WO2003053873A2 - Phase-separated glasses - Google Patents

Abstract

The invention relates to a phase-separated optical glass and to a method for preparing such a glass. The invention also relates to optical elements, especially an optical fiber and an optical amplifier, produced from the inventive phase-separated glass, and to a method for producing such an optical fiber.

Description

 PHASE SEPARATED GLASSES

description

The present invention relates to a phase-separated optical glass and a method for producing such a glass. The present invention further relates to optical elements, in particular a glass fiber and an optical amplifier, produced from the phase-separated glass according to the invention, and to a method for producing such a glass fiber.

Phase separated glasses have long been known in the art. For example, sodium borosilicate glasses are produced in which the sodium and boron compounds can be dissolved out of the glass and the silicate residue is then used to produce quartz glass by sintering at relatively low temperatures. Fluorine-tarnished glasses are also used to produce white lamp glasses.

In the case of optical glasses, however, a two-phase or multi-phase was generally regarded as a glass defect, and the use of phase-separated glasses as optical glasses has so far only been considered in exceptional cases. In this area, attempts have always been made to produce particularly homogeneous glasses.

Glass ceramics, that is, glasses with a glassy matrix and crystallites enclosed therein, are an exception. The prior art mentions several glass ceramics which are used as optical glasses. For example, US 5,483,628 and US 5,537,505 describe glass ceramics for optical waveguides. WO 99/05071 and WO 99/28255 also describe transparent glass ceramics, which can also be doped with rare earth compounds.

However, such glass ceramics have some disadvantages. On the one hand, depending on the illumination wavelength, the crystallites enclosed in the matrix can cause transmission losses due to scattering mechanisms at the phase boundaries. When used as a glass fiber for optical amplifiers, it has also been found that the width and flatness of the gain are impaired in the case of glass ceramics. Furthermore, glass fibers can be drawn from such materials only with difficulty and, depending on the crystallite size, these generally have only poor mechanical resistance. It is assumed that the crystallites or their phase boundaries form a kind of predetermined breaking points. Glass ceramics are also usually produced by tempering a green glass body. Reheating after tempering for fiber drawing can therefore change the crystal properties, such as the crystallite size and distribution, and change the properties of the glass ceramic.

Glasses which reveal discrete phases of amorphous areas in a glass matrix have not previously been proposed as optical glasses. Although WO 00/01632 describes a glass with at least two separate amorphous phases, this glass is only used as an intermediate for the production of a glass ceramic and not as an optical glass.

Heavy metal glasses such as tellurium oxide glasses (see, for example, EP 0 858 976), bismuth oxide glasses (see, for example, EP 1 127 858 A1) or antimony oxide glasses (WO 99/51537) have also been proposed as materials for optical amplifiers in the recent past, which are characterized by have a wide gain. However, such heavy metal oxide glasses have the disadvantage that they have a significantly higher refractive index of n 2 than the standard SiO ₂ Have fibers of the telecommunications network, so that when connecting such amplifier fibers with the usual SiO∑ fibers, the so-called splicing, problems occur at the phase boundaries due to scattering losses and reflections.

The object of the present invention is therefore to provide novel optical glasses which do not have the problems of the prior art. In particular, novel glasses are to be provided which can be used as materials for optical amplifiers.

The above object is achieved by the embodiments of the present invention disclosed in the claims.

In particular, a phase-separated optical glass is provided which comprises an SiO ₂ -based matrix and at least one type of discrete regions embedded in the matrix, the discrete regions embedded in the matrix having a composition different from the matrix, and these regions are essentially not crystalline.

The figures show:

FIG. 1 shows emission spectra of samples from the examples and comparative examples.

FIG. 2 shows transmission spectra of two Er-doped antimony silicate glasses.

Figures 3 to 5 show greatly enlarged photographic images of glasses according to the invention. For the purposes of the invention, “essentially crystalline” means that less than 10% by volume, preferably less than 5% by volume, more preferably less than 1% by volume and very particularly preferably that no crystallites in the matrix According to a preferred embodiment of the present invention, there are also no crystallites in the matrix.

The term “optical glasses” or glasses of optical quality are understood to mean glasses with defined linear and / or nonlinear optical properties, which are usually melted from high-purity starting components. A distinction can be made between so-called passive and active optical glasses. passive glasses "are understood to mean those which have as little or no interaction with the incident light and which have defined linear optical properties, such as transparency, refractive index, Abbe number, etc. Such passive optical glasses can be used, for example, as optical lenses be applied. In contrast, “active glasses” are understood to mean glasses which have a defined interaction with incident light, such as non-linear optical properties, frequency doubling, stimulated emission, etc. Such active optical glasses can be used, for example, as core material of optical amplifiers, as laser resonator material, etc. Of course, active optical glasses generally also have defined passive properties.

The glass according to the invention is preferably transparent.

According to the invention, the term “matrix” means the continuous phase of the phase-separated optical glass according to the invention and stands in contrast to the areas embedded in the matrix in which it is preferably not continuous, but discontinuous or discrete areas within the matrix. “Continuous” in this context means that essentially all areas of the silicate phase are connected to one another and that only in exceptional cases is a silicate “droplet” completely enclosed by the other phase.

According to a preferred embodiment, there is a type of discrete areas in the matrix of the glass according to the invention which have a composition different from the matrix. According to further embodiments, however, two or more different types of regions can also be present in the matrix. These areas can be homogeneous or in turn have further discrete areas with a composition different from the matrix and / or the first discrete areas. According to less preferred embodiments, crystallites can also be present in the amorphous regions, provided that these regions are still essentially crystal-free, as defined above.

The areas embedded in the matrix preferably have a spherical or droplet-like shape.

According to certain embodiments of the present invention, however, the regions also have a shape deviating from a spherical shape. For example, it can be advantageous according to certain embodiments that ellipsoidal regions are present in the matrix in the glass according to the invention. This makes it possible to give the glass according to the invention optically anisotropic properties. Such a deformation of the generally spherical areas within the matrix can be generated, for example, by the forces exerted on the glass during fiber drawing. The glass according to the invention preferably has a binodal phase distribution. The mixture tends to form or contain discrete spherical particles. The phase boundaries are equally sharp from the start of particle formation and during their growth. A phase separation takes place in that centers form in the metastable state and droplets form as a result of the growth of these centers, the composition of the matrix and droplets being defined from the start and remaining essentially constant at a constant temperature.

However, according to special embodiments of the present invention, a spinodal arrangement of the phases can also be present in the phase-separated glass. These systems tend to form phases with non-spherical particles that are highly interconnected. In contrast to binodal phase distributions, the phase boundary is rather diffuse at the beginning of the phase separation and becomes clearer with increasing phase separation. In the unstable state of the mixture, interconnected phases are defined from the start, with the differences in the phase compositions and the volume of the phases increasing over time.

Such spinodal arrangements can be converted into binodal arrangements.

The size of the discrete areas embedded in the matrix is preferably matched to the properties of the light irradiated during later use. For example, the discrete particles preferably have a size such that no unintended interactions occur when light is irradiated.

A clouding of a glass can occur through various mechanisms. With a particle diameter that is larger than the wavelength of the radiated light, the glass can be clouded by refraction and / or reflection. Light scattering can take place with a particle diameter which is approximately equal to the wavelength. If the particle diameter is smaller than the wavelength, the glass is transparent.

The loss of intensity by scattering mechanisms takes place according to the following simplified formula (approximation of the Raleigh relationship) V ² / λ ⁴ (1) where I is the intensity, V is the volume of the particles and λ is the wavelength of the irradiated radiation.

As a rule, the areas embedded in the matrix have a smaller diameter than the wavelength of the incident light.

For example, the average discrete regions embedded in the matrix have a diameter of at most 100 nm, particularly preferably at most 50 nm, and preferably at least 1 nm.

According to one embodiment of the present invention, the regions embedded in the matrix have a diameter of preferably at most 25 nm, more preferably at most 20 nm, particularly preferably at most 10 nm.

2 shows the transmission spectra of two glasses according to the invention which have the same composition but differ in the diameter of the regions embedded in the matrix. The maximum transmission of the glass, which have embedded areas with a larger diameter, is deteriorated compared to the glass, which have embedded areas with a smaller diameter. According to other embodiments, the diameter of the regions embedded in the matrix is in a range from 10 to 100 nm, preferably 20 to 50 nm. For example, glasses of this embodiment can be used as an intensity filter.

