Preform, method for manufacturing the preform, and optical fiber

Abstract

This invention provides a fiber optic cable-readable preform with excellent mode mixing for achieving speckle-free output. [Solution] A preform is provided for drawing into a speckle-free output optical fiber, wherein the cross-sectional structure of the preform comprises a circular inner core having a refractive index or refractive index profile, surrounded by a structured circular region having an average refractive index lower than the average refractive index of the inner core, and the preform can be drawn into a speckle-free optical fiber using standard fiber drawing techniques.

Description

Technical Field

[0001] In many applications using lasers and fiber lasers, it is preferable to have a speckle-free output at the distal output end of a fiber system instead of the typical Gaussian distribution obtained from a laser source. Such an output is often referred to as a top-hat distribution or a flat-top distribution. Generally, in most systems / applications, an efficient mode mixing fiber section is required for proper functioning. In other applications, such as for laser cleaning or for a spatial sensing sensor, a speckle-free output is required to achieve speckle-free emission. This specification discloses a manufacturing method and a preform structure that can be drawn into a desired optical fiber having a speckle-free output over the entire output surface.

Background Art

[0002] In various applications, laser welding or bonding has become a very large business. In many cases, for maximizing the benefits of these processes, it is important that the surface be very clean and very smooth all the way down to the atomic / molecular level. In addition to surface preparation for recoating and the like, laser cleaning has become the method of choice in surface preparation for precision welding and long-life welding.

[0003] The need for and pursuit of speckle-free output fiber output has existed for some time, particularly since laser and fiber laser sources began to be used in a wide range of applications. The need for ultra-clean surfaces for improved welding and joining, along with the demand for single-mode or minority-mode sources for high-density output, and the miniaturization of various imaging optical devices, have increased the need for speckle-free beams in laser processing systems for large and small parts. Laser welding, laser cleaning, and laser joining / sealing procedures can all be negatively affected by non-speckle-free beams. For example, if a surface is uneven after cleaning with a laser at speckle-containing output, a normal join may be achieved, but the ideal tight, continuous, or defect-free join required for laser joining / welding will not be realized. Furthermore, in high-power (CW or pulsed) sources, localized power peaks can lead to fiber failure. Avoiding this is highly desirable, especially in high-power applications.

[0004] Optical fibers are often used to transmit and distribute laser radiation to areas far from the laser source. This may be for the purpose of protecting the source, achieving a larger working beam, and / or for greater flexibility to reach various surface targets. Generally, these advantages are due to the use of multimode optical fibers, which have a large core and many modes for transmitting laser energy.

[0005] Optical fibers are generally drawn from preforms. The cross-sectional structure of the preform determines the cross-sectional structure of the drawn fiber. While preforms can be manufactured using several processes, the process described herein is Plasma Outside Vapor Deposition (POVD). Here, the preform is constructed by depositing continuous layers of material from a core rod to create a cladding and glass jacket. After the cladding is complete, a pure silica tube may be fused onto the preform to achieve the desired outer diameter and thickness. In such a process, the core, cladding, and outer pure silica are all coaxial with each other. Polygonal core preforms can be manufactured in a similar manner by starting with a non-circular core and depositing the cladding and jacket layers in the same way as with a circular core. Optical fibers of standard dimensions can be drawn from such preforms, which have circular or non-circular cores, depending on the shape of the starting material preform.

[0006] Laser Bonding: In electronics and high-tech miniaturization, there is a high demand for speckle-free, cleaned surfaces. Mode-mixed fibers do not always lead to true flat-top output, causing or leaving surface irregularities at the molecular scale, which can actually damage / degrade the operation of devices or high-tech applications such as supersonic jets, expensive aircraft components, and space applications. The smaller the device, the more desirable high speckle-free beam output across the entire output surface area of ​​the transmission fiber. Otherwise, serious adverse effects can occur across the entire surface of the processed part. The mode mixing required to obtain an effective clad-pumped fiber laser is relatively less demanding compared to, for example, the needs of laser processing in small to ultra-small electronic devices. Simply asymmetric or non-circular cores are not sufficient to achieve the level of mixing required to achieve true top-hat output, which is a truly speckle-free output across a wide range of input sources.

[0007] As a result, many critical applications in laser cleaning, laser bonding, and laser welding require optical fibers with excellent mode mixing to achieve speckle-free output. Ideally, such optical fibers are simply drawn from a well-constructed preform that possesses all the necessary characteristics of the final optical fiber, proportional to the drawdown ratio of the optical fiber of the required size.

