JP6705468B2 - Optical waveguide element - Google Patents

Description

The present invention relates to an optical waveguide element, and more specifically, in an optical waveguide element using a resin (EO polymer) having an electro-optical effect in a core layer that is an optical waveguide, an optical wave propagating in an optical waveguide and a modulation electrode are propagated. The present invention relates to an optical waveguide device capable of improving interaction with microwaves and improving modulation efficiency.

Conventionally, as an optical device using a polymer material for a substrate, one having a microstrip structure as a modulation electrode has been proposed (for example, refer to Patent Document 1). In addition to the microstrip structure, as a structure in which the interaction between the light wave propagating in the optical waveguide and the microwave propagating in the modulation electrode is improved, the modulation electrode is embedded in the coplanar structure (In-plane).
CPW) has been proposed (see, for example, Patent Documents 2 and 3).
Generally, in an optical device using a polymer material, a lower clad layer, a core layer and an upper clad layer are laminated on a substrate such as silicon, and the optical waveguide has a rib type structure. The core layer is made of a resin (EO polymer) having an electro-optical effect, and has a structure in which the orientation is controlled by applying a voltage to the core layer.
In the case of such a rib type structure, the thickness of the lower clad layer and the upper clad layer is about 2 to 6 μm, and the thickness of the core layer is about 0.1 to 2 μm.

FIG. 5 is a cross-sectional view showing an example of a conventional optical waveguide device having a microstrip structure for a modulation electrode, and the dimensions of the respective constituent elements are different from the actual dimensions in order to make the explanation easy to understand.
In the figure, reference numeral 1 is an optical waveguide element, and a ground electrode 3 made of a conductive material formed by metal plating or the like is formed on a substrate 2 made of silicon or the like, and dry etching or the like is performed on the ground electrode 3. A lower clad layer (first clad layer) 4 made of an insulating material processed by the above is formed, and a core layer 5 made of a resin (EO polymer) having an electro-optical effect is formed on the lower clad layer 4 by a spin coater or the like. A rib-type optical waveguide 6 that is formed and projects downward is formed on a part (two places in the figure) of the core layer 5.

An upper clad layer (second clad layer) 7 made of an insulating material that is etched by dry etching or the like is provided on the core layer 5, and the upper clad layer 7 and the optical waveguide 6 are provided directly on the upper clad layer 7. Is provided with a signal electrode (electrode layer) 8 made of a conductive material formed by metal plating or the like.
The EO polymer forming the core layer 5 is orientation-controlled by poling.

FIG. 6 is a cross-sectional view showing an example of a conventional optical waveguide device having a coplanar structure in which a modulation electrode is embedded. Similar to the optical waveguide device 1 described above, the dimensions of each component are shown in order to make the description easy to understand. It is different from the actual one.
This optical waveguide device 11 is different from the above optical waveguide device 1 in that a lower clad layer 4 is directly formed on a substrate 2 made of silicon or the like, and the lower clad layer 4 is formed on the lower clad layer 4 in the longitudinal direction. A core layer 12, 12 made of a resin (EO polymer) having an electro-optical effect is formed along with a spin coater or the like, and a rib type optical waveguide 13 protruding downward is formed on a part of the core layer 12. A signal electrode (electrode layer) 14 and a ground electrode (electrode layer) 15 made of a conductive material, which are formed on the lower clad layer 4 and sandwich the core layer 12 from both sides, are provided by metal plating or the like. The points are different.

JP, 2009-145475, A JP, 2007-25370, A Japanese Patent Publication No. 10-504664

By the way, in the case of an optical waveguide device having a microstrip structure as the modulation electrode, if the thickness of the cladding layer is increased, the electric field value effectively applied to the light wave propagating in the optical waveguide is decreased, and as a result, the driving voltage is increased. There was a problem.
Therefore, in order to solve this problem, an optical waveguide device having a buried coplanar structure (In-plane CPW) in which a modulation electrode is buried between upper and lower cladding layers has been proposed.
Compared with the case where the modulation electrode has a microstrip structure, such an optical waveguide element can directly apply an electric field to the optical waveguide through which the light wave propagates, and therefore has a higher performance than the modulation electrode having a macrostrip structure. The advantage is that efficient modulation is possible.

However, even in the optical waveguide device having such a configuration, there is a problem that the drive voltage varies greatly among products. Further, in order to suppress the variation of the driving voltage between products, it is necessary to control the thickness of the clad layer in the submicron unit, but it is difficult to control the thickness of the clad layer in the submicron unit. There was a problem.

The present invention has been made in view of the above circumstances, in which the variation of the driving voltage between the optical waveguide elements is controlled without controlling the thickness of each of the pair of cladding layers sandwiching the core layer from the vertical direction by submicron. An object is to provide an optical waveguide device that suppresses

As a result of intensive studies to solve the above problems, the present inventors have found that a first clad layer formed on a substrate and a material having an electro-optical effect formed on the first clad layer. And an electrode layer formed on the first clad layer so as to sandwich the core layer, and a second clad layer formed so as to cover the core layer and the electrode layer. In the waveguide element, if the thickness of the second clad layer is 10 μm or more, it is not necessary to control the thickness of the clad layer in the submicron unit when the clad layer is manufactured, and the driving voltage between the optical waveguide elements is not required. The inventors have found that it is possible to suppress the variation of the above, and have completed the present invention.

That is, the optical waveguide element of the present invention comprises a first clad layer formed on a substrate, a core layer made of a material having an electro-optical effect formed on the first clad layer, and the first clad layer. An optical waveguide device comprising: an electrode layer formed on a clad layer so as to sandwich the core layer; and a second clad layer formed so as to cover the core layer and the electrode layer. The clad layer has a thickness of 10 μm or more.

The thickness of the second cladding layer is preferably 15 μm or more.
The thickness of the first cladding layer is preferably 10 μm or more.
The thickness of the second cladding layer is preferably thicker than the thickness of the first cladding layer.
The material is preferably resin.

According to the optical waveguide element of the present invention, by controlling the thickness of the second cladding layer to 10 μm or more, it is not necessary to control the thickness of the cladding layer in units of submicrons, and the driving voltage between the optical waveguide elements can be reduced. Can be suppressed.

It is sectional drawing which shows the optical waveguide element of the 1st Embodiment of this invention. It is sectional drawing which shows the optical waveguide element of the 2nd Embodiment of this invention. It is a figure which shows the relationship between the thickness of the lower clad layer of the optical waveguide device of the 1st Embodiment of this invention, and the standardization voltage. It is a figure which shows the thickness of the upper clad layer of the optical waveguide device of the 1st Embodiment of this invention, and the relationship of standardized voltage. It is sectional drawing which shows an example of the conventional optical waveguide element which made the modulation electrode the microstrip structure. FIG. 11 is a cross-sectional view showing an example of a conventional optical waveguide device having a buried electrode and a modulation electrode.

A mode for carrying out the optical waveguide device of the present invention will be described.
The following embodiments are specifically described in order to better understand the spirit of the invention, and do not limit the invention unless otherwise specified.

[First Embodiment]
FIG. 1 is a cross-sectional view showing an optical waveguide device 21 having a buried coplanar structure with a modulation electrode according to a first embodiment of the present invention, and like the optical waveguide devices 1 and 11 described above, in order to make the description easy to understand. , The dimensions of each component are different from the actual ones. The two optical waveguides 6 are optical waveguides that are bifurcated in the Mach-Zehnder optical waveguide.
Further, the same components as those of the above-mentioned optical waveguide devices 1 and 11 are designated by the same reference numerals.

