JP3881584B2 - Processing method of ferrule for optical fiber and processing method of optical fiber pigtail - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for processing a ferrule for an optical fiber used for optical communication and a method for processing an optical fiber pigtail.
[0002]
[Prior art]
In recent years, optical communication using an optical fiber has been used with an increase in the amount of information in communication. In this optical communication, an optical connector is used to connect optical fibers or connect an optical fiber and various optical elements.
[0003]
As shown in FIGS. 1 and 2, the optical fiber fixture 6 used in the optical connector is obtained by fixing the support 2 to the ferrule 1, and the optical fiber pigtail 10 has a through hole 1 a of the optical fiber fixture 6. The end portion of the optical fiber 3 is held and fixed by an adhesive 4 and a pair of ferrules 1 are inserted from both ends of the sleeve 5 so that the tip surfaces 1d processed into a convex spherical shape are brought into contact with each other. It has become.
[0004]
Various materials such as ceramics, metals, plastics, and glasses have been made as materials for the ferrule 1, but most of them are made of ceramics at present. The reason for this is that ceramics have a high processing accuracy, so the tolerance of the inner and outer diameters can be as high as 1 μm or less, and ceramics have a low coefficient of friction, so they have excellent optical fiber insertability, high rigidity, and high heat. This is because the expansion coefficient is low, so that it is stable against external stress and temperature change, and has excellent corrosion resistance.
[0005]
Furthermore, even if the material is ceramics, in recent years, most of alumina has been replaced by zirconia. Since this zirconia sintered body has a Young's modulus as low as about half that of alumina, when the tip surfaces 1d of the two ferrules are brought into contact with each other, the adhesion can be increased with a small stress, and the strength and toughness are high. Therefore, reliability can be improved (see Japanese Patent Publication No. 8-30775).
[0006]
As the zirconia sintered body used for the optical ferrule 1, about 2.5 to 3.5 mol% (about 4.5 to 6.2 wt%) of Y ₂ O ₃ as a main component containing ZrO ₂ is used. A partially stabilized zirconia sintered body mainly composed of a tetragonal crystal phase in which a raw material contained is molded and fired to have an average crystal grain size of 0.4 to 0.6 μm has been proposed (Japanese Patent Laid-Open No. 6-337327). No. publication).
[0007]
Further, a tetragonal crystal phase obtained by forming and firing a raw material in which 0.2 to 0.3% by weight of Al ₂ O ₃ is added to a raw material containing ZrO ₂ as a main component and Y ₂ O ₃ as a stabilizer. There has been proposed a partially stabilized zirconia for ferrule 1 mainly composed of (see Japanese Patent Application Laid-Open No. 10-260336).
[0008]
Furthermore, in the zirconia sintered body used for the ferrule 1 containing ZrO ₂ as a main component and Y ₂ O ₃ as a stabilizer, the Y ₂ O ₃ concentration in the tetragonal phase was maintained at 3.0 mol% or more. Partially stabilized zirconia has been proposed (see Journal of the Ceramic Society of Japan, September 1999 issue).
[0009]
Even when zirconia having any of the above compositions is used, the tip surface 1d is preliminarily formed into a spherical shape by grinding the ferrule alone, and then the optical fiber 3 is inserted into the through hole 1a and fixed with the adhesive 4 Thereafter, the front end surface 1 d was finished and polished together with the front end surface of the optical fiber 3 to form an optical fiber pigtail 10.
[0010]
When finishing the front end face 1d of the optical fiber pigtail 10, a work hardened layer is formed on the optical fiber 3, so that the refractive index changes and the optical fibers 3 come into contact with each other as optical connectors. Since the reflected return light is generated from the high portion of the optical fiber, the high refractive index layer can be removed by polishing the final finish using SiO ₂ , and the tip surface of the optical fiber 3 and the ferrule 1 The pulling amount with the front end surface 1d could be suppressed to ± 50 nm or less.
