Fibre laser amplifier comprising a lateral pumping device

Abstract

The present invention relates to a fibre optical amplifier, comprising an amplifying optical fibre (1), comprising a doped core (11), at least one optical cladding (12, 13) and an outer covering (14), the optical amplifier also comprising at least one lateral pumping device (2), comprising a pumping optical fibre (21) assembled with the amplifying optical fibre (1) at a junction zone (20). According to the invention, the outer covering (14) is made of a material with high thermal conductivity, covers most of the perimeter of the amplifying optical fibre (1) at the segments (101, 102) of this fibre which surround the junction zone (20), and covers part of this perimeter at the segment (103) of this fibre comprising the junction zone (20), so that the outer covering (14) extends without interruption on the amplifying optical fibre (1).

Description

Fiber laser amplifier including a side pump device. Field of invention

[0001] The present invention relates to laser amplifiers. It relates in particular to fiber laser amplifiers, in which a light beam is amplified during its propagation in an amplifying optical fiber.

[0002] In particular, the invention relates to such fiber laser amplifiers comprising a side pump device. Prior art

[0003] Fiber laser amplifiers are optical devices well known to those skilled in the art, in which light radiation is amplified during its propagation along an amplifying optical fiber.

[0004] Amplifying optical fibers are generally composed of at least one core surrounded by an optical cladding. The core is most often made of a silica matrix that is doped, generally with rare earth ions, to form an optical amplifying medium. This core of the optical fiber is intended to guide and amplify the light beam to be amplified.

[0005] The core is usually surrounded by an optical cladding (commonly referred to as "cladding"), which is often made of silica whose refractive index is lower than that of the core it surrounds. This index jump advantageously keeps the light beam to be amplified in the core, without it being able to escape into the optical cladding.

[0006] The optical cladding itself is capable of guiding a light beam along the amplifying optical fiber. A so-called "pump" light flux is introduced into this optical cladding. By circulating along the optical cladding, this pump light flux is caused to pass through the doped core, in which its photons are absorbed by the doping ions of the core, which then pass into an excited state. These excited doping ions of the core then allow the amplification of the light beam to be amplified circulating in the core.

[0007] The optical cladding surrounding the core of the optical fiber must ensure the guidance of the pump light flux. To this end, this optical cladding can be surrounded by another optical cladding, called the external optical cladding, whose refractive index is lower than that of the optical cladding surrounding the core, so that the index jump prevents the pump light flux from escaping from the optical cladding surrounding the core.

[0008] It is also possible for the optical cladding surrounding the core, or an external optical cladding surrounding the optical cladding surrounding the core, to be surrounded by an external coating, which may for example be a reflective coating helping to maintain the pump light flux in the amplifying optical fiber. In many cases, this external coating 14 is formed from polymers. It is, most often, non-transparent, or even opaque. It generally makes it possible to protect the amplifying optical fiber against mechanical stresses.

[0009] Increasingly, fiber laser amplifiers are being used to obtain high-power laser beams. They can be included in a laser cavity, or used to amplify a laser beam previously produced in a cavity.

[0010] This use of fiber laser amplifiers to obtain high-power laser beams, however, comes up against difficulties limiting the power of the light beam obtained.

[0011] Thus, optical amplification in a fiber laser amplifier generates non-linear effects, well known to those skilled in the art, which are highly detrimental to the quality of the amplified light beam or its spectral finesse. These non-linear effects increase significantly with the length of the amplifying optical fiber. They therefore require fiber laser amplifiers to implement only a limited length of amplifying optical fiber. An increase in the amplification power of a fiber laser amplifier cannot therefore be obtained by an unlimited lengthening of the amplifying optical fiber, but on the contrary requires an increase in the amplification power per unit length of the amplifying optical fiber.

[0012] To achieve very high power amplification with a limited length of amplifying optical fiber, a very high power pump light flux must be introduced into the optical cladding of the amplifying optical fiber.

[0013] Conventionally, the pump light flux can be introduced into the optical cladding surrounding the core of the amplifying optical fiber at the ends of this amplifying optical fiber. However, such a pump method does not allow the energy of the pump light flux to be distributed homogeneously along the amplifying optical fiber, and requires the introduction of very high optical power at certain points of the amplifying optical fiber.

[0014] To improve the homogeneity of this distribution, it has been proposed to introduce the pump light flux into an amplifying optical fiber by at least one lateral pump device, placed between the two ends of the amplifying optical fiber.

