End cap assembly for hollow core optical fiber

Abstract

An end cap assembly for a hollow core optical fiber is disclosed, comprising an elongated hollow glass ferrule, the elongated hollow glass ferrule comprising a first ferrule portion having a first ferrule end and a second ferrule portion having a second ferrule end, wherein the first ferrule end is configured to seal, the second ferrule end is configured to receive a hollow core optical fiber, and the second ferrule portion is configured to secure the hollow core optical fiber.

Description

Technical Field

[0001] The present disclosure generally relates to end cap assemblies for hollow core optical fibers. More specifically, the present disclosure relates to an end cap assembly comprising a ferrule and an end cap, and in particular, to a method of sealing the ferrule such that the ferrule is hermetically sealed, and more particularly, such that a high power optical beam can be coupled into and / or out of a hollow core optical fiber without damaging the hollow core optical fiber.

Background Art

[0002] End cap assemblies are known in the field of high power laser applications, particularly in applications where a high power optical beam is coupled to a hollow core optical fiber, simply referred to as a hollow core fiber (HCF).

[0003] The reason why it is desirable to couple a high power optical beam to an HCF is that such fibers confine almost all of the energy in the hollow core, and thus appear like free space transmission. Further, since the energy is confined in the hollow core, guidance by the HCF improves the damage threshold and weakens the non-linear effects.

[0004] The reason why it is desirable to use an end cap in combination with an HCF is that the end cap protects the fiber end from contamination. By protecting the fiber end, the HCF is optimally functional as contaminants cannot enter the air-filled internal channel by capillary forces. Further, the end cap can serve to fix the HCF.

[0005] Recently, end caps for HCFs were demonstrated in (Non-Patent Literature 1). The demonstrated end caps were used for both in-coupling to and out-coupling from hollow core optical fibers. Each end cap is made from silica in the form of a monolithic unit, and each end cap is directly spliced ​​into the HCF. In this paper, it was demonstrated that an HCF with two end caps was used in a laser with a maximum input power of approximately 260 W at 1080 nm, providing an output power of 203 W and resulting in an overall transmission efficiency of 78.1%.

[0006] More recently, as described in Non-Patent Literature 2, the two end caps described above were spliced ​​more optimally, but still directly, to the HCF. This more optimal splicing resulted in a stable laser output for over an hour and still provided a high transmission efficiency of 77.5% even with an input power of 460W.

[0007] Very recently, Yulong Cui et al. (Non-Patent Literature 3) explained that while HCF is similarly directly spliced, an end cap with more optimal splicing now has a transmission efficiency of approximately 87.5% and can provide a stable laser output for over an hour with an input power of 1176W.

[0008] The aforementioned academic paper provides an end cap that is directly spliced ​​onto the HCF. This is problematic. The splicing process can damage the microstructure of the HCF, leading to cladding collapse. This can limit coupling efficiency, which can lead to excessive heat generation when using high-power lasers, thereby burning out the fiber. This needs to be avoided, and was the reason why splicing was gradually improved in the paper, particularly by carefully controlling the temperature of the splicing system. However, as further stated in the paper, a stable laser output could only be provided for about an hour.

[0009] Therefore, in particular, there is a need to provide an end cap or end cap assembly that provides stable and efficient coupling without damaging the microstructure of the HCF and provides high transmission efficiency, so that a stable laser output of a high-power laser can be provided for a long period of time.

[0010] A solution for an end cap assembly for a hollow core optical fiber is disclosed in (Patent Document 1). Here, the end cap assembly comprises a glass ferrule tube, which is laser-welded at one end to the output end of the HCF and at the other end to an output window or input lens. The output window or input end is similar to the end cap, and in this method, the end cap is not directly fixed or laser-welded to the HCF. Thus, (Patent Document 1) provides an end cap assembly in which the fiber end is not damaged. However, by laser-welding the output window or input to the glass ferrule tube, there is a very high possibility that the input surface or output surface will be damaged during manufacturing, which can reduce transmission through the end cap and lead to assembly failure.

[0011] Therefore, it is desirable to provide end cap assemblies that can be manufactured without damaging the optical surfaces for input and / or output, so that transmission is optimized. At the same time, it is also desirable to provide end cap assemblies that provide stable and efficient coupling without damaging the microstructure of the HCF. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] U.S. Patent Application Publication No. 2007 / 0041083 [Non-patent literature]

[0013] [Non-Patent Document 1] Academic paper "All-Fiber Gas Cavity Based on Anti-Resonant Hollow-Core Fibers Fabricated by Splicing with End Caps", by Jing Shi et al, in Photonics 2021, 8, 371. [Non-Patent Document 2] The paper, "Stable and Efficient Coupling of High-Power Continuous-Wave Laser With Uncooled Anti-resonant Hollow-Core Fibers With End Caps," by Yulong Cui et al., in IEEE Photonics Journal, Vol. 14, No. 1, February 2022. [Non-Patent Document 3] "Highly efficient and stable coupling of kilowatt-level continuous wave laser into hollow-core fibers," Chin. Opt. Lett. 20 (2022) [Overview of the project] [Problems that the invention aims to solve]

[0014] The purpose of this disclosure is to provide an end cap assembly that overcomes the problems of the prior art. Furthermore, an objective of this disclosure is to provide an end cap assembly with high transmission efficiency.

[0015] Furthermore, an object of the present disclosure is to provide an end cap assembly that provides stable and efficient coupling to and from a hollow core fiber (HCF) without damaging the microstructure of the HCF.

Means for Solving the Problems

[0016] These and other objects are defined in the claims and solved by the end cap assembly described below in the present disclosure. In one aspect, an end cap assembly for a hollow core optical fiber is disclosed, the end cap assembly comprising: - an elongated hollow glass ferrule, 〇 a first ferrule portion having a first ferrule end, and 〇 a second ferrule portion having a second ferrule end wherein, the first ferrule end is configured to be sealed, the second ferrule end is configured to receive a hollow core optical fiber, the second ferrule portion is an elongated hollow glass ferrule configured to fix the hollow core optical fiber. The end cap assembly comprises the above.

[0017] In a preferred embodiment of the first aspect, the end cap assembly further comprises an elongated solid end cap made of an optically transmissive material, the elongated solid end cap comprising: 〇 a first end cap portion having a first end cap end, and 〇 a second end cap portion having a second end cap end wherein, the second end cap portion is attached inside the first ferrule portion, whereby the end cap seals the first ferrule end.

[0018] This preferred embodiment provides several advantages. The elongated solid end cap can, first of all, serve to protect the hollow core optical fiber from contaminants since the hollow core optical fiber can be disposed and fixed inside the ferrule.

[0019] Second, the elongated solid end cap can serve to keep the first end cap portion and the first end cap end away from the second end cap portion. Thus, when the second end cap portion is disposed inside the first ferrule portion, the second end cap portion can be fixed inside the first ferrule portion such that the first end cap end forming the optical surface is not close to the location where the second end cap portion is fixed. In this way, it is at least physically ensured that the optical surface is not easily damaged in the process of fixing the end cap to the ferrule.

[0020] Third, the elongated solid end cap can serve to stabilize the solid end cap inside the ferrule, whereby the end cap can be fixed in a stable and / or uniform manner.

