WO2024078970A1

WO2024078970A1 - Laser light source comprising a semiconductor device

Info

Publication number: WO2024078970A1
Application number: PCT/EP2023/077630
Authority: WO
Inventors: Michael Foertsch; Kirill Spasibko
Original assignee: Q.ant GmbH
Priority date: 2022-10-10
Filing date: 2023-10-05
Publication date: 2024-04-18
Also published as: DE102022126118A1

Abstract

The invention relates to a laser light source (30), comprising a semiconductor device (10) with at least one nonlinear optical medium, in particular a nonlinear crystal, and at least one pump laser source (32) for producing a pump laser beam (35) in order to form a signal beam (37) and/or an idler beam (38) in the nonlinear optical medium by parametric down-conversion.

Description

Laser light source with a semiconductor device

Description

The present invention relates to a laser light source comprising: at least one non-linear optical medium, in particular a non-linear crystal, and at least one pump laser source for generating a pump laser beam for forming a signal beam and an idler beam in the non-linear optical medium by parametric down conversion. The invention also relates to a laser projector with such a laser light source.

Light sources that produce light with high intensity, color fidelity, bundling and suitable coherence are advantageous for visualization applications, such as projectors. For visualization applications, especially for

Projectors often use light sources that generate incoherent light, e.g. lamps or LEDs. However, such light sources have disadvantages in terms of intensity, color fidelity and beam bundling. Laser light sources are superior in all of the aspects mentioned, but emit highly coherent light, which in use in a laser projector leads to so-called speckle noise, ie a granular (ie grainy) interference effect that significantly reduces the image quality. Speckle noise does not only occur in laser projectors, but wherever laser light sources are used for imaging or measurement purposes, for example in interferometric measurement technology.

WO 2006/105259 A2 describes a system and a method for operating a multicolor laser source that has arrays of semiconductor lasers to generate light with different colors. The individual emitters or semiconductor lasers of a respective array emit essentially incoherently, e.g. with different phases, in order to suppress speckle noise. To reduce speckle noise, a spectral broadening of the laser radiation emitted by the semiconductor lasers can also be carried out. One or more of the arrays can be followed by a nonlinear frequency converter that converts an input frequency into an output frequency with a different color. Such a nonlinear frequency converter can, for example, generate a parametric down-conversion (PDC) of a green input frequency into a red output frequency. The nonlinear frequency converters can be arranged within an (external) resonator of a respective individual laser emitter or outside of such a resonator. For the nonlinear frequency conversion, a non-linear medium is required, which can be implemented, for example, by an optical fiber or a non-linear crystal. The non-linear crystal of such a laser light source is tuned to the wavelength of the pump laser beam of a respective laser emitter in such a way that a PDC process takes place in the laser-active crystal. The PDC process is based on the non-linear interaction of the pump laser beam, which is generated by the coherent pump laser source, with the non-linear medium. This interaction creates two new light fields, which in the present application - as is generally customary - are referred to as the signal beam and the idler beam. The signal beam and the idler beam receive the energy w _P and the momentum k _P of the pump laser beam, i.e. the following applies to the energy MP = w _s + Wi, where w _s denotes the energy of the signal beam and w _z the energy of the idler beam. The following applies accordingly to the momentum k _P of the pump laser beam, the momentum k _s of the signal beam and the momentum k _z of the idler beam: k _P = k _s + k _z .

Object of the invention

A first aspect of the invention is based on the object of providing a laser light source in which the pump laser radiation of the pump laser source is used as efficiently as possible.

Subject of the invention

This object is achieved by a laser light source according to claim 1. According to the invention, it is proposed that the non-linear optical medium comprises at least two, in particular several, waveguides, wherein a partial signal beam is formed in a respective waveguide and the at least two partial signal beams are combined to add the laser power of the partial signal beams.

The laser light source according to the invention, which is based on the process of parametric down conversion, requires no mechanical functional components and is therefore very small. Parametric down conversion can also be used to destroy the coherence of the laser beam generated by the laser light source, by having either only the signal beam or only the idler beam form the useful laser beam of the laser light source. This takes advantage of the fact that the signal beam and the idler beam have strong correlations due to the joint creation process in the non-linear medium, but that the idler beam or the signal beam on their own exhibit the fluctuation behavior of thermal light sources. These fluctuations are fast enough that speckle noise is practically completely eliminated. The laser light source according to the invention is therefore suitable for generating brilliant, speckle-free projection, e.g. in data glasses, in head-up displays, for the exposure of microchips in lithography and for imaging processes (for illumination) in microscopy. Due to the adjustable coherence (see below), the light source according to the invention can also be used to generate holograms or for other optical applications.

