Reduced reflection optical fiber connectors and optical fiber connectors with such a

Abstract

Optical fiber plug for an optical fiber connector for optically connecting a number N of first optical fibers to a number M of second optical fibers, wherein the optical fiber plug (1, 1', 101, 101') holds an end section (3) of each first optical fiber (4) with an optical fiber end face (5) and has a number N of lenses (6, 6'), each having an entrance surface (11) facing one of the first optical fibers and an exit surface (12) facing away from this first optical fiber, wherein each lens (6, 6') is assigned to exactly one first optical fiber and each optical fiber is assigned to exactly one lens (6, 6'), and the lenses (6, 6') are designed and arranged such that a beam emerging from one of the first optical fibers in a propagation direction is incident on the entrance surface (11) of the assigned lens (6,6') and is projected as a convergent beam onto the exit surface (12) of the associated lens (6, 6'), wherein at least one lens (6, 6') and preferably each lens is designed as a 2-section lens (6, 6') and has at least two sections, namely a first section (123, 223), which is delimited by the entrance surface (11), and a second section (124, 224), which is delimited by the exit surface (12), wherein the refractive index n, 1 of the first section (123, 223) differs from the refractive index n 2 of the second section (124, 224).

Description

[0001] The present invention relates to an optical fiber connector and an optical fiber plug for an optical fiber connector for optically connecting two or more optical fibers.

[0002] Optical fibers are cables used to transmit light signals. Optical fibers often contain quartz glass fibers. They are also colloquially referred to as fiber optic cables, even if they do not contain any glass fibers.

[0003] Such optical fibers are used particularly in communications technology for transmitting information signals. However, such optical fibers are not infinitely long, so it is necessary to connect several optical fibers together. Plug-in connectors or splice connections are often used for this purpose. During splicing, the fiber ends of two optical fibers to be joined are melted and pushed together. The connectors are generally used to detachably connect optical fibers. Plug-to-plug connections are usually used here, which are designed to minimize signal attenuation. However, the current technology always connects optical fibers with the same diameters (field diameter) that can be used for signal transmission.

[0004] A distinction is usually made between single-mode and multimode optical fibers. However, these differ in their field diameters.

[0005] However, hollow fibers with one or more cavities in their cross-section have also been known for some time. These can also be used to conduct light. Such hollow fibers, also called hollow-core fibers, generally have advantages over solid-core fibers. However, only recently have hollow-core fibers been able to be produced at acceptable costs in long lengths and with sufficient quality. Therefore, solid-core optical fibers have been and continue to be used.

[0006] Optical signal transmission systems that use hollow fibers already exist. However, connecting multiple hollow fibers together is not easy. Furthermore, there is no known way to cost-effectively connect a hollow-core fiber to a solid-core fiber without unwanted back reflections, so the optical fibers cannot be used in combination. This is due, among other things, to the fact that the usable diameter (field diameter) for light transmission in hollow-core fibers is approximately twice as large as the field diameter in solid-core fibers. This has slowed the spread of hollow-core fibers.

[0007] From US 6 282 347 B1 an optical fiber connector is known which comprises a first optical fiber, a first convex lens which focuses the light emitted by the first optical fiber, a second convex lens which further focuses the light focused by the first lens, and a second optical fiber which receives the focused light beam from the second lens.

[0008] From US 4,563,057 A a fiber optic cable connector is known which serves to couple two optical fibers which are each fixed in holders, wherein each holder has a magnifying lens which is optically aligned with the end of the respective fiber so that the lenses focus the ends of the fibers in an enlarged manner to a predetermined position, wherein a fastening device connects the holders to one another in such a way that the magnified images of the fibers overlap and thereby an optimal coupling of the adjacent fiber ends is to be achieved.

[0009] Furthermore, US 2012 / 0020619 A1 describes an optical interface that uses optical elements (e.g., lenses) to image rather than collimate light beams, wherein each connector includes a lens that focuses a diverging light beam from an origin to an image point at a predetermined distance from the lens, and the connector systems can be coupled either to a similar optical connector or to a connector without a lens by positioning the receiving optical component at the image point of the focusing optics of the first connector.

[0010] Based on the described prior art, it is therefore an object of the present invention to provide a connection technology with which both hollow core optical fibers can be connected to one another and optical fibers with different field diameters, such as a solid core optical fiber with a hollow core optical fiber, can be connected without excessive back reflections occurring during operation.

[0011] With regard to the optical fiber connector, this object is achieved by an optical fiber connector for an optical fiber connector for optically connecting a number N of first optical fibers to a number M of second optical fibers, wherein the optical fiber connector holds an end section of each first optical fiber with an optical fiber end face and has a number N of lenses, each having an entrance face facing one of the first optical fibers and an exit face facing away from this first optical fiber, wherein each lens is assigned to exactly one first optical fiber and each optical fiber is assigned to exactly one lens, and the lenses are designed and arranged in such a way thatthat a beam emerging from one of the first optical waveguides in a propagation direction strikes the entrance surface of the associated lens and is projected as a convergent beam onto the exit surface of the associated lens, wherein at least one lens and preferably each lens is designed as a 2-section lens and has at least two sections, namely a first section which is delimited by the entrance surface and a second section which is delimited by the exit surface, wherein the refractive index n, 1 of the first section depends on the refractive index n 2 of the second section.

