bars with active radiation-generating Layers that are parallel to the emission direction in a plurality of parallel, strip-shaped Emission directions are divided. Such laser diodes are usually with the contact surfaces the individual emission zones are soldered to a cooler so that the individual strip-shaped emission zones electrically are connected in parallel. Due to the parallel arrangement of the emission zones can be opposite a laser diode with a single emission zone a higher optical Achieved performance, so that such laser bars in particular for high performance applications suitable.

at High-power laser diodes are of particular importance for cooling to. Without adequate cooling would the resulting heat loss lead to a sharp increase in temperature, so that the semiconductor body within shortest time thermally overloaded and thereby destroyed in the episode would. For cooling can the semiconductor body the laser diode, for example, on a metal plate with sufficient Heat capacity and thermal conductivity be mounted.

to Achieving even higher optical services can such laser bars stacked vertically become (so-called laser stack).

to Achieving even higher optical power, which in a simple way in a multimode fiber can be coupled can laser radiation from two or more diode laser stacks through Deflection mirrors or prisms can be combined without the jet characteristics the combined laser radiation with respect to the laser radiation of a individual diode laser stacks are significantly deteriorated, under the condition that the vertical extent of the laser radiation of the individual laser bar chips after collimation less than the half the vertical distance of adjacent laser bar chips.

A possibility is in, for to provide each laser bar of the stack with its own (microchannel) cooling. However, such a device requires a comparatively high Material and manufacturing costs, since each semiconductor body initially on the respective cooling element soldered and then stacked together with the semiconductor body mounted thereon become. Each of these assembly steps has to be carried out with high precision ensure exact alignment of all emission zones around the flow of coolant ensure through all levels of the stack and also the electrical Contacting the laser bars to ensure. Especially for pumping applications with high performances is one possible good focusability of the generated radiation essential. This can at the big one lateral aperture of the laser bar achieved only by consuming optics which, in turn, increased too Costs lead.

A another possibility consists of the individual emission zones so strongly from each other spaced that during the laser operation produces a relatively small amount of heat per area, that alone due to the heat conduction to the side or behind the laser bars arranged cooling elements can be directed. A relatively large distance between the emission zones a laser bar leads however, to an even larger lateral aperture and therefore even higher Effort to focus the radiation emitted by the laser stack or to couple into a multimode optical fiber.

In summary let yourself note that the high power diode lasers known in the art (Laser stacks), although a compact design, but disadvantageously a high level of technical equipment Effort for the active cooling (between the individual billets) and poor focusability of the emitted Have radiation in an optical fiber.

It is therefore an object of the present invention, in the case of a qcw operation (quasi continuous wave - pulsed operation with duty factors of 0.1% to 30%) a compact, preferably completely brazed high-power diode laser stack with a low level of technical equipment Effort for the cooling which overcomes the aforementioned disadvantages of the prior art and Optionally the combination of the laser radiation of two or more Diode laser stacks with deflecting mirrors allows.

This is possible in qcw operation because despite the high optical output power during the pulses the accumulating average heat loss by the factor of the duty cycle is lower.

In particular, it should therefore be possible to dispense with active cooling (for example through microchannel coolers) between the individual laser bars and active cooling for example. B. suffice by a laterally or rear-mounted radiator. In addition, for the qcw operation optimized laser As a result of the smaller distance between the individual emission zones (= higher "coverage density"), the lateral aperture can be up to about 3 times smaller with the same optical power, making it possible to couple the emitted radiation into a multimode fiber with a simple and cost-effective imaged optics.

Furthermore is intended in an optional variant of the vertical spacing of the laser bar chips and the vertical collimation of the laser radiation of each laser bar chip so executed be that a union of laser radiation of two or more Diode laser stacks by deflecting mirror or prisms without noticeable Deterioration of the beam properties and thus further coupling the emitted radiation into a multi-mode fiber with a simple and cost-effective imaging optics possible is.

These Tasks are performed by a diode laser with the in claim 1 features and by a method with the in claim 26 mentioned features solved. Advantageous developments of the invention are the subject of the dependent claims.

