AUTOMATED INSTALLATION AND METHOD FOR INCORPORATING AT LEAST ONE BRAGG NETWORK IN ONE OR MORE PREDETERMINED SECTIONS OF AN OPTICAL FIBER ELEMENT

Abstract

The invention relates to an automated installation (100) and an automated method for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element (200), using: A first line (130) called a "delay" line in which the speed of the optical fiber element exiting said line is modified relative to its speed at the input; A zone (140) called an inscription zone, provided for inscribing at least one Bragg grating in one or more predetermined sections of said optical fiber element stripped of its first protective coating; A second line (160) called a "delay" line in which the speed of the optical fiber element exiting said line is modified relative to its speed at the input. Figure [1]

Description

Title of the invention: AUTOMATED INSTALLATION AND METHOD FOR REGISTERING AT LEAST ONE NETWORK DE BRAGG IN ONE OR MORE SECTIONS PREDETERMINED FROM AN OPTICAL FIBER ELEMENT technical field

[0001] The present invention relates to an automated installation and method for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element.

[0002] The invention also relates to a computer program configured to implement the steps of said process.

[0003] The invention applies to the field of Bragg grating sensors used in the civil engineering, offshore, aviation, and more consumer applications, such as automotive. State of the art

[0004] A Bragg diffraction grating is a structure that exhibits a periodic pattern of alternating high and low optical refractive indices. Bragg gratings are useful because of their ability to reflect a particular wavelength or "color" of light. The color that will be reflected by a Bragg grating is the color whose wavelength corresponds exactly to twice the effective grating period. The complete formula is written: λ_Bragg = 2 * neff * λ_Grating, where:

[0005] Lambda_Bragg: Bragg wavelength, i.e., the color reflected by the grating,

[0006] Lambda_Grating: physical pitch of the grating, i.e., the alternating period of high and low indices,

[0007] Neff: effective index of the medium, for example optical fiber.

[0008] Bragg gratings can be formed by creating an interference pattern in the glass core of an optical fiber, usually by recombining two parts of a laser beam.

[0009] It is known to inscribe Bragg gratings by applying optical radiation perpendicular to the axis of the optical fiber according to a first technique. Such a technique consists of dividing a laser beam into two subbeams and recombining these subbeams at a known and controllable angle in the core of the optical fiber. A second well-known technique consists of focusing the laser beam onto the core of the fiber through a grooved or patterned transmissive optical element under the name of phase mask. This phase mask holographically creates an interference pattern in the core of the optical fiber.

[0010] It is also known from the prior art to coat optical fibers with a standby coating which protects the delicate glass structure from chemical or mechanical attacks, and which allows the storage of these fibers in the form of reels.

[0011] Thanks to this waiting coating, the optical fiber reel can be placed in a so-called hydrogenation chamber, that is to say a sealed chamber containing hydrogen at pressures of up to 200 bars and at temperatures ranging from ambient to several tens of degrees Celsius, without risk of damage or mechanical embrittlement such as micro-scratches or cracks.

[0012] This hydrogenation step maximizes the photosensitivity of the optical fiber and allows for faster writing of the Bragg grating and / or with higher reflectivity for a given laser insolation time.

[0013] This hydrogenation step also makes it possible to maximize the regeneration rate, i.e. the reflectivity of the Bragg network obtained after the thermal regeneration treatments, relative to that of the initiating Bragg network, i.e. before said treatments.

[0014] However, the waiting coating must be eliminated at least on the portion of the fiber where the applied optical radiation must access and form a Bragg grating in the core of the optical fiber.

[0015] It is also necessary to remove the waiting coating in order to apply the final protective coating, which is also specific to the application chosen for the optical fiber.

[0016] These techniques for producing Bragg gratings on optical fiber are well established, but encounter difficulties in making production processes continuous on a large scale.

[0017] Indeed, the removal speeds of the waiting coating are not compatible with the registration speeds of optical fibers, which are generally much lower.

[0018] This has so far limited the production of Bragg gratings for optical fibers to small batch production. In these batch processes, the coating is generally chemically removed from a short length of several optical fibers. The optical fibers are then individually inscribed to form Bragg gratings in the sections of the optical fibers where the coating has been removed.

[0019] These batch production processes allow good control of the formation of Bragg gratings in a short length of optical fiber.

[0020] However, these batch production processes, due to the discontinuity between the removal of the waiting coating and the registration of the Bragg gratings, do not allow not the production of large-scale Bragg gratings, or the production of multiple Bragg gratings in a large length of optical fiber.

