Crosstalk-reduced uncoupled multi-core optical fiber

Abstract

Disclosed is an uncoupled multi-core optical fiber having at least two core portions, each of which comprises a core and a low-index cladding. Each core has a radius r1 and a relative refractive index Δ1. The low-index cladding has a radius r2 and a relative refractive index Δ2. The low-index cladding directly contacts and surrounds the core, and the volume V2 of the low-index cladding is about 15.0% Δμm 2 ~approximately 37.0%Δμm 2 In addition, this fiber has a radius r3 and a

Description

Priority

[0001] This application claims the benefit of priority under 35 U.S.C. § 120 of U.S. Provisional Patent Application No. 63 / 464,270, filed May 5, 2023, the benefit of priority to U.S. Provisional Patent Application No. 63 / 446,619, filed February 17, 2023, and the benefit of priority to U.S. Provisional Patent Application No. 63 / 401,310, filed August 26, 2022, the disclosures of all of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a multi-core optical fiber, and more particularly to an uncoupled multi-core optical fiber with reduced crosstalk between adjacent alkali-doped cores. [Background technology]

[0003] Multicore optical fibers have multiple cores embedded in a cladding matrix. Therefore, the increased fiber density of multicore optical fibers makes their use in passive optical network (PON) systems advantageous in overcoming cable size limitations and duct congestion issues. Multicore optical fibers are also useful in submarine cables designed for the transmission of telecommunication signals across land and oceans. The use of submarine cables for the transmission of telecommunication signals has increased dramatically in recent years, with over 90% of intercontinental communication signals now transmitted via submarine cables. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, the demand for transmission capacity of undersea cables is increasing due to the increasing amount of information being sent and received between different continents via the Internet. [Means for solving the problem]

[0005] The multi-core optical fiber disclosed herein has low crosstalk and dispersion between adjacent cores while maintaining a sufficiently large mode field diameter. Therefore, the multi-core optical fiber disclosed herein is useful for use in submarine cables. The multi-core optical fiber disclosed herein can be called an uncoupled fiber, in which a distance between the cores is large enough to ensure independent mode transmission within the different cores. Furthermore, the cores of the multi-core optical fiber disclosed herein are alkali-doped cores surrounded by trenches, which not only minimizes crosstalk but also reduces radiation loss.

[0006] In one embodiment of the present disclosure, there is disclosed an uncoupled multi-core optical fiber having at least two core portions, each of which comprises a core and a low-index cladding. Each core has a radius r1 and a relative refractive index Δ1 with respect to pure silica, and is doped with at least one of sodium, potassium, and rubidium. The low-index cladding has a radius r2 and a relative refractive index Δ2 with respect to pure silica, where Δ2<Δ1. The low-index cladding directly contacts and surrounds the core, and the volume V2 of the low-index cladding is about 15.0% Δμm. 2 ~approximately 37.0%Δμm 2 The fiber also includes a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica, where Δ2<Δ3<Δ1, directly surrounding the low-index cladding. Furthermore, the cable cutoff wavelength of each core is approximately 1530 nm or less, and the effective area of ​​each core at a wavelength of 1550 nm is approximately 100 μm. 2 ~about 135μm 2 The attenuation of the multi-core optical fiber at a wavelength of 1550 nm is approximately 0.165 dB / km or less, and the center-to-center spacing, which is the distance between the center lines of adjacent core portions, is approximately 48 micrometers to approximately 60 micrometers.

[0007] Additional features and advantages are set forth in the detailed description that follows, and will become apparent to those skilled in the art in part from the description, or may be learned by practice of the embodiments, claims, and accompanying drawings described herein.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and characteristics of the claimed invention.

[0009] Additionally, the accompanying drawings are included for a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate selected aspects of the disclosure by way of example and, together with the following detailed description, serve to explain the principles and operation of the methods, products, and compositions encompassed by the disclosure. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating an uncoupled multi-core optical fiber having multiple cores according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view showing an enlarged view of one core of an uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 3] FIG. 1 illustrates a relative refractive index profile of an uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a schematic cross-sectional view illustrating an uncoupled multi-core optical fiber with an outer coating according to an embodiment of the present disclosure. [Figure 5] FIG. 1 is another schematic cross-sectional view showing an uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 6A] FIG. 1 illustrates the relative refractive index profile of an exemplary uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 6B] FIG. 1 illustrates the relative refractive index profile of an exemplary uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 7A] 1 is a graph plotting the far-end crosstalk between cores of an uncoupled multi-core optical fiber according to an embodiment of the present disclosure versus the center-to-center spacing of adjacent cores. [Figure 7B] 1 is a graph plotting near-end crosstalk between cores of an uncoupled multi-core optical fiber according to an embodiment of the present disclosure versus the center-to-center spacing of adjacent cores. [Figure 8] 1 is a graph plotting radiation loss versus center-to-center spacing of adjacent cores for an uncoupled multi-core optical fiber according to an embodiment of the present disclosure. [Figure 9] Schematic diagram showing the far-end crosstalk and near-end crosstalk measurement system DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure provides enabling teachings and may be more readily understood by reference to the following description, drawings, examples, and claims. To this end, those skilled in the art will recognize and appreciate that many variations are possible in various aspects of the embodiments described herein while still achieving beneficial results. It will also be apparent that some of the desirable advantages of the embodiments can be achieved by selecting some features of the embodiments without utilizing others. Thus, those skilled in the art will recognize that many modifications and applications are possible and may even be desirable in certain circumstances, and are part of this disclosure. Accordingly, it is to be understood that, unless otherwise specified, the present disclosure is not limited to the specific compositions, articles, devices, and methods disclosed. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting.

[0012] In this specification and the claims that follow, use will be made of a number of terms that shall be defined to have the following meanings.

[0013] The term "optical fiber" refers to a waveguide having a glass portion surrounded by a coating, which includes a core and a cladding, and is referred to herein as a "glass fiber."

[0014] "Radial position," "radius," or radial coordinate "r" refers to the radial position relative to the centerline of the fiber (r=0).

[0015] Unless otherwise specified, "refractive index" refers to the refractive index at a wavelength of 1550 nm.

[0016] A "refractive index profile" is the relationship between refractive index or relative refractive index and radius. While the present specification may depict a relative refractive index profile with a step boundary between adjacent core or cladding regions, variations in processing conditions may result in interfaces between adjacent regions that do not exhibit a sharply defined step boundary. Therefore, while the present specification may depict a refractive index profile with a step-like refractive index change, it should be understood that the actual boundary may deviate from a perfect step function characteristic, such as a rounded transition. It should also be understood that the value of the relative refractive index may vary with radial position within a core or cladding region. When the relative refractive index varies with radial position within a particular region of a fiber (e.g., the core or cladding region), the relative refractive index may be expressed using an actual functional dependency, an approximation of the functional dependency, a value at a specific location within that region, or an average value applicable to the entire region. Therefore, unless otherwise specified, when the relative refractive index of a region (e.g., the core region or each cladding region) is expressed as a single value or a parameter (e.g., Δ or Δ%) applicable to the entire region, it is understood that the relative refractive index may be constant or nearly constant at that single value within the region, or may not be constant within the region but may vary with radial position, with the single value or parameter representing the average value of such relative refractive index. For example, if "i" is a glass fiber region, then unless otherwise specified, the parameter Δ i refers to the average value of the relative refractive index in a region of a glass fiber, as defined below. Note that the dependence of the relative refractive index on radial position may not be constant, such as having a gradient or a curve, whether by design or as a result of normal manufacturing variations.

[0017] In this specification, the term "relative refractive index" is defined as follows.

[0018]

number

[0019] In the formula, n i is the radial position r of the glass fiber unless otherwise specified. i is the refractive index at ref Unless otherwise specified, is the refractive index of pure silica glass. Therefore, in this specification, the relative refractive index (%) is a relative value based on pure silica glass (which has a relative refractive index of 1.444 at a wavelength of 1550 nm). In this specification, the relative refractive index is expressed as Δ ("delta") or Δ% ("delta %"), and unless otherwise specified, the value is expressed in units of "%." The relative refractive index may also be expressed as Δ(r) or Δ(r)%.

[0020] The average relative refractive index (Δ ave ) can be calculated using the following formula:

[0021]

number

[0022] In the formula, r inner is the inner radius of the region, r outer is the outer radius of the region, and Δ(r) is the relative refractive index of the region.

[0023] The refractive index of an optical fiber profile can be measured using commercially available instruments 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 instruments measure the refractive index n(r)-n relative to a reference refractive index. meas The measurement is performed using the reference refractive index n measis typically taken to be the refractive index of a calibrated refractive index matching oil or pure silica glass. The measurement wavelength can 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. This absolute refractive index, n(r), is then used to determine the relative refractive index, as defined above.

[0024] The term "α-profile" ("alpha profile") refers to a relative refractive index profile Δ(r) having a functional form defined by the following equation:

[0025]

number

[0026] In the formula, r0 is the radial position where Δ(r) is maximum, 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 is in the range of r i is the initial radial position of the α profile, r f is the final radial position of the α profile, and α is a real number. In this specification, Δ(r0) of the α profile is expressed as Δ max and Δ(r0) of a specific region i of the fiber is called Δ imax In the α profile, which represents the relative refractive index profile of the fiber core region, r0 is on the center line (r=0), and r z corresponds to the outer radius r1 of the core region, and if Δ1(r1)=0, then the above equation reduces to the simple equation

[0027]

number

[0028] When the core region has a refractive index expressed by the above formula, the outer radius r1 can be calculated from the measured relative refractive index profile by the following procedure. That is, by examining the measured relative refractive index profile, the estimated maximum relative refractive index Δ 1max , the estimated value of α, the estimated value of the outer radius r 1est Using these estimates, r = -r 1est From r=r 1est Trial function Δ trial 3 shows the relative refractive index profile of a representative glass fiber having a core described by an α profile, according to an embodiment of the present disclosure.

