JPS6263904A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To produce an inverse ridge optical waveguide with one time of an ion exchange treatment by providing a difference in the thickness of ion exchange layers by etching with a mask in an ion exchange soln. CONSTITUTION:An LiNbO3 substrate 1 is subjected to the ion exchange in phosphoric acid which is the ion exchange soln. heated to 230 deg.C. the ion exchange of Li and H takes place right under a window 3 and a high refractive index part 4a is formed. An SiO2 film 10 is etched by phosphoric acid to have 150Angstrom thickness in this stage. The etching rate of the SiO2 film 10 is 60Angstrom /min. The film 10 is thoroughly etched in 7min and 30sec after and the effect as the mask for the ion exchange is lost. The part right under the mask is ion- exchanged as well. The thickness d1 of the high refractive index layer 4a formed right under the window 3 is 0.5mum and the thickness d2 of the high refractive index layer 4b formed right under the film 10 is 0.25mum.

Description

Detailed Description of the Invention 27. - Industrial Application Field The present invention relates to a method for manufacturing a guiding waveguide used in the field of optical information processing using coherent light or the field of optical measurement and control.

Conventional technology Ion-exchange optical waveguides, which are manufactured by heat-treating a ferroelectric substrate such as LIN b O3 in an acid such as benzoic acid, which is an ion-exchange solution, have a large refractive index difference with respect to the substrate °C, making it suitable for various devices. It is very important to configure
N b O3” Abride Physics Letter, Volume 41,
No. 7, pp. 607-608 (1982) (J, L, Iac
kel, C, E, Rice and LJVeselk
a, ” Proton exchange for
high-index waveguides in
LiNbO3”, Appl, Phya, L
et t.

VOl, 41, NO, 7, PP, 607-608 (1
982)))].

The three-dimensional optical waveguide fabricated by this ion exchange method has a large propagation loss due to lateral scattering, and for this reason, it is necessary to reduce the propagation loss by using an inverted ridge shape. FIG. 2 shows a comparison of propagation loss with respect to thickness for a three-dimensional optical waveguide and an inverted ridge type optical waveguide. 20 is the characteristic of the three-dimensional optical waveguide, and 21 is the characteristic of the inverted ridge type optical waveguide. The inverted ridge type optical waveguide has weak confinement in the lateral direction and has extremely low propagation loss compared to a three-dimensional optical waveguide.

FIG. 3 shows a conventional method for manufacturing an inverted IJ, diagonal optical waveguide. In the figure a, 1 is a ferroelectric substrate L i NbO3
The substrate, 2' is an Afi film that serves as a protective mask during ion exchange, 3 is a window formed by a photo process, and 4a is a first
This is a high refractive index layer formed by ion exchange. Next, as shown in the same figure, Af! , the film 2 is removed by etching.

Next, to prevent cracking, the ion exchange treatment temperature and LiNb○3
Baking is performed to bring the temperature of the substrate 1 to the same temperature,
A second ion exchange is carried out in benzoic acid at 230°C. In this way, an inverted ridge-shaped optical waveguide is formed, as shown in FIG. 3C, in which the thickness dl of the high refractive index layer 4a immediately below the window 3 is greater than the thickness d2 of the high refractive index layer 4b immediately below the 12 film 2.

Problems to be Solved by the Invention As described above, in the method of fabricating an inverted ridge type optical waveguide by performing ion exchange in one batch, baking occurs in the middle, which reduces the JIT refractive index of the optical waveguide and the thickness of the optical waveguide. 17, the problem is that an optical waveguide is fabricated that is different from the fabrication process.)/(.Due to the use of acids such as nitric acid in the AR film removal process, chemical damage to the optical waveguide surface may cause propagation. Increased losses were a problem.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for manufacturing an optical waveguide of the present invention uses a method in which a window is opened in a part of the ferroelectric substrate J2 and can be etched with an ion exchange solution. In the second step of forming a mask, ion exchange is performed during the ion exchange to form a high refractive index layer with a thickness of dl under the window surface, a high refractive index layer with a thickness of d2 directly under the mask, and The method includes a step of forming an IJ nozzle-shaped optical waveguide whose thickness dl is smaller than the thickness d2.

Effect 6 /.-) According to the present invention, a reverse ridge type optical waveguide can be formed by one-time ion exchange by the above-mentioned means, and the steps of baking and mask removal can be omitted, thereby avoiding changes in the shape of the optical waveguide and chemical damage.

