Laser light source assembly, lighting unit and laser projection device

Abstract

The present invention relates to a laser light source assembly for a laser projection device, comprising a laser diode array having a first illumination group including at least one first laser diode and a second illumination group including at least one second laser diode, the first laser diode and the second laser diode having different emission maxima in their spectra, the present invention is characterized in that the first laser diode has an emission maximum in a wavelength region of 440-462 nm and the second laser diode has an emission maximum in a wavelength region of 462-472 nm, and the laser diode array is contained within a housing such that the beam paths of the first laser diode and the second laser diode extend spatially separated within the housing.

Description

[Technical field]

[0001] This application claims priority to U.S. Patent Application Publication No. 2021 / 023996, filed February 5, 2021, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a laser light source assembly, an illumination unit including the same, and a laser projection device equipped with the illumination unit. [Background technology]

[0003] The use of semiconductor light sources to illuminate imaging systems in projection devices, for example micromirror devices (DMDs) or liquid crystal plates, is known. Compared to large-scale lighting modules with discharge lamps, semiconductor light sources allow compact structures for illumination. In addition to LEDs (LED = Light Emitting Diodes), laser diode arrays are used as semiconductor light sources, which are characterized by an improved service life, good energy efficiency and high spectral stability, which allows for strong laser projection devices with improved color saturation.

[0004] In order to achieve a wide coverage of the visible spectrum, especially in professional laser projection devices for movie theaters, high-value home projectors and miniature projectors for smartphones, separate light source units are provided for blue, green or red emission, which are usually arranged spatially separated and the emission of the light source units is combined using a beam combining optics, see, for example, US Pat.

[0005] Patent document 3 describes a compact light source construction unit with at least two illumination modules that respectively bundle laser diode arrays for blue, green and red. The individual illumination modules are mutually orthogonal, so that beam overlay and spectral mixing are performed by means of an angularly positioned forward and backward emitting optical multiplexer, which has locally different dichroic mirror surfaces.

[0006] Laser diodes emitting in the blue, green and red parts of the visible spectrum are differentiated according to the current state of development with regard to the achievable luminous efficiency, and InGaN semiconductor-based laser diodes with an emission maximum in the green-yellow part of the visible spectrum are suitable for lower current densities than those emitting blue light. Furthermore, red light laser diodes require higher thermal stability than shorter wavelength laser diodes. For this reason, light generating devices for laser projectors with monochromatic light sources are mostly more economical. Light generating devices for laser projectors usually use high-power blue-emitting laser diodes, which provide the blue channel and are further used to excite wavelength conversion elements that provide electromagnetic radiation in the green and red regions. For this type of laser projection device, blue laser diodes are used, which excite spectrally distinct fluorescent substances, for example of the phosphorus type. For the continuous generation of spectral colors, fluorescent coated rotating elements can be used as wavelength conversion elements. Such a color wheel is disclosed, for example, in US Pat. No. 5,399,313.

[0007] To excite the wavelength conversion element, laser diodes are usually used whose emission maximum is in the wavelength range of 440-462 nm. Known laser diode arrays for this purpose provide an emission of 455 nm with a narrow spectral distribution of + / - 6 nm of this maximum. This wavelength range has been found to be particularly suitable for fluorescence generation by phosphorus substances or Cer-doped yttrium-aluminum-garnet. If blue excitation light is used to represent blue in addition, the adaptation to the wavelength conversion element leads to a restriction of the color palette (color gamut) that can be projected on the screen. The standard Rec. 2020 therefore requires a 100% saturated depiction of blue at a wavelength of 467.1 nm. This "pure blue" that is not achievable in the aforementioned wavelength range adapted for fluorescence excitation is defined by the color spaces sRGB, Rec. 709 and DCI-P3 at 467.7 nm.

