Photonic crystal fiber assembly

Abstract

To provide a good alignment of a PCF and a ferrule in a z-direction.SOLUTION: The present invention comprises a photonic crystal fiber (PCF) assembly that includes the PCF and at least one ferrule structure. The PCF has a first fiber end section that is provided with a first fiber end. The ferrule structure has a center axis, and is mounted to the first fiber end section. The ferrule structure comprises: an inner ferrule arrangement; and an outer ferrule arrangement surrounding the first fiber end section. The inner ferrule arrangement comprises: an inner ferrule front section proximally to the first fiber end; and an inner ferrule rear section distally to the first fiber end. Each of the inner ferrule sections has an inner diameter and at least a length thereof fully surrounds the PCF. The inner ferrule rear section is anchored to the first fiber end section in an anchor length section, and the inner ferrule front section supports the first fiber end section proximally to the first fiber end.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photonic crystal fiber (PCF) assembly comprising a PCF and at least one ferrule structure. The present invention also includes a laser system and an apparatus comprising the laser system. Furthermore, the present invention comprises a pair of interlocking ferrule elements. [Background technology]

[0002] Photonic crystal fibers, referred to herein as PCFs, belong to a class of fibers with optical nano- or microstructures that affect the motion of photons. PCFs (sometimes called holey fibers, hole-assisted fibers, microstructured fibers, or microstructured fibers) obtain their waveguiding properties at least in part through the configuration of their microstructures, e.g., in the form of air (or gas) holes or solid microstructures, that have a different refractive index than the surrounding background material. The large variety of hole / microstructure configurations results in PCFs with very different properties.

[0003] Examples of PCFs include those described in US Pat. No. 5,399,623, US Pat. No. 5,499,633, or US Pat. No. 5,499,623. Termination of this PCF is often more difficult, especially due to the microstructure, and optionally due to the hollow microstructure and / or hollow core.

[0004] Conventional step-index fibers, i.e., optical fiber termination structures with a core having a uniform refractive index and a surrounding cladding having a lower refractive index, where the refractive index drops abruptly at the core-cladding boundary, are well known. US Pat. No. 5,399,433 discloses a connector for large-core step-index fibers designed to reduce the risk that high-power light pumped into the end of the fiber will burn or melt the connector material. The connector comprises a holder having a metallic plug body and a radially inwardly disposed sleeve having a support configured to support the optical fiber away from the end face of the optical fiber, the support employing a transparent or translucent heat-resistant inorganic material, e.g., a ceramic material or sapphire, having a melting point of 1500° C. or higher and a refractive index higher than that of the cladding of the optical fiber. It is not described how the fiber is attached to the connector.

[0005] It is generally desirable to terminate optical fibers in a manner that is easy to handle and well protected against dust, moisture and heat. The small diameter and core diameter of PCFs, and their typically high flexibility, require that the termination of the PCF be held in a mechanically rigid structure (usually called a ferrule or ferrule structure) at the termination point in order to be practically useful in precision beam delivery systems.

[0006] Patent document 5 discloses a fiber termination combination that includes an optical fiber having a fiber core that transmits high-energy optical signals that can damage the fiber, and a structured region characterized by a plurality of channels defined by thin walls arranged around the core with an inner diameter smaller than that of the core to direct the optical signal to the core, a ferrule provided with an opening for positioning the fiber at an end of the fiber that encases the fiber end and cooperates with a block structure that prevents the optical signal from interfering with the microstructured region of the fiber, and a block structure provided at the end of the fiber that has an opening that fits with the fiber core and prevents the optical signal from interfering with the microstructured region of the fiber.

[0007] US Patent No. 6,399,633 discloses an optical fiber having a hollow fiber core, the front faces of both ends of the fiber of which are open, and each fiber end is surrounded in a dust-proof manner by a protective element, the protective element including a window on its front face in front of the fiber end for coupling and decoupling light to the hollow fiber core.

[0008] No. 6,399,433 discloses a monolithic optical ferrule in which a fiber is fused and terminated to form a monolithic unit that minimizes optical loss without damaging the fiber and ferrule, and is typically capable of transmitting high power laser radiation, preferably above about 500 W. The end cap, fiber and fusible powder are composed of materials of substantially the same physical properties such that when fused together, the structure so formed is monolithic and the optical path is transparent.

[0009] The prior art fiber terminations disclosed above are generally difficult to attach to the fiber and often result in damage to the fiber or misalignment in the z-direction (the axial direction of the fiber) and / or failure to anchor the optical fiber resulting in failure to couple the fiber to another element. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 6,985,661 [Patent Document 2] U.S. Patent No. 8,938,146 [Patent Document 3] U.S. Patent No. 7,792,408 [Patent Document 4] U.S. Pat. No. 4,737,011 [Patent Document 5] U.S. Patent No. 7,242,835 [Patent Document 6] U.S. Patent No. 7,373,062 [Patent Document 7] U.S. Patent No. 7,306,376 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide an end termination structure for a PCF that alleviates at least one of the above-mentioned disadvantages. In one embodiment, it is an object to provide an end termination structure for a PCF that provides good alignment of the PCF and ferrule in the z-direction, while being relatively simple to assemble.

[0012] In one embodiment, it is an object to provide an end termination structure for a PCF, which provides safe protection of the PCF, especially against dust, moisture and / or heat, at the terminated end of the PCF.

[0013] In one embodiment, it is an object to provide an end termination structure for a PCF that provides new options for stripping cladding modes. In one embodiment, it is an object to provide an end termination structure for a PCF that has a long life even when the PCF is operated at relatively high powers, such as powers of over 5 kW. [Means for solving the problem]

[0014] These and other objects are achieved by the present invention and its embodiments as defined in the claims and as described hereinafter. It is understood that the present invention or embodiments thereof have numerous additional advantages which will become apparent to those skilled in the art from the following description.

[0015] The term "z-direction" means in the axial direction, and the term "axially" means along an axis. The phrase "radial distance" refers to a distance determined radially from a central axis of the structure under discussion, e.g., a PCF, a ferrule structure or element thereof. "Radial" refers to a direction radially outward from the central axis, and the phrase "radially" refers to a radial orientation relative to the axis.

[0016] The term "substantially" is used herein to mean that normal product variations and tolerances are included within the scope of the term. The term "about" is generally used to include that which is within the uncertainty of measurement. When the term "about" is used in a range, it should be interpreted herein to mean that that which is within the uncertainty of measurement is included in the range.

[0017] The term "comprises / comprising" as used herein should be interpreted as an open-ended term, i.e. to specify the presence of specifically stated features, such as elements, units, integers, steps, components and combinations thereof, but not to exclude the presence or addition of one or more other stated features.

[0018] Throughout this specification or the claims, the singular encompasses the plural unless otherwise specified or required by context. All dimensions are cross-sectional dimensions unless otherwise specified.

[0019] In accordance with the present invention, an end termination structure is provided as a PCF assembly. The PCF assembly of the present invention comprises a PCF and at least one ferrule structure, the PCF having a central axis and comprising a core region and a cladding region, and a first fiber end section having a first fiber end.

[0020] The ferrule structure has a central axis and is attached to the first fiber end section. The ferrule structure comprises an inner ferrule arrangement and an outer ferrule arrangement surrounding the first fiber end section. In accordance with the present invention, it has been found that by providing the ferrule structure with an inner ferrule arrangement and an outer ferrule arrangement, a new kind of ferrule structure is provided that allows for much easier assembly of the fiber and the ferrule structure. In particular, it has been found that by shaping the inner ferrule arrangement to include an inner pre-ferrule section and an inner post-ferrule section, much easier assembly is achieved.

[0021] In one embodiment, the inner ferrule configuration comprises an inner ferrule front section proximal to the first fiber end and an inner ferrule back section distal to the first fiber end. Each of the inner ferrule sections has an inner cross-sectional diameter and completely surrounds the PCF at least along its length. The inner ferrule back section is anchored to the first fiber end section at an anchor length section, and the inner ferrule front section supports the first fiber end section proximal to the first fiber end. Advantageously, the inner ferrule front section is not fixed or anchored to the first fiber end section, but merely supports the first fiber end section to ensure accurate radial alignment.

[0022] In one embodiment, the phrase "proximal to the first fiber end" means near the first fiber end, preferably adjacent to the first fiber end. It is preferred that the central axis of the PCF of the first fiber end section and the central axis of the ferrule structure are substantially parallel. Although the PCF may in principle be positioned away from the central axis of the ferrule structure, in most applications it is desirable for the central axis of the PCF of the first fiber end section and the central axis of the ferrule structure to be coincident, thereby simplifying assembly.

[0023] During assembly, the first fiber end section is attached and anchored to the inner ferrule rear section. Then, either before or at the same time, the first fiber end section is attached to the inner ferrule front section to align the first fiber end to a desired location in the z-direction. The outer ferrule arrangement is then attached to hold the inner ferrule front section and the inner ferrule rear section in position relative to each other, thereby fixing the first fiber end alignment to the ferrule structure. By anchoring the fiber directly exclusively to the inner ferrule rear section, a much simpler alignment of the fiber end end face is obtained since the distance between the inner ferrule front section and the inner ferrule rear section is set to position the fiber end end face at a desired location in the z-direction, and then the distance between the inner ferrule front section and the inner ferrule rear section can be fixed by attaching the inner ferrule front section and the inner ferrule rear section to the outer ferrule arrangement.

[0024] In one embodiment, the inner ferrule front section and the inner ferrule rear section are not directly fixed to each other, but are merely connected and held in place by the outer ferrule configuration. Preferably, the inner ferrule front section and the inner ferrule rear section are arranged with an intermediate gap in the axial direction. The gap advantageously provides an axial distance between the inner ferrule front section and the inner ferrule rear section. This distance is preferably in the range of about 1 mm to about 10 cm, such as about 5 mm to about 2 cm.

[0025] In one embodiment, the intermediate gap between the inner ferrule pre-section and the inner ferrule post-section extends partially around the PCF, for example forming a semi-annular shaped gap. In one embodiment, the gap extends completely around the PCF, forming an annular shaped gap, thereby forming a distance between the inner ferrule pre-section and the inner ferrule post-section. In either case, a portion of the first fiber end section is not covered by the inner ferrule configuration.

[0026] In one embodiment, the assembly further comprises an alignment sleeve disposed between the inner ferrule front section and the first fiber end section, whereby the inner ferrule front section supports the first fiber end section proximate to the first fiber end via the alignment sleeve, the alignment sleeve being preferably positioned to surround and support the first fiber end section at the first fiber end.

[0027] During assembly, the alignment sleeve is attached to the first fiber end section at a desired position in the z-direction relative to the first fiber end, and then the inner ferrule front section is attached.

[0028] The alignment sleeve and its use have been found to be highly beneficial because PCFs typically vary widely in outer diameter and therefore would require individually sized inner pre-ferrule sections without the alignment sleeve, and, as described below, alignment sleeves may be provided to accommodate PCFs of different outer diameters, for example, by crimping the alignment sleeve around the fiber to provide sufficient support.

[0029] Advantageously, the alignment sleeve supports the first fiber end section by collapsing the first fiber end section over its entire length or over its support section. Suitable materials for the alignment sleeve therefore include materials that can be contracted or collapsed onto the first fiber end section, for example by the application of heat. Advantageously, the alignment sleeve is not fixed or tethered to the first fiber end section, but is preferably mechanically held in place to provide the desired axial support for the phosphor.

[0030] In one embodiment, the alignment sleeve is fused to the PCF. Advantageously, the alignment sleeve is made from glass, preferably from silica glass, such as fused silica glass, fused quartz and / or doped silica, and / or borosilicate glass, such as borosilicate glass comprising about 96% silica and 4% boron oxide, e.g., glass sold under the trade name Vycor™.

[0031] Doped glasses may include, for example, fluoride-doped silica, boron-doped silica, and / or germanium-doped silica. Doping the glass may make it more malleable and more collapsible.

[0032] It has proven advantageous to make the alignment sleeve from silica, which has a refractive index of up to 1.45 for light at 1 μm, such as for light in the range 1-2 μm.

[0033] In one embodiment, the alignment sleeve is made from down-doped silica, for example silica doped with fluorine and / or boron. In one embodiment, the alignment sleeve has a refractive index that is less than the effective refractive index of the cladding region.

[0034] Advantageously, the alignment sleeve is substantially completely transparent to the wavelengths of light transmitted or transmittable by the PCF, thereby reducing or even avoiding the risk of overheating due to optical absorption.

[0035] The alignment sleeve is preferably a capillary tube that is applied to surround the PCF and is arranged to support the first fiber end section of the PCF by being thermally collapsed at least at its support section, such as its central section. This structure is very simple and effective, and therefore economically feasible.

[0036] By simply collapsing a section of the alignment sleeve, the uncollapsed length of the alignment sleeve may be shaped to have a cross-sectional outer diameter that matches the cross-sectional inner diameter of the pre-inner ferrule section, such that the inner diameter of the pre-inner ferrule section correlates to the outer diameter of the uncollapsed alignment sleeve, allowing PCFs of different outer diameters to be attached to the alignment sleeve by collapsing the support length of the alignment sleeve.

[0037] Advantageously, the alignment sleeve is retained within said inner ferrule front section without any intermediate material between the alignment sleeve and said inner ferrule front section, hi one embodiment, the alignment sleeve is mechanically retained and / or fused to said inner ferrule front section.

[0038] Advantageously, the inner ferrule front section surrounds and holds the alignment sleeve in a preselected axial position. The inner diameter of the inner ferrule front section is advantageously correlated to the alignment sleeve by being slightly larger than the maximum outer diameter of the alignment sleeve, e.g., slightly larger to allow the alignment sleeve to be inserted into the bore of the hollow through-bore of the inner ferrule front section, e.g., by being about 0.1 μm to about 2 mm larger in diameter, such as about 1 μm to about 1 mm larger, e.g., about 0.1 mm to about 0.01 mm larger.

[0039] Advantageously, the alignment sleeve surrounds the PCF proximate to the first fiber end, and preferably the first fiber end and the end of the alignment sleeve are aligned in a plane perpendicular to the PCF central axis.

[0040] The alignment sleeve may in principle have any length (as determined in the axial direction), such as up to the length of the inner ferrule front section. In practice, the alignment sleeve is desirably relatively short, but long enough to ensure support of the electromagnetic forces. Advantageously, the alignment sleeve has an axial length of at least up to about 1 mm, such as from about 2 mm to about 5 cm, such as from about 5 mm to about 2 cm. For most PCF assemblies, the optimal length of the alignment sleeve has been found to be about 10 mm.

[0041] In one embodiment, the alignment sleeve supports the first fiber end section by having an inner diameter that matches the outer diameter of the first fiber end section, at least along its support section. In this embodiment, the inner diameter of the support section of the alignment sleeve is desirably up to about 0.5 mm larger than the inner diameter, such as up to about 0.1 mm, such as up to about 0.01 mm. When the alignment sleeve is crimped or collapsed onto the first fiber end section, the inner diameter of the alignment sleeve in an uncollapsed or uncrimped state may be larger, such as up to about 5 mm larger than the PCF diameter, such as up to about 3 mm larger, such as up to about 1 mm larger than the PCF.

[0042] In one embodiment, the inner ferrule front section supports the first fiber end section via an alignment sleeve by mechanically holding the alignment sleeve in an axial position such that an end of the alignment sleeve and an end of the inner ferrule front section are aligned in a plane perpendicular to the central axis of the ferrule structure. Preferably, the first fiber end, the end of the alignment sleeve and the end of the inner ferrule front section are aligned in a plane perpendicular to the central axis of the PCF.

[0043] During ferrule assembly, the alignment sleeve is moved in the z direction to achieve the desired z position of the fiber end face, for example, relative to the outer ferrule reference point, thereby ensuring that the desired optical focus of the ferrule is achieved, before or at the same time the fiber is secured to the inner ferrule rear section.

[0044] In one embodiment, the inner ferrule front section supports the first fiber end section directly proximal to the first fiber end with an alignment sleeve, preferably by mechanically holding the first fiber end section in an axial position relative to the first fiber end. Preferably, the end of the inner ferrule front section and the first fiber end are aligned in a plane perpendicular to the PCF central axis. Advantageously, the inner diameter of the inner ferrule front section is greater than the inner diameter by up to about 0.5 mm, such as up to about 0.1 mm, such as up to about 0.01 mm.

[0045] In practical use, at the optical exit end of the PCF, some of the light may be guided into the cladding as cladding modes, e.g., due to reflection and / or incident radiation, and at the input end of the PCF, some of the light focused and transmitted into the PCF fiber may not be guided by the core but may be guided as cladding modes, e.g., due to mismatches of beam parameters entering the fiber, imperfections in the focusing lens, and dust / imperfections on the optical surfaces, and the like. These cladding modes may become very hot when used for high-power transmission. Also, the temperature of the terminated end of the PCF, especially that sealed in the ferrule structure, may become excessively high, damaging the polymer coating of the PCF and thus the entire termination and the anchorage between the ferrule structure and the PCF.

[0046] The component of the incident radiation that is not coupled into the core propagates into the cladding until it is deflected into the protective polymer coating, where it is removed ("stripped"). If the source of the laser radiation input into the fiber is a high power laser, the intensity of the radiation in these cladding modes can easily burn through the protective polymer coating and destroy the fiber. One example is laser radiation at an object in an industrial workpiece (especially a metallic object) where substantial power returning to the fiber is reflected so that the radiation is coupled into the outer periphery of the cladding rather than into the fiber's core. For this reason, it is necessary to remove cladding mode radiation at all fiber terminations before it can deflect into the protective polymer coating and cause destruction. "Mode stripping" is the name given to a number of techniques used to remove such cladding modes.

[0047] This problem is solved by an embodiment of the present invention, which eliminates polymer from the PCF from the anchor length to the inner ferrule post-section and its first fiber end. In one embodiment, the ferrule structure comprises a hermetic solder element disposed to surround the first fiber end section to form an annular hermetic seal between the first fiber end section and the inner ferrule post-section. The hermetic solder element is disposed closer to the annular section than the anchor length of the inner ferrule post-section. Furthermore, the anchor length of the inner ferrule post-section is preferably not completely annular, thereby allowing heat to dissipate from the anchor length of the PCF, preferably to the hermetic solder element. The anchor length of the inner ferrule post-section preferably extends from about 20 degrees to about 350 degrees around the PCF, such as about 180 degrees (semi-annular).

[0048] The hermetic solder element additionally serves to protect the first fiber end from dust and other undesirable contamination. If the PCF assembly includes an end cap, the hermetic solder element ensures a hermetic seal of the first fiber end section from the first fiber end to the z-direction location of the hermetic solder element. Advantageously, the polymer coating of the PCF is stripped from the first fiber end section from the first fiber end to the z-direction location of the hermetic solder element.

[0049] In one embodiment, the first fiber end section is attached to the ferrule structure without applying substantial pressure to the PCF, which can cause stress in the fiber, which is highly undesirable in many applications because it can result in poor beam quality and even the stress can damage or shorten the life of the PCF.

[0050] In one embodiment, the first fiber end section is attached to the ferrule structure without any direct joints to the fiber, including tethers, except for one or more joints to the inner ferrule back section.

[0051] In one embodiment, the PCF is free of a polymer coating on the first fiber end section from the anchor section of the inner post-ferrule section to the first fiber end. Advantageously, the inner ferrule front section is made from a material that is at least partially transparent at wavelengths between about 200 nm and about 4 μm, such as fused silica or quartz, and the inner ferrule rear section is made from fused silica or quartz, or a metal or alloy. In one embodiment, the inner ferrule front section is made from substantially undoped silica, which has a refractive index of up to 1.45 for light at 1 μm.

[0052] Typically, the inner ferrule post section is made from a material with high conductivity and low thermal expansion to ensure high heat dissipation. Therefore, it is particularly desirable to make the inner ferrule post section from a metal or metal alloy such as Colsibro®, a high copper alloy with small additions of nickel and silicon, which help increase the strength, hardness and wear resistance of the material.

[0053] The outer ferrule configuration primarily functions to hold the inner ferrule configuration sections in place relative to one another, but advantageously the outer ferrule configuration also aids in dissipating heat from the ferrule structure.

[0054] Advantageously, the outer ferrule arrangement is made from metal, ceramic or glass, such as silica. In one embodiment, the outer ferrule arrangement is at least partially transparent to allow light to escape to an optional outer alignment jacket that absorbs the light, in particular light from cladding modes is allowed to escape through the outer ferrule arrangement, and optionally, stripped cladding mode light is allowed to escape through the outer ferrule arrangement, as described in more detail below.

[0055] In one embodiment, the outer ferrule arrangement is preferably secured to each of the inner ferrule front and rear sections of the inner ferrule arrangement to hold them in position relative to one another such that the first fiber end section of the PCF is supported substantially straight within the ferrule structure. The outer ferrule arrangement is preferably secured to the inner ferrule arrangement by at least one of an adhesive, solder, and melt or laser welding.

[0056] The PCF assembly may advantageously include an end cap arrangement, for example to protect the first fiber end against dust, moisture, and similar contamination. In one embodiment, the ferrule structure includes an end cap disposed in front of the first fiber end. The end cap may be mounted with or without separation from the inner ferrule pre-section, depending on the structure and intended application of the PCF. The end cap is secured directly to the inner ferrule pre-section or to the outer ferrule pre-section of an outer ferrule arrangement, as described in more detail below.

[0057] In one embodiment, the end cap is secured to the outer ferrule front section of the outer ferrule arrangement, which in this embodiment preferably comprises an outer ferrule front section and an outer ferrule back section, the outer ferrule back section secured to both the inner ferrule back section and the inner ferrule front section to hold the inner ferrule arrangement sections in relative position, and the outer ferrule front section secured to the inner ferrule front section and the end cap, thereby holding the end cap in place relative to the first fiber end.

[0058] The end cap may be a conventional end cap, e.g. with or without a focusing element. Advantageously, the end cap is an anti-reflection coated silica end cap. If the end cap is mounted remote from the first fiber end, it may be desirable for the end cap to have an anti-reflection coating on both sides. This is particularly desirable if the PCF is a hollow core PCF.

[0059] In one embodiment, the end cap is a lens. Preferably, the lens is provided with an anti-reflective coating on both sides thereof, i.e., on the side facing the first fiber end and on the opposite side.