In this optical waveguide element 21, a lower clad layer (first clad layer) 22 is formed on the surface (one main surface) of a substrate 2 made of silicon or the like having a rectangular plate shape, and the lower clad layer 22 is formed on the lower clad layer 22. Core layers 12 and 12 made of a resin (EO polymer) having an electro-optical effect are formed by a spin coater or the like along the longitudinal direction of the lower clad layer 22, and a part of these core layers 12 protrudes downward. Ribs 13 are formed, and a signal electrode (electrode layer) 14 and a ground electrode (electrode layer) 15 formed of a conductive material on the lower cladding layer 22 and sandwiching the core layer 12 from both sides are formed of a conductive material. An upper clad layer (second clad layer) 23 is formed so as to cover the core layers 12, 12, the signal electrode 14, and the ground electrode 15.

Here, as the resin (EO polymer) having the electro-optical effect that constitutes the core layer 12, for example, acrylic resin such as polymethylmethacrylate, epoxy resin, polyimide resin, silicone resin, polystyrene resin, polyamide Examples of the resin include a resin, a polyester resin, a phenol resin, a polyquinoline resin, a polyquinoxaline resin, a polybenzoxazole resin, a polybenzothiazole resin, and a polybenzimidazole resin.
If necessary, inorganic fine particles or other components may be added to the above polymer to adjust the refractive index, mechanical properties, etc. of the polymer.

Examples of the conductive material forming the signal electrode 14 and the ground electrode 15 include gold or its alloy, platinum or its alloy, silver or its alloy, copper or its alloy, aluminum or its alloy, and the like. When these metals or their alloys are applied to the signal electrode 14 and the ground electrode 15, the signal electrode 14 and the ground electrode 15 may be made of the same conductive material or different conductive materials. .

As a material for forming the lower clad layer 22 and the upper clad layer 23, since the high frequency characteristics of the optical waveguide element 21 can be secured and the light wave can be favorably confined in the optical waveguide 13, the dielectric constant is low and the core layer is A material having a lower refractive index than the material used for the above, for example, a resin such as a silicone resin, a fluororesin, an epoxy resin, or a polyimide resin is preferable.

The thickness t1 of the upper clad layer 23 may be within a range that satisfies the mechanical characteristics of the optical waveguide device 21 and the function as an optical waveguide, and is preferably 10 μm or more, more preferably 15 μm or more. ..
Here, the thickness t1 of the upper clad layer 23 is limited to 10 μm or more. When the thickness t1 is less than 10 μm, it is difficult to control the thickness of the upper clad layer 23 in units of submicron, and thus the upper portion This is because the accuracy of the thickness of the clad layer 23 decreases, which is not preferable.

Further, the thickness t2 of the lower clad layer 22 may be within a range that satisfies the mechanical characteristics of the optical waveguide element 21 and the function as an optical waveguide, but the thickness t2 of the lower clad layer 22 is set to 10 μm or more. It is possible to suppress the variation of the driving voltage caused by the variation. This is because when the thickness t2 of the lower clad layer 22 is 10 μm or more, the change of the driving voltage with respect to the change of the thickness t2 of the lower clad layer 22 becomes gradual.
By doing so, it becomes possible to fabricate the optical waveguide device 21 with a small variation in the driving voltage characteristic without controlling the submicron film thickness with high accuracy.

In the upper clad layer 23 and the lower clad layer 22, the thickness of the upper clad layer 23 is preferably larger than the thickness of the lower clad layer 22.
In general, the upper clad layer 23 and the lower clad layer 22 may have the same thickness due to the ease of design and manufacturing. However, by making the thickness of the upper clad layer 23 thicker than the thickness of the lower clad layer 22, the driving voltage can be further reduced.
Here, in order to realize a larger reduction of the driving voltage, the thickness of the upper clad layer 23 is preferably 10 to 20 μm.

Thus, the thickness of the upper clad layer 23 is 10 μm or more, preferably 15 μm or more, the thickness of the lower clad layer 22 is 10 μm or more, and the thickness of the upper clad layer 23 is larger than that of the lower clad layer 22. Thus, the driving voltage can be reduced as compared with the conventional optical waveguide device having the embedded coplanar structure with the modulation electrode.
Moreover, since it is not necessary to control the thickness of each of the upper clad layer 23 and the lower clad layer 22 to a thickness of submicron, it is possible to manufacture the upper clad layer 23 and the lower clad layer 22 with good reproducibility.