[0021] Moreover, in these batch production processes, the optical fiber stripped of its waiting coating is exposed, before the Bragg gratings are registered, to risks of damage.

[0022] One object of the present invention is to remedy at least one of the drawbacks of the prior art.

[0023] Another object of the invention is to provide an installation and a method for carrying out continuously and automatically the operations of removing the waiting coating and registering the Bragg networks.

[0024] Another object of the invention is to propose an automated installation and method for continuously carrying out thermal treatments for stabilizing or regenerating sections of inscribed optical fibers.

[0025] Another object of the invention is to apply a technical coating intended for an end application, for example a ceramic-type coating resistant to very high temperature. Description of the invention

[0026] To this end, the invention relates to an automated installation for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element, said installation comprising: - At the installation's input, a docking station configured to accommodate said optical fiber element wound on a first winding support and covered with a first protective coating, - Guiding means configured to scroll said optical fiber element through said installation, - At the output of the installation, a storage station configured to wind the said optical fiber element onto a second winding support, - Characterized in that the said installation further comprises, successively and downstream of the docking station: - A so-called "unstripping" area, configured to remove the first protective sheath from the said optical fiber element, - A first line, called a "delay line," equipped with means to vary its length, so that the optical fiber element travels along the said first delay line over a variable distance, the speed of the optical fiber element at the output of the said delay line being modified relative to its speed at the input, - A so-called registration zone, designed to register at least one Bragg grating in one or more predetermined sections of said optical fiber element stripped of its initial protective coating, - A second line, called a "delay line," equipped with means to vary its length, so that the optical fiber element travels in the second delay line over a variable distance, the speed of the optical fiber element at the output of the delay line being modified relative to its speed at the input. - A so-called "re-sheathing" zone, configured to coat the said optical fiber element with a second protective coating, - Control mechanisms.

[0027] Various embodiments of the invention are provided, incorporating, according to all their possible combinations, the different optional features set out below.

[0028] According to a particular embodiment, the first and / or second delay line may comprise at least two pulleys, the means for varying the length of the first, respectively the second delay line, being configured to move said two pulleys further apart or closer together.

[0029] Advantageously, the installation may further include a heat treatment station located downstream of the registration area and upstream of the second delay line.

[0030] Preferably, the heat treatment station can be a CO2 laser thermal annealing station, or a thermal annealing furnace.

[0031] According to one particular feature, the inscription area may include a source configured to emit continuous or pulsed laser radiation and associated with an optical assembly, said assembly being preferably mounted on a moving plate in translation.

[0032] The invention also relates to a method for inscribing, in an automated installation according to an embodiment of the invention, at least one Bragg grating in one or more predetermined sections of an optical fiber element, said optical fiber element being previously coated with a first protective coating, wound on a first winding support and installed on a docking station of said installation, characterized in that it comprises an inscription phase during which, simultaneously: - A step is performed to lengthen the first line, called the "delay line," so that the speed of the optical fiber element exiting said delay line is reduced to a value (V_inscription) relative to a scrolling speed value (V_nom) at the input of said delay line, - A step is carried out to register at least one Bragg grating in one or more predetermined sections of the optical fiber element moving through a so-called "registration" zone at the speed (V_inscription), - A step is taken to shorten the length of a second line called "delay line", so that the scrolling speed of the optical fiber element at the output of said delay line is increased to the value (V_nom) relative to the scrolling speed value (V_inscription) at the input of said delay line.

[0033] Various embodiments of the invention are provided, incorporating, according to all their possible combinations, the different optional features set out below.

[0034] The method may include a reloading phase, alternating with the inscription phase, during which simultaneously: - A step is performed to shorten the length of the first line, known as the "delay" line, so that the scrolling speed of the optical fiber element at the output of said delay line is increased to a value (V_sup) relative to the scrolling speed value (V_nom) at the input of said delay line, - The optical fiber element is moved at speed (V_sup) in the so-called "registration" zone, without registering said optical fiber element. - We proceed with a step of lengthening the second line called "delay line", so that the speed of scrolling of the optical fiber element at the output of said delay line is reduced to the value (V_nom) compared to its speed of scrolling (V_sup) at the input of said delay line.

[0035] Advantageously, during the registration phase and during the reloading phase, a step can be taken to remove the first protective waiting coating in a so-called "unsheathing" area of ​​said installation, said unsheathing area being located upstream of the first delay line.

[0036] Advantageously, during the registration phase and during the reloading phase, a step of depositing a second protective coating on said optical fiber element can be carried out in a so-called "re-sheathing" zone of said installation, said re-sheathing zone being located downstream of the second delay line.

