JPH04281409A - Ferrule for optical connector - Google Patents

Abstract

PURPOSE:To reduce deterioration in the extinction ratio of a polarization maintaining optical fiber due to residual stress when the polarization maintaining optical fiber is adhered to the ferrule and then a flange is fitted by employing structure wherein the flange can not move beyond a projection or step provided at the outer periphery of the front end part of the sleeve when pressed in. CONSTITUTION:A flanged projection 32 is formed at the front end of the sleeve 31 of the ferrule 1 which holds an optical fiber inside and the flange 33 is pressed in the sleeve 31 of the ferrule 1. The pressed-in flange 33 stops while abutting on the projection 32 of the sleeve 31, so even while the pressure of a spring operates on the flange 33 after assembly, the flange 33 never comes out toward the front end of the ferrule 1. The projection 32 which receives the spring pressure applied to the flange 33 is provided previously to the sleeve 31 where the flange 33 is pressed in, so sufficient fixation strength for the spring pressure is obtained without making a pressing-in margin large.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a ferrule for an optical connector used for connecting between optical fibers or between an optical fiber and an optical element, especially for polarization-maintaining optical fibers. This invention relates to a ferrule for an optical connector used in an optical connector used when it is necessary to precisely match the angle.

0002

2. Description of the Related Art Optical connectors used to facilitate connection and disconnection between optical fibers or between optical fibers and optical devices include, for example, JIS standard optical connectors.
Like the F04 type single-core optical fiber connector (generally called SC type optical connector) specified in C5973, an optical fiber is fixed at the center of a cylindrical rod (ferrule), and this is A typical method is to insert the ferrule into a hollow cylinder (alignment sleeve) and abut the end surfaces of the ferrules against each other. As described in Japanese Patent Application No. 60-11082, the ferrule used in this type of optical connector has a fine through hole with an inner diameter slightly larger than the outer diameter of the optical fiber, and is made of zirconia ceramic. Some ferrules (hereinafter referred to as zirconia ferrules) are manufactured by press-fitting a single cylindrical rod-shaped fitting part into a metal flange part. Its characteristics include (a)
Both the hardness and bending strength of the mating part are high, and the reliability is high (
b) Simple structure and low cost; (c) Patent application filed in 1980-
244050, the Young's modulus of zirconia ceramic is lower than that of other ceramics;
By polishing the ferrule end faces into a convex spherical shape and connecting them by applying pressure in the axial direction, even if the fiber retracts from the ferrule end face, the ferrule tip will deform and the core part of the fiber will be prevented. They have excellent properties such as being able to be brought into close contact with each other and achieving stable connection characteristics.

On the other hand, some optical fibers include polarization-maintaining optical fibers that can preserve the polarization state of propagating light. A polarization-maintaining optical fiber has a property of maintaining its polarization state when linearly polarized light is input in the direction of its principal axis. As a parameter to evaluate its performance, the extinction ratio, which is the ratio of the optical power on the output side in the principal axis direction and the component in the perpendicular direction when linearly polarized waves are incident in the principal axis direction, is used. In the case of a holding optical fiber, the value is −40 to −
50dB has been achieved. When connecting these optical fibers to each other, or when connecting a polarization-maintaining optical fiber to an optical element such as a laser diode that generates linearly polarized waves, it is necessary to match the direction of the main axis of the optical fiber, that is, the angle around the axis of the optical fiber. There is.

0004

When attaching the above-mentioned SC type optical connector to the above-mentioned polarization-maintaining optical fiber, it becomes necessary to align the direction of the main axis of the polarization-maintaining optical fiber with the direction of the plug housing. However, in the conventional zirconia ferrule, as shown in FIG.
1 is press-fitted into a holding part 42, and since the holding part 42, which has the function of determining the orientation around the axis of the ferrule, has a predetermined orientation, it is necessary to adjust the orientation of the main axis of the polarization-maintaining optical fiber. In this case, some kind of ingenuity is required on the plug housing side that incorporates the ferrule. An example of this technique is to use a cylindrical plug housing such as the F01 type single-core optical fiber connector (FC type optical connector) specified in JIC C 5970, and install the ferrule in the plug housing before connecting the fiber. There is a method of attaching a positioning key to the adapter according to the direction of the axis. However, there are the following problems when using a screw-fastening type optical connector such as an FC type optical connector for a polarization maintaining optical fiber.

