This patent application claims the priority of German patent application no. 10 2007 009 820.2 filed Feb. 28, 2007, the disclosure content of which is hereby incorporated by reference.
The invention relates to an optical arrangement and an optical method.
Light sources having high light intensity, high light density or high luminance find application in various areas of everyday life. Light sources for reading lamps, for endoscopy or microscopy can be mentioned here by way of example. Further applications, likewise from the area of everyday life, concern projection applications such as beamers or displays, for example, in which highly focussed light sources having high luminance are also of importance for displaying individual image pixels. Material processing, too, makes use of highly focussed light sources having high luminances. Examples can be found in the welding, engraving or cutting of workpieces.
Material processing, in particular, has hitherto been possible only with highly focussed light sources having a very high luminance. In this case, very high luminances have been attainable heretofore only by laser light sources.
Parabolic mirrors or lenses have been used heretofore for producing highly focussed light sources. This is shown for example in the document “Trichroic prism assembly for separating and recombining colors in a compact projection display”, Hoi-Sing Kwok et al., Applied Optics, Vol. 39, No. 1, Jan. 1, 2000, pp. 168-172. Optical devices of this type, as a light source, have a relatively large size and result in light sources having an extent of at least 1 mm or more. Furthermore, the light beams emitted by such light sources are not parallel to one another, but rather follow more of a star-shaped course.
In the case of image projections which display overall images formed from individual image pixels, the areal extent of an individual pixel is of crucial importance for the optical quality of the imaging. The smaller the areal extent of an individual image pixel, the better the optical quality of the imaging is perceived to be. However, the areal extent of the pixel is not the only factor of importance in this case; the brightness of the individual pixel also influences the perceived quality of the imaging. Weak light sources, in comparison with a light source having high luminous intensity, result in an image perceived as matt and having low contrast.
One object of the invention is to provide a solution which makes it possible to obtain high imaging quality, with the luminance remaining the same.
The fact that a first light-emitting element and a second light-emitting element are provided, the individual light beams thereof being additively combined to form a common light beam, results in a total luminance which is higher than each of the individual luminances of the first or second light-emitting element. The luminances are added by means of a light addition device arranged in such a way that the individual light beams of the light-emitting elements which come from mutually deviating directions are combined to form a common light beam. This measure increases the total intensity of the light source thus produced by comparison with the individual luminances of the light-emitting elements.
In accordance with one development, provision is made for forming the light-emitting elements from at least one first semiconductor-based laser diode and at least one second semiconductor-based laser diode. What is achieved by this measure is that the emitted light from each individual light-emitting element is already emitted in longitudinally directed fashion in a parallel beam, whereby the further addition of the emissive light is simplified. Moreover, semiconductor-based laser diodes have a high output power relative to their light-emitting area.
In accordance with one development, provision is made for choosing mutually deviating wavelength ranges of the emitted light for the first and the second light-emitting element. What is thereby achieved is that a variation of the hue of the light source can be obtained by means of an addition of different-colored emitted light of different wavelengths of two or more laser diodes by a variation of the individual luminances at the individual laser diodes. A light source with a color tonality that can be varied can thus be formed by means of the light addition device.
In accordance with one development, provision is made for arranging an optical converter device into the beam path of the optical arrangement. The optical converter device brings about a change, a conversion of the wavelengths of the light passing through it. Preferably, at least part of the light passing through is converted in such a way that the wavelength of the converted light is longer than the wavelength of the non-converted light. By way of example, the non-converted light is blue light, and the converted light can then be yellow light, for example.
In this case, the arrangement of the optical converter device in the beam path is possible upstream of the light addition device or downstream of the light addition device. The light emerging from the converter device has a wavelength that is different than the wavelength of the entering light. Through a combination of suitable converter material and semiconductor-based laser diodes, light sources which have an exactly predeterminable color tonality can be produced in this way. Consequently, light sources of white light having different color temperatures can also be produced in this way.
In accordance with one development, the light is forwarded to the optical addition device by means of an optical fiber. What is achieved by means of the optical fiber is that the first and/or the second light-emitting element can be arranged at a different location than the light addition device, and the light is guided to the light addition device by means of the optical fiber. In accordance with this development, it is also possible for the light to be guided away from the optical addition device by means of an optical fiber. It is thus possible for the light source to be formed at a location at a distance from the optical addition device. In this case, the converter device can also be arranged at the end of the optical fiber and thus at the light exit point. This is advantageous when individual subcomponents have to be arranged at locations at a distance from one another on account of limited spatial sizes or on account of configurational or application-dictated requirements. One example of this is endoscopy, in particular.
