Method for manufacturing optical modulation waveguide element using organic nonlinear optical compound

Abstract

To provide a method for manufacturing an optical modulation element capable of suppressing optical degradation in an optical modulator using an organic electro-optic polymer (EO polymer).SOLUTION: The present invention relates to a method for manufacturing an optical modulation element in which an optical modulator including an optical waveguide containing an organic electro-optic polymer is housed and sealed within a housing, the method including: a first step of accommodating the optical modulator inside the housing and reducing pressure at least inside the housing; and a second step of sealing the housing under the reduced pressure or in an inert gas atmosphere containing at least one gas selected from noble gases and nitrogen.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an optical modulation waveguide element, and more particularly to a method for manufacturing an optical modulation element in which an optical modulator having an optical waveguide containing an organic electro-optic polymer on a substrate is accommodated and sealed inside a housing. [Background technology]

[0002] In recent years, the development of various electronic devices using nonlinear optical materials has been progressing in fields such as optical information processing and optical communications. Among these nonlinear optical materials, those that produce a first-order electro-optic effect (Pockels effect) due to a second-order nonlinear optical effect are expected to be applied to optical switches and optical modulation. Among nonlinear optical materials that have the Pockels effect, inorganic nonlinear optical materials such as lithium niobate have already been put to practical use and are widely used. In addition, as the recent development of the information society requires more advanced information processing, it is expected that organic nonlinear optical materials, such as organic electro-optic polymer materials, which are expected to have excellent performance such as higher nonlinear optical properties and high-speed response, and have better electro-optic effects and broadband characteristics, will be put to practical use instead of conventional inorganic materials. For example, nonlinear optical materials containing acrylic nonlinear optically active copolymers into which a unit having a cycloalkane such as an adamantyl group in the side chain and a unit having an organic dye moiety have been introduced in order to adjust the glass transition temperature, and optical waveguide modulators fabricated using the nonlinear optical materials as the core material of an optical waveguide have been disclosed (e.g., Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-057415 [Patent Document 2] International Publication No. 2017 / 159815 [Patent Document 3] Japanese Patent Publication No. 2023-143173 [Non-patent literature]

[0004] [Non-Patent Document 1] J.Phys.Chem.B.108,8725-8730(2004) [Non-patent document 2] Chem.Mater.20,5047-5054(2008)) Summary of the Invention [Problem to be solved by the invention]

[0005] Various electronic devices using nonlinear optical materials and the materials for them are required to have various resistances that affect the reliability of the electronic devices, such as resistance to high temperatures and high humidity in environments accompanied by high-intensity light irradiation, and resistance to thermal shock. In the case of the above-mentioned organic electro-optical polymer (EO polymer) materials, the mechanism of deterioration when the polymer is irradiated with high-intensity laser light has been pointed out to be oxidation of substances involving oxygen and decomposition by the generated radicals (e.g., Non-Patent Documents 1 and 2). To address the issue of deterioration due to photo-oxidation, for example, an optical integrated circuit module employing an oxygen getter (oxygen adsorption layer) that adsorbs oxygen has been disclosed (Patent Document 3). However, this technology recommends activating the oxygen adsorption layer, which is made of a Zr-containing alloy or the like, by heating it in a vacuum or in an inert gas atmosphere at 300-450°C for 15 minutes or more, and the components and activation devices on which the oxygen getter (oxygen adsorption layer) is provided are required to be heat-resistant to ultra-high temperatures exceeding 300°C. Furthermore, taking into consideration the thermal degradation of EO polymers, if the oxygen adsorption layer comes into contact with oxygen when combined with other components containing EO polymers after activation, the oxygen absorption ability of the oxygen adsorption layer will be impaired. It is difficult to completely remove dissolved oxygen in the EO polymer using an oxygen getter. Furthermore, when a device is miniaturized, it may not be possible to provide a sufficient amount of oxygen getter for deoxidation. To date, no concrete measures have been proposed or demonstrated that are simpler, more feasible, and more effective to resolve the optical degradation of optical modulators using EO polymers.

[0006] An object of the present invention is to provide a method for manufacturing an optical modulation element that can suppress optical degradation in an optical modulator using an organic electro-optic polymer (EO polymer). [Means for solving the problem]

[0007] As a result of extensive research into achieving the above-mentioned object, the inventors discovered that in an optical modulator having an optical waveguide containing an organic electro-optic polymer on a substrate, deterioration of the organic electro-optic polymer can be suppressed by performing vacuum annealing to remove oxygen from the EO polymer and the package, thereby operating the modulator in an oxygen-free state, and thus completed the present invention.

