WO2014118516A1 - Fibre optical laser combiner - Google Patents

Fibre optical laser combiner Download PDF

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Publication number
WO2014118516A1
WO2014118516A1 PCT/GB2014/050203 GB2014050203W WO2014118516A1 WO 2014118516 A1 WO2014118516 A1 WO 2014118516A1 GB 2014050203 W GB2014050203 W GB 2014050203W WO 2014118516 A1 WO2014118516 A1 WO 2014118516A1
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WO
WIPO (PCT)
Prior art keywords
fibre
input
diameter
output
fibres
Prior art date
Application number
PCT/GB2014/050203
Other languages
French (fr)
Inventor
Stephen Keen
Stephen Moore
Iain Botheroyd
Original Assignee
Gsi Group Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gsi Group Limited filed Critical Gsi Group Limited
Priority to US14/764,295 priority Critical patent/US9620925B2/en
Priority to EP14701616.6A priority patent/EP2951625B1/en
Priority to PL14701616T priority patent/PL2951625T3/en
Priority to ES14701616.6T priority patent/ES2670976T3/en
Priority to CN201480006534.3A priority patent/CN104969104B/en
Publication of WO2014118516A1 publication Critical patent/WO2014118516A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0905—Dividing and/or superposing multiple light beams
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/0994—Fibers, light pipes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/04—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/255—Splicing of light guides, e.g. by fusion or bonding
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/255—Splicing of light guides, e.g. by fusion or bonding
    • G02B6/2551—Splicing of light guides, e.g. by fusion or bonding using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2856—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers formed or shaped by thermal heating means, e.g. splitting, branching and/or combining elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/43—Arrangements comprising a plurality of opto-electronic elements and associated optical interconnections
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media

