MULTI-APERTURE LASER SYSTEM

Abstract

The invention relates to an optical system with a dividing element (2), which divides the input laser beam (EL) into a number of spatially separate sub-beams, at least one optical amplifier (4), through which the spatially separate sub-beams propagate, at least one path-length adjustment element (3), which adjusts the path length of at least one of the sub-beams, and a combination element (6, 8), which coherently superimposes the sub-beams in an output laser beam. The object of the invention is to achieve a high beam quality in the output laser beam, wherein the demands on the surface quality of the optical components used are to be reduced compared with the prior art. To this end the invention proposes that at least one optical functional element (5, 5′, 6′, 7) from the group of transport element, spectral broadening element, beam deflection element, optical isolator, optical modulator and pulse compressor is provided arranged after the at least one optical amplifier (4) in the beam path, through which functional element the spatially separate sub-beams propagate.

Claims

1. Optical system, comprising a dividing element, arranged to divide an input laser beam into a number of spatially separate sub-beams, at least one optical amplifier, through which the spatially separate sub-beams propagate, at least one path-length adjustment element, which is arranged to adjust the path length of at least one of the sub-beams, and a combination element, arranged to coherently superimposes the sub-beams in an output laser beam, wherein at least one optical functional element from the group of transport element, spectral broadening element, beam deflection element, optical isolator, optical modulator and pulse compressor arranged after the at least one optical amplifier in the beam path, through which functional element the spatially separate sub-beams propagate.

2. Optical system according to claim 1, wherein the dividing element and/or the combination element are each formed as diffractive beam splitters.

3. Optical system according to claim 1, wherein the dividing element and/or the combination element are each formed as a reflective element with zones of different reflectivity.

4. Optical system according to claim 3, wherein the dividing element and/or the combination element each comprise two or more reflective elements at which the laser radiation is reflected consecutively one or multiple times.

5. Optical system according to claim 1, wherein the sub-beams form a two-dimensional array in a plane transverse to the propagation direction.

6. Optical system according to claim 1, wherein provision is made for an error signal detector, which is arranged to derive an error signal from the output laser beam or from the sub-beams, and a controller, which is arranged to derive from the error signal at least one control signal to control the at least one path-length adjustment element.

7. Optical system according to claim 1, wherein the at least one optical amplifier is an optically pumped multicore waveguide, which is doped with rare earth ions and in which a plurality of waveguide structures is integrated, wherein each waveguide structure is arranged to carry one of the sub-beams.

8. Optical system according to claim 1, wherein the at least one path-length adjustment element is arranged ahead of the at least one optical amplifier in the beam path.

9. Optical system according to claim 1, wherein the combination element is located at the location of the application of the output laser beam.

10. Optical system according to claim 1, wherein the pulse compressor is an arrangement of one or more grating pairs or prism pairs, wherein each grating or prism pair is penetrated by each of the spatially separate sub-beams single or multiple times.

11. Optical system according to claim 1, wherein the spectral broadening element is a multicore waveguide in which a plurality of waveguide structures is integrated, wherein each waveguide structure carries one of the sub-beams.

12. Optical system according to claim 1, wherein the transport element is a multicore waveguide in which a plurality of waveguide structures is integrated, wherein each waveguide structure carries one of the sub-beams.

Description

[0034] Exemplary embodiments of the invention are explained below with reference to the drawings. There is shown:

[0035] FIG. 1 a schematic depiction of an optical system according to the invention as a block diagram;

[0036] FIG. 2 a schematic depiction of an optical system according to the invention in another configuration as a block diagram;

[0037] FIG. 3 a dividing and combination element based on multiple reflection.

[0038] In the exemplary embodiment of FIG. 1, an input laser beam coming from a laser source 1 is divided into N channels. An arrangement of partially reflective mirrors or polarized beam splitters in a cascaded arrangement, diffractive elements or an arrangement of mirrors with zones of different reflectivity (see below) can be used as a dividing element 2 for this. The N spatially separate sub-beams are now spatially separately amplified by means of an optical amplifier 4. Classic individual amplifiers (e.g. fiber-based amplifiers) can be used for this or one or more multicore fibers, which implement the concept of spatially separate amplification in a compact manner. The necessary path-length adjustment elements 3 for controlling the coherent combination are ideally located in the beam path behind the dividing element 2 and ahead of the optical amplifier 4. Piezo elements, for example, EOMs or optical wedges movable via actuators are possible for this.

