Preform for a multicore optical fiber

Abstract

A preform for a multicore optical fiber is described. The preform includes an assembly of core rods arranged in a desired configuration. The core rods are placed in contact with each other to define a series of contact regions between pairs of contacting core rods. The core rods are fused at selected locations within the contact regions to secure the core rods to form a preform from which a multicore optical fiber can be formed. The preform maintains good alignment of the core rods and minimizes distortion of the core rods during the fiber drawing process. A multicore optical fiber with excellent uniformity in core diameters is produced from the preform using conventional fiber drawing processes.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 567,002, filed March 19, 2024, the contents of which are used as the basis and are incorporated herein by reference in their entirety. Technical Field

[0002] This specification relates to multi-core optical fibers. More specifically, this specification relates to a preform for a multi-core optical fiber, and to drawing said preform to form a multi-core optical fiber. Background Technology

[0003] Optical fiber is used in a variety of telecommunications applications. The most widely used optical fibers consist of single-core elements used to transmit optical signals. The core element of a single-core fiber comprises a core region surrounded by one or more cladding regions. Since the transmission capacity of a single-core fiber is currently approaching its theoretical limit, the demand for increased transmission capacity is met by increasing the number of single-core fibers included in the transmission cable. While a higher fiber count provides higher transmission capacity, this results in larger cables and makes it difficult to retrofit existing space-constrained fiber optic installations with higher-capacity cables. Therefore, it is necessary to develop solutions that can provide higher transmission capacity without increasing the size of the transmission cable.

[0004] One solution under consideration is multi-core fiber. Multi-core fiber comprises multiple core elements embedded in a common cladding. Each core element of a multi-core fiber serves as an independent signal transmission channel. Since transmission capacity increases with the number of core elements in a multi-core fiber, it is desirable to maximize the density of core elements in a given cross-sectional area of ​​the common cladding.

[0005] Multicore optical fibers are drawn from a preform comprising multiple core rods positioned within a surrounding cladding. Multicore optical fibers are formed by heating the tip of the preform and drawing the fiber from it under tension. As the fiber is drawn, its diameter decreases and it gradually cools. As the fiber cools, its viscosity increases, and the fiber diameter stabilizes at a predetermined target value (e.g., 125 micrometers).

[0006] Currently, several methods exist for forming preforms of multicore optical fibers. In one method, a hole is drilled in a cylindrical glass body, and a core rod is placed into the hole to form the preform. The composition of the glass body corresponds to the composition of the cladding region of the multicore optical fiber drawn from the preform. This method of forming multicore preforms requires the use of expensive ultrasonic drilling machines to create precisely sized holes with appropriate smoothness to match the diameter of the core rod. Furthermore, the length of the preform is limited because maintaining hole uniformity becomes increasingly difficult as the drilling depth increases.

[0007] Another method for forming preforms for multicore optical fibers is the stack-and-draw method. In this method, core rods and cladding rods are stacked within a circular glass substrate tube to form a preform assembly. The cladding rod fills the space between the core rod and the substrate tube and helps to fix the position of the core rod. The preform assembly is then heated under vacuum conditions to fill the gaps between the core rod, cladding rod, and glass substrate tube. Heating causes the core rod and cladding rod to fuse together with each other and with the glass substrate tube to form a solid preform, which is then drawn into a multicore optical fiber using a conventional draw tower. However, during the process of fusing the preform assembly, the size and position of the core rod can change, and it is difficult to manufacture multicore optical fibers with uniform core size and placement along the length of the fiber.

[0008] To address the challenge of precisely positioning the mandrel, an alternative method has been proposed, in which the outer surface of a circular mandrel is machined into a square or other shape with one or more flat surfaces. The flat surfaces of the machined mandrels are then brought into contact or stacked to form a preform assembly, which is subsequently heated and solidified to form a multicore preform. While this method may improve the alignment and positioning of the mandrels within the preform assembly, the initial machining process of flattening one or more sides of the mandrel adds a costly step to the manufacture of the multicore preform.

[0009] Therefore, new technologies are needed to manufacture preforms and preform assemblies of multi-core optical fibers in a cost-effective manner, providing precise placement and uniformity of the cores over extended preform lengths. Summary of the Invention

[0010] This disclosure provides a preform and preform assembly of a multi-core optical fiber, as well as a method for manufacturing the same. The preform is manufactured by arranging a plurality of core rods in a configuration having contacting outer surfaces to form a preform assembly; and fusing the core rods at selected locations along a contact area defined by the contacting outer surfaces to form a fusion zone, the fusion zone fixing the core rods to form the preform. The outer surface of the preform is corrugated. The multi-core optical fiber can be drawn from the preform without placing the preform into a substrate tube. The multi-core optical fiber drawn from the preform is characterized by precise and consistent positioning and dimensional accuracy of the cores along its length.

[0011] This disclosure relates to:

[0012] A preform for an optical fiber, the preform comprising:

[0013] An assembly of multiple mandrels, the assembly having a first end, a second end, and a central longitudinal axis extending from the first end to the second end, each of the mandrels having an outer surface defining a circular cross-section, the outer surface of each mandrel directly contacting the outer surface of another mandrel along a contact area aligned with the central longitudinal axis, the contact area including a first fusion region and a non-fusion region extending from the first fusion region.

[0014] This disclosure relates to:

[0015] A multi-core optical fiber comprising:

[0016] Multiple core regions, spaced apart from each other, each core region comprising glass.

[0017] A cladding region surrounds and directly contacts the core region, the cladding region comprises glass and has a relative refractive index lower than that of the core region, the cladding region defines the outer surface of the multi-core optical fiber, the outer surface being corrugated and without sharp edges.

[0018] This disclosure relates to:

[0019] A method for manufacturing a multi-core optical fiber, the method comprising:

[0020] Multi-core optical fibers are drawn from a preform comprising an assembly of multiple cores, the assembly having a first end, a second end, and a central longitudinal axis extending from the first end to the second end. Each core has an outer surface defining a circular cross-section. The outer surface of each core directly contacts the outer surface of another core along a contact area aligned with the central longitudinal axis. The contact area includes a first fusion region and a non-fusion region extending from the first fusion region.

[0021] Further features and advantages will be set forth in the following detailed description and will be apparent in part from the description or recognized by those skilled in the art through practice of the embodiments described in the written description and its claims and the accompanying drawings.

[0022] It should be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework for understanding the nature and characteristics of the claims.

[0023] The accompanying drawings are included to provide further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate selected aspects of this description and, together with the description, serve to explain the principles and operation of the methods, products, and compositions covered herein. The features shown in the drawings are illustrations of selected embodiments of this specification and are not necessarily depicted to scale. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar features.

[0024] The appended claims are incorporated in and form a part of this detailed description. Attached Figure Description

[0025] Although this specification concludes with claims that specifically point out and expressly claim the subject matter of the written description, it is believed that this specification will be better understood from the following written description, taken in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 A cross-sectional view of a mandrel with a core region and a cladding region is depicted.

[0027] Figure 2 A cross-sectional view of a mandrel having a core region, a trench cladding region, and an outer cladding region is depicted.

[0028] Figure 3 A cross-sectional view of a mandrel having a core region, an offset cladding region, a grooved cladding region, and an outer cladding region is depicted.

[0029] Figure 4A The relative refractive index distribution of a core rod with a core region, a grooved cladding region, and an outer cladding region is depicted.

[0030] Figure 4B The relative refractive index distribution of a core rod having a core region, an offset cladding region, a groove cladding region, and an outer cladding region is depicted.

[0031] Figure 5A This is a schematic depiction of soot preform deposition using the OVD process.

