JP3931834B2 - Optical wavelength multiplexer / demultiplexer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wavelength multiplexer / demultiplexer used when performing wavelength division multiplexing transmission in the field of optical communications, and more particularly to an optical wavelength multiplexer / demultiplexer capable of realizing low loss and flat passband characteristics.
[0002]
[Prior art]
In the field of optical communications, a wavelength division multiplexing system is being studied in which a plurality of signals are placed on light of different wavelengths and transmitted through a single optical fiber to increase the information capacity. In this method, an optical wavelength multiplexer / demultiplexer that multiplexes / demultiplexes light of different wavelengths plays an important role. In particular, an optical wavelength multiplexer / demultiplexer using an arrayed waveguide diffraction grating can realize multiplexing / demultiplexing with a narrow wavelength interval, and has the advantage of easily increasing the number of multiplexed communication capacities. Yes.
[0003]
Up to now, in order to allow the wavelength fluctuation of the laser beam on the transmitting side and increase the transmission speed by widening the bandwidth per channel, the characteristics of the passband in the optical multiplexer / demultiplexer using an array diffraction grating are flattened. Various studies have been made (for example, Patent Document 1).
[0004]
FIG. 4 shows an optical circuit of a conventional arrayed waveguide grating optical wavelength multiplexer / demultiplexer. 4A is an overall explanatory diagram of the optical circuit, and FIG. 4B is an enlarged explanatory diagram of a portion A of FIG. 4A. This optical wavelength multiplexer / demultiplexer includes an input channel waveguide 1 and a Mach-Zehnder on the input side of an arrayed waveguide diffraction grating 4 composed of a plurality of channel waveguides (hereinafter referred to as “arrayed waveguides”) 5. The circuit 42 and the input side slab waveguide 3 are connected. An output channel waveguide 7 and an output side slab waveguide 6 are connected to the output side of the arrayed waveguide grating 4.
[0005]
The Mach-Zehnder circuit 42 includes a pair of slab-connecting linear channel waveguides 49 connected to the input channel waveguide 1, a delay channel waveguide 410 composed of two channel waveguides of different lengths, and a 3 dB coupler 411. It is made up. The pair of slab connecting linear channel waveguides 49 are arranged close to each other, and also have the role of the other 3 dB coupler in the Mach-Zehnder circuit 42.
[0006]
In the arrayed waveguide grating optical wavelength multiplexer / demultiplexer, the light wave incident from one end of the input side slab waveguide 3 propagates in the input side slab waveguide 3 and reaches the boundary with the arrayed waveguide grating 4. To reach. The reached light wave is coupled to each arrayed waveguide 5 with a power ratio corresponding to the electric field distribution at the boundary and propagates. Due to the grating effect of the arrayed waveguide 5, the direction of the equiphase surface of the light wave in the vicinity of the boundary between the arrayed waveguide 5 and the output-side slab waveguide 6 differs depending on the wavelength. Therefore, when the wavelength changes, the output-side slab waveguide 6 The light condensing position shifts at the boundary between the output channel waveguides 7. For this reason, only the light wave having a specific demultiplexing wavelength can be extracted from each output channel waveguide 7, and a light wave multiplexing / demultiplexing function is realized.
[0007]
Here, in the optical wavelength multiplexer / demultiplexer shown in FIG. 4, a Mach-Zehnder circuit 42 is connected to the input-side slab waveguide 3. Due to the interference in the Mach-Zehnder circuit 42, light is alternately output to the input-side slab waveguide 3 with respect to the wavelength from each of the slab connection linear channel waveguides 49.
[0008]
FIG. 5 shows the wavelength dependence of the optical power output to the input-side slab waveguide 3 from each of # 1 and # 2 of the slab connection linear channel waveguide 49. When the incident position on the end face of the input-side slab waveguide 3 is changed, light of different wavelengths depending on the incident positions is collected in a certain output channel waveguide 7. Accordingly, by making the wavelength-dependent period of FIG. 5 appropriate, light of different wavelengths from the two slab connecting linear channel waveguides 49 can be condensed on the same output channel waveguide 7. It becomes possible. As a result, a wider passband can be realized (for example, Non-Patent Document 1).
[0009]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 08-122557 [Non-patent Document 1]
IEEE PHOTOTONICS TECHNOLOGY LETTERS, VOL. 14, no. 1, pp. 56-58, 2002
[0010]
[Problems to be solved by the invention]
In the conventional arrayed waveguide grating optical wavelength multiplexer / demultiplexer, the core width of each slab connecting linear channel waveguide 49 is made equal to the core width of the delay channel waveguide 410. In addition, since the gap width of the slab connecting linear channel waveguide 49 must be sufficiently widened so that the gap 412 between the cores can be filled with the clad material, between the core centers of the respective slab connecting linear channel waveguides 49 The distance cannot be reduced below a certain value.
