JP2903581B2 - Manufacturing method of optical waveguide device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide device having an optical waveguide made of an oxide optical material used for various optical devices having an optical waveguide, and relates to the oxide optical device. An optical waveguide made of a material is improved in light absorption characteristics other than the light absorption inherent to the material, and the efficiency of optical waveguide is improved.

[Summary of the Invention]

The present invention relates to a method for manufacturing an optical waveguide device using an oxide optical material, and particularly to a method for manufacturing the optical waveguide device using ozone (O ₃ ).
By performing heat treatment in an atmosphere containing, it is possible to eliminate light absorption causes other than the light absorption inherent in the oxide optical material, and to improve the light transmittance of the base material as various optical materials. .

The present invention also provides an optical waveguide device in which an optical waveguide made of an oxide optical material thin film of LiNbO ₃ is provided on a MgO-doped LiNbO ₃ single crystal substrate, and the above-described heat treatment is performed.

[Conventional technology]

Oxide optical materials have their electro-optic, acousto-optic,
It is widely used for various optical elements, optical waveguides, etc. by utilizing the characteristics such as the magneto-optical effect and the non-linear optical effect.
G, for example, to shorten the wavelength from the light source of the semiconductor laser light, for example, to use as a light source for optical recording, for example, to improve the recording density by short wavelength recording, and to improve the resolution. It is extensive.

However, in a normal oxide optical material, for example, lithium niobate (LiNbO _3, hereinafter abbreviated as LN), which has a non-linear optical effect and is attracting attention for application to SHG, its optical material base is its inherent light. Since it exhibits high light absorption characteristics other than absorption, for example, in visible light green (wavelength: 0.5145 μm), there are inconveniences such as restrictions on its use.

For example are also reports that this is transparent when the optical material remains pulled by high-temperature annealing the optical material made of crystal pulling method in an oxygen O ₂ atmosphere is darkened, but the oxygen (O ₂ ) Sufficient improvement in light absorption has not been achieved by heat treatment in an atmosphere.

[Problems to be solved by the invention]

The present invention aims to eliminate or reduce light absorption at a wavelength other than the light absorption specific to the above-described oxide optical material.

In other words, as a result of research and consideration that absorption other than absorption of light having its own wavelength occurs in this oxide optical material,
The cause is considered to be oxygen deficiency, that is, oxygen vacancies. For example, when growing an LN thin film as an optical waveguide by SPE or a liquid phase epitaxial growth (LPE) on a LiTaO ₃ substrate as an optical waveguide,
Since the melt contains V ₂ O ₅ as a flux when the LPE is applied, that is, for example, to reduce the melting point, the LN thin film obtained by the LPE has a portion of
Li (NbV _δ ³⁺ ) O substituted by (Vanadium)
_3-δ is obtained. By the way, this LN thin film absorbs green light having a wavelength other than the wavelength showing the intrinsic absorption of LN. This is oxygen O
This is thought to be due to the formation of oxygen vacancies deficient. In other words, electrons are localized due to the presence of these oxidized vacancies, or V ⁵⁺ , which should be pentavalent for charge neutralization, ie, charge compensation, changes to trivalent V ³⁺ . However, this seems to cause light absorption other than the light absorption inherent in the material, for example, in green.

Therefore, in the present invention, light absorption is improved by effectively eliminating the oxygen vacancies.

[Means for solving the problem]

In the present invention, in a method for manufacturing an optical waveguide device in which an optical waveguide made of an oxide optical material is formed on a substrate,
Heat treatment is performed in an oxygen atmosphere containing ozone (O ₃ ).

In another embodiment of the present invention, as shown in FIG. 1, an optical waveguide comprising an oxide optical material thin film (2) of LiNbO ₃ is provided on a MgO-doped LiNbO ₃ single crystal substrate (1), An optical waveguide device subjected to the heat treatment described above is configured.

