Coupling device for coupling a solid optical fiber and a hollow-core optical fiber

Abstract

The invention relates to a coupling device for coupling a solid optical fiber (1) and a hollow-core optical fiber (2). The coupling device (3) comprises at least one mode adapter (4) and a guidance system (5). The guidance system (5) is configured to position itself or to position at least one of the two fibers (1, 2) such that light sent from one of the two fibers (1, 2) passes through the at least one mode adapter (4) and then into the other of the two fibers (1, 2).

Description

Coupling device between a solid optical fiber and a hollow-core optical fiber 1. Scope of the invention

[0001] The invention lies in the field of optical data transmission, and more particularly in that of the interconnection between a solid optical fiber and a hollow-core optical fiber. 2. Prior art

[0002] Conventional optical fibers, i.e., the most commonly used, are solid fibers. When solid fibers contain one or more cores, they are called single-mode optical fiber (or SMF fiber) and multi-core optical fiber (or multi-core fiber). The core(s) of a solid fiber are generally made of silica glass. The solid fiber also includes an optical cladding surrounding the core(s) of the fiber.

[0003] A new type of fiber has recently been developed: hollow-core fiber. Hollow-core fiber consists of a hollow core surrounded by multiple air channels; it is a microstructured fiber. Hollow-core fiber is very promising because it allows for signal transmission with lower latency in the network.

[0004] One difficulty encountered, however, lies in coupling these different fibers together, and in particular a solid fiber with a hollow-core fiber. The optical beam diameter is around 9 µm for single-mode and multi-core fibers, while that of hollow-core fiber can vary between approximately 9 µm and 30 µm (specifically between 9.2 µm and 30.4 µm).

[0005] Document WO 2024 / 133462 proposes a solution to this problem using a coupling device between a solid fiber and a hollow-core fiber. However, this coupling device is limited to a single predefined mode diameter for the hollow-core fiber (namely 30 µm) and therefore cannot accommodate a range of hollow-core fibers with different mode sizes or diameters.

[0006] The present invention aims to provide a coupling device that is adaptable, that is to say, allowing coupling between two fibers regardless of the optical beam diameter of each of said fibers. 3. Description of the invention

[0007] The invention proposes for this purpose a coupling device between a solid optical fiber and a hollow-core optical fiber, said coupling device comprising at least one modal adapter and a guidance system, the guidance system being configured to position itself or to position at least one of the two fibers so that a light sent from one of the two fibers passes into at least one modal adapter and then into the other of the two fibers.

[0008] Thanks to the guidance system according to the invention, it is possible to couple fibers of different diameters. In particular, it is possible to couple a solid fiber with a hollow-core fiber of any diameter. The resulting coupling device is thus flexible and adaptable to different needs.

[0009] The invention makes it possible to reuse existing modules, and in particular modal adapters, in a hollow core fiber network.

[0010] According to one feature, the coupling device includes several modal adapters, the guidance system being configured to position itself or to position at least one of the two fibers so that light sent from one of the two fibers passes into an appropriate modal adapter among said modal adapters, and then into the other of the two fibers.

[0011] The coupling device thus configured makes it possible to offer different modal adapters on a single device.

[0012] According to one characteristic, the guidance system is a piezoelectric system configured to cause movement of at least one of the two fibers.

[0013] According to one feature, the guidance system includes two piezoelectric actuators, each of the piezoelectric actuators being configured to cause movement of one of the two fibers.

[0014] By applying a predefined electrical voltage to the piezoelectric actuators, a mechanical deformation of said actuators is generated. This deformation, translated into movement, allows for the simple and rapid displacement of at least one of the fibers in order to align the fibers and at least one adapter.

[0015] According to one characteristic, the coupling device includes a centering system configured to position at least one of the two fibers in space.

[0016] The centering system saves time during fiber alignment. It allows the fibers to be located in space, i.e., their positions to be determined. This enables the fibers to be initially positioned opposite each other, allowing for finer alignment later.

[0017] According to one characteristic, the centering system comprises four photodiodes extending around one of the two fibers or between the two fibers.

[0018] According to one characteristic, the photodiodes are arranged in a parallelepiped pattern.

[0019] Photodiodes are photodetectors capable of detecting light arriving from one of the fibers. The power of this light is measured, thus allowing the fibers to be located in space.

[0020] The parallelepiped arrangement of the photodiodes allows a movement of fibers to be scanned along a horizontal direction and a vertical direction, and therefore the fibers to be positioned along these horizontal and vertical directions.

[0021] According to one characteristic, the guidance system comprises at least two MEMS mirrors, each MEMS mirror being opposite one modal adapter among the at least one modal adapter, and one of the two fibers.

[0022] MEMS mirrors enable precise light guidance from one fiber to the other via at least one modal adapter. Furthermore, this technology is stable and robust in the face of temperature variations, vibrations, and handling.