[0012] For special applications, more than two sections may be provided. For example, the lens may have three sections, each with a different refractive index.

[0013] If the lens consists of multiple parts, these parts can be bonded together with an adhesive. The thin adhesive layer then does not form a lens section within the meaning of the present invention. In a preferred embodiment, 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 rays travels a distance of at least 0.2 or 0.3 mm in each section when passing through the lens.

[0014] As a rule, N=M will be used, since only then can the signals of all optical fibers be transmitted in both directions.

[0015] In the simplest case, N=M=1, i.e., the fiber optic connector holds an end section of a first fiber optic cable with a first fiber optic cable end face and a lens with an entrance face facing the fiber optic cable and an exit face facing away from the first fiber optic cable. The lens is designed and arranged such that a beam of rays emerging from the first fiber optic cable strikes the entrance face of the lens and is projected as a convergent beam of rays onto the exit face of the lens.

[0016] Information carried by the beam is thus projected from the first optical fiber onto the exit surface, where it can be further processed or forwarded. In a preferred embodiment, the first optical fiber is a hollow-core optical fiber.

[0017] It is particularly preferred if the beam is focused onto the exit surface of the lens, as this allows a second waveguide, which is intended to pick up the signal, to be positioned with its end face directly at the exit surface of the lens. However, unwanted back reflections occur at the transition between the lens and the second waveguide, which, among other things, reduce the signal strength.

[0018] Therefore, according to the invention, the lens is designed as a two-section lens with two sections with different refractive indices. If multiple lenses are provided, it is advantageous if as many as possible, and ideally all, of the lenses are designed as two-section lenses.

[0019] In a preferred embodiment, the refractive index n 2 of the second section is smaller than the refractive index n 1 of the first section, wherein preferably the refractive index n 2less than 1.5 and particularly preferably 1.5 > n 2 > 1.4. This choice of refractive index has proven to be effective. The refractive index n 2 can preferably be adapted to the refractive index of a solid core fiber used as a second optical fiber.

[0020] For example, the first section can be made of a different material than the second section. It is also advantageous if the refractive index n 1 within the first section and / or the refractive index n 2 is constant within the second section, as this makes it easier to manufacture the two-section lens. It has been shown that the second section in the propagation direction is particularly preferably longer than the first section in the propagation direction.

[0021] In a further preferred embodiment, the 2-section lens is formed in two parts, with a first part comprising the first section, and a second part having the second section. The parts can therefore be manufactured separately and positioned next to one another, wherein the two parts of the 2-section lens particularly preferably have mutually facing contact surfaces at which the two parts are in contact with one another directly or via an adhesive layer arranged between them, such that a beam of rays emerging from the first optical waveguide assigned to the 2-section lens strikes the entrance surface of the first part and enters the second part via the contact surfaces. 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.What is essential is that the combination of the two parts, i.e., the composite two-section lens, generates a convergent beam of rays from the light signal emerging from the end face of the first optical fiber. In a preferred embodiment, the two parts are glued together, forming a thin adhesive layer between them. Alternatively, the two parts can also touch directly at their contact surfaces without an adhesive layer.

[0022] In a further preferred embodiment, the contact surface of the second part and the exit surface are each flat but not arranged parallel to each other. The contact surface of the second part can be oriented perpendicular to the propagation direction. Alternatively, the exit surface of the second part can also be convexly curved.

[0023] Preferably, the diameter of the beam on the exit surface is less than 100 µm, particularly preferably less than 25 µm and most preferably less than 10 µm.

[0024] In a preferred arrangement, the diameter of the beam at the exit surface of the lens substantially corresponds to the exit surface of a second optical fiber, e.g., a solid-core optical fiber, so that, if the focusing is selected accordingly, the entire light signal is focused onto a portion of the exit surface whose dimensions substantially correspond to the typical dimensions of the core of the second optical fiber. By appropriately selecting the lens, the light signal can be adapted to the core diameter of the second optical fiber, into which signal transmission is to take place.

[0025] The fiber optic connector can be used for both signal transmission directions. If a light signal is provided at the exit surface of the lens, e.g., by a second fiber optic cable designed as a solid-core optical fiber, the lens projects this signal onto the end face of the first fiber optic cable, e.g., a hollow-core optical fiber.

[0026] To simplify the following description of the invention, only the case in which a light signal is provided by the first optical waveguide, designed as a hollow-core optical waveguide, and is focused onto the exit surface of the lens will be described below. However, the optical waveguide connector can also be used in the opposite signal transmission direction. Instead of the hollow-core optical waveguide, a solid-core optical waveguide, e.g., a single-mode or multimode glass fiber, can be provided as the first optical waveguide.

