CYLINDRICAL MULTICORE FERRULE AND ITS POLISHING METHOD

An object of the present disclosure is to enable a plurality of single fibers to be easily and collectively connected. The present disclosure is a cylindrical multi-fiber ferrule including through holes each having a cylindrical shape and configured to hold a plurality of optical fibers on the same circle centered on a central axis of the cylindrical shape, in which a region where the through holes are arranged at one end of the cylindrical shape in a longitudinal direction has a spherical shape, and a central region where the through holes are not arranged at one end of the cylindrical shape in the longitudinal direction is a flat surface shape perpendicular to the longitudinal direction of the cylindrical shape.

TECHNICAL FIELD

The present disclosure relates to a cylindrical multi-fiber ferrule used for collectively connecting a plurality of ports using optical fibers in an optical fiber network and a polishing method of the cylindrical multi-fiber ferrule.

BACKGROUND ART

As a technology of connecting a plurality of single-mode optical fibers, there is a multi-fiber optical connector (for example, Non Patent Literature 1). In a general multi-fiber optical connector, two guide holes are provided in a ferrule having a rectangular end face, and a guide pin is inserted into the guide hole to perform connection.

Furthermore, there has also been developed an optical connector (for example, Non Patent Literature 2) in which reflection characteristics are improved by obliquely polishing the end face of the ferrule, and convenience is improved by providing a housing and attaching and detaching the housing by a push-pull mechanism.

On the other hand, as a technology of collectively connecting a plurality of ports of an optical fiber in an optical connector using a cylindrical ferrule, an optical connector using a multicore fiber (for example, Non Patent Literature 3) has been studied. In addition, an SC type (for example, Non Patent Literature 4) optical connector with improved axial rotation accuracy has also been studied.

However, in the conventional technology disclosed in Non Patent Literature 1 described above, in order to avoid deterioration of reflection characteristics due to difficulty in physical contact on the entire core wire, it is necessary to apply a refractive index matching material and use a dedicated tool for attachment and detachment, and there is a problem that the operation process is complicated.

In the conventional technology disclosed in Non Patent Literature 2, it is difficult to control a clearance between the guide hole and the guide pin, and there is a problem that the manufacturing of a low-loss optical connector increases the cost.

In the conventional technology disclosed in Non Patent Literature 3 and Non Patent Literature 4, it is necessary to use a multicore fiber to collectively connect a plurality of ports using a cylindrical ferrule, but the multicore fiber is expensive, and there is a problem that a wiring form becomes complicated because it is necessary to use a device such as a fan-in/fan-out.

CITATION LIST

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

An object of the present disclosure is to enable a plurality of single fibers to be easily and collectively connected.

Solution to Problem

A cylindrical multi-fiber ferrule of the present disclosure includesthrough holes each having a cylindrical shape and configured to hold a plurality of optical fibers on the same circle centered on a central axis of the cylindrical shape,in which a region where the through holes are arranged at one end of the cylindrical shape in a longitudinal direction has a spherical shape curved with a predetermined curvature radius, anda central region where the through holes are not arranged at one end of the cylindrical shape in the longitudinal direction is a flat surface perpendicular to the longitudinal direction of the cylindrical shape.

A polishing method of a cylindrical multi-fiber ferrule according to the present disclosure is a method of polishing a ferrule end face of the cylindrical multi-fiber ferrule according to the present disclosure, in which polishing is performed with a predetermined curvature radius, and then flat polishing is performed. Specifically, a polishing method of a cylindrical multi-fiber ferrule of the present disclosure includes fixing an optical fiber to at least any of through holes of a ferrule formed with the through holes each having a cylindrical shape and configured to hold a plurality of optical fibers on the same circle centered on a central axis of the cylindrical shape, polishing an end face of one end of the ferrule into a spherical shape curved with a predetermined curvature radius, and then, polishing a central region where the through holes are not arranged at the one end perpendicularly to a longitudinal direction of the cylindrical shape to form a flat surface.

