JP2003270685A - Waveguide type optical modulator, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide type optical modulator using an organic nonlinear optical material having temporally and thermally stable optical characteristics and a quick response performance. <P>SOLUTION: The waveguide type optical modulator has a core 4 made of an organic material, clad layers (a lower clad layer 3 and an upper clad layer 5) formed on and under the core 4, and a pair of electrodes (a lower electrode 2 and an upper electrode 6) for applying an electric field to the core 4 and the upper and lower clad layers 3 and 5, which are laminated on a substrate 1, and the core 4 contains a high polymer liquid crystal compound having a functional group capable of cross-linking and a nonlinear optical active group and is formed by field orientating treatment and cross-linking of the high polymer liquid crystal compound. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is used for optical communication and the like,
The present invention relates to a waveguide type optical modulation element that controls the intensity or phase of light.

[0002]

2. Description of the Related Art In high-speed, large-capacity communication, development of an optical switch having high-speed response performance is required. Conventionally, in this field, inorganic ferroelectric crystals such as LiNbO ₃ have been studied as a representative material. However, in these materials, the high dielectric constant of the ferroelectric crystal causes a velocity mismatch between light and microwave, as reported in The Institute of Electronics, Information and Communication Engineers, Vol. 76, p. 1306 (1993). The operating band is limited.

On the other hand, it has been reported that a waveguide type optical modulator using an organic non-linear optical material is suitable for wide band operation utilizing its low dielectric constant. For example, Applied Physics Letters, Volume 60, p. 1538 (1992).
Discloses a waveguide-type optical modulator using an organic nonlinear optical material that covers an operating band exceeding 40 GHz. In addition, the Optoelectronic Functional Organic Materials Handbook (Asakura Shoten, Tokyo, 1995), page 434, suggests the possibility of broadband operation over 100 GHz. However, in order to develop a second-order nonlinear optical effect as an organic nonlinear optical material,
It is necessary to arrange the nonlinear optical response group in a structure lacking the inversion symmetry center. As a method therefor, an orientation treatment (poling) by an electric field is generally performed. That is, by applying a high voltage at a temperature equal to or higher than the glass transition point of the base polymer, a dipole of a molecule or a responsive group exhibiting a second-order nonlinear optical effect is oriented and then cooled to form a dipole. The technique of freezing the orientation of the child is taken. As a result, there has been a problem that the orientation characteristics are gradually lost due to structural relaxation with time or heat, and the nonlinear optical characteristics are deteriorated.

To solve this problem, it is effective to use a rigid polymer material having a sufficiently high glass transition point. Ma
terials Research Society Symposium Proceedings, No.
Volume 328, page 511 (1994) lists polyimides and the like as candidates for the base polymer. However, when a non-linear optical polymer material exhibiting such a high glass transition temperature is used, a high temperature higher than the glass transition temperature is required for its alignment treatment, and thus the substrate, lower cladding layer, core, etc. are damaged. There was a problem.

Further, in Japanese Patent No. 2865917, in a polymer having a side chain having an optically non-linear or mesomorphic property, a crosslinking group on the side opposite to the polymer main chain is bonded by photocrosslinking. At that time, a method of imparting an alignment action by applying an electric field or the like is disclosed. However, such a method has a problem that the apparatus becomes complicated in the manufacturing process. Japanese Unexamined Patent Publication No. 2000-81645 discloses a method in which a copolymer having a glycidyl group as a crosslinkable group at the side chain end is subjected to thermal crosslinking while performing electric field orientation at the glass transition temperature or higher. However, manufacturing problems such as thermal crosslinking taking a long time remain.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a waveguide type optical modulation element using an organic nonlinear optical material which has temporally and thermally stable optical characteristics and high-speed response performance. is there.

[0007]

As a result of earnest research in view of the above object, the present inventor has found that a polymer liquid crystal compound having a crosslinkable functional group and a non-linearly optically active group is aligned by applying an electric field, and after completion of the application of the electric field. Also, by cross-linking a high-molecular liquid crystal compound that retains liquid crystal orientation, a high temperature is not required for the orientation treatment, and a nonlinear optical material having stable optical characteristics with time and thermal response and fast response can be easily obtained. Discover that
The present invention was conceived.

