JP6825457B2 - Electro-optic element - Google Patents

Description

The present invention relates to an electro-optical element.

In recent years, with the progress of high-speed and large-capacity optical fiber communication systems, electro-optical elements using waveguide-type optical elements, as represented by external modulators, have been put into practical use and widely used. There is. As such an electro-optical element, a polymer waveguide layer formed by using an organic polymer material (organic electro-optical polymer) having an electro-optical effect is formed by a signal electrode and a lower ground electrode formed of a metal material or the like. A structure sandwiched from the vertical direction is known (see, for example, Patent Document 1).

JP-A-2009-145475

The electro-optical element as described above may be used in a high temperature environment, such as when the installation environment is high temperature or when devices arranged around the device generate heat for driving. In such a case, since the amount of thermal expansion differs between the organic electro-optical polymer forming the polymer waveguide layer and the metal material forming the signal electrode, there is a difference in the amount of thermal expansion between the waveguide layer and the signal electrode. It will occur. Due to this difference in the amount of thermal expansion, strain may occur in the waveguide layer.

Further, when an electro-optical element is used, resistance heat generation due to energization may occur at the electrode, and such heat may also cause distortion of the waveguide layer. Further, the heat applied to the electro-optical element at the time of manufacturing the element or mounting the electro-optical element can also be a cause of the distortion of the waveguide layer.

Here, the difference in the amount of thermal expansion between the organic electro-optical polymer and the metal material is given as an example, but not limited to the metal material, a material having a difference in the amount of thermal expansion from the organic electro-optical polymer is used as an electrode forming material. In the electro-optical element used as the above, the same problem may occur.

In an electro-optical device having a polymer waveguide layer, distortion of the polymer waveguide layer may lead to deterioration of the optical propagation characteristics of the device, that is, light loss. Therefore, improvement was required.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electro-optical element in which light loss is unlikely to occur.

In order to solve the above problems, one aspect of the present invention includes a substrate, a waveguide layer containing an organic polymer material having an electro-optical effect as a forming material and provided with an optical waveguide, and the substrate and the waveguide. A ground electrode provided between the layers, a band-shaped signal electrode provided on the waveguide layer, and a stress relaxation layer provided between the signal electrode and the waveguide layer are provided. The signal electrode is planarly overlapped with a part of the optical waveguide, and the stress relaxation layer is provided at least in a region where the signal electrode and the optical waveguide are planarly overlapped, and is a material for forming the stress relaxation layer. Provided is an electro-optical element having a thermal expansion coefficient larger than the thermal expansion coefficient of the material for forming the waveguide layer.

In one aspect of the present invention, the waveguide layer has a core layer including the optical waveguide and a clad layer made of a material having a refractive index lower than that of the core layer forming material. At least one of the core layer and the clad layer uses the organic polymer material having the electro-optical effect as a forming material, and the coefficient of thermal expansion of the forming material of the stress relaxation layer is the thermal expansion coefficient of each layer constituting the waveguide layer. The configuration may be larger than the maximum value of the coefficient of thermal expansion of the forming material.

In one aspect of the present invention, the stress relaxation layer may be provided in a region that is planarly overlapped with the signal electrode.

In one aspect of the present invention, the stress relaxation layer may be provided on the entire upper surface of the waveguide layer.

In one aspect of the present invention, the glass transition temperature of the stress relaxation layer may be lower than the glass transition point of the material for forming the waveguide layer.

According to the present invention, it is possible to provide an electro-optical element in which light loss is unlikely to occur.

The schematic perspective view which shows the electro-optical element which concerns on this embodiment. Explanatory drawing which shows the laminated structure of an electro-optical element. The figure which shows the deformation example of an electro-optical element. The figure which shows the deformation example of an electro-optical element. The figure which shows the deformation example of an electro-optical element.

Hereinafter, the electro-optical element 100A according to the present embodiment will be described with reference to FIGS. 1 to 5. In all the drawings below, the dimensions and ratios of the components are appropriately different in order to make the drawings easier to see.

FIG. 1 is a schematic perspective view showing an electro-optical element 100A according to the present embodiment. FIG. 2 is an explanatory view showing a laminated structure of the electro-optical element 100A, and is a cross-sectional view taken along the arrow in line segments II-II of FIG.

