JP2003172802A - Optical material composition and optical element manufactured by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical material composition to reduce changes in the optical path length of an optical element with temperature. <P>SOLUTION: The optical material composition is synthesized by hydrolyzing and condensing a silicon compound having at least either an organic functional group or a hydrolysable group and a germanium compound having at least either a reactive organic group or a hydrolysable group. The treatment conditions to form an optical element from the above optical material composition are controlled so as to leave the organic component to reduce changes in the optical path length with temperature. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical material and a composition for forming the same, and more particularly to an optical material for optical elements such as waveguides and filters used in the field of optical communication.

[0002]

2. Description of the Related Art Optical elements used in the field of optical communication include
Optical performance is required to be stable against changes in environmental conditions. For example, the optical path length (optical length) S in the optical element
Is given by the following equation when this is an optical system composed of one material. S = nl (1) where n is the refractive index of the material and l is the geometrical optical path length.

The temperature T dependence of the optical path length S, dS / dT, is expressed by the following equation. dS / dT = 1 (dn / dT + nα) (2) where α is the linear expansion coefficient of the material. Therefore, in order to reduce the temperature dependence of the optical path length to 0, in the case of a material having a positive linear expansion coefficient, the temperature dependence of the refractive index n is dn / dT.
Must be negative with a magnitude that cancels the positive linear expansion coefficient. That is, a material satisfying dn / dT = -nα (3) is required.

An optical waveguide type Bragg diffraction grating will be considered as a specific example of an optical element. The reflection (Bragg) wavelength λ _B of this diffraction grating is expressed by the following equation. λ _B = 2neΛ (4) Here, ne is the effective refractive index of the optical waveguide, and Λ is the period of the diffraction grating. Since the effective refractive index ne is proportional to the refractive index n ₁ of the waveguide core, and Λ is a geometrical length, the temperature T dependence dλ _B / dT of this reflection wavelength is the same as the above dS / dT. Has meaning. Therefore, in order to reduce dλ _B / dT, that is, to improve the stability of the reflection wavelength with respect to temperature, the temperature coefficient of the refractive index of the waveguide material and the linear expansion coefficient that determines the temperature change of the geometrical dimension are important factors. Becomes

Inorganic materials such as glass and ceramics have high heat resistance and high stability of optical properties such as refractive index. However, the melting temperature is high, so that molding is difficult, and the hardness is high, so that processing is difficult. On the other hand, organic materials such as resins are excellent in moldability at low temperatures, but on the other hand, they have insufficient heat resistance, have a large coefficient of thermal expansion, and have relatively large temperature dependence of optical characteristics such as refractive index. Organic-inorganic composite materials have been developed in order to make use of the advantages of such inorganic materials and organic materials and to supplement the drawbacks.

A method using a metal alkoxide is known as a typical method for synthesizing an organic-inorganic composite material. It is well known as a sol-gel method that a composition equivalent to quartz glass can be obtained by hydrolysis and condensation reaction of a metal alkoxide, but it is well known as a sol-gel method. , The organic components remain in the composition, and an organic-inorganic composite material is obtained.

For example, in order to obtain a material having high light transmittance and heat resistance, a material composed of a silicon alkoxide having an organic functional group has been studied (US Pat. No. 60).
54253). Further, using an organic-inorganic composite composed of an organic monomer and a metal alkoxide, a material having a small coefficient of linear expansion coefficient and refractive index change with temperature has been investigated (JP-A-8-157735).

[0008]

However, the organic-inorganic composite material made of silicon alkoxide having an organic functional group has a large coefficient of thermal expansion and a small temperature coefficient of refractive index. Therefore, when an optical element is formed, the optical path length is increased. The problem that the temperature change becomes large cannot be solved. In the case of an organic-inorganic composite material composed of an organic monomer and a metal alkoxide, from the compatibility of the organic monomer and the metal alkoxide,
There is a problem that the composition range that can be manufactured is limited. In order to solve such a problem, it is an object of the present invention to provide an optical material composition capable of reducing the temperature change of the optical path length of an optical element.

[0009]

The optical material composition of the present invention comprises a silicon compound having at least one of an organic functional group and a hydrolyzable group, and at least one of a reactive organic group and a hydrolyzable group. The compound is characterized by containing an organic component although it is synthesized from a germanium compound having

The first aspect of the optical material composition of the present invention is
A silicon compound represented by the general formula R ¹ _i SiX ¹ _4-i (where i = 1, 2, 3, R
¹ is an organic functional group, X ¹ is a hydrolyzable group), and a germanium compound represented by R ² _j GeX ² _4-j or R ² ₄ Ge or GeX ² ₄ (where j = 1, 2,
3, R ² is a reactive organic group, and X ² is a hydrolyzable group)
Is a main starting material, and is a composition obtained by hydrolyzing and condensing these. Here, the reactive organic group means a part of an organic functional group in which a reaction between functional groups occurs by irradiation with light or heating. The hydrolyzable group is a general term for groups that may hydrolyze.

