JPH0990155A - Optical branching filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an element which can select light different in wavelengths with simple constitution by branching wavelength multiplex light into the light of the plural different wavelengths through the use of one filter. SOLUTION: The light of the plural different wavelengths can be obtained by making plural wavelength multiple light incident on the filter whose transmission wavelength changes when the incident angle of incident light changes like an interference filter at different angles. The wavelength multiplex signal light which is made incident on an optical fiber 101 and is distributed in a star coupler 102 is made incident on 106 from the left from a fiber 103. Then, it reaches the interference filter 113. Since the incident angle to the interference filter 113 becomes smaller as light transmits from the fiber 103 to 106, the transmission wavelengths become different. Generally, the transmission wavelengths become longer as an angle formed by a filter face and light becomes smaller. Namely, the angle formed by the optical fiber and the interference filter can be set to a value sufficient for separating the transmission wavelengths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical demultiplexer for extracting a plurality of wavelength lights from wavelength multiplexed light.

[0002]

2. Description of the Related Art In optical communication, there is wavelength division multiplexing as a method of multiplexing a plurality of signal trains in one optical fiber. When performing wavelength division multiplexing transmission, a demultiplexer is an essential device for separating a plurality of different wavelength signals, and a method as shown in FIG. 6 has been conventionally proposed.

In FIG. 6, 301 is an optical fiber, and 302 is
Is a star coupler, 303 to 306 are optical fibers, 30
7 to 310 are filter holders for fixing the filter and the fiber, 311 to 314 are bandpass filters having different transmission wavelength bands, and 315 to 318 are optical fibers.

The optical fiber 301 has wavelengths λ1, λ2, λ
When the optical signals of 3 and λ4 are incident, the lights equally branched by the star coupler are respectively from the optical fibers 303 to 306.
To the filters 311 to 314 having different transmission wavelengths.
Optical signals of wavelengths λ1, λ2, λ3, and λ4 are selected, and λ1 is used for the optical fiber 315, λ2 is used for the optical fiber 316, λ3 is used for the optical fiber 317, and λ is used for the optical fiber 318.
The optical signal 4 is demultiplexed. Here, the filter is slightly tilted so that the light reflected by the filter does not return directly to the optical fiber. This makes it possible to separate multiplexed wavelengths.

In FIG. 7, 401 is an optical fiber,
Reference numeral 402 is a star coupler, 403 to 406 are optical fibers 407 are optical fiber holders, and 408 are optical fibers 403.
To 406 and the groove provided in the optical fiber holding portion, 409
412 to 412 are filters having different transmission wavelength bands.

Also in this case, as in FIG. 6, the light of four wavelengths is branched into four optical fibers by the star coupler and advances to the four optical fibers embedded in the optical fiber holding portion, each having a different transmission wavelength. It is incident on the filter.
As a result, four different wavelength signals can be obtained at the output end of the optical fiber.

[0007]

However, this has the drawback that each filter holder must be assembled individually. Further, it is necessary to prepare a filter for each desired wavelength, which increases the number of parts and complicates the assembly work.

Therefore, in view of the above problems, it is an object of the present invention to provide an element for selecting lights having different wavelengths with a simpler structure.

[0009]

According to the demultiplexer of the present invention, the wavelength-division-multiplexed light is demultiplexed into a plurality of lights having different wavelengths by using one filter. The number of the elements can be reduced, and the structure of the element can be simplified.

Specifically, the optical demultiplexer of the present invention comprises an optical wavelength filter having a different transmission wavelength depending on the incident angle, and an incident means for making a plurality of wavelength multiplexed lights incident on the optical wavelength filter at different incident angles. It is characterized by having. Furthermore, it is possible to adopt a configuration having branching means for converting one wavelength multiplexed light into the plurality of wavelength multiplexed lights. As the branching means, a star coupler or an optical waveguide provided on the substrate may be branched. It is also possible to obtain a desired number of branches by branching in multiple stages. In addition, the incident means may be configured by a light guide path that guides the plurality of wavelength-multiplexed lights into the optical wavelength filter so that they are incident at different angles, and the light guide path is an optical fiber,
There are the above-mentioned optical waveguides and the like. Regarding the arrangement of the light guide path and the optical wavelength filter, a gap may be provided in a part of the light guide path, the optical wavelength filter may be provided in the gap, or the optical wavelength filter may be provided at the end face portion of the light guide path.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a filter, such as an interference filter, whose transmission wavelength changes when the incident angle of incident light changes (in a filter in which the difference in the effective optical path length in the filter affects the transmission wavelength, By changing the angle, it is possible to change the effective optical path length and change the transmission wavelength.) By making a plurality of wavelength-multiplexed lights incident at different angles,
A plurality of different wavelength lights are obtained respectively. A more specific configuration example will be described below.

[0012]

EXAMPLE 1 FIG. 1 shows a first example of the present invention. 110 is an optical fiber, 102 is a star coupler, 1
Reference numerals 03 to 106 are optical fibers, 107 to 110 are optical fibers, 111 is an optical fiber holding portion fixing the optical fibers with an adhesive or the like, and 113 is an interference filter, which is a bandpass characteristic that transmits an optical wavelength of a certain band. And the bandpass wavelength changes depending on the incident angle of the light beam. The interference filter 113 has grooves 112 formed in the optical fibers 103 to 106 and the optical fiber holder, and is installed here.

