OVERLAP DEVICE AND OPTICAL SYSTEM

Description

[0001] The present invention relates to an optical system with a superposition device for coherently superposing four mutually coherent input beams to form a single output beam. The four mutually coherent input beams and the output beam formed by the superposition are typically laser beams.

[0002] The superposition device described above is preferably designed to superimpose the four input beams collinearly, whereby, in particular, a congruent superposition with the output beam can be achieved. The coherent superposition of the four input beams makes it possible to modulate or manipulate the properties of the output beam, for example, the power of the output beam and / or the polarization state of the output beam.

[0003] Fast polarization modulation can generally be achieved using interferometric systems that couple a single input beam and manipulate the phase using phase shifters integrated into the interferometer. See, for example, the article "The rotating linearly polarized light from a polarizing Mach-Zehnder interferometer: Production and applications", C. Pawong et al., Opt. Lasers Tec. 43, 461-468 (2011), or the article "Investigation of the use of rotating linearly polarized light for characterizing SiO2 thin-film on Si substrate", C. Pawong et al., in: Optoelectronic Materials and Devices, G. Duan, ed., Vol. 8308 of Proceedings of SPIE (2011), paper 830811.

[0004] Fast polarization modulation can be used, for example, to write polarization-influencing nanostructures into transparent materials for data storage with high storage density and extremely long lifetimes. See, for example, the article "Eternal 5D data storage by ultrafast laser writing in glass" by J. Zhang et al., Proc. of SPIE Vol. 9736, 97360U (2016). A corresponding optical data storage system based on nanogratings inscribed in a glass material, which are formed upon irradiation with light with a spatially modulated phase and polarization, is described in US Pat. No. 10,236,027 B1. A liquid crystal spatial light modulator (SLM) is used to modulate the phase and polarization.

[0005] US 10,181,336 B1 describes an optical data storage system that uses a dynamic digital hologram with independently programmable holographic zones for data storage. The dynamic digital hologram can be designed as an optically controllable SLM.

[0006] In the methods and devices described above for inscribing nanostructures or voxels into a transparent material, the dynamics are limited due to multiplexing and / or the segmentation of multispot fields with regard to their polarization state.

[0007] US9792945B1 describes a 3D optical data storage device. Light energy is used to modify the electrical properties of a memory cell. It does not explain how the adjustment of the light energy parameters required for high-rate writing, particularly with regard to polarization, is achieved.

[0008] It is also known to use coherent combining or coupling for rapid modulation of the laser power, see, for example, the article "Coherent combining of second-harmonic generators by active phase control of the fundamental waves," A. Odier et al., Optics Letters 42 (16), 2017, 3201ff. In this article, active phase control at the fundamental wavelength is used to control the combining at the frequency-converted wavelength.

[0009] US2021 / 0119707 describes an optical data transmission system in which a laser comprises a plurality of modulatable optical reflectors and is configured to emit mutually coherent optical beams from the modulatable optical reflectors. An optical power combiner has a first optical input connected to receive light from one of the optical beams emitted by a first of the modulatable optical reflectors and a second optical input connected to receive light from one of the optical beams emitted by a second of the modulatable optical reflectors. An electronic controller is connected to operate the first and second of the modulatable optical reflectors to modulate the optical beams emitted by them to transmit a first and second data stream, respectively.The optical power combiner is connected to interfere the light received from the first and second of the modulatable optical reflectors with a relative phase difference.

[0010] From DE 10 2017 104 392 A1, it is known to use an interferometer as a superposition device to modulate the amplitude of an output laser beam. In this case, a relative phase position of two beam channels of the interferometer is temporally modulated. If polarization beam splitters are used as a splitting element for splitting the input laser beam and as a combining element for coherent combination, the modulation of the relative phase position leads to a modulation of the polarization state of the coherently superimposed output beam. With the help of a wave plate and a polarizer, the modulation of the polarization state of the output laser beam can be converted into a modulation of the amplitude of the output laser beam.

[0011] US 9,042,009 B2 describes a passive device for coherent superposition which has an amplitude-splitting interferometer with at least four branches. Aufgabe der Erfindung

[0012] The invention is based on the object of providing an optical system with a superposition device which enables independent adjustment or modulation of the power and the polarization state of the coherently superimposed output laser beam. Gegenstand der Erfindung

[0013] This object is achieved according to the invention by an optical system with a superposition device of the type mentioned above, comprising: a beam source for generating a laser beam, a splitting device for splitting the laser beam into the four mutually coherent input beams, a phase modulation device for modulating the relative phase positions of the four input beams, and a superposition device for coherently superposing the four input beams to form the output beam. The optical system and the superposition device can be implemented with discrete optical components, fiber optics, integrated optics, or as a hybrid system.The superposition device comprises four inputs for the entry of one of the input beams each, an output for the exit of the output beam, a first combination device for the coherent combination of the first input beam and the second input beam to form a first superposition beam, a second combination device for the coherent combination of the third input beam and the fourth input beam to form a second superposition beam, and a third combination device for forming the output beam by coherent combination of the first superposition beam and the second superposition beam, wherein the superposition device is designed to set both a polarization state, in particular a polarization direction, and a power of the output beam independently of one another depending on relative phase positions of the individual phases of the input beams supplied to the four inputs.

[0014] In the superposition device described here, a two-stage superposition of the four input beams occurs. This means that first, two of the input beams are superimposed to form one of two superposition beams, and then the two superposition beams are superimposed to form the output beam. The three combination devices can be different optical assemblies or separate optical components. However, it is also possible for one and the same optical element or component to assume the function of two or, if necessary, all three combination devices. In this case, the superposition of the respective beams typically occurs at different positions of the optical element or component.

[0015] Unlike the case in DE 10 2017 104 392 A1 cited at the beginning, the polarization state and the power of the output beam can be adjusted or modulated independently of each other in the two-stage superposition device described here. When adjusting the polarization state of the output beam, a linear polarization of the output beam can be set, the polarization direction (azimuth angle) of which is freely selectable (from 0° to 180°).

[0016] The superheterodyne device may be a passive device that does not have any optical elements whose optical properties can be adjusted. In the event that the superheterodyne device does have optical elements whose optical properties can be adjusted, e.g., phase shifters, optical rotators, etc., such adjustment is generally not used to dynamically adjust or modulate the polarization state and / or the power of the output beam, but typically only to correct undesirable, e.g., temperature-induced changes in the optical properties of the optical components of the superheterodyne device, in order to enable, for example, complete constructive interference of the input beams (see below).

[0017] The adjustment of the polarization state and / or the power of the output laser beam is typically achieved solely by adjusting or specifying the relative phase positions of the individual phases of the input beams to one another. Since the absolute phase of the four input beams plays no role in the superposition, a phase modulation unit designed to adjust or modulate the phases of three of the four input beams is sufficient to adjust the relative phase positions. The adjustment of the polarization state and / or the power of the output beam by specifying or adjusting the (relative) phase positions of the four input beams with the aid of the phase modulation unit can be carried out highly dynamically with switching times, for example, in the MHz range.

[0018] By rapidly switching the polarization, in particular, an increased write rate can be achieved without extended multiplexing in applications involving the writing of polarization-influencing nanostructures into a transparent material or the alignment of dipole properties in a transparent material with ferroelectric properties. Furthermore, compared to writing approaches based on segmenting the regions to be written with respect to polarization, the optical requirements can be reduced and, typically, efficiency can be increased. Compared to the sequential writing of voxel fields each with the same polarization, as described in US Pat. No. 10,181,336 B1, increased efficiency can also be achieved, and the effective write rate can be increased at the same repetition frequency.Compared to approaches that use an SLM to enable 2D multi-spot distribution with independent control of power / phase and polarization direction, as is the case, for example, in US Pat. No. 10,236,027 B1, the above-mentioned advantages result from a higher modulation rate, as well as the advantages listed below, which arise from the fact that the modulation does not occur in the useful or output beam: By arranging the phase modulation unit upstream of the superheterodyne device, it is not necessary for the phase modulation unit to provide the output beam with the required output parameters directly from an input beam. This allows, for example, the use of lower-performance components for modulating the relative phase positions.Additionally, for input beams generated by an ultrashort pulse laser, the power in the phase modulation unit can be reduced by switching time-stretched pulses. Optical components with increased losses can also be used without significantly negatively impacting the efficiency of the overall system. The modulation of the relative phase positions of the input beams can also occur at a different wavelength than the wavelength of the output beam.

[0019] Preferably, the superposition device is configured to set a power of the output beam, at at least one relative phase position of the individual phases of the four input beams, which—apart from parasitic losses upon passing through the optical components of the superposition device—corresponds to the sum of the powers of the four input beams. Thus, with a suitable selection of the relative phase position of the input beams, the superposition device makes it possible to generate complete constructive interference of the input beams at the output, so that the output beam has the maximum possible power (100% of the sum of the powers of the input beams). As described above, in addition to the maximum power of the output beam in this case, the polarization state of the output beam can be adjusted independently.The superposition device is typically also designed to modulate the power independently of the polarization state, up to a complete destructive interference of the four input beams at the output, i.e. up to a power of the output beam which is 0% of the sum of the powers of the four input beams.

[0020] The power of the input beams entering the superheterodyne device at the four inputs is typically essentially the same for all four input beams, meaning that the power of each input beam is not used to dynamically adjust the polarization state or the power of the output beam. In principle, however, it is possible to deviate (usually slightly) from an identical intensity of the four input beams in order to ensure the complete constructive interference of the four input beams when superimposed to form the output beam, as described above. This may be necessary, for example, if the losses of the input beams vary as they pass through the superheterodyne device.

[0021] In addition to the output beam, the superposition device, or more precisely, at least one combination device, typically generates at least one further beam at a further ("inverting") output, which can be used as a diagnostic beam. The diagnostic beam typically has a polarization direction perpendicular to the polarization direction of the beam emerging from the other output. The sum of the power emerging at this output and at the further output is also constant and does not depend on the relative phase positions of the four input beams.