[0008] That is, in a first aspect, the present invention provides a method for manufacturing an optical modulation element in which an optical modulator having an optical waveguide including an organic electro-optic polymer on a substrate is accommodated and sealed inside a housing, a first step of housing the optical modulator in a housing and reducing the pressure inside the housing; a second step of sealing the housing under the reduced pressure or under an inert gas atmosphere of at least one kind selected from a Group 18 element and nitrogen, The present invention relates to a method for manufacturing an optical modulation element. As a second aspect, the present invention relates to the production method according to the first aspect, in which the first step is carried out at a temperature of 80° C. or less. As a third aspect, the organic electro-optical polymer The present invention relates to the production method according to the first aspect, wherein the polymer has an atomic group that exhibits nonlinear optical activity in a side chain, and the atomic group that exhibits nonlinear optical activity is an atomic group having a furan ring group represented by the following formula [3]: [ka] (In the formula, R 10 and R 11each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and the black dot represents a bond to the remaining structure constituting the atomic group that exhibits nonlinear optical activity. As a fourth aspect, the present invention relates to the production method according to the third aspect, wherein the organic electro-optical polymer is a polymer containing at least a repeating unit having a nonlinear optically active moiety represented by the following formula [2]: [ka] (In the formula, R 2 represents a hydrogen atom or a methyl group, L 1 represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain an ether bond and / or an ester bond, L 2 *-NHC(=O)O-, *-C(=O)NH- or *-C(=O)O-(* is L 1 represents the bond end with Z represents an atomic group that exhibits the nonlinear optical activity. As a fifth aspect, the atomic group exhibiting nonlinear optical activity is represented by formula [4] or formula [5] (in these chemical formulas, R 4 ~R 9 wherein one hydrogen atom is removed). [ka] (In the formula, R 4 and R 5 each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, or an optionally substituted aryl group having 6 to 10 carbon atoms; R 6 ~R 9each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, an alkylcarbonyloxy group having 2 to 11 carbon atoms, an aryloxy group having 4 to 10 carbon atoms, an aralkyloxy group having 5 to 11 carbon atoms, an arylcarbonyloxy group having 5 to 11 carbon atoms, a silyloxy group having an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, or a halogen atom; R 10 and R 11 each independently represents the same meaning as above, Ar represents a divalent aromatic group represented by formula [6] or formula [7]. [ka] (In the formula, R 12 ~R 17 each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, or an optionally substituted aryl group having 6 to 10 carbon atoms. As a sixth aspect, the atomic group exhibiting nonlinear optical activity is represented by the formula [4] or the formula [5] (in these chemical formulas, R 4 or R 5 In the fifth aspect, the present invention relates to a production method according to the fifth aspect, wherein the aryl group is an atomic group having a structure represented by the following formula (wherein one hydrogen atom is removed): [Effects of the Invention]

[0009] According to the present invention, it is possible to manufacture an optical modulation element that can suppress optical degradation in an optical modulator using an EO polymer. In particular, according to the present invention, it is possible to manufacture an optical modulation element that can be expected to suppress half-wave voltage change for more than 2000 hours, even when high-intensity light irradiation is performed in the wavelength bands of C band (1530 to 1565 nm) or O band (1260 to 1360 nm) in a high-temperature environment above room temperature, particularly above 80°C. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a schematic cross-sectional view showing one embodiment of a light modulation element. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the waveguide structure of the optical modulator. [Figure 3] FIG. 3 is a conceptual diagram of an apparatus used for analyzing the characteristics of an optical modulator having a waveguide structure manufactured in the example. [Figure 4] FIG. 4 is a diagram showing the relationship between the triangular wave voltage (applied voltage), the change in light intensity (change in emitted light intensity), and the half-wave voltage (Vπ). [Figure 5] FIG. 5 is a diagram showing the results of the optical modulation test (1) carried out in air (changes in the half-wave voltage ratio (Vπ(t) / Vπ(0)) with respect to test time). [Figure 6] FIG. 6 is a conceptual diagram of an apparatus used to analyze the characteristics of an optical modulator in an environment where the influence of oxygen is eliminated. [Figure 7] FIG. 7 is a diagram showing the results of the optical modulation test (2-1) carried out under vacuum (changes in the half-wave voltage ratio (Vπ(t) / Vπ(0)) with respect to test time). [Figure 8] FIG. 8 is a diagram showing the results of the optical modulation test (2-1) carried out under an argon atmosphere (changes in the half-wave voltage ratio (Vπ(t) / Vπ(0)) with respect to test time). [Figure 9] FIG. 9 is a diagram showing the results of the optical modulation test (2-2) carried out under vacuum (changes in the half-wave voltage ratio (Vπ(t) / Vπ(0)) with respect to test time). DETAILED DESCRIPTION OF THE INVENTION

[0011] [Method of manufacturing optical modulation element] The present invention relates to a method for manufacturing an optical modulation element. In the present invention, the optical modulation element is also called an electro-optic element, and is not particularly limited to a particular type as long as it is an optical modulator having an optical waveguide containing an organic electro-optic polymer on a substrate, which is housed inside a housing and sealed.

