JPH06308341A - Optical waveguide type element - Google Patents

Abstract

PURPOSE:To provide the optical waveguide element having an excellent refractive index distribution of a step type. CONSTITUTION:A hollow groove 12 is formed by etching molding on a crystal substrate 11 by a sol-gel method and a crystal layer 13 consisting of lithium niobate, PLZT or barium titanate having the refractive index higher than the refractive index of the substrate 11 is formed by dip coating, spin coating or mist coating of a metal alkoxide soln. of the constituting elements of the crystal and is subjected to calciniation and orientation to form the crystal layer. This crystal layer is formed as the optical waveguide 13. As a result, the optical waveguide having several cm length has a uniform depth and specified refractive index and is formable to have the larger and deeper difference in the refractive index from the substrate. The coupling efficiency with a single-mode optical fiber is, therefore, improved and the insertion loss is lessened. The formation of the optical waveguide of low propagation loss by the simple process with good reproducibility is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type device such as an optical switch, an optical modulator, an optical wavelength conversion device or the like used for optical fiber communication and the like.

[0002]

2. Description of the Related Art Currently, an optical waveguide device is LiNbO ₃
After forming an optical waveguide pattern of a metal film such as titanium by photolithography on an electro-optical crystal such as LiTaO ₃ or LiTaO ₃ and then thermally diffusing at about 1000 ° C., or by proton exchange with pyrophosphoric acid or benzoic acid, the substrate A diffusion type optical waveguide having a slightly higher refractive index is formed.

For example, a titanium thermal diffusion type optical waveguide will be described in detail with reference to FIG. In the figure, 31 indicates a LiNbO ₃ single crystal substrate, and 32 indicates titanium ions. After the optical waveguide pattern of the metal film is formed on the crystal surface, thermal diffusion is performed at about 1000 ° C. Therefore, the diffusion distribution in the depth direction becomes higher as the surface has a higher concentration and becomes deeper.
The profile was such that the refractive index increased according to this concentration, and this portion was the optical waveguide for confining light.

[0004]

However, in the optical waveguide by the diffusion method, the refractive index profile of the optical waveguide is
Depending on the diffusion of titanium ions and protons in the depth direction, the surface has a high refractive index and becomes deeper and becomes Gaussian distribution type, the difference in refractive index between the substrate and the optical waveguide is very small, and the diffusion constant is small. Therefore, the diffusion depth is shallow. In the obtained refractive index profile in the optical waveguide, when the optical waveguide element is modularized, the cross-section has a concentric circular structure, and the cladding of the outer periphery has a single core with a constant high refractive index portion. The coupling efficiency with the mode optical fiber is poor and the insertion loss increases.

Therefore, in order to improve the refractive index profile of the diffusion type optical waveguide, magnesium oxide is additionally diffused to slightly lower the refractive index of the substrate surface or annealed to deepen the diffusion depth. The method is adopted. But,
Such a method is complicated in process and has a problem of instability inside the crystal due to the method of producing the crystal, that is, a problem of uniformity of composition.
There is a problem that an optical waveguide having a uniform diffusion depth and a low propagation loss cannot be formed with good reproducibility in the optical waveguide having the length.

The present invention has an excellent refractive index profile in consideration of the problems of the conventional optical waveguide type device,
An object of the present invention is to provide an optical waveguide type device capable of forming an optical waveguide having a uniform diffusion depth and low propagation loss with good reproducibility.

[0007]

In the present invention, LiTaO
₃ or on a substrate such as glass, with a higher refractive index than the substrate,
_{LiNbO 3, (Pb 1-X} , La X) (Zr 1-y, Ti y)
A crystal layer having an electro-optical effect, such as _{1-X / 4} O ₃ (hereinafter, PLZT) or BaTiO ₃ , is formed by using crystal elements such as lithium, niobium, or lead, lanthanum, zircon, titanium,
Alternatively, a mixed metal alkoxide solution of titanium, barium, or the like is dip-coated, spin-coated, or mist-coated, and baked to cause sol-gel growth, and the crystal layer is used as an optical waveguide.

Further, by optimizing the temperature at the time of firing the sol-gel or by performing polarization on the crystal layer after firing,
Orient the crystal layer. An optical waveguide element is constructed by utilizing the electro-optical effect of the oriented crystal layer.

[0009]

According to the present invention, the refractive index profile of the optical waveguide has a constant refractive index of a uniform depth and a large refractive index difference between the substrate and the optical waveguide in the optical waveguide having a length of several cm. , It is possible to take deep.

