Disconnection device and fiber optic connector with such a

Abstract

Decoupling device for decoupling an optical signal from a hollow-core optical waveguide, wherein the decoupling device comprises: a hollow-core optical waveguide with a first end section, a second end section, each comprising an end face of the optical waveguide, and a main section arranged between the first end section and the second end section, wherein the hollow-core optical waveguide has a core designed to receive light signals and a cladding surrounding the core, and wherein the hollow-core optical waveguide has a length l, the core having a constant, non-circular cross-sectional area within the main section.

Description

[0001] The present invention relates to a decoupling device for extracting an optical signal from a hollow-core optical waveguide. The decoupling device detects the light signals emerging from the hollow-core optical waveguide and forwards them for further processing, for example to another optical waveguide, a multiplexer, a demultiplexer, an optical sensor, or a grating coupler.

[0002] The decoupling device features: - a hollow-core optical waveguide with a first end section, a second end section, each comprising an end face of the optical waveguide, and a main section arranged between the first end section and the second end section, wherein the hollow-core optical waveguide has a core designed to receive light signals and a cladding surrounding the core, and wherein the hollow-core optical waveguide has a length l, the core having a constant, non-circular cross-sectional area within the main section. - a lens with an entrance surface facing the first end section and an exit surface facing away from the second end section, - a holder that supports the first end section and the lens, the lens being configured and arranged such that a beam of light emerging from the first end section strikes the entrance surface and is projected as a convergent beam onto the exit surface; an optical waveguide with a core designed to receive light signals and a cladding surrounding the core, the optical waveguide having length l and comprising a first and a second end section, each comprising an end face of the optical waveguide, and a main section arranged between the end sections. The core within the main section has a constant cross-sectional area.

[0003] Optical fibers are well-known. In the most common cases, these fibers consist of an inner glass core and a surrounding cladding with a slightly lower refractive index. Total internal reflection at the interface between the cladding and the glass core guides the radiation. Such fibers form the core of today's high-performance telecommunications networks. However, these solid-core fibers have limited network capacity, so that with further growth in the amount of data to be transmitted, a capacity bottleneck is likely. Capacity improvements for these optical fibers are not to be expected, partly due to the nonlinear Shannon limit.

[0004] Therefore, hollow-core fibers, or hollow-core optical waveguides, have been receiving increasing attention for several years. In contrast to the solid-core fibers described above, hollow-core fibers, in which light is guided over long distances in air or a vacuum, offer several advantages. The air-filled core is surrounded by a microstructured glass cladding, which enables a high light concentration.

[0005] Of particular interest are the so-called NANFs (Nested Antiresonant Nodeless Fibers), a special type of hollow-core fiber exhibiting exceptionally low attenuation and high efficiency in light guidance. These NANFs consist of a central, hollow core surrounded by several nested cylindrical glass tubes attached to the inside of a glass sheath. Typically, there are five or six such glass tubes, with their diameters and spacing precisely calibrated to achieve antiresonance in the transverse plane. This reduces the overlap between the light source and the glass, effectively trapping the light within the hollow core, which, due to its construction, is no longer circular.

[0006] While the light guidance within the fiber is excellent, significant losses regularly occur when the light signals are extracted from the fiber or transmitted to, for example, an adjacent fiber. Specially designed connectors are used here, but these—like any component in the light beam—exhibit insertion loss. Therefore, when using hollow-core optical fibers, the performance of the entire system is limited less by the fiber itself and more by the insertion loss of other required components.

[0007] Information carried by a beam of light is thus projected from the hollow-core fiber onto the exit surface by the output coupling device and can be further processed or transmitted there. For some applications, it is preferred if the beam of light is focused onto the exit surface of the lens. Preferably, the lens is arranged and designed such that the diameter of the beam of light on the exit surface is less than 100 µm, particularly preferably less than 25 µm, and ideally less than 10 µm.

[0008] Such a coupling device in the form of an optical fiber connector is already known from EP 4 220 259 A1, the contents of which are incorporated here by reference. The detailed construction and the arrangement of the lens are described in detail in this document.

