Laser welding of hollow core optical fiber assemblies

Abstract

Disclosed are various examples for systems and methods for laser welding a hollow core optical fiber assembly. For example, a system comprises a hollow core optical fiber assembly, which includes a glass cladding tube, an outer capillary tube, and an inner capillary tube. The inner capillary tube is situated inside of the outer capillary tube. The outer capillary tube is situated inside of the glass cladding tube. A laser system comprises a laser source and laser optics. The laser source directs a laser beam to the laser optics. The laser optics directs a diverging laser beam through an opening at an end of the glass cladding tube onto a discrete welding point on an interior surface of the inner capillary tube. The diverging laser beam approaches the discrete welding point at an angle less than 90° relative to a longitudinal axis of the hollow core optical fiber assembly.

Description

LASER WELDING OF HOLLOW CORE OPTICAL FIBER ASSEMBLIES

[0001] This Application claims the benefit of priority to U.S. Provisional Patent Application Serial Number 63 / 677157 filed on July 30, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.FIELD

[0002] This application relates to hollow core optical fibers. More particularly, this application relates to methods of assembling preforms for hollow core optical fibers.BACKGROUND

[0003] Traditional optical fibers have a solid glass or plastic core. Solid core optical fibers have been used for decades by the telecommunication industry for data transmission. However, hollow core optical fibers have been recognized as having many advantages over solid core optical fibers, such as lower signal losses, lower dispersion, less susceptibility to optical damage, and other advantages. Typically, hollow core optical fibers channel light through a hollow core that is filled with air or vacuum. Hollow core optical fibers surround an air or vacuum-filled core with a structured cladding that uses photonic bandgap or anti-resonant guiding mechanisms to confine and transmit light. The air or vacuum filed core is surrounded by small tubes (e.g., capillary tubes). The negative curvature and the thickness of these small tubes provide an anti-resonant effect.

[0004] The optical properties of hollow-core optical fibers can be defined by a reflection of light on the elements of the core-clad interface. Low-loss transmission of light is achieved through coherent reflections from the thin core wails which are modelled asFabry-Perot resonators. If anti-resonance conditions are met, then the reflection coefficient from a capillary wall increases and optical losses are reduced. In a simple design, the cladding includes a single ring layer of capillaries. More complex structures include nested or double nested capillary configurations. Typically, flame-based methods of welding are used to bond various capillaries within a hollow core optical fiber assembly.SUMMARY

[0005] Examples of the present disclosure are related to systems for a hollow core optical fiber assembly. In one example, the hollow core optical fiber assembly comprises a glass cladding tube, an outer capillary tube, and an inner capillary tube. The inner capillary tube is situated inside of the outer capillary tube, and the outer capillary tube is situated inside of the glass cladding tube. A laser system comprises a laser source and laser optics. The laser source produces a laser beam and directs the laser beam to the laser optics. The laser optics is configured to produce a diverging laser beam and direct the diverging laser beam through an opening at an end of the glass cladding tube onto a discrete welding point on an interior surface of the inner capillary tube. The diverging laser beam approaches the discrete welding point at an angle relative to a longitudinal axis of the hollow core optical fiber assembly. The angle being less than ninety degrees.

[0006] In the above system example, the system further comprises an insert that is positioned within the glass cladding tube, and the insert holds the outer capillary tube against an inner wall of the glass cladding tube.

[0007] In any of the above system examples, the insert comprises an arch between a pair of protrusions.

[0008] In any of the above system examples, an end of the inner capillary tube comprises an angled face cut, and the angled face cut exposes a portion of the interior surface of the inner capillary tube to the laser beam.

[0009] In any of the above system examples, the laser beam is directed to generate an aperture in an outer surface of the inner capillary tube. An optical path of the laser beam has access to the interior surface of the inner capillary tube through the aperture.

[0010] In any of the above system examples, the laser source is operated at a power density of at least five kW / cm2.

[0011] In any of the above system examples the laser source comprises at least one of a carbon dioxide laser or a carbon monoxide laser.

[0012] In any of the above system examples, the system further comprises a gas flow control device that contacts an end of the hollow core optical fiber assembly, and the gas flow control device directs gas through the hollow core optical fiber assembly.

[0013] In any of the above system examples, the system further comprises a vacuum positioned near to an end of the hollow core optical fiber assembly, and the vacuum removes a contaminant from the generation of a weld at the discrete welding point on the interior surface of the inner capillary tube.

[0014] In any of the above system examples, the end of the hollow core optical fiber assembly is a first end, and the system further comprises a motorized chuck for gripping a second end of the glass cladding tube, and the motorized chuck is configured to rotate or translate the glass cladding tube.

[0015] Examples of the present disclosure are related to methods of making a hollow core optical fiber preform. For example, the method comprises directing adiverging laser beam to a hollow core optical fiber assembly, and the hollow core optical fiber assembly comprises an outer capillary tube situated inside of a glass cladding tube and an inner capillary tube situated inside of the outer capillary tube. The diverging laser beam passes through an end of the outer capillary tube to a discrete welding point on an interior surface of the inner capillary tube to weld the inner capillary tube and the outer capillary tube to the glass cladding tube at the discrete welding point.

