WO2008006505A2 - Dispositif laser - Google Patents

Dispositif laser Download PDF

Info

Publication number
WO2008006505A2
WO2008006505A2 PCT/EP2007/005967 EP2007005967W WO2008006505A2 WO 2008006505 A2 WO2008006505 A2 WO 2008006505A2 EP 2007005967 W EP2007005967 W EP 2007005967W WO 2008006505 A2 WO2008006505 A2 WO 2008006505A2
Authority
WO
WIPO (PCT)
Prior art keywords
laser
sections
laser device
laser light
emitters
Prior art date
Application number
PCT/EP2007/005967
Other languages
German (de)
English (en)
Other versions
WO2008006505A3 (fr
Inventor
Maxim Darsht
Aleksei Mikhailov
Vitalij Lissotschenko
Iouri Mikliaev
Original Assignee
Limo Patentverwaltung Gmbh & Co. Kg.
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 Limo Patentverwaltung Gmbh & Co. Kg. filed Critical Limo Patentverwaltung Gmbh & Co. Kg.
Publication of WO2008006505A2 publication Critical patent/WO2008006505A2/fr
Publication of WO2008006505A3 publication Critical patent/WO2008006505A3/fr

Links

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
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4031—Edge-emitting structures
    • H01S5/4062—Edge-emitting structures with an external cavity or using internal filters, e.g. Talbot filters

