JP6543183B2 - Optical circuit manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a laminated optical circuit including a plurality of optical waveguides.

  The optical waveguide constituting the silica-based optical circuit is manufactured on a quartz glass substrate or a silicon substrate using silica-based glass as a main material. This optical waveguide has low propagation loss, high reliability and stability, good machinability, good matching with the silica-based optical fiber, low loss and high reliability, and is for standard communication. It has features such as being connected to a silica-based optical fiber.

  Y-branch power splitter composed of the above optical waveguide, Mach-Zehnder Interferometer (MZI), optical switch using MZI, and arrayed Waveguide Grating (AWG) Development of optical circuits (PLC: Planar Lightwave Circuits) is underway. These optical circuits have become important key devices of photonic network systems based on wavelength division multiplexing (WDM) optical transmission systems which are under construction (see Non-Patent Documents 1, 2 and 3).

  The silica based optical waveguide is mainly manufactured as follows. First, a lower cladding layer and a core layer are formed on a quartz substrate or a silicon substrate from the substrate side. Next, after processing the desired core pattern by photolithography and reactive ion etching, an upper cladding layer is formed on the core layer. In this way, an optical waveguide comprising a light propagating core and a cladding structure is formed. By forming a desired pattern in this optical waveguide, various optical circuits including Y-branch power splitter, MZI, and AWG can be manufactured. (Non-patent documents 3 and 4).

  The above-mentioned optical circuit devices are subject to various research and development in order to meet the demand for miniaturization, high integration, high functionality, high performance, and cost reduction, along with the progress toward the advancement of photonic networks. It is in progress. One example is development for one-chip integration in which multiple elements are integrated in order to realize multiple functions on one chip. In addition to the fact that the number of fiber connection points can be reduced by the one-chip composite integration, connection loss with the fiber can be reduced as compared with the case where a plurality of chips are connected by fiber. In addition, the fiber routing space on the fiber mounting board is reduced, and in this respect, miniaturization of the device on the mounting board can be realized. Conventional devices include AWG, variable optical attenuator (VOA) to adjust light intensity, tap to branch part of signal light, and photodetector (PD) to monitor light intensity in one chip Integrated composite integrated optical circuits and the like are known (Non-Patent Documents 3 and 5).

  Furthermore, integrated optical circuits corresponding to ROADMs (Reconfigurable optical add drop multiplexers) in which a plurality of AWGs, SWs, VOAs, etc. are integrated are also known.

  Importance of technology to realize multi-layered optical circuits with two or more laminated optical waveguide layers in order to further reduce the footprint (footprint) of optical circuits on mounting boards in the future Is high. This multilayer type optical circuit is to be provided with a multilayer core, and research and development of new optical devices utilizing the function of this multilayer core are also in progress. As an example, an optical device that implements functions such as an optical circuit, a liquid crystal on silicon (LCOS), a wavelength selective switch (WSS) using a micro electro mechanical system (MEMS), and the like can be given. . The WSS optical devices disclosed in Patent Document 1 and Patent Document 2 can be made smaller by using a laminated optical circuit.

  FIG. 1 shows a method of manufacturing a conventional multilayer optical circuit (Non-patent Document 6). First, the lower cladding layer 112 and the glass film 113 are formed on the substrate 111 from the substrate side (FIG. 1A). The refractive index of the glass film 113 is higher than that of the cladding layer 112. The glass film 113 is formed by a flame deposition (FHD) method, a sputtering method, a CVD method, or the like.

  Next, the glass film 113 is processed into a desired pattern using photolithography and reactive ion etching (RIE) technology to generate a first core 114 (FIG. 1 (b)). Thereafter, the upper cladding layer 115 is formed on the lower cladding layer 112 and the exposed portion of the first core 114 (FIG. 1C), and the upper cladding layer 115 is planarized (FIG. 1D). This planarization process can be performed by polishing or heat treatment. Thus, the first waveguide layer is produced.

  The upper cladding layer 115 can be formed by forming a glass layer by a flame deposition (FHD) method, a sputtering method, a CVD method, or the like, similarly to the lower cladding layer 112 described above.

