JPH0441321B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an improvement of a star coupler that is desired to couple an optical signal from an arbitrary optical fiber to another optical fiber evenly and without loss. This invention relates to a star coupler that is easy to assemble and adjust.

(Prior Art) Fig. 1 is a diagram showing an example of a conventional star coupler.
-A' sectional view. In the figure, 1 is a transparent cylindrical glass rod with both ends cut at right angles, and 2 is an optical fiber consisting of an optical fiber core 3 and an optical fiber clad 4.

As shown in the figure, the star coupler is made by applying an optical reflective coating treatment to the inside of one side of the glass rod 1, in this case the B side, by depositing a metal film such as gold or aluminum to obtain an optical reflective coating, and on the inside of the other side, this side. In this case, the C-plane is made up of a group of optical fibers 2 bound by guides (not shown) and whose tips are flat-polished together, and made of optically transparent epoxy resin or the like. They are constructed by vertically sticking them together and butting them together using adhesive.

Next, regarding the diffusion of light in the star coupler as described above, light from any one optical fiber 2 is diffused into the glass rod 1 through its C-plane.
A part of the light diffused into the glass rod 1, for example, the diffused light H, is totally reflected at the boundary of the outer surface D of the glass rod 1 (however, the refractive index of the glass rod 1 is the refractive index of the surrounding medium). (assumed to be set higher than It progresses and reaches the C plane. Therefore, if the length of the glass rod 1 where light is repeatedly reflected is made long enough, the light from any one optical fiber 2 that reaches the C plane will be reflected in the diameter cross section of the glass rod 1, in other words, It is clear that the particles are almost uniformly diffused over the entire cross section shown in FIG. 1b. That is, a plurality of optical fibers 2 bound by guides (not shown) are closely adjacent to the C surface of the glass rod 1 (7 in FIG. 1).
Therefore, a portion of the light from any one optical fiber 2 is equally divided and transmitted to the other optical fibers (6 in this case) as diffused light, and the optical signal is This type of operation provides the function of a star coupler.

However, in the star coupler as described above, when focusing on the C surface of the glass rod 1,
There is a gap forming part 5 formed between the optical fiber cladding 4 and the bound optical fibers 2 other than the cross section of the optical fiber core 3 through which the optical fibers 2 that are in close contact with each other transmit light. Therefore, even the light that is diffused as described above and reaches the C-plane is not coupled to other optical fibers 2, resulting in a loss of optical signals.

Furthermore, in order to reduce the above-mentioned loss, it is possible to remove the optical fiber cladding 4 of each optical fiber 2 in advance and bind a plurality of optical fibers 2 in this state so that they are closely adjacent to each other. Removing only the optical fiber cladding 4 from the original optical fiber 2 requires a very difficult work process and a high level of technical skill. For example, even if the optical fiber cladding 4 is removed and only the optical fiber core 3 is obtained, gaps will still be formed between the bound optical fibers 2, and optical signal loss cannot be eliminated. .

Furthermore, in order to obtain low loss, the cylindrical diameter of the glass rod 1 needs to be the same as the diameter L of the optical fiber group made up of a plurality of bound optical fibers, and high accuracy is required in the alignment of the two. There were also manufacturing problems.

(Objects and Structure of the Invention) The present invention has been made in consideration of these points, and at the same time provides a star coupler with low loss, and at the same time, eliminates the need for alignment adjustment in the manufacturing process. That is, this type of star coupler is characterized in that an optical reflective film is formed on the plane polished portion of the optical fiber other than the optical fiber core, which eliminates the problems of the prior art. It is. Hereinafter, the present invention will be explained using figures.

Embodiment FIG. 2 is a diagram showing an embodiment of the star coupler according to the present invention, and FIG. 2A is an explanatory view thereof, and FIG. The difference between the star coupler of the present invention shown in FIG. 2 and the conventional star coupler shown in FIG.
In other words, the optical fiber cladding 4 and the gap forming part 5 formed between the optical fibers 2 are coated with an optical reflective film G, and the diameter L' of the glass rod 1 is large enough to accommodate multiple (seven) beams. It is larger than the group of optical fibers formed by binding the fibers 2 together.

Next, let's look at the diffusion of light in the star coupler as described above. Any single optical fiber 2
The light from the glass rod is diffused and reflected within the glass rod, as in the conventional case explained in FIG. 1, and returns to the C plane, which is the fiber joint side. however,
In the case of the present invention shown in FIG. 2, the part of the diffused light that is not coupled to the optical fiber core 3 of the other optical fiber 2 is reflected by the effect of the optical reflection film G formed on the C surface of the glass rod 1. Then, it is returned to the B surface, which is the reflective side of the other end of the glass rod 1, and repeatedly moves back and forth between the two reflective films. Due to these back and forth processes of the diffused light, the diffused light that could not be coupled with other optical fiber cores is given the opportunity to couple with other optical fiber cores again, and by repeating these back and forth processes, the diffused light from any optical fiber is All of these can be coupled to other optical fibers, which theoretically makes it possible to construct a lossless star coupler.

At this time, it is a matter of course that the reflectance of the optical reflective film G is perfect, and that the angle between the B surface and C surface forming both surfaces of the glass rod 1 and the central axis of the glass rod 1 is perpendicular. Conditions are necessary. Note that this condition is also necessary for the conventional star coupler described in FIG.

Here, the formation of the optical reflection film G on the optical fiber coupling part side of the glass rod 1 will be explained: (1) A plurality of optical fibers are bound using a guide and fixed adjacent to each other to form an optical fiber group. One end face is polished all at once.

(2) A protective film, such as a photoresist film, which is hardened by ultraviolet irradiation is applied to the end face of the optical fiber group polished in step (1), and then light having a wavelength to which the applied photoresist film is sensitive is applied. For example, an ultraviolet light source is irradiated from the other end of the optical fiber to solidify the photoresist film only on the optical fiber core.

(3) Develop the tips of the optical fiber group bound by the guide obtained by the process in (2) to obtain an optical fiber group in which only the optical fiber core at one tip is protected by a photoresist film.

(4) After performing a metal vapor deposition process using gold, aluminum, etc. on the tip end face of the optical fiber group in the state of (3), the solidified photoresistor film is removed by etching process.

(5) The photodist film is removed by the process in (4),
Only the cross section of the optical fiber core is exposed, and the other parts, that is, the optical fiber cladding and the gap forming part, are all covered with an optical reflective film G, which forms an optical reflective pattern covered with a film made of gold, aluminum, etc. It is. In this way, the formation of the optical reflection film G in the gas rod 1 can be achieved by using the same technology as the pattern formation technology for ordinary printed circuit boards, and it is possible to achieve extremely high-precision optical reflection without any particular difficulty. A pattern can be easily formed.

Note that in (2) above, the light irradiation does not target all optical fibers, but if, for example, five of the seven optical fibers shown in Fig. 2 are to be coupled, the light is irradiated to the remaining two optical fibers. It goes without saying that without irradiation, an optical reflective film will be formed on the optical fiber core portion of the optical fiber, and a star coupler with the desired number of optical fibers can be easily obtained.

In addition, although the cylindrical direct connection L' of the glass rod 1 is larger than the diameter L of the optical fiber group, the optical reflection film G on the C surface on the side where it is connected to the optical fiber increases the loss of the optical signal. without involvement, therefore;
Unlike conventional methods, ultra-precise adjustment is not required when aligning the optical axes, and improvements in manufacturing can be expected.

In addition, in the above explanation, the diameter of glass rod 1 is
Although L' is assumed to be larger than the diameter L of the optical fiber group,
There is no need to explain that the diameter may be the same as in the past.

Fig. 3 shows another embodiment of the star coupler according to the present invention, in which a prismatic glass rod is used instead of the cylindrical glass rod shown in the first embodiment; The front view, Figure b is a sectional view taken along line A-A', and Figure c is a side view.

In this case, the fiber group consists of four optical fibers arranged in a row as shown in the figure, and a prismatic glass rod 11.
Although the structure is in close contact with the star coupler, its operation as a star coupler is exactly the same as in the first embodiment.
Light diffusion, coupling, etc. will not be explained here.

In addition, the first aspect of the present invention explained in FIGS. 2 and 3,
It goes without saying that in the second embodiment, the number of optical fibers to be coupled can be expanded arbitrarily. However, in the case of the first embodiment shown in FIG. 2, it is easier to manufacture the fibers by arranging them adjacent to each other in an annular shape, so the number of fibers cannot be increased continuously (in the embodiment, every 6 fibers are expanded). ), but
In that case, by setting dummy fibers and limiting the number of fibers by covering them with an optical reflective film, it is possible to equivalently expand the number of fibers to any desired number.

(Effects of the Invention) As detailed above, according to the present invention, only the optical fiber core of the plurality of optical fibers bonded to the glass rod is exposed, and an optical reflective film is formed on the other portions by means such as metal vapor deposition. Therefore, excellent effects can be expected, such as a star coupler with low optical signal loss and easy manufacture without requiring special skill.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional star coupler.
FIGS. 2 and 3 also illustrate an embodiment of the star coupler according to the present invention. 1 and 11 are glass rods, 2 is optical fiber, 3
is an optical fiber core, 4 is an optical fiber clad, and 5 is an optical fiber core.
G is a gap forming part, and G is an optical reflection film.

Claims (1)

[Scope of Claims] 1. A glass rod that is optically transparent and has both ends cut at right angles, and one end of which is coated with an optically reflective film using gold, aluminum, etc.; A star coupler configured by closely adhering a plurality of optical fibers that have been plane-polished, wherein an optical reflective film is formed on a plane-polished portion of the optical fiber that is plane-polished, other than the optical fiber core.