JP3963389B2 - Optical fiber connector with lens and mode switching function - Google Patents

Description

  The present invention belongs to an optical signal transmission technique using an optical fiber, and in particular, is transmitted in an optical signal transmission using 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 possible information.

  SI type optical fibers are widely used as optical signal transmission media. There are many modes in the light propagating through the SI optical fiber. Therefore, in optical signal transmission using an SI optical fiber, higher-order mode light having a large incident angle and outgoing angle with respect to the end face of the optical fiber is lighter than low-order mode light having a small incident angle and outgoing 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 pulse shape of the signal pulse incident from the incident end is deteriorated by combining the light of the lower order mode and the light of the higher order mode at the exit end. For this reason, there is a problem that a signal having a particularly high frequency cannot be transmitted.

  The frequency range of a signal that can be transmitted is called a transmission band, and is generally represented by an upper limit frequency value that can be transmitted. A wide transmission band means that the amount of information that can be transmitted in a certain time can be increased.

  In the optical signal transmission using the SI type optical fiber, as already described, the transmission band is limited due to the signal deterioration due to the mode dispersion. For example, a typical value in 100 m transmission is several tens MHz to several tens MHz. Low.

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

According to the present invention, the object as described above is achieved.
A pair of lens surfaces (6 ′, 6 ″) that are rotationally symmetric with respect to the central axis are formed on both end faces of the translucent member (6), or the pair of translucent members (8, 9) are mutually connected. A pair of lens surfaces (10, 11) that are rotationally symmetric with respect to the central axis are formed on opposite end surfaces, and the lens surfaces (6 ′, 6 ″ or 10, 11) are within a cross section including the central axis. In each of the above, the shape of each of the two regions divided by the central axis is obtained by dividing the convex lens surface having the central axis as the optical axis by dividing the convex lens surface by the optical axis in the cross section including the optical axis. In each of the shapes, the optical axis side is the outer diameter side and the outer diameter side is the optical axis side so that the optical axis side is reversed and replaced around the direction parallel to the optical axis. lens,
Is provided.

In addition, according to the present invention, the object as described above is achieved.
An optical fiber connector interposed between a first optical fiber on a light incident side and a second optical fiber on a light output side when transmitting an optical signal using a step index type optical fiber,
This fiber optic connector
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 cylindrical first inward reflecting surface (7 ′ or 8 ′) disposed coaxially with the optical axis on the first end surface side and the second end surface side of the lens and having the same diameter as the lens, and A second inner reflective surface (7 ′ or 9 ′), respectively, the first inner reflective surface (7 ′ or 8 ′) and the second inner reflective surface (7 ′ or 9 ′); ) Has a function of condensing the incident light of the second optical fiber through the lens while reflecting the light emitted from the first optical fiber on one of its reflection surfaces,
High-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 enters the second optical fiber with a relatively large inclination with respect to the optical axis. It is configured to be incident as next mode light,
An optical fiber connector having a mode switching function,
Is provided.

  In one aspect of the present invention, the first inner reflective surface (8 ′) is formed on the outer peripheral surface of the translucent member (8), and the second inner reflective surface (9 ′) is It is formed on the outer peripheral surface of the translucent member (9).

  According to the present invention, by interposing an optical fiber connector having a mode switching function using a special lens according to the present invention or a special pair of lens surfaces and an inward reflection surface in the middle of an optical fiber transmission line, It is possible to suppress the mode dispersion, improve the transmission band, and increase the amount of information that can be transmitted.

  Hereinafter, embodiments of the present invention will be described 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 an embodiment of this optical signal transmission method, and FIG. 2 is a schematic diagram showing the entire transmission path.

  In the following, for convenience of explanation, the light in the vicinity of the optical axis is representatively illustrated and explained as the low-order mode light, and the light in the vicinity of the outer peripheral portion (peripheral part) farthest from the optical axis is representatively shown as the high-order mode light. This is illustrated and described. However, it goes without saying that the low-order mode light and the high-order mode light referred to in the present invention are not limited to those shown in the drawings.

  In FIGS. 1 and 2, reference numeral 21 denotes a first SI type optical fiber, 22 denotes a second SI type optical fiber, and 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, the optical signal is incident from one end of the optical fiber 21 (IN), emitted from the other end of the optical fiber 21, and one end of the optical fiber connector 23. , Is output from the other end of the optical fiber connector 23, is input to one end of the optical fiber 22, and is output from the other end of the optical fiber 22 (OUT).

  This will be described in more detail with reference to FIG. Low-order mode light (light having a small incident angle) A and 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 is emitted as A ′ and B ′ from the other end face of the optical fiber 21. At the time of emission, the high-order mode light B ′ has a time delay Δt with respect to the low-order mode light A ′. These lights A ′ and B ′ are incident on one end face of the optical fiber 22 through the optical fiber connector 23.

