Microbend-improved, reduced-diameter multi-core optical fiber

Abstract

This provides a multi-core optical fiber with improved microbending and reduced diameter. [Solution] The multi-core optical fiber consists of a first core made of alkali metal-doped silica glass, a first inner cladding surrounding the first core, and a 30%Δ-micrometer core surrounding the first inner cladding. 2 A first outer cladding comprising a first trench region having the above trench volume, a second core made of alkali metal-doped silica glass, a second inner cladding surrounding the second core, and surrounding the second inner cladding, 30%Δ·micrometer 2 The structure comprises a second outer cladding including a second trench region having the above trench volume, and a common cladding surrounding the first core and the second core, respectively. Each of the first core and the second core has a waveguide light signal of 1550 nm with a wavelength of 100 micrometers 2 It has the following effective area.

Description

Priority

[0001] This application claims priority to Netherlands Patent Application No. 2025271, filed on 3 April 2020, which claims priority to U.S. Provisional Patent Application No. 62 / 991278, filed on 18 March 2020, on which the contents are based and are fully cited herein. [Technical Field]

[0002] This disclosure relates to optical fibers. More specifically, this disclosure relates to optical fiber cables made for submarine environments. Most specifically, this disclosure relates to optical fibers having a reduced diameter without significantly increasing microbend sensitivity. [Background technology]

[0003] Submarine cables are designed to transmit telecommunications signals across land, sea, and air. In recent years, the volume of telecommunications signals traversing submarine cables has increased dramatically, and currently, over 90% of intercontinental communication signals are transmitted via submarine cables. Therefore, with the increase in intercontinental internet traffic, the demand for the transmission capacity of such submarine cables is also rising.

[0004] Conventional methods for increasing the transmission capacity of submarine cables include wavelength division multiplexing to increase the number of transmission channels and advanced modulation formats to increase the data transmission rate per channel. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, these methods are no longer practical because the number of channels and channel data transmission speeds are near their practical limits. Another method that could potentially increase the transmission capacity of submarine cables is to increase the number of fibers within the cable by increasing the overall diameter of the cable. However, this method is also not practical because the diameter of submarine cables is limited to facilitate cable laying. Increasing the diameter of submarine cables increases their mass, making cable management even more difficult due to the limited storage capacity of ships that lay submarine fiber optic cables. [Means for solving the problem]

[0006] This disclosure provides optical fibers having a reduced diameter to increase the total number of fibers in a submarine cable, and thus allowing the diameter of the submarine cable to be maintained at an easily layable size. Specifically, the optical fibers disclosed herein have a reduced glass diameter and / or reduced cladding thickness while still maintaining the microbend characteristics required for long-distance transmission. More specifically, the optical fibers disclosed herein provide low attenuation, low microbend sensitivity, and high puncture resistance in a compact form. The reduced glass diameter and / or reduced cladding thickness may be used to increase fiber density in a standard submarine cable design. The microbend characteristics of such reduced-diameter optical fibers, as disclosed herein, are achieved by co-optimizing the cladding characteristics of the fiber with dimensions of a reduced refractive index cladding layer in the refractive index profile to suppress optical signal leakage. The high modulus of the secondary cladding improves the puncture resistance and handling of the fiber despite the smaller cross-sectional area.

[0007] This description relates to an optical fiber having a core region made of silica glass doped with chlorine and / or alkali metals. The optical fiber further comprises a cladding region surrounding the core region, which includes an inner cladding directly adjacent to the core region, an outer cladding surrounding the inner cladding, and a trench region radially positioned between the inner and outer claddings, the trench region being approximately 30%Δ-micrometers 2 It has the above volume. In addition, this optical fiber is approximately 100 micrometers 2 It has the following effective area at 1550 nm.

[0008] This description relates to an optical fiber having a core region made of chlorine and / or alkali metal-doped silica glass, and a cladding region surrounding the core region. The cladding region includes an inner cladding directly adjacent to the core region, an outer cladding surrounding this inner cladding, and a trench region radially positioned between the inner and outer claddings, the trench region being approximately 30%Δ-micrometers 2 The optical fiber has the above volume. This optical fiber further comprises a primary coating surrounding the cladding region and a secondary coating surrounding the primary coating. The primary coating has an in-situ modulus of elasticity of about 0.5 MPa or less, and the secondary coating has an in-situ modulus of elasticity of about 1500 MPa or more. The diameter of the secondary coating is about 210 micrometers or less.

[0009] This description further includes a first core made of silica glass doped with chlorine and / or alkali metals, a first inner cladding surrounding the first core, and surrounding the first inner cladding, approximately 30% Δ-micrometers 2 The multi-core optical fiber has a first outer cladding containing a first trench region having the above volume. In addition, the multi-core optical fiber has a second core made of silica glass doped with chlorine and / or alkali metals, a second inner cladding surrounding this second core, and surrounding the second inner cladding, about 30% Δ micrometers 2It has a second outer cladding which includes a second trench region having a volume greater than or equal to the above. A common cladding surrounds the first and second cores. Furthermore, each of the first and second cores is approximately 100 micrometers 2 It has the following effective area at 1550 nm.

[0010] Additional features and advantages are described in the following detailed description, some of which will be readily apparent to those skilled in the art from that description, or will be recognized by carrying out the embodiments as described in the description and its claims, as well as in the accompanying drawings.

[0011] It should be understood that both the general description above and the detailed description below are merely illustrative and intended to provide an overview or framework for understanding the nature and features of the claims.

[0012] The accompanying drawings are included for further understanding and constitute part of this specification. The drawings illustrate selected aspects of this disclosure and, together with the description, serve to illustrate the principles and operation of the methods, products, and compositions contained herein. [Brief explanation of the drawing]

[0013] [Figure 1] Schematic diagram of a coated optical fiber according to an embodiment of the present disclosure. [Figure 2] Schematic diagram of an optical fiber ribbon according to an embodiment of the present disclosure. [Figure 3] Schematic diagram of an optical fiber cable according to an embodiment of the present disclosure [Figure 4] Schematic diagram of a cross-section of an optical fiber according to an embodiment of the present disclosure. [Figure 5] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 6A] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 6B] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 6C] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 6D] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 6E] Relative refractive index profile of an optical fiber according to an embodiment of the present disclosure [Figure 7] Plot of radiant loss versus cladding radius for two optical fibers. [Figure 8A] Schematic diagram of a multi-core optical fiber according to an embodiment of the present disclosure. [Figure 8B] Schematic diagram of a multi-core optical fiber according to an embodiment of the present disclosure. [Figure 8C] Schematic diagram of a multi-core optical fiber according to an embodiment of the present disclosure. [Figure 9] Schematic diagram of a multi-core optical fiber according to an embodiment of the present disclosure. [Figure 10] Plot of crosstalk versus core spacing of three multi-core optical fibers. [Figure 11] Relative refractive index profile of the core of a multi-core optical fiber according to an embodiment of the present disclosure [Modes for carrying out the invention]

[0014] This disclosure is provided as a feasible teaching and can be more readily understood by referring to the following description, drawings, examples, and claims. For this purpose, those skilled in the art will recognize and understand that many modifications can be made to various aspects of the embodiments described herein while obtaining beneficial results. It will also be apparent that some of the desired advantages of these embodiments can be obtained by selecting some features without utilizing others. Thus, those skilled in the art will recognize that many modifications and adaptations are possible, may even be desirable in certain circumstances, and are part of this disclosure. Therefore, it will be understood that this disclosure is not limited to any particular composition, article, apparatus, and method disclosed unless otherwise specified. It should also be understood that the technical terms used herein are for the purpose of describing specific aspects and are not intended to limit them.

[0015] Numerous terms are used herein and in the subsequent claims as defined below:

[0016] An "optical fiber" is a waveguide that has a glass portion surrounded by a sheath. This glass portion consists of a core and cladding, and is referred to here as a "glass fiber."

[0017] "Radial position," "radius," or radial coordinate "r" refers to the radial position relative to the fiber's centerline (r=0).

[0018] Unless otherwise specified, "refractive index" refers to the refractive index at a wavelength of 1550 nm.

[0019] A "refractive index profile" is the relationship between the refractive index, or relative refractive index, and the radius. For relative refractive index profiles depicted here as having a step boundary between adjacent core and / or cladding regions, normal variations in processing conditions may result in a less-than-sharp step boundary at the interface of adjacent regions. While the boundary of the refractive index profile may be expressed here as a step change in refractive index, it should be understood that the actual boundary may be rounded or deviate in other ways from the perfect step function characteristics. It should be further understood that the value of the relative refractive index may vary with the radial position in either the core or / or cladding region. When the relative refractive index varies with the radial position within a particular region of the fiber (e.g., either the core or / or cladding region), it is expressed as its actual function dependence or approximate function dependence, or as its value at a specific location within the region, or as an average value applicable to the entire region. Unless otherwise specified, when the relative refractive index of a region (e.g., either the core region and / or cladding region) is expressed as a single value or as a parameter applied to the entire region (e.g., Δ or Δ%), it is understood that the relative refractive index within that region is constant or approximately constant, and the single value corresponds to, or the single value or parameter represents the average value of the non-constant relative refractive index dependence with respect to the radial position within that region. For example, if "i" is the region of glass fiber, then the parameter Δ i Unless otherwise specified, this refers to the average relative refractive index within the region defined by equation (1) below. Whether due to design or normal manufacturing variations, the dependence of the relative refractive index on radial position may be sloped, curved, or otherwise non-constant.

[0020] The "relative refractive index" used here is expressed in equation (1) as follows:

[0021]

number

[0022] It is defined as follows, and in the formula, ni is the refractive index at the radial position r of the glass fiber, where r i is the refractive index, and n ref is the refractive index of pure silica glass, unless otherwise specified. Thus, as used herein, the relative refractive index percentage is relative to pure silica glass having a value of 1.444 at a wavelength of 1550 nm. As used herein, the relative refractive index is represented by Δ (or "delta") or Δ% (or "delta %"), and its value is given in units of "%" unless otherwise specified. Also, the relative refractive index may be represented as Δ(r) or Δ(r)%.

[0023] The average relative refractive index (Δ 平均 ) of a region of the fiber is given by Equation (2):

[0024] [Equation number]

[0025] where r 内側 is the inner radius of the region, r 外側 is the outer radius of the region, and Δ(r) is the relative refractive index of the region.

[0026] The refractive index of the optical fiber profile can be measured using commercially available devices such as the IFA-100 Fiber Index Profiler (Interfiber Analysis LLC, Sharon, Massachusetts, USA) or the S14 Refractive Index Profiler (Photon Kinetics, Inc., Beaverton, Oregon, USA). These devices measure the refractive index with respect to a reference refractive index, n(r) - n meas , where the reference refractive index n measThis is typically the calibrated refractive index that matches oil or pure silica glass. The measurement wavelength may be 632.5 nm, 654 nm, 677.2 nm, 654 nm, 702.3 nm, 729.6 nm, 759.2 nm, 791.3 nm, 826.3 nm, 864.1 nm, 905.2 nm, 949.6 nm, 997.7 nm, 1050 nm, or any wavelength in between. Next, the relative refractive index is calculated using the absolute refractive index n(r) as defined by equation (1).

[0027] The term "α-profile" or "alpha profile" is derived from formula (3):

[0028]

number

[0029] This refers to the relative refractive index profile Δ(r) having the functional form defined by , where r0 is the radial position where Δ(r) is maximum, and Δ(r0)>0, r z >r0 is the radial position where Δ(r) decreases to its minimum value, and r is r i ≦r≦r f It is within the range, where r i is the initial radial position of the α-profile, and r f is the final radial position of the α-profile, where α is a real number. Δ(r0) of the α-profile is, here, Δ max , or if a specific region i of the fiber is mentioned, Δ imax It is sometimes referred to as such. The relative refractive index profile of the fiber core region is such that r0 occurs at the center line (r=0), r z If the α-profile corresponds to the outer radius r1 of the core region and is described by Δ1(r1)=0, then equation (3) can be simplified to equation (4):

[0030]

number

[0031] If the core region has a refractive index expressed by equation (4), the outer radius r1 can be determined from the measured relative refractive index profile by the following procedure: Maximum relative refractive index Δ1 max , α, and outer radius r 1est The estimated value of is obtained by examining the measured relative refractive index profile, where r=rr 1est and r=r 1est The test function Δ between these two points trial It is used to make. The relative refractive index profiles of typical glass fibers having a core represented by an α-profile according to embodiments of the present disclosure are shown in Figures 5 and 6.

[0032] "Trench volume" is:

[0033]

number

[0034] Defined as, in the formula, r トレンチ、内側 r is the inner radius of the trench region of the refractive index profile, and r トレンチ、外側 Δ is the outer radius of the trench region of the refractive index profile. トレンチ (r) is the relative refractive index of the trench region of the refractive index profile, and r is the radial position within the fiber. The trench volume is expressed as an absolute value and has a positive value of %Δ micrometers. 2 %, %Δ-micrometer 2 , %Δ-μm 2 or %Δμm 2 These units are expressed in such units that they can be used interchangeably here. The trench region is also referred to here as the cladding region with reduced refractive index, and the trench volume is also referred to as V3.

[0035] The "mode field diameter" or "MFD" of an optical fiber is:

[0036]

number

[0037] Defined by equation (6), f(r) is the transverse component of the electric field distribution of the guided optical signal, and r is the radial position within the fiber. The "mode field diameter" or "MFD" depends on the wavelength of the optical signal, and is reported here for wavelengths of 1310 nm, 1550 nm, and 1625 nm. Here, when referring to the mode field diameter, a specific application of that wavelength is made. Unless otherwise specified, the mode field diameter is the LP at a particular wavelength. 01 It refers to a fashion trend.

[0038] The "effective area" of an optical fiber is:

[0039]

number

[0040] Defined as in equation (7), where f(r) is the transverse component of the electric field of the guided optical signal and r is the radial position within the fiber. "Effective area" or "A eff This depends on the wavelength of the light signal, and in this case, it is understood to refer to a wavelength of 1550 nm.

[0041] The term "attenuation" as used here refers to the loss of optical output as a signal propagates along an optical fiber. Attenuation was measured as specified in the IEC-60793-1-40 standard, "Attenuation measurement methods".

[0042] The bending resistance of an optical fiber, expressed here as "bending loss," can be measured by inductive attenuation under specified test conditions, such as those specified in the IEC-60793-1-40 standard, "Measurement methods and test procedures - Macrobending loss." For example, the test conditions may involve laying or winding one or more turns of fiber around a mandrel of a specified diameter, such as by winding it once around a mandrel of a 15 mm, 20 mm, or 30 mm diameter or a similar diameter mandrel (e.g., "1 × 15 mm diameter bending loss", "1 × 20 mm diameter bending loss", or "1 × 30 mm diameter bending loss"), and measuring the increase in attenuation per turn.

