JP3231190B2 - Waveguide type optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical device. More specifically, the present invention has an optical waveguide using lithium niobate as a base material,
Also, the present invention relates to a waveguide type optical element capable of suppressing abnormal short circuit development between electrodes even in a high humidity atmosphere. The waveguide type optical device of the present invention is useful as one of the key devices of an optical communication system, and is particularly useful as an optical modulator device.

[0002]

2. Description of the Related Art An optical element having an electro-optical effect, for example, a waveguide type optical element using lithium niobate as a base material,
For example, it is useful as an element of an external modulator for a high-speed optical communication system.However, in practical use, since lithium niobate crystal has a pyroelectric effect, the occurrence of temperature drift due to it has to be solved. Has become.

[0003] The temperature drift is caused by the electric charge induced on the substrate surface by the pyroelectric effect of the substrate, which generates a local electric field. Therefore, this electric charge crosses the optical waveguide formed on the substrate surface and reaches the electrode. This causes the refractive index of the optical waveguide to fluctuate (P. Skeath, C.
H.Bulmer, SCHiser, and WKBurus, Appl.Phys.Let
t., Vol. 49 (1986), 1221, and CHBulmer and WKBu
rns, Appl. Phys. Lett., Vol. 48 (1986), 1036).

As means for suppressing this temperature drift,
Japanese Patent Publication Nos. 4-22485 and 5-78016 disclose that a conductive film is formed so as to cover the surface of a substrate or a dielectric layer exposed between electrodes.

In FIG. 1A, optical waveguides 2a and 2b are formed on the surface of a substrate 1 made of lithium niobate single crystal, and the substrate 1 and the optical waveguides 2a and 2b are formed.
A dielectric layer 3 is formed thereon. This dielectric layer 3
In many cases, it is formed by silicon oxide. On the dielectric layer 3, a conductive film layer 4 made of, for example, silicon is formed. The signal electrode 5a is arranged on the optical waveguide 2a via the dielectric layer 3 and the conductive film layer 4, and the dielectric layer 3 and the conductive film layer 4 are formed on the other optical waveguide 2b. A ground electrode 5b is arranged via the signal electrode 5a.
On the other side of the ground electrode 5b, another ground electrode 5c separated from the signal electrode 5a is disposed on the conductive film layer 4. The electrodes are often formed of gold.

A thin intermediate layer made of titanium or the like may be interposed between the electrodes 5a, 5b, 5c and the conductive film layer 4 in order to enhance the adhesion of the electrodes. In general, a conductive film layer made of silicon (non-quality) is formed by sputtering, CV
It can be easily formed by a conventional method such as Method D, has good adhesion to the underlying dielectric (silicon oxide) layer, and is chemically stable.

The conventional waveguide type optical element shown in FIG. 1 (b) has almost the same configuration as that shown in FIG. 1 (c), except that the electrodes 5a, 5b, 5c is the direct dielectric layer 3
The surface of the dielectric layer between these electrodes is covered with conductive film layers 4a and 4b.

In the conventional waveguide type optical device shown in FIGS. 1A and 1B, the conductive film layers 4, 4a and 4b are generated by the pyroelectric effect to uniformly disperse the electric charge and generate a local electric field. This has the effect of suppressing temperature drift, and hence temperature drift.

FIG. 2 is a plan view of the optical device shown in FIGS. 1 (a) and 1 (b). The electrodes 5a, 5b, 5c are connected to signal output means (not shown), and the optical waveguides 2a, 2
b is connected at its input end and output end to light input means and output means (not shown), respectively.

FIG. 1 shows the temperature drift property of a waveguide type optical device.
Markedly improved by the conventional means shown in
It can be put to practical use. However, depending on the environment in which the optical element is used, for example, in a high-temperature and / or high-humidity environment, the conductive film layer and the electrode react with each other to generate a reaction product, and the generated material causes adjacent electrodes to exchange. An accident of short circuit occurs. For example, KΩ ~
The resistance value on the order of MΩ falls below the order of several hundred Ω.

Now, the above phenomenon will be described by taking a waveguide type optical element in which the conductive film layer is made of silicon and the electrode is made of gold as an example. That is, when an optical modulator element having such a combination of the conductive film layer and the electrode forming material is operated in a high humidity atmosphere with a DC bias voltage applied thereto, gold and silicon are interposed through water. It reacts electrochemically and a reaction product precipitates between the electrodes.

FIG. 3 shows a case in which an optical modulator element having the same structure as that shown in FIGS. 1A and 2 is enclosed (a case without any leakage ... a normal sample, a case with a slight leakage ... The relationship between the time and the electric resistance between the signal electrode and the ground electrode when the abnormal sample was held while continuously applying a DC bias voltage of 5 V under the conditions of temperature: 80 ° C. and humidity: 95% RH. Have been. This silicon conductive film has a thickness of about 100 nm and an electrode length of 40 nm.
mm. The electric resistance value is a holding time of 0, 100 hours,
After 200 hours, the measurement was performed in an atmosphere at 25 ° C. and 40% RH or less.