[0008] US Pat. No. 5,399,663 describes an illumination assembly for a laser projection device with two fixed, spatially separated wavelength conversion elements assigned to different spectral regions. This allows simultaneous green and red beam emission, which are superimposed in separate beam paths. To excite both wavelength conversion elements, a laser diode array is used, in which two laser diode types, which are differentiated with respect to the polarization direction and / or the spectral band of the emitted electromagnetic radiation, are arranged alternately. A beam splitter optical system arranged in the beam path between the laser diode array and the wavelength conversion element exploits this difference in emission characteristics, so that the beam from the first laser diode type is sent only to the first wavelength conversion element, and the beam from the second laser diode type is sent only to the second wavelength conversion element. For the blue part of the illumination, US Pat. No. 5,399,663 proposes a preferred form, which is the use of a third single light source coupled in the beam path after the wavelength conversion element by means of a collimating lens system. The optical system required for beam guidance results in a complex and large-scale structure of the illumination assembly. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] German Patent Application No. 102021102798.5 [Patent Document 2] US Patent Application Publication No. 2020 / 0301265A1 [Patent Document 3] US Patent Application Publication No. 2020 / 0301156A1 [Patent Document 4] German Patent Application Publication No. 102010003234A1 [Patent Document 5] German Patent Application Publication No. 112013004405B4 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to provide a laser light source assembly for a lighting unit of a laser projection device that is compact and easy to operate. Furthermore, a lighting unit with a wavelength conversion element and a laser light source assembly is mentioned, which lighting unit is characterized by a high color space coverage and requires a small construction space. In a preferred embodiment, the largest possible color gamut is provided by a complete coverage of the color space, especially in the long wavelength (blue) region, according to the standard Rec.2020. Furthermore, the object relates to provide a laser projection device with a space-saving lighting unit with high image quality and a wide color space. [Means for solving the problem]

[0011] This object is achieved by the features of claim 1. Advantageous embodiments of the laser light source assembly are the subject of the dependent claims, while claims 10 and 11 relate to lighting units and laser projection devices which include a laser light source assembly.

[0012] The laser light source assembly of the present invention includes a laser diode array having a first illumination group including at least one first laser diode and a second illumination group including at least one second laser diode, where the first laser diode and the second laser diode provide different emission maxima in the spectrum, the first laser diode providing an emission maximum in a wavelength region of 440-462 nm, and the second laser diode providing an emission maximum in a wavelength region of 462-472 nm. The laser diode array is further accommodated in a housing such that the beam paths of the first laser diode and the second laser diode extend spatially separated within the housing.

[0013] The laser light source assembly of the present invention thus forms a module operable as a structural unit, which provides a beam with an emission maximum in the blue wavelength range of 440-462 nm for fluorescence excitation by a first illumination group, and forms a single blue channel, which meets the requirement for a 100% saturated pure blue color according to one of the standards Rec.2020, sRGB, Rec.709 or DCI-P3 by a second illumination group, whose wavelength is also in the blue part of the spectrum (emission maximum in the wavelength region of 462-472 nm).The laser light source assembly of the present invention therefore allows the expansion of the color palette using components in the form of a module with compact dimensions.

[0014] In an advantageous embodiment, the first illumination group provides an emission maximum in the wavelength range of 450 to 460 nm, while the second illumination group preferably uses an emission maximum in the wavelength range of 464 to 470 nm, particularly preferably in the wavelength range of 466 to 468 nm.

[0015] Illumination in the green and red regions of the visible spectrum can be produced by excitation of the wavelength conversion element by the first illumination group, as will be detailed in the further description associated with the development of the invention regarding the illumination unit of the laser projection device, which includes a laser light source assembly.

[0016] In an advantageous embodiment of the laser light source assembly of the present invention, a separate color channel associated with direct illumination can be used. A third illumination group is preferably accommodated in a laser diode array grouped together in a common housing. The third illumination group then comprises at least one third laser diode emitting an emission maximum in the red wavelength range of 610-635 nm, preferably in the wavelength range of 627-633 nm.