[0021] Due to the above advantages, the present disclosure, particularly the elongated solid end cap, provides an end cap assembly configured to provide stable and efficient coupling of light beams to and from the HCF without damaging the microstructure of the HCF.

[0022] Furthermore, since the second ferrule end is configured to receive the hollow core optical fiber, the second ferrule end can be sealed by the hollow core optical fiber in some embodiments. In such embodiments, a sealed ferrule is provided that ensures that contaminants cannot reach the fiber.

[0023] In another aspect, the present disclosure provides an end cap-to-fiber assembly comprising an end cap assembly according to the first aspect and a hollow core optical fiber having a cladding, the fiber A first fiber portion having a fiber input end or a fiber output end, and a second fiber portion having a fiber output end or a fiber input end. Equipped with, The first fiber portion is fixed inside the second ferrule portion, thereby physically separating the fiber from the end cap. The second portion is located outside the second ferrule portion.

[0024] Therefore, when an end cap assembly is used with an HCF, the present disclosure, in particular an elongated solid end cap, provides an end cap assembly configured to provide stable and efficient coupling of a light beam to and from the HCF without damaging the microstructure of the HCF.

[0025] In a third aspect, the Disclosure provides a system for coupling a light beam into and / or out of a hollow core optical fiber, the system being: - End cap to fiber assembly according to a second embodiment, - Laser configured to generate a light beam It is equipped with.

[0026] In a preferred embodiment, the optical beam is led from the first end cap end to the fiber input end, thereby coupling the optical beam to the hollow core optical fiber, and / or the optical beam is led out from the first end cap end and out from the fiber output end, thereby coupling the optical beam out of the hollow core optical fiber.

[0027] In a fourth embodiment, the present disclosure provides a method for manufacturing an end cap assembly for a hollow core optical fiber, the method comprising: - This is the process of preparing a long, slender hollow glass ferrule, and the long, slender hollow glass ferrule is ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end The process of providing and preparing - This is a process of preparing an elongated solid end cap made of an optically transparent material, and the elongated solid end cap is ○ A first end cap portion having a first end cap end, and 〇 Second end cap portion having a second end cap end The process of providing and preparing - The process of inserting and attaching the second end cap portion inside the first ferrule portion. It is equipped with.

[0028] In a fifth embodiment, the Disclosure provides a method for manufacturing an end-cap to fiber assembly for a hollow core optical fiber, the method comprising: - A process for manufacturing an end cap assembly according to the first embodiment, - This is the process of preparing a hollow core optical fiber, and the hollow core optical fiber is ○ A first fiber portion having a fiber input end, and ○ Second fiber portion having a fiber output end The process of providing and preparing - The process of inserting and attaching the first fiber portion inside the second ferrule portion. It is equipped with.

[0029] The above-mentioned and / or additional purposes, features, and advantages of this disclosure are further described by the following exemplary and non-limiting detailed description of embodiments of this disclosure with reference to the accompanying drawings. [Brief explanation of the drawing]

[0030] [Figure 1] Figures showing embodiments of an end cap assembly and an end cap-to-fiber assembly according to a first and second embodiment, respectively. [Figure 2]A diagram showing one embodiment of a ferrule without an end cap, as part of the first and second embodiments. [Figure 3] Figures showing embodiments of an end cap assembly and an end cap-to-fiber assembly according to a first and second embodiment, respectively. [Figure 4] A figure illustrating one embodiment of a system for coupling an optical beam to and / or out of a hollow core optical fiber, according to a third aspect. [Modes for carrying out the invention]

[0031] First aspect: End cap assembly for hollow core optical fiber Arc fusion In a preferred embodiment, the second end cap portion is attached to the first ferrule portion by arc fusion, preferably by uniformly creating a fuse around the second end cap portion, and / or the hollow core optical fiber is attached to the second ferrule portion by arc fusion, preferably by uniformly creating a fuse around the hollow core optical fiber.

[0032] Arc splicing, or arc splicing, is an established method for joining optical fibers. However, arc splicing is commonly used in communication networks, guaranteeing splice loss reduced to 0.05 dB and excellent reliability. The inventors of this disclosure have found that arc splicing can be used as part of the manufacture of end cap assemblies for hollow core optical fibers.

[0033] A typical advantage of using arc fusion is the hermetically sealing of a certain length of hollow core fiber, which is important for creating gas-filled absorption cells or protecting the fiber from the ingress of humidity, dust, or vapor in harsh operating environments.

[0034] As disclosed herein, when arc fusion is used in combination with a hollow core optical fiber and a ferrule, the inventors have found that it provides hermetically sealed or hermetic sealing of the ferrule. Thus, since the fiber is configured to be inside the ferrule, the inventors have found a very effective way to protect the fiber from the environment.

[0035] In the most preferred embodiment, arc fusion is performed using a multi-electrode system such as that described in WO2008 / 098119, which is configured to generate an arc between electrodes to create a substantially uniform heated field around the outer surface of at least one optical fiber. The inventors of the present disclosure have found that in the most preferred embodiment, such a multi-electrode system can be configured to create a substantially uniform heated field around the outer surface of a ferrule, as described in the present disclosure. In other words, since the end cap and the hollow core optical fiber are inside the ferrule, the substantially uniform heated field is, in the most preferred embodiment, around the outer surface of the end cap, and the substantially uniform heated field is around the outer surface of the hollow core optical fiber.

[0036] By inserting the end cap and / or ferrule into the hollow core fiber, the arc region can be used to melt the ferrule, for example, if the ferrule is made of glass. In this way, the glass is melted around the outer surface of the elongated section, forming a fusion splice between the ferrule and the end cap, and / or between the ferrule and the hollow core optical fiber. Such a process has several advantages.

[0037] Firstly, such a process helps to keep the arc region away from the end cap surface. Keeping the arc region away from the end cap surface is beneficial because excessive heat to that surface can cause damage to the surface, which can reduce transmission through the end cap and lead to assembly failure.

[0038] Secondly, since the end cap is located inside the ferrule rather than outside it, a compact assembly is provided. This compactness provides stability to the arc region during the fusion process. This is because the radial position of the electrodes affects the stability of the arc region. In particular, if the radial position of the electrodes is far from the center of the arc region, the stability of the arc region around the end cap decreases, creating uneven heating around the assembly.

[0039] As described above, the use of arc fusion can result in the formation of a fused joint between the ferrule and the end cap, and / or between the ferrule and the hollow core optical fiber. Therefore, by inspecting the ferrule after arc fusion, it may be possible to characterize that the ferrule is sealed by arc fusion, for example, because the fused joint may be uniform.

[0040] Arc fusion can be optimally performed when the arc is a plasma arc and the heating region is a heated plasma region. Furthermore, arc fusion can be performed when a substantially uniform heating region generates a ferrule surface temperature of at least about 1600°C, because this can provide a thermally stable plasma. A thermally stable plasma can result in the fusion process being more than 10 times more thermally repeatable compared to other arc fusion processes.

[0041] End cap dimensions In one embodiment, the second end cap portion has a length of more than 1 mm, preferably about 2 mm. Such a length has the advantage of preventing the end cap from moving from side to side inside the ferrule when inserted into the ferrule, thereby providing an assembly that gives the end cap a stable and well-limited alignment inside the ferrule.

[0042] In another embodiment, the first end cap portion is located outside the ferrule and has a length of more than 2 mm, preferably about 3 mm. This provides the advantage that when the end cap is attached to the inside of the ferrule, for example by arc fusion, the length of the first end cap portion provides a stable fastener inside the arc fusion system.

[0043] In a preferred embodiment, the first end cap portion is cylindrical and has a first outer diameter greater than 1 mm, preferably about 2 mm. Having such a first end cap portion allows, firstly, a relatively large optical beam to be transmitted to the first end cap portion, and as a result, the large optical beam can be further transmitted to the ferrule and further to the hollow core optical fiber. Secondly, having a first end cap portion with a first outer diameter greater than 1 mm allows the end cap to be housed in an arc splicing system configured to hold an optical fiber, and as a result, the arc splicing system can then hold the first end cap portion.

[0044] In another preferred embodiment, the second end cap portion is cylindrical and has a second outer diameter of less than 2 mm, preferably about 1 mm. Having such a second end cap portion allows, firstly, a relatively large optical beam to be transmitted outward from the second end cap portion, and as a result, the large optical beam can be transmitted further to the ferrule and further to the hollow core optical fiber. Secondly, having a second end cap portion with a second outer diameter of less than 2 mm allows the second end cap portion to fit inside the ferrule, thereby providing a compact assembly. When such an assembly is used, as described in relation to arc fusion, the compactness can provide stability to the arc region during the fusion process.

[0045] In yet another preferred embodiment, the second end cap portion is cylindrical and has a second outer diameter greater than 0.4 mm, preferably about 1 mm. By having a second end cap portion with a second outer diameter greater than 0.4 mm and / or less than 2 mm, the second end cap portion can fit inside the ferrule, thereby providing a compact assembly. When such an assembly is used, as described in relation to arc fusion, the compactness can provide stability to the arc region during the fusion process.

[0046] In a more preferred embodiment, the first end cap portion is cylindrical and has a first outer diameter, and the second end cap portion is cylindrical and has a second outer diameter, the first outer diameter being larger than the second outer diameter. This embodiment provides that the first end cap portion can be adapted to optical input requirements such as lens or optical beam dimensions, and the second end cap portion can be adapted to other optical input requirements for a hollow core optical fiber, such as fiber dimensions.

[0047] In relation to the above-described embodiment, the end cap further comprises an intermediate end cap portion between the first end cap portion and the second end cap portion, the intermediate end cap portion being tapered from the first outer diameter to the second outer diameter. This can provide a method for low-cost production of end caps.

[0048] In the most preferred embodiment, the dimensions of the second end cap portion are configured to match the dimensions of the first ferrule portion. Such a fit can minimize angular and concentric mismatches of the fibers during the fusion process.

[0049] End cap void features In one embodiment, the end cap is made of fused silica, for example, Corning 7979 Grade 0F. In this way, the end cap can be made from the same material as the hollow core optical fiber.

[0050] In another embodiment, the first end cap end and / or the second end cap end are preferably anti-reflective (AR) coated by a dielectric coating comprising, for example, a number of layers or a thin film stack of a number of materials.

[0051] In alternative embodiments to those described above, the first and / or second end cap edges are preferably treated with an anti-reflective (AR) coating by a random pattern process. One example of treating the first and / or second end cap edges is by directly etching a nanometer-scale texture into the surface. These nanotextures exhibit high efficiency, a wide bandwidth, a wide acceptance angle, and unique functionality. Surface energy effects such as hydrophobicity and resistance to the adsorption of chemicals from the laser-emitting environment are further potential advantages of nanostructure technology. Fabricating surface relief structures in optical materials creates a stepwise transition in the material density (refractive index) encountered by the passing light. The height, shape, and spacing of the structures constituting the texture determine how effective the texture is in suppressing reflected light. Due to this gradient refractive index AR effect, the AR performance is very stable and does not depend on the wavelength of light as in the case of dielectric coatings. As a result, AR nanotextures exhibit a wide operating bandwidth, extremely low loss, and a wide acceptance angle compared to AR coatings.

[0052] If the first end cap end and / or the second end cap end are coated or treated with an anti-reflective (AR) coating as described above, the first end cap end and / or the second end cap end are quite delicate and may not withstand all types of treatments in order to maintain the AR effect. Therefore, when the end cap is mounted inside the ferrule according to this disclosure, and when the end cap is mounted after the end cap end has been AR coated or treated, the first end cap end and / or the second end cap end can, in a preferred embodiment, be protected from secondary effects resulting from the mounting process. As previously described, such a mounting process may be arc welding. If arc welding is performed near the end cap end having an AR coating or treatment, arc welding may potentially damage the AR coating or treatment. By elongating the end cap, according to the assembly now disclosed, the end cap end is physically moved away from arc welding, thereby ensuring that the AR coating or treatment is not damaged. Thus, the elongated end cap, along with the AR-coated or AR-treated end cap end, has the technical effect of preventing the AR coating or AR treatment from being damaged during arc fusion. Therefore, in a preferred embodiment, an end cap assembly for a hollow core optical fiber is provided, and the end cap assembly is, - A long, slender, hollow glass ferrule, ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end Equipped with, The first ferrule end is configured to be sealed, The second ferrule end is configured to receive a hollow core optical fiber, The second ferrule portion is configured to secure the hollow core optical fiber, and consists of an elongated hollow glass ferrule, - A long, slender, solid end cap made of optically transparent material, ○ A first end cap portion having a first end cap end, and 〇 Second end cap portion having a second end cap end Equipped with, The second end cap portion is attached to the inside of the first ferrule portion, thereby the end cap seals the end of the first ferrule. The second end cap portion is attached to the first ferrule end by arc fusion. The first end cap end and / or the second end cap end are elongated solid end caps that are treated to be anti-reflective. It is equipped with.

[0053] In this preferred embodiment and other embodiments, according to the first aspect, arc welding is performed on the second end cap portion and, therefore, on the first ferrule portion as well. To protect the first end cap end and / or the second end cap end from damage during arc welding, the inventors of the present disclosure have found that the first end cap end and / or the second end cap end must be separated from the arc welding point in the second end cap portion and the first ferrule portion by more than 0.5 mm, preferably more than 1 mm. This can be achieved, for example, when the end cap has an overall length of more than 2 mm, and more preferably when the end cap has an overall length of more than 3 mm, such as about 4 mm or 5 mm.

[0054] In one embodiment, the first end cap end is a flat surface. The flat surface can function as an optical window, allowing a light beam to diverge into the optical window and further into the end cap. The light beam can be diverged, for example, by placing a lens in front of the first end cap end. Alternatively, in another embodiment, the first end cap end is a curved surface for forming a lens that focuses inside the second ferrule portion. This can provide a compact assembly.

[0055] Ferrule Typically, a ferrule is a ceramic, plastic, or stainless steel component of an optical fiber plug that holds the end of a fiber and precisely aligns it into a socket. The fiber is inserted into the ferrule and bonded with epoxy or adhesive, which provides long-term mechanical strength and prevents contamination from the environment. The ferrules disclosed in this disclosure differ from the typical ferrules described above.

