WO2003022766A1

WO2003022766A1 - Bismuth oxide glasses containing germanium oxide

Info

Publication number: WO2003022766A1
Application number: PCT/EP2002/010059
Authority: WO
Inventors: Bianca Schreder; Rüdiger SPRENGARD; Ulrich Peuchert; Martin Letz; Joseph S. Hayden; Sally Pucilowski
Original assignee: Schott Glas; Carl-Zeiss-Stiftung Trading As Schott Glas; Carl-Zeiss-Stiftung
Priority date: 2001-09-10
Filing date: 2002-09-07
Publication date: 2003-03-20
Also published as: JP4671263B2; AU2002362276A1; JP2005502576A; EP1425250A1

Abstract

The invention relates to bismuth oxide glass, containing germanium oxide, a method for the production thereof, the use thereof and a glass fiber consisting of said inventive glass.

Description

Bismuth oxide glasses containing germanium oxide

The present invention relates to a bismuth oxide-containing glass which contains germanium oxide, a method for producing such a glass, the use of such a glass and a glass fiber which comprises the glass according to the invention.

Optical amplifier units are one of the key components of modern optical communications technology, in particular WDM technology (WDM "wavelength division multiplexing"). Until now, quartz glasses doped with optically active ions have been used as core glass for optical amplifiers , Si0 ₂ -based amplifiers enable simultaneous amplification of several closely spaced, wavelength-differentiated channels in the range around 1.5 μm.However, due to the narrow-band emission of the Er ³⁺ in SiCV glasses, these are not suitable for the increasing demand Suitable transmission power.

Accordingly, the demand for glasses from which rare earth ions emit significantly more broadband than from SiO ₂ glasses is increasing. Glasses with heavy elements are preferred, in particular heavy metal oxide glasses or glasses containing heavy metal oxide (“heavy metal oxide”, HMO glasses). As a result of their weak interatomic bonds, these heavy metal oxide glasses have large interatomic electric fields and, due to their greater strength, Splitting of the ground state and excited states to a broader emission of the rare earth ions.Examples of such glasses are glasses based on tellurium oxide, bismuth oxide and antimony oxide.

Such heavy metal oxide-containing glasses, however, have some disadvantages, particularly compared to SiO ₂ glasses, which have not yet been overcome by the prior art. Naturally, such glasses have weak interatomic binding forces and are mechanically much less stable than Si0 ₂ fibers. However, good mechanical stability is particularly relevant for the production of broadband fiber amplifiers with regard to long-term reliability. In order to be able to be installed in suitable amplifier housings, fibers drawn from the glasses must be able to be rolled up to a diameter of about 5 to 10 cm without breaking. Furthermore, the glass fibers should also remain permanently stable when rolled up.

Glasses containing heavy metal oxide also have a much lower melting and softening point than SiO ₂ . A compound of Si0 ₂ fiber with the heavy metal oxide-containing fiber z. B. by thermal welding in an arc (so-called "splicing") is therefore difficult. It is therefore desirable to have the smallest possible difference between the softening temperature of the heavy metal oxide glass and that of the SiO ₂ -based glass.

A rare earth-doped glass or glass product such as a fiber or a waveguide substrate should therefore simultaneously meet the following key requirements for use as a broadband amplifier medium in the telecommunications sector:

- wide and flat absorption and emission bands of the rare earth ion, but not only in the area of the C-transmission band around 1550 nm,

- sufficient lifetime of the emitting state or the laser level,

- the highest possible thermal load capacity, i.e. high softening point,

- high mechanical stability,

- good meltability with conventional melting processes and

- good fiber drawability.

Bismuth oxide-containing glasses have been described in the prior art, for example in JP 11-236245 and WO 00/23392, and for use as optical components. suggested more strongly. In particular, the function of cerium oxide is discussed, which is said to have a stabilizing effect on the high oxidation level of bismuth when the glass is melting and which should also be advantageous for glasses with too low phonon energy for spectroscopic reasons. However, the addition of Ce0 ₂ is disadvantageous, since even small amounts of less than 0.2 mol% Ce0 ₂ increasingly yellow the glass and shift the UV edge of the absorption into the range of the Er ³⁺ emission line at 550 nm becomes. The described positive effects on the spectroscopic properties could not be confirmed either.