Definitions

  • This invention relates to a fibre optical laser combiner.
  • it relates to a combiner for combining the output from several lasers into a single output fibre, and apparatus and methods for controlling the spatial beam profile emitted from that fibre.
  • This fibre is usually radially symmetric (of circular cross-section) and has a uniform refractive index profile (otherwise known as step-index).
  • the beam emitted from such a fibre is thus also circularly symmetric and produces a generally uniform distribution of light on a workpiece receiving a laser beam via the beam delivery optical fibre.
  • One method of producing high power fibre laser systems is to combine the outputs from several lasers via a tapered fibre bundle, spliced to an output fibre. Each laser is delivered to the bundle via a separate input fibre, the laser beams in the separate input fibres are then combined and all their inputs exit via the same single output fibre. These are known generally as output combiners.
  • One aspect of such a combining scheme is that, although the individual input fibres are located in close proximity to each other, the inputs are distinct while they remain in the tapered bundle.
  • the standard output fibre collects all of the inputs and produces a uniform output as all the inputs are overlapped by the same circularly symmetric single refractive index region.
  • WO 2011/048398 discloses a system having a tapered input fibre bundle.
  • the present invention arose in an attempt to provide a combining arrangement which can produce a non-uniform, or tailored light distribution at a workpiece.
  • an optical combiner comprising a bundle of input fibres spliced to an output fibre, said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres.
  • the secondary regions are thereby arranged such that they provide coupling from only a subset of the input fibres.
  • a secondary region is said to overlie an input fibre if the end face of the input fibre is enclosed or partially enclosed within the end face of the secondary region.
  • the first region has a diameter which is preferably equal or substantially equal to the diameter of the input fibre bundle at the splice point.
  • the output fibre may be a double-clad output fibre.
  • the first region may be a cladding.
  • the secondary region may comprise a central core.
  • the secondary region may alternatively or in addition comprise one or more annular regions.
  • the input fibre bundle comprises at least one radially outer set of input fibres, and said annular region overlies said radially outer input fibres.
  • the output fibre may have a secondary region surrounded by a first region, and the input fibre bundle may have a central fibre and a plurality of fibres radially surrounding this, such that the secondary region of the output fibre is of diameter equal to or less than the diameter of the central input fibre. It is preferably positioned with its entry face lying within the area defined by the output face of said central input fibre. It may be co-axial therewith.
  • the secondary region in this or other embodiments may be circular or elliptical, for example, or have other shapes.
  • an output fibre may have a central secondary region and surrounding first region, eg a central core and a surrounding cladding
  • the central core acts to capture the majority of the light from a central input fibre and thus tends to give a pronounced peak in the centre of an output beam profile.
  • a portion of light from the outer input 'port' (ie input fibres) can also be captured by the central core of the output fibre. This can lead to a profile having a central peak, which is beneficial for a range of laser processing operations.
  • an output fibre has an annular secondary region, such as a circular high-index ring that overlaps with the outer fibres of the input bundle
  • a majority of the input light is coupled directly to the annular pedestal which is formed by the high-index ring.
  • This method of producing an annular beam is a robust and simple method compared to other bulk optic schemes.
  • the brightness increases, typically by the ratio of the overall fibre area to the annular pedestal area. Such a profile is also beneficial for a wide range of laser processing applications.
  • the invention provides a method of providing a single output from a plurality of lasers, comprising providing an input fibre bundle having a plurality of input fibres receiving laser outputs from each of a plurality of lasers, and splicing the bundle, at a splice point, to a single output fibre; said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and also includes one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres.
  • the secondary regions may be an annular region or a plurality of annular regions, a combination of a central core and one or more annular regions, or other configurations where more than one high-index region is provided, which regions may be of different refractive indices.
  • the invention provides a laser system including an output combiner as described.
  • the invention provides a method of material processing, or of tailoring a beam profile during material processing, using a method or apparatus as described.
  • Figure 1 shows an end view of input fibre bundle
  • Figure 2 shows a matching output fibre without a secondary region
  • Figure 3 shows a plot of output intensity
  • Figure 4 shows an end view of a fibre bundle
  • Figure 5 a matching output fibre with a secondary region
  • Figure 6 shows a plot of output intensity with edge input
  • Figure 7 shows a plot of output intensity with a centre input
  • Figure 8 shows an end view of an input bundle
  • Figure 9 shows a matching output fibre a secondary region
  • Figure 10 shows a plot of output intensity
  • Figure 11 shows an output fibre similar to Figure 5;
  • Figure 12 shows the output fibre overlapped with a tapered input fibre bundle