[0032] Figure 5B An apparatus for doping and consolidating flue gas preforms is described.

[0033] Figures 6A-6C The deposition of multiple soot layers on a substrate is depicted.

[0034] Figure 7 A schematic process for forming multi-core optical fibers is described.

[0035] Figure 8 An embodiment of a preform for a multi-core optical fiber is shown, the preform comprising various components of a core rod.

[0036] Figure 9A An end view of the core pair in contact with a multi-core optical fiber preform is shown.

[0037] Figure 9B and 9C A perspective view of the contacting mandrel pair in a plane, including the centerline of the contacting mandrel pair.

[0038] Figure 10 The image depicts a 2 × 2 arrangement of core rods in a preform of a multi-core optical fiber.

[0039] Figure 11A and 11B It shows from Figure 10 The image depicts the end of a multi-core optical fiber drawn from a preform.

[0040] Figure 12A and 12B An image of the end of a multi-core optical fiber drawn from a preform with a 2 × 2 configuration is shown.

[0041] Figure 13 An image of the end of a multi-core optical fiber drawn from a preform with a 2 × 2 configuration is shown. Detailed Implementation

[0042] This disclosure is provided as an facilitating teaching and can be more readily understood by referring to the following description, drawings, examples, and claims. Therefore, those skilled in the art will recognize and understand that many changes can be made to various aspects of the embodiments described herein while still obtaining beneficial results. It will also be apparent that some desired benefits of the embodiments of the invention can be obtained by selecting some features without utilizing others. Therefore, those skilled in the art will recognize that many modifications and adaptations are possible and, in some cases, even desirable and part of this disclosure. Therefore, it should be understood that, unless otherwise stated, this disclosure is not limited to the specific compositions, articles, apparatus, and methods disclosed. It should also be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0043] Components (including materials, compounds, compositions, and method steps) that can be used with the disclosed reflective optical elements and methods for manufacturing reflective optical elements, used in conjunction with them, prepared for them, or as embodiments thereof are disclosed. It should be understood that when combinations or subsets of components, or interactions, are disclosed, each individual component and each combination of two or more components is contemplated and disclosed herein, even if not explicitly stated. For example, if a combination of components A, B, and C is disclosed, then each of A, B, and C is disclosed individually, as are each of the combinations AB, BC, AC, and ABC. Similarly, if components D, E, and F are disclosed individually, then each combination DE, EF, DF, and DEF is also disclosed. This concept applies to all aspects of this disclosure, including but not limited to components corresponding to materials, compounds, compositions, and steps in methods.

[0044] As illustrated in the exemplary embodiments, the construction and arrangement of the elements in this disclosure are merely illustrative. Although only a few embodiments of the invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily understand that many modifications (e.g., variations in the size, dimensions, structure, shape and proportions, parameter values, material selection, orientation, etc. of the various elements) can be made without departing from the novel and non-obvious teachings and advantages of the stated subject matter.

[0045] In this specification and the following claims, reference will be made to many terms, which should be defined as having the following meanings:

[0046] The terms “include”, “includes”, or similar terms mean to cover but not be limited to, that is, inclusive rather than exclusive.

[0047] Unless otherwise stated, the indefinite article “a / an” and its corresponding definite article “the” as used herein mean at least one (species), or one (species) or more (species).

[0048] As used herein, the term “or” is inclusive; more specifically, the phrase “A or B” means “A, B, or both A and B.” For example, in this document, exclusive “or” is indicated by terms such as “A or B” and “one of A or B”.

[0049] As used herein, when referring to a list of two or more items, the term "and / or" means that any one of the listed items may be used alone, or any combination of two or more of the listed items may be used. For example, if a composition is described as containing components A, B, and / or C, the composition may contain A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0050] In this document, relational terms such as first and second, top and bottom are used only to distinguish one entity or action from another, and do not necessarily require or imply any actual such relationship or order between such entities or actions.

[0051] Unless otherwise stated, the term "about" refers to all terms within the scope described. For example, about 1, 2, or 3 is equivalent to about 1, about 2, or about 3, and further includes about 1-3, about 1-2, and about 2-3. Specific and preferred values ​​disclosed for compositions, components, ingredients, additives, and the like, as well as their ranges, are for illustrative purposes only; these values ​​do not exclude other defined values ​​or other values ​​within the defined range. The compositions and methods disclosed herein include compositions and methods having any of the values ​​described herein or any combination of such values, specific values, more specific values, and preferred values.

[0052] As used herein, the term "about" means that a quantity, size, formulation, parameter, and other quantity and characteristic is not and does not need to be precise, but may be approximate and / or larger or smaller as required, reflecting tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art. When a value is referred to as about or approximately equal to a number, the value is within ±10% of said number. For example, a value of about 10 means a value between 9 and 11, including the endpoints. When the term "about" is used to describe the endpoints of a value or range, this disclosure should be understood to include the specific value or endpoint mentioned.

[0053] As used in this article, “contains” is an open-ended transition phrase. The list of elements following the transition phrase “contains” is a non-exclusive list, which allows for the existence of other elements besides those specifically stated in the list.

[0054] The terms “comprising” and “comprises”, such as “A comprises B”, are intended to include the concepts of “composed of” and “substantially composed of” as special cases, such as in “A is composed of B” or “A is substantially composed of B”.

[0055] The term “wherein” is used as an open transition phrase to introduce a statement of a series of characteristics of the structure.

[0056] As used herein, contact refers to direct or indirect contact. Direct contact is contact in the absence of an intermediate material, while indirect contact is contact via one or more intermediate materials. Elements in direct contact touch each other. Elements in indirect contact do not touch each other but are rigidly or flexibly joined together via one or more intermediate materials. Contact refers to bringing two elements into direct or indirect contact. Elements in direct (indirect) contact can be described as being in direct (indirect) contact with each other.

[0057] As used herein, “directly adjacent” means in direct contact, and “indirectly adjacent” means indirect contact. The term “adjacent” covers elements that are directly or indirectly adjacent to each other.

[0058] "Radial position", "radius", or radial coordinate "r" refers to the radial position of the corresponding core region in a multi-core optical fiber drawn from a preform formed from the mandrel (r = 0) relative to the centerline of the mandrel.

[0059] The terms "inner" and "outer" refer to the relative values ​​of the radial coordinates or relative positions of regions within a multi-core optical fiber, where "inner" means closer to the centerline of the core rod or core region than "outer." Inner radial coordinates are closer to the centerline than outer radial coordinates. Inner regions are closer to the centerline than outer regions.

[0060] "Refractive index" refers to the refractive index at a wavelength of 1550 nm.

[0061] "Refractive index distribution" refers to the relationship between refractive index or relative refractive index and radius. For the relative refractive index distribution described herein, which has a step boundary between adjacent core and / or cladding regions, normal variations in processing conditions may prevent the attainment of a clear step boundary at the interface between adjacent regions. It should be understood that although the boundary of the refractive index distribution may be described herein as a step change in refractive index, the actual boundary may be smooth or otherwise deviate from the ideal step function characteristics. It should be further understood that the value of the relative refractive index may vary with radial position within the core region and / or any cladding region. When the relative refractive index varies with radial position within a specific region (e.g., the core region and / or any cladding region) of the core rod or multi-core fiber, it is expressed as its actual or approximate functional dependence, or its value at a specific location within said region, or as an average value applicable to the entire region. Unless otherwise stated, if the relative refractive index of a region (e.g., the core region and / or any cladding region) is expressed as a single value or parameter applicable to the entire region (e.g., Δ or Δ% or %), it should be understood that the relative refractive index in the region is constant or approximately constant and corresponds to a single value, or that the single value or parameter represents the average value of a non-constant relative refractive index dependence with radial position in the region. For example, if “i” is a region of a core rod or multi-core fiber, unless otherwise stated, the parameter Δ iIt refers to Δ given in the following equation (2). ave The average relative refractive index within the defined region. Whether as a result of design or normal manufacturing variability, the dependence of the relative refractive index on radial position can be oblique, curved, or otherwise non-constant.

