JP4569440B2 - Temperature independent optical multiplexer / demultiplexer - Google Patents

Description

  The present invention relates to an arrayed waveguide type optical multiplexer / demultiplexer used for wavelength division multiplexing in the field of optical communications, and more particularly to a temperature-independent optical multiplexer / demultiplexer designed to reduce its loss. .

  In the field of optical communication, 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 multiplexer / demultiplexer that multiplexes / demultiplexes light of different wavelengths plays an important role. In particular, a waveguide type optical multiplexer / demultiplexer using a Mach-Zehnder interferometer or an arrayed waveguide is advantageous for realizing multiplexing / demultiplexing with multi-channels and narrow demultiplexing intervals, and facilitates multiplexing of communication capacity. There is an advantage that can be greatly increased.

FIG. 5 shows a conventional arrayed waveguide type optical multiplexer / demultiplexer 12. The arrayed waveguide type optical multiplexer / demultiplexer 12 of this configuration includes an input channel waveguide 1, an input side slab waveguide 2 connected to the input channel waveguide 1, an output channel waveguide 6, and an output channel. The output side slab waveguide 5 connected to the waveguide 6 and the arrayed waveguide 3 composed of a plurality of channel waveguides connected to the input side slab waveguide 2 and the output side slab waveguide 5 are provided.
The light wave input from the input channel waveguide 1 propagates through the input side slab waveguide 2 and enters the arrayed waveguide 3. When propagating through each channel waveguide of the arrayed waveguide 3, the light wave undergoes a phase change and enters the output-side slab waveguide 5. The light wave in the output-side slab waveguide 5 interferes and reaches the output channel waveguide 6. Here, since the interference pattern of the light wave varies depending on the wavelength, an optical multiplexing / demultiplexing function is realized.

  Here, when an optical circuit is configured using a normal material, when the temperature changes, the refractive index of the material changes due to the thermo-optic effect, and thereby the equivalent refractive index of the arrayed waveguide 3 changes. Furthermore, the length of the arrayed waveguide 3 also changes due to thermal expansion. For this reason, the amount of phase change received by the arrayed waveguide 3 changes with temperature. Since this change differs depending on the wavelength, the output demultiplexing wavelength changes as a result. Here, considering a case where it is made of a quartz-based material as an example, the change of the demultiplexing wavelength due to the temperature near the wavelength of 1.55 μm is 0.01 nm / ° C. Therefore, for example, when used at an ambient temperature of 0 to 60 ° C., the maximum wavelength of 0.6 nm is shifted. For this reason, it cannot be used in a practical system as it is, and it is necessary to control the temperature of an optical circuit composed of a channel waveguide, a slab waveguide, and an arrayed waveguide.

  Therefore, as a temperature independence method that does not require temperature control means, a phase change due to temperature is achieved by providing a groove in a part of the optical circuit and filling it with a material having a refractive index temperature coefficient different from that of the optical circuit. There is known a method for compensating for the wavelength dependence of (see, for example, Non-Patent Document 1).

  Generally, since there is no confinement structure in the groove, a large diffraction loss occurs. Therefore, a method of reducing the diffraction loss of the entire groove by providing a plurality of grooves and concentrating the grooves with the grooves having an optimum groove interval is often employed (for example, Non-Patent Document 2). (See, for example, Non-Patent Document 3), a structure in which this method is incorporated in an arrayed waveguide optical multiplexer / demultiplexer has also been reported.

  When grooves are formed in the channel waveguide, diffraction occurs in both the vertical and horizontal directions with respect to the substrate, and even if the grooves are incorporated in the channel waveguide, the loss cannot be reduced sufficiently.

  Therefore, there is a report example of a structure in which a plurality of wedge-shaped grooves are provided in the input-side slab waveguide (see, for example, Non-Patent Document 4). FIG. 6 shows a temperature-independent optical multiplexer / demultiplexer 16 employing this structure, in which a plurality of wedge-shaped grooves 8a to 8c are provided in the input-side slab waveguide 2 to realize wavelength dependence compensation. In the input-side slab waveguide 2, only the diffraction in the vertical direction with respect to the substrate 7 affects the loss, so that the loss can be reduced compared to the case where a groove is formed in the channel waveguide.

