Fiber laser amplifier comprising side pumping device

Abstract

The invention relates to a fiber optic amplifier comprising an amplifying fiber (1) comprising a doped core (11), at least one optical cladding (12, 13) and an outer cover layer (14), the optical amplifier further comprising at least one side pumping device (2), the side pumping device (2) comprises a pumping fiber (21) assembled with the amplifying fiber (1) at a junction region (20). According to the invention, the outer cover layer (14) is made of a material with high thermal conductivity, covers a majority of the circumference of the amplifying optical fiber (1) at a section (101, 102) of the optical fiber surrounding the joining region (20), and covers a part of the circumference at a section (103) of the optical fiber comprising the joining region (20), such that the outer cover layer (14) extends uninterruptedly on the amplifying optical fiber (1).

Description

Technical Field

[0001] The present invention relates to laser amplifiers. In particular, the present invention relates to fiber laser amplifiers in which a light beam is amplified while propagating through an amplifying optical fiber.

[0002] In particular, the invention relates to such a fiber laser amplifier comprising a side pumping arrangement. Background Art

[0003] Fiber laser amplifiers are optical devices well known to those skilled in the art, in which optical radiation (light illumination) is amplified as it propagates along an amplifying optical fiber.

[0004] Amplifying optical fibers usually consist of at least one core surrounded by an optical cladding. The core is usually a silica matrix, which is usually doped with rare earth ions to form an optical amplifying medium. Such a core of an optical fiber is designed to guide and amplify a light beam to be amplified.

[0005] The core is usually surrounded by an optical cladding, which is usually made of silica and has a lower refractive index than the core surrounded by the optical cladding. This refractive index jump advantageously keeps the light beam to be amplified within the core to ensure that the light beam does not escape into the optical cladding.

[0006] The optical cladding itself is able to guide the light beam along the amplifying fiber. A so-called "pump" light flux is introduced into the optical cladding. As the pump light flux travels along the optical cladding, this pump light flux also passes through the doped core, where the photons of the pump light flux are absorbed by the dopant ions of the core, which then enter an excited state. These excited dopant ions of the core then amplify the light beam to be amplified that circulates in the core.

[0007] The optical cladding surrounding the core of the optical fiber must guide the pump flux. To achieve this, the optical cladding can be surrounded by another optical cladding, the so-called outer optical cladding, which has a lower refractive index than the optical cladding surrounding the core, so that the refractive index jump prevents the pump flux from escaping from the optical cladding surrounding the core.

[0008] The optical cladding surrounding the core or the outer optical cladding surrounding the optical cladding surrounding the core may also be surrounded by an outer covering layer, for example, the outer covering layer may be a reflective covering layer that helps to keep the pump light flux in the amplifying optical fiber. In many cases, the outer covering layer 14 is made of a polymer. The outer covering layer is usually opaque or even opaque. The outer covering layer is usually used to protect the amplifying optical fiber from mechanical stress.

[0009] Fiber laser amplifiers are increasingly used to generate high-power laser beams. Fiber laser amplifiers can be included in the laser cavity or used to amplify a laser beam previously generated in the cavity.

[0010] However, using fiber laser amplifiers to obtain high-power laser beams encounters the difficulty of limited beam power.

[0011] Therefore, the optical amplification in the fiber laser amplifier will produce nonlinear effects well known to those skilled in the art, which are extremely detrimental to the quality of the amplified beam or its spectral sharpness. These nonlinear effects increase dramatically with the increase of the length of the amplifying fiber. Therefore, this requires that the fiber laser amplifier can only use amplifying fibers of limited length. Therefore, increasing the amplification power of the fiber laser amplifier cannot be achieved by extending the amplifying fiber indefinitely, but requires increasing the amplification power per unit length of the amplifying fiber.

[0012] In order to achieve extremely high power amplification with a finite length of amplifying optical fiber, extremely 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 fiber at the end of the amplifying fiber. However, this pumping method cannot make the energy of the pump light flux evenly distributed along the amplifying fiber, and requires extremely high optical power to be introduced into some points of the amplifying fiber.

[0014] In order to improve the uniformity of this distribution, it has been proposed to introduce the pump light flux into the amplification fiber via at least one side pumping device, which is located between the two ends of the amplification fiber.