[0027] In a preferred embodiment, the fiber optic connector has a protective housing, wherein both the end sections of the first fiber optics and at least one section of each 2-section lens are either arranged in the protective housing or close off an opening in the protective housing. The protective housing is preferably sealed dust-tight. The end sections of the fiber optics can be guided into the housing through one or more inlet openings. A section of each 2-section lens can be inserted into one or more outlet openings, such that the 2-section lenses close off the outlet openings like windows. The area between the end face of the first fiber optics and the inlet face of the 2-section lenses should be in a dust-free environment. Therefore, the inlet and outlet openings, as far as they are separated from the end sections of the first fiber optics and the outlet openings, must be dust-tight.The two-section lenses are not sufficiently closed or sealed. This can be done, for example, with the help of an adhesive, which also fixes the end sections of the first optical waveguides or the two-section lenses in the inlet and outlet openings. The protective housing should have at least the protection class IP5X and preferably the protection class IP6X. Furthermore, the protective housing should also be sealed against moisture, so that in a preferred embodiment it additionally or alternatively fulfills at least the protection class IPX1, preferably the protection class IPX3 and most preferably the protection class IPX5.

[0028] In a preferred embodiment, it is provided that the protective housing has an inlet and an outlet surface, between which a number N of through channels or grooves extends.

[0029] At least a portion of the end section of each hollow-core optical waveguide is held in one of the through-channels or in one of the grooves. Preferably, both the end section of the hollow-core optical waveguide and at least a portion of the associated lens are arranged in the through-channel or the groove. The lens is arranged closer to the output surface than the end section of the hollow-core optical waveguide.

[0030] The arrangement in the through-channel ensures that there are no external influences, such as dust or moisture, between the end face of the hollow-core optical fiber and the entrance surface. This virtually eliminates the reduction in the signal strength. It can be advantageous to seal the through-channel, meaning that both the end section of the hollow-core optical fiber and the lens seal the through-channel on both sides. The through-channel design is particularly suitable for N=1.

[0031] It is possible that the through-channel has two sections with different cross-sections, wherein the end section of the hollow-core optical waveguide is arranged at least partially in the section with the smaller cross-section and the lens is arranged in the section with the larger cross-section. In order to effect an effective focusing of the light signal onto the exit surface, the lens generally must have a certain minimum diameter. Therefore, the lens usually has a larger cross-section than the hollow-core optical waveguide. The through-channel can therefore have a smaller cross-section in the region in which the hollow-core optical waveguide is guided. This simplifies the fixation of the hollow-core optical waveguide within the through-channel. The through-channel can have a stop for the lens against which the lens abuts, such that movement of the lens in the direction of the hollow-core optical waveguide is prevented.Alternatively, or in combination with this, the through-channel can have a stop for the hollow-core optical waveguide, against which the hollow-core optical waveguide rests, thus preventing movement of the hollow-core optical waveguide toward the lens. Alternatively, or in combination with this, the stop can also be designed such that it substantially, and ideally completely, prevents lateral movement between the lens and / or hollow-core optical waveguide relative to the through-channel.

[0032] Such stops can be implemented using through-channel sections with different cross-sections. If the base element, and especially the through-channel incorporated within it, are precisely manufactured, the hollow-core optical fiber and lens can be adjusted simply by positioning the respective elements at the respective stops.

[0033] In a further preferred embodiment, the exit surface of the lens closes the through-channel at the exit surface, preferably flush with it. This measure ensures, on the one hand, that no contaminants collect in the through-channel. On the other hand, the exit surface of the lens can be accessed, e.g., for cleaning, without the through-channel having a disruptive influence.

[0034] In an alternative embodiment, the lens closes the through-channel at the exit surface, with the exit surface projecting beyond the exit surface. It is possible to coat the projecting part of the lens with an adhesive, with the exit surface not having any adhesive.

[0035] In a further preferred embodiment, the protective housing has a transverse channel which intersects the through-channel, wherein the transverse channel preferably completely traverses the protective housing. Even if the transverse channel does not necessarily have to run at a right angle to the through-channel, this is generally the preferred embodiment. The transverse channel allows external access into the through-channel in order to adjust the hollow-core optical waveguide within the through-channel and to fix it, for example, using adhesive. Once the hollow-core optical waveguide and lens are precisely positioned relative to one another, the hollow-core optical waveguide can be fixed, e.g., glued, within the through-channel.

