JP2000089184A - Structure for fixing optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new structure for fixing an optical waveguide element to reduce optical loss during an operation for the optical waveguide device using an optical waveguide element which is relatively small in the thickness of at least a portion where electrodes are formed and enables high speed modulation. SOLUTION: An optical waveguide element 10 is provided with a substrate 1 which is provided with a pair of main surfaces that are opposed to each other and has an electrooptical effect, an optical waveguide 2 which is formed on one of main surfaces 1A of the substrate 1, electrodes 3 which apply modulation signals to light waves that propagate in the waveguide 2, and a thin thickness portion 5 which is formed at least at the position where the electrodes 3 are located on the substrate 1 and has a relatively thin thickness. The element 10 is fixed to a plate shaped member 12 by first fixing adhesive 13. The member 12 is fixed to a base 11 by second fixing adhesive 15 so that the member 12 is placed between the element 10 and a casing 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device fixing structure, and more particularly to an optical waveguide device fixing structure that can be suitably used as a traveling wave type optical waveguide device capable of high-speed modulation.

[0002]

2. Description of the Related Art In recent years, optical waveguide devices have been used as external modulators with the progress of high-speed, large-capacity optical fiber communication systems. Since such an external modulator is used under the condition of a high-speed switch, a high-speed modulation characteristic is required for an optical waveguide device used for the above-mentioned external modulator. For this reason, the shape of the modulation signal application electrode of the optical waveguide device constituting the optical waveguide device is made to have a special shape, or a buffer layer such as silicon dioxide is formed between the electrode and the substrate constituting the optical waveguide device. Or attempts were made to do so.

However, the applicant of the present application has disclosed in Japanese Patent Application No. 9-85579 because of the high cost associated with the complexity of the electrode manufacturing process and the deterioration of the electrode alignment accuracy when the buffer layer is formed. An optical waveguide device capable of high-speed modulation without the above-described problem has been invented by relatively reducing the thickness of at least the portion of the substrate constituting the optical waveguide device where the electrodes are formed. Based on the above, an application has been filed for this optical waveguide element.

[0004]

However, when such an optical waveguide device is fixedly mounted on a pedestal or a housing and used as an optical waveguide device as described above,
Compared to a case where a conventional optical waveguide element having no relatively small thickness is provided and used as an optical waveguide device, light loss during operation is significantly increased and sufficient signal strength cannot be obtained. There was a problem.

The present invention relates to an optical waveguide device using an optical waveguide element capable of high-speed modulation by reducing the thickness of at least a portion where an electrode is formed.
An object of the present invention is to provide a new optical waveguide element fixing structure for reducing optical loss during operation.

[0006]

SUMMARY OF THE INVENTION The present invention provides a substrate having a pair of opposing main surfaces and having an electro-optic effect, an optical waveguide formed on one main surface of the substrate, and an optical waveguide formed on one of the main surfaces. An optical waveguide device having an electrode for applying a modulation signal to a guided light wave and a thin portion having a relatively small thickness formed at least in a portion where the electrode is located on the substrate is fixed to a pedestal. A fixing structure of the optical waveguide element for mounting the optical waveguide element, wherein the optical waveguide element is bonded and fixed to a predetermined member, and the predetermined member is bonded and fixed to the pedestal; A fixing structure of an optical waveguide element, wherein a waveguide element is fixed to the base with the predetermined member interposed therebetween.

The present inventor has found that an optical waveguide element which enables high-speed modulation and has at least a relatively thin portion at which an electrode is formed is fixed to a pedestal and causes a light loss. As a result of repeated research to find out, we found the following facts.

That is, when an optical waveguide device is mounted on an optical waveguide device, and this optical waveguide device is used, for example, as an optical modulator, the ambient temperature of the device during operation is about -40 to 80 ° C. Vary between.
Then, a thermal stress is generated between the optical waveguide element and the pedestal due to the thermal shrinkage accompanying the change in the environmental temperature, and the optical waveguide element receives the thermal stress from the pedestal. In general, when the optical waveguide element is formed of a uniform plate-shaped substrate, the thermal stress tends to be uniformly dispersed in the substrate, but a thin portion is formed on the substrate as described above. In the optical waveguide element, stress tends to concentrate on a thin portion of the substrate. Therefore, the refractive index of the substrate in the vicinity of the thin portion changes, which affects the light wave guided through the optical waveguide, and increases the light loss. The present invention has been made based on the above findings of the inventors.

