(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(19) World Intellectual Property
`Organization
`International Bureau
`
`_ (10) International Publication Number
`(43) International Publication Date
`WO 2016/062758 Al
` 28 April 2016 (28.04.2016) WIPO! PCT
`
` =
`
`(51)
`
`international Patent Classification:
`H01S 5/40 (2006.01)
`HOIS 5/14 (2006.01)
`HOIS 3/08 (2006.01)
`.
`.
`(21) International Application Number: PCT/EP2015/074348
`(22) International Filing Date:
`
`21 October 2015 (21.10.2015)
`English
`English
`
`.
`(25) Filing Language:
`(26) Publication Language:
`(30) Priority Data:
`14/521,487
`
`23 October 2014 (23.10.2014)
`
`US
`
`(72)
`
`(71) Applicant): TRUMPF LASER GMBH [DE/DE], Aich-
`halder Strasse 39, 78713 Schramberg (DE).
`17, 78647
`Inventors: KILLI, Alexander; Austrasse
`Trossingen (DE). RIED, Steffen; Uhlandstrasse 39, 78628
`Rottweil (DE). TILLKORN, Christoph; Robert-Bosch-
`Strasse 12, 78667 Villingendorf (DE). ZIMER, Hagen;
`Heubergstrasse 23, 78655 Dunningen-Seedorf (DE).
`
`re
`
`(74)
`
`Agent: TRUMPF PATENTABTEILUNG; TRUMPF
`GmbH & Co. KG, TH501 Patente und Lizenzen, Jo-
`hann-Maus-Strasse 2, 71254 Ditzingen (DE).
`
`(81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY,
`BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM,
`DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM,GT,
`HN, HR, HU,ID,IL,IN,IR, IS, JP, KE, KG, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, MX, MY, MZ, NA, NG,NI, NO, NZ, OM,
`PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW,SA, SC,
`SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN,
`TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ,
`TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU,
`TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE,
`nw we srTOENOREpeeae SE a we
`SM. TR) OAPI (BF BJ CF CG Cl CM G GN. GQ.
`GW Ker ML. MR NE SN TD TG).
`»
`GA,
`>
`>
`;
`>
`° ae eee
`,
`Published:
`
`with international search report (Art. 21(3))
`
`WO2016/062758A|HIITININNININNININNHINANNOYINGANTMEKAMM (57) Abstract: A variety of dense wavelength beam combining (DWBC) apparatusesare described herein that combine a plurality of
`
`
`
`
`
`(54) Title: OPEN-LOOP WAVELENGTH SELECTIVE EXTERNAL RESONATOR AND BEAM COMBINING SYSTEM
`
`FIG. 1
`
`
`
`
`individual input beams into a single output beam. DWBCapparatuses contemplated herein are open-loop configurations, i.e. config -
`urations where the wavelength selective optics of a feedback generation system are decoupled from a beam combining system that
`combinesa plurality of input beams each having a wavelength selected from a range of different wavelengths. Specifically, each con-
`stituent beam of the combined output beam produced by the beam combining systemtraverses an optical path that does not include
`the wavelength-selective optics of the feedback generation system. DWBC apparatuses contemplated herein further provide for
`matching the wavelength-dependent angular dispersion functions of optics of the feedback generation system with the wavelength-
`dependent angular dispersion functions of optics of the beam combining system. The external cavity laser diode array comprises
`edge-emitting LD (111A-111N), a focussing optics (112) for divergence control of the emitted beams onto diffracting optics (115), a
`retroreflector (120) and a half-wave plate (113) and a polarizer (114) for control of the output power. An intra-cavity spatial filter
`(116) may be used to contro] the spatial beam quality and an extra-cavity dispersive optics (122) for delivering a combined. mul-
`ti-wavelength high power beam.
`
`BNSDOCID: <WO.
`
`2016062758A1_I_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`OPEN-LOOP WAVELENGTH SELECTIVE EXTERNAL RESONATOR AND BEAM
`
`COMBINING SYSTEM
`
`TECHNOLOGYFIELD
`
`[0001]
`
`The present disclosure relates generally to laser systems and moreparticularly to
`
`systems and methods for narrow-bandwidth laser beam stabilization and multiple laser beam
`
`combining.
