CN1402028A - Rare earth element doped glass double-clad optical fiber and preparation method thereof - Google Patents

Abstract

A rare-earth element doped glass double-clad optical fiber and a preparation method thereof are disclosed, wherein the periphery of a fiber core of the optical fiber is coated with an inner cladding and an outer cladding on the same central axis. The material of the core is a phosphate glass system. The material of the inner cladding is a phosphate glass system or a silicate glass system that matches the core material in terms of refractive index, expansion coefficient, and softening temperature. Selecting glass raw materials of the fiber core and the inner cladding according to the matching relation, melting, preparing a prefabricated rod to form a core-cladding combination body, and finally carrying out the specific steps of optical fiber drawing to obtain the glass double-clad optical fiber. Compared with the prior art, the glass double-clad fiber has the advantages of higher concentration of doped rare earth ions, larger stimulated emission cross section, larger tunable range and larger gain. The preparation method is simple and the production cost is low.

Description

Rare earth element-doped glass double-clad optical fiber and preparation method thereof

Technical field:

The invention relates to a glass double-clad optical fiber doped with rare earth elements and a preparation method thereof, in particular to an optical fiber core material (abbreviated as core material) and a multi-component glass material whose inner cladding is a non-quartz matrix, and the outer cladding is plastic Double-clad optical fiber and its preparation method.

Background technique:

A fiber laser is a laser resonator composed of an optical fiber doped with certain rare earth elements and an optical feedback element. Under the action of pump light, stimulated emission occurs in the doped fiber medium and forms laser light in a certain wavelength range. It has the advantages of low threshold, high efficiency, narrow linewidth, and tunability. The characteristics of fiber laser determine that it has more advantages than semiconductor lasers and other large lasers. However, the original fiber laser directly coupled the pump light into the fiber core with a diameter of less than 10 μm, resulting in low coupling efficiency and low output power of the fiber laser, which limited its application range. In order to overcome the above difficulties, in recent years, a double-clad fiber has been developed internationally. Because it has an inner cladding with a large cross-section and numerical aperture, it can effectively absorb pump light with a large divergence angle. The above-mentioned shortcoming of single cladding is overcome, the output power is greatly improved, and the development of high-power fiber lasers is greatly promoted. The advantage of double-clad pumping is that the pump light is no longer required to be a single-mode laser, so that high-power multi-mode semiconductor laser pumping can be applied. The pump energy does not need to be directly coupled into the fiber core, but coupled into the inner cladding. , and continuously excite the dopant ions in the fiber core, which has a high absorption rate for the pump light, resulting in high light-to-light conversion efficiency, thereby achieving high power output. American Torch (SDL) company (see prior art [1] V.Dominc, S.MacCormack, R.Waarts.et al.110W fiber Laser.Electronics letters, 1999, Vol35:1158～1160) reported in 1999 Cladding pumped laser with output power of 110W. At present, cladding pumped lasers are widely used in communication, military, industrial processing, medical treatment, printing and so on.

The core and inner cladding of double-clad fibers used in cladding-pumped fiber amplifiers or fiber lasers are basically silica-based. There are several deficiencies in the double-clad optical fiber of silica matrix:

(1) The doping concentration of rare earth ions in the quartz matrix is low (<2wt%). Since rare earth ions are prone to clusters in the quartz matrix, causing a sharp decrease in the fluorescence lifetime, it can only be operated when the concentration of rare earth ions doped in the quartz is low, which will lead to a double-clad optical fiber absorption rate So low that the optical fiber must be very long to absorb fully, but the longer the length, the greater the loss, and it is not conducive to the miniaturization of the device. U.S. Polaroid (Polaroid) company M.Muendel et al. (see prior art [2] M.Muendel, B.Engstrom, D.Kea, et al.35-Watt CW singlemode Ytterbium FiberLaser.CLEO'97, CPD30- 2/649) reported a double-clad laser with an output power of 35W. The ^Yb3+ -doped quartz matrix double-clad fiber used was prepared by improved chemical vapor deposition (MCVD) for the core and inner cladding materials. The doping concentration of Yb ³⁺ ions is only 1.5wt%, the core diameter is 8 μm, the inner cladding with a rectangular cross section measures 170×330 μm ² , the numerical aperture (NA) formed by the inner cladding and the core material is 0.07, and the outer cladding It is an organic polymer, the diameter of the outer cladding is 500 μm, and the numerical aperture (NA) formed by the outer cladding and the inner cladding is 0.48. In order to fully absorb the pump light, the fiber length reaches 50 meters.