FIG. 1 is a perspective view showing an example of an optical waveguide element used in the fixing structure of the optical waveguide element of the present invention. FIGS. 2 and 3 show the optical waveguide element shown in FIG. 1 fixed to a pedestal. FIG. 2 is a partial cross-sectional view showing an example of a fixing structure of the optical waveguide element of the present invention. 2 and 3 show a cross section taken along line II of FIG. 1 when viewed in the direction of the arrow.

In an optical waveguide device 10 shown in FIG. 1, a Mach-Zehnder optical waveguide 2 is applied to a main surface 1A of a substrate 1 having an electro-optic effect, and a modulation signal is applied to a light wave guided through the optical waveguide 2. Electrodes 3 are formed. Further, the main surface 1 of the substrate 1 on which the optical waveguide 2 and the electrode 3 are formed
A concave portion 4 is formed in a portion of the main surface 1B opposite to the portion A where the electrode 3 is located, thereby forming a thin portion 5 of the substrate 1 as shown in FIG.

In the fixing structure of the optical waveguide device shown in FIGS. 2 and 3, the main surface 1B of the substrate 1 constituting the optical waveguide device 10 shown in FIG. 1 is covered with a plate-shaped member 12 and a first fixing adhesive 13. The plate-like member 12 is fixed to the pedestal 11 and the second
And a plate-like member 12 is interposed between the pedestal 11 and the optical waveguide element 10.

As described above, by fixing the optical waveguide element 10 to the pedestal 11 via the plate-shaped member 12, the stress from the pedestal 11 generated in the optical waveguide element 10 due to the environmental temperature change during the operation described above is reduced. The stress is relaxed by the member 12 and the stress is not concentrated on the thin portion of the substrate as described above. Therefore, when an optical waveguide device is formed from such an optical waveguide element, an increase in optical loss can be prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a fixing structure of an optical waveguide device according to the present invention will be described in detail based on an embodiment of the present invention with reference to the drawings. FIG. 2 is a view showing an example of the fixing structure of the optical waveguide element of the present invention as described above. FIG.
Then, the concave portion 4 forming the thin portion 5 formed on the main surface 1B side of the substrate 1 of the optical waveguide element 10 is filled with the filling adhesive 14.
And the first fixing adhesive 13 is applied to the main surface 12A of the plate-shaped member 12 and the main surface 1B of the substrate 1, and the plate-shaped member 12 and the optical waveguide element 10 are fixed. I have. As described above, the inside of the concave portion 4 is filled with the filling adhesive 14, that is, the adhesive is applied so as to fill the gap between the thin portion 5 of the optical waveguide element 10 and the plate-shaped member 12, thereby forming the thin portion 5. The stress concentration from the pedestal 11 can be further reduced, and the object of the present invention can be better achieved.

FIG. 3 is a partial sectional view showing another example of the fixing structure of the optical waveguide element of the present invention. In FIG. 3, the first fixing adhesive 13 is applied to the main surface 12A of the plate-like member 12 and the main surface 1B of the substrate 1 without filling the filling adhesive 14 in the concave portion 4. Member 12 and optical waveguide element 10
And fixed. That is, an adhesive is applied so that no adhesive is present between the thin portion 5 of the optical waveguide element 10 and the plate-shaped member 12, and the optical waveguide element 10 and the plate-shaped member 12 are bonded and fixed. I have. When the fixing structure shown in FIG. 3 is adopted, high-speed modulation is possible due to the presence of the air layer in the concave portion 4, and the thermal stress generated in the adhesive itself is reduced, as described above. Stress concentration on the thin portion 5 can be further reduced, and the object of the present invention can be achieved more effectively.

In the fixing structure of the optical waveguide element shown in FIGS. 2 and 3, a plate-like member 12 is interposed between the optical waveguide element 10 and the pedestal 11, but is interposed between the optical waveguide element and the pedestal. The member to be formed does not necessarily have to be plate-shaped, and any member can be used as long as the object of the present invention can be achieved, depending on the form used as the optical waveguide device.

However, the member interposed between the optical waveguide element and the pedestal is preferably plate-shaped for reasons of symmetry and workability. When such a plate-shaped member 12 is used, the present invention is applied. In order to better achieve the object, the thickness t is preferably 0.2 to 2 mm.

The material used for the plate-shaped member 12 is not particularly limited as long as the object of the present invention can be achieved, but the heat generated between the plate-shaped member 12 and the optical waveguide element 10 is not limited. From the viewpoint of reducing the stress and improving the effect of relaxing the thermal stress from the pedestal 11, it is preferable to form the optical waveguide element 10 from the same material as the substrate 1.

