Uncoupled-core multi-core optical fiber with reduced crosstalk

Abstract

An uncoupled core multi-core optical fiber is disclosed, the optical fiber comprising at least two cores, each core comprising a core and a depressed refractive index cladding. The core has a radius r1 and a relative refractive index [Delta] 1. The depressed refractive index cladding has a radius r2 and a relative refractive index [Delta] 2, the depressed refractive index cladding surrounding and directly contacting the core, the depressed refractive index cladding having a volume V2 of from about 15.0% [Delta]-[mu] 2 to about 37.0% [Delta]-[mu] 2. The optical fiber further includes an optical fiber having a radius r3 and a relative refractive index [Delta] 3 such that [Delta] 2lt; [delta] 3lt; and a common cladding of [delta] 1, the common cladding surrounding and in direct contact with the depressed refractive index cladding. Further, a cable cutoff wavelength of each core is about 1530 nm or less, and a center-to-center spacing between centerlines of adjacent cores is about 48 microns to about 60 microns.

Description

[0001] This application claims priority under 35 U.S.C. §120 to U.S. Provisional Application Serial No. 63 / 464,270 filed on May 5, 2023, U.S. Provisional Application Serial No. 63 / 446,619 filed on February 17, 2023, and U.S. Provisional Application Serial No. 63 / 401,310 filed on August 26, 2022, and this application is incorporated herein by reference in its entirety based on the contents of the said provisional applications. Technical Field

[0002] The present disclosure relates to multi-core optical fibers. More particularly, the present disclosure relates to uncoupled-core multi-core optical fibers having reduced crosstalk between adjacent cores such that the cores are alkali-doped. Background Art

[0003] Multicore optical fibers include multiple cores embedded in a cladding matrix. Thus, the fiber density is increased, making multicore optical fibers useful for overcoming cable size limitations and pipe congestion problems in passive optical network ("PON") systems. The use of multicore optical fibers is also beneficial in submarine cables, which are designed to transmit telecommunication signals over vast expanses of land and ocean. The use of submarine cables for transmitting telecommunication signals has increased dramatically over the past few years, with more than 90% of intercontinental communication signals currently being transmitted over these cables. Therefore, driven by the growth of Internet traffic between continents, the demand for transmission capacity of such submarine cables has also increased. Summary of the invention

[0004] The multi-core optical fiber disclosed herein has low crosstalk and low dispersion between adjacent cores while still maintaining a sufficiently high mode field diameter. Therefore, the multi-core optical fiber disclosed herein can be beneficial for use in submarine cables. Since the distance between the cores is large enough to ensure isolated mode transmission in different cores, the multi-core optical fiber disclosed herein can be referred to as an uncoupled optical fiber. In addition, the multi-core optical fiber disclosed herein has an alkali-doped core enclosed by a groove, which not only minimizes crosstalk but also reduces radiation loss.

[0005] In various aspects, the present disclosure includes an uncoupled core multicore optical fiber, the optical fiber including at least two cores, each core including a core and a depressed index cladding. The core has a radius r1 and a relative refractive index Δ1 relative to pure silica, the core is doped with at least one of sodium, potassium, and rubidium. The depressed index cladding has a radius r2 and a relative refractive index Δ2 relative to pure silica such that Δ2<Δ1, the depressed index cladding surrounds and directly contacts the core, and the volume V2 of the depressed index cladding is about 15.0% Δ-micrometers 2 to about 37.0% Δ-μm 2The optical fiber further includes a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica such that Δ2<Δ3<Δ1, the common cladding surrounding and directly contacting the depressed refractive index cladding, and further, the cable cutoff wavelength of each core is about 1530 nm or less, and the effective area of ​​each core is about 100 microns at a wavelength of 1550 nm 2 to about 135 microns 2 , the attenuation of the multi-core optical fiber at a wavelength of 1550 nm is about 0.165 dB / km or less, and the center-to-center spacing between center lines of adjacent cores is about 48 microns to about 60 microns.

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

[0007] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework for understanding the nature and 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 accompanying drawings are illustrative of selected aspects of the disclosure, and together with the description serve to explain the principles and operations of the methods, products, and compositions encompassed by the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic cross-sectional view of an uncoupled-core multi-core optical fiber having multiple cores according to an embodiment of the present disclosure;

[0010] Figure 2 is an enlarged cross-sectional schematic diagram of a single core of an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0011] Figure 3 depicts the relative refractive index profile of an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0012] Figure 4 is a schematic cross-sectional view of an uncoupled-core multi-core optical fiber with an outer coating according to an embodiment of the present disclosure;

[0013] Figure 5 is another schematic diagram of a cross section of an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0014] Fig. 6A depicts the relative refractive index profile of an exemplary uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0015] Figure 6B depicts the relative refractive index profile of an exemplary uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0016] Fig. 7A is a graph of co-propagating inter-core crosstalk versus center-to-center spacing of adjacent cores for an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0017] Figure 7B is a graph of counter-propagating inter-core crosstalk versus center-to-center spacing of adjacent cores for an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0018] Figure 8 is a graph of radiation loss versus center-to-center spacing of adjacent cores for an uncoupled-core multi-core optical fiber according to an embodiment of the present disclosure;

[0019] Fig. 9 is a schematic diagram of a system for measuring co-propagating crosstalk and counter-propagating crosstalk. DETAILED DESCRIPTION

[0020] The present disclosure is provided as feasible teaching and can be more easily understood by reference to the following description, drawings, examples and claims. To this end, those skilled in the relevant art will recognize and understand that many changes can be made to the various aspects of the embodiments described herein while still obtaining beneficial results. It is also obvious that some of the expected benefits of the present embodiment can be obtained by selecting some of the features without utilizing other features. Therefore, those skilled in the art will recognize that many modifications and adaptations are possible, and may even be desirable in some cases, and are part of the present disclosure. Therefore, it should be understood that unless otherwise stated, the present disclosure is not limited to the specific compositions, products, devices and methods disclosed. It should also be understood that the terms used herein are only for the purpose of describing specific aspects and are not intended to be restrictive.

[0021] Throughout this specification and the claims that follow, reference will be made to a number of terms which shall be defined to have the following meanings:

[0022] "Optical fiber" refers to a waveguide having a glass portion surrounded by a coating. The glass portion includes a core and a cladding, and is referred to herein as a "glass optical fiber."

[0023] "Radial position," "radius," or radial coordinate "r" refers to the radial position relative to the centerline of the optical fiber (r=0).

[0024] Unless otherwise specified, "refractive index" refers to the refractive index at a wavelength of 1550 nm.

[0025] "Refractive index profile" is the relationship between the refractive index or relative refractive index and the radius. For the relative refractive index profile described herein as having a step boundary between adjacent core and / or cladding regions, normal changes in processing conditions can hinder the acquisition of sharp step boundaries at the interface of adjacent regions. It should be understood that although the boundary of the refractive index profile can be described herein as a step change in the refractive index, in practice the boundary can be circular or otherwise deviate from the perfect step function property. It is further understood that the value of the relative refractive index can change with the radial position in any cladding region in the core region and / or cladding region. When the relative refractive index changes with radial position in a specific region of the optical fiber (e.g., any cladding region in the core region and / or cladding region), it is represented according to its actual or approximate functional dependence, or its value at a specific position in the region, or according to the average value applicable to the entire region. Unless otherwise specified, if the relative refractive index of a region (e.g., a core region and / or any cladding region) is expressed as a single value or parameter (e.g., Δ or Δ%) applicable to the entire region, it is understood that the relative refractive index in the region is constant or approximately constant and corresponds to a single value, or that the single value or parameter represents an average value of a non-constant relative refractive index that is related to radial position within the region. For example, if "i" is a region of a glass fiber, the parameter Δ i refers to the average of the relative refractive indices in a region defined below, unless otherwise stated. Whether by design or due to normal manufacturing variability, the dependence of the relative refractive index on radial position may be tilted, curved, or otherwise non-constant.

[0026] As used herein, "relative refractive index" is defined as: Unless otherwise stated, n i is the radial position r in the glass fiber i The refractive index at , and unless otherwise stated, n ref is the refractive index of pure silica glass. Therefore, as used herein, the relative refractive index percentage is relative to pure silica glass, which has a value of 1.444 at a wavelength of 1550 nm. As used herein, unless otherwise specified, the relative refractive index is represented by Δ (or "delta") or Δ% (or "delta%"), and its value is in "%". The relative refractive index can also be expressed as Δ(r) or Δ(r)%.

