JP2006065046A - Manufacturing method for optical waveguide device and optical waveguide device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for optical waveguide device with which a ridge type structure is accurately processed. <P>SOLUTION: A thinning process is performed after the ridge type structure is formed by (a) the step in which the ridge type structure forming face 16 is built on a first base body 11 composed of a ferroelectric substance, (b) the step in which a second base body 12 is provided which is fitted on the ridge type structure forming face side of the first base body 11 so that a material having a refractive index smaller than that of the first base body is made contact with the ridge type structure forming face of the first base body 11, and (c) a thinning step face 17 is formed by processing the back face which is opposite to the ridge type structure forming face 16 of the first base body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a ridge-type optical waveguide device using a ferroelectric material, and an optical waveguide device manufactured by the method, and more specifically, a first substrate of a ferroelectric material, The present invention relates to a method for manufacturing a ridge type optical waveguide device using a supporting second substrate to be supported, and a ridge type optical waveguide device. The present invention is used for optical waveguide devices such as an optical switch using an optical waveguide, a wavelength conversion element in which a periodic structure is formed in a ferroelectric, and a second harmonic generation element, for example.

Various optical devices are used in the fields of optical information communication systems, measuring devices such as interferometers, pickup lasers for optical disks, and printing devices.
As one of these optical devices, an optical waveguide device made by forming an optical waveguide in a ferroelectric material is used as an optical switch or a wavelength conversion element. For example, a quasi phase matching element used as a wavelength conversion element forms a periodically poled structure inside a ferroelectric bulk crystal such as LiNbO ₃ or LiTaO ₃ , and further, an optical waveguide so as to cross the periodically poled structure By forming, pseudo phase matching is performed on the light passing through the optical waveguide. The quasi phase matching element can create a phase matching element corresponding to a desired wavelength by adjusting the period of the polarization inversion layer.

  Patent Document 1 is disclosed as a conventional example of a method of forming an optical waveguide on a substrate of a ferroelectric material. According to this document, a proton exchange treatment is performed from the processed surface side of the substrate to form an exchange treatment portion, a ridge structure is formed in a part of the exchange treatment portion, and then the proton exchange treatment portion is heated. An optical waveguide is formed by diffusion treatment.

When an optical waveguide having a ridge structure is made of a ferroelectric material, the refractive index difference between the optical waveguide layer and the surrounding layers is important. That is, if the refractive index difference at the boundary surface between the optical waveguide layer and the surrounding layer is steep, light can be completely confined in the waveguide, but if the refractive index changes slowly at the boundary, Light passing through the waveguide oozes out and attenuates.

In addition, it is desirable that the shape of the light passing through the optical waveguide (guided light mode shape) is as good as possible in the vertical and horizontal symmetry as much as possible in consideration of the application to the device. For this purpose, it is necessary to make the shape of the boundary surface between the optical waveguide layer and the surrounding layer (the boundary surface where the refractive index difference occurs) symmetrical. Ideally, it is desirable that the cross-sectional shape of the optical waveguide layer is circular, such as the core layer and the clad layer of the optical fiber. However, since the optical waveguide formed on the ferroelectric crystal substrate must be manufactured on a flat substrate, it must be manufactured by a process such as pattern etching used in a semiconductor process. It is difficult to make the shape circular.
For this reason, as described in Patent Document 1, a ridge structure in which the cross section of the optical waveguide layer is processed into a mountain shape is usually formed.

  The upper surface and the left and right side surfaces (slopes) of the ridge structure described in Patent Document 1 form an interface between the air layer and the ridge type proton exchange layer, and the refractive index changes stepwise between the layers. Thus, there is little external leakage of light propagating in the optical waveguide.

  On the other hand, when looking at the lower surface of the ridge structure, the upper surface is an air layer-proton exchange layer interface, while the lower surface forms a proton exchange layer-proton non-exchange layer boundary (not a clear boundary). Has been. Therefore, the refractive index difference at the top surface is steep and the refractive index difference is large, whereas the refractive index change is not steep at the lower end surface compared to the upper end surface and the refractive index difference is small, and the shape of the boundary surface in the vertical direction However, the symmetry as an optical waveguide is not good.

Therefore, in order to solve the problem of symmetry, a bonded ridge type optical waveguide has been devised and disclosed (see, for example, Patent Document 2).
In the bonded ridge type optical waveguide device described in Patent Document 2, a periodic polarization reversal structure is formed on a ferroelectric crystal substrate itself, and the substrate is thinned and processed into a ridge type. It is fixed on the top via an adhesive layer.
JP 2003-365680 A JP 2003-107545 A

The above-described conventional bonded ridge type optical waveguide is manufactured by the following procedure.
First, the ferroelectric material in which the optical waveguide is formed is used as the upper substrate (in the case of a quasi phase matching element, a periodic polarization inversion structure is formed on the upper substrate), and the lower substrate serving as a support member is bonded to the upper substrate. Or it joins directly.
Next, the upper substrate is thinned until the thickness of the ridge structure portion is reached. Further, after the thinned upper substrate is polished, a ridge structure is formed by mechanical cutting, laser processing, etching, or the like to form a ridge optical waveguide.