That is, it has a core made of an organic material, an upper clad layer and a lower clad layer formed above and below the core so as to sandwich the core, and a pair of electrodes for applying an electric field to the core and the upper and lower clad layers. The waveguide-type light modulation element of the present invention comprises a polymer liquid crystal compound in which the layer forming the core has a crosslinkable functional group and a non-linear optically active group, and the polymer liquid crystal compound is crosslinked after an electric field is applied. It is characterized in that it is formed by. Also,
The waveguide-type light modulation element of the present invention having the above structure is characterized in that the layer forming the core contains a crosslinked polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group.

The crosslinkable functional group is preferably a crosslinkable functional group by ultraviolet irradiation. Further, the polymer liquid crystal compound has the following general formula (I):

[Chemical 2] (In the general formula (I), R¹And R²Are independent hydrogen
Represents a child or a methyl group, L ¹And L²Each independently
Represents a bond or a divalent linking group, and M is a divalent nonlinear optical activity.
Represents a sexual group. m and n each represent a mole fraction, and m is
1-100 (%), n represents 0-99 (%), m + n = 100
(%). ) Is a compound represented by
Yes.

The present invention has a core made of an organic material, an upper clad layer and a lower clad layer formed above and below the core, and a pair of electrodes for applying an electric field to the core and the upper and lower clad layers. The method for producing a waveguide-type light modulation device according to, wherein the layer forming the core is (a) a liquid crystal composition containing a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group, the lower clad layer. It is characterized in that it is formed by coating the above, (b) applying an electric field, and (c) subsequently crosslinking the polymer liquid crystal compound.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION [1] Waveguide Type Optical Modulation Element FIG. 1 shows an example of a waveguide type optical modulation element of the present invention. The waveguide type optical modulator is composed of a substrate 1 and a core 4 made of an organic material.
A clad layer (lower clad layer 3 and upper clad layer 5) formed above and below the core 4 with the core 4 in between;
And a pair of electrodes (lower electrode 2 and upper electrode 6) for applying an electric field to the upper and lower clad layers.

(1) Substrate The substrate used in the present invention is not particularly limited, but a substrate having excellent flatness is preferable. For example, a metal substrate, a silicon substrate, a transparent substrate, or the like can be used, and can be appropriately selected depending on the form of the waveguide type optical modulation element. Preferred examples of the metal substrate include a substrate made of gold, silver, copper, aluminum and the like, and preferred examples of the transparent substrate include a substrate made of glass, plastic (polyethylene terephthalate etc.) and the like.

(2) The lower electrode 2 is formed on the lower electrode substrate 1. The lower electrode 2 may be a metal vapor deposition layer, a transparent electrode layer, or the like. Gold, silver, copper, aluminum etc. are mentioned as a preferable example of the metal to vapor-deposit. Moreover, as a preferable example of the transparent electrode layer,
Examples thereof include indium tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide and the like. The substrate 1 may also serve as the lower electrode 2.

(3) Lower cladding layer A lower cladding layer 3 is formed on the lower electrode 2. The organic material forming the lower clad layer 3 is not particularly limited, but polyimide, fluorinated polyimide and the like are preferable examples.

(4) Core The layer forming the core 4 contains a polymer liquid crystal compound and is formed by subjecting the polymer liquid crystal compound to an electric field orientation treatment and then crosslinking. The layer forming the core 4 may contain an uncrosslinked polymer liquid crystal compound together with a crosslinked polymer liquid crystal compound. As the polymer liquid crystal compound, any compound having a crosslinkable functional group and a non-linear optically active group can be preferably used. Further, the crosslinkable functional group is preferably a crosslinkable functional group by ultraviolet irradiation. As a preferable example of the polymer liquid crystal compound used in the present invention, the following general formula (I):

[Chemical 3] (In the general formula (I), R¹And R²Are independent hydrogen
Represents a child or a methyl group, L ¹And L²Each independently
Represents a bond or a divalent linking group, and M is a divalent nonlinear optical activity.
Represents a sexual group. m and n each represent a mole fraction, and m is
1-100 (%), n represents 0-99 (%), m + n = 100
(%). ). here
And m is preferably 50-100, and is 70-100.
Is preferred.