[0027] The average relative refractive index of the fiber region (Δ ave ) is determined by the following equation: where r inner is the inner radius of the region, router is the outer radius of the region, and Δ(r) is the relative refractive index of the region.

[0028] The refractive index of a fiber profile can be measured using commercially available equipment such as the IFA-100 Fiber Refractive Index Analyzer (Interfiber Analysis LLC, Sharon, MA, USA) or the S14 Refractive Index Analyzer (PhotonKinetics, Inc., Beaverton, OR, USA). These instruments measure the refractive index n(r) - n relative to a measured reference refractive index. meas , where the measured reference refractive index n meas Typically a calibrated refractive index matched to oil or pure silica glass. The measurement wavelength can be 632.5nm, 654nm, 677.2nm, 654nm, 702.3nm, 729.6nm, 759.2nm, 791.3nm, 826.3nm, 864.1nm, 905.2nm, 949.6nm, 997.7nm, 1050nm or any wavelength in between. The absolute refractive index n(r) is then used to calculate the relative refractive index as defined above.

[0029] The term "α-distribution" or "alpha distribution" refers to a relative refractive index distribution Δ(r) having the functional form defined in the following equation: where r o is the radial position where Δ(r) is the maximum value, Δ(r0)>0, r z >r0 is the radial position where Δ(r) decreases to its minimum value, and r is at r i ≤r≤r f In the range of i is the initial radial position of the α-distribution, r f is the final radial position of the α-distribution, and α is a real number. Δ(r0) for the α-distribution may be referred to herein as Δ max , or when referring to a specific region i of the optical fiber, it may be referred to as Δ imax When the relative refractive index distribution in the core region of an optical fiber is described by an α-profile, where r0 occurs at the centerline (r = 0), r z Corresponding to the outer radius r1 of the core region, and Δ1(r1)=0, the above equation simplifies to:

[0030] When the core region has a refractive index described by the above equation, the outer radius r1 can be determined from the measured relative refractive index profile by the following procedure. Maximum relative refractive index Δ 1max , α, and outer radius r 1estAn estimate of is obtained by examining the measured relative refractive index profile and is used for the case where r = -r 1est and r = r 1est Create a test function Δ between trial . Figure 3 0047] The relative refractive index profile of a representative glass optical fiber having a core described by an α-profile according to an embodiment of the present disclosure is shown in .

[0031] The term "graded refractive index profile" refers to an α-profile where α<10. The term "step refractive index profile" refers to an α-profile where α≥10.

[0032] The "trench volume" is defined as: where r Trench,inner is the inner radius of the groove region of the refractive index profile, r Trench,outer is the outer radius of the groove 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 in the fiber. The trench volume is an absolute and positive number and will be expressed herein as % Δ μm 2 , %Δ-micrometer 2 、%Δ-μm 2 or %Δμm 2 The units are expressed as V2, and thus these units may 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 herein as V2.

[0033] The "mode field diameter" or "MFD" of an optical fiber is defined in the following equation: MFD=2w Where f(r) is the transverse component of the electric field distribution of the guided optical signal, and r is the radial position in the fiber. The "mode field diameter" or "MFD" depends on the wavelength of the optical signal and is reported herein for wavelengths of 1310nm, 1550nm, and 1625nm. When referring to the mode field diameter in this article, the wavelength will be specifically indicated. Unless otherwise stated, the mode field diameter refers to the LP at a specific wavelength. 01 model.

[0034] The "effective area" of a fiber is defined in the following equation: where f(r) is the transverse component of the electric field of the guided optical signal and r is the radial position in the fiber. eff ” depends on the wavelength of the optical signal and is understood herein to refer to a wavelength of 1550 nm.

[0035] As used herein, the term "attenuation" is the optical power loss at 1550 nm as a signal travels along an optical fiber. Attenuation is measured as specified in the IEC-60793-1-40 standard "Attenuation measurement method".

[0036] The bending resistance of an optical fiber (referred to herein as "bending losses") may be determined by induced attenuation under specified test conditions as specified in the IEC-60793-1-47:2017 standard "Optical fiber - Part 1-47: Measurement methods and test procedures - Macrobending loss". For example, the test conditions may require laying or winding the optical fiber around a mandrel of specified diameter, for example by winding 100 turns around a 60 mm diameter mandrel and measuring the attenuation increment for each turn.

[0037] As used herein, “cable cut-off wavelength” or “cable cut-off” refers to the 22 m cable cut-off test as specified in the IEC 60793-1-44 standard “Measurement methods and test procedures – Cut-off wavelength”.

[0038] Unless otherwise stated herein, optical properties (such as dispersion, dispersion slope, etc.) are reported for the LP01 mode.

[0039] Unless otherwise stated, the "chromatic dispersion" (referred to herein as "dispersion") of an optical fiber is the sum of material dispersion, waveguide dispersion, and intermodal dispersion. "Material dispersion" refers to the way in which the refractive index of the material used for the optical core affects the speed at which different optical wavelengths propagate within the core. "Waveguide dispersion" refers to the dispersion caused by the different refractive indices of the core and cladding of the optical fiber. In the case of single-mode waveguide fiber, the intermodal dispersion is zero. Dispersion values ​​in dual-mode mode assume that the intermodal dispersion is zero. The zero dispersion wavelength (λ0) is the wavelength at which the dispersion has a zero value. The dispersion slope is the rate of change of dispersion with respect to wavelength. As mentioned earlier, the dispersion and dispersion slope are reported herein at a wavelength of 1310nm or 1550nm and are expressed in ps / nm / km and ps / nm, respectively. 2The unit of chromatic dispersion is / km. Chromatic dispersion is measured according to the IEC 60793-1-42:2013 standard "Optical fibres - Part 1-42: Measurement methods and test procedures - Chromatic dispersion".

[0040] The term "crosstalk" in multi-core optical fiber is a measure of how much power leaks from one core portion to another adjacent core portion. As used herein, the term "adjacent core" refers to the core closest to the reference core. In an embodiment, all cores may be equally spaced from each other, meaning that all cores are adjacent to each other. In other embodiments, the cores may be unequally spaced from each other, meaning that some cores are spaced farther from the reference core than the adjacent cores are spaced from the reference core. Crosstalk can be determined based on a coupling coefficient and Δβ, which depends on the refractive index profile design of the core, the distance between two adjacent cores, and the structure of the cladding surrounding the two adjacent cores, and Δβ depends on the difference in the propagation constant β value between two adjacent cores (for example, as described herein, the two cores have a centerline separated by a minimum core-to-core separation distance). For two adjacent cores, as power P1 is emitted to the first core, the power P2 coupled from the first core to the second core can be determined according to coupled mode theory using the following equation: Where <> represents the average value, L is the fiber length, κ is the coupling coefficient between the electric fields of the two cores, ΔL is the length of the fiber, and L c is the correlation length, and g is given by: Where Δβ is the mismatch in propagation constant between the LP01 modes in two adjacent cores when the two adjacent cores are isolated. The crosstalk (in dB) is then determined using the following equation:

[0041] The crosstalk between two adjacent core sections increases linearly with fiber length on a linear scale, but does not increase linearly with fiber length on a dB scale. As used herein, crosstalk performance is referenced to a 100 km length L of fiber. However, crosstalk performance may also be expressed relative to alternative fiber lengths under appropriate scaling. For fiber lengths other than 100 km, the following equation may be used to determine the crosstalk between core sections: For example, for a 10km length of fiber, the crosstalk can be determined by adding "-10dB" to the crosstalk value of the 100km length of fiber. For a 1km length of fiber, the crosstalk can be determined by adding "-20dB" to the crosstalk value of the 100km length of fiber. For long-distance transmission in uncoupled-core multi-core fiber, the crosstalk per 100km length should be less than or equal to -30dB, less than or equal to -40dB, or even less than or equal to -50dB.

