JP5310061B2 - Laser glass, fiber laser and double clad optical fiber - Google Patents

Description

  The present invention relates to a Yb-containing phosphate glass for laser, a fiber laser, and a double clad optical fiber.

Patent Document 1 proposes a high-power laser phosphate glass using Nd ₂ O ₃ as an active substance.

Patent Document 2 proposes a phosphate glass for a communication band having a wavelength of 1.5 μm using Er ₂ O ₃ as an active substance, Yb ₂ O ₃ and Cr ₂ O ₃ as sensitizers. Yes.

Patent Document 3 proposes a phosphate glass for high-power laser using Yb ₂ O ₃ as an active substance.

Patent Document 4 proposes a double-clad optical fiber for a high-power laser that uses silica glass as a base and uses Er ₂ O ₃ and Yb ₂ O ₃ as active substances.

Japanese Patent No. 3158202 JP-A-3-275529 JP-A-8-26768 Special table 2007-523035 gazette

Conventionally known glass for lasers has a problem that the refractive index is not high, the light emission characteristics are not sufficient, or the mechanical characteristics are not sufficient.
It is an object of the present invention to provide a glass for laser, a fiber laser, and a double clad optical fiber that can solve such problems.

The present invention is expressed in terms of mole percentages based on the following oxides, P ₂ O ₅ is 50 to 65%, Al ₂ O ₃ is 5 to 20%, B ₂ O ₃ is 1 to 10%, Li ₂ O is 0 to 0%. 10%, Na ₂ O 0-10%, K ₂ O 5-20%, MgO 0-10%, CaO 0-10%, SrO 0-10%, Nb ₂ O ₅ 2-15 %, Yb ₂ O ₃ 0.1 to 10% and La ₂ O ₃ 0 to 10% glass for laser (hereinafter sometimes referred to as the glass of the present invention).

Also provided is a fiber laser having a laser medium, a resonator, and an excitation light source, wherein the laser glass is used as the laser medium.
Further, a double clad optical fiber having the laser glass as a core glass is provided.

According to the present invention, a glass for a laser having a high refractive index can be obtained, and as a result, the radiation transition probability (A _rad ) can be increased.
Moreover, the double clad optical fiber of the present invention, for example, the glass of the present invention is used as a core, the glass having a lower refractive index than the core and a higher refractive index than the second cladding is used as the first cladding, and the refractive index is higher than that of the first cladding. A double clad optical fiber having a low resin as the second clad can increase the numerical aperture (NA) of the first clad and the second clad, and can easily confine the excitation light in the clad.

Further, according to the present invention, it is possible to increase the fluorescence lifetime (τ), and in this case, it is possible to lower the laser oscillation threshold.
Moreover, since A _rad can be increased, the laser output can be increased.
However, the quantum efficiency (eta) is τ and A _rad since represented by the product of τ and A _rad is a trade-off relationship.

In addition, according to the present invention, it is possible to obtain a glass having excellent mechanical properties that are important during glass polishing, melt-drawing and fiberizing processes, or chemical durability that is important when used as a product.
Further, since the glass of the present invention is a phosphate glass containing 50 mol% or more of P ₂ O ₅ , it is difficult to devitrify even if it contains a larger amount of rare earth such as Yb as compared with silica-based glass. Since the rare earths are difficult to cluster, they have excellent light emission characteristics.

  According to the double clad optical fiber of the present invention, it becomes possible to bundle a plurality of optical fibers that propagate pump light of a multimode high-power laser diode (LD) and to input the pump light into the first clad. As a result, a higher output can be obtained than the method in which the excitation light of the single mode LD is input only to the core.

  The fiber laser of the present invention is suitably used for processing.

  In the double clad optical fiber of the present invention, the core is the glass of the present invention, the first clad having a refractive index smaller than that of the core is provided around the core, and the refractive index of the first clad is greater than that of the first clad. Has a small second cladding, which is typically a resin. Further, if the NA of the first cladding and the second cladding is increased, it becomes easier to confine the excitation light in the cladding, that is, it becomes easier to introduce the excitation light. The double clad optical fiber of the present invention can be used in either single mode or multimode.

Refractive index with respect to the helium d line of the glass of the present invention _{(n d)} is preferably from 1.52 to 1.64. If it is less than 1.52, it will be difficult to increase the refractive index difference between the first cladding and the second cladding (in many cases resin) in the double-clad optical fiber of the present invention, and it will be difficult to increase the NA. This may make it difficult to confine the excitation light. More preferably, it is 1.545 or more, More preferably, it is 1.56 or more, Most preferably, it is 1.58 or more. If it exceeds 1.64, the stability of the glass may be lowered. More preferably, it is 1.625 or less, typically 1.615 or less.