[0011]
[Problems to be solved by the invention]
However, in any of the above-described conventional examples, when the partially stabilized zirconia sintered body containing Y ₂ O ₃ is exposed to a high-temperature atmosphere in which moisture exists, the tetragonal crystal is transformed into a monoclinic crystal. Thus, there is a problem that properties such as strength and toughness deteriorate.
[0012]
Further, since the above optical connector may be used in a bad environment for a long time depending on the usage, a pair of ferrules 1 are inserted from both ends of the sleeve 5 as an acceleration test, and a convex spherical shape is formed inside. There is a case where an optical connector in a state where the front end surfaces 1d processed into a contact with each other are exposed to hot water at 80 ° C. may be subjected to a test. At this time, the ferrule 1 made of a zirconia sintered body has a phenomenon in which the abutting portion of the tip surface 1d is deformed by the above-described phase transformation, and the radius of curvature of the convex spherical surface of the ferrule tip surface 1d is increased. As a result, there is a problem in that connection failure and excessive connection loss occur.
[0013]
[Means for Solving the Problems]
Therefore, the present invention has been made in view of the above problems, and according to the method for processing an optical fiber ferrule of the present invention, a zirconia ceramic made of a through hole provided in the axial direction to hold the optical fiber. the front end face of the ferrule after grinding convex, to produce a rhombohedral phase to the tip surface by 1 × 10 13 irradiated ^{to 1} × 10 ¹⁷ ions / cm ² high energy ions in the tip end surface Then , the tip surface is polished .
[0014]
Next, in the optical fiber pigtail of the present invention, the rear end portion of the ferrule made of zirconia ceramic having a through hole in the axial direction is fixed to the support, and the front end of the optical fiber protrudes forward from the front end surface of the ferrule. In this state, an optical fiber is bonded and fixed in the through hole, and the protruding optical fiber and the tip surface of the ferrule are ground into a substantially convex spherical shape, and then high-energy ions are applied to the tip surface at 1 × 10 ^13. After the formation of a rhombohedral crystal phase on the tip surface by irradiation with ˜1 × 10 ¹⁷ ions / cm ² , the tip surface is polished .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0016]
As shown in FIG. 1, the optical fiber fixture 6 is obtained by joining the rear end side of the ferrule 1 to a support. An optical fiber pigtail 10 is obtained by attaching the optical fiber 3 to the optical fiber fixture 6.
[0017]
The ferrule 1 has a through hole 1a for inserting the optical fiber 3 in the axial direction. The rear end side of the through hole 1a includes a conical portion 1b for facilitating insertion of the optical fiber 3, and an outer peripheral portion. A chamfered portion 1e that serves as a guide surface when the sleeve is inserted is provided at the boundary between 1c and the substantially convex spherical tip surface 1d, and the optical fiber 3 is inserted into the through hole 1a in the ferrule 1 of the optical fiber fixture 6. After fixing with the adhesive 4, the optical fiber pigtail 10 is polished by polishing the optical fiber 3 projected from the front end surface 1d of the ferrule 1 and the front end surface 1d into a convex spherical shape having a curvature radius of about 7 to 25 mm. Is formed.
[0018]
As shown in FIG. 2, the optical fibers 3 can be connected by inserting a pair of ferrules 1 from both ends of the sleeve 5 and pressing them with a spring or the like to bring the tip surfaces 1d into contact with each other.
[0019]
The material of the support 2 fixed to the rear part of the optical fiber fixture 6 is a metal such as stainless steel, a copper alloy with nickel plating, brass with nickel plating, or white with nickel plating. Can be used.
[0020]
The zirconia sintered body constituting the ferrule 1 of the optical fiber fixture 6 contains ZrO ₂ as a main component and Y ₂ O ₃ as a stabilizer, and is partially stabilized zirconia mainly composed of tetragonal crystals. Use ceramics. Moreover, when manufacturing the ferrule 1 made of such zirconia ceramics, it is obtained by using the above raw material powder, forming it into a predetermined shape by extrusion molding, injection molding, press molding or the like and then firing it.
