JPH06102438A - Optical coupling device - Google Patents

Abstract

PURPOSE:To improve the optical coupling efficiency to an optical fiber and to arrange an optical axis in a connector side in parallel with the fiber, in an optical coupling device coupling the fiber to the connector having a light source. CONSTITUTION:A first refraction member 23 with a refractive index n1 and a second refraction member 24 with the refractive index n2 are provided on a case 21 in the connector side, and the refractive index n3 of the fiber 9 loaded on the connector is made nearly equal to the refractive index n1. When the inclination of an incident surface 24a is regarded as theta2, and the inclination of a joint surface 23a is regarded as theta1, and the incident angle to the joint surface 23a is regarded as theta3, when the condition of sin(theta1-theta2+theta3)=(n1/n2)Xsintheta1 is satisfied, the optical axis O from the light source becomes parallel with the central axis Of of the fiber 9, and the incident optical axis coincides with the central axis Of of the fiber 9 and the optical incident coupling efficiency is in best.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling device for coupling an optical fiber used for optical communication with a light source such as a laser diode.

[0002]

2. Description of the Related Art A conventional example will be described with reference to the drawings. Figure 3
Is a cross-sectional view showing the configuration of a conventional optical coupling device, and FIG. 4 is a schematic configuration diagram for explaining the problems of the conventional example. The optical coupling device 1 shown in FIG. 3 includes a light source 5 including a laser diode.
The optical connector 2 has a built-in optical connector 2 and a plug 3 coupled to the optical connector 2.

The optical connector 2 has a case 10 having a substantially cylindrical shape with a flange, the light source 5 fixed to the left end of the case 10 in the figure, and a laser beam emitted from the light source 5. And a condensing lens 4 that emits light. At the right end of the case 10 in the drawing, a loose insertion hole 6 is formed in which a ferrule 8 holding an optical fiber 9 at its center is loosely inserted. Further, a positioning groove 10a is formed on the right end portion of the case 10 in the drawing, and a male screw portion 10b is formed on the outer peripheral portion. The plug 3 is screwed into the right end of the case 10 in the figure.

The plug 3 has a substantially cylindrical shape in which one end of the optical fiber cord 7 is inserted in the center.
At the center of the optical fiber cord 7, an optical fiber 9 on which the laser light condensed by the condenser lens 4 is incident
Is buried. Further, a cylindrical protruding portion 11a is formed on the plug body 11 holding the optical fiber cord 7, and a female screw 12a is formed on the inner surface of the left portion of the fastening member 12 provided on the outer periphery of the plug body 11 in the drawing. Has been done.

When the optical connector 2 and the plug 3 are connected to each other, the ferrule 8 holding the optical fiber 9 at the center is inserted into the free insertion hole 6 of the optical connector 2, and the protruding portion 11a of the plug body 11 is exposed to light. It is inserted into the groove 10a of the connector 2, and the female screw 12a of the fastening member 12 and the male screw portion 10b of the optical connector 2 are screwed together. And the protrusion 11
The optical connector 2 and the plug 3 are axially positioned by bringing the tip end surface A of the a into contact with the inner end surface B of the groove 10a.

The transmission state of light in the optical coupling device 1 having the above configuration will be described with reference to FIG. In the optical coupling device 1 in which the optical connector 2 and the plug 3 are connected, the laser beam emitted from the light source 5 is condensed by the condenser lens 4, and the light condensed at the focal point of the lens 4 is the fiber. The light is incident on the incident end face 9a of the optical fiber 9 so as to coincide with the central axis Of of the fiber 9. Therefore, the incident end surface 9a of the fiber 9 is
Must be positioned so as to be orthogonal to the optical axis O from the light source 5 and be arranged so that the optical axis O of the light source 5 and the central axis Of of the fiber coincide with each other.

However, in this structure, a part of the laser beam Lf incident from the light source 5 is reflected by the end surface 9a of the optical fiber 9 and returns to the light source 5 as reflected light Lb. When the reflected light Lb returns to the light source 5 in this manner, the reflected light Lb is measured by a photoelectric conversion element (not shown) provided in the light source 5 for measuring the amount of light, and the amount of emitted light becomes larger by that amount. As a result, the drive control of the light source 5 is adversely affected.

As a measure against such a problem, as shown in FIG. 5, a quartz plate 1 having an incident end face 13a having an antireflection film formed thereon is used.
Providing 3 on the front surface of the fiber 9 has been proposed. Thereby, the reflected light Lb returning from the fiber end surface 9a to the light source 5 can be prevented, but the reflected light Lb from the quartz plate 13 is prevented.
There arises a problem that 1 returns to the light source 5.

Further, as a modification of this, as shown in FIG. 6, there is one in which the incident end surface 13a of the quartz plate 13 is formed as an inclined surface. According to such an improved example, since the incident end face 13a is formed to be inclined, the reflected light Lb1
Is reflected in a direction different from that of the light source 5, and the reflected light L
b and Lb1 do not adversely affect the drive control of the light source 5.