In accordance with one development, provision is made for forming the light addition device from at least one optical element having an interface formed in such a way that the light of a predetermined wavelength range is reflected by the interface. Light outside said wavelength range penetrates through the interface. By way of example, the light from at least two light-emitting elements can be added in this way. For this purpose, the first light-emitting element is designed in terms of its wavelength range such that the light that it emits penetrates through the interface. The second light-emitting element is designed such that the light that it emits is reflected at the interface. If the light from the first light-emitting element impinges on the interface, then it penetrates through the interface and in the process is not deflected or is only slightly deflected, but not reflected. If the light from the second light-emitting element impinges on the interface, then it is reflected by the interface. Through a selected arrangement of the interface in relation to the position of the light-emitting elements and the orientation thereof, what can thus be achieved is that the reflected light from the second light-emitting element is optically added to the light from the first light-emitting element that has penetrated through the interface.
In accordance with one development, the converter device is thermally coupled to a cooling device. What is thus achieved is that a heat arising on account of high light energy during the conversion is dissipated from the converter device and damage to the converter device is thus avoided.
Exemplary embodiments are explained in more detail below with reference to the drawings, in which:
The light emitted by the laser diodes LE1 to LE3 differs in each case by virtue of its wavelength λ. The wavelength λ of a light, in particular in the so-called visible range, is a measure of the color of the emitted light. The laser diodes LE1 to LE3 emit light of the wavelength λ1, λ2 and λ3 independently of one another. The different wavelengths λ1, λ2 and λ3 of the emitted light are also illustrated in the corresponding illustration of
A cost-effective deflection mirror can also be used instead of the first optical element OE1 since only the light from the first laser diode LE1 is applied to the optical element OE1. The optical element OE1 is not penetrated by a light beam in the case of this arrangement.
In its further beam course, the deflected beam λ1 of the first laser diode LE1 then impinges on the optical element OE2 from a rear side. The optical element OE2, in the same way as the optical element OE1 and the optical element OE3, is arranged at an angle inclined by 45° with respect to the incident light beams λ1, λ2 and λ3. The incident light beams λ1, λ2 and λ3 impinge on the optical elements OE1, OE2 and OE3 at a distance from one another in a parallel direction. This arrangement has the effect, on the one hand, that the light beam emitted by the laser diodes is deflected by 90° at the respective optical elements and thus reflected. On the other hand, this arrangement has the effect that the light beam λ1 impinging on the optical element OE2 from the rear side penetrates through this and is not reflected. The optical element OE2 is designed in such a way that it is highly reflective to light beams of the wavelength λ2, but the light beams of the wavelength λ1 can penetrate through without being reflected.
The arrangement of the optical elements inclined by 45° therefore brings about an addition of the light beams λ1 and λ2. In the further beam course, the sum of the two light beams λ1 and λ2 impinges on the third optical element OE3 from a rear side. In this case, the optical element OE3 is designed in such a way that it has the effect of being transparent to the wavelengths of the beams λ1 or λ2 and has highly reflective properties for the wavelengths λ3 of the third laser diode. Accordingly, the light beams λ1, λ2 and λ3 leave the optical element OE3 in a common parallel direction, and hence the optical light addition device 1. A light source 5 comprising the sum of the individual light beams λ1, λ2 and λ3 is thus formed. A light is thus generated having a luminance that is formed by addition from the luminances of the individual laser diodes LE1, LE2 and LE3.
The surface of the optical element OE1 is formed in such a way that it exactly reflects the wavelength of the light emitted by the laser diode LE1a and LE1b. The optical element OE2 is furthermore formed in such a way that the wavelength λ1 penetrates through the optical element OE2. The wavelengths of the laser diodes LE2a and LE2b are reflected at the surface of the optical element OE2. The light beams of the wavelength λ1 impinge on the optical element OE2 and leave the latter without experiencing a deflection, in a direction parallel to the light beams of the laser diodes LE2a and LE2b. The optical element OE2 is oriented with its surfaces with respect to the laser diodes LE2a and LE2b in such a way that the emitted beams of the wavelength λ2 are reflected at its surface and leave the optical element OE2 in a direction identical to the light beams of the wavelength λ1. The sum formed in this way from the beams λ1 and λ2 of the laser diodes LE1a, LE1b, LE2a and LE2b then impinges as a common light beam on the rear side of the optical element OE3.
