JP3562921B2 - Optical fiber connector with mode switching function - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical signal transmission technique using an optical fiber, and particularly to an optical signal transmission technique using an optical fiber of a multi-mode step index type (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 possible information.
[0002]
Problems to be solved by the prior art and the invention
SI type optical fibers are widely used as a medium for optical signal transmission. 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 in the higher-order mode having a large incident angle and emission angle with respect to the end face of the optical fiber is more light than the light in the low-order mode having a small incident angle and emission angle with respect to 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 in which the propagation speed in the longitudinal direction of the optical fiber differs depending on the mode. As a result, the signal pulse incident from the incident end degrades the pulse shape 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 signals 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.
[0004]
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. For example, a typical value in 100 m transmission is several tens MHz to one hundred and several tens MHz. Low.
[0005]
Accordingly, an object of the present invention is to provide an optical element used to significantly improve the transmission band of optical signal transmission using an SI type optical fiber and increase the amount of information that can be transmitted. .
[0006]
[Means for Solving the Problems]
According to the present invention, as achieving the above objects,
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 an optical fiber of a step index type,
It is arranged so as to have a common optical axis with the exit end of the first optical fiber and the entrance end of the second optical fiber,
A first conical-shaped transparent member and a second conical-shaped transparent member coaxially arranged so as to face each other, and a cylindrical reflecting member coaxially arranged at a position radially outward of the first and second conical-shaped transparent members; Light converging means,
Light emitted in a divergent state from the first optical fiber is incident on the first conical-shaped transparent member from the bottom surface, is internally reflected by the conical surface, and then has a diameter oblique to the optical axis from the conical surface. In the direction outward, reflected inward in the radial direction by the cylindrical reflecting member, made incident on the second cone-shaped transparent member from the conical surface, reflected internally by the conical surface, and then emitted from the bottom surface. The light is converged into the second optical fiber, and the light converging means is interposed in the above optical path;
Higher-order mode light emitted from the first optical fiber with a relatively large inclination with respect to the optical axis is converted into low-order mode light with a relatively small inclination with respect to the optical axis to the second optical fiber. Low-order mode light that is incident and emitted from the first optical fiber with a relatively small inclination with respect to the optical axis is incident on the second optical fiber with a relatively large inclination with respect to the optical axis. It is configured to be incident as the next mode light ,
A difference between the length of the first optical fiber and the length of the second optical fiber is 50% or less;
An optical fiber connector having a mode switching function,
Is provided.
[0007]
In one aspect 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.
[0008]
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.
[0009]
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.
[0010]
In one aspect of the present invention, the light converging means is formed by making the cross section including the optical axis of the reflecting surface of the cylindrical reflecting member form a concave curve.
[0011]
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 transparent member is formed.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
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.
[0014]
In the following, for convenience of explanation, light near the optical axis is typically illustrated and described as low-order mode light, and light near the outer periphery (peripheral portion) farthest from the optical axis is typically illustrated as high-order mode light. It is illustrated and described. However, the low-order mode light and the high-order mode light in the present invention are not limited to those shown in the drawings.
[0015]
1 and 2, reference numeral 21 denotes a first SI optical fiber, reference numeral 22 denotes a second SI optical fiber, and reference numeral 23 denotes an optical fiber connector for connecting the 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.
[0016]
As shown in FIG. 2, the optical signal enters from one end of the optical fiber 21 (IN), exits from the other end of the optical fiber 21, and exits from one end of the optical fiber connector 23. And exits from the other end of the optical fiber connector 23, enters the one end of the optical fiber 22, and exits from the other end of the optical fiber 22 (OUT).
[0017]
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.
[0018]
In the present embodiment, the light A ′, which was in the low-order mode at the time of incidence, is converted into high-order mode light and emitted from the optical fiber connector 23, and the light B ′, which was in the high-order mode at the time of incidence, is converted into low-order mode light. And output. 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.
[0019]
Accordingly, the lower-order mode light B ′ and the higher-order mode light A ′ that have entered the one end face of the optical fiber 22 with a time shift Δt propagate through the optical fiber 22, and are transmitted from the other end face of the optical fiber 22 to B ′. When the light is emitted as “, A”, the time shift Δt at the time of entering the optical fiber 22 is eliminated, and the low-order mode light B ″ and the high-order mode light A ″ are emitted almost simultaneously. Thereby, the mode dispersion is eliminated and the transmission band is improved.
