JP2003057500A - Optical coupling mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an NA of incident light on an optical fiber as small as possible, and also, to improve an optical coupling efficiency as compared with that in a conventional method. SOLUTION: A 1st parabola 100 has an optical axis (x-axis) between a light source and a light receiving part as a symmetry axis, and a parabola rotary- moved by taking the focus (origin) of the 1st parabola as a center is regarded as a 2nd parabola 200, the optical coupling mirror is a cylindrical rotary mirror obtained by rotating a certain part 400 of a curve 300 cut by two intersections between the 2nd parabola and the symmetry axis of the 1st parabola by taking the symmetry axis of the 1st parabola as a rotating axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling mirror that couples light from a light source into an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as a means for coupling light from a light source into an optical fiber, for example, reference 1 (Reference 1: Japanese Patent Laid-Open No. H6-6)
-209124).

According to Reference 1, a light source is arranged at the focal point of a paraboloid so that the emission direction of light is directed to the parabolic side. Then, the light emitted from the light source is reflected by this parabolic surface. The reflected light becomes parallel to the rotation axis of the paraboloid,
This collimated light is coupled into the optical fiber.

[0004]

However, as the light source, for example, an LED having a light emitting surface with a diameter of 200 μm is used, and as an optical fiber, for example, the incident end surface has a diameter of 1 μm.
When using a material of about mm, the size of the light source cannot be ignored. That is, the light source is not a point light source and has a planar spread. Therefore, with respect to light emitted from the light source and having a shallow angle (small emission angle), the reflected light is blocked by the light source and cannot reach the optical fiber, resulting in low optical coupling efficiency. There is a problem.

Therefore, an optical coupling method is conceivable in which the light source is arranged so that the light emitted from the light source is directed toward the incident end face side of the optical fiber, and a lens is interposed between the light source and the optical fiber. According to this optical coupling method, the light emitted from the light source may be condensed by the lens and coupled to the optical fiber.

However, in such a structure of the optical coupling system, only light having a shallow angle with respect to the optical axis can be coupled to the optical fiber, and a deep angle with respect to the optical axis (a large emission angle, for example, Light at angles near vertical are not collected by the lens. Also, the light source has a size. Therefore, the light near the center of the light source can be condensed by the lens, but the light emitted from the end of the light source may be diverged due to refraction by the lens. Therefore,
The desired optical coupling efficiency cannot be obtained even with such a configuration of the optical coupling system.

In view of the above-mentioned conventional structure, therefore, as an optical coupling means capable of coupling light having a shallow angle with respect to the optical axis and light having a deep angle with respect to the optical axis to, for example, a light source, It is conceivable that the light source is arranged such that the direction of the emitted light is directed to the incident end face side of the optical fiber, and the parabolic mirror is arranged on the side opposite to the optical fiber side of the light source.

However, in this structure, when the diameter of the incident end face of the optical fiber is about 1 mm and a large size light source such as 0.2 mmφ is used, the following problems occur. In other words, if a paraboloid of revolution is designed so that a light source of this size can be installed at the focal point of the parabolic mirror, the parabola that constitutes the paraboloid of revolution will become symmetric as it moves away from the focal point along the axis of symmetry. The curve is far away from the axis. That is, the curve becomes a curve that spreads to the quasi-line side. Therefore, the angle range of the light reflected by the parabolic surface and incident on the optical fiber becomes narrow,
Therefore, the angle range of the light (also referred to as direct light) traveling directly from the light source to the incident end side of the optical fiber becomes relatively wide. Therefore, since the direct light includes the light having a large emission angle, the NA of the light incident on the optical fiber is increased and the light diameter is also expanded. As a result, the coupling loss increases.

Further, in order to narrow the light diameter of the incident light to the optical fiber and reduce the NA, the parabola forming the paraboloid of revolution is designed to be close to the axis of symmetry. It becomes impossible to install such a large-sized light source. Therefore, even with this configuration, it is difficult to improve the optical coupling efficiency.

Therefore, the NA of the light entering the optical fiber is
There has been a demand for the appearance of an optical coupling means capable of reducing the optical coupling efficiency as much as possible and improving the optical coupling efficiency more than ever before.

[0011]

For this reason, the optical coupling mirror of the present invention for coupling the light from the light source to the light receiving surface of the light receiving component is designed as follows. First, the first parabola having the optical axis between the light source and the light receiving component as the axis of symmetry is rotationally moved around the focal point of the first parabola. The parabola obtained by this is referred to as a second parabola. The symmetry axis of the second parabola and the first parabola, that is, the optical axis, intersect at two intersections. Then, the curve of the second parabola cut at this intersection is further cut at a desired position on the side of each intersection. A part of the curve thus cut is rotated with the axis of symmetry of the first parabola as the axis of rotation. The cylindrical rotary mirror obtained by this rotation is called an optical coupling mirror. The position where the curve of the second parabola is further cut is determined in consideration of the usage conditions of the finally obtained rotary mirror, the optical coupling efficiency, the size of the light receiving surface, and the like.

The partial curve forming the plane of rotation of such a rotary mirror is a parabola (first parabola) whose axis of symmetry is the axis of symmetry.
The curve becomes closer to the rotation axis side. Moreover,
Since the first parabola is designed so that the second parabola does not come into contact with the light source, it is possible to install a large-sized light source in the rotary mirror. Therefore, it is possible to widen the angular range of the light reflected by the mirror surface in the light emitted from the light source. Also, the NA of the light that is directly incident on the light receiving surface from the light source.
Can be reduced. Therefore, the optical coupling loss can be reduced and the optical coupling efficiency can be improved.

Further, in such an optical coupling mirror, the first
When the light source is arranged so that the center of the light source is located at the focal point of the parabola and the second parabola, and the light receiving component is arranged so that the light receiving surface is located on the extension line of the rotation axis, it is preferable that the light coupling from the light source is performed. The average NA of the numerical aperture (NA) of the direct incident light that reaches the light receiving surface without being reflected by the mirror surface of the mirror and the NA of the reflected light that reaches the light receiving surface after being reflected by the mirror surface from the light source.
The angle of rotation (θ) of the first parabola and the part of the curve (specifically, the distance (L) between the ends of the part of the curve) are determined so that the value of is smaller than the NA of the light source. Good.