  On the other hand, by increasing the relative refractive index difference Δ between the core and the clad, a method of reducing the radius of curvature of the bent waveguide and reducing the element in size is generally known. There is a report applied to a type optical multiplexer / demultiplexer (see, for example, Non-Patent Document 5).

  When the relative refractive index difference Δ is increased, there is a problem that radiation loss in the groove cannot be sufficiently suppressed even when a groove is formed in the slab waveguide. 7A and 7B show the relationship between the groove arrangement interval and the loss when the groove width is used as a parameter when the relative refractive index difference Δ between the core and the cladding is 0.8% and 2.5%, respectively. . It can be seen that there is an optimum groove arrangement interval for each groove width for any Δ. However, it can be seen that the minimum loss increases when Δ = 2.5% compared to when Δ = 0.8% and 2.5% and the same groove width. This is because, even if a groove is formed in the slab waveguide, the diffraction loss in the vertical direction cannot be ignored as Δ increases.

  Therefore, in order to reduce the diffraction loss in the vertical direction (perpendicular to the substrate), a method of forming a core having a taper structure in the vertical direction (for example, see Non-Patent Document 6) is employed, and this structure is converted into a spot size. A method of reducing the diffraction loss by using the device as a vessel and expanding the spot size around the groove in the vertical direction is conceivable.

  In addition, as a beam spot converting optical waveguide for converting the beam spot diameter, a segmented waveguide having a plurality of cores arranged in the propagation direction of the light beam is used, and the core / cladding refractive index difference is determined along the propagation direction of the light beam. An optical transmission module is known in which the beam spot diameter is enlarged or reduced by changing the optical transmission module to improve the coupling efficiency between optical components (see, for example, Patent Document 1).

Y. Inoue, et al., “Athermal silica-based arrayed-waveguide grating (AWG) multiplexer”, ECOC 97 Technical Digest, pp. 33-36, 1997 Hoshino et al., “Diffraction loss reduction structure in PLC integrated isolators”, 1999 IEICE General Conference, C-3-138, p.292, 1999 A.Kaneko, et al., “Athermal silica-based arrayed-waveguide grating (AWG) multiplexers with new low loss groove design,” OFC'99 Technical Digest, TuO1, pp.204-206, 1999 Maru, et al., “Athermal and center wavelength adjustable arrayed-waveguide grating”, OFC 2000 Technical Digest Hida, et al., “Fabrication of low-loss and polarisation-insensitive 256 channel arrayed-waveguide grating with 25 GHz spacing using 1.5% △ waveguides”, Electron. Lett., Vol.36, no.9, pp.820- 821, 2000 Ito et al., “Ultra-Low Loss Arrayed Waveguide Grating Using 1.5%-△ Waveguide”, IEICE Technical Report, OPE2002-16, pp.27-30, 2002 JP 2002-169046 A

  However, in order to reduce the longitudinal diffraction loss in the wedge-shaped groove, when the method of forming the core with the longitudinal taper structure is adopted, the process conditions for etching and core deposition are complicated for the formation of the taper structure. Must be controlled.

  Therefore, an object of the present invention is to solve the above-mentioned problems and to realize diffraction in the groove filled with an optical resin in order to realize temperature independence even when the relative refractive index difference Δ between the core and the clad is increased. It is an object of the present invention to provide a temperature-independent optical multiplexer / demultiplexer that can keep the above small.

