WO2018234081A1

WO2018234081A1 - Optical fiber unit having a fiber end cap and method for producing an optical fiber unit

Info

Publication number: WO2018234081A1
Application number: PCT/EP2018/065391
Authority: WO
Inventors: Stefan BAUMBACH; Johannes OVERBUSCHMANN; Sebastian PRICKING
Original assignee: Trumpf Laser Gmbh
Priority date: 2017-06-23
Filing date: 2018-06-11
Publication date: 2018-12-27
Also published as: DE102017114002B4; DE102017114002A1

Abstract

The invention relates to an optical fiber unit (1) comprising an optical fiber (3), which has a light-conducting region (27) and, at a fiber end, an end surface (5) for coupling light (7) into the light-conducting region (27) or for coupling light (7) out of the light-conducting region (27), the light (7) entering or exiting the optical fiber (3) through an inner region (5A) of the end surface (5). Furthermore, the optical fiber unit (1) comprises a hollow end cap (11) having a hole element (15), which has a stop surface (15C) and an opening (16), and having an optical element (17). The hole element is fastened to the optical fiber (3) in such a way that the end surface (5) of the optical fiber (3) lies against the stop surface (15C) and the light (7) can be coupled into the light-conducting region (27) from the hollow end cap (11) through the opening (16) or can be coupled out of the light-conducting region (27) into the hollow end cap (11) through the opening (16).

Description

Optical fiber unit with fiber end cap and

Method for producing an optical fiber unit

The present invention relates generally to optical fibers, in particular optical fibers for transporting laser pulses with pulse durations in the nanosecond to

Femtoseconds. In particular, the present invention relates to the configuration of a fiber end of such optical fibers.

For the transport of short pulses, fibers with a hollow core (hollow core fiber) or photonic crystal fibers (photonic crystal fiber) are suitable. Such fibers have special light-conducting regions in which laser pulses with pulse durations in the nanosecond to femtosecond range can be transported. This is possible because the peak intensities are not present in the material of the fiber, but in substantially solid-free light-conducting regions, for example in a hollow core filled with air or generally with gas, and thus can not make any permanent material changes there. Due to this special structure, however, the fiber ends are to be specially configured to avoid, for example, contamination by particles, outgassing products or the entry of undesired gases or undesired change of the gas parameters and, correspondingly, not to impair the light conduction by such effects. WO 03/032039 A1 discloses a hermetically sealed optical fiber having voids or holes. To seal the same, a solid translucent window is provided directly at the fiber end. A manufacturing method for producing a short wavelength transport fiber, in particular a "photonic band gap" fiber, is disclosed in US 2004/0258381 Al.

EP 1 772 758 A1 discloses a fiber end of an optical fiber which is surrounded by a dust-proof protective element. For this purpose the protective element is made of outgas-free material, e.g. Metal or glass formed to seal the fiber and has a window for beam exit. The protective element surrounds the outer wall of the fiber cladding and is formed such that a gap between the fiber exit and the window is formed. The protective element also has a gas inlet or gas outlet used

Housing opening to allow adjusting gas parameters in the fiber over the gap by means of a connected pump permanently or at intervals.

In general, the coupling into fibers depends on the correct positioning of the coupling lens relative to the light-conducting region. Thus, a misalignment between coupling-in lens and the light-conducting area worsen the coupling efficiency. The same applies to the decoupling. Furthermore, there is a general risk at high (laser pulse) intensities that the end cap can be damaged by laser-induced material processing and even destroyed.

It is an object of this disclosure to propose an improved fiber end configuration that allows the use of such optical fibers at high peak intensities. Another object is to provide a method of fiber end configuration that allows to ensure specific fiber conditions over a long period of time.

At least one of these objects is achieved by an optical fiber unit having a configured fiber end according to claim 1 and by a method of manufacturing such an optical fiber unit according to claim 16. Further developments are given in the subclaims.

In one aspect, an optical fiber unit comprises an optical fiber having a light-guiding region and at one end a fiber end for coupling light into the light-guiding region or for coupling light from the light-guiding region, the light through an inner region of the end surface in the Optical fiber enters or exits. The optical fiber unit further includes a hollow end cap having a hole member having a stopper surface and an opening and an optical element, the hole member being fixed to the optical fiber such that the end surface of the optical fiber abuts against the stopper surface and the light from the hollow end cap can be coupled through the opening in the light-guiding area or out of the light-guiding area through the opening in the hollow end cap can be coupled out.

In another aspect, an optical fiber unit comprises an optical fiber having an end face for coupling or uncoupling light at a fiber end, the light entering or exiting the optical fiber through an inner, for example, centrally located, portion of the end face, and a hollow end cap on. The end cap includes a hole member having an opening and an optical element. The hole element is fastened to the end surface of the optical fiber in such a way that the inner (especially the through-hole) radiant) area of the end face with the opening overlapping, in particular completely overlapping, is arranged.

The use of the hole element affords the possibility of ensuring a fixation of the optical element of the end cap with respect to the fiber end surface, in particular the light-guiding region of the optical fiber, in the three spatial directions. In the plane of the fiber end surface, the relative position can be fixed by the (fixed) position of the hole element and in the propagation direction, the relative position can be fixed via the (fixed) geometry of the end cap, for example via the distance between the ends (side walls) of the end cap end cap.