`
`BACKGROUND
`
`[0002]
`
`Dense wavelength beam combining (DWBC)techniquesspatially superimpose a
`
`plurality of relatively low power input beamsto produce a single high power output beam. In
`
`order to ensure that the high power output beam is of high quality, DWBC require wavelength-
`locking of each individual emitter. Wavelength-locking refers to forcing a substantial majority
`of radiation emitted by an emitter to be of wavelengthsthat fall within a narrow desired
`
`wavelength spectrum. DWBCsystemsachieve wavelength-locking of each individual emitter by
`
`providing wavelength-selective feedback. Wavelength-selective feedback stimulates emission of
`
`radiation at the desired wavelengths, which crowds outradiation at undesired wavelengths.
`
`DWECsystems can utilize a resonator cavity external to the resonator cavities of the individual
`
`emitters to provide the wavelength-selective feedbackto.
`
`[0003]
`
`Without wavelength-selective feedback, individual emitters in DWBC systems will
`
`emit intolerable levels of radiation at non-desired wavelengths. Radiation having non-desired
`
`wavelengths cannot be combined into a single beam by use of spectral-angular dispersive
`
`elements, e.g. diffraction gratings. As many DWBC systemsoperate as an inverse spectrometer,
`
`the wavelength-selective feedback — and the radiation emitted by the individual emitters — need
`
`to be extremely stable under changing environmental conditions. Additionally, radiation having
`
`non-desired wavelengths can induce temporal fluctuation in the output power by means of
`
`spectral crosstalk between neighboring emitters. Spectral crosstalk refers the situation where a
`
`portion of the radiation emitted by a first individual emitter is directed into a second individual
`
`emitter as feedback.
`
`BNSDOCID: <wO
`2016062758A1_|_>
`
`

`

`-
`
`ee
`
`snreteee oo
`
`WO 2016/062758
`
`PCT/EP2015/074348
`
`In ordertolimit the levels of radiation emitted at non-desired wavelengths, DWBC
`[0004]
`systems can incorporate wavelength filtering cavities designed to remove radiation having non-
`
`desired wavelengths from the low power input beams — or components thereof — as they
`
`propagate through the wavelength filtering cavities. However, spatial filtering is a lossy
`
`procedure that can cause a significant reduction in the efficiency of the DWBCsystems. In order
`
`to limit the reduction in efficiency attributable to special filtering, some DWBC systems perform
`
`spatial filtering in a low-powerregion of an external cavity.
`
`SUMMARYOF THE INVENTION
`
`A variety ofdense wavelength beam combining (DWBC)apparatusesare described
`[0005]
`herein that combine a plurality of individual input beamsinto a single output beam. DWBC
`apparatuses contemplated herein are open-loop configurations, i.e. configurations where the
`
`wavelength selective optics of a feedback generation system are decoupled from a beam
`
`combining system that combinesa plurality of input beams cach having a wavelength selected
`
`from a range of different wavelengths. Specifically, cach constituent beam of the combined
`
`output beam produced by the beam combining system traverses an optical path that does not
`
`include the wavelength-selective optics of the feedback generation system. Therefore, DWBC
`apparatuses contemplated herein perform spatial filtering in a low-powerregion of an external
`
`cavity.
`
`[0006]
`
`DWEBCapparatuses contemplated herein further utilize a first angular provide for
`
`matching the wavelength-dependent angular dispersion functions of optics of the feedback
`
`generation system with the wavelength-dependent angular dispersion functions of optics of the
`
`beam combining system. Asa result, the quality of the output beam produced by the DWBC
`systems contemplated herein is not compromised by a mismatch in the angular dispersive
`
`characteristics of the feedback generation system and the beam combining system.
`
`An external cavity laser apparatus is provided that includes a plurality of beam
`[0007]
`emitters that collectively emit a plurality of external cavity input beams each having a primary
`componentwith aninitial linear polarization state, a beam splitter disposed in an optical path of
`
`the plurality of input beams and configured to extract, from the plurality of external cavity input
`
`beams, a plurality of first extracted component beamsandto direct the plurality of first extracted
`
`2
`
`BNSDOCID: <wO.
