AU682490B2 - Light guide for optical fibre amplifiers for the wavelength range around 1300 NM - Google Patents

Description

TRANSLATED FROM GERMAN 901-077 D. Weber PCT/EP94/00329 Optical waveguide for fiber-optic amplifiers in the wavelength range around 1300 nm The invention concerns an optical waveguide according to the characterizing clause of patent claim 1. An optical waveguide with the features mentioned therein is known in many instances, e.g. from telcom report 6 (1983) supplement: "Communication By Means Of Light", pages 29 35. Optical waveguides of such a structure and composition serve as thb transmission medium of optical communication technology.

It is known from the February 1991 Journal of Lightwave Technology, Vol.9, No.2, pages 220 227, that light in the wavelength range around 1530 nm can be amplified with such optical waveguides, if their core contains erbium as the laser-active substance. On this basis, there are fiber-optic amplifiers being used very successfully in systems operating in the wavelength range around 1530 nm.

It is an entirely different matter with the wavelength range around 1300 nm: As established in the introductory part of publication PD 12/1 to PD 12/4, OFC/IOOC '93, February 21 26, 1993, San Jose Convention Center, San Jose California, no practical realizable fiber-optic amplifiers exist so far for this wavelength range. The wavelength range around 1300 nm is used in many optical communication systems which are installed at the present time. The advantage lies in that the transmission characteristics of the optical waveguide of the kind mentioned in the beginning are more favorable in the 1300 nm range than in the 1500 nm range, e.g. the minimum dispersion of such optical waveguides is around 1310 nm. It would therefore be desirable to have an optical waveguide for amplifying light in the wavelength range around 1300 nm.

Among fiber-optic amplifiers for the 1300 nm range suggested in the above mentioned publication, the amplifier with the praseodymium (Pr)-doped fluoride fiber was indicated as the most promising. However, as is known from: "Lasers and Optronics", August 1991, pages 43 46, particularly the right column on page 44, optical waveguides with fluoride glass as the basic material exhibit great disadvantages when compared to optical waveguides with silicon dioxide as the basic material, since they are weak, hygroscopic and cannot be spliced by fusion to Sioz optical waveguides. The same problem exists for fiber-optic amplifiers containing a neodymium (Nd)-fluoride fiber.

It would therefore be desirable to have an amplifying optical waveguide for the 1300 nm range, which has silicon dioxide as its basic material. It is known from the above mentioned "Journal of Lightwave Technology" publication, left column on page 220, that it is not a practical idea to d.pe the basic silicon dioxide material with Nd to obtain a fiber-optic amplifier that is suitable for the 1300 nm wavelength range, because at this wavelength the effectiveness is strongly limited by absorption under conditions of excitation.

The task of the invention is therefore to present the composition of an amplifier-optical waveguide, which is suitable for the 1300 nm wavelength range.

One solution of the task with neodymium as the doping agent is indicated in claim 1. An alternative solution with praseodymium as; the doping agent is indicated in claim 2.

Further developments are indicated in the subclaims. An advantageous method for producing the new optical waveguide is the subject of claims 6 to 9. One aspect of the invention is that the new optical waveguide also created a new fiber-optic amplifier. This is the subject of claim 9.

The invention will now be explained in greater detail by means of the drawings, which illustrate: Figure 1 a fiber-optic amplifier for the wavelength range around 1300 nm, with the new optical waveguide as an amplifying optical waveguide, and Figure 2 a device for performing the preferred method to produce the new optical waveguide.

The reference number 10 in figure 1 denotes a schematically indicated amplifier-optical waveguide of a fiber-optic amplifier. At splicing points 11 and 12 it is connected to an optical waveguide 13 which conducts the optical input signal to be amplified, or to an optical waveguide 14 which conducts the amplified optical output signal of the fiber-optic amplifier. As is customary with fiber-optic amplifiers, a pumping light source 15 is provided, which in the depicted case is coupled to the optical waveguide 13 by a coupler 16. As is often the case in such illustrations, the amplifier-optical waveguide 10 is drawn with a thicker line to distinguish it from the normal optical waveguides 13 and 14, even though it has the same diameter. The wavelength of the light passing through such a fiber-optic amplifier is in the range of 1300 nm. A digital signal is indicated at the input as well as at the output, which in the latter case is depicted as an amplified signal.

