DE102021120516A1 - Device and method for combining coherent laser beams - Google Patents

Abstract

The present invention relates to a device for combining coherent laser beams, comprising a splitting device (110) for splitting an input laser beam (108) into a plurality of coherent laser beams (102), a phase setting device (120) for setting a respective phase of the coherent laser beams (102), and a waveguide device (112, 112', 112"), which has a plurality of cores (114) for conducting a respective coherent laser beam (102), each of the coherent laser beams (102) being assigned a mode field diameter (d _m ). which it propagates through a respective core (114). The waveguide device (112, 112', 112") is in an end region (144) of the waveguide device (112, 112', 112") for increasing the mode field diameter (d _m ) of the respective coherent laser beams (102) formed.

Description

The invention relates to a device for combining coherent laser beams, comprising a splitting device for splitting an input laser beam into a plurality of coherent laser beams, a phase adjustment device for adjusting a respective phase of the coherent laser beams, and a waveguide device which has a plurality of cores for conducting a respective coherent laser beam , each of the coherent laser beams being assigned a mode field diameter with which it propagates through a respective core.

The invention also relates to a method for combining coherent laser beams, in which an input laser beam is divided into a plurality of coherent laser beams by means of a splitting device, the coherent laser beams are passed through a waveguide device having a plurality of cores, with a coherent laser beam being passed through a respective core and wherein each of the coherent laser beams is assigned a mode field diameter with which it propagates through the respective core, and in which a respective phase of the coherent laser beams is adjusted by means of a phase adjustment device.

From the WO 2020/016336 A1 a device for combining a plurality of coherent laser beams is known, comprising a plurality of phase adjustment devices for adjusting a respective phase of one of the coherent laser beams, and a beam combination device for combining the coherent laser beams to form at least one combined laser beam, the beam combination device having a microlens array with at least two Having microlens arrays for forming the at least one combined laser beam.

From the EP 2 248 233 B1 a high peak power fiber amplifier system is known.

The invention is based on the object of providing a device mentioned at the outset and a method mentioned at the outset, by means of which a combination of coherent laser beams can be implemented with increased combination efficiency and/or a more compact optical structure.

This object is achieved according to the invention in the device mentioned at the outset in that the waveguide device is formed in an end region of the waveguide device to increase the mode field diameter of the respective coherent laser beams.

By increasing the mode field diameter of the coherent laser beams in the end region of the waveguide device, the coherent laser beams can be coupled out at an output of the waveguide device with an increased fill factor.

The decoupling of the coherent laser beams with an increased fill factor brings about a reduction in a spatial extent and/or in a cross section of an envelope of the coherent laser beams that are coupled out. In particular, this enables a spatially compact design of a combination device for combining the coupled-out coherent partial beams. For example, as a result, diffractive optical elements and/or microlens arrays provided for combining the coherent partial beams can be implemented in a compact manner.

In particular, the solution according to the invention makes it possible to increase the fill factor of the coupled-out coherent laser beams without additional collimation lenses.

In particular, coherent laser beams decoupled from the waveguide device according to the "tiled-aperture" principle or the "filled-aperture" principle or a combination of the "tiled-aperture" principle and the "filled-aperture" principle ("mixed -aperture" principle) can be combined.

In the case of the "tiled aperture" principle, the decoupled coherent laser beams are superimposed in the far field. With the "filled aperture" principle, the decoupled coherent laser beams are superimposed in the near field, for example behind a combination device such as a diffractive optical element.

Since the spatial extent and/or the cross-section of the envelope of the decoupled coherent laser beams decreases as the fill factor increases, the increased fill factor enables a combination of the coherent laser beams with increased combination efficiency, particularly in the “tiled aperture” principle.

In particular, coherent laser beams coupled out of the waveguide device can be combined by means of near-field overlapping and/or according to the "tiled aperture" principle.

In particular, it can be provided that the waveguide device has an output positioned in the end region for decoupling the coherent laser beams from the waveguide device. For example, the output is positioned at one end of the waveguide device, this end in particular being an end in Is longitudinal direction of the waveguide device and / or in the main direction of propagation of the coherent laser beams.

In particular, it can be provided that the mode field diameter is increased in the end area and/or that the mode field diameter is greatest at an output of the waveguide device for coupling out the coherent laser beams located in the end area. This makes it possible to increase the fill factor of the coherent laser beams coupled out of the waveguide device.

In particular, the mode field diameter is increased towards the output of the waveguide device and is increased in particular monotonically or approximately monotonically.

In particular, the end region of the waveguide device is designed in such a way that propagation of the coherent laser beams causes the mode field diameter to increase.

It can be provided that in the end region of the waveguide device the mode field diameter is constant at least in sections and/or does not increase. For example, the mode field diameter is constant and/or does not increase in a section adjacent to the exit.