[0009] The existing decoupling device works very satisfactorily. Nevertheless, it can be improved.

[0010] German patent DE 10 2022 102 057 A1 describes a fiber optic connector and an associated coupling device for optically connecting two optical fibers. The connector holds the fiber end and uses a lens positioned in front of it, which projects the beam of light emerging from the first optical fiber as a convergent beam. The aim is a low-loss, pluggable coupling even with different field diameters.

[0011] EP 3 839 586 A1 discloses optical components based on a hollow-core photonic crystal fiber (HC-PCF) for broadband radiation sources, particularly for metrological applications in semiconductor lithography. Among other things, gas-filled fiber arrangements with transparent end caps or cladding and sleeve arrangements are described; internal capillaries may be collapsed at the ends.

[0012] US patent 2017 / 0160467 A1 concerns the structure of anti-resonant hollow-core fibers. It describes a ring-shaped cladding element with several second, spaced-apart tubular elements that define the core, with further tubular elements nested within each of these elements. This design aims to achieve low attenuation combined with a large usable bandwidth.

[0013] Based on the described prior art, it is therefore an object of the present invention to provide a decoupling device in the use of which the insertion loss into the subsequent element is reduced.

[0014] According to the invention, this problem is solved by providing a first cross-sectional area of ​​the core in the main section that differs in size and / or shape from a second cross-sectional area of ​​the core on the end face of the first end section, wherein the second cross-sectional area is larger than the first cross-sectional area and / or the first cross-sectional area has a shape in which a circle with a maximum diameter d 1max can be inscribed, and the second cross-sectional area has a shape in which a circle with a maximum diameter d can be inscribed. 2max can be inscribed, whereby d 1max < d 2max is.

[0015] Tests have shown that changing the cross-sectional area of ​​the core in the end section can significantly reduce the insertion loss of the light signal into the subsequent element. Depending on the application, the second cross-sectional area of ​​the core in the first end section must therefore be adjusted accordingly to achieve optimal results.

[0016] The observed effect is particularly pronounced in optical fibers where the core within the main section has a non-circular cross-section. This non-circular cross-section design can offer various advantages in light guidance, such as improved mode control, reduced polarization dependence, and improved bending insensitivity. Such optical fibers are used, for example, in communication networks that require high bandwidth and low transmission losses.

[0017] Preferably, the second cross-sectional area is at least 10% larger than the first cross-sectional area.

[0018] Particularly in the case of hollow-core fibers, the cross-sectional area of ​​the core has an irregular shape, as it is only bounded by the glass tubes. However, a central section of the core emerges, which can best be characterized by an inscribed circle that touches the glass tubes. In a preferred embodiment, the first cross-sectional area has a shape in which a circle with a maximum diameter d is inscribed. 1max can be inscribed, and the second cross-sectional area a shape into which a circle with a maximum diameter d can be inscribed. 2max can be inscribed, whereby d 1max < d 2max is. Preferably, d 2max at least 10% and preferably at least 20% larger than d 1max .

[0019] Furthermore, it has been shown that it is advantageous if the shape change does not occur abruptly, but gradually in the end section, i.e., if a shape change of the core already takes place at a certain distance from the end face. Therefore, in a preferred embodiment, it is provided that in the first end section from the main section towards the end face, the cross-sectional area of ​​the core increases monotonically, preferably in the first end section from the main section towards the end face, the cross-sectional area of ​​the core increases strictly monotonically. With a monotonical increase in the cross-sectional area, intermediate regions are also possible in which the cross-sectional area of ​​the core remains constant, whereas with a strictly monotonical increase, the cross-sectional area increases continuously.

[0020] Furthermore, it is advantageous if, in the first end section of the main section in the direction of the end face, the maximum diameter of a circle inscribed in the cross-sectional area increases monotonically, preferably with the deformation, i.e. the increase in the diameter of the inscribed circle, increasing strictly monotonically.

[0021] Furthermore, it is advantageous if the first end section in the direction of the main section has a length I E has a thickness of at least 30 µm, preferably at least 50 µm, and particularly preferably at least 100 µm. In a preferred embodiment, the length of the end section is less than 1 mm, preferably less than 500 µm, and best of all between 100 and 300 µm.