The end cap optionally includes a hollow body. The hole member (e.g., a perforated plate) and the optical element may be e.g. arranged at opposite ends of the hollow body and connected to the hollow body. In alternative embodiments, the hole element and / or the optical element may be formed such that the structural function of the hollow body is taken over by one or both of these elements.

In some embodiments, the optical fiber may include a cavity structure including the light-guiding portion that terminates at the end surface in the inner region and a cladding structure associated with a cladding region surrounding the inner region of the end surface, and the hole member may be attached to the optical fiber such in that an interior of the hollow end cap is fluidly connected to the cavity structure in the optical fiber through the opening of the hole member.

In some embodiments, the end surface of the optical fiber at the abutment surface of the hole member and / or the sheath structure, in particular the outer sheath side of the optical fiber, on an inner side of a Faserbefestigungsabschnitts the opening and / or the sheath structure, in particular an outer sheath side of the optical fiber, at the hole member, in particular at one Rear side of the hole element via a fillet connection, be attached. The connections can in particular be based on (glass) welding or gluing.

In some embodiments, the end cap is gas tight except for the opening and optionally one or more gas control holes. This can prevent or at least be delayed that set parameters of the gas in the hollow core over several years undesirable and uncontrolled change.

In some embodiments, the light-guiding portion of the optical fiber may be formed as a hollow core, the access of which is kept free from the opening. The cavity structure may further include a hole cladding structure disposed between the light guiding portion of the optical fiber and the cladding structure and terminating at the end surface in the inner region. In particular, the access to the perforated shell structure can be kept free from the opening.

In some embodiments, the hole member is affixed to the end face of the optical fiber such that the opening of the hole member and the inner (irradiated) portion of the end face abut each other, that is, the inner portion is radially overlapping with the opening. Here, the radial direction is related to the plane of the end surface and the central axis of the inner region. In further embodiments, the inner region is additionally overlapping with the opening in the axial direction. In this case, the axial direction is related to the extent of the opening in the hole element, which is usually given in the direction of the central axis of the inner region, substantially in accordance with the propagation direction of the light when entering or leaving the fiber. The feature that the inner area of the end face with the opening overlapping, in particular completely overlapping, comprises herein these two layers.

In a further aspect, a method of making an optical fiber unit having at least one configured fiber end of an optical fiber comprises the steps of mounting a hollow end cap having a hole member having a stopper surface and an opening, and, in particular, for leading from the optical fiber Light transparent optical element comprises, on the optical fiber, wherein the optical fiber has a light-guiding portion and at the fiber end an end face for coupling light into the light-guiding area or outcoupling of light from the light-guiding area, and positioning the hole member so with respect to the optical fiber the end surface of the optical fiber abuts against the abutment surface, so that the light can be coupled into or out of the optical fiber, an interior of the end cap and the opening in the optical fiber. In another aspect, a method of making an optical fiber unit having at least one configured fiber end of an optical fiber, for example, for manufacturing the above optical fiber unit, comprises the steps of mounting an end cap having a hole member with an opening and a light to be transported by the optical fiber transparent optical element comprises, on an end surface of the optical fiber having an inner portion which is irradiated by the light to be transported by the fiber, and positioning the hole member so with respect to the optical fiber, that the inner portion of the end surface overlapping with the opening, in particular is completely overlapping, is arranged so that light can be coupled through the optical element, an inner space of the end cap and the opening in the optical fiber or from this auskoppelbar.

In some embodiments of the method, the end cap may be attached to the end surface such that the interior of the end cap is in fluid communication with a cavity structure of the optical fiber. Furthermore, when attaching the hollow

Endkappe first the hole element are mounted on the end face of the optical fiber before then the hollow end cap can be completed by attaching further components, which may include an optical element and optionally a hollow body, in particular to the standing in fluid communication with the cavity structure of the optical fiber interior of the Form end cap.

In some embodiments of the method, mounting the hollow end cap may further include aligning the optical element relative to the fiber end surface for an optical coupling and / or outcoupling configuration.

In some embodiments of the method, at least one gas control hole may be provided in the end cap that fluidly connects an external environment to the interior space. In this case, the method of production may further comprise the following steps: Bringing the interior of the end cap and the associated cavity fluid structure in a defined gas and / or pressure state using the at least one gas control hole and closing the at least one gas control hole, in particular by means of laser-based Material processing such as laser melting. The concepts disclosed herein are intended to provide improved fiber end configurations in which the construction of the end cap is accomplished, for example, solely by glass components and with gas tight connections between the glass components with each other and the optical fiber. This can be implemented, for example, with a gluten-free glass welding process.

In general, the fixation of the position of the fiber end to the end cap can provide a mechanically strong bond between a coupling lens and the fiber end surface, and thus an entrance region of the light into the fiber, or correspondingly between the fiber end surface and a coupling lens. This fixation with respect to the fiber end surface (in the three spatial directions) makes it possible to implement a permanently stable optical constellation in the coupling or decoupling. Further, by appropriate dimensioning of the hollow body, generally with appropriate dimensioning of the distance between Faserendfiäche and optical element (eg lens), a passage of the light beam (eg high-intensity laser pulses) by the optical element only in a region of the beam path, in which a hazard of Material due to laser-induced damage due to eg high laser pulse intensities is not present.