It can be advantageous if a respective core diameter of the cores is increased in the end region and/or if a respective core diameter of the cores is greatest at an output of the waveguide device for coupling out the coherent laser beams located in the end region. This makes it possible to increase the fill factor with which the coherent laser beams are coupled out.

In particular, the respective core diameter is increased towards the output of the waveguide device and is in particular increased monotonically or approximately monotonically.

Provision can be made for the core diameter in the end region of the waveguide device to be constant at least in sections and/or not to increase. For example, the core diameter is constant and/or does not increase in a section adjacent to the exit.

It can be advantageous if a center distance between adjacent cores is constant and, in particular, is constant in the end region. A constant center-to-center spacing of the cores, in conjunction with an increase in the mode field diameter and/or the core diameter, causes an increase in the filling factor.

In particular, it can be provided that the cores of the waveguide device are oriented at least approximately parallel to one another in the end region and/or at the output of the waveguide device and/or in a section of the end region adjacent to the output.

The fact that the cores are oriented at least approximately parallel to one another is to be understood in particular to mean that the respective longitudinal center axes of the cores are oriented at least approximately parallel to one another.

The stated object is also achieved according to the invention in that a center distance between adjacent cores is reduced in an end region of the waveguide device.

This variant according to the invention of the device for combining coherent laser beams has in particular one or more features and/or advantages of the variant described above.

In particular, provision can be made for the center-to-center distance between adjacent cores to be reduced towards the exit, and/or for the center-to-center distance between adjacent cores to be smallest at the exit. In particular, the pitch of adjacent cores is monotonically reduced towards the output.

By reducing the center distance, an increase in the fill factor can be realized in the end area. For example, an overlap and/or a combination of the coherent laser beams can then be realized in the end region and in particular at an output of the waveguide device.

In particular, it can be provided that the respective core diameter of the cores is reduced in the end region and/or that the respective core diameter of the cores is smallest at an output of the waveguide device for coupling out the coherent laser beams located in the end region. For example, a reduction in the center-to-center spacing of the cores in the end area is usually accompanied by a reduction in the core diameter in the end area when implemented using geometric fiber taping.

In particular, the respective core diameter of the cores is reduced towards the outlet and in particular is reduced monotonically or approximately monotonically.

It can be favorable if the cores in the end area are arranged so as to converge and/or converge toward an output of the waveguide device located in the end area for coupling out the coherent laser beams. As a result, the fill factor with which the coherent laser beams are coupled out of the waveguide device can be increased. In addition, this allows an overlap and/or a combination of the coherent laser beams to be implemented at the output of the waveguide device.

In particular, it can be provided that the waveguide device is produced by taping in the end region. In this way, in particular, a waveguide device can be formed with the features and/or advantages mentioned above.

The term taper is to be understood in particular as fiber taper and/or a drawing out of fibers.

A reduction in the center-to-center distance and/or the core diameter of cores located in the end region can be brought about, for example, by geometric taper.

Diffusion tapers can be used, for example, to increase the diameter of cores with, in particular, an at least approximately constant center-to-center distance between the cores in the end region.

In particular, it can be provided that the waveguide device has a jacket in which the cores are embedded and in particular all cores of the waveguide device are embedded. In particular, the cladding is a common cladding for all cores of the waveguide device. For example, the waveguide device is designed as a multi-core fiber.

The cladding of the waveguide device is also referred to in particular as a cladding.

It can be advantageous if the coherent laser beams are coupled out with a filling factor of at least 25% and preferably at least 80% and particularly preferably at least 90% at an output of the waveguide device located in the end region. As a result, the coherent laser beams can be combined with a high combination efficiency.

For the same reason, it can be advantageous if the coherent laser beams are coupled out at an output of the waveguide device in the end region with a fill factor that is greater than a fill factor with which the coherent laser beams are coupled into the waveguide device.

In one embodiment it can be provided that the waveguide device has a plurality of individual waveguides or is formed from a plurality of individual waveguides, with each individual waveguide in particular having a core and a cladding assigned to the core.

A single waveguide is to be understood in particular as a waveguide with a single core.

In particular, the individual waveguides of the waveguide device are oriented parallel to one another, at least in sections.

In particular, the individual waveguides of the waveguide device are arranged adjacent to one another and/or abutting and/or adjoining one another, with the respective jackets of the individual waveguides being arranged adjacent to one another and/or abutting and/or adjoining one another.

In one embodiment, it can be provided that the individual waveguides of the waveguide device are implemented on a “photonically integrated chip” (PIC). In this case, the sub-structure in which a large part of the optical field is concentrated is referred to as the core. For example, the individual waveguide is designed as a strip, wire or slot waveguide.

In particular, it can be provided that the device has an amplification device for amplifying the coherent laser beams passed through the cores, with the amplification device being integrated in particular in the waveguide device or being assigned to the waveguide device.