[0008] Conventional techniques have employed several approaches to create asymmetric core cross-sections by using cladding that includes asymmetric cores, non-circular cores, or changes in refractive index due to the addition of new materials or local sections of air, and by adjusting drawing parameters during the drawing process to vary the cross-section at different spots along the long axis of the optical fiber over its length. [Overview of the project] [Problems that the invention aims to solve]

[0009] Our technological advancements in preform structures enhance the potential for better, more speckle-free performance in remote processes requiring optical fibers drawn from the preforms described herein, and improve new manufacturing techniques to realize and provide the required speckle-free output performance in fibers drawn from these preforms. The primary objective is to design and fabricate optical preforms with structures that are inherently better (ideally) suited to enabling the drawing of optical fibers of various sizes with speckle-free output in transmission from Gaussian output sources or other sources without speckle-free cross-sectional output.

[0010] Another objective is to provide a speckle-free output optical fiber preform that can be drawn into a speckle-free output fiber using standard drawing processes, thus preventing losses in the output from the drawing process and limiting additional costs to the preform manufacturing process.

[0011] Another objective is to provide a manufacturing process for preforms that can be used to produce speckle-free output optical fibers.

[0012] A further objective is to provide speckle-free output optical fibers for laser processing of various materials, including laser cleaning, laser processing, and laser welding. A circular core preform structure that satisfies these objectives is the subject of this patent. The manufacture and processing of non-circular core preform structures that can be successfully drawn into speckle-free output optical fibers is also one of the subjects of this patent application. [Means for solving the problem]

[0013] In summary, this paper describes new types of circular cores, non-circular core preforms for drawing speckle-free output optical fibers with equivalent cross-sections, and methods for manufacturing them. These preforms are designed to produce better speckle-free output optical fibers. They are fibers of various dimensions with core sizes ranging from 100 μm to over 1000 μm, and effectively convert Gaussian or low-mode light source output to speckle-free work surface output such as flat-top output. New, improved speckle-free output optical fiber products made from these preforms are excellent for use in laser processing applications, including laser cleaning of surfaces and laser welding of critical surfaces, in addition to other applications that benefit from top-hat output. [Brief explanation of the drawing]

[0014] [Figure 1]As shown in Figure 1(A), this figure illustrates the basic structure of the initial preform, which has a core and is surrounded by a structured silica layer. [Figure 2] This figure shows the refractive index profile in the cross-section of the initial preform, and Figures 2(A) and 2(B) show further details. [Figure 3] This figure shows the intermediate preform with the asymmetrical region, indicated by the diagonal lines, removed. As shown in Figure 4, the inner core of the resulting preform is asymmetrical. [Figure 4] This figure shows the internal intermediate preform of Figure 3, surrounded by a reflective layer and ready for drawing the speckle-free output optical fiber. [Figure 5] This figure shows the stage preceding the intermediate preform of a non-circular core optical fiber, in relation to the initial preform in Figure 1. [Figure 6] This figure shows one of two preforms manufactured from the intermediate preform shown in Figure 5, which is ready to be drawn into a non-circular core speckle-free output optical fiber. [Figure 7] This figure basically shows a preform having a flat surface and two sets of cutting lines for creating the cores of four drawn preforms, each having a non-circular core. [Figure 8] This figure shows one of the four preforms manufactured from the initial preform in Figure 7, which is ready to be drawn into a non-circular core speckle-free output optical fiber. [Figure 9] This is a cross-sectional view of plasma external vapor phase deposition (POVD). [Figure 10] The figure on the right shows a near-field image and plot of the circular core optical fiber of the present invention with a core diameter of 300 μm, and the figure on the left shows a near-field image and plot of a standard circular core optical fiber of the prior art with a core diameter of 300 μm. [Figure 11]The figure on the right shows a near-field image and plot of the circular core optical fiber of the present invention with a core diameter of 600 μm, and the figure on the left shows a near-field image and plot of a standard circular core optical fiber of the prior art with a core diameter of 600 μm. [Figure 12] On the right is a figure showing a near-field image and plot of the non-circular core optical fiber of the present invention, which has core dimensions of 100 μm × 100 μm. [Modes for carrying out the invention]

