JPS6262306A - Plastic optical fiber and edge surface processing method - Google Patents

Abstract

PURPOSE:To improve the introducing efficiency, the coming-out efficiency, and the space factor of the light by molding the edge surface of the core part of the plastic optical fiber into the Fresnel lens shape having the prescribed focus distance. CONSTITUTION:An edge surface 12 of a core part 11 of the optical fiber is formed to the Fresnel lens shape having the prescribed focus distance. The forming process is composed of the process to push the edge surface of the core part 11 to a Fresnel lens-shaped type 33 formed on the surface of a heating plate 31, the process to heat the edge surface of the core part 11 to the thermal deformation temperature by a heating plate 31 and transfer the Fresnel lens shape formed at the type 33 to the edge surface, and the process to reduce the temperature of the heating plate 31, reduce the temperature of the edge surface of the core part and stabilize the Fresnel lens shape transferred to the edge surface of the core part. Thus, the simplification and the low cost of the introducing efficiency, the coming-out efficiency, the space factor of the light and the processing of the Fresnel lens shape of the edge surface are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention uses a transparent plastic material at least in the core portion to transmit optical signals. ! The present invention relates to plastic optical fibers used in , and 4I relates to the shape of the end face of the plastic optical fiber and an end face processing method for forming the end face into this shape.

[Background of the invention]

A plastic optical fiber is formed by covering a core made of fibers such as acrylic-based methacrylic resin with a cladding of, for example, fluorine-containing methacrylic resin, which has a lower refractive index than the core, and serves as a waveguide for transmitting light. used.

In order to use it as a light waveguide, one end face of a plastic optical fiber (hereinafter abbreviated as optical fiber) was used as the incident face from the light emitting side, and the other end face was used as the exit face. Both end faces 3c were finished as smooth as possible in the shape shown in the figure. This is because if the finish of the end surface 3e' is rough, the light may be diffusely reflected or totally reflected at the end surface 3C, causing optical loss, and the light from the exit surface may be diffused. , a predetermined light receiving element 2
The amount of light that effectively enters the light receiving side such as a decreases &
This is to help you.

As described above, it is essential for an optical fiber to have a smooth finish on the end face 3cf of the core 3a, and known methods for finishing the end face 3c include using a grinder and using a heating plate. In particular, a method of pressing the end face of an optical fiber against a heating plate having a smooth surface to make the end face smooth is known as 1% Publication No. 15241/1983.

On the other hand, no matter how smooth the end face of an optical fiber is and how much light output a light emitting diode or semiconductor laser as a single light emitting element outputs, it is meaningless unless light enters the optical fiber efficiently. There are two types of light-emitting diodes: single-face emitting type and edge-emitting type, but in either case, the intensity distribution of the light emitted is almost isotropic, and the light spread in this way is transferred to the original fiber with a small core diameter. It is difficult to put it in. Furthermore, as shown in FIG. 6, due to the difference in refractive index between the core 3a and the cladding 3b, the incident light may not be totally reflected between the core 3a and the cladding 3b, and the light may be transmitted from the core 3a to the cladding 3b side. Therefore, it is necessary to guide the light to the core 3a at a shallow angle θ. (Incidence angle at which total reflection occurs at θ beam 2 and 3b). That is, even if the core 3a is formed smoothly, only a portion of the light incident on the end face of the core 3a is introduced into the core 3aK. For this purpose, for example, as shown in FIG. 7, a lens l is inserted between the light emitting diode 2 and the optical fiber 30 to converge the light from the light emitting diode 2 and make it enter the core 3a of the optical fiber 3. be. In this structure, in order to guide light to the core 3a at a shallow angle θ, it is sufficient to bring the lens 1 close to the light emitting diode 2.
It spreads beyond the diameter a, and much light does not enter the optical fiber 3. If the light emitting area is made smaller to avoid this, the light output of the light emitting diode 2 will become smaller, so the optical fiber 3
The light output that enters is also reduced. Also.

If the lens 1 is moved further away, the image in one light emitting area will become smaller, or the angle of incidence will become deeper, and the amount of light that does not enter the lens 1 will increase. There is also the problem that the space factor is also degraded by inserting the separate lens 1 into the optical path.

For these reasons, various coupling methods are used to guide more light into the core 3b of the optical fiber 3 at a shallow angle θ. This - as an example.