[0036] In a particularly preferred embodiment, an adjusting device for adjusting the end section of the hollow-core optical waveguide is arranged in the transverse channel. This adjusting device can have a sleeve element with a transverse bore or a transverse recess, wherein the end section of the hollow-core optical waveguide is guided through the transverse bore or the transverse recess. If the sleeve element is now moved relative to the transverse channel and thus also relative to the through-channel, this leads to a movement of the end section of the hollow-core optical waveguide within the through-channel, whereby the end section of the hollow-core optical waveguide can be adjusted. For this purpose, the hollow-core optical waveguide can be subjected to a signal and the light spot projected onto the exit surface can be observed. As soon as this light spot has the desired properties (position on the exit surface, diameter of the light spot), i.e.As soon as the hollow core optical fiber has assumed the desired relative position to the entrance surface of the lens, the end section can be glued within the through-channel.

[0037] For example, it is possible for the sleeve element and the through-channel to be filled with adhesive, at least in sections in the area where the end section of the hollow-core optical fiber is located. In this case, the sleeve element remains in the optical fiber connector after adjustment.

[0038] It is also possible to construct the sleeve element in two parts, with the two parts coming from different directions of the transverse channel carrying the end section of the hollow-core optical fiber between them. This embodiment facilitates the insertion of the end section of the hollow-core optical fiber and the sleeve element.

[0039] In a further preferred embodiment, the end face of the hollow-core optical waveguide and the two-section lens are arranged at a distance from one another. This improves the imaging properties of the lens. In particular, back reflections can be reduced. In a preferred embodiment, the first and / or the second section has an anti-reflection coating. An anti-reflection coating can thus be arranged on the entrance surface and / or the exit surface. If the lens has a refractive index n Li and the medium arranged in the passage channel, ie usually air, has a refractive index n m , the refractive index n is 1 the anti-reflective coating applied to the entrance surface n1=nLinM.

[0040] In a further preferred embodiment, N > 1, preferably N ≤ 16 and most preferably N = 8. Thus, several pairs of optical fibers can be connected to one another using a plug connection.

[0041] It is further advantageous if a plurality, and preferably all, of the lenses are configured as a lens array, wherein all lenses are configured as two-section lenses, each having a first and a second section, and wherein a plurality of first sections and / or a plurality of second sections are integrally formed, wherein preferably all first sections and / or all second sections are integrally formed. This significantly facilitates the manufacture of the two-section lenses and the adjustment of the two-section lenses in the fiber optic connector.

[0042] With regard to the optical fiber connector, the object mentioned at the outset is achieved by an optical fiber connector for optically connecting a number N of first optical fibers, each having an end section, to a number M of second optical fibers, each having an end section, with a first optical fiber plug, in which the end sections of the first optical fibers are held by a first optical fiber end face, and a second optical fiber plug, in which the end sections of the second optical fibers are held by a second optical fiber end face, wherein each first optical fiber end face is assigned exactly one second optical fiber end face, wherein between each first optical fiber end face and the second optical fiber end face assigned thereto, at least one lens is arranged in such a way thatthat a light beam emerging from the first optical waveguide end face is imaged onto the second optical waveguide end face, wherein the lens has an entrance face and an exit face and at least two sections, namely a first section which is delimited by the entrance face and a second section which is delimited by the exit face, wherein the refractive index n, 1 of the first section depends on the refractive index n 2 of the second section.

[0043] It is advantageous if an optical fiber connector as described above is provided as the first optical fiber connector. In a preferred embodiment, an optical fiber connector as described above can be provided as the first and second optical fiber connector.

[0044] In order to simplify the following description of the optical fiber connector according to the invention, the following will only describe the case where N = 1 and a light signal is provided by the first optical fiber designed as a hollow core optical fiber and is focused onto the exit surface of the lens. In the case described below, a solid core optical fiber is provided as the second optical fiber. However, the optical fiber connector can also be used in the opposite signal transmission direction. Instead of the hollow core optical fiber, a monomode or multimode glass fiber can be provided as the first optical fiber. Likewise, N > 1. Finally, it is also possible for a hollow core optical fiber to be provided as the first and second optical fiber.In this case, two lenses are arranged between each first optical fiber end face and the second optical fiber end face assigned to it.

[0045] The lens is preferably arranged such that it contacts the solid core end face. An anti-reflective coating can then be applied to the exit surface. If the lens has a refractive index n Li and the core of the solid core light guide has a refractive index of n F , the refractive index n 2 the anti-reflective coating applied to the exit surface, n2=nFnM result.

[0046] Furthermore, a pretensioning device can be provided which pretensions the output surface of the lens against the solid core end face.

[0047] In a further preferred embodiment, a solid core optical waveguide is used as the second optical waveguide, the core of which has a refractive index which deviates by no more than 10%, preferably by no more than 3% and most preferably by no more than 1% from the refractive index of the second portion of the lens.

[0048] For example, already known optical fiber connectors, such as LC connectors, can also be used for connecting solid-core optical fibers with hollow-core optical fibers or for connecting hollow-core optical fibers with each other or for connecting solid-core optical fibers with different field diameters if the LC connector is designed as described.

