JPS6323106A - Optical coupler - Google Patents

Abstract

PURPOSE:To make an optical fiber to have an easily formable excellent and mechanically stabilized pointed end face so as to improve the coupling efficiency of the optical fiber, by installing a tapered section which is gently narrowed toward the end to the end of the optical fiber composed of a core and clad formed around the core and a semispherical end section to the leading edge of the tapered section. CONSTITUTION:The end section of an optical fiber 11 is gently narrowed and a tapered section 12 is formed. The end section of the tapered section 12 is cut off at a point, at which a prescribed outer diameter is obtained, and the end face 13 is heated so as to obtain a semispherical form. The semispherical form can be easily obtained due to the surface tension when the end face of the optical fiber 11 is heated. Moreover, roughness of the surface, such as a scratch, etc., formed before heating can be removed. In addition, the semispherical end face 13 acts as a lens and transforms rays of light radiated from a light source at a wide divergent angle into a narrower divergent angle. Since the tapered section 12 can be made shorter, furthermore, the mechanical stability can extensively be improved and variation of the degree of coupling caused by a positional shift can be reduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to an optical coupling device used for optical fiber communication, etc., and in particular to an optical coupling device that can improve the coupling efficiency between a light source and an optical fiber. It is related to.

(Prior Art) In optical fiber communications, improving the coupling efficiency of optical power between a light source such as a semiconductor laser or a light emitting diode and an optical fiber is an important issue indispensable for configuring an efficient system.

Conventionally, the structure of such a coupling part is the second pA (a
There are various types shown in ) to (d). In other words, the same figure (a
) is the end 2 of the fiber 1 formed into a hemispherical shape, (b) is a ball lens 4 placed close to the end of the fiber 3, and (C) is a cylindrical lens 5 instead. This is what I put. Further, (d) shows an example of the tapered fiber 6.

Among these, the one that can realize the maximum coupling efficiency allowed by Liouville's theorem is (d
) tapered fiber. In fact, it has been reported that the coupling efficiency between a tapered fiber and a semiconductor laser reaches 97%. Even when coupled with a light emitting diode, the numerical aperture is 0.
．． A coupling efficiency of 83% was achieved with 26 fibers, which is known to be overwhelmingly high efficiency.

(Problems to be Solved by the Invention) However, there are also the following problems in the case of tapered fibers.Tapered fibers require a tapered portion of about 5 mm in length, which is relatively long, and there is a risk of shrinkage. In the tapered part, the external total reflection of the cladding is used, so the medium outside the cladding is air (or n=1
) is desirable. Therefore, it is difficult to fix using an adhesive or the like, and the degree of bonding may change due to positional displacement due to temperature changes.

Furthermore, the tip of the tapered fiber should have approximately the same dimensions as the light emitting surface of the light source to provide maximum coupling efficiency. Therefore, the diameter at the tip of the taper is approximately 20 μm, which has the drawback that it is difficult to easily obtain a good surface by cutting, resulting in poor yield.

Furthermore, if the light emitting surface of the light source is small, it is extremely difficult to manufacture a tapered fiber with a minute tip diameter corresponding to this. That is, when the tip of the fiber becomes thinner, the heat capacity decreases and the heating temperature rises. Therefore, the S fiber may become too hot and break, and there is a limit to the diameter reduction.

In addition, tapered fibers with small tip diameters may have a reduced coupling effect due to imperfections such as surface irregularities or bends in the small diameter portion, or are easily affected by vibrations, which may cause misalignment. A decrease in efficiency could not be avoided.

The present invention has been made based on the above-mentioned circumstances, and it is an object of the present invention to provide an optical coupling device that is easy to manufacture, can obtain a good tip surface, is mechanically stable, and can improve coupling efficiency.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a tapered portion in which the distal end portion of an optical fiber consisting of a core and a cladding covering the core is gently thinned;
The present invention provides an optical coupling bag 4 having a hemispherical end portion formed at the tip of this tapered portion.

(Function) According to the present invention, since the tip end surface of the tapered portion is formed into a hemispherical shape by heating, the tip diameter of the tapered portion can be made relatively thick. Therefore, there is little decrease in heat capacity, and processing during heating is easy, and the tip surface can be formed into a good hemispherical surface due to surface tension during heating. In addition, the optical coupling device obtained in this way has a relatively large tip diameter and a short taper part, so it is easy to position with respect to the light source, and has high mechanical stability, so it has the advantage of increasing coupling efficiency. .

(Example) The tapered part 12 is made by gently thinning the tip part.
form. The tip of the tapered portion 12 is cut at a portion having a predetermined outer diameter, and the enlarged surface 13 is further heated to form a hemispherical shape. In the figure, 14 is the cladding, and 15 is the core.O In the case of conventional equipment that simply cuts the tapered part at a predetermined position, as shown in VIA (d), scars from the cutter usually remain. , causing scattered light. Although it is possible to polish this surface, it is not possible due to the high cost.In contrast, the coupling device of the present invention heats the end surface of the optical fiber 11 and easily obtains a hemispherical surface due to surface tension. . At this time, surface roughness such as scratches that existed before heating is also removed.

Furthermore, this hemispherical tip surface 13 acts as a lens, converting the light rays emitted from the light source with a large divergence angle into a smaller divergence angle.

Therefore, the role of reducing the divergence angle in the tapered part 12 is shared by the lens part of the distal end surface 13, and this is promoted, thereby reducing the taper ratio (the ratio of the outer diameter of the tapered end to the distal end). If the taper angle is kept constant, the length of the tapered portion 12 can be reduced.

Since the tapered portion 12 can be shortened in this manner, mechanical stability can be significantly improved, and changes in the degree of coupling caused by positional displacement can be reduced.

Furthermore, the coupling device of the present invention has the advantage that the distance from the light source can be increased when compared with the tapered fiber coupling device shown in Figure X+/(d).

That is, in the case of a tapered fiber coupling device, since the tip diameter is small, the distance from the laser must be extremely small, ie, several micrometers or less.

On the other hand, in the optical coupling device according to the present invention, the diameter of the tip can be increased, and the distance from the light source can be set to about several tens of μm. Therefore, it is easier to position and fix the laser than the conventional one, there is no risk of damaging the laser, and the amount of light reflected to the laser can be drastically reduced.

Reducing reflected light to a laser is an essential condition for stable laser operation, and the present invention is effective in satisfying this requirement.

As is clear from the above description, the present invention is characterized in that it not only simply combines the advantages of a fiber with a hemispherical end and a tapered fiber, but also further enhances these advantages. At the same time, it is possible to provide an optical coupling device that can reduce reflected light by reducing the tapered portion, thereby increasing the coupling efficiency and increasing the coupling distance with the light source.

Note that this invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist.

For example, in the above-mentioned embodiments, the tapered portion has a linear slope as shown in the figure, but a curved surface may also be used depending on the case.

〔Effect of the invention〕

According to the present invention, it is possible to obtain an optical coupling device that is mechanically stable and has high optical coupling efficiency.

[Brief explanation of the drawing]

1.3...Fiber 2...End portion 4...Spherical lens 5...Cylindrical lens 6...Tapered fiber 11°° Optical fiber 12...°Tapered portion 13...
Tip surface 14...Clad 15...F.

Claims (1)

[Claims] An optical coupling characterized in that an optical fiber consisting of a core and a cladding covering the core has a tapered portion in which the tip portion is gently thinned, and a hemispherical end portion formed at the tip of the tapered portion. Device.