JP2001059951A - Optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking of the substrate of an optical waveguide element which has a thin part formed by relatively lessening the thickness of the part where at least an electrode is formed. SOLUTION: A first substrate electrode 7-1 and a second substrate electrode 7-2 are respectively formed on side surfaces 1C, 1D of the substrate 1 which is provided with the optical waveguide 2, the electrode 3, a buffer layer and the thin part 5 which is formed by a recessed part 4. Further, a first recessed part electrode 8-1 and a second recessed part electrode 8-2 are respectively formed on side surfaces 4A, 4B of the recessed part 4. Therein, the first substrate electrode 7-1 and the first recessed part electrode 8-1 are electrically connected by a lead wire 9-1, the second substrate electrode 7-2 and the second recessed part electrode 8-2 are electrically connected by a lead wire 9-2, and, thereby, the pyroelectric charges which are revealed in the side surfaces 1C, 1D of the substrate 1 and the side surfaces 4A, 4B of the recessed part 4 are negated.

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 and, more particularly, to an optical waveguide device which 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 electrode for applying the modulation signal of the optical waveguide device constituting the optical waveguide device is made 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.

[0003] However, such an optical waveguide device has problems that the cost is high due to the complexity of the manufacturing process of the electrodes, and that the formation of the buffer layer increases the driving voltage. From this point of view, the present applicant has filed Japanese Patent Application No.
No. 85579, it has been found that the above problem can be solved by forming a thin portion in which at least the portion of the substrate of the optical waveguide element where the electrodes are formed is made relatively thin, and an application for this optical waveguide element is made. Is going.

[0004]

However, when such an optical waveguide device is actually driven and used,
When the thickness of the thin portion is reduced to about 100 μm,
In some cases, the substrate itself was broken at the thin portion. For this reason, some restrictions have been imposed on high-speed modulation by such an optical waveguide element.

According to the present invention, there is provided a substrate having a pair of opposing main surfaces and having an electro-optic effect, an optical waveguide formed on one of the main surfaces, and a modulation signal applied to a light wave guided through the optical waveguide. An electrode for applying, an optical waveguide element having a thin portion having a relatively small thickness formed at least in a portion of the substrate where the electrode is located, preventing the substrate from cracking as described above, It is an object of the present invention to provide an optical waveguide device in which the limitation of high-speed modulation is extremely widened.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a substrate having an electro-optical effect, comprising a pair of opposing main surfaces and a pair of opposing side surfaces, and a light guide formed on one main surface of the substrate. A waveguide, comprising an electrode for applying a modulation signal to a light wave guided through the optical waveguide, a thin portion having a relatively small thickness is provided at least in a portion of the substrate where the electrode is located, An optical waveguide device in which a concave portion is formed between a thin portion and the other main surface of the substrate, wherein a first conductive portion is formed on each of the pair of opposed side surfaces, and a first conductive portion is formed in the concave portion. An optical waveguide device, wherein two conductive portions are formed, and a connecting means for electrically connecting the first conductive portion and the second conductive portion is provided.

FIG. 1 is an inventor of the present invention,
FIG. 4 is a cross-sectional view showing an example of an optical waveguide device that enables a high-speed modulation by forming a thin portion in which at least a portion of a substrate where electrodes are formed is relatively thin. In addition,
In the following drawings, in order to clarify the features of the present invention, they are drawn in forms different from actual ones.

In the optical waveguide device shown in FIG. 1, an optical waveguide 2 and an electrode 3 are formed on a main surface 1A of a substrate 1 having an electro-optic effect. In the main surface 1B of the substrate 1 opposite to the main surface 1A, a concave portion 4 is formed in a portion where the electrode 3 is located.
Is formed, whereby the thin portion 5 of the optical waveguide element 10 is formed.
Is configured.

The present inventors have conducted intensive studies to prevent cracks in the thin portion 5 of the optical waveguide device having the structure shown in FIG. 1 and searched for the cause. Conventionally, as a substrate material of an optical waveguide element used for an optical waveguide device, generally, lithium niobate (LiNbO ₃ : may be abbreviated as LN) is generally used. Generally, the X-cut plate or the Z-cut plate is used.
Since these cut surfaces have advantages and disadvantages, they are used properly according to the concept of the designer.

When an optical waveguide device is manufactured by using an LN X-cut plate as a substrate, when the optical waveguide device is driven, pyroelectric charges may be induced on the side surface of the substrate by a pyroelectric action. Was. Since this pyroelectric charge causes a temperature drift, conventionally, electrodes were formed on both side surfaces of the substrate, and these electrodes were electrically connected to remove the pyroelectric charge.

