Strengthened anti-fatigue optical fiber with enhanced side irradiation

Abstract

It is proposed an optical fiber (4) comprising: an outer cladding section surrounding an inner core section, the outer cladding section having a lower refractive index than the core section, and the outer cladding section and the core section forming an optical light guide; an emission region (8) associated with an emission end (3) of the optical fiber (2), the emission region (8) extending in a longitudinal direction along the optical fiber (4) and arranged to emit radiation in a transverse direction relative to the longitudinal direction of the optical fiber (4); wherein, within the emission region (8), the core section is provided with a plurality of scattering sites (100), each of which is formed by a local change in refractive index in the core section.

Description

Technical Field

[0001] The present invention relates to a robust and fatigue-resistant all-silica optical fiber having enhanced side irradiation and preferably having sensing capabilities. Background Art

[0002] There are many applications for illumination with or without temperature / stress sensing, which are optimally achieved by uniform side radiation from a reliable and robust optical fiber.

[0003] Common techniques for achieving side radiation effects in optical fibers are to remove their reflective cladding, micro-machine the fiber surface, or taper the fiber tip, as disclosed by Hyun Wook Kang et al. in J.Biomed, Optics, 17, 8001-1(2012) and van den Bergh et al. in US5,536,265A. Defects on the fiber surface can cause such optical fibers to be more prone to mechanical failure during use because of their lower strength and greater susceptibility to fatigue. For such side-scattering optical fibers, the reduction in bending strength is significant.

[0004] A more modern approach is to produce side-radiation optical fibers by focusing the irradiation of laser pulses in the core of the optical fiber, as disclosed by Chuang et al. in US2008 / 0158905A1 and Rose et al. in US2018 / 0113247A1. These scattering centers introduce changes in the normal structure, which allows regions with different refractive indices compared to the bulk of the core material. Local changes in the structure in turn produce regions where the intensity is disrupted. The limitations of standard scattering center production techniques and currently sold standard all-silica optical fibers do not allow for the manufacture of reliable and efficient side-irradiated optical fibers. Therefore, new technologies and devices are needed to overcome the above-mentioned disadvantages and limitations of the prior art. Summary of the Invention

[0005] Starting from this related art, the present invention attempts to provide a robust and fatigue-resistant optical fiber having enhanced side irradiation and preferably sensing capabilities, and a method for its manufacture.

[0006] This object is achieved by an optical fiber and a method having the features of the independent claims. Advantageous embodiments and improvements are specified in the claims according to the above-mentioned independent claims.

[0007] The optical fiber includes a cladding section surrounding a core section, the refractive index of the cladding section being lower than that of the core section, and the cladding section and the core section forming an optical waveguide. The optical fiber further includes an emission region associated with one end of the optical fiber for emitting radiation in a direction along the longitudinal axis of the optical fiber and arranged to emit radiation in a transverse direction with respect to the longitudinal axis of the optical fiber. In the emission region, the core section is provided with a plurality of scattering sites, each scattering site being formed by a local change in refractive index in the core section. This configuration of the optical fiber provides an efficient side-irradiated solid optical fiber having one or more sites of side illumination, the optical fiber having good bending strength and good fatigue resistance.

[0008] In one embodiment, the core section surrounds an inner cladding section, the refractive index of the inner cladding section being lower than that of the core section, thereby providing a tubular shape of the core section. These optical fibers are unique structures mainly because their recesses are low-refractive-index cladding-type silica, thereby producing tubular optical fibers with a solid core. Prior tubular optical fibers have been formed from tubular preforms and have only air in the inner section of the optical fiber. This provides an optical fiber with lower bending strength and nearly twice the surface area, which will be exposed to the environment and its impact on the long-term reliability of side-illuminated optical fibers.

[0009] In another embodiment, the optical fiber further includes an innermost section having a refractive index higher than that of an adjacent surrounding section, where the refractive indices of the innermost section and the adjacent surrounding section allow the innermost section to function as a single-mode or low-mode optical waveguide. This embodiment may be provided with means for testing the stress or temperature of the optical fiber near the side-irradiated site, thereby providing feedback to the user of the device, using an all-optical sensing system to provide such localized information, especially if the longitudinally innermost section has at least one fiber Bragg grating section in the emission region and can be used as an optical fiber stress and / or temperature sensor.