Definitions

  • the present invention relates to a laser device comprising at least one semiconductor laser and / or at least one semiconductor optical amplifier having a plurality of emitters.
  • Such semiconductor lasers which are embodied, for example, as laser diode bars, represent a significant advancement in terms of beam quality over conventional wide-band laser diode bars, which can only emit multi-mode laser radiation.
  • a plurality, for example 49, single-mode individual lasers are arranged at a distance from one another in a bar.
  • Each of these single lasers has a beam quality factor M 2 of 1 or slightly more than 1.
  • the diffraction factor M 2 is a measure of the
  • Diffraction factor M 2 is approximately equal to 49 and thus much smaller than in conventional multi-mode laser diode bars. Their diffraction factor M 2 can be significantly more than 1000. But this is the light of the single-mode laser diode bar much better coupled into an optical fiber with a small cross-section.
  • a disadvantage of conventional laser devices with such single-mode laser diode bars proves to be the fact that even the diffraction factor M 2 of about 49 or more is still relatively large, so that the focusability of such Laser radiation into an optical fiber with a small cross-section is still not very good.
  • Such power densities can be achieved with single-mode
  • Laser diode bars are achieved under optimal conditions. However, then no power reserve remains.
  • the problem underlying the present invention is thus the creation of a laser device of the type mentioned, which is better focusable.
  • the laser device comprises means for r phase coupling of the laser light of at least a plurality of emitters, in particular of all emitters, wherein the means for phase coupling are arranged outside the at least one semiconductor laser.
  • Laser light of all the emitters can be achieved so that the semiconductor laser no longer lasing on a number of modes corresponding to the number of emitters, but that ideally the semiconductor laser only lasers in a single longitudinal and / or transversal mode. This would ideally result in a single
  • this laser light can be focused much better in an optical fiber of small cross-section than the light of a known from the prior art Laser device. In particular, this results in a significantly greater light power which can be coupled into an optical fiber.
  • the means for phase coupling comprise lens means for Fourier transformation of the laser light.
  • the means for phase coupling comprise lens means for Fourier transformation of the laser light.
  • Phase coupling comprise mirror means, of which the laser light can be partially reflected back into the at least one semiconductor laser.
  • the mirror means may comprise spaced first portions which may at least partially reflect the laser light, between these first portions second portions are angeord net, which have a different, in particular a lower reflectivity for the laser light than the first sections, wherein the second portions, in particular, can not reflect the laser light or only to a small degree or only scattering back into the at least one semiconductor laser.
  • the first and the second sections may be arranged such that they correspond to a Fourier-transformed intensity distribution of the phase-coupled laser light of a plurality, in particular all emitters of the semiconductor laser in the Fourier plane of the lens means.
  • the semiconductor laser becomes on a single longitudinal and / or transversal mode to lasers, so that ultimately single-mode laser light can be generated.
  • the laser device it is possible for the laser device to comprise a lens array on which the mirror means are formed, for example by means of a corresponding surface coating.
  • This lens array can simultaneously serve for collimating the laser light.
  • the reflective surface coating is formed as only partially reflective coating, so that a part of the
  • the means for phase coupling comprise a spatial filter. This can be arranged in the Fourier plane of the lens means. Due to this arrangement, also after feedback of a part of the laser light into the semiconductor laser, the phase and possibly also the wavelength of the laser light emitted by the emitters can be influenced.
  • the means for phase coupling comprise at least one seed laser whose laser light can be at least partially coupled into the semiconductor laser. It can be provided that the at least one seed laser as a single-mode
  • Laser diode or as a laser diode bar with single-mode single emitters or as an array of single-mode laser diodes is formed. In this way it can be ensured that the at least one semiconductor laser lasers in a single longitudinal and / or transverse mode. It may be provided that the seed laser is used only for adjusting the laser device.
  • the emitters of the at least one semiconductor laser are designed such that they can each generate single-mode laser light.
  • the semiconductor laser is designed as a laser diode bar with single-mode single emitters or as a stack of laser diode bars with single-mode single emitters.
  • the laser device comprises a plurality of laser diode bars with single-mode single emitters or also a plurality of stacks.
  • an antireflection coating may be provided on one or both end surfaces of the semiconductor laser, so that it no longer serves as a laser but as an optical amplifier.
  • Fig. 1 is a schematic side view of a first
  • FIG. 2 shows a first embodiment of a lens array serving as a mirror means
  • FIG. 3 shows a second embodiment of a lens array serving as a mirror means
  • Fig. 5 is a schematic side view of another
  • Fig. 6 is a schematic plan view of the embodiment of FIG. 5;
  • Fig. 7 is a schematic side view of another
  • FIG. 8 shows a schematic side view of a further embodiment of a laser device according to the invention
  • 9 shows a clarification of the separation of an incident portion of the laser light from a reflected-back portion of the laser light by means of polarization cubes;
  • Fig. 10 is a schematic side view of another embodiment of an inventive
  • FIG. 1 shows a laser device according to the invention comprising a semiconductor laser 1, a lens means 2 and a lens array 3.
