阅读说明：本技术 具有用于减弱散斑噪声的光学装置的激光光源和激光投影器以及用于运行这种激光光源和这种激光投影器的方法 (Laser light source and laser projector with optical device for reducing speckle noise and method for operating such a laser light source and such a laser projector ) 是由 K·曼特尔 M·弗奇 于 2018-10-22 设计创作，主要内容包括：本发明涉及一种激光光源(1a)用于产生具有至少两个、优选三个不同波长(λ<Sub>R</Sub>,λ<Sub>G</Sub>,λ<Sub>B</Sub>)的激光射束(2),激光射束尤其是用于无散斑成像和/或投影,激光光源包括：至少两个光学装置,尤其是至少两个光学参量振荡器(5a-c),它们分别具有非线性光学介质(6a-c)用于产生各一信号射束(S1,S2,S3)和各一闲频射束(I1,I2,I3)；以及叠加装置(4),其构造用于为了产生具有至少两个波长(λ<Sub>R</Sub>,λ<Sub>G</Sub>,λ<Sub>B</Sub>)的激光射束(2)而将至少两个光学装置(5a-c)各自的信号射束(S1,S2,S3)或闲频射束(I1,I2,I3)叠加。本发明也涉及一种激光投影器,用于在投影面上产生尤其是无散斑的图像,所述激光投影器具有这种激光光源(1a)。(The invention relates to a laser light source (1a) for generating light having at least two, preferably three, different wavelengths (lambda) R ，λ G ，λ B ) In particular for speckle-free imaging and/or projection, comprising: at least two optical devices, in particular at least two optical parametric oscillators (5a-c), each having a nonlinear optical medium (6a-c) for generating a respective signal beam (S1, S2, S3) and a respective idler beam (I1, I2, I3); and a superposition device (4) which is designed to generate a beam having at least two wavelengths (lambda) R ，λ G ，λ B ) The signal beam (S1, S2, S3) or idler beam (I1, I2, I3) of each of the at least two optical means (5a-c) are superimposed by the laser beam (2). The invention also relates to a laser projector for generating images, in particular speckle-free images, on a projection surface, comprising such a laser light source (1 a).)

1. A laser light source (1a) for generating a laser beam (2), in particular for speckle-free imaging and/or projection, having at least two, preferably three, different wavelengths (λ)_R，λ_G，λ_B) The laser light source includes:

at least two optical devices, in particular at least two optical parametric oscillators (5a-c), each having a nonlinear optical medium (6a-c) for generating a respective signal beam (S1, S2, S3) and a respective idler beam (I1, I2, I3), and

a superimposing device (4) configured to superimpose the signal beam (S1, S2, S3) or the idler beam (I1, I2, I3) of each of the at least two optical devices (5a-c) to produce a beam having the at least two wavelengths (λ [)_R，λ_G，λ_B) The laser beam (2).

2. Laser light source according to claim 1, having at least three optical arrangements (5a-c) for generating a respective signal beam (S1, S2, S3) and a respective idler beam (I1, I2, I3), wherein the superposition means (4) are configured for superposing the respective signal beam (S1, S2, S3) or idler beam (I1, I2, I3) of the at least three optical arrangements (5a-c) to generate the at least two wavelengths (λ) having a difference_R，λ_G，λ_B) The laser beam (2).

3. The laser light source according to claim 1 or 2, further comprising: at least one pump source (3a-c) for generating at least one pump beam (P1, P2, P3) for exciting a nonlinear optical medium (6a-c) of the at least two optical devices (5 a-c).

4. The laser light source of any one of the preceding claims, having at least one optical filter element (4a-c) in the optical path after each optical arrangement (5a-c) for filtering a signal beam (S1, S2, S3) or an idler beam (I1, I2, I3) of the corresponding optical arrangement (5a-c) which is not used for superposition, in particular a wavelength-selective optical filter element.

5. A laser projector (10) for producing an image (B), in particular a speckle-free image, on a projection surface (13), comprising:

laser light source (1a) according to any of the preceding claims for generating light having at least two, preferably three, different wavelengths (λ [ ])_R，λ_G，λ_B) A laser beam (2), and

a scanner device (12) for deflecting the laser beam (2) in two dimensions to produce an image (B) on a projection surface (13).

