Highly transmissive glasses with high solarisation resistance, use thereof and method for production thereof

Abstract

Glasses are provided that are highly transparent and have very good resistance to solarisation. The resistance to solarisation is favoured to a special extent by the production method. The concentrations of reduced polyvalent ion species are reduced by targeted use of bubbling with an oxidising gas. Methods for producing glasses and to the uses thereof, particularly as core glasses in optical waveguides, are also provided.

Claims

1. An optical fiber comprising a core glass having improved solarization resistance, the core glass comprising SnO.sub.2, up to 2.8% by weight Al.sub.2O.sub.3, at most 33% by weight SiO.sub.2, and at least 12% by weight and at most 24% by weight of La.sub.2O.sub.3, the core glass having an attenuation of ≤1300 dB/km at a wavelength of 1050 nm, wherein the core glass is free of oxides of Bi, and free of Lu.sub.2O.sub.3, Gd.sub.2O.sub.3, Dy.sub.2O.sub.3 and Yb.sub.2O.sub.3.

2. The optical fiber according to claim 1, wherein the attenuation of the core glass at a wavelength of 1050 nm is <400 dB/km.

3. The optical fiber according to claim 1, wherein the attenuation of the core glass at a wavelength of 1050 nm is 400 to 1300 dB/km.

4. The optical fiber according to claim 1, wherein the core glass further comprises Fe.sup.2+ and/or Fe.sup.3+ in a content of 0 to 10 ppm.

5. The optical fiber according to claim 1, wherein the core glass further comprises MnO in a concentration of <200 ppb.

6. The optical fiber according to claim 1, wherein the core glass further comprises MnO in a concentration of 200 to 500 ppb.

7. The optical fiber according to claim 1, wherein the core glass is free of PbO, As.sub.2O.sub.3 and Sb.sub.2O.sub.3.

8. The optical fiber according to claim 1, wherein the core glass further comprises a composition in percent by weight of: TABLE-US-00016 from to B.sub.2O.sub.3 0 24 SiO.sub.2 23 62.1 Al.sub.2O.sub.3 0 10 Li.sub.2O 0 10 Na.sub.2O 0 18.5 K.sub.2O 0 25.7 BaO 0 57.8 ZnO 0 40 La.sub.2O.sub.3 0 25 ZrO.sub.2 0 10 HfO.sub.2 0 14.2 SnO.sub.2 >0 2 MgO 0 8 CaO 0 8 SrO 0 24.4 Ta.sub.2O.sub.5 0 22 Y.sub.2O.sub.3 0 11.9 Rb.sub.2O 0 15 Cs.sub.2O 0 21 GeO.sub.2 0 7.5 F 0 2 Σ R.sub.2O 5 20 Σ MgO, CaO, SrO, ZnO 20 42.

9. The optical fiber according to claim 8, wherein the core glass further comprises a mass ratio of SiO.sub.2 to B.sub.2O.sub.3 that is more than 5.

10. The optical fiber according to claim 8, wherein the core glass further comprises a total content of MgO, CaO, BaO, SrO, La.sub.2O.sub.3, Ta.sub.2O.sub.5, ZrO.sub.2 and HfO.sub.2 of at least 40% by weight.

11. The optical fiber according to claim 8, wherein the core glass further comprises a portion of Sn.sup.2+ of at most 5%, based on a total content of tin.

12. The optical fiber according to claim 1, wherein the core glass further comprises a content of SnO.sub.2 of at least 0.01 and at most 1% by weight.

13. A method for the production of the optical fiber of claim 1, comprising the steps of: melting the glass mixture in a melting vessel; and refining the melt in a refining vessel.

14. The optical fiber according to claim 1, further comprising a cladding glass sheathing the core glass.

15. The method according to claim 13, further comprising the step of bubbling the melt in a conditioning vessel with an oxidizing gas after the refining step.

16. The optical fiber according to claim 1, wherein the core glass comprises more Fe.sup.3+ than Fe.sup.2+.

17. The optical fiber according to claim 1, wherein the minimum content of HfO.sub.2 in the core glass is 0.01% by weight.

