JP2001343544A - Method for producing film structural body, method for producing optical guide substrate and method for producing second harmonic generation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical guide which is low in optical damage and, further, to greatly increase the output of second harmonic. SOLUTION: In the production of an optical guide substrate which is provided with a substrate which is made of single crystal of lithium potassium niobate- lithium potassium tantalate solid solution and the optical guide which consists of the film of single crystal of lithium potassium niobate formed on the surface of the substrate, the temperature of the substrate is kept to be >=700 deg.C and <=850 deg.C and, at the same time, the film made of the single crystal of lithium potassium niobate is formed by organometallic vapor growth method. In the optical guide thus obtained, the second harmonic can be efficiently generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate composed of a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution, and a single crystal of potassium potassium niobate or lithium potassium potassium tantalate formed on the surface of the substrate. TECHNICAL FIELD The present invention relates to a coating structure including a film made of a lithium potassium solid solution single crystal, and a method for manufacturing an optical waveguide substrate and a second harmonic generation element using the same.

[0002]

2. Description of the Related Art Lithium potassium niobate single crystals and lithium potassium niobate-lithium potassium tantalate solid solution single crystals are receiving attention, in particular, as single crystals for blue light second harmonic generation (SHG) devices for semiconductor lasers. I have. Since it can generate light up to the ultraviolet region of 390 nm, by using such short wavelength light, it can be used for optical disk memory, DVD laser light source, racer pointer, display, medical use, photochemistry, various light sources. A wide range of applications such as measurement is possible. Further, since the single crystal has a large electro-optic effect, it can be applied to an optical storage element or the like utilizing the photorefractive effect.

In optical applications, particularly in second harmonic generation applications, it is necessary to transmit a laser beam having a short wavelength of, for example, about 400 nm in a single crystal at a power density as high as possible. Moreover, at this time, it is necessary to minimize optical damage. Although it is essential to suppress optical damage in this way, it is necessary that the single crystal constituting the optical waveguide has good crystallinity, and that the optical waveguide has a single domain. is necessary. Accordingly, it is required from a practical viewpoint to generate a second harmonic having a high output of, for example, 30 mW.

[0004]

In Japanese Patent Application Laid-Open No. Hei 8-6083, an epitaxial cladding layer made of a lithium potassium niobate-lithium potassium tantalate solid solution single crystal is provided on the surface of a substrate made of a lithium potassium niobate single crystal. An optical waveguide made of the solid solution single crystal is formed on the cladding layer by metal organic chemical vapor deposition. However, this device still suffers from optical damage and the second harmonic output has not yet reached the high levels mentioned above.

"Japanese J. Appl. Phys." Vol. 37 (1
998) 5582-5587, a lithium potassium niobate film is formed on a (111) Si substrate by metal organic chemical vapor deposition. However, since the crystal structure of lithium potassium niobate is significantly different from the crystal structure of (111) Si, a polycrystalline film is formed.

An object of the present invention is to provide a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution on a substrate made of a single crystal of lithium potassium niobate-lithium potassium tantalate. Is to form a film having a good quality.

Another object of the present invention is to provide an optical waveguide with less optical damage, and to further increase the output of the second harmonic.

[0008]

SUMMARY OF THE INVENTION The present invention provides a substrate comprising a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution, a lithium potassium niobate single crystal or lithium potassium niobate-tantalum tantalum formed on the surface of the substrate. In producing a coating structure comprising a film made of a lithium potassium oxide solid solution single crystal, the film is formed by metal organic chemical vapor deposition while maintaining the substrate temperature at 700 ° C. or more and 850 ° C. or less. It is characterized by doing.

The present invention also provides a substrate comprising a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution, a single crystal of lithium potassium niobate or a solid solution of lithium potassium niobate-lithium potassium tantalate formed on the surface of the substrate. In manufacturing an optical waveguide substrate including an optical waveguide formed of a single crystal film, while maintaining the substrate temperature at 700 ° C. or higher and 850 ° C. or lower,
The film is formed by a metal organic chemical vapor deposition method.