[0015] In the following description, in the configurations illustrated in Figures 1 to 8, numbers with the same last two digits indicate similar items; for example, 101, 201, 301, 401, etc., are pure silica cores constituting the inner core, while 103, 203, 303, 403, 503, etc., are structured silica mode mixed regions constructed from down-doped silica and pure silica deposition, respectively, which, as described later, surround the inner core throughout the entire figure in each case. Although most of the depositions described herein use the Plasma External Vapor Deposition (POVD) process, the Plasma Chemical Vapor Deposition (PCVD) process can also be used in different deposition steps described herein when desired for ordinary reasons. References to plasma deposition herein may refer to either process unless otherwise specified. A pure silica core rod 101 is placed in a POVD chamber, and a series of layers of alternating down-doped layers 123 and pure silica layers 121 are added to realize the structured section 103 shown in Figure 1. The difference between the diameter 102 of the pure silica core and the diameter 104 of the structured silica section determines the overall thickness of the modal mixed structured silica section 103. Inside section 103, there are a certain number of layered pairs 120, which may vary, generally ranging from 8 to 30 pairs. Within each layered pair 120, the pure silica layer 121 is often much thicker than the down-doped silica layer 123. The ratio of the two thicknesses generally ranges from about 1 to 20. This is summarized in Figures 1 and 1(A). Particularly useful ranges for these two parameters are 7 to 13 for the thickness ratio within the paired layers and 12 to 20 for the number of paired layers.

[0016] Naturally, to start with a silica core of the appropriate size, the inner cores 101, 201 may be made from thinner silica rods, with pure silica deposited on top by plasma deposition of additional pure silica in some cases to achieve the desired core diameter.

[0017] Figure 2 shows the refractive index (RI) profile of the preform 100 in cross-section. Figures 2(A) and 2(B) show how the RI changes across the cross-section. The lines represent the decrease in the refractive index of the downdoped silica layer relative to that of the core material. The sharpness of the RI change indicates a sharp change in the material during deposition, and the speckle-free bottom demonstrates the speckle-free nature of the dopant level in each downdoped layer. In one series of examples, Δn = 5×10 -3 is.

[0018] After taking the preform of FIG. 1, additional pure silica 305 is deposited thereon, and a preform having a diameter of 325 as shown in FIG. 3 is fabricated. In the next step, a portion 307 of the initial preform diameter 325 is offset from the center of the newly ground shape, and a preform with an asymmetric inner core is fabricated by preferably removing it up to one side of the preform so that the structured silica section 303 surrounding the inner core 301 has the new preform shape.

[0019] FIG. 3 illustrates the asymmetric removal of the outer material 307, where the inner core 301 is offset from the center within the outer core 305. The core 301 is concentrically surrounded by a structured silica region 303, and the diameter 302 of the inner core and the diameter 304 of the structured silica define the overall thickness of the latter region.

[0020] FIG. 4 is a cross-sectional view of the completed preform ready for scribing into a speckle-free output optical fiber. The inner core 401 is concentrically surrounded by a structured silica 403 having a thickness defined by the difference between the diameter of the structured silica 404 and the diameter of the inner core 402. The outermost core 405 is surrounded by a reflective layer 409 such as downdoped silica deposited by POVD / PCVD. Note that the center of the inner core 401 is offset by a difference 411 within the outer core 405. In one example, 411 was 4 mm.

[0021] Figure 4 can also be used to initially show a cross-section of an optical fiber drawn from the preform described above. In this case, the reflective layer 409 may be added when the optical fiber is drawn and may be selected from silicone, rigid plastic cladding, or other polymer cladding materials. The reflective layer 409 of the speckle-free output optical fiber may be composite, that is, the reflective layer may be added during the drawing process while the reflective layer is on the preform and the fiber is drawn.

[0022] One more point should be added. Although silica glass fibers are very strong when drawn, over time the glass surface is susceptible to damage from various conditions in the application, which can compromise the outermost glassy layer. Therefore, it is well known that optical fibers used in open environments, such as those found in most industrial or medical applications, generally have one or more protective jackets, which are not illustrated herein. These jackets are usually added during the drawing process, but they may also be added in further downstream processes.

[0023] Figures 5 to 8 illustrate embodiments of the fabrication of preforms and optical fibers for speckle-free output having a non-circular core. First, an initial preform, as illustrated in Figure 1, is enlarged with additional core material to form a larger preform having an inner core 501, a structured silica region 503, and a second core around the structured silica region, and having a diameter 525. The second core may be fabricated entirely by a plasma deposition process, or it may be fabricated by sleevering a pure silica tube with an inner diameter in close contact with the diameter of the initial preform, and then bonding the two together to form a larger preform with a desired diameter 525 and no bubbles. The larger preform is ground down to a width 515 and a specific height related to its width, removing material 507. The larger preform is ground down so that a portion of the second core material remains on top of the entire structured silica region 503. In most examples, the inner core 501 and the outer (second) core 505 are both pure silica material. The ground preform is cut along the cutting line 513 to produce two non-circular cores of two new preforms, each capable of being drawn into a speckle-free output optical fiber.