[0015] Such a side pumping device can be complementary to the pumping device located at the end of the amplifying fiber and generally comprises a passive pump fiber for conducting the pump light flux. For example, the pump fiber is joined to the optical cladding of the amplifying fiber by welding at a section where the outer coating of the amplifying fiber has been removed. This assembly of the pump fiber and the optical cladding is achieved in such a way that the pump light flux circulating in the pump fiber passes through the optical cladding of the amplifying fiber.

[0016] For example, EP2618191B1 or US2015 / 0007615A1 discloses introducing a pump light flux through such a side pumping device.

[0017] It is known that the temperature increase in laser amplifiers, in particular due to the release of heat during the optical amplification process, is a factor limiting the amplification power in the amplification fiber. This temperature increase can lead to a degradation of the quality of the amplified light beam and even to the destruction of the laser amplifier.

[0018] In laser amplifiers comprising one or more side pumping arrangements, the junction region between the amplification fiber and the pump fiber is particularly susceptible to temperature increases, increasing the risk of degrading the quality of the generated laser beam or damaging the laser amplifier.

[0019] At these junction regions, the amplifying fiber receives particularly high pump powers, which causes the doping ions located in this region to be particularly strongly excited. This excitation and the subsequent de-excitation (de-excitation) generate considerable heat.

[0020] Furthermore, the splice region between the pump and amplifier fibers carries a large amount of optical power, which is likely to generate heat in any impurities or irregularities that may be present, especially in the welds (seams) between the fibers.

[0021] Finally, the heat dissipation at the junction area between the amplifying fiber and the pump fiber is usually inefficient. In fact, the junction area is formed on a section where the outer coating of the amplifying fiber is stripped, which is usually made of polymer material, which helps to dissipate the heat of the amplifying fiber.

[0022] This junction area between the amplifying fiber and the side-pumping device is therefore particularly fragile and sensitive to heating. These side-pumping devices are therefore rarely used to amplify extremely high-power laser beams. Summary of the invention

[0023] The object of the present invention is to overcome these disadvantages of the prior art.

[0024] In particular, the invention has the object of realizing very high-power optical amplification in fiber laser amplifiers.

[0025] A particular object of the invention is to increase the power of optical amplification obtainable by a fiber laser amplifier equipped with a side pumping arrangement.

[0026] Another object of the present invention is to reduce the risk of thermally induced beam quality degradation or thermally induced damage of a fiber laser amplifier equipped with a side pumping arrangement.

[0027] These objects and others that will become clear later are achieved by using a fiber optical amplifier comprising an amplifying fiber, the amplifying fiber itself comprising at least one doped core, at least one optical cladding surrounding the core, and an outer covering surrounding the optical cladding, the optical amplifier comprising at least one side pumping device, the side pumping device itself comprising a pump fiber, the pump fiber being spliced ​​to the optical cladding or at least one of the optical claddings of the amplifying fiber at a splicing region located between the two ends of the amplifying fiber, so that at least a portion of the light flux propagating in the pump fiber can be transferred into the optical cladding or into at least one of the optical claddings. According to the invention, the outer covering is made of a material having a thermal conductivity greater than 1 W / m·K and covers at least 90% of the circumference of the amplifying fiber at a first section of the amplifying fiber, the first section being between the splicing region and the first end of the amplifying fiber, and at a second section of the amplifying fiber, the second section being between the splicing region and the second end of the amplifying fiber. According to the invention, the outer covering layer also covers a portion of the circumference of the amplifying optical fiber at a section of the amplifying optical fiber including the splicing area and extending between the first section and the second section of the amplifying optical fiber, so that the outer covering layer extends uninterruptedly between the first section and the second section of the amplifying optical fiber.

[0028] In this way, the outer coating of the amplifying optical fiber can effectively distribute and dissipate the heat generated in the amplifying optical fiber, including the heat generated in the splicing area which is particularly susceptible to thermal damage. This improvement in heat dissipation at the splicing area advantageously increases the amplification power of the amplifying optical fiber without increasing the risk of damaging the amplifying optical fiber.

[0029] The core and the optical cladding are designed to guide the light flux into the optical fiber. Therefore, the core and the optical cladding are made of a transparent material, usually based on silica, capable of transmitting the light flux.

[0030] In contrast, the outer covering is typically made of an opaque material, most commonly a light-impermeable material.