[0022] Even if the shape of the core in the first end section differs from the shape of the core in the main section, it is advantageous if the outer diameter of the mantle in the main section corresponds to the outer diameter of the mantle in the first end section.

[0023] In another preferred embodiment, the hollow core fiber is provided to be a photonic crystal fiber or an antiresonance fiber.

[0024] Therefore, the mantle preferably has a structure that exhibits either a photonic band gap or an antiresonant property.

[0025] In a photonic crystal fiber, light is guided through band gaps. These fibers have a core surrounded by a regular structure of tiny air channels—part of the cladding. The band gaps arise when the periodic pattern of the air channels prevents certain wavelengths of light from propagating in specific directions, thus trapping the light within the core. This allows for very precise control over the guided wavelengths.

[0026] In an antiresonant fiber, a hollow or gas-filled core is located at the center of the fiber. This core is surrounded by a structure that serves as a cladding. At least part of this structure is made of materials with different refractive indices. They are designed to be antiresonant at specific wavelengths.

[0027] The core principle behind antiresonance fibers is the use of antiresonant effects to guide light within the hollow core. Light striking the surrounding structure is reflected instead of being absorbed or transmitted. This occurs because the dimensions of the structure are chosen to generate destructive interference at specific wavelengths.

[0028] As already stated, it is advantageous that the structure has a plurality of cylindrical tubes, wherein capillaries with an outer diameter that is smaller than an inner diameter of the tubes are particularly preferably arranged in the cylindrical tubes.

[0029] In this embodiment, it is advantageous if the tubes, and preferably also the capillaries, are not circular in the second cross-sectional area and are circular in the first cross-sectional area. The enlargement of the core is thus achieved essentially by deformation of the tubes and capillaries.

[0030] Furthermore, the insertion loss can be further reduced if the lens and its entrance surface are designed and arranged in such a way that the focal point of the lens is not on the end face, but in the core of the hollow core fiber, preferably with the focal point being located in the main section or on a boundary between the first end section and the main section.

[0031] In a further preferred embodiment, the lens is designed as a 2-section lens and has at least two sections, namely a first section which is bounded by the entrance surface and a second section which is bounded by the exit surface, wherein the refractive index n1 of the first section differs from the refractive index n2 the second section differs.

[0032] For special applications, more than two sections may be provided. For example, the lens may have three sections, each differing in its refractive index.

[0033] If the lens consists of several parts, these parts can be bonded together with an adhesive. The thin adhesive layer then does not constitute a lens section within the meaning of the present invention. In a preferred embodiment, therefore, each section of the lens has a thickness of at least 0.2 mm and preferably at least 0.3 mm, so that the beam of light travels a path of at least 0.2 mm or 0.3 mm, respectively, in each section when passing through the lens.

[0034] When a beam of light exiting a hollow-core optical fiber is focused onto the exit surface of the lens, a second waveguide, intended to receive the signal, can be positioned with its end face directly adjacent to the lens's exit surface. However, unwanted back reflections occur at the interface between the lens and the second waveguide, which, among other things, reduce the signal strength.

[0035] Therefore, the lens is preferably designed as a two-section lens with two sections having different refractive indices. In a preferred embodiment, the refractive index n2 of the second section is smaller than the refractive index n1 of the first section, preferably being less than 1.5 and particularly preferably 1.5 > n2 > 1.4. This choice of refractive index has proven effective. The refractive index n2 can preferably be matched to the refractive index of a solid core fiber used as the second optical waveguide.

[0036] For example, the first section can be made of a different material than the second section. It is also advantageous if the refractive index n1 within the first section and / or the refractive index n2 within the second section is constant, as this simplifies the fabrication of the two-section lens. It has been found that, particularly preferably, the second section has a greater length in the direction of propagation than the first section.

[0037] In a further preferred embodiment, the two-section lens is formed in two parts: a first part comprising the first section and a second part comprising the second section. The parts can therefore be manufactured separately and positioned side by side. Particularly preferably, the two parts of the two-section lens have contact surfaces facing each other, where the two parts are in contact either directly or via an interposed adhesive layer. This allows a beam of light emerging from the first optical waveguide associated with the two-section lens to strike the entrance surface of the first part and pass through the contact surfaces into the second part. The second part can, for example, be a glass body with parallel or nearly parallel entrance and exit surfaces. It is not necessary for each part to have a curved surface.The essential point is that the combination of the two parts, i.e., the compound two-section lens, generates a convergent beam of light from the light signal emerging from the end face of the first optical waveguide. In a preferred embodiment, the two parts are bonded together, forming a thin layer of adhesive between them. Alternatively, the two parts can also touch directly at their contact surfaces without an adhesive layer.

[0038] Finally, the present invention also relates to a fiber optic connector for a fiber optic connector for optically connecting a hollow-core optical fiber to another optical fiber. The aforementioned problem is solved here by the fact that the fiber optic connector has the coupling device described above according to the invention.

[0039] Such a fiber optic connector enables the connection of a hollow-core fiber to a solid-core fiber. One problem here is that hollow-core fibers have a significantly larger mode field diameter than solid-core fibers. Using the described fiber optics can further increase the mode field diameter, especially in the terminal segment, exacerbating the problem. However, the described fiber optic connector is capable of accommodating even such large differences in mode field diameter.

[0040] It is of course also possible to use the fiber optic connector to connect the hollow core fiber to another hollow core fiber.

[0041] Further advantages, features and applications of the present invention will become clear with reference to the following description of a preferred embodiment and the accompanying figures. These show: Fig. 1 a longitudinal section of an optical fiber connector according to the invention with a hollow core optical fiber, Fig. 2 a detailed enlargement of Fig. 1, Fig. 3 Two cross-sectional views through the hollow core optical waveguide, Fig. 4 detailed enlargements of the cross-sectional views of Fig. 4, Fig. 5 a longitudinal section view through the hollow core optical waveguide and Fig. 6 a schematic representation of a coupling element according to the invention.

[0042] In Fig. Figure 1 shows a longitudinal section of an output coupling device according to the invention, designed as a fiber optic connector.

[0043] The optical fiber connector 1 contains one end of a hollow-core optical fiber 2. This end is held in a through-channel of a holder 3. A lens 4 is also provided.

[0044] A light beam or beam 8 emerges from an end face 7 of the hollow-core optical waveguide 2 and spreads out towards the lens 4. The lens 4 is configured such that it projects the light beam 8, which strikes an entrance surface of the lens 4, as a convergent beam onto the exit surface of the lens 4 and preferably focuses it. Ideally, the exit surface is located at the focus of the convergent beam. An arrangement outside the focus is also possible, although this is disadvantageous.

[0045] The lens has two sections 5, 6 with different refractive indices.

[0046] Although the preferred embodiment describes a light beam 8 exiting the end face 7 of the hollow-core optical waveguide 2 and striking the entrance face of the lens 4, the signal path can also be reversed. A signal coupled in via the exit face of the lens 4 can also be imaged onto the end face 7 of the hollow-core fiber 2.

[0047] It is clearly evident that the lens 4 consists of two parts, with the first part forming the first section 5 and the second part forming the second section 6. The refractive index n1 in the first section 5 is constant and greater than the refractive index n2 in the second section 6. The second section 6 has a length in the direction of propagation of the light ray that is significantly greater (in the example shown, more than twice as long) than the length of the first section 5 in the direction of propagation of the light ray.

[0048] The first section 5 has the inlet surface and is bonded to the second section 6. The second section 6 has the outlet surface. It is clearly evident that the diameter of the second section 6 is larger than the diameter of the first section 5. The diameter of the second section 6 essentially corresponds to the inner diameter of the through-channel of the holder 3. This has the advantage that the lens 4, with sections 5 and 6 already connected, can be inserted into the through-channel of the holder 3 and is then already correctly positioned laterally.