In summary, in some embodiments, a perforated disk (as a hole member) may be attached to a fiber end so that, for example, a laser beam - generally light - can be coupled or extracted into the fiber only through the hole of the disk. The hole of the disk, generally the opening of the hole member, may e.g. drilled or generated by selective laseretching. For example, the aperture may be made linear along the direction of propagation in the fiber in the end portion of constant diameter (cylindrical) or stepped diameter (partially cylindrical) or conical or in a combination of such shapes.

In some embodiments, a tube (eg cylindrical) is attached as a hollow body to the front side of the perforated disc, so that the disc terminates the interior of the tube at one end (eg gas-tight). Alternatively or additionally, the tube can also be attached to the fiber cladding (cladding) via a rear wall and the hole element can optionally be additionally attached to the tube. In some embodiments, the hole element is configured such that the hole / opening is at least as large as the hollow core of a hollow core fiber, in the case of a photonic crystal fiber preferably at least as large as a hollow core and a hole shell structure surrounding the hollow core. Usually, the hole is smaller than 1 mm in diameter, and is for example in the diameter range of 50 μιη to 500 μιη, for example in the range of 200 μιη to 400 μιη.

In some embodiments of the end cap, the other side of the tube (generally the hollow body) is terminated by an optical element. The optical element may be a (e.g., planar or wedge-shaped) protective window, a lens, a diffractive optical element, a wave plate, or an axicon. Thus, e.g. Lenses have convergence / divergence matching and diffractive optical elements generally digitized and e.g. pixel-based phase adaptation of the transmitted light through a specific (permanently set or adjustable) phase imprint.

If the connections of the individual components are to be carried out by means of a laser welding process, the components mentioned are made e.g. made of glass (fused silica (quartz) or BK7) or sapphire.

For high intensity applications, the length of the tube (generally the end cap) can be adjusted so that the power density of the light beam on the terminating optical element does not cause damage. Further, in high intensity applications, the pinhole can be HR coated such that laser light reflected back into the end cap during, for example, material processing performed with the high intensity laser beam can not be coupled back into the cladding of the optical fiber. That is, generally, a (high) reflective coating on the inside of the hole member can serve as protection against damage to the optical fiber.

Further, the distance between an optical element formed as a lens and the fiber end surface may be substantially the focal length of the lens for a collimated one

steel to be coupled or a collimated outcoupling beam correspond.

One or more of the said components of the end cap may additionally comprise one or more holes (referred to herein as gas pop holes) through which a gas orifice may pass. variety and their pressure in the interior of the end cap and thus can be adjusted in the hollow core. This hole or holes can be sealed gas-tight, without affecting the parameters set in the fiber and in the interior. The closing can be done, for example, by introducing a glass closure (for example by a laser melting process), or the hole or holes can be sealed by a mechanical arrangement.

The embodiments disclosed herein may include i.a. have the following advantages. A hermetic sealing of the fiber end is possible, in particular by gas-tight laser welding. With appropriate choice of materials for the various components (for example, quartz glass) results in a gas-free construction. In laser welding of, for example, made of glass components, a quasi-monolithic structure is possible, which is correspondingly thermally stable and, for. has comparable expansion coefficients.

With gas-tight and degassing-free end caps, the gas parameters can remain stable for years. Furthermore, due to the fixed position of the fiber end surface in the three spatial directions, the optical parameters can remain permanently the same. The fixed position of a coupling lens to Faserendfiäche simplifies the adjustment with respect to a

Coupling or decoupling of the laser beam into the fiber by reducing the possible degrees of freedom. Furthermore, the optical fiber unit can ensure that no absorbent materials such as e.g. Metals can be positioned near the laser beam at the fiber exit. This also avoids heating the arrangement by scattered radiation.

Finally, a misalignment between the input / output lens and the fiber end surface can generally be avoided, whereby the coupling / decoupling efficiency can be kept stable. The efficiency is determined in particular permanently, since a misalignment or misalignment of the fiber end in all three spatial directions can be avoided.

Herein, concepts are disclosed that allow to at least partially improve aspects of the prior art. In particular, further features and their expediencies emerge from the following description of embodiments with reference to the figures. From the figures show: 1A and 1B schematic representations to illustrate a first exemplary embodiment of an optical fiber unit,

2A, 2B and 2C are schematic representations to illustrate further exemplary embodiments of optical fiber units and

Fig. 3 is a schematic representation to illustrate the implementation of a method for setting fixed operating parameters of such a fiber optic unit.

In part, aspects described herein are further based on the recognition that by using the endface of an optical fiber, an optical configuration for coupling or decoupling can be firmly established. Thus, the end face serves as an optical reference point for, for example, a focusing lens, but at the same time serves as a mechanical reference point with respect to a fixed position of the focusing lens in the case of the optical fiber unit described herein. In general, by making a quasi-monolithic embodiment, an optical element can be fixed with respect to the light-guiding region of an optical fiber in all three spatial directions (mechanical and thermal).

