US-12619091-B2 - Superposition device and optical system

Abstract

A superposition device includes four inputs, each respective input for entry of a respective one of four input beams, an output for exit of an output beam, a first combination device for coherent combination of a first input beam and a second input beam to form a first superposition beam, a second combination device for coherent combination of a third input beam and a 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. The superposition device is configured to set both a polarization direction and a power of the output beam independently of one another based on relative phase positions of individual phases of the four input beams fed to the four inputs in relation to one another.

Inventors

• Malte Kumkar

Assignees

• Trumpf Laser—und Systemtechnik GmbH

Dates

Publication Date

20260505

Application Date

20231019

Priority Date

20210423

Claims (18)

1. 1 . A superposition device for the coherent superposition of four mutually coherent input beams to form an output beam, the superposition device comprising: four inputs, each respective input for entry of a respective one of the four input beams, an output for exit of the output beam, a first combination device for coherent combination of a first input beam and a second input beam of the four input beams to form a first superposition beam, a second combination device for coherent combination of a third input beam and a fourth input beam of the four input beams 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 configured to set both a polarization direction and a power of the output beam independently of one another based on relative phase positions of individual phases of the four input beams fed to the four inputs in relation to one another; wherein each of the first combination device, the second combination device, and/or the third combination device comprises or forms an interferometer, with a first beam channel for propagation of a first partial beam and a second beam channel for propagation of a second partial beam.
2. 2 . The superposition device as claimed in claim 1 , wherein the interferometer of the first combination device comprises: a first splitting element for splitting the coherently superposed first input beam and second input beam into the first partial beam and the second partial beam, and a first combination element for coherent superposition of the first partial beam and the second partial beam to form the first superposition beam, and/or wherein the interferometer of the second combination device comprises: a second splitting element for splitting the coherently superposed third input beam and fourth input beam into the first partial beam and the second partial beam, and a second combination element for the coherent superposition of the first partial beam and the second partial beam to form the second superposition beam.
3. 3 . The superposition device as claimed in claim 1 , wherein the interferometer of the third combination device comprises a splitting element for splitting the first superposition beam and the second superposition beam into the first partial beam and the second partial beam, and a combination element for coherent superposition of the first partial beam and the second partial beam to form the output beam.
4. 4 . The superposition device as claimed in claim 1 , wherein the interferometer comprises at least one polarization-influencing device for influencing a polarization direction of at least one of the first partial beam and the second partial beam in fixedly predefined fashion.
5. 5 . The superposition device as claimed in claim 4 , wherein the interferometer comprises a splitting element and a combination element in a form of intensity beam splitters, and the interferometer comprises, as the polarization-influencing device, an optical rotator for aligning the polarization directions of the first partial beam and the second partial beam perpendicularly relative to one another.
6. 6 . The superposition device as claimed in claim 5 , being configured to feed the first input beam and the second input beam, the third input beam and the fourth input beam, or the first superposition beam and the second superposition beam, with circular polarization and respective opposite directions of rotation, to the splitting element of the interferometer.
7. 7 . The superposition device as claimed in claim 4 , wherein the interferometer comprises a splitting element and a combination element in a form of polarization beam splitters, and the interferometer comprises, as the polarization-influencing devices, two optical rotators for rotating a polarization direction of a respective one of the first partial beam and the second partial beam by 45°.
8. 8 . The superposition device as claimed in claim 7 , further comprising: at least two polarization-rotating optical elements, arranged upstream of the splitting element of the interferometer in a beam path and configured to rotate a polarization direction of the first input beam and the second input beam, of the third input beam and the fourth input beam, or of the first superposition beam and the second superposition beam by 45°.
9. 9 . The superposition device as claimed in claim 1 , wherein the first combination device for the coherent combination of the first input beam and the second input beam, the second combination device for the coherent combination of the third input beam and the fourth input beam, and/or the third combination device for the coherent combination of the first superposition beam and the second superposition beam have/has an intensity beam splitter or a polarization beam splitter.
10. 10 . The superposition device as claimed in claim 9 , being configured to feed the first input beam and the second input beam, the third input beam and the fourth input beam, or the first superposition beam and the second superposition beam with a respective identical polarization direction, to the intensity beam splitter.
11. 11 . The superposition device as claimed in claim 9 , being configured to feed the first input beam and the second input beam, the third input beam and the fourth input beam, or the first superposition beam and the second superposition beam, having two mutually perpendicular polarization directions, to the polarization beam splitter.
