JPS6163806A - Terminal member for connecting optical fiber - Google Patents

Abstract

PURPOSE:To expand the degree of freedom allowing precise positioning at a connection point and to prevent an optical fiber connecting terminal member from damage even if slight deformation is generated by setting up the length and outer diameter of the terminal member to a specific relation so that the cylindrical part of the member is elastically deformed. CONSTITUTION:In the optical fiber connecting terminal member (ferrule) 1' having the cylindrical part having high circularness and accurately forming a through hole 6' slightly larger than the outer diameter of an optical fiber, L<2>/D is set up to 2.4 times or more the value of Ef/Sf when the outer diameter and length of the member 1' are D and L respectively and its Young's modulus and yield stress are Ef and Sf so that said cylindrical part is elastically deformed. In addition, a synthetic resin mold containing reinforcing agents such as glass fiber or carbon fiber is used for the terminal member 1'. Since the terminal member 1' having high elasticity is used, the production cost can be reduced by using plastic without requiring high accuracy. In addition, working at the operation of a connector is made easy and the optical fiver connecting method using the elasticity can be applied. For instance, an economical optical connector can be obtained by using a V-shaped rgoove.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a component (ferrule) that is placed over the terminal of an optical fiber when connecting the optical fiber used as a transmission medium for optical communication.

(Prior Art) Optical fibers, which have excellent transmission characteristics such as high bandwidth and low loss, have recently been used on a large scale as a transmission medium for information and optical energy. Along with this, there has been a need for a method for connecting thin optical fibers with a diameter of about 0.1 mm, which are used especially when transmitting high-speed information, with low connection loss and at low cost.

Optical fiber connections require more sophisticated technology than electrical connections, primarily due to the small diameter and fragility of optical fibers. In other words, in order to connect optical fibers with less energy loss at the connection point, the optical axes of the optical fibers to be connected must be aligned at once, and the optical fibers must be aligned on the order of microns to eliminate the gap between the end faces of the optical fibers. (This is called axis alignment).

Conventional optical fiber connection methods include, for example, Technical
Staff of C5ELT: ”0PTICAL
FIBERCOMMUNICATION, ”pp,
541-643.1980. McGraw-Old II
, New York, and can be roughly divided into methods for permanently connecting optical fibers and methods for connecting optical fibers in a detachable manner using optical connectors. Among these, for connections between devices, etc., a connector connection method that allows reconnection and disconnection is important.

As for the structure of conventional optical connectors, for example,
The structure shown in No. 22707, which uses a ferrule and a sleeve as basic elements, is unique.

A ferrule is a rod-shaped member with a cross section based on a circle, and a through hole for inserting an optical fiber with a diameter slightly larger than the outer diameter of the optical fiber is bored on the central axis of the reference circle. It is a cylindrical member for accurately butting the two together.

Pass the ends of the optical fibers to be connected through the through holes of the ferrules, align and secure the end faces of the optical fiber and ferrule on the same plane, and insert the ferrules into the sleeve so that the end faces of the ferrules abut. Connect the optical fiber using

If the optical axes of the optical fibers are bent (referred to as angular misalignment) or misaligned between the optical fibers at the optical fiber connection section, the splice loss will increase. For this reason, conventional ferrules have been designed so that they do not bend and are used as rigid bodies, in order to prevent optical fiber optical axes from being misaligned or angularly misaligned, which would increase splice loss. It's here. Therefore, the small diameter, which is a characteristic of optical fiber,
Flexibility could not be utilized in optical connectors.

An example of a conventional ferrule is shown in FIG. ferrule l
consists of a cylindrical part 2 and a collar 3, the diameter of the cylindrical part 2 is 2.5wm, and the length of the cylindrical part 2 from the collar 3 to the tip 4 of the ferrule (hereinafter referred to as the ferrule length) is 8. .0m. A ceramic capillary 7 with an optical fiber insertion hole 6 is fitted into the tip of a stainless steel cylindrical member 5. Set the ferrule collar 3 to the 8th
Assuming that the cantilever spring is fixed and applies force to the tip 4 as shown in the figure, the spring constant of this cantilever spring is approximately 20 kg
/ **, indicating that it is extremely stiff. If you apply force until it breaks, the force at break will be about 10 kg,
Even in this case, the amount of displacement at the tip is 0.11- or less.