As a rule, the matrix and embedded areas have a different refractive index n. According to certain embodiments, however, the difference in the refractive index between the matrix and the embedded regions can also be sufficiently small so that, even when larger particles are present, there is essentially no clouding of the glass due to light refraction and / or reflections at the phase boundaries.

The phase-separated optical glass according to the invention preferably comprises the following composition (in mol%):

SiO ₂ 20-80

GeO ₂ 0-30

AI ₂ O ₃ 0-40

Ga ₂ 0 ₃ 0-40 ln ₂ O ₃ 0-30

Ti0 ₂ 0-30

ZrO ₂ 0-30

V ₂ O ₅ 0-30

B ₂ O ₃ 0-50

R ¹ ₂ 0 0-40 (R ¹ = Li, Na, K, Rb and / or Cs)

R ² 0 0-40 (R ² = Mg, Ca, Sr, Ba, Pb and / or Zn)

F, CI, Br 0-20

P ₂ O ₅ 0-40

Heavy metal oxide 0-80 Silicon dioxide is preferably present in an amount of 30 to 75 mol%. In this area, the maximum strength of the glass composition is usually obtained.

Oxides of elements which are selected from the group of oxides of the elements Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Zn, W, Ti, Zr, Cd and / or In can also be present.

Additional oxides can be included to adjust physicochemical or optical properties or to reduce the tendency to crystallize.

For example, the addition of at least one further classic network-forming component such as B ₂ O ₃ , Al ₂ O ₃ , GeO ₂ , etc. is preferred.

Furthermore, components can be present in the glass according to the invention which bring about stabilization of the glassy phase against crystallization, such as Al ₂ O ₃ , ZπO and Li ₂ O. These components are preferably present in a total proportion of Al ₂ O ₃ + ZnO + Li ₂ O of 0.1 to 20 mol%.

Lithium oxide can be added to the glass composition according to the invention in a proportion of preferably 0.01 to 10 mol%, more preferably 0.1 to 5 mol%, in order to improve the phase separation and to prevent crystallization of the regions embedded in the matrix , Furthermore, the addition of Li ₂ O may be preferred, since it can enlarge the glass formation areas in glasses containing heavy metal oxide.

Furthermore, the glass according to the invention can contain fluorine in a proportion of 0.01 to 20 mol%, preferably 0.1 to 10 mol%, to improve the phase separation. Zinc oxide can be used to regulate particle size. Zinc oxide can occur both in the matrix phase and in the embedded areas. It is believed to change the surface tension of the embedded areas. If zinc oxide or ZnO is present in a proportion of at least about 0.4 mol%, this can result in smaller embedded areas. The addition of zinc oxide is particularly preferred if lithium oxide is present in a content of at least 0.2 mol%.

Phosphate or phosphorus compounds, such as phosphorus oxides, can support phase separation in some glass compositions. In the case of such glass compositions, the addition of phosphate is therefore particularly preferred. Phosphorus oxides also differ from the silicate matrix in terms of their physical properties and therefore tend to form a separate phase. If there are other compounds in the melt which are more compatible with the phosphate phase than with the silicate phase, these can form the regions different from the silicate matrix together with the phosphate phase. It is assumed that this process can also be used to enrich compounds in the areas other than the silicate matrix, which would just be soluble in the silicate matrix without the addition of phosphate.

The matrix is preferably a multicomponent system, with at least three components preferably being present side by side in the matrix. According to a preferred embodiment, the matrix contains silicon dioxide, aluminum oxide and potassium oxide, where potassium oxide can be replaced by other alkali metals and / or alkaline earth metals or can be present in a mixture with these. In addition to the matrix, the phase-separated optical glass according to the invention also contains discrete regions embedded in the matrix, which have a different composition from the matrix and which are essentially non-crystalline.

In addition to SiO _2, which functions to form the matrix, the composition according to the invention preferably contains a further compound which forms the main constituent of the regions embedded in the matrix. As a rule, however, part of the SiO _{2 will} also dissolve in the regions embedded in the matrix, just as part of the compound, which forms the main constituent of the regions embedded in the matrix, will also dissolve in the matrix. The further oxides which may be present can be distributed over both phases and can serve to stabilize and / or improve the physical properties of the matrix and / or of the regions embedded in the matrix.

