KR0183492B1 - Fluoride glass fiber - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to fluoride glass of certain compositions with broad infrared transmission. Fluoride optical fibers using such fluoride glass can exhibit high efficiency with low loss. The fluoride optical fiber having a secondary coating on the outer cover of the primary coating can appropriately adjust the refractive index of the primary coating.

Description

Fluoride glass fiber

The present invention relates to fluoride optical fibers capable of achieving high efficiency amplification using fluoride glass and fluoride glass with satisfactory wide infrared transmission.

Fluoride glass has improved transparency in the range of visible to infrared wavelengths. Thus, it finds use as a filter in lenses, prisms or various optical devices, or as optical fibers for optical communication, optical measurement or power transmission. Fluoride optical fiber amplifiers having a core doped with praseodymium as rare earth ions allow optical amplification in the 1.3 μm wavelength band, which is an important wavelength band in optical communication systems. Therefore, the use of fluoride glass for optical fiber amplifiers has recently become of great interest.

Light amplification is induced in the 1.3 μm wavelength band by induced emission due to the transition from praseodymium to ¹ H4 level to ³ H5 level. This induced emission is observed in glass with low lattice vibration energy (phonon energy), such as fluoride glass, but not in glass such as silicate glass with high phonon energy due to the presence of non-radiative transitions by polyphonon relaxation.

Therefore, it is necessary to use glass with low phonon energy, such as fluoride glass, to obtain such praseodymium based light amplification at 1.3 μm wavelength.

However, the quantum efficiency of amplification in the 1.3 μm band is kept low at 3.4% for ZrF ₄ -based fluoride glass currently used as the main material of praseodymium doped fibers. In order to improve this low quantum efficiency, it is important to develop fluoride glass with lower phonon energy than ZrF ₄ -based fluoride glass.

Thus, fluoride glasses with low phonon energies known to date include 4 to 48 mol% ZnF ₂ , 32 to 63 mol% PbF ₂ , 0 to 34 mol% GaF ₃ , and 0 to 43 mol% InF ₃ ( Provided that GaF ₃ + InF ₃ = 17 to 53 mol%, and ZnF ₂ + PbF ₂ + GaF ₃ + InF ₃ ≥ 70 mol%), the fluoride glass described in Japanese Patent Application Laid-Open No. 60-155549.

Such fluoride glass has a satisfactory wide infrared transmission because of its low phonon energy. If doped with praseodymium, fluoride glass can provide higher quantum efficiency than ZrF ₄ -based fluoride glass.

However, due to its insufficient thermal stability to crystallization, this fluoride glass cannot produce the jacketting tube necessary for the production of single type fibers as described below. Thus, the use of such fluoride glass does not produce a single type of fiber.

We have developed an InF ₃ -based fluoride glass having a low phonon energy as a fluoride glass having a proportion of components distinct from the above-mentioned PbF ₂ -based fluoride glass and disclosed in Japanese Patent Application No. 6-172499. We have also developed fluoride fibers comprising such fluoride glass.

In the case of Pr ³⁺ -doped single type fibers using InF ₃ -based fluoride glass disclosed in Japanese Patent Application No. 6-172499, the resulting gain factor is applied to Pr ³⁺ -doped ZrF ₄ -based fluoride fibers. Exceeded the gain factor of 0.2 dB / mW. However, the glass composition is not optimal and the optical loss of the fiber is not sufficiently reduced. Thus, such fibers do not obtain a maximum gain factor of 0.4 dB / mW expected from the spectral properties of Pr ³⁺ contained in InF ₃ -based fluoride glass.

The present invention has been accomplished under such circumstances. It is an object of the present invention to provide fluoride glass having a satisfactory wide infrared transmission and optical fibers for light amplification with low loss and high efficiency.

1 is a chart showing the glass transition temperature (Tg) and (crystallization temperature Tx-glass transition temperature Tg) according to BaF ₂ concentration in the fluoride glass of the present invention.

2 is a chart showing Tg, (Tx-Tg) and refractive index (n _D ) according to PbF ₂ concentration in the fluoride glass of the present invention.

Figure 3 is a chart showing (Tx-Tg) according to the concentration of CdF ₂ in the fluoride glass of the present invention.

4 is a chart showing the transmittance of a glass material with wavelength.

5A and 5B are schematic cross-sectional views showing steps for producing all types of fibers by a suction mold method;

6A and 6B are schematic cross-sectional views showing steps for producing all types of fibers by the rotational molding method.

7a to 7c are schematic cross-sectional views showing steps of manufacturing the optical fiber according to the present invention.

8 is a chart showing transmittance loss with wavelength in an embodiment of the optical fiber of the present invention.

9 is a chart showing the transmission loss with wavelength in another embodiment of the optical fiber of the present invention.

The first feature of the invention is 10 to 30 mol% InF ₃ , 7 to 30 mol% GaF ₃ , 10 to 19 mol% ZnF ₂ , 4 to 30 mol% BaF ₂ , 0 to 24 mol% SrF ₂ , 0-30 mol% PbF ₂ , and at least one member selected from the group consisting of LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ 1.5-10 mol%, 1.5-30 mol% LiF, 0-30 mol% NaF, and 0 to 15 mole percent of the additive, wherein the total amount of all these components is 100 mole percent.

The second feature of the present invention the matrix of the coating 10 to 30 mol% of InF _3, 7 to 30 mol% of GaF _3, 10 to 19 mol% of ZnF _2, 4 to 30 mol% of BaF _2, 0 to 24 mol % of SrF _2, 0 to 30 mol% of PbF _2, and LaF _3, YF _3, GdF ₃ and LiF, 0 of LuF one or more members of 1.5 to 10 mol%, selected from the group as consisting of _3, 1.5 to 30 mol% Provided is a fluoride optical fiber having a core and a coating comprising from 30 to 30 mol% NaF, and from 0 to 15 mol% additive, wherein the total amount of all these components is 100 mol%.

Here, the matrix of the core is 5 to 25 mol% InF ₃ , 13 to 40 mol% GaF ₃ , 4 to 25 mol% ZnF ₂ , 30 to 46 mol% PbF ₂ , 0 to 20 mol% CdF ₂ , and 1.5-12 mol%, and 0-15 mol% of additives of at least one member selected from the group consisting of LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ , the total amount of all of which is 100 mol% Is done.

