JPS5926006B2 - Manufacturing method of optical coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the coupling ratio of optical signals in an optical coupler between a plurality of optical waveguides to a desired value.

The present invention relates to a method for manufacturing an optical coupler. In an optical transmission system, an optical coupler is an important component for branching an optical signal from one waveguide that propagates light waves to another waveguide, or for monitoring the optical signal.

Conventional optical couplers consist of multiple waveguides on a glass or other dielectric substrate with appropriate coupling lengths and coupling gaps, and are used by connecting them to other major optical waveguides, such as optical fibers. Another construction method is to directly process the cladding part of the optical fiber by mechanical or etching, and determine the bonding length and bonding gap between the processed optical fibers in the same manner as the above-mentioned configuration method. It is fixed by adhesive etc. to form an optical coupler.In either method, in order to satisfy the phase matching condition of the light wave to obtain the required coupling ratio, the wavelength of the light wave must be adjusted to the manufacturing dimensions of the coupling length and coupling gap. There was a drawback that the following machining accuracy was required. The present invention makes it possible to control coupling conditions such as the coupling length and coupling gap between a plurality of waveguides that are in common contact with each other by heating the optical waveguide and diffusing the dopant that constitutes the waveguide. It is characterized by the ability to easily obtain the required coupling ratio,
The purpose is to provide a manufacturing method for realizing an optical coupler, which has conventionally been difficult to manufacture, through simple steps.

FIG. 1 shows an example of an optical coupler manufactured according to the method of the present invention, in which 1 is the cladding of an optical fiber □, and 2 is its core, which is a waveguide for optical signals.

3 is the cladding of the other optical fiber 8, and 4 is its core.

Reference numeral 5 denotes a contact surface which is a part of the optical fiber cladding 1, and is in contact with a contact surface 6 which is a negative part of the optical fiber cladding 3.

FIG. 2 schematically shows a manufacturing device for controlling the coupling ratio of the optical coupler shown in FIG. 1, where T is a pumping optical fiber, 8 is a coupling optical fiber, and 9 is a pumping laser. beam, 10 is a lens, 11 is an optical fiber holding fine movement table, 12 is an optical fiber cladding mode removal section, 13;
14 is an optical fiber holding stand, 15 is a photodetector on the excitation side,
16 is a photodetector on the coupling side, 17 and 18 are respective measuring meters, 40 and 41 are discharge electrodes for heating, and 42 is a power source thereof. Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

The diameter of the cores 2 and 4 of the optical fibers 7 and 8 is usually 100μ.
The outer diameter of the claddings 1 and 3 of the optical fiber is 100μ or less, especially for a single mode optical fiber.
That's all. In order to manufacture optical couplers using such optical fibers, it is necessary to remove the cladding by etching or polishing so that the waveguide sections to be coupled can be brought into close proximity to each other. For this purpose, an optical fiber 7 consisting of a cladding 1 and a core 2 and an optical fiber 8 consisting of a cladding 3 and a core 4 are bonded onto one substrate and polished to produce contact surfaces 5 and 6. In this case, the polishing accuracy is only several times the wavelength of the light and is relatively easy. Each optical fiber is then removed from the substrate and held side by side with contact surfaces 5 and 6 facing each other as shown in FIG. 1a. At this time, each optical fiber 7,
If a force is applied to press the contact surfaces 5 and 6 of 8 against each other, the contact position between the contact surfaces 5 and 6 can be maintained stably.
Next, heating is performed in the axial direction centering around the contact portions of the contact surfaces 5 and 6 to fuse the two optical fibers 7 and 8 together. During this fusion, if the heating range is too wide, the optical fiber will be deformed, so a device that can control temperature and heat minute parts is required.

Devices of this kind currently in practical use include those in which the beam of a carbon dioxide gas laser is focused with an infrared transmitting lens, and discharge heating devices in which high pressure is applied to a tungsten electrode. Among these, discharge heating equipment is particularly easy to control temperature, the discharge is more stable if an AC power source is used, and it is less expensive and more practical because it does not have the complicated structure of laser heating equipment. be. If you connect an optical measurement system like the one shown in Figure 2 before fusing the two optical fibers together, when a light wave of an appropriate wavelength is introduced into the core 2 of the optical fiber 7 to excite it, the other Since the light wave coupled to the core 4 of the optical fiber 8 can be measured using the photodetector 16, the coupling ratio during the process can be determined from the ratio of the outputs of both the photodetectors 15 and 16. In this state, the bonded portion is heated following fusion. When the two optical fibers 7 and 8 are simply fused together, the coupling ratio between them is small, so the coupled light within the optical fiber 8 is weak, and the output of the detector 16 is also small.

