GB1573218A - Optical fibre waveguides for signal transmission comprising multiple component glass with an adjusted expansion co-efficient between the core and mantle - Google Patents

Description

(54) OPTICAL FIBER WAVE-GUIDES FOR SIGNAL TRANSMISSION COMPRISING MULTIPLE COMPONENT GLASS WITH AN ADJUSTED EXPANSION CO-EFFICIENT BETWEEN THE CORE AND MANTLE (71) We, CARL-ZEISS STIFTUNG, trading as JENAer GLASWERK SCHOTT & GEN., a company incorporated under the laws of the Federal Republic of Germany, of Hattenbergstrasse 10, 6500 Mainz, West Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an optical fiber wave-guide with a refractive index gradient profile, the optical fiber comprising an outer mantle consisting of a silicate multiple component glass, an inner mantle, and a core, the core and the inner mantle being silicon dioxidefree.

The wave-guiding process inside the fiber occurs to the greatest extent in the core which, owing to its structure, has a refractive gradient profile. The inner, silicon dioxide-free mantle contributes only marginally to the waveguiding process. The outer silicate mantle takes no part in the wave-guiding process.

The manufacture of wave-guiding fibers with refractive gradient profiles intended for signal transmission is effected by two main processes, which to be sure are generally different although in the first stages both processes use the well-known method of oxide precipitation from the gas phase (CVD process of the semi-conductor technology (U.S.P.

2,326,059).

According to the first patent applications (DT-OS 2,122,895 and DD-S 2,300,061) in the field of glass fiber manufacture for signal technology, this method of the CVD process is used for the production of a white, soot-like deposit which allows very clean conditions according to the disclosure of the semiconductor industry.

Later patents (U.S.P. 3,778,132, DT-OS 2,546,162) go back to the older possibilities of producing glass directly from the gas phase according to the CVD pacesses (Fest W. M., Steele S. R., Ready D. W., Physics of Thin Films 5, 1969), Academic Press, N.Y., London, page 290).

The two process methods serve either to produce an outer coating (DT-OS 2,313,249, DT-OS 2,300,013) on a very clean silicon dioxide glass rod with a lower refractive index material, namely corresponding to doped silicon dioxide glass; or an inner coating on a silicon dioxide glass tube (DT-OS 2,122,895, DT-OS 2,300,061) with a higher refractive index material, namely again corresponding to doped silicon dioxide glass. After both processes, the outer coated rod or the inner coated glass tube, as the case may be, is drawn directly to form a fiber. The inner coating of a glass tube is disclosed in DT PS 1,496,542, and the manufacture of glass fibers with a wave-guide effect is disclosed in DT-PS 745,142 as well as in DT-OS 2,025,921 and U.S.P. 3,157,726.

An improved process which uses the technology of the inner coating of a tube using the MCVD processes is described by French (10. International Congress on Glass Number 6, Optical Property and Optical Wave-Guides 646) as well as by MacChesney et al, (Ibid. 6-40) and in U.S.P. 3,778.132.

(Additional literature: Appl. Phys. Lett. 23 (1973) 338 and Proc. IEE. 62 (1974) 1280).

In particular, the introduction of an intermediate stage, in which in the internal coating process the tube is collapsed to a bar or rod and not immediately drawn to a fiber, is usefui in the MCVD process. The advantage lies above all in the fact that the extremely clean condition of the inner surface of the preform which will later become the core of the fiber is sealed hermetically so that subsequent process steps can be done in a normal industrial atmosphere. These last named process steps of the MCVD processes are clearly different from those of DOS 2,122,895 and DT-OS 2,300,061. The drawing out of an inner coated glass tube to a fiber with a core and mantle has been known for a long time (DT-PS 745,142) and has already been reported for optical fiber wave-guide (DT-OS 2,025,921).

All these processes refer to the inner coaing of a tube with core material which consists of silicon dioxide alone or doped silicon dioxide, whereby this material is deposited by gas phase precipitation on the inner wall of a tube. The use of silicon dioxide or doped silicon dioxide is shown in the teachings of U.S.P. 2,326,059 and other references (Hyde and Hood) and is relatively problem-free.