The matrix is 10 to 30 mole% of the core InF _3, 7 to 30 mol% of GaF _3, 10 to 19 mol% of ZnF _2, 4 to 30 mol% of BaF _2, 0 to SrF _2, 0 of 24 mol% To 30 mol% PbF ₂ , and at least one member selected from the group consisting of LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ 1.5 to 10 mol%, 1.5 to 30 mol% LiF, 0 to 30 mol% NaF , And 0 to 15 mol% of additives, with the total amount of all of these components being 100 mol%.

The transition metal ions or rare earth ions may be contained in the core, and the relative refractive index difference Δn of the core and the coating is greater than 1.0%.

As rare earth ions Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm ³⁺ , Eu ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , Tm ³⁺ and Yb ³⁺ It may contain one or more selected from.

A third feature of the invention includes a core coating, a primary coating, and a secondary coating on the sheath of the primary coating, wherein the matrix of the primary coating is 10 to 30 mol% InF ₃ , 7 to 30 mol% GaF. _3, 10 to 19 mol% of ZnF _2, 4 to 30 mol% of BaF _2, 0 of 1 to 24 mol% of SrF _2, 0 to 30 mol% of PbF _2, and LaF _3, YF _3, GdF ₃ and LuF ₃ At least one member selected from the group consisting of 1.5 to 10 mol%, 1.5 to 30 mol% LiF, 0 to 30 mol% NaF, and 0 to 15 mol% additives, the total amount of all of these components being 100 Mol%; The matrix of the secondary coating is 10 to 30 mol% InF ₃ , 7 to 30 mol% GaF ₃ , 10 to 19 mol% ZnF ₂ , 4 to 30 mol% BaF ₂ , 0 to 24 mol% SrF 2, 0-30 mol% PbF ₂ , and at least one member selected from the group consisting of LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ 1.5-10 mol%, 1.5-30 mol% LiF, 0-30 mol% A fluoride optical fiber is provided, which comprises NaF, and an additive of 0 to 15 mol%, wherein the total amount of all of these components is 100 mol%.

Here, the second matrix of the coating is a ZrF ₄ and HfF ₄ one or more fluoride and BaF ₂ is selected from, LaF _3, GdF _3, YF _3, LiF, NaF, PbF ₂ and one selected from the group consisting of AlF ₃ Fluoride glass containing the above member is included.

The refractive index of the primary coating can be adjusted such that the refractive index of the primary coating matches the refractive index of the secondary coating, or is greater than the refractive index of the secondary coating and smaller than the refractive index of the core.

Here, the adjustment of the refractive index of the primary coating can be carried out by replacing the portion of PbF ₂ with NaF in the matrix of the primary coating.

The above and other objects, effects, features and advantages of the present invention will become more apparent from the embodiments connected with the accompanying drawings.

The present inventors have extensive studies on the glass-forming region of a fluoride glass containing _{InF 3, GaF 3, ZnF 2} , BaF 2, SrF 2, PbF 2, LaF 3, YF 3, GdF 3, LuF 3, LiF and NaF Was performed. Through this study we found that fluoride glass having a glass transition temperature close to the glass transition temperature of the ZrF ₄ -based fluoride glass (about 260 ° C.) and a glass forming region as described in claim 1 having high thermal stability against crystallization Was found.

In the fluoride glass of the present invention, InF ₃ , GaF ₃ and ZnF ₂ are the main constituents of the network former. Preferably, the glass comprises 10 to 30 mole% InF ₃ and 7 to 30 mole% GaF ₃ and preferably 20 to 30 mole% InF ₃ and 7 to 20 mole% GaF ₃ . From fluoride glass compositions of the present invention it exceeds 30 mol% of InF ₃ concentration, and the concentration of GaF ₃ can be obtained a thermally stable glass for crystallization in the region of less than 7 mol%. However, its glass transition temperature rises to about 300 ° C., so a glass transition temperature close to the glass transition temperature of ZrF ₄ -based fluoride glass cannot be achieved. On the other hand, less than 10% of the molar concentration of InF _3, and in a region where the concentration of GaF ₃ exceeds 30 mol%, the resulting glass is likely to be crystallized by the poor thermal stability against crystallization.

The concentration of ZnF ₂ is preferably 10 to 19 mol%. In the composition of fluoride glass claimed in the present invention, when containing ZnF ₂ greater than 19 mol%, single crystals of ZnF ₂ tend to form in the resulting glass. If this concentration is less than 10 mol%, crystals composed of InF ₃ and GaF ₃ will form in the glass.

BaF ₂ and SrF ₂ are the main components for modifying network formers. Preferably, the glass comprises a BaF ₂ and SrF ₂ of 0 to 24 mol% 4 to 30 mol%. BaF ₂ concentrations of 10 to 24 mol% and SrF ₂ concentrations of 0 to 14 mol% enable the production of glass with excellent thermal stability against crystallization.

1 is a composition _{28InF 3 -9GaF 3 -17ZnF 2 -12PbF 2} -xBaF 2 - (24-x) SrF 2 -5YF 3 -5LiF the fluoride BaF ₂ concentration (x mol%) in a glass charge having a (mol%) It is a chart which shows the dependence of the glass transition temperature (Tg) and (crystallization temperature Tx-glass transition temperature Tg) with respect to. In general, (Tx-Tg) is used as an index of thermal stability of glass. In Fig. 1, the left vertical axis represents the glass transition temperature (Tg) and the right vertical axis represents (Tx-Tg) (in this case, the value of Tg (black circle, _● ) is read from the left vertical axis and (Tx-Tg) The value of (black square, _■ ) is read from the right longitudinal axis). FIG. 1 shows that the value of Tg is close to 260 ° C. in all regions where the concentration of BaF ₂ varies from 0 to 24 mol%. Tx-Tg, on the other hand, exhibits a convex BaF2 dependency. The value of Tx-Tg is high in the region of 0 ≦ BaF ₂ ≦ 24 mol% of 90 ° C. or higher, especially in the region of 10 ≦ BaF ₂ ≦ 24 mol% of 100 ° C. or higher, that is, in the region of 0 ≦ SrF ₂ ≦ 14 mol%. Has a value. This is evidence of possessing high thermal stability against crystallization.