As shown in FIG. 8, there is an optical fiber called a spherical fiber in which one end of the core 3a of the optical fiber 3 is formed into the shape of a spherical lens 4. This spherical-tipped fiber is often used in fibers that use glass fiber for the core 3a, and can receive light over a wider area than the end area of the core 3a, and can introduce the received light into the core 3a at a shallow angle. However, since the tip of the optical fiber 3 is enlarged into a spherical shape, it is difficult to install it close to the light emitting element (light emitting diode) 2 and the light receiving element using a plug or connector, which poses a problem in usability.

In addition, it is not easy to finish the end face of a plastic optical fiber whose core 3a is made of a polymeric material into a spherical lens as shown in the same figure.Due to the difference in refractive index from the glass material, this spherical tip shape is made of plastic. It has rarely been applied to optical fibers. On the other hand, the end surface 3 formed smoothly
Even when light is emitted from c, as shown in Fig. 5, the light expands beyond the diameter of the core 3a, so there is a problem that the efficiency decreases unless the light receiving area of the light receiving element 2& is widened. , a condensing means such as a lens may be inserted between the end surface 3c and the light receiving element 2&.

However, inserting a lens not only costs money, but also requires space to insert the lens).
Problems also arise in terms of space factor.

[Purpose of the invention]

The present invention has been made in view of the actual state of the prior art described above, and its purpose is to provide an optical fiber that can transmit all the light incident on at least the end face by introducing it into the core. Another object is to provide an optical fiber that can efficiently emit introduced light to the light receiving side. Another object is to realize the improvement of the above characteristics with a good space factor.

Still another object is to propose a method for manufacturing an optical fiber with excellent light introduction efficiency and light output efficiency as described above.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the end face of the core portion of the optical fiber is formed into a Fresnel lens shape, and further, the end face is formed into a Fresnel lens shaped mold formed on the surface of a heating plate. a pressing step, a step of heating the end surface to a heat deformation temperature by the heating plate, and transferring a 7-Lehnel Lemme shape formed in a pattern onto the end surface, and a step of lowering the temperature of the heating plate to reduce the temperature of the end surface. The present invention is characterized in that a seven-channel lens body can be formed on the end face of the core portion of the optical fiber through a step of lowering the angle and fixing the transferred Fresnel lens shape on the end face.゛[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 are for explaining an optical fiber according to an embodiment of the present invention, and FIG. 1(a) is a diagram.

FIG. 1(b) is an enlarged end view of the core portion of the original fiber, FIG. 1(b) is a front view showing the end face shape of the optical fiber, and FIG. 2 is an exploded perspective view showing an example of how to attach the optical fiber to the light emitting element side. .

In FIGS. 1 and 2, an optical fiber 10 is shown.

For example, the core 11 consists of a core 11 made of fibers such as acrylic methacrylic resin, and a cladding 13 made by coating the core 11 with a fluorine-containing methacrylic resin having a lower refractive index than the core 11. The end surface 12 of is formed into a Fresnel lens shape. A Fresnel lens has the optical characteristics of a thick lens.
It is formed in the shape of concentric steps as shown in FIG. In this case, the setting is made to focus on the light receiving portion 14a of the light receiving element 14.

FIG. 2 shows an example of a structure in which the optical fiber 10 is opposed to the optical element 15. That is, the optical element 15 is attached to one side of the connector 1G, and the entire core 11 with the cladding 13 of the optical fiber 10 partially peeled off is attached to the plug 17'! I#, and insert the plug 17 into the connector 16 so that the Fresnel-shaped end surface 12 of the core 11 and the end surface 18 of the plug 17 almost match. Then, the collar 20 of the plug 17 is elastically engaged with the engagement protrusion 19 of the connector 16.
Just so that the optical element 150 and the semiconductor chip 21 are at the focal point of the Fresnel lens body on the end surface 12 ((((, the end surface 12
faces the optical element 15. By arranging it in this manner, when the optical element 5 is a light receiving element, light is concentrated on the semiconductor chip 21 which is a light receiving part, and the light receiving efficiency can be improved. Further, when the optical element 15 is a light emitting element, the light incident on the end face 12 out of one emitted light becomes almost parallel light and is introduced into the core 11, so that the light is transmitted to the cladding 13 side. Therefore, the optical loss due to the transmission of this light can be minimized, and the light incident on the end face 12 can be efficiently transmitted.

