JP2002318327A - Method for connecting resin optical fiber with light accepting semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting method with decreased optical transmission loss when a resin optical fiber is optically coupled with a light-accepting semiconductor device. SOLUTION: A tapered resin optical fiber is optically connected through an optical lens with a light-accepting semiconductor device. The optical lens is of thin type and preferably attached to the resin optical fiber or the light- accepting semiconductor device. The cross section of the resin optical fiber at the connection is preferably in an almost same dimension as that of the light-accepting part of the light-accepting semiconductor element. A soft light- transmitting material is preferably made present on the connecting plane between the fiber and the light-accepting semiconductor device. The light transmitting material is preferably a silicone, acrylic, epoxy or elastomer resin having the refractive index near that of the resin optical fiber and having <=50 degrees hardness according to JIS (type-A).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting a resin optical fiber and a light receiving semiconductor device at the time of optical coupling.
In particular, the present invention relates to a technique for reducing a loss in optical transmission between a resin optical fiber (referred to as POF) and a light receiving semiconductor device (referred to as a light receiving device).

[0002]

2. Description of the Related Art An optical communication system using an optical fiber includes:
A transmission system is provided at one end of an optical signal transmission path using an optical fiber, and a reception system is provided at the other end. The transmission system includes, for example, a light emitting element such as a light emitting diode or a semiconductor laser, and controls the light emitting element to emit a signal light to enter an optical fiber. On the other hand, the receiving system includes a light receiving element such as a photodiode. The light receiving element receives a signal light transmitted through an optical fiber and emitted from an emission end thereof, and converts the signal light into an electric signal.

[0003] The communication performance in such an optical communication system is greatly affected by the transmission efficiency of signal light. In particular, the transmission loss at the connection between the optical fiber and the light receiving device affects the communication performance. A conventional optical communication system has a main purpose of long-distance transmission for industrial use, and a method of precisely connecting to a light receiving device using a quartz optical fiber having a small core diameter has been adopted.

[0004] However, recently, demands for short-distance communication applications have increased, and the use of POF having a large core diameter has been studied. Going forward for consumer use (limited areas, buildings, households, etc.)
Practical use of optical communication systems in Japan is a pending issue.
It is important to develop a technology for connecting the device to the light receiving device.

For example, when a POF having a large core diameter is simply connected to a photodiode having a small light receiving portion, only a part of the signal light from the POF is incident on the photodiode. Also, in this case, even if a convex lens is interposed and connected, a part of the signal light is not received. A convex lens cannot collect random light at one point, and reflects some of the light on its surface. That is, these methods mean that a large transmission loss occurs at the connection.

The present inventor has proposed a coupling structure (JP-A-10-221573) in which a light guide surrounded by a reflection surface is interposed between an optical fiber and a light receiving element in order to reduce connection loss. However, this structure is effective only when a light guide path having an extremely long path is possible. It is theoretically difficult to condense random outgoing light from an optical fiber over a short distance. In particular, signal light with a large outgoing angle is attenuated through many reflections inside the light guide and reaches the light receiving semiconductor or reverses. Signal light returns to the optical fiber. Further, the present inventor has proposed a connection structure (JP-A-10-111429) in which a flexible light transmitting body is sandwiched between optical fibers.

The inventor of the present invention has been keen to study further practical use, and is capable of effectively transmitting signal light by processing a connection portion of a large POF into a tapered shape and optically coupling with a light receiving device having a small light receiving portion via a lens. Was found. That is, the connection portion of the POF is processed into a light guide having a long path and is optically coupled with a light receiving device and a lens to reduce connection loss. It has also been found that the optical transmission loss can be further reduced by interposing a flexible light transmitting body at the interface between the POF and the light receiving device during the optical connection.

[0008]

SUMMARY OF THE INVENTION The present invention is an optical connection method for reducing an optical transmission loss when a POF is connected to a light receiving device in an optical communication system.

[0009]

SUMMARY OF THE INVENTION The present invention is a connection method for reducing optical transmission loss by optically connecting a POF having a connection portion tapered to a light receiving device via a lens.
Another method is to reduce connection loss by interposing a flexible light transmitting body at the interface between the POF and the light receiving device.

According to a second aspect, the optical lens is mounted on a POF or a light receiving device.