As described above, according to the optical waveguide device 21 of the present embodiment, the thickness of the upper clad layer 23 formed so as to cover the core layer 12, the signal electrode 14, and the ground electrode 15 is set to 10 μm or more. By controlling the thickness of the cladding layer 23, the driving voltage can be reduced as compared with the conventional optical waveguide device having the embedded coplanar structure with the modulation electrode.
Further, by controlling the thickness t1 of the upper clad layer 23 to be 10 μm or more, it is possible to suppress the variation of the driving voltage caused by the variation of the thickness t2 of the lower clad layer 22.

[Second Embodiment]
FIG. 2 is a sectional view showing an optical waveguide device 31 having a buried coplanar structure with a modulation electrode according to a second embodiment of the present invention. The dimensions of the components are different from the actual ones. The two optical waveguides 32 are optical waveguides that are bifurcated in the Mach-Zehnder optical waveguide.
Further, the same components as those of the above optical waveguide device 21 are designated by the same reference numerals.

The optical waveguide device 31 of the present embodiment differs from the optical waveguide device 21 of the first embodiment in that the optical waveguide device 21 of the first embodiment projects downward in a part of the core layer 12. While the rib 13 is formed, in the optical waveguide element 31 of the present embodiment, the rib 32 protruding upward is formed in a part of the core layer 12, and the other constituent elements are This is exactly the same as the optical waveguide device 21 of the first embodiment.

The optical waveguide element 31 of the present embodiment can also achieve the same actions and effects as the optical waveguide element 21 of the first embodiment.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Example 1]
FIG. 3 shows the thickness of the lower clad layer 22 and the standardized drive when the drive voltage Vπ is standardized (normalized drive voltage Vπ) when the thicknesses of the upper clad layer 23 and the lower clad layer 22 are 4 μm, respectively. It is a figure which shows the relationship with voltage Vπ.
Here, in the optical waveguide device 21, when the thickness of the upper clad layer 23 is changed in 7 ways of 2 μm, 4 μm, 5 μm, 7.5 μm, 10 μm, 15 μm and 20 μm, the upper clad layer 23 has different thicknesses. On the other hand, the relationship between the thickness of the lower clad layer 22 and the standardized drive voltage Vπ when the thickness of the lower clad layer 22 is changed in 7 ways of 2 μm, 4 μm, 5 μm, 7.5 μm, 10 μm, 15 μm, and 20 μm. Shows.

FIG. 4 shows the thickness of the upper clad layer 23 and the standardized drive when standardized (normalized drive voltage Vπ) based on the drive voltage Vπ when the thicknesses of the upper clad layer 23 and the lower clad layer 22 are 4 μm, respectively. It is a figure which shows the relationship with voltage Vπ.
Here, in the optical waveguide device 21, when the thickness of the lower clad layer 22 is changed in 7 ways of 2 μm, 4 μm, 5 μm, 7.5 μm, 10 μm, 15 μm, and 20 μm, the lower clad layer 22 has different thicknesses. On the other hand, the relationship between the thickness of the upper clad layer 23 and the standardized drive voltage Vπ when the thickness of the upper clad layer 23 is changed in 7 ways of 2 μm, 4 μm, 5 μm, 7.5 μm, 10 μm, 15 μm, and 20 μm. Shows.

According to FIG. 3, when the thickness of the upper clad layer 23 is constant, the normalized drive voltage Vπ increases as the thickness of the lower clad layer 22 increases, but the thickness of the lower clad layer 22 changes. It can be seen that the variation of the standardized drive voltage Vπ with respect to is small.
In particular, when the thickness of the lower clad layer 22 is 10 μm or more, the fluctuation of the standardized drive voltage Vπ with respect to the change of the thickness of the lower clad layer 22 is very small, and it is not necessary to control the thickness of the lower clad layer 22 in the submicron range. Therefore, it is understood that the optical waveguide device can be easily manufactured.

