JPS63231408A - Optical connector - Google Patents

Abstract

PURPOSE:To obtain an optical connector which permits high-density packaging by providing a pair of ferrules fixed with ends of two optical fibers, an elastic sleeve and a spring for application of pressing force to the connector and specifying the pressing force, sleeve holding force, the length of a fitting part as well as the inside surface area and bending rigidity of the sleeve. CONSTITUTION:The following equation is required to be satisfied when the inside surface area of the sleeve 4 is designated as S, the pressing force of the ferrule 2 as FA and the sleeve holding force as FR: 2.8<=FA/FR<=(0.14S+0.5). Namely, the pressing force of the ferrule and the sleeve holding force are required to satisfy the following relation: FR, FA/FR<0.14S+0.5. The length L of the ferrule 2 fitting part is required to be L<=2.4D<3>+1.5 when the outside diameter of the ferrule is designated as D. The stable characteristics are thereby obtd. even if the outside diameter of the ferrule is set in a >=1mm and <=1.6mm range. The optical connector which is formed by using the small-diameter ferrules, is small in size and permits high-density packaging is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in optical connectors used in optical communications.

(Conventional technology) When testing, adjusting, and maintaining optical transmission equipment,
There are various types of optical connectors that are used to easily connect and disconnect optical cords, but the mainstream ones fix the optical fiber in the center of a cylindrical rod (ferrule) with an outer diameter of 2.5 mm, and connect it with a precision connector. In this method, the ferrules are inserted into a hollow cylinder (alignment sleeve) with an inner diameter, and the end surfaces of the ferrules are brought into contact with each other by the pressing force of a spring. For example, F according to the draft Japanese Industrial Standards
In the OI type single-fiber optical fiber connector, the ferrule is a ceramic capillary press-fitted into a metal cylinder with a small hole in the center for inserting and fixing the optical fiber, and the alignment sleeve is a slit on the side of the hollow cylinder. I use what is called a split sleeve. In addition, the optical connector shown in Japanese Patent Application No. 60-244050 is
The mating surfaces of the ferrules are polished to have a convex spherical surface, and the end faces of the optical fibers are placed very close to each other, increasing return loss and reducing splice loss. Furthermore, by using zirconia as the material and setting the ferrule pressing force to approximately 1 - and the sleeve holding force to an appropriate value smaller than that, the ferrules are brought into contact with each other and high-performance connection characteristics are obtained.

The above-mentioned ferrule pressing force is when the connector is connected,
This is the force applied by the spring in the axial direction of the ferrule.
The sleeve holding force is the force required to pull out one ferrule from the state in which the ferrules are inserted from both sides of the elastic sleeve so that they touch each other at the center of the sleeve.

Here, the ferrule pressing force is relative to the sleeve holding force,
It needs to be big. This relationship must be satisfied even if the tolerance of the ferrule pressing force is ±20% and the tolerance of the sleeve holding force is ±30% as specified in the draft Japanese Industrial Standard "Type F01 single-core optical fiber connector." In other words, when the minimum value of the ferrule pressing force and the maximum value of the sleeve holding force according to the above tolerance are calculated, the maximum value of the ferrule pressing force must be about 2.8 times the minimum value of the sleeve holding force.

Figure 3 shows ferrule 2-. 2' is a cross-sectional view showing a state where 2' are connected, 1' is an optical connector plug, 2' is another ferrule to be connected, 4' is an elastic sleeve, and 6' is a pressure spring. In order to bring the ferrules into contact with each other, the ferrule pressing force must be greater than the sleeve holding force, but due to the characteristics of a coil spring as a pressing spring, the line of action a of the ferrule pressing force A is generally above the center axis. As shown in FIG. 3, since the contact point C of the fiber core located on the central axis of the ferrule end face does not pass through, a bending moment M is generated in the ferrule. Therefore, when an external impact is applied, the mutual positions of the ferrule 2'' and the pressure spring 6', which are floatingly installed in the optical connector plug 1', change, and this bending moment M may further increase. As the ferrule pressing force increases, this bending moment M increases, and when the bending moment M increases with respect to the sleeve holding force, the ferrules tilt slightly to each other, creating a gap between the fiber end faces, resulting in a connection loss due to Fresnel loss. At this time, the elastic sleeve 4' bends and its inner diameter expands. This bending depends on the inner diameter and length of the elastic sleeve 4', and the inner diameter enlargement depends on the bending stiffness in the axial direction per unit length. The elastic sleeve of a conventional optical connector has an inner diameter of 2.5 mi+, a length of 11.4 m, and an axial bending stiffness of about 8 kgf-+u per unit length.

