Method for manufacturing a functionalised optical fibre

Abstract

The invention relates to a method for manufacturing a functionalised optical fibre, the method comprising: – during a functionalisation phase (110): – unwinding (114) a non-functionalised optical fibre wound onto a first spool in order to cause it to travel past a femtosecond laser which, through a temporary protective wrapper, inscribes patterns in a non-functionalised waveguide in order to obtain a functionalised optical-fibre blank, – winding (114) the functionalised optical-fibre blank onto a second spool, – during a phase (130) of depositing a permanent protective wrapper: unwinding (134) the functionalised optical-fibre blank wound onto the second spool so as to cause it to pass successively: - through a solvent bath which completely dissolves the temporary protective wrapper in order to expose the functionalised waveguide, then - through a deposition station (138) where the permanent protective wrapper is applied to the exposed waveguide.

Description

[0001] Process for manufacturing a functionalized optical fiber

[0002] [1] The invention relates to a method for manufacturing a functionalized optical fiber using laser pulses. The invention also relates to a non-functionalized optical fiber and a functionalized optical fiber blank for implementing this manufacturing method.

[0003] [2] The state of the art is known from the following documents: CN116661051A,

[0004] US2024 / 052173A1, US2004 / 052457A1, CN106772782B, CN116719121A,

[0005] CN104678486B, CN116520483A, US2001 / 020375A1, CN117008240A, US6204304B1, US2008 / 212925A1, US2019 / 113369A1 and KR20090084316A.

[0006] [3] Furthermore, a known method for manufacturing a functionalized optical fiber is for example described in application WO9739371A1. This method comprises in particular the following steps:

[0007] - the supply of a reel on which a non-functionalized optical fiber is wound, then

[0008] - the unwinding of the non-functionalized optical fiber to make it run through a manufacturing line where the optical fiber runs through different manufacturing stations to transform it into a functionalized optical fiber.

[0009] [4] In application WO9739371A1, the manufacturing chain successively comprises in particular:

[0010] - a station for removing an initial protective envelope to expose the waveguide of the non-functionalized optical fiber, then

[0011] - a functionalization station, using laser pulses, of the exposed waveguide to obtain a functionalized waveguide, then

[0012] - a station for depositing a definitive protective envelope on the functionalized waveguide.

[0013] [5] This process is interesting because there are practically no constraints on the nature of the final protective envelope. Thus, it makes it possible to manufacture functionalized optical fibers comprising a protective envelope made of metal or ceramic or any other material opaque to laser pulses. In addition, the number of manufacturing stations is limited, which simplifies the implementation of this manufacturing process.

[0014] [6] On the other hand, in such a manufacturing process, the running speed of the optical fiber in the manufacturing line is imposed by the manufacturing station which requires the slowest running speed. This is generally the functionalization station or the station for removing the initial protective envelope. Thus, for the other manufacturing stations which could accept a faster running speed, it is not possible to use the running speed as a parameter for optimizing the operation of this station. This is particularly true for the station for depositing the final envelope where the running speed is often a parameter which influences the thickness of the final envelope.Thus, since it is not possible to adjust the speed of the final envelope deposition station, the thickness of the final envelope must be adjusted by setting other parameters such as the temperature and pressure conditions under which the final envelope is deposited on the waveguide. This makes it more difficult to adjust and optimize the operation of this production line.

[0015] [7] The invention aims to overcome this drawback by proposing a manufacturing process which makes it possible to more simply optimize the manufacturing of a functionalized optical fiber without imposing any constraints on the choice of the final envelope and without complicating the manufacturing process.

[0016] [8] The invention is set forth in the attached set of claims.

[0017] [9] The invention will be better understood on reading the description which follows, given solely as a non-limiting example and made with reference to the drawings in which:

[0018] - Figure 1 is a schematic, partial and perspective illustration of a non-functionalized optical fiber,

[0019] - figure 2 is a partial longitudinal sectional view of a functionalized optical fiber blank,

[0020] - figure 3 is a partial longitudinal sectional view of a functionalized optical fiber,

[0021] - figure 4 is a schematic illustration of a fiberizing tower, - figure 5 is a schematic illustration of a functionalization chain,

[0022] - Figure 6 is a schematic illustration of a chain for depositing a final protective envelope, and

[0023] - Figure 7 is a flowchart of a process for manufacturing a functionalized optical fiber.

[0024]

[0010] In this description, the terminology, conventions and definitions of the terms used in this text are introduced in a chapter I. Then, detailed examples of embodiments are described in a chapter II with reference to the figures. In a chapter III, variants of these embodiments are presented. Finally, the advantages of the different embodiments are specified in a chapter IV.

[0025]

[0011] Chapter I: Definitions, terminologies and conventions:

[0026]

[0012] In the figures, the same references are used to designate the same elements.

[0027]

[0013] In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

[0028]

[0014] The symbol “*” denotes scalar multiplication.

[0029]

[0015] In this text, the term “laser pulse”, without further precision, designates a pulse from a femtosecond laser.

[0030]

[0016] The expression “an element made of a material A” or the expression “an element of material A” means that the material A represents 90% or 95% of the mass of this element.

[0031]

[0017] A "pure" component indicates that, if impurities are present in that component, then the mass of those impurities represents less than 1%, and typically less than 0.1% or less than 0.05%, of the total mass of the component.

[0032]

[0018] The acronym PVA stands for polyvinyl alcohol (“Poly(Vinyl Alcohol)” in English. PVA is a polymer. PVA is obtained by controlled hydrolysis or alcoholization of polyvinyl acetate.

[0033]

[0019] The hydrolysis rate of PVA is representative of the rate of replacement of acetate groups (CH3COO-) by hydroxyl groups (OH-) during the hydrolysis of polyvinyl acetate.

