JP2000231034A - Optical coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to select an optical coupling function and an optical path switching function and to attach and detach a branch line fiber to and from a trunk line fiber, to obtain the degree of optical coupling which hardly depends upon fiber mode conditions, and to mount the branch line fiber and trunk line fiber at low cost orthogonally to each other. SOLUTION: A trunk line module 26 is equipped with a 1st collimator 32 and a 2nd collimator 34 in a 1st cylindrical housing 30. The 1st collimator 32 collimates the light projected from the trunk line fiber into parallel light. The 2nd collimator 34 converges the parallel light from the 1st collimator 32 on a trunk line fiber end. The tube wall between the 1st and 2nd collimators have an opening 48 into which a branch line reflecting mirror is inserted. A branch line module 28 is equipped with a 3rd collimator 58, a 4th collimator 60, and a reflecting mirror 62 in a 2nd housing 50. When the branch line module 28 is mounted on the trunk line module 26, the reflecting mirror 62 is positioned between the 1st and 2nd collimators to guide at least part of the projection light from the 1st collimator 32 to the 3rd collimator 58 and at least part of the projection light from the 4th collimator 60 to the 2nd collimator 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber communication system for extracting a part of an optical signal transmitted through an optical fiber and coupling an external optical signal to the optical fiber. About the vessel.

[0002]

2. Description of the Related Art The configuration of a conventional optical coupler is described in, for example,
"Tokuhei 5-19131", Reference 2 "Tokohei 7-50"
No. 214, reference 3 "US Pat. No. 4,210,979" and reference 4 "US Pat. No. 4,054,366", respectively. In each of the optical couplers disclosed in these documents, two optical fibers are arranged adjacent to each other and a part of the side of one fiber is fused to the side of the other fiber, or After the side surfaces are polished to form an adhesive surface, these are adhered with an optical adhesive or the like to be integrated. FIG. 7 shows the configuration of such an optical coupler.

FIG. 7 is a plan view showing a configuration of a conventional optical coupler. The trunk fiber 10 and the branch fiber 12 are bonded by fusion or adhesion, and the bonded portion functions as an optical coupler. Optical coupling between the trunk fiber 10 and the branch fiber 12 is performed by coupling light leaked from each fiber at the adjacent boundary (coupling portion) 14. In this manner, by subjecting each fiber to fusion or side polishing, the propagation mode of light propagated by the trunk fiber 10 is intentionally broken, and the branch fiber 12
To achieve the optical coupling effect.

This optical coupler has four ports 16, 1
8, 20, and 22. One end of the trunk fiber 10 is a port 16 and the other end is a port 18. One end of the branch fiber 12 is a port 20 and the other end is a port 22. Now, in FIG.
It is assumed that light is being transmitted through the trunk fiber 10 from the port 16 to the port 18. When the light reaches the adjacent boundary portion 14 via the port 16, the light propagation mode changes because the fiber structure has changed at that portion. A part of the light having the changed mode no longer conforms to the propagation mode of the trunk fiber 10 and leaks at that part, and only the light conforming to the propagation mode of the branch fiber 12 out of the leaked light is transmitted to the port 22. Excited. Therefore, a part of the light incident from the port 16 is propagated to the port 18 and the remaining light is coupled to the port 22, so that an optical signal can be extracted from the trunk fiber 10 to the branch fiber 12.

On the other hand, part of the light incident from the port 20 is coupled to the port 18 by the same optical coupling process as described above. Therefore, a part of the optical signal can be inserted from the port 20 of the branch fiber 12 to the port 18 of the trunk fiber 10.

[0006]

However, the above-mentioned conventional optical coupler has the following problems.

[0007] 1) The trunk fiber and the branch fiber are fixed in an integrated state, and the branch fiber cannot be separated from the trunk fiber and removed or attached.

Generally, in an optical network system in which a large number of terminal devices are connected via a trunk fiber, an optical coupler is required for each terminal device. In actual system operation, it is often the case that terminal equipment is connected to the trunk fiber or removed as needed. Therefore, the optical coupler is inserted into the trunk fiber even when the terminal device is not connected. At this time, in the conventional optical coupler, since the branch fiber is always fixed as described above, an insertion loss corresponding to the degree of coupling of the optical coupler occurs. Therefore, even if the terminal equipment is not connected to the trunk fiber, an insertion loss always occurs in the optical coupler, and the number of connectable optical couplers determined by the accumulated loss is limited.

However, in general, even if the number of terminals connected to the entire system is constant, it is desirable that the number of optical couplers connected to the trunk fiber is large. This is because the greater the number of optical couplers connected, the greater the degree of freedom in the connection positions of terminal devices that can be connected to the trunk fiber. As described above, in the conventional optical coupler, the number of optical couplers connected on the trunk fiber is limited because the branch fiber cannot be attached or detached, and therefore, the degree of freedom of the connection position of the terminal device is small. There were drawbacks.

