JPH0574046B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wavelength selective optical demultiplexing device used in a wavelength division multiplexing communication system using optical fibers.
The present invention relates to a simple and compact device that integrates an optical demultiplexing function and an optical distribution function.

[Background of the invention]

One of the wavelength division multiplexing communication systems using optical fibers has been proposed to have a configuration as shown in FIG. This is for each terminal group 5A, 5 having multiple terminals.
As a signal transmission method to B,...,5N, the wavelength λ ₁ ~
Using λ _o , the above wavelength is assigned to each terminal group 5A, 5B,...
5N as λ ₁ , λ ₂ , . . . , λ _o , respectively, and transmits light. That is, the light with wavelengths λ ₁ to λ _o transmitted through the optical fiber transmission line 1A is demultiplexed by the optical demultiplexer 2A into light with wavelength λ ₁ and light with wavelengths λ ₂ to _{λ a} . The light of wavelength λ ₁ enters the optical splitter 4A through the optical fiber transmission line 3A, and the optical splitter 4A distributes the optical signal to each terminal of the terminal group 5A. Light with wavelengths λ ₂ to λ _o is transmitted through optical fiber transmission line 1B.
and enters the next optical demultiplexer 2B. The optical demultiplexing and optical distribution functions are performed by the same operation as before.

FIG. 2 shows a conventional example of a device having both the above-mentioned functions of light separation and light distribution. In this device, only the light of wavelength λ ₁ is reflected and demultiplexed by the interference film filter 6, and this demultiplexed light is reflected by the reflecting mirror 7 and enters the waveguide portion 9 of the mixing rod 8. Then, it is configured to be distributed to the optical fiber transmission lines connected to the opposite side. However, since this conventional device uses many individual parts such as lenses, filters, and mirrors, it is difficult to adjust the optical axis and assemble it, and there is also the problem that the device becomes large, and the cost is extremely high. There is also the problem that it is expensive.

[Purpose of the invention]

An object of the present invention is to provide a wavelength-selective optical demultiplexing device that is small in size, has a simple configuration, and is low in cost.

[Summary of the invention]

By processing optical fiber, the present invention
The above object is achieved by creating a wavelength selective optical demultiplexer and an optical distributor and configuring them in combination. First, a wavelength-selective optical demultiplexer is made by bringing two optical fibers into contact in parallel, heating the vicinity of their tips, stretching them to make them tapered, cutting the tips diagonally at a desired angle θ, and polishing them. It has a new configuration in which an interference film filter having desired optical characteristics is formed on the polished surface. The optical distributor uses a bundle of multiple optical fibers, which is heated and stretched while twisting one end to make it tapered. By abutting this tapered end surface against the surface of the optical demultiplexer on which the interference film filter is deposited, one wavelength selective optical demultiplexing/distributing unit is constructed. By not only stretching the end of the optical splitter to make it tapered, but also stretching the end of the optical splitter that is connected to it and making it tapered, the demultiplexing function can be improved. The light mixing effect can be fully exerted on both the distribution function side and the distribution function side. That is, according to the present invention, by sufficiently mixing the lights having different wavelengths transmitted through the input optical fiber before the interference film filter, the demultiplexing function of the interference film filter can be efficiently promoted. By sufficiently mixing the single wavelength light separated by the interference film filter, the light can be uniformly distributed to each optical fiber of the distributor. In particular, by stretching the input section of the distributor into a tapered shape while giving it a twist, broadband characteristics can be achieved, making it possible to uniformly distribute light of any wavelength. The system shown in FIG. 1 can be constructed by cascading a plurality of the units, with one of the two optical fibers of the optical demultiplexer serving as an input and the other as an output.