Preferred examples of L ¹ and L ² include 2 carbon atoms.
~ 12 alkylene groups. L ¹ and L ² may have a substituent, and preferred examples of the substituent include a lower alkyl group and a halogen atom. In addition, when the carbon atom having a substituent is an asymmetric carbon, its configuration is
Any of R, S and RS may be used.

The divalent nonlinear optically active group represented by M is, for example, a divalent non-localized π-electron structure having an electron-donating portion (or group) and an electron-accepting portion (or group). Groups. Specifically, Handbook of
Nonlinear optically active groups exemplified in Liquid Crystals, Volume 3, Chapter IV (1998) and the like can be mentioned, and among them, the groups shown below are preferable. However, the present invention is not limited to these.

[Chemical 4]

(5) The upper clad layer 5 is formed on the lower clad layer 3 with the upper clad layer core 4 interposed therebetween. The organic material forming the upper clad layer 5 is not particularly limited, but polyimide, fluorinated polyimide and the like are preferable examples.

(6) Upper electrode The upper electrode 6 is formed on the entire surface or a part of the upper clad layer 5. The material forming the upper electrode 6 is not particularly limited, and for example, gold, silver, copper, aluminum or the like can be used. The upper electrode 6 is preferably an electrode formed by depositing these materials.

(7) Waveguide As a waveguide, known waveguides described in Optical Wave Engineering (Corona Publishing Co., Ltd., 1988), Chapter 7, p. 204, for example, branching waveguide type, Mach-Zehnder type, direction A sex coupler type, a crossed waveguide type, etc. can be adopted. Of these, a branching waveguide type, a Mach-Zehnder type, and a directional coupler type are preferable. Figure 3-
5 shows a branch type optical modulator, a Mach-Zehnder type optical modulator and a directional coupler type optical modulator, respectively.

[2] Method for Manufacturing Waveguide Type Optical Modulation Element The method for manufacturing the present invention will be described below with reference to FIG. A lower electrode layer 2 is formed by providing a conductive layer such as a metal vapor deposition layer and a transparent electrode layer on a substrate 1 made of silicon resin or the like by electron beam vapor deposition or the like. Next, the lower clad layer 3 made of a polymer thin film is formed on the lower electrode layer 2. As a method of forming the polymer thin film, a method of applying the material itself of the polymer thin film and drying it, a method of applying a precursor of the polymer thin film and polymerizing it by an appropriate method, and the like can be adopted. As the coating method, known methods such as curtain coating method, extrusion coating method, roll coating method, spin coating method, dip coating method, bar coating method, spray coating method, slide coating method, and printing coating method can be adopted, and The spin coating method is preferred.

A layer (core layer) made of a polymer material for forming the core 4 is formed on the lower clad layer 3. The core layer, (a) a liquid crystal composition containing a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group is coated on the lower clad layer, (b) an electric field orientation treatment, (c) Then, it is formed by crosslinking.

The coating method of the liquid crystal composition may be a known method, for example, a method of applying the liquid crystal composition using a coating solution in which the liquid crystal composition is uniformly dissolved in a solvent is preferable. As the coating method, the method exemplified for the lower clad layer 3 can be used. The solvent is not particularly limited, but preferred examples include ester solvents (methyl acetate, ethyl acetate, etc.), ketone solvents (acetone, methyl ethyl ketone, cyclohexanone, etc.),
Halogen-containing solvent (dichloromethane, chloroform, etc.),
These mixed solvents etc. are mentioned. The concentration of the high molecular weight liquid crystal compound in the coating liquid is not particularly limited as long as it is a concentration range that can be coated, but it is preferably in the range of 1 to 60 mass% with respect to the total mass of the coating liquid, and in the range of 5 to 40 mass%. It is more preferable. If necessary, a suitable polymerization initiator, polymerization inhibitor, photosensitizer, crosslinking agent, liquid crystal alignment aid, etc. may be added to the coating liquid. The amount of the additive is not particularly limited, but the total amount of the additive is preferably 30% by mass or less, and more preferably 15% by mass or less, based on the total mass of the coating liquid.