FIGS. 3 and 9 show other examples of ferrules. The shape is the same as the previous example, but the difference is that there is no capillary and the entire ferrule is made of plastic (PPS resin containing a reinforcing agent).

In this example, the spring constant is about 10 kg, the force at break is several kg, and the displacement of the tip is less than 0.5 kg.

As described above, conventional ferrules were characterized by being able to open and not deform. Therefore, when aligning the optical axis,
It was necessary to place the entire ferrule in a precise position, not just at the connection point.

In other words, as shown in FIG. 4, at the connection position 8, the central axis of the connection end surfaces 9, 9' of the ferrule is at a certain distance from the axis where it should be defeated. ! If the ferrule 1'' is fixed to the plug lO at a position shifted by 1ItH, the plug 10 may not be able to be inserted into the adapter 11, or the ferrule 1' will be difficult to bend, so the bending stress will exceed the yield stress of the ferrule 1''. This caused either ferrule 1# to be damaged or plug 10 to be damaged, and in either case, optical axis alignment could not be performed.

For this reason, in the past, the plug and adapter were precisely machined, the ferrule was suspended from the plug by a spring, etc., and the holding force of the sleeve that tightened the ferrule was sufficiently strong to prevent axial and angular misalignment between the ferrules. I tried to prevent it from happening. Increasing the holding force of the sleeve increases the frictional force between the sleeve and the ferrule, which increases the insertion/extraction force when inserting/extracting the plug, and increases wear between the sleeve and the ferrule. The increase in insertion and removal force will become a problem when increasing the number of fibers in optical connectors in the future. Furthermore, wear debris generated by wear causes increased loss.

Furthermore, it is expected that optical fiber connectors will be mounted in high density in the future, and in this case, the ferrule, which is a basic element of the optical fiber connector, will also need to be miniaturized. Conventional ferrules are difficult to bend, so they had to have a rigid structure to deal with external forces, which required great strength. Due to this strength limitation, with conventional rigid ferrules, the ferrule diameter cannot be made very small. Furthermore, in order to connect with low loss, the length of the sleeve needs to be several times the outer diameter of the ferrule, so the length of the ferrule cannot be made too short. Therefore, conventional rigid ferrules have the disadvantage that their dimensions cannot be made very small. This stiffness of the ferrule had several drawbacks.

Furthermore, since the ferrule is rigid, an optical axis alignment mechanism that takes advantage of the flexibility of the optical fiber, such as is used in a permanent connection method of optical fibers, cannot be used in the optical fiber connector.

For example, a mechanism for permanently connecting optical fibers by taking advantage of the flexibility of optical fibers has been proposed, as disclosed in Japanese Utility Model Application Laid-Open No. 53-93241. This method uses bending stress generated by bending the optical fibers to press the optical fibers against the corners, and the optical axes of the optical fibers to be connected are precisely aligned based on the relative positional relationship between the corners and the optical fibers. Furthermore, as a splicing method that more actively utilizes the flexibility of optical fibers, a splicing method is proposed in JP-A-57-139716 in which optical axes are aligned by pressing an optical fiber against a V-groove using an individual presser spring. There is. With this connection method, unevenness in the axial direction of the optical fiber can be absorbed by the optical fiber's flexible bending, and it is expected to be economical by using the low-cost V-groove and relaxing the dimensional accuracy of optical connector parts. . In this way, conventional optical fiber connection methods that take advantage of flexibility have been proposed, but all of them require the use of bare optical fibers that are easily damaged, so it is important to apply them to detachable optical connectors. was difficult. Also,
With conventional ferrules, it was not possible to bend the ferrule flexibly, so a method that utilized such flexibility could not be used.

