JP2009188094A - Optical fiber for optical amplification and optical fiber laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber for optical amplification that is suppressed in an increase in loss caused by photo-darkening without deteriorating conversion efficiency, and an optical fiber laser using the same. <P>SOLUTION: The optical fiber 1 for optical amplification executes the incidence and transmission of an exciting light of ≥400 nm and ≤2,000 nm. The optical fiber 1 for optical amplification has a core 2 containing deuterium molecules and at least one kind of rare-earth ion, and a clad 3 covering the outer periphery of the core 2. The core is contains deuterium molecules. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber for optical amplification in which an increase in core loss due to photodarkening is suppressed in incident and transmission of excitation light having a wavelength of 400 nm to 2000 nm, and an optical fiber laser using the optical fiber.

  Optical fiber lasers have the advantages of higher efficiency than conventional solid-state lasers, as well as superior beam quality, output stability, and cooling efficiency, and their applications are rapidly expanding in recent years. However, there is a problem that the transmission loss of the core gradually increases with the incidence and transmission of the excitation light to the optical fiber, and as a result, the laser output decreases. This increase in core loss due to the incidence and transmission of excitation light is generally called photodarkening.

  Regarding photodarkening, for example, non-patent literature 1 reports optical darkening of an optical fiber added with Tm, and non-patent literatures 2 and 3 report optical darkening of an optical fiber added with Yb. Regarding the mechanism of photodarkening, it is believed that the main cause is the generation of defects in the optical fiber, but it is not completely clear.

  As a means for suppressing photodarkening, a method of containing hydrogen molecules or oxygen molecules in an optical fiber is known. For example, Patent Document 1 discloses a method for suppressing photodarkening by containing hydrogen molecules in the core. Non-Patent Document 3 reports suppression of photodarkening in a Yb-doped optical fiber containing oxygen molecules.

  On the other hand, it has been reported that in an optical fiber for ultraviolet transmission, damage and deterioration of glass due to ultraviolet rays are suppressed by containing hydrogen molecules in the optical fiber. For example, Patent Document 2 discloses an optical fiber for ultraviolet transmission in which an optical fiber is accommodated in a metal pipe filled with high-pressure hydrogen gas.

  Patent Document 3 discloses an optical fiber for transmitting ultraviolet light having a wavelength of 170 nm or more and 350 nm or less, wherein the optical fiber contains hydrogen molecules and a hydrogen diffusion prevention layer is provided on the outer peripheral surface of the cladding. An optical fiber is disclosed.

Further, Patent Document 4 discloses an optical fiber for ultraviolet transmission having a hydrogen retaining layer on the outer peripheral surface of the clad and further providing a hydrogen blocking layer on the outer periphery thereof.
JP 2007-114335 A JP-A-6-34830 JP-A-9-309742 JP 2003-19297 A M.M. M.M. Broer, et al. "Highly linear near-resonant photodarkening in a thulium-doped aluminumsilicate glass fiber", Optics Letters 18, 799-801 (1993). Koponen, et al. , “Measuring photodarkening from ytterbium doped silica fibers”, Optics Express 14, 11539-11544 (2006). S-Yoo, et al. , “Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation”, Optics Letters 32, 1626-1628 (2007).

  Patent Document 1 discloses a method for suppressing photodarkening by including hydrogen molecules in an optical fiber. However, when hydrogen molecules are included in an optical fiber, hydrogen molecules are used in a wide range of wavelengths from 1000 nm to 2000 nm. Absorption by occurs. Accordingly, in the optical fiber for optical amplification, hydrogen molecules in the optical fiber absorb the light depending on the wavelengths of the excitation light and the signal light, and as a result, the conversion efficiency is lowered.

  Non-Patent Document 3 discloses a method of suppressing photodarkening by incorporating oxygen molecules into an optical fiber, but has a drawback that the effect of suppressing photodarkening of oxygen molecules is inferior to that of hydrogen molecules.

  Patent Documents 2, 3, and 4 disclose optical fibers provided with a container or coating that prevents escape of hydrogen molecules from the optical fiber. In these publications, an optical fiber for ultraviolet transmission is disclosed. The technical idea for suppressing photodarkening in optical fibers for optical amplification used in the visible and infrared wavelength regions with wavelengths of 400 nm to 2000 nm. Is not described at all.

  Accordingly, an object of the present invention is to provide an optical fiber for optical amplification in which an increase in loss due to photodarkening is suppressed without reducing conversion efficiency, and an optical fiber laser using the optical fiber.

  In order to achieve the above object, the present invention is characterized in that a deuterium molecule is contained in a core in an optical fiber for optical amplification that performs incidence and transmission of excitation light of 400 nm or more and 2000 nm or less.