As a method of applying an electric field (electric field orientation treatment), a method of applying a DC electric field, a method of utilizing corona discharge or the like can be used, and a method of utilizing corona discharge is preferable. The electric field application is preferably performed at a temperature at which the polymer liquid crystal compound forming the core layer exhibits a liquid crystal phase or higher, and preferably at a temperature at which the polymer liquid crystal compound exhibits a liquid crystal phase or lower.

For the cross-linking reaction, a known cross-linking method using heat, electromagnetic waves or the like can be adopted, and radical polymerization by ultraviolet light using a photopolymerization initiator is particularly preferable. When the crosslinkable group is an epoxy group, it is preferable to use a method of thermally crosslinking by adding a diamine. The crosslinking reaction is preferably carried out at a temperature at which the polymer liquid crystal compound forming the core layer exhibits a liquid crystal phase or lower.

A waveguide is formed in the obtained core layer to form the core 4
To make. The waveguide is formed by patterning into a desired shape such as a Mach-Zehnder shape or a cross shape according to the purpose. A well-known method such as photolithography or dry etching can be adopted for the patterning formation.

An upper clad layer 5 made of a polymer thin film is formed on the core 4 and the lower clad layer 3. The material and method for forming the upper clad layer 5 may be the same as that for forming the lower clad layer 3.

An upper electrode 6 is formed on the upper clad layer 5. The upper electrode 6 is formed by depositing a metal on the upper clad layer 5 with heat or an electron beam to form an upper electrode layer, and then patterning the upper electrode layer into the shape of the upper electrode 6. For patterning, photolithography, dry etching, etc. can be adopted.

In the waveguide type optical modulator obtained by the above steps, the phase of propagating light can be controlled by grounding the lower electrode 2 and changing the voltage applied to the upper electrode 6. The waveguide type optical modulation element of the present invention can suppress the temperature and the applied voltage of the alignment treatment to be low. Furthermore, since the orientation of the nonlinear optically active group of the core is fixed by cross-linking and the orientation of the liquid crystal can be retained even after cross-linking, it is stable over time and thermally.

[0030]

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

Example 1 An in- waveguide type optical modulator having the structure shown in FIG. 2 was produced as follows. First, aluminum was electron beam evaporated on a silicon substrate to form a lower electrode 2. Acrylic UV curable resin was spin-coated on the lower electrode 2 and irradiated with UV light (25
4 nm, 10 W / cm, 10 minutes) and cured to form a lower cladding layer 3 having a film thickness of 10 μm. A coating liquid containing the following polymer liquid crystal compound 1 and having the composition shown below was spin-coated on the lower clad layer 3 and subjected to electric field orientation treatment by corona discharge (applied voltage: 1 kV) at 100 ° C. After aligning the electric field, keep it at 100 ° C and irradiate with ultraviolet rays (254 nm, 10W / cm, 2
Minutes). Appl. Opt., Volume 38,
According to the method described on page 966 (1999), photolithography and dry etching were performed to form a pattern to form a core 4 having a thickness of 8 μm shown in FIG.