Embodiment A first embodiment of the method for manufacturing an optical waveguide according to the present invention is shown in FIG. In the figure d, 1 is a ferroelectric substrate L I N b
The O3 substrate 10 is a mask having a window 3 with a width of 2 μm patterned by CVD and a photo process, specifically, an Sio2 film with a thickness of 450 mm. This L i
Ion exchange is performed on the N b O3 substrate 1 in phosphoric acid, which is an ion exchange solution, heated to 230°C. The figure shows the LiN b O3 substrate 1 after 6 minutes, where ion exchange of Li and H occurs directly under the window 3, forming a high refractive index region 4a. At this time, the 5102 film 10 is etched with phosphoric acid to a thickness of 160 mm. The etching rate of the Si02 film 10 is 608/min. After 7 minutes and 30 seconds, the SiO2 film 10 is completely etched.
It loses its effectiveness as a mask for ion exchange, and ions are exchanged directly under this mask. Figure C shows a cross section of the L I N b 03 substrate 1 pulled out of the phosphoric acid solution after 10 minutes, showing the high refractive index layer 4a (
7) Thickness dl is 0.51im, SiO2 film 1
The thickness d2 of the high refractive index layer 4b formed directly under o is 0.26
It was μm. The platform He-Ne laser beam, which is made by entering the He-Nθ laser beam from the end surface, propagates through the high refractive index layer 4a while seeping into the high refractive index layer 4b, and its propagation loss is 0.8 dB 7 cm. Ah-3. As described above, according to the present invention, there is no need for a mask removal process, so that chemical damage is not caused and propagation loss can be reduced. Further, by using phosphoric acid, the chemical damage caused by the phosphoric acid to the L I N b O3 substrate 1 is extremely small, resulting in a reduction in propagation loss. Furthermore, the etching rate of the S z 02 film 2 can be changed by changing the film quality, and an optical waveguide with an arbitrary ridge ratio (d2/d1) can be formed.

A second embodiment of the method for manufacturing a guiding waveguide according to the present invention will be described below. In this example, d, Afi with a thickness of 1000A
Patterning the film on L r N b O3 soil 7
x-/ Ion exchange was performed in chlorotic acid. By performing heat treatment at 220°C for 20 minutes, the thickness was reduced to 0.45 in the same process as in Example 1.
A .mu.m inverted ridge type optical waveguide was formed. The propagation loss is 1
．． It was 5 dB 76m.

In the example, a LiNbO3 substrate was used as the ferroelectric substrate, but LINbxT −0(O≦X”(I K)
Any substrate capable of forming an ion exchange waveguide such as 3≦1) may be used. In addition, although phosphoric acid and succinic acid were used as acids, the present invention is not limited to benzoic acid and boric acid. I used the oxide film SIO2 and AIt as a mask, but it was 5t.
3N4. The present invention is not limited to the above, as long as it can be etched in an ion exchange solution such as Cr, Ti, etc. Effects of the Invention According to the method for manufacturing an optical waveguide of the present invention, the ion exchange layer can be etched by etching a mask in an ion exchange solution. By providing a difference in thickness, a reverse ridge optical waveguide can be manufactured by a single ion exchange treatment. This prevents changes in the shape of the optical waveguide due to baking and optical damage during mask removal, and furthermore, it is possible to significantly shorten the process.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an example of the method for manufacturing an optical waveguide of the present invention, Fig. 2 is a characteristic diagram showing a comparison of propagation loss between a three-dimensional optical waveguide and an inverted ridge type optical waveguide, and Fig. 3 1 is a process diagram showing a conventional method for manufacturing an inverted ridge type optical waveguide. 1...L I N b Os substrate, 3...
・Window, 4...High refractive index layer, 1o...Mask 0 Name of agent Patent attorney Satoshi Nakao and 1 other person/
---LiNbO3 substrate 3-11-10-m-mask (b) CC,) Fig. 2 Thickness, L+(, um)

Claims (4)

[Claims] (1) A step of forming a mask on a ferroelectric substrate in which a window is partially opened and which can be etched with an ion exchange solution, and ion exchange is performed in the ion exchange solution so that a thickness of d_1 is formed directly under the window. forming a high refractive index layer having a thickness of d_2 directly under the mask, and forming an inverted ridge-shaped optical waveguide in which the thickness d_1 is greater than the thickness d_2. A method for manufacturing an optical waveguide. (2) LiNbxTa_(_1_-
_X_)O_3 (0≦x≦1), the method for manufacturing an optical waveguide according to claim (1). (3) A method for manufacturing an optical waveguide according to claim (1), which uses phosphoric acid as the ion exchange solution. (4) A method for manufacturing an optical waveguide according to claim (1), which uses an oxide film as a mask.