JPH0412441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a demultiplexer that branches an optical signal into a plurality of multimode optical lines in an optical communication circuit.

(b) Background of the technology The conventional communication technology, which uses electric wires to configure a circuit network and communicates using electrical signals, gradually changed to optical fiber, which configures a circuit network using optical fibers and communicates using optical signals. It is being replaced by communication technology. There is also a demand for optical communication technology to add functions that have been incorporated into conventional communication technology, and there is a demand for the development of parts and the like to carry out these functions.

(c) Conventional technology and problems Current optical communications mainly use technology for multimode lines. Since this multimode line is generally used for relatively short distance communication, it is often branched and connected to many terminal devices. Therefore, such communication lines require a large number of optical demultiplexers that branch optical signals into a plurality of multimode optical lines.

FIG. 1 is a plan view showing the most basic conventional optical demultiplexer. In the figure, 1A is an optical demultiplexer, 2A is an input optical fiber, 2B is a lens, 3A is an output optical fiber, 3B is a lens, 4A is an output optical fiber, 4B is a lens, 5 is a glass prism, and 5' is a Represents a dielectric multilayer film. optical fiber 2
The light entering the optical demultiplexer 1A from A is converted into parallel light beams by the lens 2B, and then split into two directions by the dielectric multilayer film 5' built into the glass prism 5.
The branched lights are sent to optical fibers 3A and 4A via lenses 3B and 4B, respectively.

However, an optical demultiplexer with this structure requires the same number of lenses as input and output optical fibers, and because a glass prism is inserted at each branch point, the external size becomes large and assembly work such as optical axis alignment is required. is extremely difficult.

FIG. 2 is a diagram showing an optical demultiplexer that has been attempted as a method of miniaturizing the above-mentioned optical demultiplexer and making it easier to assemble. Figure 2a shows an example of a fiber-type optical demultiplexer that uses optical fibers as optical paths and is formed by twisting multiple optical fibers together, and Figure 2b shows a waveguide formed on a substrate as an optical path. This is an example of a waveguide-type optical demultiplexer in which a waveguide is branched into a plurality of pieces, and the same objects as in FIG. 1 are represented by the same symbols.

In the fiber type optical demultiplexer 1B shown in FIG. 2a, 6A and 7A indicate the core portions of the optical fibers, and 6B and 7B indicate the cladding portions of the optical fibers. The fiber type optical demultiplexer 1B combines two core parts of the optical fibers by twisting them together and heating them, and then integrates the clad part around the core parts of the optical fibers. One end of the core section 6A and the cladding section 6B are attached to the optical fiber 2A, and one end of the core section 6A and the cladding section 6B are attached to the optical fiber 2A.
The other end of B is connected to optical fiber 3A. One end of the core section 7A and the cladding section 7B are left open, and the other end is connected to the optical fiber 4A. The light entering the optical demultiplexer 1B from the optical fiber 2A is divided into the core portion 6A and the core portion 7A.
The light is split into two directions at the merged portion, and one light is sent out to the optical fiber 3A, and the other light is sent out to the optical fiber 4A.

In the waveguide type optical demultiplexer 1C shown in FIG. 2b, 8 is a substrate, 9 is a waveguide formed on the substrate, 9A is an input waveguide, and 9B and 9C are output waveguides. The waveguide type optical demultiplexer 1C includes a substrate 8 and a waveguide 9.
An optical fiber 2A is connected to the waveguide 9A, an optical fiber 3A is connected to the waveguide 9B, and an optical fiber 4A is connected to the waveguide 9C. The light that has entered the optical demultiplexer 1C from the optical fiber 2A is split into two directions at the branch point of the waveguide, and one of the branched lights is sent to the optical fiber 3A.
and the other one is sent out to the optical fiber 4A.

The optical demultiplexer shown in FIGS. 2a and 2b is
Although the structure is simpler, more compact, and easier to assemble than the optical demultiplexer using lenses and a dielectric multilayer film as described above, these methods also do not have sufficient functions as an optical demultiplexer. The reason is that multimode optical signals are reflected and refracted by the walls of the optical fiber while being transmitted through the optical fiber. Therefore, the power branched at the branch point is not necessarily equal, and depending on the mode at that time, the power is transmitted biasedly to the optical fiber 3A, or conversely, the power is transmitted biasedly to the optical fiber 4A, that is, modal. The disadvantage is that the influence of noise is large.