[0062] As used in this paper, the "relative refractive index" is defined in equation (1) for any radial position r as follows:

[0063]

[0064] Unless otherwise specified, n is the refractive index at radial position r in the glass optical fiber, and unless otherwise specified, n ref It is the refractive index of pure quartz glass. For the purposes of this disclosure, n ref = 1.444, which is the refractive index of pure silica at 1550 nm. Therefore, as used herein, the percentage of relative refractive index is relative to pure silica glass. As used herein, unless otherwise stated, the relative refractive index is expressed as Δ (or “delta”) or Δ% (or “delta %”), and its value is given in the unit “%”. The relative refractive index can also be expressed as Δ(r) or Δ(r)%. When referring to a specific region i of the core rod or the core region of a multi-core optical fiber, the relative refractive index can also be expressed as Δ i Δ i %, Δ i (r) or Δ i (r)%.

[0065] The average relative refractive index of the region of the optical fiber ( ave The following is determined by equation (2):

[0066]

[0067] Where r 内 r is the inner radius of the region. 外 Δ is the outer radius of the region, and Δ(r) is the relative refractive index of the region.

[0068] A "groove," "groove region," or "groove cladding region" refers to a portion of the cladding surrounded by and directly adjacent to the outer cladding region. The trench is located between the outer radius r1 of the core region and the inner radius r3 of the outer cladding region, and its relative refractive index Δ3 is less than the relative refractive index Δ4 of the outer cladding region. In some embodiments, the trench is directly adjacent to the core region. In other embodiments, an offset cladding region surrounds and is directly adjacent to the core region, and a trench cladding region surrounds and is directly adjacent to the offset cladding region, wherein the relative refractive index Δ2 of the offset cladding region is less than the relative refractive index Δ1 of the core region and greater than the relative refractive index Δ3 of the trench cladding region.

[0069] The illustrative embodiments described herein will now be described in detail.

[0070] This disclosure provides preforms and preform assemblies for multi-core optical fibers, as well as methods for manufacturing the same. The preform is manufactured by arranging a plurality of core rods in a configuration having contacting outer surfaces to form a preform assembly; and fusing the core rods at selected locations along a contact area defined by the contacting outer surfaces to form a fusion zone, the fusion zone fixing the core rods to form the preform. The outer surfaces of the assembly and the preform are corrugated. The multi-core optical fiber drawn from the preform is characterized by precise and consistent positioning and dimensional alignment of the cores along its length.

[0071] A core rod is a constituent element of a preform assembly. A core rod includes a series of two or more concentric glass regions. These concentric glass regions correspond to regions in a multi-core optical fiber drawn from the preform. The core rod includes a core region and a cladding region surrounding the core region. Both the core region and the cladding region are glass. The cladding region includes one or more regions whose relative refractive indices may differ from and from the relative refractive index of the core region. The plurality of cladding regions are concentric with respect to each other and with the core region. In some embodiments, the cladding region includes a trench cladding region surrounding the core region. In some embodiments, the trench cladding region is surrounded by and directly adjacent to an outer cladding region. In some embodiments, the trench cladding region is directly adjacent to the core region. In other embodiments, the trench cladding region is directly adjacent to an offset cladding region, and the offset cladding region is directly adjacent to the core region. The core region, cladding region, trench cladding region, and outer cladding region are also referred to as core, cladding, trench, and outer cladding, respectively. The offset cladding region is optional and may also be referred to herein as offset.

[0072] It should be understood that the core region is the central area of ​​the mandrel and is substantially cylindrical, and that the surrounding optional offset cladding region, the surrounding trench cladding region, and the surrounding outer cladding region are substantially annular. The annular region can be characterized by its inner and outer radii. Radial positions r1, r2, r3, and r4 in this document refer to the outermost radii of the core region, the offset cladding region, the trench cladding region, and the outer cladding region, respectively. Radius r4 corresponds to the outer radius of the mandrel.

[0073] Whenever used herein, the relative refractive index Δ1 or Δ1(r) refers to the core region, the relative refractive index Δ2 or Δ2(r) refers to the offset cladding region, the relative refractive index Δ3 or Δ3(r) refers to the trench cladding region, and the relative refractive index Δ4 or Δ4(r) refers to the outer cladding region. Unless otherwise stated, if a single value is reported for the relative refractive index of a region, the single value corresponds to the average value of the region.

[0074] As will be further described below, the core region, offset cladding region, trench cladding region, and outer cladding region have different relative refractive indices. Each of these regions is formed from doped or undoped quartz glass. The refractive index variation relative to undoped quartz glass is achieved by using techniques known to those skilled in the art to incorporate increasing or decreasing refractive index dopants at levels designed to provide a target refractive index or refractive index distribution. Increasing refractive index dopants are dopants that increase the refractive index of the glass relative to the undoped glass composition. Decreasing refractive index dopants are dopants that decrease the refractive index of the glass relative to the undoped glass composition. In one embodiment, the undoped glass is pure quartz glass. When the undoped glass is pure quartz glass, increasing refractive index dopants include Cl, Br, Ge, Al, P, Ti, Zr, Nb, and Ta, and decreasing refractive index dopants include F and B. Regions with constant refractive indices can be formed either by being undoped (e.g., pure quartz) or by doping at a uniform concentration. Variable refractive index regions are formed by non-uniform spatial distribution of dopants and / or by incorporating different dopants in different regions. The refractive index changes approximately linearly with the concentration of increasing or decreasing refractive index dopants. For example, in quartz glass, each 1 wt% Cl dopant increases the relative refractive index by approximately 0.083%, and each 1 wt% F dopant decreases the relative refractive index by approximately 0.32%.

[0075] The core rod disclosed herein includes a core region and a cladding region surrounding the core region. Both the core region and the cladding region are glass. Figure 1 An example of a mandrel is shown in a schematic cross-sectional view. The mandrel 10 includes a core region 15 and a cladding region 50. The core region 15 has a higher refractive index than the cladding region 50. In one embodiment, the cladding region 50 is a single region (e.g., an outer cladding region), and in other embodiments, the cladding region 50 includes multiple concentric regions (e.g., a combination of an outer cladding region and offset cladding regions and / or trench cladding regions). The mandrel 10 has a center 17 defined as r = 0, through which a centerline extending along the length of the mandrel 10 passes. The core region 15 has a radius of r1, and the cladding region 50 has a radius of r4. The ratio of radius r1 to radius r4 is referred to herein as the "core-cladding ratio" and is in the range of 0.10 to 0.60, or in the range of 0.15 to 0.50, or in the range of 0.20 to 0.45, or in the range of 0.25 to 0.40.

[0076] Figure 2 and 3 A schematic cross-sectional depiction of another embodiment of the mandrel 10 is shown. Figure 2 In the core rod 10, there is a core region 15 and a cladding region 50. The cladding region 50 includes a trench cladding region 53 and an outer cladding region 55. Figure 3In the core, the core rod 10 includes a core region 15 and a cladding region 50. The cladding region 50 includes an offset cladding region 51, a trench cladding region 53, and an outer cladding region 55.

