JP3318617B2 - Ferrule for optical connector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, optical measurement, C
In fields such as ATV system, but about the ferrule for an optical connector used for optical fiber connection.

[0002]

2. Description of the Related Art Conventionally, ferrules for optical connectors used for connecting single mode optical fibers are fitted with ceramic materials such as zirconia and alumina, metal materials such as stainless steel, and amorphous materials such as glass. It was constituted by. Among them, zirconia is most widely used. This is because a low-loss connection of a single mode optical fiber requires a shape accuracy on the order of sub-μm and is excellent in strength, abrasion resistance and the like.

A conventional zirconia ferrule is JIS
FIG. 3 shows an example of the structure of a ferrule for an optical connector generally used for an F04 type single-core optical fiber connector specified in C 5973. This is configured by press-fitting a cylindrical rod-shaped fitting portion 6 made of zirconia into a metal flange 7.
However, precision processing of ceramic materials such as zirconia requires a number of difficult processes, and inevitably increases the processing cost. The appearance of a ferrule was expected.

Further, when the fitting portion of the ferrule for an optical connector is made of a metal such as stainless steel, the inner diameter is 125 μm.
Since high-precision drilling is required, which is as thin as about m and has a length of at least 30 times or more the inner diameter, it requires advanced technology and is an obstacle to cost reduction. Fig. 4 shows JIS C 59
An example of an alumina capillary type ferrule widely used at the beginning in the F01 type single core optical fiber connector specified in 70 is shown. The alumina capillary 8 having a fine through hole is press-fitted into a through hole of a stainless steel ferrule body 9 integral with a flange, and the outer periphery of the stainless steel ferrule body 9 integral with the flange is finished around the minute through hole. is there. In this case, since it is necessary to grind each piece, the manufacturing cost is higher than that of the zirconia ferrule described above. In addition, in the case of these metal ferrules, the generation of metal powder due to insertion and removal during actual use may cause connection failure, and in the case of high power connection, the metal powder generates heat and damages the optical fiber. It had drawbacks such as causing a problem.

Under such circumstances, a ferrule using a surface-reinforced borosilicate glass (JP-A-5-724) was developed.
No. 41), however, the glass material was inherently vulnerable to scratches, and had a drawback that its practical strength was reduced to about 1/10 of that of zirconia even if surface strengthening treatment was performed. Ferrules using quartz glass as a glass material have also been proposed (JP-A-55-22707, JP-A-63-500684), and are economical because of the simplicity of bonding optical fibers and polishing the end faces. Although it is reported that it is rich and has excellent environmental resistance such as temperature characteristics, the above-mentioned problem of strength has not been overcome.

On the other hand, in order to make the linear expansion coefficient of the fitting portion of the ferrule coincide with that of the optical fiber, a proposal has been made to use crystallized glass (Japanese Patent Application Laid-Open No. 63-500684). For this purpose, a brittle crystallized glass having insufficient strength was used, and the reliability was inferior in terms of strength, similarly to a glass material. Further, in order to compensate for the drawback, the outer periphery must be protected by a ductile material such as metal. Therefore, with such a design, it was not possible to form a ferrule fitting portion with high long-term reliability using only crystallized glass.

Although it is conceivable to use calcium phosphate crystallized glass for the fitting portion of the ferrule (Japanese Patent Application Laid-Open No. 1-288803), the strength of this material is also insufficient, and a stainless steel casing is not used. Cold press-fit
It was used by fitting. Also, after casting and molding into a cylindrical shape with a mold, the outer surface is polished and formed, and laser drilling is performed.
A plurality of processing steps, such as shaping the inner diameter by polishing, are individually required, and it is difficult to simplify the processing, and the cost reduction is not sufficient. Furthermore, alkali is a main component also in material, and it was inferior in chemical resistance, water resistance, etc., and had a defect in reliability.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to use a crystallized glass having excellent strength and reliability as a fitting portion of a ferrule for an optical connector. That is, the present invention is made of crystallized glass, which has never existed, in order to overcome the drawbacks of using the above-mentioned conventional type of material as a material for forming the fitting portion of the optical connector ferrule. Suitable for mass production utilizing the spinnability of glass, high processing accuracy can be realized, and strength, which was a drawback of the glass ferrule, can be improved 2.3 to 16 times as compared with the conventional one. the combined, economical, high processing precision, high weather resistance, it is intended to provide a ferrule for an optical connector having a high mechanical strength.