[0042] As used herein, using co-propagating crosstalk (XT), as described above, power P1 is emitted into the first core at the first end of the optical fiber, and power P2 coupled into the second core is determined at the second end of the optical fiber. Therefore, power P2 coupled into the second core is determined at the end of the optical fiber in the propagation direction of the optical signal. As used herein, using counter-propagating crosstalk (CXT), as described above, power P1 is emitted into the first core at the first end of the optical fiber, and power P2 coupled into the second core is determined at the first end of the optical fiber. Therefore, power P2 coupled into the second core is determined at the end of the optical fiber in the propagation direction of the optical signal. In optical fiber, counter-propagating crosstalk is generally lower than co-propagating crosstalk.

[0043] A system for measuring co-propagating crosstalk and counter-propagating crosstalk as disclosed herein is provided in Fig. 9 To measure the disclosed crosstalk, a multi-core optical fiber (e.g., a multi-core optical fiber having a 1x2 core design) with a length between 20 km and 25 km on a standard shipping spool was tested. Fig. 9 As shown, the system includes a tunable laser source (TLS) with a linewidth of 200kHz, an optical splitter for monitoring the laser output power, and a 1x 2 multi-core fiber fan-in / fan-out (FIFO 1) fused to the optical fiber to inject the source light into one core of the optical fiber while directing the reverse propagating light into the other core. The fan-out (FIFO 2) is fused at the far end of the optical fiber, and its output is connected to an optical receiver to measure the forward propagating light output by each core. Fig. 9 As shown, optical receivers #1, #2, and #3 are each high sensitivity detectors with -109dBm noise sensitivity and linearity error with <20% deviation over the entire power measurement range (+5 to -75dBm). All three optical receivers are calibrated and read the same power at one power level. The multicore fiber used to make the FIFO has the same mode field diameter and core-to-core spacing as the transmission multicore fiber being tested.

[0044] Techniques for determining crosstalk between cores in a multicore optical fiber can also be found in the following literature: M. Li et al., "Coupled Mode Analysis of Crosstalk in Multicore fiber with Random Perturbations", Optical Society of America, 2015, Journal W2A.35; and Shoichiro Matsuo et al., "Crosstalk behavior of cores in multi-core portion under bent condition", IEICE Electronics Express, Vol. 8, No. 6, pp. 385-390, published on March 25, 2011; and Lukasz Szostkiewicz et al., "Cross talk analysis in multicore optical fibers by supermode theory". "Optics Letters", Vol. 41, No. 16, pp. 3759-3762, published on August 15, 2016, the disclosures of which are incorporated herein by reference in their entirety.In addition, techniques for determining co-propagating and counter-propagating crosstalk between cores in a multi-core optical fiber can be found 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 on August 15, 2014, and Tetsuya Hayashi et al., “Uncoupled Multi-Core Fiber Design for Practical Bidirectional Optical Communications,” OFC, Optica Publishing Group, 2022, which are also incorporated herein by reference in their entirety.

[0045] As used herein, the phrase "coupling coefficient" κ relates to the overlap of the electric fields when two cores are close to each other. The square of the coupling coefficient κ 2It is related to the average power in core m of a multi-core optical fiber affected by the power of other cores. The "coupling coefficient" can be estimated using coupled power theory, 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 which are incorporated herein by reference in their entirety.

[0046] The optical fiber disclosed herein comprises a plurality of cores, an outer cladding region surrounding each core, and an optional coating surrounding the outer cladding region. The core and outer cladding regions are glass. Each core comprises a plurality of regions, the plurality of regions comprising a core and a depressed index cladding. The plurality of cladding regions are preferably concentric regions. The depressed index cladding surrounds and is directly adjacent to the core. The outer cladding region surrounds and is directly adjacent to the depressed index cladding, such that the depressed index cladding is disposed between the core and outer cladding regions in a radial direction. As discussed further below, the outer cladding region is a common cladding.

[0047] The depressed index cladding has a lower relative refractive index than each of the core and outer cladding regions. The depressed index cladding may be referred to herein as a trench or trench region. In addition, as discussed further below, the depressed index cladding helps reduce crosstalk between adjacent cores.

[0048] Whenever used herein, radial position r1 and relative refractive index Δ1 or Δ1(r) refer to the core, radial position r2 and relative refractive index Δ2 or Δ2(r) refer to the depressed index cladding, and radial position r3 and relative refractive index Δ3 or Δ3(r) refer to the outer cladding region. In addition, radial position r4 (not shown) refers to the primary coating, radial position r5 (not shown) refers to the secondary coating, and radial position r6 (not shown) refers to the optional tertiary coating.

[0049] The relative refractive index Δ1(r) has a maximum value Δ 1max 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 In embodiments where the relative refractive index is constant or approximately constant over a region, the maximum and minimum values ​​of the relative refractive index are equal or approximately equal. Unless otherwise stated, if a single value is reported for the relative refractive index of a region, the single value corresponds to the average value for the region.

[0050] It should be understood that each core is substantially cylindrical in shape and that the surrounding depressed index cladding, outer cladding region, primary coating, and secondary coating are substantially annular in shape. The annular region is characterized in terms of an inner radius and an outer radius. Radial positions r1, r2, r3, r4, r5, and r6 refer herein to the outermost radii of the core region, depressed index cladding, outer cladding region, primary coating, secondary coating, and tertiary coating, respectively. In embodiments without a tertiary coating, radius r5 also corresponds to the outer radius of the optical fiber. When a tertiary coating is present, radius r6 corresponds to the outer radius of the optical fiber.

[0051] The difference between radial position r2 and radial position r1 is the thickness of the depressed 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.

[0052] Conventionally, multi-core optical fibers can be used to increase fiber density while maintaining the outer diameter of conventional optical fibers (e.g., 125 micron outer diameter). In addition, conventional methods of achieving such high fiber density with multi-core optical fibers while also reducing crosstalk between adjacent cores include reducing the mode field diameter of the multi-core optical fiber. While the reduction in mode field diameter reduces crosstalk between adjacent cores, it also limits the amount of power that can be emitted into each core due to nonlinear effects. Therefore, conventional multi-core optical fibers typically have increased radiation and tunneling losses.

[0053] The multi-core optical fibers described herein address these deficiencies in conventional approaches to providing high fiber density in relatively small (e.g., 125 micron outer diameter) multi-core optical fibers. In particular, by incorporating a core portion including a depressed index cladding immediately adjacent to the core, the multi-core optical fibers described herein have reduced radiation and tunneling losses while still maintaining a large effective area, relatively low crosstalk, and good bending performance. In addition, the multi-core optical fibers disclosed herein have a mode field diameter compatible with standard single-mode optical fibers.

[0054] In the embodiments disclosed herein, the multi-core optical fiber is uncoupled. For the uncoupled cores of the multi-core optical fiber, the distance between the cores is large to ensure independent mode transmission within the core and low crosstalk between the cores. At a wavelength of 1550nm, the crosstalk between the cores of the uncoupled core multi-core optical fiber disclosed herein is less than or equal to -30dB per 100km length of the multi-core optical fiber (-30dB / 100km). A multi-core optical fiber having at least one pair of uncoupled cores is referred to herein as an "uncoupled core multi-core optical fiber". In contrast, the coupled cores of the multi-core optical fiber utilize the crosstalk between the cores. Therefore, in a coupled multi-core optical fiber, the distance between the cores must be much smaller than that of an uncoupled multi-core optical fiber.

[0055] The uncoupled-core multi-core optical fiber disclosed herein includes a common cladding region surrounding and directly contacting a core, and the core includes a depressed index cladding surrounding and directly contacting the core, wherein the common cladding region surrounds and directly contacts the depressed index cladding.

[0056] refer to Figure 1 , embodiments of the present disclosure relate to an uncoupled core multi-core optical fiber 10, which includes a plurality of cores 20 surrounded by a common cladding 30. In an embodiment, the optical fiber 10 is configured for use in a submarine cable. The cores 20 of the optical fiber 10 are each a glass core. Figure 1 As shown, the core 20 is disposed within a common cladding 30 and extends a length of the optical fiber 10 generally parallel to the central axis 15 of the optical fiber. Figure 1 Only two cores 20 are depicted, it should be noted that the optical fiber 10 may include more than two cores, such as 2 or more, or 4 or more, or 6 or more, or 8 or more, or 10 or more, or 12 or more cores. However, it should be noted that in some embodiments, the optical fiber 10 includes only two uncoupled cores 20.