2) It is impossible to select between the optical coupling function and the optical path switching function.

When an optical coupler is applied to an optical network system, it is needless to say that an optical coupling function between the trunk fiber and the branch fiber is required. However, in some cases, all optical signals of the trunk fiber are converted to the branch fiber. The function to switch to is required. For example, when a plurality of terminal devices are to be connected to one optical coupler position, in order to newly arrange a plurality of optical couplers around the terminal device, conventionally, the trunk fiber is cut once and the optical coupler is connected. It needed to be expanded. As described above, since the conventional optical coupler has no optical path switching function, it is impossible to add an optical coupler without cutting the trunk fiber.

3) The degree of optical coupling depends on the mode excitation condition.

In FIG. 7, when the fiber used is a multimode fiber, the degree of optical coupling from the port 16 to the port 22 and the degree of optical coupling from the port 20 to the port 18 depend on the mode distribution excited by the fiber. The values are different. Originally, it is desirable that the degree of coupling of the optical coupler is always constant with respect to any mode distribution excited in the fiber. However, the degree of optical coupling of the conventional optical coupler utilizes the characteristic of coupling a leaky mode to another port, so that the above-described problem occurs essentially.

4) Since the adjacent fibers are subjected to fine side polishing, the production cost is high and the reproducibility of characteristics as an optical coupler is hardly obtained.

A part of each fiber core having a very small diameter is polished uniformly along the axis of the fiber, and these polished surfaces are brought into close contact with each other very precisely (with a mechanical dimensional accuracy smaller than the wavelength of light). Integrate. Therefore, the characteristics of the conventional optical coupler are greatly influenced by minute parameters such as the polishing accuracy, the polishing size, and the size of the adjacent position. In order to constantly control and manufacture these parameters, the manufacturing cost becomes large, and even if desired characteristics are obtained, characteristic fluctuations due to fluctuations in parameters due to external environments are likely to occur.

5) The branch fiber cannot be mounted orthogonal to the trunk fiber.

Considering the basic configuration of the conventional optical coupler, it is impossible to mount the branch fiber in a state orthogonal to the trunk fiber. For this reason, a dead space occurs around the optical coupler.

Therefore, conventionally, the branch fiber can be arbitrarily attached to and detached from the trunk fiber, and the optical coupling function and the optical path switching function can be selected, and the optical coupling degree which is hardly dependent on the mode excitation condition can be obtained. In addition, there has been a demand for an optical coupler that can be manufactured at a low cost and that can mount a branch fiber and a trunk fiber orthogonally to each other.

[0019]

Therefore, according to the optical coupler of the present invention, there is provided an optical coupler comprising a trunk line module and a branch line module, wherein the trunk line module emits light from the end of the trunk fiber. And a second collimator that is provided to face the first collimator, and that converges the parallel light emitted from the first collimator to an end of the trunk fiber. The branch line module is configured to be attachable to the trunk line module, and includes a third collimator, a fourth collimator, and a reflection mirror. When the branch line module is mounted to the trunk line module, the reflection mirror includes a first collimator and a second collimator. A fourth collimator is disposed between the first collimator and the second collimator to reflect at least a part of the parallel light emitted from the first collimator to guide the parallel light to the third collimator, and The third collimator reflects at least a portion of the parallel light emitted from the remeter and guides the parallel light to the second collimator. The third collimator focuses the reflected light from the reflection mirror on the end of the branch fiber. The collimator is characterized in that the light emitted from the end of the branch fiber is converted into parallel light.

In this manner, one trunk fiber and the other trunk fiber are connected via the trunk module. The light emitted from one end of the trunk fiber is the first light.
After being converted into parallel light by the collimator, the light propagates through the trunk module and enters the second collimator. The second collimator focuses the incident parallel light on the end of the other trunk fiber. Therefore, light transmitted from one trunk fiber is sent to the other trunk fiber via the trunk module.

On the other hand, when the branch line module is mounted on the trunk line module, the reflection mirror of the branch line module is inserted into the optical path between the first and second collimators. As a result, at least a part of the parallel light emitted from the first collimator is reflected by the reflection mirror and guided to the third collimator. The third collimator focuses the incident parallel light on the end of the branch fiber. As described above, when the branch line module is mounted on the trunk line module, light transmitted by the trunk line fiber can be extracted to the branch line side. Further, by changing the size of the reflection mirror, the amount of light guided to the third collimator changes, so that not only an optical coupling function but also an optical path switching function can be realized.