Advantageous Effects of Invention

According to the present disclosure, it is possible to easily and collectively connect a plurality of single fibers, and thus, it is possible to achieve economical optical connection.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. These examples are merely examples, and the present disclosure can be carried out in a form with various modifications and improvements based on the knowledge of those skilled in the art. Note that components having the same reference numerals in the present specification and the drawings denote the same components.

FIG.1is a schematic diagram illustrating a cross-sectional structure of a cylindrical multi-fiber ferrule according to an embodiment of the present disclosure. A ferrule1is the cylindrical multi-fiber ferrule of the present disclosure, has a cylindrical shape, and has a through hole for holding a plurality of optical fibers2in parallel with the longitudinal direction of the cylindrical shape. One optical fiber2is arranged in each through hole.FIG.1illustrates a state in which the optical fiber2is held in each through hole. The core centers of the plurality of optical fibers2are arranged on the same circle having a core arrangement radius Rcorewith respect to the central axis of the cylindrical shape of the ferrule1.

AlthoughFIG.1illustrates an example in which eight through holes are arranged at equal intervals and the optical fibers2are arranged in all the through holes, it is sufficient that the core centers of the plurality of optical fibers2are arranged on the circumference of a circle having the core arrangement radius Rcore, and the present invention is not limited thereto. For example, it is sufficient that the optical fiber2is arranged in at least one of the eight through holes. In the present embodiment, an example in which the plurality of optical fibers2are arranged on one circumference is described, but the plurality of optical fibers2may be arranged in two or more circles. The optical fiber2is generally formed of quartz glass, but is not limited thereto as long as it is an optical fiber capable of communicating signal light in a communication wavelength band. The ferrule1is generally formed of zirconia, but is not limited thereto as long as it can hold the optical fiber2. At one end of the ferrule1in the longitudinal direction, the plurality of optical fibers2are arranged in a spherical region6arranged outside a ferrule flat surface4. The spherical region6is a curved region curved with a predetermined curvature radius. The ferrule flat surface4is arranged on the central axis of the ferrule1and is a surface with which the two ferrules are brought into contact.

FIG.2is a schematic diagram illustrating a side surface of an optical coupling portion of the cylindrical multi-fiber ferrule according to the embodiment of the present disclosure. The two ferrules1into which the optical fibers are inserted are aligned by a sleeve8. As a result, the axial deviation of the two ferrules1is controlled within a certain allowable range. In order to minimize the connection loss in the optical coupling portion of the two ferrules1, it is desirable that the cores of the plurality of optical fibers inserted into the two ferrules1have the same optical characteristics in terms of having similar mode field diameters. It is important to minimize the connection loss due to the axial deviation and the rotational deviation of the optical fibers inserted into the two ferrules1, and it is desirable that the optical fibers inserted into the two ferrules1be arranged at opposing positions on the circumference having the same core arrangement radius on the ferrule end faces of the ferrules1. In order to minimize the connection loss due to axial deviation, it is desirable that the ferrule outer diameters of the two ferrules1are substantially the same. In order to reduce the gap between the end faces of the optical fibers inserted into the two ferrules1as much as possible to reduce the excess loss due to the gap, it is important that the ferrule flat surfaces of the two ferrules1can be brought into contact with each other, and a distance D9between flanges9of the two ferrules1in the ferrule axial direction is desirably about the same as or shorter than the sum of a lengths Li of the two ferrules1in the ferrule axial direction.

FIG.3is a schematic diagram illustrating a vicinity of the ferrule end face of the optical coupling portion in more detail. The two ferrules1are in contact with each other at the ferrule flat surface4at the central portion of each end face. The ferrule flat surface4is a central region surrounded by the spherical region6where no through hole is arranged, and is perpendicular to the longitudinal direction of the cylindrical shape. Each of the plurality of optical fibers2is arranged in the spherical region6of the ferrule1in order to prevent the end face of each of the optical fibers2from being damaged by contact. In the end face of the optical fiber2, an angle θ of the end face of the optical fiber2with respect to the ferrule flat surface4is controlled in order to suppress signal characteristic deterioration due to reflection. Here, in the present disclosure, the end faces of the optical fibers2each have a spherical shape. The angle θ may be an angle of a tangent line at a core position among positions where the optical fibers2are arranged with respect to the ferrule flat surface4.