Therefore, the NA of the light emitted from the optical coupling mirror designed based on the determined rotational movement angle (θ) of the first parabola and the part (L) of the curve is smaller than that in the conventional case. Designed so that the average NA of the light emitted from the light source is small even when the ratio of light having a large emission angle that is reflected light is larger than that of light that has a small emission angle that is directly incident light. Because it is done, NA
Can be made smaller. Therefore, by using this optical coupling mirror, the optical coupling efficiency from the light source to the light receiving surface can be improved.

In the case where the reflected light reflected by the mirror surface of the light emitted from the light source is mainly coupled to the light receiving surface, θ and L are determined so that the numerical aperture of the reflected light is minimized. do it.

In such a case, for example, the amount of light with a small emission angle such as direct incident light is negligibly small, while the amount of light with a large emission angle that is reflected light is very large. In some cases, the wiring is connected near the center of the light emitting surface of the light source. If a connecting component or the like is provided near the center of the light emitting surface of the light source, light having a shallow angle from the optical axis, that is, light having a small emission angle is blocked by the component and cannot be coupled to the light receiving surface. Therefore, of the light emitted from the light source, the light having a large emission angle is coupled to the light receiving surface. Light having a large emission angle is reflected by the mirror surface of the optical coupling mirror, and the reflected light is incident on the light receiving surface. Therefore, in order to minimize the NA of the reflected light, θ
And L may be determined. As a result, the NA of the entire light incident on the light receiving surface can be reduced.

When the light amount of the direct incident light and the light amount of the reflected light are approximately the same, the maximum incident angle of the direct incident light and the maximum incident angle of the reflected light are substantially equiangular (substantially equal to each other). It is preferable that the rotational movement angle of the first parabola is determined such that the angle can be regarded as an angle.

As described above, the NA of the light incident on the light receiving surface from the rotary mirror can be reduced according to the emission pattern of the light source.

In the design stage of the optical coupling mirror of the present invention,
The rotational movement angle of the first parabola is set such that the maximum incident angle of the direct incident light and the maximum incident angle of the reflected light are substantially equiangular and the light source does not come into contact with the mirror surface. Further, the two end portions of the light emitting surface which intersect the straight line which is perpendicular to the rotation axis and which passes through the focal point are in the same plane as the curved line and the rotation axis, and among the two end portions, the curved side is based on the rotation axis. The end located at
The end is defined as the end, and the end located on the side opposite to the curved side with respect to the rotation axis is defined as the second end. At this time, a part of the curve is obtained by cutting the curve at the intersection of the straight line representing the direct incident light emitted from the second end of the light emitting surface and entering the light receiving surface at the maximum incident angle. And However, the direct incident light should not touch a part of the curve.

As a result, the NA of the light emitted from the rotary mirror is
Can be minimized, and the coupling efficiency of the light emitted from the light source to the light receiving surface can be significantly improved as compared with the conventional case.

Here, it is known to those skilled in the art that the communication frequency band of a multimode fiber having a large core diameter such as POF (plastic optical fiber) depends on the NA of the light source and the NA of the optical fiber. There is. The smaller the NA of the light source and the smaller the NA of the optical fiber, the wider the frequency band can be achieved.

Therefore, as described above, by reducing the NA of the light incident on the light receiving surface from the optical coupling mirror,
The communication frequency band between the light source and the light receiving component can be expanded as compared with the conventional case.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that each of the drawings merely schematically shows the shape, size, and arrangement relationship of each constituent component to the extent that the invention can be understood, and therefore the present invention is not limited to the illustrated examples.

<Description of Basic Concept> First, the basic concept of the present invention will be described with reference to FIGS.

The optical coupling mirror of the present invention uses, for example, an LE as a light source.
When the light receiving component is D and the light receiving surface is an optical fiber having a diameter of 1 mm, it is used as an optical coupling mirror for coupling the light of the LED to the optical fiber.

The optical fiber is installed so that the light-receiving surface, that is, the incident end surface is located at a position on the extension line of the symmetry axis of the first parabola used in the design stage of the optical coupling mirror. In addition, the light source usually has a light emitting surface that is wide. Therefore, the center of the light source, that is, the center of the light emitting surface is the first of the optical coupling mirror.
The light source is installed so as to be located at the focal points of the parabola and the second parabola. Moreover, the light is emitted from the light source toward the light receiving surface of the optical fiber. Therefore, the optical axis of the light from the light source to the optical fiber via the optical coupling mirror is the axis of symmetry of the first parabola and also the rotation axis of the optical coupling mirror.

Now, referring to FIG. 1, consider a parabola in a two-dimensional coordinate system of xy coordinates. The first parabola is on the xy coordinate plane, and the principal axis, that is, the x axis is the optical axis. Therefore, the emission direction of the light from the light source is the direction in which the value of x on the x-axis increases. As is well known, the first parabola 100 having the optical axis as the axis of symmetry is expressed by the following equation (1). In addition, the following equation (1)
Represents the first parabola when the focal point is the origin (x, y) = (0,0).

Y = √ (1 / a + 4x) / 2√a (1) In the above equation (1), a is a coefficient that determines the slope of the first parabola. The coefficient a is defined by the equation (3) shown below. The first parabola 100 is the first parabola 1
When the light source is arranged such that the light emission center of the light source having a spread on the light emitting surface is located at the focal point of the parabolic surface obtained by rotating about the axis of symmetry (x axis) of 00 as the rotation axis, the light source is parabolic. The parabola should not touch the surface. Then, the first parabola 100 is rotationally moved about the focal point by the angle θ to obtain the second parabola 200. However, the position of the light source is not moved. Then, the second parabola may come into contact with the light source depending on the size of the light source and the rotational movement angle (θ) of the first parabola. Do not let the light source contact the second parabola,
The coefficient for previously determining the slope of the first parabola is the coefficient a.