For example, a cladding area of the waveguide device and in particular an inner cladding area of the waveguide device is assigned to the amplification device. For example, pumped light for amplifying the coherent laser beams is guided through this cladding region during operation of the device.

Provision can be made for the device to have a combination device for combining coherent laser beams coupled out of the waveguide device. In this way, for example, at least one combined laser beam can be formed from the decoupled coherent laser beams.

For example, the combination device comprises at least one diffractive optical element, the at least one diffractive optical element comprising a grating structure with a periodic pattern, for example. In this way, for example, a combination of the coherent laser beams can be implemented according to the “filled aperture” principle.

It can be provided that the combination device comprises at least one microlens array for combining the coherent laser beams. In this way, for example, a combination of the coherent laser beams can be implemented according to the "mixed-aperture" principle.

In principle, it is also possible for the coherent laser beams coupled out of the waveguide device to be combined into at least one combined laser beam without a combination device. For example, the coherent laser beams are decoupled from the waveguide device in such a way that they are combined by propagation in the far field to form at least one combined laser beam (“tiled aperture” principle).

For example, at least one lens element can be provided for imaging coherent laser beams coupled out of the waveguide device into at least one combined laser beam. In this way, for example, a combination of the coherent laser beams can be implemented according to the “tiled aperture” principle.

In particular, the waveguide device is set up and configured such that the coherent laser beams are or can be combined by interference when or after they are coupled out of the waveguide device and in particular are or can be combined to form at least one combined laser beam.

In particular, a coherent laser beam is coupled into a respective core of the waveguide device by means of the splitting device.

The input laser beam is, for example, a continuous wave laser beam or a pulsed laser beam and in particular an ultrashort pulse laser beam.

In particular, the phase adjustment device is designed to adjust a respective phase of the coherent laser beams and/or a respective phase shift between the coherent laser beams.

In particular, the phase adjustment device comprises a plurality of phase adjustment elements, one phase adjustment element being assigned to one of the coherent laser beams. For example, in the case of N coherent laser beams, there are at least N-1 phasing elements, with a respective phasing element being associated with each of the N-1 laser beams.

In the method mentioned at the outset, it is provided according to the invention that the mode field diameter of the respective coherent laser beams is increased in an end region of the waveguide device.

The advantages already explained in connection with the devices according to the invention result. Advantageous embodiments of the method according to the invention have already been explained in connection with the devices according to the invention.

In particular, the method according to the invention has one or more features and/or advantages of the devices according to the invention.

In particular, the method according to the invention can be carried out using the devices according to the invention or is carried out using the devices according to the invention.

It can be favorable if the mode field diameter of the respective coherent laser beams is increased by propagation or during propagation of the coherent laser beams through the waveguide device and in particular through the end region of the waveguide device.

In particular, it can be provided that propagation of the coherent laser beams through the waveguide device and in particular through the end region of the waveguide device increases a fill factor with which the coherent laser beams are coupled out at an output of the waveguide device.

Alternatively or additionally, it can be provided according to the invention that the coherent laser beams converge and/or converge in the end area.

In particular, the statements “at least approximately” or “approximately” generally mean a deviation of no more than 10%. Unless otherwise stated, the statements “at least approximately” or “approximately” mean in particular that an actual value and/or distance and/or angle deviates by no more than 10% from an ideal value and/or distance and/or angle .

• 1 eine schematische Darstellung einer Vorrichtung zur Kombination von mehreren kohärenten Laserstrahlen;
• 2 eine schematische Darstellung eines zeitlichen Intensitätsprofils von zwei Pulszügen, durch deren Überlagerung ein kombinierter Laserstrahl gebildet wird;
• 3 eine schematische Querschnittsdarstellung einer ersten Ausführungsform einer Wellenleitereinrichtung, welche als Multikernfaser ausgebildet ist;
• 4 eine schematische Querschnittsdarstellung einer weiteren Ausführungsform einer Wellenleitereinrichtung, welche aus einer Mehrzahl von Einzelwellenleitern ausgebildet ist;
• 5 eine schematische Querschnittsdarstellung einer weiteren Ausführungsform einer Wellenleitereinrichtung, wobei Kerne der Wellenleitereinrichtung in einem Endbereich konvergierend sind;
• 6a ein als diffraktives optisches Element ausgeführtes Kombinationselement zur Kombination von aus der Wellenleitereinrichtung ausgekoppelten Strahlen;
• 6b ein Linsenelement zur Fokussierung von aus der Wellenleitereinrichtung ausgekoppelten Strahlen; und
• 6c ein als Mikrolinsenarray ausgeführtes Kombinationselement zur Kombination von aus der Wellenleitereinrichtung ausgekoppelten Strahlen.