[0043] The terms "cable cutoff wavelength" or "cable cutoff" used herein refer to the 22m cable cutoff test specified in the IEC 60793-1-44 standard, "Measurement methods and test procedures - Cut-off wavelength".

[0044] The optical fiber disclosed herein comprises a core region, a cladding region surrounding the core region, and a covering surrounding the cladding region. The core region and the cladding region are made of glass. The cladding region comprises a plurality of regions, which are preferably concentric regions. The cladding region comprises an inner cladding region, a reduced refractive index cladding region, and an outer cladding region. The inner cladding region surrounds and is directly adjacent to the core region. The reduced refractive index cladding region surrounds and is directly adjacent to the inner cladding region such that this reduced refractive index cladding region is radially positioned between the inner and outer cladding regions. The outer cladding region surrounds and is directly adjacent to the reduced refractive index cladding region. The reduced refractive index cladding region has a lower relative refractive index than the inner and outer cladding regions. The reduced refractive index cladding region may also be referred to herein as a trench or trench region. The relative refractive index of the inner cladding region may be less than, equal to, or greater than the relative refractive index of the outer cladding region. Cladding regions with reduced refractive index may contribute to reduced bending loss and microbend sensitivity. The core region, inner cladding region, reduced refractive index cladding region, and outer cladding region are also referred to as the core, cladding, inner cladding, reduced refractive index cladding, and outer cladding, respectively.

[0045] Whenever used herein, radial position r1 and relative refractive index Δ1 or Δ1(r) refer to the core region, radial position r2 and relative refractive index Δ2 or Δ2(r) refer to the inner cladding region, radial position r3 and relative refractive index Δ3 or Δ3(r) refer to the cladding region with reduced refractive index, radial position r4 and relative refractive index Δ4 or Δ4(r) refer to the outer cladding region, radial position r5 refer to the primary coating, radial position r6 refer to the secondary coating, and radial position r7 refer to an optional tertiary coating.

[0046] The relative refractive index Δ1(r) is the maximum value Δ 1max and minimum value Δ 1min It has the relative refractive index Δ2(r), which is the maximum value Δ2max and minimum value Δ 2min It has the relative refractive index Δ3(r), which is the maximum value Δ 3max and minimum value Δ 3min It has the relative refractive index Δ4(r), which is the maximum value Δ 4max and minimum value Δ 4min In embodiments where the relative refractive index is constant or nearly constant over a certain region, the maximum and minimum values ​​of the relative refractive index are equal or nearly equal. Unless otherwise specified, if a single value is reported for the relative refractive index in a certain region, that single value corresponds to the average value in that region.

[0047] It will be understood that the central core region has a substantially cylindrical shape, while the surrounding inner cladding region, reduced refractive index cladding region, outer cladding region, primary coating, and secondary coating have a substantially annular shape. The annular region can be characterized by its inner and outer radii. Radial positions r1, r2, r3, r4, r5, r6, and r7 here refer to the outermost radii of the core, inner cladding, reduced refractive index cladding, outer cladding, primary coating, secondary coating, and tertiary coating, respectively. Radius r6 also corresponds to the outer radius of the optical fiber in embodiments without a tertiary coating. If a tertiary coating is present, radius r7 corresponds to the outer radius of the optical fiber.

[0048] When two regions are directly adjacent to each other, the outer radius of the inner region is equal to the inner radius of the outer region. For example, an optical fiber may have an outer cladding region surrounded by a directly adjacent reduced-refractive-index cladding region. Radius r3 corresponds to the outer radius of the reduced-refractive-index cladding region and the inner radius of the outer cladding region. The relative refractive index profile also includes the reduced-refractive-index cladding region surrounding the inner cladding region and directly adjacent to it. Radial position r2 corresponds to the outer radius of the inner cladding region and the inner radius of the reduced-refractive-index cladding region. Similarly, radial position r1 corresponds to the outer radius of the core region and the inner radius of the inner cladding region.

[0049] The difference between radial position r2 and radial position r1 is referred to here as the thickness of the inner cladding region. The difference between radial position r3 and radial position r2 is referred to here as the thickness of the cladding region with reduced refractive index. The difference between radial position r4 and radial position r3 is referred to here as the thickness of the outer cladding region. The difference between radial position r5 and radial position r4 is referred to here as the thickness of the primary coating. The difference between radial position r6 and radial position r5 is referred to here as the thickness of the secondary coating.

[0050] As further described below, the relative refractive indices of the core region, inner cladding region, reduced refractive index cladding region, and outer cladding region may differ. Each of these regions may be formed from doped or undoped silica glass. The refractive index of undoped silica glass can be altered by incorporating up-dopants or down-dopants at levels designed to give a target refractive index or refractive index profile, using techniques known to those skilled in the art. Up-dopants are dopants that increase the refractive index of the glass relative to the undoped glass composition. Down-dopants are dopants that decrease the refractive index of the glass relative to the undoped glass composition. In one embodiment, the undoped glass is silica glass. When the undoped glass is silica glass, examples of up-dopants include Cl, Br, Ge, Al, P, Ti, Zr, Nb, and Ta, and examples of down-dopants include F and B. Regions with a constant refractive index can be formed by not doping or by doping at a uniform concentration over the thickness of that region. Regions with varying refractive indices are formed by a non-uniform spatial distribution of dopants across the thickness of the region and / or by incorporating different dopants in different regions. Down-doping can also be performed by incorporating voids in the silica glass. These voids correspond to localized regions filled with air or other gases (e.g., N2, Ar, SO2, CO2, Kr, O2) and / or vacuum spaces extending over lengths shorter than the total length of the glass fiber. Preferably, the voids are distributed randomly, i.e., aperiodicly, along the length of the glass fiber.

[0051] The values ​​for Young's modulus, elongation %, and tear strength refer to the values ​​determined under the measurement conditions according to the procedure described herein.

[0052] Here, we will refer in detail to embodiments that are useful for explaining the foregoing.

[0053] One embodiment relates to an optical fiber. This optical fiber comprises a glass fiber surrounded by a sheath. An example of an optical fiber is shown in a schematic cross-sectional view in Figure 1. The optical fiber 10 comprises a glass fiber 11 surrounded by a primary sheath 16 and a secondary sheath 18. In some embodiments, the secondary sheath 18 may contain a pigment. Further description of the glass fiber 11, the primary sheath 16, and the secondary sheath 18 is given below. In addition, one or more tertiary ink layers may surround the secondary sheath 18.

[0054] Figure 2 shows an optical fiber ribbon 30 which may comprise multiple optical fibers 20 and a matrix 32 enclosing these optical fibers. Each optical fiber 20 comprises a core region, a cladding region, a primary coating, and a secondary coating, as described above. The optical fiber 20 may also have a tertiary coating as described above.

[0055] As shown in Figure 2, the optical fibers 20 are arranged relative to each other in a substantially planar, parallel relationship. The optical fibers in the optical fiber ribbon 30 are encased by a ribbon matrix 32 in one of several known forms (e.g., edge-coupled ribbon, thin-layered ribbon, thick-layered ribbon, or multilayer ribbon) by conventional methods for manufacturing optical fiber ribbons. The optical fiber ribbon 30 in the embodiment of Figure 2 contains twelve optical fibers 20. However, any number of optical fibers 20 (e.g., two or more) may be used to form an optical fiber ribbon 30 for a particular application. The ribbon matrix 32 has tensile properties similar to those of the secondary coating and may be formed from the same, similar, or different composition used to prepare the secondary coating.

[0056] Figure 3 shows an optical fiber cable 40 comprising multiple optical fibers 20 surrounded by a jacket 42. In some embodiments, the optical fiber cable 40 is a submarine cable. The optical fibers 20 may be densely or loosely packed in a conduit surrounded by the inner surface 44 of the jacket 42. The number of fibers arranged within the jacket 42 is referred to as the “total number of fibers” of the optical fiber cable 40. As will be further described below, the optical fibers of this disclosure have a reduced diameter and therefore provide a large “total number of fibers”.

[0057] The jacket 42 is formed from an extruded polymer material and may contain multiple concentric layers of polymer or other material. The optical fiber cable 40 may contain one or more reinforcing members (not shown) embedded within the jacket 42 or placed within a conduit defined by the inner surface 44. The reinforcing members may contain fibers or rods that are more rigid than the jacket 42. The reinforcing members may be made from metal, braided steel, glass-reinforced plastic, glass fiber, or other suitable material. The optical fiber cable 40 may contain other layers surrounded by the jacket 42, such as an armor layer, a moisture-proof layer, or a rip cord. Furthermore, the optical fiber cable 40 may have a twisted loose tube core or other optical fiber cable structure.

[0058] glass fiber As shown in Figure 1, the glass fiber 11 comprises a core region 12 and a cladding region 14, as is known in the art. The core region 12 has a higher refractive index than the cladding region 14, and the glass fiber 11 functions as a waveguide. In many applications, the core region 12 and the cladding region 14 have a discernible core-cladding boundary. Alternatively, the core region 12 and the cladding region 14 may not have a clear boundary.

[0059] In some embodiments, the core region 12 has a refractive index that varies with distance from the center of the glass fiber. For example, the core region 12 may have a relative refractive index profile with an α-profile (as defined in equation (3) above) having an α value between 2 and 10, between 2 and 6, between 2 and 4, between 4 and 20, between 6 and 20, between 8 and 20, between 10 and 20, or between 10 and 40.

[0060] A schematic cross-sectional view of an exemplary optical fiber is shown in Figure 4. As previously mentioned, the optical fiber in Figure 4 may be used in submarine cables. In Figure 4, the optical fiber 46 comprises a core region 48, a cladding region 50, a primary sheath 56, and a secondary sheath 58. The cladding region 50 includes an inner cladding region 51, a cladding region with reduced refractive index 53, and an outer cladding region 55. A tertiary layer (e.g., an ink layer) surrounds or directly adjacent to the secondary sheath, as necessary.

[0061] As previously mentioned, optical fiber 46 may have a reduced glass diameter and / or reduced sheathing diameter. Such reduced diameters can increase the fiber density (e.g., "total number of fibers") of optical fiber 46 when used, for example, in a standard submarine cable design. In the smaller diameter profile of optical fiber 46, the properties of the fiber are further specifically tuned, as described below, to provide appropriate attenuation and microbend characteristics.

[0062] A typical relative refractive index profile of a glass fiber according to an embodiment of the present disclosure is shown in Figure 5. The profile of the optical fiber 60 in Figure 5 shows the outer radius r1 and the maximum relative refractive index Δ 1maxThe profile shows a core region (1) with a relative refractive index Δ1, an inner cladding region (2) extending from radial position r1 to radial position r2 with a relative refractive index Δ2, a reduced refractive index cladding region (3) extending from radial position r2 to radial position r3 with a relative refractive index Δ3, and an outer cladding region (4) extending from radial position r3 to radial position r4 with a relative refractive index Δ4. In the profile of Figure 5, the reduced refractive index cladding region (3) is sometimes referred to here as a trench and has a constant or average relative refractive index Δ3 that is smaller than the relative refractive index of the inner cladding region (2) and the outer cladding region (4). The core region (1) has the highest average and maximum relative refractive index in the profile. The core region (1) may include a region with a lower refractive index (known in the art as a "centerline dip") (not shown) at or near the centerline. The core region (1) may include a region with a higher refractive index (referred to as a "centerline spike") (not shown) on or near the centerline.

[0063] In the relative refractive index profile of Figure 5, the core region (1) of the glass fiber has an α-profile with an α value of 2 or more and 20 or less. The radial position r0(Δ 1max The (corresponding to) corresponds to the fiber's centerline (r=0), and the radial position r of the α-profile. z This corresponds to the core radius r1. In embodiments having a centerline recess, the radial position r0 is slightly offset from the fiber centerline. In some embodiments, the relative refractive index Δ1 decreases continuously radially away from the centerline. In other embodiments, the relative refractive index Δ1 varies over several radial positions between the centerline and r1, and also includes a constant or approximately constant value over other radial positions between the centerline and r1.

[0064] In Figure 5, the transition region 61 from the inner cladding region (2) to the cladding region with reduced refractive index (3) and the transition region 62 from the cladding region with reduced refractive index (3) to the outer cladding region (4) are shown as step-type transitions. It should be understood that the step-type transition is an idealized representation, and that the transition regions 61 and / or 62 may not actually be strictly perpendicular, as shown in Figure 5. Rather, the transition regions 61 and / or 62 may have a slope or curvature. If the transition regions 61 and / or 62 are not perpendicular, the inner radius r2 and outer radius r3 of the cladding region with reduced refractive index (3) correspond to the midpoints of the transition regions 61 and 62, respectively. These midpoints correspond to half the depth 63 of the cladding region with reduced refractive index (3).

[0065] The relative order of the relative refractive indices Δ1, Δ2, Δ3, and Δ4 in the relative refractive index profile shown in Figure 5 is given by condition Δ 1max >Δ4>Δ3 and Δ 1max The condition Δ2 > Δ3 is satisfied. The values ​​of Δ2 and Δ4 may be equal, or one may be greater than the other, but both Δ2 and Δ4 must satisfy Δ 1max It is between Δ3.

[0066] The relative refractive indices Δ1, Δ2, Δ3, and Δ4 are based on the materials used in the core region, inner cladding region, reduced refractive index cladding region, and outer cladding region. Descriptions of these materials with respect to relative refractive indices Δ1, Δ2, Δ3, and Δ4 are given below.

[0067] Core area The core region is made of silica glass. The silica glass of the core region may be undoped silica glass, updoped silica glass, and / or downdoped silica glass. Updoped silica glass includes silica glass doped with alkali metal oxides (e.g., Na2O, K2O, Li2O, Cs2O, or Rb2O) and / or halogens. Downdoped silica glass includes silica glass doped with fluorine. In some embodiments, the silica glass of the core region is Ge-free and / or Cl-free, i.e., the core region is made of silica glass with little germanium and / or chlorine.

[0068] The core region may be made from silica glass doped with at least one alkali metal, such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and / or francium (Fr). In some embodiments, this silica glass is doped with a combination of sodium, potassium, and rubidium. This silica glass may have peak alkali concentrations in the range of about 10 ppm to about 500 ppm, or about 20 ppm to about 450 ppm, or about 50 ppm to about 300 ppm, or about 10 ppm to about 200 ppm, or about 10 ppm to about 150 ppm. Doping with alkali metals within the disclosed range reduces Rayleigh scattering, thereby resulting in lower attenuation in the optical fiber.