[0015] Such a lateral pump device, which may be complementary to pump devices located at the ends of the amplifying optical fiber, usually comprises a passive pump optical fiber, which conducts a pump optical flow. This pump optical fiber is assembled, for example by welding, to the optical cladding of the amplifying optical fiber, at a segment of the amplifying optical fiber from which the external coating has been removed. This assembly of the pump optical fiber to the optical cladding is carried out in such a way that the pump optical flow circulating in the pump optical fiber passes into the optical cladding of the amplifying optical fiber.

[0016] The introduction of a pump light flux by such a side pump device is for example described in documents EP2618191B1 or US2015 / 0007615A1.

[0017] The temperature increase in a laser amplifier, linked in particular to the emission of heat during optical amplification, is known as a factor limiting the amplification power in an amplifying optical fiber. Indeed, this temperature increase can lead to a loss of quality of the amplified light beam, or even destruction of the laser amplifier.

[0018] In laser amplifiers comprising one or more side pump devices, the junction areas between the amplifying optical fiber and the pump optical fibers are particularly subject to temperature increases, increasing the risks of degradation of the quality of the laser beam produced or of destruction of the laser amplifier.

[0019] Indeed, at these junction zones, the amplifying optical fiber receives a particularly high pump power, which results in a particularly strong excitation of the doping ions located in this zone. This excitation, and the subsequent de-excitation, generate a significant amount of heat.

[0020] Furthermore, the junction between a pump fiber and the amplifying optical fiber carries a very high optical power. This optical power is likely to generate heating at the level of any impurities or irregularities that may appear, particularly at the level of the weld between the fibers.

[0021] Finally, thermal energy dissipation is generally less efficient at this junction zone between the amplifying optical fiber and the pump fiber. Indeed, this junction is made on a segment of the amplifying optical fiber that is stripped of its external coating, generally made of polymer materials, which participates in the dissipation of thermal energy from the amplifying optical fiber.

[0022] Such a junction zone between an amplifying optical fiber and a side pump device is therefore particularly fragile and sensitive to heating. As a result, these side pump devices are rarely implemented for the amplification of very high power laser beams.

[0023] The present invention aims to overcome these drawbacks of the prior art.

[0024] In particular, the invention aims to enable very high power light amplification to be obtained in fiber laser amplifiers.

[0025] A particular objective of the invention is to make it possible to increase the power of the light amplification which can be obtained by fiber laser amplifiers equipped with side pump devices.

[0026] Another objective of the invention is to reduce the risk of degradation of the qualities of the beams obtained, due to heat, or of destruction by heat of fiber laser amplifiers equipped with side pump devices.

[0027] These objectives, as well as others which will appear more clearly subsequently, are achieved using a fiber optic amplifier, this amplifier comprising an amplifying optical fiber, itself comprising at least one doped core, at least one optical cladding surrounding the core(s), and an external coating surrounding the optical cladding(s), this optical amplifier comprising at least one lateral pump device, itself comprising a pump optical fiber assembled to the optical cladding of the amplifying optical fiber, or to at least one of these optical claddings, at a junction zone located between the two ends of the amplifying optical fiber, so as to allow the transfer into the optical cladding, or into at least one of the optical claddings, of at least a portion of a pump light flux propagating in the pump optical fiber.According to the invention, the external coating is made of a material having a thermal conductivity coefficient greater than 1 W / mK, and covers at least 90% of the perimeter of the amplifying optical fiber, at the level of a first segment of said amplifying optical fiber, located between said junction zone and a first end of said amplifying optical fiber, and at the level of a second segment of said amplifying optical fiber, located between said junction zone and a second end of said amplifying optical fiber.The outer coating also covers, according to the invention, a part of the perimeter of said amplifying optical fiber, at the segment of said amplifying optical fiber comprising the junction zone, and extending between the first segment and the second segment of the amplifying optical fiber, such that the outer coating extends without interruption between the first and second segments of the amplifying optical fiber.

[0028] Thus, the outer coating of the amplifying optical fiber can effectively distribute and dissipate the heat generated in the amplifying optical fiber, including at the junction area, which is an area particularly prone to damage by heat. This improvement in heat dissipation at the junction area advantageously makes it possible to increase the amplification power of the fiber optic amplifier, without increasing the risks of damage to the amplifying optical fiber.