A parabola obtained by rotationally moving the first parabola 100 of the above equation (1) about the focal point (origin) in the xy plane, for example, by the angle θ, that is, the second parabola 2
00 is represented by the following equation (2).

Y = − (Sec ² θ (−√ (1+ (4aCosθ) x) + Sinθ + axSin2θ)) / (2a) (2) Then, the coefficient a is given by the following equation (3). . The half width of the light source (when the light emitting end face of the light source is circular, the half width is the radius) is defined as Din in the y direction.

A = 1 / (2 Din (1 + Sin θ)) (3) Therefore, the second parabola 200 shown by the above equation (2) is used.
Is expressed by the following equation (4), where the focal point is the origin, the rotational movement angle of the first parabola is θ, and the half width of the light source is Din.

Y = (Din (-1 + Cos2θ-2 Sinθ + 2√ (1 + Sinθ) √ (1 + (2Cosθ) x / Din + Si nθ))-(Sin2θ) x) / (1 + Cos2θ) ・.. (4) The second parabola 200 represented by the equation (4) and the symmetry axis (x axis) of the first parabola are two points, for example, P ₁ (x ₁ , 0) and P
_They intersect at ₂ (x ₂ , 0). One point P ₁ (x ₁ , 0) is on the light source side, and the other point P ₂ (x ₂ , 0) is on the light receiving component side. A curve 300 between two points cut at the intersection of these two points is partially cut out to form a part 400 of the curve (also referred to as a partial curve). A part 400 of this curve is rotated with the axis of symmetry (x axis) of the first parabola 100 as the axis of rotation.

By rotating, a cylindrical rotating surface 500 is obtained. The inner surface of the rotating surface 500 is a rotating surface mirror. This rotating mirror serves as an optical coupling mirror. FIG. 2A shows the shape of the rotating surface 500 in a three-dimensional coordinate system of xyz coordinates.

Here, the opening 600 on the light receiving component side of the rotating surface 500 is required to emit the light from the light source and couple the emitted light to the light receiving face of the light receiving component. Therefore, the opening 600 needs to be a window (emission window) having the same size as the light receiving surface even if it is large. Therefore, the above curve 300 is cut from the intersection P ₂ (x ₂ , 0) on the light receiving component side at an appropriate position P _x (x _x , y _x ) on the _one intersection P ₁ (x ₁ , 0) side. (See Fig. 1). In addition, the opening 70 on the light source side of the rotating surface 500.
It is preferable that 0 is a window (incident window) having the same size as the light emitting surface of the light source even if it is small. Thus, for example, a line (y-axis) perpendicular to the axis of rotation (x-axis) at the focal point and the curve 300 described above.
The curve 300 is cut at the intersection with and (see FIG. 1). The partial curve 400 obtained by cutting the curve 300 in this way
Is rotated about the x axis as a rotation axis, an optical coupling mirror 500 having an entrance window 700 and an exit window 600 as shown in FIG. 2A is obtained.

Then, as shown in FIG. 2B, a light source 750 is installed in the entrance window 700, and a light receiving component 650 is installed in the exit window 600. In FIG. 2B, the optical coupling mirror is shown by a cross section cut along the xy plane. Further, for example, an LED is used as the light source and an optical fiber is used as the light receiving component. Further, FIG. 2B is a diagram showing a positional relationship between the optical coupling mirror, the light source, and the light receiving component,
The shapes and sizes of the light source and the light receiving component are not limited to those shown in this figure.

Further, in this configuration example, the light emitting surface 770 of the light source 750 has the same shape and the same size as the entrance window 700. The light receiving surface 660 of the light receiving component 650 has a size equal to or smaller than the size of the emission window 600. In FIG. 2 (B),
The emission window 600 and the light receiving surface 660 have the same shape and the same size.

Next, a method for determining the rotational movement angle (θ) of the first parabola and the length (L) of a part of the curve will be described.

In the optical coupling mirror of the present invention, the NA of the direct incident light which reaches the light receiving surface from the light source without being reflected on the mirror surface of the optical coupling mirror and the NA of the light which is emitted from the light source and is reflected on the mirror surface and then reaches the light receiving surface. The value of the average NA with the NA of the reflected light is N of the light source.
The θ and L are determined so as to be smaller than A.

Here, the light quantity (light intensity) of the direct incident light is Sd
, And NA is NAd. Further, when the amount of reflected light (light intensity) is Sr and NA is NAr, the average NA of the light emitted from the optical coupling mirror is expressed by the following equation (5).

Average NA = (Sd × NAd) / (Sd + Sr) + (Sr × NAr) / (Sd + Sr) (5) Further, the exit window of the optical coupling mirror (the opening on the side of the light receiving component) The condition for making the aperture of () the size of the light receiving surface is expressed by the following equation (6), where Dout is the half width of the light receiving surface.

Y = Dout (6) Then, the condition that the reflected light of the optical coupling mirror is not reflected again on the mirror surface is expressed by the following equation (7).

Y − Dout = Tan θ (x − L) (7) Therefore, the NA (NAd) of the direct incident light is expressed by the following equation (8).

NAd = Sin (ATan (Dout / L)) (8) The NA (NAr) of the reflected light is expressed by the following equation (9).

NAr = Sin θ (9) Therefore, from the above equations (5), (8) and (9),
It suffices to determine θ and L at which the average NA becomes smaller than the NA of the light source. It is more preferable if this average NA can be made smaller than the NA of the light source to be the minimum value.

By the way, due to the size of the light source, the maximum outgoing angle of the outgoing light from the optical coupling mirror (the maximum incident angle to the light receiving surface) is deviated by α. Reference is now made to FIG. FIG. 3 shows a cross section of the optical coupling mirror of the present invention cut in the xy plane.