6. A laser projector as claimed in claim 5, wherein the scanner device (12) has a mirror (11) for deflecting the laser beam (2) in two dimensions.

7. The laser projector of claim 5 or 6, further comprising: a control device (7) which is designed to modulate the amplitude (A1, A2, A3) of the pump beam (P1, P2, P3) of the at least one pump source (3a-c) in accordance with an image (B) to be generated on the projection surface (13).

8. Method for operating a laser light source (1a) according to one of claims 1 to 4, wherein a respective signal beam (S1, S2) and a respective idler beam (I1, I2) are generated by means of a first optical device (5a) of the at least two optical devices (5a-c) and a second optical device (5b) of the at least two optical devices (5a-c), wherein the signal beam (S1) or the idler beam (I1) of the first optical device (5a) is selected to have the at least two different wavelengths (λ ™)_R，λ_G，λ_B) Of (a) a first wavelength (λ)_R) Wherein the signal beam (S2) or the idler beam (I2) of the second optical arrangement (5b) is selected to have the at least two different wavelengths (λ)_R，λ_G，λ_B) Of (d) and a first wavelength (λ)_R) A different second wavelength (λ)_G) Wherein the at least two wavelengths (λ) having different are generated_R，λ_G，λ_B) In that the respectively selected signal beam (S1, S2) or idler beam (I1, I2) of the first optical arrangement (5a) and the second optical arrangement (5b) are superimposed.

9. Method according to claim 8, wherein the signal beam (S3) and the idler beam (I3) are generated by means of a third optical device (5c) of the at least three optical devices (5a-c), wherein the signal beam (S3) or the idler beam (I3) of the third optical device (5c) is selected to have the same first wavelength (λ) as the first wavelength (λ)_R) And a second wavelength (λ)_G) A different third wavelength (λ)_B) And wherein at least three, in particular exactly three, wavelengths (λ) are generated which differ_R，λ_G，λ_B) The laser beam (2) is produced by superimposing the signal beams (S1, S2, S3) or idler beams (I1, I2, I3) selected by the first optical device (5a), the second optical device (5b) and the third optical device (5 c).

10. Method for operating a laser projector (10) according to one of claims 5 to 7, wherein the laser light source (1a) is operated by means of a method according to claim 8 or 9.

Technical Field

The invention relates to a laser light source for generating laser beams having at least two, preferably three different wavelengths, in particular for speckle-free imaging and/or projection, and to a laser projector having such a laser light source. The invention also relates to a method for operating such a laser light source and to a method for operating such a laser projector.

Background

Conventional projection systems, such as those used in conventional video projectors, utilize conventional interleaved optical paths to project an object onto a projection surface. In many cases, metal vapor lamps are used as light sources.

Since several years ago, such projection systems were competed by laser projection systems, the use of which was predicted since the 60 s, see Texas Instrument Bulletin No. d L a1324, (1966) the article "Experimental L laser Display for L image Screen Presentation" or US3,436,546. laser projection systems offer a series of advantages that are compact, have good brightness and have good contrast, long service life and are sufficiently cost-effective to be suitable not only for the home cinema market but also, for example, for heads-up displays, laser projectors that are stronger in all details than L ED projectors and that are also capable of scanning projections in addition to imaging projections, which differ significantly from conventional projectors in that instead of projecting images onto a cloth, the images are constructed in a pixel-wise manner in order to project three laser beams (typically one for red, green, blue and blue colors) or one spatial laser beam onto a single pixel of a blue mirror for use with a fast frequency of the laser beam, which is usually reflected at about 30 pixels of the laser beam and reflected at a common frequency of the blue mirror.

Laser projectors have significant drawbacks: since the laser radiation is coherent, so-called speckle noise is formed, i.e. a grainy (i.e. grainy) interference effect which significantly reduces the image quality. Speckle noise occurs not only in the case of laser projectors, but also everywhere where laser light sources are used for imaging or measurement techniques, for example also in interferometric measurement techniques.

Thus, what is needed to improve image quality is the use of a method that eliminates or at least significantly reduces speckle noise.A simple but effective method for reducing speckle noise consists, for example, of using a rotating ground glass plate made of corrugated glass.if the ground glass plate is set in motion (e.g., rotated), the resulting speckle pattern changes.Here, if the speckle pattern moves rapidly with respect to the integration time of the detector (camera or eye), many mutually independent speckle patterns integrate with one another and speckle noise is reduced.viewed from another point of view, the roughness of the ground glass plate surface produces phase fluctuations in the light field.