[0029] The core and the optical cladding(s) are capable of guiding a light flux into the optical fiber. They are therefore made of a transparent material, often silica-based, capable of transmitting the light flux.

[0030] On the contrary, the external coating is most often made of a non-transparent, most often opaque material.

[0031] The material constituting this external coating has a thermal conductivity coefficient which is preferably greater than 2 W / mK, even more preferably greater than 5 W / mK, and which may be, particularly advantageously, greater than 30 W / mK.

[0032] Preferably, the outer coating completely covers the perimeter of the amplifying optical fiber at the first and second segments of the amplifying optical fiber.

[0033] This situation corresponds to the majority of cases, in which the external coating surrounds the entire perimeter of an optical fiber. The invention can, however, also be applied to situations in which the external coating does not completely cover the perimeter of the optical fiber.

[0034] It should be noted that, if the first and second segments are located between the junction area and the ends of the optical fiber, they do not necessarily extend to these ends. Thus, for example, when the fiber optic amplifier comprises several side pump devices, these first or second segments can be located between the junction areas of two side pump devices.

[0035] According to a particularly advantageous embodiment, the external coating is made of a metallic material.

[0036] By "metallic material" is meant a metal or a metal alloy. Such external metallic coatings of optical fiber are known, in themselves, from the prior art, and the processes for obtaining them are well mastered. Their implementation on the amplifying optical fiber of the invention is particularly advantageous, due to their very good thermal conductivity which allows good heat dissipation.

[0037] Advantageously, the assembly of the pump optical fiber to the optical sheath of the amplifying optical fiber is done by welding at the junction zone.

[0038] Preferably, the outer coating covers at least 50% of the perimeter of the amplifying optical fiber, at the segment of the amplifying optical fiber comprising the junction zone and extending between the first segment and the second segment of the amplifying optical fiber.

[0039] Thus, advantageously, the external coating covers at least 50% of the perimeter of the amplifying optical fiber over the entire length of the amplifying optical fiber.

[0040] The entire length of the amplifying optical fiber is thus covered, over a significant part of its diameter, by an external coating allowing heat dissipation.

[0041] Preferably, the cross-sectional area of ​​the core, or the sum of the cross-sectional areas of the cores, is greater than 400 µm².

[0042] Such cores advantageously allow the propagation of multimode beams. For example, if there is only one core, it can advantageously have a diameter greater than 30 μm.

[0043] Advantageously, the fiber optic amplifier comprises at least two side pump devices, each of these side pump devices being assembled to the amplifying optical fiber at one of said junction zones.

[0044] The multiplication of such side pump devices makes it possible to significantly increase the amplification of the fiber optic amplifier. It is therefore advantageous, on a fiber optic amplifier, to have at least ten side pump devices.

[0045] Advantageously, these junction zones are distributed regularly along the length of the amplifying optical fiber.

[0046] According to an advantageous embodiment, the amplifying optical fiber has at least two distinct optical sheaths, a first optical sheath surrounding the core(s) and an external optical sheath surrounding the first optical sheath.

[0047] Preferably, the outer optical cladding is cut at the junction area(s).

[0048] Such cutting of the outer optical cladding allows the assembly of the pump optical fiber to the first optical cladding surrounding the core(s).

[0049] Cutting the cladding at the junction area can advantageously be achieved by laser ablation. This laser ablation can also achieve cutting of the external optical cladding, if necessary.

[0050] Thus, the present invention also relates to a method of manufacturing a fiber optic amplifier as described above, which comprises a step of local laser ablation of the external coating to form the junction zone, on a portion of the perimeter of said amplifying optical fiber not covering more than 50% of the perimeter of the amplifying optical fiber. Description of figures

[0051] The invention will be better understood upon reading the following description of preferred embodiments, given as a simple figurative and non-limiting example, and accompanied by the figures among which: La is a schematic sectional view, in an axial plane, of a segment of a fiber laser amplifier according to an embodiment of the invention. La is a perspective representation of the portion of the fiber optical amplifier represented by la.

[0052] It thus schematically represents a sectional view in an axial plane of a segment of a fiber laser amplifier in which light radiation is amplified during its propagation along an amplifying optical fiber 1. This fiber laser amplifier can be included in a laser cavity, or be used to amplify a previously formed laser beam.