Specifically, an optical fiber for optical amplification according to the present invention includes a core containing deuterium molecules and at least one kind of rare earth ions, and a clad covering the outer periphery of the core.
When the core contains rare earth ions, propagation light having a wavelength of 400 nm or more and 2000 nm or less can be amplified by stimulated emission of the rare earth ions. Furthermore, since the core contains deuterium molecules, it is possible to suppress an increase in loss due to photodarkening without reducing the conversion efficiency in a wide range from 400 nm to 2000 nm.

In the optical fiber for optical amplification according to the present invention, it is preferable that a diffusion prevention layer for preventing permeation of deuterium molecules is provided on the outer periphery of the cladding.
Since the diffusion preventing layer is provided, escape of deuterium molecules from the optical fiber for optical amplification can be prevented.

In the optical fiber for optical amplification according to the present invention, it is preferable that the diffusion prevention layer contains one or more of aluminum, titanium, copper, chromium, tin, nickel, silver, gold, and carbon.
When the diffusion preventing layer contains a material having high thermal conductivity, heat generated from the optical amplification optical fiber can be efficiently removed.

In the optical fiber for optical amplification according to the present invention, a protective coating layer containing at least one of urethane acrylate resin, fluorine resin, silicone resin, epoxy resin and polyimide resin is provided between the clad and the diffusion preventing layer. It is preferable to have.
Since the protective coating layer is provided, the mechanical strength of the core and the clad can be increased. Further, by providing the protective coating layer between the clad and the diffusion preventing layer, it becomes easy to manufacture an optical amplification optical fiber having the diffusion preventing layer and the protective coating layer.

In the optical fiber for optical amplification according to the present invention, it is preferable that the concentration of deuterium molecules contained in the core is 1 × 10 ¹⁴ molecules / cm ³ or more.
When the concentration of deuterium molecules is 1 × 10 ¹⁴ molecules / cm ³ or more, it is possible to reduce the possibility that the effect of suppressing loss increase due to photodarkening is reduced.

In the optical fiber for optical amplification according to the present invention, it is preferable that the host glass of the core is quartz glass.
Since the host glass of the core is quartz glass, it is possible to share the production equipment with the usual quartz optical fiber for optical transmission, and it is excellent in economic efficiency.

In the optical fiber for optical amplification according to the present invention, it is preferable that the rare earth ions contained in the core include one or more of Yb ions, Eu ions, Tb ions, Tm ions, and Er ions.
When the rare earth ions contained in the core are any one or more of Yb ions, Eu ions, Tb ions, Tm ions, and Er ions, propagating light having a wavelength of 400 nm or more and 2000 nm or less can be amplified.

In the optical fiber for optical amplification according to the present invention, it is preferable that the clad is formed of at least two layers having different refractive indexes.
Since the clad is a multi-clad fiber formed of two or more layers, rare earth ions existing in the core can be excited. By using a multi-clad fiber for an optical fiber laser, high-power multimode laser diode light can be used as excitation light.

Specifically, an optical fiber laser according to the present invention includes the optical amplification optical fiber according to the present invention, and a pumping light source that emits pumping light that pumps the optical amplification optical fiber.
Since the optical fiber for optical amplification according to the present invention is provided, an increase in loss due to photodarkening can be suppressed without reducing the conversion efficiency. Therefore, it is possible to provide a highly efficient optical fiber laser that does not cause a decrease in laser output over a long period of time.

In the optical fiber laser according to the present invention, the wavelength of the excitation light emitted from the excitation light source is preferably 400 nm or more and 2000 nm or less.
Since the optical fiber for optical amplification suppresses photodarkening in a wide range from 400 nm to 2000 nm, it is possible to provide a highly efficient optical fiber laser that does not cause a decrease in laser output in a wide range from 400 nm to 2000 nm. .

  ADVANTAGE OF THE INVENTION According to this invention, the optical fiber for optical amplification which suppressed the loss increase by photodarkening, without reducing conversion efficiency can be provided.

  Further, according to the present invention, by using the optical fiber for optical amplification, it is possible to provide a highly efficient optical fiber laser that does not cause a decrease in laser output over a long period of time.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment. FIG. 1 is a cross-sectional view of an optical fiber according to the first embodiment. The optical amplification optical fiber 1 according to the first embodiment includes a core 2, a cladding 3, a protective coating layer 4, and a diffusion prevention layer 5 in order from the center of the optical amplification optical fiber 1. Hereinafter, each of the above items will be described.