WO 01/55041 A1 describes a bismuth oxide-containing glass for optical fiber amplifiers, which contains at least one of Ga ₂ 0 ₃ , W0 ₃ and Te0 ₂ . However, these components are not beneficial. The addition of tellurium oxide can increase the risk of reducing Bi ³⁺ to elementary Bi ° and thus discolor the glass black. The addition of tungsten oxide to glasses containing heavy metal oxide leads to increasing instability of the glasses with regard to crystallization. Gallium oxide is a relatively expensive and less accessible component and therefore addition is not advantageous either. JP 2001-213635 A also describes glasses containing bismuth oxide, almost all of the glasses described also containing gallium oxide here. These writings do not provide a solution to the problem of how the mechanical strength and the thermal stability of glasses containing bismuth oxide can be improved.

The object of the present invention was therefore to provide bismuth oxide-containing glasses for optical amplifiers in the sense of the abovementioned catalog of requirements, which glasses can overcome the problems of the prior art and with which optical amplifiers with a broad and flat amplification characteristic can be produced. Such glasses should also have sufficient mechanical stability in order to be able to be warped into mechanically sufficiently stable fibers. The object is achieved by the embodiments described in the claims.

In particular, the present invention relates to bismuth oxide-containing glass which has the following composition (in mol%):

Bi ₂ 0 ₃ > 15

Ge0 ₂ > 0.01 further oxides 0 - 74.99

Rare earth compound 0-10 (oxide-based)

Surprisingly, it was found that the glasses according to the invention containing germanium oxide have a larger distance between the transformation temperature T _g and the crystallization temperature T _x compared to glasses free of germanium oxide. This is advantageous if, after a first cooling and cooling from the melt, the glass is to be processed further by shaping. The further the crystallization temperature T _x lies above the transformation temperature T _g , the lower is the risk that crystallization occurs when the glass is reheated and, as a rule, the glass becomes unusable. Such a glass is, for example, better suited for warping from a preform into a glass fiber, since a sufficient distance from the crystallization temperature can be maintained when warmed for warping.

Furthermore, surprisingly, the thermal load-bearing capacity of glasses containing bismuth oxide is also improved overall by the presence of germanium oxide. An improved or increased thermal load capacity of a glass is understood to mean that a higher temperature is required to set a certain viscosity of a glass than in the case of a glass with a lower or worse thermal load capacity. For example, the transformation temperature T _g and / or the softening point EW of a thermally more resilient glass are increased compared to a germanium oxide-free starting glass. Glasses containing heavy metal oxide generally have a significantly poorer thermal load capacity than glasses based on Si0 ₂ . For example, they have a lower transformation temperature T _g and a lower softening temperature EW. This can be problematic if a glass fiber made from such a glass is to be connected as an optical amplifier fiber to the standard SiO ₂ glass fiber network. This can be done, for example, by thermal welding, so-called “splicing”. In this method, the ends of the SiO ₂ fibers and the reinforcing fibers are brought into spatial proximity or in contact with one another and heated simultaneously by, for example, an arc. The softened ends can then be connected to one another merge or adhere to each other and a connection of the amplifier fiber with the Si0 ₂ fiber is formed. Such a fusion is all the more difficult the further apart the viscosities of the glasses of the fibers to be connected are at elevated temperature. Already a T _g increase by a few Kelvin can therefore be advantageous for such a coupling process.

It was also found that the introduction of the network-forming component Ge0 _2, particularly in combination with Si0 _2, improves the mechanical properties of the glass. For example, the so-called Y value is improved in the glasses according to the invention. The Y value is determined by determining the Vicker's hardness. For this purpose, the depth of penetration is determined in an indentation test on the surface of a glass plate for a given pressure. It also shows that single-mode fibers drawn from the glasses according to the invention have better Weibull statistics than corresponding germanium oxide-free glass fibers.

The figures show:

FIG. 1 shows the comparison of a Weibull statistic of a glass fiber drawn from glasses according to the invention and a comparative example not according to the invention. Figure 2 shows the Er ³⁺ term scheme.

FIG. 3 schematically shows the effect of a slight shift in the absorption band to lower wavelengths and the associated positive effect on the flatness of the gain.

Figure .4 is a photographic illustration of a glass fiber according to the invention, which was connected to a silicate telecommunications fiber by so-called "splicing".