When the light is sent from the branch fiber to the fourth collimator, it is converted into parallel light and then guided to the second collimator by the reflection mirror. Therefore, light transmitted by the branch fiber can be coupled to the trunk fiber.

As described above, according to the optical coupler of the present invention, 1) the trunk fiber and the branch fiber can be attached and detached.

Here, it is assumed that, in an optical network system to which a large number of terminal devices are connected, a large number of trunk modules are arranged without attaching branch modules on the trunk fiber. Since the optical insertion loss of the trunk module itself is extremely small, arranging the trunk module on the trunk fiber indefinitely does not cause optical loss of the entire system. If necessary, a terminal device can be connected by attaching a branch line module to a trunk line module at a desired position. Therefore, a large number of trunk modules can be arranged on the trunk fiber, and terminal equipment can be connected to an arbitrary position on the trunk fiber. In the conventional optical coupler, since it is equivalent to the fact that the branch module is always mounted, a considerable insertion loss occurs in the optical coupler itself, and thus there is no such degree of freedom.

Apart from this, it is desirable that the number of optical couplers for connecting the trunk fiber to the terminal equipment is originally equal to the number of terminal equipment. This is because arranging an expensive optical coupler on the trunk fiber more than necessary increases the system cost even when the terminal device is not connected. In the conventional case,
An unnecessary optical coupler to which no terminal device is connected may be arranged on the trunk fiber. This increases the system cost and the insertion loss of the network. On the other hand, in the present invention, the number of optical couplers can be set relatively freely, considering only the system cost.

It is to be noted that the optical coupler of the present invention has an advantage that the optical signal propagated by the trunk fiber is not instantaneously interrupted when the branch line module is attached or detached.

Also, 2) selection of an optical coupling function and an optical path switching function is possible. In the optical coupler of the present invention, the following three functions can be selected.

A) When the branch line module is not installed: a function of simply connecting trunk fibers with no loss or low loss (a function of simply connecting trunk fibers only).

B) When a branch line module whose reflection surface area of the reflection mirror viewed from the first collimator side or the second collimator side is smaller than the beam cross-sectional area of the parallel light emitted from the first collimator is installed: An optical coupling function (a function of extracting and inserting an optical signal) that couples a part of the light transmitted through the branch fiber and a part of the light transmitted through the branch fiber to the trunk fiber.

C) When a branch line module having a reflecting surface area of the reflecting mirror viewed from the first collimator side or the second collimator side that is equal to or larger than the beam cross-sectional area of the parallel light emitted from the first collimator is mounted: trunk fiber An optical path switching function (a function of switching the path of an optical signal) in which all of the light transmitted through the branch fiber is coupled to the branch fiber and all of the light transmitted through the branch fiber is coupled to the trunk fiber.

Accordingly, since the optical coupler of the present invention can have an optical path switching function, it is possible to increase the number of optical couplers without cutting the trunk fiber.

Further, the optical coupler of the present invention has a 3) structure in which the degree of optical coupling hardly depends on the excitation conditions of the multimode fiber.

The optical coupler of the present invention can accept a higher-order propagation mode from a lower-order propagation mode. Therefore,
Whatever mode is excited in the multimode fiber, a stable and constant amount of optical branching can be extracted.

Further, 4) the branch fiber can be mounted in a state of being orthogonal to the trunk fiber.

In the optical coupler according to the present invention, preferably, the main module includes a first cylindrical body formed of a tube wall having a substantially uniform thickness. First and second collimators are formed by inserting a spherical lens and a ferrule inside, and an opening is formed between the first and second collimators to allow a reflecting mirror to pass through a tube wall of the first housing. The branch line module has a second groove having a V-shaped cross-section that can be engaged with the outer wall surface of the first housing.
A housing is provided, and a reflection mirror is supported by a protruding piece provided in this groove. Two holes are formed in the second housing, and a spherical lens and a ferrule are inserted into each hole. Preferably, third and fourth collimators are configured.

As described above, a non-adjustable integrated collimator using a low-cost spherical lens with excellent processing reproducibility and a low-cost precision ferrule that has been put into practical use in large quantities is used as an element part. Since these spherical lenses and ferrules can be obtained at low cost, 5) a low-cost optical coupler can be realized.

The casing of the trunk line module has a cylindrical shape, and the casing of the branch line module is provided with a groove having a V-shaped cross section. When these are combined in a state where the cylindrical surface of the main line module is in contact with the groove surface of the branch line module, the relative angle of the branch line module to the optical axis of the collimator is always kept constant. Therefore, 6) the reproducibility of the coupling characteristics is good.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the drawings merely schematically show the shapes, sizes, and arrangements so that the present invention can be understood. The conditions and materials such as numerical values described below are merely examples. Therefore, the present invention is not limited to this embodiment.