12. 12 . The superposition device as claimed in claim 9 , wherein the first combination device is configured to rotate a polarization direction of the first superposition beam based on a relative phase position between the first linearly polarized input beam and the second linearly polarized input beam, and/or wherein the second combination device is configured to rotate a polarization direction of the second superposition beam based on a relative phase position between the third linearly polarized input beam and the fourth linearly polarized input beam, and/or wherein the third combination device is configured to rotate a polarization direction of the output laser beam, based on a relative phase position between the first superposition beam and the second superposition beam.
13. 13 . The superposition device as claimed in claim 9 , wherein the first combination device, the second combination device, and/or the third combination device, in order to generate a linear polarization of the first superposition beam, of the second superposition beam, and/or of the output beam, comprises a phase shifting element, arranged downstream of the intensity beam splitter or the polarization beam splitter in a beam path.
14. 14 . The superposition device as claimed in claim 9 , wherein the four inputs are configured for entry of at least four further input beams, and the output is configured for exit of at least one further output beam that is a coherent combination of the at least four further input beams.
15. 15 . An optical system comprising: a beam source for generating a laser beam, a splitting device for splitting the laser beam into four mutually coherent input beams, a phase modulation device for modulating relative phase positions of the four input beams, and a superposition device as claimed in claim 1 for the coherent superposition of the four input beams to form the output beam.
16. 16 . The optical system as claimed in claim 15 , wherein the splitting device is configured to split the laser beam or a further laser beam generated by the beam source into at least four further mutually coherent input beams, wherein the phase modulation device is configured to modulate relative phase positions of the at least four further input beams, and wherein the superposition device is configured for coherent superposition of the at least four further input beams to form at least one further output beam.
17. 17 . The optical system as claimed in claim 15 , being configured to feed the four input beams to the four inputs of the superposition device with substantially a same power.
18. 18 . The optical system as claimed in claim 15 , being configured to feed the four input beams to the four inputs of the superposition device with linear polarization having a predefined polarization direction or with circular polarization.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of International Application No. PCT/EP2022/060657 (WO 2022/223761 A1), filed on Apr. 22, 2023, and claims benefit to German Patent Application No. DE 10 2021 204 057.8, filed on Apr. 23, 2021. The aforementioned applications are hereby incorporated by reference herein. FIELD Embodiments of the present invention relate to a superposition device for the coherent superposition of four mutually coherent input beams to form an output beam. Embodiments of the present invention also relate to an optical system, which comprises at least one such superposition device for the superposition of four mutually coherent input beams to form an output beam. The four mutually coherent input beams and the output beam formed when they are superposed are typically laser beams. BACKGROUND The superposition device described above is preferably designed to superpose the four input beams collinearly, it being possible in particular for a congruent superposition to take place to form the output beam. 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. Rapid polarization modulation may generally be implemented using interferometric systems, into which a single input beam is input coupled and in the case of which the phase is manipulated by phase shifters integrated in the interferometer; cf. 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. The rapid polarization modulation may for example be used to write polarization-influencing nanostructures to transparent materials for data storage with a high storage density and an extremely long service life; 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 on the basis of nano-gratings which are written into a glass material and are formed when light of spatially modulated phase and polarization is radiated in is described in U.S. Pat. No. 10,236,027 B1. For the modulation of the phase and the polarization, that document makes use of a liquid-crystal spatial light modulator (SLM). U.S. Pat. No. 10,181,336 B1 describes an optical data storage system which, for the data storage, comprises a dynamic digital hologram with independently programmable holographic zones. The dynamic digital hologram may be in the form of an optically actuable SLM. In the case of the methods and apparatuses described above for writing nanostructures or voxels into a transparent material, the dynamics are limited owing to multiplexing and/or segmentation of multi-spot arrays in terms of their polarization state. U.S. Pat. No. 9,792,945B1 describes a 3D optical data storage medium. The electrical property of a storage cell is modified using light energy. It is not mentioned how the setting of the light energy parameters, which is required for writing at a high data rate, can be realized, in particular also in terms of the polarization alignment. It is likewise known to use coherent superposition or coupling for rapid modulation of the laser power; cf. 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 the article, use is made of active phase control at the fundamental wavelength in order to control the superposition at the frequency-converted wavelength. DE 10 2017 104 392 A1 discloses the use of an interferometer as superposition device to modulate the amplitude of an output laser beam, in the case of which interferometer a relative phase position is temporally modulated by two beam channels of the interferometer. If polarization beam splitters are used as splitting element for splitting the input laser beam and as combination element for coherent combination, the modulation of the relative phase position leads to modulation of the polarization state of the coherently superposed output beam. Using a waveplate and a polarizer, it is possible in this case to convert the modulation of the polarization state of the output laser beam into modulation of the amplitude of the output laser beam. U.S. Pat. No. 9,042,009 B2 describes a passive apparatus for coherent superposition, comprising an amplitude-splitting interferometer with at least four branches. SUMMARY Embodiments of the present invention provide a superpos