A series of alternatives have therefore been tried in the literature to get the speckle problem in the case of laser projectors to grasp. A review is given in the wo 2009 by riechert, f.carlu university, of "speed Reduction in project Systems". The goal of these methods is to superimpose speckle patterns that are independent of each other (i.e., uncorrelated) in a non-coherent (i.e., intensity-based) manner. The non-correlation can be achieved here, for example, by wavelength diversity or polarization diversity. But the light sources required for wavelength diversity are larger, more expensive or less intense; furthermore, the (unpredictable) influence of the structure of the curtain used proves to be problematic. The unknown effect of the curtain type on polarization and the achievable number of independent speckle patterns is too small to contradict polarization diversity. A further possibility for reducing speckle is the angular diversity of the illumination. Here again, the number of uncorrelated speckle patterns that can be achieved is limited and rather limited by the ratio between the illumination aperture and the viewing aperture. Since the area of the mirrors used in the projection is relatively small, based on the high frequencies to be generated, this method is also not optimally suited for reducing speckle noise. Similar problems exist for using spatially separated areas of the curtain to generate uncorrelated speckle patterns.

To achieve the required non-coherent overlap, different methods may be used as well. On the one hand, different mutually incoherent laser light sources can be used, even if they have the same wavelength (for example on the basis of small differences in wavelength, or accidental phase jumps). This, however, increases the cost and the overall size of the laser projector. The use of orthogonal polarizations also results in incoherent overlap, but with the limitations as described above. As a third possibility, a delay lineTemporal incoherence of the light source is exploited so that the superposition on the detector becomes incoherent. Number of incoherent superimposed speckle patternsDepending on the implementation of the delay line. Integration in time as each detector performs in the case of a rotating ground glass plate is a fourth possibility. Speckle patterns independent of each other on the basis of the rotation of the ground glass plate are added during the integration time of the detector, and interference of patterns appearing one after another in time does not occur. This solution, however, is contradictory to the fact that: the averaging must be performed within about 20ns as described above. A ground glass sheet with such a speed is mechanically too laborious and prone to failure if it is to be completely realized.

At US6,233,025B1, a method and apparatus for generating at least three laser beams of different wavelengths to render a color video image is described. In the apparatus, the output of a pulsed laser is supplied as an excitation beam to a medium having nonlinear optical properties. In one example, a nonlinear optical medium is disposed in an optical parametric oscillator. The optical parametric oscillator, in addition to the original beam, which passes through the optical parametric oscillator without frequency change, generates a signal beam and an idler beam, which in some cases, after frequency conversion, are used together with the original beam to render a monochromatic sub-image of the color video image. Illustrated at US6,233,025B1, speckle noise can be suppressed in the following manner: the pulsed laser generates laser pulses having a pulse length of less than 1ps for exciting the nonlinear optical medium.

Disclosure of Invention

The object of the present invention is to provide a laser light source and a laser projector having a laser light source, as well as a method for operating such a laser light source and a method for operating such a laser projector, which make it possible to effectively suppress speckle noise.

According to the invention, this object is achieved by a laser light source comprising: at least two optical devices, in particular at least two optical parametric oscillators, each having a nonlinear optical medium for generating a respective signal beam and a respective idler beam; and a superimposing device, which is designed to superimpose (spatially) the signal or idler beam of each of the at least two optical devices in order to produce a laser beam having at least two wavelengths (this is to be understood as superimposing the signal or idler beam of one of the optical devices with the signal or idler beam of at least one other optical device).

According to the invention, a laser beam, which can be used, for example, for projection in a laser projector, is generated by means of a plurality of, in particular three, optical devices each having a nonlinear optical medium. The optical device or the corresponding nonlinear medium is designed to carry out a so-called "parametric down conversion" (PDC). PDC is based on the nonlinear interaction of the pump beam of a coherent pump source (e.g., a conventional laser) with a nonlinear optical medium (e.g., a nonlinear crystal). In the case of this interaction, two new optical fields are formed, which are referred to as signal beam and idler beam in the present application as usual. The signal beam and the idler beam obtain the energy omega of the pump beam_PAnd momentumThis means that there is ω for energy_P＝ω_S+ω_IWherein, ω is_SRepresents the energy of the signal beam and_Irepresenting the energy of the idler beam. Momentum of pumping beamMomentum of signal beamAnd the momentum of the idler beamAlso, there are:the signal beam and the idler beam differ at least in their wavelengths. In general, beams with smaller wavelengths are referred to as signal beams and beams with larger wavelengths are referred to as idler beams. In addition, the signal beam and idler beam can be additionally used in some casesAre distinguished from each other, but depend on the non-linear medium or non-linear crystal chosen and the physical implementation.