  • Figure 13 shows an annular high-index region output fibre similar to that of Figure
  • Figure 14 shows the output fibre of Figure 13 overlapped with a tapered input fibre bundle
  • Figure 15 shows a system usable for material processing.
  • FIGs 1 to 3 show a previously proposed system.
  • An input fibre bundle comprises a bundle of seven fibres comprising a first central fibre 1 and six outer fibres 2a to 2f. Each fibre has a cladding 4 (of diameter d) and a core 3.
  • the fibre bundle is tapered in a known manner. It receives inputs from seven separate fibre lasers at a proximal end and the distal end is shown in the figure, from which the individual laser outputs are emitted via the separate fibres. This is spliced to a matching output fibre 5 typically of cladding diameter 3d.
  • the individual outputs from the separate laser which have been applied through the individual fibres of the fibre bundle shown in Figure 1 are combined the resulting beam is output at the output end of the output fibre 4.
  • Figure 3 shows approximately the relative intensity of the output across the diameter of the output phase of the fibre and it will be seen that this is generally uniform across the entire diameter. Of course, the diagram is simplified and there may be slight variations in practice.
  • Figure 4 again shows a similar input fibre bundle to that of Figure 1.
  • the input fibre bundles themselves are well known and comprise a central core 3 and an outer cladding region .
  • This is spliced to an output fibre 6 shown in Figure 5 which differs from that of Figure 2 by having a central core 7 and a surrounding cladding 8.
  • the cladding region 8 is a first region of refractive index nO
  • the core 7 is a secondary region of index nl, different to nO.
  • the cladding diameter is approximately equal to the outer diameter of the tapered input fibre bundle and thus is of diameter approximately 3d.
  • the central core is of higher refractive index than the cladding.
  • the refractive indices are as follows:
  • Figure 11 also shows the output fibre of Figure 5 and Figure 12 shows this superimposed upon a cross-sectional view of the tapered input fibre, illustrating the individual input fibres 11a to llg and the output fibre 12 having a core 13 which lies generally concentric (coaxial) with, or at least inside (or coextensive with) a central fibre llg.
  • the inner core ( 7, 13) acts to capture the majority of light from the central input fibre llf and thus gives a pronounced peak 15 in the output beam profile which is shown in Figure 6.
  • a portion of the light from the outer input fibre (input ports) 11a to llf is also captured by the central core of the output fibre.
  • a profile as shown in Figure 6 or in Figure 7 for example with a central peak 15 above a plateau level 16 is obtained.
  • Such a profile is beneficial for a range of laser-processing operations.
  • Figure 7 shows an example of a centre input (ie where the input comes mainly or wholly from the central input fibre) and Figure 6 shows an example of an edge input , in which the majority of the input comes from the ring of fibres surrounding the central input fibre. It is seen that with a centre input a much more pronounced peak is obtained but a significant peak is still obtained with an edge input.
  • a centre input a much more pronounced peak is obtained but a significant peak is still obtained with an edge input.
  • Figure 8 again shows an input fibre bundle similar to that of Figure 4.
  • Figure 9 shows an output fibre 17 having an annular relatively high-index region 18. As is shown in Figure 14, this most preferably overlaps the outer fibres (11a to llf) of the input tapered fibre bundle shown in Figure 8. That is, the inner diameter dl is greater than or equal to d (the diameter of an input fibre) and the outer diameter d2 of the annular region is less than or equal to 3 x d, as is shown in Figure 14 where the annulus is shown as being overlapped with the outer input fibres.
  • Figure 15 shows a typical application of the invention in a material processing application.
  • the laser sub units 23 shown may have an output power of up to 1.5kW and the combined beam at 26 may be up to lOkW.
  • the laser source from combiner 25 is directed via coupling optics 27 onto the material to be modified 28.
  • N individual fibre lasers sources 23 are coupled into the combiner 25 through their respective feed fibres 24.
  • the combiner is formed by the fusion of the feed fibre 24 and the delivery fibre 26.
  • the output beam profile at 28 can be controlled as described earlier in this application. Examples of the profiles are shown in figures 6, 7 and 10.
  • a further aspect of this invention is fast switching of the mode profile.
  • the output beam profile at 28 can be switched.
  • each laser may be switched ON or OFF, during a material processing operation, independently of the other laser, to alter or taoilor the beam profile.
  • the time to switch between these two profiles is limited by the response time of the control electronics for the individual lasers 23. Typically this can be of the order of tens of usees. This time is far faster than alternative bulk optic switching methods that have been used previously to control the beam profile. This rapid switching time enables the possibility of in process beam profile switching for optimised material processing.
  • One, two or more of the N lasers may be turned ON or OFF, or their output varied, to alter the beam profile.
  • the embodiments shown and described are illustrative only and other
  • Some may have a central core and one or more annular or other shape regions of relatively high-index compared to the rest of the output fibre. Other shapes may be used for different beam profiles.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Electromagnetism (AREA)
  • Lasers (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