From FIG. 3, it can be understood that when the optical element is exposed to high temperature and high humidity, the resistance between the electrodes is significantly reduced. FIG. 4 shows a high temperature under the same conditions as FIG.
It has been shown that the optical band of an optical element exposed to high humidity decreases with its holding time. That is, even if the optical element is sealed in the case, if the hermetic sealing of the case is incomplete, or if a leak occurs due to some accident, as shown in FIGS. The deterioration of the characteristics of the optical element progresses rapidly. This significantly reduces the reliability of the optical device.

Analyzing the abnormal sample in which the interelectrode resistance has been reduced, it is recognized that foreign matter has grown in a dendritic manner on the surface of the silicon layer between the electrodes having a separation distance of several tens of μm. However, no growth of such a product was observed in normal samples.

FIG. 5 shows the results of an Auger electron spectroscopic analysis of the surface of the interelectrode precipitate in the abnormal sample and the surface of the gold electrode. In FIG.
On the surface of the gold electrode, only gold (Au) and carbon (C) as a surface contaminant were detected. On the surface of the interelectrode precipitate, oxygen (O) and silicon other than gold (Au) and carbon (C) were detected. (Si) was detected. Although this precipitate was amorphous and its substance was difficult to identify, it is presumed to contain AuSi generated by the electrochemical reaction and / or its oxide and hydrate.

Since the optical element is used for a long period of time (for example, 20 years or more), during such a long-term operation, the above-mentioned reaction product precipitates are formed between the electrodes, and the characteristics of the optical element are reduced. It is necessary to completely prevent lowering.

[0017]

SUMMARY OF THE INVENTION The present invention provides a waveguide type optical device which is free from deposits between electrodes even when it is exposed to high temperature and high humidity. It is an object of the present invention to provide a waveguide type optical element having no or few waveguides.

[0018]

SUMMARY OF THE INVENTION A waveguide type optical device according to the present invention comprises a substrate having an electro-optical effect, an optical waveguide formed on a surface of the substrate, and a substrate formed on the substrate and the waveguide surface. Dielectric layer, a plurality of electrodes provided on the dielectric, and a conductive film layer formed on the dielectric layer, and disposed between the electrodes, A dividing portion is formed between all the electrodes and all the conductive film layers adjacent to the electrodes, so as to electrically separate them.

In the waveguide type optical device of the present invention, a conductive film layer may be formed between the electrode and the dielectric layer.

In the waveguide type optical device according to the present invention, the electrode may be formed directly on the dielectric layer.

In the waveguide type optical device according to the present invention, it is preferable that the substrate is made of lithium niobate.

In the waveguide type optical device according to the present invention, it is preferable that the electrode is formed of gold and the conductive film layer is formed of silicon.

[0023]

[0024]

In the waveguide type optical device according to the present invention, the dividing portion may be formed in the conductive film layer disposed between at least one pair of mutually adjacent electrodes. Further, at least a part of the dividing portion may extend along a direction of the waveguide.

[0026]

In the waveguide type optical device of the present invention, the substrate is generally formed of a single crystal of lithium niobate, and the optical waveguide is generally formed on a predetermined portion of the substrate surface by, for example, titanium,
It is formed by diffusing hydrogen or the like. In general, the electrode is generally formed of gold, the dielectric layer is formed of silicon oxide, and the conductive film layer is formed of silicon.

In the waveguide type optical device of the present invention shown in FIG. 6A, a dielectric layer 3 is formed on the surfaces of the substrate 1 and the waveguides 2a and 2b. ,
Electrodes 5a, 5b, 5c are formed (or via a conductive film layer), and a conductive film layer 4 is formed on a portion of the dielectric layer between the electrodes.
a, 4b are formed. A signal electrode (hot electrode) 5a is arranged on the waveguide 2a, and a ground electrode 5b is arranged on the other waveguide 2b. The signal electrode (hot electrode) 5a is arranged on the opposite side of the ground electrode 5b across the signal electrode 5a. The ground electrode 5c is provided. These electrodes are connected to signal output means (not shown) and can apply a signal voltage to the waveguide to modulate light propagating through the waveguide.

[0028]

[0029]

[0030]

[0031]

[0032]

In the optical device shown in FIGS. 6A and 6B, the conductive film layer 4a disposed between the electrode 5b and the electrode 5a is separated from both of the electrodes 5b and 5a. It is electrically separated and extends along the direction A of the waveguide, and is formed in, for example, a quadrilateral shape as shown in the figure. As a result, a dividing portion 6a is formed between the conductive film layer 4a and the electrode 5b, and a dividing portion 6d is formed between the conductive film layer 4a and the electrode 5a. Further, the conductive film layer 4b disposed between the electrode 5a and the electrode 5c is
a, 5c, are separated from each other via the dividing portions 6b and 6c, and extend along the direction A of the waveguide;
For example, it is formed in a quadrilateral shape as shown. That is, in the optical elements of FIGS. 11A and 11B, all the electrodes are not connected to the conductive film layer. In other words, all the conductive film layers are separated from the electrodes and do not short-circuit with each other. For this reason, even if the electrode and the conductive film layer come into contact with moisture at a high temperature and an electrochemical reaction product is generated and deposited between the electrode and the conductive film layer connected to the electrode, The deposit and the adjacent electrode do not short-circuit each other. Further, the conductive film layer disposed between the electrodes may be divided into two parts by a groove-shaped dividing part formed in an intermediate part thereof.