[0020] The mass distribution of a polymer, expressed in g / mol, corresponds to the mass average molar mass and is designated by the symbol “M w ". This is the average of the molar masses weighted by the mass of the chains of each length. This mass distribution is determined by size-exclusion chromatography known by the acronym SEC ("Size-Exclusion Chromatography"). This mass distribution is generally provided by the polymer manufacturer so it is not normally necessary to measure it.

[0034]

[0021] An optical fiber comprises at least one portion capable of guiding an optical signal along its longitudinal axis. This portion is formed of a core and an optical cladding which covers the core. The refractive index of the optical cladding is adapted so that the optical signal is confined inside the core and can propagate longitudinally with limited losses. Subsequently, this portion of the optical fiber whose function is to guide the optical signal is called a "waveguide". Thus, this waveguide comprises the core and the optical cladding of the optical fiber. On the other hand, the waveguide does not comprise the protective envelope(s) which cover the optical cladding to protect the waveguide.

[0035]

[0022] The protective sheath is the coating that forms the outer part of an optical fiber and whose function is to give this optical fiber mechanical, chemical and thermal properties that allow it to be handled and used without damaging it. In particular, the protective sheath makes it possible to protect the waveguide of this optical fiber:

[0036] - scratches on the surface of the optical cladding which form the beginnings of rupture; and

[0037] - environmental chemical attacks such as gases or liquids which can cause: a) the beginnings of ruptures by oxidation of the surface of the optical cladding or the core, b) a degradation of the optical qualities of the waveguide by the spectral absorption of compounds diffusing inside the waveguide.

[0038]

[0023] A protective envelope is said to be "transparent" to laser pulses when the transmittance, also called "transmission factor", at the wavelengths of these laser pulses is greater than 10% or 25% and, preferably, greater than 50%. The transmittance is equal to the ratio between the intensity of the laser pulse which has passed through the protective envelope and the intensity of the laser pulse incident on the outer face of this protective envelope.

[0039]

[0024] A protective envelope "opaque" to laser pulses is a protective envelope which is not transparent to these laser pulses.

[0040]

[0025] In this text, a “solvent-soluble” protective envelope means a protective envelope which is completely dissolved when it is soaked and kept static in a mass M of this solvent at a temperature T for a duration D, where:

[0041] - the mass M is one hundred times greater than the initial mass of the protective envelope to be dissolved,

[0042] - the temperature T of the solvent is between 10°C and 90°C, and

[0043] - duration D is less than 10 min and, preferably, less than 5 min or 1 min or 10 s.

[0044]

[0026] In this text, a solvent is therefore a fluid in which the protective envelope is soluble, in the sense given to this term in the preceding paragraph.

[0045]

[0027] When the solvent is water, the protective envelope is said to be “water soluble”.

[0046]

[0028] Chapter: Example of embodiment

[0047]

[0029] Figure 1 shows a portion of a non-functionalized optical fiber 2. The fiber 2 is, for example, a single-mode optical fiber or SMF (“Single Mode Fiber”) capable of guiding an optical signal over very long distances, i.e., over distances greater than one kilometer. The wavelength of the guided optical signal is typically in the visible light range, i.e., between 380 nm and 780 nm, or in the near infrared range, i.e., between 780 nm and 2000 nm, or in the far infrared, i.e., between 2 pm and 22 pm.

[0048]

[0030] For this, the fiber 2 comprises a non-functionalized waveguide 4 which guides the propagation of the optical signal along a longitudinal axis 6 of the fiber 2 and a single external protective envelope 8 which surrounds the waveguide 4.

[0049]

[0031] The waveguide 4 comprises a core 10, inside which the optical signal propagates, and an optical cladding 12 which covers this core 10. The waveguide 4 is for example made of silica. In this case, one of the core 10 and the optical cladding 12 is doped to obtain the desired refractive index different from the refractive index of the other of the core 10 and the optical cladding 12. For example, the core 10 is made of germanium-doped silica and the optical cladding 12 is then made of pure undoped silica.

[0050]

[0032] The guide 4 is non-functionalized, that is to say that the core 10 does not include any pattern inscribed using a laser pulse. Here, the core 10 does not include any defect deliberately created in this core to reflect part of the optical signal which propagates inside this core 10.

[0051]

[0033] In this embodiment, the outer diameter of the guide 4 is equal to 125 μm.

[0052]

[0034] The envelope 8 is intended to be removed during a subsequent step of manufacturing a functionalized optical fiber. Here, the envelope 8 is therefore only temporary. Thus, in the remainder of this text, the envelope 8 is also referred to as a “temporary envelope”. For this purpose, the envelope 8 is, in this embodiment, a water-soluble protective envelope. In addition, the envelope 8 is transparent to laser pulses. For this purpose, here, the envelope 8 is a protective envelope made of PVA. This envelope 8 is capable of being completely dissolved in water at 25°C in less than 5 s. In this exemplary embodiment, for this purpose, its thickness is typically less than 20 μm. The precise composition of the envelope 8 results from its manufacturing process which is described in detail with reference to FIG. 7.

[0053]

[0035] The thickness of the envelope 8 is also chosen to be greater than 10 μm so that it is capable of fulfilling its function as a protective envelope. In this exemplary embodiment, the thickness of the envelope 8 is equal to 15 μm. Here, the envelope 8 has the same mechanical protection properties as other standard protective envelopes. For example, when a large number of portions of the fiber 2 are subjected to a longitudinal tension of 16 N, only 10% of these portions of the fiber 2 have a rupture of the core 10.