It is essential for the invention that the optical waveguide, which is designed as an amplifying optical waveguide for the 1300 nm range, has the following composition: Silicon dioxide is the basic material of the entire optical waveguide; as is customary, the core of the optical waveguide contains a doping agent which increases the index of refraction, e.g. GeO 2 and additionally neodymium (Nd) and fluorine in accordance with the invention. The composition of the sheath is not significant. It is important that the neodymium is combined with fluorine, i.e.

that the neodynium is surrounded by fluorine ions, The fluorine ions may not be displaced by oxygen ions. The neodymium and fluorine medium provides the neodymium with the desired laser property, which is required to amplify light in the wavelength range around 1300 nm. One possibility of surrounding the neodymium with fluorine is for the core to contain neodymium and fluorine in the form of a compound NdF 3 Instead of neodymium, the core may also contain praseodymium The same applies to the surrounding by fluorine, and in the case of praseodymium it is also advantageous for the core to contain praseodymium and fluorine in the form of a compound PrF 3 Any method is suitable to manufacture the optical waveguide of the invention, if it combines neodymium and fluorine or praseodymium and fluorine in the core of an optical waveguide using silicon oxide as its basic material.

For example, it is possible to guide gaseous BF 3 through heated NdF 3 powder and in this way to transport the I II NdF 3 to the place where it precipitates on a substrate, in order to dope the SiO 2 material with NdF 3 In a particularly advantageous method, NdF 3 or PrF 3 is brought close to a substrate as a complex with another vaporous combination, in conjunction with output materials of a chemical vapor reaction from which the core material originates, so that it can precipitate on the substrate together with the chemical vapor reaction products. The chemical vapor reaction can be performed in a substrate tube, for example in accordance with the known MCVD process, so that the substrate tube is coated on the inside. Such a process is explained in the following as an example of a method for precipitating a chemical vapor reaction.

As an alternative to such an MCVD process, wherein the substrate is a quartz tube which is coated on the inside, the method may also he one in which the substrate tube is a rod-shaped mandrel which is coated on the outside, or it may be a base that rotates around its axis, on which the glass core material and potentially also the glass sheath material is created by coating in the axial direction through a chemical vapor reaction. The principle of these three known variations of methods to precipitate with a chemical vapor reaction is known from the above mentioned telcom report publication.

It is essential for the preferred method of producing the new optical waveguide, that NdF 3 or PrF 3 is guided to the substrate together with another suitable compound and the output materials of the chemical vapor reaction used to produce the glass core material, so that it can precipitate on the substrate together with the product of the chemical vapor reaction.

-o w 7 In the configuration example of a suitable method described below, the cited other compound is aluminum fluoride (A1F 3 Aluminum trifluoride is a compound that is suitable for forming a complex with NdF 3 or PrF 3 which has a clearly lower vaporization temperature than NdF 3 or PrF 3 Lanthanum trifluoride (LaF 3 can also be used instead of aluminum trifluoride, or any other compound which is able to form the cited complex with a clearly lower vaporization temperature. In the case of AIF 3 or LaF 3 an optical waveguide is the result which, in addition to the components cited so far, contains the further component aluminum or lanthanum, namely in an A1F 3 or LaF 3 compound. These components are a consequence of the production method and do not achieve the desired optical properties.

The following is essential for the optical properties: The core contains the neodymium or praseodymium built into a SiO 2 matrix, which has a fluorescence band that uniformly covers the range of 1280 to 1330 nr. Neodymium or praseodymium is always surrounded by fluorine. An amplifier-optical waveguide with such a core can be directly Lsed in optical waveguide communication systems that utilize the 1330 nm range.

A configuration example of a preferred method is explained in the following by means of figure 2, which illustrates a device for carrying out the method.

The manufacture of an amplifying optical waveguide takes place with an optical wavegui-3 preform in accordance with the MCDV process in such a way, that a rotating substrate tube, which is usually made of quartz glass, is clamped in a glass lathe, where it is coated with the sheath or core layers of an artificial glass during several passes.