18. A fiber glass having improved solarization resistance comprising SnO.sub.2, up to 2.8% by weight Al.sub.2O.sub.3, at most 33% by weight SiO.sub.2, and at least 12% by weight and at most 24% by weight of La.sub.2O.sub.3, the fiber glass having an attenuation of ≤1300 dB/km at a wave length of 1050 nm, wherein the refractive index of the fiber glass is between 1.55 and 1.75, and wherein the fiber glass is free of oxides of Bi, and free of Lu.sub.2O.sub.3, Gd.sub.2O.sub.3, Dy.sub.2O.sub.3 and Yb.sub.2O.sub.3.

19. The fiber glass according to claim 18, wherein the attenuation thereof at a wavelength of 1050 nm is <400 dB/km.

20. The fiber glass according to claim 18, wherein the attenuation thereof at a wavelength of 1050 nm is 400 to 1300 dB/km.

21. An optical fiber comprising a core glass comprising the fiber glass according to claim 18.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a bar graph that shows the influence of the content of SnO.sub.2 in the glass on the solarization resistance;

(2) FIG. 2 is a line graph that shows the attenuation spectrum of different glasses;

(3) FIG. 3 is a line graph that shows the effect of the bubbling procedure after the refining process;

(4) FIG. 4 is a bar graph that shows the decrease of the color temperature after irradiation;

(5) FIG. 5 is a line graph that shows the attenuation spectrum after three hours; and

(6) FIG. 6 is a line graph that shows the spectrum of attenuation.

DETAILED DESCRIPTION

Examples

(7) For the manufacture of glasses according to the present invention, compositions from conventional raw materials, irrespective of unavoidable impurities, were put in and melted in a high-frequency heated skull crucible at 1500-1580° C. over a time of 3 hours. The melt was heated to a temperature of 1550-1630° C. and subsequently refined for 45 min. The temperature was subsequently decreased to 1540° C. and bubbling was performed with oxygen over 30 min. The temperature was then, over the course of 15-20 minutes, decreased to 1450° C. and the glass was cast. From 660° C. on the cooling of the glass blocks took place with a rate of 10 K/h until it reached ambient temperature.

(8) The results are summarized in TABLE 1. The details for the composition of the optical glasses/core glasses are indicated in percent by weight on the basis of oxides and were analyzed. Furthermore, n.sub.d means the refractive index, ν.sub.d the Abbe number, Pg, F the relative fraction of dispersion for the wavelengths g and F, α.sub.20/300 the linear coefficient of thermal expansion in the range of 20° C. to 300° C. according to ISO 7991, Tg the glass trans-formation temperature according to ISO7884, the density according to the Buoyancy flotation method correspondent to the Archimedean principle, CR the climate resistance according to ISO/WD 13384, FR the staining resistance according to the SCHOTT-method and AR the resistance to alkaline according to ISO/DIN10629.