FIG. 5 shows Giles parameters of a glass fiber drawn from glasses according to the invention.

FIGS. 6 and 7 show investigations of the long-term stability (“Reliability”) of a glass fiber according to the invention.

FIGS. 8a and 8b show the maximum gain calculated from Giles parameters for a fixed number of channels as a function of the wavelength, and the change in noise as a function of the wavelength.

Figure 1 shows two Weibull statistics of bismuth oxide-containing glass fibers. In such a Weibull statistic, the probability of breakage F is plotted against the tension σ applied to the fiber, which corresponds to a specific bending radius of the fiber. In this case, a fiber should still have the lowest possible probability of breakage when the voltage applied is as large as possible. From Figure 1 it can now be seen that the Ge0 ₂ -containing fiber (square markings) with the same applied voltage σ has a lower probability of breakage F than a corresponding Ge0 ₂ -free fiber (circular markings). Both fibers comprise a core and a glass jacket formed around them and a total diameter of approximately 125 μm. They were drawn from preforms produced using the same method under the same drawing conditions and showed comparable designs, geometries and coatings. In the fiber not according to the invention, the proportion of germanium oxide would be switched to an equal proportion of gallium oxide.

FIGS. 6 and 7 show that the long-term stability of the fibers according to the invention is also good. FIG. 6 shows the result of a so-called "pull-and-bend" test which was carried out on glass fibers according to the invention. FIG. 7 shows the result of a so-called "double-cleavage-drilled compression" test (DCDC test) on a sample the glass composition according to the invention according to Example 6. An n value of approx. 16 is a comparatively good value for a fiber containing heavy metal oxide, which is already relatively close to the n value of silicate fibers of approx. 20.

The following are all data in mol% and on an oxide basis, unless stated otherwise.

The glass according to the invention contains germanium oxide in a proportion of at least 0.1 mol%, preferably at least 1 mol%, particularly preferably at least 3 mol%. The glass according to the invention preferably contains at most 60 mol%, more preferably at most 50 mol%, most preferably 40 mol%, of germanium oxide.

Bismuth oxide is present in the glass according to the invention in a proportion of at least 15 mol%. The proportion of bismuth oxide in the glass is preferably at least 20 mol%. The upper limit is preferably 80 mol%, more preferably 70 mol%, most preferably 60 mol%, of bismuth oxide in the glass. With proportions over 80 mol% bismuth oxide, the glass can easily crystallize.

In addition to the components mentioned above, the glass according to the invention can contain further oxides with a content of 0 to 74.99 mol% on an oxide basis. Such additional oxides can be included to adjust physicochemical or optical properties or to reduce the tendency to crystallize.

To improve the fiber drawability, the addition of at least one further classic network-forming component such as, B ₂ θ ₃ , Al ₂ 0 ₃ , etc., is preferred in particular when using the glass according to the invention for an optical fiber amplifier.

The addition of Si0 ₂ has a particularly positive effect on the mechanical properties of the glass, but usually worsens the spectroscopic properties. The glass according to the invention preferably contains at least 1 mol%, more preferably at least 5 mol%, of SiO ₂ . It is further preferred that the glass according to the invention contains at most 50 mol%, more preferably at most 40 mol%, most preferably at most 30 mol% Si0 ₂ .

The addition of B ₂ 0 ₃ or boric acid improves the spectroscopic properties of the glass, in particular the flatness of the gain, and the glass according to the invention therefore preferably contains at least 5 mol%, more preferably at least 10 mol% and most preferably at least 15 mol%, B ₂ 0 ₃ . The proportion of B ₂ 0 ₃ is preferably at most 60 mol%, more preferably at most 40 mol%.

In particular Al ₂ 0 ₃ can be added to facilitate glass formation. The proportion of Al ₂ 0 ₃ is preferably at least 0.5 mol%, more preferably at least 2 mol%. The proportion of Al ₂ 0 ₃ is preferably at most 30 mol%, more preferably at most 20 mol%.

Furthermore, oxides of elements can be contained which consist of the best of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Zn, Sn, Ta, Nb, W, Ti, Zr, Cd and In - selected group. The proportion of such oxides is preferably at least 1 mol%. They can be contained in a total proportion of preferably at most 60 mol%, more preferably at most 40 mol%, in the glass composition according to the invention.