[0057] The common cladding 30 may also be referred to herein as a "glass matrix". The outer diameter of the common cladding 30 is about 180 microns or less, or about 160 microns or less, or about 150 microns or less, or about 125 microns or less, or about 100 microns or less. In an embodiment, the outer diameter of the common cladding 30 is in a range from about 100 microns to about 180 microns, or from about 100 microns to about 160 microns, or from about 120 microns to about 130 microns, or from about 124 microns to about 126 microns. In some embodiments, the outer diameter of the outer cladding is 125 microns. The outer diameter of the common cladding 30 may be the glass outer diameter of the optical fiber 10. As shown in FIG. Figure 1 As shown, the cross-section of the common cladding 30 is circular. However, it is also contemplated that the common cladding 30 may include other cross-sectional shapes. Additionally, in some embodiments and as discussed further below, an outer coating may surround the common cladding 30.

[0058] The central axis 15 is located at the centerline of the optical fiber 10 and defines the radial position r=0 of the optical fiber 10. The cores 20 may be arranged so that the centerline of at least one core 20 and the central axis 15 are located along the same axis. Figure 1 As shown, the center line CL of the core 20 Ci (ie, CL C1 , CL C2 The centerline CL of each core 20 is located along the same axis A as the center axis 15. It should also be noted that the axis A is perpendicular to (or substantially perpendicular to) the center axis 15. Ci A radial position r=0 is defined for the core so that the centerline is defined using Cartesian coordinates, wherein the central axis 15 defines the origin (0,0) of an xy coordinate system that coincides with the coordinate system defined by the radial coordinate r. The centerline CL of the first core 20 C1 The position of can be defined as (x1, y1), and the center line CL of the second core 20 C2 The position of can be defined as (x2, y2).

[0059] As discussed above, the optical fiber 10 may include multiple cores 20, and the cores 20 may be arranged in various arrangements, including linear and square configurations. In some embodiments, the optical fiber 10 consists of only two cores 20. Figure 1 In the embodiment of FIG. 1 , the cores 20 are arranged in a 1×2 linear configuration, such that two cores 20 are arranged in a single row along the same axis A. More specifically, in Figure 1 In the embodiment of the present invention, the cores 20 are arranged so that the center line CL of each core 20 C1 , CL C2 The optical fiber 10 is positioned along the axis A, and the central axis 15 of the optical fiber 10 is also positioned on the axis A. Therefore, the central axis 15 of the optical fiber 10 is aligned with the center line CL of each core 20.C1 , CL C2 However, it should also be noted that the cores 20 may be arranged in other configurations and patterns. For example, in other embodiments, the centerline CL of the first core 20 C1 From the center line CL of the second core 20 C2 Offset.

[0060] Each core 20 has a higher refractive index than the common cladding 30, so that the optical fiber 10 acts as a waveguide. In some embodiments, the cores 20 each lack a discernible boundary with the common cladding 30. Alternatively, there is a distinct boundary between the cores 20 and the common cladding 30.

[0061] like Figure 2 As shown, each core 20 includes a core 22 and a depressed index cladding 24, such that the depressed index cladding 24 surrounds the core 22. In addition, the depressed index cladding 24 is adjacent to the core 22. Therefore, the depressed index cladding 24 directly contacts the core 22, such that no other glass region is disposed between the depressed index cladding 24 and the core 22. The common cladding 30 surrounds the depressed index cladding 24 and is adjacent to the depressed index cladding 24. Therefore, the common cladding 30 directly contacts the depressed index cladding 24, such that no other glass region is disposed between the common cladding 30 and the depressed index cladding 24. Although Figure 2 Only one core region 20 is depicted, and other core regions 20 in the optical fiber 10 may have the same structure. As discussed above, the common cladding 30 is common to all core regions 20 and therefore surrounds all core regions 20. Additional details of each core 22, depressed index cladding 24, and common cladding 30 are provided below.

[0062] Figure 3 1 is a graph of an idealized relative refractive index profile of optical fiber 10 as a function of relative refractive index versus radial coordinate r according to an embodiment of the present disclosure. Core 22 has a relative refractive index Δ1 with a maximum refractive index Δ0=Δ at r=0. 1MAX and gradient α profile, which will be described in more detail below. The depressed refractive index cladding 24 can be in the form of a depressed area or groove 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. In addition, as shown in the example, Δ2<Δ1, Δ2<Δ3 and Δ3<Δ1. Other configurations of relative refractive index profiles are further discussed below.

[0063] core

[0064] The core 22 includes silica glass, which is undoped silica glass, up-doped silica glass, and / or down-doped silica glass. Up-doped silica glass includes, for example, silica glass doped with an alkali, the alkali including potassium (e.g., K2O), sodium (Na2O), rubidium (e.g., Rb2O), or a combination thereof. Other up-doping agents include, for example, germanium (e.g., GeO2), phosphorus (e.g., P2O5), aluminum (e.g., Al2O 3) , chlorine, or other alkali metal oxides (e.g., Li2O or Cs2O). 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 where core 22 is doped with an alkali, the average concentration of the alkali dopant in core 22 is defined as: Among them C alkali (r) is the concentration of the alkali dopant as a function of the 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 an embodiment, the average concentration of the alkali dopant in the core 22 is in a range 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 core 22 has a maximum average alkali concentration of 500 ppm, the alkali dopant only slightly increases the refractive index of the core 22. Therefore, even with such alkali up-doping, the core 22 is still able to effectively achieve a refractive index of about 0%. When the core 22 includes two or more alkali dopants (such as both potassium and rubidium), the average concentration of the alkali dopant is the sum of the average concentrations of each individual alkali dopant. In some exemplary embodiments, the silica glass of the core 22 does not contain germanium and / or chlorine; that is, the core 22 includes silica glass lacking germanium and / or chlorine.

[0065] Down-doped silica glass includes silica glass doped with, for example, fluorine or boron.

[0066] As discussed above, the relative refractive index of each core 20 is described by an α-profile, wherein the α value is 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 greater, or about 9.0 or greater, or about 10.0 or greater, or about 11.0 or greater, or about 12.0 or greater, or about 13.0 or greater. In some embodiments, the core α value is about 10, or about 12, or about 20. Thus, the core 20 can have a graded refractive index profile or a step refractive index profile.

[0067] The outer radius r1 of the core 22 is in the range of about 2.5 microns to about 7.5 microns, or about 3.0 microns to about 7.0 microns, or about 3.5 microns to about 6.5 microns, or about 4.0 microns to about 5.0 microns, or about 3.0 microns to about 4.0 microns, or about 5.0 to about 6.5, or about 5.5 to about 6.3. In some embodiments, the outer radius r1 is about 5.3 microns, or about 5.8 microns, or about 5.9 microns, or about 6.1 microns, or about 6.3 microns, or about 6.4 microns.

[0068] The maximum relative refractive index Δ of the core 22 1max In the range from about -0.20% to about 0.20%, or in the range from about -0.15% to about 0.15%, or in the range from about -0.10% to about 0.10%, or in the range from about -0.05% to about 0.05%. In some embodiments, the relative refractive index Δ 1max The relative refractive index Δ 1max Preferably it is constant or approximately constant.

[0069] although Figure 3 , in some embodiments, the relative refractive index of the core 22 may have a centerline inclination such that the maximum refractive index of the core 22 and the maximum refractive index of the entire optical fiber 10 are located at a small distance away from the centerline of the core 22, rather than at the centerline of the core 22, such as Figure 3 As depicted in .

[0070] Depressed-index cladding

[0071] The depressed index cladding 24 comprises down-doped silica glass. In some embodiments, the depressed index cladding region 34 is down-doped with fluorine or boron.

[0072] As discussed above, the inner radius of depressed index cladding 24 is r1. The outer radius r2 of depressed index cladding 24 is in the range of about 12.0 microns to about 28.0 microns, or about 14.0 microns to about 26.0 microns, or about 16.0 microns to about 24.0 microns, or about 18.0 microns to about 22.0 microns, or about 14.0 microns to about 22.0 microns, or about 15.0 to about 20.0, or about 13.0 to about 23.0. In some embodiments, the outer radius r2 is about 16.5 microns, or about 16.8 microns, or about 18.4 microns, or about 20.0 microns, or about 21.3 microns, or about 22.1 microns.