If the light source is a point light source, the angle of the outgoing light from the light source passing through the end of the exit window of the optical coupling mirror with respect to the optical axis is the same regardless of the end. However,
As the light emitting surface of the light source becomes larger, the edge Q ₁
Therefore, there is a difference between the maximum output angle of the output light 800 passing through any one end R of the output window and the maximum output angle of the output light 900 passing through another end Q ₂ through the end R. The difference between these angles is α.

Therefore, the NA (NAd) of the direct incident light is given by the following equation (1) when the condition of the size of the light source is added to the above equation (8).
It is represented by the formula 0). The NA (NAr) of the reflected light is expressed by the following equation (11).

NAd = Sin (ATan ((Dout + Din) / L)) (10) NAr = Sin (θ + α) (11) Therefore, when considering this deviation α, From the above equations (5), (10) and (11), the average NA
It is preferable to determine θ and L that minimize.

<First Embodiment> In this embodiment, the characteristics of the optical coupling mirror of the present invention will be examined. An LED having a circular emission end face is used as a light source for making light incident on the optical coupling mirror. The LED has a radius of 0.13 of the optical coupling mirror.
A size corresponding to an entrance window of mm is used.

In this embodiment, first, an optical coupling mirror is designed. 4 and 5 are schematic design process diagrams of the optical coupling mirror.

In this embodiment, the radius of the exit window of the optical coupling mirror is 0.45 mm, and the NA of the reflected light emitted from the light source after being reflected on the mirror surface and the NA of the direct light directly emitted from the light source. So that and are equal. When calculation is performed using the above equation, the rotational movement angle (θ) of the first parabola used in the design of the optical coupling mirror satisfying this condition is about 10 °.
The distance (L) between the entrance window and the exit window of the optical coupling mirror was 2.6 mm. The shape of the first parabola is determined from the shape of the curve that satisfies the above conditions.

For example, the parabola shown in FIG. 4A is the first parabola 12. The first parabola 12 is a parabola whose focal point is the origin, and the length of the y-axis line segment 14 cut at the intersection of the first parabola 12 and the y-axis is the same as the diameter (0.26 mm) of the light emitting surface of the LED. It has the same or longer length.

Next, using this first parabola 12, in this embodiment, the second parabola 16 is obtained with the first parabola 12 as the center of rotation and the rotational movement angle θ (FIG. 4).
(B)). In this embodiment, θ is 5 °, 10 °, 1
A second parabola is formed at each θ of 5 ° and 20 °.

One curve 18 is cut out by two intersection points of the second parabola 16 and the axis of symmetry (x axis) of the first parabola 12. The first intersection 20 is an intersection on the light source side (focal side, origin side), and the second intersection is an intersection on the light-receiving surface side (plus side of the x-axis) (not shown in FIG. 4). Figure 4
(C)).

Next, this curve 18 is converted into the first curve at the focal point.
It cuts by the straight line (y-axis) which intersects with the symmetry axis (x-axis) of a parabola at right angles (FIG. 5 (A)). Furthermore, at an arbitrary point P on the symmetry axis (x axis) of the first parabola within a range of 0 to 4 mm from the focus (origin), a straight line (dotted line) intersecting the symmetry axis (x axis) at a right angle. (Fig. 5)
(B)).

As a result, a part (partial curve) 22 of the curve forming the optical coupling mirror for simulation for investigating the characteristics can be obtained. The shape obtained by rotating a part 22 of this curve with the axis of symmetry (x axis) of the first parabola 12 as the axis of rotation is the shape of the optical coupling mirror 24 of this embodiment. The cross section of the optical coupling mirror 24 of this embodiment is shown in FIG. As shown in FIG. 5C, the optical coupling mirror 24 has an entrance window 26 and an exit window 28.

NA of light emitted from such an optical coupling mirror
Is calculated from the above equations (10) and (11).

The results are shown in FIG. FIG. 6 shows the relationship between the distance (L) from the entrance window 26 to the exit window 28 of the optical coupling mirror 24 and the NA of the output light from the optical coupling mirror 24 for each rotational movement angle (θ) of the first parabola. It is a characteristic diagram shown in FIG. In FIG. 6, this characteristic is represented by an entrance window 26 and an exit window 28 on the horizontal axis.
The distance (L) between them, and the NA of the emitted light is taken on the vertical axis, and the rotational movement angle (θ: θ = 5 °, 10 °, 15 ° and 20
°).

Distance from entrance window 26 to exit window 28 (L)
Is short, of the light emitted from the light source, the optical coupling mirror 24
The angle range of the light reflected by the mirror surface is narrowed. Therefore, less light is reflected by the mirror surface of the optical coupling mirror 24. Along with this, the angular range of light that is not reflected (referred to as direct light) is widened. Therefore, the amount of direct light increases and the N
A also becomes high. As the distance (L) from the entrance window 26 to the exit window 28 increases, the direct light with a large exit angle, which causes the NA of the direct light to increase, is reflected by the mirror surface. Therefore, the amount of reflected light increases, and the NA of direct light can be reduced. However, for example, when the rotational movement angle (θ) of the first parabola is set to a relatively large angle of 20 °, the angle of the reflected light with respect to the optical axis also increases to 20 °, resulting in an increase in NA. .
Therefore, when θ is set to 20 °, the distance between the entrance window 26 and the exit window 28 as shown in FIG.
Even if (L) is longer than about 1.2 mm, the NA of the light emitted from the optical coupling mirror 24 can hardly be reduced from 0.4.

The rotational movement angle of the first parabola is 15 °, 10
The NA of the reflected light can theoretically be reduced as the angle decreases to 5 °. However, when the outgoing light from the optical coupling mirror 24 is to be coupled to an optical fiber having a core diameter of 1 mm, for example, the outgoing window 28 of the optical coupling mirror 24 is used.
Must have a diameter of about 0.9 mm. According to FIG. 6, in the optical coupling mirror having the rotational movement angle θ of 5 °, the NA of the outgoing light becomes 0.2 or less by setting the distance (L) between the entrance window and the exit window to 4 mm. However, θ is 5 °
Then, when L is set to a length of 4 mm, the diameter of the exit window 28 becomes much larger than 0.9 mm. Therefore, although it can be used in a special case of optically coupling to an optical fiber having a very large light receiving surface, it is not practical.