The τ of the glass of the present invention is preferably 0.5 ms or more. If it is less than 0.5 ms, the laser oscillation threshold may be increased. More preferably, it is 1 ms or more. Further, τ is preferably 2 ms or less. If it exceeds 2 ms, A _rad may be small and the laser output may be low. More preferably, it is 1.5 ms or less.

  The glass of the present invention preferably has a Vickers hardness (Hv) of 500 or more. If it is less than 500, the glass is easily scratched in the polishing process, the melt drawing process, and the fiber forming process. More preferably, it is 550 or more, Especially preferably, it is 600 or more. Moreover, it is preferable that Hv is 700 or less. If it is less than 700, the Young's modulus is high and there is a risk of weakening to thermal shock. More preferably, it is 650 or less.

The fracture toughness (Kc) of the glass of the present invention is preferably ^0.5 MPa · m ^0.5 or more. If it is less than ^0.5 MPa · m ^0.5 , when the glass is scratched in the glass polishing process, the melt drawing process, or the fiber forming process, the scratch is likely to extend, and the control range of the processing process is narrowed. Alternatively, the yield may be reduced. More preferably 0.53 MPa ^{· m 0.5} or more, particularly preferably 0.55 MPa ^{· m 0.5} or more. On the other hand, Kc is preferably 0.65 MPa · m ^0.5 or less. If it exceeds 0.65 MPa · m ^0.5 , the viscosity of the glass becomes too high, and there is a risk that the workability such as the polishing process, the fiber forming process, and the melt drawing process will deteriorate. More preferably, it is 0.60 MPa · m ^0.5 or less.

Next, the composition of the glass of the present invention will be described using the mole percentage display content.
P ₂ O ₅ is a main component (glass-forming oxide) that forms glass and a component that improves Hv and Kc, and is essential. If it is less than 50%, the glass tends to be devitrified and the glass may become unstable. Preferably it is 53% or more, More preferably, it is 56% or more, Most preferably, it is 59% or more. If it exceeds 65%, it becomes difficult to obtain a desired refractive index, or chemical durability is lowered. Preferably it is 62% or less, More preferably, it is 60% or less.

Al ₂ O ₃ is a component that improves Hv, Kc or chemical durability, and is essential. Al ₂ O ₃ is preferably 7% or more, more preferably 9% or more, and particularly preferably 11% or more. If Al ₂ O ₃ exceeds 20%, the glass becomes unstable. Preferably it is 18% or less, More preferably, it is 16% or less.

B ₂ O ₃ has an effect of improving Hv and Kc or stabilizing the glass, and is essential. If it is less than 1%, the above effect is small. Preferably it is 2% or more, more preferably 3% or more, and particularly preferably 4% or more. If it exceeds 10%, the refractive index becomes small, or the chemical durability decreases. Preferably it is 8% or less, More preferably, it is 6% or less.

Li ₂ O is not essential, but has an effect of increasing the refractive index and softening the glass, and may be contained in a range of 10% or less. If it exceeds 10%, the chemical durability may be reduced. Preferably it is 8% or less, More preferably, it is 6% or less. When Li ₂ O is contained, the content is preferably 1% or more. If it is less than 1%, the effect may be insufficient. More preferably, it is 2% or more, further preferably 3% or more, and particularly preferably 4% or more.

Na ₂ O is not essential, but has an effect of increasing the refractive index and softening the glass, and may be contained in a range of 10% or less. If it exceeds 10%, the chemical durability may be reduced. Preferably it is 8% or less, More preferably, it is 6% or less. When Na ₂ O is contained, the content is preferably 1% or more. If it is less than 1%, the effect may be insufficient. More preferably, it is 2% or more, further preferably 3% or more, and particularly preferably 4% or more.

K ₂ O is a component having an effect of enhancing the light emission characteristics or refractive index of glass and softening the glass, and is essential. If it is less than 5%, the effect is small. Preferably it is 7% or more, More preferably, it is 9% or more, Most preferably, it is 11% or more. If it exceeds 20%, the chemical durability is lowered. Preferably it is 17% or less, More preferably, it is 15% or less.

The total content of Li ₂ O, Na ₂ O and K ₂ O is preferably 6 to 20%. If it is less than 6%, the effect of increasing the refractive index or the effect of softening the glass may be reduced. More preferably, it is 8% or more. If it exceeds 20%, the chemical durability may be lowered. More preferably, it is 18% or less, and particularly preferably 15% or less.

