WO2011054603A2

WO2011054603A2 - Light source

Info

Publication number: WO2011054603A2
Application number: PCT/EP2010/064302
Authority: WO
Inventors: Klaus Stoppel; Karl-Heinz Nuebel; Hans-Jochen Schwarz; Manfred Vogel; Andreas Letsch
Original assignee: Robert Bosch Gmbh
Priority date: 2009-11-06
Filing date: 2010-09-28
Publication date: 2011-05-12
Also published as: WO2011054603A3; DE102009046464A1

Abstract

The invention relates to a light source, in particular for optically activating a laser device (11), such as a laser device (11) of a laser ignition system (1) of an internal combustion engine (109), comprising a diode laser (13) and a fibre-optic device (12), wherein the fibre-optic device (12) is arranged relative to the diode laser (13) such that light generated by the diode laser (13) couples into the fibre-optic device (12), characterized in that the light source comprises a photodetector (90) for detecting stray light (111) which is scattered at the transition from the diode laser (13) into the fibre-optic device (12).

Description

light source

State of the art

The invention relates to a light source according to the preamble of the independent

Claim. Such a light source is known from DE 102004 006 932 B3 and has a diode laser bar with a plurality of narrow emitters, which are arranged in a row next to each other in the direction of their longitudinal axis. The diode laser bar is a device for beam guidance and beam shaping emerging from it

Laser beam associated with a variety of in a row next to each other

arranged optical fibers contains, in which couples the laser beam.

In many cases, it is desirable to provide information about the proper operation of such a light source or information about the proper performance of a process produced by the emission of the light source.

Disclosure of the invention

The invention provides such a device, in particular a device is provided which is particularly robust, can be manufactured inexpensively and is able to provide particularly high-quality information.

The invention is based on the observation that in light sources after the

Generic term of the independent claim in the transition from the diode laser in the light guide increasingly scattered light occurs, from the conclusions about the proper operation of the light source or information about the flawless

Successes of a excited by the emission of the light source process can be drawn. Such a process excited by the emission of the light source may be, for example, the generation of a laser pulse by a laser device excited by the light source or the ignition of a combustion in an internal combustion engine. The invention is further based on the finding that this scattered light can be supplied to a photodetector in a particularly simple manner, the suitable Location, in particular in the vicinity of the area in which a transition of light between a diode laser and a light guide, in particular 5mm or less spaced from this area, is arranged. The transition of light from the diode laser in the light guide takes place in

Generally in the range of also referred to as cross-sectional transducers, encompassed by the light guide means in which a transition of the lateral

Intensity distribution of the radiation generated by the diode laser is carried out to a predetermined by the light guide lateral intensity distribution. In general, this transition occurs along the direction of propagation of the radiation generated by the diode laser front 10mm or the front 20mm of the light guide.

In the present case, a photodetector is to be understood in a broad sense as an instrument for detection, in particular for optoelectrical conversion, of light, for example a photodetector may comprise a photodiode, a CCD camera

be bolometric sensor or a photomultiplier or comprise one or more such components each single or multiple.

Developments of the invention provide that the diode laser comprises a plurality of emitters and the light guide comprises a plurality of optical fibers (hereinafter also referred to as fibers) and each fiber has a first end, wherein in a further advantageous embodiment of the invention, the first ends of such Emitters are arranged that coupled by the emitter light into the first ends of the optical fibers, wherein the light source comprises a photodetector for detecting light that is scattered in the transition from the emitters in the first ends. It is understood that the photodetector is arranged for this purpose at a suitable location, in particular in the region of the first ends of the optical fibers, in particular 5 mm or less spaced from the first ends of the optical fibers. such

Developments of the invention have, inter alia, the advantage that when passing from the diode laser into the light-conducting device, the scattered radiation starts from a spatially well-defined region and can therefore also be detected well by the photodetector. For this purpose, it is also advantageous if each fiber has a side surface and the fibers are arranged at least in the region of their first ends along their side surfaces in abutment. Here, a first end of an optical fiber is to be understood as meaning an end of an optical fiber in the direction of its longitudinal axis, for example in the case of a cylindrical fiber a base surface of the cylinder. A lateral surface of an optical fiber is to be understood as meaning the surface which delimits an optical fiber perpendicular to its longitudinal axis, for example, in the case of a cylindrical fiber, the lateral surface of the cylinder. Optical fibers which are butted along their side surfaces are understood to be optical fibers, all or almost all of which, for example, more than 90% of the optical fibers, contact immediately adjacent optical fibers along their side surfaces.

