Improved splicing of hollow-core fibers

Abstract

Processes for splicing rotationally non-invariant optical fibers, such as hollow-core fibers (HCFs), are disclosed. For some embodiments, the splicing process comprises properly aligning (both azimuthally and axially) an end of a first rotationally non-invariant optical fiber with an end of a second rotationally non-invariant optical fiber. The rotationally non-invariant optical fibers are aligned with a predefined gap between their respective ends. Upon properly aligning the to-be-joined ends, the splicing process continues to a two-stage fusion process in which: (a) the first stage applies arcs that melt together the ends of the fibers without damaging the internal microstructures o f the fibers; and (b) the second stage applies arcs to strengthen the splicing point without damaging the internal microstructures of the fiber.

Description

IMPROVED SPLICING OF HOLLOW-CORE FIBERSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patent application serial number 63 / 545, 300, filed 2023-Oct-23, by Kremp et al., and having the title "Low-Loss Mechanically Stable Hollow Core Fiber Splicing," which is incorporated herein by reference in its entirety.BACKGROUNDFIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to optics and, more particularly, to optical fibers.DESCRIPTION OF RELATED ART

[0003] For optical fibers, a discrete loss that occurs when two fibers are joined end- to-end is known as a splice loss. Splice loss occurs when there is a less-than-perfect joining of one fiber end to another fiber end (due to, for example, mismatch, misalignment, or poor splicing conditions), thereby resulting in atenuation, scatering, and / or reflection. Because splice loss contributes to the total signal loss in optical fiber networks, there are ongoing efforts to reduce splice loss.SUMMARY

[0004] The present disclosure teaches processes for splicing rotationally non- invariant optical fibers, such as hollow-core fibers (HCFs). For some embodiments, the splicing process comprises properly aligning (both azimuthally and axially) an end of a first rotationally non-invariant optical fiber with an end of a second rotationally non-invariant optical fiber. The rotationally non-invariant optical fibers are aligned with a predefined gap between their respective ends. Upon properly aligning the to-be-joined ends, the splicing process continues to a two-stage fusion process in which: (a) the first stage applies arcs that melt together the ends of the fibers without damaging the internal microstructures of the fibers; and (b) the second stage applies arcs that add strength to the splicing point withoutdamaging the internal microstructures of the fiber,

[0005] Other systems, devices, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure.Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0007] FIG. 1A is a drawing that shows a geometry for a cross-sectional view (shown as the X-Y plane) of an embodiment of a rotationally non-invariant optical fiber, such as an anti-resonant hollow-core fiber (ARHCF).

[0008] FIG. IB is a drawing that shows the square root of the fundamental mode intensity (horizontal polarization) for the ARHCF of FIG. 1A.

[0009] FIG. 2 A is a side-view projection (shown as the Y-Z plane) of an end of a rotationally non-invariant optical fiber, which was collected at one azimuthal angle (0).

[0010] FIG. 2B is a side-view projection (Y-Z plane) of an end of another rotationally non-invariant optical fiber, which shows sub-optimum azimuthal alignment with the fiber end of FIG. 2 A.

[0011] FIG. 3 is a side-view projection (Y-Z plane) for a sub-optimum azimuthal alignment of two (2) joined rotationally non-invariant optical fibers, which exhibits a lower degree of correlation between the two (2) joined ends.

[0012] FIG. 4 is a side-view projection (Y -Z plane) for an optimum azimuthal alignment of two (2) joined rotationally non-invariant optical fibers, which exhibits higher degree of correlation between the two (2) joined ends.

[0013] FIG. 5 is a graph showing simulated coupling loss (in decibels (dB)) and average coupling loss (also in dB) for different rotational angles (or azimuthal anglemismatches) for an embodiment of spliced rotationally non-invariant optical fibers.

[0014] FIG. 6 is a flowchart showing one embodiment of a process for splicing together rotationally non-invariant optical fibers.

[0015] FIG. 7 A is a side-view projection (Y-Z plane) of two (2) rotationally non- invariant optical fibers that are aligned axially and azimuthally at an initial distance (dinitiai) that separates the two (2) optical fiber ends.

[0016] FIG. 7B is a diagram illustrating the starting position and movement of the two (2) optical fibers of FIG. 7B.