Some of the aspects described herein are further based on the recognition that by gas-tightly connecting the end face of an optical fiber, a controlled environment can be established which allows the propagation condition in an optical fiber having cavity structures to be established and, in particular, ensured over a long period of time. In particular, by laser welding, it is possible to produce hermetically sealed, substantially monolithic end caps which form a fixed unit with the optical fiber. It has thus been further recognized that adjusting the gas type and / or the gas pressure can be carried out, for example, via gas control holes and subsequent sealing of these gas control holes, whereby the resulting optical parameters of the optical fiber subsequently largely do not change due to the hermetic seal.

Furthermore, it has been recognized that the end cap disclosed herein not only allows to securely locate an exit window or lens at a safe distance from the high intensities present at the fiber exit, and the end cap disclosed herein can thus protect it accordingly, but also at the same time impurity the fiber can be avoided. Exemplary optical fiber units and their associated components are explained below in conjunction with FIGS. 1A to 2C.

FIG. 1A schematically shows a sectional view through an optical fiber unit 1 in the region of a fiber end of an optical fiber 3. The fiber end has a fiber end surface 5, through which light 7 (an exemplary beam path is indicated by two dashed lines in FIG. 1A) is coupled into the fiber 3 is to be or from the light 7 is to be decoupled from the fiber 3.

The optical fiber unit 1 comprises, in addition to the optical fiber 3, an end cap 11

End cap 11 includes various components that form an interior IA, which is (in some embodiments) substantially gas-tightly isolated from the outside environment. In FIG. 1A, the end cap 11 comprises, for example, a hollow body 13, a perforated element 15 designed as a circular perforated plate, and an optical element 17. The optical element 17 is, for example, a likewise circular focusing lens 17A, as on the dashed lines of the parallel outside of the end cap 11 Beam path is visible. In alternative embodiments, the optical element 17 is, for example, a plane-parallel plate through which the light passes substantially unaffected (see FIG. 2A), a (glass) wedge, a diffractive optical element, a wave plate or an axicon.

In a sectional view shown in Figure 1B can be seen on an inner side 15A of the hole member 15. Such a view arises, for example, in the production when first the perforated plate is fixed to the fiber end 5, ie, before the end cap 11 with the hollow body 13 and optical element 17 was completed. Behind the opening 16 can be seen an inner region 5A of the end surface 5 of the optical fiber 3, through which during use of the optical fiber 3 for transporting light, the light 7 in the fiber 3, in particular in the light-guiding Area, enters or exits from this. For example, as shown in FIG. 1B, a hollow core 27 terminates in the inner region 5A of the end surface 5. Since the diameter of the opening 16 is larger than the diameter of the inner region 5A, the light 7 substantially fails to interact with the hole member 15 the opening 16. It can be seen that the inner region 5A in the radial direction with the opening 16 overlapping, in particular completely overlapping, is arranged. In the exemplary arrangement shown in FIG. 1A, a central axis 21 of the inner region 5 A coincides with an axis of symmetry 22 of the end cap 11, and thus the circular opening 16. Moreover, the central axis 21 substantially corresponds to the direction of propagation of the light in the optical fiber 3, in particular in an end region thereof.

In FIG. 1B, a cladding region 5B of the end face 5 of the optical fiber 3 which surrounds the inner region 5A can be seen. The cladding region 5B is associated with a cladding structure 3B, which essentially gives the optical fiber 3 its mechanical stability. The sheath structure 3B is bounded by an outer sheath side of the optical fiber 3. In Figure 1B, the outer diameter of the fiber 3 compared to the hole member 15 is shown enlarged for clarity.

The hole member 15 is fixed to the optical fiber 3 such that the end surface 5 of the optical fiber 3 abuts against the abutment surface 15C. The stop surface 15C is shown in phantom for clarity in Figure 2B. It adjoins the opening 16 on a rear side 15B of the perforated plate 15, for example, and extends e.g. annular up to a diameter of the optical fiber 3 according to outer diameter. In the embodiment according to FIG. 1A, the hole element 15 and the shell structure 3B are connected to one another in a gas-tight manner in the area of the abutment surface 15C.

In alternative embodiments, the connection between the end cap and the optical fiber does not occur or not exclusively in the area of the stop surface, so that the end face, e.g. partially abuts the stop surface, in the case of a gas-tight connection, however, this again around the optical fiber takes place. The abutment surface is then designed such that it defines the spatial position of the optical fiber and the end cap.

The dimensions of the end cap 11 are chosen such that - for example, in the case of a coupling of light 7 - the beam broadening to the optical element 17 can take place so far that the intensity in the irradiated by the light 7 region of the optical element 17 to no damage to the optical element 17 during operation. Accordingly, the respective application of the optical fiber unit 1, in particular the required power density, requires the necessary distance between the hole element 15 and the optical fiber unit 1. see element 17. This results in the distance also from the respective existing optical conditions (divergence, convergence) in the coupling or coupling. At the same time with the distance of the required minimum diameter of the optical element 17 is defined. For example, the diameter of the optical element 17 is in the range of a few millimeters to a few centimeters and the distance between the hole member 15 and the optical element 17 is in the range of a few centimeters.

If the hollow body 13 is formed as a cylindrical tube, the minimum diameter of the hole element 15 is correspondingly given. In alternative embodiments, the hollow body 13 may, for example, be formed with an increasing diameter from the fiber end, so that the hole element 15 is correspondingly smaller than the optical element 17. Generally, the hole member 15 and the optical element 17 are disposed at opposite ends 19A, 19B of the hollow body 13.

In some embodiments, an inner side 15A of the hole member 15 may reflect incident light into the inner space 11A to prevent unwanted, e.g. formed by back reflections or scattering light in the optical fiber 3, in particular in the cladding region 5B is coupled. For example, the inner side 15A may be provided with a reflective coating. Furthermore, the optical element 17 may be provided with an antireflective coating.

Furthermore, it can be seen in Figure 1 A gas control holes 25, which allow the interior I IA controlled to fill with gas to put under (over- / under) pressure or flush. Preferably, the gas control holes 25 can be closed when a desired filling state of the inner space 11A, and thus e.g. a cavity structure 3A in the optical fiber 3, is present. This can be done for example by melting the material of the hollow body 13 with a laser, by gluing or by mechanical sealing. See also the description of FIG. 3.

The embodiment shown in FIGS. 2A and 2B will be explained below with reference to the features different from those shown in FIGS. 1A and 1B. For identical or similar elements and their functions, the corresponding reference numerals are used and referred to the preceding description. It can be seen in the schematic sectional representation of FIG. 2A that the optical element 17 is designed as a plane-parallel plate 17B which transmits the light 7. Accordingly, the light 7 passes through the optical element 17 substantially unchanged.

Further, in Fig. 2A, an embodiment of the aperture 16 having a light irradiated (cylindrically shaped) portion 16A and a (cylindrically shaped) fiber attaching portion 16C is known.

The diameter of the light-irradiated portion 16 A of the opening 16 is selected so that the light 7 does not hit the hole member 15 and thus can be coupled or disconnected undisturbed.

The fiber attachment portion 16C is configured to receive an end portion 23 of the optical fiber 3. It is correspondingly larger in aperture diameter (at least as large as the diameter of the optical fiber 3) than the aperture diameter of the light-irradiated portion 16A in FIG. 2A.

The transition from the fiber attachment portion 16C to the light irradiated portion 16A, in this case the radially extending constriction, forms the abutment surface 15C against which the end surface 5 of the optical fiber 3 abuts and, for example, with which the end surface 5 is secured in the sheath region 5B, in particular (FIG -) is welded or glued.

Further, the fiber attachment portion 16C of the opening 16 on the inner side may be connected to the outer shell side of the end portion 23 of the optical fiber 3.

This is a measure to further stabilize the attachment of the end cap 11 to the optical fiber 3, because usually optical fibers have an outer diameter of a few 100 μιη, so that the mechanical connection between the fiber and end cap is to handle accordingly carefully.

Alternatively or in addition to the attachment of the hole member 5 to the shell structure 3B in the cladding region 5B of the end surface 5, the embodiment of Figure 2A thus allows attachment to the outer shell side in the end portion 23 of the optical fiber 3. The optical fiber 3 can thus be connected to the hole member 15 over a larger area, causing the Transition from the end portion 23 of the optical fiber 3 to the end cap 11 towards stable can be performed.

Alternatively or additionally, furthermore, the outer shell side of the end portion 23 of the optical fiber 3 may be connected to the rear side 15B of the hole member 15 in the form of a (e.g., gas-tight circumferential) fillet joint.

In FIG. 2A it can be seen that the inner region 5A is overlapping with the opening 16 not only in the radial direction (here transverse to the direction of expansion / axis of symmetry of the opening), but also in the axial direction (here along the direction of extension / axis of symmetry of the opening). is arranged overlapping with the opening 16. Thus, the inner region 5A completely overlaps with the opening 16 and thus also here assumes a position defined and fixed in all three spatial directions by the abutment surface 15B.

In a gas tight connection (e.g., by laser welding of the components), the interior IA can be reliably hermetically sealed against the environment except for fluid communication with the cavity structure 3A (and optionally the gas control holes 25). As described below, the cavity structure 3A may include both a hollow core of the optical fiber 3 and a hole cladding structure.

2B, wherein the opening diameter of the light-irradiated portion 16A corresponds to the solid circle of the opening 16 and the opening diameter of the fiber attachment portion 16C to the dashed, the optical fiber 3 bounding, Circle corresponds. In the intermediate, dashed area is the abutment surface 15C, which surrounds here by way of example the inner region 5A annular completely.

2B, a fiber end surface of a microstructured glass fiber having a cavity structure 3A (eg a photonic crystal fiber) is indicated behind the light-irradiated section 16A. Thus, one can see centrally the hollow core 27 (in particular a schematically indicated round orifice of the light-conducting region of the optical fiber 3), which is surrounded by a perforated shell structure 29. The hole jacket structure 29 is a arranged Structure surrounded by the hollow core 27 channels, which cause a guiding of the light in the hollow core 27. In FIG. 2B, the ends of the channels of the perforated jacket structure 29 are schematically represented by dots. According to the embodiment of Figure 2B, not only is the access of the hollow core 27 on the end face 5 clear of the opening 16, in its full cross-sectional area, but also the accesses of the perforated shell structure 29 from the opening (16) - in this case also completely - kept free.