Under scattered light, which is scattered in the transition from a diode laser in a light guide, is understood in the context of this application in a broad sense, such light emitted by the diode laser and then deviates from the originally intended for the light in the light source way, for example due to a residual roughness of an optical surface or due to other defects of the diode laser, the light guide and / or the interface between the diode laser and the light guide. By scattered light is meant in particular light that emerges from an optical fiber through the side surface of the optical fiber, thus traversing the fiber cladding, in particular in the range of also referred to as cross-sectional transducers, encompassed by the light guide means in which a transition of the lateral intensity distribution of the Diode laser generated radiation takes place on a predetermined by the light guide lateral intensity distribution.

In particular, scattered light in the sense of this application is pronounced as diffuse, non-directional or substantially non-directional light, which occurs in particular in the surroundings of the light source.

Additionally or alternatively, the reproducibility of the scattered light improves when the fibers are connected in the region of their first ends with a preferably transparent fiber carrier or are even arranged in the region of their first ends between two preferably transparent fiber carriers. Here are in particular the

Side surfaces of the fibers with the fiber carriers or in contact. Preferably, the photodetector is in direct contact with, or spaced from, the fiber carrier by 5mm or less. It may be that the scattered light reaching the photodetector without further

Measures does not reach the desired intensity. It is therefore advantageous to have a means for Increase the scattered light intensity from which the photodetector is hit, provide and / or provide a means for imaging the scattered light on the photodetector.

An illustration of scattered light is understood here to mean that the scattered light, in particular previously scattered, or at least parts of the scattered light, in particular previously scattered, undergo a significant change in direction during the imaging, in particular by reflection at flat or curved surfaces or by refraction at curved surfaces. On the other hand, therefore, for example, the transmission through a thin plane-parallel disc is not to be understood as imaging within the meaning of the invention, since in this case a significant change in direction of the scattered light does not occur altogether.

Advantageously, the means for increasing the intensity of scattered light from which the photodetector is struck and / or the means for imaging scattered light on the photodetector are made in one piece with the light-guiding device, and in particular a mirroring of an outer surface of one or more fiber carriers and / or a curved outer surface of one or more fiber carrier. Preferably, the reflective coating and / or a mirrored curved outer surface is located completely or partially on an outer surface of one or more fiber carriers facing away from the photodetector. Transmitting, curved outer surfaces of one or more

On the other hand, fiber carriers are preferably located completely or partially on an outer surface of one or more fiber carriers facing the photodetector.

Further very advantageous embodiments provide for the use of at least one further optical component, which may in particular be made in one piece with the light-conducting device, in particular a light guide which is shaped such that it reflects scattered light by multiple reflection onto the photodetector or lenses, in particular Fresnel lenses. Preferably, a Fresnel lens is applied on the outer surface of the fiber carrier. Other structures for increasing the scattered light intensity from which the photodetector is hit and / or for imaging scattered light onto the photodetector can also be advantageously applied to the outer surface of the fiber carrier.

Also advantageously, the means for increasing the amount of scattered light from which the photodetector is struck and / or the means for imaging scattered light on the photodetector may be a gel disposed in a space between one or more fiber carriers or optical fibers and the photodetector , This improves the light conduction, reduces reflections and refractions in the light path, especially when the optical gel has a refractive index of about 1.3 to 1.7.

Advantageously, it is provided that the light source contains at least one fluorescent substance which, in the transition from the diode laser in the

Light guide is scattered light, wherein resulting from the photodetector fluorescent light is detected. This advantageously makes it possible to use even those photodetectors whose spectral sensitivity is low for the scattered light and higher for the fluorescent light. Far-reaching functional improvements can be achieved if the light source comprises a plurality of photodetectors which are arranged at substantially different locations from one another and / or have a significantly different spectral sensitivity, in particular in combinations with the above-described measures, in particular one or more of the measures described above one, several or all of the photodetectors covered by the light source can relate.