[0017] FIG. 8 is a diagram illustrating one embodiment of the arc-discharging steps from the process of FIG. 6.

[0018] FIG. 9 is a graph showing transmitted power (in dBm) at 1543.2nm through a 10μm gap between two ARHCF fibers in a ring-of-fire (ROF) arc splicer prior to fusion splicing with optimum azimuthal alignment (shown as closed circles) and without optimum azimuthal alignment (shown as open squares).

[0019] FIG. 10 is a graph showing the difference in ARHCF-to-ARHCF splice loss with optimum azimuthal alignment (shown as closed circles) and without optimum azimuthal alignment (shown as open squares).

[0020] FIG. 11 is a graph showing the mean, median, and standard deviation of the data shown in FIG. 10.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Micro-structured fibers (such as photonic crystal fibers (PCFs), hollow-core fibers (HCFs), photonic band-gap hollow-core fibers (PBGHCFs), anti-resonant hollow-core fibers (ARHCF s), etc.) are rotationally non-invariant and, thus, their fundamental eigenmodes are not circular. For example, as shown in FIGS. I A and IB (collectively designated herein as FIG. 1), a cross-section 100a, 100b (collectively, 100) of a five-ring ARHCF 104a (with the X-Y plane representing the plane through which the cross-section is taken) exhibits a star-shaped or pentagonal fundamental mode 104b. Consequently, as shown in FIGS. 2A and 2B (with the Z axis being labeled as an axial direction of the ARHCF), a side-view projection 204 (in the Y-Z plane) of an end of an ARHCF at one azimuthal angle (0) appears different than a side view projection 208 of that same ARHCF ata different 0.

[0022] Thus, even when two ARHCFs with the same-shaped fundamental modes are spliced together, if the ARHCFs are not rotationally aligned, then (as shown in FIG. 3) the side-view projection 304 exhibits a mismatch at the splice point of the ARHCFs. If, however, the ARHCFs are rotationally aligned (as shown in FIG. 4), then the side-view projection 404 exhibits a close match at the splice point of the ARHCFs. Consequently, there have been efforts to properly align optical fibers, such as those disclosed in WO2022 / 125443 (PCT / US2021 / 062021), filed on 2021 -December-06, by OFS Fitel, LLC, and listing as inventors Kremp, et al., which is incorporated by reference herein as if expressly set forth in its entirety.

[0023] As one can appreciate, splice loss or coupling loss (in decibels (dB)) for ARHCFs with pentagonal fundamental modes exhibits a substantially sinusoidal behavior through a full rotation of 360°, as shown in the graph of FIG. 5, with the splice loss being at minima when the rotational or azimuthal mismatch is 0°, 72°, 144°, 216°, or 288°, and the splice loss being at maxima when the rotational or azimuthal mismatch is at 36°, 108°, 180°, 252°, or 324°. Although a specific example of an ARHCF is provided to illustrate splice losses that are caused by rotational or azimuthal misalignment, those having skill in the art will appreciate that similar rotational-angle-based losses occur in other rotationally non- invariant optical fibers, e.g., ARHCFs with a different number of rings or nesting levels, including ARHCF with four (4), six (6) or seven (7) instead of five (5) rings per nesting levels, which may also have three (3) or more instead of the case of two (2) nesting levels as shown in FIG. 1 . Azimuthal alignment can also reduce scatering or reflection.

[0024] In addition to splice losses from rotational misalignment, the process of fusing together optical fibers with internal microstructures affects the properties at the splice point. Specifically, for HCFs or PCFs (which have internal microstructures), different arc discharge powers from an arc splicer can affect differently the properties at the splice point. For example, an amount of arc discharge power that results in a lower splice loss may be different than an amount of arc discharge power that produces a mechanically stronger splice.

[0025] Of course, it is possible to reduce or minimize rotation-angle-dependent losses and arc-discharge-power-dependent drawbacks by meticulously setting up the equiμment and managing the environment to compensate for most (if not all) of the variables that affectsplice loss. However, employing such a meticulous process is slow, cumbersome, costly, and unsuitable as a field-deployment solution. In other words, field deployment requires a fast, portable, and (preferably) fully automated process, which can reduce or minimize as many of the adverse factors that affect splice loss.