[First Embodiment] FIG. 1 is a sectional view showing the structure of an optical coupler according to a first embodiment. This optical coupler is connected to the main line module 26 and the branch line module 28.
It is composed of The trunk line module 26 and the branch line module 28 are detachable from each other. FIG. 1 shows a state where the main line module 26 and the branch line module 28 are separated. First, FIG.
With reference to (A), FIG. 1 (B) and FIG. 2 (A), the configuration of the trunk module 26 will be described.

FIG. 2 is a perspective view showing the structure of the optical coupler. As shown in FIG. 2A, the trunk line module 26
The first housing 30 has a cylindrical shape. The cross section shown in FIG. 1A is a state of a cut along the longitudinal direction of the first housing 30. In addition, the cross section shown in FIG.
It is a state of a cut edge obtained by cutting a central portion of the zero along a direction perpendicular to the longitudinal direction.

The main line module 26 includes the first collimator 3
2 and a second collimator 34. The first collimator 32 converts light emitted from the end of the trunk fiber 36 into parallel light. In addition, the second collimator 34
It is provided so as to face the first collimator 32,
The parallel light emitted from the first collimator 32 is focused on the end of the trunk fiber 38.

The above-mentioned first housing 30 is a metal pipe constituted by a pipe wall having a substantially uniform thickness. That is, in this metal pipe, the central axis of the cylindrical surface formed by the inner wall surface coincides with the central axis of the cylindrical surface formed by the outer wall surface. A spherical lens having the same diameter as the inside diameter of the metal pipe and a ferrule having the same outside diameter as the inside diameter of the metal pipe are inserted into the inside of the metal pipe, and the first and second lenses are inserted.
Collimators 32 and 34 are configured as fiber collimators.

Specifically, a spherical lens 40 is inserted into one end of the metal pipe and fixed at a predetermined position. Subsequent to the spherical lens 40, a ferrule 42 to which the trunk fiber 36 is connected is inserted into one end of the metal pipe and fixed (the fiber is inserted into a hollow cylindrical ferrule through-hole and the fiber end face and the ferrule end face are the same. It is inserted and fixed so that it is located on a plane.) In order for these to function as the first collimator 32, the trunk fiber 3
6 is designed so that the end is located at the focal point of the spherical lens 40. Similarly, the ball lens 44 is inserted into the other end of the metal pipe and fixed at a predetermined position. Following the spherical lens 44, a ferrule 46 to which the trunk fiber 38 is connected.
Is inserted into the other end of the metal pipe and fixed. In order for these to function as the second collimator 34, the end of the trunk fiber 38 is designed to be located at the focal point of the spherical lens 44.

Incidentally, an antireflection film is formed on the surface of the spherical lens and the end face of the fiber by means such as vapor deposition.

As described above, the first collimator 32 and the second collimator 34 are fixed to face each other. Therefore, the light propagated by the trunk fiber 36 is converted into parallel light by the spherical lens 40, and then the parallel light enters the spherical lens 44 and is collected at the end of the trunk fiber 38. Therefore, the trunk fiber 36 and the trunk fiber 3
8, a substantially lossless optical coupling is realized.

The first collimator 3 of the first housing 30
An opening 48 is formed in the tube wall between the second and second collimators 34 to allow the reflection mirror 62 provided on the branch line module 28 to pass therethrough (FIG. 1B).

Next, FIG. 1 (C), FIG. 1 (D), FIG.
(E) and FIG. 2 (B), the branch line module 2
8 will be described. The branch line module 28 has a rectangular parallelepiped second housing 50 in which a groove 52 having a V-shaped cross section is formed on one side surface. Also, in the second housing 50, two parallel cylindrical holes 54 and 5 penetrating from the surface on which the groove 52 is formed to the surface facing this surface are provided.
6 are formed. These cylindrical holes 54 and 56
The grooves 52 are arranged along the extending direction. FIG. 1 (C)
The cross-section shown in FIG.
It is a state of the cut edge cut | disconnected along the extension direction of 4 and 56. The cross section shown in FIG. 1D is a cross-section taken along the direction orthogonal to the cross section shown in FIG. 1C at the position of the cylindrical hole 54. Further, the cross section shown in FIG. 1E is a cross section at the center of the second housing 50, which is parallel to the cross section shown in FIG. 1D.

The above-mentioned groove 52 of the second housing 50 is formed so as to be able to engage with the outer wall surface of the first housing 30. Therefore, the branch line module 28 can be mounted on the trunk line module 26. At the time of mounting, the extending direction of the groove 52 and the first housing 30
The first case 30 and the second case 50 are fixed such that the longitudinal direction of the first case 30 coincides with that of the first case 30, and a part of the outer surface of the first case 30 contacts the inner surface of the groove 52. Since the outer surface of the first housing 30 and the inner surface of the groove 52 are in line contact, the relative angle between the trunk module 26 and the branch module 28 is always maintained.