[0016] In the above method example, the method further comprises placing an insert into the glass cladding tube to hold the outer capillary against an inner surface of glass cladding tube.

[0017] In any of the above method examples, the method further comprises positioning the outer capillary between a pair of protrusions of the insert.

[0018] In any of the above method examples, the method further providing for an angled face cut at the end of the inner capillary tube, and the angled face cut exposes a portion of the interior surface of the inner capillary tube to the laser beam.

[0019] In any of the above method examples, welding the inner capillary tube and the outer capillary tube to the glass cladding tube further comprises generating, with the diverging laser beam, an aperture in an outer surface of the inner capillary tube.

[0020] In any of the above method examples, the method further comprises operating the laser source at a power density of at least five kW / cm2.

[0021] In any of the above method examples, the laser source is a carbon dioxide laser or a carbon monoxide laser.

[0022] Examples of the present disclosure are related to a hollow core optical fiber preform. For example, the hollow core optical fiber preform comprises a glass claddingtube and an outer capillary tube that is positioned within and welded to the glass cladding tube. Further, the hollow core optical fiber preform comprises an inner capillary tube that has an end with an angled face cut, and the inner capillary tube being positioned within the outer capillary tube, the inner capillary tube and the outer capillary tube are welded to the glass cladding tube.

[0023] In the above preform example, the end of the inner capillary tube is a first end, and the hollow core optical fiber preform further comprises a first welded region at the first end of the inner capillary tube and a second welded region at a second end of inner capillary tube. An unwelded region is situated between the first welded region and the second welded region.

[0024] In any of the above preform examples, the inner capillary tube and the outer capillary tube have a welded region at the end, and the welded region has a cross- sectional dimension in a range of 1 millimeter to 5 millimeters.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0026] FIG. 1 is a drawing of a system for laser welding a hollow core optical fiber assembly according to one example of the present disclosure.

[0027] FIGS. 2A and 2B are cross-sectional views of an end of a hollow core optical fiber assembly according to one example of the present disclosure.

[0028] FIG. 3 is a cross section view of a portion of the system for laser welding the hollow core optical fiber assembly from FIG. 1 according to one example of the present disclosure.

[0029] FIG. 4 is a flowchart illustrating one example of a method of making a hollow core optical fiber preform according to one example of the present disclosure.DETAILED DESCRIPTION

[0030] Disclosed are various approaches for laser welding hollow core optical fiber assemblies. Generally, flame-based methods of welding are used to weld various capillaries within a hollow core optical fiber assembly. These methods can be prone to contamination and can induce a large heat zone, which is problematic for welding thin glass wall tubes within a hollow core optical fiber assembly. Oftentimes, flame-based processes can cause excessive heating of the entire hollow core optical fiber assembly, which can lead to deformation of components and undesirable optical transmission properties. Flamed-based welding processes for hollow core optical fiber assemblies can also be time-consuming.

[0031] Accordingly, various examples of the present disclosure are directed to an improved approach for laser welding hollow core optical fiber assemblies. For example, the various examples use a laser beam-based system that allows for smaller heat zones during welding operations. These smaller heat zones can reduce the likelihood of compromising the optical propagation properties for the hollow core optical fiberassemblies by localizing the heat to the welding region and minimizing heating in peripheral regions. Additionally, the various examples allow for improved automation of the welding process compared to existing flamed-based processes. For example, a motorized chuck is used to position the hollow core optical fiber assemblies into various positions for welding all of the capillary tubes during the laser welding process. In addition, the various examples include components for removing containments during the welding process. As such, the various examples will increase manufacturing yields for hollow core optical fiber preform assemblies because of the reduced time for welding an assembly and because of the reduced number of manufacturing defects caused by contamination.

[0032] In the following discussion, a general description of the system and its components is provided, followed by a discussion of the operation of the same. Although the following discussion provides illustrative examples of the operation of various components of the present disclosure, the use of the following illustrative examples does not exclude other implementations that are consistent with the principals disclosed by the following illustrative examples.

[0033] With reference to FIG. 1 , shown is drawing of a system 103 for laser welding a hollow core optical fiber assembly. The system 103 includes a laser system 106, an insert 109, a hollow core optical fiber assembly 112, a gas flow control device 117, a vacuum device 118, and other suitable components.

[0034] The laser system 106 comprises a laser source 119 and laser optics 120.The laser source 119 is configured to generate a laser beam for welding discrete locations at or near the ends of the hollow core optical fiber assembly 112. In some examples, thelaser source 119 is aligned with a longitudinal plane of the hollow core optical fiber assembly 112. In some examples, the laser source 119 is positioned to provide a laser beam at an angle a relative to a longitudinal axis 124 of the hollow core optical fiber assembly 112. The angle a is in a range from 0 to ninety degrees. In the depicted FIG. 1 , the angle a is formed between the longitudinal axis 124 of the hollow core optical fiber assembly 112 and a centerline of a path of a diverging laser beam 122. However, the angle a may be specified relative to an axis or structure other than the longitudinal axis 124.

[0035] The laser source 119 produces a laser beam and the laser beam is directed to a laser optics 120. The laser optics 120 produces a diverging laser beam 122 and directs the diverging laser beam 122 through an opening at a first end 113 of the hollow core optical fiber assembly 112. In some implementations, the laser source 119 can have an average laser beam power that is less than 150 watts. In one non-limiting example, the laser radiation used in the welding process is a pulsed laser beam at typical frequency of about 10 kHz with an average power of < 150 W and a duty cycle variable in the range of 10-60%. Lasers other than pulsed lasers may be employed.

