JP2001059921A - Light guiding and light receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize light transmission loss at the time of transmitting signal light from optical fiber to a light receiving element. SOLUTION: The optical fiber and this light guiding and light receiving device which is integrated with a light receiving element are connected and light transmission is executed. The device has a structure formed by connecting an end surface of a light guide body 3 and a light receiving surface of a light receiving element 2. The light guide body 3 is surrounded by a reflection surface and, therein, is filled with a light transmitting body 4. Further, the light transmitting body 4 is brought into contact with the light receiving part of the light receiving element 2. The light transmitting body 4 has the characteristic that the light transmitting body 4 is soft, or the light receiving element 2 side thereof is hard and the optical fiber 1 side thereof is soft. The hardness of the optical fiber 1 side of the light transmitting body 4 is preferably less than 60 deg. JIS (D) hardness. Further, the refractive index of the light transmitting body 4 is preferably within the refractive index of the optical fiber ±0.2. The optical fiber 1 side surface of the light transmitting body 4 is designed in such a manner that the central part is projected and the peripheral part is rugged. Resin for the light transmitting body 4 is preferably one kind selected from silicone resin, acrylic resin, epoxy resin, thermoplastic elastomeric resin and the derivatives of these resins.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a light guide light receiving device for optically joining an optical fiber and a light receiving element, and relates to a technique for reducing a loss during optical transmission.

[0002]

2. Description of the Related Art A receiving system using an optical fiber transmits a signal light through an optical fiber and a light receiving device via a lens, and a metal-sealed or resin-sealed photodiode is used as the light-receiving device. .

[0003] The receiving performance in such an optical transmission system is greatly affected by the transmission efficiency of the signal light, and not only the performance of the optical fiber and the light receiving device but also the transmission loss of the connecting portion affects the communication performance. The current connection method involving a lens has a problem that a precision structure is required, the cost is high and the versatility is poor, and further, a connection loss of several dB to several tens dB is caused by reflection on the lens surface.

The present inventor has proposed a coupling structure in which a light guide having a light guide path surrounded by a reflection surface is interposed between an optical fiber and a light receiving element in order to reduce the connection loss. Kaihei 10-221573).

After the above-mentioned proposal, further studies have been made on practical use. When an optical fiber and a light receiving element are connected by a light guide, the light guide is directly coupled to the light receiving element to have a structure that can be separated and connected to the optical fiber. Is important.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for reducing a loss at the time of connection between an optical fiber and a light receiving element, and proposes a lens-less light guide light receiving apparatus having excellent connection performance.

[0007]

SUMMARY OF THE INVENTION The present invention is an apparatus for transmitting signal light from an optical fiber to a light receiving element via a light guide having a light guide path surrounded by a reflection surface and filled with a light transmitting body. The light guide light receiving device is characterized in that the end face of the light guide is coupled to the light receiving surface of the light receiving element, and the light transmitting body is in contact with the light receiving portion of the light receiving element. The light guide light receiving device according to claim 1, wherein the end face of the light guide and the light receiving surface of the light receiving element are electrically connected. Claim 3
Is a light guide light receiving device according to claim 1 or 2, wherein the optical fiber and the light guide are connectable and separable.

According to a fourth aspect of the present invention, the optical fiber has a light guide path in which the core dimension of the optical fiber is larger than the dimension of the light receiving portion of the light receiving element and tapers from the optical fiber side toward the light receiving element side. It is a light guide light receiving device.

According to a fifth aspect of the present invention, the light transmitting body has a characteristic of being flexible or softening from the light receiving element side toward the optical fiber side, and the hardness of the optical fiber side is JIS (D) 60 degrees or less. The light guide light receiving device according to claim 1, wherein: A sixth aspect of the present invention is the light guide light receiving device according to any one of the first to fifth aspects, wherein the refractive index of the light transmitting body is within ± 0.2 of the refractive index of the optical fiber.

According to a seventh aspect of the present invention, in the light guide light receiving device according to any one of the first to sixth aspects, the connecting surface of the light transmitting body on the optical fiber side has a convex shape in the optical fiber direction. According to a eighth aspect of the present invention, the outer peripheral portion on the optical fiber side of the light transmitting body has a shape subjected to uneven processing to allow air to escape, and the light guide light receiving device according to the first to seventh aspects, Device.