A third aspect of the present invention is an optical connection method, wherein the cross section of the connection portion of the POF is substantially the same as the light receiving portion of the light receiving semiconductor element.

According to a fourth aspect of the present invention, the optical lens is a thin synthetic lens such as a Fresnel type or a Fraunhofer type.

[0013] Claims 6 and 7 relate to an optical transmission body, and have a refractive index of ± 0.05 of the value of a resin optical fiber.
Within, the hardness is less than JIS (A type) 50 degrees or less silicone resin, acrylic resin, epoxy resin,
It is at least one selected from elastomeric resins and derivatives of these resins.

[0014] PO which is considered to be used for consumer use in the future
F has a considerably large size of the input / output light portion as compared with a normal light receiving device. POF has a core diameter of 125 to 980 μm
However, the light receiving portion of the light receiving semiconductor element is 100 to 500
μm. Further, the processing of the POF is easy, but the processing of the light receiving semiconductor element is difficult. That is, it is practical to process the POF in order to optically connect the same area.

Examples of the method of processing the POF include a method of heating and stretching the POF and a method of sandwiching the POF with a heating jig. At the time of processing, it is necessary to take care that the reflection function of the clad portion does not deteriorate, and when there is a concern that the reflection function may be reduced, it is preferable to perform a simple reflection coating treatment. For example, a method of spraying a fluorine resin or attaching a highly reflective ferrule can be used. Also, P
It is particularly preferable to use a product whose refractive index increases continuously or stepwise from the outer periphery toward the center as the OF, since the reflection loss in the grad portion can be reduced.

It is preferable that the optical lens is attached to the front end of the POF or the light receiving device from the viewpoint of workability. Further, the optical lens preferably has a thin shape (Fresnel type, Fraunhofer type, etc.). The front end of the POF or the light receiving device may be subjected to lens processing (molding, printing, cutting, etc.).

It is effective and preferable to reduce the connection loss by interposing a flexible light transmitting body at the connection interface between the POF and the light receiving device. Since the interface is in close contact and the gap is eliminated, reflection and scattering can be prevented, and efficient optical transmission can be achieved. The light transmitting body is easy to handle if it is attached to the POF or the light receiving device in advance.

The refractive index of the light transmitting body and the refractive index of the optical fiber are preferably substantially the same, and the difference in the refractive index between the two is preferably within ± 0.05. If this difference is too large, loss of optical transmission is caused by reflection or the like.

The light transmitting body is flexible and has a hardness according to JIS (A
Is preferably 50 degrees or less, particularly 6 JIS (D type).
0 degrees or less is preferable. If it is too hard, the adhesion at the time of connection will be insufficient and a gap will be created, resulting in loss during optical transmission. Suitable resins include silicones, acrylics, epoxies, thermoplastic elastomers, and derivatives thereof. Commercial products can be selected from product catalogs such as Shin-Etsu Chemical Co., Toshiba Silicone, Toagosei, Nippon Kayaku and Asahi Kasei.

FIG. 1 is a diagram showing an example of an optical connection according to the present invention (a cross-sectional view taken from the side in the connection direction), wherein (1) shows a state before connection and (2) shows a state after connection. The tapered POF 10 is connected via an optical lens 15 to a light receiving device 16 (light receiving unit 17). The tapered portion of the POF is covered with a protective member 12 (ferrule, jacket, or the like). 14 is a light transmitting body, 18 is a plug, and 19 is a socket.

FIG. 2 is a diagram showing an example of an optical connection according to the present invention. POF20 whose tip is processed into a lens shape 25
Is a light receiving device 26 (light receiving unit 27) with a light transmitting body 24 interposed therebetween.
Is connected to 22 is a protective member, 28 is a plug, 29
Is a socket.

FIG. 3 is a diagram showing an example of an optical connection according to the present invention. The tapered resin POF 30 is connected via a light transmitting body 34 to a light receiving device 36 (light receiving portion 37) in which a Fresnel lens 35 is processed. 32 is a protective material, 38 is a plug, and 39 is a socket.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples.

[0024]

Embodiment 1 A PMMA-based POF (Toray, refractive index: 1.50, core diameter: 980 μm) and a metal-sealed light-receiving device (photodiode, light-receiving part diameter: 0.2 mm; Hamamatsu Photonics) Figure 1
Connected as in (2). The connection loss at this time is 0.2d
It was as small as B or less.

The tapered shape of the POF connection portion was processed by removing the jacket, heating and stretching the fiber main body, press-coating with a large jacket, and further cutting at the target core diameter portion.
The lens is a thin acrylic convex lens, and is sandwiched between heat-cured light transmitting members of an addition-reaction silicone (Shin-Etsu Chemical Co., Ltd.) having a hardness of JIS (A) of 20 degrees. The refractive index of both the lens and the light transmitting body was 1.50.

[0026]

Example 2 The same POF as in Example 1 was processed into a lens shape by pressing a heated mold at the tip of the POF. This P
The OF and the same light receiving device as in Example 1 were connected as shown in FIG. 2 (2) with a cured rubber-modified epoxy resin (Nippon Kayaku) as a light transmitting body. The connection loss at this time was also 0.2 dB or less. The hardness of the light transmitting body was JIS (A) 10 degrees, and the refractive index was 1.50.

[0027]

Embodiment 3 An acrylic Fresnel lens (Terasaki) was adhered to the light receiving window of the light receiving device of Embodiment 1. This light receiving device and the POF of Example 1 were connected via a light transmitting body.
The connection loss in this case was also 0.2 dB or less. The light transmitting body used was a urethane elastomer sheet (Cosmo Instruments) having a hardness of 5 degrees / JIS (A).

[0028]

[Comparative Example 1] In Example 1, P was not tapered.
A connection experiment was performed using OF. In this case, the connection loss was 6.1 dB, and it is considered that the signal light was not effectively transmitted because the light receiving portion of the light receiving device was considerably smaller than the core portion of the POF.

[0029]

Comparative Example 2 In Example 1, the POF and the light-receiving device were connected without using a lens and a light transmitting body. The connection loss in this case was 1.2 dB. Although the connection loss was reduced as compared with the first embodiment due to the effect of the tapering process, a large loss was caused as compared with the first embodiment.

[0030]

Comparative Example 3 An experiment was conducted in the same manner as in Example 1 except that the hardness of the silicone was 55 degrees in accordance with JIS (A). In this case, the optical transmission loss at the connection portion was 1.5 dB. That is, it is considered that a gap is formed at the boundary between the POF and the light receiving device due to the rigidity of the light transmitting body, causing considerable connection loss.

[0031]

When the POF and the light receiving device are optically coupled by the method of the present invention, the optical transmission loss at the time of connection can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one example of an optical connection method of the present invention.

FIG. 2 is a diagram showing one example of the optical connection method of the present invention.

FIG. 3 is a diagram showing one example of the optical connection method of the present invention.

[Explanation of symbols]

 10, 20, 30 Resin optical fiber 12, 22, 32 Protective member 14, 24, 34 Light transmitting body 15, 25, 35 Lens 16, 26, 36 Light receiving semiconductor device 17, 27, 37 Light receiving section 18, 28, 38 Plug 19, 29, 39 Socket

Claims (7)

[Claims] 1. An optical connecting method, wherein a connecting portion optically couples a tapered resin optical fiber and a light receiving semiconductor device via an optical lens. 2. The optical connection method according to claim 1, wherein the optical lens is mounted on a resin optical fiber or a light receiving semiconductor device. 3. The optical connection method according to claim 1, wherein the cross section of the connection portion of the resin optical fiber is substantially the same size as the light receiving portion of the light receiving semiconductor element. 4. The optical connection method according to claim 1, wherein the optical lens is a thin synthetic lens such as a Fresnel type or a Fraunhofer type. 5. The optical system according to claim 1, wherein a flexible light transmitting body is interposed at a boundary surface between the optical lens and the resin optical fiber and / or the light receiving semiconductor device and optically coupled.
The optical connection method according to 1. 6. The optical connection method according to claim 5, wherein the refractive index of the light transmitting body is within ± 0.05 of the refractive index of the resin optical fiber. 7. The light transmitting body is at least one selected from a silicone resin, an acrylic resin, an epoxy resin, an elastomer resin and a derivative of these resins having a hardness of 50 degrees or less according to JIS (A type). The optical connection method according to claim 5, wherein: