JPH0789168B2 - Optical connector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical connector used for connecting optical fibers to each other in optical communication.

(Prior Art) Conventionally, various types of optical connectors are known for use in connecting optical fibers to each other. A typical example is a hollow cylinder having a precise inner diameter by fixing the optical fiber to the center of a cylindrical rod-shaped ferrule, such as the F01 single-core optical fiber connector defined in JIS C 5970. In some cases, the end faces of the ferrules are butted against each other by inserting the ferrules into a linear alignment sleeve.

Materials that make up this ferrule include metals, ceramics, plastics, etc., but as a high-precision ferrule used for connecting a single-mode optical fiber whose core diameter is about 10 μm, the fitting part What is called a capillary-type ferrule is widely used, which is made of stainless steel, and is made by press-fitting a cylindrical rod made of alumina ceramic that adheres and fixes the optical fiber to the center. In addition, a ferrule that has a precision equal to or better than that of a capillary ferrule and has excellent characteristics such as economic efficiency, characteristic stability, and ease of polishing, which is called a zirconia ferrule and has a fitting part made of zirconia ceramic, is also practical. Have been used for.

As the alignment sleeve, a slit sleeve having a structure in which a slit is formed in the axial direction of the cylindrical rod and the ferrule is slightly elastically deformed when the ferrule is inserted to align and hold the ferrule is widely used. There is. In order to function as a split sleeve, a material having a spring property is required, so that a material made of phosphor bronze is generally used, but another material made of zirconia ceramic is also made.

(Problems to be Solved by the Invention) As described above, various materials are used for the ferrule and the split sleeve, but if attention is paid to the hardness of these materials, depending on the combination, various problems as described below may occur. Occurs.

(I) When the hardness of the ferrule is lower than the hardness of the split sleeve When the optical connector is coupled, the outer periphery of the ferrule and the inner surface of the split sleeve rub against each other. The ferrule wears out as it is repeatedly attached and detached. Abrasion of the outer periphery of the ferrule finished with high precision causes axial misalignment between the ferrules abutted against each other, increasing the connection loss of the optical connector. As an example of this case, FIG. 15 is a diagram showing the results of repeated attachment / detachment tests in which a single mode optical connector was constructed using a capillary ferrule and a zirconia split sleeve. In the figure, the vertical axis represents the connection loss and the horizontal axis represents the number of attachments and detachments. From this figure, it can be seen that the connection loss deteriorates before the number of attachments / detachments reaches 100 times.

(Ii) When the hardness of the ferrule is higher than the hardness of the split sleeve When the hardness of the ferrule is higher than the hardness of the split sleeve, the inner surface of the split sleeve is worn when the optical connector is attached and detached. Since the split sleeve holds the ferrule by its elasticity, even if the inner surface is slightly scratched, it does not affect the highly accurate connection between the ferrules. However, there is a problem that the cutting powder of the split sleeve, which is generated due to wear of the inner surface of the split sleeve, tends to adhere to the tip of the ferrule. PC with a structure in which the end surface of the ferrule is polished into a convex spherical surface
In the case of the optical connector, when foreign matter adheres to the tip of the ferrule, a gap is created between the end faces of the optical fibers facing each other, and the return loss at the connection portion deteriorates.

FIG. 14 (b) is a diagram showing an example of the result of a repeated attachment / detachment test of a single-mode optical connector constructed by using a zirconia ferrule and a phosphor bronze split sleeve.
In the figure, the vertical axis represents the return loss and the horizontal axis represents the number of attachments and detachments. As is clear from this figure, when the optical connector plug is repeatedly inserted and removed about 100 times, dust adheres to the end face of the ferrule and the return loss deteriorates. When the end face of the ferrule is cleaned (indicated by a circle in the figure), the return loss returns to the original value as shown in Fig. 14 (b), but if the insertion and removal are repeated, the return loss deteriorates again. repeat.

As described above, when the ferrule and the split sleeve are made of materials having different hardnesses, each of them has a problem regardless of the hardness. That is, when the optical connector is repeatedly attached and detached, when the hardness of the ferrule is lower than the hardness of the split sleeve, the connection loss deteriorates, and in the opposite case, the return loss deteriorates.

Further, in the case of the optical connector having the above-mentioned structure, the ferrule and the split sleeve have a structure in which they are not fixed to the plug housing and the adapter housing, respectively, but float in order to avoid the influence of the dimensional tolerance of the plug housing and the external force. This allows the split sleeve to rotate freely within the adapter housing, but the locations where the split sleeve and ferrule contact do not normally have a uniform distribution around the central axis of the split sleeve. Therefore, every time the optical connector plug is attached or detached, the position where the split sleeve rotates and comes into contact with the ferrule changes, and the positions of the ferrules that are brought into contact with each other change slightly, so that the connection characteristics change.