According to a ninth aspect, the light transmitting member is selected from the group consisting of silicone resin, acrylic resin, epoxy resin, thermoplastic elastomer resin, and derivatives of these resins.
The light guide light receiving device according to claim 1, wherein the light guide light receiving device is a seed.

In order to efficiently transmit signal light to the light receiving element, it is important to prevent leakage of the signal light and to join the light guide and the light receiving element at the shortest distance. In other words, it is effective to integrate the end face of the light guide and the light receiving surface of the light receiving element and bring the light transmitting body into contact with the light receiving portion of the light receiving element. For this purpose, it is important that the optical semiconductor is used not in a device sealed with a metal or a resin but in an element state and directly connected by an electrical connection method without using a gold wire. Since the current light receiving device is designed on the premise of a lens structure, the size of the incident surface is large and the distance to the element is long. That is, when the current light receiving device is used, the signal light is not effectively transmitted due to light leakage, scattering or reflection.

[0013] Even when a light receiving element is used, signal light loss occurs when the entire light receiving element or the entire module section electrically connected with the gold wire is coupled with the light guide, so that the light receiving section of the light receiving element and the light transmitting body are connected. It is necessary to connect the parts directly to minimize the transmission loss. It is preferable to use a module dedicated to light transmission in which the light receiving portion of the light receiving element is exposed, or to electrically connect the outer peripheral electrode portion of the light receiving element and the end face of the light guide to prevent light leakage to portions other than the light transmitting portion.

When the light guide and the light receiving element are integrated, it is preferable that the optical fiber side of the light guide has a structure capable of connection and separation. It is functional that the light receiving element is mounted and fixed on the main body of the optical communication device or the attached equipment, and leaving the degree of freedom on the other optical fiber side has practicality.

It is preferable that the optical fiber has a core size larger than the size of the light receiving portion of the light receiving element and is tapered from the optical fiber side toward the light receiving element side. This structure is important as a simple connection technique when a plastic optical fiber having a large core size is used.

The light transmitting body is required to protect the light receiving element from the environment (confidentiality and reliability). It is necessary for the light transmitting body to protect the light receiving element from external pressure and moisture. Since the light receiving element is very sensitive to changes in pressure, temperature, and humidity, the light transmitting body is required to have a function of buffering stress and firmly protecting the light receiving element from water intrusion. That is,
The light transmitting body has the property of being flexible or becoming rigid continuously or stepwise from the optical fiber side to the light receiving element side. The optical fiber side hardness of the light transmitting body is 60 degrees or less according to JIS (D). Preferably, there is. If it is too hard, the adhesion to the optical fiber will be poor, resulting in loss of signal light during optical transmission.

It is preferable that the refractive index of the light transmitting body is substantially the same as that of the optical fiber. At least, the difference in refractive index between the light transmitting body and the optical fiber is preferably within ± 0.2. If the difference is too large, light transmission loss due to reflection or the like is caused. A method for adjusting the refractive index of the light transmitting body is known (eg, POF CONFE).
RANCE '97, JP-A-11-43605).

In the case where the light guide light receiving device is connected to the optical fiber, if air is involved in the connection surface between the light transmitting body and the optical fiber, the light causes transmission loss due to phenomena such as reflection, scattering and refraction.
For this reason, it is effective to provide a shape or device that does not involve air in the connection surface.

It is preferable that the connecting surface of the light transmitting body on the optical fiber side has a convex and concave shape, and air is pushed out from the central portion to the outer peripheral portion by a pressing force at the time of connection so as to be in close contact therewith. Specific shapes include a spherical shape, a parabolic shape, a conical shape, and a pyramid shape. It is also effective to create an escape route in the outer peripheral portion of the light transmitting body on the optical fiber side and forcibly discharge air bubbles by pressing force at the time of connection. For example, it is preferable to apply a wave-like, triangular or groove-like processing to the optical fiber side connection outer peripheral portion. In this case, it is particularly preferable to use it in combination with the convex shape of the connection surface.