On the other hand, the use of silicon dioxide alone or doped silicon dioxide or generally the presence of silicon dioxide in a waveguiding layer is a disadvantage and actually runs counter to basic optical fiber-wave-guides theory. Only the simple acceptance of this component from previously known CVD technology has justified their use in known circumstances. For the transmission art, silicon dioxide should not be used generally in the conducting part of the fiber.

In this way, generally higher apertures can be attained, which as a consequence have better mechanical properties in the fibers, the fiber can be stronger in bending and can withstand greater pressures without hindering the wave-guiding qualities (loss of the transmitted information). Additionally, a higher aperture offers the greater advantage of better and easier optical manipulation; the angle opening is greater, which makes the incoupling of information simple and cheaper. An additional greater advantage is in the increased intensity output of the incoherent light source.

A particular disadvantage with the use of silicon dioxide glass and doped silicon dioxide glass as the wave-guiding material in the fiber results from the great difference in the linear thermal expansion coefficient which already exists between the lesser doping in the silicon dioxide glass mantle with a lower refractive index and the doped silicon dioxide core. This is particularly the case with pure silicon dioxide glass which has an extremely low linear thermal expansion coefficient. Each contribution of an admixed component lets the expansion coefficient rise irregularly or spasmodically.

The same situation occurs in the case in which a doping of silicon dioxide, for example with boron oxide, is used in a surrounding mantle and pure silicon dioxide glass is used in the core material.

Also, up to now there has been no optical fiber, wave-guide for communications technology with a control of the linear thermal expansion coefficient. By a polarization tension experiment under a suitable microscope, these great linear thermal expansion coefficient differences are clearly recognizable as tension differences in the preform and in the fibers, The advantage of a control of the linear thermal expansion coefficient lies in the following facts:- Only the smallest possible tension differences (these resulting from the expansion differences) are desired for the manufacture of the inner coating, the preform and the fiber to be drawn therefrom. With the somewhat inexact procedure of the inner coating process and the collapsing process, the freshly deposited layers on the inner coating are torn; the fissures resulting therefrom which even though subsequently temperature-treated cannot be completely healed. Thus, large areas result in the subsequent fiber which leads to increased losses (in dB/KM). Thus the fiber cannot be used for its intended purpose.

Another advantage is that, with a control of the linear thermal expansion coefficients between the hollow tube and the inner coating, a later division of the preform is possible. It was because of the expansion difference and the higher tension in the manufactured preform that it has not been possible to previously saw or cut the preform. Upon cutting, the inner coating portion broke because it was under tensile stress or strain.

An additional advantage is that, by a control of the expansion coefficient and thereby an associated reduction of the tensions in the preform in future, preforms can be melted together. This has a significant meaning for the transition from batch-wise manufacturing processes to continuous finishing processes for the production of a large amount of communication fibers. Using the melting of individual preforms allows really long preform pieces to be made. Thus the fiber drawing process and the subseqent bundling for a cable can be effected continuously.

An additional advantage resulting from the equalization of the tensions inside the preform by control of the linear thermal expansion coefficient, is that the losses which result from the tensions in the fiber can be eliminated.

These losses form, up to now, a constant portion of the theoretical minimum loss in such optical fiber wave-guides. Through control of the expansion coefficients, the theoretical minimum loss boundary can be further lowered.

In this way, fibers are obtained which are particularly suited for long range signal transmission.

An adjustment of the expansion coefficient at the extreme low value of the silicon dioxide glass with values between 5 and 8 X 107/0C is not possible since the addition of further components in most cases produces an increase in the expansion coefficient. There are many possible components which can produce refractive index gradient profiles in the transmission fibers. Therefore, materials with too lower linear thermal expansion coefficients below 10 X 10-'/"C should not be used for communications fibers.

The object of the invention is a communications fiber whose linear thermal expansion coefficient in all of the fiber elements (mantle and core material) lies above 15 X 10-7/0C and in which the expansion coefficients in all fiber elements (mantle and core elements) are so mutually arranged that the lowest possible tension differences exist between these elements. This is true for the tensions between the tube and the inner coating as well as for the tensions inside a preform or a fiber.

