JPS58123512A - Optical fiber - Google Patents

Abstract

PURPOSE:To obtain optical fibers having high efficiency of optical coupling, by making the optical coupling end to a cone so as to be gradually finer at its end by forming as well a round top part having a larger diameter than a core diameter integrally with the same material as the core. CONSTITUTION:The top end part of optical fibers 8 is processed to a cone by a mechanical grinding and is processed to a round top so that the carvature (a)= about 5mum by heating intensively by a H2 burner 10 (or arc discharge). Quartz etc. of the same material as a core are stuck on the top end of the core 1 by melting to form a round top part 11 having the larger diameter than that of the core 1. The part 11 is heated by the burner 10 etc. to form a radius of carvature of the top end to about 7-12mum. By making the radius of carvature of the top end at the round top part 11 to 7-12mum, the light receiving surface is made to be larger than the core diameter, and therefore an efficiency of optical coupling is improved greatly by 35-40% as compared with 10-20% in the past.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to an optical fiber, and more particularly to the structure of an optical coupling end of an optical fiber.

Although single-mode fiber coupling is advantageous for long-wavelength laser diodes for communications, the optical coupling efficiency (also simply referred to as coupling efficiency) was poor, and commercialization was not possible.

For example, optical fibers used in optical communications to take in and transmit light from a light source such as a laser diode are usually made of a transparent material and have a uniform high refractive index, as shown in Figure 1. A core part (core) 1 and a cladding F that covers it and has a uniformly low refractive index smaller than the core part
It is composed of a steel plate 2 and a jacket 3 provided on its surface. In conventional optical fibers, as shown in the figure, the entire fiber tip, including the core and cladding layer that faces the light source, is processed into a spherical surface with a gentle curvature (spherical processing). It is designed to take in as much of the diffused laser light 4 as possible by utilizing the light condensing effect due to the lens effect. However, in spite of this, the coupling efficiency between the laser diode and the optical fiber is as low as about 10%, which has been a big problem in practice.

On the other hand, as shown in FIG.
A structure in which the fibers are guided to the core 1 is also being considered, but the coupling efficiency is as low as 20%. Furthermore, this structure has poor temperature characteristics because the cylindrical lens 7 is newly added. In other words, even if the optical coupling end of the optical fiber 8 is located at the height where the laser beam 4 of the Lebo diode chip 6 is emitted, the temperature will change due to the difference in the coefficient of thermal expansion of each member supporting the -0 element. This causes a shift in optical coupling. For this reason, since the cylindrical lens 7 is further used, the optical coupling property tends to worsen as the temperature changes.

Therefore, an object of the present invention is to provide an optical fiber with high optical coupling efficiency.

In order to achieve such an object, the present invention provides an optical fiber consisting of a core and a cladding surrounding the core having a refractive index lower than that of the core, in which the optical coupling end of the optical fiber has a conical shape whose tip gradually tapers. At the same time, the tip of the tip is integrally formed with a bulbous end made of the same material as the core and larger in diameter than the core.The present invention will be explained below with reference to Examples.

Figure 3 (al ~ (cl) and Figure 4 tal, (bl
1A and 1B are a cross-sectional view and a perspective view showing a method of manufacturing an optical fiber according to an embodiment of the present invention. □ First, as the optical fiber 8, for example, a single mode quartz fiber is prepared. That is, as shown in FIG. 3 (al), a core part 1 with a diameter r = 10 μm and a refractive index n, and a core part 1 with an outer diameter r = 125 μm and a refractive index n! (nl > An optical fiber 8 consisting of a cladding layer 2 (nw) is prepared.

Both the core 91 and the cladding layer 2 are mainly made of quartz.

S10. The cladding layer 2 is doped with impurities such as B, 01, etc. in order to reduce its refractive index. Further, the tip (optical coupling end) facing the light source is cut into a plane.

Note that 3 is a fiber jacket (film) made of, for example, nylon, which covers the optical fiber.

As shown in FIG. Figure + al
As shown in 1-, the optical fiber 8 is brought into contact with the flat surface of the rotating grindstone 9 at a predetermined angle while rotating, and polished.

The state in which the core s1 protrudes from the cladding layer 2 is determined by processing the tip of the optical fiber into a flat conical shape before processing the tip.

Next, the tip of the core portion is processed so that the curvature a is approximately 5 μm. Specifically, as shown in FIG. 4 tb+, the optical fiber is held vertically and the burner 10 is
This is done by strongly heating the tip of the core portion using an arc group 1ll. By doing this,
At the tip of Hikari 7 Eyeva, only the core part l is processed into a hemispherical shape,
On the other hand, the cladding part remains almost in the same state as when it was polished7. ),,Note that due to the heating during processing of the tip ball, the unevenness created on the polished surface during polishing, especially the unevenness of the core protrusion that affects the characteristics, is smoothed out and its influence can be removed.

Curvature a of the tip of the core product formed in this way
is the size of the apex angle θ mentioned above, H, and the degree of heating of the burner (
(time, temperature). The heating temperature is limited by the material of the optical fiber.

Next, quartz or the like made of the same material as the core is adhered to the tip of the core 1 by melting, and a tip ball portion 11 larger than the diameter of the core 1 is formed. This tip ball portion 11 is shown in FIG.
l) It is heated by an H, burner, etc. as shown in I, and the radius of curvature of the tip is 7 to 12 as shown in Figure 3 (C1).
It is formed on the order of μm.

Next, as an example of a light emitting semiconductor device with an optical fiber using an optical fiber having such an optical coupling end, a laser diode device with an optical fiber is shown in FIGS. 5 to 7. Figure 5 is the overall plan view, Figure 6 is the Vl of Figure 5.
It is a sectional view along the -Vl line. In both figures, 12 is a stem, and 5 is a submount, which are made of conductive material. 6 is a laser diode chip, and 13 is a lead electrically insulated from the stem 12, which is connected to the top electrode of the laser diode tip 6 via a gold wire 14. On the other hand, 15 is a GND IJ-de, which is coupled to the lower s'* pole of the racer chip 6 via the conductive stem 12 and the submount 5. 8 is the same optical fiber as shown in FIG. 3 (cl), and 3 is its IP
ji (fiber jacket), the optical fiber 8 faces the laser diode chip 6. A monitor fiber 16 is provided on the opposite side of the optical fiber 8 with the laser chip 6 inside.

FIG. 7 is an enlarged view of the configuration in which the laser diode chip 6 and the optical fiber 8 face each other.

The laser diode tip 6 is fixed onto the submount 5 via a conductive solder 17.

Furthermore, this submount 5 is fixed onto the stem 12 via a conductive solder 18. In addition, the output surface of the laser diode chip 6 and the tip of the optical fiber 8 f! 11
Distance l from the tip of 1, 11! For example, li4 is 25 μm.

According to such an embodiment, by setting the radius of curvature of the tip of the spherical tip portion 11 to 7 to 12 μm, the light-receiving surface can be made larger than the core diameter, so that the optical coupling efficiency is determined by the experiment shown in FIG. As shown in the graph, this is a significant improvement of 35-40% compared to the conventional 10-20%. This can also be said to be a coupling efficiency that reaches a practical level. Note that the coupling efficiency is defined as the output (W) of a racer diode received by a charging conversion element through a fixed length of optical fiber having a known loss rate. It was calculated by converting it into electricity 311 (mW).

Further, according to this embodiment, the tip of the tip ball portion 11 is set at 7 to 1
By setting the radius of curvature to 2 μm, the reflected light of the laser beam from the tip ball s11 returns to the laser diode chip 6.
Since there is a marked decrease in the number of noises that occur, there is also the effect that noise generation can be significantly reduced compared to conventional methods.

Note that the present invention is not limited to the above embodiments,
Modifications are possible based on the technical idea of the present invention. Further, the present invention can also be applied to multi-mode communication optical fibers such as stepped type and graded type having a core diameter of 50 μmφ.

As described above, according to the present invention, since it is possible to provide an optical fiber with high optical coupling efficiency, single mode optical communication is also possible.

[Brief explanation of drawings]

Figures 1 to 1 are cross-sectional views of conventional optical fibers, Figure 2 is a cross-sectional view showing the main parts of conventional optical fibers, and Figure 3 is a cross-sectional view showing the main parts of a laser diode.
, fbl&1 A cross-sectional view and a perspective view showing a method of manufacturing an optical fiber according to an embodiment of the present invention, FIG. 5 is a plan view of a laser diode incorporating the optical fiber of the present invention, and FIG. - A cross-sectional view along the Vl plum. FIG. 7 is an enlarged sectional view of the main part, and FIG. 8 is the same (a graph showing optical coupling efficiency). 1...core, 2...cladding, 4...laser light,
5... Submount, 6... Laser diode chip, 8... Optical fiber, 11... Tip bulb, 12...
...Stem, 16...Monitor fiber. (9) 65 Fig. 5 Fig. 6 Fig. 66- Fig. 7 Fig. 8 Fig. 8 -r Gi Ministry 4 (ptnt)

Claims (1)

[Claims] 1. In an optical fiber consisting of a core and a cladding that surrounds the core and has a refractive index lower than that of the core, the optical coupling end of the optical fiber has a conical shape with a tip that gradually becomes narrower, and the tip has the same shape as the core. An optical fiber that is made of a material that is integrally formed with a tip bulb that is larger than the core diameter.