JPH1164663A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To embody a process for producing an optical waveguide by forming a lithium niobate film which is added with titanium and of which the chemical compsn. formula is expressed by LiNbO3 on a substrate having an electro-optic effect by a sol-gel method. SOLUTION: This process produces the optical waveguide by forming the lithium niobate film 12 to which Ti is added and is expressed by the chemical compsn. formula LiNbO3 on the substrate 11 having the electro-optic effect by the sol-gel method. The Ti-added lithium niobate film 12 is formed by manufacturing a soln. of the precursor of the Ti-added lithium niobate by using org. acid lithium, alkoxide niobium and alkoxide titanium, applying a coating soln. prepd. by diluting the precursor soln. on the substrate 11 and baking the coating film by heating, then repeating the coating applying stage and baking stage by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical waveguide, and more particularly, to a method for manufacturing an optical waveguide used in an optical communication device.

[0002]

2. Description of the Related Art With the increase in information capacity toward the advanced information society, the practical use of optical communication has progressed, and the need for optical switching has increased. In addition, a new optical subscriber system (Switched Access Star: SAS) has been proposed, and optical switching has become an increasingly important device. However, conventional mechanical optical switching (prisms, mirrors, fibers, and the like) is not suitable for integration in terms of speed, shape, reliability, and the like. Therefore, using a ferroelectric material such as lithium niobate (LiNbO ₃ ), titanium (Ti) is diffused into a substrate to form an optical waveguide, and an electric field is applied to the optical waveguide to change the refractive index of light to electric. Development of a waveguide-type control device that performs switching and modulation by changing the phase of light transmitted through the waveguide by changing the phase by an optical effect has been promoted.

Generally, a Ti-diffused LiNbO ₃ waveguide is manufactured by, for example, an optical integrated circuit (Ohm), (1993)
The method disclosed in Hiroshi Nishihara, Masamitsu Haruna, Toshiaki Suhara, p170-175 is employed. Specifically, LiN
A resist is applied after cleaning the grease and dirt on the surface of the bO ₃ substrate, and after baking the pattern, developing is performed to form a resist pattern. Next, a Ti film is deposited by sputtering or electron beam evaporation. When a magnetron type RF sputtering apparatus is used, a Ti target having a target diameter of 10 cm is used, the RF power is set to 100 W, the sputtering atmosphere is set to an argon (Ar) gas atmosphere, and the pressure of the atmosphere is set to 2.7 Pa.
The sputtering rate was set to 24 nm / min.
Under these conditions, when the distance between the substrate and the target is 45 mm, a uniform Ti film can be obtained over a diameter of about 30 mm. Since the change amount Δn of the surface refractive index of the diffusion waveguide is mainly controlled by the Ti film thickness, the Ti sputtering rate is suitably from 0.3 nm / sec to 0.4 nm / sec or less.

Then, after removing the resist, a Ti pattern is formed. This Ti pattern is thermally diffused to produce a Ti-diffused LiNbO ₃ waveguide. An electric furnace is used for heat diffusion. At this time, in order to prevent outward diffusion of lithium oxide (Li ₂ O), argon (Ar) gas and oxygen (O ₂ ) gas were passed through warm water at about 60 ° C. to introduce a mixed gas containing water vapor into the quartz tube. And heat. This heating temperature is 1000
At 6 ° C., the heating time is about 6 hours when the Ti film thickness is 40 nm to 50 nm. When the Ti film thickness is 45 nm, the diffusion temperature is 1000 ° C., and the diffusion time is 6 hours while flowing Ar gas and 1 hour while flowing O ₂ gas, the resulting Ti-diffused LiNbO ₃ waveguide has a surface refractive index change. Δn =
0.022, diffusion depth d = 2.6 μm, propagation loss 0.5
A characteristic of dB / cm to 1.0 dB / cm is obtained.