`
`2016062758A1_!_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`component beams into a feedback branch, a reflective element disposed in the feedback branch
`
`and configuredto reflect the plurality of first extracted component beams back through the beam
`splitter such that at least a portion of the plurality of first extracted component beamsis
`
`transmitted into the plurality of beam emitters as a plurality of orthogonal feedback component
`beams each having a polarization state that is orthogonalto the initial linear polarizationstate,
`
`andafirst angular dispersive optic disposed in the feedback branch and havinga first
`
`wavelength-dependent angular dispersion function, the first angular dispersive optics being
`
`configured to impart a wavelength-dependent angular spectrum determined bythefirst
`
`wavelength-dependent angular dispersion function on the plurality of first extracted component
`
`beams.
`
`[0008]
`
`A methodis provided for stabilizing the wavelengths of a plurality of input beams
`
`collectively emitted by a plurality of emitters, cach of the plurality of input beams having a
`
`primary componentwith aninitial linear polarization state. The method involves extracting from
`
`the plurality of input beamsa plurality of extracted component beams, directing the plurality of
`
`extracted componentbeams through an angular dispersive optic that imparts a wavelength-
`
`dependent angular spectrum to the plurality of extracted component beams, directing the
`
`plurality of extracted component beams through a feedback branch that includes a wavelength
`
`selective optic so as to provide a plurality of feedback beams that each includes a componentthat
`
`has a polarization state that is orthogonalto the initial linear polarization state of the plurality of
`
`input beams; and directing the plurality of feedback beamsinto the plurality of emitters.
`
`{0009]
`
`A method is provided for producing a combined output beam formedfrom a plurality
`
`of beam combining input beams extracted from a plurality of linearly-polarized laser source
`
`output beamscollectively emitted by a plurality of emitters, each of the plurality of laser source
`
`output beams having a primary component with aninitial linear polarization state. The method
`
`involves extracting from the plurality of input beams a plurality of extracted component beams
`
`and the plurality of beam combining input beams, directing the plurality of extracted component
`
`beamsthrough an angular dispersive optic that imparts a wavelength-dependent angular
`
`spectrum to the plurality of extracted component beams, directing the plurality of extracted
`
`component beams through a feedback branch that includes a wavelength selective optic so as to
`
`provide a plurality of feedback beamsthat each includes a componentthat has a polarization
`
`3
`
`BNSDOCID: <WO.
`
`2016062758A1_I_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`state that is orthogonalto the initial linear polarization state of the plurality of input beams,
`directing the plurality of feedback beamsinto the plurality of emitters, and providing the
`combined output beam bydirecting the plurality of beam combining input beamsat an angular
`dispersive beam combining optic such that each ofthe plurality of beam combining input beams
`emerges from an overlap region ofthe angular dispersive beam combining optic with a common
`direction of propagation.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0010]
`
`The present invention will be described in even greater detail below based on the
`
`exemplary figures. The inventionis not limited to the exemplary embodiments. All features
`
`described and/or illustrated herein can be used alone or combinedin different combinationsin.
`
`embodiments of the invention. The features and advantages of various embodiments of the
`
`present invention will become apparent by reading the following detailed description with
`
`reference to the attached drawings whichillustrate the following:
`
`FIG. 1 illustrates an apparatus for producing, via dense wavelength beam combining
`(0011)
`(DWBC)techniques, a single, multi-wavelength output laser beam comprisinga plurality of
`spatially and directionally overlapped beamsthat each have a narrow wavelength spectrum;
`
`[0012]
`FIG. 2 illustrates an alternative apparatus for producing, via dense wavelength beam
`combining techniques, a single, multi-wavelength output laser beam comprising a plurality of
`spatially and directionally overlapped beams that each has a narrow wavelength spectrum;
`
`FIG. 3 illustrates an additional alternative apparatus for producing, via dense
`[0013]
`wavelength beam combining techniques, a single, multi-wavelength output laser beam
`comprising a plurality of spatially and directionally overlapped beamsthat each has a narrow
`
`wavelength spectrum;
`
`[0014]
`
`FIGS. 4A and 4Billustrate configurations of laser sources for use in an external
`
`cavity laser apparatus wherein the laser sources are arrays of diode lasers formed from horizontal
`
`stacks of diode bars;
`
`BNSDOCID: <WO___-2016062758A1_|_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`[0015]
`
`FIGS. 5A, 5B, and SC illustrate configurations of laser sources for use in an external
`
`cavity laser apparatus wherein the laser sources are arrays of diode lasers formed from vertical
`
`stacks of diode bars; and
`
`[0016]
`
`FIG. 6 illustrates a configuration of a laser source for use in an external cavity laser
`
`apparatus wherein the laser sourceis an array of diode lasers formed from a two-dimensional
`
`stack of diode bars.