Substantially different locations in the sense of the invention may be, for example, locations that are more than 5 or more than 15 mm apart, or locations whose spacing is greater than half the maximum extent of

Diode laser.

Photodetectors having a substantially different spectral sensitivity can be realized by the corresponding maxima of the spectral sensitivity (current per light power) occurring at wavelengths that differ by 100 nm or more or 300 nm or more.

Drawing Figure 1 shows a schematic representation of an internal combustion engine with a laser ignition device according to the invention.

FIG. 2 shows a laser ignition device in detail. Figures 3a, 3b, 3c and 3d show a first embodiment of a light source according to the invention. FIGS. 4a, 4b, 4c and 4d show further embodiments according to the invention

Light sources.

Description of the embodiment

An internal combustion engine carries in Figure 1 in total the reference numeral 109. It serves to drive a motor vehicle, not shown, or a generator, also not shown. The engine 109 includes a plurality of cylinders 129, one of which is shown in FIG. A combustion chamber 14 of the cylinder 129 is bounded by a piston 16. Fuel 229 enters the combustion chamber 14 directly through an injector 18, which is connected to a fuel pressure accumulator 209. Fuel 229 injected into the combustion chamber 14 is ignited by means of a laser pulse 24 which is emitted by an ignition device 27 comprising a laser device 11 into the combustion chamber 14 and focused by means of focusing optics 261. The laser device 11 is fed by a light source 10 via a light guide 12 with a pumping light. The light source 10 is controlled by a control and regulating device 32, which also controls the injector 18.

In addition to the light-conducting device 12, the light source 10 also includes a diode laser 13, which, in response to a control current, emits a corresponding pump light via the light source 12

Lichtleiteinrichtung 12 outputs to the laser device 11.

FIG. 2 schematically shows a detailed view of the solid state laser 260 of FIG

Laser device 11 from FIG. 1. As can be seen from FIG. 2, the solid-state laser 260 has a laser-active solid, hereinafter referred to as laser crystal 44, to which a crystal, also referred to as Q-switch, the passive Q-switch 46, is optically arranged downstream. The solid-state laser 260 also has a coupling-in mirror 42 and a coupling-out mirror 48. The components of the solid state laser 260 are monolithic in this example, that is, they are largely non-detachably connected to each other, for example by bonding and / or coating. To generate a laser pulse, also called a giant pulse, the

Laser crystal 44 through the coupling mirror 42 through with pumping light 28 a applied, so that optical pumping and formation of population inversion in the laser crystal 44 occurs. First, the passive Q-switch 46 is in its idle state, in which it has a relatively low transmission for the light to be generated by the laser device 11. In this way, the process of stimulated emission and thus the generation of laser radiation are initially suppressed. However, as the pumping time increases, that is, when it is exposed to the pumping light 28a, the radiation intensity in the solid-state laser 260 rises, so that the passive Q-switch 46 finally fades. This increases his

Transmission abruptly, and the generation of laser radiation begins. This state is symbolized by the double arrow 24 '. During laser operation, due to the effect of the stimulated emission, rapid degradation of the population inversion present in the laser crystal 44 occurs, so that the emission of the solid state laser 260 typically stops after a few nanoseconds, and subsequently the transmission of the Q-switch 46 also returns to its original, low value ,

In the manner described above, a laser pulse 24, also referred to as a giant pulse, which has a relatively high peak power. The laser pulse 24 is, optionally using another light guide (not shown) or directly, coupled through a likewise not shown combustion chamber window of the laser device 11 in the combustion chamber 14 (Figure 1) of the engine 109, so that existing therein fuel 229 or air / Fuel mixture is ignited. Figures 3a, 3b, 3c and 3d show a schematic view of a

Embodiment of a light source 10 according to the invention. The diode laser 13 encompassed by the light source 10 has the design of a so-called diode laser bar. It thus has a plurality of juxtaposed emitters 131. The emitters 131 have a side surface 1310 through which the light generated by the emitters 131 exits. This side surface 1310 typically has an approximately rectangular shape with a short, for example, Ιμηη long, first side 1311 and a, usually referred to as slow axis, a longer, for example 10 - 500μηη long, second side, for example, ηηηη long first page 1311 and 1312. Between those in one

Layer plane, in the direction of the slow axis juxtaposed emitters 131 are called separation trenches designated areas from which no light is emitted. The generated by the emitters 131 and emerging from the side surfaces 1310 light Each has the shape of a cone of light, wherein the half-opening angle of the light cone in the plane of the fast-axis is typically in the range of 30 ° to 60 ° and is generally significantly larger than the opening angle of the cone of light in the plane of the slow axis typically only a few degrees.