  MgO, CaO and SrO are not essential, but they have an effect of increasing the refractive index and may be contained in a range of 10% or less, respectively. If it exceeds 10%, the chemical durability may be lowered, or the glass may become unstable. Preferably each is 7% or less, more preferably 5% or less. Moreover, when it contains MgO, CaO, or SrO, Preferably each content is 1% or more, More preferably, it is 3% or more, Most preferably, it is 4% or more.

Nb ₂ O ₅ is indispensable because it has an effect of increasing the refractive index or light emission characteristics or improving Hv or Kc. If it is less than 2%, the effect is small. Preferably it is 3% or more, More preferably, it is 5% or more. If it exceeds 15%, the glass becomes unstable. Preferably it is 12% or less, More preferably, it is 9% or less.

Yb ₂ O ₃ is essential as an active substance. If it is less than 0.1%, the action as an active substance becomes insufficient, and there is a possibility that a high output cannot be obtained. Preferably it is 0.5% or more, More preferably, it is 1% or more, More preferably, it is 2% or more, Most preferably, it is 5% or more. If it exceeds 10%, the glass becomes unstable. Preferably it is 8% or less, More preferably, it is 6% or less.

La ₂ O ₃ is not essential, but has an effect of increasing the refractive index and may be contained within a range of 10% or less. If it exceeds 10%, the glass becomes unstable. Preferably it is 8% or less, More preferably, it is 6% or less. When La ₂ O ₃ is contained, the content is preferably 1% or more. More preferably, it is 2% or more, and particularly preferably 5% or more.

The glass of the present invention consists essentially of the above components, but may contain other components as long as the object of the present invention is not impaired. In such a case, the total content of the other components is preferably 5% or less, and typically 1% or less. For example, Sb ₂ O ₃ is not an essential component but can be added as a clarifier during glass melting. When Sb ₂ O ₃ is added, its content is preferably 0.01% or more, more preferably 0.05% or more, and preferably 1% or less, more preferably 0.5% or less.

It is preferable that SiO ₂ is not contained from the viewpoint of the molding temperature. For example, “not containing SiO ₂ ” means 0.05% or less even when SiO ₂ is contained.
Moreover, since BaO is a component which reduces Hv and Kc, it is preferable not to contain it.
Also, Nd ₂ O ₃ , Er ₂ O ₃ , V ₂ O ₅ , NiO, Co ₂ O ₃ , Cr ₂ O ₃ , CuO and CeO ₂ are components that may lower η, so do not contain any of them. Is preferred.
Moreover, it is preferable not to contain any of F ₂ , PbO and As ₂ O ₃ from the viewpoint of environmental aspects.

The method for producing the present glass is not particularly limited. For example, raw materials used in ordinary optical glass such as oxides, hydroxides, carbonates, nitrates, and phosphates are weighed and mixed, and crucibles used in ordinary optical glass production such as platinum crucibles, quartz crucibles, and alumina crucibles. And then melted, clarified and stirred at about 1200 to 1500 ° C. for 2 to 10 hours, cast into a mold preheated to 500 to 600 ° C., and then gradually cooled to produce.
The method for producing the double clad optical fiber of the present invention is not particularly limited. For example, a melted glass is polished and then melt-drawn to produce a preform, which is drawn into an optical fiber.

  Examples of the present invention will be described below. Examples 1 to 15 are examples of the present invention, and Example 16 is described as Example 27 in Japanese Patent Laid-Open No. 8-26768 and is a comparative example.

[Chemical composition and sample preparation]
The raw materials were weighed so as to have the chemical composition (mol%) shown in Table 1. Raw material of each _glass, P 2 in the case of _{O 5 H} 3 PO ₄ or BPO ₄ or Al _{(PO 3)} 3 or KPO _3, in the case of _Al 2 _{O 3 Al} 2 _{O 3} or Al _{(PO 3)} 3 H ₃ BO ₃ or BPO ₄ for B ₂ O ₃ , KCO ₃ or KPO ₃ for K ₂ O, SrCO ₃ for SrO, BaCO ₃ for BaO, K ₂ O In this case, K ₂ CO ₃ or KPO ₃ was used, in the case of SrO, SrCO ₃ was used, and in the case of Nb ₂ O ₅ , Yb ₂ O ₃ and ZnO, these oxides themselves were used.