[0009]

SUMMARY OF THE INVENTION The present invention has a through hole having an inner diameter slightly larger than the outer diameter of an optical fiber at its center, and has a cylindrical rod-like shape for fitting and aligning with a split sleeve or the like. A structure in which a fitting part and a covering part of the optical fiber core wire are held inside, and a flange part for being held in the optical connector housing, wherein the fitting part and the flange part are fixed. In the ferrule for an optical connector having the cylindrical rod-shaped fitting portion, a surface of the fitting portion is provided.
An outer layer on the surface side and an inner layer having the through-hole.
The outer layer is made of a silicate-based, aluminosilicate-based, or phosphosilicate-based crystallized glass or partially crystallized glass, and the inner layer is a transparent silicate-based gas.
A ferrule for an optical connector characterized by being constituted by a lath .

The ferrule for an optical connector according to claim 1, wherein the SiO ₂ component of the crystallized glass or the partially crystallized glass is 40 wt% or more.

[0011] Further, the components of the crystallized glass or the partially crystallized glass are SiO ₂ ≧ 40 wt%, Al ₂ O ₃ ≦ 35 wt%
%, TiO ₂ ≦ 15 wt%, MgO ≦ 15 wt%, CaF ₂ ≦ 30 wt%
, Li ₂ O ≦ 20 wt%, P ₂ O ₅ ≦ 15 wt%, ZrO ₂ ≦ 9 wt%, K
₂ O ≦ 5 wt%, PbO ≦ 1 wt%, Na ₂ O ≦ 5 wt%, As ₂ O ₃ ≦
The ferrule for an optical connector according to claim 1 or 2, wherein the composition is in the range of 5 wt%, SnO ≦ 1 wt%, NaF ≦ 1 wt%, and LiF ≦ 1 wt%.

[0012]

As described above, in the ferrule for an optical connector according to the present invention, the cylindrical rod-shaped fitting portion is formed on the surface side of the fitting portion.
And an inner layer having the through hole ,
The outer layer is made of a silicate or aluminosilicate or phosphorus
Silicated or partially crystallized glass
Further, since the inner layer is made of a transparent silicate glass , the moldability is superior to that of the conventional zirconia ferrule, and particularly, it comes into contact with the sleeve in which the ferrule for an optical connector is fitted. Since the outer layer was made of strong "crystallized glass or partially crystallized glass",
Sufficient strength can be obtained as a ferrule for an optical connector.
Furthermore, the cylindrical rod-shaped inner layer in contact with the optical fiber is transparent.
Since the formed silicate glass, is irradiated with UV light from the end face of the optical connector ferrule, as UV light reaches the portion where the optical fiber contact via the silicate-based glass <br/> Las of the inner layer Thus, the UV-curable adhesive is cured, and the optical fiber can be bonded and fixed. In addition, the inner layer
Since the silicate glass has the same polishing characteristics of the end face as the optical fiber, the polishing process is simplified.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors of the present invention have studied the effect of the relative displacement between the fitting portion of the optical connector ferrule and the optical fiber during a thermal cycle. As a result, the coefficients of linear expansion do not necessarily have to match. I found something. That is, as described in JP-A-63-500684,
It does not mean "the difference must be within 20%". As a result of this examination, it was clarified that what was important was the absolute value of the difference in linear expansion coefficient, not the ratio.

