WO2007147946A1

WO2007147946A1 - Method for manufacturing fibre preform

Info

Publication number: WO2007147946A1
Application number: PCT/FI2007/050373
Authority: WO
Inventors: Pekka Soininen; Sami Sneck
Original assignee: Beneq Oy
Priority date: 2006-06-22
Filing date: 2007-06-19
Publication date: 2007-12-27
Also published as: FI20065441A0; FI20065441A; FI122323B; WO2007147946A8

Abstract

The invention relates to a method for manufacturing a fibre preform and/or for modifying properties of the same by an ALD method. According to the invention, one or more fibre preforms are placed in an atomic layer deposition reactor and a first catalyst is supplied into a core of the fibre preform in order to produce a catalysing layer onto a surface of the core of the fibre preform. Next, one or more dopants are supplied into the core of the fibre preform, whereby the first catalyst causes two or more deposition layers to be formed onto the surface of the core of the fibre preform.

Description

METHOD FOR MANUFACTURING FIBRE PREFORM

BACKGROUND OF THE INVENTION

[0001] The invention relates to manufacturing or modifying a fibre preform by an atomic layer deposition method, and particularly the present in- vention relates to a method according to the preamble of claim 1 for manufacturing a fibre preform and/or for modifying properties of the same by an ALD method, wherein a surface to be grown is exposed to alternately repeated saturated surface reactions of starting materials in accordance with principles of the ALD method. The present invention further relates to a fibre preform manufactured or modified by the method according to the invention as well as to an optical fibre manufactured from a fibre preform manufactured or modified according to the present invention.

[0002] According to prior art, the manufacture of a core of a fibre preform is carried out e.g. by a Modified Chemical Vapour Deposition or MCVD method. In the MCVD method, the aim is to grow, by using a Chemical Vapour Deposition or CVD technique, a so-called soot layer inside a tubular preform in a longitudinal direction thereof. In order to produce fibres of uniform quality during manufacture, process parameters have to be adjusted extremely accurately, but despite such accuracy, growth takes place in a different manner at an inlet end and at an outlet end of the preform. Furthermore, as the process of growing the core of the fibre preform progresses, the conditions change as the diameter of the core of the preform decreases due to the grown soot layer. In practice, this means that the properties also in the direction of a radius of the preform change. The manufacture of the core of the preform takes place layer by layer to enable a refractive index distribution to be formed to be adjusted. This, in turn, leads to the requirement that the starting materials, together with a substrate, should be distributed uniformly on the surface of the core of the preform which, consequently, means that the process becomes more demandr ing to manage. The soot layer provided is made of a porous material, so it has to be sintered to make it solid prior to the manufacture of a next layer. Thus, the requirements not only of the process but also of the sintering have to be taken into account in the adjustment of a flame used in the sintering. The core of the fibre preform may also be manufactured by utilizing some other method used in the manufacture of a fibre preform, such as OVD, VAD or another corresponding method. [0003] This manufacture of a core of a fibre preform by the MCVD method or some other method for manufacturing fibre is an extremely accurate and demanding task and the required equipment is complex, as can be seen in what has been disclosed above. Despite such accuracy, it is impossible to manufacture a core of a fibre preform with an ideal accuracy and at a desired production rate, but the process is slow and the end product always includes compromises. Furthermore, between the core growing and sintering phases, the soot layer tends to absorb impurities, which impair the properties of a finished end product. [0004] It has not been economically possible nor reasonable to manufacture a fibre preform or its core by means of a conventional ALD technique since the conventional technique has allowed only one atomic layer to be grown at a time onto the surface of the core of the fibre preform. As far as the purposes of commercial production are concerned, by this known method it has been far too slow to achieve a sufficient thickness of the deposition layers.

BRIEF DESCRIPTION OF THE INVENTION

[0005] An object of the invention is thus to provide a method so as to solve the above-mentioned problems. The object of the invention is achieved by a method according to the characterizing part of claim 1 , which is characterized by the method comprising the following steps of: a) supplying a catalyst to an ALD reactor in order to produce a catalysing surface onto the surface of the fibre preform to be grown; b) supplying one or more dopants and/or substrates onto the surface of the fibre preform to be grown so that the catalyst causes two or more atomic or molecular layers to be formed onto the surface of the fibre preform to be grown.