[0022] The diagnostic beam can therefore be used, for example, to determine and monitor the polarization state and power of the output beam or of a respective superposition beam. The (indirectly) measured actual value of the polarization state and the actual value of the power of the output beam can be used to adapt or regulate the power and relative phase positions of the input beams in order to set the target value of the polarization state or power of the output beam. For this purpose, the adjustable optical component(s) of the superposition device described above, e.g. in the form of one or more phase shifters, optical rotators, etc., can also be influenced. As described above, such control typically takes place on a slower timescale than the highly dynamic adjustment of the relative phase positions of the input beams.

[0023] In one embodiment, the first, second, and / or third combination device comprises / comprising an interferometer, preferably a Mach-Zehnder interferometer, with a first beam channel for propagating a first partial beam and a second beam channel for propagating a second partial beam. In principle, all three combination devices can comprise an interferometer or be designed as an interferometer. In one embodiment, only the third combination device comprises an interferometer or is designed as an interferometer. In an alternative embodiment, both the first and second combination devices, but not the third combination device, comprise an interferometer or are designed as an interferometer.

[0024] In a further development, the interferometer of the first combination device comprises a splitting element for splitting the coherently superimposed first and second input beams into the two partial beams and a combination element for coherently superimposing the two partial beams to form the first superposition beam, and / or the interferometer of the second combination device comprises a splitting element for splitting the second and third coherently superimposed input beams into the two partial beams and a combination element for coherently superimposing the two partial beams to form the second superposition beam. As described above, in this further development, both the first combination device and the second combination device preferably have an interferometer, while the third combination device preferably does not have an interferometer.It is understood that the splitting element serves not only to split the respective input beams into the two partial beams, but also to coherently superimpose them.

[0025] In a further embodiment, the interferometer of the third combination device comprises a splitting element for splitting the first and second coherently superimposed superimposed beams into the two partial beams, as well as a combining element for coherently superimposing the two partial beams to form the output beam. As described above, in this case, the first and second combination devices are preferably not designed as interferometers.

[0026] With the help of an interferometer, in particular a Mach-Zehnder interferometer, the power of the output beam can be reduced and the polarization state or polarization direction of the output beam can be adjusted through a controlled adjustment of the phases of the individual input beams to one another via reduced constructive interference. It goes without saying that with the help of such an interferometer, only the power or only the polarization state of the output beam can be adjusted. The interferometer usually has at least one optical component or a combination of optical components for phase and / or polarization adjustment between the two partial beams orbetween the two beam channels to ensure that, with a suitable choice of the relative phase position of the two partial beams, maximum constructive interference occurs at the combining element where the coherent superposition of the two partial beams occurs. The combining element of the interferometer typically generates a diagnostic beam upon coherent superposition of the two partial beams. This diagnostic beam can be used, for example, to determine the power levels and relative phase positions of the two partial beams, as well as the phase shift between the two beam channels of the interferometer, and to adjust them if necessary, as described above.

[0027] In a further development, the interferometer has at least one polarization-influencing device for the preferably fixed influencing of a polarization state, in particular a polarization direction, of at least one of the partial beams. As described above, the polarization state of one or both partial beams can be influenced by a suitable polarization-influencing device such that maximum constructive interference occurs at the combination element for at least one phase position of the two partial beams relative to one another. A fixed influencing of the polarization state means that there is no dynamic influencing of the polarization state, since the dynamic adjustment of the polarization state and the power of the output beam occurs solely by adjusting the relative phase positions of the input beams.However, the polarization influencing device can in principle be designed to be controllable in order to compensate for different parasitic losses in the two beam channels, thermal effects, etc., as described above.

[0028] The polarization-influencing device(s) are preferably designed as polarization-rotating optical devices or elements (polarization rotators), in particular in the form of optical rotators, for example in the form of optical crystals which, due to their crystalline structure and when suitably aligned, exhibit an intrinsic polarization rotation, e.g., crystalline quartz, which exhibits high transparency and performance across a broad wavelength range from UV to NIR. In principle, Faraday rotators can also be used as polarization-influencing devices. However, Faraday rotators require an external magnetic field for polarization rotation and are therefore more complex to manufacture and operate than optical crystals. For the present application, it is advantageous or necessary that the polarization rotation of the partial beam(s) occurs independently of the polarization direction of the respective partial beam.Such a polarization rotation is typically not possible with birefringent delay devices, e.g. with λ / 2 delay elements, since these only allow a rotation of the polarization direction for a given polarization direction of the respective partial beam.

[0029] In one embodiment, the splitting element and the combining element are designed as intensity beam splitters, and the interferometer has, as a polarization-influencing device, at least one polarization-rotating optical device, in particular an optical rotator, for perpendicularly aligning the polarization directions of the two partial beams relative to one another. For the purposes of this application, an intensity beam splitter is understood to be a beam splitter that enables the splitting or combination of two or more partial beams essentially independent of their polarization state. The intensity beam splitters described here are generally designed as 50% beam splitters, i.e., they combine two beams entering the intensity beam splitter with equal weighting to form one exiting beam.The intensity beam splitter can, for example, be implemented in the form of a dielectric layer system on the surface of a transparent substrate. With a suitable orientation of the surface to the beam incidence direction, the desired polarization-independent reflectivity and transmission of essentially 50% each can be achieved.

[0030] In the simplest case, an optical rotator can be arranged in one of the two beam channels of the interferometer to align the polarization directions of the two partial beams, causing a 90° rotation of the polarization direction of the partial beam propagating in this beam channel. However, it is understood that two or possibly more than two polarization-rotating optical devices or elements can also be arranged in the beam channels of the interferometer to align the polarization directions of the two partial beams at an angle of 90° relative to each other.

[0031] In a further development of this embodiment, the superposition device or the optical system into which the superposition device is integrated is designed to feed the first and second input beams, the third and fourth input beams, or the first and second superposition beams with circular polarization and opposite rotation directions to the splitting element of the interferometer. In the three cases mentioned, the first, second, or third combination device comprises the interferometer. If the interferometer is integrated into the third combination device, the power of the first and second superposition beams can be adjusted by adjusting the relative phase position of the first and second input beams in the first combination device and the relative phase position of the third and fourth input beams in the second combination device.To adjust the power of the respective heterodyne beam, the first and / or second combination device can, for example, comprise an intensity beam splitter. In this case, the first input beam and the second input beam are typically circularly polarized and have the same direction of rotation. Accordingly, the third and fourth input beams are also circularly polarized and have a direction of rotation opposite to that of the first and second input beams. In this way, the power of the two heterodyne beams can be adjusted independently of each other.

[0032] If the output beam is to have maximum power, it is necessary for the first and second input beams in the first combination device to maximally interfere constructively with the first heterodyne beam, and for the third and fourth input beams in the second combination device to maximally interfere constructively with the second heterodyne beam. This can be the case, for example, if the first and second input beams have a relative phase position of 0° to each other or—depending on the output of the intensity beam splitter from which the heterodyne beam emerges—if the first and second input beams have a phase position of 90° to each other.In the event that the relative phase position of the input beams entering the superposition device changes prior to superposition with the respective superposition beam, for example, if a phase shift occurs during reflection, the phase position of the input beams must be adjusted accordingly so that the relative phase position in the superposition beam corresponds to 0°. The same applies to the third and fourth input beams and the second combination device.

[0033] By adjusting the relative phase position of the first and second superposition beams relative to each other, the polarization direction of the linearly polarized partial beams in the two beam channels of the interferometer can be specified. The polarization directions of the two partial beams, which are linearly polarized after coherent superposition at the interferometer's splitting element, are aligned perpendicular to each other. To ensure identical alignment of the polarization directions of the two superposition beams at the interferometer's combining element, the polarization-rotating device or element is used, which rotates the polarization direction of the two partial beams relative to each other by 90°.If the two superimposed beams have the same power, a linearly polarized output beam is generated at the output of the superimposing device. The polarization direction can be adjusted by specifying the relative phase position between the first and second superimposed beams. If the two superimposed beams have a maximum power, the superimposition at the combining element of the interferometer produces an output beam with maximum power that corresponds to the sum of the powers of the input beams. Ideally, full constructive interference always occurs during superimposition at the output of the interferometer.

[0034] In an alternative embodiment, the splitting element and the combining element are designed as polarization beam splitters, and the interferometer has two polarization-rotating optical devices, in particular two optical rotators for rotating a polarization direction of one of the two partial beams by 45°, as a polarization-influencing device. In contrast to the embodiment described above, in which it is not important how the rotation of the polarization direction of the two partial beams by 90° relative to one another is distributed between the two beam channels, when using polarization beam splitters it is advantageous if the rotation of the polarization direction is symmetrical in both beam channels, i.e. if both partial beams are rotated by 45°.

[0035] In this embodiment, the two partial beams propagating in the two beam channels of the interferometer are typically elliptically polarized partial beams. By rotating the phase position of the two partial beams by 45°, a linearly polarized output beam can be generated. With a suitable choice of the relative phase position, superposition to form an output beam with maximum constructive interference can be achieved. When using polarization beam splitters as described here, increased effort is required to ensure maximum constructive interference due to the lower symmetry compared to intensity beam splitters. In the embodiment described here, the two optical rotators described above are required for this purpose.

[0036] In a further development of this embodiment, the superposition device comprises at least two polarization-influencing, in particular polarization-rotating, optical elements, in particular in the form of optical rotators, which are arranged in the beam path upstream of the splitting element of the interferometer and which are preferably designed to rotate a polarization direction of the first and second input beams, the third and fourth input beams, or the first and second superposition beams by 45°. If the third superposition device comprises the interferometer, a polarization-rotating optical element can be arranged in the beam path of the first and second superposition beams upstream of the splitting element of the interferometer.