As shown in FIGS. 1 and 2, the electro-optical element 100A of the present embodiment includes a substrate 50, a waveguide layer 1, a signal electrode 5, a lower ground electrode (ground electrode) 9, and a stress relaxation layer 10. It has.

The waveguide layer 1 includes an inverted ridge type optical waveguide 1A having a convex shape on the substrate 50 side.

Further, in the signal electrode 5 and the lower ground electrode 9, the structure of the region in which the electric signal acts on the propagating light propagating in the optical waveguide 1A is a microstrip line (MSL). Further, in the signal electrode 5 and the lower ground electrode 9, the input portion of the electric signal is a coplanar line (CPW). That is, the signal electrode 5 and the lower ground electrode 9 are CPW-MSL conversion circuits as a whole.

The electro-optical element 100A is an optical modulator having a rectangular shape in a plan view and having a CPW-MSL conversion circuit.
Hereinafter, each configuration will be described in detail.

(substrate)
The material and shape of the substrate 50 are not particularly limited as long as they have sufficient flatness to form an optical waveguide and mechanically have sufficient strength. As the substrate 50, for example, a silicon substrate, a quartz substrate, a glass substrate, a ceramic substrate, or the like can be used. Further, as the substrate 50, a silicon substrate or a quartz substrate is preferable.

The thickness of the substrate 50 is, for example, about 0.3 to 2 mm.

(Wife path layer)
A waveguide layer 1 containing an organic electro-optical polymer as a forming material is formed above the substrate 50. The waveguide layer 1 has an optical waveguide 1A.

The waveguide layer 1 is composed of a core layer 2, a lower clad layer 3 and an upper clad layer 4. The core layer 2 is sandwiched between the lower clad layer 3 and the upper clad layer 4.

The core layer 2, the lower clad layer 3 and the upper clad layer 4 each contain at least one kind of organic polymer material. As the organic polymer material, any material having a high transmittance for light propagating through the optical waveguide 1A can be used.

Further, the refractive index of the core layer 2 is higher than the refractive index of the lower clad layer 3 and the upper clad layer 4. As a result, the light propagating through the optical waveguide 1A propagates in the core layer 2.

Examples of the organic polymer material include acrylic resins such as polymethylmethacrylate, epoxy resins, polyimide resins, silicone resins, polystyrene resins, polyamide resins, polyester resins, phenolic resins, and polyquinolin resins. , Polyquinoxaline resin, polybenzoxazole resin, polybenzothiazole resin, polybenzoimidazole resin and the like.

If necessary, other components such as organic fine particles and inorganic fine particles are added to the organic polymer material to adjust the refractive index and mechanical properties of the lower clad layer 3, the core layer 2 and the upper clad layer 4. It is possible to do.

At least one layer of the core layer 2, the lower clad layer 3 and the upper clad layer 4 is made of an organic polymer material having an electro-optical effect as a forming material. Specifically, at least one layer of the core layer 2, the lower clad layer 3 and the upper clad layer 4 contains an organic compound exhibiting non-linear optical characteristics (hereinafter, referred to as “non-linear optical organic compound”). This makes it possible to impart an electro-optical effect to the waveguide layer 1.

The nonlinear optical organic compound can be introduced into the organic polymer material by addition to the above-mentioned organic polymer material or by chemical bonding to the side chain or main chain of the above-mentioned organic polymer material.

The nonlinear optical organic compound is not particularly limited as long as it is known, but an atomic group having an electron donating property (hereinafter referred to as “donor”) and an atomic group having an electron attracting property (hereinafter referred to as “donor”) in one molecule are not particularly limited. , "Acceptor"), and a molecule having a structure in which an atomic group of a π-electron conjugate system is arranged between a donor and an acceptor is desirable. Specific examples of such molecules include Disperse Reds, Disperse Oranges, stilbene compounds and the like.

The core layer 2, the lower clad layer 3, and the upper clad layer 4 are coated on the substrate 50 by a known coating method using a solution prepared by dissolving the above-mentioned organic polymer material and nonlinear optical organic compound in an organic solvent. Can be formed with. As the coating method, known techniques such as a spin coating method, a spray coating method, a dip coating method, an printing method, a screen printing method, and a doctor blade method can be used, and the spin coating method and the like are particularly preferable.

The organic solvent can be freely selected from alcohols, ketones, esters, ethers, aromatic hydrocarbons, aliphatic hydrocarbons and the like in consideration of solubility and film forming property. These organic solvents may be used alone or in combination of two or more.