LiF and NaF are also main components for modifying network formers in claimed fluoride glasses. The incorporation of the components lowers the melting temperature of the glass melt and forms a uniform glass melt even at low temperatures. Therefore, their incorporation enhances the glass forming ability.

NaF is preferably included in an amount of 0 to 30 mole%. If the concentration of NaF exceeds 30 mol%, there is a high tendency to crystallize, so that no stable glass is obtained. LiF is a particularly important component for maintaining the thermal stability of the glass. Preferably, the concentration of LiF is between 1.5 and 30 mol%, in particular between 5 and 10 mol%, which significantly enhances thermal stability against crystallization. However, at concentrations above 30 mol%, the tendency to crystallize is strong and may fail to obtain a stable glass.

In the claimed fluoride glass, LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ are also the main components which increase the thermal stability of the glass. Preferably, at least one of the components is included in an amount of 1.5 to 15 mol%, preferably 1.5 to 10 mol%. If the concentration is less than 1.5 mol%, an increase in thermal stability cannot be assured. On the other hand, there is a strong tendency to crystallize at concentrations in excess of 15 mol%, which may fail to obtain stable glass.

In the claimed fluoride glass, PbF ₂ is an essential component capable of adjusting the refractive index, and preferably included in the range of 0 to 30 mol%. However, PbF ₂ can be partially replaced with NaF in the range of 0 to 20 mol%, in which the refractive index of the claimed fluoride glass can be controlled without compromising the thermal stability of the glass.

2 is a composition _{25InF 3 -10GaF 3 -14ZnF 2 -xPbF 2} -18BaF 2 -8SrF 2 -2.5YF 3 -2.5LaF 3 - (20-x) (LiF + NaF) the claimed fluoride glass having a (mol%) The glass transition temperature (Tg), (Tx-Tg) and refractive index n _D according to the PbF ₂ concentration (x mol%) in water are shown. In FIG. 2, the left vertical axis represents temperature, the right vertical axis represents the refractive index (wherein the Tg values (black circles, _● ) and (Tx-Tg) values (black squares, _■ ) are read from the left vertical axis, The value of the refractive index (white circle, _○ ) is read from the right longitudinal axis.

2 shows that the glass transition temperature is close to 260 ° C. in the entire region where the concentration of PbF ₂ varies from 0 to 20 mol%. The value of (Tx-Tg) shows high thermal stability above 90 ° C. On the other hand, as the concentration of PbF ₂ increases, the refractive index increases linearly from 1.46 to 1.54. Thus, by replacing all or part of the appropriate amount of PbF ₂ with NaF in the claimed fluoride glass, the refractive index can be controlled while maintaining the transition temperature close to 260 ° C., while maintaining high thermal stability.

The claimed fluoride glass and claimed fluoride optical fibers also comprise 0 to 15 mole percent additive. As an additive, 0 to 10 mol% BeF ₂ , 0 to 10 mol% MgF ₂ , 0 to 10 mol% CaF ₂ , 0 to 4 mol% CdF ₂ , 0 to 5 mol% TlF ₄ , 0 to 5 mol% MnF ₂ , 0-5 mol% SmF ₃ , 0-5 mol% ScF ₃ , 0-5 mol% HfF ₄ , 0-5 mol% ZrF ₄ , 0-10 mol% KF , 0 to 10 mol% RbF, 0 to 10 mol% CsF, 0 to 15 mol% BiF _3, and AlF ₃ 0 to 15 mol%.

In this case, CdF ₂ may replace some of the aforementioned essential components ZnF ₂ or PbF ₂ , ie 0-4 mol%. FIG. 3 shows (Tx-) according to CdF ₂ concentration (x) in glass 28InF ₃ -9GaF _3- (15-x) ZnF ₂ -xCdF ₂ -12PbF ₂ -18BaF ₂ -8SrF ₂ -5YF ₃ -5LiF (mol%) Tg) value. It can be seen from FIG. 3 that CdF ₂ can be included at a concentration of up to 4 mol% in glass without compromising thermal stability. However, at concentrations above 4 mol%, the value of (Tx-Tg) decreases drastically. At 5 mol% or more, the thermal stability of the glass is significantly impaired. Similarly, BeF _2, MgF _2, CaF may be substituted for each part of the essential component, ZnF _2, PbF _2, BaF ₂ and SrF ₂ as a _second and separate elements of MnF _2. In addition, the element ₄ TlF, SmF _{3, 3} ScF, HfF _4, and ZrF ₄ as essential component, InF _3, GaF _3, may be substituted for respective portions of the YF ₃ and LaF _3. However, if they are included as substitutes beyond the aforementioned ranges, the thermal stability of the glass can be significantly impaired.

The fluoride optical fiber of the present invention comprises a structure having a high Δn (Δn ≥ 1.0%) to achieve high efficiency optical amplification. This is because the 1.3 μm transition quantum efficiency of praseodymium is enhanced by using low phonon energy glass as the main glass and increasing Δn of the fiber which can achieve high brightness at the core.

However, in the case of using PbF ₂ -based fluoride glass described in Japanese Patent Application No. 60-155549 cited above for the production of high Δn optical fibers as a core, and using a known ZrF ₄ -based fluoride glass as the coating Crystals containing essentially PbF ₂ and ZrF ₄ grow at the interface between the core and the coating, making it difficult to obtain satisfactory optical fibers.

In contrast, in the fluoride fiber of the present invention, the use of the fluoride glass according to claim 1 as a coating does not cause crystallization at the interface between the core and the coating material, and a satisfactory optical fiber can be obtained even when PbF ₂ -based fluoride glass is used as the core glass. there was. The reason is that InF ₃ is also included in the composition of PbF ₂ -based fluoride glass, and thus there is no rapid crystal growth containing PbF ₂ and InF ₃ as main components.

It is of course also possible to produce the claimed optical fibers using the fluoride glass of claim 1 as core glass.

Single type fluoride optical fibers were prepared by the following preparation steps. A full form of fluoride fiber having a structure comprising a core and a cladding was prepared by a suction mold method. The resulting full fluoride fiber form was then inserted into the first sheath and stretched by applying heat to prepare a second fiber form. The secondary fiber former was reinserted into the secondary envelope and drawn into a single type of optical fiber.