[0005]

However, in the method of manufacturing a Ti-diffused LiNbO ₃ waveguide described in the prior art, since the waveguide is manufactured by thermally diffusing Ti, the surface refraction of the diffusion waveguide is reduced. The rate of change Δn is mainly Ti
It will be controlled by the film thickness. Since the uniform range of the thickness of the Ti film is 30 mm in diameter, a 3 inch substrate (having a diameter of
mm) is not covered. Further, the maximum value of the refractive index change is as low as Δn = 0.022. Since this uses thermal diffusion, Ti diffused into the substrate
Concentration is 1.5% or less (Δn = 0.08 at the maximum)
It is caused by that.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for manufacturing an optical waveguide which has been made to solve the above problems. That is, this is a method for producing an optical waveguide in which a lithium niobate film having a chemical composition formula of LiNbO _{3 in} which titanium is added is formed on a substrate having an electro-optical effect by a sol-gel method.

In the method of manufacturing an optical waveguide, a lithium niobate film having a chemical composition formula of LiNbO ₃ to which titanium is added is formed on a substrate having an electro-optical effect by a sol-gel method. LiNb with uniform titanium added to a large area characterized by the sol-gel method
O ₃ is formed. Furthermore, the amount of change in the surface refractive index is uniform, light scattering is reduced, and variations in optical characteristics are suppressed. Also, by controlling the amount of titanium added,
An optical waveguide having a large refractive index difference is manufactured.

[0008]

Embodiments of the present invention will be described below.

First, in a first step, lithium organic acid represented by a chemical composition formula RCOOLi, wherein R is a hydrocarbon,
chemical composition formula m is a natural number _{Nb (O-C m H 2m} + 1) 5
Alkoxide niobium represented in, by using the alkoxide of titanium represented by the chemical composition formula of n is a natural number _{Ti (O-C n H 2n} +1) 4, the chemical composition formula was added titanium L
A precursor of lithium niobate represented by iNbO ₃ is produced.

Alternatively, a chemical composition represented by the chemical formula R
Lithium organic acid represented by COOLi, chemical composition formula Li a a is a natural number _{(O-C a H 2a +} 1) and alkoxide of lithium represented by the chemical composition formula b is a natural number Nb
(O-C _b H _{2b + 1} ) ₅ , and a chemical composition formula Ti (O-C
A precursor of lithium niobate represented by a chemical composition formula LiNbO _{3 to} which titanium is added is prepared using alkoxide titanium represented by _c H _{2c + 1} ) ₄ .

Next, in a second step, the above-prepared precursor is applied on a substrate to form a coating film composed of a precursor of lithium niobate, and the coating film is heated and fired.

By repeating the step of applying the precursor of the second step on the substrate and the step of heating and baking the coating film, the substrate is represented by the chemical composition formula LiNbO _{3 in} which titanium is added to the substrate. A lithium niobate film is formed.

The lithium organic acid (RCOOLi; R represents a hydrocarbon) includes saturated lithium carboxylate (C _n H _{2n + 1} COOLi; n represents a natural number), unsaturated lithium carboxylate, and aromatic carboxylic acid. There is lithium.