An optical device for performing PDC procedures in nonlinear optical media can, for example, relate to an Optical Parametric Oscillator (OPO), which can, for example, be constructed as in the above-mentioned patent document US6,233,025B1, which is the content of the present application by reference in its entirety. The laser light source with the optical parametric oscillator can be compact and cost-effectively implemented and have a similar brightness as conventional laser light sources, i.e. it integrates the advantages of conventional laser light sources into a laser projector.

However, a laser light source with the optical arrangement or optical parametric oscillator differs from such conventional laser light sources essentially in that: based on the working principle, phase fluctuations occur in the optical field at the outlet of the corresponding OPO, which occur on a time scale of the order of picoseconds. This is related to the way light generation in PDC systems is based on the nonlinear interaction of the pump beam of a coherent pump source (e.g., conventional laser) with a nonlinear optical medium (e.g., nonlinear crystal) as described above.

The signal and idler beams have a strong correlation due to co-formation processes in a non-linear medium, whereas the signal and idler beams alone have a fluctuating appearance of a thermal light source, see M of the aelanta university.In 2015, doctor's paper "Development of a versatilide source of single viruses". The inventors have realised that: these fluctuations are fast enough to average from thousands up to tens of thousands of individual speckle patterns, for example during the above-mentioned 20ns available for generating pixels, whereby the speckle noise is practically completely eliminated. This solution physically corresponds to a ground glass plate with a correspondingly high rotational speed, wherein the non-correlation is formed by phase fluctuations and the non-coherent overlap is achieved by the final integration time of the eye or detector when observing the image.

In contrast to US6,233,025B1 cited above, in the laser light source according to the invention, the required light is preferably generated by means of an optical parametric oscillator, wherein in particular two additional frequency doubling units are eliminated. This enables a significantly more efficient and compact overall system. In US6,233,025B1, the pump light itself is used to generate the superimposed laser beam or for the monochromatic partial image. However, in the case of pump light, the phase fluctuations described above do not occur, i.e. coherent laser light is involved, so that speckle noise likewise occurs in the monochromatic sub-images generated by the pump signal. Particularly unsuitable are: the pump light is used for the green sub-image, which is particularly sensitive to the human eye. Speckle noise at this wavelength is perceived as a strong disturbance.

Preferably, the laser light source has at least three, in particular exactly three, optical arrangements for generating a signal beam and an idler beam each, and the superimposing arrangement is designed to superimpose the respective signal beams or idler beams of the (at least) three optical arrangements in order to generate a laser beam having at least two, preferably at least three, in particular exactly three, different wavelengths. Typically, three different wavelengths are sufficient to produce a color (video) image. In the case of using the laser light source for a laser projector, the three wavelengths of the laser beam used for projection are in the visible wavelength range. If necessary, the wavelength of the corresponding signal beam or of the corresponding idler beam can be varied by means of a frequency conversion device in order to generate the desired frequency or wavelength for projection.

The three wavelengths of the laser beam can be, for example, wavelengths in the red wavelength range between about 635nm to about 780nm, wavelengths in the green wavelength range between about 520nm to about 540nm, and wavelengths in the blue wavelength range between about 400nm to about 470 nm. In principle, however, other wavelengths in the visible wavelength range can also be used, which enable color video images to be produced by additive color mixing.

In order to generate signal beams with different wavelengths and idler beams, different nonlinear optical media, in particular different nonlinear optical crystals, can be used in the optical arrangement. However, it is also possible to vary the wavelengths of the signal beam and idler beam within certain limits by setting different temperatures to the same type of nonlinear optical medium or crystal. Reference is made to US6,233,025B1 cited at the outset for a nonlinear optical crystal that can be used in the present application.