[0073] The maximum relative refractive index Δ2 of depressed index cladding 24 is in the range of from about -0.50% to about -0.2%, or in the range of from about -0.40% to about -0.25%, or in the range of from about -0.35% to about -0.25%, or in the range of from 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%. The relative refractive index Δ2 is preferably constant or approximately constant.

[0074] The refractive index Δ2 of depressed index cladding 24 and the fluorine dopant used to achieve such a refractive index are selected to ensure that the optical fiber does not exhibit increased attenuation when exposed to hydrogen. The attenuation at 850 nm represents the hydrogen sensitivity of the optical fiber. In some embodiments, the attenuation of optical fiber 10 at 850 nm is less than 1.6 dB / km. In other embodiments, the attenuation of optical fiber 10 at 850 nm is less than 1.5 dB / km.

[0075] like Figure 3 As shown, the depressed index cladding 24 is a depressed index cladding region forming a groove design. The "volume" V2 of the depressed index cladding 24 is defined as: Among them, Δ 2-3 =(Δ2(r)-Δ3).

[0076] The groove volume V2 of the depressed index cladding 24 is about 5.0% Δ-micrometer 2 or greater, or about 7.0% Δ-micrometer 2 or greater, or about 10.0% Δ-micrometer 2 or greater, or about 15.0% Δ-micrometer 2 or greater, or about 17.5% Δ-micrometer 2 or greater, or about 20.0% Δ-micrometer 2 or greater, or about 22.5% Δ-micrometer 2 or greater, or about 27.5% Δ-micrometer 2 or greater, or about 30.0% Δ-micrometer 2 or greater, or about 32.5% Δ-micrometer 2 or greater, or about 35.0% Δ-micrometer 2 Additionally or alternatively, the trench volume V2 of the depressed index cladding 24 is about 37.0% Δ-micrometers 2 or less, or about 36.0% Δ-micrometer 2 or less, or about 34.0% Δ-micrometer 2 or less, or about 32.0% Δ-micrometer 2or less, or about 30.0% Δ-micrometer 2 or less, or about 28.0% Δ-micrometer 2 or less, or about 26.0% Δ-micrometer 2 or less, or about 24.0% Δ-micrometer 2 or less, or about 22% Δ-micrometer 2 or less, or about 20.0% Δ-micrometer 2 or less, or about 18.0% Δ-micrometer 2 or less, or about 15.0% Δ-micrometer 2 or less, or about 10.0% Δ-micrometer 2 or less, or about 7.0% Δ-micrometer 2 In an embodiment, the groove volume V2 of the depressed index cladding 24 is about 5.0% Δ-μm 2 to about 37.0% Δ-μm 2 , or about 7.0% Δ-μm 2 to about 37.0% Δ-μm 2 , or about 10.0 %Δ-μm 2 to about 37.0% Δ-μm 2 , or about 15.0% Δ-μm 2 to about 37.0% Δ-μm 2 , or about 5.0% Δ-μm 2 to about 36.0% Δ-μm 2 , or about 7.0% Δ-μm 2 to about 36.0% Δ-μm 2 , or about 10.0% Δ-μm 2 to about 36.0% Δ-μm 2 , or about 15.0% Δ-μm 2 to about 36.0% Δ-μm 2 , or about 16.0% Δ-μm 2 to about 35.0% Δ-μm 2 , or about 17.0 %Δ-μm 2 to about 34.0% Δ-μm 2 , or about 18.0% Δ-μm 2 to about 33.0% Δ-μm 2 , or about 20.0% Δ-μm 2 to about 30.0% Δ-μm 2 , or about 22.0% Δ-μm 2 to about 30.0 %Δ-μm 2 , or about 24.0% Δ-μm 2to about 28.0% Δ-μm 2 The groove volume V2 is at least 5.0% Δ-μm 2 , in order to achieve the low crosstalk values ​​required for uncoupled multicore fibers. In addition, the trench volume V2 is no greater than 37.0% Δ-μm 2 , in order to achieve a cable cutoff of 1530 nm or less (as discussed further below). In some embodiments, the trench volume V2 is about 19.8% Δ-micrometer 2 , or about 20.1% Δ-micrometer 2 , or about 21.7% Δ-micrometer 2 , or about 34.9% Δ-micrometer 2 , or about 36.3% Δ-micrometer 2 , or about 36.9% Δ-micrometer 2 .

[0077] Figure 3 The depressed index cladding 24 is depicted as having a rectangular shape. However, it is also contemplated that the depressed index cladding 24 may include other shapes, such as a triangle.

[0078] The transition regions from the core 22 to the depressed index cladding 24 and from the depressed index cladding 24 to the common cladding 30 are located at Figure 3 . However, it should be understood that such a step change is idealized and the transition region may not be strictly vertical in practice. Instead, the transition region may have a slope or curvature.

[0079] The depressed-index cladding 24 helps confine light within each core 22 as it propagates along the optical fiber 10 , thereby reducing crosstalk between adjacent core regions 20 .

[0080] Note that one or more core regions 20 in the optical 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 and / or radius than one or more other core regions 20. Figure 1 and Figure 2 A core region 20 is depicted having a circular cross-sectional shape. However, one or more core regions 20 may have other cross-sectional shapes, such as oval, rectangular, square, or D-shaped.

[0081] Public cladding

[0082] The common cladding 30 comprises down-doped silica glass. In some embodiments, the common cladding 30 is down-doped with fluorine or boron. In other embodiments, the common cladding 30 is composed of undoped silica glass.

[0083] As discussed above, the inner radius of the common cladding 30 is r2. In an embodiment, the outer diameter r3 of the common cladding 30 is in a range from about 40.0 microns to about 65 microns, or from about 45.0 microns to about 62.5 microns, or from about 50.0 microns to about 60.0 microns, or from about 52.5 microns to about 57.5 microns. In some embodiments, the outer radius r3 of the common cladding 30 is about 62.5 microns.

[0084] The relative refractive index Δ3 of the common cladding is in the range of from about -0.30% to about 0.00%, or in the range of from about -0.25% to about -0.05%, or in the range of from about -0.20% to about -0.10%, or in the range of from about -0.15% to about 0.00%, or in the range of from 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%. The relative refractive index Δ3 is preferably constant or approximately constant.

[0085] In some embodiments, the absolute difference between the relative refractive index Δ2 of the depressed refractive 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%.

[0086] As discussed above, the common cladding 30 can be an outer cladding common to all core regions 20 in the optical fiber 10. Thus, the common cladding 30 can surround each core region 20 in the optical fiber 10.

[0087] External coating

[0088] One or more coatings may be provided on the outer surface of the common cladding 30. For example, Figure 4 As shown, in some embodiments, primary coating 40 directly surrounds common cladding 30, and secondary coating 50 directly surrounds primary coating 40. Primary coating 40 may include a low modulus material, and secondary coating 50 may include a high modulus material. One or more of the materials may be, for example, acrylate.

[0089] Optical fiber 10 may further include a tertiary coating 60 surrounding secondary coating 50. 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 secondary coating 50.

[0090] When no tertiary layer is applied, the outer diameter of the secondary coating 50 is the outer diameter of the optical fiber 10. The outer diameter of the secondary coating 50 can be about 250 microns or less, or about 220 microns or less, or about 210 microns or less, or about 200 microns or less, or about 190 microns or less, or about 180 microns or less, or about 170 microns or less.

[0091] Core spacing

[0092] like Figure 5 As shown, adjacent core regions 20 are spaced a sufficient distance from each other to reduce crosstalk between the core regions. More specifically, the center line CL of the first core 20' C1 The center line CL of the adjacent second core 20" C2 Separation distance x. Thus, distance x is the center-to-center spacing between the center lines of adjacent cores. As defined above, using Cartesian coordinates, where the center axis 15 defines the origin (0, 0) of the xy coordinate system, the center line CL C1 The position is defined as (x1, y1), and the center line CL C2 The position is defined as (x2, y2), the distance x is the center line CL C1 and CL C2 The minimum core-to-core separation distance (or "minimum separation distance") between the two is defined as x2 = √[(x2-x1) 2 +(y2-y1) 2 As used herein, the term "adjacent cores" is used to refer to cores having centerlines that are closest to each other (i.e., there is no other core having a centerline CL that is closer to the core than the adjacent core). Ci ). In an embodiment, the centerlines of adjacent cores are separated by a minimum separation distance.