[0012] The above production method includes the following first and second steps. (1) A method for accommodating an optical modulator in a housing and reducing the pressure inside the housing. 1 process, (2) A second step of sealing the housing under reduced pressure or in an inert gas atmosphere of at least one kind selected from the group consisting of Group 18 elements and nitrogen.

[0013] The first step is to accommodate the optical modulator inside a housing and reduce the pressure inside the housing. The housing is not particularly limited in shape or material as long as it can accommodate the optical modulator, and can be, for example, a combination of a package and a lid for optical communications. The first step is preferably carried out at a temperature of 80°C or less and at a vacuum of 1 x 10 -4 It is preferable to reduce the pressure to less than 1 Pa. Above 1 x 10 -4 A vacuum of 100 Pa or less can be achieved by first using an auxiliary pump such as a rotary pump to reduce the pressure to a pressure range where the vacuum pump (described later) can operate, and then using a high-performance vacuum pump such as a molecular turbo pump (turbomolecular pump), oil diffusion pump, cryopump, titanium getter pump (supplementation pump), or ion pump (sputter ion pump). The JIS standard specifies a vacuum of 1 x 10 -1 Pa~1×10 -5 High vacuum, 1×10 Pa -5 Pa~1×10 -8 Pa is defined as ultra-high vacuum, and the above reduced pressure conditions can be said to be a vacuum level ranging from high vacuum to almost ultra-high vacuum.

[0014] The second step is a step of sealing the housing, and the sealing step is carried out under reduced pressure subsequent to the first step, i.e., vacuum sealing, or in an atmosphere of at least one inert gas selected from Group 18 elements and nitrogen, i.e., hermetically sealing. Among the inert gases, gases selected from the 18th element include helium, neon, argon, krypton, and xenon. Furthermore, it is preferable to use an inert gas (element 18 and nitrogen) with a purity of 98% or more, preferably 99% or more, and more preferably close to 100%. In particular, the second step is preferably carried out under an argon atmosphere.

[0015] In the manufacturing method, for example, an optical modulator is mounted in the package for optical communications, and the surrounding environment is depressurized in a vacuum chamber. Thereafter, the opening of the package is covered and sealed with a lid while the pressure remains reduced in the vacuum chamber, or an inert gas selected from the group consisting of element 18 and nitrogen is introduced into the vacuum chamber, and the opening of the package is covered and sealed with a lid.

[0016] A schematic cross-sectional view of a light modulation element is shown in Fig. 1. Note that the schematic view shown in Fig. 1 is just an example, and the embodiment of the light modulation element according to the present invention is not limited to this. In the optical modulation element 1 shown in FIG. 1, an optical modulator 10 is fixed in a package 2 with an adhesive 7. The optical modulator 10 has a waveguide containing an organic electro-optic polymer on a substrate. The package 2 is covered with a lid 3, and the inside is airtight. That is, in this embodiment, the package 2 and the lid 3 form the housing. An optical fiber 4 optically connected to the optical modulator 10 according to the present invention is drawn to the outside of the package 2 through a hermetic sealing pipe 5. A solder material 6 is filled between the pipe 4 and the package 2, and the periphery of the optical fiber 4 is also hermetically sealed. The device shown in this figure has an optical modulator 10 fixed inside a package 2 with adhesive 7, and then the device is placed in a vacuum chamber or the like to reduce the ambient pressure, and the lid 3 is seam-welded to the top opening of the package 2 in an atmosphere substituted with nitrogen or an 18th element such as argon as necessary. Furthermore, the area around the optical fiber 4 that is pulled out from a pipe 5 to the outside is filled with solder material 6. This results in a device that is vacuum-sealed or hermetically sealed with a gas such as nitrogen gas or argon that is nearly 100% pure.

[0017] [Optical modulator] The optical modulator according to the present invention is not particularly limited as long as it has an optical waveguide containing an organic electro-optic polymer on a substrate, and the organic electro-optic polymer can be a constituent material of the core, clad, or both the core and clad in the optical waveguide.