An additional object is a wave-guide fiber with a refractive index gradient profile in the area of the core which has a high as possible refractive index in the core material which is significantly and clearly higher than the refractive index of the silicon dioxide glass which is 1.458. These both are, by means of the invention, reached with an optical fiber waveguide according to the broadest claim.

According to the present invention, there is provided an optical fiber wave-guide for signal transmission comprising (1) an outer mantle comprising the following components: Component Weight % SiO2 51 - 92 # Al2O3 + ZrO2 + La2O3 + TiO2 + B2O3 + P2O5 1 - 40 P2O5 0 - 5 B2O3 0 - 26 Al2O3 0 - 28 ZrO2 0 - 5 Alkali Oxide # + Alkaline Earth Oxide 2 - 40 BaO 0 - 7 CaO 0 - 10 MgO 0 - 9 PbO 0 - 6 ZnO 0 - 8 La2O3 0 - 6 Na2O 0 - 12 K2O 0 - 8 Li2O 0 - 4 and which has a linear thermal expansion coefficient lying between 15 and 120 X 10-7/ C, (2) an inner, SiO2-free mantle comprising the following components: Component Weight % GeO2 50 - 100 P2O 0 - 45 B2O3 0 - 20 Al2O3 0 - 12 and corresponding in its linear thermal expansion coefficient to that of the outer mantle with a tolerance of t 5 X 107/0 C, and (3) an inner, SiO2-free core which has a refractive index gradient corresponding to the formula for a parabola with an exponent between 1.7 and 2.1 and which comprises the following components: Component Weight % GeO2 50 - 99 Sb2O, 0 - 50 ZnO 0 - 50 P2O5 0 - 50 Al2O3 0 - 15 B2O, 0 - 15 As2O3 0 - 30 BaO 0 - 10 PbO 0 - 15 Alkali Oxide 0 - 15 Alkaline Earth Oxide 0 - 15 La2O3 0 - 15 SnO2 0 - 20 TiO2 0 - 20 WO3 0 - 5 ZrO2 0 - 5 Ga2O3 0 - 14, the refractive indices of the inner mantle and the core being greater than 1.55, the refractive index of the core increasing from the outside to the inside thereof, the core having a linear thermal expansion coefficient which deviates from those of the inner and outer mantles by not more than # 12 X 10-7/ C, and the linear thermal expansion coefficients of the inner mantle and the core being greater than 15 X 10-7/ C.

Also according to the present invention, there is provided a process for the manufacture of an optical fiber wave-guide as defined in the last preceding paragraph, wherein the inner mantle and the core are produced as an inner coating on the inside surface of a tube by the vapor deposition process from the gas phase, which inner coated tube is collapsed to a preform and the preform is drawn to a fiber.

In the glass composition for the silicon dioxide tube, for the inner mantle and for the fiber core, additional elements, for example Ba, Rb, Cs, Sn, As, Sb, Bi and lanthanides can be included, as well as anions other than oxygen, even halogens.

The outer silicate mantle may be one which has been drawn from a melt.

The finished fiber wave-guide is characterised by a lower transmission loss, a higher transmission capacity and a large refractive index difference between the mantle and core material through a high aperture which lies above 0.25.

The inner silicon dioxide-free mantle consists of germanium oxide or of germanium oxide with an additional component.

In the accompanying drawings:- Figure 1 is a schematic illustration of a gas phase deposition apparatus for use in the pro duction of an optical fiber wave-guide according to the present invention, Figure 2 is a series of graphs for various glass compositions deposited on the inner surface of a glass tube, each graph plotting the relative concentrations of various components of the composition on the vertical axis against layer thickness on the horizontal axis, and, Figure 3 is a series of graphs for various glass compositions deposited on the inner surface of a glass tube, each graph plotting the refractive index of the composition on the vertical axis against the layer thickness on the horizontal axis.

An embodiment of a method of depositing glass layers on the inner surface of a glass tube will now be described.

