JPH06174971A - Optical connector - Google Patents

Abstract

PURPOSE:To provide the high-performance optical connector which can realizes ultra-low reflection connection of >=55dB reflection attenuation quantity. CONSTITUTION:Ferrules 3 are in contact with each other at the front ends, as shown in (a), when ferrule bodies 2 are brought into contact without pressurization. Optical fibers 4 are, however, not in contact with each other and are parted apart a fiber spacing u. The ferrule bodies 2 are pressurized and the ferrules 3 are deformed by the pressurizing force and the optical fibers 4 are therefore brought into contact with each other and the front ends of the optical fibers 4 are slightly deformed, as shown in (b), when such optical connectors are connected. Then, excess compressive force is not applied on the optical fibers 4 when the optical connectors are connected and the ultra-low- reflection connector is therefore realized without impairing the optical characteristics of the optical fibers 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical connector ferrule and an optical fiber used in the field of optical communication.

[0002]

2. Description of the Related Art An optical connector is used to connect an optical fiber which is a transmission line of optical communication. For example, in connection with a transmission line such as a semiconductor laser module that needs to prevent generation of noise due to reflected light, particularly in connection with a transmission line in high-speed large-capacity communication such as CATV and video communication, signal loss at the connection point is small. Performance optical connectors are required.

Generally, an optical connector is composed of a plug into which an optical fiber is inserted and fixed, and an adapter having a mechanism for fitting and aligning the plugs. Particularly, unlike the conventional electrical connector, it is important to accurately match the relative positions of the two optical fibers to be connected. For this reason, it is necessary to extremely reduce the axial deviation angle bending between the optical fibers. Therefore, the optical fiber is made to match the center of the ferrule whose outer shape is finished to the specified size, is fixed by adhesive, and the ferrule body is inserted from both ends of the sleeve incorporated in the adapter and abutted. Is often used.

The structure of the prior art will be described below with reference to the drawings. FIG. 7 is a connection cross-sectional view showing a typical example of a conventionally used optical connector, and the left end of the symmetrical drawing is omitted. Reference numeral 4 is an optical fiber made of quartz glass, 3 is a ferrule made of ceramics such as alumina or zirconia, and the optical fiber 4 is adhered and fixed to the center of the ferrule 3 with an adhesive material (not shown) with its axial center aligned. I am doing it. Reference numeral 2 is a ferrule body in which the ferrule 3 and the optical fiber 4 are integrally assembled, and 7 is a ferrule flange for holding the ferrule body 2 and pressurizing it by a spring 6 as a pressurizing means. , 8 is a plug frame for receiving the ferrule flange 7, 9 is a nut, 10 is an optical fiber 4 inserted therein, and the ferrule flange 7 and the spring 6 are incorporated in the spring together with the plug frame 8. It is a bush that receives the force of 6. Reference numeral 1 denotes a plug, which comprises the optical fiber 4, the ferrule 3, the spring 6, the ferrule flange 7, the plug frame 8, the nut 9, and the bush 10. Reference numeral 11 is an adapter, and 12 is a split sleeve incorporated in the adapter 11.

FIG. 8 is an enlarged sectional view of the tip of the ferrule body 2. Reference numeral 3 denotes a ferrule, and 4 denotes an optical fiber, in which the dimensions of the optical fiber 4 are extremely enlarged. The tip of the ferrule 3 is a convex spherical surface having a radius of curvature R, and the tip of the optical fiber 3 is a substantially convex spherical surface slightly retracted from the convex spherical surface. The radius of curvature R is often 10 to 60 mm.

Next, the optical connector is connected to the ferrule body 2 by pressing the ferrule 3 with the spring 6 through the ferrule flange 7.
, Two sets of the plugs 1 are inserted from both sides of the adapter 11 in which the split sleeve 12 is assembled in the center in advance,
This is completed by screwing and fixing each of the nuts 9. The optical fibers 4 are aligned concentrically by the split sleeve 12, and the ferrules 2 are pressed from both sides by the springs 6 having a strength of 0.8 to 1.2 kg to stabilize the connection. It is trying to make it.