Although in this example the diode laser 13 has the design of a so-called diode laser bar, the invention is not limited to such a design, but also includes, for example, diode laser 13 with other arrangements of emitters 131, for example arrangements having emitters 131 in multiple layer planes, these Layer planes are offset for example in the direction of the fast axis by a few microns to each other, for example, so-called diode laser stacks or nanosticks. A transmission of the invention to other types of lasers known per se or other types of light sources known per se instead of a diode laser 13 is conceivable.

The light guide device 12 likewise encompassed by the light source 10 has a multiplicity of fibers 121, the fibers 121 each having a first end 1211 and a second end 1212. The fibers 121 are arranged in the region of their first ends 1211 in a position next to one another. Furthermore, the fibers 121 are arranged in the region of their first ends 1211 such that the end faces 1216 of the fibers 121 associated with the first ends 1211 lie together in one plane. Furthermore, the fibers 121 are arranged in the region of their first ends 1211 along their side surfaces 1217 in abutment, that is arranged so that all fibers 121 or almost all fibers 121, for example, more than 90% of the fibers 121, immediately adjacent fibers 121 in the region touching first ends 1211.

As can be seen in FIGS. 3 a, 3 b and 3 c, the fibers 121 are connected to a fiber carrier 20 in the region of their first ends 1211. The fiber carrier 20 used in this example has the shape of a cuboidal disk, extends across the width in which the fibers 121 are arranged, for example, about 20 mm, has an in

Direction of the longitudinal axes 1219 of the fibers 121 oriented length of 1 mm to 20 mm, for example, to 10 mm. The fiber carrier 20 terminates flush on its side facing the diode laser 13 with the end faces 1216 of the fibers 121. The height of the fiber carrier 20 is in the range of a few tenths of a millimeter to a few millimeters and is typically many times higher than the height of the fibers 121. The fiber carrier 20 consists of a glass and is bonded to the fibers 121 in the region of their first ends 1211. The fiber carrier 20 consists of a glass, which compared to the type of glass or to the types of glass that make up the fibers 121, a lower hardness at room temperature, a comparable

Thermal expansion coefficient and / or a higher softening temperature has.

Types of glass used are, for example, float glasses.

The region which is referred to herein as the region of the first ends 1211 of the fibers 121 is to be understood in particular as the region of the fibers 121 in which the fibers 121 are arranged on the fiber carrier 20.

The composite of fibers 121 and fiber carrier 20 is fixed relative to the diode laser 13, for example by gluing. Another possibility is to fix by clamping so that it can be loosened at a later time, for example, for disassembly or readjustment.

It is further provided that the fibers 121 are arranged in the region of their first ends 1211 not only on a fiber carrier 20, but are arranged between the fiber carrier 20 and a second fiber carrier 21. The fiber carrier 20 and the second fiber carrier 21 each have the shape of a cuboid glass disc and are, for example, the same size.

Also between the second fiber carrier 21 and the fibers 121 is a

cohesive connection and also the second fiber carrier 21 closes with the

End faces 1216 of the fibers 121 flush.