[0026] To address these and other drawbacks, this disclosure teaches a process that axially and azimuthally aligns two (2) to-be-joined rotationally non-invariant optical fibers and, thereafter, fuses together the rotationally non-invariant optical fiber ends at the splice point. In particular, the fusing together of the optical fibers employs three (3) distinct arcs from an arc splicer while controlling the axial movement of the rotationally non-invariant optical fibers. By selectively controlling the axial movement of the rotationally non- invariant optical fibers while applying arcs with different power levels, the disclosed process permits azimuthally aligned fusion splicing of rotationally non-invariant optical fibers that is suitable for field deployment.

[0027] Having provided a broad technical solution to a technical problem, reference is now made in detail to the description of the embodiments as illustrated in the drawings. Specifically, FIG. 6 is a flowchart showing one embodiment of a process for splicing together rotationally non-invariant optical fibers; FIGS. 7A, 7B, and 8 are drawings further illustrating several of the process steps of FIG. 6; and FIGS. 9, 10, and 11 are graphs showing example data comparing the disclosed process with other fiber-splicing processes. Although several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents.

[0028] Before explaining in detail the various aspects of the disclosed processes, some of the terminology that is used throughout this disclosure is explained. By way of example, for purposes of the present invention, a fiber is referred to as "rotationally invariant" if it is circularly symmetric (if it has continuous symmetry , meaning, it maps onto itself while being rotated by an arbitrary azimuthal angle). For a "rotationally invariant" fiber, all of the material properties (e.g., refractive index, etc.) of the fiber are independent of the azimuthal angle. .An example is a single-core fiber whose core is perfectly circular and centered in the center of a perfectly circular cladding. The refractive index profile of both core and cladding is allowed to vary radially, though.

[0029] A fiber is referred to as "rotationally non-invariant" if it is not rotationally invariant Thus, rotationally non-invariant fibers are defined as those fibers whose transverse geometry or structure, which includes the refractive index profile of cores, rings and cladding (solid and / or micro-structured) as well as other material parameters such as loss or gain (imaginary part of the refractive index) or elastic modulus or stress profile and the like, depends on the azimuthal angle, meaning, those fibers that are not circularly symmetric. Examples are PBGHCFs, ARHCFs, a single-core fiber with a D-shaped cladding, or any multicore fiber.

[0030] FIG. 6 is a flowchart showing one embodiment of a process 600 for splicing together rotationally non-invariant optical fibers. The process 600 includes an aligning process 601 followed by a fusing process 602. Tire aligning process 601 aligns a first rotationally non-invariant optical fiber with a second rotationally non-invariant optical fiber. Of course, those having skill in the art will understand that any splicing equipment is calibrated using known methods prior to splicing together the rotationally non-invariant optical fibers. Insofar as calibration methods are well known to those having skill in the art, no further discussions of calibration processes are discussed and the process 600 of FIG. 6 presumes calibrated equipment for the disclosed process steps.

[0031] Additionally, to more clearly explain the process 600, anti-resonant hollow- core fibers (ARHCFs) are used as example embodiments of rotationally non-invariant optical fibers. However, it should be appreciated that other types of rotationally non-invariant optical fibers (e.g., PCFs, FICFs, PBGHCFs, etc.) can be aligned 601 and fused 602 using the process 600 of FIG. 6. Moreover, to distinguish between the two (2) to-be-joined rotationally non-invariant optical fibers, each fiber is arbitrarily designated as either a first optical fiber (e.g., first rotationally non-invariant optical fiber, first ARHCF (or ARHCF1), etc.) or a second optical fiber (e.g., second rotationally non-invariant optical fiber, second ARHCF (or ARHCF2), etc.). Additionally, although a Cartesian coordinate system (using X, Y, and Z) is used to designate the orientation and movement of the optical fibers, it should be appreciated that the directions are arbitrarily assigned for illustrative purposes only.

[0032] With this in mind, and turning to FIG. 6, some embodiments of the alignment process 601 begin with rotationally scanning 604 a first rotationally non-invariant optical fiber end (e.g., ARHCF 1 end). The rotational scanning 604 is done through a full rotation(namely, a full 360 degree (360°) rotation) at multiple azimuthal angles, 0 (e.g,, at 4° increments for ninety (90) total scans)). Each of the discrete azimuthal angles 0 produces a side-view projection of the ARHCF 1, similar to those shown in FIGS. 2A and 2B.