[0018] An example of an optical modulator according to the present invention is shown in Fig. 2. Note that the structure of the optical modulator shown in Fig. 2 is just an example, and the present invention is not limited to this. FIG. 2 is a schematic cross-sectional view showing the waveguide structure of the optical modulator. 2 has a lower electrode 12, a lower clad 13, an EO polymer layer 14, a silicon film 16, an upper clad 15, and an upper electrode 17 laminated in this order from the substrate 11 side. The silicon film 16 is provided in a strip shape on the EO polymer layer 14, and the upper clad 15 is provided so as to cover the EO polymer layer 14 and the silicon film 16. 2, light propagates around the silicon film 16, and a portion of the light intensity propagates through the EO polymer layer 14. The EO polymer layer 14 is sandwiched between the upper clad 15 and the lower clad 12, forming an optical waveguide structure. When a voltage is applied to the upper electrode 17 and the lower electrode 12 via a power supply 18 to generate an electric field, the refractive index of the EO polymer layer located between these electrodes changes, modulating the intensity of the propagating light (optical modulation). For example, the intensity optical modulator can have a Mach-Zehnder waveguide structure, as described below, but is not limited to this.

[0019] One specific example of an optical modulator that is the subject of the present invention is an optical switching element (optical communication element) such as the Mach-Zehnder optical modulator described above. In a Mach-Zehnder optical modulator, a typical optical switching element, a high-frequency voltage is applied to one or both of the branched optical waveguide structures to exhibit electro-optical properties, changing the refractive index and thereby causing a phase change in the propagating light. This phase change changes the light intensity after branching and combining, enabling high-speed modulation of light. The optical modulator referred to here is not limited to phase and intensity modulation, but can also be applied to, for example, a polarization conversion element, a wave dividing element, and a wave combining element. Furthermore, in addition to the use in communication devices, the present invention also includes applications such as electric field sensors that detect changes in an electric field as changes in refractive index.

[0020] <Organic electro-optic polymers (nonlinear optically active polymers)> The optical waveguide included in the optical modulator according to the present invention is configured to contain an organic electro-optic polymer. The organic electro-optical polymer (also called nonlinear optically active polymer) used in the present invention may be, for example, a polymer having an atomic group that exhibits nonlinear optical activity in its side chain. By incorporating an atomic group that exhibits nonlinear optical activity in the side chain of the polymer, the nonlinear optically active moiety is dispersed throughout the polymer, and it is expected that a material with optically uniform properties can be obtained. The atomic group exhibiting nonlinear optical activity refers to an atomic group derived from an organic nonlinear optical compound. The organic nonlinear optical compound is preferably a π-conjugated compound having an electron-donating group at one end of a π-conjugated chain and an electron-withdrawing group at the other end, and having a large molecular hyperpolarizability β. Examples of the electron-donating group include a dialkylamino group, and examples of the electron-withdrawing group include a cyano group, a nitro group, and a fluoroalkyl group.

[0021] For example, the atomic group exhibiting the nonlinear optical activity is an atomic group having a furan ring group represented by the following chemical formula [3]. [ka]

[0022] In the above formula, R 10 , R 11 each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and a black dot (●) represents a bond to the remaining structure constituting the atomic group that exhibits nonlinear optical activity.

[0023] Specific examples of preferred atomic groups that exhibit the nonlinear optical activity include atomic groups having a functional group derived from a structure represented by the following formula [4], and atomic groups having a functional group derived from a structure represented by the following formula [5]. That is, the atomic groups are those represented by formula [4] or formula [5] (in these chemical formulas, R 4 ~R 9 In one of the above, one hydrogen atom is removed. [ka]

[0024] In the above formula [4] or formula [5], R 4 and R 5 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, or an aryl group having 6 to 10 carbon atoms which may have a substituent. The bond of the atomic group (Z) is 4 or R 5 is preferably a bond obtained by removing one hydrogen atom from

[0025] In the above formula [4] or formula [5], R 6 ~R 9 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, an alkylcarbonyloxy group having 2 to 11 carbon atoms, an aryloxy group having 4 to 10 carbon atoms, an aralkyloxy group having 5 to 11 carbon atoms, an arylcarbonyloxy group having 5 to 11 carbon atoms, a silyloxy group having an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, or a halogen atom.

[0026] In the above formula [4] or formula [5], R 10 and R 11 are each independently expressed in the above formula [3] R in 10 and R 11that is, each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0027] In the above formula [4] or formula [5], Ar represents a divalent aromatic group represented by the following formula [6] or formula [7]. [ka]

[0028] In the above formula [6] and formula [7], R 12 ~R 17 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, or an aryl group having 6 to 10 carbon atoms which may have a substituent.

[0029] Among these, as an atomic group exhibiting nonlinear optical activity, in an atomic group having a functional group derived from the structure represented by the formula [4] or [5], R 4 or R 5 Examples of the structure include those in which one hydrogen atom has been removed from any of the above.