Further, elements such as magnesium for preventing light damage and erbium having a light amplifying effect have a problem of diffusion coefficient in thermal diffusion and require a heat treatment step of about 1000 ° C. over several degrees. In addition to being complicated, the reproducibility was poor, and doping was difficult. However, in the sol-gel method, it was possible to easily dope even a plurality of elements by adding it to the alkoxide solution of the raw material.

Therefore, in an optical waveguide type device used for optical fiber communication or the like, an optical waveguide having good coupling efficiency with a single mode optical fiber, low insertion loss, and low propagation loss can be reproduced by a very simple process. It became possible to form with good performance.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the construction of an embodiment of the optical waveguide type element of the present invention. 11 shows a glass substrate. A concave groove 12 having a depth of 1 μm and a width of 3 μm is provided on the surface of the substrate 11, and a LiNbO ₃ crystal layer 13 is further formed thereon. The groove 12 is formed by press molding glass, resin, silicon, or germanium, but it may be formed by dry etching or wet etching.

The optical waveguide of this embodiment is characterized in that the grown LiNbO ₃ layer 13 is produced by the sol-gel method. The LiNbO ₃ layer 13 is composed of LiOC ₂ H ₅ and Nb (OC ₂
Using H _{5) 5,} and mixed to prepare a LiNb (OC ₂ H _{5) 6} mixed metal alkoxide solution. By applying the mixed metal alkoxide solution to the substrate 11 by spin coating, calcining to remove the solvent, and repeating the re-application, the layers are uniformly laminated, and heated by vacuuming to remove the solvent.
A LiNb (OC ₂ H ₅ ) _X O _{3-X / 2} layer is formed. further,
By baking this at 450 ° C., a 3 μm single-crystal LiNbO ₃ layer is formed.

The operation of the optical waveguide type device constructed as described above will be explained. In the groove 12 filled with the LiNbO ₃ layer 12, the effective refractive index becomes the highest and a step type optical waveguide is formed. When light having a wavelength of 0.84 mμm is incident on the optical waveguide, an optical second harmonic is generated due to the second-order nonlinear optical effect. Filter this output light,
Used as 0.42 μm light.

FIG. 2 is a perspective view showing the construction of another embodiment of the optical waveguide device of the present invention. In the figure, 21 indicates a sapphire substrate. A groove 22 having a depth of 5 μm and a width of 8 μm is formed on the surface of the substrate 21 by etching, and a PLZT layer 23 is formed thereon. Furthermore, PL
On the upper surface of the ZT layer 23, an aluminum electrode 24 for applying an electric field for performing light modulation by utilizing the electro-optic effect,
A buffer layer 25 for preventing light absorption by the electrodes is provided to form an optical waveguide type element.

The optical waveguide of the PLZT layer 23 of this embodiment is
As a metal alkoxide solution that constitutes Pb-, La
-, Zr- and Ti- was used _{(OCH 3 OCH 2 CH 2)} 4,
Mix in dry nitrogen at a compounding ratio of 9/65/35 to obtain Pb-
A La-Zr-Ti alkoxide solution is prepared. By spraying this mixed alkoxide solution on the substrate 21 in a mist state, the mixed alkoxide solution is uniformly deposited in the groove 12 having a relatively large gap, and further heated at 600 ° C. to remove the solvent and fired at 700 ° C. Oriented single crystal PLZT (9/65/3
5) The layer 3 μm has been produced.

The operation of the optical waveguide type device constructed as described above will be described. The concave groove 2 filled with the PLZT layer 22 is described.
In the second part, the effective refractive index becomes the highest and forms a step type optical waveguide. Wavelength 1.3 μm or 1.55 μm
From the optical fiber to the optical waveguide. Electrode 2
When an electric field is applied to the optical waveguide via 4, the refractive index changes in the waveguide due to the electro-optic effect, and the polarization component of the incident optical signal can be changed according to the applied voltage. This output light is used as control light.

As described above, according to the present invention, on a substrate such as crystal or glass, LiNbO ₃ having a higher refractive index than the substrate,
A crystal layer of PLZT, BaTiO ₃ or the like is mixed with a crystal constituent element such as lithium, niobium, or lead, lanthanum, zircon, titanium, or a metal alkoxide solution of titanium, barium, or the like, and dip coating, spin coating, or mist. Laminated by coating,
After that, desolvation and baking are performed to form an oriented single crystal or amorphous oxide dielectric layer in a sol-gel state, and the crystal layer is used as an optical waveguide. Also, the sol
The crystal layer is oriented by optimizing the temperature during gel firing or by polarizing the amorphous crystal layer after firing. Utilizing the electro-optical effect of the oriented crystal layer,
It constitutes an optical waveguide device.