[0020]
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 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 can be obtained. Is recognized.
[0021]
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.
[0022]
In the present embodiment, the output end of the SI optical fiber 21 and the input end of the SI optical fiber 22 are coaxially opposed to each other. The optical fiber connector 23 is coaxially arranged between them. 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.
[0023]
The light emitted from the emission end of the optical fiber 21 is converted into parallel light traveling in the optical axis direction with a circular cross section by the convex lens 3, and vertically enters the bottom surface of the conical transparent member 6. At that 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 the central part of the convex lens 3 or its vicinity, and enters the central part of the bottom surface of the conical transparent member 6 or its vicinity. 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. The internal reflection by the conical surface described above is preferably total reflection. By appropriately setting the shapes of the conical-shaped transparent members 6 and 7 and their intervals and the inner diameter of the cylindrical-shaped 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 conical 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 converged by the convex lens 4 and is incident on the incident end of the optical fiber 22. Higher-order mode light that has entered from the optical fiber 21 to the peripheral portion of the bottom surface of the conical transparent member 6 or in the vicinity thereof has a low angle with the optical axis when entering the optical fiber 22 because it has a small angle with the optical axis. On the other hand, the low-order mode light that is introduced into the optical fiber 22 as the next mode light and enters the central portion of the bottom surface of the conical transparent member 6 or in the vicinity thereof from the optical fiber 21 when the light enters the optical fiber 22 Since the angle with the optical axis is large, the light is introduced into the optical fiber 22 as higher-order mode light. Thus, the low-order mode light and the high-order mode light are converted (replaced) by the optical fiber connector 23.
[0024]
FIG. 5 is a schematic cross-sectional view showing a second embodiment of the optical fiber connector of the present invention. In this figure, members having the same functions as those in FIGS. 1 to 4 are denoted by the same reference numerals.
[0025]
In this embodiment, the optical fiber connector 23 is composed of two conical transparent members 8 and 9 each having a convex lens surface on the bottom surface and one cylindrical reflective member 5 disposed radially outward of the conical transparent members. Become. 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.
[0026]
In the present embodiment, the light converging function of the convex lenses 3 and 4 in the embodiment of FIGS. 3 and 4 is realized by making the bottom surfaces of the conical transparent members 8 and 9 convex surfaces 10 and 11. Therefore, the present embodiment has the same operation and effect as the embodiment of FIGS. In addition, the number of components can be reduced by adopting this embodiment.
[0027]
FIG. 6 is a schematic sectional view showing a third embodiment of the optical fiber connector of the present invention. In this figure, members having the same functions as those in FIGS. 1 to 5 are denoted by the same reference numerals.
[0028]
In the present embodiment, the optical fiber connector 23 includes two convex lenses 3 and 4, two conical transparent members 6 and 7 disposed between the two convex lenses 3 and 4, and two conical transparent members 6 and 7 having a shape matching the conical surfaces of the conical transparent members. One cylindrical transparent member 12 having a concave conical surface on both end surfaces. Here, the concave conical surface refers to a surface formed corresponding to the conical surface of the conical body after removing the coaxial conical body from the end of the cylinder so as to form a concave portion. The two conical transparent members 6 and 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.
[0029]
This embodiment has the same functions and effects as the embodiments of FIGS. In addition, according to the present embodiment, the optical system adjustment such as the optical axis alignment is automatically performed by simply adjusting the conical transparent members 6 and 7 to the concave conical surface of the cylindrical transparent member 12. Easy to assemble and adjust.
[0030]
FIG. 7 is a schematic sectional view showing a fourth embodiment of the optical fiber connector of the present invention, 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.
[0031]
In this embodiment, the optical fiber connector 23 includes two conical transparent members 14 and 15 having conical surfaces bulging outward, and one cylindrical reflecting member disposed radially outward of the conical transparent members. 16 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 have outwardly convex curves (for example, arcs). It has been.