(Problems to be Solved by the Present Invention) (1) Even if the ferrule is fixed in a misaligned position, the ferrule end faces can be accurately aligned at the connection point by appropriately deforming the ferrule itself. It is an object of the present invention to provide a ferrule that has a high degree of freedom and does not break even if it is slightly deformed by dispersing external force through elastic deformation.

(2) By making the ferrule itself flexible, the force necessary for optical axis alignment can be reduced, and an optical axis alignment mechanism that utilizes flexibility can be applied to optical connectors.

(3) To provide a small ferrule that is economical and can be applied to high-density optical connectors.

(Means for Solving the Problem) The cylindrical portion of the end member for connecting optical fibers causes elastic displacement, that is, the Young's modulus and yield stress of the outer end bundle member are Ef and Sf, respectively, and L”/D -h
<E f /S f (7) 2.4 times or more.

The features of the present invention are achieved in that the ferrule can be bent to a practical extent with an appropriate amount of force, and is not damaged by this deformation. This will be explained in detail below.

In order to connect optical fibers with low connection loss, it is necessary to accurately align the ferrules at the connection point so that there is no angular or axial deviation between them. However, since the parts constituting plugs and adapters have dimensional variations (tolerances) during manufacturing, the plugs and adapters assembled from these parts also have variations in dimensional accuracy. The smaller the tolerance, the smaller the variation in dimensional accuracy, but on the other hand, the manufacturing cost increases, so in order to lower the cost, it is desirable to increase the tolerance as much as possible.

Normally, the tolerance in relatively rough manufacturing is about 0.1w, so it is expected that the misfit that occurs when a plug or adapter is assembled is about 0.5 ms.

In order to prevent such a relatively large misalignment from affecting the alignment of the ferrules at the connection point, which requires precise alignment on the order of microns, conventional optical connectors use springs, etc. to absorb the misalignment. Was. When the present invention is used, the ferrule itself elastically deforms, making it possible to absorb misalignment. Even if the fixed part of the ferrule is fixed at a position slightly offset from the extension of the optical axis at the connection point, the ferrule can be bent flexibly to ensure that the ferrule tip is placed in the correct position at the connection point. It is possible to perform optical axis alignment.

The necessary conditions for such a modification to be possible will be explained below. For the sake of simplicity, as shown in FIG. 4, it is assumed that the mating misalignment that occurs when the plug 10 and the adapter 11 are mated is only the axis misalignment H. In other words, in order to place the connection end surface 9 of the ferrule 1'' in the correct position at the connection position 8,
As shown in Fig. 5, the ferrule l'' is deformed so that the extension line of the axis at the ferrule tail 3' and the central axis at the connecting end face 9 of the ferrule are parallel and deviate by H, and there is a gentle curve between them. In such a modification, the force applied to the ferrule 1'' can be schematically represented as shown in FIG. The force Q applied at L2 from the fixed surface 12 of the ferrule collar 3'', and the force Q applied from the surface 13 at Ll from the fixed surface 12.
The ferrule 1'' is deformed due to the opposing force N. By increasing the force Q to an appropriate level or more, it is possible to position the ferrule tip at an accurate position.

Here, care must be taken to ensure that the ferrule itself does not become plastically deformed or damaged due to deformation. □Failure (including plastic deformation) occurs when the stress caused by deformation exceeds the yield stress in a certain area. When the ferrule deforms as shown in Figure 6, the maximum bending stress S occurs at the root 15 of the ferrule, reducing the Young's modulus of the ferrule material to Ef.
is expressed by the following formula.

S=3・81 DL2 Q /(6・HEl +L2'
Q) (1) Here, E is a quantity called bending stiffness.If the ferrule has a structure in which an optical fiber is placed at its center, and the diameter and Young's modulus of the optical fiber are A and Eo, respectively, the following formula is obtained. expressed.

El=0.05 ・(EoA′ +Ef(D′ −A
' ) ) (21S increases as Q increases, but converges to a constant value Sl when Q becomes sufficiently large.

51=3・HEfD/L2'' In other words, the maximum bending stress S that occurs during the deformation as shown in Figure 6 does not exceed Sl. Therefore, in order for the ferrule to be able to undergo the above deformation without being damaged, the ferrule must be It is sufficient that the yield stress Sf of the material is greater than 31 in equation (3).