[0010]

However, in the improved example shown in FIG. 6, the incident end face 13a of the quartz plate 13 is inclined, so that the laser beam is made to efficiently enter the laser beam. It is necessary to phase match the fiber 9. Therefore, as shown in FIG. 6, the axes of the light source 5, the lens 4, and the fiber 9 are displaced from each other so that the optical axis O of the light source 5 is inclined by a predetermined angle with respect to the central axis Of of the fiber 9. I have to do it.

As described above, as a result of arranging the light source 5 and the lens 4 and the fiber 9 with their axes displaced, the aberration of the lens 4 and the eclipse phenomenon of the laser beam of the light source 5 occur, and the fiber 9 of the laser beam is generated. The efficiency of incidence on light is reduced. Further, by arranging the respective axes so as to be displaced, the outer dimensions of the entire coupling device become large in the X1 and X2 directions in the drawing.

Therefore, an object of the present invention is to provide an optical coupling device capable of preventing the reflected light returning to the light source and preventing the incidence efficiency of the laser beam from entering the fiber.

[0013]

The optical coupling device of the present invention comprises:
A first refraction member having a refraction index n1 substantially equal to the refraction index n3 provided at a position where an optical fiber having a refraction index n3 abuts, and a refraction index n2 provided on the light incident side of the first refraction member. The second refraction member, and the first refraction member and the second refraction member are joined at a joint surface inclined with respect to a plane orthogonal to the axis of the optical fiber. The incident surface is also formed to be inclined with respect to the plane orthogonal to the axis of the optical fiber, and the inclination angles of the light incident surface and the joint surface are the same as those of the light incident on the incident surface parallel to the axis of the optical fiber. The optical axis of is set so as to be incident on the optical fiber in line with the axial direction of the optical fiber.

[0014]

According to the above-mentioned means, since the first refraction member having a refraction index substantially the same as that of the optical fiber is provided on the other side with which the optical fiber abuts, the first refraction member and the optical fiber are In between, no reflection of incident light occurs. Further, the second refraction member is joined to the first refraction member, and the optical axis parallel to the axis of the optical fiber is set by setting the inclination angle of the joint surface and the inclination angle of the light incident surface of the second refraction member. The light that you have
The light is transmitted through the second and first refraction members and is incident on the optical fiber. Since the optical axis of the light incident on the second refraction member is parallel to the axis of the optical fiber, the optical coupling device can be downsized.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Since the optical coupling device shown in this embodiment is the same as that shown in FIG. 3, this embodiment will explain the main part of the optical connector, which is the characteristic part of the device. FIG. 1 is a schematic configuration explanatory view showing a main part of an optical connector according to an embodiment of the present invention, and FIG. 2 is an operation explanatory view of an optical connector according to an embodiment of the present invention. In FIG. 1, reference numeral 21 denotes a case in which the fiber 9 and the ferrule 8 holding the fiber 9 are inserted. The case 21 is fixed, for example, at a position deep inside the loose insertion hole 6 inside the connector 2 shown in FIG. 3 and at a position facing the light source 5 and the condenser lens 4.

A concave groove 22 is formed on the light source side of the case 21, and a second refracting member 24 having a refractive index n2 is provided in the concave groove 22. The light incident surface 24a of the second refraction member 24 is formed to be inclined by an angle θ2 with respect to the plane perpendicular to the central axis Of of the optical fiber 9. In addition, the groove 2
A first refraction member 23 having a refractive index n1 is provided on the back side of 2. The first refraction member 23 and the second refraction member 2
4 is joined at the joint surface 23a, and the joint surface 2
The inclination angle of 3a with respect to the vertical plane of the central axis Of is θ1.
Is. The incident surface of the optical fiber 9 is processed into a spherical shape, and when the fiber 9 is inserted into the connector 2 together with the ferrule 8, the tip of the fiber 9 contacts the first refracting member 23.

Here, the condenser lens 4 emitted from the light source 5
When the optical axis O of the laser beam focused by is incident parallel to the central axis Of of the fiber, the optical axis of the laser beam coincides with the central axis Of after passing through the first and second refraction members 24 and 23. The conditions for being incident on the fiber 9 are shown below. When this condition is satisfied, the incident coupling efficiency of the laser beam on the fiber 9 becomes the best. The refractive index of air is “1”, the refractive index of the second refraction member 24 is n2,
The refractive index of the refracting member 23 is n1, and the refractive index of the fiber 9 is n3. Here, by making the refractive index n1 of the first refractive member 23 and the refractive index n3 of the fiber substantially equal to each other, it is possible to prevent the incident light from being reflected at the joint portion between the first refractive member 23 and the fiber 9. .