Depending on the field of application, the addition of lithium oxide is particularly preferred in the glasses according to the invention. It has been found that the addition of Li ₂ 0 in glasses containing bismuth oxide can increase the glass formation areas. In addition, Li ₂ 0 is advantageous if an amplifier with particularly good efficiency is to be generated in the L band. The use of preferably at least 1 mol%, more preferably at least 3 mol%, of Li ₂ O is favorable.

The addition of further alkali oxides is particularly advantageous if the glass is to be used for planar applications, such as planar waveguides and planar optical amplifiers, using the ion exchange technique.

If appropriate, the glasses according to the invention can also contain proportions of halide ions such as F ^" or CI ^" in a proportion by weight of at most about 10 mol%, particularly preferably of at most about 5 mol%.

The glass according to the invention preferably has the following composition:

In the table, M means at least one of Li, Na, K, Rb and / or Cs and M ^{M means} at least one of Be, Mg, Ca, Sr and / or Ba.

The addition of tungsten oxide to glasses containing heavy metal oxide leads to an increasing tendency of the glasses to crystallize, i.e. an instability of the glasses with regard to crystallization. A tendency to crystallize complicates further processing and / or deformation of the glass under heating, such as fiber drawing from a preform. The glass according to the invention therefore preferably contains essentially no tungsten oxide, this expression meaning that tungsten compounds are not added as a component to the glass composition, but are present at most as an impurity in a proportion of at most 0.5 mol%.

The addition of tellurium oxide to the glass according to the invention can increase the risk of reducing Bi ³⁺ to elementary Bi °. Since elemental bismuth stains the glass black, the addition of tellurium compounds is disadvantageous. The glass according to the invention is therefore preferably essentially tellurium-free, this expression meaning that tellurium or a tellurium compound is not Component are added to the glass composition, but is at most present as an impurity in a proportion of at most 0.5 mol%.

If the glass according to the invention is used as a so-called passive component, such as, for example, as a jacket around the optically active core of an amplifier fiber, it preferably contains no optically active rare earth compound. However, it can be preferred according to certain embodiments that actually passive components such as the cladding of an amplifier fiber also contain small amounts of optically active rare earth compounds.

According to one embodiment of the present invention, the glasses according to the invention preferably comprise at least one rare earth compound as a dopant. This embodiment relates in particular to the use of the glasses according to the invention as optically active glasses for optical amplifiers and lasers. 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, with oxides of Er being most preferred.

The glasses according to the invention can also contain cerium oxide, but this is not preferred since cerium can discolor the glass yellowish-orange and shift the UV edge of the absorption into the region of the Er ³⁺ emission line. The glasses according to the invention are therefore preferably cerium-free. With the glasses described here, the addition of cerium oxide can be dispensed with, since the oxidation state of the bismuth oxide can, if necessary, also be stabilized by using a suitable melting process.

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. The rare earth compounds used as dopants are preferably so-called “optically active compounds”, “optically active compounds” being understood to mean, for example, those which lead to the glass according to the invention being capable of stimulated emission if it is excited by a suitable pump source.

According to one embodiment, the glasses according to the invention contain at least two rare earth compounds in a total amount of 0.01 to 15 mol%, preferably of 0.01 to 8 mol%. Glasses with optically active rare earth ions can be codoped with optically inactive rare earth elements, for example to increase the emission lifetimes. 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. Gd can be codoped to stabilize the crystallization.

Furthermore, in order to achieve a more effective utilization of the excitation light, sensitizers such as Yb, Ho and Nd can be added in a suitable amount, for example 0.005 to 8 mol%.

The content of each individual rare earth compound in the glass is preferably at least 0.005 mol%, more preferably at least 0.01 mol%, on an oxide basis. Further, the rare earth compound content is at most 8 mol%, more preferably at most 5 mol%, on an oxide basis. In one embodiment, the rare earth compound (s) content is from 2 to 5 mole percent on an oxide basis. According to a further embodiment, the content of rare earth compound (s) is 0.01 to 2 mol% on an oxide basis.