As can be seen with reference to FIGS. 2A and 2B, the diameter of the light-irradiated portion 16A of the opening 16 is greater than an (outer) diameter of the perforated shell structure 29. This ensures that the incoming / outgoing light is not disturbed on the one hand and that the microstructured fiber, in particular the entire cavity structure 3A (hollow core 27 and perforated shell structure 29), in fluid communication with the interior 11 A is.

For example, the gas in the cavity structure 3A may be controlled for composition and pressure through the gas control holes 25, for example. For this purpose, as in the embodiment of Figures 1 A and 1B in the end cap 11 a plurality of gas control holes 25 (in this case, for example, in the hollow body 13) are provided. Through the gas control holes 25 there is a fluid connection from the outside to the interior IA to adjust gas parameters in the optical fiber unit 1 and in particular in the cavity structure 3A of the optical fiber 3.

In alternative embodiments, the accesses of the perforated sheath structure 29 may be kept free only partially or at only one end of the fiber, e.g. the optical coupling or decoupling does not interfere and the gas parameters can still be adjusted accordingly.

Similar to the stabilization by the fiber attachment portion 16C, a back wall or a structure limited to the area around the optical fiber 3 may generally serve as a support member or support plate. The latter can be provided, for example, annular in the transition region from the optical fiber to the end cap.

In the embodiment of FIG. 2C, such a measure can be seen to further stabilize the attachment of the end cap 11 to the optical fiber 3. In addition to the attachment of the hole element 5 to the shell structure 3B in the jacket region 5B, the end surface 5 a rear wall 30 on a rear side 15 B of the hole member 15 is provided. The rear wall 30 is fixedly connected to the outer periphery of the optical fiber 3 and thus stabilizes the end portion 23 of the optical fiber 3 to the end cap 11.

The back wall 30 allows the fiber end surface 5 to pass therethrough and abut against the abutment surface 15C.

Furthermore, the rear wall 30 is connected to the hollow body 13 in the illustrated embodiment in the outer region. The hole element 15 may (but need not) be connected at its back to the rear wall 30 or be connected at its outer periphery to the hollow body 13. Preferably, however, it is ensured that the inner space 11A is hermetically sealed with respect to the optical fiber 3, with the exception of the fluid connection to the cavity structure 3A (and optionally to the gas control holes 25). As described above, the cavity structure 3A may include both a hollow core of the optical fiber 3 and a hole cladding structure.

Furthermore, in FIG. 2C, a sectionally cylindrical and conical embodiment of the opening 16 can be seen. This embodiment ensures that the light 7 does not strike the hole element 15, as the opening 16 in a conical section 16B opens in the direction of the interior space IA ,

For the sake of completeness, it is noted that various aspects of the exemplary embodiments may be combined in different ways. For example, the focusing lens in the structure of Figures 2A and 2C can be used or the conical opening shape can be used in the structure of Figures 1A and 2A. Furthermore, the gas control opening may be provided in the hole element, the rear wall or the optical element.

Fig. 3 illustrates the implementation of a method for setting fixed operating parameters in the optical fiber unit 1, each with an end cap 11 at each end, which are constructed here by way of example according to the embodiment of Figures 1 A and 1B.

For setting the gas parameters, the optical fiber unit 1 is in a defined environment (illustrated by way of example with reference to a schematic housing 31) with adjustable base. ren gas parameters, ie, with adjustable gas types (eg air or inert gas) and with adjustable pressure (eg vacuum to several bar overpressure). FIG. 3 clarifies the setting of the gas parameters by means of a gas unit 33.

The desired gas state can be set in the housing 31 and thus in the optical fiber unit 1. For example, the housing 31 may first be substantially evacuated before it is flooded with a selected gas at a specific gas pressure. This can be done, for example, under defined coupling of laser light into the optical fiber unit 1 (not shown) in order to be able to set the desired optical parameters of the optical fiber unit 1 in a controlled manner.

If the desired gas state is stationary in the optical fiber unit 1, the gas control holes 25 can be closed, for example, by fusing with a laser beam 35. For this purpose, the housing 31 is provided, for example, with a window 37 for irradiating the laser beam 35 onto the gas control holes 25. FIG. 3 diagrammatically shows, by way of example, melting zones 39 at the inlet of the various gas control holes 25.

Manufacturing an optical fiber unit having at least one configured fiber end of an optical fiber generally includes attaching the hollow end cap 11 to the end surface 5 of the optical fiber 3, the end surface 5 having an inner region 5A, and positioning the hole member 15 with respect to the optical fiber 3 the end surface 5 of the optical fiber 3 abuts against the abutment surface 15C. As a result, the light 7 can be coupled into or out of the optical fiber 3 through the optical element 17, an inner space 11A of the end cap 11 and the opening 16.