By combining at least two, preferably several, for example between 2 to 20 or more, waveguides on a common semiconductor device, By adding the partial signal beams formed in the waveguides, the laser power of the partial signal beams can be combined, resulting in a higher overall power of the semiconductor device.

At the same time, a size of the semiconductor device does not need to be increased significantly, since the largest dimension, namely the extension of the semiconductor device in the direction of the length of a respective waveguide, does not need to be increased even when multiple waveguides are used.

Different methods can be used to produce a waveguide in a nonlinear crystal, for example ion implantation or a lithographic process. The waveguide is designed in such a way that it guides the pump laser beam at the pump wavelength, the signal beam at the signal wavelength and the idler beam at the idler wavelength in the nonlinear crystal with low losses.

In a further development of the invention, it is advantageous if the semiconductor device comprises at least two waveguides for forming partial signal beams of a first color and at least two waveguides for forming partial signal beams of at least a second color. For this purpose, it is necessary to select the non-linear optical media appropriately or to design the length of the non-linear optical media and their periodic polarity, in particular the periodic polarity of the respective waveguides, in order to generate the desired wavelengths. The partial signal beams of the different colors can be generated simultaneously. It can be provided that the partial signal beams of the different colors in at least one superposition device to form a common laser beam emerging from the laser light source with at least two or more, for example three wavelengths. For example, three wavelengths (red, green and blue) and their individual optical powers, which are superimposed to form the emerging laser beam, are ideally selected so that they add up to a white tone suitable for projection purposes, ideally a white tone with a color temperature of 6500 K.

In a further development of the invention, it is advantageous that each waveguide comprises a tapered coupling-out region. The coupling-out region tapers, for example, towards the waveguide or away from the waveguide. The tapered coupling-out region is, for example, bevelled. With a coupling-out region that tapers towards the waveguide, i.e. a coupling-out region that widens away from the waveguide, an almost homogeneously luminous line can be generated, for example, on a coupling-out side of the semiconductor conductor device by means of several waveguides arranged next to one another. The proposed design of the coupling-out region also makes it possible to optimize the coupling of the waveguide to optical elements, for example an optical fiber or a focusing device, for example a lens device.

In a further development of the invention, it is advantageous that a respective waveguide comprises a tapered coupling region. The coupling region tapers, for example, towards the waveguide or away from the waveguide. The tapered coupling region is for example bevelled. The proposed design of the coupling region makes it possible to optimise the coupling of the waveguide to optical elements, for example an optical fibre or a focusing device, for example a lens device. In particular, in this case, by appropriately designing the coupling region of the waveguide, the (mode) diameter of the exit surface of the optical fibre can be adapted to the (mode) diameter of the waveguide, or more precisely the entry surface of the waveguide.

In a further development of the invention, it is advantageous that the pump laser beam generated by the at least one pump laser source is divided between the at least two waveguides, in particular using evanescent coupling. For example, several waveguides can be fed by one pump laser source. The coupling is carried out, for example, by means of a lens device, for example a microlens array, or a fiber coupling.

It can also be provided that the laser light source comprises at least two pump laser sources. Each pump laser source can, for example, feed one or more waveguides.

It can be provided that the at least one pump laser source or the at least two pump laser sources comprise a solid-state laser, in particular a diode laser. The diode laser can be operated continuously (cw) or pulsed. In the case of pulsed operation of the diode laser, it is possible to use the power supplied to the diode laser for generating the The injection current supplied to the pump laser beam for the individual pulses should be selected to be greater than the cw injection current, i.e. the diode laser should be overpulsed. On average over time, overpulsing results in an injection current that essentially corresponds to the cw injection current due to the pulse pauses.

