WO2008022920A2

WO2008022920A2 - Laser light source

Info

Publication number: WO2008022920A2
Application number: PCT/EP2007/058214
Authority: WO
Inventors: Manfred Vogel; Werner Herden; Ning Qu; Heiko Ridderbusch
Original assignee: Robert Bosch Gmbh
Priority date: 2006-08-22
Filing date: 2007-08-08
Publication date: 2008-02-28
Also published as: DE102006039396A1; WO2008022920A3

Abstract

The invention relates to a laser light source (340, 340a, 340b, 340c, 340d, 340e) having a semiconductor laser chip (341, 341a, 341b), having a plurality of emitters (342) which emit laser light. According to the invention, provision is made of at least two cooling elements (345a, 345b, 345c) for cooling the semiconductor laser chip (341, 341a, 341b) which are situated in thermal contact with two different surfaces (341', 341') of the semiconductor laser chip (341, 341a, 341b).

Description

- -

description

Title laser light source

State of the art

The invention relates to a laser light source with a semiconductor laser chip having a plurality of emitter emitting laser light.

From DE 10 2004 016 835 Al, such a laser light source is already known, which is also referred to as a laser diode bar. In order to prepare a laser beam emitted by the laser diode bar, an optical device is associated with the laser diode bar, which has inter alia a coupling prism and a decoupling prism and, overall, a very complicated structure.

Disclosure of the invention

It is an object of the present invention to improve a laser light source of the type mentioned in such a way that it is versatile and in particular no complex additional optics for adjusting a beam characteristic of the laser light emitted by it needs.

This object is achieved in a laser light source of the aforementioned type according to the invention that at least two cooling elements are provided for cooling the semiconductor laser chip, which are in thermal contact with two different surfaces of the semiconductor laser chip.

Advantages of the invention

The inventively provided a plurality of cooling elements, the possibility of efficient cooling of the semiconductor laser chip is given. In contrast to conventional laser light sources, in which only one surface of the semiconductor laser chip is cooled by a single cooling element, special arrangements of the emitters can be realized in the laser light source according to the invention, for example, in conventional laser light sources with their relatively poor cooling to thermal destruction - - would result during operation of the semiconductor laser chip.

A particularly efficient cooling of the semiconductor laser chip results when the cooling elements are in thermal contact with mutually opposite surfaces of the semiconductor laser chip.

The emitters, which usually have a line or rectangular shape, are advantageously combined to form an emitter group, wherein the emitters are preferably arranged next to one another along a direction extending essentially perpendicular to their longitudinal axis. Conventional emitter arrays are designed in contrast to the laser light source according to the invention, due to the lower cooling capacity only for relatively low peak power, while according to the invention, according to investigations by the Applicant significantly higher than the previously realized peak performance can be achieved.

A particularly effective cooling of the semiconductor laser chip results when the emitter and / or emitter groups of the laser light source are each arranged in the region of the surfaces of the semiconductor laser chip provided with the cooling elements.

Advantageously, the laser light source according to the invention can also have at least one further semiconductor laser chip, each of the semiconductor laser chips at least one cooling element is assigned, so that the resulting stack configuration is again cooled according to the invention on at least two surfaces. By using identical semiconductor laser chips for the formation of the stack configuration, an increase in performance of the laser light source according to the invention can be achieved with an overall comparatively low production cost.

The plurality of semiconductor laser chips of the laser light source according to the invention can be electrically connected in parallel or in series with each other and thus allow different connection configurations or adaptation to different electrical parameters such as an operating voltage and / or an operating current. Semiconductor laser chips, each with differently doped substrates, can also be used very advantageously, which provides a further degree of freedom with regard to the electrical control of the laser light source.

Very different electrical emitter groups can be assigned to different emitter groups, so that the individual emitter groups can be controlled independently of one another, for example, to selectively apply laser light to corresponding loads connected to the laser light source. - -

Instead of using conventional laser emitters, for example, having a width of only about one micron and having a correspondingly high fast-axis divergence, it is also conceivable to use so-called photonic bandgap crystal-based emitters, which currently have emitter widths of up to can be produced to 20 microns and have a correspondingly lower fast-axis divergence.