[0017] Besides the reduced construction space requirement, the laser light source assembly according to the invention is characterized by a simplified handling as a module. For this purpose, the laser diodes of the laser diode array are arranged in the housing in such a way that the beam paths of the laser diodes of the different illumination groups run spatially separate at least until they leave the housing. The separate color channels can then be separated from the emission of the first illumination group, provided for fluorescence excitation, by simple optics, in particular by reflective elements such as stepped mirrors and microlenses. The use of dichroic optics can thus be dispensed with. It is preferred that the laser diodes are spatially arranged according to their emission properties, i.e. according to their belonging to one of the illumination groups. It is advantageous that the laser diodes are arranged on a carrier forming part of the housing in such a way that the lateral spacing between the laser diodes of the different illumination groups is at least 2 mm, preferably at least 4 mm. The lateral spacing is then defined as the distance between the centers of gravity of the active areas of the two laser diodes. An arrangement results in which the laser diodes are closely packed in each illumination group, preferably resulting in a concentration of laser diodes belonging to one of the illumination groups. The resulting laser diode region has the required lateral spacing with respect to the neighboring regions, as long as the laser diodes of the laser diode region are assigned to another lighting group. In order not to enlarge the structural size of the laser light source assembly too much, a preferred upper limit for the lateral spacing is set at 10 mm, particularly preferably 8 mm.

[0018] In a further advantageous embodiment of the laser light source assembly of the present invention, the laser diode array is assigned a beam guide device that collimates and / or separates the beam paths of the laser diodes of different illumination groups. Preferably, at least some of the components of the beam guide device are arranged in the housing and / or are integrated with the housing into a structural group. The beam guide device is used to separate the emission of the different illumination groups, from which separate color channels and spatially undesired beam-expanded excitation light can exit the housing of the laser light source assembly and be emitted preferably in different spatial directions.

[0019] Each of the illumination groups advantageously includes a number of monochromatic laser diodes, the diverging beams of which may cross inside the housing, as long as it is ensured that they do not cross the beam paths of laser diodes that are not associated with the respective illumination group. For beam guidance, a microlens array and a reflective optical system assigned to the individual laser diodes are preferably used.

[0020] In a further advantageous embodiment of the laser light source assembly, all the laser diodes of the laser diode array have a common thermal path for cooling. The common thermal path can be made integral with the carrier of the laser diode. This integral form is particularly advantageous when the third lighting group with long-wave emitting laser diodes is accommodated in the laser light source assembly formed as a module, since this creates higher demands on a constant temperature. Furthermore, the common thermal path allows the laser diodes to be mounted on the carrier for the laser diode array by a consistent process.

[0021] Furthermore, the laser light source assembly is preferably designed for external operation. For this purpose, an electrode assembly is provided for contacting the laser diode, which extends from the housing. The electrode assembly is then formed in such a way that the laser diodes of different lighting groups can be operated independently of each other. In a possible embodiment, further subgroups are formed in one lighting group, for example by row or column assemblies of co-operable laser diodes. External electrical operation allows the current intensity and output power to be adjusted separately for the laser diodes of different lighting groups.

[0022] In one development of the invention, the illumination unit comprises the aforementioned laser light source assembly. In addition, there is a wavelength conversion element and an overlay optics. The illumination unit is designed according to the invention in such a way that the wavelength conversion element is excited by the emission of the first illumination group of the laser light source assembly to emit a fluorescent beam, and the overlay optics combines the emission of the second illumination group of the laser light source assembly and the fluorescent beam in one illumination beam path. Due to the modular form of the laser light source assembly and the spatial separation of the beam for fluorescence excitation and the respective beams for the separate color channels, the optics for beam guidance assigned to the illumination unit can be designed in a simple and small structure. Furthermore, the replacement of the laser light source assemblies present as a structure group is facilitated.