[0024] In Figure 6, each composite core from Figure 5 is set up in a plasma deposition apparatus after its corners 619 have been rounded, and a reflective coating 609 is deposited on top of the composite non-circular core. The core materials 601 and 605 are entirely identical, and the core has a semicircular region 603 of structured silica inside. Its width 615 is as shown. In this particular example, the width and height are substantially equal in length, and the non-circular core is square in shape. Other shapes such as rectangles, triangles, trapezoids, hexagons, and octagons are also possible.

[0025] The optical fiber drawn from this preform will have a cross-section equivalent to that of the preform, with an actual size proportional to the preform. In one example of a preform, the inner core 501 has a diameter of 15 mm, the structured silica 503 has a diameter of 17 mm, and the structured silica 503,603 has a thickness of 2 mm. The width and height are both 18.5 mm, and the diameter of the preform 525 was 51 mm.

[0026] Figures 7 and 8 illustrate the division of a ground initial preform with a non-circular core into four equivalent square cores, and the fabrication of four new preforms having the cross-sections shown in Figure 8. Thus, in Figure 7, the inner core 701 is surrounded by structured silica 703, which in turn is surrounded by additional core material 705. The initial preform has a diameter of 725. After the initial deposition, the preform is ground into an oval composite core by removing material 707, and the resulting oval core is then cut along cutting lines 713 into four non-circular core pieces having side dimensions 735. These pieces are then rounded at the corners and a reflective layer 709 is deposited to produce four equivalent preforms as shown in Figure 8. As before, the inner core 701 and the second core 705 are of the same material overall, most likely pure silica.

[0027] As shown in Figure 8, the final preform has an arc of structured silica 803 sandwiched between core material 801 and core material 805, inside a square core having rounded corners 819 in this example, and the final preform is manufactured by depositing or otherwise adding reflective material 809 surrounding the core. The width of the non-circular core 835 is equal to the height of the core, since the core is square in this example. Other possible shapes of the non-circular core are as described above. The relative area in the optical fiber when drawn will be proportional to the area of ​​the preform shown in Figure 8, since the fiber cross-section will have the same shape as the cross-section of the preform.

[0028] In one example, the diameter of the pure silica inner core 701 was 15 mm, the diameter of the surrounding structured silica 703 was 17 mm, and the thickness of the structured silica 703,803 was 2 mm. The diameter of 725 was 51 mm. The four non-circular cores had side dimensions of 735,835, and 18.5 mm respectively.

[0029] A typical POVD setup is shown in Figure 9, where 901 is a screening box, 902 is a substrate rod, 903 is a glass lathe, 904 is a plasma torch, and 905 is a handle attached to the substrate rod 902. In many examples, the plasma torch 904 operates at power levels of 5.28 MHz and 50 kW. As mentioned above, in different cases, either plasma vapor deposition, i.e., POVD or PCVD is used.

[0030] A wide range of materials can be used as core materials within structured silica sections and reflective coatings. While pure silica is often chosen for the core and sleeve, up-doped silicon such as germanium-doped silicon (Ge-Si) or graded-index silica-based cores may also be used. The reflective layer is almost always fluorosilicate, but other low-refractive-index silicas such as borosilicates may be used. Reflective / clad-type coatings added after fiber laying include fluoroacrylate and silicone plastic materials. The choice of core material will influence the viable choice of materials for the layers of the structured silica section. For example, if pure silica is used as the core material, a down-doped (low RI) silica, such as fluorosilica with a selected fluorine dopant level, will be the first layer in the layers, and the high-RI second layer may be pure silica, or lower-doped fluorosilica, or up-doped silica such as Ge-Si, or similar materials as required for optical fibers, as long as the total refractive index of the structured silica section is lower than the refractive index of the core. If one or more of the layers within the structure are replaced with updoped silica, special effects may occur, as long as the refractive index of the structured silica section remains lower than that of the core.

[0031] The preferred combinations, the thickness ratio between layers, and the number of layers are numerous and depend on the intended application, available preforming equipment and materials, and core requirements. Several more useful ranges of the number of layers and the thickness ratio between layers within the layers are described above.

