JP2849486B2 - Ferrule for polarization maintaining optical fiber connector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrule for an optical connector used for connection between optical fibers or between an optical fiber and an optical element. The present invention relates to a ferrule for an optical connector used for an optical connector used when an angle needs to be accurately adjusted.

[0002]

2. Description of the Related Art In the connection between optical fibers or between an optical fiber and an optical element, an optical connector used for easy connection and disconnection is, for example, JIS.
An optical fiber is fixed to the center of a cylindrical rod (ferrule) as in an F04 type single-core optical fiber connector (generally called an SC type optical connector) specified in C5973, and this has a precise inner diameter. A typical example is a method in which the ferrules are inserted into a hollow cylinder (aligning sleeve) and the end faces of the ferrule abut against each other. As a ferrule used in an optical connector according to this method, for example, as described in Japanese Patent Application No. 60-11082, a zirconia ceramic having a fine through hole having an inner diameter slightly larger than the outer diameter of an optical fiber is used. There is one manufactured by press-fitting a cylindrical rod-shaped fitting portion formed as a single body into a metal flange portion (hereinafter referred to as a zirconia ferrule). As its features,
(A) The hardness and bending strength of the fitting portion are both high and high in reliability, (b) the structure is simple and low cost, and (c) zirconia ceramic as described in Japanese Patent Application No. 60-244050. Because the Young's modulus of the ferrule is lower than that of other ceramics, the ferrule end faces are polished into a convex spherical shape, and by applying an axial pressing force to each other, the fiber is pulled from the ferrule end face. The ferrule tip is deformed so that the core portions of the fibers can be brought into close contact with each other, and stable connection characteristics can be realized.

On the other hand, among optical fibers, there is a polarization-maintaining optical fiber that can maintain the polarization state of propagating light. The polarization maintaining optical fiber has a characteristic of maintaining its polarization state when linearly polarized light is incident in the main axis direction. As a parameter for evaluating the performance, an extinction ratio, which is a ratio of a component of the optical power on the emission side in a main axis direction and a direction perpendicular to the main axis direction when linearly polarized light is incident in the main axis direction, is used. In the case of a holding optical fiber, the value is -40 to 40.
-50 dB is realized. When connecting the optical fibers to each other or to an optical element such as a laser diode that generates linearly polarized light and a polarization maintaining optical fiber, it is necessary to match the direction of the main axis of the optical fiber, that is, the angle around the optical fiber axis. There is.

[0004]

When the above-mentioned SC type optical connector is attached to the above-mentioned polarization maintaining optical fiber, it is necessary to adjust the direction of the main axis of the polarization maintaining optical fiber to the direction of the plug housing. However, the conventional zirconia ferrule is, for example, as shown in FIG.
1 is press-fitted into the holding portion 42, and since the holding portion 42 having a function of determining the direction around the axis of the ferrule is determined in advance, it is necessary to adjust the direction of the main axis of the polarization maintaining optical fiber. Requires some contrivance on the plug housing side to incorporate the ferrule. As an example of this contrivance, for example, a cylindrical plug housing such as an F01 type single-core optical fiber connector (FC type optical connector) specified in JIC C 5970 is used, and after a ferrule is incorporated into the plug housing, a fiber is inserted. There is a method of attaching a positioning key to the adapter in accordance with the direction of the axis. However, there are the following problems in 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 a change in extinction ratio when an optical connector manufactured by incorporating a polarization maintaining optical fiber in a plug housing of an SC optical connector FC optical connector when plugs are repeatedly inserted and removed. is there. F
In the case of the C-type optical connector, since the ferrule is inserted before the positioning key, a torque is applied to the ferrule when the positioning key is fitted to the adapter. Further, when the coupling nut is tightened, the plug housing is slightly rotated around the positioning key with respect to the adapter, so that a torque is applied to the ferrule. When a torque is applied to the ferrule, the axes of both fibers to be connected are shifted, so that the extinction ratio changes each time the connection is made. For this reason, as the optical connector for the polarization maintaining fiber, a rectangular SC type optical connector that is of a push-pull type in which no torque is applied to the ferrule and in which the direction of the plug is uniquely determined with respect to the adapter is advantageous. As shown in FIG. 6, when the FC type optical connector is used for the plug housing, the extinction ratio greatly fluctuates each time the plug type is attached or detached due to the above-described effects. The result is as follows.

Here, in order to incorporate the polarization maintaining optical fiber into a rectangular plug housing such as an SC type optical connector, it is necessary to match the direction of the main axis of the fiber with the direction of the plug housing in advance. For this purpose, it is easy to attach the fiber to the ferrule in a fixed direction in advance, and the existing SC type optical connector plug housing can be used as it is. As a method for performing the alignment, (a) a method in which the direction of the ferrule and the direction of the main axis of the optical fiber are previously aligned and bonded, and (b) a function of determining the direction of the ferrule after bonding the ferrule to the optical fiber. A method of attaching the flange to the ferrule is conceivable.

The method (a) is described in, for example,
As described in US Pat. No. 232,308, a method is known in which a jig having a ferrule fixing portion and an optical fiber fixing portion rotatable around an axis is used, and the fiber is aligned and connected to the ferrule. However, assembling ferrules one by one using such a special jig is not very productive and may be costly.