The saturated lithium carboxylate includes lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium caronate, lithium enanthate, lithium caprylate, lithium pelargonate, lithium caprate, lithium undecanoate, lithium dodecanoate Lithium, lithium tridecanoate, lithium tetradecanoate, lithium pentadecanoate, lithium hexadecanoate, lithium peptadecanoate, lithium octadecanoate, lithium nonadecanoate, lithium eicosanoate, lithium heneicosanoate, lithium docosanoate, lithium tricosanoate, lithium tetracosanoate, Lithium pentacosanoate, lithium hexacosanoate, lithium heptacosanoate, lithium octacosanoate, lithium nonakosanoate, triacontan Lithium, Heng triacontyl lithium Tan, lithium dotriacontanoic, lithium tritriacontanoic acid, lithium tetra triacontyl Tan, lithium pentatriacontanoic Con Tan, lithium hexatriacontane, lithium heptamethylene triacontyl Tan acid,
Lithium nonatricontanate, lithium tetracontanate, lithium hentetracontanate, lithium dotetracontanate, lithium tritetracontanate, lithium tetratetracontanate, lithium pentatetracontanate, lithium hexatetracontanate, heptatetracontan Lithium oxide, lithium octatetracontanate, lithium nonatetracontanate, lithium pentacontanate, lithium hempantacontanate, lithium dopentacontanate, lithium tripentacontanate, lithium tetrapentacontanate, lithium pentapentacontanate, Lithium hexapentacontanate, lithium heptapentacontanate, lithium octapentacontanate, lithium nonapentacontanate, lithium hexacontanate, Lithium Kisakontan acid, lithium-decenoic acid, lithium undecenoic acid, lithium dodecene acid, lithium tridecene acid, lithium tetradecene acid,
Lithium pentadecenoate, lithium hexadecenoate, lithium peptadecenoate, lithium octadecenoate, lithium nonadecenoate, lithium eicosenoate, lithium heneicosenoate, lithium docosenate, lithium tricosenate, lithium tetracosenoate, lithium hentakosenate, lithium hexacosenate, lithium peptacosenate Lithium, lithium octacocene, lithium nonacocene,
Lithium oxalate, lithium malonate, lithium succinate, lithium glutarate, lithium adipate, lithium pimerate, lithium suberate, lithium azelate, lithium sebacate, and the like can be used.

As the unsaturated lithium carboxylate, lithium acrylate, lithium propiolate, lithium methacrylate, lithium crotonate, lithium isocrotonate, lithium oleate, lithium fumarate, lithium maleate and the like can be used.

As the lithium aromatic carboxylate, lithium benzoate, lithium toluate, lithium naphthoate, lithium salicylate, lithium anthranilate, lithium cinnamate, lithium mandelate and the like can be used. The organic lithium may be any organic lithium having up to 60 carbon atoms, for example.

Examples of the above alkoxydoniobium include pentamethoxydniobium, pentaethoxydniobium, pentapropoxydniobium, pentabutoxidedniobium, pentapentoxydniobium, pentahexoxidedniobium, pentaheptoxydniobium, pentaoctoxydniobium and pentadoxydniobium. Nonaxidoniobium, pentadecoxydniobium, pentown decodoxydniobium, pentadodexoxydniobium, pentatridecoxydniobium, pentatetradecoxydniobium, pentapentadecoxydniobium, pentahexadecoxydniobium, pentaheptadecoxydniobium , Pentaoctadecoxydniobium, pentanonadecoxydniobium, pentaeicoxidniobium, pentaheneicodoxyniobium, pentadoxydniobium, pentatricoxydniobium, pentad Tiger Jobs Sydney of, penta penta Jobs Sydney of, penta-hexa Jobs Sydney of, penta hepta Jobs Sydney of, penta octa Jobs Sydney of,
Pentanonacoxide niobium, 1 methoxy 2 ethoxydniobium, 2 methoxy 3 ethoxydniobium, 3 methoxy 2 ethoxydniobium, 4 methoxy 1 ethoxydniobium and the like can be used.

Examples of the above alkoxide titanium include tetramethoxide titanium, tetraethoxide titanium, tetrapropoxide titanium, tetrabutoxide titanium, tetrapentoxide titanium, tetrahexoxide titanium, tetraheptoxide titanium, tetraoctoxide titanium, tetraoctoxide titanium, and tetraoctoxide titanium. Titanium nonoxide, tetradecoxide titanium, 1 methoxy 3 ethoxide titanium, 2 methoxy 2 ethoxide titanium, 3 methoxy 1 ethoxide titanium, or the like can be used.

The lithium alkoxide includes lithium methoxide, lithium ethoxide, lithium propoxide, lithium butoxide, lithium pentoxide,
Lithium hexaoxide, lithium heptoxide, lithium octoxide, lithium nonoxide, lithium decoxide, undecoxide lithium, lithium dodecoxide, lithium tridecoxide, lithium tetradecoxide, lithium pentadecoxide, lithium hexadecoxide , Lithium heptadecoxide, lithium octadecoxide, lithium nonadecoxide, lithium eicoxide, lithium henecoxide, lithium docoxide,
Lithium trichoxide, lithium tetracoxide, lithium pentacoxide, lithium hexacoxide, lithium heptacoxide, lithium octacoxide, lithium nonacoxide, and the like can be used.