[0033] The alignment process 601 further comprises rotationally scanning 608 a second rotationally non-invariant optical fiber end (e.g., ARHCF2 end). The second rotational scan 608 is also performed through a foil 360° rotation at multiple 0 (preferably the same 0 increments as the first rotational scan 608). Each discrete 0 produces a side-view projection of the ARHCF2, similar to those shown in FIGS. 2A and 2B. It should be appreciated that the first rotational scan 604 and the second rotational scan 608 can be performed sequentially or concurrently.

[0034] The alignment process 601 correlates 612 the rotational scans of the ARHCF 1 end with the rotational scans of the ARHCF2 end. From the results of the correlation 612, the alignment process determines 616 an optimum azimuthal angle. This optimum azimuthal angle represents an angle at which the fundamental mode at the ARHCF 1 end matches as closely as possible the fundamental mode at the ARHCF2 end. By way of example, for an optical fiber with a pentagonal fundamental mode, the optimum azimuthal angle represents the minima in the graph of FIG. 5. Technically, correlating 612 the rotational scans is not exactly the same as minimizing coupling loss. However, for practical field-deployment conditions, the correlation of the rotational scans provides a sufficiently accurate approximation of when the coupling loss is minimized.

[0035] The ends of the two (2) rotationally non-invariant optical fibers (e.g., ARHCF1 end and ARHCF2 end) are azimuthally aligned 620 using the correlation results. Additionally, the two (2) ends (ARHCF 1 end and ARHCF2 end) are also axially aligned 624 and secured 628 at an initial distance (dinitial) from each other. It should be appreciated that the steps of azimuthally aligning 620 and axially aligning 624 can be repeated multiple times to more-precisely secure 628 the ARHCF 1 end in relation to the ARHCF2 end at dinitial- In other words, the gap between ARHCF 1 and ARHCF2 can be reduced (or otherwise changed) through multiple iterative steps until the gap reaches dinttiai - Additionally, it should be appreciated that the gap between ARHCF 1 and ARHCF2 can be adjusted by moving both ARHCF 1 and ARHCF2 or, alternatively, moving only one of the ARHCFs while holding steady the other of the ARHCFs. Insofar as iterative processes for aligning optical fibers isknown in the art (e.g., WO2022 / 125443), further discussion of the iterati ve process is omited herein. For some embodiments, dinitiai is less than or equal to ten micrometers (dinitial≤ 10μm ).

[0036] Consequently, by the end of the alignment process 601 , the configuration is similar to that shown in FIGS. 7 A (side-view projection (Y-Z plane) of the rotationally non- invariant optical fibers) and 7B (showing a starting position before the fusing process 602). In other words, the side-view image 704 upon completion of the alignment process 601 shows a gap 708 between the two (2) to-be-joined ends of the rotationally non-invariant optical fibers with the gap preferably being dinitial≤ 10μm . For reasons relating to the fusing process 602 (explained below), the dinitiai is small compared to conventional pre-fusion gaps.

[0037] Those having skill in the art will understand that, once the equipment has been calibrated, the alignment process 601 can be implemented automatically for field deployment by computerized processes that reside on a laptop computer or other portable device or in the splicer itself. Consequently, the disclosed alignment process 601 does not require cumbersome or costly equipment that is typically used in conventional systems (and which is unsuitable for field deployment).

[0038] For the fusing process 602, the ends of the rotationally non-invariant optical fibers (e.g., the ARHCF1 end and the ARHCF2 end) are fused together. Preferably, a multi- arc splicer (such as a ring-of-fire (ROF) arc splicer with three (3) arc-discharging electrodes) is used for fusion splicing the ARHCF1 end to the ARHCF2 end, thereby achieving a sufficiently uniform temperature environment for the fusing process 602.

[0039] Specifically, the fusing process 602 axially moves together 632 the optical fibers at a controlled rate (designated herein as an axial convergence rate (or roonvergence) or push speed). FIG. 7B illustrates this axial movement 632.

[0040] Because microstructures at the ends of the rotationally non-in variant optical fibers are susceptible to damage from conventional push speeds (e.g., greater than120 micrometers-per-second (>120pm / s)), the roonvergencein the disclosed fusing process 602 is preferably lower than 100μm / s (e.g., 90μm / s, 80μm / s, 70μm / s, 60μm / s, 50μm / s, 40μm / s, 30μm / s, or even as low as 20μm / s). The slower ^convergence reduces the likelihood or amount of possible "bump" damage to the ends of the rotationally non-invariant optical fibers.