(2) The gain of rare earth ions in the quartz matrix is small. This is mainly because the stimulated emission cross section of rare earth ions in the quartz matrix is small.

(3) The adjustable range of the double-clad optical fiber composition of the quartz matrix is small. It mainly adds a small amount of other elements (such as: P, Ge, etc.) on the pure quartz substrate to change the refractive index, and the composition range is narrow.

(4) The preparation process of the double-clad optical fiber of the quartz matrix is complicated and the cost is high. This is mainly because the preform of the double-clad optical fiber of the quartz matrix is prepared by an internal deposition method (such as: MCVD (modified chemical vapor deposition) and PCVD (plasma-activated chemical vapor deposition), etc.), and the deposition process is complicated. , the equipment requirements are expensive, and the drawing temperature is high. For example, U.S. Patent US 6345141 (see prior art [3] US6345141; date of publication: Feb.5.2002; name: Double-clad optical fiber with improved inner cladding geometry) proposes a double-clad optical fiber with improved inner cladding geometry for a variety of quartz substrates with different inner cladding shapes. layers of fiber optics.

To sum up, the silica-based double-clad optical fiber has several disadvantages, such as low doping concentration of rare earth ions, small gain, narrow composition range, high manufacturing cost, and complicated manufacturing process.

Invention content:

The purpose of the present invention is to provide a kind of non-quartz matrix multi-component glass to prepare double-clad optical fiber, which can effectively overcome the low doping concentration of rare earth ions and the gain Small, narrow composition range, high preparation cost, complex preparation process and other deficiencies.

The cross-sectional shape of the double-clad optical fiber of the present invention is shown in Figure 1 and Figure 2, and includes three parts: core 1, inner cladding 2 surrounding the core 1, and outer cladding 3 surrounding the inner cladding 2, and the central axis of the three coincides, wherein The material of core 1 is phosphate glass system, and its glass formula range is shown in Table 1. The cross-section of the core is circular, and the diameter of core 1 is usually φ5-60 μm. Among them, the core diameter of φ5-12 μm can be used as Fiber lasers output single-mode laser beams, usually called single-mode fibers, and other larger-diameter cores are called multimode fibers. The material of the inner cladding is phosphate glass system or silicate glass system, and the range of the glass formula is shown in Table 2. The inner cladding has a lower refractive index than the core, that is, _ninner < _ncore , and its cross-sectional shape is Square (as shown in Figure 1) or rectangle (as shown in Figure 2), or other polygons. The outer cladding is made of polymer material such as plastic, and the cross-sectional shape of the outer cladding is circular, and its refractive index _nout is lower than that _of the inner cladding, nin, ie, _nout < _nin .

The most important feature of the double-clad optical fiber of the present invention is that the rare earth ions in the core 1 not only have a high doping concentration in the phosphate glass (at least one order of magnitude higher than that of the quartz matrix), but also have a larger stimulated emission cross section than that of the quartz matrix, so The prepared optical fiber has a large gain per unit length (at least one order of magnitude higher than the double-clad optical fiber of the silica matrix), and the present invention has the advantages of: (a) the glass composition of the inner cladding 2 and the glass composition of the fiber core are matching. (b) A wide range of glass components can be selected. (c) In the preparation process, the preparation and wire drawing process of the preform is simple, and the preparation cost is low.