[0011]
Therefore, the light power output from each slab connection linear channel waveguide 49 is incident on the input side slab waveguide 3 from the slab connection linear channel waveguide 49 at a wavelength (λc in FIG. 5). The electric field distribution 614 obtained by superimposing the light to be abrupt has a steep double peak shape as shown in FIG. Therefore, at λc, the mismatch between the electric field distribution at the input portion and the electric field distribution at the portion connecting the output-side slab waveguide 6 to the output channel waveguide 7 becomes large. As a result, as shown in the wavelength loss characteristic of FIG. 7, if the passband is in a ripple shape or the ripple is to be suppressed, it is necessary to reduce the number of arrayed waveguides 5, and the loss increases.
[0012]
Accordingly, an object of the present invention is to provide a low-loss and flat passband characteristic without making the passband ripple, while making the gap width between the cores of the straight channel waveguide for slab connection sufficiently wide to be buried with a clad material. An object of the present invention is to provide an optical wavelength multiplexer / demultiplexer that can be realized.
[0013]
[Means for Solving the Problems]
To achieve the above object, the present invention provides an arrayed waveguide diffraction grating composed of a plurality of channel waveguides, an input-side slab waveguide connected to one end of the arrayed waveguide diffraction grating, and the arrayed waveguide diffraction An output-side slab waveguide connected to the other end of the grating and an output channel waveguide connected to the output-side slab waveguide, and a Mach-Zehnder circuit connected to the input-side slab waveguide is connected The Mach-Zehnder circuit is connected to the pair of slab-connecting linear channel waveguides connected to the input-side slab waveguide, the tapered waveguide connected to the slab-connecting linear channel waveguide, and connected to the tapered waveguide. in two different lengths of delay channel waveguide, and an optical wavelength demultiplexer comprising a 3dB coupler connected to said delay channel waveguides, the tape The waveguide has a core width that continuously changes and is formed to be narrowest at a connection portion with the straight channel waveguide for slab connection. The pair of straight channel waveguides for slab connection has a core width that is the tapered waveguide. An optical wavelength multiplexer / demultiplexer comprising a directional coupler connected to the slab waveguide in the vicinity of each other while being equal to the connecting portion . An optical wavelength multiplexer / demultiplexer is provided.
[0014]
In this way, by narrowing the width of the waveguide constituting the Mach-Zehnder circuit near the connection portion with the input side slab waveguide, the electric field distribution of the input portion to the input side slab waveguide and the output side slab waveguide are reduced. The mismatch with the electric field distribution of the portion connected from the waveguide to the output channel waveguide can be reduced. As a result, the ripple in the passband can be reduced, and loss in the band can be reduced.
[0015]
The Mach-Zehnder circuit is configured as described above, and the core width of the tapered waveguide is narrowed on the straight channel waveguide side for slab connection, so that the core width is narrowed in the vicinity of the connection portion with the input-side slab waveguide. be able to.
[0016]
The core width of the linear channel waveguide for slab connection is preferably as narrow as possible as long as mismatch loss with the input-side slab waveguide does not increase, and the relative refractive index difference between the core and the cladding is about 0.75%. In the channel waveguide, the core width is preferably 1 μm to 3 μm. The gap between the pair of straight channel waveguides for connecting slabs is preferably 3 μm or more, which allows easy embedding of a clad material. Further, the core width of the delay channel waveguide is preferably 6 μm to 8 μm, which is a pseudo single mode condition.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view of an embodiment of an arrayed waveguide grating optical wavelength multiplexer / demultiplexer according to the present invention. FIG. 1 (a) is an overall explanatory view of an optical circuit, and FIG. ) Is an enlarged explanatory view of a portion A in FIG. This optical wavelength multiplexer / demultiplexer is fabricated on a quartz substrate 8, a core made of a quartz-based material is formed on the quartz substrate 8, and an optical circuit is constituted by this core. The surface of the core and the quartz substrate 8 is covered with a clad film made of a quartz material. In the optical circuit, an input channel waveguide 1, a Mach-Zehnder circuit 2, and an input side slab waveguide 3 are connected to the input side of an arrayed waveguide diffraction grating 3 composed of a plurality of arrayed waveguides 4. An output channel waveguide 7 and an output side slab waveguide 6 are connected to the output side of the arrayed waveguide grating 4.
[0019]
The Mach-Zehnder circuit 2 includes a pair of slab connection linear channel waveguides 9 connected to the input-side slab waveguide 2, a taper waveguide 13 connected to the slab connection linear channel waveguide 9, and 2 connected to the taper waveguide 13. It consists of a delay channel waveguide 10 of different lengths and a 3 dB coupler 11 connected to the delay channel waveguide 10. The pair of slab connecting linear channel waveguides 9 and the tapered waveguides 13 are arranged close to each other and also serve as a 3 dB coupler (directional coupler).
[0020]
The core width of each of the pair of slab connecting straight channel waveguides 9 is 1.5 μm, and the core width of the delay channel waveguide 10 is 6 μm. In order to continuously change these core widths, a tapered waveguide 13 is provided.