Here, the optical fiber 103 and the interference filter 1
The angle formed by 13 is the angle a, the angle formed by the fiber 104 and the interference filter 113 is the angle b, and the angle formed by the fiber 105 and the interference filter 113 is the angle c.
The angle formed by 6 and the interference filter 113 is the angle d. Here, the angle a is slightly smaller than the right angle so that the reflected light does not return to the optical fiber, the angle b is smaller than the angle a, the angle c is smaller than the angle b, and the angle d is smaller than the angle c.

Here, the wavelength division multiplexed signal light which is incident on the optical fiber 101 and distributed by the star coupler 102 is incident on the left end of the fibers 103 to 106, and the interference filter 11
Reach 3. At this time, since the incident angle on the interference filter 113 becomes smaller as the fibers 103 to 106 change, the transmission wavelengths become different. Generally, the smaller the angle between the filter surface and the light beam, the longer the transmission wavelength. That is, the wavelength of light emitted from the optical fiber 103, transmitted through the interference filter 113 as it is, and incident on the optical fiber 107 is set to λ1, and wavelength of light emitted from the optical fiber 104 and transmitted through the interference filter 113 as it is and incident on the optical fiber 108. Is set to λ2, the wavelength of the light emitted from the optical fiber 105, transmitted through the interference filter 113 as it is, and incident on the optical fiber 109 is set to λ3, emitted from the optical fiber 106, transmitted through the interference filter 113 as it is, and transmitted to the optical fiber 110.
If the wavelength of the light incident on is λ4, the following relationship holds. [lambda] 1 <[lambda] 2 <[lambda] 3 <[lambda] 4 The optical signals are separated in this relationship.

Here, the angle formed by the optical fiber 103 and the interference filter is a, the angle formed by the optical fiber 104 and the interference filter is b, the angle formed by the optical fiber 105 and the interference filter is c, and the angle formed by the optical fiber 106 and the interference filter. Let d be the following relationship. The value of a>b>c> da to d may be set to a value sufficient to separate λ1 to λ4 according to the wavelength selection characteristic of the interference filter used. Although the star coupler and the fibers 103 to 106 are described as separate elements in the present embodiment, the star coupler and the fibers 103 to 106 may be integrated by using a star coupler using an optical fiber.

FIG. 2 shows another form of this embodiment. Reference numerals 701 and 702 are optical fiber holding portions, 703 is an interference filter, and 704 is an adhesive. The optical fiber holders 701 and 702 are the same as the original ones 701 and 70.
The interference filter 70 is cut into two pieces and vapor-deposited on the end face.
3 is formed and then joined with an adhesive.

(Embodiment 2) FIG. 3 shows a second embodiment of the present invention. Here, 201 is an optical fiber, 202
Is a star coupler, 203 to 206 are optical fibers through which incident light passes, 207 is an optical fiber holding unit, 208 is an interference filter, 209 to 212 are couplers, and 213 to 216 are optical fibers for output.

Here, the angle formed by the optical fiber 203 and the interference filter 212 is an angle e, the angle formed by the optical fiber 204 and the filter 212 is an angle f, and the angle formed by the optical fiber 205 and the interference filter 212 is an angle g. The angle formed by the optical fiber 206 and the interference filter 212 is the angle h. Here, the angle e is smaller than the right angle so that the reflected light does not return to the optical fiber, the angle f is smaller than the angle e, the angle g is smaller than the angle f, and the angle h is smaller than the angle g.

Here, the signal light distributed from the star coupler 202 through the optical fiber 201 is 203 to 20.
The light enters from the left end of the fiber No. 6 and reaches the interference filter 208. At this time, the incident angle on the interference filter 208 becomes smaller as the fibers 203 to 206 are formed.

Therefore, as described in the first embodiment, light of different wavelengths is separated and emitted to the outside. In this embodiment, if a photodetector such as a photodiode for receiving each wavelength signal is arranged near the filter 208, each signal light can be received, so that the configuration can be reduced. Since the signal light from the filter is directly incident on the photodetector, the coupling loss between the filter and the light guide path (optical fiber) for emission can be eliminated. In this embodiment, by disposing a filter on the end face portion of the light guide path, the loss is reduced as compared with the case where the filter is incident on the photodetector or the external light guide path (optical fiber or the like) through the light guide path for emission. It can be reduced.

(Embodiment 3) FIG. 4 shows a third embodiment of the present invention. Although an optical fiber is used as the light guide in the above-mentioned embodiment, in this embodiment, the wavelength-multiplexed light is made incident on the filter by using the optical waveguide provided on the substrate. Further, as a means for branching one wavelength-multiplexed light, the star coupler is used in the above-mentioned embodiment, but the branching by the waveguide branch is used in this embodiment. The desired number of branches is obtained by performing the waveguide branch in multiple stages.