[0021]
As the zirconia ceramics, those having an average crystal grain size of 0.1 μm to 1.0 μm and a porosity of 3% or less are applicable. Here, if the crystal grain size exceeds 1.0 μm, the gap between crystals becomes large and a good outer peripheral surface cannot be obtained, and the grain size is stably adjusted to 0.1 μm or less when pulverizing with a ball mill or the like when mixing raw materials. Since the crystal grows after firing and the diameter further increases, the thickness is set to 0.1 μm or more. The porosity represents the percentage of voids contained in the ferrule individual as a percentage. When the porosity exceeds 3%, the pore portion deteriorates the outer peripheral surface roughness.
[0022]
According to the method for processing an optical fiber ferrule of the present invention, the tip surface of a ferrule made of zirconia ceramic provided with a through hole in the axial direction to hold the optical fiber is ground into a convex shape, and then the height of the tip surface is increased. A rhombohedral phase is generated on the tip surface by irradiating energy ions with 1 × 10 ¹³ to 1 × 10 ¹⁷ ions / cm ² .
[0023]
Here, since rhombohedral zirconia is formed on the surface portion of zirconia, compressive residual stress is generated on the surface portion, and even if a tensile mechanical load acts on the zirconia, the surface easily It is possible to prevent cracks from occurring. In addition, the tip surface 1d has anti-deformability in hot water. Therefore, even if a tensile mechanical load is applied, the tensile stress on the surface does not increase. Therefore, the zirconia of the present invention has a feature that cracks are hardly generated from the surface and can withstand a larger tensile load.
[0024]
Therefore, the ferrule 1 of the present invention can withstand a larger tensile load. For example, the bending strength is improved by 10 to 40%, and the toughness value is improved by 2 to 3 times. Further, the strengthened ferrule 1 made of zirconia has a feature that even if the surface is damaged, the possibility that the scratch will develop into a crack that causes the zirconia to break is small. In addition, reinforced zirconia has a feature that it is not necessary to reduce the roughness of the finished surface because the notch sensitivity is small.
[0025]
FIG. 3 shows rhombohedral crystals in a lattice model. In the rhombohedral crystal, zirconium (Zr) 21 located at the center of each vertex and each surface and a sub-lattice in which a part thereof is replaced with yttrium (Y), and oxygen (O) atoms 22 are apexes therein. It is based on a fluorite structure consisting of sublattices arranged in The lattice constant of the rhombohedral phase is a = 5.12-5.24 angstroms (Å) and α = 89.2-89.8 degrees. That is, the lattice volume of the rhombohedral crystal is 0.5 to 3% larger than that of the cubic and tetragonal structures.
[0026]
In the present invention, the rhombohedral crystal is produced by irradiating the tip surface of the zirconia member with high-energy ions to cause a processing-induced transformation from a cubic crystal structure and a tetragonal crystal structure.
[0027]
Here, the surface of the zirconia material is transformed into a rhombohedral phase by ion irradiation, and the volume is expanded by 0.5 to 3% compared to cubic and tetragonal crystals, so that compressive stress is generated on the surface portion and high energy ions The surface layer of the zirconia material undergoes volume expansion due to lattice defects generated by irradiation, and the volume expansion portion is constrained by the base material, so that compressive stress is generated in the surface layer portion.
[0028]
In general, ceramics such as zirconia are weak against tensile stress and easily generate cracks, but compressive stress has a relatively strong property, and this compressive stress becomes a residual compressive stress of 5 to 500 MPa.
[0029]
In addition, a cubic phase and a tetragonal phase are present together with the rhombohedral phase in the opening peripheral portion of the through hole 1a in the distal end surface 1d of the optical fiber fixture 6, and a monoclinic phase is included therein. It doesn't matter.
[0030]
Here, if the residual compressive stress is less than 5 MPa, the stress against thermal degradation is too small, and the effect on thermal degradation is small. If the residual compressive stress exceeds 500 MPa, the residual stress becomes excessive, leading to the destruction of zirconia. There is a fear.