[0030] Examples of the polymer having an atomic group exhibiting nonlinear optical activity in a side chain include a polymer containing at least a repeating unit having a nonlinear optically active moiety represented by the following formula [2]. [ka]

[0031] In the above formula [2], R 2 represents a hydrogen atom or a methyl group. In the above formula [2], L 1 represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain an ether bond and / or an ester bond. In addition, in the above formula [2], L 2*-NHC(=O)O-, *-C(=O)NH- or *-C(=O)O-(* is L 1 represents the bond end with . Among them, L 2 is *-NHC(=O)O-(* is L 1 It is preferable that the bond is a bond end with In the above formula [2], Z represents an atomic group exhibiting nonlinear optical activity, such as an atomic group having a furan ring group represented by the above formula [3], preferably an atomic group having a structure represented by formula [4] or [5] (the definitions in these formulas are as described above).

[0032] The organic electro-optical polymer (e.g., a polymer having an atomic group exhibiting nonlinear optical activity in a side chain) may further contain, in addition to the repeating unit having the nonlinear optically active site, the following repeating units: It can contain a repeating unit represented by formula

[11] or a repeating unit represented by the following formula

[12] . By introducing these repeating units, it is expected that the glass transition temperature (Tg) of the polymer and the content of nonlinear optically active moieties can be adjusted. [ka]

[0033] In the above formula

[11] , R 21 represents a hydrogen atom or a methyl group. In addition, in the above formula

[11] , W 1 is a methyl group or -L 3 -R 22 Represents. L 3 is a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain a single bond, an ether bond and / or an ester bond, or *-L 4 represents —NHC(═O)O— (* represents the bond end with the O atom), and L 4 represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain an ether bond and / or an ester bond.

[0034] R 22represents an alkyl group having 1 to 6 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a cycloalkyl group having 4 to 8 carbon atoms, an aliphatic bridged ring group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms.

[0035] In the above formula

[12] , W 2 represents an alkyl group having 1 to 6 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a cycloalkyl group having 4 to 8 carbon atoms, an aliphatic bridged ring group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms.

[0036] Furthermore, the organic electro-optical polymer (e.g., a polymer having an atomic group exhibiting nonlinear optical activity in a side chain) may contain a repeating unit (referred to as other repeating units) other than the repeating unit represented by formula [2] having the nonlinear optically active moiety, the repeating unit represented by formula

[11] , and the repeating unit represented by formula

[12] . For example, in order to adjust the content of nonlinear optically active moieties, repeating units that form a polymer matrix can be introduced into the organic electro-optical polymer.Furthermore, in order to contribute to improving the solvent resistance and suppressing orientation relaxation in a molded article (cured film) obtained from the organic electro-optical polymer, and further to enable the formation of a molded article by thermosetting, repeating units having a structure that can be thermoset (crosslinked) can be introduced into the organic electro-optical polymer. Alternatively, in order to adjust the glass transition temperature, a repeating unit containing a cycloalkane such as an adamantyl ring may be introduced into the organic electro-optical polymer. Considering that the organic electro-optical polymer is to be used as a material for forming an optical waveguide, it is desirable to select such other repeating units having a structure that does not significantly adversely affect the transparency and moldability of the organic electro-optical polymer.

[0037] In the repeating unit forming the polymer matrix, examples of the polymer matrix include resins such as polymethyl methacrylate, polycarbonate, polystyrene, silicone-based resins, epoxy-based resins, polysulfone, polyethersulfone, and polyimide. By introducing such a repeating unit that forms a polymer matrix into the organic electro-optical polymer, the organic electro-optical polymer can be made into a form in which the repeating unit represented by formula [2] having a nonlinear optically active site, the repeating unit represented by formula

[11] , the repeating unit represented by formula

[12] , and the repeating unit of the polymer matrix are copolymerized.

[0038] In the repeating unit having a thermosetting (crosslinkable) structure, a preferred example of the thermosetting (crosslinkable) structure is an isocyanate group protected with a blocking agent. The blocking agent is not particularly limited as long as it can be dissociated (deblocked) by heating to regenerate an active isocyanate group. The repeating unit having a structure capable of being thermoset (crosslinked) can be exemplified by the repeating unit represented by the following formula

[13] . [ka] In the above formula

[13] , R 23 represents a hydrogen atom or a methyl group, and L 5 represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain an ether bond and / or an ester bond, and Y represents an isocyanate group protected with a blocking agent.

[0039] In the repeating unit containing the cycloalkane, the cycloalkane is not particularly limited and may be a single ring or a condensed ring, and these rings may be bridged. Examples of the condensed ring include a bicyclo ring and a tricyclo ring. Examples of the bridged ring include dicyclopentane and adamantyl.