Of the Diode laser according to the invention has a variety of superimposed arranged on laser bar chips, each laser bar chip a plurality of emission zones arranged parallel to one another and wherein the width of the emission zones respectively between 25 μm and 400 microns and the Distance between the emission zones in each case between 50 .mu.m and 200 .mu.m (preferred between 50 μm and 150 μm and more preferably between 50 μm and 100 μm), and the laser bar chips with a means for periodic excitation of the emission zones with a duty cycle of less than or equal to 30% (and preferably greater than 0.1%). When duty cycle will the ratio the length the excited state (pulse duration) to the period understood. The idea of the present invention is therefore the diode laser (or the emission zones) not continuously (cw-operation), but periodic (qcw operation to stimulate. Because with a periodic (pulsed) excitation less Heat is produced, On the one hand, on a complex (Microchannel) Cooling between the laser bar chips are dispensed and it is on the other hand possible, the individual emission zones of a laser bar chips are so dense to arrange next to each other that the plurality of emission zones of a Laser bar chips has a small lateral extent (aperture). Therefore, it is possible the emitted laser radiation with simple optical means, for example one cylindrical lens per laser bar (fast-axis-collimator - FAC) and an arranged behind it imaging optics for all laser bars in one Coupling optical fiber. For the optional variant of combining the radiation fields of two or more diode laser stacks, the vertical distance of the Laser bar chips and the focal length of the FAC cylindrical lens such selected that the vertical extent of the radiation fields after collimation less than or equal to half the vertical spacing of the laser bar chips is, so that the radiation fields lossless through deflecting mirrors or Prisms can be combined.

Preferably are the laser bar chips with a driver for periodic excitation the emission zones with a duty cycle of less than or equal to 30% (more preferably less than or equal to 20%, more preferably less equal to 15%). Preferably, the width of the emission zones is in each case between 25 μm and 400 μm and the distance between the emission zones is between 50 μm and 200 μm in each case.

Preferably the diode laser has at least 3 (more preferably between 10 and 20) one above the other arranged laser bar chips on. Preferably, each laser bar chip at least 3 (more preferably between 3 and 25) emission zones on. The emission zones are preferably elongated, wherein the longitudinal axes the emission zones arranged parallel to the light emission direction are. Preferably, each laser bar chip is on a carrier Stack element arranged. Preferably, each laser bar chip is on Lot (particularly preferably via a Brazing alloy) with the carrier connected stacking element connected. As Hartlot in the sense of the application is a solder joint understood that with a liquidus temperature of more than 250 ° C and of up to a maximum of 900 ° C has been produced. Preferably, the functional layers (Emission zones) formed from the material system In-Ga-Al-As-P.

Preferably Each stack element has optics for vertical collimation of the light emitted by the emission zones of the laser bar chip. The collimating optic is preferably by a cylindrical lens educated.

Preferably, for the optional variant of combining the radiation fields of two or more diode laser stacks, the focal length of the cylindrical lens is selected such that the vertical extent of the radiation field of each laser bar chip after the cylindrical lens is equal to or less than half the vertical spacing of adjacent laser bar chips, and the radiation fields of the two or more a plurality of diode laser stacks can be brought together by stacks of deflecting mirrors or deflecting prisms so that the jet property of the combined beam compared to the beam of a individual diode laser stacks are not significantly impaired.

Preferably a multimode optical fiber with an entrance facet is provided, wherein an imaging optic is arranged such that the of the Stack elements emitted light in the entrance facet of the multimode optical fiber is coupled. The technical equipment Effort for The imaging optics used can according to the invention be low be held because the requirements due to the small distances of the individual emission zones (and therefore the small lateral aperture a bar) and the low lateral divergence lower than in the devices known from the prior art. The stack elements (supports) preferably have a heat conduction coefficient of at least 150 W / m · K on.

Preferably at least one (particularly preferably: coolant-flowing) cooling element is provided, wherein at least two of the stack elements with the at least one cooling element are connected. Preferably, at each of the side surfaces of Stack elements a common cooling element provided, with all the stack elements with the two common cooling elements are connected. Alternatively, it is envisaged that at the back of the Stack elements provided a common cooling element is, with all the stack elements with the common cooling element are connected.

Preferably is an insulator and contact plate between adjacent stack elements arranged. Preferably, the stack elements via a solder with the at least a cooling element connected. Preferably, the solder is a braze. Preferably stands every laser bar chip over at least one solid trained stack element with the at least a cooling element thermally in contact.

Preferably differs the thermal expansion coefficient of the stack elements of coefficient of thermal expansion of the thus in contact at least one cooling element by less than 20%, and / or the thermal expansion coefficient differs the stack elements of the thermal expansion coefficient of it in contact with laser bar chips by less than 20%, and / or the thermal expansion coefficient differs the stack elements of the thermal expansion coefficient of it in contact with insulator and contact plate by less than 20%.

Preferred materials for the laser bar chip are a GaAs semiconductor substrate and functional layers of the material system In-Ga-Al-As-P. The stack element: is preferably made of CuW, CuMo or BeO. The insulator and contact plate is preferably formed of Al ₂ O ₃ . The elastic connecting element is preferably formed of Au, Al wire, ribbon or foil.