In view of the above-mentioned problems, an object of the present invention is to provide an optical connector with high reliability, in which the connection characteristics do not deteriorate even after repeated attachment and detachment.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides, in claim 1, a pair of ferrules to which respective end portions of an optical fiber are fixed, and a pair of ferrules having slits formed in the axial direction. In an optical connector including a split sleeve in which is inserted and abutted, a spring for applying an axial pressing force to each ferrule, a pair of plug housings for housing each ferrule, and an adapter housing for housing the split sleeve. The ferrules and the split sleeve were both made of the same material, zirconia ceramic, and had the same hardness.

In Claim 2, chamfering is performed along the axial inner edge of the slit of the split sleeve.

According to the third aspect of the invention, the protrusion that engages with the slit of the split sleeve is provided in the adapter housing.

(Operation) According to claim 1, both ferrules and split sleeves are made of zirconia ceramic of the same material, and the hardnesses of both are made to match, so that even if the optical connector plug is repeatedly attached and detached, It is possible to suppress mutual wear due to the contact of the split sleeves. According to claim 2, since the chamfering is performed along the axial inner edge of the slit of the split sleeve, even when a brittle material such as zirconia ceramic is used for the split sleeve, the inner edge of the slit is prevented from being damaged when the ferrule is inserted. it can.

According to the third aspect of the present invention, since the protrusion that engages with the slit of the split sleeve is provided on the inner surface of the adapter housing, the rotation of the split sleeve can be restrained, and the position where the ferrule and the split sleeve come into contact can be always kept constant.

(Example) As an example of the present invention, the split sleeve inner diameter 2.495 mm,
An optical connector using a zirconia split sleeve with a thickness of 0.35 mm, a length of 11.4 mm, and a slit width of 0.45 mm and a zirconia ferrule with an outer diameter of 2.499 ± 0.0005 mm was constructed, and its connection characteristics were investigated. FIG. 1 is a configuration diagram of an optical connector of the present embodiment, where 1 is a pair of optical fibers, 2 is a pair of ferrules to which each end of a pair of optical fibers 1 is fixed, 3 is a split sleeve, and 4 is the above-mentioned. A pressing spring for applying a pressing force in the axial direction to each ferrule 2, a pair of plug housings for accommodating the ferrules together with the pressing spring 4, an adapter housing for accommodating the split sleeve, a plug housing 5 and an adapter. It is a connector for connecting the housing 6. FIG. 2 is a cross-sectional view of the ferrule 2 of this embodiment, which has a structure in which a fitting insertion portion 21 made of zirconia ceramic is press-fitted into a flange portion 22. Fig. 3 (a)
(B) is a sectional view of the split sleeve 3 of the present embodiment. The inner edges of both end faces are chamfered 3a and 3b, and a slit 31 is provided in the axial direction. FIG. 13 shows the result of measuring the connection loss of 100 split sleeves using the same single-mode optical connector plug configured as described above and using a semiconductor laser beam having a wavelength of 1.3 μm. Splice loss is 0 on average.
A good value of 1 dB was obtained.

FIG. 14 shows the results of repeated attachment / detachment tests of the optical connector according to this example and the conventional optical connector using the phosphor bronze split sleeve. In this test, the return loss was measured after every 10 connections, and when the value was 25 dB or less, the ferrule end face was cleaned and the test was continued. First
As shown in Fig. 14 (b), the one using the phosphor bronze split sleeve had a deterioration in return loss before 100 times.
In the case of the optical connector according to the present invention shown in FIG. 4 (a), it can be seen that even if the attachment / detachment is repeated 200 times or more, dust is not attached to the end face of the ferrule, and stable connection characteristics are maintained.

FIG. 4 shows another embodiment, in which a chamfer 32 is provided along the axial inner edge of the slit 31 of the split sleeve 3.