It is generally known that a core / coated outer diameter ratio of at least 5 is required to produce a single type of optical fiber having a core that can be well constrained by suction molding. However, with the above-described method for producing single type fibers, it is impossible to produce fiber formers having a core / coated outer diameter ratio of 5 or more by the fiber former forming step using the suction mold method. Thus, in order to produce a single type of fiber having a core / coating ratio of greater than 5, the primary sheath, ie the secondary sheath, should preferably have the same refractive index as the sheath (primary sheath). If the secondary coating has a higher refractive index than the primary coating, the field of propagating light in the core extends into the coating and weakens the light intensity in the core. Therefore, high efficiency amplification cannot be obtained.

In contrast, the optical fiber of the present invention uses the fluoride glass claimed as the coated glass. Thus, the sheaths and secondary sheaths have a consistent refractive index, can produce single type fibers with a core / coat ratio of at least 5 and with limited high intensity light in the cores.

The core / coating ratio is not limited to five or more as long as the ratio can suppress the type of coating, if no suction molding method is used.

As can be clearly seen from the cross section of a single type fluoride fiber, the maximum value of the area of the core and the sheath is 1/16 of the total cross-sectional area of the optical fiber. Most cross sections consist of a primary shell and a secondary shell. Thus, the weight of most optical fibers is due to the sheath. This means that the price of the sheath determines the price of a single type of fiber.

Fluoride raw materials such as InF ₃ and GaF ₃ are expensive compared to ZrF ₄ . The use of InF ₃ -based fluoride glass as the shell tube inevitably raises the cost of the resulting optical fibers.

In the fluoride fibers of the present invention, the use of ZrF ₄ -based fluorides as primary sheaths, i.e., secondary coatings, can reduce the cost of the resulting single type fibers.

When using an outer shell of ZrF ₄ -based fluoride as the secondary coating, producing a satisfactory fiber with limited high intensity light in the core requires a match between the refractive index of the coating and the secondary coating. Among the fluoride fibers claimed, the concentration of PbF ₂ , the component of the coated glass, is partially replaced by NaF and can change the refractive index in the range of 1.46 to 1.54 without changing the glass transition temperature of the coated glass. Moreover, the glass transition temperature of the coated glass is close to the glass transition temperature of the ZrF ₄ -based fluoride glass. As a result, even when ZrF ₄ -based fluoride glass is used as the secondary coating, fiber forming steps such as stretching and fiber drawing can be performed without problems. In addition, the refractive index of the coated glass can be adjusted to be larger than the refractive index of the outer shell and smaller than the refractive index of the core. Thus, it is possible to produce a satisfactory single type fiber with limited high intensity light in the core.

When producing optical fibers having a relative refractive index difference (Δn) of 4% or more, it is necessary to use fluoride glass having a refractive index higher than that of the claimed fluoride glass as the core glass. The relative refractive index difference (Δn) can be defined as Δn = (core refractive index-coated refractive index) / core refractive index (%). In general, fluoride glass having a high concentration of PbF ₂ is known to have a high refractive index. Our extensive research has developed fluoride glass components containing 30-46 mol% PbF ₂ and having a high refractive index close to 1.6. Preferred fluoride glass in the present invention has a core matrix of 5 to 25 mol% InF ₃ , 13 to 40 mol% GaF ₃ , 4 to 25 mol% ZnF ₂ , 30 to 46 mol% PbF ₂ , 0 to 2 mol % Of CdF ₂ and LaF ₃ , YF ₃ , GdF ₃ , and LuF ₃ , consisting of 1.5 to 12 mol% and 0 to 15 mol% of additives selected from the group consisting of 100 mole% of all components Phosphorus fluoride glass.

In the fluoride glass of the core, InF ₃ and GaF ₃ are essential components as network formers. InF ₃ is preferably contained at a concentration of 5 to 25 mol%. If its concentration is less than 5 mol%, transparent glass cannot be obtained. If the concentration of InF ₃ exceeds 25 mol% in the core fluoride glass component, a rather high crystallization rate occurs, resulting in an unsatisfactory glass. GaF ₃ is preferably contained at a concentration of 13 to 40 mol%. If the GaF ₃ concentration is less than 13 mol% in the core fluoride glass component, no clear glass can be obtained due to crystallization. If its concentration exceeds 40 mol%, the glass melt becomes opaque yellow and no clear glass can be obtained. Moreover, in the core fluoride glass, PbF ₂ and ZnF ₂ are essential components as network modifiers. The incorporation of these ions lowers the melting temperature of the glass melt so that a homogeneous melt can be obtained at low temperatures, thus enhancing the glass forming ability. The preferred concentration of PbF ₂ in this core fluoride composition is 30 to 46 mol%. Concentrations below 30 mol% make it difficult to obtain transparent glass due to crystallization. At concentrations above 46 mol%, the glass melt becomes volatile and cannot provide stable glass. ZnF ₂ is preferably contained at a concentration of 4 to 25 mol%. At concentrations below 4 mol%, clear glass cannot be obtained due to crystallization. At concentrations above 25 mole%, a rather high crystallization rate occurs and no clear glass can be obtained. CdF ₂ may be contained as a substitute for PbF ₂ or ZnF _{2 in} the range of 0 to 20 mol%. Preferably it can be contained in the range of 0 to 7 mol% to enhance the glass forming ability and to obtain a stable glass. Moreover, LaF ₃ , YF ₃ , GdF ₃ , or LuF ₃ are essential ingredients to improve thermal stability against crystallization in the claimed fluoride glass. In the core fluoride glass composition, one or more of them may be contained at a concentration of 1.5 to 12 mole percent to improve thermal stability against reheating.

Using such a fluoride glass as a core and using the fluoride glass of the present invention as claimed in claim 1 as an sheath, an optical fiber having a Δn of 4% or more that cannot be obtained with conventional ZrF ₄ -based fluoride fibers can be produced. have.

In addition, when producing a single type optical fiber having Δn of 4% or less compared to the relative refractive index difference Δn of optical fibers made using conventional ZrF ₄ -based fluoride glass, the fluoride claimed as core and coating The use of glass makes it possible to produce optical fibers that are nearly identical to ZrF ₄ -based fluoride glass. Moreover, the claimed fluoride glass has better infrared transmission than ZrF ₄ -based fluoride glass. Thus, doping its core with rare earth ions for optical amplification allows for higher amplification efficiency than that of ZrF ₄ -based fluoride glass.