[0056] In one embodiment, the ferrule is made of a material different from fused silica, the material having a lower refractive index than that of fused silica (defined at a wavelength of 1064 nm and a temperature of 20 degrees Celsius). Thus, the ferrule can be made from a material different from that of the end cap and / or hollow core optical fiber. Specific examples of materials and their advantages are described below.

[0057] In another embodiment, the ferrule is made of a material different from fused silica, the material having a coefficient of thermal expansion (CTE) that differs from that of fused silica by a coefficient of 0.3 or more and less than 8.0, preferably in the range of about 0.5 to 6.0, and more preferably in the range of about 0.5 to 1.5.

[0058] In a preferred embodiment, the material is a borosilicate. This material is an example of a material having a CTE about six times or more than that of fused silica. Borosilicate has a higher refractive index than fused silica, i.e., a refractive index of 1.47 at a wavelength of 1064 nm instead of 1.44. The inventors of this disclosure have found that when ferrules are made of borosilicate, their very low processing / softening temperature can minimize thermal load and damage to the HC fibers.

[0059] In the most preferred embodiment, the material is fluorine-doped fused silica (fluorosilicate). This material is an example of a material having a CTE of about 0.5 compared to fused silica, but furthermore, its refractive index is lower than that of fused silica, i.e., 1.44 instead of 1.45 at a wavelength of 1064 nm. Considering arc fusion to the end cap of a hollow core optical fiber, the inventors of this disclosure have found that fluorine-doped fused silica has a low softening temperature, but not as low as borosilicate, and therefore does not minimize the thermal load on the fiber as much as borosilicate. However, the inventors of this disclosure have recognized that fluorine-doped fused silica offers significant advantages compared to borosilicate. Because fluorine-doped fused silica has a coefficient of thermal expansion (CTE) that closely matches that of the fiber (such as one made of fused silica), the inventors of this disclosure have found that fluorine-doped fused silica does not induce stress at the interface between the fiber and the ferrule, which can weaken the assembly at the fusion point. For this reason, fluorine-doped fused silica has been found to be preferable to borosilicate.

[0060] In some embodiments, the material is the same as the material for the hollow core optical fiber, i.e., fused silica. In this way, the CTE is clearly adapted to the HC fiber and does not cause stress at the interface between the fiber and the ferrule. However, fused silica has a high processing / softening temperature, and therefore, if fused silica is used, it may cause damage to the structure of the hollow core optical fiber during the fusion process. However, this damage can be prevented by various solutions.

[0061] In one embodiment, the first ferrule portion has a length of more than 1 mm, preferably about 2 mm. Such a length has the advantage of providing an assembly that prevents the end cap from moving from side to side inside the ferrule when the end cap is inserted into the ferrule, thereby giving the end cap a stable and well-limited alignment inside the ferrule.

[0062] In another embodiment, the second ferrule portion has a length greater than 3 mm, preferably about 4 mm, and more preferably about 5 mm. Such a length has the advantage of providing a semblage that prevents the hollow core optical fiber from moving from side to side inside the ferrule once it is inserted into the ferrule, thereby giving the fiber a stable and well-limited alignment inside the ferrule. As previously described, ferrules are generally alignment systems, and providing lengths such as those described herein is one solution for performing fiber alignment.

[0063] In yet another embodiment, the first ferrule portion is cylindrical and has a first inner diameter greater than 0.4 mm and / or less than 2 mm, preferably less than 1 mm. This embodiment provides a compact assembly. When such an assembly is used, as described in relation to arc fusion, the compactness can provide stability to the arc region during the fusion process.

[0064] In a preferred embodiment, the second ferrule portion is cylindrical and has a second inner diameter greater than 0.2 mm and / or less than 0.4 mm, preferably less than 0.3 mm, most preferably about 0.2 mm. This second inner diameter is preferably adapted to the dimensions of the hollow core optical fiber.

[0065] In some embodiments, the first ferrule portion is cylindrical on the inside and has a first inner diameter, and the second end cap portion is cylindrical on the inside and has a second inner diameter, with the first inner diameter being larger than the second inner diameter. This can result in the ferrule fitting the dimensions of both the end cap and the hollow core optical fiber.

[0066] In other embodiments, the ferrule further comprises an intermediate end ferrule portion between the first ferrule portion and the second ferrule portion, the intermediate ferrule portion being tapered from a first inner diameter to a second inner diameter. This can provide a method for low-cost production of ferrules, for example, when the inner diameter of the intermediate ferrule portion is proportional to the outer diameter of the intermediate ferrule portion and the intermediate ferrule portion is tapered from a first outer diameter to a second outer diameter.

[0067] In a preferred embodiment, the dimensions of the first ferrule portion are configured to match the dimensions of the second end cap portion. In another preferred embodiment, the dimensions of the second ferrule portion are configured to match the dimensions of the hollow core optical fiber. Preferably, the dimensional fit should be such that the difference between the first ferrule portion having a first inner diameter and the second end cap portion having a second outer diameter, and / or the difference between the second ferrule portion having a first inner diameter and the hollow core optical fiber having its outer diameter, is less than 50 microns, most preferably between 5 and 15 microns. In these preferred embodiments, any movement during the splicing process can be minimized, which can provide the most optimal and / or most uniform splice.

[0068] Applications of end cap assemblies In one embodiment, the end cap assembly is for coupling a light beam to a hollow core optical fiber, and the first end cap end is configured to receive the light beam, so that when the light beam enters the first end cap end, the light beam is transmitted through the end cap to the second ferrule portion.

[0069] In another embodiment, the end cap assembly is for coupling the optical beam out of the hollow core optical fiber, and the first end cap end is configured to transmit the optical beam such that when the optical beam is transmitted from the first end cap end, the optical beam is transmitted through the end cap via a ferrule.

[0070] In other words, the end cap assembly may be used as either an input or output at one end of the hollow core optical fiber, or it may be used as both an input and an output at both ends of the hollow core optical fiber.

[0071] The end cap assemblies according to this disclosure can be used in a variety of applications and with laser beams having a desired wavelength. In some embodiments, the wavelength can be about 1 micron, or from 1 micron to about 2 microns, for example, up to about 2.2 microns. For example, the wavelength can be 1500-1600 nm, or 1700-2200 nm.

[0072] The desired wavelength described above may be provided, for example, by a laser operating as a continuous-wave (CW) laser or an ultrashort-pulse (USPL) laser. The laser may also be operated as a long-pulse laser configured to supply pulses of, for example, about 1 ns to several hundred ns.

[0073] Lasers can be, for example, high-power (i.e., several hundred watts). The end cap assemblies according to this disclosure have been found to be usable in high-power applications where high-power lasers are used.

[0074] However, the end cap assemblies according to this disclosure may also be used in low-power applications where low-power lasers are used. A low-power laser can be defined as a laser configured to deliver milliwatts or tens of watts.

[0075] When end cap assemblies are used in low-power applications, desirable wavelengths may be between 300 nm and 1000 nm, for example. Such wavelengths may be used, for example, in connection with quantum setups.

[0076] Second aspect: End cap to fiber assembly In one embodiment, the first fiber portion is fixed by arc fusion, preferably by uniformly creating a fused area around the hollow core optical fiber. The advantages of this embodiment have already been described in relation to the first aspect of the present disclosure.