[0037] Preferably, the second protective coating can be a polymer coating preferably made of an acrylate, a polyimide, a PEEK, filled or unfilled, or a metallic coating preferably made of aluminium, copper, gold or a ceramic coating preferably made of boron nitride.

[0038] According to a particular aspect, after the step of depositing the second protective coating, a step of winding the optical fiber element onto a second winding support in a storage station can be carried out.

[0039] According to another particular aspect, during the inscription phase, and at the end of the inscription step, a thermal annealing step can be carried out by passing the optical fiber element through a furnace, or a CO2 laser annealing step can be performed on the sections of the optical fiber element on which the Bragg gratings have been inscribed.

[0040] According to a preferred aspect, the heat treatment step can be a thermal annealing to stabilize the Bragg lattice by inducing a partial erasure of its spectral pattern.

[0041] According to another also preferred aspect, the heat treatment step can be a regeneration heat treatment inducing the complete erasure of the Bragg grating, then the formation of a new Bragg grating at the same wavelength and with a reflectivity reduced by a factor of at least 10, or even at least 100.

[0042] After the step of winding the optical fiber element onto a second winding support, a heat treatment step can be carried out in a furnace of the optical fiber element wound on the second support, the second support preferably being a ceramic coil.

[0043] According to yet another particular aspect, during the registration step, the predetermined section(s) of the optical fiber element can receive one or more pulses from a source configured to emit laser radiation, and associated with an optical assembly mounted on a moving stage in translation at a speed equal to the scroll speed (V_inscription) of the optical fiber element in the registration area.

[0044] Alternatively, during the registration step, the predetermined section(s) of the optical fiber element may receive one or more pulses from a source configured to emit laser radiation, and associated with an optical assembly mounted on a fixed plate, the scroll speed (V_inscription) of the optical fiber element in the registration area being zero.

[0045] Advantageously, during the registration step, wavelength-multiplexed Bragg gratings and / or Bragg gratings written at the same wavelength can be created on the predetermined section(s) of the optical fiber element. Brief description of the FIGURES

[0046] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which: - Fig. 1 is a schematic representation of a non-limiting example of an automated installation for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element, according to the invention. - Fig. 2 is a schematic representation of a non-limiting example of an embodiment of a method for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element, according to the invention. - Fig. 3 is a schematic representation of another non-limiting embodiment of a method for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element, according to the invention.

[0047] It is understood that the embodiments described below are by no means limiting. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0048] In particular, all the variants and embodiments described are combinable with each other if there is no technical obstacle to this combination.

[0049] In the figures and in the rest of the description, elements common to several figures retain the same reference. Detailed description of the FIGURES

[0050] Fig. 1 is a schematic representation of a non-limiting example embodiment of an automated installation for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element, according to the invention.

[0051] The installation of [Fig.1] includes at the input a docking station 110 configured to accommodate an optical fiber element 200 wound on a first winding support 201, such as a reel, and coated with a first protective standby coating.

[0052] The term "optical fiber element" refers to a long portion of optical fiber consisting of one or more fiber cores and an optical cladding that confines the light signal within the fiber core(s). This optical fiber element is generally intended to be inserted into a mechanical cladding or protective sleeve designed for a specific application.

[0053] The optical fibers considered for the present invention may be single-mode, multi-mode, microstructured, photonic crystal, or multi-core fibers. The optical fibers considered for the present invention are in any case photosensitive, typically, for example, so-called germanosilicate optical fibers, that is, fibers whose light-guiding core is doped with germanium.

[0054] The installation includes guide means 190 configured to advance the optical fiber element through said installation. These guide means 190 may consist of pulleys or rollers mounted to rotate freely about an axis perpendicular to the axis (x) of progression of the optical fiber element through said installation.

[0055] The installation includes at the output a storage station 180 configured to wind said optical fiber element, on which at least one Bragg grating has been inscribed in one or more predetermined sections, onto a second winding support 202, which may also be a reel.

[0056] The installation also includes means (not shown in the FIGURES) configured to control and adjust the tension of the optical fiber element as it travels through the installation.

[0057] In accordance with the invention, the installation further comprises successively and downstream of the docking station 110 the equipment detailed below.

[0058] The docking station 110 unwinds the optical fiber element 200 into a sheathing area 120 which may consist of an enclosure in which the first protective coating of the optical fiber element is dissolved with an aqueous or organic solution.

