JPH0458204A - Forming method for optical waveguide - Google Patents

Abstract

PURPOSE:To ensure the light shutting-in effect by forming a film made of materials whose refractive index is lower than that of a desired plate material constituting an optical waveguide, namely, a buffer layer on one side of this plate material and joining it to a substrate made of a mechanically hard material and polishing them at an angle to the junction face and forming a optical waveguide material on a part having a proper thickness on the polished surface. CONSTITUTION:A buffer layer 2 having a low refractive index is formed on one face of a Ti-sapphire single crystal plate 1 as a plate-shaped waveguide material by sputtering or the like and is stuck to a substrate 3. Sapphire having the same mechanical characteristic as Ti-sapphire is used as the material of the substrate. After sticking, they are polished at a very shallow angle to form a part corresponding to a desired waveguide thickness on a polished surface in parallel with a boundary line 4 between the waveguide material 1 and the buffer layer 2 having a low refractive index. The area of the waveguide material having this desired thickness is patterned as desired by ion etching to form Ti-sapphire wage-guides 11 and 12.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for forming an optical waveguide.

(Prior art) Optical waveguides used as basic elements of optical ICs and optical sensors pass through a region surrounded by a medium with a low refractive index.
It is an optical transmission line in which light (electromagnetic waves) propagates while undergoing repeated total reflection at its boundary surfaces.

In order to realize such a structure, conventionally, various forming methods have been used depending on the waveguide material.

For example, in the case of a LiNbO3 waveguide, the waveguide is formed by diffusing titanium (Ti) on the substrate surface and increasing the refractive index of that portion. FIG. 7 is a perspective view showing an example of a branching interference type optical modulator using a Lib03 substrate. L i
T1 is selectively diffused into the NbO3 substrate 30 to form an optical waveguide 32, and electrodes 31 are formed at predetermined positions.

In the case of a glass waveguide, as shown in Figures 8 to 12, a glass waveguide film is formed on a silicon substrate by flame deposition and heat treatment, and then patterned by photolithography. It forms a waveguide. That is, a porous glass film is deposited on the substrate 40 by a flame deposition method, heated to make it transparent, and the refractive index becomes n2.
Glass films of nl and n2 are formed (FIG. 8). Next, the aSt was patterned using reactive ion etching (Fig. 9), and the glass film was removed by reactive ion etching using a-5i44 as a mask (Fig. 10).
Fig. 11. Depositing porous glass by flame deposition method.
(Fig. 12) and heat to make it transparent (Fig. 12). The refractive index in the thickness direction of the leading wave film is controlled by doping the core portion with T i 02 during film formation by flame deposition.

(Problems to be Solved by the Invention) The conventional method described above creates a partial refractive index difference by diffusing Ti, etc., so there are restrictions on the materials that can be applied.
It has not been possible to use materials whose refractive index is difficult to change locally (eg, Ti-sapphire single crystal).

The present invention has been made in view of the problems of the prior art described above, and its purpose is to provide a method that expands the range of usable waveguide materials and makes it possible to form a variety of waveguides. be.

(Means for Solving the Problems) An overview of typical waveguides of the present invention is as follows.

A film (buffer layer) of a material with a refractive index lower than that of the plate material is formed on one side of the desired plate material to be used as a leading waveguide, and it is bonded to a substrate made of a mechanically hard material via this buffer layer. Polish at an angle to the surface. Next, a portion of the optical waveguide material having an appropriate thickness on the polished surface is patterned into a desired pattern to form a leading waveguide. If the refractive index of the substrate material is lower than that of the optical waveguide material, the buffer layer is not necessary.

(Operation) A desired waveguide is formed using only physical processing without using chemical methods such as metal diffusion.

That is, a structure having an optical confinement effect is formed by bonding a low refractive index layer to a desired optical waveguide material. Next, apply the optical waveguide material to the required thickness (for example, 10 μm or less when using the waveguide as a single mode fiber).
Process it into In this case, it is conceivable to uniformly polish the entire surface to the desired thickness, but there is a limit to processing accuracy and it is difficult to achieve the desired thickness. Therefore, polishing is performed diagonally to the joint surface. In this case, since a region with a desired thickness is always formed, by leaving only that region by patterning, a waveguide with the required thickness (within an allowable range) can be obtained.

If necessary, the waveguide may be covered with transparent glass or the like.

Inclined polishing can be achieved with a high-precision jig. In this method, if the waveguide material exists as a bulk, the waveguide can be reliably formed by processing, and the range of usable materials can be expanded.