[0010] The extension of the scattering site is greater in the direction of the longitudinal axis of the optical fiber than in the direction transverse to the longitudinal axis, so that most of the cross-section is unaffected, thereby contributing to enhancing the strength of the optical fiber.

[0011] The scattering sites can be distributed in the optical fiber according to various regular patterns, thereby providing scattering sites across the entire cross-section of the core section. The scattering sites can be arranged in a circular pattern, the diameter of the circular pattern varying regularly or irregularly along the longitudinal axis of the optical fiber. The scattering sites can in particular be arranged in a helix, the axis of rotation of which is oriented along the longitudinal axis.

[0012] The section of the optical fiber is preferably made of silica glass, in which scattering sites for optical and infrared radiation can be generated.

[0013] The scattering sites are at a depth of at least 75 μm or at least 200 μm from the outermost silica glass surface, and / or at a depth of about 300 μm or less from the outermost glass surface, so as to provide a bending strength of at least about 0.5 GPa.

[0014] The outermost cladding section can be protected by one or more non-silica protective coatings and / or sheath layers that contribute to enhancing the bending strength of the optical fiber, and all or some of these layers are removed above the emission region.

[0015] The emission end of the optical fiber can be covered with a reflective coating. The reflective coating guides non-scattered radiation back into the diffuser, thereby improving the efficiency of the diffuser.

[0016] The reflective coating can form a dichroic mirror that reflects radiation of a first wavelength passing through the core section and transmits radiation of a second wavelength passing through the innermost core section. This embodiment allows the radiation of the second wavelength to pass through the edge of the diffuser.

[0017] A method for manufacturing an optical fiber, which generates the scattering sites by focusing femtosecond laser pulses at the intended scattering sites. This method allows the generation of scattering sites deep into the optical fiber.

[0018] While the optical fiber is exposed to the femtosecond laser pulses, the optical fiber can be moved by an xyz positioner. This method allows the generation of complex patterns for the arrangement of the scattering sites, and the complex patterns are optimized for efficient and uniform emission. Description of the Drawings

[0019] Other advantages and features of the present invention are disclosed in the following description, in which exemplary embodiments of the present invention are explained in detail based on the drawings.

[0020] Figure 1 A diagram showing the optical fiber and its dimensions;

[0021] Figure 2 is from Figure 1 an enlarged representation of the emission region of the optical fiber;

[0022] Figure 3a is a refractive index distribution curve of an embodiment having an outer cladding section and an inner core section;

[0023] Figure 3b represents Figure 3a a refractive index distribution curve of an embodiment similar to the embodiment of , which additionally has an innermost section for sensing;

[0024] Figure 3c Represents the refractive index distribution curve of an embodiment having an inner cladding section that produces a tubular core section;

[0025] Figure 3d Represents an embodiment similar to Figure 3c whose refractive index distribution curve further has an innermost section portion for sensing;

[0026] Figure 4 Depicts an apparatus for introducing a scattering site;

[0027] Figure 5 Shows a graph in which the intensity of some embodiments is plotted against the depth of the scattering site;

[0028] Figure 6 Is a graph in which the maximum depth of the scattering site is plotted against the diameter of the bare fiber;

[0029] Figure 7 Represents the results of the efficiency of radial emission using embodiments of the present disclosure;

[0030] Figure 8 Is a picture showing the distribution of scattering sites inside the optical fiber;

[0031] Figure 9 Is another picture showing the distribution of scattering sites inside the optical fiber; and

[0032] Figure 10 Shows an embodiment for guiding two wavelengths separately.

[0033] It should be noted hereinafter that the same reference numerals are used in different drawings to indicate similar or identical items. Detailed Description

[0034] Figure 1 Represents a medical probe 1 that has a light diffuser 2 at the distal end 3 of an optical fiber 4. The distal end 3 of the medical probe 1 is surrounded by a square that indicates the boundary of an enlarged view A, which is depicted in Figure 2 . The proximal end 5 of the medical probe 1 is equipped with a connector 6 for connecting the optical fiber 4 to a laser that emits radiation into the optical fiber 4. The connector 6 may be provided with an RFID jacket 7 for identifying and administering the medical probe 1. The overall probe length L of the medical probe 1 ranges between approximately 2 and 6 meters. The diffuser 2 is provided with an emission area 8, the length l e of which varies from 3 mm to 40 mm, with a typical length l e being 5 mm to 30 mm, and the distance d of the emission area 8 from the distal end 3 is approximately 1 mm, as Figure 2As shown. The emission region 8 scatters the incident light in a transverse direction with respect to the longitudinal axis 9 of the optical fiber 4.