[0031] The material constituting the outer cover layer has a thermal conductivity which is preferably greater than 2 W / m·K, even more preferably greater than 5 W / m·K, and which may particularly advantageously be greater than 30 W / m·K.

[0032] Preferably, the outer covering layer completely covers the circumference of the amplifying optical fiber at the first section and the second section of the amplifying optical fiber.

[0033] This situation corresponds to most cases where the outer coating surrounds the entire circumference of the optical fiber. However, the present invention can also be applied to the case where the outer coating does not completely cover the circumference of the optical fiber.

[0034] It should be noted that, although the first section and the second section are located between the splice region and the ends of the optical fiber, the first section and the second section do not necessarily extend to these ends. Thus, for example, when the fiber optical amplifier comprises a plurality of side pumping devices, these first or second sections may be located between the splice regions of two side pumping devices.

[0035] According to a particularly advantageous embodiment, the outer cover layer is made of a metallic material.

[0036] "Metallic material" may be understood to mean a metal or a metal alloy. Such metal outer coverings for optical fibers are well known in the prior art and methods for obtaining them are well understood. Such metal outer coverings are particularly advantageous for use on the amplifying optical fiber of the present invention due to their excellent thermal conductivity enabling good heat dissipation.

[0037] Advantageously, the pump fiber is spliced ​​to the optical cladding of the amplification fiber at the splice region by welding.

[0038] Preferably, the outer covering layer covers at least 50% of the circumference of the amplifying optical fiber at a section of the amplifying optical fiber comprising the splice region and located between the first section and the second section of the amplifying optical fiber.

[0039] Thus, advantageously, the outer covering layer covers at least 50% of the circumference of the amplifying optical fiber over the entire length of the amplifying optical fiber.

[0040] Thus, the entire length of the amplifying optical fiber is covered with the outer covering layer used for heat dissipation over a substantial portion of the diameter of the amplifying optical fiber.

[0041] Preferably, the cross-sectional area of ​​the fiber core or the sum of the cross-sectional areas of the fiber cores is greater than 400 μm 2 .

[0042] Such a core advantageously allows multimode light beam propagation.For example, if there is only one core, the core may advantageously have a diameter greater than 30 μm.

[0043] Advantageously, the fiber optic amplifier comprises at least two side pumping devices, each of which is connected to the amplifying optical fiber at one of the splicing regions.

[0044] Increasing the number of such side pumping devices significantly improves the amplification of the fiber optical amplifier. Therefore, it is advantageous to provide at least ten side pumping devices on the fiber optical amplifier.

[0045] Advantageously, these splice regions are evenly distributed along the length of the amplifying optical fiber.

[0046] In an advantageous embodiment, the amplifying optical fiber has at least two different optical claddings, including a first optical cladding surrounding the core and an outer optical cladding surrounding the first optical cladding.

[0047] Preferably, the outer optical cladding is cut at the splicing area.

[0048] Cleaving the outer optical cladding in this manner enables the pump fiber to be spliced ​​with the first optical cladding surrounding the core.

[0049] Cutting the cladding at the junction area can advantageously be achieved by laser ablation. If desired, such laser ablation can also cut the outer optical cladding.

[0050] Therefore, the present invention also relates to a method of manufacturing a fiber optic amplifier as described above, comprising the step of locally laser ablating the outer coating to form a splice region on a portion of the circumference of the amplifying fiber covering no more than 50% of the circumference of the amplifying fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention will be better understood on reading the following description of preferred embodiments given by way of simple symbolic but non-limiting examples and accompanied by the accompanying drawings, in which: - Figure 1 is a schematic cross-sectional view in an axial plane of a section of a fiber laser amplifier according to one embodiment of the present invention. - Figure 2 yes Figure 1 A perspective view of a portion of a fiber optic amplifier is shown in FIG. DETAILED DESCRIPTION

[0052] Figure 1 This schematically shows a cross-section of a section of a fiber laser amplifier in an axial plane, in which optical radiation (light illumination) is amplified while propagating along an amplifying optical fiber 1. The fiber laser amplifier may be contained in a laser cavity or used to amplify a preformed laser beam.

[0053] As is well known to those skilled in the art, the amplifying optical fiber 1 comprises a core 11 surrounded by an optical cladding 12. As is known, the core 11 consists of a silica matrix doped with rare earth ions, such as ytterbium ions, to form an optical amplifier medium. This core of the optical fiber is designed to guide a light beam 91 to be amplified. In the embodiment shown, this core has a diameter of about 50 μm.