(Example) Next, an example of the present invention will be described with reference to the drawings.

1 to 4 are process sectional views showing one embodiment of the method for forming an optical waveguide of the present invention, and FIG. 5 is a perspective view showing the completed state.

In this embodiment, Ti-sapphire single crystal is used as the optical waveguide material. This Ti-sapphire is usually used as a laser medium (bulk crystal) for tunable wavelength lasers, but it is difficult to fabricate a single crystal thin film or realize partial refractive index changes, so it is not suitable for optical waveguides. It was considered difficult to use.

Description of each process A low refractive index buffer layer (for example, a SiO2 film of 1.46 because the refractive index of Ti-sapphire is 1.76) is applied to one side of the plate-shaped waveguide material (Ti-sapphire) single-crystal plate 1. 2 is formed using sputtering or the like, and bonded to the substrate 3. The substrate material is a sapphire substrate having almost the same mechanical properties as Ti to Mil Sapphire (FIG. 1). Note that the bonding can also be realized by using an adhesive, glass fusion, or the like.

After bonding, by polishing at an extremely shallow angle, a portion corresponding to the desired waveguide thickness is formed on the polished surface 5 parallel to the boundary line 4 between the waveguide material 1 and the low refractive index buffer layer 2. (Figure 2). FIG. 3 is an enlarged sectional view of portion A in FIG. 2. By patterning the region of the waveguide material having the desired thickness into a desired pattern using ion etching or the like,
A Ti-sapphire waveguide can be formed (FIGS. 4 and 5).

The size of the waveguide is 10 μm or less in the case of a single mode, and if you want to create a waveguide with a cross section of 5 μm x 5 μm, it will be polished at an angle of 1° and 28 mm from the boundary with the buffer layer.
Buttering may be performed at positions 0 to 290 μm apart.

FIG. 6 is a diagram showing an example of the configuration of a tunable wavelength laser using the Ti-sapphire waveguide produced in the above embodiment.

When excitation light is incident on the Ti-sapphire waveguide 23 from the excitation light source 20 via the lens 21, an inverted level due to the electrons in the T3 ion is formed, and stimulated emission light is generated and the optical resonator (mirror 22, 25 , wavelength tuning mechanism 24)
The laser oscillates. In order to oscillate, the power density of the excitation light in the laser medium (Ti-sapphire) must exceed a certain threshold, but compared to the case of a bulk crystal, the guiding waveguide structure can obtain a high optical power density, and this Therefore, it is expected that the laser oscillation threshold can be significantly lowered. In this way, it is possible to expand the range of usable optical waveguide materials.

(Effects of the Invention) As explained above, according to the present invention, the following effects can be obtained.

(1) There is no need to form a thin film of waveguide material or to form a refractive index distribution, and a waveguide can be formed if a bulk crystal is present, so there are many applicable materials.

(2) By setting a shallow polishing angle, a region with a desired waveguide thickness can be obtained over a wide area, and a high degree of freedom can be obtained in waveguide design. For example, if the polishing angle is 0°5°, 4
The width of the area where a waveguide with a thickness of ±1 μm can be formed is 400 μm.
Therefore, it is fully usable in reality.

[Brief explanation of the drawing]

1 to 4 are process cross-sectional views showing one embodiment of the method for forming a leading waveguide of the present invention, FIG. 5 is a perspective view showing a completed state, and FIG. Figure 7 is a perspective view of a distributed interference optical modulator fabricated by a conventional method, and Figures 8 to 12 are diagrams showing the configuration of an example of a tunable wavelength laser device manufactured using a conventional flame deposition method. FIG. 3 is a cross-sectional view showing a manufacturing process of a quartz-based optical waveguide using an ion etching method. 1... Optical waveguide material (Ti-sapphire) 2... Buffer layer (S102 film) 3... Substrate 4... Bonding surface 5...
Slope 11.12...Patterned optical waveguide 20...
・Excitation light source 21...Lens 22...Mirror 23...Ti-sapphire waveguide 24...Wavelength tuning mechanism 25...Mirror 26...Laser light Fig. 1 Fig. 2 Fig. 3 Figure 4 Figure 1 Figure Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] A waveguide material (1) for forming an optical waveguide and a low refractive index layer (2) having a lower refractive index than the waveguide material are bonded, and the waveguide material (1) is attached to the bonded surface. The area of the optical waveguide material (1) having a desired thickness on the polished surface is patterned into a desired pattern to form an optical waveguide (11).
, 12).