For example, a fully assembled end cap 11 may be attached to the optical fiber 3. Alternatively, at first, only the hole member 15 may be fixed to the fiber end surface 5, and then, e.g. with careful alignment of the optical element, the other components of the end cap are attached. In both manufacturing methods, the optical element may be oriented with respect to the fiber end e.g. be aligned with the help of stops.

Exemplary materials for the components of the end cap are various types of glass, such as quartz glass and BK7 glass, or sapphire, etc., which allow laser welding, for example. In particular, if identical or similar materials are used for the various components, the end cap can be considered monolithic and preferably has the same or essentially the same coefficients of expansion and / or thermal conductivities for the different components. Particularly in the case of laser glass welding, the various optical elements can first be aligned with each other, for example, an adjustment light beam can be used to verify the correct orientation. Then the different components are welded together. In particular glass-glass welds ensure sufficient gas tightness with appropriate strength without introducing foreign materials such as adhesives that can change the set gas mixture inside the end cap and in the hollow core by Ausgasungsprozesse undesirable manner.

Herein, for a gas-tight connection-based end cap, the aspect "gas-tight" is understood to mean that the leakage rate from the inside of the end cap to the outside is smaller than the leaking rate from the hollow core of the fiber through the fiber sheath to the outside Thus, in general, an end cap is gas tight unless it is essentially the limiting element to the gas tightness of the fiber optic unit.

In the exemplary embodiments illustrated, the opening of the hole element and the optical element are arranged in a beam path of the light entering or leaving the optical fiber. In particular, the beam path runs without any optical deflection in the interior of the end cap. In alternative embodiments, a folding or deflection of the beam path in the interior can take place with a mirror arrangement. For example, a deflection of e.g. 90 °, so that the light passes laterally through the end cap.

In some embodiments, the end cap (some of its components) may also be glued. Thus, for example, the hole member 15 and the hollow body 13 may be made of metal, in which case a gas-tight connection between the hole member 15 and the cladding region 5B of the optical fiber 3 is ensured with corresponding bonds.

It is explicitly emphasized that all features disclosed in the description and / or the claims are considered separate and independent of each other for the purpose of the original disclosure. tion as well as for the purpose of limiting the claimed invention, regardless of the combinations of features in the embodiments and / or the claims to be considered. It is explicitly stated that all range indications or indications of groups of units disclose every possible intermediate value or subgroup of units for the purpose of the original disclosure as well as for the purpose of restricting the claimed invention, in particular also as a limit of a range indication.

Claims

claims

1. Optical fiber unit (1) with

an optical fiber (3) which has a light-guiding region (27) and at one fiber end an end surface (5) for coupling light (7) into the light-guiding region (27) or coupling light (7) out of the light-guiding region (27) wherein the light (7) enters or leaves the optical fiber (3) through an inner region (5A) of the end surface (5), and

a hollow end cap (11) having a hole member (15) having a stopper surface (15C) and an opening (16) and an optical element (17), wherein

the hole member is fixed to the optical fiber (3) such that the end surface (5) of the optical fiber (3) abuts against the stop surface (15C) and the light (7) from the hollow end cap (11) passes through the opening (16) the light-conducting region (27) can be coupled in or out of the light-guiding region (27) through the opening (16) in the hollow end cap (11) can be coupled out.

2. Optical fiber unit (1) according to claim 1, wherein

the optical fiber (3) has a cavity structure (3A) comprising the light guiding region (27) which terminates at the end surface (5) in the inner region (5A), and a cladding structure (3B) having a cladding region surrounding the inner region (5A) (5B) is associated with the end face (5), and

the hole member (15) is fixed to the optical fiber (3) such that an inner space (11A) of the hollow end cap (11) having the cavity structure (3A) in the optical fiber (3) passes through the opening (16) of the hole member (15 ) fluid is connected.

3. optical fiber unit (1) according to claim 1 or 2, wherein

the end face (5) of the optical fiber (3) on the abutment surface (15C) of the hole member (15) and / or

the sheath structure (3B), in particular the outer sheath side of the optical fiber (3), on an inner side of a fiber attachment portion (16C) of the opening (16) and / or

the jacket structure (3B), in particular an outer jacket side of the optical fiber (3), on the hole element (15), in particular on a rear side (15B) of the hole element (15) via a fillet connection,

is attached, in particular (glass) welded or glued.

4. optical fiber unit (1) according to one of the preceding claims, wherein

the light-guiding region (27) of the optical fiber (3) is designed as a hollow core whose access from the opening (16) is kept free, and / or

the cavity structure (3A) further comprising a hole cladding structure (29) disposed between the light guiding portion (27) of the optical fiber (3) and the cladding structure (3B) and terminating at the end surface (5) in the inner region (5A), and

in particular, the access to the perforated shell structure (29) from the opening (16) is kept free.

5. optical fiber unit (1) according to one of the preceding claims, wherein

the hole element (15) consists of a material which can be welded to the optical fiber (3), in particular the sheath structure (3B), such as glass, e.g. Quartz glass or BK7 glass, or sapphire.