In a further embodiment, the laser light source has at least one pump source for generating at least one pump beam (in the form of a laser beam having a pump wavelength) for exciting the nonlinear optical media of the at least two optical devices. For generating the pump beam, three identical pump sources in the form of laser light sources, for example in the form of laser diodes, can be used, the amplitudes of which can be individually set to produce the desired color for the corresponding pixel of the image. The pump source can be operated in a pulsed manner, wherein the pulse frequency can be adapted in particular to the clock frequency of the pixels used to generate the image.

In a further embodiment, the laser light source has at least one, in particular wavelength-selective, optical filter element in the beam path after the respective optical arrangement, in particular in the superposition arrangement, for filtering the signal beam of the respective optical arrangement that is not used for the superposition or the idler beam that is not used for the superposition. The use of optical filter elements is advantageous or necessary if the pump beam, the signal beam and the idler beam are emitted from the optical arrangements in a collinear manner, so that spatial separation cannot be achieved without further measures. What is needed in this case is: the other beams (idler or signal beams) and pump beams, which are not used for superposition, are filtered or eliminated before superposition. For filtering the pump beam and the signal beam or idler beam, it is possible to use the same wavelength-selective optical element, but it is also possible to use two or more different wavelength-selective optical elements for this purpose. The one or more wavelength selective optical elements may especially be part of a superimposing arrangement. In this case, the wavelength-selective optical element can be configured, for example, to divert only the signal beam or only the idler beam into a direction suitable for generating the laser beam. Instead of wavelength-selective optical elements, other types of optical filter elements can also be used, for example filter elements based on polarization filtering or in some cases on spatial filtering.

The wavelength selective optical (filtering) element can for example relate to a dichroic mirror, a prism with a wavelength selective coating, etc. Unlike the laser light source described herein, no wavelength selective optical element is required at US6,233,025B1, because there is a use of both the signal beam and the idler beam to produce the monochromatic sub-image.

The laser projector can have additional optical elements, for example a focusing device, for focusing the laser beam at an adjustable or predefined distance, at which the projection surface is usually situated, for example, a scanner device can be actuated by means of a control device in order to generate an image with a resolution of, for example, 1280 35720 pixels and an image repetition rate of, for example, 60Hz, as in the case of conventional television sets.

Instead of a laser projector in which the (superimposed) laser beam is deflected in two dimensions by means of a scanner device to produce an image on the projection surface, the laser projector can have two or more scanner devices which each deflect a signal beam or idler beam of a corresponding optical device onto the same point or pixel on the projection surface. In this case, the laser beams are superimposed to form laser beams having at least two different wavelengths, which only take place on or in the region of the projection surface.

In one embodiment, the scanner device has a mirror for the two-dimensional deflection of the laser beam. As mentioned above, a high image repetition rate requires a high dynamic movement in the deflection of the laser beam, in particular along the fast axis, i.e. along the lines of the image to be produced. Instead of a single mirror, the scanner device can also in some cases have two or more mirrors or other optical elements which enable two-dimensional deflection of the laser beam, see for example the initially cited US3, 436,546, in which a polygon mirror is used in combination with an oscillating mirror for this purpose.

In a further embodiment, the laser projector comprises a control device which is designed to modulate the amplitude of one or more pump beams of the at least one pump source in accordance with the image to be generated at the projection surface. By modulating the amplitude or power of the pump beams of the individual pump sources, the color of the corresponding pixel can be set as in conventional laser projectors. The modulation or change in the power of the pump beam can be performed directly in the respective pump source, for example in the form of a laser diode. However, it is also possible for the modulation to be carried out in an optical modulator which is arranged in the beam path downstream of the pump source, as described in US6,233,025B1 mentioned at the outset.

The laser light source described here for generating an incoherent laser beam with at least two different wavelengths can be used advantageously not only in laser projectors but also in other applications in the field of imaging technology and in the field of interferometric measuring technology.

The task is also solved by: a method for operating a laser light source according to one of the preceding embodiments is carried out. In the context of the method, a signal beam and an idler beam are each generated by a first optical device of the at least two optical devices and a second optical device of the at least two optical devices. The signal beam or idler beam of the first optical arrangement is selected to have a first wavelength of the at least two different wavelengths, and the signal beam or idler beam of the second optical arrangement is selected to have a second wavelength of the at least two different wavelengths, which is different from the first wavelength. Laser beams having at least two different wavelengths are generated by superimposing the respectively selected signal beams or idler beams of the first optical arrangement and the second optical arrangement. In the context of the method, the advantages already explained in connection with the laser light source and the laser projector result, in particular.