An optical combiner (25), comprising a bundle of input fibres (24) spliced to an output fibre (26), the output fibre having a cladding and at least one high-index portion within the cladding, such that the high index portion has a diameter substantially equal to or less than the outer diameter of the input fibre bundle at the splice point.

Description

Fibre Optical Laser Combiner
This invention relates to a fibre optical laser combiner. In particular, it relates to a combiner for combining the output from several lasers into a single output fibre, and apparatus and methods for controlling the spatial beam profile emitted from that fibre.
Many laser-processing schemes rely on beam delivery via an optical fibre. This fibre is usually radially symmetric (of circular cross-section) and has a uniform refractive index profile (otherwise known as step-index). The beam emitted from such a fibre is thus also circularly symmetric and produces a generally uniform distribution of light on a workpiece receiving a laser beam via the beam delivery optical fibre.
For many applications it is desirable to produce tailored non-uniform light distributions on the workpiece, such as an annular profile or profiles having a central peak. Schemes are available for producing such profiles but are often complex and involve the use of free-space optics. The use of these is undesirable, particularly with high-power fibre-laser systems.
One method of producing high power fibre laser systems is to combine the outputs from several lasers via a tapered fibre bundle, spliced to an output fibre. Each laser is delivered to the bundle via a separate input fibre, the laser beams in the separate input fibres are then combined and all their inputs exit via the same single output fibre. These are known generally as output combiners. One aspect of such a combining scheme is that, although the individual input fibres are located in close proximity to each other, the inputs are distinct while they remain in the tapered bundle. The standard output fibre collects all of the inputs and produces a uniform output as all the inputs are overlapped by the same circularly symmetric single refractive index region.
WO 2011/048398 discloses a system having a tapered input fibre bundle. The present invention arose in an attempt to provide a combining arrangement which can produce a non-uniform, or tailored light distribution at a workpiece.
According to the present invention in a first aspect there is provided an optical combiner, comprising a bundle of input fibres spliced to an output fibre, said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres.
The secondary regions are thereby arranged such that they provide coupling from only a subset of the input fibres.
A secondary region is said to overlie an input fibre if the end face of the input fibre is enclosed or partially enclosed within the end face of the secondary region.
The first region has a diameter which is preferably equal or substantially equal to the diameter of the input fibre bundle at the splice point. The output fibre may be a double-clad output fibre.
The first region may be a cladding.
The secondary region may comprise a central core.
The secondary region may alternatively or in addition comprise one or more annular regions. Where the secondary region comprises at least one annular region, the input fibre bundle comprises at least one radially outer set of input fibres, and said annular region overlies said radially outer input fibres. The output fibre may have a secondary region surrounded by a first region, and the input fibre bundle may have a central fibre and a plurality of fibres radially surrounding this, such that the secondary region of the output fibre is of diameter equal to or less than the diameter of the central input fibre. It is preferably positioned with its entry face lying within the area defined by the output face of said central input fibre. It may be co-axial therewith. The secondary region in this or other embodiments may be circular or elliptical, for example, or have other shapes.
Other configurations of the output fibre may be used. In embodiments in which an output fibre has a central secondary region and surrounding first region, eg a central core and a surrounding cladding, it is observed that the central core acts to capture the majority of the light from a central input fibre and thus tends to give a pronounced peak in the centre of an output beam profile. Furthermore, a portion of light from the outer input 'port' (ie input fibres) can also be captured by the central core of the output fibre. This can lead to a profile having a central peak, which is beneficial for a range of laser processing operations.