[0037] If the interferometer is integrated into the first combination device or the second combination device, a respective polarization-rotating element can be arranged in the beam path of the first and second input beams or in the beam path of the third and fourth input beams, respectively, before these are superimposed to form the first and second superposition beams, respectively. With appropriate alignment of the preferred axis(es) of the polarization beam splitters of the interferometer and the polarization beam splitters of the other combination devices (at 45° to each other), the additional polarization-rotating optical devices can be omitted.

[0038] In the embodiment described here, in which the splitting element and the combining element are designed as polarization beam splitters, the first and second input beams are typically linearly polarized, and their polarization directions are rotated by 90° to each other. Similarly, the third and fourth input beams are linearly polarized, and their polarization directions are rotated by 90° to each other. Adjusting the relative phase position of the first and second input beams and the relative phase position of the third and fourth input beams typically generates an elliptically polarized heterodyne beam.By adjusting the phase position of the first and second input beams relative to each other, the phase position of the third and fourth input beams relative to each other and the phase position of the two superposition beams relative to each other in combination with a rotation of the polarization direction of the elliptical polarization in front of or in the interferometer(s), the power and the polarization state of the output beam can also be adjusted independently of each other in this case.

[0039] In a further embodiment, the first combination device for coherently combining the first input beam and the second input beam, the second combination device for coherently combining the third input beam and the fourth input beam, and / or the third combination device for coherently combining the first heterodyne beam and the second heterodyne beam comprise an intensity beam splitter or a polarization beam splitter. In this embodiment, the respective combination device typically does not comprise an interferometer or is not designed as an interferometer. The respective combination device generally comprises precisely one polarization beam splitter or precisely one intensity beam splitter for coherently combining the first and second input beams, the third and fourth input beams, or the first and second heterodyne beams.

[0040] If the superposition device does not include an interferometer, it is typically required that both the first and second combination devices have a polarization beam splitter, or that the third combination device has a polarization beam splitter. It is understood that all three combination devices can also each have a polarization beam splitter. If the beam emerging from the respective combination device is to have a linear polarization, a phase shifting device in the form of a λ / 4 delay device is typically required, which is arranged downstream of the polarization beam splitter in the beam path (see below).

[0041] In a further development of this embodiment, the superposition device or the optical system into which it is integrated is designed to feed the first and second input beams, the third and fourth input beams, or the first and second superposition beams, each with an identical polarization state, in particular with an identical polarization direction, to the intensity beam splitter. In this case, with coherent combination, the power of the beam emerging from the intensity beam splitter can be adjusted by adjusting the relative phase position of the beams entering the intensity beam splitter. The (linear) polarization state, in particular the polarization direction, of the beams entering the intensity beam splitter is retained.By adjusting the relative phase position, both maximum constructive interference and maximum destructive interference with respect to the respective heterodyne beam or output beam can generally be generated in the coherent combination in the intensity beam splitter.

[0042] In a further embodiment, the superposition device or the optical system into which it is integrated is designed to feed a first and second input beam, a third and fourth input beam, or a first and second superposition beam to the polarization beam splitter, each having two mutually perpendicular polarization directions. In this case, the polarizer axis(es) are typically aligned parallel to the two mutually perpendicular polarization directions. The coherent combination of the beams entering the polarization beam splitter generally produces an elliptically polarized outgoing beam in which the semi-axes (preferential axes or directions) of the elliptical polarization are aligned at 45° to the two mutually perpendicular polarization directions of the incoming beams.By aligning the preferred axis of a λ / 4 delay device to coincide with the 45° preferred axis, elliptical polarization is converted to linear polarization, whose polarization direction is determined by the principal axis ratio and the direction of rotation of the elliptical polarization. Adjusting the relative phase position between the beams entering the polarization beam splitter changes the aspect ratio between the semi-axes of the elliptical polarization, but not the orientation of the semi-axes at 45° to the two mutually perpendicular polarization directions. The polarization components of the beams entering the polarization beam splitter that are not aligned parallel to a respective polarizer axis do not contribute to the power of the outgoing beam.By aligning the polarization direction of the rays entering the polarization beam splitter, the power of the outgoing beam can be adjusted.

[0043] In a further development, the first combination device is designed to adjust a polarization state, in particular to rotate a polarization direction, of the first superposition beam depending on a relative phase position between the first, preferably linearly polarized input beam and the second, preferably linearly polarized input beam, and / or the second combination device is designed to adjust a polarization state, in particular to rotate a polarization direction, of the second superposition beam depending on a relative phase position between the third, preferably linearly polarized input beam and the fourth, preferably linearly polarized input beam, and / or the third combination device is designed to adjust a polarization state of the output laser beam, in particular to rotate a polarization direction of the output laser beam,depending on a relative phase position between the first superposition beam and the second superposition beam. In the embodiment described here, the first, second, and / or third combination device for coherent combination comprise an intensity beam splitter or a polarization beam splitter. In this case, the polarization state can be adjusted using suitable optical elements, in particular the polarization direction of a respective superposition beam or the output beam can be rotated.

[0044] In a further development, the first, second and / or third combination devices for generating a linear polarization of the first superposition beam, the second superposition beam and / or the output beam have a phase shift element, in particular a λ / 4 delay device, which is arranged in the beam path after the intensity beam splitter or the polarization beam splitter. The λ / 4 delay device can, for example, be a λ / 4 delay plate, but the λ / 4 delay device can also be designed in a different way, for example as an integrated, e.g. fiber-optic component. The λ / 4 delay device can also have a plurality of optical components in order to generate the phase-shifting effect. The optical axis orThe preferred direction of the λ / 4 delay device is typically aligned parallel to one of the semi-axes, for example, the long semi-axis, of the generally elliptical polarization with which a respective beam enters the λ / 4 delay device. This ensures that the λ / 4 delay device generates a linear polarization of the respective exiting beam. If the λ / 4 delay device is arranged downstream of a polarization beam splitter in the beam path, the optical axis or preferred direction of the λ / 4 delay device is typically aligned at an angle of 45° to the polarizer axis.

[0045] By appropriately selecting the polarization state or polarization directions of the first and second input beams, the third and fourth input beams, and / or the first and second heterodyne beams, it can be ensured that the orientation of the principal axes of the elliptical polarization state of the beam entering the λ / 4 delay device is always at 45° to the optical axis of the λ / 4 delay device. As described above in connection with the polarization beam splitter, by adjusting the relative phase position of the first and second input beams, the second and third input beams, or the first and second heterodyne beams relative to one another, the aspect ratio of the elliptical polarization state can be adjusted, which causes a rotation of the polarization direction of the beam exiting the λ / 4 delay device.

[0046] In a further embodiment, the four inputs are designed for the entry of at least four further input beams, and the output is designed for the exit of at least one further output beam coherently combined from the four further input beams. In principle, it is possible to generate a number of N output beams from a number of 4 N input beams by coherent superposition with the aid of the superposition device. In this case, a plurality of groups of four input beams each can be fed to a respective first, second, and third combination device, for which the relative phase position to one another is adjusted independently of one another, such that the power and polarization state can be adjusted independently of one another for each output beam.In the simplest case, the groups of four input beams each are fed to the optical elements of the first, second and third combination device in a laterally offset manner, so that the input beams and also the superposition beams formed from them of all groups each pass through one and the same optical elements.

[0047] The beam source of the optical system is preferably a seed laser of a MOPA (Master Oscillator Power Amplifier) ​​system. In this case, the four input beams are generated by amplifying the seed laser beam. In principle, it is possible to position the phase modulation device in the beam path directly upstream of the inputs of the superposition device. However, in the case of a MOPA system, it is advantageous if the relative phase positions of the four input beams are adjusted using a phase modulation device located upstream of the final amplifier of the MOPA system. In this way, optical elements that do not require high performance or high efficiency can be used in the phase modulation device.The average power and / or peak power of the output beam of such a MOPA system can be high, for example, more than 1 W, 10 W, 1 kW, 10 kW, or even 1 MW.

[0048] The output beam is typically fed to an application device of the optical system, which is usually a processing device, e.g., a processing head, for processing a workpiece using the output beam. For positioning the output beam(s) (see below) relative to the workpiece, translation units for moving the processing head and / or the workpiece can also be provided. Dynamic beam positioning (2D, 2.5D), spatiotemporal beam shaping, position detection (before the process), and process control (in-situ, ex-situ) can also be performed.

[0049] When the output beam is fed to the workpiece, polarization can also be influenced in the application device. For example, the application device for feeding the output beam to the workpiece can have a birefringent component, e.g., an optical fiber, in particular a fiber-based amplifier. In this case, the superposition device can pre-compensate for the birefringence generated when the output beam is fed to the workpiece. Typically, the pre-compensation is performed by suitably adjusting the relative phase positions, which are set by the phase modulation device, so that the desired combination of polarization state and output beam power is achieved on the workpiece.In this way, non-polarization-maintaining transport fibers can also be used or the MOPA concept can be modified by performing the superposition before the (typically fiber-based) final amplifier, which in this case is integrated into the application device.

[0050] In addition to the above-described application of the optical system for writing voxels for data storage in transparent materials, the optical system can also be used, among other things, for the production of optical components based on spatially dependent polarization manipulation. The rapid polarization change generated by the optical system can also be advantageously used for other applications, such as analytical methods.

[0051] The optical system may also include a conversion device arranged between the phase modulation device and the superposition device. The conversion device may be an optical amplifier device, for example, the final amplifier(s) of the MOPA system described above. The conversion device may also perform another function.

[0052] The conversion device can, for example, be designed for frequency conversion of the input beams. This is advantageous because the output beam or the application for which the output beam is used often requires wavelengths for which no high-performance amplifier system, phase modulation device, or other optical components are available. In this case, the coherent coupling in the superheterodyne device can be combined with frequency conversion, which usually takes place in the beam path upstream of the superheterodyne device.

[0053] The optical system described here, in particular in the form of a MOPA system, is compatible with a frequency conversion device arranged between the beam source and the superposition arrangement.