Next, a method of processing the tip of the ferrule body 2 will be described. First, a diamond grindstone is used to grind into a conical shape, and then the tip of the ferrule 2 is pressed while rotating while the diamond film is being supplied to a strongly stretched plastic film, and the optical fiber is polished. 4 and the tip of the ferrule 3 are simultaneously formed into a convex spherical shape.

The positional relationship between the ferrule 3 of the ferrule body 2 and the optical fiber 4, which is a problem in the conventional optical connector as described above, will be described with reference to FIG. The relative position between the ferrule 3 and the optical fiber 4 is generally the amount of pull-in d, that is, the intersection Q between the axial center line of the ferrule 3 and the convex spherical surface having the radius of curvature R, and the tip of the optical fiber 4. When the tip of the optical fiber 4 is on the inside of the convex spherical surface, it is represented by −, and when it is on the outside of the same, it is represented by a sign of +.
It was generally used in the range of -50 to +100 nm.

[0009]

However, the above-mentioned range of the drawing amount d of the optical fiber in the conventional method is unsuitable for sufficiently taking out the performance of the optical connector, and the optical characteristics of the optical fiber are sufficiently protected. Not a thing. This problem will be described below with reference to FIGS. 8 and 9.

FIG. 9 is a partially enlarged sectional view in which ferrule bodies of a conventional optical connector having a radius of curvature R are butted against each other, and the size of the optical fiber portion is extremely enlarged. A ferrule 3 with a radius of curvature R = 20 mm
The case where the optical fiber 4 having a diameter of 0.125 mm is used in FIG. In FIG. 8, the distance between the tip of the ferrule 3 and the intersection Q is calculated to be 98 nm, and even if the pull-in amount d is the lower limit of −50 nm with respect to the ferrule 3, the optical fiber 4 This means that the tip has already protruded 48 nm from the tip of the ferrule 3. Therefore, when connecting and fixing an optical connector using such a ferrule body 2, first, when the tips of the ferrule body 2 are brought into contact with each other without applying pressure, as shown in FIG. The tip of No. 4 comes into contact before the ferrule 3, and when this is pressurized, as shown in FIG. Therefore, an extremely strong compressive force is applied to the optical fiber 4, which deteriorates the performance of the optical connector.

Further, in the above-described method for processing the tip of the ferrule body, the work-affected layer remains on the surface portion of the end of the optical fiber, and the return loss cannot be reduced.
The limit was about 0 dB. If the surface of the felt body is polished in order to remove the work-affected layer, the amount of pull-in d becomes large and the above range is exceeded.

The pull-in amount d is -50 to +100 nm of the conventional one.
In order to remove the work-affected layer in such a range as described above, for example, "PC optical connector having a return loss of 50 dB or more" (Proceedings of Autumn Meeting of the Institute of Electronics, Information and Communication Engineers 1991 C-224) is proposed. As described above, the ferrule is preliminarily spherical-polished, and then the optical fiber is incorporated and bonded. Then, the optical fiber is made to have a dimension slightly protruding from the ferrule tip, and then the optical fiber tip is spherically polished. After this, the work-affected layer is removed. Optical fiber
Since the work-affected layer is removed after the work-affected layer is protruded from the tip end of the tool, the pull-in amount falls within a predetermined range even if the work-affected layer is removed. However, in this method, since the spherical processing of the ferrule and the optical fiber is performed in separate steps, the center of the radius of curvature shifts to cause eccentricity, and as described above, an extremely strong compressive force is applied to the optical fiber. It has the drawback of degrading performance.

As described above, it is not easy to remove the work-affected layer without problems within the conventional range of the pull-in amount d. However, when using the ferrule body with the work-affected layer left, It is impossible to provide an optical connector that satisfies the requirements for high speed and high performance of optical transmission and that prevents generation of noise due to reflected return light. An object of the present invention is to solve the above problems and provide a high performance optical connector capable of realizing an ultra-low reflection connection with a return loss of 55 dB or more.

