JP2849703B2 - Metal oxide-based third-order nonlinear optical materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material which forms the basis of an optical device utilizing a non-linear optical effect, and more specifically, a substance having a large non-linear optical effect obtained by adding / combining an alkali metal to a metal oxide. A thin film of

[0002]

2. Description of the Related Art As a substance having a relatively large nonlinear optical effect which has been conventionally found, CdS
Glass and the like in which semiconductor fine particles such as Au are dispersed and deposited and noble metal fine particles such as Au and the like are dispersed and precipitated are known. In contrast, recently, we have discovered that certain transition metal oxides, such as V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , CuO, etc. It has been found that a large nonlinear optical effect comparable to that of a conventionally promising material is exhibited (Japanese Patent Application No. Hei 6-678).
No. 41). Such transition metal oxides have not only the advantage of exhibiting a large nonlinear optical effect, but also intense laser irradiation, which is important when used in optical devices, especially in comparison with other nonlinear optical materials that have been studied conventionally. It has excellent characteristics in that it has excellent stability, can be easily synthesized from inexpensive raw materials, hardly causes chemical changes over a long period of time, and has almost no toxicity to the human body. The third-order nonlinear optical material is considered to be applied to various optical devices by utilizing a nonlinear refractive index change and a nonlinear extinction coefficient change, which are manifested by a third-order nonlinear optical effect. The most promising is the application to all-optical computers. To achieve practical use of this all-optical computer, it is necessary to further improve the performance of the third-order nonlinear optical material. That is, the development of a material having a higher third-order nonlinear susceptibility (χ ⁽³⁾ ), a faster response speed, and a smaller light absorption (extinction coefficient: α) is required. In particular, it is important to develop a material having a large figure of merit χ ⁽³⁾ / α, which is often used as a criterion for evaluation. However, in general, since a material having a large χ ^{(3) has} a large α, there is a problem that it is difficult to greatly improve the figure of merit χ ⁽³⁾ / α.

The present inventors have conducted intensive studies in view of the current situation and problems of the above-described third-order nonlinear optical materials, and as a result, have found a transition metal oxide-based material found in the prior application (Japanese Patent Application No. 6-67841). By adding an alkali metal to the material,
^It has been found that not only ⁽³⁾ but also χ ⁽³⁾ / α can be greatly improved, and the utility as a third-order nonlinear optical material is enhanced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to stably express high third-order nonlinear optical effects (large 発 現⁽³⁾ and χ ⁽³⁾ / α) in view of the current state of nonlinear optical materials, and Another object of the present invention is to provide a new non-linear optical material which is inexpensive and excellent in safety and a method for manufacturing the same.

[0005]

Means for Solving the Problems The present invention has been made to achieve the above object, and the third-order nonlinear optical material of the present invention comprises V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , CuO
And a thin film of a material obtained by adding and combining at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs to at least one metal oxide selected from the group consisting of NiO and NiO. It is formed on a transparent substrate.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The "metal oxide" used in the present invention is exemplified by V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , CuO and NiO. Particularly preferred are V ₂ O ₅ and NiO.

In the present invention, the metal added to and combined with the metal oxide includes at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs.
More preferably, Li is used.

The ratio of the number of metal atoms in the metal oxide to the number of alkali metal atoms in the additional component is not particularly limited.
It is preferably about (1: 0.01) to (1: 0.5), more preferably about (1: 0.02) to (1: 0.2).

As the transparent substrate to which the above-mentioned thin film is applied,
Examples thereof include glass containing SiO ₂ as a main component, quartz, and sapphire made of Al ₂ O ₃ .

In the present invention, the main components of the nonlinear optical material are V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , CuO and NiO
At least one metal oxide selected from the group consisting of These oxides have a property of exhibiting a high third-order nonlinear optical effect under irradiation of strong light such as laser light. The reason why such a phenomenon occurs is not clear, but is presumed to be due to the following principle. That is, these metal oxides have semiconductor properties, and thus have continuous absorption bands in a wide wavelength range from ultraviolet to visible to near infrared. Therefore, when a metal oxide is irradiated with a laser beam having a frequency in the vicinity of the band gap, the carrier density in the excited state is significantly increased, causing saturation absorption to change the refractive index. It is presumed that an optical effect appears. Further, it is considered that the change in the refractive index due to the temperature rise accompanying the irradiation of the laser beam also contributes to the expression of the third-order nonlinear optical effect.

Such a phenomenon does not appear in all metal oxides, but satisfies the two conditions of (a) having an absorption band at the wavelength of the irradiated laser beam and (b) having semiconductor properties. It is believed that this is achieved only with metal oxides. V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , CuO
And at least one metal oxide thin film selected from the group consisting of NiO and NiO exhibits a high third-order nonlinear optical effect.

In the present invention, V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ ,
Co ₃ O ₄ , CuO and NiO, at least one metal oxide selected from the group consisting of Li, Na, K, Rb and at least one alkali metal selected from the group consisting of Cs, added and combined A compound is generated, and a thin film of such a compound is formed on a transparent substrate to obtain a nonlinear optical material. The purpose of adding the alkali metal in the compound of the present invention is to enhance the nonlinear optical effect of the metal oxide thin film, that is, to increase χ ⁽³⁾ . When no alkali metal is added, the semiconducting properties are small, and the metal oxide close to the insulator becomes a compound having a large semiconducting property by adding the alkali metal, and the nonlinear optical effect is enhanced by the increase in such semiconducting properties. , Χ ⁽³⁾ is estimated to increase. As the semiconductor properties of metal oxides increase,
^{In the} ultraviolet-visible-near-infrared region, α in the town area tends to increase at the same time as ⁽³⁾ increases. Not so, by appropriately selecting the amount of alkali metal added,
χ ⁽³⁾ can be increased substantially without increasing α. That is, both the third-order nonlinear susceptibility χ ⁽³⁾ and the figure of merit χ ⁽³⁾ / α can be increased, and the usefulness as a nonlinear optical material can be enhanced.