[0077] In another embodiment, the fiber further comprises an intermediate fiber portion between the first fiber portion and the second fiber portion, the intermediate fiber portion being peeled off from the cladding. Preferably, the intermediate fiber portion is located outside the second ferrule portion, thereby configuring the intermediate fiber portion to guide light out of the fiber. This can ensure that the final cladding modes inside the cladding are removed from the fiber. The removed cladding modes can be converted into heat and removed from the fiber.

[0078] Third aspect: A system for coupling a light beam into and / or out of a hollow core optical fiber. In one embodiment, the laser is a high-power laser having an average power of more than 200 W, preferably more than 1000 W, more preferably more than 1500 W, and most preferably more than 2000 W. Such high power is generally unusable with previous end cap products due to end cap damage. Damage to previous end cap products, particularly to the input surface to the fiber or the bonding surface, generally occurs during the fixing of the end cap, because the end cap is bonded directly to the fiber using, for example, epoxy or adhesive, and thus the epoxy or adhesive adheres to the input surface and / or bonding surface. However, damage to previous end cap products, particularly to the input surface to the fiber or the bonding surface, can also occur because the end cap is welded. The inventors of the present disclosure have found that the assembly now disclosed is configured to operate for extended periods at input average powers such as those described herein. This is because, in particular, the end cap is not directly fused to the hollow core optical fiber, and furthermore, the elongated end cap prevents damage to the end cap, especially the first end cap end, during the process of fixing the end cap to the ferrule, thereby preventing heat from accumulating at the input end of the hollow core optical fiber. Thus, the system disclosed hereby overcomes these problems and ensures that the fiber does not burn when using high-power lasers. For the same reason, the transmission efficiency of the system disclosed hereby achieves more than 85% for average input power up to at least 270W.

[0079] Fourth aspect: Method for manufacturing an end cap assembly for a hollow core optical fiber In one embodiment of the method according to the fourth aspect, the step of attaching the second end cap portion is performed by arc fusion, preferably by uniformly creating a fused area around the second end cap portion. The advantages of arc fusion have already been described in relation to the first and second aspects of the present disclosure. Furthermore, as previously described, the first end cap end and / or the second end cap end may be AR coated or treated.

[0080] In relation to the manufacturing method, in one embodiment, AR coating or AR treatment may be applied or performed before each end cap is attached to the inside of the ferrule by arc fusion. This can facilitate the production of the end cap assembly, particularly because, here, the second end cap end is located inside the ferrule, making it difficult to apply AR coating or AR treatment to the second end cap end after arc fusion.

[0081] However, since the first end cap end is outside the ferrule after installation, the AR coating or AR treatment may, in principle and in one embodiment, be applied to or performed on the first end cap end after the end cap has been installed inside the ferrule by arc fusion. Thus, for example, if the first end cap end is close to the fusion point, the installation of the end cap by arc fusion may damage the first end cap end, thereby potentially affecting, for example, transmission through the first end cap end. However, this may be acceptable if the first end cap end is not coated or treated. Therefore, in this embodiment, the first end cap end may be prepared for AR coating or treatment after installation, for example, by polishing and / or planarizing to form an optical window, or by curving to form an optical focusing surface.

[0082] In a second embodiment of the method according to the fourth aspect, the transition from the first end cap portion to the second end cap portion is performed by tapering. In the relevant embodiments, tapering is a two-step process, namely, - A first step comprising tapering the first end cap portion from a first outer diameter to an intermediate end cap portion having an intermediate outer diameter, and - A second step comprising tapering the intermediate end cap portion from the intermediate outer diameter to a second end cap portion having a second outer diameter. That is the case.

[0083] In one embodiment, the first ferrule end and / or the second ferrule end are provided by cleavage. In most embodiments, the end cap assembly is an end cap assembly according to the first embodiment.

[0084] Fifth aspect: Method for manufacturing an end cap-to-fiber assembly for a hollow core optical fiber In one embodiment of the fifth aspect of the method, the step of attaching the first fiber portion is performed by arc fusion, preferably by uniformly creating a fused area around the first fiber portion. The advantages of arc fusion have already been described in relation to the first and second aspects of the present disclosure.

[0085] In another embodiment, the first fiber input end is prepared by cleavage. In most embodiments, the end cap-to-fiber assembly is an end cap-to-fiber assembly according to a second embodiment.

[0086] Examples (Example 1) Embodiments of an end cap assembly and an end cap-to-fiber assembly according to the first and second embodiments, respectively. Figure 1 shows an embodiment of an end cap assembly 1 and an end cap to fiber assembly according to a first and second embodiment, respectively. The end cap assembly is shown as a cross section to view the inside of the end cap assembly. The end cap assembly 1 for a hollow core optical fiber 2 comprises an elongated hollow glass ferrule 3 having a first ferrule portion 4 with a first ferrule end 5 and a second ferrule portion 6 with a second ferrule end 7. The first ferrule end 5 is configured to seal, and the second ferrule end 7 is configured to receive the hollow core optical fiber 2. Furthermore, the second ferrule portion 6 is configured to secure the hollow core optical fiber 2. In this example, the hollow core optical fiber 2 is mounted inside the ferrule 3, more specifically inside the second ferrule portion 6. The end cap assembly further comprises an elongated solid end cap 8 made of an optically transparent material, which includes a first end cap portion 9 having a first end cap end 10 and a second end cap portion 11 having a second end cap end 12. The second end cap portion 11 is fitted inside the first ferrule portion 4, thereby the end cap 8 seals the first ferrule end 5.

[0087] In this example, the second end cap portion 11 is attached to the first ferrule portion 4 by arc fusion, preferably by uniformly creating a fused area around the second end cap portion 11, and the hollow core optical fiber 2 is attached to the second ferrule portion 6 by arc fusion, preferably by uniformly creating a fused area around the hollow core optical fiber 2. Thus, the arc fusion process provides a uniform fused area between the second end cap portion 11 and the first ferrule portion 4. Furthermore, the arc fusion process provides a uniform fused area between the hollow core optical fiber 2 and the second ferrule portion 6. These fused areas are not visible in the figure, but can be actually seen by inspecting the end cap assembly 1, as disclosed herein, which is created by arc fusion.

[0088] In this example, the second end cap portion 11 has a length of approximately 2 mm. As can be seen from Figure 1, the first end cap portion 9 is located outside the ferrule 3 and has a length of approximately 3 mm.

[0089] The first end cap portion 9 is cylindrical and has a first outer diameter of approximately 2 mm. The second end cap portion 11 is similarly cylindrical and has a second outer diameter of approximately 1 mm. Thus, the first outer diameter is larger than the second outer diameter. The end cap 3 further includes an intermediate end cap portion 13 between the first end cap portion 9 and the second end cap portion 11, which is tapered from the first outer diameter to the second outer diameter. The dimensions of the second end cap portion 11 are configured to match the dimensions of the first ferrule portion 4, and vice versa.

[0090] In this example, the end cap 8 is made of fused silica, and both the first end cap end 10 and the second end cap end 12 are treated with an anti-reflective coating using a random pattern process. As can be seen from Figure 1, the first end cap end 10 is a flat surface.