`
`DETAILED DESCRIPTION OF THE DRAWINGS
`
`[0017]
`
`The present disclosure describes a variety of dense wavelength beam combining
`
`(DWBC)systems that combinea plurality of individual input beamsinto a single output beam.
`
`The DWBCsystems contemplated herein are open-loop configurations, i.e. configurations where
`
`the wavelength selective optics of a feedback-generation system (which can also be referred to as
`
`a wavelength stabilization system) are decoupled from the beam combining system.
`
`Specifically, each constituent beam of the combined output beam produced by the beam
`
`combining system traverses an optical path that docs not include the wavelength-selective optics
`
`of the feedback generation system.
`
`[0018]
`
`Performing spatial filtering and cross-talk mitigation in a low powerregion of an
`
`external cavity of a DWBCsystem limits the loss in output powerattributable thereto.
`
`Therefore, as compared to configurations where the wavelength selective optics of the feedback
`
`component system form a portion of the optical path betweenthe plurality of input beam emitters
`
`and the beam combining optic of the beam combining system (i.e. “closed-loop” configurations),
`
`open-loop configurations are capable of achieving significantly greater wall-plug efficiency.
`
`[0019]
`
`Furthermore, in the DWBC systems contemplated herein, the angular dispersive
`
`behavior of the wavelength-selective optics of the feedback generation system is identical to the
`
`angular dispersive behavior of the beam combining optic of the beam combining system.
`
`Specifically, the wavelength selective optics of the feedback generation system and the beam
`
`combining components of the beam combining system have identical wavelength-angle
`
`dispersion functions(i.e. the relationship, defined for a range of wavelengths, between the
`
`wavelength of a beam andthe difference between the beam’s angles of incidence and
`
`5
`
`BNSDOCID: <wO.
`
`2016062758A1_|_>
`
`

`

`ae
`
`.
`
`re
`
`WO 2016/062758
`
`PCT/EP2015/074348
`
`transmission with respect to the optic). Therefore, for cach wavelength in the range of
`wavelengths for which the wavelength-angle dispersion function is defined, the difference
`
`between the angle of incidence and the angle of transmission of a beam will be the same with
`
`respect to both the wavelength-selective optics of the feedback generation system and the beam
`
`combining optics of the beam combining system.
`
`[0020]
`
`DWEC systems are described herein that utilize two identical optics as different
`
`systems components. Oneof the identical optics is used as a wavelength-selective component of
`
`the feedback generation system and one is used as a beam combining componentof the beam
`
`combining system. In some of the systems contemplated herein the two identical optics are
`
`identical diffraction gratings. The use of identical optics in both the feedback generation system
`
`and the beam-combining system allows for seamless matching of the wavelength-angle-position
`
`spectrum of a light cone produced by an angular dispersive component of the wavelength
`selective elementofthe feedback generation system and the wavelength-angle-position spectrum
`of a light cone incident on an angular dispersive component of the beam combining system. As a
`result, output beam quality of the DWBC systems contemplated herein is not compromised by a
`
`mismatch in the angular dispersive characteristics of the feedback generation system and the
`
`beam combining system.
`
`[0021]
`
`FIG.1 illustrates an apparatus for producing, via dense wavelength beam combining
`
`(DWBC)techniques, a single, multi-wavelength output laser beam comprisinga plurality of
`
`spatially and directionally overlapped single wavelength beams. The DWBCapparatus 100
`
`includes an input generation system 101, an adjustable beam splitting system 102, a feedback
`
`generation system 103 and a beam combining system 104.
`
`[0022]
`
`The input generation system 101 is a means for producing a plurality of individual
`
`beamsthat together constitute laser source output 151. The input generation system includes a
`
`laser source 111 (which includesa plurality of emitters) and a position-to-angle transform optic
`
`112. The position-to-angle transform optic 112 may also be considered to be part of the
`
`feedback generation system 103 as it interacts with the laser source output 151 in a mannerthat
`
`impacts the downstream properties of the feedback generation system input 153. Similarly, the
`
`position-to-angle transform optic 112 may also be consideredto be part of the beam combining
`
`BNSDOCID: <wO
`
`2016062758A1_|_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`system 104 as it interacts with the laser source output 151 in a mannerthat impacts the
`
`downstream properties of the beam combining system input 154.