  However, according to the above procedure, when the ridge structure is processed on the thinned upper substrate, the adhesive layer and the lower substrate exist immediately below the thinned upper substrate. It is easily deformed by pressure and heat. Therefore, when pressure and heat are generated when processing the ridge structure, stress is applied to the adhesive layer and the lower substrate, and stress from the adhesive layer and lower substrate is applied to the thinned upper substrate. It was difficult to process with high accuracy.

  Accordingly, the present invention provides a device manufacturing method capable of processing a ridge-type structure with high accuracy in a method for manufacturing a device having a ridge-type optical waveguide, and a ridge having a device structure capable of processing a ridge-type structure with high accuracy. An object of the present invention is to provide a type optical waveguide device.

  The ridge-type optical waveguide device manufacturing method of the present invention made to solve the above-mentioned problems includes (a) a step of processing a ridge-type structure forming surface on a first substrate made of a ferroelectric material, and (b) a first. A step of providing a second substrate to be fixed to the ridge structure forming surface side of the first substrate so that a material having a refractive index smaller than that of the substrate material is in contact with the ridge structure structure forming surface of the first substrate; And a step of thinning the back surface of the substrate opposite to the ridge type structure forming surface to form a thinning surface. The ridge type optical waveguide device of the present invention is manufactured by this manufacturing method.

Here, a ferroelectric material such as LiNbO ₃ , LiTaO ₃ , KNbO ₃ , KTP (KTiOPO ₄ ), LiNb _(1-x) Ta _x O ₃ (where 0 ≦ x ≦ 1) is used for the first substrate. It is preferable. However, the present invention is not limited to these, and other ferroelectric crystals can be applied.
The method for processing the ridge structure on the first substrate is not particularly limited. For example, a processing method such as etching using a mask, machining, laser ablation, or ion milling can be used.

  A member made of a material having a refractive index lower than that of the first base is in contact with the ridge-type structure forming surface. However, the second base itself may be used as the member made of this material. Some intermediate layer may be provided between the base and the second base, and the intermediate layer may be made of a material having a refractive index smaller than that of the first base. That is, when the second substrate has a refractive index smaller than that of the first substrate, the second substrate may be directly fixed to the first substrate. In addition, the first substrate and the first substrate are interposed through some intermediate layer made of a material having a refractive index lower than that of the first substrate (for example, an adhesive layer made of an adhesive or a refractive index adjusting layer formed with a thin film having a desired refractive index). The two substrates may be fixed.

  The method for thinning the first substrate is not particularly limited. For example, grinding or polishing can be used as appropriate.

  According to the ridge type optical waveguide device manufacturing method of the present invention, a ridge type structure forming surface is first formed on a first substrate made of a ferroelectric material, and then directed toward the ridge type structure forming surface side. Then, the second substrate is fixed. However, the light having a refractive index smaller than that of the first base material is in contact with the surface on which the ridge type structure is formed, so that the light traveling from the ridge type structure portion toward the second base side is totally reflected to return to the second base side. Make it difficult to stick out. Then, after the second substrate is fixed, the back surface, which is the back side of the ridge-type structure forming surface, is thinned to form a flat thinned surface. Since the thinning process at this time merely processes a flat surface, the processing is easy, and the thinning process with high accuracy can be performed.

  According to this manufacturing method, when the ridge structure forming surface is formed on the first substrate, the ridge structure can be formed while the first substrate is still thick. It is possible to easily process the ridge type structure with high accuracy without being subjected to this. As a result, an optical waveguide device with good processing accuracy can be provided.

  Further, in the step (b), the second substrate is fixed to the ridge-type structure forming surface of the first substrate through an adhesive layer made of an adhesive having a refractive index lower than that of the first substrate material. For example, the adhesion layer can suppress light seepage, and as a result, the limitation of material selection with respect to the refractive index of the second base material can be eliminated.

  Further, in the step (b), if the second substrate is directly fixed to the ridge-type structure forming surface of the first substrate by using the second substrate material having a refractive index smaller than that of the first substrate material, adhesion is achieved. Since the second substrate can be directly fixed without forming a layer, it is possible to avoid the influence of the adhesive layer over time and thermal deterioration.

  In step (b), a ridge-side refractive index adjustment layer having a refractive index smaller than that of the first substrate material is formed on the ridge-type structure forming surface of the first substrate. If the second substrate is fixed directly or via an adhesive layer, the ridge-side refractive index adjustment layer can suppress the light oozing out from the ridge-type structure portion. It is possible to eliminate restrictions on material selection with respect to the refractive index of the base material or the refractive index of the adhesive layer.

In addition, after the step (c), a step of forming a back side refractive index adjusting layer having a refractive index smaller than that of the first base material so as to cover at least the back side portion of the ridge type structure on the flaky surface. In this case, the back side refractive index adjusting layer can suppress the seepage of light from the back side portion of the ridge structure.
In particular, the symmetry of the refractive index between the ridge-type structure forming surface and the back surface is improved by adjusting the refractive index of the back-side refractive index adjustment layer according to the refractive index of the material in contact with the ridge-type structure forming surface. And an optical waveguide mode with good symmetry can be realized. Furthermore, if both the ridge-side refractive index adjustment layer and the back-side refractive index adjustment layer are provided at the same time and are made of the same material, an optical waveguide mode with better symmetry can be realized.