The output materials for the sheath or core layers are guided in gaseous form into the substrate tube. The continuous lengthwise heating of the substrate tube with an oxyhydrogen gas blow pipe produces a continuous layer of artificial glass of a predetermined composition on the inside wall of the substrate tube, through the precipitation from a chemical vapor reaction. The length of the substrate tube is usually 1250 mm. The output materials for producing the layers of artificial glass for example are silicon tetrachloride (SiCl4), germanium tetrachloride (GeCl 4 phosphorus oxytrichloride (OPC13), and potentially hexafluorethane (C 2

F

6 together with oxygen and helium.

Figure 2 illustrates part of a device for carrying out the method of the invention, clai'ped in a glass lathe. ThAs devioe contains the tube I with a larger diameter at the left end. Its diameter corresponds approximately to the diameter of the substrate tube 5. About in the center of the device its total length is approximately 350 mm the tube 1 narrows into a tube 2 with a smaller diameter. Tube 2 is surrounded by another larger diameter tube 3, which is closed at the left end and is connected to tube 1, and which contains an enlargement 4 with rotational symmetry.

The substrate tube 5 to be coated is fused to the right end of tube 3. It has a length of 900 mm for example.

The left end of the device, i.e. the tube 1, is able to rotate in the glass lathe 6 and is driven by drive 7.

When the device operates, the materials needed to carry out the method of the invention are contained in the enlargement 4, namely aluminum fluoride (A1F3) as the complex builder and neodymium fluoride (NdF 3 The aluminum II L- sl fluoride and neodymium fluoride output materials are available in powder form.

They are filled into the enlargement at the ratio of 3-4 to 1 (3 to 4 parts of AlF to 1 part of NdF 3 The enlargement 4 and the materials contained therein are not heated during this phase of the process. The enlargement 4 and the materials contained therein are only heated to 1400 0 C when the core layer doped with the rare earth element is to be produced.

When the mixture of aluminum trifluoride and neodymium trifluoride is heated, the two form a complex containing a considerable vapor pressure, which is sufficient to insert the vaporized complex into the substrate tube.

A melting point of over 2000°C is indicated for neodymium trifluoride. Heating this compound to a temperature of 1300 0 C would not produce the vapor pressure needed to insert this compound into the substrate tube.

The complex created with the mixture the stoichiometry is assumed to be 3 (AlF 3 x NdF, enters the substrate tube together with SiC1 4 GeCl4, oxygen, helium and potentially hexafluorethane, where it is incorporated into the oxide mass behind the burner in a controlled "thermophoretic" manner. It is important for the complex (it could be called fluoro-complex) to be incorporated; the fluorine ions may not be displaced by oxygen ions.

When carrying out the suggested method to manufacture the optical waveguide preform with a core layer doped with NdF 3 or PrF3 or both, it proved to be useful to manufacture another core layer without such doping in a subsequent step, I -I after Lhe NdF 3 or PrF 3 doped core layer has been produced, and then, before collapsing the substrate tube, to remove about 70% of the total thickness of the first and the second core layer by etching, for example with hexafluorethane.

The result is a particularly pure core layer, which has a definite rectangular core profile.

AMENDED CLAIMS Creceived on July 13, 1994 at the International Office; the original claims 1 and 2 were amended; other claims remain unchanged (I page)] 1. An optical waveguide made of silicon dioxide a the basic material, with a core and a sheath, where th core contains one or more doping agents which increade the index of refraction, characterized in that the cor additionally contains neodymium combined with fluorine, 2. An optical waveguide made of silicon dioxide as the basic material, with a core and a sheath, where the core contains one or more doping agents which increase the index of refraction, characterized in that the core additionally contains prasecdymium combined with fluorine.

3. An optical wavyguide as claimed in claim 1 or 2, characterized inthat the core contains neodymium and fluorine as the compound NdF 3 or PrV 3 4. An ptical waveguide as claimed in one of the preced ng claims, characterized in that the core additionally ccontaina sluminum or lanthanum, or an element wich is able to form a compound forming a complex with NdF, or PrF 3 the vaporization temperature of which is lower than that of Nd?3 or Prl).