As the resin of the light transmitting body, those having excellent light transmitting properties, adjustable hardness, and proven in the semiconductor field or the optical field are preferable. It is preferable to select one kind of a silicone resin, an acrylic resin, an epoxy resin, a thermoplastic elastomer resin, and derivatives of these resins.
When a plurality of resins are used, problems such as water intrusion and optical transmission loss may occur depending on the state of the contact interface. Commercial products can be selected from product catalogs of Shin-Etsu Chemical, Toshiba Silicone, Toagosei, Nippon Kayaku, Asahi Kasei, etc.
Derivatives of these resins can also be produced and used using known techniques. (JP-A-59-133220, JP-A-62-167317, JP-A-3-22553, JP-A-10-17776, JP-A-10-110102, and JP-A-10-261821).

FIG. 1 shows an example of a light guide light receiving device according to the present invention (a view in which the connection direction is viewed from the side). (1) shows a state where the light guide and the light receiving element are integrated, and (2) shows a state before the integration. 1 is an optical fiber, 2 is a light receiving element, 3 is a light guide, and 4 is a light transmitting body. The optical fiber side connection surface of the light transmitting body is 5. An electrode 6 is arranged on the light receiving element side end surface of the light guide, and is coupled to the light receiving side electrode 8 of the light receiving element.

FIG. 2 is a diagram showing another example of the light guide light receiving device according to the present invention. 1 is an optical fiber, 2 is a light receiving element,
23 is a light guide. 24a is a flexible light transmitting body, 24b
Is a rigid light transmitting body. The light receiving element is adhesively sealed with a light transmitting body. Reference numeral 25 denotes a connection surface on the optical fiber side of the light transmitting body, which is spherical. 26 is the end face of the light guide on the light receiving element side, 27
And 29, a circuit board for making an electrical connection between the light receiving element and the outside. Reference numeral 20 denotes an insulating resin for protecting the back surface of the light receiving element.

FIG. 3 is a diagram showing another example of the light guide light receiving device according to the present invention. (3) is a diagram viewed from the optical fiber side. 1 is an optical fiber, 2 is a light receiving element, 30 is an insulating resin, 33 is a light guide, and 34 is a light transmitting body. The connection surface on the optical fiber side of the light transmitting body is composed of a conical central portion 35C and a cut hexagonal pyramid-shaped outer peripheral portion 35d.

FIG. 4 is a diagram in which the light guide and light receiving device of the present invention (FIG. 1) is connected to an optical fiber. 2 is a light receiving element,
Reference numeral 3 denotes a light guide, and the optical fiber 1 and the light transmitting body 4 are
Are connected without gaps. Further, a mechanism for temporarily fixing the optical fiber to the light guide light receiving device may be provided. The attachment / detachment mechanism (spring, screw,
Existing technology such as grooves) can be used.

FIG. 5 is a view showing an example of a light guide light receiving device having a structure similar to that of the present invention. The light receiving element 2 is integrated with a light guide 53 surrounded by a reflection surface and filled with a light transmitting body 54, but is connected using a gold wire 51 by a conventional method, which is regarded as an inefficient lensless connection. be able to.

FIG. 6 is a diagram showing an example of a connection structure using a conventional lens. The optical fiber 1 and the metal-sealed light receiving device transmit signal light via a quartz ball lens 60. The light receiving device includes a light receiving element 2, a gold wire 61, a light receiving side electrode 68, an inside 64 (dry nitrogen gas), and a glass window 65.

FIG. 7 shows an example of a commercially available metal-sealed light receiving device. (1) is a view seen from the lateral direction, and (3) is a view seen from the optical fiber direction. In the glass window 75 of (3), the light receiving element 2 (the light receiving unit 70 and the light receiving side electrode 78) and the gold wire 71 can be seen. That is, the signal light from the optical fiber is
The structure is difficult to be effectively transmitted to the light receiving portion of the light receiving element.