Since the material that can be used as the substrate 1 needs to have an electro-optical effect, specific examples of the material that can be used as the plate-like member 12 include lithium niobate, potassium lithium niobate, and lithium tantalate. ,
Examples include KTP, glass, silicon, GaAs, and quartz.

First and second fixing adhesives 13 and 15
Examples include epoxy-based adhesives and UV-curable adhesives, as well as Alon ceramics C having a coefficient of thermal expansion relatively close to materials having an electro-optical effect such as lithium niobate.
(Product name, manufactured by Toa Gosei Co., Ltd.) (Coefficient of thermal expansion 13 × 10 ^-6 )
For example, a known adhesive can be used. In addition, the first fixing adhesive 13 and the second fixing adhesive 15
They may be the same or different.

As the filling adhesive 14, the same adhesive as the first and second fixing adhesives 13 and 15 or a polyimide having a low dielectric constant can be used. In actual use, the same type of adhesive as the first and second fixing adhesives 13 is preferable, but a different resin such as polyimide may be used.

The coating thickness of the first fixing adhesive 13 is preferably 2 to 10 μm on the main surface 1B of the substrate 1 and the main surface 12A of the plate-shaped member 12, and the second fixing adhesive is preferably used. The coating thickness of 15 is preferably 20 to 100 μm on the main surface 11A of the pedestal 11 and the plate-shaped member 12B.

The fixing structure of the optical waveguide device of the present invention shown in FIGS. 2 and 3 is, as described in Japanese Patent Application No. 9-85579, applied to a substrate 1 having a predetermined size by a Ti diffusion method or the like. Thus, the optical waveguide 2 is formed, and the electrode 3 made of Au or the like is formed by using both the vapor deposition and plating methods. Next, after a resist is applied to the electrode 3 portion of the substrate 1, the substrate 1 is fixed to a surface plate with an adhesive or the like, and a recess 4 is formed on the main surface 1B side of the substrate 1 by machining or laser ablation. After polishing the end surface of the substrate 1, the substrate 1 is cut into chips by dicing or the like to obtain an optical waveguide device 10 as shown in FIG.

The machining can be performed by a method such as dicing or micro grinding. In the case where the recess 4 is formed by laser ablation, ArF having a high intensity per unit area of the oscillation laser is used.
And an excimer laser such as KrF.

Next, in order to obtain the fixing structure shown in FIG. 3, a first fixing adhesive 13 is applied to a portion of the main surface 1B of the substrate 1 to be bonded, and this is applied to the main member 1 of the plate-like member 12. It is fixed by bonding to the surface 12A. On the other hand, when obtaining the fixing structure shown in FIG. 2, the filling adhesive 14 is filled in the concave portion 4 of the substrate 1, the first fixing adhesive 13 is applied to the main surface 1B of the substrate 1, and It is bonded and fixed to the main surface A of the plate-shaped member 12.

When manufacturing the fixing structure shown in FIGS. 2 and 3, from the viewpoint of working efficiency, the substrate 1 and the plate-like member 12 are bonded as described above, and the end face of the assembly is polished. Alternatively, the optical waveguide element 10 can be formed by cutting the chip.

Next, a second fixing adhesive 15 is applied to the main surface 12B of the plate-shaped member 12 and the main surface 11A of the pedestal 11, and the two are adhered to each other, thereby fixing the optical waveguide element shown in FIGS. Get the structure.

[0027]

The present invention will be described below in detail with reference to examples. Example 1 An x-cut plate of lithium niobate having a thickness of 1 mm was used as a substrate 1, an optical waveguide 2 was formed on the main surface 1A side of the substrate 1 by a Ti diffusion method, and a vapor deposition method and a plating method were used in combination. Thus, an electrode 3 made of Au having a thickness of 10 μm was formed. Next, after applying a resist on the surface of the electrode 3, using a whetstone (grinding stone) having a width of 0.2 mm and a # 400, the number of rotations is 30,000 rpm, and the feeding speed is 120 mm / m.
polished several times under the condition of “in”, and further, 0.1 mm in width, # 1
Polishing was performed in the same manner using 000 (grinding stone) to form a concave portion 4 having a depth d of 0.8 mm and a width w of 0.2 mm.

Next, Aron Ceramics C (trade name, manufactured by Toa Gosei Co., Ltd.) was used as the first fixing adhesive 13 and the filling adhesive 14, and was filled in the recess 4. A 1 μm thick plate-like member 12 made of lithium niobate is applied to the surface 1B to a thickness of 10 μm.
Then, the first fixing adhesive 13 and the filling adhesive 14 were cured by being left at room temperature for 24 hours to fix the substrate 1 and the plate-shaped member 12. Next, after polishing the end face of the assembly formed in this way, the chip is cut into 2 × 10 chips by dicing,
Next, the chip was washed to obtain an optical waveguide device 10.

