JPS62293208A - Formation of optical element - Google Patents

Abstract

PURPOSE:To easily form an optical element with good controllability by coating an acid which is liquid at <=90 deg.C on the surface of a ferroelectric substrate,a then subjecting the coating to a heat treatment. CONSTITUTION:A protective mask 2 consisting of Ta is formed on a +Z surface 3 of an LiNbO3 substrate 1 and pyrophosphoric acid 5 is coated thereon. The pyrophosphoric acid 5 is liquid at a room temp. and permits surface coating by spin coating, etc. The heat treatment is executed in an oven 6 heated to 200 deg.C and a plate 7 made of Al is used to uniform the temp. The substrate is finally taken together with the plate 7 out of the oven 6 and thereafter the protetive mask 2 consisting of Ta is removed by a soln. of sodium hydroxide. A high-refractive index layer 8 is then formed by a proton exchange right under a slit 4. The difference in the max. refractive index between the high refractive index layer 8 formed of the pyrophosphoric acid and the substrate 1 is high and the optical waveguide which confines light largely is manufactured.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Industrial Application Field The present invention relates to optical waveguides and microlenses used in the field of optical information processing using coherent light, optical communications, and optical applied measurement and control fields. The present invention relates to a method for forming an optical element used for.

Conventional technology Conventionally, a ferroelectric LiNbO3 substrate was heated at 160°C.
Heat treatment is performed in a benzoic acid solution at ~250℃.
A high refractive index layer (maximum refractive index difference Δn=about 0.13) was formed by exchanging Li in the L I Nb0a substrate with H in benzoic acid to form an optical waveguide. [J. L. Shatkel, C. E. Rice and G. J. Veselka, “Proton Exchange for High-Index Unib Guide in L I Nb0a” Applied Fixtures Letter.

Volume 41, No. 7, pp. 607-608 (19B2) (J,
L., Jackel, C.E., Rice and I.
, 1, Veselka.

”Proton exchange for high
-tndexwaveguides in LiNbO
3,” Appl, Phys, Let t.

Vo141.47. PP607-608 (1982))
See J.

Hereinafter, a method for forming an optical waveguide will be described as an example of an optical element. FIG. 5 shows a concrete block diagram of a method for forming an optical waveguide using the conventional 3.\proton exchange method in a solution. 1 is a LiNbO3 substrate which is a ferroelectric substrate;
2' is eight! A protective mask 4 is immersed in a liquid 5' onto the protective mask 2' by photoprocessing and etching. The solution 6' is maintained at a constant temperature of 200''G via a bead 10 heated by a heater 9.
After heat-treating the LiNb Oa substrate 1 for 60 minutes in the chamber, cleaning is performed with methanol.

Thus, H and L I Nb Os in the benzoic acid solution 6'
Li in the substrate 1 is exchanged to form a high refractive index layer 8. This high refractive index layer 8 becomes an optical waveguide with a thickness of about 0.5 μm.

Problems to be Solved by the Invention The method for forming an optical element in a solution as described above has the following problems. (1) Workability deteriorates due to the vapor generated by the solution. (2) Operations such as stirring are required to equalize the temperature of the solution. (3) Cracks are likely to occur due to rapid temperature changes when the board is moved in and out. (4)
The surface of the chamfer to which proton exchange is desired is also immersed in the solution, so proton exchange is performed.

(6) Since the entire sample holder is immersed in the solution, the lifespan of the solution is short and a large amount must be used.

Means for Solving the Problems The present invention solves the above problems and greatly improves workability, controllability, and mass productivity by adding new ideas to the method of forming optical elements. It is. That is, the method for forming an optical element of the present invention is based on L I NbxT a (,
-x ) O3 (0≦x≦1) The melting point is 90° on the surface of the substrate.
After applying a liquid acid having a concentration of C or less, the LiNbxT
The method includes a step of heat-treating the a(1-x)O3 (0≦x≦1) substrate at a temperature of 100° C. or higher.

Function The present invention allows proton exchange to be carried out in the same process as ordinary diffusion, annealing, etc. by the above-mentioned means, and workability, controllability, and mass productivity are greatly improved.

Embodiment A first embodiment of the method for forming an optical device according to the present invention is shown in FIG. In this first embodiment, pyrophosphoric acid (H4P2
A method for forming an optical waveguide by applying a coating film (0□) will be explained.

In Figure 1a, 1 is the L zNb Oa substrate of the +Z board (a substrate cut perpendicular to the +Z axis), and 2 is the LiNbO3 substrate 1.
This is a protective mask made of Ta formed on the +Z plane 3.

The thickness of the protective mask 2 is 300 mm. 4 is a slit formed in the protective mask 2 by a photo process and a lift-off process. First, the purity is 9 as shown in the figure.
Add 5% phosphoric acid 5 to LiNbO using a spinner.
5. Coating was performed on the +Z surface 3 of the substrate 1. Specifically, a spin code was performed for 20 seconds at a rotation speed of 3 oorpm. Purity 9
5% throat phosphoric acid 6 is liquid at room temperature and can be applied to surfaces such as spin cord.

Next, open θ heated to 200°C as shown in Figure C.
Heat treatment was carried out for 60 minutes inside. 7 is a plate made of 82 to ensure temperature uniformity. Finally, the plate 7 was taken out from the open 6 and cooled, and the protective mask 2 made of Ta was removed using a sodium hydroxide solution, as shown in FIG.