A tube from which the outer silicate mantle is formed is drawn from a fluid melt by a known process such as the Danner process or the vertical sieve process. It has a composition according to Example 1 of Table 2. This tube has, after cooling, a linear thermal expansion coefficient of 77 X 107/oC. (A named linear thermal expansion coefficients in this description were obtained by measuring between 20"C and 300"C). The tube is fastened on a glass blower's lathe between the ends and rotated with a speed of 4 rotations per second. A glass burner with a speed of 6 cm per minute runs back and forth on the support of this lathe under the rotating tube. In ths way a temperature of 860"C is reached in the glass tube.

The rotating tube is flushed with a gas mixture of oxygen, germanium chloride and eventually one or more additional components. This gas mixture is produced by an oxygen stream blowing over an exact regulatory system through the slightly vaporizable fluids, for example germanium chloride and other chloride compounds. In Figure 1 such an apparatus for the production of the gas mix ture is shown and the multi-component silicate glass tube to be coated on the inside. Gas flow regulators are designated by M, an oxygen supply by 0,, burners are designated by the letter C and the tube by T. The component A is germanium chloride, the components B, X and Y are additional fluid components chosen according to the invention; the component Z is a gaseous component whose vapor pressure lies above 1 atm (A, B, X and Y have vapor pressures below 1 atm at room temperature). P is a programmer which is set for the changing of the flow regulators M so that, in the course of the inner coating process, a refractive index gradient is obtained on the inner coating. A large number of components which can be used are shown in Table I.

The gases are produced by blowing an oxygen stream from 0 under the control of the regulators M through the slightly vaporized fluids of components X, Y, A and B. This oxygen stream entrains molecules of such components. This gas mixture is deposited in the tube in the region of the burner C as oxides and melted onto the inner wall of the silicate glass tube T as a glass film. The free-flowing anions leave the tube T in the direction of the arrow. The burner C travels along the tube T and reverses its direction of travel upon reaching the end of the tube T. With many passes of the tube, a glass layer of 0.1 to 3 microns is produced if the temperature on the inside of the tube is sufficiently high, if the viscosity of the silicate glass tube is adjusted and if the speed of travel of the burner is followed according to the above given values.

The individual changes of the oxygen streams through the fluid containers allow changes from layer to layer of the glass composition of the inner mantle and the core so that one obtains the desired concentration profile of the individual components in the total layer packet of the inner coating.

If components are used which need higher temperatures for their vaporization then the whole tube system can be put in a heating mantle.

As choices from the components in Table 2 phosphorus, boron and aluminum can be used for the lowering of the refractive index of pure germanium oxide which is 1.65 down to the limit of 1.55. For raising the refractive index of pure germanium oxide from 1.65 to higher refractive index, values, titanium, tantalum, zirconium, antimony, lanthanum and other components are mixed therewith. On the one hand, by a specific mixing of the components the different refractive index profile in the inner mantle and in the core can be produced according to an inner coating process through the deposition from the gas phase. On the other hand, by specific mixing of the components, the linear thermal expansion coefficients can be so arranged that, when the expansion coefficient of the multi-component silicate glass of the outer mantle is taken as the datum, the linear thermal expan sion coefficient of the inner mantle can be adjusted with a tolerance of + 5 X 10--'/OC and that of the core with a tolerance of + 12 x 107/ C Figure 2 shows a few possible concentration profiles for the inner coating according to the deposition process from the gas phase. In Figure 2 the multi-component silicate glass is shown by MCSG. The different oxide components are shown in Figure 2 as follows: P = P2O.; A = Awl203; B = B2Q; G = GeO2; T = TiO2 and S = Sub203. In the graphs of Figure 2, the inner coating, thick ness is that obtained directly after deposition i.e. before collapsing of the tube to produce the preform. The inner coating is destined to define the core and the inner mantle in the finished wave-guide. The graphs of figure 3 relate to the refractive index gradients result ing from figure 2 and are derived before collapsing. During collapsing of the tube, the refractive index profile changes from a linear line to a parabolic curve with an exponent in the parabolic formula between 1.7 and 2.1. In the graphs of figure 3, the letters have the same meaning as in figure 2.