(9) TABLE-US-00010 TABLE 1 Ex. 1 2 3 4 5 6 7 8 9 10 11 SiO.sub.2 48.79 42.73 47.71 48.6 51.8 33 47.5 42.8 43.73 33.47 43.31 B.sub.2O.sub.3 8 8 11.88 11.63 Al.sub.2O.sub.3 9 2 0.22 0.19 P.sub.2O.sub.5 Li.sub.2O 0.9 1.8 0.82 0.71 0 0.7 Na.sub.2O 9 6 8.3 8.2 9 4 6.86 5.8 5.67 4.9 5.8 K.sub.2O 5.8 9.1 3 1 6.48 3.7 0.66 0.57 3.7 CaO SrO BaO 20 28 0.8 0.8 22 22 0.9 9.2 29.95 40.24 9 ZnO 1 8 34.4 33 6 30 27.6 21.2 7.63 21.2 La.sub.2O.sub.3 9 5 5.64 10.7 6.32 10.8 ZrO.sub.2 3 8 1.8 3.81 4.9 2.46 4.9 HfO.sub.2 0.06 0.17 0.04 0.08 0.6 0.05 0.59 SnO.sub.2 0.15 0.10 0.25 0.3 0.2 0.2 0.31 0.39 0.26 0.17 0.15 MnO 0.00015 sum 100 100 100 100 100 100 100 100 100 100 100 properties n.sub.d 1.5828 1.6097 1.58 1.567 1.556 1.617 1.58825 1.62361 1.5830 1.6240 1.6234 v.sub.d 51.6 53.0 52.4 51.06 49.9 58.7 56 50.2 PgF 0.5538 0.5557 α.sub.(20-300° C.) 7.9 8.1 8.74 8.22 8.18 9.25 7.96 [10.sup.−6/K] Tg [° C.] 529 617 534 563 573 584 568 ρ [g/cm.sup.3] 2.97 3.49 3.13 3.44 3.23 3.6 3.44 CR [class] 1 1 1 1 AR [class] 1.0 1.0 1.0 1.0 FR [class] 0 0 0 0 D (1050 nm) — — — — — — 180 117 250 300 [dB/km]* Ex. 12 13 14 15 16 17 18 19 20 SiO.sub.2 50 45 44 31.07 30.98 24.26 25.75 29.6 27.90 B.sub.2O.sub.3 1 6 1 2.37 2.42 4.52 3.24 3.50 3.50 Al.sub.2O.sub.3 1 4 2 P.sub.2O.sub.5 0.1 4 2 Li.sub.2O 3 5 0.86 1.09 0.45 0.86 0.86 1.22 Na.sub.2O 2 2 3 1.04 1.04 K.sub.2O 2 2 7 1.55 1.55 0.28 CaO 1 6 5 SrO 0.01 0.02 BaO 9.9 6 8 22.32 17.96 34.13 23.16 16.30 23.20 ZnO 23 14 25 16.84 19.61 14.23 21.60 16.20 La.sub.2O.sub.3 5 5 15.73 13.89 13.29 23.24 18.40 18.50 Ta.sub.2O.sub.5 3.35 6.50 21.57 4.58 4.80 4.70 ZrO.sub.2 2 1 3 4.75 4.81 1.45 4.84 4.40 4.30 SnO.sub.2 0.10 0.10 0.12 0.12 0.15 0.07 0.10 0.14 0.21 HfO.sub.2 0.02 0.09 0.08 0.07 properties n.sub.d 1.5739 1.5588 1.5869 1.68826 1.69171 1.73162 1.73339 1.70863 1.72019 v.sub.d 53.03 55.63 51.29 48.23 47.06 45.35 46.93 48.02 47.19 PgF 0.5446 0.5436 0.5536 0.558 0.559 0.562 0.5591 0.5589 0.5591 α.sub.(20-300° C.) [10.sup.−6/K] 7.0 7.9 7.7 n.b. n.b. 8.4 7.71 6.60 7.51 Tg [° C.] 541 429 561 n.b. n.b. 665 631 611 597 ρ [g/cm.sup.3] 3.15 2.8 3.11 4.04 4.03 4.18 4.40 4.22 4.28 CR [class] 1 AR [class] 1.0 FR [class] 1 D (1050 nm) 1052 [dB/km]* Ex. 21 22 23 24 25 26 27 28 29 30 SiO.sub.2 28.10 27.80 27.70 28.10 28.20 29.80 28.80 29.10 29.10 29.30 B.sub.2O.sub.3 3.00 3.30 3.40 3.30 3.40 3.50 2.40 1.02 3.30 3.30 Al.sub.2O.sub.3 0.02 P.sub.2O.sub.5 Li.sub.2O 0.80 1.09 0.96 0.85 0.89 0.88 0.88 0.93 0.92 0.89 Na.sub.2O K.sub.2O CaO SrO 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 BaO 28.30 22.50 22.40 25.40 28.40 22.00 29.60 29.60 29.30 29.60 ZnO 12.50 17.10 17.60 14.90 13.70 17.80 13.10 13.90 12.40 13.00 La.sub.2O.sub.3 18.20 15.30 17.60 18.20 16.30 18.40 18.70 19.00 18.50 18.60 Ta.sub.2O.sub.5 4.60 8.30 5.70 4.70 4.60 2.90 1.90 1.80 1.80 0.67 ZrO.sub.2 4.20 4.20 4.30 4.20 4.20 4.30 4.30 4.40 4.30 4.30 SnO.sub.2 0.09 0.14 0.12 0.10 0.10 0.10 0.09 0.10 0.09 0.09 HfO2 0.07 0.06 0.07 0.07 0.08 0.08 0.08 0.08 0.08 properties n.sub.d 1.7177 1.7240 1.7211 1.7179 1.7139 1.7159 1.7145 1.7190 1.7074 1.7043 v.sub.d 47.61 46.03 46.94 47.44 47.79 46.84 48.17 47.71 48.87 49.12 PgF 0.5593 0.5600 0.5577 0.5591 0.5653 0.5591 0.5576 0.5587 0.5567 0.5569 α.sub.(20-300° C.) 7.79 7.23 7.44 7.49 7.74 7.12 7.98 7.99 7.85 7.9 [10.sup.−6/K] Tg [° C.] 624 602 613 623 612 600 631 646 618 610 ρ [g/cm.sup.3] 4.33 4.32 4.30 4.30 4.28 4.18 4.29 4.34 4.22 4.19 CR [class] 1 1 1 1 AR [class] 1.0 1.0 1.0 1.0 FR [class] 1 1 2 2 D (1050 nm) 721 883 738 518 637 660 898 714 1238 1193 [dB/km]* *not irradiated