  In the present embodiment, in the optical fiber connector 23, the light A ′ that was in the low-order mode at the time of incidence is converted into a high-order mode light and emitted, and the light B ′ that was in the high-order mode at the time of incidence is converted into low-order mode light To be emitted. Thus, the mode is switched in the optical fiber connector 23, and the light A 'enters the high-order mode and the light B' enters the one end face of the optical fiber 22 as the low-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 shift Δt propagate in the optical fiber 22 and B from the other end face of the optical fiber 22. When the light is emitted as “, 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. Thereby, mode dispersion is eliminated and the transmission band 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, but the length of the optical fiber 21 and the length of the optical fiber 22 are different. Even if it is slightly different, a sufficient effect is recognized. For example, even if the length of the optical fiber 21 and the length of the optical fiber 22 are different by about 20%, the transmission band is slightly reduced. 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 that is about twice that in the case where the transmission method of the present invention is not used can be obtained. Is recognized.

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

  In the present 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 transparent cylindrical rods 3 and 4 having the same length and the same diameter, and one gradient index cylindrical lens 5 disposed therebetween. The cylindrical lens 5 has the same diameter as the two transparent cylindrical rods 3 and 4. The outer peripheral surfaces of the transparent cylindrical rods 3 and 4 are cylindrical inner reflection surfaces 3 'and 4'. This reflection surface may use total reflection, or may be provided with a reflection film.

  5 and 6 are schematic diagrams for explaining the characteristics and functions of the cylindrical lens 5. As shown in FIG. 5, the cylindrical lens 5 has a cylindrical shape with a radius R, and the refractive index is a function of the distance r from the central axis Z. If the refractive index distribution of the cylindrical lens 5 is n (r), this refractive index distribution is as shown in FIG. That is, the refractive index distribution n (r) of the cylindrical lens 5 has the highest refractive index at the position of the central axis Z (arranged so as to coincide with the optical axes of the optical fibers 21 and 22) (that is, r = 0). It takes the form of a monotonically increasing function that is low and gradually increases in refractive index as r increases. This curve is approximated by, for example, a quadratic curve or a quartic curve. In this embodiment, the refractive index distribution n (r) has a tangent slope of 0 at r = R.

  As shown in FIG. 3, the light emitted from the emission end of the optical fiber 21 enters the one end surface of the cylindrical lens 5 through the transparent cylindrical rod 3. At that time, the high-order mode light emitted from the exit end of the optical fiber 21 is reflected inward by the inner reflecting surface 3 ′ of the transparent cylindrical rod 3 and enters the cylindrical lens 5 with a large inclination with respect to the optical axis. On the other hand, the low-order mode light is incident on the cylindrical lens 5 with a small inclination with respect to the optical axis. By appropriately setting the length and refractive index of the cylindrical lens 5 and its distribution, the high-order mode light incident on the one end surface of the cylindrical lens 5 with a large angle with respect to the optical axis has a small angle with respect to the optical axis. The light is emitted from the other end surface. Of the light exiting the cylindrical lens 5, the light traveling at a small angle with respect to the optical axis enters the incident end of the optical fiber 22 through the transparent cylindrical rod 4 and travels at a large angle with respect to the optical axis. Light undergoes inward reflection by the inward reflection surface 4 ′ of the transparent cylindrical rod 4 and enters the incident end of the optical fiber 22.

  Thus, when the higher-order mode light that has entered the cylindrical lens 5 from the optical fiber 21 through the transparent cylindrical rod 3 enters the optical fiber 22 through the transparent cylindrical rod 4, the angle formed with the optical axis is as follows. Since it is small, it is introduced into the optical fiber 22 as low-order mode light. On the other hand, when the low-order mode light incident on the cylindrical lens 5 enters the optical fiber 22 through the transparent cylindrical rod 4, Since the angle formed with the optical axis is large, it is introduced into the optical fiber 22 as high-order mode light. Thus, the low-order mode light and the high-order mode light are converted (replaced) by the optical fiber connector 23.

  As a method of manufacturing the cylindrical lens 5, for example, three or more kinds of uncured mixture composed of an organic polymer and a monomer are concentrically multilayer-spun, and the refractive index is increased from the central portion toward the outer peripheral portion. A fiber-like uncured laminate was formed, which increased in sequence, and the components between adjacent layers were interdiffused or interdiffused so that the refractive index distribution between each layer of this laminate changed continuously. Later, a method of curing the laminate to obtain a refractive index distribution type optical fiber and cutting it into an appropriate length can be mentioned. Furthermore, the refractive index distribution can be adjusted by stretching the fiber to reduce the diameter.

  FIG. 7 is a schematic cross-sectional view showing a second 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 in FIGS. 1 to 6 are denoted by the same reference numerals.

  In the present embodiment, the optical fiber connector 23 has a pair of lens surfaces 6 ′, 6 ″ formed on both surfaces of the translucent member 6 and a cylindrical shape disposed radially outward of the translucent member 6. The inner reflection surface 7 ′ is formed on the inner surface of the inner reflection member 7. The inner reflection surface 7 ′ extends in the axial direction from both ends of the translucent member 6 in the optical axis direction. And disposed adjacent to the outer peripheral surface of the translucent member 6.