Further, the refraction angle of the optical axis Oi of the light source 5 entering the second refracting member 24 from the incident surface 24a is θ3, and this optical axis Oi extends from the joining surface 23a to the first refracting member 23. The incident angle of incidence is θ4. Note that (n2> n1),
(Angle θ1> angle θ2). First, when the optical axis O from the light source 5 becomes parallel to the central axis Of of the fiber 9 and is incident on the incident surface 23a, the incident angle is represented by the angle formed by the line perpendicular to the incident surface and the optical axis O. Becomes equal to θ2. Therefore, Formula 1 is established by Snell's law.

[0019]

## EQU1 ## sin θ3 = (1 / n2) sin θ2

Further, the optical axis Oi is incident on the first refracting member 23, and the condition that the optical axis Oi is incident on the fiber 9 coincident with the central axis Of is that the optical axis Oi is incident on the first refracting member 23 from the joint surface 23a. That is, the refraction angle of the optical axis becomes equal to θ1. Therefore, it is necessary that Formula 2 is satisfied by Snell's law.

[0021]

## EQU00002 ## sin .theta.4 = (n1 / n2) sin .theta.1

When the relation between θ4 and θ1, θ2, θ3 at this time is obtained, the optical axis O and the central axis Of are parallel to each other, the angle between the optical axis Oi and the optical axis O, and the optical axis Oi and the center. The angle between the optical axis Oi and the central axis Of is (θ2−θ3) because the angle with the axis Of is in the relation of an optic angle. Therefore, θ1 and (θ2
-Θ3 + θ4) has a relation of the vertical angle, and the following Expression 3 is established.

[0023]

## EQU3 ## θ1 = θ2-θ3 + θ4

When this is transformed,

[0025]

(4) θ4 = (θ1-θ2 + θ3)

Is represented by Substituting equation 4 into equation 2,

[0027]

## EQU00005 ## sin (.theta.1-.theta.2 + .theta.3) = (n1 / n2) sin.theta.1

[0028] If the condition of this equation 5 is satisfied, the optical axis O of the laser beam from the light source 5 is emitted parallel to the central axis Of of the fiber 9, and this light is directed to the fiber 9.
The incident light can be made to coincide with the central axis Of, the matching of the light to the fiber 9 can be maintained, and the coupling efficiency becomes the best. Even if a part of the laser beam from the light source 5 is reflected by the incident surface 24a of the second refraction member 24, the reflected light does not return to the light source.

Since the refractive index n1 of the first refracting member 23 is substantially equal to the refractive index n3 of the fiber 9, no reflection of incident light occurs at the junction between the first refracting member 23 and the fiber 9. Therefore, if the case 21 including the first and second refracting members 23 and 24 is held by the connector 2 shown in FIG. 3, the fiber 9 held in the plug 3 is simply mounted as it is to maintain the refraction relationship. Therefore, the light always enters the fiber 9 with the best coupling efficiency. Further, since the optical axis O from the light source 5 is parallel to the central axis Of of the fiber 9, the incident light is directed to the central axis Of as shown in FIG.
Since it is not necessary to incline with respect to the connector 2, the structure of the connector 2 can be downsized.

[0030]

According to the present invention described in detail above, in an optical coupling device in which a fiber is joined to a connector having a light source, the light from the light source can be incident on the coupled fiber with the best coupling efficiency. Also, as shown in the embodiment, the optical axis of the light emitted from the light source can be arranged parallel to the central axis of the fiber, and a small optical device can be constructed.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing a main part of an optical connector according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a light incident action of the optical connector according to the embodiment of the present invention.

FIG. 3 is a sectional view showing a configuration of a conventional optical coupling device.

FIG. 4 is a schematic configuration diagram for explaining problems of the conventional example.

FIG. 5 is a schematic configuration diagram showing a conventional improvement example.

FIG. 6 is a schematic configuration diagram showing a conventional improvement example.

[Explanation of symbols]

 8 Ferrule 9 Fiber 21 Case 22 Groove 23 First Refractive Member 23a Bonding Surface 24 Second Refractive Member 24a Incident Surface n1 Refractive Index n1 First Refractive Member n2 Refractive Index O Optical Fiber Of Fiber Central axis of

Claims (1)

[Claims] 1. A refraction index n1 provided at a position where an optical fiber having a refraction index n3 abuts and is substantially equal to the refraction index n3.
Of the first refracting member and a second refracting member having a refractive index n2 provided on the light incident side of the first refracting member.
And the second refracting member are joined at a joint surface inclined with respect to the plane orthogonal to the axis of the optical fiber, and the light incident surface of the second refracting member is also relative to the plane orthogonal to the axis of the optical fiber. It is formed to be inclined, and the inclination angles of the light incident surface and the joining surface are such that the optical axis of light incident parallel to the axis of the optical fiber with respect to the incident surface is the same as the axial direction of the optical fiber. An optical coupling device, which is set so as to coincide with each other.