Advantageously, it can also be provided that the laser light source comprises at least one seed light source for generating a seed signal beam and/or a seed idler beam, and at least one superposition device for superimposing the seed signal beam and/or the seed idler beam with the pump laser beam for joint coupling into the non-linear optical medium. The emission spectrum of the seed signal beam or a seed idler beam contains the signal wavelength of the signal beam or the idler wavelength of the idler beam or essentially corresponds to these. By using the seed light source, the gain of the non-linear medium for the seed beam and/or the idler beam can be increased (seed gain). The superposition device can be designed to superimpose the seed signal beam and/or the seed idler beam collinearly (spatially) in order to feed them along a common beam path to the nonlinear medium. For the collinear superposition, for example, a polarizing beam splitter can be used which is reflective for the polarization direction of the seed signal beam (or the idler signal beam) and transmissive for the polarization direction of the pump laser beam, or vice versa.

Other optical devices can also be used as superposition devices. For example The different wavelengths of the pump laser beam and the seed or idler signal beam can be used to achieve superposition, e.g. with the help of a diffraction grating or a dichroic beam splitter or the like.

In an advantageous embodiment, the laser light source has at least one control device for controlling the power of the seed signal beam coupled into the non-linear optical medium and/or of the pump laser beam. The control device can be designed to adjust the power of the seed light source and/or the pump laser source in order to influence or adjust the coherence of the signal beam coupled out of the non-linear medium and/or of the idler beam. Alternatively or additionally, (optical) filtering can be carried out with an adjustable optical filter in order to adjust the power of the seed signal beam and/or the seed idler beam coupled into the non-linear medium. The same applies to adjusting the power of the pump laser source.

The seed light source is, for example, an LED, superluminescence diode or a laser diode. An LED typically has a coherence length that is so large that the radiation emerging from the seed light source is referred to as incoherent. The superluminescence diode is a laser diode without a resonator. A superluminescence diode combines the brightness of a laser diode with the low coherence (length) of light-emitting diodes, which is equivalent to a larger bandwidth of the radiation emitted by the superluminescence diode compared to the laser radiation emitted by a laser diode. The seed light source in the form of a laser diode can in particular be a multi-mode laser diode or a laser operated below the emission threshold. The seed signal beam or seed idler beam generated by such a multi-mode laser diode also has a shorter coherence length than a pump laser beam generated by a pump laser source, e.g. in the form of a single-mode laser diode.

According to one embodiment, the pump laser source is designed to generate a pump laser beam with a pump wavelength of less than 460 nm. The pump wavelength of the pump laser source should not be selected to be larger when the laser light source is used for projection, since during parametric down conversion in the non-linear medium the converted output wavelengths are larger than the pump wavelength of the pump laser beam. With a pump wavelength that is, for example, 450 nm or less, for example approximately 375 nm or less, the three primary colors blue (between approximately 420 nm and approximately 470 nm), green (between approximately 520 nm and approximately 540 nm) and red (between approximately 635 nm and 780 nm) can be generated by parametric down conversion. To generate, for example, three signal beams or For the generation of idler beams with wavelengths in the blue, green and red wavelength ranges, three pump laser sources can be used, which do not necessarily use the same pump wavelength. The generation of three signal beams or idler beams with different wavelengths can also be achieved with the help of a single pump laser source by splitting the pump laser beam between the respective waveguides. It can advantageously be provided that the

Laser light source comprises at least one focusing device for focusing the pump laser beam and/or the seed signal beam and/or the seed-ldler beam, in particular on a respective entry surface of a respective waveguide. The focusing device can be a focusing lens, for example. So-called "graded index lens" (GRIN) lenses can be used as lenses for focusing. The lenses can in particular be combined to form a monolithic hybrid microsystem. GRIN lenses have a comparatively small decentration due to the manufacturing process.

It can advantageously be provided that the pump laser beam and/or the seed signal beam and/or the seed idler beam are coupled into a respective waveguide via a respective optical fiber. In particular, in this case the (mode) diameter of the exit surface of the optical fiber can be adapted to the (mode) diameter of the waveguide, or more precisely the entry surface of the waveguide. Alternatively, the mode field diameter of the pump light source can be adapted to the mode field diameter of the waveguide and accordingly also to the acceptance angle of the waveguide, for example by means of an aperture.