[0040] The average molecular weight of the polymer having the atomic group exhibiting nonlinear optical activity in its side chain, for example, the polymer containing at least a repeating unit having a nonlinear optically active moiety represented by the formula [2], is not particularly limited, but a preferred example is one having a weight average molecular weight of 10,000 to 1,000,000. Note that the weight average molecular weight in the present invention is a value measured by gel permeation chromatography (polystyrene equivalent). In addition, in a polymer containing at least a repeating unit having a nonlinear optically active moiety represented by the formula [2], the proportion of the repeating unit represented by the formula [2] in the same molecule is not particularly limited, and can be, for example, 1 mol % to 99 mol %, 10 to 90 mol %, 20 to 80 mol %, 30 to 70 mol %, or 40 to 60 mol %.

[0041] The optical waveguide containing the organic electro-optic polymer according to the present invention is formed by dissolving the organic electro-optic polymer in an appropriate organic solvent to form a varnish, applying the varnish to a substrate such as glass or plastic, and then processing the varnish by light or electron beam lithography, wet or dry etching, nanoimprinting, etc., to form an optical waveguide structure capable of transmitting light. Typically, the optical waveguide structure is formed by applying and laminating a material with a high refractive index, such as a varnish containing an organic electro-optic polymer, on a material with a low refractive index, but is not limited to this structure. In order to develop second-order nonlinear optical properties in materials (e.g., thin films) made using a varnish containing the organic electro-optic polymer, a poling treatment is performed. The poling treatment involves heating the material to a temperature above the glass transition temperature and below the melting point of the material, applying a predetermined electric field, and then cooling the material while maintaining the electric field, thereby orienting the nonlinear optically active sites (atomic groups that develop nonlinear optical activity) contained in the polymer. This treatment allows the material to develop macroscopic nonlinear optical properties. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0043] [EO polymer] The organic electro-optical polymers (EO polymers) (1) and (2) used in this example are as follows: [ka]

[0044] EO polymer (1) is a polymer that can operate as an optical modulator in the C-band [conventional band, 1530-1565 nm] wavelength band, and EO polymer (2) is a polymer that can operate as an optical modulator in the O-band [original band, 1260-1360 nm] wavelength band.

[0045] [Manufacturing of optical modulators] As the optical modulator used in the following examples, the above EO polymer (1) or (2) was used to fabricate an optical modulator having an optical waveguide shown in FIG. 2 on a substrate. As shown in Figure 2, a bottom electrode 12 (Au and Cu, 0.3 μm thick), a bottom cladding 13 (sol-gel SiO2, 3 μm thick), and an EO polymer layer 14 (EO polymer (1) or (2), approximately 1 μm thick) were stacked in this order from the silicon substrate 11 side. A silicon film 16 (50 nm thick, approximately 5 μm wide) was then stacked on the EO polymer layer 14. An upper cladding 15 (sol-gel SiO2, 5 μm thick) was then stacked to cover the silicon film 16, and an upper electrode 17 was then stacked to form an optical modulator 10. The resulting modulator 10 was placed on a hot plate (not shown) and heated to near the glass transition point of the polymer while a voltage of 500 volts was applied. After the plate was cooled to room temperature, the voltage application was stopped, allowing the EO polymer to be oriented (poling process).

[0046] [Optical modulation test (1)] The characteristics of an optical modulator with an optical waveguide structure fabricated using the above EO polymer (1) or (2) were analyzed. A conceptual diagram of the device used for the characteristic analysis is shown in Figure 3. As shown in FIG. 3, a laser generator is attached to the end face of the optical modulator 10 using an optical fiber 22. Laser light was incident from the device 21. The wavelength of the incident laser light was 1550 nm when the EO polymer layer 4 was EO polymer (1), and 1310 nm when it was EO polymer (2). A heater for temperature control was installed below the optical modulator 10 (not shown) so that the optical modulation test (1) could be performed under heated conditions. A function generator was used as the power supply 18, and a triangular wave voltage was applied to the upper and lower electrodes (2, 7) of the optical modulator 10. The light modulated by the applied voltage inside the optical modulator 10 was extracted through an optical fiber 22 from the end face opposite to the laser light input end face, and the intensity of the emitted light was input to a photodetector 23 and measured. The power supply 18 (function generator) and photodetector 23 were connected to an oscilloscope 24, and the voltage and intensity were measured. Figure 4 shows the relationship between the triangular wave voltage (applied voltage), the change in light intensity (change in emitted light intensity), and the half-wave voltage (Vπ) measured with an oscilloscope. The emitted light intensity obtained using this measurement method changes in proportion to sin2(Γ / 2) with respect to the applied voltage (where Γ is the phase difference caused by the applied voltage, and Γ is proportional to π(V / Vπ), where V is the applied voltage and Vπ is the half-wave voltage). Therefore, the half-wave voltage (Vπ) was evaluated by analyzing the phase difference Γ caused by the applied voltage using the emitted light intensity measured by the photodetector described above.