[0014]

In order to achieve the above object, the structure of the present invention is an optical system in which two sets of ferrule bodies, in which an optical fiber is assembled to a ferrule via an adhesive, are abutted by a pressing means. In the connector, when the ends of the two ferrule bodies are opposed to each other and the optical fibers are not in contact with each other when they are brought into contact with each other without applying pressure, the optical fibers are in contact with each other when being applied with pressure by the applying means. It is characterized by

Further, the distance between the optical fibers when the two ferrule bodies are opposed to each other and are brought into contact with each other without applying pressure is determined by the applied pressure when the ferrule is pressed within the elastic limit of the ferrule. Characterized by being within the quantity.

[0016]

According to the method of connecting the optical connector of the present invention, the distance between the optical fibers of the ferrule body (hereinafter referred to as the fiber distance) when brought into butt contact with each other without applying pressure is determined by the strength of the spring pushing the ferrule. By making the elastic deformation amount of the ferrule to be determined, the compressive load on the boundary surface of the optical fiber can be reduced as much as possible, and the optical connectors can be connected to each other without deteriorating the optical characteristics.

[0017]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an enlarged cross-sectional view of a ferrule butting portion of an optical connector according to an embodiment of the present invention, and particularly, an optical fiber portion is extremely enlarged. Figure 2 is a theoretical calculation
FIG. 3 is a schematic diagram of a loop body, FIG. 3 is a graph showing experimental results of return loss and fiber spacing in the connected optical connector, and FIG. 4 similarly shows experimental results of relationship between return loss and spring strength. 5 is a graph, FIG. 5 is a graph showing an experimental result of a change in return loss when the temperature is changed, and FIG. 6 is an enlarged cross-sectional view showing a tip of a ferrule body of an optical connector of another embodiment. Is.

Embodiments of the present invention will be described in detail below with reference to the drawings. In FIG. 1, 3 is a ferrule made of zirconia, 4 is an optical fiber made of silica glass,
Reference numeral 2 is an adhesive 5 such as Epotek 353ND for which the axis of the optical fiber 4 is aligned with that of the ferrule 3.
Is a fiber body adhered and fixed by, u is a fiber interval, and g is a distance between the ferrule tip and the optical fiber tip (hereinafter referred to as an end face distance). Other configurations, assembling methods, and connecting methods are the same as those of the conventional example shown in FIG.

Both ends of the ferrule 3 and the optical fiber 4 are processed into convex spherical surfaces having substantially the same radius of curvature, and the relative positional relationship between them is a feature of the present invention. Figure 1
(A) shows a state in which the ferrule body 2 is contacted without pressure. The ferrules 3 are in contact with each other at their tips, but the optical fibers 4 are not in contact with each other and are separated by a fiber interval u. When the optical connector of the present invention is connected, the ferrule body 2 is pressed and the ferrules 3 are deformed by the pressing force as shown in FIG. The tip of the fiber 4 is slightly deformed.

Here, the deformation amount of the ferrule when the tips of the two sets of ferrules are made to face each other and brought into pressure contact with springs from both sides will be determined based on the elastic strain theory. Figure 2 (a) shows the load W
Fell butting under pressure from both in - is a schematic view of Le body, the Fel - le body Fel comprising a cylindrical portion P ₁ and the spherical portion P ₂ of the curvature radius R of the diameter d ₁ - and Le, where It consists of an omitted optical fiber. FIG. 2B is a partially enlarged cross-sectional view of the tip of the ferrule, where d ₂ is the inner diameter of the ferrule, x is the intersection of the convex spherical surface with the radius of curvature R and the axial center line of the ferrule. A variable that represents the distance from Q to an arbitrary position of the spherical portion P ₂ , x ₁ represents the distance between the intersection Q and the tip of the ferrule, and x ₂ represents the distance from the end surface of the spherical portion P ₂ .

Here, the Young's modulus of the ferrule is E, the spring strength is W, and the circular constant is π. When the deformation amount of the cylindrical portion P ₁ is λ ₁ and the deformation amount of the spherical surface portion P ₂ is λ ₂ , Formula 1 is derived.

