JP2820845B2 - Optical coupling device - Google Patents

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. FIG.
FIG. 4 is a cross-sectional view showing a configuration of a conventional optical coupling device, and FIG. 4 is a schematic configuration diagram for explaining a problem of the conventional example. The optical coupling device 1 shown in FIG.
, And a plug 3 coupled to the optical connector 2.

The optical connector 2 has a substantially cylindrical case 10 having a flange formed thereon, the light source 5 fixed to the left end of the case 10 in the drawing, and a laser beam emitted from the light source 5. And a condenser lens 4 that emits light. A play insertion hole 6 into which the ferrule 8 holding the optical fiber 9 at the center thereof is loosely formed is formed at the right end of the case 10 in the figure. A groove 10a for positioning is formed at the right end of the case 10 in the figure, and a male screw portion 10b is formed at the outer periphery. The plug 3 is screwed into the right end of the case 10 in the figure.

The plug 3 has a substantially cylindrical shape into which one end of an optical fiber cord 7 is inserted at the center.
At the center of the optical fiber cord 7, an optical fiber 9 into which the laser light focused by the focusing lens 4 is incident.
Is buried. A cylindrical projection 11a is formed on the plug body 11 holding the optical fiber cord 7, and a female screw 12a is formed on a left inner surface of a fastening member 12 provided on the outer periphery of the plug body 11. Have been.

When the optical connector 2 and the plug 3 are connected, the ferrule 8 holding the optical fiber 9 at the center is inserted into the play insertion hole 6 of the optical connector 2, and the projection 11a of the plug body 11 is The female screw 12a of the fastening member 12 and the male screw portion 10b of the optical connector 2 are screwed into the groove 10a of the connector 2. And the projection 11
By abutting the tip end face A of FIG. 1A and the inner end face B of the groove 10a, the axial positioning of the optical connector 2 and the plug 3 is performed.

Referring to FIG. 4, a light transmission state in the optical coupling device 1 having the above configuration will be described. 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 condensing lens 4 and the light condensed at the focal point of the lens 4 is transmitted to the fiber The light is incident on the incident end face 9a of the fiber 9 so as to coincide with the central axis Of of the fiber 9. For this reason, the incident end face 9a of the fiber 9
Needs to be positioned so as to be orthogonal to the optical axis O from the light source 5 and to be arranged so that the optical axis O of the light source 5 and the central axis Of of the fiber coincide.

However, in this configuration, a phenomenon occurs in which a part of the laser beam Lf incident from the light source 5 is reflected by the end face 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 as described above, the reflected light Lb is measured by a light-quantity measuring photoelectric conversion element (not shown) provided in the light source 5, and the emitted light quantity is measured to be a value correspondingly larger. As a result, the drive control of the light source 5 is adversely affected.

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

As another improvement, as shown in FIG. 6, there is a quartz plate 13 having an incident end face 13a 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 formed.
Is reflected in a direction different from that of the light source 5, and the reflected light L
The drive control of the light source 5 is not adversely affected by b and Lb1.

[0010]

However, the improved example shown in FIG. 6 has a structure in which the incident end face 13a of the quartz plate 13 is inclined. The fiber 9 needs to be phase-matched. For this reason, as shown in FIG. 6, the axes of the light source 5, the lens 4 and the fiber 9 are shifted from each other so that the optical axis O of the light source 5 is inclined by a predetermined angle with respect to the center axis Of of the fiber 9. I have to do it.

As described above, the axes of the light source 5, the lens 4, and the fiber 9 are shifted from each other. As a result, the aberration of the lens 4 and the shaking phenomenon of the laser beam of the light source 5 occur. The incidence efficiency to the light is reduced. Further, by displacing the respective axes, the external dimensions of the entire coupling device increase in the X1 and X2 directions in the figure.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical coupling device that can prevent reflected light returning to a light source and that does not reduce the efficiency of incidence of a laser beam on a fiber.

[0013]

The optical coupling device of the present invention comprises:
A first refractive member having a refractive index n1 substantially equal to the refractive index n3 provided at a position where the optical fiber having the refractive index n3 comes into contact, and a refractive index n2 provided on the light incident side of the first refractive member. A first refraction member and a second refraction member are joined at a joining surface inclined with respect to a plane orthogonal to the axis of the optical fiber, and the light of the second refraction member is The incident surface is also formed so as to be inclined with respect to the plane orthogonal to the axis of the optical fiber, and the angle of inclination of each of the light incident surface and the joint surface is such that the light incident on the incident surface in parallel with the axis of the optical fiber. Is set so as to be incident on the optical fiber in the same axial direction.

[0014]

According to the above means, the first refraction member having a refractive index substantially equal to the refractive index of the optical fiber is provided on the other side of the optical fiber in contact with the optical fiber. There is no reflection of the incident light between. Further, a second refraction member is joined to the first refraction member, and an optical axis parallel to the axis of the optical fiber is set by setting the inclination angle of the joining surface and the inclination angle of the light incident surface of the second refraction member. The light
The light passes through the second and first refraction members and enters 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 size of the optical coupling device can be reduced.