Regardless of the type of emitter used, the efficient cooling according to the invention allows a flexible arrangement of the individual emitters of the laser light source with one another, for example so-called laser stacks, the individual emitters being used, for example. can be arranged such that they correspond approximately to an entrance surface of an optical fiber device to be supplied by the laser light source and accordingly the laser can efficiently couple light into the optical fiber device without the need for complex optical coupling elements. As a result, a very simple and therefore reliable and cost-effective light coupling can be realized.

Advantageously, an input portion of an optical fiber device provided between the laser light source and a laser device to be supplied thereto may be disposed directly in front of a surface of the semiconductor laser chip having the emitters, i. In particular, no complicated and thus expensive coupling optics is required in order to couple the laser light generated by the laser light source into the optical waveguide device.

The laser light source according to the invention can be advantageously used as a pump light source for a laser-based ignition system of an internal combustion engine, with applications both in internal combustion engines of motor vehicles as well as in stationary engines are conceivable.

The efficient cooling of the semiconductor laser chip according to the invention further advantageously provides the possibility of keeping an operating temperature of the laser light source and thus also the wavelength of the laser light emitted by the emitters constant.

In principle, the inventively improved heat conduction from / to the semiconductor laser chip through the at least two cooling elements also to an improved temperature, in particular

Heating, the semiconductor laser chip can be used, provided that appropriate heat sources are provided. Such a temperature control is particularly useful in applications in the automotive field can be used to allow the emission of laser light of the desired wavelength even under extreme cold start conditions. An optional cooling or heating can be achieved, for example, by a Peltier element which is in thermal contact with at least one, but preferably all, cooling elements provided according to the invention. - -

Other features, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

Short description of the drawing

In the drawing shows:

Figure Ia is a schematic representation of an internal combustion engine with a laser-based ignition device;

Figure Ib is a schematic representation of the ignition device of Figure 1;

Figure 2 is a schematic plan view of a laser light source of the invention

Ignition device of Figure 2;

Figure 3 is a schematic side view of an embodiment of the laser light source according to the invention;

Figure 4 is a schematic side view of another embodiment of the laser light source according to the invention;

Figure 5a to 5c schematically show an embodiment of the laser light source according to the invention with two semiconductor laser chips;

Figure 6a is a schematic side view of another embodiment of the laser light source according to the invention; and

Figure 6b is a plan view of the laser light source of Figure 6a.

Embodiments of the invention

An internal combustion engine carries in FIG. 1a overall the reference numeral 10. It serves to drive a motor vehicle, not shown. The internal combustion engine 10 comprises a plurality of cylinders, of - - which is designated in Figure 1 only one with the reference numeral 12. A combustion chamber 14 of the cylinder 12 is limited by a piston 16. Fuel enters the combustion chamber 14 directly through an injector 18, which is connected to a designated also as a rail fuel pressure accumulator 20.

Injected into the combustion chamber 14 fuel 22 is ignited by means of a laser pulse 24 which is emitted by a laser device 26 comprehensive ignition 27 into the combustion chamber 14. For this purpose, the laser device 26 is fed via a light guide device 28 with a pumping light, which is provided by a pumping light source 30. The pumping light source 30 is controlled by a control unit 32, which also controls the injector 18.

As can be seen from FIG. 1 b, the pumping light source 30 feeds a plurality of optical fiber devices 28 for different laser devices 26, which are each assigned to a cylinder 12 of the internal combustion engine 10. For this purpose, the pumping light source 30 has a plurality of individual laser light sources 340, which are connected to a pulse power supply 36. As a result of the presence of the plurality of individual laser light sources 340, a "stationary" distribution of pump light to the various laser devices 26 is realized, so that no optical distributors or the like are required between the pump light source 30 and the laser devices 26.