Table 1 Glass formulations used in the core Table 2 Multi-component glass formulations used in the inner cladding Phosphate Glass System Element Content (mol%) P ₂ O ₅ 55～70 Al ₂ O ₃ 4～10 BaO 4～14 Na ₂ O 3～8 K ₂ O 3.5～15 Nb ₂ O ₅ 0.4～3.4 La ₂ O ₃ 0.3～3.0 Y ₂ O ₃ 0.2～6 Sb ₂ O ₃ 0～0.2 Yb ₂ O ₃ or Er ₂ O ₃ or Nd ₂ O ₃ or Ho ₂ O ₃ or Tm ₂ O ₃ or Dy ₂ O ₃ 0.2～6 Phosphate Glass System Silicate glass system Element Content (mol%) Element Content (mol%) P ₂ O ₅ 54.5～71 SiO ₂ 61.8～74 Al ₂ O ₃ 4～8 B ₂ O ₃ 2～15 BaO 4～16.5 Na ₂ O 0～8.2 Na ₂ O 3～8 K ₂ O 3.7～8.8 K ₂ O 5～15.5 CaO 0～4.5 Nb ₂ O ₅ 0.4～2 ZnO 0～6.6 La ₂ O ₃ 0.3～2.8 PbO 0～0.6 Y ₂ O ₃ 0.5～5.3 KHF ₂ 0～19.5 Sb ₂ O ₃ 0～0.2 Sb ₂ O ₃ 0～0.2

The concrete steps of the preparation process of the glass double-clad optical fiber of the present invention are:

① In the first step, the formula (by mole percentage) of the material of the core 1 (hereinafter referred to as the core material) and the material of the inner cladding 2 is selected.

The formula of the core material and the formula of the inner cladding should be matched with each other. When selecting the formula, first determine the specific formula of the core material, according to the matching of the core material and the inner cladding material in terms of refractive index, expansion coefficient and softening temperature. relationship to determine the composition of the inner cladding material. Firstly, it is determined that the core material glass is selected from the phosphate glass system, and the specific composition range is shown in Table 1. The molar percentage is 55-70% P ₂ O ₅ , 4-10% Al ₂ O ₃ , 4-14% BaO, 3-8% Na ₂ O, 3.5-15% K ₂ O, 0.4-3.4% Nb ₂ O ₅ , 0.3-3% La ₂ O ₃ , 0.2-6% Y ₂ O ₃ , 0-0.2% Sb ₂ O ₃ , 0.2-6% Yb ₂ O ₃ , or Er ₂ O ₃ , or Nd ₂ O ₃ , or Ho ₂ O ₃ , or Tm ₂ O ₃ , or Dy ₂ O ₃ . There are two glass systems for selecting the glass formula used in the inner cladding: (a) The formula for the phosphate glass system is (by mol%): 54.5-71% P ₂ O ₅ , 4-8% Al ₂ O ₃ , 4-16.5 %BaO, 3-8% Na ₂ O, 5-15.5% K ₂ O, 0.4-2% Nb ₂ O ₅ , 0.3-2.8% La ₂ O ₃ , 0.5-5.3% Y ₂ O ₃ , 0-0.2% Sb ₂ O ₃ , (b) for the silicate glass system formula is (by mol%): 61.8~74% SiO ₂ , 2~15% B ₂ O ₃ , 0~8.2% Na ₂ O, 3.7~8.8% K ₂ O, 0-4.5% CaO, 0-6.6% ZnO, 0-0.6% PbO, 0-19.5% KHF ₂ , 0-0.2% Sb ₂ O ₃ . Above-mentioned core material of the present invention and inner cladding glass meet following conditions in three respects of refractive index, coefficient of expansion, softening temperature:

(a) The relationship between the refractive index ncore of the core material and the refractive index _{nnei of} the inner cladding glass is: n _core is greater than _nnei , that is, n _core >n _clad , and the refractive index difference between the two selected formulas is n _core - _nnei 0.15% to 3%;

(b) The matching between the expansion coefficient of the core material glass and the expansion coefficient of the inner cladding glass is based on the fact that the two do not generate internal compressive stress after filament formation, and generally the difference is ±20×10 ^-7 /°C.

(c) The transition temperature difference between the core material and the inner cladding material is within 30°C, and the softening temperature difference can be within 50°C.

The selection of the formula of the core material and the inner cladding glass of the present invention not only achieves the above-mentioned mutual matching relationship, but also selects the overall requirements that can be achieved: the glass has good mechanical properties and good chemical stability. Crystallization is not easy to occur at high temperature.

② In the second step, the glass of the core material and the inner cladding is melted.

