JP3063816B2 - Asymmetric optical coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asymmetric optical coupler, and more particularly to an asymmetric optical coupler suitable for an optical transmission line.

[0002]

2. Description of the Related Art There are a star coupler system, a loop system, and a bus system as a system for forming a transmission line using an optical fiber. Light transmission to each device in the loop system and the bus system is usually configured using an asymmetric coupler as shown in FIG. One fiber 1 of the asymmetric coupler is called a bus line fiber or a bus fiber, and is used for a loop (bus). The other fiber 2 is referred to as a tap fiber, one of which is an input tap 2a and the other is an output tap 2b, which inputs a signal from the input tap 2a and passes through the bus fiber 1 from another output tap 2b of another coupler. An output method is adopted (see FIG. 5).

An asymmetrical coupler used in such an optical transmission line disperses a signal on a bus little by little and efficiently to an output tap in order to mount many terminals on a loop, and furthermore, a signal from an input tap. Is required to be efficiently coupled to the bus fiber. To satisfy the former requirement, the core diameter and numerical aperture of the tap fiber should be relatively large in order to efficiently couple the signal transmitted from the bus fiber to the tap fiber. The amount can be arbitrarily set by appropriately changing the tapered shape. On the other hand, in order to satisfy the latter requirement, the core diameter and numerical aperture of the tap fiber should be relatively small.

[0004]

However, as described above, since the two requirements required for the coupler of the optical transmission line have mutually contradictory properties, two optical fibers are used as in a conventional coupler. In a structure that is tapered and stretched in parallel, trying to reduce either the branch loss from the bus fiber to the tap fiber or the coupling loss from the tap fiber to the bus fiber must sacrifice the other, and the overall loss is There was a disadvantage that it increased.

[0005] The present invention solves such conventional difficulties,
It is an object of the present invention to provide an asymmetric optical coupler capable of efficiently branching a signal from a bus fiber to a tap fiber and coupling a signal from the tap fiber to a bus fiber.

[0006]

In order to achieve the above object, an asymmetric optical coupler according to the present invention is a tapered asymmetric optical coupler formed by fusion-bonding a bus fiber and a tap fiber to each other. In the fiber, an input tap fiber and an output tap fiber having different core diameters and numerical apertures are joined at a fusion portion of an asymmetric optical coupler.

Further, the asymmetric optical coupler of the present invention is an asymmetric optical coupler formed by fusing a bus fiber and a tap fiber and extending in a tapered shape. In the asymmetric optical coupler, the tap fiber has a different positional relationship between the core and the bus fiber. The input tap fiber and the output tap fiber are joined at the fusion portion of the asymmetric optical coupler.

[0008]

The tap fiber of the asymmetrical optical coupler constructed by arranging and tapping two tap fibers and bus fibers is used as an input tap fiber having different core diameters, numerical apertures, or different positions of the core with respect to the bus fiber. It is assumed that the tapping fiber is joined at the fused portion of the asymmetric optical coupler. Thereby, both the distribution of the optical signal from the bus fiber to the output tap and the coupling of the optical signal from the input tap to the bus fiber can be efficiently performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the asymmetric optical coupler of the present invention will be further described below with reference to the drawings. FIG.
1A and 1B show an embodiment of an asymmetric optical coupler according to the present invention, in which a bus fiber 10 and a tap fiber 20 are shown.
These two optical fibers are arranged in parallel, tapered, and fusion-bonded. The tap fiber 20 is formed by joining two optical fibers 21 and 22 having different parameters. Here, the parameter refers to the bus fiber 10
Of the optical fiber, which is a function of the distribution characteristic and the coupling characteristic of the optical fiber, and includes the core diameter, the numerical aperture, the outer diameter, the refractive index distribution, and also the positional relationship of the core to the bus fiber.

A multi-mode fiber is preferably used as the optical fiber 10 (21, 22). In the embodiment shown in FIG. 1A, the bus fiber 10 has a core diameter / fiber diameter of 200/250 (μm), for example.
A fiber having a core diameter of 0.26 and a large numerical aperture is used. The tap fiber 20 has a core diameter /
Fiber diameter 50/125 (μm) and numerical aperture 0.2
0, and an output tap fiber 22 having a core diameter / fiber diameter of 100/125 (μm) and a numerical aperture of 0.26, which is joined to the bus fiber 10. Is bonded to the bus fiber so as to be a fusion bonded portion. Although FIG. 1A shows an example in which the joining portion coincides with the smallest diameter portion of the tapered waist (a portion tapered into a narrow shape) which is fusion-bonded.
As shown in (b), the joining portion may be shifted from the minimum diameter portion of the tapered waist. By shifting in this way,
The optical coupling from tap to bus and from bus to tap can be adjusted. For example, when the coupling length of the incident tap 21 is increased, the amount of light coupled from the tap to the bus increases, and the amount of emission from the bus to the tap decreases.