Next, a specific manufacturing method will be described with reference to a manufacturing process diagram of FIG. FIG. 1 schematically shows the present invention so that the present invention can be understood. The materials used, numerical conditions, and the like shown here are examples within the scope of the present invention, and the present invention is not limited only to these materials and numerical conditions.

In Example 1, as the sol-gel raw material, for example, lithium acetate was used as the organic acid lithium, pentaethoxydniobium was used as the alkoxide niobium, and tetraethoxide titanium was used as the alkoxide titanium.

First, lithium acetate and pentaethoxydniobium are dissolved in an ethanol solution. This solution is stirred and refluxed for 24 hours to perform a deesterification reaction.
This reaction is represented by equation (1).

[0023]

Embedded image

As shown in the above formula (1), niobate in which lithium and niobium in the form of Li—O—Nb— (O—C _m H _{2m + 1} ) ₄ have a one-to-one bond, where m is a natural number. A precursor for lithium was made.

Further, to this solution is added tetraethoxide titanium in such an amount that 0.2% Ti is added. Tetraethoxide titanium may be produced by previously mixing and reacting lithium acetate and pentaethoxydniobium. Tetraethoxide titanium may be present alone or in a state where lithium and niobium are substituted for part of a precursor of lithium niobate having a one-to-one bond. Thus, a precursor solution of Ti-added lithium niobate was prepared. Thereafter, this precursor solution of lithium niobate was diluted with ethanol to obtain 0.2 mol / dm.
A coating solution having a concentration of ³ was prepared.

Then, as shown in FIG. 1A, the solution prepared above is applied to the substrate 11 using a spin coating apparatus to form a coating film. As the substrate 11, a lithium niobate substrate, a lithium tantalate substrate, a sapphire (α-Al ₂ O ₃ ) substrate, or a substrate obtained by depositing lithium niobate on a silicon substrate is used. Here 3
An inch (76 mm) lithium niobate substrate was used.

Next, the substrate 11 on which the coating film was formed was baked at 150 ° C. for 30 minutes, and then baked at 450 ° C.
And baking for 30 minutes to dry the coating film.

A step of applying the coating solution to the substrate 11;
The step of drying the coating film by baking is performed, for example, by 20
After repeating this process twice, crystallization annealing was performed in an oxygen atmosphere at 700 ° C. for 30 minutes to produce a Ti-added lithium niobate film 12 having a thickness of 1 μm.

Next, as shown in FIG.
After applying a resist on the i-added lithium niobate film 12 to form a resist film, a pattern was baked on the resist film and then developed to form a resist pattern 13.

Next, ECR (Electron Cycrotron Resonance) is performed by using, for example, a mixed gas of hexafluoroethane (C ₂ F ₆ ) and argon (Ar) as an etching gas.
Etching, reactive ion etching (RIE), plasma etching, etc.
The added lithium niobate film 12 is etched to form a ridge-shaped Ti-added lithium niobate film pattern 14 on the substrate 11 as shown in FIG. This Ti
The added lithium niobate film pattern 14 forms a ridge structure.

As a method of patterning the Ti-added lithium niobate film 12, for example, a lift-off method can be used in addition to the method described above. In particular,
As shown in (1) of FIG. 2, after a resist is applied on a lithium niobate substrate (hereinafter, referred to as a substrate) 21 to form a resist film, a pattern is baked on the resist film and development is performed. A resist pattern 22 is formed. The resist pattern 22 has an opening in a region where the ridge structure of the Ti-added lithium niobate film is formed.

Next, a coating solution obtained by diluting the precursor solution with ethanol is applied on the substrate 21 by a spin coating apparatus, and the substrate 21 is heated at 150 ° C. for 60 minutes to dry the coating film. This coating process and the drying process are repeated 20 times, and as shown in FIG. 2B, T.sub.T is formed on the resist pattern 22 and on the opening portion of the substrate 21.
An i-doped lithium niobate film 23 is formed. At this time,
The Ti-added lithium niobate film 23 has a resist pattern 2
It is formed thinner than 2.