[0036] Further, in another example, the laser source 119 can generate a laser beam using a carbon dioxide (CO2) laser. Such a laser beam can operate a wavelength of 10.6 pm. A carbon monoxide laser operating at a wavelength between about 5.2 pm and 6.0 pm can also be used. Additionally, various power densities are used for different phases of the welding process. For example, the laser source 119 can operate at a power density of less than five kW / cm2for welding multiple glass layers (e.g., the glass cladding tube 123, the outer capillary tube 126, the inner capillary tube 129) of the hollow coreoptical fiber assembly 112. In other examples, the laser source 119 can operate at a power density of at least 5 kW / cm2for creating an aperture in the outer capillary tube 126 in order to create a direct pathway to the interior surface of the inner capillary tube 129. However, the power density can vary based at least in part on the glass composition and glass thickness. For welding glass layers, the laser source 119 is configured for sufficient power density in order to melt and weld the multiple glass layers (e.g., the inner capillary tube 129, outer capillary tubes 126, glass cladding tube 123), but not enough to cause hole formation or glass deformation.

[0037] The laser optics 120 may include an optical device to focus the laser beam from the laser source 119 onto the hollow core optical fiber assembly 112. The laser optics 120 may be configured to form the diverging laser beam 122 that contacts the interior surface of the inner capillary tube 129. The focal point of the diverging laser beam 122 may be above the interior surface of the inner capillary tube 129. The laser optics 120 comprises one or more components that is / are positioned in an optical path 121 between the laser source 119 and the first end 113 of the hollow core optical fiber assembly 112. In some non-limiting examples, the laser optics 120 may comprise a lens, a mirror, a phase mask, a spatial light modulator, or other suitable focusing optical devices.

[0038] In some examples, the laser optics 120 can have a focal distance in a range between 20-80 millimeters and a working distance in a range between 50-125 millimeters. The focal point may be located at a position above the interior surface of the inner capillary tube 129. In some examples, the focal point is in a range from 10 millimeters to 50 millimeters away from the interior surface of the inner capillary tube 129.

[0039] In some examples, the diverging laser beam 122 is focused by the laser optics 120 (e.g., spherical optics). During welding, a convergent section of the incident diverging laser beam 122 is applied to an interior surface of the inner capillary tube 129 with a cross-section of the diverging laser beam 122 on the interior surface of the inner capillary tube 129 being of an elliptical shape due to an angle a of around or about 45 degrees or other angles.

[0040] In some examples, the diverging laser beam 122 is specified to have one or more parameters. For example, the laser optics 120 can have a focal distance in a range between 20-80 millimeters and a working distance in a range between 50-125 millimeters. The focal point may be located at a position above the interior surface of the inner capillary tube 129. In some examples, the focal point is in a range from 10 millimeters to 50 millimeters away from the interior surface of the inner capillary tube 129. During the welding process, the diverging laser beam 122 can cause the interior surface of the inner capillary tube 129 to melt and weld with the lower glass layers such as the inner capillary tube 129, the outer capillary tube 126 and the glass cladding tube 123 of the hollow core optical fiber assembly 112 together.

[0041] The hollow core optical fiber assembly 112 can represent a glass-based anti-resonant optical fiber structure that has a tubular shape with a first end 113 and a second end 114. The hollow core optical fiber assembly 112 includes an assembly of optical structures for making an optical fiber preform. The optical structures can include an array of smaller diameter hollow glass tubes or capillaries nested within each other. For example, the hollow core optical fiber assembly 112 includes glass components, such as a glass cladding tube 123, one or more outer capillary tubes 126, one or more innercapillary tubes 129 and other suitable components. In some examples, each inner capillary tube 129 is positioned within the outer capillary tube 126, and each outer capillary tube 126 is positioned within the glass cladding tube 123. The outer capillary tubes 126 are spaced along an interior surface of the glass cladding tube 123. These outer capillary tubes 126 surround a core of the hollow core optical fiber assembly 112.

[0042] In some examples, the inner capillary tube 129 has an inner diameter in a range of three to five millimeters and a wall thickness in a range of 0.5 to one millimeter. The outer capillary tube 126 has an inner diameter in a range of seven to ten millimeters and a wall thickness in a range of 0.5 to two millimeters. The glass cladding tube 126 has an inner diameter in a range of forty to one hundred and twenty millimeters and a wall thickness in a range of three to thirty millimeters.

[0043] In some examples, the system 103 produces discrete welding points at or near the first end 113 and / or the second end 114 of the hollow core optical fiber assembly 112. For instance, the laser source 119 produces a laser beam and directs the laser beam to the laser optics 120. The laser optics 120 is configured to produce a diverging laser beam 122 and direct the diverging laser beam 122 through an opening at the first end 113 of the glass cladding tube 123 onto a first discrete welding point on an interior surface of the inner capillary tube 129. The diverging laser beam 122 approaches the first discrete welding point at an angle a relative to a longitudinal axis 124 of the hollow core optical fiber assembly 112. The angle a can be less than ninety degrees. After a first weld has been produced at the first end 113, the hollow core optical fiber assembly 112 can be manipulated (e.g., rotated) in order to position the second end 114 of the hollow core optical fiber assembly 112 for a second weld. After the optical structures arewelded, the preform is heated using a furnace in order to soften and stretch the preform. The preform is stretched or extruded until the desired optical fiber specifications are reached.