(d) Object of the Invention An object of the invention is to provide an optical demultiplexer that is small in size and easy to assemble, with less influence of modal noise.

(e) Structure of the invention This purpose is to use a demultiplexer that directly branches light from one multimode optical path to multiple multimode optical paths without using any optical components. It has a demultiplexer that branches the optical fiber into at least three or more optical paths, and a multiplexer that merges at least two or more optical paths into one optical path, and connects one optical path on the input side to the output side. After branching into more optical lines than the number of optical lines connected to the output side, two or more optical lines are combined so that the power of the output light is balanced, and then merged into the number of optical lines connected to the output side. This is achieved through coercion.

(f) Embodiments of the invention Examples of the invention will be described below with reference to the accompanying drawings.
Note that the same objects as in FIG. 1 are represented by the same symbols. FIG. 3 shows an embodiment of a 1×3×2 fiber type optical demultiplexer according to the present invention. 1D in the figure
are fiber type optical demultiplexers, 11, 12 and 13
represents optical fiber.

In FIG. 3, one end of the optical fiber 11 is connected to the optical fiber 2A.
One end of an optical fiber 12 and one end of an optical fiber 13 are fused to an intermediate portion of the optical fiber 1 to form a demultiplexing section. The other end of the optical fiber 12 is fused to the intermediate part of the optical fiber 13 to form a multiplexing section, the other end of the optical fiber 11 is connected to the optical fiber 3A, and the other end of the optical fiber 13 is connected to the optical fiber 3A. Connected to fiber 4A. In other words, the light that enters the optical demultiplexer 1D from a single optical fiber 2A is once split into three directions, and then the lights from the two directions are combined in consideration of a combination that provides a good balance of light power to reduce modal noise. We are trying to reduce the impact and ultimately branch out in two directions.

FIG. 4 shows an embodiment of a 1×4×2 waveguide type optical demultiplexer according to the present invention. In the figure, 1E represents a waveguide type optical demultiplexer, 14 represents a substrate, and 15 represents a waveguide.

In FIG. 4, one end of the waveguide 15 is connected to the optical fiber 2A, and the other end of the waveguide 15 is connected to the optical fibers 3A and 4A.
And from one optical fiber 2A to optical demultiplexer 1E
After the input light is once split into four directions in the middle of the waveguide 15, the light from the two directions is combined in consideration of the combination that will improve the balance of light power, reducing the influence of modal noise, and finally is branching out in two directions.

Although it is possible to provide an optical demultiplexer that is less affected by modal noise by the embodiment shown in FIG. 3 and the embodiment shown in FIG. It requires a lot of effort to fuse and is not suitable for producing many products of the same standard. On the other hand, waveguide type optical demultiplexers are
Since waveguides can be formed using CVD, the quality is stable and this method is suitable for mass production of products of the same standard. Further, although this embodiment is an optical demultiplexer in two directions, it is also possible to realize an optical demultiplexer in three or more directions.

(g) Effects of the Invention As described above, according to the present invention, it is possible to provide an optical demultiplexer that is less affected by modal noise, is small, and is easy to assemble.

[Brief explanation of drawings]

Fig. 1 is a plan view showing a conventional basic optical demultiplexer, and Fig. 2 is an optical demultiplexer that has already been attempted to miniaturize the optical demultiplexer shown in Fig. 1 and make it easier to assemble.
FIG. 2a shows an example of a fiber-type optical demultiplexer, FIG. 2b shows an example of a waveguide-type optical demultiplexer, and FIG. 3 shows an example of a 1×3×2 fiber-type optical demultiplexer according to the present invention. Embodiment FIG. 4 shows an embodiment of a 1×4×2 waveguide type optical demultiplexer according to the present invention. In the figure, 2A is an input optical fiber, 3A is an output optical fiber, 4A is an output optical fiber, 11, 12 and 13 are optical fibers, 14
represents a substrate, and 15 represents a waveguide.

Claims (1)

[Claims] 1. A splitter that directly branches light from one multimode optical line to a plurality of multimode optical lines without using any optical components, It has a branching section that branches into more than one optical line, and a combining section that merges at least two or more optical lines into one optical line, and connects one optical line on the input side to the output side. After branching into a greater number of optical lines than the number of optical lines to be connected, two or more optical lines are combined so that the power of the output light is balanced, and the two or more optical lines are combined into the number of optical lines to be connected to the output side. An optical demultiplexer featuring