The following description of preferred embodiments serves to explain the invention in more detail in conjunction with the drawings. Show it:

• 1 a schematic representation of a device for combining a plurality of coherent laser beams;
• 2 a schematic representation of a temporal intensity profile of two pulse trains, by their superimposition a combined laser beam is formed;
• 3 a schematic cross-sectional representation of a first embodiment of a waveguide device, which is designed as a multi-core fiber;
• 4 a schematic cross-sectional representation of a further embodiment of a waveguide device, which is formed from a plurality of individual waveguides;
• 5 a schematic cross-sectional representation of a further embodiment of a waveguide device, wherein cores of the waveguide device are converging in an end region;
• 6a a combination element designed as a diffractive optical element for combining beams coupled out of the waveguide device;
• 6b a lens element for focusing beams coupled out of the waveguide means; and
• 6c a combination element designed as a microlens array for combining beams coupled out of the waveguide device.

Identical or functionally equivalent elements are provided with the same reference symbols in all figures.

An embodiment of a device for combining coherent laser beams is in 1 shown schematically and denoted by 100 there. The device 100 can be used to combine a plurality of mutually coherent laser beams 102 into a combined laser beam 104 . In particular, the device 100 can be used to carry out a coherent beam combination of the respective coherent laser beams 102 (coherent beam combining).

For example, it can be provided that a laser source 106 is used to provide an input laser beam 108 for coupling into the device 100 .

The device 100 includes in particular a splitting device 110 by means of which the input laser beam 108 is split into a plurality of coherent laser beams 102 . In 1 For example, three coherent laser beams 102a, 102b and 102c are shown.

In particular, the coherent laser beams 102 have the same properties, such as the same wavelength and/or the same repetition rate and/or the same spectrum.

The coherent laser beams 102 are guided through a waveguide device 112 of the apparatus 100, the waveguide device 112 having a plurality of cores 114. FIG. The cores 114 are those parts of the waveguide device 112 through which electromagnetic radiation and/or light can be conducted.

In particular, the waveguide device 112 is designed as an optical waveguide and/or optical fiber cable. The cores 114 are formed in particular from light-guiding fibers, for example plastic fibers.

When the device 100 is in operation, one of the coherent laser beams 102 is passed through and/or passed through one of the cores 114 .

The device 100 comprises, in particular, an amplification device 116, by means of which the coherent laser beams 104 are amplified. In particular, the amplifying device 116 is assigned to the waveguide device 112 and/or is part of the waveguide device 112. For example, the amplifying device 116 is integrated into the waveguide device 112.

The device 100 comprises a combination device 118 for combining coherent laser beams 102 coupled out of the waveguide device 112. The combined laser beam 104 is formed by combining the coherent laser beams 102 by means of this combination device 118.

In particular, the device 100 includes a phase adjustment device 120, by means of which a respective phase of the coherent laser beams 102 can be adjusted. In particular, a respective phase shift Δφ between the individual coherent laser beams 102 can be set by means of the phase setting device 120 .

The phase adjustment device 120 comprises, in particular, a plurality of phase adjustment elements 122 for adjusting the respective phase of one of the coherent laser beams 102. For example, a phase adjustment element 122 is assigned to several or all of the coherent laser beams 102 .

In the case of N coherent laser beams 102, the phase adjustment device 120 comprises, for example, N-1 or N phase adjustment elements 122.

In particular, the coherent laser beams 102 coupled out of the waveguide device 112 can be combined by interference to form the combined laser beam 104 by suitable phase adjustment using the phase adjustment device.

In 2 a temporal intensity profile of two pulse trains is shown, which each have an envelope 126a and 126b. In particular, the pulse trains with envelopes 126a and 126b are each associated with one of the coherent laser beams 102 .

Envelope pulse trains 126a and 126b each comprise an oscillating carrier wave 127a and 127b, respectively. The carrier wave 127a or 127b has a central frequency ω ₀ .

The combined laser beam 104 is formed by superimposing the envelopes 126a, 126b of the pulse trains and their carrier waves 127a, 127b.

The phase shift Δφ of the respective coherent laser beams 102 can be adjusted by means of the phase adjustment device 120 such that the envelopes of the pulse trains 126a, 126b and/or oscillating carrier waves 127a, 127b assigned to the respective coherent laser beams 102 are arranged at the same temporal positions. This results in a constructive interference of the pulse trains with envelopes 126a and 126b.

In particular, a combination of the coupled-out coherent laser beams 102 according to the tiled-aperture principle is provided in the device 100 . In particular, the coherent laser beams 102 coupled out of the waveguide device 112 can be combined according to the tiled aperture principle.

For the technical details of combining coherent laser beams, see the scientific papers "Coherent combination of ultrafast fiber amplifiers", Hanna, et al, Journal of Physics B: Atomic, Molecular and Optical Physics 49(6) (2016), 062004; "Performance scaling of laser amplifiers via coherent combination of ultrashort pulses", Klenke, Mensch und Buch Verlag; "Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier", Ramirez, et al., Optics Express 23(5), (2015), 5406-5416; and "Highly scalable femtosecond coherent beam combining demonstrated with 19 fibers", Le Dortz, et al., Optics Letters 42(10), (2017), 1887-1890.