[0023] According to one development of the invention, a laser projection device is proposed, which comprises an imaging system and an illumination unit according to the invention. Apart from a compact structure, the laser projection device is characterized by the illumination of the imaging system, which covers the projection surface with an expanded color space. Besides the high color saturation achieved thereby, a further advantage is the increased accuracy that can be achieved due to the white point correction that can be performed by the customer. Furthermore, the laser light source assembly designed as a module makes it easier to correct thermal effects during the operation of the laser projection device.

[0024] In the following, exemplary variants of the invention will be explained with reference to the drawings. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a plan view of a first embodiment of a laser source assembly according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the laser light source assembly of FIG. 1 according to the present invention. [Diagram 3] FIG. 2 is a plan view of a second embodiment of a laser source assembly according to the present invention. [Figure 4] 4 is a cross-sectional view of the laser light source assembly of the present invention of FIG. 3. [Diagram 5]4 is an electrical contact of a second embodiment of a laser source assembly according to the present invention. [Figure 6] 1 is a laser projection device with an illumination system including a first embodiment of a laser light source assembly according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] 1 shows in a schematic diagram a laser source assembly 1 according to the invention. It comprises a laser diode array 2 enclosed by a housing 7, from which arises a module which can be operated as a construction unit.

[0027] The laser diode array 2 is divided into a first illuminating group 3 and a second illuminating group 5 emitting different spectral laser light. The first illuminating group 3 then comprises first laser diodes 4.1, ..., 4.n with their emission maxima in the wavelength range of 440-462 nm, preferably in the interval of 450-460 nm. This blue emission is tuned to fluorescent excitation and does not exactly fall into the definition for pure blue color according to the color space standards Rec.2020, sRGB, Rec.709 or DCI-P3. A second illuminating group 5 is therefore provided for the introduction of the blue channel, and second laser diodes 6.1, ..., 6.4 assigned to the second illuminating group 5 have their emission maxima in the wavelength range of 462-472 nm, preferably 464-470 nm, particularly preferably 466-468 nm, and thus can emit a "pure blue" color with 100% color saturation. This means that it can cover the entire blue range according to the color standard Rec.2020.

[0028] According to the invention, the first and second laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4 are arranged in a definite manner in the laser diode array 2 such that the beam paths 8.1, 8.2 coming from the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4 of the different illumination groups 3;5 run spatially separated in the housing 7. Advantageously, on a carrier 9 forming part of the housing 7, the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4 are mounted such that the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4 that do not belong to the same illumination group 3;5 have a lateral distance D that is adapted to the beam divergence of the first laser diode 4.1, ..., 4.n and the second laser diode 6.1, ..., 6.4. With typical construction dimensions, a lateral distance D of at least 2 mm, preferably at least 4 mm, has proven to be advantageous for keeping the optical paths of the first illumination group 3 and the second illumination group 5 separated in the housing 7. The upper limit of the lateral distance D is preferably 10 mm, and more preferably 8 mm.

[0029] As a further preferred measure for spatially separating the beam paths 8.1, 8.2 of the first laser diodes 4.1, ..., 4.n and the second laser diodes 6.1, ..., 6.4, Fig. 2 shows a beam guiding device 10 in the housing 7. The beam guiding device 10 comprises a mirror 11 and a microlens 12 which deflects and collimates the beam path 8.1 emerging from the second laser diode 6.1. Correspondingly, a stepped mirror 13 and microlenses 14.1, ..., 14.7 detect only the beams emerging from the first laser diodes 4.1, ..., 4.7, bundle them and emit them on the opposite side of the housing 7.

[0030] 3 shows a second embodiment of the laser source assembly 1 according to the invention, where the same reference numbers are used for parts corresponding to the first embodiment. An additional third illumination group 15 is represented in the housing 7. The third illumination group 15 of the laser diode array 2 then comprises at least one third laser diode 16.1, ..., 16.8, which emits an emission maximum in the wavelength range of 610-635 nm, preferably in the wavelength range of 627-633 nm, which is used for illumination of the red channel. The illuminable color spectrum can thus be further expanded.