[0035] For the medical probe 1 with a short emission region 8 of 3 mm to 10 mm, the reflective coating 10 is deposited at the end face of the distal end 3 and has the required reflection coefficient at the working wavelength. This reflective coating 10 guides the non-scattered radiation back into the diffuser 2, thereby improving the efficiency of the medical probe 1.

[0036] In the diffuser 2, the length of the bare silica varies between 6 mm and 50 mm, with a typical length of 8 mm to 37 mm. Over this length of bare silica, in many cases the primary coating of the optical fiber 4 and in all cases the secondary sheath of the optical fiber 4 are stripped, and this length of bare silica is generally slightly greater than the length l of the emission region 8. e The diameter D of the silica surface of the optical fiber 4 is typically 480 μm to 960 μm.

[0037] The length l of the region of the optical fiber 4 from which the secondary sheath has been stripped. s can extend 20 mm beyond the emission region 8. Generally, the outer diameter d of the primary coating 11. pc is 520 μm to 1100 μm, while the outer diameter d of the secondary sheath 12. sc is 600 μm to 1300 μm.

[0038] The scattering within the emission region 8 is caused by a plurality of scattering sites 100 located within the emission region 8.

[0039] Figures 3a to 3d represents a possible refractive index distribution curve of the optical fiber 4, which will be the side illuminator of the present disclosure after undergoing the generation of the scattering sites 100, as will be explained in more detail below.

[0040] Figures 3a to 3d The refractive index distribution curves of each show the refractive index distribution curve along the diameter of the circular cross-section of the optical fiber 4.

[0041] In Figure 3a the simplest structure is represented as a solid core section 300, which is surrounded by a cladding section 301, and the refractive index of the cladding section 301 is lower than that of the core section 300. The core section 300 and the cladding section 301 serving as the reflective layer form an optical waveguide for the radiation emitted by the laser. The core section is typically made of undoped silica, while the cladding section is made of fluorine-doped silica. A thin final layer 302 of pure silica surrounds the reflective cladding section 301.

[0042] In Figure 3bIn [description], the optical fiber 4 is further provided with an innermost section 303, which is centered in the optical fiber and represents a low-mode core surrounded by a tubular-shaped core section 300. The tubular-shaped core section 300 has an outer cladding section 301 and a final layer 302 of pure silica on the outer cladding section 301. The innermost section 303 is typically made of silica doped with GeO2. The innermost section 303 can be a single-mode or low-mode core, sometimes referred to as an oligomode or few-mode optical fiber. An optical fiber Bragg grating (FBG) can be written into the innermost section 303 to provide stress and / or temperature sensing sites within the innermost section 303. In this case, independent radiation sources can be used for the innermost section 303 and the side-radiating core section 300.

[0043] In Figure 3c and Figure 3d an example of the refractive index distribution curve of the optical fiber with the tubular core section 300 is depicted.

[0044] In Figure 3c the optical fiber 4 further includes an inner cladding section 304 surrounded by the tubular core section 300 and the outer cladding section 301. The outer cladding section 301 typically has the same or a lower refractive index as the inner cladding section 304. The tubular core section 300 can be made of pure silica, and the outer cladding section 301 and the inner cladding section can be made of fluorine-doped silica.

[0045] Figure 3d The embodiment of [description] also has an additional high-refractive-index innermost section 303 within the inner cladding section 304 and the tubular core section 300. The innermost section 303 of this embodiment can be made of pure silica or silica doped with GeO2.

[0046] It should be noted that in Figures 3a to 3d the embodiment of [description], the outer silica surface 305 is formed by the outer surface of the final layer 302, but if the final layer 302 is omitted, it can also be formed by the outer surface of the outer cladding section 301.

[0047] The optical fiber 4 of the present invention is drawn from a special preform and is constructed in the following manner.