It can advantageously be provided that a partial signal beam formed in a respective waveguide is coupled out of a respective waveguide via a common or a respective collimation device and/or a respective optical fiber. The collimation device is, for example, in the beam path after the non-linear Medium in order to collimate the pump laser beam, the signal beam and/or the idler beam, which typically emerges divergently from the waveguide. So-called "graded index lens" (GRIN) lenses can be used as lenses for collimation. The lenses can in particular be combined to form a monolithic hybrid microsystem.

In a development of the invention, it can be provided that the laser light source comprises at least two semiconductor devices, wherein the at least two semiconductor devices are formed as a layer stack. In addition to (or even instead of) placing several waveguides next to each other, the same increase in power can be achieved by placing (stacking) several chips with one or more waveguides on top of each other, so that a two-dimensional increase in power and the number of waveguides is obtained, instead of a one-dimensional one. In this case, the waveguides on each chip should be protected from the chips on their upper side, e.g. by sputtering an additional oxide layer onto the upper side of the chip, which completely covers the waveguides from above.

The semiconductor device comprises, for example, a substrate comprising silicon (Si) or silicon carbide (SiC) or gallium nitride (GaN) and/or the non-linear crystal comprises, for example, lithium niobate (LiNbOa). However, the non-linear crystal can also comprise, for example, KTP (potassium titanyl phosphate), PP-KTP (periodically poled potassium titanyl phosphate), PP-LN (periodically poled lithium niobate), Ti:LN (titanium lithium niobate), AIN (aluminum nitride), LNol (lithium niobate on Isolation substrate), BBO (beta barium oxide) and LBO (lithium barium oxide). These nonlinear crystals are transparent for wavelengths of more than approximately 380 nm. For the laser light source, a nonlinear crystal should be selected that has low absorption and thus high transparency for the pump wavelength as well as the signal wavelength and the idler wavelength.

Further embodiments relate to a semiconductor device for a laser light source according to the described embodiments.

A further aspect of the invention relates to a laser projector which comprises a laser light source according to the embodiments described. The laser light source can be used, for example, in a laser projector in order to generate an almost speckle-free image on a projection surface. To generate the image on the projection surface, the laser projector can have a scanner device for two-dimensional deflection of the laser beam, which can, for example, comprise at least one mirror. Such a laser projector can be used in particular as a head-up display in a motor vehicle in which, for example, the windshield serves as the projection surface. The laser light source can, however, also serve as an illumination source for the projection of images for the generation of which spatially resolving modulators are used, for example so-called DMDs (Digital Mirror Devices) or SLMs (Spatial Light Modulators).

Further exemplary embodiments concern a

Laser light source comprising a semiconductor device with at least one non-linear optical medium, wherein the non-linear optical medium does not comprise at least two but only one waveguide. It is advantageously provided that the semiconductor device comprises a substrate comprising silicon carbide (SiC) or gallium nitride (GaN). The semiconductor device is, for example, an optoelectronic chip and comprises, for example, a circuit section. At least one waveguide is arranged on the circuit section. The circuit section comprises, for example, SiC. A buffer layer, for example a heat sink, can advantageously be provided on the circuit section. The heat sink comprises, for example, SiC.

SiC and GaN have significantly improved heat transport properties compared to Si. Thermal radiation from integrated circuits in silicon leads to refractive index modulations in the lithium niobate, i.e. in the waveguide. These modulations produce temporally changing phase properties of the light guided in the waveguide. This in turn leads to inefficiencies in photonic calculations and means unpredictable losses and inaccuracies for photonic computing, for example. This problem can be avoided by using SiC or GaN instead of Si. A stack made of SiC/buffer layer/LiNbO3 or GaN/buffer layer/LiNbO3 is therefore particularly well suited as a starting material for optoelectronic chips. A further exemplary embodiment therefore relates to a laser light source comprising a semiconductor device comprising a stack comprising stacked layers of SiC/buffer layer/LiNbO3 or GaN/buffer layer/LiNbO3 with at least one non-linear optical medium, wherein the non-linear optical medium comprises at least one waveguide. The embodiment of the laser light source with at least one waveguide can, as far as applicable, be combined with all of the above-described embodiments of the laser light source with at least two, in particular several, waveguides, with the proviso that only one waveguide is provided.

The invention also relates to the use of the described laser projector and/or the described semiconductor devices and/or the described laser light sources for quantum computing in a quantum processor or quantum computer.