On the one hand, it is possible that the surface of the fiber carrier 20 facing the fibers 121 and the surface of the second fiber carrier 21 facing the fibers 121 are parallel to one another, so that the gap remaining between the fiber carriers 20, 21 has a uniform height. Alternatively, the fibers 121 facing surface of the

Fiber carrier 20 and the fibers 121 facing surface of the second fiber carrier 20 to each other tilted so that the remaining between the fiber carriers 20, 21 gap in the region of the end faces 1216 of the fibers 121 has a lower height than in the end faces 1216 of the fibers 121 opposite region the fiber carrier 20,21. Preferably, a tilting takes place at an angle of 0.1 ° to 2.5 °, for example 0.2 ° to 0.5 °. According to the shape of the gap between the fiber carriers 20, 21 is in In this case, a continuous taper of the fibers 121 is provided. Due to the continuous transition between one of the coupling into the fibers 121

useful cross-sectional shape and one of the light pipe in the fibers 121 useful cross-sectional shape are abrupt transitions, the potential

represent mechanical weak points, avoided.

The two fiber carriers 20, 21 can have similar, in particular identical, properties with respect to their material. The second fiber carrier 21 preferably consists of a glass, which has a lower hardness at room temperature and / or a comparable coefficient of thermal expansion and / or a higher one compared to the type of glass or to the types of glass making up the fibers 121

Has softening temperature.

According to the invention it is provided that the light source is a photodetector 90 for

Detection of scattered light 111 which is scattered in the transition from the diode laser 13 in the light guide 12, the photodetector 90 detected scattered light 111, which is scattered in the transition from the emitters 131 in the first ends 1211 of the optical fibers 121. The photodetector 90 is spaced about 1mm from the fiber carrier 20 in this example.

The light source further comprises one or more further photodetectors 91, which also serve to detect stray light 111 which is scattered in the transition from the emitters 131 into the first ends 1211. The photodetector 90 is formed, for example, as a photodiode and formed with an associated spectral filter so that it narrow-band emission of the diode laser 13 (for example, light of wavelength 807nm to 809nm) measures.

The further photodetector 91 is, for example, likewise designed as a photodiode, but the spectral filters which prevent the emission of the diode laser 13 (for example, the light of the

Wavelength 807 nm to 809 nm) or the laser device 11 (for example, 1064 nm wavelength light). In this example, spectral filters are associated with the further photodetector so that it only detects light in the wavelength range less than 500 nm, which is primarily due to the illumination of the combustion taking place in the combustion chamber 14 (FIG. 1). By means of evaluation of the signals supplied by the detectors 90 and 91, information about an operating state of the diode laser 13 and about a combustion taking place in the combustion chamber 14 can be provided independently of one another.

The provision of a second further photodetector 91, which is selective for the

Emission of the laser device 11 (for example, light of wavelength 1064 nm) is possible. In the example, the detectors 90, 91 are located in substantially different locations, for example at locations 20mm apart, or at locations whose spacing is greater than half the maximum extension of the diode laser.

From the embodiment shown above, as shown in Figures 4a to 4d, further embodiments of the invention, which differ from this in that additionally at least one means is provided, through which the scattered light 111 is imaged on the photodetector 90 and through that the

Scattered light intensity from which the photodetector 90 is hit is increased. In the embodiment of the invention shown in FIG. 4 a, this means is embodied as a coating 122 applied on an outer surface of the fiber carrier 20, by which the light intensity incident on the photodetector 90 is approximately doubled. The provision of a mirroring 122 of further outer surfaces of the fiber carrier 20 and a reflective coating 122 on both fiber carriers 20, 21 and / or spectrally selective reflective coatings 122 are possible.

In the embodiment of the invention illustrated in FIG. 4b, this means is embodied as a coating 122 applied on an outer surface of the fiber carrier 20, and the outer surface of the fiber carrier 20 is additionally curved in such a way that the scattered light 111 is focused onto the photodetector 90. An arrangement without mirroring 122 is possible. In this case, the scattered light by a

Lens effect imaged on the photodetector. Also, the execution of the outer surface of the fiber carrier 20 and / or the other fiber carrier 21 as a Fresnel lens is possible.

In the embodiment of the invention shown in FIG. 4 c, this means is embodied as a light guide 125 applied on an outer surface of the fiber carrier 20, by which the scattered light 111 is supplied to the photodetector 90, in particular by multiple reflection.