[0048] In Figure 3aIn the simplest case, a pure silica preform is used as the starting point for plasma outside vapor deposition (POVD) of cladding-type silica to provide an outer cladding section 301 for producing an optical waveguide having a desired numerical aperture (NA) and a necessary minimum thickness, which will ensure that there is no evanescent wave leakage through the outer cladding section 301 in the optical fiber 4. In some cases, some additional pure silica may be deposited on the outer cladding section 301 to establish the total silica size. During the drawing process, the draw ratio is selected to achieve the desired size of the final optical fiber 4. During the drawing process, various primary coatings and secondary sheaths are applied to maintain the inherent strength of the section of the optical fiber made of silica. The secondary sheath may also be applied after completion of this drawing process. Typically, polyimide is first applied as the primary coating, and then Teflon (DuPont TM) or nylon is applied as the secondary sheath on top of this primary coating.

[0049] For example, a typical optical fiber 4 having a refractive index profile from Figure 3a is designated as OPTRAN® WF595 / 630 / 715 / / 760 / 900 PT, which means:

[0050] - OPTRAN® represents the trademark of CeramOptec optical fibers,

[0051] - WF (water-free) means that the core material is based on silica with a low OH content,

[0052] - 595 represents the outer diameter of the core section 300 in μm,

[0053] - 630 represents the outer diameter of the outer cladding section 301 in μm,

[0054] - 715 represents the total silica diameter of the optical fiber 4 in μm,

[0055] - 760 represents the outer diameter of the primary coating in μm,

[0056] - 900 represents the outer diameter of the secondary sheath in μm,

[0057] - P means that polyimide is used as the primary coating,

[0058] - T means that Teflon is used as the secondary sheath.

[0059] Typical tolerances for this optical fiber 4 are: silica diameter ±2%; and plastic sheath ±3%.

[0060] Figure 3bThe production of the embodiments is carried out in a similar manner, except that the process starts with providing a rod for the innermost section 303 made of silica doped with GeO2. The core section 300 is prepared by the tube-in-tube process or POVD to form the inner core section 300. The remaining process steps are the same as those of Figure 3a the embodiments.

[0061] To fabricate Figure 3c the embodiments, one can start with a cladding-type silica rod thick enough to yield the desired inner final dimensions of the inner cladding section 304 of the optical fiber 4, then apply pure silica by POVD or the tube-in-tube process to produce a tubular core section 300, subsequently add another cladding-type silica to provide the outer cladding section 301 to the preform, and apply a final outer layer of pure silica at the desired cladding / core diameter ratio to complete the preform. A protective coating is added as described above during or after drawing to the desired fiber dimensions. This embodiment has a refractive index profile as shown in Figure 3c Figure.

[0062] In Figure 3d the case of the sensing embodiment optical fiber, the innermost core-type silica rod can be used for the innermost section 303, and the cladding-type silica is deposited on the rod by the POVD process, and then pure silica with a higher refractive index is deposited by POVD or by the tube-in-tube process. Another section of the cladding-type silica is deposited on the tubular core section 300 to provide the outer cladding section 301 for producing an optical waveguide having a desired numerical aperture (NA) and a sufficient minimum thickness. Further POVD deposition of an additional pure silica layer allows for fine-tuning to achieve the desired overall dimensions. Figure 3d Figure shows the refractive index of such a preform and the refractive index of the optical fiber 4 drawn therefrom.

[0063] For typical dimensions of these optical fibers 4, the core section 300 has an outer diameter of 400 μm to 800 μm; the outer silica diameter of the final layer 302 is 480 μm to 960 μm, and the inner cladding section 304 has an outer diameter of 200 μm to 450 μm within the tubular core 300. For the sensing type of the present invention, the innermost part 303 has a diameter of 5 μm to 21 μm.

[0064] Figure 4Depicts an equipment configuration for generating a scattering site 100 within an optical fiber 4. The optical fiber 4 with its longitudinal axis 9 coinciding with the rotational axis 401 is firmly held by an adjustable fiber holder 402 and an adjustable fiber gripper 403 attached to a three-axis (XYZ) precision positioning stage 404. The fiber gripper 403 is capable of rotating the optical fiber 4 around the rotational axis 401. A femtosecond laser system 405 is positioned together with an inline attenuator 406 and a focusing system 407 to generate a scattering site 100 in the emission region 8. The process is monitored by a digital microscope 408 equipped with a camera 409, an illumination light source 410, and a microscope objective 411. During the generation of the scattering site 100, the optical fiber 4 is translated by the positioning stage 404 and rotated around the rotational axis 401 such that the focus of the laser beam is at a desired position within the optical fiber 4 to generate a scattering site 100 within the core section 300 of the optical fiber 4. By applying laser radiation to the optical fiber 4, the density of the silica is changed. This laser radiation can even create voids within the silica of the core section 300. In some cases, cracks are formed in the silica.