Sf > 3・HEf D/L2”
(41 Now, in order to bring the end faces of the ferrules into close contact with each other, an axial force is usually applied to the ferrule, but in order to prevent buckling at the tips (Japanese Patent Laid-Open No. 57-13
9716)) L2 must satisfy the following equation:

L2 ≧ 0.8 ・Shuku5) These L2 can be made as follows, for example.

L2 = 0.8・L
(5') Also, as mentioned above, due to the variation in fitting accuracy that occurs when the plug and adapter are fitted together, the maximum value is 0.
Since a mating misalignment of about 5u is expected, H can be expressed by the following equation.

■≦0.5-The maximum value H of the Japanese formula (4), L2 of formula (5') and H of formula (6)
By substituting m (=0.5 dragons), a conditional expression is found that allows the ferrule to undergo the necessary deformation without being damaged.

(L2 / B”) > 2.3 ・
(Ef/Sf) (?) Figure 1 shows the results of calculations by inserting material constants of various materials into the above conditional expression (7). For each material, the area to the right of each solid line is the area where the present invention can be realized. Considering that the wider this region is, the greater the flexibility in ferrule design, this figure shows that a material with a small bending elastic modulus and a large lateral stress, such as a plastic material, is suitable for the ferrule material. . Furthermore, considering high-precision moldability, a plastic material containing a reinforcing agent is considered to be the most suitable.

Next, the force Q is the force applied to the ferrule 1'' by the holding force of the sleeve 14 in FIG. 5, but it may also be applied by, for example, a ferrule pressing spring as described in i. It needs to be of an appropriate size.If the minimum force required to place the ferrule tip in the correct position is Q2, then Q2 can be found by setting up and solving an elastic equation, and becomes the following equation.

Q2 = 6 ・HEI / ((Ll
-L2 ) L2 2) (sl where Ll is expressed by the following formula.

L2 < Ll ≦ Shiku9) Now, Q2
Considering that it can be realized using a normal spring or the like, it is desirable that the size of the spring is, for example, about 100 g or less.

(125100g (UnL
Considering the maximum possible size of L, the length of the ferrule is set to L, and formulas (2), (5'), (6) and (10
By substituting 1 into equation (8), a conditional expression that allows the necessary deformation with a force of 100 g or less can be found.

≧0.01 ・(Eo A' + Ef (D'
-A' ) ) (11) Next, the deformation performance of the present invention will be explained. External forces act on the ferrule mainly when attaching or detaching the plug, but since the collar of the ferrule is normally held or fixed to the plug by a spring or the like, the stress generated is greatest at the base of the ferrule.

As shown in Fig. 8, when the tip of the ferrule is deformed by applying force perpendicularly to the axis with the tail of the ferrule fixed, the relationship between the displacement W of the tip and the maximum bending stress S2 that occurs is given by the following 2. It will be done.

S2 = 1.5 ・Ef DW / I,
” (12) The maximum bending stress S2 is the yield force Sf
Exceeding this will damage the ferrule. Therefore, by setting the left side of the above equation as sr and solving it, the displacement Wf (this will be referred to as the maximum deformable amount) of the tip when it starts to break can be found.

Wf = 0.67 ・Sr L” / (Ef
D) (13) Furthermore, in the present invention, formula (13)
When calculated by substituting equation (7) into , Wf becomes as follows.

Wf > 1.6m (14
) Thus, the maximum possible ferrule of the present invention is 1.6 am or more, which is at least 4 times to 1
It becomes a large value of about 00 times. For example, when comparing the conventional ferrule illustrated in FIG. 9 with a ferrule made of the same material (plastic: PPS resin with reinforcing agent), the conventional ferrule has a Wf of Q, 2 mm, which is more than 7 times larger than that of the present invention. Further, compared to other conventional ferrules illustrated in FIG. 7, the ferrule of the present invention is 45 times larger or more. As described above, the present invention has the characteristics that the maximum amount of deformation is larger than that of conventional ferrules, and that it is resistant to deformation.