[0032] Separately, to manufacture fiber lasers or amplifiers, a rare-earth doped innermost core can be incorporated into the structure of silica or other core material in the preform and subsequently in the drawn optical fiber, adding a structure such as structured silica. Alternatively, a tubular preform may be manufactured and then sleeved onto a rare-earth core or clad rare-earth core rod.

[0033] Figures 10 to 12 show some representative results for fibers made from a preform having a structured silica section housed within the core of the preform. Specifically, each figure shows near-field images on the right and corresponding output plots below for three sample fibers having a 300 μm circular core, a 600 μm circular core, and a 100 μm × 100 μm non-circular square core, respectively. For comparison, Figures 10 and 11 show the corresponding near-field images and plots on the left half for optical fibers with standard 300 μm and 600 μm cores, respectively.

[0034] At the time of filing, fibers with a 300 μm core, a 600 μm core, or a larger core would be one of the preferred examples of the present invention. For non-circular core fibers, preferred non-circular core configurations would be either a square or rectangular core having semi-circular or quarter-circular segments of structured silica.

[0035] Further potentially useful configurations include having a thin updoped layer preceding or following the structured silica section described above, or having thin updoped layers before and after the structured silica section described above. The thickness of this updoped layer must be the same as or thinner than the low RI layer of the opposing layer.

[0036] (Note) (Note 1) A preform that is drawn onto a speckle-free output optical fiber, The cross-sectional structure of the preform comprises a circular inner core having a refractive index or refractive index profile, surrounded by a structured circular region having an average refractive index lower than the average refractive index of the inner core, This preform can be wired into a speckle-free optical fiber using standard fiber wiring techniques. Preform.

[0037] (Note 2) The preform according to Appendix 1, wherein the structural circular region has a first layer having a lower refractive index (RI) than the material of the core, followed by a second layer having a higher RI than the material of the first layer, and having a plurality of pairs of layers starting from the inner core, each layer having a thickness.

[0038] (Note 3) The preform as described in Appendix 2, wherein the low RI layer is a down-doped layer, and the next layer is a core layer or an up-doped layer.

[0039] (Note 4) The preform according to Appendix 2 or 3, wherein in each of the aforementioned layers, the ratio of the thickness of the core layer to the thickness of the down-doped layer is about 1 to about 20.

[0040] (Note 5) The number of layers is approximately 8 to approximately 30, as described in Appendix 2 or 3 of the preform.

[0041] (Note 6) A preform according to any one of Appendix 1 to 5, wherein a pure silica tube is folded on the preform without creating gaps or bubbles at the interface between the inner surface of the tube and the second cladding to form a wire-drawn preform for a speckle-free output optical fiber.

[0042] (Note 7) An optical fiber drawn from a preform described in any one of the appendices 1 to 6, wherein the cross-section of the optical fiber is proportional to the cross-section of the preform, and the optical fiber has a speckle that reduces the output / transmission of the optical fiber to a high-power low-mode photonic source.

[0043] (Note 8) The aforementioned structural circular region is as described in any one of Appendices 2 to 5, the optical fiber as described in Appendice 7.

[0044] (Note 9) A method for manufacturing a preform as described in any of the appendices 1 to 6, wherein plasma vapor deposition is used to manufacture the section of the cross-section and the layer thereof of the preform as described in the appendice.

[0045] (Note 10) A preform from which a speckle-free output optical fiber can be drawn has a cross-sectional structure, It comprises a composite non-circular core surrounded by a reflective clad-type material, the composite non-circular core is A polygonal section of a core material having a refractive index, Arc segments of a structured silica circular region having an average refractive index lower than the average refractive index of the core material, within the section of the polygonal core, Furthermore, The reflective cladding material has a refractive index lower than that of the core material. The preform can be drawn into a speckle-free output optical fiber using standard fiber optic drawing techniques. Preform.

[0046] (Note 11) The preform according to Appendix 10, wherein the structural circular region comprises a down-doped layer and a subsequent core layer, and has pairs of layers starting from the inner core, each layer having a thickness.

[0047] (Note 12) The preform according to Appendix 10 or 11, wherein in each of the aforementioned layers, the ratio of the thickness of the core layer to the thickness of the down-doped layer is about 1 to about 20.

[0048] (Note 13) The number of layers is approximately 8 to approximately 30, according to the preform as described in Appendix 10 or 11.

[0049] (Note 14) The polygon is selected from the group of triangles, quadrilaterals, pentagons, hexagons, heptagons, octagons, decagons, and dodecagons, and is a preform as described in any one of the appendices 10 to 13.