[0028]

Embodiments of the present invention will be described. The present invention
Light guides 3 and 2 surrounded by a reflection surface between optical fiber 1 and light receiving element 2 and filled with light transmission bodies 4, 24 and 34.
In an optical transmission system which optically couples through the intermediary of 3, 33, the light receiving surface of the light receiving element is directly coupled to the end face of the light guide, and the light guide has a structure in which the optical fiber and the light guide can be connected and separated. It is a light receiving device. The light receiving portion of the light receiving element is sealed with a light transmitting body, and the light transmitting body is connected to the optical fiber side connection surface 5,
25 and 35. By using the light guide light receiving device of the present invention, it is possible to reduce the loss at the time of optical transmission. Less than,
This will be specifically described in Examples and Comparative Examples.

[0029]

[Embodiment 1] A step guide type acrylic optical fiber (core diameter 0.7 mm, manufactured by Mitsubishi Rayon Co., Ltd.) and a light receiving element (light receiving diameter 0.4 mmφ, manufactured by Hamamatsu Photonics) are integrated with the light guide light receiving device of FIG. Connected. The inner surface of the light guide is subjected to a plating process capable of highly reflecting light. The light transmitting body is made of a silicone-modified epoxy resin (manufactured by Nippon Kayaku) having an optical fiber side hardness of JIS (D) 30 degrees. The optical transmission loss was measured by connecting the optical fiber and the light guide and light receiving device, and was found to be extremely small at 0.7 dB.

The light refractive index is 1.50 for the optical fiber and 1.51 for the silicone-modified epoxy resin. Resin hardness is JI
Measured according to S (using durometer). The light transmitting body was injected into the light guide and cured while continuously changing the mixing ratio between the resin having a high silicone modification rate and the resin having a low silicone modification rate, and having a gradient hardness on the light receiving element side.

[0031]

Embodiment 2 A great index type acrylic optical fiber (core diameter: 0.5 mm, refractive index: 1.5 to 1.6, made by Clave) was connected to the light guide light receiving device shown in FIG. The element used was made by Hitachi, Ltd. (light receiving diameter: 0.2 mmφ). The light transmitting body is
Two kinds of acrylic-modified epoxy resins having a hardness of 10 degrees and 50 degrees (refractive index: 1.50, manufactured by Toagosei Co., Ltd.) were used. The optical transmission loss was 0.8 dB.

[0032]

[Embodiment 3] Fluorine type optical fiber (core type 0.3 mm,
(Refractive index: 1.35, manufactured by Asahi Glass Co., Ltd.) and the light-guiding device of FIG. The same light receiving element as that in Example 2 was used, and the light transmitting body was a vinyl-modified silicone resin (an optical fiber side hardness of 40).
Degree, refractive index 1.43) was used. The shape of the side surface of the optical fiber of the light transmitting body is conical at the center and hexagonal pyramid at the outer periphery, so that air can easily escape when the optical fiber is pressed.
The outer peripheral portion also has a function of assisting in positioning and temporarily fixing the optical fiber. In this embodiment, 0.
A loss of 5 dB has occurred.

[0033]

[Examination Example 1] An optical fiber and a light receiving element were connected by a light guide in the same manner as in Example 1 except that a commercially available epoxy resin (Nitto Denko, refractive index 1.55) was used as a light transmitting body. In this case, the optical transmission loss at the connection was 3.8 dB. It is considered that the epoxy resin as the light transmitting body is hard as JIS (D) 70 degrees, and the optical fiber connection surface does not adhere to each other, causing loss. The epoxy resin used for the light transmitting body was mainly composed of bisphenol A type epoxy resin and phthalic anhydride.

[0034]

[Study Example 2] An optical fiber was connected in the same manner as in Example 3 using the light guide light receiving device shown in FIG. The optical transmission loss in this case is 4.
It was 1 dB. It is considered that the signal light was transmitted to a part other than the light receiving element due to the connection structure by the gold wire, and the efficiency became poor.

[0035]

[Examination Example 3] An optical fiber and a light receiving element were connected by a light guide in the same manner as in Example 3 except that a general-purpose urethane-modified synthetic rubber (manufactured by Takeda Pharmaceutical Co., Ltd.) was used as a light transmitting body. In this case, the connection portion optical transmission loss was as high as 3.8 dB. It is considered that a loss due to reflection occurred because the refractive index of the light transmitting body was as high as 1.58.