The present invention also relates to a substrate comprising a single crystal of a lithium potassium niobate-lithium potassium tantalate solid solution, a lithium potassium niobate single crystal or a lithium potassium lithium niobate-lithium potassium tantalate solid solution formed on the surface of the substrate. When manufacturing a second harmonic generation element comprising a single crystal film and having an optical waveguide for wavelength conversion for converting a fundamental wave into a second harmonic, the temperature of the substrate is set to 700 ° C. or more and 850 ° C. The method is characterized in that the film is formed by a metal organic chemical vapor deposition method while holding below.

The inventor of the present invention has found that the film has extremely good crystallinity by forming the film by metal organic chemical vapor deposition while maintaining the temperature of the substrate at 700 ° C. or higher and 850 ° C. or lower. It has been found that light damage is significantly reduced. And by applying such a film to the second harmonic generation element, the output of the second harmonic is significantly improved,
In particular, they have found that an output of 30 mW or more can be stably obtained, and have reached the present invention.

The reason why such an effect is obtained is that the crystallinity of the lithium potassium niobate single crystal constituting the film is remarkably improved, and at the same time, the film has a single domain. large.

That is, the Curie temperature of a lithium potassium niobate-lithium potassium tantalate solid solution single crystal is as follows:
The temperature varies depending on the ratio of each element of lithium, niobium and tantalum, but is about 450-550 ° C. Therefore, even if a substrate made of a single crystal subjected to single domain processing is used, if the temperature of the substrate is maintained at 700 ° C. or higher, the substrate is naturally multi-domain, so that the film generated on the surface of the substrate may be Should be localized. In this case, the crystallinity of the film also deteriorates. Moreover, in order to use such a multi-domain film as an optical device, it is necessary to perform single-domain processing again, but the crystallinity of the film is damaged again at the stage of the single-domain processing. Give it.

However, when a film is formed by a metal organic chemical vapor deposition method at a temperature of 700 ° C. or more in the combination of the substrate material and the film material described above, the film is formed into a single domain, and its crystallinity is also reduced. It has been found that there is almost no adverse effect of the multi-domain. The reason for this is not clear,
Because the crystallinity of the film is good, the stress generated due to the shift of the crystal lattice between the material of the substrate and the material of the film is large, or the film formation temperature is high, so that the difference between the gas temperature and the film temperature become larger, the film surface is cooled by continued atmosphere, such that they are offset to some degree heat transfer to the film from the substrate can be considered.

Japanese Patent Application Laid-Open No. Hei 8-6083 has a general description that a waveguide layer is formed on a cladding layer at 500 to 700 ° C. by metal organic chemical vapor deposition. However, a lithium potassium niobate single crystal substrate is used as a substrate, and a waveguide layer is formed via a clad layer thereon. In addition, in order to make the refractive index of the waveguide layer slightly higher than the refractive index of the epitaxial cladding, after fixing the substitution ratio y of tantalum in both, the ratio of niobium to lithium in the waveguide layer is changed to niobium in the cladding layer. Is slightly larger than the ratio of lithium to niobium (the ratio of niobium is slightly increased). Therefore, in the combination of the materials of the substrate and the optical waveguide which is the premise of the present invention, the holding temperature of the substrate is set to 70.
It is not disclosed that the temperature is kept at 0 to 850 ° C., so that a remarkable effect cannot be obtained.

According to the second harmonic generation device of the present invention, for example, it is possible to generate a region of 390 nm to 470 nm. Therefore, by using such short-wavelength light, a wide range of applications such as optical disk memory, medical use, photochemistry, various types of optical measurement, and the like are possible.

In order to achieve the effects of the present invention, it is more preferable that the holding temperature of the substrate is 740 ° C. or higher, or 780 ° C. or lower.

The composition of the single crystal constituting the substrate and the film is as follows:
There is no limitation as long as a tungsten bronze structure composed of K, Li, Nb, Ta, and O is maintained. However, in order to use the film as an optical waveguide, in particular, an optical waveguide for wavelength conversion, it is necessary to adjust the difference in the refractive index between the substrate and the film. From this viewpoint, the following basic composition is particularly preferable, and in this case, the production method of the present invention is particularly preferable.

(1) The basic composition of the film is as follows. _{K 3 Li 2-X-A} (Nb 1-Y Ta Y) 5 + X + A O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 A is 0.
006-0.12, preferably 0.006-0.
02. )

(2) The basic composition of the substrate is as follows. _{K 3 Li 2-X (Nb} 1-Y-B Ta Y + B) 5 + X O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 B is 0.
005-0.5, preferably 0.03-0.1. )

In a particularly preferred embodiment, Y is 0.

