JP2007147751A - Method of manufacturing optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical waveguide for improving characteristics of the optical waveguide. <P>SOLUTION: The method of manufacturing the optical waveguide comprises a core film formation process S1 for forming a core film on a first substrate, a core film processing process S2 for forming a core having a rectangular cross sectional shape by processing the core film, a groove formation process S3 for forming a groove corresponding to the core on a second substrate, and a joint process S4 for jointing the first substrate and the second substrate by mutually allowing the core formed on the first substrate to correspond to the groove formed on the second substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical waveguide.

Conventionally, as a method for producing an optical waveguide, a core formed on a substrate is processed into a ridge shape, and overclad glass is deposited on the substrate and the core by using a flame deposition method (FHD), a plasma CVD method, or the like. There is a method of forming an overcladding that covers the top and side surfaces of the core (see Patent Document 1 below).
JP-A-11-125727

  However, in the FHD method, it is difficult to obtain a desired shape due to high temperature, and furthermore, since an additive is added to the overcladding, there is a concern about deterioration of polarization characteristics due to residual stress. Also, with the PVD method or the CVD method, voids remain and it is difficult to obtain sufficient characteristics.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing an optical waveguide capable of improving the characteristics of the optical waveguide.

  An optical waveguide manufacturing method of the present invention includes a core film forming step of forming a core film on a first substrate, and a core film that forms a core having a rectangular cross-sectional shape on the first substrate by processing the core film A first step in which a processing step, a groove forming step of forming a groove corresponding to the core on the second substrate, and a core formed on the first substrate and a groove formed on the second substrate are made to correspond to each other; A bonding step of bonding the substrate and the second substrate.

  According to the method for manufacturing an optical waveguide of the present invention, the first substrate and the second substrate are formed by associating the core having the rectangular cross-sectional shape formed on the first substrate with the groove formed on the second substrate. Since the substrate is bonded, the over clad is constituted by the second substrate. Therefore, generation | occurrence | production or deformation | transformation of the void which generate | occur | produces when depositing glass and forming an over clad can be prevented. Therefore, an optical waveguide with improved characteristics can be manufactured with reduced loss.

  In the method for producing an optical waveguide according to the present invention, it is also preferable to use an adhesive for joining the first substrate and the second substrate in the joining step. In this way, the first substrate and the second substrate can be reliably bonded.

  In the method for producing an optical waveguide of the present invention, it is also preferable that the first and second substrates are quartz glass substrates and the core film is quartz glass to which a dopant for increasing the refractive index is added. In this way, the refractive indexes of the first and second substrates can be set lower than the refractive index of the core, and the first and second substrates can function appropriately as clads with respect to the core. Further, the periphery of the core is surrounded by the first substrate and the second substrate made of the same material. Therefore, the polarization characteristics of the optical waveguide are improved, and an optical waveguide with improved characteristics can be manufactured. For example, Ge can be used as the dopant for increasing the refractive index.

  Further, the optical waveguide manufacturing method of the present invention forms the core in the core film processing step, and processes the core film so that a film thinner than the thickness of the core remains on the same plane as the core. It is also preferable to join the first substrate and the second substrate by heating to 1200 ° C. or higher.

  Thus, when the first and second substrates are quartz glass substrates and the core film is quartz glass to which a dopant for increasing the refractive index is added, the film and the core generally formed in the core film processing step are Softens at a lower temperature than the first and second substrates. And since it heats to 1200 degreeC or more in a joining process, a film | membrane and a core soften and the adhesiveness of a film | membrane and a core, a 1st board | substrate, and a 2nd board | substrate improves.

  According to the method for producing an optical waveguide of the present invention, the characteristics of the optical waveguide can be improved.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

(First embodiment)
FIG. 1 is a diagram illustrating the steps of a method for manufacturing an optical waveguide according to the present embodiment. The optical waveguide manufacturing method according to the present embodiment includes a core film forming step S1, a core film processing step S2, a groove forming step S3, and a joining step S4. Then, with reference to FIG. 2, each process of the manufacturing method of the optical waveguide which concerns on 1st Embodiment is demonstrated. FIG. 2 is a cross-sectional view showing a method of manufacturing the optical waveguide according to the first embodiment.

  In the core film forming step S1, a core film 12 is formed on the first substrate 11 as shown in FIG. The first substrate 11 is a quartz glass substrate having a diameter of about 4 inches and a thickness of about 0.5 mm. The core film 12 is formed by depositing a quartz glass film having a thickness of about 7.5 μm to which Ge is added as a refractive index increasing dopant using a plasma CVD method. As a method of forming the core film 12, an FHD method, sputtering, or the like may be used.

