JP2007003622A - Optical transmitter module, optical receiver module, and optical transceiver system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter module having a wide allowable range in a mounting error between an optical coupling device and a light emitting element. <P>SOLUTION: The optical transmitter module includes a light emitting element 103, a multimode optical fiber 105, and a core member 107 which guides light from the light emitting element 103 to the multimode optical fiber 105 and which is covered with a clad member 108, wherein the core member 107 is such that its end face 107b on the light emitting element side, in the view from the optical path direction, is greater than the end face of the core 109 of the multimode optical fiber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical transmission module, an optical reception module, and an optical transmission / reception system that realize optical signal communication, and more particularly, to a technique for reducing manufacturing costs more than before without sacrificing optical coupling efficiency.

  In recent years, the demand for high-speed signal transmission technology has increased rapidly in the interior of PCs, between PCs and displays, between AV devices and displays, between AV devices, and the like. Generally, electric signals are used for such short-distance signal transmission. However, electrical signals are said to have a barrier to speeding up at a transmission rate of about 5 Gbps due to problems such as electromagnetic radiation. Therefore, high-speed signal transmission technology using an optical signal instead of an electric signal has attracted much attention.

In the optical transmission / reception system, it is necessary to improve the optical coupling efficiency between the light emitting element and the multimode optical fiber and between the multimode optical fiber and the light receiving element in order to suppress loss of signal intensity. As a means for this, there is a technique for suppressing optical axis deviation and arrangement deviation by improving mounting accuracy.
For example, in Patent Document 1, a concave portion and a convex portion are formed with high precision in advance on a substrate main surface of a light emitting element and an optical coupling device to which a multimode optical fiber is fixed. An optical transmission module is disclosed in which the light emitting element and the optical coupling device are aligned with high precision by being fitted. By doing so, the mounting accuracy between the light emitting element and the optical coupling device is improved, and as a result, the optical coupling efficiency can be improved.
JP-A-10-223985

In order to use the optical transmission / reception system for consumer devices such as PCs and AV devices, it is important to reduce the cost of the optical transmission module.
However, in Patent Document 1, high precision is required for forming the concave portions and the convex portions for alignment between the light emitting element and the optical coupling device, and the manufacturing cost increases accordingly. Further, not only the optical transmission module but also the optical reception module has the same problem regarding the alignment of the light receiving element and the optical coupling device.

A first object of the present invention is to provide an optical transmission module that can be manufactured at a lower cost than before without sacrificing optical coupling efficiency.
A second object of the present invention is to provide a light receiving module that can be manufactured at a lower cost than before without sacrificing optical coupling efficiency.
It is a third object of the present invention to provide an optical transmission / reception system that can be manufactured at a lower cost than conventional ones.

In order to achieve the first object, an optical transmission module according to the present invention is coated with a light emitting element, a multimode optical fiber, and a cladding member that guides light from the light emitting element to the multimode optical fiber. A core member, and the end surface on the light emitting element side when viewed in the optical path direction is wider than the core end surface of the multimode optical fiber.
In order to achieve the second object, an optical receiver module according to the present invention is coated with a light receiving element, a multimode optical fiber, and a cladding member that guides light from the multimode optical fiber to the light receiving element. A core member, and the core member has an end surface on the light receiving element side that is narrower than a core end surface of the multimode optical fiber when viewed in the optical path direction.

  In order to achieve the third object, an optical transmission / reception system according to the present invention is an optical transmission / reception system in which an optical transmission module and an optical reception module are optically coupled by a multimode optical fiber, and the optical transmission module includes: A light-emitting element; and a first core member coated with a cladding member that guides light from the light-emitting element to one end of the multi-mode optical fiber. The light receiving module includes a light-receiving element and the multi-mode light. A second core member coated with a cladding member that guides light from the other end of the fiber to the light receiving element, and the first core member has an end surface on the light emitting element side when viewed in the optical path direction. The second core member is wider than the core end surface of the multimode optical fiber, and the end surface on the light receiving element side when viewed in the optical path direction is narrower than the core end surface of the multimode optical fiber.

  According to the configuration described in the means for solving the problem, since the end face on the light emitting element side is widened, the mounting error between them can be reduced without sacrificing the optical coupling efficiency between the light emitting element and the core member. The permissible range can be expanded more than before. In general, if the allowable range of mounting errors is wide, the manufacturing cost is reduced. Therefore, the optical transmission module can be manufactured at a lower cost than in the past. The core member is a part of the configuration of the optical coupling device.

  Further, according to the configuration described in the means for solving the problem, the end face on the light receiving element side is narrowed, so that the optical coupling efficiency between the light receiving element and the core member is not sacrificed between them. The allowable range of mounting error can be expanded as compared with the conventional case. In general, if the allowable range of mounting errors is wide, the manufacturing cost is reduced. Therefore, the optical receiving module can be manufactured at a lower cost than the conventional one.

Moreover, according to the structure described in the means for solving a subject, an optical transmission / reception system consists of the optical transmission module and optical reception module which were mentioned above. Therefore, similarly to the above, the optical transmission / reception system can be manufactured at a lower cost than the conventional one.
The core member may have a portion whose thickness continuously decreases toward the multimode optical fiber and may not have a portion whose thickness increases toward the multimode optical fiber.

By continuously reducing the thickness as described above, it is possible to reduce the loss of signal strength in the core member, rather than reducing the thickness stepwise.
The core member may have a portion having a constant thickness by a predetermined distance from the end surface on the light emitting element side toward the multimode optical fiber.
By making the thickness constant for a predetermined distance as described above, it is possible to reduce the loss of signal strength in the core member rather than making the entire core member tapered.