[0032]
In the present embodiment, the light converging function realized by making the bottom surfaces of the conical transparent members 8 and 9 into convex spherical surfaces 10 and 11 in the embodiment of FIG. 5 is added to the conical surfaces of the conical transparent members 14 and 15. It was a burden. 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. The main light converging function is realized at the time of internal reflection at 14a and 15a, and the auxiliary light converging function is realized at the time of passing through the conical surfaces 14b and 15b.)
[0033]
This embodiment has the same operation and effect as the embodiment of FIG.
[0034]
FIG. 9 is a schematic sectional view showing a fifth embodiment of the optical fiber connector of the present invention. In this figure, members having the same functions as those in FIGS. 1 to 8 are denoted by the same reference numerals.
[0035]
In this embodiment, the optical fiber connector 23 includes two conical transparent members 17 and 18 and one cylindrical reflective member 19 having a concave curved surface disposed radially outward of the conical transparent members. Consists of The two conical transparent members 17 and 18 are arranged such that their 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.
[0036]
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. 7 and 8 is loaded on the reflection inner surface of the cylindrical reflection member 19. It was made. 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.
[0037]
This embodiment has the same functions and effects as those of the embodiment shown in FIGS.
[0038]
Note that the use of the cylindrical transparent member 12 as in the embodiment of FIG. 6 can be implemented in combination with any of the embodiments of FIGS. 5, 7 to 8 and 9.
[0039]
【The invention's effect】
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 amount of information that can be transmitted is increased. be able to.
[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 10, 11 having convex lens surface bottom Surface convex lens surface bottom 12 Concave surface Cylindrical transparent member 13 having outer peripheral reflecting surfaces 14, 15 Conical transparent member 16 having a conical bulge Cylindrical reflecting member 17, 18 Conical transparent member 19 Cylindrical reflecting member 21, 22 having concave reflecting surface Optical fiber 23 Optical fiber connector

Claims (6)

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 an optical fiber of a step index type,
It is arranged so as to have a common optical axis with the exit end of the first optical fiber and the entrance end of the second optical fiber,
A first conical-shaped transparent member and a second conical-shaped transparent member coaxially arranged so as to face each other, and a cylindrical reflecting member coaxially arranged at a position radially outward of the first and second conical-shaped transparent members; Light converging means,
Light emitted in a divergent state from the first optical fiber is incident on the first conical-shaped transparent member from the bottom surface, is internally reflected by the conical surface, and then has a diameter oblique to the optical axis from the conical surface. In the direction outward, reflected inward in the radial direction by the cylindrical reflecting member, made incident on the second cone-shaped transparent member from the conical surface, reflected internally by the conical surface, and then emitted from the bottom surface. The light is converged into the second optical fiber, and the light converging means is interposed in the above optical path;
Higher-order mode light emitted from the first optical fiber with a relatively large inclination with respect to the optical axis is converted into low-order mode light with a relatively small inclination with respect to the optical axis to the second optical fiber. Low-order mode light that is incident and emitted from the first optical fiber with a relatively small inclination with respect to the optical axis is incident on the second optical fiber with a relatively large inclination with respect to the optical axis. It is configured to be incident as the next mode light ,
A difference between the length of the first optical fiber and the length of the second optical fiber is 50% or less;
An optical fiber connector having a mode switching function. The mode switching according to claim 1, wherein 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. Optical fiber connector with functions. 2. The mode according to claim 1, wherein the light converging means is formed by forming a bottom surface of the first conical transparent member and a bottom surface of the second conical transparent member as convex curved surfaces. Optical fiber connector with replacement function. The said light converging means is formed by giving a swelling to the conical surface of the said 1st conical-shaped transparent member, and the conical surface of a 2nd conical-shaped transparent member, respectively, The Claim 1 characterized by the above-mentioned. Optical fiber connector with mode switching function. 2. The mode switching function according to claim 1, wherein the light converging unit is formed by making a reflection surface of the cylindrical reflection member so that a cross section including the optical axis forms a concave curve. 3. With fiber optic connector. The cylindrical reflecting member is formed on an outer peripheral surface of a cylindrical transparent member, and the cylindrical transparent member has concave cones on both end surfaces for receiving the first and second conical transparent members. The optical fiber connector having a mode switching function according to any one of claims 1 to 5, wherein a surface is formed.

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