[Action]

According to the above-described method of the present invention, it is possible to reduce light absorption close to a limit value that almost depends only on the composition of the oxide optical material obtained by the heat treatment including ozone irrespective of the properties itself of the oxide optical material obtained by initial LPE, for example. Get off. This is considered to be due to the fact that active O is generated by the thermal decomposition of ozone (O ₃ ) and the oxygen vacancies in the oxide optical material are compensated to suppress the localization of electrons and the change in charge.

〔Example〕

Example 1 As shown in FIG. 1, on a LiNbO ₃ single crystal substrate (1) doped with MgO, an oxide optical material thin film (2) to be an optical waveguide made of LiNbO ₃ is generated by LPE to produce SHG. Formed. In this case, as a melt for obtaining the LPE, The sample thus obtained, that is, the optical waveguide obtained by LPE using LN, is deficient in oxygen, that is, has oxygen vacancies. That is, in the present embodiment, since oxygen was selected to be smaller than stoichiometry (stoichiometry), the use of the melt resulted in the active formation of an oxygen-deficient state and the visible light green Light (0.15
(45 μm). By the way, the stoichiometric melt contains 50 mol% of Li ₂ O, 10 mol% of Nb ₂ O ₅ and V
₂ O ₅ is 40 mol%. FIG. 2 shows the result of measuring the amount of light transmission of green light (0.5145 μm) with respect to the optical waveguide using the LN thin film thus obtained. That is, in this case, the optical power with respect to the light transmission distance was measured by coupling the prism to the optical waveguide, changing the position thereof, and measuring the optical power obtained from the prism. In Fig. 2 ●
The marks and the ▲ marks are plots of the measurement results of the optical power with respect to the light in the TE mode and the light in the TM mode, respectively, immediately after the LPE. In this case, the light absorption coefficient α for the TE mode is α5.74 cm ^−1. In this case, the light propagation loss L of the guided light was L24.9 dB / cm, and the TM mode was α17.9 cm ⁻¹ and L77.6 dB / cm.

At 600 ° C, 1
The heat treatment according to the present invention was performed in an atmosphere containing ozone (O ₃ ) for a long time. TE mode and TM after this heat treatment respectively
The results of measuring the amount of light passing through the mode are plotted as circles and triangles, respectively. When the light absorption coefficient α and the light propagation loss L of the guided light are respectively observed from these, in the TE mode, α0.36 cm ⁻¹ and L1.55 dB / c are obtained.
In the m and TM modes, α1.65 cm ⁻¹ and L 7.2 dB / cm. As is apparent from comparison between them, light absorption for green light is remarkably reduced.

In addition, the LiNbO ₃ substrate (1) containing MgO is thus placed on the LiNbO ₃ substrate.
_{(3) An} optical waveguide device formed by forming an optical waveguide by a thin film,
Since both the substrate (1) and the optical waveguide thereon are made of LiNbO ₃ , they have excellent crystallinity and can effectively reduce light absorption. In addition, the LiNbO ₃ substrate (1) containing MgO and the LiNbO ₃ thin film (2) )
That is, the difference between the refractive index of the optical waveguide and that of the optical waveguide is large, and the change in the refractive index between the two can be rapidly changed in a stepwise manner, so that the optical waveguide can have a more excellent function.

Example 2 Li (Nb _x Ta _1-x ) O ₃ thin film was formed on a LiTaO ₃ substrate Was grown by the LPE method using the melt. This thin film functions as an optical waveguide, but when HeNe laser light having a wavelength of 0.6328 μm is guided, light is transmitted only at a distance of about 1 mm. Ozone (O ₃ ) 1% by volume for 3 hours at 500 ° C
And heat treatment was carried out in an atmosphere of the remaining oxygen. After this heat treatment, light having the above-mentioned wavelength was transmitted by 7 mm or more. This shows that light absorption is improved.

Example 3 A KTiOPO ₄ (KTP) optical material grown by a flux method and having a cube of about 40 mm on each side was heat-treated at 800 ° C. for 7 hours in oxygen containing ozone (O ₃ ). Peeling was observed.