The method (b) has not been attempted so far, but as a method of attaching the flange to the ferrule in an arbitrary direction, bonding, press fitting, and welding can be considered. However, these methods have the following problems. In the case of bonding : In the case of the above-described optical connector, since both ferrules to be connected are pressed against each other, a pressing force by a spring always acts on the ferrule. This pressing force is applied to the flange of the ferrule, and a structure in which such a constantly acting force is received by the adhesive is not preferable in terms of reliability. In the case of press-fitting : Polarization-maintaining optical fibers generally have the property of maintaining the state of polarization by imparting birefringence to the inside of the core through which light propagates. Birefringence 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 remains in the fiber, and the extinction ratio may be degraded. In order to reduce this effect, it is sufficient to reduce the amount of deformation by reducing the press-fitting margin, but since a force is constantly applied to the flange as described above, in order to obtain the required large fixing strength, The press fit must be increased. In the case of welding: When a welding operation is performed on a ferrule, the temperature of the entire ferrule is temporarily increased, but the fiber, the coating of the fiber, and the like remain. Also, due to thermal stress,
The same effect as in the case of press fitting described above is also conceivable.

On the other hand, as a structure for attaching a flange to a ferrule later, a structure as shown in FIG. 5 has been known. This has a structure in which the ferrule main body 52 is made of metal, and a capillary 51 made of alumina ceramic is embedded at the tip. As such a structure, a method of integrally processing the entire ferrule is generally used. However, since a part to be fitted to the alignment sleeve, that is, the ferrule main body 51, is required to be formed of a hard material having poor workability. In FIG. 5, only the flange 53 is made of a member that can be easily cut, and is press-fitted later to improve the overall manufacturability. In this case, since the flange must be firmly fixed as described above, a strong residual stress remains in the ferrule main body after press-fitting, and it is not appropriate to perform press-fitting work after bonding the polarization maintaining fiber. . SUMMARY OF THE INVENTION An object of the present invention is to provide a ferrule for an optical connector in which the extinction ratio is less deteriorated even when a flange is attached after bonding to a polarization maintaining optical fiber.

[0010]

That is, according to the present invention, there is provided a ceramic material having a precise outer diameter and a fine through hole having an inner diameter slightly larger than the outer diameter of the polarization maintaining optical fiber. A fitting portion formed of a cylindrical rod-shaped member, and a cylindrical hole for accommodating the fitting portion at one end, and for bonding and fixing a core covering portion of the polarization maintaining optical fiber to the other end. has a hole, and is composed of a metallic holder having a flange-like projections on the outer periphery, has a structure integrated with the holding portion and the fitting portion, is housed is positioned within the housing A ferrule for a polarization-maintaining optical fiber connector , wherein the holding part is coated with a polarization-maintaining optical fiber core.
The sleeve that holds the part inside, and the two connecting ferrules
Receives spring pressure to press the rules axially against each other
And the sleeve is positioned on the housing.
From a ring-shaped flange with a positioning part
The polarization-maintaining optical fiber connector ferrule
The positioning part of the flange is the ferrule.
With respect to the main axis of polarization of the polarization-maintaining optical fiber bonded inside the fiber
With a predetermined positional relationship, the sleeve
A protrusion or a step is provided on the outer periphery of the front end of the sleeve into which the fitting portion is press-fitted, and when the flange is press-fitted, the flange is displaced from the protrusion or the step. A ferrule for a polarization-maintaining optical fiber connector characterized by having a structure that cannot move forward.

[0011]

In the ferrule according to the present invention, the flange of the ferrule for an optical connector is a separate part. After the fiber is bonded to the ferrule, the direction of the flange can be adjusted and the ferrule can be press-fitted into the ferrule, and the ferrule receives the spring pressure applied to the flange. The main feature is that the projection is provided in advance on the holding portion of the ferrule. According to this structure, the ferrule is bonded to the polarization maintaining optical fiber, and the flange can be attached after polishing the end face.
For example, the axis of the fiber and the direction of the flange can be easily adjusted by viewing the polished fiber end face with a microscope. In addition, since the projection for receiving the spring pressure applied to the flange is provided in advance on the holding portion of the ferrule, sufficient fixing strength can be obtained even when the press-fitting margin of the flange is small. The deterioration of the extinction ratio of the wave holding optical fiber can be reduced. As described above, by using the ferrule structure according to the present invention, an optical connector for a polarization maintaining fiber can be formed extremely easily using a conventional optical connector plug housing as it is. Further, 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 having extremely good reproducibility of the extinction ratio when repeatedly attached and detached.