[0059] Next, a first line 130, referred to as a "delay line," equipped with means 131 for varying its length L130, is adjacent to the stripping zone 120. Thus, the optical fiber element moves along said first delay line over a variable distance. As a result, the speed of movement of said optical fiber element exiting said delay line is modified compared to its speed of movement entering said delay line.

[0060] At the output of this first delay line 130, there is a zone 140 called registration, intended to register at least one Bragg network in one or more predetermined sections of said optical fiber element stripped of its first protective waiting coating.

[0061] At the exit of the registration zone 140, there is a second line 160 called "delayed" equipped with means 161 to vary its length L160.

[0062] Thus, the optical fiber element travels along said second delay line over a variable distance. As a result, the speed of the optical fiber element exiting said delay line is modified compared to its speed of travel entering said delay line.

[0063] A zone 170 called "re-sheathing" follows the second delay line and is configured to coat said optical fiber element with a second protective coating which constitutes the final coating.

[0064] This second protective coating allows the optical fiber element to be wound onto the storage station 180 without risk of damage. This second protective coating also possesses the properties required for the application for which the optical fiber element is intended.

[0065] The installation also includes control means 10 provided in particular for adjusting the lengths of the first and second delay line, controlling the registration means, and adjusting the unwinding and winding speeds in the receiving station and in the storage station.

[0066] According to a particular and advantageous embodiment, the means 131 for varying the length L130 of the first delay line 130 comprise a motorization for moving at least two pulleys 190 away from each other, present in the first delay line 130.

[0067] Similarly, the means 161 for varying the length of the second delay line 160 include a motorization for moving at least two pulleys 190 away from each other, present in the second delay line 160.

[0068] It is understood that, when the optical element travels through the installation in a predominantly horizontal direction (x), its trajectory is deflected by moving one or both of the pulleys along an axis, for example, vertical (z). This results in a lengthening of the path to be traveled in the delay line by the optical fiber element.

[0069] Depending on the desired footprint of the installation, the number of movable pulleys can be adjusted along an axis perpendicular to the main (x) direction of travel of the optical element within the installation. In other words, for a horizontal main travel direction, the number of movable pulleys along the vertical axis can be increased in a delay zone to avoid being constrained by excessive vertical displacement of the movable pulleys.

[0070] The inscription zone 140 includes a source 142 associated with an optical assembly, and configured to emit continuous or pulsed laser radiation.

[0071] This can be a continuous laser radiation emitting at ultraviolet wavelengths, for example 244 nm.

[0072] This can also be pulsed laser radiation, and in particular nanosecond excimer laser radiation, for example a KrF laser emitting at 248 nm or an ArF laser emitting at 193 nm.

[0073] It can also be femtosecond laser radiation, for example Ti:Sa emitting at 800nm, or Ytterbium emitting at 1030 nm, 515 nm or 266 nm.

[0074] The optical assembly associated with the laser radiation source is preferably mounted on a plate 141 that moves in translation, in order to be able to follow the moving optical fiber element, or to perform several successive inscriptions.

[0075] The registration step will be detailed in the paragraphs relating to the method according to the invention.

[0076] Advantageously, the automated installation 100 may further include a thermal treatment station 150 located downstream of the registration zone 140 and upstream of the second delay line 160.

[0077] This heat treatment station 150 can be a CO2 laser thermal annealing station, or a thermal annealing furnace.

[0078] The heat treatment step will be detailed in the paragraphs relating to the process according to the invention.

[0079] As shown in [Fig.1], this installation is an automated installation in that it requires very little intervention from an operator.

[0080] Indeed, once the optical element is loaded on the docking station 110, the optical fiber element is automatically unwound through the various stations 120, 130, 140, 150, 160, 170 and also automatically wound up at the exit 180 of the installation on the storage station.

[0081] FIGURES 2 and 3 are each a schematic representation of a non-limiting example embodiment of a method for inscribing at least one Bragg grating in one or more predetermined sections of an optical fiber element 200, according to the invention.

[0082] In this process, the optical fiber element is first coated, during its manufacture, with a first protective standby coating, then wound onto a first winding support 201, such as a reel, and hydrogenated.

[0083] The term "first protective temporary coating" means a coating that can be easily removed, for example by soaking in an aqueous or organic solution.

[0084] The coil can be placed in a so-called hydrogenation chamber, namely a sealed chamber containing H2 at pressures of up to 200 bar and at temperatures ranging from ambient to several tens of degrees Celsius. There is no longer risk of damage or mechanical weakening such as micro-scratches or cracks, since the optical fiber element is protected by the first protective coating.