[0049] Further advantages, features, and possible applications of the present invention will become clear from the following description of preferred embodiments and the accompanying figures. They show: Fig. 1 a sectional view through a fiber optic connector with fiber optic cable, Fig. 2 is a sectional view of a protective housing of the embodiment of Fig. 1, Fig. 3 a perspective view of the adjusting device of the embodiment of Fig. 1, Fig. 4 a sectional view through the protective housing with inserted adjustment device of the embodiment of Fig. 1, Fig. 5 a view as in Fig. 4, but with inserted optical fiber, Fig. 6 a sectional view through a second embodiment of an optical fiber connector, Fig. 7 a sectional view through an optical fiber connector, Fig. 8 a sectional view through a third embodiment of an optical fiber connector, Fig. 9 is a perspective sectional view of the third embodiment, Fig. 10 a sectional view through a fourth embodiment of an optical fiber connector, Fig. 11 is a perspective sectional view of the fourth embodiment, Fig. 12 a sectional view through a second embodiment of an optical fiber connector, Fig. 13 a perspective view of a fifth embodiment of an optical fiber connector according to the invention, Fig. 14 is a perspective view of the protective housing of the fifth embodiment, Fig. 15 an exploded view of the protective housing of Fig. 15, Fig. 16 a perspective view of the opened protective housing of Fig. 15, Fig. 17 a sectional view of the protective housing of Fig. 15 and Fig. 18 a perspective sectional view of the protective housing of Fig. 15.

[0050] In Fig. 1 shows a preferred embodiment of an optical fiber connector 1. In this embodiment, only one optical fiber is accommodated, so that N = 1. An end section 3 of a hollow-core optical fiber 4 is arranged in the optical fiber connector 1. This end section 3 is inserted into a through-channel 7, 8, 9 (in Fig. 2). Furthermore, a lens 6 is provided. A light beam or a bundle of rays 10 emerges from an end face 5 of the end section 3 of the hollow core optical waveguide 4 and broadens in the direction of the lens 6. The lens 6 is designed such that it projects the light beam 10, which strikes an entrance surface 11 of the lens 6, as a convergent bundle of rays onto the exit surface 12 of the lens 6 and preferably focuses it. In the best case, the exit surface 12 is located at the focus of the convergent bundle of rays. An arrangement out of focus is also possible, although this is disadvantageous.

[0051] The lens has two sections with different refractive indices, which are not shown in the figure.

[0052] In the embodiment shown, a capillary 19 is provided, which surrounds part of the end section 3 of the hollow-core optical waveguide 4. The capillary 19 can be omitted. In this case, the through-channel is preferably designed in a stepped manner.

[0053] Although the preferred embodiment describes a light beam emerging from the end face 5 of the end section 3 of the hollow-core optical waveguide 4 and striking the entrance surface 11 of the lens 6, the signal path can also be reversed. A signal coupled in via the exit surface 12 of the lens 6 can also be imaged onto the end face 5 of the end section 3.

[0054] The individual elements of the fiber optic connector are shown in Fig. 2. The protective housing 2 has a through-channel, which in the embodiment shown has three sections: a front section 7, which is intended to accommodate the lens 6, and a middle section 8, which is intended to accommodate the end section 3 of the hollow-core optical waveguide 4 and whose cross-section is reduced compared to the cross-section of the front section 7. Finally, there is a rear section 9 of the through-channel, which again has a somewhat larger cross-section. The rear section 9 is of secondary importance for the invention and can have any cross-section.

[0055] Furthermore, a transverse channel 13 is provided, via which access to the through-channel is granted from the outer surface of the protective housing 2.

[0056] In the transverse channel 13 an adjusting device 14, 15 is arranged, which in Fig. 3. The adjusting device 14, 15 consists of two elements 14 and 15, which in the assembled state, as shown in Fig. 3, have a transverse bore or a transversely extending recess through which the end section 3 of the hollow-core glass fiber 4 can be guided. In an alternative embodiment, the upper element 15 of the adjusting device 14, 15 can be omitted. In the example shown, the lower element 14 of the adjusting device has a handling recess 16, indicated in the drawing, with which the adjusting device 14, 15 can be moved in the direction of the transverse channel 13 and / or rotated about the axis of the transverse channel 13. The upper element 15 can also have a handling recess. This allows the end section 3 of the hollow-core optical fiber 4 to be adjusted relative to the protective housing 2.Once the relative position is set to the desired position, adhesive can be poured through the opening of the sleeve-shaped part 15 of the adjustment device, so that the adhesive is distributed through the transverse recess 18 toward the end section 3 and creates a firm connection between the end section 3 and the protective housing 2 within the central section 8 of the through-channel 7, 8, 9. The adjustment device 14, 15 can also be formed as a single piece, in which case the end section 3 would have to be guided through the transverse recess 18 of the adjustment device 14, 15. The two-piece design has the advantage that the assembly of the waveguide connector is easier.

