JPH10197739A - Optical fiber connector with mode switching function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the amount of information that can be transmitted by greatly improving the transmission band of optical signal transmission using a step index type optical fiber. SOLUTION: The optical fiber connector 23 is interposed between a light- incidence side optical fiber 21 and a light-projection side optical fiber 22 to perform mode switching through which high-order mode light projected from the optical fiber 21 is made incident as low-order mode light on the optical fiber 22 and low-order mode light projected from the optical fiber 21 is made incident as high-order mode light on the optical fiber 22. The light projected in a diverged state from the optical fiber 21 is made into parallel luminous flux through a convex lens 3, projected from a conic surface 6b after being made incident on a conic transparent member 6 from the bottom surface and reflected by the internal surface of a conic surface 6a, reflected by a cylindrical reflecting member 5, projected from the bottom surface after being made incident on a conic transparent member 7 from its conic surface 7b and reflecting by the internal surface of a conic surface 7a, and made incident on the optical fiber 22 in a converged state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal transmission technique using an optical fiber, and more particularly, to a multimode step index type optical fiber (hereinafter simply referred to as "SI type optical fiber"). The present invention relates to a mode switching optical fiber connector used to increase the amount of information that can be transmitted in the used optical signal transmission.

[0002]

2. Description of the Related Art SI type optical fibers are widely used as a medium for transmitting optical signals. There are many modes in light propagating through an SI type optical fiber. Therefore, in the optical signal transmission using the SI type optical fiber, the light of the higher order mode having a large incident angle and the output angle with respect to the end face of the optical fiber is more light than the light of the low order mode having the small incident angle and the output angle with the end face of the optical fiber. Since the propagation speed in the longitudinal direction of the fiber becomes slow, there is a mode dispersion phenomenon that the propagation speed in the longitudinal direction of the optical fiber differs depending on the mode. As a result, the pulse shape of the signal pulse incident from the incident end is deteriorated at the output end by combining the low-order mode light and the high-order mode light. For this reason, there is a problem that a signal of a particularly high frequency cannot be transmitted.

[0003] The frequency range of a signal that can be transmitted is called a transmission band, and is generally indicated by an upper limit frequency value at which transmission is possible. The fact that the transmission band is wide means that the amount of information that can be transmitted in a given time can be increased.

In the optical signal transmission using the SI type optical fiber, as described above, the transmission band is limited due to the signal degradation due to the mode dispersion. Low at 10 MHz.

Accordingly, an object of the present invention is to provide an optical element used to greatly improve the transmission band of optical signal transmission using an SI type optical fiber and increase the amount of information that can be transmitted. Things.

[0006]

According to the present invention, a first optical fiber on the light incident side when transmitting an optical signal using a step index type optical fiber is provided. An optical fiber connector interposed between the optical fiber and a second optical fiber on the light emitting side, the optical fiber connector having a common optical axis with the emitting end of the first optical fiber and the incident end of the second optical fiber. First and second conical-shaped transparent members and a second conical-shaped transparent member arranged coaxially so that each vertex faces each other, and a cylinder coaxially arranged at a position radially outward thereof. A shape reflecting member, and light converging means, wherein light emitted in a divergent state from the first optical fiber is made incident on the first conical-shaped transparent member from a bottom surface and internally reflected by a conical surface. Later the light from the conical surface Is emitted diagonally outward in the diagonal direction, is reflected radially inward by the cylindrical reflecting member, is incident from the conical surface on the second conical transparent member, and is internally reflected by the conical surface. After that, the light is emitted from the bottom surface and is made to enter the second optical fiber in a converged state, and the light converging means is interposed in the above optical path, and the light converging means is provided from the first optical fiber to the optical axis. Higher-order mode light emitted with a relatively large inclination is incident on the second optical fiber as low-order mode light with a relatively small inclination with respect to the optical axis, and the light is emitted from the first optical fiber. The low-order mode light emitted with a relatively small inclination with respect to the axis is incident on the second optical fiber as the high-order mode light with a relatively large inclination with respect to the optical axis. , Characterized the door, optical fiber connector having a mode replacement function is provided.