FIG.4is a diagram illustrating a flowchart illustrating an example of a polishing method of a cylindrical multi-fiber ferrule according to an embodiment of the present disclosure. In the polishing method of a cylindrical multi-fiber ferrule according to the present embodiment, steps S101to S103are sequentially performed.

Step S101: First, the optical fibers2are inserted into the through holes, and the optical fibers2and the through holes are bonded and fixed, and adhesion removal polishing of the ferrule1is performed. In general, in the ferrule1in which the optical fiber2is inserted and bonded and fixed, since an excessive adhesive adheres to the ferrule end face, polishing is performed to remove the excessive adhesive.

Step S102: Next, spherical polishing is performed on the ferrule1that has been subjected to the adhesion removal polishing. By polishing the entire end face of the ferrule1including the ferrule flat surface4and the spherical region6into a spherical shape having a predetermined curvature radius ROC, it is possible to form a spherical shape of the spherical region6in which the plurality of optical fibers2of the ferrule1are arranged.

Step S103: Subsequently, spherical polishing is performed on the ferrule flat surface4that has been subjected to the spherical polishing. In general, in polishing the ferrule1, a polishing sheet on which a polishing agent is sprayed is placed on a pad, and polishing is performed while an end face of the ferrule1is pressed against a surface of the polishing sheet. Here, it is possible to polish only the central portion of the ferrule1into a flat shape to form the ferrule flat surface4by performing polishing by adjusting the polishing time using a pad having a hard hardness.

The spherical shape is any shape in which the curvature radius ROC of the spherical region has a predetermined value. The spherical region is symmetrical with respect to the center of the spherical surface, and the center of the spherical surface may be arranged on the central axis of the cylindrical shape of the ferrule1or may be arranged at other positions.

FIG.5is a diagram illustrating an example of a relationship between an angle θ of an end face of the optical fiber2with respect to the ferrule flat surface4and a reflection attenuation amount R. In optical coupling between the optical fibers2, when there are regions having different refractive indexes between the end faces of the optical fibers2, signal characteristics are deteriorated due to reflection at boundaries having different refractive indexes. In the present disclosure, there is a gap between the end faces of the optical fibers2inserted into the two ferrules1. When this gap is air, quartz glass and air have different refractive indexes, and thus it is necessary to devise a technique for reducing reflection. In the present disclosure, reflection is reduced by controlling the angle θ.

The relationship between the angle θ (unit: degree) of the end face of the optical fiber2with respect to the ferrule flat surface4and the reflection attenuation amount R (unit: dB) can be expressed by the following expression.

Here, n1, ω1, and λ are the refractive index of the core of the optical fiber2, the mode field radius of the core of the optical fiber2, and the signal wavelength, respectively.

Ro is a reflection attenuation amount in the case of θ=0 degrees, and can be expressed by the following expression.

Here, n2is a refractive index of a light receiving medium.

In the present embodiment, since light emitted from the end face of the optical fiber2propagates air, n2is a refractive index of air. When the wavelength λ is 1310 nm and the mode field radius ω1is 4.5 μm, the reflection attenuation amount Ro at 0=0 is 14.7 dB, and by setting the angle θ of the end face of the optical fiber2with respect to the ferrule flat surface4to five degrees or more, the reflection attenuation amount R of 40 dB or more can be maintained.

FIG.6is a diagram illustrating an example of a relationship of excess loss TGwith respect to a gap G of the optical fiber2. In the optical coupling between the optical fibers2, if the gap exists between the end faces of the optical fibers2, a distribution of the emitted light of the input-side optical fiber is widened, and coupling efficiency with the core of the output-side optical fiber is reduced, which causes excess loss. The relationship between the gap G (unit: μm) and the excess loss TG(unit: dB) can be expressed by the following expression.