[0060] The PCF may in principle be any kind of PCF, such as the PCFs mentioned in the introduction above. In one embodiment, the PCF is selected from a hollow-core fiber, such as a band-gap fiber, a kagome fiber, an anti-resonant-reflection (ARS) fiber, or a solid-core fiber.

[0061] In one embodiment, the PCF has a core diameter of less than 10 μm, preferably about 50 μm or less, such as from about 5 μm to about 40 μm. In one embodiment, the PCF comprises at its first fiber end section a termination section of hollow capillary fiber to protect the end of the PCF from back reflections, which is achieved by positioning one hollow capillary fiber in front of the PCF, for example in an alignment sleeve or in the inner ferrule pre-section.

[0062] In one embodiment, the first fiber end (end face) has a metallic or anti-reflective coating. In one embodiment, the PCF is a hollow core fiber, and an end cap is fixed to the outer ferrule front section of the outer ferrule arrangement, providing an end cap space between the end cap and the inner ferrule front section. The cap space may in principle be determined to be very small in the z-direction, from 1 mm up to, for example, 5 cm. In practice, the cap space is kept to less than about 1 cm for practical reasons.

[0063] In one embodiment, the hollow core has a collapsed end portion (such as up to 2 mm long, preferably up to 1 mm long) and a metallic or anti-reflective coating on the fiber end face. In one embodiment, the inner ferrule arrangement comprises a passageway leading to the end cap space for injecting and / or extracting fluids, in particular gases. The passageway is preferably provided by at least one additional through hole in each of the inner ferrule pre-section and the inner ferrule post-section. The additional through hole is preferably substantially parallel to the axis of the ferrule structure. Preferably, the additional through hole comprises a valve arrangement at the outlet from the inner ferrule post-section.

[0064] The passages leading to the end cap spaces for injecting and / or withdrawing fluids may advantageously be used for injecting or flushing with a suitable gas, for example to ensure a moisture-free hollow core. Suitable gases include air, argon, nitrogen or a mixture containing any of the aforementioned gases. Optionally, the cap spaces for injecting and / or withdrawing fluids are arranged to generate a hollow core pressure of about 100 hPa (1 mbar) or less, such as about 10 hPa (0.1 mbar) or less, such as about 1 hPa (0.01 mbar) or less, at standard temperature.

[0065] Optionally, the cap space for injecting and / or dispensing fluids is arranged to generate a hollow core pressure of up to 200 kPa (2 bar), such as up to about 150 kPa (1.5 bar), at standard temperature.

[0066] In one embodiment, the inner ferrule arrangement comprises at least one passageway leading to the gap between the inner ferrule front section and the inner ferrule rear section. The passageway advantageously passes through the inner ferrule rear section, preferably in the form of a through hole, for example parallel to the central axis of the ferrule structure. Injection and / or ejection of fluids, such as injection and / or ejection of gases as mentioned above. In one embodiment, the inner ferrule arrangement comprises at least two passageways leading to the gap between the inner ferrule front section and the inner ferrule rear section, for example for flushing the gap, for drying the gap and / or for heat dissipation.

[0067] In one embodiment, the inner ferrule front section has a rear end where at least a radially outer portion of the rear end is angled relative to a central axis of the ferrule structure for out-coupling light, such as light propagating within the inner ferrule configuration. In one embodiment, the inner ferrule front section has a rear end where at least a radially outer semi-annular or annular radially outer portion of the rear end is angled relative to a central axis of the ferrule structure for out-coupling light. Advantageously, light may be out-coupled through the outer ferrule configuration.

[0068] In one embodiment, the inner ferrule front section has a rear end where at least a radially inner portion of the rear end is angled relative to the central axis to form a funnel shape, which may facilitate easier attachment of the PCF to the inner ferrule front section. The rear end of the inner ferrule front section may be angled over part of its extension around the fiber or over its entire annular extension around the PCF.

[0069] The rear end of the inner ferrule front section may advantageously be coated with a reflective coating to back-reflect light, such as light incidentally emitted from the first fiber end and / or light propagating within the inner ferrule arrangement.

[0070] In one embodiment, the inner ferrule front section has a front end that is coated with a reflective coating to protect the ferrule structure against at least one of incident light and back reflected light.

[0071] In one embodiment, the inner ferrule rear section has a front end, the front end is angled relative to a central axis of the ferrule structure and the front end is coated with a reflective coating to protect against at least one of incident and back reflected light, the front end is angled relative to a central axis of the ferrule structure, or the front end is coated with a reflective coating to protect against at least one of incident and back reflected light. The front end of the inner ferrule rear section may be angled over a portion of its extension around the fiber or over its entire annular extension around the PCF.

[0072] As explained above, the ferrule structure of the PCF assembly of the present invention enables several functions for stripping unwanted cladding modes by reflecting and directly stripping the cladding modes. As will be explained below, the present invention enables additional functions for stripping unwanted light.

[0073] In one embodiment, the first fiber end section comprises at least one mode stripper length, the mode stripper length comprising at least one of a mode stripping high refractive index material and a scatter layer applied in contact with the optical fiber at the mode stripper length and the fiber in the mode stripper length has a roughness Ra value of at least about 0.1 μm, the mode stripper length comprising at least one of a mode stripping high refractive index material and a scatter layer applied in contact with the optical fiber at the mode stripper length, or the fiber in the mode stripper length has a roughness Ra value of at least about 0.1 μm.

[0074] A high roughness Ra value may be provided, for example, by etching (e.g. laser etching or chemical etching) or mechanical polishing. The Ra value may be measured according to standards ISO 4287, DIN 4762 and / or DIN 4768.

[0075] The mode stripper length reduces or completely prevents forward propagating cladding light. The mode stripping high refractive index material may be, for example, a binder and / or a chemical glass containing silica particles (e.g., doped to increase the refractive index).

[0076] In one embodiment, the mode stripper length of the PCF is positioned between the pre-inner ferrule section and the post-inner ferrule section. In one embodiment, at least one of the inner ferrule pre-section and the inner ferrule post-section has a groove that exposes a mode stripper length of the PCF.

[0077] Advantageously, the groove preferably partially surrounds the fiber and preferably extends at least about 20 degrees, and for example up to about 350 degrees, preferably from about 20 degrees to about 90 degrees, in a direction around the PCF.

[0078] In one embodiment, the ferrule structure comprises a mode stripper coating disposed in direct contact with an outer surface of the inner ferrule front section, the mode stripper coating preferably being included between the inner ferrule front section and the outer ferrule structure.

[0079] In one embodiment, the ferrule structure comprises an outer alignment jacket surrounding the outer ferrule arrangement, the outer alignment jacket preferably comprising alignment means, preferably at least one of axial (z-direction) and rotational alignment means.

[0080] The main purpose of the outer alignment jacket is to ensure the rigidity and mechanical strength of the ferrule structure as well as easier alignment of the PCF with respect to the outgoing or in-coupled beam of light. Furthermore, for axial and rotational alignment, the outer alignment jacket is very beneficial.

[0081] In one embodiment, the alignment means comprises at least one of axial (z direction), radial (x,y direction) and rotational alignment means.

[0082] Advantageously, the alignment means comprises one or more flanges, one or more protrusions, one or more recesses and / or one or more markings. Preferably the alignment means comprises a mounting flange with position control.

[0083] In one embodiment, the alignment means comprises markers for rotational fiber orientation, eg PM orientation. It is generally desirable to be able to rotate the fiber in the ferrule so that the PM axis is aligned with respect to the alignment means on the outside of the ferrule. This may be provided, for example, by having corresponding markings on the inner post-ferrule section immediately adjacent the anchor length.

[0084] In one embodiment, the ferrule structure is configured to cool the outer ferrule structure with a cooling fluid and the outer alignment jacket comprises a passage with at least one inlet and at least one outlet for a cooling fluid such as water, or the ferrule structure is configured to cool the outer ferrule structure with a cooling fluid or the outer alignment jacket comprises a passage with at least one inlet and at least one outlet for a cooling fluid such as water. The passage of the outer ferrule structure and / or the outer alignment jacket are advantageously arranged to spirally surround the underlying element to provide good heat dissipation. By ensuring that the outer ferrule structure passes the light to be stripped and / or out-coupled through the inner ferrule structure, this light may escape through the outer ferrule structure and be absorbed by the outer alignment jacket. This causes the outer alignment jacket to heat up, but cooling the outer alignment jacket with the cooling fluid keeps the temperature at an acceptable level even when the PCF is transmitting light at high power.

[0085] In one embodiment, the assembly further comprises one or more sensors, such as one or more optical and / or electrical and / or chemical sensors, for at least one of monitoring temperature, monitoring connector performance and monitoring fiber damage. The sensors are advantageously arranged in the ferrule structure, such as the outer ferrule arrangement and / or the outer alignment jacket. Advantageously, the sensors are fiber sensors, but in principle non-fiber sensors are also applicable.

[0086] In one embodiment, the assembly comprises a second ferrule structure coupled to a second end section of the PCF comprising a second fiber end, the second ferrule structure being preferably a ferrule structure as described above and attached to the second end section of the PCF in a corresponding manner as described above, in one embodiment, the second end of the PCF is a fiber splice end and / or is coupled with a free space coupling.

[0087] The present invention also includes a laser system that includes the PCF assembly described above. The laser system advantageously comprises a laser light source, and the PCF assembly is optically connected to the laser light source for receiving light from the laser light source. The laser light source may in one embodiment be arranged to deliver light directly to the PCF, for example by fusing to the PCF. In one embodiment, the laser light source is arranged to deliver light to the PCF via one or more optical elements and / or via free space.

[0088] Preferably, the PCF assembly is configured to transmit light to a light collection station of a device. Preferably, the first fiber end having the ferrule structure is configured to connect to a user device.

[0089] The device may be, for example, a microscope, a surgical device, a measurement device (instrumentation), a material processing device, an illumination device, any combination thereof, and / or any device described in more detail below. The laser source may in principle be any kind of laser source, such as a CW laser source or a pulsed laser source, etc. Laser sources are well known in the art and will not be described in further detail here.

[0090] In one embodiment, the laser source is configured to generate pulses of laser light, preferably the laser source is a femtosecond laser source or a picosecond laser source or a nanosecond laser source.

[0091] In one embodiment, the laser source has a pump duration from about 30 fs to about 30 ps, ​​for example from about 100 fs to about 10 ps. In one embodiment, the laser source has a peak power determined at the exit of the laser source of at least about 5 kW, such as at least about 10 kW, such as at least about 30 kW, such as at least about 50 kW.

[0092] The laser source is advantageously a mode-locked laser source. In one embodiment, the laser source is an actively mode-locked laser. In one embodiment, the laser source is a passively mode-locked laser. A mode-locked laser preferably comprises one or more amplifiers.

[0093] In one embodiment, the laser system is configured for supercontinuum generation and the laser source is a mode-locked pumped pulsed source arranged to provide a PCF for supercontinuum generation. The PCF is preferably a solid-core PCF suitable for supercontinuum generation, such as the PCFs described in WO15144181, WO15003715, WO15003714, US2015192732, and / or US2011013652.

[0094] In one embodiment where the PCF is a solid-core PCF, the PCF is desirably a microstructured solid-core PCF comprising a plurality of non-solid and / or solid cladding inclusions. The solid-core PCF is preferably configured to guide light comprising at least one wavelength in the range of about 200 nm to about 4.5 μm, preferably at least one wavelength in the range of 1000 nm to about 1100 nm, preferably single mode light.

[0095] In one embodiment, the PCF is a hollow core PCF, and preferably the hollow core PCF is configured to guide light having at least one wavelength in the range of about 200 nm to about 4.5 μm, preferably at least one wavelength in the range of 1000 nm to about 1100 nm, preferably single mode light.

[0096] In one embodiment, the PCF is configured to guide a continuous wave of wavelengths of light, preferably spanning at least about 0.1 μm, such as at least about 0.3 μm, such as at least about 0.5 μm.

[0097] In one embodiment, the hollow-core PCF comprises an outer cladding region and N hollow tubes surrounded by the outer cladding region, each of the hollow tubes fused to the outer cladding to form a ring defining an inner cladding region and a hollow core region surrounded by the inner cladding region, preferably N is between 6 and 12, more preferably N is 7. Advantageously, the hollow tubes are not in contact with each other, and preferably the hollow tubes are spaced substantially equidistant from adjacent hollow tubes.

[0098] The hollow core PCF is advantageously as described in the Applicant's co-pending Danish Patent Application No. 201570877 entitled "HOLLOW CORE OPTICAL FIBER AND A LASER SYSTEM".

[0099] The PCF of this laser system advantageously has a core region diameter of from about 3 μm to about 100 μm, such as from about 10 μm to about 50 μm, such as from about 10 μm to about 30 μm.

[0100] The present invention also comprises a set of interlocking ferrule elements suitable for the PCF assembly described above. A set of interrelated ferrule elements comprises the elements necessary to provide a ferrule structure for a PCF to produce the PCF assembly described above.

[0101] A pair of interrelated ferrule elements are an inner ferrule pre-section and an inner ferrule post-section for forming an inner ferrule configuration; an outer ferrule configuration; Each of the inner ferrule front section, inner ferrule rear section and outer ferrule configuration has a length and a central axis and includes a main hollow through bore parallel to or coincident with the respective central axis, and the pair of interrelated ferrule elements preferably further includes an alignment sleeve having a length and a central axis and includes a main hollow through bore parallel to or coincident with the central axis.

[0102] Advantageously, the elements are correlated such that the alignment sleeve can be positioned within the main hollow throughbore of the inner front ferrule section, and the inner front ferrule section and the inner back ferrule section can be mounted within the main hollow throughbore of the outer ferrule configuration to form the inner ferrule configuration, whereby a set of correlated ferrule elements may be assembled with a PCF into a PCF assembly.

[0103] The alignment sleeve is advantageously a capillary tube, the main hollow throughbore of the alignment sleeve having an inner diameter of about 2 mm or less, such as about 1 mm or less, such as 0.5 mm or less, and the alignment sleeve is preferably collapsible over at least a portion of its length as described above.

[0104] The alignment sleeve may advantageously be as described above and made from the materials described above. In one embodiment, the alignment sleeve preferably has an axial length of at least about 1 mm, such as from about 2 mm to about 5 cm.

[0105] The inner ferrule front and rear sections and the outer ferrule arrangement are advantageously as described above and made from the materials described above. In one embodiment, the set further comprises an end cap configured to be placed in front of the inner ferrule front section by attaching to the inner ferrule front section or by attaching to the outer ferrule front section of an outer ferrule arrangement, the end cap preferably being an anti-reflective coated silica end cap, e.g., as described above.

[0106] In one embodiment, each of the inner ferrule pre-section and the inner ferrule post-section comprises one or more additional through holes for providing a fluid passageway, the additional through holes preferably being substantially parallel to the axis of the respective inner ferrule section, and optionally comprising a valve arrangement at an exit from the inner ferrule post-section, e.g. as described above.

[0107] In one embodiment, the inner ferrule front section has a rear end, at least a radially outer portion of the rear end is angled relative to a central axis of the inner ferrule front section and the rear end is preferably coated with a reflective coating for outcoupling light as described above, or at least a radially outer portion of the rear end is angled relative to a central axis of the inner ferrule front section, or the rear end is preferably coated with a reflective coating for outcoupling light as described above.

[0108] In one embodiment, the inner ferrule front section has a rear end, at least a radially inner portion of the rear end being inclined relative to the central axis to form a funnel shape to facilitate insertion of a PCF into the inner ferrule front section, for example as described above.

[0109] Advantageously, the inner ferrule front section has a front end, the front end being coated with a reflective coating. In one embodiment, the inner ferrule rear section has a front end, the front end is angled relative to a central axis of the inner ferrule rear section and the front end is preferably coated with a reflective coating as described above, or the front end is angled relative to a central axis of the inner ferrule rear section, or the front end is preferably coated with a reflective coating as described above.

[0110] In one embodiment, at least one of the inner ferrule front section and the inner ferrule rear section has a groove leading to its main hollow throughbore, the groove preferably having an annular extension extending at least about 20 degrees, such as up to about 350 degrees, such as up to about 90 degrees.

[0111] In one embodiment, the set further comprises an outer alignment jacket correlated to the outer ferrule arrangement such that it can be positioned to surround the outer ferrule arrangement, e.g., as described above. The outer alignment jacket preferably comprises an alignment means, e.g., as described above.

[0112] Advantageously, the outer ferrule arrangement and / or the outer alignment jacket are provided with a passageway with at least one inlet and at least one outlet for a cooling fluid, for example as described above.

[0113] The present invention also includes an apparatus comprising a laser system as described above, the PCF assembly being configured to transmit light to a receiving station of the apparatus. The device may in principle be any kind of device that uses laser light for its operation. In one embodiment, the device is an illumination device configured to illuminate an object, the illumination device being preferably selected from a microscope, a spectroscope or an endoscope.

[0114] In one embodiment, the illumination source is adapted for at least one of fluorescence imaging, fluorescence lifetime imaging (FLIM), total internal reflection fluorescence (TIRF) microscopy, fluorescence resonance energy transfer (FRET), pulse interleave excitation foster resonance energy transfer (PIE-FRET), broadband spectroscopy, nanophotonics, industrial testing such as flow cytometry, metrology, ring-down spectroscopy such as gas sensing, hyperspectral spectroscopy (e.g., crop analysis of fruits, time of flight spectroscopy (TCSPC)), single molecule imaging, and combinations thereof.

[0115] In one embodiment, the device is a micromachining device, preferably for material processing such as at least one of drilling, marking, cutting, and scribing. In one embodiment, the device is a surgical device, such as an eye surgical (ophthalmic) device.

[0116] All of the features of the invention and embodiments of the invention described above, including ranges and preferred ranges, can be combined in various ways within the scope of the invention, unless there is a specific reason why such features should not be combined.

[0117] The above and / or additional objects, features and advantages of the present invention will become more apparent from the following detailed description of illustrative and non-limiting embodiments of the present invention, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0118] [Figure 1] 1 is a cross-sectional view of a first embodiment of a PCF assembly according to the present invention, where a radially inner portion of the rear end is inclined relative to the central axis to form a funnel shape. [Diagram 2] 4 is a cross-sectional view of a second embodiment of a PCF assembly according to the present invention, the inner ferrule rear section having a passageway leading to a gap between the inner ferrule front section and the inner ferrule rear section. [Diagram 3] 1 is a cross-sectional view of a third embodiment of a PCF assembly according to the present invention, the PCF having a mode stripper section at its first fiber end section, the inner pre-ferrule section having a groove exposing the mode stripper length of the PCF. [Figure 4] 1 is a cross-sectional view of a fourth embodiment of a PCF assembly according to the present invention, the PCF having a mode stripper section at its first fiber end section, the inner ferrule post section having a groove exposing the mode stripper length of the PCF. [Diagram 5]FIG. 13 is a cross-sectional view of a fifth embodiment of a PCF assembly according to the present invention, in which a portion of the rear end of the inner ferrule front section is tilted relative to the central axis of the ferrule structure to outcouple light propagating within the inner ferrule configuration. [Figure 6] FIG. 13 is a cross-sectional view of a sixth embodiment of a PCF assembly in accordance with the present invention, in which the rear end of the inner ferrule rear section, along its entire annular extension, is tilted relative to the central axis of the ferrule structure to output couple light propagating within the inner ferrule configuration. [Figure 7] 13 is a cross-sectional view of a seventh embodiment of a PCF assembly according to the present invention, the PCF having a mode stripper section at its first fiber end section in the gap between the inner pre-ferrule section and the inner post-ferrule section. [Figure 8] 13 is a cross-sectional view of an eighth embodiment of a PCF assembly according to the present invention, the PCF assembly including an end cap attached to the inner ferrule front section. [Figure 9] 13 is a cross-sectional view of a ninth embodiment of a PCF assembly according to the present invention, the PCF assembly including an end cap attached to the outer ferrule front section. [Figure 9a] FIG. 10 is a cross-sectional view of a PCF assembly that is a variation of the ninth embodiment shown in FIG. [Figure 10] 13 is a cross-sectional view of a tenth embodiment of a PCF assembly according to the present invention, the PCF assembly including an outer alignment jacket. [Figure 11] 13 is a cross-sectional view of an eleventh embodiment of a PCF assembly according to the present invention, the PCF assembly including an alignment sleeve. [Figure 12] 12 is a cross-sectional view of a twelfth embodiment of a PCF assembly according to the present invention, the PCF assembly comprising an alignment sleeve, the PCF comprising a section of hollow core capillary. [Figure 12b] 13 is an enlarged cross-sectional view of the alignment sleeve and supported first fiber end section of the PCF assembly of FIG. 12. [Figure 13]23 is a cross-sectional view of a thirteenth embodiment of a PCF assembly according to the present invention, the PCF assembly including an alignment sleeve having a collapsed support section. [Figure 13b] 14 is an enlarged cross-sectional view of the alignment sleeve and supported first fiber end section of the PCF assembly of FIG. 13. [Figure 14a] 1 is a simplified cross-sectional view of a PCF fiber end section. [Figure 14b] 1 is a simplified cross-sectional view of a PCF fiber end section. [Figure 14c] 1 is a simplified cross-sectional view of a PCF fiber end section. [Figure 14d] 1 is a simplified cross-sectional view of a PCF fiber end section. [Figure 15] 1 is a schematic diagram of a laser system and user equipment according to one embodiment of the present invention. [Figure 16] 1 is a schematic diagram of an apparatus and user equipment according to an embodiment of the present invention; [Figure 17a] 1 is a schematic diagram of an apparatus and user equipment of an embodiment of the present invention in which the laser system is a supercontinuum laser system. [Figure 17b] 1 is a schematic diagram of an apparatus and user equipment of an embodiment of the present invention in which the laser system is a supercontinuum laser system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] The drawings are schematic and may be simplified for clarity, and the same reference numbers are used throughout to refer to the same or corresponding parts. The PCF assembly of Fig. 1 comprises a photonic crystal fiber (PCF) for PCF assembly having a first fiber end section 1 provided with a first fiber end section 1a, and a ferrule structure. The ferrule structure comprises an inner ferrule arrangement comprising an inner pre-ferrule section 2 proximal to the first fiber end section 1a and an inner ferrule post-section 3 distal to the first fiber end section 1a. The inner pre-ferrule section 2 and the inner ferrule post-section 3 comprise hollow through holes 2a, 3a coinciding with the central axes of the inner pre-ferrule section 2 and the inner ferrule post-section, respectively. The PCF first fiber end section is mounted in said hollow through holes 2a, 3a such that the inner ferrule arrangement surrounds the first fiber end section.

[0120] The inner ferrule rear section 3 is anchored to the first fiber end section 1 at anchor length section 3b, and the PCF is free of polymer coating from point 1c to the first fiber end. The inner ferrule front section 2 supports the first fiber end section 1 proximal to the first fiber end 1a by mechanically holding the first fiber end section in an axial position proximal to the first fiber end. As can be seen, the inner ferrule front section and the first fiber end are aligned in a plane perpendicular to the central axis of the PCF.

[0121] The ferrule structure further comprises an outer ferrule arrangement 5 arranged to surround the inner ferrule arrangement 5. The outer ferrule arrangement 5 is secured to each of the inner ferrule front section 2 and the inner ferrule rear section 3 to hold them in position relative to each other and to define a gap 4 therebetween. The outer ferrule arrangement 5 is secured at each of its ends by solder 6 to each section 2, 3 of the inner ferrule arrangement.

[0122] The PCF first fiber end section is advantageously held relatively straight in the gap 4 between the inner ferrule pre-section 2 and the inner ferrule post-section 3. In an alternative embodiment not shown, the PCF has excess length between the inner ferrule pre-section 2 and the inner ferrule post-section 3.

[0123] The radially inner portion 2c of the rear end of the inner ferrule front section 2 is tilted relative to the central axis to form a funnel shape to facilitate feeding the PCF 1 into the inner ferrule front section during assembly. The radially outer portion 2d of the rear end of the inner ferrule front section 2 is advantageously coated with a tilted reflective coating to back-reflect light propagating within the inner ferrule configuration.

[0124] Additionally, the front end 2e of the inner ferrule front section 2 is preferably coated with a reflective coating to protect the ferrule structure against incident and / or back reflected light, and the front end 3e of the inner ferrule rear section is preferably coated with a reflective coating to protect against incident and / or back reflected light.

[0125] The PCF assembly of FIG. 2 comprises a photonic crystal fiber (PCF) for assembly, having a first fiber end section 11 with a first fiber end 11a, and a ferrule structure. The ferrule structure comprises an inner ferrule arrangement comprising an inner ferrule front section 12 proximal to the first fiber end 11a and an inner back section 13 distal to the first fiber end 11a. The inner ferrule back section 13 is anchored to the first fiber end section 11 at an anchor length section 13b, such that the PCF is free of polymer coating from point 11c of the PCF to the first fiber end. The ferrule structure comprises an outer ferrule arrangement 15 fixedly disposed on each of the inner ferrule front section 12 and the inner ferrule back section 13, holding them in a fixed position relative to each other. The front end 3e of the inner ferrule back section is preferably coated with a reflective coating to protect against incident and / or back reflected light.

[0126] The front end 13e of the inner ferrule rear section 13 is inclined relative to the central axis of the ferrule structure to form an outward facing end face for out-coupling the ferrule light. The outer ferrule structure 15 is preferably substantially transparent to the out-coupled light. The inner ferrule rear section 13 includes a passage 13f that leads to a gap 14 between the inner ferrule front section 12 and the inner ferrule rear section 15. The passage may be used to fill or withdraw fluid from the gap 14 as previously described.

[0127] 3 includes a photonic crystal fiber (PCF) for PCF assembly having a first fiber end section 21 with a first fiber end 21a, and a ferrule structure. The ferrule structure includes an inner ferrule arrangement surrounding the first fiber end section 21, including an inner ferrule pre-section 22 proximal to the first fiber end 21a and an inner ferrule post-section 23 distal to the first fiber end 21a.

[0128] The inner ferrule back section 23 is anchored to the first fiber end section 21 at anchor length section 23b, and the PCF is free of polymer coating from point 21c to the first fiber end. The inner ferrule front section 22 supports the first fiber end section 21 proximal to the first fiber end 21a by mechanically holding the first fiber end section in an axial position proximal to the first fiber end.

[0129] The ferrule structure further comprises an outer ferrule arrangement 25 secured to each of the inner ferrule front section 22 and the inner ferrule rear section 23 to hold them in position relative to each other and define a gap 24 therebetween. The outer ferrule arrangement 25 is secured at each of its ends by solder 26 to the respective sections 22, 23 of the inner ferrule arrangement.

[0130] The front end 23e of the inner ferrule back section 23 is angled with respect to the central axis of the ferrule structure to provide an outward facing end face for out-coupling light propagating within the inner ferrule configuration and to reduce back reflections. The inner ferrule back section 23 further includes a passageway 23f leading to a gap 24 between the inner ferrule front section 22 and the inner ferrule back section 25. The passageway may be used to fill or withdraw fluid from the gap 24 as previously described. The PCF has a mode stripper section 27 in its first fiber end section 21, and the inner ferrule front section 22 has a groove 27a exposing the PCF mode stripper length 27.

[0131] To monitor the output coupling efficiency of the mode stripper 27, a sensor 28 is attached to the outer ferrule arrangement 25 over the groove 27a exposing the PCF mode stripper length.

[0132] The PCF assembly of FIG. 3 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 31 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 31, the inner ferrule configuration having an inner pre-ferrule section 32 proximal to the first fiber end and an inner ferrule post-section 33 distal to the first fiber end.

[0133] The inner ferrule back section 33 is anchored to the first fiber end section 31, and the PCF is free of polymer coating from point 31c of the PCF to the first fiber end of the PCF. The inner ferrule front section 32 supports the first fiber end section 31 proximal to the first fiber end 31a by mechanically holding said first fiber end section in an axial position proximal to the first fiber end.

[0134] The ferrule structure further comprises an outer ferrule arrangement 35 secured to each of the inner ferrule front section 32 and the inner ferrule rear section 33 to hold them in position relative to each other and define a gap 34 therebetween. The outer ferrule arrangement 35 is secured at each of its ends with solder 36 to the respective sections 32, 33 of the inner ferrule arrangement.

[0135] The PCF has a mode stripper section 37 on its first fiber end section 31 and the inner ferrule back section 33 has a groove 37 a exposing the PCF mode stripper length section 37 .

[0136] To monitor the output coupling efficiency of the mode stripper 37, a sensor 38 is attached to the outer ferrule arrangement 35 over the groove 37a exposing the PCF mode stripper length.

[0137] The PCF assembly of FIG. 5 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 41 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 41, the inner ferrule configuration having an inner ferrule pre-section 42 proximal to the first fiber end and an inner ferrule post-section 43 distal to the first fiber end.

[0138] The inner ferrule back section 43 is anchored to the first fiber end section 41 such that the PCF is free of polymer coating from point 41c to the first fiber end. The inner ferrule front section 42 supports the first fiber end section 41 proximal to the first fiber end 41a by mechanically holding the first fiber end section in an axial position proximal to the first fiber end.

[0139] The ferrule structure further comprises an outer ferrule arrangement 45 secured to each of the inner ferrule front section 42 and the inner ferrule rear section 43 to hold them in position relative to one another and define a gap 44 therebetween. The outer ferrule arrangement 45 is secured at each of its ends with solder 46 to the respective sections 42, 43 of the inner ferrule arrangement.

[0140] The PCF has a mode stripper section 47 at its first fiber end section 41 and the inner ferrule back section 43 has a groove 47 a exposing the PCF mode stripper length section 47 .

[0141] The front end 43e of the inner ferrule rear section 43 is tilted relative to the central axis of the ferrule structure to provide an outwardly facing end face for out-coupling light propagating within the inner ferrule configuration and to reduce back reflection of light. Portion 42b (e.g., a semi-annular shaped portion at the rear end of the inner ferrule front section) is tilted relative to the central axis of the ferrule structure to out-couple light propagating within the inner ferrule configuration and to reduce back reflection of light. The remaining portion 42c is not tilted and has an end face that is substantially perpendicular to the central axis. The non-tilted portion 42c at the rear end of the inner ferrule front section is advantageously coated with a reflective coating to reduce back reflection of light.

[0142] To monitor the output coupling efficiency of the angled portion 42b of the inner ferrule front section and the mode stripper 47, respectively, sensors 48a, 48b are attached to the outer ferrule arrangement 45 above the rear end of the inner ferrule front section and the groove 47a exposing the PCF mode stripper length section, respectively.

[0143] The PCF assembly of FIG. 6 is a variation of the PCF assembly of FIG. 5 in which the entire rear end 42b of the rear end of the inner ferrule front section is angled relative to the central axis of the ferrule structure to outcouple light propagating within the inner ferrule configuration and reduce back reflections of light.

[0144] The PCF assembly of FIG. 7 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 51 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 51, the inner ferrule configuration having an inner ferrule pre-section 52 proximal to the first fiber end and an inner ferrule post-section 53 distal to the first fiber end.

[0145] The inner ferrule back section 53 is anchored to the first fiber end section 51 such that the PCF is free of polymer coating from point 51c to the first fiber end 51a. The inner ferrule front section 52 supports the first fiber end section 51 proximal to the first fiber end 51a by mechanically holding the first fiber end section in an axial position proximal to the first fiber end.

[0146] The ferrule structure further comprises an outer ferrule arrangement 55 secured to each of the inner ferrule front section 52 and the inner ferrule rear section 53 to hold them in position relative to each other and define a gap 54 therebetween. The outer ferrule arrangement 55 is secured at each of its ends with solder 56 to the respective sections 52, 53 of the inner ferrule arrangement.

[0147] The PCF has a mode stripper section 57 in its first fiber end section 51 positioned between the pre-inner ferrule section 52 and the post-inner ferrule section 53 . The PCF assembly of FIG. 8 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 61 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 61, the inner ferrule configuration having an inner ferrule pre-section 62 proximal to the first fiber end and an inner ferrule post-section 63 distal to the first fiber end.

[0148] The inner ferrule back section 63 is anchored to the first fiber end section 61 at anchor length 63b, and from point 61c of the PCF to the first fiber end 61a, the PCF is free of polymer coating.

[0149] The ferrule structure includes a hermetic solder element 66a disposed to surround the first fiber end section 61 to form an annular hermetic seal 66a between the first fiber end section 61 and the inner ferrule rear section 63, the hermetic solder element 66a being disposed closer to the front annular section 62 than the anchor length 63b of the inner ferrule rear section. As can be seen in the drawings, the anchor length 63b of the inner ferrule rear section 63 is not completely annular, and the anchor length 63b of the inner ferrule rear section preferably extends from about 20 degrees to about 350 degrees around the PCF, such as about 180 degrees.

[0150] The ferrule structure further comprises an outer ferrule arrangement 65 secured to each of the inner ferrule front section 62 and the inner ferrule rear section 63 to hold them in position relative to each other and define a gap 64 therebetween. The outer ferrule arrangement 65 is secured at each of its ends with solder 66 to the respective sections 62, 63 of the inner ferrule arrangement.

[0151] The ferrule structure further comprises an end cap 67 disposed in front of, and preferably in direct contact with, the first fiber end 61c. The end cap 67 is secured directly to the inner ferrule front section. As explained above, this embodiment is particularly beneficial when the PCF is a solid-core PCF.

[0152] The PCF assembly of FIG. 9 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 71 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 71, the inner ferrule configuration having an inner ferrule pre-section 72 proximal to the first fiber end and an inner ferrule post-section 73 distal to the first fiber end.

[0153] The inner ferrule rear section 73 is anchored to the first fiber end section 71 at anchor length 73b, and from point 71c of the PCF to the first fiber end 71a, the PCF is free of polymer coating.

[0154] The ferrule structure includes a hermetic solder element 76a disposed to surround the first fiber end section 71 to form an annular hermetic seal 76a between the first fiber end section 71 and the inner ferrule rear section 73, the hermetic solder element 76a being disposed closer to the front annular section 72 than the anchor long section 73b of the inner ferrule rear section.

[0155] The hermetic solder element ensures a hermetic seal of the first fiber end section 71 from the first fiber end 71c to the z-direction location of the hermetic solder element 76a. The ferrule structure further comprises an outer ferrule arrangement 75, 75a comprising an outer ferrule front section 75a and an outer ferrule back section 75. The outer ferrule back section 75 is secured to each of the inner ferrule front section 72 and the inner ferrule back section 73 to hold them in position relative to each other and to form a gap 74 therebetween. The outer ferrule back section 75 is secured at each of its ends to the respective sections 72, 73 of the inner ferrule arrangement with solder 76, and the outer ferrule front section 75a is secured to the inner ferrule front section 72 with solder 76.

[0156] The ferrule structure further comprises an end cap 77 disposed in front of the first fiber end section 71c. The end cap 77 is mounted spaced apart from the inner ferrule front section 72 to define an end cap space 78 between the end cap 77 and the inner ferrule front section 72. The end cap is secured to the outer ferrule front section 75a of the outer ferrule arrangement, which thereby holds the end cap 77 in a desired position relative to the inner ferrule front section 72 and the first fiber end section 71c. As explained above, this embodiment is particularly beneficial when the PCF is a hollow core PCF.

[0157] The inner ferrule arrangements 72, 73 are provided with passages leading to the end cap space 78 for injecting and / or withdrawing fluids. The passages are provided by additional through holes 72f, 73f in the inner ferrule front section 72 and the inner ferrule rear section 73, respectively. Advantageously, a valve arrangement (not shown) is arranged to ensure the desired opening and closing functions of the through holes 72f, 73f and the end cap space 78.

[0158] The PCF assembly shown in FIG. 9a differs from that of FIG. 9 in that the end cap is a lens 77a, which preferably has an anti-reflective coating on both sides.

[0159] The PCF assembly of FIG. 10 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 81 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 81, the inner ferrule configuration having an inner ferrule pre-section 82 proximal to the first fiber end and an inner ferrule post-section 83 distal to the first fiber end.

[0160] The inner ferrule back section 83 is anchored to the first fiber end section 81 at anchor length 83b, and from point 81c of the PCF to the first fiber end 81a, the PCF is free of any polymer coating.

[0161] The ferrule structure includes a hermetic solder element 86 a disposed to surround the first fiber end section 81 to form an annular hermetic seal 86 a between the first fiber end section 81 and the inner ferrule back section 83 .

[0162] The hermetic solder element 86a ensures a hermetic seal of the first fiber end section 81 from the first fiber end 81c to the z-direction location of the hermetic solder element 86a. The outer ferrule back section 85 is secured to each of the inner ferrule front section 82 and the inner ferrule back section 83 to hold them in position relative to each other and to form a gap therebetween. The outer ferrule back section 85 is secured at each of its ends with solder 86 to the respective sections 82, 83 of the inner ferrule arrangement, and the outer ferrule front section 85a is secured to the inner ferrule front section 82 with solder 86.

[0163] The ferrule structure further comprises an end cap 87 disposed in front of the first fiber end 81c. The end cap 87 is mounted spaced apart from the inner ferrule front section 82, thereby forming an end cap space 88 between the end cap 87 and the inner ferrule front section 82. The end cap is secured to the outer ferrule front section 85a of the outer ferrule arrangement.

[0164] The ferrule structure comprises an outer alignment jacket 89 surrounding the outer ferrule arrangement 85, 85a, which preferably comprises alignment means 89a, 89b, which in the illustrated embodiment include an alignment flange 89a and a protrusion 89b for rotational alignment, e.g., for fiber rotational orientation.

[0165] The PCF assembly of FIG. 11 comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 91 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 91, the inner ferrule configuration having an inner ferrule pre-section 92 proximal to the first fiber end and an inner ferrule post-section 93 distal to the first fiber end.

[0166] The assembly further comprises an alignment sleeve 90 disposed between the inner ferrule front section 92 and the end section of the first fiber 91 to completely surround the first fiber end section 91, such that the inner ferrule front section 92 supports the first fiber end section 91 proximal to the first fiber end 91 a via the alignment sleeve 90. In the embodiment illustrated in FIG. 11, the alignment sleeve 90 is a short section of capillary tubing.

[0167] The front end of the alignment sleeve 90, the front end of the inner ferrule front section 92, and the first fiber end 91a are aligned in a plane perpendicular to the central axis of the ferrule assembly.

[0168] The inner ferrule back section 93 is anchored to the first fiber end section 91 at anchor length 93b, and from point 91c of the PCF to the first fiber end 91a, the PCF is free of any polymer coating.

[0169] The ferrule structure includes a hermetic solder element 96 a disposed to surround the first fiber end section 91 to form an annular hermetic seal 96 a between the first fiber end section 91 and the inner ferrule back section 93 .

[0170] The outer ferrule back section 95 is secured to each of the inner ferrule front section 92 and the inner ferrule back section 93 to hold them in position relative to each other and to form a gap therebetween. The outer ferrule back section 95 is secured at each of its ends to the respective sections 92, 93 of the inner ferrule arrangement with solder 96, and the outer ferrule front section 95a is secured to the inner ferrule front section 92 with solder 96.

[0171] The ferrule structure further includes an end cap 97 disposed in front of the first fiber end 91c. The end cap 97 is mounted spaced apart from the inner ferrule front section 92. The end cap is secured to the outer ferrule front section 85a of the outer ferrule arrangement.

[0172] The ferrule structure includes an outer alignment jacket 99 surrounding the outer ferrule arrangement 95, 95a, the outer alignment jacket preferably including alignment means 99a, 99b.

[0173] Sensors 98 are attached to the outer alignment jacket 99 to monitor the performance of the connector and / or to monitor the fiber for damage. The PCF assembly of Figures 12 and 12a comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 101 assembled with a ferrule structure having an inner ferrule arrangement surrounding the first fiber end section 101, the inner ferrule arrangement having an inner pre-ferrule section 102 proximal to the first fiber end and an inner ferrule post-section 103 distal to the first fiber end.

[0174] The assembly further comprises an alignment sleeve 100 disposed between the inner ferrule front section 102 and the end section of the first fiber 101, completely surrounding the first fiber end section 101, such that the inner ferrule front section 102 supports the first fiber end section 101 proximal to the first fiber end 101a via the alignment sleeve 100. In the embodiment illustrated in Figure 11, the alignment sleeve 100 is a short section of capillary tube. Figure 12a zooms in on the alignment sleeve 100 and the supported first fiber end section 101, revealing that the PCF comprises a short section of another fiber 101b, which is advantageously a section of hollow core capillary tube 101b.

[0175] The front end of the alignment sleeve 100, the front end of the inner ferrule front section 102, and the first fiber end 101a are aligned in a plane perpendicular to the central axis of the ferrule structure.

[0176] The inner ferrule back section 103 is anchored to the first fiber end section 101 at anchor length 103b, and from point 101c of the PCF to the first fiber end 101a, the PCF is free of any polymer coating.

[0177] The ferrule structure includes a hermetic solder element 86 a disposed to surround the first fiber end section 101 to form an annular hermetic seal 106 a between the first fiber end section 101 and the inner ferrule back section 103 .

[0178] The outer ferrule back section 105 is secured to each of the inner ferrule front section 102 and the inner ferrule back section 103 to hold them in position relative to each other and to form a gap between them. The outer ferrule back section 105 is secured at each of its ends to the respective sections 102, 103 of the inner ferrule arrangement with solder 106, and the outer ferrule front section 105a is secured to the inner ferrule front section 102 with solder 106.

[0179] The ferrule structure further comprises an end cap 107 disposed in front of the first fiber end 101c. The end cap 107 is mounted spaced apart from the inner ferrule front section 102. The end cap is secured to the outer ferrule front section 105a of the outer ferrule arrangement.

[0180] The ferrule structure comprises an outer alignment jacket 109 surrounding the outer ferrule arrangement 105, 105a, the outer alignment jacket preferably comprising alignment means 109a, 109b.

[0181] Sensors 108 are attached to the outer alignment jacket 109 to monitor the performance of the connector and / or to monitor the fiber for damage.

[0182] The PCF assembly of Figures 13 and 13a comprises a photonic crystal fiber (PCF) for assembly having a first fiber end section 111 assembled with a ferrule structure having an inner ferrule configuration surrounding the first fiber end section 111, the inner ferrule configuration having an inner ferrule pre-section 112 proximal to the first fiber end and an inner ferrule post-section 113 distal to the first fiber end.

[0183] The assembly further comprises an alignment sleeve 110 disposed between the inner ferrule front section 112 and the end section of the first fiber 111 to completely surround the first fiber end section 111, such that the inner ferrule front section 112 supports the first fiber end section 111 proximal to the first fiber end 111a via the alignment sleeve 110. The alignment sleeve 100 supports the first fiber end section 111 by collapsing it over the first fiber end section 111 at the support length section 110b. At the uncollapsed portion 110a of the alignment sleeve 110, the alignment sleeve 110 has an outer diameter that correlates to the inner diameter of the inner ferrule front section 112.

[0184] The inner ferrule back section 113 is anchored to the first fiber end section 111 at anchor length 113b, and from point 111c of the PCF to the first fiber end 111a, the PCF is free of polymer coating.

[0185] The ferrule structure includes a hermetic solder element 86 a disposed to surround the first fiber end section 111 to form an annular hermetic seal 116 a between the first fiber end section 111 and the inner ferrule back section 113 .

[0186] The outer ferrule back section 115 is secured to each of the inner ferrule front section 112 and the inner ferrule back section 113 to hold them in position relative to each other and to form a gap between them. The outer ferrule back section 115 is secured at each of its ends to the respective sections 112, 113 of the inner ferrule arrangement with solder 116, and the outer ferrule front section 115a is secured to the inner ferrule front section 112 with solder 116.

[0187] The ferrule structure further comprises an end cap 117 mounted spaced from the inner ferrule front section 112. The end cap is secured to the outer ferrule front section 115a of the outer ferrule arrangement.

[0188] The ferrule structure comprises an outer alignment jacket 119 surrounding the outer ferrule arrangement 115, 115a, the outer alignment jacket preferably comprising alignment means 119a, 119b.

[0189] The end section of the PCF shown in Figure 14a is a hollow core PCF, comprising a hollow core 121 and a surrounding cladding with a number of cladding holes 122. At the first fiber end 123, the PCF has a metal or anti-reflective coating on the fiber end face (fiber end) for protection against incident light and / or back reflections.