[0041] As the ARHCF I end and the ARHCF2 end move together 630 or convergeaxially (along the Z-axis), the fusing process 602 discharges 636 a first arc at a first arc power (Pi) for a first arc pulse duration (tI). The purpose of the first arc is to melt the to-be-joined ends and, therefore, the first arc is a short-but-strong arc pulse with sufficient power to melt the ends but not too much power to damage the ends. By way of example, for silica-based optical fibers, the first arc generates a first temperature (Ti) that is greater than the melting point of glass (which is greater than 1700 degrees Celsius (or Tj > 1700°C)) for a n of somewhere between approximately fifty milliseconds and approximately one-hundred- and-twenty milliseconds (meaning, ~50ms < n < ~120ms). The discharging 636 of the first arc is illustrated in FIG. 8.

[0042] Immediately after the first-arc discharge 636, the fusing process 602 discharges 640 a second arc at a second arc power (P2) for a second arc pulse duration (12). P2 < Pi; and, t2 > th- Preferably, for silica fibers, ~120ms < t2 < ~150ms. The second arc generates a second temperature (T2) that continues to be high enough to melt glass (meaning, T2 > 1700°C). The discharging 640 of the second arc is also shown in FIG. 8. Toward the end of T2, the ARHCF 1 end and the ARHCF2 end have converged and the very brief period of continued pushing results in a slight overlap of the two ends of the ARHCFs (typically overlapping between ~5μm and ~17μm).

[0043] Shortly before the end of T2, the fusing process 602 axially moves away 644 (or moves apart) the two rotationally non-invariant optical fibers (e.g., ARHCF 1 and ARHCF2) for a short distance (also designated herein as an axial divergence distance (divergence)). This slight pulling away reduces strain at the splicing point. Preferably, divergence < ~2μm. In a more-preferred embodiment, divergence ~ ~1 μm or, more preferably, ddivergence < 1μm. All axial movement is then stopped 648, and the rotationally non-invariant optical fibers (e.g., ARHCF 1 and ARHCF2) are maintained stationary,

[0044] Once the movement of the rotationally non-invariant optical fibers has been stopped 648, the fusing process 602 discharges 652 multiple lower-power arcs sequentially. For some embodiments, each lower-power arc comprises a third arc power (P3) and a third arc pulse period (13), which generates a third temperature (T3). One embodiment of the repeated arc discharges 652 is shown in FIG. 8.

[0045] The lower-power arc discharges are intended to improve structural strength at the splice point. Thus, rather than melting the now-merged ends of the rotationally non-invariant optical fibers (e.g., AHRCF 1 end and ARHCF2 end), the lower-power arcs perform an annealing function at a softening temperature (rather than above the melting temperature). As such, the lower-power arcs comprise ultra-short bursts in which 20ms < rs < 40ms. Also, for some embodiments in which the process 600 is applied to silica-based HCFs, P3 < P2 and T3 < T2, preferably within the range of 1160°C < T3 < 1700°C. Depending on the desired outcome, the number of lower-power arc discharges 652 can vary. Preferably, the fusing process 602 discharges 652 at least ten (10) lower-power arcs at the softening temperature. Those having skill in the art will understand that each of the multiple lower-power arcs need not have the same pulse length, or have the same pulse power, or generate the same temperature. Rather, each pulse can be adjusted to achieve substantially the same intended purpose of improving structural strength after the first arc discharge 636 and the second arc discharge 640.

[0046] The disclosed fusing process 602 is controlled by the same laptop computer or portable device or splicer hardware that implements the alignment process 601. In other words, the same apparatus controls both the aligning 601 within the arc splicer and the fusing 602 by the arc splicer. As such, in addition to being more cost-effective than conventional equipment, the disclosed process 600 is fast enough for field deployment. For example, upon proper calibration, the alignment process 601 and the fusing process 602 (in combination) can be performed in less than 120 seconds (<120s).