The core 2 contains deuterium molecules and at least one rare earth ion. The concentration of deuterium molecules contained in the core 2 is preferably 1 × 10 ¹⁴ molecules / cm ³ or more, particularly preferably 1 × 10 ¹⁶ molecules / cm ³ or more. If the concentration of deuterium molecules is less than 1 × 10 ¹⁴ molecules / cm ³ , the effect of suppressing loss increase due to photodarkening may be reduced. In addition, quartz glass is used as a host glass, and at least one kind of rare earth ions is included. The rare earth ions are preferably selected from any of Yb ions, Eu ions, Tb ions, Tm ions, and Er ions.

  The diameter of the core 2 is not particularly limited. In the case of a single mode optical fiber, for example, it can be in the range of 1 μm to 20 μm, preferably 3 μm to 15 μm. In the case of a multimode optical fiber, it can be in the range of, for example, 10 μm to 500 μm, preferably 20 μm to 100 μm. The thickness of the clad 3 is also not particularly limited, and can be, for example, in the range of 10 μm to 300 μm, preferably 60 μm to 200 μm. The optical fiber for optical amplification 1 is preferably a multi-clad fiber in which the cladding 3 is formed of at least two layers having different refractive indexes in order to increase the amplification factor.

  The protective coating layer 4 is not essential in the present invention, but is provided between the clad 3 and the diffusion prevention layer 5 and is one or more of urethane acrylate resin, fluororesin, silicone resin, epoxy resin, and polyimide resin. It is preferable to use a resin composed of The protective coating layer 4 is provided for the purpose of ensuring the mechanical strength of the optical amplification optical fiber 1. The thickness of the protective coating layer 4 is not particularly limited, and can be, for example, in the range of 1 μm to 300 μm, preferably 2 μm to 100 μm.

  The diffusion preventing layer 5 prevents the permeation of deuterium molecules. As what prevents the permeation | transmission of a deuterium molecule, they are aluminum, titanium, copper, chromium, tin, nickel, silver, gold | metal | money, carbon, or these combination, for example. The thickness of the diffusion preventing layer 5 is not particularly limited as long as it is a film thickness sufficient to prevent external diffusion of deuterium molecules. For example, when the diffusion preventing layer 5 is composed of one or more of aluminum, titanium, copper, chromium, tin, nickel, silver and gold, the thickness of the diffusion preventing layer 5 is 0.1 μm or more and 100 μm or less. Preferably, it can be in the range of 1 μm or more and 50 μm or less. When the diffusion preventing layer 5 is made of carbon, the thickness of the diffusion preventing layer 5 can be in the range of 0.001 μm to 0.1 μm.

The optical fiber 1 for optical amplification having the above-described characteristics can hold deuterium molecules in the core 2 over a long period of time, and can suppress an increase in loss due to photodarkening over a long period of time.
In addition, in order to form the diffusion prevention layer 5 inside the protective coating layer 4, it is necessary to incorporate the formation process of the diffusion prevention layer 5 in the spinning process, so that the production is difficult. On the other hand, the step of forming the diffusion preventing layer 5 outside the protective coating layer 4 can be performed after the spinning step. Therefore, it is preferable that the diffusion prevention layer 5 is disposed outside the protective coating layer 4.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited only to the examples. In this example, four types of optical fibers were produced and evaluated for each. The evaluation results of the optical fiber are shown in FIGS.

Example 1
The optical fiber according to Example 1 is the optical fiber for optical amplification according to the embodiment.
In the production of the optical fiber for optical amplification, the production of the optical fiber, the deuterium molecule addition treatment, and the formation of the diffusion prevention layer were carried out in order. First, manufacture of an optical fiber will be described. Soot was deposited on the inner wall of the quartz tube using high purity silicon tetrachloride (SiCl ₄ ) as a raw material by an internal chemical vapor deposition (MCVD) method. The quartz tube on which this soot was deposited was immersed in an aqueous solution of Yb and Al and then dried, and an optical fiber preform in which Yb and Al were added to the core through a collapse process was produced. The base material was melt-drawn, and a protective coating layer was formed on the clad surface with a UV curable resin to form an optical fiber. The optical fiber has a clad diameter of 125 μm and a core diameter of 7.9 μm, and the relative refractive index difference between the core and the clad is 0.30%. The concentrations of Yb and Al added to the core were 2.0% by mass and 1.7% by mass, respectively.

  In the deuterium molecule addition treatment, the optical fiber obtained as described above is loaded into a stainless steel container and treated for 72 hours under conditions of 100% deuterium gas, 100 atm and 80 ° C. Deuterium molecules were infiltrated into the core.