[0023] According to one feature, the coupling device includes a verification system configured to verify that the fibers and one modal adapter among at least one modal adapter are aligned with each other.

[0024] According to one feature, the verification system includes a power measurement device configured to measure optical power output from one of the two fibers.

[0025] The verification system checks the alignment of the fibers and the modal adapter. The fibers and modal adapter are considered aligned when maximum power is measured by the power meter.

[0026] According to one feature, the verification system includes a thermal camera.

[0027] The thermal imaging camera allows visualization of infrared radiation emitted from one of the fibers. The thermal imaging camera can be used to verify if the fibers are properly aligned.

[0028] According to one characteristic, the coupling device includes a control system configured to control the guidance system.

[0029] Depending on one characteristic, the control system is connected to the verification system and / or the centering system. The control system can be configured to automatically control the guidance system based on a measurement performed by the verification system or the centering system.

[0030] The control system enables dynamic alignment and centering of the fibers by injecting light through one fiber and measuring the output power of the other. The measured power corresponds to the output power of one of the fibers and / or the power measured by the centering system (e.g., by the photodiodes).

[0031] Depending on one characteristic, the coupling device may include a Peltier module.

[0032] The Peltier module allows the coupling device to be cooled by thermoelectric means. This makes it possible to control the temperature of the coupling device and increase its stability. 4. Presentation of the figures

[0033] Other advantages and features of the invention will become apparent in the following description with reference to the accompanying drawings, given by way of non-limiting examples: ...

[0034] 5. Detailed description of at least one embodiment of the invention

[0035] Figures 1 and 2 schematically represent two fibers 1, 2 and a coupling device 3 according to a first embodiment of the invention.

[0036] The coupling device 3 allows the interconnection or coupling between fibers 1 and 2. Fibers 1 and 2 have different optical beam diameters. Fiber 1 is a solid fiber, more precisely a single-mode fiber (but could also be a multi-core or multi-mode fiber), while fiber 2 is a hollow-core fiber.

[0037] Thus, in the embodiments shown and described, fibers 1 and 2 are respectively single-mode and hollow-core fibers. In other embodiments, the coupling device can couple other types of fibers. For example, the coupling device can couple a multi-core fiber and a hollow-core fiber, or even two hollow-core fibers of different diameters. The following description of the coupling device should therefore be understood as applicable to any type of fiber of different natures that one seeks to interconnect.

[0038] A 100 lens can also be assembled to one end of the solid fiber 1. The 100 lens allows for better focusing of the light.

[0039] The coupling device 3 includes at least one modal adapter 4. The modal adapter 4 allows the connection of optical fibers of different types or modes, including fibers with different core diameters. The modal adapter 4 aligns the propagation modes during coupling between different fibers. In other words, the modal adapter 4 modifies the received propagation mode so that the output optical beam mode corresponds to that of the hollow-core fiber 2. The modal adapter 4 thus reduces signal loss.

[0040] The modal adapter 4 can be of any known type, for example, a GRIN adapter, a TAPER adapter, a single-mode fiber (SMF fiber), etc. The GRIN (graded-index) adapter is a modal adapter whose refractive index varies gradually. In the example shown, the GRIN adapter has a lens at one end. The TAPER adapter is a conical modal adapter that allows for a gradual change in the fiber diameter. The single-mode fiber has a lens at one end, thus forming a lensed fiber. The use of a lens, regardless of the type of modal adapter, allows for better focusing of the light.

[0041] For the sake of simplicity, the model shows a single modal adapter 4. The model shown, on the other hand, uses four modal adapters 4. The number of modal adapters can vary depending on the requirements. The greater the number of modal adapters, the greater the adaptability of the coupling device between optical fibers.

[0042] The modal adapters 4 of the allow the solid fiber to be coupled to hollow core fibers with a diameter that can vary between approximately 9 µm and 30 µm.

[0043] The first modal adapter 4, in this case the lensed fiber, has a mode diameter of approximately 10.4 µm. This type of modal adapter is useful when the hollow-core fiber 2 has a diameter close to that of the solid-core fiber 1, particularly that of a single-mode fiber. This modal adapter allows the solid-core fiber 1 to be brought as close as possible to the hollow-core fiber 2 in order to couple them. This coupling can also be achieved without splicing, as the fibers are sufficiently close together thanks to the modal adapter.

[0044] The other four mode adapters shown further enlarge the propagation modes. The last adapter shown, for example, has a mode diameter of approximately 30 µm. The intermediate adapters have mode diameters ranging from 9 µm to 30 µm. The GRIN adapter, for example, has a mode diameter of approximately 20 µm.