The laser device 26 has, for example, a laser-active solid 44 with a passive Q-switching circuit 46, which form an optical resonator together with a coupling-in mirror 42 and an output mirror 44. Upon application of a pumping light generated by the pumping light source 30, the laser device 26 generates a laser pulse 24 in a manner known per se, which is focused by focusing optics 52 onto an ignition point ZP located in the combustion chamber 14 (FIG. The components present in the housing 38 of the laser device 26 are separated from the combustion chamber 14 by a combustion chamber window 58.

FIG. 2 shows a schematic plan view of a first embodiment of the laser light source 340 according to the invention. As can be seen from FIG. 2, the laser light source 340 has several

Laser light emitting emitter 342 whose laser light is used as pumping light 60 for optically pumping the laser device 26 (FIG. 1b) or the laser-active solid 44 disposed therein and accordingly coupled into the optical fiber device 28. According to the invention, at least two cooling elements, not shown in FIG. 2, are advantageously provided, which enable efficient cooling of the laser light source 340.

A schematic side view of a further embodiment of the laser light source 340a according to the invention is shown in FIG. In addition to a emitter 342 having - -

Semiconductor laser chip 341, the laser light source 340a according to the invention advantageously two cooling elements 345a, 345b, which, as shown in Figure 3, in thermal contact with opposing surfaces 341 ', 341 "of the semiconductor laser chip 341 are located.

The configuration according to the invention with the two cooling elements 345a, 345b permits the arrangement of a large number of emitters 342 in a so-called laser stack configuration, as a result of which, as can be seen from FIG. 3, a plurality of emitter groups 342a are obtained. Due to the small width of a single emitter 342 and the concomitant relatively large fast-axis divergence, the above-described juxtaposition of the emitter 342 to emitter group 342a is particularly useful because this provides a more efficient coupling of the laser light generated by the emitters 342 into a downstream optical Component such as the light guide device 28, see Figure Ib, Figure 2, is possible. In particular, as is evident from FIG. 2, no complex coupling optics known from conventional systems are required, but rather direct coupling of the laser light from the emitters 342 of the laser light source 340, 340a into the optical waveguide device 28 can take place, which not only reduces the complexity of the arrangement is reduced, but also by a required in conventional laser light sources coupling optics resulting losses can be avoided.

Due to the efficient cooling by the inventive arrangement of the cooling elements 345a, 345b, an increased temperature stability of the semiconductor laser chip 341 and thus a corresponding wavelength stability of the laser light generated by the laser light source 340, 340a laser light is also given.

The connection of the semiconductor laser chip 341 with the cooling elements 345a, 345b can take place, for example, by way of a solder connection 346 or else by pressing or the like.

The emitters 342 or corresponding emitter groups 342b, 342c are particularly advantageously arranged, as in the variant 340b of the laser light source according to the invention shown in FIG. 4, in each case in the region of the surfaces 341 ', 341 "of the semiconductor laser chip 341 provided with the cooling elements 345a, 345b.

For example, in a preferred embodiment of the laser light source 340b according to the invention, the semiconductor laser chip 341 may have a height h of about 100 microns, while the width b of the semiconductor laser chip 341 is about one millimeter. The cooling elements 345a, 345b are not shown to scale and advantageously have a height of one to - - several millimeters in order to ensure an efficient heat transfer away from the semiconductor laser chip 341.

Preferably, the cooling elements 345a, 345b are formed of a material having high thermal conductivity, with the use of copper being particularly preferred.

In a further very advantageous embodiment of the laser light source 340c according to the invention, a total of two semiconductor laser chips 341a, 341b are provided, which together form a stack configuration, compare FIG. 5a. The cooling elements 345a, 345b according to the invention are in each case connected to a surface of one of the two semiconductor laser chips 341a, 341b and thus in turn cause cooling of the laser stack 341a, 341b from two sides or the surfaces 341 ', 341 ".