    If the step (a1) includes the step of forming the periodic polarization inversion structure in the ridge type structure portion after the step (a), the wavelength conversion element is formed by forming the periodic inversion polarization layer in the ridge type structure portion. Thus, a quasi-phase matching optical waveguide device that can be used as the second harmonic element can be manufactured.

  Hereinafter, an optical waveguide device and an optical waveguide manufacturing method of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and can be applied without departing from the spirit of the present invention.

(Example 1)
FIG. 1 is a configuration diagram of an optical waveguide device according to an embodiment of the present invention. The optical waveguide device 10 includes a first substrate 11, a second substrate 12, an adhesive layer 13, and a refractive index adjustment layer 14.

The first substrate 11 is a region where a ridge structure 15 serving as an optical waveguide layer is formed, and is made of a ferroelectric material. As the ferroelectric material, for example, a crystal having a nonlinear crystal optical effect of LiNbO ₃ , LiTaO ₃ , or KNbO ₃ can be used. However, the material is not limited to these, and any ferroelectric material applicable as an optical waveguide device can be used.

  The first substrate 11 has a ridge type structure forming surface 16 on which a ridge type structure 15 is formed, and a thinning treatment surface 17 which is the opposite side surface. As will be described in detail in the description of the device manufacturing process (FIGS. 2 and 3) to be described later, the ridge-type structure forming surface 16 is first processed in a state in which the first substrate 11 has a thickness before the thinning process. .

The second substrate 12 is a member used to support the first substrate 11, has a fastness capable of supporting the first substrate 11, and has adhesiveness to the adhesive layer 13. Any material can be used. Specifically, a glass substrate, a plastic substrate, a metal substrate, a semiconductor substrate, or the like can be used.
The first substrate 11 and the second substrate 12 may be made of the same material. By using the same material, the expansion coefficient with respect to the temperature change becomes equal, the adhesion force to the adhesive layer 13 becomes equal, and it becomes difficult to peel off and the structure is less likely to cause distortion.

  For the adhesive layer 13, an adhesive such as a UV curing agent, an epoxy resin, or an acrylic resin (for example, a refractive index of 1.3 to 1.7) is used. However, as the material of the adhesive layer 13, a material having a refractive index smaller than that of the material of the first base 11 is used, and the light passing through the first base 11 is reflected at the boundary between the first base 11 and the adhesive layer 13. So that it is totally reflected. That is, the adhesive layer 13 adheres the first substrate 11 and the second substrate 12 and can confine light passing through the first substrate 11.

  The refractive index adjusting layer 14 is formed on the thinning-processed surface 17 of the first substrate 11 and has a refractive index close to the upper and lower interfaces across the ridge structure 15 of the first substrate 11, more preferably the same. Thus, the same material as the adhesive layer 12 or a material having an approximate refractive index is used.

  However, the refractive index adjustment layer 14 is not necessarily required if the required specifications for the symmetry of the optical waveguide mode shape (especially the symmetry of the fundamental wave mode shape) are not strict. That is, when the refractive index adjusting layer 14 is not provided and the upper interface is in contact with the air layer (refractive index is 1) as shown in FIG. 4, the adhesive layer 13 (for example, the refractive index is 1.3). There will be some difference in refractive index between the lower interface in contact with ~ 1.7). Therefore, although the optical waveguide mode shape is somewhat deteriorated, it is still in a sufficiently acceptable range depending on the application.

Next, a method for manufacturing this optical waveguide device will be described. FIG. 2 is a flowchart for explaining a manufacturing process of the optical waveguide device 10. FIG. 3 is a schematic view of a device cross section during the manufacturing process.
First, a ridge type structure forming surface is processed on the first substrate 11 (s101).
As shown in FIG. 3A, a first substrate 11 and a second substrate 12 are prepared. For example, LiNbO ₃ is used as these materials. These substrates are cut into a flat plate shape so as to be easily processed.
As shown in FIG. 3B, a metal film (Cr, Ni, etc.) as a mask material 21 is patterned by photolithography on a region having a waveguide width on the surface of the first substrate 11.
As shown in FIG. 3C, the ridge structure 15 is formed by dry etching, for example. The processing method is not limited to dry etching, but may be direct machining, ion milling, laser ablation, wet etching, or the like.
When the ridge structure 15 is formed, the mask material 21 is removed.

In the case of forming a periodically poled structure in order to obtain a quasi-phase matching element, a process for forming a periodically reversed polarization structure is performed on the ridge structure after FIG. 3C.
In the periodically poled structure, electrode patterning is performed on the surface of the ridge structure 15 portion, and a voltage is applied to form a periodically poled layer. Since the method of forming the periodically poled layer on the ferroelectric material is a well-known technique, the description thereof is omitted.