[0047] Although not necessary, the time for different steps within the process 600 can be reduced by reducing the number of 9 measured (for example, if it is known that the fundamental mode is pentagonal and the loss exhibits a sinusoidal behavior with minima at every 72°, then it may be unnecessary to perform a full rotational scan through 360° and only necessary to perform discrete scans through a 72° rotation). Other process steps can also be modified to reduce the total process time, such as, reducing dinitial, increasing tconvergence, increasing the ©-spacing between each discrete scan, decreasing the number of discrete scans during the rotational scanning 604, 608, decreasing the number of lower-power arc discharges 652, and so on. Of course, those having skill in the art will understand that there are limits to modifying these parameters. However, understanding those limits is well within the knowledge of one having ordinary skill in the art. Suffice it to say that the process 600 can be reduced to < -70s and, with near-perfect optimization for speed (but slight sacrificefor less-than-perfect alignment), reduced to less than a minute.

[0048] Continuing, FIGS. 9, 10, and 11 provide example experimental data to demonstrate the feasibility of applying the process of FIG. 6 during field deployment. Specifically, FIG. 9 is a graph showing transmitted power (in dBm) at a center wavelength of 1543.2nm through a 10μm wide gap between two ARHCF fibers in a three (3) arc ring-of- fire (ROF) arc splicer prior to fusion splicing; FIG. 10 is a graph showing the difference in ARHCF l-to-ARHCF2 splice loss with optimum azimuthal alignment (shown as closed circles) and without azimuthal alignment (shown as open squares); and FIG. 11 is a graph showing the mean, median, and standard deviation of the data shown in FIG. 10.

[0049] As shown in FIG. 9, a comparison of thirty (30) random azimuthal alignments (shown as open squares) with thirty (30) optimized azimuthal alignments (shown as closed circles) results in an average increase in the transmited power level of 0.08dB, which is caused by the imperfect match of the fundamental mode from the imperfect alignment.When the splice loss is measured for twenty (20) trials (as shown in FIGS. 10 and 11), the median splice loss is 0.26dB without azimuthal alignment (open squares) but 0.13dB with azimuthal alignment (closed circles). The data in FIG. 10 includes what appears to be one outlier. When that outlier is omited from the analysis, the mean with azimuthal alignment is 0.148dB and the standard deviation is 0.079dB (with the median remaining unchanged either with or without the outlier).

[0050] Ultimately, the disclosed process 600 provides a fast, reliable, and cost - effective field-deployable solution for low-loss splicing of rotationally non-invariant optical fibers, such as PCFs, HCFs, ARHCFs, PBGHCFs, etc. Even without perfectly optimizing all parameters, the disclosed process 600 exhibits a high success rate (one hundred percent (100%) in the experimental data shown) and very short splicing times (< 120s).

[0051] Any process descriptions or blocks in flow charts should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the preferred embodiment of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the presentdisclosure.

[0052] Although exemplary embodiments have been shown and described, it will be clear to those of ordinary skill in the art that a number of changes, modifications, or alterations to the disclosure as described may be made. All such changes, modifications, and alterations should therefore be seen as within the scope of the disclosure.