Next, an epoxy-based adhesive is used as the second fixing adhesive 15, and the epoxy-based adhesive is used as the second fixing adhesive 15.
2B and a thickness of 30 μm on the main surface 11A of the base 11,
These were adhered and fixed to obtain an optical waveguide element fixing structure shown in FIG. Next, using a UV-curable resin, an optical fiber (not shown) is optically aligned with and coupled to the optical waveguide 2 of the optical waveguide element 10, and after a temperature cycle test at -40 to 80 ° C is performed 1,300 times. Was examined for light loss. As a result, the light loss of the fixed structure in this embodiment is 0.2 d.
B was found.

Example 2 As shown in Example 1, a fixing structure shown in FIG. 3 was produced in the same manner as in Example 1 except that the recessed portion 4 was not filled with the filling adhesive 14. When the light loss of this fixed structure was examined in the same manner as in Example 1, it was found to be 0.3 dB.

COMPARATIVE EXAMPLE In the above embodiment, the plate-like member 12 was replaced with the optical waveguide element 1.
0 and the main surface 11A of the base 11 without being interposed between the base 11 and the base 11
Was carried out in the same manner as in the above example, except that the epoxy adhesive was applied to a thickness of 30 μm. When the light loss of this fixed structure was examined in the same manner as in the above embodiment,
It turned out to be 5 dB.

As apparent from Examples 1 to 4 and Comparative Example, according to the fixing structure of the optical waveguide device of the present invention,
It can be seen that an increase in optical loss can be prevented even when an optical waveguide device having a thin portion formed to enable high-speed modulation is mounted and used as an actual optical waveguide device.

As described above, the present invention has been described in detail with reference to specific examples in the embodiments of the present invention. However, various modifications and changes can be made without departing from the scope of the present invention.

[0034]

As described above, according to the structure for fixing an optical waveguide element of the present invention, an optical waveguide element capable of high-speed modulation in which a thin portion is formed at least in a portion where an electrode is located on a substrate is mounted. Therefore, even when used as an optical waveguide device, an increase in optical loss can be prevented,
A practical high-speed modulated optical waveguide device can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an optical waveguide element used for a fixing structure of an optical waveguide element of the present invention.

FIG. 2 is a partial cross-sectional view showing an example of a fixing structure of the optical waveguide element of the present invention.

FIG. 3 is a partial cross-sectional view showing another example of the fixing structure of the optical waveguide element of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate, 2 optical waveguides, 3 electrodes, 4 concave portions, 5 thin portions, 10 optical waveguide elements, 11 pedestals, 12 plate-like members, 13 first fixing adhesive, 14 filling adhesive, 15 second Fixing adhesive, 1A, 1B Main surface of substrate, 11A Main surface of housing, 12A, 12B Main surface of plate-shaped member, t Plate-shaped member thickness, d Depth of recess, w
Recess width

Claims (5)

[Claims] 1. A substrate having a pair of main surfaces opposed to each other and having an electro-optic effect, an optical waveguide formed on one main surface of the substrate, and a modulation signal applied to a light wave guided through the optical waveguide. An electrode for applying, and an optical waveguide element provided with a thin portion having a relatively small thickness, formed at least in a portion of the substrate where the electrode is located, is fixed to a base, and the optical waveguide element is fixed. A fixing structure of the optical waveguide element for mounting, wherein the optical waveguide element is adhesively fixed to a predetermined member, and the predetermined member is adhesively fixed to the pedestal,
The fixing structure of the optical waveguide element, wherein the optical waveguide element is fixed to the pedestal with the predetermined member interposed therebetween. 2. The fixing structure for an optical waveguide element according to claim 1, wherein said predetermined member is made of the same material as said substrate. 3. The fixing structure for an optical waveguide element according to claim 1, wherein said predetermined member is plate-shaped. 4. An adhesive fixing between the optical waveguide element and the predetermined member is performed by applying an adhesive so as to fill a gap between the thin portion of the optical waveguide element and the predetermined member. The fixing structure for an optical waveguide element according to claim 1, wherein 5. An adhesive fixing between the optical waveguide element and the predetermined member, in such a manner that an adhesive does not exist in a gap formed between the thin portion of the optical waveguide element and the predetermined member. The fixing structure for an optical waveguide element according to claim 1, wherein