[0045] As illustrated, the coupling device 3 also includes a guidance system 5, or orientation system. The guidance system 5 guides or orients the light sent from one of the two fibers to the other. To do this, the guidance system 5 can align the solid fiber 1, the appropriate modal adapter 4, and the hollow-core fiber 2. Alternatively, the guidance system 5 can position itself or be positioned to guide the light sent from one fiber, between the solid fiber 1 and the hollow-core fiber 2, so that this light passes through the appropriate modal adapter 4, and then through the other fiber between the solid fiber 1 and the hollow-core fiber 2. In this document, the appropriate modal adapter is defined as the modal adapter having the mode diameter closest to that of the hollow-core fiber 2.

[0046] In the embodiment shown in Figure 1, the guidance system 5 is piezoelectric. The guidance system 5 is configured to cause movement of the solid fiber 1 and / or the hollow-core fiber 2. The movement can be translational and / or rotational. The guidance system 5 is configured to act on the solid fiber 1 and / or the hollow-core fiber 2 so as to position at least one of these two fibers. The solid fiber 1 and / or the hollow-core fiber 2 are positioned so as to be aligned with the appropriate modal adapter 4. The guidance system 5 acts on the solid fiber 1 and / or the hollow-core fiber 2 under the effect of an electrical voltage.

[0047] The guidance system 5, according to this first embodiment, comprises two piezoelectric actuators, called the first piezoelectric actuator 50 and the second piezoelectric actuator 51. The first piezoelectric actuator 50 is configured to act on the solid fiber 1. The second piezoelectric actuator 51 is configured to act on the hollow-core fiber 2. The first piezoelectric actuator 50 and the second piezoelectric actuator 51 generate a mechanical deformation when subjected to an electrical voltage. The deformation is translated into a movement, which can be a translation or a rotation. The translational movement can be a movement along at least one of the X, Y, or Z axes, which are orthogonal to each other. The rotational movement can occur around one of these X, Y, or Z axes. The Z axis here corresponds to a longitudinal direction (i.e.in the length of the fibers), the X axis has a lateral or transverse direction, the Y axis has a vertical or height direction.

[0048] The coupling device 3 may include a support on which the first piezoelectric actuator 50 and the second piezoelectric actuator 51 are assembled. The solid fiber 1 may be positioned on the support so as to be in contact with or assembled to the first piezoelectric actuator 50. The hollow core fiber 2 may be positioned on the support so as to be in contact with or assembled to the second piezoelectric actuator 51.

[0049] The guidance system 5 can include a different number of piezoelectric actuators. In particular, the guidance system can include one or more piezoelectric actuators configured to act on the modal adapters.

[0050] The coupling device may include a stop configured to prevent a collision between the two fibers 1, 2 when one of the two fibers is moved along the Z axis.

[0051] The coupling device 3 may advantageously include a verification system 6 (not shown for simplicity). The verification system 6 is configured to verify that the fibers 1, 2 and the appropriate modal adapter 4 are aligned with each other.

[0052] The verification system 6 includes a photodetector 60 (referred to here as the central photodetector). The central photodetector 60 can be a "Large Area Detector" type photodetector.

[0053] The central photodetector 60 is positioned opposite the hollow core fiber 2. The central photodetector 60 can thus capture or absorb the light sent from the solid fiber 1 and then transform this light into a measurable quantity (an electrical current or voltage).

[0054] The verification system 6 may also include a power measurement device or wattmeter 61.

[0055] The wattmeter 61 is connected to the central photodetector 60. The wattmeter 61 is configured to measure the optical power from the quantity obtained by the central photodetector 60.

[0056] The verification system 6, using the central photodetector 60 positioned opposite the hollow-core fiber 2, measures the power output of the hollow-core fiber 2. This power measurement allows the verification system 6 to confirm that the solid fiber 1 and the hollow-core fiber 2 are properly aligned. More specifically, the verification system 6 verifies that the fibers 1 and 2, and the appropriate modal adapter 4, are correctly aligned.

[0057] In the example shown, the central photodetector 60 is separate from the wattmeter 61. In another embodiment, the wattmeter may include an integrated photodetector. The verification system may then include the wattmeter incorporating the photodetector.

[0058] The coupling device 3 may also advantageously include a centering system 7 or positioning system. The centering system 7 is configured to position the solid fiber 1 and the hollow-core fiber 2 in space, as detailed later.

[0059] The centering system 7 includes, for example, at least one photodetector 70-D, 70-G, 70-H, or 70B (referred to herein as the peripheral photodetector). The peripheral photodetector is sensitive to a wavelength window between 1.3 µm and 1.65 µm (referred to herein as the telecommunications window). The peripheral photodetector can be, for example, a photodiode. The peripheral photodetector is located near the hollow-core fiber 2.

[0060] According to the first embodiment, the centering system 7 comprises four photodiodes 70-D, 70-G, 70-H, 70B (visible in Figure 1, two of them being visible in Figure 2). The photodiodes 70-D, 70-G, 70-H, 70B are distributed around the hollow core fiber 2. The photodiodes are arranged to the right (photodiode 70-D), to the left (photodiode 70-G), above (photodiode 70-H) and below (photodiode 70-B) of the hollow core fiber 2. The photodiodes 70-D, 70-G, 70-H, 70B are distributed in a parallelepiped arrangement. According to another embodiment, the peripheral photodetectors can be arranged between the solid fiber 1 and the hollow core fiber 2, or distributed around the solid fiber 1.