The waveguide device 112 comprises a cladding 128, by which the cores 114 are each surrounded and/or in which the cores 114 are each embedded. The jacket 128 is also referred to as a cladding.

At the in 3 example shown, the cladding 128 is designed as a common cladding for all cores 114 of the waveguide device 112 . In particular, the cladding 128 is a common cladding in which all cores 114 of the waveguide device 112 are embedded.

In the embodiment according to 3 the waveguide device 112 is designed, for example, as a multi-core fiber.

During operation of the device 100 it is provided that one of the coherent laser beams 102 is passed through each of the cores 114 . The coherent laser beams 102 propagate through the cores 114 each with a specific mode field diameter d _m .

The mode field diameter d _m is to be understood as meaning a transverse distribution of a radiation intensity within a specific core 114 . For example, in the case of a Gaussian power distribution, the mode field diameter d _m results from the reduction of the electric and magnetic field strength to the amount of 1/e or from the reduction of the power to the amount of 1/e ² .

In particular, it can be provided that the jacket 128 has an inner jacket area 130 and an outer jacket area 132 . The outer cladding region 132 is arranged further outwards and/or at a greater distance from a specific core 114 in the transverse direction 134 than the inner cladding region 130, the transverse direction 134 being oriented transversely and in particular perpendicularly to a respective central longitudinal axis 135 of the cores 114.

In particular, the cores 114 extend along their respective longitudinal center axis 135. In particular, the longitudinal center axis 135 is oriented parallel to a main propagation direction 136 of the coherent laser beam 102 guided through the respective core 114.

The respective main directions of propagation 136 of all coherent laser beams 102 guided through the cores 114 are shown in FIG 3 example shown in particular oriented at least approximately parallel to each other.

In particular, the inner cladding region 130 adjoins the respective cores 114 and/or adjoins the respective cores 114 in the transverse direction 134 .

In particular, the outer cladding region 132 limits the waveguide device 112 to the outside. In particular, the inner cladding region in the interior of the waveguide device extends in sections between the inner cladding region 130.

The outer cladding region 132 forms, for example, a mechanical protective layer and/or an outer protective layer of the waveguide device 112.

The inner jacket region 130 is preferably assigned to part of the reinforcement device 116 and/or the reinforcement device 116 . In particular, the coherent laser beams 102 are amplified by the inner cladding region 130 as they pass through the cores 114 .

For example, pump light for amplifying the coherent laser beams 102 is guided through the inner cladding region 130 during operation of the device 100 .

The waveguide device 112 has an input 138 for coupling the coherent laser beams 102 into the waveguide device 112 and an output 140 for coupling the coherent laser beams 102 out of the waveguide device 112 . The outlet 140 is spaced from the inlet 138 parallel to the longitudinal central axis 135 .

In particular, the input 138 and/or the output 140 are each arranged at one end of the waveguide device 112 . In particular, the waveguide device 112 and/or the cores 114 extend between the input 138 and the output 140.

In particular, the coherent laser beams 102 are coupled into the respective cores 114 at the input 138 and coupled out of the respective cores 114 at the output 140 .

In the exemplary embodiment shown, the waveguide device 112 has a partial region 142 in which a respective core diameter d _k of the cores 114 is at least approximately constant and is at least approximately constant, in particular with respect to the main propagation direction 136 and/or with respect to a longitudinal direction 135a parallel to the longitudinal center axis 135 . In particular, the partial area 142 extends in the main propagation direction 136 and/or in the longitudinal direction 135a.

For example, sub-area 142 adjoins entrance 138 or entrance 138 is in sub-area 142.

The waveguide device 112 has an end region 144 in which the core diameter d _k of the respective cores 114 varies and varies in particular with respect to the main propagation direction 136 and/or with respect to a longitudinal direction 135a parallel to the longitudinal center axis 135. In particular, the partial area 142 extends in the main propagation direction 136 and/or in the longitudinal direction 135a.

The end region 144 adjoins the partial region 142, for example in the main propagation direction 136 and/or in the longitudinal direction 135a.

In particular, the end region 144 is to be understood as an end region of the waveguide device 112 on the output side. For example, the exit 140 is in the end area 144.

A length l ₀ of the end area 144 is, for example, in the range from millimeters to centimeters. In particular, the length l ₀ of the waveguide device 112 is a distance between a position 146 on the waveguide device 112 and the output 140 . In particular, the waveguide device 112 extends between this position 146 and the exit 140.

In the exemplary embodiment shown, the core diameter d _k of the respective cores 114 is expanded in the end region 144 towards the outlet 140 . In the end area 144, this results in an increase in the mode field diameter d _m . In particular, this allows the coherent laser beams 102 to be coupled out at the output 140 with a respective mode field diameter d _m which is larger in comparison to the corresponding mode field diameter d _m at the input 138 .

