JPH01124807A - Optical branching/coupling device - Google Patents

Abstract

PURPOSE:To eliminate loss of light by coupling even if either mode is used so that both modes can be used by forming the core part of a fiber for input/ output into a double-core structure having a single-mode waveguide part and multimode waveguide part. CONSTITUTION:The light of the single-mode waveguide part 14 of the fiber 1a for input/output is inputted through a lens 4a to a half mirror 7 and is separated to transmitted light and reflected light. The transmitted light is inputted to the single-mode waveguide part 14 of the fiber 1b and the reflected light is further reflected by a mirror 8 and is then inputted to the waveguide part 14 of the fiber 1c. On the other hand, the light form the multimode waveguide part 15 of the fiber 1a is branched to the waveguide parts 15 of the fibers 1b, 1c. The fiber is thus made into the double-core structure formed coaxially with the single-mode waveguide part and the multimode waveguide part, by which the light loss by the coupling is eliminated in spite of using any mode and the use of both the modes is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention branches light propagated through one optical transmission line to a plurality of ports. Alternatively, the present invention relates to an optical branching/coupling device having a function of coupling light from a plurality of boats to a single optical transmission line.

[Conventional technology]

Figure 6 is a cross-sectional top view showing a conventional optical branching/coupling device in which the device presented at the 1981 IEICE General Conference (2672) is applied to the optical branching/coupling device. (1a) to (1c) are input/output fibers, (2) are transmission path fibers connected to the input/output fiber (1a), (5a) and (3b) are the input/output fibers (1a), Fiber for the above transmission line (2)
Optical connectors (4a) to (4c) for connecting
is a lens for coupling light between the input/output fibers (1a) to (1C), and (5) is this lens (4a).
A glass block placed between ~(4C), (6) a spacer prism inserted between this glass block (5) and the lens (4b), ()) a glass block placed between this spacer prism (6) and the glass Half mirror 1 (8) with transmittance of 50 ocs and reflectance of 5 ocs formed between blocks (5)
is a mirror with a reflectance of 100% formed on the side surface of the glass block (5), and (9) is the upper 3Q (1a) to (I
c) This is a case where the components of (4a) to (6) are fixed. In addition, input/output fibers (1a) to (1
C) and the transmission line fiber 7 (B (2) K) are single mode fibers.

Next, the operation will be explained.

The light that has propagated through the transmission line fiber (2) is connected to the input/output fiber (1) connected by optical connectors (5a) and (3b).
a) K-coupled, converted into a parallel beam by a lens (4a), passed through a glass block (5), and a half mirror (
7). Here, the half mirror (7) transmits half of the power of the incident light and reflects the other half. The light having half the power transmitted through the half mirror (7) is transmitted through the spacer prism (6) and inputted into the input/output fiber (1b) by the lens (4b). In addition, the light with half the power reflected by the half mirror (7) is further reflected by the mirror (8) formed on the side surface of the glass block (5), and is sent to the lens (4c) through the multi-input/output fiber ( 1C)
is input. In this way, the input/output fiber (1
The light input to a) is split equally into an input/output fiber (1b) and an input/output fiber (1c).

Next, a case where the traveling direction of the light explained above is reversed will be explained.

The light propagating through the input/output fiber (1b) passes through the lens (
4b) into a parallel light beam, and the spacer prism (6
) and enters the bar mirror (7)K. Here, light with half the power of the incident light passes through the glass block (
5) and enters the multi-input/output fiber (1a) through the lens (4a). In addition, input/output fiber (1C
) is converted into a parallel beam by a lens (4C), reflected by a mirror (8), and then reflected by a half mirror (7).
) Here, the light with half the power of the incident light is reflected and passed through the input/output fiber (4a) by the lens (4a).
1a). In this way.

Input/output fiber (1b) and input/output fiber (1C)
The light from is coupled to the input/output fiber (1a).