In addition, the end surface of the core member on the light emitting element side is inclined by approximately 45 degrees with respect to the light emitting surface of the light emitting element, and the light emitted from the light emitting surface of the light emitting element is the end surface of the core member on the light emitting element side. The light emitting element and the core member may be disposed at a relational position that reflects to the end surface on the multimode optical fiber side.
According to the above configuration, even if light is incident on the end surface of the core member on the light emitting element side from the direction orthogonal to the core axis, the incident light can be bent by approximately 90 degrees in the core axis direction. Therefore, even if the light emitting element is arranged so as to emit light in the direction perpendicular to the substrate, the light can be extracted in the direction parallel to the substrate, so that the multimode optical fiber can be easily handled.

The end surface of the core member on the light emitting element side may be in contact with air.
According to the above configuration, since the ratio of the refractive index at the end face is large, the reflectance can be increased.
In addition, a light reflecting member may be disposed on the end surface of the core member on the light emitting element side.

According to the said structure, the reflectance in an end surface can further be raised depending on conditions.
The light emitting element and the core member are arranged such that an optical distance between the light emitting element side end surface of the core member and the light emitting element is within 500 μm, and the core member is viewed in the optical path direction. The diameter of the end face on the light emitting element side may be 100 μm to 120 μm.

  According to the above configuration, when a general surface emitting laser is employed as the light emitting element, the optical coupling efficiency between the surface emitting laser and the multimode optical fiber is ensured to be −5 dB or more, and the surface emitting laser, the core member, It is possible to secure 50 μm or more as an allowable range of the mounting error. If the allowable range of mounting error can satisfy the condition of 50 μm or more, mounting by outer shape recognition becomes possible.

The core member may further have an end surface on the multimode optical fiber side that is narrower than a core end surface of the multimode optical fiber when viewed in the optical path direction.
According to the above configuration, not only between the light emitting element and the core member, but also the tolerance of the mounting error between the multimode optical fiber and the core member can be expanded. Therefore, the optical transmission module can be manufactured at a lower cost.

The core member may have a diameter of an end surface on the multimode optical fiber side that is 60% to 80% of a core diameter of the multimode optical fiber.
According to the above configuration, it is possible to suppress the loss due to the misalignment between the core member and the multimode optical fiber to a level at which the loss can be ignored.
Two or more light-emitting elements, the same number of multi-mode optical fibers as the light-emitting elements, and the clad member that guides light from each light-emitting element to the multi-mode optical fiber corresponding to each light-emitting element, The core members have the same number of core members as the light emitting elements, and each of the core members has an end face on the light emitting element side as viewed in the optical path direction wider than the core end face of the multimode optical fiber, and all the core members have a predetermined pitch. The light emitting elements may be formed as a single chip at the predetermined pitch.

According to the above configuration, in addition to the same effect as described above, a plurality of sets of the core member and the light emitting element can be mounted in a lump so that an effect of further reducing the mounting cost can be achieved. .
In addition, the end surface of the core member on the light receiving element side is inclined by approximately 45 degrees with respect to the light receiving surface of the light receiving element, and the light incident from the multimode optical fiber is reflected by the end surface of the core member on the light receiving element side. Then, the light receiving element and the core member may be arranged at a relational position toward the light receiving surface of the light receiving element.

According to the above configuration, the light propagated through the core member can be bent by approximately 90 degrees in the direction perpendicular to the core axis at the end surface of the core member on the light receiving element side. Therefore, since the light propagated in the substrate parallel direction can be received by the light receiving surface directed in the substrate vertical direction, the handling of the multimode optical fiber can be facilitated.
The end surface of the core member on the light receiving element side may be in contact with air.

According to the above configuration, since the ratio of the refractive index at the end face is large, the reflectance can be increased.
In addition, a light reflecting member may be disposed on the end surface of the core member on the light receiving element side.
According to the said structure, the reflectance in an end surface can further be raised depending on conditions.

The light receiving element and the core member are arranged such that an optical distance between the light receiving element side end surface of the core member and the light receiving element is within 500 μm, and the core member is viewed in the optical path direction. The diameter of the end face on the light receiving element side may be 40 μm to 60 μm.
According to the above configuration, −5 dB or more can be secured as the optical coupling efficiency between the light receiving element and the multimode optical fiber, and 50 μm or more can be secured as an allowable range of mounting errors between the light receiving element and the core member.

The core member may further have an end surface on the multimode optical fiber side wider than the core end surface of the multimode optical fiber when viewed in the optical path direction.
According to the above configuration, not only between the light receiving element and the core member but also an allowable range of mounting error between the multimode optical fiber and the core member can be expanded. Therefore, the optical receiver module can be manufactured at a lower cost.

The core member may have a diameter of an end surface on the multimode optical fiber side that is 120% to 140% of a core diameter of the multimode optical fiber.
According to the above configuration, it is possible to suppress the loss due to the misalignment between the core member and the multimode optical fiber to a level at which the loss can be ignored.
Also, two or more light receiving elements, the same number of multimode optical fibers as the light receiving elements, and a clad member that guides light from each multimode optical fiber to the light receiving element corresponding to each multimode optical fiber. And the same number of core members as the light receiving elements, each of the core members having an end surface on the light receiving element side when viewed in the optical path direction is narrower than the core end surface of the multimode optical fiber, and all the core members are The light emitting elements may be integrally formed at a predetermined pitch, and all the light emitting elements may be formed on the same chip at the predetermined pitch.

  According to the above configuration, in addition to the same effect as described above, a plurality of sets of the core member and the light receiving element can be mounted in a lump so that the mounting cost can be further reduced. .

