WO2000031583A1

WO2000031583A1 - Second order nonlinear optical material and method for producing second order nonlinear optical device

Info

Publication number: WO2000031583A1
Application number: PCT/JP1999/006094
Authority: WO
Inventors: Kenji Kitaoka; Jinhai Si; Kazuyuki Hirao
Original assignee: Japan Science And Technology Corporation
Priority date: 1998-11-20
Filing date: 1999-11-02
Publication date: 2000-06-02
Also published as: JP2000155346A

Abstract

An organic dye having a second order nonlinear optical effect or a polymer precursor having a side chain of an organic dye and a zol-gel liquid in which a metallic oxide precursor is dispersed are cast on a substrate to form a thin film. The thin film is irradiated with lights of different wavelengths coaxial at one time to conduct optical poling of a thin film under heat treatment or after treatment. The polarization of the organic dye is stably maintained over a long period of time, thereby providing a second order linear optical device preferable to, for example, an optical modulator and an optical switch.

Description

Specification

Method of manufacturing secondary nonlinear optical material and secondary nonlinear optical element

The present invention relates to an optical modulator widely used in the field of communication equipment. A second-order nonlinear optical material and a method for manufacturing a second-order nonlinear optical element used in a wide range of fields including an optical switch. Landscape technology

In general, a second-order nonlinear optical material containing an organic dye is given a second-order nonlinear optical characteristic by polarizing an organic dye inside the material by electric polling. The temperature is set high for efficient polarization, and the polymerization reaction and densification are performed by the sol-gel method (K. Izawa et al., Jpn. J. Appl. Phys. Vol. 32 (1993) 807) -811) In the case of a polymer material, the polarization treatment is performed while increasing the fluidity of the material (Japanese Patent Application Laid-Open No. 10-239720) or irradiating with ultraviolet rays.

In electrical polling, the orientation direction of the organic dye is unidirectional. Therefore, the phase matching condition important as an optical element for transmitting the second harmonic in a waveguide structure such as an optical modulator or an optical switch is not satisfied due to the difference in chromatic dispersion of the material.

As a means for satisfying the phase matching condition of an organic dye-containing organic material having a second-order nonlinear optical effect, polarization processing by optical poling has been reported (J. Si et al "Appl. Phys. Let., Vol. 72, Vol. 7 (1998) 762-764) In this method, a pulse laser of several picoseconds (ps) to several nanoseconds (ns) is used, and the fundamental wave and its second harmonic are polarized on the same axis. As in the case of electric poling, polarization efficiency increases when poling while increasing the temperature.

However, in polymer materials, the long-term stability of the polarization structure is poor, and the second-order nonlinear optical characteristics are degraded by the relaxation of the polarization structure. Specifically, T. As reported in Goodson III et al., J. Appl. Phys., 80 (12), 6602-6609 (1996), 4- [N-ethyl N (2-hydroxyxethyl)] amino 4'2-troazobenzene In a material in which is dispersed in polymethyl methacrylate, the intensity of the second harmonic generated by polarization by optical polling becomes almost zero at about 300,000 shots of the YAG laser.

The significant attenuation of the second harmonic is due to the relaxation of the polarization structure. That is, a polymer material is generally a material that is liable to change easily due to poor stability against thermal effects of laser light and environmental temperature changes. A dye exhibiting a non-linear effect develops second-order nonlinear optical characteristics by orientation polarization by poling, but the second-order nonlinear optical characteristics deteriorate due to relaxation of the polarization structure. Disclosure of the invention

The present invention has been devised to solve such a problem. By using an oxide formed by a sol-gel method as a matrix, the stability of the polarization structure is improved, It is an object of the present invention to provide an element that exhibits stable second-order nonlinear optical characteristics over a long period of time.

In order to achieve the object, the present invention is to cast an organic dye having a second-order nonlinear optical effect or a sol-gel liquid in which a polymer precursor having an organic dye in a side chain and a metal oxide precursor are dispersed on a substrate. It is characterized in that the formed thin film is simultaneously irradiated with light beams of two wavelengths coaxially to perform light polling. Optical polling can be performed on either the heat-treated thin film or the heat-treated thin film.

The manufactured second-order nonlinear optical material or second-order nonlinear optical element is composed of an organometallic raw material to which at least one organic functional group that does not hydrolyze or an organometallic raw material to which at least one organic functional group that does not hydrolyze is added Matrix materials have been synthesized using a mixture with an organic metal raw material to which only the organic functional group to be hydrolyzed is coordinated. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic diagram of the equipment used for optical polling.