When doped into the core with transition metal ions or rare earth ions, the fluoride fibers of the invention can be used as optical fiber lasers or optical fiber amplifiers. Examples of doped transition metal ions are Cr, Ti, Fe, Co, Ni and Cu, while examples of doped rare earth ions are Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb to be. These doping elements can be contained in the range of 0.001-10 weight%. Concentrations in excess of 10% by weight are undesirable because this degrades the thermal stability of the core glass. At concentrations less than 0.001% by weight, sufficient emissions cannot be obtained due to the inherent losses of the fiber, such as scattering losses.

The invention will now be described in detail by way of examples which are intended to illustrate, but not to limit the invention.

Example 1

An _{InF 3, GaF 3, ZnF 2} , PbF 2, BaF 2, SrF 2, YF 3, LaF 3, GdF 3, LuF 3, LiF and NaF all weighed in dry form and mixed in a ratio shown in Table 1. 4 g of ammonium bifluoride was added to each mixture and placed in a crucible. The crucible was fixed in a heat resistant furnace and heated at 900 ° C. for 1 hour in an argon atmosphere to melt the contents of the crucible. The furnace temperature was lowered to 700 ° C. and the crucible was removed. The inner melt was poured into a bronze mold having an outer diameter of 8 mm and preheated to 200 ° C., and the melt was quenched to obtain a glass rod.

A portion of the glass rod was broken and the glass transition temperature (Tg) and crystallization temperature (Tx) were measured using a differential scanning calorimeter. Tg value was about 260 degreeC in all the samples. The (Tx-Tg) value is known as an index of thermal stability to crystallization of the glass. The measurement of (Tx-Tg) for all glass samples was above 90 ° C. and the resulting glass was found to have high thermal stability.

A 10 mm long cylindrical rod was cut out of the glass rod, its opposite end surface was polished and the transmission spectrum of the rod was measured. The rod was found to have a good transmittance of about 10 μm or less. A portion of the sample was measured in Raman spectrum. The peaks of all the workpieces appeared around about 500 cm ⁻¹ , and the resulting glass transition appeared to have a small phonon energy.

<Comparative Example 1>

ZrF ₄ , BaF ₂ , LaF ₃ , AlF ₃ , YF ₃ and NaF are all used as raw materials in anhydrous form and weighed to obtain 46.5ZrF ₄ -23.5BaF ₂ -2.5LaF ₃ -2.5YF ₃ -4.5AlF ₃ -20NaF ( Mole%) was formed. 20 g of this batch were mixed, 4 g of ammonium bifluoride were added and the mixture was placed in a crucible. The crucible was heated in a heat resistant furnace at 900 ° C. for 1 hour to melt the contents of the crucible. Then, the furnace temperature was lowered to 700 ° C., the internal melt was poured into a bronze mold preheated to 240 ° C., and the melt was quenched to obtain a glass rod.

A 10 mm long cylindrical rod was cut out of the resulting glass rod, its opposite end surface was polished and the transmission spectrum of the rod was measured in the same manner as in Example 1. The results are shown in dashed lines in FIG. 4. As shown, starting at a wavelength of about 5 μm, the absorption increased and at a wavelength longer than 8 μm the transmission was small.

A portion of the sample was measured in Raman spectra in the same manner as in Example 1. Peaks representing phonon energy appeared around about 500 cm ⁻¹ , and it was confirmed that the resulting glass had much greater phonon energy than the glass of Example 1.

Preparation of Core Glass Sample No. 1

The core glass of the optical fiber according to the present invention was produced by the following method.

InF ₃ , GaF ₃ , ZnF ₂ , PbF ₂ , YF ₃ and LaF ₃ are all used as raw materials in anhydrous form and weighed to determine 13InF ₃ -29GaF ₃ -12ZnF ₂ -38PbF ₂ -4YF ₃ -4LaF ₃ (mol%) A batch of compositions was formed. After adding 4 g of ammonium bifluoride to 20 g of this batch, the mixture was placed in a crucible. The crucible was fixed in a heat resistant furnace and heated at 900 ° C. for 1 hour under an argon atmosphere to melt the contents of the crucible. The temperature of the furnace was then lowered to 700 ° C. and the crucible was removed. The inner melt was poured into a bronze mold having an outer diameter of 8 mm and preheated to 200 ° C., and the melt was quenched to obtain a glass rod.

The resulting glass was measured for glass transition temperature (Tg) and crystallization temperature (Tx) using a differential scanning calorimeter. The result was Tg = 258 degreeC and Tx = 336 degreeC. From these results, the (Tx-Tg) value was 78 ° C., and it was confirmed that the resulting glass was thermally stable.

Preparation of Core Glass Sample Nos. 2 to 147

As in the core glass sample No. 1 of Preparation InF _3, GaF _3, ZnF _2, CdF _2, PbF _2, YF _3, LaF _3, GdF _3, and both the LuF ₃ and weighed on the anhydrous form, as described in Tables 2 to 5 Mix in proportions. 4 g of ammonium bifluoride was added to each mixture and the mixture was placed in a crucible. The crucible was heated in a heat resistant furnace in the same manner as in Example 1 to melt the contents of the crucible. The crucible internal melt was poured into a preheated mold and quenched to obtain a glass rod.

A 10 mm long cylindrical rod was cut out of the glass rod, its opposite end surface was polished and the transmission spectrum of the rod was measured. The rod was found to have good transmittance at wavelengths below 10 μm. A portion of the glass sample was measured in Raman spectrum. The peaks of all the measurements appeared near about 500 cm ⁻¹ , indicating that the resulting glass had a small phonon energy.

Manufacture of optical fiber

Core Glass Sample No. 1 was used as the core glass, and a fluoride glass having the composition 28InF ₃ -9GaF ₃ -17ZnF ₂ -18 BaF ₂ -6-SrF ₂ -5YF ₃ -10NaF-7LiF (mol%) as the coated glass. Fluoride fiber full form was prepared by suction molding method.

First, a mixed _{InF 3, GaF 3, ZnF 2} , PbF 2, YF 3, LaF 3, BaF 2, SrF 2, LiF and NaF were weighed for all the anhydrous form have the composition of the core and the coating. Each mixture was placed in a crucible and heated in a heat resistant furnace under an argon atmosphere to melt the contents of the crucible.