[0069] In some embodiments, the core region is made from silica glass doped with alkali metals and fluorine as a downdopant. Figures 5 and 6 show exemplary embodiments of downdoped silica glass. The fluorine concentration in the glass fiber is in the range of about 0.1% by mass to about 2.5% by mass, or about 0.25% by mass to about 2.25% by mass, or about 0.3% by mass to about 2.0% by mass.

[0070] In yet another embodiment, the core region is made from silica glass doped with a halogen such as chlorine. Figures 6B-6D show exemplary embodiments of chlorine-doped silica glass. The chlorine concentration in the glass fiber ranges from about 0.4% to about 2.2% by mass, or from about 0.6% to about 2.0% by mass, or from about 1.0% to about 1.9% by mass, or 1.6% by mass, or about 1.8% by mass.

[0071] The radius r1 of the core region is in the range of about 3.0 micrometers to about 6.0 micrometers, or in the range of about 3.5 micrometers to about 5.5 micrometers, or in the range of about 4.0 micrometers to about 5.0 micrometers, or in the range of about 4.2 micrometers to about 4.7 micrometers. In some embodiments, the core region includes a portion having a constant or substantially constant relative refractive index having a radial width of at least 1.0 micrometer, or at least 2.0 micrometers, or at least 3.0 micrometers, or at least 4.0 micrometers, or in the range of 1.0 micrometer to 4.0 micrometers, or in the range of 2.0 micrometers to 3.0 micrometers. In some embodiments, the portion of the core region having a constant or substantially constant relative refractive index is Δ 1min It has a relative refractive index of .

[0072] The relative refractive index of the core region is Δ1 or Δ 1max The minimum relative refractive index Δ in the core region is in the range of approximately -0.15% to approximately 0.30%, or approximately -0.10% to approximately 0.20%, or approximately -0.05% to approximately 0.15%, or approximately 0% to approximately 0.10%. 1min It is in the range of approximately -0.20% to approximately -0.50%, or approximately -0.30% to approximately -0.40%, or approximately -0.32% to approximately -0.37%. Δ 1max and Δ 1min The difference is greater than 0.05%, or greater than 0.10%, or greater than 0.15%, or greater than 0.20%, or in the range of 0.05% to 0.40%, or in the range of 0.10% to 0.35%.

[0073] Inner cladding region The inner cladding region consists of fluorine-doped down-doped silica glass and / or voided silica glass. The average concentration of down-dopant in the inner cladding region is greater than the average concentration of down-dopant in the core region. In some embodiments, the fluorine concentration in the inner cladding region is in the range of about 0.50% by mass to about 2.00% by mass, or about 0.60% by mass to about 1.00% by mass, or about 0.70% by mass to about 0.80% by mass.

[0074] The relative refractive index of the inner cladding region is Δ2 or Δ 2max It is in the range of approximately -0.20% to approximately -0.50%, or approximately -0.25% to approximately -0.45%, or approximately -0.30% to approximately -0.40%, or approximately -0.33% to approximately -0.37%. It is preferable that the relative refractive index Δ2 is constant or approximately constant. Δ 1max -Δ2 difference (or Δ 1max -Δ 2max The difference is greater than approximately 0.25%, greater than approximately 0.30%, greater than approximately 0.35%, or in the range of approximately 0.25% to approximately 0.45%, or in the range of approximately 0.30% to approximately 0.40%.

[0075] The radius r2 of the inner cladding region is in the range of approximately 7.0 micrometers to approximately 15.0 micrometers, or approximately 7.5 micrometers to approximately 13.0 micrometers, or approximately 8.0 micrometers to approximately 12.0 micrometers, or approximately 8.5 micrometers to approximately 11.5 micrometers, or approximately 9.0 micrometers to approximately 11.0 micrometers, or approximately 9.5 micrometers to approximately 10.5 micrometers. The thickness r2-r1 of the inner cladding region is in the range of approximately 3.0 micrometers to approximately 10.0 micrometers, or approximately 4.0 micrometers to approximately 9.0 micrometers, or approximately 4.5 micrometers to approximately 7.0 micrometers.

[0076] Cladding region with reduced refractive index The reduced refractive index cladding region is made from down-doped silica glass. As previously mentioned, the preferred down-dopan is fluorine. The concentration of fluorine in the reduced refractive index cladding region is in the range of about 0.30% to about 2.50% by mass, or about 0.60% to about 2.25% by mass, or about 0.90% to about 2.00% by mass.

[0077] Relative refractive index Δ3 or Δ 3min It is in the range of approximately -0.30% to approximately -0.80%, or approximately -0.40% to approximately -0.70%, or approximately -0.50% to approximately -0.65%. It is preferable that the relative refractive index Δ3 is constant or approximately constant. Δ 1max -Δ3 difference (or Δ 1max -Δ 3min The difference between Δ1 and Δ3, or the difference between Δ1 and Δ3, or Δ1 and Δ 3min The difference between Δ2 and Δ3 (or Δ2-Δ3) is greater than approximately 0.50%, greater than approximately 0.55%, greater than approximately 0.6%, or in the range of approximately 0.50% to approximately 0.80%, or in the range of approximately 0.55% to approximately 0.75%. 3min The difference, or Δ 2max -Δ3 difference, or Δ 2max -Δ 3min The difference is greater than approximately 0.10%, greater than approximately 0.20%, greater than approximately 0.30%, or in the range of approximately 0.10% to approximately 0.60%, or in the range of approximately 0.20% to approximately 0.60%.

[0078] The inner radius of the reduced refractive index cladding region is r2, and has the value specified above. The outer radius r3 of the reduced refractive index cladding region is in the range of approximately 10.0 micrometers to approximately 20.0 micrometers, or approximately 12.0 micrometers to approximately 19.5 micrometers, or approximately 13.0 micrometers to approximately 19.0 micrometers, or approximately 13.5 micrometers to approximately 18.5 micrometers, or approximately 14.0 micrometers to approximately 18.0 micrometers, or approximately 14.5 micrometers to approximately 17.5 micrometers. The thickness r3-r2 of the reduced refractive index cladding region is in the range of 0.5 micrometers to approximately 12.0 micrometers, or approximately 1.0 micrometers to approximately 10.0 micrometers, or approximately 1.5 micrometers to approximately 9.0 micrometers, or approximately 2.0 micrometers to approximately 8.0 micrometers.

[0079] The cladding region with reduced refractive index is approximately 30%Δ-micrometers. 2 Above or approximately 50% Δ·micrometer 2 Above or approximately 70% Δ·micrometer 2 The following, or approximately 30% Δ·micrometer 2 More than or equal to approximately 70% Δ·micrometer 2 The following, or approximately 50% Δ·micrometer 2 More than or equal to approximately 70% Δ·micrometer 2 The offset trench design may have the following trench volumes. Below the disclosed range of trench volumes, bending performance is reduced, and above the disclosed range of trench volumes, the fiber no longer functions as a single-mode fiber.

[0080] The offset trench design disclosed herein offers advantages over conventional trench designs adjacent to the core region. More specifically, the offset trench design disclosed herein reduces the restriction of the fundamental mode and provides improved bending loss at large bending diameters (e.g., bending diameter > 25 mm) for the target optical fiber mode field diameter and cable cutoff characteristics. Furthermore, the trench design disclosed herein has a trench region with a reduced refractive index, which conveniently restricts the intensity profile of the fundamental LP01 mode propagating through the optical fiber, thereby reducing the optical fiber mode field diameter.

[0081] Outer cladding region The outer cladding region consists of fluorine-doped down-doped silica glass and / or voided silica glass. The average concentration of down-dopant in the outer cladding region is greater than the average concentration of down-dopant in the core region. In some embodiments, the fluorine concentration in the outer cladding region is in the range of about 0.50% by mass to about 2.00% by mass, or about 0.60% by mass to about 1.00% by mass, or about 0.70% by mass to about 0.80% by mass.

[0082] Relative refractive index of the outer cladding region Δ4 or Δ 4max It is in the range of approximately -0.20% to approximately -0.50%, or approximately -0.25% to approximately -0.45%, or approximately -0.30% to approximately -0.40%, or approximately -0.33% to approximately -0.37%. It is preferable that the relative refractive index Δ4 is ​​constant or approximately constant. As shown in Figure 5, the relative refractive index Δ4 may be equal to the relative refractive index Δ2.

[0083] The inner radius of the outer cladding region is r3, which has the previously specified value. The outer radius r4 is preferably small to minimize the diameter of the glass fiber in order to increase the total number of fibers in the cable. The outer radius r4 of the outer cladding region is in the range of 65 micrometers or less, or 62.5 micrometers or less, or 60.0 micrometers or less, or 57.5 micrometers or less, or 55.0 micrometers or less, or 52.5 micrometers or less, or 50.0 micrometers or less, or in the range of 37.5 micrometers to 62.5 micrometers, or in the range of 40.0 micrometers to 60.0 micrometers, or in the range of 42.5 micrometers to 57.5 micrometers, or in the range of 45.0 micrometers to 55.0 micrometers. Thus, for example, the diameter of the cladding region (i.e., twice the outer radius r4) is approximately 130 micrometers or less, or approximately 125 micrometers or less, or approximately 120 micrometers or less, or approximately 115 micrometers or less, or approximately 110 micrometers or less, or 105 micrometers or less, or approximately 100 micrometers or less, or approximately 90 micrometers or less, or approximately 80 micrometers or less, or approximately 75 micrometers or less. The outer cladding region thickness r4-r3 is in the range of 10.0 micrometers to 50.0 micrometers, or 15.0 micrometers to 45.0 micrometers, or 20.0 micrometers to 40.0 micrometers, or 25.0 micrometers to 35.0 micrometers.

[0084] Characteristics of optical fibers The optical fibers according to embodiments of this disclosure may have mode field diameters ranging from about 9 micrometers to about 9.5 micrometers at 1310 nm and from about 10 micrometers to about 10.5 micrometers at 1550 nm, along with a cable cutoff of less than about 1530 nm. In some embodiments, the cable cutoff is less than about 1500 nm, or less than about 1450 nm, or less than about 1400 nm, or less than about 1300 nm, or less than about 1260 nm.

[0085] In addition, the optical fiber according to the embodiments of this disclosure is approximately 100 micrometers 2 Below, approximately 90 micrometers 2 Below, approximately 80 micrometers 2 Below, approximately 70 micrometers 2 Below, approximately 70 micrometers 2 From approximately 90 micrometers 2 The range, or approximately 75 micrometers 2 From approximately 85 micrometers 2 The range, or approximately 80 micrometers 2 It may have an effective area at 1550 nm.

[0086] The attenuation of the optical fiber disclosed herein is 0.175 dB / km or less, or 0.170 dB / km or less, or 0.165 dB / km or less, or 0.160 dB / km or less, or 0.155 dB / km or less, or 0.150 dB / km or less at a wavelength of 1550 nm.

[0087] As shown in Figure 5, the optical fiber 60 provides an exemplary embodiment of an optical fiber having an alkali-doped core, a relative refractive index Δ1 of the core region (1) from about -0.3% to about -0.42%, and a core radius (r1) between about 4 micrometers and about 6.5 micrometers. In addition, the thickness of the inner cladding region of the optical fiber 60 is between about 2 micrometers and about 12 micrometers. The optical fiber 60 has a Δ of 54.5%. 2It has an offset trench design with a trench volume of . The cladding of the optical fiber 60 is fluorine-doped, and the cladding region with reduced refractive index has a radius (r3) of approximately 17.5 micrometers. The optical properties of the optical fiber 60 are shown in Table 1 below.

[0088] [Table 1]

[0089] Figure 6A shows an alkali-doped core and approximately 50% Δ-micrometers 2 Second and third exemplary embodiments of optical fibers 64 and 65 are shown, having a trench volume, fluorine-doped cladding, and a reduced refractive index cladding region with a radius (r3) of approximately 17.5 micrometers. As shown in Table 2 below, optical fiber 64 yields a mode field diameter of 9.07 micrometers at 1310 nm, and optical fiber 65 yields a mode field diameter of 9.39 micrometers at 1310 nm. The optical properties of optical fibers 64 and 65 are shown in Table 2 below.

[0090] [Table 2]

[0091] Figure 6B shows a fourth exemplary embodiment of an optical fiber 66 having a chlorine-doped core with a chlorine concentration of approximately 1.8 mass%. The optical fiber 66 also includes an inner cladding, a reduced refractive index cladding region, and a fluorine-doped silica outer cladding. The inner cladding has a fluorine concentration of 0.73 mass%; the reduced refractive index cladding region has a fluorine concentration of 1.5 mass%; and the outer cladding has a fluorine concentration of 0.73 mass%. Furthermore, the optical fiber 66 has a glass outer diameter of 125 micrometers, a primary cladding outer diameter of 167 micrometers, and a secondary cladding outer diameter of 200 micrometers. The optical properties of the optical fiber 66 are shown in Table 3 below.

[0092] [Table 3]

[0093] Figure 6C shows a fifth exemplary embodiment of an optical fiber 67 having a chlorine-doped core with a chlorine concentration of approximately 1.8 mass%. The optical fiber 67 also includes an inner cladding, a reduced refractive index cladding region, and a fluorine-doped silica outer cladding. The inner cladding has a fluorine concentration of 0.73 mass%; the reduced refractive index cladding region has a fluorine concentration of 1.5 mass%; and the outer cladding has a fluorine concentration of 0.73 mass%. Furthermore, the optical fiber 67 has an outer diameter of 125 micrometers for the glass, an outer diameter of 167 micrometers for the primary cladding, and an outer diameter of 200 micrometers for the secondary cladding. The optical fiber 67 was drawn under conditions such that the fiber was slowly cooled in a high-temperature furnace during the drawing process. More specifically, during the drawing process, the optical fiber 67 was slowly cooled in a furnace operating at 900 degrees for a period of 0.3 seconds. The optical properties of the optical fiber 67 are shown in Table 4 below.

[0094] [Table 4]

[0095] Figure 6D shows a sixth exemplary embodiment of an optical fiber 68 having a chlorine-doped core with a chlorine concentration of approximately 1.8 mass%. The optical fiber 68 also includes an inner cladding, a reduced refractive index cladding region, and a fluorine-doped silica outer cladding. The inner cladding has a fluorine concentration of 0.73 mass%; the reduced refractive index cladding region has a fluorine concentration of 1.5 mass%; and the outer cladding has a fluorine concentration of 0.73 mass%. Furthermore, the optical fiber 68 has an outer diameter of 100 micrometers for the glass, an outer diameter of 125 micrometers for the primary cladding, and an outer diameter of 160 micrometers for the secondary cladding. The optical properties of the optical fiber 68 are shown in Table 5 below.