[0031] 4, a side view of the second embodiment, shows that the assembly of the first laser diodes 4.1, ..., 4.n, the second laser diodes 6.1, ..., 6.4 and the third laser diodes 16.1, ..., 16.8 is selected such that the beam paths 8.1, 8.2, 8.3 of the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8 of the different illumination groups 3; 5; 15 run spatially separated in the housing 7. In this respect, the aforementioned lateral spacing D is respected. Further, a beam guiding device 10 is present in the housing 7, with microlenses 18.1, ..., 18.7 assigned to the first laser diodes 4.1, ..., 4.n, mirrors 11 and microlenses 12 assigned to the second laser diode 6.1, and mirrors 17.1, 17.2 and microlenses 18.1, 18.2 assigned to the third laser diodes 16.1, 16.5, such that the different illumination groups 3;5;15 emit light to different sides of the housing 7 of the laser source assembly 1.

[0032] Furthermore, a common thermal path 20 is provided for all laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8 of the laser diode array 2. By using one cooling element integrated or forming in the carrier 9, the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8 can be easily finished in a consistent process step. Furthermore, the thermal stability during operation is improved.

[0033] Figure 5 shows the electrical contacts for a preferred form of the second embodiment. One can see the electrode assembly 21 extending from the housing 7. This allows for external independent operation of the different lighting groups 3;5;15 and thus group-by-group adjustment of the current intensity and output power for the laser diodes 4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8. The first anode 22 and first cathode 23 for the first lighting group 3, the second anode 24 and second cathode 25 for the second lighting group 5, and the third anode 26 and third cathode 27 for the third lighting group 15 are represented individually.

[0034] 6 shows an illumination unit 28 of the invention, which comprises the aforementioned laser light source assembly 1, a wavelength conversion element 29 and an overlay optics 32 forming an exchangeable module. The wavelength conversion element 29 receives a beam from the first illumination group 3 of the laser light source assembly 1, which is used to excite a first fluorescent material 30 and a second fluorescent material 31, and the wavelength conversion element 29 again emits a beam in the green and red parts of the visible spectrum. This fluorescent beam combines the overlay optics 32 with a blue channel 35, which is directly supplied by the second illumination group 5 of the laser light source assembly 1. In the shown variant, the fluorescent materials 30, 31 are spatially separated from each other.

[0035] In a modified variant, there is no spatial separation of the fluorescent materials, such as the first fluorescent material 30 and the second fluorescent material 31, but they are provided on the conversion element 29 (not shown). In another modified variant, a single broadband-emitting fluorescent material is used. Broadband-emitting fluorescent materials are provided specially for 3LCD systems, in which not one but three imagers (separate for each primary color) are provided, illuminated by a continuous illumination white light source. The beam paths of the primary colors can then be separated by wavelength-selective optics, for example dichroic mirrors (not shown).

[0036] The illumination unit 28 is housed as a structural group in a laser projection device 33 and serves to illuminate an imaging system 34. Here, the laser projection device 33 is characterized by a particularly extended color palette and a compact, easy-to-implement structure. Since the laser light source assembly 1 is formed as a module, the separate blue channel does not form an additional component, which facilitates light source replacement and white light correction. [Explanation of symbols]

[0037] 1 Laser source assembly 2 Laser Diode Array 3 First lighting group 4.1, 4.2, ..., 4.n First laser diode 5 Second lighting group 6.1, 6.2, 6.3, 6.4 Secondary laser diode 7. Housing 8.1, 8.2, 8.3 Beam path 9. Career 10 Beam guide device 11. Mirror 12 Microlenses 13 Stepped Mirror 14.1, 14.2…, 14.7 Micro Lenses 15 Third Lighting Group 16.1, 16.2…, 16.8 Third laser diode 17.1, 17.2 Mirror 18.1, 18.2 Micro Lenses 19.1, …, 19.7 Microlenses 20 Heat Path 21 Electrode Assembly 22 1st anode 23 First Cathode 24 2nd anode 25 Second Cathode 26 Third anode 27 Third Cathode 28 Lighting Unit 29 Wavelength conversion element 30 First fluorescent material 31 Second fluorescent material 32 Overlay Optical System 33 Laser Projection Device 34 Imaging System 35 Blue Channel 36 Control device 37 Illumination Beam Path D Horizontal Spacing