By applying this optical connector to a single mode optical fiber, the present inventors obtained high-performance connection characteristics with an average connection loss of 0.13 dB and an average return loss of 324 dB.

However, in recent optical transmission, high-density packaging of optical connectors is required as optical fibers become more multi-core. In such areas, the outer diameter of the ferrule should be adjusted to the conventional 2.
It is advantageous to make the optical connector thinner than the optical connector and to reduce the external dimensions of the optical connector. For example, the outer diameter of the ferrule can be changed to 2.
If the diameter is reduced to 5 fins or I' of 21.8 mm, the external dimensions of the optical connector may be approximately 6 m+s, so the cross-sectional area of the connector can be reduced to 1/3. Furthermore, since the end surface area is small, the necessary ferrule pressing force is small, and therefore the holding force of the elastic sleeve, which should be smaller than the ferrule pressing force, is also weaker. Furthermore, since the sleeve holding force is related to the area within the sleeve where the outer surface of the ferrule contacts the inner surface of the sleeve, the length of the ferrule fitting portion can be reduced as well as the sleeve size. When the diameter and length of the ferrule are reduced in this way, the process of polishing the outer periphery and the precision hole into which the fiber is inserted becomes easier when making the ferrule due to the reduction in the polishing area, resulting in (1) shorter polishing time; 2) Since the number of pieces that can be processed in one polishing process increases, the cost per piece is reduced; and (3) The yield rate improves because it becomes easier to obtain the dimensions. Therefore, reducing the diameter of the ferrule significantly reduces manufacturing costs and improves economic efficiency. Furthermore, since the ferrule pressing force can be reduced, when a large number of such ferrules are connected at once, the overall repulsive force can be reduced, and a compact multi-core optical connector can be realized.

There are no specific regulations regarding the mechanical bending strength of optical connectors, but JIS C5415r high frequency coaxial CO
Type 5 connectors are stipulated to have a cable connection strength of 5kgr or more, and optical connectors are required to have the same strength. For this purpose, the bending strength of the ferrule must be 5 kgf'.
The above is necessary. Figure 5 shows the bending strength of various materials used for the ferrule.

Among these, zirconia ceramic has the highest bending strength and is a material suitable for reducing the ferrule diameter.

(Problem to be solved by the invention) The above-mentioned mechanical strength problem of the ferrule can be solved by selecting the material, but if the outer diameter of the ferrule is reduced and a ferrule pressing force of about 1 kg is applied as before, the mechanical strength The connection characteristics become unstable due to physical impact.

Figure 2 shows that the ferrule pressing force is approximately 1 kg as before, the ferrule holding force is approximately 100 g, and only the ferrule diameter is 1. This figure shows the change in connection loss when an impact of approximately 1000 G is applied using an omm optical connector for a single mode optical fiber. This impact force of 100 OG can easily be generated when actually attaching and detaching an optical connector. As can be seen from Figure 2, the connection loss value before impact is 0.1 dB.
Although it is good as below, it may deteriorate to 1 dB or more after applying a shock. This is thought to be because, despite the reduction in the contact area between the ferrule and the sleeve, the pressing force was maintained as before, and a gap was generated due to a change in the bending moment M due to the impact.

An object of the present invention is to provide an optical connector that is small and can be mounted at high density.

(Means and actions for solving the problem) Therefore, in order to achieve stable connection characteristics with a small diameter ferrule, it is necessary to newly define the magnitude of the ferrule pressing force and sleeve holding force, as well as the characteristics of the sleeve.

First, we will discuss pressing force and holding force.

Decreasing the ferrule size reduces the sleeve retention force, and the reason for this reduction is the reduction in the contact area with the elastic sleeve. This contact area is thus the inner surface area of the elastic sleeve. In other words, if the ferrule diameter is large or the ferrule length is long, the contact area between the ferrule and the elastic sleeve becomes large, and the ferrule can be held stably. Therefore, even when the diameter of the ferrule is reduced, it is thought that a contact area larger than the -chamber is required. Therefore, in the small diameter ferrule,
We investigated the change in connection characteristics depending on the inner surface area of the elastic sleeve. Figure 4 shows the upper limit of the ferrule pressing force at which the loss variation is 0.1 dB or less when an impact force of 1000 G is applied to a connected state using a small diameter ferrule with an outer diameter of 1.0+em to 1.8 mm. The results are shown in which the ratio of the ferrule pressing force to the sleeve holding force is plotted against the inner surface area of the elastic sleeve.

As is clear from FIG. 4, the ratio of the ferrule pressing force to the sleeve holding force when achieving stable connection characteristics is approximately proportional to the inner surface area of the elastic sleeve.