The best mode for carrying out the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
1 is a cross-sectional view of an optical axis of an optical transmission module according to Embodiment 1. FIG.
FIG. 2 is a top view of the optical transmission module according to the first embodiment.
The optical transmission module 101 includes an electric circuit board 102, a light emitting element 103, an optical coupling device 104, a multimode optical fiber 105, and a refractive index matching gel 106.

The light emitting element 103 is a general surface emitting laser, and is disposed on the electric circuit substrate 102 so as to emit light in a direction perpendicular to the substrate.
The optical coupling device 104 includes two core members 107 and a clad member 108. The core member 107 is disposed between the optical paths between the light emitting element 103 and the multimode optical fiber 105. The clad member 108 covers the two core members 107. As the material of the core member 107 and the clad member 108, general materials used for the core and clad of the multimode optical fiber can be used. Note that the end surface 107 b on the light emitting element side of the core member 107 is inclined by approximately 45 degrees with respect to the light emitting surface 103 a of the light emitting element 103. With this configuration, the light from the light emitting element 103 is bent by approximately 90 degrees in the direction of the core shaft 107 a at the end face 107 b and propagates inside the core member 107.

The multimode optical fiber 105 is a general multimode fiber including a core 109 and a clad 110, and is fixed at a position where the core axis coincides with the core axis 107 a of the core member 107.
The refractive index matching gel 106 is disposed between the optical paths of the light emitting element 103 and the optical coupling device 104 for shortening the optical distance and preventing reflection.

Since the core member 107 has main features in the present invention, the core member 107 will be described in detail below.
(1) The core member 107 is characterized in that the end face 107b on the light emitting element side is wider than the core end face of the multimode optical fiber 105 when viewed in the optical path direction. With this configuration, it is possible to widen the allowable range of mounting error between the light emitting element 103 and the core member 107 as compared with the related art.
(2) The core member 107 is characterized in that the end surface 107c on the multimode optical fiber side is narrower than the core end surface of the multimode optical fiber 105 when viewed in the optical path direction. With this configuration, it is possible to widen the allowable range of mounting errors between the core member 107 and the multimode optical fiber 105.
(3) The core member 107 includes a first section 107d, a tapered section 107e, and a second section 107f along the core axis 107a from the end face 107b on the light emitting element side to the end face 107c on the multimode optical fiber side.

The core diameter of the first section 107d is maintained at the core diameter on the end face 107b on the light emitting element side. In the taper section 107e, the core diameter continuously decreases gradually toward the multimode optical fiber. The core diameter of the second section 107f is maintained at the core diameter on the end surface 107c on the multimode optical fiber side. By continuously reducing the thickness of the core member 107 as in the tapered section 107e, it is possible to reduce the loss of signal strength in the core member 107 rather than reducing it in a stepped manner. Further, by providing a section having a constant thickness by a predetermined distance such as the first section 107d and the second section 107f, the loss of signal strength in the core member 107 can be reduced rather than making the entire core member 107 tapered. Can be reduced.
(4) Regarding the diameter of the end surface 107b on the light emitting element side, specifically, the light emitting element 103 and the core member 107 are arranged so that the optical distance between the core shaft 107a and the light emitting surface 103a of the light emitting element is within 500 μm. In the case of the specified specifications, it is adjusted to be 100 μm to 120 μm when viewed in the core axis direction.

The lower limit of 100 μm is necessary to satisfy the following two conditions.
First condition: -5 dB or more is secured as an optical coupling efficiency (including a loss due to mounting dislocation) between the light emitting element 103 and the multimode optical fiber 105.
Second condition: 50 μm or more is secured as an allowable range (mounting tolerance) of mounting error between the light emitting element 103 and the core member 107.

In particular, the second condition is indispensable for mounting the optical coupling device 104 by outer shape recognition.
FIG. 3 is a diagram showing the relationship between the optical coupling efficiency and the allowable range of mounting error for each of the three types of core diameters.
Note that the radiation angle of light from the light emitting element 103 is assumed to be 17 degrees or less, which is a typical value of a multimode type surface emitting laser. As can be seen from FIG. 3, in order to ensure an optical coupling efficiency of -5 dB and an allowable range of mounting error of 50 μm, it is necessary to set the core diameter to 100 μm or more.

The upper limit of 120 μm is determined in terms of the cost of the optical coupling device 104. That is, the larger the diameter of the core member 107, the more difficult the forming process is, and thus the manufacturing cost increases. Therefore, it is desirable that the diameter of the core member 107 is smaller for cost reduction. In this case, it is appropriate to set the thickness to about 120 μm.
(5) Specifically, the diameter of the end face 107c on the multimode optical fiber side is adjusted to be 60% to 80% of the core diameter of the multimode optical fiber 105. In the case of a general multimode fiber, the multimode optical fiber 105 has a core diameter of 50 μm and a core eccentricity of about 2 μm. The mounting accuracy between the optical coupling device 104 and the multimode optical fiber 105 can be easily increased to several μm by using an optical bench 111 as shown in FIG. Assuming that the worst mounting accuracy is 10 μm, in order to suppress the loss due to the misalignment between the core member 107 and the core 109 of the multimode optical fiber 105 to a level that can be ignored, the multimode optical fiber of the core member 107 is used. The diameter of the end face 107c on the side is preferably 60% to 80% of the diameter of the core 109 of the multimode optical fiber 105.