(a) Core material glass melting: After mixing the raw materials evenly according to the formula determined in the first step above, first put them in a quartz crucible and melt them at a melting temperature of 1200-1300 ° C. After the raw materials are completely melted, pass oxygen to remove water. Until the fluorescence lifetime reaches saturation, then pour the clinker into a platinum crucible, keep the temperature at 1200-1300°C, perform stirring and clarification operations in sequence (the whole process is more than 5 hours), and finally pour it on the iron mold and move it into the Preheat to a muffle furnace at the material transition temperature (Tg) for annealing, first keep warm for 2 hours, then cool down at a rate of 2°C/hour to 50-100°C, and then cool down to room temperature at a rate of 5°C/hour , and then take it out after cooling completely.

(b) Inner cladding 2 glass melting: according to the inner cladding glass formula determined in the first step above, when the phosphate glass system is selected, the melting process and conditions are exactly the same as the core glass melting process. When the silicate glass system is selected, mix the raw materials according to the above first step formula and put them directly into the platinum crucible for melting, then stir and clarify the operation process (the whole process takes more than 5 hours), and the melting temperature is kept at 1300 ~1450°C, finally poured on the iron mold, moved into the muffle furnace whose preheating temperature is the material transition temperature (Tg) for annealing, first kept for 2 hours, and then cooled by 50-100°C at a rate of 2°C/hour , and then cooled down to room temperature at a rate of 5°C/hour, and then removed after complete cooling.

③ The third step is to prepare the preform.

Determine the diameter and length of the prepared preform according to the diameter of the optical fiber core 1 to be drawn and the size of the cross-section of the inner cladding and their length, for example: the ratio d core rod=200～500d between the two can be used _Core , d _{clad rod} = (200～500〕×(200～500)]d _pack , wherein d _{core rod} is the diameter of the core preform rod, d _core is the core diameter, and d _{clad rod} is the transverse diameter of the inner cladding preform rod Cross-sectional area, d _package is the cross-sectional area of the inner cladding.

Cutting the core material glass prepared above requires cutting out a part with good optical uniformity, grinding it into a round rod shape, and then going through steps such as grinding and polishing successively to process it into a preform of the fiber core 1 of the required size ( Hereinafter referred to as the mandrel), the surface finish of the mandrel must be level 2 or above.

The inner cladding glass material prepared above is cut, and it is required to cut out the part with good optical uniformity, and grind it into a round rod shape, and then go through steps such as grinding and polishing in turn, and then process it into the axial center of the inner cladding glass round rod. Drill the hole. The prefabricated rod made of the inner cladding is a sleeve rod, the surface of the inner hole of the sleeve rod is polished, and finally the drilled inner cladding sleeve rod is processed into a cross-sectional shape as required, such as square or rectangle or other polygons of rod shape. Then use ultrasonic wave or hydrofluoric acid to clean the surface impurities or pollutants of the processed core rod and inner cladding rod. Insert the processed mandrel into the central circular hole of the inner cladding rod, and ensure the close contact between the two and the coincidence of the central axes of the two to obtain the combination of the mandrel and the inner cladding, referred to as the core cladding combination.

④ The fourth step, fiber drawing.

Fix the above-mentioned core-clad assembly on a wire drawing machine, draw the core-clad assembly into an optical fiber at a temperature of 650-700°C, and immediately pass the optical fiber through a device equipped with molten liquid plastic as the outer cladding 3 to form The outer cladding 3, and then the double-clad optical fiber is coated with an ultraviolet curing material, irradiated and cured by a xenon lamp, and finally drawn into a double-clad optical fiber that meets the requirements. The length of qualified optical fiber produced by this production process can reach at least 1km.

The beneficial effects produced by the present invention are: providing high-power fiber lasers and double-clad optical fibers used in fiber amplifiers, meeting the requirements of current optical communication development, taking Nd ³⁺ ion doping as an example, according to the above-mentioned double-clad optical fiber of the present invention The stimulated emission cross section obtained by the multi-layer optical fiber in the silicate glass system is about 2.0×10 ^-20 cm ² , and the stimulated emission cross section in the phosphate glass system is 3.9×10 ^-20 cm ² , both of which are better than those of the prior art The stimulated emission cross-section of the doped quartz matrix used in the method is large. Compared with the quartz optical fiber in which the quartz matrix is doped with rare earth ions in the prior art, the glass double-clad optical fiber of the present invention has a higher doping concentration, a larger tunable range, a larger gain, a simpler preparation method, and a lower production cost. Low.

