JP2000330081A - Optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide element which is capable of suppressing the resonance of a substrate while improving workability. SOLUTION: The entire area of the rear surface of an element part 10 consisting of the LiNbO3 substrate formed with an optical waveguide and an electrode thin film 13 on its front surface is fixed by an adhesive 32 to a groove 21 of a holder 20 and the remaining surface is covered by a protective resin 33, by which the element part 10 is fixed in a molded state to the holder 20. An adhesive prepared by using an epoxy resin, which cures at room temperature and less generates thermal stress, as a chief material and compounding an amine compound as a hardener with this resin is used as the adhesive 32. A resin sealing material of a UV curing type is used for the protective resin 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide element used for an optical modulator or the like, and more particularly, to an optical waveguide element formed by an element portion on which an optical waveguide is formed and a holder accommodating the element portion. The present invention relates to an optical waveguide device in which the disadvantages described above are improved.

[0002]

2. Description of the Related Art An optical waveguide element used for an optical modulator or the like is formed, for example, by forming an optical waveguide pattern of a Ti (titanium) thin film on one surface of a LiNbO ₃ (lithium niobate) substrate, and then performing a thermal diffusion process. To form an optical waveguide,
An element portion having an electrode thin film formed near the optical waveguide is provided. The element section causes a change in the refractive index by the displacement of the substrate material due to the piezoelectric effect due to the electric field applied between the electrodes, thereby modulating the light passing through the optical waveguide.

[0003] Such an optical waveguide device is finally constructed such that the element portion is housed in a holder made of metal or the like. The inside of the holder is replaced with, for example, a dry gas, and is closed and sealed by seam welding. Various methods of mounting the element portion on the holder have been devised. For the purpose of preventing the stress from being applied to the entire element portion, for example, as shown in FIG. The element part 2 is joined to the holder 3 at only a few places, the element part 2 is supported in the holder 3 using a thin metal plate 4 as shown in FIG. 7, or the element part is held in the holder using a gold wire (not shown). Methods such as hanging are proposed.

[0004]

However, the accommodating method as described above requires introduction of a replacement gas, lid processing, and the like, resulting in poor workability and mass productivity, leading to an increase in element cost. is there.

When an AC electric field is applied between the electrodes to modulate light, an in-plane vibration is generated in the substrate, and the in-plane vibration becomes a transverse wave and propagates in the thickness direction of the substrate.
Then, the reflected wave reflected from the lower surface of the substrate inside the substrate interferes with the traveling wave traveling toward the lower surface of the substrate to become a standing wave, and a resonance state occurs. If this frequency component is contained in the modulation frequency band, the modulation characteristics will be adversely affected by resonance. Such a resonance phenomenon may significantly occur in the above-described housing method.

The present invention has been made in view of the above problems, and has as its object to provide an optical waveguide device capable of suppressing resonance of a substrate while improving workability.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the entire surface of the other surface of the substrate on which the optical waveguide and the electrode thin film are not formed is fixed to a holder with an adhesive, and the remaining surface is sealed with a resin. By covering with a stopper material, the element part is fixed to the holder in a molded state.

According to this configuration, by molding the element portion, the replacement work and the lid processing with the dry gas inside the holder for accommodating the element portion, which are conventionally performed, become unnecessary, and the workability is improved. It is planned. In addition, by molding the element portion and fixing it to the holder, the in-plane vibration of the substrate is suppressed at the time of the modulation action by the element portion, so that the vibration propagating in the thickness direction of the substrate is suppressed, and the occurrence of resonance is suppressed. Further, the adhesive applied to the entire other surface of the substrate has a vibration damping effect, which also contributes to suppressing the occurrence of resonance of the substrate.

Here, in order to suppress the stress generated by the adhesion between the element portion and the holder from being applied to the entire element portion, an adhesive which is hardened at room temperature, generates little thermal stress, and has a low shrinkage property is used. It is preferable to use an adhesive containing an epoxy resin as a main component and an amine compound as a curing agent. Also,
As the resin sealing material, in order to suppress the generation of thermal stress during curing, it is preferable to use, for example, an ultraviolet curable resin that is not based on thermosetting.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an element section 10 which is a component of an optical waveguide element according to an embodiment of the present invention. Hereinafter, a manufacturing process of the element unit 10 will be described.