Further advantages of the invention emerge from the description and the drawing. Likewise, the features mentioned above and those listed below can be used individually or in combination in any desired way. In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

The drawing shows:

Fig. 1a is a schematic representation of an embodiment of a semiconductor device according to a first embodiment,

Fig. 1b is a schematic representation of an embodiment of a semiconductor device according to a further embodiment, Fig. 2 is a schematic representation of an embodiment of a further semiconductor device according to a further embodiment,

Fig. 3 is a schematic representation of an embodiment of a laser light source with a semiconductor device, a pump laser source and a seed light source.

Fig. 1a shows a highly schematic example of the structure of a semiconductor device 10 for a laser light source in a sectional view/side view. The semiconductor device comprises a substrate 12, for example comprising silicon (Si) or silicon carbide (SiC) or gallium nitride (GaN). The advantages of silicon carbide and gallium nitride are explained further below with reference to the embodiment shown in Fig. 2.

A buffer layer 14, for example comprising silicon dioxide (SiCt), is applied to the substrate 12.

According to the illustration in Fig. 1a, the semiconductor device 10 comprises ten waveguides 16, in particular those running parallel to one another. The number of waveguides is freely selectable.

The waveguides 16 can be produced, for example, by ion implantation or dif-founded titanium or laser ablation or dry or wet etching in a non-linear crystal. The non-linear crystal in the example is periodically poled lithium niobate. It is essential for the selection of a non-linear crystal that in a PDC process can take place in the non-linear crystal. In order to create the geometric outer contour of the waveguide shown in the example, surface ablation can be carried out, for example by means of laser radiation. Periodic poling is not absolutely necessary, but can increase the efficiency of non-linear processes.

The generation of non-speckle light using PDC is sometimes not very efficient. For example, parametric light with only a few 100 pW of power can be generated from several mW of pump power under optimal conditions. In the example, each waveguide can generate light with a power of 100 pW. By generating and combining the partial beams in parallel, the power of the laser light source in the example can be increased to 1 mW.

Figure 1b shows a highly schematic example of the structure of a semiconductor device 10 in a top view. In the example, four waveguides 16 are shown in a simplified manner. The waveguides 16 are designed differently merely as an example for the purposes of illustration. It can be provided that in one embodiment all waveguides 16 are designed the same or different from one another.

The waveguides 16 are fed by one or more pump laser sources and optionally by one or more seed laser sources. This will be explained later with reference to the embodiment shown in Fig. 3.

The waveguides shown in Fig. 1b each comprise a tapered coupling-out region 18 according to different embodiments. According to the example, the coupling-out regions taper towards the waveguide. However, it is also possible to design the coupling-out region inversely. This is shown, for example, with the dashed lines for a coupling-out region 18a. The tapered coupling-out region is, for example, bevelled. With a coupling-out region that tapers towards the waveguide, i.e. a coupling-out region that widens away from the waveguide, an almost homogeneously luminous line or area can be generated, for example, on a coupling-out side of the semiconductor conductor device by means of several waveguides arranged next to one another. In the example, the waveguides are optimally coupled via their coupling-out region to optical elements, in the example a collimator device, for example lens device 20, for example designed as a microlens array.

The waveguides shown in Fig. 1b each comprise a tapered coupling region 22 according to various embodiments. In the left waveguide 16, the coupling region 22a tapers away from the waveguide, for example. In the other waveguides 16, the coupling region 22 tapers towards the waveguide 16.

The two left waveguides 16 are coupled to a respective optical fiber 24 via their coupling regions 22, 22a. In particular, in this case, by appropriately designing the coupling region of the waveguide, the (mode) diameter of the exit surface of the optical fiber can be adapted to the (mode) diameter of the waveguide, or more precisely, the entry surface of the waveguide. The two right waveguides 16 are coupled via their coupling regions 22, 22a to a focusing device 26, for example a lens device.

Differently designed input and output coupling areas can be provided in any combination for a particular waveguide.