  Next, a glass film 116 is deposited on the upper cladding layer 115 (FIG. 1E). Then, as in the case shown in FIG. 1B, the glass film 116 is processed into a desired pattern using photolithography and reactive ion etching (RIE) technology to generate the second core layer 117. (FIG. 1 (f)). Thereafter, an upper cladding layer 118 is formed on the exposed portions of the upper cladding layer 115 and the second core 117 (FIG. 1 (g)). Thus, the second waveguide layer is manufactured.

  The laminated optical circuit provided with the n-th waveguide layer (n = 3, 4, ...) after the second waveguide layer is manufactured by repeating Fig. 1 (d) to Fig. 1 (g). can do.

JP, 2010-117564, A JP, 2009-168840, A

Y. Hibino, IEEE CIRCUITS & DEVICES, Nov., 2000, pp. 21-27. A. Himeno, et al., J. Sel. Top. Q. E., vol. 4, 1998, pp. 913-924. M. Abe, J. Cer. Soc. J., 2008, pp. 1063-1070. M. Kawachi, Opt. Quantum Electron., 22, 1990, pp. 391-416. I. Ogawa, et al., Proc. LEOS 2005, TuL1, pp. 268-269. Senichi Suzuki, et al., Integrated-Optic Ring Resonators with Two Stacked Layers of Silica Waveguide on Si, Photon. Tech. Lett., 1992, pp. 1256.

  In the above-described conventional method for manufacturing a laminated optical circuit, it is necessary to stabilize the laminated glass film at the time of manufacturing the glass film or at the time of the heat treatment thereafter. For this reason, it is general to adjust the additional component of the glass so that the glass transition temperature or the softening point temperature of the lower glass film is higher than that of the upper glass film. When the glass transition temperature (transition point) or softening temperature (softening point) of the lower glass film is lower than that of the upper glass layer, the lower glass film is heat treated at the time of formation or patterning of the upper glass film. As it softens, the base of the lower layer will shake. As a result, the pattern in the upper layer may be distorted, or the distortion may affect the optical circuit in the lower layer, and the optical characteristics of the entire laminated optical circuit may be degraded.

  Generally, as the number of stacked optical circuits increases, it is necessary to make the glass transition temperature or softening point temperature of the lower glass film higher than that of the upper glass film, so the temperature control thereof becomes more difficult. If the temperature adjustment is not properly performed, the optical characteristics of the laminated optical circuit may be impaired. In addition, when the upper layer waveguide is manufactured, scattered light or stray light is generated by the lower layer waveguide in the photolithography and exposure steps, and the error accuracy of the waveguide manufacturing is lowered. As a result, the optical characteristics of the entire optical circuit are increased. It may deteriorate. This is more pronounced as the number of waveguide layers increases.

  In addition, when only a part of the optical circuit chip is stacked to form a waveguide, the above-described conventional optical circuit manufacturing method is inefficient because the waveguides are stacked one by one.

  The present invention has been made in view of such circumstances, and can avoid the difficulty of the photolithography and the patterning exposure process, and can relieve the restriction of the glass transition temperature condition between a plurality of waveguide layers. An object of the present invention is to provide a method of manufacturing a laminated optical circuit.

In order to solve the above problems, the present invention comprises the steps of producing a single-layer optical circuit in which a lower cladding layer, a core, and an upper cladding layer are formed on a substrate from the substrate side; one of the so surface between the upper cladding layer of the single layer optical circuit faces, and bonding two of the single-layer optical circuit, the one substrate of two of the single-layer optical circuit which is the joint Removing, and on the exposed lower cladding layer of the one single-layer optical circuit from which the substrate has been removed, a single-layer optical circuit separate from the two single-layer optical circuits joined together. Bonding the other single layer optical circuit such that the surface of the upper cladding layer is bonded .

  The step of bonding may include the step of positioning two single-layer optical circuits such that the surfaces of the cladding layers face each other.

  The bonding step may include the step of polishing the cladding layer on the bonding surface.

  According to the present invention, the restriction of the glass transition temperature condition between a plurality of waveguides can be relaxed. Moreover, the difficulty of a photolithography and a patterning exposure process can be avoided.