[0057] In the Fig. 4 and Fig. 5 are two partial sectional views of the protective housing 2 with inserted adjustment device 14, 15, one without optical fiber ( Fig. 4) and once with optical fiber ( Fig. 5) is shown in order to better recognize the arrangement of the end section 3 within the adjustment device 14, 15. It can be seen here that the adjustment device 15, 16 has a horizontally extending bore 17 into which the end section 3 can be inserted. In the direction of the middle section 8 of the through-channel, the horizontally extending bore 17 is connected to a recess 18 through which the adhesive can easily escape from the sleeve-like element 15.

[0058] In Fig. 6 shows an alternative embodiment of an optical fiber connector 1'. This embodiment essentially corresponds to the embodiment shown in Fig. 1, however, an alternatively designed lens 6' is provided. This lens can be made of quartz glass, silicon or SF11. Here too, the lens 6' has two sections with different refractive indices.

[0059] In Fig. 7 shows a fiber optic connector 20. In the left part of the Fig. 7 is the Fig. 1 shown fiber optic connector. In the right part of the Fig. 7, a solid-core optical fiber 22 is arranged within a ferrule 23, as is known from prior art LC connectors. The ferrule 23 and the optical fiber connector 1 are arranged with their end faces within a sleeve 21. The end face of the solid-core optical fiber 22 is pressed onto the exit surface 12 of the lens 6, creating physical contact. Because the second section of the lens 6, which faces the end face of the solid-core optical fiber 22, has a refractive index that is lower than the refractive index of the first section of the lens 6, back reflections are significantly reduced.

[0060] In the Fig. Figures 8 (perspective sectional view) and 9 (sectional view) show a third embodiment of an optical fiber connector 101 according to the invention. Identical or essentially identical components have been provided with the same reference numerals as in the previous figures. It can be clearly seen that the lens 123, 124 here consists of two parts, with the first part forming the first section 123 and the second part forming the second section 124. The refractive index n 1 in the first section 123 is constant and larger than the refractive index n 2 in the second section 124. The second section 124 has a length in the propagation direction that is significantly greater (in the example shown, more than twice as long) than the length of the first section 123 in the propagation direction.

[0061] The first section 123 has the entry surface 111 and is bonded to the second section 124. The second section 124 has the exit surface 112. It can be clearly seen that the diameter of the second section 124 is larger than the diameter of the first section 123. The diameter of the second section 124 essentially corresponds to the inner diameter of the through-channel of the protective housing 2. This has the advantage that the lens 123, 124, with the sections 123, 124 already connected to each other, can be inserted into the protective housing 2 and is then already correctly positioned laterally.

[0062] Furthermore, it is also possible for the diameter of the first section 123 to substantially correspond to the inner diameter of the through-channel of the protective housing 2. Lateral positioning can then also be achieved by inserting the first section 123 into the through-channel. In this case, it is advantageous if the lateral extent of the second section 124 is not greater than the lateral extent of the first section 123.

[0063] Alternatively, one or both sections of the lens can have a square or rectangular cross-section. The through-channel can then have a cross-section adapted to the cross-section of the lens sections.

[0064] In the Fig. 10 (perspective sectional view) and 11 (sectional view) show a fourth embodiment of an optical fiber connector 101' according to the invention. Identical or essentially identical components have been provided with the same reference numerals as in the previous figures. The only difference from the third embodiment is that the second section 124 of the lens is fastened at its end in or on the through-channel using an adhesive 125 such that the exit surface 112 is flush with the adhesive 125. The exit surface 112 remains unwetted by the adhesive 125. The adhesive 125 thus forms a type of meniscus. When the adhesive 125 is applied, the exit surface 112 can be wetted, in which case the exit surface 112 should then be subsequently polished in order to remove the adhesive 125 from the exit surface 112. The surrounding adhesive 125 then ensures that no sharp edges are created.

[0065] In the Fig. 12 shows a second embodiment of an optical fiber connector according to the invention. The illustration essentially corresponds to the illustration of Fig. 7, but here two optical fiber connectors 101 according to the invention according to the third embodiment are used to connect two hollow core optical fibers to each other.

[0066] In the Fig. 13 to 18 show various views of a fifth embodiment of an optical fiber connector 201 according to the invention.

[0067] While the previous embodiments concerned fiber optic connectors that had only one fiber optic cable (N = 1), this embodiment carries several fiber optic cables, in the example shown N = 8.

[0068] In the perspective view of Fig. 13 shows a connector shell 225. This connector shell 225 is basically known. The protective housing 202 held in the connector shell 225, the second section 224 of the lenses held therein, and their exit surfaces 212 can be seen.

[0069] In the perspective view of Fig. 14, the connector sheath 225 has been removed, revealing the protective housing 202, the exit surface 212, and the optical fibers 204. The adjustment opening 226 can already be seen in this view.