Reference numeral 529 is a 1 × 8 coupler using an optical waveguide, 501 is a waveguide for inputting signals, and 502 to 5
Reference numeral 09 is a waveguide for dividing the input into eight, and 510 is a groove provided in a part of each waveguide, in which an interference filter is arranged. 511 is an optical fiber holding member, 512
Are optical signal input optical fibers, 513 to 520 are optical fiber holding members, and 521 to 528 are output optical fibers.

Here, the wavelength-multiplexed light enters the optical fiber 512 and enters the waveguide 501. The incident light is guided to the waveguide from 502 to 509 via three stages of 1 × 2 branches. Here, the interference filter 510 and the waveguide 502,
503, 504, 505, 506, 507, 508, 5
If the angles formed by 09 are a, b, c, d, e, f, g, h, then a>
These are arranged so that the relationship of b>c>d>e>f>g> h holds. Thus, the demultiplexed light beams of different wavelengths are obtained from the optical fibers 521 to 528, respectively.

In this embodiment, the groove is provided and the interference filter is arranged there. However, the coupler 529 is divided into two parts at the grooved part, and the interference filter is directly formed on one end surface by vapor deposition or the like. After that, the both may be connected to form an optical demultiplexer.

(Fourth Embodiment) FIG. 5 shows a fourth embodiment of the present invention. Reference numeral 601 denotes a waveguide for inputting a signal, 6
02 to 609 are waveguides that divide the input into eight, 610
Is an interference filter provided on the end face of the waveguide, 611 is a coupler, 612 is an optical fiber for inputting optical signals, and 613 to 62
Reference numeral 0 is an optical fiber holder, 621 to 628 are output optical fibers, and 629 is a coupler.

Similar to the second embodiment, this embodiment has a feature that the photodetector for receiving the light of each wavelength can be arranged in the vicinity of the optical demultiplexer, so that the overall structure can be reduced.

In this embodiment, the interference filter provided on the end face of the waveguide can be an interference filter chip having an interference film formed on the substrate, but the interference film is formed on the end face of the waveguide by means such as vapor deposition. It may be formed directly.

In each of the above embodiments, the case where the optical fiber or the optical waveguide is used as the light guide path has been described.
A plurality of light guide paths having different incident angles to the optical wavelength filter can be configured by combining ordinary optical systems.

[0029]

As described above, according to the present invention, a demultiplexer that demultiplexes an optical signal according to the difference in different wavelengths can be realized with a simple structure. That is, only one filter for a single wavelength is required, and the filter can be integrated with the optical fiber or the waveguide.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical demultiplexer of the present invention.

FIG. 2 is a diagram showing another configuration of the first embodiment of the optical demultiplexer of the present invention.

FIG. 3 is a diagram showing the configuration of a second embodiment of the optical demultiplexer of the present invention.

FIG. 4 is a diagram showing the configuration of a third embodiment of the optical demultiplexer of the present invention.

FIG. 5 is a diagram showing the configuration of a fourth embodiment of the optical demultiplexer of the present invention.

FIG. 6 is a diagram showing a first conventional example of an optical demultiplexer.

FIG. 7 is a diagram showing a second conventional example of the optical demultiplexer.

[Explanation of symbols]

 101 optical fiber 102 star coupler 103-110 optical fiber 111,112 fiber holding layer 113 optical fiber 201 optical fiber 202 star coupler 203-206 optical fiber 207 fiber holding layer 208-211 photodetector 212 interference filter 301 optical fiber 302 star coupler 303 -306 Optical fiber 307-310 Filter holder 311-314 Filter 315-318 Optical fiber 401 Optical fiber 402 Star coupler 403-406 Optical fiber 407 Optical fiber holding layer 408 Optical fiber and groove 409-412 carved in optical fiber holding layer Filters 501 to 509 Waveguide 510 Interference filter 511 Coupler 512 Optical fiber 513 to 520 Coupler 521 to 528 Optical fiber 529 Waveguide Layers 601-609 waveguide 610 interference filter 611 coupler 612 optical fibers 613-620 coupler 621 to 628 optical fiber 629 waveguide layer 70,702 optical fiber holding unit 703 interference filter 704 adhesive

Claims (5)

[Claims] 1. A demultiplexer for extracting a plurality of lights having different wavelengths from wavelength-multiplexed light, the optical wavelength filter having a different transmission wavelength depending on an incident angle,
An optical demultiplexer comprising: an incident means for making a plurality of wavelength-multiplexed lights incident on the optical wavelength filter at different incident angles. 2. The optical demultiplexer according to claim 1, further comprising branching means for converting one wavelength multiplexed light into the plurality of wavelength multiplexed lights. 3. The optical demultiplexer according to claim 1 or 2, wherein the incident means comprises a light guide path that guides the plurality of wavelength-multiplexed lights into the optical wavelength filter so as to be incident at different angles. 4. The optical demultiplexer according to claim 3, wherein a gap is provided in a part of the light guide path, and the optical wavelength filter is provided in the gap. 5. The optical demultiplexer according to claim 3, wherein the optical wavelength filter is provided on an end face portion of the light guide path.