JP3689031B2 - Optical waveguide and method for manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a planar optical waveguide in which a core and a clad are provided on a substrate to be used for an optical communication component and the like, and a manufacturing method thereof, and more particularly to an optical waveguide suitable for an optical waveguide having a cover glass bonded on a substrate, and It relates to the manufacturing method.
[0002]
[Prior art]
As optical communication technology expands and spreads, development of optical modules such as optical branching devices and optical multiplexing / demultiplexing devices using planar optical waveguides is in progress.
[0003]
For example, in an optical branching device, a glassy thin film that becomes a core is formed on a wafer by CVD or flame deposition, and then patterned, and further a glassy thin film that becomes a cladding is formed on the core. An optical waveguide is formed.
[0004]
FIG. 10 is a side sectional view of the optical branching device. The substrate having the core and the clad formed on the surface, that is, the optical waveguide 11 is connected to the fiber arrays 12 and 13 which are input / output terminals at the left and right ends in FIG.
[0005]
Here, the thickness of the optical waveguide 11 is usually as thin as about 1 mm, and it is difficult to obtain the adhesive strength with the fiber arrays 12 and 13 as it is. In addition, in order to align the optical path end of the thick fiber core and the optical path end of the thin waveguide core, the optical waveguide 11 is bonded to the fiber arrays 12 and 13 in the thickness direction, so that the time of temperature change In particular, stress is generated or deformed due to the expansion / contraction of the adhesive 14, and PDL (polarization dependent loss) and insertion loss increase. Therefore, conventionally, a cover glass 15 is attached to the upper surface of the optical waveguide 11 with an adhesive 16 to secure an adhesive area with the fiber arrays 12 and 13, maintain adhesive strength, and expand and contract the adhesive when the temperature changes. The deformation / stress of the optical waveguide 11 is prevented.
[0006]
[Problems to be solved by the invention]
However, by attaching the cover glass 15 to the upper surface of the optical waveguide 11 with the adhesive 16, the optical waveguide 11 is stressed by expansion and contraction when the adhesive 16 is cured. At this time, if the optical waveguide 11 (wafer) before bonding the cover glass 15 is flat, the direction and magnitude of the stress generated in the optical waveguide 11 becomes substantially uniform, and a design that allows for this is possible. Since the optical waveguide 11 (wafer) is wavy, the direction and magnitude of the stress generated for each substrate is different, and even in one substrate, stress may be generated in a twisting direction, for example. In particular, PDL tended to deteriorate significantly. The waviness of the optical waveguide 11 (wafer) is often generated by stress generated by the film formation of the core and the clad, and is often generated along with the release of stress during heat treatment for removing the stress.
[0007]
For example, Japanese Patent Application Laid-Open No. 8-29632 discloses a structure in which a part of a core and a clad of an optical waveguide is divided to reduce stress applied to the core, but patterning for dividing the waveguide is extremely performed. Since it becomes complicated, it is not so preferable.
[0008]
The present invention has been devised to solve the above-mentioned problems of the prior art, and increases the adhesive strength of the connecting portion of the optical waveguide and prevents deformation without complicating the structure and process. In addition, an object of the present invention is to provide an optical waveguide capable of easily controlling PDL and a manufacturing method thereof.
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention, in the optical waveguide thereon a cover glass to a substrate formed with the core and cladding in the surface portion is bonded by an adhesive, wherein the substrate, the cover glass is adhered Before being applied, it is made of a material that is curved so as to be deformed in a flat direction as a result of contraction of the adhesive, as viewed from the direction perpendicular to the light input / output direction and along the surface. An optical waveguide is provided. In particular, the substrate is uniformly curved only when viewed from a direction orthogonal to the light input / output direction along the surface before the cover glass is bonded, that is, a tunnel dome or a bowl-like shape. It is preferable that the substrate or the substrate be made of a material that is uniformly curved as viewed from any direction along the surface before the cover glass is bonded, that is, a dome or a cup. Thereby, the direction of the stress applied to the substrate after the cover glass is bonded becomes constant, and the control becomes easy. Since the substrate is cut from a wafer that is curved with a uniform curvature as a whole, the PDL of each substrate becomes uniform without deterioration, and the quality thereof is stabilized.