The branch line module 28 includes the third collimator 5
8, a fourth collimator 60 and a reflection mirror 62. Of these, the reflection mirror 62 is connected to the branch line module 28.
Is mounted between the first collimator 32 and the second collimator 34, and reflects at least a part of the parallel light emitted from the first collimator 32 to guide it to the third collimator 58. In addition, at least a part of the parallel light emitted from the fourth collimator 60 is reflected and guided to the second collimator 34.

As shown in FIGS. 1C and 1E, the reflection mirror 62 is supported by a protruding piece 64 provided in the groove 52. The protruding piece 64 is provided at the center of the groove 52 between the cylindrical holes 54 and 56, and is a rod-shaped member extending in a direction parallel to the cylindrical holes 54 and 56 and protruding. As shown in FIG. 1 (C), the opposing side surfaces of the top of the member are wide so that they are inclined at an angle of 45 ° with respect to the extending direction of the groove 52. Reflection films are formed on these two slopes by vapor deposition or the like, and are configured as reflection surfaces 62a and 62b of the reflection mirror 62, respectively. Thus, the reflection mirror 62 is formed on the top of the protruding piece 64.
The thickness of the reflection mirror 62 is determined by the thickness of the opening 48 of the first housing 30.
Is smaller than the width.

The reflection mirror 62 is inserted into the opening 48 of the first housing 30 when the branch line module 28 is mounted on the trunk line module 26, and is stored in the trunk line module 26. The length of the projecting piece 64 is
Is designed to be located between the first collimator 32 and the second collimator 34 and near the central axis of the first housing 30. Therefore, the first end of the reflection mirror 62
The penetration depth into the housing 30 is always maintained. This is shown in FIG.

FIG. 3 is a sectional view showing the structure of the optical coupler when it is mounted. The cross section shown in FIG. 3A corresponds to the cross section shown in FIGS. 1A and 1C. The cross section illustrated in FIG. 3B corresponds to the cross sections illustrated in FIGS. 1B and 1E. As shown in FIGS. 3A and 3B, the top of the projecting piece 64 is located at a position substantially coincident with the central axis of the first housing 30. Reflection mirror 62 viewed from first collimator 32 side
Is smaller than the beam cross-sectional area of the parallel light 66 emitted from the first collimator 32 (see FIG. 3).
(B)). The upper end of the reflection surface 62a of the reflection mirror 62 is the first
It is located at the center axis of the housing 30. Therefore, the reflection mirror 6
2 reflects the component of the parallel light 66 from the beam center to the beam periphery. The reflected light propagates toward the third collimator 58, and the non-reflected light propagates toward the second collimator.

The third collimator 58 focuses the reflected light from the reflection mirror 62 on the end of the branch fiber 68, and the fourth collimator 60 controls the branch fiber 7
The light emitted from the end of 0 is made parallel light. These third and fourth collimators 58 and 60
It is configured by inserting a spherical lens and a ferrule into two cylindrical holes 54 and 56 formed in the housing 50.

Specifically, a spherical lens 72 is inserted into one end of the cylindrical hole 54 and fixed at a predetermined position. Following the spherical lens 72, a ferrule 74 to which a branch fiber 68 is connected is inserted into one end of the cylindrical hole 54 and fixed. In order for these to function as the third collimator 58, the end of the branch fiber 68 is designed to be located at the focal point of the spherical lens 72. Similarly, a spherical lens 76 is inserted into one end of the cylindrical hole 56 and fixed at a predetermined position. Following the spherical lens 76, a ferrule 78 to which the branch fiber 70 is connected is inserted into one end of the cylindrical hole 56 and fixed. In order for these to function as the fourth collimator 60, the end of the branch fiber 70 is designed to be located at the focal point of the spherical lens 76.

As described above, the branch line module 28 includes two collimators arranged in parallel with each other. Then, a part of the light passing through each of the collimators 58 and 60 is
It is configured to be incident on the reflection surfaces 62a and 62b of the reflection mirror 62, respectively. Therefore, part of the parallel light emitted from the first collimator 32 is
Is reflected by the reflecting surface 62 a of the third collimator 58 and enters the spherical lens 72 of the third collimator 58. The spherical lens 72 guides the light to the branch fiber 68 by condensing the incident light on the end of the branch fiber 68. On the other hand, the light emitted from the branch fiber 70 is converted into parallel light by the spherical lens 76 of the fourth collimator 60. Then, a part of the parallel light is reflected by the reflection surface 62b of the reflection mirror 62 and propagates to the second collimator 34 side.