As shown in FIG. 4, the optical bench 111 has a multimode optical fiber positioning groove 112 and an optical coupling device positioning groove 113. The accuracy of these grooves can be secured to about 10 μm by fabricating the optical bench 111 by performing anisotropic etching on a silicon substrate or molding a plastic material with a precision mold.
If the multimode optical fiber 105 is a silica-based GI (Grated Index) type multimode product with a diameter of 125 μm, it can be mass-produced without deterioration in quality up to a core diameter of less than 110 μm with the current general-purpose technology. . Assuming that a GI type multimode fiber having a core diameter of 100 μm is used, if the end surface 107c on the multimode optical fiber side of the core member 107 is set to 60 μm to 80 μm, a sufficient mounting tolerance is ensured and the loss is ignored. It can be made as small as possible.
(6) The difference in diameter at both ends of the core member 107 is desirably as small as possible. The degree of gradual decrease in the diameter of the tapered section 107e is determined in consideration of optical signal loss due to light emission and crosstalk between channels. Since the taper section 107e is shortened as the difference in diameter is reduced, the optical coupling device 104 can be reduced in size and cost.

The optical coupling device 104 can be manufactured by a known technique such as mold forming.
1 and 2 show only optical components in order to clarify the features of the present invention, but the actual optical transmission module 101 also includes electronic components as shown in FIGS.
FIG. 5 is a side view of the optical transmission module according to the first embodiment.

FIG. 6 is a top view of the optical transmission module according to the first embodiment.
The optical coupling device 104 is fixed to the electric circuit board 102 by the optical bench 111. A light emission driving element 114 is mounted on the main surface of the electric circuit board 102. The light emission driving element 114 receives an electric signal through the electric wiring 115, modulates the electric signal, and supplies the modulated signal to the light emitting element 103 through the electric wiring 116. The electric wiring 116 and the electrode of the light emitting element 103 are bonded by a wire 117.

Next, a method for manufacturing the optical transmission module 101 will be described.
Step S1: The light emission drive element 114 and other electrical components are mounted on the electric circuit board 102. The mounting accuracy of the electrical components is designed to such an extent that no short circuit between the lines occurs.
Step S2: The light emitting element 103 is mounted at the light emitting element mounting position of the electric circuit board 102, and wiring is performed. The mounting accuracy of the light emitting element 103 is not particularly specified.

Step S3: The optical coupling device 104 is fitted into the optical coupling device positioning groove 113 of the optical bench 111 and fixed.
Step S4: The optical coupling device 104 is aligned with the light emitting element 103 by image recognition, and the optical bench 111 is fixed to the electric circuit board 102. Since the allowable range of mounting error between the light emitting element 103 and the optical coupling device 104 is designed to be 50 μm, even if alignment by image recognition is adopted, it can be within the allowable range of mounting error.

Step S5: The multimode optical fiber 105 is fitted into the multimode optical fiber positioning groove 112 of the optical bench 111 and fixed. Since the optical bench 111 is precisely molded with an error of about 10 μm, high-precision mounting can be realized simply by fitting the optical coupling device 104 and the multimode optical fiber 105 into the grooves 112 and 113.
Step S6: Fill the gap between the light emitting element 103 and the optical coupling device 104 with the refractive index matching gel 106. At this time, care is taken so that the gel 106 does not enter the end face 107b on the light emitting element side.

By mounting in this way, the optical transmission module 101 can be easily produced if a mounting apparatus having a mounting error of 50 μm is prepared.
(Embodiment 2)
FIG. 7 is a cross-sectional view of the optical axis of the optical receiver module according to the second embodiment.
FIG. 8 is a top view of the optical receiver module according to the second embodiment.

The optical receiver module 201 includes an electric circuit board 202, a light receiving element 203, an optical coupling device 204, a multimode optical fiber 205, and a refractive index matching gel 206.
The light receiving element 203 is a general PIN photodiode, and is disposed on the electric circuit substrate 102 so that the light receiving surface faces in the direction perpendicular to the substrate.
The optical coupling device 204 includes two core members 207 and a clad member 208. The core member 207 is disposed between the optical paths between the light receiving element 203 and the multimode optical fiber 205. The clad member 208 covers the two core members 207.

The multimode optical fiber 205 is a general multimode fiber including a core 209 and a clad 210, and is fixed to the optical coupling device 204 so that the core axis thereof coincides with the core axis of the core member 207. With such a configuration, the light from the multimode optical fiber 205 propagates through the core member 207 and enters the light receiving element 203.
The refractive index matching gel 206 is disposed between the optical paths of the light receiving element 203 and the optical coupling device 204 for shortening the optical distance and preventing reflection.

Since the present invention has main features in the core member 207, the core member 207 will be described in detail below.
(1) The core member 207 is characterized in that the end surface 207b on the light receiving element side is narrower than the core end surface of the multimode optical fiber 205 when viewed in the optical path direction. With this configuration, it is possible to widen the allowable range of mounting error between the light receiving element 203 and the core member 207 as compared with the conventional case.
(2) The core member 207 is characterized in that the end surface 207 c on the multimode optical fiber side is wider than the core end surface of the multimode optical fiber 205 when viewed in the optical path direction. With this configuration, the allowable range of mounting error between the core member 207 and the multimode optical fiber 205 can be expanded as compared with the conventional case.
(3) The core member 207 includes a first section 207d, a tapered section 207e, and a second section 207f along the core axis 207a from the end face 207b on the light receiving element side to the end face 207c on the multimode optical fiber side.

The core diameter of the first section 207d is maintained at the core diameter on the end face 207b on the light receiving element side. In the taper section 207e, the core diameter gradually decreases toward the light receiving element. The core diameter of the second section 207f is maintained at the core diameter on the end surface 207c on the multimode optical fiber side. By continuously reducing the thickness of the core member 207 as in the tapered section 207e, it is possible to reduce the loss of signal strength in the core member 207 rather than reducing it in a stepped manner. Further, by providing a section having a constant thickness by a predetermined distance, such as the first section 207d and the second section 207f, the loss of signal strength in the core member 207 can be reduced rather than the entire core member 207 being tapered. Can be reduced.
(4) Regarding the diameter of the end surface 207b on the light receiving element side, specifically, the light receiving element 203 and the core member 207 are arranged so that the optical distance between the core shaft 207a and the light receiving surface 203a of the light receiving element is within 500 μm. In the case of the specifications, the thickness is adjusted to be 40 μm to 60 μm when viewed in the core axis direction.