[0061] As illustrated, the coupling device 3 may further include a control system 8. The control system 8 is configured to control the guidance system 5. The control system 8 may include a processor and memory. The memory may be a storage medium on which a computer program is stored. The computer program contains instructions for executing steps in a method for controlling the guidance system 5.

[0062] The control system 8 may include a human-machine interface allowing a user to control the guidance system 5.

[0063] The control system 8 is advantageously connected to the verification system 6. The control system 8 is, for example, connected to the wattmeter 61. The control system 8 thus receives the power measurements taken by the verification system 6.

[0064] The control system 8 can also be connected to the centering system 7. The control system 8 thus receives the electrical signal emitted by the centering system 7 (in particular by the photodiodes 70-D, 70-G, 70-H, 70B).

[0065] The power measured by the verification system 6 provides information on the alignment of the solid fiber 1, the hollow-core fiber 2, and the appropriate modal adapter. Measuring the optical power determines whether the solid fiber 1, the hollow-core fiber 2, and the appropriate modal adapter 4 are aligned. Based on the measured optical power value, the control system 8 can command or control the movement of the solid fiber 1 and / or the hollow-core fiber 2. As explained above, this movement can be a translation or a rotation along or around one of the X, Y, or Z axes. The control system 8 sends a command to the guidance system 5, specifically to the first piezoelectric actuator 50 and / or the second piezoelectric actuator 51.The guidance system 5, by means of the first piezoelectric actuator 50 and the second piezoelectric actuator 51, acts on the solid fiber 1 and / or the hollow-core fiber 2 to align the fibers 1, 2 and the appropriate modal adapter 4 with each other. If the coupling device also includes a piezoelectric actuator acting on the modal adapters, the control system can further control said piezoelectric actuator.

[0066] The control system 8 can be configured to automatically control the guidance system 5 based on the optical power measured by the verification system 6. This can be done using a computer program. A feedback loop is used to control the guidance system 5 (and thus the positioning of the solid and / or hollow-core fibers) by measuring the optical power at the output of the hollow-core fiber 2.

[0067] The process of coupling solid fiber 1 and hollow core fiber 2 takes place, for example, in the following way.

[0068] The process begins with a positioning initiation step in which the solid fiber 1 and the hollow-core fiber 2 are roughly positioned around the appropriate modal adapter 4. The initiation step assumes that the size of the hollow-core fiber 2 is known.

[0069] The process then includes a spatial centering or tracking step for the solid fiber 1. Spatial tracking is performed by injecting light and measuring the power received by at least one peripheral photodetector, here by photodiodes 70-D, 70-G, 70-H, and 70B. The at least one peripheral photodetector captures the light received by the solid fiber 1 and converts it into an electrical signal. The electrical signal is sent to the control system 8.

[0070] The power is measured at several positions of the solid fiber 1 along the X and Y axes. To do this, the first piezoelectric actuator 50 is activated. The solid fiber 1 is moved along each of the X and Y axes in a predefined step. The predefined step is, for example, a micrometer step. The power captured by the photodiodes 70-D, 70-G, 70-H, 70B is measured at each new position of the solid fiber 1. In other words, a scan is performed along each of the X and Y axes. During this scan, several power values ​​are obtained, each corresponding to a given position of the solid fiber 1, specifically to coordinates of the solid fiber 1 along the X and Y axes.

[0071] Once the scan is complete, a power value, called the upper power, corresponding to the highest power value measured during the scan, is identified for each photodiode. The measurement of a high power by the photodiodes provides information that the solid fiber 1 is not centered around (or aligned with) the hollow-core fiber 2.

[0072] The coordinates of the solid fiber 1 corresponding to the higher power (called the upper coordinates) are then identified. From the upper coordinates, centering coordinates of the solid fiber 1 are calculated so as to align the solid fiber 1 with the hollow-core fiber 2.

[0073] According to one embodiment, a scan along the X-axis can first be performed. The higher power is identified for each of the right photodiodes 70-D and left photodiodes 70-G. The X-axis position of the solid fiber 1 corresponding to this higher power is identified for each of the right photodiodes 70-D and left photodiodes 70-G. This provides the position XDsup for the right photodiode 70-D and XGsup for the left photodiode 70-G.

[0074] A Y-axis scan can then be performed. The higher power is identified for each of the top 70-H and bottom 70-B photodiodes. The Y-axis position of the solid fiber 1 corresponding to this higher power is identified for each of the top 70-H and bottom 70-B photodiodes. This provides the YHsup position for the top 70-H photodiode and the YBsup position for the bottom 70-B photodiode.