`
`[0023]
`
`The adjustable beam splitting system 102 is a meansforsplitting the beam splitting
`
`system input 152 into a feedback generation system input 153 and a beam combining system
`input 154 and also a meansfor directing the feedback generation system input 153 into the
`feedback generation system 103 and directing the beam combining system input 154 into the
`
`beam combining system 104. The adjustable beam splitting system 102 includes a means for
`
`selecting the fraction of optical power directed into the feedback generation system 103 and the
`
`fraction of optical powerdirected into the beam combining system 104. In the embodiment
`illustrated in FIG. 1, the adjustable beam splitting system 102 includes a polarizing beam splitter
`114. However, in alternative embodiments, the adjustable beam splitting system 102 may
`
`include other meansforsplitting a input beams, e.g. a thin-film polarizer.
`
`The feedback generation system 103 is a means for producing wavelength-stabilizing
`[0024]
`feedback 156, that when directed into the laser source 111 as feedback, serves to select, for each
`
`of the plurality of emitters of the laser source 111, a preferred resonant mode. The feedback
`
`gencration system 103 can be identified by the optical path from the polarizing beam splitter 114
`
`through an angular dispersive optic 115 to a reflective element 120 and from thereflective
`
`element 120 back to the polarizing beam splitter 114 in the reverse direction.
`
`[0025]
`
`The beam combining system 104 is a means for producing a single multi-wavelength
`
`combined output beam (combined output beam 160) from a plurality of individual single-
`
`wavelength input beamsthat together constitute the beam combining system input 154. The
`
`beam combining system 104 can be identified by the optical path from the polarizing beam
`
`splitter 104 to an angular-dispersive beam combining optic 122 and into the optical path of the
`
`combined output beam 160.
`
`[0026]
`
`In the embodimentillustrated in FIG. 1, the laser source 111 includes a plurality of
`
`individual emitters (e.g. 111A and 111N) that each emit a single laser beam that is a constituent
`
`beam of the laser source output 151. Each constituent beam ofthe laser source output 151 may
`
`also be called an input beam. The individual laser emitters may be diodelasers, fiber lasers,
`
`solid-state lasers, or any other type of lasers. The plurality of individual emitters that together
`
`7
`
`BNSDOCID: <WO.
`
`2016062758A1_I_>
`
`

`

`7 Ta
`
`:
`
`nel
`
`=
`
`WO 2016/062758
`
`PCT/EP2015/074348
`
`constitute the laser source 111 may be arranged in a one dimensional array, a two dimensional
`
`array, or a variety of other configurations. For example, laser source 111 may be an array of
`
`diode lasers formed from vertical or horizontal stacks of diode bars, each of which hasaplurality
`of individual diode laser emitters. The laser source 111 may beanyarray of diode lasers
`
`configured as depicted in any of FIGS. 4A-B, 5A-C, and 6. However,the laser source 111 is not
`
`limited to such configurations, and embodiments described herein contemplate that a variety of
`
`alternative laser source configurations may be used as well. The configurations of the laser
`
`source 111 depicted in FIGS. 4A-B, 5A-C, and 6 maybe any ofa geometrically stacked
`
`configuration (a geometric stack), an optically stacked configuration (an optical stack), or any
`other meansof configuring a plurality of beams as depicted in those FIGS.
`
`[0027]
`
`Although not shownin the embodimentillustrated in FIG. 1, implementations
`
`contemplate that the input generation system 101 can include a variety of optics for manipulating
`
`the beams emitted by individual emitters of the laser source 111 prior to their interaction with the
`
`position-to-angle transform optic 112. Typically, beams emitted by diode lasers have an
`
`asymmetric beam profile, i.c. the beam diverges at disparate rates along two axes defined
`
`perpendicularto its direction of propagation. The two axes can be identified as a fast axis, along
`
`which the beam diverges morerapidly, and a slow axis, upon which the beam diverges
`
`comparatively more slowly. The manipulation of the beams may bereferred to as preprocessing
`
`and can include, e.g., rotation of the beams such that downstream processing is performed along
`
`a fast axis rather than a slow axis, collimation of the beamsalongthe fast axis, and collimation of
`
`the beams along the slow axis. A variety ofpriorart literature discusses techniques for
`
`preprocessing beams emitted by diode laser emitters, such as those of the laser source 111. For
`
`example, the beams emitted by the laser source 111 may be manipulated as described in U.S.