[0091] In the embodiment shown in Figure 1, the first ferrule portion 4 has a length of approximately 2 mm, and the second ferrule portion 6 has a length of approximately 5 mm. Furthermore, the first ferrule portion 4 is cylindrical and has a first inner diameter of approximately 0.216 mm that matches the outer diameter of the hollow core optical fiber 2. The first inner diameter is larger than the second inner diameter.

[0092] The ferrule 3 further includes an intermediate end ferrule portion 14 between the first ferrule portion 4 and the second ferrule portion 6. The intermediate ferrule portion 14 is tapered from the first inner diameter to the second inner diameter.

[0093] Since the hollow core optical fiber 2 is mounted inside the second ferrule portion 6, this figure also shows an embodiment of the second aspect. Accordingly, Figure 1 shows an end cap to fiber assembly 1 comprising an end cap assembly according to the first aspect and a hollow core optical fiber 2 having cladding 15, the fiber 2 comprising a first fiber portion 16 having a fiber input end 17 or a fiber output end 17 and a second fiber portion 18 having a fiber output end 19 or a fiber input end 19. As can be seen from Figure 1, the first fiber portion 16 is fixed inside the second ferrule portion 6 so that the fiber 2 is physically separated from the end cap 8. Finally, the second fiber portion 18 is outside the second ferrule portion 6.

[0094] (Example 2) One embodiment of a ferrule as part of the first and second embodiments Figure 2 shows an embodiment of the ferrule 3 without an end cap 1 as part of the first and second embodiments. The ferrule 3 is shown in perspective. According to the first and second embodiments, the ferrule is an elongated hollow glass ferrule 3. The ferrule comprises a first ferrule portion 4 having a first ferrule end 5 and a second ferrule portion 6 having a second ferrule end 7. Both the first ferrule end 5 and the second ferrule end are configured to be sealed.

[0095] (Example 3) Embodiments of an end cap assembly and an end cap-to-fiber assembly according to the first and second embodiments, respectively. Figure 3 shows one embodiment of the end cap assembly 1 and the end cap-to-fiber assembly according to the first and second embodiments, respectively. The illustrated end cap assemblies are photographs of end cap assemblies manufactured according to the first and second embodiments, and those manufactured according to the fourth and fifth embodiments, respectively.

[0096] An end cap assembly 1 for a hollow core optical fiber 2 comprises an elongated hollow glass ferrule 3 having a first ferrule portion 4 with a first ferrule end 5 and a second ferrule portion 6 with a second ferrule end 7. The first ferrule end 5 is configured to seal, and the second ferrule end 7 is configured to receive the hollow core optical fiber 2. Furthermore, the second ferrule portion 6 is configured to secure the hollow core optical fiber 2. In this example, the hollow core optical fiber 2 is mounted inside the ferrule 3, more specifically inside the second ferrule portion 6. The end cap assembly further comprises an elongated solid end cap 8 made of an optically transparent material, having a first end cap portion 9 with a first end cap end 10 and a second end cap portion 11 with a second end cap end 12. The second end cap portion 11 is mounted inside the first ferrule portion 4, thereby the end cap 8 seals the first ferrule end 5.

[0097] In this example, the second end cap portion 11 is attached to the first ferrule portion by arc fusion, preferably by uniformly creating a fused area around the second end cap portion 11, and the hollow core optical fiber 2 is attached to the second ferrule portion 6 by arc fusion, preferably by uniformly creating a fused area around the hollow core optical fiber 2. Thus, the arc fusion process provides a uniform fused area between the second end cap portion 11 and the first ferrule portion 4. Furthermore, the arc fusion process provides a uniform fused area between the hollow core optical fiber 2 and the second ferrule portion 6. These fused areas are not visible in the figure, but can be actually seen by inspecting the end cap assembly 1, as disclosed herein, which is created by arc fusion.

[0098] In this example, the second end cap portion 11 has a length of approximately 3 mm. As can be seen from Figure 3, the first end cap portion 9 is located outside the ferrule 3 and has a length of approximately 3 mm.

[0099] The first end cap portion 9 is cylindrical and has a first outer diameter of approximately 2 mm. The second end cap portion 11 is similarly cylindrical and has a second outer diameter of approximately 1 mm. Thus, the first outer diameter is larger than the second outer diameter. The end cap 3 further includes an intermediate end cap portion 13 between the first end cap portion 9 and the second end cap portion 11, which is tapered from the first outer diameter to the second outer diameter. The dimensions of the second end cap portion 11 are configured to match the dimensions of the first ferrule portion 4, and vice versa.

[0100] In this example, the end cap 8 is made of fused silica, and both the first end cap end 10 and the second end cap end 12 are treated with an anti-reflective coating using a random pattern process. As can be seen from Figure 3, the first end cap end 10 is a flat surface.

[0101] In the embodiment shown in Figure 3, the first ferrule portion 4 has a length of approximately 3 mm, and the second ferrule portion 6 has a length of approximately 5 mm. Furthermore, the first ferrule portion 4 is cylindrical and has a first inner diameter of approximately 0.216 mm that matches the outer diameter of the hollow core optical fiber 2. The first inner diameter is larger than the second inner diameter.

[0102] The ferrule 3 further includes an intermediate end ferrule portion 14 between the first ferrule portion 4 and the second ferrule portion 6. The intermediate ferrule portion 14 is tapered from the first inner diameter to the second inner diameter.

[0103] Since the hollow core optical fiber 2 is mounted inside the second ferrule portion 6, this figure also shows an embodiment of the second aspect. Accordingly, Figure 3 shows an end cap to fiber assembly 1 comprising an end cap assembly 1 according to the first aspect and a hollow core optical fiber 2 having cladding 15, the fiber 2 comprising a first fiber portion 16 having a fiber input end 17 or a fiber output end 17 and a second fiber portion 18 having a fiber output end 19 or a fiber input end 19. As can be seen from Figure 1, the first fiber portion 16 is fixed inside the second ferrule portion 6 so that the fiber 2 is physically separated from the end cap 8. Finally, the second fiber portion 18 is outside the second ferrule portion 6.

[0104] (Example 4) A third embodiment of a system for coupling a light beam to and / or out of a hollow core optical fiber. Figure 4 shows one embodiment of a system 20 for coupling an optical beam 21 to and / or out of a hollow core optical fiber 2, according to a third aspect. In this example, the system 20 comprises an end cap-to-fiber assembly 1 according to a first aspect, and a hollow core optical fiber 2 mounted inside a ferrule 3, thereby also comprising an end cap-to-fiber assembly according to a second aspect, and a laser 22 configured to generate an optical beam 21.

[0105] The optical beam 21 is guided from the first end cap end 10 to the fiber input end 17, thereby coupling the optical beam to the hollow core optical fiber 2. From the laser, the laser light is first coupled to a large-mode-area (LMA) fiber 23, then coupled outward (in the form of a diverging light beam), and further coupled in this example to a coupling optical system in the form of a collimating lens 24 and a focusing lens 25 configured to couple the light beam to the fiber input end 17 together with an end cap 8. Thus, this example demonstrates how the present disclosure provides a setup for coupling light from the LMA fiber 23 to a hollow-core optical fiber 2.