[0077] In one embodiment (e.g., Figure 2 In this embodiment, the core rod includes a trench cladding region surrounding the core region and an outer cladding region surrounding the trench cladding region. The trench cladding region is directly adjacent to the core region, and the outer cladding region is directly adjacent to the trench cladding region. In another embodiment (e.g., Figure 3 In the core region, the core rod includes an offset cladding region surrounding the core region, a trench cladding region surrounding the offset cladding region, and an outer cladding region surrounding the trench cladding region. The offset cladding region is directly adjacent to the core region, the trench cladding region is directly adjacent to the offset cladding region, and the outer cladding region is directly adjacent to the trench cladding region.

[0078] Figure 4A and 4B The diagram presents a representative relative refractive index distribution of the core rod. One type of optical fiber is the step-index fiber, in which the relative refractive index of the core region is constant or approximately constant relative to its radial position from the centerline (r = 0). Another type of optical fiber is the graded-index fiber, in which the relative refractive index of the core region varies with its radial position from the fiber's centerline (r = 0).

[0079] Figure 4A The gradient relative refractive index distribution of the mandrel 60 is shown. The mandrel has an outer radius of r1 and a relative refractive index of Δ1, wherein the maximum relative refractive index is Δ1. 1max The core region (1), the trench cladding region (3) extending from radial position r2 = r1 to radial position r3 with a relative refractive index of Δ3, and the outer cladding region (4) extending from radial position r3 to radial position r4 with a relative refractive index of Δ4. Figure 4A In the embodiment, the relative refractive index Δ3 is constant or approximately constant from the inner radius r2 of the trench cladding region (3) to the outer radius r3 of the trench cladding region (3).

[0080] Figure 4B The gradient relative refractive index distribution of the mandrel 60 is shown. The mandrel has an outer radius of r1 and a relative refractive index of Δ1, wherein the maximum relative refractive index is Δ1. 1max The core region (1), the offset cladding region (2) extending from radial position r1 to radial position r2 > r1 and with a relative refractive index of Δ2, the trench cladding region (3) extending from radial position r2 to radial position r3 and with a relative refractive index of Δ3, and the outer cladding region (4) extending from radial position r3 to radial position r4 and with a relative refractive index of Δ4. Figure 4B In the embodiment, the relative refractive index Δ3 is constant or approximately constant from the inner radius r2 of the trench cladding region (3) to the outer radius r3 of the trench cladding region (3).

[0081] In other embodiments, Figure 4A and 4B The core region (1) shown is a step refractive index relative refractive index distribution, rather than a gradual refractive index distribution. For example, the relative refractive index of the core region could be a step refractive index distribution, which has the same characteristics as Δ. 1max A corresponding constant or approximately constant value extends over at least 70%, at least 80%, or at least 90% of the distance between the fiber's centerline (r = 0) and its outer radius r1. In another embodiment, Figure 4A and 4B The grooved cladding region (3) shown has a relative refractive index Δ3 that varies in the radial direction.

[0082] exist Figure 4A In the diagram, the transition region 62 from the core region (1) to the trench cladding region (3) and the transition region 64 from the trench cladding region (3) to the outer cladding region (4) are shown as step transitions. Figure 4B In the diagram, the transition region 62 from the offset cladding region (2) to the trench cladding region (3) and the transition region 64 from the trench cladding region (3) to the outer cladding region (4) are shown as step transitions. It should be understood that the step transitions are idealized, and the transition regions 62 and 64 may not actually be strictly vertical. Instead, the transition regions 62 and / or 64 may have slopes or curvatures. When the transition regions 62 and / or 64 are not vertical, the inner radius (r2) and outer radius (r3) of the trench cladding region (3) correspond to the midpoints of the transition regions 62 and 64, respectively. The midpoint corresponds to the depth 67 of the trench cladding region (3). Figure 4A and 4B The depth 67 corresponds to half of the outer cladding region (4), where the depth 67 is defined by the relative refractive index Δ4 relative to the outer cladding region (4).

[0083] Figure 4A and 4B The relative ordering of the relative refractive indices Δ1, Δ3, and Δ4 in the relative refractive index distribution shown satisfies condition Δ 1max > Δ4 > Δ3.

[0084] The core region comprises quartz glass. The quartz glass in the core region is undoped quartz glass, updoped silica glass, and / or downdoped silica glass. In one embodiment, the quartz glass in the core region does not contain Ge; that is, the core region comprises Ge-free quartz glass. In another embodiment, the core region comprises quartz glass doped with germanium dioxide (GeO2). Examples of updoped silica glass include quartz glass doped with alkali metal oxides (e.g., Na2O, K2O, Li2O, Cs2O, or Rb2O) and / or halogens (Cl or Br). Downdoped silica glass includes quartz glass doped with F.

[0085] The outer radius r4 of the mandrel is in the range of 5.0 mm to 30.0 mm. The ratio of the outer radius r1 of the core region to the outer radius r4 of the mandrel is in the range of 0.10 to 0.50, or in the range of 0.15 to 0.45, or in the range of 0.20 to 0.40. In an embodiment, the core region has a gradient relative refractive index distribution, with a relative refractive index Δ1 or Δ 1max Within the range of 0.20% to 0.50%, or within the range of 0.25% to 0.45%, or within the range of 0.30% to 0.40%, and with a minimum relative refractive index Δ 1min Within the range of -0.10% to 0.10%, or within the range of -0.05% to 0.05%, or within the range of -0.02% to 0.02%.

[0086] In some embodiments, the cladding includes an offset cladding region directly adjacent to the core region and a trench cladding region directly adjacent to the offset cladding region. In these embodiments, the offset cladding region has an inner radius r1 and an outer radius r2 > r1 as defined above. The ratio of the outer radius r2 of the offset cladding region to the outer radius r4 of the core rod is in the range of 0.10 to 0.60, or in the range of 0.15 to 0.55, or in the range of 0.20 to 0.50. The ratio of the thickness r2 - r1 of the offset cladding region to the outer radius r4 of the core rod is in the range of 0.03 to 0.30, or in the range of 0.05 to 0.25, or in the range of 0.07 to 0.20. The relative refractive index Δ2 of the offset cladding region is in the range of -0.10% to 0.10%, or in the range of -0.05% to 0.05%, or in the range of -0.02% to 0.02%.

[0087] The trench cladding region comprises a derefractive index-doped quartz glass. The preferred derefractive index dopant is F (fluorine). The relative refractive index of the trench cladding region is Δ3 or Δ... 3minGreater than -0.70% and / or less than -0.10%, or greater than -0.65% and / or less than -0.15%, or greater than -0.60% and / or less than -0.25%, or greater than -0.55% and / or less than -0.30%.

[0088] In some embodiments, the relative refractive index Δ3 is constant or approximately constant, and in other embodiments, the relative refractive index Δ3 monotonically decreases from the inner radius r2 to the outer radius r3. In a preferred embodiment, the monotonically decreasing Δ3 exhibits a constant or approximately constant slope. The monotonically decreasing Δ3 begins at or near the maximum value Δ3 at the inner radius r2. 3max The minimum value Δ extends to or near the outer radius r3. 3min Relative refractive index Δ 3max Within the range of -0.20% to 0.00%, or within the range of -0.15% to 0.00%, or within the range of -0.10% to 0.00%. In one embodiment, the relative refractive index Δ 3max Equal to or approximately equal to the relative refractive index Δ 1min In another embodiment, the relative refractive index Δ 3max It is equal to or approximately equal to the relative refractive index Δ2. The relative refractive index Δ 3min Within the range of -0.70% to -0.05%, or within the range of -0.60% to -0.10%, or within the range of -0.50% to -0.15%, or within the range of -0.40% to -0.20%.