The optical element OE3 is formed in such a way that it has the effect of being transmissive to light of the wavelength λ1 and λ2 and reflects the light of the wavelength λ3, which is emitted by the laser diodes LE3a and LE3b, at its surface. The surfaces of the optical element OE3 are in turn formed in such a way that the light beam having the wavelength λ3 that is incident from the light-emitting elements LE3a and LE3b is reflected and leaves the optical element OE3 together with the light beams λ1 and λ2 in a common direction. Therefore, at the end of the light addition device 1, a light source 5 is formed which cumulates from the individual light beams λ1, λ2 and λ3 and thus comprises, in its intensity, the sum of the individual intensities of the light beams of the laser diodes LE1a, LE1b, LE2a, LE2b, LE3a and LE3b.
The light source 5 thus becomes a light source having a small areal extent, the color tonality and coloration of which can be varied as desired from white light through to any other color shade. A very broad color spectrum can therefore be represented by varying the individual intensities of the individual laser diodes LE4a, LE4b, LE5a, LE5b, LE6a or LE6b. This is of great importance for applications in the area of projection technology, where light spots or image pixels of any desired color and of high intensity can be produced in this way.
This shows that light addition devices 1 of the type described above can be combined and arranged one after another as desired. Consequently, not only is it possible for a high variation of individual laser diodes to be combined and the light intensities thereof to be added, but also multifarious possibilities in respect of application and possibilities in respect of extension are then afforded. Cascades of light addition devices can thus be formed, wherein light sources of high intensity can be formed by addition.
The exemplary embodiment of
In this case, the abbreviation CER stands for cerium and thus describes a cerium-doped converter material, and the abbreviation YAG stands for yttrium aluminum garnet crystal. Consequently, Cer-doped YAG converter denotes a cerium-doped yttrium aluminum garnet crystal.
As an alternative to this, europium-based material can be used as converter material, whereby it is possible for example to achieve a red, green or blue conversion with lasers having wavelengths of 370 nm to 400 nm and a white light source can thus be produced by the combination thereof.
The exemplary embodiment of
Consequently, it is possible to find suitable exemplary embodiments for a wide variety of uses in order in each case to obtain a light source whose areal extent is very small and whose luminance is very high.
Thus, the exemplary embodiment of
Even though laser diodes are used as light-emitting elements in the exemplary embodiments described above, the concept of the invention is not thereby exclusively restricted to laser diodes. Rather, other light-emitting elements are also suitable. The use of laser diodes is particularly suitable on account of their luminance and parallel-directed light emission.
Thus, with light-emitting diodes it is likewise possible to produce light sources having a small areal extent, the luminance of which is however very low, or greatly limited. An optical power density of approximately 0.1 kW/cm2 is achieved with InGaN-based LEDs, which can have an emission area of approximately 1 mm×1 mm on a chip-size arrangement. Through a cascade-like arrangement of light addition devices, a high luminance can also be achieved by means of a multiplicity of light-emitting diodes of this type.
As an alternative to light-emitting diodes, with laser-based light sources such as, for example, InGaN-based lasers, it is possible to achieve a higher optical output power at each individual light-emitting element. The InGaN-based lasers, with an optically emissive area of 1 μm to 20 μm×0.3 μm, are significantly smaller than simple light-emitting diodes and therefore achieve an optical output power density of up to 40 000 kW/cm2. As the optical power increases, the risk of the laser diode, in particular the facet of the laser, being damaged increases. By means of the light addition device, it is possible to combine individual output powers of a plurality of laser diodes, without the risk of the facet of a laser diode being destroyed, to form a light source whose light power is significantly greater than the light power of individual laser diodes. A cascade-like arrangement of light addition devices increases the possible luminances of the light sources that can be produced by a further factor.
The invention is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.
Number | Date | Country | Kind |
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10 2007 009 820.2 | Feb 2007 | DE | national |