According to one embodiment of the present invention, the molar fraction of the matrix components is greater than the molar fraction of the components which form the regions embedded in the matrix, for example the molar fraction of SiO ₂ is 50 to 80 mol%, more preferably 60 to 70 Mol%, the molar proportion of the component which forms the main constituent of the regions embedded in the matrix, at 50 to 20 mol%, more preferably at 40 to 30 mol%.

If the matrix composition has a higher proportion of the total mixture, a phase reversal can take place, ie the silicate-based composition no longer forms the continuous phase or the matrix, but rather forms discrete areas within a phase containing, for example, heavy metal oxide. However, such a phase inversion is not preferred according to the invention. The regions embedded in the matrix preferably comprise at least one heavy metal compound. The proportion of the heavy metal compound in the glass composition is preferably at least 1 mol% on an oxide basis, more preferably at least 5 mol% on an oxide basis, particularly preferably at least 10 mol% on an oxide basis, and preferably at most 80 mol% on an oxide basis, more preferably at most 70 mol% on an oxide basis, particularly preferably at most 60 mol% on an oxide basis.

A heavy metal compound is preferably selected from a group of compounds which is selected from compounds of antimony, molybdenum, tellurium, tungsten, arsenic, bismuth, tantalum, lanthanum, niobium and / or mixtures of these compounds. It is further preferred that the heavy metal compounds are heavy metal oxides. Compounds of these elements differ in molecular size and other physical properties from the silicate matrix, so that there is a tendency for phase separation in a silicate matrix.

The glass according to the invention particularly preferably contains at least one heavy metal compound which is selected from compounds of antimony, molybdenum, tellurium, tungsten and / or mixtures of these compounds. These heavy metals in particular have a significantly lower bond strength to oxygen atoms compared to silicon. In the form of oxides, they have a much lower melting point than silicon dioxide. For these reasons, it is assumed that these heavy metal oxides are only poorly miscible, ie not compatible, with silicon dioxide in the molten state. As a result, discrete phases are formed when the starting compositions are melted in the liquid phase. When they cool down, these segregated phases remain and form a phase-separated glass. According to one embodiment of the present invention, the glass according to the invention contains antimony oxide. It has been found that with such antimony oxide-containing glasses, the addition of boric acid to the glass composition deteriorates the phase separation. For a clear phase separation, the addition of boron oxide or boric acid to the glass composition is therefore not preferred according to this embodiment of the present invention. The glass according to the invention according to this embodiment therefore preferably comprises only small amounts of at most 10 mol% and very particularly preferably essentially no boron oxide. Furthermore, it has been found that BaO can also deteriorate the phase separation in glasses containing antimony oxide, and BaO is therefore preferably also present in a proportion of at most 10 mol% according to this embodiment of the present invention, more preferably the glass according to the invention contains essentially no BaO ,

According to the invention, the expression “essentially none” means that this component is at most present as an impurity and is not added to the starting glass composition as an additional component.

According to further embodiments, the glass according to the invention contains tellurium oxide and / or bismuth oxide. According to this embodiment, the addition of ZnO to stabilize the regions embedded in the matrix against crystallization in a proportion of 0.01 to 20 mol%, in particular 0.1 to 10 mol%, is particularly preferred.

According to preferred embodiments, the glass according to the invention further comprises at least one rare earth compound in a content of 0.005 to 10 mol%, more preferably 0.01 to 5 mol%. The rare earth compound is preferably at least one oxide which is selected from oxides of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and / or Lu. Oxides of the elements Er, Pr, Tm, Nd and / or Dy are particularly preferred.

If necessary, in addition to one or more rare earth compounds), Sc and / or Y compounds can also be contained in the glass.

According to a preferred embodiment of the present invention, the rare earth compounds used are one or more so-called “optically active compounds”, “optically active compounds” being understood to mean those which lead to the glass according to the invention being stimulated to be emitted are capable if the glass is excited by a suitable pump source.