Next, the operation of the optical coupler of this embodiment will be described. The trunk fibers 36 and 38 are connected to trunk fibers of the optical network system. Here, it is assumed that an optical signal enters the trunk module 26 from the trunk fiber 36 side.

First, a) the case where the branch line module 28 is not mounted on the trunk line module 26 will be described. The light transmitted by the trunk fiber 36 is transmitted to the ferrule 42.
Emitted from the fiber end face at the end face, the spherical lens 40
Is converted into parallel light. This parallel light is transmitted to the spherical lens 4
The light is condensed by 4 and coupled to the main fiber 38.

In general, in an optical coupling system composed of mutually facing collimators, the coupling loss does not depend on the collimator interval but on the optical axis deviation and the optical axis angle deviation between the opposing collimators. In particular, it is a well-known fact that it largely depends on the optical axis angle deviation. However, this configuration
Since the ferrule and the ball lens are inserted into one metal pipe, optical axis shift and optical axis angle shift do not occur essentially, and a low-loss optical coupling system is realized.

In general, spherical lenses have the advantage of having extremely high roundness and can be manufactured at a low cost with the same diameter. Since such a spherical lens is used, a low-cost and high-precision optical coupling system can be obtained.

As described above, the main line module 26
When the branch line module 28 is not mounted on the main line fiber, the light transmitted by the main line fiber 36 can be coupled to the main line fiber 38 with low loss.

Next, b) the case where the branch line module 28 is mounted on the trunk line module 26 will be described. In this case, the reflection mirror 6 attached to the branch line module 28 is used.
2 reflects a part of the parallel light transmitted from the first collimator 32. The reflected light is coupled to a branch fiber 68 by a third collimator 58 also associated with the branch module 28. In this way, the optical coupler extracts the optical signal propagating from the trunk fiber 36 toward the trunk fiber 38 to the branch fiber 68 side.

As described above, the length of the protruding piece 64 on which the reflecting mirror 62 is supported is determined by the length of the reflecting mirror 62 in the first housing 3.
It is designed to be located at the center axis of 0, that is, at the center of the light beam. Therefore, the light from the beam center position to the beam peripheral position is branched and coupled to the branch fiber by the reflection mirror 62. With this configuration, the optical coupler having this configuration has a characteristic that the degree of optical coupling hardly depends on the mode distribution excited in the fiber.
This is because, generally, low-order modes are distributed near the center of the light beam, and higher-order modes are distributed toward the periphery of the light beam. That is, the reflection mirror 62
Reflected by the optical fiber includes all modes excited by the fiber, and does not exhibit mode dependency such that only a mode component having a high optical coupling degree is coupled to the branch fiber.

The degree of coupling as an optical coupler depends on the thickness of the reflecting mirror 62. In other words, it is determined by the cross-sectional area of the entire light beam transmitted from the first collimator 32 and the cross-sectional area of the light beam reflected by the reflection mirror 62.

Further, optical coupling from the branch fiber 70 to the trunk fiber 38 can be performed. The optical signal sent from the branch fiber 70 is converted into parallel light by the fourth collimator 60, and a part thereof is reflected by the reflection mirror 62. The reflected light is coupled to the main fiber 38 by the second collimator 34. Therefore, according to this optical coupler, it is possible to insert an optical signal from the branch fiber 70 into the trunk fiber 38.

In the optical coupler of this embodiment, the branch line module 28 can be easily attached to and detached from the main line module 26. However, even when the attachment and detachment are repeated, very high characteristic reproducibility is exhibited. The reason will be described below.

As described above, when the branch line module 28 is mounted, the groove 52 formed on the end surface of the second casing 50 of the branch line module 28 is pressed against and contacts the outer wall of the trunk line module 26. Therefore, branch line module 2
8, only the translational displacement in the extending direction of the groove 52 and the rotational displacement about the central axis of the first housing 30 are allowed, but the collimator axis of the trunk module 26 and the collimator axis of the branch module 28 Will always be maintained.

Actually, even if the mounting position of the branch line module 28 to the trunk line module 26 is shifted in the axial direction on the first housing 30, the mounting angle of the branch line module 28 (with respect to the central axis of the first housing 30). Even if the rotation angle is shifted, these shifts do not contribute to the loss of optical coupling between the collimators. Therefore, since the position parameter and the angle parameter required for the collimator coupling system are always maintained, stable optical coupling characteristics can be always ensured even when the module is attached or detached.