In the above, the reason why single mode fibers are used for the input/output fibers (1a) to (1C) is that a single twisted fiber is used for the transmission line fiber (2). For example, consider using Figure 7 the case where a multimode fiber is used as the input/output fiber (1a) even though a single mode fiber is used as the transmission line fiber (2). . FIG. 7 is a cross-sectional view showing the connection between the transmission line fiber (2) and the input/output fiber (1a). In FIG. 1, s1 is the core portion of the multimode fiber, αυ is the core portion of the single mode fiber, and α is the joining surface of the two fibers. The multimode fiber can propagate light in many propagation modes in the core portion Ql. In contrast, a single mode fiber can only propagate light in one of the lowest propagation modes. Therefore, when coupling light from a multimode fiber to a single mode fiber, most of the light in the multimode fiber that does not match the single mode propagation mode is not coupled and is lost. On the other hand, when coupling from a single mode fiber to a multimode fiber, on the other hand, all the light that has propagated through the single mode fiber is coupled to the multimode fiber. Here, the transmission line fiber (2)
FIG. 8 shows a case where multimode fibers are used as the input/output fibers (1a) to (1c) although K single mode fibers are used.

In this case, the optical connector (!a), as described above, is connected from the transmission line fiber (2) to the input/output fiber (1a).
Since the light is coupled without loss through the input/output fibers (Ib) and (Ic), the light can be branched favorably through the input/output fibers (Ib) and (Ic).

On the other hand, as mentioned above, most of the light coupled from the input/output fibers (1b) and (1c) to the input/output fiber (1a) is lost at the joint surface α, resulting in poor light coupling. I can't do it anymore. Next, contrary to the case in Fig. 8, although a multimode fiber is used for the transmission line fiber (2), the input/output fiber (1a)
FIG. 9 shows the case where a single mode fiber is used in (1C). In this case, most of the light coupled from the transmission line fiber (2) to the input/output fiber (1a) is lost at the joint surface tta, as described above, so that good light branching cannot be performed. . On the other hand, the light coupled from the input/output fibers (1b) and (1C) to the input/output fiber (1a) is connected to the optical connector (3a) j C5
b) is coupled to the transmission line fiber (2) without loss, so that good optical coupling can be achieved.

From the above, in order to obtain good characteristics with no loss for both 9 branching and coupling, k should be
), the input/output fiber (1
When a single mode fiber is always used as a) to (1c), and a multimode fiber with t is used as the transmission line fiber (2), input/output 77 i/< (1a) to (
For 1c), a multimode fiber must be used. Also, if you look at Jin, you can also use an input/output fiber (
In the optical branching/coupling device in which single mode fibers are used in 1a) to (1c).

This indicates that only a single mode fiber can be used as the transmission line fiber (2) and that a multimode fiber cannot be used.On the other hand, multimode fibers can be used as the input/output fibers (1a) to (1c). The optical multiplexing and demultiplexing equipment that
This indicates that only a multimode fiber can be used as the transmission line fiber (2), and a single mode fiber cannot be used.

[Problem that the invention seeks to solve]

Conventional optical branching/coupling devices are configured as described above, so optical branching/coupling devices that use single mode fibers as input/output fibers can only use single mode fibers as transmission line fibers; If you want to use a mode fiber as a transmission line fiber, you must prepare another optical branching and coupling device that has a multimode fiber as an input/output fiber. The optical branching/coupling device used as a transmission line fiber can only use multimode fibers as transmission line fibers.If you want to use a single mode fiber as a transmission line fiber, you need to use a new single mode fiber as an input/output fiber. Unfortunately, we had to prepare a separate optical branching and coupling device.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain an optical branching/coupling device that can use both a single mode fiber and a multimode fiber as a transmission line fiber.

[Means for solving problems]

In the optical branching/coupling device according to the present invention, the input/output fiber is a fiber having a double core structure having a single mode waveguide section and a multimode waveguide section at the same time.

[Effect]

The optical branching/coupling device according to the present invention has a dual core structure in which the core portion of the input/output fiber has a single mode waveguide portion and a multimode waveguide portion at the same time.

Regardless of whether a single mode fiber or a multimode fiber is used as a transmission line fiber, there is no loss of light due to coupling between fibers.

The transmission line fiber eliminates the inconvenience of replacing optical branching and coupling devices.

[Embodiments of the invention]

FIG. 1 is a structural sectional view showing one embodiment of the present invention.