[0054] In other embodiments, it is well known that the amplifying optical fiber may have multiple cores. The present invention is also applicable to such multi-core amplifying optical fibers.

[0055] The core 11 is surrounded by an optical cladding 12, which, as is known, is made of silica and has a lower refractive index than the core 11 surrounded by the optical cladding 12. This refractive index jump advantageously keeps the light beam 91 to be amplified within the core 11 to ensure that the light beam does not escape into the optical cladding 12.

[0056] The optical cladding 12 itself is capable of guiding a light beam along the amplifying optical fiber 1. A so-called "pump" light flux 92 is introduced into this optical cladding 12. When the pump light flux 92 propagates along the optical cladding 12, it passes through the doped core 11, where the photons of the pump light flux are absorbed by the doping ions of the core 11, which then enter an excited state. These excited doping ions of the core 11 then amplify the light beam to be amplified 91 propagating in the core 11.

[0057] The optical cladding 12 surrounding the core 11 of the amplification optical fiber 1 must guide the pump light flux 92. To achieve this, in the embodiment shown, this optical cladding 12 is surrounded by a further optical cladding, the so-called outer optical cladding 13, which has a lower refractive index than the optical cladding 12 surrounding the core 11, so that the refractive index jump prevents the pump light flux 92 from escaping from the optical cladding 12 surrounding the core 11.

[0058] In the embodiment shown, the outer optical cladding 13 surrounding the optical cladding 12 surrounding the core 11 is surrounded by an outer covering 14 which prevents any leakage of the light flux outside the amplification optical fiber 1 and helps to protect the amplification optical fiber 1 from mechanical stresses.

[0059] According to the invention, the outer covering 14 is made of a material with high thermal conductivity. Thus, this material has a thermal conductivity greater than 1 W / m·K, which is higher than the thermal conductivity of polymeric materials usually used for outer coverings of optical fibers. Preferably, the thermal conductivity is greater than 2 W / m·K. Even more preferably, the thermal conductivity is greater than 5 W / m·K. It is particularly advantageous if the thermal conductivity is greater than 30 W / m·K, which is the case for most metallic materials.

[0060] For example, the outer cover layer 14 may be made of a metallic material or another material having high thermal conductivity, such as a composite material or an organic material.

[0061] In most cases, the material constituting the outer covering 14 is an opaque material, most commonly a light-impermeable material. This solution is generally advantageous because opaque or light-impermeable materials with high thermal conductivity are readily available. Furthermore, the outer covering is generally not required to transmit the light flux. Instead, the function of the outer covering is generally to reflect the entire light flux passing through the optical fiber.

[0062] It is particularly advantageous to use a metal material for the outer covering. Such metal outer coverings for optical fibers are known per se to the person skilled in the art. In particular, it is known that metal outer coverings provide higher mechanical strength and thermal resistance than conventional polymer coverings. In addition to these properties, metal outer coverings have a much higher thermal conductivity than polymer coverings. Therefore, the metal outer covering can make a greater contribution to the distribution and dissipation of heat from the amplifying optical fiber 1.

[0063] For example, such outer coating 14 may be made of a metal such as gold, aluminum or copper having a very high thermal conductivity (typically exceeding 200 W / m·K). Methods for manufacturing optical fibers coated with such metallic outer coatings are known to those skilled in the art.

[0064] In order to achieve extremely high power amplification, an extremely high power pump light flux 92 must be introduced into the optical cladding 12 of the amplification optical fiber 1 .

[0065] According to conventional techniques well known to those skilled in the art, a portion of the pump light flux 92 can be introduced into the optical cladding 12 surrounding the core 11 of the amplification optical fiber 1 at the end of the amplification optical fiber 1 .

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

[0067] Figure 1 The section of the fiber laser amplifier shown in shows such a side pumping device 2 mounted on the amplifying fiber 1. However, the fiber amplifier may comprise a plurality of such side pumping devices 2, for example distributed along the length of the amplifying fiber 1, and may also comprise a pumping device located at the end of the amplifying fiber 1.