[0020]

As is apparent from the above description,
The present invention realizes a step type with a constant refractive index at a uniform depth in a refractive index profile of the optical waveguide in an optical waveguide having a length of several cm. Moreover, the refractive index difference between the substrate and the optical waveguide is large, and the optical waveguide can be deepened.

Elements such as magnesium that prevent optical damage and elements such as erbium that have the effect of amplifying light have the problem of diffusion coefficient and a temperature of about 1000 ° C. over several degrees in the conventional thermal diffusion method.
Since the heat treatment step is required, the process is complicated, the reproducibility is poor, and doping is difficult. However, in the sol-gel method of the present invention, the alkoxide solution of the raw material is mixed according to the compounding ratio. As a result, multi-element doping can be performed easily even at high concentration, and in optical waveguide type devices used for optical fiber communication etc., the coupling efficiency with single mode optical fiber is good and Since there is little loss and a sufficient depth can be obtained, an optical waveguide with low propagation loss can be formed with excellent reproducibility by a very simple process. Therefore, the electro-optic constant of PLZT etc. is large,
From the standpoint of deviceization, optical control at low voltage is expected, but only thin films can be produced, so materials that were not practical will become practical. As a result, the present invention provides an optical waveguide having a wide input light band and a wider application range as well as an optical I.
This makes it possible to realize C.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an optical waveguide device of the present invention.

FIG. 2 is a perspective view showing another embodiment of the optical waveguide device of the present invention.

FIG. 3 is a perspective view of an optical waveguide manufactured by a conventional diffusion method.

[Explanation of symbols]

11 substrate 12 concave groove 13 LiNbO ₃ layer 21 substrate 22 concave groove 23 PLZT layer 24 electrode 25 buffer layer 31 crystal substrate 32 titanium ion

Claims (8)

[Claims] 1. An optical waveguide device comprising an optical waveguide, which is formed by sol-gel firing and has an oxide dielectric layer having a higher refractive index than that of the substrate, formed on a substrate provided with grooves. 2. The optical waveguide device according to claim 1, wherein a substrate provided with the groove by dry etching or wet etching is used. 3. The optical waveguide device according to claim 1, wherein the substrate provided with the groove is formed by press-molding glass, resin, silicon or germanium. 4. A metal alkoxide solution of an element constituting an oxide dielectric is mixed on a grooved substrate, and the mixed metal alkoxide solution is applied by dip coating or spin coating, followed by calcination or vacuum sputtering. The mixed metal alkoxide layers are laminated in multiple layers by repeatedly removing the solvent and re-coating, and then firing at a high temperature to form an oriented single crystal or amorphous oxide dielectric layer. The optical waveguide type device according to claim 1, 2 or 3, further comprising an optical waveguide. 5. A mixed metal alkoxide solution of elements constituting an oxide dielectric is deposited by spraying on a substrate provided with a groove, and is deposited by heating or vacuuming to remove the solvent. 4. The optical waveguide device according to claim 1, further comprising an optical waveguide formed by forming a single crystal or amorphous oxide dielectric layer by firing. 6. A Li alkoxide solution and an Nb alkoxide solution are used as a metal alkoxide solution constituting an oxide dielectric, and further, in a predetermined case, a refractive index adjustment, a light amplification effect, an electro-optical constant adjustment, and a dielectric constant adjustment are performed. A metal alkoxide solution for adding and mixing to prepare a mixed metal alkoxide solution, degassing and further firing, and using the LiNbO ₃ oxide dielectric layer as an optical waveguide. The optical waveguide device according to any one of claims 1 to 5. 7. A Ba alkoxide solution and a Ti alkoxide solution are used as a metal alkoxide solution constituting an oxide dielectric, and a Sr alkoxide solution is further added as an additive, and the mixture is formed by firing. and, BaTiO ₃ or Ba _1-X Sr _X TiO ₃ oxide either optical waveguide device of claims 1 to 5, wherein the use of a dielectric layer as an optical waveguide. 8. A Pb alkoxide solution, a Ti alkoxide solution, a lanthanum alkoxide solution, and a Zr alkoxide solution are used as the metal alkoxide solution constituting the oxide dielectric, and the mixture is formed by firing.
b _1-X , La _X ) (Zr _1-y , Ti _y ) _{1-X / 4} O ₃ oxide dielectric layer is used as an optical waveguide.
6. The optical waveguide device according to claim 5.