In the optical coupling mirror used for coupling the light of the LED having the light emitting surface with the diameter of 0.26 mm to the optical fiber with the diameter of the core of 1 mm, the diameter of the emission window must be 1 mm or less. If the rotational movement angle (θ) is small, the distance (L) between the entrance window and the exit window of the optical coupling mirror will be short. Therefore, the NA of the reflected light reflected by the mirror surface
Is small, but the amount of light is small. Also, the amount of direct light that is not reflected by the mirror surface is large, and its NA is large. Therefore, the NA of the entire light emitted from the optical coupling mirror is large, and the optical coupling efficiency is low.

On the other hand, if the rotational movement angle is large, the distance between the entrance window and the exit window of the optical coupling mirror can be lengthened.
Therefore, the amount of reflected light can be increased, but its NA is increased. Further, the NA of the direct light becomes small.
Therefore, the NA of the entire emitted light from the optical coupling mirror is still large, and the optical coupling efficiency is also reduced accordingly.

As described above, the optical coupling mirror 2 of this embodiment is
Considering that the output light from 4 is optically coupled to the optical fiber with a core diameter of 1 mm, the diameter of the output window when the distance (L) is 2.6 mm when the rotational movement angle of the first parabola is about 10 °. Is about 0.9 mm. At this time, the NA of the reflected light becomes equal to the NA of the direct light, so that the NA of the light emitted from the optical coupling mirror can be minimized.

<Second Embodiment> In this embodiment, the characteristics of the optical coupling mirror different from those of the first embodiment will be examined.

In this embodiment, L is used as the light source.
Use ED. The inclination of the first parabola is 10 °. Then, the size of the light source is changed, and the change characteristic of the NA value of the emitted light with respect to the distance (L) between the incident window and the outgoing window is examined.

Changing the size of the light source means changing the radius of the entrance window of the optical coupling mirror. Here, the radius of the entrance window is 0.05 mm, 0.1 mm, 0.2
mm and 0.4 mm.

FIG. 7 shows the change characteristics of the NA of the outgoing light with respect to the distance (L) between the entrance window and the exit window depending on the size of the light source. In FIG. 7, the horizontal axis indicates the distance between the entrance window and the exit window.
(L) is shown, and NA is shown on the vertical axis.

According to FIG. 7, the smaller the size of the light source, the smaller the NA of the light emitted from the optical coupling mirror. It is also shown that even if the size of the light source is large, the NA can be reduced to some extent by increasing the distance between the entrance window and the exit window.

Reference will now be made to FIG. FIG. 8 is a characteristic diagram showing the characteristics of the distance (L) between the entrance window and the exit window with respect to the rotational movement angle (θ) of the first parabola for each size of the light source.

According to FIG. 8, when the rotational movement angle of the first parabola is increased, the distance (L) between the entrance window and the exit window becomes longer. However, this characteristic is remarkable when the size of the light source is small, and in the case of a light source of a large size such that the radius of the light emitting surface is 0.4 mm, the rotational movement angle is 20.
Even if the angle is 0, the distance (L) between the entrance window and the exit window is almost 0 mm.

Therefore, in reality, as shown in FIG. 7, when the size of the light source is large, the distance between the entrance window and the exit window is large.
(L) cannot be lengthened. Therefore, if the size of the light source is large, the NA cannot be reduced.

Therefore, it is preferable that the size of the light source is small.

The curve shown by the dotted line in FIG. 8 is the NA of the reflected light reflected from the light source to the mirror surface and incident on the light receiving surface and the NA of the direct light directly incident on the light receiving surface without being reflected on the mirror surface. Represents the rotational movement angle of the first parabola and the distance between the entrance window and the exit window of the optical coupling mirror when the values are equal. Also,
In FIG. 8, a region on the right side of this curve is a region where the NA of reflected light becomes large. As the NA of the reflected light increases, the NA of the entire light emitted from the optical coupling mirror also increases. Therefore, at the rotational movement angle (θ) and the distance between the entrance window and the exit window (L) in this region, the design of the optical coupling mirror Does not.

<Application Example of Optical Coupling Mirror> As an application example of the optical coupling mirror described above, the following configuration can be used.

For example, one configuration example will be described with reference to FIG. The rotational movement angle (θ) of the first parabola 100 is set such that the maximum incident angle of the direct incident light and the maximum incident angle of the reflected light are substantially equiangular and the light source does not come into contact with the mirror surface. Further, the second parabola 200 has a rotation axis (x
The angle is such that it makes contact with a straight line (y = S) parallel to the axis) and separated from the focal point by a predetermined distance equal to or less than the half width of the light receiving surface at one point (S).

The rotational movement angle (θ) is such an angle,
Furthermore, a point where the curve 300 and the above straight line (y = S) touch
The optical coupling mirror is designed with the part 400a of the curve cut at the position (S). The optical coupling mirror 5 is shown in FIG.
Indicates 00. When the size of the light source is sufficiently small, the NA incident on the light receiving surface from the optical coupling mirror can be reduced. Further, the shape of the optical coupling mirror 500 is a tubular shape in which the size of the cross section perpendicular to the optical axis (x axis) gradually increases from the entrance window 700 to the exit window 600. Such a shape is easy to manufacture.

Another configuration example will be described with reference to FIG. At the design stage of the optical coupling mirror, first,
The rotational movement angle (θ) of the first parabola 100 is set such that the maximum incident angle of the direct incident light and the maximum incident angle of the reflected light are substantially equal and the light source does not come into contact with the mirror surface.