Next, after removing the resist pattern 22, as shown in FIG. 2C, crystallization annealing is performed for 30 minutes in an oxygen atmosphere at 700 ° C.
A Ti-added lithium niobate film pattern 24 having a thickness of 1 μm is formed on 1. The Ti-added lithium niobate film pattern 24 forms a ridge structure.

Next, a second embodiment will be described. In Example 2, for example, lithium acetic acid as an organic acid lithium, pentaethoxydniobium as an alkoxide niobium, and tetraethoxytitanium in an amount of 2.0% Ti as an alkoxide titanium were added to the sol-gel raw material. Using. Then, a Ti-added lithium niobate film was produced in the same manner as in Example 1 above. That is, the other conditions are the same as in Example 1, except that the amount of the alkoxide titanium is different.

Next, a third embodiment will be described. In Example 3, for example, lithium acrylate which is an unsaturated lithium carboxylate was used as the organic acid lithium as the sol-gel raw material, pentaethoxydniobium was used as the alkoxide niobium, and 0.2% Ti was used as the alkoxide titanium. The amount of titanium tetraethoxide added was used. Then, a Ti-added lithium niobate film was produced in the same manner as in Example 1 above. That is, the other conditions are the same as in Example 1, except that lithium acrylate was used as the lithium organic acid.

Next, a fourth embodiment will be described. In Example 4, for example, lithium benzoate, which is lithium aromatic carboxylate, was used as the organic acid lithium as the sol-gel raw material, pentaethoxydniobium was used as the alkoxydniobium, and 0.2% Ti was used as the alkoxidetitanium. The amount of titanium tetraethoxide added was used. Then, a Ti-added lithium niobate film was produced in the same manner as in Example 1 above. That is, the other conditions are the same as in Example 1, except that lithium benzoate was used as the lithium organic acid.

Next, a fifth embodiment will be described. In Example 5, as an example, tetraethoxide titanium in an amount to which ethoxide lithium is added as lithium alkoxide, pentaethoxide niobium is used as alkoxide niobium, and 0.2% Ti is added as titanium alkoxide is added to the sol-gel raw material. Using. Then, a Ti-added lithium niobate film was produced in the same manner as in Example 1 above. That is, the other conditions were the same as in Example 1, except that lithium ethoxide was used as lithium alkoxide instead of lithium organic acid.

Next, the Ti-added lithium niobate films prepared in Examples 1 to 5 were applied with a wavelength of 1.53 μm and a T
The propagation loss was measured by guiding the M mode light. The refractive index was measured by the prism coupling method, and the refractive index difference was calculated. Table 1 shows the refractive index difference and the uniformity of the propagation loss (both in the range of ± 5%) on the 3-inch substrate.

As a comparative example, an optical integrated circuit (Ohm Co., Ltd.) described in the prior art, (1993) Hiroshi Nishihara,
The results disclosed in Masamitsu Haruna, Toshiaki Suhara, p170-175 are also shown in Table 1.

[0040]

[Table 1]

As shown in Table 1 above, since a lithium niobate film to which Ti was added was prepared by the sol-gel method, a large area uniform film thickness characteristic of the sol-gel method was obtained.
An i-doped lithium niobate film can be formed. Further, as can be seen from Example 1 and Example 2, by controlling the addition amount of Ti by the addition amount of alkoxide titanium, the refractive index difference can be increased. In addition, it is possible to control an optical waveguide having a small propagation loss.

The method of manufacturing an optical waveguide is used to form an optical waveguide utilizing the electro-optic effect and an optical waveguide such as an element (eg, optical switching, optical modulator) using the optical waveguide utilizing the electro-optic effect. It can be used.