[0070] In Fig. 15 is an exploded view of the Fig. 14. The protective housing itself consists of the housing cover 228, the base part 227, and the main housing part 229. The base part 227 has a plurality of alignment structures formed as grooves 230, into which the end sections 203 of the optical fibers 204 are inserted. With the help of the grooves 230, the end sections 203 can already be positioned relatively precisely.

[0071] The housing main part 229 has two opposite openings, the one in the Fig. 15, is closed by the first sections 223 and second sections 224, each formed as an array. It can be seen that the base element 227 is stepped on its side facing the lenses in order to provide the lens array with a stop edge 231. During assembly, the second lens array section 224, including the first lens array section 223 attached thereto, preferably glued, can be inserted into the rear opening of the main housing part 229 until it makes contact with the stop edge 231.

[0072] After the end sections 203 have been positioned in the corresponding grooves 230, the housing cover 228 is placed over the end sections 203, thus forming the upper and lower walls of the protective housing. This "sandwich" is inserted into the front opening of the housing main part 229. The housing main part 229 is designed to form the side walls of the protective housing. The end sections of the 203 and the first sections 223 are therefore arranged in a closed space of the protective housing. The reference number 210 indicates the beam path.

[0073] In the Fig. 16 shows the protective housing in an open state to illustrate the positioning of the individual elements.

[0074] The Fig. 17 and Fig.18 show sectional views of the protective housing, from which the positioning of the individual elements relative to one another can be determined. If the end sections 203 are not positioned correctly, the position can be corrected via the adjustment opening 226. For this purpose, the housing cover 228 must either also have an opening or it must be temporarily removed. For example, the grooves 230 could be designed such that they position the end sections 204 somewhat too high. With the aid of a manipulator, which can be V-groove-shaped, for example, each individual optical fiber can then be pressed downwards through the adjustment opening 226 until the correct position is assumed. The end section is fixed in the final position, e.g., using adhesive.

[0075] Once all end sections 203 are correctly positioned and fixed, the housing cover 228 is repositioned or closed. List of reference symbols 1, 1', 101, 101' fiber optic connector 2 protective housings 3 Final section 4 hollow core optical fibers 5 End face of the hollow core optical fiber 6.6' lens 7 Through channel 8 through channel 9 Through channel 10 light beam 11 Entrance area 12 Exit area 13 Cross channel 14 Adjustment device 15 Adjustment device 16 Handling recess 17 Hole 18 Recess 19 capillaries 20, 120 fiber optic connectors 21 solid-core optical fibers 22 Ferrule 123 first section 124 second section 125 Adhesive 201 fiber optic connectors 202 protective housing 203 end sections 204 hollow core optical fibers 210 light beam 211 entrance area 212 Exit area 223 first section 224 second section 225 plug sheath 226 Adjustment opening 227 Basic element 228 housing cover 229 Main housing part 230 groove 231 stop edge

Claims

[1] Optical fiber plug for an optical fiber connector for optically connecting a number N of first optical fibers to a number M of second optical fibers, wherein the optical fiber plug (1, 1', 101, 101') holds an end section (3) of each first optical fiber (4) with an optical fiber end face (5) and has a number N of lenses (6, 6'), each having an entrance surface (11) facing one of the first optical fibers and an exit surface (12) facing away from this first optical fiber, wherein each lens (6, 6') is assigned to exactly one first optical fiber and each optical fiber is assigned to exactly one lens (6, 6'), and the lenses (6, 6') are designed and arranged in such a way that a beam emerging from one of the first optical fibers in a propagation direction is incident on the entrance surface (11) of the assigned lens (6,6') and is projected as a convergent beam onto the exit surface (12) of the associated lens (6, 6'), wherein at least one lens (6, 6') and preferably each lens is designed as a 2-section lens (6, 6') and has at least two sections, namely a first section (123, 223), which is delimited by the entrance surface (11), and a second section (124, 224), which is delimited by the exit surface (12), wherein the refractive index n, 1 of the first section (123, 223) differs from the refractive index n 2 of the second section (124, 224). [2] Optical fiber connector according to claim 1, characterized by that the refractive index n 2 of the second section (124, 224) is smaller than the refractive index n 1 of the first section (123, 223), wherein preferably the refractive index n 2 less than 1.5 and particularly preferably 1.5 > n 2 > 1.