[0053] In a manner well known to those skilled in the art, the amplifying optical fiber 1 comprises a core 11 surrounded by an optical cladding 12. The core 11 is, in a manner known per se, made up of a silica matrix which is doped with rare earth ions (for example, with Ytterbium ions), in order to constitute an optical amplifying medium. This core of the optical fiber is intended to guide the light beam to be amplified 91. In the embodiment shown, this core has a diameter of the order of 50 μm.

[0054] In other embodiments, the amplifying optical fiber may, in a known manner, have several cores. The present invention applies in an identical manner to such multi-core amplifying optical fibers.

[0055] The core 11 is surrounded by an optical cladding 12 (generally referred to by the English term “cladding”), which is, in a manner known per se, made of silica whose refractive index is lower than that of the core 11 which it surrounds. This index jump advantageously maintains the light beam to be amplified 91 in the core 11, without it being able to escape into the optical cladding 12.

[0056] The optical sheath 12 is itself capable of guiding a light beam along the amplifying optical fiber 1. A light flux 92, called a “pump” light flux, is introduced into this optical sheath 12. By propagating along the optical sheath 12, this pump light flux 92 is caused to pass through the doped core 11, in which the photons are absorbed by the doping ions of the core 11, which then pass into an excited state. These excited doping ions of the core 11 then allow the amplification of the light beam to be amplified 91 propagating in the core 11.

[0057] The optical sheath 12 surrounding the core 11 of the amplifying optical fiber 1 must ensure the guidance of the pump light flux 92. For this, in the embodiment shown, this optical sheath 12 is surrounded by another optical sheath, called external optical sheath 13, whose refractive index is lower than that of the optical sheath 12 surrounding the core 11, so that the index jump prevents the pump light flux 92 from escaping from the optical sheath 12 surrounding the core 11.

[0058] In the embodiment shown, the external optical sheath 13 surrounding the optical sheath 12 surrounding the core 11 is surrounded by an external coating 14, which prevents any leakage of light flux outside the amplifying optical fiber 1 and contributes to the protection of the amplifying optical fiber 1 against mechanical stresses.

[0059] According to the invention, this external coating 14 is made of a material with high thermal conductivity. This material thus has a coefficient of thermal conductivity greater than 1 W / mK, which is higher than that of the polymer materials commonly used for external coatings of optical fibers. Preferably, this coefficient of thermal conductivity is greater than 2 W / mK. Even more preferably, this coefficient of thermal conductivity is greater than 5 W / mK. It is particularly advantageous for this coefficient of thermal conductivity to be greater than 30 W / mK, which is the case for most metallic materials.

[0060] Thus, the external coating 14 can for example be made of a metallic material, or of another material with high thermal conductivity, such as for example a composite or organic material.

[0061] In the majority of cases, the material constituting the external coating 14 is a non-transparent material, most often opaque. Such a solution is often advantageous, since such non-transparent or opaque materials with high thermal conductivity are easy to obtain. Furthermore, the external coating does not normally need to transmit a luminous flux. On the contrary, its function is often to fully reflect the luminous flux circulating in the fiber.

[0062] It is particularly advantageous to produce this coating in a metallic material. Such external metallic coatings of optical fibers are known, in themselves, to those skilled in the art. They are notably known to have mechanical strength and heat resistance which are superior to those of usual polymer coatings. In addition to these previously identified characteristics, the external metallic coatings have a thermal conductivity much higher than that of the polymer coatings. They can therefore contribute, in a stronger way, to the distribution and dissipation of the heat of the amplifying optical fiber 1.

[0063] Such an external coating 14 may for example be made of a metal such as gold, aluminum or copper, which have a very high thermal conductivity (generally greater than 200 W / m / K). The methods for manufacturing optical fibers coated with such external metallic coatings are known to those skilled in the art.

[0064] To obtain very high power amplification, a very high power pump light flux 92 is introduced into the optical sheath 12 of the amplifying optical fiber 1.

[0065] A portion of this pump light flux 92 can be introduced into the optical sheath 12 surrounding the core 11 of the amplifying optical fiber 1 at the ends of this amplifying optical fiber 1, according to a conventional technique well known to those skilled in the art.

[0066] In the embodiment shown, at least a portion of this pump light flux propagating in the amplifying optical fiber 1 is introduced by one or more lateral pump devices 2.

[0067] The fiber laser amplifier segment which is represented by shows such a lateral pump device 2, equipping the amplifying optical fiber 1. The fiber amplifier may however comprise a plurality of these lateral pump devices 2, for example distributed along its length, and may also comprise pump devices at the ends of the amplifying optical fiber 1.