To achieve the above object, the first invention provides at least one or more input channel waveguides, an input-side slab waveguide connected to the input channel waveguides, and at least one or more output channels. A channel waveguide, an output slab waveguide connected to the output channel waveguide, and the input slab waveguide and the output slab waveguide are connected to each other, and a plurality of channel guides having different waveguide lengths are connected. In a temperature-independent optical multiplexer / demultiplexer including an arrayed waveguide formed of waveguides , a plurality of divided cores are arranged at appropriate intervals in the light propagation direction in the core of the input side slab waveguide. The split core portion is formed, and the spot size diameter of light propagating through the split core portion is larger than the spot size diameter of light propagating through the undivided core portion of the input side slab waveguide. And a plurality of wedge-shaped grooves filled with an optical resin whose refractive index depends on temperature are disposed in the region of the divided core portion, and between the grooves adjacent to each other in the light propagation direction. The divided core is also formed in the region of the channel waveguide, and the phase change amount caused by the refractive index change due to the temperature in each of the channel waveguides constituting the arrayed waveguide is the phase change amount caused by the refractive index change due to the temperature of the optical resin. To compensate for the wavelength dependence of the phase change due to the temperature generated in the arrayed waveguide, making the central wavelength temperature independent, and the divided core of the divided core section periodically in the light propagation direction. And the length of the split core in the light propagation direction is gradually increased from the central portion of the split core portion toward the unsplit core portion of the input slab waveguide. A temperature-independent optical demultiplexer that is configured to so that.

According to a second aspect of the present invention, there is provided at least one input channel waveguide, an input side slab waveguide connected to the input channel waveguide, at least one output channel waveguide, and the output An output-side slab waveguide connected to a channel waveguide, an arrayed waveguide composed of a plurality of channel waveguides each connecting the input-side slab waveguide and the output-side slab waveguide, each having a different waveguide length. In the temperature-independent optical multiplexer / demultiplexer provided, the core of the input-side slab waveguide is formed with a split core portion in which split cores that are split into a plurality are arranged at appropriate intervals in the light propagation direction, The spot size diameter of the light propagating through the split core portion is set to be larger than the spot size diameter of the light propagating through the undivided core portion of the input side slab waveguide, and the split core In this region, a plurality of wedge-shaped grooves filled with an optical resin whose refractive index depends on temperature are arranged, and the divided core is also formed in the region between the grooves adjacent to each other in the light propagation direction. The arrayed waveguide is formed by canceling the phase change caused by the refractive index change due to temperature in each of the channel waveguides constituting the arrayed waveguide with the phase change caused by the refractive index change caused by the temperature of the optical resin. Compensating for the wavelength dependence of the phase change due to the temperature generated in the above, making the temperature of the central wavelength independent, and the length of the split core in the light propagation direction of the split core portion is constant, and Set so that the distance between the divided cores adjacent to each other in the light propagation direction is gradually shortened from the central part of the divided core part toward the undivided core part of the input-side slab waveguide. Alternatively, as the distance between the divided cores adjacent to each other in the light propagation direction is constant and approaches the undivided core portion of the input-side slab waveguide from the central portion of the divided core portion, The temperature-independent optical multiplexer / demultiplexer is set so that the length of the divided core in the propagation direction is gradually increased .

According to a third invention, in the first or second invention, the split core is formed in an arc shape, and the center of curvature of the arc-shaped split core is the input channel waveguide and the input side slab guide. This is a temperature-independent optical multiplexer / demultiplexer located at or near the waveguide connection.

The fourth invention is the first to third inventions, wherein the core and the cladding that forms the periphery of the core is composed of silica-based material, the relative refractive index difference of the cladding and the core 1.0 It is a temperature-independent optical multiplexer / demultiplexer that is at least%.

  The temperature-independent optical multiplexer / demultiplexer of the present invention can be used for an optical wavelength multiplexer / demultiplexer, an M × N frequency routing device, an Add / Drop filter, and the like used in an optical multiplexing transmission system.

  According to the present invention, even when the relative refractive index difference Δ between the core and the clad is increased, the diffraction loss in the groove can be suppressed, and the temperature-independent optical multiplexer / demultiplexer can be downsized. In addition, each split core of the split core section that suppresses the diffraction loss in the groove is not tapered in the vertical direction, but may have a fixed size in the vertical direction, and it is easy to create without complicating the process steps. The cost of the optical multiplexer / demultiplexer is not increased.