[0029] It should be noted that the term "graded-index profile" refers to an α-profile with α<10. The term "step-index profile" refers to an α-profile with α≧10.

[0030] "Trench volume" is defined as follows:

[0031]

number

[0032] In the formula, r Trench,inner is the inner radius of the trench region of the refractive index profile, r Trench,outer is the outer radius of the trench region of the refractive index profile, Δ Trench (r) is the relative refractive index of the trench region of the refractive index profile, and r is the radial position within the fiber. Trench volume is an absolute, positive quantity and is referred to herein as %Δ micrometers squared, %Δ-micrometers squared, and %-Δμm 2 , or %Δμm 2These units are used interchangeably in this specification. In addition, in this specification, the trench region may be referred to as a depressed-index cladding region, and the trench volume may be represented by V2.

[0033] The "mode field diameter" ("MFD") of an optical fiber is defined as follows:

[0034]

number

[0035] where f(r) is the cross-sectional electric field distribution component of the guided optical signal, and r is the radial position in the fiber. The "mode field diameter" ("MFD") varies with the wavelength of the optical signal, and in this specification, the mode field diameters are reported for wavelengths of 1310 nm, 1550 nm, and 1625 nm. Specific wavelengths are indicated when the mode field diameter is mentioned. Unless otherwise noted, the mode field diameter is the LP at the specified wavelength. 01 This refers to the mode field diameter of the mode.

[0036] The "effective area" of an optical fiber is defined as:

[0037]

number

[0038] In the formula, f(r) is the cross-sectional electric field component of the guided optical signal, and r is the radial position within the fiber. eff ") varies with the wavelength of the optical signal, and in this specification it should be understood to refer to the effective area for a wavelength of 1550 nm.

[0039] In this specification, the term "attenuation" refers to the loss of optical power at a wavelength of 1550 nm that occurs as a signal travels along an optical fiber. Attenuation measurements were made in accordance with the standard IEC 60793-1-40 "Attenuation measurement methods."

[0040] The bending resistance of an optical fiber can be measured by generating attenuation under specified test conditions that comply with the standard IEC 60793-1-47:2017, "Optical fibers - Part 1-47: Measurement methods and test procedures - Macrobending loss." For example, the test conditions can include wrapping the fiber around a mandrel of a specified diameter, such as a 60 mm diameter mandrel, wrapping the fiber 100 times and measuring the increase in attenuation with each wrap.

[0041] In this specification, "cable cutoff wavelength" ("cable cutoff") refers to a cutoff test performed on a 22 m cable in accordance with the IEC 60793-1-44 "Measurement methods and test procedures - Cut-off wavelength" standard.

[0042] Unless otherwise specified, optical properties (e.g., dispersion, dispersion slope, etc.) are 01 The optical properties of the modes are reported.

[0043] The "chromatic dispersion" of an optical fiber, referred to herein as "dispersion" unless otherwise noted, is the sum of material dispersion, waveguide dispersion, and intermodal dispersion. "Material dispersion" refers to how the refractive index of the material used in the optical core affects the speed at which light of various wavelengths propagates within the core. "Waveguide dispersion" refers to the dispersion caused by the difference in refractive index between the core and cladding of the optical fiber. In the case of a single-mode waveguide fiber, intermodal dispersion is zero. Dispersion values ​​in a two-mode system are those assuming zero intermodal dispersion. The zero-dispersion wavelength (λ0) is the wavelength at which dispersion takes on a zero value. Dispersion slope is the rate of change of dispersion with wavelength. Dispersion and dispersion slope are reported herein at wavelengths of 1310 nm or 1550 nm. Dispersion is in units of picoseconds / nm / km, and dispersion slope is in units of picoseconds / nm. 2 The unit of chromatic dispersion is / km. Chromatic dispersion is measured in accordance with the standard IEC 60793-1-42:2013 "Optical fibres - Part 1-42: Measurement methods and test procedures - Chromatic dispersion".

[0044] "Crosstalk" in a multi-core optical fiber is a measure of the amount of power leakage from a core portion to an adjacent core portion. In this specification, the term "adjacent core portion" refers to the core closest to a reference core portion. In some embodiments, all of the core portions may be equally spaced, meaning that all of the core portions are adjacent to one another. In other embodiments, the core portions may not be equally spaced, meaning that some core portions are spaced apart from the reference core portion by a distance greater than the distance between the reference core portion and the adjacent core portion. Crosstalk can be determined based on the coupling coefficient and Δβ. The coupling coefficient is a coefficient that depends on the refractive index profile design of the core portions, the distance between two adjacent core portions, and the structure of the cladding surrounding the two adjacent core portions. Δβ depends on the difference in the propagation constant β between two adjacent core portions (e.g., in this specification, two core portions whose centerlines are separated by the minimum inter-core separation distance). When power P1 is incident on the first of two adjacent core portions, power P2 coupled from the first core portion to the second core portion can be calculated using the following equation from the coupled-mode theory.

[0045]

number

[0046] In the formula, "< >" denotes the average, L is the fiber length, κ is the coupling coefficient between the electric fields of the two cores, ΔL is the change in the fiber length, and L c is the correlation length, and g is given by

[0047]

number

[0048] In the formula, Δβ is the LP of two adjacent core parts that are separated from each other. 01 The mismatch in the propagation constants of the modes. In this case, the crosstalk (unit: dB) can be calculated using the following formula:

[0049]

number

[0050] Crosstalk between two adjacent cores increases linearly with fiber length on a linear scale, but not on a dB scale. In this specification, crosstalk performance is based on an optical fiber length L of 100 km. However, with appropriate scaling, crosstalk performance for other optical fiber lengths can also be expressed. For optical fiber lengths other than 100 km, the crosstalk between cores can be calculated using the following equation:

[0051]

number

[0052] For example, the crosstalk when the optical fiber length is 10 km can be calculated by adding "-10 dB" to the crosstalk value of an optical fiber with a length of 100 km. Also, the crosstalk when the optical fiber length is 1 km can be calculated by adding "-20 dB" to the crosstalk value of an optical fiber with a length of 100 km. In long-distance transmission using uncoupled-core multicore fiber, the crosstalk per 100 km needs to be -30 dB or less, -40 dB or less, or even -50 dB or less.

[0053] In this specification, in far-end (co-propagating) crosstalk (XT), when power P1 is incident on a first core portion from a first end, as described above, power P2 coupled from the first core portion to a second core portion is determined at the second end of the optical fiber. Therefore, power P2 coupled to the second core portion is determined at the end of the optical fiber on the side of the propagation direction of the optical signal. On the other hand, in near-end (counter-propagating) crosstalk (CXT), when power P1 is incident on a first core portion from the first end, as described above, power P2 coupled from the first core portion to the second core portion is determined at the first end of the optical fiber. Therefore, power P2 coupled to the second core portion is determined at the end of the optical fiber opposite to the propagation direction of the optical signal. Generally, in a certain optical fiber, near-end crosstalk is smaller than far-end crosstalk.

[0054] FIG. 9 shows the far-end crosstalk (XT co ) and near-end crosstalk (XT counter) measurement system. To measure the crosstalk according to the present disclosure, a test was conducted using a 20-25 km long multicore fiber (e.g., a multicore fiber with a 1x2 core design) wound on a standard shipping spool. As shown in FIG. 9, the system includes a tunable laser source (TLS) with a linewidth of 200 kHz, a tap for monitoring the laser output power, and a fan-in / fan-out (FIFO1) for the 1x2 multicore fiber. FIFO1 was connected to the fiber so that light from the source was injected into one core of the fiber and light propagating in the reverse direction was guided to the other core. Meanwhile, a fan-out (FIFO2) was connected to the far end of the fiber. The output of FIFO2 was connected to an optical receiver, which measured the light propagating in the forward direction and output from each core. Optical receivers #1, #2, and #3 shown in Figure 9 are all high-sensitivity detectors with a noise sensitivity of -109 dBm and a linearity error of less than 20% across the entire power measurement range (+5 to -75 dBm). These three optical receivers were calibrated so that the power indication value for one power value was the same. Furthermore, each FIFO was fabricated using a multicore fiber with the same mode field diameter and inter-core pitch as the transmission multicore fiber under test.

[0055] Techniques for determining crosstalk between cores in a multi-core optical fiber are also described in M. Li et al., "Coupled Mode Analysis of Crosstalk in Multicore fiber with Random Perturbations," Optical Fiber Communication Conference, OSA Technical Digest (online), Optical Society of America, 2015, paper W2A.35; Shoichiro Matsuo et al., "Crosstalk behavior of cores in multi-core fiber under bent condition," IEICE Electronics Express, Vol. 8, No. 6, pp. 385-390, published March 25, 2011; and Lukasz Szostkiewicz et al., "Crosstalk analysis in multicore optical fibers by supermode theory," Optics Letters, Vol. 41, No. 16, pp. 3759-3762, published August 15, 2016, the contents of all of which are incorporated herein by reference. Furthermore, techniques for determining far-end crosstalk and near-end crosstalk between cores in a multi-core optical fiber are described in Akihide Sano et al., "Crosstalk-Managed High Capacity Long Haul Multicore Fiber Transmission With Propagation-Direction Interleaving," Journal of Lightwave Technology, Vol. 32, No. 16, pp. 2771-2779, published August 15, 2014, and Tetsuya Hayashi et al., "Uncoupled Multi-Core Fiber Design for Practical Bidirectional Optical Communications," OFC, Optica Publishing Group, 2022, the contents of all of which are also incorporated herein by reference.