After applying the above solution, it is preferable to dry the obtained coating film. Drying may be performed by blowing air, reducing the pressure, heating, or a combination thereof.

(Expression of electro-optical effect)
The optical waveguide 1A obtained by laminating the core layer 2, the lower clad layer 3, and the upper clad layer 4 in this manner is subjected to a process (polling) for orienting the nonlinear optical organic compound contained in the waveguide layer 1. As a result, the electro-optical effect is exhibited.

Specifically, the waveguide layer 1 is heated to a temperature near the glass transition point based on the glass transition point Tg of the organic polymer material containing the nonlinear optical organic compound. In the heated state, an electric field of 50 V / μm or more, preferably 80 V / μm or more is applied to the layer containing the nonlinear optical organic compound, and the layer is cooled to room temperature while maintaining the voltage application. As a result, the waveguide layer 1 has an electro-optical constant (EO constant) in the range of 10 to 300 pm / V.

In the waveguide layer 1, the thickness of the core layer 2 is preferably 0.1 μm or more and 10.0 μm or less, and the thickness of the lower clad layer 3 and the upper clad layer 4 is preferably 0.5 μm or more and 20.0 μm or less. The thickness of each of these layers may be appropriately controlled according to (i) the wavelength of light to be propagated and (ii) the refractive index of the core layer 2, the lower clad layer 3 and the upper clad layer 4.

The waveguide layer 1 has an inverted ridge type optical waveguide 1A having a convex shape toward the substrate 50 side. In the ridge type optical waveguide 1A, first, a trench 31 to be a ridge portion of the optical waveguide 1A is formed in the lower clad layer 3 by dry etching or the like, and then a core layer 2 is formed in the lower clad layer 3 in which the trench 31 is formed. Can be formed by laminating.

The shape of the optical waveguide 1A is not particularly limited, and examples thereof include a slab type, a channel type, a ridge type, and a rib type.

In the electro-optical element 100A of the present embodiment, the optical waveguide 1A is formed linearly in the longitudinal direction of the element in a plan view. However, the electro-optical element 100A of the present invention is not limited to a linear element, and has various forms such as a Y-branch type element, a directional coupling type element, a Mach-Zehnder interference type element, a Fabry-Perot resonator type element, and a polarization reversal type element. -Can be used according to the application.

(electrode)
The electro-optical element 100A of the present embodiment has a signal electrode 5, a lower ground electrode (ground electrode) 9, and upper ground electrodes 6 to 8 electrically connected to the lower ground electrode 9.

The signal electrode 5 is a band-shaped electrode provided on the waveguide layer 1. The signal electrode 5 is planarly overlapped with a part of the optical waveguide 1A, and an electric signal is applied to the light propagating in the optical waveguide 1A to modulate the light. Further, the signal electrode 5 is partially bent, and the ends 5a and 5b extend in the same direction as the optical waveguide 1A. The ends 5a and 5b are arranged on the peripheral edge of the electro-optical element 100A.

The upper grounding electrodes 6 to 8 are formed on the surface of the upper clad layer 4 and are electrically connected to the lower grounding electrode 9 described later. The upper ground electrodes 6 and 7 are arranged so as to sandwich the end portion 5a of the signal electrode 5. Further, the upper ground electrodes 7 and 8 are arranged so as to sandwich the end portion 5b of the signal electrode 5. As the material for forming the upper ground electrodes 6 to 8, the same material as the signal electrode 5 can be used.

The lower ground electrode 9 is provided between the substrate 50 and the waveguide layer 1. As the material for forming the lower ground electrode 9, the same material as the signal electrode 5 can be used.

The lower ground electrode 9 has a polygonal notch 9a formed at a position where the ends 5a and 5b overlap in a plane. In the figure, the shape of the notch 9a is shown as a pentagon.

The signal electrode 5, the upper ground electrode 6 to 8, and the lower ground electrode 9 are made of, for example, a conductive inorganic material.
The signal electrode 5, the upper ground electrode 6 to 8, and the lower ground electrode 9 are made of a material having good conductivity at high frequencies, for example, gold (Au), silver (Ag), copper (Cu), platinum (Pt), rhodium. It is possible to use one containing one or more selected from the group of (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and aluminum (Al). , Practically preferable.

The material of the signal electrode 5 and the lower ground electrode 9 may be good as long as it has good conductivity, and is not limited to metal. Although the operating temperature of the device is limited, a superconducting material may be used.

In order to increase the electric field of the high frequency signal applied to the optical waveguide, it is effective to thin the lower clad layer 3 and the upper clad layer 4 to reduce the distance between the signal electrode 5 and the lower ground electrode 9, but the optical waveguide is used. With increased loss of propagating light. As a method for reducing this light loss, a conductive material having both a small light absorption loss and good conductivity, that is, a so-called transparent electrode material, can be used for the signal electrode 5 lower ground electrode 9. As such a conductive material, a transparent electrode made of tin-added indium tin oxide (ITO), antimony-added indium oxide (Antimony Tin Oxide: ATO), tin oxide (SnO ₂ ), or the like is preferable.

The film thickness of the signal electrode 5, the upper ground electrode 6 to 8, and the lower ground electrode 9 is preferably 1 μm or more in consideration of the skin effect in the high frequency signal.

The width of the signal electrode 5 may be wider than the width of the optical waveguide 1A formed in the core layer 2 in order to ensure good electric field efficiency, and is not particularly limited. In order to ensure good high-frequency response of the device, it is necessary to design the electrode width and thickness so that the characteristic impedance is suitable for a high-frequency line, considering the dielectric constant and thickness of the materials of the core layer and clad layer. preferable. Like the electro-optical element shown in FIG. 1, the lower ground electrode 9 may be partially cut out in order to adjust the characteristic impedance.

The stress relaxation layer 10 is provided between the signal electrode 5 and the waveguide layer 1. In the present embodiment, the stress relaxation layer 10 is provided at least in a region where the signal electrode 5 and the optical waveguide 1A overlap in a plane.

The coefficient of thermal expansion of the material for forming the stress relaxation layer 10 is designed to be larger than the coefficient of thermal expansion of the material for forming the waveguide layer 1. Therefore, even when the electro-optical element 100A is used in a high temperature environment, the waveguide layer 1 made of an organic electro-optical polymer and the signal electrode 5 made of a metal material or a conductive metal oxide are used as a forming material. It is possible to suppress the strain caused by the difference in the amount of thermal expansion with. As a result, it is possible to suppress problems such as deterioration of the characteristics of the optical waveguide 1A and peeling of the optical waveguide layer 1.

When the waveguide layer 1 has a laminated structure of a plurality of layers as in the electro-optical element 100A of the present embodiment, the coefficient of thermal expansion of the material for forming the stress relaxation layer 10 is the coefficient of thermal expansion of the material for forming the core layer 2. It is designed to be larger than the maximum value of the coefficient of thermal expansion of the forming material of the lower clad layer 3 and the upper clad layer 4.

As the material for forming the stress relaxation layer 10, the resin material exemplified as the material for forming the core layer 2, the lower clad layer 3, and the upper clad layer 4 can be preferably used. From the above resin materials, the material for forming the stress relaxation layer 10 may be selected based on the relationship with the coefficient of thermal expansion of the material for forming the waveguide layer 1.

Further, the glass transition point of the stress relaxation layer 10 is preferably lower than the glass transition point of the material for forming the waveguide layer 1.

The stress relaxation layer 10 can be formed on the surface of the waveguide layer 1 by using a commonly known film forming technique.
The electro-optical element 100A of the present embodiment has the above configuration.

The electro-optical element 100A having the above configuration is high-performance with little optical loss because distortion of the optical waveguide 1A due to the difference in thermal expansion coefficient between the waveguide layer 1 and the signal electrode 5 is unlikely to occur.

Further, the electro-optical element 100A has a structure in which a stress relaxation layer 10 is provided directly under the signal electrode 5. Therefore, it is easy to relieve the stress generated at the interface between the signal electrode 5 and the waveguide layer 1. In particular, in the signal wiring for inputting a high frequency signal, the width of the signal electrode 5 in the field of view of FIG. 2 (the width of the waveguide layer 1 in the plane direction in the field of view of FIG. 2) is as narrow as several μm to several tens of μm. In addition, as shown in FIG. 1, the signal wiring for inputting a high frequency signal has a shape having a partially curved portion.

Such signal wiring tends to generate a local stress difference and tends to cause distortion around the signal wiring. Therefore, the optical waveguide formed directly under such a signal wiring is easily affected by the distortion generated in the vicinity of the signal wiring.