[0054] The beam source for generating the laser beam can be configured to generate a c / w laser beam and / or a pulsed laser beam. The beam source can, in particular, be configured to generate an ultrashort pulse laser beam with laser pulses whose pulse durations are on the order of ps or fs. So-called chirped pulse amplification (CPA) is often used in ultrashort pulse lasers, in which temporally stretched pulses are amplified and subsequently compressed. CPA technology can be combined with the coherent coupling of the four input beams to the output beam described here, and in particular with the independent adjustment of the polarization state and the power of the output beam. In this case, the conversion device can, for example, form a pulse compressor of the CPA system. However, the conversion device can also be configured generally for pulse shaping of the input beams, which in this case are pulsed.

[0055] It is understood that the conversion device can also be designed to fulfill several of the functions described above or that the optical system can have several conversion devices.

[0056] In the beam path between the beam source and the superposition device, in particular in the beam path between the conversion device and the superposition device, as well as in the beam path of the output beam behind the superposition device, a suitable beam guide can be provided, which can comprise, for example, a scanner optics.

[0057] In a further embodiment, the splitting device is designed to split the laser beam or a further laser beam generated by the beam source into at least four further coherent input beams, the phase modulation unit is designed to modulate the relative phase positions of the at least four further input beams, and the superposition device is designed to coherently superpose the at least four further input beams to form at least one further output beam.

[0058] In this embodiment, the optical system is designed to form one output beam from several groups of four input beams each by coherent superposition. Through coherent superposition, the power and polarization state can be adjusted independently of each other for each output beam, i.e., the powers and polarization states of the output beams can be modulated independently of each other. However, it is also possible for several output beams to be generated in the optical system, where the powers and polarization states cannot be modulated independently of each other. Simultaneous redistribution to different output beams or scanning of output beams based on extended coherent coupling as well as 2D or 3D multiplexing is also possible.

[0059] It is understood that the optical system may additionally be configured to generate at least one output beam that is not generated by a coherent superposition of input beams and whose power and / or polarization state are not adjustable. The use of such an output beam may be advantageous for certain applications.

[0060] In one embodiment, the optical system is designed to feed the four input beams and / or the at least four further input beams to the four inputs of the superposition device with substantially the same power. As described above in connection with the superposition device, it is advantageous for coherent superposition if the four mutually coherent input beams have substantially the same power or intensity. This can be achieved, for example, if the power of a laser beam generated by the beam source is divided equally among the four mutually coherent input beams in the splitting device. As described above, it is possible to deviate from an identical power of the four input beams if they experience different losses when passing through the superposition device.The power of the individual input beams can be adjusted to compensate for the different losses as they pass through the heterodyne device. This ensures that the power that can be coupled from the input beams into the respective heterodyne beam and the power that can be coupled from the heterodyne beams into the output beam are consistent, so that an ideally complete interference contrast can be achieved in the heterodyne beams and the output beam, respectively.

[0061] In a further embodiment, the optical system is configured to feed the four input beams and / or the four additional input beams to the four inputs of the superposition device with linear polarization in a predetermined polarization direction or with circular polarization. As described above in connection with the superposition device, it is advantageous if the input beams are fed to the superposition device with a defined polarization state.

[0062] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0063] They show: Fig. 1a-c schematic representations of three embodiments of a superposition device, which has three combination devices for the coherent superposition of four mutually coherent input beams, one or two of which are designed as Mach-Zehnder interferometers, Fig. 2a-d schematic representations of four superposition devices analogous to Fig. 1a-c , in which at least one combination device has a λ / 4 delay device arranged in the beam path after an intensity beam splitter or a polarization beam splitter, Fig. 3a,b schematic representations of superposition devices analogous to Fig. 2b or Fig. 2d , in which a common polarization beam splitter is used for two or for all three combination devices, Fig. 4 a schematic representation of a superposition device analogous to Fig. 2d , which is designed to superimpose three groups of four mutually coherent input beams to form one coherent output beam, Fig. 5a-c schematic representations of optical systems which comprise a superimposition device according to Fig. 1a-c , Fig. 2a-d or Fig. 3a,b and Fig. 6 a schematic representation of an optical system comprising a superposition device according to Fig. 4 has.

[0064] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0065] Fig. 1a-c each show a superposition device 5 for the coherent superposition of four mutually coherent input beams 1 to 4 to form a superimposed output beam 6. The superposition device 5 has four inputs E1 to E4, each of which serves for the entry of one of the four input beams 1 to 4. The superposition device 5 also has an output A, which serves for the exit of the output beam 6 formed during the coherent superposition. The superposition device 5 is designed to collinearly superpose the four input beams 1 to 4, wherein in the examples shown, a congruent superposition with the output beam 6 occurs.

[0066] The one in Fig. 1a-c What the superposition devices 5 shown and the superposition devices described below have in common is that they allow a power PA and a polarization state of the output beam 6 to be adjusted independently of one another. In the examples shown, the polarization state adjusted with the aid of the superposition device 5 is a polarization direction R of a linearly polarized output beam 6.

[0067] While the beam paths in Fig. 1a-c and are shown in the plane of the drawing in the following figures, the polarization states are shown in a propagation direction perpendicular to the plane of the drawing. The X-direction of the Fig. 1a-c The polarization states shown correspond to the s-component, the Y-direction to the p-component of the polarization.

[0068] The Fig. 1a-c The superposition devices 5 shown and the superposition devices 5 described further below make it possible to set a power PA of the output beam 6 which - apart from parasitic losses when passing through the optical elements of the superposition device 5 - corresponds to the sum of the powers P 1 to P 4 of the four input beams 1 to 4. In principle, the power PA of the output beam 6 can be continuously set between a value which corresponds to the sum of the powers P 1 to P 4 of the input beams 1 to 4, ie 100% of the input power, and a value of 0% of the input powers P 1 to P 4 of the input beams 1 to 4.

[0069] The independent adjustment of the power PA and the polarization direction R of the output beam 6 is achieved by setting the relative phase positions Δφ 1,2 ; Δφ 3,4 ; Δφ 12,34 of the Fig. 1a-c shown phases φ 1 , φ 2 , φ 3 , φ 4 of the four input beams 1 to 4. The independent adjustment of the power PA and the polarization direction R of the output beam 6 is typically carried out exclusively by adjusting the relative phase positions Δφ 1,2 ; Δφ 3,4 ; Δφ 12,34 of the four input beams 1 to 4, i.e. without other parameters of the four input beams 1 to 4 or parameters of optical components of the superposition device 5 being changed for this purpose. The powers P 1 to P 4 of the four input beams 1 to 4 are generally the same or are selected to be different in order to pre-compensate for parasitic losses. The powers P 1 to P 4 of the four input beams 1 to 4 are also not changed for the adjustment.Since the relative phase positions Δφ 1.2 ; Δφ 3.4 ; Δφ 12.34 of the four input beams 1 to 4 can be adjusted highly dynamically, the power PA and the polarization direction R of the output beam 6 can also be adjusted highly dynamically with the aid of the superposition device 5.

[0070] The one in Fig. 1a-c What is common to the superposition devices 5 shown and those described below is that they are designed to carry out a two-stage coherent superposition with the aid of three combination devices K1 to K3: A first combination device K1 serves to coherently combine the first input beam 1 and the second input beam 2 to form a first superposition beam U1. A second combination device K2 serves to coherently combine the third input beam 3 and the fourth input beam 4 to form a second superposition beam U2. A third combination device K3 serves to form the output beam 6 by a coherent superposition of the first superposition beam U1 and the second superposition beam U2.

[0071] The properties of the first superposition beam U1 formed during the coherent combination or superposition of the first and second input beams 1, 2 in the first combination device K1 depend on the relative phase position Δφ 12 of the first and second input beams 1, 2, which corresponds to the phase difference Δφ 12 = φ 1 - φ 2 between the phase φ 1 of the first input beam 1 and the phase φ 2 of the second input beam 2. Accordingly, the properties of the second superposition beam U2 formed during the coherent combination or superposition of the third and fourth input beams 3, 4 in the second combination device K2 depend on the relative phase position Δφ 34 of the third and fourth input beams 3, 4, which corresponds to the phase difference Δφ 34 = φ 3 - φ 4 between the phase φ 3 of the third input beam 3 and the phase φ 4 of the fourth input beam 4.

[0072] The properties of the output beam 6 depend on the properties of the first superposition beam U1, the properties of the second superposition beam U2 and the relative phase difference Δφ 12,34 between the first and second input beams 1, 2 and the third and fourth input beams 3, 4. Since an absolute phase of the four input beams 1 to 4 plays no role in the formation of the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34, the relative phase difference Δφ 12,34 can be defined, for example, as the phase difference Δφ 12,34 = (φ 1 + φ 2 ) / 2 - (φ 3 + φ 4 ) / 2 between the first input beam 1 and the third input beam 3. The parameters used to independently adjust the power PA and the polarization direction R during coherent superposition are therefore the three relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34 of the four input beams 1 to 4 described here.

[0073] The Fig. 1a-c The superposition devices 5 shown each have at least one combination device K1, K2, K3, which forms a Mach-Zehnder interferometer 7a-c. Fig. 1a,b The third combination device K3 is designed as a Mach-Zehnder interferometer 7c, in which Fig. 1c In the example shown, the first and second combination devices K1, K2 are designed as Mach-Zehnder interferometers 7a,b.

[0074] The Fig. 1a The superposition device 5 shown has a first combination device K1, which has an intensity beam splitter 8a for the coherent superposition of the first and second input beams 1, 2 to form the first superposition beam U1. Accordingly, the second combination device K2 of the superposition device 5 also has an intensity beam splitter 8b for the coherent superposition of the second and third input beams 3, 4 to form the second superposition beam U2.