The end region 144 of the waveguide device 112 is produced in particular by taping (also referred to as drawing). With regard to the technical details on the tapering of the waveguide device 112 to form the end region 144, reference is made to the scientific publication "Tapered singlemode fibers and devices. Part 1: Adiabaticity criteria” by J.D. Love et al., IEE Proceedings J (Optoelectronics), Volume 138, Issue 5, October 1991, p. 343 - 354, DOI: 10.1049/ip-j.1991.0060, Print ISSN 0267-3932, Online ISSN 2053-9088.

In particular, the end region 144 is produced by diffusion taping. It can be done with it realize an increase in the core diameter d _k in the end region 144 .

The length l ₀ of the end region 144 is defined in particular via the adiabatic condition described in the cited scientific publication.

The core diameter d _k of the respective cores 114 preferably increases in the end region 144 towards the outlet 140 and in particular increases monotonically. Provision can be made for the core diameter d _k in the end region 144 to be constant or approximately constant, at least in sections.

For example, the core diameter d _k is at least approximately constant in a section 148 of the end region 144 adjoining the outlet 140 (indicated in 3 ). The section 148 with an at least approximately constant core diameter d _k results in particular from the production of the end region 144 by means of tapers.

Adjacent cores 114 of the waveguide device 112 are each spaced apart from one another by a center distance d ₀ , a spacing direction of the center distance d ₀ being oriented in particular parallel to the transverse direction 134 . In particular, the center distance d ₀ corresponds to a distance between the respective longitudinal center axes 135 of adjacent cores 114.

The center distance d ₀ between adjacent cores 114 is also referred to as pitch.

In the embodiment according to 3 the respective longitudinal central axes 135 of mutually adjacent cores 114 are oriented at least approximately parallel and/or the center distance d ₀ of mutually adjacent cores 114 is at least approximately constant.

In particular, the center distance d ₀ is at least approximately constant with respect to the main propagation direction 136 and/or the longitudinal direction 135a and is at least approximately constant in particular in the end region 144 .

The coherent laser beams 102 are coupled out with a specific fill factor F at the output 140 of the waveguide device 112 . This fill factor F is defined as the quotient of mode field diameter d _m and center distance d ₀ , ie F=d _m / d ₀ applies.

At the in 3 In the exemplary embodiment shown, an increase in the fill factor F of the coherent laser beams 102 to be coupled out results in the end region 144 by increasing the mode field diameter d _m with an at least approximately constant center distance d ₀ of the cores 114. In particular, the fill factor F of the coherent laser beams 102 coupled out at the output 140 is greater as the fill factor F of the coherent laser beams 102 coupled in at the input 138.

a in 4 The exemplary embodiment of a waveguide device 112′ shown differs from the example of the waveguide device 112 described above essentially in that the waveguide device 112′ is formed from a plurality of individual waveguides 150 and, in particular, is not formed as a multi-core fiber.

Otherwise, the waveguide device 112′ is designed in the same way as the waveguide device 112 described above, so that reference is made to its description in this respect.

In particular, the waveguide device 112' has one or more features and/or advantages of the waveguide device 112 described above.

For example, the waveguide device 112′ comprises a plurality of individual waveguides 150 which are each arranged adjacent to and/or adjacent to one another. The respective central longitudinal axes 135 of the cores 114 are in particular oriented at least approximately parallel to one another and, in particular, are oriented at least approximately parallel to one another in the end region 144 .

The individual waveguides 150 each include a core 114 and a cladding 128 assigned to the core 114 , the cladding 128 having in particular the inner cladding region 130 and the outer cladding region 132 .

In particular, the respective claddings 128 and in particular the respective outer cladding regions 132 of the individual waveguides are arranged adjacent to one another and/or adjacent to one another and/or adjacent to one another.

In particular, the individual waveguides 150 are formed in the end region 144 by taping.

In particular, the respective core diameters d _k of the respective cores 112 of the individual waveguides 150 in the end region 144 are increased towards the outlet 140, with the center distance d ₀ between adjacent cores 114 in the end region 144 being kept at least approximately constant. This results in an increase in the fill factor F, with which the coherent laser beams 102 are coupled out at the output 140.

a in 5 The exemplary embodiment shown of a waveguide device 112" differs from the exemplary embodiments described above essentially in that the cores 114 of the waveguide device 112" are arranged in the end region 144 so as to converge and/or run towards one another.

Otherwise, the waveguide device 112" is designed in the same way as the waveguide devices 112, 112' described above, so that reference is made to their description in this respect.

In particular, the waveguide device 112'' has one or more features and/or advantages of the waveguide devices 112, 112' described above.

For example, the waveguide device 112" is designed as a multi-core fiber.