[0056] In this specification, the term "coupling coefficient" or "κ" refers to the overlap of the electric field distributions that occurs when two cores are close to each other. The square of the coupling coefficient (κ 2 ) relates to the average power in a core of a multicore optical fiber as affected by the power of other cores. The "coupling coefficient" can be estimated using power coupling theory, and such estimation can be performed using the method disclosed in M. Koshiba, K. Saitoh, K. Takenaga, and S. Matsuo, "Analytical Expression of Average Power-Coupling Coefficients for Estimating Intercore Crosstalk in Multicore Fibers," IEEE Photonics J, 4(5), 1987-95 (2012), and T. Hayashi, T. Sasaki, E. Sasaoka, K. Saitoh, and M. Koshiba, "Physical Interpretation of Intercore Crosstalk in Multicore Fiber: Effects of Macrobend, Structure Fluctuation, and Microbend," Optics Express, 21(5), 5401-12 (2013), the contents of all of which are incorporated herein by reference.

[0057] The optical fiber disclosed herein comprises multiple cores and an outer cladding region surrounding each core, and may optionally comprise a coating surrounding the outer cladding region. The cores and the outer cladding region are made of glass. Each core comprises multiple regions, such as a core and a low-index cladding. The multiple cores are preferably concentric regions. The low-index cladding is immediately adjacent to and surrounds the core. The outer cladding region is immediately adjacent to and surrounds the low-index cladding, such that the low-index cladding is located radially between the core and the outer cladding region. As will be described in more detail below, the outer cladding region is a common cladding.

[0058] The low-index cladding has a lower relative refractive index than the core and outer cladding region. The low-index cladding may also be referred to herein as a trench or trench region. As described in more detail below, the low-index cladding also contributes to reducing crosstalk between adjacent cores.

[0059] Throughout this specification, radial position r1 and relative refractive index Δ1 or Δ1(r) refer to the radial position and relative refractive index of the core, radial position r2 and relative refractive index Δ2 or Δ2(r) refer to the radial position and relative refractive index of the low-index cladding, and radial position r3 and relative refractive index Δ3 or Δ3(r) refer to the radial position and relative refractive index of the outer cladding region. Furthermore, radial position r4 (not shown) refers to the radial position of the primary coating, radial position r5 (not shown) refers to the radial position of the secondary coating, and radial position r6 (not shown) refers to the radial position of the optional tertiary coating.

[0060] The relative refractive index Δ1(r) is the maximum value Δ 1max , minimum value Δ 1min The relative refractive index Δ2(r) is the maximum value Δ 2max , minimum value Δ 2min The relative refractive index Δ3(r) is the maximum value Δ 3max , minimum value Δ 3minIn embodiments where the relative refractive index within a region is constant or nearly constant, the maximum and minimum values ​​of the relative refractive index are equal or nearly equal. Note that unless otherwise specified, when a single value is reported for the relative refractive index of a region, that value corresponds to the average value for that region.

[0061] It is understood that each core has a substantially cylindrical shape, and the surrounding low-index cladding, outer cladding region, primary coating, and secondary coating have a substantially annular shape. The annular regions can be characterized by an inner radius and an outer radius. In this specification, radial position r1 refers to the outermost radius of the core region, radial position r2 refers to the outermost radius of the low-index cladding, radial position r3 refers to the outermost radius of the outer cladding region, radial position r4 refers to the outermost radius of the primary coating, radial position r5 refers to the outermost radius of the secondary coating, and radial position r6 refers to the outermost radius of the tertiary coating. In embodiments without a tertiary coating, radius r5 also corresponds to the outer radius of the optical fiber. On the other hand, when a tertiary coating is used, radius r6 corresponds to the outer radius of the optical fiber.

[0062] The difference between radial position r2 and radial position r1 is the thickness of the low-index cladding. The difference between radial position r3 and radial position r2 is the thickness of the outer cladding region. The difference between radial position r4 and radial position r3 is the thickness of the primary coating. The difference between radial position r5 and radial position r4 is the thickness of the secondary coating.

[0063] Until now, multi-core optical fibers have been adopted to increase fiber density while maintaining the outer diameter of conventional optical fibers (e.g., 125 micrometers). Furthermore, in conventional methods, the mode field diameter of a multi-core optical fiber has also been reduced to reduce crosstalk between adjacent cores while achieving high fiber density. However, although reducing the mode field diameter reduces crosstalk between adjacent cores, it also limits the amount of power that can be launched into each core due to nonlinear effects. Therefore, conventional multi-core optical fibers usually suffer from increased losses due to radiation and tunneling.

[0064] The multi-core optical fiber described herein addresses the above-mentioned problems associated with conventional approaches to increasing fiber density in relatively small (e.g., 125 micrometer outer diameter) multi-core optical fibers. Specifically, by including multiple core sections each having a core and a low-index cladding immediately adjacent to the core, the multi-core optical fiber described herein reduces radiation and tunneling losses while maintaining a large effective area, relatively low crosstalk, and good bending performance. Furthermore, the multi-core optical fiber disclosed herein has a mode field diameter compatible with that of a standard single-mode fiber.

[0065] In the embodiments disclosed herein, the multi-core optical fiber is an uncoupled type. When the cores of a multi-core optical fiber are uncoupled, the distance between the cores is large to ensure independent mode transmission in each core and reduce crosstalk between the cores. The inter-core crosstalk at a wavelength of 1550 nm of the uncoupled multi-core optical fiber disclosed herein is −30 dB per 100 km length of the multi-core optical fiber (−30 dB / 100 km) or less. In this specification, a multi-core optical fiber having at least one pair of uncoupled cores is referred to as an “uncoupled-core multi-core optical fiber.” In contrast, a multi-core optical fiber with coupled cores utilizes crosstalk between the cores. Therefore, in a coupled multi-core optical fiber, the distance between the cores needs to be significantly smaller than in an uncoupled multi-core optical fiber.

[0066] The uncoupled multicore fiber disclosed in this specification comprises a common cladding region that directly contacts and surrounds the cores, and since the cores comprise low-refractive-index cladding that directly contacts and surrounds the cores, the common cladding region is configured to directly contact and surround the low-refractive-index cladding.

[0067] Referring to FIG. 1 , an embodiment of the present disclosure is directed to an uncoupled multi-core optical fiber 10 having multiple cores 20 surrounded by a common cladding 30. In an embodiment, the fiber 10 is configured for use in a submarine cable. Each core 20 of the fiber 10 is a glass core. As shown in FIG. 1 , the cores 20 are disposed within the common cladding 30 and extend generally parallel to the central axis 15 of the fiber along the length of the fiber 10. It should be noted that although FIG. 1 illustrates two cores 20, the fiber 10 may include more than two cores, for example, two or more, four or more, six or more, eight or more, ten or more, or twelve or more cores. However, it should also be noted that in some embodiments, the fiber 10 includes only two uncoupled cores 20.

[0068] The common cladding 30 is sometimes referred to herein as a "glass matrix." The outer diameter of the common cladding 30 is about 180 micrometers or less, or about 160 micrometers or less, or about 150 micrometers or less, or about 125 micrometers or less, or about 100 micrometers or less. In embodiments, the outer diameter of the common cladding 30 ranges from about 100 micrometers to about 180 micrometers, or from about 100 micrometers to about 160 micrometers, or from about 120 micrometers to about 130 micrometers, or from about 124 micrometers to about 126 micrometers. In some embodiments, the outer diameter of the outer cladding is 125 micrometers. The outer diameter of the common cladding 30 may also be the outer glass diameter of the fiber 10. As shown in FIG. 1, the cross section of the common cladding 30 is circular. However, other cross-sectional shapes of the common cladding 30 are contemplated. Additionally, in some embodiments, the common cladding 30 may be covered by an outer coating, as discussed in more detail below.

[0069] The central axis 15 is on the center line of the fiber 10, and the central axis 15 is defined as the radial position r=0 of the fiber 10. The cores 20 can be arranged so that the center line of at least one core 20 and the central axis 15 are positioned on the same axis line. For example, as shown in FIG. 1, the center line CL of the core 20 Ci (i.e., CL C1 , C.L. C2 The center line CL of each core portion 20 is aligned along the same axis A. Note also that the axis A is perpendicular (or substantially perpendicular) to the center line 15. Ci The center line CL is defined as the radial position r=0 in the core. Ci is defined using Cartesian coordinates in an xy coordinate system that coincides with the coordinate system defined by the radial coordinate r and has the central axis 15 as the origin (0,0). C1 The position of the second core portion 20 is defined as (x1, y1), and the center line CL C2The position of can be defined as (x2, y2).

[0070] As described above, the fiber 10 can include multiple cores 20, and the cores 20 can be arranged in various configurations, such as linear or square. In some embodiments, the fiber 10 is configured with only two cores 20. In the embodiment shown in FIG. 1, the cores 20 are arranged in a 1×2 linear configuration, in which both cores 20 are aligned along the same axis A. More specifically, in the embodiment shown in FIG. 1, the center line CL of each core 20 is C1 , C.L. C2 are arranged on the axis A, and the core portions 20 are arranged so that the central axis 15 of the optical fiber 10 is also arranged on this axis A. Therefore, the central axis 15 of the optical fiber 10 is aligned with the center line CL of each core portion 20. C1 , C.L. C2 However, it should be noted that the core portions 20 may be arranged in other configurations or patterns. For example, in other embodiments, the center line CL of the first core portion 20 is aligned with the center line CL of the second core portion 20. C1 The center line CL of the second core portion 20 is C2 can be offset from

[0071] To enable fiber 10 to function as a waveguide, each core 20 has a higher refractive index than the common cladding 30. In some embodiments, each core 20 has no discernible boundary with the common cladding 30. Alternatively, there can be a distinct boundary between the core 20 and the common cladding 30.