The required value of the difference in linear expansion coefficient depends on the characteristics of the material used for the fitting portion of the ferrule, the conditions for polishing the end face, and the like. For example, the elastic modulus of the fitting portion is equivalent to that of the optical fiber. Assuming that the polishing radius of the end face is within 20 mm, the drawing amount of the optical fiber is 0.05 μm or less, and the pressing force between the ferrules at the time of coupling the optical connector is equivalent to that of the zirconia ferrule, the line of the fitting portion with the optical fiber is assumed. If the expansion coefficient difference is within about 1 × 10 ⁻⁵ / ° C., highly reliable connection between optical connectors is maintained within a temperature range of −40 to 85 ° C.

Although this value also depends on the characteristics of the adhesive used for bonding the optical fiber and the fitting portion, usually, the epoxy adhesive or U-type adhesive used for bonding the optical fiber is used.
No problem occurred with the V-curable adhesive. Therefore,
When crystallized glass is used for the fitting part of the optical connector ferrule, the required range for the linear expansion coefficient is greatly relaxed compared to conventional ideas, and even if crystallized glass of the same material system has a higher strength than ever Can be used.

In the crystallized glass, the coefficient of linear expansion, strength, transparency and the like can be controlled by the composition, but the composition for obtaining a low coefficient of linear expansion and high strength is generally different. These two characteristics are not necessarily compatible.
Therefore, clarifying the requirements for the coefficient of linear expansion has a very important meaning in selecting a composition when crystallized glass is used for the fitting portion. The inventor of the present invention found that the strength of the surface made of a ductile material, which was required when crystallized glass was used for the fitting portion of the ferrule, became unnecessary.

Also, if a transparent material is used as the crystallized glass, it is not necessary to use a thermosetting adhesive for fixing the optical fiber to the fitting portion, etc., and the use of a UV curing adhesive greatly increases the bonding process. This makes it possible to reduce the length of the optical connector, thereby contributing to a reduction in the price of the optical connector.

In consideration of reliability such as chemical resistance and water resistance, crystallized glass containing alkali as a main component cannot be used, and crystallized glass containing silica as a main material cannot be used from the viewpoint of reliability. Has been confirmed to be optimal as a material for a fitting portion of a ferrule for an optical connector.

Here, the composition of SiO ₂ is limited. SiO ₂ is 4
With a glass composition of 0 wt% or less, it is a network former to maintain environmental resistance
As the proportion of SiO ₂ decreases, the relative proportion of the alkali component increases, so that the chemical resistance decreases. For example, as shown in FIG. 5, in a 5% HCl solution, which is a measure of chemical resistance, a treatment for 3 hours at 92 ° C. results in a loss of elution of 1.0 mg / cm ² or more for glass having 40% by weight or less of SiO _2. , eluting weight loss under the same processing conditions SiO ₂ together with an increase in the proportion of SiO ₂ is 40 wt% or more of the glass decreases significantly, about the SiO ₂ is 45 wt% 0.3 mg / c
About 0.1 mg / cm ^{2 for} m ² and 55 wt%, and about 0.1 mg / cm ² for 65 wt%.
It is below the detection limit of 01 mg / cm ² , and the acid resistance is greatly improved. Accordingly, the composition of the crystallized glass used for the fitting portion is basically based on that the SiO ₂ content is 40 wt% or more.

Further, the composition of the crystallized glass is limited.
From the viewpoint of workability, Al ₂ O ₃ is limited to 35 wt% or less in order to prevent the viscosity from increasing and the workability from deteriorating. This is Al ₂ O
_The higher the ratio of _3, the higher the acid resistance, as with SiO ₂ , but above 35 wt%, the softening temperature exceeds 600 ° C and the working temperature increases to around 800 ° C. The reason for this is that the workability due to wire drawing is reduced, and that the defoaming treatment becomes difficult due to the increase in viscosity, making it difficult to obtain optically uniform glass.