In FIG. 1, (5a) to (9) are the same as the conventional device described above. (1a) to (1c) are input/output fibers, which have a 92-fold core structure different from the conventional device described above. I is the input/output fiber (1a) to (1c)
), am is a single mode waveguide, α field is a multimode waveguide, and the single mode waveguide a and the multimode waveguide α are coaxial. There is. Input/output fibers (1a), (1b) and lenses (4a)t(4b) are input/output fibers (1a) and input/output fibers (1b).
) are aligned so that efficient light coupling can be obtained between the single mode waveguides (14) of the input/output fibers (1a), (1c) and the lens (14).
aa) and (4c) are the mutual single mode waveguides (14) of the input/output fiber (1a) and the input/output fiber (1c), which are aligned so that efficient light coupling can be obtained between them. Here, the input/output fibers (1a) to (1
Since the single 7-mode waveguide section a4 and the multimode waveguide member in c) are coaxial, the space between the input/output fiber (1a) and the multimode waveguide section a of the input/output fiber (1b).

and input/output fiber (1a) and input/output fiber (1a)
At the same time, efficient optical coupling between the multimode waveguide sections 19 in b) is also obtained.

Next, the operation will be explained with reference to FIG.

The light emitted from the single mode waveguide a4 of the input/output fiber (1a) through the lens (4a) is converted into a parallel beam of light by the lens (4a), and then enters the half mirror (7).

The light incident on this half mirror (7) is separated into transmitted light and reflected light, and the transmitted light is input into the single mode waveguide I of the multi-input/output fiber (1b) through the lens (4b). 9 The reflected light is further reflected by the mirror (8).

The light is input to the single mode waveguide section a4 of the multi-input/output fiber (1c) through the lens (4C). On the other hand, the light from the single mode waveguide section 4 of the input/output fiber (1b) and the input/output fiber (1c) passes through the optical path opposite to the above and leads to the single mode guide of the input/output fiber (1a). It is coupled to the wave portion aS.

In addition, the light emitted from the multimode waveguide part a of the input/output fiber (1a) to the lens (4a) is transmitted to the multimode waveguide parts of the input/output fiber (1b) and the input/output fiber (1c). The light from the α field of the multimode waveguide of the input/output fiber (1b) and the input/output fiber (1c) is coupled to the multimode waveguide (1cJ) of the input/output fiber (1a). Ru.

In such a structure, both cases where a single twisted fiber and a multimode fiber are used as the transmission line fiber (2) are shown. First, FIG. 2 shows a case where a single mode fiber is used as the transmission line fiber (2). In Figure 2, the light that has propagated through the transmission line fiber (2) is input to the single mode waveguide aJK of the 231 core portion of the input/output fiber (1a) through the connectors (3a) and (3b). Ru. As mentioned above, the light propagated through the single mode waveguide section 04 of the input/output fiber (1a) is
The input/output fiber (1b) is branched into the single mode waveguide section a◆ of t(1C). on the other hand.

The light propagating through the single mode waveguide a◆ of the input/output fibers (1b) and (1c) is transferred to the input/output fiber (1a).
The single mode waveguide (14) is JC coupled, and further coupled to the transmission line fiber (2) via optical connectors (3a) and (3b) IC. Here, at the bonding surface a3, there is no deterioration in coupling efficiency due to mismatching of the core portions of the fibers, and good branching/coupling characteristics can be obtained for the transmission line fiber (2) k using a single mode fiber. Next, FIG. 3 shows a case where a multimode fiber is used as the transmission line fiber (2). In Figure 93, the transmission line fiber (2
) is the light propagating through the connector (3a)? (31)), the input/output fiber (1a) which is input to the multimode waveguide (II) of the double core part of the input/output fiber (1a)
As described above, the light propagated through the multimode waveguide a9 of 1a) is branched to the multimode waveguide a$ of the input/output fibers (1b) and (1C). On the other hand, the input/output fiber (1
b), the light propagating through the multimode waveguide section (L!9) of (1a) passes through the multimode waveguide section (L!9) of the input/output fiber (1a).
1! ! IC is coupled, and optical connectors (3a), (5
b) is coupled to the transmission line fiber (2). Here, at the bonding surface a, there is no deterioration in coupling efficiency due to mismatching of the core portions of the fibers, and good branching/coupling characteristics can be obtained for the transmission line fiber (2) k using a multimode fiber.

As described above, if a fiber with a structure in which a single mode waveguide section and a multimode waveguide section are coaxially provided as an input/output fiber is used, both a single mode fiber and a multimode fiber can be used as a transmission line fiber. becomes possible to use.