In a further variant of the method, a further signal beam and a further idler beam are generated by means of a third optical device of the at least three optical devices, wherein the signal beam or the idler beam of the third optical device is selected to have a third wavelength that is different from the first wavelength and the second wavelength. In this case, laser beams having the at least two, preferably at least three, in particular exactly three, different wavelengths are generated by superimposing the respectively selected signal beams or idler beams of the first, second and third optical arrangements.

Another aspect of the invention relates to a method for operating a laser projector according to one of the preceding embodiments. In the context of the method, the laser light source is operated in a method for operating the laser light source. In the context of the method, the advantages already explained in connection with the laser light source, the laser projector and the method for operating the laser light source result, in particular.

Drawings

Further advantages of the invention emerge from the description and the drawings. The features mentioned above and those yet to be mentioned below can likewise be used individually by themselves or in any combination in the case of a plurality of features. The embodiments shown and described are not to be understood as exhaustive enumeration but rather have exemplary character for the interpretation of the present invention.

The figures show:

FIG. 1 is a schematic diagram of a laser projector having a laser light source for generating laser beams having three different wavelengths to produce a color image, an

Fig. 2 is a diagram of a laser light source for the laser projector of fig. 1 that produces an incoherent laser beam in order to suppress speckle noise.

Detailed Description

In the following description of the figures, identical or functionally identical components are provided with the same reference symbols.

Fig. 1 shows an exemplary configuration of a laser light source 1 with three light sources 3a-c in the form of three laser diodes. The three light sources 3a-c are designed to generate three laser beams P1, P2, P3, wherein the first laser beam P1 has a wavelength λ in the red wavelength range_RThe second laser beam P2 has a second wavelength λ in the green wavelength range_GAnd the third laser beam P3 has a third wavelength λ in the blue wavelength range_B. The three laser beams P1, P2, P3 generated by the three light sources 3a-c are respectively turned by 90 ° and superimposed collinearly by three mirrored cube-shaped prism cubes 4a-c, so that at the exit of the laser light source 1 three laser beams with three different wavelengths λ are generated_R，λ_G，λ_BOnly one laser beam 2.

As can also be recognized in fig. 1, the laser light source 1 forms part of a laser projector 10, which laser projector 10 is used to produce an image B on a projection surface 13 (curtain). The laser projector 10 has a scanner device 12 for generating an image B, the scanner device 12 having a scanner mirror 11, which can be rotated about two axes for two-dimensionally deflecting the laser beam 2. In order to generate a two-dimensional deflection movement of the scanner mirror 11, the scanner device 12 has a rotary drive 9. The rotary drive 9 deflects the laser beam 2 at a high scanning frequency onto the projection surface 13 in order to build up an image B there line by line.

The laser projector 10 also has a focusing device 8 to focus the laser beam 2 on a projection surface 13. In the example shown, the focusing device 8 relates to a lens which is arranged between the laser light source 1 and the scanner mirror 11. It is clear, however, that the focusing device 8 can also be arranged downstream of the scanner device 12 in the beam path of the laser beam 2.

The laser projector 10 also has a control device 7 which drives the three light sources 3a-c to individually modulate the amplitudes a1, a2, A3 of the three laser beams P1, P2, P3. The control device 7 is also used to control the rotary drive 9 in synchronism with the modulation of the amplitudes a1, a2, A3 to ensure that the desired color is produced at the corresponding pixel of the image B on the projection surface 13.

Generated by the laser light source 1 of fig. 1 with three different wavelengths λ_R，λ_G，λ_BIs coherent and thus causes speckle noise of the image B produced on the projection plane 13. In order to avoid the occurrence of speckle noise or to suppress speckle noise to the greatest possible extent (in practice up to 100%), a laser light source 1a is used in the laser projector 10 of fig. 1 for generating the incoherent laser beam 2, the laser light source 1a being shown in fig. 2.