The thin film is usually formed on a transparent substrate such as glass, quartz or sapphire. The method for forming the thin film is not particularly limited, and a so-called gas phase method such as a sputter deposition method, a vacuum deposition method, or a CVD method, or a solution such as a metal alkoxide, a metal nitrate, or a metal salt of an organic acid is applied on a substrate and thermally decomposed How to do
Various known methods can be applied. For example, a solution of a metal oxide or a metal alkoxide serving as a precursor of a metal to be added, a metal nitrate, a metal salt of an organic acid, or the like is mixed, and a film is formed on a substrate by a spin coating method or the like. For example, a method of baking under an atmosphere including the above can be applied.

In the present invention, these metal oxides can be used alone or as a mixture. Further, it may be used not only as an oxide of a single component metal element but also as a composite oxide.

The thickness of the thin film is not particularly limited. However, in the case where the thin film is used as a nonlinear optical material by transmitting laser light, if the thin film is too thick, the light transmission ratio is reduced, and the output light is reduced. And is weakened by being re-absorbed, thereby deteriorating its usefulness as a nonlinear optical material. Usually, in the case of a dense thin film such as a thin film formed by a sputter deposition method,
Usually, a film thickness of about 2 to 50 nm, preferably 5 to 20 nm is appropriate.In the method of applying a solution and thermally decomposing, the formed thin film is not relatively dense, so even a thicker film can be used as a nonlinear optical material. Can be used. On the other hand, when a thin film of a non-linear optical material is formed on the surface of an optical waveguide and an evanescent wave oozing out of the optical waveguide is used, there is no problem in using the film even if the thin film is too thick. In order not to become an excellent material, the thickness of the thin film is preferably 2 nm or more, more preferably 2 to 100 nm, and further preferably about 5 to 50 nm.

[0016]

According to the present invention, it is possible to provide a new non-linear optical material which stably exhibits a high non-linear optical effect, is inexpensive and has excellent safety, and a method of manufacturing the same.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

EXAMPLE 1 A mixture of nickel octylate and lithium naphthenate (nickel: lithium = 100: 5) was placed on a glass substrate (one side).
(Atomic ratio) was formed by spin coating, and baked at 380 ° C. for 2 hours to prepare a light brown transparent lithium-added nickel oxide thin film having a thickness of about 80 nm. The third-order nonlinear susceptibility (χ ⁽³⁾ ) of this lithium-doped nickel oxide thin film is 532 nm.
The result was 1.4 × 10 ⁻⁹ esu as measured by degenerate four-wave mixing (DFWM) using a laser beam with a pulse width of 7 ns.
The value reached at least 20 times the value of χ ⁽³⁾ of the nickel oxide thin film to which lithium was not added. The extinction coefficient (α) at a wavelength of 532 nm of the lithium-added nickel oxide thin film and the nickel oxide thin film without lithium addition was 6.5 × 10 ³ cm ^−1, respectively.
And 7.7 × 10 ³ cm ⁻¹ , and an undesired increase in α was not observed even with the addition of lithium, but slightly decreased.
As a result, in the lithium-doped nickel oxide thin film, not only χ ⁽³⁾ but also the figure of merit (χ ⁽³⁾ / α) was improved by at least 20 times as compared with the nickel oxide thin film to which lithium was not added.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sakaguchi 1-8-31 Midorigaoka, Ikeda-shi, Osaka Prefecture Inside the Industrial Technology Research Institute Osaka Institute of Technology (72) Inventor Masaru Miya 1--8th Midorioka, Ikeda-shi, Osaka No. 31 Osaka Institute of Technology (58) Investigated field (Int. Cl. ⁶ , DB name) G02F 1/35 505 JICST file (JOIS)

Claims (6)

(57) [Claims] 1. A method according to claim 1, wherein V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe
_At least one metal oxide selected from the group consisting of ₂ O ₃ , Co ₃ O ₄ , CuO, and NiO includes Li, N
A third-order nonlinear optical material obtained by forming a thin film of a substance obtained by adding and combining at least one kind of alkali metal selected from the group consisting of a, K, Rb and Cs on a transparent substrate. 2. The third-order nonlinear optical material according to claim 1, wherein the metal oxide is NiO. 3. The third-order nonlinear optical material according to claim 1, wherein the metal oxide is V ₂ O ₅ . 4. The third-order nonlinear optical material according to claim 1, wherein the alkali metal is Li. 5. The third-order nonlinear optical material according to claim 1, wherein the thin film is a lithium-doped nickel oxide thin film. 6. V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe
_At least one metal oxide selected from the group consisting of ₂ O ₃ , Co ₃ O ₄ , CuO and NiO, or V,
Li, Na, Fe, Co, a solution of at least one metal alkoxide, nitrate or organic acid salt selected from the group consisting of Cr, Mn, Fe, Co, Cu and Ni;
A solution of at least one alkali metal alkoxide, nitrate or organic acid salt selected from the group consisting of Cu and Ni is applied or mixed, formed into a film on a substrate by a spin coating method, and then fired in an atmosphere containing oxygen. A method of manufacturing a third-order nonlinear optical material.