[0050] (Note 15) The section of the polygonal core is a rectangular / square core for a polygon having four sides, or a roughly sectoral core for all other polygons, as described in any one of the preforms in appendices 10 to 14.

[0051] (Note 16) The preform as described in Appendix 15, wherein the arc segments of the structured silica circular region differ for different polygonal core shapes and are substantially a portion of the circular region divided by the number of sides in the polygon.

[0052] (Note 17) The preform according to Appendix 16, wherein the arc segment of the structured silica circular region inside the rectangular / square core has a semicircular shape if the precursor original rectangular core was cut only once through the long side of the precursor rectangular core before the reflective cladding layer was deposited around the noncircular core.

[0053] (Note 18) An optical fiber drawn from a preform described in any one of appendices 10 to 17, wherein the cross-section of the optical fiber is proportional to the cross-section of the preform, and the output / transmission of the optical fiber as a high-power low-mode photonic source is speckle-free output.

[0054] (Note 19) The aforementioned structural circular region is as described in any of the appendices 10 to 17, the optical fiber as described in appendice 18.

[0055] (Note 20) A method for manufacturing a preform as described in any of Appendix 10 to 17, wherein plasma vapor deposition is used to manufacture the section of the cross-section and the layer thereof of the preform as described in the Appendix.

[0056] (Note 21) The preform according to any one of Annexes 1 to 6 or 10 to 17, further comprising an innermost core of a high refractive index rare-earth doped material so that the optical fiber can be used as an optical fiber laser / amplifier or sensing medium when it is drawn.

[0057] (Note 22) An optical fiber according to any one of Appendix 7 to 8 or Appendix 18 to 19, wherein the corresponding preform has an innermost core of rare earth-doped material so that the fiber can function as a fiber laser / amplifier or for sensing purposes.

Claims

1. A preform, The cross-sectional structure of the preform from which a speckle-free output optical fiber can be drawn is: It features a composite non-circular core surrounded by a reflective clad-type material, The aforementioned composite non-circular core is A polygonal section of a core material having a refractive index, Arc segments of a structured silica circular region having an average refractive index lower than the average refractive index of the core material, within the section of the polygonal core, Furthermore, The reflective cladding material has a refractive index lower than that of the core material. This preform can be wired into a speckle-free optical fiber using standard fiber wiring techniques. Preform.

2. The preform according to claim 1, wherein the structured silica circular region comprises a down-doped layer and a subsequent core layer, having pairs of layers starting from the inner core, each layer having thickness.

3. Having multiple layers, The preform according to claim 1 or 2, wherein in each of the aforementioned layers, the ratio of the thickness of the core layer to the thickness of the down-doped layer is about 1 to about 20.

4. Having multiple layers, The preform according to claim 1 or 2, wherein the number of layers is approximately 8 to approximately 30.

5. The preform according to any one of claims 1 to 4, wherein the polygon is selected from the group consisting of triangles, quadrilaterals, pentagons, hexagons, heptagons, octagons, decagons, and dodecagons.

6. The preform according to any one of claims 1 to 5, wherein the sections of the polygonal core are rectangular / square cores for polygons having four sides, or substantially sectoral cores for all other polygons.

7. The preform according to claim 6, wherein the arc segments of the structured silica circular region differ for different polygonal core shapes and are substantially a portion of the circular region divided by the number of sides in the polygon.

8. The preform according to claim 7, wherein the arc segment of the structured silica circular region inside the rectangular / square core has a semicircular shape if the precursor original rectangular core is cut only once through the long side of the precursor rectangular core before the reflective cladding layer is deposited around the noncircular core.

9. An optical fiber drawn from a preform according to any one of claims 1 to 8, wherein the cross-sectional area of ​​the optical fiber is proportional to the cross-sectional area of ​​the preform, and the output / transmission of the optical fiber of a high-power low-mode photonic source is speckle-free output.

10. The optical fiber according to claim 9, wherein the structured silica circular region is as described in any one of claims 1 to 8.

11. A method for manufacturing a preform according to any one of claims 1 to 8, wherein plasma vapor deposition is used to manufacture sections of the cross-sectional area of ​​the preform and layers thereof.

12. The preform according to any one of claims 1 to 8, further comprising an innermost core of a high refractive index rare-earth doped material so that the optical fiber can be used as an optical fiber laser / amplifier or sensing medium when it is drawn.

13. The optical fiber according to claim 9 or 10, wherein the corresponding preform has an innermost core of rare earth doped material so that the fiber can function as a fiber laser / amplifier or for sensing purposes.

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