However, in the optical waveguide device having the structure shown in FIG. 1, it is found that pyroelectric charges are generated not only on the side surfaces 1C and 1D of the substrate 1 but also on the side surfaces 4A and 4B of the concave portion 4. Was. Further, when the depth D of the concave portion 4 is increased and the thickness t of the thin portion 5 is reduced, the side surface 4A
And that the amount of pyroelectric charge becomes extremely large because the area of 4B becomes large. When the amount of the pyroelectric charge becomes extremely large, the effect of the piezoelectric effect caused by the pyroelectric charge also increases, and it is found that the internal stress is concentrated on the thin portion 5 and the thin portion 5 is broken. The present invention has been made based on the discovery of this fact.

FIG. 2 is a sectional view showing an example of the optical waveguide device of the present invention. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals. The optical waveguide device 20 shown in FIG. 2 is different from the optical waveguide device shown in FIG.
On the side surfaces 1C and 1D of the substrate 1, a first substrate electrode 7-1 and a second substrate electrode 7-2 made of carbon paste are provided as first conductive portions. Further, on the side surfaces 4A and 4B of the concave portion 4, a first concave electrode 8-1 and a second concave electrode 8-2 made of carbon paste are provided as second conductive portions. Then, the first substrate electrode 7-
1, the first concave electrode 8-1, and the second substrate electrode 7-2
And the second concave electrode 8-2 are connected to the conductive wires 9-1 and 9 respectively.
-2 are electrically connected.

Therefore, the pyroelectric charge induced on the side surface 1C of the substrate 1 and the pyroelectric charge induced on the side surface 4A of the concave portion 4;
Pyroelectric charge induced on the side surface 1D of the substrate 1 and the concave portion 4
And the pyroelectric charges induced on the side surface 4B are canceled each other. Therefore, the development of the piezoelectric effect is suppressed, and the thin portion 5
The stress is not concentrated on the substrate and it does not lead to destruction.

Further, the first concave electrode 8-1 and the second concave electrode 8-2 are electrically connected by a conductive wire 11. Thereby, the potential in the substrate 1 is kept constant, and the effect of canceling the pyroelectric charge is promoted.

According to the present invention, even when the thickness of the thin portion is extremely thin, the substrate is not broken by the internal stress generated by the piezoelectric effect caused by the pyroelectric charge, so that the light is guided through the optical waveguide. The speed matching between the light wave and the high-frequency electric field which is a modulation signal can be performed in a wide range. Therefore, higher high-speed modulation can be performed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments of the present invention. Optical waveguide device 20 shown in FIG.
In this embodiment, the second conductive portion is constituted by concave electrodes 8-1 and 8-2 made of carbon paste. by this,
Since the electrical contact between the second conductive portion and the side surfaces 4A and 4B of the concave portion 4 can be made firmly, the pyroelectric charges generated on the side surface 1C of the substrate 1 and the side surface 4A of the concave portion 4 can be more effectively used. Can be countered.

The recessed electrodes 8-1 and 8-2 can be formed of a conductive material such as gold, aluminum, copper, and silver paste in addition to the above-mentioned carbon paste. Also,
Instead of the conductive wires 9-1 and 9-2, a conductive electrode having the same form as the first substrate electrode or the like can be formed on the main surface 1B of the substrate 1.

In FIG. 2, the first concave electrode 8-1 is shown.
The second concave electrode 8-2 is electrically connected to the second concave electrode 8-2 by the conductive wire 11, but such an electrical connection is not always required. However, by electrically connecting them, the potential in the substrate 1 is kept constant, so that the effect of canceling the pyroelectric charge is promoted and the object of the present invention can be achieved more effectively.

FIG. 3 is a sectional view showing another example of the optical waveguide device of the present invention. In FIG. 3, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

The optical waveguide device 30 shown in FIG. 3 has a conductive resin portion 18 as a second conductive portion formed by filling the concave portion 4 of the optical waveguide device shown in FIG. 1 with carbon. are doing. The air layer 17 is formed so as to be in contact with the thin portion 5 above the concave portion 4. Then, a first conductive electrode 19-1 and a second conductive electrode 19-2 made of carbon paste are formed on the main surface 1B of the substrate, respectively, with the first substrate electrode 7-1, the conductive resin portion 18, and the second conductive electrode 19-2. Is formed so as to contact the substrate electrode 7-2 and the conductive resin portion 18.