Claims

What is claimed is:I . A process for splicing together anti-resonant hollow-core fibers (ARHCFs), the process comprising: aligning a first anti -resonant hollow-core fiber (ARHCF I) with a second anti-resonant hollow-core fiber (ARHCF2), wherein the aligning comprises: rotationally scanning an ARHCF 1 end through a 360° rotation, wherein the rotational scanning of the ARHCF 1 end comprises discrete scans at multiple azimuthal angles (9); rotationally scanning an ARHCF2 end through the 360° rotation, wherein the rotational scanning of the ARHCF2 end comprises discrete scans at the multiple 0; correlating the discrete scans of the ARHCF 1 end with the discrete scans of the ARHCF2 end; determining an optimum azimuthal alignment between the ARHCF 1 end and the ARFICF2 end in response to the correlating; azimuthally aligning the ARHCF 1 end and the ARHCF2 end at the optimum azimuthal alignment; axially aligning the ARHCF 1 end with the ARHCF2 end; and securing the ARHCF 1 end at an initial distance from the ARHCF2 end, wherein the initial distance is less than ten micrometers (dinitial< 10μm); and fusing the ARHCF 1 end with the ARHCF2 end with a ring-of-fire (ROF) arc splicer, wherein the fusing comprises: axially moving together the ARHCF 1 and the ARHCF2 at an axial convergence rate, wherein the axial convergence rate is less than 100 micrometers-per-second ( roonvergence<100gm / s); discharging a first arc at a first arc power (P1) for a first arc pulse period (t I), wherein the discharging of the first arc occurs while axially moving together the ARHCF 1 and the ARHCF2, wherein the first arc generates a first temperature (Ti), wherein:Tj is greater than 1700 degrees Celsius (T1 > 1700ºC); and tI is between 50 milliseconds and 120 milliseconds (50ms < 11 < 120ms);discharging a second arc at a second arc power (P2) for a second arc pulse period (r2), wherein the discharging of the second arc overlaps with the moving together of the ARHCF 1 and the ARHCF2, wherein the second arc generates a second temperature (T2), wherein:T2> 1700°C;P2 < Pi; and120ms < T2 < 150ms; axially moving away the ARHCF1 from the ARHCF2 for an axial divergence distance of less than one micrometer (divergence < 1μm), wherein the axially moving away occurs before the end of t2; stopping the axially moving away of the ARHCF 1 from the ARHCF2; and discharging at least ten (10) lower-power arcs after stopping the axially moving away of the ARHCF 1 from the ARHCF2, wherein each lower-power arc comprises a third arc power (P3) for a third arc pulse period (T3), wherein each lower-power arc generates a third temperature (T3), wherein:1160°C < T3< 1700°C;P3 < P2; and20ms < T3 < 40ms.

2. A process for splicing together rotationally non-invariant optical fibers, the process comprising: aligning a first rotationally non-invariant optical fiber with a second rotationally non- invariant optical fiber, wherein the aligning comprises: rotationally scanning a first rotationally non-invariant optical fiber end; rotationally scanning a second rotationally non-invariant optical fiber end; correlating the rotationally scanned first rotationally non-invariant optical fiber end with the rotationally scanned second rotationally non-invariant optical fiber end; determining an optimum azimuthal alignment between the first rotationally non-invariant optical fiber end and the second rotationally non-invariant optical fiber end in response to the correlating; azimuthally aligning the first rotationally non-invariant optical fiber end andthe second rotationally non-invariant optical fiber end at the determined optimum azimuthal alignment; axially aligning the first rotationally non-invariant optical fiber end with the second rotationally non-invariant optical fiber end; and securing the first rotationally non-invariant optical fiber end at an initial distance from the second rotationally non-invariant optical fiber end; and fusing the first rotationally non-invariant optical fiber end with the second rotationally non-invariant optical fiber end, wherein the fusing comprises: axially moving together the first rotationally non-invariant optical fiber and the second rotationally non-invariant optical fiber at an axial convergence rate: discharging a first arc at a first arc pulse power (Pi) for a first arc pulse duration (ti), wherein the discharging of the first arc occurs while axially moving together the first rotationally non-invariant optical fiber and the second rotationally non-invariant optical fiber, wherein the first arc generates a first temperature (T)); discharging a second arc at a second arc pulse power (P2) for a second arc pulse duration (TZ X wherein the discharging of the second arc occurs after the discharging of the first arc, wherein the discharging of the second arc overlaps with the axially moving together of the first rotationally non-invariant optical fiber and the second rotationally non- invariant optical fiber, wherein the second arc generates a second temperature (T2), wherein:P2 < Pj; andT2 > Ti; axially moving away the first rotationally non-invariant optical fiber from the second rotationally non-invariant optical fiber for an axial divergence distance, wherein the axially moving away occurs before the end of T2; stopping the axially moving away; and discharging lower-power arcs, wherein each lower-power arc comprises a third arc power (P3) for a third arc pulse period (T3), wherein the discharging of the lower- power arcs occurs after the stopping of the axially moving away, wherein each lower-power arc generates a third temperature (T3), wherein:T3< T2;P3 < P2; and3. The process of claim 2, wherein the first rotationally non-invariant optical fiber is an optical fiber selected from the group consisting of: a hollow-core fiber (HCF); a photonic band-gap hollow-core fiber (PBGHCF); and an anti-resonant hollow-core fiber (ARHCF).

4. The process of claim 2, wherein the second rotationally non-invariant optical fiber is an optical fiber selected from the group consisting of: a hollow-core fiber (HCF); a photonic band-gap hollow-core fiber (PBGHCF); and an anti-resonant hollow-core fiber (ARHCF).