The waveguide device 112" comprises the partial area 142 in which the core diameters d _k of the respective cores 114 and/or the respective center distances d ₀ of adjacent cores 114 are at least approximately constant in the longitudinal direction 135a. For example, in the partial area 142 the cores 114 and in particular the respective central longitudinal axes 135 of adjacent cores 114 are oriented at least approximately parallel to one another.

At the in 5 In the exemplary embodiment shown, the cores 114 converge in the end region 144 in the direction of the exit 140, ie the cores 114 run towards one another in the end region 144 towards the exit 140. In particular, the respective longitudinal center axes 135 of cores 114 adjacent to one another are angled towards one another in the end region 144 .

The respective center-to-center distances d ₀ of adjacent cores 114 are reduced in the end region 144 towards the exit 140 . In particular, the respective center distances d ₀ with respect to the main propagation direction 136 and/or the longitudinal direction 135a are reduced and in particular are reduced monotonically.

The respective core diameters d _k of the cores 114 are reduced in the end region 144 toward the outlet 140 . In particular, the respective core diameters d _k are reduced with respect to the main propagation direction 136 and/or the longitudinal direction 135a, and in particular are reduced monotonically.

For example, the end area 144 of the waveguide device 112'' is produced by geometric taper. In this way, in particular, a reduction in the center distances d ₀ and/or a reduction in the core diameter d _k in the end area 144 can be implemented.

Due to the reduction in the core diameter d _k of the respective cores 114 in the end region 144, there is a reduction in the mode field diameter d _m of the coherent laser beams 102 guided through the respective cores 114 in the end region 144.

The coherent laser beams 102 are coupled out at the output 140 with the fill factor F. In particular, the reduction in the center distance d ₀ between adjacent cores 114 and the reduction in the core diameter d _k of the respective cores 114 in the end region 144 are selected such that the fill factor F is increased in the end region 144 . In particular, the fill factor F of the coherent laser beams 102 coupled in at the input 138 is smaller than the fill factor F of the coherent laser beams 102 coupled out at the output 140.

The coherent laser beams 102 passed through the waveguide device 112, 112', 112'' are combined to form the combined laser beam 104, with a corresponding combination of the coherent laser beams 102 taking place in particular when they are coupled out or after they have been coupled out.

In order to combine the coherent laser beams 102, the combination device 118 mentioned above can be provided in particular, through which the coherent laser beams 102 coupled out of the output 140 propagate.

For example, the combination device 118 is designed as a free jet structure or includes a free jet structure.

In the 6a , 6b and 6c an envelope 152 of the coherent laser beams 102 coupled out of the waveguide device 112 is indicated in each case.

For example, the combination device 118 includes a diffractive optical element 154 for combining the coherent laser beams 102 ( 6a) . In order to focus the coherent laser beams 102 onto the diffractive optical element 154, a lens element 156 arranged in front of the diffractive optical element 144 in the beam propagation direction is provided, for example.

For example, the diffractive optical element 154 is or includes a grating structure with a periodic pattern.

With regard to the technical details on the combination of coherent laser beams using diffractive optical elements, reference is made to the scientific publications "Coherent combination of ultrashort pulse beams using two diffractive optics", Zhou et al., Opt. Lett. 42, 4422-4425 (2017) and "Diffractive-optics-based beam combination of a phase-locked fiber laser array", Cheung et al., Opt. Lett. 33, 354-356 (2008).

Alternatively or additionally, it can be provided that the combination device 118 comprises a microlens array 158 for combining the coherent laser beams 102 ( 6c ).

With regard to the technical details on the combination of coherent laser beams by means of one or more microlens arrays, reference is made to WO 2020/016336 A1 and to the unpublished German patent application with file number 10 2020 201 161.3 by the same applicant. This is expressly and fully referred to.

In principle, it is also possible for the coupled-out coherent laser beams 102 to form the combined laser beam 104 to be combined without a combination device 118 .

For example, the waveguide device 112, 112′, 112″ and in particular its end region 144 can be designed such that after the coherent laser beams 102 have been coupled out, the combined laser beam 104 is formed by propagation of the coherent laser beams 102 in the far field.

For example, a lens element 160 for focusing the decoupled coherent laser beams 102 can be provided in the propagation direction following the exit 140 ( 6b) .

In the case of the waveguide device 112" ( 5 ) it can be provided that the coherent laser beams 102 are combined to form the combined laser beam 104 in the end region 144 and/or at the output 140 of the waveguide device 112". In particular, by means of the convergence of the cores 114 in the end region 144 and/or or achieve an overlap of the modes associated with the coherent laser beams 102 at the output 140. In particular, the formation of a “supermode” in the end region 144 and/or at the output 140 can be achieved by means of this overlap.