  • the semiconductor laser 1 may be formed, for example, as a laser diode bar with single-mode single emitters.
  • the lens means 2 may be a plano-convex or biconvex lens or a multiple lens.
  • the lens array 3 may for example be a cylindrical lens array, wherein in the illustrated embodiment, the cylinder axes may extend into the plane of the drawing.
  • the distance between the lens means 2 to the semiconductor laser 1 and to the lens array 3 is in each case the same size, in particular as large as the focal length of the lens means 2.
  • a Fourier transformation results in the intensity distribution of the laser light in the
  • Fig. 1 the individual emitter 6 of the semiconductor laser 1 are illustrated by dots.
  • the laser light emanating from them is superimposed by the lens means 2 in the entry plane 5 in such a way that there arises a Fourier transformation of the intensity distribution in the exit plane 4.
  • FIG. 2 an exemplary embodiment of the lens array 3 is indicated.
  • the lens array 3 comprises on its entrance side a plurality of parallel aligned cylindrical lenses 7, on whose crests first sections 8 are arranged, which are partially mirrored.
  • the first portions 8 may have a reflectivity between 10% and 20%.
  • the second sections 9 arranged between these first sections 8 consist in part of the flanks of the cylindrical lenses 7 and partly of the wave troughs 10 of the cylindrical lenses 7.
  • These wave troughs 10 can in particular be roughened or coated in a targeted manner, so that no reverse reflection can take place from these areas. From the flanks of the cylindrical lenses 7, no direct or only a very small back reflection of the laser light can take place. Only the first sections 8 are provided with a partially reflective coating, so that the laser light 1 1 occurring on these first sections 8 is reflected back as a reflecting laser light 12. The non-reflected portions of the laser light 1 1 pass through the lens array 3 and can be collimated by this, for example, in a manner known per se from the prior art.
  • the arrangement of the first sections 8 in the entrance plane 5 or in the Fourier plane of the lens means 2 corresponds to a Fourier transformation of an intensity distribution of the laser light, which would result if all emitters 6 were phase-locked.
  • Words can by the in Fig. 2 or in Fig. 3 example indicated arrangement of the first sections 8 can be achieved that only laser light 12 is reflected back, which corresponds to a phase-locked operation of all the emitter 6 of the semiconductor laser 1.
  • the width of the first portions 8 in the direction in which the first and the second portions 8, 9 arranged side by side are, is small compared to the center distance (pitch) P 2 of the first portions 8.
  • the pitch P 2 is about 50 times as large as the width of each of the first portions 8
  • the pitch P 2 may be about 0.5 mm and the width of the first portion may be about 10 ⁇ m. This corresponds to a Fourier transformation of the phase-coupled intensity distribution of the emitters 6. In this Fourier transformation, narrow maxima are separated by large regions in which the intensity is zero or approximately zero.
  • a phase-coupled state of the back-reflected laser light 12 is indicated.
  • levels 13 of the same phase of the laser light 12 are indicated.
  • the laser light 12 is reflected back from the first portions 8 by the lens means 2 in the emitter 6 and affects after entering the emitter 6 the
  • Phase and possibly also the wavelength of the emitted from these emitters 6 laser light Due to the feedback of the laser light 12 according to the invention, it would be possible, in the ideal case, to achieve that all the emitters are phase-coupled, and thus the entire semiconductor laser only lasers in a longitudinal and / or transversal mode.
  • a phase-coupled state indicated in FIG. 4 can be found both in the embodiments according to FIGS. 1 to 3 and in the embodiments of FIGS. 5 and 6, FIG. 7, described in detail below. 8 and Fig. 10 are present.
  • Fig. 3 shows a Fig. 2 corresponding embodiment in which the first portions 14 are formed in the troughs of the cylindrical lenses 7.
  • the wave crests 15 are coated or roughened, so that they can not be targeted back reflection.
  • second sections 16 extend, which in addition to the flanks of the cylindrical lenses 7 also include the correspondingly treated wave crests 15.
  • the spacing between the individual sections 8, 14 relative to one another in the direction in which the sections 8, 14 are arranged next to one another can be significantly greater than the spacing of the individual emitters 6 relative to one another.
  • the pitch P 2 of the first sections 8, 14 (see FIG. 2) relates to the center distance Pi of the emitter 6 (see FIG. 4) as well
  • the center distance P 2 of the first sections are selected to each other.
  • the center distance can be chosen to be significantly larger than the center distance Pi of the emitter to each other.
  • a lens array 3 can also be manufactured with respect to devices known from the prior art with considerably less effort, so that the laser light can collimate.
  • Laser diode bar with significantly smaller center distance Pi as is common nowadays, by a suitable choice of the focal length of the lens means 2, a lens array 3 are used for collimating the laser light. In particular, it is no longer necessary, as known from the prior art, to position a lens directly in front of each emitter 6.
  • phase coupling achieved with the device according to the invention can stabilize the wavelength of the Laser light can be achieved. Furthermore, the laser light emitted by the semiconductor laser 1 can have a smaller spectral width than the laser devices known from the prior art. Furthermore, the phase coupling makes the laser device more stable, in particular more independent of external influences such as temperature changes, vibrations and the like.
  • a spatial filter 17 is used which is arranged in a Fourier plane 18. Furthermore, a partially transmissive mirror 51 is provided.
  • the laser light 52 emanating from the semiconductor laser 1 is collimated by collimating lens means disposed behind the semiconductor laser 1.