[0075] As described above, the third combination device K3 is designed as a Mach-Zehnder interferometer 7c and has a first beam channel 10 and a second beam channel 11. The Mach-Zehnder interferometer 7c also comprises a splitting element 12 for the coherent superposition and splitting of the two superposition beams U1, U2 into a first partial beam T1, which propagates in the first beam channel 10, and a second partial beam T2, which propagates in the second beam channel 11. A combination element 13 serves for the coherent superposition of the two partial beams T1, T2 to form the output beam 6. A first reflector 14 is arranged in the first beam channel 10 and deflects the first partial beam T1 by 90° toward the combination element 13. Accordingly, a second reflector 15 is arranged in the second beam channel 11, which deflects the second partial beam T2 by 90° to the combination element 13.

[0076] At the Fig. 1a In the superposition device 5 shown, the splitting element 12 and the combining element 13 are designed as (non-polarizing) 50% intensity beam splitters. The Mach-Zehnder interferometer 7c of Fig. 1a has a polarization-influencing device in the form of a polarization-rotating optical element, which is an optical rotator 16 in the form of a suitably aligned quartz crystal. The optical rotator 16 causes a rotation of a polarization direction R2 of the second partial beam T2 by 90°, so that the polarization direction R2 of the second partial beam T2, after passing through the optical rotator 16, is aligned parallel to the polarization direction R1 of the first partial beam T1. It is understood that such a parallel alignment of the two partial beams T1, T2 can also be achieved if, instead of a single optical rotator 16, two or more optical rotators are arranged in the respective beam channels 10, 11, which cause a suitable rotation of the respective polarization directions R1, R2 of the two partial beams T1, T2.

[0077] At the Fig. 1a In the superposition device 5 shown, the first and second combination devices K1, K2 each have an intensity beam splitter 8a, 8b for coherent superposition. For the coherent superposition in the superposition device of Fig. 1a The first input beam 1 and the second input beam 2 are fed with circular polarization, i.e., with a circular polarization state, to the first combination device K1. Accordingly, the third input beam 3 and the fourth input beam 4 are fed with circular polarization to the second combination device K2. A rotation direction D1 of the circular polarization state of the first and second input beams 1, 2 is opposite to a rotation direction D2 of the circular polarization state of the third and fourth input beams 3, 4.

[0078] By adjusting the relative phase position Δφ 12 between the first input beam 1 and the second input beam 2, the value of the power of the first superposition beam U1 can be set between 0% and 100% of the sum of the powers P 1 , P 2 of the first and second input beams 1, 2 during coherent superposition in the intensity beam splitter 8a of the first combination device K1. Correspondingly, by adjusting the relative phase position Δφ 34 between the third input beam 1 and the fourth input beam 2 during coherent superposition in the intensity beam splitter 8b of the second combination device K2, the value of the power of the first superposition beam U2 can be set between 0% and 100% of the sum of the powers P 3 , P 4 of the third and fourth input beams 3, 4. In this way, the power PA orthe intensity of the output beam 6 can be adjusted by means of the first and second combination devices K1, K2.

[0079] The polarization direction R of the output beam 6 is determined in the Fig. 1a shown example by setting or specifying the phase position Δφ 12,34 between the two pairs of input beams 1,2 and 3,4: During the coherent superposition at the splitting element 12 of the Mach-Zehnder interferometer 7c of the third combination device K3, the two linearly polarized partial beams T1, T2 described above are formed from the two counter-circularly polarized superposition beams U1, U2, the polarization directions R1, R2 of which are initially rotated by 90° to one another, but are aligned parallel to one another with the aid of the optical rotator 16, so that the linearly polarized output beam 6 is generated with the desired polarization direction R, which can be set independently of the power PA.

[0080] The Fig. 1a The superposition device 5 shown has three diagnostic outputs D, which form a respective second, inverted output of the first intensity beam splitter 8a of the first combination device K1, the second intensity beam splitter 8b of the second combination device K2, or the combination element 13 of the third combination device K3. Three diagnostic beams emerge from the three diagnostic outputs D, which can be used to determine and monitor the polarization state or polarization direction R and the power PA of the output beam 6 or a respective superposition beam U1, U2.

[0081] This is possible because the sum of the power of the diagnostic beam at the diagnostic output D and the power at the output A of the third combination device K3 is constant and independent of the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34 . The polarization direction of the diagnostic beam is also perpendicular to the polarization direction R of the output beam 6. Therefore, the actual value of the polarization direction R and the actual value of the power PA of the output beam 6 can be indirectly measured at the diagnostic output D. This measurement can be used to adapt or regulate the respective power P 1 to P 4 and the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34 of the input beams 1 to 4 in order to set the target value of the polarization direction R or the power PA of the output beam 6.For this purpose, the optical rotator 16 or other optical components of the superposition device 5 can also be influenced, which can be configured to be adjustable for this purpose. However, control using the diagnostic outputs D typically runs on a longer time scale than the highly dynamic adjustment of the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34 of the input beams 1 to 4.

[0082] Since the diagnostic beam exiting at diagnostic output D is inverted from output beam 6, this can be used not only for diagnostic purposes but also as an additional output beam, which, like output beam 6, is used in an application. For example, in an application involving writing voxels for optical data storage in the volume of transparent materials, diagnostic output D or the diagnostic beam can be used for the parallel writing of "inverted" voxels, which can be used to improve data security and for error correction during data readout. The same applies to diagnostic outputs D of the superposition devices 5 described below.

[0083] Fig. 1b shows a superposition device 5, which differs from the one shown in Fig. 1a shown superposition device 5 essentially in that the first combination device K1 and the second combination device K2 comprise a polarization beam splitter 9a and 9b respectively instead of the polarization beam splitter 9a and 9b shown in Fig. 1a The intensity beam splitter 8a,b shown in Fig. 1. The splitting element 12 and the combining element 13 of the Mach-Zehnder interferometer 7c are also Fig. 1b shown example is designed as a polarization beam splitter. The polarization beam splitters 9a,b, 12, 13 are in Fig. 1b and marked in the following figures with a dot and a double arrow (s / p polarization) to distinguish them from the intensity beam splitters.

[0084] The Fig. 1b The superposition device 5 shown differs from that shown in Fig. 1a shown superposition device also in that the interferometer 7c has two polarization influencing devices in the form of two polarization-rotating optical rotators 16a,b, which are designed to rotate a polarization direction R1, R2 of one of the two partial beams T1, T2 by 45° and which are arranged in the first beam channel 10 and in the second beam channel 11, respectively.

[0085] The Fig. 1b The superposition device 5 shown differs from that shown in Fig. 1a shown superposition device in that in the beam path after a respective polarization beam splitter 9a,b of the first or second combination device K1, K2, a further polarization-rotating optical element 17a,b is arranged for rotating the polarization direction of the first superposition beam U1 by 45° and for rotating the polarization direction of the second superposition beam U2 by 45°.

[0086] As in Fig. 1b As can be seen, the first and second input beams 1, 2, which are fed to the first combination device K1, are linearly polarized and their polarization directions are aligned perpendicular to each other. Accordingly, the third and fourth input beams 3, 4, which are fed to the second combination device K2, are also linearly polarized and their polarization directions are aligned perpendicular to each other. As shown in Fig. 1b As indicated, in the general case, a first, elliptically polarized superposition beam U1 is formed from the first and second input beams 1, 2, the polarization direction of which (long semi-axis of the elliptical polarization) is rotated by 45° with the aid of the further optical rotator 17a of the first combination device K1, and a second, elliptically polarized superposition beam U2 is formed from the third and fourth input beams 3, 4, the polarization direction of which is rotated by 45° with the aid of the further optical rotator 17b of the second combination device K2.

[0087] The Fig. 1b The superposition device 5 shown enables, in an analogous manner to the one shown in Fig. 1a shown superposition device 5 allows independent adjustment of the power PA and the polarization direction R of the output beam 6. As shown in Fig. 1b As can be seen, the superposition device 5 has only a single "inverting" diagnostic output D on the third combination device K3.

[0088] Deviating from the representation in Fig. 1b the further optical rotators 17a,b in the first and second combination device 17a,b can be dispensed with if the preferred axes of the polarization beam splitter 9a,b in the first and second combination device K1, K2 are rotated by 45° relative to the preferred axes of the splitting element 12, designed as a polarization beam splitter, and the combination element 13 of the third combination device K3.

[0089] Fig. 1c shows a superposition device 5, which differs from the one shown in Fig. 1b shown superposition device 5 in that not the third combination device K3, but the first and second combination devices K1, K2 are designed as Mach-Zehnder interferometers 7a,b. Fig. 1c In the example shown, in the beam path of the first and second input beams 1, 2, in front of the splitting element 12 of the interferometer 7a of the first combination device K1, a further optical rotator 17a, b is arranged, which causes a rotation of the respective polarization direction by 45°. Correspondingly, in the beam path of the third and fourth input beams 3, 4, in front of the splitting element 12 of the interferometer 7b of the second combination device K2, a further optical rotator 17c, d is arranged, which causes a rotation of the polarization direction by 45°. The superposition beams U1, U2 formed in the first and second combination devices K1, K2 are coherently superposed in a third combination device K3, which is designed as an intensity beam splitter 8c. The polarization directions of the four input beams 1 to 4 from Fig. 1c correspond to the polarization directions of the four input beams 1 to 4 of Fig. 1b .

[0090] As described above, with the help of the Fig. 1a-c described superposition devices 5, in which at least one of the combination devices K1 to K3 has an interferometer 7a-c, the polarization direction R and the power PA of the output beam 6 are adjusted independently of each other solely by adjusting the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34. Fig. 1a-c The superposition devices 5 shown can also be carried out using interferometers that are not Mach-Zehnder interferometers 7a-c.