By employing the structure shown in FIG. 3, the inside of the concave portion 4 is filled to a considerable extent, so that the strength of the substrate is increased. Therefore, there is an advantage that handling of the optical waveguide element is facilitated.

Further, by forming the air layer 17, a high-frequency electric field applied to the electrode 3 leaks to the air layer 17 having a low refractive index. Therefore, the effective refractive index of the high-frequency electric field is reduced, and the speed matching between the light wave guided through the optical waveguide 2 and the high-frequency electric field can be increased. Therefore, the object of the present invention can be achieved without impairing the high-speed modulation, which is the original purpose of forming the thin portion 5.

The thickness d of the air layer 17 is not particularly limited as long as it achieves the object of the present invention and enables high-speed modulation by predetermined speed matching.
However, in general, for the depth D of the concave portion 4, d /
D is 1/50 to 3/4, preferably 1/10 to 1/2
It is formed so that

Further, instead of the air layer 17, a low dielectric constant layer made of at least one material selected from silicon oxide, titanium oxide, polyimide, SOG, resist and epoxy having a low dielectric constant is formed in the concave portion 4. It can be formed on the side in contact with the thin portion 5. This also achieves the same effect as described above.

In FIG. 3, the first conductive electrode 1
The conductive resin portion 18 and the first substrate electrode 7-1 and the second substrate electrode 7 are formed by the 9-1 and the second conductive electrode 19-2.
-2 is electrically connected. However, without providing such an electrode, both can be electrically connected by a conductive wire or carbon paste as shown in FIG.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Example 1 In this example, an optical waveguide device having a configuration as shown in FIG. 2 was manufactured.

(Preparation of Optical Waveguide Element) An X-cut plate of lithium niobate having a thickness of 1 mm was used as the substrate 1, and a waveguide pattern mask was formed on the main surface 1 A side of the substrate 1 by photolithography. Next, a titanium thin film was formed on the substrate via the waveguide pattern mask by an evaporation method. Thereafter, the waveguide pattern mask was removed with an organic solvent to form a waveguide pattern made of titanium. Next, the substrate 1 was placed in a high-temperature electric furnace and subjected to heat treatment, and the titanium constituting the waveguide pattern was thermally diffused into the substrate 1 to form an optical waveguide 2 made of titanium. Next, a 10 μm-thick electrode 3 made of gold was formed by using both an evaporation method and a plating method.

Then, after a resist is applied to the surface of the electrode 3, a concave portion 4 having a depth D of 0.9 mm and a width W of 150 μm is formed over the entire length of the substrate 1 by laser ablation using an excimer laser. Formed. Next, the substrate 1 is cut into chips of 2 × 10 × 1 tmm by dicing, and the chips are cleaned to obtain a thickness t.
A thin portion 5 having a thickness of 10 μm was formed on the substrate 1. Then
After preparing a single-core fiber array using 1.5 μm single-mode fiber and aligning the substrate 1 on which the optical waveguide 2 and the electrode 3 are formed, the single-core fiber array and the substrate 1 are made of an ultraviolet curable resin. Glued.

Thereafter, the carbon paste is applied to the side surfaces 1C and 1D of the substrate 1 and the side surfaces 4A and 4B of
5 μm was applied. Next, the carbon paste is dried by baking at 60 ° C. for 1 hour, and the first substrate electrode 7-1 and the second substrate electrode 7-2, and the first concave electrode 8-1 and the second concave electrode are formed. 8-2 was formed.

The first substrate electrode 7-1 is provided on the main surface 1B of the substrate 1 at both ends in the longitudinal direction of the substrate 1.
And the first concave electrode 8-1 and the second substrate electrode 7-
A conductive electrode (not shown) for electrically connecting the second and second recessed electrodes 8-2 to each other was formed, and conduction between these electrodes was established. Further, the first recessed electrode 8-1 and the second recessed electrode 8-2 were electrically connected by the conductive electrode, and an optical waveguide device as shown in FIG. 2 was manufactured.

(Evaluation of Characteristics of Optical Waveguide Element) The optical waveguide element produced as described above was placed in a high-temperature layer,
A temperature cycle test of の 85 ° C. was performed. Then, the fluctuation (loss fluctuation) of the amount of light output from the optical waveguide element by the temperature cycle test was measured. For the modulation band of the optical waveguide device, the optical response characteristics were measured and the light intensity was 3 dB.
It was determined from the decreasing band (3 dB band). Table 1 shows the results.