Description of drawings:

Fig. 1 is the multi-component glass double-clad optical fiber sectional schematic diagram that the inner cladding of the present invention is a square

Fig. 2 is the multi-component glass double-clad optical fiber sectional schematic view that inner cladding of the present invention is a rectangle

Detailed ways:

The present invention will be further described below in combination with specific embodiments.

The first choice is to determine the core and inner cladding glass formulations. Table 3 and Table 4 give 6 groups of core material and inner cladding glass formulations, in which the core material and inner cladding glass of the 3 combinations in Table 3 are all phosphate glass systems, and the core material of the three combinations in Table 4 is phosphoric acid Salt glass system, inner cladding is silicate glass system.

Specific embodiment 1-the 1st group material

table 3 Group 1 Group 2 group 3 Component (mol%) Fiber core Inner cladding Fiber core Inner cladding Fiber core Inner cladding P ₂ O ₅ 60.0 61.0 55.0 54.5 70 71 Al ₂ O ₃ 4.0 4 5.0 5.0 7 8 BaO 10.0 10.0 14.0 16.5 4 4 Na ₂ O 4.0 4.5 3.0 3.0 8 8 K ₂ O 15.0 15.5 13.0 13.0 5.6 5 Nb ₂ O ₅ 0.4 0.4 2 2 0.5 0.5 La ₂ O ₃ 0.3 0.3 1.5 1.5 0.3 2.8 Y ₂ O ₃ 0.2 5.3 4.5 4.4 0.5 0.5 Group 1 Group 2 group 3 Component (mol%) Fiber core Inner cladding Fiber core Inner cladding Fiber core Inner cladding Sb ₂ O ₃ 0.1 0 0 0.1 0.1 0.2 Yb ₂ O ₃ 6 - 2 - 4 - Stimulated emission cross section (×10 ^-20 cm ² ) 1.69 - 1.72 - 1.65 - Fluorescence lifetime (ms) 2.2 - 2.3 - 2.3 - Fiber core diameter (μm) 10μm 6μm 30μm Core Glass Refractive Index n _Core 1.530 1.528 1.511 Numerical aperture 0.10 0.08 0.12

Follow the steps above. The first step: select the glass formula, according to Table 3. First select the first group of formulations in Table 3. The refractive index n _core of the core material that meets the above conditions is greater than the refractive index n _{inner of} the inner cladding glass, and the difference between the two (n _core - n _inner ) is between 0.15% and 3%. between.

In the second step, the melting rules of the core material and the inner cladding glass are the same, that is, about 2,500 grams of the mixed raw materials of the above formula are weighed for the core material, and about 5,000 grams of the inner cladding glass mixed raw materials are weighed. First, melt the raw material in a 1.5 liter quartz crucible at a melting temperature of 1250°C. After the raw material is completely melted, pass oxygen to remove water until the fluorescence lifetime reaches saturation. Then pour the clinker into a 1.2-liter platinum crucible, and perform operations such as stirring and clarification in sequence. The whole process takes about 5 hours. Finally, pour it on an iron mold with a size of 150mm×70mm×60mm, move it into a muffle furnace preheated to a material transition temperature Tg of 430°C for annealing, keep it warm for 2 hours, and then cool it down to 380°C at a rate of 2°C/hr. Then lower it to room temperature at 5°C/hr, and take it out after complete cooling.

The test results show that the refractive index of the prepared core glass is 1.530, and the stimulated emission cross section of Yb ³⁺ ions in the core glass is 1.6×10 ^-20 cm ² .