Since TiO ₂ , MgO, Li ₂ O, P ₂ O ₅ , and ZrO ₂ are each used as a crystal nucleating agent, the composition ratio of TiO ₂ is 15 wt% or more and MgO is 15 wt% or more. When the content of Li ₂ O is 20 wt% or more, the content of P ₂ O ₅ is 15 wt% or more, and the content of ZrO ₂ is 9 wt% or more, crystal nucleation proceeds rapidly, and it becomes difficult to control the formation of crystal grains of a certain size. The most important strength property among the properties of fossilized glass deteriorates, and the material of the fitting part for connector ferrule of the present invention lacks practicality.
It becomes a crystallized glass of 0 MPa or less. Therefore, TiO ₂ , Mg
O, Li ₂ O, P ₂ O ₅ , and ZrO ₂ do not hinder uniform crystal formation, so that 15 wt%, 15 wt%, 20 wt%, 15 wt%,
Limited to 9 wt% or less.

Also, CaF ₂ , K ₂ O, PbO, Na ₂ O, As
₂ O ₃ , SnO, NaF, and LiF are not essential materials, but each component ratio is 30 wt%, 5 wt%, 1 wt%, 5 wt%,
wt%, 1wt%, 1wt% , when more than 1 wt%, respectively SiO ₂
Is relatively reduced, and the percentage of network formers is reduced, thereby reducing chemical resistance. In particular, since CaF ₂ , K ₂ O, Na ₂ O, NaF, and LiF are alkaline, they are 30 wt%, 5 wt%, 5 wt%,
When the content is 1 wt% or more, the decrease in chemical resistance and water resistance is increased. At the same time, CaF ₂ , NaF, and LiF also have a role of a crystal nucleating agent. Therefore, when the content is 30 wt%, 1 wt%, or 1 wt% or more, respectively, the crystal nucleation proceeds too quickly, and as described above, the crystallized glass has a low content. It leads to strengthening. Therefore, CaF ₂ , K ₂
O, PbO, Na ₂ O, As ₂ O ₃ , SnO, NaF, LiF are each 30 wt%, 5 wt%, 1 wt%,
5 wt%, 5 wt%, 1 wt%, 1 wt%, limited to 1 wt% or less.

Further, by using silicate glass for the inner layer of the fitting portion of the ferrule for an optical connector and using crystallized glass for the outer layer, UV light can be applied from the end face by utilizing the transparency of the inner glass. Can be used, so that a UV-curable adhesive can be used for fixing the optical fiber to the fitting portion or the like.
Therefore, in this case, since the requirement for transparency is a characteristic out of consideration for the crystallized glass, the range of selection of the composition to be used is further expanded, and the strength is further improved. Also, if a material having a high ratio of silicic acid is used as the silicate glass of the inner layer , the polishing characteristics of the end face become equivalent to those of the optical fiber, so that the polishing process can be simplified and the cost can be reduced. Furthermore, if the surface of the fitting portion made of crystallized glass or partially crystallized glass is formed with a compression layer using a means such as ion exchange,
It is possible to further improve the strength of the fitting portion.

With respect to the production means, a glass base material having a through-hole is precisely produced by utilizing the properties of crystallized glass, and then processed into a cylindrical rod having substantially the same diameter as the fitting portion by a drawing process. By performing the treatment, a precise fitting portion can be formed. At this time, since there is no need to press-fit into a ductile material or the like due to the high strength of the material itself, there is no need for a grinding step as compared with conventional ceramic materials such as zirconia, which greatly contributes to the reduction in the price of optical connectors. .

Hereinafter, the present invention will be described in more detail with reference to the drawings. However, the embodiments disclosed below are merely exemplifications of the present invention, and do not limit the scope of the present invention. FIG. 1 is a view showing a ferrule for an optical connector for a single mode optical fiber according to a first embodiment of the present invention.
Is a fitting portion, 2 is a flange portion, and 3 is a fine through hole into which an optical fiber is inserted and fitted. Table 1 shows the composition (wt%) of the fitting portion 1 of the ferrule for an optical connector using crystallized glass. The fitting portion 1 was made of aluminosilicate crystallized glass having the composition shown in Table 1.