As described above, a tungsten bronze structure made of K, Li, Nb, Ta, and O is considered as each material of the substrate and the film. However, substitution of each element is possible within a range that maintains this structure, for example, substitution of K and Li by Na, Rb, and the like.
In this case, the substitution ratio is preferably 10 atomic% or less when potassium or lithium is 100 atomic%. It is also possible to add a laser oscillation doping agent such as a rare earth element such as Cr, Er or Nd.

The substrate is disclosed in Japanese Patent Application Laid-Open No. Hei 8-25937.
No. 5, JP-A-8-319191, preferably obtained by the micro-pull-down method.

In the metal organic chemical vapor deposition method, a potassium source, a lithium source, a niobium source and a tantalum source are used. As a potassium source, potassium dipivaloylmethanato [K (C ₁₁ H ₁₉ O ₂ )] is preferable. As a lithium source, dipivaloyl methanatolithium [Li (C
₁₁ H ₁₉ O ₂ )]. As a niobium source,
Pentaethoxyniobium [Nb (OC ₂ H ₅ ) ₅ ]
Is preferred. As a tantalum source, pentaethoxy tantalum [Ta (OC ₂ H ₅ ) ₅ ] can be used.

[0025]

EXAMPLE A substrate made of the solid solution single crystal was produced by a micro pulling-down method. Specifically, potassium carbonate, lithium carbonate, niobium chloride and tantalum oxide
The mixture was prepared at a composition ratio of 30.0: 24.0: 45.08: 0.92 to produce a raw material powder. About 50g of this raw material powder
Into a platinum crucible and heated to 1150 ° C.
The raw material was melted. The temperature of the space inside the upper furnace
The temperature was adjusted to 1200 ° C., and the raw material in the crucible was melted. The temperature of the single crystal growing section is set to 1050 ° C. to 1150 ° C., and a nozzle provided on the bottom of the crucible is set at 10 mm /
At the speed of time, the C-plane plate was pulled down along the direction of the a-axis of the crystal. As a result, a thickness of 1 mm and a width of 30 m
A single crystal substrate having a length of 100 mm and a length of 100 mm could be grown. This substrate was used as an under cladding part. The composition of the _{substrate, K 3 Li 1.9 (Nb 0} .97 Ta 0.03)
_5.1 O _15.2 .

Next, a single bond is formed by metalorganic vapor phase epitaxy.
A crystalline film was prepared. Specifically, as starting materials,
Baroyl methanate potassium [K (C₁₁H
₁₉O ₂)] And dipivaloyl methanatolithium [L
i (C₁₁H₁₉O₂)] And pentaethoxy niobium
[Nb (OC₂H₅)₅]It was used. these
After filling each dedicated raw material container,
The gas is heated to the gasification temperature to generate gas, and the flow rate of each gas is controlled.
Introduced into the reaction chamber using argon carrier gas
Was. Dilute each gas with 880 sccm of argon gas
Was. The flow rate of the oxygen gas was 200 sccm. Argo
Total flow rate of gas and each source gas is 2000sccm
And The flow rate, temperature, and pressure of each gas are shown in Table 1.
It is.

[0027]

[Table 1]

The pressure in the reaction chamber was set to 40 Torr, and the temperature of the substrate was changed as shown in Table 2. The piping to the reaction chamber was heated to 250 ° C. The film formation time was 8 hours. As a result, a single crystal film having a smooth surface was obtained. The film thickness was measured by the prism coupling method.
0 to 4.5 μm. The ordinary light refractive index of the film is 2.278.
5, and the extraordinary light refractive index was 2.131. The composition of the obtained film was K ₃ Li _1.85 Nb _5.15 O
_15.3 . The half width of the X-ray rocking curve of each film was measured and is shown in Table 2.

On this epitaxial film, a thickness of 1 μm, a width of 5 μm,
A titanium film pattern having a length of 25 mm was formed in stripes at intervals of 2 mm. This sample was processed by a reactive ion etching method. At this _time, using the C 2 _{F 6} gas and _{O 2} gas, pressure 0.02 Torr, and processed for 100 minutes at an RF power 250 W, to produce an optical waveguide of the ridge structure.