Example 2 In this example, a buffer layer 6 as shown in FIG. 3 was formed between the substrate and the electrode of the optical waveguide device manufactured in Example 1. After forming the optical waveguide 2, the buffer layer 6 is formed by uniformly depositing silicon oxide on the main surface 1 </ b> A of the substrate 1 by a vapor deposition method, and then by photolithography to a thickness of 1.1 μm.
m. The obtained optical waveguide device is the same as that of the first embodiment.
In the same manner as described above, the fluctuation of the light amount and the light response characteristics were measured and evaluated. Table 1 shows the results.

Example 3 In this example, an optical waveguide device 30 as shown in FIG. 3 was manufactured. (Preparation of Optical Waveguide Element) After forming the optical waveguide 2, the buffer layer 6, and the electrode 3 on the substrate 1 in the same manner as in Example 2,
The recess 4 was formed in the substrate 1 and cut into chips. Next, the single-core fiber array was connected to the substrate 1 in the same manner as in Example 2.

Thereafter, the concave portion 4 was filled with a carbon paste having a high viscosity, so that the conductive resin portion 18 was formed. However, the air layer 17 having a thickness d of 100 μm was made to remain in a portion in contact with the upper thin portion 5 in the concave portion 4. Thereafter, baking was performed at 90 ° C. for 30 minutes, and the carbon paste was dried to form the conductive resin portion 18. Next, a carbon paste is applied to the side surfaces 1C and 1D of the substrate 1 to a thickness of 15 μm,
The first substrate electrode 7-1 and the second substrate electrode 7-2 were formed by performing baking for a time and drying the carbon paste.

Electrical connection was established between these electrodes by forming conductive electrodes (not shown) similar to those in the first embodiment. Thus, an optical waveguide device 30 as shown in FIG. 3 was manufactured.

(Evaluation of Characteristics of Optical Waveguide Device) With respect to the optical waveguide device formed as described above, the fluctuation of the light amount and the optical response characteristics in the 3 dB band were measured by the same temperature cycle test as in Example 1. Table 1 shows the results.

Embodiment 4 In this embodiment, the air layer of the optical waveguide device shown in Embodiment 3 is
An optical waveguide element 30 was manufactured in place of the low dielectric constant layer. (Preparation of Optical Waveguide Element) In this embodiment, before filling the recess 4 with the conductive resin, a resist (dielectric constant: 2.
5) was filled in the recess 4 so that the thickness d became 100 μm. Next, the resist was dried by baking at 90 ° C. for 30 minutes to form a low dielectric constant layer 17.

Next, after filling the concave portion 4 with a carbon paste having a high viscosity in the same manner as in Example 3,
Was performed for 60 minutes to form a conductive resin portion 18. Further, the first substrate electrode 7 is formed in the same manner as in the above embodiment.
After forming the first substrate electrode 7-2 and the second substrate electrode 7-2, an electrical connection was established by forming a conductive electrode, and the optical waveguide element 30 was manufactured.

(Evaluation of Characteristics of Optical Waveguide Device) With respect to the optical waveguide device formed as described above, the fluctuation of the light quantity and the optical response characteristics in the 3 dB band were measured by the same temperature cycle test as in Example 1. Table 1 shows the results.

Embodiment 5 In this embodiment, an optical waveguide device 4 as shown in FIG.
0 was produced. The optical waveguide device 40 shown in FIG. 4 is a modified example of the optical waveguide device 30 shown in FIG. That is, without the buffer layer 6, the first substrate electrode 17-1 and the second substrate electrode 17-2 extend upward along the side surfaces 1C and 1D of the substrate 1 and come into contact with the side surface of the electrode 3. It is formed so that it does.

The constituent material of the optical waveguide element 40 is the same as that used in the third embodiment.
It carried out similarly to.

Next, in the same manner as in Example 1, the optical waveguide device manufactured as described above was placed in a high-temperature layer, and
A temperature cycle test of 40 to 85 ° C was performed. And
The fluctuation (loss fluctuation) of the light amount output from the optical waveguide element by the temperature cycle test was measured in the same manner as in the above-described example. Table 1 shows the results.