Claims (10)

1. An optical waveguide made of silicon dioxide as the basic material, with a core and a sheath, where the core contains one or more doping agents which increase the index of refraction, wherein the core additionally contains neodymiurr combined with fluorine and/or praseodymium combined with fluorine, and wherein the core contains neodymium and fluorine and/or praseodymium and fluorine as the compounds NdF, or PrF 3 respectively whereby the waveguide exhibits laser action in the 1300 nm region.

2. An optical waveguide as claimed in claim 1, wherein the core additionally contains aluminum or lanthanum, or an element which is able to form a compound forming a complex with NdF 3 or PrF 3 the vaporization temperature of which is lower than that of NdF 3 or PrF,.

3. An optical waveguide as claimed in claim 2, wherein the core contains aluminum or lanthanum in a compound AlF3 or LaF 3 15

4. A method for manufacturing an optical waveguide of the type claimed in any one of the preceding claims, in which the core material is produced by precipitation from a chemical vapour reaction on a substrate, and wherein the core material is further processed into an optical waveguide, characterized in that a complex is formed with neodymium fluoride (NdF.) or praseodymi-n (PrF 3 and another compound, and is supplied in vapour form to the substrate together with the output materials of the chemical vapour reaction, so that the product of the chemical vapour reaction and the complex are p'ecipit e9d on the substrate.

5. A method as claimed in claim 4, wherein a sheath material is produced by precipitation from a chemical vapour reaction on a substrate. 25

6. A method as claimed in claim 4 or claim 5, wherein aluminum trifluoride (AtF) or lanthanum trifluoride (La 3 or another compound is used as the compound which forms a complex with NdF or PrFP, whose vaporization temperature is clearly lower than that of NdFa or PrF.

7. A method as claimed in any one of claims 4 to 6, in which a quartz tube is used as a substrate, and the output products of a chemical vapour reaction are inserted into the substrate tube, wherein the output products of the chemical vapour reaction are Y 11 inserted into the sub rote tube together with the vapourized complex, so that the substrate tube is coated on the inside by precipitation of the products from the chemical vapour reaction and the complex, and that the internally coated subsrate tube is further processed into an optical waveguide.

8. An optical waveguide substantially as herein desribed with reference to the accompanying drawings,

9. A method of manufacturing an optical waveguide preform or an optica; waveguide substantially as herein described with reference ot the accompanying drawings,