It is a figure for demonstrating the manufacturing method of the conventional laminated | stacked optical circuit. It is a figure for demonstrating an example of the manufacturing method of the single layer optical circuit laminated | stacked in order to produce the laminated type optical circuit of embodiment. It is a figure for demonstrating an example of the manufacturing method of the laminated | stacked optical circuit which laminated | stacked several single layer optical circuits. It is the schematic which shows the structural example of a hot press apparatus. It is a figure which shows the structural example of 3 layer laminated | stacked optical circuit. FIG. 6 is a diagram showing an example of transmission spectrum characteristics of a second optical circuit in the arrayed waveguide grating wavelength division multiplexer as the three-layer laminated type optical circuit of FIG. 5. It is a figure which shows an example of the transmission optical characteristic of an arrayed waveguide grating wavelength multiplexer / demultiplexer.

  Hereinafter, a laminated optical circuit according to an embodiment of the present invention will be described. The laminated optical circuit is one in which a single layer optical circuit 10 having one waveguide layer is laminated. First, a method of manufacturing the single-layer optical circuit 10 will be described with reference to FIG.

[Method of producing single-layer optical circuit]
FIG. 2 is a diagram for explaining a method of manufacturing the single-layer optical circuit 10. As shown in FIG.

  As shown in FIG. 2, the lower cladding layer 11 and the glass layer 13 are formed on the substrate 11 from the substrate side (FIG. 2 (a)). The substrate 11 is, for example, a Si substrate. The refractive index of the glass layer 13 is higher than that of the lower cladding layer 12.

In this embodiment, the lower cladding layer 11 is formed on the thermal oxide film layer using a flame deposition (FHD) method, and the SiO ₂ -Ta ₂ O ₅ glass layer 13 is formed on the lower cladding layer 11 by sputtering. accumulate.

  Next, after forming the processing mask layer 14 (FIG. 2B), the exposure processing and patterning processing of the processing mask layer 14 are performed using a photolithographic technique (FIG. 2C). Thereafter, the glass layer 13 is processed into a desired pattern by reactive ion etching (RIE) to form a core 15 (FIG. 2 (d)).

  The remaining processed mask layer 14 is removed (FIG. 2 (e)), the upper cladding layer 16 is formed on the lower cladding layer 12 and the exposed portion of the core 15, and the core 15 is embedded with the upper cladding layer 16 (FIG. 2). (F)).

  Thus, a single-layer optical circuit 10 including one waveguide layer (cladding layers 12 and 16 and core 15) is produced. In FIG. 2, the relative refractive index difference (Δ) of the core to the cladding layers 12 and 16 is 2.5%. The thickness of the cladding layer 12 is 20 μm, and the size of the core 15 is 3.5 μm × 4.0 μm (width × height).

  Next, a method of manufacturing the laminated optical circuit 51 of the present embodiment will be described with reference to FIGS. FIG. 3 is a view for explaining an example of a method of manufacturing the laminated optical circuit 51. As shown in FIG. FIG. 4 is a view for explaining the inside of the hot press chamber 50 of the hot press 5.

  The laminated optical circuit 51 is obtained by joining two single layer optical circuits 10 and 20. The method of manufacturing the single-layer optical circuit 20 is the same as that shown in FIGS. 2 (a) to 2 (f). That is, the single-layer optical circuit 20 includes the lower layer cladding layer 22, the core 25, and the upper layer cladding layer 26 on the substrate 21 as in the single-layer optical circuit 10. Here, in the single-layer optical circuit 20, the thickness of the lower layer cladding layer 22 is 5 μm, and the thickness of the upper layer cladding layer 26 is 10 μm.

  First, two single-layer optical circuits 10 and 20 are prepared (FIG. 3A). Next, the junction positions of the two single-layer optical circuits 10 and 20 are adjusted so that the corresponding upper layer cladding layers face each other and are joined (FIG. 3 (b)), the two single-layer optical circuits 10, 20 are joined (Fig. 3 (c)). At this time, each upper cladding layer is polished, and the single-layer optical circuits 10 and 20 can be joined on a flat surface.

  Then, the substrate 21 is removed by dry etching (FIG. 3 (d)). Thus, a laminated optical circuit 81 including two waveguide layers is manufactured.

  The manufacturing method of FIG. 3 described above is realized by the hot press device 5.

  In the hot press device 5 shown in FIG. 4, the heater 51, the first optical circuit holder 52, the second optical circuit holder 53, and the first IR (Infrared Camera) camera 54 are provided in the hot press chamber 50. And a second IR (Infrared Camera) camera 55, a microscope 56, and a scope holder 57.