In one embodiment of the present invention, the light converging means is a convex lens disposed adjacent to the bottom surface of the first conical transparent member and the bottom surface of the second conical transparent member.

In one aspect of the present invention, the light converging means is formed by forming the bottom surface of the first conical transparent member and the bottom surface of the second conical transparent member into convex curved surfaces.

In one aspect of the present invention, the light converging means is formed by giving bulges to the conical surface of the first conical transparent member and the conical surface of the second conical transparent member. .

In one aspect of the present invention, the light converging means is formed by making a cross section including the optical axis of the reflecting surface of the cylindrical reflecting member form a concave curve.

In one embodiment of the present invention, the cylindrical reflecting member is formed on an outer peripheral surface of a cylindrical transparent member, and the cylindrical transparent member has the first conical transparent member and the second conical transparent member on both end surfaces. A concave conical surface for receiving the conical-shaped transparent member is formed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

First, an optical signal transmission method using an optical fiber connector having a mode switching function according to the present invention will be described. FIG. 1 is a schematic sectional view showing one embodiment of this optical signal transmission method, and FIG. 2 is a schematic view showing the entire transmission line.

In the following, for convenience of explanation, light near the optical axis is representatively illustrated and described as low-order mode light, and light near the outer peripheral portion (peripheral portion) farthest from the optical axis is described as high-order mode light. A representative illustration will be given. However, the low-order mode light and the high-order mode light referred to in the present invention are, of course, not limited to these illustrated ones.

1 and 2, reference numeral 21 denotes a first SI.
Reference numeral 22 denotes a second SI type optical fiber, and reference numeral 23 denotes an optical fiber connector for connecting these two optical fibers 21 and 22. The optical fiber 21 includes a core 21a and a clad 21b, and the optical fiber 22 includes a core 22a and a clad 22b.

As shown in FIG. 2, an optical signal is input from one end of the optical fiber 21 (IN), is output from the other end of the optical fiber 21, and is output from one end of the optical fiber connector 23. Optical fiber connector 2
The light exits from the other end of the optical fiber 22, enters one end of the optical fiber 22, and exits from the other end of the optical fiber 22 (OUT).

This will be described in more detail with reference to FIG. The low-order mode light (light having a small incident angle) A and the high-order mode light (light having a large incident angle) B simultaneously incident on one end face of the optical fiber 21 propagate through the optical fiber 21, respectively. The light exits from the other end face of the optical fiber 21 as A ′ and B ′. At the time of this emission, the higher-order mode light B ′ has a time delay Δt with respect to the lower-order mode light A ′. These lights A ′ and B ′ enter one end face of the optical fiber 22 via the optical fiber connector 23.

In this embodiment, the optical fiber connector 23
At the time of incidence, the light A ', which was in the low-order mode at the time of incidence, is converted into high-order mode light and emitted, and the light B', which was at the high-order mode at the time of incidence, is converted into low-order mode light and emitted. Thus, the mode is switched in the optical fiber connector 23, and the light A ′ enters the one end face of the optical fiber 22 as the higher-order mode and the light B ′ enters the lower-order mode.

Accordingly, the low-order mode light B ′ and the high-order mode light A ′ incident on one end face of the optical fiber 22 with a time lag Δt propagate through the optical fiber 22, and the other end of the optical fiber 22. When the light is emitted from the end face as B ″ and A ″, the time shift Δt at the time of incidence on the optical fiber 22 is eliminated, and the low-order mode light B ″ and the high-order mode light A ″ are emitted almost simultaneously. This eliminates mode dispersion,
The transmission bandwidth is improved.

In principle, the length of the optical fiber 21 and the length of the optical fiber 22 should be equal. In this case, the effect of improving the transmission band is maximized. Even if the length is slightly different, a sufficient effect is recognized. For example, even if the length of the optical fiber 21 differs from the length of the optical fiber 22 by about 20%, the decrease in the transmission band is slight. Further, even if the difference between the length of the optical fiber 21 and the length of the optical fiber 22 is increased to about 50%, a transmission band about twice as large as when the transmission method of the present invention is not used can be obtained, and a clear effect is obtained. Is recognized.