  • This can be a fast-axis collimation lens
  • lens means 55 are provided, which in the illustrated embodiment consist of three separate lenses 56, 57, 58.
  • the lenses 56, 58 are cylindrical lenses whose cylinder axes extend in the Y direction, so that they only influence the slow axis of the laser light 52.
  • the middle lens 57 is a cylindrical lens whose cylinder axis extends in the X direction so as to influence only the fast axis of the laser light 52.
  • the focal lengths of the lens means 55 are chosen so that a
  • the plane 59 may have a distance from the exit plane 4, which corresponds to twice the focal length f of the fast-axis collimating lens 53.
  • the Distance of the central lens 57 from both the plane 59 and the Fourier 18 correspond to twice their focal length F.
  • the spatial filter 17 arranged in the Fourier plane 18 may consist of a disk with a hole or a gap. But there is also the possibility of a hole or
  • gap pattern that corresponds to a Fourier transform an intensity distribution of the laser light, which would result if all emitters 6 were phase-coupled.
  • Embodiment is designed as a biconvex lens.
  • the distances between the spatial filter 17 and 51 the lens means 60 and between the lens means 60 and the partially transmissive mirror 51 respectively correspond to the focal length F of the lens means 60.
  • the intensity distribution in the Fourier plane 18 is thus Fourier-transformed into the plane of the partially transmissive mirror 51, so that an inverse transformation takes place.
  • lens means 61 are provided which can couple the laser light passing through the mirror 51 into an optical fiber 62.
  • the laser light reflected back from the partially reflecting mirror is coupled into the individual emitters 6 and, after entering the emitters 6, influences the phase and possibly also the wavelength of the laser light emitted by these emitters 6.
  • a phase-locked operation can be realized, as in
  • Fig. 4 is shown.
  • correction elements for optical path extension and thus for phase matching in the To arrange device may be, for example, glass blocks or glass wedges.
  • Such correction elements for the optical extension of partial beams of the laser light 52 may be required if the individual emitters 6 are offset from one another, for example due to a so-called "smiley face".
  • Glass wedges have the advantage that they can be displaced, thereby changing the path difference caused by them.
  • "Preferred locations for the arrangement of the optical extension elements are the plane 59 and the Fourier plane 18.
  • the laser light 20 of the seed laser 19 is coupled via a collimating lens 21 and a lens array 22 into the side opposite the exit side of the emitter 6 of the semiconductor laser 1 (from the left in FIG. 7).
  • the light emerging from this to the right in FIG. 7 may be phase-locked and is collimated, for example, by a lens array 23.
  • Lens array 23 arranged at the same time for coupling in the laser light of the seed laser 19.
  • the generally linearly polarized laser light 20 is deflected via a polarization cube 24 to a Faraday rotator 25, which in particular the Polarization direction of the laser light can rotate by 45 °. Since the Faraday rotator 25 irrespective of the direction of propagation of the light passing through it, the polarization direction each time in the same direction d re, the polarization direction by another 45 ° gedet by the repeated passage, so that the exiting from the emitters laser light 26th to the right in Fig. 8 passes through the polarizing cube 24 hind.
  • another non-reciprocal optical element may be used.
  • FIG. 9 a quarter wavelength plate 28 and a mirror 29 are shown in FIG. 9 next to the polarization cube 24.
  • the light 27 entering the polarizing cube 24 from above in FIG. 9 is deflected to the left in FIG. 9 because of its linear polarization direction.
  • This light 30 is reflected on the mirror 29 and undergoes a phase jump. Due to the phase jump, the back-reflected light 31 is linearly polarized by the quarter wavelength plate 28
  • the laser light 20 emanating from the seed laser 19 is deflected onto a lens array 34 via a beam splitter optics 33. After passing through the lens array 34, the laser light 20 passes through an additional collimating lens 35 and is then from a polarization cube 36 to the left in Fig. 10 deflected.
  • a left side adjoining quarter wavelength plate 37 converts the laser light 20 into circularly polarized laser light 38.
  • This laser light 38 is split in a further polarization cube 39 into two linearly polarized laser light components 40, 41 with mutually perpendicular polarization direction. These laser light components 40, 41 are coupled via lenses 42, 43 and lens arrays 44, 45 into two semiconductor lasers 1, 1 'and influence their mode spectra.
  • a half-wavelength plate 46 is still arranged to the
  • Polarization direction to rotate by 90 ° (see the polarization directions clarifying arrows 47, 48 in Fig. 10). This polarization direction rotated by 90 ° corresponds to that of the semiconductor laser 1, so that a more efficient coupling or phase coupling is made possible.
  • the laser light components 40, 41 coupled into the semiconductor lasers 1, 1 'undergo reflection on the rear sides of the semiconductor lasers 1, 1' and thus a phase jump.
  • a phase jump As a result, after merging the laser light components 40, 41 in the polarization cube 39, that propagates to the right in FIG.
  • Laser light 49 has a circular polarization which rotates the other way round than that of the oppositely moving laser light 38. However, after passing through the quarter wavelength plate 37, laser light 50 with a linear polarization perpendicular to that of the originally coupled laser light 20 of the
  • Seed laser 19 is aligned.
  • Laser light 20 are performed on the exit plane 4 of the semiconductor laser 1.
  • an image of the laser light on the exit plane 4 of the semiconductor laser 1 can be performed.
  • the semiconductor laser 1 does not function as a laser but as an optical amplifier for that of the seed laser
  • partially reflective coatings may also be provided on one or both end surfaces.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)