[0021]
The electric field distribution 14 obtained by superimposing the light incident on the input-side slab waveguide 3 from the slab-connecting linear channel waveguide 9 in this embodiment is as shown in FIG. In the present invention, the core width of the slab connecting linear channel waveguide 9 is made narrower than before, so that even if the width of the gap 12 between the slab connecting linear channel waveguides 9 is the same, each slab connecting The center of gravity of the electric field distribution 14 of the light output from the straight channel waveguide 9 can be made closer. Further, since the core width of the slab connecting linear channel waveguide 9 is narrow, the evanescent region in each electric field distribution of the slab connecting linear channel waveguide 9 can be expanded. For these reasons, the mismatch between the electric field distribution at the input portion and the electric field distribution at the portion connected from the output-side slab waveguide 6 to the output channel waveguide 7 can be reduced. Therefore, the ripple in the pass band can be reduced and the loss in the band can be reduced.
[0022]
The wavelength loss characteristic in the present embodiment is as shown in FIG. 3, and it can be seen that the passband ripple can be reduced as compared with the conventional example of FIG.
[0023]
【The invention's effect】
As described above, the present invention includes an arrayed waveguide diffraction grating composed of a plurality of channel waveguides, an input-side slab waveguide connected to one end of the arrayed waveguide diffraction grating, and the arrayed waveguide diffraction grating. An output-side slab waveguide connected to the other end of the output channel, and an output channel waveguide connected to the output-side slab waveguide, and a Mach-Zehnder circuit connected to the input-side slab waveguide. In the multiplexer / demultiplexer, there is provided an optical wavelength multiplexer / demultiplexer in which the width of the waveguide constituting the Mach-Zehnder circuit is narrowly formed in the vicinity of the connection portion with the input-side slab waveguide. The mismatch between the electric field distribution at the input portion to the slab waveguide and the electric field distribution at the portion connected from the output-side slab waveguide to the output channel waveguide can be reduced. As a result, the ripple in the passband can be reduced, and loss in the band can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of an optical wavelength multiplexer / demultiplexer according to the present invention, FIG. 1 (a) is an overall explanatory diagram, and FIG. 1 (b) is an A part of FIG. 1 (a). FIG.
FIG. 2 is an explanatory diagram showing an electric field distribution of light incident on an input-side slab waveguide from a slab-connecting linear channel waveguide according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of wavelength loss characteristics according to an embodiment of the present invention.
4A and 4B are explanatory diagrams of a conventional optical wavelength multiplexer / demultiplexer, in which FIG. 4A is an overall explanatory diagram, and FIG. 4B is an enlarged explanatory diagram of a portion A in FIG.
FIG. 5 is an explanatory diagram of wavelength dependency of optical power incident on an input-side slab waveguide from a slab connection linear channel waveguide of a conventional optical wavelength multiplexer / demultiplexer.
FIG. 6 is an explanatory diagram showing an electric field distribution of light incident on an input-side slab waveguide from a conventional slab connection linear channel waveguide.
FIG. 7 is an explanatory diagram of wavelength loss characteristics of a conventional example.
[Explanation of symbols]
1: input channel waveguide 2: Mach-Zehnder circuit 3: input side slab waveguide 4: array waveguide diffraction grating 5: array waveguide 6: output side slab waveguide 7: output channel waveguide 8: substrate 9: slab Connecting linear channel waveguide 10: delay channel waveguide 11: 3 dB coupler 12: gap 13: taper waveguide 14: overlapping electric field distribution

Claims (2)

An arrayed waveguide diffraction grating composed of a plurality of channel waveguides, an input side slab waveguide connected to one end of the arrayed waveguide diffraction grating, and an output side connected to the other end of the arrayed waveguide diffraction grating A Mach-Zehnder circuit connected to the input-side slab waveguide , wherein the Mach- Zehnder circuit is connected to the input-side slab waveguide. A pair of slab connecting linear channel waveguides connected to the waveguide, a tapered waveguide connected to the slab connecting linear channel waveguide, and two different length delays connected to the tapered waveguide In an optical wavelength multiplexer / demultiplexer comprising a channel waveguide and a 3 dB coupler connected to the delay channel waveguide ,
The taper waveguide has a core width that continuously changes and is formed to be narrowest at a connection portion with the straight channel waveguide for slab connection, and the core width of the pair of straight channel waveguides for slab connection is the taper. An optical wavelength multiplexer / demultiplexer comprising a directional coupler connected to the slab waveguide adjacent to each other while being equal to a connection portion with the waveguide . The core width of the straight channel waveguide for slab connection is 1 μm to 3 μm, the gap between the pair of straight channel waveguides for slab connection is 3 μm or more, and the core width of the delay channel waveguide is 6 μm to 8 μm. Item 4. The optical wavelength multiplexer / demultiplexer according to Item 1 .

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