JP2800532B2 - Line monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line monitor used for optical communication and optical information processing, and more particularly to a monitor of a transmission signal and a reception signal at a terminal station when bidirectional communication is performed with one fiber, and an optical fiber. And a line monitor used for monitoring output light and reflected light.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, a line monitor of this type splits forward light and reverse light into split fibers 24 and 25 by a fusion type coupler 23 which joins an input fiber 21 and an output fiber 22. The power is observed by a light receiving module for forward light observation 28 and a light receiving module 29 for backward light observation connected to the branch fibers 24 and 25 through connection points 26 and 27, respectively. Have been.

In this line monitor, the power of the forward light is as strong as about +15 dBm, and the power of the backward light is-.
If it is assumed to be as weak as about 5 dBm (power difference 20 dBm), the branching ratio of the fusion type coupler 23 can be practically only about 10 to 1 due to the restriction of the interval setting accuracy between adjacent fiber cores at the time of manufacturing. As the light receiving module 29 for observing the directional light, a normal light receiving module with a lens can be used. However, the light receiving module 28 for observing the forward light has a large incident power to the light receiving element and the light receiving element does not operate properly. It was necessary to attenuate the incident power by attaching a film.

[0004]

In this conventional line monitor, when the light receiving sensitivity difference between the forward light and the backward light is provided, as described above, the branching ratio of the fusion type coupler can be only about 10: 1. Therefore, two types of light receiving modules with an attenuating film for observing high power and a light receiving module with a lens for observing low power are required, and the configuration is complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a line monitor capable of simplifying a configuration in which a difference in light receiving sensitivity between forward light and backward light is provided.

[0006]

SUMMARY OF THE INVENTION A line monitor according to the present invention reflects an input fiber and an output fiber of signal light, and a part of a forward light and a backward light input from the output fiber. It has a half mirror and light receiving elements for respectively receiving the forward light and the backward light reflected by the half mirror, and the half mirror is inserted in a divergent beam of the forward light.

Preferably, the half mirror is provided so as to be movable along an optical axis.

[0008]

In the above means, the reflected forward light enters the light receiving element with a large spot size, and the reflected backward light enters the light receiving element with a small spot size.

Further, since the half mirror is provided so as to be movable along the optical axis, the ratio of the spot size of the beam incident on each light receiving element can be adjusted.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a line monitor according to an embodiment of the present invention.

An input fiber 1 and an output fiber 2 for signal light
Are coupled in a cross beam coupling system by two convex lenses 3 and 4. In the divergent beam (divergent ray bundle) of the forward light incident on the convex lens 4 on the exit fiber 2 side, the forward light incident from the entrance fiber 1 and the exit fiber 2
A half mirror 5 composed of a dielectric mirror that reflects a part of the backward light that has entered from above is inserted. In the vicinity of the half mirror 5, the forward light and the backward light reflected by the half mirror 5 are reflected. Light receiving elements 6 for receiving light respectively
7 are arranged. The half mirror 5 is provided so as to be movable along the optical axis together with the light receiving elements 6 and 7.

In the line monitor having the above structure, if forward light of +15 dBm is incident from the incident fiber 1 and 10% of the light is reflected by the half mirror 5,
Although the power of the forward light is +5 dBm, it is incident on the light receiving element 6 while increasing the spot size, so that only a part of the light is received.

When the backward light of -5 dBm enters from the output fiber 2, the power of the reflected light reflected by the half mirror 5 is -15dBm, but the light is focused on the light receiving surface of the light receiving element 7 because it is focused. Combine with high efficiency.

On the other hand, by moving the half mirror 5 along the optical axis, the ratio of the spot size of the beam incident on each of the light receiving elements 6 and 7 can be adjusted, without using two half mirrors. A line monitor can be configured according to the power ratio of the signal to be observed.

The half mirror 5 is connected to the output fiber 2
It is not limited to the case where the light is inserted into the divergent beam of the forward light incident on the convex lens 4 on the side. For example, as shown in FIG.
It may be inserted into the divergent beam of the forward light incident on the convex lens 3 on the incident fiber 1 side.

The branching ratio of the half mirror 5 can be selected to an appropriate value according to the application.

[0018]

As described above, according to the line monitor of the present invention, the reflected forward light is incident on the light receiving element in a state where the spot size is large, and the reflected backward light is reflected in the spot size. Since the light enters the light receiving element in a small state, only the reflected forward light is received, and the same effect as when an attenuation film is attached is obtained, and the reflected backward light is received via the lens. In this case, the same effect as the above case can be obtained, and it is not necessary to use an attenuating film and a lens in the light receiving portion as in the related art, and the structure can be simplified.

Further, since the half mirror is provided so as to be movable along the optical axis, the ratio of the spot size of the beam incident on each light receiving element can be adjusted, so that the two half mirrors are not used. In addition, a line monitor can be configured according to the power ratio of the signal to be observed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a line monitor according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a main part of a line monitor according to another embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional line monitor.

[Description of Signs] 1 Incident fiber 2 Outgoing fiber 3 Convex lens 4 Convex lens 5 Half mirror 6 Light receiving element 7 Light receiving element

Claims (2)

(57) [Claims] 1. An input fiber and an output fiber of a signal light, a half mirror that reflects a part of a forward light and a backward light that is input from the output fiber from the input fiber, and a half mirror that is reflected by the half mirror. A line monitor, comprising: a light receiving element that receives forward light and backward light, respectively, wherein the half mirror is inserted in a divergent beam of forward light. 2. A line monitor according to claim 1, wherein said half mirror is provided so as to be movable along an optical axis.