At least two rare earth compounds in a total amount of 0.01 to 15 mol% can also be used. Glasses with optically active rare earth ions can be codoped with optically inactive rare earth elements, for example to increase the emission lifespan of the glass. For example, it can be coded with La and / or Y. In order to increase the pump efficiency of the amplifier, it can, for example, also be codoped with other optically active rare earth compounds, such as Yb.

If necessary, in addition to one or more rare earth compounds, Sc and / or Y compounds can also be present in the glass according to the invention. By doping with other rare earth ions such as Tm, other wavelength ranges can be developed, such as the so-called S band between 1420 and 1520 nm in the case of Tm.

Furthermore, in order to make more effective use of the excitation light, sensitizers such as Yb, Ho and Nd can be added in an appropriate amount, for example 0.005 to 8 mol%.

The content of each individual rare earth compound is preferably from 0.005 to 8 mol% on an oxide basis.

It has been found that such rare earth compounds accumulate preferentially in the discrete areas embedded in the matrix, provided that these are areas containing heavy metal oxide. It is assumed that the rare earth compounds also dissolve in the silicate matrix only when these areas are supersaturated.

The areas embedded in the matrix can contain, in addition to the heavy metal oxide compound and possibly the rare earth compounds, further oxides, for example alkali and / or alkaline earth compounds and / or portions of network formers, such as SiO ₂ , Al ₂ O ₃ . Such further oxides can therefore usually dissolve both in the matrix and in the regions embedded in the matrix and they can also be present in both phases at the same time. In the embedded areas, these additional oxides can be used to stabilize against crystallization.

According to a further embodiment of the present invention, the phase-separated glass according to the invention is used as an optically active glass of an optical amplifier. To improve the fiber drawability for Table fiber amplifier is particularly preferred, the addition of at least one component such as B ₂ 0 ₃ , Al ₂ 0 ₃ , Ge0 ₂ , etc. is particularly preferred.

Furthermore, oxides of W and or Ga can serve to increase the Dλ value, ie to broaden the emission cross section. The addition of alkali oxides is particularly advantageous if the glass is to be used for planar optical amplifiers using the ion exchange technique. Li ₂ 0 as a glass component is advantageous according to this embodiment if an optical amplifier with particularly good efficiency is to be generated in the L-band.

The present invention further relates to a method for producing the phase-separated optical glass according to the invention, which comprises the steps of mixing the starting composition and melting these starting components.

In the molten state, phase separation is preferably carried out solely by the starting composition of the components. According to the present invention, it is preferably not necessary to introduce special tempering steps in order to cause the at least two phases to separate.

Demixing can occur, for example, in the case of glasses containing antimony oxide even at high temperatures of greater than 1000.degree.

It was found that the heavy metal oxides also dissolve to a certain extent in the silicate phase, even if the majority of the heavy metal oxides form the discrete areas embedded in the matrix, and that Si0 _{2 also} to a certain extent also in the heavy metal oxide-containing areas Phase solves. Therefore, depending on the solubility of the respective heavy metal oxide from the silicate matrix used may be preferred according to certain embodiments to add larger proportions of heavy metal oxide compounds to the starting mixture than is present later as a separate phase in the glass according to the invention. In cases in which La ₂ 0 ₃ , Nb ₂ 0 ₅ , Ta ₂ 0 ₅ , Sb 0 ₃ , W0 ₃ , and / or mixtures thereof are used as the heavy metal compound in the glass according to the invention, the heavy metal compound preferably has a proportion of 1 to 60 mol% of the starting batch. In cases in which Mo0 ₃ , Bi ₂ θ3, Te0 ₂ and / or mixtures thereof are used as the heavy metal compound in the glass according to the invention, the heavy metal compound preferably has a proportion of 1 to 80 mol% of the starting mixture.

To achieve a fluorine content of the glass according to the invention, fluorides, preferably alkali and / or alkaline earth fluorides, can be added to the mixture in a proportion of preferably at most 10 mol%, particularly preferably at most 5 mol%. The fluorides NaF, CaF ₂ , AIF ₃ and / or mixtures thereof are particularly preferably added to the mixture.

The starting components of the glass according to the invention are preferably predried before melting, since even a lower moisture content generally worsens the active and passive optical properties of glasses and, for example, can lead to shorter fluorescence lifetimes for glasses containing Er.