FIG. 3 is a schematic sectional view showing a first embodiment of the optical fiber connector 23 of the present invention used in the above-described optical transmission method, and FIG. 4 is a schematic perspective view thereof.

In this embodiment, the exit end of the SI optical fiber 21 and the entrance end of the SI optical fiber 22 are coaxially opposed to each other. Between these, the optical fiber connector 23 is coaxially arranged. The optical fiber connector 23 includes two convex lenses 3 and 4, two conical transparent members 6 and 7 disposed therebetween, and one cylindrical reflective member disposed radially outward of the conical transparent members. 5 The two conical transparent members 6 and 7 are arranged such that the vertices face each other (that is, the bottom surfaces face outward). In the present embodiment, the “cone shape” does not necessarily have to be a conical shape in a strictly geometrical sense, and a conical surface and a bottom surface exist in a desired optically effective area. Anything should do. The cylindrical reflecting member 5 has, for example, a metal reflecting film provided on the inner surface.

The light emitted from the emission end of the optical fiber 21 is converted into parallel light traveling in the optical axis direction in a circular cross section by the convex lens 3, and vertically enters the bottom surface of the conical transparent member 6. At this time, the higher-order mode light emitted from the emission end of the optical fiber 21 passes through the periphery of the convex lens 3 or its vicinity and enters the periphery of the bottom surface of the conical transparent member 6 or its vicinity. The low-order mode light emitted from the emission end passes through or near the center of the convex lens 3 and enters the center or the vicinity of the bottom surface of the conical transparent member 6. These lights are internally reflected radially inward by the conical surface 6 a of the conical transparent member 6, are translated in the cross section of FIG. 3, and are conical with the conical surface 6 b of the conical transparent member 6. Is emitted from another region) and is reflected by the cylindrical reflecting member 5. Then, the light reaches the transparent member 7 having a conical shape, enters from the conical surface 7b, is internally reflected in the direction of the optical axis by the conical surface 7a (an area different from the area where the light enters), exits perpendicularly from the bottom surface, and becomes parallel light. Become. It is preferable that the internal reflection by the conical surface is total reflection. By appropriately setting the shapes of the conical transparent members 6, 7 and their intervals and the inner diameter of the cylindrical reflecting member 5, as shown in FIG. The higher-order mode light incident on the vicinity is guided to or near the center of the bottom surface of the conical transparent member 7, and the lower-order mode light incident on or near the center of the bottom surface of the conical transparent member 6 is conically transparent. The light can be guided to the peripheral portion of the bottom surface of the member 7 or the vicinity thereof, and further, these lights can be converted into parallel light traveling in the optical axis direction. By setting the apex angle of the conical transparent members 6 and 7 to about 60 degrees, refraction during passage through a conical surface (incoming and outgoing) can be advantageously avoided.
The parallel light emitted from the conical transparent member 7 is
And is incident on the incident end of the optical fiber 22.
Higher-order mode light that has entered the peripheral portion of the bottom surface of the conical transparent member 6 or its vicinity from the optical fiber 21 has a low angle with the optical axis when entering the optical fiber 22 because it has a small angle with the optical axis. The second mode light is introduced into the optical fiber 22, while the optical fiber 21 transmits the conical transparent member 6.
When entering the optical fiber 22, the low-order mode light that has entered the central portion of the bottom surface of the optical fiber or in the vicinity thereof has a large angle with the optical axis. be introduced. Thus, the low-order mode light and the high-order mode light are converted (replaced) by the optical fiber connector 23.

FIG. 5 shows a second embodiment of the optical fiber connector according to the present invention.
It is a typical sectional view showing an embodiment. In this figure, members having the same functions as those in FIGS. 1 to 4 are denoted by the same reference numerals.

In this embodiment, the optical fiber connector 23
Consists of two conical transparent members 8 and 9 each having a convex lens surface on the bottom surface and one cylindrical reflecting member 5 disposed radially outward of the conical transparent members. The two conical transparent members 8 and 9 are arranged so that the vertices face each other, and the bottom surfaces are convex lens surfaces 10 and 11.