[0190] The end section of the PCF shown in Figure 14b is a hollow core PCF, comprising a hollow core 131 and a surrounding cladding with a number of cladding holes 132. In a short end portion adjacent the first fiber end 133, for example an end portion having a length l up to about 2 mm in length, the PCF cladding holes are otherwise collapsed or sealed. The hollow core 131 is not sealed.

[0191] Figure 14c shows another view of the hollow core PCF illustrated in Figure 14b. It can be seen that due to the sealed cladding holes 133, the light transmitted into the PCF is not completely confined at the end portion of length l, and the light spreads out into a cone shape 144. To mitigate this, a lens may be placed, for example, in front of the first fiber end 133.

[0192] In FIG. 14e, the hollow core PCF illustrated in FIG. 14c is further provided with a metal coating 133a for protection against incident light and / or back reflections. The laser system illustrated in FIG. 15 comprises a laser source 141 and a fiber transmission cable 142 for transmitting light from the laser source 141 to a user device 144. The fiber transmission cable 142 comprises as its waveguide the hollow core PCF described above with one or more low loss transmission bands associated with the user device. As shown, the fiber transmission cable 142 may be quite long and still be capable of transmitting single mode light in the fundamental mode with high efficiency and low loss to the user device 144. The fiber transmission cable 142 has a first end 143a and a second end 143b. In the illustrated embodiment, each of the first end 143a and the second end 143b are attached to the ferrule structure described above for connection to the user device 144 and the laser source 141, respectively.

[0193] The apparatus of FIG. 16 comprises the laser system of FIG. The apparatus of Figures 17a and 17b comprises a laser source 151 for transmitting pulsed light and a cable of supercontinuum generating PCF 152 arranged to generate and transmit supercontinuum light to a user device 154. The fibre transmission cable 152 comprises as its waveguide a solid core PCF as shown in Figure 17b comprising a number of microstructures 166 surrounding a solid core 155.

Claims

1. 1. A photonic crystal fiber (PCF) assembly comprising: a PCF and at least one ferrule structure, the PCF having a central axis and comprising a core region and a cladding region and a first fiber end section having a first fiber end, the ferrule structure having a central axis and attached to the first fiber end section, the ferrule structure comprising an inner ferrule arrangement and an outer ferrule arrangement surrounding the first fiber end section, the inner ferrule arrangement comprising an inner ferrule pre-section proximal to the first fiber end and an inner ferrule pre-section distal to the first fiber end. and a rear ferrule section, each of the inner ferrule sections having an inner diameter and completely surrounding the PCF by at least its length, the inner ferrule rear section being anchored to the first fiber end section by an anchor length section, the inner ferrule front section supporting the first fiber end section proximate to the first fiber end, a central axis of the PCF of the first fiber end section and a central axis of the ferrule structure are preferably substantially parallel, and more preferably a central axis of the PCF of the first fiber end section and a central axis of the ferrule structure are coincident.

2. 2. The PCF assembly of claim 1, further comprising an alignment sleeve disposed between the inner ferrule front section and the first fiber end section, the inner ferrule front section supporting the first fiber end section proximate to the first fiber end via the alignment sleeve, the alignment sleeve preferably being positioned to surround and support the first fiber end section at the first fiber end.

3. 3. The PCF assembly of claim 2, wherein the inner ferrule front section surrounds and retains the alignment sleeve at a preselected axial position, and the inner diameter of the inner ferrule front section is slightly larger than the maximum outer diameter of the alignment sleeve, such as about 0.1 μm to about 2 mm larger in diameter, such as about 1 μm to about 1 mm larger, such as about 0.1 mm to about 0.01 mm larger.

4. 4. The PCF assembly of claim 2 or 3, wherein the inner ferrule front section supports the first fiber end section via the alignment sleeve by mechanically holding the alignment sleeve in an axial position, preferably such that an end of the alignment sleeve and an end of the inner ferrule front section are aligned in a plane perpendicular to a central axis of the ferrule structure, and more preferably such that the first fiber end, the end of the alignment sleeve and the end of the inner ferrule front section are aligned in a plane perpendicular to a central axis of the PCF.

5. The PCF assembly of any one of claims 2 to 4, wherein the alignment sleeve surrounds the PCF proximal to the first fiber end, preferably such that the first fiber end and the end of the alignment sleeve are aligned in a plane perpendicular to a central axis of the PCF, and the alignment sleeve preferably has an axial length of at least about 1 mm, such as from about 2 mm to about 5 cm, for example from about 5 mm to about 2 cm.

6. The PCF assembly of any one of claims 2 to 5, wherein the alignment sleeve supports the first fiber end section by having an inner diameter at least along its support section that is adapted to the outer diameter of the first fiber end section, and preferably the inner diameter of the support section of the alignment sleeve is greater than the inner diameter by up to about 0.5 mm, such as up to about 0.1 mm, such as up to about 0.01 mm.

7. The PCF assembly of any one of claims 2 to 6, wherein the alignment sleeve supports the first fiber end section by collapsing the first fiber end section over its entire length or onto the support section, the alignment sleeve being preferably a capillary tube applied to surround the PCF and arranged to support the first fiber end section of the PCF by being thermally collapsed over at least its support section, such as a central section, and the alignment sleeve is preferably fused to the optical fiber, preferably without intermediate material.

8. 8. The PCF assembly of claim 2, wherein the alignment sleeve is made from glass, preferably silica glass, such as fused silica glass, fused quartz and / or doped silica, and / or borosilicate glass, for example borosilicate glass containing about 96% silica and 4% boron oxide.

9. A PCF assembly according to any one of claims 2 to 8, wherein the alignment sleeve has a refractive index of up to 1.45 for light at 1 μm, such as for light in the range 1 μm to 2 μm.

10. A PCF assembly according to any one of claims 2 to 9, wherein the alignment sleeve is made from down-doped silica, for example silica doped with fluorine and / or boron.

11. The PCF assembly of any one of claims 2 to 10, wherein the alignment sleeve has a refractive index lower than the effective refractive index of the cladding region.

12. 12. The PCF assembly of claim 2, wherein the alignment sleeve is retained within the inner ferrule pre-section without any intermediate material between the alignment sleeve and the inner ferrule pre-section, and preferably the alignment sleeve is mechanically retained and fused to the inner ferrule pre-section, or mechanically retained or fused to the inner ferrule pre-section.

13. 13. The PCF assembly according to any one of claims 1 to 12, wherein the inner ferrule pre-section and the inner ferrule post-section are not directly fixed to each other, preferably the inner ferrule pre-section and the inner ferrule post-section are arranged with an intermediate gap in the axial direction, preferably the gap provides an axial distance between the inner ferrule pre-section and the inner ferrule post-section, preferably the distance being in the range of about 1 mm to about 10 cm, such as about 5 mm to about 2 cm.

14. 14. The PCF assembly of claim 1, wherein the inner ferrule front section supports the first fiber end section directly proximal to the first fiber end, preferably by mechanically holding the first fiber end section proximal to the first fiber end at an axial position, preferably such that the end of the inner ferrule front section and the first fiber end are aligned in a plane perpendicular to a central axis of the PCF.

15. 15. The PCF assembly of claim 1, wherein the ferrule structure comprises a hermetic solder element disposed surrounding the first fiber end section to form an annular hermetic seal between the first fiber end section and the inner ferrule post section, the hermetic solder element disposed closer to the front annular section than the anchor length of the inner ferrule post section, preferably the anchor length of the inner ferrule post section is not completely annular, and the anchor length of the inner ferrule post section preferably extends at about 20 degrees to about 350 degrees, such as about 180 degrees, relative to the PCF.

16. The PCF assembly of any one of claims 1 to 15, wherein the PCF is free of a polymer coating on the first fiber end section from the anchor section of the inner post-ferrule section to the first fiber end.

17. 17. A PCF assembly according to any one of claims 1 to 16, wherein the inner ferrule front section is made from a material that is at least partially transparent at wavelengths from about 200 nm to about 4 μm, the inner ferrule front section being made from, for example, fused silica or quartz, such as substantially undoped silica having a refractive index of 1.45 for 1 μm light.

18. The PCF assembly of any one of claims 1 to 17, wherein the inner ferrule post section is made from fused silica or quartz or a metal or alloy.

19. The PCF assembly of any one of claims 1 to 18, wherein the outer ferrule arrangement is made from metal, ceramic or glass, for example silica.

20. 20. The PCF assembly of claim 1, wherein the outer ferrule arrangement is secured to each of the inner ferrule front section and the inner ferrule rear section of the inner ferrule arrangement to hold them in a fixed position relative to each other, the first fiber end section of the PCF is preferably supported substantially straight within the ferrule structure, and the outer ferrule arrangement is secured to the inner ferrule arrangement by at least one of an adhesive, solder and melting or laser welding.

21. The PCF assembly of any one of claims 1 to 20, wherein the first fiber end section is attached to the ferrule structure substantially without applying stress that creates pressure on the fiber.

22. 22. The PCF assembly of claim 1, wherein the first fiber end is attached to the ferrule structure without any direct joint to the fiber, including the anchoring, except for one or more joints to the inner ferrule back section.

23. 23. The PCF assembly of claim 1, wherein the ferrule structure comprises an end cap disposed in front of the first fiber end, the end cap being attached with or without being spaced apart from the inner ferrule front section, the end cap preferably being fixed directly to the inner ferrule front section or to an outer ferrule front section of the outer ferrule arrangement.

24. 24. The PCF assembly of claim 23, wherein the end cap is secured to the outer ferrule front section of the outer ferrule arrangement, the outer ferrule arrangement preferably comprising the outer ferrule front section and the outer ferrule back section, the outer ferrule back section secured to both the inner ferrule back section and the inner ferrule front section, and the outer ferrule front section secured to the inner ferrule front section.

25. 25. A PCF assembly according to claim 23 or claim 24, wherein the end cap is an anti-reflection coated silica end cap, the end cap preferably being or comprising a lens.

26. The PCF assembly according to any one of claims 1 to 25, wherein the PCF is a hollow-core fiber or a solid-core fiber, and preferably the first fiber end (end face) has a metallic or anti-reflective coating.

27. A PCF assembly according to any preceding claim, wherein the PCF has a core diameter of less than 100 μm, preferably about 50 μm or less, such as from about 5 μm to about 40 μm.

28. 28. The PCF assembly of any one of claims 23 and 25-27, wherein the PCF is a hollow core fiber, the end cap is secured to the outer ferrule front section of the outer ferrule arrangement to provide an end cap space between the end cap and the inner ferrule front section, and optionally the hollow core has a collapsed end portion and a metal or anti-reflective coating on the fiber end face.

29. 29. The PCF assembly of claim 28, wherein the inner ferrule arrangement comprises a passageway leading to the end cap space for injecting and / or extracting fluid, the passageway preferably being provided by at least one additional through hole in each of the inner ferrule pre-section and the inner ferrule post-section, the additional through hole preferably being substantially parallel to the axis of the ferrule structure, and more preferably the additional through hole comprising a valve arrangement at an outlet from the inner ferrule post-section.