[0044] In some examples, the hollow core optical fiber assembly 112 is attached to a motorized chuck or a lathe, which is configured for rotating and translating the hollow core optical fiber assembly 112. The motorized chuck or lathe is controlled by a controller or a computing device for automating the operation of the motorized chuck or lathe (and the other components of the system 103) during a welding process. A fixed structure is used for holding the hollow core optical fiber assembly 112 and the motorized chuck.

[0045] The gas flow control device 117 provides for purging gas through interior components of the hollow core optical fiber assembly 112. The second end 114 of the hollow core optical fiber assembly 112 is attached to the gas flow control device 117. The gas flow control device 117 provides for positive pressure within the interior components of the hollow core optical fiber assembly 112 in order to prevent volatile compounds (e.g. , silicon oxides formed as a byproduct of laser welding) from redepositing onto surfaces inside the interior components (e.g., tubes, capillaries, etc.). Further, the purging gas that flows through the hollow core optical fiber assembly 112 provides a cooling effect to lower the temperature during and / or after the welding process. The cooling that results from the flow of gas helps minimize glass deformation during the welding process. In some examples, the gas flow control device 117 is integrated with a motorized chuck, attached to a motorized chuck, integrated with a motorized lathe, or attached to the motorized lathe.

[0046] The vacuum device 118 is configured to collect gas that exits the first end 113 of the hollow core optical fiber assembly 112. For example, the gas flow control device 117 is situated at the second end 114 of the hollow core optical fiber assembly 112 and the vacuum device 118 is situated at the first end 113 of the hollow core optical fiber assembly 112. The vacuum device 118 collects volatile compounds in gas and particulate form in order to prevent such volatile compounds from condensing within the hollow core optical fiber assembly 112 or on the laser optics 120. The collection of the gas that exits the first end 113 of the hollow core optical fiber assembly also prevents the gas and particulate matter from interfering with a laser beam generated from the laser source 119. In one approach, a portion of the vacuum device 118 is attached to or otherwise comes into contact with the hollow core optical fiber assembly 112. In such case, the vacuum device 118 has an opening to provide access to laser beam during the welding process.

[0047] The insert 109 is a removable structural component that is situated within a glass cladding tube 123 of the hollow core optical fiber assembly 112. The insert 109 is situated within hollow core optical fiber assembly 112 in order to hold the outer capillary tubes 126 in position for welding. After the welding has been completed, the insert 109 is removed from the hollow core optical fiber assembly 112.

[0048] In some examples, the insert 109 includes multiple protrusions that extend from a center. An arch is created between adjacent ones of the protrusions, where the curvature of the arch corresponds to the outer circumference of the outer capillary tubes 126. In some examples, the insert 109 can be printed in a plastic or other suitable materials using a three-dimensional printer.

[0049] As described herein, silica (or other glass) tubes are welded in a nested configuration with the glass cladding tube 123, where the inner capillary tubes 129 (e.g., the smaller tubes) are located inside an outer capillary tube 126 (e.g., a larger tube). The outer capillary tube 126 is in contact with an interior surface of the glass cladding tube 123, along a direction parallel to a longitudinal axis of the glass cladding tube 123. In some examples, the inner capillary tubes 129 generally have thinner walls (e.g., 0.5 mm to 1.0 mm) compared to the outer capillary tubes 126 (e.g., 3.0 mm to 10.0 mm).

[0050] In one example, the laser source 119 can generate a laser beam from a carbon dioxide laser at a mid-infrared radiation (IR) wavelength (9-11 pm), which is strongly absorbed by the silica glasses of the hollow core optical fiber assembly 112. The combination of the carbon dioxide laser beam and a laser optics 120 can provide a localized small heat affected zone and at the same time enable a high degree of welding strength at the welding location. At the welding location, the heat affected zone and its depth is effectively controlled by the selection of the laser optics 120, the laser power from the laser source 119, and the duration of the laser exposure. Regardless of the high absorption of carbon dioxide based laser radiation on a glass surface and the dissipation of heat in the glass volume, the focusing of the laser beam in the vicinity of the glass surface and the control of the laser power creates special laser-induced heat propagation. This heat propagation can enable highly localized penetration of the heat through the glass volume and also through the contact surfaces between the tubes, which causes local melting and glass welding at the interfaces or points of contact between respective pairs of the inner capillary tubes 129, outer capillary tubes 126, and the glass cladding tube 123.

[0051] In some examples, the duration of the laser exposure is in a range of ten (10) seconds to twenty (20) seconds to form one welding spot (see e.g., welded region 209 in FIGS. 2A). This allows deeper and more uniform heat propagation through the thickness of the glass, and it avoids overheating of the interior surface of the inner capillary tube 129. The exposure time can depend on tube thicknesses. Process optimization enables formation of the welded area without creation of excessive stress, which can lead to formation of cracks around the area. In some instances, a typical single welded spot has a “tilted shark tooth” shape or a tilted triangular shape. The number of such spots typically varies from 1 to 3 for one area, but it is not limited.