`
`Patent Application Serial No. 14/053,187 or as describe in U.S. Patent No. 8,724,222.
`
`[0028]
`
`In the embodiment depicted in FIG. 1, each constituent beam of the system input 151
`
`is substantially linearly-polarized. Each emitter of a diode array laser source, such as the laser
`
`source 111, emits a beam that theoretically consists only of a componentthat has aninitial linear
`
`polarization. In various different reference frames, the initial linear polarization can be said to be
`
`a p-polarization, an s-polarization, or a combination of p-polarization and s-polarization.
`However,as a result of various factors (c.g. manufacturing defects), the emitters of a diode array
`
`8
`
`BNSDOCID: <wo
`
`2016062758A1_I_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`laser source each emits a beam that may include an unpolarized componentor that may include
`various components that have a polarization that is at an angle with respect to the theoretical
`
`initial linear polarization. Therefore, in practice, each beam emitted by an emitter in the laser
`
`source 111 may be described as including a primary componentwith aninitial linear polarization
`
`and additional secondary components that can be characterized, at least at a particular instant in
`time, as unpolarized, elliptically polarized, or linearly polarized at an angle with respect to the
`initial linear polarization of the primary component. Such beams can besaid to be primarily
`linearly polarized. A primarily linearly polarized beam is a beam in whichalinearly polarized
`primary componentcarriesat least 80% ofthe total optical power of the beam, preferably carries
`
`at least 90%, and particularly preferably carries at least 94%.
`
`[0029]
`
`Typically, diode laser emitters are marketed as transverse electric (TE) or transverse
`
`magnetic (TM), where the TE or TM describes the manner in which the emitted beams are
`
`primarily linearly polarized. In the remaining discussion of FIG. 1, it is assumed that each
`
`constituent beam ofthe laser source output 151 is primarily p-polarized with respect to the
`principle plane of the polarizing beam splitter 114. However, embodiments herein contemplate
`that each constituent beam ofthe laser source output 151 can also be primarily s-polarized with
`
`respectto the principle plane of the polarizing beam splitter 114 or can be primarily linearly
`polarized in a direction that is neither entirely s-polarized or p-polarized with respect to the
`principle plane of the polarizing beam splitter 114.
`
`[0030]
`
`Each emitter in the laser source 111 hasa particular, fixed location with respect to the
`
`position-to-angle transform optic 112. Therefore, the laser source output 151 has a position
`
`spectrum that corresponds to the spatial distribution of the emitters in the laser source 111. For
`
`example, the position of constituent beam 151A of the laser source output 151 correspondsto the
`
`position of the individual emitter 111A, while the position of the constituent beam 151N of the
`
`laser source output 151 corresponds to the position of the individual emitter 111N.
`
`[0031]
`
`Theposition-to-angle transform optic 112 transforms the position spectrum of the
`
`laser source output 151 into an angular spectrum of the beam splitting system input 152. In the
`
`embodiment depicted in FIG. 1, the angular spectrum of the beam splitting system input 152
`
`refers to the set of angles of transmission with respect to the position-to-angle transform optic
`
`BNSDOCID: <wO.
`
`2016062758A1_|_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`112 of the beam splitting system input 152. The position-to-angle transform optic 112 converts a
`position of each constituent beam ofthe laser source output 151 (which correspondsto a position
`
`of an emitter of the laser source 111) into an angle of incidence with respect to the angular
`
`dispersive optics of both the feedback system (i.e. the angular dispersive optic 115) and the beam
`combining system (ic, the angular dispersive beam combining optic 122). Specifically, the
`angular spectrum of the beam splitting system input 152 determinesthe set of angles of
`
`incidence, with respect to the angular dispersive optic 115 and the angular dispersive beam
`
`combining optic 122, of the constituent beams of the feedback generation system input 153 and
`
`the beam combining system input 154. Therefore, the feedback generation system input 153 and
`
`the beam combining system input 154 both have an angular spectrum that is determined by the
`
`angular spectrum of the beam splitting system input 152. For example, the position-to-angle
`
`transform optic 112 transforms a position of the constituent beam 151A into an angle of
`
`incidence with respect to the angular dispersive optic 115 (whichis transferred to the constituent
`
`beam 153A of the feedback generation system input 153) and also transforms a position of the
`
`constituent beam 151A into an angle of incidence with respect to the angular-dispersive beam
`
`combining optic 122 (whichis transferred to the constituent beam 154A of the beam combining
`
`system input 154).