5. The process of claim 2, wherein: the initial distance is less than or equal to ten micrometers (dinitial< 10μm).

6. The process of claim 2, wherein: the axial convergence rate is less than one-hundred micrometers-per-second ( roonvergence100μm / s).

7. The process of claim 2, wherein: the axial divergence distance is less than one micrometer (divergence < 1 μm).

8. The process of claim 2, wherein:T1 is greater than 1700 degrees Celsius (T1 > I700°C);T2> 1700°C;1160°C < Ts < 1700°C; t 1I is between 50 milliseconds and 120 milliseconds (50ms < t1 < 120ms);120ms < T2 < 150ms; and20ms < T3 < 40ms.

9. A process comprising: aligning a first rotationally non-invariant optical fiber with a second rotationally non- invariant optical fiber at an initial distance and with an optimum azimuthal alignment; and fusing the first rotationally non-invariant optical fiber with the second rotationally non-invariant optical fiber, the fusing comprising: axially moving together the first rotationally non-invariant optical fiber and the second rotationally non-in variant optical fiber at an axial convergence rate; discharging a first arc while axially moving together the first rotationally non- invariant optical fiber and the second rotationally non-invariant optical fiber; discharging a second arc, the discharging of the second arc overlapping with the axially moving together of the first rotationally non-invariant optical fiber and the second rotationally non-invariant optical fiber , the discharging of the second arc occurring after the discharging of the first arc; axially moving away the first rotationally non-invariant optical fiber from the second rotationally non-invariant optical fiber for an axial divergence distance, the axially moving away occurring before the end of the discharging of the second arc; stopping the axially moving away; and discharging lower-power arcs after the stopping of the axially moving away.

10. The process of claim 9, wherein: the first rotationally non-invariant optical fiber is a first hollow-core fiber (HCF); and the second rotationally non-invariant optical fiber is a second HCF.

11. The process of claim 10, wherein: the first HCF is a first photonic band-gap hollow-core fiber (PBGHCF); and the second HCF is a second PBGHCF.

12. The process of claim 10, wherein: the first HCF is a first anti-resonant hollow-core fiber (ARHCF); and the second HCF is a second ARHCF.

13. The process of claim 9, wherein : the initial distance is less than or equal to ten micrometers (dinitial< 10μm).

14. The process of claim 9. wherein: the axial convergence rate is less than one-hundred micrometers-per-seeond ( roonvergence100μm / s).

15. The process of claim 9, wherein: the axial divergence distance is less than two micrometers ( roonvergence< 2μm).

16. The process of claim 15, wherein: divergence < 1μm.

17. The process of claim 9, wherein the discharging of the first arc comprises: discharging the first arc with a multi-arc splicer, the first arc comprising a first arc power (Pi) and a first arc pulse period (n), the first arc generating a first temperature (Ti). wherein:Ti is greater than 1700 degrees Celsius (T1 > 1700°C); and ti is between 50 milliseconds and 120 milliseconds(50ms < t1 < 120ms);18. The process of claim 17, wherein the discharging of the second arc comprises: discharging the second arc with the multi-arc spicer, the second arc comprising a second arc power (P2) and a second arc pulse period (t2), the second arc generating a second temperature (T2), wherein:T2> 1700°C;P2 < P1; and120ms < T2 < 150ms;19. The process of claim 18, wherein the discharging of the lower-power arcs comprises:discharging at least ten (10) lower-power arcs with the multi-arc splicer, each arc comprising a third arc power (P3) and a third arc pulse period (T3), wherein each lower-power arc generates a third temperature (T3), wherein:1160°C <T3 < 1700°C;P3 < P2; and20ms < T3 < 40ms.

20. The process of claim 9, wherein the axially moving together of the first rotationally non-invariant optical fiber and the second rotationally non-invariant optical fiber comprises at least one of: axially moving the first rotationally non-invariant optical fiber toward the second rotationally non-invariant optical fiber while keeping stationaiy the second rotationally non- invariant optical fiber; axially moving the second rotationally non-invariant optical fiber toward the first rotationally non-invariant optical fiber while keeping stationary the first rotationally non- invariant optical fiber; axially moving both the first rotationally non-invariant optical fiber and the second rotationally non-invariant optical fiber toward each other.

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