The configuration of this embodiment is highly effective in an electro-optical element having such a thin signal electrode 5.

In this embodiment, as an example, the stress relaxation layer 10 is formed on the upper surface of the waveguide layer 1 as shown in FIGS. 1 and 2, and at least in the region where the signal electrode 5 and the optical waveguide 1A overlap in a plane. The configuration is provided, but the configuration is not limited to this.

3 to 5 are diagrams showing a modified example of the electro-optical element. FIG. 3 is a schematic cross-sectional view corresponding to FIG. 2 described above. 4 and 5 are schematic perspective views corresponding to FIG. 1.

First, in the present embodiment, the stress relaxation layer 10 is formed on the upper surface of the waveguide layer 1, but the upper surface of the waveguide layer 1 is partially dug down as in the electro-optical element 100B shown in FIG. A stress relaxation layer may be embedded inside the formed recess.

Further, in the present embodiment, the signal electrode 5 and the optical waveguide 1A are provided at least in a region where they overlap in a plane, but as in the electro-optical element 100C shown in FIG. The stress relaxation layer 11 may be provided in the plane-overlapping regions. In the electro-optical element 100C, a stress relaxation layer 11 is always provided below the signal electrode 5. As the stress relaxation layer 11, the same forming material as the stress relaxation layer 10 described above can be adopted.

In such a configuration, since the stress relaxation layer 10 is always present at the position where the signal electrode 5 is formed, the electrical characteristics around the signal electrode 5 are changed as compared with the electro-optical element 100A of FIGS. Difficult to do. Therefore, the electro-optical element 100C is preferable because, in addition to the effect of the electro-optical element 100A, impedance matching when supplying a signal current to the signal electrode 5 is facilitated.

Further, the stress relaxation layer 12 may be formed on the entire upper surface of the waveguide layer 1 as in the electro-optical element 100D shown in FIG. As the stress relaxation layer 12, the same forming material as the stress relaxation layer 10 described above can be adopted. The electro-optical element 100D is preferable because it easily forms the stress relaxation layer 12 in addition to the effects of the electro-optical elements 100A and 100C.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. The various shapes and combinations of the constituent members shown in the above-mentioned example are examples, and can be variously changed based on design requirements and the like within a range not deviating from the gist of the present invention.

1 ... Waveguide layer, 1A ... Optical waveguide, 2 ... Core layer, 3 ... Lower clad layer (clad layer), 4 ... Upper clad layer (clad layer), 5 ... Signal electrode, 9 ... Lower ground electrode (ground electrode) 10, 11, 12 ... Stress relaxation layer, 50 ... Substrate, 100A-100D ... Electro-optical element

Claims (4)

With the board
A waveguide layer containing an organic polymer material having an electro-optical effect as a forming material and provided with an optical waveguide,
A ground electrode provided between the substrate and the waveguide layer,
A band-shaped signal electrode provided on the waveguide layer and
A stress relaxation layer provided between the signal electrode and the waveguide layer is provided.
The signal electrode overlaps a part of the optical waveguide in a plane, and
The stress relaxation layer is provided at least in a region where the signal electrode and the optical waveguide overlap in a plane.
Thermal expansion coefficient of the material for forming the stress relieving layer is much larger than the thermal expansion coefficient of the material for forming the waveguide layer,
The waveguide layer includes a core layer including the optical waveguide and
It has a clad layer having a material having a refractive index lower than that of the core layer forming material as a forming material.
The clad layer includes a lower clad layer arranged on the substrate side of the core layer and
It has an upper clad layer arranged on the signal electrode side of the core layer.
At least one of the core layer and the clad layer is made of an organic polymer material having the electro-optical effect as a forming material.
An electro-optical element in which the coefficient of thermal expansion of the material for forming the stress relaxation layer is larger than the maximum value of the coefficient of thermal expansion of the material for forming each layer constituting the waveguide layer . The electro-optical element according to claim 1, wherein the stress relaxation layer is provided in a region that overlaps the signal electrode in a plane. The electro-optical element according to claim 2 , wherein the stress relaxation layer is provided on the entire upper surface of the waveguide layer. The electro-optical element according to any one of claims 1 to 3 , wherein the glass transition point of the stress relaxation layer is lower than the glass transition point of the material for forming the waveguide layer.

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