[0006] Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The idea underlying the invention is that a digitally accurate Atomic Layer Deposition or ALD method is used for manufacturing and/or modifying a fibre preform, particularly for manufacturing and/or modifying a core of a fibre preform. The ALD method and its applications relating to doping of a fibre preform and other materials have been further described e.g. in Finnish Patent Application No. 20045490 of the same Applicant. According to the invention, a substrate and/or a dopant of a fibre preform is supplied by the ALD method to a surface of the fibre preform to be grown. According to the invention, the ALD method for manufacturing a fibre preform utilizes a so-called catalytic ALD deposition such that the surface of the fibre preform to be grown, the fibre preform having been placed inside an ALD reactor, is first exposed to a catalyst which reacts with the surface of the fibre preform, forming a catalytic surface. Next, the surface of the fibre preform to be grown is exposed to a substrate and/or a dopant in order to produce deposition layers onto the surface of the fibre preform to be grown and/or in order to dope the substrate of the fibre preform with the dopant. Because of the catalyst, the number of atomic or molecular layers being formed onto the surface of the fibre preform to be grown is not only one but the catalyst enables the surface reaction of the substrate and/or the dopant to continue such that during one cycle, which comprises exposing the surface to be grown once to the catalyst and once to the substrate and/or dopant, two or more atomic or molecular layers are formed onto the surface of the fibre preform to be grown, together forming a deposit layer produced by one cycle. Catalysed reactions are temperature and dose dependent such that it is possible to adjust the number of atomic and molecular layers and thus the thickness of the deposition layer being formed by means of process temperatures as well as the magnitude of doses of catalyst and/or substrate and/or dopant supplied onto the surface of the fibre preform to be grown.

[0008] The reactions of the substrate and/or the dopant catalysed by a catalyst enable even large deposition layers to be formed onto the surface of the fibre preform to be grown during each ALD cycle. A large deposition layer herein refers to the formation of two or more atomic or molecular layers during one ALD cycle, preferably to the formation of ten or more atomic or molecular layers during one cycle, or even to the formation of 30 to 100 atomic or molecular layers during one ALD cycle. According to the invention, such a catalytic ALD deposition enables an extremely rapid ALD deposition, whereby it becomes possible to manufacture or modify a fibre preform by the ALD method for commercial production. In addition, while the use of ALD becomes possible, it becomes possible to manufacture fibre preforms of higher quality since as a method, ALD provides a digitally accurate fibre preform manufacture which allows the amounts and ratios of the dopants to be adjusted accu- rately. Furthermore, the equipment used in the ALD method can be designed to be significantly simpler than the complex equipment of the MCVD method. No sintering phase, which is required in an MCVD process, is thus needed, either. Hence, in terms of quality, pureness and accuracy, a fibre preform manufactured by the method as well as an optical fibre further manufactured therefrom are better than those manufactured by the known methods.

DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following, the manufacture of a core of a tubular fibre preform by a method according to the invention is examined by way of example. According to the present invention, ALD technique is utilized for the manufacture of a fibre preform and/or a core thereof. In the present context, a fibre preform refers to any fibre preform which is suitable for manufacturing an optical fibre. Furthermore, in the present context, the manufacture of a fibre preform may comprise the manufacture of a fibre preform itself, the manufacture of a core of a fibre preform, modifying a fibre preform and/or modifying a core of a fibre preform. In other words, the method according to the invention may be utilized in a part of a manufacturing process of a fibre preform or its core, or in the entire process.

[0010] For the method according to the invention, an ALD apparatus, an ALD reactor in particular, in which one or more fibre preforms are placed, is provided. The ALD reactor is preferably provided with a reaction chamber in which preforms are placed such that the starting materials may be supplied into the tubular preform, i.e. to a core of the preform. In practice, this can be implemented by placing the preforms between inlets and outlets of the reaction chamber such that from the inlet the starting materials flow into the core of the preform from its first end and exit the preform from its second end, directly to the outlet. Thus, only the core of the preform is exposed to the starting materials. When two or more preforms are to be placed in the ALD reactor, it is possible to provide the reaction chamber with an inlet and outlet for a larger number of preforms. This enables fibre preforms having different properties to be manufactured simultaneously in the ALD reactor by feeding different starting materials and/or amounts or ratios of starting materials to different preforms.