In embodiments in which an output fibre has an annular secondary region, such as a circular high-index ring that overlaps with the outer fibres of the input bundle, then a majority of the input light is coupled directly to the annular pedestal which is formed by the high-index ring. This leads to an intensity profile of light output against the diameter which has an annular peak. This method of producing an annular beam is a robust and simple method compared to other bulk optic schemes. Furthermore, the brightness increases, typically by the ratio of the overall fibre area to the annular pedestal area. Such a profile is also beneficial for a wide range of laser processing applications. In a further aspect, the invention provides a method of providing a single output from a plurality of lasers, comprising providing an input fibre bundle having a plurality of input fibres receiving laser outputs from each of a plurality of lasers, and splicing the bundle, at a splice point, to a single output fibre; said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and also includes one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres. The secondary regions may be an annular region or a plurality of annular regions, a combination of a central core and one or more annular regions, or other configurations where more than one high-index region is provided, which regions may be of different refractive indices. In a further aspect, the invention provides a laser system including an output combiner as described.
In a further aspect, the invention provides a method of material processing, or of tailoring a beam profile during material processing, using a method or apparatus as described.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:
Figure 1 shows an end view of input fibre bundle;
Figure 2 shows a matching output fibre without a secondary region;
Figure 3 shows a plot of output intensity;
Figure 4 shows an end view of a fibre bundle;
Figure 5 a matching output fibre with a secondary region;
Figure 6 shows a plot of output intensity with edge input;
Figure 7 shows a plot of output intensity with a centre input; Figure 8 shows an end view of an input bundle;
Figure 9 shows a matching output fibre a secondary region;
Figure 10 shows a plot of output intensity;
Figure 11 shows an output fibre similar to Figure 5;
Figure 12 shows the output fibre overlapped with a tapered input fibre bundle;
Figure 13 shows an annular high-index region output fibre similar to that of Figure
9;
Figure 14 shows the output fibre of Figure 13 overlapped with a tapered input fibre bundle; and
Figure 15 shows a system usable for material processing.
Figures 1 to 3 show a previously proposed system. An input fibre bundle comprises a bundle of seven fibres comprising a first central fibre 1 and six outer fibres 2a to 2f. Each fibre has a cladding 4 (of diameter d) and a core 3. The fibre bundle is tapered in a known manner. It receives inputs from seven separate fibre lasers at a proximal end and the distal end is shown in the figure, from which the individual laser outputs are emitted via the separate fibres. This is spliced to a matching output fibre 5 typically of cladding diameter 3d. In the output fibre, the individual outputs from the separate laser, which have been applied through the individual fibres of the fibre bundle shown in Figure 1 are combined the resulting beam is output at the output end of the output fibre 4.
Figure 3 shows approximately the relative intensity of the output across the diameter of the output phase of the fibre and it will be seen that this is generally uniform across the entire diameter. Of course, the diagram is simplified and there may be slight variations in practice.
Figure 4 again shows a similar input fibre bundle to that of Figure 1. Note that the input fibre bundles themselves are well known and comprise a central core 3 and an outer cladding region . This is spliced to an output fibre 6 shown in Figure 5 which differs from that of Figure 2 by having a central core 7 and a surrounding cladding 8. Thus, the cladding region 8 is a first region of refractive index nO, and the core 7 is a secondary region of index nl, different to nO. The cladding diameter is approximately equal to the outer diameter of the tapered input fibre bundle and thus is of diameter approximately 3d. The central core is of higher refractive index than the cladding. In one embodiment, the refractive indices are as follows:
Core = 1.459
Cladding = 1.455
NA = 0.11