  Weighed raw materials were mixed, put in a platinum crucible with an internal volume of about 300 cc, melted, clarified and stirred at about 1200-1500 ° C. for 2-3 hours, then preheated to about 500-600 ° C. length 100 mm × width 50 mm × After casting into a rectangular mold with a height of 20 mm, it was gradually cooled at about 1 ° C./min to prepare a sample. About the solubility of glass, etc., as a result of visual observation at the time of the above sample preparation, there is no problem in solubility for any of Examples 1 to 16, and the obtained glass sample has no bubbles or striae It was confirmed.

[Evaluation method]
Refractometer refractive index n _d for the helium d line (Kalnew Optical Industry Co., Ltd., trade name: KRP-2) was measured in. The value of the refractive index was measured to the fourth decimal place and rounded off to the third decimal place.

The fluorescence lifetime τ (ms) was calculated from the time decay curve of the fluorescence intensity of the ² F _5/2 → ² F _7/2 transition. Excitation was performed at a wavelength of 980 nm, and monitoring was performed at a wavelength of 1020 to 1060 nm where the emission intensity was strongest. Excitation was performed with a pulse of τ / 10 or less, and light emission from the sample was dispersed with a spectroscope (xxx manufactured by SPEX), and detected with an InGaAs photodiode (IGA-020-A manufactured by Electro-Optical-System). The signal was taken into a digital oscilloscope (TDS520 manufactured by Electronics), and the obtained attenuation curve was subjected to least square fitting with a single exponential function to obtain a fluorescence lifetime.

Vickers hardness Hv (GPa) was evaluated by an indentation test method using a Vickers hardness measuring machine (trade name: MVK-H2 manufactured by AKASHI). Specifically, a Vickers indenter was pushed into a smooth sample surface at a room temperature and in an air atmosphere at an indentation load of 25 g and an indentation time of 15 seconds. Measurement was performed 5 times per sample, and Vickers hardness was determined from the average of 3 points excluding the maximum and minimum values.
Vickers hardness Hv (GPa) = (1.854 P / d2) × 9.8.
Here, P is the indentation load (kg), and d is the diagonal length (mm) of the indentation.

Fracture toughness Kc (MPa · mm ^1/2 ) was determined by using a Vickers hardness measuring machine (manufactured by AKASHI, trade name: MVK-H2) to generate cracks with an indentation load P of 0.2 kg. The diagonal length 2a (m) and the crack length 2c (m) 30 s after unloading were measured and calculated by the following equation using the Young's modulus E (Pa) obtained by the ultrasonic pulse method. The measurement is performed at room temperature in an air atmosphere and satisfies c / a> 2.5. The measurement was performed five times per sample, and the fracture toughness was determined from the average of three points excluding the maximum value and the minimum value.
Fracture toughness Kc = 0.026 × E ^1/2 × P ^1/2 × a / c ^3/2 .
Here, P is the indentation load (kg), a is the diagonal length (m) of the indentation, and c is half the crack length (m). Kc may be labeled as K _IC .

  The glass of the present invention can be used for a laser. The double clad optical fiber of the present invention can be used for a high-power fiber laser.

Claims (11)

A molar percentage based on the following _oxides, P 2 _{O 5} 50 to 65% of _{Al 2 O 3 5~20%, B} 2 O 3 1-10% 0-10% of Li ₂ O, Na ₂ O 0-10%, K ₂ O 5-20%, MgO 0-10%, CaO 0-10%, SrO 0-10%, Nb ₂ O ₅ 2-15%, Yb ₂ O ₃ 0.1 to 10%, the glass for laser containing _La 2 _{O 3} 0%. Laser glass according to claim 1 containing no SiO _2.   The glass for laser according to claim 1 or 2, which does not contain BaO. _{Nd 2 O 3, Er 2 O} 3, V 2 O 5, NiO, Co 2 O 3, Cr 2 O 3, CuO and none of CeO ₂ not containing claim 1, 2 or 3 of the glass for laser. F _2, PbO and _As 2 _O none of ₃ free claims 1 to 4 of the laser glass.   The laser glass according to any one of claims 1 to 5, wherein a refractive index with respect to helium d-line is 1.52 to 1.64.   The glass for laser according to any one of claims 1 to 6, which has a fluorescence lifetime of 0.5 ms or more.   The glass for laser according to any one of claims 1 to 7, which has a Vickers hardness of 500 or more. The glass for laser according to any one of claims 1 to 8, which has a fracture toughness of 0.5 MPa · m ^0.5 or more.   A fiber laser having a laser medium, a resonator, and an excitation light source, wherein the laser glass according to claim 1 is used as the laser medium.   The double clad optical fiber which uses the glass for lasers in any one of Claims 1-9 as a core glass.