The laser light source 1a of fig. 2 has three optical arrangements in the form of optical parametric oscillators 5a-c, into which three pump beams P1, P2, P3 are coupled, which, as in fig. 1, are generated by three laser light sources or pump sources 3a-c in the form of laser diodes. In contrast to fig. 1, in the case of the laser light source 1a shown in fig. 2, the three pump beams P1, P2, P3 are generated by three laser diodes of identical construction, i.e. the wavelength λ of the three pump beams P1, P2, P3_P1，λ_P2，λ_P3In the example shown, this is consistent and can be, for example, in the range between 350nm and 400 nm.

The optical parametric oscillators 5a-c have nonlinear optical media in the form of nonlinear crystals 6a-c, respectively. The nonlinear optical crystals 6a-c can for example be lithium triborate crystals, but other optically nonlinear crystals can also be involved, for example barium metaborate (BBO). Importantly, parametric down-conversion (PDC) processes can occur in the corresponding nonlinear crystal. An example of a nonlinear crystal in which this process can occur is illustrated in US6,233,025B1.

In the PDC process, the respective pump beams P1, P2, P3 form an interaction with the nonlinear crystals 6a-c, wherein two new optical fields are generated, which are referred to hereinafter as signal beams S1, S2, S3 and idler beams I1, I2, I3. The PDC process obtains the energy ω of the corresponding pump beams P1, P2, P3_P1，ω_P2，ω_P3And momentumI.e. energy omega_Pi＝ω_Si+ω_IiWherein, ω is_SiRepresenting the energy of the corresponding signal beam S1, S2, S3_IiRepresenting the energy of the corresponding idler beams I1, I2, I3. The corresponding momentum is also conserved, i.e.:

the three optical parametric oscillators 5a-c form optical resonators, respectively, in which nonlinear optical crystals 6a-c are arranged. The optical parametric oscillator 5a-c is operated below the lasing threshold (i.e. not in a Gain-condition) to avoid the occurrence of (partial) stimulated emission which may cause an undesired phase relationship. When the optical parametric oscillator 5a-c is operated below the laser threshold, the power of the signal beams S1, S2, S3 and the idler beams I1, I2, I3 generally scales substantially linearly with the power of the corresponding pump beams P1, P2, P3.

Energy ω of the corresponding pump beam P1, P2, P3_PiDuring the PDC process, the corresponding signal beams S1, S2, S3 and the corresponding idler beams I1, I2, I3, i.e. the corresponding signal beams S1, S2, S3 and the corresponding idler beams I1, I2, I3, respectively, have a different wavelength than the associated pump beams P1, P2, P3. By a suitable selection of the corresponding nonlinear optical crystal 6a-c and by a suitable setting of, for example, the temperature of the corresponding nonlinear optical crystal 6a-c, the energy ω of the corresponding pump beam P1, P2, P3 can be adjusted_PiTo the corresponding signal beams S1, S2, S3 and the corresponding idler beams I1, I2, I3, as desired.

Energy ω of the corresponding pump beam P1, P2, P3_PThe distribution of (c) can be carried out in particular by: in the case of the first nonlinear optical crystal 6a, the signal beam S1 has a wavelength λ in the red wavelength range between about 635nm to about 780nm_R. Accordingly, the signal beam S2 generated by the second nonlinear crystal 6b can have a wavelength λ in the green wavelength range, i.e., between about 520nm to about 540nm_G. In the first placeIn the case of nonlinear interaction in the three nonlinear crystals 6c, it is possible to produce a crystal having a wavelength λ in the blue wavelength range between about 400nm and about 470nm_BThird signal beam S3.

In the example shown in fig. 2, three signal beams S1, S2, S3 generated by three optical parametric oscillators 5a-c are superimposed in a superimposing device 4, which for this purpose has three optical elements 4a-c in the form of cube-shaped prisms. In fig. 2, the optical elements 4a-c of the superimposing means 4 relate to wavelength selective optical elements which are provided with (respectively different) wavelength selective coatings.

On the first wavelength selective element 4a, has a red wavelength λ_RIs diverted, while the first pump beam P1 and the first idler beam I1 are filtered. Correspondingly, on the second wavelength selective element 4b, there is a green wavelength λ_GIs diverted while the second idler beam I2 and the second pump beam P2 are filtered. On the third wavelength selective element 4c, has a blue wavelength λ_BIs diverted, while the third idler beam I3 and the third pump beam P3 are filtered.