FIG. 9 is a diagram showing the relationship between the optical coupling efficiency and the allowable range of mounting errors for each of the three types of core diameters.
Note that the light receiving diameter of the light receiving element 203 is assumed to be 80 μm and 100 μm. According to FIG. 9, it can be seen that, if the optical coupling efficiency is the same, the allowable range of mounting error can be increased as the core diameter is reduced. However, if the diameter of the core member 207 is smaller than 40 μm, multimode transmission cannot be performed. Therefore, the diameter of the end face 207b on the light receiving element side must be 40 μm or more.

On the other hand, the light receiving diameter of the light receiving element 203 needs to be increased in order to improve the optical coupling efficiency, but needs to be decreased in order to improve the communication speed. Therefore, the light receiving diameter is determined by these balances.
As shown in FIG. 10, there is a correlation between the communication speed and the light receiving sensitivity, and it is necessary to improve the light receiving sensitivity in order to improve the communication speed. In order to improve the light receiving sensitivity, it is necessary to reduce the electric capacity. For this purpose, it is necessary to reduce the light receiving surface. The electric capacity is caused by a signal conversion element 214 described later. Usually, when a communication speed of about 3 Gbps is guaranteed, the light receiving diameter of the light receiving element 203 can be about 100 μm. If it is 4 Gbps, it is about 80 μm, and if it is 10 Gbps, it is about 40 to 50 μm. That is, to increase the communication speed, the light receiving diameter must be reduced.

Considering the above points, it can be seen that the light receiving diameter of the light receiving element 203 and the diameter of the end face of the core member 207 on the light receiving element side need to be optimized according to the communication speed.
Assuming a communication speed of about 2.5 Gbps per channel, it is appropriate that the light receiving diameter of the light receiving element 203 is 100 μm and the diameter of the core member 207 is 40 to 60 μm. Within this range, the following two conditions can be satisfied.

First condition: -5 dB or more is secured as an optical coupling efficiency (including a loss due to mounting dislocation) between the light emitting element 103 and the multimode optical fiber 105.
Second condition: 50 μm or more is secured as an allowable range (mounting tolerance) of mounting error between the light emitting element 103 and the core member 107.
(5) Specifically, the diameter of the end surface 207c on the multimode optical fiber side is adjusted to be 120% to 140% of the core diameter of the multimode optical fiber 205. In the case of a general multimode fiber, the multimode optical fiber 205 has a core diameter of 50 μm and a core eccentricity of about 2 μm. The mounting accuracy between the optical coupling device 204 and the multimode optical fiber 205 can be easily increased to several μm by using an optical bench 111 as shown in FIG. Assuming that the worst mounting accuracy is 10 μm, in order to suppress the loss due to the misalignment between the core member 207 and the core 209 of the multimode optical fiber 205 to a negligible level, the multimode optical fiber of the core member 207 It is desirable that the diameter of the end face 207c on the side be 120% to 140% of the diameter of the core 209 of the multimode optical fiber 205.

If the multimode optical fiber 205 is a silica-based GI (Grated Index) type multimode product with a diameter of 125 μm, it can be mass-produced without deterioration in quality up to a core diameter of about 110 μm with the current general-purpose technology. . If a GI type multimode fiber having a core diameter of 100 μm is used, if the end surface 207c of the core member 207 on the multimode optical fiber side is 120 μm to 140 μm, a sufficient mounting tolerance is ensured and the loss is ignored. It can be made as small as possible.
(6) The difference in diameter between both ends of the core member 207 is preferably as small as possible. The reason is as described in the first embodiment.

The optical coupling device 204 can be manufactured by a known technique such as mold forming.
7 and 8 show only the optical components for clarifying the characteristics of the present invention, but the actual optical receiving module 201 also includes electronic components as shown in FIGS. 11 and 12.
FIG. 11 is a side view of the optical receiver module according to the second embodiment.

FIG. 12 is a top view of the optical receiver module according to the second embodiment.
The optical coupling device 204 is fixed to the electric circuit board 202 by the optical bench 111. A signal conversion element 214 is mounted on the main surface of the electric circuit board 202. The signal conversion element 214 receives a current signal from the light receiving element 203 via the electric wiring 216, converts it into a voltage signal, and outputs the voltage signal to the outside via the electric wiring 215. The electric wiring 216 and the electrode of the light receiving element 203 are bonded by a wire 217.

Since the manufacturing method of the optical receiver module according to the second embodiment is the same as the manufacturing method of the optical transmitter module according to the first embodiment, description thereof is omitted.
The optical transmission / reception system can be configured by the optical transmission module according to the first embodiment and the optical reception module according to the second embodiment.
FIG. 13 is a top view of the optical transmission / reception system according to the present invention.

In the optical transmission / reception system, the optical transmission module 101 and the optical reception module 201 are optically coupled by a common multimode optical fiber 218.
FIG. 14 is a diagram illustrating loss evaluation of the optical transmission / reception system according to the present invention together with a comparative example.
In order to increase the communication speed, it is necessary to increase the light receiving power (minimum light receiving sensitivity). For example, if the communication speed is 2.5 Gbps, a minimum light receiving sensitivity of about −18 dBm is required from the performance of a general signal processing LSI on the receiving side (see FIG. 13).