In the present embodiment, the light converging function of the convex lenses 3 and 4 of the embodiment shown in FIGS.
This is realized by making the bottom surface of 9 a convex lens surface 10 or 11. Therefore, the present embodiment corresponds to FIGS.
The same operation and effect as those of the embodiment are exerted. In addition, the number of components is reduced by adopting this embodiment.

FIG. 6 shows a third embodiment of the optical fiber connector according to the present invention.
It is a typical sectional view showing an embodiment. In this figure, members having the same functions as those in FIGS. 1 to 5 are denoted by the same reference numerals.

In this embodiment, the optical fiber connector 23
1 has two convex lenses 3 and 4, two conical transparent members 6 and 7 disposed therebetween, and two concave conical surfaces on both end surfaces having a shape conforming to the conical surfaces of the conical transparent members. And two columnar transparent members 12. Here, the concave conical surface refers to a surface formed corresponding to the conical surface of the cone after removing the coaxial cone from the end of the cylinder so as to form a concave portion. Two conical transparent members 6,7
Are arranged such that the vertices face each other.
The outer peripheral surface 13 of the cylindrical transparent member 12 has a function of a cylindrical reflecting member.

This embodiment has the same operation and effect as those of the embodiment shown in FIGS. In addition, according to the present embodiment, the optical system adjustment such as the optical axis alignment is automatically performed by simply fitting the conical transparent members 6 and 7 to the concave conical surface of the cylindrical transparent member 12. Easy to assemble and adjust.

FIG. 7 shows a fourth embodiment of the optical fiber connector according to the present invention.
FIG. 8 is a schematic cross-sectional view showing the embodiment, and FIG. 8 is a schematic perspective view thereof. In these drawings, members having the same functions as those in FIGS. 1 to 6 are denoted by the same reference numerals.

In this embodiment, the optical fiber connector 23
Is composed of two conical transparent members 14 and 15 whose conical surfaces bulge outward and one cylindrical reflecting member 16 arranged radially outward of these conical transparent members. 2
The two conical transparent members 14 and 15 are arranged such that their vertices face each other, and in a cross section including the optical axis, the conical surfaces 14a, 14b, 15a, and 15b form a curve (for example, an arc) that is outwardly convex. Have been.

In this embodiment, the light converging function realized by making the bottom surfaces of the conical transparent members 8, 9 in the embodiment of FIG.
4, 15 conical surfaces are loaded. Note that this light convergence function is mainly realized when the light is internally reflected by the conical surface, and is also auxiliaryly realized when the light passes through the conical surface. 14
The main light converging function is realized at the time of internal reflection at a, 15a, and the auxiliary light converging function is realized at the time of passing through the conical surfaces 14b, 15b.)

This embodiment has the same operation and effect as the embodiment of FIG.

FIG. 9 shows a fifth embodiment of the optical fiber connector according to the present invention.
It is a typical sectional view showing an embodiment. In this figure, members having the same functions as those in FIGS. 1 to 8 are denoted by the same reference numerals.

In this embodiment, the optical fiber connector 23
Consists of two conical transparent members 17 and 18 and one cylindrical reflecting member 19 having a reflecting surface composed of a concave curved surface disposed radially outward of the conical transparent members. The two conical transparent members 17 and 18 are arranged such that vertices face each other. Further, the cylindrical reflecting member 19 has a reflecting surface whose cross section including the optical axis has a concave curve (for example, an arc) shape.

In this embodiment, the light converging function realized by giving the conical surfaces of the conical transparent members 14 and 15 bulges in the embodiment of FIGS. It was a burden on the inside. Therefore, in the present embodiment, the light is in a divergent state up to the cylindrical reflecting member 19, and the light is in a converging state after being reflected by the cylindrical reflecting member 19.

This embodiment has the same operation and effect as those of the embodiment shown in FIGS.

The use of the cylindrical transparent member 12 as in the embodiment of FIG. 6 can be carried out in combination with any of the embodiments of FIGS. 5, 7 to 8 and FIG.