From this, even when the ferrule pressing force, which is the cause of the bending moment M, is larger than the sleeve holding force, that is, when the ferrule tends to tilt due to impact, the characteristics are stable as long as the inner surface area of the elastic sleeve is large. I understand that.

Here, when reducing the diameter of the ferrule, the lower limit of the inner surface area is a problem. As mentioned earlier, the ratio of the ferrule pressing force to the sleeve holding force when tolerances are taken into account is 2.
8 or more is required, so from FIG. 4 it follows that the inner surface area of the sleeve cannot be less than 20 squares. At this time, the ferrule pressing force was set at the upper limit, but it is the shaded area in FIG. 4 that actually provides stable connection characteristics. That is, when calculating the slope of 0.14 and the Y-ring intercept of 0.5 from the graph, and assuming that the inner surface area of the sleeve is 81, the ferrule pressing force is F1, and the retaining force of the sleeve is FR, the following equation must be satisfied.

2.8≦FA/FR≦(0.14S +0.5
) In other words, the ferrule pressing force and sleeve holding force must satisfy the following relationship, and in that case, the inner surface area of the sleeve must be 20 cm or more. .

The value of the ferrule pressing force can be determined by calculating the sleeve holding force in the actual small diameter connector from this formula.

Next, from Figure 4, which describes the characteristics of the elastic sleeve,
It can be seen that the ratio of the ferrule pressing force to the sleeve holding force is determined only by the inner surface area of the sleeve and is not directly dependent on the inner diameter or length of the sleeve. On the other hand, when the ferrule is tilted by the bending moment M, the elastic sleeve is bent and its inner diameter is expanded. Here, the bending of the elastic sleeve is a value that depends on the inner diameter and length, and the inner diameter expansion is a value that depends on the bending stiffness El around the axis of the elastic sleeve. E is the Young's modulus of the material of the elastic sleeve, and . (see figure). From Figure 4, we can see that the connection characteristics are determined by the inner surface area and are relatively independent of the inner diameter and length of the elastic sleeve, so when the ferrule is tilted within the elastic sleeve, the inner diameter expansion acts on the elastic sleeve rather than bending. It is determined that there is. Therefore, the ferrule
In order to suppress the inclination of the ferrule when both the elastic sleeve is reduced, it is necessary to specify the bending stiffness El/L in the axial direction per unit length rather than specifying the inner diameter and length, that is, specifying the wall thickness of the sleeve. There is a need to. Regarding the sample used to obtain the relationship shown in FIG. 4, the elastic sleeve was made of phosphor bronze and had a wall thickness of about 0.2 mm, and the EI/L at this time was 8 kgf11ffil.

Next, the mechanical strength of the ferrule will be described.

The maximum stress σ generated in the ferrule under the bending moment M is expressed as σ-M/Z. Here, 2 is the section modulus, which is Z-πD3/32 when the ferrule outer shape is D. The length of the ferrule fitting part is L, and it is 1 from the tip.
．． When force P is applied at 5 mm, the maximum bending moment M is at the base of the ferrule, M-P (L-1,
5) Therefore, the maximum stress σ is a−M/Z= 32 P (L−1,5)/πD”−
(f). If σ is replaced with the bending strength σV of the material, P becomes the bending strength of this ferrule.

FIG. 6 shows the results of calculating the bending strength with respect to the outer diameter of a ferrule made of zirconia ceramic. however,
It is assumed that a force is applied at a position 1.5 mm from the tip of the ferrule, the inner surface area of the elastic sleeve is 2011I112, and the bending strength of zirconia is 120 kgr/1 square. or,
The distance between the elastic sleeve and the ferrule collar is 0.7 m, which is a sufficient value so that the collar does not get in the way of the pressing force of the spring pressing the ferrules together in the optical connector.
It was set as m.

Here, it is assumed that the force is applied at a point 1.5 mm from the tip of the ferrule, because when the ferrule is inserted into the elastic sleeve in an actual optical connector, the tip of the ferrule first comes into contact with the elastic sleeve. At this time, the ferrule is tilted by the force in the direction of tilting, using the tip as a fulcrum.

Since the elastic sleeve is built into the adapter, the ferrule collides with the end of the ferrule insertion hole of the adapter (the part indicated by the reference numeral 3'' in FIG. 1), thereby preventing the ferrule from tilting. In other words, this point of collision is the point where the force is actually received, and is approximately 1.5 m+e from the tip of the ferrule.