In the gas production apparatus according to figure 1, the concentration of the germanium component can be either held constant or it can be lowered stepwise, preferably by adding index-increasing-components additively or the concentration of the germanium component can be correspondingly lowered. With the regulator M which can be regulated electrically, either form of control is possible. By adding P2Od to the germanium oxide as well as using other components which has a lower refractive index than pure germanium oxide usable refractive indices are obtained if one lowers the concentration of P2Os from the outside to the inside and raises the concentration of the germanium from the outside to the inside. This inverse behaviour can be applied with all components whose refractive index in the particular oxide is lower than that of germanium oxide.

Through the mixing of two or more components, the adjustment of the refractive index and the linear thermal expansion coefficient is possible, when the flow velocity of the oxygen through the gas-producing vessels, the vapor pressure of the different liquids at standardized temperatures in the vaporizing vessels and the reaction temperatures in the tube are adjusted.

By controlling the through flow quantities of oxygen according to a table of calibration curves, the required molar compositions can be regulated for the production of the intended layer composition. The linear thermal expansion coefficient of the obtained layer composition can be ascertained experimentally through mixing metallic organic fluids as carriers of the respective oxides, hydrolysis of the mixture and final fusion. Measuring is done on a rod of 5 cm length and 1 mm diameter in a dilatometer.

The inner silicon dioxide-free mantle, as already known, consists of pure germanium oxide alone or of a mixture of several components, of which one is germanium oxide and of another with a compound which lowers the refractive index. For that purpose one or more of P2O:, B2O and Awl203 are used.

Employing a tube according to Example 1 hereinafter with a linear thermal expansion coefficient of 77 X 10-;/"C, pure germanium oxide is used as material for the inner, silicon dioxide-free mantle. The above-described ex pansion coefficient measurement of the pure germanium oxide gives a linear thermal expan sion coefficient of 78 X 10-'/"C.

After a sufficiently thick layer packet for the inner, silicon-dioxide-free mantle has been obtained by 25 passes of the gas-burner over the tube at a speed of 6 cm per minute the concentration of germanium is linearly decreased from 100 weight percent within 40 layers to 93 weight percent while at the same time the concentration of antimony oxide is increasing linearly in the same number of layers from zero to 7 weight percent. The change of the linear thermal expansion coefficient can be obtained through the use of B203 as well in the boundary so that on one hand a linear reflective index increase in the layer packet is reached and on the other hand the linear thermal expansion coefficient does not change over the tolerance of t 6 X 10-'/ OC.

According to another example a multicomponent silicate glass tube example 5, hereinafter is internally coated by vapor phase deposition first with a silicon-dioxide-free mantle consisting of 52 weight percent germanium oxide, 13 weight percent boron oxide, 7 weight percent aluminum oxide, 25 weight percent phosphorus oxide, and 2 weight percent zinc oxide. This inner, silicon-dioxide-free mantle has 12 layers. Finally, the layer packet for the core material is made by gas phase deposition.

This core material consists of the same components as the inner, silicon dioxide-free mantle, however additionally a mixture of antimony oxide, lanthanum oxide and titanium oxide is added to these components. The concentration of this second mixture of antimony oxide, lanthanum oxide and titanium oxide begins with zero weight percent and increases to 8 percent by weight at the layer which subsequently forms the core axis. The ratio of the antimony oxide, lanthanum oxide and titanium oxide is 2:1:1. Under tension tests, the preform attained with the inner coating of this material shows only a slight stress. The preforms can be sawn without difficulty and joined by melting with other similarly made preforms to form an endless preform for the continuous manufacture of wave-guide fibers.

Numerous further silicate glass tubes with an inner, silicon dioxide-free mantle which show a difference in the linear thermal expansion coefficient of not more than T 5 X 1(h7/0C on the inside are possible, wherein the coating with the core glass material follows so that the linear thermal expansion coefficient of the core material deviates by not more than t 12 X 10-?/OC from that of the inner mantle and that of the outer mantle.

Particularly good wave-guiding fibers are obtained when the refractive index gradient in the core is such that it follows the formula for parabola with the exponent between 1.7 and 2.1. Thus the refractive index of all the material formed in the gas phase deposition process in the gas phase has a value over 1.55 i.e., clearly above that of pure silicon dioxide glass which is 1.458. Particularly preferred in the core material besides the germanium oxide are the components antimony, phosphorus, and/or zinc in an oxide concetration between 1 and 50 percent by weight. The silicate glass tube for the outside mantle has a composition such that the sum of Al2O3, ZrO2, La2O3, TiO2, B2O3 and P2O5 is 1 to 40 weight percent and such that the sum of the alkali oxides and the alkaline earth oxides is 2 to 40 weight percent.