[0011] Preferably, however, the ALD reactor may be provided such that the preforms may be placed in the reaction chamber successively in a flow connection with one another. In such a case, a starting material fed into a first preform passes through all preforms before exiting the reactor. In other words, the preforms may be attached by appropriate attaching means provided in the reactor which allow the starting materials supplied into the core of the preforms to flow successively through all the preforms. This enables preforms to be manufactured efficiently since it is possible to process several preforms simul- taneously during the same starting material cycle. In addition to connecting the preforms in series as disclosed above, preforms may also be placed in the ALD reactor in parallel, in which case a catalyst and/or a substrate and/or a dopant is fed to each preform separately, simultaneously or non- simultaneously. The preforms are placed normally in the reaction chamber, which may be e.g. a vacuum chamber, of the ALD reactor. Alternatively, the preforms may be provided in the ALD reactor such that the tubular preforms themselves constitute the walls of the reaction chamber to which the starting materials, such as the catalyst, substrate and dopant, are fed, in which case no separate vacuum chamber is necessarily needed but in some cases the pre- forms may form this vacuum chamber. Furthermore, the method according to the invention may be carried out by the ALD technique also in a device for the manufacture of a preform or in a device for the modification thereof, such as an MCDV lathe, or during the manufacture of a preform.

[0012] Preforms are made of a glass material, which may be any oxide forming conventional glass, such as SiO₂, B₂O₃, GeO₂ and P₄O₁₀.

[0013] As described above, according to the invention a catalyst, which forms a catalysing layer onto the surface of the core as a result of a surface reaction of the surface of the core and the catalyst, is first supplied into the core of the tubular preforms provided in the ALD reactor. A catalyst to be used may be trimethylaluminium (Me₃AI), which reacts with OH groups residing on the surface of the core of the preform, forming aluminium-oxygen bonds and a surface comprising methylaluminium. Alternatively, aluminium dimethyl- amide (AI₂(NMe₂^) may be used as a catalyst. In addition to the above- mentioned aluminium compounds, trimethyl lanthanum, trimethyl zirconium, trimethyl hafnium or a compound of another trimethyl and metal or another compound comprising aluminium, lanthanum, zirconium, hafnium or another metal, which causes a catalysing effect in order to grow a plurality of atomic layers onto the surface of the core of the fibre preform during one cycle, can be used as a catalyst. In such a case, the catalyst each time forms onto the sur- face of the core a metal-oxygen bond and/or a surface comprising methyl metal and having a catalytic effect, thus forming a catalytic layer onto the surface of the core of the preform.

[0014] Next, one or more dopants and/or substrates are supplied into the core of the preform, whereby a first catalyst causes the formation of two or more atomic or molecular layers onto the surface of the core of the fibre preform. In other words, the catalyst enables two or more atomic layers to be formed onto the surface of the core by catalysing a surface reaction of the substrate and/or the dopant. In the present connection, silanol, such as tris(tert- butoxy)silanol ((BuO)₃SiOH), which reacts with the catalytic surface, can be used as a substrate. When the aforementioned silanol is used together with aluminium dimethylamide, a siloxane polymer is formed which forms bonds through an aluminium layer. When said silanol is further supplied into the core of the preform, it diffuses through the previously formed deposition layers to the aluminium-oxygen bonds, forming a new deposition layer beneath the previous ones by means of the above-described mechanism. This catalysed reaction progresses until said silanol is no longer capable of diffusing to the aluminium-oxygen bonds through the previous deposition layers. This reaction mechanism and catalytic effect have been disclosed and explained in more detail e.g. in publication "Rapid Vapor Deposition of Highly Conformal Silica Nanolaminates", Science, VOL 298, 11 OCTOBER 2002, pp. 402 to 406. Another silanol or another corresponding substance or compound which enables a catalytic ALD process may also be used as a substrate.

[0015] The core of the preform may also be provided with a dopant, which may be added to the substrate or it may be supplied thereto separately, simultaneously or non-simultaneously with the substrate. Any material used for a normal doping of the fibre preform may be used as a dopant. These dopants may thus comprise one or more materials or compounds, and the dopant may be in elementary or compound form. For instance, the dopant may comprise a rare earth metal, such as erbium, ytterbium, neodymium or cerium, a material of boron group, such as boron or aluminium, a material of carbon group, such as germanium, tin and silicon, a material of nitrogen group, such as phosphorus, a material of fluorine group, such as fluorine, or silver or any material or compound suitable for doping. In the method according to the invention, the dopant may be an additive, auxiliary substance, filling material, colouring agent or another additional material of the material to be doped. Particularly, the dopant may be an auxiliary, reinforcement, softener, pigment or a sintering additive for thermal, light or electrical conductivity. The dopant may be supplied into the core of the fibre preform also by carrying out an ordinary ALD cycle without the assistance of a catalyst. In such a case, in order to grow the core of the fibre preform, a catalyst and a substrate may be supplied into the core of the fibre preform by utilizing catalytic ALD cycles while the dopant, in turn, is supplied in separate ALD cycles to be carried out between the catalytic cycles.