[0106] Further details are explained in the following sections. item [Item 1] An end cap assembly for a hollow core optical fiber, - A long, slender, hollow glass ferrule, ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end Equipped with, The first ferrule end is configured to be sealed, The second ferrule end is configured to receive a hollow core optical fiber, The second ferrule portion is configured to secure the hollow core optical fiber, and the elongated hollow glass ferrule, - A long, slender, solid end cap made of optically transparent material, ○ A first end cap portion having a first end cap end, and 〇 Second end cap portion having a second end cap end Equipped with, The second end cap portion is attached to the inside of the first ferrule portion, thereby the end cap seals the end of the first ferrule, and is an elongated solid end cap. An end cap assembly equipped with [a specific feature].

[0107] [Item 2] The end cap assembly according to item 1, wherein the second end cap portion is attached to the first ferrule portion by arc fusion, preferably by uniformly creating a fused portion around the second end cap portion, and / or the hollow core optical fiber is attached to the second ferrule portion by arc fusion, preferably by uniformly creating a fused portion around the hollow core optical fiber.

[0108] [Item 3] The end cap assembly according to item 1 or 2, wherein the second end cap portion has a length of more than 1 mm, preferably about 2 mm.

[0109] [Item 4] An end cap assembly according to any one of items 1 to 3, wherein the first end cap portion is located outside the ferrule, and the first end cap portion has a length of more than 2 mm, preferably about 3 mm.

[0110] [Item 5] The end cap assembly according to any one of items 1 to 4, wherein the first end cap portion is cylindrical and has a first outer diameter greater than 1 mm, preferably about 2 mm.

[0111] [Item 6] The end cap assembly according to any one of items 1 to 5, wherein the second end cap portion is cylindrical and has a second outer diameter of less than 2 mm, preferably about 1 mm.

[0112] [Item 7] The end cap assembly according to any one of items 1 to 6, wherein the second end cap portion is cylindrical and has a second outer diameter greater than 0.4 mm, preferably about 1 mm.

[0113] [Item 8] The end cap assembly according to any one of items 1 to 7, wherein the first end cap portion is cylindrical and has a first outer diameter, and the second end cap portion is cylindrical and has a second outer diameter, with the first outer diameter being larger than the second outer diameter.

[0114] [Item 9] The end cap assembly according to item 8, wherein the end cap further comprises an intermediate end cap portion between the first end cap portion and the second end cap portion, and the intermediate end cap portion is tapered from the first outer diameter to the second outer diameter.

[0115] [Item 10] An end cap assembly according to any one of items 1 to 9, wherein the dimensions of the second end cap portion are configured to match the dimensions of the first ferrule portion.

[0116] [Item 11] The end cap assembly according to any one of items 1 to 10, wherein the end cap is made of fused silica.

[0117] [Item 12] The end cap assembly according to any one of items 1 to 11, wherein the first end cap end and / or the second end cap end are preferably coated with an anti-reflective dielectric coating.

[0118] [Item 13] An end cap assembly according to any one of items 1 to 12, wherein the first end cap end and / or the second end cap end are preferably treated to be anti-reflective by a random pattern process.

[0119] [Item 13] The end cap assembly according to any one of items 1 to 12, wherein the first end cap end is a flat surface.

[0120] [Item 14] The end cap assembly according to any one of items 1 to 13, wherein the first end cap portion is a curved surface for forming a lens that focuses inside the second ferrule portion.

[0121] [Item 15] The end cap assembly according to any one of items 1 to 14, wherein the ferrule is made of a material different from fused silica, and the material has a refractive index lower than that of fused silica (as defined at a wavelength of 1064 nm and a temperature of 20 degrees Celsius).

[0122] [Item 16] The end cap assembly according to any one of items 1 to 15, wherein the ferrule is made of a material different from fused silica, and the material has a coefficient of thermal expansion (CTE) that differs from the coefficient of thermal expansion (CTE) of fused silica by a coefficient of 0.3 or more and less than 8.0, preferably the coefficient is in the range of about 0.5 to 6.0, and more preferably the coefficient is in the range of about 0.5 to 1.5.

[0123] [Item 17] The end cap assembly described in item 16, wherein the material is a borosilicate. [Item 18] The end cap assembly according to item 15 or 16, wherein the material is fluorine-doped fused silica (fluorosilicate).

[0124] [Item 19] The end cap assembly according to any one of items 1 to 18, wherein the first ferrule portion has a length of more than 1 mm, preferably about 2 mm.

[0125] [Item 20] The end cap assembly according to any one of items 1 to 19, wherein the second ferrule portion has a length of more than 3 mm, preferably about 4 mm, and more preferably about 5 mm.

[0126] [Item 21] The end cap assembly according to any one of items 1 to 20, wherein the first ferrule portion is cylindrical and has a first inner diameter greater than 0.4 mm and / or less than 2 mm, preferably less than 1 mm.

[0127] [Item 22] The end cap assembly according to any one of items 1 to 21, wherein the second ferrule portion is cylindrical and has a second inner diameter greater than 0.2 mm and / or less than 0.4 mm, preferably less than 0.3 mm, most preferably about 0.216 mm.

[0128] [Item 23] The end cap assembly according to any one of items 1 to 22, wherein the first ferrule portion is cylindrical on the inside and has a first inner diameter, and the second end cap portion is cylindrical on the inside and has a second inner diameter, the first inner diameter being larger than the second inner diameter.

[0129] [Item 24] The end cap assembly according to item 23, wherein the ferrule further comprises an intermediate end ferrule portion between the first ferrule portion and the second ferrule portion, and the intermediate ferrule portion is tapered from the first inner diameter to the second inner diameter.

[0130] [Item 25] An end cap assembly according to any one of items 1 to 24, wherein the dimensions of the first ferrule portion are configured to conform to the dimensions of the second end cap portion.

[0131] [Item 26] The end cap assembly according to any one of items 1 to 25, wherein the end cap assembly is for coupling a light beam to the hollow core optical fiber, and the first end cap end is configured to receive the light beam, so that when the light beam enters the first end cap end, the light beam is transmitted through the end cap to the second ferrule portion.

[0132] [Item 27] The end cap assembly according to any one of items 1 to 26, wherein the end cap assembly is for coupling a light beam out of the hollow core optical fiber.

[0133] [Item 28] - The end cap assembly described in any of items 1 to 27, - The hollow core optical fiber having cladding An end cap-to-fiber assembly comprising, The aforementioned fiber, A first fiber portion having a fiber input end or a fiber output end, A second fiber portion having a fiber output end or a fiber input end Equipped with, The first fiber portion is fixed inside the second ferrule portion, thereby physically separating the fiber from the end cap, and An end cap-to-fiber assembly in which the second portion is located outside the second ferrule portion.

[0134] [Item 29] The end cap-to-fiber assembly according to item 28, wherein the first fiber portion is fixed by arc fusion, preferably by uniformly creating a fused area around the hollow core optical fiber.

[0135] [Item 30] The end cap-to-fiber assembly according to item 28 or 29, wherein the fiber further comprises an intermediate fiber portion between the first fiber portion and the second fiber portion, and the intermediate fiber portion is peeled off from the cladding.

[0136] [Item 31] The end cap-to-fiber assembly according to item 30, wherein the intermediate fiber portion is located outside the second ferrule portion, thereby configuring the intermediate fiber portion to guide light out of the fiber.