It can be provided that the waveguides 16 of the semiconductor device 10 are designed to generate partial signal beams of different colors. For example, at least two or more waveguides 16 are designed to form partial signal beams of a first color and at least two or more waveguides 16 are designed to form partial signal beams of at least a second color. For this purpose, it is necessary to suitably select and adapt the non-linear optical media or to suitably design the length of the non-linear optical media and their periodic polarity, in particular the periodic polarity of the respective waveguides, in order to generate the respective desired wavelengths. The waveguides 16 for generating partial signal beams of different colors can also be fed by different pump laser sources.

Fig. 2 shows a further exemplary embodiment of a semiconductor device 10 with a non-linear optical medium, wherein the non-linear optical medium comprises only one waveguide 16. It is advantageously provided that the semiconductor device 10 comprises a substrate 12 comprising silicon carbide (SiC) or gallium nitride (GaN). The semiconductor device 10 is, for example, an optoelectronic chip and comprises, for example, a Circuit section, in particular integrated into the silicon carbide layer 12. At least one waveguide 16 is arranged on the circuit section. The circuit section comprises, for example, SiC or GaN. A buffer layer 14, for example a heat sink, can advantageously be provided on the circuit section. The heat sink comprises, for example, SiC or GaN.

SiC or GaN has significantly improved heat transport properties compared to Si. The thermal radiation from integrated circuits in silicon leads to refractive index modulations in the lithium niobate, i.e. in the waveguide 16. These modulations produce temporally changing phase properties of the light guided in the waveguide 16. This in turn leads to inefficiencies in photonic calculation and means, for example, unpredictable losses and inaccuracies for photonic computing. This problem can be avoided by using SiC instead of Si. A stack structure made of SiC/buffer layer/LiNbOS or GaN/buffer layer/LiNbOS is therefore particularly well suited as a starting material for optoelectronic chips.

Fig. 3 shows a highly schematic example of a laser light source 30, which comprises a pump laser source 32 in the form of a diode laser, a semiconductor device 10 and a seed light source 34. In the example shown, the pump laser source 32 is designed to generate a pump laser beam 35 with a pump wavelength A _P of 375 nm or greater than 375 nm. For visualization applications using a parametric down-conversion (PDC) process, the The pump wavelength A _P should not be chosen too large and should be smaller than approx. 460 nm or approx. 450 nm. For other applications, wavelengths in other ranges can be selected. For example, both the signal and the idler wavelength can be in the infrared range. If, for example, the generated signal and/or idler beams are used as seeds for high-power lasers or in photonic data processing, the pump wavelength can be up to 2000 nm, typically in the range of 520-540 nm, 750-850 nm or 1000-1100 nm.

The pump laser beam 35 is coupled into the non-linear crystal of the semiconductor device, more precisely into the waveguide 16 formed there, in the example four. The PDC process takes place in the non-linear crystal. During the PDC process, the pump laser beam 35 interacts with the non-linear crystal, generating two new light fields, which are formed as a signal beam 37 with a signal wavelength X _s and as an idler beam 38 with an idler wavelength

In the PDC process, the energy w _P of the pump laser beam 35 is preserved, i.e. the law of conservation of energy w _P = w _s + w _s applies, where w _{s is} the energy of the signal beam 37 and

denote the energy of the idler beam 38 . In order to also satisfy the momentum conservation law k _P = k _s + k _z for the momentum k _P of the pump laser beam 35 , the momentum k _s of the signal beam 37 and the momentum k _z of the idler beam 38 , a phase adjustment is required, which in the example shown is achieved by a periodic polarization 39 of the nonlinear crystal . The periodic polarization 39 is indicated in Fig. 3 by vertical lines which form the interfaces between the reversely polarized ferroelectric domains of the nonlinear crystal . The periodic poling 39 also increases the nonlinearity of the crystal and thus the efficiency of the PDC process.

A first beam splitter 40 is arranged in the beam path after the non-linear crystal, which separates the idler beam 38 from the pump laser beam 35 emerging from the non-linear crystal, which is not converted during the PDC process. The first beam splitter 40 is designed as a dichroic beam splitter, i.e. it has a wavelength-selective element in the form of a wavelength-selective coating in order to separate the pump laser beam 35 with the pump wavelength X _P from the idler beam 38 with the idler wavelength

to separate. In the beam path after the first beam splitter 40 there is a second beam splitter 41 which separates the pump laser beam 35 from the signal beam 37. The second beam splitter 41 is designed as a polarization beam splitter and/or dichroic beam splitter. The separation of the signal beam 37 and the idler beam 38 in a polarization beam splitter 41 is possible because both beams are polarized perpendicular to one another in the design of the laser light source 30 chosen here, i.e. there is a type II phase adjustment. Alternatively, a phase adjustment can also be implemented in which the signal beam 37 and the idler beam 38 have the same polarization (type I). In both cases (type I and type II) the beam splitter can also be designed as an optical filter or as a wavelength-selective optical element.