[0065] Although the present invention works well with an optical fiber 4 having a refractive index profile curve such as Figure 3a , Figure 3b , a better and preferred embodiment is an optical fiber whose refractive index profile curve follows Figure 3c and Figure 3d , especially an optical fiber 4 having a tubular core section 300. In these optical fibers 4, compared to the previous case, the core section 300 can have more space to have a scattering site 100. Some reasoning for this effect is disclosed in the analysis of Figure 6 .

[0066] It has been found that the strength of the optical fiber significantly depends on the distance from the scattering defect to the outer silica surface of the optical fiber 4. Figure 5 This dependence is shown. For practical reasons, a bending strength of 0.5 GPa is selected as the minimum acceptable strength, Figure 5 indicating that for a probe 1 that can be well manipulated, the scattering defect of the diffuser 2 should be generated at 75 μm or deeper from the outer silica surface 305 of the optical fiber 4.

[0067] On the other hand, the change in the refractive index within the optical fiber body and the presence of the cylindrical outer silica surface 305 of the optical fiber 4 create interference in precisely focusing the laser beam deep within the core section 300, which is due to the effective cylindrical lens effect of the laser beam of the femtosecond laser system 405 caused by the cylindrical shape of the optical fiber 4. A larger diameter of the optical fiber 4 results in a smaller curvature of the outer silica surface 305, enabling the laser beam to be focused deeper within the core section 300. Figure 6Shows the effect of the diameter of the outer silica surface 305 on the maximum depth of the useful and efficient scattering site 100. As the diameter of the optical fiber 4 becomes larger, the curvature of the outer silica surface 305 becomes less significant. Naturally, the attenuation through the silica material also affects the efficiency of generating non-uniformities deep within the core section 300 of the optical fiber 4. In fact, the scattering site 100 can be generated to a depth of up to 200 μm to 300 μm deep from the outer silica surface 305.

[0068] In summary, it is shown that simply placing the refractive index non-uniformity within the core at least 75 μm deep from the outer silica surface 305 provides a robust and manipulable side-illuminating optical fiber 4 for various applications.

[0069] The scattering site 100 can be generated only within the tubular volume of the optical fiber 4, with a depth of 75 μm to 200 μm - 300 m, where the maximum depth depends on the diameter of the optical fiber. Within the diameters studied, the scattering site 100 cannot be generated within the central part of the optical fiber 4. To compare the side-irradiation efficiency of different optical fiber designs, the unwanted power propagating in the forward direction was studied for various optical fiber designs. The designs studied were Figure 3a the standard optical fiber design and Figure 3c the tubular core design. The results are shown in the table of Figure 7

[0070] Figure 7 Evidence is provided of how the tubular core structure enhances the side-radiation efficiency; including the effect of the size of the inner cladding section 304. The diameter of the inner cladding section 304 of the EI2 optical fiber is larger than the corresponding diameter of the EI1, and for all optical fibers, the length of the region of non-uniformity is 20 mm. It can be seen that in the standard core (leftmost column), a large amount of light passes through the non-uniformity section compared to either size of the tubular core. It should also be noted that the larger inner cladding section 304 provides a thinner cross-section of the tubular core section 300, and the efficiency of side-illuminating scattering is greater, as shown by the reduced forward power levels in the rightmost column.

[0071] The optical fiber 4 having a solid tubular core section 300 is a preferred structure, and the most preferred embodiment of the present invention is particularly suitable for including a low-mode innermost section 303, which can be used as a continuous all-optical sensor to detect the temperature and / or stress of the side-illuminating section in-situ and in real-time when using the probe 1.