As described above, in the case of the method of the present invention, an improvement in light absorption is clearly obtained.

As described above, light absorption can be reduced to the limit value specific to the material by the heat treatment in ozone according to the method of the present invention, but the ozone (O ₃ ) concentration in the atmosphere of this heat treatment is 0.01% by volume or more. Although the effect can be obtained, the effect is saturated at 20% by volume, which is close to the limit of a commercially available ozone generator. Therefore, the amount is preferably 20% by volume or less, for example, about 10% by volume.

Further, the heating temperature is 300 ° C. or more, the effect of improving the light absorption can be obtained.However, the heating temperature is limited to a temperature that does not affect the film destruction or the crystal characteristics, for example, 1000 ° C. The following is assumed.

In the method of the present invention, the heat treatment is performed in an oxygen atmosphere containing ozone. In this case, the heat treatment in the ozone causes damage to the surface of the oxide optical material, thereby reducing the magnetostatic property, for example. If, for example, a problem arises in the characteristics when applied to a medium for surface wave propagation or the like, before the heat treatment in ozone, the SiO ₂ film is formed on the surface of the oxide optical material, for example, on the surface of the film formed by LPE. , A protective film such as SiN can be formed. The thickness of the protective film is, for example, not less than 50.degree. Which can cover the surface of the optical material uniformly without generating a cut-off portion, and is not more than 5 .mu.m, for example, so that the optical characteristics are not lost by the deposition. Further, for example, when a non-reflection coat or a light-trapping cladding layer is formed on the surface of the optical material, the non-reflection coating or the cladding layer can be used as a protective film.

Incidentally, the film thickness of the anti-reflection code is λ / 2n (λ: wavelength, n:
(Refractive index).
Since the thickness is selected to be about 3000 ° and the cladding layer is 1600 °, it can be sufficiently used as a protective film for heat treatment in O ₃ .

In addition, the oxide optical material is not limited to the above-described example, and may be, for example, KNbO ₃ , β-BaB ₂ O ₄ , Y ₃ Al ₅ O ₁₂ , LiB ₃ O ₅ , TeO ₂ , B
The present invention can be applied to the improvement of the light absorption characteristics for a ₂ NaNb ₅ O ₁₅ , BaTiO ₃ , Bi ₁₂ SiO ₂₀ , Bi ₁₂ GeO ₂₀ , ZnO and the like.

〔The invention's effect〕

As described above, in the present invention, after the oxide optical material is grown, heat treatment is performed in an oxygen atmosphere containing ozone (O ₃ ) to improve the absorption of light other than the absorption of the wavelength unique to the material. This is due to the localization of electrons due to the generation of oxygen vacancies due to oxygen deficiency as described above, or to the light that does not originally occur due to the change in charge to neutralize the charge due to the presence of these vacancies. The absorption is compensated by the heat treatment in an ozone atmosphere, that is, the supply of active oxygen to compensate for oxygen vacancies, thereby avoiding the above-described localization of electrons and changes in charge, and improving light absorption characteristics other than material-specific absorption. It seems to come off.

Further, according to the method of the present invention described above, since the light loss in the optical waveguide can be reduced by improving the light absorption characteristics of the optical waveguide, an efficient optical waveguide device, for example, an optical integrated circuit or the like can be constructed. You can do it.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of an optical waveguide device according to the present invention. FIG. 2 shows the results of measuring the light transmission of the oxide optical crystal before and after heat treatment in ozone. (1) is a substrate, and (2) is an oxide optical material thin film.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C30B 28/00-35/00 G02F 1/29-7/00

Claims (2)

(57) [Claims] 1. A method for manufacturing an optical waveguide device, comprising: forming an optical waveguide made of a thin film of an oxide optical material on a substrate; and performing heat treatment in oxygen containing ozone. 2. An optical waveguide device comprising: forming an optical waveguide made of an oxide optical material thin film made of LiNbO ₃ on a MgO-doped LiNbO ₃ single crystal substrate; and performing heat treatment in oxygen containing ozone. Manufacturing method.