Consider a configuration of an optical transmission / reception system that guarantees a minimum light reception sensitivity of −17 dBm with a margin of 1 dB with respect to this minimum light reception sensitivity. Here, as the multimode optical fiber 218, a general multimode fiber having a core diameter of 50 μm is assumed. Then, when the optical coupling devices 104 and 204 are not mounted, the light receiving power that can be guaranteed falls to −25 dBm (see FIG. 14A). There is also a shortage of 8 dB against the target of -17 dBm. On the other hand, when the optical coupling devices 104 and 204 are mounted, the received light power that can be guaranteed is improved to −15.5 dBm (see FIG. 14B). A power margin of 1.5 dBm can be generated for a target of -17 dBm.
(Embodiment 3)
FIG. 15 is a side view of the optical transmission module according to the third embodiment.

FIG. 16 is a top view of the optical transmission module according to the third embodiment.
The optical transmission module 301 includes an electric circuit board 302, a light emitting element 303, an optical coupling device 304, a multimode optical fiber 305, a refractive index matching gel 306, and a submount 318.
The third embodiment is different from the first embodiment in that the light emitting element 303 emits light in the direction parallel to the substrate. The light emitting element 303 is fixed to the electric circuit board 302 via the submount 318. The end surface of the core member 307 on the light emitting element side is substantially parallel to the light emitting surface of the light emitting element 303.

Next, a method for manufacturing the optical transmission module 301 will be described.
Step S1: A light emitting drive element (not shown) and other electric components are mounted on the electric circuit board 302. The mounting accuracy of the electrical components is designed to such an extent that no short circuit between the lines occurs.
Step S2: The light emitting element 303 is mounted at the light emitting element mounting position of the submount 318, and wiring is performed. The mounting accuracy of the light emitting element 303 is about 40 μm as will be described later.

  Step S3: The submount 318 is mounted at the submount mounting position of the electric circuit board 302. The mounting accuracy of the submount 318 is not particularly specified. One ends of the electrodes 320 and 321 are connected to the electrical wirings 316 and 322 by solder on the bottom surface of the submount 318, respectively. Therefore, it is not necessary to perform wire bonding between the submount 318 and the electric circuit board 302.

Step S4: The optical coupling device 304 is aligned with the light emitting element 303 by image recognition, and the optical coupling device 304 is directly fixed to the electric circuit board 302.
With the current general-purpose technology, the optical coupling device 304 can be formed with a processing accuracy of about 10 μm. Therefore, if the optical coupling device 304 is directly fixed to the main surface of the electric circuit board 302, the accuracy of the core axis 307a in the board vertical direction can be mounted with about 10 μm. Then, the mounting accuracy of the light emitting element 303 on the submount 318 may be mounted with an accuracy of about 40 μm in the substrate vertical direction.

  Step S5: The multimode optical fiber 305 is fitted into the guide groove 319 of the optical coupling device 304 and fixed. Since the guide groove 319 is precisely molded with an error of about 10 μm, high-precision mounting can be realized only by fitting the multimode optical fiber 305 into the guide groove 319. As a result, the coupling loss between the optical coupling device 304 and the multimode optical fiber 305 is reduced to a level that is almost negligible.

Step S6: Fill the gap between the light emitting element 303 and the optical coupling device 304 with the refractive index matching gel 306.
Note that electrodes 320 and 321 are formed on the submount 318 from the side surface to the bottom surface. A partial region of the submount 318 is chamfered so that the electrodes 320 and 321 are not interrupted between the surfaces.

  In the third embodiment, the optical structure is such that the end surface 307b of the core member 307 on the light emitting element side and the light emitting surface of the light emitting element 303 face each other. Therefore, these intervals can be made smaller than those in the first embodiment (for example, an optical distance of 200 to 300 μm). If the optical distance is short as shown in FIG. 17, the optical coupling efficiency increases. Therefore, by increasing the optical coupling efficiency, it is possible to widen the allowable range of mounting errors.

Further, alignment of the optical coupling device 304 and the light emitting element 303 is performed using image recognition as in the first embodiment. If the mounting accuracy at this time can be reduced to 50 μm or less, the same transmission power as in the first embodiment can be obtained.
(Embodiment 4)
FIG. 18 is a side view of the optical receiver module according to the fourth embodiment.

FIG. 19 is a top view of the optical receiver module according to the fourth embodiment.
The optical receiving module 401 includes an electric circuit board 402, a light receiving element 403, an optical coupling device 404, a multimode optical fiber 405, a refractive index matching gel 406, and a submount 418.
The optical receiving module 401 includes an electric circuit board 402, a light receiving element 403, an optical coupling device 404, a multimode optical fiber 405, a refractive index matching gel 406, and a submount 418.

The fourth embodiment is different from the second embodiment in that the light receiving element 403 receives light in the direction parallel to the substrate. The light receiving element 403 is fixed to the electric circuit board 402 via the submount 418. The end surface of the core member 407 on the light receiving element side is substantially parallel to the light emitting surface of the light receiving element 403.
Next, a method for manufacturing the optical receiving module 401 will be described.

Step S1: A signal conversion element (not shown) and other electric components are mounted on the electric circuit board 302. The mounting accuracy of the electrical components is designed to such an extent that no short circuit between the lines occurs.
Step S2: The light receiving element 403 is mounted at the light receiving element mounting position of the submount 418, and wiring is performed. The mounting accuracy of the light receiving element 403 is about 40 μm as will be described later.

Step S3: The submount 418 is mounted at the submount mounting position of the electric circuit board 402. The mounting accuracy of the submount 418 is not particularly specified. One end of the electrode 420 is connected to the electrical wiring 416 by wire bonding. One end of the electrode 421 is connected to the electrical wiring 422 by solder on the bottom surface of the submount 418.
Step S4: The optical coupling device 404 is aligned with the light receiving element 403 by image recognition, and the optical coupling device 404 is directly fixed to the electric circuit board 402.