Next, FIG. 4 shows an example of the refractive index distribution in the cross section of a fiber having a single mode waveguide section and a multimode waveguide section on the same axis. In FIG. 4, the horizontal axis is the distance from the central axis of the fine chimney cross section, and the vertical axis is the refractive index. The refractive index is constant at the refractive index n1 from the center to the radius a, and at the position of the radius a, the refractive index decreases n2) and gradually decreases in a parabolic manner until the radius is It has a refractive index distribution as follows. Furthermore, there is a relationship of <λ between the radius a, the refractive index n1 within the radius a, the refractive index n2 outside the radius a, and the wavelength λ of the light propagating in the fiber. It has been established. At this time, the area within radius a becomes one core.

By satisfying the above relationship, it becomes a single mode waveguide. Moreover, the inside of the radius becomes a graded index type multimode waveguide. FIG. 5 shows another example of the refractive index distribution in the cross section of a fiber having a single mode waveguide section and a multimode waveguide section on the same axis.

The refractive index is n1 from the center to radius a, and n2 from the center to radius a. It has a refractive index distribution that decreases stepwise to n5 above the radius n5. Also, the radius a and the refraction '4n1
The relationship 4a 2n1 (nl-n2) < λ holds between the refractive index n2 and the wavelength λ of the light propagating within the fiber. At this time, the area within the radius a becomes a single mode waveguide.

Moreover, the inside of the radius becomes a step-index type multimode waveguide.

〔Effect of the invention〕

As described above, according to the present invention, the input/output fiber of the optical branching/coupling device has a coaxial double-core structure with a core part serving as a single mode waveguide and a core part serving as a multimode waveguide. This has the effect that it becomes possible to use both a single mode fiber and a single mode fiber for the transmission line.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional top view showing an optical branching/coupling device according to an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional top views of the optical branching/coupling device for explaining the invention in detail, and FIG. and FIG. 5 is a diagram showing a refractive index distribution in a cross section of an input/output fiber constituting an optical branching/coupling device according to an embodiment of the present invention.
Figure 6 is a cross-sectional top view showing a conventional optical branching and coupling device;
The figure is a cross-sectional view showing the connection between a single mode fiber and a multimode fiber, and Figure 8 is a diagram showing a case where a single seven-mode fiber is used as the transmission line fiber and a multimode fiber is used as the input/output fiber. FIG. 3 is a diagram in which a multimode fiber is used as the transmission path fiber and a single mode fiber is used as the input/output fiber. In the figure, e (1a), (1b), (1a) are input/output fibers, (2) is a transmission line fiber, (sa
), (3b) are optical connectors, (4a), (4b),
(4c) is the lens, (5) is the glass block, (6) is the spacer prism, (7) is the no-7 mirror, (81 is the mirror, (9) is the case, Ql is the core of the multimode fiber, ( 11) is the core part of the single mode fiber. Q3 is the input/output fiber (1a) and the transmission line fiber (
2), αj is the double core part, (14 is the single mode waveguide part of the double core part α), and 9 is the double core part (11
This is a multimode waveguide. Note that the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) In an optical branching/coupling device consisting of at least one branching/coupling element having the function of branching or coupling optical power and one or more optical fibers for inputting/outputting light, at least one The above-mentioned optical fiber has a coaxial double core structure, with the inner core of the double core being a single mode waveguide and the outer core of the double core being a multimode waveguide. An optical branching/coupling device characterized by: (2) As the optical fiber, the refractive index distribution of the cross section of the optical fiber is directed outward from the center of the optical fiber with a radius a
The refractive index n_1 is constant up to a distance of , decreases to a refractive index n_2 lower than the refractive index n_1 at the position of the radius a, and continuously decreases parabolically from the refractive index n_2 from the radius a to the radius It has a refractive index distribution shape such that the refractive index is n_3 above b, and the refractive index n_1 and n_2 are
At least 4n√ between the radius a and the wavelength λ of the light used
Claim 1, characterized in that an optical fiber having a relationship of [2n_1-(n_1-n_2)]<λ is used.
Optical branching/coupling device described in Section 1. (3) As the optical fiber, the refractive index distribution of the cross section of the optical fiber is directed outward from the center of the optical fiber with a radius a
The refractive index n_1 is constant up to a distance of , and decreases to the refractive index n_2 lower than the refractive index n_1 at the position of the radius a, and the refractive index n_2 is constant from the radius a to the radius b, and the refractive index n_2 is constant at the position of the radius b. It has a step-like refractive index distribution shape that decreases to a refractive index n_3 lower than the refractive index n_2, and at least 4n√[2n_1−(n_1− The optical branching/coupling device according to claim 1, characterized in that an optical fiber having a relationship of: n_2)]<λ is used.