FIG. 2 is a diagram illustrating a process of manufacturing the second harmonic element. BEST MODE FOR CARRYING OUT THE INVENTION

Organic dyes exhibiting a second-order nonlinear optical effect are not particularly limited in material, and include para-nitroaline, styryl-pyridin-ma-line, 414'tricyanovinyldimethylamino-diazostilbene, 3 Methyl 4-nitropyridine 1 oxide, 4—4 ′ dimethylaminocyanobiphenyl, dimethylaminophenyl urea, 4-amino 4 ′ nitrodiphenyl sulfide, 4-1 [diethyl (2H Deguchi quichetyl)] Amino 4'nitroazobenzene or the like is used. The polymer precursor having an organic dye in the side chain is not particularly limited, either. [3 (triethoxysilyl) propyl] 2,4 dinitrophenylamine, 3 (4formylphenoxy) Examples include propyl triethoxysilane, methacrylic acid having a second-order nonlinear optical dye added to a side chain, and polyamic acid having a second-order nonlinear optical dye added to a side chain.

The organic dye or the polymer precursor having the organic dye in the side chain is mixed with a metal oxide raw material and a solvent constituting the matrix to prepare a uniform sol-gel solution. The metal oxides used as the matrix are made of precursors such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxy titan, tetrabutoxy zirconium, tetrapropoxy zirconium, and trisecondary butoxy aluminum. Examples include silica, titania, zirconia, and alumina. The sol-gel solution is not particularly limited as a raw material in which an organic functional group that does not cause hydrolysis is added to the side chain of the metal oxide precursor, but is not particularly limited. Methyltriethoxysilane, 3-methacryloxypropyl Trimethoxysilane, phenylethoxysilane, diphenyldimethoxysilane, etc. are added. You.

Raw materials such as organic dyes, polymer precursors having organic dyes in the side chain, and metal oxide precursors are dispersed in solvents such as lower alcohols such as ethanol, isopropanol, and 2-methoxyphenol, and acetic acid. When the metal oxide precursor is unstable to hydrolysis, a stabilizer such as diethanolamine, monoethanolamine, dimethylformamide, etc. can be used in addition to the alcoholic solvent. Stabilizers not only stabilize the metal oxide precursor against hydrolysis, but also coordinate with the organic precursor and the polymer precursor having an organic dye in the side chain to improve dispersibility. The stabilizer is usually added in a proportion of 0.01 to 20 mol%, preferably 1 to 18 mol%.

In the sol-gel solution, the amount of water or acid to be introduced into the sol is appropriately adjusted depending on the type of the precursor so that the hydrolysis of the metal oxide precursor proceeds to some extent before the film formation. Specifically, precursors with a high rate of hydrolysis reaction do not require the introduction of water or acid, because they are hydrolyzed by atmospheric moisture even if they are left indoors after film formation. For the building, hydrolysis is promoted by adding an appropriate amount of water or acid.

The sol-gel liquid containing various raw materials is cast into a thin film on a heat-resistant substrate and gelled. Examples of the heat-resistant substrate include quartz glass. Glass substrates such as non-alkali glass, glass substrates coated with transparent electrodes such as ITO, and silicon substrates. Spin coating, immersion, spraying, etc. are used. The sol-gel solution is cast by the method. The coating thickness of the sol cast on the substrate is not particularly limited, but is generally adjusted to 100 to 100 nm, preferably to 100 to 500 nm. You.

After a gel film is formed from the sol cast on the substrate, it is placed in an oven and heat-treated at 80 to 300 ° C, preferably 130 to 220 ° C. When the thin film is fixed on the substrate by heat treatment, light poling is performed at the same time. You can also.

Specifically, as shown in Fig. 1, the thin film sample S is housed in an oven 1 that can transmit a laser beam and can control the temperature, and lenses 2 and 3 are placed before and after the oven 1.

The polling laser beam has a pulse width on the order of nanoseconds to femtoseconds, and is emitted from the laser oscillator 11. The laser beam passes through the lens 12 and is split by the beam splitter 13. Then, the light transmitted through the shutter 14, the second-order nonlinear optical crystal 15, the fundamental wave power filter 16, the mirror 17, the polarization rotator 18, and the light simply reflected by the mirror 19 are Are combined by a dichroic mirror 20, then irradiate a thin film sample S in an oven 1, and enter a light intensity detector 23 via a fundamental wave power filter 21 and a shirt filter 22. The angles and distances of the respective optical systems are adjusted so that the fundamental wave having the same polarization direction and its second harmonic are simultaneously and coaxially incident. The laser beam may be incident on the thin film sample S in any thickness direction or in any direction that guides the light in the plane of the thin film sample S. When one of the simultaneously incident laser beams is twice as long as the other, interference results in a polarization structure that satisfies the phase matching condition in the thin film sample S due to the two beams. . As a result, an SHG element that generates a second harmonic by making a long-wavelength laser beam incident is produced.