[0010]
Further, in the present invention, there is provided a method of manufacturing an optical waveguide , which is a substrate having a core and a clad formed on a surface portion , and a cover glass bonded thereto with an adhesive, and has at least one portion forming the optical waveguide. The formed wafer is placed on a curved surface so as to be deformed in a flat direction as a whole as seen from a direction orthogonal to the light input / output direction of the optical waveguide and in a flat direction by shrinkage of the adhesive. There is provided a method of manufacturing an optical waveguide , wherein the cover glass is bonded to the heat-treated wafer . In particular, the wafer is mounted on a surface that is uniformly curved as a whole when viewed from a direction that is along the surface and orthogonal to the light input / output direction of the optical waveguide, that is, a surface that has a bowl shape or a kamaboko shape. Place the wafer on a surface that is uniformly curved as viewed from any direction along its surface, that is, a spherical surface or a cup-shaped surface. Good. As a result, unevenness (undulation) of the wafer is removed and the wafer is uniformly bent, so that the stress generated by subsequent processing can be easily controlled. Further, by bonding a cover glass to the heat-treated wafer and cutting it into the substrate shape, the direction of stress applied to the substrate after the cover glass is bonded becomes constant, and the control becomes easy. In addition, by placing the wafer on a concave or convex surface having a uniform curvature and performing a heat treatment, the curvature of the cut-out substrate becomes even more uniform and the quality thereof is stabilized. Further, the heating / pressurizing process by, for example, a hot isostatic pressing method for removing voids generated in the core and the clad also serves as the heating process of the wafer, thereby simplifying the process.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0012]
FIG. 1 is a perspective view showing an optical branching device as an optical waveguide to which the present invention is applied and an optical fiber array connected to the optical branching device, and FIG. 2 is a sectional side view taken along line II-II. The core 1a and the clad layer 1b are formed on the surface, and the patterned substrate, that is, the optical waveguide 1, has a cover glass 5 adhered to the surface thereof with an adhesive 6, and input and output terminals at both left and right ends in FIG. The fiber arrays 2 and 3 are bonded and connected by an adhesive 4.
[0013]
Here, as schematically shown in FIG. 3, the optical waveguide 1 is curved in a concave spherical shape with a uniform curvature with the side on which the core and the clad are formed before the cover glass 5 is bonded (FIG. 3). On the left). This is deformed in a flattening direction due to the shrinkage of the adhesive 6 (right side in FIG. 3). The amount of deformation is about 5 m to 20 m in the radius of curvature of the optical waveguide 1 before the cover glass 5 is bonded to the optical waveguide 1 having a width and length of several centimeters. By setting in consideration only the amount after the deformation of the waveguide 1, it is a range that hardly causes a problem. In practice, the cover glass 5 is also deformed to some extent according to its thickness. Moreover, although stress due to the shrinkage of the adhesive 6 is also generated, the direction and size thereof are constant, so that the PDL of the optical waveguide 1 is not deteriorated and is constant, and the quality is stable.
[0014]
On the other hand, as shown on the left side of FIG. 4, when the optical waveguide has an uneven shape before bonding the cover glass, the right side of FIG. 4 is caused by the shrinkage of the adhesive by bonding the cover glass. As shown in FIG. 5, not only the direction of deformation is irregular, but also the direction and magnitude of the generated stress varies depending on the location, for example, twisting stress is also generated, and as a result, the PDL varies greatly for each optical waveguide. , Its quality deteriorates.
[0015]
Below, the manufacturing procedure of the said optical branching device is demonstrated. First, a core layer mainly composed of SiO ₂ is formed on a glass wafer A made of quartz or the like by, for example, a plasma CVD method. At this time, one or more kinds of dopes selected from phosphorus, titanium, germanium, aluminum, boron, fluorine and the like so that the refractive index is higher by about 0.2% to 0.8% than that of the glass wafer A. Agent is added to the core layer. Since the refractive index of the core 1a is desirably equal to the refractive index of the optical fiber core, the refractive index may be adjusted by appropriately selecting a dopant. In addition to plasma CVD, film formation is performed using a so-called low-temperature film formation apparatus capable of forming a film at about 500 ° C. or lower, such as atmospheric pressure CVD, PVD, vacuum deposition, sputtering, ion plating, etc. Good. This is heat-treated at a temperature higher than the deposition temperature and lower than the melting point, a predetermined waveguide pattern is formed on the surface of the core 1a with a photoresist, and etching such as RIE is performed, whereby the core 1a having a predetermined pattern is formed. Form. Thereafter, a low-refractive-index upper cladding layer 1b containing SiO ₂ as a main component is formed by the same low-temperature film formation method as described above.
[0016]
Next, in a state where the upper clad layer 1b is exposed, by heating and pressurizing from the surroundings by a hot isostatic pressing method (hereinafter referred to as HIP method), the void is reduced to a practically no problem level, Alternatively, it is eliminated, and the film-forming stress generated in each film-forming layer is removed. Therefore, the HIP method is desirably maintained for about 2 hours in the range of 1000 ° C. to 1200 ° C. and 1000 kgf / cm ^{2 to} 1700 kgf / cm ² .
[0017]
Here, when performing the heating and pressurizing treatment by the HIP method, the glass wafer A is placed on the concave spherical seat B having a curvature radius of 5 m to 20 m as shown in FIG. By doing so, the heated and softened glass wafer A becomes a shape curved substantially along the surface shape of the concave spherical seat B. Thereby, the unevenness | corrugation (undulation) as shown in FIG. 6 of the said glass wafer A is extended, and it is removed with the said void and residual stress. Further, even if the irregularities (swells) of the glass wafer A are left slightly, the glass wafer A is curved in the same direction, so the direction of stress due to the shrinkage of the adhesive that occurs later is constant, and the control is easy. Become. Depending on the processing temperature, the weight and thickness of the glass wafer A, the radius of curvature is larger than the radius of curvature of the concave spherical seat B.
[0018]
On the other hand, when performing the above heating and pressure treatment, if a flat seating surface is used, the unevenness (swells) will not grow and there will be no escape and voids and residual stress will be removed, but the unevenness (swells) will remain. The direction of stress due to the contraction of the agent is not constant and cannot be controlled. Moreover, even if the removal of voids is not required and the HIP treatment is not performed, heat treatment may be performed for the purpose of stabilizing the refractive index and removing residual stress. At this time, even if there is no unevenness (undulation) on the wafer before the heat treatment, residual stress at the time of film formation occurs in the formed film, so that the unevenness (undulation) is extended when a flat seat surface is used as described above. As a result, there are no reliefs and undulations remain.
[0019]
If the radius of curvature of the concave spherical seat B is 20 m or more, there is no difference from the case where it is placed on the flat seat and processed, and if it is less than 5 m, the adhesive layer becomes thick and undergoes significant curing shrinkage. , PDL increases. In addition, connection position alignment with the input / output connection terminals becomes troublesome, and there is a risk of increasing insertion loss.
[0020]
Next, several tens to several hundreds of optical waveguides 1 patterned on the glass wafer A are cut out by a dicing apparatus (not shown). The size to be cut out is not an individual waveguide chip but a strip C of 5 to 10 chips (FIG. 7).
[0021]
Next, a cover glass is affixed on the surface of the strip C with an adhesive 6 made of, for example, an ultraviolet curable resin. This cover glass preferably has the same thermal expansion characteristics as the strip C, that is, the substrate of the optical waveguide 1. For example, the same material as the substrate of the optical waveguide 1 may be used. The thickness is preferably about the same as or greater than that of the optical waveguide 1 in view of the reinforcing effect. However, if the cover glass side of the optical waveguide 1 is set to be greatly deformed by the shrinkage of the adhesive, the deformation amount of the optical waveguide 1 is increased. Can be reduced, and the design becomes easy. And it cuts out to the chip | tip of each optical waveguide 1, optically polishes an end surface of a core, the fiber arrays 2 and 3 are adhere | attached with the adhesive agent 4, and an optical branching device is completed.
[0022]
FIG. 8 shows the relationship between the amount of warpage of the optical waveguide chip and the PDL, heat-treated using the concave spherical seat B, cut out from the curved glass wafer, and heat treated using the flat seat and the optical waveguide bonded with the cover glass described later. The graph compared with the optical waveguide which cut out from the done glass wafer and adhere | attached the cover glass is shown. An optical waveguide that has been heat-treated using a concave spherical seat B, cut out from a curved glass wafer, and bonded with a cover glass has a PDL of significantly less than 0.1 dB regardless of the amount of warpage of the optical waveguide chip. I understand. Here, the amount of warpage of the optical waveguide chip is the maximum distance between the front surface and the back surface of the optical waveguide chip.
[0023]
In the above embodiment, the glass wafer is heat-treated using the concave spherical seat B. However, the glass wafer may be heat-treated using a convex spherical seat B ′ as shown in FIG. A concave or convex aspherical seat may be used so as to be uniformly curved in consideration of the softening characteristics of the lens.
[0024]
Further, a bowl-like shape which is curved along the surface of the waveguide as shown in FIG. 9 (b) and which is uniformly concavely curved as viewed from the direction (side surface direction) orthogonal to the light input / output direction of the waveguide. The glass wafer may be heat-treated using a seat B ″ or a semi-cylindrical seat B ′ ″ that is curved uniformly and convex as viewed from the side as shown in FIG. 9C. In that case, since most of the stress generated by the shrinkage of the adhesive that bonds the cover glass is applied to the light input / output direction x, it does not affect the TE wave (z) and TM wave (y) orthogonal to the direction x, The PDL expressed as the difference in power does not change and becomes constant.
[0025]
Moreover, in the said embodiment, although the glass wafer was curved at the time of the heating and pressurizing process by HIP method, you may separately heat-process, for example about 500 to 1200 degreeC using a concave spherical seat or a convex spherical seat. .
[0026]
Further, in the above embodiment, the ultraviolet curable resin is used as the adhesive for attaching the cover glass to the surface of the optical waveguide 1, but a thermosetting adhesive or the like may be used instead.
[0027]
In addition, in the said embodiment, although the glass wafer was cut out in strip shape and the cover glass was affixed, you may affix a cover glass with a glass wafer.
[0028]
【The invention's effect】
As apparent from the above description, according to the optical waveguide according to the present invention, the substrate of the optical waveguide in which the core and the clad are provided on the substrate and the cover glass is bonded to the substrate before the cover glass is bonded. The direction of the stress applied to the substrate after the cover glass is bonded to the substrate by being curved in a concave or convex shape as a whole along the surface and perpendicular to the light input / output direction. Becomes constant, and its control becomes easy. In particular, the substrate is generally uniformly curved only when viewed from a direction perpendicular to the light input / output direction along the surface before the cover glass is bonded, i.e., a tunnel dome or a bowl-shaped one. The substrate is preferably made of a substrate that is uniformly curved as viewed from any direction along its surface before the cover glass is bonded, that is, a dome or a cup. Further, since the substrate is cut from a wafer that is curved with a uniform curvature as a whole, the PDL of each substrate becomes uniform without deterioration, and the quality thereof is stabilized.
[0029]
Further, according to the method of manufacturing an optical waveguide according to the present invention, the wafer on which one or more portions forming the optical waveguide are formed is uniform as a whole when viewed from a direction orthogonal to the light input / output direction of the optical waveguide. When the wafer is placed on a concave or convex surface that is curved and heat-treated, the irregularities (waviness) of the wafer is removed and the wafer is uniformly curved, so that the stress generated by subsequent processing can be easily controlled. In particular, the wafer is placed on a surface that is uniformly curved when viewed from a direction that is along the surface and perpendicular to the light input / output direction of the optical waveguide, that is, a bowl-shaped or kamaboko-shaped surface. The wafer may be heat-treated, or the wafer may be placed on a surface that is uniformly curved as viewed from any direction along the surface, that is, placed on a spherical surface or a cup-shaped surface. Further, by bonding the cover glass after the heat treatment, the direction of the stress applied to the substrate after the cover glass is bonded becomes constant, and the control becomes easy. In addition, by placing the wafer on a concave or convex surface with a uniform curvature and heat-treating it, the curvature of the cut out substrate becomes even more uniform, and stress that deteriorates PDL is not applied. Is stable.
[0030]
In addition, the process is simplified by serving also as the heat treatment of the wafer by heating / pressurizing treatment by, for example, hot isostatic pressing for removing voids generated in the core and clad of the optical waveguide.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an optical branching device as an optical waveguide to which the present invention is applied and an optical fiber array connected to the optical branching device.
2 is a side sectional view taken along line II-II in FIG.
FIG. 3 is a schematic side view of an optical waveguide according to the present invention.
FIG. 4 is a schematic side view of a conventional optical waveguide.
FIG. 5 is a view showing a state in which a glass wafer A is placed on a concave spherical seat B;
FIG. 6 is a diagram schematically showing how the irregularities (swells) of glass wafer A are stretched by heat treatment.
FIG. 7 is a perspective view showing a state in which a glass wafer A is cut into strips.
FIG. 8 is a graph showing the relationship between the amount of warpage of an optical waveguide chip and PDL.
FIGS. 9A to 9C are perspective views showing a heat treatment seat for a glass wafer for explaining another embodiment of the present invention. FIGS.
FIG. 10 is a side sectional view showing a conventional optical branching device and an optical fiber array connected thereto.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical waveguide 1a Core 1b Clad layer 2, 3 Fiber array 4 Adhesive 5 Cover glass 6 Adhesive 11 Optical waveguide 12, 13 Fiber array 14 Adhesive 15 Cover glass 16 Adhesive A Glass wafer B Concave spherical seat B 'Convex spherical surface Seat B ″ Sagittarius B ″ ″ Kamaboko Seat C Strip

Claims (15)

In the optical waveguide in which the core and the clad are formed on the surface portion , and the cover glass is adhered thereon with an adhesive,
The substrate is deformed in a flat direction along the surface of the substrate before the cover glass is bonded, and as a whole when viewed from a direction orthogonal to the light input / output direction, and in a flat direction due to the shrinkage of the adhesive. optical waveguide, characterized in that it consists of those curved.     2. The substrate according to claim 1, wherein the substrate is uniformly curved as a whole along the surface of the cover glass before being bonded and when viewed from a direction orthogonal to the light input / output direction. The optical waveguide according to 1.     2. The optical waveguide according to claim 1, wherein the substrate is made of a material that is uniformly curved as viewed from any direction along the surface of the substrate before the cover glass is bonded. 3.     4. The optical waveguide according to claim 1, wherein the curvature of curvature of the substrate is uniform throughout.     5. The optical waveguide according to claim 1, wherein the substrate is curved so that a side on which the core and the clad are provided is concave.     The optical waveguide according to any one of claims 1 to 4, wherein the substrate is curved so that a side on which the core and the clad are provided is convex.     The optical waveguide according to claim 1, wherein an optical fiber array is connected to an optical input / output end of the substrate by bonding. A substrate having a core and a clad formed on a surface portion , and a manufacturing method of an optical waveguide having a cover glass bonded thereon with an adhesive ,
The wafer on which one or more portions forming the optical waveguide are formed is deformed in a uniform manner as viewed from the direction orthogonal to the light input / output direction of the optical waveguide, and in a flat direction due to the shrinkage of the adhesive. A method of manufacturing an optical waveguide , comprising: placing on a curved surface, heat-treating , and bonding the cover glass to the heat-treated wafer .     The wafer is heat-treated by being placed on a surface that is uniformly curved as a whole only when viewed from a direction perpendicular to the light input / output direction of the optical waveguide along the surface thereof. The manufacturing method of the optical waveguide of Claim 8.     9. The method of manufacturing an optical waveguide according to claim 8, wherein the wafer is placed on a surface that is uniformly curved as viewed from any direction along the surface thereof and heat-treated.     The wafer is placed on a concave or convex spherical surface that is curved with a uniform curvature only when viewed from a direction that is along the surface and perpendicular to the light input / output direction of the optical waveguide. 10. The method for manufacturing an optical waveguide according to claim 8, wherein the optical waveguide is manufactured.     11. The heat treatment is performed by placing the wafer on a concave or convex spherical surface that is curved with a uniform curvature when viewed from any direction along the surface thereof. Manufacturing method of the optical waveguide. 13. The method of manufacturing an optical waveguide according to claim 8 , wherein an optical fiber array is bonded to the light input / output end after the wafer is cut out from the wafer . Heating and pressing treatment to remove voids generated in the core and cladding, a method of manufacturing an optical waveguide according to any one of claims 8 to 13, characterized in that also serves as a heat treatment of the wafer . Heat treatment of the wafer, method for manufacturing an optical waveguide according to any one of claims 8 to 14, characterized in that by hot isostatic pressing process (HIP process).

Images