[0031]
Note that the opening peripheral edge of the through hole 1a preferably has a diameter of at least 250 μm with the axis of the ferrule 1 as the center. Here, the diameter of 250 μm is set to 250 μm in consideration of a margin such as a center deviation because the diameter with which the tip surface 1d of the ferrule 1 of the pair of optical fiber pigtails 10 abuts within the sleeve 5 is about 200 μm.
[0032]
By the way, the conventional ferrule 1 made of zirconia has a rhombohedral phase formed on the front end surface 1d in order to perform grinding in the processing stage of the single end surface 1d. After fixing, when the tip surface 1d is polished together with the zirconia and the tip surface 1d of the optical fiber 4, the rhombohedral crystal phase generated during the processing of the bent ferrule 1 alone is removed. As a result, the optical fiber pigtail 10 is removed. When this is exposed to a high temperature and high humidity environment, there is a thermal degradation problem that the surface becomes rough. In addition, when exposed to a high temperature and high humidity environment in the state of contact as an optical connector, thermal degradation that causes a flattening phenomenon that the contacted part is plastically deformed and the size of the spherical surface increases. A problem has occurred.
[0033]
This is because a processing-affected layer at the front end surface of the optical fiber is generated during polishing, and the refractive index of the processed-affected layer is high, so that the light propagating through the optical fiber 3 is reflected back by the high-refractive index layer. Since the reflected return light becomes noise in the optical communication system, the work-affected layer, which is a high refractive index layer, can be removed by final polishing with a SiO ₂ abrasive paper during polishing, which is an optical connector. So it was common sense.
[0034]
However, since the final finish polishing also removes the rhombohedral phase that can suppress the thermal degradation of zirconia, the thermal degradation problem of the ferrule 1 described above occurs.
[0035]
According to the processing method of the present invention, it is possible to increase the thickness of the rhombohedral phase by further irradiating the rhombohedral phase generated by grinding with high energy ions. Therefore, even if the surface rhombohedral phase is partially removed by the final polishing of the optical fiber pigtail 10, the rhombohedral phase can be left.
[0037]
Here, a method for confirming the presence of rhombohedral crystal phase is that X-ray diffraction is performed on the ferrule tip surface 1d, and the peak positions of tetragonal crystal and cubic crystal overlap, and separation is performed using the Rietveld method. The rhombohedral peak can be confirmed on the low angle side of the tetragonal and cubic peaks.
[0038]
Further, the residual compressive stress was measured using X-ray diffraction, and Cr was used for the X-ray target. In the case of Cr, using the peak of the tetragonal crystal (213) plane, the angle (ψ) formed by the normal of the ferrule tip surface 1d and the lattice plane normal was changed, and the following formula was obtained from the measurement of 7 points.
[0039]
_{σ = - {Ecotθ 0/2} (1 + ν)} × (δ2θ / δsin 2 ψ)
Here, E is the Young's modulus of Cr, 15500 Kgf / mm ² , ν is the Poisson's ratio of Cr, 0.29, θ ₀ is the diffraction angle of zirconia in the unloaded state, and δ 2θ / δ sin ² ψ is a 2θ-sin 2ψ plot diagram. Use the slope obtained from.
[0040]
From the above, the residual compressive stress can be obtained.
[0041]
The confirmation of the rhombohedral crystal and the measurement of the residual compressive stress are not limited to the X-ray diffraction, and the same result can be obtained by a method performed by Raman spectroscopic analysis.
[0042]
Next, the processing method of the present invention will be described in detail.
[0043]
First, ZrO _{2 as} a starting material contains Al ₂ O ₃ , SiO ₂ , TiO ₂ , CaO, Na ₂ O, Fe ₂ O _3, etc. as impurities. Or purify it by techniques such as gravity beneficiation using the specific gravity difference. Then, ₃ to 5 mol% of Y ₂ O ₃ is added to ZrO ₂ and mixed and reacted and dissolved by a method such as neutralization coprecipitation or hydrolysis.