The laser light source 30 shown in Fig. 3 has a seed light source 34 in the form of a superluminescence or laser diode, which is used to generate a seed signal beam 37 ' The seed light source 34 generates a seed

Signal beam 37 ' whose wavelength coincides with the signal

Wavelength X _s of the signal beam 37. The seed light source 34 generates the seed signal beam 37 ' with a coherence length that is smaller than the coherence length of the pump laser beam 35 generated by the pump laser source 32. The seed signal beam 37 ' is collinearly superimposed with the pump laser beam 35 in a superposition device 46 in the form of a dichroic mirror. This takes advantage of the fact that the pump laser source 32 generates the pump laser beam 35 with a (linear) polarization that is aligned perpendicular to the (linear) polarization of the seed signal beam 37 '. For the superposition in the superposition device 16, it is advantageous if the pump laser beam 35 and the seed signal beam 37 ' are collimated. The laser light source 30 has a collimation lens 47 for collimating the pump laser beam 5 emerging divergently from the pump laser source 32. Accordingly, a further collimation lens 48 for collimating the seed signal beam 37' is arranged between the seed light source 34 and the superposition device 16.

The superimposed pump laser beam 35 and the seed signal beam 37' are divided into four waveguides 16 according to the example. The division is carried out, for example, by means of a suitable beam splitter 44, in particular comprising a micromirror arrangement. The beam splitter 44 divides the superimposed pump laser beam 35 and the seed signal beam 37' into four partial beams 35-T, 37'-T. In the example, the four partial beams 35-T, 37'-T are focused onto an entrance surface 21 of a respective waveguide 16 by means of a respective focusing lens 26, in the example a lens arrangement. The focusing lenses 26 are designed such that the respective partial beams 35-T, 37'-T are adapted to the mode field diameter of the respective waveguide 16. The acceptance angle of a respective waveguide 16 can be adapted by a common guidance of a respective partial beam 35-T, 37'-T in an optical fiber 24. The focusing lens 26 and the optical fiber 24 can also be realized in the form of a single optical component, for example in the form of a GRIN lens. Alternatively or additionally, the adaptation to the mode field diameter or to the acceptance angle of the waveguide 6 can be carried out in another way, for example by using an aperture or by the tapered coupling-in/out regions 18, 22 of the waveguides or the like described with reference to Fig. 1.

In a respective waveguide 16, a partial beam comprising a partial signal beam 37-T and a partial idler beam 38-T is formed by means of PDC.

It can be provided that the partial signal beams 37-T and the partial idler beams 38-T are superimposed again to form a common beam before the beam splitters 40, 41 by means of a superposition device 42. Additional optical elements, such as a common or respective collimation device 20 (as shown in Fig. 1, for example) and/or a respective optical fiber, can be arranged between the semiconductor device 10 and the superposition device 42. It can also be provided that a separate beam splitter 40, 41 is assigned to each respective waveguide in the beam path after the waveguides 16. For certain applications, for example for holography, it can be useful if the laser light source 30 has a switchable or adjustable coherence (length). The laser light source 30 shown in Fig. 3 has a control device 52 for setting the coherence length of the signal beam 37 used as the useful laser beam. The control device 52 makes it possible to set the intensity of the seed signal beam 37' coupled into the nonlinear crystal by controlling the injection current which is supplied to the seed light source 34 for generating the seed signal beam 37'. For example, the coherence can be set, for example by adjusting the stability of the pump beam, by changing from a frequency-stabilized to a non-frequency-stabilized range. In this way, a desired coherence of the signal beam 37 emerging from the laser light source 30 can be set.