[0047] An optical modulation test was conducted in air at 80°C using EO polymer (1) as the EO polymer layer of the optical modulator, and using laser light (wavelength: 1550 nm) with a light intensity of 10 mW or 40 mW. The change in half-wave voltage was evaluated by the ratio of the half-wave voltages (Vπ(t) / Vπ(0)), where Vπ(0) is the half-wave voltage immediately after the start of the test and Vπ(t) is the half-wave voltage after a certain time (t). The results are shown in Figure 5. As shown in Figure 5, when the laser light intensity was set to 10 mW, the half-wave voltage ratio (Vπ(t) / Vπ(0)) remained almost unchanged at 1, and the device operated stably for more than 500 hours. On the other hand, when the laser light intensity was set to 40 mW, a large increase in the half-wave voltage was observed within 100 hours, and the half-wave voltage continued to increase thereafter. The increase in half-wave voltage that occurs when high-intensity laser light is used is presumably the result of oxygen remaining in the EO polymer layer that makes up the optical modulator and oxygen in the air surrounding the optical modulator becoming active oxygen, which causes deterioration of the EO polymer.

[0048] [Optical modulation test (2)] A conceptual diagram of the equipment used to analyze the characteristics of the optical modulator in an environment where the effects of oxygen are eliminated is shown in Figure 6. Note that in Figure 6, some of the cables connecting the various components have been omitted. The test was carried out by placing the optical modulator 34 under vacuum as shown in Fig. 6. The optical modulator 34 used here has the same configuration as the optical modulator 10 shown in Fig. 3 above. An optical modulator 34 was placed in a stainless steel vacuum chamber 31, and the optical modulator 34 was connected to a laser generator 42 outside the chamber by an optical fiber 35 via an optical fiber connection terminal 37. The optical modulator 34 was also connected to a power source 41 outside the chamber by a power cable 36 via a power cable connection terminal 38. Light incident from the laser generator 42 and modulated within the optical modulator 34 was measured and detected by a photodetector 43 and an oscilloscope 44 via the optical fiber 35 and the optical connection terminal 37. A heater 40 for temperature control was connected to the optical modulator 34. The inside of the vacuum chamber 31 is evacuated by connecting a molecular turbo pump 32 and a rotary pump 33, and the vacuum gauge 39 always shows a vacuum of 1×10 -4 The pressure was kept at or below Pa. At this time, the heater 40 for adjusting the temperature was not operated, and evacuation was carried out at room temperature. Furthermore, an argon gas generator 45 was connected to the vacuum chamber 31 via a flow rate control valve 46 . The heater 40 was operated to control the temperature at 80°C, and the -4The optical modulation test was carried out in the same manner as in the optical modulation test (1) under an environment of 100 Pa or less or an argon atmosphere, and the half-wave voltage after time (t) was defined as Vπ(t), and the half-wave voltage ratio (Vπ(t) / Vπ(0)) was used for evaluation.

[0049] This testing device embodies, so to speak, the manufacturing method of the optical modulation element of the present invention and the optical modulation element of the present invention; that is, it embodies the manufacturing method of the present invention by housing the optical modulator 34 in a vacuum chamber 31 (housing), reducing the pressure inside the chamber (evacuating it), and further introducing argon, which is an inert gas of the 18th element.

[0050] Optical Modulation Test (2-1): EO Polymer (1) The EO polymer (1) was used as the EO polymer layer of the optical modulator, and laser light (wavelength: 1550 nm) with a light intensity of 35 mW was used under vacuum (1 × 10 -4 Figure 7 shows the results of an optical modulation test conducted at 80°C and 1000kJ / s. As shown in FIG. 7, it was confirmed that the half-wave voltage ratio (Vπ(t) / Vπ(0)) hardly changed even after 2000 hours or more had passed.

[0051] Following the above test, argon gas was introduced into the vacuum chamber 31 from the argon generator 45, and the pressure was adjusted to 1 Pa using the flow control valve 46, thereby conducting a test in an argon atmosphere (using EO polymer (1), at a light intensity of 35 mW or 60 mW, and at 80°C). The results are shown in FIG. 8. As shown in Figure 8, the half-wave voltage ratio (Vπ(t) / Vπ(0)) remained almost unchanged even after more than 500 hours for both laser light intensities of 35 mW and 60 mW, demonstrating stable operation.