[0072] It should be noted that a very regular and precise pattern of the scattering site 100 can be introduced along the length of the optical fiber 4. Compared with the prior art that earlier attempted to provide an extended region of side-illumination, this results in a more uniform side-irradiation pattern from the optical fiber 4 during use. Figure 8 ​An embodiment is shown in which the scattering section 100 forms five helices 101 having different diameters but the same pitch. The helices 101 are aligned along the longitudinal axis 9 of the optical axis. The scattering section 100 has a length of 20 μm along the longitudinal axis 9 and a diameter of approximately 5 μm in a direction transverse to the longitudinal axis 9. More generally, the scattering section 100 can have the dimensions of its major axis vary in the range of 13 μm to 31 μm and the dimensions of its minor axis vary between approximately 4 μm and 6 μm according to the depth of the section, and the dimensions of the minor axis are independent of the depth. Figure 8 Sector B in

[0073] is an enlarged view of the scattering section 100. Figure 9 The pitch of the helices 101 can also vary along the longitudinal axis 9, as can be appreciated from Figure 9 In the picture depicted in

[0074] Embodiments of the present invention provide a tubular core optical fiber with excellent side-irradiation ability, which has a solid inner low refractive index region mainly composed of a low refractive index cladding type glass. The low refractive index region covering the inner surface of the tubular core 300 allows for more efficient side-irradiation of the optical fiber.

[0075] The optical fiber can also include an innermost section 303 that functions as an innermost single-mode or low-mode core (sometimes referred to as an oligomode or few-mode optical fiber), where at least one fiber Bragg grating is written along the optical fiber to provide a stress / temperature sensing section in the innermost core of the side-irradiated optical fiber. The innermost core is positioned at the center of the all-silica optical fiber 4 and can be used for temperature and stress sensing. The innermost core does not significantly participate in guiding the optical power to be scattered in the diffuser section.

[0076] The innermost section 303 can also guide radiation independently of the radiation guided in the tubular core. Figure 10 An embodiment is shown that corresponds to Figure 3bEmbodiments, and wherein radiation of wavelength λ1 is guided through the core section 300 to the emission region 8, where the radiation of wavelength λ1 is scattered in a lateral direction relative to the longitudinal axis 9 of the optical fiber 4 by the scattering sites 100. The innermost core section 303 is free of scattering sites 100 and is used to guide radiation of wavelength λ2 through the emission region 8 to the dichroic mirror 306, which reflects the radiation of wavelength λ1 and transmits the radiation of wavelength λ2. The radiation of wavelength λ2 can be used to provide a visible aiming beam or to provide the possibility of observing the reflectivity of the surrounding tissue, without at least one fiber Bragg grating, or in combination with at least one fiber Bragg grating. The embodiments can be modified accordingly Figure 3d of the embodiments.

[0077] Embodiments of the present disclosure create desired scattering sites within approximately 75 μm to 300 μm of the outermost surface of the outer cladding of the tubular core optical fiber.

[0078] Embodiments of the present disclosure use femtosecond pulsed lasers to create desired scattering sites within the tubular core to enhance uniform lateral irradiation along a desired portion of the optical fiber.

[0079] In the present disclosure, a solid all-silica optical fiber with a tubular core is provided, wherein within the core, a series of scattering sites have been induced by focusing pulses of a femtosecond high-power density laser at the expected scattering sites. These scattering sites are generally created at locations between 75 μm and 300 μm from the outer surface of the outermost cladding of the silica glass. The minimum depth of the scattering sites defines the fiber strength and is the same for optical fibers of different diameters. The optical fiber itself acts as a cylindrical lens, and this effect defines the maximum depth of the scattering sites. The maximum depth is mainly defined by the fiber diameter. Such an optical fiber has enhanced, uniform lateral irradiation during use.

[0080] In contrast to earlier attempts, the new enhanced lateral irradiation optical fiber has a more uniform longitudinal scattering power distribution, does not contain any plastic material in the diffusive section, can simultaneously monitor temperature and stress during operation, and has sufficient mechanical strength and thermal strength for most applications. In contrast to earlier attempts at lateral irradiation optical fibers, these new all-silica optical fibers are robust and fatigue-resistant in use, and the design of the tubular core allows for efficient lateral irradiation of optical fibers with different silica diameters. The bending strength is at least about 0.5 GPa.

[0081] The probe described herein is particularly suitable for laser-induced thermal therapy (LITT) and photodynamic therapy (PDT) in the power range of 1 watt to 10 watts.