FIG. 2 shows an embodiment of the present invention, in which the ferrule material is a reinforcing agent-containing epoxy resin, the ferrule diameter is 0.8M, and the ferrule length is 20III. Ferrule 1
A fiber insertion hole 6'' is provided in the tip 4'' of the ferrule so that there is no eccentricity on the central axis of the ferrule.The root 15' of the narrow diameter portion is subject to stress concentration during deformation; The diameter is gradually changed to disperse stress and provide strength.

In this embodiment, when a cantilever spring is used as shown in FIG. 8, the spring constant is several log/II, which is extremely soft compared to a conventional ferrule. In addition, if a load perpendicular to the axis is applied to the tip of the ferrule in this state, the tip will be
No damage or plastic deformation occurs even when displaced.

This is more than 10 times the deformation compared to the conventional ferrule. Furthermore, if the tail and tip of the ferrule are deformed so that their axes are parallel to each other as shown in Figure 6, the axes can be shifted by up to 0.5 degrees. As a result, even if the fixed part of the ferrule is slightly deviated from the extension of the optical axis at the connection point, the ferrule itself can be flexibly deformed and the tip can be accurately positioned at the connection point.

Next, when aligning the ferrule using a sleeve, the force required to tighten the sleeve can be reduced because the ferrule itself is flexible in the present invention compared to conventional rigid ferrules. As a result, the frictional force between the sleeve and the ferrule is reduced, and it is possible to reduce the amount of abrasion powder that causes increased loss and the insertion/extraction force.

Furthermore, in the future it will be required to package optical fibers at high density. In this case, it is necessary to downsize the optical connector components, especially the ferrule. Conventional ferrules have a thick ferrule diameter to provide strength and prevent the ferrule from deforming or breaking even when external forces are applied (rigid structure), so it was necessary to make the ferrule a certain degree thicker. In the present invention, the external force is dispersed by elastic deformation of the ferrule (flexible structure), and the deformation performance is large enough to prevent damage due to flexible deformation even with a small diameter.Furthermore, a sleeve is used to align the ferrule. If this is the case, experience has shown that in order to do this correctly, the length of the sleeve needs to be several times the outer diameter of the ferrule!
J is known. By making the ferrule smaller in diameter, the sleeve can be made smaller. In addition to this, the aforementioned reduction in force for tightening the sleeve also facilitates miniaturization of the sleeve. Thus, according to the present invention, a compact optical connector element that can be applied to a high-density multi-core connector can be realized.

Furthermore, according to the invention, light requiring flexibility.

Align the optical axis of the optical connector with the axis alignment mechanism 4! -A new optical connector applied to the mechanism becomes possible. In particular, if the ferrule is designed to satisfy equation (11), it can be deformed with a force of 100 g or less, so it is also possible to align the optical axis by pressing the ferrule against the V-groove using a small spring. . Although various specific structures can be considered, for example, it is possible to use a structure as shown in FIG. 3 to form an optical connector. This is JP-A-57
-139716, which is applied to an optical connector using an optical axis alignment mechanism using an individual pressing spring and a V groove.
ll itself bends flexibly, and the ferrule tip 4'' is pressed against the V-groove 18 of the V-series stand 17, and at the same time, due to the bending stress generated by the deformation, the ferrule 1'' is pushed into the V-groove 1.
The zero alignment fixed at point 8 is performed using both sides of the V-groove 18 as reference surfaces. V-grooves are less expensive than sleeves, and economical optical connectors can be realized. Also plug 10'
Even if the position of the V-groove 18 is slightly shifted, the deflection of the ferrule absorbs the shift and allows accurate alignment at the connection point 28'. The parts other than the grooves may be manufactured somewhat roughly, and this can be expected to lower the cost of the optical connector and improve the scratchability.