[0011] The second embodiment of the optical material forming composition of the present invention have the general formula R ¹ _i SiX ¹ _4-i or R ¹ ₄ Si, or SiX ¹ ₄ in the silicon compound represented by (where, i = 1, 2, 3, R
¹ is an organic functional group, X ¹ is a hydrolyzable group), and a germanium compound represented by R ² _j GeX ² _4-j (where j = 1, 2,
3, R ² is a reactive organic group, and X ² is a hydrolyzable group)
Is a main starting material, and is a composition obtained by hydrolyzing and condensing these.

In particular, the organic functional group R ¹ and the reactive organic group R ² are preferably alkenyl groups, and the silicon compound is ≡.
It is preferably a silicon alkoxide having a methacryloxypropyl group. Alternatively, the germanium compound is preferably germanium chloride having an allyl group.

It is important that these compositions contain an organic component, which allows the thermal expansion of the material to be compensated by the temperature coefficient of the refractive index. By forming an optical element using these compositions, stable element performance with respect to temperature changes can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the process of completing the present invention, a material capable of compensating a change in optical path length due to thermal expansion by a temperature change in refractive index was searched for based on an alkoxide. First, it is represented by the following general formula (5) R ¹ _i SiX ¹ _4-i (5) (where i is an integer of 1 to 3, R ¹ is an organic functional group, and X ¹ is a hydrolyzable group). is in the optical material composition comprising silicon compounds of silicon alkoxides, generally polymer organic functional group R ¹ is produced by the reaction dn /
Since dT is too large negatively, dS / dT becomes negative and the temperature dependence of the optical path length S becomes worse. Therefore, the present inventors have examined reducing the temperature dependence of the optical path length by adjusting dn / dT to be larger than that of this material.

As a result, the temperature dependence of the refractive index of germania is dn / dT = 18.8 × 10 ⁻⁶ K ^−1, which has a relatively large positive value, so that the material containing germanium is an optical material. Envisioned to obtain the composition. From this idea, the following general formula (6) R ² _j GeX ² _4-j (6) (where j is an integer of 1 to 3, R ² is a reactive organic group, X ²
Represents a hydrolyzable group) and a silicon compound represented by the above general formula (5) are added, and an optical material composition obtained by hydrolyzing and condensing the same is used. Got the prospect of being able to achieve.

The starting material of the present invention represented by the formulas (5) and (6) contains an organic functional group, a reactive organic group and a hydrolyzable group. Here, the reactive organic group means an organic functional group having reactivity. Therefore, both R ¹ and R ² may be reactive organic groups. An unreacted organic group can be left in an optical material composition obtained by hydrolyzing and condensing these, and further in an optical element finally produced by polymerizing the optical material composition. . Silica and germania themselves have a positive dS / dT, but it is possible to give a negative dn / dT to the remaining unreacted organic groups and the like. In consideration of this point, by adjusting the hydrolysis or condensation reaction or adjusting the polymerization reaction to leave the organic component, it is possible to form an optical element having small temperature dependence.

Even when the starting material does not contain an organic functional group, unreacted hydrolyzable groups can be left in the optical element produced from the optical material composition of the present invention. Can have a negative dn / dT. Thus, (5) is a germanium compound to the silicon compound of the formula, one does not contain any reactive organic group R ² or hydrolyzable group X ^2, a R ² ₄ Ge or GeX ² ₄ (7) Good. Further, when a germanium compound is represented by the equation (6), the silicon compound does not contain either an organic functional group R ¹ or a hydrolysable group X ^1, R ¹ ₄ Si, or SiX ¹ ₄ (8 ) May be.

A typical reactive organic group that can be used as R ¹ and R ² is an alkenyl group. Specifically, vinyl group, ≡
-Methacryloxypropyl group, allyl group and the like. The alkenyl group can be polymerized by irradiation with ultraviolet rays or the like. In addition, examples of the organic functional group that can be used as R ¹ include a methyl group and a phenyl group. Examples of the hydrolyzable group include an alkoxyl group, a halogen group such as chlorine, and a hydroxyl group.