Next, the design of the split sleeve when using zirconia ceramic will be described. FIG. 7 shows an example of the result of measuring the vicinity of the ferrule end surface on the inner surface of the split sleeve with a circularity measuring device when the zirconia ferrule was inserted into the zirconia split sleeve. Since the circularity of the ferrule is much higher than that of the sleeve, it can be considered that the inscribed circle in FIG. 7 corresponds to the inserted ferrule. As is apparent from FIG. 7, the split sleeve and the ferrule are in contact with each other at the slit portion and the side opposite to the slit. Therefore, assuming that concentrated load acts on these parts, the deformation of the split sleeve is calculated using the finite element method, and the ferrule is inserted when the diameter of the inscribed circle of the split sleeve matches the outer diameter of the ferrule. Assuming the state, the reaction force Fr of the concentrated load was obtained. Fr is defined as the gripping force. In the calculation, Young's modulus of zirconia ceramic was 20000 kgf / mm ² and Poisson's ratio was 0.31.

Here, in order to confirm the validity of the calculation, FIG. 8 shows the result of comparison between the measured value of the ferrule extraction force, which is the evaluation value of the split sleeve, and the gripping force. As is clear from FIG. 8, it is proportional to the product of the ferrule withdrawing force, which is the gripping force, and the ferrule insertion length, which is consistent with the conventional idea that the ferrule withdrawing force is the static frictional force due to the gripping force. However, the ferrule withdrawal force was the force required to remove one ferrule from the state in which the ferrules were inserted into the split sleeve from both sides, and a stainless steel ferrule was used for the measurement as in the conventional method.

Based on the results of Fig. 8 and Fig. 9, the ferrule outer diameter is 2.5m.
The relationship between the ferrule extraction force and the value (normalized load Fr / (1-Din / Df)) obtained by normalizing the gripping force with the initial inner diameter of the split sleeve is shown for m and the sleeve length is 11.4 mm. , Din is the inner diameter of the split sleeve, Df is the outer diameter of the ferrule Furthermore, the maximum stress generated in the split sleeve during deformation can be obtained to secure a safety factor = 8 and a safety factor = 10 against the allowable stress of zirconia ceramic. The range is shown together and the relationship between the thickness t of the split sleeve and the standardized load is shown in Fig. 10. However, the width of the slit is 0.45.
mm.

The dimensions of each part of the split sleeve can be determined within the range in which the strength of the split sleeve can be guaranteed from the target ferrule removal force shown in FIGS. 9 and 10. In accordance with the F01 type single-core optical fiber connector standard specified in JIS C 5970, and FC type optical connectors that are widely used at present, a value of 300 to 600 g is used as the ferrule extraction force. , To obtain this value, refer to Fig. 9 and Fig. 10.
If the split sleeve thickness is 0.35 mm, the sleeve inner diameter is 2.
The safety factor can be set to 8 or more in this case, if the range is 491 to 2.495 mm. If the split sleeve has a thickness of 0.4 mm, the inner diameter of the sleeve should be in the range of 2.493 to 2.497 mm, and in this case, the safety factor can be 10 or more.

Also, the ferrule outer diameter is 1.25 mm, and the split sleeve length is
In the case of 7.2 mm, the relationship between the ferrule removal force and the standardized load is as shown in Fig. 11, and the relationship between the standardized load and the split sleeve thickness is as shown in Fig. 12. However, the width of the slit was 1.22 mm. As a result, if the split sleeve thickness is 0.15 mm, the ferrule removal force is 100 to 200 g in the sleeve inner diameter range of 1.242 to 1.246 mm, and if the thickness is 0.2 mm, the sleeve inner diameter is 1.244 to
In the range of 1.248, ferrule pullout force is 100-300g, thickness 0.25mm
If so, the ferrule removal force will be 150 to 400 g in the range of the sleeve inner diameter of 1.245 to 1.248 mm, and the safety factor can be 5 or more in each case. The ferrule withdrawal value was set to a value of 120 to 400 g described in the example of Japanese Patent Application No. 62-43741. The safety factor was made smaller than that of the ferrule with an outer diameter of 2.5 mm because the ferrule with an outer diameter of 2.5 mm is mainly used as a single-core connector, and force is applied in the direction of twisting the ferrule during operation, that is, in the direction of expanding the split sleeve. It is easy to work, but in the case of a ferrule with an outer diameter of 1.25 mm, it can be considered to be mainly used as a multi-core connector,
This is because the force that can be generated in the split sleeve by the external force is considered to be small.

Here, the above calculation is performed for the case where the width of the slit is relatively smaller than the diameter of the sleeve, as in the case of the conventional split sleeve. Since the portion and the slit are in contact with each other on the opposite side, it is possible to dispose the action point of the gripping force on the object around the center axis of the ferrule by widening the width of the slit. FIG. 5 is a view showing the shape of the split sleeve in which the slit 31 has an opening angle of 120 ° with respect to the central axis of the split sleeve 3. With such a shape, the action points of the gripping force acting on the ferrule can be evenly distributed to three points with respect to the central axis.