A straight line parallel to the optical axis (x-axis) and separated from the focal point by a predetermined distance equal to or less than the half width of the light receiving surface (y =
When T) and the curve 300 have two intersections T ₁ and T ₂ , the cut portion of the curve forming the opening (emission window) on the light receiving component side is the intersection T ₁ on the light source side of the above two intersections. And In addition, the cut section of the curve forming the opening (incident window) on the light source side is a straight line (y) perpendicular to the optical axis (x axis) at the focal point.
Cut at the intersection of the axis) and the curve 300. By this cutting, a partial curve 400b, that is, a part of the curve is obtained. When a part 400b of this curve is rotated around the x-axis as the rotation axis, the optical coupling mirror 50 having the structure as shown in FIG.
0 is obtained. The optical coupling mirror 500 includes an entrance window 700 and an exit window 600.

If a straight line parallel to the optical axis (x-axis) and separated from the focal point by a predetermined distance less than the half width of the light receiving surface does not intersect with the curved line, the position where the curved line is closest to the straight line is not present. A section of the curve is obtained by cutting the curve at. The optical coupling mirror obtained by rotating a part of this curve has the same shape as the optical coupling mirror shown in FIG.

The optical coupling mirror designed as described above is
Each of them has a tubular shape whose cross section gradually increases from the entrance window 700 to the exit window 600. Therefore, it is easier to manufacture than an optical coupling mirror having a shape in which the tube is largely swollen in the middle between the entrance window 700 and the exit window 600.
However, this optical coupling mirror has a narrow angle range of light reflected by the mirror surface and can only reflect light having a large emission angle of light from the light source. Therefore, the NA of the direct incident light becomes large. Therefore, it becomes an effective optical coupling mirror when the NA of the light emitted from the light source is large, that is, when the light amount of the light emitted from the light source is large.

Further, another application example of the optical coupling mirror of the present invention will be described with reference to FIG. The optical coupling mirror 500 of the present invention has a window 150 having the same shape as the exit window 600 of the optical coupling mirror 500, and extends substantially parallel to the extension line of the optical axis (x axis). The extending cylindrical reflecting mirror 250 may be formed so as to communicate between the emission window 600 of the optical coupling mirror 500 and the light receiving surface.

The entrance window 700 of the designed optical coupling mirror 500
In addition, when the distance (L) between the output windows 600 becomes short, it becomes difficult to connect the optical coupling mirror 500 and the light receiving component, or when a problem occurs due to the short distance (L), such reflection occurs. If the mirror 250 is formed continuously with the emission window 600, the light emitted from the emission window 600 to the reflection mirror 250 is reflected by the mirror surface of the reflection mirror 250 and reaches the light receiving component. Therefore, it is possible to solve the problem that the distance (L) between the entrance window 700 and the exit window 600 of the optical coupling mirror 500 becomes short.

[0083]

Next, the optical coupling mirror of the present invention will be described with reference to more specific design examples. The following embodiments are all preferable examples of the present invention, and the present invention is not limited to the numerical conditions mentioned in the embodiments.

<First Embodiment> In this example, an LED whose light emitting surface has a diameter of 260 μm is used as a light source, and a light receiving surface, that is, an optical fiber whose core diameter is 1 mm is used as a light receiving component.

An optical coupling mirror for efficiently coupling the light emitted from the LED with an optical fiber with a small NA is designed.

From the above equations (1) to (3), the rotational movement angle of the first parabola whose focus is the origin is θ, and the radius of the light source is Di.
If n, the second parabola is represented by the above equation (4).

Next, since the diameter of the core of the optical fiber for coupling light is 1 mm, this embodiment is designed to couple the light within the diameter range of 900 μm within this diameter.

Therefore, Dout of the above equation (6) is 0.45 m
m (450 μm).

Next, in this example, the reflected light from the optical coupling mirror is 2
Avoid reflections. Therefore, the above equation (7) is added to the design conditions.

Further, the maximum incident angle of the direct incident light incident on the optical fiber and the maximum incident angle of the reflected light are made substantially equal to each other.

Therefore, from the above equations (8) and (9), the rotational movement angle (θ) of the first parabola is set so that the NA of the direct incident light and the NA of the reflected light are substantially equal and the minimum value is obtained. ) And the length of a part of the curve. The length of a part of the curve corresponds to the distance (L) between the entrance window and the exit window of the optical coupling mirror. Therefore, the curve cut at the intersection of the second parabola and the optical axis is further cut at the focal position. Then, according to the distance (L) obtained by the calculation, the curved portion on the opposite side (optical fiber side) from the focus is cut.

In this example, θ is 9.5 ° and L is 3.
A value of 5 mm was calculated.

As a result, the part 30 of the curve for constructing the optical coupling mirror becomes as shown by the thick line in FIG. Then, the cross-section cut along the xy coordinate plane of the optical coupling mirror obtained by rotating a part 30 of this curve is indicated by a thick line 30 and a thin line 32 (FIG. 12).

According to this optical coupling mirror, the light (H) directly incident on the optical fiber from the ends Q ₁ and Q _{2 of} the LED at the maximum incident angle that can be coupled to the optical fiber, and the rotation axis (x-axis) from the LED. ), The reflected light (h) of the light emitted perpendicularly to
There is no danger of interference with the optical coupling mirror. These lights H and h
Are all shown by dotted lines in FIG.

As a result, the NA of the light entering the optical fiber from the optical coupling mirror can be 0.20. And
The theoretical optical coupling efficiency at this time is such that the reflectance of the mirror surface of the optical coupling mirror is 90% and the loss due to Fresnel reflection is 7.6%.
Even so, a high efficiency of 90% can be obtained.

<Second Embodiment> As a second embodiment, the rotational movement angle (θ) of the first parabola is set so that the second parabola after rotational movement is parallel to the rotation axis and from the focal point to the aperture of the core. An example will be described in which the angle is such that a straight line separated by a predetermined distance of half or less is in contact with one point.

Here, 0.45 mm from the origin (focus)
Make the separated straight line (y = 0.45) and the second parabola touch at one point. Then, the curve is cut at the contact point.

Therefore, the distance L between the entrance window and the exit window is L
Corresponds to the value of x when y of the second parabola becomes 0.45.

As a result of the calculation, θ was 9.7 °. Then, the point where the second parabola and the straight line (y = 0.45) contact is L =
The position was 2.6 mm.

