JP2585272Y2 - Fiber type optical isolator - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber type optical isolator used for blocking return light returning to a light source through an optical fiber as a transmission line in optical communication.

[0002]

2. Description of the Related Art In optical communication, when return light enters a semiconductor laser which is a light source,
Interference and resonance occur inside the semiconductor laser, resulting in noise and deteriorating the S / N ratio of the signal. For this reason, an optical isolator is installed immediately before a semiconductor laser, which is usually a light source. This optical isolator has a function of passing outgoing light from a light source but removing return light.

Usually, as this type of optical isolator, the transmission deflection directions of the Faraday rotator are set to 45
A type in which a polarizer in a rotated state is provided and a magnet is provided around the polarizer is used.

However, this type of optical isolator requires a lot of time and labor to assemble, is difficult to integrate because it has many components, and is difficult to use between optical fibers. The transmitted light is unpolarized).

On the other hand, an optical isolator of the type using an optical waveguide or an optical fiber has been developed. This type of optical isolator has a structure in which return light is attenuated by connecting a large number of Y branch portions formed of an optical waveguide or an optical fiber. However, when the Y-branch is formed of an optical waveguide and a large number of these are connected to form an optical isolator, the size of the optical isolator becomes large. On the other hand, when the Y-branch is composed of an optical fiber and a large number of these are connected to form an optical isolator, the number of parts used is small and does not increase so much. There is a problem that it is necessary to process and join, and the processing is difficult.

The present invention has been made in view of the above points, and provides a fiber type optical isolator which can be constituted only by optical fibers and which can be easily processed and manufactured.

[0007]

In order to solve the above-mentioned problems, the present invention comprises two optical fibers 3 and 5 each composed of a core and a clad. The two optical fibers 3 and 5 are brought into contact with each other so that the two optical fibers 3 and 5 are parallel to each other. The one of the two optical fibers 3 and 5 on the side branched into two by the tapered Y-branch portion 7, and the one optical fiber 3 side is defined as a light incident side. The fiber type optical isolator 1 was configured with the other end of the other optical fiber 5 on the side where no fusion was performed as a free end.

[0008]

With the configuration described above, light incident from the light incident side of the optical fiber 3 propagates through the core 31.
Then, distribution coupling is performed with the core 51 of the other optical fiber 5 approaching at the tapered Y-shaped branch portion 7, and a part of the incident light propagates inside the core 51. Then, the light propagating in the core 51 is emitted into the clad when the core 51 is interrupted, but the emitted light is gradually coupled and absorbed again into the other core 31, resulting in an optical fiber with almost no loss. 3.

On the other hand, the return light returning to the optical fiber 3 from the opposite direction is distributedly coupled to the core 51 of the other adjacent optical fiber 5 at the portion of the tapered Y-branch portion 7 and one of the return light is returned. The part propagates in the optical fiber 5. The light split into the optical fiber 5 is emitted from the end and removed.

The necessary isolation can be realized by connecting the required number of fiber type optical isolators 1 in series.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a side sectional view showing a fiber type optical isolator 1 according to the present embodiment. As shown in FIG. 1, the fiber-type optical isolator 1 includes two optical fibers 3 and 5 including cores 31 and 51 and clads 32 and 52, and a side surface of one optical fiber 3 and another optical fiber 5 Are connected by a tapered Y-shaped branch portion 7.

Here, a manufacturing procedure of the fiber type optical isolator 1 will be described with reference to FIG. First, as shown in FIG. 3A, two optical fibers 3 and 5 having different lengths each comprising a core and a clad are prepared, and both are aligned. At this time, as shown in FIG. 4A, one end 55 of the shorter optical fiber 5 contacts the side surface of the longer optical fiber 3.