Coating Liquid for Core Formation: Polymer Liquid Crystal Compound 1
(20 mass%), trimethylolpropane triacrylate (0.1 mass%), Irgacure 651 (0.3 mass%),
Methyl ethyl ketone (79.7% by mass) Polymer liquid crystal compound 1

[Chemical 5]

Acrylic UV curable resin was spin-coated on the lower clad layer 3 and the core 4 thus obtained, and then cured by irradiation with UV light (254 nm, 10 W / cm, 10 minutes) to obtain a film thickness.
An upper clad layer 5 having a thickness of 15 μm was formed. Next, aluminum was laminated on the upper clad layer 5 to a thickness of 0.5 μm by electron beam evaporation, and an upper electrode 6 for applying a signal voltage was patterned. Finally, it was cut into chips by a dicer and the end face was polished to obtain a waveguide type optical modulator. It was confirmed that the obtained device exhibited an electro-optical effect. Furthermore, it was confirmed that the effect was retained even after 6 months.

Example 2 A Mach-Zehnder type optical modulator shown in FIG. 4 was produced in the same manner as in Example 1 except that a Mach-Zehnder type waveguide was formed in the core pattern formation.

[0035]

As described above, in the waveguide type optical modulator of the present invention, a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group is used as a non-linear optical material. After the application, a cross-linking reaction is carried out in the liquid crystal alignment state which is held, so that it can be easily manufactured. Since the obtained waveguide type optical modulator has the non-linear optically active group of the core fixed by cross-linking, it has optical characteristics that are stable over time and is thermally stable, and has high-speed response performance.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a waveguide type optical modulator according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view of a waveguide type optical modulator according to an embodiment of the present invention.

FIG. 3 is a schematic perspective view of a branch type optical modulator including a waveguide type optical modulator according to an embodiment of the present invention.

FIG. 4 is a schematic perspective view of a Mach-Zehnder interferometer type optical modulator including a waveguide type optical modulator according to an embodiment of the present invention.

FIG. 5 is a schematic perspective view of a directional coupler type optical modulator including a waveguide type optical modulator according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Substrate 2 ... Lower electrode 3 ... Lower clad layer 4 ... Core 5 ... Upper clad layer 6 ... Upper electrode

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H047 KA04 NA03 PA02 PA21 PA24                       PA28 QA05 RA08                 2H079 AA02 AA12 BA01 BA03 DA08                       EA04 EA05 EB04                 2H088 EA45 EA46 EA47 GA06 HA10                       MA10 MA11 MA16 MA18                 2K002 AB04 BA06 CA14 DA07 DA08                       DA14 EA08 HA02

Claims (5)

[Claims] 1. A core comprising an organic material, an upper clad layer and a lower clad layer formed above and below the core so as to sandwich the core, and a pair of electrodes for applying an electric field to the core and the upper and lower clad layers. In the waveguide type light modulation element, the layer forming the core contains a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group, and crosslinks after applying the electric field to the polymer liquid crystal compound. A waveguide-type optical modulation element characterized by being formed by. 2. A core made of an organic material, an upper clad layer and a lower clad layer formed above and below the core, and a pair of electrodes for applying an electric field to the core and the upper and lower clad layers. In the waveguide type light modulation element, the layer forming the core contains a crosslinked body of a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group. 3. The waveguide type optical modulation element according to claim 1, wherein the crosslinkable functional group is a functional group which is crosslinkable by ultraviolet irradiation. 4. The waveguide according to claim 1.
In the light modulation device of the type, the polymer liquid crystal compound is
General formula (I): [Chemical 1] (In the general formula (I), R¹And R²Are independent hydrogen
Represents a child or a methyl group, L ¹And L²Each independently
Represents a bond or a divalent linking group, and M is a divalent nonlinear optical activity.
Represents a sexual group. m and n each represent a mole fraction, and m is
1-100 (%), n represents 0-99 (%), m + n = 100
(%). ) Waveguide type characterized by being represented by
Light modulator. 5. A core made of an organic material, an upper clad layer and a lower clad layer formed above and below the core so as to sandwich the core, and a pair of electrodes for applying an electric field to the core and the upper and lower clad layers. In the method of manufacturing a waveguide type light modulation element, the layer forming the core is (a) a liquid crystal composition containing a polymer liquid crystal compound having a crosslinkable functional group and a non-linear optically active group on the lower clad layer. And (b) an electric field is applied, and (c) the polymer liquid crystal compound is then crosslinked to form a waveguide-type optical modulator.