In addition, in the case of the laser light source 340c, a contact 347 arranged between the semiconductor laser chips 341a, 341b is provided, which serves for the electrical control of the semiconductor laser chips 341a, 341b. The contacting 347 may be connected, for example, to a ground potential or another reference potential of the pumping light source 30 (FIG. 1b) or the pulse power supply 36 arranged therein. The connection of

Semiconductor laser chips 341a, 341b with a potential corresponding to an operating voltage advantageously takes place directly via the also electrically conductive cooling elements 345a, 345b.

In the exemplary embodiment according to FIG. 5a, the two semiconductor laser chips 341a, 341b can be embodied identically, for example, so that an electrical parallel connection of the semiconductor laser chips 341a, 341b results under the above-described contacting.

In contrast to this, the exemplary embodiment 34Od according to FIG. 5b shows an electrical series connection of the semiconductor laser chips 341a, 341b, which are in turn identically designed, whereby a correspondingly higher, approximately twice the operating voltage is required in comparison with the exemplary embodiment according to FIG large operating current sets. Since the emitter 342 of the upper semiconductor laser chip 341b in FIG

Configuration are arranged according to Figure 5a is not directly in the vicinity of the cooling element 345b or a cooling element 345b contacting surface 341 ", is given a slightly lower efficiency in the cooling of the laser light source 34Od.

In particular, in those applications in which a vertical distance between the emitter groups of the two semiconductor laser chips 341a, 341b a predefinable threshold value, for example, from an input cross-section or diameter of a light guide device 28th - - depends, must not exceed, arranged between the semiconductor laser chips 341a, 341b and unspecified in Figure 5b Kontaktierungszwischenschicht must have a correspondingly low height and thus can itself cause no significant heat transfer away from the semiconductor laser chips 341a, 341b.

In a further particularly advantageous embodiment 34Oe of the invention

Laser light source, cf. 5c, the semiconductor laser chips 341a, 341b disposed adjacent to one another each have differently doped substrates. For example, the semiconductor laser chip 341a may have an n-type substrate while the semiconductor laser chip 341b has a p-type substrate, resulting in a different polarity for the electrical operation of the semiconductor laser chips 341a, 341b. As a result, in the case of the laser light source 34Oe, it is advantageously possible to realize an electrical series connection, wherein the first cooling element 345a is connected, for example, to a potential corresponding to an operating voltage of the pulse power supply 36 (FIG. 1b) and the second cooling element 345b accordingly has a ground potential or any other lower reference potential.

Another very advantageous embodiment of the laser light source according to the invention is shown schematically in Figure 6a in a side view. As can be seen from FIG. 6a, the laser light source has a first cooling element 345a, which is in thermal contact with a semiconductor laser chip 341, analogously to the embodiments described above. The semiconductor laser chip 341 has a total of four different emitter groups 342d, 342e, 342f, 342g, which are spaced apart as shown and configured such that all emitters 342 of a corresponding emitter group 342d, 342e, 342f, 342g couple laser light generated therefrom to a corresponding optical fiber device can, which is shown in Figure 6a schematically by the circles 28a ', 28b', 28c ', 28d'.

Separate cooling elements 345b, 345c, 345d, 345e are advantageously assigned to the individual emitter groups 342d,..., 342g, which, as described above, are simultaneously associated with the electrical

Contacting the respective emitter groups 342d, ..., 342g of the semiconductor laser chip 341 serve. That is, the contacting of a particular emitter group of the laser light source according to the invention shown in Figure 6a takes place on the one hand via one of the cooling elements 345b, ..., 345e arranged separately from one another and the common cooling element 345a, which is connected to the four emitter groups 342d, ..., 342g. connected to the ground potential.