[0093] In an embodiment, the distance x is about 48 microns or more, or about 50 microns or more, or about 52 microns or more, or about 55 microns or more, or about 58 microns or more. Additionally or alternatively, the distance x is about 60 microns or less, or about 58 microns or less, or about 55 microns or less, or about 50 microns or less. In some embodiments, the distance x is about 48 microns to about 60 microns, or about 50 microns to about 60 microns, or about 50 microns to about 58 microns, or about 50 microns to about 55 microns, or about 51 microns to about 54 microns.

[0094] like Figure 5As shown, the distance y is the minimum distance between the outer diameter of the core region 20 and the outer diameter of the common cladding 30, and is measured from the edge of each of the plurality of core regions 20 to the outer surface 32 of the common cladding 30. In an embodiment, y is about 5 microns or more, or about 10 microns or more, or about 12 microns or more, or 15 microns or more, or about 18 microns or more, or about 20 microns or more, or about 22 microns or more, or about 25 microns or more, or about 28 microns or more, or about 30 microns or more. Additionally or alternatively, the distance y is about 30 microns or less, or about 28 microns or less, or about 25 microns or less, or about 22 microns or less, or about 20 microns or less. In an embodiment, the distance y is about 5 microns to about 30 microns, or about 10 microns to about 28 microns, or about 12 microns to about 25 microns, or about 15 microns to about 20 microns. Without intending to be bound by theory, it is believed that the extent of signal loss due to tunneling and radiation depends on the distance y. More specifically, it is believed that as the distance y becomes larger, an increase in the distance y corresponds to an exponential increase in tunneling and radiation losses due to increased coupling to external modes. Thus, in general, an increase in the distance y corresponds to a decrease in radiation and tunneling losses.

[0095] nature

[0096] Without intending to be limited by theory, the combination of the depressed index cladding 24 directly surrounding the core 22 and the core spacing (distance x) between adjacent cores provides low cable cutoff and low crosstalk. Therefore, the optical fiber disclosed herein has excellent bending performance and is suitable for use in submarine cables. In addition, since the depressed index cladding 24 directly surrounds the core 22, the optical fiber disclosed herein does not include an inner cladding region between these components. Therefore, the optical fiber disclosed herein can be produced in a cost-effective manner (by not requiring the additional time and resources required to manufacture such an inner cladding region).

[0097] In particular, the optical fibers produced herein have a cable cutoff of 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 cable cutoff is about 1250 nm or greater, or about 1280 nm or greater, or about 1300 nm or greater, or about 1320 nm or greater, or about 1350 nm or greater, or about 1380 nm or greater, or about 1400 nm or greater, or about 1420 nm or greater, or about 1450 nm or greater. In some embodiments, the cable cutoff is about 1300 nm to about 1530 nm, or about 1320 nm to about 1515 nm, or about 1350 nm to about 1500 nm, or about 1375 nm to about 1475 nm.

[0098] As discussed above, the cable cutoff of the optical fiber 10 is preferably high in order to improve the bending performance of the optical fiber disclosed herein. It should also be noted that the effective area of ​​the optical fiber is relatively high (as discussed below), thus facilitating a higher cable cutoff.

[0099] The optical fiber disclosed in this article has a wavelength of about 100 microns at 1550 nm. 2 or larger, or about 105 microns 2 or larger, or about 110 microns 2 or larger, or about 115 microns 2 or larger, or about 120 microns 2 or larger, or about 125 microns 2 or larger, or about 130 microns 2 Alternatively or additionally, the optical fiber has an effective area of ​​about 135 microns at a wavelength of 1550 nm. 2 or smaller, or about 130 microns 2 or smaller, or about 125 microns 2 or smaller, or about 120 microns 2 or smaller, or about 115 microns 2 In one embodiment, the effective area is about 100 microns. 2 to about 135 microns 2 , or about 105 microns 2 to about 130 microns 2 , or about 110 microns 2 to about 125 microns 2 , or about 115 microns2 to about 120 microns 2 In some exemplary embodiments, the active area is about 110 microns 2 , or about 111 microns 2 , or about 112 microns 2 , or about 114 microns 2 .

[0100] At a wavelength of 1550 nm and at a bend diameter of 140 mm, the co-propagation crosstalk between adjacent cores in the optical fiber produced herein is less than about -35 dB or less than about -40 dB per 100 km of optical fiber length. In embodiments, at a wavelength of 1550 nm and at a bend diameter of 140 mm, the co-propagation crosstalk between adjacent cores 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 optical fiber length. Additionally or alternatively, in some embodiments, at a wavelength of 1550 nm and at a bend diameter of 140 mm, the co-propagation crosstalk between adjacent cores 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 optical fiber length.

[0101] At a wavelength of 1550 nm and at a bend diameter of 140 mm, the counter-propagating crosstalk between adjacent cores in the optical fiber produced herein is less than about -70 dB, 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 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 per 100 km of optical fiber length. Additionally or alternatively, in some embodiments, at a wavelength of 1550 nm and at a bend diameter of 140 mm, the counter-propagating crosstalk between adjacent cores 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 optical fiber length.

[0102] 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 1550 nm of about 11.0 microns or more, or about 11.5 microns or more, or about 12.0 microns or more, or about 12.5 microns or more, or about 13.0 microns or more, or about 13.5 microns or more, or about 14.0 microns or more, or about 14.5 microns or more, or about 15.0 microns or more. Additionally or alternatively, each core 20 has a mode field diameter at a wavelength of 1550 nm of about 15.0 microns or less, or about 14.5 microns or less, or about 14.0 microns or less, or about 13.5 microns or less, or about 13.0 microns or less, or about 12.5 microns or less, or about 12.0 microns or less, or about 11.5 microns or less. In some embodiments, each core 20 has a mode field diameter of about 11.0 microns to about 15.0 microns, or about 11.5 microns to about 14.5 microns, or about 12.0 microns to about 14.0 microns, or about 12.5 microns to about 13.5 microns at a wavelength of 1550 nm. In an exemplary embodiment, the mode field diameter is about 11.5 microns, or about 12.0 microns, or about 12.5 microns, or about 13.0 microns.

[0103] According to aspects of the present disclosure, each core 20 has a dispersion of less than about 22 ps / nm / km at 1550 nm. For example, the dispersion at 1550 nm is about 17 ps / nm / km to about 22 ps / nm / km, or about 18 ps / nm / km to about 22 ps / nm / km, or about 18 ps / nm / km to about 21 ps / nm / km, or about 19 ps / nm / km to about 21 ps / nm / km, or about 20 ps / nm / km to about 22 ps / nm / km.

[0104] The dispersion slope of each core 20 at 1550 nm is less than about 0.1 ps / nm 2 / km, or about 0.04ps / nm 2 / km to about 0.1ps / nm 2 / km, or about 0.05ps / nm 2 / km to about 0.1ps / nm 2 / km, or about 0.055ps / nm 2 / km to about 0.1ps / nm 2 / km, or about 0.06ps / nm 2 / km to about 0.1ps / nm 2 / km, or about 0.08ps / nm 2 / km to about 0.1ps / nm 2 / km, or about 0.04ps / nm 2 / km to about 0.08ps / nm 2 / km, or about 0.05ps / nm 2 / km to about 0.08ps / nm 2 / km, or about 0.55ps / nm 2 / km to about 0.08ps / nm 2 / km, or about 0.06ps / nm 2 / km to about 0.08ps / nm2 / km, or about 0.04ps / nm 2 / km to about 0.06ps / nm 2 / km, or about 0.05ps / nm 2 / km to about 0.06ps / nm 2 / km, or about 0.55ps / nm 2 / km to about 0.06ps / nm 2 / km. For example, the dispersion slope at 1550nm can be about 0.04ps / nm 2 / km, about 0.05ps / nm 2 / km, about 0.055ps / nm 2 / km, about 0.057ps / nm 2 / km, about 0.058ps / nm 2 / km, about 0.059ps / nm 2 / km, about 0.06ps / nm 2 / km, about 0.061ps / nm 2 / km, about 0.07ps / nm 2 / km, about 0.08ps / nm 2 / km or any value in between these values.