A substrate 11 for manufacturing the element section 10 includes:
The substrate 11 is formed of a LiNbO ₃ (lithium niobate) crystal, which is a piezoelectric material.
Polishing of not less than 00 and not more than # 1200 is performed, and the average roughness Ra
Is finished to 0.1 μm or more and 1 μm or less.

An optical waveguide 12 made of a Ti (titanium) thin film is formed on one surface (ie, the surface side) of the LiNbO ₃ substrate 11.
After forming the pattern of FIG.
2 is obtained. In the present embodiment, the optical waveguide 12 is a Y-branch type, and the pair of electrode thin films 13 and 13 is formed so as to sandwich one of the branched waveguides. is there.

The optical waveguide 12 is formed by the following steps. First, a photoresist is applied to a LiNbO ₃ substrate 1
Coat 1 Thereafter, a resist waveguide pattern is formed on the substrate 11 using a waveguide pattern mask. Next, a Ti film having a thickness of several tens nm is formed by an electron beam evaporation method or the like. Thereafter, the LiNbO ₃ substrate 11 on which the Ti film is formed is subjected to ultrasonic cleaning while being immersed in acetone, lift-off is performed, and unnecessary Ti adhered to portions other than the optical waveguide pattern.
The film is removed with the photoresist. Then, the LiNbO ₃ substrate 11 on which the optical waveguide pattern is formed is
Heat at about 00 ° C for several hours to convert Ti to LiNbO ₃ substrate 1
Diffusion into 1. The portion where Ti is diffused is LiNbO ₃
Since the refractive index is higher by about 10 ⁻² than that of the optical waveguide 12, this portion becomes the optical waveguide 12 for confining light.

The electrode thin film 13 is formed by the following steps. That is, a photoresist is coated on the LiNbO ₃ substrate 11 and an electrode pattern is formed using an electrode pattern mask in the same manner as the patterning of the optical waveguide 12. Thereafter, the electrode thin film 13 is formed by electron beam evaporation. Au was used for the electrode thin film 13. Further, Ti was deposited on the upper and lower surfaces of the Au film to a thickness of several nm in order to improve the adhesion between the Au film and LiNbO ₃ and the protective layer 14 described later.
Then, unnecessary electrode films other than the electrode pattern are removed together with the photoresist by a lift-off method. First, the protective layer 14 is formed by depositing a protective film of SiO ₂ (silicon dioxide) using LiN
A film is formed on the bO ₃ substrate 11. Thereafter, patterning of a window for leading out an electrode is performed, and a protective film window is formed by chemical etching.

Optical waveguide 12, electrode thin film 13, and protective layer 1
The LiNbO ₃ substrate 11 on which the substrate 4 is formed is cut into a block of an appropriate size, and the end surface is polished to a mirror surface in order to couple light to the optical waveguide 12. Thereafter, each block is cut for each optical waveguide element, and the element section 10 is completed.

Referring to FIG. 3, holder 20 for fixing element portion 10 has a thermal expansion coefficient of Li in this embodiment.
It is formed of a stainless material, which is a material close to that of NbO ₃ , and has a groove (recess) 21 for housing the element unit 10 and an electrode terminal 22 for extracting an electrode.

Referring to FIGS. 4 and 5, the entire surface of element portion 10 where optical waveguide 12 is not formed (that is, the rear surface side) is fixed to the bottom surface of groove 21 of holder 20 by adhesive 32. The adhesive 32 cures at room temperature, generates less thermal stress even in the subsequent thermal history, and has an epoxy resin as a main component and an amine as an optimal adhesive for suppressing resonance due to a transverse wave propagating in the thickness direction of the substrate. An adhesive containing a compound as a curing agent was used.

After that, the electrode thin film 13 of the element section 10 and the holder 2 are formed with an aluminum wire 31 having a diameter of about 30 μm by a known wire bonding method utilizing, for example, ultrasonic vibration.
0 electrode terminal 22 is joined. Further, the protective resin 33 is filled over the entire surface into the groove 21 of the holder 20 from the upper surface side of the element portion 10 and is cured by covering the surface of the element portion 10 and both side surfaces in the longitudinal direction. In the present embodiment, the protective resin 33 is used.
In order to suppress the generation of thermal stress at the time of curing, a transparent ultraviolet-curable resin sealing material containing a modified methacrylate ester as a main component was used.