Matrix made from inorganic compounds is strong and can maintain the polarized structure for a long time. On the other hand, when a raw material having an organic functional group added to the side chain is used, the organic functional group remains in the matrix after hydrolysis and heat treatment. The resulting matrix has a three-dimensional structure due to the organic functional group, which suppresses the generation of fine bubbles as compared to a matrix composed of only an inorganic material, and makes the film structure itself dense. In general, pulsed lasers are used for optical poling, but dye energy sublimation can be a problem depending on the energy of the pulsed laser. In such a case, The effective film structure effectively suppresses the sublimation of the dye. In addition, although the dye is liable to change with time slightly as compared with a matrix containing only an inorganic compound, a large second-order nonlinear optical effect is obtained because the dye is easily polarized. Hereinafter, the present invention will be described more specifically with reference to examples. Example 1:

Ethanol: tetraethoxysilane: dimethylformamide: 4 _ [N-ethyl N (2 hydroxyshethyl)] amino 4 'nitroazobenzene: hydrochloric acid: water = 4: 1: 2: 0 in molar ratio. A sol-gel solution containing each component at a ratio of 05: 1. 18: 6 was prepared as follows. First, tetraethoxysilane and dimethylformamide are added to half the amount of ethanol, and the mixture is stirred. Further, 41- [N-ethyl N (2-hydroxyethyl)] amino 4'-nitroazobenzene is added, and the mixture is stirred. A solution was prepared. Separately from the solution, the remaining ethanolamine, hydrochloric acid and water were mixed to prepare a solution. The solution B was added dropwise to the solution to prepare a sol-gel solution.

After the sol-gel solution was stirred for 1 hour, it was applied to a non-alkali glass substrate at 2,000 rpm by spin coating. Immediately after the application, it was placed in an oven and dried at 150 ° C for 5 minutes. Coating and drying were repeated twice, and finally a gel film was prepared by drying for 20 minutes. The obtained gel film was subjected to optical poling during a heat treatment at 230 ° C. for 10 minutes using a polling apparatus shown in FIG. A 50 mJ, 50 Hz Nd: YAG laser with a pulse time of 3 to 3.5 nanoseconds was used for optical polling. The laser intensity was set to 0.23 W as the light intensity of the fundamental wave before focusing. The thin film that had been optically poled at 230 ° C was cooled to room temperature and irradiated with 1064 nm light of the fundamental wave used for optical poling to evaluate the success or failure of optical polling. As a result, the second harmonic of 532 ηm was detected. The intensity of the second harmonic is such that the second-order nonlinear optical constant Xeff for quartz is about 1.5, and the pulse of 1064 nm The signal intensity did not degrade even after irradiation with the laser for more than 30,000 shots. Example 2:

Ethanol: tetraethoxysilane: diphenyldimethoxysilane: dimethylformamide: 4— [N-ethyl N (2-hydroxicetyl)] amino 4'nitroazobenzene: hydrochloric acid: water = 4 in molar ratio : 0.95: 0.05: 2: 0.05: 1.18: 6 A sol-gel solution containing each component at a ratio of 6 was prepared as follows. First, tetraethoxysilane and dimethylformamide are added to half the amount of ethanol, and the mixture is stirred. Further, 4- [Nethyl N (2hydroxyshethyl)] amino 4'nitroazobenzene is added, and the mixture is stirred. was prepared solution a ₂ were uniformly dispersed. Apart from the solution A _2, it was prepared a solution B ₂ were mixed remaining Etanoruami down and hydrochloric acid, water. The solution B ₂ dropwise mixed Zoruge Le solution was prepared in solution A _2.

After the sol-gel solution was stirred for 1 hour, the solution was applied to an alkali-free glass substrate at 2,000 rpm by spin coating. Immediately after the application, it was placed in an oven and heat-treated at 210 ° C for 20 minutes to produce a dye-dispersed phenyl group-silicone composite thin film.

The obtained thin film was subjected to optical polling using a laser beam of 1064 nm and 532 ηm in the same manner as in Example 1. The laser intensity was set to 0.22 W as the light intensity of the fundamental wave before focusing. Optical polling was performed separately from the heat treatment.

In order to evaluate the success or failure of the optical polling, the light of 1064 nm of the fundamental wave used for the optical polling was irradiated. As a result, a second harmonic of 532 nm was detected. Regarding the intensity of the second harmonic, the second-order nonlinear optical constant _e ff for quartz was about 3. When the pulse laser of 1064 nm was continuously irradiated, the signal intensity decreased to about 20% up to 30,000 shots, but after that, it was irradiated for more than 30,000 shots. After the test, there was almost no deterioration of the signal strength. Example 3:

The components were stirred at a molar ratio of 2 methoxyethanol: titanium trisopropoxide: paranitroaline = 15: 1: 0.05 to prepare a sol-gel bath in which the components were uniformly dispersed. After stirring the sol-gel bath for 1 hour, the solution was applied to an alkali-free glass substrate at 2000 rpm by spin coating. Immediately after the application, it was placed in an oven and subjected to a heat treatment at 150 ° C for 20 minutes to produce a dye-dispersed titania thin film.