Although the deposited crystal layers of the respective crystallized glass were different from each other due to the heat treatment, the linear expansion coefficient of the fitting portion 1 was 14.5 × 10 ^{−7 to} 107 × 10 ⁻⁷ / ° C. It does not have a great difference from the linear expansion coefficient of the silica-based optical fiber, and long-term reliability against a temperature change can be ensured in that the thermal behavior of the fitting portion 1 and the optical fiber match. Table 1 shows the bending strength of the material of these fitting parts.
As shown in FIG. 7, the pressure is 165 to 1107 MPa, which is about 2.4 to 16 times that of the fitting portion made of quartz glass, and shows high strength characteristics. The highest strength gave values comparable to zirconia.

[0027]

[Table 1]

When the grain size of the crystal is controlled to 1 μm or less by heat treatment, an almost transparent appearance can be obtained. These materials are chemically stable and have excellent resistance to acids and alkalis other than hydrofluoric acid. When using the fitting part made of transparent crystallized glass, in assembling the optical connector, the optical fiber was fixed using a UV-curable adhesive taking advantage of the transparency of the material, but the curing time was 3 minutes. It was enough. If opaque, the optical fiber was fixed to the fitting using a thermosetting adhesive as in the prior art. The curing time was 10 minutes. The connection loss was 0.1 dB or less in each case. Also,
As part of the reliability test, -10 to 25 to 65 ° C, 93
% R.I. H, 24h / cycle temperature / humidity cycle test
After performing 0 cycles, the measurement was performed in the range of -40 to 85 ° C. It was confirmed that there was no change in the return loss, and that the optical fiber was not retracted enough to form a gap between the optical fiber end faces.

Further, when a compression layer was formed on the surface of the fitting portion 1 by ion exchange, the bending strength was increased about twice in many samples. This treatment also increased the surface hardness and further improved the abrasion resistance. FIG. 2 shows a state in which the optical connector ferrule is incorporated in an optical connector housing, 4 is a plug housing, and 5 is an optical cord.

Embodiment 2 In the same manner as in Embodiment 1, a ferrule for an optical connector for a single mode optical fiber comprising a fitting portion 1, a flange portion 2, and a fine through hole 3 into which an optical fiber is inserted and fitted is provided. Produced. The fitting portion 1 has a structure in which the inner layer is made of high silicate glass and the outer layer is made of crystallized glass. The composition of crystallized glass is SiO ₂ 6
2%, Al ₂ O ₃ 25%, Li ₂ O 5%, ZrO ₂ 1%, TiO ₂ 4%
, P ₂ O ₅ 2% and others.

As a method of manufacturing the fitting portion of the ferrule for an optical connector, first, a high silicate glass and a glass having the above composition are integrated, and a glass base material having a through hole is precision-processed. By performing wire drawing, a cylindrical rod having an inner diameter and an outer diameter equivalent to the fitting portion of the ferrule for an optical connector was produced. After grinding and shaping both end faces of this cylindrical rod, the outer layer is
-A crystallized glass having a spodumene solid solution as a main crystal phase. Further, this was immersed in a solution of 75% NaNO _{3 and} 15% NaSO ₄ at 450 ° C. for 15 minutes to perform surface strength treatment.
The shape accuracy of the fitting part 1 satisfied the standard of the CS connector. The bending strength was about 400 MPa, which was equivalent to the strength of alumina.

The materials are chemically stable and have excellent resistance to acids and alkalis other than hydrofluoric acid. This optical connector ferrule makes use of the transparency of high silicate glass
The optical fiber was fixed by irradiating the end face with a V-curable adhesive, but a fixing time of 5 minutes was sufficient. In addition, since the inner layer is made of high silicate glass, the polishing characteristics are equivalent to those of an optical fiber. In end face polishing, it is not necessary to use diamond abrasive grains, and the polishing time is half that of the conventional case. Further, since the linear expansion coefficient of the high silicate glass is close to the linear expansion coefficient of the optical fiber, the environmental resistance is also very stable, and is -10 to +25 to 65 ° C and 93% R.F. H, after performing 20 cycles of a temperature / humidity cycle test of 24 h / cycle,
The measurement was performed in the range of 40 to 85 ° C., but there was no change in the return loss.