[0016] In accordance with what has been disclosed above, during one ALD cycle, wherein first, a dose of catalyst and next, a dose of a substrate and/or dopant are supplied into the core of the preform, due to the influence of the catalyst it is possible to form a deposition layer having a thickness of several atomic layers. This makes a core of a fibre preform fast to manufacture as well as preforms and thus an optical fibre of extremely high quality to be produced since it is possible to utilize the digitally accurate ALD method while growth of the material takes place three-dimensionally. [0017] In the method, the reaction of the catalyst and substrate and/or dopant supplied into the core of the preform may be adjusted by heating the preform after it has been placed in the ALD reactor by heating means to a first predetermined temperature and/or by heating the preform to a second predetermined temperature after feeding the catalyst prior to feeding the sub- strate and/or the dopant. Thus, the temperature of the fibre preform is adjusted in order to produce a predetermined number of deposition layers onto the surface of the core of the fibre preform and/or in order to produce a predetermined thickness of deposition layers onto the surface of the core of the fibre preform. This is possible since the reactions of the catalyst and e.g. silanol are tempera- ture-dependent. Thus when silanol and trimethylaluminium are used, the temperature is preferably 200 to 300 ⁰C. This temperature is low compared to the temperatures of known methods for manufacturing and modifying a preform. Hence, in the method according to the invention, the glass material does not soften, which enables the above-disclosed use of a tubular preform as a reac- tion chamber.

[0018] When necessary, an ALD cycle, which comprises supplying a catalyst as well as a substrate and/or a dopant, can be repeated as many times as desired in order to produce a desired or predetermined deposition layer or a desired doping structure into the core of the fibre preform. The same catalyst, dopant and substrate may be used in successive cycles or, alternatively, the catalyst and/or dopant and/or substrate may be changed between cycles so as to provide the fibre preform with the desired properties. In addition, the mutual ratio or amount of catalyst, substrate and/or dopant may be varied between different cycles. Furthermore, in each cycle it is also possible to supply one or more dopants into the core of the fibre preform simultane- ously; similarly, two or more substrates and/or catalysts may also be used in one cycle.

[0019] It is to be noted that although the manufacture and/or modification of a core of a tubular preform by utilizing the method according to the present invention has been disclosed above by way of example, this method may also be used for manufacturing or modifying a cladding of a preform by exposing this cladding to the catalytic ALD method. It is further to be noted that the core of the fibre preform may be grown or formed also from inside out instead of from outside in, as disclosed above. In such a case, the core of the preform is grown around e.g. a wire or a rod. [0020] In accordance with the above, the accurate and highly manageable manufacturing method enables a fibre preform whose properties are of higher quality than those of a prior art fibre preform to be manufactured. Furthermore, the fibre preform may be manufactured quickly and economically, and further, its properties may be adjusted extremely accurately during manu- facture. From a fibre preform thus provided, an optical fibre may be further manufactured which is of higher quality than that of the prior art, whereby, as a result of the more accurate method of manufacturing the fibre preform, it has a more accurate structure.

[0021] The catalytic ALD method according to the present invention may also be utilized in other applications. Such applications include hermetic coating, i.e. encapsulating, antireflective coating, active optical filters enabling e.g. band-pass filters to be provided, coating or encapsulating of fuel cells and solar panels, coating or passivating of pieces of jewellery, as well as coating, encapsulating or passivating of other metals, as well as Micro-Electro- Mechanical Systems or MEMS applications. In all these applications, the above-described catalytic ALD method is utilized such that the product being processed is placed in an ALD reactor wherein it is processed according to what has been disclosed above in order to achieve the desired properties. In other words, these other applications are carried out by replacing a fibre pre- form disclosed above by a product to be processed or a product whose properties are to be modified. Until now, this has not been possible by the ALD method due to its slowness, but now this catalytic method enables fast production of deposit layers with the growth rate being up to 100 times or more compared with the conventional ALD method.