Figure 11 also shows the output fibre of Figure 5 and Figure 12 shows this superimposed upon a cross-sectional view of the tapered input fibre, illustrating the individual input fibres 11a to llg and the output fibre 12 having a core 13 which lies generally concentric (coaxial) with, or at least inside (or coextensive with) a central fibre llg. It is observed that the inner core ( 7, 13) acts to capture the majority of light from the central input fibre llf and thus gives a pronounced peak 15 in the output beam profile which is shown in Figure 6. Furthermore, it is also observed that a portion of the light from the outer input fibre (input ports) 11a to llf is also captured by the central core of the output fibre. Thus, a profile as shown in Figure 6 or in Figure 7 for example with a central peak 15 above a plateau level 16 is obtained. Such a profile is beneficial for a range of laser-processing operations.
Figure 7 shows an example of a centre input (ie where the input comes mainly or wholly from the central input fibre) and Figure 6 shows an example of an edge input , in which the majority of the input comes from the ring of fibres surrounding the central input fibre. It is seen that with a centre input a much more pronounced peak is obtained but a significant peak is still obtained with an edge input. By varying the type of input and also the index and size of the central core and/or cladding different outputs can be obtained for different uses.
Figure 8 again shows an input fibre bundle similar to that of Figure 4. Figure 9 shows an output fibre 17 having an annular relatively high-index region 18. As is shown in Figure 14, this most preferably overlaps the outer fibres (11a to llf) of the input tapered fibre bundle shown in Figure 8. That is, the inner diameter dl is greater than or equal to d (the diameter of an input fibre) and the outer diameter d2 of the annular region is less than or equal to 3 x d, as is shown in Figure 14 where the annulus is shown as being overlapped with the outer input fibres.
This leads to an output profile as shown schematically in Figure 10 having an annulus 20, 21 above a plateau 22. In such an output fibre which has an annular high- index region that overlaps with the outer fibres of the tapered input bundle, the large majority of the input light is coupled directly to this annular pedestal. The efficiency of the system tends to be very high compared with free space methods of annular beam generation. In addition, it is found that the brightness of the source actually increases (by the ratio of the overall fibre area to the annular pedestal area).
Figure 15 shows a typical application of the invention in a material processing application. The laser sub units 23 shown may have an output power of up to 1.5kW and the combined beam at 26 may be up to lOkW. The laser source from combiner 25 is directed via coupling optics 27 onto the material to be modified 28.
N individual fibre lasers sources 23 are coupled into the combiner 25 through their respective feed fibres 24. The combiner is formed by the fusion of the feed fibre 24 and the delivery fibre 26. Through the choice of refractive index profile of the delivery fibre 26 and the orientation of the feed fibres 24 relative to this fibre the output beam profile at 28 can be controlled as described earlier in this application. Examples of the profiles are shown in figures 6, 7 and 10.
A further aspect of this invention is fast switching of the mode profile. By individually addressing/controlling the component lasers 23 the output beam profile at 28 can be switched. For example using the combiner described in figures 4 and 5 excitation of all the lasers produces a broad near flat top profile ideal for welding and thick section cutting. Excitation of just the central port laser on the other hand produces a narrow beam profile which is ideal for thin section cutting. Thus, each laser may be switched ON or OFF, during a material processing operation, independently of the other laser, to alter or taoilor the beam profile. The time to switch between these two profiles is limited by the response time of the control electronics for the individual lasers 23. Typically this can be of the order of tens of usees. This time is far faster than alternative bulk optic switching methods that have been used previously to control the beam profile. This rapid switching time enables the possibility of in process beam profile switching for optimised material processing.
One, two or more of the N lasers may be turned ON or OFF, or their output varied, to alter the beam profile. The embodiments shown and described are illustrative only and other
embodiments may be used. Some may have a central core and one or more annular or other shape regions of relatively high-index compared to the rest of the output fibre. Other shapes may be used for different beam profiles.