[0068] Figure 1 The side pumping device 2 shown in FIG. 1 comprises a pump fiber 21 that conducts a light flux 93 generated by a light emitting diode 22. For example, the pump fiber 21 is joined to the optical cladding 12 of the amplifying optical fiber 1 by welding at a joining region 20 where the outer coating 14 of the amplifying optical fiber 1 has been removed. Such assembly of the pump fiber 21 and the optical cladding 12 is achieved in such a way that at least a portion of the light flux 93 propagating in the pump fiber 21 enters the optical cladding 12 at the joining region 20 to form the pump light flux 92.

[0069] In the illustrated embodiment, the portion of the light flux 93 that does not pass directly through the optical cladding 12 but remains in the pump fiber 21 is reflected by the mirror 23 placed at the end of the pump fiber 21. This portion can then enter the optical cladding 12 during a second pass through the splice region 20.

[0070] As is known, assembling a side pumping arrangement on an amplification optical fiber 1 involves removing the outer cladding 14 from a portion of the amplification optical fiber 1 .

[0071] In prior art solutions, when the outer coating is made of a polymer, it is possible to cut the outer coating on a portion of the optical fiber to remove it, thereby stripping off the entire portion of the amplifying optical fiber.

[0072] However, according to the present invention, a different method is used to remove the outer coating 14 from a portion of the amplification optical fiber 1. Therefore, it is advantageous to remove the outer coating 14 only on the portion of the circumference of the amplification optical fiber 1 to be welded to the pump fiber 21, rather than on the entire circumference.

[0073] Figure 2 It shows Figure 1 A perspective view of a portion of a fiber optic amplifier is shown in, Figure 2 Such a cut-out 140 in the outer covering 14 is also shown. Three successively connected sections can be distinguished on the shown portion of the amplifying optical fiber 1. The outer covering 14 completely covers the amplifying optical fiber 1 at a first section 101 of the amplifying optical fiber 1 located on one side of the splicing region 20 (i.e. between the splicing region 20 and the first end of the amplifying optical fiber 1). Likewise, the outer covering 14 completely covers the amplifying optical fiber 1 at a second section 102 of the amplifying optical fiber 1 located on the other side of the splicing region 20 (i.e. between the splicing region 20 and the second end of the amplifying optical fiber 1). In contrast, a section 103 of the amplifying optical fiber 1 extending between the first section 101 and the second section 102 corresponds to the portion of the amplifying optical fiber 1 in which the cut-out 140 is formed in the outer covering. Therefore, this section 103 includes the splicing region 20 formed in the cut-out 140 of the outer covering 14. At this section 103, the outer covering 14 covers only a part of the circumference of the amplifying optical fiber 1. However, the outer coating is not completely removed at the splice region 20, so that the outer coating extends uninterruptedly between the first section 101 and the second section 102 of the amplifying optical fiber.

[0074] Thus, advantageously, the outer covering 14 surrounding the amplification fiber 1 extends continuously over the amplification fiber 1. In fact, the outer covering 14 completely surrounds the amplification fiber 1 on both sides of the junction area 20 of the side pumping device 2 on the amplification fiber 1 and covers a portion of the circumference of the amplification fiber 1 at the junction area 20. Preferably, the outer covering 14 covers 50% to 80% of the circumference of the amplification fiber 1 at the junction area 20.

[0075] Removal of the outer coating 14 on the portion of the circumference of the amplification fiber 1 to be welded to the pump fiber 21 can advantageously be achieved by laser ablation of the outer coating 14, and the laser ablation of the outer coating 14 is advantageously limited to the area where the joint is to be formed. To achieve this, the laser is focused on the surface to be ablated, and the photons heat and strip the material. The surface to be ablated is determined by moving the focus.

[0076] This laser ablation of the outer covering 14 has the advantage of being able to be performed efficiently, regardless of the material that constitutes the outer covering. In this way, laser ablation can effectively remove coverings, such as some metal coverings, which are firmly adhered to the optical fiber surrounded by the covering and cannot be easily removed by a mechanical stripping operation.

[0077] When removing the outer covering layer 14 , in case the amplification optical fiber 1 comprises an outer optical cladding 13 , such outer optical cladding 13 may also be cut so that the pump fiber 21 can be welded directly to the optical cladding 12 surrounding the core 11 .

[0078] The continuous presence of the outer cladding layer 14 over at least a portion of the circumference of the amplifying optical fiber 1 enables a more efficient distribution and dissipation of thermal energy than previous amplifying optical fiber side pumping solutions.