[0054]

[0036] Figure 2 represents a blank of functionalized optical fiber 20. This blank 20 is identical to the optical fiber 2 except that patterns 22 are inscribed in its core 10 to functionalize the waveguide 4.

[0055]

[0037] The patterns 22 are inscribed using laser pulses from a femtosecond laser. Such a pattern corresponds to a sudden variation in the refractive index in the core 10. More precisely, a pattern inscribed using a femtosecond laser consists of one or more bubbles all located in the same transverse plane, i.e. in a plane perpendicular to the axis 6. Each of these bubbles is created by a laser pulse. The bubble appears at the focal point on which the laser pulse is focused. Each bubble creates a significant variation in the refractive index of the core 10 in the direction of propagation of the optical signal. For this, the difference between the index n r io of refraction of the heart 10 and the index n rB of refraction of a bubble is greater than 0.3 or 0.4. Here, the interior of each bubble is empty or practically empty which corresponds to a difference between the indices n r io and n rB greater than or equal to 0.4.

[0056]

[0038] Furthermore, for the refractive index variation to be abrupt, the diameter of each bubble is less than 500 nm and, preferably, less than 100 nm. Generally, the diameter of each bubble is also greater than 10 nm or 50 nm. Each bubble is predominantly spherical. Thus, the diameter of a bubble is equal to the diameter of the smallest volume sphere that entirely contains that bubble. Here, that diameter is less than 100 nm.

[0057]

[0039] When the pattern 22 is formed from several bubbles located in the same transverse plane, these bubbles can be disjointed or, on the contrary, overlap to form, for example, furrows.

[0058]

[0040] It is emphasized that currently only laser pulses, typically femtosecond, generating non-linear effects in the optical fiber make it possible to obtain a pattern 22 having the above characteristics without damaging the protective coating. Thus, by observing the dimensional characteristics of the pattern 22 it is possible to know that it was created using laser pulses from a femtosecond laser.

[0059]

[0041] In this embodiment, the patterns 22 are grouped into several distinct sets of patterns 22 and the patterns 22 of each set are arranged relative to each other to form a Bragg grating. Typically a Bragg grating is formed of at least three and, preferably, at least ten patterns 22. Thus, the waveguide 4 comprises a succession of Bragg gratings arranged one behind the other along the axis 6.

[0060]

[0042] The pitch A between two immediately consecutive patterns 22 along the axis 4 of the same Bragg grating is constant and chosen to place the wavelength at which this Bragg grating reflects the incident optical signal at the desired value.

[0043] Figure 3 shows a functionalized optical fiber 30 identical to the fiber 20 except that the sheath 8 is replaced by a definitive protective sheath 32. Unlike the sheath 8, the sheath 32 is not necessarily intended to be easily removed. Thus, the sheath 32 is not necessarily made of a material that can be easily removed. Furthermore, unlike the sheath 8, the sheath 32 can be made of a material that is opaque to laser pulses. In fact, the material from which the sheath 32 is made can be any material as long as it is suitable for the sheath 32 to fulfill its function of protecting the waveguide 4.Under these conditions, the material of the envelope 32 is chosen according to the field of use of the fiber 30. For example, the envelope 32 is made of one of the following materials: metal or ceramic or carbon.

[0061]

[0044] Figure 4 shows a fiberizing tower 40 used to manufacture the fiber 2. This tower 40 is similar to the known fiberizing towers for the manufacture of non-functionalized optical fibers in which the waveguide is made of silica. Thus, only the elements necessary for understanding the invention are shown in Figure 4 and described subsequently. In particular, in Figure 4 the absence of representation of certain manufacturing stations is represented by dotted lines.

[0062]

[0045] The tower 40 comprises successively, going from top to bottom, in particular: a furnace 42 for drawing the waveguide 4, a station 44 for depositing the envelope 8 and a winder 46.

[0063]

[0046] The furnace 42 melts a silica preform 48 to obtain a silica filament 50 which then passes through various stations (not shown) until the waveguide 4 is obtained which passes through the station 44 while moving at a production speed v p . The speed v p is typically greater than 80 mm / s and less than 350 mm / s. For example, the speed v p is often equal to or close to 120 mm / s and, preferably, even greater than 120 mm / s.

[0064]

[0047] The station 44 comprises a bucket 52 and an annealing tunnel 54 for depositing the envelope 8 on the guide 4. Thus, at the outlet of the station 44, the fiber 2 is obtained.

[0065]

[0048] The cup 52 makes it possible to deposit a PVA solution directly onto the optical sheath 12 and all around this optical sheath 12. For this purpose, the cup 52 contains the PVA solution to be deposited. The cup 52 is shaped so that the guide 4 enters from the top inside the cup 52, then passes through the PVA solution, then exits via a vertical tubular channel located on the bottom of the cup 52. Here, the cup 52 is shaped so that the PVA solution it contains is at ambient temperature and at ambient pressure. Thus, the station 44 is devoid of a device for heating the PVA solution and a device for pressurizing the PVA solution. The ambient temperature is typically greater than 18°C ​​and most often between 18°C ​​and 35°C. Ambient pressure is typically between 980 hPa and 1060 hPa and, most often, between 1000 hPa and 1025 hPa, i.e. close to 1013 hPa.Under these conditions, the thickness of the PVA solution deposited on the optical cladding 12 essentially depends on the viscosity of this PVA solution. The viscosity of this solution is adjusted by adjusting the amount of water in the solution. Here, the viscosity of the PVA solution is adjusted so that the thickness of the envelope 8 on the waveguide is between 10 μm and 20 μm. This corresponds to a mass of water in the solution of between 70% and 80% of the mass of this solution, the remainder of this solution being PVA. In this embodiment, to obtain an envelope 8 of 15 μm thickness, the amount of water in the PVA solution is taken equal to 75% of the mass of the solution so that the PVA represents 25% of the mass of this solution.

[0066]

[0049] The tunnel 54 dries the PVA solution deposited on the waveguide 4 by the bucket 52. For this purpose, the envelope 8 passes through, at the speed v p, the tunnel 54. The interior of the tunnel 54 is heated to a temperature sufficient for the deposited PVA solution to be completely dry at the exit of this tunnel 54. Thus, at the exit of the tunnel the envelope 8 is obtained. Generally, the temperature inside the tunnel 54 is greater than 200°C or 250°C. Here, the temperature inside the tunnel 54 is also kept less than or equal to 360°C so as not to damage the envelope 8.

[0067]

[0050] The winder 46 winds the fiber 2 which leaves the station 44 onto a reel 58. Once the manufacturing of the fiber 2 is complete, it is entirely wound onto the reel 58. The length L2 of the fiber 2 wound onto the reel 58 is typically greater than 1 km or 5 km. The reel 58 can then be removed from the winder 46 to store it while waiting to be used during a subsequent functionalization phase. For example, the reel 58 is stored in a storage site and the tower 40 can then be used to manufacture a new reel 58 without waiting for the stored reel 58 to be used during a functionalization phase.

[0068]

[0051] Figure 5 represents a chain 60 for functionalizing the fiber 2 which transforms the fiber 2 into the blank 20 of functionalized optical fiber. For this, the chain 60 comprises successively, going in the direction of travel of the optical fiber: an unwinder 62, a functionalization station 64 and a winder 66. In Figures 5 and 6 the direction of travel of the optical fiber is represented by an arrow.

[0069]

[0052] The unwinder 62 makes it possible to unwind the fiber 2 wound on the reel 58 at a writing speed v so that the fiber 2 runs in the station 64 at this speed v.

[0070]

[0053] The station 64 writes, in the core 10, the patterns 22 as the fiber 2 moves at the speed v, in this station 64. Thus, the fiber which leaves the station 64 is the blank 20 of functionalized optical fiber. For this, the station 64 is equipped with a femtosecond laser 68 whose laser pulses are focused at a point located in the core 10. Thus, each laser pulse creates a bubble. Here, each pattern 22 is formed of one or more bubbles. Under these conditions, the station 64 writes, in the core 10, the patterns 22 one after the other using a temporal succession of laser pulses while the fiber 2 moves in front of the femtosecond laser 68. The frequency of the laser pulses is adjusted taking into account the speed v, to obtain the desired distance between two immediately consecutive patterns 22 of the same Bragg grating.Conversely, when no Bragg grating is to be inscribed in the portion of fiber 2 which passes in front of the femtosecond laser 68, the generation of laser pulses is inhibited.

[0071]

[0054] Here, the laser pulses pass through the envelope 8 before reaching the core 10. Thus, the patterns 22 are written through the envelope 8. This is possible because the envelope 8 is transparent to the laser pulses.

[0072]

[0055] The winder 66 winds the blank 20 onto a reel 70 as it is produced at the speed v,. The length L20 of the blank 20 wound onto the reel 70 is typically close to the length L2, i.e. for example between 0.95*L2 and L2. Once the blank 20 is completely manufactured, the reel 70 can then be removed from the winder 66 to store it while awaiting a subsequent phase of depositing the envelope 32.

[0073]

[0056] Typically, the speed v, is much smaller than the speed v p and often ten or a hundred times lower than the speed v p . For example, the speed v, is often between 0.05 mm / s and 10 mm / s. Here, the speed v, is equal to 0.1 mm / s. A low speed v makes it possible to improve the precision of the pitch A of the inscribed Bragg gratings.

[0074]

[0057] Figure 6 shows a chain 80 for depositing the final envelope 32 which transforms the blank 20 into functionalized fiber 30. In Figure 6, only the elements necessary for understanding the invention have been shown. The chain 80 comprises successively, going in the direction of travel of the optical fiber: an unwinder 82, a station 84 for removing the envelope 8, a station 86 for depositing the envelope 32 and a winder 88.

[0075]

[0058] The unwinder 82 makes it possible to unwind the blank 20 wound on the reel 70 at a deposition speed v dso that the blank 20 passes through stations 84 and 86 at this speed v d . Typically, the speed v d is greater than the speed v, and often ten or fifty times greater than the speed v,. The speed v d is generally limited by the maximum speed at which it is possible to deposit the envelope 32 on the waveguide 4. Generally, the speed v d is less than 340 mm / s or 240 mm / s and greater than 1 mm / s.

[0076]

[0059] The station 84 comprises a water bath through which the blank 20 passes. For this, for example the station 84 is arranged in a similar manner to that described with reference to FIG. 3 of application US2006134324 or to one of FIGS. 6 and 7 of application US2016025925A1. Thus, in this embodiment, the station 84 comprises a tube in which a solvent, for example water, circulates permanently. The blank 20 enters the interior of the rectilinear tube through one end of this tube and exits this tube via the opposite end. Inside the tube, the blank 20 is directly in contact with the solvent over the entire length or practically the entire length of the tube. The length of the tube is adjusted so that, at the speed v d, the contact time between the blank 20 and the solvent allows the envelope 8 to be completely dissolved. In the case where the solvent is water, the contact time necessary to completely dissolve the envelope 8 is between 2 s and 5 s. In this case, the length of the tube is less than or equal to 1.5 m or 1 m.

[0077]

[0060] At the exit of station 84, the envelope 8 is completely removed and only the functionalized waveguide 4 remains which enters station 86.