6. Optical fiber unit (1) according to one of the preceding claims, wherein

the end cap (11) comprises a hollow body (13), the hole element (15) with the opening (16) and the optical element (17), in particular transparent to the light guide fiber (3), and

wherein in particular the hole element (15) and the optical element (17) at opposite ends (19A, 19B) of the hollow body (13) are connected to the hollow body (13).

7. optical fiber unit (1) according to claim 6, wherein

the hollow body (13), the hole element (15) and / or the optical element (17) are made of materials which can be welded together, such as glass, e.g. Quartz glass or BK7 glass, or sapphire, and are interconnected, in particular (glass) welded, or glued.

8. optical fiber unit (1) according to claim 6 or 7, wherein

the hollow body (13) is tubular, in particular with a circular or polygonal cross-section, and / or

wherein a length of the hollow body (13) is such that light (7) emerging from the inner region (5A) expands in the inner space (HA) in such a way that the optical element (17) with an intensity which is below a damage threshold intensity of the optical element (17), and / or

wherein, in the case of an optical element (17) designed as a focusing lens, the length of the hollow body (13) is within the focal length of the focusing lens so that the optical fiber unit (1) is operable with a collimated input beam and / or a collimated output beam.

9. optical fiber unit (1) according to one of the preceding claims, wherein

the optical element (17) is designed as a plane-parallel plate (17B), wedge, lens (17A), diffractive optical element, wave plate or axicon.

10. Optical fiber unit (1) according to one of the preceding claims, wherein

the optical fiber unit (1) is gas-tight and

in particular components of the optical fiber unit (1), in particular the hole element (15) and the optical fiber (3), and / or components of the end cap (11), in particular the hollow body (13), the hole element (15) and / or the optical element (17) are connected to each other gas-tight, in particular gas-tight (glass) welded or glued gas-tight.

11. Optical fiber unit (1) according to one of the preceding claims, wherein

the hole element (15) plate-shaped, in particular as a circular disc in which the opening (16) is arranged centrally, is formed and / or

wherein the opening (16) as a cylindrical hole (16 A) or as in the direction of the interior (11 A) in diameter enlarging, in particular conically opening hole (16 B) is formed and / or

wherein a central axis (21) of the inner region (5A) is aligned along an axis of symmetry (22) of the end cap (11).

12. Optical fiber unit (1) according to one of the preceding claims, wherein

the opening (16) is at least as large in diameter as a diameter of the light-guiding region (27) and in particular as large as a diameter of the perforated shell structure (29) and / or

wherein the opening (16) in diameter is less than 1 mm, in particular less than 500 μιη, and is for example in the range of 50 μιη to 500 μιη, and / or wherein at least one of the opening (16) surrounding region of an inner side (15A) of the hole member (15), in particular in the region of the light guide fiber (3) provided for wavelength, reflective coated, in particular reflective coated.

13. Optical fiber unit (1) according to one of the preceding claims, wherein

the end cap (11) further has a rear wall (30), which is arranged with respect to the inner space (11A) on a rear side (15B) of the hole element (15) and with an outer sheath side of the optical fiber (3) and the hollow body (13 ) and / or the hole element (15), in particular gas-tight, is connected.

14. Optical fiber unit (1) according to one of the preceding claims, wherein

at least one gas control hole (25) in the end cap (11) is provided, that the environment with the interior space (11 A) connects fluid, the gas control hole (25) in particular has an opening diameter, for example by means of laser-based material processing such as laser melting, is closable, and / or

wherein the optical fiber unit (1) has an end cap (11) at each end of the optical fiber (3), wherein in particular at least one of the end caps (11) has a gas control hole (25) closed, for example by means of laser-based material processing.

15. Optical fiber unit (1) according to one of the preceding claims, wherein

the end cap (11) is gas-tight except for the opening (16) and optionally the at least one gas control hole (25) and / or

wherein the opening (16) of the hole element (15) and the optical element (17) in a beam path of the optical fiber (3) entering or exiting light (7) are arranged.

16. A method for producing an optical fiber unit having at least one configured fiber end of an optical fiber (3), in particular an optical fiber unit (1) according to one of the preceding claims, comprising the steps:

Mounting a hollow end cap (11) comprising a hole member (15) having a stopper surface (15C) and an opening (16), and an optical element (15) transparent to light to be guided by the optical fiber (3) 17), on the optical fiber (3), wherein the optical fiber (3) has a light-guiding region (27) and at the fiber end an end-face che (5) for coupling light (7) in the light-guiding region (27) or coupling of light (7) from the light-guiding region (27), and

Positioning the hole element (15) with respect to the optical fiber (3) so that the end face (5) of the optical fiber (3) abuts against the abutment surface (15C) so that the light (7) passes through the optical element (17); 11A) of the end cap (11) and the opening (16) in the optical fiber (3) can be coupled or decoupled from this.

17. The method of claim 16, wherein

at least one gas control hole (25) is provided in the end cap (11) which fluidly connects an external environment to the interior space (HA), further comprising the steps of:

Bringing the interior (HA) of the end cap (11) and the associated with this fluid cavity structure (3A) in a defined gas and / or pressure state using the at least one gas control hole (25) and

Closing the at least one gas control hole (25), in particular by means of laser-based material processing such as laser melting.