According to a particularly preferred embodiment, the glasses according to the invention contain at least Er ₂ 0 ₃ as a dopant. Figure 2 shows the energy term scheme of Er ³⁺ . Excited by a suitable pump radiation is the upper laser level lι _{_3/2} either indirectly (980 nm via ln ^_4/2) populated directly or (1480 nm). An incoming signal photon brings excited Er ³⁺ ions to the stimulated emission, ie electrons relax to the ground state ⁴ li _5/2 with emission of photons in the signal wavelength. Depending on the degree of splitting of the multiplet (Stark levels) from the upper and lower laser level, it emits ³⁺ in the 1550 nm band narrower or wider. This splitting depends on the local environment of the Er ³⁺ in the glass matrix.

Surprisingly, it was found that germanium oxide in Er-doped bismuth oxide-containing glasses has a significant influence on the position of the intensity maximum of the absorption and / or emission bands of the erbium around 1550 nm and thus has a positive influence on the flatness of the gain in the C-band.

Due to the proportion of germanium oxide in the glass according to the invention, the flank of the absorption band in the short-wave range is shifted towards higher intensities. Since an amplification spectrum results from the superposition of absorption and emission spectrum, even with only a slight shift in the maximum of the absorption band, based on a wavelength window of interest, e.g. B. the C-band range between about 1528 and 1565 nm, a flatter and wider gain characteristic. FIG. 3 schematically shows a slight shift in the absorption band and the resulting positive effect on the gain.

FIG. 5 shows Giles parameters obtained using a glass according to the invention compared to those obtained using a silicate glass. It can clearly be seen that the band in the range around 1500 nm is significantly broadened by the glass according to the invention. Figures 8a and 8b show the gain and the noise of a doped HMO double cladding fiber according to the invention compared to Si0 ₂ amplifier fibers depending on the wavelength and the number of channels. For this application, the so-called Giles parameters are determined using methods known in the prior art for the amplifier fibers, from which the maximum gain and the noise at a specific wavelength are then determined when the number of channels is fixed. FIG. 8a shows on the one hand that with a set number of 120 channels [ch], a maximum gain of approximately 25 dB is achieved with an amplifier fiber according to the invention, while for a silicatic amplifier fiber with the same number of channels only a maximum gain of almost 20 dD is achieved. For a comparable gain of 25 dD, the number of channels must be reduced from 120 to 80 channels for a silicate amplifier fiber. At the same time, with the same number of channels, the noise of the glass fiber according to the invention is significantly lower than that of a silicic fiber. Even with a further increase to 180 channels (Figure 8b), the same picture results: the fiber according to the invention has a higher maximum gain with less noise. These FIGS. 8a and 8b show that a broadband transmission is possible with the HMO glass fiber according to the invention with low noise.

According to this embodiment of the present invention, it is preferred that the glass according to the invention contains boric acid or boron oxide in a proportion of in particular 5 to 60 mol%, more preferably 10 to 40 mol% (calculated as B ₂ O ₃ ). It has been found that boron oxide can further improve the flatness of the gain in optical amplifying glasses.

Furthermore, Si0 ₂ can preferably be contained, as a result of which the service life τ of the upper laser level can advantageously be extended.

By doping with other rare earth ions, other wavelength ranges can be developed, such as the so-called S band between 1420 and 1520 nm in the case of Tm. forms of the present invention, other rare earth ions such as Tm, Yb, Pr ³⁺ , Nd ³⁺ and / or Dy ³⁺ may therefore be preferred as dopants. Tm, Pr, Nd and / or Dy dopings are particularly preferred in the glasses with lower phonon energies because they can prevent radiationless transitions.

Surprisingly, it was found that gallium oxide, as described below, is not advantageous in glasses containing bismuth oxide in many cases and that, in particular, a shift from gallium oxide to germanium oxide leads to glasses with very particularly good properties.

The glass according to the invention therefore preferably contains essentially only a small amount of gallium oxide, for example at most 10 mol%, preferably at most 5 mol% and more preferably essentially no gallium oxide. The expression "essentially no gallium oxide" means that gallium oxide is contained in the glass at most as an impurity, i.e. at most in a proportion of 0.5 mol%, and no gallium compound is added to the starting mixture as an additional component.

According to this first embodiment, the addition of aluminum oxide in a proportion of 2 to 30 mol% is particularly preferred.