[0044]
Next, the obtained raw material is formed into a predetermined shape by extrusion molding, press molding, injection molding, or the like, and if necessary, cut or the like, and then fired in an air atmosphere.
[0045]
At this time, in order to obtain an average crystal grain size as small as 0.5 μm or less, it must be fired at a low temperature of 1200 to 1550 ° C. and a dense sintered body, but this reduces the primary particle size of the raw material. This can be achieved by increasing the specific surface area. The ferrule 1 can be obtained by further polishing and grinding the sintered body.
[0046]
Here, the firing temperature and the average crystal grain size are in a proportional relationship, and the average crystal grain size increases as the firing temperature increases. The zirconia sintered body of the present invention has an average particle size of 0.12 μm at a firing temperature of 1200 ° C., 0.23 μm at 1370 ° C., and 0.5 μm at 1550 ° C.
[0047]
Prior to ion irradiation, the surface of the tip surface 1d of the ferrule 1 is previously ground or polished to eliminate unevenness that causes stress concentration, and further washed with an organic solvent such as ethanol or acetone. It is good to keep.
[0048]
Further, at least the tip surface 1d is irradiated with high energy ions, but the entire portion of the ferrule 1 may be irradiated with the ions.
[0049]
The ion to be irradiated may be any ion that can be easily accelerated by an electric field. In particular, if it is in a gaseous state at room temperature, the irradiation work is easy. Specifically, helium (He), argon (Ar), xenon (Xe), neon (Ne), oxygen (O), nitrogen (N), boron (B), phosphorus (P), titanium (Ti ), Chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), or the like.
[0050]
As an example of ion irradiation, there is a method using the ion irradiation apparatus shown in FIG. 4. This apparatus mainly includes an ion generation unit 31, an ion extraction unit 32, an ion beam deflection unit 33, an acceleration unit 34, and an ion beam scanning unit 35. The irradiation vacuum chamber 36, the irradiation table 37, the ion beam current amount measuring unit 38, and the like, and the front end surface 1 d of the ferrule 1 as the irradiation object is installed on the irradiation table 37. The degree of vacuum of the ion irradiation vacuum chamber 36 is preferably about 1.33 × 10 ⁻⁴ torr.
[0051]
Ion irradiation can be performed using the above-described apparatus or the like. First, an ion source material is supplied to the ion generation unit 31 to be in a plasma state to form ions, and the ions are extracted to the outside by the ion extraction unit 32 to form an ion beam. These ions pass through the ion beam deflecting unit 33 and can select only the desired ion species. Further, only selected ions are guided to the acceleration unit 34 and accelerated at a desired acceleration voltage. In this way, the tip surface 19 is irradiated with ions having a desired type and desired energy as a beam. At this time, the ion beam scanning unit 35 scans the front end surface 1d to perform a desired amount of irradiation. The ion irradiation amount can be measured by the ion beam current amount measuring unit 38.
[0052]
The energy given to the ions is at least about 30 KeV to 1 MeV, and at most about 10 MeV due to the relationship between the penetration depth of the ions into the tip surface 1d and the damage given to the material. If it is 10 MeV or more, the zirconia material is thermally damaged, and conversely, its strength is lowered.
[0053]
The irradiation dose is preferably 1 × 10 ¹³ to 1 × 10 ¹⁷ ions / cm ² per 1 cm ^{3 of} irradiation area. Irradiation with more than 1 × 10 ¹⁷ ions / cm ² does not significantly increase the strength of the zirconia material. Further, at 1 × 10 ¹³ ions / cm ² or less, since the amount is small, no remarkable improvement in strength is observed.
[0054]
By the above method, rhombohedral zirconia is induced in the surface layer of the tip surface 1d of the ferrule 1.
[0055]
The abundance ratio of the rhombohedral phase generated by the processing and the depth from the surface can be controlled by each of the above conditions.