Subsequently, the first substrate 11 is bonded to the second substrate 12 (s102).
As shown in FIG. 3D, the ridge-type structure forming surface 16 of the first substrate 11 is bonded to the second substrate 12 with an adhesive layer 13.

Subsequently, a thinning process is performed on the first substrate 11 (s103).
As shown in FIG. 3E, a rough grinding process, a precision lapping process, and a polishing process are performed in this order on the back surface of the substrate 11 opposite to the ridge-type structure forming surface 16, and the first substrate 11 is formed. Flakes to 2-5 μm. Since the thinning process surface 17 at this time is a simple process in which the flat surface is simply thinned, the influence of stress and the like is small, and a precise process can be performed.

Subsequently, the refractive index adjustment layer 14 is formed (s104).
As shown in FIG. 3 (f), using the adhesive (or a material whose refractive index approximates that of the adhesive) used when forming the adhesive layer 13 so as to cover the surface of the thinning treatment surface 17, The refractive index adjustment layer 14 is formed. The refractive index adjusting layer 14 can also serve as a protective layer for the thinning treatment surface 17 by covering not only the back side portion of the ridge structure 15 but also the entire thinning treatment surface 17.

  As shown in FIG. 1, the optical waveguide device 10 manufactured by the above steps includes an adhesive layer 13 made of the same material or a material having an approximate refractive index, and a refractive index adjustment layer on both the upper and lower surfaces and the left and right surfaces of the ridge structure 15. 14, and a material having a refractive index smaller than that of the ridge structure 15 is used, so that light is sufficiently confined. In addition, the ridge structure 15 is processed with high accuracy and becomes an optical waveguide having a good refractive index symmetry.

  It is more preferable to execute the process up to step s104 to form the refractive index adjustment layer 14. However, as described above, even if the structure shown in FIG. As long as the required specifications for the mode shape are not strict, it can be fully utilized.

  FIG. 5 is a diagram showing the optical waveguide device when a process of forming a periodically inverted polarization structure is performed on the ridge structure 15 after FIG. 3C. A periodically poled structure in which the polarization polarity changes alternately is formed on the surface of the ridge type structure portion, and functions as a quasi phase matching element.

(Example 2)
FIG. 6 is a configuration diagram of an optical waveguide device according to another embodiment of the present invention. In the figure, the same components as those in FIG. 1 and FIG. The optical waveguide device 30 includes a first substrate 11 and a second substrate 31.

  The first substrate 11 is a region where the ridge structure 15 serving as an optical waveguide layer is formed, and a ferroelectric material similar to that described in FIG. 1 is used. The first substrate 11 has a ridge type structure forming surface 16 on which a ridge type structure 15 is formed, and a thinning treatment surface 17 which is the opposite side surface. As will be described in detail later in the description of the device manufacturing process (FIGS. 7 and 8), the ridge-type structure forming surface 16 is first processed in a thick state before the thinning process of the first substrate 11. .

  The second substrate 31 is a member used to support the first substrate 11, has a refractive index smaller than that of the first substrate 11, and has a robustness capable of supporting the first substrate 11. And the material which can adhere to the 1st base | substrate 11 is used. For example, the second substrate 31 can be formed by bringing the polymer material such as plastic or synthetic resin into contact with the first substrate 11 in a molten state and then solidifying and molding. Specifically, a UV curable resin, an epoxy resin, an acrylic resin or the like (a main component material of an adhesive and a refractive index of 1.3 to 1.7) is used as the second substrate 31.

  Furthermore, similarly to the case shown in FIG. 1, a refractive index adjusting layer 14 may be further formed on the upper side of the first substrate 11 to have a structure as shown in FIG. In this case, the refractive index adjusting layer 14 is made of the same material as that of the second substrate or a material whose refractive index is approximate. Thereby, the symmetry of the optical waveguide mode shape can be improved.

Next, a method for manufacturing the optical waveguide device 30 shown in FIGS. 6 and 9 will be described. FIG. 7 is a flowchart for explaining a manufacturing process of the optical waveguide device 30. FIG. 8 is a schematic view of a device cross section during the manufacturing process.
First, the ridge structure forming surface 16 is processed on the first substrate 11 (s201).
As shown to Fig.8 (a), the 1st base | substrate 11 is prepared. For example, LiNbO ₃ is used as the material of the first substrate 11. The base 11 is cut into a flat plate shape so as to be easily processed.
As shown in FIG. 8B, a metal film (Cr, Ni, etc.) as a mask material 21 is patterned on the surface of the first base 11 on the region to be the waveguide width by photolithography.
As shown in FIG. 8C, the ridge structure 15 is formed by dry etching, for example. The processing method is not limited to dry etching, but may be direct machining, ion milling, laser ablation, wet etching, or the like.
After the ridge structure 15 is formed, the mask material 21 is removed.

In order to form a quasi phase matching element, when a periodically poled structure is formed, a process for forming a periodically reversed polarization structure is applied to the ridge structure 15 after FIG. 8C.
In the periodically poled structure, electrode patterning is performed on the surface of the ridge structure 15 portion, and a voltage is applied to form a periodically poled layer.