However, when the joint is heated to an appropriate temperature, the dopants such as germanium oxide and phosphorus pentoxide contained in the cores 2 and 4 of the two optical fibers 7 and 8 are diffused, and the equivalent core diameter is expanded. , the power distribution of the light waves excited in the cores 2 and 3 also expands, the coupling ratio between them increases, and the output of the photodetector 16 on the core 4 side increases.
Therefore, if the magnitude of the optical output supplied to the core 2 of the optical fiber 7 is known in advance by the photodetector 15, the coupling ratio becomes clear. It is possible to stop heating. The magnitude of the diffusion due to heating at this time is 10 to 0 to 10-8 square centimeters/second when the core dopant is phosphorus pentoxide at the heating temperature for fusing the silica-based optical fiber.
It is known that in the case of germanium oxide, the diameter is about one-tenth that of phosphorus pentoxide, and if the diameter of the core doped with phosphorus pentoxide is 5μ, in order to equivalently double the core diameter, , a heating time of about 0.5 minutes is sufficient.

FIG. 3 is a diagram showing the state in which the optical coupler manufactured as described above is housed in a jig and stably held. 19 is the jig main body (only the lower half is shown in the figure), 20 is each Micrometers 21 and 22 provided in the jig main body 19 to accommodate the optical fiber
23 is a covered optical fiber, 23 is a joint formed of an optical fiber wire as shown in FIG. 1, and 24 is a joint formed at the center of the jig body so that the joint 23 does not come into contact with the jig body. It is a hollow part. As shown in the figure, after the optical fiber is placed in the groove 20 so that the coupling part 23 is held in the cavity 24, the upper half (not shown) of the jig body is covered and glued to integrate it. be. FIG. 4 shows a second example of an optical coupler manufactured by the method of the present invention, in which optical waveguides 25 and 26 provided in a dielectric substrate 24 are arranged close to each other in parallel. It was manufactured by heating the section as before to allow diffusion of the dopant forming the waveguide, and stopping the heating when the desired coupling ratio was obtained.

FIG. 5 is an example in which the method of the present invention is applied to an optical fiber branching element.

27 is a core on the excitation side, and 28 and 29 are cores on each branch side.

30, 31, and 32 are respective clads, and 33 is a branching joint.

As shown in the figure, the ends of each optical fiber are polished and butt-fused using a suitable jig. In this state, the coupling between each core is weak and the branching coupling is insufficient, so the heating is continued to diffuse the cores until the branched light output increases to an appropriate value. As explained above, by heating the coupling part at a high temperature that does not cause extreme deformation of the optical waveguide, the dopant contained in the waveguide is diffused. This is equivalent to finely adjusting the length, and by directly observing the coupled light, there is an advantage that it is possible to realize an optical coupler with a desired coupling ratio.

Another advantage is that it is relatively easy to branch light waves propagating through an optical fiber.

[Brief explanation of drawings]

Fig. 1 is a plan view and a sectional view taken along the line B-B of an example of an optical coupler to which the present invention is applied, Fig. 2 is a diagram schematically showing an apparatus implementing the present invention, and Fig. 3 is an optical fiber coupling. The perspective view of the holder of the container, FIGS. 4 and 5 are views showing other examples to which the method of the present invention is applied. 1, 3... Clad, 2, 4... Core, 5, 6... Contact diagram, 7, 8... Optical fiber, 9... ... Laser beam, 15, 16...
...Photodetector.

Claims (1)

[Claims] 1. In a method for manufacturing an optical coupler between a plurality of optical waveguides,
The coupling ratio between the waveguides is controlled by heating the common contact portion of each waveguide to cause diffusion of the waveguide portion of the waveguide, and when the desired coupling ratio is obtained, the heating is stopped. A method for manufacturing an optical coupler, characterized in that the optical coupler is stopped. 2. When diffusing the waveguide portion of a waveguide, the coupling ratio between the waveguides is monitored by injecting light into the input waveguide to excite it and measuring the coupled light from other waveguides. A method of manufacturing an optical coupler according to claim 1, characterized in that: