Multi-fiber optical fiber with reduced crosstalk

Abstract

The multicore optical fiber comprises four cores arranged in a linear configuration, each core's centerline spaced from the centerline of an adjacent core by a distance x of about 30 micrometers or less, each core having a relative refractive index Δ1. A cladding surrounds each of the four cores, the cladding including an inner cladding region having a relative refractive index Δ2, a depressed-index cladding region having a relative refractive index Δ3, and an outer cladding region having a relative refractive index Δ4, where Δ1 > Δ2 > Δ3 and Δ1 > Δ4 > Δ3. Furthermore, each of the four cores has a mode field diameter of about 8.1 micrometers or less at a wavelength of 1310 nm, and crosstalk between adjacent cores is about -18 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

Description

Priority

[0001] This application claims the benefit of priority under 35 U.S.C. §120 of U.S. Provisional Patent Application No. 63 / 399,420, filed August 19, 2022, the contents of which are relied upon and incorporated herein by reference in its entirety. [Technical Field]

[0002] This disclosure relates to optical fibers, and more particularly to optical fibers having single-mode operation at both 1310 nm and 1550 nm wavelengths while having reduced crosstalk between adjacent cores. [Background technology]

[0003] Multi-fiber optical fibers have multiple cores embedded in a cladding matrix. Therefore, fiber density is increased, making multi-fiber useful in overcoming cable size limitations and duct congestion issues in passive optical network ("PON") systems. The use of multi-fiber optical fibers is also beneficial in high-speed optical interconnects, where increased fiber density is necessary to realize compact, high-fiber-count connectors. To have sufficiently high performance, multi-fiber optical fibers must have low crosstalk, low dispersion, and a large mode-field diameter compatible with standard single-mode fiber. By matching the mode-field diameter to that of standard single-mode fiber, multi-fiber optical fibers can be easily inserted into existing cable systems. Summary of the Invention

[0004] The multicore fiber disclosed herein can achieve the beneficial characteristics of low crosstalk between adjacent cores, low dispersion, and a sufficiently large mode field diameter. Therefore, the multicore fiber disclosed herein is highly useful in high-speed optical interconnects (as well as other telecommunications systems). The unique combination of offset trenches combined with the core spacing between adjacent cores provides such beneficial characteristics. Furthermore, the optical fiber disclosed herein has a low cable cutoff such that the fiber is single-mode in both the O-band (1260 nm to 1360 nm) and C-band (1530 nm to 1565 nm) frequency ranges, while also achieving good crosstalk and attenuation performance at O-band and C-band wavelengths. Therefore, the optical fiber is single-mode at both 1310 nm and 1550 nm operation, allowing the optical fiber to be used in telecommunications sources operating at these wavelengths without signal distortion from modal dispersion.

[0005] In aspects, the present disclosure includes a multicore optical fiber having four cores arranged in a linear configuration such that the centerline of each core is aligned along an axis A, where the centerline of each core is spaced from the centerline of an adjacent core by a distance x of about 30 micrometers or less, and each core has a relative refractive index Δ1. A cladding surrounds each of the four cores, the cladding having an inner cladding region having a relative refractive index Δ2, an inner cladding region having a relative refractive index Δ3, and a 20% Δμm cladding region having a relative refractive index Δ4. 2 and an outer cladding region having a relative refractive index Δ4, where Δ1 > Δ2 > Δ3 and Δ1 > Δ4 > Δ3. Further, the multi-core optical fiber has an outer diameter of about 125 micrometers or less, each of the four cores has a mode field diameter of about 8.1 micrometers or less at a wavelength of 1310 nm, each of the four cores has a cable cutoff of about 1260 nm or less, and crosstalk between adjacent cores of the four cores is about -18 dB or less at wavelengths of 1310 nm and 1550 nm per 2 km of fiber length.

[0006] Additional features and advantages will be set forth in the detailed description which follows, and in part will become readily apparent to those skilled in the art from that description, or may be learned by practicing the embodiments as set forth in the written description and claims thereof, as well as the accompanying drawings.

[0007] 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 character of the claims.

[0008] The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate selected aspects of the present disclosure and, together with the description, serve to explain the principles and operation of methods, products, and compositions encompassed by the present disclosure. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a cross section of an optical fiber having multiple cores, according to an embodiment of the present disclosure; [Figure 2] 1 is a schematic diagram of an enlarged cross section of a single optical fiber according to an embodiment of the present disclosure; [Figure 3] 1 is a graph illustrating the relative refractive index profile of an optical fiber according to an embodiment of the present disclosure. [Figure 4] 1 is a schematic diagram of a cross section of an optical fiber having an outer coating according to an embodiment of the present disclosure; [Figure 5] 1 is another schematic diagram of a cross section of an optical fiber according to an embodiment of the present disclosure. [Figure 6] 1 is a schematic diagram of a cross section of an optical fiber with markers according to an embodiment of the present disclosure; [Figure 7] 1 is a schematic diagram of a cross section of an optical fiber with markers according to an embodiment of the present disclosure; DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure is provided as an enabling teaching and may be more readily understood by reference to the following description, drawings, examples, and claims. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made in various aspects of the embodiments described herein while still obtaining beneficial results. It will also be apparent that some of the desired advantages of the embodiments can be obtained by selecting some of the features without utilizing other features. Accordingly, those skilled in the art will recognize that many modifications and adaptations are possible and may even be desirable in particular circumstances and are a part of this disclosure. Accordingly, it is to be understood that the present disclosure is not limited to the specific compositions, articles, devices, and methods disclosed, unless otherwise specified. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0011] In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings.

[0012] An "optical fiber" is a waveguide having a glass portion surrounded by a cladding, the glass portion comprising a core and a cladding, and is referred to herein as a "glass fiber."

[0013] "Radial position," "radius," or radial coordinate "r" refers to the radial position relative to the centerline of the fiber (r=0).

[0014] "Refractive index" refers to the refractive index at a wavelength of 1550 nm unless otherwise specified.

[0015] A "refractive index profile" is the relationship between refractive index or relative refractive index and radius. For relative refractive index profiles depicted herein as having step boundaries between adjacent core and / or cladding regions, normal variations in processing conditions may result in less than sharp step boundaries at the interfaces of the adjacent regions. While the boundaries of the refractive index profile may be expressed herein as step changes in refractive index, it will be understood that actual boundaries may be rounded or otherwise deviate from a perfect step function characteristic. It will further be understood that the value of the relative refractive index may vary with radial position in either the core and / or cladding regions. When the relative refractive index varies with radial position within a particular region of the fiber (e.g., either the core and / or cladding regions), it will be expressed in terms of its actual or approximate functional dependence, or its value at a specific location within the region, or 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 the cladding region) is expressed as a single value or as a parameter (e.g., Δ or Δ%) that applies to the entire region, it is understood that the relative refractive index within that region is constant, or nearly constant, and corresponds to the single value, or that the single value or parameter represents an average value of the non-constant dependence of the relative refractive index with radial position within that region. For example, if "i" is a region of a glass fiber, then the parameter Δ i Unless otherwise specified, refers to the average value of the relative refractive index within a region as defined below. Whether by design or as a result of normal manufacturing variations, the dependence of the relative refractive index on radial position may be sloped, curved, or otherwise non-constant.

[0016] As used herein, "relative refractive index" means

[0017]

number

[0018] where n iis the radial position r of the glass fiber unless otherwise specified. i is the refractive index at ref is the refractive index of pure silica glass, unless otherwise specified. Thus, as used herein, relative refractive index percentages are relative to pure silica glass, which has a value of 1.444 at a wavelength of 1550 nm. As used herein, relative refractive index is expressed as Δ (or "delta") or Δ% (or "delta%"), and its value is given in units of "%" unless otherwise specified. Relative refractive index is also sometimes expressed as Δ(r) or Δ(r)%.

[0019] The average relative refractive index (Δ 平均 ) is expressed as:

[0020]

number

[0021] where r 内側 is the inner radius of the region, and r 外側 is the outer radius of the region and Δ(r) is the relative refractive index of the region.

[0022] 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 relative to a reference index, n(r)-n meas , where the metric refractive index n measis typically a calibration 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. The absolute refractive index, n(r), is then used to calculate the relative refractive index as defined above.

[0023] The term "α-profile" or "alpha profile" refers to the following formula:

[0024]

number

[0025] where r is the radial position at which Δ(r) is a maximum, and Δ(r)>0, r z >r0 is the radial position where Δ(r) decreases to a minimum, and r is the radial position where r i ≦r≦r f 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 defined herein as Δ max , or if a specific region i of the fiber is mentioned, Δ imax The relative refractive index profile of the core region of the fiber is such that r occurs at the centerline (r = 0) and r z corresponds to the outer radius r1 of the core region and is described by an α-profile with Δ1(r1)=0, the above equation becomes

[0026]

number

[0027] is simplified to

[0028] When the core region has a refractive index expressed by the above formula, the outer radius r1 can be determined from the measured relative refractive index profile by the following procedure: max , α, and outer radius r 1est An estimate of is obtained by examining the measured relative refractive index profile, r=rr 1est and r = r 1est Test function Δ trial The relative refractive index profile of a representative glass fiber having a core represented by an α-profile according to an embodiment of the present disclosure is shown in FIG.

[0029] "Trench Volume" is:

[0030]

number

[0031] where r トレンチ、内側 is the inner radius of the trench region of the refractive index profile, and r トレンチ、外側 is the outer radius of the trench region of the refractive index profile, and Δ 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, has a positive value, and is %Δ micrometers. 2 , %Δ-micrometers 2 , %Δ-μm 2 or %Δμm 2 and whereby these units can be used interchangeably herein. The trench region is also referred to herein as the depressed-index cladding region, and the trench volume is also referred to as V3, V4, or V5.

[0032] The "mode field diameter" or "MFD" of an optical fiber is:

[0033]

number

[0034] where 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 herein for wavelengths of 1310 nm, 1550 nm, and 1625 nm. When referring to the mode field diameter herein, the wavelength-specific application is made. Unless otherwise specified, the mode field diameter is the LP at a particular wavelength. 01 It is called a mode.

[0035] The "effective area" of an optical fiber is:

[0036]

number

[0037] 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. eff " depends on the wavelength of the optical signal and is understood herein to refer to a wavelength of 1550 nm.

[0038] As used herein, the term "attenuation" is the loss of optical power as a signal propagates along an optical fiber. Attenuation was measured as specified in the IEC-60793-1-40 standard, "Attenuation measurement methods."

[0039] As used herein, "cable cut-off wavelength" or "cable cut-off" refers to the 22 meter cable cut-off test as specified in the IEC 60793-1-44 standard, "Measurement methods and test procedures - Cut-off wavelength."

[0040] The optical fiber disclosed herein comprises multiple core regions, cladding regions surrounding the core regions, and a coating surrounding the cladding regions. The core and cladding regions are glass. The cladding region includes multiple regions, which are preferably concentric. The cladding regions include at least an inner cladding region, a depressed-index cladding region, and an outer cladding region. The inner cladding region surrounds and is directly adjacent to the core region. The depressed-index cladding region surrounds and is directly adjacent to the inner cladding region such that the inner cladding region is radially disposed between the core region and the depressed-index cladding region. The outer cladding region surrounds and is directly adjacent to the depressed-index cladding region such that the inner cladding region is radially disposed between the inner and outer cladding regions.

[0041] The depressed-index cladding region has a lower relative refractive index than each of the inner and outer cladding regions. 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. The depressed-index cladding region is sometimes referred to herein as a trench or trench region. Additionally, as further described below, the depressed-index cladding region and the inner cladding region contribute to reducing crosstalk between adjacent cores.

[0042] As used herein, radial location r1 and relative refractive index Δ1 or Δ1(r) refer to the core region, radial location r2 and relative refractive index Δ2 or Δ2(r) refer to the inner cladding region, radial location r3 and relative refractive index Δ3 or Δ3(r) refer to the depressed-index cladding region, and radial location r4 and relative refractive index Δ4 or Δ4(r) refer to the outer cladding region. Additionally, radial location r5 (not shown) refers to the primary coating, radial location r6 (not shown) refers to the secondary coating, and radial location r7 (not shown) refers to the optional tertiary coating.

[0043] The relative refractive index Δ1(r) is the maximum value Δ1max and the minimum value Δ 1min The relative refractive index Δ2(r) has a maximum value Δ 2max and the minimum value Δ 2min The relative refractive index Δ3(r) has a maximum value Δ 3max and the minimum value Δ 3min The relative refractive index Δ4(r) has a maximum value Δ 4max and the minimum value Δ 4min In embodiments where the relative refractive index is constant or nearly constant over a region, the maximum and minimum values of the relative refractive index are equal or nearly equal. Unless otherwise specified, when a single value is reported for the relative refractive index over a region, that single value corresponds to the average value for that region.

[0044] It will be understood that the central core region is substantially cylindrical in shape, and that the surrounding inner cladding region, depressed-index cladding region, outer cladding region, primary coating, and secondary coating are substantially annular in shape. The annular regions can be characterized by inner and outer radii. Radial positions r1, r2, r3, r4, r5, r6, and r7 refer herein to the outermost radii of the core region, inner cladding region, depressed-index cladding region, outer cladding region, 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. When a tertiary coating is present, radius r7 corresponds to the outer radius of the optical fiber.

[0045] The difference between radial position r2 and radial position r1 is the thickness of the inner cladding region. The difference between radial position r3 and radial position r2 is the thickness of the depressed-index cladding region. The difference between radial position r4 and radial position r3 is the thickness of the outer cladding region. The difference between radial position r5 and radial position r4 is the thickness of the primary coating. The difference between radial position r6 and radial position r5 is the thickness of the secondary coating.

[0046] Referring to FIG. 1 , embodiments of the present disclosure relate to a multicore optical fiber 10 including multiple cores 20 surrounded by a cladding 30. As described further below, an outer coating may surround the cladding 30. The cladding 30 may also be referred to herein as a "glass matrix." The outer diameter of the 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, or about 90 micrometers or less, or about 80 micrometers or less. In embodiments, the outer diameter of the cladding 30 ranges from about 80 micrometers to about 180 micrometers, or from about 90 micrometers to about 160 micrometers, or from about 100 micrometers to about 150 micrometers, or from about 125 micrometers to about 150 micrometers. The outer diameter of the cladding 30 may be the outer diameter of the optical fiber 10 (without any additional coating layers disposed on the cladding 30). 1, the cross section of cladding 30 is circular, however, it is contemplated that cladding 30 may have other cross-sectional shapes.

[0047] Each of the cores 20 is a glass core. The optical fiber 10 can include a plurality of cores 20, such as, for example, two or more, or four or more, or six or more, or eight or more, or ten or more, or twelve or more cores. The cores can be arranged in various arrangements, including linear and square arrangements. In some embodiments, at least two of the plurality of cores are arranged such that their centerlines are positioned along the same axis. In yet some other embodiments, at least two of the plurality of cores are arranged such that their centerlines are positioned along the same axis, and the centerline of the optical fiber 10 is also positioned along the same axis. The centerline CL of each core C defines the radial position r=0 of the core, and the center line CL of the optical fiber 10 F defines the radial position of the fiber r=0.

[0048] In the embodiment of FIG. 1, the cores 20 are arranged in a 1×4 linear configuration such that all four cores are arranged in a single row along the same axis A. More specifically, in the embodiment of FIG. 1, the cores 20 are all aligned along the centerline CL of each core. C is positioned along the axis A, and the centerline CL of the optical fiber 10 F The optical fiber 10 is also arranged so that the center line CL of the optical fiber 10 is also positioned on the axis A. F is the center line CL of the core 20 C Such a 1x4 linear arrangement is beneficial because it allows optical fiber 10 to be directly coupled to a transmitting source and a receiving source without the need for logical input and output devices. However, it should be noted that cores 20 may be arranged in other configurations and patterns. For example, in other embodiments, cores 20 may be arranged in a 2x2 square arrangement. In yet other embodiments, optical fiber 10 may comprise six cores arranged in a 1x6 linear arrangement.

[0049] In some other embodiments, the optical fiber 10 comprises four cores 20 arranged in a 1x4 configuration. However, in this embodiment, the centerline CL of at least one core is C is positioned along the axis A, while the centerline CL of at least one other core C are not positioned along axis A. Thus, in this embodiment, at least one core is slightly offset from another core.

[0050] Each core 20 has a higher refractive index than the cladding 30 so that the optical fiber 10 functions as a waveguide. In one embodiment, the cores 20 and cladding 30 are configured so that light guidance within the optical fiber 10 is single-mode at the operating wavelength (i.e., the cutoff wavelength of each core is lower than the operating wavelength), which in one embodiment are 1310 nm and 1550 nm. In other embodiments, at least some of the cores 20 may be configured to support multiple guided modes at the operating wavelength.

[0051] In some embodiments, each of the cores 20 has no discernible boundary with the cladding 30. Alternatively, there is a clear boundary between the cores 20 and the cladding 30.

[0052] As shown in Figure 2, the cladding 30 can comprise an inner cladding region 32, a depressed-index cladding region 34, and an outer cladding region 36 surrounding each core 20. Although Figure 2 shows only one core 20, it is contemplated that each core 20 in the optical fiber 10 can be surrounded by the same cladding regions 32, 34, 36. And, as described further below, the outer cladding region 36 can be a common cladding surrounding all of the cores.

[0053] 3 is a plot of an ideal relative refractive index profile of optical fiber 10 as relative refractive index Δ versus radial coordinate r, according to an embodiment of the present disclosure. Core 20 has Δ=Δ at r=0. 1MAX The inner cladding region 32 has a relative refractive index Δ1 and a radius r2. The depressed-index cladding region 34, which may be in the form of a depressed region or trench, has a radius r3 and a relative refractive index Δ3. The outer cladding region 36 has a radius r4 and a relative refractive index Δ4. Furthermore, as shown by way of example, Δ3<Δ2 and Δ3<Δ4. Other configurations of relative refractive index profiles are discussed further below.

[0054] core The core 20 is made from silica glass, which may be undoped, updoped, and / or downdoped. Updoped silica glass includes, for example, silica glass doped with germanium (e.g., GeO), phosphorus (e.g., P2O5), aluminum (e.g., Al2O3), chlorine, or alkali metal oxides (e.g., Na2O, KO, Li2O, Cs2O, or Rb2O). In some embodiments, the core is made from germanium-doped glass having a germanium concentration between about 5% and about 10% by weight. In embodiments in which the core is doped with an alkali dopant, the peak alkali concentration in the silica glass may range from about 10 ppm to about 500 ppm, or from about 30 ppm to about 400 ppm. In still other embodiments, the silica glass of the core 20 is free of germanium and / or chlorine, i.e., the core region is made from silica glass free of germanium and / or chlorine.

[0055] Down-doped silica glass includes, for example, silica glass doped with fluorine or boron.

[0056] As previously mentioned, the relative refractive index of each core 20 is described by an α-profile having an α value in 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 some other embodiments, the α value 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 α value of the core is about 10, or about 12, or about 20.

[0057] The outer radius r1 of the core 20 is in the range of about 2.5 micrometers to about 7.0 micrometers, or about 3.0 micrometers to about 6.5 micrometers, or about 3.5 micrometers to about 5.0 micrometers, or about 4.0 micrometers to about 4.5 micrometers, or about 3.0 micrometers to about 3.5 micrometers. In some embodiments, the outer radius r1 is about 3.0 micrometers, or about 3.2 micrometers, or about 3.3 micrometers, or about 3.6 micrometers, or about 4.0 micrometers, or about 4.2 micrometers, or about 4.4 micrometers.

[0058] Maximum relative refractive index of core 20 Δ 1max is in the range of about 0.80% or less, or about 0.75% or less, or about 0.70% or less, or about 0.65% or less, or about 0.60% or less, or about 0.55% or less, or about 0.50% or less, or about 0.45% or less, or about 0.40% or less, or about 0.35% or less, or about 0.30% or less, or about 0.25% or less. 1max is about 0.20% or more, or about 0.25% or more, or about 0.30% or more, or about 0.35% or more, or about 0.40% or more, or about 0.45% or more, or about 0.50% or more, or about 0.55% or more, or about 0.60% or more, or about 0.65% or more, or about 0.70% or more, or about 0.75% or more. In some embodiments, the maximum relative refractive index Δ of core 20 1max is about 0.35%, or about 0.40%, or about 0.52%, or about 0.57%, or about 0.60%, or about 0.65%, or about 0.70%.

[0059] Although not shown in FIG. 3, in some embodiments, the relative refractive index of core 20 may have a centerline dip such that the maximum refractive index of core 20, and therefore of the entire optical fiber 10, is located a short distance away from the centerline of core 20, rather than at the centerline of core 20 as shown in FIG.

[0060] It should be noted that one or more cores 20 in optical fiber 10 may be different from one or more other cores 20. For example, one or more cores 20 may have a different refractive index profile and / or radius than one or more other cores 20. Furthermore, Figures 1 and 2 depict cores 20 as having a circular cross-sectional shape. However, one or more cores 20 may have other cross-sectional shapes, such as elliptical, rectangular, square, or D-shaped.

[0061] Inner cladding region The inner cladding region 32 may be made of undoped silica glass. In some other embodiments, the inner cladding region 32 is updoped or downdoped. The inner radius of the inner cladding region 32 is r1, as previously described. The outer radius r2 of the inner cladding region 32 ranges from about 6.0 micrometers to about 14.0 micrometers, or from about 6.5 micrometers to about 13.5 micrometers, or from about 7.0 micrometers to about 13.0 micrometers, or from about 7.5 micrometers to about 12.5 micrometers, or from about 8.0 micrometers to about 12.0 micrometers. In some embodiments, the outer radius r2 is about 7.14 micrometers, or about 7.46 micrometers, or about 8.0 micrometers, or about 8.5 micrometers, or about 8.8 micrometers, or about 9.14 micrometers, or about 10.2 micrometers, or about 10.56 micrometers.

[0062] The relative refractive index Δ2 of the inner cladding region 32 is in the range of about −0.20% to about 0.20%, or about −0.15% to about 0.15%, or about −0.10% to about 0.10%, or about −0.05% to about 0.05%. In some embodiments, the relative refractive index Δ2 is about 0.0%. It is preferred that the relative refractive index Δ2 be constant or nearly constant.

[0063] The inner cladding region 32 helps to confine light within each core 20 as it is transmitted along the optical fiber 10 , and therefore reduces crosstalk between adjacent cores 20 .

[0064] Depressed-index cladding region The depressed-index cladding region 34 is made of down-doped silica glass, and in some embodiments, the depressed-index cladding region 34 is down-doped with fluorine or boron.

[0065] The inner radius of the depressed-index cladding region 34 is r2, as previously described. The outer radius r3 of the depressed-index cladding region 34 ranges from about 8.0 micrometers to about 20.0 micrometers, or from about 10.0 micrometers to about 19.0 micrometers, or from about 12.0 micrometers to about 18.0 micrometers. In some embodiments, the outer radius r3 is about 10.2 micrometers, or about 12.0 micrometers, or about 12.3 micrometers, or about 13.0 micrometers, or about 13.1 micrometers.

[0066] In some embodiments, depressed-index cladding region 34 is a depressed-index cladding region that forms a trench design. The "volume" V3 of depressed-index cladding region 34 is

[0067]

number

[0068] where Δ 3-4 =(Δ3(r)-Δ4).

[0069] The trench volume V3 of the depressed-index cladding region 34 is approximately 20.0%Δ-micrometers 2 or more, or approximately 25.0%Δ-micrometers 2 or more, or approximately 30.0%Δ-micrometers2 or greater than or equal to approximately 35.0%Δ-micrometers 2 or more, or approximately 40.0%Δ-micrometers 2 or greater than or equal to approximately 45.0%Δ-micrometers 2 or more, or approximately 50.0%Δ-micrometers 2 or greater than or equal to approximately 55.0%Δ-micrometers 2 or more, or approximately 60.0%Δ-micrometers 2 In an embodiment, the depressed-index cladding region 34 has a trench volume V3 of about 20.0%Δ-micrometers. 2 to approximately 80.0%Δ-micrometers 2 , or approximately 30.0%Δ-micrometers 2 to approximately 70.0%Δ-micrometers 2 , or approximately 35.0%Δ-micrometers 2 to approximately 65.0%Δ-micrometers 2 , or approximately 40.0%Δ-micrometers 2 to approximately 60.0%Δ-micrometers 2 In some embodiments, the trench volume V3 is about 50.9%Δ-micrometers 2 , or approximately 51.0%Δ-micrometers 2 , or approximately 53.3%Δ-micrometers 2 , or approximately 56.13%Δ-micrometers 2 , or approximately 57.0%Δ-micrometers 2 , or approximately 62.1%Δ-micrometers 2 is.

[0070] The transition regions from the inner cladding region 32 to the depressed-index cladding region 34 and from the depressed-index cladding region 34 to the outer cladding region 36 are shown as step changes in Figure 3. However, it should be understood that such step changes are idealized and that in practice the transition regions may not be strictly vertical. Instead, the transition regions may have a slope or curvature.

[0071] outer cladding region The outer cladding region 36 may be made of undoped silica glass. In some other embodiments, the outer cladding region 36 is updoped or downdoped. The inner radius of the outer cladding region 36 is r3, as previously described. The outer radius r4 of the outer cladding region 36 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 r4 of the outer cladding region 36 is about 62.5 micrometers.

[0072] The relative refractive index Δ4 of the outer cladding region 36 is in the range of about −0.20% to about 0.20%, or about −0.15% to about 0.15%, or about −0.10% to about 0.10%, or about −0.05% to about 0.05%. In some embodiments, the relative refractive index Δ4 is about 0.0%. It is preferred that the relative refractive index Δ4 be constant or nearly constant. Furthermore, in some embodiments, the relative refractive index Δ4 is equal to or substantially equal to the relative refractive index Δ2.

[0073] As previously mentioned, the outer cladding region 36 may be an outer cladding common to all of the cores 20 in the optical fiber 10. Thus, the outer cladding region 36 may surround each core 20 within the optical fiber 10.

[0074] Outer coating One or more coatings can be disposed on the exterior surface of cladding 30. For example, as shown in Figure 4, in some embodiments, primary coating 40 immediately surrounds cladding 30 and secondary coating 50 immediately surrounds primary coating 40. Primary coating 40 can be made from a low modulus material and secondary coating 50 can be made from a high modulus material. One or more of these materials can be, for example, an acrylate.

[0075] The optical fiber 10 may further include a tertiary coating 60 surrounding the secondary coating 50. The tertiary coating 60 may include a pigment, ink, or other colorant to mark the optical fiber for identification purposes, and the tertiary coating typically has a Young's modulus similar to that of the secondary coating 50.

[0076] The outer diameter of the secondary coating 50 is the outer diameter of the optical fiber 10 if no tertiary layer is applied. 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.

[0077] Core Spacing As shown in Figure 5, adjacent cores 20 are spaced apart from one another by a distance x. More specifically, the centerline CL of the first core C is the center line CL of the adjacent second core C 5, the cores 20a-d are spaced apart by a distance x from the center line CL of the cores 20a-d. Thus, the distance x is the center-to-center distance between adjacent cores. In the embodiment of FIG. C Each of the adjacent cores is aligned with the center line CL CThe cores are arranged in a 1x4 linear arrangement a distance x from each other. In embodiments, the distance x is about 35 micrometers or less, or about 30 micrometers or less, or about 29 micrometers or less, or about 28 micrometers or less, or about 27 micrometers or less, or about 26 micrometers or less, or about 25 micrometers or less, or about 24 micrometers or less, or about 22 micrometers or less, or about 20 micrometers or less. In embodiments, the distance x is in the range of about 15 micrometers to about 35 micrometers, or about 20 micrometers to about 30 micrometers, or about 22 micrometers to about 28 micrometers, or about 24 micrometers to about 26 micrometers, or about 24 micrometers to about 30 micrometers. In some embodiments, the distance x is about 24 micrometers, or about 26 micrometers, or about 27 micrometers. It is also contemplated that the first set of cores may be spaced a different distance from the second set of cores. For example, referring to FIG. 5, cores 20a and 20b may be spaced apart by a first distance (distance x-1) and cores 20b and 20c may be spaced apart by a second distance (distance x-2) such that the first distance is not equal to the second distance (x-1 ≠ x-2).

[0078] As shown in FIG. 5, the center line CL of the outermost core 20 C The distance y can be defined as the minimum distance between the center line CL of the outermost cores 20a and 20d and the outer diameter of the cladding 30. Therefore, in the example of FIG. Cis spaced a minimum distance y from the outer diameter of the cladding 30. In embodiments, the distance y ranges from about 15 micrometers to about 30 micrometers, or from about 20 micrometers to about 28 micrometers, or from about 22 micrometers to about 26 micrometers, or from about 20 micrometers to about 25 micrometers, or from about 22 micrometers to about 24 micrometers. In some embodiments, the distance y is about 23.5 micrometers, or about 24 micrometers, or about 24.5 micrometers, or about 25 micrometers. It is also contemplated that the first core may be spaced a different distance from the outer diameter of the cladding 30 than the second core. For example, referring to FIG. 5, core 20a may be spaced a first distance (distance y-1) from the outer diameter of cladding 30, and core 20d may be spaced a second distance (distance y-2) from the outer diameter of cladding 30, such that the first distance is not equal to the second distance (y-1 ≠ y-2).

[0079] marker As shown in FIG. 6 , for example, a marker 70 can be placed within the cladding 30 to mark one or more cores 20. For example, the marker 70 can be used to identify the relative position of a “first core” within the optical fiber 10. Other cores can then be identified based on their relative positions to the “first core.” Thus, in embodiments, the marker 70 is placed within the cladding 30 in a position that clearly identifies the “first core.” Note that the first end of the optical fiber is a mirror image of the second end of the optical fiber. Placing the marker 70 on the centerline of the optical fiber may not be useful for distinguishing between different cores. More specifically, with reference to FIG. 6 , placing the marker 70 on the centerline of the optical fiber 10 between the central two cores is not useful for distinguishing between these two cores because the core located to the right of the middle is located to the left of the middle at the opposite end of the fiber. Thus, in embodiments, the marker 70 is placed on the centerline CL of the optical fiber 10. F is not placed in

[0080] In the embodiment of FIG. 6, the marker 70 is positioned between the centerlines CL of two adjacent cores 20, such that at least one of these adjacent cores is an outer core. C 6 and 7 are not located on the axis of symmetry of fiber 10. Marker 70 can be made from doped silica glass such that marker 70 has a relative refractive index Δ5 that is not equal to that of cladding 30 (Δ5 ≠ Δ4). In some embodiments, the silica glass of marker 70 is doped with a downdopant such that marker 70 forms a trench region in cladding 30. In other embodiments, marker 70 is updoped, for example, with germanium.

[0081] nature Without intending to be limited by theory, the staggered trenches in the depressed-index cladding region 34, in combination with the core spacing distance between adjacent cores, result in lower cable cutoff and reduced crosstalk. Accordingly, the optical fiber disclosed herein provides single-mode operation in both the O-band (1260 nm to 1360 nm) and C-band (1530 nm to 1565 nm) frequency ranges. The optical fiber produced herein is therefore single-mode for both 1310 nm and 1550 nm operation, allowing the optical fiber to be used in telecommunications sources operating at these wavelengths without signal distortion from modal dispersion.

[0082] Specifically, the cabled cutoff of the optical fiber produced herein is about 1300 nm or less, or about 1260 nm or less, or about 1250 nm or less, or about 1240 nm or less, or about 1230 nm or less, or about 1220 nm or less, or about 1210 nm or less, or about 1205 nm or less, or about 1200 nm or less, or about 1195 nm or less, or about 1190 nm or less, or about 1185 nm or less, or about 1180 nm or less, or about 1175 nm or less, or about 1170 nm or less. For example, the cabled cutoff is about 1189 nm, or about 1216 nm, or about 1219 nm, or about 1221 nm, or about 1228 nm, or about 1232 nm.

[0083] The optical fiber produced herein has a crosstalk between adjacent cores at 1310 nm of less than about −35 dB per 2 km of fiber. In embodiments, the crosstalk between adjacent cores at 1310 nm is less than about −40 dB, or 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 2 km of fiber. Additionally or alternatively, in some embodiments, the crosstalk between adjacent cores at 1310 nm is greater than −80 dB per 2 km of fiber.

[0084] The optical fiber produced herein has a crosstalk between adjacent cores at 1550 nm of less than about −15 dB per 2 km of fiber. In embodiments, the crosstalk between adjacent cores at 1550 nm is less than about −20 dB, or less than about −25 dB, or less than about −30 dB, or less than about −35 dB, or less than about −40 dB, or less than about −45 dB per 2 km of fiber. Additionally or alternatively, in some embodiments, the crosstalk between adjacent cores at 1550 nm is greater than about −50 dB per 2 km of fiber.

[0085] Thus, the optical fiber produced herein has low cable cutoff and low crosstalk at both 1310 nm and 1550 nm, hi some embodiments, the crosstalk between adjacent cores in the optical fiber produced herein is less than about -10 dB per 2 km length of fiber at both 1310 nm and 1550 nm wavelengths. In still other embodiments, the crosstalk between adjacent cores is about −15 dB or less, or about −18 dB or less, or about −20 dB or less, or about −22 dB or less, or about −24 dB or less, or about −25 dB or less, or about −28 dB or less, or about −30 dB or less, or about −32 dB or less, or about −34 dB or less, or about −35 dB or less, or about −38 dB or less, or about −40 dB or less, or about −42 dB or less, or about −44 dB or less, or about −45 dB or less, or about −48 dB or less, or about −50 dB or less, or about −52 dB or less, or about −54 dB or less, or about −55 dB or less, or about −58 dB or less, or about −60 dB or less, per 2 km length of fiber, at both wavelengths of 1310 nm and 1550 nm.

[0086] In addition to the low cable cutoff and low crosstalk disclosed above, each core 20 disclosed herein has a mode field diameter at a wavelength of 1310 nm of about 6.0 micrometers or greater, or about 6.2 micrometers or greater, or about 6.4 micrometers or greater, or about 6.5 micrometers or greater, or about 6.6 micrometers or greater, or about 6.8 micrometers or greater, or about 7.0 micrometers or greater, or about 7.25 micrometers or greater, or about 7.5 micrometers or greater, or about 7.75 micrometers or greater, or about 8.0 micrometers or greater. Additionally or alternatively, each core 20 has a mode field diameter at a wavelength of 1310 nm of about 9.0 micrometers or less, or about 8.5 micrometers or less, or about 8.4 micrometers or less, or 8.2 micrometers or less, or about 8.1 micrometers or less, or about 8.0 micrometers or less, or about 7.8 micrometers or less, or about 7.6 micrometers or less, or about 7.4 micrometers or less, or about 7.2 micrometers or less, or about 7.0 micrometers or less. In some embodiments, the mode field diameter at a wavelength of 1310 nm is in the range of about 5.0 micrometers to about 9.0 micrometers, or about 5.0 micrometers to about 8.4 micrometers, or about 5.0 micrometers to about 8.2 micrometers, or about 8.0 micrometers to about 8.0 micrometers, or about 5.0 micrometers to about 7.8 micrometers, or about 6.2 micrometers to about 7.75 micrometers.

[0087] Each of the cores 20 disclosed herein has a mode field diameter at a wavelength of 1550 nm of about 6.0 micrometers or greater, or about 6.25 micrometers or greater, or about 6.5 micrometers or greater, or about 6.75 micrometers or greater, or about 7.0 micrometers or greater, or about 7.25 micrometers or greater, or about 7.5 micrometers or greater, or about 7.75 micrometers or greater, or about 8.0 micrometers or greater, or about 8.25 micrometers or greater, or about 8.5 micrometers or greater, or about 8.75 micrometers or greater, or about 9.0 micrometers or greater. Additionally or alternatively, each core 20 has a mode field diameter at a wavelength of 1550 nm of about 9.75 micrometers or less, or about 9.5 micrometers or less, or about 9.4 micrometers or less, or about 9.2 micrometers or less, or about 9.0 micrometers or less, or about 8.8 micrometers or less, or about 8.75 micrometers or less, or about 8.6 micrometers or less, or about 8.5 micrometers or less, or about 8.4 micrometers or less, or about 8.2 micrometers or less, or about 8.0 micrometers or less, or about 7.8 micrometers or less, or about 7.75 micrometers or less, or about 7.6 micrometers or less. In some embodiments, each core 20 has a mode field diameter at a wavelength of 1550 nm in the range of about 6.0 micrometers to about 9.6 micrometers, or about 6.0 micrometers to about 9.4 micrometers, or about 6.0 micrometers to about 9.2 micrometers, or about 6.0 micrometers to about 9.0 micrometers, or about 6.0 micrometers to about 8.8 micrometers, or about 6.0 micrometers to about 8.75 micrometers, or about 6.0 micrometers to about 8.6 micrometers, or about 6.5 micrometers to about 9.6 micrometers, or about 6.5 micrometers to about 9.4 micrometers.

[0088] Additionally, the optical fiber disclosed herein has a fiber optics wavelength of approximately 55.0 micrometers at a wavelength of 1310 nm. 2 Less than or equal to about 50.0 micrometers 2 Less than or equal to about 45.0 micrometers 2 Less than or equal to about 40.0 micrometers 2 Less than or equal to about 35.0 micrometers 2 Less than or equal to about 30.0 micrometers 2 This optical fiber has an effective area of approximately 30.0 micrometers at a wavelength of 1510 nm. 2 or greater than, or approximately 35.0 micrometers 2 More than or equal to approximately 40.0 micrometers 2 or more, or approximately 45.0 micrometers 2 More than or equal to approximately 50.0 micrometers 2 Additionally or alternatively, the effective area at a wavelength of 1550 nm is about 70.0 micrometers. 2 Less than or equal to approximately 65.0 micrometers 2 Less than or equal to about 60.0 micrometers 2 In some embodiments, the effective area at a wavelength of 1550 nm is about 30 micrometers. 2 and about 70 micrometers 2 It is in the range between.

[0089] Each of the cores 20 disclosed herein has a zero-dispersion wavelength of about 1380 nm or less, or about 1370 nm or less, or about 1360 nm or less, or about 1350 nm or less, or about 1345 nm or less, or about 1340 nm or less, or about 1335 nm or less, or about 1330 nm or less, or about 1325 nm or less, or about 1320 nm or less, or about 1315 nm or less, or about 1310 nm or less, or about 1300 nm or less. In some embodiments, the zero-dispersion wavelength is from about 1290 nm to about 1380 nm. For example, the zero-dispersion wavelength can be from 1295 nm to about 1370 nm, or from about 1300 nm to about 1360 nm, or from about 1305 nm to about 1350 nm. For example, the zero dispersion wavelength can be about 1300 nm, about 1310 nm, about 1320 nm, about 1330 nm, about 1340 nm, about 1350 nm, about 1360 nm, about 1370 nm, or about 1380 nm.