Reference List

Δφ

phase shift

d0

center distance

dk

core diameter

dm

mode field diameter

f

fill factor

l0

length

ω0

center frequency

100

contraption

102

coherent laser beam

102a

coherent laser beam

102b

coherent laser beam

102c

coherent laser beam

104

combined laser beam

106

laser source

108

input laser beam

110

splitting facility

112

waveguide device

112'

waveguide device

112"

waveguide device

114

core

116

reinforcement device

118

combination device

120

phase adjuster

122

phase adjuster

126a

pulse train

126b

pulse train

127a

carrier wave

127b

carrier wave

128

Coat

130

inner mantle area

132

outer mantle area

134

transverse direction

135

longitudinal central axis

135a

longitudinal direction

136

main direction of propagation

138

Entry

140

Exit

142

subarea

144

end area

146

position

148

Section

150

single waveguide

152

enveloping

154

diffractive optical element

156

lens element

158

Microlens Array

160

lens element

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2020016336 A1 [0003, 0147]
• EP 2248233 B1 [0004]

Claims (14)

Device for combining coherent laser beams, comprising splitting means (110) for splitting an input laser beam (108) into a plurality of coherent laser beams (102), phase adjusting means (120) for adjusting a respective phase of the coherent laser beams (102), and waveguide means (112 , 112', 112"), which has a plurality of cores (114) for the passage of a respective coherent laser beam (102), wherein each of the coherent laser beams (102) is assigned a mode field diameter (d _m ), with which it passes through a respective core (114), characterized in that the waveguide device (112, 112', 112") in an end region (144) of the waveguide device (112, 112', 112") for increasing the mode field diameter (d _m ) of the respective coherent laser beams (102) is formed. device after claim 1 , characterized in that the mode field diameter (d _m ) is increased in the end region (144) and/or that the mode field diameter (d _m ) at an output (140) of the waveguide device (112, 112') located in the end region (144) , 112") for decoupling the coherent laser beams (102) is greatest. device after claim 1 or 2 , characterized in that a respective core diameter (d _k ) of the cores (114) in the end region (144) is increased, and/or that a respective core diameter (d _k ) of the cores (114) at one end region (144) lying output (140) of the waveguide device (112, 112', 112") for coupling out the coherent laser beams (102) is greatest. Device according to one of the preceding claims, characterized in that a center distance (d ₀ ) between adjacent cores (114) is at least approximately constant and is at least approximately constant in particular in the end region (144). Device according to the preamble of claim 1 , characterized in that in an end region (144) of the waveguide device (112, 112', 112") a center distance (d ₀ ) between adjacent cores (114) is reduced. device after claim 5 , characterized in that in the end area (144) a respective core diameter (d _k ) of the cores (114) is reduced, and/or that a respective core diameter (d _k ) of the cores (114) at one end area (144) lying output (140) of the waveguide device (112, 112', 112") for coupling out the coherent laser beams (102) is smallest. device after claim 5 or 6 , characterized in that the cores (114) in the end region (144) converge toward an output (140) of the waveguide device (112, 112', 112") located in the end region (144) for coupling out the coherent laser beams (102). and/or arranged to run towards one another. Device according to one of the preceding claims, characterized in that the waveguide device (112, 112', 112'') is produced in the end region (144) by taping. Device according to one of the preceding claims, characterized in that the coherent laser beams (102) with a filling factor (F) of at least 25 % and preferably at least 80% and particularly preferably at least 90% are coupled out. Device according to one of the preceding claims, characterized by an amplification device (116) for amplifying the coherent laser beams (102) passed through the cores (114), the amplification device (116) being integrated in particular in the waveguide device (112, 112', 112") or is associated with the waveguide device (112, 112', 112"). Device according to one of the preceding claims, characterized by a combination device (118) for combining coherent laser beams (102) coupled out of the waveguide device (112, 112', 112"), and in particular characterized in that the combination device (118) has at least one microlens - Array (158) and / or at least one diffractive optical element (154). Method for combining coherent laser beams, in which an input laser beam (108) is divided into a plurality of coherent laser beams (102) by means of a dividing device (110), the coherent laser beams (102) are distributed by a waveguide device (112, 112', 112") with a A plurality of cores (114) are passed through, a coherent laser beam (102) being passed through a respective core (114) and wherein each of the coherent laser beams (102) is assigned a mode field diameter (d _m ) with which it passes through the respective Core (114) propagates, and in which a respective phase of the coherent laser beams (102) is adjusted by means of a phase adjustment device (120), characterized in that the mode field diameter (d _m ) of the respective coherent laser beams (102) in an end region (144) of the waveguide device (112, 112', 112"). procedure after claim 12 , characterized in that the mode field diameter (d _m ) of the respective coherent laser beams (102) is increased by propagation or during propagation of the coherent laser beams (102) through the end region (144) of the waveguide device (112, 112', 112"). Procedure according to the preamble of claim 12 , characterized in that the coherent laser beams (102) converge in the end region (144) and/or converge.

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