  The pair of lens surfaces 6 ′ and 6 ″ formed on the translucent member 6 are rotationally symmetric with respect to the optical axis, but each of two regions divided by the optical axis in a cross section including the optical axis. The shape is such that the convex lens is divided by the optical axis and the optical axis side and the outer diameter side are interchanged with each other, and a pair of lenses at the outer diameter position of the translucent member 6. The direction of the surface normal of the surfaces 6 ′ and 6 ″ is parallel to the optical axis, and the direction of the surface normal on the optical axis has the greatest inclination with respect to the optical axis.

  In the present embodiment, the function of the cylindrical lens 5 of the embodiment of FIGS. 3 and 4 is imposed on the pair of lens surfaces 6 ′, 6 ″ of the translucent member 6, and this embodiment is illustrated in FIG. And there exists an effect equivalent to embodiment of FIG.

  FIG. 9 is a schematic sectional view showing a third embodiment of the optical fiber connector of the present invention, and FIG. 10 is a schematic perspective view thereof. In these drawings, members having functions similar to those in FIGS. 1 to 8 are denoted by the same reference numerals.

  In the present embodiment, the optical fiber connector 23 includes a pair of lens surfaces 10 and 11 formed on end surfaces of the pair of translucent members 8 and 9 facing each other, and an outer peripheral surface of the translucent members 8 and 9. And inward reflecting surfaces 8 'and 9' formed on the surface.

  In this embodiment, the function of the pair of lens surfaces 6 ′, 6 ″ in the embodiment of FIGS. 7 and 8 is imposed on the pair of lens surfaces 10, 11, and this embodiment is shown in FIGS. There exists an effect equivalent to embodiment of FIG.

It is a typical sectional view showing one embodiment of an optical signal transmission method. It is a schematic diagram which shows the whole transmission line of the optical signal transmission method of FIG. It is a typical sectional view showing an embodiment of an optical fiber connector of the present invention. FIG. 4 is a schematic perspective view of the optical fiber connector of FIG. 3. It is the schematic for demonstrating the characteristic and function of a gradient index type | mold cylindrical lens used for the optical fiber connector of this invention. It is the schematic for demonstrating the characteristic and function of a gradient index type | mold cylindrical lens used for the optical fiber connector of this invention. It is a typical sectional view showing an embodiment of an optical fiber connector of the present invention. It is a schematic perspective view of the optical fiber connector of FIG. It is a typical sectional view showing an embodiment of an optical fiber connector of the present invention. FIG. 10 is a schematic perspective view of the optical fiber connector of FIG. 9.

Explanation of symbols

3, 4 Transparent cylindrical rod 3 ', 4' Inward reflecting surface 5 Gradient index type cylindrical lens 6 Translucent member 6 ', 6 "Lens surface 7 Inward reflecting member 7' Inward reflecting surface 8, 9 Translucent 8 ', 9' Internal reflection surface 10, 11 Lens surface 21, 22 Optical fiber 23 Optical fiber connector

Claims (3)

A pair of lens surfaces (6 ′, 6 ″) that are rotationally symmetric with respect to the central axis are formed on both end faces of the translucent member (6), or the pair of translucent members (8, 9) are mutually connected. A pair of lens surfaces (10, 11) that are rotationally symmetric with respect to the central axis are formed on opposite end surfaces, and the lens surfaces (6 ′, 6 ″ or 10, 11) are within a cross section including the central axis. In each of the above, the shape of each of the two regions divided by the central axis is obtained by dividing the convex lens surface having the central axis as the optical axis by dividing the convex lens surface by the optical axis in the cross section including the optical axis. In each of the shapes, the optical axis side is the outer diameter side and the outer diameter side is the optical axis side so that the optical axis side is reversed and replaced around the direction parallel to the optical axis. lens. An optical fiber connector interposed between a first optical fiber on a light incident side and a second optical fiber on a light output side when transmitting an optical signal using a step index type optical fiber,
This fiber optic connector
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 cylindrical first inward reflecting surface (7 'or 7' or 2) arranged coaxially with the optical axis on the first end surface side and the second end surface side of the lens according to claim 1. 8 ') and a second inner reflective surface (7' or 9 '), respectively, the first inner reflective surface (7' or 8 ') and the second inner reflective surface (7). 'Or 9') has a function of condensing the light emitted from the first optical fiber at the incident end of the second optical fiber through the lens while being reflected by one reflection surface thereof. ,
High-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 enters the second optical fiber with a relatively large inclination with respect to the optical axis. It is configured to be incident as next mode light,
An optical fiber connector having a mode switching function. The first inner reflective surface (8 ′) is formed on the outer peripheral surface of the translucent member (8), and the second inner reflective surface (9 ′) is formed of the translucent member (9). The optical fiber connector having a mode switching function according to claim 2, wherein the optical fiber connector is formed on an outer peripheral surface.

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