[0090] Additionally, the optical fiber disclosed herein has an attenuation of about 0.40 dB / km or less at a wavelength of 1310 nm, about 0.35 dB / km or less at a wavelength of 1310 nm, or about 0.32 dB / km or less at a wavelength of 1310 nm.

[0091] According to an embodiment of the present disclosure, the optical fiber has an absolute value at 1310 nm within a range between about -6.0 ps / nm / km and about 1.0 ps / nm / km, and a .DELTA.F of about 0.015 ps / nm 2 / km and 0.1ps / nm 2 / km. For example, the absolute value of the dispersion at 1310 nm is about -5.5 ps / nm / km to about 0.8 ps / nm / km, or about -5.0 ps / nm / km to about 0.5 ps / nm / km, or about -4.5 ps / nm / km to about 0.2 ps / nm / km, or about -4.0 to about 0.1 ps / nm / km, or about -3.5 ps / nm / km to about 0.08 ps / nm / km, or about -3.0 ps / nm / km to about 0.05 ps / nm / km. For example, the absolute value of the dispersion at 1310 nm is about -5.5 ps / nm / km, or about -4.0 ps / nm / km, or about -3.8 ps / nm / km, or about -3.4 ps / nm / km, or about -2.8 ps / nm / km, or about 0.08 ps / nm / km. In one example, the dispersion slope at 1310 nm is about 0.015 ps / nm 2 / km to approximately 0.095ps / nm 2 / km, approx. 0.025ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.03ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.035ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.04ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.045ps / nm 2 / km to approximately 0.09ps / nm 2 / km.

[0092] According to an aspect of the present disclosure, the optical fiber has a dispersion at 1550 nm of less than about 22 ps / nm / km and a dispersion at 1550 nm of less than about 0.1 ps / nm 2For example, the dispersion at 1550 nm can be from about 10 ps / nm / km to about 22 ps / nm / km, or from about 10 ps / nm / km to about 22 ps / nm / km, or from about 10 ps / nm / km to about 20 ps / nm / km, or from about 10 ps / nm / km to about 15 ps / nm / km, or from about 15 ps / nm / km to about 22 ps / nm / km, or from about 15 ps / nm / km to about 20 ps / nm / km. For example, the dispersion at 1550 nm can be about 10 ps / nm / km, about 15 ps / nm / km, about 16 ps / nm / km, about 17 ps / nm / km, about 17.5 ps / nm / km, about 18 ps / nm / km, about 19 ps / nm / km, about 19.5 ps / nm / km, about 19.6 ps / nm / km, about 20 ps / nm / km, about 20.1 ps / nm / km, about 22 ps / nm / km, or any value between these values. In one example, the dispersion slope at 1550 nm is about 0.04 ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.05ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.055ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.06ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.08ps / nm 2 / km to approximately 0.1ps / nm 2 / km, approx. 0.04ps / nm 2 / km to approximately 0.08ps / nm 2 / km, approx. 0.05ps / nm 2 / km to approximately 0.08ps / nm 2 / km, approx. 0.055ps / nm 2 / km to approximately 0.08ps / nm 2 / km, approx. 0.06ps / nm 2 / km to approximately 0.08ps / nm 2 / km, approx. 0.04ps / nm 2 / km to approximately 0.06ps / nm 2 / km, approx. 0.05ps / nm 2 / km to approximately 0.06ps / nm 2 / km, or approximately 0.055ps / nm 2 / km to approximately 0.06ps / nm 2 For example, the dispersion slope at 1550 nm is about 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, or approximately 0.08ps / nm 2 / km.

[0093] Illustrative Embodiments Exemplary embodiments of the optical fiber disclosed herein are provided below, along with comparative examples. The following exemplary embodiments are intended to be examples and are not intended to limit the scope of the present disclosure.

[0094] Table 1 below provides five examples of multi-core optical fibers, each fiber having four cores arranged in a 1x4 linear configuration. Each of the optical fibers in Table 1 below has an outer diameter of 125 micrometers. Examples 2-3 in Table 1 below each have a relatively smaller mode field diameter than Comparative Example 1, and therefore lower crosstalk between adjacent cores.

[0095] [Table 1]

[0096] Table 2 below provides three exemplary embodiments of multi-core optical fibers, each fiber having four cores arranged in a 1 x 4 linear configuration. Each of the optical fibers in Table 2 below has an outer diameter of 125 micrometers.

[0097] [Table 2]

[0098] Table 3 below provides three exemplary embodiments of multi-core optical fibers, each fiber having four cores arranged in a 1 x 4 linear configuration. Each of the optical fibers in Table 3 below has an outer diameter of 125 micrometers.

[0099] [Table 3]

[0100] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the present invention. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments that embody the spirit and scope of the invention will occur to those skilled in the art, the present invention is to be construed as including all within the scope of the appended claims and equivalents thereof.

[0101] Preferred embodiments of the present invention will be described below in detail.

[0102] Embodiment 1 In multi-core optical fiber, four cores arranged in a linear arrangement such that the centerline of each core is aligned along an axis A, each core's centerline being spaced from the centerline of an adjacent core by a distance x of about 30 micrometers or less, each core having a relative refractive index Δ1; and A cladding surrounding each of the four cores, an inner cladding region having a relative refractive index Δ2; Relative refractive index Δ3 and 20% Δ micrometers 2 a depressed-index cladding region having a volume V3 or greater; an outer cladding region having a relative refractive index Δ4; Cladding, including Equipped with Δ1>Δ2>Δ3 and Δ1>Δ4>Δ3, the multi-fiber optical fiber has an outer diameter of about 125 micrometers or less; each of the four cores has a mode field diameter of about 8.1 micrometers or less at a wavelength of 1310 nm; each of the four cores having a cable cutoff of about 1260 nm or less; A multi-core optical fiber, wherein the crosstalk between adjacent cores of the four cores is about -18 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0103] Embodiment 2 2. The multi-core optical fiber of embodiment 1, wherein the distance x is between about 22 micrometers and about 28 micrometers.

[0104] Embodiment 3 3. The multi-core optical fiber of embodiment 2, wherein the distance x is between about 24 micrometers and about 26 micrometers.