Next, when the two optical fibers 3 and 5 are heated with the one end portion 55 of the optical fiber 5 as a heating center, the two optical fibers 3 and 5 are fused and become as shown in FIG. .
Then, when the optical fibers 3 and 5 are extended from both sides of the fused portion, as shown in FIG.
Is formed, and the fiber type optical isolator 1 shown in FIG. 1 is completed. Since the tapered Y-shaped branch 7 extends from both sides, the cores 31 and 51 of the two optical fibers 3 and 5 are tapered at the tapered Y-shaped branch 7 as shown in FIG. At the same time, the distance between the two cores is reduced, and the cores are in a distributed coupling state.

The side branched into two by the tapered Y-shaped branch portion 7 (ie, the tapered Y-shaped branch portion 7 shown in FIG. 1).
Of the two optical fibers 3 and 5 on the left side of the figure, the longer optical fiber 3 is used as the light incident side and the shorter optical fiber 5 is used.
The end 57 of this is the open end.

Next, FIG. 3 is a diagram showing the core 31 of the optical fiber 3 and the core 51 of the optical fiber 5 for explaining the operation of the fiber type optical isolator 1, and FIG. It is a diagram showing a state of light intensity distribution of light,
FIG. 6B is a diagram showing a state of the intensity distribution of the return light.

As shown in FIG. 1A, incident light incident from the left side of the core 31 of the optical fiber 3 is guided inside the core 31 while light leaks into the cladding to some extent. In the portion of the tapered Y-shaped branch portion 7 where the diameter of the core 31 is gradually reduced, the light leaked from the core 31 into the clad is increased, and the other optical fiber 5 approaching the other end.
And a part of the incident light is guided inside the core 51 as well. The light guided in the core 51 is emitted into the clad when the core 51 becomes thinner, and the emitted light is gradually coupled and absorbed by the core 31 again and guided. Thus, the incident light propagates with almost no loss.

On the other hand, as shown in FIG. 1B, the return light returning from the right side of the core 31 of the optical fiber 3 is guided through the core 31 while a little light leaks into the cladding. Then, in the portion of the tapered Y-shaped branch portion 7 where the diameter of the core 31 is gradually reduced, the leakage light from the core 31 into the clad becomes large, and the taper of the core 51 of the other optical fiber 5 adjacent thereto becomes large. Parts and gradually become separated after increasing the bond. The light separated by the core 51 is emitted from the end of the core 51 and removed. That is, the core 31
Return light propagating through the inside decreases at a predetermined rate. Note that the branching ratio of the return light of the optical fibers 3 and 5 differs depending on the shape and length of the fusion-stretched portion.

FIG. 4 shows a fiber type optical isolator 10 in which a plurality of optical fibers 5 are sequentially connected to one long optical fiber 3 to thereby provide a large number of tapered Y-shaped branch portions 7.
FIG. With this configuration, the return light propagating in the optical fiber 3 is removed by a predetermined ratio at each of the tapered Y-shaped branch portions 7 and hardly returns to the incident side end face of the optical fiber 3. Conversely, the required isolation can be set by the number of the tapered Y-shaped branch portions 7.

Here, it is assumed that the tapered Y-shaped branch portion 7 of the return light is used.
When the branching ratio is 0.5, half of the return light in each of the tapered Y-shaped branch portions 7 is emitted to the optical fiber 5 side and does not return to the light source. In this case, the isolation Pt (dB) is given assuming that the number of the tapered Y-shaped branch portions 7 is n. It is represented by

FIG. 5 is a view showing a specific example when the fiber type optical isolator 100 having the structure shown in FIG. 4 is mounted immediately before a semiconductor laser. In the figure, the input end of the fiber type optical isolator 100 is connected to a semiconductor laser module 81 by an optical connector 80, and the output end is connected to a normal optical fiber 87 by an optical connector 83 and an adapter 85.

Although one embodiment of the fiber-type optical isolator according to the present invention has been described in detail, the present invention is not limited to the above-described embodiment, and for example, the following various modifications are possible.