From FIG. 6, in order to satisfy the ferrule bending strength of 5 kgf, the ferrule outer diameter must be 1 mm or more. At this time, the upper limit of the length at each outer diameter becomes L −1,5−πσ D3/32P by transforming the equation (2), and L−2,4D +1.5 by substituting the above values. Therefore, when the ferrule outer diameter is D, the length of the ferrule fitting part is L≦2.4 D3+1. Must be Tl.

(Example) As an example of the present invention, an optical connector using a ferrule with an outer diameter of 1.25 mm was applied to a single mode optical fiber, and the connection characteristics were investigated using semiconductor laser light with a wavelength of 1.3 μm. FIG. 1 is a configuration diagram of the optical connector of this embodiment.

1 is an optical connector plug, 2 is a zirconia ferrule with an outer diameter of 125 mm to which the end of the optical fiber is fixed, 3 is an adapter, 4 is an elastic sleeve into which ferrule 2 is fitted, 5
6 is a coupling nut, 6 is a pressing spring that applies an axial pressing force to the ferrule 2, 7 is an optical fiber, 8 is a rotation stopper pin, and 9 is a rubber holder.

The elastic sleeve 4 has an axial bending stiffness of 8 kgrΦ per unit of stiffness, and an inner surface area of 28 to 34 m.
It is m. The ferrule pressing force is 0.4 to 1 kg, the sleeve holding force is 120 to 400 g, and the length of the fitting part of the ferrule 2 is 5 mm or 6 mm. An optical connector was constructed by combining these values to satisfy the above design conditions. FIGS. 8(a) and 8(b) show histograms of splice loss and return loss. As can be seen from the figure, the average connection loss was 0.08 dB and the average return loss was 38.6 dB, and the characteristics were equal to or better than those of the conventional optical connector using a ferrule with a diameter of 2.5 mm.

(Effect of the invention) As explained above, the present invention reduces the diameter of the ferrule,
Stability against mechanical shock when miniaturizing optical connectors is solved by optimizing the ferrule pressing force and sleeve holding force, and defining the characteristics of the ferrule and sleeve.According to the present invention, the ferrule outer diameter 1 or more 1
, 6 mm or less, stable characteristics similar to those of conventional optical connectors can be obtained. Therefore, a compact optical connector using a small diameter ferrule can be realized. The use of this optical connector enables high-density packaging, which was impossible with conventional optical connectors, and has the advantages of being able to construct a multi-fiber optical connector, and also improving economic efficiency.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical connector showing an embodiment of the present invention;
Figure 2 shows an optical connector with a ferrule outer diameter of 1.0 mm.
A diagram showing an example of loss fluctuation when a 0OG impact is applied. Figure 3 is a partial cross-sectional view of the main part showing the state of ferrule connection.
Fig. 4 is a diagram showing the relationship between the ratio of ferrule pressing force and sleeve holding force to the inner surface area of the elastic sleeve when realizing a stable connection, and Fig. 5 is a diagram showing the bending strength of the material used for the ferrule. Figure 6 shows the inner surface area of the elastic sleeve 20
A diagram showing the relationship between ferrule diameter and ferrule bending strength in mm2, FIG. 7 is a diagram illustrating the second moment of area in the axial direction per unit length of the elastic sleeve,
FIGS. 8(a) and 8(b) are histograms showing the connection characteristics of the optical connector according to the present invention. 1.1'... Optical connector plug, 2.2-2'...
Zirconia ferrule, 3...adapter, 4゜4''
, 4'... Elastic sleeve, 5... Coupling nut, 6, 6'... Pressing spring, 7... Optical fiber, 8
... Rotation stop pin, 9... Rubber holder.

Claims (2)

[Claims] (1) A pair of ferrules to which the ends of two optical fibers to be coupled are respectively fixed, and the pair of ferrules are fitted so that the ends of the respective optical fibers are mutually aligned and connected in the axial direction. and an elastic sleeve that is butted together;
In the optical connector, the optical connector has a spring that applies a pressing force in the axial direction to each of the ferrules, and the outer diameter of each of the ferrules is set to 1.0 to 1.6 mm, wherein the ferrule is applied to each of the ferrules by the spring. The pressing force is F_A, and the sleeve holding force, which is the force required to pull out the ferrule from the elastic sleeve, is F_
R, and when the inner surface area of the elastic sleeve is S, the following relationship is satisfied: F_R<F_A F_A/F_R<0.14S+0.5 When the outer diameter of the ferrule is D, the ferrule fits into the elastic sleeve. The length of the mating part is 2.6D^
3+1.5 mm or less, the inner surface area of the elastic sleeve is 20 mm^2 or more, and the bending stiffness in the axial direction per unit length is 8 kgf·mm or more. (2) The optical connector according to claim 1, wherein the ferrule is made of zirconia ceramic.