[0072] As shown in FIG. 2 , each core region 20 includes a core 22 and a low-index cladding 24 surrounding the core 22. Furthermore, the low-index cladding 24 is directly adjacent to the core 22. Therefore, there is no other glass region between the low-index cladding 24 and the core 22, and the low-index cladding 24 is in direct contact with the core 22. The common cladding 30 surrounds the low-index cladding 24 and is directly adjacent to the low-index cladding 24. Therefore, there is no other glass region between the common cladding 30 and the low-index cladding 24, and the common cladding 30 is in direct contact with the low-index cladding 24. Although FIG. 2 shows only one core region 20, the other core regions 20 of the fiber 10 can have the same structure. As mentioned above, the common cladding 30 is common to all of the core regions 20, and therefore, all of the core regions 20 are surrounded by the common cladding 30. Further details of each core 22, the low-index cladding 24, and the common cladding 30 will be described below.

[0073] 3 is a graph plotting relative refractive index Δ versus radial coordinate r for an idealized relative refractive index profile of fiber 10, according to an embodiment of the present disclosure. The relative refractive index Δ1 of core 22 has a maximum refractive index Δ0=Δ1 at r=0. 1MAX and has a gradient α profile. Details of the α profile of the relative refractive index Δ1 of the core 22 are described below. The low-index cladding 24 may be in the form of a recessed region or trench and has a relative refractive index Δ2 and a radius r2. The common cladding 30 has a radius r3 and a relative refractive index Δ3. Furthermore, as shown by example in the figure, Δ2<Δ1, Δ2<Δ3, Δ3<Δ1. Other configurations of the relative refractive index profile are described below.

[0074] core Core 22 can be composed of silica glass (either undoped, up-doped, or down-doped). Up-doped silica glass can include alkali-doped silica glass, such as potassium (e.g., KO), sodium (NaO), rubidium (e.g., RbO), or a combination thereof. Other up-dopants can include germanium (e.g., GeO), phosphorus (e.g., PO), aluminum (e.g., AlO), chlorine, or other alkali metal oxides (e.g., LiO or CsO). In some exemplary embodiments, core 22 is doped with both potassium and rubidium. In other exemplary embodiments, core 22 is doped with both sodium and potassium. In embodiments in which core 22 is alkali-doped, the average concentration of the alkali dopant in core 22 is defined as follows:

[0075]

number

[0076] In the formula, C alkaliwhere (r) is the concentration of alkali dopant as a function of radial distance from the center of the core, and MFD is the mode field diameter of the core at a wavelength of 1550 nm. In embodiments, the average alkali dopant concentration in the core 22 ranges from 10 ppm to 500 ppm, or from 20 ppm to 500 ppm, or from 25 ppm to 400 ppm, or from 50 ppm to 300 ppm. Because the average alkali concentration in the core 22 is at most 500 ppm, doping with alkali dopants only slightly increases the refractive index of the core 22. Therefore, even with this alkali updoping, the effective refractive index of the core 22 can still be maintained at approximately ±0%. Note that if the core 22 contains two or more alkali dopants (e.g., both potassium and rubidium), the average alkali dopant concentration is the sum of the average concentrations of the individual alkali dopants. In some exemplary embodiments, the silica glass of the core 22 does not contain germanium, chlorine, or both. That is, the core 22 is made of silica glass that does not contain germanium, chlorine, or both.

[0077] On the other hand, examples of down-doped silica glass include silica glass doped with fluorine or boron.

[0078] As described above, the relative refractive index of each core 22 is described by an α profile in which the value of α is within the range of about 7.0 or less, or about 6.0 or less, or about 5.0 or less, or about 4.0 or less, or about 3.0 or less, or about 2.0 or less, or about 1.0 or less. In other embodiments, the value of α of the core is about 8.0 or more, or about 9.0 or more, or about 10.0 or more, or about 11.0 or more, or about 12.0 or more, or about 13.0 or more. In some embodiments, the value of α of the core is about 10, or about 12, or about 20. Thus, the refractive index profile of the core 22 may be a graded-index profile or a step-index profile.

[0079] The outer radius r1 of core 22 is in the range of about 2.5 micrometers to about 7.5 micrometers, or about 3.0 micrometers to about 7.0 micrometers, or about 3.5 micrometers to about 6.5 micrometers, or about 4.0 micrometers to about 5.0 micrometers, or about 3.0 micrometers to about 4.0 micrometers, or about 5.0 to about 6.5, or about 5.5 to about 6.3 micrometers. In some embodiments, the outer radius r1 is about 5.3 micrometers, or about 5.8 micrometers, or about 5.9 micrometers, or about 6.1 micrometers, or about 6.3 micrometers, or about 6.4 micrometers.

[0080] The maximum relative refractive index Δ of the core 22 1max is in the range of about −0.20% to about 0.20%, or in the range of about −0.15% to about 0.15%, or in the range of about −0.10% to about 0.10%, or in the range of about −0.05% to about 0.05%. 1max is about 0.0%. Preferably, the relative refractive index Δ 1max is assumed to be constant or approximately constant.

[0081] Note that, although not shown in FIG. 3, in some embodiments, there may be a dip in the relative refractive index at the centerline of core 22, such that the maximum refractive index of core 22 and the maximum refractive index of the entire fiber 10 is located some distance away from the centerline of core 22 rather than on the centerline of core 22 as shown in FIG.

[0082] Low refractive index cladding The low-index cladding 24 is composed of down-doped silica glass, and in some embodiments, the low-index cladding region 24 is down-doped with fluorine or boron.

[0083] The inner radius of the low-index cladding 24 is r1, as described above. The outer radius r2 of the low-index cladding 24 is in the range of about 12.0 micrometers to about 28.0 micrometers, or about 14.0 micrometers to about 26.0 micrometers, or about 16.0 micrometers to about 24.0 micrometers, or about 18.0 micrometers to about 22.0 micrometers, or about 14.0 micrometers to about 22.0 micrometers, or about 15.0 micrometers to about 20.0 micrometers, or about 13.0 micrometers to about 23.0 micrometers. In some embodiments, the outer radius r2 is about 16.5 micrometers, or about 16.8 micrometers, or about 18.4 micrometers, or about 20.0 micrometers, or about 21.3 micrometers, or about 22.1 micrometers.

[0084] The relative refractive index Δ2 of the low-index cladding 24 is in the range of about −0.50% to about −0.2%, or about −0.40% to about −0.25%, or about −0.35% to about −0.25%, or about −0.30% to about −0.25%. In some embodiments, the relative refractive index Δ2 is about −0.27%, or about −0.29%, or about −0.31%, or about −0.34%, or about −0.37%. Preferably, the relative refractive index Δ2 is constant or nearly constant.

[0085] The refractive index Δ2 of the low-index cladding 24 and the fluorine dopant used to impart the refractive index Δ2 to the low-index cladding 24 are selected so that the optical fiber does not experience an increase in attenuation when exposed to hydrogen. The hydrogen sensitivity of the optical fiber is manifested in the attenuation at 850 nm. In some embodiments, the attenuation of the fiber 10 at 850 nm is less than 1.6 dB / km. In other embodiments, the attenuation of the fiber 10 at 850 nm is less than 1.5 dB / km.

[0086] 3, the low-index cladding 24 is a low-index cladding region having a trench structure. The "volume" V2 of the low-index cladding 24 is defined as follows:

[0087]

number

[0088] In the formula, Δ 2-3 =(Δ2(r)-Δ3).

[0089] The trench volume V2 of the low refractive index cladding 24 is approximately 5.0% Δμm 2 or more, or about 7.0% Δμm 2 or more, or about 10.0% Δμm 2 or more, or about 15.0% Δμm 2 or more, or about 17.5% Δμm 2 or more, or about 20.0% Δμm 2 or more, or about 22.5% Δμm 2 or more, or about 25.0% Δμm 2 or more, or about 27.5% Δμm 2 or more, or about 30.0% Δμm 2 or more, or about 32.5% Δμm 2 or more, or about 35.0% Δμm 2 In addition to or instead of this, the trench volume V2 of the low refractive index cladding 24 is about 37.0% Δμm 2 or less, or about 36.0% Δμm 2 or less, or about 34.0% Δμm 2 or less, or about 32.0% Δμm 2 Less than or equal to about 30.0% Δμm 2 or less, or about 28.0% Δμm 2 or less, or about 26.0% Δμm 2 or less, or about 24.0% Δμm 2 or less, or about 22% Δμm 2 Less than or equal to about 20.0% Δμm 2 or less, or about 18.0% Δμm 2 Less than or equal to about 15.0% Δμm 2 Less than or equal to about 10.0% Δμm 2 Less than or equal to about 7.0% Δμm 2 In an embodiment, the trench volume V2 of the low index cladding 24 is about 5.0% Δμm 2 ~approximately 37.0%Δμm2 , or about 7.0% Δμm 2 ~approximately 37.0%Δμm 2 , or about 10.0% Δμm 2 ~approximately 37.0%Δμm 2 , or about 15.0% Δμm 2 ~approximately 37.0%Δμm 2 , or about 5.0% Δμm 2 ~approximately 36.0%Δμm 2 , or about 7.0% Δμm 2 ~approximately 36.0%Δμm 2 , or about 10.0% Δμm 2 ~approximately 36.0%Δμm 2 , or about 15.0% Δμm 2 ~approximately 36.0%Δμm 2 , or about 16.0% Δμm 2 ~approximately 35.0%Δμm 2 , or about 17.0% Δμm 2 ~approximately 34.0%Δμm 2 , or about 18.0% Δμm 2 ~approximately 33.0%Δμm 2 , or about 20.0% Δμm 2 ~approximately 30.0%Δμm 2 , or about 22.0% Δμm 2 ~approximately 30.0%Δμm 2 , or about 24.0% Δμm 2 ~approximately 28.0%Δμm 2 To achieve the low crosstalk required for uncoupled multi-core optical fibers, the trench volume V2 must be at least 5.0% Δμm 2 Furthermore, in order to make the cable cutoff value 1530 nm or less (details will be described later), the trench volume V2 must be 37.0%Δμm 2 In some embodiments, the trench volume V2 should be about 19.8% Δμm 2 , or about 20.1% Δμm 2 , or about 21.7% Δμm 2 , or about 34.9% Δμm 2 , or about 36.3% Δμm 2 , or about 36.9% Δμm 2 is.