[0049] In Fig. 2 is a close-up of Fig. Figure 1 shows the hollow-core fiber or hollow-core optical waveguide 2, which is held in the holder 3 and has the end face 7. A beam of light 8 is also shown schematically. The hollow-core fiber 2 has a core 15, which is designed to receive light signals, and a cladding that surrounds the core 15. The hollow-core fiber 7 has a main section 10, which is bounded by a first end section 9. The hollow-core fiber 7 can be very long, e.g., several kilometers long. A second end section is located at the end of the main section 10 opposite the first end section 9 and is therefore not shown in the figure.

[0050] In Fig. 2. It can also be seen that the core has a larger extent in the region of the first terminal section 9 than in the region of the main section 10. In Fig. Figure 2 also indicates two cross-sections through the hollow core fiber 2, which are in Fig. 3 are shown enlarged.

[0051] In Fig. Figure 3 shows on the left a first cross-section of the hollow core fiber 2 in the main section 10 and on the right a second cross-section of the hollow core fiber 2 in the first end section 9.

[0052] The hollow-core optical waveguide has a core 15, which is designed to receive light signals, and a cladding that surrounds the core 15. The cladding, in turn, consists of a sheath 11 and an antiresonant structure 16. The antiresonant structure 16 consists of a plurality of cylindrical tubes 12 in which capillaries 13 are arranged. In the illustrated embodiment, further capillaries 14 with an even smaller outer diameter are contained within the capillaries 13. The light is guided within the core 15, which is not circular, with the result that the light beam within the hollow-core optical waveguide 2 also exhibits a non-circular intensity distribution.

[0053] In the right view of Fig. 3 the tubes 12 and capillaries 13 and 14 are strongly deformed, so that the area occupied by the core 15 has become larger.

[0054] In Fig. 4 are the same views as in Fig. Figure 3 shows that the enclosing 11 has been omitted to allow for larger cross-sections. Since the area of ​​the core 15, i.e., the area not occupied by the enclosing 11 and the antiresonant structure 16, is difficult to determine, a circle with maximum diameter has been inscribed within the area of ​​the core 15 in each figure. The diameter d 1max The diameter of the section in the left cross-section from main section 10 is significantly smaller than the diameter d. 2max of the right cross-section from the first end section 9.

[0055] In Fig. Figure 5 shows a longitudinal section of a portion of the hollow core fiber 2, which comprises the first end section 9 and part of the main section 10. The core 15 widens towards the end face 7. In the embodiment shown, the cross-sectional area of ​​the core 15 thus increases strictly monotonically in the end section 9 towards the end face 7.

[0056] In Fig. Figure 6 schematically illustrates the structure of an output coupling device according to the invention. The essential elements of the output coupling device are the hollow core fiber 2 with a specially shaped first end section 9 and the lens 4. A light beam 8 guided in the hollow core fiber 2 is schematically indicated in the illustration. The light beam 8 exiting the first end section of the hollow core fiber 2 strikes the entrance surface of the lens 4 and is projected by it as the convergence of the beam onto the exit surface of the lens 4. The lens 4 is in Fig.6 is not designed as a 2-section lens. The lens 4 is designed and arranged such that the focus 17 of the lens 4 lies within the hollow core fiber 2, specifically, in the example shown, within the main section 10 or in the immediate vicinity of the connection between the main section 10 and the first end section 9.

[0057] The described widening of the core 15 in the first end section 9, which faces the lens 4, makes the light-guiding core 15 rounder, so that when coupled to a further element, an angular orientation around the optical waveguide axis can usually be omitted. Reference symbol list 1 fiber optic connector 2 hollow core optical waveguides 3 brackets 4 lenses 5 first section 6 second section 7 Front surface 8 beams 9 first final section 10 Main Section 11. Envelope 12 tubes 13, 14 capillaries 15 core 16 antiresonant structure 17 Focus