[Equation 1]

Here, the numerical value of the ferrule of the embodiment is given by
That is, E = 10000 kg / mm ² , W = 1 kg, d ₁ = 2.5
Substituting mm, l ₁ = 10 mm, R = 20 mm, and d ₂ = 0.125 mm, λ ₁ = 136 and λ ₂ = 8 are obtained. If the total amount of deformation is λ, then λ = λ ₁ + λ ₂ = 136 + 8
= 144 nm. The results obtained represent the amount of deformation of one side of the zirconia ferrule when two zirconia ferrules with a radius of curvature of 20 mm are butted against each other and pressed by a spring with a strength of 1 kg, and most of the amount of deformation is in the cylindrical portion P ₁ . It is shown that the effectiveness of the spherical surface portion P ₂ is small.

Therefore, the end face distance g is the deformation amount 144 nm.
Within the range, the tip of the ferrule is compressed by the spring, and the tip of the optical fiber jumps out from the tip of the ferrule and comes into contact with the tip of the opposing optical fiber. That is, if the fiber spacing u is within 144 × 2 = 288 nm, the tips of the optical fibers facing each other may contact each other.
Predicted by calculation.

Next, the process of processing the tip shape of the ferrule body of the optical connector of the present invention will be described. The process up to the step of polishing with diamond abrasive grains is the same as the conventional process. In this polishing step, the end faces of the optical fiber and the ferrule can be processed with almost no step, but a work-affected layer occurs on the surface of the optical fiber. Therefore, in order to remove the work-affected layer, plane lapping is performed using a fine particle abrasive such as SiO ₂ or Ce O ₂ .

Since there is a hardness difference between the ferrule made of ceramics such as alumina and zirconia and the optical fiber made of quartz glass, in the flat lapping process using the fine particle material, the tips of the optical fiber and the ferrule are It is difficult to finish-polish the same surface, and a step is formed at the tip of the optical fiber and the ferrule in which the optical fiber retracts in proportion to the polishing amount.

In the present invention, as theoretically studied, it is predicted that a shape in which the end face distance g of the ferrule body is 144 nm and the end face of the optical fiber is retracted from the tip of the ferrule is acceptable. Therefore, a step up to about 144 nm may occur in the polishing step for removing the work-affected layer. That is, it is easy to remove the work-affected layer.

Next, in order to confirm the performance of the optical connector according to the present invention, various samples of the same ferrous body as in the embodiment were prepared in the above-mentioned detailed steps, and the results of the performance measurement were shown in the drawings. explain. FIG. 3 plots the return loss of samples at various fiber intervals. The return loss increases as the fiber spacing increases, and exceeds 60 dB. However, when the fiber spacing reaches around 250 nm or more, the optical fibers are separated from each other to form a gap, so the return loss is extremely reduced. That is, if the fiber spacing is within the deformation amount of two sets of ferrules, it can be understood that the smaller the compressive force applied to the optical fiber, the more the return loss increases.

A conventional optical fiber drawing amount d is -50 to
In the polishing process of diamond abrasive grains in the range of +100 nm and with a plastic film, the reflection attenuation amount, which was at most 40 dB, was greatly improved and a characteristic of 55 dB or more was obtained. Fiber spacing 0 to 250 in this experiment
When nm is applied to the pull-in amount d, d is the distance between the optical fiber tip and the intersection of the axis center line of the ferrule and the convex spherical surface with the radius of curvature R. Therefore, the intersection and the tip of the ferrule. Is equal to the distance calculated above, or 98 nm previously calculated, plus the end face distance, or half the fiber spacing. Therefore, the pull-in amount d of the ferrule body with the radius of curvature R = 20 mm is-(98
+0) to − (98 + 125), that is, approximately −100 to −22.
This corresponds to the range of 5 nm.

In the present invention, the marginal area where the optical fibers are not in contact with each other is obtained by model calculation and further verified by experiments. However, in actual use, variations in spring pressure and differences in the coefficient of thermal expansion between the ferrule and the optical fiber are used. It is necessary to set a region where the contact state is not released due to changes in environmental conditions and manufacturing quality, taking into consideration the effects of the above.