[0090] It should be noted that although FIG. 3 illustrates the low-index cladding 24 as having a rectangular shape, configurations in which the low-index cladding 24 has other shapes, such as a triangle, are also contemplated.

[0091] 3 also illustrates the transition regions from the core 22 to the low-index cladding 24 and from the low-index cladding 24 to the common cladding 30 as step-like changes. However, it should be understood that such step-like changes are idealized, and that in practice the transition regions may not be strictly vertical. Rather, the actual transition regions may have a slope or curve.

[0092] The low-index cladding 24 aids in transmitting light along the optical fiber 10 while confining it to each core 22 , thereby reducing crosstalk between adjacent core regions 20 .

[0093] It should be noted that one or more core regions 20 of fiber 10 may be different from one or more other core regions 20. For example, one or more core regions 20 may have a different refractive index profile, a different radius, or both, than one or more other core regions 20. Furthermore, although the cross-sectional shapes of the core regions 20 are illustrated in Figures 1 and 2 as being circular, one or more core regions 20 may have other cross-sectional shapes, such as elliptical, rectangular, square, or D-shaped.

[0094] Common Cladding Common cladding 30 is comprised of down-doped silica glass. In some embodiments, common cladding 30 is down-doped with fluorine or boron. In yet other embodiments, common cladding 30 is comprised of undoped silica glass.

[0095] The inner radius of common cladding 30 is r2, as described above. The outer radius r3 of common cladding 30 ranges from about 40.0 micrometers to about 65 micrometers, or from about 45.0 micrometers to about 62.5 micrometers, or from about 50.0 micrometers to about 60.0 micrometers, or from about 52.5 micrometers to about 57.5 micrometers. In some embodiments, the outer radius r3 of common cladding 30 is about 62.5 micrometers.

[0096] The relative refractive index Δ3 of the common cladding is in the range of about −0.30% to about 0.00%, or about −0.25% to about −0.05%, or about −0.20% to about −0.10%, or about −0.15% to about 0.00%, or about −0.25% to about 0.00%. In some embodiments, the relative refractive index Δ3 is about −0.22%, or about −0.23%, or about −0.25%. Preferably, the relative refractive index Δ3 is constant or nearly constant.

[0097] In some embodiments, the absolute value of the difference between the relative refractive index Δ2 of the low-index cladding 24 and the relative refractive index Δ3 of the common cladding 30 is about 0.02% to about 0.30%, or about 0.03% to about 0.28%, or about 0.04% to about 0.25%, or about 0.05% to about 0.22%, or about 0.06% to about 0.20%, or about 0.08% to about 0.18%.

[0098] As mentioned above, the common cladding 30 may be an outer cladding common to all of the core regions 20 of the fiber 10. Thus, each core region 20 of the fiber 10 may be surrounded by the common cladding 30.

[0099] Outer coating One or more coatings may be provided on the outer surface of common cladding 30. For example, as shown in Figure 4, in some embodiments, a primary coating 40 contacts and covers common cladding 30, and a secondary coating 50 contacts and covers primary coating 40. Primary coating 40 is comprised of a low modulus material, and secondary coating 50 is comprised of a high modulus material. One or both of these materials may be, for example, an acrylate.

[0100] The optical fiber 10 may further include a tertiary coating 60 overlying the secondary coating 50. The tertiary coating 60 may include a colorant, such as a pigment or ink, to mark the optical fiber for identification, and typically has a Young's modulus similar to that of the secondary coating 50.

[0101] If no tertiary coating is provided, the outer diameter of the secondary coating 50 will be the outer diameter of the fiber 10. The outer diameter of the secondary coating 50 can be about 250 micrometers or less, or about 220 micrometers or less, or about 210 micrometers or less, or about 200 micrometers or less, or about 190 micrometers or less, or about 180 micrometers or less, or about 170 micrometers or less.

[0102] Core Spacing 5, adjacent core regions 20 are spaced apart from each other by a sufficient distance to reduce crosstalk between the core regions. More specifically, the center line CL of the first core portion 20′ is C1 is the center line CL of the adjacent second core portion 20 ″ C2 , and is spaced a distance x from the center line CL. Therefore, the distance x is the center-to-center spacing between the center lines of adjacent cores. As defined above, the center line CL is spaced a distance x from the center line CL using Cartesian coordinates in the xy coordinate system with the center axis 15 as the origin (0,0). C1 The position of is defined as (x1, y1), and the center line CL C2 If the position is defined as (x2, y2), the distance x is C1 and center line CL C2is the minimum core-to-core separation distance (or "minimum separation distance") between x = √[(x2 - x1) 2 +(y2-y1) 2 In this specification, the term "adjacent core portions" is used to refer to core portions whose centerlines are closest to each other (i.e., for a given core portion, the centerline CL is closer to the centerline of the given core portion than the centerline of its adjacent core portion). Ci (No core has a centerline less than 100 mm). In an embodiment, the centerlines of adjacent cores are spaced apart by a minimum separation distance.

[0103] In embodiments, distance x is about 48 micrometers or more, or about 50 micrometers or more, or about 52 micrometers or more, or about 55 micrometers or more, or about 58 micrometers or more. Additionally or alternatively, distance x is about 60 micrometers or less, or about 58 micrometers or less, or about 55 micrometers or less, or about 50 micrometers or less. In some embodiments, distance x is about 48 micrometers to about 60 micrometers, or about 50 micrometers to about 60 micrometers, or about 50 micrometers to about 60 micrometers, or about 50 micrometers to about 58 micrometers, or about 50 micrometers to about 55 micrometers, or about 51 micrometers to about 54 micrometers.

[0104] 5 , distance y is the smallest distance between the outer diameter of a core region 20 and the outer diameter of the common cladding 30, measured from the edge of each core region 20 of the multiple core regions 20 to the outer surface 32 of the common cladding 30. In embodiments, y is about 5 micrometers or more, or about 10 micrometers or more, or about 12 micrometers or more, or 15 micrometers or more, or about 18 micrometers or more, or about 20 micrometers or more, or about 22 micrometers or more, or about 25 micrometers or more, or about 28 micrometers or more, or about 30 micrometers or more. Additionally or alternatively, distance y is about 30 micrometers or less, or about 28 micrometers or less, or about 25 micrometers or less, or about 22 micrometers or less, or about 20 micrometers or less. In some embodiments, the distance y is between about 5 micrometers and about 30 micrometers, or between about 10 micrometers and about 28 micrometers, or between about 12 micrometers and about 25 micrometers, or between about 15 micrometers and about 20 micrometers. Without intending to be bound by any particular theory, it is believed that the magnitude of signal loss due to tunneling and radiation depends on the distance y. More specifically, it is believed that as the distance y increases, the coupling of the outer modes increases, resulting in an exponential increase in tunneling and radiation losses. Therefore, in general, increasing the distance y reduces tunneling and radiation losses.

[0105] characteristics Without intending to be limited to any particular theory, the combination of having the low-index cladding 24 immediately surrounding the core 22 and providing a spacing (distance x) between adjacent cores results in shorter cable cutoff wavelengths and reduced crosstalk. Accordingly, the optical fiber disclosed herein has excellent bend performance, making it suitable for use in submarine cables. Furthermore, because the low-index cladding 24 immediately surrounds the core 22, the fiber disclosed herein does not have an inner cladding region between the low-index cladding 24 and the core 22. Accordingly, the fiber disclosed herein can be manufactured cost-effectively (since the additional time and resources required to create such an inner cladding region are not required).

[0106] Specifically, the cabled cutoff of the optical fiber produced herein is about 1530 nm or less, or about 1520 nm or less, or about 1515 nm or less, or about 1510 nm or less, or about 1500 nm or less, or about 1480 nm or less, or about 1450 nm or less, or about 1420 nm or less, or about 1400 nm or less, or about 1380 nm or less, or about 1350 nm or less, or about 1320 nm or less, or about 1300 nm or less, or about 1280 nm or less, or about 1250 nm or less. Additionally or alternatively, the cabled cutoff is about 1250 nm or more, or about 1280 nm or more, or about 1300 nm or more, or about 1320 nm or more, or about 1350 nm or more, or about 1380 nm or more, or about 1400 nm or more, or about 1420 nm or more, or about 1450 nm or more. In some embodiments, the cable cutoff is from about 1300 nm to about 1530 nm, or from about 1320 nm to about 1515 nm, or from about 1350 nm to about 1500 nm, or from about 1375 nm to about 1475 nm.

[0107] As mentioned above, to improve the bend performance of the fibers disclosed herein, it is preferable to increase the cabled cutoff of fiber 10. It should also be noted that the present fibers have a relatively large effective area (discussed below), which also contributes to a longer cabled cutoff wavelength.

[0108] The optical fiber disclosed herein has an effective area of ​​approximately 100 μm at a wavelength of 1550 nm. 2 or more, or approximately 105 μm 2 or more, or about 110 μm 2 or more, or about 115 μm 2 or more, or about 120 μm 2 or more, or about 125 μm 2 or more, or about 130 μm 2 In addition to or instead of this, the effective area of ​​the present optical fiber at a wavelength of 1550 nm is about 135 μm 2 Less than or equal to 130 μm 2 Less than or equal to about 125 μm 2 Less than or equal to 120 μm 2 Less than or equal to about 115 μm 2 In an embodiment, the effective area is about 100 μm 2 ~about 135μm 2 , or about 105 μm 2 ~approx. 130 μm 2 , or about 110 μm 2 ~about 125μm 2 , or about 115 μm 2 ~about 120μm 2 In some exemplary embodiments, the effective area is about 110 μm 2 , or about 111 μm 2 , or about 112 μm 2 , or about 114 μm 2 is.