1 0. A fibro-optic amplifior including as the amplifying element an optical woveguide as claimed in tiny one of clairrs 1 to 3 or claim 8. DATED THIS SIXTEENTH DAY OF~ JULY 1997 ALCATEL N. 00 :6 0 00 INTERNATIONAL SEARCH- RFPORT FI'Iem kt Applicaton~ No PCT,'EP 1,4/00329 A. CLASSIFICATION OF SUWiECT'MA'ITER IPC 5 HO1S3/06 HOIS3/17 C03("3/095 0'03C13/04 According to IntemAional Patent Clmroicatn (lPC) or to both national clascation and IPC D, FIELDS SEARCHIED Minimum documentation searched (claxsallation system followed by classification symbols) IPC 5 HolS Documentation search~d oitier than rmirmum documnentation to the extent taat susch documeints are included In the fields searched Electronic datat bWe consulted durnng the in'irnatiosial "iarch (name of data bame and, where practical, search terms used) DOCUMENTS CONSIDERED TO [IF RELEVANT Category* Citaizon of documnt,4 Win1 miliabon, where appropriate, of the relevant Piagaet Relevant to lao. X EP,At0 466 932 (FURUKAWA ELECTRIC) 22 19 January 19?9 see pagje 6, Tine 5 line see page 8, line 23 -line 24; table 1 A see page line 53 -page 14, line 25;, 2-5,7 claims 1,6,8 A DEtA,41 20 054 (HITACHI CABLE) 2 January 0 1992 see column 10, lino 3 -line see column 10, 1~ne 39 line 44 see figures 8,9 [LM Furthe cloctinenti art listd ins the watnuAiln of box C, P Iatait family manbci' are listed in annex *Sliecia eategosses of cd dcuntU IT tau documnent published after the International fii date or rirtt dle ndnot In conflct with the Applcation but document definig the general tte of the art which is not d th P or thelo of the considered to be of pArticulatr~da metinUrywikdice VI eadier doment but publiahed on or suet the Iitersialoral dovcent ofpartlcular relevance; the claihned invention filing dOAt cannot be Corudered novel or cannot be conisidered to IL document which may throw dw~btt on. priority elainsi(s) or involve a&4 Inventive stp when the documrent is taken aloe which is cited to establith the putittaios dAte of another 'Y documcnt of patiular relevance; the dallita4$maendo" citation or other spMcIl rero (as specified) cano be co~ee to involve an invo e s wup ep when the V~ docurnent refinig to an oral disslos, use, exhibiutl or document Is combined with one or more other such doeu- other mexa Rets such eornbtdton being obvious to a person skled P' docunient publisned pior to the Inntmiuonal flling date but OteLt laer thant the priority, date claimed *W document mimber of the same patent family Date of the actual compieton of tW lInerational $earch Date of miling of the IntemaioWa Mearch report 13 May 1994 01, JWUN 199 Nam tr andmetn&4"aaes of&th ISA zise t c c e puropean PAtent Mfet, P.11. At Itratentlais I NL 2210 tY Ripmijk T41.(+ 3003402040,T~ U i 310 Ba ipde III FAx (4 31-70) 34.3014Bttpde Frm KC?/IS t121bciro m t)tu 14YIMI page I of 2 INTERNATIONAL SEARCH REPORT Intern, it Alplikauon No IPCT/EP 94/00329 C.(Conunuauon) DOCUMENTS C0NSlDH1,'Ji-D TO BEi RELEWtNT Category Citaton ofdocurnent with tndicauot., where appropriate, efteev., (.sges Relevant to claim No. A JOURNAL OF LIGHTWAVE TECHNOLOGY., 1.2 vol.9, no.2, February 1991, NEW YORK US pages 234 250, XP000225314 WJ. MINISCALCO 'Erbium !Ioped glasses for fiber amplifiers at 1500 nm' see page 231, left colqmn, last paragraph -right column, line 14 see page 238, left column, paragraph 4 A ELECTRONICS LETTERS,, vol.23, no.15, 16 July 1987, ST8ENAGE GB pages 768 769 M, SHIMIZU ET AL. 'High-efficiency Nd-doped fibre lasers using direct-coated dielectric mirror' see page 768, right column, paragraph 3 A OPTICAL FIBER COMMUNICATION CONFERENCE. 1,3,4 1988 TECHNICAL DIGEST SERIES, POSTCONFERENCE EDITION, vol.1, 1988, WASHINGTON DC, US page 1S., XP000014097 W.J. MINISCALCO ET AL. 'Nd3+ doped fiber laser at 1,3 mum' see page 154, lef~t column, last paragraph A OPTICS LETTERS.2 vol.16, noA.2, 15 November 1991, NEW YORK Us pages 1747 1749, XP000244440 Y. OIIISHI ET AL. 'Pr3+ doped fluoride fiber amplifier operating at 1.31 mum' see abstract A IEEE JOURNAL OF QUANTUM ELECTRONICS., vol .25, no.10, October 1989, NEW YORK US pages 2119 2123, XP000084392 R.M. PERCIVAL ET AL. 'Characterization of spontaneous and stimulated emission from Praseodymium (Pr3+) ions doped into a silica-based monomode optical fiber' 7mm ?CTJIsA'2t (.tviuto at said khuq (Julty 192 page 2 of 2 INTERNATIONAL SEARCH REPORT Ap~tnN ron~e~ np I'~'PCT/EP 94/00329 Patent document I Publication Patent ramly Publication cited In search report T date Member(s) -L date EP-A-0466932 22-01-92 AU-A- 7185591 21-08-91 CA-A- 2051104 06-08-91 JP-A- 3265537 26-11-91 WO-A- 9111401 08-08-91 US-A- 5262365 16-11-93 DE-A-4120054 02-01-92 JP-A- 4060618 26-02-92 CA-A- 2040527 30-12-91 GB-A- 2245984 15-01-92 US-A- 5206925 27-04-93 Foerm PM /15A21 (p.tat fAMilY VAAeX) (Jualy IM)