[0089] The inner radius of the trench cladding region is r2 = r1 (in embodiments without an offset cladding region) or r2 > r1 (in embodiments with an offset cladding region) and has the value specified above. The ratio of the outer radius r3 of the trench cladding region to the outer radius r4 of the mandrel is in the range of 0.10 to 0.70, or in the range of 0.15 to 0.65, or in the range of 0.20 to 0.60. The ratio of the thickness r3 – r2 of the trench cladding region to the outer radius r4 or the mandrel is in the range of 0.05 to 0.30, or in the range of 0.07 to 0.25, or in the range of 0.10 to 0.20.

[0090] The relative refractive index Δ4 or Δ in the outer cladding region 4maxThe relative refractive index Δ4 is ​​preferably constant or approximately constant, within the range of -0.10% to 0.10%, or within the range of -0.05% to 0.05%, or within the range of -0.02% to 0.02%. The inner radius of the cladding region is r3 and has the value specified above. The thickness r4–r3 of the cladding region to the outer radius r4 of the mandrel is within the range of 0.30 to 0.90, or within the range of 0.35 to 0.85, or within the range of 0.40 to 0.80, or within the range of 0.45 to 0.75.

[0091] Multi-core optical fibers are drawn from preforms, which are formed from core rod assemblies as described herein. Core rods are typically formed by redrawing a larger blank consisting of identical concentric regions of core rods with larger dimensions. Redrawing reduces the size of the blank to the dimensions of the core rods described herein. The blank includes a central core region surrounded by an annular cladding region. The composition of the core and cladding regions of the blank corresponds to the composition of the core and cladding regions of the core rod redrawn from the blank. The diameter of the core region and the thickness of the cladding region of the blank are proportional to the diameter of the core region and the thickness of the cladding region of the core rod drawn from the blank. Multi-core optical fiber preforms are formed from core rods, as described below. Drawing the preform produces a multi-core optical fiber. During drawing, each core rod in the preform becomes a core element of the multi-core optical fiber. The core region diameter and cladding thickness of the core element are proportional to the core region diameter and cladding thickness of the core rod of the preform from which the core element was drawn. The shape of the cross-section defined by the outer surface of the multi-core optical fiber is similarly proportional to the shape of the cross-section defined by the outer surface of the preform for drawing the multi-core optical fiber.

[0092] Quartz and doped quartz can be produced from the core and cladding regions of mandrel blanks using methods known in the art. Suitable methods include flame combustion, flame oxidation, flame hydrolysis, external vapor deposition (OVD), internal vapor deposition (IVD), axial vapor deposition (VAD), dual-crucible method, rod-tube method, cane-in-soot method, and doped quartz deposition processes. Various chemical vapor deposition (CVD) and plasma-enhanced CVD processes are known and suitable for producing quartz or doped quartz.

[0093] Quartz formation occurs through the reaction or decomposition of quartz precursors. Suitable precursors for quartz include octamethylcyclotetrasiloxane (OMCTS) and SiCl4. Doping is achieved using doping precursors. Doping precursors can be introduced along with the quartz precursor during the deposition process or used to treat the quartz body formed from the quartz precursor. Preferred doping precursors include halogen-containing gases. Suitable precursors for bromine-doped quartz include SiBr4. Suitable precursors for chlorine-doped quartz include Cl2, SiCl4, Si2Cl6, Si2OCl6, and CCl4. Suitable precursors for fluorine-doped quartz include F2, CF4, and SiF4. Quartz precursors and / or doping precursors are preferably provided as gases to the deposition process. Gas-phase quartz precursors or gas-phase doping precursors are supplied in undiluted form or in combination with inert diluent gases (e.g., He, N2, Ar).

[0094] The billet is manufactured by forming the core and cladding regions in one or more process steps. Typical process steps include soot deposition, doping, and consolidation. This is for illustrative purposes and not intended to be limiting. Figure 5A and 5B The image shows the formation of quartz or doped quartz in the form of core soot particles according to the OVD method. Figure 5A In this process, a core soot body 20 is formed by depositing quartz-containing soot 22 onto the outer surface of a rotating and translating mandrel 24. The mandrel 24 is preferably conical. A glass / soot precursor 28 in gaseous form is provided to the flame 30 of the burner 26 to oxidize, hydrolyze, burn, or otherwise react or decompose the glass / soot precursor, thereby forming the soot 22 of the core soot body 20. Fuel 32, such as methane (CH4), and combustion-supporting gas 34, such as oxygen, are provided to the burner 26 and ignited to form the flame 30. Optionally, a dopant compound 36 is also provided to the burner 26. A mass flow controller labeled V meters appropriate amounts of the glass / soot precursor 28, fuel 32, combustion-supporting gas 34, and dopant compound 36 (all preferably in gaseous form) to the burner 26. The glass / ash precursor 28 is a glass forming agent compound (e.g., a quartz precursor) and is oxidized in flame 30 to form a generally cylindrical core ash region 23.

[0095] Figure 5B Another process for doped core fumigation body 20 is demonstrated. Before consolidation, the core fumigation body 20 is removed. Figure 5AThe bait rod 24 shown is used to form a hollow cylindrical core soot body. During the doping and consolidation processes, the core soot body 20 is suspended, for example, by means of a holding mechanism 21, inside a pure quartz muffle tube 27 of the furnace 29. Optionally, the core soot body 20 is exposed to a doping precursor before or during the consolidation step. The doping precursor is preferably provided in gaseous form and supplied directly to the core soot body 20 before or during consolidation. In one embodiment, the gaseous doping precursor is a vapor formed by heating or evaporating a liquid precursor. The doping precursor is supplied in pure (undiluted) form or in combination with a diluent gas. The doping concentration can be controlled by controlling, but is not limited to, the doping temperature, the evaporation temperature of the liquid doping precursor, the pressure or partial pressure of the gaseous doping precursor in the processing environment of the core soot body, the doping time, the number of doping cycles, and the porosity or surface area of ​​the core soot body (high porosity and / or high surface area promote higher doping concentrations).

[0096] In one embodiment, after doping, the core soot mass is consolidated to form a densified glass with a core region having a composition and refractive index distribution of a core rod. Typical consolidation temperatures are in the range of 1100°C to 1600°C. The density of the densified glass is at least 1.90 g / cm³. 3 After densification, the densified core glass is optionally redrawn to the desired size and used as a substrate for depositing additional concentric soot layers having the composition and relative refractive index of the cladding region of the mandrel. Alternatively, additional concentric soot cladding layers can be deposited on the core soot body prior to consolidation, and the combination of layers can be consolidated to form a billet from which the mandrel is redrawn.

[0097] Figures 6A-6C The fabrication of a soot body with three porous soot layers is demonstrated. However, it should be recognized that the outlined procedure is generally applicable to soot bodies with any number of porous soot layers.

[0098] Figure 6AA quartz-based soot layer 112 is deposited on a substrate 120. The quartz-based glass soot is formed by providing a gaseous quartz-based glass precursor material, such as SiCl4 or octamethylcyclotetrasiloxane (OMCTS), to a burner 122. A feed-in burner 122 is supplied with fuels such as H2, CH4, D2 (deuterium), CD4, or CO. Oxygen is also supplied to the burner 122, and the fuel and oxygen are burned to produce a flame 126. In some embodiments, the gaseous quartz-based glass precursor material is SiCl4, and the feed-in burner 122 is supplied with a non-hydrogenated fuel such as D2, CD4, or CO to limit the amount of residual OH in the deposited quartz-based glass soot. The gaseous quartz-based glass precursor material can be delivered to the burner at a flow rate of about 4 L / min to about 10 L / min, while the fuel can be supplied to the burner at a flow rate of about 10 L / min to about 40 L / min.