Claims

1. A laser light source assembly for a laser projection device (33), comprising: A laser light source assembly comprising a laser diode array (2) having a first illumination group (3) comprising at least one first laser diode (4.1, ..., 4.n) and a second illumination group (5) comprising at least one second laser diode (6.1, ..., 6.4), said first laser diode (4.1, ..., 4.n) and said second laser diode (6.1, ..., 6.4) having different emission maxima in the spectrum, the first laser diode (4.1, ..., 4.n) has an emission maximum in a wavelength region of 440 to 462 nm, and the second laser diode (6.1, ..., 6.4) has an emission maximum in a wavelength region of 462 to 472 nm, The laser diode array (2) is accommodated in a housing (7) such that beam paths (8.1, 8.2) of the first laser diodes (4.1, ..., 4.n) and the second laser diodes (6.1, ..., 6.4) extend spatially separated within the housing (7).

2. 2. The laser light source assembly of claim 1, wherein the first laser diodes (4.1, . . . , 4.n) have an emission maximum in the wavelength range of 450-460 nm.

3. 3. A laser light source assembly according to claim 1 or 2, wherein the second laser diode (6.1, ..., 6.4) has an emission maximum in the wavelength range of 464-470 nm.

4. 4. The laser light source assembly according to claim 1, wherein the laser diode array (2) comprises a third illumination group comprising at least one third laser diode (16.1, ..., 16.8) having an emission maximum in the wavelength range of 610 to 635 nm.

5. 5. The laser light source assembly according to claim 1, wherein the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) are arranged on the carrier (9) of the laser diode array (2) such that the lateral spacing (D) between the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) of the different illumination groups (3, 5, 15) is at least 2 mm.

6. 6. The laser light source assembly according to claim 5, wherein the lateral spacing (D) between the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) within each one of the illumination groups (3, 5, 15) is smaller than the lateral spacing (D) between the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) of different illumination groups (3, 5, 15).

7. 7. The laser light source assembly according to claim 1, wherein the laser diode array (2) is assigned a beam guiding device (10) for collimating and / or separating the beam paths (8.1, 8.2, 8.3) of the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) of different illumination groups (3, 5, 15).

8. 8. The laser light source assembly according to claim 7, wherein at least some of the components of the beam guiding device (10) are arranged within the housing (7) and / or are integrated with the housing (7) into one structural group.

9. 9. The laser light source assembly according to claim 1, wherein all laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) of the laser diode array (2) are assigned a common thermal path (20) for cooling.

10. 10. The laser light source assembly according to claim 1, wherein an electrode assembly (21) for electrically operating the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) extends from the housing (7), the electrode assembly (21) being formed such that the laser diodes (4.1, ..., 4.n; 6.1, ..., 6.4; 16.1, ..., 16.8) of different lighting groups (3, 5, 15) can be operated independently of each other.

11. A laser light source assembly (1) according to any one of claims 1 to 10, A wavelength conversion element (29), and An illumination unit including an overlay optical system (32), The illumination unit (28) is designed such that the wavelength conversion element (29) is excited to emit a fluorescent beam by the emission of a first illumination group (3) in the laser light source assembly (1), and the overlay optical system (32) combines the emission of a second illumination group (5) of the laser light source assembly (1) and the fluorescent beam into one illumination beam path (37).

12. A laser projection device comprising an imaging system and an illumination unit (28) according to claim 11 for illuminating said imaging system (34).

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