[0105] Each core 20 may have the same or different dispersion and dispersion slope at 1550 nm.

[0106] The average attenuation of the optical fiber disclosed herein is determined by measuring the attenuation of each core 20 of the uncoupled core multi-core optical fiber 10 at a wavelength of 1550 nm, and then calculating the average attenuation of the entire uncoupled core multi-core optical fiber 10 based on the individual attenuation measurements of each core 20. In an embodiment, the average attenuation of the uncoupled core 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. In addition, the average attenuation of the uncoupled core 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 (also as discussed above). It should be understood that the average attenuation of the uncoupled-core multi-core optical fiber 110 may be within a range formed by any attenuation lower limit value and any attenuation upper limit value described herein.

[0107] The respective attenuation of each core 20 is also determined 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 20 in the uncoupled-core multi-core optical fiber 10 is about 0.148 dB / km, and the attenuation of the second core 20 in the uncoupled-core multi-core optical fiber 10 is about 0.147 dB / km.

[0108] Furthermore, the uncoupled optical fibers disclosed herein may have an average attenuation of less than or equal to about 1.6 dB / km at a wavelength of 850 nm, less than or equal to about 1.5 dB / km at a wavelength of 850 nm, or less than or equal to about 0.145 dB / turn at a wavelength of 850 nm.

[0109] The core 20 has a radiation loss of 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 at a wavelength of 1550 nm.

[0110] In embodiments, the disclosed multi-core optical fiber has bending losses of about 0.6 dB or less, or about 0.5 dB or less, or about 0.4 dB or less at 1625 nm when wound 100 times on a 60 mm mandrel diameter.

[0111] Reference again Figure 2 and Figure 3 In an embodiment, each core 20 is manufactured so that the varying relative refractive index Δ2 of the depressed index cladding region 24 is determined by the down dopant concentration D as a function of the radial coordinate r, i.e., D=D(r). In an embodiment, the down dopant is fluorine, and D(r) is expressed as the radially dependent fluorine concentration F(r). Therefore, F(r) within the depressed index cladding 24 can be at a minimum value F min and the maximum value F max In the embodiment, F min At radial position r1, and F max At radial position r2. In the embodiment, F max Greater than or equal to 0.75 wt.% and less than or equal to 2.2 wt.%, or greater than or equal to 0.9 wt.% and less than or equal to 2.2 wt.%.

[0112] The down dopant concentration (e.g., F max and F min ) determines the refractive index profile therein, and therefore determines the trench volume V2 of the depressed 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 losses and inter-core crosstalk of each core 20. In order to achieve a 100 micron at a wavelength of 1550 nm, the trench volume V2 is preferably 100 microns. 2 and 135 microns 2 In order to achieve an effective area between 100 nm and 1500 nm, a cable cutoff wavelength of less than 1530 nm, a dispersion of less than 22 ps / nm / km at 1550 nm, and a crosstalk of less than -30 dB / 100 km at 1550 nm, the groove volume V2 of the depressed refractive index cladding 24 of each core 20 should be greater than or equal to 15% Δ-micrometer 2 and less than or equal to 37% Δ-micrometer 2 .

[0113] Exemplary Embodiments

[0114] The following provides exemplary embodiments of the uncoupled-core multi-core optical fiber disclosed herein. The following exemplary embodiments are intended to be illustrative and are not intended to limit the scope of the present disclosure.

[0115] Table 1 below provides five modeled examples of uncoupled core multicore optical fibers (exemplary examples AE), each of which includes 2 cores arranged in a 1×2 linear configuration. The core refractive index, radius, and α value for the two cores of each exemplary optical fiber in Table 1 apply. The optical fibers in Table 1 below each have an outer diameter of 125 microns. In addition, the crosstalk at 1550 nm for each optical fiber in Table 1 is determined at different center-to-center spacing lengths (i.e., different distances of x) between the centerlines of adjacent cores. More specifically, the crosstalk at 1550 nm is determined for each optical fiber having a center-to-center spacing of adjacent cores ranging from 44 microns to 66 microns. Table 1

[0116] As shown in Table 1 above, center-to-center spacing between adjacent core centerlines of 48 microns and above generally produces better crosstalk between adjacent cores.

[0117] An optical fiber was produced based on the above modeled Exemplary Example A. The performance of the produced optical fiber is shown in Table 2 below as Exemplary Example A'. Additionally, an optical fiber was produced based on the above modeled Exemplary Example E. The performance of the produced optical fiber is shown in Table 2 below as Exemplary Example E'. Exemplary Examples A' and E' both had a center-to-center spacing of 50 microns between the centerlines of adjacent cores. Table 2

[0118] As shown in Table 2 above, the manufactured fibers of both illustrative examples A' and E' have very low attenuation while still achieving high mode field diameter and low crosstalk.

[0119] Fig. 6A The refractive index profile of exemplary examples AD with respect to the radial coordinate r is shown. In addition, at a wavelength of 1550 nm, the co-propagating core-to-core crosstalk (in dB / 100 km) of exemplary examples AD is Fig. 7A is plotted as a function of the center-to-center spacing (micrometers) of adjacent cores. At a wavelength of 1550 nm, the counter-propagating inter-core crosstalk (in dB / 100 km) of the exemplary example AD is Figure 7B is plotted as a function of the center-to-center spacing of adjacent cores (in micrometers). And the radiation loss (dB / km) of the exemplary example AD is Figure 87 is plotted as a function of the center-to-center spacing of adjacent cores (in microns). As discussed herein, radiation losses represent mode leakage losses due to the smaller cladding diameter and overlap of the mode field intensity with the high refractive index primary coating. The center-to-center spacing of adjacent cores is selected so that the inter-core crosstalk at a wavelength of 1550nm is less than -30dB / 100km and the radiation losses are less than 1dB / km. In addition, FIG7 shows that as the center-to-center spacing of adjacent cores increases, the inter-core crosstalk between adjacent cores decreases. However, Figure 8 It is shown that as the center-to-center spacing of adjacent cores increases, the radiation loss also increases. Thus, as the distance x increases, the crosstalk between the cores decreases, but the radiation loss increases.

[0120] Example Process The uncoupled cores of the multi-core optical fibers of the present disclosure may be made using any suitable method for forming a multi-core optical fiber. See, for example, U.S. Patent No. 11,370,689 B2, the entire contents of which are incorporated herein by reference. Figures 1 to 8 An exemplary method of forming an uncoupled-core multi-core optical fiber 10 (or any alternative embodiment thereof) includes forming a glass blank for a common cladding 30. The formation of the glass blank may involve first forming a soot body via an outside vapor deposition ("OVD") process, a soot pressing method, a vapor axial deposition ("VAD") process, or any other known method, and then dehydrating and consolidating into a fully densified 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 and then a plurality of holes are drilled along the length of the glass blank for inserting a core rod therein. In some embodiments, the common cladding glass blank is doped with a down dopant (such as fluorine).

[0121] Next, a core region of the core rod may be formed. In some embodiments, the core region is composed of at least one base at a concentration between 0.1 wt% and 5 wt%. In some embodiments, the core is doped with potassium. In other embodiments, the core is doped with two base components selected from potassium, sodium, rubidium, and cesium. The core rod may be formed by the method disclosed in U.S. Patent No. 7,536,076 B2, the entire contents of which are incorporated herein by reference. .

[0122] Next, a cladding is deposited on the core region. In an embodiment, a silica-based soot soot outer cladding (multiple) is formed on the core region via an OVD or VAD process. The outer cladding (multiple) has a composition corresponding to the depressed index cladding of the core of the multi-core optical fiber. For example, the outer cladding can include separate layers having a composition corresponding to the depressed index cladding 24. The outer clad core region is positioned in a consolidation furnace, and consolidation of the outer clad core region is initiated. For example, the outer clad core region can be heated to a peak sintering temperature to initiate consolidation.

[0123] During consolidation, after the consolidation is initiated, the overclad core region is exposed to the down dopant for a period of time T. The soot preform resulting from the completion of the consolidation process includes a core region and an overcladding layer surrounding the core region. The core region (e.g., in an unconsolidated or partially consolidated state) and the overcladding layer may be placed inside a consolidation furnace. The consolidation furnace may be heated to a peak sintering temperature of the overcladding layer to initiate consolidation.