Claims

[1] Coupling device for coupling an optical signal from a hollow core optical waveguide (2), wherein the coupling device comprises: - a hollow-core optical waveguide (2) with a first end section (9), a second end section, each comprising an end face of the optical waveguide, and a main section (10) arranged between the first end section (9) and the second end section, wherein the hollow-core optical waveguide (2) has a core (15) intended to receive light signals and a cladding surrounding the core (15), and wherein the hollow-core optical waveguide (2) has a length l, wherein the core (15) has a constant, non-circular cross-sectional area within the main section (10), - a lens (4) with an entrance surface facing the first end section (9) and an exit surface facing away from the second end section, - a holder (3) which holds the first end section (9) and the lens (4), wherein the lens (4) is designed and arranged such that a beam of rays (8) exiting from the first end section hits the entrance surface and is projected as a convergent beam of rays (8) onto the exit surface, characterized by , that a first cross-sectional area of ​​the core in the main section (10) differs in size and / or shape from a second cross-sectional area of ​​the core (15) on the end face (7) of the first end section (9), wherein the second cross-sectional area is larger than the first cross-sectional area and / or the first cross-sectional area has a shape in which a circle with a maximum diameter d 1max can be inscribed, and the second cross-sectional area has a shape in which a circle with a maximum diameter d can be inscribed. 2max can be inscribed, whereby d 1max < d 2max is. [2] Disconnecting device according to claim 1, characterized by , that in the first end section (9) of the main section (10) in the direction of the end face (7) the size of the cross-sectional area of ​​the core (15) increases monotonically, wherein preferably in the first end section (9) of the main section (10) in the direction of the end face (7) the size of the cross-sectional area of ​​the core (15) increases strictly monotonically. [3] Disconnecting device according to claim 1 or 2, characterized by , that in the first end section (9) of the main section (10) in the direction of the end face (7) the maximum diameter of a circle inscribed in the cross-sectional area increases, wherein preferably in the first end section (9) of the main section (10) in the direction of the end face (7) the maximum diameter of a circle inscribed in the cross-sectional area increases monotonically and particularly preferably strictly monotonically. [4] Disconnecting device according to any one of claims 1 to 3, characterized by , that the first end section (9) in the direction of the main section (10) has a length I E has a thickness of at least 30 µm, preferably at least 50 µm and particularly preferably at least 100 µm. [5] Disconnecting device according to any one of claims 1 to 3, characterized by , that the first end section (9) in the direction of the main section (10) has a length l E has a size smaller than 1 mm, preferably smaller than 500 µm and best between 100 and 300 µm. [6] Disconnecting device according to any one of claims 1 to 5, characterized by , that an outer diameter of the mantle in the main section (10) corresponds to an outer diameter of the mantle in the first end section (9). [7] Disconnecting device according to any one of claims 1 to 6, characterized by that the hollow core fiber is a photonic crystal fiber or an antiresonance fiber. [8] Disconnecting device according to claim 7, characterized bythat the mantle has a structure which either has a photonic band gap or an antiresonant property. [9] Disconnecting device according to claim 8, characterized by , that the structure has a plurality of cylindrical tubes (12), wherein preferably capillaries (13,14) with an outer diameter that is smaller than an inner diameter of the tubes (12) are arranged in the cylindrical tubes (12). [10] Disconnecting device according to claim 9, characterized by that the tubes (12) and preferably also the capillaries (13,14) are not circular in the second cross-sectional area and are circular in the first cross-sectional area. [11] Disconnecting device according to any one of claims 1 to 10, characterized by, that the lens (4) and its entrance surface are designed and arranged such that the focal point of the lens (4) is not on the end face (7) but in the core (15) of the hollow core fiber, preferably the focal point being in the main section (10) or on a boundary between first end section and main section (10). [12] Disconnecting device according to any one of claims 1 to 11, characterized by , that the lens (4) is designed as a 2-section lens and has at least two sections, namely a first section (5) which is bounded by the entrance surface and a second section (6) which is bounded by the exit surface, wherein the refractive index n1 of the first section (5) differs from the refractive index n2 of the second section (6). [13] Optical fiber connector for an optical fiber connector for optically connecting a hollow core optical fiber (2) to another optical fiber, characterized by , that the optical fiber connector (1) has the coupling device according to one of claims 1 to 12.

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