Abstract

L'invention concerne un dispositif laser comprenant au moins un laser à semi-conducteur (1, 1') et/ou au moins un amplificateur à semi-conducteur optique doté d'une pluralité d'émetteurs (6). Le dispositif laser comporte des moyens de couplage de phase de la lumière laser (11) d'au moins plusieurs émetteurs (6), notamment de tous les émetteurs (6), les moyens de couplage de phase étant disposés à l'extérieur du laser à semi-conducteur (1, 1').
PCT/EP2007/005967 2006-07-14 2007-07-05 Dispositif laser WO2008006505A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE102006033070 2006-07-14
DE102006033070.6 2006-07-14
DE102007007412.5 2007-02-12
DE102007007412 2007-02-12

Publications (2)

Publication Number Publication Date
WO2008006505A2 true WO2008006505A2 (fr) 2008-01-17
WO2008006505A3 WO2008006505A3 (fr) 2008-02-28

Family

ID=38442572

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2007/005967 WO2008006505A2 (fr) 2006-07-14 2007-07-05 Dispositif laser

Country Status (1)

Country Link
WO (1) WO2008006505A2 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102017131000A1 (de) * 2017-12-21 2019-06-27 LIMO GmbH Kollimationsvorrichtung für einen Nanostack
US11752571B1 (en) 2019-06-07 2023-09-12 Leonardo Electronics Us Inc. Coherent beam coupler

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4813762A (en) * 1988-02-11 1989-03-21 Massachusetts Institute Of Technology Coherent beam combining of lasers using microlenses and diffractive coupling
EP0661785A2 (fr) * 1993-12-28 1995-07-05 Fuji Photo Film Co., Ltd. Appareil laser
US20030103534A1 (en) * 2001-11-30 2003-06-05 Braiman Yehuda Y. Master laser injection of board area lasers

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4813762A (en) * 1988-02-11 1989-03-21 Massachusetts Institute Of Technology Coherent beam combining of lasers using microlenses and diffractive coupling
EP0661785A2 (fr) * 1993-12-28 1995-07-05 Fuji Photo Film Co., Ltd. Appareil laser
US20030103534A1 (en) * 2001-11-30 2003-06-05 Braiman Yehuda Y. Master laser injection of board area lasers