Here, W1and W2are mode field radii of cores of the optical fibers2on the input side and the output side, respectively.FIG.6is a diagram illustrating a loss when the mode field radii of the cores of the optical fibers inserted into the two ferrules1are both 4.5 μm. For example, by adjusting the gap between the end faces of the optical fibers2inserted into the two ferrules1to equal to or less than 20 μm, the excess loss can be suppressed to equal to or less than 0.1 dB.

FIG.7is a diagram illustrating an example of a relationship between an angle θ of an end face of the optical fiber2with respect to the ferrule flat surface4and the curvature radius ROC. When the optical connector is manufactured, the end face of the ferrule1is polished in order to control the reflection attenuation amount of the optical connector. According to the polishing conditions, the end face shape of the ferrule1to which the optical fiber2is inserted is controlled, and a desired reflection attenuation amount can be obtained.

In general, in polishing the ferrule1, a polishing sheet on which a polishing agent is sprayed is placed on a pad, and polishing is performed while an end face of the ferrule is pressed against a surface of the polishing sheet. It is possible to adjust the curvature radius of the end face of the ferrule by performing polishing using the hardness of the pad, the pressing force of the ferrule1, the polishing time, and the like as parameters. The relationship between the angle θ (unit: degree) of the end face of the optical fiber2with respect to the ferrule flat surface4and the curvature radius ROC (unit: mm) can be expressed by the following expression.

In the example illustrated inFIG.7, the core arrangement radius Rcoreis 850 μm and 1700 μm. For example, when the core arrangement radius Rcoreis 850 μm, the angle θ of the end face of the optical fiber2can be set to equal to or greater than five degrees by setting the curvature radius ROC to equal to or less than 9.7 mm, and the reflection attenuation amount R of equal to or greater than 40 dB can be achieved. In addition, in order to enable more optical fibers2to be arranged, when the core arrangement radius Rcoreis increased to 1700 μm, the angle θ of the end face of the optical fiber2can be set to equal to or greater than five degrees by setting the curvature radius ROC to equal to or less than 19.5 mm, and the reflection attenuation amount R of equal to or greater than 40 dB can be achieved.

FIG.8is a diagram illustrating an example of a relationship between an angle θ of the end face of the optical fiber2with respect to the ferrule flat surface4and an amount of recess from the vertex. Here, the amount of recess from the vertex represents a difference in the retraction position of the end face of the optical fiber2at the core arrangement radius Rcorefrom the position of the vertex of the spherical surface of the ferrule end face polished with the curvature radius illustrated inFIG.7in the axial direction of the ferrule1. In the example illustrated inFIG.8, the core arrangement radius Rcoreis 850 μm and 1700 μm. For example, when the angle θ of the end face of the optical fiber2is five degrees, the amount of recess is 37 μm to 74 μm when the core arrangement radius Rcoreis 850 μm to 1700 μm. For this reason, when the ferrules polished with the curvature radius described above are connected to each other, a large gap is generated between the optical fibers2.

FromFIG.6, it is necessary to set the gap to equal to or less than 20 μm in order to suppress the excess loss due to the gap. For this reason, after polishing is performed so as to have the curvature radius ROC illustrated inFIG.7, polishing is performed using a pad having a harder hardness, and the distance from the ferrule flat surface4to the end face of the optical fiber2is set to 10 μm or less. As a result, it is possible to flatly polish only the central portion of the end face of the ferrule polished with the curvature radius ROC to reduce the difference between the position of the ferrule flat surface4at the center of the ferrule end face and the retraction position of the end face of the optical fiber2at the core arrangement radius Rcorein the axial direction of the ferrule.

For example, in the ferrule end face polished so that the core arrangement radius Rcoreis 850 μm, the angle θ of the end face of the optical fiber2is five degrees, and the curvature radius is 9.7 mm, by performing flat polishing to a depth of 27 μm from the vertex of the ferrule end face, a reflection attenuation amount of equal to or greater than 40 dB and an excess loss due to a gap of equal to or less than 0.1 dB can be achieved. In addition, for example, in the ferrule end face polished so that the core arrangement radius Rcoreis 1700 μm, the angle θ of the end face of the optical fiber2is five degrees, and the curvature radius is 19.5 mm, by performing flat polishing to a depth of 64 μm from the vertex of the ferrule end face, a reflection attenuation amount of equal to or greater than 40 dB and an excess loss due to a gap of equal to or less than 0.1 dB can be achieved.

FIG.9is a diagram illustrating an example of a relationship of the number of cores Ncoreof the optical fiber2with respect to the core arrangement radius Rcore.FIG.9is an example illustrating the number of cores of the optical fiber2when the optical fibers2are arranged at equal intervals in an annular shape on the core arrangement radius and the distance between cores of the adjacent optical fibers2is 250 μm. For example, by arranging the optical fibers2at equal intervals such that the core arrangement radius Rcoreis 850 μm and the distance between adjacent cores is 250 μm,21optical fibers2can be collectively connected. In addition, by setting the core arrangement radius Rcoreto 1700 μm,42optical fibers2can be collectively connected.

FIG.10is a diagram illustrating an example of a relationship between a rotational angle deviation and an excess loss TRdue to a rotational angle deviation @. In the configuration of the optical coupling portion of the cylindrical multi-fiber ferrule of the present disclosure, the rotational angle deviation at the time of manufacturing the optical connector causes excess loss. When the excess loss due to the rotational angle deviation is denoted by TR(unit: dB), the rotational angle deviation is denoted by @ (unit: degree), and the core arrangement radius is denoted by Rcore(unit: μm), the relationship among these can be expressed by the following expression.

Here, w1and w2are mode field radii of cores of the optical fibers2, respectively.

In the example illustrated inFIG.10, the core arrangement radius Rcoreis 850 μm. As the rotational angle deviation @ increases, the excess loss TRincreases, and the connection characteristics deteriorate. In the example illustrated inFIG.10, the mode field radius w1is 4.5 μm, 5.5 μm, and 6.5 μm. As is clear from these comparisons, by using the optical fiber2having a larger mode field radius w1, it is possible to reduce excess loss due to rotational angle deviation as compared with the optical fiber2having a smaller mode field radius.

According to the present disclosure, the ferrule end face of the cylindrical multi-fiber ferrule is polished with a desired curvature radius, and then the ferrule central portion is flatly polished, so that the central portion of the cylindrical multi-fiber ferrule has a flat shape, and the end faces of the optical fibers2arranged in an annular shape each have a spherical shape. Therefore, in optical connector connection using the cylindrical multi-fiber ferrule of the present disclosure, excellent optical characteristics are achieved with preferable reflection characteristics and reduced excess loss due to a gap. In addition, in the polishing method of a cylindrical multi-fiber ferrule of the present disclosure, the ferrule end face is polished so as to have a desired curvature radius, and then only the central portion of the ferrule is subjected to flat polishing. Therefore, a special polishing device or polishing jig is not required, and the ferrule can be polished by a simple and economical method.

First Embodiment

FIG.11is a schematic diagram illustrating a fitting form of an optical coupling portion in an optical connector according to a first embodiment of the present disclosure. Two ferrules1are inserted into the sleeve8so as to face each other, and ferrule flat surfaces of the two ferrules1are brought into contact with each other by applying pressure by a spring12, and thereby, optical fibers2are connected in a state where a gap is provided between end faces of the optical fibers2. In order to facilitate attachment and detachment in connection, the sleeve8is incorporated in an adapter17, and each of the two ferrules1is incorporated in a plug frame14attached to a housing15.

Each of the two ferrules1is attached with a flange9for protecting the optical fibers2. As illustrated inFIG.12, the optical fibers2can be easily inserted into the ferrules by inserting a plurality of capillaries23into the flanges9and arranging the capillaries23at the same positions as through holes24for holding the optical fibers2.

As illustrated inFIG.13, by tapering the capillaries23in the longitudinal direction and making the diameter of the tip of the tapered shape close to the diameter of the through holes24for holding the optical fibers2, it is possible to prevent the optical fiber2from being caught due to a step when the optical fiber2is inserted into the ferrule1and to prevent the optical fiber2from being broken.