Further, even when the distribution of the gripping force is not uniform around the central axis, a protrusion 61 is provided on the inner surface of the adapter housing as shown in FIG. 6, and the protrusion 61 is locked in the slit 31 of the split sleeve 3 to form the adapter housing. By restraining the free rotation of the split sleeve 3 within the ferrule, a gripping force always acts on the ferrule in a fixed direction, so that an optical connector in which the connection characteristics vary little even if the optical connector is repeatedly attached and detached You can

(Effect of the Invention) As described above, according to claim 1, since both ferrules and split sleeves are made of zirconia ceramic of the same material, and the hardnesses of both are made the same, they can be repeatedly attached and detached. Also, there is no generation of cutting chips due to wear and wear, and it is possible to reliably prevent deterioration of the return loss due to axial misalignment between ferrules due to wear and adhesion of wear powder, and to maintain good connection characteristics. Claim 2
According to the above, since the axial inner edge of the slit of the split sleeve is chamfered, even if a brittle material is used for the split sleeve,
It is possible to realize a highly reliable optical connector. According to the third aspect of the present invention, since the protrusion that engages with the slit of the split sleeve is provided on the inner surface of the adapter housing to restrain the rotation of the split sleeve, the contact position between the ferrule and the split sleeve is always kept constant. You can As described above, it is possible to realize an optical connector in which variations in connection characteristics are small even after repeated attachment and detachment.

[Brief description of drawings]

1 is a sectional view showing an embodiment of an optical connector according to the present invention, FIG. 2 is a sectional view showing a structure of a ferrule of the optical connector according to the present invention, and FIGS. 3 (a) and 3 (b) are sectional views according to the present invention. FIG. 4 is a sectional view showing the shape of the sleeve, FIG. 4 is a view showing a chamfered state of the slit of the split sleeve, FIG. 5 is a view showing the shape of the split sleeve having a wide slit, and FIG. 6 is a rotation stopper structure of the split sleeve. Fig. 7 is a sectional view showing the shape of the split sleeve when the ferrule is inserted, Fig. 8 is a diagram showing the relationship between the ferrule removal force and the gripping force, and Fig. 9 is an outer diameter of 2.5 m.
Fig. 10 shows the relationship between the ferrule extraction force and the standardized load for the ferrule of m, and Fig. 10 shows the relationship between the split sleeve thickness and the standardized load for the ferrule with an outer diameter of 2.5 mm.
Fig. 11 is a diagram showing the relationship between the ferrule removal force and standardized load for a ferrule with an outer diameter of 1.25 mm, and Fig. 12 is a diagram showing the relationship between the split sleeve thickness and standardized load for a ferrule with an outer diameter of 1.25 mm. FIG. 14 is a diagram showing the measurement results of the connection loss in one embodiment of the optical connector according to the present invention, FIG. 14 (a)
(B) is a diagram showing the results of repeated attachment / detachment tests using the optical connector of the present invention and a conventional optical connector, and FIG. 15 is a diagram showing the results of repeated attachment / detachment tests using a zirconia split sleeve and a capillary ferrule. Is. In the figure, 1 ... Optical fiber, 2 ... Ferrule, 3 ... Split sleeve, 4 ... Pressing spring, 5 ... Plug housing, 6 ... Adapter housing, 21 ... Fitting insertion portion, 22 ...
Flange, 31 …… Slit, 32 …… Chamfer,

Front page continuation (72) Inventor Shinichi Iwano 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Etsuji Sugita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Corp. (72) Inventor Yasuhiro Ando 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (56) Reference JP 61-13205 (JP, A) JP 61- 170709 (JP, A) JP 59-125706 (JP, A) Actual development 59-43921 (JP, U)

Claims (3)

[Claims] 1. A pair of ferrules to which each end of an optical fiber is fixed, a split sleeve in which a slit is formed in the axial direction and a pair of ferrules are fitted and abutted, and a pressing force in the axial direction is applied to each ferrule. In an optical connector having a spring to be applied, a pair of plug housings for housing each ferrule, and an adapter housing for housing a split sleeve, both ferrules and split sleeves are formed of the same material zirconia ceramic, and An optical connector characterized by matching hardness. 2. The optical connector according to claim 1, wherein chamfering is performed along the axial inner edge of the slit of the split sleeve. 3. The optical connector according to claim 1 or 2, wherein a protrusion that engages with the slit of the split sleeve is provided on the inner surface of the adapter housing.