[0091] At the Fig. 1a In the superposition device 5 shown, only intensity beam splitters 8a,b, 12, 13 were used, in which Fig. 1b In the superposition device 5 shown, only polarization beam splitters 9a,b, 12, 13 were used. However, it is understood that combinations of polarization and intensity beam splitters can also be used, as is the case, for example, with the superposition device 5 of Fig. 1c is the case. The Fig. 1a-c The superposition devices 5 shown are conceptually scalable, cascadable and flexible with regard to the order of the interferometers 7a,b,c and the other superposition components.

[0092] Fig. 2a-d show examples of superposition devices 5, which also allow the independent adjustment of the polarization direction R and the power PA of the output beam 6 and in which a maximum constructive interference of the four input beams 1 to 4 can be generated. Fig. 2a-d The superposition devices 5 shown are used for this purpose in contrast to the ones shown in Fig. 1a-c In the example shown, no interferometer 7a-c is required.

[0093] The one in Fig. 2a-d The superposition devices 5 shown have in common that the first, second and third combination devices K1, K2, K3 for the coherent superposition of the first and second input beams 1, 2, the third and fourth input beams 3, 4 and the first and second superposition beams U1, U2 each comprise either an intensity beam splitter 8a-c or a polarization beam splitter 9a-c. For the coherent superposition, it is typically necessary that at least one combination device K1, K2, K3 comprises a polarization beam splitter 9a-c. In the case of the Fig. 2a In the superposition device 5 shown, the third combination device K3 has a polarization beam splitter 9c, in which Fig. 2b-d In the superposition devices 5 shown, the first and second combination devices K1, K2 each have a polarization beam splitter 9a, 9b. A splitting into two partial beams T1, T2, as is the case with the interferometers 7a-c of Fig. 1a-c If this is the case, the combination devices K1 to K3 are Fig. 2a-d shown superposition devices 5 are not.

[0094] The one in Fig. 2a-d The superposition devices 5 shown also have in common that at least one of the first, second and third combination devices K1, K2, K3 for generating a linear polarization of the first superposition beam U1, the second superposition beam U2 or the output beam 6 has a phase shift element, in the examples shown in the form of a λ / 4 delay device 20a-c, which is arranged in the beam path after the intensity beam splitter 8a-c or the polarization beam splitter 9a-c of the respective combination device K1 to K3. The λ / 4 delay device 20a-c makes it possible, by setting a phase difference Δφ 12 ; Δφ 34 ; Δφ 12.34 between the first and second input beams 1, 2, the third and fourth input beams 3, 4 and the first and second superposition beams U1, U2, the polarization direction R1, R2, R of the first superposition beam U1, the second superposition beam U2 and the first and second superposition beams U1, U2 formed during the coherent superposition.of the output beam 6. In combination with the other stage in the two-stage superposition, this results in additional adjustability of the power PA of the output beam 6.

[0095] In the Fig. 2a-d The incoming beams are each fed to a respective intensity beam splitter 8a-c of the first, second or third combination device K1, K2, K3 with an identical polarization state, in Fig. 2a-c with an identical polarization direction: In the Fig. 2a In the superposition device 5 shown, the first and second input beams 1, 2, which are coherently superposed in the intensity beam splitter 8a of the first combination device K1, each have a linear polarization with an identical polarization direction. Accordingly, the third and fourth input beams 3, 4 of the second combination device K2 of the superposition device 5 of Fig. 2a each have a linear polarization state with identical polarization direction. Fig. 2c and shown superposition device 5, the two superposition beams U1, U2, which are fed to the intensity beam splitter 8c of the third combination device K3, have a linear polarization state with the same polarization direction. Fig. 2d The first and second superposition beams U1, U2 are fed to the third combination device K3, each with an identical elliptical polarization state, via the superposition device 5 shown.

[0096] In the event that a respective combination device K1 to K3 has a polarization beam splitter 9a-c for coherent superposition, the polarization directions R1, R2 of the beams entering it are Fig. 2a-d shown examples are aligned perpendicular to each other: In the Fig. 2a ,b, in which the third combination device K3 for coherent superposition has a polarization beam splitter 9c, the polarization directions R1, R2 of the first and second superposition beams U1, U2 are aligned perpendicular to each other. The same applies to the polarization directions R1, R2 of the first and second superposition beams U1, U2 shown in Fig. 2b shown superposition device 5. This is necessary in order to generate a power PA of the output beam 6 of 100% or 0% of the sum of the powers P 1 to P 4 of the input beams 1 to 4, ie in order to maximize the interference in order to be able to set a complete constructive interference or a complete destructive interference. In the event that the deflection device 5 is not intended to generate maximum or minimum constructive interference, a vertical alignment of the polarization directions R1, R2 can be deviated from if necessary. Likewise, in the Fig. 2b-d shown superposition devices 5, the polarization directions R1, R2 of the first and second input beams 1, 2 and the third and fourth input beams 3, 4, which enter the respective polarization beam splitters 9a,b of the first and second combination devices K1, K2, are each aligned perpendicular to each other. The polarizer axes of the polarization beam splitters 9a-c of the combination devices K1, K2, K3 of the superposition devices 5 of Fig. 2a-d are each aligned parallel to the polarization directions R1, R2 of the respective input beams 1 to 4.

[0097] At the Fig. 2a In the superposition device 5 shown, with the aid of the first combination device K1, the power of the first superposition beam U1 can be adjusted by adjusting the relative phase position Δφ 12 between the first input beam 1 and the second input beam 2 between 0% and 100% of the sum of the powers P 1 , P 2 of the two input beams 1, 2. The same applies to the second superposition beam U2, whose power is adjusted as a function of the relative phase position Δφ 34 between the third and fourth input beams 3, 4. The relative phase position Δφ 12 between the first and second input beams 1, 2 and the relative phase position Δφ 34 between the third and fourth input beams 3, 4 are preferably selected to be the same size, so that the two superposition beams U1, U2 strike the polarization beam splitter 9c of the third combination device K3 with the same power.

[0098] By adjusting the relative phase angle Δφ 12.34 between the first superposition beam U1 and the second superposition beam U2, the ellipticity, or more precisely the aspect ratio between the two semi-axes of the elliptical polarization at the output of the polarization beam splitter 9c of the third combination device K3, is adjusted. Due to the parallel alignment of the polarizer axes of the polarization beam splitter 9c to the polarization directions R1, R2 of the two superposition beams U1, U2, an elliptical polarization is generated during the coherent superposition in the polarization beam splitter 9c of the third combination device K3, the semi-axes of which are aligned at 45° to the polarization directions R1, R2 of the two superposition beams U1, U2.By means of the λ / 4 delay device 20c following in the beam path, which in the example shown is designed as a λ / 4 plate and whose preferred direction is parallel to the preferred direction of the elliptical polarization (ie in the case of the . Fig. 2b shown example at 45° to the polarizer axes or the polarization directions R1, R2), the elliptical polarization is converted into a linear polarization of the output beam 6. The polarization direction R of the output beam 6 depends on the aspect ratio of the elliptical polarization and can therefore be adjusted by adjusting the relative phase position Δφ 12.34.

[0099] At the Fig. 2b In the superposition device 5 shown, the first and second combination devices K1, K2 each have a polarization beam splitter 9a,b instead of an intensity beam splitter 8a,b, each of which is followed by a λ / 4 delay device 20a,b in the form of a λ / 4 plate. The operation of the first and second combination devices K1, K2 corresponds to that of the third combination device K3 of Fig. 2a : A superposition beam U1 is formed from the first and second input beams 1, 2, which is initially elliptically polarized before being linearly polarized at the λ / 4 delay device 20a of the first combination device K1. The same applies to the third and fourth input beams 3, 4, from which the second superposition beam U2 is formed in the second combination device K2. By adjusting the relative phase position Δφ 12 of the first and second input beams 1, 2 and the relative phase position Δφ 34 of the third and fourth input beams 3, 4, the respective linear polarization direction R1, R2 of the first and second superposition beams U1, U2 can be adjusted.The alignment of the polarization directions R1, R2 of the superposition beams U1, U2 relative to the preferred axis V of the polarization beam splitter 9c of the third combination device K3 makes it possible to adjust the distribution of the power of the superposition beams U1, U2 to the output A and to the diagnostic output D and thus the power PA of the output beam 6.

[0100] Deviating from the Fig. 2b In the illustration shown, the two λ / 4 delay devices 20a,b can be dispensed with if the polarizer axis V of the polarization beam splitter 9c of the third combination device K3 is aligned at an angle of 45° to the first and second polarization directions R1, R2, as shown in Fig. 2b Instead of the λ / 4 delay devices 20a,b, Fig. 2b Optical rotators can also be used, which cause a rotation of the polarization direction of the two superimposed beams U1, U2 by 45° and thus produce the same effect as the rotation of the polarization axis V of the polarization beam splitter 9c of the third combination device K3 by 45° to the first and second polarization direction R1, R2. In this case, the polarizer axes of the polarization beam splitter 9c of the third combination device K3 are aligned parallel to the first and second polarization direction R1, R2. In all cases described here, the preferred directions of polarization of the superimposed beams U1, U2 are aligned parallel to the polarizer axes of the polarization beam splitter 9c of the third combination device K3, since otherwise part of the power of the superimposed beams U1, U2 is fed to the diagnostic output D and cannot be introduced into the output beam 6.

[0101] The polarization directions R1, R2 of the two superimposed beams U1, U2 are preferably selected so that they introduce equal power components into the output beam 6. In this way, as in the superimposing device 5 of Fig. 2b an elliptical polarization aligned at 45° to the polarization directions R1, R2 of the two superimposed beams U1, U2 is generated. With the aid of the λ / 4 delay device 20c of the third combination device K3, a linear polarization state of the output beam 6 with an adjustable polarization direction R is formed from the elliptical polarization state of the output beam 6.

