JP2001059920A - Light guide body for joining optical fiber and optical semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize light transmission loss. SOLUTION: Optical fiber 1 and a light receiving and emitting semiconductor 2 are jointed with a light guide body 3 which is filled with a light transmitting body 4a, 4b which are surrounded by a reflection body and are different in hardness. The light transmitting body 4a, 4b have the characteristic in such a manner that 4a of the light receiving and emitting semiconductor 2 side is hard and 4b of the optical fiber 1 side is soft. The hardness of the light transmitting body 4a, 4b is set in such a manner that 4b of the optical fiber 1 side preferably has JIS (D) hardness less than 60, and the refractive index thereof is preferably set within refractive index of the optical fiber ±0.2. Resin for the transmitting body 4a, 4b is preferably at least one kind selected from silicone resin, acrylic resin, epoxy resin, thermoplastic elastomeric resin and the derivatives of these resins. A joint structure in which the light receiving and emitting semiconductor 2 and the light guide body 3 are combined and the optical fiber 1 and the light guide body 3 are connected is preferably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical connection and coupling structure between an optical fiber and a light emitting / receiving semiconductor, and to a technique for reducing a loss during optical transmission.

[0002]

2. Description of the Related Art An optical transmission system using an optical fiber comprises:
The optical fiber is connected to the light emitting and receiving semiconductor device to transfer the signal light. Transmitting semiconductor devices include resin-sealed light-emitting diodes (LEDs) and metal-sealed semiconductor lasers (L
D) A metal-sealed or resin-sealed photodiode (PD) is used as the receiving semiconductor device.

[0003] The communication performance of such an optical transmission system is greatly affected by the transmission efficiency of signal light, and the transmission loss not only of the optical fiber but also of the connecting portion affects the communication performance. The current connection structure mainly includes a lens interposed between an optical fiber and a semiconductor device. However, this structure has a problem that not only the precision connection is required, the cost is high and the versatility is poor, but also 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 emitting / receiving semiconductor in order to reduce the connection loss (see FIG. 1). JP-A-10-221573, JP-A-10-22
1574).

[0005] After the above proposal, further studies for practical use have been earnestly conducted. When an optical fiber and a light receiving / emitting semiconductor are connected by a light guide, it is important to fill the inside of the light guide with a light transmitting body having different hardness. I found something.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for reducing the loss at the time of joining an optical fiber and a light-receiving / emitting semiconductor. It proposes a structure to have.

[0007]

According to the present invention, there is provided an optical transmission system comprising a light guide having a light guide path surrounded by a reflective surface between an optical fiber and a light receiving / emitting semiconductor and filled with a light transmitting body. And a light guide for bonding, characterized in that the light transmitting body has a characteristic of being continuously or stepwise flexible from the light receiving / emitting semiconductor side to the optical fiber side.

[0008] A second aspect of the present invention is a silicone resin, an acrylic resin, an epoxy resin, a thermoplastic elastomer resin, wherein the light transmitting body has a characteristic value whose hardness on the optical fiber side is 60 degrees or less according to JIS (D). The bonding light guide according to claim 1, wherein the light guide is one kind selected from resin derivatives.

According to a third aspect of the present invention, the optical fiber has a light guide path in which a core dimension of the optical fiber is larger than a dimension of the light emitting / receiving section of the light emitting / receiving semiconductor and tapers from the optical fiber side toward the light emitting / receiving semiconductor side. 3. A light guide for joining an optical fiber and an optical semiconductor according to item 1.

According to a fourth aspect of the present invention, there is provided the joining light guide according to any one of the first to third 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 fifth aspect of the present invention, the light receiving / emitting semiconductor and the light guide are integrated with each other, and the optical fiber and the light guide can be connected and separated. Is a light guide for bonding.

The characteristics of the light transmitting body that directly contacts the optical semiconductor are important. The light transmitting body is required to have a function of protecting the optical semiconductor from the environment (especially, moisture) and a resistance to environmental confidentiality. The light transmitting body also needs to protect the semiconductor from external pressure.
Since the optical semiconductor is very sensitive to pressure fluctuations, the light transmitting body is required to have a performance of buffering the external pressure and firmly protecting the optical semiconductor. Further, adhesion between the optical fiber and the light transmitting body is also important. If a gap is formed at the interface between the optical fiber and the light transmitting body, light transmission loss is caused by reflection or scattering.

That is, it is preferable that the light transmitting body is designed to be rigid on the optical semiconductor side and flexible on the optical fiber side. As for the hardness of the light transmitting body, it is preferable that the light becomes flexible continuously or stepwise from the optical semiconductor side to the optical fiber side. The optical fiber side hardness of the light transmitting body is preferably 60 degrees or less in JIS (D). If it is too hard, the adhesion to the optical fiber will be poor, resulting in loss of signal light during optical transmission.