[0068] The lateral pump device 2 which is represented by the comprises a pump optical fiber 21, which conducts a light flux 93 produced by a light-emitting diode 22. This pump optical fiber 21 is assembled, for example by welding, to the optical cladding 12 of the amplifying optical fiber 1, at a junction zone 20 at which the outer coating 14 of the amplifying optical fiber 1 has been removed. This assembly of the pump optical fiber 21 to the optical cladding 12 is carried out in such a way that at least a part of the light flux 93 propagating in the pump optical fiber 21 passes, at the junction zone 20, into the optical cladding 12, to form the pump light flux 92 there.

[0069] In the embodiment shown, the part of the light flux 93 which does not pass directly into the optical sheath 12 and which remains in the pump optical fiber 21 is reflected by a mirror 23 placed at the end of the pump optical fiber 21. It can then pass into the optical sheath 12 during a second passage at the level of the junction zone 20.

[0070] The assembly of the side pump device on the amplifying optical fiber 1 requires, in a known manner, removing the external coating 14 at the level of a portion of this amplifying optical fiber 1.

[0071] In the prior art solutions, when the external coating is made of polymers, it is possible to cut this external coating, on a section of the optical fiber, to remove it and thus strip an entire section of the amplifying optical fiber.

[0072] However, according to the invention, it is provided to implement a different method for removing the external coating 14 at the level of a portion of the amplifying optical fiber 1. Thus, advantageously, the removal of the external coating 14 is carried out only on the portion of the perimeter of the amplifying optical fiber 1 on which the pump optical fiber 21 must be welded, and not on the entirety of this perimeter.

[0073] The, which shows a perspective representation of the portion of the fiber optic amplifier represented by the, shows such a cutout 140 in the external coating 14. It is possible to distinguish, on the represented portion of the amplifying optical fiber 1, three successive segments. At a first segment 101 of the amplifying optical fiber 1, located on one side of the junction zone 20 (i.e. between this junction zone 20 and a first end of the amplifying optical fiber 1), the external coating 14 completely covers the amplifying optical fiber 1. Similarly, at a second segment 102 of the amplifying optical fiber 1, located on the other side of the junction zone 20 (i.e. between this junction zone 20 and a second end of the amplifying optical fiber 1), the external coating 14 completely covers the amplifying optical fiber 1.On the other hand, the segment 103 of the amplifying optical fiber 1, which extends between the first segment 101 and the second segment 102, corresponds to the part of the amplifying optical fiber 1 on which the cutout 140 is formed in the outer covering. This segment 103 therefore comprises the junction zone 20, which is formed in the cutout 140 of the outer covering 14. At this segment 103, the outer covering 14 only covers a part of the perimeter of the amplifying optical fiber 1. This outer covering is however not removed entirely at the junction zone 20, so that it extends without interruption between the first segment 101 and the second segment 102 of the amplifying optical fiber.

[0074] Thus, advantageously, the external coating 14 surrounding the amplifying optical fiber 1 continues continuously on the amplifying optical fiber 1. Indeed, this external coating 14 completely surrounds this amplifying optical fiber 1 on both sides of the junction zone 20 of the lateral pump device 2 on this amplifying optical fiber 1, and covers part of the perimeter of this amplifying optical fiber 1, at the level of this junction zone 20. Preferably, at the level of this junction zone 20, the external coating 14 thus covers between 50% and 80% of the perimeter of the amplifying optical fiber 1.

[0075] The removal of the external coating 14, on the portion of the perimeter of the amplifying optical fiber 1 on which the pump optical fiber 21 is to be welded, can advantageously be done by laser ablation of this external coating 14, which is advantageously limited to the area on which the junction is to be made. For this, a laser is focused on the surface to be ablated and the photons come by heating to tear off the material. The displacement of the focal point determines the surface to be ablated.

[0076] Such laser ablation of the outer coating 14 has the advantage of being able to be carried out efficiently, independently of the material composing the outer coating. Thus, it can efficiently remove coatings, such as certain metallic coatings, which adhere strongly to the optical fiber which they surround, and which cannot be easily removed by a mechanical stripping operation.

[0077] When this removal of the external coating 14 is carried out, it may be provided to also cut the external optical sheath 13, when the amplifying optical fiber 1 comprises such an external optical sheath 13, in order to allow the welding of the pump optical fiber 21 directly onto the optical sheath 12 surrounding the core 11.