[0085] This hydrogenation step maximizes the photosensitivity of the optical fiber and allows for faster writing of Bragg gratings, with higher reflectivity for a given laser insolation time.

[0086] This hydrogenation step also makes it possible to maximize the regeneration rate, i.e. the reflectivity of the Bragg networks obtained after regeneration compared to that of the initiating Bragg networks, i.e. before regeneration.

[0087] The optical fiber element, wound on the first winding support 201, is installed on the docking station 110 of said installation.

[0088] The method according to the invention includes a PHI registration phase during which the steps detailed below are carried out simultaneously.

[0089] An extension step El30 is carried out on the length L130 of the first line 130 called "delayed", so that the scrolling speed of the optical fiber element at the output of said delayed line is lowered to a value V_inscription relative to a scrolling speed value V_nom at the input of said delayed line.

[0090] An El40 registration step is carried out of at least one Bragg grating in one or more predetermined sections of the optical fiber element moving in the so-called "registration" zone 140 at the speed V_registration.

[0091] A shortening step El60 is carried out on the length L160 of the second line 160 called "delayed", so that the scrolling speed of the optical fiber element at the output of said delayed line is increased to the value V_nom relative to the scrolling speed value V_inscription at the input of said delayed line.

[0092] In other words, the optical fiber element is actually unwound in a continuous step El 10 from the docking station 110 at a speed V_nom which is greater than the registration speed V_inscription.

[0093] It is understood that the elongation step E130 of the length L130 of the first line 130 called "delayed", makes it possible to slow down the speed of scrolling the optical fiber element.

[0094] In parallel, it is also understood that the shortening step E160 of the length L160 of the second line 160 called "delay" makes it possible to accelerate the speed of scrolling of the optical fiber element so that it recovers its speed V_nom at which it is continuously wound in the storage station 180.

[0095] At the end of the PHI registration phase, it is understood that the length L130 of the first line 130, known as "delayed", is at its maximum, while the length L160 of the second line 160, known as "delayed", is at its minimum.

[0096] Therefore, the process includes a PHI' reloading phase, alternating with the PHI inscription phase, during which the steps detailed below are carried out simultaneously.

[0097] A shortening step E130' is carried out on the length L130 of the first line 130 called "delayed", so that the scrolling speed of the optical fiber element at the output of said delayed line is increased to a value V_sup with respect to the value of the scrolling speed V_nom at the input of said delayed line.

[0098] The optical fiber element is moved E140' at the speed V_sup in the so-called "inscription" zone 140, without any inscription being made on the optical fiber element.

[0099] An extension step E160' is carried out on the length L160 of the second line 160 called "delayed", so that the speed of scrolling of the optical fiber element at the output of said delayed line is reduced to the value V_nom compared to its speed of scrolling V_sup at the input of said delayed line.

[0100] This scrolling speed V_sup can typically be, for example, from 5 to 25 m / minute.

[0101] Thus, it is understood that the process allows continuous operation at speed V_name of the installation 100 with an alternation between the registration phase PHI and the reloading phase PHI'.

[0102] Regarding the registration step E140, the predetermined section(s) of the optical fiber element 200 can receive one or more pulses from the source 142 configured to emit laser radiation, and associated with an optical assembly mounted on the plate 141, which is movable in translation at a speed equal to the scroll speed V_registration of the optical fiber element 200 in the registration area 140.

[0103] Alternatively, the lengthening of the first delay line and the shortening of the second delay line can be adjusted so that the scrolling speed V_inscription of the optical fiber element 200 in the inscription zone 140 is zero. In this so-called "Stop and Go" configuration, the moving plate 141 remains stationary during inscription.

[0104] During the registration step E140, wavelength-multiplexed Bragg gratings can be produced using several settings of the source 142, and / or Bragg gratings written at the same wavelength can be produced using a single setting of the source 142.

[0105] During the registration step E140, Bragg gratings can be produced in one place or in several places, either by means of a beam-separating optical setup or by moving the movable stage 141.

[0106] During the E140 inscription step, type I Bragg gratings can be produced, which are inscribed at a moderate writing intensity and which have gratings indexed over the whole core, or type II gratings which can be written at higher intensities for a very short time, generally with a single nanosecond pulse from an excimer laser.

[0107] It should be noted that during the registration phase PHI and the reloading phase PHI', the removal step E120 of the first protective standby coating in the so-called "unsheathing" zone 120 of the installation is advantageously carried out continuously at the nominal speed V_nom. The first protective standby coating is dissolved by immersion in an aqueous or organic solution. A removal speed V_nom of 1 to 10 m / minute can be used in the case of removal in an aqueous solution, for example 3 m / minute.