An embodiment of an arrayed waveguide temperature-independent optical multiplexer / demultiplexer 11 according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a top view of an optical circuit of a temperature-independent optical multiplexer / demultiplexer 11 according to an embodiment of the present invention. 2 is a cross-sectional view of the center of the input-side slab waveguide 2 (enlarged cross-sectional view taken along the line AA ′ in FIG. 1). This temperature-independent optical multiplexer / demultiplexer 11 is formed on a quartz glass substrate 7 on an input channel waveguide 1, an input-side slab waveguide 2, an arrayed waveguide 3, an output-side slab waveguide 5, and an output channel waveguide 6. These waveguides are formed by the core 10, and the quartz glass substrate 7 and the core 10 are covered with the clad 15. Here, the refractive index of the clad 15 is 1.457, the same as that of the quartz glass substrate 7, and the refractive index of the core 10 is 1.495 (relative refractive index difference Δ = 2.5%).

  A plurality of channel waveguides constituting the arrayed waveguide 3 connected between the input-side slab waveguide 2 and the output-side slab waveguide 5 are bent in an arc shape in order to reduce the size of the optical multiplexer / demultiplexer. The length increases from the inside toward the outside channel waveguide.

  A plurality of wedge-shaped (or curved wedge-shaped) grooves 8a to 8c are formed at predetermined intervals in the center of the input-side slab waveguide 2, and all the grooves 8a to 8c are filled with the optical resin 14. ing. In this embodiment, the quartz glass substrate 7, the core 10, and the clad 15 constituting the optical circuit are made of a quartz material, and the temperature dependency of the refractive index of the quartz material is a positive value. A silicone resin having a negative refractive index temperature dependency is used (an epoxy resin having a negative refractive index temperature dependency may be used as the optical resin 14 as well). With this structure, the phase change amount caused by the refractive index change due to temperature in each channel waveguide having a different waveguide length of the arrayed waveguide 3 is the phase change amount caused by the refractive index change due to the temperature of the wedge-shaped optical resin 14. The wavelength dependence of the phase change due to the temperature generated in the arrayed waveguide 3 can be compensated, and the temperature dependence of the center wavelength is realized.

  The core around the grooves 8a to 8c of the input-side slab waveguide 2 is a divided core portion 21 in which a plurality of divided cores 22 are periodically arranged at a period of 5 μm in the light propagation direction. The cores before and after the split core portion 21 are undivided core portions 23a and 23b in a state where the cores are continuous as before. The length of each divided core 22 (length in the light propagation direction) is substantially constant in the central portion of the divided core portion 21 near the grooves 8a to 8c, but the core is not divided from the central portion of the divided core portion 21. The length of the split core 22 is set to gradually increase as the portions 23a and 23b are approached. Further, each divided core 22 has an arc shape, and the center of curvature of the arc-shaped divided core 22 is located at or near the connection portion between the input channel waveguide 1 and the input side slab waveguide 2.

  Light waves of a plurality of wavelengths emitted from the input channel waveguide 1 are expanded by diffraction in the input-side slab waveguide 2 and are incident on each channel waveguide of the arrayed waveguide 3. It is known that the spot size of light propagating through a core that is periodically divided and divided is larger than the spot size of light propagating through an undivided core (Z. Weissman et al., (See “2-D mode tapering via tapered channel waveguide segmentation”, Electron. Lett., Vol. 28, No. 16, pp. 1514-1516, 1992). Therefore, by providing the split core portion 21 obtained by dividing the core around the grooves 8a to 8c, the spot size around the grooves 8a to 8c can be expanded in the vertical direction (direction perpendicular to the quartz glass substrate 7). it can. As a result, it is possible to reduce diffraction loss in the grooves 8a to 8c.

  In addition, the length of the split core 22 is not split by gradually increasing the length of the split core 22 as it approaches the core portions 23a and 23b that are not split from the central portion of the split core portion 21 with a substantially constant length. The spot size of the guided light can be smoothly changed between the core portions 23a and 23b and the split core portion 21, and the transition loss due to the spot size expansion can be reduced.