In the asymmetric optical coupler constructed as described above, as shown in FIG.
Optical power P ₃ which is inputted from binding to the bus fiber 10. At this time, since the core diameter of the bus fiber 10 is sufficiently larger than the core diameter of the tap fiber 21, coupling from the tap fiber 21 to the bus fiber 10 is likely to occur. Further, since the numerical aperture of the input taps 21a is small, only slightly pulling the tapered, optical power P ₃ that enters the input taps fiber 21 is spread throughout the cladding, which binds with high efficiency and bus fiber 10. On the other hand, the light power P ₁ from the input bus 10a of the bus fiber 10, since the diameter of the taper waist is still large enough, are emitted almost directly output bus. At this time, the output tap fiber 2
For second core diameter and numerical aperture is large, entered from the input bus fiber 10a, the optical power P ₂ that leaked in the tapered portion is coupled with high efficiency to the output taps. The coupling state of these optical powers is shown in the graph of FIG.

FIG. 3 is a diagram showing another embodiment of the asymmetric optical coupler of the present invention. The bus fiber 10 has a core diameter / fiber diameter of 100/125 (μm) and a numerical aperture of 0.26.
The tap fiber 20 'has a smaller core diameter and a smaller numerical aperture than the bus fiber 10, and has the same core diameter and numerical aperture, for example, a core diameter / fiber diameter of 50/125 (μ).
m), two optical fibers 2 having a numerical aperture of 0.20
1 ′ and 22 ′ are joined, but the position of the core of one fiber 21 ′ is close to the bus fiber 10, and the position of the core of the other fiber 22 ′ is is seperated.

In such an asymmetric optical coupler in which the bus fiber 10 and the tap fiber 20 are tapered and fused, the input tap enters the input tap because the core position of the input tap is close to the bus fiber. Optical power couples to the output bus with high efficiency. The optical power from the input bus 10a of the bus fiber 10 is emitted to the output bus almost as it is because the diameter of the tapered waist is still sufficiently large as in the embodiment of FIG. Input bus fiber 1)
Optical power incident from Oa and exuding at the tapered portion is coupled to the output tap with high efficiency.

Such an asymmetric optical coupler can be suitably used alone as an optical coupler or an optical distributor, or can be suitably used for a loop-type or bus-type optical transmission line or the like in which a plurality is connected.

[0015]

As is apparent from the above embodiments, according to the asymmetric optical coupler of the present invention, the tap fiber to be fused with the bus fiber is constituted by two optical fibers having different parameters. The distribution of the optical signal from the bus fiber to the output tap and the coupling of the optical signal from the input tap to the bus fiber can be efficiently performed.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing an embodiment of an asymmetric optical coupler according to the present invention, respectively.

FIG. 2A is a diagram showing a coupling relationship of optical power in an asymmetric optical coupler of the present invention, and FIG. 2B is a graph of the coupling relationship.

FIG. 3 is a diagram showing another embodiment of the asymmetric optical coupler of the present invention.

FIG. 4 is a diagram showing a conventional optical coupler.

FIG. 5 is a diagram showing an optical transmission line using a conventional optical coupler.

[Explanation of symbols]

 10 Bus fiber 20, 20 'Tap fiber 21, 21' Fiber for input tap 22, 22 'Fiber for output tap

Continued on the front page (72) Inventor Takeo Senuma 2-4-15-703, Atsugigaoka, Akishima-shi, Tokyo (72) Inventor Yutaka Nakazawa 1-39-2-2-305, Kuboyama-cho 1-305-305, Hachioji-shi, Tokyo (72) Inventor Shinichiro Ina 67-10 Shimoootsuki, Hadano-shi, Kanagawa Prefecture 2-1-1, Showa Electric Wire & Cable Co., Ltd. (72) Inventor Nobuo Kohata 2-1-1, Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Electric Wire & Cable Co., Ltd. (56) References JP-A-3-110525 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/28-6/293

Claims (2)

(57) [Claims] 1. An asymmetric optical coupler formed by fusing a bus fiber and a tap fiber and extending in a tapered shape.
The tap fibers have input cores with different core diameters and numerical apertures.
Tsu asymmetric optical coupler fiber and the output tap for fiber-flop is characterized in that it is joined at fused portion of the asymmetric <br/> optical coupler. 2. A fusion bonding of a bus fiber and a tap fiber.
In an asymmetric optical coupler formed by extending in a tapered shape,
The tap fiber has a core for the bus fiber.
Fiber for input tap and output tap with different positional relationship
For the asymmetric optical coupler at the fused part
An asymmetric optical coupler characterized by being joined .