[0075] The order of the scans along the X, Y axes does not matter and can be reversed.

[0076] The process then involves calculating the centering coordinates (Xcen, Ycen) (or centering position) of the solid fiber 1 from the positions XDsup, XGsup, YHsup and YBsup. The calculation is, for example, as follows: Xcen = (XDsup + XGsup) / 2 and Ycen = (YHsup and YBsup) / 2.

[0077] According to the example described, the control system 8 receives the power values ​​measured by the photodiodes, records said values ​​and determines the upper powers for each of the photodiodes and along each of the X, Y axes. The identification of the upper coordinates of the solid fiber and the calculation of the centering coordinates are also carried out by the control system 8.

[0078] The process further includes aligning the solid fiber 1 and hollow core fiber 2 along the Z-axis. This allows them to get as close as possible to the modal adapter 4. The solid fiber 1 can, for example, be moved along the Z-axis by means of the first piezoelectric actuator 50.

[0079] The process also includes a measurement of the output power of the hollow core fiber 2 using the verification system 6. The power measured at the output of the hollow core fiber 2 allows verification that the two fibers 1, 2 are properly aligned.

[0080] The process can further include a final adjustment along the X, Y axes by means of the first piezoelectric actuator 50. This allows for fine-tuning the alignment of the solid fiber 1 and hollow core fiber 2.

[0081] The alignment steps along the z-axis and the final adjustment steps along the X, Y axes are repeated as many times as necessary until a maximum power value is reached, measured at the output of the hollow core fiber 2. The maximum power can correspond to a predefined power or simply to the highest power measured since the beginning of the process.

[0082] The process can finally include a step of rotating the hollow core fiber 2 around the Z-axis. The rotation of the hollow core fiber 2 is carried out by means of the second piezoelectric actuator 51. The rotation can also make it possible to obtain the maximum power output of the hollow core fiber 2. Since the fibers are not necessarily perfectly symmetrical, a rotation can make it possible to align the fibers with each other and collect the maximum power output of the hollow core fiber 2.

[0083] In summary, the coupling process of the solid fiber 1 and hollow core fiber 2 according to the example described above includes the following steps: initiation of positioning by a rough positioning of the solid fiber 1 and the hollow core fiber 2 around the appropriate modal adapter 4; scanning (or displacement) of the solid fiber 1 in the X axis by means of the first piezoelectric actuator 50; scanning (or displacement) of the solid fiber 1 in the Y axis by means of the first piezoelectric actuator 50; identification, for each photodiode, of the upper coordinates or upper positions XDsup, XGsup, YHsup and YBsup of the solid fiber 1 corresponding to the upper power for each of the photodiodes; calculation of the centering coordinates (Xcen,Ycen) of the solid fiber 1 from the upper positions XDsup, XGsup, YHsup and YBsup;positioning of the solid fiber 1 at the centering coordinates (Xcen,Ycen), said positioning being able to be carried out automatically by the feedback loop; alignment of the solid fiber 1 along the Z axis by means of the first piezoelectric actuator 50; measurement of the power output of the hollow core fiber 2 by means of the verification system 6.;

[0084] If necessary, the process further includes a final adjustment comprising the following substeps: displacement of the solid fiber 1 along the X, Y and / or Z axes by means of the first piezoelectric actuator 50, and / or rotation of the hollow core fiber 2 around the Z axis by means of the second piezoelectric actuator 51; and verification of the alignment by measuring the output power of the hollow core fiber 2 by means of the verification system 6.

[0085] As explained above, the initial positioning step assumes that the size of the hollow core fiber 2 is known. If this size is not known, the process can be repeated until the appropriate modal adapter 4 is found.

[0086] In the example described above, the power output measurement of the hollow-core fiber 2 is performed after the solid fiber 1 has been positioned and aligned along the X, Y, and Z axes. The procedure can be carried out differently. The power output measurement of the hollow-core fiber 2 can be performed after the solid fiber 1 has been positioned at the centering coordinates (Xcen, Ycen). Depending on the power measured at the output of the hollow-core fiber 2, the procedure can continue by aligning along the Z axis or by refining the positioning along the X and Y axes. In the second case (refining the positioning along the X and Y axes), the steps of scanning along the X and Y axes, identifying the upper coordinates, and calculating the centering coordinates are repeated. These steps can be repeated by reducing the predefined displacement step of the solid fiber 1.This variant of the fiber coupling process allows for time savings during fiber centering.

[0087] In one embodiment, the control system 8 can store the steps performed to align two fibers, as well as the fiber characteristics (fiber types and diameters). The information from the stored steps can be reused to subsequently align fibers with the same characteristics. This reduces the fiber coupling time.