While heating the obtained thin film at 230 ° C. for 10 minutes, it was subjected to optical polling using laser beams of 1064 nm and 532 nm in the same manner as in Example 1. The laser intensity was set to 0.22 W, which is the light intensity of the fundamental wave before focusing.

The thin film that had been optically polled at 230 ° C was cooled to room temperature and irradiated with the fundamental wave of 1064 nm used for optical poling to evaluate the success or failure of the optical polling. As a result, a 532 nm second harmonic was detected. Regarding the intensity of the second harmonic, the second-order nonlinear optical constant Xeff for quartz was about 0.8, and there was no deterioration in signal intensity even after irradiating a pulse laser of 1064 nm for 30,000 shots or more. Example 4:

Acetone: N [3 (triethoxysilyl) propyl] 2,4 dinitrophenylamine: Tetraethoxysilane: Hydrochloric acid: Water = 20: 0.5: 0.5: 0.1: Mole ratio A sol-gel solution containing each component at a ratio of 6 was prepared as follows. First, § seton half volume by adding N [3 (Application Benefits triethoxysilyl) propyl] 2, 4 Gini Torofueniruami emissions and Te tiger silane stirred to prepare a solution A _4. Apart from the solution A _4, it was prepared a solution B ₄ was mixed remaining acetone and hydrochloric acid, water. Solution B ₄ was added dropwise to Solution A ₄ to prepare a sol-gel solution.

After the sol-gel solution was stirred for 10 minutes, the solution was applied to a glass substrate without spinning at 2000 rpm by spin coating. Immediately after the application, it was placed in an oven and dried at 130 ° C for 5 minutes to produce a gel film. While heating the obtained thin film at 230 ° C. for 10 minutes, it was subjected to optical polling using laser beams of 1064 nm and 532 nm in the same manner as in Example 1. The laser intensity was set to 0.22 W, which is the light intensity of the fundamental wave before focusing.

The thin film that had been optically polled at 230 ° C was cooled to room temperature, and irradiated with 1044 nm of the fundamental wave used for optical polling to evaluate the success or failure of optical polling. As a result, a 532 nm second harmonic was detected. Regarding the intensity of the second harmonic, the second-order nonlinear optical constant Xeff for quartz was about 1, and the signal intensity did not deteriorate even after irradiation with a pulse laser of 1064 nm for 30,000 shots or more. Example 5:

A second harmonic element was manufactured using the thin film provided on the substrate. As the thin film, as shown in FIG. 2, a gel film b provided on a glass substrate a without any force in Example 2 was used. After removing the thin film b while leaving the waveguide portion by reactive ion etching using the polyimide film c, the polyimide film d is further spin-coated on the surface on which the waveguide has been formed, and is formed at 150 °. C was thermally cured, and both end surfaces of the waveguide were polished. Two luminous fluxes 6 of 800 nm and 400111 ^ were incident from the end face of the waveguide, and were subjected to optical poling to produce a second harmonic element ί. When a laser beam of 800 nm, which is the fundamental wave g, was incident on the second harmonic element f, a second harmonic h of 400 nm was detected. This confirms that the required second harmonic element was obtained. Industrial applicability As described above, in the present invention, a sol-gel solution containing a non-linear optical organic dye is cast on a support such as a substrate to produce a gel film in which the non-linear optical organic dye is dispersed. By subjecting the thin film formed by the sol-gel method to heat treatment and optical polling, a second-order nonlinear optical material can be obtained. The thin film formed by the sol-gel method is a second-order nonlinear optical material with stable performance because the polarization state of the organic dye is fixed stably over a long period of time. In addition, since a polarization state that satisfies the phase matching condition can be obtained by optical poling, a nonlinear optical element such as a second harmonic element is manufactured.

Claims

The scope of the claims

1. An organic dye having a second-order nonlinear optical effect or a sol-gel liquid in which a polymer precursor and a metal oxide precursor having an organic dye are dispersed in a side chain are cast on a substrate, and two wavelengths are formed on the formed thin film. A method for producing a second-order nonlinear optical material, comprising simultaneously irradiating a plurality of light beams coaxially and performing light polling.

2. The method for producing a second-order nonlinear optical material according to claim 1, wherein the thin film being heat-treated or the heat-treated thin film is subjected to optical polling.

3. Organometallic raw material to which one or more non-hydrolyzable organic functional groups are added, or organometallic raw material to which one or more non-hydrolyzable organic functional groups are added and only organic functional groups to be hydrolyzed are coordinated 2. The method for producing a second-order nonlinear optical material or a second-order nonlinear optical element according to claim 1, wherein the matrix material is synthesized with a mixture of the following.