The study example shows that the optical transmission loss is larger than that of the embodiment but smaller than that of the comparative example, indicating that the structure of the light guide and light receiving device and the characteristics of the light transmitting body have an influence.

[0037]

Comparative Example As shown in FIG. 6, optical transmission was performed by a conventional method.
The optical fiber of Example 1 and a commercially available light receiving device (glass window diameter 3
mmφ, manufactured by Hamamatsu Photonics) was connected via a ball lens (manufactured by Nippon Molex). In this case, the optical transmission loss at the connection portion was 11 dB. Reflection at the lens surface had an adverse effect and caused extremely high losses.

[0038]

The light guide light receiving device of the present invention has a joint structure for directly coupling to the light receiving element and connecting to the optical fiber. When the optical fiber and the light guide light receiving device of the present invention are connected, the optical transmission loss during optical communication becomes extremely small. That is, the present invention greatly contributes to increasing the versatility of the optical communication system.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a light guide light receiving device of the present invention.

FIG. 2 is a diagram illustrating an example of a light guide light receiving device of the present invention.

FIG. 3 is a diagram showing an example of the light guide light receiving device of the present invention.

FIG. 4 is a diagram showing a connection example using the light guide light receiving device of the present invention.

FIG. 5 is a diagram showing an example of a conventional light guide light receiving device using gold wire connection.

FIG. 6 is a diagram showing an example of a conventional lens connection structure.

FIG. 7 is a diagram showing an example of a commercially available metal-sealed light receiving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Light receiving element 3, 23, 33, 53 Light guide 4, 24, 34, 54 Light transmitting body 5, 25, 35 Optical fiber side surface of light transmitting body 6, 26 Light receiving element side end face of light guide 8 , 68, 78 Light receiving side electrode of light receiving element 20, 30 Insulating resin 27, 29 Circuit board 51, 61, 71 Gold wire 60 Ball lens 64 Dry nitrogen gas 65, 75 Glass window 70 Light receiving part of light receiving element

Claims (9)

[Claims] An apparatus for transmitting signal light from an optical fiber to a light receiving element through a light guide having a light guide path surrounded by a reflective surface and filled with a light transmitting body, and transmitting the signal light to an end face of the light guide. A light guide light receiving device, wherein a light receiving surface of a light receiving element is coupled, and a light transmitting body and a light receiving portion of the light receiving element are in contact with each other. 2. The light guide light receiving device according to claim 1, wherein an end face of the light guide and a light receiving surface of the light receiving element are electrically connected. 3. The light guide light receiving device according to claim 1, wherein the optical fiber and the light guide have a structure that can be connected and separated. 4. The light-guided light-receiving device according to claim 1, wherein a core dimension of the optical fiber is larger than a size of a light-receiving portion of the light-receiving element, and the optical fiber has a light guide path that tapers from the optical fiber side toward the light-receiving element. apparatus. 5. The light transmitting body is characterized in that it is flexible or softens from the light receiving element side to the optical fiber side, and the hardness of the optical fiber side is JIS (D) 60 degrees or less. The light guide light receiving device according to claim 1, wherein: 6. The light guide light receiving device according to claim 1, wherein the refractive index of the light transmitting body is within ± 0.2 of the refractive index of the optical fiber. 7. The optical fiber-side connecting surface of the light transmitting body has a convex shape such as a spherical shape, a parabolic shape, a conical shape, a pyramid shape, etc. in the optical fiber direction. The light guide light receiving device according to claim 6. 8. The method according to claim 1, wherein an outer peripheral portion of the light transmitting body on the optical fiber side is formed into a corrugated shape, a polygonal shape, a groove shape or the like in order to release air. The light guide light receiving device according to claim 7. 9. The method according to claim 1, wherein the light transmitting body is one selected from a silicone resin, an acrylic resin, an epoxy resin, a thermoplastic elastomer resin, and a derivative of these resins. The light guide light receiving device according to claim 8.