  After the core film forming step S1, a core film processing step S2 is performed. As shown in FIG. 2B, in the core film processing step S2, the core film 12 is processed to form a core 12a having a rectangular cross-sectional shape. A photomask corresponding to the waveguide circuit pattern is formed on the upper surface of the core film 12, and the core 12a along the waveguide circuit pattern is formed using photolithography and reactive ion etching.

  In the present embodiment, the core film 12 around the core 12a is removed, and the core 12a is formed so that the cross section is a square having a width of 7.5 μm and a height of 7.5 μm. Thereafter, the first substrate 11A on which the core 12a is formed is annealed in an oxygen atmosphere at a temperature of 1000 ° C. for 8 hours.

  In the groove forming step S3, the grooves 14 corresponding to the cores 12a are formed in the second substrate 13. First, as shown in FIG. 2C, a second substrate 13 made of quartz glass, which is the same material as the first substrate 11, and having a diameter of about 4 inches and a thickness of about 0.5 mm is prepared. . Subsequently, as shown in FIG. 2D, a photomask corresponding to the pattern of the core 12a is formed on the main surface of the second substrate 13, and the core 12a is formed using photolithography and reactive ion etching. A groove 14 corresponding to the pattern is formed. The cross section of the groove 14 is a rectangle having a width of 8.5 μm and a depth of 7.7 μm, and the core 12 a is formed in the groove 14.

  Then, the first substrate 11A on which the core 12a is formed and the second substrate 13A on which the groove 14 is formed are washed with a cleaning liquid containing buffered hydrofluoric acid and dried. Thereafter, the cleaned surfaces of the first substrate 11A and the second substrate 13A are treated with a silane coupling agent, and an adhesive is applied to the surface of the second substrate 13A in which the grooves 14 are formed by a spin coater. . As the adhesive, for example, an epoxy UV adhesive having a viscosity of about 100 cP or less is used.

  Next, in the joining step S4, as shown in FIGS. 2E and 2F, the first substrate 11A and the second substrate 13A are joined with the core 12a and the groove 14 corresponding to each other. First, the first substrate 11A and the second substrate are arranged such that the surface of the first substrate 11A on which the core 12a is formed and the surface of the second substrate 13A on which the groove 14 is formed are spaced apart from each other. 13A is set in the exposure machine. The exposure machine is a contact type exposure machine used in photolithography. The first substrate 11A is set on the photomask holder of the exposure machine, and the second substrate 13A is set on the substrate holder of the exposure machine.

  Then, the pattern of the core 12a and the pattern of the groove 14 are viewed with the eyepiece of the exposure machine, and the first substrate 11A and the second substrate 13A are aligned so that both patterns overlap. When the patterns overlap, the first substrate 11A and the second substrate 13A are brought into close contact with each other, the entire surface of the first and second substrates 11A and 13A is irradiated with UV light to cure the adhesive, and the first substrate 11A and the second substrate 13A are bonded. In this way, the optical waveguide 10A is manufactured.

  In the optical waveguide 10A, the first substrate 11 and the second substrate 13A bonded to each other with an adhesive function as a clad for the core 12a. One surface of the core 12a having a quadrangular cross section is in contact with the first substrate 11, and the other three surfaces of the core 12a are in contact with the three surfaces constituting the groove 14 of the second substrate 13A. That is, the periphery of the core 12a is in contact with the first and second substrates 11 and 13A made of the same material.

  Subsequently, effects of the method for manufacturing an optical waveguide according to the present embodiment will be described. According to the method for manufacturing an optical waveguide of the present embodiment, the first core 11a having a rectangular cross-sectional shape formed on the first substrate 11A and the groove 14 formed on the second substrate 13A are associated with each other. Since the board | substrate 11 and the 2nd board | substrate 13A are joined, an over clad will be comprised with the 2nd board | substrate 13A. Therefore, generation | occurrence | production and deformation | transformation of the void which generate | occur | produce when depositing glass and forming an over clad can be prevented. Therefore, the optical waveguide 10A with improved characteristics with less loss can be manufactured.

  In addition, an optical waveguide produced by forming a core on a substrate and depositing an overclad glass on the substrate and the core as in the prior art has different characteristics between the substrate and the overclad. In other words, the polarization characteristics deteriorate due to the different characteristics of the cladding surrounding the four sides of the core.