In the embodiment of the invention shown in FIG. 4 d, this means is embodied as a gel 140, which is arranged in a spatial region between the fiber carrier 20 or the fiber carriers 20, 21 and the photodetector 90. Alternatively or additionally, an arrangement of the optical gel 140 between the optical fibers 121 and the photodetector 90 would be possible. In the embodiment of the invention illustrated in FIG. 4e, this means is embodied as a fluorescent substance 128 which is applied to an outer surface of the fiber carrier 20, the photodetector 90 detecting the resulting fluoroscopic light 112.

Claims

claims

1. Light source, in particular for the optical excitation of a laser device (11),

For example, a laser device (11) of a laser ignition system (1) of a

Internal combustion engine (109) comprising a diode laser (13) and a

Light guide (12), wherein the light guide (12), are arranged to the diode laser (13) that by the diode laser (13) generated light in the

Coupled light guide device (12), characterized in that the light source comprises a photodetector (90) for detecting stray light (111), the

Transition from the diode laser (13) in the light guide (12) is scattered.

2. Light source according to claim 1, characterized in that the diode laser (13) comprises a plurality of emitters (131) and the light guide (12) comprises a plurality of optical fibers (121) and each fiber (121) has a first end (1211). wherein the first ends (1211) are disposed to the emitters (131) such that light generated by the emitters (131) couples into the first ends (1211) of the optical fibers (121), the photodetector (90) being stray light (111) scattered at the transition from the emitters (131) to the first ends (1211).

3. Light source according to claim 2, characterized in that each fiber (121) has a side surface (1217) and the optical fibers (121) at least in the region of their first ends (1211) along their side surfaces (1217) are arranged in abutment.

4. Light source according to claim 2 or 3, characterized in that the optical fibers (121) in the region of their first ends (1211) are connected to a fiber carrier (20).

5. Light source according to claim 4, characterized in that the light guide device (12) comprises a second fiber carrier (21), wherein the optical fibers (121) in the region of their first ends (1211) between the fiber carriers (20, 21) are arranged.

6. Light source according to claim 4 or 5, characterized in that the fiber carrier (20) or the fiber carrier (20,21) optically transparent, in particular for one of the Diode laser (13) and / or by the light source (11) generated light are.

7. Light source according to claim 6, characterized in that the scattered light (111)

first scattered at the junction of the diode laser (13) in the light guide (12) and subsequently transmitted through the fiber carrier (20) or the fiber carrier (20,21) and subsequently detected by the photodetector (90).

8. A light source according to claim 6 or 7, characterized in that a means for increasing the scattered light intensity from which the photodetector (90) is hit, is provided and / or a means for imaging the scattered light (111) on the

Photodetector (90) is provided.

9. A light source according to claim 8, characterized in that the means for increasing the scattered light intensity from which the photodetector (90) is hit, and / or the means for imaging the scattered light (111) on the photodetector (90) a

Is mirrored (122) of an outer surface of the fiber carrier (20) or the fiber carrier (20,21), deflected by the scattered light (111) on the photodetector (90),

reflected in particular, is.

10. A light source according to claim 8 or 9, characterized in that the means for increasing the scattered light intensity from which the photodetector (90) is hit, and / or the means for imaging the scattered light (111) on the photodetector (90) has a curved Outer surface (123) of the fiber carrier (20) or the fiber carrier (20,21) is deflected by the scattered light (111) in a focusing manner on the photodetector (90), in particular reflected or refracted.

11. Light source according to one of claims 8 to 10, characterized in that the means for increasing the scattered light intensity from which the photodetector (90) is hit, and / or the means for imaging the scattered light (111) on the photodetector (90) a gel (140) which is in a space between the fiber carrier (20) or the

Fiber carriers (20,21) or the optical fibers (121) and the photodetector (90) is arranged.

12. Light source according to one of the preceding claims, characterized in that the light-guiding device (12) comprises a light guide (125) which controls the scattered light (111) by multiple reflection on the photodetector (90).

13. Light source according to one of the preceding claims, characterized in that the light source contains at least one fluorescent substance (128), which is excited by the scattered light (111), wherein by the photodetector (90), the resulting fluorescent light (112) is detected.

14. Light source according to one of the preceding claims, characterized in that the light source comprises a plurality of photodetectors (90,91), wherein the plurality of photodetectors (90,91) are arranged at substantially different locations from each other and / or have a substantially different spectral sensitivity.