`
`[0032]
`
`The embodiment depicted in FIG. 1 eliminates a source of output beam quality
`
`degradation present in DWBC apparatuses in whicha position-to-angle transform optic used to
`
`generate angles of incidence with respect to a feedback system angular dispersive optic is distinct
`
`from a position-to-angle transform optic used to generate angles of incidence with respect to a
`beam combining system angular dispersive optic. In such systems,slight differencesin the
`distinct transform optics (even in such cases where the distinct transform optics are
`
`manufactured to identical specifications) can create slight differences in the angular spectrum
`
`they produce and thereby cause degradation in output beam quality. The embodiment depicted
`
`in FIG. 1 eliminates such output beam quality degradation attributable to differences falling
`
`within manufacturing tolerances of position-to-angle transform optics.
`
`[9033]
`
`The adjustable beam splitting system 102 includes a birefringent optic 113 in addition
`
`to the polarizing beam splitter 114. In various embodiments, depending on the system design,
`
`the birefringent optic 113 maybe, ¢.g., a half wave plate or a quarter wave plate. In the
`
`10
`
`BNSDOCID: <wO____2016062758A1_I_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`embodimentdepicted in FIG. 1, the birefringent optic 113 is a half wave plate that rotates the
`
`polarization of the beam splitting system input 152. Specifically, the birefringent optic 113
`
`rotates the primarily linear polarization of each constituent beam of the beam splitting system
`
`input 152. In other words, the birefringent optic 113 rotates the primarily linear polarization of
`
`the beam splitting system input 152 such that each beam emerging from the birefringent optic
`
`113 has a linear polarization that can be represented as the sum of a p-polarized component and
`
`an s-polarized component (wherein p-polarized and s-polarized are defined with respect to the
`
`principle plane of the polarizing beam splitter). Therefore, in the embodimentillustrated in FIG.
`
`1, the beam splitting system input 152, which includes substantially a primary p-polarized
`
`component, is converted bythe birefringent optic 113 into a superimposed combination of an s-
`
`polarized componentand a p-polarized component. Asaresult, after interacting with the
`
`birefringent optic 113, the beam splitting input 152 includes a plurality of altered input
`
`component beams that each includesa first altered input component beam (i.c. a constituent
`
`beam of the s-polarized component) and a second altered input component beam(i.e. a
`
`constituent beam of the p-polarized component).
`
`[0034]
`
`The polarizing beam splitter 114 extracts, from each constituent beam of the beam
`
`splitting system input 152 a first extracted component beam and a second extracted component
`
`beam. The plurality of first extracted component beams collectively constitute the feedback
`
`generation system input 153 andthe plurality of second component beamscollectively constitute
`
`the beam combining system input 154. Specifically, the polarizing beam splitter 114 extracts,
`
`from the beam splitting system input 152, the s-polarized componentanddirects it into the
`
`feedback generation system 103 as the feedback generation system input 153. The polarizing
`
`beam splitter 114 also extracts the p-polarized componentand directs it into the beam combining
`
`system 104 as the beam combining system input 154. In this manner, the adjustable beam
`
`splitting system 102 extracts first and second components of each input beam of the laser source
`
`output 151 and directs the first component into the feedback generation system 103 and the
`
`second componentinto the beam combining system 104.
`
`{0035]
`
`The birefringent optic 113 can itself be rotated in order to adjust the fractions of the
`
`optical powerof the beam splitting system input 152 that is directed to the feedback generation
`
`system 103 and to the beam combining system 104. Therefore, the birefringent optic 113 and the
`
`11
`
`BNSDOCID: <WO.
`
`2016062758A1_|_>
`
`

`

`WO 2016/062758
`
`PCT/EP2015/074348
`
`polarizing beam splitter 114 together provide an “adjustable” meansfor splitting each constituent
`
`beam of the beam splitting system input 152. The adjustability of the adjustable beam splitting
`
`system 102 enables the apparatus 100 to be adjusted to account for variations