30. 30. The PCF assembly of any one of claims 1 to 29, wherein the inner ferrule front section has a rear end, and at least a radially outer portion of the rear end is angled relative to the central axis of the ferrule structure to output couple light propagating within the inner ferrule arrangement, e.g., a radially semi-annular or annular shaped outer portion of the rear end is angled relative to the central axis of the ferrule structure to output couple light propagating within the inner ferrule arrangement.

31. The PCF assembly of any one of claims 1 to 30, wherein the inner ferrule front section has a rear end, at least a radially inner portion of the rear end being angled relative to the central axis to form a funnel shape.

32. 32. The PCF assembly of claim 1, wherein the inner ferrule front section has a rear end, the rear end being coated with a reflective coating to back reflect light, such as light propagating within the ferrule.

33. 33. The PCF assembly of claim 1, wherein the inner ferrule front section has a front end, the front end being coated with a reflective coating to protect the ferrule structure against at least one of incident light and back-reflected light.

34. 34. The PCF assembly of any one of claims 1 to 33, wherein the inner ferrule rear section has a front end, the front end being angled relative to the central axis of the ferrule structure and the front end being coated with a reflective coating to protect against at least one of incident light and back reflected light, the front end being angled relative to the central axis of the ferrule structure, or the front end being coated with a reflective coating to protect against at least one of incident light and back reflected light.

35. 35. The PCF assembly of any one of claims 1 to 34, wherein the first fiber end section has at least one mode stripper length, the mode stripper length comprising at least one of a mode stripping high refractive index material and a scatter layer applied in contact with the optical fiber at the mode stripper length and the fiber at the mode stripper length has a roughness Ra value of at least about 0.1 μm, or the mode stripper length comprising at least one of a mode stripping high refractive index material and a scatter layer applied in contact with the optical fiber at the mode stripper length, or the fiber at the mode stripper length has a roughness Ra value of at least about 0.1 μm.

36. 36. The PCF assembly of claim 35, wherein the mode stripper length of the PCF is positioned between the inner ferrule pre-section and the inner ferrule post-section.

37. 36. The PCF assembly of claim 35, wherein at least one of the inner ferrule pre-section and the inner ferrule post-section has a groove exposing the mode stripper length of the PCF, preferably the groove partially surrounding the fiber, preferably extending at least about 20 degrees.

38. 38. The PCF assembly of claim 1, wherein the ferrule structure comprises a mode stripper coating disposed in direct contact with an outer surface of the inner pre-ferrule section, the mode stripper coating preferably being included between the inner pre-ferrule section and the outer ferrule arrangement.

39. 39. A PCF assembly according to any one of claims 1 to 38, wherein the ferrule structure comprises an outer alignment jacket surrounding the outer ferrule arrangement, the outer alignment jacket preferably comprising alignment means, preferably at least one of the axial (z direction), radial (x, y direction) and rotational alignment means.

40. 40. The PCF assembly of claim 39, wherein the alignment means comprises one or more flanges, such as a mounting flange with positioning control.

41. 41. A PCF assembly according to claim 39 or 40, wherein the alignment means comprises markers for rotational fibre orientation, e.g. PM ​​orientation.

42. 42. The PCF assembly of claim 1, wherein the ferrule structure is configured to cool the outer ferrule structure with a cooling fluid and the outer alignment jacket comprises a passage with at least one inlet and at least one outlet for the cooling fluid, or the ferrule structure is configured to cool the outer ferrule structure with a cooling fluid, or the outer alignment jacket comprises a passage with at least one inlet and at least one outlet for the cooling fluid.

43. The PCF assembly of any one of claims 1 to 42, further comprising one or more sensors, such as one or more optical and / or electrical and / or chemical sensors, for at least one of temperature monitoring, connector performance monitoring, and fiber damage monitoring.

44. A PCF assembly as claimed in any one of claims 1 to 43, wherein the assembly comprises a second ferrule structure connected to a second end section of the PCF, the second ferrule structure preferably being a ferrule structure as claimed in any one of claims 1 to 43.

45. A laser system comprising a PCF assembly according to any one of claims 1 to 44.

46. 46. ​​The laser system of claim 45, wherein the laser system comprises a laser source, the PCF assembly being optically connected to the laser source to receive light from the laser source and configured to transmit the light to a light collection station of an apparatus, and preferably the first fiber end provided with the ferrule structure is configured to connect to the user device.

47. 47. The laser system of claim 45 or 46, wherein the laser source is configured to generate pulses of laser light, preferably the laser source is a femtosecond laser source.

48. 48. The laser system of claim 47, wherein the laser source has a pump duration of from about 30 fs to about 30 ps, ​​such as from about 100 fs to about 10 ps.

49. 50. The laser system of claim 47 or 48, wherein the laser source has a peak power determined at the exit of the laser source of at least about 5 kW, such as at least about 10 kW, such as at least about 30 kW, such as at least about 50 kW.

50. 50. The laser system of any one of claims 47 to 49, wherein the laser source is a mode-locked laser, such as an actively or passively mode-locked laser, the mode-locked laser preferably comprising one or more amplifiers.

51. 51. The laser system of any one of claims 45 to 50, wherein the PCF is a hollow core PCF, preferably configured to guide light comprising at least one wavelength in the range of about 200 nm to about 4.5 μm, preferably at least one wavelength in the range of 1000 nm to about 1100 nm.

52. 52. The laser system of claim 51, wherein the PCF is configured to guide a continuous wave of optical wavelengths spanning at least about 0.1 μm, such as at least about 0.3 μm, such as at least about 0.5 μm.

53. 53. The laser system of claim 51 or 52, wherein the hollow-core PCF comprises an outer cladding region and N hollow tubes surrounded by the outer cladding region, each of the hollow tubes fused to the outer cladding to form a ring defining an inner cladding region, the hollow core region surrounded by the inner cladding region, preferably N is 6 to 12, more preferably N is 7.

54. 454. The laser system of claim 453, wherein the hollow tubes are not in contact with each other, and preferably the hollow tubes are positioned at substantially equal distances from adjacent hollow tubes.

55. 51. The laser system of any one of claims 45 to 50, wherein the PCF is a solid-core PCF, preferably a microstructured solid-core PCF comprising a plurality of non-solid and / or solid cladding inclusions, and wherein the solid-core PCF is configured to guide light comprising at least one wavelength in the range of about 200 nm to about 4.5 μm, preferably at least one wavelength in the range of 1000 nm to about 1100 nm.

56. 56. The laser system of any one of claims 45 to 55, wherein the PCF has a core region diameter of from about 3 μm to about 100 μm, such as from about 10 μm to about 50 μm, such as from about 10 μm to about 30 μm.

57. A set of interlocking ferrule elements suitable for a PCF assembly according to any one of claims 1 to 44, said set of ferrule elements comprising: - an inner ferrule pre-section and an inner ferrule post-section to form an inner ferrule configuration; an outer ferrule arrangement; a set of correlated ferrule elements, each of the inner ferrule front section, the inner ferrule back section and the outer ferrule configuration having a length and a central axis and comprising a main hollow through bore parallel to or coincident with said respective central axes, the set of correlated ferrule elements preferably further comprising an alignment sleeve having a length and a central axis and comprising a main hollow through bore parallel to or coincident with said central axis.

58. 46. ​​The set of correlated ferrule elements of claim 45, wherein the elements are correlated such that the alignment sleeve can be positioned within the main hollow throughbore of the inner ferrule front section and the inner ferrule front section and the inner ferrule back section can be installed within the main hollow throughbore of the outer ferrule configuration to form the inner ferrule configuration.

59. 59. A set of interrelated ferrule elements as described in claim 57 or 58, wherein the alignment sleeve is a capillary tube and the main hollow throughbore of the alignment sleeve has an inner diameter of about 2 mm or less, such as about 1 mm or less, such as about 0.5 mm or less, and the alignment sleeve is preferably collapsible over at least a portion of its length.

60. A set of interrelated ferrule elements according to any one of claims 57 to 59, wherein the alignment sleeve preferably has an axial length of at least about 1 mm, such as from about 2 mm to about 5 cm.

61. 61. A set of correlated ferrule elements according to any one of claims 57 to 60, wherein the set further comprises an end cap configured to be positioned in front of the inner ferrule front section by attaching to the inner ferrule front section or by attaching to an outer ferrule front section of the outer ferrule arrangement, the end cap preferably being an anti-reflective coated silica end cap.

62. 62. A set of correlated ferrule elements as claimed in any one of claims 57 to 61, wherein each of the inner ferrule pre-section and the inner ferrule post-section comprises one or more additional through holes for providing a fluid passageway, the additional through holes preferably being substantially parallel to the axis of the respective inner ferrule section, and more preferably the additional through holes comprise a valve arrangement at an outlet from the inner ferrule post-section.

63. 63. The set of correlated ferrule elements of any one of claims 57 to 62, wherein the inner ferrule front section has a rear end, at least a radially outer portion of the rear end being angled relative to the central axis of the inner ferrule front section and the rear end being coated with a reflective coating, or at least a radially outer portion of the rear end being angled relative to the central axis of the inner ferrule front section, or the rear end being coated with a reflective coating.

64. 64. The set of interrelated ferrule elements of any one of claims 57 to 63, wherein the inner ferrule front section has a front end, the front end being coated with a reflective coating.

65. 65. The set of correlated ferrule elements of any one of claims 57 to 64, wherein the inner ferrule rear section has a front end, the front end being angled relative to a central axis of the inner ferrule rear section and the front end being coated with a reflective coating, or the front end being angled relative to the central axis of the inner ferrule rear section, or the front end being coated with a reflective coating.

66. 66. A set of interrelated ferrule elements according to any one of claims 57 to 65, wherein at least one of the inner ferrule front section and the inner ferrule rear section has a groove leading to its main hollow throughbore, the groove preferably having an annular extension extending at least about 20 degrees.

67. 67. A set of correlated ferrule elements according to any one of claims 57 to 66, wherein the set further comprises an outer alignment jacket correlated to the outer ferrule arrangement so as to be arranged to surround the outer ferrule arrangement, the outer alignment jacket preferably comprising alignment means.

68. 57. An apparatus comprising the laser system of any one of claims 45 to 56, wherein the PCF assembly is configured to transmit light to a receiving station of the apparatus.

69. 69. The apparatus of claim 68, wherein the apparatus is an illumination apparatus configured to illuminate an object, the illumination apparatus being preferably selected from a microscope, a spectroscope, or an endoscope.

70. 70. The apparatus of claim 69, wherein the illumination source is adapted for at least one of fluorescence imaging, fluorescence lifetime imaging (FLIM), total internal reflection fluorescence (TIRF) microscopy, fluorescence resonance energy transfer (FRET), pulsed alternating excitation Förster resonance energy transfer (PIE-FRET), broadband spectroscopy, nanophotonics, flow cytometry, industrial testing such as metrology, ring-down spectroscopy such as gas sensing, hyperspectral spectroscopy, spectroscopic methods such as crop analysis and time-of-flight spectroscopy (TCSPC) of e.g. fruits, single molecule imaging, and combinations thereof.

71. 69. Apparatus according to claim 68, wherein the apparatus is a micro-machining apparatus, preferably for material processing such as at least one of drilling, marking, cutting and scribing.

72. 69. The device of claim 68, wherein the device is a surgical device, such as an eye surgical (ophthalmic) device.

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