[0088] In the first embodiment described above, the photodiodes are distributed around the hollow-core fiber 2. According to another embodiment not shown, the photodiodes can be distributed around the other fiber among fibers 1 and 2, here solid fiber 1. In other words, the photodiodes can be distributed around fiber 1 or fiber 2. When the photodiodes are distributed around solid fiber 1, the coupling process comprises the same steps except that the displaced fiber is the hollow-core fiber 2. Hollow-core fiber 2 is displaced by means of the second piezoelectric actuator 51. The verification system 6 is in this case connected to the output of the non-displaced fiber. In other words, the fiber coupling process can comprise the following steps: initiation of positioning by a rough positioning of the solid fiber 1 and the hollow-core fiber 2 around the appropriate modal adapter 4;scanning (or displacement) of one of the two fibers 1, 2 (called displaced fiber) along the X axis by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51; scanning (or displacement) of the displaced fiber along the Y axis by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51; identification, for each photodiode, of the upper coordinates or upper positions of the displaced fiber corresponding to the upper power for each of the photodiodes; calculation of the centering coordinates (Xcen,Ycen) of the displaced fiber from the upper positions; positioning of the displaced fiber at the centering coordinates, said positioning being able to be carried out automatically by the feedback loop; alignment of the displaced fiber along the Z axis by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51;measurement of the output power of the other fiber 1, 2 (called non-displaced fiber) using the verification system 6.;

[0089] If necessary, the method further includes a final adjustment comprising the following substeps: displacement of the displaced fiber along the X, Y and / or Z axes by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51, and / or rotation of the undisplaced fiber or the displaced fiber around the Z axis by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51; and verification of the alignment by measuring the output power of the undisplaced fiber by means of the verification system 6.

[0090] According to another embodiment not shown, the photodiodes can be arranged between the fibers 1 and 2. In other words, the photodiodes can extend in a plane between the two fibers. In this case, each fiber can be centered with respect to the photodiodes. The fiber coupling process can include the following steps: initiating positioning by roughly positioning the solid fiber 1 and the hollow-core fiber 2 around the appropriate modal adapter 4; scanning (or moving) the solid fiber 1 along the X-axis by means of the first piezoelectric actuator 50; scanning (or moving) the solid fiber 1 along the Y-axis by means of the first piezoelectric actuator 50; identifying, for each photodiode, the upper coordinates or upper positions of the solid fiber 1 corresponding to the upper power for each of the photodiodes;calculation of the centering coordinates (Xcen_1,Ycen_1) of the solid fiber 1 from the upper positions of the solid fiber 1; positioning of the solid fiber 1 at the centering coordinates (Xcen_1,Ycen_1), said positioning being able to be carried out automatically by the feedback loop; scanning (or displacement) of the hollow core fiber 2 in the X axis by means of the second piezoelectric actuator 51; scanning (or displacement) of the hollow core fiber 2 in the Y axis by means of the second piezoelectric actuator 51; identification, for each photodiode, of the upper coordinates or upper positions of the hollow core fiber 2 corresponding to the upper power for each of the photodiodes; calculation of the centering coordinates (Xcen_2,Ycen_2) of the hollow core fiber 2 from the upper positions of the hollow core fiber 2;positioning of the hollow core fiber 2 at the centering coordinates (Xcen_2,Ycen_2), said positioning being able to be carried out automatically by the feedback loop; alignment of the solid fiber 1 and / or the hollow core fiber 2 along the Z axis by means of the first piezoelectric actuator 50 and / or the second piezoelectric actuator 51; measurement of an output power of at least one of the fibers 1, 2 by means of the verification system 6.;

[0091] If necessary, the method further includes a final adjustment comprising the following substeps: displacement of the solid fiber 1 and / or the hollow core fiber 2 along the X, Y and / or Z axes by means of the first piezoelectric actuator 50 and / or the second piezoelectric actuator, and / or rotation of the solid fiber 1 and / or the hollow core fiber 2 around the Z axis by means of the first piezoelectric actuator 50 or the second piezoelectric actuator 51; and verification of the alignment by measuring the output power of at least one of the two fibers by means of the verification system 6.

[0092] Figure 1 schematically represents the solid fiber 1, the hollow-core fiber 2, and the coupling device 3 according to a second embodiment of the invention. The second embodiment differs from the first embodiment in that the coupling device does not include a centering system. In particular, the coupling device does not include photodiodes 70-D, 70-G, 70-H, and 70-B. The other elements of the coupling device in the second embodiment are similar to those of the first embodiment.

[0093] The process of coupling solid fiber 1 and hollow core fiber 2 therefore does not include fiber centering (or spatial positioning).

[0094] The method of coupling solid fiber 1 and hollow core fiber 2 may include the following steps: initiation of positioning by a rough positioning of the solid fiber 1 and the hollow core fiber 2 around the appropriate modal adapter 4; measurement of a power output of the hollow core fiber 2 using the verification system 6.

[0095] If the measured power is equal to the maximum power (predefined or non-predefined power), the coupling process can be stopped.