Comparative Example In this comparative example, an optical waveguide device having a conventional configuration as shown in FIG. 1 was fabricated without forming a first conductive portion such as a first substrate electrode and a second conductive portion. . The form of the optical waveguide element is the same as that of the first embodiment except that the step of applying a carbon paste or the like is omitted and the first substrate electrode and the like are not provided. With respect to the optical waveguide device formed as described above, the fluctuation of the light amount before and after the temperature cycle test and the optical response characteristics in the 3 dB band were measured in the same manner as in Example 1. Table 1 shows the results
Shown in

[0044]

[Table 1]

As is clear from Table 1, the first conductive portion such as the first substrate electrode and the first conductive portion according to the present invention are provided.
It can be seen that the optical waveguide device formed with the second conductive portion such as the concave electrode has a larger light quantity fluctuation before and after the temperature cycle test than the optical waveguide device having no conductive portion. A large variation in the amount of light indicates a large amount of pyroelectric charge, which is a factor of generating an internal electric field that changes the effective refractive index of the optical waveguide. Therefore, it can be seen that the pyroelectric charge induced on the side surface of the substrate and the pyroelectric charge induced on the side surface of the concave portion are almost completely canceled out in the optical waveguide device of the present invention.

As is apparent from Examples 3 to 5, Examples 1 and 2, and Comparative Example, the conductive resin portion formed by filling the concave portion with the conductive resin in the second conductive portion. It can be seen that the optical response characteristics do not deteriorate even in the case of

As described above, the present invention has been specifically described based on the embodiments of the present invention with specific examples, but the present invention is not limited to the above contents and does not depart from the scope of the present invention. All modifications and changes are possible.

[0048]

According to the present invention, pyroelectric charges in a thin portion of a substrate formed to enable high-speed modulation can be removed at a high rate. Can be prevented.
As a result, since the thin portion can be considerably thinned, the speed matching between the light wave guided through the optical waveguide and the high-frequency electric field as the modulation signal can be achieved in a sufficiently wide range. Therefore, it is possible to provide an optical waveguide device capable of further high-speed modulation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a conventional optical waveguide device.

FIG. 2 is a cross-sectional view showing one example of the optical waveguide device of the present invention.

FIG. 3 is a sectional view showing another example of the optical waveguide device of the present invention.

FIG. 4 is a sectional view showing still another example of the optical waveguide device of the present invention.

[Explanation of symbols]

Reference Signs List 1 substrate, 2 optical waveguides, 3 electrodes, 4 recesses, 5 thin portions, 6 buffer layer, 7-1, 17-1 first substrate electrode, 7-2, 17-2 second substrate electrode, 8-1
First concave electrode, 8-2 Second concave electrode, 9-1, 9
−2, 11 conductor, 10, 20, 30, 40 optical waveguide element, 17 air layer (low dielectric layer), 18 conductive resin section, 19-1 first conductive electrode, 19-2 second conductive electrode , 1C, 1D Side view of substrate, 4A, 4B Side view of recess

Claims (7)

[Claims] 1. A substrate having an electro-optic effect having a pair of main surfaces facing each other and a pair of side surfaces facing each other, an optical waveguide formed on one main surface of the substrate, and a waveguide for guiding the optical waveguide. An electrode for applying a modulation signal to the wave of the wave, a thin portion having a relatively small thickness is provided at least in a portion of the substrate where the electrode is located, and the thin portion and the other of the substrate. An optical waveguide device having a concave portion formed between the optical waveguide device and a main surface, wherein a first conductive portion is formed on each of the pair of opposed side surfaces, and a second conductive portion is formed in the concave portion. An optical waveguide device, further comprising a connecting means for electrically connecting the first conductive portion and the second conductive portion. 2. The method according to claim 1, wherein the second conductive portion is made of gold, aluminum,
The optical waveguide device according to claim 1, wherein the electrode is an electrode made of at least one conductive material selected from copper, carbon, silver paste, and carbon paste. 3. The device according to claim 2, wherein the second conductive portion is composed of a plurality of electrodes that are electrically connected.
3. The optical waveguide device according to claim 1. 4. The method according to claim 1, wherein the second conductive portion is made of a conductive resin filled in the concave portion, and has an air layer on a side of the concave portion in contact with the thin portion.
3. The optical waveguide device according to claim 1. 5. The second conductive portion is made of a conductive resin filled in the concave portion, and has a low dielectric constant layer made of a low dielectric constant material on a side of the concave portion in contact with the thin portion. The optical waveguide device according to claim 1, wherein: 6. The conductive resin is at least one of a carbon paste and a silver paste.
The optical waveguide device according to claim 4. 7. The optical waveguide device according to claim 5, wherein the low dielectric constant material is at least one selected from silicon oxide, titanium oxide, polyimide, SOG, resist, and epoxy. .