The inventive method for generating laser radiation with one or more diode laser stacks, each of which has a plurality of superimposed laser bar chips, wherein each laser bar chip has a plurality of parallel to each other arranged emission zones, and wherein the width of the emission zones each between 25 microns and 400 μm and the distance between the emission zones is between 50 μm and 200 μm in each case characterized in that the emission zones of the laser bar chips with a duty cycle be excited by less than or equal to 30% to the emission.

Preferably become the emission zones of the laser bar chips with a duty ratio of smaller than or equal to 20% (more preferably less than or equal to 15%) to emission stimulated. The excitation is preferably carried out by applying a Electric current with a current between 50 A and 300 A. (preferably between 100A ... 200A) where the current pulse duration is between 1 μs and 500 ms (preferably between 10 μs and 50 ms).

Preferably becomes the radiation emitted by the laser bar chips each vertically collimated and subsequently onto the entrance facet of a multimode fiber imaged and coupled into this. Preferably becomes the vertical Collimating a cylindrical lens and for coupling an imaging Optics used. For the optional combination of the laser radiation of two or more Diode laser stacks, the focal length of the cylindrical lens is preferably chosen so that the vertical extent of the laser radiation is smaller than half the vertical spacing of adjacent laser bar chips, and the Laser radiation of the diode laser stacks is preferably by stacks from deflecting mirrors or deflecting prisms or corresponding individual elements merged.

When imaging optics is preferably an (aspheric) Einzellinse or cylindrical lenses (instead of a round lens two cylindrical lenses are necessary) used. The heat generated in the emission zones becomes preferably passively (i.e., by heat conduction) over the Side surfaces and / or over the back the stack elements removed.

The Invention will be described below with reference to embodiments and the accompanying drawings explained in more detail.

It demonstrate:

1 1 is a schematic sectional view of a diode laser stack according to the invention with one cylindrical lens per laser bar chip for vertical collimation and one imaging optics for coupling the radiation into a multimode optical fiber;

2 1 is a schematic sectional view of a diode laser stack according to the invention with a lens array for vertical collimation of the radiation of the laser bar chips and imaging optics for coupling the radiation into a multimode optical fiber;

3 FIG. 2 a schematic sectional view of a diode laser stack according to the invention along an axis transverse to the direction of light propagation, the contacting of the n side of the laser bar chips being effected by direct soldering to the overlying stack element, FIG.

4 3 is a schematic sectional view of a diode laser according to the invention according to an alternative embodiment along an axis transverse to the direction of light propagation, the contacting of the n-side of the laser bar chips being effected by an elastic connecting element to the insulator and contact plate.

5 a schematic perspective view of a laser bar chip having a plurality of emission zones for the diode laser stack according to the invention, and

6 a schematic perspective view of the combination of the laser radiation of two diode laser stacks by a stack of deflecting mirrors.

1 shows a schematic sectional view of a diode laser according to the invention in stack (stack) construction, each laser bar (stacking element) a laser bar chip 1 which is on a support 2 (also called stack element) is supported. The variety of laser bar chips 1 emits the laser radiation, first for each chip 1 by means of a cylindrical lens 3 is vertically collimated and subsequently by means of an optical element 4 on the entrance facet 6 a multimode optical fiber 5 imaged and thus into the multimode light-fiber 5 is coupled. Alternative to the large number of cylindrical lenses 3 in 1 It is also possible to have a single lens array 3 with a large number of collimating areas ( 2 ).

The structure of the diode laser stack according to the invention is in 3 and 4 described in more detail. The laser bar chips 1 can be between the stack elements 2 be arranged.

In both possible in 3 and 4 shown construction variants are the stack elements 2 with the chips soldered on them 1 electrically connected in series. Therefore, on the active coolers 8th Insulated solder pads are created to not short circuit the series connection when soldering the stack elements with the coolers.

In the body variant according to 3 the series connection happens only through the current flow stack element 2 → Chip 1 → stack element 2 → Chip 1 etc. The insulator and contact plate 9 in this case serves only as a support element and insulator plate. In the body variant according to 4 the series connection is effected by the current flow stack element 2 → Chip 1 → elastic connection 10 → Insulator and contact plate 9 → stack element 2 → Chip 1 → elastic connection 10 → Insulator and contact plate 9 → stack element 2 etc.

The Parts 1, 9 and 2 are preferably by means of age resistant braze joints joined together. Preferably used brazing materials are an Au / Sn alloy, an Au / Ge alloy or an Au / Si alloy (particularly preferably 80% Au / 20% Sn alloy, 88% Au / 12% Ge alloy or 96.76% Au / 3.24% Si alloy).