  Further, when the core 10 is divided in the input-side slab waveguide 2, it is necessary to reduce aberration due to a light phase change due to a change in refractive index. Therefore, in the present embodiment, each divided core 22 has an arc shape, and the center of curvature of the arc-shaped divided core 22 is positioned at or near the connection portion between the input channel waveguide 1 and the input-side slab waveguide 2. Accordingly, the light propagating through the input-side slab waveguide 2 while being enlarged from the connecting portion is prevented from generating aberrations.

  FIG. 3 shows the minimum length of the split cores 22 arranged periodically with respect to the plurality of wedge-shaped groove structures of the input-side slab waveguide 2 of the above embodiment (the length of the split cores 20 near the grooves 8a to 8c). The calculation result of the groove | channel arrangement | positioning space | interval and the transition loss of the division | segmentation core part 21 and groove | channels 8a-8c when (S) is made into a parameter is shown. The calculation was performed by a two-dimensional beam propagation method. In the case of the conventional structure in which the split core portion 21 is not formed (the split core 22 is arranged with a period of 5 μm, so that when the split core 22 has a length of 5 μm, it is the same as the core portions 23 a and 23 b that are not continuously split. Therefore, the structure in which the divided core portion 21 is formed can reduce the minimum loss when the groove interval is optimized, as compared with the conventional structure corresponding to the length of the divided core 22 = 5 μm. It can also be seen that when the minimum length of the split core 22 is reduced to 1 μm, the minimum loss can be greatly reduced to 0.7 dB.

  FIG. 4 shows a manufacturing procedure of the arrayed waveguide type optical multiplexer / demultiplexer according to the embodiment of the present invention. First, (1) a core (core film) 10 is deposited on a quartz glass substrate 7 by an electron beam evaporation method or the like. Next, (2) an optical circuit pattern mask 13 is formed on the surface of the core 10 by photolithography, and (3) input / output channel waveguides 1 and 6 and input / output side slab guides are formed by reactive ion etching. The cores 10 other than the core portions of the waveguides 2 and 5, the arrayed waveguide 3 and the split core portion 21 are etched to form a waveguide core pattern. Next, (4) the mask 13 is peeled off, and (5) the clad 15 is deposited by chemical vapor deposition. Finally, (6) the grooves 8a to 8c are formed and the resin 14 is filled. In this manufacturing procedure, the waveguides 1, 2, 3, 5, 6 and the split core portion 21 can be formed at the same time. Therefore, the spot size of the groove, which has been a problem when the conventional structure is employed. It is possible to suppress an increase in process distance due to the formation of the conversion structure.

  In the above-described embodiment, the divided cores 22 divided into a plurality of divided cores 21 are periodically arranged. However, the length of the divided cores 22 of the divided cores 21 is constant, and adjacent divided parts are divided. You may make it the space | interval between the cores 22 and 22 gradually shorten as the core parts 23a and 23b which are not divided | segmented from the center part of this division | segmentation core part 21 approach. Alternatively, the interval between the adjacent divided cores 22 and 22 is made constant, and the length of the divided core 22 is gradually increased as approaching the core portions 23a and 23b that are not divided from the central portion of the divided core portion 21. It may be.

1 is a top view showing an optical circuit of an embodiment of a temperature-independent optical multiplexer / demultiplexer according to the present invention. It is an expanded sectional view of the A-A 'line of the input side slab waveguide of FIG. In one Embodiment of this invention, it is a figure which shows the relationship between the groove | channel arrangement | positioning space | interval in an input side slab waveguide, and the loss of a division | segmentation core part and a groove | channel. It is a figure which shows the preparation procedure of the temperature independent optical multiplexer / demultiplexer which concerns on one Embodiment of this invention. It is a figure which shows the optical circuit of the conventional array waveguide type | mold optical multiplexer / demultiplexer. It is a figure which shows the optical circuit of the conventional temperature independent optical multiplexer / demultiplexer. It is a figure which shows the relationship between the groove | channel arrangement | positioning space | interval and loss in a waveguide with relative refractive index difference (DELTA) = 0.8% and 2.5%.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input channel waveguide 2 Input side slab waveguide 3 Array waveguide 5 Output side slab waveguide 6 Output channel waveguide 7 Quartz glass substrate 8a-8c Groove 10 Core 15 Cladding 21 Division | segmentation core part 22 Division | segmentation core 23a, 23b Undivided core