The resin of the light transmitting body is preferably a resin having excellent light transmitting property, capable of adjusting hardness, and having a proven track record in the semiconductor field or the optical field. 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).

The joint structure of the present invention is effective when the core size of the optical fiber is larger than the size of the light emitting / receiving portion of the light emitting / receiving semiconductor, and is tapered from the optical fiber side toward the light emitting / receiving semiconductor side. In particular, it is important as a simple joining technique when a plastic optical fiber having a large core size is used.

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).

It is preferable that the optical semiconductor and the light guide are integrated, and that the light guide and the optical fiber are connected and separated.
The optical semiconductor is functionally mounted and fixed on a main body or an attached facility of the optical communication device, and it is preferable to couple the light guide and the optical semiconductor to shorten the transmission distance in order to efficiently transmit the signal light. In addition, it is practical to leave the degree of freedom by connecting the other optical fiber side of the light guide body.

In order to efficiently transmit the signal light from the light receiving and emitting semiconductor and the signal light to the light receiving and emitting semiconductor, it is also effective to embed the light receiving and emitting semiconductor in the light guide and couple the light receiving and emitting semiconductors at the shortest distance. Since the current optical semiconductor device is designed on the premise of a lens structure, the size of the input / output surface is large and the distance to the optical semiconductor is long, so that signal light is not effectively transmitted due to light leakage, scattering or reflection.

Further, it is preferable that the connection surface of the light transmitting body on the optical fiber side has a convex and concave shape so that air is expelled and brought into close contact with the pressing force at the time of connection. It is also effective to create an escape route for air at the optical fiber side connection outer peripheral portion to discharge air bubbles.

FIG. 1 shows an example of a light guide according to the present invention (a diagram viewed from the side in the connection direction). 3 is a light guide, 4a and 4
b is a light transmitting body. The connecting surface between the flexible light transmitting body 4b and the optical fiber 1 is 5. The optical semiconductor 2 is bonded by a rigid light transmitting body 4a.

FIG. 2 is a view showing another example of the light guide according to the present invention. (1) is a view from the side of the connection direction,
(2) is the figure which looked at the light guide from the optical fiber side. 1 is an optical fiber, 2 is an optical semiconductor, and 3 is a light guide. The central part 25 of the optical fiber side connection surface of the light transmitting body 24 is spherical, and the outer peripheral part 29 is processed into a wavy shape to allow air to escape. The light transmitting body 24 has a hard inclined structure on the optical semiconductor side and a flexible inclined structure on the optical fiber side.

FIG. 3 is a diagram in which an optical fiber and an optical semiconductor are connected using the light guide (FIG. 1) of the present invention. The optical fiber 1 and the light transmitting body 4b are connected at the surface 35 without any gap. Further, a device for temporarily fixing the optical fiber and the light guide may be provided. An attachment / detachment mechanism (existing technology such as a spring, a screw, and a groove) used in a general connector can be used.

FIG. 4 is a diagram showing an example of a connection structure using a conventional lens. Optical fiber 1 and optical semiconductor device 4
Numeral 2 transmits light via a ball lens 40 made of quartz.

[0024]

Embodiments of the present invention will be described. The optical fiber 1 and the optical semiconductor 2 are optically connected by interposing a light guide 3 which is surrounded by a reflection surface and filled with light transmitting bodies 4 and 24 having different hardnesses. It is preferable that the optical semiconductor and the light guide are integrated, and the optical fiber and the light guide have a structure that can be connected and separated. The light transmitting body is the optical fiber side connection surface 5, 2
5 and 5 are flat and 25 are spherical.
If the outer periphery of the light transmitting body is devised so that air can escape easily and the adhesion is improved, the light transmission efficiency increases. The outer peripheral portion 29 is processed into a wavy shape. The use of the light guide of the present invention can reduce the loss at the time of optical transmission. Hereinafter, specific examples will be described with reference to examples and comparative examples.

[0025]

Embodiment 1 A step index type acrylic optical fiber (manufactured by Toray) and an LED (manufactured by NEC) were connected using the light guide of FIG. The inner surface of the light guide is subjected to a plating process capable of highly reflecting light. Inside the light guide, LED side is J
The optical fiber side is composed of two stages of a rubber-modified epoxy resin (manufactured by Nippon Kayaku) having characteristics of IS (A) 60 degrees and JIS (D) 20 degrees (refractive index 1.50). When the optical fiber and the light guide were connected and the optical transmission loss at the connection was measured,
It was as low as 1.8 dB.