[Embodiments of the invention]

FIG. 3 shows an overview of the wavelength selective optical demultiplexing device of the present invention. 10 is an optical demultiplexer, 14 is an optical splitter in which the number of input ports to the number of output ports is 1:n, 11 is an input side optical fiber, 12 is an output side optical fiber, 1
3 is an interference film filter that has the characteristic of transmitting light with wavelength λ ₁ and reflecting light with wavelengths λ ₂ to λ _o (for example, if λ ₁ < λ ₂ , λ ₃ , ..., λ _o , it is in the short wavelength band). ₂₂ is _a distribution output _{optical fiber} bundle.
The operation of this unit is such that the optical signal (wavelengths λ ₁ to λ _o ) from the optical fiber transmission line 1A is transmitted to the input side optical fiber 1.
1 and reaches the interference film filter 13.
This interference film filter 13 transmits only the optical signal with the wavelength λ ₁ and reflects the remaining optical signals with the wavelengths λ ₂ to λ _o . The transmitted light propagates as indicated by the arrow 3A and is equally distributed to each distribution output optical fiber of the optical distributor 14. The reflected light is coupled to the output optical fiber 12 at the taper portion 15 and transmitted to the next optical fiber transmission line 1B.

FIG. 4 shows the cross-sectional structure of the optical demultiplexer of the present invention, in which a is a front cross-sectional view, b is a cross-sectional view of the optical fibers 11 and 12 seen from the left, and c is a cross-sectional view of the tapered portion seen from the right. FIG.

The tapered portion 15 is formed by fusing and heating the optical fibers 11 and 12 and drawing them. Tapered part 15
The core portion 20A of the optical fiber 11 and the core portion 20B of the optical fiber 12 at the tip end are elliptical. This is because the outer diameter of the cladding portion 19 at the tip of the tapered portion is kept approximately circular. The cladding portion between the core portions 20A and 20B of the tapered portion 15 also becomes narrower toward the tip, as shown at 16. This is an interference film filter 1 inside the optical fiber 11.
This is because signals having wavelengths λ ₂ to λ _o out of the light transmitted toward the optical fiber 3 are reflected by the interference film filter 13, and these reflected lights are coupled to the optical fiber 12 with little loss. That is, if the thickness of the cladding part 16 between the core part 20A and the core part 20B near the tip of the tapered part 15 is large, the core part 2
Since the light reflected by the interference film filter 13 deposited on the 0A has a spread, it cannot be made to efficiently enter the core portion 20B of the optical fiber 12, resulting in optical loss. For example, core parts 20A and 2
If the 0B interval is 50 μm, the optical loss will be approximately 0.3 dB. Therefore, the core part 20 can be efficiently and with low loss.
In order to make the light incident on B, it is better that the thickness of this cladding part 16 is thin. The preferred value is from several μm to several tens of μm.
m, in which case the optical loss will be 0.1 dB or less.
The reason why the cladding part 16 between the core part 20A and the core part 20B of the tapered part 15 is made thinner toward the tip is that as the light transmitted in the input optical fiber 11 approaches the interference film filter 13, the cladding part 16 becomes thinner toward the tip. This is to make it easier to couple to the core portion 20B of the optical fiber 12 and to make it easier for the light reflected by the interference film filter 13 to enter the core portion 20B with low loss.

The reason why the surface on which the interference film filter 13 is formed at the tip of the tapered portion 15 is made obliquely at an angle θ is to allow the reflected light to enter the core portion 20B. All you have to do is choose. However, this θ influences the isolation characteristics between wavelengths. In other words, the smaller θ is, the greater the isolation between wavelengths can be, so θ is a small value, 15~
It is more preferable to choose from a range of 22.5°. λ ₁ , λ ₂ ,
_.

Core portion 20A at the tip of tapered portion 15 and core portion 2
The combined cross-sectional area of 0B is made approximately equal to the cross-sectional area of a core group consisting of a plurality of core sections on the input side of the optical distributor 14. By doing so, the optical loss between the optical demultiplexer and the optical distributor can be reduced, and the optical signal can be equally distributed to each optical fiber of the distribution output optical fiber 22. The shape of the core portions 20A and 20B at the tip of the tapered portion 15 may be circular, but
The closer the shape is to an ellipse, the more the reflected light from the interference film filter 13 can enter the core portion 20B with low loss, and the optical loss with the optical distributor 14 can also be reduced. Note that 17A and 17B are optical fibers 11 and 1.
The core portions 18A and 18B of No. 2 are clad portions.