Subsequently, the surface of the first substrate 11 on which the ridge structure is formed is brought into contact with a molten resin layer (raw material of the second substrate 12) such as a UV curable resin (s202).
Subsequently, the molten resin layer is solidified, and the second substrate is fixed to the ridge-type structure forming surface (s203).
That is, as shown in FIG. 8D, the ridge-type structure forming surface 16 of the first base 11 is directed to the second base 31, and the second base 31 is directly fixed.

Subsequently, a thinning process is performed on the first substrate 11 (s204).
As shown in FIG. 8E, a rough grinding process, a precision lapping process, and a polishing process are performed in this order on the back surface of the substrate 11 opposite to the ridge structure forming surface 16, and the first substrate 11 is formed. Flakes to 2-5 μm. Since the thinning process surface 17 at this time is a simple process in which the flat surface is simply thinned, the influence of stress and the like is small, and a precise process can be performed.

Subsequently, when the structure shown in FIG. 9 is used, the refractive index adjustment layer 14 is formed (s205).
As shown in FIG. 9, when the refractive index adjustment layer 14 is formed, the refractive index is adjusted by using the molten resin used when forming the second base 31 so as to cover the thinned surface 17. Layer 14 is formed. The refractive index adjusting layer 14 can also serve as a protective layer for the thinning treatment surface 17 by covering not only the back side portion of the ridge structure 15 but also the entire thinning treatment surface 17.

  As shown in FIG. 9, the optical waveguide device 30 manufactured by the above steps is covered with the same material (second base 31 and refractive index adjusting layer 14) on both the upper and lower surfaces and the left and right surfaces of the ridge structure 15. In addition, since a material having a refractive index smaller than that of the ridge structure 15 is used, light is sufficiently confined. In addition, the ridge-type structure 15 portion is processed with high accuracy and becomes an optical waveguide with good refractive index symmetry.

  It is more preferable to execute the process up to step s205 to form the refractive index adjustment layer 14. However, as described above, the refractive index adjustment layer 14 is omitted and a refractive index adjustment layer as shown in FIG. Even if the structure is not formed, it can be fully utilized unless the required specification for the optical waveguide mode shape is strict.

  FIG. 10 is a diagram showing the optical waveguide device when a process for forming a periodically inverted polarization structure is performed on the ridge structure 15 after FIG. 8C. A periodically poled structure in which the polarization polarity changes alternately is formed on the surface of the ridge-type structure 15 and functions as a quasi-phase matching element.

(Example 3)
FIG. 11 is a configuration diagram of an optical waveguide device according to another embodiment of the present invention. In the figure, the same components as those in FIGS. 1, 4, 6, and 9 are denoted by the same reference numerals, and description thereof is partially omitted. The optical waveguide device 40 includes a first base 11, a second base 31, a ridge side refractive index adjustment layer 41, and a back side refractive index adjustment layer 42.

  The first substrate 11 is a region where a ridge structure 15 serving as an optical waveguide layer is formed, and a ferroelectric material similar to that shown in FIG. 1 is used. The first substrate 11 has a ridge type structure forming surface 16 on which a ridge type structure 15 is formed, and a thinning treatment surface 17 which is the opposite side surface. As will be described in detail later in the description of the device manufacturing process (FIGS. 12 and 13), the ridge-type structure forming surface 16 is first processed in a state in which the first substrate 11 is thick before the thinning process. .

A ridge-side refractive index adjustment layer 41 made of a material having a refractive index smaller than that of the first substrate 11 is formed on the ridge structure forming surface 16 of the first substrate 11. For the ridge side refractive index adjustment layer 41, for example, a SiO ₂ film (refractive index 1.5), a SiON film, or the like is used. These films can be formed using a film forming method such as sputtering or vapor deposition.

  And the 2nd gas 31 as a support member adheres so that the ridge side refractive index adjustment layer 41 may be contact | connected. The second base 31 is made of a material that can support the first base 11 and can adhere to the ridge-side refractive index adjustment layer 41. However, since the ridge side refractive index adjustment layer 41 is provided, there is no restriction on the refractive index. Also in this case, specifically, as in the case of FIG. 6, a UV curable resin, an epoxy resin, an acrylic resin, or the like (a main component material of the adhesive and a refractive index of 1.3 to 1.7) is used. It can be used as the second substrate 31.

  Furthermore, a back side refractive index adjustment layer 42 may be formed on the upper side of the first substrate 11 to have a structure as shown in FIG. For the back side refractive index adjusting layer 42, it is preferable to use the same material as the ridge side refractive index adjusting layer 41 or a material having an approximate refractive index. Thereby, the symmetry of the optical waveguide mode shape can be improved.