It is further preferred to dry the melt by blowing in preferably dry oxygen, so-called 0 ₂ -bubbling.

Drying of the melt can also be achieved by adding some of the starting components to the batch as bromides. In front- up to 25 mol% of the alkali and / or alkaline earth compounds and / or of Al ₂ 0 ₃ can preferably be added in the form of bromides.

After melting, the glass may be annealed prior to molding in accordance with one embodiment of the present invention.

According to preferred embodiments, the glass according to the invention is cooled to room temperature after molding. It is preferred according to the invention that the glasses are relatively quick, i.e. with cooling rates of preferably at least 5 K h, more preferably of at least 10 K / h. Such cooling rates, which are fast for optical glasses, can result in a smaller diameter of the regions embedded in the matrix, which is preferred according to some embodiments of the present invention.

According to other embodiments, however, a larger diameter of the regions embedded in the matrix may be desired, so that, according to these embodiments, slower cooling rates are preferred.

According to one embodiment of the present invention, the glass is quenched, i.e. cooled very quickly to room temperature. Larger glass volumes can be quenched by water cooling and or roller cooling. However, since, for example, only a relatively small amount of gias leaves the heated part of the apparatus during fiber drawing, water cooling is generally not required in such glass products in order to achieve rapid cooling rates.

Tempering or tempering the glasses near the melting point of the heavy metal oxide generally did not lead to any optical change in the glasses according to the invention. However, if the glass is heated to a temperature above the melting point of the areas embedded in the matrix warms, the heavy metal oxide-rich areas can melt, which in some glasses can lead to crystallization when the sample cools. According to the invention, the glasses according to the invention are therefore preferably no longer heated to a temperature above the melting temperature of the heavy metal oxide after the production.

The phase-separated glass according to the invention can be used particularly advantageously as optically active glass for an optical amplifier. Since glasses according to the invention can also be warped into fibers, for example, single-mode fibers can be produced with a rare earth-doped core for optical fiber amplifiers.

Surprisingly, it was found that a widening of the emission spectrum and thus of the gain can only be observed when amorphous regions are embedded in the matrix. If, on the other hand, the areas embedded in the matrix are crystallized, the result is a comparatively narrower emission and thus a narrower and inhomogeneous amplifier characteristic.

FIG. 1 shows emission spectra of glasses according to the invention and not according to the invention for use as optically active glass for an optical amplifier.

Three types of spectra can be distinguished in the emission spectra shown in FIG. The glasses each have emission spectra of different widths, with the widest possible emission spectrum being preferred since this leads to a widened gain of the optical amplifier and optical amplifiers with a wide gain are desired in telecommunications. The first type (type A) has the narrowest and therefore the most unfavorable emission band. These glasses are compositions in which there are no two-phase glasses or in which the glass has crystallites in a proportion of> 10% by volume. In the case of erbium doping, these glasses have a pink color.

In contrast, glasses of the second type (type B) have a much wider emission band. These glasses are phase-separated glasses according to the invention according to one embodiment, which are essentially not crystalline. These glasses are usually yellowish in color.

The broadest emission curve (curve type C) was measured on a pure Er-doped antimony oxide glass. In addition to the disadvantages mentioned in the introduction, such antimony oxide glasses are, however, difficult to manufacture, since, because of the volatility of the antimony, the starting composition can only be melted in a closed crucible and only by rapid cooling of the melt, so-called quenching, for example by rapidly introducing one containing the melt Ampoule can be obtained in a larger volume of water.

FIG. 1 thus shows that the phase-separated glasses according to the invention can achieve almost the same width of the emission spectrum as that of a pure antimony oxide glass, but at the same time its disadvantages, such as the difficult manufacture, can be avoided. There is therefore a “glass in glass” in which different functionalities can be achieved in one material and these functionalities could not be present simultaneously in a homogeneous glass. The ones shown in FIG. 1 Glasses according to the invention have, for example, the following combination of properties:

• A high refractive index of the areas embedded in the matrix - good emission spectroscopic properties (wide emission),

• a low refractive index of the matrix - simple connection of a glass fiber containing the glass according to the invention to a conventional Si0 ₂ fiber and

• good mechanical stability of the fiber thanks to the silicate matrix.