  In the formation of the diffusion preventing layer, the diffusion preventing layer having a thickness of 30 μm was formed by performing copper plating on the outer peripheral surface of the optical fiber after the above deuterium molecule addition treatment.

  The evaluation results of the optical amplification optical fiber manufactured as described above are shown in FIG. The evaluation results indicate transmission loss after the excitation light from the excitation light source is incident and photodarkened. An LD was used as the excitation light source. The excitation wavelength of the excitation light source was 980 nm, the excitation light power was 400 mW, and the irradiation time was 100 minutes. The transmission loss at a wavelength of 800 nm is suppressed to a low value of 1.6 dB / m as shown in FIG. 3 after the deuterium treatment.

(Example 2)
For comparison, transmission loss after optical darkening was measured for the optical fiber manufactured in the same manner as in Example 1 except that the deuterium molecule addition treatment was not performed. As shown in FIG. 3, the loss at a wavelength of 800 nm was a large value of 5.0 dB / m.

(Example 3)
In the deuterium molecule addition treatment, except that the treatment was performed for 72 hours under the conditions of 100% hydrogen gas, 300 atm, and 65 ° C., an optical fiber was produced and a diffusion prevention layer was formed in the same manner as in Example 1, The transmission loss after photodarkening was measured in the same manner as described above. As shown in FIG. 3, the loss at a wavelength of 800 nm was 0.8 dB / m, which was lower than that in Example 1.

Example 4
The optical fiber for optical amplification according to Example 4 differs from Example 1 in the production of the optical fiber and the formation of the diffusion prevention layer. An optical fiber manufacturing method will be described. Soot was deposited on the inner wall of the quartz tube using high purity silicon tetrachloride (SiCl ₄ ) as a raw material by an internal chemical vapor deposition (MCVD) method. The quartz tube on which the soot was deposited was dipped in an aqueous solution of Yb and Al and then dried, and an optical fiber preform in which Yb and Al were added to the core 2 was manufactured through a Collabs process. The base material was melt-drawn, and a diffusion barrier layer was formed by forming a carbon coating around the cladding by a CVD method of a hydrocarbon gas raw material.

  In the deuterium molecule addition treatment, the optical fiber obtained as described above was subjected to deuterium molecule addition treatment for 72 hours under the conditions of 100% hydrogen gas, 300 atm, and 65 ° C.

  In the same manner as in Example 1, the transmission loss after photodarkening was measured. As shown in FIG. 3, the transmission loss at a wavelength of 800 nm was 0.7 dB / m, which was lower than those in Examples 1 and 3.

It is sectional drawing perpendicular | vertical to the longitudinal direction which shows an example of the optical fiber for optical amplification concerning this embodiment. It is a graph which shows the evaluation result of the optical fiber for optical amplification which concerns on Example 1, and shows the wavelength dependence of the loss in each optical fiber which performed the deuterium molecule addition non-processing and the deuterium molecule addition process. It is an evaluation result of each optical fiber which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber for optical amplification 2 Core 3 Clad 4 Protective coating layer 5 Diffusion prevention layer

Claims (10)

A core containing deuterium molecules and at least one rare earth ion;
An optical fiber for optical amplification comprising: a clad covering an outer periphery of the core.   The optical fiber for optical amplification according to claim 1, further comprising a diffusion prevention layer that prevents permeation of deuterium molecules on an outer periphery of the clad.   3. The optical fiber for optical amplification according to claim 2, wherein the diffusion prevention layer includes at least one of aluminum, titanium, copper, chromium, tin, nickel, silver, gold, and carbon.   The protective coating layer containing any one or more of urethane acrylate resin, fluororesin, silicone resin, epoxy resin, and polyimide resin is provided between the clad and the diffusion prevention layer. The optical fiber for optical amplification as described. 5. The optical fiber for optical amplification according to claim 1, wherein the concentration of deuterium molecules contained in the core is 1 × 10 ¹⁴ molecules / cm ³ or more.   6. The optical fiber for optical amplification according to claim 1, wherein the host glass of the core is quartz glass.   7. The light according to claim 1, wherein the rare earth ions contained in the core are any one or more of Yb ions, Eu ions, Tb ions, Tm ions, and Er ions. Optical fiber for amplification.   The optical fiber for optical amplification according to any one of claims 1 to 7, wherein the clad is formed of at least two layers having different refractive indexes. An optical fiber for optical amplification according to any one of claims 1 to 8,
An excitation light source that emits excitation light for exciting the optical fiber for optical amplification;
An optical fiber laser comprising:   The optical fiber laser according to claim 9, wherein the wavelength of the excitation light emitted from the excitation light source is 400 nm or more and 2000 nm or less.

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