[0124] The gas source is in fluid communication with the interior of the consolidation furnace, providing a gas containing a down dopant to the interior. The down dopant (e.g., fluorine) then diffuses through the overcoat during consolidation. In an embodiment, the diffusion rate of the down dopant through the overcoat depends on the composition and material properties (e.g., porosity, density, etc.) of the overcoat. As the overcoat consolidates, the porosity of the overcoat decreases, so that the diffusion rate of the down dopant can decrease as the overcoat consolidates.

[0125] In an embodiment, the region surrounding and directly contacting the core corresponds to the depressed index cladding 24. In an embodiment, the depressed index cladding 24 has a concentration of a down dopant.

[0126] After the core region is consolidated into a glass preform, the glass preform is inserted into the hole drilled in the glass blank formed during the step. After each core rod is inserted into the glass blank, the optical fiber preform is assembled by thermally closing the gap between the inserted core rod and the drilled hole. The assembled preform is then drawn into a multi-core optical fiber. An example method of forming a core rod-based optical fiber preform is discussed in U.S. Patent No. 11,370,689, the entire contents of which are incorporated herein by reference.

[0127] It is obvious to those skilled in the art that various modifications and changes can be made without departing from the spirit or scope of the present invention. Since those skilled in the art can think of modifications, combinations, sub-combinations and variations of the disclosed embodiments that include the spirit and essence of the present invention, the present invention should be understood to include everything within the scope of the attached claims and their equivalents.

Claims

1. An uncoupled core multi-core optical fiber, comprising: At least two cores, each core comprising: 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; and A depressed refractive index cladding having a radius r2 and a relative refractive index Δ2 relative to pure silica such that Δ2<Δ1, the depressed refractive index cladding surrounding and directly contacting the core, the volume V2 of the depressed refractive index cladding being about 5.0% Δ-micrometers 2 to about 37.0% Δ-μm 2 ;as well as a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica such that Δ2<Δ3<Δ1, the common cladding surrounding and directly contacting the depressed-index cladding, in: The cable cutoff wavelength of each core is about 1530nm or less, The effective area of ​​each core at 1550 nm is about 100 microns 2 to about 135 microns 2 , Each core includes an attenuation of about 0.165 dB / km or less at a wavelength of 1550 nm, and The center-to-center spacing between the centerlines of adjacent cores is from about 48 microns to about 60 microns.

2. The uncoupled-core multi-core optical fiber according to claim 1, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -30 dB or less per 100 km of optical fiber.

3. The uncoupled-core multi-core optical fiber according to claim 2, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -40 dB or less per 100 km of optical fiber.

4. The uncoupled-core multi-core optical fiber according to claim 3, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -50 dB or less per 100 km of optical fiber.

5. The uncoupled-core multi-core optical fiber according to claim 4, wherein: The co-propagation crosstalk between the at least two cores is about -60 dB or less per 100 km of optical fiber.

6. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 5, wherein: The counter-propagating crosstalk between the at least two cores is about -35 dB or less per 100 km of optical fiber.

7. The uncoupled-core multi-core optical fiber according to claim 6, wherein: The counter-propagating crosstalk between the at least two cores is about -40 dB or less per 100 km of optical fiber.

8. The uncoupled-core multi-core optical fiber according to claim 7, wherein: The counter-propagating crosstalk between the at least two cores is about -45 dB or less per 100 km of optical fiber.

9. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 8, wherein: The at least two cores consist of only two cores.

10. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 9, wherein: The centerline of each of the at least two cores is located along axis A.

11. The uncoupled-core multi-core optical fiber according to claim 10, wherein: The axis A extends through the central axis of the multi-core optical fiber.

12. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 11, wherein: The effective area of ​​each core is about 110 microns at a wavelength of 1550 nm. 2 .

13. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 12, wherein: The attenuation of each core is about 0.160 dB / km or less at a wavelength of 1550 nm.

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

15. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 14, wherein: The relative refractive index Δ1 is about −0.20% to about 0.20%.

16. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 15, wherein: The average concentration of alkali in the core is from about 20 ppm to about 500 ppm.

17. The uncoupled-core multi-core optical fiber according to claim 16, wherein: The average concentration of alkali in the core is from about 5 ppm to about 300 ppm.

18. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 17, wherein: The mode field diameter of each core is about 11.0 microns to about 15.0 microns at a wavelength of 1550 nm.

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

20. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 19, wherein: The center-to-center spacing between centerlines of adjacent cores is from about 50 microns to about 55 microns.

21. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 20, wherein: The radius r3 is about 120 microns to about 130 microns.

22. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 21, wherein: The radius r3 is about 125 microns.

23. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 22, wherein: The radius r2 is about 13.0 microns to about 23.0 microns.

24. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 23, wherein: The radius r1 is about 3.0 micrometers to about 7.0 micrometers.

25. The uncoupled-core multi-core optical fiber according to any one of claims 1 to 24, wherein: The volume V2 of the depressed index cladding is about 15.0% Δ-micrometers 2 to about 37.0% Δ-μm 2 .

26. The uncoupled-core multi-core optical fiber according to claim 25, wherein: The volume V2 of the depressed index cladding is about 20.0% Δ-micrometers 2 to about 30.0% Δ-μm 2 .

27. An uncoupled core multi-core optical fiber, comprising: At least two cores, each core comprising: A core having a radius r1 and a relative refractive index Δ1 relative to pure silica, wherein each portion comprises an attenuation of less than about 0.150 dB / km at a wavelength of 1550 nm.

28. The uncoupled-core multi-core optical fiber of claim 27, wherein: the core is doped with at least one of sodium, potassium and rubidium, The optical fiber further comprises: A depressed refractive index cladding having a radius r2 and a relative refractive index Δ2 relative to pure silica such that Δ2<Δ1, the depressed refractive index cladding surrounding and directly contacting the core, the volume V2 of the depressed refractive index cladding being about 5.0% Δ-micrometers 2 to about 37.0% Δ-μm 2 ,as well as a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica such that Δ2<Δ3<Δ1, the common cladding surrounding and directly contacting the depressed-index cladding, The cable cutoff wavelength of each core is about 1530nm or less, The effective area of ​​each core at 1550 nm is about 100 microns 2 to about 135 microns 2 ,as well as The center-to-center spacing between the centerlines of adjacent cores is from about 48 microns to about 60 microns.

29. The uncoupled-core multi-core optical fiber according to claim 27 or claim 28, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -30 dB or less per 100 km of optical fiber.

30. The uncoupled-core multi-core optical fiber according to claim 29, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -40 dB or less per 100 km of optical fiber.

31. The uncoupled-core multi-core optical fiber according to claim 30, wherein: For a bend diameter of 140 mm, the co-propagating crosstalk between the at least two cores is about -50 dB or less per 100 km of optical fiber.

32. The uncoupled-core multi-core optical fiber according to claim 31, wherein: The co-propagation crosstalk between the at least two cores is about -60 dB or less per 100 km of optical fiber.

33. The uncoupled-core multi-core optical fiber according to any one of claims 27 to 32, wherein: The counter-propagating crosstalk between the at least two cores is about -35 dB or less per 100 km of optical fiber.

34. The uncoupled-core multi-core optical fiber according to claim 33, wherein: The counter-propagating crosstalk between the at least two cores is about -40 dB or less per 100 km of optical fiber.

35. The uncoupled-core multi-core optical fiber according to claim 34, wherein: The counter-propagating crosstalk between the at least two cores is about -45 dB or less per 100 km of optical fiber.

36. The uncoupled-core multi-core optical fiber according to any one of claims 27 to 35, wherein: The at least two cores consist of only two cores.

37. The uncoupled-core multi-core optical fiber according to any one of claims 27 to 36, wherein: The centerline of each of the at least two cores is located along axis A.

38. The uncoupled-core multi-core optical fiber according to claim 37, wherein: The axis A extends through the central axis of the multi-core optical fiber.

39. The uncoupled-core multi-core optical fiber according to any one of claims 27 to 38, wherein: The attenuation of each core is about 0.149 dB / km or less at a wavelength of 1550 nm.

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