[0078]

[0061] Station 86 deposits envelope 32 directly onto waveguide 4 at speed v d. In the case where the envelope 32 is metallic, this station 86 is for example identical to that described in application US2016025925A1. If the envelope 32 is made of ceramic, the station 86 can be produced as described in application FR3137911A1. In the case where the envelope 32 is made of polymer, the arrangement of the station 86 is deduced from the arrangement of the station 44 previously described. However, in this case, the polymer deposited on the waveguide 4 is not PVA. In this case and depending on the polymer used, to obtain the desired viscosity of the solution contained in the cup, it may be necessary to heat this cup. In addition, in the case of a polymer other than PVA, the solution of this polymer contained in the cup is often pressurized so that the deposition takes place at a pressure higher than ambient pressure. The temperature and the length of the drying tunnel must also be adapted to the polymer deposited.

[0079]

[0062] At the output of station 86, fiber 30 is obtained.

[0080]

[0063] The winder 88 winds, as it is produced, the fiber 30 onto a reel 90. Thus, at the end of the manufacture of the fiber 30, this fiber 30 is completely wound onto the reel 90 which can then be removed from the winder 88 to store it before being delivered to a customer. The length L30 of the fiber 30 wound onto the reel 90 is, for example, close to the length L20, that is to say between 0.95*L20 and L20, where L20 is the length of the blank 20 wound onto the reel 70.

[0081]

[0064] The method of manufacturing the fiber 30 will now be described with reference to FIG. 7.

[0082]

[0065] The method begins with a phase 100 of production of the fiber 2. This phase 100 includes in particular a step 102 of preparation of the PVA solution to be used in the cup 52. Here, this PVA solution is prepared by dissolving, in pure water, a PVA whose mass distribution, before its dissolution, is between 30,000 g / mol and 70,000 g / mol and whose hydrolysis rate is between 87% and 90%. It has been observed that this particular composition of the PVA before its dissolution in water makes it possible to obtain a PVA solution which can be deposited at room temperature and at ambient pressure, which is generally not the case for compositions other than PVA.

[0083]

[0066] The mass distribution of PVA is measured using the SEC method. The hydrolysis rate of PVA can be characterized by different methods, including DRX (X-Ray Diffraction) analysis or DSC (Differential Scanning Calorimetry) thermal analysis or FTIR (Fourier Transform Infrared Spectroscopy) analysis. FTIR analysis also makes it possible to highlight the ratio between the acetate (CH3COO-) and hydroxyl (OH-) groups of PVA. These different analysis methods are described in the following article: M Hdidar et al.: “Effect of hydrolysis and mass molecular weight on the structure and properties of PVA films”, ionics 2017, 23 3125-3155. After its dissolution in water, the hydrolysis rate of PVA can vary. However, the rate of hydrolysis of dissolved PVA is a function of the rate of hydrolysis of PVA before it is dissolved.Thus, it is possible to determine whether the hydrolysis rate, before dissolution, of the PVA used to obtain an AA solution of PVA, is between 87% and 90% by performing the following steps:.

[0084] - Step 1): The characteristics of this AA solution are measured by DRX, DSC and FTIR analysis.

[0085] - Step 2): BB samples of PVA solutions are prepared. Each BB sample is obtained by dissolving, in pure water, PVA having, before its dissolution, a known hydrolysis rate. The known hydrolysis rate is different for each of the BB samples. In addition, for each of the BB samples the mass distribution of PVA is identical to that of the AA solution.

[0086] - Step 3): The characteristics of the BB samples are measured by applying the same analyses as those used in step 1).

[0087] - Step 4): The characteristics measured during step 3) are compared with the characteristics measured during step 1). The BB samples whose characteristics are closest to the characteristics of the AA solution make it possible to estimate the hydrolysis rate, before dissolution, of the PVA used to prepare the AA solution.

[0088]

[0067] It is also emphasized that it is possible to know whether a PVA protective envelope has been obtained by depositing a PVA solution as described here in the same way as described above for the AA PVA solution. Indeed, for this, the PVA envelope is dissolved in pure water in order to obtain a PVA solution.

[0089]

[0068] Here, during step 102, the amount of dissolved PVA represents between 20% and 30% of the mass of the solution. For example, to obtain an envelope 8 of 15 μm thickness, the amount of dissolved PVA represents 25% of the mass of the solution.

[0090]

[0069] Once the PVA solution has been prepared and poured into the cup 52, a production step 104, at speed v p , fiber 2 is executed using the fiberizing tower 40. During this step 104, the waveguide 4 runs through the PVA solution prepared during step 102 at speed v p . During step 104, the PVA solution crossed by the waveguide is at ambient temperature and at ambient pressure.

[0070] At the end of this step 104, the coil 58 on which the fiber 2 is wound is obtained. Phase 100 is then completed and the coil 58 is then stored, during a step 108, before being used during a functionalization phase 110. During step 108, the coil 58 can be stored for several hours or several days before being used during phase 110.

[0091]

[0071] Phase 110 consists of functionalizing the waveguide 4 of the fiber 2 to obtain the blank 20 of functionalized optical fiber. Phase 110 is carried out by the functionalization chain 60.

[0092]

[0072] For this, just before the start of phase 110, the reel 58 is supplied, that is to say here removed from storage, then, during a step 112, the fiber 2, wound on this supplied reel 58, is installed in the functionalization chain 60. For this, the reel 58, which has been supplied, is mounted in the unwinder 62 and an empty reel 70 is mounted in the winder 66. The free end of the fiber 2 wound on the reel 58 is then pulled to pass it through the writing station 64 until it reaches the reel 70. The free end which has been thus pulled is then fixed on the reel 70.