[0099] A gaseous quartz-based glass precursor material reacts in a flame 126 to produce a quartz-based glass soot 128, which is deposited as a soot layer 112 on a substrate 120 as the burner rotates. The rotation speed can be from about 20 rpm to about 400 rpm, or preferably from 30 rpm to about 100 rpm. The soot layer 112 can have the same, higher, or lower refractive index compared to undoped quartz. Higher or lower refractive indices can be achieved by supplying a rising or falling refractive index dopant precursor to the burner 122. The soot layer 112 can form a single-layer soot cladding or the innermost (smallest radius) layer of a multi-layer soot cladding. As the burner rotates, the flame 126 of the feed-in burner 122 travels back and forth along the axial length of the substrate 120 as indicated by arrow 124, thereby constructing the quartz-based glass soot and forming the soot layer 112 on the substrate 120.

[0100] Figure 6B The deposition of soot layer 116 on soot layer 112 is depicted. Soot layer 116 can be formed in a similar manner to soot layer 112. For example, a gaseous quartz-based glass precursor material such as SiCl4 or OMCTS can be supplied to a feed-gas burner 122 and reacted in flame 126 to form quartz-based glass soot, which is deposited as soot layer 116 on soot layer 112 as the burner rotates. Soot layer 116 can have the same, higher, or lower refractive index than soot layer 112.

[0101] Figure 6CThe deposition of soot layer 114 on soot layer 116 is depicted. Soot layer 114 can be formed in a similar manner to soot layer 112 or soot layer 116. For example, a gaseous quartz-based glass precursor material such as SiCl4 or OMCTS can be supplied to a feed-gas burner 122 and reacted in flame 126 to form quartz-based glass soot, which is deposited as soot layer 114 on soot layer 116 as the substrate 120 rotates. Soot layer 114 can have the same, higher, or lower refractive index compared to soot layer 116 or soot layer 112. Additional layers can be deposited similarly to obtain a soot body with any desired number of layers. After depositing the soot layers, the soot body is consolidated to form a billet, from which a mandrel is drawn again.

[0102] The process conditions for forming different layers of multilayer soot can be the same or different. Process variables include flame temperature, flow rate of silicon or dopant precursor, burner travel rate along the length of the substrate, and substrate rotation rate. Dopant concentration can be controlled by varying the flow rate of the dopant precursor, the choice of dopant precursor, and the doping temperature. A uniform or variable dopant concentration distribution in the radial direction can be achieved. To form a trench cladding region with a monotonically decreasing relative refractive index in the radial direction, the concentration of a derefractive index dopant precursor (e.g., SiF4) gradually increases during soot deposition, as concentric monolayers of trench cladding soot are formed. The flow of the derefractive index dopant precursor terminates at the transition from the soot layer corresponding to the trench cladding region to the soot layer corresponding to the outer cladding region. Variations in process conditions can control the soot deposition rate and the density of the soot in the deposited state. Flame temperature can be 1500°C or higher. Higher flame temperatures promote higher deposited soot density. Conversely, lower flame temperatures result in lower deposited soot density.

[0103] In one embodiment, substrate 120 is a bonded glass having the composition and refractive index of the core region of a mandrel to be redrawn from a blank. In this embodiment, soot layers 112, 116, and 114 correspond to different portions of the cladding region (e.g., offset cladding region, trench cladding region, and outer cladding region). In another embodiment, substrate 120 is a mandrel, soot layer 112 corresponds to the core region, and soot layers 116 and 114 correspond to two different portions of the cladding region (e.g., offset cladding region and trench cladding region, or trench cladding region and outer cladding region). The soot layers provide a blank upon bonding, the blank being configured to allow redrawing of a mandrel having the relative refractive index distribution disclosed herein.

[0104] Figure 7 A process for fabricating multicore optical fibers from a blank comprising a core region surrounded by a cladding region is described. Although the cladding region is described as a single region, it should be understood that the cladding region may include, as described herein, a single region. Figure 1-4B The process involves creating a series of two or more concentric regions to produce a core rod consistent with the embodiments disclosed herein. In this process, a blank is redrawn to form multiple core rods. The multiple core rods are assembled to form a multicore preform, and the multicore preform is drawn to form a multicore optical fiber.

[0105] In the redrawing process, a billet is stretched and thinned by heating and drawing to form a mandrel. The billet, or a portion thereof, enters a heated zone (e.g., a furnace). The heat in the heated zone softens the billet, allowing it to flow, stretch, and thin. Tension may be applied to facilitate redrawing. The length of the heated zone, or the time it takes for the billet to reach a temperature sufficient to allow it to flow, determines the degree of stretching and thinning, and thus the diameter of the mandrel. The billet is typically a dense, solid piece of glass with a diameter of about 30 mm to 150 mm. The diameter of the mandrel redrawn from the billet is about 10 mm to 60 mm. Multiple mandrels are produced by cutting the redrawn billet into lengths of about 1 m to 2 m. The diameter of the mandrels is uniform across the multiple mandrels. In embodiments, the diameter of each mandrel among the multiple mandrels is within ±3.0%, ±2.0%, ±1.5%, ±1.0%, or ±0.5% of the average diameter of the multiple mandrels. The outer surface and cross-section of the mandrel are circular, and preferably perfectly circular. During the redrawing process, deviations from perfect roundness may occur, and slight deformations may occur in the cross-section of the mandrel, deviating from a perfect circle. For example, such deformations may be slightly elliptical. However, the outer surface and cross-section of the mandrel remain circular, with curvature, and without rectangular features such as sharp corners, vertices, straight sections, or edges. In embodiments, the outer surface defines a cross-section with a radius of curvature greater than 100 micrometers, or greater than 500 micrometers, or greater than 1000 micrometers, or greater than 2000 micrometers, or greater than 3000 micrometers, or greater than 5000 micrometers. When used for a circular cross-section, the term "diameter" refers to the average linear dimension of the cross-section passing through its center.

[0106] A multicore preform is formed into an assembly of core rods. The core rods of the assembly can be drawn from the same or different blanks. A core rod assembly is formed by placing multiple core rods in contact with each other and rigidly joining the core rods. In the assembly, the core rods are arranged in a configuration consistent with the arrangement of the desired core elements in a multicore optical fiber drawn from the multicore preform. The assembly has a cross-section with a center, through which the central longitudinal axis of the assembly passes. In the assembly, the centerlines of the core rods are parallel or substantially parallel to each other and parallel or substantially parallel to the central longitudinal axis of the assembly. The outer surface of each core rod is in direct contact with the outer surface of at least one other core rod in a contact area extending along the length of the core rod. The contact area is aligned with the direction of the central longitudinal axis of the assembly. The core rods of the assembly are rigidly joined by fusion at selected locations within the contact area to form a fusion zone that rigidly joins the core rods together in the multicore preform. The fusion zone is formed by localized heating at selected locations within the contact area. Localized heating can be accomplished, for example, with a flame torch (e.g., an oxy-hydrogen flame).

[0107] Figure 8 The diagram illustrates the arrangement of core rods in selected assemblies of preforms that can be used as multi-core optical fibers, in a cross-section perpendicular to the central longitudinal axis. Preform (a) comprises an assembly of two core rods arranged in a 1 × 2 linear arrangement. Preform (b) comprises an assembly of four core rods arranged in a 1 × 4 linear arrangement. Preform (c) comprises an assembly of four core rods arranged in a 2 × 2 square arrangement. Preform (d) comprises a hexagonal assembly of seven core rods. Preform (e) comprises a hexagonal assembly of 19 core rods. It should be noted that in… Figure 8 The outer surface of each preform depicted is corrugated, with undulations or peaks and valleys defined by the radius of curvature and the arrangement of the core rods within the preform. It should also be noted that... Figure 8 Each of the preforms depicted in the image is without a surrounding substrate tube. Further attention should be paid to... Figure 8 The preforms (c), (d), and (e) depicted each include one or more internal cavities aligned with the centerline and central longitudinal axis of the core region of the assembly and the preform. The internal cavity is an unfilled area defined by the circular outer surface of the contacting core of the assembly. Figure 8 The preforms shown are for illustrative purposes only and do not limit the number or arrangement of the mandrels. It will be apparent to those skilled in the art that other arrangements of other numbers of mandrels can be similarly conceived and implemented according to this disclosure.

[0108] In an embodiment, the preform assembly includes two or more, three or more, four or more, six or more, eight or more, ten or more, or twelve or more mandrels arranged in a linear (n × 1), square (n × n), rectangular (n × m), hexagonal or other polygonal configuration.

[0109] Figure 9A and 9B An enlarged view of the contact area between the mandrels is shown. Figure 9A A pair of mandrels in contact is shown. Although only one pair of mandrels is depicted, it should be understood that... Figure 9A This describes any contacting mandrel pairs in the assembly of the mandrels in the preforms disclosed herein. For example, Figure 8 Components (b)–(e) each contain multiple contacting mandrel pairs, each of the multiple contacting mandrel pairs as follows: Figure 9A and 9B The illustration is schematic. Figure 9A Each mandrel 10 depicted has a center 17, a core region 15, and a cladding region 50. The center 17 defines a corresponding centerline extending along the length of the contacting mandrel 10. A contact region 40 is also shown, along which the outer surface of the contacting mandrel 10 contacts.

[0110] Figure 9B A perspective view of the contact area 40 in a direction parallel to the center line of the contacting mandrel 10 is shown. Figure 9B The perspective view depicted in the middle and through Figure 9A The center 17 corresponds to the plane containing the center line of the contacting mandrel 10. For each contacting mandrel 10, Figure 9B It shows Figure 9A The core region 15, cladding region 50 and center 17 are depicted in the image. Figure 9B The centerline 42, first end 44, and second end 46 of each contacting mandrel 10 are further shown. When assembled into a preform, the first end 44 and second end 46 of the contacting mandrel 10, together with the corresponding ends of any other mandrels in the preform assembly, define the ends of the preform assembly. The preform assembly includes a central longitudinal axis parallel to the centerline 42, which passes through the center of the preform assembly. If the preform assembly only includes Figure 9B If the mandrel pair 10 is depicted, the central longitudinal axis of the preform assembly will be aligned with the contact area 40.

[0111] Contact area 40 extends from a first end 44 to a second end 46. In the initial assembly of mandrel 10, the outer surfaces are placed in contact and not permanently joined. After initial contact, selected areas of contact area 40 are fused by heating, thereby permanently joining mandrel 10. The fusion creates a fusion zone 48 at selected locations in contact area 40. The unfused portions of contact area 40 are unfused areas 49 of contact area 40. One or more unfused areas 49 extend from each of the fusion zones 48. One or more fusion zones are formed between contacting mandrel pairs in the preform to secure the mandrels to each other in the assembly. Fusion occurs by locally heating the contact areas at the locations of the fusion zones. Local heating can be done, for example, with a spray gun. In one embodiment, fusion zone 48 is formed near one end of the assembly. In another embodiment, fusion zone 48 is formed near both ends of the assembly, and unfused areas 49 extend between fusion zones 48. Figure 9C Preferably, at least one fusion zone is formed in the contact region between each contacting mandrel pair in the assembly. In some embodiments, two or more fusion zones are formed in the contact region of one or more contacting mandrel pairs in the assembly. In other embodiments, the fusion zones are formed away from the end of the preform assembly, for example, toward the center of the contact region 40.

[0112] For the purposes of this disclosure, a fusion region is referred to as the end near the preform assembly if any portion of the fusion region is within 25% of the length of the contact area 40 from one end, wherein the length of the contact area 40 is the distance between the first end 44 and the second end 46 measured in a direction parallel to the centerline 42. In some embodiments, a portion of one or more fusion regions is within 20%, 15%, 10%, or 5% of the length of the contact area 40 from one end of the preform assembly. In other embodiments, the entire one or more fusion regions are within 20%, 15%, 10%, or 5% of the length of the contact area 40 from one end of the preform assembly. In some embodiments, one or more fusion regions extend from one end of the preform assembly along the contact area 40. The length of the fusion zone is less than or equal to 30.0 mm, or less than or equal to 20.0 mm, or less than or equal to 10.0 mm, or less than or equal to 7.0 mm, or less than or equal to 5.0 mm, or greater than or equal to 1.0 mm, or greater than or equal to 3.0 mm, or greater than or equal to 5.0 mm, or greater than or equal to 10.0 mm, or in the range of 1.0 mm to 30.0 mm, or in the range of 2.0 mm to 20.0 mm, or in the range of 3.0 mm to 15.0 mm.

[0113] Once the core is laid and fused, the optical fiber is drawn from the preform. In continuous optical fiber manufacturing processes, the optical fiber is drawn from a heated preform positioned in a drawing furnace and passes through a series of processing stages. These stages typically include metrology units (e.g., fiber diameter control) for evaluating fiber quality and other properties, a heating stage, a primary coating stage, a secondary coating stage, an ink layer stage, and a spool or other winding stage for receiving and storing the coated fiber. The path the optical fiber takes from the drawing furnace to the winding stage can be straight or may include bends. The drawing speed of the optical fiber from the preform is greater than 30 m / s, or greater than 35 m / s, or greater than 40 m / s, or greater than 45 m / s, or greater than 50 m / s.

[0114] As described herein, multi-core optical fibers drawn from the preform of this disclosure have a corrugated outer surface, the outer surface having undulations and features defined by the size and placement of the core rods in the assembly defining the preform. The cross-sectional dimension of the multi-core optical fiber is the maximum linear dimension passing through the center of the cross-section of the multi-core optical fiber. Each core region of the multi-core optical fiber further has a cross-sectional dimension corresponding to the maximum linear dimension passing through its center. In some embodiments, the cross-sectional dimension of the multi-core optical fiber is less than or equal to 500 μm, and the cross-sectional dimension of each core of the multi-core optical fiber is greater than or equal to 50 μm. In other embodiments, the cross-sectional dimension of the multi-core optical fiber is less than or equal to 250 μm, and the cross-sectional dimension of each core of the multi-core optical fiber is greater than or equal to 60 μm. In one embodiment, the multi-core optical fiber drawn from the preform is coated with one or more coatings to form a coated multi-core optical fiber with a circular outer surface. The circular outer surface is non-corrugated and preferably defines a circular or approximately circular cross-section for the coated multi-core optical fiber.

[0115] Example 1

[0116] A blank containing a core region surrounded by a cladding region was fabricated using an external vapor deposition process. The core region was quartz glass doped with approximately 7 wt% GeO2, and the cladding region was undoped quartz. The blank was redrawn at a temperature of approximately 1900°C and a redrawing speed of 10 mm / s, and cut to form a mandrel with a diameter of 11 mm and a length of 1 m. The core-cladding ratio of the mandrel was 0.33. Four mandrels were assembled in an approximately 2 × 2 square configuration. Figure 10The image depicts an approximately 2 × 2 square assembly. Limitations in the alignment system used to form the assembly preclude achieving a perfectly square configuration. Quadrilateral ABCD connects the centers of the four mandrels of the preform. The preform includes four contact areas 40 between adjacent mandrels of the assembly. The mandrels are secured by applying a flame torch for approximately 30 to 60 seconds to create fusion zones at the top and bottom of the preform. The preform further includes an internal cavity 57 surrounded by the mandrels. The internal cavity 57 is aligned with the centerline of the core region of the mandrel and the central longitudinal axis of the preform. The internal cavity 57 is parallel or substantially parallel to the contact areas 40.