FIG. 6 is a diagram showing the change in extinction ratio when plugs are repeatedly attached and detached for optical connectors manufactured by incorporating polarization maintaining optical fibers into the plug housings of SC type optical connectors and FC type optical connectors. be. F
In the case of a C-type optical connector, the ferrule is inserted before the positioning key, so torque is applied to the ferrule when aligning the positioning key with the adapter. Also, when tightening the coupling nut, the plug housing rotates around the positioning key, albeit slightly, relative to the adapter, which applies torque to the ferrule. When torque is applied to the ferrule, the axes of both fibers to be connected shift, resulting in a change in extinction ratio each time the ferrule is connected. Therefore, as an optical connector for a polarization maintaining fiber, it is advantageous to use a push-pull coupling method in which no torque is applied to the ferrule, and a rectangular SC type optical connector in which the direction of the plug relative to the adapter is uniquely determined. As shown in Figure 6,
When an FC type optical connector is used for the plug housing, the extinction ratio fluctuates greatly each time it is attached/detached due to the above-mentioned effects, but when an SC type optical connector is used, a very stable result can be obtained.

In order to incorporate a polarization maintaining optical fiber into a rectangular plug housing such as an SC type optical connector, it is necessary to align the direction of the main axis of the fiber with the direction of the plug housing in advance. For this purpose, a simple method is to attach the fiber to the ferrule in advance in a fixed direction, and the existing SC type optical connector plug housing can be used as is. Methods for performing this alignment include (a) a method in which the direction of the ferrule and the direction of the main axis of the optical fiber are aligned in advance and bonded; and (b) a method that determines the direction of the ferrule after bonding the ferrule to the optical fiber. One possible method is to attach the flange to the ferrule.

[0007] As the method (a), for example, Japanese Patent Application Laid-Open No. 1999-1-
As described in Japanese Patent No. 232,308, a method is known in which a fiber is orientated and connected to a ferrule by using a jig having a ferrule fixing part and an optical fiber fixing part rotatable around an axis. However, assembling ferrules one by one using such a special jig is not very productive and may result in high costs.

Although the method (b) has not been tried so far, adhesion, press-fitting, and welding are conceivable methods for attaching the flange to the ferrule in any direction. However, these methods may have the following problems. In the case of adhesion: In the case of the above-mentioned optical connector, in order to press both ferrules to be connected together, a pressing force from a spring is always applied to the ferrules. This pressing force is applied to the flange of the ferrule, and a structure in which such constantly acting force is received by an adhesive is not desirable in terms of reliability. In the case of press-fitting: Polarization-maintaining optical fibers generally have the property of maintaining the polarization state by imparting birefringence inside the core through which light propagates, but when an external force acts on this fiber, the inside of the core becomes different. Birefringence in the direction occurs and the extinction ratio deteriorates. Therefore, if an operation such as press-fitting is performed after bonding the fiber to the ferrule, strong residual stress may remain in the fiber and the extinction ratio may deteriorate. In order to reduce this effect, the amount of deformation can be reduced by reducing the press-fitting allowance, but as mentioned above, force is constantly acting on the flange, so in order to obtain the required large fixing strength, There is no choice but to increase the press-fitting allowance. In the case of welding: When welding is performed on a ferrule, the entire ferrule becomes hot, albeit temporarily, which affects the fiber and its coating. In addition, due to thermal stress,
The same influence as in the case of press-fitting described above is also considered.