FIG. 5 shows another embodiment of the optical demultiplexer of the present invention. In this process, two optical fibers 11 and 12 are inserted into a glass tube 21, the glass tubes are fused together, heated, and stretched to form a tapered portion 23. After diagonally cutting and polishing the tips, the interference film filter 13 is formed. ' is vapor-deposited. Optical fibers 11 and 12 are glass tubes 2
1, it is mechanically stable and its optical properties are also stable. Furthermore, the glass processing for forming the tapered portion is easier than in the case of using only optical fibers, since it is carried out by inserting it into a glass tube, and the yield is good and manufacturing accuracy is also improved. Furthermore, the deposition of the interference film filter 13' becomes easier. The optical distributor 14 may also be made by inserting an optical fiber bundle into a glass tube and then heating, twisting, and stretching the entire tube, as previously proposed by the present inventor (Japanese Patent Application No. 58-133354). good. The number n of output ports of the optical distributor takes an integer value of 2 or more. In place of the glass tube 21, a polymeric material (for example, a heat-shrinkable tube) may be used. Optical fiber 11, 12, 2
2 may be an optical fiber whose outer periphery is coated with a polymer material.

〔Effect of the invention〕

According to the present invention, it is possible to create an optical splitter by processing optical fibers, and it is possible to achieve small size, simple configuration, and low cost.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a wavelength division multiplexing communication system using conventional optical fibers, Fig. 2 is a schematic diagram of a conventional wavelength selective optical demultiplexing device, and Fig. 3 is a schematic diagram of a wavelength division multiplexing communication system using conventional optical fibers. Overview of selective optical demultiplexing device,
4 and 5 show the cross-sectional structure of an optical demultiplexer according to an embodiment of the present invention. 1A, 1B,..., 1N, 3A, 3B,..., 3N
...Optical fiber transmission line, 2A, 2B,..., 2N,
10...Optical demultiplexer, 4A, 4B,..., 4N, 14
...Optical distributor, 5A, 5B, ..., 5N ... Terminal group, 6, 13, 13' ... Interference film filter, 7...
... Reflector, 8... Mixing rod, 9... Waveguide, 11, 12... Optical fiber, 15, 23...
Tapered part, 16... Clad part, 17A, 17
B, 20A, 20B...core part, 18A, 18
B, 19... Clad part, 21... Glass tube, 2
2... Optical fiber bundle.

Claims (1)

[Claims] 1. An input side optical fiber and an output side optical fiber are brought into contact with each other in parallel, one end of the fiber is heated and stretched to make it tapered, and the tip is cut diagonally at a desired angle. An interference film filter having desired wavelength selection characteristics is formed on the cut surface of the interference film filter, and n optical fibers are bundled into one, heated and stretched while twisting one end to form a tapered shape. 1. A wavelength-selective optical demultiplexing device, characterized in that the input part of an optical splitter with a ratio of input ports to output ports of 1:n (n≧2) is connected. 2. Claim 1, wherein the input-side optical fiber and the output-side optical fiber are inserted into a common glass tube, and one end of the glass tube is heated and stretched together with the glass tube to form a narrow tapered shape. wavelength-selective optical demultiplexing device. 3 Using a plurality of wavelength-selective optical demultiplexing devices according to claim 1, the input optical fiber of the next stage device is connected to the output side optical fiber of the first stage device, and the output of the next stage device is connected to the output side optical fiber of the first stage device. A wavelength selective optical demultiplexing device in which devices are interconnected such that the input side optical fiber of the third stage device is connected to the side optical fiber.