[0052] In some examples, the welding process involves controlling the average laser power during a laser exposure cycle, which, along with other features, such as air cooling, helps to enable better uniformity of the heating process through the glass thickness and to avoid excessive heating of the surface. The average power control includes programming a power profile over the exposure period for the laser source 119. The power profile can include a simple step function, a step function with a ramp down at the end of the cycle, two steps of different powers, two steps with lower power in between and other possible variations. In some examples, the system 103 can include a computing device that programs or provides a command for the power profile (e.g., the average laser power, step functions for powering up and powering down) to the laser source 119. Additionally, the computing device can provide instructions to other components in the system 103 in order to automate the welding process. Other components can include the laser system 119, a chuck, a lathe, the gas flow control device 117, the vacuum device 118, and other suitable components.

[0053] During the welding process, a melting range is achieved when the glass is fluid enough to fill the gaps and to enable a strong welded area. In some examples, the welding process (with fusion of the welded components) occurs at a glass viscosity of less than 107Poise, such as from < 104Poise to 106Poise (e.g., glass temperature exceeds 1800 °C (1800 °C-2100 °C) for silica or silica-based glasses).

[0054] In some examples, the heat affected zone has a length within 0.5 mm - 5 mm depending on the heating conditions. Prior methods of welding nested glass tubes involved gas burners which have much broader heat affected zones with lengths on the scale of several centimeters or even larger. As a result, gas burners used for welding can cause thermal distortion of the entire hollow core optical fiber assembly 112 which may negatively affect the dimensional stability of the hollow core optical fiber assembly 112.

[0055] In contrast, the various examples use a laser source 119 that provides more precision, stability, and control in comparison to flame-based processes. Further, the various examples can provide better geometrical accuracy of the final preform product, which enables lower optical losses. Additionally, the laser source 119 enables a more consistent process during a welding procedure and a smaller number of rejects. As such, a manufacturing process based on laser welding would have a higher yield of preform products.

[0056] Additionally, upon heating the hollow core optical fiber assembly 112 to temperatures required to weld silica or other glass material, some volatilization can occur, which can condense in areas with a lower temperature away from the welding location. Gas burners intrinsically generate a large flow of flue gases, which carry the condensate particles to areas that are difficult to reach and clean. The localized heat provided by thelaser source 119 can also result in volatilization, but such volatilization occurs in an environment or areas where it is possible to bring gas flow to bear. For example, the gas flow is directed through the tubes and out of the first end 113 by use of gas flow control device 117 and / or vacuum device 118. In some non-limiting examples, the gas flow control device 117 is an air purge system, which is used along with an external air-knife and the vacuum device 118 (e.g., a vacuum exhaust). As a result, the various examples are directed to a cleaner process with much lower contamination of the hollow core optical fiber assembly 112, which in turn provides better welding strength characteristics for the hollow core optical fiber assembly 112.

[0057] In some examples, the system 103 is implemented as an automated mechanical system which can translate and rotate the axis for handling of the hollow core optical fiber assembly 112. Additionally, a motorized chuck (e.g., a component of the gas flow control device 117) can manipulate the orientation of the hollow core optical fiber assembly 112. This allows for the laser source 119 to remain stationary and at the same time provides flexibility to position the hollow core optical fiber assembly 112 at various orientations to weld different discrete spots. The system 103 is used for precise rotation about the circumference and translation along a longitudinal axis of the hollow core optical fiber assembly 112. The mechanical motion of the system 103 is synchronized with a laser shutter of the laser source 119. The laser shutter can control the timing of the laser ON / OFF function and a duration of the laser exposure for each individual welding area. In some examples, the entire welding sequence is fully automated, which would reduce manual operations, increase accuracy of the final assembly and reduce overall fabrication time.

[0058] With reference to FIG. 2A, shown is a cross-sectional view of the first end 113 of the hollow core optical fiber assembly 112. In this depicted example, FIG. 2A illustrates that the inner capillary tube 129a has an angled face cut 203. The angled face cut 203 begins at the end of the inner capillary tube and is flush with the end of the outer capillary tube 126. The angled face cut 203 extends at an angle relative to a longitudinal axis of the inner capillary tube 129a. The angled face cut 203 results in the distance from the end of the inner capillary tube 129a to the first end 113 of the hollow core optical fiber assembly increasing from the bottom of the inner capillary tube 129a to the top.

[0059] The angled face cut 203 is implemented on the inner capillary tubes 129a in order to expose the interior surface 206 of the inner capillary tubes 129a to the diverging laser beam 122. As such, the diverging laser beam 122 generates a longer welded region 209 at the first end 113 because the angled face cut 203 exposes more area of the inner capillary tubes 129a for welding.

[0060] The welded region 209 can take different shapes. In some examples, the welded region 209 can have a triangular shape, a “shark tooth” shape, an oval shape, a circular shape, a rectangular shape, and other suitable shapes. Further, the welded region 209 can include multiple instances that are adjacent. For example, the welded region 209 can include two adjacent tilted triangular shapes, two adjacent oval shapes, and other suitable multi-instance shapes that may include a gap therebetween.

[0061] FIG. 2A illustrates the welded region 209 and an unwelded region 212. The welded region 209 represents a discrete welding location that has been generated by the laser source 119 at the first end 113. The welded region 209 includes a welding of the inner capillary tube 129a, the outer capillary tube 126 and the glass cladding tube 123.During the welding process, the diverging laser beam 122 creates a heat affected zone 218 that causes the welding of the inner capillary tube 129a, the outer capillary tube 126 and the glass cladding tube 123. The welded region 209 is a first welded region 209 for the first end 113. A second welded region 209 is made for the same inner capillary tube 129a at the second end 114 of the hollow core optical fiber assembly 112. In this respect, the respective inner capillary tubes 129a, the outer capillary tubes 126 and the glass cladding tubes 123 are welded at both ends of the hollow core optical fiber assembly 112.

[0062] The unwelded region 212 represents a portion of the hollow core optical fiber assembly 112 that is not welded. The unwelded region 212 extends from the first welded region 209 at a first welded location to the second welded region 209 made at a second welding location proximate to the second end 114 of the hollow core optical fiber assembly 112.

[0063] In some examples, the cross-sectional dimension of the welded region 209 is based at least in part on the distance of the focal point of the laser optics 120 from the interior surface 206 of the inner capillary tube 129. For example, a focal point of about thirty millimeters from the interior surface 206 of the inner capillary tube 129 can generate a welded region 209 with a cross-sectional dimension of three and a half millimeters. In this example, the power density of the laser source 119 is about 1 .5 kW kW / cm2. In some examples, the cross-sectional dimension of the welded region 209 has a range of 0.5 millimeter to 10 millimeters, 1 millimeter to 5 millimeters, or other cross-sectional dimensions. In some examples, the welded region 209 can have an oval shape. As such, the length of the welded region 209 can represent a major or minor axis. The welded region 209 can have other suitable shapes as previously described.

[0064] Next, FIG. 2B illustrates a cross-sectional view of another example of the first end 113 of the hollow core optical fiber assembly 112. FIG. 2B illustrates that the inner capillary tube 129b has an aperture 221. In this non-limiting example, the inner capillary tube 129b does not have an angled face cut 203 found in FIG. 2A. In this example, the end of the inner capillary tube 129b is flush with the end of the outer capillary tube 126 at the first end 113. In this non-limiting example, the inner capillary tube 129b can restrict the amount of access of the diverging laser beam 122 to the interior surface 206 of the inner capillary tube 129b.

[0065] In an effort to increase the available access, the laser source 119 is configured to create the aperture 221 before the welding process. In some examples, the laser source 119 is operated at a power density of at least 5 kW / cm2to form the aperture. However, the power density can vary based at least in part on the glass composition and glass thickness. Additionally, the shape and / or size of the aperture 221 can vary.

[0066] After the aperture 221 has been formed, the laser source 119 can direct a diverging laser beam 122 through the aperture 221 in order to weld the inner capillary tube 129a, the outer capillary tube 126 and the glass cladding tube 123. In some examples, the power density of the laser source 119 is adjusted to less than 5 kW / cm2for welding the multiple glass layers together. However, the power density for aperture formation and welding glass layers can vary based at least in part on the glass composition and glass thickness.

[0067] In another example, neither an angled face cut 203 nor an aperture 221 is needed. In such case, the diverging laser beam 122 may have sufficient access to the interior surface 206 of the inner capillary tubes 129 by entering the interior of innercapillary tube 129 at the first end of the hollow core optical fiber assembly 112. However, the length of the weld may be limited by the diameter of the inner capillary tubes 129 as well as the angle between the laser and the longitudinal axis of the hollow core optical fiber assembly 112.

[0068] With reference to FIG. 3, shown is a cross-sectional view of the second end 114 of the hollow core optical fiber assembly 112 attached to the gas flow control device 117. The gas flow control device 117 includes a chuck with multiple gas openings 301. In some examples, each gas opening 301 is mated with a corresponding one of the outer capillary tubes 126. The gas flow control device 117 can inject purging gas 305a-305c (collectively referred to as “gas 305”) through the gas openings 301 , into the outer capillary tubes 126, and out the first end 113 of the outer capillary tubes 126 of the hollow core optical fiber assembly 112. In some examples, the gas 305 can be air or other suitable gases.

[0069] The purging gas 305 is injected during the welding process by the laser source 119 in order to push contaminants out of the assembly. This keeps contaminants from depositing onto the various surfaces within the hollow core optical fiber assembly 112. In some examples, a vacuum device 118 is attached to the first end 113 of the hollow core optical fiber assembly 112 in order to facilitate collection of contaminants.

[0070] In some examples, the gas flow control device 117 comprises part of a motorized chuck. As such, the gas flow control device 117 can rotate the hollow core optical fiber assembly 112 about its axis or translate the hollow core optical fiber assembly 112 along its longitudinal axis 124 (FIGS. 1 and 2A). The gas flow control device 117 can receive rotation and / or translation commands from a computing device. The gas flowcontrol device 117 can use the motorized chuck to rotate and / or translate the hollow core optical fiber assembly 112 according to the commands.

[0071] Referring next to FIG. 4, shown is a flowchart that provides an example method 400 of a laser welding operation for the system 103 (FIG. 1) in order to create discrete laser welds that affix the inner capillary tubes 129 (FIG. 1), the outer capillary tubes 126 (FIG. 1), and the glass cladding tubes 123 (FIG. 1) of the hollow core optical fiber assembly 112 (FIG. 1) to each other. The flowchart of FIG. 4 provides merely an example of the many different types of functional arrangements that can be employed to implement or execute the operation of the system 103.

[0072] In block 401 , the method 400 begins with providing a glass cladding tube 123 of the hollow core optical fiber assembly 112. In some examples, the glass cladding tube 123 is provided in an automated manner. For example, the motorized component is used to retrieve and position the glass cladding tube 123 for the assembly of a hollow core optical fiber assembly 112.

[0073] In block 404, the method 400 includes placing one or more outer capillary tubes 126 inside of the glass cladding tube 123. The inner capillary tubes 129 are placed within the outer capillary tubes 126. In some examples, one or more inserts 119 are placed within the hollow core optical fiber assembly 112 in order to hold or brace the outer capillary tubes 126 against the interior wall of the glass cladding tube 123. In some examples, the inner capillary tube 129 is first welded inside of the outer capillary tube 126. Then, the welded product of the inner capillary tube 129 and the outer capillary tube 126 are placed inside of the glass cladding tube 123. Alternatively, the inner capillary tube126, the outer capillary tube 129, and the glass cladding tube 123 can be welded in a single step.

[0074] In block 407, the method 400 includes positioning a laser source 119 (FIG.1) at an angle a (FIG. 1) directed toward a targeted welding point through the first end 113 of the hollow core optical fiber assembly 112. In some examples, the hollow core optical fiber assembly 112 is attached to a motorized chuck or a gas flow control device 117 (FIG. 1) that has a motorized chuck. The motorized chuck can rotate or translate the hollow core optical fiber assembly 112 to an appropriate position for laser welding. As such, in some examples, the laser source 119 may be in a fixed position and the hollow core optical fiber assembly 112 is moved by a motorized chuck to the appropriate position for producing discrete welding spots at the ends of the inner capillary 129. Alternatively, the hollow core optical fiber assembly 112 may be maintained in a stationary position and the laser source 119 may be positioned to direct the laser to welding points.

[0075] In block 410, the method 400 includes positioning laser optics 120 (FIG. 1) in an optical pathway 121 (FIG. 1) of a laser beam of the laser source 119. The laser optics 120 are positioned between the first end 113 of the hollow core optical fiber assembly 112 and the laser source 119. In some examples, the laser optics 120 may comprise a lens or other focusing element. The laser beam 122 passes through the lens or other focusing element. A diverging laser beam 122 is formed from the lens or other focusing element. The diverging laser beam 122 enters the first end 113 of the hollow core optical fiber assembly 112.

[0076] In block 413, the method 400 includes directing the diverging laser beam122 to a discrete weld point (see e.g., welded region 209 in FIG. 2A) the first end 113 ofthe hollow core optical fiber assembly 112. The diverging laser beam 122 can pass through the first end 113 of the hollow core optical fiber assembly 112 to weld the inner capillary tube 129, the outer capillary tube 126, and the glass cladding tube 123 together. The diverging laser beam 122 is directed to the interior surface 206 of the inner capillary tube 129. The diverging laser beam 122 produces a discrete welding spot at the end of the inner capillary tube 129.

[0077] In one example, the diverging laser beam 122 is directed to an interior surface 206 (FIGS. 2A, 2B) of the inner capillary tube 129 in order to weld the inner capillary tube 129, the outer capillary tube 126, and the glass cladding tube 123 together. However, in some situations, the end of the inner capillary tube 129 can limit the area for the interior surface 206 of the inner capillary tube 129 that the laser beam can access. Limited access to the interior surface 206 may limit the length of the welded region 209 along the longitudinal axis 124 extending inward from the first end 113 of the hollow core optical fiber assembly 112.

[0078] Different approaches can be implemented in order to increase the length of the discrete welding spot to provide greater laser access to the interior surface 206 from the first end 113. In one non-limiting example, the inner capillary tube 129 is configured with an angled face cut 203 (FIG. 2A). The angled face cut 203 can slant radially inward away from the first end 113. The angled face cut 203 allows the laser beam to reach further inside the inner capillary tube 129.

[0079] Alternatively, in scenarios without an angled face cut 203, the laser source119 can generate an aperture 221 (FIG. 2B) in the inner capillary tube 129b. In this example, the laser source 119 is operated at a power density of at least 5 kW / cm2. Atthis power density, the laser source 119 can create an aperture 221 in the inner capillary tube 129b. After the aperture 221 has been formed, the laser source 119 can adjust the power density to less than five kW / cm2in order to weld the inner capillary tube 129b, the outer capillary tube 126, and the glass cladding tube 123. However, the power density for aperture formation and welding glass layers can vary based at least in part on the glass composition and glass thickness as well as the type of laser that is used. In some examples, after the discrete welding spot has been produced at a first location, the motorized chuck can rotate the hollow core optical fiber assembly 112 in order to weld a second location at a second inner capillary tube 129. After the welding has been completed, one or more inserts 119 can be removed from the hollow core optical fiber assembly 112.