On the other hand, as a structure in which a flange is later attached to a ferrule, a structure as shown in FIG. 5 has been known. This has a structure in which a ferrule main body 52 is made of metal, and a capillary 51 made of alumina ceramic is embedded in the tip. For such a structure, it is common to process the entire ferrule in one piece, but the part that fits with the alignment sleeve, that is, the ferrule body 51, is required to be made of a hard material with poor workability. In the case shown in FIG. 5, only the flange 53 is made of a free-cutting material and press-fitted later, thereby improving the overall manufacturability. In this case, as mentioned above, the flange needs to be firmly fixed, so strong residual stress will remain in the ferrule body after press-fitting, so it is not appropriate to perform press-fitting after bonding the polarization-maintaining fiber. . SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a ferrule for an optical connector that exhibits less deterioration in extinction ratio even if a flange is attached after bonding to a polarization-maintaining optical fiber.

0010

[Means for Solving the Problems] That is, according to the present invention, a cylindrical bar-shaped ceramic rod having a precise outer diameter and a minute through hole having an inner diameter slightly larger than the outer diameter of the optical fiber element. a fitting part made of a member, a cylindrical hole at one end for accommodating the fitting part, and a hole at the other end for adhesively fixing the coated part of the optical fiber, and In the ferrule for an optical connector, the ferrule is composed of a metal holding part having a brim-like protrusion on the outer periphery, and has a structure in which the fitting part and the holding part are integrated, and the holding part holds the optical fiber coated part inside. a sleeve that holds the
It is composed of a ring-shaped flange that receives spring pressure to press both ferrules to be connected together in the axial direction, and the flange has a structure that is press-fitted into the sleeve in the axial direction, and the fitting part is press-fitted. A ferrule for an optical connector is provided, characterized in that a protrusion or step is provided on the outer periphery of the front end of the sleeve, and the flange cannot move forward than the protrusion or step when the flange is press-fitted. be done.

[0011]

[Operation] In the ferrule according to the present invention, the flange of the ferrule for optical connectors is a separate part, and after bonding the fiber to the ferrule, the flange can be oriented and press-fitted into the ferrule, and it can receive the pressure of the spring applied to the flange. The main feature is that the protrusion is already provided on the holding part of the ferrule. According to this structure, the flange can be attached after bonding the ferrule to the polarization-maintaining optical fiber and polishing the end face.
For example, the orientation of the fiber axis and flange can be easily aligned by viewing the polished fiber end face with a microscope. In addition, by providing a protrusion in advance on the ferrule holding part to receive the pressure of the spring applied to the flange, sufficient fixing strength can be obtained even if the press-fitting margin for the flange is small. Deterioration of the extinction ratio of the wave-maintaining optical fiber can be reduced. As explained above, by using the ferrule structure according to the present invention, it is possible to extremely easily form an optical connector for polarization maintaining fiber by using a conventional optical connector plug housing as is. Furthermore, since the present invention can be applied to a rectangular plug housing such as an SC type optical connector, it is possible to form an optical connector for a polarization-maintaining fiber with extremely good reproducibility of extinction ratio during repeated attachment and detachment.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 are diagrams showing the construction of one embodiment of a ferrule according to the present invention. The ferrule 1 has a precise outer diameter and is composed of a fitting part 2 that holds the optical fiber therein and a holding part 3, and the holding part 3 is a sleeve that holds the coated part of the optical fiber inside. 31, and a flange 33 which serves to hold the ferrule 1 in a fixed orientation within the plug housing and to receive the pressure of a spring to press both ferrules to be connected together. FIG. 1 shows a state before the flange 33 is press-fitted into the sleeve 31, and a protrusion 32 is provided at the front end of the sleeve 31. The flange 33 is passed through the optical fiber core 4 before bonding the ferrule, and the sleeve 31 is inserted after the fiber bonding and ferrule end face polishing work is completed.
It is press-fitted from the rear end. FIG. 2 is a diagram illustrating the state of the ferrule after press-fitting, in which (a) is a front view seen from the front end of the ferrule, and (b) is a side view. Since the press-fitted flange 33 stops when it abuts against the protrusion 32 of the sleeve 31, the flange 33 will not come off toward the front end of the ferrule 1 even when spring pressure is applied to the flange 33 after assembly. Furthermore, during press-fitting, the keyway 34 provided in the flange 33 can be set in any direction around the ferrule axis, so that it can be aligned with the direction of the main axis of the bonded polarization-maintaining optical fiber. moreover,
This orientation adjustment work can be done after polishing the ferrule end face, so the main axis can be determined by observing the fiber end face with a microscope at the ferrule end face, or by inputting linearly polarized light from the other end and monitoring the output light. The flange 33 can be press-fitted in accordance with the determined direction, and the workability is good.