[0079] This solution therefore makes it possible to significantly increase the pump power introduced into the amplification fiber 1, and thus the amplification power of the amplification fiber 1. The outer coating, which preferably extends continuously along the entire length of the fiber, enables the heat to be distributed and dissipated, thereby significantly reducing the risk of beam quality degradation due to local temperature increases and the risk of damage to the fiber optical amplifier due to excessive temperatures. This good temperature dissipation makes it possible to introduce very high pump powers via the side pumping device 2, so that the pump energy is evenly distributed over the length of the pump.

[0080] Employing the solution according to the invention thus makes it possible to overcome the limitations that prevent the generation of very high-power laser beams by means of amplifying optical fibres.

Claims

1. A fiber optical amplifier, the amplifier comprising an amplifying optical fiber (1), the amplifying optical fiber (1) comprising: - at least one doped core (11), - at least one optical cladding (12, 13) surrounding said core (11), and - an outer covering layer (14) surrounding said optical cladding (12, 13), The optical amplifier comprises at least one side pumping device (2), the side pumping device (2) comprising a pump fiber (21), the pump fiber (21) being spliced ​​to the optical cladding (12) of the amplifying optical fiber (1) or to at least one of the optical claddings (12, 13) of the amplifying optical fiber (1) at a splicing region (20) located between two ends of the amplifying optical fiber (1), so that at least a portion of the light flux (93) propagating in the pump fiber (21) can be transmitted into the optical cladding (12) or into at least one of the optical claddings (12, 13), characterized in that the outer covering layer (14) - Made of materials with a thermal conductivity greater than 1W / m·K, - covers at least 90% of the circumference of the amplifying optical fiber (1) at a first section (101) of the amplifying optical fiber (1), the first section (101) being located between the splicing region (20) and the first end of the amplifying optical fiber (1), and at a second section (102) of the amplifying optical fiber (1), the first section (101) being located between the splicing region (20) and the second end of the amplifying optical fiber (1), - covering a portion of the circumference of the amplifying optical fiber (1) at a section (103) of the amplifying optical fiber (1) that includes the splicing region (20) and extends between the first section (101) and the second section (102) of the amplifying optical fiber (1), such that the outer covering layer (14) extends uninterruptedly between the first section (101) and the second section (102) of the amplifying optical fiber (1).

2. A fiber optical amplifier according to the preceding claim, characterized in that The outer covering layer (14) completely covers the circumference of the amplifying optical fiber (1) at the first section (101) and the second section (102) of the amplifying optical fiber (1).

3. A fiber optical amplifier according to any one of the preceding claims, characterized in that The outer covering layer (14) is made of metal material.

4. A fiber optical amplifier according to any one of the preceding claims, characterized in that The assembly of the pump fiber (21) and the optical cladding (12) of the amplification fiber (1) is achieved by welding at the joint area (20).

5. A fiber optical amplifier according to any one of the preceding claims, characterized in that The outer covering layer (14) covers at least 50% of the circumference of the amplifying optical fiber (1) over the entire length of the amplifying optical fiber (1).

6. Fiber optic amplifier according to the preceding claim, characterized in that The cross-sectional area of ​​the fiber core (11) or the sum of the cross-sectional areas of the fiber cores is greater than 400 μm 2 .

7. A fiber optical amplifier according to any one of the preceding claims, characterized in that The fiber optical amplifier comprises at least two side pumping devices (2), each of which is connected to the amplifying optical fiber (1) at one of the splicing regions (20).

8. Fiber optic amplifier according to the preceding claim, characterized in that The splicing regions (20) are evenly distributed along the length of the amplifying optical fiber (1).

9. A fiber optical amplifier according to any one of the preceding claims, characterized in that The amplifying optical fiber (1) has at least two different optical claddings (12, 13), the optical claddings (12, 13) comprising a first optical cladding (12) surrounding the core (11) and an outer optical cladding (13) surrounding the first optical cladding (12).

10. Fiber optic amplifier according to the preceding claim, characterized in that The outer optical cladding (13) is cut at the bonding region (20).

11. A method of manufacturing a fiber optical amplifier according to any one of the preceding claims, characterized in that: The method comprises the step of locally laser ablating the outer covering layer (14) on a portion of the circumference of the amplifying optical fiber (1) covering no more than 50% of the circumference of the amplifying optical fiber (1) to form the splicing region (20).

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