[0109] Optical fibers manufactured herein have a far-end crosstalk between adjacent cores at a wavelength of 1550 nm of less than about −35 dB or less than about −40 dB per 100 km of fiber length when the bend diameter is 140 mm. In embodiments, the far-end crosstalk between adjacent cores at a wavelength of 1550 nm is less than about −45 dB, or less than about −50 dB, or less than about −60 dB, or less than about −65 dB, or less than about −70 dB, or less than about −75 dB per 100 km of fiber length when the bend diameter is 140 mm. Additionally or alternatively, in some embodiments, the far-end crosstalk between adjacent cores at a wavelength of 1550 nm is greater than about −80 dB, or greater than about −75 dB, or greater than about −70 dB, or greater than about −65 dB, or greater than about −60 dB per 100 km of fiber length when the bend diameter is 140 mm.

[0110] The optical fiber manufactured herein has a near-end crosstalk between adjacent cores at a wavelength of 1550 nm, assuming a bend diameter of 140 mm, of less than about -70 dB per 100 km of fiber length, or less than about -69 dB, or less than about -68 dB, or less than about -67 dB, or less than about -66 dB, or less than about -65 dB, or less than about -64 dB, or less than about -63 dB, or or less than about -63 dB, or less than about -62 dB, or less than about -61 dB, or less than about -60 dB, or less than about -55 dB, or less than about -53 dB, or less than about -50 dB, or less than about -47 dB, or less than about -45 dB, or less than about -43 dB, or less than about -40 dB, or less than about -37 dB, or less than about -35 dB, or less than about -33 dB, or less than about -30 dB. Additionally or alternatively, in some embodiments, the near-end crosstalk between adjacent cores at a wavelength of 1550 nm is greater than about -100 dB, or greater than about -95 dB, or greater than about -90 dB, or greater than about -85 dB, or greater than about -80 dB per 100 km of fiber length when the bend diameter is 140 mm.

[0111] Each core 20 disclosed herein has a mode field diameter at a wavelength of 1550 nm of about 11.0 micrometers or more, or about 11.5 micrometers or more, or about 12.0 micrometers or more, or about 12.5 micrometers or more, or about 13.0 micrometers or more, or about 13.5 micrometers or more, or about 14.0 micrometers or more, or about 14.5 micrometers or more, or about 15.0 micrometers or more, while having the short cable cutoff and low crosstalk disclosed above. Additionally or alternatively, each core 20 has a mode field diameter at a wavelength of 1550 nm of about 15.0 micrometers or less, or about 14.5 micrometers or less, or about 14.0 micrometers or less, or about 13.5 micrometers or less, or about 13.0 micrometers or less, or about 12.5 micrometers or less, or about 12.0 micrometers or less, or about 11.5 micrometers or less. In some embodiments, the mode field diameter at a wavelength of 1550 nm of each core 20 is about 11.0 micrometers to about 15.0 micrometers, or about 11.5 micrometers to about 14.5 micrometers, or about 12.0 micrometers to about 14.0 micrometers, or about 12.5 micrometers to about 13.5 micrometers. In exemplary embodiments, the mode field diameter is about 11.5 micrometers, or about 12.0 micrometers, or about 12.5 micrometers, or about 13.0 micrometers.

[0112] According to an embodiment of the present disclosure, the dispersion at 1550 nm of each core 20 is less than about 22 picoseconds / nm / km. For example, the dispersion at 1550 nm is about 17 picoseconds / nm / km to about 22 picoseconds / nm / km, or about 18 picoseconds / nm / km to about 22 picoseconds / nm / km, or about 18 picoseconds / nm / km to about 21 picoseconds / nm / km, or about 19 picoseconds / nm / km to about 21 picoseconds / nm / km, or about 20 picoseconds / nm / km to about 22 picoseconds / nm / km.

[0113] The dispersion slope of each core 20 at 1550 nm is approximately 0.1 picoseconds / nm2 / km, or about 0.04 picoseconds / nm 2 / km ~ approx. 0.1 picoseconds / nm 2 / km, or approximately 0.05 picoseconds / nm 2 / km ~ approx. 0.1 picoseconds / nm 2 / km, or approximately 0.055 picoseconds / nm 2 / km ~ approx. 0.1 picoseconds / nm 2 / km, or approximately 0.06 picoseconds / nm 2 / km ~ approx. 0.1 picoseconds / nm 2 / km, or approximately 0.08 picoseconds / nm 2 / km ~ approx. 0.1 picoseconds / nm 2 / km, or approximately 0.04 picoseconds / nm 2 / km ~ approx. 0.08 picoseconds / nm 2 / km, or approximately 0.05 picoseconds / nm 2 / km ~ approx. 0.08 picoseconds / nm 2 / km, or approximately 0.055 picoseconds / nm 2 / km ~ approx. 0.08 picoseconds / nm 2 / km, or approximately 0.06 picoseconds / nm 2 / km ~ approx. 0.08 picoseconds / nm 2 / km, or approximately 0.04 picoseconds / nm 2 / km ~ approx. 0.06 picoseconds / nm 2 / km, or approximately 0.05 picoseconds / nm 2 / km ~ approx. 0.06 picoseconds / nm 2 / km, or approximately 0.055 picoseconds / nm 2 / km ~ approx. 0.06 picoseconds / nm 2 For example, the dispersion slope at 1550 nm is about 0.04 picoseconds / nm 2 / km, approximately 0.05 picoseconds / nm 2 / km, approximately 0.055 picoseconds / nm 2 / km, approximately 0.057 picoseconds / nm 2 / km, approximately 0.058 picoseconds / nm 2 / km, approximately 0.059 picoseconds / nm 2 / km, approximately 0.06 picoseconds / nm 2 / km, approximately 0.061 picoseconds / nm 2 / km, approximately 0.07 picoseconds / nm 2 / km, approximately 0.08 picoseconds / nm2 / km, or any value between these values.

[0114] The dispersion and dispersion slope at 1550 nm of the core portions 20 may be the same or different among the core portions 20 .

[0115] The average attenuation of the optical fiber disclosed in the present specification is determined by first measuring the attenuation of each core 20 of the uncoupled multi-core optical fiber 10 at a wavelength of 1550 nm, and then calculating the average attenuation of the entire uncoupled multi-core optical fiber 10 based on the individual attenuation measurements of each core 20. In an embodiment, the average attenuation of the uncoupled multi-core optical fiber 10 at a wavelength of 1550 nm is less than about 0.165 dB / km, or less than about 0.160 dB / km, or less than about 0.155 dB / km, or less than about 0.150 dB / km, or less than about 0.149 dB / km, or less than about 0.145 dB / km, or less than about 0.140 dB / km, or less than about 0.135 dB / km, or less than about 0.130 dB / km. Furthermore, the average attenuation of the uncoupled multi-core optical fiber 10 at a wavelength of 1850 nm is less than about 1.6 dB / km or less than about 1.5 dB / km (calculated in the same manner as above). It should be understood that the average attenuation of the uncoupled multi-core optical fiber 110 can be within a range defined by any one of the lower attenuation limits and any one of the upper attenuation limits described in this specification.

[0116] The individual attenuation of each core portion 20 is also measured and is found to be less than about 0.165 dB / km, or less than about 0.160 dB / km, or less than about 0.155 dB / km, or less than about 0.150 dB / km, or less than about 0.149 dB / km, or less than about 0.145 dB / km, or less than about 0.140 dB / km, or less than about 0.135 dB / km, or less than about 0.130 dB / km at a wavelength of 1550 nm. In an embodiment, the attenuation of the first core portion 20 of the uncoupled multi-core optical fiber 10 is about 0.148 dB / km, and the attenuation of the second core portion 20 of the uncoupled multi-core optical fiber 10 is about 0.147 dB / km.

[0117] Additionally, the uncoupled optical fiber disclosed herein has an average attenuation at a wavelength of 850 nm of about 1.6 dB / km or less, about 1.5 dB / km or less, or about 0.145 dB / turn or less.

[0118] The radiation loss of the core 20 at a wavelength of 1550 nm is about 0.020 dB / km or less, or about 0.010 dB / km or less, or about 0.005 dB / km or less, or about 0.003 dB / km or less.

[0119] In embodiments, the bend loss at 1625 nm of a multicore fiber of the present disclosure wrapped 100 times around a 60 mm diameter mandrel is about 0.6 dB or less, or about 0.5 dB or less, or about 0.4 dB or less.

[0120] 2 and 3, in an embodiment, each core region 20 is fabricated to provide a varying relative refractive index Δ2 in the low-index cladding region 24 with a down-dopant concentration D that varies with radial coordinate r, i.e., D=D(r). In an embodiment, the down-dopant is fluorine, and D(r) is represented by a fluorine concentration F(r) that varies with radial direction. Thus, within the low-index cladding 24, F(r) reaches a minimum value F min to maximum value F max In the embodiment, the rotational speed can be varied between F min At the radial position r2, F max In the embodiment, F max is 0.75% by mass or more and 2.2% by mass or less, or 0.9% by mass or more and 2.2% by mass or less.

[0121] The down-dopant concentration (e.g., F) in the low-index cladding 24 max and F minThe value of V2 determines the refractive index profile of the low refractive index cladding 24, and thus the trench volume V2 of the low refractive index cladding 24. Without wishing to be bound by theory, it is believed that the trench volume V2 affects the cable cutoff wavelength, effective area, dispersion, bending loss, and inter-core crosstalk of each core portion 20. When the effective area at a wavelength of 1550 nm is 100 μm 2 ~135μm 2 To achieve a cable cutoff wavelength of less than 1530 nm, a dispersion at 1550 nm of less than 22 picoseconds / nm / km, and a crosstalk at 1550 nm of less than -30 dB / 100 km, the trench volume V2 of the low refractive index cladding 24 of each core 20 must be less than 15% Δμm 2 More than 37%Δμm 2 It is desirable to do the following:

[0122] Illustrative Embodiments Exemplary embodiments of the uncoupled multi-core optical fiber disclosed herein are presented below, and are intended to be illustrative and not limiting of the scope of the present disclosure.