5 shows a schematic, perspective view of a laser bar chip 1 with a variety of emission zones 7 , According to the invention, the width d2 of the emission zones 7 each between 25 microns and 400 microns and the distance d1 between the emission zones 7 each between 50 microns and 200 microns. Due to the duty cycle of less than or equal to 30% (and thus the lower heating compared to the cw operation), the distance d1 between the emission zones 7 relatively low (between 50 microns and 200 microns) can be selected. Therefore, leads to a variety of emission zones 7 to a relatively small overall width (aperture) W. For this reason succeeds in a precise coupling of the emitted radiation in the multimode optical fiber 5 , wherein the used imaging optics 4 can be chosen inexpensively.

6 shows the inventive combination of the radiation fields of two identical diode laser stacks with the FAC lenses 3 with the help of a stack of deflecting mirrors 11 , The vertical extent of the radiation fields of the individual laser bar chips is by suitable choice of the focal length of the cylindrical lenses less than half the vertical distance of adjacent laser bar chips P, so that the individual beams do not overlap in the union. The combined laser radiation then has the same lateral extent and divergence and the same vertical divergence as the laser radiation of a single diode laser stack. The vertical dimension increases only by half the vertical spacing of adjacent laser bar chips P. Therefore, the combined beam can be coupled into multimode fibers just as easily as a single diode laser stack.

1

Laser bar chip / laser bars

2

Stack element / carrier

3

cylindrical lens (Fast axis collimator)

4

imaging optics

5

optical fiber

6

entrance facet

7

Single emitter / active Material / active area / emission zone

8th

active cooler

9

Insulator- and contact plate

10

elastic Connection (Ribbon, Wire; soldered, welded)

11

deflecting

d1

distance adjacent single emitter

d2

width the single emitter

W

width of the light exit area / aperture

P

vertical Distance between adjacent laser bar chips

Claims (33)