Subsequently, the whole fiber was produced by the suction mold method shown in FIG. That is, the temperature of the glass melt formed by heating in a heat resistant furnace for 1 hour at 900 ° C was lowered to 700 ° C. Subsequently, the coated glass melt 2 was poured into a bronze mold 1 preheated to 220 ° C. up to its upper portion. Then, when the coated glass melt 2 began to solidify, the core glass melt 3 was poured onto the coated glass melt 2, and its upper center began to sink as shown in FIG. 5A. Significant volume shrinkage occurred during cooling and solidification. This volume shrinkage of the coated glass 2a resulted in the inhalation of the core glass 3a above the sinking center of the coated glass 2a. The core glass 3a sucked inside was solidified at the center of the cylindrical clad glass 2a to form the fiber form 4 as shown in FIG. 5B. The resulting fiber former (4) had a sheath outer diameter of 5 mm, a gradually varying core outer diameter of 0.2-1.7 mm, and a length of 30 mm.

Subsequently, an outer shell having the same composition as the coated glass was produced by the rotary casting method as shown in FIG. 6. That is, the raw materials were weighed, mixed so as to have a composition of coated glass, placed in a crucible, and heated in a heat resistant furnace to melt the contents of the crucible. The resulting envelope melt 12 was poured into a preheated bronze mold 11 as shown in FIG. 6A. The mold 11 was laid horizontally and rotated at high speed as shown in FIG. 6B. The melt 12 was cooled and solidified during rotation under these conditions to obtain a fluorofluoride glass shell 13 having an outer diameter of 15 mm, an inner diameter of 5 mm, and a length of 140 mm.

Subsequently, glass fiber former 4 was inserted into the glove box of the outer shell tube 13 supplied with nitrogen gas having a dew point of -60 ° C or lower. As shown in FIG. 7A, the envelope 13 was supported by the full-form support 22 via the O-ring 21. The interior was then evacuated and the former form 4 was injected into the heating furnace 23 at a rate of 3 mm / min as shown in FIG. 7B together with the envelope 13. The bottom of the composite heated to softening temperature was pulled down to obtain a glass fiber form (24) having an outer diameter of 5 mm.

Subsequently, the portion having a core diameter of 0.2 mm was cut out from the former form 24 and integrated with the outer shell 13 'made by the same method in the heating vacuum chamber. Surface treatment was carried out in a F2-HF mixed gas atmosphere. Inside the glove box supplied with nitrogen gas having a dew point of -60 ° C. or less, the former form 24 is inserted into the envelope 13 ', and the envelope 13' is inserted into the O-shaped support 22 by the former support 22. Sustained via the ring 21. The interior was then evacuated and the former form 24 was fed to the fiber drawing furnace 25 along with the envelope 13 'at a rate of 3 mm / min as shown in FIG. 7C. The composite was heated to a softening temperature and the bottom was pulled down via a tension gauge 26 by a capstan driver 27 to draw the composite into a fiber having an outer diameter of 125 μm.

The resulting optical fiber was a single type fiber with Δn = 8%, core diameter of 1 μm, and its transmittance loss at wavelength 1.3 μm was 0.2 dB / m.

The compositions of the sheaths (13) and (13 ') have a composition of 47.5HfF ₄ -23.5BaF ₂ -2.5LaF ₃ -2YF ₃ -4.5AlF ₃ -20NaF or 47.5ZrF ₄ -23.5BaF ₂ -2.5LaF ₃ -2YF ₃ -4.5 AlF ₃ -20NaF or the composition of the outer tube _{(13) 47.5HfF 4 -23.5BaF 2 -2.5LaF} 3 -2YF 3 -4.5AlF 3 -20NaF , in which the composition of the outer tube (13 ') 47.5ZrF ₄ -23.5 Fibers with a low permeability loss of BaF ₂ -2.5LaF ₃ -2YF ₃ -4.5AlF ₃ -20NaF can be produced in the same manner as described above.

Optical fibers were prepared in the same manner as described above except that the core glass-coated glass composite was changed as in Table 6. The resulting optical fiber was a single type fiber with Δn = 1 to 8% and its transmittance loss at wavelength 1.3 μm was 0.2 dB / m.

Comparative Example 2

Comparative optical fibers were prepared in the same manner as in Example 2 with fluoride glass of 16InF ₃ -19GaF ₃ -15ZnF ₂ -22CdF ₂ -28PbF ₂ (mol%) composition as core glass, 28InF ₃ -9GaF ₃ -12ZnF ₂ -as coated glass. 18BaF ₂ -6SrF ₂ -5YF ₃ was prepared using the composition of the fluoride glass of -10NaF-7LiF-5CdF ₂ (mol%).

As the core glass as used herein, a fluoride glass, CdF concentration is less than more than 20 mol%, 30 mol% PbF concentration and, LaF _3, YF _3, GdF ₃ and LuF ₃ not containing at least one member selected from the group consisting of Different from that used in Example 2 in that it does not. The fluoride glass used here as the coated glass is different in that it contains 5 mol% CdF ₂ as used in Example 2.

The resulting optical fiber was a single type fiber having a length of 100 m, an internal diameter of 1.7 μm and a cutting wavelength of 0.95 μm, but at a wavelength of 1.3 μm its transmission loss was 10 dB / m.

Example 3

The optical fibers were prepared in the same manner as in Example 2 except that the blending of the core glass composition and the coated glass composition was changed as shown in Table 7. The resulting optical fiber was a single type fiber with Δn = 1 to 4% and its transmittance loss at wavelength 1.3 μm was 0.1 dB / m. 8 shows the transmission loss spectrum of the optical fiber at 1 to 4 μm. The transmittance loss decreased with longer wavelength, and a minimum loss of 0.025 dB / m was obtained at the wavelength of 3.3 mu m.

Example 4

Optical fibers were prepared in the same manner as in Example 2 except that the core glass was doped with 500 ppm Pr ³⁺ . The resulting optical fiber had an outer diameter of 125 μm, Δn = 8%, a core diameter of 1 μm, and a cutting wavelength of 1 μm. Its transmittance loss was 0.2 dB / m at 1.3 mu m wavelength.