TABLE 1 Part 1

Vapaor Vapor Melting Pressure Melting Pressure Point at 760mm Oxide Refractive Point at 760mm Oxide Refractive Formula in C at C Index Formula in C at C Index AlB3H12 - 64.5 45.9 Al2O3 1.65 PbI 402.0 872.0 PbO 2.61 BCl3 -107.0 12.7 B2O3 1.64 PCl3 -111.8 74.2 P2O5 1.509 POCl3 2.0 105.1 P2O5 1.509 AlBr3 97.5 256.3 Al2O3 1.65 LiBr 547.0 1310.0 Li2O 1.644 AlCl3 192.4 180.3 Al2O3 1.65 LiCl 614.0 1382.0 Li2O 1.644 SbBr3 96.6 275.0 Sb2O3 2.35 Mg 651.0 1107.0 MgO 1.736 SbCl3 73.4 219.0 Sb2O3 2.35 MgCl2 712.0 1418.0 MgO 1.736 SbI3 167.0 401.0 Sb2O3 2.35 MnCl2 650.0 1190.0 MnO2 2.16 Sb2O3 656.0 1425.0 Sb2O3 2.35 MgBr2 237.0 319.0 HgO 2.55 As 814.0 610.0 As2O3 1.755 MgCl2 277.0 304.0 HgO 2.55 HgI2 259.0 354.0 HgO 2.55 AsCl3 - 18.0 130.4 As2O3 1.755 MoF6 17.0 36.0 MoO3 1.68 AsF3 - 5.9 56.3 As2O3 1.755 PBr3 - 40.0 175.3 P2O3 1.509 AsF5 - 79.8 - 52.8 As2O3 1.755 KBr 730.0 1383.0 K2O 1.608 As2O3 312.8 457.2 As2O3 1.755 KCl 790.0 1407.0 K2O 1.608 Ba 850.0 1638.0 BaO 1.98 KF 880.0 1502.0 K2O 1.608 BeB2H8 123.0 90.0 BaO 1.73 KI 723.0 1324.0 K2O 1.608 B2O3 1.64 TABLE 1 Part 2

Vapor Vapor Melting Pressure Melting Pressure Point at 760mm Oxide Refractive Point at 760mm Oxide Refractive Formula in C at C Index Formula in C at C Index BeCl2 405.0 487.0 BaO 1.73 Rb 38.5 679.0 Rb2O 1.642 BeJ2 488.0 487.0 BeO 1.73 RbBr 682.0 1352.0 Rb2O 1.642 BiBr3 218.0 461.0 Bi2O3 1.91 RbCl 715.0 1381.0 Rb2O 1.642 BiCl3 <SE TABLE 2

Example Nr. 1 2 3 4 5 6 7 8 9 10 SiO2 69.8 79.7 91.1 69.5 75.5 56.0 55.5 51.5 64.1 57.4 P2O5 - - - - - - 0.5 4.0 - 4.0 B203 9.2 10.3 4.6 1.4 9.0 10.5 15.7 1.0 25.0 - Al2O3 5.1 3.1 0.4 4.2 5.0 20.0 5.0 19.1 - 4.8 ZrO2 - - - - - 0.3 3.0 1.5 - 0.5 BaO - - - - 3.6 - 6.0 0.9 - 6.9 CaO 1.0 0.8 1.6 7.8 - 4.8 - 9.5 0.5 4.0 MgO 3.8 0.9 - - - 8.0 1.5 4.5 - PbO - - - - - - 4.0 1.0 - 6.0 ZnO - - 0.5 - - - - 7.0 - 3.2 La2O3 - - - - 0.4 - 1.5 - 0.3 Na2O 4.9 5.2 1.5 10.8 5.3 0.4 2.1 - 5.3 5.2 K2O 6.2 - - 5.3 1.2 - 3.0 - 4.8 8.0 Li2O - - 0.3 - - - 2.2 - - a x 107/ C 77 32 16 70 50 38 56 61 43 104 Example 11.