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
D'AMATO F X ET AL INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING: "MODE CONTROL OF AN ARRAY OF ALGAAS LASERS USING A SPATIAL FILTER INA TALBOT CAVITY" LASER DIODE TECHNOLOGY AND APPLICATIONS LOS ANGELES, JAN. 18 - 20, 1989, PROCEEDINGS OF SPIE:, BELLINGHAM, SPIE, US, Bd. VOL. 1043, 18. Januar 1989 (1989-01-18), Seiten 100-106, XP000129172 *
GRUNWALD R ET AL: "Microlens arrays for segmented laser architectures" PROCEEDINGS OF THE SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING USA, Bd. 2383, 1995, Seiten 324-333, XP002433962 ISSN: 0277-786X *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102017131000A1 (de) * 2017-12-21 2019-06-27 LIMO GmbH Kollimationsvorrichtung für einen Nanostack
US11752571B1 (en) 2019-06-07 2023-09-12 Leonardo Electronics Us Inc. Coherent beam coupler

Also Published As

Publication number Publication date
WO2008006505A3 (fr) 2008-02-28

Similar Documents

Publication Publication Date Title
EP2973899B1 (fr) Dispositif de couplage de longueurs d'onde de rayons laser
DE112013007759B3 (de) Halbleiterlaservorrichtung
EP0829120B1 (fr) Source accordable de lumiere laser a reglage stable et a sortie spectrale filtree
DE112017000432B4 (de) Prismen zur verbesserung der strahlqualität und bandbreitenverminderung nutzende wellenlängenstrahlkombinationslasersysteme
DE69731148T2 (de) Festkörperlaserverstärker
DE69324869T2 (de) Vielfachlasersystem mit schmaler Bandbreite
DE112011100813T5 (de) System und verfahren zur selektiven repositionier- und drehwellenlängenstrahlkombination
DE102010031199B4 (de) Vorrichtung und Verfahren zur Strahlformung
EP1145390B1 (fr) Systeme d'amplification laser
DE3942385B4 (de) Beugungsgitter-Verschiebungsmeßgerät
WO2005024516A2 (fr) Dispositif d'eclairage pour une installation d'exposition par projection microlithographique
WO2006045303A2 (fr) Laser multispectral comprenant plusieurs elements de gain
DE112004000773B4 (de) Halbleiterlaservorrichtung
EP2399158B1 (fr) Disposif pour homogeneisation de radiation laser
DE112015005587T5 (de) Optische kreuzkopplung-abschwächungssysteme für wellenlänge-strahl-kombinierende lasersysteme
DE112019003882B4 (de) Lasersystem mit treppenförmig angeordneten slow-axis-kollimatoren
WO2004021525A2 (fr) Dispositif laser a semi-conducteur
EP0961152B1 (fr) Procédé et dispositif pour former un faisceau de lumière collimaté à partir des émissions de plusieurs sources de lumière
DE19752416A1 (de) Verfahren und Vorrichtung zum Kombinieren der Strahlungsleistung einer linearen Anordnung von Strahlenquellen
EP1601072B1 (fr) Système et module de mise en forme des faisceaux optiques pour montage des lasers à diodes
DE112020000301T5 (de) Systeme und verfahren zur ausrichtung von wellenlängenstrahlkombinierenden resonatoren
WO2008006505A2 (fr) Dispositif laser
EP1384105B1 (fr) Dispositif de modelage de faisceau permettant le modelage de la section d'un faisceau lumineux
DE10322806B4 (de) Optische Anordnung zur Homogenisierung eines zumindest teilweise kohärenten Lichtfeldes
WO2003075074A1 (fr) Dispositif de modulation

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 07785906

Country of ref document: EP

Kind code of ref document: A2

NENP Non-entry into the national phase

Ref country code: DE

NENP Non-entry into the national phase

Ref country code: RU

122 Ep: pct application non-entry in european phase

Ref document number: 07785906

Country of ref document: EP

Kind code of ref document: A2