The optical waveguide device 30 according to the present embodiment is configured as described above. Therefore, by a configuration in which the element unit 10 is molded with the adhesive 32 and the protective resin 33 as in the present embodiment, a complicated operation such as replacing the periphery of the element unit with a dry gas and sealing the same as in the related art is performed. Thus, the element portion 10 can be housed in the holder 20 by a simpler method than in the conventional case, and the workability can be improved and the work cost can be reduced.

The element part 10 is molded and the holder 2 is formed.
0, the occurrence of resonance of the LiNbO ₃ substrate 11 at the time of the modulation action by the element section 10 can be suppressed, thereby suppressing the adverse effect on the modulation characteristics due to the resonance, and improving the reliability of the optical waveguide element 30. Can be secured.

The adhesive 32 has a function of buffering vibration on the back surface of the substrate 11, so that the substrate 1
1 is suppressed. In addition, since the average surface roughness of the back surface of the LiNbO ₃ substrate 11 is formed to be 0.1 μm or more and 1 μm or less, vibrations propagating to the back surface of the substrate are scattered by the back surface by this configuration, thereby attenuating the vibration. Can be.

Although the embodiment of the present invention has been described above, the present invention is, of course, not limited to this, and various modifications can be made based on the technical idea of the present invention.

[0024] In the form of, for example, or more embodiments, the optical waveguide element 30 has been described taking as an example the light modulation elements according to an electro-optical effect using a LiNbO ₃ substrate include, but not limited, for example, as a substrate such as LiTaO ₃ The present invention is also applicable to a light polarizing element using an acousto-optic effect using another piezoelectric material or using LiNbO ₃ for a substrate.

[0025]

As described above, according to the optical waveguide device of the present invention, the element portion can be housed in the holder by a simpler method than before, and the workability is improved and the work cost is reduced. be able to. Further, since the adverse effect on the modulation characteristics due to the resonance of the substrate can be suppressed, the reliability of the optical waveguide device can be ensured.

According to the second aspect of the present invention, since the adhesive which cures at room temperature, generates less thermal stress, and has low shrinkage is used, the stress generated by the bonding between the element portion and the holder is reduced. It is possible to prevent the entire element portion from being extended.

According to the third aspect of the present invention, since an adhesive that is not based on heat curing is used, it is possible to prevent the occurrence of thermal stress during curing.

[Brief description of the drawings]

FIG. 1 is a partially broken plan view of an element portion which is a component of an optical waveguide element according to an embodiment of the present invention.

FIG. 2 is a side view of the same.

FIG. 3 is a perspective view showing an entire holder which is a component of the optical waveguide element according to the embodiment of the present invention.

FIG. 4 is a perspective view showing the entire optical waveguide element according to the embodiment of the present invention.

FIG. 5 is an enlarged sectional view of a main part in FIG. 4;

FIG. 6 is a side sectional view showing a mounting mode between a conventional element portion and a holder.

FIG. 7 is a side cross-sectional view showing a mounting configuration between another conventional element portion and a holder.

[Explanation of symbols]

10 ... element unit, 11 ... LiNbO ₃ substrate, 12 ... optical waveguide, 13 ... electrode thin film, 14 ... protective layer, 20 ... holder, 2
DESCRIPTION OF SYMBOLS 1 ... groove (concave part), 22 ... electrode terminal, 30 ... optical waveguide element, 31 ... bonding wire, 32 ... adhesive, 33 ...
Protective resin.

Claims (4)

[Claims] 1. An optical waveguide device comprising: an element portion in which an optical waveguide and an electrode thin film are formed on one surface of a substrate; and a holder for accommodating the element portion, wherein the entire surface of the other surface of the substrate is bonded. An optical waveguide element fixed to the holder with an agent and the remaining surface of the substrate covered with a resin sealing material. 2. The optical waveguide device according to claim 1, wherein the adhesive is mainly composed of an epoxy resin and an amine compound as a curing agent. 3. The optical waveguide device according to claim 1, wherein the resin sealing material is an ultraviolet curable resin. 4. The optical waveguide device according to claim 1, wherein said element portion is fixed in a recess formed on an upper surface of said holder.