[Second Embodiment] Next, an optical coupler according to a second embodiment will be described with reference to FIG. FIG.
FIG. 3 is a cross-sectional view illustrating a configuration of an optical coupler according to a second embodiment. FIG. 4 shows a state where the branch line module 28 is mounted on the main line module 26. In the optical coupler of this embodiment, the size of the reflecting mirror 62 provided in the branch line module 28 is different from that of the optical coupler of the first embodiment. Other configurations are the first
This is not different from the configuration of the embodiment. The reflecting mirror of this configuration example is represented by reference numeral 80. The reflecting surface of the reflecting mirror 80 is represented by reference numerals 80a and 80b. Further, a branch line module provided with the reflection mirror 80 is represented by reference numeral 82.

The cross section shown in FIG. 4A corresponds to the cross section shown in FIG. The cross section shown in FIG.
This corresponds to the cross section shown in FIG. As shown in FIGS. 4A and 4B, the top of the protruding piece 64 is the first housing 30.
Are located above the center axis in FIG. First collimator 3
The area of the reflection surface 80a of the reflection mirror 80 viewed from the second side is:
It is equal to or larger than the beam cross-sectional area of the parallel light 66 emitted from the first collimator 32 (FIG. 4B). Therefore, the reflection mirror 8
0 reflects the entire beam of parallel light 66. The reflected light propagates toward the third collimator 58 and is coupled to the branch fiber 68. Accordingly, an optical path switching function of coupling an optical signal transmitted from the trunk fiber 36 to the branch fiber 68 is realized.

As described above, the common trunk module 26 is replaced with the branch module 28 of the first embodiment and the second module.
By selecting and installing any one of the branch line modules 82 of the embodiment, the optical coupling function for the purpose of optical branching coupling and the optical path switching function for the purpose of optical path switching can be selectively used.

[Third Embodiment] Next, a method of expanding an optical system by using the optical coupler described in the first and second embodiments will be described with reference to FIGS. explain. FIG. 5 and FIG. 6 are block diagrams showing an optical system extension example. In the drawing, the optical coupler to which the branch line module 28 of the first embodiment is mounted is indicated by reference numeral 84.
Further, reference numeral 86 denotes an optical coupler on which the branch line module 82 according to the second embodiment is mounted.

First, in the configuration shown in FIG. 5A, a plurality of optical couplers 84 are inserted in the trunk fiber 88. In this example, the optical coupler 84 is used as a normal branch coupler, and one terminal is connected to each optical coupler 84.

Next, in the configuration shown in FIG. 5B, a plurality of optical couplers 84 and 86 are inserted into the trunk fiber 88. One terminal is connected to the optical coupler 84, but a plurality of terminals can be connected to the optical coupler 86. The optical coupler 86 in the trunk fiber 88 has an optical path switching function, and converts the optical signal transmitted by the trunk fiber 88 into a third signal.
The light is sent to the branch fiber 90 connected to the collimator. The other end of the branch fiber 90 is connected to the fourth collimator side of the optical coupler 86, and the optical signal is sent to the trunk fiber 88 via the reflection mirror and the second collimator. A plurality of optical couplers 84 are inserted into the branch fiber 90, and one terminal is connected to each of the optical couplers 84. As described above, by attaching the branch line module 82 having the optical path switching function to the trunk module 26 connected to the trunk fiber 88, the number of terminals can be increased.

Next, in the configuration shown in FIG. 6, a plurality of optical couplers 86 are inserted into the trunk fiber 88. A branch fiber 90 is connected to one of the optical couplers 86. Optical couplers 84 and 86 are inserted into the branch fiber 90. A terminal is connected to the optical coupler 84, and a branch fiber 92 is connected to the optical coupler 86. Further, an optical coupler 84 is inserted into the branch line fiber 92, and a terminal is connected to the optical coupler 84.

Further, to another optical coupler 86 inserted into the trunk fiber 88, branch fibers 94a and 94b are connected to the third and fourth collimators of the optical coupler 86, respectively. To these branch fibers 94a and 94b, a photodiode 96, a laser diode 98, and an electric circuit 100 are connected as a regenerative repeater 102 (the electric signal line connects between the photodiode 96, the electric circuit 100, and the laser diode 98). It is connected.). Therefore, the optical signal transmitted by the trunk fiber 88 is sent to the branch fiber 94a in the optical coupler 86, enters the regenerative repeater 102, and is converted into an electric signal by the photodiode 96. This electric signal is amplified by the electric circuit 100 and then converted into an optical signal by the laser diode 98.
This optical signal passes through the branch fiber 94b and passes through the optical coupler 86.
And sent to the trunk fiber 88. In this way, the regenerative repeater 102 absorbs a decrease in the optical level of the optical signal. Therefore, even if the number of terminals is increased, such a regenerative repeater 102 can be connected via the optical coupler 86, so that erroneous recognition of an optical signal does not occur.

As described above, the main line module 26
If a fiber to which is connected is prepared, a large number of terminals can be connected by selecting and attaching both the branch line modules 28 and 82.