  On the other hand, according to the manufacturing method of the optical waveguide according to the present embodiment, the core 12a having the rectangular cross-sectional shape formed on the first substrate 11A and the groove 14 formed on the second substrate 13A are made to correspond to each other. Since the first substrate 11 and the second substrate 13A made of the same material are bonded to each other, the core 12b can be surrounded by the first substrate 11 and the second substrate 13A made of the same material. Therefore, the polarization characteristics of the optical waveguide 10B are improved.

  Conventionally, an apparatus for depositing overclad glass has been required. In particular, when using the HIP method in which deposition is performed in a higher temperature and higher pressure atmosphere in order to reduce voids, a larger apparatus is required.

  On the other hand, in the present embodiment, the first and second substrates 11 and 13A cover the periphery of the core 12a to form a clad, so that a process and an apparatus for depositing glass are unnecessary. In the present embodiment, since the apparatus used for bonding the first substrate 11A and the second substrate 13A is an exposure machine used in photolithography, no new apparatus is required in the bonding step S4.

  Moreover, in order to mount the optical waveguide produced by the conventional method, it is necessary to attach a reinforcing plate to the optical waveguide. On the other hand, in the method for manufacturing an optical waveguide according to the present embodiment, the second substrate 13A constituting the overclad can have a thickness that is a combination of the thickness of the conventional overclad and the thickness corresponding to the reinforcing plate. . Therefore, it is not necessary to attach a reinforcing plate when mounting the optical waveguide. That is, by producing an optical waveguide by the method for producing an optical waveguide according to the present embodiment, the total number of steps when considering the sticking of a reinforcing plate in a device mounting process can be reduced.

  The optical waveguide 10A manufactured by the optical waveguide manufacturing method according to the first embodiment was diced and divided into chips, the end face was polished, an optical fiber array was connected to the end face, and an optical waveguide device was manufactured. . The insertion loss of the straight waveguide having a length of 3.5 cm produced in this manner (the loss combining the loss of the optical fiber connecting portion and the waveguide loss at both ends) was 1 dB.

(Second Embodiment)
The optical waveguide manufacturing method according to the second embodiment includes a core film forming step S1, a core film processing step S2, a groove forming step S3, and a joining step S4, as in the first embodiment. With reference to FIG. 3, each process of the manufacturing method of the optical waveguide which concerns on 2nd Embodiment is demonstrated. FIG. 3 is a cross-sectional view showing a method for manufacturing an optical waveguide according to the second embodiment.

  In the core film forming step S1, the core film 12 is formed on the first substrate 11 which is a quartz glass substrate having a diameter of about 4 inches and a thickness of about 0.5 mm, as in the first embodiment. The core film 12 is a quartz glass film to which Ge is added as a refractive index increasing dopant, and is formed by being deposited to a thickness of about 8.0 μm by using a plasma CVD method (FIG. 3A).

  After the core film forming step S1, a core film processing step S2 is performed. As shown in FIG. 3B, in the core film processing step S2, the core film 12 is processed to form a core 12b and a film 12c having a rectangular cross-sectional shape. A photomask corresponding to the waveguide circuit pattern is formed on the upper surface of the core film 12, and the core 12b along the waveguide circuit pattern is formed using photolithography and reactive ion etching.

  The core 12b is formed, and the periphery of the core 12b is processed while leaving a film 12c thinner than the thickness of the core 12b. The core 12b is processed so that the cross section has a width of 7.5 μm, a height of 7.5 μm, and the film 12c has a thickness of 0.5 μm.

  In the groove forming step S3, as in the first embodiment, the groove 14 corresponding to the core 12b is formed on the second substrate 13 which is a quartz glass substrate having a diameter of about 4 inches and a thickness of about 0.5 mm (see FIG. FIG. 3 (c), (d)). Then, the first substrate 11B on which the core 12b and the film 12c are formed and the second substrate 13A on which the grooves 14 are formed are both washed with a cleaning liquid containing buffered hydrofluoric acid and dried.

  Next, in the bonding step S4, as shown in FIG. 3E, the first substrate 11B and the second substrate 13A are bonded so that the core 12b and the groove 14 correspond to each other. First, the first substrate 11B and the second substrate are arranged such that the surface of the first substrate 11B on which the core 12b is formed and the surface of the second substrate 13A on which the groove 14 is formed are opposed to each other with a gap therebetween. 13A is set in the exposure machine. The exposure machine is a contact type exposure machine used in photolithography. The first substrate 11B is set on the photomask holder of the exposure machine, and the second substrate 13A is set on the substrate holder of the exposure machine.