[0123] Table 1 below shows five modeling examples (Examples A to E) of uncoupled multi-core optical fibers having two cores arranged in a 1x2 linear arrangement. Note that the core refractive index, radius, and alpha value of these exemplary optical fibers shown in Table 1 apply to both of the two cores of each fiber. Also, the outer diameter of each optical fiber shown in Table 1 below is 125 micrometers. Furthermore, the length of the center-to-center spacing, which is the spacing between the center lines of adjacent core portions of each optical fiber shown in Table 1, was changed (i.e., the distance x was changed), and crosstalk at 1550 nm was measured. More specifically, for each optical fiber, the center-to-center spacing of adjacent core portions was changed in the range of 44 micrometers to 66 micrometers, and crosstalk at 1550 nm was measured.

[0124] [Table 1-1]

[0125] [Table 1-2]

[0126] As shown in Table 1 above, when the center-to-center spacing, which is the distance between the center lines of adjacent core portions, was set to 48 micrometers or more, the crosstalk between adjacent cores was improved overall.

[0127] An optical fiber was then manufactured based on the above modeling example A. The properties of the optical fiber manufactured in this manner are shown in Example A' in Table 2 below. An optical fiber was also manufactured based on the above modeling example E. The properties of the optical fiber manufactured in this manner are shown in Example E' in Table 2 below. The center-to-center spacing, which is the distance between the center lines of adjacent core portions, in both Examples A' and E' was 50 micrometers.

[0128] [Table 2]

[0129] As shown in Table 2 above, in both Example A' and Example E', the manufactured optical fibers have a large mode field diameter, small crosstalk, and very low attenuation.

[0130] FIG. 6A shows the refractive index profiles versus the radial coordinate r for Examples A to D. Furthermore, FIG. 7A is a graph plotting the far-end crosstalk (dB / 100 km) between cores at a wavelength of 1550 nm for Examples A to D as a function of the center-to-center spacing (micrometers) between adjacent core sections. Furthermore, FIG. 7B is a graph plotting the near-end crosstalk (dB / 100 km) between cores at a wavelength of 1550 nm for Examples A to D as a function of the center-to-center spacing (micrometers) between adjacent core sections. FIG. 8 is a graph plotting the radiation loss (dB / km) for Examples A to D as a function of the center-to-center spacing (micrometers) between adjacent core sections. Herein, radiation loss refers to the modal leakage loss that occurs due to the overlap of the high-index primary coating and the mode field strength when the cladding diameter is relatively small. The center-to-center spacing of adjacent core sections is selected so that the inter-core crosstalk at a wavelength of 1550 nm is less than -30 dB / 100 km and the radiation loss is less than 1 dB / km. Furthermore, from Figures 7A and 7B, it can be seen that the greater the center-to-center spacing between adjacent core sections, the less inter-core crosstalk there is between adjacent core sections. However, from Figure 8, it can be seen that the greater the center-to-center spacing between adjacent cores, the greater the radiation loss. Therefore, as the distance x increases, the inter-core crosstalk is reduced, but the radiation loss increases.

[0131] Example Process The uncoupled multi-core optical fiber of the present disclosure can be manufactured using any appropriate multi-core optical fiber molding method. See, for example, U.S. Pat. No. 1,137,0689, the entire contents of which are incorporated herein by reference. An exemplary method used to mold the uncoupled multi-core optical fiber 10 (or any of its alternative embodiments) described in the description of FIGS. 1 to 8 herein includes molding a glass blank for the common cladding 30. Molding the glass blank may include first forming a soot body using a known method such as outside vapor deposition (OVD), soot pressing, or vapor axial deposition (VAD), followed by dehydrating and consolidating the soot body until it becomes a fully dense glass. The soot body may be formed from a glass precursor material. In an embodiment, the soot body is formed from a silica-based material. Then, multiple holes for inserting core canes are drilled along the length of the glass blank. In some embodiments, the glass blank for the common clad is doped with a downdopant such as fluorine.

[0132] The core region of the core cane can then be formed. In some embodiments, the core region comprises at least one alkali at a concentration of 0.1% to 5% by weight. In some embodiments, the core is doped with potassium. In other embodiments, the core is doped with two alkali components selected from the group consisting of potassium, sodium, rubidium, and cesium. The core cane can be formed by the methods disclosed in U.S. Patent No. 7,536,076, the entire contents of which are incorporated herein by reference.

[0133] A cladding layer is then deposited on the core region. In an embodiment, one or more soot overcladding layers of silica-based soot are formed on the core region by an OVD or VAD process. The overcladding layer has a composition corresponding to the low-index cladding of the core portion of the multi-core optical fiber. For example, the overcladding layer may include multiple separate layers having a composition corresponding to the low-index cladding 24. The overcladded core region is then placed in a consolidation furnace to cause consolidation of the overcladded core region. For example, the overcladded core region may be heated to a peak sintering temperature to cause consolidation.

[0134] The consolidation process involves exposing the overclad core region to a downdopant for a period of time T from the start of consolidation. Upon completion of the consolidation process, a soot matrix is ​​obtained comprising a core region and an overclad layer surrounding the core region. The core region (e.g., an unconsolidated or semi-consolidated core region) and the overclad layer can be placed in a consolidation furnace. The consolidation furnace can then be heated to the peak sintering temperature of the overclad layer to induce consolidation.

[0135] A gas containing a downdopant is supplied to the furnace from a gas source in fluid communication with the interior of the integration furnace. This causes the downdopant (e.g., fluorine) to diffuse into the overclad layer during the integration process. In embodiments, the diffusion rate of the downdopant into the overclad layer depends on the compositional and material properties (e.g., porosity, density, etc.) of the overclad layer. Additionally, because the porosity of the overclad layer decreases as the overclad layer is integrated, the diffusion rate of the downdopant is also expected to decrease as the overclad layer is integrated.

[0136] In embodiments, the region of the core immediately surrounding the core corresponds to the low-index cladding 24. In some embodiments, the low-index cladding 24 has a concentration of a downdopant.

[0137] Once the core region is integrated into the glass preform, the glass preform formed in this step is inserted into a hole drilled in the glass blank. A core cane is then inserted into the glass blank, and a fiber preform is constructed by thermally sealing the gap between the inserted cane and the drilled hole. A multi-core optical fiber is then drawn from the constructed fiber preform. An exemplary method for forming a cane-based optical fiber preform is described in U.S. Pat. No. 1,137,0689, the entire contents of which are incorporated herein by reference.

[0138] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the present invention. Since those skilled in the art can conceive of variations, combinations, subcombinations, and modifications of the embodiments of the present disclosure while incorporating the intent and spirit of the present invention, the present invention should be construed as including all within the scope of the appended claims and their equivalents.

[0139] Preferred embodiments of the present invention will be described below in detail.

[0140] Embodiment 1 An uncoupled multi-core optical fiber having at least two core portions, Each core part is a core having a radius r1 and a relative refractive index Δ1 with respect to pure silica, the core being doped with at least one of sodium, potassium, and rubidium; a low-index cladding having a radius r2 and a relative refractive index Δ2 referenced to pure silica, where Δ2<Δ1, the low-index cladding directly surrounds the core, and a volume V2 of the low-index cladding of about 5.0% Δμm 2 ~approximately 37.0%Δμm 2 a low refractive index cladding, a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica, where Δ2<Δ3<Δ1, the common cladding immediately surrounding the low refractive index cladding; The cable cutoff wavelength of each core is approximately 1530 nm or less, The effective area of ​​each core at a wavelength of 1550 nm is approximately 100 μm 2 ~about 135μm 2 and The attenuation of each core at a wavelength of 1550 nm is approximately 0.165 dB / km or less, An uncoupled multi-core optical fiber in which the center-to-center spacing, which is the distance between the center lines of adjacent core portions, is approximately 48 micrometers to approximately 60 micrometers.

[0141] Embodiment 2 2. The uncoupled multi-core optical fiber according to embodiment 1, wherein far-end crosstalk between the at least two core portions is about −30 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0142] Embodiment 3 3. The uncoupled multi-core optical fiber according to embodiment 2, wherein far-end crosstalk between the at least two core portions is about −40 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0143] Embodiment 4 4. The uncoupled multi-core optical fiber according to embodiment 3, wherein far-end crosstalk between the at least two core portions is about −50 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0144] Embodiment 5 5. The uncoupled multi-core optical fiber according to embodiment 4, wherein far-end crosstalk between the at least two core portions is about −60 dB or less per 100 km of optical fiber.

[0145] Embodiment 6 6. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 5, wherein near-end crosstalk between the at least two core portions is about −35 dB or less per 100 km of optical fiber.

[0146] Embodiment 7 7. The uncoupled multi-core optical fiber according to embodiment 6, wherein near-end crosstalk between the at least two core portions is about −40 dB or less per 100 km of optical fiber.

[0147] Embodiment 8 8. The uncoupled multi-core optical fiber according to embodiment 7, wherein near-end crosstalk between the at least two core portions is about −45 dB or less per 100 km of optical fiber.

[0148] Embodiment 9 The uncoupled multi-core optical fiber according to any one of embodiments 1 to 8, wherein the at least two core portions consist of only two core portions.

[0149] Embodiment 10 10. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 9, wherein the center lines of the at least two core portions are both arranged along the axis A.

[0150] Embodiment 11 11. The uncoupled multi-core optical fiber according to embodiment 10, wherein the axis A extends through a central axis of the uncoupled multi-core optical fiber.