FIG. 3 shows the ferrule according to the present invention
FIG. 2 is a partial cross-sectional view showing the structure of an optical connector built into a plug housing of a C-type optical connector. Since the orientation of the keyway 34 of the flange 33 of the ferrule 1 is aligned with the orientation of the main axis of the fiber as described above, the optical connector is completed simply by incorporating the ferrule into the plug housing 21. The ferrule 1 is pressed forward by a pressure spring 22, and when a pair of plugs are connected, the ferrule 1 is held in a slightly retracted state with respect to the plug housing 21, and the end faces of both ferrules are pressed against each other. It has a structure that can be pressed against it. At this time, the flange 33 of the ferrule is always pushed toward the front end of the ferrule by the spring 22, but due to the above structure,
The press-fitted flange 33 will not come off.

[0014]

[Effects of the Invention] As detailed above, the ferrule according to the present invention has a structure in which the flange can be press-fitted after bonding the fibers, so that the direction of the flange can be adjusted to match the direction of the main axis of the bonded polarization-maintaining optical fiber. It is suitable for use by being incorporated into a rectangular plug housing such as an SC type optical connector. In addition, since the protrusion that receives the spring pressure applied to the flange is provided in advance on the sleeve into which the flange is press-fitted, it is possible to provide sufficient fixing strength against the spring pressure without requiring a large margin for press-fitting. It is possible to prevent the extinction ratio of the polarization-maintaining optical fiber from deteriorating due to stress.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view illustrating a state of an embodiment of an optical connector ferrule according to the present invention before a flange is attached.

FIG. 2 is a front view and a side view showing the state of the optical connector ferrule according to the present invention after the flange is attached.

FIG. 3 is a partial cross-sectional view illustrating the structure of an SC type optical connector assembled using the optical connector ferrule according to the present invention.

FIG. 4 is a side view showing an example of a conventional zirconia ferrule.

FIG. 5 is a side view showing another example of a conventional ferrule.

FIG. 6 is a diagram showing changes in extinction ratio when plugs are repeatedly attached and detached for optical connectors manufactured by incorporating polarization-maintaining optical fibers into SC type optical connectors and FC type optical connectors.

[Explanation of symbols]

1 Ferrule 2,41 Fitting part 3,42 Holding part 31 Sleeve 32 Protrusion 33 Flange 34 Keyway 4 Optical fiber wire 51 Capillary 52 Ferrule body 53 Flange

Claims (1)

[Claims] Claim 1: A fitting part consisting of a cylindrical bar-shaped member made of ceramics having a precise outer diameter and a fine through hole having an inner diameter slightly larger than the outer diameter of the optical fiber strand; A metal member having a cylindrical hole for accommodating the fitting portion, a hole for adhesively fixing the coated portion of the optical fiber at the other end, and a flange-shaped protrusion on the outer periphery. In the ferrule for an optical connector, the holding part has a structure in which the fitting part and the holding part are integrated. It is composed of a ring-shaped flange that receives spring pressure to press the ferrules together in the axial direction, and the flange has a structure that is press-fitted into the sleeve in the axial direction, and the front end of the sleeve is press-fitted with the fitting part. A ferrule for an optical connector, characterized in that a protrusion or a step is provided on the outer periphery, and the flange cannot move forward beyond the protrusion or step when the flange is press-fitted.