According to a further embodiment of the present invention, the glass according to the invention contains at least 15 mol% germanium oxide, preferably at least 20 mol%. In such a glass, silicon oxide can be essentially completely replaced by germanium oxide. According to this embodiment, the glass according to the invention preferably contains at most 5 mol% Si0 ₂ , more preferably at most 1 mol%, Si0 ₂ . The glass can also be essentially Si0 ₂ -free, the expression "essentially SiO ₂ -free" meaning that Si0 _{2 occurs} at most as an impurity, ie in a proportion of at most 0.5 mol%, in the glass composition and is not added to the starting batch as an additional component. Since both silicon oxide and germanium oxide are network formers, the mechanical stability of the glass does not deteriorate due to the shift from silicon oxide to germanium oxide. However, the increase in the transformation temperature T _g and the softening temperature EW of the glass caused by the levy is, as described above, particularly advantageous when the glass according to the invention is used as a fiber amplifier.

A replacement of Si0 ₂ with Ge0 ₂ is particularly advantageous if the waveguides are to be written into the glasses by ion exchange. The introduction of Ge instead of Si expands the glass network, which facilitates the diffusion of loosely bound particles, in particular alkalis.

According to this embodiment, the glass according to the invention can essentially consist of bismuth oxide and germanium oxide, this expression meaning that the sum of the proportions of bismuth oxide and germanium oxide is preferably at least 60 mol%, more preferably at least 80 mol%.

The present invention further relates to a method for producing the glasses according to the invention.

The glass according to the invention is preferably produced under oxidizing conditions. Such oxidizing conditions can preferably be achieved by blowing oxygen into the glass melt, so-called oxygen bubbling.

Furthermore, it is preferred according to the invention that dry oxygen is blown in. As a further positive effect, the drainage of the melt is also promoted to a considerable extent. To dry the glass composition or the melt, it is further preferred to pretreat the mixture of the starting materials thermally, for example by drying the mixture, preferably under vacuum. The addition of halo Generated oxygen promotes dewatering, so blowing halogenated oxygen is also preferred in accordance with certain embodiments of the present invention. The above measures for drying the batch or the melt can be used individually or in combination with one another.

Another possibility, to set oxidizing conditions during the glass manufacturing process, is the addition of oxides of polyvalent pentavalent cations, e.g. B. Sb as NaSb (OH) ₆ , Nb ₂ 0 ₅ , Sn0 ₂ , Cr ₂ 0 ₃ , V ₂ 0 ₅ , As ₂ 0 ₃ and / or mixtures thereof to form the glass composition. Since, for example, antimony has a higher electronegativity than bismuth , antimony will always oxidize possibly reduced bismuth. On the other hand, antimony is not reduced to the elemental metal, so that the glass cannot turn black due to the separation of elemental metal. According to this embodiment, preferably about 0.01 to 10% by weight, more preferably up to 5% by weight (on an oxide basis) of a pentavalent compound is added to the glass composition.

The present invention further relates to the use of a glass according to the invention for optical amplifiers, which can be fiber amplifiers or planar amplifiers. In these amplifiers, the glass according to the invention can be used as matrix or core glass and / or cladding glass. In such glass fibers, a composition that is similar except for the doping is preferably used as cladding glass.

Furthermore, the glass according to the invention can be used as a matrix glass, i.e. optically active component, and / or passive component of a laser can be used.

Furthermore, the glasses according to the invention can be used as so-called upconversion glasses.

Furthermore, the glasses according to the invention can be used as so-called non-linear optical glasses. The present invention further relates to a glass fiber which contains the glass according to the invention and optical amplifiers which contain a glass fiber according to the invention or the glass according to the invention.

A glass fiber for an optical fiber amplifier comprises a core doped with an optically active rare earth ion and at least one cladding. The core and / or sheath or sheaths of this glass fiber preferably comprise a glass according to the invention. More preferably, both the core and at least part of the cladding region comprise the glass composition according to the invention. Furthermore, the cladding glass used preferably has a composition very similar to that of the core glass. The cladding surrounding the core preferably contains no optically active rare earth doping and / or has a lower refractive index than the core. One or more further glass jackets likewise preferably comprise the glass according to the invention and / or preferably contain absorbent agents, such as transition metal oxides, for example oxides of Fe, Co and / or Ni, cobalt being particularly preferred.