According to FIG. 4, when the thickness of the lower clad layer 22 is constant, the normalized drive voltage Vπ decreases as the thickness of the upper clad layer 23 increases, and the thickness of the upper clad layer 23 decreases. It can be seen that the variation of the standardized drive voltage Vπ with respect to the change is also small.
In particular, when the thickness of the upper clad layer 23 is 10 μm or more, the fluctuation of the standardized drive voltage Vπ with respect to the change of the thickness of the upper clad layer 23 is very small, and it is not necessary to control the thickness of the upper clad layer 23 by submicron. Therefore, it is understood that the optical waveguide device can be easily manufactured.

Further, when the thickness of the upper clad layer is 15 μm or more, the fluctuation of the standardized drive voltage Vπ with respect to the change of the thickness of the upper clad layer 23 becomes further smaller, so that the control of the thickness of the upper clad layer 23 becomes easier. I understand.

Further, FIG. 4 also shows a characteristic curve when the thicknesses of the upper cladding layer 23 and the lower cladding layer 22 are the same, which is a simple structure. As can be seen from FIG. 4, when the thickness of the upper cladding layer 23 is thicker than the thickness of the lower cladding layer 22, the normalized drive voltage Vπ can be further reduced. In this case, by controlling the thickness of the upper clad layer 23 to be in the range of 10 to 20 μm, compared with an optical waveguide device in which the thickness of the upper clad layer 23 and the thickness of the lower clad layer 22 are the same, which is a general configuration. Thus, it can be seen that a larger reduction of the standardized drive voltage Vπ can be realized.

Although the configuration of the optical waveguide has been described here as a Mach-Zehnder optical waveguide, the present invention is not limited to this. As long as the configuration is such that the signal electrode and the ground electrode are formed so as to sandwich the optical waveguide from both sides, it can be applied to a configuration having one optical waveguide or three or more optical waveguides.

The optical waveguide device of the present invention comprises a first clad layer formed on a substrate, a core layer formed on the first clad layer and made of a resin having an electro-optical effect, and the first clad layer. An optical waveguide device comprising: an electrode layer formed above and sandwiching the core layer; and a second clad layer formed so as to cover the core layer and the electrode layer. Since the thickness of the clad layer is 10 μm or more, it is not necessary to control the thickness of the clad layer in the unit of submicron, and it is possible to suppress the variation of the driving voltage between the optical waveguide elements. In addition to the optical waveguide element used for the above, the degree of freedom in design can be increased and its industrial value is great even in an optical device that requires high frequency and high integration.

21 optical waveguide device 2 substrate 12 core layer 13 rib protruding downward 14 signal electrode (electrode layer)
15 Ground electrode (electrode layer)
22 Lower clad layer (first clad layer)
23 Upper clad layer (second clad layer)
31 optical waveguide element 32 rib protruding upward

Claims (5)

Forming a first cladding layer formed on the substrate;
Forming a core layer made of a resin having an electro-optical effect on the first cladding layer;
Forming a signal electrode and a ground electrode sandwiching the core layer on the first clad layer from both sides in the surface direction of the upper surface of the first clad layer;
And a step of forming a second clad layer using a resin material having a refractive index lower than that of the resin so as to cover upper surfaces of the core layer, the signal electrode, and the ground electrode. And
A method of manufacturing an optical waveguide device, characterized in that the thickness of the second cladding layer is formed to 10 μm or more. The method of manufacturing an optical waveguide device according to claim 1, wherein a rib, a part of which protrudes in a stacking direction of the first cladding layer and the second cladding layer, is formed on the core layer. 3. The method for manufacturing an optical waveguide device according to claim 1, wherein the second clad layer is formed to have a thickness of 15 μm or more. 4. The method for manufacturing an optical waveguide device according to claim 1, wherein the first clad layer is formed to have a thickness of 10 μm or more. 5. The method of manufacturing an optical waveguide device according to claim 1, wherein the second clad layer is formed to have a thickness larger than that of the first clad layer.

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