[0039]

As described above, by interposing the optical fiber connector having the mode switching function according to the present invention in the middle of the optical fiber transmission line, the mode dispersion is suppressed, the transmission band is improved, and the transmission is possible. The amount of information can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of an optical signal transmission method.

FIG. 2 is a schematic diagram showing the entire transmission path of the optical signal transmission method of FIG.

FIG. 3 is a schematic sectional view showing an embodiment of the optical fiber connector of the present invention.

FIG. 4 is a schematic perspective view of the optical fiber connector of FIG.

FIG. 5 is a schematic sectional view showing an embodiment of the optical fiber connector of the present invention.

FIG. 6 is a schematic sectional view showing an embodiment of the optical fiber connector of the present invention.

FIG. 7 is a schematic sectional view showing an embodiment of the optical fiber connector of the present invention.

FIG. 8 is a schematic perspective view of the optical fiber connector of FIG. 7;

FIG. 9 is a schematic sectional view showing an embodiment of the optical fiber connector of the present invention.

[Explanation of symbols]

 3,4 Convex lens 5 Cylindrical reflective member 6,7 Conical transparent member 6a, 6b, 7a, 7b Conical surface 8,9 Conical transparent member with convex lens planar bottom 10,11 Convex lens planar bottom 12 Concave concave surface Column-shaped transparent member 13 Outer peripheral reflecting surface 14, 15 Conical transparent member with conical bulge 16 Cylindrical reflecting member 17, 18 Conical transparent member 19 Cylindrical reflecting member with concave reflecting surface 21, 22 Optical fiber 23 Optical fiber connector

Claims (6)

[Claims] 1. An optical fiber connector interposed between a first optical fiber on a light incident side and a second optical fiber on a light emitting side when transmitting an optical signal using a step index type optical fiber. Wherein a light-emitting end of the first optical fiber and a light-entering end of the second optical fiber are arranged so as to have a common optical axis, and a third coaxially arranged such that vertexes face each other. A first conical transparent member and a second conical transparent member, a cylindrical reflecting member disposed coaxially at a position radially outward of the first transparent member, and light converging means. The light emitted in the divergent state
The first cone-shaped transparent member is made incident from the bottom surface, internally reflected by the conical surface, and then emitted obliquely to the optical axis outward from the conical surface with respect to the optical axis. The light is reflected inward, is incident on the second conical-shaped transparent member from the conical surface, is internally reflected by the conical surface, is emitted from the bottom surface, is incident on the second optical fiber in a convergent state, and The light converging means is interposed in the above optical path, and the higher-order mode light emitted from the first optical fiber with a relatively large inclination with respect to the optical axis is transmitted to the second optical fiber. The low-order mode light that is incident as a lower-order mode light with a relatively small inclination with respect to the optical axis and is emitted from the first optical fiber with a relatively small inclination with respect to the optical axis is the second light. To fiber An optical fiber connector having a mode switching function, wherein the optical fiber connector is configured to be incident as higher-order mode light with a relatively large inclination with respect to the optical axis. 2. The light converging means is a convex lens disposed adjacent to a bottom surface of the first conical transparent member and a bottom surface of the second conical transparent member, respectively. An optical fiber connector having the mode switching function described in (1). 3. The light converging means is formed by forming a bottom surface of the first conical-shaped transparent member and a bottom surface of the second conical-shaped transparent member into convex curved surfaces, respectively. 2. An optical fiber connector having the mode switching function according to 1. 4. The light converging means is formed by giving bulges to the conical surface of the first conical transparent member and the conical surface of the second conical transparent member, respectively. An optical fiber connector having a mode switching function according to claim 1. 5. The light converging means according to claim 1, wherein the reflecting surface of the cylindrical reflecting member is formed by making a cross section including the optical axis form a concave curve.
An optical fiber connector having the mode switching function described in (1). 6. The cylindrical reflecting member is formed on an outer peripheral surface of a cylindrical transparent member, and the cylindrical transparent member has the first conical transparent member and the second conical transparent member on both end surfaces. The optical fiber connector having a mode switching function according to any one of claims 1 to 5, wherein a concave conical surface for receiving is formed.