Based on the arrangement of the three wavelength selective elements 4a-c in a line, the three signal beams S1, S2, S3 are superimposed collinearly and form a beam having three different wavelengths λ in the red, green and blue wavelength ranges_R，λ_G，λ_BTo produce a desired color image B on the projection surface 13. It is clear that the wavelength-selective optical elements 4a-c do not necessarily form part of the superposition means 4, but can in some cases be arranged in the beam path between the respective optical parametric oscillator 5a-c and the superposition means 4 in order to suppress the respective unwanted radiation fraction. Instead of the wavelength selective optical elements 4a-c, other (optical) filter elements can also be used.

Alternatively, not shown in fig. 2, a superposition of the three signal beams S1, S2, S3 can also be realized on the projection surface 13. In this case, only on the projection surface 13 or in the region of the projection surface 13 are three different wavelengths λ generated_R，λ_G，λ_BOf the laser beam 2. In this case, instead of three cube-shaped prisms 4a-c of the type described, in particular three scanner devices are provided, each having at least one scanner mirror for two-dimensionally deflecting the first signal beam S1, the second signal beam S2 and the third signal beam S3, wherein the three signal beams S1, S2, S3 are each deflected onto a corresponding pixel of the image B on the projection surface 13. In this case, three scanner devices are formed for generating a laser beam having three different wavelengths λ_R，λ_G，λ_BThe laser beam 2 of (1).

As described further above, the incoherent laser beam 2 generated by the laser light source 1a shown in fig. 2 does not actually cause speckle noise on the projection surface 13, because the signal beams S1, S2, S3 respectively have phase fluctuations on the order of picoseconds on the time scale based on their generation in the nonlinear crystals 6 a-c. Thus, the three signal beams S1, S2, S3 respectively have a fluctuating behavior of the thermo-optic source, i.e. each single one of the three signal beams S1, S2, S3 is incoherent. In contrast, the corresponding signal beams S1, S2, S3 and the corresponding idler beams I1, I2, I3, which are jointly generated in the same nonlinear optical crystal 6a-c, are strongly correlated. For this reason, in the laser light source 1a shown in fig. 2, only the signal beams S1, S2, S3 of the corresponding optical parametric oscillators 5a-c are superimposed, respectively.

It is clear that instead of the signal beams S1, S2, S3 being superimposed as laser beam 2, three idler beams I1, I2, I3 can also be superimposed. It is likewise possible to superimpose one idler beam, for example the first idler beam I1, with two signal beams, for example the second and third signal beams S2, S3, or to superimpose two idler beams, for example the first and second idler beams I1, I2, with one signal beam, for example the third signal beam S3.

A method of the aforementioned type for operating the laser light source 1a is described later. The signal radiation is generated by a first optical device 5a of the three optical devices 5a-c, a second optical device 5b of the three optical devices 5a-c and a third optical device 5c of the three optical devices 5a-cBeams S1, S2, S3 and idler beams I1, I2, I3. In this case, either the signal beam S1 or the idler beam I1 of the first optical arrangement 5a is selected to have three different wavelengths λ_R，λ_G，λ_BOf a first wavelength λ_RWherein either the signal beam S2 or the idler beam I2 of the second optical arrangement 5b is selected to have three different wavelengths λ_R，λ_G，λ_BOf medium and first wavelength lambda_RA different second wavelength λ_GAnd wherein either the signal beam S3 or the idler beam I3 of the third optical arrangement 5c is selected to have three different wavelengths λ_R，λ_G，λ_BOf medium and first wavelength lambda_RAnd a second wavelength lambda_GA different third wavelength λ_B. Here, three different wavelengths λ are generated_R，λ_G，λ_BThe laser beam 2 of (2) is obtained by superimposing the signal beams S1, S2, S3 or idler beams I1, I2, I3 selected by the first optical device 5a, the second optical device 5b and the third optical device 5c, respectively.

A method of the aforementioned type for operating the laser projector 10 is described later. In the context of this method, the laser light source 1a is operated in the manner described above for operating the laser light source 1 a.

In summary, the laser projector 10 can be realized by means of the laser light source 1a shown in fig. 2, wherein the image B is practically free of speckle noise. It is clear that the laser light source 1a of fig. 2 or a suitably modified laser light source 1a, for example, which generates laser beams 2 with only two or in some cases more than three different wavelengths, can also be used to advantage in other imaging methods or measurement techniques.