[0022] It is apparent to one skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the above- described examples but may vary within the scope of the claims.

Claims

1. A method for manufacturing a fibre preform and/or for modifying properties of the same by an ALD method, wherein a surface to be grown is exposed to alternately repeated saturated surface reactions of starting materi- als in accordance with principles of the ALD method, characterized by the method comprising the following steps of: a) supplying a catalyst to an ALD reactor in order to produce a catalysing surface onto the surface of the fibre preform to be grown; b) supplying one or more dopants and/or substrates onto the sur- face of the fibre preform to be grown so that the catalyst causes two or more atomic or molecular layers to be formed onto the surface of the fibre preform to be grown.

2. A method as claimed in claim 1, characterized by repeating steps a) and b), which constitute one cycle, again once or more times when necessary.

3. A method as claimed in claim 1 or 2, characterized by supplying in step c) one dopant and/or substrate into a core of the fibre preform.

4. A method as claimed in claim 3, characterized by supply- ing, when steps b) and c) are repeated, in a next cycle a catalyst and/or dopant and/or substrate different than that in the previous cycle onto the surface of the fibre preform to be grown.

5. A method as claimed in claim 3, characterized by supplying, when steps b) and c) are repeated, in a next cycle a same catalyst as and/or a different dopant and/or substrate than that in the previous cycle onto the surface of the fibre preform to be grown.

6. A method as claimed in any one of the preceding claims 1 to 5, characterized by using trimethylaluminium as a catalyst.

7. A method as claimed in any one of the preceding claims 1 to 5, characterized by using as a catalyst trimethyl lanthanum, trimethyl zirconium, trimethyl hafnium or a compound of another trimethyl and metal or a compound comprising another aluminium, lanthanum, zirconium, hafnium or a another metal, which causes a catalysing effect in order to grow a plurality of atomic or molecular layers onto the surface of the core of the fibre preform dur- ing one cycle.

8. A method as claimed in claim 7, characterized by the dopant comprising erbium, ytterbium, neodymium, cerium, boron or aluminium, germanium, tin, phosphorus, fluorine, or silver or any other material suitable for doping a fibre preform.

9. A method as claimed in any one of the preceding claims 1 to 8, characterized by the substrate comprising silanol, glass or oxide forming a glass material.

10. A method as claimed in any one of the preceding claims 1 to 9, characterized by heating the fibre preform to a first predetermined tem- perature prior to step a), and/or to a second predetermined temperature after step a) prior to step b).

11. A method as claimed in claim 10, c h a r a c t e r i z e d by adjusting the temperature of the fibre preform in order to produce a predetermined number of atomic or molecular layers onto the surface of the fibre pre- form to be grown and/or in order to produce a predetermined thickness of a deposition layer onto the surface of the fibre preform to be grown.

12. A method as claimed in any one of the preceding claims 1 to 11, characterized by adjusting the amount of catalyst and/or substrate and/or dopant to be supplied to the ALD reactor in one cycle in order to pro- duce a predetermined number of atomic or molecular layers onto the surface of the fibre preform to be grown and/or in order to produce a predetermined thickness of a deposit layer onto the surface of the fibre preform to be grown.

13. A method as claimed in any one of the preceding claims 1 to 12, characterized by providing two or more fibre preforms that are arranged successively in a flow connection with one another such that a catalyst and a dopant and/or a substrate supplied into a core of a first tubular fibre preform flows through the core of all fibre preforms.

14. A method as claimed in any one of the preceding claims 1 to 12, characterized by providing two or more tubular fibre preforms that are arranged parallelly so as to enable a catalyst and a dopant and/or a substrate to be supplied to the core of each of them simultaneously or non- simultaneously.

15. A method as claimed in any one of the preceding claims 1 to 14, characterized by carrying out the method such that the tubular preforms themselves constitute walls of a reaction chamber.

16. A method as claimed in any one of the preceding claims 1 to 14, characterized by exposing the surface of the preform to be grown to a dopant by utilizing an ordinary ALD technique without using a catalyst.

17. A method as claimed in any one of the preceding claims 1 to 16, characterized by carrying out the method in a device for manufacturing and/or modifying a preform.

18. A fibre preform for the manufacture of an optical fibre, characterized in that the fibre preform has been manufactured or modified by a method according to claims 1 to 17.

19. An optical fibre manufactured from a fibre preform, characterized in that the fibre preform has been manufactured or modified by a method according to claims 1 to 17.