[0093]

[0073] Once the fiber 2 is installed in the chain 60, during a step 114, the unwinder 62 unwinds the fiber 2 at the speed v, and the winder 66 winds the blank 20 produced at the exit of the writing station 64 at the speed v,. Thus, the optical fiber passes through the writing station 64 at the speed v,.

[0094]

[0074] At the same time, during a step 116, as the fiber 2 advances, the station 64 writes, through the envelope 8, the patterns 22 in the portion of the core 10 present in front of the femtosecond laser 68.

[0095]

[0075] Once the fiber 2 has been completely unwound from the reel 58, the functionalization phase 110 is completed. During a step 118, the reel 70 on which the blank 20 of functionalized optical fiber is entirely wound, is then stored before being used during a phase 130 of depositing the envelope 32. During step 118, the reel 70 can be stored for several hours or several days before being used during phase 130.

[0096]

[0076] Phase 130 consists of replacing the envelope 8 with the envelope 32 to obtain the functionalized optical fiber 30. Phase 130 is carried out by the chain 80 for depositing the envelope 32.

[0097]

[0077] The execution of phase 130 is for example triggered only when the material to be used for the envelope 32 is known. Thus, once this material is known and before triggering the execution of phase 130, a station capable of depositing the envelope 32 made of this material is installed in the line 80 to form the station 86. Thus, phases 100 and 110 are the same regardless of the material of the envelope 32. On the other hand, phase 130 is customizable which allows the manufacture of functionalized optical fibers using different materials for the production of the envelope 32 while keeping phases 100 and 110 unchanged.

[0098]

[0078] During a step 132, the blank 20 is installed in the chain 80 for depositing the envelope 32. For this, the reel 70, which was stored, is mounted in the unwinder 82 and an empty reel 90 is mounted in the winder 88. The free end of the blank 20 wound on the reel 70 is then pulled to pass it through the stations 84 and 86 until it reaches the reel 90. The free end which has been thus pulled is then fixed on the reel 90.

[0099]

[0079] Once the blank 20 is installed in the chain 80, during a step 134, the unwinder 82 unwinds the blank 20 at the speed v d and the winder 88 winds the fiber 30 produced at the outlet of the station 86 at the speed v d . Thus, the optical fiber successively crosses station 84 then station 86 at speed v d .

[0100]

[0080] At the same time, during a step 136, at the removal station 84, the blank 20 passes into a solvent bath, for example water, which completely dissolves the envelope 8 and exposes the functionalized waveguide 4. The waveguide 4 thus exposed then enters the station 86 for depositing the envelope 32.

[0101]

[0081] At the station 86 for depositing the envelope 32, during a step 138, the envelope 32 is deposited on the exposed waveguide 4. Thus, the functionalized optical fiber 30 is obtained at the output of the station 86.

[0102]

[0082] Once the blank 2 has been completely unwound from the reel 70, the phase 130 of depositing the envelope 32 is completed. During a step 140, the reel 90 on which the functionalized optical fiber 30 is entirely wound is then stored before being delivered to a customer. During step 140, the reel 90 can be stored for several hours or several days or even for several years, before being sent to a customer.

[0103]

[0083] Chapter III: Variants:

[0104]

[0084] Variants of the manufacture of the non-functionalized optical fiber:

[0085] Other formulations are possible for the PVA dissolved in water in order to obtain the solution to be deposited to form the envelope 8. For example, as a variant, the following formulation of the PVA, before dissolution, is possible to obtain an envelope 8 which dissolves quickly in water: mass distribution between 146,000 g / mol and 186,000 g / mol and hydrolysis rate between 87% and 89% and a mass concentration in water of less than 10%. In the case of this last formulation, during the deposition of the envelope 8, the PVA solution is heated between 35°C and 90°C. Similarly, the PVA solution is pressurized. The pressure is then typically between 100 kPa (1 bar) and 400 kPa (4 bar) depending on the temperature.

[0105]

[0086] The PVA may also include additives that do not modify or only very little modify its solubility in water. For example, as a variant, the PVA includes a carbon-based additive such as graphene or carbon nono-tubes. Such an additive improves the mechanical properties of the casing 8.

[0106]

[0087] Pressurization of the PVA solution is also possible even with the PVA formulation described in Chapter II above. Similarly, it is also possible to heat the PVA solution described in Chapter II, for example, to adjust its viscosity and therefore the thickness of the envelope 8.

[0107]

[0088] The thickness of the envelope 8 is chosen taking into account the speed v d of deposit implemented during step 130 of depositing the envelope 32. Indeed, the higher the speed v dis slow, the greater the thickness of the envelope 8 can be because the time allowed to remove the envelope 8 during the removal step 136 is longer. Thus, the thickness of the envelope 8 can be greater than 20 μm. Conversely, the higher the speed v d is high, the lower the thickness of the envelope 8 must be in order to be able to dissolve it completely during the removal step 136. Thus, the thickness of the envelope 8 can also be less than 10 μm. However, the thickness of the envelope 8 will still be chosen to be sufficient to give the optical fiber the desired mechanical, chemical and thermal properties.

[0108]

[0089] The speed v p production speed depends on the configuration of the fiberizing tower and, for example, its height. Thus, for fiberizing towers 12 meters high, the speed v p can reach 1.66 m / s. In another fiber tower, the speed v p may be less than 80 mm / s.

[0109]

[0090] The envelope 8 may be made of water-soluble materials other than PVA. For example, as a variant, the PVA is replaced by one of the waxes disclosed in application US2006134324A1 or in application US2016025925A1 or by another water-soluble polymer such as one of those cited in application US2016025925A1.

[0110]

[0091] The soluble envelope can also be made of a material soluble in a solvent other than water. For example, as a variant, as described in application US2016025925A1, the PVA is replaced by an acrylate soluble in acetone. The envelope 8 can also be made of a material soluble in an alcohol such as ethanol.

[0111]

[0092] Variants of functionalization phase 110:

[0112]

[0093] Other embodiments of the inscribed Bragg gratings are possible. For example, the patterns are not necessarily bubbles but may be, as variants, filaments, densifications of silica or nanogratings or colored centers resulting from the recombination of the bonds between germanium and silica. Alternatively, the Bragg gratings are tilted fiber Bragg gratings or chirped fiber Bragg gratings. In the case of frequency-drift Bragg gratings, the pitch A between the patterns of the same Bragg grating is not constant but, on the contrary, varies according to a predefined law.

[0113]

[0094] The functionalization phase 110 does not necessarily consist of inscribing Bragg gratings in the core of the optical fiber. In fact, the patterns 22 inscribed in the core 10 during the phase 110 can be arranged relative to each other to form optical devices other than Bragg gratings. For example, as a variant, the patterns 22 inscribed in the core 10 form a juxtaposition, along the axis 6, of Fabry-Perot cavities. In another variant, at regular intervals, for example every millimeter, a pattern 22 is inscribed in the core 10 and this continuously over the entire length of the core 10.

[0114]

[0095] Alternatively, during phase 110, several patterns 22 are simultaneously written in the core 10. A method for doing this is for example known as the “phase mask scanning technique”. This method is for example described in application US2007236796A1. Other writing methods mentioned in this application US2007236796A1 may be used to write the patterns 22 in the core 10 during phase 110.

[0096] The patterns 22 are not necessarily written only in the core 10 but may also, in addition, extend into the optical cladding 12.

[0115]

[0097] Variants of the deposit of the new protective envelope:

[0116]

[0098] Alternatively, instead of using liquid water to remove the envelope 8, water vapor is used.

[0117]

[0099] Other embodiments of the station 84 for removing the envelope 8 are possible. For example, as a variant, the removal station 84 is arranged as one of those described with reference to FIGS. 4, 6, 7 and 8 of application US2006134324.

[0118]

[0100] Alternatively, only a portion of the fiber 2 wound on the spool 70 is unwound so that the length of the fiber 30 manufactured is less than the length of the blank 20. In such a case, the same spool 70 can be used to manufacture several spools 90 of fibers 30.

[0119]

[0101] Alternatively, during the deposition step 138, the deposited envelope 32 is a multi-layer envelope comprising several layers deposited directly on top of each other. The different layers may be made of the same material. In this case, the envelope 32 is a single-material multi-layer envelope and the number of layers may be greater than four or eight. The different layers may also be made of different materials. In this case, the envelope 32 is a multi-material multi-layer envelope. For example, the envelope 32 may comprise one or more of the following alternations of layers:

[0120] - an alternation of layers comprising a ceramic layer and a carbon layer,

[0121] - an alternation of layers comprising a polymer layer and a ceramic layer, and

[0122] - an alternation of layers comprising a polymer layer and a carbon layer.

[0123]

[0102] Optical fiber variants:

[0124]

[0103] Other embodiments of the waveguide 4 are possible. For example, the core 10 may be made of pure silica and the optical cladding 12 is silica doped with fluorine. The core 10 may also be made of other materials capable of guiding the optical signal, such as, for example, rare earth-doped aluminosilicates, sapphire or plastic. In these latter cases, the optical cladding 12 is not necessarily made of the same material as the core 10.

[0104] The optical fiber may be a multimode optical fiber or MMF (Multi-Mode Fiber).

[0125]

[0105] The optical fiber can also comprise several waveguides 4 surrounded by the same protective envelope.

[0126]

[0106] Several of the variants described above can be combined in the same embodiment.

[0127]

[0107] Chapter IV: Advantages of the embodiments described:

[0128]

[0108] The fact of executing the functionalization phase 110 independently of the phase 130 of depositing the final envelope, makes it possible to use a scrolling speed v, during the phase 110 which is independent of the scrolling speed v d during phase 130. Thus, the speeds v, and v d can be chosen independently of each other. This facilitates the optimization, respectively, of the registration phase 110 and the final envelope submission phase 130. In particular, the speed v d can be chosen to be much higher than the speed v,, which makes it possible to optimize and accelerate the deposition of the final envelope 32.

[0129]

[0109] In addition, the blank 20 of functionalized optical fiber can be stored while waiting to know the nature of the final envelope 32 of the functionalized optical fiber to be manufactured. This makes the manufacturing process of functionalized optical fibers more flexible.

[0130]

[0110] Finally, the fact of inscribing the patterns 22 through the temporary envelope 8 avoids having to remove this temporary envelope 8 during the inscription phase 110. Thus, the manufacturing method described here comprises a single step of removing the temporary envelope 8, that is to say the same number of removal steps as in the method of application WO9739371A1. This manufacturing method therefore remains particularly simple and limits the number of manufacturing stations.

[0131]

[0111] The fact of completely removing the temporary envelope 8 using only a solvent makes it possible to avoid resorting to a mechanical action likely to damage the waveguide 4 of the optical fiber. Thus, the method described here makes it possible to manufacture functionalized optical fibers of very good quality.

[0132]

[0112] The fact that the solvent used is water makes it possible to avoid the use of toxic solvents which are more difficult to handle and recycle. Thus, the use of water as a solvent simplifies the manufacturing process.

[0113] PVA is a non-toxic and biocompatible material. It is therefore not necessary to take specific precautions when handling it. This simplifies the implementation of the manufacturing process.

[0133]

[0114] The fact that the thickness of the PVA envelope 8 is between 10 μm and 20 μm makes it possible to provide mechanical protection for the waveguide 4 while allowing rapid removal of this envelope 8 when it is soaked in water. In particular, the envelope 8 can be removed while the waveguide 4 is moving at a speed v d important deposit of the final envelope.