[0108] Similarly, during the PHI registration phase and during the PHI reloading phase, an E170 deposition step of a second protective coating on said optical fiber element is advantageously carried out continuously and at the speed V_nom, in a zone 170 called "re-sheathing" of said installation, said re-sheathing zone being located downstream of the second delay line.

[0109] The second protective coating can be made of polymer (acrylate, polyimide, PEEK, filled or unfilled), or of metal (aluminium, copper, gold) or of ceramic (boron nitride).

[0110] According to an advantageous embodiment shown in [Fig.2], during the PHI registration phase, and at the end of the registration step E140, a heat treatment step 150 is carried out.

[0111] Thermal annealing can be carried out by passing the material through a furnace, or preferably by means of a CO2 laser emitting, for example, at 10.6 pm. This type of laser makes it possible to apply a controlled temperature to the Bragg grating that has just been inscribed, and not to the entire optical fiber element.

[0112] The heat treatment step 150 can be a thermal annealing to stabilize the Bragg lattice by inducing a partial erasure of its spectral pattern.

[0113] Alternatively, the heat treatment step 150 can be a regeneration heat treatment inducing the complete erasure of the Bragg grating, then the formation of a new Bragg grating at the same wavelength and with a lower reflectivity.

[0114] This so-called "regeneration" heat treatment consists of applying a high temperature, typically 900°C (but it can also be lower temperatures, such as 600°C, for longer periods or higher temperatures, such as 1000°C, for shorter periods). This type of heat treatment induces a complete erasure of the type I (so-called initiator) Bragg lattice and leads to the formation of a new Bragg grating at the same wavelength but with lower reflectivity. This new, so-called regenerated, Bragg grating exhibits high-temperature stability properties, typically up to the regeneration temperature, over long periods or over shorter periods at temperatures above the regeneration temperature.

[0115] It is understood that when only the portion of the optical element containing a Bragg grating is exposed to thermal laser annealing, this limits the unnecessary embrittlement of sections of the optical element devoid of a pattern to be stabilized.

[0116] The length of the Bragg grating processed by the CO2 type laser is an input data provided to the CO2 type laser module by the control means 10, and is adjustable by determining, for example, the length of the optical fiber element scanned by the laser beam through the optical setup which may include a galvanometric mirror combined with an f-theta lens ensuring the focusing and maintenance of a focal point along the optical fiber element regardless of the angle of deflection of the laser beam by the galvanometric mirror.

[0117] The optical setup may also include an f-theta lens, which can also be mounted on a translation stage to adjust the distance between its focal plane and the optical fiber element, thereby adjusting the laser energy density and consequently the core heating temperature. More simply, with a fixed focal length setting, the energy of the laser pulses can be adjusted to regulate the heating temperature. During the adjustment phase, it is possible to register a Bragg grating and measure its spectral shift to deduce the heating temperature to which it is exposed.

[0118] It is understood that the online heat treatment step 150 not only saves production time, but also allows adaptation of the heat treatment to be carried out for each Bragg network.

[0119] It is also understood that, since the inline heat treatment step 150 is prior to the deposition step E170 of the second final protective coating, it becomes possible to apply a second protective coating which would be incompatible with the annealing temperature of the Bragg lattice.

[0120] During the winding step E180 at the exit of the installation 100, the optical fiber element coated with the second final protective coating is wound onto a second winding support 202, typically a reel.

[0121] In the case where the heat treatment step E150 has not been carried out in the installation 100, and as shown in [Fig.3], a heat treatment step E150' is carried out outside the installation 100, in a furnace, on the optical fiber element wound on its second support 180.

[0122] It should be noted that thanks to a ceramic-type protective coating compatible with high temperatures, it becomes possible to regenerate or stabilize thermally heat the Bragg gratings directly in doored furnaces outside the installation 10, by placing the optical fiber element wound on its second support 180 such as a reel of refractory material such as a ceramic.

[0123] Thus, collective regeneration of Bragg gratings in a furnace can be carried out, independently of the length of the optical fiber element. Until now, furnace regeneration was performed in furnaces, for example tubular ones, whose geometry limited the possible length of the Bragg gratings.

[0124] All the steps of the process according to the invention are implemented by the control means 10 which execute one or more computer programs comprising instructions relating to said steps.