[0056]
As mentioned above, although embodiment of this invention was illustrated, this invention is not limited to these embodiment. The present invention can be in any form without departing from the object of the invention.
[0057]
For example, according to the present invention, the processing method can be applied to both single mode and multimode.
[0058]
2 shows an optical connector for connecting the optical fibers 4 to each other, the ferrule 1 and the sleeve 2 may be used in an optical module for connecting an optical element such as a laser diode or a photodiode to the optical fiber. it can.
[0059]
The processing method of the present invention can be applied to various members used for connecting the optical fibers 3 or between the optical fiber 3 and various optical elements, and is not limited to the ferrule 1 described above. For example, the present invention can be applied to a splicer used for completely connecting the optical fibers 3 to each other, a dummy ferrule used for an optical module, and the like.
[0073]
【The invention's effect】
As described above, according to the processing method of the present invention, since the rhombohedral phase is generated on the tip surface of the ferrule by irradiating the tip surface of the ferrule with high energy ions, the rhombohedral zirconia is formed on the surface portion of zirconia. Therefore, even if a compressive residual stress is generated in the surface portion and a tensile mechanical load acts on the zirconia, it is possible to prevent the surface from being easily cracked. In addition, the tip surface has anti-deformability in hot water.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an optical fiber pigtail having an optical fiber ferrule of the present invention.
FIG. 2 is a cross-sectional view showing an optical connector using the optical fiber pigtail of the present invention.
FIG. 3 shows a rhombohedral lattice model of the present invention.
FIG. 4 is a diagram showing a method for processing a ferrule used in the optical fiber fixture of the present invention.
FIGS. 5A and 5B are X-ray diffraction diagrams of a tip surface of an optical fiber pigtail of a conventional example. FIG.
[Explanation of symbols]
1: Ferrule 1a: Through hole 1b: Conical portion 1c: Outer peripheral portion 1d: Tip surface 1e: Chamfered portion 2: Support body 3: Optical fiber 4: Adhesive 5: Sleeve 6: Optical fiber fixture 10: Optical fiber pig Tail 21: Zirconium 22: Oxygen 31: Ion generator 32: Ion extractor 33: Ion beam deflector 34: Accelerator 35: Ion beam scanner 36: Irradiation vacuum chamber 37: Irradiation table 38: Ion beam current measurement Part

Claims (6)

After grinding the distal end surface of the zirconia ceramic ferrules having a axial to the through hole to hold the optical fiber in a convex shape, 1 high energy ions in the tip end surface ^× 10 13 ~1 × 10 ¹⁷ wherein after generating the rhombohedral the end surface processing method of the ferrule for optical fibers, characterized by polishing the front end surface by ion / cm ² irradiation. 2. The ferrule for an optical fiber according to claim 1, wherein the high energy ions are any one of He, Ne, Ar, Xe, B, N, P, O, Al, Ti, and Cr. Method. The method for processing a ferrule for an optical fiber according to claim 1, wherein the high energy ions have an energy of 30 KeV to 10 MeV. The rear end of a ferrule made of zirconia ceramic having a through hole in the axial direction is fixed to the support, and the optical fiber is bonded into the through hole with the front end of the optical fiber protruding forward from the front end surface of the ferrule. fixed, said after the a protruded optical fiber was distal end surface of the ferrule is machined on substantially convex spherical surface, be ¹ × 10 13 ~1 × 10 ¹⁷ ions / cm ² irradiation with high-energy ions in the tip end surface A method for processing an optical fiber pigtail , comprising: generating a rhombohedral phase on the tip surface by the step, and polishing the tip surface . 5. The processing of an optical fiber pigtail according to claim 4, wherein the high energy ions are any of ions of He, Ne, Ar, Xe, B, N, P, O, Al, Ti, and Cr. Method. 5. The method for processing an optical fiber pigtail according to claim 4, wherein the high energy ions have an energy of 30 KeV to 10 MeV.

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