[0105] Embodiment 4 The multi-core optical fiber according to any one of embodiments 1 to 3, wherein a center line of the multi-core optical fiber is positioned along the axis A.

[0106] Embodiment 5 The multi-core optical fiber according to any one of embodiments 1 to 4, wherein the four cores are arranged in a 1x4 linear arrangement.

[0107] Embodiment 6 6. The multi-core optical fiber according to any one of embodiments 1 to 5, wherein each of the four cores has a mode field diameter of about 8.0 micrometers or less at a wavelength of 1310 nm.

[0108] Embodiment 7 The effective area of the multi-core optical fiber at a wavelength of 1310 nm is about 55.0 micrometers. 2A multi-core optical fiber according to any one of embodiments 1 to 6, wherein:

[0109] Embodiment 8 The effective area of the multi-core optical fiber at a wavelength of 1310 nm is about 30.0 micrometers. 2 The multi-core optical fiber according to any one of the first to seventh embodiments is as described above.

[0110] Embodiment 9 9. The multi-core optical fiber according to any one of embodiments 1 to 8, wherein the minimum distance y between the center line of the outermost core of the four cores and the outer diameter of the cladding is between about 2 micrometers and about 4 micrometers.

[0111] Embodiment 10 10. The multi-core optical fiber of embodiment 9, wherein the minimum distance y is between about 2.25 micrometers and about 3.75 micrometers.

[0112] Embodiment 11 11. The multi-core optical fiber according to any one of embodiments 1 to 10, wherein crosstalk between adjacent cores of the four cores is about −20 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0113] Embodiment 12 12. The multi-core optical fiber according to embodiment 11, wherein the crosstalk between adjacent cores of the four cores is about −25 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0114] Embodiment 13 13. The multi-core optical fiber according to embodiment 12, wherein the crosstalk between adjacent cores of the four cores is about −30 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0115] Embodiment 14 14. The multi-core optical fiber according to embodiment 13, wherein the crosstalk between adjacent cores of the four cores is about −50 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0116] Embodiment 15 15. The multi-core optical fiber according to embodiment 14, wherein the crosstalk between adjacent cores of the four cores is about −55 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

[0117] Embodiment 16 16. The multi-core optical fiber according to any one of embodiments 1 to 15, wherein a cabled cutoff of each core is about 1240 nm or less.

[0118] Embodiment 17 17. The multi-core optical fiber according to embodiment 16, wherein the cabled cutoff of each core is equal to or less than about 1230 nm.

[0119] Embodiment 18 18. The multi-core optical fiber according to any one of embodiments 1 to 17, wherein the cladding includes a marker that is not positioned on the axis of symmetry of the multi-core optical fiber.

[0120] Embodiment 19 19. The multi-core optical fiber according to any one of embodiments 1 to 18, wherein the α value of each core is about 10 or more.

[0121] Embodiment 20 The volume V3 is about 40%Δ micrometers 2 The multi-core optical fiber according to any one of the first to nineteenth embodiments is as described above.

[0122] Embodiment 21 The volume V3 is about 50%Δ micrometers 2 The multi-core optical fiber according to embodiment 20 is as described above.

[0123] Embodiment 22 22. The multi-core optical fiber according to any one of embodiments 1 to 21, wherein each core has a mode field diameter of about 9.5 micrometers or less at a wavelength of 1550 nm.

[0124] Embodiment 23 23. The multi-core optical fiber according to embodiment 22, wherein the mode field diameter at a wavelength of 1550 nm is about 9.2 micrometers or less.

[0125] Embodiment 24 24. The multi-core optical fiber according to any one of embodiments 1 to 23, wherein each core has a zero dispersion wavelength of about 1380 nm or less.

[0126] Embodiment 25 25. The multi-core optical fiber according to embodiment 24, wherein the zero dispersion wavelength is about 1350 nm or less.

[0127] Embodiment 26 26. The multi-core optical fiber according to embodiment 25, wherein the zero dispersion wavelength is about 1345 nm or less. [Explanation of symbols]

[0128] 10 Multi-core optical fiber 20, 20a~d Core 30 Clad 32 inner cladding region 34 Decreased-index cladding region 36 outer cladding region 40 Primary Coating 50 Secondary Coating 60 Tertiary Coating 70 markers

Claims

1. In multi-core optical fiber, Four cores arranged in a linear configuration such that the centerline of each core is aligned along an axis A, the centerline of each core being spaced from the centerline of an adjacent core by a distance x of less than or equal to about 30 micrometers, and each core having a relative refractive index Δ １ four cores, a cladding surrounding each of the four cores, Relative refractive index Δ ２ an inner cladding region having Relative refractive index Δ ３ and 20% Δ micrometers ２ The volume V ３ a depressed-index cladding region having Relative refractive index Δ ４ an outer cladding region having Cladding, including Equipped with Δ １ >Δ ２ >Δ ３ and Δ １ >Δ ４ >Δ ３ and the multi-fiber optical fiber has an outer diameter of about 125 micrometers or less; each of the four cores has a mode field diameter of about 8.1 micrometers or less at a wavelength of 1310 nm; each of the four cores having a cable cutoff of about 1260 nm or less; A multi-core optical fiber, wherein the crosstalk between adjacent cores of the four cores is about −18 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

2. 2. The multi-core optical fiber of claim 1, wherein the distance x is between about 22 micrometers and about 28 micrometers.

3. 2. The multi-fiber optical fiber of claim 1, wherein a centerline of said multi-fiber optical fiber is positioned along said axis A.

4. 2. The multi-core optical fiber according to claim 1, wherein said four cores are arranged in a 1x4 linear configuration.

5. 5. The multi-core optical fiber according to claim 1, wherein each of the four cores has a mode field diameter of about 8.0 micrometers or less at a wavelength of 1310 nm.

6. The effective area of the multi-core optical fiber at a wavelength of 1310 nm is about 55.0 micrometers. ２ 5. The multi-core optical fiber according to claim 1, wherein:

7. 5. The multi-core optical fiber according to claim 1, wherein a minimum distance y between the center line of the outermost core of the four cores and the outer diameter of the cladding is between about 2 micrometers and about 4 micrometers.

8. 5. The multi-core optical fiber according to claim 1, wherein the crosstalk between adjacent cores of said four cores is about −25 dB or less per 2 km of fiber length at wavelengths of 1310 nm and 1550 nm.

9. 5. The multi-core optical fiber according to claim 1, wherein each core has a cable cutoff of about 1240 nm or less.

10. The multi-core optical fiber according to claim 1 , wherein the cladding includes markers that are not positioned on an axis of symmetry of the multi-core optical fiber.

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