  Then, the pattern of the core 12b and the pattern of the groove 14 are viewed with the eyepiece of the exposure machine, and the first substrate 11B and the second substrate 13A are aligned so that both patterns overlap. When the patterns overlap, the first substrate 11B and the second substrate 13A are brought into close contact with each other. The upper and lower surfaces of the first and second substrates 11B and 13A that are in close contact with each other are sandwiched between heat resistant plates (for example, SiC plates), and heat treatment is performed in an oxygen atmosphere at 1300 ° C. for 20 hours.

  The quartz glass film 12c and the core 12b to which Ge is added soften at a lower temperature than the first and second substrates 11B and 13A, which are quartz glass substrates. That is, by heating at 1300 ° C. for 20 hours, the film 12c and the core 12b are softened, and the adhesion between the film 12c and the core 12b and the first substrate and the second substrate can be improved. If the Ge-added quartz glass film 12c is made thick, light leaks from the core 12b and causes loss. However, if the layer has a thickness of about 1 μm or less, the effect on the optical characteristics is small.

  In this way, the optical waveguide 10B is manufactured. In the optical waveguide 10B, the first substrate 11 and the second substrate 13A bonded to each other function as a clad for the core 12a. The first substrate 11 and the second substrate 13A are bonded via a film 12c made of the same material as the core 12b. One surface of the core 12b having a quadrangular cross section is in contact with the first substrate 11, and the other three surfaces of the core 12b are in contact with the second substrate 13A. That is, the periphery of the core 12b is in contact with the first and second substrates 11 and 13A made of the same material.

  According to the method for manufacturing an optical waveguide of the second embodiment, the core 12b having a rectangular cross-sectional shape formed on the first substrate 11B and the groove 14 formed on the second substrate 13A are associated with each other. Since the substrate 11 and the second substrate 13A are joined, the overcladding is constituted by the second substrate 13A. Therefore, it is possible to prevent the occurrence of voids or deformation that occurs when glass is deposited to form an overcladding. Therefore, the optical waveguide 10B having improved characteristics with less loss can be manufactured.

  Further, the first substrate 11 and the second substrate made of the same material are made to correspond to the core 12b having a rectangular cross-sectional shape formed on the first substrate 11B and the groove 14 formed on the second substrate 13A. Since 13A is joined, the periphery of the core 12b can be surrounded by the first substrate 11 and the second substrate 13A made of the same material. Therefore, the polarization characteristics of the optical waveguide 10B are improved.

  In addition, the optical waveguide 10B produced by the optical waveguide production method according to the second embodiment was diced and divided into chips, the end face was polished, and an optical fiber array was connected to the end face to produce an optical waveguide device. . The insertion loss of the straight waveguide having a length of 3.5 cm produced in this manner (the loss combining the loss of the optical fiber connecting portion and the waveguide loss at both ends) was 1 dB.

It is a figure which shows the process of the manufacturing method of the optical waveguide which concerns on this embodiment. It is sectional drawing which shows the preparation methods of the optical waveguide which concerns on 1st Embodiment. It is sectional drawing which shows the preparation methods of the optical waveguide which concerns on 2nd Embodiment.

Explanation of symbols

  10A, 10B ... optical waveguide, 11 ... first substrate, 11A ... first substrate, 12a, 12b ... core, 12 ... core film, 13 ... second substrate, 13A ... second substrate, 14 ... groove.

Claims (4)

A core film forming step of forming a core film on the first substrate;
A core film processing step of processing the core film to form a core having a rectangular cross-sectional shape on the first substrate;
A groove forming step of forming a groove corresponding to the core on the second substrate;
A bonding step of bonding the first substrate and the second substrate by causing the core formed on the first substrate and the groove formed on the second substrate to correspond to each other;
A method for producing an optical waveguide, comprising:   The method for manufacturing an optical waveguide according to claim 1, wherein an adhesive is used for joining the first substrate and the second substrate in the joining step.   2. The method of manufacturing an optical waveguide according to claim 1, wherein the first and second substrates are quartz glass substrates, and the core film is quartz glass to which a dopant for increasing a refractive index is added. In the core film processing step, the core film is processed and the core film is processed so as to leave a film thinner than the core thickness on the same plane as the core,
The method for manufacturing an optical waveguide according to claim 3, wherein in the joining step, the first substrate and the second substrate are joined by heating to 1200 ° C. or higher.

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