Claims (4)

At least one input channel waveguide, an input side slab waveguide connected to the input channel waveguide, at least one output channel waveguide, and the output channel waveguide A temperature-independent optical waveguide comprising: an output-side slab waveguide; and an arrayed waveguide that connects the input-side slab waveguide and the output-side slab waveguide and has a plurality of channel waveguides each having a different waveguide length. In the duplexer,
The core of the input-side slab waveguide is formed with a split core portion in which a plurality of split cores are arranged at appropriate intervals in the light propagation direction, and the spot size of light propagating through the split core portion The diameter is set to be larger than the spot size diameter of light propagating through the undivided core portion of the input side slab waveguide,
A plurality of wedge-shaped grooves filled with an optical resin whose refractive index depends on temperature are disposed in the region of the divided core portion, and also in the region between the grooves adjacent to each other in the light propagation direction. The split core is formed ;
A phase change amount caused by a refractive index change due to temperature in each of the channel waveguides constituting the array waveguide is canceled by a phase change amount caused by a refractive index change due to the temperature of the optical resin, and is generated in the array waveguide. Compensates the wavelength dependence of the phase change due to temperature, makes the central wavelength temperature independent,
The light propagation direction as the divided cores of the divided core part are periodically arranged in the light propagation direction and approach the undivided core part of the input side slab waveguide from the central part of the divided core part. The temperature-independent optical multiplexer / demultiplexer is set so that the length of the split cores in (2) is gradually increased . At least one input channel waveguide, an input side slab waveguide connected to the input channel waveguide, at least one output channel waveguide, and the output channel waveguide A temperature-independent optical waveguide comprising: an output-side slab waveguide; and an arrayed waveguide that connects the input-side slab waveguide and the output-side slab waveguide and has a plurality of channel waveguides each having a different waveguide length. In the duplexer,
The core of the input-side slab waveguide is formed with a split core portion in which a plurality of split cores are arranged at appropriate intervals in the light propagation direction, and the spot size of light propagating through the split core portion The diameter is set to be larger than the spot size diameter of light propagating through the undivided core portion of the input side slab waveguide,
A plurality of wedge-shaped grooves filled with an optical resin whose refractive index depends on temperature are disposed in the region of the divided core portion, and also in the region between the grooves adjacent to each other in the light propagation direction. The split core is formed;
A phase change amount caused by a refractive index change due to temperature in each of the channel waveguides constituting the array waveguide is canceled by a phase change amount caused by a refractive index change due to the temperature of the optical resin, and is generated in the array waveguide. Compensates the wavelength dependence of the phase change due to temperature, makes the central wavelength temperature independent,
As the length of the split core in the light propagation direction of the split core portion is constant and approaches the non-split core portion of the input slab waveguide from the central portion of the split core portion, The interval between the divided cores adjacent in the propagation direction is set to be gradually shortened, or the interval between the divided cores adjacent in the light propagation direction is constant, and from the center of the divided core unit The temperature-independent optical multiplexing / demultiplexing is set such that the length of the divided core in the light propagation direction is gradually increased as approaching the undivided core portion of the input-side slab waveguide vessel. 3. The temperature-independent optical multiplexer / demultiplexer according to claim 1, wherein the split core is formed in an arc shape, and the center of curvature of the arc-shaped split core is the input channel waveguide and the input side. A temperature-independent optical multiplexer / demultiplexer, which is located at or near a connection portion of a slab waveguide. 4. The temperature-independent optical multiplexer / demultiplexer according to claim 1, wherein the core and the clad forming the periphery of the core are made of a quartz-based material, and the relative refractive index difference between the core and the clad is A temperature independent optical multiplexer / demultiplexer characterized by being 1.0% or more.

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