[0096] [Table 5]

[0097] Figure 6E shows a seventh exemplary embodiment of an optical fiber 69 having a chlorine-doped core with a chlorine concentration of approximately 1.8 mass%. The optical fiber 69 also includes an inner cladding, a reduced refractive index cladding region, and a fluorine-doped silica outer cladding. The inner cladding has a fluorine concentration of 0.73 mass%; the reduced refractive index cladding region has a fluorine concentration of 1.4 mass%; and the outer cladding has a fluorine concentration of 0.73 mass%. Furthermore, the optical fiber 69 has a glass outer diameter of 100 micrometers, a primary cladding outer diameter of 131 micrometers, and a secondary cladding outer diameter of 172 micrometers. The optical properties of the optical fiber 69 are shown in Table 6 below.

[0098] [Table 6]

[0099] The offset trench design for optical fibers 60 and 64-69 provides improved microbend sensitivity to the smaller diameter fibers disclosed herein. More specifically, the offset trench design disclosed herein provides optimized microbend without sacrificing cable cutoff and mode field diameter.

[0100] Primary coating and secondary coating The transmittance of light passing through an optical fiber largely depends on the properties of the coating applied to the glass fiber. As previously mentioned (see Figure 4), the coating typically includes a primary coating 56 and a secondary coating 58, where the secondary coating surrounds the primary coating and the primary coating is in contact with the glass fiber (including the central core region surrounded by the cladding region). An optional tertiary layer (e.g., an ink layer) surrounds and is in direct contact with the secondary coating.

[0101] The secondary sheath 58 may be made of a harder material (higher Young's modulus) than the primary sheath 56 and is designed to protect the glass fiber from damage caused by abrasion or external forces during processing, handling, and laying of the optical fiber. The primary sheath 56 may be made of a softer material (lower Young's modulus) than the secondary sheath 58 and is designed to buffer or dissipate stress resulting from forces applied to the outer surface of the secondary sheath. Stress dissipation within the primary sheath attenuates stress and minimizes the stress reaching the glass fiber. The primary sheath is particularly important in dissipating stress caused by microbends that the optical fiber encounters when laid within the cable. Microbend stress transmitted to the glass fiber creates local perturbations in the refractive index profile of the glass fiber, so it is necessary to minimize microbend stress. Local refractive index perturbations result in a loss of intensity of light transmitted through the glass fiber. By dissipating stress, the primary sheath minimizes the intensity loss caused by microbends.

[0102] Examples of coatings - preparation and measurement techniques As disclosed herein, the properties of the primary and secondary coatings were determined using the measurement techniques described below.

[0103] Tensile properties. The curable secondary coating composition was cured and prepared in the form of a cured rod sample for measuring Young's modulus, tensile strength at break, yield strength, and elongation at break. This cured rod was prepared by injecting the curable secondary coating composition into a Teflon® tube with an inner diameter of approximately 0.025 inches (approximately 6.35 mm). The rod sample exhibited a Young's modulus of approximately 2.4 J / cm². 2The coating was cured using a Fusion D bulb at a dose (measured over the wavelength range of 225–424 nm using the Light Bug model IL390 from International Light). After curing, the "Teflon" tube was stripped off to provide cured rod samples of the secondary coating composition. The cured rods were conditioned for 18–24 hours at 23°C and 50% relative humidity prior to testing. Young's modulus, tensile strength at break, yield strength, and elongation at break were measured using a Sintech MTS Tensile Tester on defect-free rod samples with a gauge length of 51 mm and a test speed of 250 mm / min. Tensile properties were measured according to ASTM standard D882-97. Properties were determined as the average of at least five samples, and defective samples were excluded from the average.

[0104] In-situ glass transition temperature. In-situ Tg measurements were performed on tube samples removed from coated fibers, considering both the primary and secondary coatings. The coated fibers consisted of a glass fiber with a diameter of 125 micrometers, a primary coating with a thickness of 32.5 micrometers surrounding and in direct contact with the glass fiber, and a secondary coating with a thickness of 26.0 micrometers surrounding and in direct contact with the primary coating. The glass fiber and primary coating were identical for all samples measured. The primary coating was formed from the standard primary coating composition described below. Samples with comparative secondary coatings and secondary coatings according to this disclosure were measured.

[0105] The following procedure was used to obtain a tube sample removed from the fiber: A 0.0055-inch (approximately 0.14 mm) Miller stripper was tightened approximately 1 inch (approximately 2.54 cm) from the end of the coated fiber. This 1-inch area of ​​the fiber was placed in a stream of liquid nitrogen and held in the liquid nitrogen for 3 seconds. The coated fiber was then removed from the liquid nitrogen stream and quickly stripped to remove the coating. The stripped end of the fiber was inspected for residual coating. If residual coating remained on the glass fiber, the sample was discarded and a new sample was prepared. The stripping process resulted in a hollow tube of stripped coating containing a clean glass fiber and intact primary and secondary coatings. This hollow tube is referred to as the "removed tube sample." The diameters of the glass and primary and secondary coatings were measured from the end face of the unstripped fiber.

[0106] Using a sample gauge length of 9 to 10 mm, in-situ Tg measurements were performed on the removed tube sample using a Rheometrics DMTA IV test apparatus. The width, thickness, and length of this removed tube sample were entered into the test apparatus's operating program. The removed tube sample was then mounted and cooled to approximately -85°C. Once stable, the temperature was increased using the following parameters: Frequency: 1Hz Distortion: 0.3% Heating rate: 2℃ / min Final temperature: 150℃ Initial static force=20.0g Static force > dynamic force by only 10.0%.

[0107] The in-situ Tg of the coating is defined as the maximum value of tan δ in a plot of tan δ as a function of temperature, where tan δ is: tan δ = E” / E’ It is defined as follows: E'' is the loss modulus, which is proportional to the loss of energy as heat during the deformation cycle, and E' is the storage modulus, which is proportional to the energy stored during the deformation cycle.

[0108] The removed tube samples showed distinct maximum values ​​in the tan δ plots for the primary and secondary coatings. The maximum value at lower temperatures (approximately -50°C) corresponded to the in-situ Tg of the primary coating, while the maximum value at higher temperatures (above 50°C) corresponded to the in-situ Tg of the secondary coating.

[0109] The in-situ modulus of elasticity of the primary coating. The in-situ modulus was measured using the following procedure. A 6-inch (approximately 15 cm) sample of fiber was obtained, and a 1-inch (approximately 2.5 cm) portion from the center of the fiber was stripped in a window-like manner and wiped with isopropyl alcohol. This window-like stripped fiber was mounted on a sample holder / alignment stage equipped with 10 mm x 5 mm rectangular aluminum tabs used for mounting the fiber. The two tabs were positioned horizontally, with their shorter 5 mm sides facing each other and separated by a 5 mm gap. The window-like stripped fiber was placed horizontally on the sample holder, across the tabs and across the gap between them. One end of the coating of the window-like stripped region of the fiber was positioned over one tab and extended to the middle of the 5 mm gap between the tabs. This 1-inch (approximately 2.5 cm) window-like stripped region extended across the other tab, across the remaining half of the gap. After alignment, the sample was removed, and a small dot of adhesive was applied to half of each tab closest to the 5mm gap. The fiber was then returned to its original position, and the alignment stage was raised until the adhesive was just touching the fiber. Next, the coating end was pulled away from the gap through the adhesive until most of the 5mm gap between the tabs was occupied by the windowed stripped area of ​​the fiber. The portion of the windowed stripped area remaining on the opposite tab was in contact with the adhesive. The very tip of the coating end remained extended beyond the tab into the gap between the tabs. This portion of the coating end was not embedded in the adhesive and was the subject of the in-situ modulus measurement. The adhesive was dried along with the fiber sample in this configuration, and the fiber was attached to the tabs. After drying, the length of the fiber fixed to each tab was cut to 5mm. The coating length embedded in the adhesive, the coating length not embedded (the portion extending into the gap between the tabs), and the diameter of the primary coating were measured.

[0110] The measurement of the in-situ modulus was carried out at room temperature (21 °C) for 45 minutes at a constant strain rate of 9×10 -6 1 / s using a Rheometrics DMTA IV dynamic mechanical testing apparatus. The gauge length was 15 mm. The changes in force and length were recorded and used to calculate the in-situ modulus of the primary coating. The fiber sample attached to this tab was prepared by removing any epoxy that would interfere with the 15 mm clamping length of the testing apparatus to ensure that there was no contact between the clamp and the fiber and that the sample was directly fixed to the clamp. The force of the instrument was set to zero. Next, the tab with the uncoated end of the fiber attached was mounted on the lower clamp (measurement probe) of the testing apparatus, and the tab with the coated end of the fiber attached was mounted on the upper (fixed) clamp of the testing apparatus. Next, the test was conducted, and once the analysis was completed, the sample was removed.

[0111] The in-situ modulus of elasticity of the secondary coating. For the secondary coating, the in-situ modulus was measured using a sample prepared by removing the fiber tube from the fiber sample. Approximately 1 inch (about 2.54 cm) from the end of the fiber sample was clamped with a 0.0055 inch (about 0.14 mm) Miller stripper. The 1-inch region of the fiber sample was placed in a liquid nitrogen stream and held for 3 seconds. Next, the fiber sample was removed and quickly stripped. The stripped end of the fiber sample was inspected. If there was any coating remaining on the glass portion of the fiber sample, the removed tube sample was considered defective and a new removed tube sample was prepared. A proper removed tube sample consists of a hollow tube cleanly stripped from the glass and having a primary coating and a secondary coating. The diameters of the glass, primary coating, and secondary coating were measured from the end face of the fiber that was not stripped.

[0112] To obtain the in-situ modulus of the secondary coating, the in-situ modulus of a fiber-removed tube sample was measured using a Rheometrics DMTA IV instrument with a sample gauge length of 11 mm. The width, thickness, and length were determined and provided as input to the instrument's operating software. The sample was mounted and measured using a time sweep program at ambient temperature (21°C) with the following parameters: Frequency: 1 Rad / second Distortion: 0.3% Total time: 120 seconds Measurement time: 1 second Initial static force=15.0g Static force > Dynamic force by 10.0% Once completed, the average value of the last five E' (storage modulus) data points was calculated. For a total of 15 data points, each sample was measured three times (a new sample for each measurement). The average value of the three measurements was reported.

[0113] Puncture resistance of secondary covering. Puncture resistance measurements were performed on samples equipped with glass fibers, a primary coating, and a secondary coating. The diameter of the glass fibers was 125 micrometers. The primary coating was formed from the standard primary coating compositions listed in Table 7 below. Samples with various secondary coatings were prepared as described below. The thicknesses of the primary and secondary coatings were adjusted to vary the cross-sectional area of ​​the secondary coating as described below. For all samples, the ratio of the thickness of the secondary coating to the thickness of the primary coating was maintained at approximately 0.8.

[0114] Puncture resistance is described in the Proceedings of the 52 ndThe measurement was performed using the technique described in the paper "Quantifying the Puncture Resistance of Optical Fiber Coatings" by G. Scott Glaesemann and Donald A. Clark (pp. 237-245, 2003), published at the International Wire & Cable Symposium. A summary of the method is given here. This method is the indentation method. A 4 cm long optical fiber was placed on a 3 mm thick glass slide. One end of this optical fiber was attached to a device that allowed for controlled rotation of the optical fiber. The optical fiber was investigated for transmission at 100x magnification and rotated until the thickness of the secondary coating was equal on both sides of the glass fiber in a direction parallel to the glass slide. At this position, the thickness of the secondary coating was equal on both sides of the glass fiber in a direction parallel to the glass slide. In a direction perpendicular to the glass slide, the thickness of the secondary coating above or below the glass fiber differed from the thickness of the secondary coating in a direction parallel to the glass slide. One thickness perpendicular to the glass slide is greater than the thickness parallel to the glass slide, and the other thickness perpendicular to the glass slide is less than the thickness parallel to the glass slide. This position of the optical fiber was fixed by taping both ends of the optical fiber to the glass slide. This is the position of the optical fiber used in the indentation test.

[0115] The indentation was performed using a universal testing machine (Instron Model 5500R or equivalent). An inverted microscope was placed directly beneath the crosshead of the testing machine. The microscope's objective lens was positioned directly beneath a 75° diamond wedge indenter mounted inside the testing machine. A glass slide with the fiber taped to it was placed on the microscope's sample stage and positioned directly beneath the indenter so that the width of the wedge was perpendicular to the direction of the fiber. The optical fiber was placed in position, and the diamond wedge was lowered until it contacted the surface of the secondary coating. Next, the diamond wedge was indented into the secondary coating at a speed of 0.1 mm / min, and the load on the secondary coating was measured. The load on the secondary coating was increased as the diamond wedge was indented deeper into the secondary coating until perforation occurred. A sharp decrease in load was observed at the time of perforation. The indentation load at which puncture was observed was recorded. The load is reported here in grams-force (g) and is referred to here as the "puncture load." The experiment was repeated for optical fibers oriented in the same direction to obtain 10 measurement points. The puncture load for that direction was determined by averaging these measurement points. The 10 measurement points for the second group were determined by rotating the optical fiber direction by 180°.

[0116] Microbend loss. Microbend loss was determined using the mandrel wrapping test specified in standard IEC 60793-1-47. In the mandrel wrapping test, a fiber is wrapped one or more times around a cylindrical mandrel of a specified diameter, and the increase in attenuation at a specified wavelength due to bending is determined. The attenuation in the mandrel wrapping test is expressed in units of dB / turn, where one turn refers to one rotation of the fiber around the mandrel. Microbend loss at wavelengths of 850 nm and 1625 nm was determined for selected examples described below using mandrel wrapping tests with mandrels of 15 mm and 30 mm diameter.

[0117] Exemplary embodiments of primary and secondary coatings To provide sufficient robustness and microbend characteristics for the smaller diameter fibers disclosed herein, specific properties of the primary and secondary coatings 56 and 58 can be adjusted. For example, the primary coating 56 may have a low Young's modulus and / or a low in-situ modulus. The Young's modulus of the primary coating is in the range of about 0.7 MPa or less, or about 0.6 MPa or less, or about 0.5 MPa or less, or about 0.4 MPa or less, or in the range of about 0.1 MPa to about 0.7 MPa, or in the range of about 0.3 MPa to about 0.6 MPa. The in-situ modulus of the primary coating is in the range of about 0.50 MPa or less, or about 0.30 MPa or less, or about 0.25 MPa or less, or about 0.20 MPa or less, or about 0.15 MPa or less, or about 0.10 MPa or less, or in the range of about 0.05 MPa to about 0.25 MPa, or in the range of about 0.10 MPa to about 0.20 MPa.

[0118] The primary coating 56 preferably has a higher refractive index than the cladding region 50 of the glass fiber so that it can remove erroneous optical signals away from the core region 48. The primary coating 56 maintains proper adhesion to the glass fiber during thermal and hydrolytic degradation, but should still be able to be stripped from the glass fiber for splicing purposes.

[0119] To reduce the diameter of the optical fiber, the secondary sheath 58 may be thinner than that of conventional cables. However, the secondary sheath 58 must still maintain the required robustness and puncture resistance for the optical fiber. As the thickness of the secondary sheath decreases, its protective function diminishes. Puncture resistance is a measure of the protective function of the secondary sheath. A secondary sheath with higher puncture resistance can withstand greater impacts without breaking and provides better protection for the glass fiber.

[0120] To provide the required robustness and puncture resistance, the secondary coating 58 may have an in-situ modulus of elasticity of approximately 1500 MPa or more,

[0121] The primary and secondary coatings are typically formed by applying a curable coating composition as a viscous liquid to the glass fiber and allowing it to cure. The optical fiber may also have a tertiary coating surrounding the secondary coating. The tertiary coating may contain pigments, inks, or other colorants to mark the optical fiber for identification purposes and typically has a Young's modulus similar to that of the secondary coating.

[0122] The secondary coating 58 may consist of a trifunctional monomer. The glass transition temperature (Tg) of the secondary coating 58 may be above approximately 50°C, or above approximately 60°C, or above approximately 70°C, or above approximately 80°C, or above approximately 90°C, or above approximately 100°C.

[0123] Appropriate primary coatings 56 and / or secondary coatings 58 may be used so that the optical fiber 46 has a puncture resistance of approximately 5g or more, or approximately 10g or more, or approximately 15g or more, or approximately 20g or more, or approximately 25g or more, or approximately 30g or more, or approximately 35g or more, or approximately 40g or more, or approximately 45g or more, or approximately 50g or more, or approximately 55g or more, or approximately 60g or more.

[0124] Exemplary embodiment with reduced diameter As previously stated, the optical fibers of the embodiments disclosed herein may have a reduced diameter, including the diameter of the glass and / or the diameter of the cladding. In some embodiments, the cladding region 50 may have an outer diameter of about 125 micrometers or less, and the secondary cladding 58 may have an outer diameter of about 210 micrometers or less. The cladding region 50 may have an outer diameter of about 110 micrometers or less, or about 100 micrometers or less, or about 90 micrometers or less, or about 80 micrometers or less. Furthermore, the secondary cladding 58 may have an outer diameter of about 210 micrometers or less, or about 200 micrometers or less, or about 180 micrometers or less, or about 170 micrometers or less, or about 160 micrometers or less. Note that the outer diameter of the cladding region 50 is the diameter of the glass of the optical fiber 46, and the outer diameter of the secondary cladding 58 may be the outer diameter of the entire optical fiber 46 (if there is no outer tertiary ink layer).

[0125] In some examples, the clad region 50 has an outer diameter of approximately 125 micrometers and the secondary coating 58 has an outer diameter of approximately 200 micrometers or less, or the clad region 50 has an outer diameter of approximately 125 micrometers and the secondary coating 58 has an outer diameter of approximately 180 micrometers or less, or the clad region 50 has an outer diameter of approximately 125 micrometers and the secondary coating 58 has an outer diameter of approximately 170 micrometers or less, or the clad region 50 has an outer diameter of approximately 125 micrometers and the secondary coating 58 has an outer diameter between approximately 155 micrometers and approximately 175 micrometers, or the clad region 50 has an outer diameter of approximately 125 micrometers and the secondary coating 58 has an outer diameter between approximately 160 micrometers and approximately 170 micrometers. In further exemplary embodiments, the cladding region 50 has an outer diameter of approximately 110 micrometers or less and the secondary coating 58 has an outer diameter of approximately 200 micrometers or less; or the cladding region 50 has an outer diameter of approximately 90 micrometers or less and the secondary coating 58 has an outer diameter of approximately 180 micrometers or less; or the cladding region 50 has an outer diameter of approximately 90 micrometers and the secondary coating 58 has an outer diameter between approximately 155 micrometers and approximately 175 micrometers; or the cladding region 50 has an outer diameter of approximately 90 micrometers and the secondary coating 58 has an outer diameter between approximately 160 micrometers and approximately 170 micrometers.

[0126] As previously stated, the reduced diameter optical fiber profile design of this disclosure offers certain advantages, such as a greater total number of fibers in a submarine cable. However, when the diameter of the optical fiber cladding is reduced, some light may leak through the cladding due to the reduced profile of the cladding. Therefore, the offset trench design of this disclosure conveniently reduces the "tunneling" or "radiation" loss caused by light leakage through the reduced diameter cladding by about 30% Δ·micrometer. 2 It has the above trench volume.

[0127] Figure 7 shows the radiated loss as a function of cladding diameter for two optical fibers having a mode field diameter of 9.2 micrometers at 1310 nm and a cable cutoff of 1430 nm. The optical fiber 72 illustrated in the embodiments of this disclosure has a radiated loss of approximately 58% Δ·micrometer. 2 It has a trench volume of Δ·micrometer, while the optical fiber 74 has a trench volume of only about 8% Δ·micrometer. 2 It has a trench volume of Δ·micrometer. As shown in Figure 7, the exemplary optical fiber 72 has lower radiant loss over the same cladding diameter range compared to the comparative optical fiber 74. The larger trench volume disclosed herein conveniently provides reduced radiant loss and therefore gives a more efficient optical fiber. In addition, it has about 30% Δ·micrometer 2 Offset trench designs with the above trench volumes also help reduce microbend losses in optical fibers with reduced cladding diameter. Typically, optical fibers with reduced cladding diameter exhibit increased microbend sensitivity. However, as disclosed here, approximately 30% Δ·micrometer 2 An offset trench design with the above trench volume provides reduced microbend loss to the optical fiber.

[0128] The primary and secondary coatings may also have a reduced diameter compared to the coating configuration of conventional optical fibers. The radius r5 of the primary coating is approximately 85.0 micrometers or less, or approximately 80.0 micrometers or less, or approximately 75.0 micrometers or less, or approximately 70.0 micrometers or less. To promote a reduction in the diameter of the optical fiber, it is preferable to minimize the thickness r5-r4 of the primary coating. The thickness r5-r4 of the primary coating is approximately 25.0 micrometers or less, or approximately 20.0 micrometers or less, or approximately 15.0 micrometers or less, or approximately 10.0 micrometers or less, or in the range of approximately 5.0 micrometers to 25.0 micrometers, or in the range of approximately 8.0 micrometers to 20.0 micrometers, or in the range of approximately 10.0 micrometers to 17.0 micrometers.

[0129] The radius r6 of the secondary coating is approximately 95.0 micrometers or less, or approximately 90.0 micrometers or less, or approximately 85.0 micrometers or less, or approximately 80.0 micrometers or less. It is also preferable to minimize the secondary coating thickness r6-r5. The secondary coating thickness r6-r5 is approximately 25.0 micrometers or less, or approximately 20.0 micrometers or less, or approximately 15.0 micrometers or less, or approximately 10.0 micrometers or less, or in the range of approximately 5.0 micrometers to 25.0 micrometers, or in the range of approximately 8.0 micrometers to 20.0 micrometers, or in the range of approximately 10.0 micrometers to 18.0 micrometers, or in the range of approximately 12.0 micrometers to 16.0 micrometers.

[0130] The ratio of the thickness of the secondary coating to the thickness of the primary coating may be approximately 0.50 to 1.40, or approximately 0.60 to 1.3, or approximately 0.65 to 1.2, or approximately 0.70 to 1.10, or approximately 0.75 to 1.00, or approximately 0.80.

[0131] Therefore, optical fibers according to embodiments of the present disclosure have a reduced sheathing diameter, a reduced glass diameter, or both a reduced sheathing diameter and a reduced glass diameter compared to conventional optical fibers. This helps, for example, increase the "total number of fibers" in a submarine cable.

[0132] Table 7 below shows the average coating thickness for five secondary coating samples. Examples 1 and 2 show that, compared to Examples 3, 4, and 5, an average secondary coating thickness in the range of 8.0 to 20.0 micrometers resulted in higher tensile strength than an average thickness smaller than this range. The higher tensile strength shown in Examples 1 and 2 allows for the use of thinner secondary coatings in optical fibers, such as those used in submarine cables.

[0133] [Table 7]

[0134] Example of primary and secondary coatings The primary and secondary coatings described below, along with measurements of coating strength and puncture resistance, are explained below.

[0135] Primary coating composition. The primary coating composition includes the formulations given in Table 8 below and is typical of commercially available primary coating compositions.

[0136] [Table 8]

[0137] Here, the oligomeric material was prepared from H12MDI, HEA, and PPG4000 as described herein, using a molar ratio n:m:p = 3.5:3.0:2.0, SR504 was ethoxylated (4) nonylphenol acrylate (available from Sartomer), NVC was N-vinyl caprolactam (available from Aldrich), TPO (photoinitiator) was (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (available from BASF), and Irganox 1035 (antioxidant) is benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxythiodi-2,1-ethanediyl ester (available from BASF), 3-acrylooxypropyltrimethoxysilane is an adhesion promoter (available from Gelest), and pentaerythritol tetrakis(3-mercaptopropionate) (also known as tetrathiol, available from Aldrich) is a chain transfer agent. The concentration unit "pph" refers to the amount relative to the base composition, including all monomers, oligomers, and photoinitiators. For example, a concentration of 1.0 pph for Irganox 1035 corresponds to 1 g of Irganox 1035 per 100 g total of oligomer material, SR504, NVC, and TPO.

[0138] In a 500 mL flask, at room temperature, H12MDI (4,4'-methylenebis(cyclohexyl isocyanate)), dibutyltin dilaurate, and 2,6-di-tert-butyl-4-methylphenol were mixed to prepare an oligomer. This 500 mL flask was equipped with a thermometer, a CaCl2 drying tube, and a stirrer. While continuously stirring the contents of the flask, PPG4000 was added using an addition funnel over a period of 30 - 40 minutes. When adding PPG4000, the internal temperature of the reaction mixture was monitored and the introduction of PPG4000 was controlled to prevent excessive heating (caused by the exothermic nature of the reaction). After adding PPG4000, the reaction mixture was heated in an oil bath at about 70 °C to 75 °C for about 1 hour to 1.5 hours. At various intervals, samples of the reaction mixture were collected for analysis by Fourier transform infrared spectroscopy (FTIR) to monitor the progress of the reaction by determining the concentration of unreacted isocyanate groups. The concentration of unreacted isocyanate groups was evaluated based on the intensity of the characteristic isocyanate stretching mode near 2265 cm -1 . The flask was removed from the oil bath and its contents were cooled below 65 °C. Additionally, HEA was added to ensure complete quenching of the isocyanate groups. The additional HEA was added dropwise over 2 - 5 minutes using an addition funnel. After adding the additional HEA, the flask was returned to the oil bath and its contents were reheated to about 70 °C to 75 °C for about 1 hour to 1.5 hours. FTIR analysis was performed on the reaction mixture to assess the presence of isocyanate groups, and this process was repeated until sufficient additional HEA was added to completely react any unreacted isocyanate groups. The reaction was considered complete when no detectable isocyanate stretching intensity was detected in the FTIR measurement.

[0139] Secondary coating - composition. Four curable secondary coating compositions (A, SB, SC, and SD) are listed in Table 9.

[0140]

Table 9

[0141] PE210 is bisphenol-A epoxy diacrylate (available from Miwon Specialty Chemical, South Korea), M240 is ethoxylated (4) bisphenol-A diacrylate (available from Miwon Specialty Chemical, South Korea), M2300 is ethoxylated (30) bisphenol-A diacrylate (available from Miwon Specialty Chemical, South Korea), M3130 is ethoxylated (3) trimethylolpropane triacrylate (available from Miwon Specialty Chemical, South Korea), TPO (photoinitiator) is (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (available from BASF), Irgacure 184 (photoinitiator) is 1-hydroxycyclohexyl phenyl ketone (available from BASF), and Irganox 1035 (antioxidant) is benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxythiodi-2,1-ethanediyl ester (available from BASF). DC190 (slip agent) is silicone-ethylene oxide / propylene oxide copolymer (available from Dow Chemical). The concentration unit "pph" refers to the amount relative to the base composition including all monomers and photoinitiators. For example, for secondary coating composition A, a concentration of 1.0 pph for DC-190 corresponds to 1 g of DC-190 per 100 g total of PE210, M240, M2300, TPO, and Irgacure 184.

[0142] Secondary coating - tensile strength. The Young's modulus, yield point tensile strength, yield strength, and yield point elongation of secondary coatings prepared from secondary coating compositions A, SB, SC, and SD were measured using the technique described above. The results are summarized in Table 10.

[0143] [Table 10]

[0144] These results indicate that secondary coatings prepared from compositions SB, SC, and SD exhibited higher Young's modulus and yield strength than secondary coatings prepared from the comparative composition A. In addition, secondary coatings prepared from compositions SB, SC, and SD showed higher fracture toughness than those prepared from composition A. The higher values ​​exhibited by compositions SB, SC, and SD allow for the use of thinner secondary coatings on optical fibers without sacrificing performance. As mentioned earlier, thinner secondary coatings reduce the overall diameter of the optical fiber, resulting in a greater total number of fibers in a given cross-sectional area cable (such as a submarine cable).

[0145] Exemplary optical fiber embodiment The experimental examples and principles disclosed herein demonstrate that sufficient microbend and puncture resistance characteristics can be achieved in reduced-diameter optical fibers by adjusting the coating characteristics of the optical fiber. More specifically, a higher modulus of elasticity of the secondary coating provides sufficient puncture resistance for the reduced-diameter optical fiber profile. The aforementioned thickness ratio of the secondary coating to the primary coating provides a reduced-diameter optical fiber without sacrificing puncture resistance. Furthermore, the experimental examples and principles disclosed herein demonstrate that sufficient attenuation can be achieved in reduced-diameter optical fibers by providing an alkali-doped core.

[0146] To investigate the effects of primary and secondary coating thickness and elastic modulus on radial force transmission to glass fibers, a series of modeling examples were examined. In the models, a radial external load P was applied to the surface of the secondary coating of the optical fiber, and the resulting load on the glass fiber surface was calculated. Glass fibers with a Young's modulus of 73.1 GPa (matching silica glass) and a diameter of 125 μm were modeled. The Poisson's ratio ν of the primary and secondary coatings was considered. p and ν sThese values ​​were fixed at 0.48 and 0.33, respectively. Comparative sample C1 and six samples M1-M6 according to this disclosure were examined. The comparative sample had a primary and secondary coating with thickness and modulus consistent with optical fibers known in the art. Samples M1-M6 are examples of reduced thickness of the primary and / or secondary coatings according to embodiments of this disclosure. The parameters describing the configuration of the primary and secondary coatings are summarized in Table 11.

[0147] [Table 11]

[0148] Table 12 below summarizes the load P1 on the outer surface of the glass fiber as a function of the load P applied to the surface of the secondary coating. The ratio P1 / P is referred to here as the load transfer parameter and corresponds to the ratio of the external load P transferred to the surface of the glass fiber through the primary and secondary coatings. Load P is a radial load, and the load transfer parameter P1 / P was calculated from a model based on equations (9) to (11):

[0149]

number

[0150] During the ceremony,

[0151]

number

[0152] and

[0153]

number

[0154] In equations (9) to (11), νp and νs are the Poisson's ratios of the primary and secondary coatings, r4 is the outer radius of the glass fiber, r5 is the outer radius of the primary coating, r6 is the outer radius of the secondary coating, and E p is the in-situ modulus of the primary coating, and E s is the Young's modulus of the secondary coating. The scaled load transfer parameter P1 / P (scaled) in Table 11 corresponds to the ratio P1 / P of each sample to the comparative sample C1.

[0155] [Table 12]

[0156] The model example shows that, despite the smaller coating thickness, optical fibers with the primary and secondary coatings described herein exhibit a reduction in the forces experienced by the glass fiber compared to a comparative optical fiber with conventional primary and secondary coatings of conventional thickness. Reducing the overall size of the optical fiber described herein allows for an increase in the total number of fibers in a given size cable (or a decrease in the cable diameter relative to a given total number of fibers) without increasing the risk of damage to the glass fiber due to external forces.

[0157] The scaled load transfer parameter P1 / P (scaled) of the secondary covering is less than approximately 0.99, or less than approximately 0.97, or less than approximately 0.95. The load transfer parameter P1 / P of the secondary covering is less than approximately 0.005, or less than approximately 0.0045, or less than approximately 0.00445, or less than approximately 0.00444, or less than approximately 0.0043, or less than approximately 0.0042, or less than approximately 0.0041, or in the range of approximately 0.005 to approximately 0.0041, or in the range of approximately 0.0045 to approximately 0.0042, or in the range of approximately 0.00445 to approximately 0.00420, or in the range of approximately 0.00440 to approximately 0.004200.

[0158] Table 13 below provides additional modeling examples according to embodiments of the present disclosure. Samples M7 to M18 are examples having primary and secondary coatings with reduced thickness. The parameters describing the configuration of the primary and secondary coatings are summarized in Table 12.

[0159] [Table 13]

[0160] Fiber optic cable drawing process The optical fibers disclosed herein can be formed from a continuous optical fiber manufacturing process, during which glass fibers are drawn from a heated preform to a target diameter size. The glass fibers are then cooled and directed to a coating system that applies a liquid primary coating composition to the glass fibers. After the liquid primary coating composition has been applied to the glass fibers, there are two process options. In the first process option (wet-on-dry process), the liquid primary coating composition is cured to form a solidified primary coating, and a liquid secondary coating composition is applied to this cured primary coating, and this liquid secondary coating composition is cured to form a solidified secondary coating. In the second process option (wet-on-wet process), a liquid secondary coating composition is applied to the liquid primary coating composition, and both liquid coating compositions are cured simultaneously to provide solidified primary and secondary coatings. After the fibers have left the coating system, the fibers are collected and stored at room temperature. Fiber collection typically inevitably involves winding the fibers onto a spool and storing the spool.

[0161] In some processes, the coating system applies a tertiary coating composition to a secondary coating and cures this tertiary coating composition to form a solidified tertiary coating. Typically, the tertiary coating is an ink layer used to mark the fibers for identification purposes, contains a pigment, and otherwise has a composition similar to the secondary coating. The tertiary coating is applied to and cured over the secondary coating. The secondary coating is typically cured at the time of application of the tertiary coating. The primary, secondary, and tertiary coating compositions can be applied and cured in a general continuous manufacturing process. Alternatively, the primary and secondary coating compositions can be applied and cured in a general continuous manufacturing process, the coated fibers can be collected, and the tertiary coating composition can be applied and cured in a separate offline process to form the tertiary coating.

[0162] Multi-core optical fiber The optical fibers disclosed herein can be used in multi-core optical fiber designs. The optical fibers disclosed herein make it possible to achieve multi-core optical fiber designs with the maximum number of cores in a smaller profile cable while maintaining low inter-fiber crosstalk, low tunneling loss from corner fibers to edges, and good bending performance. For example, a multi-core optical fiber may comprise the small profile fibers disclosed herein, each having a halogen and / or alkali metal-doped core and offset trench design as described above. Therefore, the single-core optical fibers described above can be used in the multi-core optical fiber to provide the same mode field diameter, effective area, and attenuation as described above.

[0163] Figure 8A shows a cross-sectional view of an exemplary multi-core optical fiber 80 having a circular contour. As shown in Figure 8A, the multi-core optical fiber 80 comprises a central fiber axis 85 (the centerline of the multi-core optical fiber 80), a plurality of cores 90, and a cladding matrix 94 that forms a common cladding 98. The cores 90 are arranged within the cladding matrix 94, and each core 90 forms core fibers CF1, CF2 that generally extend in the longitudinal direction of the multi-core optical fiber 80 parallel to the central fiber axis 85.

[0164] Each core 90 has a central axis or centerlines CL1 and CL2, as well as outer radii r1 and r2. Note that the outer radii r1 and r2 are similar to radius r1, as previously mentioned with reference to Figure 5. As shown in Figure 8A, the respective positions of centerlines CL1 and CL2 within the multi-core optical fiber 80 can be defined using Cartesian coordinates, where the central fiber axis 85 defines the origin (0,0) of the xy coordinate system, which coincides with the coordinate system defined by the radial coordinate R. The position of centerline CL1 can be defined as (x1,y1), and the position of centerline CL2 can be defined as (x2,y2). Next, the distance D between centerlines CL1 and CL2 is C1-C2 is √[(x²-x¹) 2 +(y2-y1) 2 ] can be defined as follows. Thus, the center line CL i A predetermined core 90 and center line CL having j For adjacent cores 90 having distance D Ci-Ci As further described below, √[(x j -x i ) 2 +(y j -y i ) 2 It is defined as ].

[0165] The core 90 may be similar to the core region 48 (as previously described with reference to the single-core optical fiber), made from the same material, and having the same properties, and the cladding matrix 94 may be similar to the cladding region 50 (also as previously described with reference to the single-core optical fiber), made from the same material, and having the same properties. Therefore, each core 90 of the multi-core optical fiber 80 may be surrounded by a cladding region having an offset trench design, as described above. According to embodiments of the present disclosure, the multi-core optical fiber comprises a first core, a first inner cladding surrounding the first core, a second core, a second inner cladding surrounding the second core, and a common cladding surrounding the first and second cores. In addition, a primary cladding, a secondary cladding, and optionally a tertiary cladding may be arranged on the cladding matrix 94, as also described above.

[0166] Although Figure 8A shows only two cores 90, the multi-core optical fiber 80 may have three or more cores, as will also be described below. Furthermore, the multi-core optical fiber 80 may have a circular cross-sectional profile (as shown in Figure 8A) or a rectangular ribbon cross-sectional profile. Figure 8B shows an additional exemplary embodiment of the multi-core optical fiber 80.

[0167] The multi-core optical fiber 80 may have any number of cores 90 in any form known in the art. For example, the total number of cores 90 may be 2 to 20, 2 to 18, 2 to 16, 2 to 12, 2 to 10, 2 to 8, 2 to 6, 2 to 4, 2 to 3, 4 to 20, 4 to 18, 4 to 16, 4 to 12, 4 to 10, 4 to 8, 4 to 6, 6 to 20, 6 to 18, 6 to 16, 6 to 12, 6 to 10, 6 to 8, 8 to 20, 8 to 18, 8 to 16, 8 to 12, 8 to 10, 10 to 20, 10 to 18, 10 to 16, 10 to 12, 12 to 20, 12 to 18, or 12 to 16. For example, the total number of cores 90 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any total number of cores between these values. The total number of cores 90 can be even or odd, and can be arranged in any pattern within the cladding matrix 94. Non-limiting examples of the pattern include square, rectangular, circular, and hexagonal grid patterns. For example, Figure 9 shows a multi-core optical fiber containing four cores arranged in a square pattern.

[0168] As shown in Figure 8C, one or more of the multiple cores 90 of the multi-core optical fiber 80 are surrounded by an inner cladding 95 and an outer cladding 97, so that the outer cladding 97 surrounds the inner cladding 95 between the inner cladding 95 and the common cladding 98. Each inner cladding 95 has an outer radius r IC1 The inner cladding 95 has an inner radius corresponding to the outer radius r1 of the core 90. IC1 Width δr defined by IC1 It has. Core 90 has 2 * It can have a diameter d corresponding to r1, and the inner cladding 95 is 2 * r IC1 Diameter d corresponding to IC1 Each outer cladding 97 has an outer radius r OC1 and the outer radius r of the inner cladding 95 IC1has an inner radius corresponding thereto. The outer cladding 97 has a width δr IC1 defined by the outer radius r of the inner cladding 95 OC1 and the outer radius r of the outer cladding 97 OC1 As previously described with reference to FIG. 5, note that the outer radius r of the inner cladding 95 IC1 is similar to the radius r2, and the outer radius r of the outer cladding 97 OC1 is similar to the radius r3. The common cladding 98 has an outer radius R OC as shown in FIG. 8A.

[0169] The inner cladding 95 is similar to the inner cladding region 51 (as previously described with reference to the single-core optical fiber), may be made of the same material, and may have the same properties. The outer cladding 97 is similar to the cladding region 53 with a reduced refractive index (as previously described with reference to the single-core optical fiber), may be made of the same material, and may have the same properties. The common cladding 98 is similar to the outer cladding region 55 (as previously described with reference to the single-core optical fiber), may be made of the same material, and may have the same properties. Therefore, for example, the outer cladding 97 may form a trench region similar to the cladding region 53 with a reduced refractive index.

[0170] Referring to FIGS. 8A to 8C, each of the cores 90 has a diameter "d" (r1×2 or r2×2) in the range of from about 4 micrometers to about 20 micrometers, or from about 5 micrometers to about 18 micrometers, or from about 6 micrometers to about 16 micrometers, or from about 7 micrometers to about 14 micrometers, or from about 8 micrometers to about 12 micrometers, or from about 9 micrometers to about 12 micrometers. The diameter d of each core 90 may be the same as or different from one or more other cores 90 in the multi-core optical fiber 80. The spacing D between each core 90 may be constant between each core 90 and may be about 20 micrometers or more, or about 25 micrometers or more, or about 30 micrometers or more, or about 35 micrometers or more. In addition, or alternatively, the spacing D may be about 50 micrometers or less, or about 45 micrometers or less, or about 40 micrometers or less, or about 35 micrometers or less. In some embodiments, the spacing D is in the range of from about 20 micrometers to about 40 micrometers, or from about 25 micrometers to about 35 micrometers, or about 35 micrometers. In still other embodiments, the spacing between two or more cores 90 may be different from the spacing between two or more other cores 90. The spacing between the cores 90 should be sufficient to reduce crosstalk between the cores, as further described below.

[0171] When the multi-core optical fiber 80 is in ribbon form, as shown in FIG. 8B, it has a cross-sectional width W and thickness TH. The cores 90 can be arranged in one or more rows along the thickness TH and one or more columns along the width W. The width W may be from about 0.5 mm to about 3 mm, or from about 1 mm to about 2.5 mm, or from about 1 mm to about 2 mm. The thickness may be from about 0.1 to about 0.5 mm, or from about 0.2 to 0.4 mm. In one embodiment, the multi-core optical fiber 80 has a rectangular ribbon cross-sectional profile, includes eight cores, and has a width W of about 2 mm and a thickness TH of about 0.3 mm.

[0172] In a circular cross-section design, the width W of the cladding matrix 94 is equal to the diameter (R) of the common cladding 98. OC (×2) and may be in the range of approximately 200 micrometers or less, or approximately 150 micrometers or less, or approximately 125 micrometers or less, or approximately 80 micrometers or less, or approximately 80 micrometers to approximately 125 micrometers, or approximately 120 micrometers to approximately 130 micrometers, or approximately 125 micrometers. In other embodiments, the diameter of the common cladding 98 may be approximately 140 micrometers or more, or approximately 150 micrometers or more, or approximately 160 micrometers or more, or approximately 170 micrometers or more, or approximately 180 micrometers or more, or approximately 190 micrometers or more. In addition, or alternatively, the diameter of the common cladding 98 may be approximately 200 micrometers or less, or approximately 190 micrometers or less, or approximately 180 micrometers or less, or approximately 170 micrometers or less, or approximately 160 micrometers or less, or approximately 150 micrometers or less, or approximately 140 micrometers or less. In one example, the diameter of the common cladding 98 ranges from approximately 120 micrometers to approximately 140 micrometers.

[0173] Figure 9 shows an exemplary multi-core optical fiber 100 having four cores 90 arranged in a square design. As shown in Figure 9, the distance D1 between the centerline of the first core (CL1) and the centerline of the adjacent core (CL2) is less than about 50 micrometers, as previously stated, measured using the Cartesian coordinate system. For example, the distance D1 between adjacent cores may be greater than about 20 micrometers, greater than about 25 micrometers, greater than about 28 micrometers, greater than about 30 micrometers, greater than about 35 micrometers, or greater than about 40 micrometers. In addition, or alternatively, the distance D1 may be less than about 45 micrometers, less than about 40 micrometers, or less than about 35 micrometers. For example, the distance D1 could be approximately 20 to 50 micrometers, 20 to 45 micrometers, 20 to 30 micrometers, 28 to 50 micrometers, 28 to 40 micrometers, 28 to 30 micrometers, 30 to 50 micrometers, 30 to 40 micrometers, or 40 to 45 micrometers. The distance D1 between adjacent cores 90 may be the same or different for each core.

[0174] For example, in a 4x4 square pattern, the distance D2 between two cores separated by the maximum distance can be approximately 20 micrometers or more, approximately 25 micrometers or more, approximately 30 micrometers or more, approximately 35 micrometers or more, or approximately 40 micrometers or more. In addition, or alternatively, the distance D2 can be approximately 50 micrometers or less, approximately 45 micrometers or less, approximately 40 micrometers or less, approximately 35 micrometers or less, or approximately 30 micrometers or less.

[0175] As shown in Figure 9, the distance D3 between the centerline of the core 90 and the outer radius of the common cladding 98 may be approximately 40 micrometers or less, approximately 35 micrometers or less, approximately 30 micrometers or less, approximately 25 micrometers or less, or approximately 20 micrometers or less. In addition, or alternatively, the distance D3 may be approximately 25 micrometers or more, approximately 30 micrometers or more, approximately 35 micrometers or more, or approximately 40 micrometers or more. In some examples, the distance D3 is in the range of approximately 25 micrometers to approximately 40 micrometers, or approximately 30 micrometers to approximately 35 micrometers. It is also conceivable that D3 may be the same or different for each core 90.

[0176] The distance D4 between the outer radius of the core 90 and the outer radius of the common cladding 98 may be approximately 25 micrometers or less, approximately 20 micrometers or less, approximately 18 micrometers or less, approximately 16 micrometers or less, approximately 14 micrometers or less, approximately 13 micrometers or less, approximately 12 micrometers or less, approximately 10 micrometers or less, approximately 8 micrometers or less, or approximately 6 micrometers or less. In addition, or alternatively, the distance D4 may be approximately 8 micrometers or more, approximately 10 micrometers or more, approximately 13 micrometers or more, approximately 16 micrometers or more, or approximately 18 micrometers or more. In some examples, the distance D4 is in the range of approximately 10 micrometers to approximately 20 μm, or approximately 12 micrometers to approximately 16 micrometers. It is also conceivable that the distance D4 may be the same or different for each core 90.

[0177] Furthermore, as shown in Figure 9, distance D5 can be the radius of each core 90 (e.g., r1, r2). Distance D5 may be in the range of approximately 2 micrometers to approximately 30 micrometers, or approximately 2.5 micrometers to approximately 22.5 micrometers, or approximately 5 micrometers to approximately 20 micrometers, or approximately 7 micrometers to approximately 14 micrometers, or approximately 8 micrometers to approximately 12 micrometers, or approximately 9 micrometers to approximately 11 micrometers. For example, D5 may be approximately 9 micrometers, approximately 10 micrometers, approximately 10.5 micrometers, approximately 11 micrometers, approximately 11.5 micrometers, approximately 12 micrometers, approximately 12.5 micrometers, approximately 13 micrometers, approximately 14 micrometers, approximately 15 micrometers, approximately 15.5 micrometers, approximately 16 micrometers, approximately 16.5 micrometers, approximately 17 micrometers, approximately 17.5 micrometers, or approximately 18 micrometers. It is also possible that the distance D5 may be the same or different for each of the 90 cores.

[0178] In one embodiment, the exemplary multi-core optical fiber 100 includes four core regions in a 4x4 square design, such that the fiber width W is approximately 125 micrometers, the distance D1 is approximately 45 micrometers, the distance D2 is approximately 63.6 micrometers, the distance D3 is approximately 30.7 micrometers, the distance D4 is approximately 13 micrometers, and the distance D5 is approximately 17.6 micrometers.

[0179] As mentioned earlier, Core 90 has reduced crosstalk to ensure good system performance. Crosstalk depends on the distance between cores and the length of the fiber. The average crosstalk between cores is given by equation (12). X = 2k 2 LL c (12) It can be calculated from the formula, where k is the coupling coefficient, L is the fiber length, and Lc is the correlation length which depends on the uniformity of the fiber and the laying conditions.

[0180] In some embodiments, the average crosstalk between adjacent cores 90, measured over a 100km length of multi-core optical fiber operating at 1550nm, is less than or equal to -20dB, or less than or equal to -30dB, or less than or equal to -35dB, or less than or equal to -40dB, or less than or equal to -45dB, or less than or equal to -50dB, or less than or equal to -55dB, or less than or equal to -60dB.

[0181] Figure 10 shows a plot of crosstalk and spacing between adjacent cores 90 in a multi-core optical fiber design along a fiber length of 100 km. Line 200 represents a stepped profile and 80 micrometers. 2 This represents a multi-core optical fiber design having an effective area of ​​210, where line 210 is an offset trench design (as disclosed herein) and 80 micrometers 2 This represents a multi-core optical fiber design having an effective area of ​​220, where line 220 is an offset trench design (as disclosed herein) and 100 micrometers 2 This represents a multi-core optical fiber design with an effective area of ​​80 micrometers. As shown in Figure 10, line 220 has lower crosstalk than line 200 as the spacing between cores increases. Furthermore, line 210 has lower crosstalk than line 220 as the spacing between cores increases. Thus, Figure 10 shows that each of them has an effective area of ​​80 micrometers. 2 With a multi-core design featuring a core and offset trench design with an effective area of ​​100 micrometers 2 This demonstrates that it conveniently provides lower crosstalk than a core with a larger effective area or a fiber with a stepped profile.

[0182] In the multi-core optical fiber design disclosed herein, the core 90 may have attenuation at 1550 nm of 0.18 dB / km or less, or 0.175 dB / km or less, or 0.170 dB / km or less, or 0.165 dB / km or less, or 0.160 dB / km or less, or 0.155 dB / km or less, or 0.150 dB / km or less, as also described above. Each core 90 may have the same or different attenuation.

[0183] The cores 90 of the multi-core optical fibers disclosed herein may have theoretical cutoff wavelengths of less than approximately 1500 nm, less than approximately 1400 nm, less than approximately 1300 nm, less than approximately 1260 nm, or less than approximately 1200 nm. For example, the theoretical cutoff wavelength may be from approximately 1300 nm to approximately 1500 nm, or from approximately 1300 nm to approximately 1400 nm. For example, the theoretical cutoff wavelength may be approximately 1300 nm, approximately 1310 nm, approximately 1320 nm, approximately 1329 nm, approximately 1330 nm, approximately 1340 nm, approximately 1350 nm, approximately 1360 nm, approximately 1370 nm, approximately 1380 nm, approximately 1400 nm, approximately 1500 nm, or any theoretical cutoff wavelength between these values. Each core 90 may have the same or different theoretical cutoff wavelengths.

[0184] According to one embodiment, the cable cutoff wavelength of core 90 is less than approximately 1500 nm, less than approximately 1400 nm, less than approximately 1300 nm, less than approximately 1260 nm, or less than approximately 1200 nm. For example, its cable cutoff wavelength may be from approximately 1200 nm to approximately 1500 nm, from approximately 1200 nm to approximately 1400 nm, from approximately 1200 nm to approximately 1300 nm, from approximately 1300 nm to approximately 1500 nm, from approximately 1300 nm to approximately 1400 nm, or from approximately 1400 nm to approximately 1500 nm. For example, the cable cutoff wavelength could be approximately 1200nm, 1209nm, 1210nm, 1220nm, 1230nm, 1240nm, 1250nm, 1260nm, 1300nm, 1310nm, 1350nm, 1400nm, 1410nm, 1420nm, 1430nm, 1440nm, 1450nm, 1460nm, 1500nm, or any cable cutoff wavelength between these values. Each core 90 may have the same or different cable cutoff wavelengths.

[0185] According to one embodiment, the core 90 may have zero-dispersion wavelengths ranging from approximately 1280 nm to approximately 1340 nm. For example, its zero-dispersion wavelengths could be approximately 1290 nm to approximately 1330 nm, approximately 1295 nm to approximately 1325 nm, approximately 1300 nm to approximately 1320 nm, or approximately 1305 nm to approximately 1315 nm. For example, the zero-dispersion wavelengths could be approximately 1280 nm, approximately 1285 nm, approximately 1289 nm, approximately 1290 nm, approximately 1300 nm, approximately 1301 nm, approximately 1305 nm, approximately 1306 nm, approximately 1310 nm, approximately 1315 nm, or approximately 1320 nm, or any zero-dispersion wavelength between these values. Each core 90 may have the same or different zero-dispersion wavelengths.

[0186] According to aspects of this disclosure, the core 90 has a dispersion of less than approximately 3 ps / nm / km in absolute value at 1310 nm and 0.1 ps / nm 2 Each core 90 may have a dispersion gradient of less than ps / nm / km at 1310nm. Each core 90 may have the same or different dispersion and dispersion gradient at 1310nm. For example, the absolute values ​​of the dispersion at 1310nm could be approximately 0.3 ps / nm / km to approximately 3 ps / nm / km, approximately 0.3 ps / nm / km to approximately 2.5 ps / nm / km, approximately 0.3 ps / nm / km to approximately 2.25 ps / nm / km, approximately 0.3 ps / nm / km to approximately 2 ps / nm / km, approximately 0.3 ps / nm / km to approximately 1.75 ps / nm / km, approximately 0.3 ps / nm / km to approximately 1.5 ps / nm / km, or approximately 0.3 ps / nm / km to approximately 1 ps / nm / km. For example, the absolute value of the dispersion at 1310 nm could be approximately 0.3 ps / nm / km, 0.35 ps / nm / km, 0.4 ps / nm / km, 0.5 ps / nm / km, 0.75 ps / nm / km, 1 ps / nm / km, 1.25 ps / nm / km, 1.5 ps / nm / km, 1.75 ps / nm / km, 2 ps / nm / km, 2.25 ps / nm / km, 2.5 ps / nm / km, 2.75 ps / nm / km, 3 ps / nm / km, or any value between these. In one example, the dispersion gradient at 1310 nm is approximately 0.075 ps / nm. 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.08ps / nm2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.085ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.09ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.075ps / nm 2 Approximately 0.09 ps / nm from / km 2 / km, approx. 0.08ps / nm 2 Approximately 0.09 ps / nm from / km 2 / km, or approximately 0.085 ps / nm 2 Approximately 0.09 ps / nm from / km 2 It can be as high as / km. For example, the dispersion gradient at 1310nm is approximately 0.075 ps / nm. 2 / km, approx. 0.08ps / nm 2 / km, approx. 0.085ps / nm 2 / km, approx. 0.086ps / nm 2 / km, approx. 0.087ps / nm 2 / km, approx. 0.088ps / nm 2 / km, approx. 0.089ps / nm 2 / km, approx. 0.09ps / nm 2 / km, approx. 0.01ps / nm 2 It can be / km, or any value between these values.

[0187] According to aspects of this disclosure, the core 90 has a dispersion of less than 22 ps / nm / km at 1550 nm and 0.1 ps / nm 2It may have a dispersion gradient at 1550 nm of less than ps / nm / km. Each core 90 may have the same or different dispersion and dispersion gradient at 1550 nm. For example, the dispersion at 1550 nm could be approximately 10 ps / nm / km to approximately 22 ps / nm / km, approximately 10 ps / nm / km to approximately 22 ps / nm / km, approximately 10 ps / nm / km to approximately 20 ps / nm / km, approximately 10 ps / nm / km to approximately 15 ps / nm / km, approximately 15 ps / nm / km to approximately 22 ps / nm / km, or approximately 15 ps / nm / km to approximately 20 ps / nm / km. For example, the dispersion at 1550 nm could be approximately 10 ps / nm / km, 15 ps / nm / km, 16 ps / nm / km, 17 ps / nm / km, 17.5 ps / nm / km, 18 ps / nm / km, 19 ps / nm / km, 19.5 ps / nm / km, 19.6 ps / nm / km, 20 ps / nm / km, 20.1 ps / nm / km, 22 ps / nm / km, or any value between these. In one example, the dispersion gradient at 1550 nm is approximately 0.04 ps / nm. 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.05ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.055ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.06ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.08ps / nm 2 Approximately 0.1 ps / nm from / km 2 / km, approx. 0.04ps / nm 2 Approximately 0.08 ps / nm from / km 2 / km, approx. 0.05ps / nm 2 Approximately 0.08 ps / nm from / km 2 / km, approx. 0.055ps / nm 2 Approximately 0.08 ps / nm from / km 2 / km, approx. 0.06ps / nm 2 Approximately 0.08 ps / nm from / km 2 / km, approx. 0.04ps / nm 2 Approximately 0.06 ps / nm from / km 2 / km, approx. 0.05ps / nm 2 Approximately 0.06 ps / nm from / km 2 / km, or approximately 0.055 ps / nm 2 Approximately 0.06 ps / nm from / km 2 It can be as high as / km. For example, the dispersion gradient at 1550nm is approximately 0.04 ps / nm. 2 / km, approx. 0.05ps / nm 2 / km, approx. 0.055ps / nm 2 / km, approx. 0.057ps / nm 2 / km, approx. 0.058ps / nm 2 / km, approx. 0.059ps / nm 2 / km, approx. 0.06ps / nm 2 / km, approx. 0.061ps / nm 2 / km, approx. 0.07ps / nm 2 / km, approx. 0.08ps / nm 2 It can be / km, or any value between these values.

[0188] According to one embodiment, the bending loss of each core 90 in the multi-core optical fiber disclosed herein at 1550 nm, as determined by a mandrel winding test using a mandrel having a diameter of 10 mm, may be less than about 3 dB / winding, less than about 2.5 dB / winding, less than about 2 dB / winding, less than about 1.5 dB / winding, or less than about 1 dB / winding. For example, the bending loss could be approximately 0.5 dB / turn to 3 dB / turn, approximately 0.5 dB / turn to 2.5 dB / turn, approximately 0.5 dB / turn to 2 dB / turn, approximately 0.5 dB / turn to 1.5 dB / turn, approximately 0.5 dB / turn to 1 dB / turn, approximately 0.5 dB / turn to 1 dB / turn, approximately 1 dB / turn to 3 dB / turn, approximately 1 dB / turn to 2.5 dB / turn, approximately 1 dB / turn to 2 dB / turn, approximately 1 dB / turn to 1.5 dB / turn, approximately 1.5 dB / turn to 3 dB / turn, approximately 1.5 dB / turn to 2.5 dB / turn, approximately 1.5 dB / turn to 2 dB / turn, approximately 2 dB / turn to 3 dB / turn, or approximately 2 dB / turn to 2.5 dB / turn, using a mandrel with a diameter of 10 mm. For example, the bending loss could be approximately 0.5 dB / turn, 0.75 dB / turn, 0.9 dB / turn, 1 dB / turn, 1.5 dB / turn, 2 dB / turn, 2.5 dB / turn, 3 dB / turn, or any value between these values, using a mandrel with a diameter of 10 mm.