[0052] Optical Modulation Test (2-2): EO Polymer (2) The EO polymer (2) was used as the EO polymer layer of the optical modulator, and laser light (wavelength: 1310 nm) with a light intensity of 27 mW or 60 mW was used under vacuum (1 × 10 -4The results of the optical modulation test conducted at a temperature of 1000 K (or less than 1000 KPa) and 80°C are shown in Figures 9(a) and 9(b). As shown in Figure 9(a), when the laser light intensity is 27 mW, it was confirmed that the half-wave voltage ratio (Vπ(t) / Vπ(0)) hardly changed even after 780 hours or more. Also, as shown in Figure 9(b), when the laser light intensity is 60 mW, it was confirmed that the half-wave voltage ratio (Vπ(t) / Vπ(0)) hardly changed even after 2000 hours or more.

[0053] The results shown in Optical Modulation Test (2-1) (Fig. 7) and Optical Modulation Test (2-2) (Figs. 8 and 9) suggest that removing the oxygen remaining in the EO polymer layer that constitutes the optical modulator and the oxygen present around the optical modulator and placing it under a high vacuum or argon atmosphere suppressed the photodegradation of the EO polymer and the change in half-wave voltage. [Explanation of symbols]

[0054] 1 Optical modulation element, 2 Package, 3 Lid, 4 Optical fiber, 5 Pipe, 6 Solder material, 7 Adhesive 10 Optical modulator, 11 Silicon substrate, 12 Lower electrode, 13 Lower clad, 14 EO polymer layer, 15 Upper clad, 16 Silicon film, 17 Upper electrode, 18 Power supply (function generator) 21...laser generator, 22...optical fiber, 23...photodetector, 24...oscilloscope, 31...Vacuum chamber, 32...Molecular turbo pump, 33...Rotary pump, 34...Optical modulator, 35...Optical fiber, 36...Power cable, 37...Optical fiber connection terminal, 38...Power cable connection terminal, 39...Vacuum gauge, 40...Heater, 41...Power supply, 42...Laser generator, 43...Photodetector, 44...Oscilloscope, 45...Argon gas generator, 46...Flow rate adjustment valve

Claims

1. A method for manufacturing an optical modulation element in which an optical modulator having an optical waveguide including an organic electro-optic polymer on a substrate is accommodated and sealed inside a housing, the method comprising: a first step of housing the optical modulator in a housing and reducing the pressure inside the housing; a second step of sealing the housing under the reduced pressure or under an inert gas atmosphere of at least one kind selected from a Group 18 element and nitrogen, A method for manufacturing an optical modulation element.

2. The method according to claim 1 , wherein the first step is carried out at a temperature of 80° C. or less.

3. The organic electro-optic polymer A polymer having an atomic group exhibiting nonlinear optical activity in a side chain, 2. The method according to claim 1, wherein the atomic group exhibiting nonlinear optical activity is an atomic group having a furan ring group represented by the following formula [3]: 【Chemical 1】 (In the formula, R １０ and R １１ each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and the black dot represents a bond to the remaining structure constituting the atomic group that exhibits nonlinear optical activity.

4. 4. The method according to claim 3, wherein the organic electro-optical polymer is a polymer containing at least a repeating unit having a nonlinear optically active moiety represented by the following formula [2]: 【Chemistry 2】 (In the formula, R ２ represents a hydrogen atom or a methyl group, L １ represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain an ether bond and / or an ester bond, L ２ *-NHC(=O)O-, *-C(=O)NH- or *-C(=O)O- (* is L １ represents the bond end with Z represents an atomic group that exhibits the nonlinear optical activity.

5. The atomic group exhibiting nonlinear optical activity is represented by formula [4] or formula [5] (wherein R ４ ~R ９ The method according to claim 3 or 4, wherein one hydrogen atom is removed from the group represented by the formula (I). 【Chemistry 3】 (In the formula, R ４ and R ５ each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, or an optionally substituted aryl group having 6 to 10 carbon atoms; R ６ ~R ９ each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, an alkylcarbonyloxy group having 2 to 11 carbon atoms, an aryloxy group having 4 to 10 carbon atoms, an aralkyloxy group having 5 to 11 carbon atoms, an arylcarbonyloxy group having 5 to 11 carbon atoms, a silyloxy group having an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, or a halogen atom; R １０ and R １１ each independently represents the same meaning as above, Ar represents a divalent aromatic group represented by formula [6] or formula [7]. 【Chemistry 4】 (In the formula, R １２ ~R １７ each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, or an optionally substituted aryl group having 6 to 10 carbon atoms.

6. The atomic group exhibiting nonlinear optical activity is represented by the formula [4] or [5] (in these chemical formulas, R ４ or R ５ The method according to claim 5, wherein one hydrogen atom is removed from the group represented by the formula (I).

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