[0125] The installation and method according to the invention, in summary, allow the following steps to be carried out automatically and continuously: - Removal of the waiting layer at a speed compatible with the registration speeds of Bragg networks and the speeds of the terminal layer, - The registration of Bragg gratings with the possibility of using multiple pulses by optical fiber tracking or with a so-called "stop&go" operation, while maintaining scroll speeds in other areas, - Stabilization or regeneration of Bragg networks by thermal annealing, - The application of a terminal coating dedicated to the application.

[0126] The installation and method according to the invention make it possible in particular to control the stabilization of the temperature behavior of Bragg networks according to the type of Bragg networks (I or II) that one wishes to obtain.

[0127] It is also possible to carry out regeneration by CO2 laser with an optical fiber element passing through a sheath or cell made of material transparent at the wavelength of the CO2 laser and minimizing convective phenomena between the optical fiber element and the ambient atmosphere;

[0128] It is also possible to carry out a regeneration or stabilization at high temperature of Bragg grating assemblies wound directly on a coil (for example in refractory material) and this for arbitrary lengths or arbitrary topologies of the Bragg grating assemblies.

[0129] The installation and method according to the invention make it possible to obtain: - Temperature-stabilized Bragg gratings by thermal annealing, whether wavelength-multiplexed or quasi-continuous type, regenerated or not; - Quasi-continuous Bragg gratings regenerated by thermal annealing and re-covered with final protective coatings adapted to a particular application; - Wavelength-multiplexed Bragg gratings regenerated by thermal annealing and re-clad with final protective coatings adapted to a particular application; - Bragg networks with optimized reflectivity due to the possibility of multi-pulse writing and the possibility of controlling the thermal treatments for stabilization and regeneration.

[0130] Optical fiber elements inscribed with Bragg gratings stabilized at low temperatures according to the process of the invention are used for the manufacture of sensors usable at temperatures up to 500°C for applications in civil engineering, land or sea transport, aeronautics, energy infrastructure, cryogenic applications.

[0131] Optical fiber elements inscribed with high-temperature stabilized Bragg gratings according to the process of the invention are used for the manufacture of sensors usable at temperatures up to 1300°C for applications such as space launchers, nuclear, hydrogen production components, leak detection on hot pipes.

[0132] Of course, the invention is not limited to the examples just described.

Claims

1. Demands An automated installation (100) for registering at least one Bragg grating in one or more predetermined sections of an optical fiber element (200), said installation comprising: - At the installation's input, a docking station (110) configured to accommodate said optical fiber element (200) wound on a first winding support (201) and covered with a first protective waiting coating, - Guiding means (190) configured to scroll said optical fiber element through said installation, - At the output of the installation, a storage station (180) configured to wind said optical fiber element onto a second winding support (202), Characterized in that the said installation further comprises successively and downstream of the docking station (110): - A zone (120) referred to as the "unsheathing" zone, configured to remove the first protective sheath from said optical fiber element, - A first line (130) called a "delay line" equipped with means (131) for varying its length (L130), so that said optical fiber element moves along said first delay line over a variable distance, the speed of movement of said optical fiber element at the output of said delay line being modified relative to its speed of movement at the input, - A zone (140) called the registration zone, intended to register at least one Bragg grating in one or more predetermined sections of said optical fiber element stripped of its first protective waiting coating, - A second line (160) called a "delay line" equipped with means (161) for varying its length (L160), so that said optical fiber element moves along said second delay line over a variable distance, the speed of movement of said optical fiber element at the output of said delay line being modified relative to its speed of movement at the input, - A zone (170) called "re-sheathing", configured to coat said optical fiber element with a second protective coating, - Control means (10).

2. Automated installation (100) according to claim 1, characterized in that the first (130) and / or the second (160) delay line comprise at least two pulleys (190), the means (131, 161) for varying the length of the first (130), respectively the second (160) delay line, being configured to move said two pulleys (190) away from or closer to each other.

3. Automated installation (100) according to claim 1 or 2, characterized in that it further comprises a heat treatment station (150) disposed downstream of the registration zone (140) and upstream of the second delay line (160).

4. Automated installation (100) according to any one of the preceding claims, characterized in that the inscription area (140) comprises a source (142) configured to emit continuous or pulsed laser radiation and associated with an optical assembly, said assembly being preferably mounted on a translationally movable plate (141).