Optically active cores of glass fibers for fiber amplifiers generally have to be coated with a glass jacket with a lower refractive index than that of the core glass in order to ensure adequate light conduction in the core. The glass of the cladding should otherwise have essentially the same physical properties and a similar chemical composition as the core glass, in order to allow a simultaneous warping of the core and cladding glass to form a fiber. In contrast to the optically active core, the cladding generally does not contain any rare earth doping.

To set a specific refractive index stroke, for example between the core and the sheath, it is advantageous that a proportionately large amount of a component with a high refractive index is transferred to a component with a low refractive index or refractive index. Then a balance error only a slight effect on the refractive index stroke. In order to adjust the refractive index of the cladding glass, a proportion of the bismuth oxide in the glass composition of the core glass is usually switched over to silicon dioxide. However, because due to the very low refractive index of silicon dioxide compared to the very high refractive index of bismuth oxide, very small levies are sufficient to set the desired refractive index stroke, even minor weighting errors have a major impact on the refractive index stroke between the jacket and core. However, this refractive index deviation is critical for the numerical aperture, which is calculated from the refractive index of the core and the cladding and from which the angle is determined at which a light wave is reflected at the interface between the core and cladding glass.

In this context, an allocation of bismuth oxide to germanium oxide proves to be very advantageous compared to an allocation to SiO ₂ in the same molar proportion, since it reduces the refractive index of the glass per proportion significantly less. Relatively large amounts of germanium oxide are therefore required in order to set the same refractive index stroke. This is advantageous for the reasons mentioned above.

A allocation from Bi ₂ 0 ₃ to Ge0 ₂ also has an advantageous effect on the production process of a coated fiber or a preform for producing a coated fiber. When a coated fiber or preform of a covered fiber is produced by a double crucible process, the core composition is melted in an inner crucible and the shell composition is melted in an outer crucible lying around this inner crucible. The presence of a germanium oxide-rich jacket melt has the advantage that the glass melt contained in the outer crucible is somewhat tougher than the melt contained in the inner crucible at the same temperature due to the higher softening point of a germanium oxide-rich jacket. In such a case, the inner crucible can be heated via the outer crucible and the glass in the inner crucible will still be melted well. This is particularly advantageous for glasses with a steep viscosity curve over temperature.

Examples

All of the glass compositions of the examples and comparative examples were melted from pure raw materials which had not yet been optimized with regard to trace impurities in Pt crucibles. After about 1.5 hours, the liquid glass was poured into preheated graphite molds and cooled in the cooling furnace from T _g to room temperature at cooling rates of up to 15 K / h.

Table 1 summarizes the compositions of the glasses of the examples and comparative examples, and the properties of the glasses obtained.

Notes on Table 1:

1) C-band: 1530 to 1562 nm

2) Inversion: characteristic value for inversion in a band, should be as high as possible

3) Flatness: The characteristic value for flatness of the gain in a band should be as low as possible

4) Ext. C-band: Extended C-band, from 1528 to 1570 nm

5) Integral absorption or emission cross section, should be as large as possible

6) Absorption or emission cross section FWHM (fill width at half maximum), should be as large as possible

All glasses according to the invention have a large distance between the transformation temperature Tg and the crystallization temperature T _x compared to the glasses of the comparative examples. The further the crystallization temperature T _{x is} above T _g , the better the glass is suitable for warping into a glass fiber, since the crystallization temperature is not reached when heated for warping.

The glasses of the examples according to the invention have very good Y values of at least 74 for glasses containing heavy metal oxide, which roughly corresponds to the strength of window glass. For example, only Y values from 57 to 63 are achieved for glasses containing tellurium oxide.

The lifetimes τ of the upper laser level listed in Table 1 are comparatively short compared to that of silicate glasses. However, they are sufficient to produce an efficient amplifier using a suitable amplifier design.

Example 1 and Comparative Example 1 have a relatively high B ₂ O ₃ content. The spectroscopic properties, in particular the flatness in the C band and the absorption and emission cross section of these glasses tend to be relatively good. As can be seen from the comparison of Example 1 with Comparative Example 1 is, the Ge0 ₂ -containing glass according to the invention additionally has a softening temperature EW increased by approximately 50 ° C., an improved Y value and a larger distance between the transformation temperature and the crystallization temperature. Furthermore, the lifespan of the upper laser level 1 of Er is increased and the other spectroscopic properties of the glass are also slightly improved.