A wave-guiding fiber with a refractive index gradient profile is manufactured according tc the invention in which a glass tube with the composition given below has layers deposited dn the inside of the glass tube according to the modified vapor deposition process. The composition of the glass tube is: Component Weight % SiO2 71.0 B2O3 18.8 Al2O3 3.1 Na2O 5.9 K20 1.2 This layering on the inside is an oxide deposition from a mixture from a carrier gas oxygen (excess oxygen) and additional gas mixtures, which results from oxygen blowing through liquids as shown in Fig. 1 and the entrained components deposited as oxides in the partially heated tube of Fig. 1.

The fluids in the example are: A = GeCI4 at 250C B = POC1, at 20 C X = SbCl5 at 450C Y = GaCIB at 900C These fluids are in thermostatic containers which keep the nominal temperature at # 0.5 degrees in order to maintain a constant vapor pressure.

An additional gas-forming component is added to the gas mixture which is designated Z and is BCI3 and is thermostatically maintained at - 40C. Altogether 56 layers are deposited on the inside of the silicate glass tube used. The viscosity of the glass tube of the above composition is characterised by a transformation temperature of 470 C, a melting point of 740 C and an operating temperature of 11000 C. For the adequate separation of the oxides from the metal chloridesloxygen gas mixture, a minimum temperature of 890 C is employed. For this reason, the burner shown in Fig. 1 should bring a maximum of only half of the circumference of the tube to the deposition temperature at each position which it occupies during forward and reverse travel under the tube. Thus, the other half of the circumference remains below 700 C. Deforma tion of the tube under influence of temperature is achieved by a sufficiently slow rotation of the tube. In this embodiment, a rotation of 18 revolutions per minute was used. The temperature in the heated area of the tube was 9700 C, the temperature in the cold part of the tube circumference lay between 570 and 630 C. The composition of layers 1-15 was held constant. For layers 115, 300 ml/min O2 (excess oxygen) was 15 ml/min BCl3 as well as 270 ml/min oxygen which had flowed through the GeCl4 vessel and 10 ml/min oxygen which had flowed through the POCl3 vessel were mixed and passed through the heated glass tube. (See Figure 1). The glass tube in this embodiment was 1.15 m long, and had an outside diameter of 24 mm and an inside diameter of 15 mm.

The nozzle distance which the oxygen nozzle (smaller than 0.5 mm) must penetrate in the liquid containing vessels is larger than 20 cm and smaller than 22 cm. This gas mixture, which includes additional oxygen, is decomposed in the tube at the above given temperature. The burner is heated with hydrogen and oxygen. The temperature is detected pyrometrically and serves for the regulation of the hydrogen stream in the burner. The tube guide, through which the gas mixture streams, is heated to 900C by a heating sleeve.

The sixteenth layer differs considerably from the first 15 layers. The oxygen flow through the germanium chloride is raised about 4 ml/min, and the flow of BCl3 is drastically lowered to 3 ml/min. The amount of oxygen which flows through the vessel with POCI3 is also raised to 14 ml/min. Added to the gas mixture for the first time in layer 16 is oxygen which has flowed through the vessel with SbCl5. During the production of layer 16, 4 ml/min of oxygen flows through the SbCIs vessel. Also for the first time in layer 16, 3 ml/min of oxygen flows through the vessel containing gallium chloride. The subsequent layers 17 to 56 differ from layer 15 in that from layer to layer, the oxygen flows through the germanium chloride, phosphorus oxychloride, antimony chloride and gallium chloride vessels are increased step by step.

The increase for the vessel with GeCl4 is about 4 ml/min for POCl3 about 2 ml/min, for SbCl5 about 2 ml/min and for GaCl3 about 1 ml/min from layer to layer.