[0077]

According to the optical coupler of the present invention, one trunk fiber and the other trunk fiber are coupled via the trunk module. The light emitted from one end of the trunk fiber is converted into parallel light by the first collimator, propagates through the trunk module, and enters the second collimator. The second collimator focuses the incident parallel light on the end of the other trunk fiber. Therefore, light transmitted from one trunk fiber is sent to the other trunk fiber via the trunk module.

On the other hand, when the branch line module is mounted on the trunk line module, the reflection mirror of the branch line module is inserted into the optical path between the first and second collimators. As a result, at least a part of the parallel light emitted from the first collimator is reflected by the reflection mirror and guided to the third collimator. The third collimator focuses the incident parallel light on the end of the branch fiber. As described above, when the branch line module is mounted on the trunk line module, light transmitted by the trunk line fiber can be extracted to the branch line side. Further, by changing the size of the reflection mirror, the amount of light guided to the third collimator changes, so that not only an optical coupling function but also an optical path switching function can be realized.

When the light is transmitted from the branch fiber to the fourth collimator, it is converted into parallel light and then guided to the second collimator by the reflection mirror. Therefore, light transmitted by the branch fiber can be coupled to the trunk fiber.

Therefore, according to the optical coupler of the present invention,
1) The trunk fiber and the branch fiber can be attached and detached, and 2) The optical coupling function and the optical path switching function can be selected. Further, 3) the degree of optical coupling hardly depends on the excitation condition of the multimode fiber, and 4) the branch fiber is mounted in a state orthogonal to the trunk fiber. In addition, 5) it can be manufactured at low cost, and 6) good reproducibility of the coupling characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an optical coupler according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of an optical coupler.

FIG. 3 is a diagram illustrating a configuration of an optical coupler when mounted.

FIG. 4 is a diagram illustrating a configuration of an optical coupler according to a second embodiment.

FIG. 5 is a diagram illustrating an example of expanding an optical system.

FIG. 6 is a diagram illustrating an example of expanding an optical system.

FIG. 7 is a diagram illustrating a configuration of a conventional optical coupler.

[Explanation of symbols]

10, 36, 38, 88: Trunk fiber 12, 68, 70, 90, 92, 94a, 94b: Branch fiber 14: Adjacent boundary 16-22: Port 26: Trunk module 28, 82: Branch module 30: First Housing 32: first collimator 34: second collimator 40, 44, 72, 76: spherical lens 42, 46, 74, 78: ferrule 48: opening 50: second housing 52: groove 54, 56: cylindrical hole 58 : Third collimator 60: Fourth collimator 62, 80: Reflecting mirror 62a, 62b, 80a, 80b: Reflecting surface 64: Projecting piece 66: Parallel light 84, 86: Optical coupler 96: Photodiode 98: Laser diode 100: Electric circuit 102: Regenerative repeater

Claims (4)

[Claims] 1. An optical coupler comprising a trunk line module and a branch line module, wherein the trunk line module converts a light emitted from an end of a trunk fiber into parallel light, and a first collimator. A second collimator that is provided to face and collects parallel light emitted from the first collimator at an end of the trunk fiber, wherein the branch line module is configured to be attachable to the trunk module. A third collimator, a fourth collimator, and a reflection mirror, wherein the reflection mirror is located between the first collimator and the second collimator when the branch module is mounted on the trunk module. Reflecting at least a part of the parallel light emitted from the first collimator and guiding the parallel light to the third collimator; Reflecting at least a part of the parallel light emitted from the second collimator, the third collimator condenses the reflected light from the reflection mirror to the end of the branch fiber, The optical coupler, wherein the fourth collimator converts light emitted from the end of the branch fiber into parallel light. 2. The optical coupler according to claim 1, wherein the main module includes a first cylindrical housing formed of a tube wall having a substantially uniform thickness. The first and second collimators are configured by inserting a spherical lens and a ferrule inside a housing, and the reflecting mirror is inserted through a tube wall of the first housing between the first and second collimators. The branch line module includes a second housing having a groove having a V-shaped cross-section capable of engaging with the outer wall surface of the first housing, and is provided in the groove. The reflection mirror is supported by the protruding piece, two holes are formed in the second housing, and a spherical lens and a ferrule are inserted into each hole to constitute the third and fourth collimators. An optical coupler characterized by the fact that: 3. The optical coupler according to claim 1, wherein the area of the reflection surface of the reflection mirror viewed from the first collimator side or the second collimator side is a parallel light beam emitted from the first collimator. An optical coupler having a smaller cross-sectional area. 4. The optical coupler according to claim 1, wherein the area of the reflection surface of the reflection mirror viewed from the first collimator side or the second collimator side is a parallel light beam emitted from the first collimator. An optical coupler having a sectional area or more.