The glass from Example 3 contains a relatively large amount of Si0 ₂ . For this reason, the mechanical properties of this glass are relatively good. The comparatively longer service life is also caused by the high Si0 ₂ content. At the same time, however, the spectroscopic properties, in particular the flatness of the gain in the C band, have deteriorated somewhat compared to the other glasses according to the invention. The difference between T _g and T _x is also smaller.

It can be seen from the comparison of example 5 according to the invention with comparative example 5 that even small allocations of Ga ₂ θ ₃ to Ge0 ₂ of only 3.5 mol% cause a slight, but nevertheless influential shift of the emission maximum to shorter wavelengths, which is reflected in an improved flatness of the gain from 0.255 to 0.248. The significant increase in the difference between T _g and T _x in example 1 according to the invention is remarkable.

A double cladding fiber was produced using the glass composition from Example 5 as core glass and cladding glasses set as required for the refractive index stroke (cf. Table 2). First, a preform was made from the core and the first jacket using a double crucible. This preform was then provided with the second jacket using the rod-in-tube process. The preform obtained was then drawn out to a glass fiber with a diameter of 125 μm. The fiber was then coated with an acrylic polymer coating for mechanical protection. Table 2

Claims

Expectations

1. Bismuth oxide-containing glass, which has the following composition (in mol%):

Bi ₂ 0 ₃ > 15

Ge0 ₂ > 0.01 further oxides 0-74.99

Rare earth compound 0-15 (oxide-based)

»

2. Glass according to claim 1, wherein the glass contains at least 3 mol% Ge0 ₂ .

3. Glass according to claim 1 or 2, wherein the glass contains at least one rare earth compound in a proportion of 0.005 to 8 mol% on an oxide basis, which consists of oxides of Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and / or Lu is selected.

4. Glass according to one of the preceding claims, wherein at least Er ₂ 0 _{3 is contained} as a rare earth compound.

5. Glass according to one of the preceding claims, which comprises the following composition (in mol%):

Bi ₂ 0 ₃ 15-70

Ge0 ₂ 1 - 60

La ₂ 0 ₃ 0-20

Si0 ₂ 0.5 - 60

B ₂ 0 ₃ 5-60

Al ₂ 0 ₃ 0.5-50

Ga ₂ 0 ₃ 0-50

W0 ₃ 0-30

Nb ₂ 0 ₅ 0-30 Ta ₂ 0 ₅ 0 - 15

Ti0 ₂ 0-30

ZnO 0 - 40

Zr0 ₂ 0-30

Sn0 ₂ 0-30

M ' ₂ O 0 - 40

M "O 0-30

F and / or CI 0-10

Bi ₂ 0 ₃ + Geθ2 + B ₂ 0 ₃ + AI ₂ 0 ₃ 5 - 85

Rare earth compound 0-8 (oxide based) where M ^{1 is} at least one of Li, Na, K, Rb and / or Cs and M ^{11 is} at least one of Be, Mg, Ca, Sr and / or Ba.

6. A method of manufacturing a glass according to any one of claims 1 to 5, wherein the glass is melted under oxidizing conditions.

7. The method according to claim 6, wherein the oxidizing conditions are brought about by blowing oxygen into the glass melt.

8. The method according to claim 6 or 7, wherein the mixture to be melted is a polyvalent compound selected from Nb ₂ O _δ , Sb ₂ θ ₅ , Sn0 ₂ , Cr ₂ 0 ₃ , As ₂ 0 ₃ , V ₂ 0 ₅ and mixtures thereof Oxides, is added.

9. Use of a glass according to one of claims 1 to 5 optically active glass for optical amplifiers.

10. Use of a glass according to claim 9, wherein the optical amplifier is a fibrous amplifier.

11. Use according to claim 10, wherein the optical amplifier is a planar amplifier.

12. Use of a glass according to one of claims 1 to 5 as optically active glass for a laser.

13. Use of a glass according to one of claims 1 to 5 as a non-linear optical glass.

14. Glass fiber comprising a core and at least one cladding surrounding the core, the glass of the core and / or the glass of the cladding comprising a glass according to one of claims 1 to 5.

15. Glass fiber according to claim 14, comprising an optically active core glass according to one of claims 1 to 5 and / or at least one cladding glass according to one of claims 1 to 5.

16. Glass fiber according to claim 15, further comprising at least one further cladding, which comprises a plastic.