[0151] Embodiment 12 The effective area of ​​each core at a wavelength of 1550 nm is approximately 110 μm 2 ~approx. 130 μm 2 The uncoupled multi-core optical fiber according to any one of Embodiments 1 to 11, wherein

[0152] Embodiment 13 13. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 12, wherein the attenuation of each core portion at a wavelength of 1550 nm is about 0.160 dB / km or less.

[0153] Embodiment 14 14. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 13, wherein the attenuation of each core at a wavelength of 1550 nm is about 0.150 dB / km or less.

[0154] Embodiment 15 15. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 14, wherein the relative refractive index Δ1 is about −0.20% to about 0.20%.

[0155] Embodiment 16 16. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 15, wherein an average alkali concentration in the core is about 20 ppm to about 500 ppm.

[0156] Embodiment 17 17. The uncoupled multi-core optical fiber according to embodiment 16, wherein an average alkali concentration in the core is about 5 ppm to about 300 ppm.

[0157] Embodiment 18 18. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 17, wherein each core portion has a mode field diameter of about 11.0 micrometers to about 15.0 micrometers at a wavelength of 1550 nm.

[0158] Embodiment 19 19. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 18, wherein the cable cutoff wavelength of each core portion is about 1300 nm to about 1530 nm.

[0159] Embodiment 20 20. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 19, wherein the center-to-center spacing, which is the spacing between center lines of adjacent core portions, is about 50 micrometers to about 55 micrometers.

[0160] Embodiment 21 21. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 20, wherein the radius r3 is about 120 micrometers to about 130 micrometers.

[0161] Embodiment 22 22. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 21, wherein the radius r3 is about 125 micrometers.

[0162] Embodiment 23 23. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 22, wherein the radius r2 is about 13.0 micrometers to about 23.0 micrometers.

[0163] Embodiment 24 24. The uncoupled multi-core optical fiber according to any one of embodiments 1 to 23, wherein the radius r1 is about 3.0 micrometers to about 7.0 micrometers.

[0164] Embodiment 25 The volume V2 of the low refractive index cladding is about 15.0% Δμm 2 ~approximately 37.0%Δμm 2 The uncoupled multi-core optical fiber according to any one of Embodiments 1 to 24, wherein

[0165] Embodiment 26 The volume V2 of the low refractive index cladding is about 20.0% Δμm 2 ~approximately 30.0%Δμm 2 26. The uncoupled multi-core optical fiber according to embodiment 25,

[0166] Embodiment 27 An uncoupled multi-core optical fiber having at least two core portions, Each core portion has a core having a radius r1 and a relative refractive index Δ1 with respect to pure silica; An uncoupled multi-core optical fiber in which the attenuation of each core at a wavelength of 1550 nm is less than approximately 0.150 dB / km.

[0167] Embodiment 28 the core is doped with at least one of sodium, potassium, and rubidium; The uncoupled multi-core optical fiber is a low-index cladding having a radius r2 and a relative refractive index Δ2 referenced to pure silica, where Δ2<Δ1, the low-index cladding directly surrounds the core, and a volume V2 of the low-index cladding of about 5.0% Δμm 2 ~approximately 37.0%Δμm 2 a low refractive index cladding, a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica, where Δ2<Δ3<Δ1, the common cladding directly surrounding the low refractive index cladding; The cable cutoff wavelength of each core is approximately 1530 nm or less, The effective area of ​​each core at a wavelength of 1550 nm is approximately 100 μm 2 ~about 135μm 2 and 28. The uncoupled multi-core optical fiber according to embodiment 27, wherein a center-to-center spacing between center lines of adjacent core portions is about 48 micrometers to about 60 micrometers.

[0168] Embodiment 29 29. The uncoupled multi-core optical fiber according to embodiment 27 or 28, wherein far-end crosstalk between the at least two core portions is about −30 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0169] Embodiment 30 30. The uncoupled multi-core optical fiber according to embodiment 29, wherein far-end crosstalk between the at least two core portions is about −40 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0170] Embodiment 31 31. The uncoupled multi-core optical fiber according to embodiment 30, wherein far-end crosstalk between the at least two core portions is about −50 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

[0171] Embodiment 32 32. The uncoupled multi-core optical fiber according to embodiment 31, wherein far-end crosstalk between the at least two core portions is about −60 dB or less per 100 km of optical fiber.

[0172] Embodiment 33 33. The uncoupled multi-core optical fiber according to any one of embodiments 27 to 32, wherein near-end crosstalk between the at least two core portions is about −35 dB or less per 100 km of optical fiber.

[0173] Embodiment 34 34. The uncoupled multi-core optical fiber according to embodiment 33, wherein near-end crosstalk between the at least two core portions is about −40 dB or less per 100 km of optical fiber.

[0174] Embodiment 35 35. The uncoupled multi-core optical fiber according to embodiment 34, wherein near-end crosstalk between the at least two core portions is about −45 dB or less per 100 km of optical fiber.

[0175] Embodiment 36 The uncoupled multi-core optical fiber according to any one of embodiments 27 to 35, wherein the at least two core portions consist of only two core portions.

[0176] Embodiment 37 The uncoupled multi-core optical fiber according to any one of embodiments 27 to 36, wherein the center lines of the at least two core portions are both arranged along the axis A.

[0177] Embodiment 38 38. The uncoupled multi-core optical fiber according to embodiment 37, wherein the axis A extends through a central axis of the uncoupled multi-core optical fiber.

[0178] Embodiment 39 The uncoupled multi-core optical fiber according to any one of embodiments 27 to 38, wherein the attenuation of each core at a wavelength of 1550 nm is about 0.149 dB / km or less. [Explanation of symbols]

[0179] 10 Uncoupled multi-core optical fiber 15 Center axis 20 Core section, core area 22 cores 24 Low refractive index cladding region 30 Common Cladding 32 Outer surface 40 Primary Coating 50 Secondary Coating 60 Tertiary Coating

Claims

1. An uncoupled multi-core optical fiber having at least two core portions, Each core part is radius r １ and the relative refractive index Δ １ a core having a doped layer of at least one of sodium, potassium, and rubidium; radius r ２ and the relative refractive index Δ ２ and a low index cladding having Δ ２ <Δ １ the low-index cladding directly surrounds the core, and the volume V ２ is about 5.0% Δμm ２ ~ about 37.0% Δμm ２ a low refractive index cladding, radius r ３ and the relative refractive index Δ ３ and a common cladding having Δ ２ <Δ ３ <Δ １ a common cladding directly surrounding the low refractive index cladding; The cable cutoff wavelength of each core is approximately 1530 nm or less, The effective area of ​​each core at a wavelength of 1550 nm is approximately 100 μm ２ ~Approx. 135μm ２ and The attenuation of each core at a wavelength of 1550 nm is about 0.165 dB / km or less; An uncoupled multi-core optical fiber, wherein the center-to-center spacing, which is the distance between the center lines of adjacent core portions, is about 48 micrometers to about 60 micrometers.

2. 2. The uncoupled multi-core optical fiber according to claim 1, wherein far-end crosstalk between the at least two core portions is about −30 dB or less per 100 km of optical fiber with a bending diameter of 140 mm.

3. 2. The uncoupled multi-core optical fiber according to claim 1, wherein near-end crosstalk between the at least two core portions is about −35 dB or less per 100 km of optical fiber.

4. 4. The uncoupled multi-core optical fiber according to claim 3, wherein near-end crosstalk between the at least two core portions is about −40 dB or less per 100 km of optical fiber.

5. The uncoupled multi-core optical fiber according to any one of claims 1 to 4, wherein the at least two core portions consist of only two core portions.

6. 5. The uncoupled multi-core optical fiber according to claim 1, wherein the center lines of the at least two core portions are both arranged along an axis A.

7. The uncoupled multi-core optical fiber according to claim 6 , wherein the axis A extends through a central axis of the uncoupled multi-core optical fiber.

8. The effective area of ​​each core at a wavelength of 1550 nm is approximately 110 μm ２ ~ about 130 μm ２ The uncoupled multi-core optical fiber according to any one of claims 1 to 4, wherein

9. 5. The uncoupled multi-core optical fiber according to claim 1, wherein the attenuation of each core portion at a wavelength of 1550 nm is about 0.160 dB / km or less.

10. The relative refractive index Δ １ The uncoupled multi-core optical fiber according to any one of claims 1 to 4, wherein is about -0.20% to about 0.20%.

11. 5. The uncoupled multi-core optical fiber according to claim 1, wherein an average alkali concentration in the core is about 20 ppm to about 500 ppm.

12. 12. The uncoupled multi-core optical fiber according to claim 11, wherein an average alkali concentration in the core is about 5 ppm to about 300 ppm.

13. An uncoupled multi-core optical fiber having at least two core portions, Each core has a radius r １ and the relative refractive index Δ １ and a core having An uncoupled multi-core optical fiber, wherein each core has an attenuation at a wavelength of 1550 nm of less than about 0.150 dB / km.

14. the core is doped with at least one of sodium, potassium, and rubidium; The uncoupled multi-core optical fiber is radius r ２ and the relative refractive index Δ ２ and a low index cladding having Δ ２ <Δ １ the low-index cladding directly surrounds the core, and the volume V ２ is about 5.0% Δμm ２ ~ about 37.0% Δμm ２ a low refractive index cladding, radius r ３ and the relative refractive index Δ ３ and a common cladding having Δ ２ <Δ ３ <Δ １ and a common cladding directly surrounding the low refractive index cladding, The cable cutoff wavelength of each core is approximately 1530 nm or less, The effective area of ​​each core at a wavelength of 1550 nm is approximately 100 μm ２ ~Approx. 135μm ２ and 14. The uncoupled multi-core optical fiber according to claim 13, wherein a center-to-center spacing between centerlines of adjacent core portions is about 48 micrometers to about 60 micrometers.

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