Claims

Claims
1. An optical combiner, comprising a bundle of input fibres spliced to an output fibre, said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres.
2. An optical combiner as claimed in any preceding claim, wherein the secondary region comprises a central core.
3. An optical combiner as claimed in any preceding claim, wherein the secondary region comprises one or more annular regions.
4. An optical combiner as claimed in any preceding claim, wherein the secondary region comprise at least one annular region, the input fibre bundle comprising at least one radially outer set of input fibres, and wherein said annular region overlies said radially outer set of input fibres.
5. An optical combiner as claimed in Claim 4, wherein the annular region has an inner diameter and an outer diameter and the inner diameter is equal to or greater than the diameter of one of the input fibres and the outer diameter is equal to or less than 3 times the diameter of one of the input fibres.
6. An optical combiner as claimed in Claim 5, wherein the input fibres are all of substantially the same outer diameter.
7. An optical combiner as claimed in Claim 5 or 6, wherein the bundle of input fibres comprises an inner fibre and a plurality of fibres surrounding the inner fibre, the annular secondary region not overlying said inner fibre.
8. An optical combiner as claimed in any preceding claim, wherein the output fibre comprises a central core and a surrounding cladding, and the input fibre bundle comprise a central fibre and a plurality of fibres radially surrounding this, such that the central core of the output fibre is of diameter equal to or less than the diameter of the central input fibre.
9. An optical combiner as claimed in Claim 8, wherein the central core of the output fibre is positioned with its entry face lying within the area defined by the output face of said inner input fibre.
10. A combiner as claimed in Claim 8 or Claim 9, wherein the central core of the output fibre is co-axial with the inner input fibre.
11. A method of providing a single output from a plurality of lasers, comprising providing an input fibre bundle having a plurality of input fibres receiving laser outputs from each of a plurality of lasers, and splicing the bundle, at a splice point, to a single output fibre; said output fibre comprising a first region with refractive index nO and diameter equal to or greater than the input fibre bundle diameter and also includes one or more secondary regions within the first region, the second regions each having refractive index that differs from nO, each of the secondary regions not overlying all of the input fibres.
12. A method as claimed in Claim 11, which is a method of providing a single output from a plurality of fibre lasers.
13. A method as claimed in Claim 11 or Claim 12, wherein the relatively high-index region or regions is one or more annular regions.
14. A method as claimed in Claim 13, wherein an annular high-index region is provided and wherein the input fibre bundle comprises a central fibre and a plurality of radially outer fibres, the annular region overlapping the radially outer fibres.
15. A method as claimed in Claim 14, wherein annular high-index region has a diameter which is greater than or equal to the diameter of one of the input fibres and less than or equal to 3 times the diameter of one of the input fibres.
16. A method as claimed in Claim 15, wherein the input fibres are all of the same diameter.
17. A method as claimed in any of Claims 11 to 16, wherein a high-index region comprises a central core which is of diameter equal to or less than the diameter of a central input fibre.
18. A method as claimed in Claim 17, wherein the central core of the output fibre is positioned with its entry face lying within the area defined by the output face of said inner one of the input fibres.
19. A method as claimed in Claim 18, wherein the central core is co-axial with an inner input fibre.
20. A method as claimed in any of Claims 11 to 19, comprising controlling the outputs of each of the plurality of lasers independently to select or adjust the beam profile of a beam output from the output fibre.
21. A method as claimed in Claim 20, wherein the outputs of each of the plurality of lasers is adjusted during operation to alter the output beam profile during an operation.
22. A method as claimed in any of Claims 11 to 21, used in a material processing operation.
23. An optical combiner substantially as hereinbefore described with reference to, and as illustrated by, any of the accompanying drawings.
24. A method of providing an optical combiner substantially as hereinbefore described.
PCT/GB2014/050203 2013-01-31 2014-01-27 Fibre optical laser combiner WO2014118516A1 (en)

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US14/764,295 US9620925B2 (en) 2013-01-31 2014-01-27 Fiber optical laser combiner
EP14701616.6A EP2951625B1 (en) 2013-01-31 2014-01-27 Fibre optical laser combiner
PL14701616T PL2951625T3 (en) 2013-01-31 2014-01-27 Fibre optical laser combiner
ES14701616.6T ES2670976T3 (en) 2013-01-31 2014-01-27 Fiber optic laser combiner
CN201480006534.3A CN104969104B (en) 2013-01-31 2014-01-27 Optical-fiber laser synthesizer

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GB1301745.4A GB2510370A (en) 2013-01-31 2013-01-31 Fibre Optical Laser Combiner
GB1301745.4 2013-01-31

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CN104969104A (en) 2015-10-07
CN104969104B (en) 2018-12-04
ES2670976T3 (en) 2018-06-04
EP2951625A1 (en) 2015-12-09
US20150372444A1 (en) 2015-12-24
GB2510370A (en) 2014-08-06
PL2951625T3 (en) 2018-08-31
US9620925B2 (en) 2017-04-11
GB201301745D0 (en) 2013-03-20
EP2951625B1 (en) 2018-04-04

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