[0012]

1 and 2 show a ferrule according to an embodiment of the present invention. The ferrule 1 has a precise outer diameter, and is composed of a fitting portion 2 and a holding portion 3 for holding the optical fiber in the inside, and the holding portion 3 is a sleeve for holding the coated portion of the optical fiber core in the inside. 31
And a flange 33 which serves to hold the ferrule 1 in a fixed orientation in the plug housing and to receive the pressure of a spring for pressing the two ferrules to be connected together.
It is composed of FIG. 1 shows a state before the flange 33 is pressed into the sleeve 31, and a projection 32 is provided at a front end of the sleeve 31. The flange 33 is passed through the optical fiber 4 before the ferrule is bonded, and after the fiber bonding and the ferrule end surface polishing work are completed, the sleeve 3 is closed.
1 from the rear end. 2A and 2B are diagrams illustrating a state of the ferrule after press-fitting. FIG. 2A is a front view as viewed from a front end of the ferrule, and FIG. 2B is a side view. Since the press-fitted flange 33 stops when it comes into contact with the projection 32 of the sleeve 31, the flange 33 does not come off in the front end direction of the ferrule 1 even when a spring pressure is applied to the flange 33 after assembly. Further, at the time of press-fitting, the key groove 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. Furthermore, since the adjustment work of this direction can be performed after the ferrule end face is polished, observe the fiber end face with a microscope at the ferrule end face part, or input linearly polarized light from the other end and monitor the emitted light. Thus, the direction of the main shaft is determined, and the flange 33 may be press-fitted in accordance with the direction, and the workability is good.

FIG. 3 shows a ferrule according to the present invention,
FIG. 3 is a partial cross-sectional view illustrating a structure of an optical connector configured to be incorporated in a plug housing of a C-type optical connector. Since the direction of the key groove 34 of the flange 33 of the ferrule 1 matches the direction of the main axis of the fiber as described above, the optical connector is completed only by incorporating the ferrule into the plug housing 21. The ferrule 1 is pressed forward by a pressing spring 22. When a pair of plugs are connected, the ferrule 1 is held in a state of being slightly retracted with respect to the plug housing 21, and both ferrule end faces are mutually connected. It has a structure that can be pressed. At this time, the flange 33 of the ferrule is always pushed by the spring 22 toward the front end of the ferrule.
The press-fitted flange 33 does not come off.

[0014]

As described in detail above, the ferrule according to the present invention is particularly biased as an optical fiber to be bonded by a structure in which a flange provided with a positioning portion for positioning the sleeve in the housing of the connector can be press-fitted after bonding the fiber. When a wave holding optical fiber is used, the direction of the flange can be adjusted according to the direction of its main axis, and the SC
It is suitable to be used by being incorporated in a rectangular plug housing such as an optical connector. In addition, since the projection for receiving the spring pressure applied to the flange is provided in advance on the sleeve for press-fitting the flange, it is possible to give sufficient fixing strength to the spring pressure without having to take a large press-fit margin. It is possible to prevent the extinction ratio of the polarization maintaining optical fiber from deteriorating due to the stress .

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view illustrating a ferrule for a polarization-maintaining optical fiber connector according to an embodiment of the present invention before a flange is mounted.

FIGS. 2A and 2B are a front view and a side view showing a state after a flange is attached to a ferrule for a polarization-maintaining optical fiber connector according to the present invention.

FIG. 3 is a partial cross-sectional view illustrating a structure of an SC type optical connector assembled using a ferrule for a polarization maintaining optical fiber connector 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 illustrating a change in extinction ratio when an optical connector manufactured by incorporating a polarization maintaining optical fiber into an SC type optical connector and an FC type optical connector is repeatedly plugged and unplugged.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ferrule 2, 41 Fitting part 3, 42 Holding part 31 Sleeve 32 Projection 33 Flange 34 Key groove 4 Optical fiber strand 51 Capillary 52 Ferrule main body 53 Flange

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-253207 (JP, A) JP-A-63-261308 (JP, A) JP-A-61-219910 (JP, A) JP-A-61-219910 39004 (JP, A) JP-A-1-234807 (JP, A) JP-A-57-172414 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6/36 G02B 6 / 38

Claims (1)

(57) [Claims] 1. A fitting part comprising a ceramic cylindrical rod-shaped member having a fine outer diameter and a fine through-hole having an inner diameter slightly larger than the outer diameter of the polarization maintaining optical fiber. Has a cylindrical hole at one end for accommodating the fitting portion, a hole at the other end for bonding and fixing the core coated portion of the polarization-maintaining optical fiber, and a brim-shaped outer periphery. A ferrule for a polarization-maintaining optical fiber connector, comprising a metal holding portion having projections, having a structure in which the fitting portion and the holding portion are integrated, and positioned and housed in a housing. The holding section receives a spring pressure for pressing the two ferrules to be connected to each other in the axial direction, with the sleeve holding the polarization-maintaining optical fiber core covered portion inside, and
A ferrule for a polarization-maintaining optical fiber connector comprising a ring-shaped flange provided with a positioning portion for positioning the sleeve to the housing, wherein the flange has a positioning portion bonded to the ferrule. A structure in which the sleeve is axially press-fitted into the sleeve with a predetermined positional relationship with respect to the polarization main axis of the optical fiber, and a protrusion or a step is provided on the outer periphery of the sleeve front end where the fitting portion is press-fitted. The ferrule for a polarization-maintaining optical fiber connector, wherein the flange cannot be moved forward from the protrusion or the step when the flange is press-fitted.