5. A method for inscribing, in an automated installation (100) according to any one of claims 1 to 4, at least one Bragg grating in one or more predetermined sections of an optical fiber element (200), said optical fiber element being previously coated with a first protective holding coating, wound on a first winding support (201) and installed on a docking station (110) of said installation, characterized in that it comprises an inscription phase (PHI) during which, simultaneously: - A lengthening step (El30) is carried out on the length (L130) of a first line (130) called a "delay line", so that the speed of the optical fiber element at the output of said delay line is reduced to a value (V_inscription) relative to a speed value (V_nom) at the input of said delay line, - An inscription step (El40) is performed on at least one Bragg grating in one or more predetermined sections of the optical fiber element moving through a zone (140) called the "inscription" zone at the speed (V_inscription), - A shortening step (E160) is carried out on the length (L160) of a second line (160) called "delayed", so that the scrolling speed of the optical fiber element at the output of said delayed line is increased to the value (V_nom) relative to the scrolling speed value (V_inscription) at the input of said delayed line.

6. A method for inscribing at least one Bragg grating according to claim 5, characterized in that it comprises a reloading phase (PHI'), alternating with the inscription phase (PHI), during which simultaneously: - A shortening step (E130') is performed on the length (L130) of the first line (130) called the "delay" line, so that the scrolling speed of the optical fiber element at the output of said delay line is increased to a value (V_sup) relative to the scrolling speed value (V_nom) at the input of said delay line, - The optical fiber element is moved (E140') at the speed (V_sup) in the zone (140) called "inscription", without inscription of said optical fiber element, - We proceed with an extension step (E160') of the length (L160) of the second line (160) called "delayed", so that the speed of scrolling of the optical fiber element at the output of said delayed line is reduced to the value (V_nom) compared to its speed of scrolling (V_sup) at the input of said delayed line.

7. A method for inscribing at least one Bragg grating according to claim 6, characterized in that, during the inscription phase (PHI) and during the reloading phase (PHI'), a step (El20) is carried out involving the removal of the first protective standby coating in a zone (120) referred to as the "unsheathing" zone of said installation, said unsheatheing zone being located upstream of the first delay line.

8. A method for registering at least one Bragg grating according to claim 6 or 7, characterized in that, during the registration phase (PHI) and during the reloading phase (PHI'), a deposition step (El70) of a second protective coating is carried out on said optical fiber element, in a zone (170) referred to as the "re-sheathing zone" of said installation, said re-sheathing zone being disposed downstream of the second delay line.

9. A method for inscribing at least one Bragg grating according to claim 8, characterized in that the second protective coating is a polymer coating preferably made of an acrylate, a polyimide, a PEEK, filled or unfilled, or a metallic coating preferably made of aluminum, copper, gold, or a ceramic coating preferably made of boron nitride.

10. Method for inscribing at least one Bragg grating according to claim 9, characterized in that after the deposition step (El70) of the second protective coating, a winding step (E180) of the optical fiber element is carried out on a second winding support (202) in a storage station (180).

11. A method for inscribing at least one Bragg grating according to any one of claims 6 to 10, characterized in that, during the inscription phase (PHI), and at the end of the inscription step (E140), a thermal annealing step (150) is carried out by passing the optical fiber element through a furnace, or alternatively, a CO2 laser annealing step is carried out on the sections of the optical fiber element on which the Bragg gratings have been inscribed.

12. A method for inscribing at least one Bragg grating according to claim 11, characterized in that the heat treatment step (150) is a regeneration heat treatment inducing the complete erasure of the Bragg grating, then the formation of a new Bragg grating at the same wavelength and with a reflectivity reduced by a factor of at least 10, or even at least 100.

13. A method for inscribing at least one Bragg grating according to claim 10, characterized in that at the end of the winding step (E180) of the optical fiber element on a second winding support (202), a heat treatment step (150') is carried out in a furnace of the optical fiber element wound on the second support, the second support being preferably a ceramic reel.

14. A method for inscribing at least one Bragg grating according to any one of claims 6 to 13, characterized in that, during the inscription step (E140), the predetermined section(s) of the optical fiber element (200) receive one or more pulses from a source (142) configured to emit laser radiation, and associated with an optical assembly mounted on a plate (141) that moves in translation at a speed equal to the scroll speed (V_inscription) of the optical fiber element (200) in the inscription zone (140).

15. A method for inscribing at least one Bragg grating according to any one of claims 6 to 13, characterized in that, during the inscription step (E140), the predetermined section(s) of the optical fiber element (200) receive one or more pulses from a source (142) configured to emit laser radiation, and associated with an optical assembly mounted on a fixed plate (141), the scroll speed (V_inscription) of the optical fiber element (200) in the inscription area (140) being zero.

Images