In the embodiment shown in FIG. 1, two optical fibers 3 and 5 having the same core diameter and the same clad diameter are fused and drawn, but any one of the two optical fibers 3 and 5 is used. By pre-drawing one of the optical fibers, the core diameter and the cladding diameter of the two optical fibers 3 and 5 may be made different, and then the two may be fused and drawn. With this configuration, it is possible to realize a wideband optical isolator having less wavelength dependence of the branching ratio. As a result, the power of the return light is distributed at a fixed rate to the two optical fibers regardless of the change in the wavelength. Note that the branching ratio between the two is arbitrarily good (for example, 1: 2).

A fiber type optical isolator 1 shown in FIG.
In the example of 00, an example is shown in which a large number of optical fibers 5 are sequentially connected to one optical fiber 3, but the optical fiber 3 does not have to be constituted by one. That is, for example, as shown in FIG.
A plurality of fiber type optical isolators 1 having two tapered Y-shaped branch portions 1 are prepared, and the optical fibers 3 of the fiber type optical isolators 1 are sequentially fused and connected in series as shown in FIG. A fiber optical isolator having a shape may be formed. Each optical fiber 3 may be connected by a connector and an adapter.

According to the manufacturing method shown in FIG. 2, the optical fiber 5 is fused and drawn on the side surface of the optical fiber 3, but at the stage shown in FIG. It is exposed. Therefore, in some cases, the end face of the core of the optical fiber 5 after the fusion stretching may be exposed to the outside. For this reason, as shown in FIG. 6, a clad member 59 made of only the same material as the clad is previously fused to the end face of the optical fiber 5 composed of the core and the clad. 5 may be melt-stretched. By doing so, the core end face on the side where the optical fiber 5 is fused is not exposed to the outside, and the loss caused by the exposure can be prevented.

[0025]

As described in detail above, the fiber type optical isolator according to the present invention has the following excellent effects. Since it can be composed only of optical fibers, the number of parts can be reduced and cost can be reduced.

Since the optical fiber can be manufactured by a fusion-splicing operation, the manufacturing becomes easy.

Since a magnet is unnecessary and has almost no wavelength dependence,
Its performance is stable and its reliability is high.

The required isolation can be easily set by increasing or decreasing the number of tapered Y-shaped branches.

It has a small polarization characteristic and can be easily used between optical fibers. The coupling portion of the two optical fibers has a tapered distribution coupling
Since both the optical fibers are heated and melted
Of the tapered Y-branch based on the processing conditions
By setting the length and shape arbitrarily, both optical fibers
Can be easily changed.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a fiber type optical isolator 1 according to one embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing procedure of the fiber type optical isolator 1.

FIG. 3 is a diagram illustrating a state of intensity distribution of incident light and return light propagating through a core 31 portion of the optical fiber 3 and a core 51 portion of the optical fiber 5;

FIG. 4 is a diagram showing a fiber type optical isolator 100 provided with a large number of tapered Y-shaped branch portions 7;

FIG. 5 is a diagram showing a specific example when the fiber-type optical isolator 100 is mounted immediately before a semiconductor laser.

FIG. 6 is a diagram illustrating a method of manufacturing a fiber type optical isolator according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fiber type optical isolator 3, 5 Optical fiber 31, 51 Core 32, 52 Cladding 7 Tapered Y branch part

Claims (1)

(57) [Scope of request for utility model registration] 1. An optical fiber comprising a core and a clad, wherein one end of the other optical fiber is connected to the side of one optical fiber such that the two optical fibers are parallel to each other.
Contacting the head together, by heat sealing stretched core and the cladding of Ryohikari fiber around the end periphery of the other optical fibers said contact,
In a distributed coupling state, the branching ratio of the two becomes a predetermined arbitrary value.
A tapered Y-branch portion having an arbitrary length and shape is formed, and the one optical fiber side of the two optical fibers branched into two at the tapered Y-branch portion is used for light. A fiber-type optical isolator, wherein an end on the non-fusion side of the other optical fiber which is an incident side is an open end.