Therefore, a change in the actual measurement value of the return loss is shown in FIG. 4 when a spring with a strength of 1 kg is used in a sample with a reduced return loss and only one spring is replaced with a stronger spring. Shown in. According to the calculation, the amount of deformation of both ferrules is 288 nm when both springs with a strength of 1 kg are used.
If one spring is replaced with a spring having a strength of 1.25 kg, the deformation amount is 324 nm, and if the spring having a strength of 1.5 kg is replaced, the deformation amount is 360 nm. The difference in deformation amount is 36
nm and 72 nm. On the other hand, the actual fiber spacing u is 2
The sample A of 74 nm and the sample B of 291 nm have a fiber spacing difference of 24 nm and 41 nm, respectively, while the fiber spacing limit value of 250 nm, which was the limit value in the previous experiment, is 24 nm and 41 nm, respectively. It was theoretically predicted that a spring exchange of 0.25 kg would improve the properties of the spring exchange of 1.5 kg for sample B, which is consistent with the experimental results of FIG.

Next, the result of investigation on the influence of the return loss on temperature will be described with reference to FIG. Room temperature to 0 ° C
→ -25 ° C → 0 ° C → 25 ° C → 50 ° C → 75 ° C → 50 ° C →
The temperature was changed to 25 ° C., the residence time at each temperature was set to 1 hour, and the change time to the next temperature was set to 30 minutes. The fiber spacing u of samples C, D, E, F, G and H are 56, 93, 160, 195 and 24, respectively.
6, 252 nm. The solid line shows the set temperature, the alternate long and short dash line shows the change in return loss of sample F, and the broken line shows the change of return loss of sample G. The return loss of samples C, D, E, and F having a fiber spacing u of 200 nm or less did not change. This state is represented by sample F as a representative. Samples G and H with fiber spacing u around 250 nm are from 50 ° C to 7
The return loss decreases sharply between 5 ° C. This state is represented by Sample G as a representative. That is, in order to maintain the performance with respect to the temperature change of 100 ° C., the fiber interval u is 5
It may be reduced to about 0 nm.

FIG. 6 shows a sectional view of the tip of the ferrule body of the optical connector according to another embodiment of the present invention which is suitable for removing the work-affected layer. Here, since the constituent elements are the same as those in FIG. 8, the same constituent elements are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the convex spherical surface shape polishing process performed after the conical grinding process is devised. That is, the plastic film is strongly stretched to control the tension constantly, and the pressing force of the tip of the ferrule body 2 against the plastic film is controlled to be constant, and the tip end shape of the ferrule body 2 is convexly spherical-polished. To a mirror surface. According to this processing method, the optical fiber 4
It is possible to process the protrusion of the ferrule 3 protruding from the tip, and it is possible to cope with the case where the thickness of the process-altered layer is large.

[0033]

As described above, according to the present invention, an excessive compressive force is not applied to the optical fiber when two sets of optical connectors facing each other are connected. In addition to the fact that the work-affected layer of the optical fiber can be easily removed, an ultra-low reflection optical connector having a return loss of 55 dB or more can be realized without impairing the optical characteristics of the optical fiber.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view of an optical connector according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a Ferule body for theoretical calculation.

FIG. 3 is a graph showing the relationship between return loss and fiber spacing.

FIG. 4 is a graph showing the relationship between return loss and spring strength.

FIG. 5 is a graph showing changes in return loss with temperature.

FIG. 6 is a partially enlarged sectional view of a ferrule body according to another embodiment of the present invention.

FIG. 7 is a connection cross-sectional view of a conventional optical connector.

FIG. 8 is a partially enlarged sectional view of a conventional ferrule body.

FIG. 9 is an enlarged cross-sectional view of a butted portion of a conventional ferrule body.

[Explanation of symbols]

 2 Ferrule body 3 Ferrule 4 Optical fiber 5 Adhesive 6 Spring

Claims (2)

[Claims] 1. An optical connector comprising a ferrule and two sets of ferrule bodies assembled by an adhesive with which a ferrule body is butted against each other by a pressing means. The ends of the two ferrule bodies are opposed to each other and pressed. An optical connector characterized in that the optical fibers are separated from each other without contact when they are contacted without each other, and the optical fibers are contacted with each other when pressed by the pressing means. 2. The deformation of the ferrule, wherein the distance between the optical fibers when two sets of ferrule bodies are opposed to each other and are brought into contact with each other without pressure is determined by the pressure applied when pressure is applied within the elastic limit of the ferrule. The optical connector according to claim 1, wherein the optical connector is within the quantity.