Next, a method for manufacturing the optical waveguide device 40 shown in FIGS. 11 and 14 will be described. FIG. 12 is a flowchart for explaining a manufacturing process of the optical waveguide device 40. FIG. 13 is a schematic view of a device cross section during the manufacturing process.
First, a ridge type structure forming surface is processed on the first substrate 11 (s301).
As shown to Fig.13 (a), the 1st base | substrate 11 is prepared. For example, LiNbO ₃ is used as the material of the first substrate 11. The base 11 is cut into a flat plate shape so as to be easily processed.
As shown in FIG. 13B, a metal film (Cr, Ni, etc.) as a mask material 21 is patterned by photolithography on the region having the waveguide width on the surface of the first substrate 11.
As shown in FIG. 13C, the ridge structure 15 is formed by dry etching, for example. The processing method is not limited to dry etching, but may be direct machining, ion milling, laser ablation, wet etching, or the like.
After the ridge structure 15 is formed, the mask material 21 is removed.

In the case of forming a periodically poled structure in order to obtain a quasi-phase matching element, a process for forming a periodically reversed polarization structure is performed on the ridge structure 15 after FIG. 13C.
In the periodically poled structure, electrode patterning is performed on the surface of the ridge structure 15 portion, and a voltage is applied to form a periodically poled layer.

Subsequently, a ridge side refractive index adjustment layer is formed on the ridge structure forming surface 16 (S302).
As shown in FIG. 13D, a SiO ₂ film is formed as the ridge-side refractive index adjustment layer 41 on the ridge-type structure forming surface 16 by sputtering (other film forming methods may be used).

Subsequently, the ridge-type structure forming surface 16 on which the ridge-side refractive index adjustment layer 41 is laminated is brought into contact with a molten resin layer (raw material of the second base 31) such as a UV curable resin (s303).
Subsequently, the molten resin layer is solidified, and the second substrate is fixed to the ridge type structure forming surface (s304).
That is, as shown in FIG. 13E, the second substrate 31 is fixed to the ridge side refractive index adjustment layer 41 with the ridge structure forming surface 16 of the first substrate 11 facing the second substrate 31.

Subsequently, a thinning process is performed on the first substrate 11 (s305).
As shown in FIG. 13 (f), a rough grinding process, a precision lapping process, and a polishing process are performed in this order on the back surface of the substrate 11 opposite to the ridge structure forming surface 16, and the first substrate 11 is formed. Flakes to 2-5 μm. Since the thinning process surface 17 at this time is a simple process in which the flat surface is simply thinned, the influence of stress and the like is small, and a precise process can be performed.

Subsequently, the back side refractive index adjustment layer 42 is formed (s306).
The back-side refractive index adjustment layer 42 is formed using the same material as the ridge-side refractive index adjustment layer 41 or a material having an approximate refractive index so as to cover the thinned surface 17. To do.
The back side refractive index adjusting layer 42 can be used as a protective layer for the thinning treatment surface 17 by covering not only the back side portion of the ridge structure 15 but also the entire thinning treatment surface 17.

  As shown in FIG. 14, the optical waveguide device 40 manufactured by the above steps is made of the same material (ridge side refractive index adjustment layer 41, back side refractive index adjustment layer 42) on both the upper and lower sides and the left and right sides of the ridge structure 15. In addition, since a material having a refractive index smaller than that of the ridge structure 15 is used, light is sufficiently confined. In addition, the ridge-type structure 15 portion is processed with high accuracy to form an optical waveguide having a good refractive index symmetry.

  It is more preferable to execute the process up to step s306 to form the back side refractive index adjustment layer 42, but as described above, the back side refractive index adjustment layer 42 is omitted and the back side refraction as shown in FIG. Even if the rate adjusting layer is not formed, the structure can be fully utilized unless the required specification for the optical waveguide mode shape is strict.

  Further, after the process shown in FIG. 8C, the case where the process of forming the periodically inverted polarization structure is performed on the ridge-type structure 15 is not shown, but as in the structures shown in FIGS. A periodically poled structure whose polarization polarity changes is formed on the surface of the ridge structure 15 and functions as a quasi-phase matching element.

In the above description, a material obtained by solidifying a molten resin is used for the second base 31, but other materials may be used as long as they can be fixed to the ridge side refractive index adjustment layer 41.
For example, when an SiO ₂ film is used for the ridge side refractive index adjustment layer 41, an SiO ₂ glass substrate having a groove corresponding to the ridge structure portion 15 of the ridge structure forming surface 16 is prepared, and this is formed on the ridge side. It is good also as the 2nd base | substrate 31 by making it contact with the refractive index adjustment layer 41 and joining.
For bonding in this case, hydrofluoric acid bonding in which hydrofluoric acid is applied to the SiO ₂ film as the ridge-side refractive index adjustment layer 41 or bonding is performed on the both surfaces of the optical fiber so that the bonding surfaces on both sides are finished very smoothly. A joining method such as contact can be used.

(Example 4)
FIG. 15 is a configuration diagram of an optical waveguide device according to another embodiment of the present invention. In the figure, the same components as those in FIGS. 1, 4, 6, 9, 11, and 14 are denoted by the same reference numerals, and the description thereof is partially omitted. The optical waveguide device 50 includes a first substrate 11, a second substrate 12, an adhesive layer 13, a ridge side refractive index adjustment layer 41, and a back side refractive index adjustment layer 42.