  In the example of FIG. 4, the single-layer optical circuit 10 is held by the first optical circuit holder 52, and the single-layer optical circuit 20 is held by the second optical circuit holder 53. The IR cameras 54, 55 are provided in corresponding optical circuit holders and image the single layer optical circuits 10, 20.

  The optical circuit holder 53 is configured to be able to move the single-layer optical circuit 20 along the vertical direction R1 shown in FIG.

  A microscope 56 is mounted between the two single layer optical circuits 10,20. The scope holder 57 is configured to be movable along the left-right direction R2 shown in FIG. 4 in order to adjust the bonding position of the two single-layer optical circuits 10 and 20.

  In FIG. 3 (b), the junction positions of the two single-layer optical circuits 10 and 20 are confirmed by the IR cameras 54 and 55 and the microscope 56. At this time, when it is necessary to adjust the bonding position, the single layer optical circuit 20 is moved along the directions R1 and R2 by the optical circuit holder 53 and / or the scope holder 57. Thereby, appropriate positioning of the single-layer optical circuits 10 and 20 can be implemented. After alignment, the microscope 56 moves to a position away from the space area at the top of the optical circuit.

  In FIG. 3 (c), the two single layer optical circuits 10 and 20 are joined as follows. After adjusting the position, the optical circuit is brought into contact with the upper surface as it is, sandwiched between the upper optical circuit holder 53 and the lower optical circuit holder 52, and a slight pressure (about 3N) is applied between the substrates. Make it After heating by the heater 51 of the hot press and raising the temperature to 900 ° C., the pressure is further increased to about 100 N, and then while the pressure is applied, the first optical circuit 10 and the second The upper surfaces of the optical circuit 20 are bonded to each other.

  Although the case where two single layer optical circuits 10 and 20 are joined has been described above with reference to FIGS. 3 and 4, the number of single layer optical circuits to be stacked can be three or more.

  For example, FIG. 5 is a diagram showing a configuration example of a three-layer laminated type optical circuit (laminated optical circuit) 82 in the case where three single-layer optical circuits 10, 20, and 30 are joined. Sectional drawing of the laminated type optical circuit 82, (b) shows the perspective view of AWG (Arrayed Waveguide Grating) wavelength multiplexer / demultiplexer as the three-layered laminated type optical circuit 82. FIG.

  The configuration of the single layer optical circuit 30 is the same as that of the single layer optical circuit 20. That is, the single-layer optical circuit 30 includes the lower cladding layer 32, the core 35, and the upper cladding layer 36 on the substrate 31. The thickness of the lower layer cladding layer 32 is 5 μm, and the thickness of the upper layer cladding layer 36 is 10 μm.

In the example of FIG laminated optical circuit 82 of 5 (a), on the stacked light circuit 81 of the lower clad layer 22 shown in FIG. 3 (d), the upper cladding layer 36 of a single-layer optical circuit 30 is bonded ( 3 (c)), and the substrate 31 of the single-layer optical circuit 30 is removed (similar to the removal of the substrate 21 of FIG. 3 (d)).

  FIG. 6 shows transmission spectrum characteristics of the second waveguide layer in the AWG wavelength division multiplexer as the laminated optical circuit 82. As shown in FIG. The second waveguide layer means a layer comprising the cladding layers 22 and 26 and the core 25 of FIG.

  According to the transmission spectrum characteristics shown in FIG. 6, it can be seen that good demultiplexing characteristics are obtained. Regarding the first waveguide layers (cladding layers 12 and 16 and core 15 in FIG. 5) and the third waveguide layers (cladding layers 32 and 36 and core 35 in FIG. 5) other than the second waveguide layer Similarly, good branching characteristics could be obtained.

  In general, the AWG wavelength multiplexer / demultiplexer significantly impairs the transmission spectrum characteristics when there are distortions and fabrication errors that occur in the arrayed waveguide portion or the slab waveguide portion. However, as described above, since the transmission spectrum characteristics of the laminated optical circuit 82 of the present embodiment are good, the waveguide is well manufactured.