This sample was cut to obtain a chip-like element having a length of 10 mm and a width of 2 mm in the optical waveguide direction. The input end face and output end face of this element are optically polished, and a wavelength of 8
An anti-reflection coating with a reflectance of 0.5% was applied at 60 nm, and an anti-reflection coating with a reflectance of 0.5% at 430 nm was applied on the emission side. When a titanium-sapphire laser beam was incident on this device, phase matching was performed at a wavelength of 857 nm. The input power was 100 mW, and the output power of the second harmonic was measured.

[0031]

[Table 2]

[0032]

As described above, according to the present invention, a film having good crystallinity made of a single crystal of lithium potassium niobate is formed on a substrate made of a solid solution of lithium potassium niobate-lithium potassium tantalate solid solution. It can be generated, and by using this, an optical waveguide with less optical damage can be provided, and further, the oscillation output of the second harmonic can be greatly increased.

Continued on the front page (72) Inventor Takashi Yoshino 2-56, Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Insulator Co., Ltd. F term (reference) 2H047 KA05 LA00 PA05 PA06 PA12 PA14 PA24 QA03 RA04 RA08 TA11

Claims (9)

[Claims] 1. A substrate comprising a lithium potassium lithium niobate-lithium potassium tantalate solid solution single crystal; and a lithium potassium niobate single crystal or a lithium potassium lithium niobate-lithium potassium tantalate solid solution single crystal formed on the surface of the substrate. When manufacturing a film structure having a film, the film is formed by metal organic chemical vapor deposition while maintaining the temperature of the substrate at 700 ° C. or more and 850 ° C. or less. A method for producing a coating structure. 2. The chemical composition of the film is as follows: K ₃ Li _2- XA (Nb _{1 -Y} Ta _Y ) _{5 + X + A} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 A is 0.
006-0.12, preferably 0.006-0.
02. 2. The method for producing a coated structure according to claim 1, wherein 3. The method according to claim 1, wherein the chemical composition of the substrate is K ₃ Li _2-X (Nb _1−Y−B Ta _{Y + B} ) _{5 + X} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 B is 0.
005-0.5, preferably 0.03-0.1. 2. The method for producing a coated structure according to claim 1, wherein 4. A substrate comprising a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution, and a single crystal of lithium potassium niobate or a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution formed on the surface of the substrate. When manufacturing an optical waveguide substrate having an optical waveguide made of a film, the film is formed by metal organic chemical vapor deposition while maintaining the temperature of the substrate at 700 ° C. or more and 850 ° C. or less. A method for manufacturing an optical waveguide substrate, comprising: 5. The chemical composition of the film is as follows: K ₃ Li _2- XA (Nb _{1 -Y} Ta _Y ) _{5 + X + A} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 A is 0.
006-0.12, preferably 0.006-0.
02. 5. The method for producing a coating structure according to claim 4, wherein 6. The chemical composition of the substrate is as follows: K ₃ Li _2-X (Nb _1−Y−B Ta _{Y + B} ) _{5 + X} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 B is 0.
005-0.5, preferably 0.03-0.1. 5. The method for producing a coating structure according to claim 4, wherein 7. A substrate comprising a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution, and a single crystal of lithium potassium niobate or a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution formed on the surface of the substrate. When manufacturing a second harmonic generation element comprising a film and having a wavelength conversion optical waveguide for converting a fundamental wave into a second harmonic, the temperature of the substrate is set to 700 ° C or higher and 850 ° C or lower. A method for manufacturing a second harmonic generation element, wherein the film is formed by metal organic chemical vapor deposition while holding the film. 8. The chemical composition of the film is K ₃ Li _2- XA (Nb _{1 -Y} Ta _Y ) _{5 + X + A} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 A is 0.
006-0.12, preferably 0.006-0.
02. The method for producing a coating structure according to claim 7, wherein 9. The chemical composition of the substrate is as follows: K ₃ Li _2-X (Nb _1−Y−B Ta _{Y + B} ) _{5 + X} O
_{15 + 2X} (where X is 0.10-0.50, preferably 0.10-0.20; Y is 0.00-0.05, preferably 0.00-0.01 B is 0.
005-0.5, preferably 0.03-0.1. The method for producing a coating structure according to claim 7, wherein