(Effects of the Invention) As described above, by using the present invention, the excellent mechanical characteristic of optical fibers, such as elasticity, can be utilized for connector connection of optical fibers. by this,
There is an advantage in that it becomes possible to replace some parts of an optical connector that conventionally required high-level processing techniques with parts that do not require processing precision. Furthermore, in the present invention, the ferrule can be made of plastic, which has low material cost and can be manufactured by an economical manufacturing method such as a molding method, so that a reduction in the price of the ferrule can be expected. Furthermore, there is an advantage that an optical connector that can be operated more easily than a conventional optical connector can be realized when the optical connector is scraped. Furthermore, it becomes possible to apply an optical fiber connection method that utilizes elasticity, and for example, by using a V-groove, an economical optical connector can be realized.

[Brief explanation of the drawing]

In Figure 1, the outer diameter and length of the cylindrical portion of the terminal member (ferrule) are D and L, respectively, and the Young's modulus and yield stress of various ferrules are Bf and S (r (L” /D)> 2.3 A graph showing the relationship between the outer diameter and length of the ferrule obtained from the equation (Ef/Sf). Figure 2 is a partial cross-sectional view of an embodiment of the present invention, and Figure 3 is a graph showing the relationship between the outer diameter and length of the ferrule determined from the formula of 2.3.(Ef/Sf). Figures 4 and 5 are partial cross-sectional views of the composite layer of the plug and adapter, and Figure 6 is a partially cross-sectional perspective view of an embodiment of an optical connector using the ferrule. Figure 7 is a partially cross-sectional perspective view of a conventional ferrule (capillary type), and Figure 8 is a diagram showing how to deform a ferrule by applying an appropriate force to it. In addition, Fig. 9 is a partially sectional perspective view of a conventional ferrule (nozzle shape). 1.1', 1.1.1.1 ... Ferrule 2.2 '... Ferrule cylindrical portion 3.3', 3'' 3111, 31111... Ferrule collar 4.4', 4'' 4 III... - Ferrule tip 5.5'... Cylindrical member 6.6' , 6"...Optical fiber insertion hole 7...Capillary 8.8'...Connection position 9.9', 9"...Ferrule contact vc end surface 10,
10', 10"... Plug 11. 11'... Adapter 12... Ferrule collar fixing surface 13... Pressing surface 14... Sleeve 1
5...Ferrule base 16...Individual pressing spring 17...V series 18.
...V groove. Fig. 6 Fig. 7 Fig. 8 Fig. 9 Procedural amendment dated March 30, 1982 1. Indication of the case 1984 Patent application No. 184440 2. Name of the invention Terminal member for optical 7 eyeper connection amendment Incident 5! Relationship between patent applicant (422) Nippon Telegraph and Telephone Public Corporation (1) [Low price] on page 2, line 9 of the specification is corrected to 1, from 1 low price. (2) Between “diameter D:” and “ga” on page 8, line 18,
Add the next token. (hereinafter referred to as the outer diameter of the ferrule)” (3
) Delete the 4 characters "Fig. 8," in the 4th line of the same @S page0 (4) Correct the [7 errule diameter] in the 3rd line of the 7th page to ``The outer diameter of the ferrule.'' (5) "(Problem to be solved by the present invention)" on page 8, line 17 of the same page has been replaced with "(Leap point to be solved by the invention)"
Correct. (6) Change r(L!/Dν” in the second line of the same page to r(
L"/D) J. (TE) Correct "7 errule diameter D" in the first line of page 1111'F of the same to "outer diameter DJ of 7 errule. (8) Page 18 of the same, 18 Correct "7 ferrule diameter" to "ferrule outer diameter" in the row.

Claims (1)

[Scope of Claims] 1. An optical fiber connecting terminal member having a highly circular cylindrical portion in which a through hole slightly larger than the outer diameter of the optical fiber is accurately provided in the center, The cylindrical portion can undergo elastic displacement, that is, the outer diameter and length of the cylindrical portion are D and L, respectively, and the Young's modulus and yield stress of the end member are Ef and S, respectively.
An optical fiber connection terminal member characterized in that f is L^2/D which is 2.4 times or more of Ef/Sf. 2. The terminal member for optical fiber connection according to claim 1, wherein the terminal member is a molded article of synthetic resin containing a reinforcing agent such as glass fiber, carbon fiber, or silica particles.