For example, the silicon compound represented by the general formula (5) includes vinyltriethoxysilane, allyltriethoxysilane, ≡-methacryloxypropyltriethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane and phenyltriethoxy. Examples of the silicon compound represented by the general formula (8) such as silane include tetramethoxysilane and tetraethoxysilane. The germanium compound represented by the general formula (6) includes allyltrichlorogermane, methacryloxytriethylgermane,
Examples of the germanium compound represented by the general formula (7) such as methyltrichlorogermane and allyltrichlorogermane include tetraethoxygermane, tetramethoxygermane and tetraisopropoxygermane.

In the optical material composition of the present invention, the ratio of the silicon compound and the germanium compound can be arbitrarily changed. Furthermore, if necessary, a catalyst such as a metal alkoxide, a compound derived from a metal alkoxide, and a photoreaction initiator can be added. Next, examples in which an optical element is produced from the optical material composition of the present invention will be described.

[Example] In order to produce an optical waveguide using the optical material composition of the present invention, a first optical material composition containing a photoreaction initiator and a second optical material composition not containing a photoreaction initiator are prepared. .

From ≡-methacryloxypropyltrimethoxysilane: 13 mmol, isobutoxyaluminoxytriethoxysilane: 3 mmol, allyltrichlorogermane: 1 mmol, 0.1N hydrochloric acid aqueous solution: 23.5 mmol, isopropanol: 7 mmol The resulting solution is stirred at room temperature to form a uniform solution, which is used as the second optical material composition. Next, a 2-
Hydroxy-2-methyl-1-phenylpropane-1-
One drop of ON was dropped to obtain a first optical material composition having photoreactivity.

When the first optical material composition was spin-coated on a silicon substrate and dried, a coating film with a film thickness of 9.8≡m was obtained. When the surface of this coating film was spin-coated with the second optical material composition and dried, a coating film with a film thickness of 3 μm was obtained. When the two-layer coating film is irradiated with a high-pressure mercury lamp, the reactive organic groups in the first layer containing the photoreaction initiator are polymerized to increase the refractive index of the first layer. Since the second layer does not have photoreactivity, the refractive index does not change and a difference in refractive index occurs between the second layer and the first layer. That is, an optical waveguide having the first layer as a core and the second layer as a clad can be manufactured.

A Bragg diffraction grating was formed on this optical waveguide by a two-beam interference exposure method. The optical system of the two-beam interference exposure method used is shown in FIG. The laser beam 40 having a wavelength of 325 nm from the He-Cd laser 10 is reflected by the reflecting mirror 20, and the two beams 42 and 44 are formed by the beam splitter 22.
Divide into The two light fluxes are crossed on the substrate 30 by the reflecting mirrors 24 and 26, respectively, and interfere with each other. Polymerization of the core layer of the first coating film on the substrate was further promoted by the generated interference fringe pattern, and a structure in which the refractive index periodically changed was generated. Then, it heat-processed at 110 C and obtained the flat plate type optical waveguide which has a Bragg diffraction grating.

As shown in FIG. 2, the obtained optical waveguide 50
LED light 4 with a wavelength of 1300 nm at the end face 52 of the
6 was coupled and guided. When the spectrum of the outgoing light 48 from the other end surface 54 of the optical waveguide 50 is observed, the dip 45
Was found to have occurred. This indicates that only a certain wavelength in the wavelength range of the guided light is reflected by the Bragg diffraction grating 54. Similarly, when the temperature of the optical waveguide was changed and the wavelength (λ _B ) reflected by the Bragg grating was measured, the temperature dependence of λ _B (dλ _B / dT) was −
It was 0.77 × 10 ^-10 mK ^-1 .

Comparative Example ≡-methacryloxypropyltrimethoxysilane: 14 mmol, isobutoxyaluminoxytriethoxysilane: 3 mmol, 0.1N aqueous hydrochloric acid solution 23.5 mmol, isopropanol: 7 mmol, water: 30 mmol. A solution consisting of
A uniform solution is prepared, which is the second optical material composition. Next, 2-hydroxy- was added to this composition as a photoreaction initiator.
One drop of 2-methyl-1-phenylpropan-1-one was dropped to obtain a first optical material composition having photoreactivity.

When the first optical material composition was spin-coated on a silicon substrate and dried, a coating film having a film thickness of 9.5≡m was obtained. The surface of this coating film was spin-coated with the second optical material composition and dried to obtain a second coating film with a film thickness of 3 μm. The two-layer coating film was irradiated with a high-pressure mercury lamp to fabricate an optical waveguide having the first layer as a core and the second layer as a clad. A Bragg diffraction grating was formed on this optical waveguide by the two-beam interference exposure method as described above. Similarly, by changing the temperature of the optical waveguide, the wavelength reflected by the Bragg grating
When (λ _B ) was measured, the temperature dependence of λ _B (d λ _B / d
T) was −1.59 × 10 ⁻¹⁰ mK ⁻¹ .