[0080] In some examples, the vacuum device 118 is configured to collect gas that exits the first end 113 of the hollow core optical fiber assembly 112. For example, the gas flow control device 117 is situated at the second end 114 of the hollow core optical fiber assembly 112 and the vacuum device 118 is situated at the first end 113 of the hollow core optical fiber assembly 112. The gas flow control device 117 purges gas through the hollow core optical fiber assembly 112 during the welding process. The vacuum device 118 collects the gas and volatile compounds in the gas in order to prevent such volatile compounds from condensing within the hollow core optical fiber assembly 112.

[0081] Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof(e.g., X, Y, and / or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain examples require at least one of X, at least one of Y, or at least one of Z to each be present.

[0082] It should be emphasized that the above-described examples of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described example(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

CLAIMSTherefore, the following is claimed:1 . A system for laser welding a hollow core optical fiber assembly, comprising: a hollow core optical fiber assembly, the hollow core optical fiber assembly comprising a glass cladding tube, an outer capillary tube, and an inner capillary tube; the inner capillary tube being situated inside of the outer capillary tube, the outer capillary tube being situated inside of the glass cladding tube; a laser system comprising a laser source and laser optics, the laser source producing a laser beam and directing the laser beam to the laser optics, the laser optics being configured to produce a diverging laser beam and direct the diverging laser beam through an opening at an end of the glass cladding tube onto a discrete welding point on an interior surface of the inner capillary tube, the diverging laser beam approaching the discrete welding point at an angle relative to a longitudinal axis of the hollow core optical fiber assembly, the angle being less than ninety degrees.

2. The system of claim 1 , further comprising an insert that is positioned within the glass cladding tube, the insert holding the outer capillary tube against an inner wall of the glass cladding tube.

3. The system of any one of claims 1 or 2, wherein the insert comprises an arch between a pair of protrusions.

4. The system of any one of claims 1 -3, wherein an end of the inner capillary tube comprises an angled face cut, wherein the angled face cut exposes a portion of the interior surface of the inner capillary tube to the laser beam.

5. The system of any one of claims 1 -4, wherein the laser optics is configured to direct the divergent laser beam through an outer surface of the inner capillary tube to the discrete welding point on the interior surface of the inner capillary tube.

6. The system of claim 5, wherein the laser source is operated at a power density of at least five kW / cm2.

7. The system of any one of claims 1 -6, wherein the laser source comprises at least one of a carbon dioxide laser or a carbon monoxide laser.

8. The system of any one of claims 1 -7, wherein the system further comprises a gas flow control device that contacts an end of the hollow core optical fiber assembly, the gas flow control device directing gas through the hollow core optical fiber assembly.

9. The system of any one of claims 1 -8, wherein the system further comprises a vacuum positioned near to an end of the hollow core optical fiber assembly, the vacuum removing a contaminant from the generation of a weld at the discrete welding point on the interior surface of the inner capillary tube.

10. The system of any one of claims 1 -9, wherein the end is a first end, and the system further comprises a motorized chuck for gripping a second end of the glass cladding tube, the motorized chuck rotating or translating the glass cladding tube.

11. A method of making a hollow core optical fiber preform, comprising: directing a diverging laser beam to a hollow core optical fiber assembly, the hollow core optical fiber assembly comprising an outer capillary tube situated inside of a glass cladding tube and an inner capillary tube situated inside of the outer capillary tube, the diverging laser beam passing through an end of the outer capillary tube to a discrete welding point on an interior surface of the inner capillary tube to weld the inner capillary tube and the outer capillary tube to the glass cladding tube at the discrete welding point.

12. The method of claim 11 , further comprising placing an insert into the glass cladding tube to hold the outer capillary against an inner surface of the glass cladding tube.

13. The method of claims 11 or 12, further comprising positioning the outer capillary between a pair of protrusions of the insert.

14. The method of any one of claims 11-13, further comprising providing for an angled face cut at the end of the inner capillary tube, wherein the angled face cut exposes a portion of the interior surface of the inner capillary tube to the laser beam.

15. The method of any one of claims 11-14, wherein welding the inner capillary tube and the outer capillary tube to the glass cladding tube further comprises generating, with the diverging laser beam, an aperture in an outer surface of the inner capillary tube.

16. The method of claim 15, further comprising operating the laser source at a power density of at least five kW / cm2.

17. The method of any one of claims 11-16, wherein the laser source comprises at least one of a carbon dioxide laser or a carbon monoxide laser.

18. A hollow core optical fiber preform, comprising: a glass cladding tube; an outer capillary tube that is positioned within and welded to the glass cladding tube; and an inner capillary tube that has an end with an angled face cut, the inner capillary tube being positioned within and welded to the outer capillary tube.

19. The hollow core optical fiber preform of claim 18, wherein the end of the inner capillary tube is a first end, and further comprising: a first welded region at the first end of the inner capillary tube; and a second welded region at a second end of inner capillary tube; and an unwelded region situated between the first welded region and the second welded region.

20. The hollow core optical fiber preform of any one of claims 18 or 19, wherein the inner capillary tube and the outer capillary tube having a welded region at the end, the welded region having a cross-sectional dimension in a range of 1 millimeter to 5 millimeters.

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