From layer 17 to 56, the temperature remains constant. At the end of layer 56, the tube is stepwise collapsed in 8 passes of the burner, while the excess oxygen is halved stepwise. The temperature for the first collapsing step is 12350C. For the 7th and 8th passes of the burner, the temperature is raised to 13000C. The other components of the gas mixture have already turned off during the collapsing process. Also before the final collapsing step, the remaining oxygen is turned off. Thus, a 80 cm preform with a preform diameter of 16 mm is obtained. From this preform at 1400 C in a carbon resistance oven, a 3062 m fiber having a diameter of 115 microns is drawn at a rate of 25 m/min. The optical loss or attenuation at a wave length of 860 nm compared with a corresponding laser beam gives a value of 5 dB/km, the pulse dispersion of a test pulse is 3 nsec/km.

The core diameter of the fiber is 45 microns.

The tensile strength of the fiber is 400 N/mm.

The refractive index profile in the fiber, based on layers 17 to 56, corresponds to an exponent a = 1.9 in the parabolic formula y = xa.

The linear thermal expansion coefficient of the glass tube is 53 X 10-7/0C. The linear thermal expansion coefficient of the core material, which is the result of the inner layering, is adjusted to the coefficient of the glass tube. By wet-chemical analysis of the core material and subsequent melting of the analytically established concentration in a platinum crucible at 16500C a glass is obtained which has a linear thermal coefficient of expansion of 56 X 10-/0C in the area between 20 and 3000 C. The refractive index of this glass is 1.58.

Claims (4)

WHAT WE CLAIM IS:

1. An optical fiber wave-guide for signal transmission comprising (1) an outer mantle comprising the following components: Component Weight //O SiO2 5192 # Al2O3 + ZrO2 + La2O3 + TiO2 + B2O8 + P2O5 1 - 40 P2O5 0 - 5 B2O3 0 - 26 Al2O3 0 - 28 ZrO2 0 - 5 # Alkali Oxide + Alkaline Earth Oxide 2 - 40 BaO 0 - 7 CaO 0 - 10 MgO 0 - 9 Pbo 0 - 6 ZnO 0 - 8 La2Os 0 - 6 Na2O 0 - 12 K2O 0- 8 Li2O 0 - 4 and which has a linear thermal expansion coefficient lying between 15 and 120 X 10-7/ C, (2) an inner, SiO2-free mantle comprising the following components: Component Weight % GeO2 50 -- 100 P206 0 - 45 B2O3 0 - 20 Al2O3 0 - 12 and corresponding in its linear thermal expansion coefficient to that of the outer mantle with a tolerance of + 5 X 10-7/ C, and (3) an inner, SiO-free core which has a refractive index gradient corresponding to the formula for a parabola with an exponent between 1.7 and 2.1 and which comprises the following components.

Component Weight % GeO2 50 - 99 Sb2O 0 - 50 ZnO 0 - 50 P205 0 - 50 Al2O3 0 - 15 B2O3 0 - 15 As2O3 0 - 30 BaO 0 - 10 PbO 0 - 15 Alkali oxide 0 - 15 Alkaline Earth Oxide 0 - 15 La2O3 0 - 15 SnO2 0 - 20 TiO2 0 - 20 WO, 0 - 5 ZrO2 0 - 5 Ga2O3 0 - 14 the refractive indices of the innner mantle and the core being greater than 1.55, the refractive index of the core increasing from the outside to the inside thereof, the core having a linear thermal expansion coefficient which deviates from those of the inner and outer mantles by not more than j 12 X 10-7/ C, and the linear thermal expansion coefficients of the inner mantle and the core being greater than 15 X 10-7/ C.

2. A process for the manufacture of an optical fiber wave-guide as claimed in Claim 1, wherein the inner mantle and the core are produced as an inner coating on the inside surface of a tube by the vapor deposition process from the gas phase, which inner coated tube is collapsed to a preform and the preform is drawn to a fiber.

3. A wave-guide as claimed in Claim 1 wherein the wave-guiding region of the waveguide consists of at least two zones, in which the outer zone has no refractive index gradient and consists of a mixture of germanium oxide and one or more of Sb2O3, P20S, and ZnO, while the inner zone has a refractive index gradient and consists of a mixture of 50 to 99 weight percent germanium oxide and 1 to 50 weight percent of at least one of Sb203, P2Os, and ZnO.

4. A wave-guide as claimed in any preceding claim wherein the outer mantle is one which has been drawn from a melt.