  The first substrate 11 is a region where the ridge-type structure 15 serving as an optical waveguide layer is formed, and a ferroelectric material similar to that shown in FIG. 1 is used. The first substrate 11 has a ridge-type structure forming surface 16 on which a ridge-type structure 15 is formed, and a thinning treatment surface 17 that is the opposite side surface. As will be described in detail later in the description of the device manufacturing process (FIGS. 16 and 17), the ridge-type structure forming surface 16 is first processed in a state in which the first substrate 11 has a thickness before the thinning process. .

A ridge-side refractive index adjustment layer 41 made of a material having a refractive index smaller than that of the first substrate 11 is formed on the ridge structure forming surface 16 of the first substrate 11. Specifically, a layer made of the same material as that shown in FIG. 11 such as a SiO ₂ film is formed by the same film forming method.

  Then, the second substrate 12 as a support member is fixed by the adhesive layer 13 so as to be in contact with the ridge side refractive index adjustment layer 41. The second substrate 12 is made of a material that is strong enough to support the first substrate 11 and that can adhere to the ridge-side refractive index adjusting layer 14. However, since the ridge side refractive index adjustment layer 41 is provided, there is no restriction on the refractive index. Specifically, as in the case of FIG. 1, a glass substrate, a plastic substrate, a metal substrate, a semiconductor substrate, or a UV curable resin, an epoxy resin, an acrylic resin, or the like is used as in the case of FIG. Can be used as

Further, the back side refractive index adjustment layer 42 is formed on the upper side of the first substrate 11. For the back side refractive index adjusting layer 42, it is preferable to use the same material as the ridge side refractive index adjusting layer 41 or a material having an approximate refractive index. Thereby, the symmetry of the optical waveguide mode shape can be improved.
However, as in the case of the relationship between FIG. 11 and FIG. 14, a structure as shown in FIG. 18 in which the refractive index adjustment layer 42 on the back side is omitted may be used.

Next, a method for manufacturing the optical waveguide device 50 shown in FIGS. 15 and 18 will be described. FIG. 16 is a flowchart for explaining a manufacturing process of the optical waveguide device 50. FIG. 17 is a schematic view of a device cross section during the manufacturing process.
First, a ridge type structure forming surface is processed on the first substrate 11 (s401).
As shown to Fig.17 (a), the 1st base | substrate 11 and the 2nd base | substrate 12 are prepared. For example, LiNbO ₃ is used as the material of the first substrate 11. The base 11 is cut into a flat plate shape so as to be easily processed. For the base 12, for example, a glass substrate is used.
As shown in FIG. 17B, a metal film (Cr, Ni, etc.) as the mask material 21 is patterned by photolithography on the region having the waveguide width on the surface of the first substrate 11.
As shown in FIG. 17C, the ridge structure 15 is formed by dry etching, for example. The processing method is not limited to dry etching, but may be direct machining, ion milling, laser ablation, wet etching, or the like.
After the ridge structure 15 is formed, the mask material 21 is removed.

In the case of forming a periodically poled structure in order to obtain a quasi-phase matching element, a process of forming the periodically poled structure in the ridge structure 15 is performed after FIG.
In the periodically poled structure, electrode patterning is performed on the surface of the ridge structure 15 portion, and a voltage is applied to form a periodically poled layer.

Subsequently, the ridge side refractive index adjustment layer 41 is formed on the ridge structure forming surface 16 (S402).
As shown in FIG. 17D, an SiO ₂ film is formed as the ridge-side refractive index adjustment layer 41 on the ridge-type structure forming surface 16 by sputtering (or other film forming methods may be used).

Subsequently, the second substrate 12 is bonded to the ridge side refractive index adjustment layer 41 (s403).
As shown in FIG. 17 (e), the ridge-type structure forming surface 16 of the first substrate 11 is bonded to the second substrate 12 with the adhesive layer 13.

Subsequently, a thinning process is performed on the first substrate 11 (s404).
As shown in FIG. 17 (f), rough grinding processing, precision lapping processing, and polishing processing are performed in this order on the back surface of the substrate 11 opposite to the ridge structure forming surface 16, and the first substrate 11 is formed. Flakes to 2-5 μm. Since the thinning process surface 17 at this time is a simple process in which the flat surface is simply thinned, the influence of stress and the like is small, and a precise process can be performed.

Subsequently, the back side refractive index adjustment layer 42 is formed (s405).
When the back side refractive index adjustment layer 42 is formed, the back side refractive index adjustment is performed by using the same material as the ridge side refractive index adjustment layer 41 or a material having an approximate refractive index so as to cover the thinned surface 17. Layer 42 is formed.
The back side refractive index adjusting layer 42 can be used as a protective layer for the thinning treatment surface 17 by covering not only the back side portion of the ridge structure 15 but also the entire thinning treatment surface 17.