Surprisingly, it has also been found that the phase-separated glass according to the invention has a longer fluorescence lifetime τ than the glasses from the comparative examples. The glasses according to one embodiment of the invention have fluorescence lifetimes τ of> 3 ms, preferably> 5 ms. The fluorescence lifetime τ is the time at which the intensity of the fluorescence has dropped to 37% of the maximum intensity after the excitation light has been switched off.

The present invention thus also relates to a glass fiber which comprises the glass according to the invention. To produce such a glass fiber, it is preferred to melt the starting components of the glass by means of a multi-crucible process and, if necessary, to draw the molten glass directly into a glass fiber after a refining step, without the glass being solidified and reheated beforehand. By means of a double or triple crucible, one or more outer glass jackets can also be applied to the fiber core simultaneously during the fiber drawing process.

Such a glass fiber for an optical amplifier preferably has a core with a thickness of 1 to 15 μm and one or more glass jackets, so that an outer diameter of, for example, about 125 μm results.

Surprisingly, it was found that the glass according to the invention macroscopically has a refractive index which corresponds approximately to that of a conventional SiO ₂ -based glass or is of the same order of magnitude. The glasses according to the invention macroscopically have a refractive index of π <1.7 at 1300 nm. This low refractive index makes it possible, for example, for an amplifier fiber made from the glass according to the invention to be connected to the silicate glass fibers of the telecommunications network for optical amplifiers with little technical problems or outlay using methods customary in the prior art.

Silicate glasses can also be selected for the coats. A cladding of an optical fiber should have physical properties similar to the core of an optical fiber. Since the glass according to the invention has the same macroscopic properties as a silicate glass, when using the glass according to the invention as the core glass of a glass fiber, the cladding glasses can also be of silicatic origin. This has the considerable advantage that the antimony oxide-containing shells required for homogeneous antimony oxide-containing glasses can be avoided, which are not advantageous for reasons of environmental protection and with regard to undesired crystallization. For example, crystallization-stable lead silicate glasses can be used as cladding glasses.

Examples:

The glass compositions given in the table below became glasses of the examples according to the invention and the glasses similar examples produced. High-purity raw materials were used. Anti-monoxide was dried to reduce the water content. Then all the glasses were melted in silica glass crucibles at about 1500 ° C. The silica glass crucible was arranged in an inductively heated platinum crucible. Dry oxygen was introduced into the melted mixture at 1550 ° C. for about 90 minutes. Subsequently, the molten glass composition was ^Λ A hour at about 1500 ° C allowed to stand before it was poured into pre-heated graphite molds. The samples were cooled uniformly at 450 ° C. for half an hour and cooled to room temperature at a rate of 15 K / h.

Table 1

Table 1 (continued)

Table 1 (continued)

Note on the table: No entry in fields of lines that describe physical properties means that this property has not been determined for this glass so far.

Samples cooled at 450 to 500 ° C show no to negligible crystallization both macroscopically and TEM microscopically.

The glasses of Examples A to L according to the invention all have the advantageous properties of an emission curve of type B, fluorescence lifetimes τ of> 5 ms and a refractive index n at 1300 nm of approximately 1.6. The glasses from Examples B, C, D and F could be annealed at 700 ° C. without a significant change in the properties, such as, for example, separation of the phases.

The heavy metal oxide content can be varied within a wide range, as examples A to F show. Furthermore, various other components can be contained in the glass according to the invention without the optical properties of the glass being impaired.

In the case of Er-doped antimony oxide-containing glasses, the color of the glass can give an indication of the internal structure of the glass. Erbium (Er) usually dissolves in a phase containing heavy metal oxide in a yellowish color, whereas in the absence of a phase containing heavy metal oxide it dissolves in the silicate phase to form a pink or pink color. The color of the glass thus gives a first rough indication of whether the phase-separated glass according to the invention is present or not.

An exception to this is the glass from example L, which is colored strongly pink, but nevertheless has an emission curve of type B. This glass contains a relatively high proportion of erbium, and it is suspected that not all erbium oxide was able to dissolve in the heavy metal oxide-containing phase and therefore remains in the silicate phase and gives it its pink color, which gives the yellow color to the heavy metal-containing ones Phase covered. However, this exemplary embodiment is less preferred since the fluorescence lifetime τ is deteriorated to a value below 5 ms compared to the other examples. This is attributed to concentration quenching due to the high Er concentration. The glass from comparative example 1 is a pure antimony oxide glass which was melted in a closed system. The glass from comparative example 2 is an Er-doped silicate glass without heavy metal oxide.

The compositions of the glasses from comparative examples 3 and 4 contain boron oxide in different contents. Both glasses only have an emission spectrum of type A, i.e. these glasses are only less suitable as glasses for optical amplifiers. Furthermore, the fluorescence lifetime τ is deteriorated compared to that of the silicate glass from Comparative Example 2.

Although the glass from comparative example 5 contains no boron oxide, it still has only one type A emission curve. This behavior is attributed to the presence of barium oxide in the glass.

Figures 3 and 4 show photographic images of antimony oxide-containing glasses according to the invention. FIG. 3 shows the edge area of a two-phase glass, in which the areas different from the matrix can be clearly recognized as dark areas. In this case, the areas have a diameter of approximately 10 to 20 nm. FIG. 4 shows the recording of a glass which was produced by quenching the melt in water. The areas which contain antimony oxide and which are different from the matrix can be seen in dark areas and have a diameter of about 5 to 10 nm.

FIGS. 5 a to c show photographic images of TEM microscopic images in different magnifications. The areas different from the matrix can also be clearly seen in these figures and have a diameter of approximately 10 to 20 nm. The 5c, the finer structuring contained is an artifact of the measurement and not due to the glass structure.

Claims

Expectations 1. Phase-separated optical glass, comprising an SiO ₂ -based matrix and at least one type of discrete regions embedded in the matrix, which have a different composition from the matrix and which are essentially non-crystalline. 2. Glass according to claim 1, wherein the areas embedded in the matrix comprise at least one heavy metal compound. 3. Glass according to claim 1 or 2, wherein the regions embedded in the matrix comprises at least one heavy metal compound which is selected from the group of compounds of Sb, Mo, Te, W, As, Bi, Ta, La, Nb and mixtures of these compounds is. 4. Glass according to one of the preceding claims, which has the following composition (in mol%): Si0 ₂ 20-80 Ge0 ₂ 0-30 Al ₂ 0 ₃ 0-40 Ga ₂ 0 ₃ 0-40 ln ₂ 0 ₃ 0-30 Ti0 ₂ 0-30 Zr0 ₂ 0-30 V ₂ 0 ₅ 0-30 B ₂ 0 ₃ 0-50 R ¹ ₂ 0 0-40 (R ¹ = Li, Na, K, Rb and / or Cs) R ² 0 0-40 (R ² = Mg, Ca, Sr, Ba, Pb and / or Zn) F, CI. Br 0-20 P ₂ 0 ₅ 0 - 40 Heavy metal oxide 0 - 80. 5. Glass according to one of the preceding claims, wherein the glass has a binodal phase distribution. 6. Glass according to one of the preceding claims, wherein the areas embedded in the matrix have an average diameter of at most 100 nm, preferably at most 50 nm. 7. Glass according to one of the preceding claims, wherein at least the regions embedded in the matrix contain a rare earth compound in a content of 0.005 to 10 mol%. 8. The glass of claim 7, wherein the rare earth compound is an erbium compound. 9. Glass according to one of the preceding claims, wherein the glass contains substantially no B2O3. 10. A method for producing a phase-separated optical glass according to one of claims 1 to 9, comprising the steps of mixing and melting the starting components. 11. The method of claim 10, wherein the glass is not annealed. 12. Glass fiber containing a glass according to one of claims 1 to 9. 13. A method of manufacturing a glass fiber according to claim 12, comprising the step of drawing a fiber from a glass according to any one of claims 1 to 9. 14. The method according to claim 13, wherein by means of a multi-crucible method, the starting components of the glass are drawn directly into a glass fiber after melting and optionally refining, without the glass being solidified and reheated. 15. An optical amplifier comprising an optically active glass according to one of claims 1 to 9.