The optical device shown in FIG. 7 is similar to the optical device shown in FIG.
It has a configuration similar to that of the optical element of (b), except that the exposed portion of the dielectric layer 3 is small and the temperature drift is suppressed. That is, in this case, the conductive film layer was formed below the conductive film layer (dielectric layer) by grounding the conductive film layer end that reached the element end without contacting the conductive film layer and the electrode. Since the charge can be removed and the floating can be prevented, the effect of suppressing the occurrence of the temperature drift can be enhanced.

In the optical device of the present invention, the conductive film layer
The dividing portion formed so as to be divided into two is formed in the direction A of the waveguide.
, May extend in a straight line. In this way, it is possible to prevent a direct short circuit between the portions of the electrode parallel to the direction A of the waveguide due to the electrochemical reaction product precipitate. Further, since the exposed area of the dielectric layer is small, the effect of preventing the occurrence of temperature drift can be enhanced.

[0036]

In the optical device of the present invention, the growth of the (electrochemical) reaction product of the electrode material, particularly gold, and the film material, particularly silicon, is divided by the effect of the dividing portion, and the adjacent electrodes are electrically connected. Connection, that is, a short circuit can be suppressed. However, if the reaction progresses violently, the corrosion of the electrode due to the reaction becomes remarkable, and the electrode characteristics, for example, the band may fluctuate, so that the optical device having the configuration of the present invention, depending on the use environment, It is desirable that the case is housed in a case having sufficient sealing performance.

[0038]

According to the present invention, it is possible to stabilize the electrode characteristics and increase the reliability of the electro-optical element utilizing the electro-optical effect.

[Brief description of the drawings]

FIG. 1A is a cross-sectional explanatory view showing a configuration of an example of a conventional waveguide type optical element. FIG. 1B is an explanatory sectional view showing the configuration of another example of the conventional waveguide type optical element.

FIG. 2 is a plan view of the optical device of FIG. 1 (a) or (b).

FIG. 3 is a graph showing an example of a relationship between a voltage application time and a resistance between electrodes of a conventional waveguide optical element under high temperature and high humidity conditions.

FIG. 4 is a graph showing an example of a relationship between a voltage application time and an optical band of an optical device similar to that of FIG. 3 under similar conditions.

FIG. 5 is a graph showing the results of elemental analysis of the surface of the electrode and the surface of the precipitate formed between the electrodes.

FIG. 6A is an explanatory plan view showing a configuration of an example of a waveguide type optical element of the present invention. FIG. 6B is an explanatory cross-sectional view of the optical device of FIG.

FIG. 7 is an explanatory plan view showing the configuration of another example of the optical element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2a, 2b ... Optical waveguide 3 ... Dielectric layer 4, 4a, 4b ... Conductive film layer 5a, 5b, 5c ... Electrode 6a, 6b, 6c, 6d ... Dividing part A ... Waveguide direction

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Shinki 585 Tomicho, Funabashi-shi, Chiba Sumitomo Cement Co., Ltd. Optoelectronics Division (72) Inventor Toshihiro Sakamoto 585 Tomihiro-cho, Funabashi-shi, Chiba Sumitomo Cement Co., Ltd. (56) References JP-A-3-253815 (JP, A) JP-A-5-264936 (JP, A) JP-A-62-273207 (JP, A) JP-A-2-15245 (JP, A A) JP-A-4-19714 (JP, A) JP-A-5-224164 (JP, A) European Patent Application Publication 553568 (EP, A1) European Patent Application Publication 315350 (EP, A1) European Patent Application Publication 444959 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/00-1/035 G02F 1/29-1/313

Claims (7)

(57) [Claims] 1. A substrate having an electro-optical effect, an optical waveguide formed on a surface of the substrate, a dielectric layer formed on the substrate and the waveguide surface, and provided on the dielectric. A plurality of electrodes, and a conductive film layer formed on the dielectric layer and disposed between the electrodes, wherein all the electrodes and all the conductive films adjacent thereto are provided. A waveguide type optical element, wherein a division part for electrically separating them from each other is formed between the layers. 2. The waveguide type optical device according to claim 1, wherein a conductive film layer is also formed between said electrode and said dielectric layer. 3. The waveguide type optical device according to claim 1, wherein said electrode is formed directly on said dielectric layer. 4. The optical waveguide device according to claim 1, wherein said substrate is made of lithium niobate. 5. The waveguide type optical device according to claim 1, wherein said electrode is formed of gold, and said conductive film layer is formed of silicon. 6. The method according to claim 1, wherein the dividing portion is formed in the conductive film layer disposed between at least one pair of mutually adjacent electrodes. Waveguide type optical element. 7. The waveguide-type optical device according to claim 1, wherein at least a part of the dividing portion extends along a direction of the waveguide.