[0033]

As described above, in the ferrule for an optical connector according to the present invention, the cylindrical rod-shaped fitting portion has the fitting portion.
An outer layer on the surface side of the joining portion and an inner portion having the through hole
The outer layer is made of silicate or aluminosilicate
Crystallized glass or partial crystallization based on salt or phosphosilicate
Constituted by glass, wherein the inner layer is transparent
Because it is composed of silicate glass, it has better moldability than conventional zirconia ferrules, and especially the outer layer that comes in contact with the sleeve into which the ferrule for optical connectors is fitted has strong "crystallized glass or partially crystallized glass". Therefore, sufficient strength as a ferrule for an optical connector can be obtained. Furthermore, since the cylindrical rod-shaped inner layer that is in contact with the optical fiber is formed of transparent silicate glass, when the UV light is irradiated from the end face of the ferrule for an optical connector, the optical fiber comes into contact with the silicate glass of the inner layer. U in part
The V light arrives, the UV-curable adhesive is cured, and the optical fiber can be bonded and fixed. Further, since the silicate glass of the inner layer has the same polishing characteristics of the end face as the optical fiber, the polishing process is simplified, and the ferrule for an optical connector can be provided at a low price.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a structure of a ferrule for an optical connector for a single mode optical fiber according to a first embodiment of the present invention.

FIG. 2 is a partial side sectional view illustrating a state in which an optical connector in which a ferrule for an optical connector according to the present invention is incorporated in a plug housing is configured.

FIG. 3 is a side view showing the structure of a conventional zirconia ferrule.

FIG. 4 is a side sectional view showing the structure of a conventional alumina capillary ferrule.

FIG. 5 is a graph showing the relationship between the SiO ₂ content and the loss of glass elution in a 5% HCl solution at 92 ° C. for 3 hours.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fitting part 2 Flange part 3 Fine through hole 4 Plug housing 5 Optical code 6 Cylindrical rod-shaped fitting part 7 Flange part 8 Alumina capillary 9 Stainless steel ferrule body with integral flange part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-69212 (JP, A) JP-A-59-62812 (JP, A) JP-A-6-94944 (JP, A) JP-A-5-92 286734 (JP, A) Special table 63-500684 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/36 G02B 6/38

Claims (3)

(57) [Claims] 1. A cylindrical rod-shaped fitting portion having a through hole having an inner diameter slightly larger than the outer diameter of an optical fiber at the center thereof for fitting and aligning with a split sleeve or the like, and an optical fiber core wire. the covered portion of the held inside, and is composed of a flange portion for being held in the optical connector housing, the optical connector ferrule having a structure fixed between said engaging portion and the flange portion, wherein The cylindrical rod-shaped fitting portion is an outer portion on the surface side of the fitting portion.
A part layer and an inner layer having the through hole , wherein the outer layer is made of a silicate-based, aluminosilicate-based, or phosphosilicate-based crystallized glass or partially crystallized glass, and further, the internal layer is A ferrule for an optical connector, comprising a transparent silicate glass . 2. The ferrule for an optical connector according to claim 1, wherein the SiO ₂ component of the crystallized glass or the partially crystallized glass is at least 40 wt%. 3. The composition of the crystallized glass or the partially crystallized glass is as follows: SiO ₂ ≧ 40 wt%, Al ₂ O ₃ ≦ 35 wt%, Ti
O ₂ ≦ 15 wt%, MgO ≦ 15 wt%, CaF ₂ ≦ 30 wt%, Li ₂ O
≦ 20 wt%, P ₂ O ₅ ≦ 15 wt%, ZrO ₂ ≦ 9 wt%, K ₂ O ≦ 5
wt%, PbO ≦ 1wt%, Na 2 O ≦ 5wt%, As 2 O 3 ≦ 5wt%,
The ferrule for an optical connector according to claim 1, wherein the ferrule has a composition in the range of SnO ≦ 1 wt%, NaF ≦ 1 wt%, and LiF ≦ 1 wt%.