  With the current general-purpose technology, the optical coupling device 404 can be formed with a processing accuracy of about 10 μm. Therefore, if the optical coupling device 404 is directly fixed to the main surface of the electric circuit board 402, the core axis 407a can be mounted with an accuracy of about 10 μm in the board vertical direction. Then, the mounting accuracy of the light receiving element 403 on the submount 418 may be mounted with an accuracy of about 40 μm in the substrate vertical direction.

  Step S5: The multimode optical fiber 405 is fitted into the guide groove 419 of the optical coupling device 404 and fixed. Since the guide groove 419 is precisely molded with an error of about 10 μm, high-precision mounting can be realized only by fitting the multimode optical fiber 405 into the guide groove 419. As a result, the coupling loss between the optical coupling device 404 and the multimode optical fiber 405 is reduced to a level that is almost negligible.

Step S6: Fill the gap between the light receiving element 403 and the optical coupling device 404 with the refractive index matching gel 406.
Note that electrodes 420 and 421 are formed on the submount 418 from the side surface to the bottom surface. A partial region of the submount 418 is chamfered so that the electrodes 420 and 421 are not interrupted between the surfaces.

  The fourth embodiment has an optical structure in which the end surface 407b of the core member 407 on the light receiving element side and the light receiving surface of the light receiving element 403 face each other. Therefore, these intervals can be reduced as compared with the second embodiment (for example, an optical distance of 200 to 300 μm). If the optical distance is short, the optical coupling efficiency increases. Therefore, by increasing the optical coupling efficiency, it is possible to widen the allowable range of mounting errors.

Further, the alignment between the optical coupling device 404 and the light receiving element 403 is performed using image recognition as in the second embodiment. If the mounting accuracy at this time can be reduced to 50 μm or less, the reception power similar to that of the second embodiment can be obtained.
An optical transmission / reception system can be configured by the optical transmission module according to the third embodiment and the optical reception module according to the fourth embodiment.

The optical transmission module, the optical reception module, and the optical transmission / reception system according to the present invention have been described based on the embodiments. However, the present invention is not limited to these embodiments. For example, the following modifications can be considered.
(1) In the first embodiment, the optical bench 111 is used to facilitate the alignment between the optical coupling device 104 and the multimode optical fiber 105. However, the present invention is not limited to this as long as the alignment accuracy can be easily secured. For example, as shown in FIGS. 20 and 21, a guide groove 519 having a diameter slightly larger than the outer diameter of the multimode optical fiber 505 may be formed in the optical coupling device 504. The same applies to the second embodiment.
(2) In Embodiment 1, since it can be expected that the end face 107b on the light emitting element side is substantially totally reflected, no special treatment is applied to the end face. However, when the reflectance can be further improved by disposing the light reflecting member, the light reflecting member 623 may be disposed on the end face as shown in FIGS. As the light reflecting member 623, a dielectric multilayer film or a metal film can be considered. In the case of metal coating, care should be taken so that the metal does not go around the bottom surface of the optical coupling device 604 and the connection surface with the multimode optical fiber 605 so as not to block the optical path. The same applies to the second embodiment.
(3) Although the cross-sectional shape of the core member is circular in the embodiment, the present invention is not limited to this. For example, the cross-sectional shape may be an ellipse or a rectangle.
(4) Although the embodiment has been described with a two-channel configuration, the present invention is not limited to this. For example, AV equipment has specifications for inputting / outputting four types of signals R, G, B, and CLK. In such a case, a 4-channel configuration may be used.

  The present invention can be used for optical signal communication.

2 is a cross-sectional view of the optical axis of the optical transmission module according to Embodiment 1. FIG. 4 is a top view of the optical transmission module according to Embodiment 1. FIG. It is the figure showing the relationship between the optical coupling efficiency and the tolerance | permissible_range of a mounting error for every three types of core diameters. It is a three-plane figure which shows the external shape of an optical bench. 2 is a side view of the optical transmission module according to Embodiment 1. FIG. 4 is a top view of the optical transmission module according to Embodiment 1. FIG. FIG. 6 is an optical axis cross-sectional view of an optical receiver module according to Embodiment 2. 6 is a top view of an optical receiver module according to Embodiment 2. FIG. It is the figure showing the relationship between the optical coupling efficiency and the tolerance | permissible_range of a mounting error for every three types of core diameters. It is a figure which shows the relationship between a communication speed and the minimum light reception sensitivity. 6 is a side view of an optical receiver module according to Embodiment 2. FIG. 6 is a top view of an optical receiver module according to Embodiment 2. FIG. 1 is a top view of an optical transmission / reception system according to the present invention. It is the figure which represented the loss evaluation of the optical transmission / reception system which concerns on this invention with the comparative example. 6 is a side view of an optical transmission module according to Embodiment 3. FIG. 6 is a top view of an optical transmission module according to Embodiment 3. FIG. It is a figure which shows the coupling efficiency with respect to the space | interval of a light emitting element and an optical coupling device. FIG. 6 is a side view of an optical receiver module according to a fourth embodiment. 6 is a top view of an optical receiver module according to Embodiment 4. FIG. FIG. 6 is an optical axis cross-sectional view of an optical transmission module according to Modification 1. FIG. 10 is a top view of an optical transmission module according to Modification 1. FIG. 10 is an optical axis cross-sectional view of an optical transmission module according to Modification 2. 10 is a top view of an optical transmission module according to Modification 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical transmission module 102 Electric circuit board 103 Light emitting element 104 Optical coupling device 105 Multimode optical fiber 106 Refractive index matching gel 107 Core member 108 Cladding member 114 Light emission drive element 201 Optical receiving module 202 Electric circuit board 203 Light receiving element 204 Optical coupling device 205 Multimode Optical Fiber 206 Refractive Index Matching Gel 207 Core Member 208 Clad Member 214 Signal Conversion Element