Therefore, a part 40 of the curve forming the optical coupling mirror of this embodiment becomes a curve shown by the thick line in FIG. The cross section of the optical coupling mirror obtained by rotating a part 40 of this curve along the xy coordinate plane is shown in FIG.
3 is indicated by a thick line 40 and a thin line 42.

The optical coupling mirror of this example has a tubular shape such that the diameter of a circle formed in a cross section perpendicular to the optical axis (x axis) from the entrance window 44 to the exit window 46 is large. Therefore, for example, when a mold of resin is formed using a mold that reflects the mirror surface shape of the optical coupling mirror, and a metal is vapor-deposited on the outside of the resin to manufacture an optical coupling mirror, Since the exit window 46 of the optical coupling mirror has the largest diameter, it is easy to take out the resin inside the deposited metal. Therefore, there is an advantage that it is easier to manufacture than the optical coupling mirror of the first embodiment.

However, the distance (L) between the entrance window 44 and the exit window 46 of the optical coupling mirror of this embodiment is shorter than that of the optical coupling mirror of the first embodiment. Therefore, the light (H) that can enter the optical fiber at the maximum incident angle from the end of the LED
Light (J) at an angle larger than (dotted line in FIG. 13) by Δθ
Light in the angular range up to (the one-dot chain line in FIG. 13) is not reflected by the optical coupling mirror, and cannot be directly coupled to the optical fiber as incident light.

Further, since the rotational movement angle (θ) of the first parabola becomes larger than that in the first embodiment, the incident angle of the reflected light to the optical fiber becomes large, so that the NA may increase. is there. In this embodiment, the rotational movement angle (θ)
In comparison with the first embodiment, the change of the angle is as small as 0.2 °, so that the NA does not increase so much.

In this example, the NA of the light entering the optical fiber from the optical coupling mirror was 0.22.

In the first and second embodiments, the NA of the light incident on the optical fiber can be set to about 0.2.
As a result, the conventional S in which the NA of the optical fiber is 0.5
Even if I-POF (step index type plastic optical fiber) 100 m is used, the communication frequency band can be 100 MHz or more.

<Third Embodiment> As a third embodiment, an example using an LED having a light emitting surface with a diameter of 200 μm will be described. Hereinafter, points different from the first and second embodiments will be described, and detailed description of the same points will be omitted.

The optical coupling mirror is designed under the same conditions as in the first embodiment except for the light source.

As a result, the rotational movement angle (θ) of the first parabola
Is 7.1 °, the distance from the entrance window to the exit window (L)
Was 4.4 mm.

Therefore, the smaller the entrance window (smaller diameter of the light emitting surface of the light source), the smaller the rotational movement angle of the first parabola, and the longer the distance from the entrance window to the exit window of the optical coupling mirror. Become.

Further, the NA of the light incident on the optical fiber from the optical coupling mirror of this embodiment was 0.15, which was a very low value.

<Fourth Embodiment> As a fourth embodiment, an LED having a light-emitting surface with a diameter of 200 μm is used as in the third embodiment.
And the optical coupling mirror is designed under the same conditions as in the second embodiment except for the light source.

As a result, the rotational movement angle (θ) of the first parabola
Was 7.2 °. Also, with the second parabola, y = 0.45
The position of the contact point with the straight line was a position where the distance between the entrance window and the exit window of the optical coupling mirror was 3.6 mm.

Rotational movement angle (θ) of the first parabola in this example
And the rotational movement angle (θ) of the third embodiment is 0.1 °.
It was a little. Therefore, the NA of the light entering the optical fiber from the optical coupling mirror is 0.15, which is the same as that in the third embodiment.
That was a low value.

In the third and fourth embodiments, the NA of the light incident on the optical fiber can be made smaller than that in the first and second embodiments. This can be expected to further widen the frequency band.

<Fifth Embodiment> As a fifth embodiment, an example using an LED having a light emitting surface with a diameter of 300 μm will be described. Hereinafter, differences from the first to fourth embodiments will be described, and detailed description of the same points will be omitted.

The optical coupling mirror is designed under the same conditions as in the first embodiment except for the light source.

As a result, the rotational movement angle (θ) of the first parabola
Was 11.3 °, and the distance (L) from the entrance window to the exit window was 3.0 mm.

The NA of the light incident on the optical fiber from this optical coupling mirror was 0.24, and a sufficiently low NA value was obtained for the light incident on the optical fiber.

<Sixth Embodiment> As a sixth embodiment, an LED whose light emitting surface has a diameter of 300 μm as in the fifth embodiment.
And the optical coupling mirror is designed under the same conditions as in the second embodiment except for the light source.

As a result, the rotational movement angle (θ) of the first parabola
Became 11.5 °. Also, with the second parabola, y = 0.45
The position of the contact point with the straight line was a position where the distance between the entrance window and the exit window of the optical coupling mirror was 2.2 mm.

The NA of the light incident on the optical fiber from this optical coupling mirror was 0.26. This NA value is larger than the NA value of the optical coupling mirror of the fifth embodiment, but is within a range that can be sufficiently utilized.

In the fifth and sixth embodiments, the NA of the light incident on the optical fiber is 0.24 to 0.26.
This is a large size L with a light emitting surface diameter of 300 μm.
Considering that the ED is used, the NA is much lower than the conventional one. Therefore, the frequency band can be made much wider than before.

Incidentally, the distance between the entrance window and the exit window of the designed optical coupling mirror becomes short, which makes it difficult to connect the optical coupling mirror and the light receiving component, and the short distance causes a problem. In this case, a cylindrical reflecting mirror may be provided so as to communicate with the emitting end face of the optical coupling mirror. This reflecting mirror has an end face having the same shape as the emitting end face of the optical coupling mirror. Then, it is assumed that it extends along the extension line of the rotation axis (optical axis) substantially parallel to the extension line. As a result, the light that has entered the reflecting mirror from the emission end face of the optical coupling mirror is reflected by the mirror surface of the reflecting mirror and reaches the light receiving component. Therefore, it is possible to solve the problem caused by the reduction in the distance between the entrance window and the exit window of the optical coupling mirror.