[0039] If the system is a continuously (cw) emitting laser system, spatially separate propagation of the sub-beams (multi-aperture emission) can now take place directly up to the application. Elements for beam deflection (e.g. scanners, acousto-optic deflectors etc.) and elements for output modulation (shutters, EOMs, AOMs etc.) or fiber-optic transport fibers (e.g. multicore fibers or multicore hollow-core fibers) are penetrated by the multi-aperture emission. These elements are summarized by the reference character 5. These elements are optical functional elements in the sense of the invention. It is also possible in this case that the deflection or modulation acts only on a portion of the sub-beams. The sub-beams are superimposed and coherently combined only shortly before the application (“filled aperture” combination), to be precise by means of a combination element 6, which is constructed in a complementary manner to the dividing element 2. Let a “tiled aperture” combination be explicitly excluded here.

[0040] If the system is a pulsed and in particular an ultra-short-pulsed laser system, the approach according to the invention has other advantages compared with the prior art. Following division and spatially separate amplification, the spatially separate, yet extremely compactly arranged sub-beams propagate through a pulse compressor (e.g. grating arrangement) as an optical functional element 5. The sub-beams do not exceed the thresholds of material destruction or non-linear pulse or beam degradation here, as the surface scaling succeeds via the division into sub-beams. Following pulse compression, beam combination can take place. The spatially separate sub-beams can likewise each experience spectral broadening beforehand. This is done, for example, in spatially separately arranged waveguides (e.g. glass fibers or gas-filled hollow-core fibers). The now spectrally broadened sub-beams can then be individually compressed (e.g. by chirped mirrors) or propagate spatially separately as far as the application. Instead of the spectral broadening or in addition to this, other elements for beam or pulse modification can be passed through. Elements for pulse selection, pulse or output modulation or beam deflection are conceivable. These functionalities are summarized in FIG. 1 as a whole by reference character 5. The amplified, if applicable spectrally broadened and modulated pulses can now propagate as far as the application as spatially separate and collimated sub-beams before coherent combination finally takes place according to the “filled aperture” principle in 6.

[0041] In the exemplary embodiment of FIG. 2, a rare-earth-doped multicore fiber (core number=N) is used as an optical multichannel amplifier 4. Division into N sub-beams following the laser source 1 is achieved by the use of a mirror arrangement 2 (see FIG. 3) based on reflectors with zones of different reflectivity, which can generate a high number of sub-beams in a compact design. The N-1 path-length adjustment elements are realized by a piezo array 3, which is adapted in its arrangement to the geometry of the sub-beams. The emitted laser radiation of the amplifying multicore fibers 4 is collimated and the resulting beam bundle passes through a grating compressor 5′. After the grating compressor 5′, spectral broadening takes place in a passive multicore fiber or gas-filled multi-hollow-core fiber 6′. To this end the sub-beam array from the amplifying multicore fiber 4 can be replicated, after passing through the grating compressor 5′, directly into the multicore broadening fiber 6′. Multi-aperture propagation takes place at 7, e.g. to bridge the distance to the application 11 and/or to insert a power modulation or beam deflection. For coherent combination, a small fraction of the multi-aperture emission is diverted onto a photodiode array 9 for detecting a error signal. A controller (not shown) calculates the necessary corrections by the path-length adjustment elements 3 from this. Immediately before the application 11, beam combination takes place at 8. Pulse compression by means of chirped mirrors follows at 10.

[0042] FIG. 3 shows a dividing and combination element based on multiple reflection such as can be used in the exemplary embodiments in FIGS. 1 and 2.

[0043] The element consists of four sub-elements A, B, C, D. The first sub-element A is a mirror with the highest possible reflectivity. The second sub-element B comprises (in the example depicted) four zones of different reflectivity. The laser beams take the path depicted in FIG. 3. The reflectivities of the zones of the sub-element B can be selected such that the incident input laser beam EL is divided into sub-beams in a certain ratio. One example is division into equal portions to all sub-beams. This is achieved by selecting the reflectivities of the four zones at 75%, 66%, 50% and 0%. The exiting four sub-beams then fall on plane-parallel surfaces of the two sub-elements C and D, which are tilted towards the sub-elements A, B. The sub-element C is again highly reflective. The sub-element D comprises in turn four zones of different reflectivity (as before). As a result, as depicted, a two-dimensional array of 16 sub-beams is generated in a plane perpendicular to the beam path. The number of zones of different reflectivity can be arbitrary in the case of sub-elements B and D according to the desired number of sub-beams, i.e. according to the division ratio.

[0044] The combination element can, as said previously, be implemented identically and arranged in the manner that the resulting path length differences of the 16 sub-beams precisely cancel one another out. Due to the integration of division and combination in a single element, a compact design is possible, and simple adjustment is guaranteed. Nor does any angular dependence of the sub-beams on the wavelength exist, the element is thus also suitable for spectrally broadband radiation and thus for the use for ultra-short pulses.