[0078] The presence of the external coating 14 continuously, over at least part of the perimeter of the amplifying optical fiber 1, allows a much more efficient distribution and dissipation of thermal energy than in previous solutions of lateral pumps of amplifying fibers.

[0079] This solution according to the invention therefore makes it possible to significantly increase the pump power injected into the amplifying optical fiber 1, and therefore the amplification power of this amplifying optical fiber 1. The external coating, preferably continuous over the entire length of the fiber, thus allows a distribution and dissipation of the heat which greatly limits the risk of degradation of the light beam due to the local rise in temperature and the risk of destruction of the fiber optic amplifier by an excessive rise in temperature. This good temperature dissipation allows the introduction of a very high pump power, by lateral pump devices 2, which allow a homogeneous distribution of the pump energy over the length of the pump.

[0080] The use of the solution according to the invention therefore makes it possible to push back the limits hindering the production of very high power laser beams by amplifying optical fibers.

Claims

Fiber optic amplifier,said amplifier comprising an amplifying optical fiber (1), comprisingat least one doped core (11),at least one optical cladding (12, 13) surrounding said core(s) (11), andan external coating (14) surrounding said optical cladding(s) (12, 13),said optical amplifier comprising at least one lateral pump device (2), comprising a pump optical fiber (21) assembled to said optical cladding (12) of said amplifying optical fiber (1), or to at least one of said optical claddings (12, 13) of said amplifying optical fiber (1), at a junction zone (20) located between the two ends of said amplifying optical fiber (1), so as to allow the transfer into said optical cladding (12), or into at least one of said optical claddings (12, 13), of at least a portion of a luminous flux (93) propagating in said pump optical fiber (21),characterized in that said external coating (14) is made of a material having a thermal conductivity coefficient greater than 1 W / mK, covers at least 90% of the perimeter of said amplifying optical fiber (1), at a first segment (101) of said amplifying optical fiber (1), located between said junction zone (20) and a first end of said amplifying optical fiber (1), and at a second segment (102) of said amplifying optical fiber (1), located between said junction zone (20) and a second end of said amplifying optical fiber (1), covers a part of the perimeter of said amplifying optical fiber (1), at a segment (103) of said amplifying optical fiber (1) comprising said junction zone (20), and extending between said first segment (101) and said second segment (102) of said amplifying optical fiber (1),such that said outer coating (14) extends without interruption between said first segment (101) and second segment (102) of said amplifying optical fiber (1)., Fiber optic amplifier according to the preceding claim, characterized in that said external coating (14) completely covers the perimeter of said amplifying optical fiber (1) at the level of said first segment (101) and second segment (102) of said amplifying optical fiber (1). Fiber optic amplifier according to any one of the preceding claims, characterized in that said external coating (14) is made of a metallic material. Fiber optic amplifier according to any one of the preceding claims, characterized in that the assembly of said pump optical fiber (21) to said optical sheath (12) of said amplifying optical fiber (1) is made by welding at said junction zone (20). Fiber optic amplifier according to any one of the preceding claims, characterized in that said external coating (14) covers at least 50% of the perimeter of said amplifying optical fiber (1), over the entire length of said amplifying optical fiber (1). Fiber optic amplifier according to the preceding claim, characterized in that the surface area of ​​the section of said core (11), or the sum of the surface areas of the sections of said cores, is greater than 400 µm². Fiber optic amplifier according to any one of the preceding claims, characterized in that it comprises at least two side pump devices (2), each of said side pump devices (2) being assembled to said amplifying optical fiber (1) at one of said junction zones (20). Fiber optic amplifier according to the preceding claim, characterized in that said junction zones (20) are distributed regularly over the length of said amplifying optical fiber (1). Fiber optic amplifier according to any one of the preceding claims, characterized in that said amplifying optical fiber (1) has at least two separate optical claddings (12, 13), a first optical cladding (12) surrounding said core(s) (11) and an external optical cladding (13) surrounding said first optical cladding (12). Fiber optic amplifier according to the preceding claim, characterized in that said external optical cladding (13) is cut at said junction zone(s) (20). Method for manufacturing a fiber optic amplifier according to any one of the preceding claims, characterized in that it comprises a step of local laser ablation of said external coating (14) to form said junction zone (20), on a portion of the perimeter of said amplifying optical fiber (1) not covering more than 50% of the perimeter of said amplifying optical fiber (1).

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