[0043]

As described above, according to the present invention,
On a substrate having an electro-optic effect, by a sol-gel method,
Since the chemical composition formula to which titanium is added forms a lithium niobate film represented by LiNbO ₃ , a lithium niobate film to which titanium is uniformly added over a large area, which is a feature of the sol-gel method, is formed. be able to. Further, the amount of change in the surface refractive index is made uniform, light scattering is reduced, and variations in optical characteristics can be suppressed. Further, by controlling the amount of titanium added, it becomes possible to manufacture an optical waveguide having a large difference in refractive index.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram for explaining a manufacturing method of the present invention.

FIG. 2 is a manufacturing process diagram for explaining a manufacturing method by a lift-off method.

[Explanation of symbols]

 11 Substrate 12 Ti-doped lithium niobate film

Claims (10)

[Claims] 1. A chemical composition formula LiNbO in which titanium is added on a substrate having an electro-optical effect by a sol-gel method.
_{3. A} method of manufacturing an optical waveguide, comprising forming a lithium niobate film represented by ₃ . 2. The method of manufacturing an optical waveguide according to claim 1, wherein a lithium niobate substrate represented by a chemical composition formula LiNbO ₃ is used as the substrate. 3. The method of manufacturing an optical waveguide according to claim 1, wherein a substrate in which a lithium niobate film represented by a chemical composition formula LiNbO ₃ is laminated on the substrate is used. Method. 4. The method of manufacturing an optical waveguide according to claim 1, wherein the lithium-niobate film represented by the chemical composition formula LiNbO ₃ to which titanium is added is: lithium organic acid represented by the chemical composition formula RCOOLi the R hydrocarbon, chemical composition formula m is a natural number _{Nb (O-C m H 2m} + 1) 5
Alkoxide niobium represented in the chemical composition formula of n is a natural number _{Ti (O-C n H 2n} + 1) 4
A first step of preparing a precursor of lithium niobate represented by a chemical composition formula LiNbO ₃ to which titanium is added by using titanium and an alkoxide titanium represented by the formula: Performing a second step of heating and firing the coating film to form a lithium niobate film represented by a chemical composition formula LiNbO _{3 to} which titanium is added on the substrate, the method comprising the steps of: . 5. The method for manufacturing an optical waveguide according to claim 4, wherein the step of applying the precursor of the second step on a substrate and the step of heating and baking the coating film are repeatedly performed, thereby obtaining the substrate. Chemical composition formula LiNb with titanium added
A method for manufacturing an optical waveguide, comprising forming a lithium niobate film represented by O ₃ in a plurality of layers. 6. The method for manufacturing an optical waveguide according to claim 4, wherein said lithium organic acid has a chemical composition formula C wherein n is a natural number.
_A method for manufacturing an optical waveguide, comprising using a saturated lithium carboxylate represented by nH2n ₊ 1COOLi. 7. The method for manufacturing an optical waveguide according to claim 4, wherein an unsaturated lithium carboxylate is used for the lithium organic acid. 8. The method of manufacturing an optical waveguide according to claim 4, wherein lithium organic carboxylate is used as the lithium organic acid. 9. The method for manufacturing an optical waveguide according to claim 1, wherein the lithium niobate film represented by the chemical composition formula LiNbO ₃ to which titanium is added is: chemical composition formula Li a a is a natural number _{(O-C a H 2a +} 1) and alkoxide of lithium represented by the chemical composition formula b is a natural number _{Nb (O-C b H 2b} + 1) 5
And a chemical composition formula Ti (O—C _c H _{2c + 1} ) _{4 where} c is a natural number.
A first step of preparing a precursor of lithium niobate represented by a chemical composition formula LiNbO ₃ to which titanium is added by using titanium and an alkoxide titanium represented by the formula: Performing a second step of heating and firing the coating film to form a lithium niobate film represented by a chemical composition formula LiNbO _{3 to} which titanium is added on the substrate, the method comprising the steps of: . 10. The method of manufacturing an optical waveguide according to claim 9, wherein the step of applying the precursor of the second step on a substrate and the step of heating and baking the coating film are repeatedly performed, whereby the substrate is formed. Chemical composition formula LiNb with titanium added
A method for manufacturing an optical waveguide, comprising forming a lithium niobate film represented by O ₃ in a plurality of layers.