[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, the present embodiment will explain a main part of the optical connector which is a characteristic portion thereof. FIG. 1 is a schematic structural explanatory view showing a main part of an optical connector according to one embodiment of the present invention, and FIG. 2 is an operational explanatory diagram of the optical connector according to one embodiment of the present invention. In FIG. 1, reference numeral 21 denotes a case where the fiber 9 and the ferrule 8 holding the fiber 9 at the center are inserted. The case 21 is fixed, for example, at a position deep inside the play 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 refractive 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 a plane perpendicular to the central axis Of of the optical fiber 9. Also, groove 2
A first refraction member 23 having a refractive index n1 is provided on the back side of the second refraction member 2. The first refraction member 23 and the second refraction member 2
4 is joined at the joining surface 23a.
The angle of inclination of the central axis Of with respect to the vertical plane of 3a is θ1.
It is. The incident surface of the optical fiber 9 is processed into a spherical shape. When the fiber 9 is inserted into the connector 2 together with the ferrule 8, the tip of the fiber 9 comes into contact with the first refraction member 23.

Here, the condenser lens 4 emitted from the light source 5
When the optical axis O of the laser beam condensed by the laser beam is incident parallel to the central axis Of of the fiber, the optical axis coincides with the central axis Of after passing through the first and second refraction members 24 and 23. The condition for the light to be incident on the fiber 9 is shown below. When this condition is satisfied, the incident coupling efficiency of the laser beam to the fiber 9 becomes the best. The refractive index of air is “1”, the refractive index of the second refractive member 24 is n2,
The refractive index of the refractive 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 substantially equal to the refractive index n3 of the fiber, it is possible to prevent the incident light from being reflected at the junction 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 refraction member 24 from the incident surface 24a is θ3, and the refraction angle of the optical axis Oi is from the joining surface 23a to the first refraction member 23. The incident angle of incidence is assumed to be θ4. (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 this is incident on the incident surface 23a, the incident angle is represented by the angle formed by the perpendicular to the incident surface and the optical axis O. Becomes equal to θ2. Therefore, Equation 1 holds according to Snell's law.

[0019]

## EQU1 ## sin θ3 = (1 / n2) sin θ2

The condition that the optical axis Oi is incident on the first refraction member 23 and that the optical axis Oi is incident on the fiber 9 so as to coincide with the central axis Of is such that the optical axis Oi is incident on the first refraction member 23 from the bonding surface 23a. The refraction angle of the optical axis becomes equal to θ1. Therefore, it is necessary that Equation 2 be established according to Snell's law.

[0021]

## EQU2 ## sin θ4 = (n1 / n2) sin θ1

When the relationship between θ4 and θ1, θ2, θ3 at this time is obtained, the optical axis O and the central axis Of are parallel, the angle between the optical axis Oi and the optical axis O, and the angle between the optical axis Oi and the center. Since the angle with the axis Of has an illusional angle, the angle between the optical axis Oi and the central axis Of is (θ2−θ3). Therefore, θ1 and (θ2
−θ3 + θ4) is the relationship of the vertical angle, and the following Expression 3 is established.

[0023]

Equation 3 θ1 = θ2−θ3 + θ4

[0024] When this is transformed,

[0025]

Equation 4 θ4 = (θ1−θ2 + θ3)

## EQU2 ## Substituting Equation 4 into Equation 2 gives

[0027]

Sin (θ1−θ2 + θ3) = (n1 / n2) sin θ1

## EQU1 ## If the condition of Equation 5 is satisfied, the optical axis O of the laser beam from the light source 5 is emitted in parallel with the central axis Of of the fiber 9, and this light is transmitted to the fiber 9.
The light can be incident so as to be coincident with the central axis Of, so that the matching of 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 on 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 refractive member 23 is substantially equal to the refractive index n3 of the fiber 9, the incident light is not reflected at the junction between the first refractive member 23 and the fiber 9. Therefore, if the case 21 provided with the first and second refracting members 23 and 24 is held by the connector 2 shown in FIG. 3, the above-described refraction relationship is maintained only by mounting the fiber 9 held by the plug 3 as it is. The light is always incident on 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 transmitted through the central axis Of as shown in FIG.
It is not necessary to incline the connector 2, and the structure of the connector 2 can be reduced in size.

[0030]

According to the present invention described in detail above, in an optical coupling device for joining a fiber to a connector having a light source, light from the light source can be incident on the fiber to be coupled with the best coupling efficiency. Further, as shown in the embodiment, the optical axis of the light emitted from the light source can be arranged in parallel with the central axis of the fiber, so that a compact optical device can be constructed.

[Brief description of the drawings]

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

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

FIG. 3 is a cross-sectional view illustrating a configuration of a conventional optical coupling device.

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

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

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

[Explanation of symbols]

 Reference Signs List 8 ferrule 9 fiber 21 case 22 concave groove 23 first refraction member 23a joining surface 24 second refraction member 24a incident surface n1 refraction index of first refraction member n2 refraction index of second refraction member O optical axis Of fiber Center axis of

Claims (1)

(57) [Claims] 1. A refractive index n1 substantially equal to the refractive index n3 provided at a position where an optical fiber having a refractive index n3 abuts.
And a second refractive member having a refractive index n2 provided on the light incident side of the first refractive member.
The second refraction member and the second refraction member are joined at a joining surface inclined with respect to the plane orthogonal to the axis of the optical fiber, and the light incident surface of the second refraction member also extends with respect to the plane orthogonal to the axis of the optical fiber. The angle of inclination of each of the light incident surface and the bonding surface is 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 be coincidentally incident.