(10) In TABLE 2 two cladding glasses with their respective compositions are listed (according to analysis in percent per weight on the basis of oxides). Furthermore, n.sub.d means the refractive index, α.sub.20/300 the linear coefficient of thermal expansion in the range of 20° C. to 300° C. according to ISO 7991, EW the softening temperature at a viscosity of 10.sup.7,6 dPas, S the resistance to acids according to ISO 12116, L the resistance to bases according to DIN ISO 695.

(11) TABLE-US-00011 TABLE 2 Example A B type of cladding glass group 1 group 2 SiO.sub.2 73.9 69.9 B.sub.2O.sub.3 9.60 1.0 Na.sub.2O 6.60 12.6 K.sub.2O 2.56 3.2 MgO 0.01 2.7 CaO 0.63 5.1 BaO 0.04 2.1 Al.sub.2O.sub.3 6.62 4.0 TiO.sub.2 0.1 F 0.08 0.2 Cl 0.18 Fe.sub.2O.sub.3 4.E−02 Sb.sub.2O.sub.3 <0.005 As.sub.2O.sub.3 <0.005 0.1 Sum 100.26 101 Properties n.sub.d 1.49 1.514 α .sub.(20-300° .sub.C.) [10.sup.−6/K] 5.5 9.1 EW [° C.] 790 720 S [class] 1 1 L [class] 2 2

(12) Because the glasses according to this invention are particularly suitable as core glasses for optical fibers, selected core glasses of TABLE 1 together with selected cladding glasses of TABLE 2, optical fibers with a diameter of 30, 50 and 70 μm were manufactured and their physical data determined which are shown in TABLE 3.

(13) The manufacture of fibers was carried out according to the established rodpipe pulling process on a conventional rod-pipe pulling machine with a cylindrical oven according to prior art. The attenuation of the fibers was determined according to DIN 58141 part 1. ÖW is the opening angle and was determined according to DIN 5814-3, ΔÖW is the difference of the opening angles of the 1 m long and 3.8 m long and in average 50 μm wide fibers.

(14) The color temperature [K] of the emitted light from the fiber after the passage of a certain fiber distance was determined after irradiation of norm light D65 (color temperature 6504 K). The results are listed in table 3. The attenuation at different light wavelengths was indicated in dB km.sup.−1 and the opening angle as well as the difference of the opening angles was indicated in degrees.