[0102] The Fig. 2c The superposition device 5 shown has a first and second combination device K1, K2, which, as in the case of the Fig. 2b shown superposition device 5 and which make it possible to specify the linear polarization direction R1, R2 of the first and second superposition beams U1, U2 by adjusting the respective relative phase positions Δφ 12 , Δφ 34 of the first and second input beams 1, 2 and of the third and fourth input beams 3, 4. In the Fig. 2c In the superposition device 5 shown, the relative phase positions Δφ 12 , Δφ 34 are preferably adjusted such that the two superposition beams U1, U2 have an identical polarization direction R1, R2. The power of the input beams 1 to 4 is adjusted such that, without the superposition, equal powers are transferred to the output beam 6. By adjusting the relative phase position Δφ 12,34 between the two superposition beams U1, U2, the power PA of the output beam 6 can be adjusted with the aid of the intensity beam splitter 8c of the third combination device K3 described above, specifically in a value range between 0% and 100% of the sum of the powers P 1 to P 4 of the input beams 1 to 4.

[0103] At the Fig. 2d In the superposition device 5 shown, the first and second combination devices K1, K2 for the coherent superposition each have a polarization beam splitter 9a,b, which generate a first and second elliptically polarized superposition beam U1, U2. With the identical powers P1 to P4 of the four input beams 1 to 4 assumed here, this results in elliptical polarization with main axes oriented at 45° to the polarizer axes V or to the two polarization directions R1, R2 of the respective input beams 1, 2 and 3, 4. By varying the relative phase positions Δφ12; Δφ34, the extreme values ​​of circular polarization and linear polarization can be traversed. In addition, the power coupled into the first superposition beam U1 and the second superposition beam U2 can be adjusted.Preferably, the two relative phase positions Δφ 12 ; Δφ 34 are selected to be equal in order to supply the two superimposed beams U1, U2 to the intensity beam splitter 8c of the third combination device with substantially equal power. The polarization, or more precisely, the elliptical polarization state of the two superimposed beams U1, U2, is also set identically in this way. In this way, upon superposition of the two superimposed beams U1, U2, a linearly polarized output beam 6 with an adjustable polarization direction R is generated by a λ / 4 delay device 20c arranged downstream of the intensity beam splitter 8c of the third combination device K3.

[0104] In the Fig. 2a-d In the superposition devices 5 shown, the three combination devices K1, K2, K3 for coherent superposition each have either an intensity beam splitter 8a-c or a polarization beam splitter 9a-c in the form of separate optical components. However, this is not necessarily the case; rather, two or more combination devices K1, K2, K3 can use one or more common optical components for coherent superposition.

[0105] Fig. 3a shows a superposition device 5, the functioning of which is the same as in Fig. 2b shown superposition device 5 and in which the three polarization beam splitters 9a-c are combined in a single optical component in the form of a common polarization beam splitter. The first and second input beams 1, 2, the third and fourth input beams 3, 4 and the two superposition beams U1, U2 are superposed at different positions along the common polarization beam splitter 9a, b, c. The two λ / 4 delay devices 20a, b of the first and second combination devices K1, K2 of the superposition device 5 of Fig. 2b are also designed in the form of a common λ / 4 delay plate 20a,b. Two deflection mirrors 14, 15 serve to deflect the first and second superimposed beams U1, U2 to the common polarization beam splitter 9a,b,c for coherent superposition to the output beam 6.

[0106] The Fig. 3b The superposition device 5 shown corresponds in its functionality to that shown in Fig. 2d The first and second combination devices K1, K2 are designed in the form of a common polarization beam splitter 9a,b. A deflection mirror 14 serves to deflect the first superposition beam U1 to the intensity beam splitter 8c, which, together with the λ / 4 delay plate 20c, forms the third combination device K3 of the superposition device 5.

[0107] The superposition devices 5 described above are designed for the coherent superposition of four input beams 1 to 4 to form a coherently superimposed output beam 6. However, the superposition device 5 can also be used to superimpose several groups of four input beams onto one output beam each assigned to the respective group.

[0108] Fig. 4 shows an example of such a superposition device 5', which is designed for the coherent superposition of three groups of four input beams 1a-c, 2a-c, 3a-c, 4a-c to form a respective common output beam 6a-c. As in the Fig. 3a,b In the examples shown, this is achieved by the two polarization beam splitters 9a, 9b being sufficiently large to enable the coherent superposition of the first and second input beams 1a-c, 2a-c and the third and fourth input beams 3a-c, 4a-c at different, laterally offset positions. The coherent superposition of the superposition beams formed in each case takes place accordingly at different, laterally offset positions of a common intensity beam splitter 8c. In this way, both the Fig. 4 The indicated linear polarization states of the three output beams 6a-c as well as their powers can be adjusted independently of one another. It is understood that not only three groups of input beams 1a-c, 2a-c, 3a-c, 4a-c, but a larger or smaller number of groups of input beams can be coherently superimposed using a suitably designed superposition device 5'.

[0109] Fig. 5a -cshow an optical system 30 which has a beam source 31 for generating a laser beam E and a splitting device 32 for splitting the laser beam E (more precisely the power of the laser beam E) equally between the four mutually coherent input beams 1 to 4, so that the four input beams 1 to 4 have identical powers P 1 to P 4 after splitting. The optical system 30 further comprises a phase modulation device 33 which is used for the rapid modulation of the relative phase positions Δφ 1,2 , Δφ 2,3 , Δφ 12,34 (cf. Fig. 1a ) of the four input beams 1 to 4. In the beam path after the phase modulation device 33, the superposition device 5 is arranged, which coherently superposes the four input beams 1 to 4 and forms the output beam 6. The superposition device 5 can, for example, be designed as in Fig. 1-c , Fig. 2a-d oder Fig. 3a,b shown.

[0110] The optical system 30 also has an application device 34, which in the example shown is a processing device in the form of a processing head used to process a workpiece using the output beam 6. For positioning the output beam 6 or multiple output beams 6a-c (see below) relative to the workpiece, the application device 34 can have translation units for moving the processing head and / or the workpiece. The application device can also have a scanner device for dynamic beam positioning (2 D, 2.5 D) and / or be designed to perform spatiotemporal beam shaping, position detection (before the process), and / or process control (in-situ, ex-situ).

[0111] In the Fig. 5a In the optical system 30 shown, the splitting device 32 is arranged in the beam source 31 and the beam source 31 couples the four input beams 1 to 4 into the phase modulation device 33. In the Fig. 5b In the optical system 30 shown, the splitting device 32 is arranged in the phase modulation device 33 and the beam source 31 couples the laser beam E into the phase modulation device 33. In the Fig. 5c In the optical system 30 shown, a conversion device 35 is arranged between the phase modulation device 33 and the superposition device 5. The conversion device 35 can fulfill one or more functions and be designed in different ways, as will be described in more detail below.

[0112] In the Fig. 5c In the example shown, the beam source 31 is a seed laser of a MOPA (Master Oscillator Power Amplifier) ​​system. The conversion device 35 in this case is a final amplifier of the MOPA system, in which the four input beams 1 to 4 are amplified before being fed to the superposition device 5. The phase modulation device 33 is in this case arranged in the beam path before the final amplifier or the conversion device 35. This is advantageous because in this case, optical components can be used in the phase modulation device 33 that do not need to have high performance or high efficiency. In contrast, the average power and / or peak power of the output beam 6 is high in an optical system 30 in the form of a MOPA system due to the use of the final amplifier.However, the conversion device 35 of the optical system 30 may also be a different type of optical amplifier.

[0113] The beam source 31 can be configured to generate a c / w laser beam and / or a pulsed laser beam E. The beam source 31 can, for example, generate an ultrashort pulse laser beam with laser pulses whose pulse durations are on the order of ps or fs. So-called chirped pulse amplification (CPA) is often used with ultrashort pulse lasers, in which temporally stretched pulses are amplified and subsequently compressed. The CPA technology can be combined with the coherent coupling of the four input beams 1 to 4 to the output beam 6 in the superposition device 5, as described here. In this case, the conversion device 35 can, for example, form or contain a pulse compressor of the CPA system. However, the conversion device 35 can also be configured generally for pulse shaping of the input beams 1 to 4, which in this case are pulsed.

[0114] The conversion device 35 can also serve for frequency conversion of the four input beams 1 to 4. In this case, the coherent superposition in the superposition device 5 is combined with a frequency conversion taking place in the conversion device 35 in the beam path upstream of the superposition device 5. The optical system 30, also in the form of a MOPA system, is compatible with a frequency conversion device arranged between the beam source 31 and the superposition arrangement 5.

[0115] It is understood that the conversion device 35 can also be configured to perform several of the functions described above or other functions. For example, the conversion device 35 can be used to adjust or adapt the beam or pulse parameters required for the respective application, such as pulse energy, pulse duration, etc. The conversion device 35 can also be used for beam transport or for flexible beam guidance. The optical system 30 can also have multiple conversion devices 35.

[0116] For example, a conversion device 35 can be integrated into the application device 34 and serve to influence the polarization of the output beam 6. For example, the application device 34 or the conversion device 35 for feeding the output beam 6 to the workpiece can have a birefringent component, e.g. an optical fiber, in particular a fiber-based amplifier. In this case, the superposition device 5 can pre-compensate for the birefringence generated when the output beam 6 is fed to the workpiece. Typically, the pre-compensation is carried out by suitably adjusting the relative phase positions Δφ 12 ; Δφ 34 ; Δφ 12,34 , which are set by the phase modulation device 33, so that the desired combination of polarization state or polarization direction R and power PA of the output beam 6 is achieved on the workpiece.In this way, non-polarization-maintaining transport fibers can also be used in the optical system 30, or the MOPA concept can be modified by performing the superposition before the (typically fiber-based) final amplifier, which in this case is integrated into the application device 34.