4. [3] Optical fiber connector according to claim 1 or 2, characterized by that the first section (123, 223) is made of a different material than the second section (124, 224), wherein preferably the refractive index n 1 within the first section (123, 223) and / or the refractive index n 2 is constant within the second section (124, 224), wherein particularly preferably the second section (124, 224) has a greater length in the propagation direction than the first section (123, 223) in the propagation direction. [4] Optical fiber connector according to claim 1, 2 or 3, characterized bythat the 2-section lens (6, 6') is formed in two parts with a first part which comprises the first section (123, 223), and a second part which has the second section (124, 224), wherein particularly preferably the two parts of the 2-section lens (6, 6') have contact surfaces facing one another, at which the two parts are in contact with one another directly or via an adhesive layer (125) arranged therebetween, so that a beam of rays emerging from the first optical waveguide assigned to the 2-section lens (6, 6') strikes the entrance surface (11) of the first part and enters the second part via the contact surfaces. [5] Optical fiber connector according to claim 4, characterized by that the contact surface of the second part and the exit surface (12) are each flat but not arranged parallel to each other. [6] Optical fiber connector according to one of the preceding claims, characterized bythat the 2-section lens (6, 6') is designed and arranged such that a beam emerging from the first optical waveguide strikes the entrance surface (11) and is focused onto the exit surface (12). [7] Optical fiber connector according to one of the preceding claims, characterized by that the optical fiber connector (1, 1', 101, 101') has a protective housing (202), wherein both the end sections of the first optical fibers and at least one section of each 2-section lens (6, 6') are either arranged in the protective housing (202) or close an opening of the protective housing (202). [8] Optical fiber connector according to claim 7, characterized bythat the protective housing (202) comprises an input and an output surface, between which a number N of through-channels (7, 8, 9) extend, wherein preferably in each through-channel (7, 8, 9) both the end section of one of the first optical waveguides and at least the first section (123, 223) of the 2-section lens (6, 6') and preferably also at least partially the second section (124, 224) of the 2-section lens (6, 6') are arranged. [9] Optical fiber connector according to claim 8, characterized by that the 2-section lens is arranged completely in one of the through-channels, wherein preferably the exit surface (12) of the 2-section lens (6, 6') closes the corresponding through-channel (7, 8, 9) flush at the exit surface. [10] Optical fiber connector according to one of claims 8 to 9, characterized bythat the protective housing has a transverse channel (13) which intersects one of the through-channels (7, 8, 9), wherein preferably the transverse channel (13) completely traverses the protective housing (202). [11] Optical fiber connector according to claim 10, characterized by that an adjusting device (14, 15) for adjusting the end section of the first optical waveguide arranged in the corresponding through-channel is arranged in the transverse channel (13), wherein the adjusting device (14, 15) preferably has a sleeve element with a transverse bore or a transverse recess, wherein the end section of the first optical waveguide is guided through the transverse bore or the transverse recess, wherein preferably the sleeve element and the through-channel (7, 8, 9) are filled with adhesive at least in sections in the region in which the end section of the corresponding first optical waveguide is arranged. [12] Optical fiber connector according to one of the preceding claims, characterized by that the end face (5) of the first optical waveguide and the associated 2-section lens (6, 6') are arranged at a distance from one another. [13] Optical fiber connector according to one of the preceding claims, characterized by that N = 1. [14] Optical fiber connector according to one of claims 1 to 12, characterized by that N >1, preferably N ≤ 16 and most preferably N = 8. [15] Optical fiber connector according to claim 14, characterized bythat a plurality of, and preferably all, lenses (6, 6') are designed as a lens array, wherein all lenses are designed as 2-section lenses (6, 6'), each having a first and a second section, and wherein a plurality of first sections and / or a plurality of second sections are formed in one piece, wherein preferably all first sections and / or all second sections are formed in one piece. [16] Optical fiber connector according to claim 14 or 15 as far as dependent on claim 7, characterized by that the protective housing (202) is formed in several parts, wherein at least one part has a plurality of grooves (230) for receiving a respective section of the first optical waveguides, wherein preferably the protective housing (202) fulfills at least the protection class IP, particularly preferably the protection class IP5X and best the protection classes IP6X. [17] Optical fiber connector for optically connecting a number N of first optical fibers, each having an end section (3), to a number M of second optical fibers, each having an end section (3), comprising a first optical fiber plug, in which the end sections of the first optical fibers are held by a first optical fiber end face, and a second optical fiber plug, in which the end sections of the second optical fibers are held by a second optical fiber end face, wherein each first optical fiber end face is assigned exactly one second optical fiber end face, wherein at least one lens is arranged between each first optical fiber end face and the second optical fiber end face assigned thereto such that a light beam emerging from the first optical fiber end face is imaged onto the second optical fiber end face,wherein the lens has an entrance surface (11) and an exit surface (12) and at least two sections, namely a first section which is delimited by the entrance surface (11) and a second section which is delimited by the exit surface (12), wherein the refractive index n, 1 of the first section depends on the refractive index n 2 of the second section. [18] Optical fiber connector according to claim 17, characterized by that an optical fiber connector (1, 1', 101, 101') according to one of claims 1 to 16 is provided as the first optical fiber connector, wherein an optical fiber connector according to one of claims 1 to 16 is preferably provided as the first optical fiber connector and as the second optical fiber connector [19] Optical fiber connector according to claim 17 or 18, characterized bythat the lens is arranged such that it contacts the second optical waveguide end face, wherein preferably a biasing device is provided which biases the output face of the lens against the second optical waveguide end face.

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