[0117] A multi-core optical fiber with a length of 470 m is drawn from a preform. Images of both ends of the optical fiber are shown below. Figure 11A and 11B As shown, the multi-core optical fiber has four core regions spaced apart from each other, and each core region is surrounded by a cladding region. The cladding region defines the outer surface of the multi-core optical fiber, which is corrugated. An internal cavity exists along the central longitudinal axis of the optical fiber.

[0118] Table 1 summarizes the measurements of the core diameter and the spacing between the cores at both ends of the preform and the optical fiber along quadrilateral ABCD.

[0119] Table 1. Geometric measurements of the preform and optical fiber in Example 1

[0120]

[0121] The results in Table 1 show that the core diameter and inter-core spacing at both ends of the fiber are similar. The core diameter variation at both ends is less than 0.45 μm, and the inter-core spacing variation is less than 1.25 μm. The results also show that the aspect ratio of the 2 × 2 configuration fiber is slightly improved compared to the preform.

[0122] Example 2

[0123] In the second example, an alignment device is used to assemble four mandrels of the type described in Example 1 into a 2 × 2 square configuration to improve the accuracy of the mandrel position in the preform.

[0124] Multi-core optical fibers with a length of 1050 m are drawn from preforms. Figure 12A and 12B Images of both ends of the optical fiber are shown, demonstrating a significant improvement in the fiber core geometry. The multi-core fiber has four core regions spaced apart from each other, and each core region is surrounded by a cladding region. The cladding region defines the outer surface of the multi-core fiber, which is corrugated.

[0125] Table 2 summarizes the preformed rods ( Figure 10 (Depicted in the middle) and the measurement of the core diameter and the spacing between the cores along the two ends of the optical fiber along the quadrilateral ABCD.

[0126] Table 2. Geometric measurements of the optical fiber in Example 2

[0127]

[0128] The results in Table 2 show that the core diameter and intercore spacing at both ends of the optical fiber are similar. Over a length of approximately 1 km, the core diameter variation at both ends of the optical fiber is less than 1.25 μm, and the intercore spacing variation at both ends of the optical fiber is less than 1.52 μm.

[0129] Example 3

[0130] In the third example, an alignment device is used to assemble four core rods with a diameter of 11 mm into a 2 × 2 square configuration. The core rods are similar to those in Examples 1 and 3, but have a smaller core radius to obtain a single-mode core in the fiber drawn from the preform.

[0131] Multi-core optical fibers with a length of 2050 m are drawn from preforms. Figure 13 An image of one end of an optical fiber is shown. The multi-core fiber has four core regions spaced apart from each other, and each core region is surrounded by a cladding region. The cladding region defines the outer surface of the multi-core fiber, which is corrugated.

[0132] Table 3 shows the preforms ( Figure 10 (Depicted in the middle) and the measurement of the core diameter and the spacing between the cores along the two ends of the optical fiber along the quadrilateral ABCD.

[0133] Table 4. Geometric measurements of the optical fiber in Example 3

[0134]

[0135] For each of the four cores of the multi-core fiber, the mode field diameter (MFD) at 1310 nm and 1550 nm, the fiber cutoff wavelength, and the attenuation at 1310 nm and 1550 nm were measured. The results are summarized in Table 4. The MFD, fiber cutoff wavelength, and attenuation of each core region of the multi-core fiber conform to the industry standards for single-mode fiber.

[0136] Table 4. Optical Measurements of the Fiber in Example 3

[0137]

[0138] Unless otherwise expressly stated, it is not intended to interpret any method described herein as requiring its steps to be performed in a particular order. Therefore, no particular order is intended to be inferred where the method claims do not actually describe the order in which the steps are followed, or where the claims or description do not otherwise specifically specify that the steps are limited to a particular order.

[0139] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the illustrated embodiments. Because modifications, combinations, sub-combinations, and variations of the disclosed embodiments that may be conceived by those skilled in the art and incorporated into the spirit and substance of the illustrated embodiments are possible, this specification should be construed as including all contents within the scope of the appended claims and their equivalents.

Claims

1. A preform for a multi-core optical fiber, the preform comprising: An assembly of multiple mandrels, the assembly having a first end, a second end, and a central longitudinal axis extending from the first end to the second end, each of the mandrels having an outer surface defining a circular cross-section, the outer surface of each mandrel directly contacting the outer surface of another mandrel along a contact area aligned with the central longitudinal axis, the contact area including a first fusion region and a non-fusion region extending from the first fusion region.

2. The preform of claim 1, wherein the component comprises three or more of the mandrels.

3. The preformed rod according to claim 1 or 2, wherein the mandrel is arranged in a linear configuration, a square configuration, a rectangular configuration, or a hexagonal configuration.

4. The preform according to any one of claims 1 to 3, wherein the radius of curvature of the circular cross-section is greater than 1000 micrometers.

5. The preform according to any one of claims 1 to 4, wherein each of the preforms comprises a core region and a cladding region, the cladding region surrounding and being directly adjacent to the core region, the relative refractive index of the core region being greater than the relative refractive index of the cladding region.

6. The preform according to claim 5, wherein the cladding region comprises a grooved cladding region.

7. The preformed rod according to any one of claims 1 to 6, wherein the preformed rod comprises one or more internal cavities aligned with the central longitudinal axis.

8. The preform according to any one of claims 1 to 7, wherein the first fusion zone is adjacent to the first end of the component.

9. The preform of claim 8, wherein the entire first fusion zone is adjacent to the first end of the component.

10. The preform according to any one of claims 1 to 9, further wherein the contact area further includes a second fusion zone.

11. The preform of claim 10, wherein the second fusion zone is adjacent to the second end of the component.

12. The preformed rod according to any one of claims 1 to 11, wherein the preformed rod has a corrugated outer surface.

13. The preform according to claim 12, wherein the outer surface is without sharp edges.

14. A multi-core optical fiber, comprising: Multiple core regions, spaced apart from each other, each core region comprising glass; A cladding region surrounds and directly contacts the core region, the cladding region comprises glass and has a relative refractive index lower than that of the core region, the cladding region defines the outer surface of the multi-core optical fiber, the outer surface being corrugated and without sharp edges.

15. The multi-core optical fiber of claim 14, wherein the outer surface is further free of straight sections.

16. The multi-core optical fiber according to claim 14 or 15, further comprising a coating having a circular outer surface.

17. The multi-core optical fiber according to any one of claims 14 to 16, wherein the cross-sectional dimension of the multi-core optical fiber is less than 500 μm, and the cross-sectional dimension of each core region of the multi-core optical fiber is greater than 50 μm.

18. The multi-core optical fiber according to any one of claims 14 to 17, wherein the plurality comprises three or more of the core regions.

19. The multi-core optical fiber according to any one of claims 14 to 18, wherein the core region is arranged in a linear configuration, a square configuration, a rectangular configuration or a hexagonal configuration.

20. A method for manufacturing a multi-core optical fiber, the method comprising: Multi-core optical fibers are drawn from a preform comprising an assembly of multiple core rods having a first end, a second end, and a central longitudinal axis extending from the first end to the second end. Each of the core rods has an outer surface defining a circular cross-section. The outer surface of each core rod directly contacts the outer surface of another core rod along a contact area aligned with the central longitudinal axis. The contact area includes a first fusion region and a non-fusion region extending from the first fusion region.

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