[0117] The Fig. 6 The optical system 30' shown differs from that shown in Fig. 5a-c shown optical system 30 in that the superposition device 5', which as in Fig. 4 shown, three groups, each with four input beams 1a to 4a, 1b to 4b, 1c to 4c are supplied. The four input beams 1a to 4a, 1b to 4b, 1c to 4c of the respective group are coherently combined in the superposition device 35' to form a respective common output beam 6a-c, which is supplied to an application device 34'. The phase modulation device 33' and the splitting device 32' are adapted to the total number of twelve input beams 1a to 4a, 1b to 4b, 1c to 4c. It is understood that the beam source 31' in the Fig. 6 shown example does not necessarily have to generate a single input beam E, which is divided into the total of twelve input beams 1a to 4a, 1b to 4b, 1c to 4c, since only the four input beams 1a to 4a, 1b to 4b, 1c to 4c in a respective group have to be coherent with each other.

[0118] The optical system 30' of Fig. 6 can therefore also have a beam source 31', which comprises three laser sources for generating a separate laser beam E for each group of input beams 1a to 4a, 1b to 4b, 1c to 4c. The phase modulation unit 33' is designed in this case as described above and serves to adjust the relative phase positions for each group of four input beams 1a to 4a, 1b to 4b, 1c to 4c independently of one another. The conversion device 35 can also be designed to perform the conversion for each of the three groups of input beams 1a to 4a, 1b to 4b, 1c to 4c independently of one another.This enables, in particular, the combination of different parameters in the three output beams 6a-c, for example, by operating the three laser sources of the beam source 31' with different parameters or by performing a different conversion of the three groups of input beams 1a to 4a, 1b to 4b, 1c to 4c in the conversion device 35. The different parameters can relate to the power, the repetition frequency, the pulse duration, the wavelength, or even a temporal offset between the three groups of input beams 1a to 4a, 1b to 4b, 1c to 4c or the associated output beams 6a-c.

[0119] The three in Fig. 6 The output beams 6a-c shown can also be spatially superimposed or combined in a spatial combination device 36 of the superposition device 5', as shown in Fig. 4is indicated. In the (optional) spatial combination, only a single output beam 6 is fed to the application device 34'. The superposition of the output beams 6a-c can be achieved, for example, by wavelength multiplexing if the conversion device 35 converts the three groups of input beams 1a to 4a, 1b to 4b, 1c to 4c into a different spectral distribution, or if the beam source 31' is designed to generate three laser beams with different wavelengths, which enables wavelength-selective deflection for the superposition in the spatial combination device 36. It is understood that, as an alternative to the three output beams 6a-c, the input beams 1a to 4a, 1b to 4b, 1c to 4c of a respective group can also be spatially superimposed in or upstream of the superposition device 5'.

[0120] The optical system 30, 30' described above can be used, for example, for writing voxels into transparent materials for data storage. The optical system 30, 30' can also be used for the manufacture of optical components based on spatially dependent polarization manipulation. The rapid polarization change generated by the optical system 30, 30' can also be advantageously used for other applications, e.g., for analytical methods.

[0121] It is understood that the functionalities realized with the aid of the optical components of the optical system 30, 30' described above can also be realized with the aid of optical components designed in a different way which fulfill the same functionality.

Claims

1. An optical system (30, 30'), comprising: a beam source (31, 31') for generating a laser beam (E), a splitting device (32, 32') for splitting the laser beam (E) into four input beams (1 to 4, 1a to 4a) that are coherent with each other, a phase modulation device (33, 33') for modulating the relative phase positions (Δφ1,2, Δφ2,3, Δφ12,34) of the four input beams (1 to 4, 1a to 4a), and a superimposing device (5, 5') for coherently superimposing the four input beams (1 to 4, 1a to 4a) that are coherent with each other to form an output beam (6, 6a), comprising: four inputs (E1 to E4) each for the entry of one of the input beams (1 to 4, 1a to 4a), one output (A) for the exit of the output beam (6, 6a), a first combination device (K1) for the coherent combination of the first input beam (1, 1a) and the second input beam (2, 2a) to form a first superimposed beam (U1), a second combination device (K2) for the coherent combination of the third input beam (3, 3a) and the fourth input beam (4, 4a) to form a second superimposed beam (U2), and a third combination device (K3) for forming the output beam (6, 6a) by coherent combination of the first superimposed beam (U1) and the second superimposed beam (U2), wherein the superimposing device (5, 5') is designed to control both a polarization state, in particular a polarization direction (R), and a power (PA) of the output beam (6, 6a) independently from one another as a function of relative phase positions (Δφ12; Δφ34 Δφ12,34) of the individual phases (φ1, φ2, φ3, φ4) of the input beams (1 to 4, 1a to 4a) fed to the four inputs (E1 to E4) relative to one another.

2. The optical system according to claim 1, in which the first, second, and / or third combination device (K1, K2, K3) comprise or form an interferometer, preferably a Mach-Zehnder interferometer (7a-c), with a first beam channel (10) for propagating a first partial beam (T1) and a second beam channel (11) for propagating a second partial beam (T2).

3. The optical system according to claim 2, in which the interferometer (7a) of the first combination device (K1) comprises a splitting element (12) for splitting the coherently superimposed first and second input beams (1) into the two partial beams (T1, T2) and a combination element (13) for coherently superimposing the two partial beams (T1, T2) to form the first superimposed beam (U1), and / or in which the interferometer (7b) of the second combination device (K3) comprises a splitting element (12) for splitting the second and third coherently superimposed input beams (3, 4) into the two partial beams (T1, T2) and a combination element (13) for coherently superimposing the two partial beams (T1, T2) to form the second superimposed beam (U2).

4. The optical system according to claim 2 or 3, in which the interferometer (7c) of the third combination device (K3) comprises a splitting element (12) for splitting the first and second superimposed input beams (U1, U2) into the two partial beams (T1, T2) and a combination element (13) for coherently superimposing the two partial beams (T1, T2) to form the output beam (6).

5. The optical system according to any one of claims 2 to 4, in which the interferometer (7a-c) has at least one polarization influencing device (16) for the preferably fixed influencing of a polarization state, in particular a polarization direction (R1, R2), of at least one of the partial beams (T1, T2).

6. The optical system according to claim 5, in which the splitting element (12) and the combination element (13) are designed as intensity beam splitters and the interferometer (7c) as a polarization influencing device has a polarization-rotating optical device, in particular an optical rotator (16), for the perpendicular alignment of the polarization directions (R1, R2) of the two partial beams (T1, T2) relative to each other.

7. The optical system according to claim 6, wherein the superimposing device is designed to feed the first and second input beams (1, 2), the third and fourth input beams (3, 4) or the first and second superimposed beams (U1, U2) with circular polarization and each with opposite directions of rotation (D1, D2) to the splitting element (12) of the interferometer (7c).

8. The optical system according to claim 5, in which the splitting element (12) and the combination element (13) are designed as polarization beam splitters and the interferometer (7c) has two polarization-rotating optical devices as polarization influencing devices, in particular two optical rotators (16a, b), for rotating a polarization direction (R1, R2) of each of the two partial beams (T1, T2) by 45°.

9. The optical system according to claim 8, the superimposing device further comprising: at least two polarization-influencing, in particular polarization-rotating optical elements (17a, b; 17c, d) which are arranged in the beam path in front of the splitting element (12) of the interferometer (7a-c) and which are preferably designed to rotate a polarization direction of the first and second input beams (1, 2), of the third and fourth input beams (3, 4) or of the first and second superimposed beams (U1, U2) around 45°.

10. The optical system according to any one of the preceding claims, in which the first combination device (K1) for the coherent combination of the first input beam (1) and the second input beam (2), the second combination device (K2) for the coherent combination of the third input beam (3) and the fourth input beam (4) and / or the third combination device (K3) for the coherent combination of the first superimposed beam (U1) and the second superimposed beam (U2) have an intensity beam splitter (8a-c) or a polarization beam splitter (9a-c).

11. The optical system according to claim 10, wherein the superimposing device is designed to feed the first and second input beams (1, 2), the third and fourth input beams (3, 4) or the first and second superimposed beams (U1, U2) with an in each case identical polarization state, in particular with an identical polarization direction (R1, R2), to the intensity beam splitter (8a, 8b, 8c).

12. The optical system according to claim 10 or 11, wherein the superimposing device is designed to feed a first and second input beam (1, 2), a third and fourth input beam (3, 4) or a first and second superimposed beam (U1, U2), each of which have two mutually perpendicular polarization directions (R1, R2), to the polarization beam splitter (9a-c).

13. The optical system according to any one of claims 10 to 12, in which the first combination device (K1) is designed to adjust a polarization state, in particular to rotate a polarization direction (R1), of the first superimposed beam (U1) depending on a relative phase position (Δφ12) between the first, preferably linearly polarized input beam (1) and the second, preferably linearly polarized input beam (2), and / or in which the second combination device (K2) is designed to adjust a polarization state, in particular to rotate a polarization direction (R2), of the second superimposed beam (U2) depending on a relative phase position (Δφ34) between the third, preferably linearly polarized input beam (3) and the fourth, preferably linearly polarized input beam (4), and / or in which the third combination device (K3) is designed to adjust a polarization state of the output laser beam (6), in particular to rotate a polarization direction (R), of the output laser beam (6) depending on a relative phase position (Δφ12;34) between the first superimposed beam (U1) and the second superimposed beam (U2).

14. The optical system according to any one of claims 10 to 13, in which the first, second, and / or third combination device (K1, K2, K3) for generating a linear polarization of the first superimposed beam (U1), the second superimposed beam (U2) and / or the output beam (6) has a phase-shifting element, in particular a λ / 4 delay device (20a-c), which is arranged in the beam path after the intensity beam splitter (8a-c) or the polarization beam splitter (9a-c).

15. The optical system according to any one of the previous claims, in which the splitting device (32') is designed to split the laser beam (E) or another laser beam generated by the beam source (31') into at least four further input beams (1b, c to 4b,c), that are coherent to each other, in which the phase modulation device (33') is designed to modulate the relative phase positions of the at least four further input beams (1b, c to 4b, c), and in which the superimposing device (5') is designed to coherently superimpose the at least four further input beams (1b, c to 4b,c) into at least one further output beam (6b, 6c).