The control device 52 is also designed to adjust the power of the pump laser source 32. This can be useful, for example, in projection applications in which several signal beams 37 are superimposed, since in this case the color of the light generated during the superposition can be changed by changing the intensity of a respective signal beam 37. The pump laser source 32 can be operated continuously or in a pulsed manner. In the latter case, overpulsing can take place, i.e. the (maximum) power of the pump laser source 32 is selected to be greater during the pulse duration than during continuous operation of the pump laser source 32. By overpulsing the pump laser source 32, the efficiency of the PDC process in the nonlinear crystal can be increased. The arrangement of pump laser source 32 and seed laser source 34 described and shown in Fig. 3 is merely exemplary.

Only one pump laser source 32 or several pump laser sources 32 without a seed laser source 34 or several pump laser sources 32 with several seed laser sources 34 can be provided.

In particular, if the waveguides 16 of the semiconductor device 10 are designed to generate partial signal beams of different colors, it can be advantageous if the waveguides 16 are fed by different pump laser sources 32 for generating partial signal beams of different colors.

In the example it is shown that the non-linear crystal is passed through by a pump laser beam in a single pass. It can also be provided that the pump laser beam passes through the non-linear crystal in a double pass.

In another exemplary embodiment, a laser light source 30 comprises a semiconductor device 10 according to the embodiment described with reference to Fig. 2.

Claims

Claims Laser light source (30), comprising a semiconductor device (10) with at least one nonlinear optical medium, in particular a nonlinear crystal, and at least one pump laser source (32) for generating a pump laser beam (35) for forming a signal beam (37) and/or an idler beam (38) in the nonlinear optical medium by parametric down conversion, characterized in that the nonlinear optical medium comprises at least two, in particular several, waveguides (16), wherein a partial signal beam (37-T) is formed in a respective waveguide (16) and the at least two partial signal beams (37-T) are combined to add the laser power of the partial signal beams (37-T). Laser light source (30) according to claim 1, characterized in that the semiconductor device (10) comprises at least two waveguides (16) for forming partial signal beams (37-T) of a first color and at least two waveguides (16) for forming partial signal beams (37-T) of at least a second color. Laser light source (30) according to one of claims 1 or 2, characterized in that a respective waveguide (16) comprises a tapered coupling-out region (18).

4. Laser light source (30) according to one of the preceding claims, characterized in that a respective waveguide (16) comprises a tapered coupling region (22).

5. Laser light source (30) according to one of the preceding claims, characterized in that the pump laser beam (35) generated by means of the at least one pump laser source (32) is divided between the at least two waveguides (16), in particular using evanescent coupling.

6. Laser light source (30) according to one of the preceding claims, characterized in that the laser light source (30) comprises at least two pump laser sources (32).

7. Laser light source (30) according to one of the preceding claims, characterized in that the at least one pump laser source (32) or the at least two pump laser sources (32) comprise a solid-state laser, in particular a diode laser.

8. Laser light source (30) according to one of the preceding claims, characterized in that the laser light source (30) comprises at least one seed light source (34) for generating a seed signal beam (37') and at least one superposition device (46) for superimposing the seed signal beam (37') on the pump laser beam (35) for joint coupling into the nonlinear optical medium.

9. Laser light source (30) according to one of the preceding claims, characterized in that the Laser light source (30) comprises at least one focusing device (26) for focusing the pump laser beam (35) and/or the seed signal beam (37'), in particular on a respective entry surface (21) of a respective waveguide (16). Laser light source (30) according to one of the preceding claims, characterized in that the pump laser beam (35) and/or the seed signal beam (37') are coupled into a respective waveguide (16) via a respective optical fiber (24). Laser light source (30) according to one of the preceding claims, characterized in that a partial signal beam (37-T) formed in a respective waveguide (16) is coupled out of a respective waveguide (16) via a common or a respective collimation device (20) and/or a respective optical fiber. Laser light source (30) according to one of the preceding claims, characterized in that the semiconductor device (10) comprises a substrate (12) comprising silicon (Si) or silicon carbide (SiC) or gallium nitride (GaN) and/or that the non-linear crystal (16) comprises lithium niobate (LiNbOa). Semiconductor device (10) for a laser light source (30) according to one of claims 1 to 12. Laser projector comprising a laser light source (30) according to one of claims 1 to 12. Use of a laser projector according to claim 14 and/or a semiconductor device according to claim 13 and/or a laser light source according to one of claims 1 to 12 for quantum computing.