[0082] Preferred embodiments of the present invention have been described with reference to the accompanying drawings. It should be understood that the present invention is not limited to the exact embodiments, and various changes and modifications can be made by those skilled in the art without departing from the scope of the present invention as defined in the appended claims.

Claims

1. An optical fiber, comprising: An outer cladding section (301) that surrounds an inner core section (300), the refractive index of the outer cladding section (301) being lower than that of the core section (300), and the outer cladding section (301) and the core section (300) forming an optical waveguide; An emission region (8) associated with an emission end (3) of the optical fiber, the emission region (8) extending along the optical fiber in the direction of a longitudinal axis (9) and being arranged to emit radiation in a transverse direction with respect to the longitudinal axis (9) of the optical fiber; Wherein, within the emission region (8), the core section (300) is provided with a plurality of scattering sites (100), each scattering site being formed by a local variation in the refractive index within the core section (300).

2. The optical fiber according to claim 1, wherein, The core section (300) surrounds an inner cladding section (304), the refractive index of the inner cladding section (304) being lower than that of the core section (300), thereby providing a tubular shape for the core section (300).

3. The optical fiber according to claim 1 or 2, Among them, The optical fiber further includes an innermost section (303) having a refractive index higher than that of adjacent surrounding sections (300, 304), wherein the refractive indices of the innermost section (303) and the adjacent surrounding sections (300, 304) allow the innermost section (303) to function as a single-mode or low-mode optical waveguide.

4. The optical fiber according to claim 3, Among them, The innermost section (303) has at least one fiber Bragg grating section in the emission region and can be used as an optical fiber stress and / or temperature sensor.

5. The optical fiber according to any one of claims 1-4, wherein, Among them, The extension of the scattering site (100) is greater in the direction of the longitudinal axis (9) of the optical fiber than in a direction transverse to the longitudinal axis (9).

6. The optical fiber according to any one of claims 1-5, wherein, The scattering sites (100) are regularly distributed throughout the core section (300).

7. The optical fiber according to any one of claims 1-5, Among them, The scattering sites (100) are arranged in a circular pattern, the diameter of the circular pattern varying regularly or irregularly along the longitudinal axis (9) of the optical fiber.

8. The optical fiber according to claim 7, Among them, The scattering sites (100) are arranged in a helix (101), the axis of rotation of the helix (101) being oriented along the longitudinal axis (9) of the optical fiber.

9. The optical fiber according to any one of claims 1-8, Among them, The sections (300, 301, 303, 304) of the optical fiber are made of silica glass.

10. The optical fiber according to claim 9, Among them, The scattering site (100) is at least 75 μm deep or at least 200 μm deep from the outermost silica glass surface (305), and / or Wherein, the scattering site (100) is at a depth of about 300 μm or less from the outermost silica glass surface (305).

11. The optical fiber according to any one of claims 1-10, Among them, The bending strength of the optical fiber is at least about 0.5 GPa.

12. The optical fiber according to any one of claims 1-11, wherein, The outer cladding section (301) is protected by one or more non-silica protective coatings and / or sheath layers (11, 12), and some or all of these layers are removed above the emission region (8).

13. The optical fiber according to any one of claims 1-12, wherein, The emission end (3) of the optical fiber is covered with a reflective coating (10, 306).

14. The optical fiber according to claim 3 and 13, wherein, The reflective coating forms a dichroic mirror that reflects radiation of a first wavelength passing through the core section (300) and transmits radiation of a second wavelength passing through the innermost core section (303).

15. A method for manufacturing an optical fiber, the optical fiber comprising: An outer cladding section (301) that surrounds the inner core section (300), the refractive index of the outer cladding section (301) being lower than that of the core section (300), and the outer cladding section (301) and the core section (300) forming an optical light guide; An emission region (8) associated with an emission end (3) of the optical fiber, the emission region (8) extending along the optical fiber in the direction of the longitudinal axis (9) and being arranged to emit radiation in a transverse direction relative to the longitudinal axis (9) of the optical fiber; wherein, within the emission region (8), the core section (300) is provided with a plurality of scattering sites (100), each scattering site being formed by a local change in the refractive index within the core section (300) The method includes the following steps: Generating the scattering sites (100) by focusing femtosecond laser pulses at the intended scattering sites (100).

16. The method according to claim 15, Among them, While the optical fiber is exposed to the femtosecond laser pulses, the optical fiber is moved by an xyz positioner (404).

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