其中a为纤芯的半径，λ为光纤内传输光的波长，n_芯为芯纤1的折射率，n_内为内包层的折射率。所以选择芯料预制棒纤芯加工成直径为2mm(d_芯棒＝200d_芯)，长度为60mm，并且玻璃表面抛光成3级光洁度。内包层的预制棒加工尺寸为25mm×25mm×80mm(d_包棒＝(200×200)d_包)，上下端面正中心处钻直径为2mm的内孔，深度为60mm，内孔表面要抛光。用超声波对芯棒和外包层套棒表面进行去污清洗处理。将芯棒插入内包层套棒中心孔中，构成两者的芯包组合体。Step 3: Prepare the preform. First, consider making a single-mode optical fiber. The core diameter d _core is less than 12 μm. The single-mode optical fiber must meet the following conditions:

Where a is the radius of the fiber core, λ is the wavelength of light transmitted in the fiber, n _core is the refractive index of the core fiber 1, and n _is the refractive index of the inner cladding. Therefore, the core material prefabricated rod core is selected to be processed into a diameter of 2 mm (d _{core rod} = 200d _core ), a length of 60 mm, and the glass surface is polished to a grade 3 finish. The processing size of the preform rod of the inner cladding is 25mm×25mm×80mm (d _{package rod} = (200×200) d _package ), and an inner hole with a diameter of 2mm is drilled at the center of the upper and lower end faces, the depth is 60mm, and the surface of the inner hole should be polished. Ultrasonic waves are used to decontaminate and clean the surface of the core rod and the outer cladding rod. The mandrel is inserted into the center hole of the inner cladding rod to form a core-clad combination of the two.

The fourth step is fiber drawing. Put the above-mentioned core package assembly into the heating furnace of the wire drawing machine. Slowly raise the temperature to 650°C (it takes at least 1.5 hours to rise from normal temperature to 650°C, and the temperature rise rate should be slower in the range from room temperature to below 250°C), the prefabricated bar head is dropped, and it is drawn into an optical fiber with a wire drawing machine. The drawing speed is 10m/min. After fiber formation, the outer cladding is formed after passing through a device equipped with molten liquid plastic. Then the double-clad fiber is coated with UV-curable material and cured by xenon lamp irradiation, and finally drawn into a fiber core with a numerical aperture of NA=0.100, a core diameter of 10 μm, and a cross-sectional shape of the inner cladding of a square with a side length of 125 μm , ytterbium-doped glass double-clad optical fiber with an outer cladding diameter of φ170 μm, the qualified optical fiber length can be at least 1 km produced by the above preparation method.

Specific embodiment 2-the 2nd, 3 groups of materials

The glass formulations of groups 2 and 3 are shown in Table 3, and the melting process of the core material and inner cladding glass is the same as that of the above-mentioned embodiment 1.

For the second group, the core rod glass is processed into a preform rod with a diameter of 3mm (d _{core rod} = 500d _core ) and a length of 60mm, and the inner cladding preform rod is processed into a processing size of 50mm × 50mm × 80mm (d _{package rod} = (400×400)d _package ), drill an inner hole with a diameter of 2mm at the center of the upper and lower end faces, and an inner cladding rod with a depth of 60mm. Its follow-up steps and drawing process are identical with embodiment 1. The final numerical aperture of the double-clad fiber composed of the second group of core materials and inner cladding materials is 0.08, the core diameter is 6 μm, the side length of the inner cladding is 125 μm, and the outer diameter is φ170 μm. For the third group, the core rod glass is processed into a diameter of 6mm (d _{core rod} = 200d _core ), and the length is 60mm preform rod, and the inner cladding preform rod is processed into a processing size of 25mm × 25mm × 80mm (d _{package rod} = ( 200×200)d _package ), drill an inner hole with a diameter of 2mm at the center of the upper and lower end faces, and an inner cladding rod with a depth of 60mm. Its follow-up steps and drawing process are identical with embodiment 1. The final numerical aperture of the double-clad fiber composed of the third group of core materials and inner cladding materials is 0.12, the core diameter is 30 μm, the inner cladding cross-section forms a square with a side length of 125 μm, and the outer diameter of the entire fiber is φ170 μm.

Specific embodiment 3-the 4th, 5, 6 groups of materials

Groups 4, 5, and 6 in Table 4 all have a phosphate glass system as the core material and a silicate glass system as the inner cladding.