[0096] If the measured power is less than the maximum power, then the process further includes the following steps: moving the solid fiber 1 by means of the first piezoelectric actuator 50 along at least one of the X, Y and Z axes; and measuring the output power of the hollow core fiber 2 by means of the verification system 6.

[0097] The displacement and measurement steps are repeated until the measured power output of core fiber 2 equals the maximum power. The measured power values ​​can be recorded, and the displacement of solid fiber 1 can take these recorded values ​​into account. In particular, solid fiber 1 can be moved to position itself as close as possible to the location that yielded the highest recorded power value.

[0098] The power measurement at the output of the hollow core fiber 2 can be performed after one or more displacements of the solid fiber 1.

[0099] Figure 1 schematically represents the solid fiber 1, the hollow-core fiber 2, and the coupling device 3 according to a third embodiment of the invention. This third embodiment differs from the second embodiment by the verification system 6. In this embodiment, the verification system 6 comprises the central photodetector 60 and a thermal camera 62.

[0100] The central photodetector 60 can be an infrared detector. The central photodetector 60 is also compatible with hollow core fiber 2.

[0101] The thermal camera 62 is connected to the central photodetector 60. The thermal camera 62 allows visualization in thermal images of infrared radiation at the output of the central photodetector 60. The thermal camera 62 allows verification if the fibers 1, 2 are approximately well aligned.

[0102] The thermal camera 62 is sensitive to wavelengths between 1.3µm and 1.65µm (corresponding to the telecommunications window).

[0103] The verification system 6 of this third embodiment can be used alone or in combination with the verification system 6 of the second embodiment. When the two systems are used in combination, a user can alternately verify the alignment of the fibers and the appropriate modal adapter with either verification system 6.

[0104] The thermal camera 62 can enable a quick visual verification and can help accelerate the positioning of fibers 1 and 2, and in particular the initial positioning (or rough positioning) step of fibers 1 and 2. A user can, in particular, verify during the coupling process, using the thermal camera 9, whether fibers 1 and 2 are approximately aligned with each other.

[0105] In an example not shown, the coupling device may include the centering system 7 as described above, the infrared detector 60 and the thermal camera 62.

[0106] Figures 5 and 6 schematically represent the solid fiber 1, the hollow-core fiber 2, and the coupling device 3 according to a fourth embodiment of the invention. The coupling device differs from the second embodiment in its guidance system. The other elements of the coupling device of the fourth embodiment are similar to those of the second embodiment.

[0107] The guiding system 5 comprises at least two MEMS mirrors 52, 53. MEMS (Micro-Electro-Mechanical Systems) mirrors are miniaturized mirrors that use microelectronic and mechanical technologies to control light reflection. The guiding system 5 comprises n+1 MEMS mirrors 52, 53, where n is the number of modal adapters in the coupling device 3. Each MEMS mirror 52, 53 is positioned opposite one of the modal adapters and one of the following fibers: the solid fiber 1 and the hollow-core fiber 2. The mirrors 52, 53 are configured to guide light between the two fibers, specifically from the solid fiber 1 to the hollow-core fiber 2.

[0108] The guidance system 5 in this example comprises five mirrors: one mirror, called the input mirror 52, and four mirrors, called output mirrors 53. The input mirror 52 is positioned opposite the solid fiber 1 and one of the modal adapters (here, the lensed fiber). The output mirrors are each positioned opposite the hollow-core fiber 2. Each output mirror 53 is also positioned opposite one of the modal adapters.

[0109] The angle at which each MEMS mirror is oriented or tilted, called the mirror angle, is controlled by applying a voltage to the mirror. The mirror angle depends on the applied voltage. The angle of each mirror is controlled by applying a predetermined voltage to guide the light from the solid fiber 1 to the hollow fiber via the appropriate modal adapter 4.

[0110] As shown in the figure, the light sent from the solid fiber 1 arrives at the input mirror 52. Depending on the angle of the input mirror 52, the light is guided towards one of the modal adapters (towards the lensed fiber in the example shown). The modal adapter 4 towards which the light is guided corresponds to the appropriate modal adapter. The output mirror 53, located opposite the appropriate modal adapter 4, is also tilted at a predetermined angle so as to guide the light towards the hollow-core fiber 2. The other output mirrors are oriented vertically (i.e., each parallel to its corresponding modal adapter). The other output mirrors are thus in their rest position.

[0111] The method for coupling the solid fiber 1 and hollow-core fiber 2 may include a step of applying a first predetermined electrical voltage to the input mirror 52 and a second predetermined electrical voltage to the output mirror 53 associated with the appropriate modal adapter 4. The electrical voltage is predetermined according to the size of the hollow-core fiber 2. The first predetermined electrical voltage causes the input mirror 52 to tilt at a certain angle so as to guide the light towards the appropriate modal adapter 4. The second predetermined electrical voltage causes the output mirror 53 associated with the appropriate modal adapter 4 to tilt at a certain angle so as to guide the light towards the hollow-core fiber 2.