[0189] According to one embodiment, the bending loss of each core 90 in the multi-core optical fiber disclosed herein at 1550 nm, as determined by a mandrel winding test using a mandrel having a diameter of 15 mm, may be less than about 1 dB / winding, less than about 0.75 dB / winding, less than about 0.5 dB / winding, or less than about 0.3 dB / winding. For example, the bending loss could be approximately 0.1 dB / turn to approximately 1 dB / turn, approximately 0.1 dB / turn to approximately 0.75 dB / turn, approximately 0.1 dB / turn to approximately 0.5 dB / turn, approximately 0.2 dB / turn to approximately 1 dB / turn, approximately 0.2 dB / turn to approximately 0.75 dB / turn, approximately 0.2 dB / turn to approximately 0.5 dB / turn, approximately 0.3 dB / turn to approximately 1 dB / turn, approximately 0.3 dB / turn to approximately 0.75 dB / turn, or approximately 0.3 dB / turn to approximately 0.5 dB / turn, using a mandrel with a diameter of 15 mm. For example, the bending loss, using a mandrel with a diameter of 15 mm, could be approximately 0.2 dB / turn, approximately 0.23 dB / turn, approximately 0.25 dB / turn, approximately 0.3 dB / turn, approximately 0.5 dB / turn, approximately 0.6 dB / turn, approximately 0.75 dB / turn, approximately 1 dB / turn, or any value between these values.

[0190] According to one embodiment, the bending loss of each core 90 in the multi-core optical fiber disclosed herein at 1550 nm, as determined by a mandrel winding test using a mandrel having a diameter of 20 mm, may be less than about 3 dB / winding, less than about 2 dB / winding, less than about 1 dB / winding, less than about 0.5 dB / winding, less than about 0.3 dB / winding, or less than about 0.2 dB / winding. For example, the bending loss, using a mandrel with a diameter of 20 mm, ranges from approximately 0.1 dB / turn to approximately 3 dB / turn, approximately 0.1 dB / turn to approximately 2.5 dB / turn, approximately 0.1 dB / turn to approximately 2 dB / turn, approximately 0.2 dB / turn to approximately 3 dB / turn, approximately 0.2 dB / turn to approximately 2.5 dB / turn, approximately 0.2 dB / turn to approximately 2 dB / turn, approximately 0.3 dB / turn to approximately 3 dB / turn, approximately 0.3 dB / turn to approximately 2.5 dB / turn, or approximately 0. It could be 3dB / turn to approximately 2dB / turn, approximately 0.1dB / turn to approximately 1dB / turn, approximately 0.1dB / turn to approximately 0.75dB / turn, approximately 0.1dB / turn to approximately 0.5dB / turn, approximately 0.5dB / turn to approximately 3dB / turn, approximately 0.5dB / turn to approximately 2.5dB / turn, approximately 0.5dB / turn to approximately 2dB / turn, approximately 1dB / turn to approximately 3dB / turn, approximately 1dB / turn to approximately 2.5dB / turn, or approximately 1dB / turn to approximately 2dB / turn. For example, the bending loss could be approximately 0.2 dB / turn, 0.23 dB / turn, 0.25 dB / turn, 0.3 dB / turn, 0.5 dB / turn, 0.6 dB / turn, 0.75 dB / turn, 0.8 dB / turn, 0.9 dB / turn, 1 dB / turn, 2 dB / turn, 2.1 dB / turn, 2.5 dB / turn, 3 dB / turn, or any value between these values, using a mandrel with a diameter of 20 mm.

[0191] According to one aspect, the bend loss of each core 90 in the multi-core optical fiber disclosed herein at 1550 nm, determined by a mandrel winding test using a mandrel having a diameter of 30 mm, may be less than about 1 dB / turn, less than about 0.5 dB / turn, less than about 0.25 dB / turn, less than about 0.1 dB / turn, less than about 0.05 dB / turn, less than about 0.01 dB / turn, or less than about 0.005 dB / turn. For example, the bend loss may be from about 0.01 dB / turn to about 1 dB / turn, from about 0.01 dB / turn to about 0.5 dB / turn, from about 0.01 dB / turn to about 0.25 dB / turn, from about 0.01 dB / turn to about 0.2 dB / turn, from about 0.01 dB / turn to about 0.1 dB / turn, from about 0.01 dB / turn to about 0.005 dB / turn, from about 0.05 dB / turn to about 1 dB / turn, from about 0.05 dB / turn to about 0.5 dB / turn, from about 0.05 dB / turn to about 0.25 dB / turn, or from about 0.05 dB / turn to about 0.2 dB / turn, from about 0.2 dB / turn to about 1 dB / turn, from about 0.2 dB / turn to about 0.5 dB / turn, or from about 0.5 dB / turn to about 1 dB / turn, using a mandrel having a diameter of 30 mm. For example, the bend loss may be about 0.005 dB / turn, about 0.01 dB / turn, about 0.05 dB / turn, about 0.06 dB / turn, about 0.07 dB / turn, about 0.08 dB / turn, about 0.09 dB / turn, about 0.1 dB / turn, about 0.12 dB / turn, about 0.13 dB / turn, about 0.15 dB / turn, about 0.2 dB / turn, about 0.23 dB / turn, about 0.24 dB / turn, about 0.24 dB / turn, about 0.25 dB / turn, about 0.3 dB / turn, about 0.31 dB / turn, about 0.4 dB / turn, about 0.5 dB / turn, about 0.51 dB / turn, about 1 dB / turn, or any value between these values, using a mandrel having a diameter of 30 mm.

[0192] Multi-core optical fibers according to embodiments of this disclosure may have the same properties as those described above with respect to single-core optical fibers. For example, the glass core of a multi-core optical fiber may have the same trench volume, mode field diameter, effective area, and attenuation as previously disclosed. Thus, the optical fibers constituting the multi-core optical fiber of this disclosure may have a reduced profile while still maintaining sufficient microbend and robustness necessary for long-distance transmission.

[0193] Table 14 below provides examples of multi-core optical fibers 310-340 according to embodiments of the present disclosure. Each multi-core optical fiber 310-340 is formed from four cores arranged in a square design, as shown in Figure 9. Each of the fibers 310-340 has an outer glass diameter of 125 micrometers and an outer cladding diameter of 242 micrometers. The radius (r1) of each core in the fibers 310-340 is approximately 17.5 micrometers, and each core is chlorine-doped. Furthermore, each core has an offset trench design and a common cladding (as disclosed herein) located outside the trenches. The refractive index of the common cladding is -0.245%. The distance D1 between the centerlines of the first core and the second core in the fibers 310-340 is 40 micrometers. The distance D3 between the centerlines of the cores and the outer radius of the common cladding in the fibers 310-340 is 34.2 micrometers. The optical properties of fibers 310-340 are shown in Table 14 below, and the relative refractive index profiles of each core are shown in Figure 11.

[0194] [Table 14-1]

[0195] [Table 14-2]

[0196] Unless otherwise specified, none of the methods described herein are intended to be interpreted as requiring the steps to be performed in a specific order. Therefore, if a claim for a method does not actually enumerate the order in which the steps should be performed, or if it is not otherwise specifically stated in the claim or description that the steps are limited to a particular order, no particular order is intended to be implied.

[0197] It will be apparent to those skilled in the art that various modifications and alterations can be made without departing from the spirit or scope of the present invention. Since modifications, combinations, partial combinations and alterations of the disclosed embodiments, including the spirit and substance of the present invention, will be conceivable to those skilled in the art, the present invention should be considered to encompass all within the scope of the accompanying claims and their equivalents.

[0198] Preferred embodiments of the present invention are described below in separate sections.

[0199] Embodiment 1 In multi-core optical fibers, The first core is made from silica glass doped with alkali metals. The first inner cladding surrounding the first core, Surrounding the aforementioned first inner cladding, approximately 30% Δ-micrometer 2 A first outer cladding including a first trench region having the above volume, The second core is made from alkali metal-doped silica glass. The second inner cladding surrounding the second core, Surrounding the aforementioned second inner cladding, approximately 30% Δ-micrometer 2 A second outer cladding including a second trench region having the above volume, and A common cladding surrounding the first core and the second core, Equipped with, Each of the first core and the second core is approximately 100 micrometers 2 A multi-core optical fiber having the following effective area at 1550nm.

[0200] Embodiment 2 Each of the i additional cores is made from alkali metal-doped silica glass, where i is an additional core ranging from 1 to 18. The inner cladding surrounding the aforementioned additional core, Each additional core surrounds approximately 30% Δ-micrometers. 2 An outer cladding including a trench region having the above volume, and A common cladding surrounds each additional core, Furthermore, Each of the additional cores is approximately 100 micrometers. 2 A multi-core optical fiber according to Embodiment 1, having the following effective area at 1550 nm.

[0201] Embodiment 3 A multi-core optical fiber according to Embodiment 2, wherein i is 2.

[0202] Embodiment 4 The multi-core optical fiber according to any one of embodiments 1 to 3, wherein the multi-core optical fiber has a circular cross-sectional shape with a width of about 80 micrometers to about 125 micrometers.

[0203] Embodiment 5 The multi-core optical fiber according to any one of embodiments 1 to 3, wherein the multi-core optical fiber has a ribbon-shaped cross-sectional shape with a width of approximately 0.5 mm to approximately 3 mm.

[0204] Embodiment 6 A multi-core optical fiber according to any one of embodiments 1 to 5, wherein the distance between the center line of the first core and the center line of the second core is in the range of about 10 micrometers to about 50 micrometers.

[0205] Embodiment 7 The multi-core optical fiber according to Embodiment 6, wherein the distance between the center line of the first core and the center line of the second core is in the range of about 20 micrometers to about 45 micrometers.

[0206] Embodiment 8 The multi-core optical fiber according to Embodiment 7, wherein the distance between the center line of the first core and the center line of the second core is approximately 45 micrometers.

[0207] Embodiment 9 A multi-core optical fiber according to any one of embodiments 1 to 8, wherein the crosstalk between the first core and the second core is less than approximately -30 dB per 100 km of fiber length.

[0208] Embodiment 10 The multi-core optical fiber according to Embodiment 9, wherein the crosstalk between the first core and the second core is less than approximately -40 dB per 100 km of fiber length.

[0209] Embodiment 11 The multi-core optical fiber according to Embodiment 10, wherein the crosstalk between the first core and the second core is less than approximately -50 dB per 100 km of fiber length.

[0210] Embodiment 12 A multi-core optical fiber according to any one of embodiments 1 to 11, wherein the distance between the centerline of each core and the outer radius of the common cladding is in the range of about 25 micrometers to about 40 micrometers.

[0211] Embodiment 13 A multi-core optical fiber according to Embodiment 12, wherein the distance between the centerline of each core and the outer radius of the common cladding is in the range of about 30 micrometers to about 35 micrometers.

[0212] Embodiment 14 A multi-core optical fiber according to any one of embodiments 1 to 13, wherein the radius of each of the first core and the second core is in the range of about 2.5 micrometers to about 9 micrometers.

[0213] Embodiment 15 The multi-core optical fiber according to Embodiment 14, wherein the radius of each of the first core and the second core is in the range of about 3.5 micrometers to about 7 micrometers.

[0214] Embodiment 16 A multi-core optical fiber according to any one of embodiments 1 to 15, wherein the attenuation of each of the first core and the second core at 1550 nm is approximately 0.175 dB / km or less.

[0215] Embodiment 17 The multi-core optical fiber according to Embodiment 16, wherein the attenuation at 1550 nm is approximately 0.170 dB / km or less.

[0216] Embodiment 18 The multi-core optical fiber according to Embodiment 17, wherein the attenuation at 1550 nm is approximately 0.160 dB / km or less.

[0217] Embodiment 19 A multi-core optical fiber according to any one of embodiments 1 to 18, wherein each of the first core and the second core has a peak alkali metal concentration in the range of about 10 ppm to about 500 ppm.

[0218] Embodiment 20 A multi-core optical fiber according to any one of embodiments 1 to 19, wherein the alkali metal of the first core and the second core is at least one of sodium, potassium, and rubidium.

[0219] Embodiment 21 A multi-core optical fiber according to any one of embodiments 1 to 18, wherein each of the first core and the second core has a chlorine concentration in the range of about 0.4% by mass to about 2.2% by mass.

[0220] Embodiment 22 The effective area at 1550 nm is approximately 70 micrometers. 2 From approximately 90 micrometers 2A multi-core optical fiber according to any one of embodiments 1 to 21, within the range of [the specified range].

[0221] Embodiment 23 The effective area at 1550 nm is approximately 80 micrometers. 2 The multi-core optical fiber described in Embodiment 22.

[0222] Embodiment 24 The volumes of the first trench region and the second trench region are approximately 70%Δ-micrometers. 2 A multi-core optical fiber according to any one of embodiments 1 to 23, as described below.

[0223] Embodiment 25 A multi-core optical fiber according to any one of embodiments 1 to 24, wherein the mode field diameters of the first core and the second core are in the range of about 9 micrometers to about 9.5 micrometers at 1310 nm and in the range of about 10 to about 10.5 micrometers at 1550 nm. [Explanation of Symbols]

[0224] 10, 20, 46 optical fibers 11. Glass fiber 12, 48 core areas 14, 50 Clad areas 16, 56 Primary covering 18, 58 Secondary coating 30 Fiber Optic Ribbons 32 Ribbon Matrix 40 Fiber Optic Cables 42 Jacket 51 Inner cladding region 53 Cladding region with reduced refractive index 55 Outer cladding region 80, 100 multi-core optical fiber 85 Central fiber axis 90 Multiple cores 94 Clad Matrix 95 Inner cladding 97 Outer cladding 98 Common cladding

Claims

[Claim 1] In multi-core optical fibers, The first core is made from alkali metal-doped silica glass. The first inner cladding surrounding the first core, Surrounding the first inner cladding, 30% Δ micrometer ２ A first outer cladding including a first trench region having the above trench volume, The second core is made from alkali metal-doped silica glass. The second inner cladding surrounding the second core, Surrounding the aforementioned second inner cladding, 30% Δ micrometer ２ A second outer cladding including a second trench region having the above trench volume, and A common cladding surrounding the first core and the second core, Equipped with, Each of the first core and the second core has a waveguide light signal of 1550 nm with a wavelength of 100 micrometers ２ A multi-core optical fiber having the following effective area.

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