Although the example in which the plurality of capillaries23are inserted into the flanges9has been described in the present embodiment, the present invention is not limited thereto as long as the optical fibers2have a shape that allows the optical fibers2to be inserted into the through holes24of the ferrules1and that can protect the optical fibers2at the time of manufacturing the optical connector.

The flange9attached to one of the two ferrules1is provided with a cutout (not illustrated), and axial rotation of the cutout of the flange9is fixed by a guide of a cutout provided in the plug frame14. The other ferrule1is attached with a mechanism (not illustrated) that enables rotation and fixation inside the plug frame14.

When an optical connector is manufactured, that is, when the optical fibers2are connected, a housing (connector plug) incorporating a ferrule attached with a flange with a cutout is inserted into one side of an adapter, a housing (connector plug) attached with a ferrule capable of rotating and fixing inside a plug frame is inserted into the other side of the adapter, a device (for example, a light source and a light receiver) capable of transmitting and receiving is attached to each of the optical fibers2, the ferrule is rotated while monitoring an optical signal, and axial rotation of the ferrule is fixed at a position where received light power is maximized, and thereby a low-loss optical connector can be manufactured.

FIG.14is a diagram illustrating an example of a mechanism that enables the cylindrical multi-fiber ferrule to be rotated and fixed inside the plug frame according to the first embodiment of the present disclosure.FIG.14is a cross-sectional view of a connector plug attached with the mechanism that enables the ferrule1to be rotated and fixed inside the plug frame14. A grooved flange19is attached to the ferrule1, and a fixing spring20is attached in a shape in which a tip thereof is sandwiched between the grooves. By pressing the fixing spring20in the direction of the arrow in the drawing, the tip of the fixing spring20is detached from the groove of the grooved flange19, which enables the grooved flange19to axially rotate. By releasing the pressing force of the fixing spring20at a position where the monitored received light power is maximized, the grooved flange19is fixed, that is, the ferrule1is fixed, and the axial rotation direction of the inserted optical fiber2is fixed. For example, as illustrated inFIG.15, by attaching a plurality of annular portions21provided with grooves to the flange in an overlapping manner, it is possible to perform finer rotation angle control.

Second Embodiment

FIG.16is a diagram illustrating an example of a mechanism that enables a cylindrical multi-fiber ferrule to be rotated and fixed inside a plug frame according to a second embodiment of the present disclosure.FIG.16is a cross-sectional view of a connector plug attached with the mechanism that enables the ferrule to be rotated and fixed inside the plug frame. A flange9is attached to the ferrule1, and a fixing magnet22is attached to the outside of the flange9. By detaching the fixing magnet22, the flange9is enabled to axially rotate and by attaching the fixing magnet22at a position where the monitored received light power is maximized, the flange9is fixed, that is, the ferrule is fixed, and the axial rotation direction of the inserted optical fiber2is fixed. Here, the flange9may be made of a material having magnetism.

Effects of Present Disclosure

The cylindrical multi-fiber ferrule according to the present disclosure uses a single-mode fiber that is a single fiber generally used similarly to a normal optical connector as a connection technology for collectively connecting a plurality of ports by the optical fibers2. Therefore, a device such as a fan in/fan out is not required as a transmission path configuration, and simple and economical optical connection can be achieved. In addition, since the central portion of the cylindrical multi-fiber ferrule has a flat shape and the end faces of the optical fibers2arranged in an annular shape each have a spherical shape, the excellent optical characteristics are achieved with preferable reflection characteristics and reduced excess loss due to a gap. Moreover, in the polishing method of a cylindrical multi-fiber ferrule of the present disclosure, the ferrule end face is polished so as to have a desired curvature radius, and then only the central portion of the ferrule is subjected to flat polishing. Therefore, a special polishing device or polishing jig is not required, and the ferrule can be polished by a simple and economical method.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to information communication industry.

REFERENCE SIGNS LIST