  As described above, in the method of manufacturing the laminated optical circuit 81 of the present embodiment, a single-layer optical circuit in which the lower cladding layer 12, the core 15, and the upper cladding layer 16 are laminated on the substrate 11 from the substrate side 10, and bonding the single-layer optical circuits 10 and 20 such that the surfaces of the clad layers 16 and 26 on the top of the two single-layer optical circuits 10 and 20 formed are opposed to each other. And removing one substrate 21 of the bonded single layer optical circuit. Here, since the manufacturing method of each single-layer optical circuit 10 and 20 becomes the same, the glass transition temperature or the softening point temperature of the glass film to be the core can be all the same for each layer. In this point, the glass between the plurality of waveguide layers is adjusted as compared with the conventional case (FIG. 1) in which the additional component of glass is adjusted so that the lower glass film is higher than the upper glass film. Constraints on transition temperature conditions can be relaxed.

  In addition, a highly accurate laminated optical circuit can be manufactured without performing waveguide manufacture by steps such as film formation, photolithography, exposure, and processing on an optical circuit laminated in one or more layers.

  The specific configuration of the present embodiment can also be changed.

  The bonding method of two single layer optical circuits can be modified. For example, in FIG. 3C, after cleaning the upper surfaces of the clad layers 16 and 26 of the two polished single-layer optical circuits 10 and 20, the single-layer optical circuits 10 and 20 are bonded by an adhesive. It is also good. As the adhesive, for example, a thermosetting adhesive having a cure shrinkage of 3% or less can be considered. The curing of the adhesive is realized by raising the temperature to 250 ° C. In this case, the thickness of the upper cladding layer 26 is preferably 15 μm.

  Also in this case, the laminated optical circuit 82 similar to the laminated optical circuit 81 of the above embodiment can be manufactured.

  FIG. 7 shows transmission spectrum characteristics in the second waveguide layer in the AWG wavelength division multiplexer as the laminated optical circuit 82. As shown in FIG.

  From FIG. 7, it can be seen that the waveguide is well manufactured because the transmission spectrum characteristics of the laminated optical circuit 82 of the present embodiment are also good.

As mentioned above, although an embodiment and a modification were explained in full detail, the modification etc. which were individually described in the embodiment can be carried out combining with the laminated optical circuit 81, 82 of the embodiment. In addition, the materials, pressures, temperatures and layer thicknesses described above are not limited to the present embodiment, and design changes can be freely made within the scope of the present embodiment. For example, the glass material to be the core may be made of any of SiO ₂ -GeO ₂ glass, SiO ₂ -TiO ₂ glass, SiOx glass, SiON and the like.

  Also, in the planarization process of the upper cladding layer, the average of the surface accuracy is flattened to about 1 nm or less, and the bonding surface of the upper cladding layer is irradiated with atoms or ions to activate the bonding surface, light is obtained even at room temperature. It is possible to join circuits and optical circuits.

11, 21 and 31 substrate 12, 22 and 32 lower layer clad layer 15, 25 and 35 core 16, 26 and 36 upper layer clad layer 81 and 82 laminated optical circuit

Claims (5)

Manufacturing a single-layer optical circuit in which a lower cladding layer, a core, and an upper cladding layer are formed on the substrate from the substrate side;
As surfaces on each of the upper cladding layer of two of the single-layer optical circuit wherein the fabricated faces, and bonding two of the single-layer optical circuit,
Removing one substrate of the two bonded single layer optical circuits ;
On top of the exposed lower cladding layer of the one single layer optical circuit from which the substrate has been removed, the upper cladding layer of a single layer optical circuit separate from the two single layer optical circuits joined together And b. Bonding the other single layer optical circuit such that the surfaces of the layers are joined .   2. The method according to claim 1, wherein the step of bonding includes the step of positioning two single layer optical circuits so that the surfaces of the cladding layers face each other. In the step of the joining method for manufacturing a multilayer optical circuit according to claim 1 or 2, characterized in that it comprises a step of polishing the cladding layer of the bonding surface. In the bonding step, an adhesive is applied to the upper surface of the cladding layer on the upper part of the single-layer optical circuit to be joined, and the single-layer optical circuits are adhered and fixed via the adhesive. A method of producing a laminated optical circuit according to any one of 1 to 3 . The method for manufacturing a laminated optical circuit according to any one of claims 1 to 3, wherein in the bonding step, the single-layer optical circuit is pressed and heated.