The large peak shown in FIG. 9 was an absorption line due to Pr ³⁺ . An amplifying agent for amplifying signal light having a wavelength of 1.31 mu m by pumping with light having a wavelength of 1.017 mu m was prepared using the optical fiber obtained in Example 4. A gain factor of 5 dB / mW was obtained.

A single type optical fiber of the type shown in FIG. 8 is prepared and the fiber core glass with Δn = 2.5% of it is doped with 1000 ppm Pr ³⁺ , or the core for fiber with Δn = 3.7%, 6.6% or 8%. The glass was doped with 500 ppm Pr ³⁺ . An amplifying agent for amplifying signal light at a wavelength of 1.31 μm by pumping with light of 1.017 μm wavelength was produced using the resulting optical fiber. The optical fiber with Δn = 2.5% obtained a gain factor of 0.25 dB / mW. The optical fiber with Δn = 3.7% obtained a gain factor of 0.3 dB / mW. The optical fiber with Δn = 6.6% obtained a gain factor of 0.4 dB / mW. The optical fiber with Δn = 8% obtained a gain factor of 0.5 dB / mW.

Comparative Example 3

Comparative optical fiber as core glass 500ZrF ₄ -15BaF ₂ -3.5LaF ₃ -10PbF ₂ -2YF ₃ -2.5AlF ₃ -10LiF-7NaF (mol%) composition with 500 ppm PrF ₃ -doped ZrF ₄ -based fluoride It prepared using the glass in the same way as in example 2, a coated glass _{47.5ZrF 4 -23.5BaF 2 -2.5LaF 3 -2YF 3} -4.5AlF 3 -20NaF ZrF 4 having a (mol%) composition-based flow Prepared in the same manner as in Example 2 using a ride glass.

The resulting optical fiber is a single type fiber with Δn = 3.7%, internal diameter of 1.7 μm and cutting wavelength of 0.95 μm, and its transmittance loss at wavelength 1.3 μm was 0.2 dB / m. An amplifying agent for signal light having a wavelength of 1.31 μm was prepared using the optical fiber obtained in Comparative Example 3 by pumping with light having a wavelength of 1.017 μm. A gain factor of 0.2 dB / mW was obtained.

The gain factor obtained with high Δn fibers (Δn = 6.1%) according to reported Japanese Patent No. 5-281112 was 0.25 dB / mW, which was lower than the gain coefficient of the claimed fluoride fiber.

A comparison between Example 4 and Comparative Example 3 showed that the use of the claimed fluoride fibers inhibited the non-radioactive relaxation of Pr ³⁺ as the release efficiency increased.

Example 5

The optical fibers were prepared in the same manner as in Example 2 except that the blend of the core glass composition and the coated glass composition was changed as shown in Table 9 and each core glass was doped with the rare earth ions shown in Table 9. Transmission spectra of the resulting optical fibers were measured for optical losses. The results show an increase in transmittance loss at the absorption wavelength of the doped rare earth ions.

Example 6

The same method as in Example 2, except that the optical fibers were changed in the blend of the core glass composition and the coated glass composition as shown in Tables 10 to 11, and each core glass was doped with the rare earth ions shown in Tables 10 to 1. It was prepared by. Transmission spectra of the resulting optical fibers were measured for optical losses. The results show an increase in transmittance loss at the absorption wavelength of the doped rare earth ions.

Example 7

Table 8 shows the formulation of the optical glass compositions for the core, sheath, and sheath of the claimed single type of optical fiber, with the formulation providing 2.5%, 3.7%, 6.6%, and 8% relative refractive index differences. The amounts of PbF ₂ and substitute NaF replaced in Table 8 were adjusted so that the refractive index of the coating was consistent with the primary envelope refractive index for using the composition of the coated glass.

Example 8

An optical fiber laser was produced using fibers doped with 2 meters of optical fiber No. 3 described in Tables 10 and 11, 1000 ppm of Tm and 4000 ppm of Yb as rare earth ions. Each end of the rare earth ion doped optical fiber was bonded to a dielectric mirror to form a Fabry-Perot laser cavity. An Nd-YAG laser operating at 1.12 μm was used as the pump source. Light from this pump source was focused by the lens on the fiber end. A dielectric mirror was used that was transparent to the pump wavelength and had a high refractive index for the lasing wavelength of 450-500 nm. Optical fiber lasers with this arrangement showed blue laser oscillations at wavelengths 455 nm and 480 nm.

Example 9

The same laser cavity as in Example 8 was prepared using optical fibers No. 4 2 meters described in Tables 10 and 11, fibers doped with a Tm of 1000 ppm as rare earth ions. The pump source was a krypton ion laser and the pump wavelengths were 647 nm and 676 nm. A dielectric mirror was used that was transparent to the pump wavelength and had a high refractive index for the lasing wavelength of 450-500 nm. Optical fiber lasers of this type showed blue laser oscillations at wavelengths of 455 nm and 480 nm. In addition, a high power LD operating at 1.48 μm was added to the pump source of Example 9 to perform two wavelength pumpings of 647 nm and 1.48 μm to increase the blue laser power.

Example 10

The same laser cavity as in Example 7 was fabricated using optical fibers No. 6 2 meters described in Tables 10 and 11, fibers doped with Er at 2000 ppm as rare earth ions. The pump source was a laser diode operating at 0.8 μm or 0.98 μm and the mirror was highly refracted for a laser wavelength of 540-545 nm. This type of optical fiber laser showed green laser oscillation at wavelength 540 nm.

In addition, the laser oscillation degree was doped with Nd, a rare earth ion (No. 2, 12) at 412 nm, a fiber doped with Pr at 492 nm (No. 1, 10) and Ho at 549 nm. In the fibers (No. 5).

Example 11

1.15 micrometer band optical amplifier was produced using the optical fiber 11 of 10 meters of Tables 10 and 11, the fiber doped with 1000 ppm Er as a rare earth ion. That is, the pump light (wavelength 1.48 mu m) from the signal light (wavelength 1.55 mu m) and LDs were coupled by a WDM fiber coupler and ranch to the fiber ends. The output signal was obtained from the product end via an optical isolator. Gains of more than 25 dB were obtained with a pumping force of 150 mW in the wavelength band of 1530-1560 nm.

Example 12

A 1.4 μm band optical amplifying agent was prepared using optical fiber No. 7, Table 10 and 11, fibers doped with rare earth ions, 0.5 wt% Tm and 1 wt% Ho. The pump source was a laser diode operating at 0.8 μm. A gain of 20 dB or more was achieved with a pump power of 100 mW.

Example 13

A 1.65 μm band optical amplifying agent was prepared using optical fiber No. 8 described in Tables 10 and 11, fibers doped with a rare earth ion of 2000 ppm Tm and 4000 ppm Tb. The pump source was a laser diode operating at 1.2 μm. A yield of 20 dB or more was obtained with a pump power of 100 mW.

Example 14

A 1.3 micrometer band optical amplifying agent was produced using 20 meters of optical fiber No. 9 described in Tables 10 and 11. The pump source was a laser diode operating at 0.98 μm. Yields above 20 dB were obtained with a pumping power of 200 mW.

The invention has been described in detail in various embodiments, and modifications and variations will be possible by those skilled in the art from within the scope without departing from the broader aspects, objects of the invention, and therefore, the appended claims are intended to provide the true object of the invention. Such changes and modifications can be included within.

As mentioned above, the present invention has succeeded in providing fluoride glass with satisfactory infrared transmission. The present invention also enables the production of optical fibers for optical amplification with low loss and high potency (Δn). Accordingly, the present invention increases the gain factor and the efficient gain, and makes it possible to manufacture an optical amplifier for semiconductor laser pumping which is essential for practical use. Moreover, the present invention provides the advantage of reducing the cost and increasing the performance of the optical communication system.

Claims (10)

10 to 30 mol% InF ₃ , 7 to 30 mol% GaF ₃ , 10 to 19 mol% ZnF ₂ , 4 to 30 mol% BaF ₂ , 0 to 24 mol% SrF ₂ , 0 to 30 mol% At least one member selected from the group consisting of PbF ₂ , and LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ , 1.5 to 10 mol%, 1.5 to 30 mol% LiF, 0 to 30 mol% NaF, and 0 to Fluoride glass comprising 15 mol% of additives, wherein the total amount of all of these components is 100 mol%. Having a core and a coating, the matrix of the coating is 10 to 30 mol% of InF _3, 7 to 30 mol% of GaF _3, 10 to 19 mol% of ZnF _2, 4 to 30 mol% of BaF _2, 0 to 24 mol % of SrF _2, 0 to 30 mol% of PbF _2, and LaF _3, YF _3, GdF ₃ and LiF, 0 of LuF one or more members of 1.5 to 10 mol%, selected from the group as consisting of _3, 1.5 to 30 mol% Fluoride optical fiber comprising from 30 to 30 mol% NaF, and from 0 to 15 mol% additive, wherein the total amount of all of these components is 100 mol%. The matrix of claim 2 wherein the matrix of the core is from 5 to 25 mol% InF ₃ , from 13 to 40 mol% GaF ₃ , from 4 to 25 mol% ZnF ₂ , from 30 to 46 mol% PbF ₂ , from 0 to 20 mol % Of CdF ₂ , and 1.5-12 mol% of one or more members selected from the group consisting of LaF ₃ , YF ₃ , GdF _3, and LuF ₃ , and 0-15 mol% of additives, the total amount of all of which 100 mol% fluoride optical fiber. The method of claim 2 wherein the core matrix is 10 to 30 mol% of InF _3, 7 to 30 mol% of GaF _3, 10 to 19 mol% of ZnF _2, 4 to 30 mol% of BaF _2, 0 to 24 mol % of SrF _2, 0 to 30 mol% of PbF _2, and LaF _3, YF _3, GdF ₃ and LiF, 0 of LuF one or more members of 1.5 to 10 mol%, selected from the group as consisting of _3, 1.5 to 30 mol% Fluoride optical fiber comprising from 30 to 30 mol% NaF, and from 0 to 15 mol% additive, wherein the total amount of all of these components is 100 mol%. The fluoride optical fiber of claim 2, wherein the core may contain transition metal ions or rare earth ions, and the relative refractive index difference Δn between the core and the coating is at least 1.0%. The method of claim 2, wherein Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm ³⁺ , Eu ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , Tm ³⁺ and Fluoride optical fiber containing at least one selected from Yb ³⁺ as rare earth ions. Having a secondary coating on the core, the primary coating, and the sheath of the primary coating, the matrix of the primary coating being 10-30 mol% of InF ₃ , 7-30 mol% GaF ₃ , 10-19 mol% ZnF _2, 4 to 30 mol% of BaF _2, 0 to 24 mol% of SrF _2, 0 to 30 mol% of PbF _2, and LaF _3, YF _3, GdF ₃ and at least one selected from the group consisting of LuF ₃ A matrix of secondary coating, comprising 1.5 to 10 mol% of members, 1.5 to 30 mol% of LiF, 0 to 30 mol% of NaF, and 0 to 15 mol% of additives, the total amount of all components being 100 mol% Is 10 to 30 mol% InF ₃ , 7 to 30 mol% GaF ₃ , 10 to 19 mol% ZnF ₂ , 4 to 30 mol% BaF ₂ , 0 to 24 mol% SrF ₂ , 0 to 30 mol % PbF ₂ , and at least one member selected from the group consisting of LaF ₃ , YF ₃ , GdF ₃ and LuF ₃ 1.5-10 mol%, 1.5-30 mol% LiF, 0-30 mol% NaF, and 0 To 15 mole% of additives Fluoride optical fiber with a total amount of components of 100 mol%. The method of claim 7, wherein the secondary coating matrix is in the group consisting of BaF ₂ , LaF ₃ , GdF ₃ , YF ₃ , LiF, NaF, PbF ₂ and AlF ₃ and at least one fluoride selected from ZrF ₄ and HfF ₄ . Fluoride optical fiber comprising fluoride glass comprising at least one member selected from. The fluoride optics of claim 7 or 8, wherein the refractive index of the primary coating is adjusted such that the refractive index of the primary coating matches the refractive index of the secondary coating or is greater than the refractive index of the primary coating and smaller than the refractive index of the core. fiber. 10. The fluoride optical fiber of claim 9, wherein the refractive index of the primary coating is adjusted by replacing the portion of PbF ₂ with NaF in the matrix of the primary coating.

Images