6.＼.

A high refractive index layer 8 was formed directly under the slit 4 by proton exchange. This high refractive index layer 8 has a thickness of 0.5 μm and functions as an optical waveguide. The maximum refractive index difference Δn between the high refractive index layer 8 formed of pyrophosphoric acid and the L I NbO5 substrate 1 is 0.145, which is higher than that of benzoic acid solution treatment, making it possible to fabricate an optical waveguide with greater light confinement. becomes. By the way, the amount of evaporation of pyrophosphoric acid 6 is extremely small compared to benzoic acid, etc., and the amount used for one time optical device fabrication is very small, so it requires safety and maintenance such as changing the solution and opening. When considering this aspect, work efficiency is dramatically improved.

Another feature of this method is that it does not require a pre-annealing process or equipment for preventing cracking of the LiNbO3 substrate 1.

Furthermore, Ta can be used as a protective mask that is not etched by phosphoric acids such as pyrophosphoric acid 6, and pattern formation is also considered to be simple and effective.

A second embodiment of the method for forming an optical element of the present invention will be described. The second embodiment shows a method of forming a microlens as an optical element. FIG. 2 is a perspective view of the microlens forming method. 1 is L I Nb0a substrate 6 is 1K pyrophosphoric acid. Pyrophosphoric acid 5 does not spread due to surface tension and maintains a constant size. By performing proton exchange in a quartz tube at 260° C. for e hours, the liquid gradually spreads, and a high refractive index layer 8 having a convex central portion as shown in FIG. 3 is formed. This high refractive index layer 8 becomes a microlens.

As described above, when this method is used, proton exchange can be performed even at temperatures of 260° C. or higher, which cannot be achieved with benzoic acid, the diffusion constant can be increased, and the process time can be shortened. Furthermore, it can be applied only to desired areas, and the process of manufacturing a protective mask can be omitted.

Regarding the third embodiment of the method for forming an optical element of the present inventionL
The case where an optical waveguide is formed on the ITaOs substrate 1' will be explained. FIG. 4 is a cross-sectional view of the method for forming the optical element. 1' is the L iT aos board, 2 is the L I
Ta formed on the -2 surface 3' of the Ta03 substrate 1'
It is a protective mask. 4 is a slit formed on the protective mask 2 by a photo process and a lift-off process. The LiTaO3 substrate 1' was heated to 70''G and 100% pure pyrophosphoric acid 6 was applied using a syringe. Next, heat treatment was performed for 10 hours in an oven heated to 280°C.Finally, the protective mask was removed. In this way, a high refractive index layer (Δn-0,1) similar to that of the previous example was formed directly under the slit 4 by proton exchange.

This high refractive index layer becomes an optical waveguide.

As described above, the present invention allows LiTaO to be easily processed at high temperatures.
It is also possible to form an optical waveguide on the third substrate 1'.

Although the heat treatment was performed at 200° C. or higher in the examples, it is possible to form optical elements at 100° C. or higher if time is taken. i! It is difficult to apply at temperatures above 90°C.
It is desirable to apply the coating at temperatures below ℃.

Further, although the optical element was formed on a +Z plate, it is possible to form a high quality optical element on a -Z plate or the like without chemical damage. In particular, +
The use of the Z plate or -Z plate is preferable because the surface is less roughened (chemically damaged) by acid than other X or Y plates.

Effects of the Invention As described above, according to the method for forming an optical element of the present invention, 9
Optical devices can be easily fabricated with good control by applying a liquid acid at 0"C or less to the surface of a ferroelectric substrate and then heat-treating it. In addition, it is possible to easily create optical devices with good controllability. Since proton exchange can be performed through heat treatment similar to that described above, workability and mass productivity are greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the method for forming an optical element in the first embodiment of the present invention, FIG. 2 is a perspective view for explaining the method of the second embodiment, and FIG. 3 is a process diagram for explaining the method of the second embodiment. FIG. 4 is a cross-sectional view for explaining the method of the third embodiment, and FIG. 6 is a configuration diagram for explaining the conventional method for forming an optical element. 1...LtNbO3 substrate, 2...Protective mask, 3...+Z surface, 4...Slit, 6...Pyrophosphoric acid, 8 ...High refractive index layer. Name of agent: Patent attorney Toshio Nakao and 1 other person
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Claims (4)

[Claims] (1) LiNb_xTa_(_1_-_x_)O_3(
0≦x≦1) After coating the surface of the substrate with a liquid acid having a melting point of 90°C or less, the LiNb_xTd_(_1_-
_x_)O_3 (0≦x≦1) A method for forming an optical device, comprising a step of heat-treating a substrate at a temperature of 100° C. or higher. (2) LiNb_xTa_(_1_-_x_)O_3(
0≦x≦1) The method for forming an optical element according to claim (1), wherein the substrate is a +Z plate or a -Z plate. (3) A method for forming an optical element according to claim (1) using an acid whose main component is pyrophosphoric acid (H_4P_2O_7). (4) LiNb_xTa_(_1_-_x_)O_3(
0≦x≦1) The method for forming an optical device according to claim (1), wherein a protective mask pattern made of Ta is formed on the surface of the substrate.