The difference between the above-mentioned Examples and Comparative Examples is whether or not it contains allyltrichlorogermane, which is a germanium chloride having an allyl group. That is, as compared with an optical element using an optical material composition consisting only of a silicon compound having a reactive organic group and a hydrolyzable group, when an optical material composition obtained by mixing such a silicon compound and a germanium compound is used, The temperature dependence of the optical path length of the optical element can be made extremely small. This is because the organic component remains in the material forming the optical element, so that the temperature change in the refractive index is adjusted to an appropriate value that compensates for the dimensional change due to the thermal expansion coefficient of the material.

If it has the above-mentioned functions,
The reactive organic group is not limited to the allyl group, and the hydrolyzable group is not limited to the halogen (chlorine) group. Examples of groups that can be used are as described above. The catalyst to be added such as a photoreaction initiator can also be selected according to the required function.

Further, in the above embodiment, the production of the optical waveguide type Bragg diffraction grating as the optical element was explained, and the effect of stabilizing the reflection wavelength thereof with respect to the temperature change was explained, but the optical element and its improved characteristics are explained. Is not limited to this. The optical material composition of the present invention can be applied to the production of a wide range of optical elements utilizing the optical path length. Optical elements that utilize the optical path length include various optical functional elements of optical waveguide type (for example, arrayed waveguide diffraction grating and Mach-Zehnder type interference element) and bulk type optical elements such as prisms and etalons.

[0031]

EFFECT OF THE INVENTION By using an optical material composition of the present invention which is synthesized from a silicon compound having an organic functional group and a hydrolyzable group and a germanium compound and contains an organic component, the optical path length can be increased. It is possible to manufacture an optical element having a small temperature dependency of.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an optical system of a two-beam interference exposure method for manufacturing an optical element of an example of the present invention.

FIG. 2 is a schematic diagram showing an optical element of an example of the present invention.

[Explanation of symbols]

46 LED light 48 outgoing light 50 optical waveguide 54 Bragg diffraction grating

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C08G 77/58 G02B 6/12 FN (72) Inventor Hiroaki Yamamoto 4 Kitahama, Chuo-ku, Osaka-shi, Osaka C-No. 7-28 Nippon Sheet Glass Co., Ltd. F-term (reference) 2H047 KA02 LA02 PA30 QA05 TA11 2H049 AA34 AA43 AA44 AA51 AA59 AA62 4J027 AF05 BA04 CB10 CC05 CD00 4J030 CB03 CB13 CE06 CC11 CE11 CE05 CE05 CC11 CE11 LB20

Claims (8)

[Claims] 1. A compound synthesized from a silicon compound having at least one of an organic functional group and a hydrolyzable group, and a germanium compound having at least one of a reactive organic group and a hydrolyzable group to obtain an organic component. An optical material composition comprising: 2. The silicon compound is represented by the general formula R ¹ _i SiX ¹ _4-i (where i = 1, 2, 3, R ¹ is an organic functional group, and X ¹ is a hydrolyzable group), The germanium compound has the general formula R ² _j GeX ² _4-j or R ² ₄ Ge or GeX ² ₄ (where j = 1, 2, 3, R ² is a reactive organic group, and X ² is a hydrolyzable group. (Shown) respectively, and is obtained by hydrolyzing and condensing these. Wherein the silicon compound has the general formula R ¹ _i SiX ¹ _4-i or R ¹ ₄ Si, or SiX ¹ ₄ (however, i = 1, 2, 3, R ¹ is an organic functional group, X ¹ is Hydrolyzable group), the germanium compound is represented by the general formula R ² _j GeX ² _4-j (where j = 1, 2, 3, R ² is a reactive organic group, and X ² is a hydrolyzable group). (Shown) respectively, and is obtained by hydrolyzing and condensing these. 4. The optical material composition according to claim 1, 2 or 3, wherein the organic functional group R ¹ and the reactive organic group R ² are alkenyl groups. 5. The silicon compound is a silicon alkoxide having an ≡-methacryloxypropyl group.
The optical material composition as described in 2 or 3. 6. The optical material composition according to claim 1, 2 or 3, wherein the germanium compound is germanium chloride having an allyl group. 7. An optical element comprising a thin layer material obtained by polymerizing at least one kind of the optical material composition according to any one of claims 1 to 6, wherein the thin layer material contains an organic component. 8. An optical element in which a plurality of thin layer materials are laminated, wherein at least one layer of the thin layer material is processed by a photopolymerization reaction.