  As shown in FIG. 15, the optical waveguide device 50 manufactured by the above steps is made of the same material (ridge side refractive index adjustment layer 41, back side refractive index adjustment layer 42) on both the upper and lower sides and the left and right sides of the ridge structure 15. In addition, since a material having a refractive index smaller than that of the ridge structure 15 is used, light is sufficiently confined. In addition, the ridge-type structure 15 portion is processed with high accuracy to form an optical waveguide having a good refractive index symmetry. Furthermore, since there is no restriction | limiting regarding a refractive index about the 2nd base | substrate 12 or an adhesive agent, if it is a robust material which can be adhere | attached on the ridge side refractive index adjustment layer 41 with the adhesive agent 13, various materials will be utilized as a 2nd base | substrate. be able to.

  It is more preferable to execute the process up to step s405 to form the back side refractive index adjusting layer 42, but as described above, the back side refractive index adjusting layer 42 is omitted and the back side refractive index as shown in FIG. Even if the rate adjusting layer is not formed, the structure can be fully utilized unless the required specification for the optical waveguide mode shape is strict.

  In addition, when a process for forming a periodically inverted polarization structure is applied to the ridge-type structure 15 after FIG. 17C, the polarization polarity changes alternately as in the structures shown in FIGS. A periodic polarization reversal structure is formed on the surface of the ridge structure 15 and functions as a quasi phase matching element.

  The present invention can be used for manufacturing an optical waveguide and an optical waveguide device using the same.

The figure which shows the structure of the optical waveguide device which is one Embodiment of this invention. The flowchart explaining the manufacturing process of the optical waveguide device which is one Embodiment of this invention. The schematic diagram explaining the manufacturing process of the optical waveguide which is one Embodiment of this invention. The figure which shows the structure which deform | transformed a part of optical waveguide device which is one Embodiment of this invention. The figure which shows the structure of the optical waveguide device which has a periodic polarization inversion structure which is one Embodiment of this invention. The figure which shows the structure of the optical waveguide device which is other one Embodiment of this invention. The flowchart explaining the manufacturing process of the optical waveguide device which is other one Embodiment of this invention. The schematic diagram explaining the manufacturing process of the optical waveguide which is other one Embodiment of this invention. The figure which shows the structure which deform | transformed a part of optical waveguide device which is other one Embodiment of this invention. The figure which shows the structure of the optical waveguide device which has the periodic polarization inversion structure which is other one Embodiment of this invention. The figure which shows the structure of the optical waveguide device which is other one Embodiment of this invention. The flowchart explaining the manufacturing process of the optical waveguide device which is other one Embodiment of this invention. The schematic diagram explaining the manufacturing process of the optical waveguide which is other one Embodiment of this invention. The figure which shows the structure which deform | transformed a part of optical waveguide device which is other one Embodiment of this invention. The figure which shows the structure of the optical waveguide device which is other one Embodiment of this invention. The flowchart explaining the manufacturing process of the optical waveguide device which is other one Embodiment of this invention. The schematic diagram explaining the manufacturing process of the optical waveguide which is other one Embodiment of this invention. The figure which shows the structure which deform | transformed a part of optical waveguide device which is other one Embodiment of this invention.

Explanation of symbols

10, 20, 30, 40 Optical waveguide device 11 First substrate 12 Second substrate 13 Adhesive layer 14 Refractive index adjusting layer 15 Ridge type structure 16 Ridge type structure forming surface 17 Thinning treatment surface 31 Second substrate (resin)
41 Ridge side refractive index adjustment layer 42 Back side refractive index adjustment layer

Claims (7)

(A) a step of processing a ridge-type structure forming surface on a first substrate made of a ferroelectric material;
(B) a step of providing a second substrate fixed to the ridge type structure forming surface side of the first substrate so that a material having a refractive index smaller than that of the first substrate material is in contact with the ridge type structure forming surface of the first substrate;
(C) A method of manufacturing an optical waveguide device comprising: a step of thinning a back surface of the first substrate opposite to the ridge-type structure forming surface to form a thinning surface. In the step (b), the second substrate is fixed to the ridge-type structure forming surface of the first substrate via an adhesive layer made of an adhesive having a refractive index smaller than that of the first substrate material. The manufacturing method of the optical waveguide device of Claim 1. The step (b) is characterized in that the second substrate is fixed directly to the ridge-type structure forming surface of the first substrate using a second substrate material having a refractive index lower than that of the first substrate material. The manufacturing method of the optical waveguide device as described in any one of Claims 1-3. In the step (b), a ridge-side refractive index adjusting layer having a refractive index smaller than that of the first substrate material is formed on the ridge-type structure forming surface of the first substrate, and further directly on the ridge-side refractive index adjusting layer. The method for manufacturing an optical waveguide device according to claim 1, wherein the second substrate is fixed through an adhesive layer. (C) After the step, (c1) a step of forming a back side refractive index adjusting layer having a refractive index smaller than that of the first base material so as to cover at least the back side portion of the ridge structure on the flaky surface. The method for manufacturing an optical waveguide device according to any one of claims 1 to 4. 6. The method of manufacturing an optical waveguide device according to claim 1, further comprising (a1) a step of forming a periodically poled structure in the ridge structure portion after the step (a). An optical waveguide device formed by the method for manufacturing an optical waveguide device according to claim 1.