(15) TABLE-US-00012 TABLE 3 core glass Ex. from Tab. 1 19 20 21 22 23 24 cladding glass-Ex. from Tab. 2 A A A A A A properties step-index fibers attenuation 550 nm, Ø 50 μm, [dB/km] 287 292 215 240 401 339 attenuation 610 nm Ø 50 μm, [dB/km] 374 411 306 333 469 386 ÖW 1 m, Ø 50 μm [°] 117 103 121 122 123 122 ÖW 3.8 m, Ø 50 μm [°] 99 83 113 104 108 113 Δ ÖW betw. 1 m and 3.8 m, Ø 50 μm [°] 18 20 8 18 15 9 core glass Ex. from Tab. 1 25 26 27 28 29 30 26 cladding glass-Ex. from Tab. 2 A A A A A A B properties step-index fibers attenuation 550 nm, Ø 50 μm, 200 274 206 276 264 244 420 [dB/km] attenuation 610 nm Ø 50 μm, 275 373 313 357 424 393 490 [dB/km] ÖW 1 m, Ø 50 μm [°] 121 109 120 65 118 118 102 ÖW 3.8 m, Ø 50 μm [°] 113 100 113 54 114 112 84 Δ ÖW betw. 1 m and 3.8 m Ø 50 μm 8 9 7 9 4 6 18 [°]

(16) The following TABLE 4 shows the effects of measures according to the present invention on a variety of variants of example glass 8:

(17) TABLE-US-00013 TABLE 4 Ex. 8 D (920 nm) D 1050 nm T.sub.Bubbling t.sub.Bubbling Variant Bubbling [dB/km] Δ (900-700 nm) [dB/km] [° C.] [min] a yes 158 32 170 1450 30 b yes 196 44 207 1430 30 c yes 339 132 368 1450 15 d yes 286 102 310 1450 30 e yes 206 54 238 1400 30 f yes 266 95 290 1450 30 g yes 225 61 245 1450 30 h yes 117 17 129 1440 30 i yes 116 19 125 1450 30 j yes 116 −5 118 1480 30 k yes 174 22 183 1450 30 l yes 208 48 222 1480 30 m yes 127 16 136 1480 30 n no 801 338 864 — — o no 663 255 714 — —

(18) The different attenuations result on the one hand from different refining temperatures and on the other hand from the fact that the raw materials have been purchased from different producers. It can be seen that from all measures the bubbling process has the strongest effect on the attenuation.

(19) TABLE-US-00014 TABLE 5 Ex. 7 D (920 nm) D 1050 nm T.sub.Bubbling t.sub.Bubbling Variant Bubbling [dB/km] Δ (900-700 nm) [dB/km] [° C.] [min] a no 338 126 410 — — b yes 253 94 279 1460 30

(20) Also for example glass 7 a clear relationship between the bubbling and the attenuation was shown.

(21) The following table 6 shows the relationship between the content of Sn.sup.2+ in a sample and the refining temperature on the one hand and the bubbling on the other hand (quantities in % by weight).

(22) TABLE-US-00015 TABLE 6 Glass LT* (° C.) Bubbling Sn.sup.g Sn.sup.2+ Sn.sup.2+/Sn 8 1700 yes 0.1  0.005  5% 8 1550 no 0.1  0.005  5% 7 1800 no 0.11 0.010 10% 8 1700 no 0.11 0.010 10% 8 1710 no 0.11 0.014 13% *refining temperature; .sup.gtotal amount of Sn

(23) It can be seen that at high temperatures a larger part of the tin is present in reduced form. So that SnO.sub.2 acts as a refining agent however very high temperatures are necessary. The table shows that in the case of bubbling according to the present invention after the refining step the content of Sn.sup.2+ is decreased. The influence of the bubbling process is particularly obvious. The ratio of Sn.sup.2+ to the total content of tin is in the same order than the ratio of Fe.sup.2+ to the total content of iron.

(24) The determined values are associated with a high measurement error. Therefore, the glasses according to the present invention are characterized by the attenuation in dB/km. The following example shows that a reduced content of Fe.sup.2+ in the glass has a strong positive influence on the attenuation. This is promoted by the relatively low refining temperatures which allow a refining process with SnO.sub.2, by additional O.sub.2 bubbling which oxidizes and homogenizes the glass and reduces scattering terms, and by the use of highly pure raw materials.