[0112] The control system 8 can, for example, include in its memory a table in which each fiber diameter is associated with an output mirror 53, and angle values ​​for the input mirror 52 and the associated output mirror 53 (or voltage to be applied to the input and output mirrors). The user only needs to specify the fiber type or its diameter to the control system 8 (via, for example, the human-machine interface). The control system 8 then sends the first and second electrical voltage commands to the input mirror 52 and output mirror 53 associated with the appropriate modal adapter 4.

[0113] The application of predetermined electrical voltages to the input mirror 52 and output mirror 53, described above, implies that the size of the hollow core fiber 2 is known.

[0114] The coupling device 3 may include a verification system similar to that described above. This is particularly useful if the size of the hollow-core fiber 2 is unknown. The modal adapters are tested sequentially until a maximum power output from the hollow-core fiber 2 is measured using the verification system 6 (specifically the wattmeter 61). The maximum power may correspond to a predefined power or simply to the highest power measured after testing the various modal adapters. Alternatively, the modal adapters may be tested sequentially until infrared radiation is detected on the thermal camera 62.

[0115] The control system 8 can store the steps performed to guide light between the fibers, as well as the fiber characteristics (fiber types and diameters). The information from these stored steps can be reused to subsequently couple fibers with the same characteristics. This information includes identifying the appropriate output mirror and the orientation or angle of each of the appropriate input and output mirrors. This reduces the fiber coupling time.

[0116] In the various embodiments described, the fibers are positioned (for the first three embodiments) or the mirrors are oriented (for the fourth embodiment) so that the light is injected at the center of the fiber, specifically at the center of the hollow-core fiber 2. Depending on the fiber type, it may be possible to inject the light at a point other than the center. When one of the fibers is a multi-core fiber, the light can be injected toward one of the cores that are offset from the center of the fiber.

[0117] The coupling device according to the invention allows for flexible and adaptable interconnection to various optical fibers, regardless of their type and diameter. Embodiments using a piezoelectric guidance system offer flexibility and the possibility of manually manipulating the coupling device. This is particularly advantageous for laboratory testing. The embodiment using a guidance system with MEMS mirrors, on the other hand, provides greater stability and enables fast and efficient coupling. This is particularly advantageous for industrial-scale coupling.

Claims

Coupling device between a solid optical fiber (1) and a hollow-core optical fiber (2), said coupling device (3) comprising at least one modal adapter (4) and a guidance system (5), the guidance system (5) being configured to position itself or to position at least one of the two fibers (1, 2) so that light sent from one of the two fibers (1, 2) passes through at least one modal adapter (4) and then through the other of the two fibers (1, 2). Coupling device according to claim 1, comprising several modal adapters (4), the guidance system (5) being configured to position itself or to position at least one of the two fibers (1, 2) so that a light sent from one of the two fibers (1, 2) passes into an appropriate modal adapter (4) among said modal adapters (4), and then into the other of the two fibers (1, 2). Coupling device according to claim 1 or claim 2, wherein the guidance system (5) is a piezoelectric system configured to cause movement of at least one of the two fibers (1, 2). Coupling device according to claim 3, wherein the guidance system (5) comprises two piezoelectric actuators (50, 51), each of the piezoelectric actuators (50, 51) being configured to cause movement of one of the two fibers (1, 2). Coupling device according to any one of claims 1 to 4, comprising a centering system (7) configured to position at least one of the two fibers (1, 2) in space. Coupling device according to claim 5, wherein the centering system (7) comprises four photodiodes (70-D, 70-G, 70-H, 70B) extending around one of the two fibers (1, 2) or between the two fibers (1, 2). Coupling device according to claim 6, in which the photodiodes (70-D, 70-G, 70-H, 70B) are arranged in a parallelepiped arrangement. Coupling device according to claim 1 or claim 2, wherein the guidance system (5) comprises at least two MEMS mirrors (52, 53), each MEMS mirror (52, 53) being opposite on the one hand a modal adapter (4) among the at least one modal adapter (4), and on the other hand one of the two fibers (1, 2). Coupling device according to any one of claims 1 to 8, comprising a verification system (6) configured to verify that the fibers (1, 2) and a modal adapter (4) among at least one modal adapter (4) are aligned with each other. Coupling device according to claim 9, wherein the verification system (6) includes a power measurement device (61) configured to measure optical power at the output of one of the two fibers (1, 2). Coupling device according to claim 9 or claim 10, wherein the verification system (6) includes a thermal camera (62). Coupling device according to any one of claims 1 to 11, comprising a control system (8) configured to control the guidance system (5). Coupling device according to claim 12 taken in combination with one of claims 9 to 11 or with one of claims 5 to 7, wherein the control system (8) is configured to control the guidance system (5) automatically from a measurement carried out by the verification system (6) or by the centering system (7).

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