[0137] [Item 32] A system for coupling a light beam to and / or out of a hollow core optical fiber, - The end cap-to-fiber assembly described in any of items 28 to 31, - A laser configured to generate the aforementioned light beam, The light beam is guided from the first end cap end to the fiber input end, thereby coupling the light beam to the hollow core optical fiber, and / or The light beam is guided out from the first end cap end and out from the fiber output end, thereby coupling the light beam out from the hollow core optical fiber, laser A system that includes these features.

[0138] [Item 33] The system according to item 32, wherein the laser is a high-power laser having an average output of more than 200 W, preferably more than 1000 W, more preferably more than 1500 W, and most preferably more than 2000 W.

[0139] [Item 34] A method for manufacturing an end cap assembly for a hollow core optical fiber, - This is the process of preparing a long, slender hollow glass ferrule, and the long, slender hollow glass ferrule is ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end The process of providing and preparing - This is a process of preparing an elongated solid end cap made of an optically transparent material, and the elongated solid end cap is ○ A first end cap portion having a first end cap end, and 〇 Second end cap portion having a second end cap end The process of providing and preparing - The step of inserting and attaching the second end cap portion inside the first ferrule portion. A method that includes [a certain feature].

[0140] [Item 35] The method according to item 34, wherein the step of attaching the second end cap portion is performed by arc fusion, preferably by uniformly creating a fused area around the second end cap portion.

[0141] [Item 36] The method according to item 34 or 35, wherein the transition from the first end cap portion to the second end cap portion is performed by tapering.

[0142] [Item 37] The aforementioned tapering is a two-step process, namely, - A first step comprising tapering the first end cap portion from a first outer diameter to an intermediate end cap portion having an intermediate outer diameter, and - A second step comprising tapering the intermediate end cap portion from the intermediate outer diameter to the second end cap portion having a second outer diameter. The method described in item 36.

[0143] [Item 38] The method according to any one of items 34 to 37, wherein the first ferrule end and / or the second ferrule end are provided by cleavage.

[0144] [Item 39] The method according to any one of items 34 to 37, wherein the end cap assembly is the end cap assembly described in any one of items 1 to 27.

[0145] [Item 40] A method for manufacturing an end cap-to-fiber assembly for a hollow core optical fiber, - A process for manufacturing the end cap assembly as described in any of items 34 to 39, - This is the process of preparing a hollow core optical fiber, and the hollow core optical fiber is ○ A first fiber portion having a fiber input end, and ○ Second fiber portion having a fiber output end The process of providing and preparing - The step of inserting and attaching the first fiber portion inside the second ferrule portion. A method that includes [a certain feature].

[0146] [Item 41] The method according to item 40, wherein the step of attaching the first fiber portion is performed by arc fusion, preferably by uniformly creating a fused area around the first fiber portion.

[0147] [Item 42] The method according to item 40 or 41, wherein the first fiber input end is prepared by cleavage.

[0148] [Item 43] The method according to any one of items 40 to 42, wherein the end cap-to-fiber assembly is the end cap-to-fiber assembly described in any one of items 28 to 31.

Claims

1. An end cap assembly for a hollow core optical fiber, - A long, slender, hollow glass ferrule, ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end Equipped with, The first ferrule end is configured to be sealed, The second ferrule end is configured to receive a hollow core optical fiber, The second ferrule portion is configured to fix the hollow core optical fiber, and the ferrule is an elongated hollow glass ferrule, - A long, solid end cap made of optically transparent material, ○ A first end cap portion having a first end cap end, and ○ Second end cap portion having a second end cap end Equipped with, The second end cap portion is attached to the inside of the first ferrule portion, so that the end cap seals the end of the first ferrule, forming an elongated solid end cap. An end cap assembly equipped with [a specific feature].

2. The end cap assembly according to claim 1, wherein the second end cap portion is attached to the first ferrule end by arc fusion, preferably by uniformly creating a fused portion around the second end cap portion, and / or the hollow core optical fiber is attached to the second ferrule portion by arc fusion, preferably by uniformly creating a fused portion around the hollow core optical fiber.

3. The end cap assembly according to claim 1 or 2, wherein the second end cap portion has a length of more than 2 mm.

4. The end cap assembly according to any one of claims 1 to 3, wherein the first end cap end and / or the second end cap end are anti-reflective, preferably by a random pattern process.

5. The end cap assembly according to any one of claims 1 to 4, wherein the first end cap portion has a length of more than 2 mm.

6. The end cap assembly according to any one of claims 1 to 5, wherein the ferrule is made of a material different from fused silica, and the material has a refractive index lower than that of fused silica.

7. The end cap assembly according to any one of claims 1 to 6, wherein the ferrule is made of a material different from fused silica, and the material has a coefficient of thermal expansion (CTE) that differs from the coefficient of thermal expansion (CTE) of fused silica by a coefficient of 0.3 or more and less than 8.0, preferably the coefficient is in the range of about 0.5 to 6.0, and more preferably the coefficient is in the range of about 0.5 to 1.

5.

8. The end cap assembly according to claim 6 or 7, wherein the material is fluorine-doped fused silica (fluorosilicate).

9. The end cap assembly according to any one of claims 1 to 8, wherein the dimensions of the first ferrule portion are configured to conform to the dimensions of the second end cap portion.

10. - The end cap assembly according to any one of claims 1 to 9, - A hollow core optical fiber with cladding, An end cap to fiber assembly comprising, The aforementioned fiber, A first fiber portion having a fiber input end or a fiber output end, A second fiber portion having a fiber output end or a fiber input end Equipped with, The first fiber portion is fixed inside the second ferrule portion, thereby physically separating the fiber from the end cap. An end cap to fiber assembly in which the second portion is located outside the second ferrule portion.

11. A system for coupling a light beam to and / or out of a hollow core optical fiber, - The end cap-to-fiber assembly according to any one of claims 1 to 9, - A laser configured to generate the aforementioned light beam, The light beam is guided to the first end cap end and to the fiber input end, thereby coupling the light beam to the hollow core optical fiber, and / or The light beam is guided outward from the first end cap end and outward from the fiber output end, thereby coupling the light beam outward from the hollow core optical fiber, and A system equipped with these features.

12. The system according to claim 11, wherein the laser is a high-power laser having an average output of more than 200 W, preferably more than 1000 W, more preferably more than 1500 W, and most preferably more than 2000 W.

13. A method for manufacturing an end cap assembly for a hollow core optical fiber, - This is a process for preparing an elongated hollow glass ferrule, and the elongated hollow glass ferrule is ○ A first ferrule portion having a first ferrule end, and ○ Second ferrule portion having a second ferrule end A process that includes, - This is a process of preparing an elongated solid end cap made of an optically transparent material, wherein the elongated solid end cap is ○ A first end cap portion having a first end cap end, and ○ Second end cap portion having a second end cap end A process that includes, - The step of inserting and attaching the second end cap portion inside the first ferrule portion. A method that includes [a certain feature].

14. The method according to claim 13, wherein the step of attaching the second end cap portion is performed by arc fusion, preferably by uniformly creating a fused portion around the second end cap portion.

15. The method according to claim 13 or 14, wherein the end cap assembly is the end cap assembly according to any one of claims 1 to 9.

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