DETAILED DESCRIPTION

(25) FIG. 1 shows the influence of the content of SnO.sub.2 in the glass on the solarization resistance. The figure illustrates only a selection of many experiments and analyses which have been conducted for determining the optimum content of the refining agent with respect to the solarization resistance.

(26) The results shown are mean values of several measurements. The single bars show the extent of the decrease of the color temperature D65 in K after irradiation for a certain time. The irradiation was conducted with a 300 W xenon high pressure short-arc lamp. It can be seen that the solarization always was low enough that the decrease of the color temperature has never reached the limit of 150 K. As mentioned above, with the naked eye a decrease of the color temperature starting from about 150 K is discernible. The glass used had the following composition, see example glass 8.

(27) Higher amounts of SnO.sub.2 did not result in a further improvement of the solarization resistance. Rather there is an optimum with respect to the solarization behavior and an optimum with respect to the refining effect. These two optima are not identical so that an average between a good refining process and a lower solarization had to be found.

(28) FIG. 2 shows the attenuation spectrum of different glasses. It can be seen that the glasses differ in two ranges with respect to the attenuation, namely on the one hand in the range of small wave lengths around 400 nm (blue edge) and on the other hand in the range around 920 to 1100 nm.

(29) It can be seen that conventional core glasses containing PbO indeed have good properties (glass B). Glasses which have had contact with platinum components show strong absorption in the UV range (glass A).

(30) The glasses A and B are fiber glasses containing lead. With As.sub.2O.sub.3 refining they indeed have good IR attenuation values. But nevertheless, they show high attenuation values in the UV range, when produced in a conventional tank (glass A) consisting of a Quarzal basin, Pt refining chamber and homogenization system, i.e. these glasses were in contact with platinum during their production.

(31) Also glass B is a lead glass which was produced in a silica glass crucible and thus had no contact with platinum.

(32) Glass C is a lead-free fiber glass which was molten in the conventional tank and refined with As.sub.2O.sub.3. As.sub.2O.sub.3 refines at lower temperatures than SnO.sub.2 and promotes the redox ratios in the glass so that also in the IR range good attenuation values are achieved. But however due to its toxicity and the solarization effects caused (not shown here) it is not desirable.

(33) Also glass D is a lead-free glass produced with Sb.sub.2O.sub.3 refining in a silica glass crucible without platinum contact. The attenuation values of this glass in the UV range and also in the IR range are very good. But also Sb.sub.2O.sub.3 is not desirable due to its toxicity and the solarization provably caused (not shown here).

(34) Example glass 8 is the glass according to the present invention with SnO.sub.2 refining. It was bubbled with oxygen after the refining process. The attenuation values of this glass in the UV range and also in the IR range are very good.

(35) FIG. 3 shows very nicely, how strong the effect of the bubbling procedure after the refining process is. It can easily be seen that with an increase of the refining temperature also the attenuation increases very strongly. But according to the present invention it has to be refined at high temperatures. With bubbling after the refining process the attenuation is even improved in such a high extent that better values are achieved than in the case of a refining process at low temperature.

(36) FIG. 4: The single bars show the extent of the decrease of the color temperature D65 in K after irradiation for a certain time for an As.sub.2O.sub.3 and an Sb.sub.2O.sub.3 refined glass. The irradiation was conducted with a 300 W xenon high pressure short-arc lamp. The length of the optical fiber was 1 m. Already after 3 h (in the case of the As.sub.2O.sub.3 refined glass) and after 30 h (in the case of the Sb.sub.2O.sub.3 refined glass) of irradiation, respectively, the decrease of the color temperature is >150 K and the effect is strengthened at least by a factor of two in the case of an irradiation time which is longer than 3 h.

(37) FIG. 5 shows the attenuation spectrum of a glass containing manganese (Ex. 11) prior and after irradiation. The band at approximately 550 nm already induced by a 3 h irradiation with a 300 W xenon high pressure short-arc lamp results in an increase of the attenuation in this wave length range to higher than 300 dB/km.

(38) FIG. 6 shows the spectrum of attenuation of example glass 25.