This advantageously results in a separate controllability of the respective emitter group 342d,... 342g, so that by means of the laser light source according to the invention depicted in FIG. 6a, for example via corresponding optical waveguide devices 28a, 28b, 28c, 28d (see FIG. 6b). A total of four different laser devices 26 (FIG. 1 a, 1 b) can be supplied with laser light 60 (FIG. 2) independently of one another, which can be used for optically pumping the respective laser device 26 or the laser-active solid 44 arranged therein. The laser light source according to the invention shown in Figure 6a, 6b can thus be used to realize a "stationary pump light distribution." Also simplifies the installation of the laser light source, since instead of four separate laser light sources only the inventive arrangement, which is preferably monolithic, to arrange in the ignition device 27 Furthermore, a common adjustment of the light guides 28a,..., 28d can advantageously take place.

Particularly advantageously, the arrangement according to the invention allows the emitter in the emitter groups 342d,..., 342g shown in FIG. 6a to couple the laser light 60 directly into the corresponding optical waveguide device 28a,..., 28d, in particular without the need for an optical coupling element ,

In a further very advantageous embodiment of the laser light source according to the invention, the use of photonic bandgap crystal-based emitters is provided which, due to their relatively large emitter width of up to 20 micrometers, has a lower fast-axis divergence and accordingly an even more efficient coupling of laser light 60 into one allow corresponding light guide device 28.

In addition to the above-described cooling elements 345a,..., 345e, other cooling elements (not shown) may also be provided, which are in particular also arranged on lateral surfaces of the semiconductor laser chip 341, 341a, 341b.

The laser light source according to the invention can generally be advantageously used in laser-based ignition systems of internal combustion engines 10, e.g. of motor vehicles or even in stationary engines used. In general, due to the high achievable output power, which is made possible by the inventively optimized cooling, other applications conceivable.

Claims

- -Claims

A laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) comprising a semiconductor laser chip (341, 341a, 341b) having a plurality of laser light emitting emitters (342), characterized in that at least two cooling elements (345a, 345b, 345c , 345d, 345e) for cooling the semiconductor laser chip (341, 341a, 341b) which are in thermal contact with two different surfaces (341 ', 341 ") of the semiconductor laser chip (341, 341a, 341b).

2. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to claim 1, characterized in that the cooling elements (345a, 345b, 345c) in thermal contact with opposing surfaces (341 ', 341 ") of the semiconductor laser chip ( 341, 341a, 341b).

A laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to any one of the preceding claims, wherein the emitters (342) are substantially rectangular in shape, characterized in that a plurality of emitters (342) each form an emitter group (342a, 342b, 342c), wherein the emitters (342) are preferably arranged next to each other along a direction extending substantially perpendicular to their longitudinal axis.

4. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to any one of the preceding claims, characterized in that the emitter (342) and / or emitter groups (342a, 342b, 342c) in each case in the region of cooling elements (345a , 345b) provided on the surfaces (341 ', 341 ") of the semiconductor laser chip (341, 341a, 341b) are arranged.

5. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to any one of the preceding claims, characterized in that at least one further semiconductor laser chip (341b) is provided, which forms a stacked configuration together with the semiconductor laser chip (341a), and each semiconductor laser chip (341a, 341b) is associated with at least one cooling element (345a, 345b).

6. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to claim 5, characterized in that the semiconductor laser chips (341, 341a, 341b) are electrically connected in parallel or in series with each other.

7. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to claim 5 or 6, characterized in that adjacent to each other semiconductor laser chips (341a, 341b) each have differently doped substrates. - -

8. laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to one of claims 3 to 7, characterized in that different emitter groups (342d, .., 342g) are each assigned separate electrical contacts.

9. Ignition device for an internal combustion engine (10), in particular of a motor vehicle, having at least one laser device (26) which generates a laser pulse (24) for emission into a combustion chamber (14), characterized by a laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) according to any one of the preceding claims, which provides laser light (60) for optically pumping the laser device (26).

10. Ignition device according to claim 9, characterized in that at least one light guide device (28, 28a, 28b, 28c, 28d) for supplying the laser device (26) with the laser light source (340, 340a, 340b, 340c, 34Od, 34Oe) generated Laser light (60) is provided, and that an input portion of the optical fiber device (28, 28a, 28b, 28c, 28d) is arranged directly in front of the emitter (s) (342).