The refractive index of the optical fiber is 1.495 and the core diameter is 0.9 mm. The LED is a chip of 0.2 mm square having a wavelength of 650 nm sealed with epoxy resin. The hardness of the rubber-modified epoxy resin was measured according to JIS (using a durometer).

[0027]

Embodiment 2 A great index type acrylic optical fiber (manufactured by Clave) and a metal-sealed PD (manufactured by Hamamatsu Photonics, light receiving diameter: 0.5 mm) were connected using the light guide of FIG. The optical fiber connection surface of the light transmitting body is spherical. or,
The outer peripheral portion of the light transmitting body on the optical fiber side is wavy, and 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. The light transmitting body has a refractive index of 1.49 and a hardness of P
Optical fiber side JIS (D) from 70 degree D side JIS (A)
It is composed of a rubber-modified acrylic resin (manufactured by Toa Gosei) having a gradient hardness of 30 degrees. This connection section is used for 1.
A loss of 2 dB occurred.

The rubber-modified acrylic resin having a gradient hardness was injected into the light guide and cured while continuously changing the mixing ratio of the acrylic resin having a high rubber modification rate and the acrylic resin having a low rubber modification rate.

[0029]

Embodiment 3 A step index type fluororesin optical fiber having a refractive index of 1.35 and a core diameter of 0.3 mm was connected to an LD (chip cross section: 0.3 mm square, manufactured by Sony) using the light guide of FIG. . The inside of the light guide is made of a fluorine-modified silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd.) having a JIS (D) of 10 degrees and a refractive index of 1.38. The measured optical transmission loss at this connection was 0.9 dB.

[0030]

[Examination Example 1] An optical fiber and an LED 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 portion was 4.2 dB. It is considered that the light transmitting body was hard as JIS (D) 70 degrees and did not adhere to the optical fiber, resulting in loss. The epoxy resin used for the light transmitting body was mainly composed of bisphenol A type epoxy resin and phthalic anhydride.

[0031]

[Examination Example 2] An optical fiber and an LD were connected by a light guide in the same manner as in Example 3 except that a general-purpose epoxy-modified acrylic resin (manufactured by Takeda Chemical Industries) was used as a light transmitting body. In this case, the connection portion optical transmission loss was as high as 3.3 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.

[0032]

Comparative Example As shown in FIG. 4, optical transmission was performed by a conventional method.
The optical fiber of Example 1 and the LED were connected via a ball lens (manufactured by Molex Japan). In this case, the connection portion optical transmission loss was 13 dB. Reflection at the lens surface had an adverse effect and caused extremely high losses.

[0033]

The light guide of the present invention has a structure in which the light guide is surrounded by a reflective surface and is filled with light transmitting members having different hardnesses. When an optical fiber and a light receiving / emitting semiconductor are joined using the light guide of the present invention, 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 a light guide structure example of the present invention.

FIG. 2 is a diagram showing a light guide structure example of the present invention.

FIG. 3 is a view showing an example of a structure after bonding according to the present invention.

FIG. 4 is a diagram showing an example of a conventional lens connection structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Optical semiconductor 3 Light guide 4a, 4b, 24 Light transmitting body 5, 25 Optical fiber side surface of light transmitting body 29 Optical fiber side outer peripheral part of light transmitting body 35 Contact surface between light guide and optical fiber 40 Ball Lens 42 Optical semiconductor device

Claims (5)

[Claims] 1. A light guide having a light guide path surrounded by a reflection surface between an optical fiber and a light receiving / emitting semiconductor and filled with a light transmitting body, wherein the light transmitting body is located between the light receiving / emitting semiconductor side and the optical fiber side. A light guide for joining an optical fiber and an optical semiconductor, characterized in that the light guide has a characteristic of being continuously or stepwise flexible. 2. The light transmitting member according to claim 1, wherein the hardness of the optical fiber side is JIS.
(D) a silicone resin having a characteristic value of 60 degrees or less,
2. The light guide according to claim 1, wherein the light guide is one selected from an acrylic resin, an epoxy resin, a thermoplastic elastomer resin, and a derivative of these resins. 3. The optical fiber according to claim 1, wherein a core dimension of the optical fiber is larger than a dimension of the light receiving / emitting section of the light receiving / emitting semiconductor, and a light guide path tapering from the optical fiber side toward the light receiving / emitting semiconductor side. A light guide for joining an optical fiber and an optical semiconductor. 4. The light guide for joining an optical fiber and an optical semiconductor 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. body. 5. The optical fiber according to claim 1, wherein the light receiving / emitting semiconductor and the light guide are integrated, and the optical fiber and the light guide have a structure that can be connected and separated. And a light guide for bonding optical semiconductors.