Next, a method for processing the end face of the core 11 of the optical fiber 10 will be explained with reference to FIGS. 3 and 4.

Fig. 83 shows an example of a heating device with a mold 33 in the shape of a Fresnel lens formed on the surface used in this processing method. The heating plate 31 consists of a heating plate 31 and heat sources 32 such as electric heaters attached to both ends of the heating plate 31 to heat the heating plate 31.

This processing method consists of the following three steps.

In the first step, as shown in FIG. 4, the end surface 12 of the core 11 of the optical fiber 10 is pressed perpendicularly to the Fresnel lens-shaped ring 33 of the heating plate 31. This is done by setting the right angle and appropriate pressing force.

In the second step, the end surface 1 of the core 11 is heated by the heating plate 31.
Since the shape of the mold 33 is transferred to the end surface 12 by heating the mold 33 to a heat deformation temperature of, for example, about 80°C, the heating part 1 is
The heating time is appropriately set depending on the material of the core 11.

In the third step, the temperature of the heating plate 31 is lowered to, for example, 40°C to room temperature, and the temperature of the end face 12 is lowered to the core 1.
The curing temperature is lowered to No. 1, and the Fresnel lens shape transferred to the end face 12 is fixed to the end face. At this time, weir 33
Since the concavities and convexities are set to approximately 30 to 50 .mu.m, a concentric groove-shaped Fresnel lens body having concavities and convexities of approximately 30 to 50 .mu.m is also formed on the end face 12. The focal length of this Fresnel lens body can be freely set depending on the refractive index and the inclination angle of the convex portion.

As described above, according to this embodiment, by simply pressing the end face of the core 11 against the mold a3 and heating it, the end face can be easily processed into a Fresnel lens body having a predetermined focal length. . This effort is the same as the conventional process of smoothing the end face, making it possible to process the end face of a complex Fresnel lens shape at extremely low cost.

〔Effect of the invention〕

The present invention is configured as described above.

This has the effect of providing a plastic fiber with excellent light introduction efficiency and light output efficiency, and a good space factor. Further, according to the method of the present invention, there is an effect that the end face of an optical fiber can be easily and efficiently processed into an end face shape having the above characteristics.

[Brief explanation of the drawing]

1 and 2 are for explaining the original fiber according to the embodiment of the present invention, FIG. 1(a) is a conceptual diagram showing the end face shape of the core, and FIG. 1(b) is a conceptual diagram showing the end face shape of the core. FIG. 2 is an exploded perspective view showing an optical fiber, an optical element, and a coupling device for these, and FIGS. 3 and 4 are for explaining the method of the present invention. , FIG. 3 is a perspective view of the heating device, FIG. 4 is a conceptual diagram showing an end face processing method, and FIGS. 5 to 8 are for explaining conventional examples. FIG. 5(a) is a conceptual diagram of an optical fiber with a smooth end surface, FIG. 5(b) is a front view showing a smooth end surface, FIG.
FIG. 7 and FIG. 8 are conceptual diagrams showing the introduction path of light, respectively. 3.10...Optical fiber, 3a, 11...
··core. 3b, 13...Clad, 3o, 12...
···End face. 31... Heating plate, 32... Heat source, 33
・・・・・・Type. Figure 1 Figure 3 (a) 14σ Figure 4 Figure 5 Figure 6 tσ Figure 7 Figure 8

Claims (2)

[Claims] (1) A core part made of a transparent plastic material and a clad part covering this core part, which allows light to enter from one end surface of the core part and transmit the received light through the core part. 1. A plastic optical fiber that emits light from an end face, wherein the end face of the core portion is formed into a Fresnel lens shape having a predetermined focal length. (2) Press the end face of the core part of an optical fiber, which has a core part made of a transparent plastic material and a clad part covering this core part, into a Fresnel lens-shaped mold formed on the surface of a heating plate. a step of heating the end surface to a heat deformation temperature by the heating plate to transfer the Fresnel lens shape formed in the mold onto the end surface; and a step of lowering the temperature of the heating plate to transform the end surface. A method for processing an end face of a plastic optical fiber, comprising the steps of lowering the temperature and fixing a Fresnel lens shape on the end face.