For the fourth, fifth, and sixth groups, the melting of the core material glass is the same as in the specific example 1, and the melting of the inner cladding glass is a raw material synthesized according to the inner cladding formula selected from the above-mentioned silicate glass system. Take 3,000 grams, mix them evenly, and melt them directly in a 2.0-liter platinum crucible at a melting temperature of 1350°C. Stirring and clarification are carried out successively. The whole process takes more than 5 hours. Finally, pour it on an iron mold with a size of 120mm×70mm×50mm, move it into a muffle furnace preheated to a material transition temperature Tg of 460°C for annealing, first keep it warm for 2 hours, and then cool it down to 380°C at a rate of 2°C/hr. Then lower it to room temperature at 5°C/hr, and take it out after complete cooling. The preform processing and wire drawing process of the following core rod and inner cladding are also the same as in Embodiment 1.

Table 4 Group 4 Group 5 Group 6 Core (mol%) Inner cladding (mol%) Core (mol%) Inner cladding (mol%) Core (mol%) Inner cladding (mol%) P ₂ O ₅ 55.0 SiO ₂ 61.8 P ₂ O ₅ 70 SiO ₂ 72 P ₂ O ₅ 60.0 SiO ₂ 73.4 Al ₂ O ₃ 10.0 B ₂ O ₃ 15.0 Al ₂ O ₃ 7 B ₂ O ₃ 3.3 Al ₂ O ₃ 4.0 B ₂ O ₃ 2.0 BaO 10.0 Na ₂ O 0 BaO 8 Na ₂ O 6.0 BaO 10.0 Na ₂ O 8.2 Na ₂ O 3.0 K ₂ O 3.7 Na ₂ O 6 K ₂ O 8.8 Na ₂ O 4.0 K ₂ O 7.5 K ₂ O 12.0 CaO 0.0 K ₂ O 3.5 CaO 2.9 K ₂ O 15.0 CaO 4.5 Nb ₂ O ₅ 3.4 ZnO 0 Nb ₂ O ₅ 0.5 ZnO 6.6 Nb ₂ O ₅ 0.4 ZnO 2.8 La ₂ O ₃ 3.0 PbO 0 La ₂ O ₃ 1.4 PbO 0.3 La ₂ O ₃ 0.2 PbO 0.6 Y ₂ O ₃ 2.5 KHF ₂ 19.5 Y ₂ O ₃ 0.5 KHF ₂ 0 Y ₂ O ₃ 6 KHF ₂ 0.8 Sb ₂ O ₃ 0.1 Sb ₂ O ₃ 0 Sb ₂ O ₃ 0.1 Sb ₂ O ₃ 0.1 Sb ₂ O ₃ 0.2 Sb ₂ O ₃ 0.2 Yb ₂ O ₃ 1.0 Yb ₂ O ₃ 3 Yb ₂ O ₃ 0.2 Refractive index 1.494 1.488 1.523 1.522 1.520 1.518 Expansion coefficient (10 ^-7 /℃) 106 91 100 94 104 91 Softening temperature (℃) 480 500 487 514 491 508

Claims (2)

1. rare earth doped glass doubly-clad light, comprise fibre core (1), surround the inner cladding (2) of fibre core (1), surround the surrounding layer (3) of inner cladding (2), the same central axis of three, it is characterized in that said fibre core (1) is that phosphate glass system by doped with rare-earth elements constitutes, concrete prescription by mole number percent is: contain 55～70% P ₂O ₅, 4～10% Al ₂O ₃, 4～14% BaO, 3～8% Na ₂O, 3.5～15% K ₂O, 0.4～3.4% Nb ₂O ₅, 0.3～3.0% La ₂O ₃, 0.2～6% Y ₂O ₃, 0～0.2% Sb ₂O ₃, 0.2～6% Yb ₂O ₃, or Er ₂O ₃, or Nd ₂O ₃, or Ho ₂O ₃, or Tm ₂O ₃, or Dy ₂O ₃

Said inner cladding (2) is to be made of the phosphate glass system of doped with rare-earth elements or silicate glass system;

System specifically fills a prescription for phosphate glass, by mole number percent is: contain 54.5～71% P ₂O ₅, 4～8% Al ₂O ₃, 4～16.5% BaO, 3～8% Na ₂O, 5～15.5% K ₂O, 0.4～2% Nb ₂O ₃, 0.3～2.8%La ₂O ₃, 0.5～5.3% Y ₂O ₃, 0～0.2% Sb ₂O ₃

System specifically fills a prescription for silicate glass, by mole number percent is: contain 61.8～74% SiO ₂, 2～15% B ₂O ₃, 0～8.2% Na ₂O, 3.7～8.8% K ₂O, 0～4.5% CaO, 0～6.6% ZnO, 0～0.6% PbO, 0～19.5% KHF ₂, 0～0.2% Sb ₂O ₃

2. the preparation method of rare earth doped glass doubly-clad optical fiber according to claim 1 is characterized in that the concrete steps of preparation process are:

＜1〉for the formulation selection of fibre core (1) material and inner cladding (2) material:

At first determine the prescription of fibre core (1) material, come to determine the prescription of inner cladding (2) material according to inner cladding (2) material and fibre core (1) material again at the matching relationship that exists aspect three of refractive index, expansion coefficient and the softening temperatures then, the matching relationship of said three aspects is: the 1. refractive index n of fibre core (1) material _CoreRefractive index n greater than inner cladding (2) material _Bag2. the expansion coefficient of fibre core (2) expansion coefficient and inner cladding (2) material differ ± 20 * 10 ^-7/ ℃ 3. the transition temperature between fibre core (1) material and inner cladding (2) material differs less than 30 ℃, and softening temperature differs less than 50 ℃; For this reason, after fibre core (1) material selection phosphate glass system, inner cladding (2) material selection phosphate glass system or silicate glass system;

＜2〉glass smelting of fibre core (1) and inner cladding (2):

1. founding of fibre core (1) phosphate glass system: according to the above-mentioned raw material of choosing prescription, after raw material mixed, at first be placed in the silica crucible and melt, temperature of fusion is 1200～1300 ℃, after raw material melts fully, logical oxygen dewaters, reach capacity up to fluorescence lifetime, then its grog is poured in the platinum crucible, temperature still remains on 1200～1300 ℃, stir successively, the operating process of clarification, be cast at last on the swage, be moved in the muffle furnace that preheat temperature is material transition temperature (Tg) and anneal, insulation earlier 2 hours, then with after 50～100 ℃ of 2 ℃/hour the speed coolings, be cooled to room temperature with 5 ℃/hour speed again;

2. founding of inner cladding (2) glass: when inner cladding (2) material was the phosphate glass system, the process of founding of founding process and above-mentioned fibre core (1) phosphate glass system was identical; When inner cladding (2) material is the silicate glass system, after mixing by above-mentioned raw material, directly putting into platinum crucible melts, the operating process of stirring successively and clarifying, keep temperature of fusion is 1300～1450 ℃ always, is cast on the swage at last, be moved in the muffle furnace that preheat temperature is material transition temperature (Tg) and anneal, insulation earlier 2 hours is lowered the temperature 50～100 ℃ with 2 ℃/hour speed then, and then is cooled to room temperature with 5 ℃/hour speed;

＜3〉preparation prefabricated rods:

At first according to the size and the definite size that will prepare prefabricated rods of their length of the diameter and inner cladding (2) cross-sectional area of the fiber core (1) that will draw; Found fibre core (1) the glass cutting that obtains and be polished into round bar shape above-mentioned, pass through frosted, polishing then successively, be processed into fibre core (1) prefabricated rods of required size; Found inner cladding (2) the glass cutting that obtains and be polished into round bar shape above-mentioned, carry out frosted and polishing then successively; Hole to the center in the glass pole axon of inner cladding (2) again, the prefabricated rods of making inner cladding (2) is a cover rod, polish overlapping excellent bore area again, the sharp processing that to overlap excellent xsect again becomes desired square or rectangular or other polygon, with ultrasound wave or hydrofluorite to above-mentioned make fibre core (1) prefabricated rods and cover rod and clean after, the prefabricated rods of fibre core (1) is inserted in the cover rod, constituted core package zoarium;

＜4〉fibre-optical drawing:

Above-mentioned core package zoarium is fixed on the wire drawing machine, under 650～700 ℃ temperature, after core package zoarium is drawn into optical fiber, optical fiber is passed be equipped with device to form surrounding layer (3) as the melt liquid plastics of surrounding layer (3), its doubly clad optical fiber is passed after ultraviolet-curable materials applies, solidify with the xenon lamp irradiation.

Images