[0134]

[0115] Using PVA with a mass distribution of between 30,000 g / mol and 70,000 g / mol and a hydrolysis rate of between 87% and 90% before dissolving in water to prepare the solution used for depositing the casing 8 makes it possible to deposit the casing at ambient pressure. Under these conditions, the thickness of the casing 8 does not depend on the speed v p production of the waveguide 4. This simplifies the implementation of the manufacturing process. Indeed, the speed v p can be freely chosen.

[0135]

[0116] Not having to heat the PVA solution used to deposit the envelope 8 simplifies the manufacturing process.

[0136]

[0117] When the PVA represents between 20% and 30% by mass of the solution, the viscosity of this solution makes it possible to deposit a temporary envelope of 10 μm to 20 μm thickness while working at ambient temperature and at ambient pressure.

Claims

Claims 1. Method for manufacturing a functionalized optical fiber using laser pulses, this method comprising: - a step of providing a first reel on which a non-functionalized optical fiber is wound, this non-functionalized optical fiber comprising a waveguide capable of guiding an optical signal and a temporary protective envelope which covers the waveguide, then - a phase (110) of functionalization of the waveguide to obtain a functionalized waveguide, this functionalization step comprising the inscription (116) of patterns in the waveguide using laser pulses, then - a phase (130) of depositing a definitive protective envelope on the functionalized waveguide to obtain the functionalized optical fiber, characterized in that: - the functionalization phase (110) comprises: - unwinding (114) the non-functionalized optical fiber wound on the first reel to make it run, at a writing speed, in front of a femtosecond laser which writes, through the temporary protective envelope, the patterns in the non-functionalized waveguide as the non-functionalized optical fiber runs in front of this femtosecond laser to obtain a blank of functionalized optical fiber, and - winding (114) the functionalized optical fiber blank onto a second reel, - phase (130) of filing the final protective envelope includes: - unwinding (134) the blank of functionalized optical fiber wound on the second reel to make it run, at a deposition speed, successively, in a station for removing the temporary protective envelope then in a station for depositing the definitive protective envelope, - at the removal station, the passage (136) of the optical fiber blank into a solvent bath which completely dissolves the temporary protective envelope to expose the functionalized waveguide, and - at the level of the station for depositing the final protective envelope, the deposit (138) of the final protective envelope on the exposed waveguide.

2. Method according to claim 1, in which during the phase (130) of depositing the final protective envelope, at the removal station, the solvent used is only water.

3. Method according to claim 2, in which, during the supplying step, the temporary envelope of the non-functionalized optical fiber wound on the first reel, is made of polyvinyl alcohol.

4. Method according to claim 3, wherein, during the supplying step, the thickness of the temporary envelope of the non-functionalized optical fiber wound on the first reel is between 10 pm and 20 pm.

5. A method according to claim 3 or 4, wherein before the step of providing the first coil, the method comprises: - the dissolution (102), in water, of a polyvinyl alcohol whose mass distribution is between 30,000 g / mol and 70,000 g / mol and whose hydrolysis rate, before its dissolution in water, is between 87% and 90%, to obtain a solution of polyvinyl alcohol, then - producing (104), at a production speed, the non-functionalized waveguide, then scrolling, at the production speed, the non-functionalized waveguide produced in the polyvinyl alcohol solution to form, around the non-functionalized waveguide, the temporary protective envelope.

6. The method of claim 5, wherein, when the non-functionalized waveguide is running in the polyvinyl alcohol solution, the solution is at ambient pressure.

7. The method of claim 6, wherein, when running the non-functionalized waveguide in the polyvinyl alcohol solution, the solution is at room temperature.

8. A method according to any one of claims 5 to 7, wherein the solution obtained by dissolving the polyvinyl alcohol in water comprises between 20% and 30%, by mass, of polyvinyl alcohol and the remainder being water.

9. Method according to claim 1, in which during the phase of depositing the final protective envelope, at the removal station, the solvent used contains an alcohol.

10. Method according to any one of the preceding claims, in which: - during the supply step, the waveguide of the supplied non-functionalized optical fiber comprises a non-functionalized core, and - the phase (110) of functionalization of the waveguide comprises the inscription (116) of patterns in the core of the waveguide using the femtosecond laser.

11. Method according to any one of the preceding claims, in which the final protective envelope is opaque to the laser pulses used during the functionalization phase.

12. Non-functionalized optical fiber for implementing a method according to any one of the preceding claims, this non-functionalized optical fiber comprising: - a waveguide (4) capable of guiding at least one optical signal, - a temporary protective envelope (8) which covers the waveguide to protect it from attacks from the external environment, this temporary protective envelope being made of polyvinyl alcohol, characterized in that the temporary envelope (8) is obtained by depositing a solution of polyvinyl alcohol dissolved in water, on the waveguide and then drying this solution of polyvinyl alcohol deposited on the waveguide, the poly(vinyl alcohol) used to obtain the solution of polyvinyl alcohol having, before its dissolution in water, a mass distribution of between 30,000 g / mol and 70,000 g / mol and a hydrolysis rate of between 87% and 90%.

13. Functionalized optical fiber blank for implementing a method according to any one of claims 1 to 9, this functionalized optical fiber blank comprising: - a waveguide (4) capable of guiding at least one optical signal, and - a temporary protective envelope (8) which covers the waveguide to protect it from attacks from the external environment, this temporary protective envelope (8) being made of water-soluble polyvinyl alcohol, characterized in that the waveguide comprises patterns (22) inscribed using laser pulses from a femtosecond laser.

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