Claims (21)

A light emitting element;
A multimode optical fiber;
A core member coated with a clad member that guides light from the light emitting element to the multimode optical fiber;
The optical transmission module, wherein the core member has an end face on a light emitting element side as viewed in an optical path direction wider than a core end face of the multimode optical fiber. The core member has a portion in which the thickness continuously decreases toward the multimode optical fiber and does not have a portion in which the thickness increases toward the multimode optical fiber. The optical transmission module according to 1. The optical transmission module according to claim 2, wherein the core member has a portion having a constant thickness by a predetermined distance from the end face on the light emitting element side toward the multimode optical fiber. The end surface on the light emitting element side of the core member is inclined by approximately 45 degrees with respect to the light emitting surface of the light emitting element,
The light emitting element and the core member are arranged in a relational position such that light emitted from the light emitting surface of the light emitting element is reflected by the end surface on the light emitting element side of the core member and is directed to the end surface on the multimode optical fiber side. The optical transmission module according to claim 1. The optical transmission module according to claim 4, wherein an end surface of the core member on a light emitting element side is in contact with air. The optical transmission module according to claim 4, wherein a light reflecting member is disposed on an end surface of the core member on a light emitting element side. The light emitting element and the core member are arranged such that an optical distance between the light emitting element side end surface of the core member and the light emitting element is within 500 μm,
2. The optical transmission module according to claim 1, wherein the core member has a diameter of an end face on a light emitting element side in the optical path direction of 100 μm to 120 μm. 2. The optical transmission module according to claim 1, wherein the core member further has an end surface on the multimode optical fiber side narrower than a core end surface of the multimode optical fiber when viewed in the optical path direction. 9. The optical transmission module according to claim 8, wherein the core member has a diameter of an end face on the multimode optical fiber side that is 60% to 80% of a core diameter of the multimode optical fiber. Two or more light emitting elements;
The same number of multimode optical fibers as the light emitting elements;
A core member of the same number as the light emitting elements, which is covered with a clad member, guides light from each light emitting element to a multimode optical fiber corresponding to each light emitting element;
Each of the core members has a wider end surface on the light emitting element side when viewed in the optical path direction than the core end surface of the multimode optical fiber,
All core members are integrally molded at a predetermined pitch,
All the light emitting elements are formed in the same chip | tip with the said predetermined pitch, The optical transmission module characterized by the above-mentioned. A light receiving element;
A multimode optical fiber;
A core member coated with a clad member that guides light from the multimode optical fiber to the light receiving element;
The optical receiver module, wherein the core member has an end surface on the light receiving element side that is narrower than a core end surface of the multimode optical fiber when viewed in the optical path direction. The light according to claim 11, wherein the core member has a portion in which the thickness continuously decreases toward the light receiving element and does not have a portion in which the thickness increases toward the light receiving element. Transmission module. The optical transmission module according to claim 12, wherein the core member has a portion having a constant thickness by a predetermined distance from an end surface on the multimode optical fiber side toward the light receiving element. The end surface on the light receiving element side of the core member is inclined by approximately 45 degrees with respect to the light receiving surface of the light receiving element,
The light receiving element and the core member are arranged at a relative position such that light incident from the multimode optical fiber is reflected by the end surface of the core member on the light receiving element side and directed toward the light receiving surface of the light receiving element. The optical receiver module according to claim 11. The optical receiver module according to claim 14, wherein an end surface of the core member on a light receiving element side is in contact with air. The optical transmission module according to claim 14, wherein a light reflecting member is disposed on an end surface of the core member on a light receiving element side. The light receiving element and the core member are arranged such that an optical distance between an end surface of the core member on the light receiving element side and the light receiving element is within 500 μm,
The optical receiver module according to claim 11, wherein the core member has a diameter of an end face on a light receiving element side in the optical path direction of 40 μm to 60 μm. The optical receiving module according to claim 11, wherein the core member further has an end surface on the multimode optical fiber side wider than a core end surface of the multimode optical fiber when viewed in the optical path direction. The optical receiving module according to claim 18, wherein the core member has a diameter of an end surface on the multimode optical fiber side of 120% to 140% of a core diameter of the multimode optical fiber. Two or more light receiving elements;
The same number of multimode optical fibers as the light receiving elements;
A core member having the same number as the light receiving elements, which is covered with a clad member, guides light from each multimode optical fiber to a light receiving element corresponding to each multimode optical fiber;
Each of the core members has an end face on the light receiving element side when viewed in the optical path direction, which is narrower than the core end face of the multimode optical fiber,
All core members are integrally molded at a predetermined pitch,
All the light emitting elements are formed in the same chip | tip with the said predetermined pitch, The optical receiver module characterized by the above-mentioned. An optical transmission / reception system in which an optical transmission module and an optical reception module are optically coupled by a multimode optical fiber,
The optical transmission module includes:
A light emitting element;
A first core member coated with a cladding member that guides light from the light emitting element to one end of the multimode optical fiber;
The optical receiving module is:
A light receiving element;
A second core member coated with a cladding member that guides light from the other end of the multimode optical fiber to the light receiving element;
The first core member has a wider end surface on the light emitting element side when viewed in the optical path direction than the core end surface of the multimode optical fiber,
The optical transmission / reception system, wherein the second core member has an end surface on the light receiving element side that is narrower than a core end surface of the multimode optical fiber when viewed in the optical path direction.

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