A diode laser stack, comprising: a plurality of superimposed laser bar chips ( 1 ), each laser bar chip ( 1 ) a plurality of mutually parallel emission zones ( 7 ), wherein the width (d2) of the emission zones ( 7 ) each between 25 microns and 400 microns and the distance (d1) between the emission zones ( 7 ) is between 50 μm and 200 μm in each case, and the laser bar chips ( 1 ) with a driver for the periodic excitation of the emission zones ( 7 ) are connected to a duty ratio of less than or equal to 30%. Diode laser stack according to claim 1, characterized in that the laser bar chips ( 1 ) with a driver for the periodic excitation of the emission zones ( 7 ) are connected to a duty ratio of less than or equal to 20%. Diode laser stack according to one of the preceding claims, characterized in that the diode laser at least 3 superimposed laser bar chips ( 1 ) having. Diode laser stack according to one of the preceding claims, characterized in that the diode laser between 10 and 20 superimposed laser bar chips ( 1 ) having. Diode laser stack according to one of the preceding claims, characterized in that each laser bar chip ( 1 ) at least 3 emission zones ( 7 ) having. Diode laser stack according to one of the preceding claims, characterized in that each laser bar chip ( 1 ) between 3 and 25 emission zones ( 7 ) having. Diode laser stack according to one of the preceding claims, characterized in that each laser bar chip ( 1 ) on a stack element serving as a carrier ( 2 ) is arranged. Diode laser stack according to one of the preceding claims, characterized in that each laser bar chip ( 1 ) via a solder on a stack element ( 2 ) is arranged. Diode laser stack according to one of claims 7 and 8, characterized in that each stack element ( 2 ) an optic ( 3 ) for vertical collimation of the emission zones ( 7 ) of the laser bar chip ( 1 ) emitted light. Diode laser stack according to claim 9, characterized in that the collimating optics ( 3 ) is formed by a cylindrical lens. Diode laser stack according to one of claims 7 and 8, characterized in that an optical system ( 4 ) for scaling down the image of all stack elements ( 2 ) emitted light is provided. Diode laser stack according to one of Claims 9-11, characterized in that a multimode optical fiber ( 5 ) with an entrance facet ( 6 ) is provided, wherein the imaging optics ( 4 ) is arranged such that the of the stack elements ( 2 ) emitted light in the entrance facet ( 6 ) of the multimode optical fiber ( 5 ) is coupled. Diode laser stack according to claim 12, characterized in that the entrance facet ( 6 ) of the multimode optical fiber ( 5 ) is formed circular with a diameter between 0.3 and 3 mm. Diode laser stack according to one of the preceding claims, characterized in that the stack elements ( 2 ) have a thermal conductivity of at least 100 W / m · K. Diode laser stack according to one of claims 7-14, characterized in that at least one coolant element ( 8th ), wherein at least two of the stack elements ( 2 ) with the at least one cooling element ( 8th ) are connected. Diode laser stack according to one of claims 7-15, characterized in that on each of the side surfaces of the stack elements ( 2 ) a common cooling element ( 8th ) is provided, with all stack elements ( 2 ) with the two common cooling elements ( 8th ) are connected. Diode laser stack according to one of claims 7-15, characterized in that on the back of the stack elements ( 2 ) a common cooling element ( 8th ) is provided, with all stack elements ( 2 ) with the common cooling element ( 8th ) are connected. Diode laser stack according to one of claims 7-15, characterized in that between adjacent stack elements ( 2 ) an insulator and contact plate ( 9 ) is arranged. Diode laser stack according to one of claims 7-15, characterized in that the stack elements ( 2 ) via a solder with the at least one cooling element ( 8th ) and / or the stack elements ( 2 ) in each case via a solder with the laser bar chip ( 1 ) and / or the stack elements ( 2 ) in each case via a solder with the insulator and contact plate ( 9 ) are connected. Diode laser stack according to one of claims 8 and 19, characterized in that the solder is a brazing material. Diode laser stack according to one of claims 15-20, characterized in that each laser bar chip ( 1 ) directly to the overlying stack element ( 2 ) and electrically connected thereto or that each laser bar chip ( 1 ) via an elastic connecting element ( 10 ), a solidly formed insulator and contact plate ( 9 ) with the overlying stack element ( 2 ) is electrically connected. Diode laser stack according to one of claims 15-21, characterized in that all the laser bar chips are electrically connected in series are switched. Diode laser stack according to one of claims 7-22, characterized in that the thermal expansion coefficient of the stack elements ( 2 ) of the thermal expansion coefficient of the at least one cooling element in contact therewith ( 8th ) differs by less than 20%, and / or the thermal expansion coefficient of the stack elements ( 2 ) of the thermal expansion coefficient of the laser bar chip in contact therewith ( 1 ) differs by less than 20%, and / or the thermal expansion coefficient of the stack elements ( 2 ) of the thermal expansion coefficient of the insulator plate in contact therewith ( 9 ) or the insulator and contact plate ( 9 ) differs by less than 20%. Diode laser stack according to one of claims 10-23, characterized in that the focal length of the cylindrical lenses ( 3 ) is selected such that the collimated radiation fields of the individual laser bar chips ( 1 ) have a vertical extent that is less than or equal to half the spacing (P) of adjacent laser bar chips ( 1 ). System comprising two or more diode laser stacks according to claim 24, characterized in that deflecting mirrors ( 11 ) and / or deflecting prisms are provided so that the radiation fields of the diode laser stacks involved by the deflecting mirror ( 11 ) and / or the deflection prisms are combined in such a way that the lateral beam extent, the lateral beam divergence and the vertical beam divergence equal to that of a single of the participating diode laser stack ( 1 ) and the vertical beam extent only by a maximum of half a vertical distance (P) of adjacent laser bar chips ( 1 ) increases. Method for generating laser radiation using a diode laser stack comprising a multiplicity of laser bar chips ( 1 ), each laser bar chip ( 1 ) a plurality of mutually parallel emission zones ( 7 ), and wherein the width (d2) of the emission zones ( 7 ) each between 25 microns and 400 microns and the distance (d1) between the emission zones ( 7 ) is in each case between 50 μm and 200 μm, characterized in that the emission zones ( 7 ) of the laser bar chips ( 1 ) are excited to emission with a duty cycle of less than or equal to 30%. Method according to claim 26, characterized in that the emission zones ( 7 ) of the laser bar chips ( 1 ) are excited to emission with a duty cycle of less than or equal to 20%. Method according to one of claims 26 and 27, characterized in that the laser bar chips ( 1 ) radiation is vertically collimated each vertically and subsequently to the entrance facet ( 6 ) of a multi-mode fiber ( 5 ) and coupled into this. A method according to claim 28, characterized in that for vertical collimation a cylindrical lens and for coupling into the multimode fiber an imaging optics ( 4 ) is used. A method according to claim 29, characterized in that as imaging optics ( 4 ) a single lens is used. A method according to claim 30, characterized in that as imaging optics ( 4 ) an aspherical single lens is used. A method according to claim 30, characterized in that as imaging optics ( 4 ) Cylindrical lenses are used. Method according to one of claims 26-32, characterized in that in the emission zones ( 7 ) generated heat over the side surfaces and / or over the back of the stack elements ( 2 ) is discharged.