[0124]

As is apparent from the above description, the optical coupling mirror of the present invention can be obtained by the following design. First, the first parabola having the optical axis between the light source and the light receiving component as the axis of symmetry is rotationally moved around the focal point of the first parabola. The parabola obtained by this is referred to as a second parabola.
The second parabola and the symmetry axis of the first parabola intersect at two intersections. Then, a part of the curve cut at this intersection is rotated with the axis of symmetry of the first parabola as the axis of rotation. The cylindrical rotary mirror obtained by this rotation is called an optical coupling mirror.

In such a rotating surface mirror, the curve forming the rotating surface is a curve closer to the rotation axis than a parabola (first parabola) having the rotation axis as the axis of symmetry. Moreover, it is possible to install a large-sized light source in the rotary mirror.
Therefore, the amount of light reflected by the mirror surface and reaching the light receiving surface can be increased. Therefore, the coupling loss can be reduced,
The optical coupling efficiency can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic concept of the present invention.

2A and 2B are explanatory diagrams of the basic concept of the present invention.

FIG. 3 is an explanatory diagram of a basic concept of the present invention.

4A to 4C are schematic design process diagrams of the optical coupling mirror of the present invention.

5A to 5C are design process diagrams of the optical coupling mirror following FIG.

FIG. 6 is a graph showing the relationship between the distance from the entrance window to the exit window of the optical coupling mirror and the NA of the light emitted from the optical coupling mirror, which is used in the description of the first embodiment; It is a characteristic view shown for every.

FIG. 7 is a diagram showing the relationship between the distance between the entrance window and the exit window and the NA of the exit light for each size of the light source, which is used in the description of the second embodiment.

FIG. 8 is a characteristic diagram showing the characteristics of the distance between the entrance window and the exit window with respect to the rotational movement angle of the first parabola for each size of the light source, which is used in the description of the second embodiment.

FIG. 9A is a design diagram showing an application example of an optical coupling mirror, and FIG. 9B is a configuration diagram of an optical coupling mirror of the application example.

10A is a design diagram showing another application example of the optical coupling mirror, and FIG. 10B is a configuration diagram of the optical coupling mirror of this application example.

FIG. 11 is a configuration diagram showing an application example of an optical coupling mirror.

FIG. 12 is a diagram schematically illustrating a part of a curve forming an optical coupling mirror and a cross section of the optical coupling mirror, which is used in the description of the first embodiment.

FIG. 13 is a diagram schematically illustrating a part of a curve forming an optical coupling mirror and a cross section of the optical coupling mirror, which is used in the description of the second embodiment.

[Explanation of symbols]

12, 100: First parabola 14: Line segment 16,200: Second parabola 18,300: Curve 20: First intersection 22, 30, 40, 400, 400a, 400b: Part of curve (thick line, partial curve) ) 24: Optical coupling mirrors 26, 44: Incident windows 28, 46: Output windows 32, 42: Fine line 150: Window 250: Reflecting mirror 500: Rotating surface (optical coupling mirror) 600: Opening on the light receiving component side (emission window) ) 650: Light receiving component 660: Light receiving surface 700: Light source side opening (incident window) 750: Light source 770: Light emitting surface 800: Outgoing light passing through end Q ₁ to end R 900: End Q ₂ to end R Outgoing light passing through

Claims (5)

[Claims] 1. An optical coupling mirror for coupling light from a light source to a light receiving surface of a light receiving component, wherein a first parabola having an optical axis between the light source and the light receiving component as an axis of symmetry is a focal point of the first parabola. The parabola rotated about the center as a second parabola, the second parabola, a part of the curve of the second parabola cut at two intersections of the axis of symmetry of the first parabola,
An optical coupling mirror, characterized in that it is composed of a cylindrical rotary mirror obtained by rotating about a symmetry axis of the first parabola as a rotation axis. 2. The optical coupling mirror according to claim 1, wherein the focal point is a center of a light emitting surface of the light source, and the light receiving surface is arranged on an extension line of the rotation axis, the light receiving surface is received from the light source. The average numerical aperture value of the numerical aperture of the direct incident light that directly enters the surface and the numerical aperture of the reflected light that reaches the light receiving surface after being reflected from the light source by the mirror surface is smaller than the numerical aperture of the light source. Thus, the rotation coupling angle of the first parabola and a part of the curve are determined. 3. The optical coupling mirror according to claim 1, wherein the focal point is the center of the light emitting surface of the light source, and the light receiving surface is arranged on an extension line of the rotation axis. When the reflected light that is reflected mainly on the mirror surface of the optical coupling mirror among the emitted light of (1) is coupled to the light receiving surface, the first numerical value is set so that the numerical aperture of the reflected light is minimized.
An optical coupling mirror, wherein a rotational movement angle of a parabola and a part of the curve are determined. 4. The optical coupling mirror according to claim 1, wherein the focal point is a center of a light emitting surface of the light source, and the light receiving surface is arranged on an extension line of the rotation axis, the light receiving surface is received from the light source. The first parabola so that the maximum incident angle of the direct incident light that is directly incident on the surface and the maximum incident angle of the reflected light that reaches the light receiving surface after being reflected by the light source on the mirror surface are substantially equiangular. An optical coupling mirror characterized in that the rotational movement angle of is determined. 5. The optical coupling mirror according to claim 4, wherein two ends of the light emitting surface which intersect the straight line which is perpendicular to the rotation axis and which passes through the focus are flush with the curve and the rotation axis. An end located on the curved side with respect to the rotation axis as a first end of the two ends, and an end located on the opposite side to the curved side with respect to the rotation axis. When the portion is the second end, a part of the curve is a straight line representing the direct incident light emitted from the second end of the light emitting surface and incident on the light receiving surface at the maximum incident angle, and the curve. An optical coupling mirror, which is obtained by cutting the curve at an intersection.