JPH0711608B2 - How to create an optical waveguide - Google Patents

Description

The present invention relates to a method for producing a waveguide for an optical circuit having functions such as photosynthesis, light demultiplexing and light deflection.

Conventionally, a ferroelectric substrate has been used as a waveguide substrate with excellent piezoelectricity.
When using a LiNbO ₃ single crystal, an optical waveguide has been produced by the method shown below. A Ti film is formed on the above-mentioned substrate by a method such as an electron gun or sputtering, and then 1000 ° C in a heating furnace.
A waveguide furnace having a thickness of 1 to 2 μm is formed by performing heat treatment in the vicinity for several hours and thermally diffusing Ti into the crystal. However, when the above-mentioned waveguide furnace is made, a high-temperature treatment step at around 1000 ° C. is included, and when the input light intensity to the waveguide exceeds 1 to 2 mW (at a wavelength of 0.6328 μm). , Optical damage to the waveguide [RL Holman, Appl. Phys. Letl, 32 , 280
(1978)].

On the other hand, as a method of reducing the optical damage of the waveguide,
In some cases, the substrate is immersed in a strong acid, hydroxide, or molten salt heated to about 200 ° C to 400 ° C. 〔J.Jacke
l, Appl.Phys.Letl, 37 , 739 (1980)] For example, molten salts include TlNO ₃ and AgNO _3, but since it is necessary to completely immerse the substrate in the molten salt, the harmful gas NO There was a problem that a large amount of _2nd grade occurred.

An object of the present invention is to provide a new method for producing an optical waveguide, which eliminates the drawbacks associated with the conventional method for producing an optical waveguide described above.

The above-mentioned object of the present invention is to include a solid material containing an ionic species on the surface of a substrate, and heat the solid material by irradiating the solid material with light to melt the solid material. An optical waveguide characterized by monitoring a change in the refractive index of the substrate surface by diffusing ion species into the substrate and observing a change in reflectance or transmittance or both of the irradiation light on the substrate surface. Achieved by the method of creating. Furthermore, before applying heat to melt the solid material, preheating the entire substrate to raise it to a certain temperature, of course, to a temperature at which the ionic species do not dissolve, creates an optical waveguide efficiently. it can.

In the method for producing a waveguide of the present invention, while lowering the temperature of the production process and reducing the generation of harmful gas, while monitoring the progress of the formation of an optical waveguide with less optical damage and less optical propagation loss. It is possible to form.

Hereinafter, the present invention will be described in detail.

In FIG. 1, reference numeral 1 is a substrate on which an optical waveguide is formed, and 2 is a solid material for forming ionic species.
Provided on top of. The substrate 1 may be a ferroelectric crystal such as LiNbO ₃ or LiTaO ₃ crystal having excellent piezoelectricity, or glass such as BK7. 2 is Mg (NO ₃ ) ₂ 6H ₂ O, C ₆ H ₅ COOH, TlNO ₃ ,
Examples include AgNO ₃ , KNO ₃ , NaNO ₃ .

FIG. 2 is a diagram showing an embodiment of the method according to the present invention, 3 is a laser light source, 4 and 5 are lenses, 6 is a beam splitter, 7 and 8 are photodetectors, 9 is a heating furnace, and 10 is It is a window for the light opened in the furnace 9. As the light source, it is desirable to use a laser having a wavelength with high absorption for the substrate material,
For example, Ar, He-Ne, YAG, CO ₂ laser and the like can be mentioned. The light beam 11 emitted from the laser light source 3 passes through the beam splitter 6 and is expanded by the lens 4 into a light beam 12 having uniform intensity. The light flux 12 is applied to the entire surface of the substrate 1 on which the solid 2 containing diffused species is stacked. When the solid 2 melts, a part of the light flux 12 is reflected and a part thereof is transmitted. The reflected light returns to the lens 4 and the beam splitter 6 causes the detector 7
Be led to. On the other hand, the light flux that has passed through the substrate is squeezed by the lens 5 and enters the detector 8.

The surface of the substrate 1 is locally heated by the light flux 12, ion exchange proceeds, the refractive index near the surface increases, and a waveguide is formed. The generation rate of harmful gas is suppressed as compared with the case where the entire substrate is heated. Further, as the heat bias, appropriate heating in advance by the furnace 9 may be used together. When the refractive index of the surface changes according to the above-mentioned principle, the reflectance and the transmittance of the light flux 12 on the substrate surface also change. Therefore, if the fluctuation of the light intensity is observed by the detector 7 or 8, the waveguide at that time is observed. The state of can be monitored.

A planar waveguide having a predetermined waveguide thickness can be manufactured by the above method.

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Referring to FIG. 2, the yz plane of an X-cut LiNbO ₃ single crystal was double-sided polished so that the surface precision was within a few Neutring rings. The dimensions of the substrate were 1 inch and 1/2 inch in the y and z directions, respectively, and the thickness was 1 mmt. After polishing, the substrate was ultrasonically cleaned and then thoroughly dried in ethanol vapor, and about 2 g of TlNO ₃ powder was uniformly deposited on the upper surface of the substrate by a doctor blade. Place this stacked substrate in a low temperature heating furnace and
CO ₂ laser light (output 20
watt) was adjusted by a Si lens so that the entire surface of the substrate was exposed to light, and within a few minutes the TlNO ₃ deposited on the substrate melted,
By irradiating CO ₂ laser light for about 60 minutes in this state, a TE ₀ mode waveguide could be formed on the substrate by the internal diffusion of Tl ions. When the propagation loss of the waveguide fabricated by the prism coupling method was measured, a value of 1.0 db / cm was obtained. Further, an improvement of 50% was also observed with respect to the improvement of the threshold value of optical damage, and it was found that the waveguide fabrication according to the present invention was superior to the conventional method.

As described above, the optical waveguide manufacturing method according to the present invention not only enables an optical waveguide with less optical damage and low light propagation loss, but is also manufactured by immersing a substrate in a conventional melt heated to a high temperature. Compared with the method described above, low-temperature treatment becomes possible and the generation rate of harmful gas can be suppressed.

Further, since the state of the waveguide can be monitored by observing the heating light when the waveguide is formed, it is not necessary to irradiate the monitoring light different from the heating light. Since the state at the time of fabrication can be monitored, it is also possible to control the number of excited modes and control the thickness of the waveguide to enhance the interaction with the surface acoustic wave.

[Brief description of drawings]

FIG. 1 and FIG. 2 are views for showing an embodiment of a method for producing an optical waveguide according to the present invention. 1 ... Substrate, 2 ... Solid containing diffused ion species, 3 ... Light source, 4,5 ... Lens, 6 ... Beam splitter, 7,8 ...
… Photodetector, 9 …… Heating furnace, 10 …… Window, 11,12 …… Luminous flux.

Claims (1)

[Claims] 1. A method for producing an optical waveguide by diffusion from the surface of a substrate, wherein a solid material containing ionic species is deposited on the surface of the substrate,
The solid material is heated and melted by irradiating the solid material with light, and the ionic species contained in the melted solid material are diffused into the substrate by ion exchange, and the irradiation light is reflected on the substrate surface. A method for producing an optical waveguide, characterized in that a change in the refractive index of the substrate surface is monitored by observing a change in the refractive index, the transmittance, or both.